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abstract | The invention concerns a method of producing a cladding tube for nuclear fuel for a nuclear boiling water reactor. According to the method, a tube is formed which comprises an outer cylindrical component (10) mainly containing zirconium and an inner cylindrical component (20) metallurgically bonded to the outer component (10), wherein also the inner component (20) at least mainly contains zirconium. The inner component (20) has a lower recrystallization temperature than the outer component (10). The cladding tube is final annealed at a temperature and during a time such that the inner component (20) substantially completely recrystallizes and such that the outer component (10) partly recrystallizes but to a lower extent than the inner component (20). The invention also concerns a cladding tube, a fuel assembly for a boiling water reactor as well as the use of a cladding tube. |
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042499950 | description | In the example shown in FIG. 1, the reference numeral 1 generally designates the lower portion of a fast nuclear reactor which is cooled by a liquid metal. Said reactor comprises in particular a main vessel 2 which is open at the top portion (not shown) and constituted by a lateral cylindrical shell 3 which terminates in a substantially hemispherical bottom wall 4. The main vessel 2 is surrounded externally in known manner by a second vessel 5 having a parallel wall or so-called safety vessel. The reactor core 6 is placed within the main vessel 2 beneath the level (not shown) of the liquid metal contained within this latter and rests on a core support diagrid 7 which is applied against the bottom wall 4 of the vessel 2 by means of a support structure 8. The reactor core and diagrid support structure 8 are completely immersed in the liquid metal contained in the main vessel 2 and usually consisting of sodium. This volume of liquid metal is also supplied through holes 9 formed in the base of the diagrid support structure 8 to a narrow annular space 10 formed first between the bottom wall 4 of the main vessel 2 and a sheet metal member 11 which is parallel to this latter, then extends opposite to the lateral cylindrical shell 3 by means of two parallel walls 12 and 13 which define two spaces 14 and 15. During reactor operation, the main vessel 2 is cooled by the flow of liquid metal which is circulated upwards within the space 14, then downwards within the space 15. At the bottom of the space 15, this coolant flow is discharged through holes 16 formed in the wall 13 in order to return to the volume contained within the main vessel 2. In accordance with an arrangement which is also conventional, the reactor core 6 is placed within an inner vessel, the lateral wall 17 of which has a substantially conical contour in the example of construction under consideration in order to be joined tangentially to a portion of torus 18 which extends annularly around the axis of the reactor core and of the main vessel. This portion of torus 18 which forms a skew wall is extended by a second conical portion 19 which is bent downwards and joined to the wall 13 of the cooling structure which forms an internal jacket for the lateral cylindrical shell 3 of the main vessel. Under these conditions, the skew wall 18 and its conical extensions 17 and 19 separate the volume of liquid metal within the main vessel 2 into two regions 20 and 21 respectively which are located in one case above said skew wall and in the other case below this latter. The nuclear reactor shown in FIG. 1 corresponds to a general arrangement known in the technique as an integrated design. Provision is accordingly made for a series of heat exchangers 22 and circulating pumps 23 placed within the interior of the main vessel 2 and disposed at suitable intervals around the reactor core 6 in such a manner that the bodies of said heat exchangers and of said pumps extend vertically through the skew wall 18 which forms a separation between said regions 20 and 21. Each heat-exchanger body 22 is provided with inlet ports or windows 24 located in the region 20 above the skew wall 18 and outlet windows 25 provided beneath said skew wall in the region 21 between the inner vessel 17 and the main vessel 2. The skew wall 18 is traversed by each body of the heat exchangers 22 or pumps 23 through wells each constituted by a cylindrical sleeve 26 which surrounds the heat-exchanger or pump body and is welded to the skew wall. In the case of the heat exchanger, said sleeve is in turn covered by a bell-cap 27 connected to the heat exchanger and forming a space 28 in which is trapped a suitable quantity of neutral blanket gas. The levels of liquid metal inside and outside the sleeve 26 are in communication respectively with the regions 20 and 21 and are represented in the drawing by the references 29 and 30. In accordance with the invention, the baffle 18 together with its conical extensions 17 and 19 towards the inner vessel and the main vessel is associated with a baffle 31 designed in the form of a single and substantially horizontal sheet metal plate 32 as shown in the example of construction of FIG. 1. Said baffle is provided with sliding contacts or shoes 33 which rest on bearing members of the L-section type, for example, these latter being rigidly fixed either to a support bracket 35 extending from the outer surface of the cylindrical sleeve 26 or provided at the top of the lateral neutron shield 36 which surrounds the reactor core 6 within the inner vessel. The plate 32 is provided at its periphery with a bent-back edge 37 which leaves a small clearance space with respect to the wall 13. Finally, the plate 32 is advantageously provided with circumferential ribs 38 for absorbing thermal shocks and especially for reducing stresses within the baffle at the time of variations in operating regime. During reactor operation, the liquid metal which has passed upwards through the reactor core 6 is collected within the region 20 within the inner vessel above the skew wall 18, then penetrates into the heat-exchanger bodies 22 through their inlet windows 24. After cooling, said liquid metal is discharged from said heat exchangers through the windows 25 and collected within the region 21 beneath the skew wall 18, between the inner vessel and the main vessel. In this region, the cooled liquid metal is recirculated by the pumps 23. After suction through the diffusers 39 of said pumps which are supported by beams 40, the liquid metal is returned into the diagrid 7 through large-section ducts 41, then undergoes a further passage through the reactor core 6, thus maintaining a continuous circulation. By positioning the baffle 31 above the skew wall 18, there is thus defined with this latter an internal region 42 which is capable of constituting an effective thermal screen during operation by virtue of the quantity of liquid metal which is contained within this region and remains practically static. Furthermore, the use of sliding bearing members permits of free expansion of the baffle whilst the ribs 38 formed in this latter ensure a reduction of thermal stresses. Finally, the solution which is contemplated offers great simplicity of construction and is of very limited overall size. FIG. 2 illustrates an alternative form of the embodiment described in the foregoing in which the baffle 31 is no longer designed as a single unit as in the previous embodiment but is constituted by adjacent sectors 31a, 31b, 31c . . . , each sector being joined to a cylindrical sleeve 26 in which a pump body or heat-exchanger body passes through the baffle and the skew wall. Preferably, these sectors are provided with edges 31'a, 31'b, 31'c, . . . , which overlap successively in order to ensure continuity of the baffle. In this alternative form, there are again shown the circumferential ribs 38 in the form of circular undulations which are intended to endow the baffle with the necessary degree of flexibility by virtue of the inherent elasticity of said ribs. In the first alternative form of a second embodiment shown in FIG. 3, the elements which were already illustrated in FIG. 1 are again shown partially. In this variant, the baffle 51 is self-supporting and has a flat portion 52 which is inclined towards the axis of the main vessel and rests on a lateral cylindrical shell 53 which is mounted within the inner vessel and the lower end of which in turn rests on the diagrid support structure 8. At the opposite end which is directed towards the periphery, the baffle 51 has a downwardly-extending side portion 54 which leaves a narrow clearance space with respect to the wall 13. In order to confine the volume within the region 42, the baffle 51 is also provided with a flange 55 opposite to each of the skirts 26 through which the bodies of the heat exchangers or pumps 22 and 23 traverse the skew wall 18. Both the flange 55 and the downwardly-extending side portion 54 extend to the bottom level of the baffle in order to prevent circulation of liquid metal by natural convection. In this embodiment as in the previous form of construction, the liquid metal contained between the skew wall and the baffle remains practically stagnant during operation. In a second alternative form of the second embodiment shown in FIG. 4, the baffle 51 is again self-supporting as in the alternative embodiment shown in FIG. 3 and also has a portion 52 which is inclined towards the axis of the main vessel. In this variant, the baffle is arranged as indicated hereinafter with a view to ensuring leak-tightness between the regions 42 and 20. The baffle 51 is provided at its periphery with an upwardly-directed side portion 56 which extends parallel to the wall 13 to the neutral gas atmosphere 60 located above the free level 58 of liquid metal. The baffle 51 is also provided with a side portion which is similar to the side portion 56 around each of the penetrations (not shown) provided in the skew wall 18 for the cylindrical sleeves 26 which surround the pump bodies. At the point of penetration of the skew wall 18 by the heat-exchanger bodies 22, the baffle 51 is provided with a side wall 57 which extends upwards and terminates in the neutral gas space 28. The foregoing arrangements make it possible to prevent any circulation between the region 42 located between the skew wall and the baffle and the region 20 containing the hot sodium. Equalizing of pressures between the region 20 and the confined region 42 is obtained by means of orifices 59 formed in the lower portion of the cylindrical shell 53 which supports the baffle 51. FIG. 5 illustrates another alternative embodiment in which the baffle associated with the skew wall is mounted in a floating arrangement. In this alternative embodiment, the baffle 62 has a flat surface 63 which extends horizontally above the skew wall 18. This surface rests on supports such as those designated by the reference 64 and formed in the wall 13 on the side nearest the main vessel or in a cylindrical shell 65 on the side nearest the reactor core, or alternatively in the external surface of the cylindrical sleeves 26 through which the pump and heat-exchanger bodies traverse the skew wall. The surface 63 of the baffle is provided with downwardly-bent side portions 66 extending beneath the level of the liquid metal which is trapped within the supports 64, thus confining beneath the baffle a blanket layer 67 of suitable neutral gas such as argon or helium. By virtue of these arrangements, total leak-tightness is accordingly obtained between the volume of hot liquid metal above the baffle and the volume of colder liquid metal located beneath this latter, thus permitting an appreciable reduction in friction forces at the time of differential radial expansions of the baffle. Finally, the presence of the gas blanket ensures more efficient thermal insulation and serves to lower the temperature of the practically static volume of liquid metal between the baffle and the skew wall. 9n |
abstract | An ion beam processing apparatus includes an ion beam irradiation optical system that irradiate a rectangular ion beam to a sample held on a first sample stage, an electron beam irradiation optical system that irradiates an electron beam to the sample, and a second sample stage on which a test piece, extracted from the sample by a probe, is mounted. An angle of irradiation of the ion beam can be tilted by rotating the second sample stage about a tilting axis. A controller controls the width of skew of an intensity profile representing an edge of the rectangular ion beam in a direction perpendicular to a first direction in which the tilting axis of the second sample stage is projected on the second sample stage surface so that the width will be smaller than the width of skew of an intensity profile representing another edge of the ion beam in a direction parallel to the first direction. |
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abstract | A particle therapy system includes a building having a first floor and second floors and, a particle beam generator installed on the first floor and configured to generate a particle beam, a first transport system configured to transport a particle beam from the particle beam generator to a first irradiation system in a first treatment room, and a second transport system configured to transport a particle beam to a second irradiation system in a second treatment room, branched from the first transport system, via a second floor. The second transport system has a first bending magnet that bends a particle beam to the direction of the second floor different from the installation surface of the particle beam generator. The building has a shielding wall configured to shield the first floor and the second floor and the second transport system is provided penetrating the shielding wall. |
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abstract | In a jet pump measurement pipe repair method according to the present embodiment, a breakage part of a measurement pipe horizontally fixed to a lower part of a jet pump provided in reactor water in a reactor pressure vessel is repaired. The method has: a step of cutting and removing the measurement pipe including the breakage part; a step of retaining a connection pipe for connecting the remaining measurement pipe on the jet pump by means of a clamp; and a step of connecting ends of the remaining measurement pipe by means of the connection pipe. |
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047568720 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention: The invention relates to a nuclear reactor housed in a prestressed concrete pressure vessel secure against bursting. The station includes a gas cooled high temperature reactor having primary loop components comprising steam generators and blowers in a large cavity clad with a liner of the prestressed concrete pressure vessel. A liner cooling system and at least one shut-down system are also included. A reactor core, the spherical fuel elements whereof comprise coated particles of a fissionable material embedded in a graphite matrix, is cooled by helium flowing from top to bottom through the reactor core as the cooling gas. 2. Background of the Art: The THTR-300 MW.sub.el prototype nuclear power station is a nuclear power installation of the aforementioned high temperature, gas-cooled type. It comprises a high temperature reactor with spehrical fuel elements utilizing helium as the cooling gas. Such reactor is often referred to as a pebble bed reactor which provides the environment of the present invention. A high temperature reactor of this configuration possesses a series of specific safety characteristics, whereby the risk of an accident in the course of the operation of such a power plant is reduced to a minimum. Even in the case of hypothetical incidents (accidents) the system's inherent safety characteristics of such high temperature reactors act to restrict environmental effects to relatively low values. The characteristics of a high temperature reactor include the negative temperature and power coefficient under all operating conditions. The use of a gaseous and, thus phase stable coolant, specifically a neutron physically neutral inert gas is also characteristic whereby, even in the case of a pressure relief accident, the coolant cannot be lost entirely. A low ratio of power density/heat capacity is another characteristic. In the case of interference with the production or removal of heat, only slow changes occur in the temperature of the core. A further characteristic of high temperature reactors is the high temperature strength of the core material comprising ceramic material (graphite) and the fuel elements, wherein the fuel is embedded in the form of particles coated with pyrocarbon in a gas tight manner, so that fission products are retained in the graphite shell. SUMMARY OF THE INVENTION It is an object of the present invention to provide a nuclear power station of the aforedescribed structural type, which may be operated economically in a capacity range of 300-600 MW.sub.el and wherein simultaneously high safety standards may be maintained by utilizing the favorable accident behavior of the high temperature reactor. This and other objects are attained by a nuclear power station for a gas-cooled high temperature pebble bed reactor having a pebble bed reactor core housed in a prestressed concrete pressure vessel 2, an operating cooling circuit comprising at least one steam generator 7 and blower 8, a secondary cooling circuit 9 and primary loop for flow of cooling medium through the reactor core from top to bottom and at least one reactor shutdown system 13. The nuclear power station according to the present invention comprises: a reactor protection building surrounding the prestressed concrete pressure vessel and cooling circuits, means for relieving the pressure in the reactor protection building, means for filtering radioactive contaminants in the reactor protection building in combination with the pressure relief means, a plurality of auxiliary cooling circuits separate and independent from the operating and secondary cooling circuits and means for removal of decay heat of the reactor core in the event of failure of the auxiliary cooling circuits the means including a liner cooling circuit for the prestressed concrete pressure vessel. The assurance of the retention of activities in case of incidents up to hypothetical accidents is to be considered the primary measure to reduce or eliminate risks in the operation of a nuclear power station. The retention of activities is determined essentially by the operating and accident temperatures and operating and accident pressures. The safety of a nuclear power station, therefore, depends primarily on the control of temperature and pressure problems; i.e. exceeding the failure temperature of the fuel elements and of the prestressed concrete pressure vessel must be sufficiently unlikely or excluded and the pressure integrity of the installation must be assured. In a nuclear power station according to the invention, the aforementioned temperature and power problems are safely under control. |
claims | 1. A neutron capture therapy system comprising:an accelerator, wherein the accelerator generates a charged particle beam;a neutron generator, wherein the neutron generator generates a neutron beam after being irradiated by the charged particle beam;a vacuum tube, wherein the vacuum tube transports the charged particles accelerated by the accelerator to the neutron generator;a beam shaping assembly, wherein the beam shaping assembly comprises a moderator and a reflector surrounding the moderator, the moderator moderates the neutrons generated by the neutron generator to a preset spectrum, and the reflector leads the deflected neutrons back to increase the neutron intensity within the preset spectrum; anda collimator, wherein the collimator concentrates the neutrons generated by the neutron generator,wherein the spectrum of the neutron beam is changed by changing the spectrum of the charged particle beam. 2. The neutron capture therapy system according to claim 1, wherein the neutron capture therapy system further comprises a microwave generator capable of injecting microwaves into the accelerator, the spectrum of the charged particle beam output by the accelerator changes according to the injected microwaves at different frequencies, when the spectrum of the charged particle beam is at a first value, the charged particle beam reacts with the neutron generator and generates a spectrum of neutron beam at a first value, and when the spectrum of the charged particle beam is at a second value, the charged particle beam reacts with the neutron generator and generates a spectrum of neutron beam at a second value, wherein the spectrum of the first value of the charged particle beam is lower than that of the second value, and the spectrum of the first value of the neutron beam is lower than that of the second value, and wherein the neutron capture therapy system indirectly changes the spectrum of the neutron beam by changing the beam energy spectrum of the charged particle beam, and then changes the neutron depth dose distribution. 3. The neutron capture therapy system according to claim 1, wherein the spectrum of the charged particle beam changes as the changing of electric field intensity of the accelerator, an electric field generating device is provided outside the vacuum tube and/or the neutron generator, the electric field generating device is capable of generating an electric field and so as to accelerate or decelerate the charged particle beam before the charged particle beam irradiates to the neutron generator. 4. The neutron capture therapy system according to claim 1, wherein the neutron capture therapy system further comprises a beam energy spectrum adjusting member capable of adjusting the spectrum of the charged particle beam, when the beam energy spectrum adjusting member is located in the vacuum tube and is in front of the neutron generator, the spectrum of the charged particle beam is adjusted after irradiating to the beam energy spectrum adjusting member, and then the charged particle beam irradiates to the neutron generator to generate the neutron beam. 5. The neutron capture therapy system according to claim 4, wherein the vacuum tube is provided with an accommodating portion, the beam energy spectrum adjusting member is accommodated in the accommodating portion and is connected with a driving mechanism capable of moving the beam energy spectrum adjusting member, when the driving mechanism controls the beam energy spectrum adjusting member to move to the front of the neutron generator, the spectrum of the charged particle beam changes after irradiating to the beam energy spectrum adjusting member and then irradiates to the neutron generator; when the driving mechanism controls the beam energy spectrum adjusting member to be accommodated in the accommodating portion but not in front of the neutron generator, the charged particle beam directly irradiates to the neutron generator. 6. The neutron capture therapy system according to claim 5, wherein the neutron capture therapy system comprises a plurality of beam energy spectrum adjusting members, and the driving mechanism drives each beam energy spectrum adjusting member to move separately to adjust the spectrum of the charged particle beam. 7. The neutron capture therapy system according to claim 5, wherein the beam energy spectrum adjusting members are made of different materials. 8. The neutron capture therapy system according to claim 1, wherein the neutron generator is connected to a power supply device and energized by the power supply device, and the beam spectrum of the charged particle beam changes after the charged particle beam irradiates to the energized neutron generator. 9. A neutron capture therapy system comprising:an accelerator, wherein the accelerator generates a charged particle beam;a neutron generator, wherein the neutron generator generates a neutron beam after being irradiated by the charged particle beam;a vacuum tube, wherein the vacuum tube transports the charged particles accelerated by the accelerator to the neutron generator;a beam shaping assembly, wherein the beam shaping assembly comprises a moderator and a reflector surrounding the moderator, the moderator moderates the neutrons generated by the neutron generator to a preset spectrum, and the reflector leads the deflected neutrons back to increase the neutron intensity within the preset spectrum;a collimator, wherein the collimator concentrates the neutrons generated by the neutron generator; andat least a beam energy spectrum adjusting member, wherein before the charged particle beam irradiates to the neutron generator, the charged particle beam irradiates to the beam energy spectrum adjusting member and achieves adjustment of the charged particle beam spectrum. 10. The neutron capture therapy system according to claim 9, wherein the beam energy spectrum adjusting member is located in the vacuum tube and is able to move from a first location to a second location, when the beam energy spectrum adjusting member is in the first location, the charged particle beam irradiates to the beam energy spectrum adjusting member before irradiating to the neutron generator; when the beam energy spectrum adjusting member is in the second location, the charged particle beam directly irradiates to the neutron generator. 11. The neutron capture therapy system according to claim 10, wherein a plurality of beam energy spectrum adjusting members are located in the vacuum tube and move from a first location to a second location separately. 12. The neutron capture therapy system according to claim 11, wherein the vacuum tube is provided with an accommodating portion located below the neutron generator, the beam energy spectrum adjusting members are accommodated in the accommodating portion, and each beam energy spectrum adjusting member is able to move upward to the first location or downward to the second location separately. 13. The neutron capture therapy system according to claim 11, wherein the beam energy spectrum adjusting members are in the same structure but with different thicknesses. 14. The neutron capture therapy system according to claim 11, wherein the beam energy spectrum adjusting members are made of different materials. 15. The neutron capture therapy system according to claim 14, wherein at least one of the beam energy spectrum adjusting members is made of materials capable of generating a neutron beam. 16. The neutron capture therapy system according to claim 9, wherein the cross sections of the beam energy spectrum adjusting member and the neutron generator perpendicular to the irradiation direction of the charged particle beam are circular. 17. A neutron capture therapy system comprising:an accelerator for generating a charged particle beam;a neutron generator for generating a neutron beam after being irradiated by the charged particle beam;a vacuum tube for transporting the charged particles accelerated by the accelerator to the neutron generator;a beam shaping assembly including a moderator for moderating the neutrons generated by the neutron generator to a preset spectrum and a reflector surrounding the moderator for leading the deflected neutrons back to increase the neutron intensity within the preset spectrum;a collimator for concentrating the neutrons generated by the neutron generator; andmeans for changing the spectrum of the charged particle beam whereby the spectrum of the neutron beam changes. 18. The neutron capture therapy system according to claim 17, wherein a plurality of beam energy spectrum adjusting members are located in the vacuum tube, and move from the first location to the second location separately. |
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claims | 1. A writing error diagnosis method for a charged beam photolithography apparatus, the apparatus irradiates a charged beam on a target object to write a desired pattern, comprising:collecting processing result data of a pattern writing circuit at a position where a pattern writing error occurs after the pattern writing error occurs; andcomparing the collected processing result data with correct data. 2. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 1, whereinthe collection of processing result data of a pattern writing circuit at a position where a pattern writing error occurs is performed by:inputting position information of the position where the pattern writing error occurs and a pattern writing condition in pattern writing at the position where the pattern writing error occurs to the pattern writing circuit;executing processing of the pattern writing circuit; andstopping the processing of the pattern writing circuit at the position where the pattern writing error occurs. 3. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 1, whereinthe correct data is simulation result data processed in the charged beam photolithography apparatus. 4. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 1, whereinthe correct data is processing result data of the pattern writing circuit obtained by executing a pattern writing process in advance. 5. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 1, whereinthe position information is data obtained in such a manner that layout data including a pattern at the pattern writing error occurrence position is converted for the charged beam photolithography apparatus. 6. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 1, whereinwhen the pattern writing circuit is constituted by a plurality of circuit boards, the collection of the processing result data and the comparison of the processing result data with correct data are performed for each of the circuit boards. 7. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 1, whereina result obtained by the comparison is displayed on a display device. 8. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 2, whereinstopping of the processing of the pattern writing circuit at the position where the pattern writing error occurs is performed on the basis of a coordinate position of the error occurrence position. 9. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 2, whereinthe collection of processing result data of the pattern writing circuit at a position where the pattern writing error occurs is performed by storing the processing result data of the pattern writing circuit at a timing when the processing is stopped at the pattern writing error occurrence position in storage means, and reading the processing result data stored in the storage means. 10. The writing error diagnosis method for a charged beam photolithography apparatus according to claim 1, whereinthe charged beam is an electron beam. 11. A charged beam photolithography apparatus, the apparatus irradiates a charged beam on a target object to write a desired pattern, comprising:collecting means for collecting processing result data of a pattern writing circuit at a position where a pattern writing error occurs after the pattern writing error occurs; andcomparing means for comparing the collected processing result data of the pattern writing circuit at the position where the pattern writing error occurs with correct data. 12. The charged beam photolithography apparatus according to claim 11, whereinthe collecting means includes:input means for inputting position information of the position where the pattern writing error occurs and a pattern writing condition in pattern writing at the position where the pattern writing error occurs to the pattern writing circuit;executing means for executing processing of the pattern writing circuit; andstop means for stopping the processing of the pattern writing circuit at the position where the pattern writing error occurs. 13. The charged beam photolithography apparatus according to claim 11, whereinthe correct data is simulation result data processed in the charged beam photolithography apparatus. 14. The charged beam photolithography apparatus according to claim 11, whereinthe correct data is processing result data of the pattern writing circuit obtained by executing a pattern writing process in advance. 15. The charged beam photolithography apparatus according to claim 11, whereinthe position information is data obtained in such a manner that layout data including a pattern at the pattern writing error occurrence position is converted for the charged beam photolithography apparatus. 16. The charged beam photolithography apparatus according to claim 11, whereinwhen the pattern writing circuit is constituted by a plurality of circuit boards, the collection of the processing result data and the comparison of the processing result data with correct data are performed for each of the circuit boards. 17. The charged beam photolithography apparatus according to claim 11, further comprisingdisplay means for displaying a result obtained by the comparing means on a display device. 18. The charged beam photolithography apparatus according to claim 12, whereinthe stop means is means for stopping the processing on the basis of a coordinate position of the error occurrence position. 19. The charged beam photolithography apparatus according to claim 12, whereinthe collecting means includes storage means for storing the processing result data of the pattern writing circuit at a timing when the processing is stopped at the pattern writing error occurrence position, and reading means which reads the processing result data stored in the storage means. 20. The charged beam photolithography apparatus according to claim 11, whereinthe charged beam is an electron beam. |
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063103559 | abstract | A covering or shield attenuating the flux of electromagnetic radiation from an article. The shield includes a matrix, a radiation attenuating material provided in the matrix, and at least one space provided in the matrix. The space reduces the overall weight of the shield. The space can be a variety of shapes, including round, honeycombed, triangular, rectangular, or other configuration. |
046631119 | summary | The present invention relates generally to the production of tritium and more particularly to a specific way of producing the tritium as well as a specific way of retaining it. One of the most promising prime fuels in fusion reaction is deuterium-tritium (D-T) fuel, and for this reason, tritium breeding has been given much attention in fusion reactor design. Some of the conceptual studies for tritium breeding can be found in the following publications: G. H. MILEY, Fusion Energy Conversion, American Nuclear Society, LaGrane Park, Ill. (1976). PA1 R. J. DeBELLIS and Z. A. SABRI, "Fusion Power: Status and Options", EPRI ER-510-SR, Electric Power Research Institute (June 1977). PA1 "STARFIRE--A Commercial Tokamak Fusion Power Plant Study", ANL/FPP-80-1, Vol. 1, Argonne National Lab. (Sep. 1980). PA1 "NUWMAK, A Tokamak Reactor Design Study", UWFDM-330, University of Wisconsin (Mar. 1979). An important aspect of the D-T fuel cycle is that a lithium blanket is required to breed tritium as an integral part of the fusion reactor. On the other hand, it is also possible to produce tritium separately by subjecting lithium to neutron irradiation as described for example in U.S. Pat. Nos. 3,100,184 or 3,079,317. The production of tritium by means of neutron irradiation is also discussed in U.S. Pat. Nos. 3,037,922; 3,510,270; and 3,791,921. As will be seen hereinafter, the present invention is also concerned with the production of tritium by means of neutron irradiation and, accordingly, one object of the present invention is to produce tritium in an efficient and yet uncomplicated and reliable manner. Another object of the present invention is to provide an uncomplicated and yet reliable way of retaining the tritium once it is produced. A more particular object of the present invention is to provide an efficient tritium breeding material, an efficient tritium retaining material and reliable means for containing both in a way which allows each to function efficiently in its intended manner. As will be seen hereinafter, for the reasons to be discussed, the preferred material selected to produce the tritium is lithium bismuth and the preferred material selected to retain the tritium once produced is nickel. These two materials are preferably contained in a common tubular housing which is pervious to neutrons, at least to a limited extent, and impervious to tritium. In this way, the entire tubular housing can be placed in an appropriate location within a nuclear reactor for exposing the lithium bismuth to the neutrons produced by the reactor. The nickel can be placed in sufficiently close vicinity to the lithium bismuth to dissolve and thereby retain any tritium produced by the lithium bismuth as a result of this bombardment of neutrons. |
claims | 1. A radiation image storage panel comprising an energy storable phosphor layer formed by a gas phase-accumulation method, wherein the energy storable phosphor layer gives off an emission having a luminescence width d in the range of 150 to 395 μm when it is exposed to radiation and then excited with a stimulating light of 50 μm half-width, where d represents the range of the resulting emission profile at half maximum. 2. The radiation image storage panel of claim 1, wherein the luminescence width d is in the range of 290 to 380 μm. 3. The radiation image storage panel of claim 1, wherein the energy storable phosphor layer has a packing ratio in the range of 80 to 90% and a thickness in the range of 130 to 800 μm. 4. The radiation image storage panel of claim 1, wherein the energy storable phosphor layer comprises a stimulable alkali metal halide phosphor represented by the formula (I):MIX.aMIIX′2.bMIIIX″3:zA (I)in which MI is at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs; MII is at least one alkaline earth metal or divalent metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ni, Cu, Zn and Cd; MIII is at least one rare earth element or trivalent metal selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In; each of X, X′ and X″ independently is at least one halogen selected from the group consisting of F, Cl, Br and I; A is at least one rare earth element or metal selected from the group consisting of Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Ag, Tl and Bi; and a, b and z are numbers satisfying the conditions of 0≦a<0.5, 0≦b<0.5 and 0<z<1.0, respectively. 5. The radiation image storage panel of claim 4, wherein MI is Cs, X is Br, A is Eu, and z is a number satisfying the condition of 1×10−4≦z≦0.1. 6. The radiation image storage panel of claim 5, wherein the energy storable phosphor layer has a density in the range of 3.6 to 4.0 g/cm3 and a thickness in the range of 130 to 800 μm. 7. A process for reading out a radiation image stored in a radiation image storage panel which comprises the steps of:moving a radiation image storage panel of claim 1 in which the radiation image is stored, relatively to a set of a stimulating means and a light-detecting means in which the stimulating means applies to one surface of the storage panel a stimulating light extended linearly in a width direction of the storage panel and in which the light-detecting means is equipped with an isometric erect image-forming means and comprises a plurality of photoelectrically converting pixels aligned in the width direction of the storage panel, each of the pixels having a size D under such conditions that 25 μm≦D≦400 μm and 0.5≦d/D≦4 in the width direction of the storage panel;applying the stimulating light to one surface of the storage panel linearly in the width direction of the storage panel and detecting a stimulated emission given off by the storage panel by the light-detecting means through the equivalent erect image-forming means to produce a series of electric signals; andprocessing the electric signals in relation to an information of the relative movement between the storage panel and the set of a stimulating means and a light-detecting means, to obtain a reproduced radiation image in the form of a series of electric image signals. 8. The process of claim 7, wherein the light-detecting means is a line sensor which comprises plural photoelectric converting elements arranged linearly. 9. The process of claim 8, wherein each photoelectric converting element corresponds to each pixel of the light-detecting means. |
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abstract | A device for circumscribing a target site with a beam. The target site is located within a target body. The path of the beam is varied rotationally so as to form a cone with an isocenter at the cone's apex. The isocenter is fixed on the approximate center of the target site. The target body is rotated about a vertical axis passing approximately through the center of the target site, and the rates of rotation of the beam path and body, respectively correspond so that the beam intersects an axis passing through the target site at an approximately constant angle. |
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048896632 | summary | BACKGROUND OF THE INVENTION 1. Technical Field The invention relates to methods of manufacturing uranium oxide base pellets for use as nuclear fuel and more particularly to manufacture of "green" pellets by cold compression of a powder whose major component is uranium dioxide. The invention makes use of uranium dioxide powder obtained by a dry process (i.e., by direct reduction of UF.sub.6 into dioxide). The powders obtained by the dry conversion process, described in French No. 2,060,242 and U.S. Pat. No. 4,397,824, including water vapor hydrolysis followed by pyrohydrolysis of the uranyl fluoride UO.sub.2 F.sub.2 obtained, have the advantage of being readily sinterable. On the other hand, the green pellets obtained by compression are relatively fragile. Handling thereof is delicate; the rejects are numerous if special care is not exercised. 2. Prior Art Different methods have been proposed for reducing the fragility of green pellets. Attempts have been made to increase the density in green condition by increasing the compacting pressure, which has the drawback of causing premature wear of the compression dies. It has been proposed to add a binder and to granulate the powder and/or to subject the powder to different treatments (French 2,561,026). All of these solutions have drawbacks. Those which use water or a binder raise criticality problems. The methods are generally applicable only to small batches, practically not exceeding 50 kg. The fragility of the green pellets obtained by compression of UO.sub.2 powder obtained by dry conversion may probably be attributed to the fact that the powder is formed of fine crystallites more or less rounded, with a very low oxygen over-stoechiometry (ratio O/U of from 2.02 to 2.06). Reoxidation of the powder improves the strength of the pellets. Surface oxidization of the uranium oxide UO.sub.2 redivides the grains into jagged aggregates with intertwining ramifications. The powder then has properties comparable to those of a powder obtained by a wet process: during compression of the pellets into shape, the grains engage each other and provide coherence. But limited surface oxidization to UO.sub.2 powder is difficult to achieve industrially. Oxidation tends to bolt until the whole of the oxide has oxidized to U.sub.3 O.sub.8 which is difficult to sinter into pellets free of cracks, unless a slow controlled reduction step is added to the manufacture during presintering. Moreover, oxidation generates islets of U.sub.3 O.sub.8 which, during sintering, shrink more than the UO.sub.2 grains, whence a heterogeneous texture. It is moreover practically impossible to carry out oxidation in a reactor for direct conversion of UF.sub.6, such as described in U.S. Pat. No. 4,397,824. It is, moreover, current practice to recycle waste from manufacture of the pellets, such as the oxidized grinding muds, the rejected pellets, the splinters and residues of powders in the form of U.sub.3 O.sub.8 (French 2,001,113). These oxidized powders, while they slightly improve the strength of the green pellets if mixed with UO.sub.2 before compacting and sintering, have a very unfavorable effect on the density and texture of the sintered pellets, for the U.sub.3 O.sub.8 is in the form of dense and coarse grains. The percentage of recycled U.sub.3 O.sub.8 in the green pellets is generally limited to 12% wt. at most. It has further been suggested to mix UO.sub.2 obtained by a wet process with an amount of U.sub.3 O.sub.8 prepared for that purpose and whose function is to generate pores which collect fission gases in the sintered pellets (French No. 1,412,878). SUMMARY OF THE INVENTION It is an object of the invention to provide a manufacturing method which appreciably increases the strength of the green pellets without having an unfavorable effect on the properties of the sintered pellets. With that purpose in mind, there is provided a method in which fine powder of uranium oxide UO.sub.2 obtained by dry conversion is mixed with a proportion less than 40% by weight of uranium oxide powder substantially in the state of reactive U.sub.3 O.sub.8 and having a grain size less than 350 microns. The total content of U.sub.3 O.sub.8 in the mixture is preferably higher than 5%, typically from 15 to 25% wt. The fine powder typically consists of elementary particles whose size is in the micron and sub-micron range, agglomerated into grains which pass across a 350 .mu.m sieve. The fine powder representing 60% wt. at least of the mixture may include up to 10% wt. of an oxide of at least another element, such as Pu, Th and Gd. The U.sub.3 O.sub.8 powder is advantageously obtained by oxidation in air of UO.sub.2 at a temperature lesser than 800.degree. C. It must be continued until the O/U ratio corresponds substantially to the stoechiometry of the U.sub.3 O.sub.8 oxide. To avoid sintering of the U.sub.3 O.sub.8 powder and obtaining a good desaggregation of this U.sub.3 O.sub.8 during subsequent mixing with the UO.sub.2 powder, the oxidation is preferably carried out at a temperature between 250.degree. C. and 350.degree. C. When so prepared, U.sub.3 O.sub.8 has no pore forming action comparable to that of the U.sub.3 O.sub.8 used in the process according to French No. 1,412,878. The improvement in the strength of the green pellets increases with the content of oxidized powder. In practice, it is desirable to use a U.sub.3 O.sub.8 content of at least 5% by weight. Thus the rejects and the faults caused by handling are reduced and the manufacturing yield is increased. The method of the invention is applicable not only to the manufacture of uranium oxide pellets but also to that of combined oxide UO.sub.2 base pellets, the best known of which are of UO.sub.2 --PuO.sub.2, UO.sub.2 --ThO.sub.2, UO.sub.2 --Gd.sub.2 O.sub.3 types. Recycled UO.sub.3 may also be incorporated in an amount not exceeding 10% wt. In all cases, it is necessary to achieve intimate mixing of the powders before compacting to obtain pellets. This mixing may particularly be achieved: from UO.sub.2 and U.sub.3 O.sub.8 powders crushed together in a hammer crusher, PA1 from UO.sub.2 and U.sub.3 O.sub.8 powders mixed in an arm mixer and equipped with a disaggglomeration turbine. Before mixing, the powders may be disagglomerated by crushing and/or sifting, the desired result being the absence of U.sub.3 O.sub.8 agglomerates. In all cases, the mixing may be carried out in industrial equipment so as to obtain large homogeneous batches, which may exceed two tons of powder when the enrichment is sufficiently low for there to be no problem of criticality. The invention also provides a complete method for manufacturing uranium dioxide based pellets in which green pellets are prepared by the above described steps, so as to obtain pellets formed by an intimate mixture of UO.sub.2 and U.sub.3 O.sub.8 without isolated U.sub.3 O.sub.8 agglomerates. Then the green pellets are sintered at a temperature allowing consolidation to be obtained, usually from 1500.degree. to 1800.degree. C., when the sintering takes place in a reducing atmosphere, from 1200.degree. to 1350.degree. C. when the sintering takes place in a slightly oxidizing atmosphere. Different embodiments of the invention will now be given, it being understood that they are in no wise limitative. |
059600497 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 schematically represents an overview 10 of the functional components associated with the reactor power cutback system (RPCS)12. When in service and confronted with certain transients, the reactor power cutback system sends control signals to the control rod drive mechanisms 14, and interacts with the turbine control system 16, to stabilize the power of the NSSS at a reduced, but non-zero level. If the RPCS cannot stabilize the NSSS by a combination of turbine runback and adjustment of the regulating control rod groups, the RPCS trips one or more groups of control rods. For purposes of the present invention, a logic scheme is associated with the conditions under which a reactor power cutback system trip demand signal is generated at demand block 18, for processing in the RPCS 12. The processing in functional block 12 includes, for example, the control rod selection criteria 20, which in turn is dependent on NSSS data 22 supplied by sensors in the plant. Other calculated conditions of the NSSS are supplied from block 24, to the RPCS 12. The RPCS 12 is also subject to action taken at the reactor power cutback control panel 26, and alarms are generated by the RPCS 12 for display at the alarm section of the operator console at 28. FIG. 2 shows the pump selection logic circuit 100 for three main feedwater pumps, A, B, and C. This circuit can be divided into four functional sections: (1) the pump selection and enablement section 102; (2) the feedwater pump trip signal section 104; (3) the logic implementation section 106; and (4) the RPCS trip demand section 18. The function of the demand section 18 in FIG. 2 can, for purposes of the present description, be considered to be the same as the function of block 18 in FIG. 1. The section 102 has, for each main feed water pump A, B, and C, at least one switch 108, and preferably at least one more switch 110, by which the operator can select whether or not that particular pump is intended to be fully operational for normal power production in the plant. When fully operational, pump speed control above e.g., 5% plant power, would automatically be adjusted by an automatic feedwater control system (not shown). When not fully operational, the pump is either on but in standby, or off and out of service. Thus, the operator can designate which, if any, of the pumps have been intentionally disabled from automatically controlled operation. The automatic feed water control system controls the variables of pump speed and valve position to maintain a preset water level in the steam generators. Although not normally utilized in the operation of an NSSS, an operational pump could, under the manual control of the operator, in effect be in a "stand-by" condition, whereby the pump rotates at a minimum recirculation speed corresponding to the flow to the steam generators produced by the other pumps. In the illustrated embodiment, main feed pump A has associated therewith, a switch 108A which can be manually toggled to the start or stop position, at either the main panel in the plant control room, or locally at, for example, the motor control center associated with the feed pump system. "Start" corresponds to selection of the pump as intended for full operation. "Stop" designates disablement from full operation, i.e., "off" or in standby. As used hereinafter, "operational" means "fully operational". The logical condition of each switch 108A, 110A, is delivered to a pair of logical OR gates 112A, 114A, the outputs of which are delivered to a flip-flop circuit 116A. The output Q of the circuit 116A on line 118A, will be a logical "1" when the operator selects the start condition for pump A at either switch 108A or 110A. This logical "1" is delivered to AND gate 120A, which operates as an enabling latch, indicative of whether the particular pump status is intended to be operational. It should be appreciated that each of the main feed water pumps B and C has associated switches 108B and C; 110B and C; 112B and C; 114B and C; 116B and C; 118B and C; and 120B and C. Preferably, the status latches are also arranged with redundancy, such that the logical conditions at outputs 118A, 118B and 118C, are each delivered to a respective second AND gate 122A, 122B, and 122C. Thus, by way of example, if the operator manually selects the start condition for main feedwater pump A via either switch 108A, or 110A, latches 120A and 122A, will both be enabled, redundantly. The feedwater pump trip signal section 104, includes the three main feedwater pumps A, B and C indicated respectively 124A, 124B and 124C, each of which is responsive to inputs from the main control panel, as indicated at 126A, B and C, as well as from one or more feedwater control systems, indicated at 128. The feedwater control system 128 and associated control logic for generating a trip signal, form no part of the present invention. It should be appreciated, however, that for each pump such as 124A, a trip of that pump will result in the generation of two trip signals 130A, 132A, which are delivered to the latches 120A and 122A, respectively. In similar fashion, trip signals 130B, 132B and 130C, 132C are delivered to the latches 120B, 122B, and 120C, 122C, respectively. When the inputs to any particular latch gate 120A, B, C or 122A, B or C are both logical "1", a respective logical "1" output signal is generated on a respective line 134A, B or C, or 136A, B or C. The logic implementation section 106 includes a RPCS trip control gate 138, which under specified conditions, passes a RPCS trip control signal on line 142 to the RPCS system 18. Preferably, another RPCS trip control gate 140 is also present, from which a trip control signal is passed along line 144 to the demand block 18. Thus, in the preferred embodiment, the actual RPCS trip demand signal is not generated at 18 for delivery to the reactor power cut back system 12 (see FIG. 1), unless a trip control signal is present on both lines 142 and 144. The OR gate 138 receives signals from three AND gates 146, 148, and 150. If any one of these AND gates generates a logical "1" output, the gate 138 generates a control signal on line 142. Similarly, as part of the redundancy described above, the OR gate 140 will pass a trip control signal on line 144, if the output of any one of the AND gates 152, 154, or 156 is a logical "1". Each of the AND gates 146-156 will generate a logical "1" output signal, if and only if a logical "1" is input to the AND gate, from signals corresponding to the condition of two different pumps. It should be appreciated that the invention is especially significant in distinguishing between an initial condition wherein only two of the three feedwater pumps are intended to be in operation, from the condition wherein all three of the feedwater pumps are intended to be in operation. The OR gates 160-182 interposed between the AND gate arrays 120, 122 and 146-156, play a role in, for example, the generation of a RPCS trip demand signal if one of only two operational pumps is tripped, while inhibiting the generation of a trip demand signal, if only one of three operational pumps trips. In essence, the AND gates 146-156 require a two out of three pump trip condition in order to pass a logical "1" signal to OR gate 138, 140. If, for example, main feed pump A is not in operational service, i.e., is being used as a spare, it is considered equivalent to a tripped pump in a configuration where three pumps are intended to be in operation. Therefore, when both switches 108A, 110A are in the stop condition, the Q output signal at flip flop 116A is a logical "1" on line 158A. In this condition, the output signal Q is a logical zero, and therefore gate 120A is not enabled. Nevertheless, in order to achieve the desired generation of a trip control signal on line 142 (and line 144) when one of either pump B or C trips, the logic section 106 must produce the same output, as it would under the conditions of pumps A and B tripping during plant operation for which all three pumps A, B and C are intended to be operational. Therefore, the logical "1" from the Q output of the flip flop 116A is delivered to the OR gate 160, such that the logical "1" can be passed to the AND gate 146. If, in the example of a trip of pump B, the AND gate 120B passes a logical "1" through the OR gate 162 to the AND gate 146, gate 146 will pass a logical "1" to the OR gate 138, and on to the demand section 18 via line 142. In this manner, gate 146 is responsive to the condition of both pumps A and B. Due to the redundancy described above, gate 152 is similarly influenced by the condition of pumps A and B. Output of gates 146 and 152, will be a logical "1" if, and only if, (a) pump A or B is considered non-operational as a result of the "stop" settings in section 102, and a trip of pump B or A occurs, respectively; or, (b) pumps A and B are both intended to be operational as indicated by the "start" settings on the switches in section 102, and trip signals from both pumps A and B are generated. It can also be appreciated that, if all the pumps that are intended to be in operation, trip coincidentally, neither of the gates 138 or 140 passes a RPCS trip control signal to the trip demand section 18. Under this condition, the reactor will fully trip on low steam generator level, thereby reducing the power from fission essentially to zero, rather than merely cutting the power back to a lower but non zero value, as a result of the actuation of the RPCS 12. In NSSS with three main feedwater pumps, each provides about 33.3% of the feed water required for the steam generators, but with a maximum capacity of at least 50% each. The Reactor Power Cutback System according to the invention is preferably used in the following manner: ______________________________________ Power RPCS Plant Level Feedwater Status Status Operator Actions Response ______________________________________ 0 to One FW pump Out of Prior to raising If the 40% ON (running at service power above 5% operating operating speed, place Feedwater feedwater supplying water Control System in pump trips to the steam automatic. will likely generators); Operator will result in a second pump ON make selection of plant trip. but at standby pumps in (running at operation or minimum speed, standby via pump not supplying selection logic. water to the steam generators); third pump OFF. 40% Two feedwater Placed At approximately If one to pumps are ON in 40% power, the feedwater 70% running at service second FW pump pump at operating speed at will be placed in operating and the third ON approxi- service. The speed is in standby. mately operator will tripped, the 50% to choose the pumps speed of the 60% in operation at the second power. FW system operating control panel and feedwater the choices are pump will be recognized by the increased by RPCS selection the logic. feedwater control system. Depending on the initial power level, the RPCS will generate a trip demand signal to cut back power by dropping rods to quickly reduce power and will initiate turbine runback. If both feedwater pumps trip, the reactor will trip on low level in steam generator. 40% Two feedwater Placed At approximately If one pump to pumps ON and In 40% power the trips, RPCS 100% third OFF and service second pump will will generate out of service at be placed in an RPCS trip approxi- service. The demand mately operator will signal. If 50% to choose the pumps both FW 60% in operation at the pumps trip, power FW system the plant will control panel and trip. the choices are recognized by the RPCS selection logic. 70% All three In At about 70%, the If one pump to feedwater pumps service third feedwater trips, the 100% are ON and pump is placed in other two running at service and this is pumps will operating speed. recognized by compensate RPCS selection for the loss logic. of the third pump. If two pumps are lost, RPCS will generate an RPCS trip demand signal. ______________________________________ It can thus be appreciated from the foregoing description, that the RPCS is in service only when at least two feedwater pumps are in full operation and the feed water control system is in the automatic mode. The conventional RPCS (inventive RPCS) is always in service when the reactor power is at least 50% (50%-60%), and the feedwater control system is in the automatic mode. The feedwater control system is always on, when power is at least 50%. This relationship between the reactor power cut back system and the feedwater control system can be implemented in a variety of ways. Preferably, the RPCS will automatically sense (without operator intervention) from the feedwater control system, which of the feedwater pumps are intended to be operational. Therefore, the switch means for manually selecting which of the pumps are intended for pumping operation and designating which of the pumps have been disabled from pumping operation, can be the same switch means used by the operators at the control panel, for placing pumps in service. As the power level passes 50% and the RPCS is placed in service, the RPCS will "read" the pump status as previously selected by the operator. Alternatively, the RPCS could be designed such that as the power level increases through approximately 50%, and the RPCS is placed in service, the operator manually selects via switches dedicated to the RPCS, which of the feedwater pumps are intended to be operational. It should also be understood that the functionality described above can be implemented in a variety of ways that would be readily available to one of ordinary skill in this field of technology. For example, programmable logic controllers, or other programmed logic via computer software, may be substituted. |
description | This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2002-347795 filed on Nov. 29, 2002, the entire contents of which are incorporated herein by reference. The present invention relates to a multi-slice X-ray CT apparatus. X-rays being irradiated to a patient by an X-ray CT apparatus that reconstructs image data from the penetration data is known. With a multi-slice X-ray CT apparatus, it is possible to collect two or more slices of data at once from different positions (multi-slice scanning), using the X-ray detector which has two or more segments of detection elements, such as a combination of a scintillator and a photodiode, which detects the X-rays. By using the multi-slice scan (it is also called a cone beam scan) together with a helical scan, data from a large scanning range can be collected in short time, and the multi-slice X-ray CT apparatus has become popular. When using the multi-slice scan together with a helical scan, an important issue is the reduction of the X-ray dose. For example, Japanese Patent Publication (Kokai) No. 2002-17716 and Japanese Patent Publication (Kokai) No. 10-248835 describe that a scanning range is set on a scanogram to include an object, such as an internal organ of a patient, an opening of a collimator is set according to the scanning range and a scan is performed of the internal organ. However, in fact, a part of the internal organ may not be included in the scanning range. As a result, insufficient data may be collected and a repeated scan may be necessary. The purpose of this invention is to offer a multi-slice X-ray CT apparatus that reduces the X-ray dose received by a patient. In order to ameliorate the above problem, according to one aspect of the present invention, there is provided an X-ray CT apparatus, including: at least one X-ray irradiation source configured to irradiate X-rays to a volume of interest; at least one X-ray detector including a plurality of detection element segments configured to detect the X-rays penetrated through the volume of interest; at least one collimator configured to create an opening that is movable at least in a slice direction and a channel direction; at least one image processing part configured to generate volume data from the detected X-rays and to extract a portion of the volume data corresponding to the volume of interest; at least one controller configured to set the opening of the at least one collimator to a second opening size to irradiate a second scanning range corresponding to the portion of the volume data and configured to perform a second scan of the second scanning range; and at least one reconstruction part configured to reconstruct image data based on data collected by the second scan. Additionally, an X-ray CT apparatus is provided that includes: at least one X-ray irradiation source configured to irradiate X-rays to a volume of interest; at least one X-ray detector including a plurality of detection element segments configured to detect the X-rays penetrated through the volume of interest; at least one collimator configured to create an opening that is movable at least in a slice direction and a channel direction; at least one image processing part configured to generate volume data from the detected X-rays and to extract a portion of the volume data corresponding to the volume of interest; at least one reconstruction part configured to reconstruct image data based on data collected by a second scan, wherein the at least one collimator comprises, a plurality of movable collimator blades configured to create the opening, and a plurality of auxiliary blades configured to create a slit corresponding to detection element segments other than detection element segments corresponding to the opening. The present invention also relates to an X-ray CT apparatus, including: at least one X-ray irradiation source configured to irradiate X-rays to a volume of interest; at least one collimator including a first opening configured to transmit the X-rays and a second opening that is more distant than the first opening from a center of the X-rays in both slice and channel directions; at least one X-ray detector including a plurality of detection element segments configured to detect the X-rays that pass through at least one of the first opening and the second opening and that penetrate through the volume of interest; and at least one reconstruction part configured to reconstruct image data based on data collected using the X-rays detected by the at least one X-ray detector. The present invention also provides a method for reconstructing image data based on data collected by an X-ray CT apparatus that includes at least one X-ray irradiation source configured to irradiate X-rays to a volume of interest, at least one collimator including a first opening through which the X-rays pass and a second opening that is more distant than the first opening from a center of the X-rays in both slice and channel directions, and at least one X-ray detector including a plurality of detection element segments configured to detect the X-rays that pass through at least one of the first opening and the second opening and that penetrate through the volume of interest, the method including: reconstructing image data around the volume of interest based on the X-rays that pass through the first opening; and reconstructing peripheral image data around the image data based on the X-rays that pass through the second opening. With reference to the drawings, the first non-limiting embodiment of an X-ray CT apparatus of the present invention will be explained. There are many types of X-ray CT apparatus, such as a rotation/rotation type where an X-ray tube and an X-ray detector rotate around a patient as one unit. Another type of X-ray CT apparatus is a fix/rotation type where a plurality of detection elements are arranged in a ring shape and an X-ray tube rotates around a patient. The invention may be applied to each type of X-ray CT apparatus. Hereinafter, a rotation/rotation type X-ray CT apparatus is explained as one example. A mechanism for changing an incidence X-ray into an electric charge is mainly grouped into a direct conversion type and an indirect conversion type. In the direct conversion type, the X-ray is changed into an optical signal by a fluorescent substance, such as a scintillator, and the optical signal is changed into the electric charge. The indirect conversion type uses a photoconduction phenomenon where a pair of an electron and a hole in a semiconductor is generated by the X-ray and the electron and the hole move to corresponding electrodes. As the X-ray detector, each type may be used. Hereinafter, the indirect type X-ray detector is explained as one example. In addition, in recent years, a so-called multi-tube type X-ray CT apparatus that includes a plurality of pairs of X-ray tubes and X-ray detectors located in a rotation frame is developing as a commercial product, and surrounding technology is also progressing. The present invention may be applied to a single tube type X-ray CT apparatus or the multi-tube type X-ray CT apparatus, as well as other equivalent devices. Hereinafter, the single tube type X-ray CT apparatus is explained as a non-limiting example. FIG. 1 is a block diagram showing the composition of the X-ray CT apparatus of the first embodiment of the present invention. The X-ray CT apparatus has a gantry 100. The gantry 100 has a ring shaped rotation frame 102 that is rotatable around a rotation center axis RA. An X-ray tube 101 is located in the rotation frame 102, and an X-ray detector 103 is located at an opposite side in the rotation frame to the X-ray tube 101 so as to place the rotation center axis is therebetween. The X-ray detector 103 can be used for a multi-slice scanning. That is, the X-ray detector 103 has a plurality of detection element segments that are arranged along a direction parallel to the rotation center axis (slice direction). The number of the detection element segments is 64 segments, for example. It is assumed that a detection width of each detection element in the slice direction is 0.5 mm as a corresponding value on the rotation center axis RA. Each detection element segment has a plurality of detection elements arranged along a channel direction. In addition, it is assumed that a Z-axis is set as the rotation center axis RA, and a XY coordinate system is a rotation coordinate system centering on the Z-axis. In this case, an X-ray center axis that connects a focus of the X-ray tube 101 and a center of the X-ray detector 103 is defined as the Y-axis, and an axis that is perpendicular to the Y-axis and the Z-axis is defined as the X-axis. These X, Y, and Z-axes are used suitably below. A collimator 108 is located between the X-ray tube 101 and the rotation center axis RA. The collimator 108 is attached to an X-ray radiation window of the X-ray tube 101. The collimator 108 is used as an X-ray limiting device that arbitrarily trims a position and a size of the X-ray generated on the focus of the X-ray tube 101 and irradiated from the X-ray radiation window, and is called an X-ray diaphragm. The collimator 108 has a plurality of members for blocking the X-ray, such as four collimator blades 11 through 14 that are respectively movable along the X or Y-axis, as shown in FIG. 5. The collimator is controlled by a collimator driving unit 107. A data collection circuit 104 referred to as DAS (Data Acquisition System) is connected to the X-ray detector 103. The data collection circuit 104 changes the output (current signal) of each channel of the X-ray detector 103 into a voltage signal, amplifies the voltage signal, and converts the voltage signal into a digital signal. A pre-processing unit 106 that corrects non-homogeneity between channels of the DAS outputs, etc. is connected to the DAS 104 via a non-contacting type data communication unit 105 using light or magnetism as a medium. The data on which the pre-processing is executed is stored in a memory storage 112. The memory storage 112 is connected to a system controller 111 via a data/control bus as well as to an image reconstruction unit 114 for reconstructing an image based on projection data, a display 116, an input unit 115 including a pointing device, such as a mouse, and a keyboard device, an image-processing unit 113 and a scanning controller 110 for controlling the gantry 100 and a high-voltage generating unit 109. FIG. 2 shows a flow of a series of processes of the non-limiting first embodiment. First, a scanogram is taken (Step S1). An imaging of the scanogram is then performed as rotation of the rotation frame 102 stops, the X-ray is generated continuously, a signal is repeatedly read from the X-ray detector 103 at a fixed cycle, and a bed plate moves at a constant speed. Based on the data collected by the scanogram imaging, scanogram data is created in the image-processing unit 113, and the created scanogram data is displayed on the display 116 (Step S2). An operator sets a scanning range (first scanning range) shown in FIG. 3 on the displayed scanogram with the input unit 115, and a first scanning condition is also set up (Step S3). In this embodiment, helical scanning is performed at least twice. The first scan is performed for scanning a large area by low resolution, and the second scan aims at scanning a narrow area in which an object internal organ is targeted by high resolution. The first scan is clearly distinguished from the second scan. The first scanning range may, as an example, be a cylinder form, but is set up as a rectangle for showing a main section on the scanogram. For the first scanning range to include a body width of the patient, a radius (FOV) is set in the range of 300 to 500 mm, for example. In addition, the first scanning range is set comparatively long in the body axis direction (slice direction) to include both an object internal organ, such as a heart, and a surrounding internal organ. Moreover, as the first scanning condition, 32 through 64 detection element segments that are comparatively more segments from 64 detection element segments are selected and used. In addition, a helical pitch (a plate movement distance per rotation) is set up comparatively fast, such as in the range of 8 to 32 mm. Additionally, in the first scanning, a tube current value is set as regulation value corresponding to low X-ray dose comparatively by the system controller 111, and in order to compensate for sensitivity decrease by the low X-ray dose, the number of views per rotation is set as 500. The setting range or the regulation value is set by the system controller 111. The first scanning is performed by the scanning controller 110 under the first scanning condition to the first scanning range (Step S4). In the first scan, as shown in FIG. 5A, the opening of the collimator 108 is set in the X-direction by the width according to the comparatively large diameter of the first scanning range, and is set in the Z-direction by the comparatively long length according to slice width and the number of the segments. That is, a fan angle of the X-ray is set according to the diameter of the first scanning range and a cone angle of the X-ray is set according to the length of the first scanning range. Based on the projection data of the first scanning range collected by the first scanning, the reconstruction unit 114 performs reconstruction processing (Step S5). Volume data covering a comparatively large area according to the first scanning condition is generated by comparatively low resolution. For example, a cone-beam reconstruction method may be adopted as the reconstruction processing method. The cone-beam reconstruction method uses an approximate 3-dimensional reconstruction algorithm that is obtained by expanding a mathematically accurate fan-beam reconstruction algorithm (2-dimensional plane) to the Z-axis direction. In the cone-beam reconstruction method, a weighted coefficient corresponding to the Z-coordinate is multiplied by the projection data, and a convolution processing is performed between the weighted data and the same reconstruction function as the fan beam data is applied. Eventually, as a back projection processing, the convolution data is back-projected on a path (from the focus to the channel of the detector) which the X-ray passes, and the back projection processing is repeated for 360°. One such cone-beam reconstruction method is known as the Feldkamp reconstruction method, which extends a reconstruction processing method of a conventional scanning method. The volume data is used for diagnosis of the object internal organ, the surrounding internal organ and a tissue structure in a large area, and may also be used for setting the scanning range of the second scanning (second scanning range). The image-processing unit 113 extracts an area of the object internal organ, such as the heart (by way of non-limiting example), from the volume data, and a 3-dimentional image (3D image) is created and displayed on the display 116 (Step S6). As the 3D image, a surface image or wire frame image is suitable, as shown in FIG. 4. The operator operates the input unit 115 and arbitrarily rotates the 3D image on a screen to set the second scanning range (having an approximate cylinder form) covering the area of the heart in all directions (Step S7). In fact, in consideration of the expansion and contraction movement of the heart, the second scanning range is set larger than the area of the heart, to include a margin. Although it has been explained that the second scanning range is set on the 3D image, instead of or in addition to the 3D image, an MPR (Multi-Planar Reconstruction) image, such as three tomographic images (axial, coronal, and sagittal images), may be created from the volume data or from the data of the extracted heart area, and the second scanning range may be set on the tomographic images. Moreover, although it has been explained that the second scanning range is manually set by the operator, the diameter and the length of the second scanning range may be automatically set to include the extracted heart area. In this case, in order to include the above-mentioned margin, expansion processing is performed on the extracted heart area by a predetermined ratio, and the second scanning range is set up to the expanded heart area. The radius (FOV) of the second scanning range is set, for example, in the range of about 50 to 150 mm, so that the heart area (object internal organ) is included, and the second scanning range is set up in the body axis direction (the slice direction) to be comparatively short, so that the heart area is limited with the above-mentioned margin. Additionally, as the second scanning condition, the number of detection element segments used in the second scan is set comparatively few (i.e., 4–16 segments from 64 segments), and the helical pitch is set, for example, to about 0.5–2.0 mm, corresponding to the comparatively slow plate movement. Moreover, in the second scan, the tube current value is set as the regulation value corresponding to the comparatively high X-ray dose by the system controller 111, and the number of views per rotation may be set as approximately 1000. The setting range or the regulation value is set by the system controller 111. In addition, although it has been explained that the number of detection element segments is selected from the range of about 4–16 segments in the second scan, the number of detection element segments is determined by the limit of the fan-beam reconstruction. Although the cone-beam reconstruction method includes the correction processing about a cone-angle as mentioned above, the accuracy of the correction cannot be enough, and an artifact may appear. Therefore, although there is little influence on a comparatively low resolution scan like the first scan, the influence cannot be ignored at a comparatively high resolution scan like the second scan. Therefore, the cone-beam reconstruction method should not be used substantially, and the fan-beam reconstruction method (the fan-beam reconstruction which is used together with the helical filter interpolation method (HFI) is adopted) is adopted. Since the cone-angle is not corrected in the fan-beam reconstruction method, artifacts caused by the cone-angle can occur. The limit for preventing the artifacts caused by the cone-angle from having significant influence is 16 segments (8 mm), for example, and the maximum of the number of used segments is restricted to 16 segments, for example, in the second scan conditions. The second scan is performed under the second scanning condition to the second scanning range (Step S8). In the second scan, as shown in FIG. 5B, the opening of the collimator 108 is set in the X-direction by the width according to the comparatively small diameter of the second scanning range under the control of the scanning controller 110, and the opening is set in the Z-direction by the comparatively narrow length according to the slice width and the number of the segments. That is, the fan-angle of the X-ray is set up according to the diameter of the second scanning range, and the cone-angle of the X-ray is set up according to the length of the second scanning range. If necessary, by using a shift function in Y-direction of the X-ray tube 101 and the X-ray detector 102 and by increasing the number of the channels of the second scanning range to more than before or the maximum, the resolution can be improved. Although the X-ray tube 101 and the X-ray detector 103 rotate around the patient, the center axis of the second scanning range that is set for the object internal organ, such as the heart, may shift from the rotation center axis RA of the rotation frame 102. If the rotation frame 102 rotates when the position of the opening of collimator 108 is fixed, it is difficult to scan the second scanning range. To ameliorate this problem, as shown in FIG. 6 and FIGS. 7A–7D, according to a shift direction and a shift distance of the center axis of the second scanning range to the rotation center axis RA of the rotation frame 102, when the width of the opening of collimator 108 is fixed, the center position of the opening is moved in the X-direction according to the rotation of the X-ray tube 101. When the height and the right-left position of the bed plate is controlled by the system controller 111 so that the center axis of the second scanning range corresponds to the rotation center axis RA of the rotation frame 102, it may not be necessary to move the center position of the opening of the collimator 108 according to the rotation of the X-ray tube 101. Based on the projection data of the second scanning range that is collected by Step S8, the reconstruction processing is performed in the reconstruction unit 114 (Step S9). Since data in an external range of the second scanning range is not collected in the second scan, the external image cannot be reconstructed. Therefore, the external data of the second scanning range is compensated by the data collected in the first scan as shown by a distribution of the projection data of the view in FIG. 8. As mentioned above, the fan-beam reconstruction method that is used together with the helical filter interpolation method (HFI). In the helical filter interpolation method, as shown in FIG. 8, a weighted filter function where a weighted coefficient decreases gradually according to the distance from a reconstruction position is convolved to the data collected in a plurality of separated positions near the reconstruction position by each view, and the total is treated as the data on the reconstruction position. When the helical filter interpolation method is used, an effective slice width is given as a total distance of separated positions for the interpolation. In order to improve slice resolution by making the effective slice width as thin as possible, as shown in FIG. 9, it is desirable to set the helical pitch at N times (where N is not an even number) the pitch (slice pitch) of the detection element segment, so that an orbit of the detection element segment is located between previous orbits of detection element segments. In FIG. 9, it is shown that N=1.5, for example. As for the external data of the second scanning range that is collected in the first scan, the data on the reconstruction position is calculated by the helical filter interpolation method based on the data collected by the first scan on a plurality of separated positions near the reconstruction position. In addition, since the X-ray dose is different between the first scan and the second scan, it is desirable to correct the data collected by the first scan or the data calculated by the helical filter interpolation method according to the X-ray dose ratio. Moreover, although data of the view that is collected by the first scan but not by the second scan exists, the data is compensated by the data of the nearest view or the data calculated from data of several near views as the data of the second scan. Although it has been explained that the external data of the second scanning range, which is not collected in the second scan, is compensated by the data collected in the first scan, the external data of the second scanning range may be compensated by the data collected in the scanogram scan (Step S1). Otherwise, the external data of the second scanning range may be assumed based on the internal data of the second scanning range that is collected in the second scan, such as the data that is averaged between the most outside part data within the second scanning range. In a heart inspection, an electrocardiographic synchronization method may be used together with the fan-beam reconstruction method. In the electrocardiographic synchronization method, while the scan is repeated over several heart beats, the projection data is stored in relationship to electrocardiographic data collected from the patient. The projection data close in phase to each other are read out among the data from several heart beats, and the image is reconstructed based on the readout projection data of (360°) or (180+the fan-angle degrees). By using the electrocardiographic synchronization method, the influence of the movement caused by the heart beat on the quality of the image can be reduced. The reconstruction processing is repeated on several reconstruction positions, eventually the volume data is created, and the 3D image, the MPR image, or other arbitrary image is created based on the volume data and displayed in the image-processing unit 113 (Step S10). In the above reconstruction method, the external data of the second scanning range is not collected in the second scan and the external data is compensated by the data collected by the first scan, etc, which is called as “Method A.” In the non-limiting embodiment, the following “Method B” may be adopted as an alternative to the method A. In method B, the external data is collected in the second scan in addition to the internal data. In order to reduce the X-ray dose, although the internal data of the second scanning range is collected at high X-ray dose, the external data of the second scanning range is collected at low X-ray dose. Some non-limiting examples are described below. A collimator shown in FIG. 10A has two collimator blades 11 and 12 that are used to limit the X-ray in the Z-direction and that include a lead member which is thick enough to block the X-ray. In addition, the collimator has other two collimator blades 15 and 16 that are used to limit the X-ray in the X-direction and that include a member whose attenuation coefficient is lower than that of lead, such as an Mo member or an alloyed metal member including lead. The collimator blades 15 and 16 block the X-ray in moderation. Thus, the high dose X-ray goes directly through the opening of the collimator 108 and is irradiated to the second scanning range, and the low dose X-ray attenuated by the semi-block collimator blades 15 and 16 is irradiated to the external area of the second scanning range. When the image is reconstructed, an X-ray dose correction is performed to the external data of the second scanning range, and the corrected external data and the internal data are used for the fan-beam reconstruction method with the HFI method. As another example, a collimator shown in FIG. 10B has two collimator blades 11 and 12 that are used to limit the X-ray in the Z-direction and has four collimator blades 17 through 20 that are movable in the X and Z directions for blocking the X-ray. The four collimator blades 17 through 20 are set on a position in the X-direction corresponding to the second scanning range, and are set at such a position in the Z-direction that a slit narrower than a central opening corresponding to the second scanning range is created. For instance, if the central opening is 8 mm (=0.5 mm×16 segments), the slit is created as 2 mm (=0.5 mm×4 segments). While the high dose X-ray directly passes through the opening of collimator 108 to the second scanning range, the thin X-ray limited by the slit is irradiated to the external area of the second scanning range. When the image is reconstructed, an X-ray dose correction is performed to the external data of the second scanning range, and the corrected external data and the internal data are used for the fan-beam reconstruction method with the HFI method. As another example, a collimator shown in FIG. 10C has a plurality of movable collimator blades 11 through 14 that create a central opening, and has a plurality of movable auxiliary blades 21 and 22, which create a slit corresponding to a part of detection element segments (four segments close to the outside) other than the central 16 detection element segments. That is, in addition to the four collimator blades 11–14 for limiting the X-ray in the Z-direction, the L-shaped two auxiliary blades 21 and 22 for blocking the X-ray block a central portion of the X-ray and open the peripheral part. The two auxiliary blades 21 and 22 are respectively movable in both X and Z directions, and shifted in the Y-direction so that it is possible to partially overlap on the central part. By adjusting the overlapped area on the central part, it is possible to arbitrarily change the central block area width. In the Z-direction, by adjusting the position of the four collimator blades 11 to 14, it is possible to open the slit at an arbitrary width out of the four collimator blades 11 to 14. Thus, the two auxiliary blades 21 and 22 are set at such a position in the X-direction that the area has the same width as the opening created by the four collimator blades 11 to 14, and are set on such a position in the Z-direction that the slit narrower than the opening according to the second scanning range is created on the peripheral part. For example, if the opening created by the four collimator blades 11 to 14 according to the second scanning range is 8 mm (=0.5 mm×16 segments), the slit created by the auxiliary blades outside of the second scanning range is 2 mm (=0.5 mm×4 segments). Thus, the high dose X-ray goes directly through the opening created by the four collimator blades 11–14 to the second scanning range, and the two thin split X-rays limited by the auxiliary blades 21 and 22 are irradiated to the external area of the second scanning range. When the image is reconstructed, the external data and the internal data are used for the fan-beam reconstruction method with the HFI method. Since the external data of the second scanning range is shifted from the internal data in the Z-direction, the quality of the image may decrease near a border between the external and internal area. However, since the second scan is primarily used for an increasingly accurate diagnosis of the object internal organ and the external area of the second scanning range is not used for the diagnosis usually, there is substantially little negative influence. In method B as well as method A, even if the center axis of the second scanning range is shifted from the rotation center axis RA of the rotation frame 102, as shown FIG. 11A to 11D, it is possible to continuously irradiate the high dose X-ray to the second scanning range by moving the collimator blade in the X-direction according to the rotation and by moving the irradiation range of the high dose X-ray to the second scanning range. It has been explained that the second scanning range is set as a cylinder form including the object internal organ, such as the heart. However, as shown in FIGS. 12 and 13, the diameter of the second scanning range may be changed according to the size of the object internal organ in the Z-direction. For example, the second scanning range may be set as a group of small cylinders, each of which has the length of the detection element segment pitch multiplied by the number of the segments, and the width of the opening of the collimator 108 may be changed according to the relative movement of the gantry 100 to the patient in the Z-direction by the helical scan in order to reduce the X-ray dose. In the non-limiting embodiment, the X-ray dose can be reduced in the multi slice X-ray CT apparatus. Another non-limiting exemplary modification of the above mentioned embodiment is explained referring to FIG. 14. A collimator of the modification has a slit A in a center area for imaging the object internal organ, such as the heart, and has a plurality of movable auxiliary blades 21′ and 22′ for imaging a peripheral part of the object internal organ. An X-ray going through the slit A is irradiated to 16 central detection element segments, and an X-ray going through the slit B is irradiated to 4 detection element segments that are adjacent to the slit A in the slice direction and that have wider range in the channel direction than that of the slit A. The image reconstruction unit 114 reconstructs the image data of the object internal organ, such as the heart of the patient, from data collected based on the X-ray which goes through the slit A, and reconstructs the image data of the peripheral part of the object internal organ, such as the heart of a patient, from data collected based on the X-ray which goes through the slit B. Image processing is performed by the image-processing unit 113 so that the image from the both image data is smoothly connected, and the image is displayed on the display 116. The present invention may not be limited to the above embodiments, and various modifications may be made without departing from the spirit or scope of the general inventive concept. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced differently than as specifically described herein. Although the above embodiment and modification includes various steps or various elements, several steps or elements may be arbitrarily selected. For instance, some steps or elements described as the embodiment or modification may be omitted. |
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059463660 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a wall, in particular a bottom part, of a core melt collection space which is disposed in a reactor building, for example as in FIG. 11 of German Published, Non-Prosecuted Patent Application DE 43 39 904 A1, corresponding to U.S. application Ser. No. 08/651,307, filed May 22, 1996. Structural concrete 2 defining a wall 1 supports a layer part 3 made of refractory concrete, which is laid out in the form of prefabricated blocks 5. The blocks 5 are jointed together by engaging above one another along joints 6 with projections 7 and 8 which are offset in height. A layer part 10 which is seated on the layer part 3, is formed of ceramic bricks, in particular ZrO.sub.2 bricks 11. The ceramic bricks 11 are likewise jointed together by engaging with a tongue 12 in a groove 13 of the neighboring brick 11 in each case. An anchoring 15 of the blocks 5 to the structural concrete 2 is seen in FIG. 2 to include a threaded bushing 17 which is screwed onto a steel reinforcement 18 embedded in the structural concrete 2. A screw 19 engages from the top in the screw-threaded bushing 17 and presses a washer 20 against a surface 21 of the block 5 at the bottom of a hole 22 in the block. The hole 22 is closed off at the top by a zirconium dioxide screw plug 23. As a result of the jointing, that is to say the mutual engagement of the tongue and groove, the ceramic bricks 11 of the layer part 10 only need to be fastened to the layer part 3 at a few points. To this end, steel anchors 25 are embedded in particular individual blocks 5. The steel anchors have a screw-threaded bore 26 into which screws 27 can be screwed. The anchors 25, which may also be made of ceramic in this case, press a washer 28 against a surface of the ceramic brick 11 at the bottom of a hole 29 in the ceramic brick. The hole 29 is subsequently closed off in a leak-tight manner with a screw-threaded plug 30 made of zirconium dioxide. In the embodiment according to FIGS. 4 and 5, the layer parts 3 and 10 are fastened to the structural concrete 2 with ceramic anchors 32, but in all other respects are composed of blocks 5 and jointed bricks 11 in the same way as in the embodiment of FIG. 1. The ceramic anchors 32 contain a screw-threaded sleeve 33 into which a screw-threaded stem 35 of a steel screw-reception piece 34 is screwed. The screw-reception piece 34 has a rectangular profile in cross-section and carries a ceramic sleeve 36 for reducing thermal loading. Particular individual bricks 11 are then once again fastened with screws 27 in a screw-threaded bore 37 which leads to the upper side. As in FIG. 3, these screws 27 engage in a hole 29 and are covered with a screw plug 30. FIG. 6 shows an embodiment of a common fastening 40 of particular individual bricks 11 of the layer part 10 and of blocks 5 of the layer part 3, which is represented on an enlarged scale in FIG. 7. The common fastening 40 includes a metal anchoring screw 41 which has a baseplate 42 and extends through a block 5 and a brick 11 lying on top. An upper side of the block 5 has a diametrically enlarged hole 43 in which a ceramic sleeve 44, optionally with an inner metal lining, is seated as a nut and presses on the block 5 at the bottom of the hole 43. If the ceramic sleeve 44 is to be used only for thermal insulation and will not be mechanically stressed, then it is possible to use a separate nut which will be covered only by the ceramic sleeve 44 after tightening. The anchoring screw 41 furthermore extends through the brick 11 into a hole 46. There the anchoring screw 41 carries a nut 47 which presses on the brick 11 at the bottom of the hole 46. After the nut 47 is tightened, the hole 46 can be closed off with a zirconium dioxide plug 48 which is screwed, by a screw-threaded bush 49, onto that end of the anchoring screw 41 which protrudes above the nut 47. FIG. 8 shows that the tongue 12 of the brick 11 protrudes in two mutually perpendicular directions from a shape which is cubic in principle. Accordingly, the groove 13 is also drawn in two mutually perpendicular directions. The jointing which results therefrom is represented in FIG. 9. The jointing achieves the effect that one fastening point 40 suffices for more than one brick 11, in particular nine or more bricks 11. Direct fastening of each individual brick is likewise possible. FIG. 10 shows that, despite the jointing, the bricks 11 can also be fastened with a steel rail 50 which has a T-shaped cross-section. The bricks 11 are fitted onto the steel rail 50 through the use of a groove 51, which likewise has a T-shaped cross-section. The steel rail 50 is fastened to an anchoring plate 52 which is embedded in the upper side of particular individual blocks 5 and is fastened with anchoring rods 53. The anchoring plate 52 extends in the direction perpendicular to the plane of the drawing. Like the fastening 40 represented in FIG. 9, the anchoring plate 52 is only disposed on a few bricks 11, so that nine or more bricks are fastened through the use of one anchoring plate 52. In the embodiment according to FIG. 11, the bricks 11 have a profile with a T-shaped cross-section. The T-shaped cross-section has a projection 55 with a height being equal to that of an undercut 56, so that the bricks 11 can be stacked in each other by alternate rotation. Each brick 11 has a base adjoining the lower part 3. The bases of the bricks 11 of every other row contain an anchor 57 with a widened T-shaped head piece 58 which protrudes from the brick. The head pieces 58 of the anchors 57 are inserted into a rail 59 with a C-shaped profile in the underlying block 5. In this way, the bricks 11 with the anchors 57 are fixed and at the same time they hold down a neighboring row of bricks 11, which do not have anchors 57, through the use of their projection 55. As has been explained with reference to FIG. 8, the projections 55 and the undercuts 56 may also extend in two mutually perpendicular directions. This undercutting of the projections 55 in the case of T-shaped bricks 11 which alternate (that is to say they are respectively rotated through 180.degree.) is shown in FIG. 12 in a similar manner to FIG. 8. The pattern of the bricks 11 which results from this configuration is represented in FIG. 13. Thus, as is seen in a direction perpendicular to the rail 59, every other brick 11 is anchored with a corresponding rail 59. FIG. 14 is an enlarged, longitudinal-sectional view showing one way of anchoring neighboring bricks 11, in which a ceramic anchor 32 is embedded in the layer part 3 made of refractory concrete. This anchor may also be twisted in or screwed. The ceramic anchor 32 engages at a meeting point of four adjoining bricks 11, as a tongue in a respectively corresponding groove in the bricks 11. In this case the bricks 11 are constructed as represented in FIG. 8, with a corresponding modification only being made at the point where the anchor 32 engages. To this end, each brick 11 has a hole at a corner point in which one quarter of the anchor 32 is received. Four bricks 11 thus enclose one anchor 32 and are thereby fixed. The anchor 32 has a double-T profile and is fastened in the layer part 3 by a split steel washer 20 which is screwed to the layer part 3. The anchor 32 may also be directly embedded in the layer part 3. It is likewise possible to construct the anchor 32 as a rail similar to the rail 59 represented in FIG. 11 and in FIG. 13. FIG. 15 and FIG. 16 respectively show a longitudinal section and a plan view of a connection of blocks 5 of the layer part 3 made of refractory concrete. A metal plate 24 which is disposed on an end surface 16 of a block 5, extends along the end surface 16 and is securely fastened to the block 5 by four steel anchors 25. A hole 31 which is provided in a region between the steel anchors 25 is open towards the top, that is to say towards the layer part 10, and a screw 19 is fed through the plate 24 in the hole 31. Two neighboring blocks 5 respectively abut at their plates 24, so that the screw 19 is fed through both plates 24 and is firmly tightened with a nut 47. In this way, the two plates 24, and therefore the two blocks 5, are securely connected to each other. A pocket which is formed in the refractory concrete by virtue of the corresponding holes 31 in the two blocks 5 can be closed off with a non-illustrated ceramic plug. The use of such a connection between blocks 5 of the layer part 3 also permits only particular individual blocks to be connected to the structural concrete 2 lying underneath the blocks 5. The invention is distinguished by a multilevel protective layer which is disposed, in particular, on the bottom part of the collection chamber. A first layer part, made of refractory concrete, is constructed in the form of prefabricated blocks and extends over the structural concrete of the collection chamber. Fastening of the blocks to one another and/or interlocking of the blocks by virtue of mutually engaging projections leads to fastening of the blocks to the structural concrete at a few individual points, so that only a few blocks are securely connected directly to the structural concrete, for example by corresponding anchors. A layer part which is formed by virtue of mutual engagement of likewise prefabricated ceramic bricks lies on top of the layer part made of refractory concrete, and is likewise securely connected to the latter only at particular individual ceramic bricks. This produces decoupling of the fastening of the individual layer parts, which effectively prevents the danger of core melts penetrating along the fastening points in the structural concrete. A simple assembly of the protective layers is furthermore achieved. The embodiments which have been described, or other embodiments, can be combined with each other. |
description | This application is filed under 35 U.S.C. §371 from International Application No. PCT/IL01/00475, bearing an International Filing date of May 24, 2001. This invention relates to semen analysis. According to WHO statistics, 8-10% of all married couples consult medical professionals after failing to conceive. Over 40 million couples are currently being treated for infertility. Among these infertile couples, it is estimated that the infertility in 40% of the couples is due to male originating causes, and another 20% is due to combined male and female originating causes. Semen analysis is a major technique in evaluating male originating causes. Standard semen analysis protocol involves the determination of at least three major semen parameters: 1. total sperm concentration (TSC); 2. percentage of motile sperm; and 3. percentage of normal sperm morphologies. For all practical purposes, semen analysis, a key factor in human male fertility medicine, has not changed since the 1930's and is still done today by microscopic inspection. In fact, it is one of the very few remaining in vitro, body fluid analysis still performed almost solely via manual methods. This manual methodology involves carefully observing the sperm cells, counting them to determine their concentration, classifying their motility, identifying their morphology, etc. This work requires high expertise, is very labor intensive and if done according to standard protocols, takes at least an hour per test. Manual assessments are known to be quite inaccurate due to numerous sources of error. The main sources of error are: Subjectivity of the observer. The varying criteria used in the different labs and by different observers. The large statistical errors due to the limited number of sperm analyzed. The WHO manual (WHO laboratory manual for the examination of human semen and sperm-cervical mucus interaction. 4th edition, Cambridge University Press, 1999) recommends observing not less than 200 sperm and classifying the morphology and motility of each. This itself is an error introducing procedure due to the tediousness and time consuming nature of the task. In practice, 50 to 100 sperm cells at most are analyzed. Even if the observer introduces no errors, the statistical error alone reaches tens of percentages. As a result of the above methodology, semen analysis test results are globally recognized to be highly subjective, inaccurate and poorly reproducible. Inter lab and inter technician variations are of such proportions that this issue is of major concern in male fertility medicine and the unresolved subject of discussion in the vast majority of symposiums, congresses and conventions on the subject. In order to overcome these difficulties, medical instrumentation companies have introduced dedicated computerized systems based on image analysis (CASA—Computer Assisted Semen Analyzers). These systems require an extremely high quality image because all their results are based on image processing. Although these systems have attempted to replace manual analysis and establish industry accepted standards, they have not succeeded in either of these objectives. The first objective could not be achieved because analysis results continue to be dependent on manual settings and on the different makes of equipment. Replacing routine manual analysis is totally impracticable because the systems are extremely expensive, complex and difficult to use. The fact is that such systems are generally not found in routine semen analysis but have rather established their niche almost solely in research centers, university hospitals and occasionally in highly specialized fertility centers. An additional approach for semen measurements is described in U.S. Pat. Nos. 4,176,953 and 4,197,450, whose entire contents are incorporated herein. These patents describe a method for measuring sperm motility using electro-optical means and an analog signal analyzer. A suspension of sperm cells is continuously examined in a predetermined field in order to detect variations in optical density by the motion of the sperm. An amplitude-modulated analog electrical signal is generated in response to the variations, and the peaks and valleys of this signal are counted over a predetermined time period to provide an abstract parameter termed Sperm Motility Index (SMI). This parameter is related to motility and gives readings which are proportional to the number of motile cells multiplied by their respective velocity. An automatic sperm analyzer called the Sperm Quality Analyzer (SQA), which provides the SMI parameter, has been on the market for a number of years. The analyzer is used in the following manner: a sperm specimen is taken up by a disposable chamber which has a rubber bulb at one end to aspirate the sample, and a thin measuring compartment at the other end. After aspirating the sample, the measuring compartment is inserted into the SQA and the SMI of the sample is automatically determined. The SMI parameter, although useful in some applications, was not significantly accepted by the medical community as a viable alternative to the conventional microscopic semen measurements. It is common knowledge that in some fields of veterinary fertility analysis, total sperm concentration (TSC), is evaluated by measuring optical turbidity of the specimen. The physical principle behind this approach is that sperm cells are more opaque than the surrounding seminal plasma, and absorption of a light beam by the specimen is therefore proportional to the TSC. For example, U.S. Pat. No. 4,632,562 discloses a method of measuring sperm density by measuring the optical absorbance of a sperm containing sample and relating the absorbance output signal to the density by using at least three summing channels. The disclosed method is intended for use in artificial insemination in the cattle breeding industry, and measures the optical absorbance in the range of 400-700 nm. This technology however, has not and could not be adopted for human use for the following reasons: (1) Human sperm concentrations in the normal range (and even in higher than normal cases), are more than an order of magnitude lower than in most of their veterinary counterparts—where this technology has been adopted. (2) Human cases are treated even when sperm concentrations are far below their normal levels. This of course is not the case for animals. Infertile animals are normally culled—in any case, they are not treated for infertility. (3) TSC in humans is a parameter, which in itself, is totally insufficient for fertility investigations, and microscopic analysis is in any case required for all the other data in the standard semen analysis protocol. To a large degree, this also holds for veterinary applications. This fact made optical absorption measurements superfluous, and no real effort has been invested in this field. There is thus a need for a simple, objective technique for measuring TSC in human semen. According to the WHO manual, sperm motility assessment (considered by most to be the most important single semen parameter) can be carried out manually using a grid system under the microscope or, alternatively, by use of CASA. CASA provides some advantages over manual methods. However, accuracy and provision of quantitative data are totally dependent on precise semen preparation techniques and instrument settings. These factors (high expertise and sophisticated environment) along with the prohibitive cost of such instrumentation, rule out for all practical purposes their application for routine semen analysis. U.S. Pat. No. 4,896,966 discloses a motility scanner for characterizing the motion of sperm, bacteria and particles in fluid. The scanner comprises an optical system including a collimating lens, condensing lens, imaging lens and a pair of reflecting elements, a source of illumination, radiation sensing means, signal processing means, and display means. The imaging lens has a useful depth of field at its object plane of at least about 0.2 mm. It is an object of the present invention to provide a method for measuring TSC. It is a further object of the invention to provide a method for determining the motile sperm concentration (MSC) and % motility. It is a still further object of the invention to provide a sampling device for use in the determination of semen parameters. It is another object of the invention to provide a system for the determination of semen parameters. In a first aspect of the invention, there is provided a method for measuring the total sperm concentration (TSC) in a sample. The method comprises (i) placing the sample in a transparent container between a synchronically pulsed light source and a photodetector; and (ii) measuring the optical absorbance of the sample in the range of 800-1000 nm, the TSC of the sample being proportional to the absorbance. The method of the invention provides an objective measurement of TSC which is not dependent on image analysis, and which can measure human TSC. However, the method may also be used to measure animal TSC. In a second aspect of the invention, there is provided a sampling device for use in optically analyzing a biological fluid comprising: (i) an aspirator for aspirating the fluid into the device; (ii) a thin measuring chamber having an upper and lower wall, the distance between the walls being in the range of 100-500 microns; (iii) a thick measuring chamber having an upper and lower wall, the distance between the walls being in the range of 0.5-3 cm; and (iv) means for excluding air from the measuring chambers. In a preferred embodiment, the biological fluid is semen, most preferably human semen. The device serves both as a sampler and dual test chamber, enabling simultaneous testing of TSC and MSC. No dilution is required for any of the measurements. This not only saves labor but also eliminates a significant source of errors—namely, dilution inaccuracy. The device also enables (when required) built-in visualizations of the specimen without transferring it to a separate viewing chamber. The thick chamber is also referred to as an optical densitometer. In a third aspect of the invention, there is provided a method for measuring motile sperm concentration (MSC) in a semen sample comprising: (i) placing the sample in a transparent container between a light source and a photodetector, wherein the sperm motion in the sample modulates the light transmitted therethrough, thereby generating a signal; (ii) sampling the signal so as to produce a plurality of signal samples; (iii) selecting acceptable signals; (iv) calculating an absolute value for each of the acceptable signal samples; (v) calculating an average a of the absolute values; and (vi) calculating the MSC based on the average a. It has now been discovered that analysis of waveforms of the analog signals derived from a light beam which traverses a semen sample can provide an indication of the MSC. Using appropriately selected criteria, excellent correlation was found to exist between the averaged area covered by the waveform and the MSC. The MSC of a sperm sample is obtained in accordance with the invention by analyzing optical properties of the sample, which vary over time due to the motility of the sperm. This is in fact, the average signal amplitude in the relevant portions of the waveform, as will be described in more detail below. In a fourth aspect of the invention, there is provided a method of determining the average velocity (AV) of sperm cells comprising: (i) obtaining a Sperm Motility Index (SMI) of the sperm cells as defined in U.S. Pat. No. 4,176,953; (ii) obtaining the MSC; and (iii) calculating AV using an algebraic expression involving the ratio SMI/MSC. Reference is made here to U.S. Pat. No. 4,176,953 issued Dec. 4, 1979, and which has been implemented in various versions of Sperm Quality Analyzers produced by Medical Electronic Systems, Israel. This patent, when applied to semen analysis, provides a parameter called SMI (Sperm Motility Index). As disclosed in the above patent and proven in numerous supporting studies, SMI is a function of both the concentration of motile cells (what is referred to as MSC) and their average velocity (AV). For the sake of simplification, we can say that SMI is a function of MSC×AV, or AV is a function of SMI/MSC. The average velocity of a sperm sample can provide an indication of the quality of the motility of the sperm. Not withstanding that which is stated above, SMI as a function of MSC and AV is more complex than a direct multiplication. After observing, analyzing and measuring over a hundred semen samples, the correct inter-relationship (formula) between them has been developed. In general terms, the formula for extracting the average velocity can be defined as: AV=f(SMI/MSC), “f” being a polynomial of the third degree. Working with f(x)=1/1000x3+1/10x2+0.89x, provided a correlation factor of r=0.82. It should be noted that most semen analysis protocols require data on the % of sperm having progressive motility rather than their average velocity. Progressive motility is defined as those sperm having an average velocity of 5 microns/second or more. This parameter too, can readily be extracted from the average velocity if a normal spread of velocities is assumed around the average. Even in cases where the velocity spread is not normal, the error in calculating the % of progressively motile sperm is not significantly affected. Moreover, when different minimal velocities are defined as progressively motile, this varying threshold is readily entered into the calculation, thereby giving extra flexibility in providing this parameter. This is important when working in different diluting media, ambient temperatures or in fact different species in vet measurements. In a fifth aspect of the invention, there is provided a system for analyzing sperm viability comprising: (i) means for measuring TSC; (ii) means for measuring MSC; and (iii) a video visualization system. The system of the invention combines the measurement of the two major sperm parameters TSC and MSC, with the traditional visualization of the sperm, thus enabling acquiring the third parameter—sperm morphology. In a preferred embodiment, TSC and/or MSC are determined according to the methods of the invention. In another preferred embodiment, the system further comprises the sampling device of the invention. It should be emphasized that there is a basic difference between the video visualization system used in the system of the invention and other sperm visualization systems (such as CASA). The other systems require extremely high quality images because all their results are built on image processing. In the present invention, on the other hand, visualization is used only as a complementary tool to view atypical or suspect cases, to add confidence to processed results, to identify specific pathologies and to enable manual sperm morphology assessment, when required. In order to fulfill these tasks, the video visualization system used in the invention is designed as a compact, inexpensive subsystem, which although of limited use as a stand-alone, precisely fills a complementary role in the system of the invention. An additional important advantage of the visualization system as compared to microscopic procedures, is that pipetting, preparation of slides, dilutions and filling of hemocytometers is unnecessary. Use, together with the video visualization system, of the device of the invention, which doubles as a complete test chamber, obviates all of the above. These features, in effect permit and enable the use of the system of the invention in any small clinic or even office environment. The video visualization system allows one to obtain the following supplementary information regarding the tested sample: 1. Measurement of Very Low Sperm Concentrations Measuring TSC at very low concentrations (below 5 million sperm/ml) is inherently limited in accuracy. This is due to the fact that light absorption by factors other than sperm cells, may become relatively significant at these low levels. Light absorption may be due to seminal plasma variability or to the presence of cells other than sperm. The latter include WBCs (white blood cells indicating infections) and other immature or non-spermic cells from various sources, etc. Since according to the invention TSC is measured by optical absorption, without visualization there would be a possibility for ambiguity in the very low ranges due to the above mentioned considerations. When TSC is considered important in the low ranges, visualization enables differentiation between the different cells contributing to the light absorption. Since MSC is measured independently of light absorption, the % motility (MSC/TSC) can be calculated using the visually determined TSC parameter. 2. Identifying Foreign Cells in the Semen The system is useful in identifying the presence of other cells which may have an effect on semen quality and/or assist in diagnosing patient ailment. For instance, leukocytes indicate infection, immature cells indicate a problem in spermatogenesis, agglutination may be due to a number of causes, etc. 3. Manual Sperm Morphology Assessment Although the system of the invention automatically assesses the % of sperm with normal morphologies, it does so according to a given criteria (e.g. the WHO criteria). Regretfully this criteria is not universally accepted. Such universally accepted criteria do not yet exist, and are often a factor of application. For example, morphology criteria for IVF and ICSI applications are normally far stricter than in normal cases. Other international standards (such as strict or Krueger criteria) are also widely applied. Visualization allows the fertility practitioner to select his own criteria as well as to identify the specific defects present (head deformity, tail problem, etc.) 4. Vasectomy Validation and Azoospermia Diagnosis In order to fully validate the outcome of vasectomy or to obtain a conclusive diagnosis of azoospermia, it is necessary to determine that there are absolutely no sperm in the semen under evaluation. This is generally not possible with the light absorption technology, because the concentrations that are to be measured can be very low. In this case, manual visualization is necessary in order to carefully scan large fields of view in search of individual sperm cells. The sperm visualization system used in the system of the invention is specifically tailored to optimally address these applications. 5. Hard Copy The video visualization system enables “freezing” a given selected view (or a few views) which may then be printed and attached to the Semen Analysis Report. This is of great value for consultations and validation of treatment efficacy. A by-product of the freezing option is viewing the semen sample under static conditions. This strongly facilitates analysis and counting. In microscopic assessments, this can only be done by demobilizing (killing) the sperm prior to viewing. Even then, all dead sperm will end up in one layer, a condition which normally complicates analysis due to high concentration and sperm overlap in the said layer. As stated above, the automatic optical measurement of TSC in human semen samples as opposed to animal samples has been hampered in the past due to the low concentration of sperm cells. This, together with the high background electronic and optical noise due e.g. to seminal plasma variability has prevented the application of methods routinely used in veterinary fertility analysis. The method of the present invention comes to overcome these obstacles by combining the following features: (i) the sample is placed in a transparent container between a synchronically pulsed light source and a synchronically enabled photodetector. The use of a synchronically pulsed light source and photodetector enables the distinction of sperm cells at low concentrations over electronic noise levels. (ii) measuring the optical absorbance of the sample in the range of 800-1000 nm. It has been found that measuring the absorbance in the near infrared region provides the optimal conditions for obtaining strong absorption by sperm cells and low absorption by seminal plasma. Preferably the measured range is 850-950 nm. Most preferably, the range is 880-900 nm. By using the method of the invention, the TSC of a sample may be determined as a function of the absorbance. Although the method of the invention is preferably used with samples of human semen or human sperm, it may also be used with animal semen and animal sperm, preferably after appropriate dilution. An example of an optical system using one embodiment of the method of the invention is illustrated in FIG. 1. The system, indicated generally by the numeral 2, comprises a light source 4, a photodetector 6 and a sample holder 8 interposed therebetween. A preferred light source may be a fast-switching synchronically pulsed light emitting diode (LED) which emits light in the near infrared region. The light source may be controlled by a light intensity controller 10 which in turn is regulated by a modulator 12. The photodetector is capable of detecting synchronically pulsed light. The photodetector transmits the measured analog signals to a demodulator 14, which is also regulated by the modulator 12, and from there to output 16 of the signal in digital form. The beam path through the sample is preferably vertical. The length of the beam path through the sample is generally between 5 and 15 mm, preferably 10 mm. The sample holder must be fully transparent to light waves in the near infra-red region of between 800 and 1000 nm. The plastic material from which the sample holder is made must be totally non toxic to sperm cells. A preferred material is polystyrene PG-79. The sample holder should preferably be designed to totally prevent penetration and forming of air bubbles in the sample, which interefere with the optical measurement. By using the method of the invention, TSC detection levels down to appr. 2 million cells/ml. have been achieved. This level already indicates extreme semen pathology. FIG. 2 illustrates one embodiment of a sampling device 20 according to the invention, for use in measuring semen. The device comprises an anterior optical viewing section 22, a posterior aspirating section 24 and an intermediate air exclusion section 26. The optical viewing section 22 comprises a thin measuring chamber 28 and a thick measuring chamber 30. The thin chamber is used to measure MSC and/or for visualization, while the thick chamber is used to measure TSC. In this way, multiple parameters can be measured simultaneously using the same sampling device and sampling step. The aspirating section 24 comprises a cylinder 32 and a plunger 34 slidingly inserted therein. These parts match each other and function as in a standard syringe. This section serves for the aspiration of the semen sample into the measuring chambers. The air exclusion section 26 comprises a separating valve 36 for separation of the measuring chambers from the cylinder volume after filling. The aspirator, thin measuring chamber, thick measuring chamber and air exclusion section are all in fluid communication. An adapter 38 in the form of a rectangular rail extends along one side of the device 20 and serves for the correct sliding in and aligning of the device upon insertion into an optical instrument by which the sample is evaluated. It also provides the mechanical support and stability required for precision electro-optical measurements. The parts of the device may be seen more clearly in FIG. 3. The thin measuring chamber 28 is an internal cavity having an upper 40 and a lower 42 parallel transparent wall through which the optical beam may pass. The distance between the walls is in the range of 100-500 microns, preferably 250-350 microns, most preferably approximately 300 microns. In the later case, the volume of liquid in the chamber is approximately 25 μl. The anterior end 44 of the chamber has an aperture through which the sample may be drawn into the device. In the illustrated embodiment, the chamber is approximately 4 mm wide. The thin measuring chamber serves for evaluation of sperm motility and may be positioned between a light source e.g. opposite the lower wall 42 and a photodetector e.g. opposite the upper wall 40. It will be understood that the light source and photodetector may also be positioned on the opposite sides of the chamber. A light beam is transmitted through the chamber containing a semen sample. The detector on the other side of the chamber registers optical density variations caused by moving sperm cells. The optical density variations are translated into an electrical signal by the photo-detector which is then routed to the electronic circuits to be filtered, digitized and processed so as to indicate the MSC. The thin measuring chamber may also be used with a video visualization system, as will be further explained below. The thick measuring chamber 30 has an upper 46 and a lower 48 transparent wall through which an optical beam may pass. The distance between the walls is in the range of 0.5-3 cm, preferably 0.8-1.2 cm, most preferably approximately 1 cm. The approximate volume held by the thick compartment in the latter case would be approximately 0.5 ml. This chamber serves for electro-optical absorption measurements of sperm concentration. A light beam, which may be the same or different from that of the thin chamber 28, is transmitted through the upper and lower walls of the chamber and detected by a photo-detector. The chamber volume should be completely filled with a sperm sample in order to avoid inaccuracies due to air bubbles. The attenuation of the light beam as it passes through the chamber is proportional to the sperm concentration. The light beam intensity is measured after passing through the chamber and translated to units of TSC by electronic means. The order of the chambers in the sampling device may be exchanged. The cylinder 32 is in fluid communication with the two measuring chambers 28 & 30, so that by drawing the plunger 34, fluid is drawn into the chambers. This method of aspiration allows large sample volumes to be aspirated into the device. In order to prevent air bubbles from remaining in the measuring chambers, a separating valve 36 is interposed between the cylinder and the measuring chambers, and is in fluid communication with them. The valve is shown in detail in FIG. 4 and comprises a piston 50 slidingly held in a valve housing 52. A connecting bore 54 connecting between the measuring chamber 30 and the cylinder 32 passes through the piston 50. When the valve is in the upper position, there is a connection between the measuring chambers and the aspirating cylinder. Pressing the valve down breaks that connection and ensures that no air remains in the measuring chambers where the samples are measured and no leakage will occur even when there is a temperature variation. This technique is equivalent to positive displacement since air is excluded from the measured fluid volumes (except at the anterior end 44). This design enables working with samples of virtually all viscosities, while at the same time preventing leakage and the penetration of air bubbles into the specimen volumes to be analyzed. Although the means for excluding air from the measuring chambers has been exemplified by a separating valve, other means may also be used, such as a positive displacement pipette All parts of the device may be manufactured from any material which is not toxic to the measured cells. Preferably, the material is relatively cheap, such as plastic materials, so that the device can be disposable. An example of a polymer which may be used to produce the device is polystyrene PG79. The separating valve, cylinder and piston may be made from polypropylene. The thin measuring compartment is by far the most toxi-sensitive part of the device due to the very high area to volume ratio of the seminal liquid in that section. In order to aspirate a sample into the device 20, the tip 44 of the thin measuring compartment 28 is dipped approximately 5 mm deep into the semen sample, which is then aspirated into the device past the separating valve 36. Only app. 0.6 cc are required for a complete filling of the device. The separating valve is then pushed down, and the device may be inserted into an optical measuring apparatus. As mentioned above, determination of the MSC according to the invention requires the generation of a voltage signal which is proportional to the MSC. FIG. 5 shows one embodiment of a system for semen analysis capable of generating such a signal. An optical capillary 100 having a rectangular cross-section is used to hold a semen sample 102. The capillary 100 is illuminated with an incident light beam 105 produced by a light source 110. The capillary 100 has an optical path of 300 μm through which the light beam 105 passes. After passing through the capillary, the scattered beam 106 is collimated by a round aperture 108 having a diameter of 70 μm. The collimated beam 107 impinges upon a photodetector 115. The photodetector 115 produces an analog voltage signal 120 proportional to the intensity of the beam 107. The analog signal varies in time due to the motility of the sperm in the semen sample 102, as shown for example in FIG. 8. The analog signal 120 is inputted to an analog-to-digital converter 125 that samples the analog signal 120 at a rate of e.g. 8000 Hz and generates a digital output signal 128. The digital output signal may be stored in a memory 130. Sperm motion in the sample 102 leads to a modulation in the intensity of the beam 107, which in turn affects the analog signal 120 and digital signal 128. A processor 135 is configured to carry out an analysis of data stored in the memory 130 in order to produce an analysis of the semen sample 102. The results of the analysis may be displayed on any display device such as a CRT screen 140 of a personal computer 145, or on an internal LCD screen 148 of the measuring device. FIG. 6 shows a flow chart diagram for one embodiment of an algorithm for calculating the MSC as carried out by e.g. the processor 135 of FIG. 5, in accordance with the invention. In step 200, the digital signal 128 of FIG. 5 is digitally filtered in order to remove high and low frequencies that are not relevant to the dominant frequency of the signal, which is determined by the motility characteristics of the semen sample 102. This is done in order to optimize the signal to noise ratio. The DC component of the signal 128 is also removed. For human sperm samples, for example, the optimal relevant frequency range was found to be between 5 and 30 Hz. In step 205, digital samples having an absolute value below a first predetermined threshold, which may be determined empirically, are excluded. In step 210 the same threshold value is subtracted from all remaining samples. In step 215, a waveform selection procedure is carried out to discard all waveforms due to artifacts such as from non-relevant cells, etc. A preferred embodiment of waveform selection with human sperm is to eliminate all waveforms not satisfying the following criteria: Minimum height—10 millivolts. Minimum width—37.5 milliseconds. Maximum width—500 milliseconds. Minimum rise/fall time—2.5 milliseconds. The correct definition (and detection) of the beginning and end of sperm associated waveforms are defined as those where significant changes of waveform direction occur. The time difference between two such points defines the time width of a given wave. The manner of selection may be understood by way of example with reference to FIG. 8 (not drawn to scale), which shows the amplitude of the analog signal (120 in FIG. 5) as a function of time. The threshold 302 is determined empirically to provide optimal linearity between the output signal and the microscopically measured MSC. The waveforms that are used for the calculation of MSC are labeled 304, 305, 306 and 307. The other waveforms have been rejected for various reasons: 308 because its peak is less than the threshold; 310 because it is too wide; and 312 because it is too narrow. In step 220 of FIG. 6 the absolute value of all selected samples is calculated, and in step 225, the average a of the absolute values is calculated. In step 230, the MSC of the sample 102 is calculated based upon the average a. For example, it was found that the dependency of MSC on a can be described by a linear equation of the form:MSC=αawhere α is an empirically derived constant. In a preferred embodiment, the dependency of MSC on a may be described by a quadratic equation of the form:MSC=Aa2+Ba With reference to FIG. 9, a specific human sperm sample was analyzed in accordance with the invention. It was found that the dependency of MSC on a could be described by the following algebraic expression:MSC=0.0047a2+0.869a (I)A good linear correlation was found to exist for small values of a. Using formula (I), the correlation factor (r) for fresh sperm over the entire range was >0.98. Analysis of treated semen samples with varying viscosity was also performed using thawed samples, washed sperm, diluted samples (both in 3% Sodium Citrate and Test Yolk buffer) as well as with samples containing up to 20% glycerol having artificially raised viscosity. It was found that varying sample viscosity (and therefore sperm velocity), did not significantly affect the correlation between MSC and average signal (“r” in all case remained above 0.96). Using centrifugal enrichment techniques, a very wide range of motile human sperm concentrations were measured (up to 250 M/ml). No significant saturation was found. The slight non-linearity at the highest ranges is easily corrected by a simple second-degree polynomial correction—given above. Analysis of bovine semen was also carried out and correlation factors between bovine MSC and identically averaged signals (same methodology as for humans) provided similarly excellent results. It is to be noted however, that bovine semen has to be diluted prior to measurements. This is due to their MSC being typically an order of magnitude above that of human. As explained above, the average velocity is a function of SMI and MSC. With reference to FIG. 7, the SMI is calculated in step 235. This may be done, for example, as disclosed in U.S. Pat. No. 4,176,953, or using an SQA analyzer. In step 240 the MSC is calculated by any known method. In a preferred embodiment, MSC is calculated by the algorithm of the invention (see Example 3 above). In step 245 the average velocity AV is calculated using an algebraic expression involving the ratio SMI/MSC. In one embodiment AV is calculated using the algebraic expression: AV = 0.001 ( SMI MSC ) 3 + 0.1 ( SMI MSC ) 2 + 0.89 ( SMI MSC ) In step 250 the results are displayed on the display device 145 or 148 (FIG. 5). One embodiment of a video visualization subsystem (VVS) which may be used with the analyzing system of the invention is illustrated in FIG. 10. A semen sample 300 is placed before a diffused, phase contrasted illuminator 305. The sample may be held in a standard laboratory slide or smear, or may be held in a sampling device according to the invention. Light from the illuminator 305 passes through the sample 300 and through a switchable dual lens system 310, preferably with amplifications of 20 and 40. The amplified light is then conveyed to a miniature CCD video camera 315. The resulting image may be displayed on a built-in internal viewing screen 320 or on external displaying means 325 such as PCs, screens, printing devices, etc. In a preferred embodiment, the VVS is built around the sampling device of the invention, and particularly the thin measuring compartment. The object of this feature is that no extra preparations will be necessary to incorporate this function to the normal testing procedure. One simply takes the semen filled device on which the automated test is performed and inserts it—as such, into the viewing port. However, the VVS is not limited to use with the sampling device of the invention, and may be used with standard laboratory slides or smears. The front end of the VVS is similar to that of the microscope. Two objective lenses are selectable for optimizing magnification and field of view, according to the application (×20 or ×40). However, instead of the eyepieces of the microscope, the image from the objective is conveyed to a miniature CCD video camera. The size of the CCD (diagonal) is 6 mm. The viewing screen is a 100 mm LCD. This provides a video amplification of app. 17. This in effect gives a potential overall amplification of 340 or 680. Although amplification factors of only 200 and 400 are required, this set up is selected so that the above amplification could be reached in a much smaller construction. This is desirable e.g. for a compact and robust desk-top unit (decreasing the specified image distance decreases the amplification to what is required). The lenses and their magnification set-up may be selected so that the “Working distance” (from object to lenses) can be varied to enable scanning throughout the whole depth of the thin measuring compartment (e.g. 300 microns). This is opposed to normal microscopic viewing which does not require such scanning, because the object is normally enclosed in a slide which is just 20 microns deep and the whole depth can be viewed without scanning or refocusing. As mentioned above, an overall amplification factor of 200 or 400 may be selected. An amplification of 400 will be the choice when it is necessary to identify non-spermic cells (white blood cells, round cells, etc.), as well as to investigate and evaluate various morphological pathologies of sperm cells (agglutinations, immature cells, sperm head or tall defects, etc.). An amplification of 200 will be preferable for cell counting—irrespective of whether they are sperm or others. The lower amplification provides a larger field of view (4 times larger) and thereby improved counting statistics. The possibility of freezing images greatly enhances both applications. In order to facilitate cell counts and acquire a truly quantitative result using the VVS, in a preferred embodiment a calibrated grid may be charted directly on the LCD viewing screen. The grid comprises 2 cm squares which are equivalent to a pre-amplification size of 0.1 mm in the semen filled measuring compartment (amplification factor of 200). This approach precludes the very difficult task of precisely charting a minute grid on the measuring compartment itself. The latter expensive solution is incorporated in the Mackler Counting Chamber as well as some other hemacytometers—precluding their use as disposables. In the present invention this is unnecessary and the VVS allows the grid to be a part of the viewing screen. The VVS may be useful in the following applications: (a) Measuring very low sperm concentrations. (b) Identifying foreign cells in the semen (other than sperm cells). (c) Manual morphology analysis according to any selected criteria. (d) Vasectomy efficacy validation. (e) Diagnosing Azoospermia. (f) On the spot comparison of computerized results with visual analysis. (g) Providing hard copy “Snap shots” of immobilized images of various semen layers. The immobilization is achieved by electronic freezing of the images. |
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051981831 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT(S) The present invention shown in FIG. 1 is an apparatus for close packing of nuclear fuel assemblies. A nuclear fuel assembly (10) has an array of fuel rods (12) evenly spaced within an envelope (13) with narrow spaces (14) and wider spaces (16) between the fuel rods (12). Close packing of nuclear fuel assemblies (10) is accomplished by inserting a plate (18), having an effective amount of neutron absorbing material, between fuel rods (12) within the nuclear fuel assembly (10). It is preferred that the plate (18) is placed between an outer row (20) and a next outer row (22) of fuel rods (12). Placement of the plate (18) may be between any rows of the nuclear fuel assembly (10) where there are no interfering guide tubes (such as may be found in boiling water reactor assemblies). The number of plates (18) placed within an assembly (10) may depend upon the burnup status or reactivity of the fuel. Fresh fuel may require that plates (18) completely surround and enclose the center of the nuclear fuel assembly. Spent fuel may require plates on one side or a few plates (18) on all sides appropriate for the activity of the spent fuel. The plates (18) may be of any thickness but preferably have a thickness (24) permitting insertion between nuclear fuel rods (12) within the nuclear fuel assembly (10). Moreover, it is preferred that the plate (18) has a width and a length permitting insertion between grid spacers and other structural elements within said nuclear fuel assembly. The apparatus may further include a releasable lock (30) for securing the plate (18) within the nuclear fuel assembly (10). The releasable lock (30) may be of any type but it is preferred to be operable under water using spent fuel handling tools. These tools are required to reach up to 40 ft. underwater manipulated by an operator on a platform above the water surface. Hence, the operator has poor visibility of the nuclear fuel assemblies beneath the water surface and must rely on the feel of a tool in knowing whether a task is successfully completed. Therefore, it is preferred that the releasable lock (30) is attached to the plate (18) and actuated by a simple linear or rotary motion. The releasable lock (30) may have flexible elements, rigid elements, or a combination of rigid and flexible elements. It is further preferred that the releasable lock (30) remain within the fuel assembly envelope (13) when engaged thereby permitting a fuel assembly (10) to touch either a container wall or another fuel assembly. Maintaining the releasable lock (30) within the envelope (13) further prevents catching or snagging the releasable lock (30) on other structures during handling of the fuel assembly (10). Releasable locks (30) with a flexible element include but are not limited to locks having a spring or a pressurized element. The releasable lock (30) may be a spring clip that engages a nuclear fuel rod when the plate (18) is inserted into the nuclear fuel assembly. The force required to engage the clip would be felt by the operator. A further embodiment of a flexible releasable lock (30) comprises a flexible element compressibly inserted through a narrow space (14) between nuclear fuel rods then expanded into a wide space (16) between nuclear fuel rods. Flexible elements include but are not limited to tapered spring elements, springs attached to tapered elements, and spiral springs. Flexible elements further include pressurized and energized elements including but not limited to pneumatic cylinders, hydraulic cylinders, and electrical solenoids. An advantage of flexible elements is that the additional force required to actuate them provides the feel that the operator needs to know the status of the lock. Releasable locks (30) having rigid elements may also be used. A preferred embodiment of a rigid releasable lock (30) is illustrated in FIGS. 2 and 3. The rigid releasable lock (30) in these figures comprises an elongated member (32) having a first end (34) and a second end (35). The first end (34) has a key (36), and the second end (35) is rotatably attachable to the plate (18). The key (36) may be of any shape, but is preferably shaped to interface with a remotely operated handling tool to rotate the elongated member (32) for locking and releasing the plate (18). A locking disk (40) is attached on the elongated member (32) between the key (36) and said second end, (35) and has a thickness (42) less than the narrow space (14) between said fuel rods (12) and has a width (46) greater than the narrow space (14). The thickness (42) of the locking disk (40) permits the locking disk (40) to be inserted between nuclear fuel rods (14), then locked between them by rotating the locking disk (40) within the wide space (16) with the key (36) so that the width (46) of the locking disk (40) prevents its removal from between the nuclear fuel rods (14). The rigid releasable lock (30) may be secured in either a locked position or an open position with a retainer (47). In a preferred embodiment, the retainer (47) comprises at least one ball detent (48) mounted on an end of the plate (18) near the key (34) with the ball (48) in contact with the key (34). The key (34) is held in position when the ball (48) rests in a depression (50) on the key (34). A further embodiment of a retainer (47) is a slotted key with a flat spring. The flat spring is mounted on an end of the plate (18) with a surface pressing on the key (34). The slots in the key (34) may be tapered and rounded to facilitate reversible actuation of the releasable lock (30). Upon rotation of the key (34), a slot will align with the flat spring thereby restraining the key (34) from rotating until additional torque is applied. The plate (18) may be of any neutron absorbing material, but it is preferred to use a structural metal, compatible with the water chemistry in storage pools such as aluminum or stainless steel, alloyed or clad with a neutron absorbing material including but not limited to boron, cadmium, and hafnium. A plate (18) has an effective amount of neutron absorbing material when the concentration of the alloying neutron absorbing material is within standard alloying practice of, for example, up to 4 weight percent boron in aluminum or up to 2 weight percent boron in stainless steel. The structural or cladding metal may be any metal compatible with the water chemistry in spent fuel storage pools including but not limited to aluminum, and stainless steel. The thickness (22) of the plate (18) may depend upon the amount of neutron absorbing material, but is preferred to be about the same as plates currently used between nuclear fuel assemblies (10). By using plates (18) which are similar to those already in use, the resulting control of neutrons will also be similar. In operation, close packing of nuclear fuel assemblies (10) is permitted by placing a plate (18) having an effective amount of neutron absorbing material between nuclear fuel elements (12) within a nuclear fuel assembly (10). Placing a plate (18) within a nuclear fuel assembly (10) allows multiple nuclear fuel assemblies to touch, thereby minimizing the volume necessary for storing or transporting multiple nuclear fuel assemblies. The plate (18) may be releasably locked within the nuclear fuel assembly (10) thereby ensuring that the plate (18) stays in place. While a preferred embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention. |
054254280 | claims | 1. An apparatus for permitting the passage of a core barrel through the interior of a pipe used in coring operations, comprising: a first pipe section having an interior diameter of a selected dimension and having threaded connection ends at each end of said first pipe section, said threaded connection ends having an interior diameter less than the interior diameter of said first pipe section; a second pipe section having an interior diameter substantially equal to the interior diameter of said first pipe section and having threaded connection ends at each end, said threaded connection ends having an interior diameter less than the interior diameter of said second pipe section and one of said second pipe threaded connection ends being connected to one of said first pipe section threaded connection ends to create a pipe joint having an interior wall of a diameter less than the interior diameters of said first and second pipe sections, said interior wall defining a pipe joint bore; and at least one groove across said interior wall of said pipe joint for permitting the transport of fluid between the interior of said first pipe section and the interior of said second pipe section when the core barrel is positioned within said pipe joint bore. connecting a first pipe section connection end to a second pipe section connection end to create a pipe joint, said pipe joint joining a first pipe section and a second pipe section, said first pipe section and said second pipe section having a predetermined interior diameter, said pipe joint having an interior wall defined by a diameter less than the interior diameter of said first and second pipe sections, said interior wall defining a pipe joint bore, said pipe joint including a groove on the interior wall of said pipe joint; installing said first and second pipe sections in a well; placing fluid into the interior of said first and second pipe sections; and transporting the tool through said first pipe section and then through said pipe joint bore, wherein said groove permits the transport of the fluid across said pipe joint as the tool moves through said pipe joint bore. connecting a first pipe section connection end to a second pipe section connection end to create a pipe joint, said pipe joint joining a first drill pipe section and a second drill pipe section, said first and second drill pipe sections having a predetermined interior diameter, said pipe joint having an interior wall defined by a diameter less than the interior diameter of said first and second drill pipe sections said pipe joint interior wall defining a pipe joint bore, said pipe joint interior wall having a groove; installing said first and second pipe sections in a well; placing fluid into the interior of said first and second pipe sections; and transporting the core barrel through said first pipe section and through said pipe joint bore, wherein said groove permits the passage of the fluid through said groove, as the core barrel moves through said pipe joint and displaces the fluid within said first and second drill pipe sections, to equalize the fluid pressure acting on the core barrel. a first pipe section having a first connection end formed at one end of said first pipe section, said first pipe section and said first connection end oriented about a common center line, said first pipe section having a bore defined by a first radius, said first connection end having a bore defined by a radius less than said first radius; and a first fluid passage extending across said first connection end, said first fluid passage being disposed from said centerline at a distance greater than the radius of said connection end bore. a second pipe section having a second connection end formed at one end, said second pipe section and said second connection end oriented about said common centerline, said second pipe section having a bore defined by a second radius, said second connection end having a bore defined by a radius less than said second radius; and a second fluid passage extending across said second connection end, said second fluid passage being disposed from said centerline at a distance greater than the radius of said second connection end bore, said first connection end engaging said second connection end to form a pipe joint, said first fluid passage being in fluid communication with said second fluid passage. a first pipe section joined to a second pipe section at a joint, said first and second pipes sections and said joint oriented about a common centerline, said first pipe section having a bore defined by a predetermined first radius, said second pipe section having a bore defined by a second predetermined radius, said joint having a bore defined by a radius less than the radii of said first and said second pipe section bores; and a fluid passage across said joint permitting fluid communication between said first pipe section and said second pipe section, said fluid passage being disposed from said common centerline at a distance greater than the radius of said joint bore. 2. An apparatus as recited in claim 1, wherein said groove is substantially parallel to said first pipe section. 3. An apparatus as recited in claim 1, wherein said first and second pipe sections comprise drill pipe. 4. An apparatus as recited in claim 1, further comprising a plurality of grooves across the interior wall of said pipe joint for permitting the transport of fluid between the interior of said first pipe section and the interior of said second pipe section. 5. A method for permitting the passage of a tool through the interior of a pipe, comprising the steps of: 6. A method as recited in claim 5, further comprising the step of operating the tool to sever a core sample from the well. 7. A method as recited in claim 6, further comprising the step of transporting the tool through said pipe joint bore to move said core sample from the interior of said first pipe section to the interior of said second pipe section. 8. A method for transporting a core barrel through the interior of a drill pipe, comprising the steps of: 9. A method as recited in claim 8, further comprising the step of severing a core sample from the wellbore. 10. A method as recited in claim 9, further comprising the step of transporting the core sample through said pipe joint. 11. A method as recited in claim 10, further comprising the step of circulating the fluid through said pipe joint as the core sample is transported through said pipe joint. 12. A pipe assembly comprising: 13. A pipe assembly as described in claim 12, further comprising: 14. A pipe assembly as recited in claim 13, wherein said first and second connection ends are in threaded engagement. 15. A pipe assembly as recited in claim 13, wherein said first and second pipe sections comprise drill pipe. 16. A pipe assembly as recited in claim 13, wherein said pipe joint has an interior wall, and wherein said first and second fluid passages are grooves in said interior wall. 17. A pipe assembly as recited in claim 13, wherein said fluid passages comprise a port through said pipe joint permitting fluid communication between said first and second pipe sections. 18. A pipe assembly comprising: |
