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claims | 1. A radiation attenuating device, comprising:at least two directly communicating adjacent chambers;at least one communication channel connecting the chambers;at least one fluid, wherein one of the at least one fluid is a radiation attenuating fluid moveable between the chambers; anda control circuit configured to oscillate the radiation attenuating fluid between the chambers. 2. The radiation attenuating device according to claim 1, wherein a height of the radiation attenuating fluid in each chamber is varied by moving a portion of the fluid from one chamber to another chamber through the communicating channel. 3. The radiation attenuating device according to claim 1, wherein an amount of time the radiation attenuating fluid resides in any one chamber is smaller than an exposure time to radiation incident to the chamber. 4. The radiation attenuating device according to claim 1, wherein the radiation attenuating fluid is one of liquid metal or a high density powder dispersed in a non-settling colloidal suspension. 5. The radiation attenuating device according to claim 1, wherein each chamber comprises a shape such that an occupying fluid is in a reduced potential energy state. 6. The radiation attenuating device according to claim 1, wherein the at least one communication channel between the adjacent chambers comprises at least one potential energy barrier for at least one of the fluids. 7. The radiation attenuating device according to claim 1, further comprising:at least one operational state wherein a volume of the radiation attenuating fluid at least fills the volume of one of the adjacent chambers. 8. The radiation attenuating device according to claim 1, further comprising:a radiation transparent fluid directly moveable between the adjacent chambers such that movement of one of the fluids displaces the other fluid; andwherein a total volume of the chambers is filled by the radiation attenuating fluid and the radiation transparent fluid. 9. The radiation attenuating device according to claim 8, wherein the at least one communication channel includes a first channel configured to transport one of the fluids from a first chamber directly to a second chamber, and a second channel configured to transport the other fluid from the second chamber directly to the first chamber. 10. The radiation attenuating device according to claim 8, wherein the radiation attenuating fluid comprises a property of high surface tension and acts as a single deformable object. 11. The radiation attenuating device according to claim 8, further comprising a control circuit that includes at least three electrodes essentially transparent to radiation, the electrodes configured to have a voltage potential applied across at least two of the electrodes. 12. The radiation attenuating device of claim 11 wherein the control circuit controlling each chamber further comprises a dielectric material layer placed between one of the electrodes and the chamber, the dielectric material being of high electric permittivity and essentially transparent to radiation. 13. The radiation attenuating device of claim 11 wherein at least one of the electrodes overlaps a boundary between the two fluids when the fluids are at rest. 14. The radiation attenuating device of claim 12 wherein the dielectric material layer comprises a barium titanate compound. 15. The radiation attenuating device according to claim 1, wherein one of the fluids has different electric properties than the other fluid. 16. The radiation attenuating device according to claim 15, wherein the different electrical properties are one of a group of properties comprising electric permittivity and electric conductivity. 17. The radiation attenuating device of claim 1, wherein a plurality of the radiation attenuating devices are abutted together, forming a two-dimensional x-y array of individually controlled radiation attenuating devices. 18. The radiation attenuating device of claim 1, wherein a radiation shield is formed of multiple two-dimensional arrays of radiation attenuating devices stacked in a z-axis to form a three-dimensional matrix, wherein a stack of radiation attenuating devices in the z-axis are aligned in a substantially overlapping mode and are configured to impede the progress of incident radiation in a cumulative manner. 19. A radiation imaging system configured to dynamically modulate an amount of radiation incident to a target to be radiated, comprising:a radiation source;a radiation shield further comprising a plurality of radiation attenuating devices, each radiation attenuating device comprising:a dynamically configurable radiation attenuating property;at least two directly communicating adjacent chambers;at least one communication channel directly connecting the adjacent chambers;a radiation attenuating fluid directly moveable between the adjacent chambers; anda control unit configured to generate at least one control signal to each radiation attenuating device, the control signal operable to oscillate the radiation attenuating fluid between the directly communicating adjacent chambers. 20. A radiation imaging system, according to claim 19, further comprising:a radiation detection array in electrical communication with the control unit and configured to generate an output signal received by the control unit;wherein the control unit is configured to dynamically modulate the radiation attenuating property of each radiation attenuating device based upon the received output signal generated by the radiation detection array. 21. A method of attenuating radiation incident to a radiation attenuating element, the method comprising:oscillating at least one fluid between at least two directly communicating adjacent chambers, the at least one fluid having a radiation attenuating property. 22. The method of claim 21, wherein oscillating at least one fluid comprises:exchanging a radiation transmitting fluid in one of the two directly communicating adjacent chambers with a radiation attenuating fluid in the second chamber in a time shorter than a radiation exposure time. 23. The method of claim 21, wherein oscillating the at least one fluid comprises generating a force based on at least one of electric, magnetic, electro-phoretic, dielectric-phoretic, electro-wetting, and magnetic-hydro-dynamic principles. 24. The method of claim 21, further comprising:stacking a plurality of the radiation attenuating elements in a z-axis;oscillating the at least one fluid between the directly communicating adjacent chambers of a radiation attenuating element in a predetermined number of stacked radiation attenuating elements whereby a total amount of radiation that is blocked is based upon a total amount of fluid incident to radiation at any one time. |
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abstract | Apparatuses (devices, systems) and methods for shielding (protecting) surroundings around periphery of regions of interest located inside objects (e.g., patients) from radiation emitted by X-ray systems towards the objects. Apparatus includes: at least one radiation shield assembly including a support base connectable to an X-ray system radiation source or detector, and a plurality of radiation shield segments sequentially positioned relative to the support base, thereby forming a contiguous radiopaque screen configured for spanning around the region of interest periphery with a radiopaque screen edge opposing the object. Radiation shield segments are individually, actively controllable to extend or contract to selected lengths with respective free ends in directions away from or towards the support base(s), for locally changing contour of the radiopaque screen edge. Applicable for shielding (protecting) medical personnel, and patients, from exposure to X-ray radiation during medical interventions or/and diagnostics. |
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042499941 | summary | This invention relates to a method for unclogging an electromagnetic filter and to an installation for carrying out said method. It is known that an electromagnetic filter is essentially constituted by a casing of non-magnetic material filled with a magnetizable packing and placed within the interior of a winding. The passage of an electric current in the winding results in the appearance of a magnetic field which has the effect of magnetizing the packing. The packing can be fixed in the form of padding, of woven steel-wire fabric or of a stack of grids. In the majority of instances, however, the packing is formed by a bed of steel beads. The application of a magnetic field to the packing beads results in magnetization of these latter and correlatively in the appearance of high magnetic-field gradients in the spaces between beads. When a fluid charged with ferromagnetic impurities passes through the bed of beads which have thus been magnetized, the impurities are transferred from the zones of low magnetic field to the zones of high magnetic field, that is to say towards the magnetic poles of the beads. The action of the magnetic forces is such that the ferromagnetic impurities adhere to the beads and the packing thus performs the function of a filter. The use of electromagnetic filters of this type has already been contemplated for a large number of installations and especially nuclear reactors in which they can be installed either in the primary circuits or in the secondary circuits. This use in nuclear reactors is described in particular in French Pat. No. 72 25870 filed on July 18, 1972 and entitled "Water treatment installation for steam generators in nuclear power plants of the pressurized-water reactor type " and in French Pat. No. 72 45355 filed on Dec. 20, 1972 and entitled "Water purification device for a nuclear power plant of the pressurized-water reactor type." In order to unclog a filter of this type, the operation is performed as follows. The first step consists in isolating the filter from the installation in which it is inserted. This operation is performed by closing valves. The packing is then demagnetized by applying a low-frequency alternating-current voltage to the terminals of the winding, the amplitude of said voltage being such as to decrease progressively to zero. Finally, a stream of liquid derived from a wash duct which is independent of the water circulation systems of the nuclear reactor is passed into the filter in order to wash the latter. This upwardly flowing liquid stream dislocates the bed of beads which accordingly undergo disordered motion during which they come into collision with each other many times. This has the effect of detaching the clogging products which are carried away by the wash liquid. On completion of this operation, the beads fall back into position at the bottom of the filter and reconstitute the bed, simply under the action of gravity. The bed of beads is then remagnetized and the filter is ready to be used again. This unclogging operation lasts a few minutes approximately. In known methods of this type, the wash water is not withdrawn from the primary (or secondary) circuit of the nuclear reactor and, in general, is therefore neither at the temperature nor at the pressure of the water which circulates within said circuit. Moreover, the unclogging operation takes place by means of a stream of water which has essentially a continuous character and is circulated upwards within the filter. Methods of the type described are subject to a large number of disadvantages. The first disadvantage arises from the fact that they call for a very large quantity of wash water which, in the case of each regeneration, is of the order of 1% of the hourly quantity of water treated by the filter. By way of explanation in the case of a filter which is capable of treating 1000 metric tons of water per hour, 15 metric tons of water are required in order to effect unclogging of the filter by means of a method of the prior art. It is therefore impossible by means of this method to withdraw such a large quantity of water from the nuclear reactor circuit over a short period of time. For this reason, it is necessary to have recourse to an auxiliary source connected to the filter by means of a wash water supply duct. This need to make use of a large quantity of water further leads to two difficulties: in the event that the filter is placed in the primary circuit of a nuclear reactor, the effluents discharged from the filter are radioactive and represent a large quantity of water to be treated, thus constituting an appreciable capital investment in the exploitation of the reactor. In the event that the filter is placed in the secondary circuit of a nuclear reactor, the water employed in this filter is usually conditioned and especially de-aerated and the need to employ a large volume of water is again objectionable in this case. The second disadvantage arises from the temperature difference observed in methods of the prior art between the filtering stage and the unclogging stage. The wash water is usually at a lower temperature than that of the water circulated within the nuclear reactor circuit. Unclogging therefore calls for a reduction in temperature at the beginning of the cycle followed by an increase in temperature at the end of the cycle; the length of the unclogging operation is increased accordingly. As a secondary consideration, it can be observed that the steels constituting the beads which form the filter bed are usually liable as a result of chemical corrosion to form products of corrosion in a different form and especially in a less magnetizable form. In consequence, it is also an advantage from this point of view to carry out washing of the filter at a temperature which is as high as possible. The present invention overcomes the foregoing disadvantages in that it proposes a method of unclogging which calls for the use of a much smaller quantity of wash water than the quantity employed in methods of the prior art. This permits