claims | 1. A method of cone beam CT scanning, the method comprising:performing cone beam CT scanning to acquire two-dimensional projection images of a patient;for each of a plurality of projection images, using a feature within the projection image to determine breathing phase for that projection image; andapplying respiration correlation techniques directly to the projection images based on the determined breathing phase. 2. A method of cone beam CT scanning according to claim 1 in which projection images that have comparable breathing phases are selected from the complete data set on completion of the acquisition and are used to reconstruct the volume data. 3. A method of cone beam CT scanning according to claim 1 in which the feature is the position of the patient's diaphragm. 4. A method of cone beam CT scanning according to claim 1 in which visual and/or audible prompts are provided for the patient's breathing. 5. A method of cone beam CT scanning according to claim 1 in which therapeutic radiation is delivered during the scan at times correlated with the patient's breathing cycle. 6. A cone beam CT scanner comprising:means for performing cone beam CT scanning to acquire two-dimensional projection images of a patient;means for using a feature within the projection image for each of a plurality of projection images to determine breathing phase for that projection image; andmeans for applying respiration correlation techniques directly to the projection images based on the determined breathing phase. 7. A cone beam CT scanner according to claim 6 arranged to select projection images that have comparable breathing phases from the complete data set on completion of the acquisition and to use these to reconstruct the volume data. 8. A cone beam CT scanner according to claim 6 in which the feature is the position of the patient's diaphragm. 9. A cone beam CT scanner according to claim 6 including means to provide visual and/or audible prompts for the patient's breathing. 10. A radiotherapy device comprising a cone beam CT scanner and a source of therapeutic radiation, wherein the CT scanner:performs cone beam CT scanning to acquire two-dimensional projection images of a patient;uses a feature within the projection image for each of a plurality of projection images to determine breathing phase for that projection image; andapplies respiration correlation techniques directly to the projection images based on the determined breathing phase to deliver therapeutic radiation during the scan. |
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abstract | A device and method for measuring the back pressure in chemical reactor tubes includes many automated features. Inflatable tube seals may be automatically inflated. The device may measure several tubes at once. It may transmit data electronically to a remote computer for analysis and graphic display. |
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abstract | An irradiated state diagram that expresses a relation of a degree of long range order S to a variable R of an irradiated state related to a damage rate and an irradiation temperature is prepared according to an ordered structure of an alloy on basis of an evaluation formula related to an effect of irradiation on an irradiated state of the alloy by using, as parameters, a first threshold value Sth1 at which the degree of long range order begins to decrease greatly under irradiation, a second threshold value Sth2 at which the degree of long range order substantially reaches equilibrium after this decrease, and a degree of long range order in an equilibrium state Seq. An R-value is calculated and an S-value corresponding to the R-value is found. An Sth1-value, an Sth2-value and an Seq-value at the R-value are found and compared. |
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claims | 1. A method, implemented by a computing system programmed to perform the following, comprising:determining a full motion range of a target, wherein the full motion range of the target defines an internal target volume (ITV);identifying a partial motion range of the target, wherein the partial motion range is an untracked portion of the full motion range of the target comprising one of an untracked plane or an untracked axis; andgenerating a partial-ITV based on the identified partial motion range, wherein the partial-ITV is a volume swept by the target as the target moves through the partial motion range, the partial-ITV being smaller than the ITV. 2. The method of claim 1, wherein determining the full motion range of the target comprises:acquiring two preoperative images of the target that show two different positions of the full motion range;receiving delineations of the target in the two preoperative images; andinterpolating the full motion range of the target based on the delineations of the target in the two preoperative images. 3. The method of claim 1, further comprising:generating a treatment plan to deliver treatment to the partial-ITV. 4. The method of claim 3, wherein identifying the partial motion range comprises at least one of receiving a user selection of the partial motion range or automatically computing the partial motion range based on at least one of a tracking mode or a treatment mode identified in the treatment plan. 5. The method of claim 1, wherein the target travels through the full motion range during a respiration cycle of a patient, the method further comprising:monitoring the respiration cycle of the patient based on external markers; andgenerating a respiration model that correlates positions of the external markers to phases of the respiration cycle and to a target position. 6. The method of claim 5, further comprising:when the patient is in one or more particular phases of the respiration cycle, activating a radiation treatment beam to treat the partial-ITV, wherein the partial-ITV includes all possible target positions during the one or more particular phases of the respiration cycle; andwhen the patient is in other phases of the respiration cycle, deactivating the radiation treatment beam. 7. The method of claim 1, the method further comprising:determining when the target is located at positions that are within the partial-ITV;while the target is located at the positions within the partial-ITV, activating a radiation treatment beam to treat the volume swept by the target as the target moves through the partial motion range; anddeactivating the treatment beam while the target is outside of the partial-ITV. 8. The method of claim 1, wherein a tracking mode that tracks the target along a single axis will be used during treatment, the method further comprising:identifying the partial motion range by projecting the full motion range of the target onto a plane that is normal to the tracked axis, wherein the partial-ITV covers a motion range of the target the untracked plane. 9. The method of claim 1, wherein a tracking mode that tracks the target along a single imaging plane will be used during treatment, the method further comprising:identifying the partial motion range by projecting the full motion range of the target onto an axis that is normal to the single imaging plane, wherein the partial-ITV covers a motion range of the target in the untracked axis. 10. The method of claim 1, further comprising:aligning a reference structure to a treatment center of a treatment system in three dimensions (3D) by acquiring images by a first image detector and a second image detector and registering the images to a preoperative 3D image;aligning a center of the partial-ITV to the treatment center based on a known offset between the reference structure and the center of the partial-ITV;tracking target position in an imaging plane that is parallel to a treatment plane that intersects the treatment center using one of the first image detector or the second image detector; andconverting image data from the first image detector or the second image detector into 3D positional data by projecting a 2D target position identified in the image data onto the treatment plane. 11. The method of claim 1, further comprising:aligning the target to a treatment center of a treatment system in three dimensions (3D) by acquiring a 3D image of the patient and performing a registration between said 3D image and a previous 3D image of the patient; andtracking target position in an imaging plane using a first image detector. 12. A treatment planning system, comprising:a memory to store instructions for image guided treatment planning; anda processing device coupled to memory, the processing device configured to:determine a full motion range of a target, wherein the full motion range of the target defines an internal target volume (ITV);identify a partial motion range of the target, wherein the partial motion range is an untracked portion of the full motion range of the target comprising one of an untracked plane or an untracked axis;generate a partial-ITV based on the identified partial motion range, wherein the partial-ITV is a volume swept by the target as the target moves through the partial motion range, the partial-ITV being smaller than the ITV; andgenerate a treatment plan that includes instructions for delivering treatment to the partial-ITV. 13. The system of claim 12, wherein the processing device is further configured to:receive delineations of the target in two preoperative images that show two different positions of the motion range; andinterpolate the full motion range of the target based on the delineations of the target in the two preoperative images. 14. The system of claim 12, wherein identifying the partial motion range comprises at least one of receiving a user selection of the partial motion range or automatically computing the partial motion range based on at least one of a tracking mode or a treatment mode identified in the treatment plan. 15. The system of claim 12, further comprising:a motion tracking system to monitor a respiration cycle of a patient based on external markers, wherein the target travels through the full motion range during the respiration cycle of the patient;wherein the processing device is further configured to generate a respiration model that correlates positions of the external markers to phases of the respiration cycle and to a target position; andwherein the treatment plan is for gated radiation treatment in which a radiation treatment beam is activated while the target is located within the partial-ITV and is deactivated while the target is located outside of the partial-ITV. 16. The system of claim 1, wherein the tracking mode tracks the target along a single axis, and wherein the processing device is further configured to identify the partial motion range by projecting the full motion range of the target onto a plane that is normal to the tracked axis, wherein the partial-ITV covers a motion range of the target in the untracked plane. 17. The system of claim 1, wherein the tracking mode tracks the target along a single imaging plane, and wherein the processing device is further configured to identify the partial motion range by projecting the full motion range of the target onto an axis that is normal to the single imaging plane, wherein the partial-ITV covers a motion range of the target in the untracked axis. 18. A treatment delivery system comprising:a treatment bed to support a patient during a treatment;at least one imager to generate images of the patient that include a target during treatment;a radiation source to generate a radiation treatment beam; anda processor to perform the following, comprising:load a treatment plan, wherein the treatment plan identifies a partial internal target volume (partial-ITV), the partial-ITV including a volume swept by the target as the target moves through a partial motion range, wherein the partial motion range is a subset of a full motion range of the target that defines an internal target volume (ITV);align a center of the partial-ITV to a treatment center of the treatment delivery system based on positioning the treatment bed;monitor a current target position based on images generated by the at least one imager; andactivate the radiation source to deliver the radiation treatment beam to the partial-ITV while minimizing radiation delivered to areas outside of the partial-ITV. 19. The treatment delivery system of claim 18, wherein the at least one imager comprises an x-ray imager that has an imaging plane, and wherein the partial motion range corresponds to motion along an untracked axis that is normal to the imaging plane, further comprising the processor to:track the current target position within the imaging plane in two dimensions (2D) based on x-ray images generated by the x-ray imager;convert a 2D target position determined from the x-ray images into three dimensional (3D) positional data by projecting the 2D target position onto a treatment plane, wherein the treatment plane is a plane that passes through the treatment center and that is plane parallel to the imaging plane; andreposition the radiation source to deliver the radiation treatment beam to the target based on the current target position. 20. The treatment delivery system of claim 18, wherein the treatment delivery system is a gantry based system configured to perform gated treatment delivery, and wherein the processor is configured to activate the radiation source when the target is located within the partial-ITV and to deactivate the radiation source when the target is located outside of the partial-ITV. 21. The treatment delivery system of claim 20, further comprising:a motion detecting device to track positions of one or more external markers disposed on the patient;wherein the processing device is further configured to determine when the target is located within the partial-ITV and when the target is located outside of the partial-ITV based on correlating the positions of the one or more external markers to locations of the target using a respiratory model. 22. The treatment delivery system of claim 18, wherein the at least one imager includes an electronic portal imaging device (EPID), and wherein the processor is further configured to perform the following, comprising:track the current target position within an imaging axis in one dimension (1D) based on the images, which are generated by the EPID; andreposition the radiation source to deliver the radiation treatment beam to the target based on the current target position, wherein the processor accounts for target motion outside of the imaging axis by treating the partial-ITV, the partial-ITV including the volume swept by the target in a plane to which the imaging axis is normal. |
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055984509 | description | BEST MODE FOR CARRYING OUT THE INVENTION This invention relates to an improved fuel bundle assembly, one of which is shown in FIG. 1 at 10. It will be understood that the fuel bundle assembly is not shown in its true length, and instead is broken away so as to illustrate the bottom and top portions of the bundle only. The assembly includes an upper handle 12 and a lower nose piece 14. A channel 16 extends upwardly from the nose piece end substantially the full length of the fuel bundle assembly 10. Individual fuel rods 20 are disposed in a matrix interior of the fuel assembly, i.e., surrounded by the channel 16. The full length fuel rods (FLR's) 20 extend between a lower tie plate 22 and an upper tie plate 24 in a well known manner, whereas partial length fuel rods (PLR's) 20' extend upwardly from the lower tie plate 22 but terminate short of the upper tie plate 24 as explained in greater detail below. The rods 20 (including PLR's 20') are normally arrayed in rows and columns. Further, and because of the length of the fuel assemblies (on the order of 160 inches), spacers, e.g., S.sub.1, S.sub.2 -S.sub.N are placed along the length of the fuel assembly to retain the rods in the desired array and to minimize or eliminate lateral vibration of the fuel rods. Typically, seven such spacers, roughly evenly spaced at 20 inch intervals, extend from the top to the bottom of the fuel assembly. As has been mentioned above, this invention relates to a new fuel bundle design for placement interior of the channels 16. Referring particularly to FIG. 2, fuel rods 20 are arranged in a 9.times.9 matrix or array. Were it not for the presence of the central water rod 26, eighty-one (81) individual fuel rods would extend the length of the matrix of fuel rods shown in FIG. 2. The invention constitutes modifying preferably the upper two thirds of the fuel assembly. Specifically, the invention here relates to the modification of the PLR's 20' which extend at least one-half of the length of the fuel assembly. As already noted, the PLR's 20' extend from the bottom tie plate 22 and extend upwardly toward the upper tie plate 24. The PLR's terminate short of the upper tie plate 24, however, preferably adjacent a spacer, e.g., S.sub.2 as shown in FIGS. 1-3; and S.sub.3 as shown in FIG. 4. For purposes of this invention, it is not important where the PLR's terminate, although PLR's will typically extend into the upper two phase region of the bundle. It is preferred that the PLR's 20' be located at least within the second row of the array removed from the channel 16. In order to illustrate the location of these PLR's in the perspective of FIG. 2, the first row of rods has been omitted from that portion of the perspective that is towards the viewer. What the viewer sees, then, is the second row of rods. The invention here, however, is not limited to any particular location for the PLR's within the bundle. With reference now to FIG. 4, a removable extension rod, or unfueled follower 32, is secured to the upper end of a PLR 20', extending upwardly from spacer S.sub.3 through spacers S.sub.1 and S.sub.2 to the upper tie plate 24 where they are secured by any suitable means. A similar follower or extension would be installed for each PLR 20' in the bundle. The followers or extension rods 32 may be secured to the uppermost ends of the PLR's 20' by any suitable fastening means such as a bayonet joint, screw threads or the like. The followers or extension rods 32 may be secured at their upper ends directly to the upper tie plate 24, or they may terminate or a few inches above the uppermost spacer S.sub.1, depending on the design of the upper tie plate. In other words, if the upper tie plate 24 is not designed to accommodate such followers, the latter can simply terminate short of the tie plate, adjacent the uppermost spacer S.sub.1. The followers or extension rods 32 may be tubular or solid in form, depending on desired reactivity characteristics as discussed below. It also may be desirable to have a number of such unfueled followers or rod extensions 32 attached to each other to facilitate easy removal from the bundle during a reactor outage. From a geometric standpoint, it will be appreciated that PLR's 20' with extensions 32 mimic FLR's 20 in terms of coolant pressure drop particularly in the two phase region of the channel, by increasing flow resistance and decreasing flow. In further accordance with the invention, power of reload bundles incorporating the extensions 32 can be adjusted to better match power requirements of the existing fuel bundles in the core. For example, the extensions 32 may be provided as hollow Zircaloy tubes and filled almost entirely with a single phase water in order to increase reactivity, i.e., increase power. On the other hand, the extensions 32 (solid or hollow) may be devoid of any hydrogen bearing material to thereby decrease reactivity and decrease power. Reactivity may be further reduced via addition of gadolinium (via natural uranium, for example) to a hollow Zircaloy follower. By thus being able to adjust both bundle flow and reactivity characteristics, control rod movement can be minimized and operating margins improved. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. |
045335141 | abstract | Control rods are inserted into the core of a nuclear reactor in operation to shut down the reactor output. Before completion of entire control rod insertion, a high-temperature coolant flowing in piping for a reactor water clean-up system is sprayed into the space in the upper portion of the reactor vessel. As the space is under negative pressure, oxygen existing in the water droplets of the sprayed coolant is separated. After completion of entire control rod insertion, a residual heat removal system is operated. The spraying operation is discontinued and a low-temperature coolant cooled by a heat exchanger in the residual heat removal system is sprayed into said space. The coolant sprayed by said first spraying operation is not cooled by the heat exchanger in said residual heat removal system. |
description | Photolithography is a process by which a photomask having a pattern is irradiated with light to transfer the pattern onto a photosensitive material overlying a semiconductor substrate. Over the history of the semiconductor industry, smaller integrated chip minimum features sizes have been achieved by reducing the exposure wavelength of optical lithography radiation sources to improve photolithography resolution. Extreme ultraviolet (EUV) lithography, which uses extreme ultraviolet (EUV) light having an exposure wavelength of between 10 nm and 130 nm, is a promising next-generation lithography solution for emerging technology nodes (e.g., 22 nm, 14 nm, 10 nm, etc.). The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. Extreme ultraviolet (EUV) photolithography systems generally use extreme ultraviolet radiation having a 13.5 nm wavelength. One method of producing 13.5 nm wavelength radiation that has recently emerged is to shot a carbon dioxide (CO2) laser beam at droplets of tin (Sn). The tin droplets are typically provided into an EUV source vessel. As the droplets enter the EUV source vessel, the CO2 laser beam hits the tin droplets and heats the tin droplets to a critical temperature that causes atoms of tin to shed their electrons and become a plasma of ionized tin droplets. The ionized tin droplets emit photons having a wavelength of approximately 13.5 nm, which is provided as EUV radiation to a scanner having downstream optics configured to focus the EUV radiation onto a workpiece. Typically, the primary laser used to ignite the plasma from the tin droplets is aimed along an axis that is coincident with an axis to which EUV radiation is sent to the downstream optics. To prevent the CO2 laser beam from entering into the downstream optics, and damaging optical components, a protection bar is typically designed in a center of an intermediate focus unit located between the EUV source vessel and the scanner. The protection bar is designed to block the CO2 laser beam from entering the downstream optics. However, the protection bar also stands in a portion of the path of the EUV radiation, thereby reducing the power of the EUV system. For example, the protection bar may reduce a cross-section of the EUV radiation entering into the downstream optics by around 15%, thereby reducing power output from the EUV radiation source by approximately 15%. Accordingly, the present disclosure relates to an EUV radiation source having an angled primary laser beam configured to generate improved EUV power, and an associated method. In some embodiments, the EUV radiation source comprises a fuel droplet generator that provides a plurality of fuel droplets to an EUV source vessel along a first trajectory. A primary laser is configured to generate a primary laser beam along a second trajectory that intersects the first trajectory at a non-perpendicular angle. The primary laser beam has a sufficient energy to ignite a plasma that emits EUV radiation from the plurality of fuel droplets. A collector mirror, located between the laser and the first trajectory, has a concave curvature configured to focus the EUV radiation to an exit aperture of the EUV source vessel that is not linearly aligned with the second trajectory of the primary laser beam. By changing the orientation of the primary laser beam to be angled with respect to the exit aperture, the protection element can be moved to a position that no longer blocks EUV radiation from entering into downstream EUV optics, thereby increasing the power output and throughput of an EUV photolithography system. FIG. 1 illustrates a block diagram of some embodiments of an extreme ultraviolet (EUV) radiation source 100 having an angled primary laser. The EUV radiation source 100 comprises a fuel droplet generator 102 configured to generate a plurality of fuel droplets 104. The plurality of fuel droplets 104 generated by the fuel droplet generator 102 are provided into an EUV source vessel 103 along a first trajectory. In some embodiments, the plurality of fuel droplets 104 may comprise tin (Sn). In other embodiments, the plurality of fuel droplets 104 may comprise a different metal material. A primary laser 106 is configured to generate a primary laser beam 108 that intersects the fuel droplets 104. The primary laser beam 108 extends along a second trajectory that intersects the first trajectory at a non-perpendicular angle φ. In various embodiments, the non-perpendicular angle φ may be an obtuse angle (i.e., an angle greater than 90° and less than 180°) or an acute angle (i.e., an angle less than 90°). In some embodiments, the primary laser 106 may comprise a carbon dioxide (CO2) laser. In other embodiments, the primary laser 106 may comprise alternative types of lasers. When the primary laser beam 108 strikes the plurality of fuel droplets 104, the primary laser beam 114 heats the plurality of fuel droplets 104 to a critical temperature. At the critical temperature, the fuel droplets 104 shed their electrons and become a plasma 110 comprising a plurality of ions. The plurality of ions emit EUV radiation 118 (e.g., having a wavelength of approximately 13.5 nm) to a collector mirror 112 having a concave curvature that curves around the plasma 110. The collector mirror 112 is configured to focus the EUV radiation 118 to an exit aperture 120 of the EUV source vessel 103, which is not linearly aligned with the second trajectory of the primary laser beam 114 (e.g., to focus the EUV radiation 118 to a focal point 122 not intersecting a line of the primary laser beam 114). A remnant of the primary laser beam 114 remaining after igniting the plasma 110 (i.e., after passing through the first trajectory of the plurality of fuel droplets 104) may extend along a line of the primary laser beam 108. A protection element 116 is configured to intersect the remnant of the primary laser beam 114. The protection element 116 is configured to absorb the remnant of the primary laser beam 114, so that the remnant of the primary laser beam 114 does not enter into and damage downstream optics. The protection element 116 is located along a line of the primary laser beam 114 (i.e., is linearly aligned with the primary laser beam 114) at a position that is external to a path of the EUV radiation 118 focused by the collector mirror 112 to the focal point 122 (e.g., outside an area defined by lines extending between edges of the collector mirror 112 and the focal point 122). By positioning the protection element 116 in an area that is outside of the path of the EUV radiation 118, the protection element 116 will not negatively impact the power of the EUV radiation 118. Therefore, EUV radiation source 100 is able to maximize the output power of the EUV radiation 118. FIG. 2A illustrates a block diagram of some additional embodiments of an EUV radiation source 200 having an angled primary laser. The EUV radiation source 200 comprises a tin droplet generator 202 configured to generate a plurality of tin droplets 204. The plurality of tin droplets 204 enter into an EUV source vessel 203 along a first trajectory extending in a first direction 205. The EUV source vessel 203 comprises a chamber held under vacuum (e.g., at a pressure of less than 10−2 mbar). In some embodiments, a tin droplet collection element 206 may be located below the tin droplet generator 202. The tin droplet collection element 206 is configured to collect tin droplets that are not vaporized during formation of the EUV radiation and/or fragments of tin droplets generated during formation of the EUV radiation. A carbon dioxide (CO2) primary laser 208 is configured to generate a primary laser beam 210. The primary laser beam 210 may comprise a plurality of pulses of infrared light. In some embodiments, the primary laser beam 210 may have principal wavelength bands centered around a range of between approximately 9 um and approximately 11 um and an energy of greater than or equal to approximately 11.9 MeV. The primary laser beam 210 follows a second trajectory extending along a second direction 209 that is not perpendicular to the first direction 205. The second trajectory extends through an opening 113 in a collector mirror 112 located within the EUV source vessel 203. The primary laser beam 210 intersects the tin droplets 204 and generates a plasma 211 that emits EUV radiation 216. In some embodiments, the EUV radiation 216 may have a wavelength of approximately 13.5 nm. In other embodiments, the EUV radiation 216 may have a wavelength of between greater than approximately 13.5 nm and less than approximately 100 nm. In yet other embodiments, the EUV radiation 216 may have a wavelength of between greater than approximately 10 nm and less than approximately 13.5 nm. A remnant of the primary laser beam 214 remaining after igniting the plasma 211 (i.e., after passing through the first trajectory of the plurality of tin droplets 204) may extend along a line of the primary laser beam 210 to intersect a protection element 116 configured to absorb the remnant of the primary laser beam 214. In some embodiments, the protection element 116 may be located between the plasma 211 and a corrugated surface of a tin collection element 215 configured to collect tin droplets 204 atoms from the plasma 211. In some embodiments, the protection element 116 may comprise a bar shaped structure. In other embodiments, the protection element 116 may comprise alternative shapes (e.g., a circular shape). In various embodiments, the protection element 116 may comprise titanium (e.g., a titanium alloy), aluminum, etc. The collector mirror 112 comprises a concave curvature configured to focus the EUV radiation 216 generated by the plasma 211 toward an intermediate focus (IF) 218 separated from the plasma 211 in a third direction 219 that is non-parallel to the second direction 209. The intermediate focus 218 is comprised within an exit aperture of the EUV source vessel 203 that is not linearly aligned with a second trajectory of the primary laser beam 210. The intermediate focus 218 is located between the EUV source vessel 203 and a scanner 220 comprising optical elements configured to direct the EUV radiation 216 to a workpiece (e.g., a semiconductor substrate). In some embodiments, the intermediate focus 218 may comprise a cone shaped aperture configured to provide for separation of pressures between the EUV source vessel 203 and the scanner 220. FIG. 2B illustrates a front-view 222 of the collector mirror 112 of FIG. 2A. As shown in front-view 222, the opening 113 within the collector mirror 112 is offset from a center line 212 passing through a center of the collector mirror 112, so that the opening 113 is located at a position that is asymmetric with respect to the curvature of the collector mirror 112. The distance d between the center line 212 of the collector mirror 112 and the opening 113 depends upon an angle β between the center line 212 and the primary laser beam 210. For example, if the angle β is larger, the opening 113 will be at a greater distance d from the center line 212. In some embodiments, the collector mirror 112 may comprise a multi-layer coating having alternating layers of different materials. For example, in some embodiments, the collector mirror 112 may comprise alternating layers of molybdenum and silicon configured to operate as a Bragg reflector. FIG. 3 illustrates a block diagram of some additional embodiments of an extreme ultraviolet (EUV) radiation source 300 having a pre-pulse laser. The EUV radiation source 300 comprises a pre-pulse laser 302 configured to generate a pre-pulse laser beam 304 that is incident on a plurality of fuel droplets 104 generated by a fuel droplet generator 102. The pre-pulse laser beam 304 has an energy that is less than a primary laser beam 108 generated by a primary laser 106. The energy of the pre-pulse laser beam 304 is insufficient to ignite a plasma from the fuel droplets 104 (e.g., is less than 11.9 MeV), but does deform the fuel droplets 104 (e.g., increase a target size/diameter of the tin droplets) to generate deformed fuel droplets 306. In some embodiments, the pre-pulse laser 302 may comprise a carbon-dioxide (CO2) laser that has a lower energy than the primary laser 106. FIG. 4 illustrates a block diagram of some additional embodiments of an extreme ultraviolet (EUV) radiation source 400 having an angled pre-pulse laser. The EUV radiation source 400 comprises a fuel droplet generator 102 configured to provide a plurality of fuel droplets 104 along a first trajectory. A primary laser 106 is configured to generate a primary laser beam 108 that extends along a second trajectory that intersects the first trajectory at a first non-perpendicular angle φ (e.g., an obtuse angle or an acute angle). An angled pre-pulse laser 402 is configured to generate a pre-pulse laser beam 404 that extends along a third trajectory that intersects the first trajectory at a second non-perpendicular angle θ (e.g., an obtuse angle or an acute angle). In some embodiments, the first non-perpendicular angle φ is equal to the second non-perpendicular angle θ. In other embodiments, the first non-perpendicular angle φ is different than the second non-perpendicular angle θ. FIG. 5 illustrates a block diagram of some additional embodiments of an extreme ultraviolet (EUV) radiation source 500 having multiple fuel droplet generators and angled primary lasers. The use of multiple fuel droplet generators and angled primary lasers increases the amount of EUV radiation produced by the EUV radiation source 500, thereby improving the output power of the EUV radiation source 500. The EUV radiation source 500 comprises a first tin droplet generator 202a and a second tin droplet generator 202b. The first tin droplet generator 202a is configured to generate a first plurality of tin droplets 204a that are provided to an EUV source vessel 501 along a first tin droplet trajectory. The second tin droplet generator 202b is configured to generate a second plurality of tin droplets 204b that are provided to the EUV source vessel 501 along a second tin droplet trajectory. In some embodiments, the first tin droplet generator 202a and the second tin droplet generator 202b are located at adjacent positions within a ceiling of the EUV source vessel 501. In some embodiments, the first tin droplet generator 202a and the second tin droplet generator 202b, respectively comprise an internal chamber configured to hold a plurality of tin droplets. The internal chamber is separated from the EUV source vessel 501 by a valve, which upon opening releases one or more tin droplets into the EUV source vessel 501. The internal chamber may be held at a high internal pressure (e.g., greater than 100 atm), so that upon opening the valve, one or more tin droplets are injected into an EUV source vessel 501 along a tin droplet trajectory. By changing the pressure, the tin droplet trajectory may be adjusted. In some embodiments, the first tin droplet generator 202a and the second tin droplet generator 202b may have internal chambers with different pressures. The EUV radiation source 500 further comprises a first CO2 laser 208a configured to generate a first primary laser beam 210a, and a second CO2 laser 208b configured to generate a second primary laser beam 210b. In some embodiments, the first primary laser beam 210a is provided through a first opening 503a in a collector mirror 502, while the second primary laser beam 210b is provided though a second opening 503b in the collector mirror 502. In some embodiments, a trajectory of the first primary laser beam 210a is different than a trajectory of the second primary laser beam 210b. In other embodiments, the trajectories of the first primary laser beam 210a and the second primary laser beam 210b may be the same (i.e., parallel). The first primary laser beam 210a is configured to intersect the first tin droplet trajectory of the first plurality of tin droplets 204a and the second primary laser beam 210b is configured to intersect the second tin droplet trajectory of the second plurality of tin droplets 204b. In some embodiments, the first primary laser beam 210a may intersect the first tin droplet trajectory along an obtuse angle, while the second primary laser beam 210b may intersect the second tin droplet trajectory along an acute angle. The first primary laser beam 210a ignites a first plasma that emits EUV radiation 504 from one or more of the first plurality of tin droplets 204a. Similarly, the second primary laser beam 210b ignites a second plasma that also EUV radiation 504 from one or more of the second plurality of tin droplets 204b. The collector mirror 502 is positioned around the first and second plasmas and has a surface with a concave curvature that is configured to focus the EUV radiation 504 into a downstream intermediate focus 218. A first protection element 116a is linearly aligned with the first primary laser beam 210a at a position that is external to a path of the EUV radiation 504 focused by the collector mirror 502 to the intermediate focus 218. The first protection element 116a is configured to absorb a remnant of the first primary laser beam 210a. A second protection element 116b is linearly aligned with the second primary laser beam 210b at a position that is external to the path of the EUV radiation 504 focused by the collector mirror 502 to the intermediate focus 218. The second protection element 116b is configured to absorb a remnant of the second primary laser beam 210b. In some embodiments, the first protection element 116a and the second protection element 116b may be arranged on opposing sides of the intermediate focus 218. In some embodiments, the first protection element 116a and the second protection element 116b may be symmetrically arranged around the intermediate focus 218. FIG. 6 illustrates a block diagram of some additional embodiments of an extreme ultraviolet (EUV) radiation source 600 having multiple angled primary and pre-pulse lasers. Although FIG. 6 is illustrated as having two angled primary and pre-pulse lasers, it will be appreciated that the disclosed EUV radiation source 600 is not limited to two primary and pre-pulse lasers. Rather, the disclosed EUV radiation source may comprise more than two primary and pre-pulse lasers. The EUV radiation source 600 comprises a first pre-pulse laser 302a configured to generate a first pre-pulse laser beam 304a that intersects a first tin droplet trajectory of a first plurality of tin droplets 204a at a non-perpendicular angle. The EUV radiation source 600 further comprises a second pre-pulse laser 302b configured to generate a second pre-pulse laser beam 304b that intersects a second tin droplet trajectory of a second plurality of tin droplets 204b at a non-perpendicular angle. In some embodiments, a trajectory of the first pre-pulse laser beam 304a is different than a trajectory of the second pre-pulse laser beam 304b. For example, the first pre-pulse laser beam 304a may intersect the first tin droplet trajectory at an obtuse angle, while the second pre-pulse laser beam 304b may intersect a second tin droplet trajectory at an acute angle. In other embodiments, the trajectories of the first pre-pulse laser beam 304a and second pre-pulse laser beam 304b may be the same (i.e., parallel). FIG. 7 illustrates a block diagram of some additional embodiments of an EUV lithography system 700. The EUV lithography system 700 comprises a primary laser 701 having a CO2 laser source 702 configured to produce a laser beam 704. In some embodiments, the CO2 laser source 702 may comprise a multi-stage laser having a plurality of stages configured to amplify laser light produced by a prior stage. The laser beam 704 passes through a beam transport system 706 configured to provide the laser beam to a focusing system 708. The focusing system 708 comprises one or more lenses 708a, 708b and/or mirrors arranged within a beam line and configured to focus the laser beam 704. The laser beam 704 is output from the focusing system 708 to an EUV source vessel 203. In some embodiments, the EUV source vessel 203 may be coupled to an underlying source pedestal 710 by one or more damping elements 712. The laser beam 704 follows a second trajectory that intersects a plurality of tin droplets 204 provided from a tin droplet generator 202, located within a ceiling of the EUV source vessel 203, to form a plasma 211 that emits EUV radiation 216. The EUV radiation 216 is reflected by a collector mirror 112 to an intermediate focus 218 that provides a connection to a scanner 220. In some embodiments, the EUV lithography system 700 may comprise a droplet metrology system 714 configured to determine the position and/or trajectory of the plurality of tin droplets 204. In some embodiments, the information from the droplet metrology system 714 may be provided to the focusing system 708, which can make adjustments to the position of the laser beam 704 to intersect the first trajectory of the plurality of tin droplets 204. The scanner 220 comprises an optical train having a plurality of optical elements (e.g., lenses and/or mirrors) configured to scan the EUV radiation 216 along a surface of a semiconductor workpiece. The optical train of the scanner 220 may be held under vacuum (e.g., at a pressure of less than 10−2 mbar) to avoid attenuation of the EUV radiation 216. In some embodiments, the scanner 220 may be coupled to an underlying scanner pedestal 716 by one or more damping elements 718. FIG. 8 illustrates a block diagram of some additional embodiments of an EUV photolithography system 800. Although the EUV photolithography system 800 is illustrated as having a certain configuration of components, it will be appreciated that the disclosed EUV radiation source may be implemented in EUV photolithography systems having additional components (e.g., additional mirrors) or having less components (e.g., less mirrors). The EUV photolithography system 800 comprises EUV radiation source 801 configured to supply EUV radiation 216 (i.e., with wavelengths in a range of between about 10 nm and about 130 nm) to an EUV photomask 802 having a patterned multi-layered reflective surface (e.g., comprising alternating layers of molybdenum and silicon). In some embodiments, the EUV radiation source 801 is configured to generate the EUV radiation 216 by hitting tin droplets 204 with a primary laser beam 210 to generate a plasma 211 comprising ions that emit photons at a wavelength of between approximately 10 nm and approximately 130 nm. The EUV radiation 216 output from the EUV radiation source 801 is provided to a condenser 806 by way of an intermediate focus 218. In some embodiments, the condenser 806 comprises first and second surfaces, 808a and 808b, configured to focus the EUV radiation 216, and a reflector 810 configured to reflect the EUV radiation 812 towards the EUV photomask 802. The EUV photomask 802 is configured to reflect the EUV radiation 812 to form a pattern on a surface of a semiconductor workpiece 804. To produce the pattern, the EUV photomask 802 comprises a plurality of absorptive features 814A-814C arranged on a front surface of the EUV photomask 802. The plurality of absorptive features 814A-814C are configured to absorb the EUV radiation 812, such that the reflected rays of EUV radiation 816 conveys a patterned defined by the EUV photomask 802. The EUV radiation 816 is filtered through reduction optics comprising a series of first through fourth mirrors 818a-818d, which serve as lenses to reduce a size of the pattern carried by the EUV radiation 816. The fourth mirror 818d conveys the EUV radiation 816 onto a on a layer of photoresist disposed on a surface of the semiconductor workpiece 804. The EUV radiation patterns the layer of photoresist so that subsequent processing can be performed on selected regions of the semiconductor workpiece 804. FIG. 9 illustrates a flow diagram of some embodiments of a method 900 of performing an EUV photolithography process. While the disclosed method 900 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. At 902, a plurality of fuel droplets are provided along a trajectory. The plurality of fuel droplets may be provided along a first trajectory extending in first direction. In some embodiments, the plurality of fuel droplets may comprise tin droplets. At 904, one or more of the plurality of fuel droplets may be struck with a pre-pulse laser extending along a trajectory intersecting the trajectory of the plurality of fuel droplets at a non-perpendicular angle, in some embodiments. The pre-pulse laser is configured to change the shape of the fuel droplets. At 906, one or more of the plurality of fuel droplets are struck with a primary laser beam intersecting the trajectory of the plurality of fuel droplets at a non-perpendicular angle. In some embodiments, the primary laser beam follows a second trajectory extending in second direction and intersecting the first trajectory at a second non-perpendicular angle. The primary laser beam ignites a plasma from the fuel droplets that emits extreme ultraviolet (EUV) radiation. In some embodiments, the primary laser beam may comprise a laser beam generated by a carbon dioxide (CO2) laser. At 908, the EUV radiation is focused at a focal point not intersecting a line of the laser beam. In some embodiments, the focal point is separated from the plasma along a third direction different than the second direction. In some embodiments, one or more of acts 902-908 may be concurrently repeated (illustrated by line 909) by different pre-pulse and/or primary lasers, so as to increase an amount of EUV radiation generated by the method 900. For example, a second plurality of fuel droplets may be provided (at act 902), struck by a second pre-pulse laser (at act 904) and by a second primary laser (at act 906). The radiation generated by the second primary laser may be subsequently focused at the focal point (at act 908), where the radiation generated by the second primary laser is added to radiation generated by other iterations of acts 902-908. At 910, remnants of the primary laser beam passing through the trajectory of the fuel droplets are absorbed by a protection element located outside a path of the focused EUV radiation. Since the remnants of the primary laser beam are absorbed by a protection element located outside a path of the focused EUV radiation, the protection element does not block the EUV radiation from entering into downstream EUV optics, thereby increasing the power output and throughput of the EUV photolithography system. At 912, the EUV radiation is provided to a workpiece via an EUV photomask (e.g., reticle) having a patterned multi-layered reflective surface (e.g., comprising alternating layers of molybdenum and silicon). Therefore, the present disclosure relates to an extreme ultraviolet (EUV) radiation having an angled primary laser beam configured to generate improved EUV power, and an associated method. In some embodiments, the present disclosure relates to an extreme ultraviolet (EUV) radiation source. The EUV radiation source comprises a fuel droplet generator configured to provide a plurality of fuel droplets to an EUV source vessel along a first trajectory. The EUV radiation source further comprises a primary laser configured to generate a primary laser beam along a second trajectory that intersects the first trajectory at a non-perpendicular angle, wherein the primary laser beam has a sufficient energy to ignite a plasma that emits extreme ultraviolet radiation from the plurality of fuel droplets. The EUV radiation source further comprises a collector mirror located between the primary laser and the first trajectory and having a concave curvature configured to focus the extreme ultraviolet radiation to an exit aperture of the EUV source vessel that is not linearly aligned with the second trajectory of the primary laser beam. In other embodiments, the present disclosure relates to an EUV radiation source. The EUV radiation source comprises a tin droplet generator configured to provide a plurality of tin droplets to an EUV source vessel along a first trajectory extending in a first direction. The EUV radiation source further comprises a collector mirror having a concave curvature and an opening that extends through the collector mirror at a location offset from a center of the collector mirror, and a carbon dioxide (CO2) laser configured to generate a primary laser beam along a second trajectory extending through the opening in a second direction that is not perpendicular to the first direction. The EUV radiation source further comprises a protection element linearly aligned with the primary laser beam and configured to absorb remnants of the primary laser beam passing through the first trajectory of the plurality of tin droplets. In yet other embodiments, the present disclosure relates to a method of generating extreme ultraviolet (EUV) radiation. The method comprises providing a plurality of fuel droplets along a first trajectory extending in a first direction. The method further comprises striking the fuel droplets with a primary laser beam following a second trajectory extending in a second direction and intersecting the first trajectory at a non-perpendicular angle, wherein the primary laser beam ignite a plasma that emits EUV radiation. The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. |
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051788225 | claims | 1. In combination with a steam generator having a plurality of generator tube support plates, each said generator tube support plate having a plurality of openings, and a plurality of generator tubes, each said generator tube passing through aligned said openings in said support plates, a corrosion monitoring system including a mockup probe, comprising: a. a probe tube support plate having an upper side and a lower side and having substantially the same thickness and being constructed of substantially the same material as said generator tube support plate, having at least one opening of substantially the same size and shape as said openings of said generator tube support plates; b. at least one probe tube having a sidewall, an upper end and a lower end, having substantially the same diameter as said generator tubes and being constructed of substantially the same material as said generator tubes, said probe tube passing through said opening of said probe tube support plate; and wherein said mockup probe is positioned within said steam generator such that said mockup probe is exposed to chemical cleaning fluids within said steam generator during chemical cleaning operations. c. a means for electronically determining corrosion within said steam generator; inserting into said steam generator a mockup probe such that said mockup probe is exposed to chemical cleaning fluids within said steam generator during chemical cleaning operations, said mockup probe including: at least one probe tube having substantially the same diameter as said generator tubes and being constructed of substantially the same material as said generator tubes, said probe tube passing through said opening of said probe tube support plate; conducting chemical cleaning operations; removing said mockup probe; and observing actual corrosion of said mockup probe. prior to said step of conducting chemical cleaning operations, inserting into said steam generator a means for electronically determining corrosion of said tube support plates such that said means is exposed to chemical cleaning fluids within said steam generator during chemical cleaning operations, said means being electronically connected to a data acquisition means; and monitoring said data acquisition means during said step of conducting chemical cleaning operations. c. an insulating sleeve having a sidewall said probe tube above said upper side of said probe tube support plate and below said lower side of said probe tube support plate. d. a protective sleeve, having a sidewall surrounding said insulating sleeve. c. an upper insulating sleeve having a sidewall surrounding said probe tube above said upper side of said probe tube support plate; and d. a lower insulating sleeve having a sidewall surrounding said probe tube below said lower side of said probe tube support plate. e. an upper protective sleeve, having a sidewall surrounding said upper insulating sleeve; and f. a lower protective sleeve, having a sidewall surrounding said lower insulating sleeve. 2. A combination according to claim 1, further comprising: 3. A combination according to claim 2, wherein said means for electronically determining corrosion within said steam generator includes a zero resistance ammetry probe, having an anode constructed of substantially the same material as said generator tube support plates, and a cathode constructed of substantially the same material as said generator tubes; wherein said zero resistance ammetry probe is positioned within said steam generator such that said zero resistance ammetry probe is exposed to chemical cleaning fluids within said steam generator during chemical cleaning operations; and wherein said zero resistance ammetry probe is electronically connected to a data acquisition means. 4. A combination according to claim 3, wherein said means for electronically determining corrosion within said steam generator includes a linear polarization probe, having an electrode constructed of substantially the same material as said generator tube support plates; wherein said linear polarization probe is positioned within said steam generator such that said linear polarization probe is exposed so chemical cleaning fluids within said steam generator during chemical cleaning operations; and wherein said linear polarization probe is electronically connected to a data acquisition means. 5. A combination according to claim 4, wherein said steam generator includes interior components connected by welds and wherein said linear polarization probe includes an electrode constructed of substantially the same material as said welds. 6. In a steam generator having a plurality of generator tube support plates, each said generator tube support plate having a plurality of openings, and a plurality of generator tubes, each said generator tube passing through aligned said openings in said support plates, a method for monitoring corrosion, comprising the steps of: 7. A method for monitoring corrosion according to claim 6, further comprising the steps of: 8. A. corrosion monitoring system according to claim wherein said sidewall of said probe tube is provided with at least one opening therein. 9. A corrosion monitoring system according to claim 1, wherein a plurality of said openings are provided in said probe tube support plate; wherein a plurality of said probe tubes are provided, each said probe tube passing through one said opening of said probe tube support plate; and wherein said probe tubes are of such length that the galvanic corrosion of said probe tube support plate during exposure to a chemical cleaning solvent approximates that of said generator tube support plates. 10. A corrosion monitoring system according to claim 1, wherein said mockup probe further comprises: 11. A corrosion monitoring system according to claim 10, wherein said mockup probe further comprises: 12. A corrosion monitoring system according to claim 1, wherein said mockup probe further comprises: 13. A corrosion monitoring system according to claim 12, wherein said upper insulating sleeve extends upward at least to said upper end of said probe tube and wherein said lower insulating sleeve extends downward at least to said lower end of said probe tube, and wherein said mockup probe further comprises: 14. A corrosion monitoring system according to claim 10, wherein said sidewall of said insulating sleeve is provided with a least one opening therein. 15. A corrosion monitoring system according to claim 11, wherein said sidewall of said insulating sleeve is provided with a least one opening therein, and said sidewall of said protective sleeve is provided with at least one opening therein aligned with said opening in said sidewall of said insulating sleeve. 16. A corrosion monitoring system according to claim 12, wherein said sidewall of said upper insulating sleeve is provided with a least one opening therein and said sidewall of said lower insulating sleeve is provided with a least one opening therein. 17. A corrosion monitoring system according to claim 13, wherein said sidewall of said upper insulating sleeve is provided with a least one opening therein, said sidewall of said lower insulating sleeve is provided with a least one opening therein, said sidewall of said upper protective sleeve is provided with at least one opening therein aligned with said opening in said sidewall of said upper insulating sleeve, and said sidewall of said lower protective sleeve is provided with at least one opening therein aligned with said opening in said sidewall of said lower insulating sleeve. |
claims | 1. A method of operating a nuclear fission traveling wave reactor, the method comprising:migrating at least one nuclear fission fuel assembly in a first direction from a first location in a nuclear fission traveling wave reactor core to a second location in the nuclear fission traveling wave reactor core, the second location having predominantly nuclear fission reactions and being different from the first location; andmigrating the at least one nuclear fission fuel assembly in a second direction toward a propagating wave burnfront in the nuclear fission traveling wave reactor from the second location to a third location in the nuclear fission traveling wave reactor core, the third location having predominantly nuclear absorption reactions, and the second direction being different from the first direction. 2. The method of claim 1 wherein the operation of migrating the at least one nuclear fission fuel assembly from the first location to the second location further includes crossing the propagating wave burnfront, and the operation of migrating the at least one nuclear fission fuel assembly from the second location to the third location further includes crossing the propagating wave burnfront. 3. The method of claim 1 wherein the first location is radially inward from the second location. |
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abstract | The present disclosure relates to a shield cover for a radiation source machine and a security inspection apparatus. The shield cover for a radiation source machine comprises: a frame body provided with a receiving chamber for receiving the radiation source machine, an end opening and an ray exit through which rays are emitted out from the radiation source machine; an end cover disposed at the end opening of the frame body and provided with a sealed chamber communicating with the receiving chamber; and a connecting member disposed between the end cover and the frame body and provided with an opening for communicating the sealed chamber of the end cover with the receiving chamber of the frame body, and the end cover being movably connected to the frame body by the connecting member such that a distance of the end cover from the end opening of the frame body is adjustable. |
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abstract | The inspection methods and systems of the present invention are mobile, rapidly deployable, and capable of scanning a wide variety of receptacles cost-effectively and accurately on uneven surfaces. The present invention is directed toward a portable inspection system for generating an image representation of target objects using a radiation source, comprising a mobile vehicle, a detector array physically attached to a movable boom having a proximal end and a distal end. The proximal end is physically attached to the vehicle. The invention also comprises at least one source of radiation. The radiation source is fixedly attached to the distal end of the boom, wherein the image is generated by introducing the target objects in between the radiation source and the detector array, exposing the objects to radiation, and detecting radiation. |
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042257905 | claims | 1. In radiographic apparatus for manipulating a quantity of radioactive material between a stored position and a use position including a capsule of said radioactive material, a storage unit with a passage through it for storing the capsule in the passage and shielding the surrounding environment from the stored radioactive material, manipulating means for location remote from said storage unit, first flexible conduit means connectible to said storage unit between one end of said passage and the manipulating means, and flexible elongated drive means movable within said conduit means and said passage for moving said capsule between a stored position and a use position under control of said manipulating means, the improvement comprising: reel means mounting said manipulating means and providing a form for coiling said conduit means externally around said reel means, and second conduit means permanently coiled on said reel means for housing a supply of said drive means. 2. Apparatus according to claim 1 wherein said second conduit means is coiled within said form. 3. Apparatus according to claim 1 wherein said second conduit means is permanently coiled in a shape including straight-linear and curved-linear portions. 4. Apparatus according to claim 3 including means for supporting said second conduit means at the outer peripheries of said curved linear portions. 5. Apparatus according to claim 1 wherein said second conduit means is a tube made of a flexible material characterized by low sliding friction to drive means housed therein. 6. Apparatus according to claim 1 wherein said first conduit means is a tube reinforced to resist crushing and external abrasion and said second conduit means is a substantially lighter-weight tube devoid of such reinforcing means. 7. Apparatus according to claim 1 including disconnectible coupler means comprised of a first component fixed to said storage unit at said one end of said passage and a second component of tubular shape fixed at one end to an end of said flexible conduit means remote from said manipulating means, said first component having a tubular aperture for receiving said second component endwise therein, and means for releasably locking said second component to said first component. 8. Apparatus according to claim 1 including a support affixed to said form and mounting said manipulating means, said form including wall means providing a housing, said second conduit means being fixed to said wall means within said housing. 9. Apparatus according to claim 8 including closure means for said housing, said manipulating means including a portion within said housing communicating with both of said conduit means, and a hand crank portion outside of said housing. 10. Apparatus according to claim 9 wherein said first-named conduit means extends through said wall means for communicating with said manipulating means inside said housing. |
claims | 1. A detection apparatus usable to detect a neutron absorption capability of a control element of a nuclear installation, the detection apparatus comprising:a processor apparatus comprising a processor and a storage;a robot apparatus in communication with the processor apparatus and comprising a number of manipulators;a neutron radiograph apparatus comprising an neutron emission source, a detector array, and a mask apparatus, the neutron radiograph apparatus being structured to receive the control element generally between the neutron emission source and the detector array;the neutron emission source being switchable between an ON state and an OFF state, the neutron emission source in the ON state being in an electrically energized condition structured to generate a neutron stream, the neutron emission source in the OFF state being in an electrically de-energized condition structured to output no meaningful neutron stream;the detector array being structured to detect an unabsorbed portion the neutron stream that passes without being absorbed through the control element, the detector array being further structured to generate an output signal that is representative of the unabsorbed portion the neutron stream; andthe mask apparatus being movable by at least a first manipulator of the number of manipulators among a number of positions, a position of the number of positions being that in which the mask apparatus is disposed at least partially between the neutron emission source and the detector array, another position of the number of positions being that in which the mask apparatus is removed from between the neutron emission source and the detector array. 2. The detection apparatus of claim 1 wherein the mask apparatus comprises a mask system having an orifice formed therein, the mask system being structured to generally resist the passage therethrough of the neutron stream but permitting passage of at least a part of the neutron stream through the orifice. 3. The detection apparatus of claim 2 wherein the orifice has a number of physical dimensions in a number of directions transverse to the part of the neutron stream, and wherein the robot apparatus is operable to change at least one physical dimension of the number of physical dimensions between a first size and a second size different than the first size. 4. The detection apparatus of claim 3 wherein the mask system comprises a first mask having a first opening formed therein and a second mask having a second opening formed therein, the robot apparatus being operable to manipulate at least one of the first mask and the second mask to overlie at least a portion of at least one of the first opening and the second opening with at least a portion of the other of the first opening and the second opening to form the orifice from the overlying at least portions of the first and second openings. 5. The detection apparatus of claim 4 wherein whereby movement of one of the first mask and the second mask with respect to the other of the first mask and the second mask changes the at least one physical dimension between the first size and the second size. 6. The detection apparatus of claim 4 wherein the robot apparatus is operable to at least partially receive at least one of the first mask and the second mask between the neutron emission source and the detector array separately from the other of the first mask and the second mask. 7. The detection apparatus of claim 4 wherein at least one of the first opening and the second opening has a length and a width that are controlled by the robot apparatus at the direction of the processor apparatus. 8. The detection apparatus of claim 4 wherein at least one of the first mask and the second mask is of a generally plate-like configuration. 9. The detection apparatus of claim 1 wherein the neutron emission source comprises an accelerator of variable strength which, in the ON state of the neutron emission source, is structured to accelerate light atomic ions, typically, but not limited to hydrogen isotopes, with variable beam current and acceleration velocity so as to induce nuclear fusion reactions in a target on which the beam is focused and thereby emit neutrons into the source assembly. 10. The detection apparatus of claim 1 wherein the mask apparatus in the position disposed at least partially between the neutron emission source and the detector array is structured to at least one of block and absorb at least a portion of the neutron stream. 11. A method of operating the detection apparatus of claim 1 to detect a neutron absorption capability of a control element of a nuclear installation wherein the nuclear installation has a pool of water, the method comprising:receiving into the pool of water the neutron emission source in the OFF state;submerging the neutron emission source in the OFF state in the pool of water to a predetermined water depth; andswitching the neutron emission source from the OFF state to the ON state when the depth of the neutron emission source in the pool of water meets or exceeds the predetermined water depth to enable safe operation of the neutron emission source. 12. The method of claim 11, further comprising:receiving the detector array and the mask apparatus into the pool of water;receiving at least a portion of the control element generally between the neutron emission source and the detector array; andmonitoring the detector array for the possible outputting therefrom of an output signal that would be representative of an unabsorbed portion the neutron stream passing without being absorbed through the at least portion of the control element. 13. The method of claim 12, further comprising moving at least one of the neutron radiograph apparatus and the control element with respect to the other of the neutron radiograph apparatus and the control element while performing the monitoring. 14. The method of claim 12, further comprising:receiving from the detector array an output signal that is representative of an unabsorbed portion the neutron stream passing without being absorbed through the at least portion of the control element; andresponsive to the receiving, processing and reporting the condition of the control element. 15. The method of claim 14 wherein the mask apparatus comprises a mask system having an orifice formed therein, the mask system being structured to strongly resist the passage therethrough of the neutron stream but permitting passage of at least a part of the neutron stream through the orifice, and further comprising:receiving the output signal when the mask apparatus is in the another position removed from between the neutron emission source and the detector array;responsive to the receiving, moving the mask apparatus from the another positions to the position in which the mask apparatus is disposed at least partially between the neutron emission source and the detector array; andmonitoring the detector array for the possible outputting therefrom of another output signal that would be representative of at least a part of the unabsorbed portion of the neutron stream passing through the orifice. 16. The method of claim 15, further comprising:moving at least one of the control element and the orifice among a plurality of positions of the orifice with respect to the control element;detecting a number of instances of the another output signal in a number of positions from among the plurality of positions; andrecording the control element wing inspection elevation, neutron source strength, mask configuration, measured detector array response and expected detector array response. 17. The method of claim 16 wherein the orifice has a number of physical dimensions in a number of directions transverse to the part of the neutron stream, and further comprising:detecting the number of instances of the another output signal when a physical dimension of the number of physical dimensions is of a first size;changing the physical dimension from the first size to a second size smaller than the first size;moving at least one of the control element and the orifice in the second size among a plurality of further positions within the number of positions;detecting a number of further instances of the another output signal in a number of further positions from among the plurality of further positions; andrecording the number of further positions. 18. The method of claim 17, further comprising:positioning the neutron emission source in the ON state at least a predetermined distance from the detector array; andemploying the water in the pool to slow the neutron stream sufficiently that the unabsorbed portion is detectable by the detector array. 19. The method of claim 17 wherein the mask system comprises a first mask having a first opening formed therein and a second mask having a second opening formed therein, at least one of the first opening and the second opening having a length and a width that are controlled by the mask robot and control system, further comprising:manipulating at least one of the first mask and the second mask to overlie at least a portion of at least one of the first opening and the second opening with at least a portion of the other of the first opening and, the second opening to form the orifice from the overlying at least portions of the first and second openings;moving one of the first mask and the second mask with respect to the other of the first mask and the second mask to at least one of:change the at least one physical dimension between the first size and the second size; andmove the position of the orifice with respect to the control element among the plurality of positions. 20. The method of claim 19, further comprising operating the robot apparatus to at least partially receive at least one of the first mask and the second mask between the neutron emission source and the detector array separately from the other of the first mask and the second mask. |
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summary | ||
059149949 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a fragmentary, longitudinal-sectional view of a fuel element storage rack 13 which has a carrying structure 12 with a plate 12b supported on feet 12a. A multiplicity of elongate carrying wells 23 having a square cross-sectional area are set up on the plate 12b. The carrying wells 23 extend along a main axis 7 which is perpendicular to the plane of the plate 12b. Only one carrying well 23 is illustrated for the sake of clarity. A control rod 5 of a boiling water reactor is introduced into the carrying well 23. The control rod 5 has a foot part 11 with which it sits on a bottom plate 28 of the carrying well 23. The control rod 5, which has a cruciform cross section (seen in FIG. 5) and the dish-shaped foot part 11, has a storage basket 1 slipped over it. The storage basket 1 has four inserts 2 which extend along the main axis 7 and rest on a base plate 15 that comes to rest above the foot part 11 of the control rod 5. The base plate 15 of the inserts 2 is connected to a tubular supporting element 10. The supporting element 10 surrounds the foot part 11 of the control rod 5 and is releasable fixed to the bottom plate 28 of the carrying well 23, in particular through the use of four pins. A fuel element 3 is disposed in each insert 2, although again only one of these fuel elements is illustrated for the sake of clarity. Adjacent inserts 2 are fixedly welded to one another through a plurality of connecting elements 8 which are constructed as connecting sheets 9. A geodetically upper region of each insert 2 has a locking element constructed as a drop latch 19. The drop latch 19 is rotatable about a center of rotation 20 and rests largely against the carrying well 23, in a position assumed as a result of its own weight. The carrying well 23 has a holding-down device 26 (seen in FIG. 2) geodetically above the drop latch 19. When the storage basket 1 is being lifted, it is prevented from executing an unintended upward movement due to the fact that the drop latch 19 rests against the holding-down device 26. A centering device 27 which is provided geodetically below the drop latch 19 ensures that the storage basket 1 and the control rod 5 are centered in the carrying well 23. The placement of the inserts 2, each of which receives a fuel element 3, around the cruciform control rod 5, achieves a combined and compressed intermediate storage of fuel elements 3 and control rods 5 in the fuel element storage rack 13 in a fuel element storage basin. This configuration can be obtained for any desired control rod having a cruciform cross section. The actual structure of the foot part 11 of the control rod 5 is also not important for achieving a compressed intermediate storage of fuel elements 3 and control rods 5. A compact storage of control rods 5 of the common structure is thus possible. FIG. 2 shows an upper region of FIG. 1 on an enlarged scale, in which the rotatability of the drop latch 19 about the center of rotation 20 is clearly visible. This drop latch 19 can be rotated out of a locked position by an illustrated gripping appliance 25 which is led into the insert 2 from above. The insert 2 can thereby be lifted out of the carrying well 23 past the holding-down device 26 of the carrying well 23. The insert 2 is lifted with a cruciform reinforcing element 17 in the geodetically upper region or end 16 of the insert 2 for securing the insert 2 against rotation. This reinforcing element 17 is provided with a carrying bracket 18, on which a non-illustrated lifting appliance can engage. This ensures that the carrying well 23 can be loaded with a control rod 5 and the storage basket 1 as well as the fuel elements 3 and that it can be correspondingly unloaded in a simple way. For this purpose, the fuel elements 3 and the control rod 5 likewise have corresponding carrying brackets 18a, 18b (seen in FIG. 1). The carrying bracket 18a of the fuel element 3 projects out of the carrying well 23 further than the carrying bracket 18b of the control element 5. The carrying well 23 is loaded by first inserting the control element 5, then the storage basket 1 and finally the fuel elements 3. Unloading takes place in reverse order. The storage basket 1 may also be constructed as a transport container, so that a storage basket 1 that is already loaded with fuel elements 3 can be introduced into and taken out of the carrying well 23. FIG. 3 is a cross-sectional view of a region around a holding-down device 26. The holding-down device 26 is fastened to the carrying well 23, so that locking elements 19 of two adjacent storage baskets 1 are blocked against upward movement by the holding-down device 26. FIG. 4 shows a portion of the storage rack 13 according to FIG. 1 on an enlarged scale in a region between the carrying structure 12 and the base plate 15 of the inserts 2. The meaning of the reference symbols is the same as that in FIG. 1. FIG. 5 illustrates a cross section through the storage rack 13. For the sake of clarity, only one storage basket 1, which is introduced in a corresponding carrying well 23, is shown completely. Adjacent carrying wells 23 are fixedly connected to one another through cruciform spacer elements 21. The spacer elements 21 have wings which are not orthogonal to one another. The storage basket 1 has a quadratic cross-sectional area 6. A cruciform gap 4 is formed by four inserts 2 which are disposed within a square, are symmetrical to the main axis 7 and likewise have a quadratic cross-sectional area. A cruciform control rod 5 is introduced in the gap 4, likewise symmetrically to the main axis 7. Adjacent inserts 2 are connected to one another through respective connecting sheets 9 in such a manner as to close off the cruciform gap 4, so that the inserts form a unit. A fuel element 3 is disposed within each insert. In this case, the inserts 2 surround the control rod 5. Four fuel elements 3 and one control rod 5 can be introduced in each carrying well 23 by placing the inserts 2 in such a way as to surround the control rod 5. This makes it possible to achieve a particularly compact intermediate storage of fuel elements 3 and control rods 5 of a boiling water reactor. The quadratic carrying wells 23 are disposed in the manner of a checkered pattern, with intermediate positions 24 which are formed between the carrying wells 23 and can likewise be supplied with a storage basket 1 and a control rod 5. The invention is distinguished by a storage basket which can be slipped over a cruciform control rod of a boiling water reactor. For this purpose, the storage basket preferably has four inserts which are spaced from one another and are fixedly connected to one another in such a way as to form a cruciform gap between them in which the control rod can be positioned. One control rod and four fuel elements can be accommodated in a single carrying well of a fuel element storage rack by virtue of this configuration. This achieves a particularly compact and combined intermediate storage of fuel elements and control rods of a boiling water reactor in a fuel element storage basin. |
052934128 | summary | FIELD OF THE INVENTION The invention relates to a process and an apparatus for dismantling an irradiated component of a nuclear reactor, particularly a vessel of a nuclear reactor cooled by pressurized water. BACKGROUND OF THE INVENTION Water-cooled nuclear reactors, particularly pressurized-water nuclear reactors, comprise a vessel which is intended for containing the core of the nuclear reactor and which is connected to the reactor cooling circuit in which the cooling water circulates. The wall of the reactor vessel which is in contact with the cooling fluid and which is exposed to the radiation emitted by the reactor core can be activated and contaminated after the reactor has been in operation for some time. In the case of nuclear power stations which have reached the end of their life and which require a complete shutdown, the solution adopted in the past has been to leave these power stations in their existing state and to allow the activity of the constituent materials of their components to decrease, in order subsequently to dismantle them under more satisfactory conditions than at the time of the shutdown, without the need to employ complex remotely controlled equipment. The number of power stations put out of industrial operation will increase appreciably in the future, and it is therefore necessary to consider dismantling these power stations in order to restore the site where they are installed to its original state. The dismantling of the conventional part of the power station presents no particular problem, but, in contrast, the dismantling of the part of the power station constituting the actual nuclear reactor poses problems which are difficult to solve in view of the radioactive emissions of the constituent materials of the reactor components. In particular, the vessel of water-cooled nuclear reactors, which contains the fuel assemblies and which is in contact with the cooling water of the reactor during its operation, is activated and contaminated where reactors which have reached the end of their life are concerned. As regards pressurized-water nuclear reactors in operation at the present time, the reactor vessel takes the form of a body of generally cylindrical shape closed by domed bottoms, of large size and having a considerable wall thickness. The vessel, which has a very high mass, is arranged within a vessel well made in a concrete structure which also delimits one or more pools located above the upper level of the vessel. The vessel which contains not only the fuel assemblies but also various internal structures, is connected by means of connection pieces to pipelines of the primary circuit of the reactor. The core assemblies and some components of the internal structures can be dismantled and removed from the vessel, in order to ensure their disposal and, if appropriate, their elimination at the time when the reactor is put out of operation. Some components of the highly activated internal structures of the reactor, such as the shroud of the core, may need to be kept inside the vessel so as to be cut under water (radiological protection). Their dismantling has to be carried out within the vessel and during the operations of dismantling the vessel itself. To date, no process and apparatus is known which enables the vessel of a pressurized-water nuclear reactor to be dismantled under very good safety conditions without the risk of radioactive contamination in the work zone, while at the same time using machining and handling means of relatively simple design in order to carry out the fragmentary disposal and elimination of the material of the vessel. SUMMARY OF THE INVENTION The object of the invention is, therefore, to provide a process for dismantling an irradiated component of a nuclear reactor, comprising at least one wall of tubular shape arranged with its axis in the vertical direction and fastened inside a well made in a concrete structure, this process making it possible under very good safety conditions and in a simple way to carry out the fragmentation of the wall of the component and the disposal and elimination of the fragments obtained. To achieve this object: the connecting elements between the concrete structure and the component are destroyed, PA0 the component is displaced some distance in the vertical direction along its axis on the inside of the well and in successive steps, PA0 the wall of the component is cut over a height corresponding substantially to the vertical displacement distance, so as to obtain blocks of the irradiated material of the wall, at the upper level of the well of the concrete structure after each displacement of the component, PA0 the cut blocks are disposed of for the purpose of effecting their elimination or storage, and PA0 the cutting of the component is carried out in successive steps separated by a vertical displacement. PA0 first means for raising the component are placed under a lower part of the component and so as to bear on a stationary support resting on the concrete structure of the reactor, in the vicinity of the bottom of the vessel well, PA0 the component is lifted by a push of the first raising means on the lower part of the component, PA0 a first modular supporting element is introduced between the lower part of the component and the stationary support on which the modular element comes to bear, PA0 the first raising means are actuated oppositely to the lifting direction, in order to bring the lower part of the component to bear on the first modular element, PA0 a unit lift of the component over a specific vertical distance is executed by second raising means bearing on the support and in engagement with a modular supporting element interposed between the component and the stationary support and resting on the stationary support before the unit lift of the component, PA0 a modular supporting element, the height of which is smaller than the vertical distance of unit lift of the component, is introduced between the modular element with which the second raising means interact and the stationary support, and PA0 the second raising means are actuated oppositely to the lifting direction, in order to bring the component to bear on the support by means of the superposed modular elements. Advantageously, and in order to increase the safety of the process, to carry out the displacement of the component in the vertical direction in successive steps: and for each of the subsequent successive displacement steps of the component: |
description | The present invention relates to a container having thick walls (“thick container”) such as a cask for housing, transporting and storing used nuclear fuel aggregate and substance contaminated by radioactivity, for example. Particularly this invention relates to a thick container in which a body section and a bottom section are formed integrally, or a thick drum which can be used as a cylinder of a large size pressing machine, or a canister for storing substance contaminated by radioactivity. The invention relates to a container or a drum which requires less troublesome steps for manufacturing and has an excellent end surface form, a manufacturing apparatus thereof and a manufacturing method thereof. As a cylinder or the like to be used in a cask or a large size pressing machine for containing and transferring and temporarily storing used nuclear fuel generated from a nuclear reactor, a container in which height, diameter and the like of its drum reach several meters is used. Containers having a wall that is several dozens centimeter in thickness have been suggested from a viewpoint of shielding from γ rays or high pressure resistance. A cask for containing and transporting and temporarily storing used nuclear fuel will be exemplified and there will be explained below a conventional container which has been used for these applications. FIG. 29 is a sectional view showing one example of the conventional cask. The cask 500 is composed of a container 501 which is formed with a body section 501a and a bottom section 501b made of stainless or carbon steel, a basket 502 for used containing nuclear fuel aggregate which is arranged in the container 501, and a neutron shielding body 503 provided on an outer periphery of the container 501. The neutron shielding body 503 is charged into a space between an outer drum 504 and the container 501, and a plurality of heat transfer fins (not shown) are provided between the container 501 and the outer drum 504. As the basket 502, a material to which boron having neutron absorbing ability is added is used. The bottom plate 501b made of stainless or carbon steel is welded with tungsten-inert gas (TIG welding) or welded with submerged-arc (SAW welding) to the container 501. A neutron shielding material 506 is sealed into the bottom plate 501b. Moreover, a primary cover 507 and a secondary cover 508 are attached to an upper section of the container 501 by bolts. A neutron shielding material 509 is sealed into the secondary cover 508. γ rays generated from used nuclear fuel aggregate are shielded by the body section 501, the bottom plate 501b, the primary cover 507 and the secondary cover 508. Moreover, neutron is shielded by the neutron shielding material 503 provided on the outer periphery of the container 501, the bottom plate 501b, the neutron shielding material 506 sealed into the secondary cover 508, and the secondary cover 508. A degradation heat of the used fuel aggregate is transmitted from the container 501 via the heat transfer fins to the outer drum 504 and is radiated to the outside therefrom. Next, how a container having a bottom (“bottomed container”) for the cask shown in FIG. 29 is manufactured will be explained below. FIGS. 30(a) through 30(e) are explanatory diagrams showing one example of the method of manufacturing the bottomed container of the cask shown in FIG. 29. As shown in FIG. 30(a), a metal billet 61 which is cogged into a predetermined dimension is upset onto an anvil with bore and is bored by a punch 63. As shown in FIGS. 30(b) and 30(c), a mandrel 65 is inserted through a hole 64 of the metal billet 61 and while it is being rotated, the hole 64 is widened by a hammer 66. As shown in FIG. 30(d), the mandrel 65 is replaced by a large-diameter mandrel 67 and hollow cogging is carried out by a hammer 68. As a result, the metal billet 61 is thinned so that a cylindrical body is formed (FIG. 30(e)). FIGS. 31(a), 31(a′), 31(b) and 31(b′) are explanatory diagrams showing the method of manufacturing the bottomed container according to an Erhardt boring method. This method is for pushing a punch 410 into a metal billet 200 put into a container so as to form the metal billet 200 into a cylindrical shape. This metal billet 200 has a rectangular section, and its diagonal length is equal with an inner diameter of a body section 300 of the container. Moreover, since the section of the metal billet 200 is rectangular, spaces 350 exist between the metal billet 200 and the container 200 (FIG. 31(a′)). When the metal billet 200 is upset into the body section 300 of the container and the punch 410 is pushed into a center axis of the metal billet 200, metal flow occurs due to metal swelling function of the punch 410. While this metal flow is filling the spaces 350 and a part of the metal flow is rising in the body section 300 of the container, and the metal billet 200 is formed into the cylindrical form (FIG. 31(b)). In addition, the bottomed container of the cask can be manufactured also by a backward extrusion pressing method (not shown). In the backward extrusion pressing method, after the metal billet having a circular section substantially equal with the inner diameter of the container is upset into the container, metal flow is generated between the punch and the container by a compressive force of the punch pressurizing along the center axis of the metal billet. While the metal is being raised to a backward direction, the metal billet is formed into a long cylindrical form. After the cylindrical body section 501a is formed by one of the above-mentioned methods, the bottom plate 501b is welded to its lower section. Further, in order to remove a thermal stress due to the welding, the container 501 is subject to heating treatment. However, in order to obtain the bottomed container of the conventional cask 500, since the bottom plate 501b is jointed to the cylindrical body section 501a by welding, the container should be subject to the heating treatment after the welding. For this reason, there arose a problem that the manufacturing requires troublesome steps. Moreover in the Erhardt boring method, as shown in FIG. 31, a drop of a temperature in a metal forward end portion rising in the spaces 350 causes scratches and wave-shaped defects. Further, as shown in the diagrams, since a faulty form portion (FIG. 31(b)) is inevitably generated in the cylindrical end section, this portion should be eliminated by a constant amount, and thus yield is greatly lowered. In addition, in the backward extrusion pressing method, the metal billet is formed while high friction is generated between the container and metal billet. For this reason, a lot of defects such as pockmarks and ribs are generated on an outer surface of the metal billet, and it takes a long time to remove these defects. Further, in both the Erhardt boring method and the backward extrusion pressing method, when a dimension and a thickness of the container to be formed become large, a pressure which is required for pressing becomes extremely large. Therefore, in these methods, it was difficult to manufacture a container having large dimension and thickness. Therefore, the present invention is devised in order to solve the above-mentioned problems, and its object is to provide a container which requires less troublesome manufacturing steps or a container in which defects generated on its cylindrical end portion and its surface can be suppressed. The radioactive substance container according to this invention comprises a thick bottomed container in which a bottom section and a body section are formed integrally by hot-dilating a metal billet in a container for forming. The radioactive substance container according to the next invention comprises a thick bottomed container in which when a metal billet is hot-dilated in a container for forming and its body section is worked, a boring uncompleted section remains on one end side of the body section so as to be a bottom section and the bottom section and the body section are formed integrally. As the above-mentioned radioactive substance container, a bottomed container in which the bottom section and the body section are formed integrally is used so that the conventional welding of a bottom plate is not required, and heating treatment of the welding can be omitted. Moreover, since the bottomed container is formed by the hot dilation, only a press pressure, which is lower than that at the time of hot backward extrusion forming, for example, is required. Here, at the time of the hot press working and the upsetting drawing, punching and drawing which are normally known can be combined, and they are not limited to detailed working methods described below. Moreover, the radioactive substance container according to the present invention can store not only used nuclear fuel but also substances and the like contaminated by radioactive rays. The bottomed container provided to the radioactive substance container includes a so-called thick container in which a thickness is thick with respect to its radius like a container to be used for a cask for transporting and storing used nuclear fuel. Here, the thick container is such that a ratio of a difference between an outer radius R0 and an inner radius Ri, namely, a thickness t=R0−Ri to an average radius R=(Ro−Ri)/2 is (t/R)>1/10. When the section of the container is not circular, an equivalent diameter de=s/π may be used for calculating the outer radius R0, the inner radius Ri and the average radius. Here, s is a peripheral length of the section, and when a length of one side is a, s=4×a in the case of quadrate section. In addition, the bottomed container of the invention is suitable for a container in which a ratio (L/Di) of an axial length L to an inner diameter Di is not less than 1 like a cask for storing used nuclear fuel in which an axial length reaches a several meters. Moreover, the present invention may be applied to a canister as a radioactive substance container. When (L/Di) is less than 1, a certain effect is produced, but as (L/D1) becomes larger than 1, the effect according to this invention is produced more remarkably. The radioactive substance container according to the next invention is the radioactive substance container described above in which a section of the metal billet vertical to an axial direction is polygonal and a shape in a section of the container for forming vertical to an axial direction is circular. As this radioactive substance container, a bottomed container in which the bottom section and the body section are formed integrally is used so that the conventional welding of a bottom plate is not required. Moreover, as for the bottomed container is hot-dilated by setting the metal billet having a polygonal section vertical to the axial direction into the container for forming having a circular internal shape of the section vertical to the axial direction. At this forming step, since the container is dilated to be formed by a function which bends each side of the polygon, the bottomed container in which the bottom section and the body section are integral can be formed with a lower pressure than conventional one. The radioactive substance container according to the next invention is the radioactive substance container described above in which a section of the metal billet vertical to an axial direction is polygonal and a section of the container for forming vertical to an axial direction is polygonal. As this radioactive substance container, a bottomed container in which the bottom section and the body section are formed integrally is used so that the conventional welding of a bottom plate is not required. Moreover, the bottomed container is hot-dilated by setting the metal billet having a polygonal section vertical to the axial direction into the container for forming having a polygonal internal shape of the section vertical to the axial direction. At this forming step, since the container is dilated to be formed by a function which bends each side of the polygon, the bottomed container in which the bottom section and the body section are integral can be formed with a lower pressure than conventional one. Moreover, an internal shape of the container for forming is changed so that bottomed containers having external forms according to various radioactive substance containers can be formed easily. The radioactive substance container according to the next invention comprises a bottomed container for storing a basket for used nuclear fuel aggregate in which a bottom section and a body section is integral by hot dilation forming in a container for forming. Here, the basket is constituted by collecting angular pipes, for example, its section vertical to the axial direction has like an internal shape of a section of the bottomed container shown in FIG. 15(d). Moreover, its outer diameter reaches about 2 to 2.5 m. As this radioactive substance container, the thick bottomed container for containing used nuclear fuel aggregate, in which a dimension in the axial direction reaches a several meters and inner diameter reaches 2 to 2.5 meters, is used so that the conventional welding of a bottom plate is not required and the heat treatment after the welding can be omitted. Particularly in the bottomed container whose thickness is thick and dimension in the axial direction is a several meters and inner diameter reaches 2 to 2.5 meters, the effect which can omit the steps is extremely great. In this container having such a size, the bottomed container of the present invention can be manufactured about one month earlier than a conventional container in which a bottom plate is welded. This difference depends upon time required for the welding itself and time required for the post-welding heat treatment and cooling. Since the bottomed container according to this invention does not require theses processes, the manufacturing time can be greatly shortened. The radioactive substance container according to the next invention is the radioactive substance container described above in which a boring punch used for hot dilation forming has a dimension and a shape which approach to the section of the basket for used nuclear fuel aggregate. Since this radioactive substance container has a dimension such that the section of the boring punch is approximate to the section of the basket for used nuclear fuel aggregate, an operation for cutting the inside of the container becomes easy after the hot dilation forming, and the manufacturing does not require the troublesome steps. Here, “dimension such that the section of the boring punch is approximate to the section of the basket for used nuclear fuel aggregate” means a relationship that the dimension of the section of the boring punch is substantially equal with a difference between the dimension of the basket for used nuclear fuel aggregate and a cutting allowance of the inner side of the bottomed container to be formed. As the boring punch of the present invention, a boring punch 27c or 27d shown in FIGS. 27(c) and 27(d), for example, can be used. Moreover, the sectional shape of the basket is like the internal shape of the section of the bottomed container shown in FIGS. 15(c) and 15(d), for example, the sectional shape of the boring punch of the invention can be approximate to the these shapes. Further, it is considered that when the sectional shape of the basket for used nuclear fuel aggregate is the internal shape of the section of the bottomed container shown in FIG. 15(d), for example, the inner side of the bottomed container having the inner shape of the section shown in FIG. 15(c) is cut so as to be formed into the internal shape of the section shown in FIG. 15(d). In this case, the section of the boring punch where the internal shape of the section shown in FIG. 15(c) is formed has a dimension that it is approximate to the section of the basket. The radioactive substance container according to the next invention comprises a bottomed container, in which a dosage equivalent factor of γ rays on an outer wall surface of a substantially center portion of a side surface of the body is not more than 200 μSv/h in the case where radioactive substance is contained in a bottomed container in which its bottom section and body section are formed integrally by hot dilation forming in a container for forming. Since the bottomed container to be used as this radioactive substance container transports and stores used nuclear fuel, it requires the function for shielding the γ rays radiated from the used nuclear fuel. It is desirable that the dosage equivalent factor of the γ rays on the outer wall surface of the substantially center portion of the sides surface of the radioactive substance container is smaller, not more than 2000 μSv/h confirms to the standard of transportation and storing based on “The rules relating to transportation of nuclear fuel substance and the like outside factory and business establishment (dated on Dec. 28, 1978, Prime Minister's Office Statute No. 57) (Final Amendment dated Nov. 28, 1990, Prime Minister's Office Statute No. 56)”, “The notice for defining details relating the technical standards relating to transportation of nuclear fuel substance and the like outside factory and business establishment (dated Dec. 28, 1978 Science and Technology Agency Notice No. 11) (Final Amendment dated Nov. 28, 1990, Science and Technology Agency Notice No. 5)” and “The technical study relating to storing of used fuel in a dry type cask (July, 1992, Agency of Natural Resources and Energy)”. The bottomed container to be used as the radioactive substance container of the present invention takes the safety into consideration, and the bottomed container is formed into a thick container made of stainless steel or carbon steel where the thickness reaches several dozens cm so that the dosage equivalent factor can be lowered to about 1/10 of this value. In this radioactive substance container, since the body section and the bottom section of the thick container are formed integrally, the conventional welding of a bottom plate is not required, and the heat treatment after the welding can be omitted. Particularly in such a thick bottomed container, the effect which can omit the above-mentioned steps is extremely great. The radioactive substance container according to the next invention is the radioactive substance container described above in which an outer diameter of the bottomed container is not less than 1000 mm to not more than 3000 mm and its thickness is not less than 150 mm to not more than 300 mm. As this radioactive substance container, a bottomed container in which the bottom section and the body section are formed integrally is used so that the conventional welding of a bottom plate is not required, and the heat treatment after the welding can be omitted. Particularly in such a thick bottomed container, the effect which can omit the above-mentioned steps is extremely great. The radioactive substance container comprises a bottomed container where a metal billet, in which at least a section vertical to an axial direction on a forward side with respect to the pressing direction (“pressing forward side”) is formed into a polygonal shape, is set into a container for forming and a boring punch is pushed into the metal billet and the metal billet is hot-dilated so that a bottom section and a body section are formed integrally. This radioactive substance container has the bottomed container where the body section and the bottom section are formed integrally. When such a bottomed container is used, the conventional welding of a bottom plate is not required, and the heat treatment after the welding can be omitted. Moreover, since this bottomed container can be formed with lower press pressure than the conventional one and the movement of the metal to the axial direction of the container is minimum, defects generated on an end portion and a container surface is less. For this reason, the adjustment of these defects requires less troublesome steps. The bottomed container of the radioactive substance container is suitable for a container in which a ratio (L/Di) of an axial length L to an inner diameter Di is not less than 1 like a cask for storing used nuclear fuel in which an axial length reaches a several meters. When such a thick bottomed container which is long with respect to the axial direction is tried to be formed by the conventional hot working method, the press pressure of several dozen-thousand ton is required, and a lot of defects occur on the end portion or the surface of the formed bottomed container. Therefore, such a thick container was conventionally manufactured by welding the bottom to a thick cylinder which was manufactured by the roll forging method or the like. On the contrary, the bottomed container according to this invention can be manufactured by one-time working as a thick bottomed container which is long with respect to the axial direction and can store used nuclear fuel aggregate. Moreover, since the press pressure is about ten-thousand tons, an existing large pressing machine can be used. Moreover, since defects do not occur on the end portion or the surface of the container, adjustment after the forming is seldom required. In addition, in the case where the container does not have such a large dimension, even if the thick container in which (t/R) exceeds 1/10 is formed by the hot press forming, high press pressure is not required. However, a lot of defects occur on the end portion or the surface of the formed bottomed container. For this reason, it is difficult to form such a container according to hot press forming, but this thick bottomed container in which (t/R) exceeds 1/10 can be formed by one-time working, and defects seldom occur on the end portion or the surface. The radioactive substance container according to the next invention comprises: a bottomed container where a bottom section and a body section are formed integrally by hot press pressure and γ rays generated from radioactive substance such as used fuel is shielded; a neutron shielding member which is provided around the bottomed container and shields neutron generated from the radioactive substance; and a cover for covering an opening of the bottomed container. The radioactive substance container according to the next invention comprises: a bottomed container which contains a radioactive substance such as used fuel into a body section with a bottom section and shields γ rays generated from the radioactive substance; a neutron shielding material which is arranged around the bottomed container and shields neutron generated from the radioactive substance, wherein a metal billet is heated and is upset and drawn so that the bottom section and the body section are formed integrally. In this radioactive substance container, the bottomed container, where the body section and the bottom section are integral, is formed. When such a bottomed container is used, the conventional welding of a bottom plate is not required, and the heat treatment after the welding can be omitted. At the time of the hot press working and upsetting draw forming, the punching and drawing which are normally known can be combined, the forming is not limited to the detailed working method mentioned below. This radioactive substance container can contain not only used fuel but also substances contaminated by radioactive rays. The radioactive substance container according to the next invention is the radioactive substance container described above in which a spot facing section is further formed integrally with the bottom section at the time of forming the bottomed container. This radioactive substance container is a bottomed container in which the metal billet is hot-dilated and simultaneously the spot facing section is also provided on the bottomed section. In a cask, since the bottomed section has a neutron absorbing member, the spot facing section is provided on the bottomed section of the container. Since the spot facing section has been conventionally provided by the cutting work or by welding a bottom plate previously provided with a spot facing section to the body section, the manufacturing requires the troublesome steps. In the bottomed container, since the spot facing section is formed integrally at the time of the hot-dilation forming, the step of forming the spot facing section can be omitted. The radioactive substance container according to the next invention is the radioactive substance container described above in which a flange is further provided integrally with the body section of the bottomed container. In the conventional radioactive substance container, since the flange section is separately manufactured and is welded to the body section so as to be attached, the heat treatment after the welding is required, namely, the manufacturing requires the troublesome steps. Moreover, since the radioactive substance container itself requires sealing property and strength, the welded portion requires high solidity. According to the bottomed container of the present invention, since the flange and the body section are formed integrally, the welding and post-welding heat treatment steps are omitted, and simultaneously the sealing property and the strength of the container itself can be secured. The radioactive substance container according to the next invention is the radioactive substance container described above in which at least one of an external section and an internal section of the bottomed container vertical to the axial direction is polygonal. Since a basket is contained in the bottomed container to be used particularly for a cask as the radioactive substance container, it is preferable that the sectional shape of the inside of the bottomed container is formed according to the shape the basket. In the conventional method, after the section of the inside of the bottomed container is formed into a circular shape, it is formed into a shape according to the basket by the cutting or the like. When this radioactive substance container is hot-dilated, the section of the inside of the container can be formed into a shape according to the basket. For this reason, the cutting step which was conventionally required can be omitted. The polygonal shape of the inner section of the body section includes so-called polygonal shapes such as triangular and tetragonal shapes and also shapes shown in FIGS. 15(c) and 15(d). Thereafter, this is applied also to the following inventions. The hot dilation forming-use metal billet according to the next invention in which at least a section vertical to an axial direction on a pressing forward side is formed into a polygonal shape. Since this hot dilation forming-use metal billet is formed so that at least the section vertical to the axial direction on the pressing forward side is formed into a polygonal shape, the metal billet is dilated towards the inner wall of the container by a function for bending each side of the polygon at the time of the hot dilation forming. Since the metal billet is dilated in a space between the pressing forward side and the body of the container at the time of the hot dilation forming, the phenomenon that the metal flows to the opposite direction to the pressing direction is suppressed. Due to these functions, with this hot dilation forming-use metal billet, a thick container where a ratio of the axial length to the diameter is not less than 1 can be formed with a press pressure which is a several part of the conventional press pressure. Moreover, defects which occurs on the end portion or the surface of the container after the forming can be suppressed. The hot dilation forming-use metal billet according to the next invention in which at least one plane is provided on at least one of a side surface on a pressing forward side and a side surface on a backward side with respect to the pressing direction (“pressing backward side”). In this hot dilation forming-use metal billet, since its side surface has at least one plane and the metal billet is hot-dilated by the function for bending the plane towards the inner wall of the container for forming, the press pressure required at the time of the hot dilation forming is lower than the case where the side surface is a curved surface. Therefore, the thick container which is long in the axial direction can be formed with the press pressure smaller than the conventional pressure. Moreover, internal defects such as cracks can be reduced in comparison with the case where the side surface is a bent surface. The hot dilation forming-use metal billet according to the next invention is the hot dilation forming-use metal billet described above in which a taper which becomes thinner towards the pressing direction is provided on the pressing forward side of the metal billet. The hot dilation forming-use metal billet according to the next invention is the hot dilation forming-use metal billet described above in which at least one or more stepped sections are provided so that the pressing forward side of the metal billet becomes thinner gradationally towards the pressing direction. In the above-mentioned hot dilation forming-use metal billet, since the timing at which the metal fills the vicinity of the bottom of the container for forming can be delayed at the final stage of the hot dilation forming, the upsetting of the metal billet can be suppressed at the final stage of the hot dilation forming. As a result, thus the press pressure can be reduced at the time of the hot dilation forming. The hot dilation forming-use metal billet according to the next invention is the one in which at least one plane is provided on a side surface and an extended section which engages with an end portion of an inlet of a container for forming is provided on an end portion on a pressing backward side. Since this hot dilation forming-use metal billet is provided with the extended section at the end portion on the pressing backward side, the metal billet is engaged with the end portion of the container by the extended section at the time of the hot dilation forming. With this function, constraint of the container on the metal billet becomes stronger so that the upsetting of the metal billet on the pressing forward side can be suppressed. Moreover, since the side surface is provided with at least one plane, the function for bending this plane and the function for suppressing the upsetting of the metal billet accrue. Therefore, due to their interaction, the press pressure can be suppressed to be small. Moreover, the metal billet is previously provided with the extended section on the pressing backward side at the time of the manufacturing. For this reason, since the step of forming the extended section which is extended to above the body section of the container on the pressing backward side is not required before the hot dilation forming step, the container manufacturing step can be simplified. Here, in this metal billet, the sectional shape is uniform along the axial direction. The hot dilation forming-use metal billet according to the next invention is the one in which at least a section vertical to an axial direction on a pressing forward side is formed into a polygonal shape, and an extended section which engages with an end portion of an inlet of a container for forming is provided on a pressing backward side. Since this hot dilation forming-use metal billet is provided with the extended section on the pressing backward side, this extended section engages the metal billet with the end portion of the container at the time of the hot dilation forming. With this function, the constraint of the container on the metal billet becomes stronger, and the upsetting of the metal billet on the pressing forward side can be suppressed. Moreover, since at least the section vertical to the axial direction on the pressing forward side was formed into a polygonal shape, the function for bending each side of the polygonal section and the function for suppressing the upsetting of the metal billet accrue. Therefore, the press pressure can be suppressed to be small by their interaction. Moreover, the metal billet is previously provided with the extended section on the pressing backward side at the time of the manufacturing. For this reason, since the step of forming the extended section which is extended to above the body section of the container on the pressing backward side is not required before the hot dilation forming step, the steps of manufacturing the container can be simplified. The hot dilation forming-use metal billet according to the next invention is the one in which at least a section vertical to an axial direction on a pressing forward side is formed into a polygonal shape, and at least one or more stepped sections are provided so that the pressing forward side becomes thinner gradationally towards a pressing direction, and an extended section which engages with an end portion of an inlet of a container for forming is provided on a pressing backward side. Since this hot dilation forming-use metal billet is provided with the extended section on the pressing backward side, the extended section latches the metal billet with the end portion of the container at the time of the hot dilation forming. With this function, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, since at least the section vertical to the axial direction on the pressing forward side was formed into a polygonal shape, the function for bending each side of the polygonal section and the function for suppressing the flow of the metal accrue. Further, since the pressing forward side becomes thinner gradationally towards the pressing direction, the timing at which the metal fills the bottom section of the container for forming can be delayed. Therefore, the press pressure can be suppressed to be small by their interaction. Moreover, the metal billet is previously provided with the extended section on the pressing backward side at the time of the manufacturing. For this reason, since the step of forming the extended section which is extended to above the body section of the container on the pressing backward side is not required before the hot dilation forming, the steps of manufacturing the container can be simplified. Here, since the pressing forward side becomes thinner gradationally, the forming becomes comparatively easy. The hot dilation forming-use metal billet according to the next invention is the one in which at least one plane is provided on at least one of a side surface on a pressing forward side and a side surface on a pressing backward side, and at least one or more stepped sections are provided so that the pressing forward side becomes thinner gradationally towards the pressing direction, and an extended section which engages with an end portion of an inlet of a container for forming is provided on the pressing backward side. Since this hot dilation forming-use metal billet is provided with the extended section on the pressing backward side, the extended section latches the metal billet with the end portion of the container at the time of the hot dilation forming. With this function, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, since at least one of the side surfaces of the metal billet has at least one plane, the function for bending the plane and the function for suppressing the flow of the metal accrue. Further, since the pressing forward side becomes thinner gradationally towards the pressing direction, the timing at which the metal fills the bottom section of the container for forming can be delayed. Therefore, the press pressure can be suppressed to be small by their interaction. Moreover, the metal billet is previously provided with the extended section on the pressing backward side at the time of the manufacturing. For this reason, since the step of forming the extended section which is extended to above the body section of the container on the pressing backward side is not required before the hot dilation forming, the steps of manufacturing the container can be simplified. Here, since the pressing forward side becomes thinner gradationally, the forming becomes comparatively easy. The container according to the next invention is the one in which a metal billet is hot-dilated in a container for forming, and a bottom section and body section are formed integrally and a thick bottomed container is obtained. The container according to the next invention is the one in which, when a metal billet is hot-dilated in a container for forming and a body section is worked, a boring uncompleted section is allowed to remain on one end side of the body section so as to be a bottom section, and an integrally thick bottomed container is obtained. As the container of the above-mentioned invention, a bottomed container in which the bottom section and the body section are formed integrally is used so that the conventional welding of a bottom plate is not required, and heat treatment after that can be omitted. Moreover, since the bottomed container is formed by the hot dilation, only a press pressure, which is lower than that at the time of hot backward extrusion forming, for example, is required. Here, at the time of the hot press working and the upsetting drawing, punching and drawing which are normally known can be combined, and they are not limited to detailed working methods described below. In addition, like a cylinder or the like for a large pressing machine, the above-mentioned container includes a so-called thick container in which a thickness is thick with respect to its radius. Here, the thick container is such that a ratio of a difference between an outer radius R0 and an inner radius Ri, namely, a thickness t=R0−Ri to an average radius R=(Ro−Ri)/2 is (t/R)>1/10 . When the section of the container is not circular, an equivalent diameter de=s/π may be used for calculating the outer radius R0, the inner radius Ri and the average radius. Here, s is a peripheral length of the section, and when a length of one side is a, s=4×a in the case of quadrate section. The container according to this invention is suitable for a container in which a ratio (L/Di) of an axial length L to an inner diameter Di is not less than 1. Another container of the present invention includes a comparatively thin container like a boiler as a pressure container. Further, another container of the invention includes a container for chemical plant, a reactor container for petroleum refining plant, an ammonia synthetic cell, a heat exchange container, a pressure container such as a boiler, a casing for a large rotational equipment for containing a hydroelectric water turbine, a container to be used as a body of submarine and ship. The container according to the next invention is a container described above in which a section of the metal billet vertical to an axial direction is polygonal and an internal shape of a section of the container for forming vertical to the axial direction is circular. As this container, a bottomed container in which the bottom section and the body section are formed integrally is used so that the conventional welding of a bottom plate is not required. Moreover, since the metal billet, where a section vertical to the axial direction is polygonal, is set into the container for forming, where an internal shape of the section vertical to the axial direction is circular so that the bottomed container is hot-dilated. At this forming step, since the metal billet is dilated by the function for bending one side of the polygonal section, the bottomed container can be formed with a press pressure which is lower than the conventional pressure. The container according to the next invention is a container described above in which a section of the metal billet vertical to an axial direction is polygonal and an internal shape of a section of the container for forming vertical to the axial direction is polygonal. As this container, a bottomed container in which the bottom section and the body section are formed integrally is used so that the conventional welding of a bottom plate is not required. Moreover, since the metal billet, where a section vertical to the axial direction is polygonal, is set into the container for forming, where an internal shape of the section vertical to the axial direction is circular so that the bottomed container is hot-dilated. At this forming step, since the metal billet is dilated by the function for bending each side of the polygonal section, the bottomed container where the bottom section and the body section are integral can be formed with a press pressure which is lower than the conventional pressure. Moreover, the internal shape of the container for forming is changed so that bottomed containers having external shapes according to appellations can be obtained. The container according to the next invention is a container described above in which an outer diameter of the bottomed container is not less than 200 mm to not more than 4000 mm, and a thickness is not less than 20 mm to not more than 400 mm. As this container, a bottomed container in which the bottom section and the body section are formed integrally is used so that the conventional welding of a bottom plate is not required, and the heat treatment after the welding can be omitted. Particularly in the thick bottomed container, the effect that the above-mentioned steps can be omitted is great. The container according to the next invention is the one in which a metal billet, where at least a section vertical to an axial direction on a pressing forward side is polygonal, is set into a container for forming, and a boring punch is pushed into the metal billet and the metal billet is hot-dilated to be formed into a bottomed container where a bottom section and a body section are integral. This container is a thick container and includes both a drum without a bottom and a bottomed container where a bottom section and a body section are integral. Particularly in the case of the thick bottomed container, the conventional welding of a bottom plate is not required, and the heat treatment after the welding can be omitted. Moreover, since the pressure required for pressing is lower than the conventional pressure, even in the case of a container which is thick and whose axial dimension reaches a several meters particularly like a container to be used as a cylinder or the like for a large pressing machine, it can be manufactured by the conventional facilities. Moreover, since a number of defects which occur on the end portion of the container surface is small, only less steps of correcting these defects after the forming are required. The container according to the next invention is a container described above in which the bottomed container is constituted so that at least one of an external section and an internal section of the bottomed container vertical to the axial direction is polygonal. Since a basket is contained in the bottomed container to be used particularly for a cask as the radioactive substance container, it is preferable that the inner section of the bottomed container is formed into a shape according to the basket. In the conventional method, after the inner section of the bottomed container is formed into a circular shape, and it is formed into the shape according to the basket by the cutting or the like. Since the inner section of this container can be formed into the shape according to the basket when the bottomed container is dilated, the cutting step which was required conventionally can be omitted. The bottomed container manufacturing apparatus according to the next invention comprises: a container for forming having at least a container body section and a container bottom section in which the container body section and the container bottom section can move relatively with respect to an axial direction of the container body section; and a boring punch which is mounted to a pressing machine and pressurizes a metal billet for hot dilation forming set into the container for forming. This bottomed container manufacturing apparatus has the container in which the bottomed section and the body section can move relatively. For this reason, when the body section of the container is tried to moved to the opposite direction to the pressing direction at the time of the hot dilation forming, the body section of the container moves to the opposite direction to the pressing direction together with the metal billet. Namely, since the body section of the container and the metal billet to be formed seldom move relatively, an increase in the press pressure at the time of the hot dilation forming can be suppressed. The bottomed container manufacturing apparatus according to the next invention comprises: a container for forming having at least container body sections and container bottom sections divided in an axial direction in which the container body section and the container bottom section can move relatively with respect to an axial direction of the container body section; and a boring punch which is mounted to a pressing machine and pressurizes a metal billet for hot dilation forming set into the container for forming. In this bottomed container, since the body section of the container extends along the whole axial direction, even in the case where the metal billet which is long in the axial direction, deformation of the metal billet in the axial direction at the time of the hot dilation forming can be absorbed by the whole container. Therefore, even in the case of the container which is long in the axial direction, an increase in the press pressure can be suppressed. The radioactive substance method of manufacturing a container according to the next invention comprises: the step of rounding a drum-shaped bottomed container where a bottom section and a body section are formed integrally by hot dilation and setting a tool so as to cut an external side of the bottomed container; and the step of cutting an internal section of the bottomed container into a shape according to at least one portion of an outer peripheral shape of a basket for containing used nuclear fuel aggregate. In this radioactive substance method of manufacturing a container, the outer side of the bottomed container where the bottom section and the body section are formed integral is finished by cutting, and the inner side is cut into a stepped shape so that a portion for containing a basket for used nuclear fuel aggregate is provided, or the inner side is finished by cutting so that the radioactive substance container is manufactured. The radioactive substance method of manufacturing a container according to the next invention comprises: the step of hot-dilating a bottomed container so that its bottom section and body section are integral; and the step of cutting an internal section of the bottomed container into a shape according to at least one portion of an outer peripheral shape of a basket for containing used nuclear fuel aggregate. In this radioactive substance method of manufacturing a container, the bottomed container where the bottom section and the body section are integral is formed by the hot dilation forming, and the outer side of the bottomed container is finished by cutting, and the inner side is cut into a stepped shape so that a portion for containing a basket for used nuclear fuel aggregate is provided, or the inner side is finished by cutting so that the radioactive substance container is manufactured. The method of manufacturing a container according to the next invention comprises: the step of setting a metal billet having at least one plane on a side surface into a container for forming with a gap from an inner wall; and the step of pushing a boring punch into the metal billet and bending the plane towards the inner wall so as to hot-dilate the metal billet. In this method of manufacturing a container, the metal billet is extended towards the inner wall of the container for forming by the function for bending the plane on the side surface of the metal billet. Moreover, since the metal billet is extended in space between the metal billet and the inner wall of the container for forming, the upsetting phenomenon of the metal billet can be suppressed. With these function, the method of manufacturing a container requires the press pressure which is lower than the conventional pressure, and defects which occurs on the end portion or the surface of the container after the forming can be suppressed. The method of manufacturing a container according to the next invention comprises: the step of setting a metal billet, which has at least one plane on a side surface and an extended section engaging with an end portion of an inlet of a container for forming on an end portion of a pressing backward side, into the container for forming with a gap from an inner wall; and the step of pushing a boring punch into the metal billet and bending the plane towards the inner wall so as to hot-dilate the metal billet. In this method of manufacturing a container, since the metal billet provided with the extended section engaging with the end portion of the opening of the container for forming is used for the end portion of the pressing backward side, the extended section engages the metal billet with the end portion of the container at the time of hot dilation forming. With this function, the constraint of the container on the metal billet becomes stronger, and the upsetting of the pressing forward side can be suppressed. Moreover, since at least one plane is provided on the side surface, the bending function and the function for suppressing the phenomenon that the metal flows to the opposite side to the pressing direction accrue. Therefore, the press pressure can be suppressed small by their interaction, and deterioration of the end surface shape can be also suppressed. The method of manufacturing a container according to the next invention is characterized in that a metal billet, where at least a section vertical to an axial direction on a pressing forward side is formed into a polygonal shape, is set into a container for forming, and a boring punch is pushed into the metal billet and the metal billet is hot-dilated. In this method of manufacturing a container, on the pressing forward side, since the metal billet is extended in the space between the pressing forward side and the container body, the flow of the metal directing to the opposite side of the pressing direction can be suppressed. For this reason, the phenomenon of the metal billet can be suppressed. For this reason, the method of manufacturing a container requires the press pressure which is lower than the conventional one, and defects which occur on the end portion or the surface of the container after the forming can be suppressed. The method of manufacturing a container according to the next invention is characterized in that a metal billet having at least one plane on at least one of a side surface on a pressing forward side and a side surface on a pressing backward side is set into a container for forming, and a boring punch is pushed into the metal billet and the metal billet is hot-dilated. In this method of manufacturing a container, since the metal billet having at least one plane on the side surface is hot-dilated, a force required for the hot dilation forming is weaker than the case where the side surface is a curved surface. Therefore, the press pressure is lower than the conventional method of manufacturing a containers, and internal defects such as cracks can be reduced. The hot pressing method of manufacturing a thick metal-made drum or a cylindrical container according to the next invention is characterized in that a metal billet having different diameter sections without joint, where its pressing forward side is composed of a member having a section with an outer diameter smaller than an inner diameter of a container or an outer diameter of a diagonal length or a member having a section with an outer diameter of a diagonal length equal with the inner diameter of the container and its backward side is composed of a member having a section with an outer diameter or a diagonal length equal with the inner diameter of the container, is set into the container for press forming which was heated to a press working temperature, and while a center of a workpiece of the metal billet without joint is being bored by a punch, the metal billet is press-worked. In this pressing method, the metal on the thick portion on the pressing backward side fills the container and simultaneously is worked, the constraint force is heightened, and the upsetting phenomenon of the metal billet without joint is suppressed, and the shape of the end surface is made to be satisfactory. Moreover, since the metal is supplied from the pressing backward side to the pressing forward side and the pressing forward side is pushed to be spread sideways and is simultaneously worked according to the effect of satisfactory plastic working of the steel heated to high temperature, it fills the space of the container to be formed. For this reason, a pressed product having a predetermined shape is manufactured from the metal billet without joint. As a result, the metal billet without joint reduces a pressing forming load and improves yield of the product, and a pressed product having excellent end surface shape can be obtained. The method of manufacturing a drum or a container of setting a metal billet into a container for forming and hot-dilating the metal billet by means of a boring punch to be operated by a pressing machine according to the next invention comprises: the step of setting the metal billet, where its pressing forward side has a section having an outer diameter with a diagonal length of not more than an inner diameter of the container and its backward side has a section having an outer diameter substantially equal with the inner diameter of the container, into a container for press forming which was heated to a press working temperature; and the step of boring a center of a workpiece of the metal billet by means of the boring punch and simultaneously press-working the metal billet. In this method, since the metal billet, where the pressing forward side has a quadrate section whose the diagonal length of the pressing forward side is smaller than the inner diameter of the container, is used, the press pressure can be small by the function for bending the side surface composing the plane on the pressing forward side. Moreover, since the pressing backward side of the metal billet suppresses the upsetting of the pressing forward side, defects on the end portion and the container surface can be suppressed, and the press pressure can be reduced. The method of manufacturing a drum or a container of setting a metal billet into a container for forming and hot-dilating the metal billet by means of a boring punch to be operated by a pressing machine, according to the next invention comprises: the step of setting the metal billet, where its pressing forward side has a section having an outer diameter with a diagonal length of smaller than an inner diameter of the container and its backward side has a section having a diagonal length substantially equal with the inner diameter of the container, into a container for press forming which was heated to a press working temperature; and the step of boring a center of a workpiece of the metal billet by means of the punch and simultaneously press-working the metal billet. In this method, since the metal billet, where the pressing forward side has a quadrate section whose the diagonal length of the pressing forward side is smaller than the inner diameter of the container, is used, the press pressure can be small by the function for bending the side surface composing the plane on the pressing forward side. Moreover, the metal billet to be used in this method can be worked comparatively easier than the case of a circular sectional shape because the pressing forward side and backward side have angular sectional shape. The method of manufacturing a drum or a container of setting a metal billet into a container for forming and hot-dilating the metal billet by means of a boring punch to be operated by a pressing machine, according to the next invention comprises: the step of setting the metal billet, where its pressing forward side has a section with an outer diameter smaller than an inner diameter of the container and its backward side has a section with an outer diameter substantially equal with the inner diameter of the container, into a container for press forming which was heated to a press working temperature; and the step of boring a center of a workpiece of the metal billet by means of the punch and simultaneously press-working the metal billet. In the above-mentioned method of manufacturing a container, since the pressing forward side has a circular section whose diagonal length is smaller than the inner diameter of the container, the metal billet is extended to the space between the metal billet and the inner wall of the container for forming. For this reason, the press pressure can be lower than the conventional pressure. Moreover, since the pressing backward side of the metal billet suppresses the upsetting of the pressing forward side, defects on the end portion and the container surface can be also suppressed, and the press pressure can be also reduced. The method of manufacturing a container according to the next invention comprises: the step of setting a metal billet having at least one plane on a side surface into a container for forming with a gap from an inner wall; the step of pushing the metal billet so as to extend a pressing backward side of the metal billet to an end portion of an inlet of the container for forming; and the step of pushing a boring punch into the metal billet and bending the plane towards the inner wall so as to hot-dilate the metal billet. This method of manufacturing a container includes the step of extending the pressing backward side of the metal billet to above the body section of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet with the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes strong, and the upsetting on the pressing forward side can be suppressed. Moreover, the metal billet is extended by the function for bending the plane of the metal billet towards the inner wall of the container for forming. With their interaction, this method of manufacturing a container can form a thick container by the lower press pressure than the backward extrusion method or the like. The method of manufacturing a container according to the next invention comprises: the step of setting a metal billet, where at least one plane is provided on a side surface and an extended section engaging with an end portion of an inlet of a container for forming is provided on a pressing backward side, into a container for forming with a gap from an inner wall; and the step of pushing a boring punch into the metal billet and bending the plane towards the inner wall so as to hot-dilate the metal billet. Since the metal billet to be used in this method of manufacturing a container is previously provided with the extended section engaging with the end portion of the inlet of the container for forming on the end portion on the pressing forward side. For this reason, since the step of extending the pressing backward side of the metal billet to above the body section of the container before the hot dilation forming, time required for the hot dilation is shortened. As a result, since the forming can be ended until the temperature of the metal billet is lowered, the end portion shape becomes more satisfactory. Moreover, since the extending step can be also omitted, the manufacturing does not require troublesome steps. The method of manufacturing a container according to the next invention comprises: the step of setting a metal billet, where at least a section vertical to an axial direction on a pressing forward side is formed into a polygonal shape, into a container for forming; the step of pushing the metal billet so as to extend a pressing backward side of the metal billet to an end portion of an inlet of the container for forming; and the step of pushing a boring punch into the metal billet so as to hot-dilate the metal billet. This method of manufacturing a container includes the step includes the step of extending the pressing backward side of the metal billet to above the body section of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet with the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes strong, and the upsetting on the pressing forward side can be suppressed. Moreover, since the metal billet, in which at least the section vertical to the axial direction on the pressing forward side is formed into a polygonal shape, is dilated to be formed, the function for bending each side of the polygon towards the inner wall of the container for forming acts. With their interaction, the thick container can be formed with lower press pressure than the backward extrusion method or the like. The method of manufacturing a container according to the next invention comprises: the step of setting a metal billet, where at least one plane is provided on at least one of a side surface of a pressing forward side and a side surface of a pressing backward side, into a container for forming; the step of pushing the metal billet so as to extend a pressing backward side of the metal billet to an end portion of an inlet of the container for forming; and the step of pushing a boring punch into the metal billet so as to hot-dilate the metal billet. This method of manufacturing a container includes the step includes the step of extending the pressing backward side of the metal billet to above the body section of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet with the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes strong, and the upsetting on the pressing forward side can be suppressed. Moreover, since the metal billet, which is provided at least one plane on at least one side, is dilated to be formed, the function for bending the plane of the metal billet towards the inner wall of the container for forming acts. With the interaction, this method of manufacturing a container can form the thick container with lower press pressure than the backward extrusion method or the like. The method of hot pressing a thick metal-made cylinder or a cylindrical container according to the next invention is characterized in that a metal billet having different diameter sections without joint, where its pressing forward side is composed of a member having a section with an outer diameter smaller than an inner diameter of a container or an outer diameter of a diagonal length or a member having a section with an outer diameter of a diagonal length equal with the inner diameter of the container and its backward side is composed of a member having a section with an outer diameter or a diagonal length equal with the inner diameter of the container, is set into the container for press forming which was heated to a press working temperature, and the metal billet is pushed so that the pressing backward side of the metal billet is extended to an end portion of an inlet of the container for forming, and while a center of a workpiece of the metal billet without joint is being bored by a punch, the metal billet is press-worked. This thick metal made cylinder or cylindrical container hot pressing method includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet wit the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, since the metal is supplied from the pressing backward side to the pressing forward side and the pressing forward side is pushed to be spread sideways and is simultaneously worked according to the effect of satisfactory plastic working of the steel heated to high temperature, it fills the space of the container to be formed. For this reason, a pressed product having a predetermined shape is manufactured from the metal billet without joint. With their interaction, in this manufacturing method, the thick container can be formed with lower press pressure than the backward extrusion method or the like. The method of manufacturing a drum or a container of setting a metal billet into a container for forming and hot-dilating the metal billet by means of a boring punch to be operated by a pressing machine, according to the next invention comprises: the step of setting the metal billet, where its pressing forward side has a section having an outer diameter with a diagonal length of not more than an inner diameter of the container and its backward side has a section having an outer diameter substantially equal with the inner diameter of the container, into a container for press forming which was heated to a press working temperature; the step of pushing the metal billet so as to extend the pressing backward side of the metal billet to an end portion of an inlet of the container for forming; and the step of boring a center of a workpiece of the metal billet by means of the boring punch and simultaneously press-working the metal billet. This method of manufacturing a drum or a container includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet wit the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, since the metal billet, in which the pressing forward side is a tetragonal section with its diagonal length is smaller than the inner diameter of the container, is used, the metal billet is dilated by the function for bending each side of the tetragonal section. Moreover, the pressing backward side of the metal billet suppresses the upsetting on the pressing forward side. With their interaction, in this manufacturing method, the thick container can be formed with lower press pressure than the backward extrusion method or the like. The method of manufacturing a drum or a container of setting a metal billet into a container for forming and hot-dilating the metal billet by means of a boring punch to be operated by a pressing machine, according to the next invention comprises: the step of setting the metal billet, where its pressing forward side has a section having an outer diameter with a diagonal length of smaller than an inner diameter of the container and its backward side has a section having a diagonal length substantially equal with the inner diameter of the container, into a container for press forming which was heated to a press working temperature; the step of pushing the metal billet so as to extend the pressing backward side of the metal billet to an end portion of an inlet of the container for forming; and the step of boring a center of a workpiece of the metal billet by means of the punch and simultaneously press-working the metal billet. This method of manufacturing a drum or a container includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet with the container end portion at the time of hot dilation forming, the constraint of the container on the metal billet becomes stronger, and upsetting on the pressing forward side can be suppressed. Moreover, since the metal billet, in which the pressing forward side is a tetragonal section with a sectional length smaller than the internal diameter of the container, is used, the metal billet is dilated to be formed by the function for bending each side of the tetragonal section. Moreover, the pressing backward side of the metal billet suppresses upsetting on the pressing forward side. With their interaction, in this manufacturing method, the thick container can be formed with lower press pressure than the backward extrusion method or the like. Further, since the metal billet to be used in this method has the pressing forward side and backward side whose sections are angular shape, the metal billet is worked comparatively easier than the metal billet having one round section. The method of manufacturing a drum or a container of setting a metal billet into a container for forming and hot-dilating the metal billet by means of a boring punch to be operated by a pressing machine, according to the next invention comprises: the step of setting the metal billet, where its pressing forward side has a section with an outer diameter smaller than an inner diameter of the container and its backward side has a section with an outer diameter substantially equal with the inner diameter of the container, into a container for press forming which was heated to a press working temperature; the step of pushing the metal billet so as to extend the pressing backward side of the metal billet to an end portion of an inlet of the container for forming; and the step of boring a center of a workpiece of the metal billet by means of the punch and simultaneously press-working the metal billet. This method of manufacturing a drum or a container includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet with the container end portion at the time of hot dilation forming, the constraint of the container on the metal billet becomes stronger, and upsetting on the pressing forward side can be suppressed. Moreover, since the pressing backward side of the metal billet has a diameter substantially equal with the inner diameter of the container for forming, upsetting on the pressing forward side can be suppressed. With their interaction, in this manufacturing method, the thick container can be formed with lower press pressure than the backward extrusion method or the like. Further, since the metal billet to be used in this method has the pressing forward side and backward side whose sectional shapes are circular, the metal billet can be worked comparatively easier than the metal billet having different sectional shapes. The method of manufacturing a container according to the next invention depending from the above-mentioned method of manufacturing a container comprises the step of forming the metal billet by means of a forging step and forming at least the pressing forward side of the metal billet into an angular section. The method of manufacturing a container according to the next invention depending from the above-mentioned method of manufacturing a container is characterized in that the forging step includes the step of providing a taper which becomes thinner towards the pressing direction on the pressing forward side of the metal billet. The method of manufacturing a container according to the next invention depending from the above-mentioned method of manufacturing a container is characterized in that the forging step includes the step of providing at least one stepped section so that the pressing forward side of the metal billet becomes thinner gradationally towards the pressing direction. In this method of manufacturing a container, at the final stage of the hot dilation forming, timing at which the metal fills the vicinity of the bottom of the container for forming can be delayed. With this function, since the upsetting phenomenon of the metal billet can be suppressed, an increase in the press pressure at the final stage of the hot dilation forming can be suppressed. The method of manufacturing a container according to the next invention depending from the above-mentioned method of manufacturing a container comprises: the step of providing a drum-shaped member between the metal billet and the bottom of the container for forming and setting the metal billet into the container for forming; the step of pushing the boring punch into the metal billet and hot-dilating the metal billet so as to form the bottomed container where the bottom section and the body section are integral; the step of removing the drum-shaped member from the bottom section of the bottomed container after the forming; and the step of removing a pillar-shaped portion formed on the bottom section of the bottomed container by means of the drum-shaped member. In this manufacturing method, the bottomed container is formed by a drum-shaped member provided at the bottom of the metal billet, and simultaneously a spot facing section is formed on the bottom of the bottomed container. Since the spot facing section has been conventionally provided by cutting, the working requires troublesome steps. However, according to this method, since a pillar-shaped section which remains on the bottom of the container is only removed after the dilation forming, the working does not require less troublesome steps than the conventional method. Here, the drum-shaped member includes polygonal members whose section vertical to the axial direction is triangular, tetragonal or the like, a polygonal member whose angle of the polygon is rounded off and an elliptic member, so the shape is not limited to the drum. The method of manufacturing a container according to the next invention comprises: the step of providing a pillar-shaped member between the metal billet and the bottom of the container for forming and setting the metal billet into the container for forming; the step of pushing the boring punch into the metal billet and hot-dilating the metal billet so as to form the bottomed container where the bottom section and the body section are integral; and the step of removing the pillar-shaped member from the bottom section of the bottomed