withdrawal of said water from the nuclear reactor circuit and therefore the introduction of the water into the filter substantially at the temperature and pressure of withdrawal since the unclogging operation takes place in a series of washing and draining-off cycles and not by means of a continuous flow of wash water as in the prior art. By way of explanation, when the method in accordance with the invention is employed in the case of a filter which is capable of treating 1000 metric tons of water per hour it is possible to unclog the filter with only 3 to 4 tons of water instead of the 15 tons which were required by the methods of the prior art. This small quantity of water can accordingly be withdrawn from the water circuit of the nuclear reactor (namely either the primary or secondary circuit); in consequence, the filter receives water to be filtered and wash water which are substantially at the same temperature and at the same pressure. In the wash cycles which take place in accordance with the method of the invention, the bed of beads undergoes successive displacements of small amplitude with a sufficiently high degree of efficacy to dispense with any need to cause complete dislocation of the bed of beads within a relatively large free internal space provided at the bottom of the filter. It is therefore always possible to employ a filter which is packed to practically the full height of this latter, as was not the case with methods of washing in the prior art. So far as the installation is concerned, the invention finally provides further advantages which are related in particular to elimination of the wash duct and of the auxiliary source of wash water. This modification of the technology of the installation results in a reduction of capital cost of this latter. In more exact terms, the present invention is therefore directed to a method for unclogging an electromagnetic filter having a magnetizable packing and placed in a water circuit of a nuclear reactor. The method essentially consists first in isolating the filter from the circuit, then in subjecting the filter to a series of washing and draining-off cycles. The washing operation consists in withdrawing from said circuit a fraction of the water which is circulated therein and in introducing said water into the filter substantially at the temperature and pressure of withdrawal and under such conditions as to impart turbulent flow motion to said water within the packing. The draining-off operation consists in discharging the wash water contained in the filter. It is preferably ensured that, when the filter is placed in the primary circuit of a nuclear reactor of the pressurized-water type, unclogging takes place at a temperature within the range of 200.degree. C. to 300.degree. C. It is also preferably ensured that the pressure of the water employed for the unclogging operation is within the range of 100 to 160 bar. When the filter is placed in the primary circuit of a pressurized-water reactor comprising a pressurizer, withdrawal of the wash water is preferably carried out within said pressurizer. The invention is also concerned with an installation for the practical application of the method hereinabove defined and for unclogging an electromagnetic filter of the magnetized-packing type, said filter being placed in the water circuit of a nuclear reactor. The installation essentially comprises means for isolating said filter from the circuit, means whereby part of the water which circulates in said circuit is withdrawn therefrom, means for introducing the water into the filter substantially at the temperature and pressure of withdrawal under conditions which impart turbulent flow motion to said water within the packing, and means for discharging the wash water contained in the filter. In a first alternative embodiment, the installation comprises a closed wash circuit constituted by an accelerating pump connected at the upstream end by means of a pipe fitted with a valve to the top portion of the filter and at the downstream end by means of a pipe fitted with a valve to the bottom portion of said filter, said circuit being connected at the top portion thereof to the water circuit of the nuclear reactor by means of an introduction valve end and at the bottom portion thereof to an effluent tank by means of a drain-off valve. In a second alternative embodiment, the installation comprises a water admission duct which connects the bottom portion of the filter to the water circuit of the nuclear reactor by means of a water introduction valve and a drain-off pipe which is connected to the bottom portion of the filter and is fitted with a drain-off valve. When the filter is placed in the primary circuit of a nuclear reactor of the pressurized-water type comprising a pressurizer, the installation comprises a pipe connected to said pressurizer and a valve placed in said pipe. When the filter is placed in the secondary circuit of a pressurized-water reactor, said circuit being equipped with at least one high-pressure heater followed by a steam generator, the filter is accordingly placed between said high-pressure heater and said steam generator. It is preferably ensured that the magnetizable packing is constituted by a bed of beads. |
050200836 | claims | 1. An arrangement comprising: a membrane of an X-ray transparent material having a first thickness; a structurally rigid support for holding said membrane at a portion of said membrane; said X-ray transparent material having a plurality of gaps extending at least partially through said membrane; an X-ray opaque material included within said gaps and forming a structure with said X-ray transparent material; said X-ray opaque material filling each of said gaps substantially entirely and extending out of said membrane. said X-ray opaque material is a metal silicide. said X-ray opaque material is a metal. said gaps filled with X-ray opaque material extend only partially through said X-ray transparent material. said gaps filled with X-ray opaque material extend only partially through said X-ray transparent material. said gaps filled with X-ray opaque material extend only partially through said X-ray transparent material. 2. An arrangement as in claim 1, wherein: 3. An arrangement as in claim 1, wherein: 4. An arrangement as in claim 1, wherein: 5. An arrangement as in claim 2, wherein: 6. An arrangement as in claim 3, wherein: |
description | This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-247206, filed Sep. 25, 2007, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to an X-ray diagnostic apparatus, and particularly relates to setting of a radiation field of X-rays. 2. Description of the Related Art Traditional X-ray diagnostic apparatus generally comprises a tabletop, an X-ray tube, and an X-ray detector. The tabletop is put a subject, the X-ray tube irradiates X-rays, and the X-ray detector detects X-rays that permeate the subject. The X-ray tube and X-ray detector are arranged on both sides of the tabletop. X-ray detecting elements are arranged to the detection range of the X-ray detector that detects X-rays. A retention feature maintains the X-ray tube. The X-ray tube is composed movable along longer direction of the tabletop (direction of body axis of a subject) through the retention feature. The X-ray detector moves with the X-ray tube in a unified manner. The tabletop is composed movable along shorter direction of own. A controller moves the tabletop, the retention feature, and the X-ray detector respectively according to the above-mentioned composition, and the center of the detection range of the X-ray detector can be matched to a test object of subject on the tabletop. Four diaphragm blade units are located between the X-ray tube and the tabletop. A pair of diaphragm blade unit in the longer direction moves antithetically in the longer direction of the tabletop as a center of the detection range of the X-ray detector. A pair of diaphragm blade unit in the shorter direction moves antithetically in the shorter direction of the tabletop as a center of the detection range of the X-ray detector. Each a pair of diaphragm blade unit narrows the detection range of the X-ray detector from the longer direction of the tabletop and the shorter direction of the tabletop, and forms the exposure field on the X-ray detector. The diaphragm blade unit narrows the detection range of the X-ray detector, cuts unnecessary X-rays, prevents unnecessary radiation exposure, and improves the image quality of the radiographic view. In the diagnostic radiography, first, an operator matches the center of the detection range of the X-ray detector to the test object of Subject. Concretely, the X-ray tube and the X-ray detector move to the longer direction of the tabletop, and the tabletop moves to the shorter direction of own. Next, the operator confirms the area in the detection range of the X-ray detector to the inspection object of the subject. When the detection range of the X-ray detector is wide compared with the inspection object of the subject, it is necessary to narrow the detection range of the X-ray detector. Then, the diaphragm blade unit narrows the detection range of the X-ray detector and forms the exposure field on the X-ray detector. Next, the X-ray tube irradiates X-rays to the subject, the X-ray detector detects X-rays that passed the subject, the radiographic view is made and is displays it in the monitor. When the test object of the subject is changed, the controller moves the tabletop, the retention feature, and the X-ray detector respectively to match the center of the detection range of the X-ray detector to the test object after it changes. However, when the retention feature is moved, the center of the detection range of the X-ray detector might not be able to be matched to the test object of the subject, because the retention feature have a constant movement stroke's and evades interference with the tabletop etc. the retention feature, and the movement of the retention feature is limited. The retention feature is not stopped easily at a prescribed position, and there is a problem that easily matching the center of the detection range of the X-ray detector to the test object after it changes becomes difficult because the inertia of the retention feature is large. There is a problem of becoming a large encumbrance for the subject when the endoscope is inserted in the inside of the body of subject on the tabletop when the tabletop is moved. When the test object of the subject is changed within the detection range of the X-ray detector, it only has to operate each a pair of diaphragm blade unit and to expand the exposure field. The test object of the subject can be fit in the broadening exposure field. As a result, the retention feature need not move. However, the retention field expands and outside of test object is unnecessarily exposed to radiation. To correspond to the change of test object of the subject without expanding exposure field, the controller open and shut each a pair of diaphragm blade unit individually, to move exposure field within the detection range of the X-ray detector, and to match the center of exposure field to the test object of the subject. However, a past device has the problem that the operation of the diaphragm blade unit becomes complex, because it needs the opening and closing operation of each diaphragm blade unit to do the opening and closing movement individually as for each diaphragm blade unit. As for a past technology, the X-ray tube and the X-ray detector are composed as one body and rotatably. When it changes the test object of the subject, the X-ray tube and the diaphragm blade unit are rotated as one body, and moves the center of the exposure field to the test object after it changes. As for a past technology, it has an edge detector of the edge of the X-ray detector and rotates as one body the X-ray tube and diaphragm blade unit, and moves the center of the exposure field. When the edge of the exposure field of X rays hangs to the edge detector, one side of a pair of diaphragm blade unit is individually moved from the edge to the center, and the controller limits it so that an X-ray beam doesn't exceed the detection range of the X-ray detector. However, the above-mentioned technology needs the mechanism that composes the X-ray tube and diaphragm blade unit as one body and rotatably. It needs the other mechanism to drive the mechanism. Accordingly, an advantage of an aspect of the present invention is to provide the X-ray diagnostic apparatus that the center of the exposure field can be easily matched to the inspection object of subject and unnecessary exposure of test object of subject can be suppressed. In order to achieve the above-described advantage, a first aspect of the invention may comprise a tabletop configured to put on a subject; a X-ray tube configured to irradiates X-rays; a X-ray detector configured to detect X-rays that penetrate subject and to arrange on the other side of the X-ray tube; a pair of diaphragm blade unit of a longer direction and a pair of diaphragm blade unit of a shorter direction configured to form a exposure field on X-ray detector and arrange between the tabletop and the X-ray tube; a beam-limiting drive unit configured to drive the each diaphragm blade unit individually; a beam-limiting control unit configured to receive a information of a moving amount and a moving direction when a center of the exposure field moves and to control the beam-limiting drive unit and to move the each diaphragm blade unit individually and to form the exposure field of the moving center is concentric. In order to achieve the above-described advantage, a sixth aspect of the invention may comprise a tabletop configured to put on a subject; a X-ray tube configured to irradiates X-rays; a X-ray detector configured to detect X-rays that penetrate subject and to arrange on the other side of the X-ray tube; a pair of diaphragm blade unit of a longer direction and a pair of diaphragm blade unit of a shorter direction configured to form a exposure field on X-ray detector and arrange between the tabletop and the X-ray tube; a beam-limiting drive unit configured to drive the each diaphragm blade unit individually; a imaging system drive unit comprised to drive the tabletop, the X-ray tube, and X-ray detector respectively so that the detection range of X-ray detector is relative movement in the longer direction and the shorter direction of the tabletop; an aperture information holding unit comprised to hold aperture information of the longer direction provided beforehand and aperture information of the shorter direction provided beforehand; a center transfer operation unit comprised to indicate the moving direction of the center of exposure field; a judgment unit comprised to judge whether part or all in the exposure field exceed the detection range of X-ray detector or part or all the exposure field enter a operation switching area formed the edge of detection range based on a moving amount and a moving direction information of center of the exposure field and an aperture information held on the aperture information holding unit. Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. A first embodiment in accordance with the present invention will be explained with reference to FIGS. 1 to 11. FIG. 1 is an oblique perspective figure of an X-ray diagnostic apparatus according to a first embodiment. As shown in FIG. 1, a X-ray diagnostic apparatus 1 is composed tabletop 2 that puts a subject, a X-ray tube 3 that irradiates X-rays, a X-ray detector 4 that detects X-rays that passed the subject, and a beam-limiting device 5 that forms the exposure field of X-rays to X-ray detector 4. X-ray tube 3 and X-ray detector 4 are put on both sides of tabletop2. Tabletop 2 is composed movable in a shorter direction of tabletop 2 (X-way in FIG. 1). The shorter direction of tabletop 2 is an orthogonal direction in the direction of body axis of a subject. The longer direction of tabletop2 (Z-way in FIG. 1) is equal to the direction of the direction of body axis of a subject. X-ray tube 3 is maintained in a retention feature 11. Retention feature 11 has a brace 12 that run on a rail and a lateral-arm 13 that move up and down along brace 12. X-ray tube 3 is fit in an apical end of lateral-arm 13. Beam-limiting device 5 is maintained in lateral-arm 13. X-ray tube 3 and beam-limiting device 5 are composed movable through retention feature 11 along the longer direction of tabletop 2 (Z-way in FIG. 1). X-ray detector 4 is composed movable with X-ray tube 3 and beam-limiting device 5 as one body. By the above-mentioned composition, X-ray tube 3, X-ray detector 4, and beam-limiting device 5 are composed that a relative movement is possible to tabletop 2 in the longer direction and the shorter direction. When the operator changes the test object of the subject on tabletop 2, and the changed test object comes off from the detection range of X-ray detector 4, the controller moves X-ray tube 3, X-ray detector 4, and beam-limiting device to tabletop 2 respectively and the center of the detection range of X-ray detector 4 is matched to the changed test object. According to the first embodiment, when the changed test object is in the detection range of X-ray detector 4, the controller operates beam-limiting device 5, and moves the center of the exposure field, and matches the center of the exposure field to the changed test object. In this case, the controller moves X-ray tube 3, X-ray detector 4, and beam-limiting device to tabletop 2 respectively and the center of the detection range of X-ray detector 4 is matched to the changed test object. FIG. 2A is a circuit diagram of an X-ray detector, FIG. 2B is a circuit diagram of an X-ray detecting element. X-ray detector 4 is classified into a direct conversion formula and an indirect conversion formula by a X-ray detection formula. The direct conversion formula is a method to use the material that converts the x-ray energy into the charge as a X-ray detecting coat. The indirect conversion formula is a method to convert X-rays into light once, and to convert the light into the charge-signal by the light-receiving element such as photodiodes. The X-ray detection formula of X-ray detector 4 is the indirect conversion formula. As shown in FIG. 2A, multi line and row X-ray detecting elements are distributed to the detection range of X-ray detector 4 that detects X-rays. The X-ray has the element 41 that detecting elements convert X-rays into optical-wavelength, and forms the charge corresponding to quantities of light of optical-wavelength. As shown in FIG. 2B, each elements 41 is composed a photodiode 42 that picks up the optical-wavelength and forms the charge corresponding to incident light volume, and a capacitor 43 accumulates the charge formed from photodiode 42. The charge accumulated in the capacitor 43 is read out as imaging signal in each element sequentially from topmost scan line 44-1 to topmost signal line 45-1 through a scan line 44. An image signal is converted into a X-ray image-data where image-data lined up in an element alignment coordinate system in read order. X-ray image-data is maintained in a fluorography image memory 94, and displayed in a monitor 95. Fluorography image memory 94 and monitor 95 are described later. Beam-limiting device 5 is explained in reference to FIGS. 1 and 3. FIGS. 3A to 3E are a figure for explaining X-ray tube 3, X-ray detector 4, and beam-limiting device 5. As shown in FIGS. 3A to 3E, beam-limiting device 5 is equipped between tabletop 2 and X-ray tube 3. Beam-limiting device 5 has an above and below pair of diaphragm blade unit 51 and a right and left pair of diaphragm blade unit 51. FIG. 3A is a figure of a diaphragm blade unit 51 etc. were seen from Z-way (the longer direction of tabletop 2). As shown in FIG. 3A, a right and left pair of diaphragm blade unit 51 narrows the detection range of X-ray detector 4 from the shorter direction of tabletop 2 (X-way), and forms the exposure field on X-ray detector 4. When the center of the exposure field is moved in the X-way, right and left pair of diaphragm blade unit 51 moves the prescribed-times of the moving amount to X-way. FIG. 3B is figure for explaining the mode that moved center of exposure field in the X-way. A right and left pair of diaphragm blade unit 51 corresponds to a pair of diaphragm blade unit 51 in the shorter direction. FIG. 3C is a figure of a diaphragm blade unit etc. were seen from X-way. As shown in FIG. 3C, an above and below pair of diaphragm blade unit 51 narrows the detection range of X-ray detector 4 from the longer direction of tabletop 2 (Z-way), and forms the exposure field on X-ray detector 4. When the center of the exposure field is moved in the Z-way, above and below pair of diaphragm blade unit 51 moves the prescribed-times of the moving amount to Z-way. FIG. 3D is figure for explaining the mode that moved center of exposure field in the Z-way. An above and below pair of diaphragm blade unit 51 corresponds to a pair of diaphragm blade unit 51 in the longer direction. For example, a distance from a focus of X-ray tube 3 to diaphragm blade unit 51 is assumed to be H1, and a distance from a focus of X-ray tube 3 to X-ray detector 4 is assumed to be H2. The amount of the movement to the X-way or the Z-way of each diaphragm blade unit 51 is (H1/H2) times the amount of the movement at the center of the exposure field. Detail of Beam-limiting device 5 is explained in reference to FIG. 4. FIG. 4 is an exploded perspective view of a beam-limiting device. As shown in FIG. 5, beam-limiting device 5 are arranged a pair of diaphragm blade unit 51 in the Z-way (the longer direction) and a pair of diaphragm blade unit 51 in the X-way (the shorter direction) on a base component 511. The combination of a stepping motor 512, a back-diaphragm blade 515, a lower-diaphragm blade 516, and a block 517 is arranged above each diaphragm blade unit 51 respectively. The amount of the rotation of the stepping motor 512 transmits to diaphragm blade unit 51 through a pulley 513 and the driving belt 514. The amount of the rotation of the stepping motor 512 transmits to back-diaphragm blade 515 and lower-diaphragm blade 516 through block 517. According to the above-mentioned composition, diaphragm blade unit 51, back-diaphragm blade 515, and lower-diaphragm blade 516 corresponding to stepping motor 512 move to the X-way or the Z-way by a prescribed amount according to the amount of the rotation of stepping motor 512. A rectangular exposure field is formed on X-ray detector 4 by each diaphragm blade unit 51. The medial edge in each diaphragm blade unit 51 corresponds to each edge of the exposure field. Each diaphragm blade unit 51, each back-diaphragm blade 515, each lower-diaphragm blade 516, and X-ray shield unit cover X-rays so that X-rays irradiated from X-ray tube 3 are not irradiated except the exposure field. Composition in which each diaphragm blade unit 51 is individually driven will be explained in reference to FIG. 5. FIG. 5 is a functional block diagram of the X-ray diagnostic apparatus. As shown in FIG. 5, X-ray diagnostic apparatus 1 has a beam-limiting drive unit 52 that individually drives each diaphragm blade unit 51 and a beam-limiting control unit 62 that controls beam-limiting drive unit 52. Beam-limiting drive unit 52 has an upside beam-limiting drive unit 53, an underneath beam-limiting drive unit 54, a left side beam-limiting drive unit 55, and a right side beam-limiting drive unit 56 to drive each diaphragm blade unit 51 severally. Upside beam-limiting drive unit 53 and underneath beam-limiting drive unit 54 individually drive each diaphragm blade unit 51 of upper and lower, and narrow the detection range of X-ray detector 4 from the longer direction of tabletop 2 (the Z-way). Left side beam-limiting drive unit 55 and right side beam-limiting drive unit 56 individually drive each diaphragm blade unit 51 of left side and right side, and narrow the detection range of X-ray detector 4 from the shorter direction of tabletop 2 (the X-way). Beam-limiting control unit 62 has an upside beam-limiting control unit 63, an underneath beam-limiting control unit 64, a left side beam-limiting control unit 65, and right side beam-limiting control unit 66 to control upside beam-limiting drive unit 53, underneath beam-limiting drive unit 54, left side beam-limiting drive unit 55, and right side beam-limiting drive unit 56 severally. A basic composition of upside beam-limiting drive unit 53 to right side beam-limiting drive unit 56 is the same. A basic composition of upside beam-limiting control unit 63 to right side beam-limiting control unit 66 is the same. Upside beam-limiting drive unit 53 and upside beam-limiting control unit 63 will explained on behalf of beam-limiting drive unit 52 and beam-limiting control unit 62. The explanation of underneath beam-limiting drive unit 54, left side beam-limiting drive unit 55, right side beam-limiting drive unit 56, underneath beam-limiting control unit 64, a left side beam-limiting control unit 65, and right side beam-limiting control unit 66 is omitted. Upside beam-limiting drive unit 53 has stepping motor 512 in FIG. 4. X-ray diagnostic apparatus has a diaphragm blade position detecting unit 57 that is the encoder that detects the amount of the rotation corresponding to the stepping motor. Upside beam-limiting control unit 63 calculates a pulse-member data that corresponds to the amount of the rotation of the stepping motor of upside beam-limiting drive unit 53 based on the moving amount of diaphragm blade unit 51. Upside beam-limiting control unit 63 generates a command pulse signal based on a pulse-member data, converts a generated command pulse signal into a power current, and thrown to the stepping motor. The moving amount of diaphragm blade unit 51 receives the instruction of the moving destination at the center of the exposure field and is calculated. An operator operates a center transfer operation unit 74, and the moving destination at the center of the exposure field is directed. Next, an operation panel 7 will be explained. Operation panel 7 is installed in a control booth. As shown in FIG. 5, operation panel 7 has aperture operation unit 71, center transfer operation unit 74, an imaging system operation unit 77, and a field size selector switch 78. Aperture operation unit 71 will be explained in reference to FIGS. 6A to 6D. FIG. 6A is an elevation view of an aperture operation unit. Aperture operation unit 71 has an upside-underneath aperture operation unit 72 that is switching operation a pair of diaphragm blade unit 51 in the longer direction of tabletop 2 (Z-way) and left side-right side aperture operation unit 73 that is switching operation a pair of diaphragm blade unit 51 in the shorter direction of tabletop 2 (X-way). FIGS. 6B to 6D are figures of relation between the diaphragm blade unit that opening and closing operation is done by the aperture operation unit and exposure field. FIG. 6B is figure for explaining the mode that diaphragm blade unit 51 forms the exposure field 4a on X-ray detector 4. The center of the detection range of X-ray detector 4 is at position O. The center of the exposure field 4a is at position O1. In FIG. 6B, each diaphragm blade unit 51 is shown as a unit. Each diaphragm blade unit 51 is shown expanded at prescribed-times (H2/H1 in FIG. 3) on X-ray detector 4. In FIGS. 6C and 6D as well as FIG. 6B, each diaphragm blade unit 51 is shown expanded at prescribed-times. When the exposure field 4a is a state shown in FIG. 6b, upside-underneath aperture operation unit 72 outputs an upside-underneath aperture command signal to upside beam-limiting control unit 63 and an underneath beam-limiting control unit 64. Upside beam-limiting control unit 63 and an underneath beam-limiting control unit 64 operates upside beam-limiting drive unit 53 and underneath beam-limiting drive unit 54 respectively based on the upside-underneath aperture command signal. As shown in FIG. 6C, the distance (the aperture) between above and below diaphragm blade unit 51 that is opened on the longer direction of tabletop 2 (Z-way) changes. In this case, the position of the center O1 of the exposure field 4a doesn't move. When the exposure field 4a is a state shown in FIG. 6b, left side-right side aperture operation unit 73 outputs an left side-right side aperture command signal to left side beam-limiting control unit 65 and right side beam-limiting control unit 66. Left side beam-limiting control unit 65 and right side beam-limiting control unit 66 operates left side beam-limiting drive unit 55 and right side beam-limiting drive unit 56 respectively based on the left side-right side aperture command signal. As shown in FIG. 6D, the distance (the aperture) between left side and right side diaphragm blade unit 51 that is opened on the shorter direction of tabletop 2 (X-way) changes. In this case, the position of the center O1 of the exposure field 4a doesn't move. Information of the distance (the aperture) between above and below diaphragm blade unit 51 that is opened on the longer direction of tabletop 2 (Z-way) and information of the distance (the aperture) between left side and right side diaphragm blade unit 51 that is opened on the shorter direction of tabletop 2 (X-way) are preserved in an aperture information holding unit 84. Center transfer operation unit 74 will be explained in reference to FIGS. 5, 7A and 7B. FIG. 7A is a elevation view of a center transfer operation unit. Center transfer operation unit 74 is put in operation panel 7 in the control booth. Center transfer operation unit 74 has a vertical transfer operation unit 75 and a left-right transfer operation unit 76. As shown in FIGS. 7A and 7B, the operator operates vertical transfer operation unit 75 and directs the moving destination at the center of the exposure field 4a. A manipulate signal from vertical transfer operation unit 75 is output to an operating information processing unit 8. The manipulate signal corresponds to the moving amount to the longer direction of tabletop 2 (Z-way). As shown in FIGS. 7A and 7B, the operator operates left-right transfer operation unit 76 and directs the moving destination at the center of the exposure field 4a. A manipulate signal from left-right transfer operation unit 76 is output to an operating information processing unit 8. The manipulate signal corresponds to the moving amount to the shorter direction of tabletop 2 (X-way). The operator may operate center transfer operation unit 74 on the obliquely upward and downward. In that case, the manipulate signal from center transfer operation unit 74 is output to operating information processing unit 8 separately for the moving amount to Z-way component (component of the direction of above and below) and the moving amount to X-way component (component of the direction of left and right) element. FIG. 7B is a figure for explaining the mode that a center of the exposure field moves. As shown in FIG. 7B, the center of the exposure field 4a is the position O1. Operating information processing unit 8 receives the manipulate signal from vertical transfer operation unit 75, calculates the distance Z1 of the Z-way at the center of the exposure field, and output to upside beam-limiting control unit 63 and an underneath beam-limiting control unit 64. Upside beam-limiting control unit 63 and an underneath beam-limiting control unit 64 calculate each distance and direction of motion of above and below diaphragm blade unit 51, and control upside beam-limiting drive unit 53 and underneath beam-limiting drive unit 54. Upside beam-limiting drive unit 53 and underneath beam-limiting drive unit 54 move the above and below diaphragm blade unit 51 respectively by just Z1. And, the center of the exposure field moves from position O1 to position O1′. Operating information processing unit 8 receives the manipulate signal from left-right transfer operation unit 76, calculates the distance X1 of the X-way at the center of the exposure field, and output to left side beam-limiting control unit 65 and right side beam-limiting control unit 66. Left side beam-limiting control unit 65 and right side beam-limiting control unit 66 calculate each distance and direction of motion of left and right diaphragm blade unit 51, and control left side beam-limiting drive unit 55 and right side beam-limiting drive unit 56. Left side beam-limiting drive unit 55 and right side beam-limiting drive unit 56 move the left and right diaphragm blade unit 51 respectively by just X1. And, the center of the exposure field moves from position O1′ to position O2. Next, an imaging system control unit 101, an imaging system drive unit 102, and an imaging system position detecting unit 103 will be explained. Imaging system control unit 101 generates the control signal based on the manipulate signal from imaging system operation unit 77, and output to imaging system drive unit 102. Imaging system drive unit 102 has the stepping motor that drives tabletop 2 and has the stepping motor that drives retention feature 11. When each stepping motor of imaging system drive unit 102 begins rotating in a prescribed direction, an imaging system construction moves relativity. Imaging system position detecting unit 103 detects the amount of the rotation of each stepping motor of imaging system drive unit 102, and it is output to imaging system control unit 101. Imaging system control unit 101 obtains the position of tabletop 2 and the position of X-ray detector 4 respectively from the amount of the rotation of each stepping motor. Information at the position of tabletop 2 and the position of X-ray detector 4 is preserved in an imaging system position information holding unit 83. Next, operating information processing unit 8 will be explained. Operating information processing unit 8 has a moving amount compute unit 81 that obtains the moving amount and moving direction of center of exposure field 4a, a center position information holding unit 82 that maintains the position information of center of exposure field 4a, imaging system position information holding unit 83, and an aperture information holding unit. When center transfer operation unit 74 prescribes the moving destination at the center of the exposure field 4a, moving amount compute unit 81 calculates the moving amount and moving direction of center of exposure field 4a from location information before moving of center of exposure field and location information in moving destination at center of exposure field. The location information in the moving destination at the center of the exposure field 4a is preserved in center position information holding unit 82. Imaging system position information holding unit 83 maintains the location information of tabletop 2 and the location information of X-ray detector 4 that operating information processing unit 8 acquired from imaging system control unit 101. Operating information processing unit 8 obtains the position O of the center of the detection range of X-ray detector 4 from the location information of tabletop 2 and the location information of X-ray detector 4. Operating information processing unit 8 obtains the edge in the detection range of X-ray detector 4 from the size of the detection range of X-ray detector 4. The edge in the detection range of X-ray detector 4 is the edge in the detection range in the X-way and Z-way. The vicinity of edge of X-way of X-ray detector 4 shows X2 and X3 in FIG. 7B. The vicinity of edge of Z-way of X-ray detector 4 shows Z2 and Z3 in FIG. 7B. Operating information processing unit 8 obtains the edge of exposure field 4a from location information in moving destination at center of exposure field 4a, information of the distance (the aperture) between left side and right side diaphragm blade unit 51 that is opened on the shorter direction of tabletop 2 (X-way), and information of the distance (the aperture) between above and below diaphragm blade unit 51 that is opened on the longer direction of tabletop 2 (Z-way). When operating information processing unit 8 receives the instruction of the moving destination at the center of the exposure field from center transfer operation unit 74, operating information processing unit 8 make judgments whether part or all in the exposure field 4a exceed the detection range of X-ray detector 4. When part or all in the exposure field 4a exceed the detection range of X-ray detector 4, operating information processing unit 8 corrects the moving amount calculated by moving amount compute unit 81 and operating information processing unit 8 outputs the moving amount after correction to beam-limiting control unit 62. Beam-limiting control unit 62 controls beam-limiting drive unit 52 based on the moving amount after correction, and is moves diaphragm blade unit 51. The edge in the exposure field 4a coincides with the edge in the detection range of X-ray detector 4 and the exposure field 4a is set in the detection range of X-ray detector 4. As a result, an unnecessary irradiation outside the detection range of X-ray detector 4 is limited. Next, composition of a display control unit 91 will be explained in reference to FIG. 5. As shown in FIG. 5, X-ray image-data that be converted the image signal read from X-ray detector is associated with coordinates in the detection range of X-ray detector 4, and preserved in fluorography image memory 94. Display control unit 91 associates the center of the detection range of X-ray detector with a center position in the monitor 95, and displays the detection range of X-ray detector 4. Monitor 95 is set up in the control booth. Display control unit 91 obtains relative position of exposure field 4a to range of detection of X-ray detector 4 based on the information on the moving amount between each diaphragm blade unit 51 maintained in aperture information holding unit 84 and the location information of the center of the exposure field 4a maintained in center position information holding unit 82, and displays the exposure field 4a at a prescribed position in monitor 95. The operator operates center transfer operation unit 74 while seeing the detection range of X-ray detector 4 and the exposure field 4a displayed in monitor 95. Display control unit 91 has a scroll processing unit 92. Scroll processing unit 92 associates a center position of the exposure field 4a on X-ray detector 4 with a standard position (For example, it is a center in display) in the display of providing beforehand, and displays the exposure field 4a. As a result, even if the center of the exposure field 4a moves by operating center transfer operation unit 74, the screen of the monitor can follow to the exposure field 4a. An appropriate exposure field 4a can be easily and for a short time selected. Display control unit 91 has a selector 93. Selector 93 selects the mode that associates center of range of detection of X-ray detector 4 with center position in monitor 95, and displays range of detection of X-ray detector 4 or the mode that associates center of exposure field 4a on X-ray detector 4 with center position in monitor 95, and displays exposure field 4a. Display control unit 91 receives the instruction signal from the field size selector switch 78, enlarges or reduces a prescribed range in coordinates of the X-ray image-data to the multistep within the range decided beforehand in the display, and displays the X-ray image-data in the monitor 95. Next, procedure for moving diaphragm blade unit 51 will be explained in reference to FIG. 8. FIG. 8 is a flowchart of procedure of the diaphragm blade unit moves. As shown in FIG. 8, the operator operates center transfer operation unit 74 while seeing the detection range and the exposure field 4a of X-ray detector 4 displayed in the monitor. For example, as shown in FIG. 9A, the operator prescribes position O1′ in the moving destination at the center of the exposure field 4a by center transfer operation unit 7. When moving amount compute unit 81 received the instruction of the moving destination at the center of the exposure field 4a from center transfer operation unit 74, moving amount compute unit 81 calculates the moving amount (Z1) at the center of the exposure field 4a based on information at the position O1 of the movement origin at the center of the exposure field 4a and the position O1′ of the moving destination at the center of the exposure field 4a. The direction of the movement is included in the moving amount (Z1). For example, a positive moving amount is an upper direction, and a negative moving amount is a lower direction. Operating information processing unit 8 sends beam-limiting control unit 62 the calculated moving amount (S101). Upside beam-limiting control unit 63 to right side beam-limiting control unit 66 of beam-limiting control unit 62 makes the moving amount at the center of the exposure field 4a prescribed-times ((H1/H2) times in FIG. 3), calculates the moving amount of each diaphragm blade unit 51 in the upper part, the lower side, and the left part and the right part respectively (S102). For example, Upside beam-limiting control unit 63 obtains the amount of the rotation of the stepping motor of upside beam-limiting drive unit 53 from the moving amount of diaphragm blade unit 51. Upside beam-limiting control unit 63 calculates the pulse-member data that corresponds to the amount of the rotation, generates the command pulse signal based on a pulse-member data, converts a generated command pulse signal based on the pulse-member data, converts the command pulse signal into the current, and thrown to the stepping motor (S103). Upside beam-limiting drive unit 53 moves diaphragm blade unit 51 (S104). Upside beam-limiting control unit 63 judges whether the edge from the position of diaphragm blade unit 51 detected by diaphragm blade position detecting unit 57 to the exposure field 4a moved to the edge Z2 in the detection range of X-ray detector 4 while diaphragm