container after the forming. In this method, the bottomed container is formed by the pillar-shaped member provided at the bottom of the metal billet, and simultaneously the spot facing section is formed on the bottomed container. Since the spot facing section has been conventionally provided by the cutting, the working requires troublesome steps. According to this method, since the spot facing section can be formed simultaneously with the dilation forming, the working requires less troublesome steps than the conventional method. Moreover, since the step of removing the pillar-shaped member can be omitted, troublesome steps are not required for forming the spot facing section in comparison with the method where the spot facing section is formed. The method of manufacturing a container according to the next invention depending from the above-mentioned method of manufacturing a container is characterized in that the body section of the container for forming can move relatively with respect to the bottom section of the container for forming. In this method of manufacturing a container, the metal billet is set into the container where the body section and the bottom section can move relatively so as to be hot-dilated. For this reason, when the metal billet tries to move the body section of the container to the opposite direction to the pressing direction at the time of the hot dilation forming, the body section of the container moves together with the metal billet to the opposite direction to the pressing direction. Namely, since the body of the container and the metal billet to be formed hardly move relatively, an increase in the press pressure can be suppressed at the time of the hot dilation forming. The method of manufacturing a container according to the next invention is characterized in that the body section of the container for forming is divided in an axial direction. In this method of manufacturing a container, since the body section of the container extends along the whole axial direction, even in the case where the metal billet which is long in the axial direction is formed, deformation of the metal billet with respect to the axial direction can be absorbed by the whole container at the time of the hot dilation forming. Therefore, even in the case where the thick container which is long along the axial direction is formed, an increase in the press pressure can be suppressed. The method of manufacturing a container according to the next invention comprises: the upsetting step of placing a pressurizing platform into a ring-shaped die formed with an opening at its inner end portion and putting a metal billet into a mold composed of the die and the pressurizing platform so as to pressurize the metal billet by means of a boring punch; and the metal billet drawing step of supporting the die by means of a drum-shaped spacer and pushing the metal billet by means of the boring punch. At the upsetting step, the metal billet is pressurized by the boring punch so that a material flows to between the opening portion of the die and the boring punch, and the metal billet is deformed into a dish shape. At this time, since the boring punch is held by the metal billet, the boring punch and the die including the metal billet are once allowed to recede. At the drawing step, the spacer is arranged below or above the die so as to support the die, and the boring punch is pushed into so that the metal billet is drawn by the die. As a result, the metal billet is deformed into a cup shape. These two steps are repeated plural times as the need arises so that the metal billet is formed into a final shape. Here, since these steps are heat working, it is necessary to heat the metal billet before the forming. This invention includes the case where the above-mentioned two steps are carried out once so that the metal billet is formed into a final shape. Moreover, the metal billet may be pressurized from above (see FIGS. 21 through 27), or pressurized from below (see FIG. 28). In such a manner the upsetting and the drawing are combined to be used so that an excessive pressure which is required in the backward extrusion forming is not required. For this reason, since the bottomed container can be formed by a normal large-size pressing machine, it is easily manufactured. The method of manufacturing a container according to the next invention comprises: the upsetting preparation step of stacking a plurality of ring-shaped dies formed with an opening on its inner end portion and stacking a plurality of pressurizing platforms respectively in the dies and putting a metal billet into a mold composed of the die and the pressurizing platform; the upsetting step of pressurizing the metal billet from above the mold using a boring punch to be operated by a pressing machine; the receding step of allowing the boring punch and the whole metal billet including and the upper die to recede; the drawing preparation step of removing the used pressurizing platform and placing a drum-shaped spacer onto the next die and placing the receded whole metal billet including the die onto the spacer; the drawing step of pushing the metal billet by means of the boring punch and drawing the metal billet by means of the die; and the repeating step of repeating the above-mentioned steps on the next pressurizing platform and die using a spacer of a length according to deformation of the metal billet. At the upsetting step, the metal billet is pressurized by the boring punch so that a material flows between the opening portion and the boring punch, and the metal billet is deformed with the boring punch being held. At the drawing step, the space is provided below the die and the metal billet is pressurized so that the die is allowed to pass and the metal billet is subject to the draw working. As a result, the metal billet is deformed into a cup shape. Here, the spacer may have any shape as long as it has a drum shape into which the drawn metal billet can be put. The upsetting preparation step through the drawing step are ended, these are further repeated. At this time, as for the die and pressurizing platform, the second ones from the top of the stacked dies and platforms are used. Since the spacer should be longer as the metal billet deforms, they are prepared for each step. In this manufacturing method, since the upsetting and the drawing are combined to be used, the pressurizing force can be suppressed small in comparison with the backward extrusion forming. For this reason, the container can be formed by a normal large-size pressing machine. The present invention will be detailed below with reference to the diagrams. However, the present invention is not limited to the embodiments described below. Moreover, a manufacturing method of a container or a drum of the present invention is not limited to methods to be disclosed below. Further, components of the following embodiments include ones which can be assumed by person skilled in the art. FIGS. 1(a) and 1(b) are explanatory diagrams showing one example of a bottomed container according to the first embodiment. FIGS. 2(a) through 2(e), 2(a′) through 2(e′) and 2(e″) are explanatory diagrams showing the steps of manufacturing the bottomed container 1 shown in FIGS. 1(a) and 1(b). FIGS. 3(a) through 3(c) are perspective views showing one example of a metal billet 200 to be used in the first embodiment. As shown in FIGS. 1(a), a bottom section 1b of the bottomed container 1 according to the first embodiment is formed integrally with a body section 1a, and as is clear from FIG. 1(b), a sectional form of the bottomed container 1 of the first embodiment is circular. In this manufacturing method, the bottomed container 1 is manufactured by a punch according to hot dilation forming. Firstly there will be explained below the metal billet to be used in the manufacturing steps. The metal billet 200 is manufactured by cutting or free forging a foundry molding lump or a metal lump of molten metal before the hot dilation forming step, explained next. At the forging step, it is desirable that at least forward side of the metal billet in a pressing direction is formed into an angular section. As a result, an effect of the hot dilation forming can be utilized more effectively. Here, in the first embodiment, the metal lump is freely forging so that the integral metal billet 200 without a joint is manufactured, but a metal billet which can be used in the present invention is not limited to this. As shown in FIGS. 3(a) through 3(c), a sectional form of the metal billet 200 used in the present embodiment is circular on a backward side in the pressing direction (hereinafter, pressing backward side) 200a, and is square on a forward side in the pressing direction (hereinafter, pressing forward side) 200b. An outer diameter of the pressing backward side 200a is larger than a diagonal length of the pressing forward side 200b, and the outer diameter of the pressing backward side 200a is substantially equal with an inner diameter of a container 300, and the diagonal length of the pressing forward side 200b is shorter than the inner diameter of the body section 300 of the container for forming (FIG. 3(b)). Here, the inner diameter of the body section 300 of the container for forming is represented by a broken line. Further in this example, a section 970 of the metal billet 200 vertical to an axial direction on the pressing forward side 200b includes a projection image 920 of a section of a boring punch 410 vertical to the axial direction (FIGS. 3(b) and 3(e)). Here, the sectional form, dimension, outer form and the like of the metal billet 200 are not limited to this example. Another example of the billet which can be applied to the present invention will be explained later. Next, there will be explained below the hot dilation forming steps. Prior to the hot dilation forming, the metal billet 200 is heated to a temperature where it is easily hot-dilated by a heating furnace (not shown). Since the heating temperature is determined by a material and the like of the metal billet 200, it is not determined ultimately. Here, as for a carbon steel material which is used for a body of the cask for containing and transporting and temporarily storing used nuclear fuel, it is desirable that the heating temperature is set to 1100° C. to 1300° C. When the heating temperature exceeds this range, crystal grains become coarse and oxidation and decarbonization occur on the surface, and the material is embrittled and is easily cracked. In the case of the carbon steel, as a percentage of the carbon is higher, the heating temperature becomes lower within the range. The metal billet 200, which is heated to the temperature at which it is easily hot-dilated by an electric furnace or the like, is upset into a body section 300 of the container for forming as shown in FIG. 2(a). The metal billet 200 which is upset into the body section 300 of the container for forming is upset by a large punch 400 having an outer diameter substantially equal with or larger than the outer diameter of the metal billet 200, and an extended section 201 extended to the container 300 is provided on the pressing backward side 200a of the metal billet 200 (see FIG. 2(b)). The extended section 201 is provided on an end portion of the metal billet 200 so that a constraint force in the axial direction of the metal billet 200 can be heightened at the hot dilation forming step by means of the punch. Since the upsetting phenomenon of the metal billet 200 is suppressed by this function and metal flow towards the pressing direction and the opposite direction can be reduced, a rise in the press pressure can be suppressed. At the same time, the form of the end surface of the bottomed container after the forming can be satisfactory. Here, even if the extended section 201 is not provided on the metal billet 200, the upsetting phenomenon can be suppressed by a friction force which is generated between an inner wall of the body section 300 of the container for forming and a side surface of the pressing backward side 200a of the metal billet 200. However, in order to lower the press pressure and obtain more organized end surface form, it is desirable that the extended section 201 is provided. After the extended section 201 is formed on the end portion of the metal billet 200, the sequence goes to the hot dilation forming step by means of a boring punch 410. In order to bore a hole at the center of the metal billet 200, firstly the punch 410 is placed on the center of the end surface of the metal billet 200 by a locating guide 310 attached to the body section 300 of the container for forming (see FIG. 2(c)). Next, the boring punch 410 is pushed by a pressing machine (not shown) so that the metal billet 200 is hot-dilated. When the boring punch 410 is pushed into the metal billet 200 by the pressing machine, the extended section 201 of the metal billet 200 is engaged with the upper end portion of the body section 300 of the container for forming, and the upsetting phenomenon of the metal billet 200 is suppressed. Moreover, the metal of the thick portion on the pressing backward side 200a of the metal billet 200 is deformed so as to fill the container 300 (see FIG. 2(d)). As a result, since the metal of the pressing backward side 200a is pushed against the inner wall of the body section 300 of the container for forming, the upsetting phenomenon of the metal billet 200 can be suppressed also by this function. As a result, the rise in the press pressure is suppressed, and the end surface form of the bottomed container after the forming can be satisfactory. When the boring punch 410 is pushed into the metal billet 200, the metal which exists just below the boring punch 410 becomes a hemispheric metal lump and moves to the pressing forward side 200b together with the boring punch 410. Due to this phenomenon, a cross section of the pressing backward side 200a of the metal billet 200 vertical to the axial direction should be larger than that of the pressing forward side 200b. Further, when the boring punch 410 is pushed into the metal billet 200, the metal on the pressing forward side 200b of the metal billet 200 is deformed so as to be spread towards the inner wall of the container 300 due to excellent property of plastic deformation owned by the steel heated to high temperature and a phenomenon that the metal lump is supplied from the pressing backward side 200a. Namely, it is the hot dilation forming. When the boring punch 410 is pushed to a predetermined depth previously set, the hot dilation forming is ended there (see FIG. 2(e)). There will be explained below types of the metal billet 200 applicable to the manufacturing method of the present invention. As shown in FIG. 3(a), at least the metal billet which is formed so that a sectional form vertical to the axial direction on the pressing forward side is polygonal can be applied to the manufacturing method of the present invention. When such a metal billet is used, since the metal billet is deformed so as to be spread towards the inner wall of the container for forming in the hot dilation forming, the press pressure can be suppressed in comparison with backward extrusion or the like. Here, the section of the metal billet 200 vertical to the axial direction shown in FIG. 3(a) is tetragonal, but the section is not limited to this. Further, the metal billet applicable to the manufacturing method of the present invention may have the following relationship. Namely, the section vertical to the axial direction on the pressing backward side has a relationship that it contains a projection image of a section vertical to the axial direction on the pressing forward side. Moreover, a projection image of the section vertical to the axial direction on the pressing backward side has a relationship that it is contained in the inner side of the section of the container for forming vertical to the axial direction. Here, the form of the inner side of the section of the container for forming vertical to the axial direction may be identical to the projection image of the section vertical to the axial direction on the pressing backward side. It is desirable that the metal billet which satisfies these relationships is used when a large bottomed container with large thickness is formed. The projection image will be explained below with reference to FIGS. 3(c) and 3(d). Here, the projection image is represented by a broken line, and the section is represented by a continuous line. FIG. 3(c) shows a state that a section 950 vertical to the axial direction on the pressing backward side of the metal billet contains a projection image 900 of the section vertical to the axial direction on the pressing forward side. FIG. 3(d) shows a state that a projection image 910 of the section vertical to the axial direction on the pressing backward side is contained in an inner side 960 of the section of the container for forming vertical to the axial direction. Moreover, FIG. 3(e) shows a state of the boring punch having a relationship that a projection image 920 of the section vertical to the axial direction is contained in a section 970 vertical to the axial direction on the pressing forward side of the metal billet. Here, the projection image 920 of the section vertical to the axial direction in FIG. 3(e) is a projection image of the boring punch. “Containing” in the present invention means that a whole portion surrounded by the broken line representing the projection image exists on the inside of a portion surrounded by the continuous line representing the section. In the case where even a part of the portion surrounded by the broken line exist on the outside of the portion surrounded by the continuous line, this is not included in the concept of “containing”. Moreover, in the case where the form of the section is identical to the projection image, this is not included in the concept of “containing”. It is desirable that the projection image of the boring punch is contained in the section vertical to the axial direction on the pressing forward side of the metal billet (see FIG. 3(e)). However, the projection image of the boring punch vertical to the axial direction may be identical to the section of the metal billet vertical to the axial direction on the pressing forward side. Moreover, the section of the boring punch vertical to the axial direction may contain the projection image of the section of the metal billet vertical to the axial direction on the pressing forward side. However, in the case of a relationship that the section of the boring punch vertical to the axial direction contains the projection image of the section vertical to the axial direction on the pressing forward side of the metal billet, when the cross section of the boring punch becomes large, a thickness of the body section of the container to be formed becomes thin. For this reason, the body section of the container easily ruptures during the hot dilation forming. Therefore, in the case of the relationship that the section of the boring punch vertical to the axial direction contains the projection image of the section of the metal billet vertical to the axial direction on the pressing forward side, it is necessary to suppress the cross section of the boring punch within a range that the body section of the container does not rapture. FIGS. 4(a) through 4(e) are explanatory diagrams showing examples of another metal billet according to the first embodiment. As is clear from FIGS. 4(a) through 4(d), these examples satisfy a condition that the section 950 vertical to the axial direction on the pressing backward side 200a of the metal billet 200 contains the projection image 900 of the section vertical to the axial direction of the pressing forward side 200b (FIG. 3(c)). In the case where the section of the pressing forward side 200b is tetragonal as shown in FIGS. 4(a) and 4(b), the metal billet 200 is deformed by mainly a force which directs towards an outer side in the radial direction of the body section 300 of the container, namely, a force which bends the side surface of the metal billet having a plane to the inner wall side of the body section 300 of the container for forming at the time of the hot dilation forming. FIG. 5 is a conceptual diagram showing a state of the deformation. A broken line in the diagram shows a process that the metal billet 200 is expanded towards the inner wall of the body section 300 of the container for forming. In the case where section vertical to the axial direction is tetragonal, the boring punch is pushed into so that a force F, which directs from the center of the metal billet 200 to the outside in the radial direction of the body section 300 of the container for forming, acts. Since the force F bends the side surface of the metal billet 200 towards the inner wall of the container for forming, the metal billet 200 is dilated to the inner wall of the container for forming by this bending function. Particularly this bending function acts effectively when the metal billet having a plane on the side surface is set into the container for forming having a circular inside of the section. Therefore, when the metal billet is dilated by the bending function, the hot dilation forming requires less press pressure, and defects such as a crack generated at the time of the forming can be suppressed. Even if the metal billet whose section vertical to the axial direction has a tetragonal shape is hot-dilated by using the boring punch whose section vertical to the axial direction has a tetragonal shape, the metal billet is dilated by the bending function. Therefore, also in this case, the hot dilation forming requires the less press pressure, and the defects such as a crack generated at the time of the forming can be suppressed. In the case where the section vertical to the axial direction on the pressing forward side 200b is circular as shown in FIG. 4(c), the above-mentioned effect is slightly reduced, but the metal billet 200 has spaces between the pressing forward side 200b and the inner wall of the body section 300 of the container. Therefore, since the metal on the pressing forward side is dilated in the spaces at the time of the hot dilation forming, the dilating deformation of the metal billet is not constrained by the body section 300 of the container for forming, and the press pressure can be suppressed small. Moreover, in this case, when the metal billet is hot-dilated by using the boring punch whose section vertical to the axial direction has a tetragonal shape, the bending function acts. For this reason, the press pressure is less than the case where the metal billet is hot-dilated by using the boring punch having a circular section vertical to the axial direction. As shown in FIGS. 4(a), 4(c) and 4(d), in the case where the section of the pressing backward side 200a vertical to the axial direction is circular and its diameter is substantially equal with the diameter of the body section 300 of the container, the extended section 201 formed on the body section 300 of the container for forming (see FIG. 3(b)) can be formed uniformly. Therefore, at the time of hot dilation forming, since the upsetting phenomenon of the metal billet 200 can be suppressed effectively by the extended section 201, the press pressure can be suppressed low, and the form of the end surface of the container after the forming can be satisfactory. As shown in FIG. 4(b), in the case where the section of the pressing backward side 200a is tetragonal and its diagonal length is substantially equal with the diameter of the body section 300 of the container for forming, the extended section 201 is formed partially on the upper end of the body section 300 of the container. For this reason, in comparison with the case where the extended section 201 is not provided, the upsetting phenomenon of the metal billet 200 can be suppressed more effectively, but in comparison with the case where the extended section 201 is formed along the whole periphery of the upper end of the body section of the container for forming, this effect is slightly reduced. Further, the metal billet, which is formed so that the form of the section vertical to the axial direction of the pressing forward side 200b or the pressing backward side 200a of the metal billet 200 is pentagonal (or more) or triangular, can also be applied to the manufacturing method according to the first embodiment. Moreover, as shown in FIGS. 4(d), when the side surface of the pressing forward side 200b has at least one or more planes, since this portion is hot-dilated by the bending, the press pressure can be suppressed low. In addition, when a number of planes on the side surfaces of the metal billet 200 is not less than three, namely, the section of the metal billet 200 vertical to the axial direction is triangular or more, the press pressure can be suppressed lower. However, when a number of planes increases, namely, a number of angles of the polygonal section vertical to the axial direction increases, since the form of the polygonal section closes to a circle, the effect which suppresses the press pressure low is reduced. Therefore, it is desirable that a number of the planes of the side surface on the pressing forward side 200b is selected within the range that the press pressure can be suppressed low. Moreover, even in the case where the form of the section of the metal billet 200 vertical to the axial direction is of substantially drum as shown in FIG. 4(e), it is included in the metal billet of the present invention as long as the planes are provided on the side surface of the metal billet 200. FIGS. 6(a) through 6(c) are perspective views showing another metal billet applicable to the first embodiment. The metal billet 200 is provided with a stepped section on the pressing forward side 200b so that it becomes thinner gradationally towards the pressing direction. As a result, at the time of the hot dilation forming, the timing that the metal of the pressing forward side 200b fills the vicinity of the bottom of the body section 300 of the container for forming can be slow. Therefore, particularly at the final state of the hot dilation forming, a rise in the press pressure can be suppressed. Moreover, since slight flow to the pressing direction is formed by this stepped section, a forging degree of a molded form can be heightened, and shortage of forging materials can be prevented. Further, since a change of the section is gradate, the manufacturing becomes easier than the case where a taper, mentioned later, is provided. Here, a number of the stepped sections is not limited to the above example, but the number can be suitably increased or decreased according to a pressing condition and the like. In addition, as shown in FIG. 6(b), even if the pressing forward side 200b is provided with a taper which becomes thinner towards the pressing direction, the function and effect which are similar to the case where the stepped section is provided on the pressing forward side 200b can be obtained. Further, as shown in FIG. 6(c), when the metal billet 200 is manufactured, the extended section 201 which is engaged with the upper end portion of the container 300 for forming may be previously provided on the metal pressing backward side 200a. As a result, the step of forming the extended section 201, which is extended to the body section 300 of the container, on the pressing backward side 200a of the metal billet 200 of is not required before the hot dilation forming, and the container manufacturing steps can be simplified. FIGS. 7(a) through 7(c) are explanatory diagrams showing another metal billet applicable to the first embodiment. As shown in the diagrams, the metal billet 200 is characterized in that the section vertical to the axial direction is constant along the pressing direction and the extended section 201 which is engaged with the upper end portion of the container 300 for forming is provided on its one end. Even in the case where such a metal billet 200 is used, since the upsetting phenomenon of the metal billet can be suppressed by the extended section 201 at the time of hot dilation forming, a rise in the press pressure can be suppressed. Here, the sectional form of the metal billet 200 is not limited to a tetragonal form, and it maybe polygonal, and the side surface of the metal billet 200 may provided with at least one plane. Moreover, the extended section 201 may be previously provided on the metal billet 200, or the metal billet 200 is set into the container 300 for forming and the extended section 201 may be provided. When the metal billet 200 is dilated to be deformed so as to be spread towards the inner wall of the container 300 (see FIGS. 2(d) and 2(e)), a friction force is generated between the metal of the metal billet 200 and the inner wall of the container 300. This friction force is caused by transfer of the metal of the pressing forward side 200b to the opposite direction to the pressing direction along the inner wall of the body section 300 of the container. Here, at the middle process of the hot dilation forming in the manufacturing method according to the first embodiment, this friction force is hardly generated. However, at the final stage of the hot dilation forming, since the metal fills the lower section of the container for forming, this friction force is generated. Due to this friction force, the body section 300 of the container for forming tries to move to the opposite direction to the pushing direction of the punch 410. When the body section 300 of the container for forming and the bottom section 301 of the container for forming are fixed, the metal of the pressing forward side moves against the friction force, and at the final stage of the hot dilation forming, excessive load is required. In order to solve this problem, in the first embodiment, the body section 300 of the container for forming and the bottom section 301 of the container for forming can move relatively. With such a structure, when the body section 300 of the container for forming tries to move to the opposite direction to the pushing direction of the punch 410 due to the friction force, the body section 300 of the container for forming also moves to the opposite direction to the pushing direction of the punch 410 together with the metal billet 200 to be formed (FIG. 2(e)). Namely, since the body section 300 of the container for forming and the metal billet 200 to be formed seldom move relatively, an increase in the load can be suppressed at the final stage of the hot dilation forming. In the present embodiment, the body section 300 of the container for forming and the bottom section 301 of the container can move relatively, and also the body section 300 of the container for forming is divided so as to capable of moving along the whole metal billet 200. As a result, even in the case where the bottomed container which is long in the axial direction is formed, an increase in the load can be suppressed at the final stage of the hot dilation forming. FIGS. 8(a) and 8(b) are sectional views showing divided sections of the body section 300 of the container for forming to be used in the first embodiment. The divided sections of the body section 300 of the container for forming may be constituted so as to be overlapped with each other as shown in FIG. 8(a) and the body sections 300a and 300b of the container for forming may move relatively at the time of hot dilation forming. Moreover, as shown in FIG. 8(b), a concave section is formed on the one body section 300a of the container for forming, and a convex section is provided on the other body section 300b of the container for forming so as to be combined. As a result, the body sections 300a and 300b of the container for forming may move relatively at the time of hot dilation forming. In the present embodiment, the body section 300 of the container for forming is divided into two, but a number of divisions can be changed suitably according to the height of the metal billet 200. Moreover, the body section 300 of the container for forming is only divided, or the body section 300 of the container is not divided and the body section 300 and the bottom section 301 of the container for forming can only move relatively. As a result, an increase in the load can be suppressed at the time of hot dilation forming. When the punch 410 is pushed into a set predetermined depth, the hot dilation forming is ended there (FIG. 2(e)). As shown in FIG. 2(e″), a cylindrical spacer 302 is placed instead of the bottom section 301 of the container for forming and the bottom section of the metal billet 200 is punched so that a drum can be formed by this manufacturing method. When the thick container whose length in the axial direction reaches a several meters is manufactured by the manufacturing method, since the press pressure can be reduced to a several part of the conventional press pressure, the container can be manufactured by the conventional facilities. Moreover, since the bottomed container in which the bottom section and the body section are integral with each other can be manufactured by one-time working, the manufacturing requires less steps, and this method is suitable also for mass production. The metal billet 200 which was subject to the hot dilation forming is cooled to normal temperature by natural cooling, forced cooling or control cooling. In order that the sectional form is adjusted or the external shape or the internal shape of the formed container is finished to a predetermined dimension, the container may be subject to the cutting or the like. Next, a result of the concrete example that an integrally cylindrical bottomed container is manufactured by the above-mentioned method will be shown. As a comparative example, a result of manufacturing the integrally cylindrical bottomed container by applying the Erhardt (elrhardt or Ehrhard) boring method which has been conventionally used is also shown. In both the concrete example and the comparative example, the cylindrical container was formed by using a cylindrical container having an inner diameter of 943 mm. As a material of the cylindrical container, carbon steel in which a percentage of carbon (C) is 0.1% was used, but stainless steel may be used. Firstly after the metal billet of carbon steel was heated to 1250° C., it was forged into a metal billet in which its section in the axial direction has a T-shaped different diameter section by the free forging method. The pressing forward side of this metal billet has a quadrate section whose diagonal length is 875 mm smaller than an inner diameter of the container for forming, and a length of the axial direction is 1896 mm. The pressing backward side has a circular section having an outer diameter of 928 mm substantially equal with the inner diameter of the container for forming, and a length of the axial direction is 574 mm. After the metal billet was again heated to 1250° C., it is set into the container for forming, and the center of the workpiece is hot-dilated by the punch so that an elongate cup-shaped cylindrical container having length of 2420 mm and thickness of 165 mm was formed. Meanwhile, in the comparative example, the carbon steel which is the same as the concrete example was used as the material of the cylindrical container, and after the metal billet was heated to 1250° C., it was forged into an angular metal billet having uniform sectional form along the whole length of the axial direction was manufactured by the free forging method. The sectional form of this metal billet is quadrate, and a length of its diagonal is 928 mm which is substantially equal with the inner diameter of the container for forming. Moreover, a length of the axial direction is 2470 mm. After the metal billet was again heated to 1250° C., it was hot-dilated so that the cylindrical container whose size is the same as the concrete example was manufactured. Table 1 shows evaluated results of the forming load and the end surface form in both the pressing methods. As is clear from the comparison, according to the manufacturing method of the present invention, the press forming load is smaller and the product yield is higher than the conventional manufacturing method. Moreover, since defective portions of the end surface form which are seen in the conventional manufacturing method seldom exist, the product can be finished by simple working after the hot dilation forming. TABLE 1EVALUATION RESULTS OF BOTH METHODSPress formingSectionalMethodloadformYieldMethod of the2400 tonSatisfactory70%PresentInventionMethod of the3980 tonDefective60%Comparativeportions ofExampleform aregenerated There will be explained below an example of cutting an outer side and an inner side of the bottomed container formed to be used as the radioactive substance container such as a cask or a canister. FIG. 9 is a schematic diagram showing an apparatus for cutting the outer side of the hot-dilated bottomed container. The bottomed container 1 is placed on a rotation supporting platform 154 having a roller and can be rotated freely in a circumferential direction. A fixing table 141 is provided on the outer side of the bottomed container 1, and a movable table 142 which slides on the fixing table in the axial direction of the bottomed container 1 is provided. A cutting tool 160 is attached to the movable table 142, and the cutting tool 160 cuts the outer circumference of the bottomed container 1. A roller 161 attached to the rotation supporting platform 154 is connected to a motor 162. The rotation of the motor 161 is transmitted to the bottomed container 1 via the roller 161 so as to rotate the bottomed container 1. When the motor 161 rotates and the bottomed container 1 starts to rotate to a direction of an arrow in the diagram, a servo motor 157 and a ball screw 158 which are provided to the end portion of the fixing table 141 moves the movable table 142 to the axial direction of the bottomed container 1, and the cutting tool 160 attached to the movable table 142 cuts the outer circumference of the bottomed container 1. Moreover, when the outer circumference is cut by a face mill or the like so that a plane is provided, not only the bottomed container having a circular section vertical to the axial direction but also the polygonal bottomed container can be formed. There will be explained below an example that the inner side of the formed bottomed container is cut. FIG. 10 is a schematic diagram showing an apparatus for working the inner side of the bottomed container. A machining apparatus 140 is composed of a fixing table 141 which pierces through a body 101 and is placed and fixed inside the bottomed container 1, a movable table 142 which slides on the fixing table 141 in the axial direction, a saddle 143 which is located and fixed onto the movable table 142, a spindle unit 146 which is composed of spindles 144 and a driving motor 145 provided on the saddle 143, and a face mill 147 provided on a spindle axis. Moreover, a reactive force receiver 148 which is formed with a contact portion according to the internal shape of the bottomed container 1 is provided on the spindle unit 146. The reactive force receiver 148 is detachable and slides along a dovetail groove (not shown) in a direction of an arrow in the diagram. Moreover, the reactive force receiver 148 has a clamp device 149 for the spindle unit 146, and is fixed to a predetermined position. Further, a plurality of clamp devices 150 are attached into a lower groove of the fixing table 141. The clamp devices 150 is composed of a hydraulic cylinder 151, a wedge-shaped moving block 152 which is provided on an axis of the hydraulic cylinder 151, and a fixing block 153 whose tilt surface comes in contact with the moving block 152. The shaded portions in the diagram are attached to the groove inner surface of the fixing table 141. When the axis of the hydraulic cylinder 151 is driven, the moving block 152 comes in contact with the fixing block 153, and the moving block 152 moves slightly downward due to the wedge effect (represented by dotted line). As a result, since the lower surface of the moving block 152 is pushed against the inner surface of a cavity 102, the fixing table 141 can be fixed inside the bottomed container 1. In addition, the bottomed container 1 is placed on a rotation supporting platform 154 composed of a roller, and is freely rotated in a radial direction. Moreover, a spacer 155 is attached between the spindle unit 146 and the saddle 143 so that a height of the tool 147 on the fixing table 141 can be adjusted. A thickness of the spacer 155 is the same as a dimension of one side of an angular pipe composing the basket. A servo motor 156 provided on the movable table 142 is driven so that the saddle 143 moves in the radial direction of the body 101. The movement of the movable table 142 is controlled by a servo motor 157 and a ball screw 158 provided on the end portion of the fixing table 141. Here, as the working proceeds, the shape of the inside of the bottomed container 1 changes, and thus it is necessary that the reactive force receiver 148 and the moving block 152 of the clamp devices 150 are replaced by ones having suitable shape. FIGS. 11(a) through 11(d) are explanatory diagrams showing one example of the method of working the inner side of the bottomed container 1. Firstly the fixing table 141 is fixed to a predetermined position inside the bottomed container 1 by the clamp devices 150 and the reactive force receiver 148. As shown in FIG. 11(a), the spindle unit 146 is moved along the fixing table (not shown) at a predetermined cutting speed, and the inner side of the bottomed container 1 is cut by the tool 147. When the cutting in this position is finished, the clamp devices 150 are removed so that the fixing table 141 is released. As shown in FIG. 11(b), the body 101 is rotated through an angle of 90° on the rotation supporting platform 154, and the fixing table 141 is fixed by the clamp devices 150. Similarly the cutting is carried out by the tool 147. Thereafter, the similar steps are repeated twice. Next, the spindle unit 146 is rotated through an angle of 180°, and as shown in FIG. 11(c), the inside of the cavity 102 is cut successively. Also in this case, similarly to the above-mentioned case, while the body 101 is being rotated through an angle of 90°, the working is repeated. Thereafter, as shown in FIG. 11(d), the spacer 155 is attached to the spindle unit 146 so that the height of the spindle unit is heightened. The tool 147 is fed in the axial direction in this position, and the inside of the bottomed container 1 is cut. This is repeated while the body 101 is being rotated through an angle of 90° so that a shape which is required for inserting an angular pipe (not shown) for containing used nuclear fuel is inserted is approximately finished. Here, the working can be carried out not only by a special machine but also by general horizontal boring machine and vertical boring machine. The above explanation referred to the example that the bottomed container 1 is laid and the outer side and the inner side are cut. However, the bottomed container 1 stands upright and the outer side and the inner side of the container may be cut by a working machine, explained below. Concretely, this working machine has a rotation table where a bottomed container to be worked is placed and the container is rotated, a crane for placing the bottomed container on the rotation table and moving it from the rotation table after the working, a movable table placed on a base, a saddle which is placed on the movable table and can move in a movable direction and a right angle direction of the movable table, a column which is placed on the saddle and supports an arm moving up and down, and the arm which is mounted to the column to be movable up and down in a vertical direction and has an attachment with a tool on its forward end and moves up and down with respect to a workpiece so as to work the workpiece. The attachment to be attached to the forward end of the arm is replaced so that this working machine can cope with various workings such as milling and boring. When the bottomed container is started to be worked, the bottomed container as a workpiece is placed on the rotation table by the crane, it is centered and is fixed onto the rotation table. When the outside of the bottomed container is cut into a cylindrical shape, a cutting tool is mounted to the attachment attached to the arm, and while the rotation table is being rotated at a predetermined number of revolution, the bottomed container is cut by this cutting tool. Here, since the column to which the arm is attached is placed on the saddle, the saddle and the movable table are moved so that the arm can be moved. Therefore, the arm is moved to an arbitrary position, and an arbitrary cutting amount can be set. Moreover, since the arm can be moved up and down, the arm is moved along the axial direction of the bottomed container so that the whole side surface of the bottomed container can be cut. Since these movements require accuracy, it is desirable that the rotating movement of the servo motor or the stepping motor is converted into a linear motion by a ball screw or the likes and the movable table or the like is moved. When the outer circumference of the bottomed container having circular sectional shape in a radial direction is cut and the container is desired to be worked into a polygonal shape such as an octagonal prism, an attachment for a face mill is attached to the arm, and the side surface of the bottomed container is cut by face milling cutting. When the arm is moved up and down and one surface of the bottomed container in the whole axial direction is cut, the rotation table is rotated through an angle of 45°, and a next side surface is worked. When this work is repeated eight times, the bottomed container whose external shape of the section in the radial section is octagonal can be manufactured. In such a manner, the bottomed container having an arbitrary polygonal section can be manufactured. When the bottomed container is used as a cask for containing used nuclear fuel, it is desirable that the internal shape of the bottomed container matches with at least one part of the outer periphery of a basket for containing used nuclear fuel aggregate. This is because the basket can be easily inserted and fixed into the container. Such a sectional shape is shown in FIG. 15(d), for example. In order to form the inner side of the bottomed container into such a shape, the attachment to be mounted to the arm is replaced by one for end mill, for example, and an angular portion inside the section is worked into a stepped form. Firstly, the saddle and the movable table are moved, the arm is moved to above the bottomed container placed on the rotation table. Next, the arm is lowered and the attachment with the end mill is inserted into the bottomed container so that the end mill is located. Thereafter, the inner side of the bottomed container is cut with a predetermined cutting amount. The cutting is given to the bottomed container some times and its inner side is cut, and when a predetermined shape is obtained, the cutting at the first stage is finished. When the necessary stepped form is obtained at one angular portion, the rotation table is rotated through an angle of 90°, and a next angular portion is worked. When this work is repeated four times, the bottomed container for the cask having the sectional shape in the radial direction as shown in FIG. 15(d) can be manufactured. Here, when the inner side of the bottomed container is cut, since there is not space for cutting chips and cutting oil, the cutting cannot be carried out during the working. For this reason, it is desirable that the cutting chips and the like are removed from the inner side of the on-working bottomed container by discharging means such as a vacuum pump. When the bottomed container is cut with it is in the upright state, the process for the cutting chips and the like is required unlike the case of the laid state, but an influence of deformation due to gravity can be reduced. When this working machine is inverted to be constituted, since the bottomed container is worked with its opening faces downward, when the inner side of the bottomed container is cut, the cutting chips and the like can be easily discharged. There will be explained below an example that the bottomed container manufactured by the method of the present invention is applied to the cask as the used nuclear fuel container. FIGS. 12(a) and 12(b) show the cask according to the embodiment of the invention: FIG. 12(a) is an axially sectional view; and FIG. 12(b) is a radially sectional view. The cask 100 is composed of a bottomed container 1 having a basket 3 in its inner side, a neutron shielding material 2 such as resin or silicone rubber provided on the outer side of the bottomed container 1, and an outer drum 4 to be the outer surface of the cask 100. The bottomed container 1 is formed with the inner side and the outer side by the above-mentioned cutting. A primary cover 5 and a secondary cover 6 are provided on the upper section of the bottomed container 1, and resin 7 for shielding neutron is sealed into the secondary cover 6. Moreover, the bottomed container 1 has a cylindrical shape with a bottom formed by punching draw working, and is made of carbon steel or stainless steel having γ rays shielding function. The neutron shielding material 2 is a polymeric material containing a lot of hydrogen and has a neutron shielding function. Moreover, a shielding body 9 into which a neutron shielding material 8 such as resin or silicone rubber is sealed is mounted to the lower section of the bottomed container 1. The basket 3 is constituted so that cells for containing used nuclear fuel aggregate (no shown) are arranged in a lattice form, and is composed of a composite martial of boron and aluminum. In addition, in order to secure sealing performance for a pressure resistant container, a metal gasket is provided between the primary cover 5, the secondary cover 6 and the bottomed container 1. A plurality of internal fins 10 made of copper for heat conduction are welded between the bottomed container land the outer drum 4, and the neutron shielding material 2 is poured into spaces formed by the internal fins 10 in a flow state and is heated to be solidified. The primary cover 5 and the secondary cover 6 are made of carbon steel or stainless steel having γ rays shielding function. Since the cask 100 uses the bottomed container 1, in comparison with the conventional case where a bottom plate is welded, the manufacturing steps can be reduced. Moreover, since a bottom plate was conventionally welded to the bottomed container, the sealing property of the welded portion depends upon the quality of the welding, but a problem of the sealing property on this welded portion in the bottomed container 1 is extremely low. Here, in order to realize the cask 100 of the present invention, shape and material of the basket 3, a charging state of the neutron shielding material 2, and a number and positions of the internal fins 10 in the bottomed container 1 are not limited to the example shown in FIGS. 12(a) and 12(b). The method of manufacturing the bottomed container according to the first embodiment is suitable for manufacturing a so-called thick container having a thickness with respect to the diameter of the cylinder. Further, the manufacturing method of the present invention is suitable particularly for the case where a container, in which a ratio of the axial length to the inner diameter is 1:1 or more, is manufactured in the thick containers. When the ratio exceeds the above-mentioned numerical value, as the forming proceeds in general hot working, the press pressure increases, but in the manufacturing method according to the embodiment the press pressure does not greatly increase at the beginning and the end of the working. Concretely, the manufacturing method according to the embodiment is particularly suitable for the case where a cask or the like as a large bottomed container, in which the thickness is thick with respect to the diameter and the axial length reaches a several meters, is manufactured. In order to manufacture such a large and thick bottomed container with its bottom integral, a several ten-thousand ton scale pressing machine was conventionally required. However, when such a so-called thick and large bottomed container is manufactured by the manufacturing method of the present invention, the press pressure of only about ten-thousand ton is required. For this reason, even if a pressing machine of several ten-thousand ton is not used, the bottomed container can be formed by an existing large pressing machine. Moreover, since the formed container has excellent sectional form and defects do not occur on the surface and the inner side, adjustment after the forming is seldom required. Here, the manufacturing method of the present invention is not limited to such a thick and large bottomed container, and a canister as a radioactive substance container with comparatively thin thickness can be manufactured by this method. In addition, with the manufacturing method of the present invention, a cylinder for a large pressing machine, a container for chemical plant, a reactor container for petroleum refining plant, an ammonia synthetic cell, a heat exchange container, a pressure container such as a boiler, a casing for a large rotational equipment for containing a hydroelectric water turbine, a body of submarine and ship can be manufactured. Moreover, the material which can be used in the method of the present invention is not limited to carbon steel, and the material includes iron materials such as stainless steel, low alloy steel and the like, nonferrous metal such as nickel alloy, aluminum metal, copper metal and magnesium metal. FIG. 13 is a perspective view showing the bottomed container according to a second embodiment of the present invention. The bottomed container 1 shown in FIG. 13 is characterized in that its external shape and internal shape are octagonal. Moreover, at least one of the external shape and the internal shape of the container may be octagonal. Since a basket for supporting a fuel bar aggregate is housed in the bottomed container of the cask as a radioactive substance container, it is preferable that the internal shape of the bottomed container is formed into a shape which matches with the basket particularly in a cask. Therefore, the internal shape of the cask is desirably octagonal instead of circular. Moreover, in the case where the internal shape of the cask is octagonal, since it is advantageous to a dimension and a weight that the thickness of the cask body is uniform as much as possible, it is desirable that the external shape of the cask body is also octagonal. This bottomed container can cope with such requirements. FIGS. 14(a) and 14(b) are sectional view showing the container body and a punch for manufacturing the bottomed container according to the second embodiment. A sectional shape of the inside of a body section 300 of the container for forming is substantially octagonal, and the external shape of the boring punch 410 is also substantially octagonal. When the body section 300 of the container for forming and the boring punch 410 are used in the hot dilation forming described in the first embodiment, an increase in the load at the time of the hot dilation forming is suppressed, and defects on a surface of a workpiece is suppressed after the forming, and the bottomed container having excellent end surface shape and a polygonal section can be manufactured. FIGS. 15(a) through 15(d) are sectional views vertical to the axial direction showing examples of the bottomed container capable of being formed by the manufacturing method according to the second embodiment. The section of the body section of the container for forming and the external shape of the boring punch are changed suitably so that the bottomed container having such a sectional shape can be formed. It is desirable that particularly the boring punch 410 for forming the internal shape of the cask is changed suitable according to the shape of the basket for containing used nuclear fuel. When the boring punch whose external shape is the internal sectional shape shown in FIG. 15(d) is used, for example, the internal shape can be formed according to the shape of the basket. FIGS. 16(a) through 16(d) are axially sectional views showing examples of the bottomed container capable of being formed by the manufacturing method according to the second embodiment. The internal shape of the bottom section of the container 300 for forming and the forward end shape of the boring punch 410 match with the shape of the bottom of the bottomed container so that these containers can be formed. The container shown in FIG. 16(d) may be bored on the bottom section after the forming, or may be formed by the boring punch provided with a protrusion at its forward end. The container formed in such a manner can be used as a container, in which its bottom section formed integrally with the body section requires not a plane but a curved surface. For example, this container can be applied to a casing and the like for a large rotating equipment for containing a hydroelectric water turbine. FIG. 17 is a axially sectional view showing the bottomed container according to a third embodiment. The bottomed container 1 is characterized in that a body and a bottom are formed integrally and a spot facing section is also formed on the bottom of the container. The bottom provided with the spot facing section was conventionally mounted to a thick cylinder by welding, but in the manufacturing method, besides the step of providing the spot facing section on the bottom, the welding step and the heat treating step after the welding are required. For this reason, there arises a problem that the manufacturing requires troublesome steps. According to the method of manufacturing a bottomed container of the present invention, since the bottom provided with the spot facing section can be formed integrally with the body by one step, there is an advantage that the manufacturing becomes very easy. FIGS. 18(a) through 18(e), 18(b′), 18(c′) and 18(e′) are explanatory diagrams showing a method of providing the spot facing section 800 on the bottomed container. As shown in FIG. 18(a), before the punch 410 is pushed into so that the hot dilation forming is carried out, a cylinder 302 which is a cylindrical member is previously provided on the bottom section 301 of the container for forming. Here, the spot facing section 800 can be formed only by the cylinder 302, but in order to easily taken out the cylinder 302 after the metal billet 200 is formed, an annular metal plate 303 may be previously placed on the upper section of the cylinder 302 (see FIG. 18(a)). The annular metal plate 303 is constituted so that its radial width is slightly larger than a radial width of the cylinder 302. As a result, after the metal billet 200 is formed into the bottomed container, the cylinder 302 can be taken out easily. In this case, the annular metal plate 303 is fitted into the bottom section after the bottomed container is formed. When the spot facing section 800 is formed only by the cylinder 303, it is desirable that the diameter of the cylinder on a side coming in contact with the metal billet 200 is smaller than the diameter of the cylinder on a side coming in contact with the bottom section 301 of the container 300 for forming. Namely, it is desired that a taper is provided on the cylinder 302 so that the diameter of the cylinder 302 becomes larger towards the pressing direction. As a result, the cylinder 302 is removed from the metal billet 200 which was subject to the hot dilation forming. The metal billet 200 is set into the body section 300 of the container and is placed on-the cylinder 302 and the annular metal plate 303 (FIG. 18(b)), and the punch 410 is pushed into the billet 200 so that the metal billet 200 is hot dilated into the shape of the bottomed container (FIG. 18(c)). As shown in FIG. 18(d), an annular groove is formed on the bottom section of the metal billet 200 formed in such a manner by the cylinder 302 and the annular metal plate 303. In this state, only a simple annular groove is provided, and thus a column section as a pillar section existing in the annular groove is cut by cutting means (not shown) such as gas burner in order to form the spot facing section 800. As a result, the bottomed container having the spot facing section 800 on the bottom section can be manufactured (FIG. 18(e)). The spot facing section 800 may be finished by cutting or the like as the need arises. In addition, as shown in FIG. 18(b′), a column 304 is used instead of the cylinder 301 so that the spot facing section 800 can be formed on the bottom section of the bottom container. Also in this case, the metal plate 305 is placed on the column 304 so that the spot facing section 800 can be formed (FIG. 18(c′)). In the case where the column 304 is used, unlike the case of using the cylinder 302, the bottomed container is formed and simultaneously the spot facing section 800 can be formed on its bottom section (FIG. 18(e′)). For this reason, the step of cutting the column section shown in FIG. 18(d) is not required, but the press pressure which is larger than the case of using the cylinder 302 is required. Therefore, the performance of the pressing machine, a size of the bottomed container to be produced and the like are taken into consideration, and it is desirable that a determination is made as to which is used the cylinder 302 or the column 304. Here, in the case where the spot facing section 800 is formed only by the column 304, it is desirable that a taper which becomes larger towards the pressing forward side is provided. Namely, it is desirable that the axial section of the column 304 is trapeziform. As a result, the column 302 is easily removed from the metal billet 200 which was subject to the hot dilation forming. The shapes of the sections of the cylinder 302 and the column 304 vertical to the axial direction are changed so that the spot facing section 800 having a desired sectional shape can be formed. For example, the shape of the section vertical to the axial direction is polygonal so that the spot facing section 800 whose internal surface shape is polygonal can be formed. As a result, since the spot facing section can be formed according to the external shape of the bottomed container, the thickness of the spot facing section in the radial direction can be kept constant. FIGS. 19(a) through 19(c) are axially sectional views showing examples of the bottomed container capable of being formed by the manufacturing method of the present invention. The bottomed container 1 shown in FIGS. 19(a) and 19(b) can be formed by selecting suitably a diameter of the cylinder or the column in the above explanation. FIG. 19(c) shows the example that two-staged spot facing section 800 is provided on the bottom section. In order to provide the two-staged spot facing section 800, for example, a forming tool, in which two columns having different diameters are stacked and its axially section has a convex shape, is set on the bottom of the metal billet 200. Moreover, the two-staged spot facing section 800 can be formed also by setting two cylinder shaving different diameters and heights on the bottom of the metal billet 200. Moreover, a step section may be provided on the external surface of the cylinder in an axial direction so as to be used. FIGS. 20(a) and 20(b) are axially sectional views showing the bottomed container according to a fourth embodiment of the present invention. The bottomed container 1 is characterized in that in the manufacturing method described in the first embodiment the extended section 201 formed before the hot dilation forming (see FIG. 2(b)) is directly utilized as the flange of the container. Since the cask as the used nuclear fuel container is constituted so that helium gas of a several atm. is sealed between the primary cover and the secondary cover, a great pressure is applied to the mounting portion of the secondary cover. Moreover, since the secondary cover occasionally receives impact of falling, the flange section as the mounting portion of the secondary cover requires the firm structure. Since the container of the present invention is formed so that the flange and the body are integral and a diameter of the flange is larger than a diameter of the body, measure such that bolts are arranged in two lines is easily taken. Therefore, the secondary cover can be fixed firmly. Since in the conventional cask the flange section is manufactured separately and is welded to the cask body, troublesome steps are required. According to the manufacturing method of the present invention, since the thick bottomed container having excellent end surface shape can be manufactured, the extended section 201 formed on the end surface of the container (see FIG. 2(b)) is seldom worked and can be utilized as the flange. Therefore, the welding step and the post-welding hot processing step can be omitted, and thus the manufacturing steps can be simplified. Here, in FIGS. 20(a) and 20(b), the extended section 201 formed before the hot dilation forming (see FIG. 2(b)) is directly used as the flange of the container, but the extended section 201 is removed by cutting or the like and the inner side of the opening of the container is worked so that a flange without extended section ever used can be formed. Also in this case, since the flange section and the body section are formed integrally, strength and sealing property can be secured sufficiently. There will be explained below another manufacturing method of the bottomed container 1. FIGS. 21 through 26 are explanatory diagrams showing the manufacturing steps of the bottomed container 1 of the cask 100 shown in FIG. 12. The bottomed container 1 is formed by combining the upsetting step and the punching draw step. Firstly, ring-shaped first die 21, second die 22 and third die 23 are stacked on a slide table 20 of the pressing machine (not shown), and first pressurizing platform 24 second pressurizing platform 25 and third pressurizing platform 26 are placed in the first through third dies 23 so that a mold is structured (FIG. 21(a)). A boring punch 27 is positioned on an upper surface of a metal billet W. The boring punch 27 is pressurized by a stem 28 attached to a punch of the pressing machine (FIG. 21(b)). The metal billet W is set in the first die 21. The metal billet W is made of low carbon steel or stainless steel formed by vacuum forging, and its upper surface is circular and its lower surface has a circular shape smaller than the upper surface so that the metal billet W is conically trapeziform (angle of tilt surface is not shown). At the time of pressurizing, the metal billet W is heated within a range of 1000° C. to 1200° C. The heating is carried out in an electric oven and the metal billet W in a red state is placed on the slide table 20. The cylinder 302 and the annular metal plate 303 (see FIG. 18(a)) are provided between the first die 21 and the metal billet W so that a spot facing section may be formed on the bottom. Next, when the metal billet W is placed, the boring punch 27 is pressurized so as to be upset (FIG. 21(c)). Since the inner end portion of the first die 21 is an opened, material flows between the boring punch 27 and an opening portion 21a of the first die so that the metal billet W is deformed into a dished shape. A hang tool 29 is used so as to hang the stem 28 together with the first die 21 (FIG. 21(d)), and the slide table 20 is moved to be conveyed out so that the first pressurizing platform 24 is removed (FIG. 21 (e)). When the first die 21 including the metal billet W is hung, in this state a spacer 30 is placed on the second die 22 (FIG. 22(a)). Thereafter, the slide table 20 is moved and the mold is conveyed in (FIG. 22(b)), and the boring punch 27 is pushed down so that the metal billet W is subject to the punching draw working by the first die 21 (FIG. 22(c)). As a result, when the metal billet W passes through the first die 21, the dished section at the top is drawn so that the metal billet W has a cup shape and is positioned in the second die 22. Next, the stem 28 and the hang tool 29 are allowed to recede upward and the slide table 20 is moved so that the metal billet W and the mold are conveyed out and the spacer 30 is removed (FIG. 22(d)). In this state, the boring punch 27 remains at the bottom of the metal billet W having cup shape (FIG. 23(a)). Next, the stem 28 in a state that the spacer 30 is removed is lowered and is pressurized by the boring punch (FIG. 23(b)). As a result, the metal billet W is further upset, and the material flows from between an opening section 22a of the second die 22 and the boring punch 27 so that the metal billet W is deformed. The hang tool 29 is used so as to hang the second die 22 together with the metal billet W (FIG. 23(c)). In this state the slide table 20 is moved so that the mold is conveyed out, and the second pressurizing platform 25 is removed (FIG. 23(d)). Next, the spacer 31 is placed on the third die 23 (FIG. 24(a)). The slide table 20 is moved so that the mold is conveyed in (FIG. 24(b)), and the boring punch 27 is pushed down so that the punching draw working is carried out by the second die 22 (FIG. 24(c)). As a result, when the metal billet W passes through the second die 22, its bellied portion is drawn and the metal billet W has a cup shape. Next, the stem 28 and the hang tool 29 are allowed to recede upward, and the slide table 20 is moved so that the metal billet W and the mold are conveyed out and the spacer 31 is removed (FIG. 24(d)). In this state the boring punch 27 remains at the bottom of the metal billet W having a cup shape. Next, the slide table 20 is moved and the metal billet W is positioned below the stem 28 (FIG. 25(a)), and the stem 28 is lowered so that the metal billet W is pressurized by the boring punch 27 (FIG. 25(b)). As a result, the metal billet W is further upset, and the material flows from between an opening section 23a of the third die 23 and the boring punch 27 so that the metal billet W is deformed. Thereafter, the hang tool 29 is used so as to hang the third die 23 together with the metal bit W (FIG. 25(c)). In this state, the slide table 20 is moved, and the third pressurizing platform 26 is removed (FIG. 25(d)). Next, the spacer 32 is placed on the slide table 20 (FIG. 26(a)). The slide table 20 is moved and the spacer 32 is conveyed in (FIG. 26(b)), and the boring punch 27 is pushed down so that the punching draw working is carried out by the third die 23 (FIG. 26(c)). As a result, when the metal billet W passes through the third die 23, its bellied portion is drawn. Next, the step 28 and the hang tool 29 are allowed to recede upward, and the slide table 20 is moved so that the metal billet W is conveyed out and the spacer 32 is removed (FIG. 26(d)). In this state the boring punch 27 remains at the bottom of the metal billet W having a cup shape, but it is directly used as the bottom of the bottomed container 1. The boring punch 27 is removed and the metal billet W can be used. Moreover, when the slide table 20 is moved and the spacer 32 is conveyed in (FIG. 26(b)), a cylindrical spacer 302 is provided in the spacer 32 (see FIG. 2(e″)), and the bottom of section the metal billet W is punched by the boring punch 27. The cylindrical container can be formed by this method. When the above-mentioned forming is finished, predetermined heat treatment is given to the bottomed container, and its inner surface is mechanically worked. The bottomed container 1 formed in such a manner has a percentage that its section is reduced from the metal billet W becomes about 40%. Moreover, in comparison with the case where the bottomed container is formed by the normal backward extrusion forming, in the case of the backward extrusion forming, the bottom section of the bottomed container becomes thick, and this causes an increase in the weight of the cask. Moreover, the pressing machine requires a great pressure, and a bottomed container cannot be occasionally manufactured depending upon its scale. On the contrary, according to the manufacturing method of this embodiment, since the bottomed container is formed by combining the upsetting and the punching draw as mentioned above, only low pressure is required at the time of the upsetting or the draw. For this reason, a large-sized pressing machine which has been conventionally used is used so as to enable the forming. FIGS. 27(a) through 27(d) are explanatory diagrams showing another manufacturing method of the bottomed container. As mentioned above, in the above-mentioned manufacturing method, the cylindrical boring punch 27, the pressurizing platforms 24 through 26, and the dies 21 through 23 having annular ring-shaped inner side were used, but the boring punch 27, etc. are not limited to these shapes. For example as shown in FIG. 27(b), in the case where the outer shape of the bottomed container 1 is octagonal, the internal shapes of a first die 21b through a third die may be octagonal. In this case, a pressurizing platform 24b is also octagonal. In addition, in the case where the internal shape of the bottomed container 1 is octagonal, as shown in FIG. 27(c), a boring punch 27c may be a octagonal prism. The metal billet W in this case has a octagonal cone trapezoid shape (detail of a tapered angle is not shown). Further, in the case where the internal shape of the bottomed container 1 has a step, as shown in FIG. 27(d), a boring punch 27d may be a prism having steps. Here, as not shown, in the case where the internal and external shapes of the bottomed container are octagonal, the die 21b shown in FIG. 27(b) and the boring punch 27c shown in FIG. 27(c) may be used. Moreover, also in the case where these shapes are not octagonal, according to the manufacturing method of the present invention, the bottomed container can be formed similarly to the above-mentioned method by changing the shapes of the boring punch, die and the like. Here, the boring punches 27c and 27d shown in FIG. 27 can be applied also to the manufacturing method according to the first embodiment. FIGS. 28(a) through 28(f) are explanatory diagrams showing an embodiment of different manufacturing method. This manufacturing method is realized in that a stem 51 is set on a slide table 52 of a pressing machine and a boring punch 53 is attached to a top portion of the stem 51, and a pressurizing platform 54 is mounted to a punch 55 of the pressing machine. Namely, as shown in FIG. 28(a), the metal billet W is placed on the boring punch 53, and the punch 55 of the pressing machine is lowered so that the metal billet W is upset by the first die 56. Next, after the lower end of the metal billet W is deformed into a dished shape, the punch 55 is allowed to recede so that the metal billet W is conveyed out (not shown). A plurality of spacers 57 are placed on the upper portion of the first die 56h so as to be conveyed in below the punch 55. Moreover, the pressurizing platform 54 is removed from the punch 55. When the punch 55 is lowered and pressurizes the metal billet W in this state, as shown in FIG. 28(b), the metal billet W is drawn by the first die 56. The first die 56 directly recedes downward. Next, similarly the metal billet W is conveyed out so that the spacer 57 is removed and the pressurizing platform 54 is mounted, and the metal billet W is conveyed in below the punch 55 again (not shown). Moreover, a second die 58 is mounted to the punch 55 side. In this state the punch 55 is lowered so as to upset and pressurize the metal billet W (FIG. 28(c)). The metal billet W is once conveyed out, and a plurality of spacers 59 are placed on the second die 58 and simultaneously the pressurizing platform 54 is removed, and the metal billet W is again conveyed in below the punch 55. In this state when the punch 55 is lowered and the pressurizes the metal billet W, as shown in FIG. 28(d), the bellied portion of the bottomed container 1 is drawn. The second dice 58 directly recedes downward. Thereafter, similarly the metal billet W is conveyed out and the spacer 59 is removed, and the metal billet W is again conveyed in below the punch 55 (not shown). Moreover, a third die 60 and the pressurizing platform 54 are attached to the punch 55 side. In this state when the punch 55 is lowered so as to pressurize the metal billet W, as shown in FIG. 28(e), the metal billet W is further deformed. The metal billet W is once conveyed out and a plurality of spacers 61 are placed on the third die 60, and simultaneously the pressurizing platform 54 is removed so that the metal billet W is again conveyed in. When the punch 55 is lowered so as to pressurize the metal billet W in this state, as shown in FIG. 28(f), the bellied portion of the bottomed container 1 is drawn. The third die 60 recedes downward. Here, the material which can be used in the method according to this invention includes ferrous materials such as carbon steel, stainless steel and low-alloy steel, and also nonferrous metal such as nickel alloy, aluminum alloy, copper alloy and magnesium alloy. There will be explained below concrete forming conditions. When a metal billet made of low carbon steel is heated to 1000° C. and a distortion speed is 0.1 to 1 s, the deformation resistance becomes 1.5 to 3 kgf/mm2. For example, if a length of 1 cm is punched within 1 minute, in the case where the outer diameter is reduced from 2500 mm to 2200 mm by a die of 30°, when the inner diameter is 1420 mm, the distortion becomes:1n ((25002−14202)/(22002−14202))=0.4and the metal billet is worked for time (2500−2200/2/tan 30°)/(1000/60)=15.6 sec. Therefore, the distortion speed becomes 0.025−1 s. Next, when the distortion resistance is 3 kgf/mm2 and the friction coefficient is 0.3, the punching force becomes:3×π/4×(22002−14202)×1n ((25002−14202)/(22002−14202))×(1+0.1×0.3/tan 30°)+4σ/(6·3·√3)=5460640 kgf However, since the temperature is initially high, the punching force is reduced to half, namely, becomes 2730 tonf. Moreover, the final thickness which prevents the bottom from dropping off at the time of punching is:54640/(3/√3)/π/1420=7.7 mm Therefore, the thickness of more than this value is required. When a length of a product is 4885 mm, since a length of a material is:4885×(22002−14202)/22002=2850 nm,an upsetting amount for one time is reduced to ⅓, namely, 950 mm and a height up to the mold constraining portion is set to the final bottom thickness of 700 mm, a necessary upsetting force becomes:3×π/4×14202×(1+0.3×1420/700/2)=61967With the pressure of this value, the bottomed container can be formed by pressing of 8000 ton which has usage accomplishment. On the contrary, since the extruding force in the case of the backward extrusion forming becomes:3×π/4×22002×1n((22002/(22002−14202))×(1+2×0.5/tan 45°))+4π(4·3·√3)=19186103 kgfthe pressing force of 20000 ton is required. As mentioned above, in the radioactive substance container and the container of the present invention, the bottomed container in which the bottom and the body are formed integrally is used so that the conventional welding of a bottom plate is not required, and the heating treatment thereafter can be omitted. As a result, troublesome manufacturing steps can be reduced greatly. Moreover, since the bottomed container is formed by the hot dilation, only a press pressure, which is lower than that at the time of hot backward extrusion forming, for example, is required. In addition, as for the radioactive substance container and the container of the present invention, the bottomed container was formed by using the metal billet having a polygonal section vertical to the axial direction and the container for forming having a circular internal shape of the section vertical to the axial direction. For this reason, since the conventional welding of a bottom plate is not required, troublesome steps required for the manufacturing can be reduced. Further in the dilation forming, the bottomed container can be formed with a lower pressure than conventional one due to a function which bends one side of the polygon of the metal billet. In addition, as for the radioactive substance container and the container of the present invention, the bottomed container was formed by the metal billet having a polygonal section vertical to the axial direction and the container for forming having polygonal internal shape of the section vertical to the axial direction. For this reason, since the conventional welding of a bottom plate is not required, troublesome steps required for the manufacturing can be reduced. Further in the dilation forming, the bottomed container can be formed with a lower pressure than conventional one due to the function which bends one side of the polygon of the metal billet. Further, bottomed containers having external shapes according to various applications can be formed easily. In addition, as for the radioactive substance container of the present invention, the bottomed container, which is enough long in the axial direction to contain the basket of used nuclear fuel aggregate used as fuel of nuclear reactor and has large inner diameter, namely, is thick, was formed by the hot dilation forming in the container for forming so that the bottom and the body were integral. For this reason, since the conventional welding of a bottom plate is not required and the post-welding heat treatment can be omitted, troublesome steps required for the manufacturing can be reduced. Particularly in the bottomed container whose thickness is thick and dimension in the axial direction is a several meters and inner diameter reaches 2 to 2.5 meters, the effect which can omit the steps is extremely great. In addition, since the radioactive substance container of the present invention has a dimension such that the section of the boring punch is approximate to the section of the basket for used nuclear fuel aggregate, an operation for cutting the inside of the container becomes easy after the hot dilation forming, and the manufacturing does not require the troublesome steps. In addition, as for the radioactive substance container of the present invention, in the case where radioactive substance is stored in the bottomed container in which the bottom and the body are formed integrally by the hot dilation forming in the container for forming, a dosage equivalent factor of the γ rays is not more than 200 μSv/h. In order to satisfy the requirement that a dosage equivalent factor of the γ rays is not more than 200 μSv/h on the surface of an external wall on the substantially center of the side surface of the container, it is necessary to manufacture the container whose thickness reaches several dozens cm using stainless steel, carbon steel or the like. Since the body and the bottom of such a thick container were formed integrally, the conventional welding of a bottom plate is not required, and since the post-welding heat treatment can be omitted, the manufacturing does not require troublesome steps. Particularly in such a thick bottomed container, the effect which can omit the steps is extremely great. In addition, as for the radioactive substance container of the present invention, in the above-mentioned radioactive substance container and the container, the outer diameter of the bottomed container was not less than 1000 mm to not more than 3000 mm, and the thickness was not less than 150 mm to not more than 300 mm. Since the thick container was formed so that the bottom and the body were integral, the conventional welding of a bottom plate is not required, and since the post-welding heat treatment is omitted, the manufacturing does not require troublesome steps. Particularly in the thick bottomed container whose axial dimension is large, the effect which can omit the above-mentioned steps is extremely great. In addition, as for the radioactive substance container and the container of the present invention, the metal billet, whose section vertical to the axial direction on the pressing forward side was at least formed into polygonal shape, was set into the container for forming, and the boring punch is pushed into the metal billet so that the metal billet is hot-dilated. For this reason, the conventional welding of a bottom plate is not required, and the post-welding heat treatment can be omitted. In addition, since a number of defects caused on the end portion and the surface of the bottomed container is small, only less troublesome steps of correcting these defects are required after the forming, and thus the manufacturing does not require troublesome steps. In addition, in the radioactive substance container of the present invention, the bottom and the body were formed integrally by hot press working. Moreover, in the radioactive substance container of the present invention, the metal billet was heated and was upset and drawn so that the bottom and the body were formed integrally. For this reason, since the welding step and the heat treating step after that can be omitted, the manufacturing does not require troublesome steps. In addition, the radioactive substance container of the present invention, the spot facing section was provided integrally with the bottom section of the bottomed container. Since in the bottomed container the spot facing section is also formed integrally at the time of the hot dilation forming, the step of providing the spot facing section can be omitted, and thus the manufacturing does not require troublesome steps. In addition, as for the radioactive substance container of the present invention, since the flange was provided integrally with the body of the bottomed container, the welding step and the post-welding heat treating step can be omitted, and troublesome steps for the manufacturing can be omitted. Moreover, the sealing performance and the strength of the container itself can be secured. In addition, as for the radioactive substance container and the container of the present invention, at least one of the section outside the body and the section inside the body of the bottomed container was polygonal. For this reason, when the bottomed container is dilated to be formed, the internal section of the container can be formed into a shape according to a basket. As a result, the step of cutting the inside of the container which has been conventionally required can be omitted, and thus the manufacturing does not require troublesome steps. In addition, the metal billet for the hot dilation forming according to the present invention was formed so that at least the section vertical to the axial direction on the pressing forward side was polygonal. For this reason, the performance for bending a side of the polygon and the function for restraining the upsetting of the metal billet accrue. Because of these functions, the thick container, in which a ratio of the length to the diameter in the axial direction is not less than 1, can be formed with a lower press pressure than conventional one. Moreover, the defects caused on the end portion and the surface of the container after the forming can be suppressed. In addition, the metal billet for the hot dilation forming of the present invention was provided with at least one plane on at least one of the side surface on the pressing forward side and the side surface of the pressing backward side. At the time of the hot dilation forming, since the metal billet is dilated to be formed by the function for bending this plane, a force required for the hot dilation forming is weaker than the case where the side surface is a curbed surface. Therefore, the thick container which is long in the axial direction can be formed with a lower press pressure than conventional one. Moreover, in comparison with the case where the side surface is a curved surface, defects on the inner side such as a crack can be reduced. In addition, the metal billet for the hot dilation forming of the present invention was further provided with a taper which becomes thinner toward the pressing direction on the pressing forward side of the metal billet in the above-mentioned metal billet for the hot dilation forming. Moreover, in the metal billet for the hot dilation forming of the present invention, at least one or more step sections were provided so that the pressing forward side of the metal billet becomes thinner gradationally towards the pressing direction. As for the metal billet, timing at which the metal fills the vicinity of the bottom of the container for forming can be delayed at the final stage of the hot dilation forming. For this reason, the upsetting is suppressed at the final stage of the hot dilation forming, and thus the press pressure can be reduced at the time of the hot dilation forming. In addition, since the metal billet for the hot dilation forming of the present invention is provided with the extended section at the end portion on the pressing backward side, the metal billet is engaged with the end portion of the container by the extended section at the time of the hot dilation forming. With this function, constraint of the container on the metal billet becomes stronger so that the upsetting on the pressing forward side can be suppressed. Moreover, since the side surface is provided with at least one plane, the function for bending this plane and the function for suppressing the upsetting of the metal billet accrue. Therefore, due to their interaction, the press pressure can be suppressed to be small. Moreover, since the metal billet is previously provided with the extended section on the pressing backward side at the time of the manufacturing, the step of manufacturing the container can be simplified. In addition, since the metal billet for the hot dilation forming of the present invention is provided with the extended section on the pressing backward side, this extended section engages the metal billet with the end portion of the container at the time of the hot dilation forming. With this function, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, since at least the section vertical to the axial direction on the pressing forward side was formed into a polygonal shape, the function for bending each side of the polygonal section and the function for suppressing the upsetting of the metal billet accrue. Therefore, the press pressure can be suppressed to be small by their interaction. Moreover, since he metal billet is previously provided with the extended section on the pressing backward side at the time of the manufacturing, the step of forming the extended section on the pressing backward side is not required, and thus the steps of manufacturing the container can be simplified. In addition, since the metal billet for the hot dilation forming of the present invention was provided with the extended section on the pressing backward side, this extended section engages the metal billet with the end portion of the container at the time of the hot dilation forming. With this function, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, since at least the section vertical to the axial direction on the pressing forward side was formed into a polygonal shape, the bending function and the function for suppressing flow of the metal accrue. Further, the pressing forward side was set to be thinner gradationally towards the pressing direction, the upsetting phenomenon is suppressed at the final stage of the hot dilation forming, and an increase in the press pressure can be suppressed. Therefore, the press pressure can be suppressed to be small due to their interaction. Moreover, since the metal billet is previously provided with the extended section on the pressing backward side at the time of the manufacturing, the step of forming the extended section on the pressing backward side is not required. In addition, since the metal billet for the hot dilation forming of the present invention is provided with the extended section on the pressing backward side, the extended section latches the metal billet with the end portion of the container at the time of the hot dilation forming. With this function, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, since at least one plane is provided on at least one of the side surfaces of the metal billet, the bending function and the function for suppressing the flow of the metal accrue further, since the pressing forward side becomes thinner gradationally, the upsetting phenomenon is suppressed at the final stage of the hot dilation forming, and an increase in the press pressure can be suppressed. Therefore, the press pressure can be suppressed to be small by their interaction. Moreover, since the metal billet is previously provided with the extended section on the pressing backward end at the time of the manufacturing, the step of forming the extended section on the pressing backward side is not required. In addition, in the above-mentioned radioactive substance container and the container, the bottomed container of the present invention has an outer diameter of not less than 200 mm to not more than 4000 mm and a thickness of not less than 20 mm to not more than 400 mm. Since such a thick container is formed so that the bottom and the body are integral, the conventional welding of a bottom plate is not required, and the post-welding heat treatment can be can be omitted so that the manufacturing does not require troublesome steps. Particularly in the thick bottomed container having a large axial dimension, the effect which can omit the above-mentioned steps is extremely great. In addition, since the container manufacturing apparatus of the present invention is provided with the container for forming, whose body and the bottom can relatively move with respect to the axial direction of the body of the container, and the boring punch which is attached to the pressing machine and pressurizes the metal billet set in the container for forming. For this reason, since the body of the container and the metal billet hardly relatively move at the time of hot dilation forming, increase in the press pressure can be suppressed at the time of the hot dilation forming. In addition, in the method of manufacturing a container of the present invention the body section of the container for forming is divided in the axial direction. For this reason, even in the case where the metal billet which is long in the axial direction is formed, the deformation of the metal billet in the axial direction at the time of hot dilation forming can be absorbed by the whole container. Therefore, an increase in the press pressure can be suppressed. In addition, according to the manufacturing method of the radioactive substance container of the present invention, the container in which the bottom and body are formed integrally is finished by cutting its external side, and its internal side is cut into a stepped shape so that a portion for containing a basket for used nuclear fuel aggregate is provided, or the internal section is cut to be finished so that the radioactive substance container is manufactured. For this reason, the internal side of the bottomed container can be cut and finished easily. In addition, according to the manufacturing method of the radioactive substance container of the present invention, the bottomed container is formed by hot dilation forming so that the bottom and the body are integral, and the external side of the bottomed container is cut to be finished, and the internal section is cut into a stepped shape so that a portion for storing a basket for used fuel aggregate is provided, or the internal side is cut to be finished so that the radioactive substance container is manufactured. For this reason, the inner side of the bottomed container can be cut and finished easily. In addition, according to the method of manufacturing a bottomed container of the present invention, the boring punch is pushed into the metal billet, and the plane of the metal billet is bent by the force directing to the inner wall of the container so that the metal billet is dilated to a gap existing between the container for forming and the metal billet. In this method of manufacturing a container, the metal billet is dilated to the inner wall side of the container for forming by function for bending the plane of the metal billet on the side surface. Moreover, since the metal billet is dilated to the space existing between the metal billet and the inner wall of the container for forming, the upsetting phenomenon of the metal billet can be suppressed. With these functions, in this method of manufacturing a container, only lower press pressure than the conventional one is required, and defects caused on the end portion and the surface of the container after the forming can be suppressed. In addition, according to the method of manufacturing a bottomed container of the present invention, the metal billet provided with the extended section engaging with the end portion of the opening of the container for forming is used for the end portion of the pressing backward side. For this reason, the extended section engages the metal billet with the end portion of the container at the time of hot dilation forming. With this function, the constraint of the container on the metal billet becomes stronger, and the upsetting of the pressing forward side can be suppressed. Moreover, since at least one plane is provided on the side surface, the bending function and the function for suppressing the phenomenon that the metal flows to the opposite side to the pressing direction accrue. Therefore, the press pressure can be suppressed small by their interaction. Further, the defects which are caused on the end portion and the surface of the container after the forming can be also suppressed. In addition, in the method of manufacturing a bottomed container of the present invention, the metal billet, in which at least the section vertical to the axial direction on the pressing forward side is formed into polygonal, is hot-dilated. For this reason, on the pressing forward side, since the metal billet is dilated in the space existing between the pressing forward side and the body of the container, the upsetting phenomenon of the metal billet can be suppressed. Therefore, in this method of manufacturing a container, only lower press pressure than conventional one is required, and the defects which are caused on the end portion and the surface of the container after the forming can be suppressed. In addition, in the method of manufacturing a bottomed container of the present invention, the metal billet, which is provided with at least one plane on at least one of the side surface of the pressing forward side and the side surface of the pressing backward side, is hot-dilated. For this reason, only a weak force suffices for the hot dilation forming in comparison with the case where the side surface is a curved surface. Therefore, a lower press pressure is required in comparison with the conventional method of manufacturing a container, and internal defects such as a crack can be also reduced. In addition, in the hot pressing method of the thick metal cylinder or the cylindrical container of the present invention, a metal billet without joint of different diameter sections, in which its pressing forward side is composed of a member having a section with an outer diameter smaller than the inner diameter of the container or an outer diameter equal with the diagonal length, or a member having a section with an outer diameter of the diagonal length equal with the inner diameter of the container, and its pressing backward side is composed of a member having a section with an outer diameter or a diagonal length equal with the inner diameter of the container, is heated to a pressing temperature and is set into the container for press forming, and thereafter while the center of the workpiece as the metal billet without joint is being bored by the punch, the billet is pressed. For this season, the metal billet without joint reduces a press forming load and improves yield of the product. Further, a press formed product having excellent end surface shape can be obtained. In addition, in the method of manufacturing a drum or a container of the present invention, the metal billet, in which its pressing forward side has a section with an outer diameter smaller than the inner diameter of the container and its backward side has a section with an outer diameter substantially equal with the inner diameter of the container, is hot-dilated. For this reason, the thick container can be formed with lower press pressure than conventional one, and a number of defects caused on the end portion or the surface of the container is small. As a result, less steps are suffice for correcting the defects after the forming. Moreover, since both the pressing forward side and backward side have angular section, the metal billet can be worked comparatively easily in comparison with a billet having a circular sectional. Therefore, the manufacturing does not require troublesome steps. In addition, in the method of manufacturing a drum or a container of the present invention, the metal billet, in which the pressing forward side has a section with a diagonal length smaller than the inner diameter of the container and the backward side has a section with a diagonal length substantially equal with the inner diameter of the container, is hot-dilated. For this reason, the thick container can be formed with lower press pressure than conventional one, and a number of defects caused on the end portion and the container surface is small. As a result, less troublesome steps suffice for correcting the defects after the forming. Moreover, since both the pressing forward side and backward side have angular sections, the metal billet can be worked comparatively easily in comparison with a metal billet having a round section. In addition, in the method of manufacturing a drum or a container of the present invention, the metal billet, in which the pressing forward side has a section with an outer diameter smaller than the inner diameter of the container and the backward side has a section with an outer diameter substantially equal with the inner diameter of the container, is hot-dilated. For this reason, the press pressure can be lower than conventional one, and a number of defects caused on the end portion and the container surface is small. As a result, only less troublesome steps suffice for correcting these defects after the forming. In addition, the method of manufacturing a container of the present invention includes the step of extending the pressing backward side of the metal billet to above the body of the container before hot dilation forming. Moreover, in this container forming method, the metal billet is dilated by the function for bending the plane of the metal billet towards the inner wall of the container for forming. Since the extended section has the function for engaging the metal billet with the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes strong, and the upsetting on the pressing forward side can be suppressed. Moreover, the press pressure can be reduced by the function for bending the plane of the metal billet towards the inner wall of the container for forming. With their interaction, this method of manufacturing a container can form the thick container with lower press pressure than the backward extrusion method or the like. In addition, in the method of manufacturing a container of the present invention, the metal billet, which is previously provided with the extended section engaging with the opening end portion of the container for forming on the end portion of the pressing backward side, is hot-dilated. For this reason, since the step of extending the pressing backward side of the metal billet to above the body of the container is not required before the hot dilation forming, time required for the hot dilation becomes short. As a result, since the forming can be finished until the temperature of the metal billet drops, the shape of the end portion becomes satisfactory. Moreover, since the extending step can be also omitted, the manufacturing does not require troublesome steps. In addition, the method of manufacturing a container of the present invention includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since the extended section has the function for engaging the metal billet with the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes strong, and the upsetting on the pressing forward side can be suppressed. Moreover, since the metal billet, in which at least the section vertical to the axial direction on the pressing forward side is formed into a polygonal shape, is dilated to be formed, the function for bending each side of the polygon towards the inner wall of the container for forming acts. With their interaction, the thick container can be formed with lower press pressure than the backward extrusion method or the like. In addition, the method of manufacturing a container of the present invention includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since the extended section has the function for engaging the metal billet with the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes strong, and the upsetting on the pressing forward side can be suppressed. Moreover, since the metal billet, which is provided at least one plane on at least one side, is dilated to be formed, the function for bending the plane of the metal billet towards the inner wall of the container for forming acts. With the interaction, this method of manufacturing a container can form the thick container with lower press pressure than the backward extrusion method or the like. In addition, the thick metal-made cylinder or drum container hot pressing method includes the step of extending the pressing backward side of the metal billet to the body of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet wit the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, the pressing forward side is a member having a section with an outer diameter smaller than the inner diameter of the container or an outer diameter of the diagonal length, or a member having a section with an outer diameter of the diagonal length equal with the inner diameter of the container. For this reason, as the metal is supplied from the pressing backward side and due to the function of the satisfactory plastic working of steel heated to high temperature, the metal billet is pushed to be spread sideways and simultaneously is worked, and is formed to fill the space of the container. As a result, the metal billet without joint is manufactured into a press product having a predetermined shape. With these interaction, the thick container can be formed with lower press pressure than the backward extrusion method or the like. In addition, the method of manufacturing a drum or a container of the present invention includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet wit the container end portion at the time of the hot dilation forming, the constraint of the container on the metal billet becomes stronger, and the upsetting on the pressing forward side can be suppressed. Moreover, since the metal billet, in which the pressing forward side is a tetragonal section with its diagonal length is smaller than the inner diameter of the container, is used, the metal billet is dilated by the function for bending each side of the tetragonal section. Moreover, the pressing backward side of the metal billet suppresses the upsetting on the pressing forward side. With their interaction, in this manufacturing method, the thick container can be formed with lower press pressure than the backward extrusion method or the like. In addition, the method of manufacturing a drum or a container of the present invention includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet with the container end portion at the time of hot dilation forming, the constraint of the container on the metal billet becomes stronger, and upsetting on the pressing forward side can be suppressed. Moreover, since the metal billet, in which the pressing forward side is a tetragonal section with a sectional length smaller than the internal diameter of the container, is used, the metal billet is dilated to be formed by the function for bending each side of the tetragonal section. Moreover, the pressing backward side of the metal billet suppresses upsetting on the pressing forward side. With their interaction, in this manufacturing method, the thick container can be formed with lower press pressure than the backward extrusion method or the like. Further, the metal billet to be used in this method is worked comparatively easier than the metal billet having one round section. In addition, the method of manufacturing a drum or a container of the present invention includes the step of extending the pressing backward side of the metal billet to above the body of the container before the hot dilation forming. Since this extended section has the function for engaging the metal billet with the container end portion at the time of hot dilation forming, the constraint of the container on the metal billet becomes stronger, and upsetting on the pressing forward side can be suppressed. Moreover, since the pressing backward side of the metal billet has a diameter substantially equal with the inner diameter of the container for forming, upsetting on the pressing forward side can be suppressed. With their interaction, in this manufacturing method, the thick container can be formed with lower press pressure than the backward extrusion method or the like. Further, the metal billet to be used in this method can be worked comparatively easier than the metal billet having different sectional shapes. Moreover, in the method of manufacturing a container of the present invention, the metal billet is formed by the forging step, and this method includes the step of forming at least the pressing forward side of the metal billet so as to provide an angular section. Moreover, the container manufacturing method of the present invention includes the step of providing a taper which becomes narrower towards the pressing direction on the pressing forward side of the metal billet. Further, in the method of manufacturing a container of the present invention, the forging step includes the step of providing at least one stepped section so that the pressing forward side of the metal billet becomes narrow gradationally towards the pressing direction. In this method of manufacturing a container, at the final stage of the hot dilation forming, timing at which the metal fills the vicinity of the bottom of the container for forming can be delayed. For this reason, the upsetting phenomenon of the metal billet can be suppressed, and the press pressure at the final stage of the hot dilation forming can be low. In addition, in the method of manufacturing a container of the present invention, the bottomed container is formed by a drum-shaped member provided at the bottom of the metal billet, and simultaneously a spot facing section is formed on the bottom of the bottomed container. Since the spot facing section has been conventional provided by cutting, the working requires troublesome steps. However, since a pillar-shaped section which remains on the bottom of the container is only removed after the dilation forming, the working does not require less troublesome steps than the conventional method. In addition, in the method of manufacturing a container of the present invention, the bottomed container is formed by the pillar-shaped member provided at the bottom of the metal billet, and simultaneously the spot facing section is formed on the bottomed container. For this reason, since the metal billet can be dilated and the spot facing section can be formed simultaneously, the working requires less troublesome steps than the conventional method. Moreover, since the step of removing the pillar-shaped member can be omitted, troublesome steps are not required for forming the spot facing section in comparison with the method where the spot facing section is formed. In addition, in the method of manufacturing a container of the present invention, the aforementioned method of manufacturing a container can relatively move the body of the container for forming with respect to the bottom of the container for forming. For this reason, since the body of the container and the metal billet to be formed hardly move relatively at the time of the hot dilation forming, an increase in the press pressure can be suppressed. In addition, in the method of manufacturing a container of the present invention, the aforementioned method of manufacturing a container divides the body of the container for forming in the axial direction. For this reason, even in the case where the metal billet which is long in the axial direction is formed, an increase in the press pressure can be suppressed. In addition, the radioactive substance container manufacturing method of the present invention includes the upsetting step of setting the pressurizing platform in a ring-shaped die provided with an opening on its inner end portion and putting the metal billet into the mold composed of the die and the pressurizing platform so as to pressurize the metal billet by means of the boring punch, and the metal billet drawing step of setting a spacer to the lower portion of the mold and pushing the metal billet by means of the boring punch. For this reason, the bottomed container is easily formed. In addition, this radioactive substance container manufacturing method includes the upsetting preparation step of stacking a plurality of ring-shaped dies provided with an opening on its inner end portion and stacking a plurality of pressurizing platforms in the dies and putting the metal billet into the mold composed of the die and the pressurizing platform, the upsetting step of pressurizing the metal billet from above the mold using the boring punch operated by the pressing machine, and the receding step of allowing the whole metal billet including the boring punch and the upper die to recede, the drawing preparation step of removing the used pressurizing platform and setting the drum-shaped spacer onto the next die and placing the whole metal billet including the receded die onto the spacer, the drawing step of pushing the metal billet using the boring punch and drawing the metal billet by means of the die, and the repeating step of repeating the above-mentioned steps using the next pressurizing platform and die and a spacer with a length according to deformation of the metal billet. For this reason, the pressurizing force can be suppressed small, and thus the manufacturing becomes easy. As mentioned above, the radioactive substance container, the radioactive substance container manufacturing apparatus and manufacturing method of the present invention are practical for a thick container such as a cask for containing, transporting and storing used nuclear fuel aggregate and substances contaminated with radioactive rays, and are suitable for providing a container such that manufacturing does not require troublesome steps and suppressing defects generated on an end portion of a cylinder and a surface of the container. |
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description | 1. Field of the Invention This invention relates generally to a tool for handling high torque, more specifically, a locking nut for a handling pole in a nuclear reactor pressure vessel. 2. Description of Related Art Repairs and inspections performed within a reactor pressure vessel (RPV) such as a boiling water reactor (BWR) are generally performed with ropes and poles for manual manipulation of tools and/or delivery of dedicated automated tools. The RPV is generally a cylindrical shaped vessel and is closed at both ends (e.g., a bottom head and a removable top head). During a reactor shut down, the top head of the RPV is removed so as to inspect or repair a selected component within. Other components in the RPV located between a top guide and a core plate or below the core plate may also be removed. To perform the inspections and/or repairs, an operator stands on a bridge positioned over the RPV and lowers the tool using ropes and poles, which may extend about eighty (80) feet below. The ability to perform such inspections and/or repairs depends on the dexterity of the operator. Due to the difficulty in accessing certain locations within the RPV, performing the repairs and/or inspections at such locations can be time consuming and burdensome. It is desirable to limit the time required to perform the repairs and/or inspections in a RPV due to the enormous daily cost of the reactor being shut down (up to almost a million dollars a day in lost revenue). Reducing the amount of time required to perform such inspections and/or repairs also would facilitate reducing radiation exposure to operators, technicians arid maintenance personnel, for example. An approach to repairing and/or inspecting equipments in the RPV has been to use handling poles to attach tools for repairing and servicing. The handling poles are light-weight and thus easy to maneuver within the RPV. Further, handling poles may be designed specifically to handle high-torque. The handling poles may be generally constructed in 10-foot sections and assembled to work in depths of over 80 feet. However, conventional handling poles typically employ a single nut to connect and lock the adjoining poles together. The single nut is typically hand tightened by an operator to lock the two poles together, and then an adhesive tape (i.e., duct tape) is attached around the nut to prevent it from inadvertently unlocking during operation. However, use of adhesive tape is not an effective manner to retain the nut on two adjoining metal poles, because the adhesive tape maybe exposed to hot water which degrades the adhesive on the tape and cause separation of the adjoining poles. Even further, during pole disconnection, it maybe necessary to first unwrap the tape. This action causes droplets of contaminated water to occasionally be expelled from the tape and may contact workers causing skin contamination. The degraded tape also leaves the glue behind on the pole sections in which radiological contaminations may stick to the adhesive tape residue and cause radiological exposure to operators and radioactive contamination issues. Exemplary embodiments of the present invention provide a handling pole for use in a nuclear reactor. The handling pole may include a pole section, a pole adapter connected to one end of the pole section, a spade member connected to the other end of the pole section, and a nut assembly for connecting adjoining poles. The pole adapter may include an upper sleeve and the spade member includes a lower sleeve. Another exemplary embodiment of the present invention provides a nut assembly for connecting adjoining poles in a nuclear reactor. The nut assembly may include an upper nut having threads on inside surface, and a lower nut having threads on the inside surface and the outside surface, wherein the upper nut threads on to the lower nut's outside surface threads. Another exemplary embodiment of the present invention provides a method of assembling a nut assembly for a handling pole. The method may include connecting a pole adapter to a spade member of the handling pole, rotating a lower nut towards the connected pole adapter and spade member, and rotating an upper nut in an opposite direction to lock the lower nut. It should be noted that these Figures are intended to illustrate the general characteristics of method and apparatus of exemplary embodiments of this invention, for the purpose of the description of such exemplary embodiments herein. These drawings are not, however, to scale and may not precisely reflect the characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties of exemplary embodiments within the scope of this invention. The relative dimensions and size of pole assembly may be reduced or exaggerated for clarity. Like numerals are used for liked and corresponding parts of the various drawings. Exemplary embodiments of the present invention may prevent and/or reduce radiological contaminations and doses during assembling and dis-assembling of the handling tool. Exemplary embodiments of the present invention may prevent and/or reduce inadvertent pole disassembly during operation. Exemplary embodiments of the present invention may provide easier and quicker connections of the pole assembly. The connection may be assembled and operated by a single operator. Thus, reduced pole assembly and disassembly time are achieved. FIG. 1A a side view of a handling pole in accordance with an exemplary embodiment of the present invention. Referring to FIG. 1A, the handling pole 10 includes a pole section 15, a pole adapter 20 connected at one end and a spade member 40 connected at the other end. As an example, the pole adapter 20 and the spade member 40 may be welded to the pole section 15. However, it should be appreciated that other attachments may be employed to connect the pole adapter 20 and spade member 40 to the pole section 15. The entire or section of the handling pole 10 may be composed of a lightweight metal, such as, but not limited to, aluminum. The handling pole 10 is adaptable to produce torque over 100 ft-lb. Each section of the handling pole 10 may be 10 feet in length, and designed to work up to 100 feet depth in the reactor. However, it should be appreciated that each handling pole 10 may be designed as 3 feet, 5 feet or other lengths, depending on the application of the pole. The handling pole 10 may also be the same size as an existing pole, and thus interchangeable with the existing pole (e.g., used for general purpose or non-high torque applications). As a result, the handling pole 10 may reduce the overall job time and may save the cost of developing, building and shipping alternate tooling, such as jet pump breaker poles. It should be appreciated that the handling pole 10 may also be used as a replacement for heavy-weight high torque poles used, for example, in jet pump beam tensioning. The heavy-weight high torque pole is described in co-pending U.S. application entitled “Apparatus and Method for Measuring Rotation During Jet Pump Tensioning” assigned to General Electric Co., which is hereby incorporated by reference in its entirety. FIG. 2 is a cross-section A-A of the handling pole of FIG. 1A in accordance with an exemplary embodiment of the present invention. As shown in FIG. 2, the pole adapter 20 has a pair of J-shaped slots 25 (only one of which is shown in FIG. 2) which may receive and interlock with a corresponding pin 45 on spade member 40 (adjacent handling pole). The J-shaped slots 25 provide a slot for pin 45 to slide into so as to provide an engagement between adjacent handling poles 10. The J-shaped slots 25 may be machined into the pole adapter 20. The pole adapter 20 may be made of, for example, aluminum or any other lightweight metal. An upper sleeve 21 may surround the pole adapter 20 as shown in FIG. 2 for reinforcement. The upper sleeve 21 may be made from stainless steel so as to prevent the J-shaped slots 25 from spreading (deforming) when torque greater than, for example, 50 ft lbs is applied. It should be appreciated that the upper sleeve 21 may be made from other materials, such as steel, aluminum, engineered plastic materials and/or any combination thereof. The pole adapter 20 includes a pair of dowel pins 27 attached to the pole section 15. The dowel pins 27 may be welded to the upper sleeve 21 at both sides (shown in FIG. 1B) to prevent the pole section 15 from buckling around the pins 27. In other words, the dowel pins 27 penetrate the upper sleeve 21, the adapter pole 20 and the pole section 15, and penetrate through the other side (e.g., the pole section 15, the adapter pole 20 and the upper sleeve 21). The dowel pins 27 may be welded to the upper sleeve 21 on both sides to transmit the torque from the J-slot 25 to the pole section 15. The pins 27 may be made from, for example, but not limited to, stainless steel. The pins 27 may be ¼ inch in diameter. It should be appreciated that other diameter sizes may be employed. FIG. 3 is a side view of the handling pole rotated in accordance with an exemplary embodiment of the present invention. As shown in FIG. 3, the pole adapter 20 includes a drain hole 28. The drain hole 28 is provided to flush out any fluid trapped in the pole adapter 20. The drain hole 28 may have a diameter of ¼ inch. It should be appreciated that there may be more than one drain hole 28 in the adapter 20. It should further be understood by one of ordinary skilled in the art that the size of the drain hole 28 and pins 27 may vary according to the application of the handling pole. Referring again to FIG. 2, the pole section 15 is also attached to a spade member 40. The spade member 40 slidably fits within a thinned section 35 of the pole section 15. In other words, the spade member 40 may act as a male connector for engaging with the pole adapter 20. The thinned section 35 of the pole section 15 may be embodied as having a larger bore diameter than the bore diameter of the adapter pole 20. As an example, the pole section 15 attached to the spade member 40 may have a bore diameter of approximately 0.905 inches and the pole section 15 attached to the adapter pole 20 may have a bore diameter of approximately 0.860 inches. The spade member 40 may be made from, for example, but not limited to, aluminum. The spade member 40 includes a spade pin 45 to slidably engage into the J-shaped slots 25. The spade pin 45 has a dimension to engage with the J-shaped slots 25 and withstand the produced torque without failure. The spade member 40 may be bored with a hole (i.e., approximately 6 mm) through both sides of the spade member 40 so that the spade pin 45 can be inserted. The spade pin 45 is welded to the spade member 40 at both sides (shown in FIG 1C) so as to prevent buckling. In other words, the spade member 40 is machined with holes on both side of the spade member 40 for spade pin 45 to be inserted and welded within the hole. The spade pin 45 is then centered in the spade member 40 and welded at least in four areas (e.g., on both sides of the spade pin 45 and on both sides of the spade member 40). The spade pin 45 may extend approximately 0.178 inches out from the surface of the space member 40. The spade pin 45 may be made from, for example, but not limited to, stainless steel. It should be appreciated by one skilled in the art that the dimensions of the spade pin 45 may be employed with different sizes. The spade member 40 is attached to the pole section 15 via a pair of lower pins 37. The lower pins 37 may be similar and may function the same as the dowel pins 27 found in the pole adapter 20. The area engaging the spade member 40 and the pole section 15 is surrounded with a lower sleeve 30 for reinforcing the connection. The lower sleeve 30 is also attached to the spade member 40 through the pair of lower pins 37. The pins 37 are welded to the sleeve 30 at both sides so as to prevent the pole section 15 from buckling around pins 37. In other words, the lower pins 37 may penetrate the lower sleeve 30, the pole section 15 and then the spade member 40, and penetrate out the other side (e.g., the spade member 40, the pole section 15 and then the lower sleeve 30). The lower pins 37 are welded to the lower sleeve 30 on both sides to prevent buckling of the thinned area of the section pole 15 and transmit torque through the spade pins 45. The lower sleeve 30 may be made of, for example, but not limited to, stainless steel, aluminum, steel, engineered plastic materials and/or any combination thereof. As an example, the lower sleeve 30 may be made from the same material as the upper sleeve 21 for ease in manufacturing. The pins 37 may be made from, for example, but not limited to, stainless steel. The lower pins 37 may be ¼ inch in diameter. It should be appreciated that other diameter sizes may be employed. The handling pole 10 includes a nut assembly 49 (shown in FIG. 4). The nut assembly 49 may include an upper nut 51 and a lower nut 52 on the spade member 40. The upper nut 51 and the lower nut 52 are used to connect, and lock together, handling poles 10 that are used to service nuclear reactor internal components. FIG. 4 is a schematic view in detail of the nut assembly in accordance with an exemplary embodiment of the present invention. As shown in FIG. 4, the lower nut 52 is threaded around the spade member 40, and the upper nut 51 is threaded around the lower nut 52. The upper nut 51 has threads in its inside surface and the lower nut 52 has threads on the inside and the outside surface. As an example, the thread of the upper nut 51 has 1 3/16 12 thread/in, and the thread of the lower nut 52 has 1 3/16 12 thread/in on the outside and 1 1/16 8 thread/in on the inside. It should be appreciated that there are no threads exposed so as to protect the threads from damages caused by inadvertent knocking and striking. When the pole 10 is connected to another pole, the lower nut 52 rotates toward (e.g., clockwise CW) the connected pole and tightened by the operator. In other words, the lower nut 52 provides the hand-tightened locking function between the connected poles. Then the upper nut 51 is threaded and tightened in the opposite direction (e.g., counterclockwise CCW) of the lower nut 52 to provide an additional locking force to the lower nut 52. The lower nut 52 may be a brass material, and the upper nut 51 may be a stainless steel material. However, it should be appreciated that the upper nut 51 and the lower nut 52 may be formed with other materials, such as, for example, steel, copper, stainless steel, iron, aluminum, zinc, and/or combination thereof. Each of the surfaces of the upper nut 51 and the lower nut 52 is formed with a non-slip grip via, for example, a knurling procedure. As an example, the non-slip grip may be shaped as a diamond-like shape. It should be appreciated that other shapes may be employed besides the diamond-like shape. FIG. 5 is a flowchart illustrating the method for attaching the nut assembly in accordance with an exemplary embodiment of the present invention. As shown in FIG. 5, initially one section of a handling pole 10 is connected to another section of an adjacent pole (S100). In other words, the spade pin 45 in the spade member 30 of one handling pole engages in the J-shaped slot 25 in the pole adapter 20 of another handling pole. Once the poles 10 are connected, the lower nut rotates (e.g., clockwise CW) until it engages with the connected poles 10 and lock the poles 10 together (S200). Then the upper nut 51 is rotated in the opposite direction (e.g., counterclockwise CCW) until it becomes taut so as to lock the lower nut 52 (S300). The operator then rotates the lower nut 52 in the opposite direction from the initial rotation (e.g., counterclockwise CCW) to provide a final tightening procedure (S400). As a result, the nut assembly 49 provides a tight connection between the adjoining poles. Exemplary embodiments of the present invention may prevent and/or reduce inadvertent pole disassembly during operation. Exemplary embodiments of the present invention may provide easier and quicker connections of the pole assembly. The connection may be assembled and operated by a single operator. Thus, reduce pole assembling time Exemplary embodiment of the present invention provides the pole adapter having a J-shaped slot which receive and interlock with a corresponding pin on an adjacent handling pole. The J-shaped slot prevents and/or reduces the pole adapter from dis-engaging with the spade member. Exemplary embodiment of the present invention provides a pair of upper pins welded to the upper sleeve at both sides to prevent the pole section from buckling around the upper pins. Exemplary embodiment of the present invention provides a pair of lower pins welded to the lower sleeve at both sides to prevent the pole section from buckling around the lower pins. Exemplary embodiment of the present invention provides the spade member having a spade pin to slidably engage into J-shaped slots. The spade pin welded to the spade member at both sides of the spade member prevents buckling. Exemplary embodiment of the present invention provides machining at least one hole in both sides of the upper sleeve, adapter pole and the pole section, inserting at least one upper pin into the hole, and welding the at least one upper pin on the upper sleeve. Exemplary embodiments of the present invention may provide an apparatus tool for handling high-torque over 100 ft lbs. The handling tool may be lightweight so as to be assembled by hand and easily manipulated by the operator without the need of a overhead crane or hoist. The exemplary embodiments of the present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as departure from the spirit and scope of the exemplary embodiments of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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abstract | The present invention provides an optical head with a single or multiple sub-wavelength light beams, which can be used in arenas such as photolithography, optical storage, optical microscopy, to name a few. The present invention includes a transparent substrate, a thin film, and a surface structure with sub-wavelength surface profile. The incident light transmits through the transparent substrate, forms a surface plasma wave along the sub-wavelength aperture located within the thin film, and finally re-emits through spatial coupling with the sub-wavelength profile of the surface structure. As the coupled re-emitting light beam or light beams can maintain the waist less than that of the diffraction limit for a few micrometers out of the surface with sub-wavelength profile in many cases, this invention can have applications ranging from micro or nano manufacturing, metrology, and manipulation by using light beams with waist smaller than the diffraction limit. |
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042082498 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to nuclear reactors and, more particularly, to hydraulic apparatus for absorbing shocks that are applied to fuel assemblies, and the like. 2. Description of the Prior Art To produce useful power from a nuclear reactor, it is necessary to assemble fissionable uranium in a sufficient concentration and in a physical configuration that will sustain a continuous sequence of neutron-induced fission reactions within the uranium nuclei. The heat generated through these reactions in this assembly, or reactor core, usually is absorbed in a stream of pressurized water. This heated pressurized water then is pumped to one or more heat exchangers in which the absorbed heat is transferred to secondary coolant water. It is, of course, this secondary coolant water that rises into the steam which drives the turbines, or other electrical power generating machinery. To provide a proper concentration of uranium for the reactor core, it has often been the practice to prepare pellets of uranium dioxide. These pellets are loaded into long, slender, hollow tubes which, when the tube ends are sealed off, are referred to as fuel rods. In order to enhance the structural integrity of the reactor core, these fuel rods are arranged into subgroups, each of about two hundred fuel rods, that are called fuel assemblies. The assemblies, in turn, are mounted in a generally right circular cylindrical array to form the reactor core. Naturally, the reactor core is environmentally hostile to the structural integrity of its component parts. The temperature, water flow velocity, pressure, radiation and the like within the reactor core all combine to place great stresses on the core materials. In addition to these environmental extremes, adequate provision also must be made to enable structural components of the reactor core to cope with other forces of a more unusual and, perhaps, of a more violent nature than those which are imposed through ordinary operating conditions. Seismic or earthquake shocks and the thermal shocks to physical structure that might attend an accident in which a significant portion of the pressurized water evaporates from or drains out of the reactor core are typical of the situations in which forces far in excess of those generated in the course of routine operation could be encountered. The customary response to this problem is the addition, in one way or another, of more materials and more metal to the reactor core. This direct approach although probably providing the needed structural protection, has a number of undesirable features. Additional materials in the reactor core, for example, exhibit a "parasitic" effect that absorbs a portion of the neutron population within the core. Neutrons, absorbed in this manner do not contribute to the energy production and hence, are used wastefully and inefficiently. Accordingly, there is a need for improvements to reactor core structures that will enable the core to safely attenuate or absorb shocks and other forces of unusual and major character without adding materials to the core structure that will not increase parasitical neutron losses. SUMMARY OF THE INVENTION These and other problems that have characterized the prior art are overcome to a large extent through the practice of the invention. Illustratively, the internal pads that brace the fuel assemblies to restrict longitudinal movement, bear against movable spring pads that are mounted on the upper end fitting of the respective fuel assemblies. At least some of these spring pads have plungers that are pinned to the respective pads. These plungers are slidably received within hollow tubular guide posts. Longitudinal slots formed in the guide posts accommodate the pins in order to permit the plungers to move in a longitudinal direction relative to the posts. The guide posts, in turn, are secured to the upper grids of the individual fuel assemblies. Within tubular guide posts, moreover, and partially blocking the open end of each of the posts are individual disk-shaped plates each with an orifice or hole. Thus, as an earth tremor, or the like, compels the plunger and spring pad assemblies to move in a longitudinal direction relative to the respective guide posts, pressurized water within the guide posts arrests this motion. This water, squirting through the holes in the plates, permits the guide posts and spring pads to move relative to each other in a longitudinal direction at a controlled rate in which the applied forces are absorbed in a safe manner. In accordance with a feature of the invention, however, the pin and plunger combinations, moving in a longitudinal direction through the respective hollow guide posts produce a progressive braking effect. Thus, as the pins which connect the plungers to their respective spring pads move longitudinally through the guide post slots, the pins and their associated plungers gradually block these slots, thereby continuously decreasing the discharge area through which the water within the guide post can flow. This technique provides a continuously increasing resistance to the further longitudinal relative movement of the plungers and orificed plates. The resistance increases, moreover, in a progressive manner that protects reactor core structure from sustaining severe damage that otherwise might occur through a more abrupt attenuation of imposed shocks, and the like. Thus, there is provided in accordance with the terms of the invention an improved technique for coping with the application of major forces that might be applied to the core of a nuclear reactor while eliminating substantial quantities of parasitical neutron absorbing material from the core. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operation and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention. |
description | 1. Field This invention relates generally to nuclear reactor systems, and in particular, to a method and apparatus for refueling a nuclear reactor. 2. Description of Related Art A pressurized water reactor has a large number of elongated fuel assemblies mounted within an upright reactor vessel. Pressurized coolant is circulated through the fuel assemblies to absorb heat generated by nuclear reactions in fissionable material contained in the fuel assemblies. The primary side of such a nuclear reactor power generating system which is cooled with water under pressure comprises an enclosed circuit which is isolated from and in heat exchange relationship with a secondary circuit for the production of useful energy. The primary side comprises the reactor vessel enclosing a core a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. In conventional nuclear plants of that type each of the parts of the primary side comprising the steam generator, a pump and a system of pipes which are connected to the reactor vessel form a loop of the primary side. For the purpose of illustration, FIG. 1 shows a simplified conventional nuclear reactor primary system, including a generally cylindrical pressure vessel 10 having a closure head 12 enclosing a nuclear core 14. A liquid coolant, such as water or borated water, is pumped into the vessel 10 by pumps 16 through the core 14 where heat energy is absorbed and is discharged to a heat exchanger 18, typically referred to as a steam generator, in which heat is transferred to a utilization circuit (not shown), such as a steam driven turbine generator. The reactor coolant is then returned to the pump 16, completing the primary loop. Typically, a plurality of the above described loops are connected to a single reactor vessel 10 by reactor coolant piping 20. An exemplary conventional reactor design is shown in more detail in FIG. 2. In addition to the core 14 comprised of a plurality of parallel, vertically co-extending fuel assemblies 22, for the purpose of this description, the other vessel internal structures can be divided into the lower internals 24 and the upper internals 26. In conventional designs, the lower internals function to support, align and guide core components and instrumentation as well as direct flow within the vessel. The upper internals restrain or provide a secondary restraint for the fuel assemblies 22 (only two of which are shown for simplicity in FIG. 2), and support and guide instrumentation and components, such as control rods 28. In the exemplary reactor shown in FIG. 2, coolant enters the reactor vessel through one or more inlet nozzles 30, flows down through an annulus between the reactor vessel and the core barrel 32, is turned 180° in a lower plenum 34, passes upwardly to a lower support plate 37 and a lower core plate 36 upon which the fuel assemblies are seated and through and about the fuel assemblies 22. In some designs, the lower support plate 37 and the lower core plate 36 are replaced by a single structure, a lower core support plate having the same elevation as 37. The coolant flow through the core and surrounding area 38 is typically large on the order of 400,000 gallons per minute at a velocity of approximately 20 feet per second. The resulting pressure drop and frictional forces tend to cause the fuel assemblies to rise, which movement is restrained by the upper internals, including a circular upper core plate 40. Coolant exiting the core 14 flows along the underside of the upper core plate and upwardly through a plurality of perforations 42. The coolant then flows upwardly and radially to one or more outlet nozzles 44. The upper internals 26 can be supported from the vessel or the vessel head and include an upper support assembly 46. Loads are transmitted between the upper support assembly 46 and the upper core plate 40 primarily by a plurality of support columns 48. Each support column is aligned above a selected fuel assembly 22 and perforations 42 in the upper core plate 40. Rectilinearly moveable control rods 28 which typically include a drive shaft or drive rod 50 and a spider assembly 52 of neutron poison rods, are guided through the upper internals 26 and into aligned fuel assemblies 22 by control rod guide tubes 54. The guide tubes are fixedly joined to the upper support assembly 46 and the top of the upper core plate 40. The support column 48 arrangement assists in retarding guide tube deformation under accident conditions which could detrimentally affect control rod insertion capability. To control the fission process, a number of control rods 28 are reciprocally moveable in guide thimbles located at predetermined positions in the fuel assemblies 22. Specifically, a control rod mechanism positioned above the top nozzle of the fuel assemblies supports a plurality of control rods. The control rod mechanism (also known as a rod cluster control assembly) has an internally threaded cylindrical hub member with a plurality of radial extending flukes or arms that form the spider 52 previously noted with regard to FIG. 2. Each arm is interconnected to a control rod 28 such that the control rod assembly mechanism 72 is operable to move the control rods 28 vertically within the guide thimbles within the fuel assemblies to thereby control the fission process in the fuel assembly 22, under the motive power of the control rod drive shaft 50 which is coupled to the control rod mechanism hub, all in a well known manner. The upper internals 26 also have a number of in-core instrumentation that extend through axial passages within the support columns 48 and into instrumentation thimbles generally, centrally located within the fuel assemblies. The in-core instrumentation typically includes a thermocouple for measuring the coolant core exit temperature and axially disposed neutron detectors for monitoring the axial and radial profile of neutron activity within the core. Nuclear power plants, which employ light water reactors require periodic outages for refueling of the reactor. New fuel assemblies are delivered to the plant and temporarily stored in a fuel storage building, along with used fuel assemblies which may have been previously removed from the reactor. During a refueling outage, a portion of the fuel assemblies in the reactor are moved from the reactor to the fuel storage building. A second portion of the fuel assemblies are moved from one support location in the reactor to another core support location in the reactor. New fuel assemblies are moved from the fuel storage building into the reactor to replace those fuel assemblies which were removed. These movements are done in accordance with a detailed sequence plan so that each fuel assembly is placed in a specific location in accordance with an overall refueling plan prepared by the reactor core designer. In conventional reactors, the removal of the reactor internal components necessary to access the fuel and the movement of the new and old fuel between the reactor and the spent fuel pool in the fuel storage building is performed under water to shield the plant maintenance personnel. This is accomplished by raising the water level in the refueling cavity and canal that is integral to the plant's building structure. The water level of more than 20 feet provides shielding for the movement of the reactor internal structures and the fuel assemblies. Refueling activities are often on a critical path for returning the nuclear plant to power operation, therefore, the speed of these operations is an important economic consideration for the power plant owner. Furthermore, the plant equipment and fuel assemblies are expensive and care must be taken not to cause damage or unnecessary radiation exposure due to improper handling of the reactor components that have to be removed to access the fuel assemblies, the fuel assemblies or fuel transfer equipment. The precision of these operations is also important since the safe and economical operation of the reactor core depends upon each fuel assembly being in its proper location. A typical pressurized water reactor needs to be refueled every 18 to 24 months. Commercial power plants employing the conventional designs generally illustrated in FIGS. 1 and 2 are typically on the order of 1,100 megawatts or more. More recently, Westinghouse Electric Company LLC has proposed a small modular reactor in the 200 megawatt class. The small modular reactor is an integral pressurized water reactor with all primary loop components located inside the reactor vessel. The reactor vessel is surrounded by a compact, high pressure containment. Due to both limited space within the containment and the low cost requirement for integral pressurized light water reactors, the overall number of auxiliary systems including those associated with refueling needs to be minimized without compromising safety or functionality. For example, the compact high pressure containment associated with the design of some small modular reactors does not allow for the incorporation of a large floodable cavity above the reactor vessel in which the transferred components can be shielded. Even in conventional designs, it would be desirable to reduce the amount of flooding required for refueling to save time and the expense of the operation. Accordingly, it is an object of this invention to provide a method and apparatus for shielding the movement of a fuel assembly that does not require flooding of the containment. It is a further object of this invention to provide such a method and apparatus that does not require the addition of motorized components to deploy shielding during fuel movement. It is an additional object of this invention to provide such a method and apparatus which practically does not require additional storage space over that currently required. These and other objects are achieved by a machine for moving a nuclear plant component from a first location to another that has a bridge assembly for positioning the machine over the nuclear plant component to be moved. A stationary mast is supported from the bridge assembly at a first end and extends down from the bridge assembly in the direction of the nuclear plant component. A moveable mast is telescopically nested within the stationary mast and configured to extend from the stationary mast and retract within the stationary mast under the control of an operator. A mast shield canister has an axially extending central opening through which the moveable mast can extend. The mast shield canister has an upper end portion and a lower end portion with a first stop on the upper end portion of the mast shield canister and/or on a lower end of the moveable mast preventing the lower end of the moveable mast from withdrawing out of the upper end portion of the mast shield canister. A second stop is provided on either or both the stationary mast or the mast shield canister that prevents the mast shield canister from moving more than a preselected distance from the stationary mast; the mast shield canister being sized at least to fit over substantially the full length of the nuclear plant component. A gripper assembly is supported at a lower end of the moveable mast and is configured to grip the nuclear plant component through the lower end portion of the mast shield canister. Preferably, the preselected distance is substantially long enough to place the mast shield canister on top of the nuclear plant component. In one embodiment the first stop comprises a first set of rollers circumferentially supported around an inner wall of the central opening on the upper end portion of the mast shield canister, that is at least in part in axial and circumferential alignment with a second set of rollers on the lower end of the moveable mast, below the first set of rollers. Preferably the second stop is a rod or cable attached to the upper end portion of the mast shield canister at a first end of the rod or cable and slidably coupled to the stationary mast at a second end portion of the rod or cable through an opening in an eyelet or tube that is affixed to the stationary mast with a second end of the second end portion of the rod or cable being larger than the opening in the eyelet or tube. Desirably, the mast shield canister is configured so that a downward movement of the mast shield canister relative to the moveable mast is powered solely under the force of gravity and an upward movement of the mast shield canister relative to the stationary mast is solely under the power of the moveable mast. The machine may also include a transfer cart having a moveable platform for moving the nuclear plant component from a first location to a second location. The transfer cart has a transfer cart shield canister having a central opening substantially completely enclosed by a shield wall system except for an open end providing access to the central opening with the central opening being sized to substantially enclose the nuclear plant component. The transfer cart also includes a rotatable coupling between the moveable platform and the transfer cart shield canister for rotating the transfer can shield canister from a generally horizontal position, where the nuclear plant component within the transfer cart shield canister is on its side, to a generally vertical position, where the open end is facing substantially in an upward direction to face the gripper assembly, and back to the horizontal position. In another embodiment, the central opening in the transfer cart shield canister substantially matches the central opening through the mast shield canister and the gripper assembly is configured to extend through the lower end portion of the mast shield canister into the central opening of the transfer cart shield canister to place the nuclear plant component within the transfer cart shield canister. The invention also contemplates a method for relocating the nuclear plant component with the machine described above including the step of moving the bridge assembly to position the machine over the nuclear plant component to be relocated with the gripper assembly aligned with the nuclear plant component. Then the moveable mast is moved downward with the mast shield canister suspended below the gripper. The method then supports the lower end portion of the mast shield canister above the nuclear plant component with the nuclear plant component in line with the central opening through which the moveable mast can extend. The moveable mast is then lowered through the central opening and the gripper assembly engages on a top surface of the nuclear plant component. The method then raises the moveable mast to withdraw the moveable mast and the nuclear plant component upward within the central opening and moves the bridge assembly to position the nuclear plant component at a new location. The method may also include the steps of lowering the moveable mast at the new location; disengaging the gripper assembly from the nuclear plant component; and raising the moveable mast. In still another embodiment the new location is a transfer cart comprising a moveable platform for transporting the nuclear plant component; wherein the moveable platform has a transfer cart shield canister with a central opening substantially completely enclosed by a shield wall system except for an open end providing access to the central opening, with the central opening being sized to substantially enclose the nuclear plant component; and a rotatable coupling between the moveable platform and the transfer cart shield canister for rotating the transfer cart shield canister from a generally horizontal position where the nuclear plant component within the transfer cart shield canister is on a side, to a vertical position, where the open end is facing substantially in an upward direction to face the gripper assembly, and back to a horizontal position. In this embodiment, the method includes the step of rotating the rotatable couplings so that the transfer cart shield canister is in the vertical position. Then the method lowers the moveable mast so a lower end of the mast shield canister substantially rests on a top surface of the shield wall system. Then the method lowers the moveable mast through the central opening in the mast shield canister to lower the nuclear plant component within the opening in the shield wall system. The gripper assembly is then disengaged from the nuclear plant component and the moveable mast is raised. Preferably, the transfer cart shield canister is then rotated to a horizontal position and transported to a new destination. Desirably, in this embodiment, the step of raising the moveable mast after disengaging the gripper assembly includes the step of raising the mast shield canister so that an upper end of the mast shield canister substantially rests against the lower end of the stationary mast. The foregoing apparatus and method is particularly suited for moving nuclear fuel assemblies between a reactor and a spent fuel pool. This invention provides a practical means to incorporate gamma radiation shielding into the mast of a refueling machine. A shielded canister is incorporated into the mast design. The shielded canister is raised and lowered with a mast similar in design to those already in use in pressurized water reactor plants. The moveable mast telescopes within a stationary mast. The stationary mast is attached to a conventional bridge of the refueling machine. The invention allows for the addition of shielding that is positioned with the movement of the moveable mast. It does not require the addition of motorized components to deploy the shielding during fuel movement. The fuel is drawn up into the shielded canister as the moveable mast lifts the fuel assembly from the reactor core. The fuel assembly is then placed into a transfer cart which is also fitted with a shielded canister. The transfer is made without exposing the fuel assembly. The result is completely shielded fuel movement. The shielded material employed in the mast and the fuel transfer cart could be any high density material that is typically used to shield gamma radiation, e.g., concrete, etc. FIG. 3 shows a schematic cross sectional view of one embodiment of the fuel transfer machine 56 with a bridge assembly 58 for positioning the machine over the fuel assembly 22 to be moved. A stationary mast 60 is supported from the bridge assembly 58 at a first end and extends down from the bridge assembly in the direction of the fuel assembly 22. A moveable mast 62 is telescopingly nested within the stationary mast 60 and configured to extend from the stationary mast and retract within the stationary mast under the control of an operator (not shown). To that extent, the refueling machine illustrated in FIG. 3 is substantially conventional with the bridge assembly riding on wheels that are guided on tracks on the operating deck of a nuclear plant. In accordance with this embodiment, the mast shield canister 64 has an axially extending central opening 102 through which the moveable mast can extend and is suspended from a lower end of the moveable mast 62 during the mast shield canister's travel downward. The mast shield canister 64 has an upper end portion, with a first stop 68 on the upper end portion of the mast shield canister 64 and/or on a lower end of the moveable mast 62 preventing the lower end of the moveable mast from withdrawing out of the upper end portion 104 of the mast shield canister 64 and a second stop 70 on either or both the stationary mast 60 or the mast shield canister 64 that prevents the mast shield canister from moving more than a preselected distance from the stationary mast. The mast shield canister 64 is sized at least to fit over substantially the full length of the nuclear component. A gripper assembly 82 is supported at a lower end of the moveable mast 62 and is configured to grip the nuclear plant component (in this example a fuel assembly) through the lower end portion 104 of the mast shield canister 64. The first stop 68 illustrated in the embodiments shown in FIGS. 3-11 comprises a first set of rollers 78 circumferentially supported around an inner wall of the central opening 102 on the upper end portion 104 of the mast shield canister 64, that is at least in part in axial and circumferential alignment with a second set of rollers 80 on the lower end of the moveable mast 62, below the first set of rollers 78. The roller guides ensure lateral alignment while allowing the moveable mast 62 to move up and down. The rollers can ride in axial grooves to assure rotational stability. The interference of the rollers 78 and 80 prevents the mast shield canister from leaving the end of the moveable mast 62. However, a mechanical release can be provided for the rollers 78 so they can withdraw into their socket and release the mast shield canister 64 from the moveable mast 62 so it can be exchanged for corresponding mast shield canisters having other interior dimensions that will accommodate other core components that need to be removed from the reactor vessel. Accordingly, though the nuclear component transfer device shown in FIGS. 3-11 is illustrated in a configuration to transfer fuel assemblies, it should be appreciated that this invention has applicability to transfer other nuclear components as well. Additionally, the mast shield canister 64 illustrated in the figures is also shown to have an upper flange 110 which can also serve as a mechanical stop against the gripper 82 at the end of the moveable mast 62 to prevent the mast from being withdrawn entirely from the central opening 102. Other mechanical stops can also be configured for this purpose. A similar stop arrangement is provided between the stationary mast 60 and the moveable mast 62 to prevent the moveable mast 62 from being completely withdrawn from the stationary mast 60. A second mechanical stop 70 is configured between the upper portion 104 of the mast shield canister 64 and the lower end of the stationary mast 60. The second mechanical stop is a rod or cable 84 that is threaded through an eyelet or sleeve 88 that is attached to the outside of the lower end of the stationary mast 60. The cable or rod 84 is attached to the upper end portion 104 of the mast shield canister 64 at a first end of the rod or cable and slidably coupled to the stationary mast 60 at the second end portion of the rod or cable 84 through an opening in the eyelet or tube 88 with an end portion 86 of the rod or cable being larger than the opening in the eyelet or tube 88 so that the mast shield canister 64 can be lowered a preselected distance which in this embodiment is substantially equal to the length of the cables 84. As can be seen in FIG. 4 as the moveable mast 62 is lowered, the mast shield canister 64 lowers under the force of gravity against the stop 68 until the limit of the stop 70 is reached. Desirably, the length of the cables 84 are long enough to place the central opening 102 at the lower end of the mast shield canister 64 right over the fuel assembly 22 as shown in FIG. 4. Then the moveable mast 62 continues traveling downward until the gripper assembly can engage the fuel assembly 22 as shown in FIG. 5. Desirably, the length of the central opening 102 below the completely withdrawn gripper assembly is at least substantially equal to the height of the fuel assembly 22 so the fuel assembly can be totally withdrawn within the mast shield canister 64 as the moveable mast 62 is raised after the fuel assembly has been engaged, as shown in FIG. 6. Then the lower end of the moveable mast 62 engages the first stop 68 and raises the mast shield canister 64 into engagement with the lower end of the stationary mast 60 as shown in FIG. 7. Thus, the fuel assembly 22 can be removed from the reactor core, or from the spent fuel pool, as the case may be, completely shielded within the mast shield canister 64 and the bridge assembly can then be moved to a fuel transfer cart that can move the fuel assembly between the reactor and the spent fuel pool. FIGS. 8-11 illustrate the reverse operation where the fuel assembly is loaded into a transfer cart 90 for transport between the reactor and the spent fuel pool. The bridge assembly 58 positions the mast shield canister 64 over a transfer cart shield canister 92 having a central opening 100 substantially completely enclosed by a shield wall system 96, except for an open end 98 providing access to the central opening. The central opening is sized to substantially enclose the nuclear fuel assembly 22 and the transfer cart is connected to a moveable platform 93 through a rotatable coupling 94. The rotatable coupling rotates the transfer cart shield canister 92 from a generally horizontal position, where the nuclear fuel assembly within the transfer cart shield canister is on a side, to a generally vertical position, as shown in FIG. 8, where the open end 98 is facing substantially in an upward direction to face the gripper assembly 82. Desirably, the central opening 100 in the transfer cart shield canister 92 substantially matches the central opening 102 through the mast shield canister 64 and the gripper assembly 82 is configured to extend through the lower end portion of the mast shield canister into the central opening 100 of the transfer cart shield canister 92 to seat the nuclear fuel assembly 22 within the transfer cart shield canister as shown in FIG. 9. The moveable mast 62 is then raised as shown in FIG. 10, preferably to rest the top of the mast shield canister 64 against the bottom of the stationary mast 60. The transfer cart shield canister 92 is then rotated to a horizontal position for transport as shown in FIG. 11. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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054593662 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma radiation field intensity meter, and more particularly to an electroscope-type dosimeter which is supplied a constant current from an energy source to provide rate of radiation dose rather than total accumulated dose. 2. Background of the Related Art Electroscope-type dosimeters have been developed over the years to measure the accumulated or total dose of gamma radiation. Specifically, the prior art electroscope-type dosimeter determines the total gamma radiation exposed to it. Typically, the electroscope-type dosimeter, more commonly known as the Lauritsen electroscope, is precharged by a conventional dosimeter charger. The electroscope-type dosimeter includes a quartz fiber and a metal frame used as a charge acceptor, and during the charging process a potential is applied between the frame and the exterior of the dosimeter. Electrical charges of the same polarity appear on both the fiber and frame, causing the fiber to be repelled from the frame by a distance proportional to the applied voltage. The chamber walls or exterior of the electroscope-type dosimeter provides an electrostatic shield for the electroscope-type dosimeter. If the electroscope-type dosimeter is exposed to additional ionizing gamma radiation, the charge on the quartz fiber decreases and the fiber tends to return to the discharge position which is closer to the frame. An image of the fiber in the new position resulting from the additional gamma radiation is projected onto a reticle scale and viewed through an eyepiece lens of the dosimeter. The scale, typically calibrated in Milliroentgens or Roentgens, indicates total accumulated radiation dose, and may be read by looking through the eyepiece toward a lamp or other light source. Thus, the prior art electroscope-type dosimeters have been unable to measure the radiation dose rate experienced when exposed to an ionizing gamma radiation field. It is, therefore, desirable to reliably measure the radiation dose rate which a meter is exposed to in a radiation field to further indicate whether the ionizing gamma radiation field is dangerous. In addition, it is also desirable that the gamma radiation field intensity meter be compact. SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a gamma radiation field intensity meter which is able to measure the dose rate at which the meter is exposed to the ionizing gamma radiation. It is another object of the present invention to provide a gamma radiation field intensity meter which is compact. To achieve these and other objects, the gamma radiation intensity meter of the present invention includes a current source generating a current which is essentially constant and a dose rate determining unit which determines the dose rate of the radiation field exposed to the gamma radiation intensity meter. The dose rate determining unit includes an ionization chamber having gas, a conductive frame disposed in the ionization chamber conducting the current generated by the tritium battery and a charge accepting fiber connected to the conductive frame. The gamma radiation intensity meter also includes a resistor, connected between the conductive frame and the ionization chamber wall which conducts the current forming a potential across the resistor. When the gamma radiation intensity meter is exposed to a radiation field, the radiation field penetrates the gamma radiation intensity meter and ionizes the gas in the ionization chamber forming ionized gas, and the ionized gas conducts a current proportional to the radiation field intensity from the conductive frame to the wall of the ionization chamber, thereby shunting that amount of current away from the resistor. The reduced current through the resistor proportionally reduces the voltage on the conductive frame and the fiber and the charge accepting fiber moves toward the conductive frame to a new position indicating the dose rate. These, together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, with reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. |