blade unit 51 is moving (S105). Upside beam-limiting drive unit 53 moves diaphragm blade unit 51 continuous when upside beam-limiting control unit 63 judges that the edge in the exposure field 4a doesn't move to the edge Z2 in the detection range of X-ray detector 4 (S105; NO). When upside beam-limiting drive unit 53 move diaphragm blade unit 51 prescribed amount (S106; Yes), Upside beam-limiting drive unit 53 stops moving of diaphragm blade unit 51. As explained above, when the operator operates center transfer operation unit 74 and the moving destination at the center of the exposure field 4a is directed, each diaphragm blade unit 51 follows to the movement of the center of the exposure field 4a. And, the center of the exposure field 4a can be easily matched to the test object of subject after is changed. An appropriate exposure field 4a can be easily selected for a short time without moving tabletop 2, retention feature 11, and X-ray detector 4. When upside beam-limiting control unit 63 judges that the edge of exposure field 4a moves to the edge Z2 of detection range of X-ray detector 4 (S105; Yes), upside beam-limiting drive unit 53 stops moving of diaphragm blade unit 51. A part of the exposure field 4a isn't go over the detection range of X-ray detector 4, and the unnecessary exposure place run out. Similarly, underneath beam-limiting control unit 64, left side beam-limiting control unit 65, and right side beam-limiting control unit 66 control underneath beam-limiting drive unit 54, left side beam-limiting drive unit 55, and right side beam-limiting drive unit 56 severally. After underneath beam-limiting drive unit 54, left side beam-limiting drive unit 55, and right side beam-limiting drive unit 56 moves prescribed amount each diaphragm blade unit 51, it is stopped. Part or all of exposure field 4a does not exceed detection range of X-ray detector 4 and each diaphragm blade unit 51 becomes states in FIG. 9B. Operating information processing unit 8 calculates the movement amount and the movement direction of the center of exposure field 4a until the edge of the exposure field 4a matches the edge of the detection range of X-ray detector 4. The calculated moving amount etc. is sent to beam-limiting control unit 62, beam-limiting control unit 62 may controls beam-limiting drive unit 52. Part of exposure field 4a does not exceed detection range of X-ray detector 4 and a useless irradiation place can be lost. As shown in FIG. 9B, when center transfer operation unit 74 prescribes position of moving destination at center of exposure field 4a, upside beam-limiting control unit 63, underneath beam-limiting control unit 64, left side beam-limiting control unit 65, and right side beam-limiting control unit 66 control upside beam-limiting drive unit 53, underneath beam-limiting drive unit 54, left side beam-limiting drive unit 55, and right side beam-limiting drive unit 56 severally. After upside beam-limiting drive unit 53, underneath beam-limiting drive unit 54, left side beam-limiting drive unit 55, and right side beam-limiting drive unit 56 moves prescribed amount each diaphragm blade unit 51, it is stopped. Each diaphragm blade unit 51 becomes states in FIG. 9C. When left side beam-limiting control unit 65 judges that the edge of exposure field 4a moves the edge X2 of detection range of X-ray detector 4, left side beam-limiting drive unit 55 stops moving of diaphragm blade unit 51. A useless irradiation place can be lost. When underneath beam-limiting control unit 64 judges that the edge of exposure field 4a moves the edge Z3 of detection range of X-ray detector 4, underneath beam-limiting drive unit 54 stops moving of diaphragm blade unit 51. When right side beam-limiting control unit 66 judges that the edge of exposure field 4a moves the edge X3 of detection range of X-ray detector 4, right side beam-limiting drive unit 56 stops moving of diaphragm blade unit 51. A useless irradiation place can be lost. When the test object of subject after is changed enters detection range of X-ray detector 4, to be suitable for the test object of the center of the exposure field 4a, the center of the exposure field 4a in the moving destination may be directed by center transfer operation unit 47. When the test object of subject after is changed exceeds detection range of X-ray detector 4, tabletop 2, retention feature 11, and X-ray detector 4 do relative movement. Specifically, tabletop 2 moves the shorter direction (X-way), X-ray tube 3, X-ray detector 4, and beam-limiting device 5 move the longer direction of tabletop 2 (Z-way). Procedure for matching center of detection range of X-ray detector 4 to test object of subject after is changed will be explained in reference to FIG. 10. FIG. 10 is a flowchart of procedure of imaging system construction is relative movement. As shown in FIG. 11A, when the center of detection range of X-ray detector 4 is position O, imaging system operation unit 77 directs position O′ of moving destination at center. As shown in FIG. 10A, imaging system control unit 101 receives position O′ of moving destination at center of detection range of X-ray detector 4 (S201). Imaging system control unit 101 calculates the amount of relative movement of imaging system structure from the moving amount and the moving direction of the center of detection range of X-ray detector 4. Specifically, imaging system control unit 101 calculates the moving amount where X-ray tube 3 and X-ray detector 4 move along direction of Z-way and the moving amount where tabletop 2 moves X-way (S202). Imaging system control unit 101 generates the control signal from the calculated moving amount of X-ray tube 3 etc. and the moving amount of tabletop 2, and output to imaging system drive unit 102 (S203). X-ray tube 3, X-ray detector 4, and beam-limiting device 5 move along the longer direction of tabletop 2 (Z-way) as one body. Tabletop 2 moves the shorter direction (X-way) (S204). When X-ray tube 3, X-ray detector 4, and beam-limiting device 5 move the prescribed amount (S205; Yes), imaging system drive unit 102 stops moving of X-ray tube 3 etc., and stops moving tabletop 2. And, the center of the exposure field 4a can be easily matched to the test object of subject after is changed. FIG. 11B shows the states that the center of detection range of X-ray detector 4 becomes the position O′ by relative movement of imaging system structure. A second embodiment in accordance with the present invention will be explained with reference to FIG. 12. FIG. 12 is a functional block diagram of the X-ray diagnostic apparatus according to a second embodiment. The second embodiment is different from the first embodiment in the following two points. The first different point is the relative movement of imaging system structure by operating of center transfer operation unit 74. In the second embodiment, the moving destination at the center of the exposure field is directed by operating center transfer operation unit 74. To locate the center of the exposure field in the moving destination at the directed center, imaging system structure is relative movement. The second different point is operating information processing unit 8 has judgment unit 85. Judgment unit 85 judges whether part or all in the exposure field 4a exceed the detection range of X-ray detector 4 when the center of exposure field 4a move based on the position of edge of exposure field 4a and the position of edge of detection range of X-ray detector. Operating information processing unit 8 decides the relative movement of imaging system structure or moving of beam-limiting unit 5 based on the result of judgment unit 85. Operating information processing unit 8 has moving amount compute unit 81, center position information holding unit 82, imaging system position information holding unit 83, and aperture information holding unit 84. Moving amount compute unit 81 receives direction from center transfer operation unit 74, calculates the moving amount and the moving direction of the center of exposure field 4a. Center position information holding unit 82 holds the position information of the center of exposure field 4a. Imaging system position information holding unit 83 holds the each position information of tabletop 2 and X-ray detector 4. Aperture information holding unit 84 holds the distance (aperture) between each diaphragm blade unit 51. Operating information processing unit 8 calculates position of moving destination at center of exposure field 4a and position of edge of exposure field 4a from the moving amount and moving direction of the center of exposure field 4a, location information of movement origin at center of exposure field 4a, and information on the distance (aperture) between each diaphragm blade unit 51. Operating information processing unit 8 calculates the center position and the position of edge of detection range of X-ray detector 4 side (position of about four in rectangular detection range) from the information of each position of tabletop 2 and X-ray detector 4. When Judgment unit 85 judges that exposure field 4a enters the detection range of X-ray detector 4 by moving of the center of exposure field 4a, operating information processing unit 8 send the moving amount and the moving direction of the exposure field 4a to beam-limiting control unit 62. Beam-limiting control unit 62 controls beam-limiting drive unit 52, and moves each diaphragm blade unit 51 individually, and the center of the exposure field 4a is matched to the test object of subject. When Judgment unit 85 judges that part or all of exposure field 4a exceed the detection range of X-ray detector 4 by moving of the center of exposure field 4a, operating information processing unit 8 send the moving amount and the moving direction of the exposure field 4a to imaging system control unit 101. Imaging system control unit 101 controls imaging system drive unit 102, and tabletop 2, X-ray tube 3, and X-ray detector 4 do relative movement, and the center of the exposure field 4a is matched to the test object of subject. Operating procedure by center transfer control unit 74 will be explained in reference to FIG. 13. FIG. 13 is a flowchart of operating procedure by the center transfer operation unit. Operating information processing unit 8 receives instruction from center transfer operation unit 74. Moving amount compute unit 81 calculates the moving amount of the center of exposure field 4a based on the position of movement origin at center of exposure field 4a and the position information of moving destination at center of exposure field 4a (S301). Judgment unit 85 judges whether the distance (aperture) between each diaphragm blade unit 51 opens completely based on aperture information on diaphragm blade unit 51 maintained in aperture information holding unit 84 (S302). When the distance (aperture) between each diaphragm blade unit 51 is completely open (S302; Yes), the imaging system structure does relative movement (S307). When the distance (aperture) between each diaphragm blade unit 51 is not completely open (S306; No), operating information processing unit 8 calculates coordinates on the edge of the exposure field 4a based on information at position of moving destination at center of exposure field 4a and the aperture information on diaphragm blade unit 51 preserved in aperture information holding unit 84 (S303). Operating information processing unit 8 calculates coordinates on the edge of detection range of -ray detector 4 based on location information of imaging system position information holding unit 83 maintained in tabletop 2 and location information of X-ray detector 4. Judgment unit 85 compares the edge of the exposure field 4a and the edge of the detection range of X-ray detector 4 (S304). When judgment unit 85 judges that at least one of the edges of exposure field 4a exceeds the detection range of -ray detector 4 (S304; Yes), and moving of the imaging system structure begins (S307). When judgment unit 85 judges that exposure field 4a enters the detection range (S304; No), and moving of diaphragm blade unit 51 begins (S306). Moving of diaphragm blade unit 51 will explained in reference to FIG. 14. FIG. 14 is a flowchart of procedure of the diaphragm blade unit moves. The moving amount and the moving direction of the center of the exposure field 4a is sent to beam-limiting control unit 62 in FIG. 14 (S401). Beam-limiting control unit 62 calculates the moving amount and the moving direction of diaphragm blade unit 51 based on the moving amount and the moving direction of the center of the exposure field 4a (S402). Beam-limiting control unit 62 generates the control signal from the moving amount and the moving direction of diaphragm blade unit 51, and output it to beam-limiting drive unit 52 (S403). Beam-limiting drive unit 52 moves diaphragm blade unit 51 (S404). When beam-limiting drive unit 52 moves diaphragm blade unit 51 prescribed amount (S405; Yes), beam-limiting drive unit 52 stops moving of diaphragm blade unit 51. When the operator directs the moving destination at the center of the exposure field 4a by center transfer control unit 74, each diaphragm blade unit 51 follows to the movement of the center of the exposure field 4a. And, the center of the exposure field 4a can be easily matched to the test object of subject after is changed. Next, the relative movement of the imaging system structure will explained in reference to FIG. 15. FIG. 15 is a flowchart of procedure of an imaging system construction is relative movement. As shown in FIG. 15, the moving amount and the moving direction of the center of the exposure field 4a is sent to imaging system control unit 101 (S501). Imaging system control unit 101 calculates amount where X-ray tube 3 and X-ray detector 4 move along Z-way and amount where tabletop 2 moves in X-way from moving amount and moving direction the center of exposure field 4a (S502). Imaging system control unit 101 generates the control signal from the calculated moving amount, and output it