description | This invention was made with government support under Contract Number DE-AC07-05ID14517 awarded by the United States Department of Energy. The government has certain rights in the invention. Embodiments of the disclosure generally relate to zirconium-based metal alloy compositions, to nuclear fuel rods including such alloy compositions, nuclear reactors including such fuel rods, and to methods of making and using such alloys, fuel rods, and reactors. Nuclear reactors are used to generate power (e.g., electrical power) using nuclear fuel materials. For example, heat generated by nuclear reactions carried out within the nuclear fuel materials may be used to boil water, and the steam resulting from the boiling water may be used to rotate a turbine. Rotation of the turbine may be used to operate a generator for generating electrical power. Nuclear reactors generally include what is referred to as a “nuclear core,” which is the portion of the nuclear reactor that includes the nuclear fuel material and is used to generate heat from the nuclear reactions of the nuclear fuel material. The nuclear core may include a plurality of fuel rods, which include the nuclear fuel material. Most nuclear fuel materials include one or more of the elements of uranium and plutonium (although other elements such as thorium are also being investigated). There are, however, different types or forms of nuclear fuel materials that include such elements. For example, nuclear fuel pellets may comprise ceramic nuclear fuel materials. Ceramic nuclear fuel materials include, among others, radioactive uranium oxide (e.g., uranium dioxide, UO2, which is often abbreviated as “UOX”), which is often used to form nuclear fuel pellets. Mixed oxide radioactive ceramic materials (which are often abbreviated as “MOX”) are also commonly used to form nuclear fuel pellets. Such mixed oxide radioactive ceramic materials may include, for example, a blend of plutonium oxide and uranium oxide. Such a mixed oxide may include, for example, U1-xPuxO2, wherein x is between about 0.2 and about 0.3. Transuranic (TRU) mixed oxide radioactive ceramic materials (which are often abbreviated as “TRU-MOX”) also may be used to form nuclear fuel pellets. Transuranic mixed oxide radioactive ceramic materials include relatively higher concentrations of minor actinides such as, for example, neptunium (Np), americium (Am), and curium (Cm). Carbide nuclear fuels and mixed carbide nuclear fuels having compositions similar to the oxides mentioned above, but wherein carbon is substituted for oxygen, are also being investigated for use in nuclear reactors. In addition to ceramic nuclear fuel materials, there are also metallic nuclear fuel materials. Metallic nuclear fuels include, for example, metals based on one or more of uranium, plutonium, and thorium. Other elements such as hydrogen (H), zirconium (Zr), molybdenum (Mo), and others may be incorporated into uranium- and plutonium-based metals. In nuclear reactors that employ metallic nuclear fuels, the metallic nuclear fuel is often formed into rods or pellets of predetermined size and shape (e.g., spherical, cubical, cylindrical, etc.) that are at least substantially comprised of the metallic nuclear fuel. The nuclear fuel material is contained within and at least partially surrounded by a cladding material, which may comprise, for example, an elongated tube. The cladding material is used to hold and contain the nuclear fuel. The cladding material typically comprises a metal or metallic alloy, such as stainless steel. During operation of the nuclear reactor, the cladding material may separate (e.g., isolate and hermetically seal) the nuclear fuel bodies from a liquid (e.g., water or molten salt) that is used to absorb and transport the heat generated by the nuclear reaction occurring within the nuclear fuel. Zirconium-based metal alloys have been employed as cladding materials, since they may exhibit relatively low absorption of thermal neutrons. For example, a class of such zirconium-based metal alloys is referred to in the art as “Zircaloys.” Another zirconium-based alloy that has been employed as cladding material is referred to in the art as “M5” alloy. M5 alloy has been reported to contain, in weight percentages: niobium 0.81-1.2 wt %; oxygen 0.090-0.149 wt %, zirconium—the balance (Mardon et al., Update on the Development of Advanced Zirconium Alloys for PWR Fuel Rod Claddings, International Topical Meeting on Light Water Reactor Fuel Performance, Portland, Oreg. (Mar. 2-6, 1997) (Published by the American Nuclear Society, Inc., La Grange Park, Ill. 60526, USA). It is known that Zircaloys and M5 Alloy have a relatively affinity to hydrogen. Absorption of hydrogen in Zircaloys and M5 Alloy may lead to hydrogen embrittlement. When such alloys are employed as cladding material in nuclear fuel bodies and reactors, such hydrogen embrittlement can lead to failure of the cladding material. In some embodiments, the present disclosure includes zirconium-based metal alloy compositions that comprise zirconium, a first additive in which the permeability of hydrogen decreases with increasing temperatures at least over a temperature range extending from 350° C. to 750° C., and a second additive having a solubility in zirconium over the temperature range extending from 350° C. to 750° C. At least one of a solubility of the first additive in the second additive over the temperature range extending from 350° C. to 750° C. and a solubility of the second additive in the first additive over the temperature range extending from 350° C. to 750° C. is higher than the solubility of the second additive in zirconium over the temperature range extending from 350° C. to 750° C. In additional embodiments, the present disclosure includes nuclear fuel rods for use in a nuclear reaction that comprise a volume of nuclear fuel material, and a cladding material at least partially surrounding the volume of nuclear fuel material. The cladding material comprises a zirconium-based metal alloy composition that includes zirconium, a first additive in which the permeability of hydrogen decreases with increasing temperatures at least over a temperature range extending from 350° C. to 750° C., and a second additive having a solubility in zirconium over the temperature range extending from 350° C. to 750° C. At least one of a solubility of the first additive in the second additive over the temperature range extending from 350° C. to 750° C. and a solubility of the second additive in the first additive over the temperature range extending from 350° C. to 750° C. is higher than the solubility of the second additive in zirconium over the temperature range extending from 350° C. to 750° C. In yet further embodiments, the present disclosure includes nuclear reactors that comprise a reactor core for generating thermal energy in which at least one fuel rod is disposed within a liquid. The at least one fuel rod includes at least one nuclear fuel material at least partially surrounded by a cladding material. The cladding material comprises a zirconium-based metal alloy composition that includes zirconium, a first additive in which the permeability of hydrogen decreases with increasing temperatures at least over a temperature range extending from 350° C. to 750° C., and a second additive having a solubility in zirconium over the temperature range extending from 350° C. to 750° C. At least one of a solubility of the first additive in the second additive over the temperature range extending from 350° C. to 750° C. and a solubility of the second additive in the first additive over the temperature range extending from 350° C. to 750° C. is higher than the solubility of the second additive in zirconium over the temperature range extending from 350° C. to 750° C. In additional embodiments, the present disclosure includes methods of making and using such alloy compositions, fuel rods, and nuclear reactors. For example, in some embodiments, the present disclosure includes methods of forming zirconium-based metal alloy compositions. In accordance with such methods, a particle mixture is formed, the particle mixture is pressed to form a green body, and the green body is sintered. For example, zirconium particles, first additive particles, second additive particles, and third additive particles may be mixed together to form the particle mixture. The first additive particles may be selected to comprise one or more elements in which the permeability of hydrogen decreases with increasing temperatures at least over a temperature range extending from 350° C. to 750° C. The second additive particles may be selected to comprise an element having a solubility in zirconium over the temperature range extending from 350° C. to 750° C. At least one of a solubility of the element of the first additive particles in the element of the second additive particles over the temperature range extending from 350° C. to 750° C. and a solubility of the element of the second additive particles in the element of the first additive particles over the temperature range extending from 350° C. to 750° C. is higher than the solubility of the element of the second additive particles in zirconium over the temperature range extending from 350° C. to 750° C. The third additive particles may be selected to comprise a dispersed grain-growth inhibitor that impedes the growth of grains of a zirconium-based metal alloy composition over the temperature range extending from 350° C. to 750° C. FIG. 1 is a simplified schematic diagram illustrating an example embodiment of a nuclear reactor 10 of the disclosure, which includes a zirconium-based metal alloy composition, as described in further detail below (in nuclear fuel rods 14 employed in the nuclear reactor 10). The nuclear reactor 10 includes a reactor core 12 that includes the fuel rods 14, which are located within a chamber 16. The fuel rods 14 may be elongated and oriented at least substantially parallel to one another in an ordered array. The fuel rods 14 include a cladding comprising a zirconium-based metal alloy composition as described herein. The cladding may at least partially surround bodies of nuclear fuel material. Nuclear reactions that generate themial energy may be carried out in the bodies of nuclear fuel within the fuel rods 14. The reactor core 12 also includes control rods 18 that may be positioned between the fuel rods 14 for controlling the nuclear reactions carried out within the fuel rods 14. For example, the control rods 18 may comprise a material or materials that will absorb neutrons emitted as part of, and that contribute to, the nuclear reactions carried out within the fuel rods 14. Thus, by controlling the relative positions between the control rods 18 and the fuel rods 14, the number of neutrons that are absorbed by the control rods 18 may be selectively increased or decreased, thereby effectively increasing or decreasing (in a selective manner) the rate at which the nuclear reaction carried out within the fuel rods 14 proceeds. The fuel rods 14 may be immersed within a reactor liquid 20 contained within the chamber 16. The reactor liquid 20 may absorb heat generated by the nuclear reaction carried out within the fuel rods 14. The reactor liquid 20 may comprise, for example, water, liquid metal, a liquid salt, etc. The heated reactor liquid 20 may be caused to flow through a closed loop circuit that includes a heat exchanger 22. For example, the heated reactor liquid 20 may be caused to flow from the chamber 16 to the heat exchanger 22 through a conduit 24. A pressurizing device 26 may be provided along the conduit 24 for maintaining the reactor liquid 20 within the conduit 24 at or above a selected pressure. The reactor liquid 20 may flow through the heat exchanger 22 and back to the chamber 16 of the reactor core 12 through another conduit 28. A pump 30 may be provided along the conduit 28 for pumping the reactor liquid 20 through the closed loop circuit extending from the chamber 16 of the reactor core 12, to the heat exchanger 22, and back to the chamber 16. With continued reference to FIG. 1, the nuclear reactor 10 further includes a turbine 32 and a generator 34. The generator 34 may be coupled to the turbine 32 through a drive shaft 36. As the turbine 32 is caused to rotate, the turbine 32 rotates the drive shaft 36, and the generator 34 generates electricity responsive to rotation of the drive shaft 36. The turbine 32 may comprise a steam turbine, and the steam used to rotate the turbine 32 may be generated by heating water or another liquid within the heat exchanger 22 using the heat of the reactor liquid 20 flowing through the heat exchanger 22. In other words, the heat in the reactor liquid 20 may be exchanged to the water or other liquid within the heat exchanger 22. The heated water and/or steam generated within the heat exchanger 22 may be carried to the turbine 32 through a conduit 38. If desirable, a pressurizing device 40 may be provided along the conduit 38 for maintaining the heated water and/or steam within the conduit 38 at, or above, a selected pressure. The steam may be used to drive rotation of the turbine 32, as previously mentioned, after which the steam may be cooled and condensed to water, which may be returned to the heat exchanger 22 through a conduit 42. A pump 44 may be provided along the conduit 42 for pumping the water back to the heat exchanger 22. Thus, the nuclear reactor 10 of FIG. 1 may be used to generate electricity from the heat provided by the nuclear reaction carried out within the fuel rods 14 in the reactor core 12. Embodiments of nuclear reactors of the present disclosure may be of various types and configurations that include a zirconium-based metal alloy composition as described below in a component, such as a fuel rod 14, of the nuclear reactor 10, and may differ in type and configuration from the nuclear reactor 10 of FIG. 1, which is described herein as a non-limiting example of a nuclear reactor that may embody the present disclosure. As previously mentioned, the fuel rods 14 may comprise a zirconium-based metal alloy composition in accordance with additional embodiments of the disclosure. FIG. 2 is a perspective view of a fuel rod 14 of the nuclear reactor 10 of FIG. 1. As shown in FIG. 2, the fuel rod 14 may be elongated, and may be generally cylindrical. In other embodiments, the fuel rod 14 may have a cross-sectional shape (i.e., a shape in a plane transverse to a longitudinal axis AL of the fuel rod 14) that is triangular, square, hexagonal, octagonal, etc. The fuel rod 14 comprises at least one volume of nuclear fuel material that is at least partially surrounded by a cladding material. For example, FIG. 3 is a simplified, longitudinal cross-sectional view of the fuel rod 14 of FIG. 2. As shown in FIG. 3, the fuel rod 14 may comprise an elongated hollow cylindrical cladding tube 50. The cladding tube 50 may comprise a zirconium-based metal alloy composition as described in further detail below. A plurality of nuclear fuel bodies 52 may be disposed within the cladding tube 50. The nuclear fuel bodies 52 may comprise pellets, slugs, balls, or other shaped particles that comprise nuclear fuel material. The nuclear fuel bodies 52 may have an outer diameter that is similar in size, but slightly smaller than, an inner diameter of the cladding tube 50, and the nuclear fuel bodies 52 may be stacked in an end-to-end configuration within the cladding tube 50, as shown in FIG. 3. As shown in FIG. 3, caps or plugs 54 may be provided at the ends of the cladding tube 50, such that the cladding tube 50 is at least substantially hermetically sealed. The plugs 54 may comprise a material similar or identical in composition to that of the cladding tube 50. The nuclear fuel bodies 52 may not occupy the entire space within the cladding tube 52, and a spring member 56 (e.g., a coil spring) may be provided between an end of a stack of the nuclear fuel bodies 52 and a plug 54, as shown in FIG. 3. Any void or space within the cladding tube 50 not occupied by the nuclear fuel bodies 52 may be occupied by an inert gas such as argon. As previously mentioned, the cladding tube 50 may comprise a zirconium-based metal alloy composition. The zirconium-based metal alloy composition may comprise zirconium, a first additive comprising a metal other than zirconium, and a second additive comprising another metal other than zirconium and the first additive. In some embodiments, the zirconium may comprise about ninety percent by weight (90.0 wt %) or more of the zirconium-based metal alloy composition, about ninety-three percent by weight (93.0 wt %) or more of the zirconium-based metal alloy composition, or even about ninety-nine percent by weight (99.0 wt %) or more of the zirconium-based metal alloy composition. The first additive may comprise one or more metal elements in which the permeability of hydrogen decreases with increasing temperature, at least over a temperature range extending from 350° C. to 750° C. By way of example and not limitation, the first additive may comprise one or more elements selected from the group consisting of niobium (Nb), tantalum (Ta), and vanadium (V). The first additive may comprise, for example, between about one-tenth of one percent by weight (0.1 wt %) and about nine percent by weight (9.0 wt %) of the zirconium-based metal alloy composition. The second additive comprises one or more elements that are selected to induce phase segregation within the zirconium-based metal alloy composition, such that a secondary phase comprising the second additive is formed, and further to cause the first additive to be drawn out from the primary zirconium-based phase into the secondary phase comprising the second additive. For example, the second additive may comprise one or more elements having a higher affinity for the first additive relative to zirconium. The second additive may have little to no solubility in zirconium over the temperature range extending from 350° C. to 750° C. The second additive may be selected such that a solubility of the first additive in the second additive and/or a solubility of the second additive in the first additive is higher than any solubility of the second additive in zirconium over the same temperature range (350° C. to 750° C.). It may be desirable in some embodiments to select the second additive such that the solubility of the second additive in the first additive over the temperature range extending from 350° C. to 750° C. is higher than the solubility of the second additive in zirconium over the temperature range extending from 350° C. to 750° C. By way of example and not limitation, the second additive may comprise one or more elements selected from the group consisting of molybdenum (Mo), antimony (Sb), and palladium (Pd). The second additive may comprise, for example, between about one-hundredth of one percent by weight (0.01 wt %) and about one percent by weight (1.0 wt %) of the zirconium-based metal alloy composition. In some embodiments, the first additive and the second additive may exhibit at least substantially ideal solid solution behavior with respect to one another over the temperature range extending from about 350° C. to about 750° C. For example, molybdenum exhibits at least substantially ideal solid solution behavior with niobium. Molybdenum is insoluble in zirconium at temperatures up to about 730° C., but is soluble in the beta phase of zirconium (β-Zr) at temperatures over about 863° C. The first additive is used to increase permeability of hydrogen with decreasing temperature. The second additive is used to induce phase-segregation of one or more elements of the first additive from the zirconium-based primary phase. These first and second additives may be used to mitigate or avoid the phenomenon of hydrogen embrittlement within the zirconium-based metal alloy composition, which may result in increased useable lifetime of, for example, cladding tubes 50 that comprise the zirconium-based metal alloy composition. Since the permeability of hydrogen in the first additive decreases with increasing temperature, when the cladding tube 50 is being heated during startup of the nuclear reactor 10 and being cooled during shutdown of the nuclear reactor 10, a temperature gradient may exist across the thickness of the cladding tube 50, such that exterior surfaces of the cladding tube 50 are cooler than interior surfaces of the cladding tube 50. Thus, there will be a driving force causing the hydride precipitation zones toward the colder exterior surfaces of the cladding tube 50. At least a fraction of the first additive may reside on the boundaries of the primary phase grains to promote transport of hydrogen. Optionally, the zirconium-based metal alloy composition may include a third additive, which may serve as a dispersed grain growth inhibitor that impedes the growth of grains of the zirconium-based metal alloy composition over the temperature range extending from 350° C. to 750° C. For example, the dispersion of grain growth inhibitor particles may impede the growth of grains of the primary zirconium-based phase in the zirconium-based metal alloy composition. The grain growth inhibitor may present a separate phase within the zirconium-based metal alloy composition, and may not dissolve in any significant quantity in zirconium or the first and second additives. Further, if the grain growth inhibitor comprises a compound, the grain growth inhibitor compound may be relatively more stable than compounds of zirconium and other elements present within the composition over the intended operating temperatures and conditions. For example, the third additive grain growth inhibitor may comprise one or more oxide materials. As non-limiting example, the third additive may comprise one or more materials selected from thorium oxide (ThO2), yttrium oxide (Y2O3), the group of lanthanum oxides, such as La2O3, neodymium oxide (Nd2O3), cerium oxide (CeO2), dysprosium oxide (Dy2O3), etc. The third additive may comprise, for example, between about five-hundredths of one percent by weight (0.05 wt %) and about five-tenths of one percent by weight (0.50 wt %) of the zirconium-based metal alloy composition. As the cladding tube 50 may be subjected to repeated heating and cooling thermal cycles during the operation of the nuclear reactor 10, a thermal driving force may exist for microstructural evolution, such as grain growth, within the zirconium-based metal alloy composition of the cladding tube 50. Thus, the third additive comprising the grain growth inhibitor may be employed to inhibit grain growth within the zirconium-based metal alloy composition during such thermal cycles. The grain growth inhibitor may also stabilize any zirconium oxide (ZrO2) scale that might form on surfaces (e.g., exterior surfaces) of the cladding tube 50. FIG. 4 is a highly simplified drawing illustrating how a microstructure 60 of a zirconium-based metal alloy composition may appear under magnification. As shown in FIG. 4, a zirconium-based metal alloy composition as described above may have a microstructure 60 that includes primary phase grains 62 of a zirconium-based metal alloy. A secondary phase 64 (shown as the shaded areas on FIG. 4) comprising a metal or metal alloy that includes the second additive may be located between the primary phase grains 62 (e.g., on and around the primary phase grains). In other words, the microstructure 60 may comprise a first plurality of grains 62 comprising a first phase, and a second phase 64 disposed at grain boundaries of the first plurality of grains 62. The first phase is the primary phase comprising grains 62 of a zirconium-based metal alloy, and the second phase 64 comprises a metal alloy based on the second additive. In some embodiments, the primary phase grains 62 comprising the zirconium-based metal alloy may have an average grain size of between about seven hundred fifty nanometers (750 nm) and about one hundred microns (100 μm). For example, in some embodiments, the primary phase grains 62 comprising the zirconium-based metal alloy may have an average grain size of between about one micron (1.0 μm) and about one hundred microns (100 μm), or even between about five microns (5 μm) and about fifty microns (50 μm). The primary phase grains 62 comprising the zirconium-based metal alloy may comprise between about ninety percent (90%) and about ninety-nine and one-half percent (99.5%) of the volume of the zirconium-based metal alloy composition. The second phase 64 that comprises a metal or metal alloy that includes the second additive may comprise between about three-tenths of one percent (0.3%) and about ten percent (10%) of the volume of the zirconium-based metal alloy composition. In some embodiments, the second phase 64 may comprise a second plurality of grains having an average grain size of between about ten nanometers (10 nm) and about one thousand nanometers (1,000 nm). For example, in some embodiments, the second phase grains may have an average grain size of between about twenty-five nanometers (25 nm) and about five hundred nanometers (500 nm), or even between about fifty nanometers (50 nm) and about two hundred fifty nanometers (250 nm). Further, in embodiments in which the zirconium-based metal alloy composition includes a third additive that serves as a grain growth inhibitor, the microstructure of the zirconium-based metal alloy composition may further include grains 66 of a third phase comprising the third additive. These third phase grains 66 may be disposed between the primary phase grains 62 of the zirconium-based metal alloy, and may be disposed at triple points between the primary phase grains 62. Such triple points are locations at which the intersections of at least three primary phase grains 62. The third phase grains 66 that include the third grain growth inhibitor additive may comprise between about six-hundredths of one percent (0.06%) and about six-tenths of one percent (0.6%) of the volume of the zirconium-based metal alloy composition. In some embodiments, the third phase may comprise a third plurality of grains 66 having an average grain size of between about two nanometers (2 nm) and about one hundred nanometers (100 nm). For example, in some embodiments, the third phase grains 66 may have an average grain size of between about five nanometers (5 nm) and about fifty nanometers (50 nm), or even between about ten nanometers (10 nm) and about thirty nanometers (30 nm). The average grain size of the grains of any of the phases in the microstructure of embodiments of zirconium-based metal alloy compositions of the disclosure may be further determined in accordance with the standard test methods defined in ASTM (American Society for Testing and Materials) International Standard Test Method Designation E112-10, which is entitled “Standard Test Methods for Determining Average Grain Size,” and is incorporated herein in its entirety by this reference. In some embodiments, the primary phase grains 62 may have an average Grain Size No. (G) of between about 3.5 and about 17.8, which ASTM International Standard Test Method Designation E112-10. In some embodiments, the primary phase grains 62 may have an average Grain Size No. (G) of between about 3.5 and about 17. In some embodiments, the primary phase grains 62 may have an average Grain Size No. (G) of between about 5.5 and about 12.5. As non-limiting examples, the cladding tube 50 may comprise a zirconium-based metal alloy composition having an overall chemical composition of any of the Sample Compositions 1 through 8 identified in Table 1 below: TABLE 1Elemental Composition in Weight PercentEx.ZrNbTaVMoPdLaThYOHOther1bal.9.00——1.00—0.051——0.0340.0020.0102bal.4.50——0.50——0.053—0.0370.0050.0153bal.0.90——0.10———0.0470.0380.0100.0104bal.1.20———0.200.2130.220—0.0920.0250.0155bal.—1.20—0.20——0.2200.1970.1130.0020.0106bal.—1.20——0.10——0.3600.1530.0050.0157bal.——1.200.10——0.2640.2360.1250.0100.0108bal.——1.20—0.900.085—0.3940.1510.0250.015(Ex. = Example; bal. = balance) Additional embodiments of the disclosure include methods of forming zirconium-based metal alloy compositions such as those described above. In some embodiments, a zirconium-based metal alloy composition as described herein may be formed by providing a particle mixture including particles of the various components to be incorporated into the zirconium-based metal alloy composition, pressing the particle mixture to form a “green” (i.e., unsintered) body, and sintering the green body to consolidate the particles and form a three-dimensional body, such as a cladding tube 50 of a fuel rod 14. Explaining further, a particle mixture may be formed by mixing zirconium particles, particles of a first additive, particles of a second additive, and optionally particles of a third additive, wherein the first, second, and third additives are as previously described hereinabove. Thus, the first additive particles may be selected to comprise one or more elements in which the permeability of hydrogen decreases with increasing temperature at least over a temperature range extending from 350° C. to 750° C. The second additive particles may be selected to comprise an element, such that the solubility of the element of the first additive particles in the element of the second additive particles and/or a solubility of the element of the second additive particles in the element of the first additive particles, over the temperature range extending from 350° C. to 750° C., is higher than any solubility of the element of the second additive particles in zirconium over the same temperature range. The third additive particles may be selected to comprise a grain-growth inhibitor that impedes the growth of grains 62 of a zirconium-based metal alloy composition over the temperature range extending from 350° C. to 750° C. The particle mixture may further include one or more various additives such as, for example, binders, plasticizers, lubricants, emulsifiers, etc. Such additives may comprise one or more organic materials (e.g., wax and/or oil). In some embodiments, such additives may comprise one or more liquids, such that the powder mixture and the liquids together form a slurry, which may be subsequently dried and further processed. In another embodiment, the third additive may undergo thermal decomposition to yield particles comprising a dispersed grain-growth inhibitor that impedes the growth of grains 62 of a zirconium-based metal alloy composition over the temperature range extending from about 350° C. to about 750° C. After forming the particle mixture, the particle mixture may be pressed to form a green body having a shape corresponding to the shape of the article to be formed. For example, in embodiments in which the article to be formed comprises a cladding tube 50 of a fuel rod 14, the green body may have a solid cylindrical shape (like a rod) or a generally hollow cylindrical shape like that of the cladding tube 50 to be formed. During the subsequent sintering process, the green body may undergo shrinkage of between about ten percent (10%) and about thirty percent (30%). Thus, the green body may be formed to have a size larger than the desired size of the article to be formed. The particle mixture may be pressed to form the green body using, for example, an axial pressing process in a die or mold, or using an isostatic pressing process. Further, the particle mixture optionally may be heated prior to and/or during the pressing process to further enhance the compaction of the particles during the pressing process. Further, one or more of the individual components of the particle mixture may be heated prior to mixing, for example, to facilitate sublimation and dispersion of one or more components. After forming the green body, the green body may be sintered to a desirable final density. For example, the green body may be heated in a furnace to cause the particles in the green body to consolidate, such that bonds are formed between the particles and porosity between the particles is at least substantially eliminated (with corresponding shrinkage in the green body as the green body is sintered). The sintering temperatures and sintering time may depend upon the particular composition being sintered, as well as on the desired microstructure to be attained in the resulting zirconium-based metal alloy composition. As non-limiting examples, however, the sintering temperature or temperatures may be between about 1,000° C. and about 1,200° C., and the sintering times may range from a few minutes (e.g., five minutes) to several hours or more (e.g., from about eight hours to about ten hours). In additional embodiments, the sintering temperature or temperatures may be between about 1,600° C. and about 1,800° C., and the sintering times may range from a few minutes (e.g., five minutes) to several hours or more (e.g., from about one hour to about five hours). In some embodiments, the green body may be subjected to an electric current while in a vacuum chamber such that the actual temperature of the green body results from its electrical resistance under the passage of electric current therethrough. Additionally, in some embodiments, pressure may be applied to the green body using, for example, a fluid pressure transmission medium (e.g., an inert gas) during at least a portion of the sintering process. In some embodiments, at least one component of the third additive particles may be sublimated while sintering the green body in an effort to improve the distribution of the grain-growth inhibitor throughout the microstructure of the resulting sintered body. For example, certain oxide species (e.g., ThO, YO, NdO) may sublime and exist in a gaseous state so as to exhibit some vapor pressure under sintering conditions at elevated temperatures and under vacuum. These gaseous species may promote diffusion and transport through the green body during sintering to result in a uniform distribution of the grain-growth inhibitor throughout the microstructure. Upon cooling, these gaseous species may solidify and be incorporated into the grain-growth inhibitor phase within the microstructure of the resulting fully sintered body. As a result, the uniformity of the distribution of the grain-growth inhibitor phase within the microstructure of the resulting fully sintered body may be improved. Thus, the composition of the third additive particles may be selected to comprise an oxide compound, such as Y2O3, which has elements that are capable of forming one or more volatile components, such as YO, under sintering conditions. In embodiments in which the green body comprises a solid cylindrical rod, the fully sintered rod then may be formed (e.g., by machining or by extrusion) into a hollow, cylindrical tube. While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the following appended claims and their legal equivalents. For example, any of the elements and features disclosed in relation to one embodiment may be combined with any of the elements and features disclosed in relation to another embodiment to provide yet further embodiments of the invention. As a non-limiting example, in additional embodiments of the disclosure, the zirconium-based metal alloy composition may only include the first additive and the third additive described herein, and may not include a second additive as described herein. |
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050193287 | summary | FIELD OF THE INVENTION AND RELATED ART STATEMENT This invention relates to a natural circulation type boiling light-water reactor. In a typical nuclear power plant employing a boiling light-water reactor, main steam generated in the boiling light-water reactor is supplied to a turbine system including turbines so as to convert thermal energy of the main steam into electric energy. Since the main steam generated contains radioactive substance, a reactor system, a turbine system, and a piping system for interconnecting therebetween are shielded by radiation shield structures, respectively. This results in the prevention of leakage of the radiation from the radioactive substance to the outside. The main radioactive substance contained in the main steam is nitrogen isotope .sup.16 N. .sup.16 N is produced by the following reaction of neutron with oxygen isotope .sup.16 O contained in light water in a reactor core or coolant (that is, reaction of neutrons with nuclei, i.e., charged particle production reaction or (n, p) reaction): EQU .sup.16 O+n.fwdarw..sup.16 N+.sup.1 H In ordinary coolant, .sup.16 N produced soon becomes anions of strong nonvolatility such as, NO.sub.2.sup.- or NO.sub.3.sup.-. Therefore, the amount of .sup.16 N contained in the main steam is small. In recent years, it has been practiced to pour deoxidizer into the coolant for the purpose of improving the quality of coolant. Pouring the deoxidizer into the coolant results in the reduction in oxidation potential of the coolant. Due to such reduction, cations such as NH.sub.4.sup.+, which are readily converted into volatile isotope .sup.16 N are increased. Further, there are known H.sub.2, NH.sub.3, N.sub.2 H.sub.4 and the like as substance to be poured into the coolant besides the deoxidizer. These substances are also important factors for the increase of .sup.16 N, the same as the deoxidizer is. To cope with this increase of .sup.16 N, not only a reactor pressure vessel but also the turbine and the piping systems are shielded by the radiation shield structures made of concrete or iron, with the result that the leakage of the radiation from .sup.16 N to the outside is suppressed satisfactorily. However, with the increase of .sup.16 N in the main steam, the shield structures have become heavy and thick and enlarged, thus bringing about an increase of the plant construction cost. OBJECT AND SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a natural circulation type boiling light-water reactor which makes a contribution to the reduction in weight and dimensions of shielding structures of turbine and piping systems. To this end, there is provided according to the present invention a natural circulation type boiling light-water reactor comprising: a pressure vessel divided into a steam/water chamber and a steam chamber; a reactor core disposed within the steam/water chamber to generate main steam which contains radioactive isotope .sup.16 N, the reactor core including a plurality of fuel elements; a shroud disposed within said steam/water chamber encircling the reactor core; a steam dryer assembly through which the main steam generated flows from said shroud into the steam chamber to reduce a wetness fraction of the main steam; a chimney connected at one end thereof to the shroud and extending within the steam/water chamber toward the steam chamber, through which the main steam flows together with said radioactive isotope .sup.16 N, the chimney being filled with light water as coolant and having the other end thereof opened toward the steam dryer assembly; a steam outlet through which the main steam generated is drawn out of the pressure vessel, the steam outlet being provided in a wall of the pressure vessel; and steam passage means through which the main steam generated flows from said shroud to said steam outlet via said steam dryer assembly. The inventory of the radioactive substance .sup.16 N in the pressure vessel depends upon the time period while .sup.16 N flows within the pressure vessel. According to the present invention, the radioactive substance .sup.16 N contained in the main steam generated by the reactor core is allowed to flow within the pressure vessel of the reactor taking a time period longer than a half-life of .sup.16 N (about seven seconds). Namely, according to the present invention, the time period while the main steam flows within the pressure vessel is prolonged by controlling the velocity of the main steam and/or increasing the length of the path for the main steam. Accordingly, the inventory of the radioactive substance .sup.16 N is reduced in the reactor pressure vessel so that the amount of .sup.16 N contained in the main steam directed from the reactor pressure vessel towards the turbine system becomes smaller. In consequence, it is possible to reduce the weight and dimensions of the shielding structures for the piping and the turbine systems. In addition, it is possible to further improve the shielding effect in case of the use of conventional shield structures. Effects and functions of the present invention will become more clear from the description of a preferred embodiment to be described in the following with reference to the accompanying drawings. |
claims | 1. An apparatus comprising:a pressure vessel including a lower vessel section, an upper vessel section, and a mid-flange connecting the lower vessel section and the upper vessel section;a suspended basket including a plurality of plates connected together by tie rods, the suspended basket configured to support upper internals of a nuclear reactor;control rod drive mechanisms (CRDMs) with CRDM motors mounted in the suspended basket by at least two plates of the suspended basket; andguide frames mounted in the suspended basket by at least two plates of the suspended basket;wherein the suspended basket includes adjustable length threaded connections between ends of tie rods and at least one of the plates,wherein the suspended basket is connected to the lower vessel section by the mid-flange,the suspended basket hangs from the mid-flange;the CRDMs are bottom supported by a first plate of the plurality of plates and have upper ends laterally supported by a second plate of the plurality of plates located above the first plate in the suspended basket; andthe guide frames are hung from the first plate of the plurality of plates and have lower ends laterally supported by a third plate of the plurality of plates located below the first plate in the suspended basket. 2. The apparatus of claim 1, wherein each adjustable length threaded connection comprises:a plate thread feature extending from the plate;a threaded end of the tie rod; anda tie rod coupling portion having threading engaging both the plate thread feature and the threaded end of the tie rod;wherein rotating the tie rod coupling portion adjusts the position of the tie rod respective to the plate. 3. The apparatus of claim 2, wherein:the plate thread feature has outside threading;the threaded end of the tie rod has outside threading; andthe tie rod coupling portion comprises a sleeve with inside threading engaging both the outside threading of the plate thread feature and the outside threading of the threaded end of the tie rod. 4. The apparatus of claim 1, further comprising:a nuclear reactor core comprising fissile material disposed in the pressure vessel;wherein the suspended basket is suspended inside the pressure vessel above the nuclear reactor core with the mounted CRDMs arranged to control insertion of control rods into the nuclear reactor core. 5. The apparatus of claim 4, wherein the suspended basket is disposed inside the lower vessel section. 6. An apparatus comprising:a pressure vessel including a lower vessel section, an upper vessel section, and a mid-flange connecting the lower vessel section and the upper vessel section; anda suspended basket including a plurality of plates connected together by tie rods; andcontrol rod drive mechanisms (CRDMs) with CRDM motors mounted in the suspended basket;guide frames mounted in the suspended basket;wherein the tie rod couplings to the plates comprise threaded turnbuckle connections each including a rod coupling portion that is rotatable to adjust the position of the tie rod respective to the plate,wherein the suspended basket is connected to the lower vessel section by the mid-flange,the suspended basket hangs from the mid-flange;the plurality of plates of the suspended basket include an upper hanger plate, a mid-hanger plate, and a lower hanger plate;the CRDMs are mounted in the suspended basket via the upper hanger plate and the mid-hanger plate; andthe guide frames are mounted in the suspended basket via the mid-hanger plate and the lower hanger plate. 7. The apparatus of claim 6, wherein each threaded turnbuckle connection further includes:a plate thread feature threadedly engaged with the rod coupling portion; anda threaded end of the tie rod threadedly engaged with the rod coupling portion. 8. The apparatus of claim 7, wherein:the plate thread feature has outside threading;the threaded end of the tie rod has outside threading; andthe tie rod coupling portion comprises a sleeve with inside threading engaging the outside threading of the plate thread feature and the outside threading of the threaded end of the tie rod. 9. The apparatus of claim 6, further comprising:a nuclear reactor core comprising fissile material disposed in the pressure vessel;wherein the suspended basket is suspended inside the pressure vessel above the nuclear reactor core with the mounted CRDMs arranged to control insertion of control rods into the nuclear reactor core. 10. An apparatus comprising:a plurality of plates;tie rods;adjustable length threaded tie rod couplings connecting threaded ends of the tie rods with threaded features of the plates to form a suspended basket;control rod drive mechanisms (CRDMs) with CRDM motors mounted in the suspended basket;a pressure vessel including a lower vessel section, an upper vessel section, and a mid-flange connecting the lower vessel section and the upper vessel section;a nuclear reactor core comprising fissile material disposed in the pressure vessel; andguide frames mounted in the suspended basket between the CRDMs and the nuclear reactor core to guide portions of the control rods withdrawn from the nuclear reactor core,wherein the suspended basket is suspended inside the pressure vessel above the nuclear reactor core with the mounted CRDMs arranged to control insertion of control rods into the nuclear reactor core,wherein the suspended basket is connected to the lower vessel section by the mid-flange,the suspended basket hangs from the mid-flange,the plurality of plates includes an upper hanger plate, a mid-hanger plate, and a lower hanger plate, the upper hanger plate being furthest from the nuclear reactor core and the lower hanger plate being closest to the nuclear reactor core;the CRDMs are mounted in the suspended basket via the upper hanger plate and the mid-hanger plate; andthe guide frames are mounted in the suspended basket via the mid-hanger plate and the lower hanger plate. 11. The apparatus of claim 10, wherein each adjustable length threaded tie rod coupling includes a threaded sleeve that is threaded onto the threaded end of the tie rod and is threaded onto the threaded feature of the plate, the sleeve being rotatable to adjust the position of the tie rod respective to the plate. 12. The apparatus of claim 10, wherein each adjustable length threaded tie rod coupling comprises a turnbuckle coupling. |
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description | The following description explains the transmission type X-ray lens as an embodiment of the present invention using FIGS. 1a and 1b. FIG. 1a is an oblique view schematic drawing showing the transmission type X-ray lens of an embodiment of the present invention. FIG. 1b is a horizontal cross section drawing showing the internal structure of the transmission type X-ray lens shown in FIG. 1a. In FIGS. 1a and 1b, 2 is first substrate, 3 is second substrate, 4 is a pipe-shaped lens component and 5 is a liquid. Substrate 2 and substrate 3 are processed in advance so that one face is a flat surface. Such things as silicon wafers (Si wafer) etc. may be used for the materials for substrate 2 and substrate 3. The structure of the pipe-shaped component 4 used shall have a cylindrically formed shape at least in the area that X-rays are irradiated. In this embodiment a carbon nanotube was used. A carbon nanotube can be made a diameter of several nm and a length of several xcexcm (10xe2x88x929 m) by growing on a silicon carbide (SiC) substrate and if arc discharging is used, a carbon nanotube bundle of a length of several hundred xcexcm can be synthesized. The liquid 5 shown in FIG. 1b, is preferably one which has little X-ray absorption as well as one which causes little damage such as scattering of X-rays. Specifically, an appropriate liquid might be something such as a lubricating fluid, such as silicon grease which has had its viscosity reduced by addition of a solvent. In this embodiment, flat face 2a of substrate 2 and flat face 3a of substrate 3 are disposed so they are opposite and these flat faces 2a of substrate 2 and 3a of substrate 3 each contact the outer face of the side of pipe-shaped lens component 2. Because the pipe-shaped lens component 4 of this embodiment has a diameter the order of a nanometer as was described earlier, the width of the spaces formed by flat face 2a, flat face 3a and the exterior face of pipe-shaped lens component 2 are of the same order and are narrow and be called gaps. Because liquid 5 is filled in this gap, the separation of flat face 2a, flat face 3a and the exterior face of pipe-shaped lens component 2 and liquid 5 is suppressed by the adhesive power of liquid 5. That is to say, because liquid 5 functions like a glue due to its fluidity and adhesive power, when pipe-shaped lens component 4 is contacting an adjacent pipe-shaped lens component 4 so that they are as close as possible, the flat face 2a of substrate 2 and the exterior face of the adjacent pipe-shaped lens component 4 are in a state of being stuck together by liquid 5. Similarly, the flat face 3a of substrate 3 which is in a position opposite to this and the exterior face of the adjacent pipe-shaped lens component 4 are also in a state of being stuck together by liquid 5. As explained above, due to the reciprocal mechanism of the gap formed by the respective components and liquid 5, transmission type X-ray lens 1 which is a structure which holds numerous pipe-shaped lens components 4 between substrate 2 and substrate 3 is structurally stable. In addition, since numerous pipe-shaped lens components 4 are arranged so that they contact flat surface 2a of substrate 2 and flat surface 3a of substrate 3, flat surface 2a and flat surface 3a fulfill the role of positioning pipe-shaped lens components 4. Because of this, the center of pipe-shaped lens components 4 can be precisely aligned on the axis 6 of an X-ray lens upon which X-rays will be incident. The degree of flatness such as the surface roughness required in flat face 2a of substrate 2 and flat face 3a of substrate 3 is determined by the properties of the X-rays incident, such as wave length and such things as the tolerance of the previously noted axis 6 and the center of the pipe-shaped lens component 4. For example, when using carbon nanotubes for pipe-shaped lens component 4, since the diameter is several nm, the side face of substrate 2 and substrate 3 would be mirror polished etc. and made a smooth surface so that they would fall within a tolerance of subnanometers or less. By adopting a substrate with this configuration, while precision processing in manufacturing is required in making the surface roughness of the flat surfaces of the two substrates uniform, this can make manufacturing of transmission type X-ray lenses easier when compared with boring holes in a substrate and can better ensure the precision of the previously noted positioning. X-rays are incident in the transmission type X-ray lens of the embodiment explained above centering on previously noted axis 6. As shown in FIG. 1a, X-ray XI is an X-ray which is incident upon transmission type X-ray lens 1, and is incident upon this transmission type X-ray lens from an X-ray source via a slit etc. Alignment of the direction of the incident X-ray with the axis of the transmission type X-ray lens is adjusted using a multi-axis staging device which is outfitted with a precision angle measuring instrument such as a goniometer. Here the diameter of pipe-shaped lens components 4 and the length of the circular cross section area are set so that they will not be smaller than the width of incident X-ray XI. In addition, as previously noted, carbon nanotubes are used for the pipe-shaped lens components which transmit X-rays in this embodiment and these have a cylindrical shape where X-rays are transmitted. At this time air or a gas in the atmosphere when carbon nanotubes are synthesized may be in them or this may be an atmosphere that will not have an adverse influence on the X-rays that they will transmit such as an atmosphere with a low X-ray absorbing coefficient of the previously noted liquid 5. It does not matter whether the carbon nanotubes are single layered tubes or multi-layered tubes. As explained earlier, in the present embodiment, by arranging pipe-shaped lens components 4 contiguous and parallel, a converging effect, the same as when numerous concave lenses have been arranged can be obtained, because the surface of the inner perimeter of pipe-shaped lens components 4 act artificially to fulfill the role of a concave lens (See FIG. 1b). Thus, X-ray XI which is incident, by successively passing through numerous pipe-shaped lens components and liquid 5 which holds these, because it gradually refracts, it ultimately converges and becomes X-ray XO. Here we have utilized a structure in which the carbon nanotubes which are pipe-shaped lens components 4 are arranged so that their outer peripheries contact each other, but it is not necessary to have carbon nanotubes fit tightly with other contiguous carbon nanotubes. It may also have a structure in which carbon nanotubes are contiguous via liquid 5. Next, we shall explain the method of manufacturing the transmission type X-ray lens of an embodiment of this invention with FIGS. 2a through 2c, which are oblique view simplified drawings showing each of the manufacturing processes of the transmission type X-ray lens of this invention. Components with the same numbers as in FIGS. 1a and 1b have the same function in FIGS. 2a through 2c. Beginning with FIG. 2a, a liquid layer is formed on substrate 2 with liquid 5. In this embodiment a liquid layer is formed by dripping liquid 5 on the flat surface 2a of this substrate 2 using dripping mechanism 21. Since it is sufficient if the liquid layer formed with liquid 5 covers a specified area on flat surface 2a, the mechanism for forming the liquid layer is not restricted to the method using dripping mechanism 21 and a layer may be formed using methods such as painting and spraying as well. In addition, in this embodiment the liquid layer formed with liquid 5 has a configuration which forms it over the entire surface of flat surface 2a of substrate 2, since ultimately it is sufficient if liquid 5 fills the gaps formed by flat surface 2a, flat surface 3a and the exterior periphery of pipe-shaped lens components 2, it may be scattered over flat surface 2a. Then, in FIG. 2b, numerous pipe-shaped lens components 4 are placed on substrate 2. After completing the process shown in FIG. 2a, pipe-shaped lens components 4 are successively placed on the liquid layer of liquid 5 formed in that process and made so that the pipe-shaped lens components are held by liquid 5. Here, pipe-shaped lens components 4 are respectively lined up and placed so that they follow the orienting axis 22 which extends in a direction parallel to the flat surface 2a of substrate 2. When the manufacturing process is fully completed and this is completed as an X-ray lens, the direction that axis 22 extends which is the standard when placing these will be perpendicular to the direction that X-rays are transmitted in the transmission type X-ray lens. When placing pipe-shaped lens components 4 parallel, one may place them in a layer formed by liquid 5 in a state in which their exterior walls are contacting each other, or may use a method in which one places the pipe-shaped lens components 4 on the liquid layer with a slight gap between a pipe-shaped lens component 4 and another pipe-shaped lens component and subsequently relies on using the phenomenon of moving them with the surface tension of liquid 5 to make adjacent pipe-shaped lens components 4 contact each other. In addition while the number of pipe-shaped lens components 4 which are placed is selected to correspond to the required focal length, as a general rule, as the number of pipe-shaped lens components 4 is increased, the focal length becomes smaller. Then, in FIG. 2c, the pipe-shaped lens components 4 placed on substrate 2 are enclosed and held with substrate 3. After the process shown in FIG. 2b is completed, the flat face 2a of substrate 2 and the flat face 3a of substrate 3 are made to face each other and these flat surfaces 2a and 3a hold pipe-shaped lens component 4 between them, At this time liquid 5 fills up spaces and gaps formed by the flat surface 2a of flat surface 3a and pipe-shaped lens components 4 by capillary action, etc. As previously noted, by liquid 5 filling up these gaps, the adhesive power of liquid 4 unifies substrate 2, substrate 3 and pipe-shaped lens component 4 and ensures and maintains structural stability. This adjustment of the position of pipe-shaped lens components in the end of the X-ray lens that X-rays will be incident upon will be done using electron microscopes etc. By adopting the method previously noted, even though the pipe-shaped lens components 4 are small diameter components like carbon nanotubes, precision processing required in manufacturing is accomplished easily because the lens components which refract X-rays are independent structures. In addition, while precision processing is required in making the surface of the substrates flat, because processing a flat surface compared to processing a curved surface can be accomplished with greater precision, precision processing required to line up numerous pipe-shaped lens components following a specific axis is accomplished with ease. Moreover, by using the X-ray lenses manufactured using this method of manufacturing, the size of devices can be reduced together with shortening of the focal length and it becomes possible to realize X-ray electron microscopes that can be used practicably. By virtue of this, interfaces and internal structures which could not be observed with X-ray electron microscopes in the past can be observed at the electron level and we can expect these X-ray electron microscopes to be used in the field of medicine as well as in industry. As previously explained, with the invention of claim one, short focal length X-ray lenses can be manufactured with realizable precision by adopting a process of first arranging tube shaped lens components on a substrate finished with a liquid layer and then holding them with a substrate. In addition, with the invention of claim two, a practical method of manufacturing X-ray lenses which converge incident X-rays with precision in microscopic areas of the order of nanometers can be made available by adopting carbon nanotubes as tube shaped lens components. Also with the invention of claim three, X-ray lenses with short focal lengths can be made available by holding tube shaped lens components placed parallel with substrates and adopting a configuration in which tube shaped lens components are held between the substrates by a liquid. Finally with the invention of claim four, practical X-ray lenses which converge incident X-rays in microscopic areas of the order of nanometers can be made available by adopting carbon nanotubes as tube shaped lens components. Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention. |
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description | This application is a divisional application of U.S. patent application Ser. No. 14/333,627 filed on Jul. 17, 2014, which is incorporated herein in its entirety by reference. The United States Government has rights in this invention pursuant to contract no. DE-AC05-00OR22725 between the United States Department of Energy and UT-Battelle, LLC. Tritium release from FLiBe is a significant safety issue in Molten Salt Reactors (MSRs) including both Fluoride Salt-Cooled High-Temperature Reactors (FHRs) and dissolved fuel MSRs, and fusion reactors. Tritium is formed in FLiBe through neutron interactions with both lithium and beryllium. The tritium generally either exists in the salt as tritium fluoride (TF), a dissolved ion (T+), or as dissolved tritium gas (HT or T2). Shifting the redox potential of the fluoride salt to a more reducing condition shifts the chemical equilibrium away from tritium-fluoride. Metallic beryllium contact has been shown to effectively reduce TF to T+ in FLiBe. Excess beryllium in the salt will keep the FLiBe TF concentration below 20 ppt. Tritium gas has a very low solubility in FLiBe. The equilibrium partial pressure of tritium gas over FLiBe with 1 ppm T2 is 105 Pa. The tritium will transport along with the salt. The generated tritium can be trapped by the carbonaceous materials in the primary loop, escape through the primary coolant surface into the cover gas, permeate through the reactor vessel or piping, or permeate through the heat exchanger tubing. The large surface area and thin tubing walls combined with the turbulent mixing within the heat exchanger makes tritium escape through the heat exchanger tubes a significant tritium escape mechanism. Tritium has been calculated and experimentally demonstrated at the Molten Salt Reactor Experiment (MSRE) at the Oak Ridge National Laboratory to significantly transfer from FLiBe under turbulent flow through heat exchanger tubes. The calculated tritium production rate at the MSRE was 54 Ci/day, and the observed disposition of tritium, not including retention in the off-gas system, amounted to 80% of this production rate: 48% discharging from fuel off-gas system, 2% discharging from coolant off-gas system, 7% discharging in coolant radiator air, 9% appearing in cell atmosphere, and 14% going into the core graphite. Most of the remainder was probably held up in oil residues in the fuel off-gas systems. Further information and attribution can be found in the references listed at the end of the specification. Tritium can be a hazardous radioactive contaminant under the above described and other conditions, but if it can be sequestered, tritium would be a valuable commodity, being useful for various applications, particularly as the parent isotope for 3He for which there is currently a global shortage. There has been heretofore a need for an effective and practical mechanism to strip tritium from FLiBe that is used in nuclear power plants. In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a nuclear reactor system including a nuclear reactor, a utilization means for utilizing heat energy generated by the nuclear reactor, and a flowing stream of molten salt for transferring the heat energy from the nuclear reactor to the utilization means, wherein the improvement includes a tritium-separating membrane structure having a porous support, a nanoporous structural metal-ion diffusion barrier layer, and a gas-tight, nonporous palladium-bearing separative layer, means for directing the flowing stream of molten salt into contact with the palladium-bearing layer so that tritium contained within the molten salt is transported through the tritium-separating membrane structure, and means for contacting a sweep gas with the porous support for collecting the tritium. In accordance with another aspect of the present invention, a method of stripping tritium from a flowing stream of molten salt includes providing a tritium-separating membrane structure having a porous support, a nanoporous structural metal-ion diffusion barrier layer, and a gas-tight, nonporous palladium-bearing separative layer; directing the flowing stream of molten salt into contact with the palladium-bearing layer so that tritium contained within the molten salt is transported through the tritium-separating membrane structure; and contacting a sweep gas with the porous support for collecting the tritium. Functionally like components are identified with the same callout numerals throughout the figures in order to show how the components interrelate in various configurations. For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings. Palladium and palladium-silver alloy films are commercially used as gaseous hydrogen separation membranes. Palladium has very high affinity for disassociating molecular hydrogen (and therefore tritium) into the atomic state, enabling fast absorption and desorption. Palladium can absorb large amounts of tritium while maintaining its physical properties, and has a high tritium transport (diffusion) rate. In order to apply the above principle to tritium-contaminated salt, especially FLiBe, a tritium-stripping transport membrane structure has been devised wherein molten salt turbulently flows on one side of the membrane structure, and a sweep gas flows on the other side thereof, neither able to pass through the membrane structure. Tritium, however, is transported through the membrane structure, effectively transferring from the salt into the sweep gas, which can generally comprise any gas that does not contain unbound hydrogen and is chemically compatible with the membrane structure. Examples of sweep gases can include, for example, dry air, nitrogen, helium, argon, and a combination of any of the foregoing. The apparatus and method disclosed herein thus mitigate tritium contamination in the salt, sequestering the tritium in the sweep gas, from which it can be easily concentrated and utilized in applications such as those described hereinabove. Referring to FIG. 1 a layered, tritium-separating membrane structure 10 (henceforth called membrane structure) can be comprised of a porous support 12 (henceforth called support), a nanoporous structural metal-ion diffusion barrier layer 14 (henceforth called barrier layer), and a gas-tight, nonporous palladium-bearing separative layer 16 (henceforth called separative layer). The layers 12, 14, 16 that make up the membrane structure 10 should have compatible thermal expansion characteristics and also should be respectively compatible with the molten salt 18 and sweep gas 20, the flows of which are shown by respective arrows A and B. FIG. 1 shows only a small portion of the membrane structure 10 in order to illustrate the layers. The membrane structure 10 can be made in any suitable shape and configuration, such as a tube or a plate, for example. The support 12 can comprise a sintered or fritted metal, ceramic, or cermet material, limited only by mechanical strength and compatibility to process fluids and other components of the membrane structure 10. An important aspect of the support 12 is the ability to join it to upstream and downstream piping. Using a similar alloy as that of the piping can significantly decrease the difficulty of creating a compatible joint. While alumina or other ceramics can be formed into suitable structural supports, ceramics are much more difficult to effectively join to the piping. Suitable materials for the support 12 can include any alloy typically used in nuclear applications; some examples include, but are not limited to 316 stainless steel (also known as SS316), 304L stainless steel, 310 stainless steel, 347 stainless steel, 430 stainless steel, Hastelloy® B, Hastelloy® B-2, Hastelloy® C-22, Hastelloy® C276, Hastelloy® N, Hastelloy® X, Inconel® 600, Inconel® 625, Inconel® 690, Monel® 400, Nickel 200, Alloy 20, titanium, other stainless steel compositions, nickel-based alloys, and the like. (Hastelloy® trademark is owned by Haynes International, Inc. Monel® and Inconel® trademarks are owned by Special Metals Corporation.) A key function of the support 12 is to provide mechanical integrity to the membrane structure 10. Hence the thickness of the support 12 depends on the mechanical loads imposed thereon, which are generally dominated by flow induced vibration due to the turbulent flow of molten salt. The skilled artisan will recognize that standard, well-known mechanical strength and support guidelines for tube performance can be applied to the support 12. A wide range of thicknesses and porosities can be used with the general understanding that as porosity decreases, the overall surface of the support 12 must be increased; for example, a support tube would have to be of greater length and/or diameter, or multiple tubes could be employed. Moreover, as porosity of the support 12 is increased, mechanical strength thereof decreases. The support 12 can be made thicker to compensate for the lower strength of higher porosity materials. Since gaseous hydrogen (hence, tritium) has very high mobility, the support 12 primarily has an economic (thicker requires more metal) rather than a performance thickness limit. A mean support 12 thickness of about 1-5 mm, typically about 2 mm, is suggested as suitable for some applications. The porosity of the support 12 must be interconnected to allow tritium to be rapidly transported therethrough from one surface to the other as indicated by arrow C. Minimum pore size is dependent on achievable manufacturing tolerances. Porous metal supports are generally manufactured as sintered powder structures. The size and shape of powder material used in the fabrication process determines the pore size. A mean powder size in a range of 0.2-5 μm, typically about 0.5 μm is suggested as suitable for some applications, but the key requirement is to have interconnected porosity; tritium gas will be transported readily through a support 12 comprised of any interconnected pore size. The barrier layer 14 is adherently deposited on the surface of the support 12 that will face the molten salt 18. The barrier layer 14 serves a plurality of important functions while allowing tritium to pass freely therethrough. A first function is to mitigate the generally large, rough porosity of the support 12 in order to provide a suitably smooth, adherent substrate for subsequent deposition of an essentially defect-free separative layer 16. At the high temperatures characteristic of molten salts, inter-diffusion of support 12 and separative layer 16 materials can perniciously degrade permeation of hydrogen through palladium alloys. Hence, a second function of the barrier layer 14 is to mitigate deleterious metal inter-diffusion between the support 12 and the separative layer 16. Sol-gel derived mesoporous yttria stabilized zirconia (YSZ) has been shown to be an effective barrier to the diffusion of metallic atoms from the support 12 to the separative layer 16. Other suitable barrier layer 14 materials include, but are not limited to scandia stabilized zirconia, alumina, titania, chromia, chromium nitrides, and the like. The particular material selected will depend on the maximum operating temperature and desired lifetime of the component; YSZ is known to have the highest demonstrated temperature performance. The barrier layer 14 can be made by a sol-gel process wherein nanoscale particles are formed in the solvent. The particles aggregate during the gelation and fuse together due to calcining providing small uniform scale pores. Calcination at higher temperatures will result in smaller pore size. The minimum thickness that is deposited in each dip-dry cycle of sol deposition—gelation is generally about 0.5 μm. A mean barrier layer 14 thickness of about 3-20 μm, typically about 5-10 μm, is suggested as suitable for some applications. Average pore size of the barrier layer 14 should be no more than 30 nm to prevent structural atoms from diffusing therethrough. Thicker layers should be used with higher temperature operation to adequately limit metal atom diffusion. Minimum thickness of the barrier layer 14 is limited by the requirement for suitably smooth, adherent substrate for subsequent deposition of an essentially defect-free separative layer 16. Maximum barrier layer 14 thickness is limited by corresponding decrease in gas permeability. The separative layer 16 is deposited on the barrier layer 14 by any suitable conventional means such as, for example, an electroless deposition process. The separative layer 16 can be comprised of palladium or palladium alloy such as, for example, a palladium-silver alloy such as for example, those described by Jayaraman, V. and Lin, Y. S. in Synthesis and hydrogen permeation properties of ultrathin palladium-silver alloy membranes. J. Membr. Sci. 1995, 104, 241. Other palladium-bearing alloys can include Pd—Cu. Average thickness of the separative layer 16 should be in the range of about 10 to about 50 μm. A separative layer 16 that is thinner than 10 μm may lack sufficient structural integrity for the intended application. Moreover, a separative layer 16 that is too thick may not transport tritium with sufficiently desirable efficiency. Turbulent molten salt 18 flows as shown by arrow A across and contacts the surface of the membrane structure 10 so that essentially all of the tritium within the flowing salt 18 rapidly impinges upon the palladium-bearing separative layer 16. The membrane structure 10 rapidly strips tritium from flowing molten salt 18. The tritium is transported as shown by arrow C through the layers of the membrane structure 10 and into the inert sweep gas 20 from which it can be readily extracted and isolated for utilization. Sweep gas 20 is shown by arrow B as flowing in the same direction as the molten salt 18 but they can flow in different directions. The sweep gas 20 is generally at thermal equilibrium with the molten salt 18 and does not transfer significant heat therefrom. Referring to FIG. 2, an example of a single-tube tritium-stripping system 21 comprises an inner, tubular membrane structure 10 disposed within an outer containment structure 22 that may be tubular as shown, but can be any suitable shape and configuration. Arrows show typical flows of molten salt 18 and sweep gas 20, but other flow directions may be used. Referring to FIG. 3, an example of a multiple-tube tritium-stripping system 31 comprises a plurality of inner, tubular membrane structures 10 disposed within a single outer containment structure 30 that may be tubular as shown, but can be any suitable shape and configuration. Molten salt 18 flows through the tubular membrane structures 10 and sweep gas 20 flows outside the tubular membrane structures 10 and within the outer containment structure 30. Referring to FIG. 4, an example of a multiple-tube tritium-stripping system 41 comprises a plurality of inner, tubular membrane structures 10 disposed within a single outer containment structure 30 that may be tubular, but can be any suitable shape and configuration. A heating jacket 32 can be employed in order to maintain the salt 18 in a molten state. Baffles 34 are optional, as well as U-shaped membrane structures 10, which can be straight, coiled, or any other suitable shape and configuration. Arrows show typical flows of molten salt 18 and sweep gas 20, but other flow directions may be used. Means for promoting turbulence (not shown in the figs.) can be employed anywhere within the flow-path of the molten salt 18, including the membrane structure 10 itself. Such means can include active or passive vanes, blades, slats, tubes, baffles, fins, rods, jets, venturi, ports, diverters, contours, corrugations, and the like, and any combination of the foregoing. An example of a turbulence promoter can be found in U.S. Pat. No. 3,302,701 issued on Feb. 7, 1967 to David G. Thomas, entitled “Turbulence Promoter for Increased Heat and Mass Transfer.” Referring to FIG. 5, a nuclear reactor facility 51 includes a reactor 50 and a utilization means 52 which can be an electricity generation plant or any other means for utilizing heat energy generated by the nuclear reactor. The skilled artisan will recognize that FIG. 5 is a very simple, general illustration intended to be applicable to various nuclear systems that are very complicated. Only the most basic components are described in order to illustrate an example of a general application of the invention. A circulating molten salt stream 56 transfers the heat energy from the nuclear reactor to the utilization means 52. A circulating molten salt stream 58 passes through a tritium-stripping system 54 where tritium is removed as described hereinabove. A sweep gas system 60 circulates a sweep gas stream 62 into and out of the tritium-stripping system 54. Two circulating molten salt streams 56, 58 are shown but a single circulating molten salt stream can be used. While there has been shown and described what are at present considered to be examples of the invention, it will be obvious to those skilled in the art that various changes and modifications can be prepared therein without departing from the scope of the inventions defined by the appended claims. |
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claims | 1. A floating nuclear power reactor, comprising:a floating vessel having a bottom positioned beneath the water level of a body of water, sides extending upwardly from said bottom, and an upper end which is positioned above the water level of the body of water;a nuclear power reactor supported on said vessel;at least a portion of said nuclear power reactor being submerged in the body of water;said nuclear power reactor having a lower end, an upstanding side wall, and an upper end;a water passageway, having inner and outer ends, extending through said floating vessel and into said nuclear power reactor;a normally closed hatch movably associated with said water passageway;said hatch being movable between a normally closed position and an open position;said hatch, when in said closed position, closing said water passageway;said hatch, when in said open position, permitting water from the body of water to flow inwardly through said water passageway into said nuclear power reactor;a latch associated with said hatch which is movable from a latched position to an unlatched position;said latch, when in said latched position, maintaining said hatch in said closed position;said latch, when in said unlatched position, permitting said hatch to move from said closed position to said open position;and a condition responsive actuator positioned within said nuclear power reactor which causes said latch to move from said latched position to said unlatched position upon a condition within said nuclear power reactor reaching a predetermined level. 2. The floating nuclear power reactor of claim 1 wherein said condition responsive actuator is a temperature condition responsive actuator. 3. The floating nuclear power reactor of claim 1 wherein said condition responsive actuator is a pressure condition responsive actuator. 4. The floating nuclear power reactor of claim 1 wherein said water passageway extends into the lower end of said nuclear power reactor. 5. The floating nuclear power reactor of claim 1 wherein said water passageway extends through the upstanding side wall of said nuclear power reactor. 6. The floating nuclear power reactor of claim 1 wherein said water passageway extends into the upper end of the nuclear power reactor. 7. The floating nuclear power reactor of claim 6 wherein a second water passageway extends from the body of water through the upstanding side wall of the nuclear power reactor. 8. The floating nuclear power reactor of claim 7 wherein a third water passageway extends from the body of water into the lower end of the nuclear power reactor. |
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summary | ||
description | This application is a National Phase of PCT/EP2009/061516, filed Sept. 7, 2009, entitled, “DEVICE FOR GRIPPING FUEL ELEMENTS, AND RELATED CLAW AND HANDLING SYSTEM”, and claims priority of French Patent Application No. 08 56016, filed Sep. 8, 2008. This invention relates to the field of handling fuel elements. More particularly, it relates to a device designed for this purpose which, if a failure occurs, could provide a solution for safely putting down the handled fuel element. LWR type fuel elements are handled by gripping fuel elements, the elements to be handled being usually in an initial vertical gripping position. In the current design, a vertical lifting system is installed within a feed cell so that spent fuel elements partially immersed in a pool in the vertical position can be gripped or picked up. When the fuel element is gripped, a pushing chain makes the vertical lift and pushes horizontally to a shear cell in which spent fuel elements are sheared into segments before being dissolved in a tank called a dissolver, full of acid. This handling operation must be done safely and it must always be possible to put the fuel elements down in a safe place if any failure arises, particularly in order to put the installation back into good condition. Furthermore, if a failure occurs, it must be possible to make a repair without any human intervention, in other words solely by remote operated means. Currently known equipment for handling fuel elements of are either vertical handling equipment or pusher systems. At the moment, there is no device that performs vertical handling and horizontal pushing functions, but horizontal pushing is necessary to shear the fuel. Therefore, the purpose of this invention is to disclose a solution for handling fuel elements that performs vertical handling and horizontal pushing functions to safely remove fuel elements, even if there is a failure in all or some of the handling system. Consequently, the first aspect of the invention relates to a fuel element gripping device comprising: a main carriage with a longitudinal axis; a clamp coupled to the main carriage and adapted to grip the head of fuel elements; a secondary carriage with a longitudinal axis comprising attachment means. According to the invention, the main carriage and the secondary carriage are coupled to each other by means of transmitting forces applied on the attachment means when a device is lifted and when the device is pushed horizontally, the force transmission means being removably connected between the main carriage and the secondary carriage, and the main carriage and the secondary carriage are uncoupled from each other when the secondary carriage is blocked at its attachments by disassembly of the connection of the force transmission means with the carriages, disassembly being made by a single pull/push movement applied on the main carriage, tension being made towards the secondary carriage. The invention thus lies in the fact that it discloses a fuel element gripping device that performs a handling function for fuel elements picked up in the vertical position, a pushing function for fuel elements picked up in the horizontal position (due to the carriages) that enables remote repair by so-called remote operated means (due to possible uncoupling between the carriages). In other words, uncoupling between carriages of the gripping device makes it possible to release picked up fuel elements in the case of a failure in the vertical or horizontal position, and to perform maintenance operations. Therefore, the advantage of an easily removable coupling between the different parts of the gripping device is that it offers a solution for putting the load (picked up fuel elements and their support) down if a failure occurs in complete safety, and enables repair operations. Failure cases considered are blocking of the lifting/pushing chain and gripping device electrical power supply failure. Uncoupling as defined in this invention is easily done using a single mechanical pull/push movement between the carriages. Thus, no complex equipment is necessary to do the uncoupling if a failure occurs. The head of the fuel elements gripped by the gripping device according to the invention is in the form either of a handle for BWR type fuel elements, or a part with an internal recess for PWR type fuel elements. Thus, any LWR (BWR+PWR) type fuel element may be gripped by the gripping device according to the invention. According to one advantageous embodiment, recoupling between the main carriage and the secondary carriage is done when the secondary carriage is blocked at its attachments, by reassembling the connection of force transmission means with the carriages, the connection being reassembled following a single push/pull movement applied to the main carriage, the pushing being made towards the secondary carriage. Advantageously, the force transmission means in removable connection between the main carriage and the secondary carriage comprise: a first key mounted on the main carriage, tipping transverse to the longitudinal axis and stopped against the secondary carriage to enable forces applied on the attachment means to be transmitted during the horizontal push; a second key mounted on the main carriage, pivoting orthogonally to the longitudinal axis and stopped against the secondary carriage to enable forces applied on the attachment means to be transmitted during lifting; device in which the tension applied on the main carriage enables tipping of the first key, the relative movement of the main carriage towards the secondary carriage and then pivoting of the second key, the first tipped key and the second pivoted key each remaining in a position without a stop in contact with the secondary carriage. The main carriage may comprise two rigid parts flexibly connected to each other, in which: one is coupled with the clamp and comprises an electronic weigh scale to electrically test tension or compression forces applied on said rigid part supporting the clamp; the other comprises a so-called head carriage coupled with the secondary carriage and a gripping socket by which the uncoupling pull/push movement between the head carriage and the secondary carriage is performed. According to one variant embodiment, the main carriage comprises: an electric motor; a hollow shaft mounted in translation with one of its ends fitted with a screw/nut type drive engaged with the electric motor, and the other of its ends bearing on part of the clamp gripping arms, actuation of the electric motor causing translation of the shaft in one direction and simultaneously moving the clamp gripping arms towards or away from each other by tipping orthogonally to the axis. The gripping device according to the invention advantageously comprises a coupling lever fixed to the main carriage and arranged to form a lever arm to translate the shaft and uncouple it from the clamp, the lever arm being adapted so that it can be manipulated by remotely operated means. Thus, if a failure occurs in the electric motor, the remote operated means can be used to uncouple the clamp gripping the head of the fuel elements and thus release them, for example into a fuel element shear cell. Any remote-operated means that are usually used or that can be used in a nuclear fuel recycling environment, particularly in the feed and control cell on the input side of the shear cell of the spent fuel to be recycled, are suitable for the invention. According to one embodiment of the gripping device, the clamp comprises a body on which the gripping arms are installed free to tip and on which a rod is installed free to slide along the axis between the arms; the hollow shaft comprises a rod fixed inside it, the rod of the hollow shaft bearing in contact with the clamp rod, the length of the clamp rod being such that in the near or the far extreme position of the clamp arms corresponding to the gripping position of the fuel element head, there is a direct contact between the head and the clamp rod. Preferably: the rod fixed inside the hollow shaft comprises a projection that extends transverse to the axis forming a flag; the main carriage comprises a first position detector arranged so as to be facing the flag so that it electrically detects direct contact between the head of the fuel elements and the clamp rod. According to one advantageous embodiment of the invention, the main carriage comprises pins installed to tip orthogonally to the longitudinal axis, the clamp body comprises a wall with steps; the shaft comprises relief fixed to its periphery; coupling between the clamp and the shaft being made by the relief tipping the pins and by the tipped pins bearing in contact with the steps in the clamp body. The means of locking the coupling between the main carriage and the clamp advantageously may consist of a pin inserted inside the wall of the clamp body transverse to the longitudinal axis of the main body to block one in translation relative to the other, the pin being designed so that it can be removed by remote-operated means. Thus as explained later, if a failure occurs the clamp can be released from the main carriage by using remote-operated means to remove this pin. According to one variant embodiment: the hollow shaft comprises a projection that extends transverse to the axis forming a flag; the main carriage comprises a first and a second position detector each arranged so as to be facing the flag in a given translated position of the hollow shaft to electrically detect a given translated position of the relief and therefore detect whether or not the pins are tipped. According to another advantageous variant embodiment: the clamp body comprises a projection that extends transverse to the axis, forming a flag; the main carriage comprises a third position detector arranged to be facing the flag when the clamp is coupled with the main carriage, and the flag thus electrically detects the presence of the clamp. According to another aspect, the invention relates to a fuel element handling system comprising: a tipping crane comprising a drum inside which carriages of the gripping device as described above are installed free to slide; a handling system comprising a lifting/pushing system, part of which is fixed to the attachment means of the secondary carriage of the gripping device as described above, the lifting/pushing system rolling the gripping device into the horizontal position towards the outside of the tipping crane drum. The invention also relates to a clamp comprising: a body with a longitudinal axis; gripping arms installed free to tip orthogonally to the longitudinal axis on the body and comprising recesses; a rod installed free to slide inside the body along the longitudinal axis, the rod comprising tabs arranged as claws that extend transverse to the axis and with a shape complementary to the shape of the recesses, the claws being arranged to engage in the recesses of the gripping arms in a translated position of the rod and thus block the gripping arms in an extreme open or closed position. The rod of the clamp according to the invention is made sufficiently long at the free end of the gripping arms so as to detect the presence of an element to be picked up by direct contact when the claws block the arms in the extreme open or closed position. Obviously, a specific type of clamp is associated with a fuel element type to be handled. According to another aspect, the invention relates to a method for handling fuel elements in which if a failure occurs during a handling operation: part of a device for gripping fuel elements is attached to mechanical standby handling means; part of the gripping device attached to the mechanical standby means is uncoupled from the remaining of the gripping device attached to the mechanical operational handling means using remote-operated means. The handling operation may be either lifting, or horizontal tipping or horizontal pushing. Actuation of the remote-operated means advantageously makes a single pull-push movement separating the parts of the gripping device from each other. Thus as mentioned above, the invention consists of designing and making a gripping device and associated clamp and handling means that enable: 1/ normal operation (in other words without a failure): vertical and horizontal handling of many types of fuel elements; gripping of these fuel elements; checking the presence of the picked up fuel elements; selection and placement of various gripping clamps as a function of the family of fuels to be picked up; an electrical check of the presence of a clamp; check forces passing through the kinematic handling chain; check the position of the various movements (presence of the fuel element, presence of the clamp, check the two extreme positions of the clamp pins, namely clamp closed and clamp open). 2/ degraded mode (in other words if a failure occurs): A/ in the vertical position: uncoupling of part of the gripping device comprising the clamp and the picked up fuel element, from the operational lifting chain; gripping of the uncoupled part of the gripping device comprising the clamp and the picked up fuel element, by another lifting means; release of the picked up fuel element from the uncoupled part of the gripping device and then placement in an appropriate rack; B/ in the horizontal position: uncoupling between the part of the gripping device comprising the clamp and the picked up fuel element and the operational pushing chain; push the fuel element into the destination location provided for this purpose, for example a cutting machine; release the fuel element; C/ regardless of the position: put the gripping device and the handling system assembly back into configuration. The fuel element handling system S according to the invention comprises firstly a gripping device P. This gripping device P comprises a main body 1 and a secondary body 2 with a longitudinal axis (XX′) each provided with rolling means 3 such as rollers, thus forming carriages. The terms main carriage and secondary carriage are used herein with reference to the fuel elements to be gripped. Thus, the main carriage 1, also called the grab, is the carriage that supports the fuel element gripping clamp 6 while the secondary carriage 2 is the intermediate carriage between the main carriage 1 and the front part of a lifting/pushing chain 200 that for example does the horizontal and vertical handling. This front part is also called the pushing chain nose. In the handling system S according to the invention S, the secondary carriage 2 is attached by its attachments means 20 to a lifting and pushing system which is adapted to be lifted by motor 4 fixed to a tipping crane not shown (FIG. 1). The tipping crane enables the gripping device P to tip from the vertical to the horizontal. The kinematic handling chain comprises the lifting/pushing chain actuated by a motor drive assembly. Handling systems with chains or cables were used in previous devices according to the state of the art, since handling was only vertical. The gripping device P comprises firstly a main body 1 rolling in a U-shaped drum 5 of the tipping crane through rolling means 3. This drum 5 of the tipping crane firstly enables guidance of the gripping device P by bearing of the gripping device in the horizontal and the vertical position, and secondly sliding of the picked up fuel elements during their horizontal transfer to an appropriate cutting machine (FIG. 1A). This main body 1 is coupled with a gripping clamp 6 for gripping fuel elements (not shown). In the lifting position, the clamp 6 thus coupled is in the lower part of body 1. FIG. 2A shows a clamp 6 suitable for use with the invention. It comprises the following elements: 1/ a tubular block 60, for which the inner shape is suitable for coupling with the main body 1; 2/ fuel elements gripping arms 61 that are installed free to tip orthogonally to the XX′ axis, each of which comprises a part forming a gripper 610 the shape of which is adapted to the type of fuel element to be handled, and a part 611 with a shape adapted to make the different tipping movements (moving the arms 61 closer or further apart), as described below; 3/ a fuel element presence detection rod 62 assembled free to translate in guides 620 fixed to the tubular block 60; 4/ a mechanical lock 63 fixed to the detection rod 62 prevents any manoeuvring movement of the grippers 610 firstly when the fuel element is not detected (gripping manoeuvre) and secondly during handling of the fuel element (unexpected opening - the rod drops during clearance correction during the lifting operation). In the embodiment shown (FIGS. 2 and 2A), the mechanical lock 63 is composed of claws 630 fixed transverse to the rod 63 that engage into complementary shaped recesses 6100 formed inside the grippers 610 in a translated position of the rod 62. In other words, the clamp 6 thus defined comprises a sort of a solely mechanical system self-locking its arms 61 by engaging the claws 630 inside the arms in the extreme open or closed position corresponding to the fuel element gripping position. In the embodiment shown in FIG. 2, a secondary locking system 64 is also provided that locks said coupling once the clamp 6 has been coupled with the main body 1. As shown, this system is composed of a stud 64 fixed to the clamp 6 that is arranged to be orthogonal to the longitudinal axis XX' of the main body 1 and that may be actuated by remote-operated means. The main body 1 comprises firstly a control system to enable coupling with the clamp 6. This control system is controlled manually by remote-operated means. This control system comprises a lever 10 that drives a cylindrical hollow shaft 11 in translation, a relief system being formed on the hollow shaft making it act like a cam 110, and this shaft drives several pins 111 in rotation. The coupling lever 10 may be blocked by a self-locking device 100 fixed to the main body 1. The cylindrical hollow shaft 11 is located around another hollow shaft 12 that controls fuel element gripping arms 61. The rod 62 of the fuel element presence detection system is inserted in one end 120 of this hollow shaft 12. The gripping position of the clamp 6 in the embodiment shown in FIG. 2A corresponds to a mutual movement of the arms of the clamp 61 towards each other in an extreme closed position blocked in translation by pins 111. This position is electrically controlled by a mechanical flag 7a composed of a projection that extends transverse to the axis and that is positioned in front of an electrical position detector 8b. Another electrical position detector 8a detects the extreme open position when the flag 7a is placed in front of it. The body 1 also comprises a control system for the fuel element gripping clamp 6. This system comprises an electric motor drive 9 that uses a gear 90 and a screw-nut type reduction gear 91 to drive one end of the hollow shaft 12 in translation. The other end of the shaft 12 is widened with a shape 120 that enables transmission of the movement by bearing on part 611 of the clamp 6. The characteristic movement positions and the presence of the clamp body are electrically controlled by means of mechanical flags 7a, 7b that are placed in front of the position detectors 8a, 8b and 8c respectively. More precisely, the presence of a gripped fuel element is detected by a flag 7a and two electrical detectors 8a, 8b. The presence of the clamp 6 is detected by a flag 7b and a detector 8c, the position of the clamp 6 and a fuel element is detected by a flag 7a and two detectors 8a, 8b. The motor 9 with the gear 90 and the screw-nut system 91 can be manually disassembled by remote-operated means. It is electrically connected to an electrical box 13 through a remote-operated connector. This electrical box 13 is supported by the electrical power supply device for the motor 9, not shown. The position detectors 8, 8a, 8b are contained in a box 14 electrically connected to the box 13 and also supported by the electrical power supply device. The electrical box 13 is a box that groups the various electrical connections arriving on the grab 1, 6 and is electrically connected to the drum of the tipping crane through a cable-support chain. The main body 1 also comprises an electronic weigh scale 15 connecting the gripping part 6, 7, 8, 9, 90, 91, 10, 11, 110, 111, 12, 120 of the permanent body 1 to an intermediate connecting system 16. This weigh scale 15 controls forces applied in the pulling and pushing directions during a lifting operation and a pushing operation respectively of the gripping device. This weigh scale 15 is electrically connected through a connector to the box 13 supported by the electrical power supply device. In the embodiment shown, the weigh scale 15 may be disassembled by remote-operated means, just like the plugged in connector. The intermediate connecting system 16 comprises a fastener 160 connecting it to a head carriage 17 and a gripping socket 161 with a shape adapted to cooperate with lifting means fitted on a feed cell in which fuel elements to be picked up are immersed in a pool. The fastener 160 is in the shape of a U connected to the weigh scale 15. The fastener 160 is fixed to the head carriage 17 by means of an inserted pin 162. This pin 162 is adapted so that it can be removed by remote-operated means. The gripping socket 161 is used only if there is a failure in the operating chain. The rolling manoeuvre of the device P in the drum 5 of the tipping crane will be actuated using the socket 161 (in vertical handling). The gripping device also comprises a secondary carriage 2 provided with rolling means 3 and coupled with the head carriage 17 of the main body 1. This secondary carriage 2 comprises attachment means 20 that are fixed to the lifting/pushing chain of the handling system. Coupling between carriages 1 and 2 is also done by force transmission means transmitting forces exerted on the attachment means 20 when lifting the device and during a horizontal push on the device. As shown, the force transmission means are composed of an assembly of two keys 170, 171. The first key 170 is installed free to tip transverse to the XX' axis. A pin 163 fixes the gripping socket 161 to the base 164 that slides on the carriage 17 and between parts 1640, 1641 and 1642 the base 1640 of which supports a pin 1643 (FIGS. 3A and 3C). A spring 1644 holds the assembly composed of the socket 161 and the pin 163 in the end stop position (FIGS. 3A and 3C). The second T-shaped key 171 is installed free to pivot about a pivot axis 172 fixed to the head carriage 17 orthogonal to the XX′ axis. Thus, during normal operation of the fuel element handling system, the keys 170 and 171 bear in contact with a front part of the secondary carriage 2 composed of pads 2121 such that: during lifting, the non-pivoted key 171 bears in contact with the pads 2121 of the secondary carriage 2 (see view in solid lines in FIG. 3E), during pushing, the secondary carriage 2 bears in contact with the key non-tipped 170 (FIG. 3A). A lever arm system 173 described below is also installed free to pivot around the pivot axis 172 (FIGS. 3A to 3E). This lever arm system 173, arranged below the second key 171 is locked to it in two angular positions through a lock system 174 described later. Thus, the lever arm system 173 and the second key 171 are fixed in rotation in these two angular positions by the lock 174, but are free in rotation from each other between these two angular positions. The secondary carriage 2 comprises a frame 21 with a U-shaped cross section and a base 210. A pin 211 is fixed on this base 210. The base 210 is closed on the top by a cover 212 (FIGS. 3B and 3E). This cover 212 comprises firstly a slot 2120, arranged to block the lever arm system 173 vertically in position inside the frame 21 when the head carriage 17 and the secondary carriage 2 are coupled to each other (FIGS. 3B and 3E). The slot 2120 has a first portion 2120a closed on the side of the attachment means 20 and with width L larger than the bottom of the T of the key 171 and a second portion 2120bflush with the first portion 2120a (FIGS. 3B and 3E). The cover 212 also comprises pads 2121 that form projections arranged on each side of the open portion 2120b of the slot 2120. These pads form the front part of the secondary carriage 2 on which keys 170 and 171 bear to transmit forces between the head carriage 17 and the secondary carriage 2 coupled to each other. Thus, as described below, the shapes of the carriage 2 and the pivoting key 171 are designed to enable coupling and uncoupling of a part (main carriage 1) of the gripping device P of the lifting/pushing chain (to which the secondary carriage 2 remains fixed) in the case of incidents or for maintenance operations, using the surrounding cell remote-operated and lifting means only. Furthermore, for some maintenance operations on the kinematic handling chain of the handling system S, the connecting arm of the socket 161 shall be provided with ducts 1610 that broach the gripping device P onto the drum 5 of the tipping crane. The case of a failure of the handling chain that affects the gripping device P and solutions to overcome this failure in accordance with the embodiment shown are described below: Blockage of the lifting chain in the vertical position: Repair operations are as follows: a/ gripping of the gripping device P and its load (fuel elements gripped by the clamp 6) at the socket 161 using the handling means of the cell in which the fuel elements are located; b/ lifting: this movement drives the base 164 by compressing the spring 1644 and thus releasing the tipping key 170. This generates relative movement between the head carriage 17 and the secondary carriage 2; the key 171 then pivots from its angular bearing position against the pads 2121 (see the solid lines in FIG. 3B) to another position in which it can slide in the groove 2120a but cannot bear against the pads 2121 (see the chain dotted lines in FIG. 3B); c/ lowering: this movement does not make key 171 pivot. The bottom of the T of the key 171 prevents rotation because it is guided in the portion 2120b of the slot 2120; d/ after lowering according to c/, the device P and its load (fuel elements gripped by the clamp 6) are released from the lifting/pushing chain and may be transferred using the cell lifting apparatus. For the transfer, the socket 161 can be pivoted by removing the pin 163. The socket 161 then rotates about an axis fixed to the intermediate connecting system 16 after the socket 161 translates upwards. Rotation of the socket 161 enables the grab 1, 16, 6 to come into an equilibrium position once it has been removed from the drum of the tipping crane. Once the device P and its load have been put down in a safe position, the load (fuel elements and their gripped support) may be released from the gripping device and the clamp 6 by the following operations: electrical power is supplied to the load gripping motor 9 if the motor is still operational; or release the clamp 6 of the main body 1 (actuation of the coupling lever 10), lifting of the device generates a relative movement between the body 1 and the clamp 6 and this movement moves the load gripping fingers 610 apart and consequently releases the load, the clamp 6 then being driven and released by means of the safety lock 64.Blockage of the Lifting Chain in the Horizontal Position: Two cases can arise: the situation allows a return to the vertical position: repair is done as described above after tipping using the tipping crane; it is impossible to return to the vertical position: *repeat the operations described in the previous section, using a push/pull means instead of the cell lifting means. After disconnecting the gripping device P from the lifting/pushing chain, the device P and its load (fuel elements gripped by the clamp 6) are pushed into a safe position; *uncoupling of the load (fuel elements) from the clamp 6 according to the principles described above; *removal of the device P with its clamp 6 for repair. We will now describe steps b/ and c/ in which the main carriage 1 and the secondary carriage 2 are uncoupled, in more detail. Firstly, note that the lever arm system 173 in the embodiment shown (FIGS. 3A to 3E), is a single piece part composed of two pairs of two arms 173-1, 173-3 and 173-2, 173-4. Each pair is arranged on different levels along the pivoting axis 172, the two arms 173-1, 173-3 and 173-2, 173-4 in one pair are approximately diametrically opposite each other relative to the pivot axis 172, while two arms 173-1, 173-2 of two different pairs form an angle of the order of 90° . Thus, in the view shown along axis 172, the lever arm system 173 is approximately in the form of a right-angled cross (See FIG. 3B). Apart from the pin 211 fixed onto the base 210, the secondary carriage according to the invention includes another pin 213 fixed below the cover 212 in the area of the reduced slot 2120b. Relative translation of the head carriage 17 towards the secondary carriage 2 (corresponding to an upwards movement of the blocked carriage 2 or a downwards movement of the blocked carriage 17) firstly makes the base 164 tip the key 170. This translation then brings one of the lever arms 173-1 into contact with the pin 211 fixed onto the base 210 that then turns the fixed key 171 in rotation by a quarter of a turn; the key 171 is then positioned such that its length is parallel to the translation movement (see key 171 in chain dotted lines in FIG. 3B). This position is authorised because the key 171 is free to turn in the widened slot 2120a. This allows the secondary carriage 2 to be uncoupled from the main carriage 1. Then, by relative translation of the head carriage 17 by separating it from the secondary carriage 2, the pin 213 comes into contact with another of the lever arms 173-2 located at a different level from the level of the lever arm 173-1, which once again pivots the arm system 173 by a quarter of a turn, but not the key 171 that is blocked in rotation. The bottom of the key 171 is blocked in rotation in the area of the slot 2120b. This final quarter-turn rotation repositions the lever arm system 173 into an angular position 180° from its initial position. The result is recoupling of secondary carriage 2 and main carriage 1 by reassembly of the connection between the key 171 that once again bears in contact with the pads 2121, following a single push/pull movement exerted on the main carriage 1. Thus in summary, the following operations are done in the embodiment shown in FIGS. 3A to 3E: 1/ Uncoupling operation: a tension movement towards the back of the secondary carriage 2 blocked in translation brings the arm 173-1 in bearing in contact with the pin 211, which pivots the key 171 into its angular release position (see the illustration in chain dotted lines in FIG. 3B). A forward pushing movement then brings the arm 173-4 that is on a different level from the arm 173-1, into contact with the pin 213, which makes the lever arm system assembly 173 pivot without pivoting the key 171, following a second rotation, on an identical travel distance in the same direction as the first rotation caused by the pin 211. The key 171 is prevented from pivoting during this second rotation by the locking system 174 that enables rotation of the lever arm system 173 relative to the key 171 when the key is held blocked in rotation (in slot 2120b). 2/ Recoupling operation: a pushing movement of the head carriage 17 or the main carriage 1 assembly by inserting the key 171 into the slot 2120b in the secondary carriage brings one of the arms 173-1, 173-3 once again in contact with the pin 211 and thus positions the key 171 fixed in rotation once again in its blocked position by pads 2121. In the embodiment shown in FIG. 3B, since the arm in contact with the pin 211 was arm 173-1 during uncoupling, the arm in contact with the pin 211 during recoupling is the other arm 173-3. In the embodiment shown in FIG. 3A, the lock 174 is composed of a ball/recess pushing system arranged between the pivoting key 171 and the lever arm system 173. More precisely, balls 1740 are fitted in the single-piece part 173 and are blocked in four angular positions at 90° from each other, in recesses 1741 with a complementary shape formed in the lower part of the key 171. A spring not shown (included in the balls 1740) is used to hold the balls 1740 in their recesses 1741, and these balls require application of a minimum force to rotate the system 173 without rotating the key 171. Another spring 1742 holds the arm system 173 in the notches. In the embodiment shown in FIG. 2A, the clamp 6 is a clamp in which the fingers 610 move towards each other to pick up the fuel elements. Obviously, a clamp in which the arms are separated from each other to pick up the fuel element head would be within the scope of the invention, provided that it can be coupled with the main body. The clamp 6 according to the invention, although shown in the context of the invention to grip fuel elements, can be perfectly well used in other applications in which it is required to lock the arms of the clamp onto the element gripped by the clamp. |
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description | This disclosure relates generally to the field of microprocessors. In particular, the disclosure relates to context switch sampling of process or thread events based on hardware event triggers in a processor. In multitasking, multiprocessing and/or multithreading systems, monitoring performance metrics may be complicated. Techniques that have been used in the past such as time-based sampling or event-based sampling employ a consistent regular grid of measurement to outline and characterize the behavior of applications whose activity may at times be anything but regular. Previous attempts to monitor activity within the context of a particular process may have required specially instrumented versions of the operating system. These techniques may also have the side effect of monitoring the special instrumentation as well as the desired performance metrics in the context of the particular process of interest. Thus results of previous techniques may have been contaminated by activity from other processes, threads or operating system instrumentation. To date, more efficient performance monitoring in multitasking, multiprocessing and/or multithreading systems to avoid contamination by events captured from other processes and/or threads have not been fully explored. Methods for performance monitoring in a computing system are described below. In some embodiments, an addressable memory stores data and instructions for performing context switch sampling. A processor includes hardware event counters for performance monitoring, and is coupled with the addressable memory to access said instructions and in response to said instructions, the processor counts occurrences of a first hardware event in a first hardware event counter and counts occurrences of a second hardware event in a second hardware event counter. After a specified number of occurrences of the first hardware event have been counted, it can be determined that a context switch has occurred. The second hardware event counter is then sampled and the hardware event counters are reset. In some embodiments the processor counts occurrences of segment register load events in the first hardware event counter and then records the sampled second hardware event counter value together with a process identifier value and/or a thread identifier value. Thus, such techniques may be used to more accurately capture and measure events for a particular process and/or thread without including contamination from events captured from other processes and/or threads. These and other embodiments of the present invention may be realized in accordance with the following teachings and it should be evident that various modifications and changes may be made in the following teachings without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense and the invention measured only in terms of the claims and their equivalents. FIG. 1 illustrates one embodiment of a multiprocessing system 101 for performing context switch sampling. Embodiments of system 101 may include addressable memory 140 having storage areas 141-149 to store data and machine executable instructions for performing context switch sampling. Multiple processes 111-131 are coupled with addressable memory 140 via a bus or any other interconnect 110 and processes 111-131 concurrently execute their respective threads. It will be appreciated that embodiments of processes 111-131 may include software processes or hardware threads or multiple individual processor cores on different dies or on the same die. Some embodiments of system 101 may also include processors such as processor 102, which has multiple hardware thread processes 111 and 121. Processes 111-131 respectively include execution units 112-132, registers 113-133, and hardware event counters 114-134 and 115-135. It will be appreciated that in some embodiments one or more of execution units 112-132 may be physically shared by some of processes 111-131. It will also be appreciated that in some embodiments of processes 111-131, registers 113-133, and/or hardware event counters 114-134 and 115-135 may also be shared or used in common by some of processes 111-131. One or more processes 111-131 may be coupled with the addressable memory 140 to access machine executable instructions 149, and responsive to machine executable instructions 149, one or more of processes 111-131 may count occurrences of a first hardware event in hardware event counters 114-134 respectively. In some embodiments the first hardware event may be a segment register load event, as is used in context switches on “x86” processors, such as those manufactured by Intel Corp. of Santa Clara, Calif. It will be appreciated that by counting occurrences of a hardware event such as a segment register load event in hardware event counters 114-134 respectively, the one or more processes 111-131 may be able to determine when a context switch has occurred. For example, a given operating system running on a specific x86 processor may need to execute four segment register loads in order to perform a context switch between application processes at ring 3. By setting a sample-after value (SAV) to sample hardware event counters after the count of exceeds four, the value of the sampled hardware event counters more accurately capture and measure events for a particular process and/or thread without including contamination from events captured from other processes and/or threads. In particular, if a SAV count is set to eight (twice four) a context switch between processes will have been detected. On the other hand if a SAV count is set to five (one more than four) a context switch between threads of the same process will have been detected. If a SAV count is set at or below the critical value (in this example, four) then sampling will fail to capture the desired application data, since sampling will occur prior to collecting event statistics in the desired application. It will be appreciated that the number of segment register loads needed to detect a context switch may vary greatly (e.g. between 1 and over 100 segment register loads) from operating system to operating system depending on the particular operating system and on the particular processor. It will be appreciated that some embodiments may use other techniques or instructions rather than segment register loads in order to perform context switch sampling. For example, a context switch may also be associated with loading of descriptor tables, and so triggering the sampling of event count data following the loading of descriptor tables (either global or local) may provide an alternative technique to perform context switch sampling. In another alternative embodiment, a particular address in addressable memory 140 may be selected for the express purpose of triggering context switch sampling, whenever that address is accessed. In yet another alternative embodiment, a hardware event trigger whenever a process and/or thread identifier is changed may be used, or a special instruction may be added to the processor architecture specifically to trigger context switch sampling. After the specified number of occurrences of the first hardware event have been counted in hardware event counters 114-134 respectively, the second hardware event counters, 115-135 respectively, are sampled and the first and second hardware event counters 114-134 and 115-135 respectively, are reset. As pointed out above, it will be appreciated that embodiments of processes 111 and 121, may share or use in common hardware event counters 114-124 and 115-125, so processor 102, for example, may have just a single set of hardware event counters. After the specified number of occurrences of the first hardware event have been counted and the second hardware event counters, 115-135 respectively, have been sampled the sampled second hardware event counter 115-135 values may be recorded and/or accumulated in storage locations 143-147 with a process identifier 141-145 value in addressable memory 140. In some embodiments the sampled second hardware event counter 115-135 values may also be recorded and/or accumulated in storage locations 143-147 with a thread identifier 144-148 value in addressable memory 140. It will be appreciated that such techniques may be used to more accurately capture and measure hardware events for a particular process and/or thread without including contamination from hardware events captured from other processes and/or threads. FIG. 2 illustrates a flow diagram for one embodiment of a process 201 to perform context switch sampling for performance monitoring in a multiprocessing system. Process 201 and other processes herein disclosed are performed by processing blocks that may comprise dedicated hardware or software or firmware operation codes executable by general purpose machines or by special purpose machines or by a combination of both. In processing block 211, I occurrences of a first hardware event are counted in a first hardware event counter (e.g. one of ECs 114-134). In processing block 212, J occurrences of a second hardware event are counted in a second hardware event counter (e.g. one of ECs 115-135). In processing block 213, it is determined whether I is equal to a predetermined SAV value N. If not counting continues in processing block 211. Otherwise processing proceeds to processing block 214 where the count J of second hardware event occurrences in the second hardware event counter is sampled. Then in processing block 215 the first and second hardware event counters are reset, and in processing block 216, the sampled count J is recorded (e.g at locations 143-147) in addressable memory 140 with a process identifier (e.g 141-145) value. FIG. 3 illustrates a flow diagram for an alternative embodiment of a process 301 for performing context switch sampling. In processing block 311, I occurrences of a segment register load event are counted in a first hardware event counter (e.g. one of ECs 114-134). In processing block 312, J occurrences of a second hardware event are counted in a second hardware event counter (e.g. one of ECs 115-135). In processing block 313, it is determined whether I is equal to a predetermined SAV value N. If not counting continues in processing block 311. Otherwise processing proceeds to processing block 314 where the count J of second hardware event occurrences in the second hardware event counter is sampled. Then in processing block 315 the segment register load event count and the second hardware event count in the first and second hardware event counters are reset, and in processing block 316, the sampled count J is recorded (e.g at locations 143-147) in addressable memory 140 with a process identifier (e.g 141-145) value. It will be appreciated that processes 201 and 301 may be able to determine when a context switch has occurred, and hence be used to accurately capture and measure hardware events for a particular process and/or thread without including contamination from hardware events captured during execution of other processes and/or threads. The above description is intended to illustrate preferred embodiments of the present invention. From the discussion above it should also be apparent that especially in such an area of technology, where growth is fast and further advancements are not easily foreseen, the invention may be modified in arrangement and detail by those skilled in the art without departing from the principles of the present invention within the scope of the accompanying claims and their equivalents. |
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claims | 1. An image processing apparatus that reconstructs block-level image data obtained by dividing the image data into a predetermined number of blocks and transmitting the image data, comprising:a reception unit configured to receive position information indicating a position of the block-level image data in the image data, together with the block-level image data;a determination unit configured to determine whether or not there is an error in the transmission of the position information received by said reception unit;a storage unit configured to store the block-level image data received by said reception unit; anda reconstruction unit configured to reconstruct the block-level image data stored in said storage unit if the number of transmission error(s) determined by said determination unit is one. 2. An X-ray image diagnostic system comprising:the image processing apparatus according to claim 1; andan imaging apparatus that transmits, to said image processing apparatus, image data captured by irradiating a subject with X-rays. 3. An image processing method performed in an image processing apparatus that reconstructs block-level image data obtained by dividing the image data into a predetermined number of blocks and transmitting the image data, the method comprising:a reception step of receiving position information indicating a position of the block-level image data in the image data, together with the block-level image data;a determination step of determining whether or not there is an error in transmission of the position information received in said reception step;a storage step of storing the block-level image data received in said reception step in a first storage unit; anda reconstruction step of reconstructing the block-level image data stored in the storage unit if the number of transmission error(s) determined in said determination step is one. 4. A non-transitory computer-readable storage medium storing, in executable form, a program for causing a computer to execute the image processing method according to claim 3. |
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claims | 1. A multileaf collimator comprising:a first set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the first set being disposed in an opposed relationship and longitudinally movable relative to each other in a first direction; anda second set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the second set being disposed in an opposed relationship and longitudinally movable relative to each other in a second direction generally parallel to the first direction; whereinthe first and second sets of pairs of leaves are disposed in different planes,each of the first and second sets includes an inner first section of a plurality of pairs of leaves having a first cross section and an outer second section of a plurality of pairs of leaves having a second cross section, andthe first cross section of the leaves in the first section of the first set is thinner than the first cross section of the leaves in the first section of the second set; andwherein the second section in each of the first and second sets includes a plurality of pairs of leaves at each side of the inner first section. 2. The multileaf collimator of claim 1 wherein the second cross section of the leaves in the second section of the first set is thinner than the second cross section of the leaves in the second section of the second set. 3. The multileaf collimator of claim 1 wherein the first cross section of the plurality of leaves in the first section of the first set is thinner than the second cross section of the plurality of leaves in the second section of the first set, and/or the first cross section of the plurality of leaves in the first section of the second set is thinner than the second cross section of the plurality of leaves in the second section of the second set. 4. The multileaf collimator of claim 3 wherein the leaves in each of the second sections of the first and second sets are symmetrically disposed relative to each of the first sections of the first and second sets respectively. 5. A multileaf collimator, comprising:a first set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the first set being disposed in an opposed relationship and longitudinally movable relative to each other in a first direction; anda second set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the second set being disposed in an opposed relationship and longitudinally movable relative to each other in a second direction generally parallel to the first direction;wherein the first and second sets of pairs of leaves are disposed in different planes, and the leaves in the first and second sets substantially focus on a converging virtual point located substantially at a radiation source; andwherein the leaves in the first and second sets have a substantially trapezoidal cross section where the parallel sides of the trapezoidal cross-section have different dimensions, andthe leaves in the first set include a main portion having a height and an end portion having a curved end surface extended beyond the height of the main portion. 6. The multileaf collimator of claim 5 wherein the leaves in the first and second sets have generally flat side surfaces. 7. The multileaf collimator of claim 5 wherein each leaf in the first set is offset from a leaf in the second set in a direction generally transverse to the first and second directions. 8. The multileaf collimator of claim 5 wherein the first set has a first number of pairs of leaves, and the second set has a second number of pairs of leaves different from the first number. 9. The multileaf collimator of claim 5 wherein the leaves in the first set have a first cross section and the leaves in the second sets have a second cross section different from the first cross section. 10. The multileaf collimator of claim 5 wherein the leaves in the first and second sets are supported by one or more movable carriages. 11. The multileaf collimator of claim 5 wherein the leaves in the first set include a main portion having a height and an end portion having one or two projections extended beyond the height of the main portion. 12. A multileaf collimator, comprising:a first set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the first set being disposed in an opposed relationship and longitudinally movable relative to each other in a first direction; anda second set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the second set being disposed in an opposed relationship and longitudinally movable relative to each other in a second direction generally parallel to the first direction;wherein the first and second sets of pairs of leaves are disposed in different planes, and each leaf in the first set is offset from a leaf in the second set by about half a leaf width in a direction generally traverse to the first and second directions, andwherein each leaf in the first set has a substantially same first cross-section, and each leaf in the second set has a substantially same second cross-section, and the first cross-section is different from the second cross-section. 13. The multileaf collimator of claim 12 wherein a quantity of the leaves in the first set is different from a quantity of the leaves in the second set. 14. The multileaf collimator of claim 12 wherein the leaves in the first and second sets are arranged to substantially focus on a single converging point. 15. The multileaf collimator of claim 12 wherein the leaves in the first and second sets have a substantially trapezoidal cross section. 16. The multileaf collimator of claim 15 wherein the leaves in the first and second sets have generally flat side surfaces. 17. The multileaf collimator of claim 12 wherein the leaves in the first and second sets are supported by one or more movable carriages. 18. The multileaf collimator of claim 12 wherein the leaves in the first set include a main portion having a height and an end portion having a curved end surface extended beyond the height of the main portion. 19. The multileaf collimator of claim 12 wherein the leaves in the first set include a main portion having a height and an end portion having one or two projections extended beyond the height of the main portion. 20. A method of shaping radiation beams from a radiation source, comprising:providing a multileaf collimator between a radiation source and an isocenter, said multileaf collimator comprising first and second sets of a plurality of beam blocking leaves disposed in first and second planes, leaves in each of the first and second sets being arranged in two opposing arrays forming a plurality of pairs of leaves in the first and second sets respectively, leaves of each pair being arranged in an opposed relationship and longitudinally movable relative each other, and the longitudinal moving directions being substantially parallel generally traverse to a beam direction; andmoving selected pairs of leaves in the first and second sets from the two opposing arrays in a substantially parallel direction to close ends of opposing leaves of the selected pairs to block a selected portion of a radiation beam;wherein in moving the selected pairs of leaves to close the ends of opposing leaves to block the selected portion of the radiation beam, a pair of leaves in the first set close at a first location, a corresponding pair of leaves in the second set close at a second location, and the first and second locations are offset from a beam's point of view. 21. The method of claim 20 wherein at the first location, the pair of leaves in the first set are in contact. 22. The method of claim 21 wherein at the second location, the pair of leaves in the second set are in contact. |
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047770120 | claims | 1. A gas cooled high temperature reactor comprising: a core of spherical fuel elements; a reflector surrounding said core on all sides; a hot gas collector compartment adjoining the lower part of said reflector; a plurality of first graphite columns forming the bottom of said reflector; a plurlaity of graphite blocks in layers forming the bottom of said hot gas collector compartment; means for removal of fuel elements from said reactor core, said means including at least one ceramic tube for the removal of spherical fuel elements from said core, said ceramic tube extending through the bottom of said reflector, said hot gas collector compartment, and said graphite block layers, and at least one metal tube for the removal of spherical fuel elements form said core, said metal tube adjoining said ceramic tube; a ring of second graphite columns having recesses therein and surrounding said ceramic tube in the bottom of said reflector and said hot gas collector compartment, and a first plurality of boron bodies arranged in said bottom of said reflector and said hot gas collector compartment in said recesses in said second graphite columns. 2. The gas cooled nuclear reactor of claim 1, further comprising a second plurality of boron bodies arranged directly around said ceramic tube. 3. The gas cooled nuclear reactor of claim 1, wherein said first plurality of boron bodies are rod-shaped and said recesses comprise vertically extending bores in said second graphite columns. 4. The gas cooled nuclear reactor of claim 3, wherein said rod-shaped boron bodies are about equal in length to said second graphite columns. 5. The gas cooled nuclear reactor of claim 3, wherein said rod-shaped boron bodies are arranged in at least two rows around said ceramic tube. 6. The gas cooled nuclear reactor of claim 5, wherein said rows of rod-shaped boron bodies are staggered with respect to one another. 7. The gas cooled nuclear reactor of claim 2, wherein said second plurality of boron bodies comprise plate-shaped members which surround said ceramic tube. 8. The gas cooled nuclear reactor of claim 1, further comprising a plurality of ceramic tubes each surrounded by a ring of graphite columns. |
claims | 1. An electron accelerator comprising:a resonant cavity comprising a hollow closed conductor, wherein:the conductor comprises an outer wall having an outer cylindrical portion of central axis, and an inner surface forming an outer conductor section;the conductor comprises an inner wall enclosed within the outer wall and having an inner cylindrical portion of central axis and an outer surface forming an inner conductor section andthe resonant cavity is symmetrical with respect to a mid-plane normal to the central axis and intersects the outer cylindrical portion and inner cylindrical portion;an electron source configured to radially inject a first beam of electrons into the resonant cavity from an introduction inlet opening on the outer conductor section to the central axis along the mid-plane;an RF system coupled to the resonant cavity and configured to generate an electric field between the outer conductor section and the inner conductor section, the electric field oscillating at a frequency to accelerate electrons of the first beam of electrons along radial trajectories in the mid-plane extending from the outer conductor section towards the inner conductor section and from the inner conductor section towards the outer conductor section;a magnet unit comprising a deflecting magnet comprising first and second permanent magnets positioned on either side of the mid-plane and configured to generate a magnetic field in a deflecting chamber in fluid communication with the resonant cavity by a first deflecting window, the magnetic field being configured to deflect a second electron beam emerging out of the resonant cavity through the first deflecting window along a first radial trajectory in the mid-plane and to redirect the second electron beam into the resonant cavity through one of the first deflecting window or a second deflecting window towards the central axis along a second radial trajectory in the mid-plane, the second radial trajectory being different from the first radial trajectory,wherein:the resonant cavity further comprises a first half shell, a second half shell, and a central ring element;the first half shell has a cylindrical outer wall having an inner radius and a central axis,the second half shell has a cylindrical outer wall having an inner radius and a central axis;the central ring element has an inner radius sandwiched at the level of the mid-plane between the first and second half shells; andthe surface forming the outer conductor section is formed by an inner surface of the cylindrical outer wall of the first and second half shells, and by an inner edge of the central ring element. 2. The electron accelerator of claim 1, wherein a portion of the central ring element extends radially beyond an outer surface of the outer wall of the first and second half shells, and wherein the magnet unit is fitted onto the portion of the central ring element. 3. The electron accelerator of claim 2, wherein:the deflecting chamber of the magnet unit is formed by a hollowed cavity in a thickness of the central ring element; andthe first and second deflecting windows are formed in the inner edge of the central ring element, facing the central axis. 4. The electron accelerator of claim 3, further comprising N magnet units, with N>1, wherein the deflecting chambers of the magnet units are formed by individual hollowed cavities in the thickness of the central ring element, with N deflecting windows being formed in the inner edge of the central ring element, facing the central axis. 5. The electron accelerator of claim 3, wherein:the central ring element is made of a ring shaped plate comprising first and second main surfaces separated by a thickness of the ring shaped plate; andeach cavity is formed by a recess open at the first main surface and at the inner edge of the ring shaped plate, the central ring element having a cover plate coupled to the first main surface to seal the recess and to form a cavity opened only at the inner edge to form the first and second deflecting windows. 6. The electron accelerator of claim 1, wherein the first and second half shells have an identical geometry and are coupled to the central ring element with a seal providing tightness of the resonant cavity. 7. The electron accelerator of claim 6, wherein:each of the first and second half shells comprises the cylindrical outer wall, a bottom lid, and a central pillar jutting out of the bottom lid; andan outer surfaces of the central pillars of the first and second half shells forms a portion of the inner conductor section. 8. The electron accelerator of claim 7, further comprising:a central chamber sandwiched between the central pillars of the first and second half shells, the central chamber comprising a cylindrical peripheral wall of the central axis, with openings radially aligned with corresponding first and second windows and the introduction inlet opening;wherein the surface forming the inner conductor section is formed by outer surfaces of the central pillars and by the peripheral wall of the central chamber. 9. The electron accelerator of claim 1, wherein the RF system is coupled to the first half shell, and wherein the central ring and central chamber are mounted onto the first half shell with different angular orientations about the central axis so as to vary the orientation of an electron beam outlet for discharging the electron beam out of the resonant cavity at a desired energy. 10. The electron accelerator of claim 1, wherein the first and second magnets are permanent magnets. 11. The electron accelerator of claim 10, wherein:the first and second permanent magnets are formed by a plurality of discrete magnet elements; andthe magnet elements are in the shape of prisms, arranged side by side in an array parallel to the mid-plane to form rows of discrete magnet elements, the magnet elements being disposed on either side of the deflecting chamber with respect to the mid-plane. 12. The electron accelerator of claim 10, further comprising N magnet units and N-n first and second deflecting magnets, wherein:N is greater than 1;the first and second deflecting magnets are permanent magnets; andn is between 0 and N−1. 13. The electron accelerator of claim 10, wherein:the magnet unit forms a magnetic field in the deflecting chamber; andthe magnetic field is between 0.05 T and 1.3 T. 14. The electron accelerator of claim 13, wherein the magnetic field is between 0.1 T and 0.7 T. 15. A method of accelerating electrons, the method comprising:providing a resonant cavity comprising a hollow closed conductor, wherein:the conductor further comprises an outer wall having an outer cylindrical portion of central axis, and an inner surface forming an outer conductor section;the conductor further comprises an inner wall enclosed within the outer wall and having an inner cylindrical portion of central axis, and an outer surface forming an inner conductor section; andthe resonant cavity is symmetrical with respect to a mid-plane normal to the central axis and intersects the outer cylindrical portion and inner cylindrical portion;radially injecting, by an electron source, a first beam of electrons into the resonant cavity from an introduction inlet opening on the outer conductor section to the central axis along the mid-plane;generating, by an RF system coupled to the resonant cavity, an electric field between the outer conductor section and the inner conductor section, the electric field oscillating at a frequency so as to accelerate electrons of the first beam of electrons along radial trajectories in the mid-plane, the trajectories extending from the outer conductor section towards the inner conductor section and from the inner conductor section towards the outer conductor section; andgenerating, by a magnetic unit comprising a deflecting magnet composed of first and second permanent magnets positioned on either side of the mid-plane, a magnetic field in a deflecting chamber, the deflecting chamber being in fluid communication with the resonant cavity via a first deflecting window, the magnetic field being configured to:deflect a second electron beam emerging out of the resonant cavity through the first deflecting window along a first radial trajectory in the mid-plane, andredirect the second electron beam into the resonant cavity through one of the first deflecting window or a second deflecting window towards the central axis along a second radial trajectory in the mid-plane the second radial trajectory being different from the first radial trajectory; wherein:the resonant cavity further comprises a first half shell, a second half shell, and a central ring element;the first half shell has a cylindrical outer wall, having an inner radius and a central axis;the second half shell has a cylindrical outer wall, having an inner radius and a central axis;the central ring element has an inner radius, sandwiched at the level of the mid-plane, between the first and second half shells; andthe surface forming the outer conductor section is formed by:an inner surface of the cylindrical outer wall of the first and second half shells; andan inner edge of the central ring element. 16. The method of claim 15, further comprising coupling the RF system to the first half shell;wherein the central ring and central chamber are mounted onto the first half shell with different angular orientations about the central axis so as to vary the orientation of an electron beam outlet to discharge the electron beam out of the resonant cavity at a desired energy. 17. The method of claim 15, further comprisingradially extending a portion of the central ring element beyond an outer surface of the outer wall of the first and second half shells; andfitting the magnet unit onto the portion of the central ring element. 18. The method of claim 17, wherein:the deflecting chamber of the magnet unit comprises a hollowed cavity in a thickness of the central ring element; andthe first and second deflecting windows are formed in the inner edge of the central ring element, facing the central axis. 19. The method of claim 15, wherein:each of the first and second half shells further comprises the cylindrical outer wall, a bottom lid, and a central pillar jutting out of the bottom lid; andan outer surface of the central pillars of the first and second half shells form a portion of the inner conductor section. 20. The method of claim 19, further comprising providing a central chamber sandwiched between the central pillars of the first and second half shells, wherein:the central chamber comprises a cylindrical peripheral wall of central axis, with openings radially aligned with corresponding first and second deflecting windows and the introduction inlet opening, andthe surface forming the inner conductor section is formed by an outer surface of the central pillars and by the peripheral wall of the central chamber sandwiched therebetween. |
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claims | 1. An apparatus comprising:a spider including a casing having an upper surface and a lower surface, the spider being connectable with a lower end of an associated connecting rod of an associated CRDM and with upper ends of a plurality of associated control rods;a J-lock attachment assembly including a female attachment assembly, a male attachment assembly and a first plunger, the female attachment assembly being fixed with respect to the spider, the male attachment assembly being mounted to the connecting rod and configured to selectively engage the female locking assembly, and the first plunger being mounted to the spider for reciprocating movement with respect to the spider so that the first plunger exerts upward force on the male locking assembly when the male locking assembly is engaged with the female locking assembly; anda kinetic energy absorbing element including a second plunger mounted to the spider for reciprocating movement, a first spring and a second spring supported by the spider for absorbing kinetic energy during a SCRAM event;wherein the second plunger protrudes from the lower surface of the casing for engagement with another surface during the SCRAM event, andwherein the first spring and the second spring are coaxially aligned, are axially coextensive along at least a portion of their respective lengths, the first spring has a first end that abuts the first plunger and a second end that abuts the second plunger, and the second spring has a first end that is axially fixed with respect to the spider and a second end that abuts the second plunger. 2. The apparatus as set forth in claim 1, wherein the second plunger is supported in a bore of the spider, said bore opening to the lower surface of the casing, and wherein the second spring is interposed between the plunger and the casing of the spider for biasing the plunger away from the top surface of the casing. 3. The apparatus as set forth in claim 1, wherein the casing includes a bore extending axially between the upper surface and the lower surface thereof, the female attachment assembly and the first plunger being supported in the bore. 4. The apparatus as set forth in claim 3, wherein the second plunger is supported within the bore of the spider. 5. The apparatus as set forth in claim 4, wherein the second plunger is biased away from the upper surface of the casing by the second spring which is interposed between the second plunger and the female coupling member. 6. The apparatus as set forth in claim 1, wherein the spider has an elongation in a SCRAM direction that is at least as large as a largest dimension of the spider transverse to the SCRAM direction. 7. The apparatus of claim 1, wherein one of the first spring and the second spring further comprises a stack of Belleville washers. 8. The apparatus of claim 1, wherein the first spring and the second spring bias the plunger away from the top surface of the casing. 9. An apparatus comprising:a spider having a casing with an upper surface and a lower surface, the spider being configured to connect with a connecting rod of a CRDM and support a plurality of mutually parallel control rods;a J-lock attachment assembly including a female attachment assembly, a male attachment assembly and a first plunger, the female attachment assembly being fixed with respect to the spider, the male attachment assembly being mounted to the connecting rod and configured to selectively engage the female locking assembly, and the first plunger being mounted to the spider for reciprocating movement with respect to the spider so that the first plunger exerts upward force on the male locking assembly when the male locking assembly is engaged with the female locking assembly; anda kinetic energy absorbing element disposed at least partially in a central bore of the spider and including a first spring, a second spring and a second plunger arranged to stop descent of the spider during a SCRAM event with kinetic energy developed during the SCRAM event being absorbed by the kinetic energy absorbing element disposed in the central bore of the spider;wherein the second plunger protrudes from the lower surface of the casing for engagement with another surface during the SCRAM event, andwherein the first spring and the second spring are coaxially aligned, are axially coextensive along at least a portion of their respective lengths, the first spring has a first end that abuts the first plunger and a second end that abuts the second plunger, and the second spring has a first end that is axially fixed with respect to the spider and a second end that abuts the second plunger. 10. The apparatus of claim 9 wherein one of the first spring and the second spring of the kinetic energy absorbing element further comprises a stack of Belleville washers disposed in a central bore of the spider. 11. The apparatus of claim 10 wherein the stack of Belleville washers does not extend outside of the central bore of the spider. 12. The apparatus of claim 10 further comprising:a plurality of mutually parallel control rods having ends connected with the spider and extending away from the spider in a first direction. 13. The apparatus of claim 12 further comprising:a control rod drive mechanism (CRDM) detachably engaging the connecting rod wherein detachment of the connecting rod from the CRDM initiates a SCRAM event. |
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044951477 | abstract | Heat retarding closure system for partitions having pressure relief openings formed therein especially in nuclear reactor buildings where main coolant nozzles of a reactor pressure vessel penetrate a biological shield, including lightweight construction closure elements having a side facing the reactor and anchors for holding the closure elements, the closure elements being pushable out of the anchors by an overpressure in a given pressure difference direction on the reactor side, and an outer sealing blowout skin, the closure elements being in the form of heat-retarding cassette inserts having a front surface with a peripheral shearing edge formed thereon resting against the blowout skin, and the blowout skin having a given thickness in the given pressure difference direction enabling the cassette insert to shear off the blowout skin and be pushed out of the anchors when a given pressure difference is at least reached. |
abstract | A neutron tube or generator is based on a RF driven plasma ion source having a quartz or other chamber surrounded by an external RF antenna. A deuterium or mixed deuterium/tritium (or even just a tritium) plasma is generated in the chamber and D or D/T (or T) ions are extracted from the plasma. A neutron generating target is positioned so that the ion beam is incident thereon and loads the target. Incident ions cause D-D or D-T (or T-T) reactions which generate neutrons. Various embodiments differ primarily in size of the chamber and position and shape of the neutron generating target. Some neutron generators are small enough for implantation in the body. The target may be at the end of a catheter-like drift tube. The target may have a tapered or conical surface to increase target surface area. |
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062333062 | description | FIG. 1 is a graphic representation of the intensity of the X-rays as generated by a known X-ray tube, illustrating the problem imposed by the X-ray absorption by a beryllium X-ray window. This graph has been obtained by theoretically calculating the intensity of X-rays as a function of the wavelength thereof (expressed in the reciprocal unit keV) as emitted by a nickel anode irradiated by an electron beam with an energy of 50 keV and a beam current of 60 mA. The intensity of this radiation is represented in an arbitrary measure; in this case it is expressed as a number of counting pulses per second (cps) of an arbitrary detector. This graph shows that at a relevant wavelength of the L.alpha. line of nickel of 146 nm (corresponding to an energy of 0.852 keV), an intensity of approximately 2.times.10.sup.12 cps is reached. FIG. 2 is a graphic representation of the absorption of the X-rays in a beryllium window of a known X-ray tube, illustrating the problem imposed by the X-ray absorption. For this Figure it is assumed that the X-rays must pass a beryllium window having a thickness of 100 .mu.m. The radiation is incident on this window as shown in FIG. 1. This graph shows that an intensity of approximately 2.times.10.sup.6 cps is reached for the above-mentioned wavelength of the La line of nickel of 1.46 nm (corresponding to an energy of 0.852 keV), thus implying an attenuation by a factor 10.sup.6. This attenuation is thus due to the presence of the 100 .mu.m beryllium window in the path of the X-rays. FIG. 3 shows a part of a known X-ray analysis apparatus which is of relevance to the invention and in which the X-ray source according to the invention can be used, the apparatus in this case being an X-ray spectrometer. The X-ray spectrometer includes an X-ray tube 2 for generating a beam of X-rays 10. The beam 10 irradiates a specimen 4 of a material to be examined by means of the X-ray spectrometer; the specimen is arranged in a specimen location for accommodating the specimen. The specimen 4 is arranged in a specimen holder 6 in a separate specimen space 8. X-ray fluorescent radiation which propagates in all directions is generated in the specimen as denoted by solid lines in the Figure. The fluorescent radiation irradiates an entrance slit 14 so that this entrance slit performs the function of the object 16 to be imaged for the imaging Rowland geometry to be described with reference to FIG. 2. In the Figure the width of the slit 14 is not shown to scale for the sake of clarity; in practical circumstances the width of this slit is of the order of from some tens of microns to some millimeters, depending on the relevant application. After having left the entrance slit 14, the beam of fluorescent radiation 18 is incident on an analysis crystal 28 which has a curved reflecting surface 29. The shape of the surface will be described in detail hereinafter with reference to FIG. 3. In this context it is to be noted merely that the surface 29 of the analysis crystal 28 has a cylindrical shape, i.e. the line of intersection of the crystal surface and the plane of drawing is a curved line (i.e. the line 29 in the Figure), but the line of intersection of the crystal surface and a plane perpendicular to the plane of drawing (for example, the plane perpendicular to the plane of drawing and also perpendicular to the line 29) is a straight line. In this arrangement the analysis crystal has a dual function: it selects the desired wavelength, determined by the angle of incidence, from the beam of fluorescent radiation on the basis of said Bragg relation (2d.sin'=n.lambda.), and it focuses the beam emanating from the apparent object point 16 in the image point 24. This image point is imaged on an exit slit 26 which constitutes the entrance collimator for an X-ray detector 20. Via an entrance window 22, the X-rays thus deflected are incident on the detector 20 in which they are detected, after which further signal processing is performed by means of electronic means (not shown). The analysis crystal 28 is mounted on a holder which is not shown in the Figure and is displaceable in two directions in the plane of drawing (as denoted by the arrows 30) and also rotatable about an axis 32 perpendicular to the plane of drawing. By virtue of these possibilities for displacement, the analysis crystal can be adjusted in an accurately defined orientation and position. The beam path from the X-ray tube 2 to the detector 20 extends through a hermetically sealable measuring space 24 which, in the case of X-rays of long wavelength, can be evacuated, if desired, or be filled with a gas which is suitable for such measurements. The known X-ray analysis apparatus utilizes a known X-ray tube which is provided with an exit window for the X-rays 10. When the invention is used, the X-ray window can be omitted because the function of this element is performed by the bundle of X-ray conducting capillary tubes, with the X-ray window provided thereon, which forms part of the X-ray source according to the invention. FIG. 4 is a diagrammatic representation of an X-ray source according to the invention. The X-ray source consists of an X-ray tube 7 in which an anode 40 is provided. The anode is irradiated by an electron beam 42 which forms a focal spot 56 on the anode so that X-rays 44 are generated in the anode in known manner; the X-rays can leave the X-ray tube 7 via a window opening 54. The X-ray source according to the invention is also provided with a bundle of capillary tubes 46 which conduct X-rays and one end of which is connected to the window opening 54 in a vacuum tight manner. The capillary tubes at that end of the bundle are directed towards the location 56 on the anode where the X-rays are generated. Even though FIG. 4 shows the bundle of capillary tubes as a bundle with gaps between the capillary tubes, a variety of constructions of this bundle is feasible. It is notably possible to construct an embodiment in which the capillary tubes are arranged against one another and are rigidly interconnected. The desired vacuumtightness of the bundle, required so as to enable vacuumtight connection of the bundle to the window opening 54 of the X-ray tube, can then be achieved by providing the exterior of the bundle with a layer of a synthetic material which is also connected to the inner side of the window opening 54. In FIG. 4 the vacuum sealing is diagrammatically represented by a plate-shaped support 58 in which the capillary tubes are provided in a vacuumtight manner. This plate-shaped support itself is mounted in the window opening 54 in a vacuumtight manner. An evacuated space is present in the housing 52 of the X-ray tube 7. This space is in vacuum contact with the interior of the capillary tubes, the other end 48 of which is sealed in a vacuumtight manner by means of an X-ray transparent X-ray window 50 which is made of a synthetic material or diamond of a very small thickness. This small thickness is possible because the ends of the capillary tubes of the bundle 46 act as a fine-meshed supporting grid having a periodic structure of, for example 10 .mu.m, so that a thickness of 1 .mu.m is feasible without special steps being required. At the end 48 of the bundle 46 the capillary tubes may be oriented in such a manner that the X-rays emanating therefrom are concentrated onto one location again. The specimen 10 to be examined in the apparatus can be arranged in that location. The X-ray power taken up by the bundle 46 is dependent on the space angle at which the entrance side of the bundle is perceived from the X-ray focus 56, on the transmission of the X-rays by the capillary tubes, and on the extent to which the window 50 transmits the X-rays. These parameters can all be varied within broad limits. In order to make a coarse estimate nevertheless of the improved X-ray yield according to the invention, it will be assumed that said space angle equals 0.2 staradian (corresponding to a receiving surface area of 1 cm.sup.2 at a distance of 2 cm from the anode), that said transmission is of the order of magnitude of 10% (see the cited article Proceedings of SPIE, "Polycapillary Focusing . . .", Table 2, paragraph 3.2) and that the X-ray absorption in the X-ray window is negligibly small because of the small thickness and the suitable choice of material. This means that a fraction of approximately 3% (i.e. 0.2/2.pi.) of the total amount of X-rays emitted by the anode in a space angle of 2.pi. staradians enters the capillary tubes which pass on this fraction with a transmission efficiency of 10%, so that ultimately 0.3% of the radiation generated in the anode comes to the benefit of the irradiation of the specimen. Even if all X-rays generated in the anode in the known X-ray tubes were situated within the space angle used (which is certainly not the case), the intensity at the area of the specimen would still be improved by a factor of approximately 3000 (0.3% of 10.sup.6) by carrying out the invention. |
abstract | An X-ray flat panel detector includes sensor elements constituted by a plurality of effective pixels that detect X-rays and a plurality of dummy pixels that are arranged adjacent to the effective pixel area and generate electrical signals irrelevant to X-rays, signal lines which read out electrical signals from the respective pixels, scanning lines which scan the respective pixels, a first electrostatic wiring line which distributes static electricity accumulated in the signal lines, and a second electrostatic wiring line which distributes static electricity accumulated in the scanning lines. A plurality of dummy pixels are classified into a DA area where noise superposed on the signal lines are removed and a DB area where noise superposed on the scanning lines are removed. The first and second electrostatic wiring lines are laid out around the sensor elements, and physically disconnected between the DA area and the DB area. |
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abstract | A water filling system for a reactor water level gauge is provided for filling a reactor water level gauge instrumentation pipe in a reactor building with water and filling the reactor water level gauge with water even in an unexpected abnormal event where the reactor building is brought into a highly radioactive environment. The water filling system for a reactor water level gauge includes a water filling instrumentation pipe guided from the reactor water level gauge instrumentation pipe in the reactor building to an outside of the reactor building and filling the reactor water level gauge instrumentation pipe in the reactor building with water even in an unexpected abnormal event of a nuclear power plant. |
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043604960 | claims | 1. Cooling system for auxiliary systems of a nuclear installation for heat removal from heat exchangers, the heat exchangers being connected on the primary side thereof to lines which may contain radioactive liquids or gases, the heat exchangers being disposed within a containment wall in a secured area of the nuclear installation, and the heat exchangers having connections on the secondary side thereof for cooling liquid lines, the improvement comprising an outgoing line for the cooling liquid connected to the connection on the secondary side of the heat exchangers, additional external heat exchangers being disposed outside of the containment wall and having an inlet and an outlet side, said inlet side of said additional heat exchangers being connected to said outgoing line, a return line for the cooling liquid being connected to said outlet side of said additional heat exchangers, said additional heat exchangers being in the form of a dry cooling tower having cooling elements connected to said outgoing and return lines on the inlet and outlet sides thereof, respectively, a refrigeration loop having a supplemental heat exchanger with the primary side thereof connected in said return line, a bypass line connected from said outgoing to said return line parallel to said cooling elements and supplemental heat exchanger, and a control valve connected in said bypass line. 2. Cooling system according to claim 1, including a rising line connected to said return line in the secured area, and an expansion tank being connected to said rising line and disposed in the secured area. 3. Cooling system according to claim 1, wherein the cooling liquid is an antifreeze medium which ensures unrestrained operation of said dry cooling tower for safe heat removal from the nuclear installation. 4. Cooling system according to claim 1, wherein a plurality of redundant cooling systems are provided for one nuclear installation, said dry cooling towers of said individual cooling systems being disposed at different locations. |
042253900 | summary | BACKGROUND OF THE INVENTION This invention pertains to homogenous nuclear reactor control systems and more particularly to a system for varying the amount of boron in the coolant fluid for a nuclear reactor system. The presently utilized system for changing the boric acid concentration in the coolant fluid of a nuclear reactor system generally accomplishes same by drawing off a portion of the coolant and replacing that portion with an equivalent amount of either demineralized and deaerated water, or water which has been previously blended so as to have a high concentration of boric acid. In general, the coolant removed from the coolant system of a nuclear reactor plant is first conveyed to an evaporator which concentrates the boric acid to a fixed amount or percentage by weight of boron and stores this concentrated boric acid solution in one tank and the generally demineralized and deaerated water from the evaporator in another tank. The two storage tanks might then be used to feed either demineralized and deaerated water or to mix the highly concentrated boric acid concentrate with water so as to vary the boration of the solution fed to the nuclear reactor. More recently, the use of anion exchange beds containing basic anion resins which operate to directly change the boric acid in the primary coolant stream, depending upon the temperature of the influent to such a bed, have been contemplated for this purpose. Such a system is shown and described in U.S. Pat. No. 3,666,626 - Gramer et al entitled "Method and Means for Reversibly Changing the Boric Acid Concentration in the Coolant of a Nuclear Reactor" assigned to the same assignee as the invention. In accordance with that invention, the enrichment or depletion of boric acid in the primary coolant water is accomplished by passing a portion of that coolant through an anion exchange resin bed charged with boric acid. The temperature of the water flowing through the bed is varied such that boric acid enters the coolant at relatively higher temperatures and is taken from the coolant and stored in the resin bed at relatively lower temperatures. Each of the above systems has inherent advantages and disadvantages. For example, the evaporative recycle system is capable of concentrating a great amount of boric acid and storing same. However, if it must perform this function rapidly, the evaporator and associated equipment becomes exceedingly large and expensive. On the other hand, the ion exchangers can perform the function of rapidly varying the quantity of borate ions in the primary coolant of the reactor system. However, the storage capacity of the ion exchangers is rather limited unless the ion exchange tanks are made exceedingly large or numerous and such a large quantity of resin is used so as to make the system prohibitively expensive. Further, ion exchange beds of the prior art have been contemplated for use simultaneously while either connected in series or in parallel. Thus all of the ion exchangers would handle an equal portion of the total required concentration change. It is now known that the storage capacity of a resin bed is lower for lower concentrations of borate ions in the flow passing therethrough. Accordingly, the simultaneous use of a plurality of ion exchangers necessitates an amount of resin in excess of that which might be used when the variation in storage capacity with concentration is taken into account. SUMMARY OF THE INVENTION The aforementioned disadvantages of the described prior art systems can be minimized by utilizing ion exchange beds for load follow purposes and a reduced size evaporator for reduction in boron concentration with core life and other purposes. The size of the ion exchange beds can be further reduced by operating them sequentially. In contrast with the prior art, the ion exchange beds are used primarily for load follow purposes. This would mean a utilization of the beds for concentration changes in the primary coolant of about 100 parts per million which would correspond to a 50% load follow capability. The coolant, which is drawn from the primary system, is first conveyed to a single ion exchange bed; this bed may be used for example to store boric acid from the flow and to consequently lower the boric acid concentration in the primary coolant. The single ion exchanger to which the flow is directed is used until a boric acid metering device indicates an increasing readout on the boric acid concentration thus indicating that the first ion exchanger has been saturated. The flow is then directed to a second ion exchange bed until the same phenomenon indicating saturation takes place and then to a third bed and so on. This sequential utilization of the ion exchange beds produces a more efficient utilization of the resin and the amount of resin can be decreased accordingly. The evaporative recycle system handles the effluent produced only during reactor operations other than load follow. Thus the amount of effluent which must be stored and processed can be greatly reduced. An evaporator has the capability of concentrating the boric acid in the flow diverted from the primary coolant system to a high degree. If it is only necessary to concentrate boric acid over a long period of time an extremely small evaporator can be used. In accordance with this invention for example, after fuel reloading and the operation, the evaporator would be used to remove that boric acid from the system which is no longer necessary to compensate for the fresh fuel reloading. That is, as an amount of fuel is burned in the reactor, a proportional amount of boric acid concentrate can be removed from the system. In certain systems the time period over which this removal can take place approximates one year. On the other hand, if ion exchangers were used to store the boric acid at the concentration level at which it was removed from the reactor as well as for those other purposes in which boron concentrations are employed, a substantially larger number of ion exchange beds would be necessary. Accordingly, a combination of the above systems produces a highly efficient operation wherein each system is used for the function it most suitably performs. The particular combination of ion exchangers and evaporators to be used on a plant depends upon equipment cost and required operation sequences. |
description | The present invention relates to a method of moisture content adjustment of materials such as pulverulent materials, and more particularly, to a method effective in moisture content adjustment of bentonite used for disposals such as geological disposals of radioactive wastes. High-level radioactive wastes included in radioactive wastes yielded from nuclear power generation include liquid wastes separately obtained by spent nuclear fuel reprocessing. More specifically, the high-level radioactive wastes show a high radioactivity level, and besides, contain a large number of radioactive nuclides having so extended life as to continue to hold radioactivity over a long period of time. For that purpose, such high-level radioactive wastes are given stabilizing by being processed into vitrified wastes in such a manner as to pour these radioactive wastes in a molten state into stainless steel canisters together with glass materials, followed by being reserved for several ten years for the sake of cooling. Afterwards, the canisters containing the vitrified wastes are received etc. in an airtight state into thick steel plate-made airtight containers called overpack to provide waste matters, causing the waste matters to be buried in stable underground stratums having a depth of 300 m or more (specified in the law). This type of geological disposals of the radioactive wastes is supposed to take measures to guarantee the safety with a multiple barrier system constructed by a combination of artificial barriers including bentonite buffer materials around the waste matters with natural barriers including bedrock. The artificial barriers serve to reduce a rate of emission of nuclides from the waste matters to the natural barriers. The natural barriers serve to retard migration of the nuclides toward the biosphere. The bentonite is a general term of a group of resource minerals containing, as main components, montmorillonite included in clay minerals, and, as coexistent mineral components, minerals such as quartz, calcite and plagioclase. The montmorillonite is in the form of thin planar crystals (about 0.2 μm in length), and presents impermeability because application of pressures by processing such as compaction after swelling by absorption of water into inter-crystal voids brings about stratification. The montmorillonite also may prevent interlayer water from being migrated because water molecules suffer ion-mannered attraction in electric double layers, causing inter-layer clearances to be narrowed under pressures. For the above reasons, the bentonite is used as impermeable materials. As for the geological disposals of the radioactive wastes, use of the bentonite is made from the viewpoint of its performances such as impermeability with respect to underground water, buffering with respect to bedrock pressures and retardation of radioactive nuclide migrations. In the existing idea of the geological disposals of the radioactive wastes, the bentonite-contained artificial barriers are schemed in such a manner as to be constructed by giving compaction with a heavy construction machine to, or static compression to the bentonite having undergone adjustment to a prescribed moisture content. It is indefinitely supposed that moisture content adjustment in this case is made by means of water adding in advance of sufficient stirring and mixing or by means of water sprinkling. By the way, Patent documents 1 to 6 are in existence as prior art literatures related to the present invention. Inventions described in Patent documents 1 and 2 are those relating to a bentonite preparation method. Inventions described in Patent Documents 3 to 6 are those relating to a concrete preparation method of kneading concrete using small cakes of ice as a substitute for water. [Patent Document 1] Japanese Patent Laid-open Hei 8-277108 [Patent Document 2] Japanese Patent Laid-open Hei 6-293512 [Patent Document 3] Japanese Patent Laid-open 2002-144325 [Patent Document 4] Japanese Patent Laid-open 2002-11709 [Patent Document 5] Japanese Patent Laid-open 2001-293718 [Patent Document 6] Japanese Patent Laid-open Hei 6-179209 The moisture content adjustment of bentonite is indefinitely supposed to be made by means of water adding in advance of sufficient stirring and mixing or by means of water sprinkling, in which case, however, an attempt to merely add water to the pulverulent bentonite or sprinkle the pulverulent bentonite with water causes only the bentonite in contact with water to be turned into granular lumps having high moisture contents, resulting in a remarkable lack in uniformity. Further, a powerful mixer is required to stir and mix hydrous bentonite until its uniformity is obtained, and besides, it is necessary to stop the mixer several times during stirring and mixing in order to remove the bentonite cohered to a mixing blade and/or a mixing tank. For this reason, an attempt to make the moisture content adjustment of a huge quantity of bentonite required for construction of the bentonite-contained artificial barriers is at variance with the reality. In addition, stirring and mixing in a continuous manner have been impossible of attainment. Further, the bentonite having undergone the moisture content adjustment with a conventional method is turned into the granular lumps (of large grain size), causing a bentonite condition immediately after compaction to go into “raising”. Thus, when the moisture content-adjusted bentonite obtained with the conventional method is compacted for the sake of use as a cut-off material, no cut-off performance could be expected before the bentonite in the form of granular lumps so swells in association with seepage as to fill up voids. Furthermore, the moisture content-adjusted bentonite obtained with the conventional method is lacking in uniformity of moisture content distribution, so that drying of the bentonite of this type causes remarkable shrinkage of its high moisture content portions, resulting in creation of a large number of great cracks. The present invention is intended to provide a material moisture content adjustment method, which is adaptable, when making moisture content adjustment by adding liquid such as water to a raw material such as pulverulent material including bentonite, to uniformly mix the liquid such as water with the raw material such as pulverulent material using relatively simple facilities, also to easily attain moisture content adjustment of a large quantity of raw materials, and further to obtain a material having satisfactory performances such as impermeability through uniform moisture content adjustment. The invention according to Claim 1 of the present invention relates to a method of adjusting a moisture content by adding liquid (water or other solutions) to a raw material such as pulverulent material and granular material, more specifically, a material moisture content adjustment method, which comprises: stirring and mixing a low-temperature raw material and fine granular ice, followed by restoring the raw material uniformly mixed with the fine granular ice to its normal temperature state to obtain a material of a prescribed moisture content. The present invention is to make the moisture content adjustment under low temperature environments by giving, after adding the granular ice to the material such as the pulverulent material having undergone adjustment to low temperatures, stirring and mixing of fellow pulverulent materials. The finer the granular ice used is, the moisture content of a mixture of the material such as the pulverulent material is made more uniform. Stirring and mixing are given using equipment such as a mixing tank kept at low temperatures with gas such as low temperature gas. Otherwise, when the method of the present invention is taken in cold districts, utilization of the fallen snow and the cold weather permits contributions also toward a reduction in cost. Further, the method of the present invention is also adaptable to give stirring and mixing over forcible feeding in such a manner as to put the material such as the pulverulent material, together with the fine granular ice, into a pipe through which low-temperature gas is flowing. With respect to the moisture content adjustment method according to Claim 1, the invention according to Claim 2 of the present invention relates to a material moisture content adjustment method, which comprises: providing a mixing tank, and putting fine granular ice into the mixing tank in such a manner as to, after sucking up liquid with low-temperature high-pressure gas (such as nitrogen gas), atomize the sucked-up liquid into the mixing tank, followed by giving, within the mixing tank kept at low temperatures, stirring and mixing of a low-temperature raw material and the fine granular ice. The above method is adapted to meet batch-mannered moisture content adjustment by the use of the mixing tank, specifically, relates to a case where the fine granular ice is put into the low-temperature mixing tank while being prepared. For instance, the fine granular ice is supplied into the mixing tank by, after sucking up the liquid such as water from a container with low-temperature high-pressure nitrogen gas supplied from a liquid nitrogen bomb, atomizing the sucked-up liquid through a liquid atomizer, while cooling. Mere additional installation of simple equipment to a normal powder mixer is enough to permit uniform stirring and mixing of the material such as the pulverulent material and the fine granular ice. With respect to the moisture content adjustment method according to Claim 1, the invention according to Claim 3 of the present invention relates to a material moisture content adjustment method, which comprises: providing a mixing tank, and putting prepared fine granular ice into the mixing tank, followed by giving, within the mixing tank kept at low temperatures, stirring and mixing of a low-temperature raw material and the fine granular ice. The above method is adapted to meet batch-mannered moisture content adjustment by the use of the mixing tank, specifically, relates to a case where the prepared fine granular ice is put into the low-temperature mixing tank. For instance, after the material such as low-temperature preserved pulverulent material is received in the mixing tank kept at low temperatures with low-temperature nitrogen gas supplied from a liquid nitrogen bomb, the fine granular ice is put into the mixing tank placed in the above condition. In this case, mere additional installation of simple equipment to the normal powder mixer is also enough to permit uniform stirring and mixing of the material such as the pulverulent material and the fine granular ice. With respect to the moisture content adjustment method according to Claim 1, the invention according to Claim 4 of the present invention relates to a material moisture content adjustment method, which comprises: providing a forcible feed pipe, and putting a low-temperature raw material and fine granular ice into the forcible feed pipe, followed by giving, within the forcible feed pipe kept at low temperatures with low-temperature high-pressure gas, stirring and mixing of the low-temperature raw material and the fine granular ice over forcible feeding through the low-temperature high-pressure gas. The above method is adapted to meet continuous-mannered moisture content adjustment by the use of the forcible feed pipe, specifically, relates to a case where the material such as the pulverulent material and the fine granular ice are stirred and mixed within the forcible pipe. For instance, the material such as the low-temperature preserved pulverulent material and the fine granular ice are put into the forcible feed pipe kept at low temperatures with the low-temperature nitrogen gas supplied from a liquid nitrogen bomb, followed by being stirred and mixed while being forcibly fed through a low-temperature gas flow. Stirring and mixing of the material such as the pulverulent material and the fine granular ice are uniformly given with a relatively simple device, enabling the moisture content adjustment to be made continuously. The present invention is particularly effective in making the moisture content adjustment of the bentonite, and involves use of the pulverulent bentonite and the fine granular ice available as the equivalent pulverulent material. Under the low temperature environments like the low-temperature mixing tank or forcible feed pipe, both the pulverulent bentonite and the fine granular ice take the form of fine grains, specifically, behave as pulverulent materials, and therefore, may be given stirring and mixing uniformly without absorption of water into the bentonite. Restoration of the pulverulent material to its normal temperature state after uniform mixing may cause the uniformly moisture content-adjusted bentonite to be obtained. In addition, mere mixing of the fellow pulverulent materials is enough, so that the need for the powerful mixer is eliminated, enabling use of the normal powder mixer to be made. Further, no cohesion of the material to the mixing blade and/or the mixing tank of the mixer is caused, enabling the moisture content adjustment of a large quantity of materials to be easily attained as well. Furthermore, pneumatic conveyance of the material such as the moisture content-adjusted pulverulent material becomes also attainable by giving stirring and mixing over forcible feeding through the low-temperature gas, and further keeping the mixture at low temperatures. Moreover, no possibility exists that the material such as the pulverulent material is turned into the granular lumps, resulting in almost no change in grain size distribution even after the moisture content adjustment. It is noted that the present invention is not limited to the moisture content adjustment of the bentonite, and applications to the moisture content adjustment of other types of pulverulent materials, granular materials and the like are possible as well. The present invention is provided based on the above constitution, and thus may produce the following effects. (1) The material such as the pulverulent material and the is fine granular ice are supposed to be stirred and mixed within the mixing tank kept at low temperatures or the forcible feed pipe kept at low temperatures. Thus, both the material such as the pulverulent material and the fine granular ice take the form of fine grains, specifically, behave as the pulverulent materials, and therefore, may be given stirring and mixing uniformly without absorption of water into the material such as the pulverulent material, enabling the uniformly moisture content-adjusted material to be obtained. (2) With respect to the geological disposals of the radioactive wastes, satisfactorily impermeable bentonite-contained artificial barriers may be obtained with the bentonite having the uniform moisture content. (3) Mere mixing of the fellow pulverulent materials is enough for the moisture content adjustment, so that the need for the powerful mixer is eliminated, enabling use of the normal powder mixer to be made, resulting in contributions toward a reduction in cost. (4) In addition to elimination of the need for the powerful mixer, no cohesion of the material to the mixing blade and/or the mixing tank of the mixer is caused, enabling the moisture content adjustment of a large quantity of materials to be attained as well. Applications to huge-scale bentonite-contained artificial barriers with respect to the geological disposals of the radioactive wastes are supposed to be particularly effective. (5) The pneumatic conveyance of the material such as the moisture content-adjusted pulverulent material becomes also attainable by giving stirring and mixing over forcible feeding through the low-temperature gas, and further keeping the mixture at low temperatures. Thus, the moisture content adjustment may be made continuously, enabling an increase in capacity to be easily attained. (6) The material such as the moisture content-adjusted pulverulent material obtained with the conventional method is turned into the granular lumps (of large grain size), causing the material condition immediately after compaction to go into “raising”. Conversely, the material such as the moisture content-adjusted material obtained with the method of the present invention results in almost no change in grain size distribution, and besides, causes an increase in dry density with respect to the same compaction energy, permitting uniform and dense conditions to be obtained immediately after compaction. Accordingly, when the material such as the pulverulent material is compacted for the sake of use as the cut-off material, it can be expected that a high cut-off performance is attainable with a low coefficient of initial permeability even immediately after seepage. (7) The moisture content-adjusted bentonite obtained with the method of the present invention shows a uniform moisture content distribution, resulting in less creation of cracks even after dried. On the other hand, the moisture content-adjusted bentonite obtained with the conventional method is lacking in uniformity of the moisture content distribution, so that drying of the bentonite of this type causes remarkable shrinkage of its high moisture content portions, resulting in creation of a large number of great cracks. Hereinafter, the present invention is described with reference to illustrative embodiments. The embodiments shown are those applied to moisture content adjustment of bentonite. FIG. 1 shows a first embodiment of a moisture content adjusting apparatus for carrying out a moisture content adjustment method according to the present invention. FIG. 2 shows a second embodiment of the same, and FIG. 3 shows a third embodiment of the same. The first embodiment shown in FIG. 1 relates to a batch-mannered moisture content adjusting apparatus, which involves use of a mixing tank 1 kept at low temperatures, and is adapted to give, within the mixing tank 1, stirring and mixing of pulverulent bentonite A and fine granular ice B, followed by restoring the pulverulent bentonite A uniformly mixed with the fine granular ice B to its normal temperature state to obtain prescribed moisture content bentonite. A normal powder mixer having a mixing blade 3 rotationally driven by a motor 2 may be used for the mixing tank 1. The mixing tank 1 is configured as a low temperature tank in such a manner as to surround an outer circumference of a lower part of the tank with a heat-insulating material or a cooling jacket 4. The low-temperature preserved pulverulent bentonite A is put into the low-temperature mixing tank 1 obtained as described the above. The fine granular ice B is supplied into the mixing tank 1 using a liquid atomizer 10, for instance. The normal powder mixer has, at its upper part, an inlet port 11, and a feed pipe 13 of a liquid-nitrogen bomb 12 is connected to the inlet port 11, permitting an upper end of a suction pipe 15 of a liquid container 14 to communicate with the middle of the feed pipe 13. Liquid such as water contained in the liquid container 14 is sucked up under negative pressure with low-temperature high-pressure nitrogen gas supplied from the liquid-nitrogen bomb 12, followed by being atomized into the mixing tank 1 while being cooled down with the nitrogen gas, causing the fine granular ice B to be supplied into the mixing tank 1. It is noted that a high-pressure relief valve 5 for making a relief from excessive pressure is connected to the upper part of the mixing tank 1. Within the mixing tank 1, the pulverulent bentonite A and the fine granular ice B are given stirring and mixing by the mixing blade 3. Both the pulverulent bentonite A and the fine granular ice B take the form of fine grains, specifically, behave as the pulverulent materials, and therefore, may be uniformly mixed without absorption of liquid such as water into the bentonite. Restoration of the pulverulent bentonite to its normal temperature state after uniform mixing may cause the uniformly moisture content-adjusted bentonite to be obtained. With respect to the geological disposals of the radioactive wastes, satisfactorily impermeable bentonite-contained artificial barriers may be obtained with the bentonite having the uniform moisture content. It is noted that the liquid added to the bentonite is not limited to water, and use of various solutions is also included. For this type of stirring and mixing, mixing of the fellow pulverulent materials is enough, so that the need for a powerful mixer is eliminated, enabling use of the normal powder mixer to be made. Further, no cohesion of the material to the mixing blade and/or the mixing tank is caused, enabling applications to the moisture content adjustment of a large quantity of materials, and hence, easy adaptations to construction of huge-scale bentonite-contained artificial barriers for the geological disposals of the radioactive wastes as well. The moisture content-adjusted pulverulent bentonite results in almost no change in grain size distribution, and besides, causes an increase in dry density with respect to the same compaction energy as compared with a conventional method, so that uniform and dense conditions are obtained immediately after compaction. Thus, when the pulverulent bentonite is compacted for the sake of use as a cut-off material, it can be expected that a high cut-off performance is attainable with a low coefficient of initial permeability even immediately after seepage. The moisture content-adjusted bentonite obtained with the conventional method is lacking in uniformity of moisture content distribution, so that drying of the bentonite of this type causes remarkable shrinkage of its high moisture content portions of the above bentonite, resulting in creation of great cracks. Conversely, the moisture content-adjusted bentonite obtained with the method of the present invention shows a uniform moisture content distribution, resulting in less creation of cracks even after dried. The second embodiment shown in FIG. 2 relates to a batch-mannered moisture content adjusting apparatus, which has a fine granular ice inlet port 20 at the upper part of the same mixing tank 1 as that shown in FIG. 1, and is adapted to put prepared fine granular ice B into the mixing tank 1. A liquid-nitrogen bomb 21 is connected to the upper part of the mixing tank 1, causing the inside of the mixing tank 1 to be kept at low temperatures with the nitrogen gas supplied from the bomb 21. Within the mixing tank 1, the low-temperature preserved pulverulent bentonite A and the fine granular ice B are given stirring and mixing by the mixing blade 3. The same actions and effects as those in the previously described first embodiment shown in FIG. 1 are obtained. Adjustment up to 100% moisture content having been supposed to be impossible of attainment with the conventional method by mixing even by the use of a large-sized mixer could be attained with a household table mixer thanks to the use of the fine granular ice according to the present invention. Further, even only slight stirring for about several seconds by human strength could bring sufficient moisture content adjustment into attainment without using the mixer. Furthermore, with respect to 20% target moisture content, the moisture content with the conventional method reached 20.4%, whereas 20.1% moisture content was obtained with the method of the present invention. FIG. 4 shows measured results, obtained with a vane-shearing testing apparatus, of required mixer torque for stirring and mixing according to the method shown in FIG. 2. The method of the present invention enables stirring and mixing to be given with low torque independently of the moisture content. The third embodiment shown in FIG. 3 relates to a continuous-mannered moisture content adjusting apparatus, which is adapted to give, within a forcible feed pipe 30 kept at low temperatures, stirring and mixing of the low-temperature pulverulent bentonite A and the fine granular ice B without using the mixing tank, causing the pulverulent bentonite A uniformly mixed with the fine granular ice B to be obtained. A liquid-nitrogen bomb 31 is connected to the forcible feed pipe 30, causing the inside of the forcible feed pipe 30 to be kept at low temperatures with the low-temperature nitrogen gas supplied from the bomb 31. Further, there is provided a compressed air feed port 34 at the upstream side of a bentonite inlet port 32 and a fine granular ice inlet port 33, causing the pulverulent bentonite A and the fine granular ice B to be stirred and mixed while being forcibly fed through a low-temperature gas flow. In this case, the same actions and effects as those of the mixing tank are obtained as well. There is also provided a normal-temperature reservoir tank 35 at the end of the forcible feed pipe 30, causing the pulverulent bentonite A uniformly mixed with the fine granular ice B within the forcible feed pipe 30 to be restored to its normal temperature state, enabling the uniformly moisture content-adjusted bentonite to be obtained. The low-temperature preserved pulverulent bentonite A and the same parts by weight of fine granular ice B as the pulverulent bentonite were put into the forcible feed pipe with a diameter of about 10 cm, followed by being stirred and mixed while being forcibly fed by a distance of about 5 m. The moisture content of the bentonite after forcible feeding reached 100%. Thus, it is seen that it is possible to attain mixing over forcible feeding with respect to even the high moisture content bentonite, which has been supposed to be impossible of attainment so far. It is also seen that it is possible to attain continuous-mannered moisture content adjustment. It is noted that the foregoing has been described as related to the applications to the moisture content adjustment of the bentonite with respect to the projects of the geological disposals of the radioactive wastes, but is not limited to the above, and applications to the moisture content adjustment of other types of materials such as subsurface materials, pulverulent materials and granular materials are possible as well. |
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description | The subject application is a continuation of PCT Patent Application No. PCT/US15/55172, filed Oct. 12, 2015, which claims priority to U.S. Provisional Patent Application No. 62/064,346, filed on Oct. 15, 2014, and U.S. Provisional Patent Application No. 62/063,382, filed on Oct. 13, 2014, all of which are incorporated by reference herein in their entirety for all purposes. The embodiments described herein relate generally to pulsed plasma systems and, more particularly, to systems and methods that facilitate merging and compressing compact tori with superior stability as well as significantly reduced losses and increased efficiency. The Field Reversed Configuration (FRC) belongs to the class of magnetic plasma confinement topologies known as compact toroids. It exhibits predominantly poloidal magnetic fields and possesses zero or small self-generated toroidal fields (see M. Tuszewski, Nucl. Fusion 28, 2033 (1988)). The attractions of such a configuration are its simple geometry for ease of construction and maintenance, a natural unrestricted divertor for facilitating energy extraction and ash removal, and very high average (or external) β (β is the ratio of the average plasma pressure to the average magnetic field pressure inside the FRC), i.e., high power density. The β metric is also a very good measure of magnetic efficiency. A high average β value, e.g. close to 1, represents efficient use of the deployed magnetic energy and is henceforth essential for the most economic operation. High average β is also critically enabling the use of aneutronic fuels such as D-He3 and p-B11. The traditional method of forming an FRC uses the field-reversed θ-pinch technology, producing hot, high-density plasmas (see A. L. Hoffman and J. T. Slough, Nucl. Fusion 33, 27 (1993)). A variation on this is the translation-trapping method in which the plasma created in a theta-pinch “source” is more-or-less immediately ejected out of the formation region and into a confinement chamber. The translating plasmoid is then trapped between two strong mirrors at the ends of the confinement chamber (see, for instance, H. Himura, S. Okada, S. Sugimoto, and S. Goto, Phys. Plasmas 2, 191 (1995)). Once in the confinement chamber, various heating and current drive methods may be applied such as beam injection (neutral or neutralized), rotating magnetic fields, RF or ohmic heating, etc. This separation of source and confinement functions offers key engineering advantages for potential future fusion reactors. FRCs have proved to be extremely robust, resilient to dynamic formation, translation, and violent capture events. Moreover, they show a tendency to assume a preferred plasma state (see e.g. H. Y. Guo, A. L. Hoffman, K. E. Miller, and L. C. Steinhauer, Phys. Rev. Lett. 92, 245001 (2004)). Significant progress has been made in the last decade developing other FRC formation methods: merging spheromaks with oppositely-directed helicities (see e.g. Y. Ono, M. Inomoto, Y. Ueda, T. Matsuyama, and T. Okazaki, Nucl. Fusion 39, 2001 (1999)) and by driving current with rotating magnetic fields (RMF) (see e.g. I. R. Jones, Phys. Plasmas 6, 1950 (1999)), which also provides additional stability. FRCs consist of a torus of closed field lines inside a separatrix, and of an annular edge layer on the open field lines just outside the separatrix. The edge layer coalesces into jets beyond the FRC length, providing a natural divertor. The FRC topology coincides with that of a Field-Reversed-Mirror plasma. However, a significant difference is that the FRC plasma can have an internal β of about 10. The inherent low internal magnetic field provides for a certain indigenous kinetic particle population, i.e. particles with large larmor radii, comparable to the FRC minor radius. It is these strong kinetic effects that appear to at least partially contribute to the gross stability of past and present FRCs, such as those produced in the recent collision-merging experiments. The collision-merging technique, proposed long ago (see e.g. D. R. Wells, Phys. Fluids 9, 1010 (1966)) has been significantly developed further: two separate theta-pinches at opposite ends of a confinement chamber simultaneously generate two plasmoids (e.g., two compact tori) and accelerate the plasmoids toward each other at high speed; they then collide at the center of the confinement chamber and merge to form a compound FRC. In the construction and successful operation of one of the largest FRC experiments to date, the conventional collision-merging method was shown to produce stable, long-lived, high-flux, high temperature FRCs (see e.g. M. Binderbauer, H. Y. Guo, M. Tuszewski et al., Phys. Rev. Lett. 105, 045003 (2010), which is incorporated herein by reference). In a related experiment, the same team of researchers combined the collision-merging technique with simultaneous axial acceleration and radial compression to produce a high density transient plasma in a central compression chamber (see V. Bystritskii, M. Anderson, M. Binderbauer et al., Paper P1-1, IEEE PPPS 2013, San Francisco, Calif. (hereinafter “Bystritskii”), which is incorporated herein by reference). This latter experiment reported in Bystritskii utilized a multitude of acceleration and compression stages before final collisional merging and represents a precursor concept to the system subject to this patent application. In contrast to the embodiments described here, the precursor system described in Bystritskii featured simultaneous compression and acceleration of compact tori within the same stage by using active fast magnetic coils. Five such stages were deployed on either side of a central compression chamber before magnetically compressing the merged compact tori. While the precursor experiment achieved respectable performance, it exhibited the following deficiencies: (1) Simultaneous compression and acceleration led to inefficient use of driver energy deployed for magnetic compression due to a timing mismatch; (2) Temperature and density decreased as plasma expanded during transit between sections; (3) Abrupt transitions between adjacent sections led to large losses due to plasma-wall contact and generation of shockwaves. Aside from the fundamental challenge of stability, pulsed fusion concepts in the medium density regime will have to address adequate transport timescales, efficient drivers, rep-rate capability and appropriate final target conditions. While the precursor system has successfully achieved stable single discharges at encouraging target conditions, the collective losses between formation and final target parameters (presently about 90% of the energy, flux, and particles) as well as the coupling efficiency between driver and plasma (at present around 10-15%) need to be substantially improved. In light of the foregoing, it is, therefore, desirable to provide improved systems and methods for pulsed fusion concepts that facilitate a significant reduction of translation and compression losses and an increase in driver efficiency. The present embodiments provided herein are directed to systems and methods that facilitate merging and compressing compact tori with superior stability as well as a significant reduction of translation and compression losses and an increase in coupling efficiency between drivers and plasma. Such systems and methods provide a pathway to a whole variety of applications including compact neutron sources (for medical isotope production, nuclear waste remediation, materials research, neutron radiography and tomography), compact photon sources (for chemical production and processing), mass separation and enrichment systems, and reactor cores for fusion for the future generation of energy and for fusion propulsion systems. The systems and methods described herein are based on the application of successive, axially symmetric acceleration and adiabatic compression stages to accelerate and heat two compact tori towards each other and ultimately collide and fast magnetically compress the compact tori within a central compression chamber. In certain embodiments, a system for merging and compressing compact tori comprises a staged symmetric sequence of compact tori formation, axial acceleration by fast active magnetic coils, passive adiabatic compression by way of a conically constricting flux conserver, and ultimately merging of the compact tori and final fast magnetic compression in a central compression chamber. The intermediate steps of sufficient axial acceleration followed by adiabatic compression can be repeated multiple times to achieve adequate target conditions before merging and final compression. In this way, a reactor can be realized by adding further sections to the system. The formation and accelerations stages or sections and the central compression chamber are preferably cylindrically shaped with walls formed of non-conducting or insulating material such as, e.g., a ceramic. The compressions stages or sections are preferably trunco-conically shaped with walls formed from conducting material such as, e.g., a metal. Aside from a magnetic bias field (DC guide field) supplied by slow coils, the formation sections, the acceleration sections, and the compression chamber include modular pulsed power systems that drive fast active magnetic coils. The pulsed power systems enable compact tori to be formed in-situ within the formation sections and accelerated and injected (=static formation) into the first compression sections, accelerated in the acceleration sections and injected into the next compression sections, and so on, and then be magnetically compressed in the compression chamber. The slow or DC magnetic coil systems located throughout and along the axis of the system provide an axial magnetic guide field to center the compact tori appropriately as it translates through the section toward the mid-plane of the central compression chamber. Alternatively, the modular pulsed power systems of the formation sections can also drive the fast active magnetic coils in a way such that compact tori are formed and accelerated simultaneously (=dynamic formation). The systems and methods described herein deploy FRCs, amongst the highest beta plasmas known in magnetic confinement, to provide the starting configuration. Further passive and active compression builds on this highly efficient magnetic topology. The process of using axial acceleration via active fast magnet sections followed by adiabatic compression in simple flux conserving conic sections provides for the most efficient transfer of energy with the least complex pulsed power circuitry. Furthermore, these basic building blocks can be sequenced to take additional advantage of the inherently favorable compressional scaling, i.e. Δp∝R4. In another embodiment, the system is configured to deploy spheromaks instead of FRC starter plasmas. In another embodiment, the system comprises a staged asymmetric sequence from a single side of the central compression chamber comprising compact tori formation, axial acceleration by fast active magnetic coils, passive adiabatic compression by way of a conically constricting flux conserver, and ultimately merging of the compact tori and final fast magnetic compression in the central compression chamber. Such an asymmetric system would include a mirror or bounce cone positioned adjacent the other side of the central compression. In yet another embodiment, the system comprises a thin cylindrical shell or liner comprised of conductive material such as, e.g., a metal, for fast liner compression within the central compression chamber. Other systems, methods, features and advantages of the example embodiments will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It should be noted that the figures are not necessarily drawn to scale and that elements of similar structures or functions are generally represented by like reference numerals for illustrative purposes throughout the figures. It also should be noted that the figures are only intended to facilitate the description of the various embodiments described herein. The figures do not necessarily describe every aspect of the teachings disclosed herein and do not limit the scope of the claims. The present embodiments provided herein are directed to systems and methods that facilitate merging and compressing compact tori with superior stability as well as a significant reduction of translation and compression losses and an increase in coupling efficiency between drivers and plasma. Such systems and methods provide a pathway to a whole variety of applications including compact neutron sources (for medical isotope production, nuclear waste remediation, materials research, neutron radiography and tomography), compact photon sources (for chemical production and processing), mass separation and enrichment systems, and reactor cores for fusion for the future generation of energy and for fusion propulsion systems. The systems and methods described herein are based on the application of successive, axially symmetric acceleration and adiabatic compression stages to accelerate and heat two compact tori towards each other and ultimately collide and fast magnetically compress the compact tori within a central compression chamber. FIG. 1 illustrates the basic layout of a system 10 for forming, accelerating, adiabatically compressing, merging and finally magnetically compressing the compact tori. As depicted, the system comprises a staged symmetric sequence of compact tori formation in formation sections 12N and 12S, axial acceleration through sections 12N, 12S, 16N and 16S by fast active magnetic coils 32N, 32S, 36N and 36S, passive adiabatic compression by way of a conically constricting flux conserver in sections 14N, 14S, 18N and 18S, and ultimately merging of the compact tori and final fast magnetic compression in a central compression chamber 20 by fast active magnetic coils 40. As illustrated, the intermediate steps of sufficient axial acceleration followed by adiabatic compression can be repeated multiple times to achieve adequate target conditions before merging and final compression. In this way, a reactor can be realized by adding further sections to the depicted system. As depicted the formation and accelerations stages or sections 12N, 12S, 16N and 16S and the central compression chamber 20 are preferably cylindrically shaped with walls formed of non-conducting or insulating material such as, e.g., a ceramic. The compressions stages or sections 14N, 14S, 18N and 18S are preferably trunco-conically shaped with walls formed from conducting material such as, e.g., a metal. Aside from a magnetic bias field (DC guide field) supplied by slow passive coils 30, the formation sections 12N and 12S, the acceleration sections 16N and 16S, and the compression chamber 20 include modular pulsed power systems that drive fast active magnetic coils 32N, 32S, 36N, 36S and 40. The pulsed power systems enable compact tori to be formed in-situ within the formation sections 12N and 12S and accelerated and injected (=static formation) into the first compression sections 14N and 14S, accelerated in the acceleration sections 16N and 16S and injected into the next compression sections 18N and 18S, and so on, and then be magnetically compressed in the compression chamber 20. The slow passive magnetic coil systems 30 located throughout and along the axis of the system provide an axial magnetic guide field to center the compact tori appropriately. Alternatively, the modular pulsed power systems of the formation sections can also drive the fast magnetic coils in a way such that compact tori are formed and accelerated simultaneously (=dynamic formation). The systems and methods described herein deploy FRCs, amongst the highest beta plasmas known in magnetic confinement, to provide the starting configuration. Further passive and active compression builds on this highly efficient magnetic topology. The process of using axial acceleration via active fast magnet sections followed by adiabatic compression in simple flux conserving conic sections provides for the most efficient transfer of energy with the least complex pulsed power circuitry. Furthermore, these basic building blocks can be sequenced to take additional advantage of the inherently favorable compressional scaling, i.e. Δp∝R4. Based on experimental and theoretical research to date, a precursor experiment as describe by Bystritskii, using FRC starter plasmas has achieved densities of about 1017 cm−3 at 1 keV. The embodiments proposed herein are estimated to reach densities of about 1018 cm−3 at 1 keV, while adding further stages and appropriate upgrades to the central chamber and fast magnetic coils can yield ultimate densities of about 1018 cm−3 at full Lawson conditions. In another embodiment, the system is configured to deploy spheromaks instead of FRC starter plasmas. In another embodiment, the system comprises a staged asymmetric sequence from a single side of the central compression chamber comprising compact tori formation, axial acceleration by fast active magnetic coils, passive adiabatic compression by way of a conically constricting flux conserver, and ultimately merging of the compact tori and final fast magnetic compression in the central compression chamber. Such an asymmetric system would include a mirror or bounce cone. In yet another embodiment, the system comprising a thin cylindrical shell or liner comprised of conductive material such as, e.g., a metal, for fast liner compression within the central compression chamber. Fusion concepts today are focused on either steady state or ultra-short pulsed regimes. Both approaches require large capital investment: in steady state magnetic fusion, high expense arises from large superconducting magnets and auxiliary heating/current drive technologies; inertial regimes are dominated by high driver cost due to large energy delivery over nanosecond timescales. The embodiments advanced herein are characterized by compact size and sub-millisecond time scales. This leads to a regime that has relaxed peak power requirements and attractive intermediate time scales. Turning in detail to the drawings, as depicted in FIG. 1, a system 10 for merging and compressing compact tori plasma includes a central compression chamber 20 and a pair of north and south diametrically opposed compact tori formation sections 12N and 12S. The first and second formation sections 12N and 12S include a modularized formation and acceleration systems 120 (discuss below in detail with regard to see FIGS. 2-4) for generating first and second compact plasma tori and axially accelerating and translating the compact tori towards a mid-plane of the compression chamber 20. As depicted, the system 10 further includes a first pair of north and south diametrically opposed compression sections 14N and 14S coupled on a first end to an exit end of the north and south formation sections 12N and 12S. The north and south compression sections 14N and 14S being configured to adiabatically compress the compact tori as the compact tori traverse the north and south compression sections 14N and 14S towards the mid-plane of the compression chamber 20. As depicted, the system 10 further includes a pair of north and south diametrically opposed acceleration sections 16N and 16S coupled on a first end to a second end of the first pair of north and south compression sections 14N and 14S. The north and south acceleration section 16N and 16S include modularized acceleration systems (discussed below with regard to FIGS. 2-4) for axially accelerating and translating the compact tori towards the mid-plane of the compression chamber 20. As further depicted, the system 10 further includes a second pair of north and south diametrically opposed compression sections 18N and 18S coupled on a first end to a second end of the north and south acceleration sections 16N and 16S and on a second end to first and second diametrically opposed ends of the compression chamber, the second pair of north and south compression sections 18N and 18S being configured to adiabatically compress the compact tori as the compact tori traverse the second pair of north and south compression sections 18N and 18S towards the mid-plane of the compression chamber 20. The compression chamber includes a modularized compression systems configured to magnetically compress the compact tori upon collision and merger thereof. As depicted the north and south formation sections 12N and 12S, the north and south acceleration sections 16N and 16S and the compression chamber 20 are cylindrically shaped. The diameter of the north and south acceleration sections 16N and 16S is smaller than the diameter of the north and south formation sections 12N and 12S, while the diameter of the compression chamber 20 is than the diameter of the north and south acceleration sections 16N and 16S. The first and second pairs of north and south compression sections 14N, 14S, 18N and 18S are truncated conically shaped with their diameter being larger on a first end than on a second end enabling a transition in the overall diameter of the system 10 from the formation sections 12N and 12S to the acceleration sections 16N and 16S to the compression chamber 20. As depicted, the north and south formation sections 12N and 12S, the first pair of north and south compression sections 14N and 14S, the north and south acceleration sections 16N and 16S, and the second pair of north and south compression sections 18N and 18S are axially symmetric. As depicted, first and second sets of a plurality of active magnetic coils 32N and 32 are disposed about and axially along the north and south formation sections 12N and 12S, third and fourth sets of a plurality of active magnetic coils 36N and 36S are disposed about and axially along the north and south acceleration sections 16N and 16S, and a fifth set of a plurality of active magnetic coils 40 are disposed about and axially along the compression chamber 20. The compression sections 14N, 14S, 18N and 18S are preferably formed from conducting material such as, e.g., a metal, while the central compression chamber 20 and the formation and acceleration sections are 12N, 12S, 16N and 16S are preferably formed from non-conducting or insulating material such as, e.g., a ceramic. As depicted, a plurality of DC magnetic coils 30 are disposed about and axially along the central compression chamber 20 and the formation, compression and acceleration sections 12N, 12S, 14N, 14S, 16N, 16S, 18N and 18S to form a bias or DC guide field within and extending axially through the central compression chamber and the formation, compression and acceleration sections. Triggering control and switch systems 120, shown in FIGS. 2-4, are configured to enable a staged symmetric sequence of compact tori formation by active magnetic coils 32N and 32S in the north and south formation sections 12N and 12S, axial acceleration by active magnetic coils 36N and 36S in the north and south acceleration sections 16N and 16S, and compression by active magnetic coils 40 in the compression chamber 20. The triggering control and switch systems 120 are configured to synchronize compact tori formation and acceleration in the north and south formation sections 12N and 12S, compact tori acceleration in the north and south acceleration sections 16N and 16S, and compact tori merge and compression in the compression chamber 20. Turning to FIGS. 2-4, there is individual pulsed power system 120 corresponding to and powering individual ones of the first, second, third, fourth and fifth sets of the plurality of active magnets 32N, 32S, 36N, 36S and 40 of the formation sections 12N and 12S, the acceleration sections 16N and 16S, and the compression chamber 20. In the formation sections, the pulse power system 120 operates on a modified theta-pinch principle to form the compact tori. FIGS. 2 through 4 illustrate the main building blocks and arrangement of the pulsed power systems 120. The pulsed power system 120 is composed of a modular pulsed power arrangement that consists of individual units (=skids) 122 that each energize a sub-set of coils 132 of a strap assembly 130 (=straps) that wrap around the section tubes 140. Each skid 122 is composed of capacitors 121, inductors 123, fast high current switches 125 and associated trigger 124 and dump circuitry 126. Coordinated operation of these components is achieved via a state-of-the-art trigger and control system 124 and 126 that allows synchronized timing between the pulsed power systems 120 on each of the formation sections 12N and 12S, the acceleration sections 16N and 16S, and compression chamber 20, and minimizes switching jitter to tens of nanoseconds. The advantage of this modular design is its flexible operation. In the formation sections 12N and 12S, FRCs can be formed in-situ and then accelerated and injected (=static formation) or formed and accelerated at the same time (=dynamic formation). In operation, a DC guide field is generated by the passive coils 30 within and axially extending through the compression chamber 20, the formation sections 12N and 12S, the acceleration sections 16N and 16S, and the compression sections 14N, 14S, 18N and 18S. Compact tori are then formed and accelerated in a staged symmetric sequence within the formation sections 12N and 12S and the acceleration sections 16N and 16S towards a mid-plane of the central chamber 20, passively adiabatically compressed within the compression sections 14N, 14S, 18N and 18S, and merged and magnetically compressed within the central chamber 20. These steps of forming, accelerating and compressing compact tori results in the compact tori colliding and merging within the central chamber 20. The compact tori are formed and accelerated by powering active magnetic coils 32N and 32S extending about and axially along the formation sections 12N and 12S, further accelerated by powering active magnetic coils 35N and 36S extending about and axially along the acceleration sections 16N and 16S, and compressed by powering active magnetic coils 40 extending about and axially along the compression chamber 20. The steps of forming, accelerating and compressing the compact tori further comprises synchronously firing diametrically opposed pairs of active magnetic coils 32N and 32S, and 36N and 36S positioned about and along the formation 12N and 12S and acceleration sections 16N and 16S, and a set of active magnetic coils 40 positioned about and along the compression chamber 20. As the compact tori are accelerated towards the mid-plane of the compression chamber 20, the compact tori are compressed as the compact tori translate through the conically constricting flux conservers of the compression stages 14N, 14S, 18N and 18S. Turning to FIG. 5, an alternative embodiment of a system 100 for merging and compressing compact tori plasma is illustrated. As depicted, the system 100 comprises a staged asymmetric sequence from a single side of the central compression chamber 20. The system 100 includes a single compact toroid formation section 12S, a first compression section 14S coupled on a first end to an exit end of the formation section 12S, an acceleration section 16N coupled on a first end to a second end of the compression section 14S, a second compression section 18S coupled on a first end to a second end of the acceleration section 16S and on a second end to a first end of the compression chamber 20. A mirror or bounce cone 50 is positioned adjacent the other end of the central compression 20. In operation, a first compact toroid is formed and accelerated in a staged sequence within the formation section 12S and then accelerated in one or more acceleration stages 16S towards a mid-plane of the central chamber 20 to collide and merge with a second compact toroid. The first compact toroid is passively adiabatically compressed within one or more compression stages 14S and 18S, and then magnetically compressed as a merged compact toroid with the second compact toroid within the central chamber 20. The second compact toroid in formed and accelerated in a staged sequence within the formation section 12S and the one or more acceleration stages 16S towards a mid-plane of the central chamber 20, passively adiabatically compressed within the one or more compression stages, and then biased back toward the mid-plane of the central chamber 20 as it passes through the central chamber 20 with a mirror or bounce cone 50 positioned adjacent an end of the central chamber 20. Turning to FIG. 6, an alternative embodiment of a system 200 for merging and compressing compact tori plasma is illustrated in a partial detail view showing the compression chamber 20 with diametrically opposed compression section 18N and 18S coupled to opposing sides of the chamber 20. The system 200 further comprise a cylindrical shell or liner 60 positioned within the central compression chamber 20 for fast liner compression. While the invention is susceptible to various modifications, and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the appended claims. In the description above, for purposes of explanation only, specific nomenclature is set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details are not required to practice the teachings of the present disclosure. The various features of the representative examples and the dependent claims may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. It is also expressly noted that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure, as well as for the purpose of restricting the claimed subject matter. Systems and methods for merging and compressing compact tori have been disclosed. It is understood that the embodiments described herein are for the purpose of elucidation and should not be considered limiting the subject matter of the disclosure. Various modifications, uses, substitutions, combinations, improvements, methods of productions without departing from the scope or spirit of the present invention would be evident to a person skilled in the art. For example, the reader is to understand that the specific ordering and combination of process actions described herein is merely illustrative, unless otherwise stated, and the invention can be performed using different or additional process actions, or a different combination or ordering of process actions. As another example, each feature of one embodiment can be mixed and matched with other features shown in other embodiments. Features and processes known to those of ordinary skill may similarly be incorporated as desired. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents. |
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description | This disclosure relates to ion sources, systems and methods. Ion sources and systems can produce ion beams which are used to investigate and/or modify a sample. The disclosure relates to ion sources, systems and methods. In some embodiments, the ion sources, systems and methods can exhibit relatively little undesired vibration and/or can sufficiently dampen undesired vibration. This can enhance performance (e.g., increase reliability, stability and the like). In certain embodiments, the ion sources, systems and methods can enhance the ability to make tips having desired physical attributes (e.g., the number of atoms on the apex of the tip). This can enhance performance (e.g., increase reliability, stability and the like). In one aspect, the disclosure generally features a system that includes a charged particle column, a detector and an optical reflective element having a first position and a second position. When in the first, position, the optical reflective element can reflect light passing through the charged particle column to the detector. When in the second position, the optical reflective element cannot reflect light passing through the charged particle column to the detector. In some embodiments, the system further includes a positioning device configured to move the optical reflective element between its first and second positions. In certain embodiments, the charged particle column is an ion column. In some embodiments, the system further includes a charged particle source. The charged particle source can be configured so that during use at least some of the charged particles generated by the charged particle source pass through the charged particle column. The charged particle source can be configured so that, when it emits light, the light goes into the column and can be reflected by the optical reflective element when it is in the first position. In certain embodiments, the detector is configured to detect light reflected by the optical reflective element. In another aspect, the disclosure generally features a system that includes a charged particle column and an optical reflective element having an optical reflective portion and an aperture. The optical reflective element is in the charged particle column. The optical reflective portion of the optical reflective element can reflect light passing through the charged particle column. Charged particles emitted by a charged particle source can pass through the aperture of the optical reflective element. In some embodiments, the optical reflective element is fixed with respect to the charged particle column. In certain embodiments, the charged particle column is an ion column. In some embodiments, the system further includes the charged particle source. The charged particle source can be configured so that during use at least some of the charged particles generated by the charged particle source pass through aperture in the optical reflective element. The charged particle source can be configured so that, when it emits light, the light goes into the column and can be reflected by the optical reflective portion of the optical reflective element. The charged particle column has an axis, and the optical reflective element can be positioned along the axis of the charged particle column. In some embodiments, the system further includes a detector configured to detect light reflected by the optical reflective element. In a further aspect, the disclosure generally features a system that includes a charged particle column having an axis, and an optical reflective element positioned within the charged particle column and displaced off-axis with respect to the axis of the charged particle column. The optical reflective element is coupled to the charged particle column. In some embodiments, the optical reflective element is fixed with respect to the charged particle column. In certain embodiments, the system further includes a support to which the optical reflective element is mounted. The support can be fixed with respect to the charged particle column. In some embodiments, the charged particle column is an ion column. In certain embodiments, the system further includes a charged particle source. The charged particle source can be configured so that during use at least some of the charged particles generated by the charged particle source pass through the charged particle column without interacting with the optical reflective element. The charged particle source can be configured so that, when it emits light, the light goes into the column and can be reflected by the optical reflective element. In some embodiments, the system further includes a detector configured to detect light reflected by the optical reflective element. In an additional aspect, the disclosure generally features a system that includes a charged particle column and a moveable optical reflective element having a first position in the charged particle column and a second position outside the charged particle column. In one aspect, the disclosure generally features a charged particle system that includes any of the preceding systems. In some embodiments, the charged particle system can be a gas field ion microscope. In another aspect, the disclosure generally features a method that includes emitting light from a charged particle source so that the light enters a charged particle column, and reflecting at least a portion of the light in the charged particle column to a detector. In some embodiments, the method also includes using the detected light to determine one or more parameters for preparing a tip of the charged particle source. Examples of parameters include the temperature of the tip of the charged particle source, the gas pressure of a chamber housing the charged particle source, and the intensity of light emitted by the charged particle source. In certain embodiments, the method further includes, based on the detected light, increasing at least one parameter selected from the group consisting of a charged particle source temperature and a gas pressure in a chamber housing the charged particle source. In some embodiments, the charged particle source is an ion source, such as a gas field ion source. In an further aspect, the disclosure generally features a method that includes using any of the systems described above to make a tip of a charged particle source. In an additional aspect, the disclosure generally features a system that includes a vacuum housing having a door and a stage assembly. The stage assembly includes a stage configured to support a sample, and a support member connected to the door. The stage is connected to the support via a friction mechanism. In some embodiments, the friction mechanism includes at least one friction bearing. In certain embodiments, the friction mechanism includes a tube that is friction fit within an aperture. In some embodiments, the stage is tillable relative to the door. In certain embodiments, the friction mechanism can be used to tilt the stage relative to the door. In some embodiments, the system further includes a charged particle source, such as an ion source (e.g., a gas field ion source). In certain embodiments, the system is a gas field ion microscope. In another aspect, the disclosure generally features a system that includes a sample holder having a first surface and a second surface opposite the first surface. The second surface has a plurality of holes. They system also includes a stage having a surface with support positions. The holes in the second surface of the sample holder are configured to engage with the support positions of the stage. The system further includes at least one magnet configured to secure the sample holder to the stage. In some embodiments, the at least one magnet is a plurality of magnets. In certain embodiments, an exposed surface of the at least one magnet coincides with the second surface of the sample holder. In some embodiments, the system further includes a charged particle source, such as an ion source (e.g., a gas field ion source). In certain embodiments, the system is a gas field ion microscope. Other features and advantages will be apparent from the description, drawings, and claims. Like reference symbols in the various drawings indicate like elements. When used to investigate properties of various samples, ion beams can provide qualitative and/or quantitative measurements that are precise and accurate to atomic resolution. Sample images measured with an ion beam (e.g., images that are derived from measurements of secondary electrons and/or scattered ions and/or scattered neutral atoms) can have very high resolution, revealing sample features that are difficult to observe using other imaging techniques. Optionally, ion beams can be used to provide qualitative and/or quantitative material constituent information about a sample. An example of a sample is a semiconductor article. Semiconductor fabrication typically involves the preparation of an article (a semiconductor article) that includes multiple layers of materials sequentially deposited and processed to form an integrated electronic circuit, an integrated circuit element, and/or a different microelectronic device. Such articles typically contain various features (e.g., circuit lines formed of electrically conductive material, wells filled with electrically non-conductive material, regions formed of electrically semiconductive material) that are precisely positioned with respect to each other (e.g., generally on the scale of within a few nanometers). The location, size (length, width, depth), composition (chemical composition) and related properties (conductivity, crystalline orientation, magnetic properties) of a given feature can have an important impact on the performance of the article. For example, in certain instances, if one or more of these parameters is outside an appropriate range, the article may be rejected because it cannot function as desired. As a result, it is generally desirable to have very good control over each step during semiconductor fabrication, and it would be advantageous to have a tool that could monitor the fabrication of a semiconductor article at various steps in the fabrication process to investigate the location, size, composition and related properties of one or more features at various stages of the semiconductor fabrication process. As used herein, the term semiconductor article refers to an integrated electronic circuit, an integrated circuit element, a microelectronic device or an article formed during the process of fabricating an integrated electronic circuit, an integrated circuit element, a microelectronic device. In some embodiments, a semiconductor article can be a portion of a flat panel display or a photovoltaic cell. Regions of a semiconductor article can be formed of different types of material (electrically conductive, electrically non-conductive, electrically semiconductive). Exemplary electrically conductive materials include metals, such as aluminum, chromium, nickel, tantalum, titanium, tungsten, and alloys including one or more of these metals (e.g., aluminum-copper alloys). Metal silicides (e.g., nickel silicides, tantalum silicides) can also be electrically conductive. Exemplary electrically non-conductive materials include borides, carbides, nitrides, oxides, phosphides, and sulfides of one or more of the metals (e.g., tantalum borides, tantalum germaniums, tantalum nitrides, tantalum silicon nitrides, and titanium nitrides). Exemplary electrically semiconductive materials include silicon, germanium and gallium arsenide. Optionally, an electrically semiconductive material can be doped (p-doped, n-doped) to enhance the electrical conductivity of the material. Typical steps in the deposition/processing of a given layer of material include imaging the article (e.g., to determine where a desired feature to be formed should be located), depositing an appropriate material (e.g., an electrically conductive material, an electrically semiconductive material, an electrically non-conductive material) and etching to remove unwanted material from certain locations in the article. Often, a photoresist, such as a polymer photoresist, is deposited/exposed to appropriate radiation/selectively etched to assist in controlling the location and size of a given feature. Typically, the photoresist is removed in one or more subsequent process steps, and, in general, the final semiconductor article desirably does not contain an appreciable amount of photoresist. FIG. 1 shows a schematic diagram of a gas field ion microscope system 100 that includes a gas source 110, a gas field ion source 120, ion optics 130, a sample manipulator 140, a front-side detector 150, a back-side detector 160, and an electronic control system 170 (e.g., an electronic processor, such as a computer) electrically connected to various components of system 100 via communication lines 172a-172f. A sample 180 is positioned in/on sample manipulator 140 between ion optics 130 and detectors 150, 160. During use, an ion beam 192 is directed through ion optics 130 to a surface 181 of sample 180, and particles 194 resulting from the interaction of ion beam 192 with sample 180 are measured by detectors 150 and/or 160. As shown in FIG. 2, gas source 110 is configured to supply one or more gases 182 to gas field ion source 120. Gas source 110 can be configured to supply the gas(es) at a variety of purities, flow rates, pressures, and temperatures. In general, at least one of the gases supplied by gas source 110 is a noble gas (helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe)), and ions of the noble gas are desirably the primary constituent in ion beam 192. In general, as measured at surface 181 of sample 180, the current of ions in ion beam 192 increases monotonically as the pressure of the noble gas in system 100 increases. In certain embodiments, this relationship can be described by a power law where, for a certain range of noble gas pressures, the current increases generally in proportion to gas pressure. Optionally, gas source 110 can supply one or more gases in addition to the noble gas(es); an example of such a gas is nitrogen. Typically, while the additional gas(es) can be present at levels above the level of impurities in the noble gas(es), the additional gas(es) still constitute minority components of the overall gas mixture introduced by gas source 110. Gas field ion source 120 is configured to receive the one or more gases 182 from gas source 110 and to produce gas ions from gas(es) 182. Gas field ion source 120 includes an electrically conductive tip 186 with a tip apex 187, an extractor 190 and optionally a suppressor 188. Electrically conductive tip 186 can be formed of various materials. In some embodiments, tip 186 is formed of a metal (e.g., tungsten (W), tantalum (Ta), iridium (Ir), rhenium (Rh), niobium (Nb), platinum (Pt), molybdenum (Mo)). In certain embodiments, electrically conductive tip 186 can be formed of an alloy. In some embodiments, electrically conductive tip 186 can be formed of a different material (e.g., carbon (C)). During use, tip 186 is biased positively (e.g., approximately 20 kV) with respect to extractor 190, extractor 190 is negatively or positively biased (e.g., from −20 kV to +50 kV) with respect to an external ground, and optional suppressor 188 is biased positively or negatively (e.g., from −5 kV to +5 kV) with respect to tip 186. Because tip 186 is formed of an electrically conductive material, the electric field of tip 186 at tip apex 187 points outward from the surface of tip apex 187. Due to the shape of tip 186, the electric field is strongest in the vicinity of tip apex 187. The strength of the electric field of tip 186 can be adjusted, for example, by changing the positive voltage applied to tip 186. With this configuration, un-ionized, gas atoms 182 supplied by gas source 110 are ionized and become positively-charged ions in the vicinity of tip apex 187. The positively-charged ions are simultaneously repelled by positively charged tip 186 and attracted by negatively charged extractor 190 such that the positively-charged ions are directed from tip 186 into ion optics 130 as ion beam 192. Suppressor 188 assists in controlling the overall electric field between tip 186 and extractor 190 and, therefore, the trajectories of the positively-charged ions from tip 186 to ion optics 130. In general, the overall electric field between tip 186 and extractor 190 can be adjusted to control the rate at which positively-charged ions are produced at tip apex 187, and the efficiency with which the positively-charged ions are transported from tip 186 to ion optics 130. In general ion optics 130 are configured to direct ion beam 192 onto surface 181 of sample 180. Ion optics 130 can, for example, focus, collimate, deflect, accelerate, and/or decelerate ions in beam 192. Ion optics 130 can also allow only a portion of the ions in ion beam 192 to pass through ion optics 130. Generally, ion optics 130 include a variety of electrostatic and other ion optical elements that are configured as desired. By manipulating the electric field strengths of one or more components (e.g., electrostatic deflectors) in ion optics 130, He ion beam 192 can be scanned across surface 181 of sample 180. For example, ion optics 130 can include two deflectors that deflect ion beam 192 in two orthogonal directions. The deflectors can have varying electric field strengths such that ion beam 192 is rastered across a region of surface 181. When ion beam 192 impinges on sample 180, a variety of different types of particles 194 can be produced. These particles include, for example, secondary electrons, Auger electrons, secondary ions, secondary neutral particles, primary neutral particles, scattered ions and photons (e.g., X-ray photons, IR photons, visible photons, UV photons). Detectors 150 and 160 are positioned and configured to each measure one or more different types of particles resulting from the interaction between He ion beam 192 and sample 180. As shown in FIG. 1, detector 150 is positioned to detect particles 194 that originate primarily from surface 181 of sample 180, and detector 160 is positioned to detect particles 194 that emerge primarily from surface 183 of sample 180 (e.g., transmitted particles). As described in more detail below, in general any number and configuration of detectors can be used in the microscope systems disclosed herein. In some embodiments, multiple detectors are used, and some of the multiple detectors are configured to measure different types of particles. In certain embodiments, the detectors are configured to provide different information about the same type of particle (e.g., energy of a particle, angular distribution of a given particle, total abundance of a given particle). Optionally, combinations of such detector arrangements can be used. In general, the information measured by the detectors is used to determine information about sample 180. Typically, this information is determined by obtaining one or more images of sample 180. By rastering ion beam 192 across surface 181, pixel-by-pixel information about sample 180 can be obtained in discrete steps. Detectors 150 and/or 160 can be configured to detect one or more different types of particles 194 at each pixel. The operation of microscope system 100 is typically controlled via electronic control system 170. For example, electronic control system 170 can be configured to control the gas(es) supplied by gas source 110, the temperature of tip 186, the electrical potential of tip 186, the electrical potential of extractor 190, the electrical potential of suppressor 188, the settings of the components of ion optics 130, the position of sample manipulator 140, and/or the location and settings of detectors 150 and 160. Optionally, one or more of these parameters may be manually controlled (e.g., via a user interface integral with electronic control system 170). Additionally or alternatively, electronic control system 170 can be used (e.g., via an electronic processor, such as a computer) to analyze the information collected by detectors 150 and 160 and to provide information about sample 180 (e.g., topography information, material constituent information, crystalline information, voltage contrast information, optical property information, magnetic information), which can optionally be in the form of an image, a graph, a table, a spreadsheet, or the like. Typically, electronic control system 170 includes a user interface that features a display or other kind of output device, an input device, and a storage medium. In certain embodiments, electronic control system 170 can be configured to control various properties of ion beam 192. For example, control system 170 can control a composition of ion beam 192 by regulating the flow of gases into gas field ion source 120. By adjusting various potentials in ion source 120 and ion optics 130, control system 170 can control other properties of ion beam 192 such as the position of the ion beam on sample 180, and the average energy of the incident ions. In some embodiments, electronic control system 170 can be configured to control one or more additional particle beams. For example, in certain embodiments, one or more types of ion beam source and/or electron beam sources can be present. Control system 170 can control each of the particle beam sources and their associated optical and electronic components. Detectors 150 and 160 are depicted schematically in FIG. 1, with detector 150 positioned to detect particles from surface 181 of sample 180 (the surface on which the ion beam impinges), and detector 160 positioned to detect particles from surface 183 of sample 180. In general, a wide variety of different detectors can be employed in microscope system 200 to detect different particles, and a microscope system 200 can typically include any desired number of detectors. The configuration of the various detector(s) can be selected in accordance with particles to be measured and the measurement conditions. In some embodiments, a spectrally resolved detector may be used. Such defectors are capable of detecting particles of different energy and/or wavelength, and resolving the particles based on the energy and/or wavelength of each detected particle. Detection systems and methods are generally disclosed, for example, in US 2007-0158558, the entire contents of which are incorporated herein by reference. In general, the accuracy of ion beam measurements depends, in part, on the stability of the ion beam daring measurement. For example, fluctuations in the position of the ion beam on the surface of a sample during a measurement can lead to errors in spatially resolved measurements. One source of such fluctuations in the position of the ion beam can be mechanical vibrations which lead to displacement of the sample relative to the ion beam during the course of a measurement. Ion beam sources typically use a variety of components such as pumps and drive mechanisms that produce low frequency vibrations when activated. Such low frequency vibrations can couple through intermediate components, inducing motion of the sample relative to the ion beam. As an example, such low frequency vibrations can couple through components formed of relatively rigid materials (e.g., stainless steel) and into the sample holder. A sample holder assembly 1510 that provides for improved stability and reduced vibrational coupling to a sample is shown in FIG. 3. Assembly 1510 is mounted to a body 1511 having an opening 1512 to insert a sample. In some embodiments, body 1511 does not include an opening, and is instead a solid member that corresponds to a door of a sample chamber. To insert a sample, body 1511 swings open on a side-mounted hinge, exposing the sample holder assembly for sample mounting. Body 1511 is connected to arms 1518 of the sample holder assembly through adjustable connectors 1522. Arms 1518 support a sample stage 1514 via friction bearing 1520. Sample stage 1514 includes a mounting surface 1516 having an aperture 1524. Sample holder assembly 1510 can be connected to an ion microscope such that a tip from which the ion beam is generated is pointed towards aperture 1524 on sample stage 1514. Body 1511 can be formed from suitable rigid materials such as hardened steel stainless steel, phosphor bronze, and titanium. Typically, for example, body 1511 corresponds to a door of a sample chamber and is square or rectangular in shape, with a thickness of between 0.25 inches and 2 inches or more. By forming body 1511 from a relatively thick piece of metal, body 1511 is relatively highly resistant to deformation, and therefore does not transmit mechanical vibrations efficiently. Sample stage 1514 is supported by arms 1518 connected to body 1511 along adjustable connectors 1522. Adjustable connectors 1522 comprise rails with recesses that mate cooperatively with flanges 1521 of arms 1518. Arms 1518 are movable in the vertical direction of FIG. 3 with respect to body 1511 by sliding flanges 1521 within the recesses of adjustable connectors 1522. In FIG. 3, the vertical direction is parallel to the optical axis 1513 of the ion beam system. In other words, arms 1518 are movable in a direction that is parallel to optical axis 1513 of the ion beam system. Following movement in the vertical direction, arms 1518 (and stage 1514 connected thereto) can be locked in a specific position. Stage assembly 1510 includes pneumatic or vacuum clamps (not shown in FIG. 3) positioned on the opposite side of body 1511 from arms 1518, and connected to arms 1518 through apertures in body 1511. To lock arms 1518 in position relative to body 1511, the pneumatic or vacuum clamps are engaged, pulling arms 1518 tight against body 1511 and preventing further relative motion between body 1511 and arms 1518. During operation of assembly 1510, body 1511, which corresponds to a door of the sample chamber, swings open to expose stage 1514. A sample is mounted on stage 1514, and then body 1511 swings closed to seal the sample chamber. A suitable height for the mounted sample is selected by releasing the pneumatic (or vacuum) clamps that fix the position of arms 1518 relative to body 1511, and then translating arms 1518 along the vertical direction in FIG. 3. Flanges 1521 of arms 1518 move relative to connectors 1522 during the vertical translation of arms 1518. When the sample has been positioned at a desired vertical position, the pneumatic (or vacuum) clamps are re-engaged, rigidly locking arms 1518 in place against body 1511 and preventing further relative motion between arms 1518 and body 1511 in the vertical direction. The rigid locking of arms 1518 to body 1511 has the added benefit of increasing the resistance of body 1511 to flexural deformation when vibrations (e.g., from pumps and other sources) are coupled to body 1511. Sample stage 1514 is connected to arms 1518 via friction bearings 1520. Friction bearings 1520 include a hollow cylindrical shaft that extends from arm 1518 and into a mating aperture on stage 1514. Stage 1514 includes two such friction bearings, as shown in FIG. 3. The cylindrical shaft is sized to provide an interference fit with the mating aperture on stage 1514. As a result, the two friction bearings 1520 allow stage 1514 to tilt relative to arms 1518, without using moving parts such as oil coated hall bearings that can introduce contaminants into the sample chamber. As shown in FIG. 3, the tilt axis (e.g., the axis about which stage 1514 is rotatable) is perpendicular to the optical axis of the ion beam system (e.g., optical axis 1513). In certain embodiments, friction bearings 1520 include a hollow cylindrical shaft that extends from stage 1514 and into a mating aperture on arm 1518. Two such friction bearings 1520 can be provided, one on each side of stage 1514 as shown in FIG. 3. The cylindrical shaft is sized to provide an interference fit with the mating aperture on arm 1518. As a result, the friction bearings 1520 allow stage 1514 to tilt relative to arms 1518. The tilt axis (e.g., the axis about which stage 1514 is rotatable), as shown in FIG. 3, is perpendicular to the optical axis of the ion beam system (e.g., optical axis 1513). The interference fit in each friction bearing 1520 is sufficiently restrictive so that stage 1514 can be tilted to an angle of 45 degrees or more without undergoing slip relative to arms 1518. Generally, a motor is used to adjust the tilt angle of stage 1514. Due to the friction bearings, tilt motion of the stage is typically not continuous, but occurs in a series of tiny jumps, each corresponding to an angular displacement of less than about 0.25 degrees (e.g., less than 0.20 degrees, less than 0.15 degrees, less than 0.10 degrees, less than 0.05 degrees). In other words, the diameter of the cylindrical shaft and of die mating hole in friction bearing 1520 are selected so that the tiny jumps in angular displacement of stage 1514 relative to arms 1518 during relative motion are about 0.25 degrees or less. Sample stage 1514 further includes mounting surface 1516 which can have an opening 1524. A sample can be placed on mounting surface 1516 and a sample position control system can be used to move the sample in the plane of surface 1516. In certain embodiments, surface 1516 (or a portion thereof) can be rotated about its center to rotate the sample. As shown in FIG. 3, in some embodiments, the tilt angle of stage 1514 is zero. Accordingly, a rotation axis of surface 1516 (e.g., the axis about which surface 1516 is rotated) is oriented in the vertical direction of FIG. 3, parallel to the direction of optical axis 1513 of the ion beam system. Surface 1516 can be formed from various types of rigid materials, such as stainless steel, ceramic, glass and polymers. Movement of surface 1516 in the horizontal place (e.g., perpendicular to the vertical direction in FIG. 3) is typically controlled by piezoelectric devices. The relatively high stillness of piezoelectric devices ensures that surface 1516 remains rigidly fixed in position in the horizontal plane of FIG. 3 (e.g., the plane perpendicular to optical axis 1513), and external vibrations do not effectively couple into surface 1516 along the horizontal plane of FIG. 3. A particular advantage of the stage assembly 1510, as discussed above, is the absence of ball bearings in the assembly, which are typically coated with a hydrocarbon-based lubricants. Such lubricants act as impurities within a sample chamber, depositing on chamber surfaces and even on the surface of the sample during exposure to the ion beam. By eliminating the use of such bearings, a potential source of contaminants is also eliminated from the ion beam system. To ensure secure but removable mounting, samples are mounted to stage 1514 using a magnetic sample holder. An embodiment of a magnetic sample holder 1600 is shown in FIG. 4. FIG. 4 depicts the underside of sample holder 1600 which mates with mounting surface 1516 of assembly 1510. Sample holder 1600 includes three support structures 1610 and three magnetic contacts 1620. Each of the three support structures 1610 includes two holes 1630 that are sized to accommodate two corresponding conical pins that extend upwards from surface 1516. By positioning sample holder 1600 with each of the six pins that extend upwards from surface 1516, sample holder 1600 can be reproducibly positioned relative to surface 1516 with a tolerance of a one micron or less. To rigidly affix sample holder 1600 to surface 1516, each of the three magnetic contacts 1620 is positioned adjacent to a corresponding piece of magnetic steel which is mounted in surface 1516. The correct positioning of the magnetic contacts 1620 is achieved automatically by engaging holes 1630 with the conical pins of surface 1516. Strong magnetic field interactions between contacts 1620 and the corresponding steel magnets in surface 1516 ensure that sample holder 1600 is affixed to surface 1516 with significant force. Each of the magnetic contacts includes two strong permanent magnets 1635 encased in a 5-sided enclosure of mu-metal. Only the lower surface of the mu-metal enclosure is left open (e.g., the surface adjacent to the steel magnets in surface 1516. The other surfaces of the mu-metal enclosure are closed to restrict the spatial extent of the magnetic field extending from magnets 1635. The two permanent magnets 1635 in each contact 1620 are oriented to that their poles are opposed. As a result, magnetic field lines extending from the two magnets are relatively restricted spatially. Because of this, and because of the mu-metal enclosure, the magnetic fields generated by contacts 1620 do not perturb the ion beam during sample exposure. To introduce a sample onto mounting surface 1516, the sample is first mounted to the underside of sample holder 1600 in FIG. 4. Then, sample holder 1600 is placed on a mounting arm, which engages with recessed lip 1640 of holder 1600. The mounting arm (not shown in FIG. 4) is extended toward surface 1516, and rotated to ensure alignment of the conical pins with holes 1630. As the mounting arm is lowered toward surface 1516, the magnetic force between contacts 1620 and the corresponding magnets in surface 1516 fix holder 1600 in place atop surface 1516, supported by the six conical pins extending from surface 1516. In this fixed position, contacts 1620 are positioned within 500 microns of the magnets in surface 1516. The mounting arm is then carefully withdrawn, and sample holder 1600 (and the sample mounted thereon) remain fixed to surface 1516. In some embodiments, the magnets positioned in surface 1516 are permanent magnets. In certain embodiments, the magnets positioned in surface 1516 can be switched on and off (e.g., by changing the position of the magnets in surface 1516 via rotation, and/or by applying a counteracting electromagnetic field via one or more magnetic coils that balances the magnetic field of the magnets in surface 1516). Switchable magnets can be particularly advantageous when positioning sample holder 1600 relative to surface 1516. For example, with the magnets switched off, sample holder 1600 can be positioned atop the supporting conical pins that extend from surface 1516. When sample holder 1600 is in the correct position, the magnets can be switched on to lock sample holder 1600 in place relative to surface 1516. Typically, the magnetic force between contacts 1620 and the magnets in surface 1560 is sufficiently strong to prevent relative movement of sample holder 1600 at tilt angles of 45 degrees or more. As noted above, tips for ion beam sources can be produced by first forming a tip from a material such as, for example, tungsten. In some embodiments, forming the tip involves sharpening a rod (e.g., a tungsten rod) to form a sharpened tip, and field evaporating the sharpened tip to produce a desired terminal shelf of the apex of the tip. In some embodiments, it is desirable for the terminal shelf of the apex of the tip that includes only a small number of atoms (e.g., from 1 to 20 atoms). During field evaporation, the tip is usually heated, and light emanating from the tip can be observed optically (e.g., using the eye, using a light detector). In some instances, the temperature of the tip can be estimated based on the observed tip color. During field evaporation of the tip, the geometry of the tip apex can be monitored by observing the field emission pattern from the tip under an appropriate applied potential (by using heat and electrical potential during field evaporation). Observing the tip during fabrication can be difficult because the sharpening and field evaporation steps are typically performed under vacuum in a sample chamber. In addition, the tip is typically oriented such that at least some of the light goes through the ion optics (ion column) which can make it difficult to observe the light. To facilitate observation of the ion source (e.g., during field evaporation when making the tip), the sample chamber can include one or more source viewing optics fixed on a retractable positioner. FIG. 5 shows a retractable positioner 1700 configured for use with a sample chamber in an ion beam system. As shown in FIG. 5, retractable positioner is mounted within a flange 1704 of a sample chamber 1702. Positioner 1700 includes a first actuator 1706 for moving positioner 1700 in an axial direction, and a second actuator 1708 for moving positioner 1700 within a plane perpendicular to the axial direction of the positioner. Also mounted to a flange of chamber 1702 is a measurement device 1710 (e.g., a camera, or a bolometer, or a linear sensor, or another device). Positioner 1700 can include a variety of optical elements. In some embodiments, positioner 1700 includes a mirror inclined at an angle to the central axis of chamber 1702 (e.g., perpendicular to the plane of FIG. 5). The inclined mirror 1712 is configured to direct light 1714 emitted by the glowing tip to measurement device 1710, as shown in FIG. 6. Light captured by measurement device 1710 can be used to monitor the tip during fabrication. For example, in certain embodiments, measurement device 1710 can be a camera, and photons produced by the glowing tip during sharpening can be detected, by the camera to form an image of the glowing tip. By monitoring the color of the tip, for example, the temperature of the tip can be estimated. In some embodiments, positioner 1700 can include an angled mirror 1716 as discussed above, and a scintillator material 1718. The scintillator material can be positioned to convert ions produced during field evaporation of the tip to photons. The photons are then directed by angled mirror 1716 to be incident on a camera or other measurement device (e.g., measurement device 1710). In certain embodiments, positioner 1700 can include a device to measure ion current such as a Faraday cup 1720. The Faraday cup 1720 can be moved into the beam path to capture ions from the tip during field, evaporation of the tip. The ion current due to the captured ions can then be measured, and the information used to assess the progress of tip building. In some embodiments, positioner 1700 can include one or more apertures 1722. Aperture 1722 provides spatial filtering for the ion beam generated from the tip, and can be used to produce an ion beam with particular properties. When multiple apertures are present on positioner 1700, the desired ion beam properties can be selected by selecting a particular aperture. In certain embodiments, chamber 1702 does not include a positioner 1700. Instead, chamber 1702 includes an angled mirror 1724 mounted in an off-axis position within chamber 1702 to a fixed mount 1726, as shown in FIG. 7. Mirror 1724 is positioned to direct oblique light rays 1728 emerging from the tip to measurement device 1710 for observation. The position of angled mirror 1724 is selected so that the mirror does not interfere with the ion beam when the ion beam system is in use. In some embodiments, chamber 1702 includes an angled mirror 1730 mounted (via a fixed mount 1732) in the path of the ion beam, as shown in FIG. 8. Angled mirror 1730 includes a central aperture 1734 that permits the ion beam to pass through the mirror. However, the portions of the mirror surface surrounding aperture 1734 are positioned to direct optical radiation from the glowing tip to measurement device 1710 for observation. Embodiments of positioner 1700 (and also fixed mounts 1726 and/or 1732) can also include a variety of other elements to perform various beam filtering and tip observation functions. For example, positioner 1700 (and mounts 1726 and/or 1732) can include optical filters, adjustable apertures, phosphor-based devices, materials for frequency conversion of optical radiation, various types of electronic measurement devices (e.g., cameras, line sensors, photodiodes, bolometers), and, in general, any type of device that can be mounted on positioner 1700 (and/or mounts 1726 and 1732) and which is suitable for use in the environment of chamber 1702. As an example, while examples have been described in which a gas field ion source is used, other types of ion sources may also be used. In some embodiments, a liquid metal ion source can be used. An example of a liquid metal ion source is a Ga ion source (e.g., a Ga focused ion beam column). As another example, while embodiments have been described in which an ion source is used, more generally any charged particle source can be used. In some embodiments, an electron source, such as an electron microscope (e.g., a scanning electron microscope) can be used. As a further example, while embodiments have been described in which samples are in the form of semiconductor articles, in some embodiments, other types of samples can be used. Examples include biological samples (e.g., tissue, nucleic acids, proteins, carbohydrates, lipids and cell membranes), pharmaceutical samples (e.g., a small molecule drug), frozen water (e.g., ice), read/write heads used in magnetic storage devices, and metal and alloy samples. Exemplary samples are disclosed in, for example, US 2007-0158558. As an additional example, while embodiments have been disclosed in which a sample is inspected, alternatively or additionally, the systems and methods can be used to modify (e.g., repair) a sample (e.g., to repair a region of the article at or near the portion of the article exposed by the cross-section). Such modification can involve gas assisted chemistry, which can be used to add material to and/or remove material to a sample (e.g., a given layer of the sample). As an example, gas assisted chemistry can be used for semiconductor circuit editing in which damaged or incorrectly fabricated circuits formed in semiconductor articles are repaired. Typically, circuit editing involves adding material to a circuit (e.g., to close a circuit that is open) and/or removing material from a circuit (e.g., to open a circuit that, is closed). Gas assisted chemistry can also be used in photolithographic mask repair. Mask defects generally include an excess of mask material in a region of the mask where there should be no material, and/or an absence of mask material where material should be present. Thus, gas assisted chemistry can be used in mask repair to add and/or remove material from a mask as desired. Typically, gas assisted chemistry involves the use of a charged particle beam (e.g., ion beam, electron beam, both) that interacts with an appropriate gas (e.g., Cl2, O2, I2, XeF2, F2, CF4, H2O, XeF2, F2, CF4, WF6). As another example, modification of a sample can involve sputtering. In some instances, when fabricating articles, it can be desirable during certain steps to remove materials (e.g., when removing undesired material from a circuit to edit the circuit, when repairing a mask). An ion beam can be used for this purpose where the ion beam spatters material from the sample. In particular, an ion beam generated via the interaction of gas atoms with a gas field ion source as described herein can be used for sputtering a sample. Although He gas ions may be used, it is typically preferable to use heavier ions (e.g., Ne gas ions, Ar gas ions, Kr gas ions, Xe gas ions) to remove material. During the removal of material, the ion beam is focused on the region of the sample where the material to be removed is located. Examples of such inspection are disclosed, for example, in US 2007-0158558. Combinations of features can be used in various embodiments. Other embodiments are covered by the claims. |
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claims | 1. A method of generating a positive ion beam sequence for providing a prescriptive dose of high energy polyenergetic positive ions to a target volume, comprising the steps of:a) providing a plurality of beam angles, plan prescription, and dose constraints;b) providing a plan optimization process based on a beam scanning sequence;c) applying said beam scanning sequence to said beam angles, plan prescription and dose constraints to generate plan optimization results;d) comparing the plan optimization results to the plan prescription; ande) modulating the beam scanning sequence and iteratively repeating steps b), c) and d) until the plan optimization results are acceptable. 2. The method of claim 1, wherein the beam scanning sequence comprises, lateral scanning of beamlets, depth scanning or beamlets, 3D scanning of beamlets, or any combination thereof. 3. A method of providing a prescriptive dose of high energy polyenergetic positive ions to a target volume, comprising the steps of:a) providing a plurality of beam angles, plan prescription, and dose constraints;b) providing a plan optimization process based on a beam scanning sequence;c) applying said beam scanning sequence to said beam angles, plan prescription and dose constraints to generate plan optimization results;d) comparing the plan optimization results to the plan prescription;e) modulating the beam scanning sequence and iteratively repeating steps b), c) and d) until the plan optimization results are acceptable; andf) irradiating the target volume with a plurality of beamlets according to the plan optimization results. 4. The method of claim 3, wherein the beam scanning sequence comprises, lateral scanning of beamlets, depth scanning or beamlets, 3D scanning of beamlets, or any combination thereof. 5. A method of providing a proton radiation dose to a targeted region, comprising:providing a plurality of modulated polyenergetic proton beamlets; andirradiating said targeted region with said plurality of modulated polyenergetic proton beamlets. 6. The method of claim 5, wherein each of said polyenergetic beamlets is modulated, individually, according to at least one of: beamlet energy distribution, beamlet intensity, beamlet direction, beamlet area, or beamlet shape. 7. The method of claim 5, wherein at least a portion of said plurality of modulated polyenergetic beamlets is modulated in three dimensions. 8. The method of claim 5, wherein at least a portion of said plurality of modulated polyenergetic beamlets is modulated in intensity. 9. The method of claim 5, wherein at least a portion of said plurality of modulated polyenergetic beamlets is modulated in energy distribution. 10. The method of claim 5, wherein at least a portion of said plurality of modulated polyenergetic beamlets is modulated to irradiate the targeted region in the depth direction. 11. The method of claim 5, wherein said plurality of modulated polyenergetic beamlets are modulated to optimize the dose to minimize irradiation of organs external to said targeted region. 12. The method of claim 5, wherein said plurality of modulated polyenergetic beamlets are modulated to minimize irradiation of areas external to said targeted region. 13. The method of claim 5, wherein said plurality of modulated polyenergetic beamlets are modulated to maximize a prescriptive dose to said targeted region. 14. The method of claim 5, wherein said plurality of modulated polyenergetic beamlets are modulated to optimize the dose to minimize irradiation of critical structures and maximize a prescriptive dose to said targeted region. 15. The method of claim 5, wherein said plurality of modulated polyenergetic proton beamlets are provided byforming a laser-accelerated high energy polyenergetic ion beam comprising a plurality of high energy polyenergetic protons, said high energy polyenergetic protons characterized as having a distribution of energy levels;collimating said laser-accelerated ion beam using a collimation device;spatially separating said high energy polyenergetic protons according to their energy levels using a first magnetic field;modulating the spatially separated high energy polyenergetic protons using an aperture; andrecombining the modulated high energy polyenergetic protons using a second magnetic field. 16. The method of claim 5, wherein each of said modulated polyenergetic proton beamlets is modulated, individually, in energy and intensity. 17. The method of claim 5, wherein said irradiating gives rise to a desired prescriptive dose to the targeted region in both longitudinal and lateral directions relative to said polyenergetic beamlets. 18. A method of providing a positive ion radiation dose to a targeted region, comprising:providing a plurality of modulated polyenergetic positive ion beamlets; andirradiating said targeted region with said plurality of modulated polyenergetic positive ion beamlets, wherein each of said polyenergetic beamlets is modulated, individually, according to at least one of: beamlet energy distribution, beamlet intensity, beamlet direction, beamlet area, or beamlet shape. 19. A method of providing a proton radiation dose to a targeted region, comprising:providing a plurality of modulated polyenergetic proton beamlets, wherein each of said polyenergetic beamlets is modulated, individually, according to at least one of: beamlet energy distribution, beamlet intensity, beamlet direction, beamlet area, or beamlet shape; andirradiating said targeted region with said plurality of modulated polyenergetic proton beamlets, wherein said plurality of modulated polyenergetic proton beamlets maximizes said proton radiation dose to the targeted region and minimizes said proton radiation dose to areas external to the targeted region. 20. A method of providing a prescriptive dose to a targeted region in a patient, comprising:a) providing a plurality of polyenergetic proton beamlets; andb) modulating said polyenergetic proton beamlets, wherein said modulating gives rise to an acceptable dose distribution to the targeted region according to the prescriptive dose in both longitudinal and lateral directions relative to said beamlets. 21. The method of claim 20, wherein said modulating step is carried out in three dimensions. 22. The method of claim 20, wherein the intensities of said polyenergetic proton beamlets are modulated. 23. The method of claim 20, wherein the energies of said polyenergetic proton beamlets are modulated. 24. The method of claim 20, wherein said polyenergetic proton beamlets are modulated to irradiate the target in the depth direction. 25. The method of claim 20, wherein said modulating step comprises optimizing the dose to minimize irradiation of organs external to said target. 26. The method of claim 20, wherein said modulating step comprises optimizing the dose to minimize irradiation of critical structures. 27. The method of claim 20, wherein said modulating step comprises optimizing the dose distribution based on a prescribed physical or biologically equivalent dose to said target. 28. The method of claim 20, wherein said modulating step comprises optimizing the dose to minimize irradiation of critical structures and optimizing the dose distribution based on a prescribed physical or biologically equivalent dose to said target. 29. The method of claim 20, wherein said polyenergetic proton beamlets are provided byforming a laser-accelerated high energy polyenergetic ion beam comprising a plurality of high energy polyenergetic protons, said high energy polyenergetic protons characterized as having a distribution of energy levels;collimating said laser-accelerated ion beam using a collimation device;spatially separating said high energy protons according to their energy levels using a first magnetic field;modulating the spatially separated high energy polyenergetic protons using an aperture; andrecombining the modulated high energy polyenergetic protons using a second magnetic field. 30. The method of claim 20, wherein the energies and intensities of said polyenergetic proton beamlets are modulated. 31. A method of providing a positive ion radiation dose, comprising:a) providing a plurality of polyenergetic positive ion beamlets; andb) modulating said polyenergetic positive ion beamlets, wherein said modulating gives rise to a desired dose distribution based on a prescribed dose to a target in both longitudinal and lateral directions relative to said beamlets. 32. A method of providing intensity modulated proton therapy to a targeted region in a patient, comprising:providing a plurality of high energy positive ion beamlets;modulating at least one of the high energy positive ion beamlets in depth relative to the patient to provide a depth-modulated beamlet;modulating at least one of the depth-modulated beamlets in a lateral direction relative to the patient to provide a lateral-modulated beamlet; andirradiating said targeted region with at least one of the lateral-modulated beamlets to the patient. 33. The method of claim 32, wherein said plurality of high energy positive ion beamlets comprise high energy polyenergetic positive ions. 34. The method of claim 33, wherein said plurality of high energy positive ion beamlets comprise high energy polyenergetic protons. 35. The method of claim 32, wherein said plurality of high energy positive ion beamlets comprise high energy monoenergetic positive ions. 36. The method of claim 35, wherein said plurality of high energy positive ion beamlets comprise high energy monoenergetic protons. 37. The method of claim 18, wherein said polyenergetic positive ion beamlets are provided byforming a laser-accelerated high energy polyenergetic ion beam comprising a plurality of high energy polyenergetic positive ions, said high energy polyenergetic positive ions characterized as having a distribution of energy levels;collimating said laser-accelerated ion beam using a collimation device;spatially separating said high energy polyenergetic positive ions according to their energy levels using a first magnetic field;modulating the spatially separated high energy polyenergetic positive ions using an aperture; andrecombining the modulated high energy polyenergetic positive ions using a second magnetic field. 38. The method of claim 32, wherein said polyenergetic proton beamlets are provided byforming a laser-accelerated high energy polyenergetic ion beam comprising a plurality of high energy polyenergetic protons, said high energy polyenergetic protons characterized as having a distribution of energy levels;collimating said laser-accelerated ion beam using a collimation device;spatially separating said high energy polyenergetic protons according to their energy levels using a first magnetic field;modulating the spatially separated high energy polyenergetic protons using an aperture; andrecombining the modulated high energy polyenergetic protons using a second magnetic field. |
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summary | ||
048204773 | abstract | A method of decreasing the danger associated with nuclear reactors is disclosed. According to the method, the coolant is treated to remove deuterium to prevent formation of dangerous tritium. The preferred process uses a distillation colummn to continuously remove heavy and intermediate-weight water from a bleed stream. Light water is returned to the coolant circuit. |
052767183 | summary | BACKGROUND OF THE INVENTION The present invention relates to a control blade for use in nuclear reactors for adjusting and controlling the power of a boiling water reactor or the like, and, more particularly, to an excellent reactivity and long-lived type control blade for nuclear reactors capable of controlling undesirable swelling of a neutron absorber or capable of preventing deterioration in the mechanical and physical life if swelling takes place. Since the neutron absorption power (capacity) of a control blade for use in boiling water nuclear reactors is gradually deteriorated when it absorbs neutrons, the control blade must be taken out from the core of the nuclear reactor after it has been used for a predetermined period so as to be replaced by a new control blade. However, the above-described replacement work must be performed while shutting down the operation of the nuclear reactor, causing a large scale work to be performed which takes a too long time. Therefore, the time in which the operation of the nuclear reactor must be shut down takes a too long time, causing the availability to be deteriorated. What is even worse, there is a risk for operators to be exposed to radiation. Furthermore, since the used control blade is a large and strong radioactive waste disposal, there recently arises a desire to lengthen the life of the control blade. As a result, a variety of novel long-lived type control blades for nuclear reactors have been developed, resulting a kind of them to be put into practical use. The inventor of the present invention has promptly recognized the necessity of realizing a long-lived type control blade and thereby has disclosed a control blade for nuclear reactors for the purpose of lengthening the life thereof in Japanese Patent Laid-Open No. 53-74697 (Japanese Patent Publication No. 59-138987). The control blade for nuclear reactors according to the above-made disclosure is basically arranged in such a manner that a long-lived type neutron absorber exemplified by Hf metal or an Ag-In-Cd alloy is, in place of a boron compound, disposed in a portion which is exposed to a relatively large amount of neutrons. A control blade for nuclear reactors is detachably inserted from a lower portion of the core into a gap having a cross-shaped lateral cross section and formed between fuel assemblies each of which is a set composed of four fuel assemblies loaded in the core portion of a nuclear reactor. The front portion of insertion and the outer end portion (the outer side end portion of the wing) of the control blade for nuclear reactors are exposed to a particularly large amount of neutrons. Therefore, hafnium (Hf), the neutron absorption power (capacity) of which cannot be largely deteriorated even if it is exposed to a large amount of neutrons, is disposed in the above-described portions so as to lengthen the life of the control blade for nuclear reactors. Furthermore, cheap and light boron carbide (B.sub.4 C) is disposed in the other portion of the control blade. A conventional control blade for nuclear reactors is basically arranged as shown in FIGS. 34 to 36 in such a manner that a plurality of tie members 1 each of which has a cross-shaped connecting portion are disposed in the axial direction at predetermined intervals. Furthermore, four wings 2 each of which is formed into an elongated rectangular plate are secured to the above-described connecting member 1 in such a manner that the four wings 2 form a cross-shape. Reference numeral 3 represents a handle connected to the front portions of the four wings 2. Each of the wings 2 has-a plurality of accommodating holes 2a formed in its widthwise direction, each of the accommodating holes 2a being formed in line in the lengthwise direction of the wing 2. In the accommodating hole 2a formed in the front insertion portion of the wing 2, a long-lived type neutron absorber 3a composed of Hf is disposed. Furthermore, a neutron absorber 4 made of B.sub.4 C powder is enclosed in the residual accommodating holes 2a. In the outer side end portion (periphery) of the wing 2 which corresponds to the outer periphery of the control blade A for nuclear reactors, a space 2b is formed in the lengthwise direction of the wing 2 in such a manner that it is communicated with each of the accommodating holes 2a. In the above-described space 2b, a long-lived type neutron absorber 3b composed of Hf is disposed to close an end portion of each of the accommodating holes 2a. The neutron absorber 3b acts to prevent the B.sub.4 C powder drop from the accommodating holes 2a. A stainless steel member 5 for use at the time of welding work is disposed between the neutron absorber 3b and the outer periphery of the wing 2. When the wing 2 thus-arranged is assembled, the neutron absorbers 3a and 4 are inserted (injected) into the accommodating hole 2a through an opening portion 2c (FIG. 35) formed at a position confronting the outer periphery of the wing 2. Then, the neutron absorber 3b and the stainless steel member 5 are placed in the space 2b before a pair of plate portions 2d confronting each other in the opening portion 2c are bent inward so as to be closed by welding. Since the melting point of the neutron absorber 3b made of Hf is 2200.degree. C. which is considerably higher than the melting point 1400.degree. C. of the stainless steel member 5, the neutron absorber 3b is not melted at the time of the welding work but is held in the outer periphery of the wing 2 made of stainless steel. Therefore, the undesirable mixture of Hf atoms of the neutron absorber 3b with the metal present in the portion to be welded can be prevented. As a result, sound weld portion can be obtained. It is preferable that range 1.sub.1 (see FIG. 34) in which the long-lived type neutron absorbers 3a are disposed 3 cm or longer and as well as 35 cm or shorter from the front insertion portion of the wing which constitutes the control blade for nuclear reactor. If it is shorter than 3 cm, the B.sub.4 C powder which constitutes the neutron absorber 4 is undesirably placed in the region which is exposed to a large amount of neutrons. On the contrary, if it is longer than 35 cm, the reactivity worth will be deteriorated at the time of shutting down the nuclear reactor because Hf displays insufficient neutron absorption effect in comparison to B.sub.4 C. Furthermore, the expensive Hf is excessively used and its weight is heavy, causing an economical disadvantage to be taken place and the overall weight of the control blade for nuclear reactors to be increased undesirably in comparison to the conventional control blade for nuclear reactors. It is preferable that the length of range 1.sub.2 of the neutron absorber 3b disposed in the outer periphery of the wing 2 be about 0.5 to, 2 cm. If it is shorter than 0.5 cm, the B.sub.4 C powder which constitutes the neutron absorber 4 is undesirably placed in the region which is exposed to a large amount of neutrons. If it exceeds 2 cm, Hf which constitute the neutron absorber 3b is undesirably placed in the region (the region adjacent to the central portion of the wing) in which the value of the neutron flux has been reduced, causing the problem similar to the above-made description to arise. The inventor of the present invention has, in Japanese Patent Laid-Open No. 1-202691, disclosed a novel control blade for nuclear reactors arranged in such a manner its structure is similar to that shown in FIG. 34 and an Hf diluted alloy which is an alloy of Hf and zirconium (Zr) or an alloy of Hf and titanium (Ti) is used in place of stainless steel. Hafnium forms an all-solid solution type alloy in association with Zr or Ti at an arbitrary ratio. Although a fact is well known that Hf, Zr and Ti are able to maintain satisfactory soundness in nuclear reactors, another fact is known that they absorbs hydrogen, thereby forms a hydride and will generate swelling, which is the cubical expansion, in a state where the quantity of hydrogen is excessively large but oxygen is insufficient. Hf is an excellent neutron absorber possessing multiple types of isotopes and it is known as a typical long-lived type neutron absorber because it is able to prevent the deterioration in the neutron absorbing performance even if it is exposed to neutrons. Furthermore, Hf has a characteristic of particularly absorbing resonance neutrons and its neutron absorption power (capacity) is not rapidly deteriorated even if it is diluted by a diluent to a certain degree. As described above, although Hf possesses the excellent nuclear neutron-absorbing characteristic, it suffers from an excessively large density (about 13.1 g/cm.sup.3). Therefore, there arises a problem in that it cannot be easily employed as a material for the control blade for the conventional nuclear reactors. On the other hand, Zr has a small density (6.5 g/cm.sup.3) and it is able to form an excellent alloy in association with Hf as described above. Also Ti has a small density (4.5 g/cm.sup.3) and it is able to form an excellent alloy with Hf. Therefore, an alloy of Hf and Zr or an alloy of Hf and Ti (since Zr or Ti serves as a diluent in view from Hf, they are called diluted alloy in this specification) is able to maintain excellent characteristics in nuclear reactors. Furthermore, the neutron absorption power is not deteriorated in comparison to the structure in which Hf is employed. Furthermore, the density of the diluted alloy can be reduced so that the density of the level possessed by stainless steel (about 8 g/cm.sup.3) can easily be realized. Therefore, a control blade for nuclear reactors which can be adapted to conventional nuclear reactors and which is constituted similarly to that shown in FIG. 34 can be constituted. In this case, the stainless steel member for welding and represented by reference numeral 5 can be omitted from the structure shown in FIGS. 34 to 36. Therefore, it might be feasible to employ a member made of the above-described diluted alloy as the member for performing the welding work. However, as described above, Hf or the Hf alloy will absorb hydrogen and generate swelling when an excessively large quantity of hydrogen is present and the quantity of oxygen is insufficient. The above-described novel control blade for nuclear reactors (see Japanese Patent Laid-Open No. 1-202691) is arranged in such a manner that accommodating holes are formed in the Hf diluted alloy sheet and the B.sub.4 C (boron carbide) powder is enclosed in the accommodating holes. .sup.10 B of B.sub.4 C reacts with neutrons to generate .sup.4 He and .sup.7 Li and as well as .sup.3 T (tritium). If the amount of neutrons exposed to the control blade increases, the amount of .sup.3 T produced cannot be neglected. Although the major portion of .sup.3 T is left in B.sub.4 C, a portion of it is removed from B.sub.4 C. Since tritium is hydrogen, it can be absorbed by Hf, Zr or Ti. Therefore, there arises a problem in that the soundness of Hf, the Hf-Zr alloy or the Hf-Ti alloy which also serves as the structure member of the Control blade will be deteriorated. The control blade for nuclear reactors of the type described above is arranged in such a manner that a multiplicity of the accommodating holes are formed in a sheet made of a diluted alloy prepared by diluting Hf by Zr or Ti serving as a diluent and the boron compound is enclosed in a portion or the major portion of the accommodating holes. There is a fear that tritium (.sup.3 T) produced when boron reacts with neutrons and hydrogen produced due to a radiolysis of water introduced at the manufacturing process move between accommodating holes and thereby hydrides HfH.sub.2 (Hf.sup.3 T.sub.2) , ZrH.sub.2 (Zr.sup.3 T.sub.2) ,TiH.sub.2 (Ti.sup.3 T.sub.2) or the like is produced with Hf, Zr or Ti. It leads to cubical expansion (swelling) due to the increase in the volume from the original Hf alloy. Therefore, there is a possibility that the stress will be generated in the Hf-Zr alloy or the Hf-Ti alloy from the inner surface of the accommodating hole, the Hf-Zr alloy or Hf-Ti alloy serving as the structure material. Another long-lived type control blade has been disclosed by the inventor of the present invention in Japanese Patent Publication No. 1-45598 (Japanese Patent Laid-Open No. 57-171291). The control blade for nuclear reactors according to the above-made disclosure employs a neutron absorbing rod. The neutron absorbing rod is arranged in such a manner that boron carbide (B.sub.4 C) powder and a Hf metal rod or an Ag-In-Cd alloy rod are enclosed in an elongated covered pipe made of stainless steel. Furthermore, metal wool is disposed between the above-described two elements. In the front end portion which is exposed to a large amount of neutrons when viewed in the direction into which the control blade is inserted, the Hf metal rod or the Ag-In-Cd alloy rod is placed, while the B.sub.4 C powder is enclosed in the end portion opposing the front insertion portion because the amount of the neutron exposure is relatively small in this portion. However, a fact has been found from the ensuing research that there is a room for improvement in the neutron absorbing rod, which is arranged in such a manner that both the boron compound and the Hf metal or the Ag-In-Cd alloy rod are enclosed. That is, a portion of tritium (.sup.3 T) produced as a result of boron-neutron reaction in the boron compound is absorbed into the surface layer of the Hf metal or the Ag-In-Cd alloy, which is sealed together, causing swelling to be generated in the neutron absorber. Therefore, the soundness of the covered pipe can be deteriorated. Furthermore, a portion of water left in the covered tube at the time of the manufacturing process is changed into hydrogen due to radiolysis. Furthermore, since hydrogen is able to transmit the stainless pipe, hydrogen generated due to the radiolysis of the reactor core water can be introduced into the covered pipe. The above-described introduction of hydrogen will cause swelling since it can be absorbed into the surface layer of the Hf metal or the Ag-In-Cd alloy similarly to the above-described case about tritium. SUMMARY OF THE INVENTION A major object of the present invention is to provide a large reactivity and long-lived type control blade for nuclear reactors capable of effectively preventing generation of a swelling phenomenon in a long-lived type neutron absorber thereof to improve soundness and thereby lengthening the life while maintaining the mechanical life. Another object of the present invention is to provide a long-lived type control blade for nuclear reactors capable of, even if hydrogen or tritium, which easily reacts with Hf, Zr or Ti, is present in accommodating holes or the like formed in the wing, restricting production of hydride or preventing generation of stress in accommodating holes if hydride is produced, capable of improving soundness and lengthening the life. Another object of the present invention is to provide a neutron absorbing rod for use in the long-lived type control blade for nuclear reactors. Another object of the present invention is to provide a neutron absorbing rod capable of preventing generation of a swelling phenomenon in a neutron absorber, reducing stress generated in a covered pipe due to the swelling if takes place and maintaining soundness. In order to achieve the above-described objects, a control blade for use in nuclear reactors according to the present invention comprises: an upper structure means; a lower structure means; a central tie means disposed between the upper structure means and the-lower structure means; a wing means having a plurality of wings connected to each other by the central tie means in such a manner that a plurality of the wings are disposed to form a cross-shape lateral cross section; and neutron absorber means enclosed in at least a major portion of a multiplicity of accommodating holes formed in a widthwise direction of each wing and in line disposed in a lengthwise direction of the wing, wherein the wing means is arranged in such a manner that each of the wings is constituted by a plate member made of hafnium metal, a hafnium alloy composed of hafnium and zirconium or titanium, or an alloy the main component of which is zirconium or titanium, the neutron absorber means comprises a long-lived type neutron absorber which is enclosed in the accommodating holes formed in the front insertion portion of the wing which is exposed to a large amount of neutrons and made of hafnium, metal the main component of which is hafnium, a silver-indium-cadmium Ag-In-Cd alloy and a neutron absorber which is inserted into at least the major portion of the residual accommodating holes and which contains boron, and a mixture of a material containing boron and at least one hydrogen absorber composed of at least either zirconium particles or hafnium powder is enclosed in the accommodating holes among the accommodating holes for accommodating the neutron absorber containing boron disposed in a range from a front insertion portion, which is exposed to a large amount of neutrons, to 1/4.multidot.L of the height L of an effective heating portion of a reactor core. In order to achieve the above-described objects, a control blade for use in nuclear reactors according to the present invention comprises: an upper structure means; a lower structure means; a central tie means for establishing a connection between the upper structure means and the lower structure means; a sheath plate means connected to the central tie means and having a U-shaped lateral cross section to constitute wings disposed to form a cross-shaped lateral cross section; and a neutron absorber rod means accommodated in the sheath plate means in line, wherein the neutron absorber rod means is constituted by inserting the long-lived type neutron absorber made of hafnium metal, metal the main component of which is hafnium or a silver-indium-cadmium (Ag-In-Cd) alloy or the like into a covered pipe while forming a gap or sleeve around the neutron absorber or while forming an oxide film on the surface of the neutron absorber. In order to achieve the above-described objects, a neutron absorbing rod according to the present invention comprises: an tubular covering(cladding) pipe; a plug means for sealing two end portions of the covering pipe; and a neutron absorber means accommodated in the covering pipe, wherein said neutron absorber means comprises a long-lived type neutron absorber enclosed in one side of the covering pipe, which is exposed to a large amount of neutrons, and made of hafnium metal, alloy the main component of which is hafnium or a silver-indium-cadmium alloy and a neutron absorber enclosed in the residual region and composed of a boron compound, and the long-lived type neutron absorber is enclosed in the covering pipe while forming a gap or a sleeve around the long-lived type neutron absorber or while forming an oxide film on the surface of the long-lived type neutron absorber. According to the present invention constituted as described above, a boron compound such as boron carbide (B.sub.4 C) and europium hexaboride (EuB.sub.6) and a hydrogen absorber composed of at least either pure zirconium (Zr) particle exhibiting an excellent hydrogen absorbing efficiency or hafnium (Hf) powder (since Hf displays lower activity than that of Zr, it is preferable that the particle size of it be small). Therefore, tritium (.sup.3 T) atoms which are produced as a direct or indirect reaction between boron with neutrons and active hydrogen (H) atoms which are produced as a radiolysis of water introduced when the control blade has been manufactured can be effectively absorbed. Therefore, the hydrogenative reaction at the inner surface of the accommodating hole formed in the wing can be effectively prevented. Furthermore, another hydrogenative reaction of the Hf metal or the Ag-In-Cd alloy to be inserted into a portion of the accommodating holes formed in the wing can also be effectively prevented. Since the volume of the Zr particles and the Hf powder increases their volume due to the hydrogen absorption, the enclosing mixture density of the boron compound and at least either the Zr particles or the Hf powder must be adjusted while previously estimating the volume increase. Furthermore, a zirconium (Zr) sheet exhibiting satisfactory hydrogen absorbing efficiency and reduced hardness is, in a manner to form a sleeve, placed on the inner surface of the accommodating hole formed in the wing. In addition, the boron compound such as B.sub.4 C and EuB.sub.6 is enclosed in the sleeve. In this case, a manufacturing process may be employed which is arranged in such a manner that a tubular member made of Zr is used to surround it before they are inserted into the accommodating hole. As a result, a gap having a certain size is necessarily formed between the tubular member made of Zr and the inner surface of the accommodating hole. Therefore, if swelling takes place because the tubular member made of Zr absorbed hydrogen, the above- described gap absorbs the cubic expansion, causing the stress induction start moment in the accommodating hole can be significantly delayed. In a case where no hydrogen or little hydrogen has been absorbed since the density of hydrogen in the tubular member made of Zr is low, the tubular member made of Zr or the above-described gap absorbs the cubic expansion due to the swelling of the boron compound. Therefore, the moment at Wee which the stress acts on the accommodating hole can be significantly delayed. Furthermore, the Hf metal rod or the Ag-In-Cd alloy rod to be inserted into the accommodating hole formed in the wing is longitudinally divided into pieces. A Zr strip is interposed between the above-described pieces. Therefore, if stress acts on the inner surface of the accommodating hole due to some reason, the strip can be crushed, and the generation of excessively large stress can be prevented. Since Zr exhibits satisfactory hydrogen absorbing performance, it absorbs hydrogen if the density of hydrogen has been raised so that the density can be reduced. As a result, swelling generated due to the hydrogen absorption by the insertion member such as the Hf metal rod or the Ag-In-Cd alloy rod to be inserted into the accommodating hole can be significantly prevented. Furthermore, swelling which will take place due to the hydrogen absorption by Hf, the Hf-Zr alloy or the Hf-Ti alloy which forms the accommodating hole can be significantly delayed. Furthermore, the tubular members made of Zr are inserted into a portion of the accommodating holes formed in the vicinity of front insertion portion. The above-described tubular member is formed into a non-sealed type and a hollow shape to form a gas plenum. If hydrogen or tritium is contained in the gas, it can be absorbed by the Zr tubular member. Therefore, the absorption of hydrogen or tritium into the inner surface of the accommodating hole can be prevented. As a result, the soundness of the accommodating hole can be maintained. That is, it possesses a function as a hydrogen getter and a function as a gas plenum. The Hf or the Hf alloy or the Ag-In-Cd alloy constituting the long-lived type neutron absorber to be enclosed in the neutron absorbing rod for use in the control blade for nuclear reactors will absorb, to the surface thereof, hydrogen generated due to the radiolysis of water left when the neutron absorbing rod was manufactured, hydrogen supplied from the nuclear core water and introduced after it has transmitted the covering pipe and tritium generated and discharged from the reaction taken place between boron and neutrons, in a case where the boron compound is enclosed together. However, according to the present invention, a gap is formed between the long-lived type neutron absorber and the covering pipe, the long-lived type neutron absorber is surrounded by the thin sleeve made of zirconium, hafnium, titanium or stainless steel, or an oxide film is formed on the surface of the long-lived type neutron absorber before it is accommodated in the covering pipe. Therefore, the generation of stress in the covering pipe due to the swelling of the long-lived type neutron absorber can be significantly prevented. That is, in a case where the gap is formed between the long-lived type neutron absorber and the covering pipe, the influence of the swelling, if taken place, upon the covering pipe can be significantly reduced. In a case where the thin sleeve is formed around the long-lived type neutron absorber and the sleeve is made of Zr, Hf or Ti, the sleeve serves as the hydrogen getter. Therefore, the swelling of the long-lived type neutron absorber due to the hydrogen absorption can be prevented. Although the sleeve member encounters swelling, the influence upon the covering pipe can be reduced because the gap of a certain size, which serves as the space capable of absorbing swelling, is necessarily formed between the inner surface of the tubular pipe and the outer surface of the sleeve and between the inner surface of the sleeve and the surface of the long-lived type neutron absorber. In the case where the sleeve is made of stainless steel, the long-lived type neutron absorber will generate swelling. However, the formed gap serves as the swelling absorbing space, causing the generation of stress in the covering pipe can be significantly reduced. In the case where the oxide film is formed on the surface of the long-lived type neutron absorber, the oxide film serves as a barrier against the hydrogen absorption. Therefore, the generation of swelling in the long-lived type neutron absorber can be prevented. In the case where both the above-described long-lived type neutron absorber and the boron compound are enclosed in the covering pipe, the Zr particles or the Hf powder serving as the hydrogen getter is mixed with the boron compound powder placed in a region which is exposed to a relatively large amount of neutrons. As a result, tritium generated when the boron compound is exposed to neutrons is caused to be absorbed by the Zr particles or the Hf powder. Therefore, the discharge of tritium can be prevented, causing swelling of the long-lived type neutron absorber to be prevented. Although the boron compound generates swelling due to He gas generated due to the reaction of the boron compound with neutrons, the generation of stress acting on the covering pipe can be prevented by adjusting the density of enclosing the boron compound. Another method can be employed in which the boron compound present in a region which is exposed to a relatively large amount of neutrons is enclosed in the inner pipe made of Zr, Hf or stainless steel. In a case where the inner pipe is made of Zr, it is able to serve as the hydrogen getter or a stress relaxer. In the case where it is made of Hf, it possesses a functions as the hydrogen getter and the stress relaxer and as well as a function as the long-lived type neutron absorber. The inner pipe made of stainless steel serves as the stress relaxer realized by forming the gap. However, it is preferable in this case that Zr particles or Hf powder be mixed with the boron compound. Also in this case, the diffusion of tritium discharged from the boron compound into the long-lived type neutron absorber can be substantially prevented. The swelling of the boron compound generated due to the He gas can be absorbed by the inner pipe so that stress generated in the covered pipe is significantly reduced. Therefore, according to the present invention, the soundness of the covered pipe can significantly be improved. Other and further objects, features and advantages of the invention will be appear more fully from the following description. |