to imaging system drive unit 102 (S503). The imaging system structure moves respectively (S504). When the imaging system structure moves prescribed amount (S105; Yes), imaging system drive unit 102 stops moving of the imaging system structure. The center of the exposure field 4a can be easily matched to the test object of subject after is changed. Next, the relative movement of the imaging system structure will be explained by illustrating the movement of the center of the exposure field 4a. FIGS. 16A to 16C are a figure for explaining the mode that the imaging system construction is relative movement. FIG. 16A shows the position of the movement origin at the center of the range detection of X-ray detector 4 and the position O1 of the movement origin at the center of the exposure field 4a. By operating center transfer operation unit 74, the center of exposure field 4a move to the longer direction of tabletop 2 (Z-way) to Z1, move to the shorter direction of tabletop 2 (X-way) to X1. And, the center of exposure field 4a becomes the position O2 from the position O1. FIG. 16B shows the exposure field 4a exceeds the detection range of X-ray detector 4 when the center of exposure field 4a is position O2. FIG. 16 shows exposure field 4a and doesn't shows diaphragm blade unit 51. As shown in FIG. 16B, when judgment unit 85 judges that exposure field 4a goes over the detection range of X-ray detector 4, imaging system control unit 101 controls imaging system drive unit 102 and does relative movement of the imaging system structure. And, the center of exposure field 4a changes the position O2 from the position O1. The center of detection range of X-ray detector 4 changes the position O′ from the position O. FIG. 16C shows state after center of exposure field 4a becomes position O2 from position O1. In the second embodiment, when part or all in the exposure field 4a exceed the detection range of X-ray detector 4 by moving the exposure field 4a, diaphragm blade unit 51 is moved until the exposure field 4a exceeds the detection range of X-ray detector 4. When the exposure field 4a exceeds the detection range of X-ray detector 4, beam-limiting control unit 62 may controls beam-limiting drive unit 52 to do the movement of diaphragm blade unit 51 and the relative movement of imaging system structure continuously, and imaging system control unit 102 may controls imaging system drive unit 102. When judgment unit 85 judges that part or all of exposure field 4a exceed the detection range of X-ray detector 4, imaging system control unit 101 controls imaging system drive unit 102, and tabletop 2, X-ray tube 3, and X-ray detector 4 are moved respectively. In doing so, the position of the center of detection range of X-ray detector matches position of moving destination at center of exposure field 4a. The operation switching area is equipped the edge of detection range. Smooth operation switch of movement of diaphragm blade unit 51 and relative movement of the imaging system structure will be explained in reference to FIGS. 17 to 19. FIG. 17 is a figure of movement switch area of range of detection. FIG. 18 is a figure of one example of change in operation speed of the movement switch area. FIG. 19 is a flowchart of procedure of the movement switch area. Operating information processing unit 8 receives instruction from center transfer operation unit 74. Moving amount compute unit 81 calculates the moving amount of the center of exposure field 4a based on the position of movement origin at center of exposure field 4a and the position information of moving destination at center of exposure field 4a (S601). Judgment unit 85 judges whether the distance (aperture) between each diaphragm blade unit 51 opens completely based on aperture information on diaphragm blade unit 51 maintained in aperture information holding unit 84 (S602). When the distance (aperture) between each diaphragm blade unit 51 is completely open (S602; Yes), the imaging system structure does relative movement (S608). When the distance (aperture) between each diaphragm blade unit 51 is not completely open (S602; No), operating information processing unit 8 calculates coordinates on the edge of the exposure field 4a based on information at position of moving destination at center of exposure field 4a and the aperture information on diaphragm blade unit 51 preserved in aperture information holding unit 84 (S603). Operating information processing unit 8 calculates coordinates on the edge of detection range of -ray detector 4 based on location information of imaging system position information holding unit 83 maintained in tabletop 2 and location information of X-ray detector 4. Judgment unit 85 compares the edge of the exposure field 4a and the edge of the detection range of X-ray detector 4 (S604). When judgment unit 85 judges that at least one of the edges of exposure field 4a enters the operation switching area of edge of detection range (S506; Yes), moving of each diaphragm blade unit 51 begins decelerating, and moving of the imaging system structure begins acceleration at the same time (S607). Flow shifts to the step S305 in FIG. 13. To be concrete, as shown in FIG. 18, a speed is controlled that it is the movement speed of each diaphragm blade unit 51=H1/H2×the movement speed of the imaging system structure. In doing so, movement on the screen is kept at a constant speed. The movement of each diaphragm blade unit 51 ends by the edge of the exposure field 4a goes out of the operation switching area. The movement speed of the imaging system structure steadies, and a relative movement is done. When judgment unit 85 judges that the exposure field 4a doesn't enter the operation switching area (S304; No), diaphragm blade unit 51 moves (S306). In the first and second embodiments, retention feature 11 maintains X-ray tube 3 and beam-limiting device 5. It is composed to move along the longer direction of tabletop 2, and it is composed to move X-ray detector 4 with X-ray tube 3 and beam-limiting device 5 as one body. In the third embodiment, X-ray tube 3 and X-ray detector 4 is composed the vertical plane including the body axis of subject rotatably with one arbitrary point between X-ray tube 3 and X-ray detector 4 is centers. FIG. 20 is a conceptual diagram of the X-ray diagnostic apparatus according to a third embodiment. As shown in FIG. 20, C-arm 14 (imaginary line in FIG. 20) is supported to the retention feature rotatably. X-ray tube 3 and diaphragm blade unit 51 are installed on part of C-arm 14. X-ray detector 4 is installed on other edges of C-arm 14. As shown in FIG. 20, C-arm 14 (chain line in FIG. 20) rotates, and the exposure field 4a approaches the test object of subject. When the center of the exposure field 4a is not suitable for the test object of subject, the center of the exposure field 4a can be matched to the test object of subject by individually moving diaphragm blade unit 51. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. |
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abstract | Systems and methods for objective Deployment Failure risk assessments are provided, which may include fault trees. Systems and methods for the analysis of fault trees are provided as well. The risk assessments system may involve the development of a fault tree, assigning initial values and weights to the events within that fault tree, and the subsequent revision of those values and weights in an iterative fashion, including comparison to historical data. The systems for analysis may involve the assignment of well-ordered values to some events in a fault tree, and then the combination those values through the application of specialized, defined gates. The system may further involve the revision of specific gates by comparison to historical or empirical data. |
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055815898 | description | DETAILED DESCRIPTION OF THE INVENTION As result of the intensive studies conducted in order to attain the objects of the invention, the present inventors found that the problem of the prior art could effectively be solved by adopting the following three design features. First, the overall system was configured as shown in FIG. 1, comprising a magnetron oscillator 1, circulator A designated by 2, directional coupler A designated by 3, incident and reflected wave power meter 4, stub tuner 5, circulator B designated by 6, directional coupler B designated by 7, cavity resonator 8, spectrum analyzer 9, discharge detector/interlocking signal transmitter 10, gelling stock solution or sol supplying/small droplet forming unit 11, and gel particle receptacle 12. Components 1-3 are interconnected by waveguides 13, and components 3-8 are also interconnected by waveguides 13. It should be noted here that a commercial power source consists typically of components 1-3 or 1-5. Secondly, the resonator 8 shown in FIG. 1 was fitted with a micrometer-type drive mechanism 15 that permitted a quartz rod 14 for fine tuning of the resonant state to be inserted into or withdrawn out of the resonator 8. As in the Ledergerber process, a quartz tube 16 for protecting the resonator against fouling by the deposition of falling droplets and other contaminants was set in the center of the resonator so that the small droplets of the stock solution or sol would fall down through the center of the quartz tube 16. Thirdly, a microwave power source commercially available for use in dielectric heating which had a frequency spectrum width of several megahertz was adapted to be capable of fine tuning over 1 MHz. In addition to these three alterations, the present inventors proposed that the resonator be positioned to create a vertical electric field as shown in FIG. 2b in contrast with the layout shown in FIG. 2a adopted by Ledergerber to create a horizontal electric field. Referring to the block diagram shown in FIG. 1, circulator A designated by 2 is for protecting the magnetron oscillator 1, whereas circulator B designated by 6 is provided to insure isolation of the resonator 8 from the stub tuner 5. The stub tuner 5 is provided for varying the incident energy to be launched into the resonator 8. Directional coupler A designated by 3 is provided so that the energy supplied from the magnetron oscillator 1 and the energy reflected by the stub tuner are read on the incident and reflected wave power meter 4, thereby indicating the effective energy that will be supplied to the resonator 8, Directional coupler B designated by 7 is provided chiefly for the purpose of matching the resonator 8 by monitoring with the spectrum analyzer 9 the frequency spectrum of the microwave being reflected from the resonator 8. Matching of the resonator 8 is roughly accomplished by combining the width of the iris provided at the entrance to the resonator with the length of the resonator. However, considering that the resonant frequency of the system varies with the temperature of the resonator, the position of the quartz tube and the presence or absence of small droplets, the quartz rod 14 for fine tuning of the resonant state is moved up and down by means of the drive mechanism 15 with the spectrum of the reflected microwaves from the resonator being monitored with the spectrum analyzer, so that the resonant frequency will lie within the frequency spectrum of the incident microwaves (defined by minimum value f.sub.min and maximum value f.sub.max) as shown in FIG. 3. In addition, the center of the resonant frequency for the case where there are no small droplets in the system (f.sub.0 in FIG. 3b) differs from the value for the case where such small droplets are present in the system (f.sub.1 in FIG. 3c) and the latter is lower than the former by about 0.7 MHz. Therefore, in the warmup process of resonating the system before starting to have the small droplets fall down, the quartz rod 14 for fine tuning of the resonant state must be manipulated to insure that f.sub.0 is positioned in such a way that both f.sub.0 and f.sub.1 will lie between f.sub.min and f.sub.max. Such fine tuning of the resonant state may be obviated by using microwaves having a wide frequency spectrum. However, when microwaves having a wide spectrum are to be used, the heating efficiency will deteriorate in proportion to the spectrum width and it becomes necessary to use a microwave power source having an even higher output or frequency. In the present invention, a commercial power source was adapted for achieving variations in the frequency spectrum width with a view to achieving an improvement in heating efficiency. Discharge may occur within the resonator 8 for certain reasons such as the deviation of the path in which the small droplets will fall down, whereby the droplets are deposited on the inner surface of the quartz tube within the resonator. The discharge detector/interlocking signal transmitter 10 is provided for the purpose of detecting the occurrence of such discharge by sensing the increase in the reflected power toward directional coupler B on account of the departure from the resonant state and then transmitting a signal for interlocking the power supply unit so that the stock solution or sol will not be supplied any more. As FIG. 2a shows, the resonator which is so positioned as to create a horizontal electric field (according to the Ledergerber process) produces a field intensity distribution where the intensity is zero at top and bottom ends of the resonator and maximal in the center. The velocity of small droplets falling down through the resonator is accelerated by gravity and the time over which they pass through the Position of great field intensity is comparatively short. In contrast, the resonator shown in FIG. 2b which is one characteristic portion of the invention and which is so positioned as to create a vertical electric field produces a field intensity distribution where the intensity is maximal at any position in the central portion of the resonator through which the small droplets pass. Hence, efficient heating is