claims | 1. A flexible penetration attachment for resiliently interconnecting a suction line through an aperture in a wall of a pool of liquid, comprising: a boot defining an outer circumference of the aperture, the aperture having a first diameter; first and second fasteners, a suction pipe having an outer surface and an outer diameter, said suction pipe extending through and movable within the aperture, said outer diameter being less than said first diameter such that a space is defined between said outer circumference and said outer surface; and a resilient seal having a first end and a second end, wherein said first end is fixedly secured to said movable suction pipe outer surface by the first fasteners extending through said resilient seal and said second end is fixedly secured to said aperture outer circumference by the second fasteners extending through said resilient seal. 2. A flexible penetration attachment as in claim 1 , wherein said resilient seal is generally U-shaped. claim 1 3. A flexible penetration attachment as in claim 1 , wherein said space is annular. claim 1 4. A flexible penetration attachment as in claim 3 , wherein said space is sized so that said suction pipe moves a pre-determined transverse, radial or rotational distance within said space in response to a force. claim 3 5. In a nuclear power plant having at least one suction line in communication with liquid in a wet-well pool thorough an aperture in a wall of the wet-wall, a flexible penetration attachment for connecting the suction line to the aperture in the pool, comprising: a boot defining an outer circumference of the aperture; first and second fasteners; a suction pipe having an outer surface, said suction pipe extending through and movable within the aperture such that a space is defined between said aperture outer circumference and said suction pipe outer surface; and a resilient seal within said space, said resilient seal having a first end and a second end, wherein said first end is fixedly secured to said movable pipe outer surface by the first fasteners extending through said resilient seal and said second end is fixedly secured to said outer circumference by the second fasteners extending through said resilient seal. 6. A flexible penetration attachment as in claim 5 , wherein said resilient seal is generally U-shaped. claim 5 7. A flexible penetration attachment as in claim 5 , wherein said first and second ends are secured by straps. claim 5 8. A flexible penetration attachment as in claim 5 , wherein said space is annular. claim 5 9. A flexible penetration attachment as in claim 8 , wherein said space is sized so that said suction pipe moves a pre-determined transverse, radial or rotational distance within said space in response to a force. claim 8 10. A flexible penetration attachment as in claim 5 , wherein said boot is separately fabricated. claim 5 11. A flexible penetration attachment as in claim 1 , wherein said first and second ends are secured by straps. claim 1 12. A flexible penetration attachment as in claim 11 , wherein said first and second fasteners extending thorough said resilient seal also extend through said straps. claim 11 13. A flexible penetration attachment as in claim 7 , wherein said first and second fasteners extending through said resilient seal extend through said straps. claim 7 14. A flexible penetration as in claim 1 , wherein said resilient seal is fabricated from an elastomeric compound. claim 1 15. A flexible penetration as in claim 1 , wherein said first fasteners extending through said resilient seal also extend through said suction pipe. claim 1 16. A flexible penetration as in claim 1 , wherein said fasteners extending through said resilient seal are bolts. claim 1 17. A flexible penetration as in claim 5 , wherein said resilient seal is fabricated from an elastomeric compound. claim 5 18. A flexible penetration as in claim 5 , wherein said first fasteners extending through said resilient seal also extend through said suction pipe. claim 5 19. A flexible penetration as in claim 5 , wherein said fasteners extending through said resilient seal are bolts. claim 5 |
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description | The present invention relates to electronic emission devices emitting electron beams, and more particularly a multibeam emission device comprising several electron emission sources capable of putting out several electron beams in parallel, with a system for focussing these electron beams. In the industrial sector, the electronic emission devices are utilised as means for observation and microscopic analysis, better known as scanning electron microscopy (SEM), such as insulation and etching (lithography) means, especially in integrated circuit lithography, or as testing and measuring means, or again as writing or storage means. In industrial applications, monosource electronic emission devices are still being used, which emit a single electron beam. Industrial applications are considerably limited by the utilisation of monosource devices offering only a small accessible field surface and a low etching/writing speed for integrated circuits inherent in the slow rate of electronic beam scanning. In order to be free of such constraints, current development is leaning towards <<parallelisation>> of several sources, each scanning a less significant surface. In the field of multibeam electronic emission devices, two distinct types of structures are known, the assembled structure and the monolithic structure. The document entitled <<Arrayed miniature electron beam columns for high throughput sub-100 nm lithography>> written by T. H. P. Chang and D. P. Kern, published in the <<Journal of Vacuum Science Technology (American Vacuum Society)>>, volume B10(6), pages 2743 to 2748, publishing in November/December 1992, describes a multibeam electronic emission device 1 made up of individual miniature columns 10 having a structure assembled in a matrix, such as illustrated in FIG. 1A. As detailed in FIG. 1B, each column 10 is made up of a point 12 with electron field emission, connected to an extraction grid 13, a diaphragm 14 and a series of Einzel microlenses 15, 16, 17 to focus the electron beam, and to a group of several lateral deflectors 18 for deflecting the beam in order to obtain a point of focus of electrons which scans a small surface on a substrate pellet 1000 corresponding to the integrated circuit chip 100 to be etched. Each column comprises an assembly of electrostatic microlenses made of silicon, independently made by MEMS technology (in English <<Micro Electro Mechanical System>>). Each column further comprises a double retroaction system, on the one hand between the field emission point 12 and the scanning microscope 11 with tunnel effect, and on the other hand between the sample 1000 and the STM microscope to control and rectify the position of the emitting point 12 and the focus of the beam. A certain number of these individual independent columns 10 is combined and assembled in a checkered or mosaic layout 1 for etching in parallel a series of integrated circuits chips. The drawback to such a structure is that no element is integrated, neither axially to the core of a column 10, nor at a transversal level between the adjacent columns 1. The density of emitters thus remains low and the writing time is long. The matricial monolithic structures are able to integrate a greater number of emission sources of electron beams in a single device of given size and thus envisages vastly greater writing speeds. Typically, pitches de a few tens of microns can be obtained. The document WO 89/11157 describes a multibeam electronic emission device with integrated matricial structure on a substrate. As illustrated in FIG. 2, each emitting source 21 of an electron beam 29 comprises only one electron emitting point 22 (cathode) and an annular grid 23 for extraction of electrons, the sources 21 being connected to a primitive focussing system formed by a metallic plate 24 to the rear of the resistive substrate 20 which generates field lines 25,25′ projecting to the front of the substrate, except in front of the sources themselves. The drawback of this focussing system is being placed in proximity and above all in a rear position relative to the emission sources of the electron beam. It actually does not comprise any adequate focussing optics arranged on the trajectory of the beam (neither electrode, nor focussing lens). It therefore cannot attain resolutions of less than 50 nm. The document U.S. Pat. No. 5,430,347 describes an individual emission device of an electron beam intended for displaying images and made by depositing layers and depositing metallisation on a substrate illustrated in FIG. 3. The source comprises an emitting point, an annular grid and one or two focussing grids, a luminescent cathode screen being arranged opposite, in front of the source. The document U.S. Pat. No. 5,430,347 announces resolution of an image point in the focal plane of a diameter of ten micrometers at a distance of one millimeter of focussing (spot from 10 μm to 1 mm). Such resolution is quite insufficient for applications such as electronic microscopy or the production of integrated circuits, a field in which the aim is to obtain a resolution clearly less than a micrometer, of about few tens of nanometers, which is the order of magnitude of the patterns to be made. The document entitled <<Digital Electrostatic Electron-Beam Array Lithography>> by L. R. Baylor et al. published in the <<Journal of Vacuum Science Technology>>, volume B20 (6), appearing in November/December 2002, describes a multibeam matrix structure for electron emission integrated on a silicon substrate and illustrated in FIGS. 3A and 3B. Each beam emission site 31 of the matrix 30 comprises a localised source 32 formed by an emitting point made of nanometric carbon, in the axis of which is superposed a series of annular electrodes 33,34,35,36. The first electrode 33 is an extraction grid, whereof the function is to extract electrons from the emitting point 32 forming the cathode. The function of the following successive electrodes 34,35,36, subjected to potentials VE, VC, VA, is to focus the beam 39 of emitted electrons on an anode 38 facing the device. The resolution specified for this device is 50 nm in diameter at a focal distance W of 100 μm only. The disadvantage of all these monolithic structures is that they require extremely advanced alignment control of etching of layers. In particular, the different successive levels of metallisation of electrodes 33,34,35,36 must be etched with openings and very precise alignment, one above the other, and this at a depth of 4 μm, particularly delicate in auto-aligned microelectronic technology. Another problem, the depositing of each emitter 32 at the bottom of the cavity 31′ formed by the stacking of the annular electrodes, can be solved only by depositing after the cavity is fully finished. The emitter must be precisely aligned and oriented according to the axis of the openings of the electrodes and also limited in height. Furthermore, this depositing must be controlled homogeneously for all the emitters of the matrix to provide homogeneous optical behaviour during focussing of each source, which creates major constraints on the depositing. Furthermore, the field-effect emitters inherently have emission homogeneities between emitters (divergence of the beams varies from one source to the other). In the same way, the emission from each field-effect source exhibits instabilities over time, which are generally impossible to foresee and control. These inhomogeneities and instabilities will be resulted, in the case of the device presented by Baylor, in variation in the resolution of an emitter over time, as well as by inhomogeneity in resolution between the different emitters, which is incompatible with high-resolution applications. In fact, for this type of application, it is necessary to have a stable spot size over time, which is homogeneous between each source. The object of the invention is thus to provide a programmable multibeam electronic emission device, compact without the abovementioned disadvantages and with stable optical resolution over time and homogeneous between the emitters. In particular, an objective of the invention is to provide a set of sources of electron beams whereof the divergence is low and stable over time. Another objective of the invention is to be able to utilise this device to form a set of electronic spots of nanometric dimension. To solve these problems, the invention provides hybridising a diaphragm structure, or means forming a diaphragm, a structure comprising a plurality of emission sources of electron beams or means forming an electron emission source. On the one hand, this contributes an improvement to the problem of resolution limitation connected to the excessive divergence of each emitting source, and, on the other hand, a solution to the problems of instability and inhomogeneity of emitting sources or angular openings over time and from one source to the other. The hybridisation device aligns and separates, at a given distance, the diaphragm structure relative to the structure of electron emission sources. On the other hand, the invention ensures that the diaphragm structure simultaneously acts as an electrostatic focussing system. This means that each diaphragm opening is polarised and shaped to form an electrostatic lens. In addition, the invention provides utilising this hybridised emission source in a magnetic focussing system known here as magnetic or electrostatic or electromagnetic projection optics. The invention thus provides hybridising a diaphragm electrode structure on a structure of matrix base of emitters implanted in a substrate. The electrode structure especially acts as a diaphragm for each electron beam emitted by each corresponding source with field effect. According to one embodiment, the matrix emitter structure can be a simple base structure, not comprising a focussing system, that is, without an integrated focussing level in the substrate. The invention applies in particular to matrix emitter structures in which the emission sources are arranged according to a network with micrometric steps, that is, with a space between sources of about one micrometer to one millimeter. Making the matrix emitter structure is advantageously greatly simplified according to the invention. The invention is made with an electronic emission device having several electron beams, comprising a first structure, or first means, comprising a plurality of emission sources of electron beams hybridised with a second structure, or second means, comprising a plurality of diaphragm openings. According to the invention the second structure is formed by an electrode or a membrane, metallic or conductive. According to the invention, hybridisation between the first structure of emission of electron beams and the second structure of diaphragm electrode is carried out by interposition of metallic balls, especially balls made of an alloy of fusible metals or balls made of gold. Alternatively, hybridisation between the first and the second structure can be carried out by the interposition of one or more anisotropic conduction films. Preferably, the first structure comprises a periodic arrangement of electron emission sources, the first structure having for example a matricial arrangement or a multilinear arrangement or a linear arrangement; the arrangement can be periodic and regular or irregular. Similarly, the second structure preferably has a periodic arrangement of the diaphragm openings, the second structure for example having a matricial arrangement or a multilinear arrangement or a linear arrangement, periodic and regular or irregular. This arrangement can be similar to that of the first structure or different according to the application. It is provided that at least one side of the electrode diaphragm structure is dipped in an electric acceleration field of electrons. The device according to the invention can also comprise an electrostatic and/or magnetic focussing system arranged outside the second structure, that is, after the hybridisation interval between the first emission structure having electron beams and the second diaphragm structure opening. Advantageously, the device will be able to bathe in a uniform magnetic field resulting from a magnetic projection device. The first emission source structure can also comprise an electrostatic collimation system of electrodes participating in focussing and arranged above each emission source implanted on the substrate. According to the invention it is provided that the second electrode diaphragm structure is subjected to potential polarisation and thus contributes to the focussing process of the beams. According to a refined embodiment, the second diaphragm electrode structure has asymmetrical diaphragm openings on one side relative to the other side of the wall formed by the diaphragm. According to one embodiment, each diaphragm opening comprises bevelled opening edges, for example in a flat bevel, or opening edges concave in shape or again opening edges convex in shape. It is provided especially that each opening, or at least one diaphragm opening, has a bigger opening surface on one side of the diaphragm relative to the opening surface opposite the other side of the diaphragm. By way of advantage in this case, it is provided that the diaphragm openings are oriented such that the largest surface opening is facing an electric field of greater value than the smallest surface opening. According to another embodiment, the second structure comprises two levels of electrodes or two levels of distinct metallic or conductive membranes separated by an insulating material or dielectric layers, so as to independently control the electric field at the diaphragm input and output. According to another embodiment, it is provided that each opening of the electrode structure undergoes electrical polarisation different to the other openings, the openings being arranged in portions of conductive or metallic membrane, separated from one another by insulating parts. According to another embodiment, the first structure comprises a substrate, a cathode, electron emitter means, an extraction grid, and in which the second structure forms current collection means, insulated from the extraction grid and arranged so as to collect part of the current emitted by the emitter means, means for measuring the collected current, and control means, as a function of measuring the collected current, the current emitted by the electron emitter means. Advantageously, the electron emitter means comprise at least one micro-point or a nanotube. According to one embodiment, the current control means emitted by the electron emitter means comprise pulsed polarisation means of the extraction grid. According to another embodiment, the current control means emitted by the electron emitter means comprise pulsed polarisation means of the cathode. Advantageously, the substrate is a CMOS substrate. According to a particular embodiment, electrical crossings connect the collection means and the extraction grid to the CMOS substrate. According to another particular form, the collection means are connected by electrical and mechanical interconnection means formed by the balls or a pillar to a zone conductive. Advantageously, the current-measuring means are located in the substrate. It can also be provided that the current-measuring means are made on a substrate on which the collection means are located. Advantageously, the current-measuring means comprise an amplifier on which a condenser or a resistor is mounted in counter-reaction and in particular, the current-measuring means comprise a measuring setup by current mirror. Preferably, the openings are circular or comprise circular sectors. FIGS. 4 and 5 show the general architecture of the electronic emission device used by the invention. According to the general view of a complete device illustrated by FIG. 5, the electronic emission device according to the invention can especially be implemented within a global high-resolution multibeam electronic emission system 5 which comprises an anode 40 and a focussing system 4, here known as <<focussing optic>>. The focussing optic 4 is designed to focus each electron beam 59 emitted by a localised source with field effect, in the form of an electronic spot, that is, a localised image concentrated in the focal plane, embodied here by the anode 40, which can be also a screen or a sample, or it could be a microscopic sample to be observed or a semiconductor substrate (<<wafer>>) covered with resin to be isolated. The anode 40 acts to accelerate the electron beams. The focussing optic 4 can be a magnetic projection system, or a system combining electrostatic and/or magnetic lenses. In the case of magnetic projection, the focussing optic 4 is distributed over the entire device. FIG. 4 illustrates the architecture of the electronic emission device 50 itself, according to the invention. The device, according to the invention, comprises a first structure 6 formed for example by a semiconductive substrate plate 60, for example made of silicon, on which an addressing circuit is implanted, in CMOS technology for example, and comprising a plurality of sources 61 for emission of electron beams, arranged in matrix form or at least according to a periodic regular, or irregular, arrangement. The device 50 according to the invention comprises on the other hand a second structure 7 formed by an electrode structure 70 comprising a plurality of diaphragm openings 8 also arranged according to a matrix arrangement or at least according to a periodic regular, or irregular arrangement, and which advantageously corresponds to the arrangement of the emission sources of the first structure 6. According to the invention, the substrate plate 60 comprising the plurality of emission source with field effect 61 forming the base structure 6 is hybridised with the structured electrode 70 comprising the plurality of diaphragm openings 8 and forming the second structure 7, by means of a hybridisation system 9-9′. The second structure 7 comprising diaphragm openings 8, is preferably made of a metallic electrode or a conductive membrane 70. In general, part or the totality of the second structure 7 is conductive to be able to evacuate the electronic charges transferred by the electrons whereof propagation is interrupted by the diaphragm 70. According to the embodiment illustrated in FIG. 4, the hybridisation system 9 is composed of hybridisation balls 90 made advantageously of metal or fusible metallic alloy and spherical or oblong in shape, in the shape of a plug or mushroom, for example. The hybridisation system 9, 9′ advantageously positions horizontally and vertically the structure 7 on the structure 6. The spread distance X between these two structures is defined by the size of the hybridisation balls 90. It can be selected from a very extended range of value from about a micrometer to about a millimeter. As illustrated in FIG. 4, the advantage of the invention is that each opening 8 transmits only one emerging electron beam 59 of reduced divergence, relative to the initial divergence of the electron beam 69 originating from the emitting source 61. This divergence becomes particularly independent of the instabilities of the sources and the emission inhomogeneities of the sources. According to the diagram of FIG. 4, the device according to the invention comprises three distinct structures: the matrix emission structure 60 which comprises a plurality of electron beam emission sources 61, an electrode structure 7 comprising a plurality of diaphragm structure openings, and a hybridisation system 9-9′ interposed between the matrix emission structure 6 and the electrode structure 7. The invention allows to control, on the one hand, the dimensions of the openings 8, and, on the other hand, the spacing of the second diaphragm structure 7 relative to the first electron emission structure 6, which allows to control the divergence of each electron beam emerging from a diaphragm opening and provides the desired divergences. With a reasonable magnetic projection optic (corresponding to a uniform magnetic field of 0.3 teslas), divergence of a few degrees allows to foresee focussing of the beams in the form of localised spots of a resolution of nanometric order. The electrode 70 drilled by diaphragm openings 8, which form the second structure 7 when it is placed in a non-zero anode field, has the effect of a lens. This effect must be controlled, since it can disrupt or participate in focussing as per the case. It is provided for the majority of applications, that the complete device 5 in placed in an electric acceleration field, such a uniform electric field E able to be generated by the polarisation of the emitter matrix 60, of the hybridised electrode 70 and an anode 40 facing the electron emission device 50. Each opening 8 arranged in the hybridised electrode 70 thus has a focussing lens effect. According to an advantageous embodiment, the openings of the diaphragm 8 can have a bevelled profile, which limits the aberrations of the electronic beam at the edge of the openings and increases the resolution accessible with this device. This is why the electronic emission device 50, according to the invention, integrates advantageously as an emission source in a high-resolution multibeam electronic system 5, such as that illustrated in FIG. 5, comprising a focussing system 4 and an acceleration anode 40 of the electron beams 59/49. The invention provides a series of parallel electron beams 59 at the output of the electronic emission device 50, each beam exhibiting only one angle of divergence of about a fraction of a degree to a few degrees. By using a focussing system 4 (for example a magnetic projection system generating a magnetic field B of about a few hundred Tesla to several tens of Tesla), the invention provides nanometric resolutions. The invention therefore advantageously enables: separate production of a first structure 6 comprising a matrix in one or two dimensions of emission sources for electron beams, and a second structure 7 comprising a matrix of diaphragm openings; transfer of the second structure 7 to the first structure 6; control of the spacing X between the second structure 7 and the first structure 6; control of alignment between the openings 8 of the second structure 7 and the emission sources 61 of the first structure 6; and, put into electrical contact certain conductive parts 60 of the first structure 6 and certain conductive parts 70 of the second structure 7. Embodiments of the first electron emission structure, of the diaphragm electrode forming the second structure, the diaphragm openings and the hybridisation system will now be detailed herebelow. FIG. 6 illustrates an embodiment of the structure for emission of electron beams used according to the invention. As shown in FIG. 6, the electron emission source structure is integrated on a semiconductor substrate support 60, for example silicon, on which an integrated circuit such as a matrix addressing circuit for writing and programming the electron beams is implanted, capable of comprising logic gates or memories, created in CMOS technology (technology for implantation of a component on Complementary Metal Oxide Semiconductor). The emitting electron sources 62 are implanted at the surface of the substrate 60 which is reconnected to ground. The emitters 62 can be constituted by metallic points or semiconductive points, nanometric tubes made of carbon fibres (<<carbon nanofibers>>), or even thin films made of carbon or porous silicon, for example. Several emitting points 62 can optionally be combined to make up a single electronic emission source 61. The emitting sources 62 can be implanted in a matrix network in one dimension or two dimensions, especially according to regular periodic arrangement in two dimensions, or a regular linear arrangement in one dimension, or a multilinear arrangement on several parallel axes in one dimension, or even according to an irregular arrangement. The emitting sources 62 are deposited in openings arranged in a dielectric layer 63 made of insulating material, for example an oxide layer. The thickness of the oxide layer 63 is of about a few tens to a few thousand nanometers. A metallisation surface 64 is deposited on the surface of the insulating layer 63 to form an extraction electrode polarised to a positive voltage Vg. Openings, typically circular, are arranged in the axis of the emitting sources 62 so as to form an annular grid around each emitting point 62 constituting a cathode. The opening of the annular grid can reach a dimension of about a few tens of micrometers to a few micrometers, according to the type of emitting source used. According to the alternative embodiment illustrated in FIG. 6, the extraction electrode 64 is topped by another dielectric layer 65 and by another metallisation surface 66 forming a second electrode insulated electrically from the extraction electrode 64. This second electrode 66 is drilled by openings, typically circular, of dimensions generally greater than the extraction grid openings of the first electrode 64. The second electrode 64 is polarised to a voltage Ve, to form a first level of focussing lenses. The typical thickness of the conductive electrodes is of about a few hundreds of nanometers. According to the invention, the diaphragm electrode 70 making up the second structure 7 is transferred by hybridisation 9 to the first emission structure 6 formed by the base plate substrate 60, on which the matricial arrangement of the emitting sources with field effect 61 is stacked out. Hybridisation consists of transferring and assembling the second structure 70 to the first structure 60 by intercalating hybridisation means 9 and 9′. According to the embodiment described earlier (FIG. 4), the hybridisation means 9 are formed by metallic balls 90. In a first embodiment, the hybridisation balls are composed of fusible metal alloys. The balls can be circular or oblong in shape, or in any other form, for example especially in the form of a mushroom. The height X of the hybridisation balls 90 controls the spacing between the diaphragm electrode 70 forming the second structure 7 and the emission substrate 60 forming the first base structure 6. The hybridisation balls 90 preferably have micrometric dimensions, these microballs preferably having a size between one micrometer and several hundred micrometers. Such hybridisation means maintain a spacing distance X between the second structure 7 and the first structure 6 of between a fraction of a micrometer and a millimeter, according to the hybridisation means utilised. Hybridisation techniques by fusible alloy ball further enable automatic alignment and control (to the nearest micrometer) of the diaphragm openings 8 of the second structure 7 relative to the emitting sources 61 of the first structure 6. It is the fusing of the balls which allows (via surface voltage forces) this auto-alignment between the structures 6 and 7. This technique thus especially enables auto-alignment between the emission means of electron beams and the divergence reduction means according to the invention. In the case of hybridisation by gold balls, assembly is achieved not by fusion of the balls but by thermocompression. The assembly precision is ensured by the precision of the machines for aligning the structures to be assembled. These different hybridisation techniques are described for example in the article: <<Electronic production and test Advanced Packaging>>, pp. 32-34, April 1999. FIGS. 9 to 9′C illustrate several hybridisation configurations at the interface between the second electrode diaphragm structure 70 and the first electronic emission base structure 60. FIG. 9 shows a first embodiment in which the hybridisation balls 90 are arranged in the peripheral zones of the device between the edges of the second structure 7 and the edges of the first structure 6. Therefore, according to this embodiment, the hybridisation balls 90 are arranged outside the propagation zones of the electron beams and at the place where the diaphragm electrode 70 forming the second structure 7 can be thick enough to reinforce its mechanical performance. FIG. 9′ illustrates another embodiment in which several microhybridisation balls 90 are arranged, not only in the peripheral zones between the edge of the diaphragm electrode 7 and the edge of the substrate plate 60 forming the second electronic emission structure 6, but also in the central zone corresponding to the active part of the substrate 60 comprising the electron emission sources 61 and the central zone of the diaphragm electrode 70 which comprises the diaphragm openings 8. The microhybridisation balls 90 are arranged around each emission cell with field effect, and rise like columns in the intervals separating the propagation spaces from the parallel electron beams. The function of the microhybridisation balls arranged in the central zone or active part of the device, alternatively or cumulatively, is to reinforce the behaviour of the mechanical assembly between the thin diaphragm electrode 70 (second structure) and the substrate plate 60 (first structure), and/or to put the electrical conductive parts of the diaphragm electrode 70 in contact with certain conductive parts of the substrate plate 60. Such an arrangement applies particularly to making a device according to the invention comprising a diaphragm electrode 7 with reticulated or alveolar structure and comprising insulating partitions made or insulators separating conductive boxes in which the diaphragm openings 8 are arranged. FIG. 9′A illustrates a first embodiment in which the hybridisation microballs 91 arranged in the central zone place parts of the substrate 60 are directly in contact with the conductive zones 70 surrounding the openings 80. FIG. 9′B illustrates a variant embodiment in which the hybridisation microballs 92 of the central zone are supported on the electrode 64 of the extraction grid of the electrons deposited on a dielectric layer which separates it and insulates it from the substrate 60, in which the electron emitting sources 61 are arranged or implanted. Here, the hybridisation balls 92 electrically connect the zones of the diaphragm electrode 70 extending around the openings 80 with the electronic extraction electrode 64 which is subjected to a potential or extraction grid voltage Vg. FIG. 9′C illustrates another variant embodiment in which hybridisation microballs 93 are supported on the focussing electrode 66 which is provided in certain embodiments of the first structure 6, for example that of FIG. 6, and which tops the electronic extraction grid electrode 64 deposited above the semiconductor substrate 60 in which the electron emitting sources 61 are stacked out. In this embodiment, the hybridisation microballs arranged in the central part electrically connect the zones of the diaphragm electrode 70 surrounding the openings 80 with the focussing electrode 66 which is subjected to a potential or polarisation voltage Ve. FIGS. 7A and 7B illustrate two embodiments of the second structure and show the general course of the hybridised electrode 70. The bevelled profiles of the diaphragm openings, detailed later, are not illustrated in FIGS. 7A and 7B. FIG. 7A illustrates a first embodiment in which the second structure is composed by a conductive membrane 70 topped by an oversize 72 of the conductive material or the depositing thickness 72 of a layer of another material which equally can be conductive, semiconductive or dielectric. The thickness of the conductive diaphragm membrane 70 which intercepts the electron beams around the diaphragm openings 8, is of about a fraction of micrometers (for example 0.1 μm) to several hundreds of micrometers (e.g. 500 μm). Outside the zones surrounding the diaphragm openings 8, the thickness of the second structure can reach much more significant values, for example cumulative thicknesses of up to approximately one millimeter, especially on the edges and on the periphery of the second structure so as to improve the mechanical performance or resistance to deformation of thermal origin of the whole of the second structure 7A. The conductive part 70 of the hybridised electrode 7A is subjected to a potential polarisation Vd to control the electric acceleration field of the electrons between the emission device and the anode and/or provide an electrostatic focussing effect, as specified herebelow. FIG. 7B illustrates another embodiment more complex than the second structure 7B which here comprises two successive electrodes 70 and 75, for increasing the polarisation strategies of the structure 7B. In the implementation in FIG. 7B, as in the example of FIG. 7A, the second structure 7B comprises a first conductive or semiconductive membrane 70 forming a first electrode drilled by diaphragm openings 8. The membrane is topped by a layer of dielectric material 71, of average thickness of about one micrometer, drilled by openings 73 in the corresponding emplacements to the right of the diaphragm openings 8, the recesses 73 preferably being of a size greater than the size of the diaphragm openings themselves. The thickness of the conductive part 70 can be reduced to a thickness of about a few tens of micrometers. The dielectric layer is topped by a conductive uniform membrane 75 which forms a second electrode. The thickness of the dielectric layer 71 electrically insulating the electrodes 70 and 75 from one another can range from one micron to tens of microns. The thickness of the conductive membrane 70 in the zones which intercept the electron beams, around the diaphragm openings 8, can range from about a tenth of a micrometer to several hundred micrometers (for example 500 μm). All the same, the second electrode 75 can be made excessively thick or can be topped by a layer 76-77 of another conductive, semiconductive or dielectric material, whereof the thickness can reach approximately one millimeter. These excess thicknesses, whether arranged in the actual body of the material of the second electrode 75, or in a different conductive or insulating material 77, are arranged outside the zones of diaphragm openings 8, especially on the peripheral edges of the electrode to improve the mechanical or thermal performance of the second structure 7B. Openings 78 are arranged in front of the diaphragm openings 8. According to the example of FIG. 7B, the openings 78 arranged in the oversizes of the second electrode have dimensions greater than the dimensions of the diaphragm openings 8 arranged in the second electrode 75 itself. The diameter of the smallest diaphragm openings 8 arranged in the electrodes can reach a tenth of a micrometer to several tens of micrometers (for example 50 μm), while the greater dimension of the biggest diaphragm openings is not limited. Each electrode 70, 75 formed by a conductive membrane is subjected to a respective polarisation potential to form an electrostatic acceleration field of the electrons of each side of the second structure and between the two electrodes 70, 75. In the embodiments of FIGS. 7A and 7B, each electrode 70 or 75 is subjected to a potential Vd, Vd1 or Vd2 uniform over the entire surface of each electrode 70 or 75. All the diaphragm openings 8 of each electrode 70 or 75 are thus subjected to the same electrical potentials. Alternatively, according to another embodiment not illustrated, it is provided that the openings can be subjected respectively to distinct individual potentials. The second structure can thus be implanted in a substrate or a material having an alveolar or reticulated structure, comprising silicon boxes separated by bands of insulates, especially using bricks according to technology known as SIBOX. In this type of technological material, each semiconductive box is insulated electrically from the other adjacent semiconductive boxes. The second structure 7 is implanted in this substrate or this technological material, each individual insulated box then being drilled by one or more diaphragm openings 8. The opening or the group of openings belonging to a box can be subjected individually to a respective potential, in order to focus each electron beam which passes through these diaphragm openings either individually or in groups. An advantage of this embodiment is to control the divergence and the optical quality of the transmitted beams. FIG. 8C is a diagram representing the course of the paths of the electrons originating from a localised emission source through a diaphragm opening 70 with bevelled profile. As it can be seen in the lower angle of FIG. 8C, the first effect of the diaphragm opening is to limit the angular opening of the electron beam transmitted through the second diaphragm structure 70. For example, with a diaphragm opening of 5 micrometers in size, arranged at a distance of 20 micrometers from the localised emitting source, the narrowest part of the diaphragm opening 84 limits the angular opening of the beam to +/−4 degrees of angle. In the example of FIG. 8C, the electric field is zero (E1=0) between the emitting source situated at the origin and the first side 85 of the diaphragm structure 70. On the other side of the second structure 70, a uniform electric field of about 1 volt/micrometer (E2=106 V/m) is imposed by an anode (not illustrated) which faces the electrode 70 formed by the second structure. All the trajectories of electrons are subjected to a uniform magnetic field of about a few tens of Tesla (for example 0.3 T). It is observed that the trajectories of the electrons 86, 87, 88, 89 curve and fold back towards the propagation axis 89 under the effect of electrostatic acceleration and magnetic focussing. The bevelled opening profile 80 limits the aberrations of the electronic beam to the crossing of the diaphragm 70, along the opening edge 83. The diaphragm effect is realised in the part of the second diaphragm structure 70 where the opening is the most reduced 84. Such a disposition provides excellent quality of the electronic beam. The beveling of the upper part 83 of the diaphragm reaches a resolution less than 10 nm and divides by five the spot dimensions (focal point) obtained with the device according to the invention, relative to those diaphragm openings without beveling, which is the consequence of the reduction in aberrations at the crossing of the diaphragm 70. In an advantageous manner the beveling of the diaphragm openings of the device according to the invention quintuples the resolution of the point of focus of an electronic beam. In addition, the invention provides that the electric field E is not uniform when crossing of the diaphragm, each side of the diaphragm electrode being exposed to electric fields E1, E2 of different values. According to the invention, the orientation of the opening of the bevel 83 preferably depends on the orientation of the gradient of electric field at the crossing of the diaphragm 70. It is provided that the narrowest part 81 or 84 of the diaphragm opening 80 faces an electric field less important than the widest part 82 or 83 of the diaphragm opening 80. The orientation of the bevel 83 of the opening 80 thus depends on the polarisation of the electrode 70 vis-à-vis the electronic emission device 60 and vis-à-vis the accelerating or focussing anode 40, for example. FIG. 8A illustrates a first embodiment in which the openings 80 70 of the diaphragm form bevels 83 opening in the direction of propagation of the electronic beams, and are subjected to a gradient of electric field E1/E2 growing in the direction of propagation of the electrons. The bevel 83 of the opening 80 is oriented such that the first side of the diaphragm 70 presenting the narrowest opening 81, or presenting the lower opening section 81, is exposed to an electric field E1 having a first value less than a second electric field value E2 which bathes the other side 82 of the diaphragm 70. The second side of the opening 80 which has a width of opening 82 greater than the first opening 81, or at least an opening section having an area 82 greater than the area of opening 81 of the first side, is exposed to a second electric field value E2 greater than the first electric field value E1 which faces the first side 81 of the diaphragm 70. In particular, the electric field can be absent, that is, of a substantially zero value (E1≅0) between the diaphragm and the emission device. This particular case corresponds to the case where the electrode of the diaphragm structure 70 is polarised to the same potential electrical as the emission device 50 (Vd=Vg or Vd=Ve or Vd1=Vg or Vd1=Ve). In the case of FIG. 8A, after having been diaphragmed at the place where the diaphragm opening 80 is the narrowest 81, the electron beams are secondly focussed or accelerated by the strong electric field E2 on the place where the opening 80 is the widest 82. Strong electrostatic effects occur in this zone, but as the trajectories of the electron beams transmitted at this level pass further away from the end opening edges, the trajectories undergo fewer aberrations. The device according to the invention comprises means for applying polarisation potentials or electrical voltages to each of the abovementioned electrodes. FIG. 8B discloses another embodiment in which, this time, the electron beams are exposed to a gradient of electric field decreasing in their direction of propagation, as they cross the openings 80′ of the diaphragms 70. In this case, as illustrated in the realisation in FIG. 5B according to the invention, the openings with bevelled profile are preferably oriented such that each diaphragm opening 80′ shrinks in the direction of propagation of the electron beams. In this case, the bevelled diaphragm openings 80′ are oriented such that the opening of greater width 81′ is arranged on the first side facing the electron emitting sources, and are exposed to an electric field of value E1′ greater than the electric field value E2′ which bathes the second side of the diaphragm 70. The second side of the diaphragm comprises openings 82′ presenting a narrower width or a section of opening 82′ of lesser area, these narrow openings 82′ facing the accelerating or focussing anode 40. In the case of FIG. 8B, the electron beams are exposed to a decreasing gradient of electric field E1′/E2′ in their direction of propagation and are first focussed or accelerated by the strong electric field E1′ at the place where the opening 80′ is the widest 81′, prior to being diaphragmed at the place where the diaphragm opening 80′ is the narrowest 82′, which proves to be the place where the electric field value E2′ is the lowest, even zero. The electric field can in fact optionally be absent from the second side of the diaphragm 70, which corresponds for example to a case where the anode is polarised at the same potential as the diaphragm 70. In an advantageous manner according to the invention, the diaphragm effect is achieved on the side of the diaphragm where the electric field E2 is the weakest, which corresponds to the narrowest side of openings 82′. The trajectories of the electron beams which pass near the edge of the opening thus undergo few aberrations. It is noted that, due to the invention, the greater the angle of bevel of the openings, the more the preceding effects are marked and the fewer aberrations are created at the crossing of the diaphragm. The value of the angle of the bevel of the openings is limited only by the emitter density at the surface of the device. FIG. 8C shows a bevelled diaphragm opening profile with a strong angle of inclination θ of around 15° relative to the axis of propagation of the electrons. In other embodiments, not illustrated here, the diaphragm openings can be bevelled with a non-linear profile, that is, the bevel is not rigorously flat, but may be convex or concave, for example. Such opening profiles are also favourable for reduction of aberrations when the electron beam passes through the diaphragm. The embodiment of an electronic emission device according to the invention can be the object of several embodiments and variants of the base architecture with even steps, in particular of a matricial arrangement in two dimensions, a linear arrangement in one dimension or a multilinear arrangement in two dimensions, with even or uneven steps. FIG. 10 illustrates a general view of an achievement of matricial architecture in two regular dimension with even steps, comprising a network of emitting sources 6 and diaphragm openings 8 7 arranged according to a regular grid. FIG. 11 illustrates a general view of a realisation of an electronic emission device according to the invention, comprising an emission structure 6 comprising a single row of sources and a diaphragm structure 7 comprising a row of corresponding openings 8 arranged in linear rods according to a periodic arrangement in one dimension at even steps. Alternatively, the emitting sources and the diaphragm openings 8 can be arranged at uneven intervals. FIG. 12 illustrates a general view of another achievement of an electronic emission device according to the invention, in which the first structure 6 and the second structure 7 comprise several relatively spaced parallel rows of emitting sources and diaphragm openings 8 arranged in two dimensions at even periodic intervals. Alternatively, the emitting sources and the diaphragm openings 8 can be arranged at uneven intervals. The spacing of the emitting sources and the corresponding openings 8 can vary from about one micrometer to a hundred micrometers, the matricial interval typically being a few micrometers or a few tens of micrometers, for example around fifty micrometers. Such a structure integrates particularly advantageously into a high-resolution multibeam electronic emission system, according to the diagram of FIG. 5B which further comprises a focussing optic 57 and an electrostatic acceleration anode. At the output of the diaphragm openings of the emission device 50, the angular opening of the beams is reduced to a few degrees, even on this side of the degree due to the invention. The focussing optic 57 is preferably a magnetic projection optic generating a magnetic field of about few hundred Tesla to a few Tesla, typically a few tens of Tesla. Advantageously, such a device according to the invention provides electron spots having a resolution of nanometric order. FIGS. 13A to 16B show another embodiment in which the diaphragm also forms collection means on the one hand of the current emitted by the emitter means so as to collect part of the emitted current, and is attached to measuring means of this part of emitted current, said measuring means being connected to polarisation means of the electron emitter means. According to the embodiment illustrated in FIGS. 13A and 13B, the electron emitter means comprise a cathode 120, electron micro-emitters 124 (point or nanotube) and a first extraction grid 126, the extraction grid-cathode distance being regulated by the thickness of a dielectric 128, which is for example of about one micrometer. Polarisation means 134 polarise respectively the extraction grid and the cathode and thus control the current emitted by the micro-emitters. The inventive device also comprises collection means 140, for example comprising an electrode or a collection grid, and can be positioned above the emission site. They are connected to means 142 for measuring the current. These collection means are thus placed on the trajectory of the electrons emitted so as to take part thereof and to allow passage of the rest of the electrons emitted to the anode. For this, orifices (or openings) are provided on these collection means. These orifices can be circular, oval or rectangular, and they can also exhibit other advantageous geometries. As illustrated in FIGS. 15A and 15B, they can also have the form of circular sectors 100, 102, 104 or even the form illustrated in FIG. 15C (scalloped circle). As a function of the selected geometry and applied polarisation, and according to standard laws of optics and electromagnetics, the part of the collected electrons and that of the electrons effectively transmitted to the anode can be determined. Therefore, measuring the collected current will give a precise indication of the electrons arriving at the anode (and thus of the dose emitted). Relative to a circular orifice, these orifices cut out of FIGS. 15A to 15C enable the collection of electrons at several levels of electronic beam and not just at the edges of the beam, thus allowing them to be less sensitive to the inhomogeneities which can appear on the edges. As a function of the application envisaged these orifices typically have diameters of about a few microns to a few tens of microns. The current collection means 140 are positioned in the emission axis, the distance relative to the first extraction grid 126 being adjusted by hybridisation means 90, for example a micro-ball 90 or any other means of interconnection (pillar, . . . ). In fact, the grid or the collection means are connected by the means 90 to a conductive zone 171, located in the standard emission device at the level of the extraction grid but insulated in this extraction grid by the insulating zone 127 (for example SiO2). The hybridisation means 90 retain a clearance between these elements which, combined with the insulating zone 127, ensures the insulating effect between them. The height of these hybridisation balls 90 controls the spacing between the electrode 140 and the substrate which comprises the emission means 124. Such hybridisation means retain a fairly precise clearance distance between the means 140 and the emission grid 126, typically of about a few hundred microns and with precision of about a fraction of microns. By placing the current-measuring means 142 (amperemeter) in the feed circuit of the collection means, it is possible to measure the electronic beam, or a magnitude proportional to the anode current, and interact on the current of the micro-emitter, or via the extraction grid 126 control and/or via the cathode 120 control. Adjustment can be done by way of counter-reaction means. These counter-reaction means can for example be made up of a voltage current converter connected to an amplification module and to an inverter, if needed. They therefore establish the voltage to be applied to the cathode and/or the extraction grid from the current collected at the collection grid. The invention thus makes use of the control and anode current regulation means separate from the extraction grid. The grids 126 are metallic in type. More generally, they are conductive (for example made of polycrystalline silicon). The emitting points 124 are conductive, for example made of silicon or molybdenum. The extraction grid 126 is for example a few hundred nm to a few micrometers thick. The thickness of the dielectric 128 is typically of a few hundred nm (for example between 0.4 and 0.7 μm). The distance between the substrate 120 and the anode 136 is around 1 mm for the application envisaged. It can vary from 10 μm to 10 mm according to the application. A first voltage generator 134 creates for example a positive ddp between the first extraction grid 126 and the cathode 120 to allow the electrons to escape from the point into the vacuum. The electron beam is oriented to the anode 136 with a certain angular opening. To collect electrons, the anode 136 is for example brought to a few hundred volts positively. The means 140 collect electrons, converted by the means 142 to current, information which the counter-reaction means can utilise to adjust the extraction of electrons as a function of a threshold value of the current emitted, for example. The operating frequencies of the source are preferably in the field of high frequencies, outside 1 Mhz. The physical realisation of micro-sources known according to the prior art imposes non-ideal structures. Interfering capacitors, between the point 124 and the grid 140, especially cause substantial displacement currents, at the moment of switching. In the embodiment illustrated in FIGS. 13A and 13B, it is conceivable to connect the extraction grids 126 and collection grids 140 to current control blocks and grid control located in the CMOS substrate, by electrical crossings. These processing blocks utilise mixed LV/HV technology (low voltage/high voltage), the control and command executed in LVCMOS and emission control in HVCMOS. A collective manufacturing process can align the collection grid 140 on the emitting point 124. As illustrated in FIG. 13A, a silicon wafer can be utilised as a substrate for making the collection grid. This substrate will also be used to create, at the same level as the collection grid, the current-measuring means and associated processing means. This can be referred to as an <<active>> collection grid. An advantage of this variant is increasing the available surface for making electronic processing blocks and above all to differentiate the low-voltage analog part at the silicon substrate from the collection grid 140, and the high-voltage analog commutation part 134 at the silicon base substrate 160; inter alia this limits the problems of interference between these two parts and furthermore permits the use of two substrates of totally different technologies. In the device illustrated in FIG. 13B, it is a <<passive>> collection grid, where the current-measuring means 142 and the processing of the collected current are localised in the CMOS substrate 160. In an embodiment, control is executed by the extraction grid, the cathode potential is maintained at a constant voltage, the potential of the extraction grid is pulsed between a high level and a low level (see the voltage Vg on the chronogram of FIG. 16A). The high level corresponds to a period during which the micro-emitter emits, the low level corresponds to a period during which the micro-emitter does not emit (see the anode current Ia in FIG. 16A). According to the invention it is possible, from the current Ig collected at the collection grid (proportional to the anode current in its central part), to act on the potential of the extraction grid to modulate emission from the micro-emitter. For this, either the level high of the voltage Vg can be modulated, or the emission duration can be modified by playing on the duration of this high level. Significant, peaks in current, transitionally at the level of the current of the collection grid, can be noticed in FIG. 16A at the moment of switching of the potential of the extraction grid. It can thus be of interest to defer measuring the collection current so as to avoid the perturbations associated with these commutations. In another embodiment, control of the micro-emitter is regulated by the cathode. The potential of the extraction grid is thus constant, whereas the cathode potential is pulsed between a high level and a low level, the latter level corresponding to the emission period of the micro-emitter. According to the invention, from the collected current Ig the potential of the cathode (Vcathode) can be acted on to modulate emission of the micro-emitter. The low level of the cathode voltage can be modulated in amplitude or in duration. It can be noted from FIG. 16B that the current collected in case where control of the microemitter is regulated by the cathode, is less sensitive to the commutations of the cathode voltage than in the preceding case. The example of FIG. 14A illustrates the current-measuring means of a measuring signal amplified by an amplifier 180 on which a condenser 182 is mounted in counter reaction. It is possible to convert the current voltage measure, a variable more easily exploitable with a limited number of components (CTIA). The variation in output voltage is thus expressed by: Δ V s ( G ) = - Igate * T Cfb where T illustrates the current integration time, or the analysis time. This structure is fairly insensitive to the rapid variations in current. The value of the condenser 182 is for example of about 10 fF, which results in sensitivities of about 20 μV/electron. The structure illustrated in FIG. 14B, with a counter-reaction resistor 184, represents instantaneous variations in output voltage on instantaneous variations of the input current. The variation in output voltage is in this case expressed as:ΔVs=−R·Igate Finally, FIG. 14C illustrates a measuring setup by current mirror: an image of the current of collection grid Ig can be used to generate a current of difference Iref−Ig, which can be utilised. A device according to the invention, irrespective of the embodiment envisaged, is able to compensate technological spatial non-uniformities or non-uniformities of known electron sources. Other arrangement forms, variants and embodiments will be able to be utilised by the specialist, without departing from the scope of the present invention. |
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description | The invention is in the medical field and in particular in real-time X-ray or fluoroscopy. The use of real-time, or continuous, X-ray is increasing rapidly because of the increased use of percutaneous medical procedures such as coronary stents, atrial ablation and gastric procedures. The doctors or other users in the operating room are forced to wear heavy lead aprons and sometimes goggles made of thick lead glass to avoid the cumulative effects of the X-ray radiation. A smaller dose of X-ray may reach persons far away from the X-ray machine. The most common X-ray procedure is fluoroscopy, in which a portable arm carries an X-ray source at one end and a digital X-ray image sensor at the other end, with the patient placed between them. A screen connected to the image sensor via an image processing system displays real time images of the procedure. Some previous attempts to reduce the radiation used stationary lead shields, adjusted by the user. This is a time consuming operation. Other prior art solutions use an electrically controlled masks that allows radiation to reach only part of the image. This is less than optimal, as without seeing the whole image it is difficult for the doctor to orient himself. The invention takes advantage of the fact that most of the image is changing very slowly and does not need as frequent updates as the area of interest. It is an object of the invention to reduce the X-ray exposure both for the patient and the doctor without degrading the image quality. A further object is to supply a system than can easily be incorporated into the design of existing fluoroscopy systems, or used as an add-on to existing systems. A further object is to introduce minimal changes in the use of the X-ray equipment compared to current practice, in order to avoid re-training. These and further objects will become clear by reading the disclosure in conjunction with the drawings. To reduce X-ray exposure, an area of interest is selected in the image. The image of the selected area is updated frequently, comparable to rate of updates used today for the whole image. The rest of the image is updated at a significantly lower rate. Since the area of interest normally is a small part of the overall area, the total exposure is reduced significantly. A movable X-ray shield placed near the X-ray source blocks the radiation from areas outside the area of interest. The shield automatically retracts when the complete image is updated. The area of interest can be selected by the user or automatically selected based on activity in the image. A typical X-ray fluoroscopy system is shown in FIG. 1. An arm 1 carries an X-ray source 4 at one end and a digital X-ray image sensor 6 at the other end. A patient 3 is supported on table 3 and placed between source 4 and sensor 6. The system is typically mounted on a cart (not shown) via column 5 which allows positioning arm 1 in any position relative to patient 2. An automatic X-ray masking unit 7 is added near source 4. Masking unit 7 can automatically change the beam from a wide beam 8 to a narrow beam 9 directed at the area of interest. Since the radiation is mainly used in the form of narrow beam 9 and only used in the full width beam 8 to update the less important image parts, a significant reduction of radiation is achieved both for the patient and the doctor. In this disclosure the terms X-ray and fluoroscopy are used interchangeably and the terms “mask” and “shield” should be broadly interpreted as anything that can interfere with the normal propagation of X-ray, not only by absorption but also by refraction, diffraction or any other interaction mechanism. The reduction of radiation can be appreciated from FIG. 2. A screen 10 displays a real-time X-ray image 11. By the way of example, a tool such as guide-wire 13 is inserted into the body. The area of interest is at the tip 14 of the guide wire, since the rest of the wire is not free to move (e.g. it is usually confined to a blood vessel or other lumen). A small area of interest 12 is chosen and this area is updated at the full rate. The rest of the image 11 is updated at a significantly lower rate. By the way of example, if the area of interest is 10% in width and 10% in height of image 11 it occupies 1% of the area. If this 1% is updated at the full rate while the rest of the image is updated at 1/30 of the rate (i.e. once per second compared to 30 frames per second), the total radiation will be 1%+ 1/30 of 100%=4.3% of the previously used dose. This represents a reduction of 23 fold. In practical terms this will allow the lead aprons to be significantly lighter and may eliminate the need for the lead glass goggles. The area of interest 14 can be manually selected by the user or can be automatically selected by a computer based on the activity in the image 11. Typically areas with very slow changes in image 11 are of little interest. Areas of interest, like the end of a guide wire or an angioplasty balloon, change rapidly as they are being manipulated by the doctor. By looking at the rate of change in the image the area of interest can be automatically selected. Sometimes there could be multiple areas of interest, requiring multiple windows 14 in image. The higher radiation level area 14 is exposed to radiation comparable to the radiation density the whole area was exposed to in prior art systems. The areas outside the higher radiation area 14 are now exposed to a significantly lower radiation level. A block diagram of such automatic selection based on activity is shown in FIG. 4. An X ray image sensor, or detector, 6 is connected to a display via a computer or display controller 30. A motion detector 28 determines the area of interest by monitoring the rate of change in the image. The algorithms for rate of change are well known in the art, and are typically based on subtracting consecutive frames. The larger the rate of change, the larger the difference between consecutive frames. An aperture size is selected by module 29, covering the area or areas where the rate of change exceeded a set threshold. This is fed to display controller 30 as well as to the controller 25 activating the variable masking mechanism which is explained later. A manual over-ride aperture control 26 can also be used to allow the user to change the dimensions of the selected aperture. The variable aperture mask comprises of X-ray shields mounted on actuators. X-ray shields are typically made of lead but any heavy metal and some non-metals can be used. When lead is used the thickness of the shield, or mask, is in the range of 1-20 mm. The actuators control the shields to form an aperture. This aperture limits the radiation for most of the time. The actuators open up the aperture to expose the whole image for a small fraction of the time, typically between 1% to 10% of the time. Two embodiments are disclosed, one based on rotary actuators is shown in FIG. 3 and one based on linear actuators is shown in FIG. 5. Referring now to FIG. 3, a masking unit 7 comprises of two rotary masks 15 and 20, typically made of lead sheet, rotated by two servo motors 18 and 23, having shaft encoders 19 and 24. A motor controller 25 controls the speed and relative position of the motors and triggers the activation of the X-ray source 4 whenever the masks are at the correct position. Each mask has a plurality of narrow slots 16 and 21 as well as at least one wide slot 17 and 22. When the wide slots 17 and 22 overlap the full image is exposed by a wide beam 8. When the narrow slots overlap a small aperture 27 is formed, allowing only a narrow beam 9 to expose the patient and update the area of interest in the image. The relative position of aperture 27 in the image is controlled by advancing or retarding the position of one motor relative to the other. For example, if the position of mask 15 will be advanced clockwise relative to mask 20, aperture 27 will move to the right. Similarly, if the position of mask 20 will be advanced clockwise, aperture 27 will move up. Masks 15 and 20 can be continuously rotated or stepped by stepper motors. The can be slaved to the firing rate of X-ray source 4 or the firing of source 4 can be slaved to the position of the masks. For highest speed operation (i.e. the highest rate of frames per second) it is best to have the masks rotate continuously and slave the firing of the source to the position of the masks. The system of FIG. 3 allows positioning of the aperture 27 anywhere in the image but does not allow changing the aperture size. By replacing each mask wheel by two parallel wheels, each having its own motor, the size of the mask can be controlled by the relative position of the mask wheels, as the mask will be the overlap of the two slots in each direction. An alternate embodiment has only two wheels, as shown in FIG. 3, but each wheel has multiple sets of slots, each set of a different width. This allows selecting the aperture width and aperture height independently is discrete steps. The desire aperture position and size can be selected automatically or manually, by using an interface device such a trackball 26 or any other pointing device such as a computer mouse, joystick, touch screen etc. A linear masking embodiment is shown in FIG. 5. Masking shields 31, 32, 33 and 34 are moved by linear actuators 35, 36, 37 and 38. The opening between the masks forms the aperture 27. The operation is similar to the rotary mask. Both the position and size of aperture 27 is easily variable. Most of the time aperture 27 is small, periodically opening for a full exposure. Actuators 35-38 can be of the moving coil type, commercially available from companies such as Kimco (www.beikimco.com/actuators_linear.php). They can incorporate linear encoders (not shown) when operated in close-loop mode. The linear masking is typically more versatile than the rotary but slower (for a given size and input power). Both types of masking units can be easily added to existing X-ray equipment by mounting them just below the X-ray source. Other methods of changing the X-ray beam dimensions can also be used, such as multi-electrode X-ray tubes. Such methods should also be considered part of the invention. Another embodiment can take advantage of longer integration times for the slower changing image areas. In this embodiment the X-ray shields are made of an X-ray attenuating material, such as thin lead. The transmission of the attenuator can be in the range of 1% to 30%. The shields are positioned once to form a given aperture and only moved if aperture needs to change. The area in the aperture receives full X-ray exposure, while the rest of the image receives attenuated exposure. Since the rest of the image is updated slowly, longer integration times leading to higher sensitivity can be used. |
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description | This application is a continuation-in-part of U.S. patent application Ser. No. 11/648,506, filed Dec. 29, 2006, now abandoned which is a continuation of U.S. patent application Ser. No. 10/887,426, filed on Jul. 8, 2004, now U.S. Pat. No. 7,185,602, which is a divisional of U.S. patent application Ser. No. 10/170,512, filed Jun. 12, 2002, now U.S. Pat. No. 7,107,929, which is a continuation of International Patent Application No. PCT/US00/33786, filed Dec. 13, 2000, which claims priority of and benefit of U.S. Provisional Patent Application No. 60/170,473 filed on Dec. 13, 1999, U.S. Provisional Patent Application No. 60/250,080 filed on Nov. 30, 2000. 1. Field of Invention The present invention relates to an ion source for use in semiconductor fabrication and more particularly to an ion source configured with its cathode located external to the ionization chamber, the ion source being operable in a first mode of operation or may be configured as a dual mode ion source that is selectively operable in both a first mode of operation, such as an arc discharge mode and a second mode of operation, such as a direct electron impact mode of operation, with a single electron emitter that can be used for ionizing gases and vapors and producing monatomic ions in an arc discharge mode of operation and molecular ions, such as cluster ions in a direct electron impact mode of operation. 2. Description of the Prior Art Electron emitters (also known as electron guns) with both directly heated and indirectly heated cathodes (IHC) are known in the art to be used in ion implantation systems. In known ion implantation systems, electron emitters with such heated and indirectly heated cathodes are normally disposed within an ionization chamber and are therefore subject to a relatively harsh environment as a result of the plasma developed within the ionization chamber. Electron emitters with IHCs offer advantages over those with directly heated cathodes in reliability and life time. In particular, emitters with directly heated cathodes include a relatively small wire that forms a filament. These filaments are known to fail in such harsh environments in a relatively short time. On the other hand, electron emitters which include Indirectly heated cathodes include a relatively massive cathode that is heated indirectly by electron bombardment from a filament. In the case of the IHC electron emitters, the cathode emits electrons thermionically. Although, the IHC is exposed to a harsh plasma environment, the massive cathode having a substantially larger mass than the filament of a directly heated cathode provides a relatively longer life than such directly heated cathodes. As such, IHC electron emitters are typically used to ionize feed materials in hot arc discharge mode, where the IHC emitter sits inside the ionization chamber. The filament inside the IHC electron emitter is heated with electrical current, and biased into negative potential with respect to the solid emitter block. This allows electrons from the filament to be accelerated into the solid emitter heating it up. The emitter block in turn is biased negatively with respect to the ion source body. When the emitter reaches sufficient temperature, it will start emitting electrons igniting arc discharge between the emitter and the source wall forming plasma. In order to further increase the operating lifetime of such IHCs, devices have been developed which include a cathode and a filament in which the cathode is located inside the ionization or arc chamber of the ion implantation system while the filament is located outside the ionization chamber, as described in detail in Varian U.S. Pat. No. 7,138,768. With such a configuration, by locating the filament outside the harsh environment of the ionization chamber, the operating lifetime of such IHCs is relatively longer than IHCs which are totally located within the ionization chamber. In recent development of cluster ion sources, heat management has become increasingly important, as many of the cluster molecules are quite fragile and can be dissociated when exposed to hot surfaces like the IHC emitter. It is thus beneficial to remove the electron emitter form the source and situate it externally, namely, outside the ionization chamber, for example, as disclosed in SemEquip U.S. Pat. No. 7,185,602, hereby incorporated by reference. Also the significant material deposits that some of the cluster materials produce favor the removal of the emitter from the source, as there is a risk of building up flakes that will short the IHC to the ionization chamber potential. This will change the operational parameters of the emitter somewhat. Now the emitter is removed from the higher gas pressure of the ionization chamber into the usually pumped source housing, where the gas pressure can be an order of magnitude or more lower, striking an arc discharge between the IHC emitter and the source will become more difficult. If plasma is ignited, there will be significant diffusion losses before the bulk of the plasma would get into the ionization chamber. For cluster ionization, the required extracted beam current densities are typically an order of magnitude lower than for traditional atomic implant species. This means that dense plasma is not needed in order to create sufficient ion beam currents. Externally located electron gun which forms an electron beam either from a directly or indirectly heated emitter will be able to inject sufficient electron current into the ionization chamber. To form an electron beam that can be efficiently injected into the source, i.e, ionization chamber, electron optics are normally used to pull and focus the beam. Typically this means placing an anode electrode between the source and emitter. The electrons are pulled from the emitter with the assistance of the anode potential and accelerated to energy e*Vcathode+e*Vanode going across the emitter-anode gap and through the anode. At the anode-source gap the electron beam is decelerated to e*Vcath and focused by the decel lens effect. This setup will allow for refined tuning of the electron beam current, size and emittance. The downside is that the distance the electrons are traveling will increase by the extent of the anode and anode gap. Typically the anode voltages are higher than the cathode voltage. This can lead into voltage holding issues. Ion beams are produced from ions extracted from an ion source. An ion source typically employs an ionization chamber connected to a high voltage power supply. The ionization chamber is associated with a source of ionizing energy, such as an arc discharge, energetic electrons from an electron-emitting cathode, or a radio frequency or microwave antenna, for example. A source of desired ion species is introduced into the ionization chamber as a feed material in gaseous or vaporized form where it is exposed to the ionizing energy. Extraction of resultant ions from the chamber through an extraction aperture is based on the electric charge of the ions. An extraction electrode is situated outside of the ionization chamber, aligned with the extraction aperture, and at a voltage below that of the ionization chamber. The electrode draws the ions out, typically forming an ion beam. Depending upon desired use, the beam of ions may be mass analyzed for establishing mass and energy purity, accelerated, focused and subjected to scanning forces. The beam is then transported to its point of use, for example into a processing chamber. As the result of the precise energy qualities of the ion beam, its ions may be implanted with high accuracy at desired depth into semiconductor substrates. The Ion Implantation Process The conventional method of introducing a dopant element into a semiconductor wafer is by introduction of a controlled energy ion beam for ion implantation. This introduces desired impurity species into the material of the semiconductor substrate to form doped (or “impurity”) regions at desired depth. The impurity elements are selected to bond with the semiconductor material to create electrical carriers, thus altering the electrical conductivity of the semiconductor material. The electrical carriers can either be electrons (generated by N-type dopants) or “holes” (i.e., the absence of an electron), generated by P-type dopants. The concentration of dopant impurities so introduced determines the electrical conductivity of the doped region. Many such N- and P-type impurity regions must be created to form transistor structures, isolation structures and other such electronic structures, which collectively function as a semiconductor device. To produce an ion beam for ion implantation, a gas or vapor feed material is selected to contain the desired dopant element. The gas or vapor is introduced into the evacuated high voltage ionization chamber while energy is introduced to ionize it. This creates ions which contain the dopant element (for example, in silicon the elements As, P, and Sb are donors or N-type dopants, while B and In are acceptors or P-type dopants). An accelerating electric field is provided by the extraction electrode to extract and accelerate the typically positively charged ions out of the ionization chamber, creating the desired ion beam. When high purity is required, the beam is transported through mass analysis to select the species to be implanted, as is known in the art. The ion beam is ultimately transported to a processing chamber for implantation into the semiconductor wafer. Similar technology is used in the fabrication of flat-panel displays (FPD's) which incorporate on-substrate driver circuitry to operate the thin-film transistors which populate the displays. The substrate in this case is a transparent panel such as glass to which a semiconductor layer has been applied. Ion sources used in the manufacturing of FPD's are typically physically large, to create large-area ion beams of boron, phosphorus and arsenic-containing materials, for example, which are directed into a chamber containing the substrate to be implanted. Most FPD implanters do not mass-analyze the ion beam prior to its reaching the substrate. Many ion sources used in ion implanters for device wafer manufacturing are “hot” sources, that is, they operate by sustaining an arc discharge and generating a dense plasma; the ionization chamber of such a “hot” source can reach an operating temperature of 800° C. or higher, in many cases substantially reducing the accumulation of solid deposits. In addition, the use of BF.sub.3 in such sources to generate boron-containing ion beams further reduces deposits, since in the generation of a BF.sub.3 plasma, copious amounts of fluorine ions are generated; fluorine can etch the walls of the ion source, and in particular, recover deposited boron through the chemical production of gaseous BF.sub.3. With other feed materials, however, detrimental deposits have formed in hot ion sources. Examples include antimony (Sb) metal, and solid indium (In), the ions of which are used for doping silicon substrates. A typical commercial ion implanter is shown in schematic in FIG. 1. The ion beam I is shows propagating from the ion source 42 through a transport (i.e. “analyzer”) magnet 43, where it is separated along the dispersive (lateral) plane according to the mass-to-charge ratio of the ions. A portion of the beam is focused by the magnet 43 onto a mass resolving aperture 44. The aperture size (lateral dimension) determines which mass-to-charge ratio ion passes downstream, to ultimately impact the target wafer 55, which typically may be mounted on a spinning disk 45. The smaller the mass resolving aperture 44, the higher the resolving power R of the implanter, where R=M/.DELTA.M (M being the nominal mass-to-charge ratio of the ion and .DELTA.M being the range of mass-to-charge ratios passed by the aperture 44). The beam current passing aperture 44 can be monitored by a moveable Faraday detector 46, whereas a portion of the beam current reaching the wafer position can be monitored by a second Faraday detector 47 located behind the disk 45. The ion source 42 is biased to high voltage and receives gas distribution and power through feedthroughs 48. The source housing 49 is kept at high vacuum by source pump 50, while the downstream portion of the implanter is likewise kept at high vacuum by chamber pump 51. The ion source 42 is electrically isolated from the source housing 49 by dielectric bushing 52. The ion beam is extracted from the ion source 42 and accelerated by an extraction electrode 53. In the simplest case (where the source housing 49, implanter magnet 43, and disk 45 are maintained at ground potential), the final electrode of the extraction electrode 53 is at ground potential and the ion source is floated to a positive voltage V.sub.a, where the beam energy E=qV.sub.a and q is the electric charge per ion. In this case, the ion beam impacts the wafer 55 with ion energy E. In other implanters, as in serial implanters, the ion beam is scanned across a wafer by an electrostatic or electromagnetic scanner, with either a mechanical scan system to move the wafer or another such electrostatic or electromagnetic scanner being employed to accomplish scanning in the orthogonal direction. As shown, in FIG. 2, a Bernas ion source a is mounted to the vacuum system of the ion implanter through a mounting flange b which also accommodates vacuum feedthroughs for cooling water, thermocouples, feed material as a dopant gas feed, N2 cooling gas, and power. The gas feed c feeds gas into the arc chamber d in which the gas is ionized. Also provided are dual vaporizer ovens e, f in which solid feed materials such as As, Sb2 O3, and P may be vaporized. The ovens, gas feed, and cooling lines are contained within a cooled machined aluminum block g. The water cooling is required to limit the temperature excursion of the aluminum block g while the vaporizers, which operate between 100° C. and 800° C., are active, and also to counteract radiative heating by the arc chamber d when the source is active. The arc chamber d is mounted to the aluminum block g. The gas introduced to arc chamber d is ionized through electron impact with the electron current, or arc, discharged between the cathode h and the arc chamber d. To increase ionization efficiency, a uniform magnetic field i is established along the axis joining the cathode h and an anticathode j by external Helmholz coils, to provide confinement of the arc electrons. An anticathode j (located within the arc chamber d but at the end opposite the cathode h) is typically held at the same electric potential as the cathode h, and serves to reflect the arc electrons confined by the magnetic field i back toward the cathode h and back again repeatedly. The trajectory of the thus-confined electrons is helical, resulting in a cylindrical plasma column between the cathode h and anticathode j. The plasma density within the plasma column is typically high, on the order of 1012 per cubic centimeter; this enables further ionizations of the neutral and ionized components within the plasma column by charge-exchange interactions, and also allows for the production of a high current density of extracted ions. The ion source a is held at a potential above ground (i.e., the silicon wafer potential) equal to the accelerating voltage Va of the ion implanter: the energy of the ions E as they impact the wafer substrate is given by E=qVa, where q is the electric charge per ion. The cathode h is typically a hot filament or indirectly-heated cathode, which thermionically emits electrons when heated by an external power supply. It and the anticathode are typically held at a voltage Vc between 60V and 150V below the potential of the ion source Va. High discharge currents D can be obtained by this approach, up to 7 A. Once an arc discharge plasma is initiated, the plasma develops a sheath adjacent to the surface of the cathode h (since the cathode h is immersed within the arc chamber and is thus in contact with the resulting plasma). This sheath provides a high electric field to efficiently extract the thermionic electron current for the arc; high discharge currents can be obtained by this method. If the solid source vaporizer ovens e or f are used, the vaporized material feeds into the arc chamber d through vaporizer feeds k and l, and into plenums m and n. The plenums serve to diffuse the vaporized material into the arc chamber d, and are at about the same temperature as the arc chamber d. In this case a co-gas could be introduced either via tube c into chamber d if the co-gas was from a gaseous stock, It would also be possible to utilize whichever solid vaporizer (e or f) was not in use for the primary feedstock to generate a co-gas from an appropriate solid material. Cold ion sources, for example the RF bucket-type ion source which uses an immersed RF antenna to excite the source plasma (see, for example, Leung et al., U.S. Pat. No. 6,094,012, herein incorporated by reference), are used in applications where either the design of the ion source includes permanent magnets which must be kept below their Curie temperature, or the ion source is designed to use thermally-sensitive feed materials which break down if exposed to hot surfaces, or where both of these conditions exist. Cold ion sources suffer more from the deposition of feed materials than do hot sources. The use of halogenated feed materials for producing dopants may help reduce deposits to some extent, however, in certain cases, non-halogen feed materials such as hydrides are preferred over halogenated compounds. For non-halogen applications, ion source feed materials such as gaseous B.sub.2H.sub.6, AsH.sub.3, and PH.sub.3 are used. In some cases, elemental As and P are used, in vaporized form. The use of these gases and vapors in cold ion sources has resulted in significant materials deposition and has required the ion source to be removed and cleaned, sometimes frequently. Cold ion sources which use B.sub.2H.sub.6 and PH.sub.3 are in common use today in FPD implantation tools. These ion sources suffer from cross-contamination (between N- and P-type dopants) and also from particle formation due to the presence of deposits. When transported to the substrate, particles negatively impact yield. Cross-contamination effects have historically forced FPD manufacturers to use dedicated ion implanters, one for N-type ions, and one for P-type ions, which has severely affected cost of ownership. Recently, cluster implantation ion sources have been introduced into the equipment market (see for example, U.S. Pat. Nos. 6,107,634; 6,288,403; and 6,958,481). U.S. Pat. Nos. 6,452,338; 6,686,595; and 6,744,214, hereby incorporated by reference, disclose ion sources that are unlike the Bernas-style sources in that they have been designed to produce “clusters”, or conglomerates of dopant atoms in molecular form, including ions of the form Asn+, Pn+, or BnHm+, where n and m are integers, and 2≦n≦18. Such ionized clusters can be implanted much closer to the surface of the silicon substrate and at higher doses relative to their monomer (n=1) counterparts, and are therefore of great interest for forming ultra-shallow p-n transistor junctions, for example in transistor devices of the 65 nm, 45 nm, or 32 nm generations. These cluster sources preserve the parent molecules of the feed gases and vapors introduced into the ion source. The most successful of these have used electron-impact ionization, and do not produce dense plasmas, but rather generate low ion densities at least 100 times smaller than produced by conventional Bernas sources, for example, as disclosed in the cluster ion sources mentioned above The use of B18H22 as an implant material for ion implantation of B18Hx+ in making PMOS devices is disclosed in Horsky et al. U.S. Patent Application Publication No. US 2004/0002202 A1, hereby incorporated by reference. FIG. 3 shows in schematic a cluster ion source 1 as described in more detail in U.S. Pat. No. 6,452,338, hereby incorporated by reference. The vaporizer 2 is attached to the vaporizer valve 3 through an annular metal gasket 4. The vaporizer valve 3 is likewise attached to the ionization chamber 5 by a second annular metal gasket 6. This ensures good thermal conduction between the vaporizer, vaporizer valve, and ionization chamber 5 through intimate contact via thermally conductive elements. A mounting flange 7 attached to the ionization chamber 5 allows mounting of the ion source 1 to the vacuum housing of an ion implanter, and contains electrical feedthroughs (not shown) to power the ion source, and water cooling feedthroughs 8, 9 to cool the ion source. The water feedthroughs 8, 9 circulate water through the source shield 10 to cool the source shield 10 and cool the attached components, the beam dump 11 and electron gun 12 (further described below). The exit aperture 13 is mounted to the ionization chamber 5 face by metal screws (not shown). Thermal conduction of the exit aperture 13 to the ionization chamber 5 is aided by an annular seal 14 which can be made from metal or a thermally conductive polymer. When the vaporizer valve 3 is in the open position, vaporized gases from the vaporizer 2 can flow through the vaporizer valve 3 to inlet channel 15 into the open volume of the ionization chamber 5. These gases are ionized by interaction with the electron beam transported from the electron gun 12 to the beam dump 11. The ions can then exit the ion source from the exit aperture 13, where they are collected and transported by the ion optics of the ion implanter. The vaporizer 2 is made of machined aluminum, and houses a water bath 17 which surrounds a crucible 18, wherein resides solid feed materials 19. The water bath 17 is heated by a resistive heater plate 20 and cooled by a heat exchanger coil 21 to keep the water bath at the desired temperature. The heat exchanger coil 21 is cooled by de-ionized water provided by water inlet 22 and water outlet 23. Although the temperature difference between the heating and cooling elements provides convective mixing of the water, a magnetic paddle stirrer 24 continuously stirs the water bath 17 while the vaporizer is in operation. A thermocouple 25 continually monitors the temperature of the crucible 18 to provide temperature feedback for a PID vaporizer temperature controller (not shown). The ionization chamber 5 is made of aluminum, graphite, or molybdenum, and operates near the temperature of the vaporizer 2 through thermal conduction. In addition to low-temperature vaporized solids, the ion source can receive gases through gas feed 26, which feeds directly into the open volume of the ionization chamber 16 by an inlet channel 27. In prior art systems, when the gas feed 26 is used to input feed gases, the vaporizer valve 3 is closed, however, in an embodiment of the invention, the feed material is vaporized in the vaporizer 2 and provided to the chamber 5 as a gas and the co-material gas is also provided to the chamber 5 via gas feed 26. The co-gas is introduced and metered via a commercial mass-flow-controller. FIG. 4 illustrates the geometry of the ion source with the exit aperture removed; the ion beam axis points out of the plane of the paper. An electron beam 32 is emitted from the cathode 33 and focused by the electron optics 34 to form a wide beam. The electron beam may be asymmetric, in that it is wider perpendicular to the ion beam axis than it is along that axis. The distribution of ions created by neutral gas interaction with the electron beam roughly corresponds to the profile of the electron beam. Since the exit aperture 13 is a wide, rectangular aperture, the distribution of ions created adjacent to the aperture 13 should be uniform. Also, in the ionization of decaborane and other large molecules, it is important to maintain a low plasma density in the ion source This limits the charge-exchange interactions between the ions which can cause loss of the ions of interest. Since the ions are generated in a widely distributed electron beam, this will reduce the local plasma density relative to other conventional ion sources known in the art. The electron beam passes through an entrance channel 35 in the ionization chamber and interacts with the neutral gas within the open volume 16. It then passes through an exit channel 36 in the ionization chamber and is intercepted by the beam dump 11, which is mounted onto the water-cooled source shield 10. Since the heat load generated by the hot cathode 33 and the heat load generated by impact of the electron beam 32 with the beam dump 11 is substantial, these elements, as well as the electron optics or anodes 34, are kept outside of the ionization chamber open volume 16 where they cannot cause dissociation of the neutral gas molecules and ions. Borohydrides Borohydride materials such as B.sub.10H.sub.14 (decaborane) and B.sub.18H.sub.22 (octadecaborane) under the right conditions form the ions B.sub.10H.sub.x.sup.+, B.sub.10H.sub.x.sup.−, B.sub.18H.sub.x.sup.+, and B.sub.18H.sub.x.sup.−. When implanted, these ions enable very shallow, high dose P-type implants for shallow junction formation in CMOS manufacturing. Since these materials are solid at room temperature, they must be vaporized and the vapor introduced into the ion source for ionization. They are low-temperature materials (e.g., decaborane melts at 100° C., and has a vapor pressure of approximately 0.2 Torr at room temperature; also, decaborane dissociates above 350° C.), and hence must be used in a cold ion source. They are fragile molecules which are easily dissociated, for example, in hot plasma sources. Contamination Issues of Borohydrides Boron hydrides such as decaborane and octadecaborane present a severe deposition problem when used to produce ion beams, due to their propensity for readily dissociating within the ion source. Use of these materials in Bernas-style arc discharge ion sources and also in electron-impact (“soft”) ionization sources, have confirmed that boron-containing deposits accumulate within the ion sources at a substantial rate. Indeed, up to half of the borohydride vapor introduced into the source may stay in the ion source as dissociated, condensed material. Eventually, depending on the design of the ion source, the buildup of condensed material interferes with the operation of the source and necessitates removal and cleaning of the ion source. Contamination of the extraction electrode has also been a problem when using these materials. Both direct ion beam strike and condensed vapor can form layers that degrade operation of the ion beam formation optics, since these boron-containing layers appear to be electrically insulating. Once an electrically insulating layer is deposited, it accumulates electrical charge and creates vacuum discharges, or so-called “glitches”, upon breakdown. Such instabilities affect the precision quality of the ion beam and can contribute to the creation of contaminating particles. It is desirable at times to be able to run an ion implantation system for implanting either monatomic ions or molecular ions, such as cluster ions. U.S. Pat. No. 7,107,929 and US Patent Application Publication No. 2007/0108394 A1, assigned to the same assignee as the present invention, are examples of ion sources that are configured to operate in dual modes and generate monatomic ions in an arc discharge mode of operation and molecular ions, such as cluster ions in a direct electron impact mode of operation. Some known dual mode ion sources are known utilize a first electron emitter which includes a cathode and an associated anode, remote from the ionization chamber which are configured to operate in a direct electron impact mode for the cluster ion feed material and also employ a second electron emitter disposed within the ionization chamber, to ionize the monatomic ion feed material. These electron emitters either use small gaps around the cathode (with remote support insulators) or adjacent insulators to prevent the cathode from shorting out to the ionization chamber. While such dual mode ion sources are a significant improvement over single mode ion sources, the need for multiple electron emitters in a single ion source adds a substantial amount of complexity. Thus, there is a need to provide an ion implantation system which includes an ion source which includes a single electron emitter, such as an electron emitter that includes a cathode that is located external to the ionization chamber which eliminates the need for an associated anode and which can be used in an arc discharge mode or alternatively incorporated into a dual mode ion source operable in a direct electron impact mode and an arc discharge mode. Briefly, the present invention relates to an ion source with an electron emitter that includes a cathode mounted external to the ionization chamber for use in fabrication of semiconductors. In accordance with an important aspect of the invention, the electron emitter is employed without a corresponding anode or electron optics. As such, the distance between the cathode and the ionization chamber can be shortened to enable the ion source to be operated in an arc discharge mode of and generate a plasma. Alternatively, the ion source can be operated in a dual mode with a single electron emitter by selectively varying the distance between the cathode and the ionization chamber. The present invention relates to an ion source which includes a single electron emitter that is configured with a cathode mounted external to the ionization chamber for use in fabrication of semiconductors. The ionization chamber is formed with an electron entrance aperture in one wall thereof. In accordance with one aspect of the invention, the cathode portion of the electron emitter, which may be either directly heated or indirectly heated, is located external to the ionization chamber. The cathode is juxtaposed so that emitted electrons are received by the electron entrance aperture and directed into the ionization chamber in order to ionize feed gases or vapors within the ionization chamber. In accordance with an important aspect of the present invention, the anode or other electron optics normally associated with the electron emitter are eliminated to enable the distance, i.e. gap, between the electron emitter and the ionization to be shortened. By shortening this distance, the ion source can be configured to operate in an arc discharge mode with an electron emitter that is completely external to the ionization chamber, thereby removing the entire electron emitter from the harsh plasma environment within the ionization chamber. In accordance with another important aspect of the invention, the ion source may be operated in both a direct electron mode of operation and an arc discharge mode of operation utilizing a single electron emitter. In this embodiment, the electron emitter is selectively located at a first distance from the ionization chamber for operation in an arc discharge mode and at a second distance for operation in a direct electron impact mode. In this embodiment, the electron emitter may be movably mounted and selectively secured to a desired position relative to the ionization chamber. Alternatively, the electron emitter can be rigidly mounted to a desired position. Accordingly, depending on the distance between the cathode and the ionization chamber, the ion source can be operated in a dual mode by selectively varying the distance between the cathode and the ionization chamber. The salient aspects of the present invention that relate to an ion source with a single electron emitter with an cathode external to the ionization chamber operable in single mode of operation or a dual mode of operation are illustrated in FIGS. 13-17 and described below. FIGS. 1-12 illustrate the general principles of an ion source that are applicable to the present invention. The ion source may include i) a vaporizer, ii) a vaporizer valve, iii) a gas feed, iv) an ionization chamber, v) an electron gun, vi) a cooled mounting frame, and vii) an ion exit aperture. Included are means for introducing gaseous feed material into the ionization chamber, means for vaporizing solid feed materials and introducing their vapors into the ionization chamber, means for ionizing the introduced gaseous feed materials within the ionization chamber, and means for extracting the ions thus produced from an ion exit aperture adjacent to the ionization region. In addition, means for accelerating and focusing the exiting ions are provided. The vaporizer, vaporizer valve, gas feed, ionization chamber, electron gun, cooled mounting frame, and ion exit aperture are all integrated into a single assembly in the ion source. Each of the features of the ion source is described below. Vaporizer: The vaporizer is suitable for vaporizing solid materials, such as decaborane (B.sub.10H.sub.14) and TMI (trimethyl indium), which have relatively high vapor pressures at room temperature, and thus vaporize at temperatures below 100° C. The temperature range between room temperature and 10° C. is easily accommodated by embodiments in which the vaporizer is directly associated with a water heat transfer medium, while other preferred arrangements accommodate novel material which produce significant vapor pressures in the range up to 200° C. For example, solid decaborane has a vapor pressure of about 1 Torr at 20° C. Most other implant species currently of interest in the ion implantation of semiconductors, such as As, P, Sb, B, C, Ar, N, Si, and Ge are available in gaseous forms. However, B.sub.10 and In are not, but can be presented in vapors from solid decaborane and TMI. The vaporizer of an embodiment of the invention is a machined aluminum block in which resides a sealed crucible containing the solid material to be vaporized, entirely surrounded by a closed-circuit water bath, which is itself enclosed by the aluminum block. The bath is held at a well-defined temperature by a closed-loop temperature control system linked to the vaporizer. The closed-loop temperature control system incorporates a PID (Proportional Integral Differential) controller. The PID controller accepts a user-programmable temperature setpoint, and activates a resistive heater (which is mounted to a heater plate in contact with the water bath) to reach and maintain it's setpoint temperature through a thermocouple readback circuit which compares the setpoint and readback values to determine the proper value of current to pass through the resistive heater. To ensure good temperature stability, a water-cooled heat exchanger coil is immersed in the water bath to continually remove heat from the bath, which reduces the settling time of the temperature control system. The temperature difference between the physically separate heater plate and heat exchanger coil provides flow mixing of the water within the bath through the generation of convective currents. As an added mixing aid, a rotating magnetic mixer paddle can be incorporated into the water bath. Such a temperature control system is stable from 20° C. to 100° C. The flow of gas from the vaporizer to the ionization chamber is determined by the vaporizer temperature, such that at higher temperatures, higher flow rates are achieved. The flow of gas from a vaporizer to the ionization chamber is determined by the vaporizer temperature, such that at higher temperatures, higher flow rates are achieved. The vaporizer communicates with the ionization chamber via a relatively high-conductance path between the crucible and the ionization chamber. This may be achieved by incorporating a relatively short, large-diameter, line-of-sight conduit between the two components. High-conductance gate valves (large diameter gates with a thin dimensioned housing) are used in the flow path between the vaporizer and source body, so as not to limit this conductance. By providing a high conductance for the transport of vapor to the ionization chamber, the pressure within the vaporizer and the temperature excursion required are lower than in prior vaporizers. In one embodiment of the ion source, a relatively low conductance supply path is achieved employing a 5 mm diameter, 20 cm long conduit, providing a conductance of about 7.times.10.sup.−2 L/s between crucible and ionization chamber. This would require a pressure within the vaporizer of about 2 Torr to establish an ionization chamber pressure of about 4.5 mTorr. Another embodiment employs an 8 mm diameter conduit of the same length, providing a conductance of about 3.times.10.sup.−1 L/s, allowing a pressure within the vaporizer of 0.5 Torr to achieve the same flow rate of material, and hence the same pressure of 4.5 mTorr within the ionization chamber. The static vapor pressure of a material at a given temperature and the dynamic pressure in the vaporizer crucible during the evolution and transport of vapor out of the crucible during operation are not the same. In general, the steady-state dynamic pressure is lower than the static vapor pressure, the extent depending on the distribution of source material within the vaporizer crucible, in addition to other details of construction. According to the invention, the conductances are made large to accommodate this effect. In addition, in certain preferred embodiments, the added openness of the ionization chamber to the vacuum environment of the source housing due to electron entrance and exit ports into the ionization chamber requires about twice the flow of gaseous material as a conventional Bernas-style source. Generally according to the invention, it is preferred that the conductance be in the range of about 3.times.10.sup.−2 to 3.times.10.sup.−1 L/s, preferably the length of the conduit being no less than 30 cm while its diameter is no less than about 5 mm, the preferred diameter range being between 5 and 10 mm. Within these limits it is possible to operate at much lower temperatures than conventional vaporizers, no large addition of temperature being required to elevate the pressure to drive the flow to the ionization chamber. Thus the temperature-sensitive materials are protected and a broad range of materials are enabled to be vaporized within a relatively small temperature range. In several of the embodiments of the vaporizer presented, the construction of the vaporizer, following these guidelines, allows operation at temperatures between 20° C. and 100° C. or 200° C. Given the high conductance of the vaporizer, and such temperature ranges, I have realized that the wide range of solid source materials that can be accommodated include some materials which have not previously been used in ion implantation due to their relatively low melting point. (It generally being preferred to produce vapors from material in solid form). An additional advantage of enabling use of only a relatively low pressure of vaporized gas within the crucible is that less material can be required to establish the desired mass flow of gas than in prior designs. In another embodiment a different vaporizer PID temperature controller is employed. In order to establish a repeatable and stable flow, the vaporizer PID temperature controller receives the output of an ionization-type pressure gauge which is typically located in the source housing of commercial ion implanters to monitor the sub-atmospheric pressure in the source housing. Since the pressure gauge output is proportional to the gas flow into the ion source, its output can be employed as the controlling input to the PID temperature controller. The PID temperature controller can subsequently raise or diminish the vaporizer temperature, to increase or decrease gas flow into the source, until the desired gauge pressure is attained. Thus, two useful operating modes of a PID controller are defined: temperature-based, and pressure-based. In another embodiment, these two approaches are combined such that short-term stability of the flow rate is accomplished by temperature programming alone, while long-term stability of the flow rate is accomplished by adjusting the vaporizer temperature to meet a pressure set-point. The advantage of such a combined approach is that, as the solid material in the vaporizer crucible is consumed, the vaporizer temperature can be increased to compensate for the smaller flow rates realized by the reduced surface area of the material presented to the vaporizer. In another embodiment of the vaporizer, a fluid heat transfer medium is not used. Rather than a water bath, the crucible is integral with the machined body of the vaporizer, and heating and cooling elements are embedded into the aluminum wall of the vaporizer. The heating element is a resistive or ohmic heater, and the cooling element is a thermoelectric (TE) cooler. The vaporizer is also encased in thermal insulation to prevent heat loss to the ambient, since the desired vaporizer temperature is typically above room temperature. In this embodiment, the heating/cooling elements directly determine the temperature of the walls of the vaporizer, and hence the temperature of the material within the crucible, since the material is in direct contact with the walls of the vaporizer which is e.g. machined of a single piece of aluminum. The same PID temperature controller techniques can be used as in the previously described embodiment, enabling the vaporizer to reach a temperature in excess of 100° C., preferably up to about 200° C. In another embodiment, the vaporizer consists of two mating, but separate components: a vaporizer housing and a crucible. The crucible is inserted into the housing with a close mechanical fit. The surface of the vaporizer housing which makes contact with the crucible contains a pattern of rectangular grooves, into which sub-atmospheric pressurized conductive gas is introduced. The pressurized gas provides sufficient thermal conductivity between the crucible and the temperature-controlled housing to control the temperature of the crucible surface in contact with decaborane or other solid feed material to be vaporized. This embodiment allows the crucible to be easily replaced during service of the vaporizer. The same PID temperature controller techniques can be used as in the previously described embodiment. In some embodiments, the vaporizer, while still close to the ionization chamber, communicating with it through a high conductance path, is physically located outside of, and removably mounted to, the main mounting flange of the ion source and the vaporizer communicates through the main mounting flange to the ionization chamber located within the vacuum system. In some embodiments, two vaporizers, independently detachable from the remainder of the ion source, are provided, enabling one vaporizer to be in use while the other, detached, is being recharged or serviced. Vaporizer Valve In the above described vaporizer embodiments, the vapors leave the vaporizer and enter the adjacent ionization chamber of the ion source through an aperture, which is preferably coupled to a thin, high conductance gate valve with a metal seal or other thermally conductive seal placed between the vaporizer and ionization chamber. The gate valve serves to separate the vaporizer from the ionization chamber, so that no vapor escapes from the vaporizer when the valve is shut, but a short, high-conductance line-of-sight path is established between the ionization chamber and vaporizer when the valve is open, thus allowing the vapors to freely enter the ionization chamber. With the valve in the closed position, the vaporizer with the valve attached may be removed from the ion source without releasing the toxic vaporizer material contained in the crucible. The ion source may then be sealed by installing a blank flange in the position previously occupied by the vaporizer valve. In another embodiment, two isolation valves are provided in series, one associated with the removable vaporizer and one associated with all of the other components of the ion source, with the disconnect interface being located between the two valves. Thus both parts of the system can be isolated from the atmosphere while the parts are detached from one another. One of the mating valves (preferably, the valve isolating the ion source body) has a small, valved roughing port integrated internal to the valve body, which enables the air trapped in the dead volume between them to be evacuated by a roughing pump after the two valves are mated in a closed position. If the source housing of the implanter is under vacuum, the vaporizer can be installed with its valve in a closed state after being refilled. It is mated to the closed valve mounted to the ion source in the implanter. The vaporizer valve can then be opened and the vaporizer volume pumped out through the roughing port (along with the gas trapped in the dead volume between the valves). Then the ion source valve can be opened, without requiring venting of the source housing. This capability greatly reduces the implanter down time required for servicing of the vaporizer. In another system, two such vaporizers, each with two isolation valves in series, as described, are provided in parallel, suitable to vaporize different starting materials, or to be used alternatively, so that one may be serviced and recharged while the other is functioning. Gas Feed In order to operate with gaseous feed materials, ion implanters typically use gas bottles which are coupled to a gas distribution system. The gases are fed to the ion source via metal gas feed lines which directly couple to the ion source through a sealed VCR or VCO fitting. In order to utilize these gases, embodiments of the ion source of the present invention likewise have a gas fitting which couples to the interior of the ionization chamber and connects to a gas distribution system. Ionization Chamber The ionization chamber defines the region to which the neutral gas or vapor fed to the source is ionized by electron impact. In certain embodiments, the ionization chamber is in intimate thermal and mechanical contact with the high conductance vaporizer valve or valves through thermally conductive gaskets, which are likewise in intimate thermal contact with the vaporizer through thermally conductive gaskets. This provides temperature control of the ionization chamber through thermal contact with the vaporizer, to avoid heat generated in the ionization chamber from elevating the temperature of the walls of the chamber to temperatures which can cause decaborane or other low-temperature vaporized materials or gases to break down and dissociate. In other embodiments, the ionization chamber, as a removable component, (advantageously, in certain instances, a regularly replaced consumable component) is maintained in good heat transfer relationship with a temperature-controlled body, such as a temperature controlled solid metal heat sink having a conventional water cooling medium or being cooled by one or more thermoelectric coolers. The ionization chamber in some embodiments is suitable for retrofit installation is sized and constructed to provide an ionization volume, extraction features, and ion optical properties compatible with the properties for which the target implanter to be retrofitted was designed. In some embodiments, the ionization chamber is rectangular, made of a single piece of machined aluminum, molybdenum, graphite, silicon carbide or other suitable thermally conductive material. Because contact of the ionization chamber with a fluid transfer medium is avoided in designs presented here, in certain instances the ionization chamber and extraction aperture are uniquely formed of low cost graphite, which is easily machined, or of silicon carbide, neither of which creates risk of transition metals contamination of the implant. Likewise for the low temperature operations (below its melting point) an aluminum construction may advantageously be employed. A disposable and replaceable ionization chamber of machined graphite or of silicon carbide is a particular feature of the invention. The ionization chamber in some embodiments is approximately 7.5 cm tall by 5 cm wide by 5 cm deep, approximating the size and shape of commercially accepted Bernas arc discharge ionization chambers. The chamber wall thickness is approximately 1 cm. Thus, the ionization chamber has the appearance of a hollow, rectangular five-sided box. The sixth side is occupied by the exit aperture. The aperture can be elongated as are the extraction apertures of Bernas arc discharge ion sources, and located in appropriate position in relation to the ion extraction optics. The flow rate of the gas fed into the ionization chamber is controlled to be sufficient to maintain proper feed gas pressure within the ionization chamber. For most materials, including decaborane, a pressure between 0.5 mTorr and 5 mTorr in the ionization chamber will yield good ionization efficiency for the system being described. The pressure in the source housing is dependent upon the pressure in the ionization chamber. With the ionization chamber pressure at 0.5 mTorr or 5 mTorr, the ion gauge mounted in the source housing, typically used in commercial ion implanters to monitor source pressure, will read about 1.times.10.sup.−5 Torr and 1.times.10.sup.−4 Torr, respectively. The flow rate from the vaporizer or gas feed into the ionization chamber required to sustain this pressure is between about 1 sccm and 10 sccm (standard cubic centimeters per minute). Electron Gun Except as mentioned below, the general principles of an electron gun suitable for use with the invention illustrated in FIGS. 13-17 are generally described below. However, those embodiments of the electron gun, for example, as illustrated in FIGS. 4, 4B, 4C, which illustrate an anode 34 or other electron optics between the cathode 33 and the electron entrance aperture 35 are not applicable to the invention illustrated in FIGS. 13-17 and are provided to provide a better understanding of the invention. For ionizing the gases within the ionization chamber, electrons of controlled energy and generally uniform distribution are introduced into the ionization chamber by a broad, generally collimated beam electron gun as shown in the illustrative figures described below. A high-current electron gun is mounted adjacent one end of the ionization chamber, external to that chamber, such that a directed stream of primary energetic electrons is injected through an open port into the ionization chamber along the long axis of the rectangular chamber, in a direction parallel to and adjacent the elongated ion extraction aperture. The cathode of the electron gun is held at an electric potential below the potential of the ionization chamber by a voltage equal to the desired electron energy for ionization of the molecules by the primary electrons. Two ports, respectively in opposite walls of the ionization chamber are provided to pass the electron beam, one port for entrance of the beam as mentioned above, and the second port for exit of the beam from the ionization chamber. After the electron beam exits the ionization chamber, it may be intercepted by a beam dump located just outside of the ionization chamber; the beam dump being aligned with the electron entry point, and preferably maintained at a potential somewhat more positive than that of the ionization chamber. The electron beam is of an energy and current that can be controllably varied over respective ranges to accommodate the specific ionization needs of the various feed materials introduced into the ionization chamber, and the specific ion currents required by the ion implant processes of the end-user. In particular embodiments, the electron gun is constructed to be capable of providing electron beam energy programmable between 20 eV and 500 eV. The lowest beam energies in this energy range accommodate selective ionization of a gas or vapor below certain ionization threshold energies, to limit the kinds of end-product ions produced from the neutral gas species. An example is the production of B.sub.10H.sub.x.sup.+ ions without significant production of B.sub.9H.sub.x.sup.+, B.sub.8H.sub.x.sup.+, or other lower-order boranes frequently contained in the decaborane cracking pattern when higher electron impact energies are used. The higher beam energies in the energy range of the electron gun are provided to accommodate the formation of multiply-charged ions, for example, As.sup.++from AsH.sub.3 feed gas. For the majority of ion production from the various feed gases used in semiconductor manufacturing, including the production of B.sub.10H.sub.x.sup.+from decaborane, an electron beam energy between 50 eV and 150 eV can yield good results. In some embodiments, the electron gun is so constructed that the electron beam current can be selected over a range of injected electron beam currents between 0.1 mA and 500 mA, in order to determine the ion current extracted from the ion source in accordance with the implant demand. Control of electron current is accomplished by a closed-loop electron gun controller which adjusts the electron emitter temperature and the electron gun extraction potential to maintain the desired electron current setpoint. The electron emitter, or cathode, emits electrons by thermionic emission, and so operates at elevated temperatures. The cathode may be directly heated (by passing an electric current through the cathode material), or indirectly heated. Cathode heating by electron bombardment from a hot filament held behind the cathode is an indirect heating technique well-practiced in the art. The cathode may be made of tungsten, tantalum, lanthanum hexaboride (LaB.sub.6), or other refractory conductive material. It is realized that LaB.sub.6 offers a particular advantage, in that it emits copious currents of electrons at lower temperatures than tungsten or tantalum. As discussed further below, the preferred separate mounting of the electron beam gun, thermally isolated from the ionization chamber, is an advantageous factor in keeping the ionization chamber cool. Electron beam guns having cathodes mounted close to the ionization chamber on a cooled support, which discharge directly into the chamber, are shown in the first two embodiments described below. The electron beam, however produced, has a significant cross-sectional area, i.e. it is a broad generally collimated beam as it transits the ionization chamber, to the beam dump with which it is aligned. In preferred embodiments, the electron beam within the ionization chamber has a generally rectangular cross section, e.g. in one embodiment approximately 13 mm.times.6 mm as injected into the ionization chamber, to match with a relatively wide extraction aperture of a high current machine, or the rectangular cross section is e.g. of a square cross-section profile for use with a narrower ion extraction aperture. In the case of direct injection, the shape of the injected electron beam can be determined by the shape of the electron optics, e.g. the grid and anode apertures of an electron gun, which, for example, may both be approximately 13 mm.times.6 mm, and also by the shape of the cathode or electron emitter, which, for the first example given, is somewhat larger than the grid and anode apertures, approximately 15 mm.times.9 mm. The advantage of generating a generally rectangular electron beam profile is to match the conventionally desired ion beam profile as extracted from the ion source, which is also rectangular. The rectangular exit aperture from which the ion beam is extracted is approximately 50 mm tall by 3.5 mm wide in many high-current implanters; in such cases the electron beam (and thus the ions produced by electron impact) can present a profile to the exit aperture within the ionization chamber of approximately 64 mm.times.13 mm. If the end-user wishes, an enlarged exit aperture may be employed to obtain higher extracted currents. As mentioned above, in the walls of the ionization chamber, there are both an electron entrance port and an aligned electron exit port for the electron beam, which departs from the conventionally employed Bernas ion source. In Bernas ion sources. energetic electrons produced by an emitter located typically internal to the ionization chamber strike the walls of the chamber to form the basis of an “arc discharge”. This provides a substantial heat load which elevates the temperature of the ionization chamber walls. In the present invention, the ionizing electrons (i.e the energetic or “primary” electrons) pass through the ionization chamber to the defined beam dump, substantially without intercepting the general chamber walls. “Secondary” electrons, i.e. low-energy electrons produced by ionization of the feed gas, still can reach the general walls of the ionization chamber but since these are low energy electrons, they do not provide significant heat load to the walls. The feature of through-transit of the primary electrons allows the ionization chamber to be conductively cooled, e.g. by the vaporizer, or by a cooled block against which the ionization chamber is mounted in substantial thermal contact, without providing a large heat load on the temperature controller of the vaporizer or block. To avoid the heat generated by the electron gun and the energetic electron beam, the electron gun and the electron beam dump are mounted in thermally isolated fashion, preferably either or both being mounted on respective water-cooled parts of a cooled mounting frame. This frame is dynamically cooled, e.g. by high-resistivity, de-ionized water commonly available in commercial ion implanters. Electron Repeller To maximize the source ionization efficiency, anti cathodes may be disposed at the opposite end of the ionization chamber from the electron emitter. The anti cathode typically operates at the same potential as the emitter, thus reflecting the electron beam back and forcing multiple passes of electrons through the ionization chamber. Alternatively, a magnetic reflector can be used. When charged particles travel towards a volume of increasing magnetic flux density, a condition exists where most of the electrons are reflected back into the direction where they came from. This effect is called magnetic mirror effect and is well characterized phenomena in plasma physics. To use this idea instead of an electrostatic anti cathode, a permanent magnet can be place at the opposite side of the ionization chamber from the emitter. This creates a strong magnetic field towards the end of the ionization chamber thus reflecting most of the ionizing electrons back towards the emitter end of the chamber. The magnetic repeller has the advantage of being in the same potential as it's surroundings, thus making it more reliable as an electrostatic anti cathode. Cooled Mounting Frame and Beam Dump: The cooled mounting frame is e.g. a water-cooled sheet metal assembly on which the electron gun and an electron beam dump may be mounted. The beam dump may be used alternatively to the electron repeller. The frame consists of two separate mechanical parts which allow the electron gun and a beam dump to be independently biased. By mounting these two components to this frame, a heat load to the ionization chamber can be substantially avoided. The frame provides a mechanical framework for the thus-mounted components, and in addition the frame and the mounted components can be held at an electric potential different from the potential of the ionization chamber and vaporizer by mounting to the ion source assembly on electrically insulating standoffs. In embodiments discussed below, the beam dump is discretely defined and isolated, preferably being removed from direct contact with the ionization chamber, with the electron beam passing through an exit port in the ionization chamber prior to being intercepted by the beam dump. The beam dump can readily be maintained at a potential more positive than the walls of the chamber to retain any secondary electrons released upon impact of primary electrons up on the beam dump. Also, the beam dump current can be detected for use in the control system as well as for diagnostics. Also, in a multi-mode ion source, by being electrically isolated, the voltage on the dump structure can be selectively changed to negative to serve an electron-repeller (anticathode) function, as described below. In another construction, the distinctly defined beam dump though can be in physical contact with the exit port in such a way that thermal conduction between the cooled beam dump and the exit port is poor e.g., by point contact of discrete elements. Electrical insulation, which has thermal insulation properties as well, can be provided to enable a voltage differential to be maintained while preventing heating of the general walls of the ionization chamber. One advantage of this embodiment is a reduced conduction of the source gas out of the ionization chamber, reducing gas usage. The extraction of ions from the ionization chamber is facilitated by an asymmetric relationship of the electron beam axis relative to the central chamber axis, locating the site of ionization closer to the extraction aperture. By maintaining a voltage on the aperture plate through which the ions are extracted that is lower than that of the other chamber walls, the ions are drawn toward the extraction path. In use of the ion source in a mode different from that used for decaborane as described above, e.g. using BF.sub.3 feed gas, the electron beam dump may be biased to a negative potential relative to the ionization chamber, e.g. to a voltage approximating that of the cathode potential, in a “reflex geometry” whereby the primary electrons emitted by the electron gun are reflected back into the ionization chamber and to the cathode, and back again repeatedly, i.e. instead of serving as a beam dump, in this mode the dump structure serves as a “repeller”, or anticathode. An axial magnetic field may also be established along the direction of the electron beam by a pair of magnet coils external to the ion source, to provide confinement of the primary electron beam as it is reflected back and forth between the cathode and beam dump. This feature also provides some confinement for the ions, which may increase the efficiency of creating certain desired ion products, for example B.sup.+ from BF.sub.3 feed gas. Such a reflex mode of operation is known per se by those practiced in the art, but is achieved here in a unique multi-mode ion source design capable of efficiently producing e.g. decaborane ions. A multimode ion source includes an electron gun for the purposes as described, disposed coaxially within a magnet coil that is associated with the source housing and ionization chamber contained within. FIG. 3 shows in schematic an embodiment of ion source 1. The vaporizer 2 is attached to the vaporizer valve 3 through an annular thermally conductive gasket 4. The vaporizer valve 3 is likewise attached to the mounting flange 7, and the mounting flange 7 is attached to ionization chamber body 5 by further annular thermally conductive gaskets 6 and 6A. This ensures good thermal conduction between the vaporizer, vaporizer valve, and ionization chamber body through intimate contact via thermally conductive elements. The mounting flange 7 attached to the ionization chamber 5, e.g., allows mounting of the ion source 1 to the vacuum housing of an ion implanter, (see FIG. 8) and contains electrical feedthroughs (not shown) to power the ion source, and water-cooling feedthroughs 8, 9 for cooling. In this preferred embodiment, water feedthroughs 8, 9 circulate water through the cooled mounting frame 10 to cool the mounting frame 10 which in turn cools the attached components, the electron beam dump 11 and electron gun 12. The exit aperture plate 13 is mounted to the face of the ionization chamber body 5 by metal screws (not shown). Thermal conduction of the ion exit aperture plate 13 to the ionization chamber body 5 is aided by conductive annular seal 14 of metal or a thermally conductive polymer. When the vaporizer valve 3 is in the open position, vaporized gases from the vaporizer 2 can flow through the vaporizer valve 3 to inlet channel 15 into the open volume of the ionization chamber 16. These gases are ionized by interaction with the electron beam transported from the electron gun 12 to the electron beam dump 11. The ions produced in the open volume can then exit the ion source from the exit aperture 37, where they are collected and transported by the ion optics of the ion implanter. The body of vaporizer 2 is made of machined aluminum, and houses a water bath 17 which surrounds a crucible 18 containing a solid feed material such as decaborane 19. The water bath 17 is heated by a resistive heater plate 20 and cooled by a heat exchanger coil 21 to keep the water bath at the desired temperature. The heat exchanger coil 21 is cooled by de-ionized water provided by water inlet 22 and water outlet 23. The temperature difference between the heating and cooling elements provides convective mixing of the water, and a magnetic paddle stirrer 24 continuously stirs the water bath 17 while the vaporizer is in operation. A thermocouple 25 continually monitors the temperature of the crucible 18 to provide temperature readback for a PID vaporizer temperature controller (not shown). The ionization chamber body 5 is made of aluminum, graphite, silicon carbide, or molybdenum, and operates near the temperature of the vaporizer 2 through thermal conduction. In addition to low-temperature vaporized solids, the ion source can receive gases through gas feed 26, which feeds directly into the open volume of the ionization chamber 16 by an inlet channel 27. Feed gases provided through channel 27 for the ion implantation of semiconductors include AsH.sub.3, PH.sub.3, SbF.sub.5, BF.sub.3, CO.sub.2, Ar, N.sub.2, SiF.sub.4, and GeF.sub.4, and with important advantages GeH.sub.4, SiH.sub.4, and B.sub.2H.sub.6, described below. When the gas feed 26 is used to input feed gases, the vaporizer valve 3 is closed. In the case of a number of these gases, the broad beam electron ionization of the present invention produces a mid-to-low ion current, useful for mid-to-low dose implantations. For higher doses, an embodiment capable of switching mode to a reflex geometry, with magnetic field, can be employed. The vaporizer 2 of FIG. 3, or that of FIG. 3A to be described, can be demounted from the ion source 1 by closing the vaporizer valve 3 and removing the unit at seal 6, (parting line D), compare FIGS. 3B and 3C. This is useful for recharging the solid feed material in the crucible 18, and for maintenance activities. In the embodiment of FIG. 3D, two valves, 3 and 3A are provided in series, valve 3 being permanently associated, as before, with removable vaporizer 28 and valve 3A being permanently associated with mounting flange 7, with the demounting plane D disposed between the two valves. In the embodiment of the ion source shown in FIG. 3A, the vaporizer 28 is of a different design from that of FIG. 3, while the rest of the ion source is the same as in FIG. 3. In vaporizer 28, there is no water bath or water-fed heat exchanger. Instead, the volume occupied by water bath 17 in FIG. 3 is occupied by the machined aluminum body 29 of vaporizer 28. A resistive heater plate 20 is in direct thermal contact with the vaporizer body 29 to conductively heat the body 29, and a thermoelectric (TE) cooler 30 is in direct thermal contact with the vaporizer body 29 to provide conductive cooling. A thermally insulating sleeve 31 surrounds the vaporizer 28 to thermally insulate the vaporizer from ambient temperature. If desired, several heater plates 20 and TE coolers 30 can be distributed within the vaporizer body 29 to provide more conductive heating and cooling power, and also to provide a more spatially uniform temperature to the crucible. This construction permits the vaporizer to operate at temperatures in excess of 100° C., up to about 200° C. FIG. 3B illustrates an embodiment in which successive mounting flanges of the series of vaporizer 28, isolation valve 3 and the ion source 1, are of increasing size, enabling access to each flange for detachment. Mounting flange 70 enables bolt-on of the assembled ion source to the ion source housing, see e.g. FIG. 8. Mounting Flange 7a enables attachment and detachment of the vaporizer 28 and its associated valve 3 from flange 7 at parting line D, see FIG. 3C. Mounting Flange 7b enables detachment of the valve 3 from the main body of the vaporizer for maintenance or recharging the vaporizer. The embodiment of FIG. 3D has two valves 3 and 3a, valve 3 normally staying attached to the vaporizer and valve 3a normally attached to ion source mounting flange 7. These enable isolation of both the vaporizer 28 and the ion source 1 before demounting the vaporizer at parting line D. The body of mated valve 3a includes roughing passage 90 connected by valve 92 to roughing conduit 91 by which the space between the valves may be evacuated, and, upon opening valve 3, by which the vaporizer may be evacuated prior to opening valve 3a. Thus attachment of vaporizer 28 need not adversely affect the vacuum being maintained in the ion source and beam line. The vent line 93, and associated valve 94 enables relief of vacuum within the vaporizer prior to performing maintenance and as well may be used to evacuate and outgas the vaporizer after recharging, to condition it for use. The embodiment of FIG. 3E illustrates a dual vaporizer construction, having the capabilities previously described. The vapor passage 15 in metal block heat sink 5a bifurcates near mounting flange 7, the branches 15′ leading to respective demountable vaporizers VAP1 and VAP2, each having two isolation valves separable at parting line D. The ionization chamber body 5b is of discrete construction, demountably mounted in intimate heat transfer relationship to temperature controlled mounting block 5a. Separate coolant passage 66 and 67 telescopically receive so-called squirt tubes which centrally conduct cold, deionized water to the dead end of the passage. The emerging cooled water has its maximum effect that that point, in the outward regions of respectively the mounting block 5a and the cooled frame 10, the water returns through the annular space defined between the exterior of the squirt tube and the passage in which the tube resides. FIG. 3F shows a vaporizer similar to that of FIG. 3A, but instead of a one-piece aluminum construction, the body of the vaporizer has two mating, but separate components: a vaporizer housing 29.sup.1 and a crucible 18.sup.1. The crucible is inserted into the housing 29.sup.1 with a close mechanical fit. The surface of the vaporizer housing which makes contact with the crucible contains a pattern of rectangular grooves, into which pressurized gas (typically at sub-atmospheric pressure) is introduced through gas inlet 93.sup.1. The pressurized gas provides sufficient thermal conductivity between the crucible 18.sup.1 and the temperature-controlled housing 291 to control the temperature of the crucible surface 65 in contact with decaborane or other solid feed material 19 to be vaporized. This embodiment allows the crucible 181 to be easily replaced during service of the vaporizer. Gas is also fed into the volume surrounding heat exchanger 21, to promote thermal conduction between the heat exchanger 21 and the housing 29.sup.1. The heat exchanger 21 is shown as a water-fed coil, but may alternatively comprise a TE cooler, such as cooler 30 in FIG. 3A. The electron beam passes through a rectangular entrance port 35 (FIG. 4) in the ionization chamber and interacts with the neutral gas within the open volume 16, defined within the ionization chamber body 5. The beam then passes directly through a rectangular exit port 36 in the ionization chamber and is intercepted by the beam dump 11, which is mounted on the water-cooled mounting frame 10. Beam dump 11 is maintained at a positive potential relative to the electron gun, and preferably slightly positive relative to the walls of the ionization chamber as well. Since the heat load generated by the hot cathode 33 and the heat load generated by impact of the electron beam 32 with the beam dump 11 is substantial, their location outside of the ionization chamber open volume 16 prevents their causing dissociation of the neutral gas molecules and ions. The only heat load from these elements to the ionization chamber is limited to modest radiation, so the ionization chamber can be effectively cooled by thermal conduction to the vaporizer 2 (FIG. 3) or by conduction to a massive mounting block 5a (FIG. 3E). Thus, the general walls of the ionization chamber can be reliably maintained at a temperature below the dissociation temperature of the neutral gas molecules and ions. For decaborane, this dissociation temperature is about 350° C. Since the ion exit aperture 37 in plate 13, shown in FIGS. 4B, 5 and 6, is a generally rectangular aperture, the distribution of ions created adjacent to the aperture by the broad, collimated beam of generally uniformly dispersed electrons should be likewise uniform. In the ionization of decaborane and other large molecules, according to this embodiment, an arc plasma is not sustained, but rather the gas is ionized by direct electron-impact ionization by the primary (energetic) electrons, in the absence of containment by any major confining magnetic field. The absence of such magnetic field limits the charge-exchange interactions between the ions and relatively cool secondary electrons as they are not strongly confined as they are in an arc plasma (confined secondary electrons can cause loss of the ions of interest through multiple ionizations). The decaborane ions are generated in the widely distributed electron beam path. This reduces the local ion density relative to other conventional ion sources known in the art. The absence of magnetic field can improve the emittance of the extracted ion beam, particularly at low (e.g., 5 keV) extraction energy. The absence of an arc plasma as in a Bernas source also can improve emittance since there is no plasma potential present in the ionization and extraction region. (I recognize that the presence of an arc plasma potential in conventional plasma-based ion sources introduces a significant random energy component to the ions prior to being extracted, which translates directly into an added angular spread in the extracted ion beam. The maximum angular spread theta. due to a plasma potential phi. is given by: .theta.=2 arcsin {.phi./E}.sup.½, where E is the beam energy. For example, for a plasma potential of 5 eV and a beam energy of 5 keV, .theta.=2.5 deg. In contrast, the random energy of ions produced by direct electron-impact ionization is generally thermal, much less than 1 eV.) FIG. 4A shows a top view of the electron exit port 36 in the open volume 16 of ionization chamber body 5, and its proximity to the ion exit aperture 37 in aperture plate 13. To enable the ions to be removed from the ionization chamber by penetration of an electrostatic extraction field outside of the ion source 1 through the ion exit aperture 37, the electron beam 32 and electron exit port 36 are situated close to the exit aperture plate 13 and its aperture 37. For example, a separation of between 6 mm and 9 mm between the edge of the ionization region and the ion extraction aperture can result in good ion extraction efficiency, the efficiency improving with larger width extraction apertures. Depending upon the particular parameters chosen, the broad, collimated electron beam 32 may not fully retain its rectangular profile due to scattering, and also due to space charge forces within the electron beam 32. The electron exit port 36 is sized appropriately in accordance with such design choices to allow passage of the electron beam without significant interception by the general walls of the ionization chamber body 5. Thus, in certain advantageous instances, port 36 is larger than port 35 so that it is aligned to receive and pass at least most of the residual electron beam. The embodiment of FIG. 4B illustrates a discretely defined beam dump 11′ which is sized and shaped to fit within port 36′ such that its inner, electron receiving surface lies flush with the inner surface of the surrounding end wall of the chamber body 5. Beam dump 11′ is mounted upon and is cooled by cooled frame 10, as before. As shows, a clearance space c, e.g., of 1 mm, is maintained between the beam dump structure and the wall of the chamber. Preferably, as shown, the structures are cooperatively shaped as in a labyrinth L.sub.s to limit the outflow of the dopant gas or vapor, while maintaining thermal and electrical isolation of the dump structure 11′ from the walls of the ionization chamber, maintaining electrical isolation of the beam dump 11′ while preventing loss of dopant gas or vapor. In the embodiment of FIG. 4C electrical insulation Z fills the space between the beam dump and the wall of the ionization chamber, maintaining electrical isolation of the beam dump 11′ while preventing loss of dopant gas or vapor. Referring to FIGS. 4D and 4E, a thermoelectrically or water-cooled outer housing H.sub.c defines a space into which a chamber-defining member 5c of heat-conductive and electrically-conductive material is removably inserted with close operational fit. Gas inlets G.sub.i introduce conductive gas of a subatmospheric pressure (e.g., between 0.5 and 5 Torr), that is significantly higher than that of the operational vacuum V.sub.o within the overall ion source housing 49 which contains the ionization chamber assembly. The conductive gas (for example, N.sub.2, Ar, or He) is introduced to the interface I.sub.f between matching surfaces of the housing and the chamber in regions remote from exposure of the interface to operational vacuum V.sub.o, and isolated from the vaporizer and process gas feed lines. In a preferred embodiment, the cooling gas is fed through an aluminum block or cooled housing and exits between the demountable ionization chamber and the block or housing, at the interface between them, into cooling channels machined into the aluminum block. The cooling channels have the form of linear grooves (e.g., 1 mm wide by 0.1 mm deep) which populate a significant percentage of the surface area between the two mating components. This construction allows the flat mating surfaces (the grooved aluminum surface and the flat surface of the separate ionization chamber) of the two components to mate flush with one another. Simple elastomeric o-rings encompass the surface area which contains the cooling channel grooves, ensuring that the gas confined to the cooling channels is isolated from regions which contain feedthroughs and passages for process gas or vapor within this interface, and also isolates the cooling gas from the ionization volume and from the vacuum housing. The spacing between those surfaces and the pressure of the conductive gas in the interface are so related that the mean-free path of the conductive gas molecules is of the order of or less than the spacing of opposed surface portions at the interface. The conductive gas molecules, by thermal motion, conduct heat across the interface from the chamber wall to the surrounding cooled housing elements. Any regions of actual physical contact between the solid material of the chamber body and of an outer housing element likewise promotes cooling by conduction. It is to be noted that the mode of conductive gas cooling described here does not depend upon convectional gas flow, but only upon the presence in the interface of the gas molecules. Therefore, in some embodiments, it may be preferred to form seals at the interface to capture the gas, as discussed above, although in other embodiments exposure of the interface at edges of the assembly with leakage to the operational vacuum V.sub.o can be tolerated just as is the case with respect to cooling of semiconductor wafers as described, e.g., in the King U.S. Pat. No. 4,261,762. In other embodiments, the cooling housing of the ionization chamber assembly or similar side wall elements of other structures of the ion source are water-cooled in the manner of cooling the mounting frame 10 as described herein. In some embodiments, depending upon the heat load on the ionization chamber, the heat conduction resulting from the inclusion of thermally conductive gasket seals, as well as regions of physical point contact between the matching surfaces of the chamber and housing elements is sufficient to keep the chamber within the desired temperature range, and the conductive gas-cooling feature described is not employed. It is recognized that the heat-transfer relationships described here have general applicability throughout the ion source and the other structural components of the implanter as well. Thus, the temperature of the vaporizer may be controlled by the heat transfer from a disposable crucible to surrounding elements via gas conduction at an interface, for operating conditions which require less than, for example, 2 W/cm.sup.2 of heat transfer through the gas interface. Likewise, surfaces of the electron gun, the electron beam dump, the mounting frame and the aperture plate may serve as conductors via a conductive gas interface to temperature-control elements such as the thermoelectrically or water-cooled housing that has been described, as illustrated in FIG. 4E. FIGS. 4F and 5 show different sizes of a broad, collimated electron beam passing through the ionization chamber, the profiles of these beams matched in profile to the wide and narrower apertures of the respective ionization chambers of FIGS. 4F and 5. FIG. 6 shows the ion exit aperture plate 13 with the axis of the ion beam directed normal to the plane of the paper. The dimensions of the exit aperture plate conform to the dimensions of the ionization chamber within body 5, approximately 7.6 cm tall.times.5.1 cm wide. The exit aperture plate contains an opening 37 which is approximately 5.1 cm in height, s, by 1.3 cm wide, r, suitable for high current implanters, and has a bevel 38 to reduce strong electric fields at its edges. It is matched by a broad, collimated electron beam having width g of 19 mm and depth p of 6 mm, cross-sectional area of 114 square mm. The aperture of the embodiment of FIG. 5, has similar features but a much narrower width, e.g. a width r.sup.1, 4 mm, matched by an electron beam of width g.sup.1 6 mm and a depth p.sup.1 of 6 mm. FIG. 7 shows the shape of the cathode 33, or electron emitter. In a preferred embodiment, it defines a planar emitting surface, it's dimensions being roughly 15 mm long.times.9 mm.times.3 mm thick. It can be directly heated by passing an electric current through it, or it can be indirectly heated, as shown, with an electric current flowing through filament 39 via leads 40, heating it to emit thermionic electrons 41. By biasing the filament 39 to a voltage several hundred volts below the potential of cathode 33, thermionic electrons 41 heat the cathode 33 by energetic electron bombardment, as is known in the art. FIG. 8 illustrates the assembly of an ion source according to FIG. 3A into a retrofit volume 60 of a previously installed ion implanter while FIG. 8A illustrates the complete ion implanter. In this particular embodiment nothing has been disturbed except that the Bernas ion source for which the implanter was originally designed has been removed and, into the vacated volume 60, the ion source of FIG. 3A has been installed, with its flange 7 bolted to the ion source housing flange. The extraction electrodes 53 remain in their original position, and the new ion source presents its aperture 37 in the same region as did the arc discharge Bernas source. The magnet coils 54 are shown remaining, available e.g., for operation in reflex mode if desired, or for applying a containment field for electrons proceeding to the beam dump 11. Water Cooled Block and Demountable Ionization Chamber In the embodiment of FIG. 3E, the ionization volume 16′ is defined by a demountable end module 5b which is mounted with conductive thermal contact on the end of solid mounting block 5a via thermally conductive seal 6″. For achieving demountability, the conductive seal 6″ is compressed via metal screws through mating surfaces of the block 5a and the demountable end module 5b. This construction enables the member 5b defining the ionization chamber 16′ to be removed from the block 5a and replaced with an unused member, advantageously of disposable construction. It also enables a different, and in some cases more efficient cooling of walls of the ionization chamber 16′ than in previous embodiments. For construction of the demountable member, in addition to aluminum (which is inexpensive and less injurious to the wafers being implanted than molybdenum, tungsten or other metals if transported to the wafer in the ion beam), the ionization chamber member Sb and exit aperture plate 13 are advantageously constructed from graphite or SiC, which removes altogether the possibility of metals contamination of the wafer due to propagation from the ion source. In addition, demountable ionization chambers of graphite and SiC may be formed cheaply, and thus can be discarded during maintenance, being less expensive to be replaced than a one-piece structure. In another embodiment, for conductively controlling the temperature of the block 5a and the chamber body 5b, they have mating smooth surfaces, the surface of the block containing machined cooling channels which admit conductive cooling gas between the block 5a and the chamber body 5b, so that that gas, introduced under vacuum, transfers heat by heat conduction (not convection) in accordance with the above description of FIGS. 4D and 4E, and cooling techniques used for the different situation of cooling wafers that are being implanted, see King U.S. Pat. No. 4,261,762. In this case, gaskets at the vapor and gas passages prevent mixing of the conductive heat transfer gas, such as argon, with the gas or vapor to be ionized. As shown, block 5a is cooled by water passages 24a, either associated with its own thermal control system, FIG. 3E or associated with the cooling system 24 that cools frame 10 on which the beam dump 11 is mounted. By being based upon heat conduction through solid members, water contact with the walls of the ionization chamber is avoided, making it uniquely possible to fabricate the ionization chamber of materials, such as low cost machined or molded graphite, which cannot conveniently be exposed to water. The remote location of the cathode and its heat effects combine with these mounting features to achieve desired cool-running of the ionization chamber. Electron Injection for High Current Applications For some ion implant applications, it is desired to obtain an ion current approaching the highest ion currents of which the technology is capable. This depends critically on the value of electron beam current traversing the ionization chamber, since the ion current produced is roughly proportional to the value of this electron current. The electron current injected into the ionization chamber is limited by the effects of space charge forces that act on the electron trajectories within the electron gun optics and the ionization chamber. In the space charge limit, these forces can add an increased width to a tightly focused beam waist produced by a lens, and can introduce an increased angular divergence to a beam as it diverges downstream of the waist. The maximum electron current which can be transported through a tube of diameter D and length L can be produced by focusing the beam on a point at the center of the tube with an angle a=D/L expressed in radians. In such case, the maximum current is given by: I.sub.max=0.0385 V.sup. 3/2a.sup.2 (1) where I.sub.max is the electron current measured in mA, and V is the voltage in volts corresponding to electrons of energy E=eV, where e is the electronic charge. Also, in this example the minimum waist diameter w is given by w=0.43 D. Inserting a=15.degree. and V=100V into equation (1) yields I.sub.max=10 mA, whereas inserting a=5.degree. and V=100V yields I.sub.max=106 mA. Referring to the embodiment of FIGS. 11-11B, biasing of the aperture plate is accomplished by forming it of an insulating material such as boron nitride, coating the exterior and interior surfaces which are exposed to the ions with an electrically conductive material such as graphite, and electrically biasing the conductor. In other embodiments insulator standoffs are employed, see FIG. 11C, to join the electrically conductive extraction aperture plate to the chamber while maintaining its electrical independence. In embodiments of this feature, gas loss from the ionization chamber at the edges of the aperture plate can be minimized by interfitting conformation of the edges of the electrically isolated aperture plate and the body of the ionization chamber (involuted design) to effect labyrinth seal effects such as described in relation to FIG. 4B. In accordance with the embodiment of FIGS. 12A, B and C, an electrically conductive aperture plate insert is mounted in an electrically insulating frame which holds the aperture plate in place, and provides an electrical contact to the insert. The embodiment facilitates change of aperture plates in accordance with changes of the type of implant run. In some embodiments thermoelectric coolers may be associated with the aperture plates to keep them from over-heating. In other embodiments, an extension of cooled frame 10 or a separate cooled mounting frame is employed to support the aperture plate. Universal Ion Source Controller A universal controller for the ion source of the invention uniquely employs the user interface that is used with arc discharge ion sources such as the Bernas and Freeman types. FIG. 9 shows, in diagrammatic form, a typical control system 200 for operating a Bernas type ion source. The operator for such existing machines programs the implanter through an Operator Interface 202 (OI), which is a set of selectable graphical user interfaces (GUI's) that are selectively viewed on a computer screen. Certain parameters of the implanter are controlled directly from the OI, by either manually inputting data or by loading a predefined implant recipe file which contains the desired parameters that will run a specific implant recipe. The available set of GUI's includes controls and monitoring screens for the vacuum system, wafer handling, generation and loading of implant recipes, and ion beam control. In many implanter systems, a predetermined set of ion source parameters is programmable through the Beam Control Screen of the OI represented in FIG. 9, including user-accessible setpoint values for Arc Current, Arc Voltage, Filament Current Limit, and Vaporizer Temperature. In addition to these setpoints, the actual values of the same parameters (for example, as indicated by the power supply readings) are read back and displayed to the operator on the OI by the control system. Many other parameters that relate to the initial set up of the beam for a given implant are programmed and/or displayed through the Beam Screen GUI, but are not considered part of the operator's ion source control. These include beam energy, beam current, desired amount of the ion, extraction electrode voltages, vacuum level in the ion source housing, etc. As indicated in FIG. 9, a dedicated Ion Source Controller 204 reads and processes the input (setpoint) values from the OI, provides the appropriate programming signals to the stack of power supplies 206, and also provides read backs from the power supplies to the OI. A typical power supply stack 206 shown in FIG. 9, includes power supplies for the Arc, Filament, and Vaporizer Heater, power supplies 208, 210 and 212, respectively. The programming and power generation for the Source Magnet Current may be provided in the screen, but is typically provided separate from the Ion Source Controller in many machines of the presently installed fleet. FIG. 9a shows the same elements as FIG. 9, but for a Bernas-style ion source of the kind which uses an indirectly-heated cathode (IHC). FIG. 9a is identical to FIG. 9, except for the addition of a Cathode power supply 211, and its read back voltage and current. The additional power supply is necessary because the IHC (indirectly heated cathode element) is held at a positive high voltage with respect to the filament, which heats the IHC by electron bombardment to a temperature sufficient that the IHC emits an electron current equal to the Arc Current setpoint value provided through the OI. The arc control is accomplished through a closed-loop control circuit contained within the Ion Source Controller. In general, the arc control of Bernas, Freeman, and IHC Bernas sources are accomplished through similar means, namely by on-board closed-loop control circuits contained within the Ion Source Controller. In order to physically retrofit the ion source of an existing ion implanter with an ion source of the present invention, the original ion source is removed from the source housing of the implanter, the power cables are removed, and the Ion Source Controller 204 and the power supplies 206 or 206.sup.1, i.e. the Filament Power Supply, Vaporizer Power Supply, Arc Power Supply, and Cathode Power Supply (if present) are removed from the gas box of the implanter. The Electron Beam Ion Source 1 of the present invention is inserted into the retrofit volume of the implanter, and the Electron Beam Ion Source Controller 220 and associated Power Supplies 207 are inserted into the vacated volume of the gas box. A new set of cables is connected. The desired mechanical configuration of the ion source is prepared prior to installation into the source housing of the implanter. For example, for decaborane production, a large width ion extraction aperture and a large dimension limiting aperture at the exit of the electron gun can be installed, to provide a large ionization volume. Additionally, if the implanter has installed a variable-width mass resolving aperture 44, the width of that aperture may be increased in order to pass a larger mass range of decaborane ions. Otherwise, the set-up proceeds in a conventional manner, modified according to the various features that are explained in the present text. In addition to the electron beam controls that have just been explained, a temperature control mechanism is provided for the vaporizer 2. The vaporizer is held at a well-defined temperature by a closed-loop temperature control system within the Controller 220. As has been explained above, the closed-loop temperature control system incorporates PID (Proportional Integral Differential) control methodology, as is known in the art. The PID controller accepts a temperature setpoint and activates a resistive heater (which is mounted to a heater plate in contact with the water bath (see FIG. 3), or in heat transfer relationship with the mass of the vaporizer body 29 (FIG. 3A) to reach and maintain its setpoint temperature through a thermocouple read back circuit. The circuit compares the setpoint and read back values to determine the proper value of current to pass through the resistive heater. To ensure good temperature stability, a water-cooled heat exchanger coil 21 is immersed in the water bath (in the case of the water-cooled vaporizer of FIG. 3), or a thermoelectric (TE) cooler 30 (in the embodiment of a solid metal vaporizer of FIG. 3A), or a heat-exchanger coil surrounded by heat-conducting gas (in the embodiment of a vaporizer utilizing pressurized gas to accomplish thermal conduction between the various elements as in FIG. 3F) to continually remove heat from the system, which reduces the settling time of the temperature control system. Such a temperature control system is stable from 20° C. to 200° C. In this embodiment, the flow of gas from the vaporizer to the ionization chamber is determined by the vaporizer temperature, such that at higher temperatures, higher flow rates are achieved. A similar temperature control system can be employed to control the temperature of conductive block 5a of FIG. 3E or 9B. As has also previously been explained, in another embodiment a different vaporizer PID temperature controller is employed. In order to establish a repeatable and stable flow, the vaporizer PID temperature controller receives the output of an ionization-type pressure gauge which is typically located in the source housing of commercial ion implanters to monitor the sub-atmospheric pressure in the source housing. Since the pressure gauge output is proportional to the gas flow into the ion source, it output can be employed as the controlling input to the PID temperature controller. The PID temperature controller can subsequently raise or diminish the vaporizer temperature, to increase or decrease gas flow into the source, until the desired gauge pressure is attained. Thus, two useful operating modes of a PID controller are defined: temperature-based, and pressure-based. In the embodiments of FIGS. 3 and 3A, temperature of the ionization chamber is controlled by the temperature of the vaporizer. Temperature control for the embodiment of FIG. 3E is achieved by a separate temperature sensing and control unit to control the temperature of the metal heat sink by use of a heat transfer medium or thermoelectric coolers or both. Calculations of Expected Ion Current The levels of ion current production that can be achieved with this new ion source technology are of great interest. Since the ion source uses electron-impact ionization by energetic primary electrons in a well-defined sizeable ionization region defined by the volume occupied by the broad electron beam in traversing the ionization chamber, its ion production efficiency can be calculated within the formalism of atomic physics: I=I.sub.0[I−exp {−n l s}] (3) [0268] where I.sub.0 is the incident electron current, I is the electron current affected by a reaction having cross section s, n is the number density of neutral gas molecules within the ionization volume, and I is the path length. This equation can be expressed as follows: f=1−exp {−L s pl} (4) [0269] where f is the fraction of the electron beam effecting ionization of the gas, L is the number density per Torr of the gas molecules at 0° C. (=3.538.times.10.sup.16 Torr.sup.−1 cm.sup.−3), s is the ionization cross section of the specific gas species in cm.sup.2, and pl is the pressure-path length product in Torr-cm. The peak non-dissociative ionization cross section of decaborane has not been published, so far as the inventor is aware. However, it should be similar to that of hexane (C.sub.6H.sub.14), for example, which is known to be about 1.3.times.10.sup.−15 cm.sup.2. For an ion source extraction aperture 5 cm long and an ionization chamber pressure of 2.times.10.sup.−3 Torr, equation (2) yields f=0.37. This means that under the assumptions of these calculations described below, 37% of the electrons in the electron current produce decaborane ions by single electron collisions with decaborane molecules. The ion current (ions/sec) produced within the ionization volume can be calculated as: I.sub.ion=fI.sub.el (5) [0271] where I.sub.ion is the ion current, and I.sub.el is the electron current traversing the ionization volume. In order to maximize the fraction of ion current extracted from the ion source to form the ion beam, it is important that the profile of the electron beam approximately matches in width the profile of the ion extraction aperture, and that the ions are produced in a region close to the aperture. In addition, the electron current density within the electron beam should be kept low enough so that the probability of multiple ionizations, not taken into account by equations (3) and (4), is not significant. The electron beam current required to generate a beam of decaborane ions can be calculated as: I.sub.eI=I.sub.ion/f (6) Given the following assumptions: a) the decaborane ions are produced through single collisions with primary electrons, b) both the gas density and the ion density are low enough so that ion-ion and ion-neutral charge-exchange interactions do not occur to a significant degree, e.g., gas density <10.sup.14 cm.sup.−3 and ion density <10.sup.11 cm.sup.−3, respectively, and c) all the ions produced are collected into the beam. For a 1 mA beam of decaborane ions, equation (6) yields I.sub.eI=2.7 mA. Since electron beam guns can be constructed to produce electron current densities on the order of 20 mA/cm.sup.2, a 2.7 mA electron beam current appears readily achievable with the electron beam gun designs described in this application. The density of primary electrons n.sub.e within the ionization volume is given by: n.sub.e=J.sub.e/e v.sub.e (7) [0275] where e is the electronic charge (=1.6.times.10.sup.−19 C), and v.sub.e is the primary electron velocity. Thus, for a 100 eV, 20 mA electron beam of 1 cm.sup.2 cross-sectional area, corresponding to a relatively wide ion extraction aperture as illustrated in FIG. 4F, equation (7) yields n.sub.e.apprxeq.2.times.10.sup.10 cm.sup.−3. For a narrow extraction aperture, as illustrated in FIG. 5, a 100 eV, 20 mA of 0.4 cm.sup.2 cross-sectional area would provide an electron density n.sub.e.apprxeq.5.times.10.sup.10 cm.sup.−3. Since the ion density, n.sub.i within the ionization volume will likely be of the same order of magnitude as n.sub.e, it is reasonable to expect n.sub.i<10.sup.11 cm.sup.−3. It is worth noting that since n.sub.e and n.sub.i are expected to be of similar magnitude, some degree of charge neutrality is accomplished within the ionization volume due to the ionizing electron beam and ions being of opposite charge. This measure of charge neutrality helps compensate the coulomb forces within the ionization volume, enabling higher values of n.sub.e and n.sub.i, and reducing charge-exchange interactions between the ions. An important further consideration in determining expected extraction current levels from the broad, collimated electron beam mode is the Child-Langmuir limit, that is, the maximum space charge-limited ion current density which can be utilized by the extraction optics of the ion implanter. Although this limit depends somewhat on the design of the implanter optics, it can usefully be approximated as follows: J.sub.max=1.72 (Q/A).sup. ½U.sup. 3/2d.sup.−2 (8) [0277] where J.sub.max is in mA/cm.sup.2, Q is the ion charge state, A is the ion mass in amu, U is the extraction voltage in kV, and d is the gap width in cm. For B.sub.10H.sub.x.sup.+ ions at 117 amu extracted at 5 kV from an extraction gap of 6 mm, equation (6) yields J.sub.max=5 mA/cm.sup.2. If we further assume that the area of the ion extraction aperture is 1 cm.sup.2, we deduce a Child-Langmuir limit of 5 mA of B.sub.10H.sub.x.sup.+ ions at 5 keV, which comfortably exceeds the extraction requirements detailed in the above discussion. Ion Extraction Aperture Considerations for the Broad, Aligned Beam Electron Gun Ion Source For the broad electron beam ion source, it is possible to employ a larger width ion extraction aperture than typically employed with high current Bernas arc discharge sources. Ion implanter beam lines are designed to image the extraction aperture onto the mass resolving aperture, which is sized to both achieve good transmission efficiency downstream of the mass resolving aperture, and also to maintain a specified mass resolution R (.ident.M/.DELTA.M, see discussion above). The optics of many high-current beam lines employ unity magnification, so that, in the absence of aberrations, the extent of the ion extraction aperture as imaged onto the resolving aperture is approximately one-to-one, i.e., a mass resolving aperture of the same width as the ion extraction aperture will pass nearly all the beam current of a given mass-to-charge ratio ion transported to it. At low energies, however, space charge forces and stray electromagnetic fields of a Bernas ion source cause both an expansion of the beam as imaged onto the mass resolving aperture, and also a degradation of the mass resolution achieved, by causing significant overlap of adjacent beams of different mass-to-charge ratio ions dispersed by the analyzer magnet. In contrast, in the ion source the absence of a magnetic field in the extraction region, and the lower total ion current level desired, e.g. for decaborane relative say to boron, uniquely cooperate to produce a much improved beam emittance with lower aberrations. For a given mass resolving aperture dimension, this results in higher transmission of the decaborane beam through the mass resolving aperture than one might expect, as well as preserving a higher R. Therefore, the incorporation of a wider ion extraction aperture may not noticeably degrade the performance of the beam optics, or the mass resolution of the implanter. Indeed, with a wider aperture operation of the novel ion source can be enhanced, 1) because of the greater openness of the wider aperture, the extraction field of the extraction electrode will penetrate farther into the ionization volume of the ionization chamber, improving ion extraction efficiency, and 2) it will enable use of a relatively large volume ionization region. These cooperate to improve ion production and reduce the required density of ions within the ionization volume to make the ion source of the invention production worthy in many instances. Care can be taken, however, not to negatively impact the performance of the extraction optics of the implanter. For example, the validity of equation (8) can suffer if the extraction aperture width w is too large relative to the extraction gap d. By adding the preferred constraint that w is generally equal to or less than d, then for the example given above in which d=6 mm, one can use a 6 mm aperture as a means to increase total extracted ion current. For retrofit installations, advantage can also be taken of the fact that many installed ion implanters feature a variable-width mass resolving aperture, which can be employed to open wider the mass resolving aperture to further increase the current of decaborane ions transported to the wafer. Since it has been demonstrated that in many cases it is not necessary to discriminate between the various hydrides of the B.sub.10H.sub.x.sup.+ ion to accomplish a well-defined shallow p-n junction (since the variation in junction depth created by the range of hydride masses is small compared to the spread in junction location created by boron diffusion during the post-implant anneal), a range of masses may be passed by the resolving aperture to increase ion yield. For example, passing B.sub.10H.sub.5.sup.+ through B.sub.10H.sub.12.sup.+ (approximately 113 amu through 120 amu) in many instances will not have a significant process impact relative to passing a single hydride such as B.sub.10H.sub.8.sup.+, and yet enables higher dose rates. Hence, a mass resolution R of 16 can be employed to accomplish the above example without introducing deleterious effects. Decreasing R through an adjustable resolving aperture can be arranged not to introduce unwanted cross-contamination of the other species (e.g., As and P) which may be present in the ion source, since the mass range while running decaborane is much higher than these species. In the event of operating an ion source whose ionization chamber has been exposed to In (113 and 115 amu), the analyzer magnet can be adjusted to pass higher mass B.sub.10H.sub.x.sup.+ or even lower mass B.sub.9H.sub.x.sup.+molecular ions, in conjunction with a properly sized resolving aperture, to ensure that In is not passed to the wafer. Furthermore, because of the relatively high concentration of the desired ion species of interest in the broad electron beam ion source, and the relatively low concentration of other species that contribute to the total extracted current (reducing beam blow-up), then, though the extracted current may be low in comparison to a Bernas source, a relatively higher percentage of the extracted current can reach the wafer and be implanted as desired. Benefits of Using Hydride Feed Gases, Etc. Beam currents obtainable with the broad electron beam ion source described can be maximized by using feed gas species which have large ionization cross sections. Decaborane falls into this category, as do many other hydride gases. While arc plasma-based ion sources, such as the enhanced Bernas source, efficiently dissociate tightly-bound molecular species such as BF.sub.3, they tend to decompose hydrides such as decaborane, diborane, germane, and silane as well as trimethyl indium, for example, and generally are not production-worthy with respect to these materials. It is recognized, according to the invention, however that these materials and other hydrides such as phosphene and arsine are materials well-suited to the ion source described here (and do not present the fluorine contamination problems encountered with conventional fluorides). The use of these materials to produce the ion beams for the CMOS applications discussed below, using the ion source principles described. For example, phosphene can be considered. Phosphene has a peak ionization cross section of approximately 5.times.10.sup.−16 cm.sup.2. From the calculations above, equation (6) indicates that a broad, collimated electron beam current of 6.2 mA should yield an ion current of 1 mA of AsH.sub.x.sup.+ ions. The other hydrides and other materials mentioned have ionization cross sections similar to that of phosphene, hence under the above assumptions, the ion source should produce 1 mA for all the species listed above with an electron beam current of less than 7 mA. On the further assumption that the transmission of the implanter is only 50%, the maximum electron beam current required would be 14 mA, which is clearly within the scope of electron beam current available from current technology applied to the specific embodiments presented above. It follows from the preceding discussion that ion currents as high as 2.6 mA can be transported through the implanter using conventional ion implanter technology. According to the invention, for instance, the following implants can be realized using the indicated feed materials in an ion source of the present invention: TABLE-US-00003 Low energy boron: vaporized decaborane (B.sub.10H.sub.14) Medium energy boron: gaseous diborane (B.sub.2H.sub.6) Arsenic: gaseous arsine (AsH.sub.3) Phosphorus: gaseous phosphene (PH.sub.3) Indium: vaporized trimethyl indium In(CH.sub.3).sub.3 Germanium: gaseous germane (GeH.sub.4) Silicon: gaseous silane (SiH.sub.4). The following additional solid crystalline forms of In, most of which require lower vaporizer temperatures than can be stably and reliably produced in a conventional ion source vaporizer such as is in common use in ion implantation, can also be used in the vaporizer of the present invention to produce indium-bearing vapor: indium fluoride (InF.sub.3), indium bromide (InBr), indium chloride (InCl and InCl.sub.3), and indium hydroxide {In(OH).sub.3}. Also, antimony beams may be produced using the temperature-sensitive solids Sb.sub.20.sub.5, SbBr.sub.3 and SbCl.sub.3 in the vaporizer of the present invention. In addition to the use of these materials, the present ion source employing the broad, aligned electron beam in a non-reflex mode of operation can ionize fluorinated gases including BF.sub.3, AsF.sub.5, PF.sub.3, GeF.sub.4, and SbF.sub.5, at low but sometimes useful atomic ion currents through single ionizing collisions. The ions obtainable may have greater ion purity (due to minimization of multiple collisions), with lessened space charge problems, than that achieved in the higher currents produced by Bernas sources through multiple ionizations. Furthermore, in embodiments of the present invention constructed for multimode operation, all of the foregoing can be achieved in the broad, aligned electron beam mode, without reflex geometry or the presence of a large magnetic confining field, while, by switching to a reflex geometry and employing a suitable magnetic field, a level of arc plasma can be developed to enhance the operation in respect of some of the feed materials that are more difficult to ionize or to obtain higher, albeit less pure, ion currents. To switch between non-reflex and reflex mode, the user can operate controls which switch the beam dump structure from a positive voltage (for broad, aligned electron beam mode) to a negative voltage approaching that of the electron gun, to serve as a reseller (anticathode) while also activating the magnet coils 54. The coils, conventionally, are already present in the implanters originally designed for a Bernas ion source, into which the present ion source can be retrofit. Thus a multi-mode version of the present ion source can be converted to operate with an arc plasma discharge (in the case of a short electron gun in which the emitter is close to the ionization volume as in FIGS. 4A-4D), in a manner similar to a Bernas source of the reflex type, or with a plasma without an active arc discharge if the emitter is remote from the ionization volume. In the embodiment described previously the existing magnet coils can be removed and modified magnet coils provided which are compatible with the geometry of a retrofitted, long, direct-injection electron gun. When these magnet coils are energized, the resultant axial magnetic field can confine the primary electron beam (both within the electron gun and in the ionization chamber) to a narrower cross-section, reducing the spreading of the electron beam profile due to space charge, and increasing the maximum amount of useful electron current which can be injected into the ionization volume. Since the electron emitter of this embodiment is remote from the ionization chamber, it will not initiate an arc discharge, but depending on the strength of the external magnetic field, will provide a low-density plasma within the ionization region. If the plasma density is low enough, multiple ionizations induced by secondary electron collisions with the ions should not be significant; however, the presence of a low-density plasma may enhance the space charge neutrality of the ionization region, enabling higher ion beam currents to be realized. Benefits of Using Dimer-Containing Feed Materials The low-temperature vaporizer of the present invention can advantageously use, in addition to the materials already mentioned, other temperature-sensitive solid source materials which cannot reliably be used in currently available commercial ion sources due to their low melting point, and consequently high vapor pressure at temperatures below 200° C. I have realized that solids which contain dimers of the dopant elements As, In, P, and Sb are useful in the ion source and methods presented here. In some cases, vapors of the temperature-sensitive dimer-containing compounds are utilized in the ionization chamber to produce monomer ions. In other cases, the cracking pattern enables production of dimer ions. Even in the case of dimer-containing oxides, in certain cases, the oxygen can be successfully removed while preserving the dimer structure. Use of dimer implantation from these materials can reap significant improvements to the dose rate of dopants implanted into the target substrates. By extension of equation (8) which quantifies the space charge effects which limit ion extraction from the ion source, the following figure of merit which describes the easing of the limitations introduced by space charge in the case of molecular implantation, relative to monatomic implantation, can be expressed: .DELTA.=n(V.sub.1N.sub.2).sup. 3/2(m.sub.1/m.sub.2).sup.−½ (9) where .DELTA. is the relative improvement in dose rate achieved by implanting a molecular compound of mass m.sub.1 and containing n atoms of the dopant of interest at an accelerating potential V.sub.1, relative to a monatomic implant of an atom of mass m.sub.2 at an accelerating potential V.sub.2. In the case where V.sub.1 is adjusted to give the same implantation depth into the substrate as the monomer implant, equation (9) reduces to .DELTA.=n.sup.2. For dimer implantation (e.g., As.sub.2 versus As), .DELTA.=4. Thus, up to a fourfold increase in dose rate can be achieved through dimer implantation. Table Ia below lists materials suitable for dimer implantation as applied to the present invention. TABLE-US-00004 TABLE IA Compound Melting Pt (deg C.) Dopant Phase As.sub.2O.sub.3 315 As.sub.2 Solid P.sub.2O.sub.5 340 P.sub.2 Solid B.sub.2H.sub.6—B.sub.2 Gas In.sub.2(SO.sub.4).sub.3 times. H.sub.2O 250 In.sub.2 Solid Sb.sub.2O.sub.5 380 Sb.sub.2 Solid Where monomer implantation is desired, the same dimer-containing feed material can advantageously be used, by adjusting the mode of operation of the ion source, or the parameters of its operation to sufficiently break down the molecules to produce useful concentrations of monomer ions. Since the materials listed in Table Ia contain a high percentage of the species of interest for doping, a useful beam current of monomer dopant ions can be obtained. Use of the Ion Source in CMOS Ion Implant Applications In present practice, ion implantation is utilized in many of the process steps to manufacture CMOS devices, both in leading edge and traditional CMOS device architectures. FIG. 10 illustrates a generic CMOS architecture and labels traditional implant applications used in fabricating features of the transistor structures (from R. Simonton and F. Sinclair, Applications in CMOS Process Technology, in Handbook of Ion Implantation Technology, J. F. Ziegler, Editor, North-Holland, N.Y., 1992). The implants corresponding to these labeled structures are listed in Table I below, showing the typical dopant species, ion energy, and dose requirements which the industry expects to be in production in 2001. TABLE-US-00005 TABLE I Energy Label Implant Specie (keV) Dose (cm.sup.−2) A NMOS source/drain As 30-50 1e15-5e15 B NMOS threshold adjust (V.sub.t) P 20-80 2e12-1e13 C NMOS LDD or drain P 20-50 1e14-8e14 extension D p-well (tub) structure B 100-300 1e13-1e14 E p-type channel stop B 2.0-6 2e13-6e13 F PMOS source/drain B 2.0-8 1e15-6e15 G PMOS buried-channel V.sub.t B 10-30 2e12-1e13H PMOS punchthrough P 50-100 2e12-1e13 suppression I n-well (tub) structure P 300-500 1e13-5e13 J n-type channel stop As 40-80 2e13-6e13 K NMOS punchthrough B 20-50 5e12-2e13 suppression L PMOS LDD or drain B 0.5-5 1e14-8e14 extension M Polysilicon gate doping As, B 2.0-20 2e15-8e15 In addition to the implants listed in Table I, recent process developments include use of C implants for gettering, use of Ge or Si for damage implants to reduce channeling, and use of medium-current In and Sb. It is clear from Table I that, apart from creating the source/drains and extensions, and doping the polysilicon gate, all other implants require only low or medium-dose implants, i.e. doses between 2.times.10.sup.12 and 1.times.10.sup.14 cm.sup.−2. Since the ion current required to meet a specific wafer throughput scales with the desired implanted dose, it seems clear that these low and medium-dose implants can be performed with the broad, aligned electron beam ion source of the present invention at high wafer throughput with ion beam currents below 1 mA of P, As, and B. Further, of course, the decaborane ion currents achievable according to the present invention should enable producing the p-type source/drains and extensions, as well as p-type doping of the polysilicon gates. It is therefore believed that the broad, aligned electron beam ion source described above enables high wafer throughputs in the vast majority of traditional ion implantation applications by providing a beam current of 1 mA of B.sub.10H.sub.14, As, P, and B or B.sub.2. The addition of Ge, Si, Sb, and In beams in this current range, also achievable with the present invention, will enable more recent implant applications not listed in Table I. Features of a further embodiment of the invention are shown in FIG. 13. In this embodiment, reference is made to the electron gun in which the emitter is close to the ionization volume as in FIGS. 4A-4D. However; a feature of this embodiment in contrast to FIGS. 3 and 4A-4D. More specifically, in contrast to known embodiments of ion sources which include electron emitters that include electron optics and/or an anode 34, as illustrated in FIGS. 4A-4D, the embodiment of the invention illustrated in FIGS. 4A-4D eliminates the need for an anode or other electron optics. Accordingly, in this embodiment of the invention, the electron gun 12 and specifically cathode emitter 33 may be located closer to the ionization volume than known ion sources, for example as illustrated in FIGS. 4A-4D forming a broad electron beam, consisting of dispersed electrons. In addition, a static or dynamic magnetic field B may be employed, e.g., by means of a permanent magnet or magnetic coils (not shown), as is known in the art. As shown in FIG. 13, the ion source 12 including the cathode 33 are immersed in a magnetic field B in a direction as shown by the arrow in the plane of the figure and transverse to the beam extraction direction which is perpendicular to the plane of the figure. It should be noted that the magnetic field direction can be opposite to the direction shown. In the embodiment of the invention shown in FIG. 13, the cathode 33 sits outside the ionization chamber volume. With such a configuration, the magnetic field traps the electrons emitted from the cathode 33 forming a column of electrons thus permitting operation without the electron optics. In particular, an electron beam is emitted from the cathode 33 and accelerated over the cathode-source gap, i.e the gap between the cathode 33 and the ionization chamber 5 while being trapped by the B-field. The resulting electron beam gyrates along the B-field lines maintaining its shape until hitting the electron beam dump 11 at an opposing end of the ionization chamber. In this mode, electrons have a single pass through the ionization chamber. Alternatively, a magnetic repeller may be installed in the beam dump location. In such an embodiment, the magnetic repeller is magnetized in the same direction as the main source B-field. This produces a magnetic mirror from which electrons are reflected before hitting the beam dump. This enables most of the electrons to pass more than once through the ionization chamber thus improving the efficiency of the source. Referring to FIG. 13, in operation, the electron beam 32 passes through an entrance port 45 in the ionization chamber 5 and interacts with the neutral gas within the open volume 16, defined within the ionization chamber body. The electron beam then passes directly through a exit port 36 in the ionization chamber 5 and is intercepted by the beam dump 11, which is mounted on the water-cooled mounting frame 10. The beam dump 11 may be biased, positive or negative, relative to the electron gun 12, i.e. cathode 33, and to the walls of the ionization chamber 5 as well, as is known in the art. In addition, the beam dump 11 may be maintained at the same or negative potential relative to the electron gun 12 or may employ a magnetic field, such that in both instances the beam dump 11 acts as a repeller. Alternatively, the beam dump 11 may be electrically isolated from the ionization chamber 5 and allowed to float electrically. In this case, the beam dump 11 is self-biased by the electron beam to a voltage within a few volts of the cathode voltage, which determines the kinetic energy of the electron beam, as is also known in the art. The cathode 33 may be an indirectly-heated cathode (IHC), or a directly heated filament. As is known in the art, the IHC element is held at a positive high voltage with respect to the filament, which heats the IHC by electron bombardment to a temperature sufficient for the IHC to emit an electron current. Feed gas is introduced into the ionization chamber 5 through gas vias, for example, the vias 15 or 27 illustrated in FIG. 3, depending upon the gas to be ionized, i.e., a cluster molecule or a monatomic feed material. Once inside the chamber 16, the electron beam 32 interacts with the gas to produce the ions, cluster or monatomic. The benefits of an anode free electron source as in the present invention include: a reduction in the source elements, elimination of the anode power supply, both of which reduce complexity of the design, improved transmission of the electron beam into the ionization chamber due to reduced electron beam space charge blow up, and elimination of failure modes associated with the anode held at a high positive voltage relative to the cathode, namely: a reduction in thermal loading of the anode, a reduction in glitches, that is, vacuum discharges between anode and chamber or anode and cathode; overloading of the anode voltage power supply and a reduction in electrical shorts associated with deposited material on or about the chamber entrance port 45 or the electron gun 12. An advantageous feature of the present invention is that by placing the cathode external to the ionization chamber, but still being proximate to said chamber, for example at a separation, d1, measured between the cathode 33 and the chamber 5, an extraction field between the cathode and ionization chamber can be established to efficiently extract and inject electrons into the ionization chamber, without the aid of intermediate electron optics. In this regard, a separation distance d1 between the cathode 33 and the ionization chamber 5, substantially equal to the distance in known ion sources as illustrated in FIGS. 4A-4D between the electron optics or anodes and the ionization chamber 5, for example 3 millimeters or more, as illustrated in FIG. 16. Such a configuration produces sufficient electron current to produce the necessary ionized beam of cluster gas molecules for the ion system. More significantly, FIG. 22 shows that with the elimination of the electron optics of the present invention, the extraction current versus cathode electron current for a monomer gas is substantially linear. Once a plasma is formed at the surface of the cathode, the electric field between cathode and ionization chamber will increase due to the formation of a plasma sheath. As established in the art, the plasma will settle at a potential within several volts of the ionization chamber potential. Since the sheath will be much narrower than the separation between cathode 33 and ionization chamber 5, the extraction field gradient increases. This allows a high extraction current which increases the ion beam current. Accordingly, the present invention is also able to generate a plasma or operate in an arc discharge mode and ionize suitable amounts of monomer feed gases as well as cluster molecule feed gases in a direct electron impact mode for commercial ion implantation depending on the separation distance d between the cathode 33 and the ionization chamber 5. In accordance with a further advantageous feature of the present invention, is that by adjusting the separation distance d1 of the cathode external to the ionization chamber with respect to the dimension of the entrance port d2, applicants can affect the ionization current of monomer gases. Specifically, FIG. 16 shows the ionization current of a monomer gas versus the separation distance d1. In this regard, a separation distance d1 substantially less than the dimension d2 of the entrance port 45, i.e., d1<d2 produces improved monomer ion beam current. In this example, applicants have found that a separation distance of about 3 mm produces the optimum bean current for monomer gas. As explained above, an advantageous feature of the present invention is obtained by placing the cathode external to the ionization chamber, but still proximate to said chamber, for example at a separation distance d1, an extraction field between the cathode 33 and ionization chamber 5 can be established to efficiently extract and inject electrons into the ionization chamber, without the aid of intermediate electron optics. In this case, an electron beam can be established. In some cases, it is also advantageous to inject plasma into the ionization chamber 5 in order to achieve a higher ion density, and hence higher ion beam currents. Since the external cathode 33 is necessarily in a rarified vacuum relative to the ionization chamber volume, conditions for creating a plasma are not typically met unless higher electron currents can be generated. Accordingly, in a further embodiment of the invention, this condition can be overcome by artificially raising the local pressure at the emitting surface of the cathode. A means to accomplish this is illustrated in FIG. 15 similar to FIG. 4. A wall member or baffle 37′ is shown attached to ionization chamber 5 and partially surrounds cathode 33 to increase the localized pressure proximate to the cathode 33. The baffle 37′ leaves an opening 2301 for the gas to flow to the vacuum pump (not shown). As is known in the art, the vacuum pump reduces the outside pressure P0 to a level about 100 times lower than the pressure P within the ionization chamber, for example the pressure within the chamber P is on the order of 10−3 Torr, whereas the pressure outside the chamber is on the order of P0 10−5 Torr. Insertion of baffle 37′ has the effect of limiting the conductance between the volume 2302 in the vicinity of the emitting surface of the cathode 33 and the pump 38′, raising the pressure Pk of the volume 2302 to a level Pk>P0. By tailoring the geometry of the baffle or wall member 37′ surrounding the cathode 33 to adjust its conductance, the pressure at the surface of cathode 33 can be adjusted to a given range. Raising the volume 2302 pressure Pk will allow a plasma to form more readily, while reducing the pressure Pk will restrict the formation of plasma. In this way, the onset of plasma formation which tends to characterize the transition from electron impact ionization to creation of a diffuse plasma discharge can be “tuned” for a given cathode and source geometry, while still maintaining the benefits of a remotely placed cathode. Once a plasma is formed at the surface of the cathode, the electric field between cathode 33 and the ionization chamber will increase due to the formation of a plasma sheath. As established in the art, the plasma will settle at a potential within several volts of the ionization chamber potential. Since the sheath will be much narrower than the separation between cathode 33 and ionization chamber 5 of FIG. 15, the extraction field increases. This enables higher electron currents to be drawn from the cathode, increasing the plasma density, thus further narrowing the sheath. This “positive feedback” mechanism for plasma production enables the onset of plasma formation to sensitively follow the local pressure at the surface of the cathode 33, making adjustment of this pressure by appropriate design of baffle 37′ of particular utility when the higher current is required. A magnetic field B, produced by a permanent magnet or energized coils (not shown), as disclosed above, is used in combination with this embodiment of the ion source 1, i.e., without the electron optics or anodes. The magnetic field B can confine the primary electron beam (both from the electron gun 12 and in the ionization chamber 16) to a narrowed cross-section, to reduce the spreading of the electron beam profile due to space charge, and increasing the maximum amount of useful electron current which can be injected into the ionization volume. As discussed, these features of the embodiments of the invention as shown in FIGS. 13 through 17 have significant benefits other than those associated with for example, simplicity, improvement in beam transmission, elimination of shorting by material deposition, mentioned above, that allows an ion source to run in multiple modes: the first mode is electron impact and the second is a plasma discharge, similar to the prior art arc discharge. This has the advantage of allowing these embodiments of the ion source to produce high currents of conventional monomer, such as, As, P & B as well as ion beams of cluster molecules. The fact that the ionization properties of the emitter change with the distance of the emitter 33 from the ionization chamber 5 can be exploited by incorporating a single emitter 33 which can be deployed such that its position is variable between a distance d1 and d2 from the ionization chamber. Alternatively, a single emitter 33 can be deployed whose position d is mechanically switchable between d1 and d2. FIG. 17 shows the latter embodiment, which is useful when switching between purely electron impact ionization (for molecular ion or cluster ion formation) and arc discharge plasma formation (for production of high currents of monomer ions) is desired. In this embodiment, cathode 33 could also extend into the ionization volume 16 of ionization chamber 5 to mimic the operation of a Bernas-style immersed cathode, as indicated in FIG. 17. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above. What is claimed and desired to be secured by a Letters Patent of the United States is: |
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056595905 | description | BEST MODE FOR CARRYING OUT THE INVENTION With reference to FIG. 1, an advanced boiling water reactor (ABWR) 10 is illustrated which incorporates a welded-in type core shroud. Prior to discussing the shroud configuration, however, it may be helpful to briefly describe the reactor construction in general. The reactor pressure vessel (or RPV) 12 is a substantially cylindrical vessel with a single full diameter removable head 14 bolted to the vessel as shown at 16. The RPV 12 houses the core shroud 18, the top guide assembly 20, the core plate assembly 22, steam separators 24 and steam dryers 26. Also included in the reactor assembly are the reactor internal pumps 28 (also referred to herein as jet pumps), control rods 30 and associated drives 32. The control rods 30 occupy alternate spaces between fuel assemblies within the core in a conventional fashion, and may be withdrawn into the guide tubes below the core during plant operation. An annular pump deck 34 extends around the core shroud 18, in the annular space or annulus 36 between the shroud 18 and the inside of the RPV sidewall. Pumps 28 project through the bottom of the RPV and include diffusers 38 which extend upwardly through pump openings or inlets 39 in the deck 34 and into the annulus 36 as best seen in FIG. 2. All major internal components of the conventional BWR type reactor can be removed except the jet pump diffusers 38, the core shroud 18, the jet pumps 28 and the high pressure coolant injection inlet piping. The invention here specifically has to do with the core shroud 18 and the pump deck 34, best seen in FIG. 2. As shown there, the jet pump discharge diffusers (one shown at 38) penetrates the pump deck 34 below the core elevation to introduce the coolant into the inlet plenum or annulus 36. The pump deck 34 itself is welded to the vessel wall at 12' as well as to the thickened base portion 18A of the shroud 18 at 40. The shroud base 38, in turn, is welded to an annular support leg 42 welded to the bottom of the vessel at 44. Thus, it will be appreciated that the shroud 18 and the pump deck 34 are intended to be permanent installations in the conventional BWR construction. With reference now to FIG. 3, a new removable core shroud 118 and pump deck 134 in accordance with this invention are illustrated. For convenience, similar reference numerals as used in FIGS. 1 and 2 are used in FIG. 3 where appropriate to identify corresponding elements, but with the prefix "1" added. In accordance with this invention, the annular shroud support leg 142 now extends upwardly above the pump inlet 139 and includes horizontal flow openings (one shown) 152. The support leg 142 has an upper edge or support surface 154 which is adapted to support the pump deck 134. At the same time, the outer periphery of the pump deck 134 is supported within an interior, radially inwardly facing annular groove 156 in the RPV wall at 112', the base of which is at the same height as surface 154 on support leg 142. This allows the pump deck 134 to be supported horizontally within the annulus 136 via insertion in the groove 156 and atop the support leg 142. It should be noted here that the annular pump deck 134 is provided in the form of ten part annular segments, the annular extent of each of which is made apparent from FIGS. 5 and 8, as discussed further hereinbelow. The shroud 118 and its thickened (but now axially shortened) base 118A are provided with a radially inwardly directed annular flange ring 158 which is welded to the bottom of the shroud base, and sized and located to seat fully on the surface 154. The flange ring 158 is formed with a through bore 160 which is aligned with a bore 162 in the pump deck and a bore 164 in the support leg 142 which opens into a radially inwardly facing, open recess 166. This arrangement allows a bolt 168 to pass through the bore 160 of flange 158, through the bore 162 in the pump deck 134, and into the recess 166 where it is threadably secured by a block nut 170 which is snugly received in the similarly shaped recess 166. It will be appreciated that a plurality of such bolt holes and bolts are circumferentially spaced about the flange ring, as best seen in FIG. 6. These bolts 168 restrain vertical loading on the shroud 118. Each block nut 170 is provided with a bail 171 which facilitates removal of the block nut 170 remotely (from above) with the aid of a specialized lifting tool (not shown), after the bolt has been disengaged from the nut. Bolts 168 are also provided with hex heads 172, and locking hex heads 174 which may be spot welded upon assembly. By this arrangement, it is not necessary to tap directly into the support leg 142, and no additional welds are required. With specific reference now to FIGS. 4 and 5, a plurality of wedge support blocks 176 are located on the segments of the pump deck 134 (for example, two wedge segment blocks per segment) at circumferentially spaced locations about the base portion 118A of the core shroud 118. These blocks 176 are radially outwardly spaced from the shroud base 118A and have radially inner tapered surfaces 178 (best seen in FIG. 4). This allows space for wedge elements 180 (two per support block) to be inserted between the shroud and the support blocks. The wedges 180 each have a mating tapered surface 182 for engagement with surface 178 of the respective block 176. The base 118A of the core shroud 118 as well as each block 176 are formed with aligned recessed grooves or keys 184, 186, respectively, for receiving the wedge elements 180, as further described below, and as best seen in FIG. 5. Each wedge element 180 is also provided with a lifting bail 188 to facilitate removal of the wedge element, again, by remote tooling. It will be understood that the wedging action between blocks 176 and wedge elements 180 serves to transfer horizontal loading on the shroud to the pump deck. As noted above, the annular pump deck 134 is divided into ten segments, nine of which are similar to that shown at 134A in FIG. 5. An otherwise conventional RIP diffuser 138 is located in the middle (circumferentially) of each segment. Turning now to FIGS. 6, 7 and 8, the tenth pump deck segment 134B serves as a keylock segment, which is the last segment installed and the first segment removed. This keyed segment 134B does not seat in a groove in the RPV wall, but rather, is seated on an arcuate support ledge 190 formed by the RPV wall by removing the upper part of the groove 156 in an arcuate portion substantially equal to the arcuate length of the segment 134B (FIG. 6). At annularly spaced locations along this keyed segment, the latter is bolted into the pressure vessel support ledge 190 as shown in FIGS. 7 and 8. A bolt and block nut/bail assembly 192, similar to the bolt 168, block nut 170 assembly, is utilized to secure the keyed segment to the RPV support ledge 190. Note also the recess 194 in the RPV wall which receives the block nut of the assembly 192. Once again the block nut of assembly 192 includes a bail element 196 to facilitate removal. With reference now to FIG. 9, it will be appreciated that removal of all bolts 168 and wedge elements 180 will enable the core shroud 118 to be lifted upwardly away from the core. The pump deck key segment 134B can then be unbolted and removed. The remaining pump deck segments 134A can then be pulled laterally out of the groove 156 in the RPV wall portion 112' (after its corresponding RIP diffuser 138 has been removed). It will be appreciated that, with the exception of the welds at the juncture of the shroud support leg 142 and the bottom of the RPV, virtually all horizontal welds are contained in removable elements, i.e., the shroud 118, shroud base 138 and pump deck 134, so that faulty welds can be relatively easily repaired and/or replaced. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. |
claims | 1. A projection exposure apparatus comprising: a light source providing radiation light; an illumination optical system directing said radiation light to a reflection mask on which a predetermined pattern is formed; a projection optical system directing said radiation light reflected by said reflection mask to a work for forming an image of a predetermined pattern on said work; and a scanning driver relatively moving at least one of said reflection mask and said work; wherein said illumination optical system includes a field stop located close by a position conjugate with said reflection mask. 2. A projection exposure apparatus according to claim 1 , wherein said illumination optical system includes a relay optical system to make said field stop substantially conjugate with said reflection mask. claim 1 3. A projection exposure apparatus according to claim 2 , wherein said relay optical system is a catoptric system. claim 2 4. A projection exposure apparatus according to claim 1 , wherein said light source provides radiation light having wavelength shorter than 50 nm. claim 1 5. A projection exposure apparatus according to claim 1 , further comprising at least one optical element located between said light source and said field stop, wherein a position of at least one optical element is adjustable in order to change illuminance distribution on said reflection mask or on said exposed substrate. claim 1 6. A projection exposure apparatus, for directing radiation light to a reflection mask on which a predetermined pattern is formed, and for projecting an image of said predetermined pattern on a work by said radiation light reflected by said reflection mask, the projection exposure apparatus comprising: a radiation light source; an illumination optical system located in an optical path between said radiation light source and said reflection mask, and directing said radiation light provided from said radiation light source to said reflection mask; a projection optical system located in an optical path between said reflection mask and said work, directing said radiation light reflected by said reflection mask to the work, and forming the image of said predetermined pattern on said work; a scanning driver relatively changing positional relationship between at least one of said reflection mask and said work, and said projection optical system; and a field stop located close by a position conjugate with said reflection mask. 7. A projection exposure apparatus according to claim 6 , wherein said field stop is located in said illumination optical system. claim 6 8. A projection exposure apparatus according to claim 7 , wherein said illumination optical system includes a relay optical system, located in an optical path between said field stop and said reflection mask, projecting an image of said field stop on said reflection mask. claim 7 9. A projection exposure apparatus according to claim 6 , wherein said radiation light source provides radiation light having wavelength below 50 nm. claim 6 10. An illumination apparatus, for using in a photolithography apparatus forming an image of a reflection mask, on which a predetermined pattern is formed, on a work, the illumination apparatus comprising: a radiation light source; and an illumination optical system located in an optical path between said radiation light source and said reflection mask, and for directing said radiation light provided from said radiation light source to a predetermined illumination area on said reflection mask; wherein said illumination optical system includes a field stop and a relay optical system forming an image of said field stop on said reflection mask as said predetermined illumination area. 11. An illumination apparatus according to claim 10 , wherein said radiation light source provides radiation light having wavelength shorter than 50 nm. claim 10 12. An illumination apparatus according to claim 10 , wherein said relay optical system is a catoptric system. claim 10 13. A method of projecting and exposing a predetermined pattern formed on a reflection mask onto a work, comprising the steps of: providing a radiation light source; illuminating the reflection mask on which the predetermined pattern is formed with said radiation light by means of an illumination optical system; projecting said pattern of said reflection mask onto said work by reflected light from said reflection mask; and relatively moving at least one of said reflection mask and said work; wherein said illuminating step further comprising a step of forming an image of a field stop positioned within said illumination optical system on said reflection mask. 14. A method according to claim 13 , wherein said radiation light having wavelength shorter than 50 nm. claim 13 15. A method according to claim 14 , further comprising a step of adjusting illuminance distribution on said reflection mask or on said work by changing a position of at least one optical element located along an optical path of said radiation light directed to said field stop. claim 14 16. A projection exposure apparatus, for directing radiation light to a reflection mask on which a predetermined pattern is formed, and for projecting an image of said predetermined pattern on a work by said radiation light reflected by said reflection mask, the projection exposure apparatus comprising: a radiation light source; an illumination optical system located in an optical path between said radiation light source and said reflection mask, and directing said radiation light provided from said radiation light source to said reflection mask; and a projection optical system located in an optical path between said reflection mask and said work, directing said radiation light reflected by said reflection mask to said work, and forming the image of said predetermined pattern on said work; wherein a position of at least one of reflection optical elements located along the optical path of said radiation light in said illumination optical system is adjustable in order to adjust illuminance distribution of said radiation light on said work, and said illumination optical system includes a field stop disposed near a plane conjugate with said reflection mask. 17. A projection exposure apparatus according to claim 16 , wherein said radiation light source provides radiation light having wavelength shorter than 50 nm. claim 16 18. A method of projecting and exposing a predetermined pattern formed on a reflection mask onto a work, comprising the steps of: providing a radiation light source; illuminating the reflection mask on which the predetermined pattern is formed with said radiation light by means of an illumination optical system having a field stop disposed near a plane conjugate with said reflection mask and optical elements positioned along an optical path of said radiation light directed to said field stop; projecting said pattern of said reflection mask onto an exposure area of said work by reflected light from said reflection mask; adjusting a position of at least one of said optical elements in order to change illuminance distribution on said exposure area of said work. 19. A method according to claim 18 , wherein said radiation light source provides light with wavelength shorter than 50 nm. claim 18 20. A projection exposure apparatus for projecting an image of a predetermined pattern formed on a reflection mask on a work, the projection exposure apparatus comprising: a radiation light source; an illumination optical system located in an optical path between said radiation light source and said reflection mask for directing radiation light from said radiation light source to said reflection mask, having at least one reflection optical element located along an optical path of said radiation light; and a projection optical system located in an optical path between said reflection mask and said work for directing light reflected by said reflection mask to the work and forming the image of said predetermined pattern on said work; wherein a position of at least one of said reflection optical element is adjustable in order to adjust distortion of said illumination optical system and illuminance distribution of said radiation light on said work. 21. A projection exposure apparatus according to claim 20 , wherein said radiation light source provides radiation light having wavelength shorter than 50 nm. claim 20 22. A method of projecting and exposing a predetermined pattern formed on a reflection mask onto a work, comprising the steps of: providing a radiation light source; illuminating the reflection mask on which the predetermined pattern is formed with radiation light from said radiation light source by means of an illumination optical system having a field stop and optical elements positioned along an optical path of said radiation light directed to said field stop; projecting said pattern of said reflection mask onto an exposure area of said work by reflected light from said reflection mask; and adjusting position of at least one of said optical elements in order to change distortion of said illumination optical system and illuminance distribution on said exposure area of said work. 23. A method according to claim 22 , wherein said radiation light source provides light with wavelength shorter than 50 nm. claim 22 24. A projection exposure apparatus for projecting an image of a predetermined pattern formed on a reflection mask on a work, the projection exposure apparatus comprising: a radiation light source; an illumination optical system located in an optical path between said radiation light source and said reflection mask for directing radiation light from said radiation light source to said reflection mask; and a projection optical system located in an optical path between said reflection mask and said work for directing light reflected by said reflection mask to the work and forming the image of said predetermined pattern on said work; wherein said illumination optical system includes a field stop arranged near a plane conjugate with said reflection mask, and the field stop includes a movable blade. 25. A projection exposure apparatus according to claim 24 , wherein said field stop includes a plurality of movable blades. claim 24 26. A projection exposure apparatus according to claim 24 , further comprising a scanning driver relatively moving at least one of said reflection mask and said work, claim 24 wherein said field stop adjusts a width in scanning direction. 27. A projection exposure apparatus according to claim 26 , wherein said radiation light source provides radiation light with wavelength shorter than 50 nm. claim 26 28. A projection exposure apparatus, for directing radiation light to a reflection mask on which a predetermined pattern is formed, and for projecting an image of said predetermined pattern on a work by radiation light reflected by said reflection mask, the projection exposure apparatus comprising: a radiation light source; an illumination optical system, located in an optical path between said radiation light source and said reflection mask, for directing said radiation light provided from said radiation light source to said reflection mask; a projection optical system, located in an optical path between said reflection mask and said work, for directing said radiation light reflected by said reflection mask to the work, and for forming the image of said predetermined pattern on said work; a mask stage for holding said reflection mask; a work stage for holding said work; a scanning driver, connected to at least one of said mask stage and said work stage, for relatively changing positional relationship between at least one of said reflection mask and said work, and said projection optical system along a sweeping direction; and a movable blade, located in an optical path between said radiation light source and said reflection mask, which is movable along a direction corresponding to said sweeping direction. 29. A projection exposure apparatus according to claim 28 , wherein said movable blade defines a width in the sweeping direction of an exposure area on said work. claim 28 30. A projection exposure apparatus according to claim 29 , wherein movement of said movable blade is synchronized with movement of at least one of said mask stage and said work stage. claim 29 31. A projection exposure apparatus according to claim 28 , wherein said radiation light source provides radiation light with wavelength shorter than 50 nm. claim 28 32. A method for projecting an image of a predetermined pattern formed on a reflection mask on a work with a projection optical system, the method comprising the steps of: providing radiation light; directing said radiation light to said reflection mask; directing said radiation light reflected by said reflection mask to the work; forming the image of said predetermined pattern on said work; changing positional relationship between at least one of said reflection mask and said work, and said projection optical system along a sweeping direction; and moving a movable blade along a direction corresponding to said sweeping direction. 33. A method according to claim 32 , wherein said movable blade defines a width in the sweeping direction of an exposure area on said work. claim 32 34. A method according to claim 33 , wherein movement of said movable blade is synchronized with movement of at least one of said mask and said work. claim 33 35. A method according to claim 32 , wherein said radiation light has wavelength shorter than 50 nm. claim 32 |
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041394135 | claims | 1. In a blow-off device for limiting excess pressure in nuclear power plants, at least one condensation tube disposed so that a lower outflow end thereof is immersed in a volume of water in a condensation chamber having a gas cushion located in a space above the volume of water, and an upper inflow end of the condensation tube extends out of the volume of water and is connectible to a source of steam that is to be condensed or a steam-air mixture, said outflow end of the condensation tube, for stabilizing the condensation, being provided with an assembly of wall parts forming passageways extending in axial direction for subdividing the steam flow and bubbles produced in the volume of water, said passageways of said assembly of wall parts being stepped in axial direction at both axial ends of said assembly of wall parts, said assembly of wall parts constitutes a plurality of tubes in mutually stepped disposition, said telescoped tubes are spaced from one another, defining annular zones therebetween and respective intermediate metal sheets are disposed in said annular zones. 2. Device according to claim 1 wherein said intermediate metal sheets in said annular zones are formed as axially oriented, circular wave-shaped metal sheets subdividing the respective annular zones and serving as spacers. 3. Device according to claim 2 including a tube bundle received in the passageway of the innermost of said telescoped tubes, said innermost passageway being subdivided by said tube bundle. 4. In a blow-off device for limiting excess pressure in nuclear power plants, at least one condensation tube disposed so that a lower outflow end thereof is immersed in a volume of water in a condensation chamber having a gas cushion located in a space above the volume of water, and an upper inflow end of the condensation tube extends out of the volume of water and is connectible to a source of steam that is to be condensed or a steam-air mixture, said outflow end of the condensation tube, for stabilizing the condensation, being provided with an assembly of wall parts forming passageways extending in axial direction for subdividing the steam flow and bubbles produced in the volume of water, said passageways of said assembly of wall parts being stepped in axial direction at both axial ends of said assembly of wall parts, said assembly of wall parts constitutes a plurality of tubes in mutually stepped disposition, said plurality of tubes having mutually stepped configurations at the axial inflow and outflow ends thereof that are mirror-images of one another. 5. In a blow-off device for limiting excess pressure in nuclear power plants, at least one condensation tube disposed so that a lower outflow end thereof is immersed in a volume of water in a condensation chamber having a gas cushion located in a space above the volume of water, and an upper inflow end of the condensation tube extends out of the volume of water and is connectible to a source of steam that is to be condensed or a steam-air mixture, said outflow end of the condensation tube, for stabilizing the condensation, being provided with an assembly of wall parts forming passageways extending in axial direction for subdividing the steam flow and bubbles produced in the volume of water, said passageways of said assembly of wall parts being stepped in axial direction at both axial ends of said assembly of wall parts, said assembly of wall parts constitutes a plurality of tubes in mutually stepped disposition, said mutually stepped disposition of said plurality of tubes constituting a substantially double conical structure and being formed by at least one central tube of relatively maximal length and annular zones with stepped tubes of decreasingly shorter relative length disposed around said central tube, one substantially conical end of said structure extending out of said condensation tube, the tubes of said structure extending farthest out of said condensation tube being also the tubes extending farthest into said condensation tube. |
claims | 1. A system for separating and coupling a top nozzle having a flow channel plate with guide holes and a fixing hole formed thereto, from/to a nuclear fuel assembly with guide thimbles, the system comprising:a lock insert configured to couple the guide thimbles of the nuclear fuel assembly to the flow channel plate of the top nozzle by being inserted into the guide holes provided in the flow channel plate of the top nozzle; anda separation part configured to separate the lock insert from the flow channel plate of the top nozzle,wherein the lock insert comprises a body in a hollow shape, and an insertion part provided on a top of the body and configured to be inserted into the guide holes,the insertion part comprising:a first latching member having a step, being fixed by being brought into contact with a latching step; anda second latching member having a projection, being fixed by being brought into contact with a latching groove,the insertion part being provided with at least one slot at a predetermined interval along a circumference of the insertion part to make the size of the circumference variable,the guide holes comprising:the latching step provided at an upper portion of an inner circumferential surface of the guide holes and configured to fix the lock insert; andthe latching groove provided at a predetermined portion of the inner circumferential surface of the guide holes and configured to fix the lock insert,wherein engagement of the first and second latching members with the latching step and latching groove alone locks the nuclear fuel assembly to the top nozzle,wherein the separation part comprises a separation member configured to release the coupling of the lock insert and the flow channel plate, and a fixing member configured to be engaged with a bottom surface of the flow channel plate through the fixing hole of the flow channel plate, wherein as the separation part is lowered, the coupling of the lock insert and the flow channel plate is released by the separation member and the fixing member is engaged with the bottom surface of the flow channel plate at the same time; and then as the separation part is lifted, the lock insert remains released from the flow channel plate and the flow channel plate of the top nozzle is lifted in engagement with the fixing member at the same time,wherein the separation member has a predetermined accommodation space formed therein to accommodate one side of the insertion part of the lock insert, and when the one side of the insertion part of the lock insert is inserted into the predetermined accommodation space, a surface of the separation member defining the accommodation space applies a force to the one side of the insertion part, thereby the size of the circumference of the insertion part is reducibly variable by the force and then the coupling between the lock insert and the flow channel plate is released, andwherein one end of the fixing member is provided with a fixing latching member having a step to be engaged with the bottom surface of the flow channel plate, thereby the flow channel plate of the top nozzle is lifted as the separation part is lifted. |
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description | The present application is a divisional of U.S. patent application Ser. No. 10/306,834, filed on Nov. 27, 2002 and entitled “THIN GAAS DIE WITH COPPER BACK METAL STRUCTURE,” the entirety of which is incorporated by reference herein. This invention relates generally to semi-conductor devices, and more particularly to Gallium Arsenide (GaAs) semiconductor devices. Two of the most common types of semiconductor die packages currently used are plastic packages and ceramic packages. Ceramic packages are preferred over plastic packages in some instances (e.g. when hemeticity and/or high frequency is required), but plastic packages are generally preferred over ceramic packages because plastic packages are less expensive. Plastic packages are routinely used to package silicon die, however, attempts to package GaAs semiconductor die in plastic packages have proven somewhat problematic. For example, although relatively thick GaAs die (i.e. those die having a thickness greater than about 3 mils) can be packaged in plastic, power dissipation characteristics of thick GaAs die limit the maximum power capabilities that can be implemented. In order to overcome the power dissipation problems and allow more complex circuits, attempts have been made to reduce the thickness of the GaAs die to less than 3 mils. However, the die handling processes associated with packaging are incompatible with thin, i.e. less than 3 mils, GaAs die. The use of a thick, about 18 μm, gold back metal layer has been proposed in an attempt to strengthen GaAs die thinned for power dissipation purposes. Unfortunately, the thick gold back-metal layer is incompatible with plastic packaging processes for at least two reasons: 1) the thick gold causes embrittlement of the soft-solder used in plastic packaging processes to attach the semiconductor die to the lead-frame; and 2) gold tends to de-laminate from a plastic package. What is needed, therefore, is a way to allow high-powered GaAs semiconductor die to be used in plastic packages. By allowing a high-powered semiconductor die to be used in a plastic package, substantial cost savings could be achieved without performance loss. FIGS. 1–3 illustrate a thin GaAs die with a copper back-metal structure suitable for use in a plastic package, in accordance with the present disclosure. In certain embodiments, various anti-stress and oxidation resistant layers are shown in addition to the copper back-metal layer. FIG. 2 illustrates a completed semiconductor die encapsulated in a plastic package. FIG. 3 illustrates the die of FIG. 1 in the plastic package of FIG. 2. FIG. 3 illustrates the die of FIG. 1 in the plastic package of FIG. 2. By providing a copper back-metal structure, a thin, high power, GaAs semiconductor die can be used in a plastic package. In general, the GaAs substrate is less than 2 mils (about 50 microns) thick, and particular embodiments of the GaAs substrate of the semiconductor die have thicknesses of approximately 1–2 mils (about 25–50 microns), less than approximately 1.5 mils (about 38 microns), or less than or equal to approximately 1 mil (about 25 microns). Approximately (and about), as used herein, generally refers to process limitations. For example, if a particular process for polishing a semiconductor substrate is conventionally performed to within 10 percent of the desired process parameter, then a substrate having a nominal thickness of approximately 1 mil (about 25 microns) will have an actual thickness of 0.9 mils (about 22 microns) to 1.1 mils (about 28 microns). The copper back-metal layer provides both mechanical strength and improved heat dissipation properties to the GaAs die, and makes the GaAs die compatible with soft-solder die attach technologies. Soft solder die attach refers to die attach methods using soft solders that generally comprise about 5% tin and 95% lead. Since soft-solder die attached methods are used when preparing a semiconductor die for encapsulation in a plastic package, the thin GaAs substrate with copper back-metal layer can be packaged in a plastic package. In discussing the structure of the semiconductor die illustrated in FIGS. 1–2, it will be appreciated that various processes known to those skilled in the art may be used in constructing the thin GaAs semiconductor die, the copper back-metal layer and other layers used for mechanical stress reduction, oxidation resistance, etc. The various layers described may be deposited using conventional sputtering, coating, crystalline growth, implantation, and/or other appropriate methods known to those skilled in the art. Referring now to FIG. 1, a thin GaAs semiconductor die with a copper back-metal layer will be discussed, wherein the semiconductor die is designated generally as Die 300. Die 300 includes a GaAs Substrate 310 in which a semiconductor circuit is formed using methods known to those skilled in the art. While not shown in FIG. 1, GaAs Substrate 310 may also include various interconnection terminals on top of GaAs Substrate 310 for connecting Die 300 to leads during the packaging process. A Diffusion Barrier 320 is formed over the bottom of GaAs Substrate 310, such that any subsequent layers formed over Diffusion Barrier 320 will not adversely impact the semiconductor circuits within GaAs Substrate 310. In at least one embodiment, Diffusion Barrier 320 includes an adhesion metal such as tantalum deposited in the form of tantalum nitride, or another suitable diffusion barrier known to those skilled in the art. It will be appreciated that the term “over” or “overlying” is used to describe a layer formed completely or partially over another layer or surface. For purposes of discussion herein the term “overlying” is used irrespective of the surface of the substrate on which overlying layer is formed. For example, a layer formed on the backside surface of a substrate and a layer formed on an active surface of a substrate are both considered to be overlying the substrate. A Stress Relief Layer 330 is formed over Diffusion Barrier 320 in at least one embodiment. Stress Relief Layer 330 provides protection for GaAs Substrate 310 and or diffusion layer 320 from uneven expansion, contraction or other physical movements of a back-metal or other layer overlying Stress Relief Layer 330. In at least one embodiment gold is used as a stress relief layer. While FIG. 1 illustrates a single stress relief layer, using more than one stress relief layer does not depart from the spirit and scope of the present invention. On top of Stress Relief Layer 330, a Copper Back-metal Layer 340 is formed. Copper Back-metal Layer 340 has a thickness chosen to be sufficient to provide the necessary support for GaAs Substrate 310 during the packaging process, including the process of soft-solder die attach. For example, a 3-mil-thick (about 76 microns) GaAs die needs very little, if any, additional mechanical support. Consequently, a 3-mil-thick (about 76 microns) GaAs die may not include Copper Back-metal Layer 340. However, a 1 mil thick (about 25 microns) GaAs die may include a Copper Back-metal layer 340 having a thickness of between about 11–15 microns to provide the additional mechanical support. An appropriate thickness for Copper Back-metal Layer 340 can be selected empirically. For example, if it is known that 18–19 microns of gold are needed to provide adequate mechanical strength for a 25 micron thick GaAs die, then using the known physical properties of gold and copper, for example tensile strength, malleability, etc., the thickness of copper needed to provide an equivalent mechanical stability can be calculated. In addition to mechanical support, Copper Metal Back layer 340 provides improved heat dissipation as compared to a thick GaAs substrate. As a result, GaAs Substrate 310 can be made thinner and still dissipate enough heat through the use of the Copper Metal Back layer 340 to support high power circuits formed overlying the thin GaAs Substrate 310. Those skilled in the art can readily calculate the amount of heat dissipation required by the circuits, and incorporate that information in their decision regarding the thickness of Copper Back-metal Layer 340. Finally, an Oxidation Resistant Layer 350 is formed over Copper Back-metal Layer 340 to prevent oxidation of Copper Back-metal Layer 340. Oxidation of Copper Back-metal Layer 340 is undesirable, since oxidation can adversely affect both the electrical and heat transfer properties of Copper Back-metal Layer 340. In addition, the oxidation can adversely affect the bonding of Copper Back-metal layer 340 to the packaging (e.g. to the solder). In at least one embodiment, Oxidation Resistant Layer 350 is a thin layer of gold about 1500 Angstroms thick, which is referred to as a flash of gold. It will be appreciated that the thickness of Oxidation Resistant Layer 350 should be limited, particularly when gold is used, because solder embrittlement may occur due to soft-solder attachment of Die 300 to a lead frame if the Oxidation Resistant Layer 350 is formed too thick. The semiconductor die shown in FIG. 1 is compatible with soft-solder die attach processes that are commonly used during packaging operations. In at least one embodiment, the GaAs Substrate 310 is less than 2 mils thick, thereby allowing a relatively high power circuit to be formed in GaAs Substrate 310. In other embodiments, GaAs Substrate 310 is less than 1 mil thick, and in at least one embodiment, GaAs Substrate 410 is nominally 1 mil (about 25 microns). The use of Copper Back-metal Layer 340 also permits Die 300 to be packaged in a plastic package, because Semiconductor Die 300 is compatible with soft-solder die attach methods. Referring next to FIG. 2 a semiconductor die having a thin GaAs substrate and a copper back-metal layer are illustrated inside of a plastic package according to an embodiment of the present invention. The packaged die will be referred to as Plastic Die Package 500. The semiconductor die illustrated in FIG. 2 includes a thin GaAs Substrate 510 (in one embodiment having a thickness in the range of 15–35 microns), a Diffusion Barrier 520, a Copper Back-metal Layer 530 and an Oxidation Resistant Layer 540. The semiconductor die is attached to Flag 560 using a soft-solder die attach method. Flag 560 is coated with Soft-solder Layer 590. Soft-solder Layer 590 is a layer of soft-solder, which in at least one embodiment comprises 5% tin and 95% lead. In alternate embodiments, eutectic solder or conductive epoxies can be used. In order to attach the semiconductor die to Flag 560, Soft-solder Layer 590 is heated, and brought into contact with the oxidation resistant layer 540 of the semiconductor die. The Oxidation Resistant Layer 540, a portion of the Copper Back-metal Layer 530 and Soft-solder Layer 590 melt such that the components of each of the layers intermingle with the others to form a solder joint when the heat is removed and the materials are allowed to cool. In at least one embodiment, when the solder process is complete, Soft-solder Layer 590 is adjacent to Copper Back-metal Layer 530, and the material in Oxidation Resistant Layer 540 (e.g. gold) is present within Soft-solder Layer 590, and at the interface between Soft-solder Layer 590 and Copper Back-metal Layer 530. Once the semiconductor die is attached to Flag 560, Flag 560 can provide an excellent thermal sink for the semiconductor die. After the semiconductor die is attached to Flag 560, Bonding Wires 582 are bonded to the die and Bonding Fingers 580, and then the assembly is in a mold die. Usually a plurality of such assemblies, e.g. as exist in a lead frame, is placed in a mold die. A thermoset plastic compound is transferred into a cavity of the mold die to encapsulate the semiconductor die, thus forming a completed semiconductor package such as Plastic Die Package 500. The thermoset plastic may be cured, and further processing (e.g. lead trim and form, package marking, and test) occur in a conventional manner. In summary, then, a thin GaAs Substrate can be provided with a copper back-metal layer to allow the GaAs Substrate to be packaged using conventional plastic packaging technologies. By providing the GaAs Substrate with a copper metal back layer, the GaAs substrate can be made thinner than 2 mils (about 50 microns), thereby reducing heat dissipation problems as well as allowing the semiconductor die to be compatible with soft-solder techniques. By enabling the semiconductor die to be packaged in a plastic package substantial cost savings can be achieved. In the preceding detailed description of the figures, reference has been made to the accompanying drawings, which form a part thereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that logical, mechanical, chemical, and electrical changes may be made without departing from the spirit or scope of the disclosure. Furthermore, many other varied embodiments that incorporate the teachings of the disclosure may be easily constructed by those skilled in the art. For example, additional diffusion layers and/or stress relief layers can be used in addition to those described. Accordingly, the present disclosure is not intended to be limited to the specific form set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents, as can be reasonably included within the spirit and scope of the invention. The preceding detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined only by the appended claims. |
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description | This application claims priority to foreign Patent Application KR 10-2009-0066455, filed on Jul. 21, 2009, the disclosure of which is incorporated herein by reference in its entirety. The present invention relates to a method for recovery of residual actinide elements from chloride molten salts and, more particularly, to a method for recovery of residual actinide elements from a chloride molten salt. Pyroprocess is a dry process for treatment of nuclear fuel using chloride molten salts at a high temperature in order to reduce the volume of a spent metal nuclear fuel and reuse the fuel materials. Actinide elements such as uranium (U) and transuranics (TRU) etc. remaining in a molten salt are recovered by electro-refining that uses a solid electrode to isolate pure uranium and by electro-winning that uses a liquid metal electrode to recover uranium and transuranics. For instance, the spent metal nuclear fuel is introduced into an anode in a LiCl—KCl eutectic salt, electric power is applied thereto to melt uranium and transuranic elements, and such uranium and transuranic elements are subjected to electro-deposition on an iron cathode or a liquid cadmium cathode (LCC), thereby recovering uranium and transuranic elements. Where a large amount of nuclear fuel is subjected to electro-refining and electro-winning, nuclear fission products are accumulated in a molten salt and a process for treatment of waste molten salt is required to eliminate such fission products. A volume of high radiation level waste and an amount of actinide elements for disposal generating from pyroprocessing must be minimized as much as possible, so as to reduce environmental burden and/or problems while improving the economic advantage of the pyroprocess. However, since some actinide elements such as uranium and transuranic elements remain in the molten salt, such actinide elements should be sufficiently removed prior to the treatment process of the waste molten salt. Conventional methods for recovery of residual actinide elements include, for example: reductive extraction, electrochemical treatment, oxidation and so forth. In Japan, a number of studies and investigations into development of a countercurrent flow type multi-staged reductive extraction method, which has high practical applicability in order to recover residual actinide elements from waste molten salts, have been conducted at the Central Research Institute of Electric Power Industry (CRIEPI). However, it is difficult to construct a multi-staged reductive extraction apparatus that flows a molten salt and a liquid metal to face each other in three to five stages according to a countercurrent flow way and allows these materials to come into contact with each other in two phases, wherein a difference between specific gravities of both the molten salt and the liquid metal is considerably high and operation of such apparatus is complicated. Moreover, in an aspect of practical utility, when a great amount of waste molten salt generated in a large scaled pyroprocess should be treated, the foregoing multi-staged reductive extraction apparatus requires increased capacity and has difficulties in continuous operation, causing deterioration in processing rate and efficiency. Argonne national laboratory (ANL) in the United States examined electrochemical recovery method using a Li—Cd anode material and an iron-based solid cathode. However, in such an electrochemical recovery using a solid cathode, disproportionation reaction wherein an electrodeposited metal portion reacts with a trivalent(+3) ion to produce a divalent(+2) ion unavoidably occurs, causing drastic decrease in recovery efficiency. One aspect of the present invention advantageously provides a method for recovery of residual actinide elements from a chloride molten salt that is formed after electro-refining and electro-winning of a spent nuclear fuel and contains rare-earth elements as well as actinide elements. Another aspect of the present invention advantageously provides a method for recovery of residual actinide elements from a chloride molten salt, that, if formed after electro-refining and/or electro-winning of a spent nuclear fuel, contains rare-earth elements as well as actinide elements, wherein this method is a hybrid process that adopts electro-winning using LCC for recovery of fuel materials used in a sodium fast reactor (SFR) for a future nuclear system and utilizes a CdCl2 oxidant and LCC electrolysis, so as to recover residual actinide elements. Embodiments of the present provide a method for recovery of residual actinide elements from a chloride molten salt, comprising: conducting electrolysis using a liquid cadmium cathode (LCC) in the chloride molten salt that is formed after electro-refining and/or electro-winning of a spent nuclear fuel and contains rare-earth elements and actinide elements; electro-depositing the actinide elements contained in the chloride molten salt on the LCC in order to reduce a concentration of the actinide elements; and adding a CdCl2 oxidant to the chloride molten salt containing the LCC-metal alloy in order to oxidize the rare-earth elements co-deposited on the LCC, thereby forming the rare-earth chlorides in the chloride molten salt. The method for recovery of residual actinide elements has various advantages, including a concentration of residual actinide elements may be decreased to 100 ppm or less by electro-depositing actinide elements remaining in the chloride molten salt, for example, waste molten salt such as LiCl—KCl eutectic salt on an LCC; an existing electro-winning apparatus and accessories thereof used for recovering uranium and transuranic fuel materials are also utilized without modification thereof, so that no additional equipment is required and an improved process with excellent convenience and simplicity is embodied, compared to conventional multi-staged reductive extraction processes currently developed in foreign countries including Japan. Accordingly, residual actinide elements, including uranium and transuranics remaining in a waste molten salt such as LiCl—KCl eutectic salt generated after electro-refining and electro-winning of a spent nuclear fuel, may be effectively removed to obtain a residual concentration of not higher than 100 ppm, and then, recovered. Therefore, a volume of high radiation level waste generating from pyroprocessing which is a dry process for treatment of a spent nuclear fuel as well as an amount of actinide elements for disposal may be considerably decreased, thereby proposing an important technology to overcome conventional problems such as mass generation of high radiation level waste and to improve the economic advantage of the pyroprocess. The present invention advantageously provides a considerably convenient and simple process capable of effectively removing and recovering residual actinide elements that remain in LiCl—KCl eutectic salts, compared to existing multi-staged reductive extraction processes. Embodiments of the present invention provide a method for recovery of residual actinide elements from a chloride molten salt that is formed after electro-refining and/or electro-winning of a spent nuclear fuel and contains actinide elements and rare-earth elements. The above method comprises conducting electrolysis using a liquid cadmium cathode (LCC) in the chloride molten salt that is formed after electro-refining and/or electro-winning of a spent nuclear fuel and contains rare-earth elements and actinide elements; electro-depositing the actinide elements contained in the chloride molten salt on the LCC in order to reduce a concentration of the actinide elements; and adding a CdCl2 oxidant to the chloride molten salt containing the LCC-metal alloy in order to oxidize the rare-earth elements co-deposited on the LCC, thereby forming the rare-earth chlorides in the chloride molten salt. The chloride molten salt may be a LiCl—KCl eutectic salt. The inventive method further comprises heating the chloride molten salt to 500° C. or more, preferably 500 to 700° C. in order to melt the same, before the electrolysis process wherein the LCC is used in the chloride molten salt. The electrolysis process in the inventive method wherein the LCC is used in a LiCl—KCl eutectic salt as the chloride molten salt may be conducted at a current density of 10 to 100 mA/cm2. Alternatively, the electrolysis process in the inventive method wherein the LCC is used in a LiCl—KCl eutectic salt as the chloride molten salt may be conducted at a current density of 10 to 100 mA/cm2, while using a glassy carbon as an anode material added to the chloride molten salt and generating chlorine gas at the anode. The foregoing electrolysis process wherein the LCC is used in the LiCl—KCl eutectic salt as the chloride molten salt, is substantially conducted at a current density of 10 to 100 mA/cm2 while using a glassy carbon as an anode material added to the chloride molten salt and generating chlorine gas at the anode. In this case, stepwise controlling the current density may enable recovery of actinide elements with a residual concentration of the same in the LiCl—KCl eutectic salt of not higher than 100 ppm. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The present invention relates to a method for recovery of residual actinide elements from a chloride molten salt by adopting a hybrid process utilizing LCC electrolysis and a CdCl2 oxidant. In the foregoing method for recovery of residual actinide elements from the chloride molten salt, LCC electrolysis of waste molten salt generated after electro-winning is firstly conducted and actinide elements remaining in the waste molten salt are electrodeposited on the LCC in order to considerably decrease a residual concentration of the actinide elements in the waste molten salt. Then, some rare-earth metal excessively co-deposited on the LCC during electrochemical recovery of the actinide elements deposited on the LCC are oxidized by adding the CdCl2 oxidant to the treated mixture and are extracted in the molten salt phase. The LCC with reduced content of rare-earth materials is reused in LCC electrochemical recovery of residual actinide elements and the actinide elements are removed, while the waste molten salt containing only rare-earth metals is forwarded to a salt waste treatment process (see FIG. 1 and FIG. 2). The inventive method for recovery of the residual actinide elements has a significant characteristic in that an existing electro-winning apparatus and accessories thereof used for recovering TRU fuel materials are directly utilized without modification thereof, thus not requiring alternative equipment. Moreover, the inventive method is advantageously simplified, compared to other multi-staged reductive extraction processes developed in foreign countries including Japan. The electrochemical recovery using LCC to recover the residual actinide elements from the waste molten salt has advantages of increasing a recovery efficiency of americium (Am) co-existing in both of divalent(+2) and trivalent(+3) states, when practically treating the used nuclear fuel. Electrochemical recovery using a solid cathode entails an unavoidable disproportionation reaction wherein deposited metals react with trivalent ions to produce divalent ions, causing a decrease in recovery efficiency. However, LCC may considerably reduce generation capability of the disproportionation reaction, thus enhancing the recovery efficiency. Consequently, the present invention uses LCC as an electrochemical recovery cathode. A process of oxidizing some rare-earth metals co-deposited on the LCC in the molten salt using a CdCl2 oxidant and chlorinating the same has been proposed from a principle wherein rare-earth elements only are selectively oxidized and extracted by thermodynamic property based on a difference of Gibbs free energy, ΔG, of formation of metal chloride (see TABLE 1). The inventive method for recovery of residual actinide elements from a chloride metal salt was subjected to practical experiments under various conditions and, as a result of the experiments, it was found that the method for recovering residual actinide elements from the chloride molten salt under the aforementioned conditions is preferable. Hereinafter, the present invention will be described in greater detail by the following examples and experimental examples, which are given for illustrative purposes but are not construed to restrict the scope of the present invention as defined by the appended claims. TABLE 1Free Energies of Formation of Chlorides at 500° C. kJ/g − equiv. Chlorine−ΔGf0−ΔGf0(KJ/g − (KJ/g − Compoundequiv. −Cl)Compoundequiv. −Cl)KCl363.76AmCl3266.38LiCl345.27CmCl3284.99PuCl3261.41LaCl3293.62NpCl3242.91CeCl3287.37UCl3232.35NdCl3281.45ZrCl2194.18GdCl3273.02CdCl2136.30YCl3272.50FeCl2124.38NbCl5107.62MoCl367.96TeCl344.33Ions in salt phaseMetals in Cd phase An experiment for recovering residual actinide elements in a waste molten salt was conducted by electro-depositing actinide elements in the molten salt on an LCC and electro-depositing the actinide elements at a current density of 10 to 100 mA/cm2 until a residual concentration of the actinide elements is decreased to 100 ppm or less, and then, measuring cyclic voltammetry CV (see FIG. 3). Afterward, most rare-earth metals excessively co-deposited on the LCC were oxidized and extracted by adding a CdCl2 oxidant to the molten salt. For the selective oxidation of CdCl2 process, a change in amount of actinide elements and rare-earth metals in the molten salt was determined using CV by each interval of 30 minutes and a variation in status of the molten salt was observed in real time, so as to determine progress of the reaction (see FIG. 4). The electrochemical recovery experiment was conducted using five representative rare-earth elements such as Nd, Ce, Gd, La and Y as well as actinide elements. As a result of experiments for LCC electro-deposition under different conditions, preferable electrochemical recovery conditions were defined. With about 1.5 wt % concentration of the actinide elements and five rare-earth elements, the electrochemical recovery experiment was carried out using a glassy carbon anode at an agitation speed of 50 rpm and a current density of 30 mA/cm2. From a result of ICP quantitative analysis and CV results measured by experiment, it was found that the residual concentration of actinide elements in the waste molten salt may be decreased to 100 ppm or less (see FIG. 5). The selective oxidation experiment was conducted to determine a constitutional composition of the rare-earth element chloride generated in the molten salt depending on an amount of an oxidant added to the same molten salt electrolysis bath as used for electrochemical recovery of actinide elements, thereby evaluating the composition. For this purpose, RE metals only were selectively oxidized by stepwise increasing an amount of the CdCl2 oxidant in the molten salt. In order to decrease the residual concentration of actinide elements to 100 ppm or less by electro-depositing rare-earth elements as well as the actinide elements on the LCC, the molten salt was subjected to electro-deposition. Following this, the amount of the CdCl2 oxidant was pre-metered to oxidize 50%, 75% and 90% of a total amount of the rare-earth elements co-deposited on the LCC and was stepwise added to the molten salt. From the experiment, it was found that the rare-earth metals only were selectively oxidized. As a result of ICP quantitative analysis of metal concentration in the molten salt, it was found that controlling an amount of the added oxidant may favorably maintain the residual concentration of actinide elements to 100 ppm or less which is a target value of the foregoing experiment. While the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various modifications and variations may be made therein without departing from the scope of the present invention as defined by the appended claims. |
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description | This disclosure-relates generally to quality assurance for radiation delivery systems, and in particular but not exclusively, relates to a respiration phantom. In radiosurgery or radiotherapy (collectively referred to as radiation treatment) very intense and precisely collimated doses of radiation are delivered to a target region in the body of a patient in order to treat or destroy lesions. Typically, the target region is composed of a volume of tumorous tissue. Radiation treatment requires an extremely accurate spatial localization of the targeted lesions. As a first step in performing radiation treatment, it is necessary to determine with great precision the location of a lesion and any surrounding critical structures, relative to the reference frame of the treatment device. Computed tomography (“CT”), magnetic resonance imaging (“MRI”) scans, and other imaging modalities enable practitioners to precisely locate a lesion relative to skeletal landmarks or implanted fiducial markers. However, it is also necessary to control the position of the radiation source so that its beam can be precisely directed to the target tissue while avoiding adjacent critical body structures. Thus radiation treatment necessitates high precision diagnosis and high precision radiation source control. The consequences of deviating outside the prescribed tolerances for the diagnosis and the radiation source control can be potentially devastating to a patient. Accordingly, quality assurance mechanisms should be implemented to ensure proper alignment and configuration of the radiation delivery system prior to delivering a prescribed radiation dose to a patient. Conventional quality assurance mechanisms include pointing the radiation source at an alignment marker, delivering a radiation dose to the alignment marker, and then analyzing the alignment marker itself to determine if the prescribed dose was actually delivered to the correct location. If the prescribed dose was delivered as expected, then the radiation treatment delivery system is deemed properly aligned. If the prescribed dose was not delivered as expected, then the radiation treatment delivery system is deemed misaligned. Conventional alignment markers include silver loaded gels capsules or photographic film canisters that can store readable information about the distribution of the radiation dose delivered to the alignment marker. However, these alignment markers are static objects that neither resemble an actual patient nor move as a patient would due to breathing. As such, prior art alignment markers do not adequately recreate the actual conditions that exist during delivery of a prescribed dose of radiation to a living patient. Embodiments of a system and method for respiration phantom for quality assurance testing of a radiation delivery system are described herein. In the following description numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. FIG. 1 is diagram illustrating execution of a quality assurance (“QA”) test procedure on a radiation delivery system 100 using a respiration phantom 102, in accordance with an embodiment of the invention. The illustrated embodiment of radiation delivery system 100 includes a radiation source 105, a source positioning system 107, a treatment couch 110, a couch positioning system 112 (also referred to as a patient positioning system), imaging detectors 115 (also referred to as imagers, only one is illustrated), and imaging sources 120 (only one is illustrated). Radiation delivery system 100 may be used to perform radiotherapy or radiosurgery to treat or destroy lesions within a patient. During radiation treatment, the patient rests on treatment couch 110, which is maneuvered to position the lesion or volume of interest (“VOI”) to a preset position or within an operating range accessible to radiation source 105 (e.g., field of view). Similarly, radiation source 105 is maneuvered with multiple degrees of freedom (e.g., rotational and translational freedom) to one or more locations during delivery of a treatment plan. At each location, radiation source 105 delivers a dose of radiation as prescribed by the treatment plan. In one embodiment, radiation delivery system 100 is an image guided radiation treatment delivery system. Together, imaging sources 120 and imaging detectors 115 form an image guidance system that provides visual control over the position of treatment couch 110 and the patient thereon. In one embodiment, couch positioning system 112 receives feedback from the image guidance system to provide accurate control over both the displacement and orientation of the VOI within the patient. In one embodiment, visual feedback from the image guidance system is further used by source positioning system 107 to position, align, and track the target VOI within the patient. Prior to delivery of a treatment plan to a patient, QA mechanisms may be executed to ensure radiation delivery system 100 is properly aligned, configured, and capable of delivering the treatment plan as prescribed. These QA mechanisms, also referred to as confidence checks, validate that the image guidance system, couch positioning system 112, source positioning system 107, and radiation source 105, itself, are all calibrated and aligned with each other and delivering a treatment plan as desired. If anyone of these subsystems is misaligned with one or more other subsystems, a treatment plan could be erroneously delivered to a patient's detriment. Respiration phantom 102 is an anthropomorphic QA marker that dynamically moves with a respiration-like motion. To implement a QA test, a dose of radiation can be delivered to respiration phantom 102 while it is caused to move with the respiration-like motion. Subsequently, respiration phantom 102 may be analyzed to determine whether the dose of radiation was delivered as expected. Since respiration phantom 102 simulates human-like breathing, it is capable of testing the ability of radiation delivery system 100 to track a VOI within a patient that is moving due to natural breathing. In one embodiment, respiration phantom 102 is fabricated of components that image (e.g., x-ray image, ultra-sound image, CT image, MR image, etc.) substantially similar to the human anatomy. Since respiration phantom 102 is anthropomorphic (e.g., includes human-like skeletal structure and major internal organs), respiration phantom 102 tests the ability of the image guidance system to identify human features, lock onto these features, and even track these features while moving due to respiration. In one embodiment, the internal organ-like and skeletal-like components of respiration phantom 102 are fabricated of materials that attenuate radiation in a similar manner to their living counterparts (e.g., water equivalent attenuation). As such, respiration phantom 102 can be used to accurately determine the dose of radiation delivered to a selected VOI and the amount of radiation exposure to the surrounding organs and skeletal structures. FIG. 2 is a perspective view of respiration phantom 102, in accordance with an embodiment of the invention. The illustrated embodiment of respiration phantom 102 includes a base 205, a respiration actuator 210, a human-like skeletal structure 215, organ components 220, and a skin-like sheath 225. Respiration phantom 102 is an anthropomorphic QA phantom that resembles the middle portion of the human anatomy between the waist and neck. In one embodiment, human-like skeletal structure 215 includes a rib cage, a sternum, and a spin. However, other embodiments of human-like skeletal structure 215 may include more or fewer human-like bone structures. For example, human-like skeletal structure 215 may further include a pelvic bone or exclude the spinal cord. Human-like skeletal structure 215 may be fabricated of materials having similar x-ray imaging qualities (or other imaging modalities) and radiation attenuation properties as the corresponding human skeletal structures. For example, human-like skeletal structure 215 may be fabricated of barium infused hardened foam, such as fabricated by Sawbones, A Division of Pacific Research Laboratories, Inc. of Vashon, Wash. FIG. 3 is a representative x-ray image of respiration phantom 102 illustrating human-like skeletal structure 215, in accordance with an embodiment of the invention. As illustrated, the individual bone structures of human-like skeletal structure 215 are radiographically distinct and image similar to a real human skeleton. The radiographical distinctness of human-like skeletal structure 215 enables visual tracking via image registration using the imaging system of radiation delivery system 100. Returning to FIG. 2, respiration phantom 102 includes a plurality of organ components 220 internal to human-like skeletal structure 215. Organ components 220 each have a shape resembling a different organ of the human anatomy. In one embodiment, each one of organ components 220 is fabricated of materials having similar x-ray imaging qualities (or other imaging modalities) and radiation attenuation properties as the corresponding human organs. For example, organ components 220 may be fabricated of foam or plastic. In one embodiment, each organ component 220 is removable from respiration phantom 102 and replaceable with a similarly shaped gel organ. The gel organ may be a sack or container having a shape of the corresponding organ and filled with a radiologically sensitive gel (e.g., BANG® polymer gel by MGS Research, Inc. of Madison, Conn.). If it is desired to determine the exposure a particular organ of a patient will received during delivery of a treatment plan, then the corresponding organ component 220 (and possibly the surrounding organ components 220) can be replaced with a gel organ filled with the radiologically sensitive gel. After the treatment plan is delivered, the gel organs are removed and analyzed to determine the dose delivered to the intended VOI and the exposure to surrounding tissue, organs, or bones. Since respiration phantom 102 is anthropomorphic, and organ components 220, human-like skeletal structure 215, and skin-like sheath 225 are all fabricated to attenuate radiation in a similar manner to the corresponding human structures, respiration phantom 102 provides a realistic simulation of the actual three dimensional dose delivery and exposure distribution. FIG. 4 is a diagram illustrating example component organs 220 of respiration phantom 102 that are removable and replaceable with gel organs, in accordance with an embodiment of the invention. The illustrated embodiment of respiration phantom 102 includes lung components 305, a heart component 310, a liver component 315, a spleen component 320, a stomach component 325, kidney components 330, a gallbladder component 335, a large intestine component 340, a pancreas component 345, a small intestine component 350, reproductive organ components 355, a bladder component 360, and an appendix component 365. It should be appreciated that component organs 220 illustrated in FIG. 4 are merely representative of possible organs that may be included within respiration phantom 102. However, other organs not illustrated may be included while some components illustrated may be excluded. For example, one embodiment of respiration phantom 102 excludes large intestine component 340, small intestine component 350, reproductive organ components 355, bladder component 360, and appendix component 365. Returning to FIG. 2, respiration phantom 102 includes respiration actuator 210 to impart a respiration-like motion on component organs 220, human-like skeletal structure 215, and skin-like sheath 225. In the illustrated embodiment, respiration actuator 210 includes a motor 211 coupled to a push rod 212 and push plate 213 to reciprocally compress component organs 220 along an inferior to superior axis 240. The motorized components (e.g., push rod 212 and push plate 213) that are in the anatomical field of view may be fabricated of radiolucent materials (e.g., plastic). In one embodiment, component organs 220 are deformable. By compressing component organs 220 along inferior to superior axis 240, component organs 220 simultaneously expand or bulge along a posterior to anterior axis 245. When component organs 220 expand along axis 245, they press against the rib cage of human-like skeletal structure 215 creating a human-like sinusoidal breathing motion. The rate of reciprocal compression may be adjusted to simulate at rest breathing, high activity breathing, or anywhere in between. Human breathing is created by a diaphragm that simultaneously pushes down on component organs 220 (axis 240) located in the abdominopelvic cavity to draw air into lungs 305 causing the thoracic cavity to expand outwards (axis 245). The respiration motion generated by the embodiment of respiration actuator 210 pushes component organs 220 upwards causing them to simultaneously bulge outwards. While the directions of motion are reversed, respiration actuator 210 illustrated in FIG. 2 replicates simultaneous motions along axes 240 and 245. Accordingly, if a VOI is located on one of lungs 305, then the VOI will experience an inferior to superior motion, as well as, a simultaneous posterior to anterior motion. Generating simultaneous motion along both axes 240 and 245 provides a mechanism to fully test the visual tracking capabilities of radiation delivery system 100. In one embodiment, respiration actuator 210 includes a programmable control system. The control system can be programmed to change breathing patterns imparted to the component organs 220 to test various different respiration scenarios. For example, pre-recorded breathing data from a living patient can be imported into the control system so that respiration actuator 210 can simulate the breathing motion. The pre-recorded breathing data could be data collected during a previous treatment and then imported into the control system to recreate or simulate the respiration-like motion of a particular VOI under similar conditions. FIG. 2 illustrates only one of many possible configurations for respiration actuator 210. For example, in the illustrated embodiment, respiration actuator 210 is illustrated with a mechanical motor 211; however, respiration actuator 210 may be implemented with a pneumatic cylinder as well. In one embodiment, push rod 212 of respiration actuator 210 may couple to the sternum of the rib cage to transfer the upward pushing force thereon. In one embodiment, respiration phantom 102 may include a diaphragm member (e.g., diaphragm 370 illustrated in FIG. 4) located below lungs 305 and above liver 315. In this embodiment, push rod 212 may push directly on the diaphragm member. Furthermore, respiration phantom 102 may include a thoracic cavity and an abdominopelvic cavity separated by the diaphragm member. In this diaphragm member embodiment, respiration actuator 210 may comprise a pump to force the diaphragm member up and down using air pressure. In yet another embodiment, the thoracic cavity and/or the abdominopelvic cavity may be liquid filled and respiration actuator 210 may use hydraulic pressure to impart the respiration-like motion. Respiration phantom 102 may further include skin-like sheath 225 pulled tight over human-like skeletal structure 215. Skin-like sheath 225 may have a slit down the center of the pelvic region and/or sternum to facilitate removal of component organs 220. Skin-like sheath 225 may be formed of rubber, plastic, silicon, or other pliable materials. The material used to fabricate may be selected for its radiation attenuation properties, such that it attenuates radiation in a manner similar to human skin. In one embodiment, respiration phantom 102 may include radiation sensors embedded within the individual component organs 220 or strategically positioned in a grid like fashion throughout the body cavity for measuring radiation exposure. For example, the radiation sensors may include arrays of metal oxide semiconductor (“MOS”) field effect transistors (“FET”) sensors, TLD sensors, or the like. FIG. 5 is a flow chart illustrating a process 500 to implement a QA test procedure on radiation delivery system 100 using respiration phantom 102, in accordance with an embodiment of the invention. The order in which some or all of the process blocks appear in process 500 should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated. In a process block 505, respiration phantom 102 is configured for the QA test. If it is desired to test delivery of a treatment plan to a VOI in a particular component organ 220 (e.g., component liver 315), then configuring respiration phantom 102 may include removing the selected component organ 220 (e.g., a foam organ) and replacing it with a radiologically sensitive gel organ having a corresponding size and shape (e.g., gel liver organ). Additionally, the component organs 220 surrounding the target organ with the VOI may also be replaced for measuring their exposure to radiation during delivery of the treatment plan. In an embodiment using electronic radiation sensors (e.g., MOS FET sensors or TLD sensors) respiration phantom 102 may not need configuration or the sensors may be positioned for redistributed within the body cavity or component organs 220. With respiration phantom 102 configured, respiration phantom 102 may be temporarily placed onto treatment couch 110 for execution of the QA testing procedure. In a process block 510, treatment couch 110 is positioned to a preset target position to place respiration phantom 102 into the field of view or operating envelope of radiation delivery system 100. In the embodiment illustrated in FIG. 1, positioning treatment couch 110 includes instructing couch positioning system 112 to move respiration phantom 102 to the preset target position. Maneuvering treatment couch 110 may include guiding couch positioning system 112 using the image guidance system visually tracking recognizable features of respiration phantom 102. Recognizable features of respiration phantom 102 may include human-like skeletal structure 215 or even tracking fiducials (e.g., metal seeds) implanted into respiration phantom 102. In a process block 515, radiation source 105 is maneuvered to a source position from which radiation source 105 is able to target the VOI within respiration phantom 102. Maneuvering radiation source 105 to the source position may include instructing source positioning system 107 to translate and rotate radiation source 105 under visual feedback from the image guidance system. In a process block 520, respiration actuator 210 is turned on to commence respiration-like motion by respiration phantom 102. In a process block 525, the image guidance system locks onto recognizable features of respiration phantom 102 to lock onto the VOI and compensate for the respiration-like motion. If the VOI is within hard tissue (e.g., human-like skeletal structure 215), then human-like skeletal structure 215 itself may be used for tracking purposes. If the VOI is within soft tissues (e.g., one of component organs 220), then tracking fiducials can be embedded within the soft tissue surrounding the VOI and tracked by the image guidance system. In yet other embodiments, tracking emitters (e.g., light emitting diodes (“LEDs”), ultrasonic emitter, etc.) may be strategically placed on the outer surface of respiration phantom 102 and their motion tracked using one or more motion sensors (e.g., infrared camera, ultrasonic receiver, etc.) mounted around respiration phantom 102 (e.g., on the walls or ceiling of the room housing radiation delivery system 100, on treatment couch 110, or otherwise). The motion sensors can monitor the motion of the tracking emitters and provide real-time feedback for dynamic tracking. The tracking emitters and motion sensors may be used in addition to the above x-ray based image guidance system using human-like skeletal structure 215 and/or the implanted tracking fiducials. Respiration-like motion data can be collected by a tracking system including the tracking emitters and motion sensors and this motion data correlated with the data collected from the x-ray based imaging system as it simultaneously tracks the internal VOI respiration-like motion (process block 527). The correlation of these data sets can be used to help characterize respiration-like motion of a particular VOI within a living patient based solely on real-time feedback from the tracking emitters mounted to the living patient. In this manner, the x-ray based imaging system is used to precisely track a VOI within respiration phantom 102, correlate this motion to feedback data received from the non-x-ray based tracking system, which would then be used during delivery of a treatment plan to a living patient to reduce exposure of the living patient to the x-ray radiation of the image guidance system. In one embodiment, a Synchrony Respiratory Tracking System from Accuray, Inc. of Sunnyvale, Calif. may be used to implement the tracking emitter and motion sensor based tracking system. In a process block 530, a dose of radiation is delivered to the respiration phantom 102. Process block 530 may include delivering an entire treatment plan including multiple individual dose deliveries. In one embodiment, the treatment plan may be created prior to delivering the treatment plan by CT scanning (other imaging modalities may also be used) respiration phantom 102 using a breathing protocol to obtain reference images of respiration phantom 102, to isolate the VOI, and to generate a four dimensional (three spatial dimensions plus time) treatment plan that is delivered by radiation delivery system 100 in process block 530. Once the treatment plan has been delivered, the radiologically sensitive gel organs are removed from respiration phantom 102 (process block 535) and analyzed (process block 540). Exposure to radiation causes the radiologically sensitive gel to change optical density by an amount that is related to its exposure. Accordingly, the gel organs can be optically scanned in three dimensions to generate a three dimensional exposure image. By analyzing the three dimensional exposure image, dose measurements can be extracted to determined whether the treatment plan was delivered as expected and whether radiation delivery system 100 is properly calibrated and aligned (process block 545). FIG. 6 is a block diagram illustrating a therapeutic patient treatment system 4000 for generating diagnostic images, generating a treatment plan, and delivering the treatment plan to a patient, in which features of the present invention may be implemented. As described below and illustrated in FIG. 6, systems 4000 may include a diagnostic imaging system 1000, a treatment planning system 2000 and a radiation delivery system 100. Diagnostic imaging system 1000 may be any system capable of producing medical diagnostic images of the VOI within a patient that may be used for subsequent medical diagnosis, treatment planning and/or treatment delivery. For example, diagnostic imaging system 1000 may be a computed tomography (“CT”) system, a magnetic resonance imaging (“MRI”) system, a positron emission tomography (“PET”) system, an ultrasound system or the like. For ease of discussion, diagnostic imaging system 1000 may be discussed below at times in relation to a CT x-ray imaging modality. However, other imaging modalities such as those above may also be used. Diagnostic imaging system 1000 includes an imaging source 1010 to generate an imaging beam (e.g., x-rays, ultrasonic waves, radio frequency waves, etc.) and an imaging detector 1020 to detect and receive the beam generated by imaging source 1010, or a secondary beam or emission stimulated by the beam from the imaging source (e.g., in an MRI or PET scan). In one embodiment, diagnostic imaging system 1000 may include two or more diagnostic X-ray sources and two or more corresponding imaging detectors. For example, two x-ray sources may be disposed around a patient to be imaged, fixed at an angular separation from each other (e.g., 90 degrees, 45 degrees, etc.) and aimed through the patient toward (an) imaging detector(s) which may be diametrically opposed to the x-ray sources. A single large imaging detector, or multiple imaging detectors, can also be used that would be illuminated by each x-ray imaging source. Alternatively, other numbers and configurations of imaging sources and imaging detectors may be used. The imaging source 1010 and the imaging detector 1020 are coupled to a digital processing system 1030 to control the imaging operation and process image data. Diagnostic imaging system 1000 includes a bus or other means 1035 for transferring data and commands among digital processing system 1030, imaging source 1010 and imaging detector 1020. Digital processing system 1030 may include one or more general-purpose processors (e.g., a microprocessor), special purpose processor such as a digital signal processor (“DSP”) or other type of device such as a controller or field programmable gate array (“FPGA”). Digital processing system 1030 may also include other components (not shown) such as memory, storage devices, network adapters and the like. Digital processing system 1030 may be configured to generate digital diagnostic images in a standard format, such as the DICOM (Digital Imaging and Communications in Medicine) format, for example. In other embodiments, digital processing system 1030 may generate other standard or non-standard digital image formats. Digital processing system 1030 may transmit diagnostic image files (e.g., the aforementioned DICOM formatted files) to treatment planning system 2000 over a data link 1500, which may be, for example, a direct link, a local area network (“LAN”) link or a wide area network (“WAN”) link such as the Internet. In addition, the information transferred between systems may either be pulled or pushed across the communication medium connecting the systems, such as in a remote diagnosis or treatment planning configuration. In remote diagnosis or treatment planning, a user may utilize embodiments of the present invention to diagnose or treatment plan despite the existence of a physical separation between the system user and the patient. Treatment planning system 2000 includes a processing device 2010 to receive and process image data. Processing device 2010 may represent one or more general-purpose processors (e.g., a microprocessor), special purpose processor such as a DSP or other type of device such as a controller or FPGA. Processing device 2010 may be configured to execute instructions for performing treatment planning operations discussed herein. Treatment planning system 2000 may also include system memory 2020 that may include a random access memory (“RAM”), or other dynamic storage devices, coupled to processing device 2010 by bus 2055, for storing information and instructions to be executed by processing device 2010. System memory 2020 also may be used for storing temporary variables or other intermediate information during execution of instructions by processing device 2010. System memory 2020 may also include a read only memory (“ROM”) and/or other static storage device coupled to bus 2055 for storing static information and instructions for processing device 2010. Treatment planning system 2000 may also include storage device 2030, representing one or more storage devices (e.g., a magnetic disk drive or optical disk drive) coupled to bus 2055 for storing information and instructions. Storage device 2030 may be used for storing instructions for performing the treatment planning steps discussed herein. Processing device 2010 may also be coupled to a display device 2040, such as a cathode ray tube (“CRT”) or liquid crystal display (“LCD”), for displaying information (e.g., a 2D or 3D representation of the VOI) to the user. An input device 2050, such as a keyboard, may be coupled to processing device 2010 for communicating information and/or command selections to processing device 2010. One or more other user input devices (e.g., a mouse, a trackball or cursor direction keys) may also be used to communicate directional information, to select commands for processing device 2010 and to control cursor movements on display 2040. It will be appreciated that treatment planning system 2000 represents only one example of a treatment planning system, which may have many different configurations and architectures, which may include more components or fewer components than treatment planning system 2000 and which may be employed with the present invention. For example, some systems often have multiple buses, such as a peripheral bus, a dedicated cache bus, etc. The treatment planning system 2000 may also include MIRIT (Medical Image Review and Import Tool) to support DICOM import (so images can be fused and targets delineated on different systems and then imported into the treatment planning system for planning and dose calculations), expanded image fusion capabilities that allow the user to treatment plan and view dose distributions on any one of various imaging modalities (e.g., MRI, CT, PET, etc.). Treatment planning systems are known in the art; accordingly, a more detailed discussion is not provided. Treatment planning system 2000 may share its database (e.g., data stored in storage device 2030) with a treatment delivery system, such as radiation delivery system 100, so that it may not be necessary to export from the treatment planning system prior to treatment delivery. Treatment planning system 2000 may be linked to radiation delivery system 100 via a data link 2500, which may be a direct link, a LAN link or a WAN link as discussed above with respect to data link 1500. It should be noted that when data links 1500 and 2500 are implemented as LAN or WAN connections, any of diagnostic imaging system 1000, treatment planning system 2000 and/or radiation delivery system 100 may be in decentralized locations such that the systems may be physically remote from each other. Alternatively, any of diagnostic imaging system 1000, treatment planning system 2000 and/or radiation delivery system 100 may be integrated with each other in one or more systems. Radiation delivery system 100 includes a therapeutic and/or surgical radiation source 105 to administer a prescribed radiation dose to a target volume in conformance with a treatment plan. Radiation delivery system 100 may also include an imaging system 3020 (including imaging sources 120 and detectors 115) to capture inter-treatment images of a patient volume (including the target volume) for registration or correlation with the diagnostic images described above in order to position the patient with respect to the radiation source. Radiation delivery system 100 may also include a digital processing system 3030 to control radiation source 105, imaging system 3020, and a patient support device such as a treatment couch 110. Digital processing system 3030 may include one or more general-purpose processors (e.g., a microprocessor), special purpose processor such as a DSP or other type of device such as a controller or FPGA. Digital processing system 3030 may also include other components (not shown) such as memory, storage devices, network adapters and the like. Digital processing system 3030 may be coupled to radiation treatment source 105, imaging system 3020 and treatment couch 110 by a bus 3045 or other type of control and communication interface. FIG. 7 is a perspective view of a radiation delivery system 100, in accordance with an embodiment of the invention. In one embodiment, radiation delivery system 100 may be an image-guided, robotic-based radiation treatment system such as the CyberKnife® system developed by Accuray, Inc. of California. In FIG. 7, radiation source 105 may be a linear accelerator (“LINAC”) mounted on the end of a source positioning system 3012 (e.g., robotic arm) having multiple (e.g., 5 or more) degrees of freedom in order to position the LINAC to irradiate a pathological anatomy (target region or volume) with beams delivered from many angles in an operating volume (e.g., a sphere) around the patient. Treatment may involve beam paths with a single isocenter (point of convergence), multiple isocenters, or with a non-isocentric approach (i.e., the beams need only intersect with the pathological target volume and do not necessarily converge on a single point, or isocenter, within the target). Treatment can be delivered in either a single session (mono-fraction) or in a small number of sessions (hypo-fractionation) as determined during treatment planning. With radiation delivery system 100, in one embodiment, radiation beams may be delivered according to the treatment plan without fixing the patient to a rigid, external frame to register the intra-operative position of the target volume with the position of the target volume during the pre-operative treatment planning phase. Imaging system 3020 (see FIG. 6) may be represented by imaging sources 120A and 120B and imaging detectors (imagers) 115A and 115B in FIG. 7. In one embodiment, imaging sources 120A and 120B are X-ray sources. In one embodiment, for example, two imaging sources 120A and 120B may be nominally aligned to project imaging x-ray beams through a patient from two different angular positions (e.g., separated by 90 degrees, 45 degrees, etc.) and aimed through the patient on treatment couch 110 toward respective detectors 115A and 115B. In another embodiment, a single large imager can be used that would be illuminated by each x-ray imaging source. Alternatively, other numbers and configurations of imaging sources and detectors may be used. Digital processing system 3030 may implement algorithms to register images obtained from imaging system 3020 with pre-operative treatment planning images in order to align the patient on the treatment couch 110 within the radiation delivery system 100, and to precisely position the radiation source 105 with respect to the target volume. In the illustrated embodiment, treatment couch 110 is coupled to a couch positioning system 112 (e.g., robotic couch arm) having multiple (e.g., 5 or more) degrees of freedom. Couch positioning system 112 may have five rotational degrees of freedom and one substantially vertical, linear degree of freedom. Alternatively, couch positioning system 112 may have six rotational degrees of freedom and one substantially vertical, linear degree of freedom or at least four rotational degrees of freedom. Couch positioning system 112 may be vertically mounted to a column or wall, or horizontally mounted to pedestal, floor, or ceiling. Alternatively, the treatment couch 110 may be a component of another mechanical mechanism, such as the Axum™ treatment couch developed by Accuray, Inc. of California, or be another type of conventional treatment table known to those of ordinary skill in the art. Alternatively, radiation delivery system 100 may be another type of treatment delivery system, for example, a gantry based (isocentric) intensity modulated radiotherapy (“IMRT”) system or 3D conformal radiation treatments. In a gantry based system, a therapeutic radiation source (e.g., a LINAC) is mounted on the gantry in such a way that it rotates in a plane corresponding to an axial slice of the patient. Radiation is then delivered from several positions on the circular plane of rotation. In IMRT, the shape of the radiation beam is defined by a multi-leaf collimator that allows portions of the beam to be blocked, so that the remaining beam incident on the patient has a pre-defined shape. The resulting system generates arbitrarily shaped radiation beams that intersect each other at the isocenter to deliver a dose distribution to the target. In IMRT planning, the optimization algorithm selects subsets of the main beam and determines the amount of time that the patient should be exposed to each subset, so that the prescribed dose constraints are best met. It should be noted that the methods and apparatus described herein are not limited to use only with medical diagnostic imaging and treatment. In alternative embodiments, the methods and apparatus herein may be used in applications outside of the medical technology field, such as industrial imaging and non-destructive testing of materials (e.g., motor blocks in the automotive industry, airframes in the aviation industry, welds in the construction industry and drill cores in the petroleum industry) and seismic surveying. In such applications, for example, “treatment” may refer generally to the application of radiation beam(s). The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation. |
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claims | 1. A molten salt reactor, comprising:a reactor core comprising graphite, the reactor core defining an internal space;multiple fuel wedges that each define a fuel channel,wherein the fuel wedges are received within the internal space of the reactor core, andwherein the fuel channel is configured to allow a fissionable fuel to flow from a first end of each of the wedges to a second end of each of the wedges,wherein the reactor core is disposed within a reactor housing,wherein the reactor core comprises a fuel ingress port and a fuel egress port, andwherein the reactor core is configured to rotate within the housing such that the fuel ingress and egress ports become at least one or more occluded and less occluded as the reactor core rotates. 2. The reactor of claim 1, further comprising a fuel pin rod disposed between at least two of the fuel wedges. 3. The reactor of claim 1, wherein the reactor core comprises:a reactor core tube with a first opening and a second opening;a first reactor end cap that caps the first opening; anda second reactor cap that caps the second opening. 4. The reactor of claim 3, further comprising a diffuser that is disposed between a portion of the first reactor end cap and the internal space of the reactor core. 5. The reactor of claim 1, wherein at least one of the fuel wedges defines a standoff space that is disposed between the fuel channel and the first end of the at least one of the fuel wedges. 6. The reactor of claim 1, wherein the reactor core is rotatably received within a graphite reflector, and wherein the graphite reflector is disposed within a reactor housing. 7. The reactor of claim 1, wherein the reactor core and the fuel wedges are configured to allow the wedges to expand between about 0.5% and about 10% as the wedges are heated within the reactor core. 8. A molten salt reactor, comprising:a reactor core comprising graphite, the reactor core defining an internal space;multiple fuel wedgesthat are received within the internal space andthat each define a fuel channel that is configured to allow a thorium molten salt fuel to flow from a first end to a second end of each of the wedges;a fuel pin rod that is disposed between at least two of the wedges,the fuel pin rod defining an internal fuel conduit; anda reactor housing,wherein the reactor core further comprises a fuel ingress port and a fuel egress port, andwherein the reactor core is rotatably received within the reactor housing such that the fuel ingress and egress ports are configured to become at least one of (i) more occluded and (ii) less occluded as the reactor core rotates within the housing. 9. The reactor of claim 8, wherein at least one of the fuel wedges defines a standoff space that is disposed between the fuel channel and the first end of the at least one of the fuel wedges. 10. The reactor of claim 8, wherein the reactor comprises a rotation gear that is coupled to the reactor core. 11. The reactor core of claim 8, wherein the reactor core comprises:a reactor core tube with a first terminal end and a second terminal end;a first reactor end cap that is disposed at the first terminal end and is sealed with the reactor core tube; anda second reactor cap that is disposed at the second terminal end and is sealed with the reactor core tube. 12. The reactor core of claim 8, wherein the reactor core further comprises a diffuser that is disposed between the fuel ingress port and the first end of the fuel wedges. 13. The reactor core of claim 8, further comprising a graphite reflector that is disposed within the reactor housing that rotatably receives the reactor core. 14. The reactor core of claim 8, wherein the fuel pin rod defines a standoff space that is disposed between a first terminal end of the fuel pin and the internal fuel conduit. |
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abstract | Devices and methods are provided to allow rapid deflection of a charged particle beam. The disclosed devices can, for example, be used as part of a hadron therapy system to allow scanning of a target area within a patient's body. The disclosed charged particle beam deflectors include a dielectric wall accelerator (DWA) with a hollow center and a dielectric wall that is substantially parallel to a z-axis that runs through the hollow center. The dielectric wall includes one or more deformed high gradient insulators (HGIs) that are configured to produce an electric field with an component in a direction perpendicular to the z-axis. A control component is also provided to establish the electric field component in the direction perpendicular to the z-axis and to control deflection of a charged particle beam in the direction perpendicular to the z-axis as the charged particle beam travels through the hollow center of the DWA. |
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abstract | The invention comprises a system for determining the state of a charged particle beam, such as beam position, intensity, and/or energy. For example, the charged particle beam state is determined at or about a patient undergoing charged particle cancer therapy using one or more film layers designed to emit photons upon passage of a charged particle beam, which yields information on position and/or intensity of the charged particle beam. The emitted photons are used to calculate position of the treatment beam in imaging and/or during tumor treatment. Optionally and preferably, updating a tomography map uses the same hardware with the same alignment used for cancer therapy at proximately the same time. |
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description | FIG. 1 is a cross-sectional view of a window 3 built up in two parts from a diamond foil 1 and a separate annular retaining element 2, wherein the foil 1 and the retaining element 2 are connected to one another by means of an adhesive or fusion layer 4. The diamond foil 1 has a thickness of up to 10 xcexcm and is transparent to an electron ray. The material of the retaining element 2 is characterized in that it is a temperature-resistant metal and has a linear thermal expansion coefficient whose value is preferably lower than 9xc3x9710xe2x88x926/K, i.e. similar or equal to the coefficient of expansion of the diamond. An example of this is molybdenum. It is also conceivable, however, that the foil transparent to electron rays is made of molybdenum and that the retaining element is manufactured from a material whose thermal expansion behavior matches that of molybdenum. It should be emphasized that the retaining element 2 did not take part in the actual manufacture of the diamond foil, acting as a carrier substrate, but that it was connected to the diamond foil only after the latter had been manufactured. The manufacture of thin diamond layers is known and takes place by means of gas deposition methods. The diamond foil is then fully divested of the carrier substrate on which it was depositedxe2x80x94for example, by etching or possibly by grinding away of the substratexe2x80x94and is connected to the retaining element 2 by its peripheral or edge regions, such that a transparent transmission zone 5 is created. The thin diamond layer 10 is provided with thickenings 16a,b,c acting as structural or reinforcement elements on its surface facing away from the retaining element 2 for mechanical stabilization of the thin diamond layer, as is shown for the embodiment in FIG. 2. Similar components have been given the same reference numerals as in FIG. 1. These thickenings 16a,b,c are also formed from diamond and in this embodiment extend parallel next to one another, which is more clearly shown in the plan view of FIG. 3. Embodiments with irregularly spaced thickenings are equally conceivable; and other geometries or patterns in which the thickenings are arranged are also possible. In the window shown in FIG. 2, the thickenings 16a,b,c have a triangular geometry. Their thickness does not come to the total thickness of the diamond foil, but it should be at least 10% of the total thickness of the foil. It is furthermore possible to provide both surfaces of the diamond foil with thickenings, or only the surface facing towards the retaining element. A balance should always be sought between the influence of a mechanical stabilization and sufficient areas of higher transparency acting as transmission zones for the electron ray. The thickenings may be added to the diamond foil, for example, through a suitable structuring of the CVD carrier substrate to be coated during the deposition process. It is also possible, however, to remove regions, for example by laser ablation or with an ion ray applied to a thicker foil, which regions will then form the subsequent regions transparent to electron rays. Besides the solution principle of a fixed connection through the use of an adhesion of fusion layer between the diamond foil and the retaining element of a material having a low linear thermal expansion coefficient, the solution principle of an integral window is proposed according to the invention, which window consists entirely of diamond. FIG. 4 is a cross-sectional view of such a window. The foil (300a) and the retaining element 300b in this embodiment form an integral whole, i.e. the window 300. A diamond plate having a thickness of more than 10 xcexcm, preferably of up to 1000 xcexcm, is used for this, which plate is thinned by laser or ion ablation down to a thickness which is transmissive to electrons over a surface area which corresponds to at least the diameter of the electron ray. This creates the actual window region 307 within the retaining element 300b. Besides this regular arrangement of the window region, the embodiment of FIG. 5, also made integrally from diamond, shows an irregularly thinned diamond plate, i.e. a transmission zone 308 reinforced with thickened portions 310a,b. The electron ray can pass through the regions 311a,b,c transparent to electron rays between the thickened portions. In the advantageous embodiment shown in FIG. 6, the thickened portions, i.e. the non-reduced regions 312a,b lie in the outermost region of the processed zone or transmission zone 309; the difference with the window of FIG. 5 is shown in dotted lines. With a sufficient stabilization, the actual transmission zone 309 still remains unaffected. It is clarified in the diagram of FIG. 7 that the windows with the proposed construction show a better pressure resistance than the known windows which are formed by a carrier substrate with a diamond foil provided in the deposition process. The bursting pressure is indicated as a measure for this. The thickness and the diameter indicate geometric values for the respective window. The diameter is understood to be the greatest longitudinal dimension of the window opening, i.e. of the transmission zone in cm here, corresponding, for example, to the diameter in circular openings, to the major axis of the ellipse in elliptical openings, and to the major side length in the case of rectangular openings. It is apparent that the window samples with less strongly adhering foils on silicon carrier substrates (triangles) became detached at a pressure of 3 to 4 bar. To achieve higher bursting pressures (dots), the diamond foil was fully removed from the carrier substrate, according to the invention, and fixedly connected to a separate retaining element or window frame from a material having a comparatively low linear thermal expansion coefficient by means of a separate connecting layer, or alternatively it was manufactured in one piece. The dotted line corresponds to the experimentally found limit value for the bursting pressure of the window, for which it holds that bursting pressure (bar)=1.3xc3x97[thickness(xcexcm)/diameter(cm)], whereby a difference from the known relation xe2x80x83bursting pressure (bar)=1xc3x97[thickness(xcexcm)/diameter(cm)] was found. The window thickness in xcexcm should accordingly be greater than 0.7 times the product of diameter (cm) and pressure difference between the two sides of the window. FIG. 8 diagrammatically shows an X-ray device 20 operating by the LIMAX process, in which a window 3 according to the invention with its modifications described above may advantageously be used. The X-ray device is formed by the X-ray tube 21 and a liquid metal circulation system 22. The X-ray tube 21 is closed off by the window 3 in a vacuumtight manner. In the vacuum space of the X-ray tube 21, there is an electron source in the form of a cathode 23 which in the operational state emits an electron ray 24 which hits a liquid metal through the window 3, which metal is being passed over a steel plate. The liquid metal circulation system 22 is provided for this purpose, composed from a tubular duct system 25 in which the liquid metal is propelled by a pump 26 so as to flow past the outer side of the window 3 in a region 27. After passing through the region 27, it enters a heat exchanger 28 from which the generated heat is removed by means of a suitable cooling system. The interaction of the electrons passing through the window with the liquid metal generates X-ray radiation (i.e. the liquid metal acts as a target), which issues through the window 3 and an X-ray emission window 29 in the bulb 21 to the exterior. It is advisable to use a doped diamond, especially if the proposed windows are used in such X-ray devices, so as to prevent a charging of the window during operation by means of the conductivity, and thus to prevent a deflection, deceleration, or complete stoppage of the electron ray. Boron is suitable for a doping process so as to reduce the resistivity to less than 1000 xcexa9cm. |
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abstract | A system and a method for capturing gaseous, particulate and liquid radioactive material released from primary containment of a Light Water Reactor (LWR) during severe accident conditions. The system includes a below-grade media area, connected to a reactor pressure vessel (RPV) and portions of primary containment, providing varying levels of adsorption/absorption of the radioactive material. The media area is located on-site to offer a passive, self-regulating structure for stabilizing a nuclear reactor. The capture system provides for liquid drainage and gaseous venting of the radioactive material, and a treatment capable of treating the media following stabilization of the reactor. |