insured even at the top end of the resonator where the velocity of falling small droplets is minimal and the resonator is capable of comparable heating to the type shown in FIG. 2a, although it is shorter in the vertical direction. The particles that have gelled upon dielectric heating are typically recovered into an aqueous fluid but the gel particles, which appear solid, are very low in strength and prone to deform or break. In order to avoid such deformation or breakage, the gel particles should plunge into the recovery fluid at the smallest possible rate. In this respect, the resonator used in the present invention which is shorter in the vertical direction than the Ledergerber resonator is advantageous because it reduces the chance of the deformation or breakage of gel particles, whereby the scope of its application is expanded. The following examples are provided for the purpose of further illustrating the invention but are in no way to be taken as limiting. EXAMPLE 1 A copper resonator (200 mm.sup.H .times.62 mm.sup.W .times.27 mm.sup.D) was set up in such a way as to produce a horizontal electric field. A quartz tube (o.d., 10.5 mm; i.d., 7.5 mm) was placed in the center of the resonator. A microwave with an effective power of 3 kW (readings on an incident and reflected wave power meter: 5 kW for the incident wave; 2 kW for the reflected wave) was launched into the system. After the resonant frequency of the system was stabilized to lie within the incident spectrum width, the small particles of an aqueous stock solution at 2.degree. C. (having ammonium nitrate and urea each dissolved at a concentration of 1 mol per liter) that were formed 30 mm above the top end of the resonator were allowed to fall down through a nozzle (o.d., 0.7 mm), with one drop passing per second. The small droplets that passed through the resonator were at 82.degree. C., having experienced a temperature rise of 80K. EXAMPLE 2 The procedure of Example 1 was repeated, except that the effective power of the launched microwave was 3.2 kW (5.0 kW for the incident wave and 1.8 kW for the reflected wave). The small droplets that passed through the resonator were at 87.degree. C., having experienced a temperature rise of 85K. EXAMPLE 3 A microwave with an effective power of 2.7 kW (4.6 kW for the incident wave and 1.9 kW for the reflected wave) was launched into a resonator of the same type as used in Example 1. A stock solution at 2.degree. C. for the production of UO.sub.2 particles (consisting of U, nitrate ions, urea and HMTA at respective concentrations of 1.5 mol, 2.25 mol, 1.5 mol and 1.5 mol per liter) was added dropwise to the resonator from the position 35 mm above its top end through a nozzle (o.d., 0.7 mm). The droplets were passed through the resonator and recovered into pure water the surface level of which lied 55 mm below the bottom end of the resonator. The particles thus recovered had gelled in a satisfactory way. EXAMPLE 4 A copper resonator (55 mm.sup.H .times.74 mm.sup.W .times.110 mm.sup.D) was set up in such a way as to produce a vertical electric field. A quartz tube (o.d., 10.5 mm; i.d., 7.5 mm) was placed in the center of the resonator. A microwave with an effective power of 3 kW (readings on an incident and reflected wave power meter: 4 kW for the incident wave; 1 kW for the reflected wave) was launched into the system. After the resonant frequency of the system was stabilized to lie within the incident spectrum width, the small particles of an aqueous stock solution at 2.degree. C. (having ammonium nitrate and urea each dissolved at a concentration of 1 mol per liter) that were formed 30 mm above the top end of the resonator were allowed to fall down through a nozzle (o.d., 0.7 mm), with one drop passing per second. The small droplets that passed through the resonator were at 83.degree. C., having experienced a temperature rise of 81K. EXAMPLE 5 At the last stage of the experiment in Example 1, the nozzle was vibrated so that the path in which the small droplets were falling down would shift, causing the droplets to deposit on the inner surface of the central quartz tube. As a result, discharge occurred and the high-frequency power source and the power supply to the stock solution feeding/small droplet forming unit were both interlocked. The method of gelation by dielectric heating with microwaves was first applied by Ledergerber to the production of gel particles as a precursor of particulate ceramic fuels but in that method, communication frequencies of 8.2-12.4 GHz had to be used and this made it necessary to fabricate a special power source at high cost. According to the present invention, it has been demonstrated that a dielectric heating power source that operates at an engineering frequency of 2.45 GHz needs only small design changeovers to realize a method and apparatus that enable the temperature elevation of about 80K necessary to cause internal gelation of the small particles of a stock solution or sol. The present invention also uses a cavity resonator of a layout that produces a vertical electric field and this contributes a lot to the purpose of avoiding the deformation or breakage of gel particles. Additionally, the installation of a discharge detector/interlocking signal transmitter improves the safety of the overall system, thereby reducing much of the burden on the operating personnel of the gelling apparatus of the invention. |
abstract | This document's object is to provide an axial power distribution control method in which only the control of an axial power distribution in a nuclear reactor with a simple operation with a clear operational target keeps the control of a xenon oscillation, thereby suppressing the xenon oscillation to an extremely small magnitude in advance at the same time. An axial power distribution control method comprises an axial offset calculation step of calculating an axial offset of the current power distribution (AOP) and axial offsets of the power distributions (AOX, AOI) which would give the current xenon and iodine distributions under equilibrium conditions, respectively, based on relative powers (PT, PB) in the upper and lower halves of the nuclear reactor core, a parameter calculation step of calculating parameters (DAOPX, DAOIX), a trajectory display step of displaying a trajectory to plot the parameters (DAOPX, DAOIX) on one and the other axis, respectively, an allowable range excess judgment step of judging if the axial offset of the current power distribution (AOP) exceeds an allowable range, an alarming step of giving the alarm when the AOP exceeds the allowable range, and a control rod moving step of controlling the movement of control rods to guide the plot to the major axis of an ellipse formed by the trajectory of said parameters upon receipt of the alarm. |
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description | The present invention relates to a fuel assembly loaded into the reactor core of a nuclear reactor, and particularly to nuclear fuel rods and fuel assemblies loaded into the reactor core of a light water reactor. Light water reactors such as boiling-water reactors (BWR) and pressurized-water reactor (PWR) typically include fuel assemblies loaded into the reactor core as nuclear fuel. The fuel assembly includes a plurality of uranium-containing nuclear fuel rods (or simply, “fuel rods”) arrayed and supported with an upper tie plate and a lower tie plate. Each nuclear fuel rod includes uranium fuel pellets charged into a fuel cladding tube about 4 meters long, and the both ends of the tube are sealed with end plugs. Traditionally, a zirconium alloy (zircalloy), which has a small thermal neutron absorption cross section and desirable corrosion resistance, has been used as material of the fuel cladding tube and the end plugs. This material has good neutron economy, and has been safely used in typical nuclear reactor environments. In light water reactors using water as a coolant, generated heat from the uranium fuel raises the temperature inside the nuclear reactor, and a high-temperature water vapor generates in case of a loss-of-coolant accident (LOCA), a rare event where the coolant water fails to enter the nuclear reactor. In the event where the lack of the coolant (coolant water) exposes the fuel rods from coolant water, the temperature of the fuel rods well exceeds 1,000° C., and causes the zirconium alloy of the fuel cladding tube to chemically react with water vapor (the zirconium alloy is oxidized, and the water vapor is reduced) to generate hydrogen. Various safety measures are taken against a loss-of-coolant accident (LOCA), including, for example, an emergency core cooling system (ECCS). Such safety measures are not confined to system designs, but extend to the constituent materials of the reactor core. For example, there are studies directed to using ceramic materials for fuel cladding tubes and end plugs, instead of using a zirconium alloy, which becomes a cause of hydrogen generation. Particularly, silicon carbide (SiC), which has desirable corrosion resistance, high heat thermal conductivity, and a small thermal neutron absorption cross section, has been a focus of active research and development as a promising material of fuel cladding tubes and end plugs. It is also expected that SiC greatly reduces hydrogen generation in case of a loss-of-coolant accident (LOCA), because the oxidation rate of SiC is two orders of magnitude smaller than the oxidation rate of a zirconium alloy in a high-temperature steam environment above 1,300° C. For example, PTL 1 proposes a fuel cladding tube and end plugs configured from a SiC material. PTL 1 discloses a configuration in which a fuel cladding tube, and end plugs for sealing the both end portions of the fuel cladding tube are formed of a SiC fiber reinforced composite reinforced with silicon carbide continuous fibers, and in which the fuel cladding tube and the end plugs are directly joined to each other without interposing a dissimilar material, in at least a joint portion that comes into contact with the reactor coolant. This publication also describes a configuration in which the fuel cladding tube and the end plugs are directly joined to each other without interposing a dissimilar material on the side that comes into contact with the reactor coolant (the outer periphery surface side of the fuel cladding tube), and in which the side that does not come into contact with the reactor coolant (the inner periphery surface side of the fuel cladding tube) is joined by solid-state welding via a dissimilar material (a composite of titanium silicon carbide and titanium silicide, or silicon carbide containing aluminum and yttrium). PTL 1: JP-A-2012-233734 In normal operation, a nuclear reactor undergoes repeated starts and stops in its operation cycle. This causes fluctuations in the internal-external pressure difference across the fuel rods, and places multiple loads on the joint between the fuel cladding tube and the end plugs. This may lead to crack initiation and propagation. In the event of a possible earthquake or falling accident, the fuel rods are expected to receive a larger bending load than during normal operation. The end-plug joints of a fuel rod where the solid end plugs and the hollow fuel cladding tube are connected to each other are regions that undergo abrupt changes in cross sectional area. Accordingly, an applied bending load on the fuel rod with the fixed end plugs translates into a concentrated stress at the end-plug joints. The end-plug joints of a traditional zirconium alloy fuel rod undergo plastic deformation under an applied stress that exceeds the proof strength, and cracks do not penetrate through the fuel rod until the applied stress reaches a stress at rupture. However, the end-plug joints connecting the fuel cladding tube and the end plugs using a ceramic base material do not undergo plastic deformation, and a crack propagates once it generates. The crack has a high probability of penetrating through the fuel rod. In the event where stress concentrates at the end-plug joint, and cracking occurs at the interface between the fuel cladding tube and the joint material interposed at the joint surfaces (end-plug joints) of the end plugs, the configuration of PTL 1 has the risk of a crack propagating toward the outer periphery surface of the fuel cladding tube or the end plugs along the joint surface, and penetrating into the fuel cladding tube or the end plugs. It is accordingly an object of the present invention to provide a fuel rod and a fuel assembly for light water reactors in which crack penetration to a fuel cladding tube or end plugs can be prevented even when cracking occurs at the joint between the fuel cladding tube and the end plugs for which a ceramic base material is used. As a solution to the foregoing problems, a fuel rod for light water reactors of the present invention includes: a cylindrical cladding tube formed of a ceramic base material; a connection formed of the same or similar material to the cladding tube; and an end plug having a concave portion of a continuously curved surface shape adapted to house the connection, wherein the end plug is formed of the same or similar material to the cladding tube, wherein a slanted surface formed at an end portion of the cladding tube, and a slanted surface formed at an end portion of the end plug are joined in contact with each other with a metallic joint material, and wherein the joint is supported by the connection. A fuel assembly according to the present invention is a fuel assembly that includes a plurality of fuel rods bundled with a spacer, and that is to be loaded into a reactor core of a nuclear reactor, wherein the fuel rods include: a cylindrical cladding tube formed of a ceramic base material; a connection formed of the same or similar material to the cladding tube; and an end plug having a concave portion of a continuously curved surface shape adapted to house the connection, the end plug being formed of the same