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description | This patent application claims priority to U.S. Provisional Application No. 61/106,497 entitled “Systems and Methods for Calculating Carbon Emissions of a Shipment” and filed Oct. 17, 2008, which is herein incorporated by reference in its entirety. As awareness of environmental issues has grown, logistics, supply chain, and shipping customers have become increasingly concerned with the impact of their transportation activities on the environment. Many customers are now requesting reports on the carbon footprint of their shipments, which they may use as gauges for purchasing carbon credits and for monitoring their environmental impact. Currently, transportation companies calculate the carbon dioxide emissions of shipments based on estimates of a given shipment's weight and the distance it is transported. In particular, standard emissions factors, such as those provided by the World Resources Institute (WRI), are applied to weight and distance statistics to estimate carbon dioxide emissions. These calculations are currently done manually and can take a significant amount of time to complete. In addition, the distance estimates and standard emissions factors used in the calculations do not take into account the efficiencies in the transportation process established by a transportation company. Accordingly, there is a need in the art for an improved system and method for calculating the emissions resulting from transporting a shipment through a transportation network. According to various embodiments of the invention, an emissions calculation system calculates emissions resulting from transporting a shipment from an origin address to a destination address through a carrier's transportation network. The emissions calculation system includes at least one computer processor and a memory, and the at least one computer processor is configured for: (1) receiving at least a portion of shipment parameters associated with a particular shipment, the received shipment parameters comprising an origin address and a destination address for the particular shipment; (2) identifying a transportation path along which the particular shipment is expected to travel from the origin address to the destination address; (3) retrieving one or more emissions factors related to at least one of the shipment parameters, each of the one or more emissions factors being based at least in part on an amount of fuel used during a particular time period by the carrier to transport previously shipped packages along at least a portion of the transportation path; and (4) estimating an amount of emissions resulting from transporting the particular shipment along the at least a portion of the transportation path based at least in part on the one or more retrieved emissions factors and at least a portion of the shipment parameters. In certain embodiments, the at least one computer processor is further configured for estimating the amount of fuel used during the particular time period to transport packages along the at least a portion of the transportation path based at least in part on an expected amount of time for transporting the packages along the at least a portion of the transportation path, and the expected amount of time based on historical shipment data of the carrier. According to other various embodiments, an emissions calculation system calculates emissions factors used to estimate emissions resulting from transporting a particular shipment from an origin carrier facility to a destination carrier facility through a carrier's transportation network. The emissions calculation system includes at least one computer processor and a memory, and the at least one computer processor configured for: (A) retrieving data comprising: (1) an amount of time expected for transporting a package along at least a portion of a transportation path between the origin carrier facility and the destination carrier facility, the at least a portion of the transportation path having a distance that is within a distance range and (2) a number of packages transported by the carrier within the distance range during a particular time period via a mode of transportation; (B) allocating a portion of a total amount of fuel used by the carrier during the particular time period for transporting the number of packages within the distance range via the mode of transportation, the allocated portion of fuel being based on at least the amount of time expected for transporting the package along the at least a portion of the transportation path, the number of packages transported by the carrier within the distance range; and (C) calculating an amount of emissions for transporting the number of packages based on the allocated amount of fuel. In other various embodiments, an emissions calculation system calculates emissions factors used to estimate emissions resulting from transporting a particular shipment from an origin carrier facility to a destination carrier facility through a carrier's transportation network. The emissions calculation system includes at least one computer processor and a memory, and the at least one computer processor configured for: (A) retrieving data comprising: (1) an amount of time expected for transporting a package along at least a portion of a transportation path between the origin carrier facility and the destination carrier facility, the at least a portion of the transportation path being a route leg, and (2) a number of packages transported by the carrier along the route leg during a particular time period via a mode of transportation; (B) allocating a portion of a total amount of fuel used by the carrier during the particular time period for transporting the number of packages along the route leg via the mode of transportation, the allocated portion of fuel being based on the amount of time expected for transporting the package along the route leg, and the number of packages transported by the carrier along the route leg; and (C) calculating an amount of emissions for transporting the number of packages based on the allocated amount of fuel. According to various other embodiments, an emissions calculation system calculates emissions factors used to estimate emissions resulting from picking up a particular shipment in a carrier's transportation network. The emissions calculation system comprises at least one computer processor and a memory, and the at least one computer processor configured for: (A) retrieving data comprising: (1) a number of stops made by the carrier during a particular time period for picking up packages associated with a service product, (2) a number of packages associated with the service product that were picked up by the carrier during the particular time period, and (3) an amount of time expected per stop for picking up packages associated with the service product; (B) allocating a portion of a total amount of fuel used by the carrier during the particular time period for picking up the number of packages associated with the service product, the allocated portion of fuel being based on at least a portion of the retrieved data; and (C) calculating an amount of emissions per stop associated with picking up packages associated with the service product based on the allocated amount of fuel per stop. In other various embodiments, an emissions calculation system calculates emissions factors used to estimate emissions resulting from delivering a particular shipment in a carrier's transportation network. The emissions calculation system includes at least one computer processor and a memory, and the at least one computer processor configured for: (A) retrieving data comprising: (1) a number of stops made by the carrier during a particular time period for delivering packages associated with a service product, (2) a number of packages associated with the service product that were delivered by the carrier during the particular time period, and (3) an amount of time expected per stop for delivering packages associated with the service product; (B) allocating a portion of a total amount of fuel used by the carrier during the particular time period for delivering the number of packages associated with the service product, the allocated portion of fuel being based on at least a portion of the retrieved data; and (C) calculating an amount of emissions per stop associated with delivering packages associated with the service product based on the allocated amount of fuel per stop. Various embodiments of the present invention now will be described more fully with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, various embodiments of the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like numbers refer to like elements throughout. As will be appreciated by one skilled in the art, various embodiments of the present invention may be embodied as a method, a data processing system, or a computer program product. Accordingly, various embodiments of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, various embodiments of the present invention may take the form of a computer program product on a computer-readable storage medium having computer-readable program instructions (e.g., computer software) embodied in the storage medium. More particularly, various embodiments of the present invention may take the form of web-implemented computer software. Any suitable computer-readable storage medium may be utilized including hard disks, CD-ROMs, optical storage devices, or magnetic storage devices. Various embodiments of the present invention are described below with reference to block diagrams and flowchart illustrations of methods, apparatuses (e.g., systems) and computer program products. It will be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, respectively, can be implemented by computer program instructions. These computer program instructions may be loaded onto a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions which execute on the computer or other programmable data processing apparatus create a means for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including computer-readable instructions for implementing the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Accordingly, blocks of the block diagrams and flowchart illustrations support combinations for performing the specified functions, combinations of steps for performing the specified functions, and program instructions for performing the specified functions. It will also be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, can be implemented by special purpose hardware-based computer systems that perform the specified functions or steps, or combinations of special purpose hardware and computer instructions. According to various embodiments of the present invention, an emissions calculation system calculates the emissions resulting from transporting a shipment through a transportation network from pickup to delivery. The shipment may include an individual or group of packages. In certain embodiments, the calculated emissions are based on estimated or actual amounts of fuel used in the transportation process. For example, in one embodiment, the calculated emissions are based on estimated amounts of fuel used during a particular time period based on the amount of planned transportation time expected by the carrier to transport a package within the carrier's transportation network from one point to another via a particular mode of transportation. The planned transportation time, according to one embodiment, is based on historical shipment data of the carrier. In addition, various embodiments of the system generate and display (or otherwise make available) one or more reports of the calculated emissions information. For example, the report may provide a breakdown of the amount of fuel used and/or carbon dioxide emitted into the atmosphere resulting from various operational activities in the transportation process (e.g., pickup and delivery activities, movement of the shipment within a transportation carrier facility, and/or transportation between carrier facilities). In addition, the report may provide a total amount of fuel and/or carbon dioxide emitted from the transportation of a particular shipment or group of shipments. FIG. 1 illustrates an exemplary flow diagram of a method 1000 of using an emissions calculation system to calculate emissions resulting from transporting a shipment according to one embodiment. In particular, the method 1000 begins at Step 1002 with a user accessing the emissions calculation system via the user's computing device and entering a request for the system to calculate an amount of emissions for a particular shipment (or group of shipments) to be transported (or that have been transported). If the request is approved by the system, the shipment parameters (e.g., number of packages in the shipment, volume of the packages, weight of packages, service level for the shipment, and/or origin/destination of the packages) are retrieved by the system in Step 1004. In one embodiment, the user may enter the shipment parameters into the system in this step. In another embodiment, the user may have entered the shipment parameters previously, and these parameters may be retrieved by the system from storage. Next, in Step 1006, the system then uses one or more of the shipment parameters to retrieve one or more emissions factors that are relevant to the amount of emissions resulting from (or estimated to result from) the shipment. The one or more emissions factors retrieved and the shipment parameters provided by the user are then used by the system to calculate (or estimate) the amount of emissions resulting from (or estimated to result from) the shipment, which is shown in Step 1012. Finally, in Step 1016, the system generates a report detailing the calculated amount of emissions resulting from (or estimated to result from) the transportation process. For example, this report may include details on the amount of carbon dioxide emitted during various operational activities in the transportation process. In the embodiment shown in FIG. 1, the emissions calculated is carbon dioxide, but, in various other embodiments, other types of emissions may be calculated based at least in part on the amount of fuel used or estimated to be used during the transportation process. For example, the other types of emissions that may be calculated include methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). Exemplary operational activities in the transportation process and various exemplary sources of data used to calculate the amount of emissions resulting from (or estimated to result from) the transportation process are described below. Following this description, exemplary architectures for the system are described along with an exemplary operation of the system. Exemplary Operational Activities in the Transportation Process According to various embodiments, an exemplary shipment being transported via a carrier's transportation network is picked up from a transportation customer at an origin location, is transferred to one or more sorting and processing facilities of the carrier (referred to hereinafter as “carrier facilities”), and is ultimately delivered to the intended recipient of the shipment at a destination location. Operational activities in the transportation process include various mobile activities (e.g., transporting the shipment between the origin location and a carrier facility, transporting the shipment between carrier facilities, transporting the shipment from a carrier facility to the destination location, and transporting the shipment via a vehicle from an airplane, ship, or train to a nearby carrier facility) and stationary activities (e.g., unloading, loading, sorting, and processing the shipment at each carrier facility). In an exemplary transportation network, the carrier may maintain one or more local carrier facilities and one or more regional carrier facilities. The local carrier facilities are typically smaller in size and more numerous than the regional carrier facilities, and the regional carrier facilities are typically located near a large airport, seaport, or other major intersection of travel (e.g., one or more interstate highways or rail lines). In addition, the modes of transportation used during each mobile operational activity may include small delivery trucks (which are typically used for residential pickup and delivery operational activities), larger delivery trucks (which are typically used for commercial pickup and delivery operational activities), transportation trailers (which are typically used for movement of consolidated shipments between carrier facilities, but may be used occasionally to pickup and/or deliver large shipments), small aircraft (which may be used for movement of consolidated shipments between a smaller carrier facility and a larger carrier facility), large aircraft (which may be used for movement of consolidated shipments between larger carrier facilities), ships (which are typically used for movement of consolidated international shipments), and rail (which are typically used for movement of consolidated shipments between carrier facilities). According to various embodiments, the transportation carrier identifies a planned amount of time (e.g., hours) per package expected for performing each operational activity. This planned amount of time may be based on route legs associated with the origin and destination addresses, zones, service levels, and/or service products. In certain embodiments, the identified planned amount of time is generated from industrial engineering studies and is stored by the transportation carrier on a transportation carrier server, for example. Exemplary Sources of Data Related to Emissions According to various embodiments, the transportation carrier stores data related to: (1) the types of fuel used by its transportation vehicles and facilities (e.g., diesel, gasoline, clean natural gas, jet fuel, etc.), (2) the amount of each type of fuel used by the carrier within a particular time period, and (3) the number of packages shipped within the carrier's transportation network over the particular time period via each service level and/or associated with each service product. In addition, the transportation carrier may store data related to an estimated amount of volume occupied by each package or an estimated weight of the package based on the service level associated with the package or type of package. The types of fuel used and the amount of each type of fuel used by the carrier may be allocated among the various operational activities. In addition, the amount of fuel may be further allocated based on the number of packages (or volume and/or weight of packages), and these allocations may be further based on the service level, service products, zones, and/or origin/destination pairs. In certain embodiments, the planned amount of time for each operational activity may also be considered when allocating fuel usage among the various operational activities. Various methods of allocating fuel among the various operational activities are described in more detail below in relation to FIGS. 7A-9A. In certain other embodiments, the carrier may further store data related to the amount of emissions resulting from (or estimated to result from) operation of a carrier facility, amount of emissions resulting from (or estimated to result from) operation of a particular vehicle or type of vehicle, and the type(s) and actual amount(s) of fuel used for certain operational activities. Exemplary Flow of Each Package within the Carrier's Transportation Network In various embodiments, the carrier identifies a particular route or flow for transporting a package within the transportation network based on the origin and destination addresses associated with the package, the type of shipment, and the service level. According to various embodiments, the type of shipment may be characterized as, for example, cargo or freight (e.g., shipments of one or more pallets of packages that are bundled together for at least a portion of the transportation process) or individual package (e.g., packages to be shipped individually throughout transportation network). Types of service levels, according to various embodiments, may include, for example, next day delivery, two-day delivery, three-day delivery, ground, and/or international. For example, for a package being shipped from an origin address in or near Atlanta, Ga. to a destination address in or near Jacksonville, Fla. via ground delivery, the identified transportation flow may include movement of the package from its origin address to a local carrier facility in Atlanta via a small delivery truck, consolidation within the Atlanta facility onto a large tractor trailer, movement of the consolidated shipment to a carrier facility in Jacksonville via the large tractor trailer, sorting of the package at the Jacksonville facility onto a small delivery truck, and movement of the package from the Jacksonville facility to the destination address via the small delivery truck. As another example, FIG. 6 illustrates the path of an exemplary shipment 800 from a customer origin location 840 to a customer destination location 870 for a particular service level involving air shipping (e.g., next day, second day, or third day delivery) according to one embodiment. As shown, the items to be transported are transferred from the transportation customer to the transportation carrier at the customer origin location 840, and the transportation carrier transports the items to a local carrier facility 850 located near the customer origin location 840, typically via a small truck 810. The shipment is then processed at the local carrier facility 850 and transported to a larger, regional carrier facility 860, typically via a larger truck 820. The exemplary shipment 800 is then transported from the regional carrier facility 860 to another regional carrier facility 865 by airplane 830. Next, the exemplary shipment 800 is transported from the regional carrier facility 865 to a local carrier facility 855 located near the customer destination location 870, typically via another large truck 825, and from the local carrier facility 855 to the customer destination location 870, typically via another small truck 815. In certain embodiments, the carrier may associate various route legs with a particular “origin/destination pair,” wherein the “origin” refers to the location of the carrier facility to which the shipment would be routed directly from the origin address (typically a carrier facility near the origin address) and the “destination” refers to the location of the carrier facility from which the shipment would be routed directly to the destination address (typically a carrier facility near the destination address). Each origin/destination pair may be divided into route legs, and each route leg may be associated with a particular mode of transportation. The route legs associated with the origin/destination pair and the mode of transportation associated with each route leg may vary depending on the type of service and service level. In other (or further) embodiments, a set of zones is associated with each carrier facility, and each zone indicates a relative distance (or range of distances) from the carrier facility. In one embodiment, the carrier may adopt the shipment (or postal) zones established by the United States Postal Service. For example, destinations within 200 miles of a particular carrier facility may be designated as Zone 2 relative to the carrier facility, and destinations between 200 miles and 400 miles of the carrier facility may be designated as Zone 3 relative to the carrier facility. In this example, a higher zone number indicates a larger distance from the carrier facility. However, it should be understood that in various other embodiments, a higher zone number may be indicate a smaller distance from the carrier facility, or the zone may be indicated with a letter, symbol, or combination thereof. For the exemplary shipment described above from Atlanta to Jacksonville, the carrier facility in Jacksonville may be identified as within Zone 3 of the Atlanta carrier facility, whereas a shipment from the Atlanta carrier facility to the Miami carrier facility may be identified as within Zone 4 of the Atlanta carrier facility. According to various embodiments, mobile operational activities involving the movement of shipments between remote locations within the carrier's transportation network may include, for example, a pickup operational activity, a transport operational activity, and a delivery operational activity. In particular the pickup operational activity includes transporting the shipment from the origin address to the local carrier facility located near the origin address (or regional carrier facility if one is located near the origin), and the delivery operational activity includes transporting the shipment from the local carrier facility located near the destination address (or regional carrier facility if one is located near the destination) to the destination address. The transport operational activity includes transporting the shipment between carrier facilities (e.g., through one or more other local or regional carrier facilities in the transportation network). For example, as shown in the embodiment of FIG. 6, the pickup operational activity includes transporting the shipment from the origin 840 to the local carrier facility 850, and the delivery operational activity includes transporting the shipment from the local carrier facility 855 to the destination 870. The transport operational activity includes transporting the shipment from the local carrier facility 850 to the regional carrier facility 860, from the regional carrier facility 860 to the regional carrier facility 865, and from the regional carrier facility 865 to the local carrier facility 855. System Architecture An emissions calculation system 5 according to one embodiment is shown in FIG. 2. As may be understood from this figure, in this embodiment, the system 5 includes one or more user computers 10, 12, 13 that are connected, via a network 15 (e.g., a LAN or the Internet), to communicate with a transportation entity server 200. The emissions calculation system 5 is configured for retrieving data from and storing data to a database 30 that may be stored on (or, alternatively, stored remotely from) the transportation entity server 200. FIG. 3 is a schematic diagram of the transportation entity server 200 according to various embodiments. The transportation entity server 200 includes one or more computer processors 60 that communicate with other elements within the transportation entity server 200 via a system interface or bus 61. Also included in the transportation entity server 200 are one or more display device/input devices 64 for receiving and displaying data. This display device/input device 64 may be, for example, a keyboard and/or pointing device that is used in combination with a monitor. The transportation entity server 200 further includes memory 66, which preferably includes both read only memory (ROM) 65 and random access memory (RAM) 67. The server's ROM 65 is used to store a basic input/output system 26 (BIOS), containing the basic routines that help to transfer information between elements within the transportation entity server 200. In addition, the transportation entity server 200 includes at least one storage device 63, such as a hard disk drive, a floppy disk drive, a CD Rom drive, or optical disk drive, for storing information on various computer-readable media, such as a hard disk, a removable magnetic disk, or a CD-ROM disk. As will be appreciated by one of ordinary skill in the art, each of these storage devices 63 is connected to the system bus 61 by an appropriate interface. The storage devices 63 and their associated computer-readable media provide nonvolatile storage for a personal computer. It is important to note that the computer-readable media described above could be replaced by any other type of computer-readable media known in the art. Such media include, for example, magnetic cassettes, flash memory cards, digital video disks, and Bernoulli cartridges. A number of program modules may be stored by the various storage devices and within RAM 67. Such program modules include an operating system 80, a fuel factor calculation module 300, an emissions calculation module 400, an emissions factor calculation module 600, and a reporting module 500. According to various embodiments, the fuel factor calculation module 300, the emissions calculation module 400, the emissions factor calculation module 600, and the reporting module 500 control certain aspects of the operation of the transportation entity server 200 with the assistance of the processor 60 and an operating system 80. In general, the fuel factor calculation module 300 is configured to calculate a fuel factor representing an amount of fuel used per volume (e.g., ft3, m3) or weight (e.g., lbs., kg) shipped (e.g., actual or estimated amount) and per stop for each service type, service level, and/or service product. According to various embodiments, the fuel factor is calculated for shipments traveling between particular origin/destination pairs and/or within particular zones of the origin (e.g., a first fuel factor is calculated for any package traveling within Zone 2 of its origin and a second fuel factor is calculated for any package traveling within Zone 3 of its origin). The emissions factor calculation module 600 is configured to calculate an amount of emissions resulting from transporting a shipment per volume or weight shipped (or per stop) based on each fuel factor calculated by the fuel factor calculation module 300. The emissions calculation module 400 calculates an amount of emissions resulting from transporting a particular shipment using one or more relevant emissions factors generated by the emissions factor calculation module 600 and at least a portion of the shipment parameters associated with the particular shipment. The reporting module 500 is configured to generate and make available to the user a report that includes the calculated emissions data. Embodiments of these modules are described in more detail below in relation to FIGS. 5, 7A, 8A, 9A, 10, 11, and 12. In a particular embodiment, these program modules 300, 400, 500, 600 are executed by the transportation entity server 200 and are configured to generate graphical user interfaces accessible to users via the Internet or other communications network. In other embodiments, the modules 300, 400, 500, 600 may be stored locally on the users' computers 10, 12, 13 and executed by one or more processors of the computers 10, 12, 13. According to various embodiments, the modules 300, 400, 500, 600 may utilize data contained in the database 30, and the database 30 may be comprised of one or more separate, linked databases. For example, in the embodiment shown in FIG. 4, the database 30 includes a global transportation entity database 31 that contains data related to transportation statistics for past shipments processed by a transportation entity, a shipment information database 32 that contains data pertaining to the shipment parameters for one or more particular shipments, and an active emissions calculation database 33 that stores data used by and calculated by the fuel factor calculation module 300 and emissions factor calculation module 600. The contents and structure of these databases are described below in more detail. Also located within the transportation entity server 200 is a network interface 74, for interfacing and communicating with other elements of a computer network. It will be appreciated by one of ordinary skill in the art that one or more of the transportation entity server 200 components may be located geographically remotely from other transportation entity server 200 components. Furthermore, one or more of the components may be combined, and additional components performing functions described herein may be included in the transportation entity server 200. Exemplary System Flow According to various embodiments of the invention, the emissions calculation system 5 calculates the carbon dioxide and/or other emissions resulting from transporting a shipment through a carrier's network. In certain embodiments, the amount of emissions calculated by the system 5 is based at least in part on an estimated or actual amount of fuel used in the transportation process. As noted above, in one embodiment, the transportation entity server 200 of the system 5 includes one or more processors 60 that are configured for executing the fuel factor calculation module 300, the emissions factor calculation module 600, the emissions calculation module 400, and the reporting module 500 to calculate and report the amount of emissions resulting from transporting a shipment through the carrier's network. FIG. 5 illustrates the working relationship between the above-mentioned databases and modules according to various embodiments of the invention. In particular, the fuel factor calculation module 300 retrieves data from the global transportation entity database 31, the shipment information database 32, and the active emissions calculation database 33 to calculate one or more fuel factors. The fuel factor calculation module 300 then transmits the calculated fuel factors to the emissions factor calculation module 600 according to one embodiment. In other embodiments, these fuel factors are retrieved by the emissions factor calculation module 600. The emissions factor calculation module 600 then calculates an emissions factor corresponding to each fuel factor. The emissions calculation module 400 retrieves (or receives) shipment parameters from the shipment information database 32 about the particular shipment for which the emissions are being calculated and retrieves (or receives) one or more emissions factors that relate to at least a portion of the shipment parameters for the particular shipment (e.g., the emissions factors corresponding to each operational activity encountered by the particular shipment based on the shipment's service level and origin and destination addresses). The emissions calculation module 400 uses these one or more emissions factors to calculate an estimated or actual amount of emissions resulting from the transportation of the shipment through the transportation network. The data calculated by the emissions calculation module 400 is retrieved by (or transmitted to) the reporting module 500. Embodiments of each of these databases and modules are discussed in more detail below. Global Transportation Entity Database According to various embodiments, the global transportation entity database 31 generally contains data pertaining to shipments previously transported by the carrier and acts a repository for shipment-related data recorded by the carrier. Exemplary data contained in the global transportation entity database 31 includes, but is not limited to: (1) logistical planning data (e.g., specific routes of shipment for each origin/destination pair, zones (or a distance range) associated with each carrier facility, sort schedules for each carrier facility (e.g., twilight, day, evening), pickup and delivery locations for residential and commercial shipments, the location of local and regional carrier facilities, modes of transportation associated with movement of packages between facilities based on service level and sort schedules, and the type of fuel used by each transportation vehicle); (2) statistical shipment data (e.g., mileage and/or estimated travel time between each origin/destination pair and/or route legs associated therewith, an amount of time estimated for performing each operational activity during the transportation process (e.g., based on industrial engineering studies), a number of stops for pickup and delivery on each pickup and delivery route, an estimated amount of time per stop (e.g., based on industrial engineering studies), an estimated amount of volume (e.g., ft3, m3) occupied by a package having a particular weight (e.g., pounds, kilograms) or being within a particular range of weights (e.g., based on industrial engineering studies), an estimated amount of weight (e.g., lbs., kg) for a package being transported via a particular mode of transportation and/or via a particular service level (e.g., based on industrial engineering studies), and an estimated amount of volume (e.g., ft3, m3) for a package being transported via a particular mode of transportation and/or via a particular service level (e.g., based on industrial engineering studies); and (3) other shipment data that may be tracked and stored by the carrier. For example, in one embodiment, logistical planning data may have been created by the carrier to evaluate and run its transportation operations, and this data is stored on the global transportation entity database 31 for future use. Similarly, statistical shipment data may have been calculated and/or recorded during the planning and execution of past shipments and stored on the global transportation entity database 31. In addition, as noted above, according to various embodiments, at least a portion of the data may be arranged according to the various zones through which (and/or routes along which) shipments travel and by operational activities within the transportation process (e.g., pickup, delivery, transport, and sorting and/or processing). At least a portion of the data may be further arranged according to service type, service level, and/or service product associated with each shipment and/or the type of vehicle used for each operational activities. Shipment Information Database According to various embodiments, the shipment information database 32 contains data pertaining to the particular shipment(s) for which the amount of emissions is to be calculated. The data generally includes shipping parameters associated with the particular shipment that may affect, directly or indirectly, the amount of emissions resulting from transporting the shipment from the origin address to the destination address. For example, the data may include, but is not limited to: (1) the origin address and destination address of the particular shipment, (2) the service type, (3) the service level, (4) the service product, (5) the volume and/or weight of the particular shipment (and/or the volume and/or weight of each of the one or more packages in the shipment), (6) number of packages in the shipment, and (7) one or more tracking numbers associated with the shipment and/or the one or more packages included in the shipment. In addition, according to various embodiments, data may also include the business unit of the carrier (if the carrier has multiple business units), a pickup type, and average daily pickup (if available). According to various embodiments, this data may be provided by the customer to the carrier via a data file (e.g., CVS) or otherwise, or this data may be previously stored and extracted from the carrier's system upon request. Active Emissions Calculation Database According to various embodiments, the active emissions calculation database 33 stores data that is used by the fuel factor calculation module 300 to calculate various fuel factors. For example, data contained in the active emissions calculation database may include, but is not limited to: (1) data retrieved by the fuel factor calculation module 300 from the global transportation entity database 31 that is relevant to the amount of fuel used for certain types of shipments and certain operational activities; (2) volume and/or weight of past shipments; (3) allocation of fuel used during the shipment for various operational activities; (4) typical numbers of stops for pickups and deliveries; (5) transit times for pickups and deliveries; (6) calculated fuel factors; and/or (7) calculated emissions factors. In addition, according to various embodiments, the data in the active emissions calculation database 33 may be organized or related by: (1) zones, (2) mode of transportation, (3) origin-destination pairs, (4) route legs, (5) service types, (6) service level, (7) service product, and/or (8) operational activity. In various other embodiments, the data described above as being stored on each database 31, 32, and 33 may be stored on one or more databases or in one or more storage areas. Fuel Factor Calculation Module According to various embodiments, the fuel factor calculation module 300 is configured to calculate at least one fuel factor that is associated with at least one operational activity, which, depending on the operational activity associated with the fuel factor, may be expressed as an amount of fuel used per volume shipped or per weight shipped (e.g., for transportation between carrier facilities or movement through a carrier facility) or an amount of fuel per stop (e.g., for pickup and delivery operational activities), for example. For example, in certain embodiments, the amount of fuel may be expressed as gallons or liters, and the volume may be expressed as a “cube,” which represents a generic unit of volume (e.g., ft3, m3). In other embodiments, the amount of fuel may be expressed as gallons or liters, and the weight may be expressed as an amount of pounds or kilograms, for example. In various embodiments, the fuel factor calculation module 300 calculates a fuel factor for each operational activity in the transportation process. In certain embodiments, the fuel factor calculation module 300 calculates a fuel factor for each operational activity based on each service level and on each origin/destination pair, zone, and/or relative distances traveled by shipments. Because each operational activity may utilize a different type and/or amount of fuel, calculating separate fuel factors for each activity results in a more accurate calculation of the total amount of fuel used (or estimated to be used) for shipping the particular shipment, according to various embodiments. In other embodiments, each fuel factor calculated may be associated with two or more operational activities. For example, according to various embodiments, the fuel factor calculation module 300 calculates one or more fuel factors associated with a transport operational activity using a zone-based approach and/or a route-based approach. In general, the zone-based approach includes allocating fuel consumption based on the number of packages (or planned hours for transporting packages) shipped via each service level, zone, and mode of transportation and calculating a fuel factor indicating an amount of fuel used per package cube (or weight) for each service level, zone, and mode of transportation based on the amount of fuel allocated. The route-based approach includes allocating fuel consumption based on the number of packages (or planned hours for transporting packages) shipped via each service level between the origin/destination pair and calculating fuel factors that each indicate the amount of fuel used to transport each package cube (or weight) between each origin/destination pair via each service level. As discussed below in more detail, FIG. 7A illustrates the steps executed by the fuel factor calculation module 300 to calculate fuel factors using the zone-based approach for the transport operational activity according to various embodiments. FIG. 8A illustrates the steps executed by the fuel factor calculation module 300 to calculate fuel factors using the route-based approach for the transport operational activity according to various embodiments. FIG. 9A illustrates the steps executed by the fuel factor calculation module 300 to calculate fuel factors for the pickup and delivery operational activities according to various embodiments. As shown in FIGS. 7A, 8A, and 9A and described below, the fuel factor calculation module 300 is configured for calculating fuel factors for the transport operational activity using either (or both) the zone-based approach or the route-based approach and is configured for calculating fuel factors for the pickup and delivery operational activities. However, in other various embodiments (not shown), one or more of these calculations may be performed by one or more separate modules. Calculating Fuel Factors for the Transport Operational Activity using Zone-Based Approach FIG. 7A illustrates the steps executed by the fuel factor calculation module 300 to calculate fuel factors using the zone-based approach for the transport operational activity according to one embodiment of the invention. The exemplary steps shown in FIG. 7A are performed to calculate a fuel factor associated with each zone (e.g., Zone 2, Zone 3, etc.) and mode of transportation (e.g., large airplane, small airplane, tractor trailer, large truck, rail, boat) for each service level (e.g., next day delivery, second day delivery, third day delivery, ground, international, freight). The module 300 begins at Step 310 by retrieving data indicating (1) a number of planned transportation time (e.g., minutes, hours) associated with transporting a package between two carrier facilities for each zone and mode of transportation associated with each service level and (2) a total number of packages shipped within each zone via each mode of transportation associated with each service level during a particular time period. For example, the data retrieved by the module 300 may indicate that two hours are expected for transporting a package within Zone 3 of a regional facility via airplane via next day delivery service, and 34 million packages were transported via airplane within Zone 3 of a carrier facility via next day delivery service in 2007. Next, in Step 311, for each zone, mode of transportation, and service level, the fuel factor calculation module 300 multiples the retrieved number of planned transportation time for each package by the retrieved total number of packages shipped associated with the respective zone, mode of transportation, and service level. Using the example introduced above, the product of Step 311 is 68 million hours*packages. Next, in Step 312, this product is multiplied by the average volume (or “cube”) per package shipped via each mode of transportation and service level to determine the total number of “cube-hours” associated with each zone, mode of transportation, and service level. Building on the example above, if the average volume per package being shipped via airplane and next day delivery is 0.5 cubic feet per package, the product of Step 312 is 34 million cubic feet-hours, which is the number of cube-hours for all of the packages transported via airplane via next day delivery within Zone 3 of a carrier facility in 2007. Alternatively, in other embodiments (not shown), the number of cube-hours associated with each zone, mode of transportation, and service level may be calculated and stored previously by the carrier, and instead of executing Steps 310 and 311, the module 300 may retrieve this pre-calculated data. In addition, in other various embodiments, the average volume per package may be the same for all packages, regardless of mode of transportation or service level, or may be based on service level, mode of transportation, zone, and/or origin/destination pair. In Step 313, a total amount of fuel used by the carrier during the particular time period for each mode of transportation is retrieved. According to various embodiments, the total amount of fuel used by the carrier during the particular time period for each (or a particular type of) mode of transportation may be tracked and stored by the carrier for one or more operational activities and/or service levels, or the total amount of fuel used by the carrier for each (or a particular type of) mode of transportation and one or more operational activities and/or service levels may be estimated (allocated) from a total amount of fuel used for the respective mode of transportation for all operational activities and service levels. For example, in a particular embodiment (not shown), the total amount of jet fuel used by the carrier is allocated based on flight classification and service level. Flight classifications may include, for example, international (packages to be transported between a U.S. airport and an international airport or between two international airports), cargo (packages that are typically bundled together (e.g., on one or more pallets) and shipped by the same customer, and the packages are being transported between two U.S. airports), and domestic (individually shipped packages to be transported between two U.S. airports). The carrier may designate a particular plane to carry packages associated with a certain flight classification, but the carrier may also include packages having different flight classifications on the same plane. In addition, in one embodiment, the carrier assigns any empty positions on the plane to the flight designation assigned to the plane. To allocate the amount of jet fuel used for each flight classification, the fuel factor calculation module retrieves the number of positions associated with (or assigned to) each flight classification during the particular time period and calculates the percentage of positions associated with each flight classification. The percentage associated with each flight classification is then multiplied by the total amount of jet fuel to determine the total amount of jet fuel associated with each flight classification. Next, the fuel factor calculation module retrieves the number of positions occupied on the planes (or assigned) by packages associated with each service level associated with each flight classification and calculates the percentage of positions associated with each service level. The percentage of positions associated with each service level is then multiplied by the total amount of jet fuel associated with the respective flight classification to determine the total amount of jet fuel associated with each service level. Thus, when the mode of transportation is a jet, the total amount of fuel retrieved in Step 313 is the total amount of jet fuel associated with each service level, according to certain embodiments. In certain embodiments, the amount of fuel used by tractor trailers, which are typically used for moving shipments between carrier facilities, is associated with the transport operational activities. However, in some embodiments, tractor trailers may be used to pickup or deliver shipments en route between carrier facilities during a transport operational activity. Thus, in certain embodiments, the module 300 allocates a portion of the fuel used by the tractor trailers that would otherwise be included in the total amount of fuel used for ground vehicles associated with transport operational activities to the amount of fuel used by ground vehicles for pickup/delivery operational activities. In particular, according to one embodiment (not shown), the module 300 identifies the percentage of cube-hours (or weight-hours) attributable to shipments that are picked up or delivered by tractor trailers en route between carrier facilities, subtracts an amount of fuel equal to this percentage from the amount of fuel indicated as used for transport operational activities, and adds the amount of fuel to the amount of fuel indicated as used for pickup/delivery operational activities. In Step 314, the total amount of fuel for each mode of transportation and service level is divided by the sum of the total amount of cube-hours for the packages transported in all zones via the respective mode of transportation and service level within the particular time period. These quotients are then normalized to one cubic-foot by dividing each quotient by the average cube per package (e.g., 0.5 cubic feet/package) for the respective service level. Next, in Step 315, the module 300 calculates a fuel factor associated with each zone, mode of transportation, and service level by multiplying the number of gallons of fuel used per cube-hour for shipments within the respective zone via the respective mode of transportation and the respective service level by the number of planned transportation time associated with transporting a shipment within the respective zone via the respective mode of transportation and respective service level. The fuel factors associated with each zone, mode of transportation, and service level are stored by the transportation entity server 200 (e.g., in the active emissions calculation database 33). Although not shown in FIG. 7A, the fuel factor calculation module 300, according to certain embodiments, may send the data it retrieves and/or calculates to the active emissions calculation database 33 after each step described above or after selected steps. For example, FIG. 7B illustrates three tables—Table A, Table B, and Table C—that store data calculated by the fuel factor calculation module 300. Each table stores data related to transportation of shipments between two carrier facilities via a particular service level. For example, Table A stores the cube-hours calculated in Step 312 that are associated with a particular service level for shipments that were transported in the particular time period within each zone and via each mode of transportation. Table B stores the number of gallons allocated in Step 313 as being used to transport shipments during the particular time period between two carrier facilities within each zone via each mode of transportation and service level. Table C stores the fuel factors calculated in Step 315 associated with each zone, mode of transportation, and service level. In other embodiments, instead of zones, fuel factor calculations for transport operational activities may be based on an estimated or actual distance (or range of distances) between the origin and destination and/or the carrier facilities through which shipments may be transported. In addition, in other embodiments, instead of the fuel factors being based on the volume of the packages, the fuel factors may be based on the weight of the packages (e.g., gallons (or liters) per pound (or kilogram)). Calculating Fuel Factors for the Transport Operational Activity using Route-Based Approach FIG. 8A illustrates the steps executed by the fuel factor calculation module 300 to calculate fuel factors using the route-based approach for the transport operational activity according to one embodiment of the invention. The exemplary steps shown in FIG. 8A are performed to calculate a fuel factor associated with each origin/destination pair for each service level (e.g., next day delivery, second day delivery, third day delivery, ground, international, freight). As noted above, in each origin/destination pair, the “origin” is the location of the first carrier facility that receives the shipment from the transportation customer's origin location, and the “destination” is the location of the last carrier facility that processes the shipment before the shipment reaches its destination location. Furthermore, each origin-destination pair may be divided into one or more route legs, and each route leg may be, for example, associated with travel by a particular vehicle (mode of transportation). In various embodiments, the route legs (and/or modes of transportation associated with them) may vary based on service level. To calculate fuel factors for each origin/destination pair, the module 300 begins at Step 320 by retrieving data indicating (1) a number of planned transportation time (e.g., minutes, hours) associated with transporting a package along each route leg associated with each origin/destination pair via each service level and (2) a total number of packages shipped along each route leg via each service level during a particular time period. Next, in Step 321, for each route leg and service level, the fuel factor calculation module 300 multiples the retrieved number of planned transportation time for each package by the retrieved total number of packages shipped associated with the respective route leg and service level. Next, in Step 322, this product is multiplied by the average volume (or “cube”) per package shipped via each service level to determine the number of cube-hours associated with each route leg of each origin/destination pair for each service level. Alternatively, in other embodiments (not shown), the number of cube-hours associated with each route leg and service level may be calculated and stored previously by the carrier, and instead of executing Steps 321 and 322, the module 300 may retrieve this pre-calculated data. In addition, in other various embodiments, the average volume per package may be the same for all packages or may be based on service level, mode of transportation, zone, and/or origin/destination pair. In Step 323, a total amount of fuel used by the carrier during the particular time period for each mode of transportation associated with each service level is retrieved, and in Step 324, the total amount of fuel for each mode of transportation associated with each service level is divided by the sum of the total amount of cube-hours for the packages transported via the respective mode of transportation associated with each service level for all origin-destination pairs within the particular time period. These quotients are then normalized to one cubic-foot by dividing the quotients by the average cube per package associated with the respective service level and mode of transportation. Next, in Step 325, the module 300 calculates a fuel factor associated with each origin/destination pair and each service level. In one embodiment, the module 300 multiplies the respective number of gallons of fuel used per cube-hour associated with the respective mode of transportation and service level by the number of planned transportation time associated with transporting a shipment along each route leg of the respective origin/destination pair via the respective service level. These products are then summed together to calculate the fuel factor associated with the respective origin/destination pair and service level and are stored by the transportation entity server 200 (e.g., in the active emissions calculation database 33). Although not shown in FIG. 8A, the fuel factor calculation module 300, according to certain embodiments, may send the data it retrieves and/or calculates to the active emissions calculation database 33 after each step described above or after selected steps. For example, FIG. 8B illustrates three tables—Table D, Table E, and Table F—that store data calculated by the fuel factor calculation module 300. In particular, Table D stores the cube-hours calculated in Step 322 that are associated with a particular service level and each route leg associated with each origin/destination pair. Table E stores the number of gallons allocated in Step 323 as being used to transport shipments during the particular time period between each origin/destination pair via each service level. Table F stores the fuel factors calculated in Step 325 associated with each origin/destination pair for each service level. In other embodiments, instead of the fuel factors being based on the volume of the packages, the fuel factors may be based on the weight of the packages (e.g., gallons (or liters) per pound (or kilogram)). In addition, in other various embodiments (not shown), the fuel calculation module 300 may be configured to execute steps 310 through 314, and then calculate a fuel factor associated with each origin/destination pair and service level by multiplying the normalized quotient from in Step 314 by the number of planned transportation hours associated with each route leg associated with the respective origin/destination pair via the respective service level. These products are then summed together to calculate the fuel factor associated with the respective origin/destination pair and service level. Calculating Fuel Factors for Pickup and Delivery Operational Activities As shown in FIG. 6, the pickup and delivery operational activities occur at the beginning and end of each shipment, respectively. The pickup operational activity includes transporting a shipment from an origin address (e.g., origin 840) to the first carrier facility that processes the shipment, which is typically located near the origin address (e.g., local carrier facility 850) and is referred to hereinafter as an “origin facility.” The delivery operational activity includes transporting the shipment from the last carrier facility that processes the shipment, which is typically located near the destination address (e.g., local carrier facility 855) and is referred to hereinafter as a “destination facility,” to the destination address (e.g., destination 870). According to various embodiments, for residential services, pickup and delivery operational activities are typically performed using small trucks that travel between various shipment origins, destinations, and the origin and destination carrier facilities (e.g., carrier facilities 850, 855), and for commercial services, these operational activities are typically performed by larger trucks. In addition, each truck may travel to multiple addresses to pickup or deliver a plurality of shipments before returning to the origin or destination carrier facility, which requires the trucks to stop and start along the pickup and delivery routes. As a result, according to various embodiments, it is difficult to calculate fuel factors associated with the pickup and delivery operational activities using the zone-based or route-based approaches described above. Thus, in various embodiments, the fuel factor calculation module 300 bases its fuel factor calculations for pickup and delivery operational activities on: (1) the number of stops made for pickup and delivery operational activities, respectively, (2) total planned time for pickup and delivery operational activities, respectively, based on an estimated amount of time per stop and the number of stops made, and (3) the amount of fuel used for pickup and delivery operational activities based on the total planned time for pickup and delivery operational activities. In certain embodiments, at least a portion of this data related to pickup operational activities is organized by service product and pickup type, and at least a portion of the data related to delivery operational activities is organized by service product. Service products generally indicate whether the shipment is being shipped by a commercial or residential customer, the service level, and the type of package being transported (e.g., commercial/residential ground letter, commercial/residential ground package, commercial/residential ground package, commercial/residential next day air letter, commercial/residential next day air package, freight, etc.), and pickup type generally indicates the frequency with which customers utilize the carrier's pickup transportation services (e.g., daily pickup, occasional pickup, occasional air pickup, temporary air pickup, one time pickup). In other embodiments, this data may be organized by service level, which includes one or more service products. FIG. 9A shows exemplary steps executed by the fuel factor calculation module 300 to calculate fuel factors for the pickup and delivery operational activities according to one embodiment. For each of the pickup and delivery operational activities, as shown in Step 331, the fuel factor calculation module 300 retrieves data related to: (1) the number of stops made during a particular time period for pickups or deliveries associated with each service product, (2) the number of packages associated with each service product that were picked up or delivered by the carrier during the particular time period, (3) the average planned time per stop (e.g., planned hours) for pickup or delivery associated with each service product, and (4) the average volume per package associated with each service product. The average planned time per stop and/or the average volume per package may be derived from industrial engineering studies conducted by the carrier or a third party entity, according to various embodiments. In addition, in certain embodiments, for pickup operational activities, the data retrieved in Step 331 may be further organized based on the pickup type associated with each package. In certain embodiments, the number of stops made during the particular time period associated with each service product is the total number of “equivalent stops” associated with the respective service product. For example, if the carrier delivers three packages at one stop, and of the three packages, the first package is associated with a first service product, a second package is associated with a second service product, and a third package is associated with a third service product, the carrier assigns 0.33 equivalent stops to each package. The number of equivalent stops for picking up or delivering each package associated with each service product during the particular time period are summed together to provide a total number of equivalent stops associated with each service product during the particular time period. For the purposes of illustration, an example of the pickup data that may be retrieved in Step 331 is provided as follows: the number of stops made during 2007 for pickups associated with commercial customers having daily pickups and shipping next day air letter packages may be 7.4 million stops, the number of next day air letter packages picked up from these commercial customers in 2007 may be 43 million packages, the planned time per stop for picking up next day air letter packages from these commercial customers may be 0.05 hours, and the average volume per next day air letter package picked up from these commercial customers may be 0.6 ft3/package. Similarly, for the purposes of illustration, an example of the delivery data that may be retrieved in Step 331 is provided as follows: the number of stops made during 2007 for deliveries of next day air letter packages from commercial customers may be 23.3 million stops, the number of next day air letter packages from commercial customers delivered in 2007 may be 56.5 million packages, the planned time per stop for delivering next day air letter packages from commercial customers may be 0.04 hours, and the average volume per next day air letter package delivered from commercial customers may be 0.6 ft3/package. Next, in Step 333, for each of the pickup and delivery operational activities, the fuel factor calculation module 300 calculates the total “cube-hours” associated with each service product by multiplying the data retrieved in Step 331. Thus, given the exemplary data noted above, the module 300 calculates in Step 333 that the number of cube-hours associated with picking up next day air letter packages from commercial customers having daily pickups during 2007 is 9.546 trillion hours*ft3, and the number of cube-hours associated with delivering next day air letter packages from commercial customers during 2007 is 31.6 trillion hours*ft3. In Step 335, for each of the pickup and delivery operational activities, the fuel factor calculation module 300 allocates the total amount of fuel used by each mode of transportation for pickup and delivery operational activities for each service product. The allocation is based on the percentage of cube-hours associated with each service product, and this allocated amount is then normalized based on the average volume per package. In particular, in one embodiment, the number of cube-hours associated with each service product and respective mode of transportation is divided by the total amount of cube-hours for all service products associated with each pickup or delivery operational activity and mode of transportation, and this quotient is multiplied by the total amount of fuel used by each mode of transportation during the particular time period for pickup and delivery activities. According to certain embodiments, this allocation step may be repeated for each type of fuel (e.g., diesel, gasoline, clean natural gas) used in pickup and delivery activities to estimate the amount of each type of fuel used for picking up or delivering shipments associated with each service product. In other embodiments, the calculations performed in Steps 331 through 335 may be calculated using the average weight of the packages (e.g., gallons (or liters) per pound (or kilogram)) associated with each service product. In Step 337, the fuel factor calculation module 300 then calculates a fuel factor for each service product by dividing the normalized amount of fuel allocated for the respective service product in Step 333 by the total number of stops for the respective service product retrieved in Step 331. These fuel factors are then stored by the transportation entity server 200 (e.g., in the active emissions calculation database 33). Although not shown in FIG. 9A, the fuel factor calculation module 300, according to certain embodiments, may send the data it retrieves and/or calculates to the active emissions calculation database 33 after each step described above or after selected steps. For example, FIG. 9B illustrates four tables—Table G, Table H, Table I, and Table J—that store data calculated by the fuel factor calculation module 300. In particular, Table G stores the number of stops retrieved in Step 331 for each service product for each of the pickup and delivery operational activities. Table H stores the total amount of calculated planned time for pickup and delivery operational activities associated with each service product. Table I stores the total amount of fuel allocated for each service product for pickup and delivery operational activities. Table J stores the fuel factors calculated in Step 337 for each service product for pickup or delivery. Calculation of Fuel Factors for Stationary Operational Activities The embodiments of the fuel factor calculation module 300 described above recite steps performed by the fuel factor calculation module 300 for calculating fuel factors that may be used to estimate the amount of fuel used by the carrier to perform mobile operational activities, such as transporting packages from between carrier facilities, between the origin address and an origin carrier facility, and between a destination carrier facility and the destination address. However, according to various embodiments, the fuel factor calculation module 300 may further be configured for calculating fuel factors related to stationary operational activities, such as movement and processing of a package volume (or weight) through each carrier facility (or type of carrier facility). In particular, according to various embodiments, the fuel factor calculation module 300 calculates a fuel factor for a stationary operation activity by first retrieving (1) a total amount of fuel used by all (or a portion of) the carrier's facilities during the particular time period and (2) a total number of packages, volume of packages, and/or weight of packages transported by the carrier during the time period. Then, the fuel factor calculation module 300 divides the total amount of fuel retrieved by the total number of packages, volume of packages, or weight of packages retrieved. This quotient is the fuel factor associated with movement of a package through each carrier facility. In other embodiments, instead of (or in addition to) retrieving the total number of packages, volume of packages, and/or weight of packages, the fuel factor calculation module 300 may retrieve the total revenue (and/or total number of invoices) associated with transporting packages during the particular time period, and the fuel factor may be the quotient of the total amount of fuel divided by the total revenue (or total number of invoices) retrieved. In various other embodiments, the fuel factor calculation module 300 is configured for calculating a fuel factor for each carrier facility. In particular, the fuel factor calculation module 300 retrieves the total amount of fuel used at each carrier facility during a particular time period and the total number of packages (and/or volume or weight of packages) that were transported through each facility during the particular time period. The fuel factor calculation module 300 then calculates a fuel factor for each facility by dividing the total amount of fuel retrieved by the total number of packages (and/or volume or weight of packages) retrieved. In other embodiments, instead of (or in addition to) retrieving the total number of packages, volume of packages, and/or weight of packages, the fuel factor calculation module 300 may retrieve the total revenue (and/or total number of invoices) associated with transporting packages through each carrier facility during the particular time period, and the fuel factor may be the quotient of the total amount of fuel divided by the total revenue (or total number of invoices) retrieved. Emissions Factor Calculation Module The emissions factor calculation module 600 according to various embodiments calculates an emissions factor based on each fuel factor calculated by the fuel factor calculation module 300. For example, in certain embodiments, for transport operational activities, each emissions factor may be expressed as an amount of emissions (e.g., lbs. or kg of CO2) per volume (or weight) of package transported, and for pickup or delivery operational activities, each emissions factor may be expressed as an amount of emissions per stop. In certain embodiments, the amount of emissions expressed in the calculated emissions factors is an amount of emissions by weight, but in other embodiments, the module 600 may calculate the amount of emissions in other acceptable units. FIG. 10 illustrates the steps executed by the emissions factor calculation module 600 according to various embodiments for calculating an amount of emissions per cube. Beginning at Step 601, the emissions factor calculation module 600 retrieves one or more of the fuel factors calculated by the fuel factor calculation module 300. Then, in Step 603, for each retrieved fuel factor, the module 600 calculates an amount of emissions corresponding to each fuel factor by multiplying the fuel factor by an amount of energy per amount of fuel (e.g., Gigajoules of energy per gallon of fuel) and by an amount of emissions per amount of energy (e.g., kilograms or pounds of emissions per Gigajoule). The amount of energy per amount of fuel and the amount of emissions per amount of energy are known standards. For example, in one embodiment, the emission factor module 600 calculates the weight of carbon dioxide emitted per package volume (“cube”) (or weight) for transport operational activities by executing the following formula: ( Liters of Fuel Used Cube ) × ( Gigajoules Liters of Fuel ) × ( Kilograms of CO 2 Gigajoule ) = Kilograms of CO 2 Emitted Cube Similarly, the emissions factor module 600 calculates the weight of carbon dioxide emitted per stop for pickup and delivery operational activities by executing the following formula: ( Liters of Fuel Used Stop ) × ( Gigajoules Liters of Fuel ) × ( Kilograms of CO 2 Gigajoule ) = Kilograms of CO 2 Emitted Stop According to various embodiments, the emissions factor calculation module 600 may send the data it retrieves and/or calculates to the active emissions calculation database 33 after each step described above or only after Step 603. In the example described above, the module 600 calculates an amount of carbon dioxide emitted per package volume (or weight) resulting from a particular operational activity of the carrier, but in other various embodiments, the module 600 may calculate emissions factors associated with other types of emissions, such as, for example, methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). In various embodiments, the emissions factor calculation module 600 is further configured for calculating emissions resulting from stationary operational activities. In certain embodiments, the emissions factor calculation module 600 calculates emissions factors based on the fuel factors calculated by the fuel factor calculation module 300 as described above. However, in other various embodiments, the emissions factor calculation module 600 calculates one or more emissions factors based on a total amount of emissions resulting from operations of carrier facilities during a particular time period. In particular, according to various embodiments, the emissions factor calculation module 600 calculates an emissions factor for a stationary operational activity by first retrieving (1) a total amount of emissions resulting from operation of all (or a portion of) the carrier's facilities during the particular time period and (2) a total number of packages, volume of packages, and/or weight of packages transported by the carrier during the time period. Then, the emissions factor calculation module 600 divides the total amount of emissions retrieved by the total number of packages, volume of packages, or weight of packages retrieved. This quotient is the emissions factor associated with movement of a package through each carrier facility. In other embodiments, instead of (or in addition to) retrieving the total number of packages, volume of packages, and/or weight of packages, the emissions factor calculation module 600 may retrieve the total revenue (and/or total number of invoices) associated with transporting packages during the particular time period, and the emissions factor may be the quotient of the total amount of emissions divided by the total revenue (or total number of invoices) retrieved. In various other embodiments, the emissions factor calculation module 600 is configured for calculating an emissions factor associated with each carrier facility. In particular, the emissions factor calculation module 600 retrieves the total amount of emissions resulting from operations at each carrier facility during a particular time period and the total number of packages (and/or volume or weight of packages) that were transported through each facility during the particular time period. The emissions factor calculation module 600 then calculates an emissions factor for each facility by dividing the total amount of emissions retrieved by the total number of packages (and/or volume or weight of packages) retrieved. In other embodiments, instead of (or in addition to) retrieving the total number of packages, volume of packages, and/or weight of packages, the emissions factor calculation module 600 may retrieve the total revenue (and/or total number of invoices) associated with transporting packages through each carrier facility during the particular time period, and the emissions factor may be the quotient of the total amount of emissions divided by the total revenue (or total number of invoices) retrieved. According to certain embodiments, the total amount of emissions for each facility may be determined using E-Grid or other smart grid technology software that provides an estimated (or actual) amount of energy (or fuel) used based on the location of the facility (e.g., postal zip code, region, state, etc.). Emissions Calculation Module The emissions calculation module 400 according to various embodiments is configured for calculating an amount of emissions (or estimated amount) resulting from the transportation of a particular shipment through the carrier's transportation network. FIG. 11 illustrates an embodiment of the emissions calculation module 400. Beginning at Step 401, the emissions calculation module 400 retrieves one or more emissions factors for each operational activity associated with the particular shipment and at least a portion of the shipment parameters associated with the particular shipment. For example, using the exemplary shipment 800 shown in FIG. 6, if the particular shipment is a letter shipped via second day delivery service level by a commercial customer that has daily pickups by the carrier, the emissions calculation module 400 retrieves (1) the pickup operational activity emissions factor associated second day delivery letter service products shipped by commercial customers having daily pickup, (2) the delivery operational activity emissions factor associated second day delivery letter service products shipped by commercial customers, (3) one or more transport operational activity emissions factors associated with second day delivery, and (4) one or more stationary operational activity emissions factors associated with processing and sorting at each carrier facility and movement of the particular shipment between the airports and the regional facilities located near each airport. Next, in Step 403, the module 400 calculates an amount of emissions corresponding to the particular shipment for non-pickup and delivery operational activities. For example, the module 400 calculates the amount of emissions corresponding to the transport operational activity by multiplying the volume of the shipment (e.g., cubic feet) by each volume-based transport operational activity emissions factor. In other embodiments in which the emissions factors are weight-based, the amount of emissions corresponding to the particular shipment is calculated by multiplying the weight of the shipment by each weight-based emissions factor. And, in embodiments in which the emissions factors are based on number of packages, revenue, or invoices, the amount of emissions corresponding to the particular shipment is calculated by multiplying the number of packages in the shipment, the cost of transporting the shipment, or the number of invoices associated with the shipment, respectively. For pickup and delivery operational activities, according to various embodiments, the emissions calculation module 400 calculates the amount of emissions based on the average daily pickup or delivery volume for each customer (or account associated with each customer). As shown in FIG. 11, to calculate the amount of emissions for a pickup operational activity, the module 400 proceeds to Step 410 shown in FIG. 13 (Step 404 in FIG. 11), and to calculate the amount of emissions for a delivery operational activity, the module 400 proceeds to Step 450 shown FIG. 14 (Step 406 in FIG. 11). After the amount of emissions for the pickup and delivery operational activities have been calculated, the module 400 sums together the emissions calculated for each operational activity to calculate the total emissions for the particular shipment, as shown in Step 408 of FIG. 11. In particular, in the embodiment shown in FIG. 13, with respect to a pickup operational activity for a particular shipment, the emissions calculation module 400 retrieves an average number of packages (or volume or weight of packages) picked up per day for the customer (or the account associated with the customer) by the carrier at Step 410. In certain embodiments, the module 400 retrieves the average number of packages for the particular service level associated with the shipment or the service product associated with the shipment. In addition, the average number of packages retrieved may be received by the system 5 from the customer or retrieved based on historical shipment data associated with the customer that has been previously stored by the transportation entity server 200. Next, in Step 412, the average number of packages retrieved in Step 410 is multiplied by the average volume (or weight) per package associated with the customer. In alternative embodiments, the average number of packages retrieved may be multiplied by the average volume (or weight) per package associated with the service level of each package. In one alternative embodiment, the average volume (or weight) is customer-specific (average volume or weight per package for all pickups for the customer at the particular service level). Then, in Step 414, the product from Step 412 is divided by the average total volume associated with a pickup/delivery truck. In certain embodiments, the average total volume associated with the pickup/delivery truck depends on the type of pickup/delivery truck expected to pickup the particular shipment and may vary over time as characteristics of packages change. If the quotient from Step 414 is less than or equal to one, then the emissions calculation module 400 treats the pickup of the particular shipment as being performed (or will be performed) by a small or large pickup/delivery truck, and if the quotient from Step 414 is greater than one, then the emissions calculation module 400 treats the pickup of the particular shipment as being performed by a larger tractor trailer. In particular, if the quotient from Step 414 is less than or equal to one, the emissions calculation module 400 proceeds to Step 416 and retrieves the pickup emissions factor associated with the particular service product (or service level) calculated by the emissions factor calculation module 600 for a small or large pickup/delivery truck. Next, in Step 418, the pickup emissions factor retrieved in Step 416 is divided by the average number of packages retrieved in Step 410. Then, in Step 420, the average volume per package is retrieved. For example, in one embodiment, the average volume per package may be retrieved from a table that associates an average weight per package with the average volume per package, and the average weight per package may be determined by dividing the total weight by the total number of packages. In various other embodiments, the average volume is determined on a daily basis (e.g., average volume for all of the customer's shipments shipped on a particular day), on a per service level basis (e.g., average volume for all of the customer's shipments being shipped via a particular service level), or on a per origin/destination level (e.g., average volume for all of the customer's shipments being shipped between a particular origin and destination). In Step 422, the total volume per shipment is calculated by multiplying the average volume per shipment retrieved in Step 420 by the number of packages per shipment. The module 400 then proceeds to Step 424 in which the total volume per shipment is multiplied by the quotient from Step 418 to calculate the amount of emissions per package. If the quotient from Step 414 is greater than one, the emissions calculation module 400 proceeds to Step 426 and rounds the quotient from Step 414 to the next highest integer. Then, in Step 428, the pickup emissions factor associated with the particular service product (or service level) for a tractor trailer is retrieved. Next, in Step 430, the pickup emissions factor retrieved in Step 428 is divided by the average number of packages retrieved in Step 410. Then, in Step 432, the average volume per shipment is retrieved. In various other embodiments, the average volume is determined on a daily basis (e.g., average volume for all of the customer's shipments shipped on a particular day), on a per service level basis (e.g., average volume for all of the customer's shipments being shipped via a particular service level), or on a per origin/destination level (e.g., average volume for all of the customer's shipments being shipped between a particular origin and destination). In Step 434, the total volume per shipment is calculated by multiplying the average volume per shipment retrieved in Step 432 by the number of packages per shipment. The module 400 then proceeds to Step 436 in which the total volume per shipment is multiplied by the quotient from Step 430 to calculate the amount of emissions per package. FIG. 14 illustrates an embodiment of steps performed by the emissions calculation module 400 in calculating the amount of emissions resulting from a delivery operational activity for the particular shipment. In particular, with respect to a delivery operational activity for a particular shipment, the emissions calculation module 400 retrieves an average number of packages (or volume or weight of packages) delivered per day to the customer (or the account associated with the customer) by the carrier at Step 450. In certain embodiments, the module 400 retrieves the average number of packages for the particular service level associated with the shipment or the service product associated with the shipment. In addition, the average number of packages retrieved may be received by the system 5 from the customer or retrieved based on historical shipment data associated with the customer that has been previously stored by the transportation entity server 200. Next, in Step 452, the total number of packages retrieved in Step 450 is multiplied by the average volume (or weight) per package associated with the customer. In alternative embodiments, the total number of packages retrieved may be multiplied by the average volume (or weight) per package associated with the service level of each package. In one alternative embodiment, the average volume (or weight) is customer-specific (average volume or weight per package for all deliveries for the customer at the particular service level). Then, in Step 454, the product from Step 452 is divided by the average total volume associated with a pickup/delivery truck. In certain embodiments, the average total volume associated with the pickup/delivery truck depends on the type of pickup/delivery truck expected to deliver the particular shipment and may vary over time as characteristics of packages change. If the quotient from Step 454 is less than or equal to one, then the emissions calculation module 400 treats the delivery of the particular shipment as being performed (or will be performed) by a small or large pickup/delivery truck, and if the quotient from Step 454 is greater than one, then the emissions calculation module 400 treats the delivery of the particular shipment as being performed by a larger tractor trailer. In particular, if the quotient from Step 454 is less than or equal to one, the emissions calculation module 400 proceeds to Step 456 and retrieves the delivery emissions factor associated with the particular service product (or service level) calculated by the emissions factor calculation module 600 for a small or large pickup/delivery truck. Next, in Step 458, the delivery emissions factor retrieved in Step 456 is divided by the average number of packages retrieved in Step 450. Then, in Step 460, the average volume per package is retrieved. For example, in one embodiment, the average volume per package may be retrieved from a table that associates an average weight per package with the average volume per package, and the average weight per package may be determined by dividing the total weight by the total number of packages. In various other embodiments, the average volume is determined on a daily basis (e.g., average volume for all of the customer's shipments shipped on a particular day), on a per service level basis (e.g., average volume for all of the customer's shipments being shipped via a particular service level), or on a per origin/destination level (e.g., average volume for all of the customer's shipments being shipped between a particular origin and destination). In Step 462, the total volume per shipment is calculated by multiplying the average volume per shipment retrieved in Step 460 by the number of packages per shipment. The module 400 then proceeds to Step 464 in which the total volume per shipment is multiplied by the quotient from Step 458 to calculate the amount of emissions per package. If the quotient from Step 454 is greater than one, the emissions calculation module 400 proceeds to Step 466 and rounds the quotient from Step 454 to the next highest integer. Then, in Step 468, the delivery emissions factor associated with the particular service product (or service level) for a tractor trailer is retrieved. Next, in Step 470, the delivery emissions factor retrieved in Step 468 is divided by the average number of packages retrieved in Step 450. Then, in Step 472, the average volume per shipment is retrieved. In various other embodiments, the average volume is determined on a daily basis (e.g., average volume for all of the customer's shipments shipped on a particular day), on a per service level basis (e.g., average volume for all of the customer's shipments being shipped via a particular service level), or on a per origin/destination level (e.g., average volume for all of the customer's shipments being shipped between a particular origin and destination). In Step 474, the total volume per shipment is calculated by multiplying the average volume per shipment retrieved in Step 470 by the number of packages per shipment. The module 400 then proceeds to Step 476 in which the total volume per shipment is multiplied by the quotient from Step 470 to calculate the amount of emissions per package. According to various other embodiments, Steps 410 through 470 described above as being performed by emissions calculation module 400 can be used with the fuel factors calculated by module 300 to calculate an amount of fuel used per package. The resulting amounts of emissions calculated from each emissions factor are then summed together to calculate a total amount of emissions estimated for transportation of the shipment through the carrier's transportation network. Reporting Module The reporting module 500 is configured to report the calculated amount of emissions to the user. FIG. 12 illustrates an exemplary flow of the steps executed by the reporting module 500 according to various embodiments. Beginning at Step 501, the reporting module 500 receives from the emissions calculation module 400 the amount of emissions resulting from transporting the particular shipment. Next at Step 502, the reporting module 500 generates a report for the user based on the data received or retrieved in Step 501, which may include, but is not limited to, the total amount of carbon dioxide and/or other emissions resulting from transporting the shipment or the amounts resulting from each operational activity (or groups thereof). This data may be further be organized by each service level and/or service product, each type of shipment vehicle, and by specific groups of packages, for example. In addition, in various embodiments, the report generated by the reporting module 500 may include the results of any of the calculations described above in relation to the fuel factor calculation module 300, the carbon factor calculation module 600, or the carbon calculation module 400, including, for example, the amount of fuel estimated (or actually) used for transporting a particular shipment or used to perform one or more operational activities. Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Accordingly, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the invention. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for the purposes of limitation. |
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claims | 1. A radioactive shielding composition comprising:an asphalt hydrocarbon component, wherein the hydrocarbon component is blended with Solvent De-asphalted Pitch (SDA) bottoms to produce asphalt having a viscosity of 500 to 2000 poise at 60° C. (140° F.);a radiation shielding and absorbing material that includes leaded glass particles derived from recycled glass waste or virgin glass, and wherein the leaded glass particles are supplied to the composition with diameter sizes of 2 millimeters or less; anda polymer which is other than said asphalt hydrocarbon component. 2. The radioactive shielding composition of claim 1, wherein the radiation shielding and absorbing material is substantially free of materials that can leach from the radiation shielding and absorbing material. 3. The radioactive shielding composition of claim 1, wherein the radioactive shielding and absorbing material comprises approximately 0.10 to 95.0 percent of an overall weight of the radioactive shielding composition. 4. The radioactive shielding composition of claim 1 further comprising, at least one of a cross linking agent and a curing agent. 5. The radioactive shielding composition of claim 4, wherein the at one of the cross linking agent and the curing agent includes at least one of elemental sulfur and sulfur donors. 6. The radioactive shielding composition of claim 1 further including at least one of:sulfur comprising approximately 0.01 to 5.0 percent of an overall weight of the radioactive shielding composition;polycarbodiimide modified diphenylmethane comprising approximately 0.01 to 15.0 percent of the overall weight;an antioxidant, wherein the antioxidant includes at least one of butylated phenol and metal hydrocarbyl dithiophosphates;hydrocarbyl dithiophosphates comprising approximately 0.10 to 2.0 percent of the overall weight;butylated phenol comprising approximately 0.10 to 5.0 percent of the overall weight;anionic emulsifiers;cationic emulsifiers;non-ionic emulsifiers;dispersants;plasticisers;gellants;mineral spirits;napthas;aromatic solvents;kerosene;compounds of D'Limolene;methyl esters of fatty acids;biodiesel compounds;fuel oils;extender and fluxing oils including at least one of FCC light cycle oil, FCC heavy naptha, FCC slurry oil, clarified slurry oil, gas oil, vacuum gas oil, coker naptha, coker gas oil, hydrotreated napthenic or parafinnic oils, neutral oils, footes oil, vegetable oils, esters of fatty acids, and aromatic extracts;fire retardants; andfiber reinforcements. 7. The radioactive shielding composition of claim 1, wherein the radiation shielding and absorbing material also includes at least one:man-made and naturally occurring compounds of Boron, including at least one of borax, boron carbide, boron nitride, bauxite, Cryolite, Boehmite, gibbsite, Diaspore, alumina trihydrate, and aluminum silicates;titanium compounds including at least one of limonite, rutile, brookite, anatase, and titano-magnetite;sulfur;sulfates;sulfites;gypsum;anhydrite;barite;iron;hematite;magnetite;siderite;goethite;limonite;lithium;lepidolite;spodumene;petalite;amblygonite;beryllium;cobalt;nickel;copper;zinc;strontium;zirconium;tin;depleted uranium;plastics;polyethylenes;polypropylenes;amorphous polypropylenes;metallocene polyethylene copolymers;parafinnic and microcrystalline waxes;fischer-tropsch waxes;water;ground concrete;recycled crumb rubber;ground tire rubber;limestones; andhydrated lime. 8. The radioactive shielding composition of claim 1 further comprising at least one of:Styrene Butadiene (SB) diblock polymers comprising approximately 0.10 to 95.0 percent of an overall weight for the radioactive shielding composition;Styrene-Butadiene-Styrene (SBS) triblock polymers which may be either linear or radial;styrene-isoprene-styrene (SIS) polymers;hydrotreated SBS;Styrene Ethylene Butadiene Styrene polymers (SEBS);Styrene Butadiene Rubber (SBR);Natural Latex;polyacrylamide;crumb rubber;glycidyl-containing ethylene terpolymers;Ethylene Vinyl Acetate;Ethylene Acrylic Acid;Polychloroprene rubber;polyethylene;metallocene polyethylenes;amorphous polypropylene;polypropylene;2-ethyl-1,3-hexane diol;glycols;polyether polyols;polyester polyols;hydroxyl terminated polybutadiene polymers;amine terminated polybutadiene polymers;copolymers of acrylonitrile;castor oil;vegetable oils;styrene acrylic copolymers;acrylic copolymers; andvinyl acrylic copolymers. |
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048658049 | abstract | A nuclear reactor fuel rod end plug (100) is adapted to be welded within each end of a nuclear reactor fuel rod cladding tube, especially by means of laser beam welding techniques, although TIG welding techniques may also be employed, wherein an annular groove (126) is defined about the external periphery of the end plug (100) so as to extend radially inwardly of the long land region (118) of the plug (100) within the vicinity of the juncture of the land surface (118) and the shoulder portion (120) at which location the girth weld between the end plug (100) and the cladding tubing will be defined. When employing laser beam welding techniques to accomplish the butt-type girth weld between the plug (100) and the cladding tube, the groove (126) serves to eliminate porosity defects within the weldment, and when employing TIG welding techniques to accomplish the butt-type girth weld between the plug (100) and the cladding tube, the groove (126) serves to eliminate porosity defects within the weldment without requiring the plug land (118 ) and shoulder (120) surfaces to be accurately machined in accordance with precisely critical dimensional tolerances, and similarly for the mating surfaces of the cladding tube, as had previously been mandatory in accordance with prior art TIG welding techniques. |
description | This application claims priority to Japanese Patent Application No. 2018-046529 filed on Mar. 14, 2018, the entire contents of which are incorporated by reference herein. The present invention relates to a method and an apparatus to detect gas leakage from a metallic canister of a concrete module. More specifically, the present invention relates to a method and an apparatus to detect leakage of an inert gas such as helium charged into a horizontally-installed canister in a horizontal silo storage. As a means to store highly radioactive waste materials such as spent nuclear fuel, attention is paid to a concrete module in which spent fuel is contained in a metallic canister and stored in a concrete construction storage-facility. There are types of concrete modules including: a concrete cask in which a canister is vertically installed and housed in a concrete storage-facility; and a horizontally-installed silo storage in which the canister is horizontally installed and loaded in a concrete storage-facility for safekeeping. Both are dry-type storage facilities that effectively remove decay heat of spent fuel inside the canister by circulating external air by natural convection through air communication ports provided at an upper side and a lower side of the concrete storage-facility (hereinafter simply referred to as “silo”), respectively. In the case of the above-described concrete modules, the canister adopts a structure sealed by welding, and therefore, there is no obligation to monitor gas leakage. However, considering long-term storage, it is important to monitor integrity of the canister, and development in a technology to detect leakage of the inert gas such as helium is desired. To respond to such desired development, the applicant of the present application proposes a helium leakage detection method in a concrete cask, in which a temperature difference between a temperature at a center of a canister bottom portion and a temperature at a center of a canister lid portion is monitored, and in a case where a value of the temperature difference is increased and a supply air temperature is decreased, it is determined that gas leakage has occurred (JP 2005-265443 A). Additionally, the applicant of the present application also proposes a helium leakage detection method in a concrete cask, in which presence/absence of gas leakage is determined by paying attention to a change in a temperature difference between a temperature at a lid portion and a temperature at a bottom portion of a canister (JP 2017-58240 A). The applicant of the present application further proposes a method in which a temperature at a canister bottom portion and a supply air temperature of external air passing between the canister and a concrete storage container are monitored, and when there is a significant change in correlation between actually-measured temperature data of the temperature at the canister bottom portion and actually-measured temperature data of the supply air temperature, or when there is a change in a physical amount linked to the actually-measured temperature data and associated with inert gas leakage, it is determined that inert gas leakage has occurred (JP 2017-75949 A). However, all of the technologies of JP 2005-265443 A, JP 2017-58240 A, and JP 2017-75949 A relate to a vertical concrete cask in which a canister is vertically installed for safekeeping and do not relate to a horizontal silo storage in which a canister is horizontally installed for safekeeping. There is no research made on gas leakage detection in the horizontally-installed canister, and relevance between gas leakage and a change in a surface temperature of a metallic canister is not clarified yet. Accordingly, whether a helium leakage detection mechanism in a vertical concrete cask can be directly applied is also unknown. On the other hand, in a case of the horizontal silo storage, the canister is not needed to be suspended at a high level because the canister is loaded into a concrete silo while being kept in a horizontally-installed state, and there is an advantage of high safety against a fall accident. From this point, development and establishment of a technology to detect gas leakage from the horizontally-installed canister is desired. The present invention is directed to providing a method and an apparatus in which gas leakage in a horizontally-installed canister can be detected. To achieve the above-described object, the inventor of the present application has conducted various kinds of tests and research on the relevance between the gas leakage in the horizontally-installed canister and a change in a surface temperature of the metallic canister. As a result, it is found that the following phenomena occur when a pressure inside the canister is decreased by gas leakage: temperatures in all of surfaces of the canister are changed; a temperature at a canister bottom portion that is one end portion in a lateral direction in the horizontally-installed attitude and a temperature at a lower portion of a canister side surface that is a lower half portion of a canister body portion in the horizontally-installed attitude are increased; and a temperature at a canister lid portion that is the other end portion in the lateral direction in the horizontally-installed attitude and a temperature at an upper portion of the canister side surface that is an upper half portion of the canister body portion in the horizontally-installed attitude are decreased. Additionally, it is found that: temperature increase at the canister bottom portion and temperature decrease at the canister lid portion are large at the time of gas leakage, and it is effective to use these characteristics of temperature differences for detection. Furthermore, it is found that a change amount of a temperature difference between the upper portion of the canister body portion and the lower portion of the canister body portion in the horizontally-installed attitude is smaller than a change amount of a temperature difference between the canister bottom portion and the canister lid portion, but responsiveness to gas leakage is good. The above-described findings can be hardly predicted from the findings in the related art in which temperatures are presumably changed by natural convection in the vertically-installed canister, more specifically, a temperature at the canister lid portion is decreased while a temperature at the canister bottom portion is increased and there is almost no change in a temperature at the canister body portion between the canister lid portion and the canister bottom portion. A gas leakage detection method in a horizontally-installed canister in order to achieve the above-described object is based on the above-described findings, and the method includes: monitoring at least two temperatures out of a temperature TB at a canister bottom portion to be one end portion in a lateral direction in a horizontally-installed attitude of the canister that is horizontally installed and housed inside a concrete silo, a temperature TSB at a canister side surface lower portion located below a horizontal plane passing through a center of the canister in the horizontally-installed attitude, a temperature TT at a canister lid portion to be the other end portion in the lateral direction in the horizontally-installed attitude, and a temperature TST at a canister side surface upper portion located above the horizontal plane passing through the center of the canister in the horizontally-installed attitude; and determining occurrence of leakage of an inert gas inside the canister when there is a change in a temperature difference between the at least two temperatures. Note that the canister side surface represents a peripheral surface of a body portion of the canister in the horizontally-installed attitude. The gas leakage detection method may further include determining occurrence of leakage of the inert gas inside the canister when there is a change in a temperature difference between one or both of the temperature TB at the canister bottom portion and the temperature TSB at the canister side surface lower portion and one or both of the temperature TT at the canister lid portion and the temperature TST at the canister side surface upper portion. The temperature TB at the canister bottom portion may be a temperature at a center of the canister bottom portion, the temperature TSB at the canister side surface lower portion may be a temperature at a bottom portion of the canister side surface to be a lowermost portion in the horizontally-installed attitude, the temperature TT at the canister lid portion may be a temperature at a center of the canister lid portion, and the temperature TST at the canister side surface upper portion may be a temperature at a top portion of the canister side surface to be an uppermost portion in the horizontally-installed attitude. A temperature difference to determine occurrence of leakage of the inert gas may also be a temperature difference ΔTBT (where ΔTBT=TB−TT) between the temperature TT at the canister lid portion and the temperature TB at the canister bottom portion. The temperature difference to determine occurrence of leakage of the inert gas may also be a temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. The temperature difference to determine occurrence of leakage of the inert gas may also be a temperature difference ΔTSBST (where ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion. The temperature difference to determine occurrence of leakage of the inert gas may also be the sum ΔT4 (where ΔT4=ΔTBT+ΔTSBST) obtained by adding the temperature difference ΔTBT (ΔTBT=TB−TT) between the temperature TT at the canister lid portion and the temperature TB at the canister bottom portion to the temperature difference ΔTSBST (where ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion. The temperature difference to determine occurrence of leakage of the inert gas may also be the sum ΔT3GR (where ΔT3GR=ΔTBT+ΔTBST) obtained by adding the temperature difference ΔTBT(ΔTBT=TB−TT) between the temperature TB at the canister bottom portion and the temperature TT at the canister lid portion to the temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. Additionally, the temperature difference to determine occurrence of leakage of the inert gas may also be the sum ΔT3R(where ΔT3R=ΔTSBST+ΔTBST) obtained by adding the temperature difference ΔTSBST (ΔTSBST=TSB−TST) between the temperature TSB at the canister side surface lower portion and the temperature TST at the canister side surface upper portion to the temperature difference ΔTBST (where ΔTBST=TB−TST) between the temperature TB at the canister bottom portion and the temperature TST at the canister side surface upper portion. Additionally, a gas leakage detection apparatus in a horizontally-installed canister in order to achieve the above-described object includes: at least two sensors out of a first temperature sensor adapted to measure a temperature TB at a canister bottom portion to be one end portion in a lateral direction in a horizontally-installed attitude of the canister that is horizontally installed and housed inside a concrete silo, a third temperature sensor adapted to measure a temperature TSB at a canister side surface lower portion located below a horizontal plane passing through a center of the canister in the horizontally-installed attitude, a second temperature sensor adapted to measure a temperature TT at a canister lid portion to be the other end portion in the lateral direction in the horizontally-installed attitude, and a fourth temperature sensor adapted to measure a temperature TST at a canister side surface upper portion located above the horizontal plane passing through the center of the canister in the horizontally-installed attitude; a monitoring unit adapted to monitor measurement values of the at least the two sensors out of the first temperature sensor, the third temperature sensor, the second temperature sensor, and the fourth temperature sensor; and a gas leakage determination unit adapted to determine occurrence of leakage of an inert gas inside the canister when a change in a difference between the at least two measurement values to be monitored exceeds a threshold value. The gas leakage detection apparatus may include at least one of the first temperature sensor and the third temperature sensor and at least one of the second temperature sensor and the fourth temperature sensor, and the monitoring unit may monitor a measurement value of at least one of the first temperature sensor and the third temperature sensor and a measurement value of at least one of the second temperature sensor and the fourth temperature sensor. According to the gas leakage detection method and the gas leakage detection apparatus in a horizontally-installed canister of the present invention, temperatures are changed at the time of gas leakage in the four parts (specifically, all of surfaces/parts of the canister) including the canister bottom portion, canister lid portion, canister side surface lower portion, and canister side surface upper portion. Furthermore, the four parts are separated into: two parts where surface temperatures are decreased; and the two parts where surface temperatures are increased. Also, temperature increase parts are separated into a part having large temperature increase and a part having little temperature increase, and temperature decrease parts are separated into a part having large temperature decrease and a part having little temperature decrease, and a change is caused in any temperature difference obtained between any parts. Therefore, it is possible to determine occurrence of leakage of the inert gas such as helium by paying attention to a change in a temperature difference between at least two parts out of the four parts when there is a change in the temperature difference. Furthermore, among the above-described four temperature monitoring parts (in other words, temperature measurement positions), a temperature difference is obtained by combining two or more of the temperature monitoring parts from among, specifically, the temperature monitoring parts where temperature increase is observed and the temperature monitoring parts where temperature decrease is observed. As a result, it is possible to suitably select a combination exhibiting a large change in a temperature difference at the time of pressure decrease, a combination having good responsiveness to a pressure change, and a combination satisfying both a significant change in a temperature difference and good responsiveness to a pressure change. In the following, structures of the present invention will be described based on embodiments illustrated in the drawings. FIG. 1 illustrates one embodiment of a concrete dry-type horizontally-installed spent fuel storage silo to which a gas leakage detection method and a gas leakage detection apparatus according to the present invention is applied. The concrete dry-type horizontally-installed spent fuel storage silo according to the present embodiment includes, for example: a concrete storage-facility (hereinafter referred to as “silo 2”) having a shielding function; and a metallic canister (hereinafter referred to as “canister 1”) having a structure housing spent fuel and being sealed by welding. The horizontally-installed spent fuel storage silo also has a structure in which decay heat of the spent fuel inside the canister 1 is removed by circulating external air by natural convection through a supply air port 3 for cooling air and an exhaust air port 4 which are provided on an upper side and a lower side of the silo 2, respectively. Note that, in FIG. 1, reference sign 5 indicates a silo shielding lid, reference sign 6 indicates a rail-shaped supporting base supporting the canister 1 horizontally installed, reference sign 7 indicates a first temperature sensor, reference sign 8 indicates a second temperature sensor, reference sign 9 indicates a third temperature sensor, reference sign 10 indicates a fourth temperature sensor, reference sign 11 indicates a temperature measurement device, reference sign 12 indicates a computer, reference sign 13 indicates a gas leakage determination unit, reference sign 14 indicates a display device, and reference sign 15 indicates a warning unit. The canister 1 is made of, for example, stainless steel and generally has a sealed structure in which a double lid including an inner cover plate and an outer cover plate is installed, by welding, in a cylindrical container having a bottom. For example, stainless steel partitions having a honeycomb structure (hereinafter referred to as “basket”) is inserted in the canister 1, and spent nuclear fuel that is a radioactive material is charged into each of the partitions. The canister 1 adopts a structure hermetically sealed by welding so as not to leak the enclosed radioactive material to the outside, and also has a structure in which an inert gas such as helium having heat conductivity higher than that of the air is enclosed inside the canister, and decay heat of the spent fuel inside the canister is transferred to an outer surface/surface of the canister via the inert gas such as helium and via the basket. For example, using helium as the gas to be enclosed inside the canister 1 is preferable, but the gas is not necessarily limited to helium, and another inert gas having heat conductivity higher than the heat conductivity of the air may also be used. In the case of the present embodiment, the canister 1 includes: the first temperature sensor 7 to measure a temperature at the canister bottom portion 1B that is one end portion in a lateral direction in the horizontally-installed attitude (referred to as a “canister bottom portion temperature TB” in the present specification); the third temperature sensor 9 to measure a temperature at a lower portion 1SB of the canister side surface that is a side surface region lower than a horizontal plane passing through the center of the canister 1 in the horizontally-installed attitude (referred to as a “canister side surface lower portion temperature TSB” in the present specification); the second temperature sensor 8 to measure a temperature at the canister lid portion 1T that is the other end portion in the lateral direction in the horizontally-installed attitude (referred to as a “canister lid portion temperature TT” in the present specification); and the fourth temperature sensor 10 to measure a temperature at an upper portion 1ST of the canister side surface that is a side surface region higher than the horizontal plane passing through the center of the canister 1 in the horizontally-installed attitude (referred to as a “canister side surface upper portion temperature TST” in the present specification). As measurement parts of surface temperatures of the canister 1, at least two parts out of the canister bottom portion 1B, canister side surface lower portion 1SB, canister lid portion 1T, and canister side surface upper portion 1ST may be selected. However, it is preferable that at least two parts are selected, in which the two parts includes: at least one part out of the canister bottom portion 1B and the canister side surface lower portion 1SB; and at least one part of the canister lid portion 1T and the canister side surface upper portion 1ST. Additionally, in a case where three parts or four parts (specifically, all of the parts) are selected, the number of combinations of temperature differences is increased, a more sensitive gas leakage detection can be achieved, and gas leakage can be detected with higher accuracy. Preferably, the first temperature sensor 7 and the second temperature sensor 8 measure temperatures at the centers, specifically, respective center positions in a radial direction of the surfaces of the canister bottom portion 1B and the canister lid portion 1T. Temperature changes in the canister bottom portion 1B and the canister lid portion 1T in occurrence of inert gas leakage are largest at the center positions of the respective surfaces. Therefore, detection sensitivity can be more improved by measuring the canister bottom portion temperature TB at the center of the canister bottom portion and the canister lid portion temperature TT at the center of the canister lid portion, and furthermore, highly-reliable gas leakage detection can be further expected. However, the first temperature sensor 7 and the second temperature sensor 8 are not limited to measuring the temperatures at the center of the canister bottom portion 1B and the center of the canister lid portion 1T, and may be arranged at positions close to edges of the respective surfaces so as to measure temperatures at positions away from the centers of the respective surfaces. Preferably, the third temperature sensor 9 measures the canister side surface lower portion temperature TSB at a bottom portion of the canister side surface to be a lowermost portion of the cylindrical body portion of the canister 1 in the horizontally-installed attitude (note that a peripheral surface of the body portion is the canister side surface). Preferably, the fourth temperature sensor 10 measures the canister side surface upper portion temperature TST at a top portion of the canister side surface to be an uppermost portion of the cylindrical body portion of the canister 1 in the horizontally-installed attitude. A temperature change in the canister side surface lower portion 1SB in occurrence of inert gas leakage is largest at the bottom portion of the canister side surface to be the lowermost portion in the horizontally-installed attitude. Additionally, a temperature change in the canister side surface upper portion 1ST in occurrence of inert gas leakage is largest at the top portion of the canister side surface to be the uppermost portion in the horizontally-installed attitude. Furthermore, preferably, the canister side surface lower portion temperature TSB and the canister side surface upper portion temperature TST are respectively the temperatures at the centers or approximate center positions in the axial direction of the cylindrical body portion of the canister 1 (specifically, in the lateral direction in the horizontally-installed attitude). A temperature change on the canister side surface in occurrence of inert gas leakage is largest at the center position in the axial direction of the body portion of the canister 1 in each of the canister side surface top portion and the canister side surface bottom portion. However, the third temperature sensor 9 and the fourth temperature sensor 10 are not limited to measuring the temperatures at the canister side surface bottom portion and the canister side surface top portion, and may measure respective temperatures at an arbitrary position of the canister side surface lower portion 1SB and an arbitrary position of the canister side surface upper portion 1ST. As the first to fourth temperature sensors 7, 8, 9, and 10, it is preferable to use a temperature measurement means such as a thermocouple or a thermistor. In this case, besides advantages of being simple in structure and being inexpensive, long-term stable operation can be expected because of the simple and sturdy structure. For example, in the case where thermocouples are used as the temperature sensors 7, 8, 9, and 10, these thermocouples are electrically connected to the temperature measurement device 11 and temperatures can be measured by utilizing thermoelectromotive force by the Seebeck effect. In the view of improving detection sensitivity of inert gas leakage, it is preferable that each of the temperature sensors 7, 8, 9, and 10 is set in a manner directly contacting the surface of the canister 1 to directly measure the temperature at each of the points, but in some cases, it is also possible to measure a surface temperature or a temperature extremely close to the surface by using a non-contact type thermometer. In the description of the present invention, the surface temperature and the temperature extremely close to the surface will be collectively referred to simply as “surface temperature”. Temperature information of the four parts (specifically, all of the surfaces/parts of the canister 1) including the canister bottom portion, canister lid portion, canister side surface lower portion, and canister side surface upper portion, which is obtained by the first to fourth temperature sensors 7, 8, 9, and 10, includes information of pressure changes inside the canister. Specifically, it is found by the inventor of the present application through tests that: the surface temperatures of the canister are changed as follows when the pressure inside the horizontally-installed canister is decreased by gas leakage: the canister bottom portion temperature TB and the canister side surface lower portion temperature TSB are increased; and the canister lid portion temperature TT and the canister side surface upper portion temperature TST are decreased. Furthermore, it is found that increase in the canister bottom portion temperature TB is larger than increase in the canister side surface lower portion temperature TSB when comparing the canister bottom portion temperature TB with the canister side surface lower portion temperature TSB, and the canister lid portion temperature TT is decreased more than the canister side surface upper portion temperature TST when comparing the canister lid portion temperature TT with the canister side surface upper portion temperature TST. Therefore, there is a change caused by gas leakage in any temperature difference between any parts. Accordingly, among the surface temperatures of the canister 1 obtained at the temperature measurement positions of the four parts, measurement values of the surface temperatures at at least two parts are monitored and a temperature difference between the measured values are monitored, and when there is a change in the temperature difference, it is grasped that pressure decrease by gas leakage is caused inside the canister. For example, in the canister 1 horizontally installed and housed inside the concrete silo 2, one or both of two surface temperature increase parts including the canister bottom portion 1B (temperature TB) and the canister side surface lower portion 1SB (temperature TSB) and one or both of the two surface temperature decrease parts including the canister lid portion 1T (temperature TT) and the canister side surface upper portion 1ST(temperature TST) are monitored. When a change indicating gas leakage is observed in a temperature difference between at least two parts out of the surface temperature increase parts and the surface temperature decrease parts, specifically, when there is increase of a certain amount or more in the temperature difference, it can be determined that gas leakage is occurring. Here, in a combination including the two surface temperature increase parts 1B and 1SB (temperatures TB and TSB) and the two surface temperature decrease parts 1T and 1ST(temperatures TT and TST), one increase part and one decrease part may be used. Alternatively, any one of following cases is also applicable: a case of using three parts including the two increase parts and one decrease part in order to emphasize a change in a temperature difference, a case of using three parts including the two decrease parts and one increase part, and also a case of using all of the four parts including the two increase parts and the two decrease parts. Additionally, it is possible to cancel a change in an external air temperature from two target temperatures by calculating and using a temperature difference, and influence of a change in the external air temperature can be hardly received. For example, in a case of combining one surface temperature increase part and one surface temperature decrease part, temperature differences can be obtained by calculation from four combinations including ΔTBT (where ΔTBT=TB−TT), ΔTSBST (where ΔTSBST=TSB−TST), ΔTBST (where ΔTBST=TB−TST), and ΔTSBT (where ΔTSBT=TSB−TT). Additionally, since the temperature difference ΔTBT is larger than the temperature difference ΔTSBST between the two temperature monitoring parts having relatively small change amounts as illustrated in FIG. 10, using the temperature difference ΔTBT between the two temperature monitoring parts (in other words, temperature measurement positions) having large change amounts in the surface temperatures is preferable from the viewpoint of a temperature difference. On the other hand, using the temperature difference ΔTSBST between the two temperature monitoring parts having the relatively small change amounts in the surface temperature is preferable in the viewpoint of responsiveness to a pressure change because, as illustrated in FIG. 11, the responsiveness is more excellent in a region surrounded by a broken line than in the temperature monitoring parts in which the temperature difference ΔTBT is obtained despite a fact that the temperature difference ΔTSBST is smaller than the temperature difference ΔTBT between the two temperature monitoring parts having the large change amounts. Furthermore, combining a temperature monitoring part having a large change amount in the surface temperature with a temperature monitoring part having a small change amount in the surface temperature, specifically, using the temperature difference ΔTBST is preferable in a viewpoint of achieving both pressure responsiveness and temperature difference clarity because, as illustrated in FIG. 12, the responsiveness to a pressure change is excellent and a large temperature difference can be obtained despite a fact that the temperature difference ΔTBST is slightly smaller than ΔTBT while being larger than ΔTSBST. Additionally, as illustrated in FIG. 13, using ΔTSBT has an advantage of having a large temperature difference although responsiveness to a pressure change of ΔTSBT is inferior to that of ΔTSBST. In the case of using the three parts including the two surface temperature increase parts and one surface temperature decrease part, it is possible to have two kinds of combinations including, for example, the sum ΔT3R of the temperature differences (where ΔT3R=ΔTSBST+ΔTBST) using the canister side surface upper portion temperature TST having a relatively small decrease amount of the surface temperature and the sum ΔT3R of the temperature differences (where ΔT3R=ΔTSBT+ΔTBT) using the canister lid portion temperature TT having a medium temperature decrease amount of the surface temperature. In this case, it is preferable to use the sum ΔT3R of the temperature differences (where ΔT3R=ΔTSBST+ΔTBST) using the canister side surface upper portion temperature TST. In the case of using the sum ΔT3R of the temperature differences (where ΔT3R=ΔTSBST+ΔTBST), combinations having respectively excellent pressure responsiveness are summed. Therefore, the pressure responsiveness is excellent and the temperature difference can be increased approximately 1.5 times compared to ΔTBT as illustrated in FIG. 15. In the case of using all of the four parts including the two surface temperature increase parts and the two surface temperature decrease parts, it is possible to have two kinds of combinations including, for example: the sum ΔT4 of the temperature differences (where ΔT4=ΔTBT+ΔTSBST) in which the two temperature monitoring parts both having the large change amounts in the surface temperatures are paired and the two temperature monitoring parts both having the relatively small change amounts in the surface temperatures are paired; and the sum ΔT4 of the temperature differences (where ΔT4=ΔTBST+ΔTSBT) in which each of the temperature monitoring parts having the large change amounts in the surface temperatures is paired with each of the temperature monitoring parts having the relatively small change amounts in the surface temperatures. In this case, it is preferable to use ΔT4=ΔTBT+ΔTSBST as ΔT4. In the case of using ΔT4=ΔTBT+ΔTSBST, the temperature difference can be increased 1.5 times compared to ΔTBT as illustrated in FIG. 14. Furthermore, in the case of using three parts including the two surface temperature decrease parts and one surface temperature increase parts, it is possible to have two kinds of combinations including, for example: the sum ΔT3GR of the temperature differences (where ΔT3GR=ΔTBT+ΔTBST) in which the canister bottom portion temperature TB is used; and the sum ΔT3GR of the temperature differences (where ΔT3GR=ΔTSBST+ΔTBST) in which the canister side surface lower portion temperature TSB is used. In this case, it is preferable to use ΔT3GR using the canister bottom portion temperature TB. As illustrated in FIG. 16, in the case of using ΔT3GR=ΔTBT+ΔTBST, the temperature difference can be increased substantially twice compared to the temperature difference ΔTBT. The above-described gas leakage detection method can be implemented by using, for example, a computer and can be implemented as a system capable of automatically detecting gas leakage. For example, as illustrated in FIG. 1, the gas leakage detection apparatus including the computer 12 executes a gas leakage detection program stored in a memory unit (not illustrated) so as to: read, from the temperature measurement device 11, measurement values of the first temperature sensor 7 to fourth temperature sensor 10; calculate a difference between at least selected two measurement values, specifically, a temperature difference; monitor a change in the temperature difference; determine occurrence of gas leakage by the gas leakage determination unit 13 when the change in the temperature difference exceeds a threshold value; and output a determination result to the display device 14 or the warning unit 15. Specifically, the computer 12 reads, from the temperature measurement device 11, the canister bottom portion temperature TB and the canister lid portion temperature TT detected by the first and second temperature sensors 7 and 8 respectively, and calculates the temperature difference ΔTBT between the canister bottom portion temperature TB and the canister lid portion temperature TT by execution of the gas leakage detection program stored in the memory unit. Next, the gas leakage determination unit 13 of the computer 12 estimates presence/absence of gas leakage by determining whether there is a change indicating gas leakage in the temperature difference ΔTBT to be monitored, for example, determining whether there is a change exceeding the threshold value. For example, a preferable method is to detect gas leakage before 10% leakage of the inert gas inside the canister. In the tests conducted by the inventor of the present application, a temperature difference of 11° C. (about 21° C. in some cases) when 100% leakage occurs. Accordingly, occurrence of gas leakage can be determined when a change in the temperature difference reaches 2° C. by setting 2° C. as a threshold to indicate a change in the temperature difference at the time of 10% leakage, for example. Therefore, even when gas leakage occurs rapidly, time elements do not affect the determination. A difference between at least two measurement values, specifically, a temperature difference is constantly monitored, and whether the value is plus or minus is determined in a computer logic circuit. A state in which the temperature difference is constantly plus is determined as gas leakage. Additionally, as a gas leakage detection system, the computer 12 may be made to execute various warning behaviors such as warning sound and warning light emission when conditions by which the computer 12 determines occurrence of gas leakage are fulfilled. Note that it is preferable to visualize the warning behaviors in terms of checking a non-abnormal state. For example, the computer 12 is made to function as a display control unit that constantly displays, on the display device 14, a temperature difference to be monitored and displays, for comparison, the temperature difference to be monitored in parallel with a temperature difference in a normal state having no gas leakage as a reference temperature difference. With such a display, an operator can visually and intuitively determine occurrence of abnormality, specifically, occurrence of gas leakage. Meanwhile, the above-described embodiment is an example of a preferred embodiment of the present invention, but a specific mode to implement the present invention is not limited to the above-described embodiment, and various modifications can be made to implement the present invention within a range not departing from the scope of the present invention. For example, in the gas leakage detection apparatus according to the above-described embodiment, occurrence of gas leakage is determined by monitoring, as a monitoring target, the temperature difference ΔTBT between the canister bottom portion temperature TB and the canister lid portion temperature TT. However, the temperature difference to be monitored is not limited to ΔTBT. There are two temperature monitoring parts in each of the parts, specifically, the parts include the two parts where the surface temperatures are decreased and the two parts where the surface temperatures are increased. Therefore, there is the plurality of possible combinations as described above. Moreover, it is possible to suitably select gas leakage detection having a different characteristic depending on a combination of the respective temperature monitoring parts, specifically, it is possible to select a combination exhibiting a large change in a temperature difference at the time of pressure decrease and/or a combination exhibiting good responsiveness to a pressure change. Furthermore, in the present invention, due to a phenomenon caused by the internal structure of the canister and peculiar to the horizontally-installed canister, temperatures are changed at the time of gas leakage at the four parts (specifically, all of the surfaces/parts of the canister) including the canister bottom portion, canister lid portion, canister side surface lower portion, and canister side surface upper portion. Additionally, the four parts are separated into: two parts where surface temperatures are decreased; and the two parts where surface temperatures are increased. Also, the temperature increase parts are separated into a part having large temperature increase and a part having little temperature increase, and temperature decrease parts are separated into a part having large temperature decrease and a part having little temperature decrease. Therefore, a change is caused in any temperature difference obtained between any parts. Additionally, in the present invention, since attention is paid to change amounts in the temperature differences as for the temperature changes in the four parts, it is possible to adopt, as information to determine occurrence of gas leakage, a change in a difference between at least two measurement values out of the temperatures TB, TSB, TT, and TST. The information to determine occurrence of gas leakage further includes a temperature difference ΔTBSB (where ΔTBSB=TB−TSB) between the surface temperature increase parts and a temperature difference ΔTTST (where ΔTTST=TT−TST) between the surface temperature decrease parts. A relation between an internal pressure and a temperature at each of the portions of the apparatus was studied by conducting tests (here, two cases including Case 1 and Case 2) while setting, as parameters, internal pressures (concretely, 5 atm, 3 atm, and 1 atm) and calorific values (concretely, 11.5 W and 36.6 W) by using a canister model having a size of 1/18 of an actual machine. (1) Test Apparatus FIG. 2 illustrates a structure of a test apparatus. The test apparatus was formed of a canister model (hereinafter referred to as “canister 21”), a DC power source 22, and a measurement system. A center portion of the canister 21 was fixed to an outer frame with a wire so as to keep a horizontally-installed attitude. The canister 21 was surrounded by an acrylic plate 23 so as not to be exposed to external air as disturbance. FIGS. 3A to 3E illustrate an internal structure of the test apparatus and temperature measurement positions. As the canister 21, a stainless steel cylinder having a height of 260 mm, an outer diameter of 101 mm, and an inner diameter of 97 mm was used. Inside the canister 21, twelve rod-shaped electric heaters 25 simulating nuclear reactor spent fuel rods were loaded inside an aluminum basket 24. The rod-shaped electric heater 25 had a diameter of 10 mm and had a heat generation unit having a length of 150 mm, and a hollow aluminum pipe having an outer diameter of 10 mm, a thickness of 1 mm, and a length of 35 mm is attached to both ends in a longitudinal axis direction of the rod-shaped electric heater 25. Thermocouples D1-1ch to D1-3ch were bonded to respective positions of a rod-shaped electric heater 25A, and thermocouples D1-4ch to D1-6ch were bonded to respective positions of a rod-shaped electric heater 25B. The rod-shaped electric heater 25 (concretely, 25A, 25B) was made to generate heat by using the DC power source 22, and a calorific value was calculated as the product of actually-measured voltage and current applied to the rod-shaped electric heater 25. Additionally, thermocouples D1-7ch and D1-8ch were used to measure a temperature of a gas inside the canister 21. FIGS. 4A to 4C illustrate temperature measurement positions of an outer surface of the canister. Particularly, a canister lid portion temperature TT, a canister bottom portion temperature TB, a canister side surface top surface temperature TST (corresponding to the canister side surface upper portion temperature), and a canister side surface bottom surface temperature TSB (corresponding to the canister side surface lower portion temperature) were respectively used as temperature monitoring parts, and therefore, were important temperature measurement points. Note that the peripheral surface of the body portion of the canister 21 in the horizontally-installed attitude was a canister side surface, and a peripheral surface of a body portion of the basket 24 in the horizontally-installed attitude was a basket side surface. (2) Test Conditions and Test Method In the canister 21 simulating the horizontally-installed canister, air was used as an internal gas, and temperature changes in the respective temperature monitoring parts of the canister 21 were checked at the time of stepwisely changing the air pressure from 5 atm, 3 atm, and to 1 atm (specifically, atmospheric pressure). The test conditions in Case 1 were a calorific value of 36.6 W and an external air temperature of 25.9° C., and the test conditions in Case 2 were a calorific value of 11.5 W and the external air temperature of 25.1° C. In the tests, the rod-shaped electric heaters 25 were made to generate heat under a pressurized state, and the pressure was adjusted to 5 atm after confirming that a steady state was obtained. In leakage tests, the pressure was changed stepwisely from 5 atm, 3 atm, and to 1 atm, and temperature data in the steady state at the respective pressures were acquired. Meanwhile, pressure adjustment was performed because pressure increase was caused by increase in the internal temperature when a valve 26 was closed when the pressure was decreased to 3 atm. Additionally, when the pressure was decreased to 1 atm, the valve 26 was opened so as to avoid pressure increase caused by temperature increase. Note that the air was used as the internal gas in the tests. The reason was that, considering a similarity rule between the actual machine and the model simulating a heat flow phenomenon inside the canister, the closer a Rayleigh number Ra of the model was to a Rayleigh number Ra of the actual machine, the more the test simulating to an actual heat flow phenomenon could be performed. Accordingly, in the tests using the canister model having the 1/18 scale of the actual machine size, the air that could increase the Rayleigh number Ra was used instead of an inert gas such as helium. (3) Test Results <Test Results of Case 1> FIG. 7 illustrates temperatures at the respective temperature measurement points at the time of changing the pressure. Additionally, FIG. 8 illustrates only temperature changes extracted at main temperature measurement points. Note that respective test data was corrected to a value at the external air temperature of 25° C. According to results illustrated in FIGS. 7 and 8, it was confirmed that a heating element center temperature THC was increased along with pressure decease. A rod-shaped electric heater 25A positioned on an inner side tends to have a temperature higher than a temperature at a rod-shaped electric heater 25B positioned on an outer side, and in the same rod-shaped electric heater, a temperature at the canister bottom portion 1B side tended to be higher than a temperature at the canister lid portion 1T side. The canister lid portion temperature TT was decreased along with pressure decrease. On the other hand, the canister bottom portion temperature TB was increased. As for the canister side surface, a temperature was increased along with pressure decrease in a region from the canister side surface bottom surface 1SB (temperature TSB) to be a lowermost portion of the body portion of the canister 21 in the horizontally-installed attitude to a position D2-090 located at 90 degrees with respect to the lowermost portion (specifically, a horizontal plane passing through the center of the canister 21), whereas a temperature was decreased along with pressure decrease at a position D2-135 located at 135 degrees with respect to the lowermost portion and at the canister side surface top surface 1ST (temperature TST) to be an uppermost portion of the body portion of the canister 21 in the horizontally-installed attitude. Note that FIGS. 7 and 8 illustrate, from the left, three kinds of bar graphs representing values at the respective temperature measurement points at the time of decreasing the pressure to 5 atm, 3 atm, and 1 atm. FIG. 9 illustrates temporal changes in temperatures at the main temperature measurement points relative to the pressure change, in which the temperatures include the heating element center temperature THC, canister lid portion temperature TT, canister bottom portion temperature TB, canister side surface top surface temperature TST, and canister side surface bottom surface temperature TSB. When the pressure was decreased by gas leakage, heat removal efficiency by heat conduction was degraded, and the heating element center temperature THC was increased. Since a bottom portion of the heater (in other words, one end in a longitudinal axis direction of a rod-shaped electric heater 25) contacted or was close to the canister bottom portion, heat of the rod-shaped electric heater 25 was transferred to the canister bottom portion and the canister bottom portion temperature TB was largely increased. Also, as illustrated in FIG. 6, since the basket 24 also contacted a lower surface on an inner side of the canister side surface due to gravity, heat of the basket 24 was transferred to the lower surface on the inner side of the canister side surface, and the canister side surface bottom surface temperature TSB was slightly increased. On the other hand, there was a space 28 between a top portion of the heater (in other words, the other end in the longitudinal axis direction of the rod-shaped electric heater 25) and the canister lid portion, and heat was hardly transferred. Additionally, since a slight space 27 was formed between a top surface of the basket side surface and a top surface on the inner side of the canister side surface, heat of this portion was hardly transferred. Since the calorific value was constant regardless of a pressure change, it could be considered that: the canister bottom portion temperature TB and the canister side surface bottom surface temperature TSB were increased; and the canister lid portion temperature TT and the canister side surface top surface temperature TST were decreased by an amount corresponding to the increase in a heat radiation amount from these portion to the atmospheric air; and as a result, the canister lid portion temperature TT and the canister side surface top surface temperature TST were decreased. FIG. 10 illustrates temporal changes in a temperature difference ΔTBT at the time of pressure decrease, in which the temperature difference ΔTBT is obtained by subtracting the canister lid portion temperature TT from the canister bottom portion temperature TB. The temperature change between the canister bottom portion temperature TB and the canister lid portion temperature TT was greater than the temperature change on the canister side surface at the time of pressure decrease, and the temperature difference ΔTBT between the canister bottom portion temperature TB and the canister lid portion temperature TT was increased by about 11° C. relative to decrease of 4 atm. FIG. 11 illustrates temporal changes in a temperature difference ΔTSBST at the time of pressure decrease, in which the temperature difference ΔTSBST is obtained by subtracting the canister side surface top surface temperature TST from the canister side surface bottom surface temperature TSB. The temperature difference ΔTSBST was increased by about 5.5° C. relative to decrease of 4 atm. As reasons for that the temperature difference ΔTSBST was smaller than ΔTBT, it could be considered that the high-temperature heating element (specifically, rod-shaped electric heater 25 here) contacted or was close to the canister bottom portion while the basket 24 contacted the canister side surface lower portion, and also it could be considered that a decrease rate of a heat flux generated by the gas at the time of pressure decrease was smaller because: a temperature of the basket 24 was lower than that of the rod-shaped electric heater 25; and an amount of the gas enclosed in the space 27 between the top surface on the inner side of the canister side surface and the top surface of the basket side surface was smaller due to the structure in which the space 27 was narrower than the space 28 between the canister lid portion and the basket 24. However, the temperature change at the time of pressure change surrounded by the broken line, specifically, responsiveness to the pressure change of ΔTSBST was better than the responsiveness relative to the pressure change of ΔTB. As a reason for having the good responsiveness, it could be considered that a change rate of a heat flux transferred from the gas to the canister 21 was faster in the canister side surface top surface temperature TST than in the canister lid portion temperature TT due to the structure in which the space 27 between the top surface on the inner side of the canister side surface and the top surface of the basket side surface was narrower than the space 28 between the canister lid portion and the basket top portion. FIG. 12 illustrates temporal changes in the temperature difference ΔTBST at the time of pressure decrease, in which the temperature difference ΔTBST is obtained by subtracting the canister side surface top surface temperature TST from the canister bottom portion temperature TB. Responsiveness to the pressure change was kept excellent. Meanwhile, since the canister bottom portion temperature TB having a large temperature increase rate at the time of pressure decrease was adopted, the temperature difference ΔTBST was larger than TSBST and a change amount was about 10° C. before and after pressure decrease. FIG. 13 illustrates temporal changes in a temperature difference ΔTSBT at the time of pressure decrease, in which the temperature difference ΔTSBT is obtained by subtracting the canister lid portion temperature TT from the canister side surface bottom surface temperature TSB. A change amount before and after the pressure decrease was about 8° C. FIG. 14 illustrates temporal changes in the sum ΔT4 of the temperature differences at the time of pressure decrease, and the sum ΔT4 is obtained by adding ΔTBT and ΔTSBST and uses, as the temperature monitoring parts, all of the parts of: the canister bottom portion temperature TB and the canister side surface bottom surface temperature TSB both having the surface temperatures increased at the time of pressure decrease; and the canister lid portion temperature TT and the canister side surface top surface temperature TST both having the surface temperatures decreased at the time of pressure decrease. A change amount before and after the pressure decrease was about 16.5° C. FIG. 15 illustrates temporal changes of the sum ΔT3R of the temperature differences at the time of pressure decrease, and the sum ΔT3R is obtained by adding ΔTSBST and ΔTBST both having good responsiveness to the pressure change and uses, as the temperature monitoring parts, the three parts of: the canister bottom portion temperature TB and the canister side surface bottom surface temperature TSB both having the surface temperatures increased at the time of pressure decrease; and the canister side surface top surface temperature TST having the surface temperature decreased at the time of pressure decrease. In this case, a change amount before and after the pressure decrease is more increased to about 15° C. while keeping good responsiveness to the pressure change. Additionally, FIG. 16 illustrates temporal changes of the sum ΔT3GR of the temperature differences at the time of pressure decrease, and the sum ΔT3GR is obtained by adding ΔTBT and ΔTBST both having large temperature differences relative to the pressure change and uses, as the temperature monitoring parts, three parts of: the canister bottom portion temperature TB having the surface temperature increased at the time of pressure decrease; and the canister lid portion temperature TT and the canister side surface top surface temperature TST both having the surface temperatures decreased at the time of pressure decrease. A change amount before and after the pressure decrease was about 21° C. <Test Results of Case 2> FIG. 17 is a graph illustrating temperatures at the respective temperature measurement points of the canister 21 at the time of changing the pressure under a test condition in which a calorific value of a heating element (here specifically, the rod-shaped electric heater 25) is reduced to about 30%, compared to Case 1. Note that respective test data was corrected to a value at the external air temperature of 25° C. A tendency of the temperature change was substantially same as the tendency in Case 1, but the temperatures were generally low because the caloric value was small. Additionally, the canister lid portion temperature TT was decreased in proportion to the pressure at the time of pressure decrease while the canister bottom portion temperature TB had a small temperature change at the time of decrease from 5 atm to 3 atm. Furthermore, no temperature change in proportion to the pressure change was observed in the canister side surface bottom surface temperature TSB and the canister side surface top surface temperature TST at the time of pressure decrease. FIG. 18 illustrates temporal changes of temperatures at the main temperature measurement points relative to the pressure change. Additionally, FIG. 19 illustrates temporal changes of the temperature difference ΔTBT relative to the pressure change, and a change amount before and after the pressure decrease was about 3.5° C. FIG. 20 illustrates temporal changes of the temperature difference ΔTSBST relative to the pressure change, and a change amount before and after the pressure decrease was about 1.5° C. From the above test results, it was found that even when a calorific value was decreased along with decrease in decay heat of spent fuel, a change in temperature difference indicating gas leakage could be detected. (4) Conclusion From the above test results, it is clarified that a factor that causes, in the horizontally-installed canister, the temperature changes different from temperature changes of a vertically-installed canister was a peculiar phenomenon caused by the internal structure of the canister. Specifically, the lattice-like partitions called the basket (in other words, honeycomb structure) are housed inside the canister, and the spent fuel that is the radioactive material is stored in each of the cells. Additionally, the space between the basket (reference sign 24 in Example) and the canister (21) is extremely narrow, and even when the basket (24) contacts, due to gravity, the inner peripheral surface of the canister side surface bottom portion to be the lower portion of the canister body portion by horizontally installing the canister (21), the space (27) formed between the basket (24) and the inner peripheral surface of the canister side surface upper portion to be the upper portion of the body portion of the canister (21) is extremely narrow such as about 4 mm relative to the actual machine having the length of, for example, about 2.5 m. Furthermore, since the spent fuel is suspended and charged from the top into the canister that is made to stand inside a reactor pool, the spent fuel contacts or is close to the canister bottom portion even though the canister is horizontally installed. Also, since a gas around the spent fuel is surrounded by the basket (24) and can be moved only in the horizontal direction, heat is moved only in the lateral direction. Due to this, as illustrated in FIG. 5A, the hot gas around the spent fuel is moved mainly in the lateral direction along the basket 24 at the time of high pressure before gas leakage. Therefore, heat having large heat capacity is accumulated in a space on the canister lid portion 1T side, and the heat is released from the space via the canister lid portion 1T, and therefore, the temperature of the canister lid portion 1T is increased. On the other hand, since the spent fuel contacts or is close to the canister bottom portion 1B side, and the heat of the spent fuel is largely transferred by heat conduction. Additionally, the hot gas is also accumulated in the space between the inner peripheral surface upper portion of the body portion and the basket 24 of the horizontally-installed canister although the accumulation amount is not much. Due to such hot gas accumulation, the temperature in this space is also increased. Furthermore, the basket 24 contacts, due to gravity, the inner peripheral surface lower portion of the canister on the canister side surface lower portion 1SB side to be the inner peripheral surface lower portion of the body portion of the horizontally-installed canister. Therefore, the heat of the spent fuel is transferred to the canister by heat conduction via the basket 24. However, when the internal pressure of the canister is decreased by gas leakage, natural convection of the gas contributing to heat removal of the spent fuel is reduced as illustrated in FIG. 5B. Therefore, cooling-effect is decreased, and as a result the temperature of the spent fuel is increased. This temperature increase of the spent fuel is largely transferred by heat conduction to the canister bottom portion 1B side that contacts the spent fuel, and the temperature of the canister bottom portion 1B is increased. On the other hand, an amount of hot gas accumulated in the space on the canister lid portion 1T side is reduced due to decrease of natural convection of the gas, and a heat flux on the canister lid portion 1T side is reduced, and then the temperature of the canister lid portion 1T is decreased. Additionally, since the space between the side surface upper portion 1ST and the basket 24 of the horizontally-installed canister is narrow and slight, the hot gas is accumulated little inherently. Therefore, an amount of temperature decrease caused by decrease in the amount of the hot gas due to the decrease in natural convection is also little. Furthermore, since the heat of the spent fuel having the increased temperature is transferred to the canister by heat conduction via the basket 24, the temperature is increased at the canister side surface lower portion 1SB. However, this change is smaller than the temperature increase at the canister bottom portion 1B that contacts the spent fuel. From the above facts, it is found that temperatures are changed in the horizontally-installed canister at the time of gas leakage in the four parts (specifically, all of surfaces/parts of the canister) including the canister bottom portion, canister lid portion, canister side surface lower portion, and canister side surface upper portion. Additionally, the four parts are separated into: two parts where surface temperatures are decreased; and the two parts where surface temperatures are increased. Also, temperature increase parts are separated into a part having large temperature increase and a part having little temperature increase, and temperature decrease parts are separated into a part having large temperature decrease and a part having little temperature decrease. Therefore, there is a change caused by gas leakage in any temperature difference between any parts. |
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