or similar material to the cladding tube, a slanted surface formed at an end portion of the cladding tube, and a slanted surface formed at an end portion of the end plug being joined in contact with each other with a metallic joint material, and the joint being supported by the connection. The present invention can provide a fuel rod and a fuel assembly for light water reactors in which crack penetration to a fuel cladding tube or end plugs can be prevented even when cracking occurs at the joint between the fuel cladding tube and the end plugs for which a ceramic base material is used. Other objects, configurations, and advantages will be apparent from the descriptions of the embodiments below. The following specifically describes embodiments of the present invention with reference to the accompanying drawings. The same reference numerals may be used to refer to the same members or parts, and descriptions of such members or parts may be omitted to avoid redundancy. The present invention is not limited to the embodiments described below, and various combinations and modifications may be appropriately made without departing from the technical idea of the present invention. Such appropriate combinations or modifications of configurations are intended to also fall within the scope of the present invention. Nuclear Fuel Rod FIG. 1 is a partial schematic cross sectional view of a nuclear fuel rod according to an embodiment of the present invention. A nuclear fuel rod 10a according to the present embodiment includes a fuel cladding tube 11, and a lower end-plug 12a and an upper end-plug 12b joined to the ends of the fuel cladding tube 11 to seal the fuel cladding tube 11. The fuel cladding tube 11 is charged with a plurality of fuel pellets 13. The nuclear fuel rod 10a is provided with a retainer spring 15 to retain the fuel pellets 13 charged inside the cylindrical fuel cladding tube 11. The upper end portion of the retainer spring 15 is connected to the upper end-plug 12b, and the lower end portion of the retainer spring 15 presses the fuel pellets 13. The fuel cladding tube 11, the upper end-plug 12a, and the lower end-plug 12b are configured from a ceramic base material. The following descriptions will be given through the case where these components are configured from a silicon carbide (SiC) material. FIG. 2 is an enlarged schematic cross sectional view representing an example of the joint between the fuel cladding tube and the end plug of a comparative example. The joint illustrated in FIG. 2 is the joint between the fuel cladding tube 11 and the lower end-plug 12a. However, the structure is the same for the joint between the upper end-plug 12b and the fuel cladding tube 11. In FIG. 2, the fuel pellets 13 charged inside the fuel cladding tube 11 are omitted to more clearly illustrate the joint between the fuel cladding tube 11 and the lower end-plug 12a. As illustrated in FIG. 2, the lower end-plug 12a is a solid columnar member with a straight barrel insert 12c projecting into the fuel cladding tube 11 in a region other than the outer edge portion. The outer diameter of the straight barrel insert 12c is slightly smaller than the inner diameter of the fuel cladding tube 11, and the lower end-plug 12a has an outer diameter about the same as the outer diameter of the fuel cladding tube 11. This forms a circular step, having a flat top surface and extending substantially perpendicular to the axial direction of the fuel cladding tube 11, between the straight barrel insert 12c and the periphery of the base of the straight barrel insert 12c (outer edge portion) in the lower end-plug 12a. The circular step with a flat top surface faces the lower end surface of the fuel cladding tube 11, and represents a butt joint interface 12d that is joined to the lower end surface of the fuel cladding tube 11 via a metallic joint material 20. In the configuration of the comparative example represented in FIG. 2, repeated starts and stops in a normal operation cycle of a nuclear reactor creates a pressure difference across the hollow cylindrical fuel cladding tube 11 charged with the fuel pellets 13 (not illustrated). Specifically, an internal-external pressure difference is created. A repeated stress due to such an internal-external pressure difference concentrates in the vicinity of the metallic joint material 20 having an interface with a dissimilar material, and may cause fatigue-induced crack initiation and propagation. In the event where an earthquake or a fall exerts a bending load on the nuclear fuel rod, a stress concentrates in the vicinity of the metallic joint material 20 lying at the base of the straight barrel insert 12c where abrupt changes occur in the transverse sectional area, and, with the lower end-plug 12a acting as a fixed end, a crack may occur and propagate when there is a large gap between the outer periphery surface of the straight barrel insert 12c and the inner periphery surface of the fuel cladding tube 11. A repeated stress during normal operation often acts to push the hollow cylindrical fuel cladding tube 11 outward. In other words, a repeated stress pushes the hollow cylindrical fuel cladding tube 11 in a direction that increases the inner diameter and the outer diameter of the fuel cladding tube 11. Here, the displacement of the fuel cladding tube 11 becomes greater toward the upper side of FIG. 2, from the butt joint interface 12d of the lower end-plug 12a, specifically from the base of the straight barrel insert 12c. Accordingly, cracking due to a repeated stress is believed to occur most frequently in the vicinity of the uppermost part of the metallic joint material 20 that is in contact with the outer periphery surface of the straight barrel insert 12c in the gap between the inner periphery surface of the fuel cladding tube 11 and the straight barrel insert 12c. A crack generated at the uppermost part of the interface between the metallic joint material 20 and the straight barrel insert 12c propagates downwardly toward the base of the straight barrel insert 12c along the outer periphery surface of the straight barrel insert 12c. Upon reaching the base of the straight barrel insert 12c, the crack radially propagates at the interface between the butt joint interface 12d of the lower end-plug 12a and the metallic joint material 20 toward the outer periphery portion of the circular butt joint interface 12d, before possibly penetrating through the nuclear fuel rod. FIG. 3 is an enlarged schematic cross sectional view representing another example of the joint between the fuel cladding tube and the end plugs of the comparative example. The difference from the comparative example represented in FIG. 2 is that the butt joint interface 12d of the lower end-plug 12a in FIG. 3 is slanted with respect to the axial direction of the fuel cladding tube 11. Specifically, the butt joint interface 12d of the lower end-plug 12a has a slanted surface so that the diameter of the lower end-plug 12a constituting the butt joint interface 12d increases toward the lower side of FIG. 3 from the base of the straight barrel insert 12c. The fuel cladding tube 11 has lower end surface of a shape that conforms to the butt joint interface 12d of the lower end-plug 12a. Specifically, the lower end surface of the fuel cladding tube 11 is slanted so that the inner diameter of the fuel cladding tube 11 increases toward the lower end-plug 12a. In the structure of the comparative example represented in FIG. 3, a repeated stress pushes the hollow cylindrical fuel cladding tube 11 outward, as with the case of FIG. 2. A crack generated at the interface between the straight barrel insert 12c and the metallic joint material 20 is more likely to propagate along the outer periphery surface of the straight barrel insert 12c, and the interface between the butt joint interface 12d of the lower end-plug 12a and the metallic joint material 20, and penetrate through the nuclear fuel rod than in the configuration of FIG. 2. FIG. 4 is an enlarged schematic cross sectional view representing an example of the joint between the fuel cladding tube 11 and the lower end-plug 12a constituting the nuclear fuel rod 10a according to the embodiment of the present invention shown in FIG. 1. The joint illustrated in FIG. 4 is the joint between the fuel cladding tube 11 and the lower end-plug 12a. However, the structure is the same for the joint between the upper end-plug 12b and the fuel cladding tube 11 shown in FIG. 1. In FIG. 4, the fuel pellets 13 charged inside the hollow cylindrical fuel cladding tube 11 are omitted to more clearly illustrate the joint between the fuel cladding tube 11 and the lower end-plug 12a. As illustrated in FIG. 4, the lower end-plug 12a is a solid columnar member with a concave portion 12f of a curved surface shape provided at an upper region including the butt joint interface 12d to be joined to the lower end surface of the fuel cladding tube 11. The concave portion 12f of a curved surface shape is a portion with a depression approximated to a portion of a spherical surface in the vicinity of the bottom portion, and a cylindrical portion having an inner surface that is continuous to the depression. The upper end surface of the lower end-plug 12a defining the concave portion 12f of a curved surface shape represents the butt joint interface 12d that can be brought into contact with the butt joint interface 11a (described later) representing the lower end surface of the fuel cladding tube 11. As illustrated in FIG. 4, the butt joint interface 12d of the lower end-plug 12a has a surface that is slanted upward from the inner periphery surface side to the outer periphery surface side (toward the fuel cladding tube 11). Specifically, the butt joint interface 12d of the lower end-plug 12a has such a shape that the inner diameter of the concave portion 12f of a curved surface shape becomes larger toward the fuel cladding tube 11. In other words, the butt joint interface 12d, which appears circular as viewed from the top, has a shape similar to the shape of an inverted hollow circular cone that becomes taller from the inner diameter to the outer diameter side. The butt joint interface 11a representing the lower end surface of the fuel cladding tube 11 facing the butt joint interface 12d of the lower end-plug 12a is a surface that is slanted upward from the inner periphery surface side to the outer periphery surface side of the fuel cladding tube 11. In other words, the butt joint interface 11a of the fuel cladding tube 11 has a surface that is slanted toward the lower end-plug 12a from the outer periphery surface side to the inner periphery surface side of the fuel cladding tube 11. As illustrated in FIG. 4, the nuclear fuel rod 10a also has a connection 21 that is disposed in a region extending from the concave portion 12f of a curved surface shape of the lower end-plug 12a to a predetermined height inside the fuel cladding tube 11 past the butt joint interface 12d of the lower end-plug 12a and the butt joint interface 11a of the fuel cladding tube 11. The connection 21 has a solid columnar portion, and a curved surface portion 21a approximated to a portion of a spherical surface, and provided at one end or both ends of the connection 21 relative to the lengthwise direction. The columnar portion and the curved surface portion 21a have outer surfaces that are continuous to each other. In the example represented in FIG. 4, the connection 21 having the curved surface portion 21a approximated to a portion of a spherical surface is shown opposite the depression of the concave portion 12f of a curved surface shape of the lower end-plug 12a. The connection 21 supports the fuel cladding tube 11 and the lower end-plug 12a. Preferably, the curved surface portion 21a of the connection 21 approximated to a portion of a spherical surface, and the depression of the concave portion 12f of a curved surface shape of the lower end-plug 12a should have as large a curvature as possible, or should be approximated to a sphere having as large a radius as possible. As illustrated in FIG. 4, the inner periphery surface of the fuel cladding tube 11, and the outer periphery surface of the connection 21 are joined to each other with the metallic joint material 20 in a region including the butt joint interface 12d of the lower end-plug 12a and the butt joint interface 11a of the fuel cladding tube 11, and covering a predetermined distance above the end portion of the butt joint interface 12d opposite the connection 21. The metallic joint material 20 may flow into the gap formed between the outer periphery surface of the connection 21 and the inner periphery surface of the concave portion 12f of a curved surface shape of the lower end-plug 12a, or may be applied beforehand to the outer periphery surface of the connection 21, or to the concave portion 12f of a curved surface shape of the lower end-plug 12a, and the gap may be closed with the metallic joint material 20 at the time of joining. With the structure shown in FIG. 4 in which the fuel cladding tube 11 and the lower end-plug 12a according to the embodiment of the present invention are joined to each other with the metallic joint material 20 with the support of the connection 21, a crack occurring at the interface between the outer periphery surface of the connection 21 and the metallic joint material 20 under a repeated stress can be prevented from penetrating and propagating to the nuclear fuel rod 10a. The following describes the mechanism by which crack penetration and propagation is prevented. In the structure of the comparative examples represented in FIGS. 2 and 3, the base of the straight barrel insert 12c constituting the lower end-plug 12a (a region in the vicinity of the joint between the fuel cladding tube 11 and the lower end-plug 12a) is a region where the transverse sectional area of the solid lower end-plug 12a undergoes abrupt changes. In contrast, in the structure shown in FIG. 4, abrupt changes in the transverse sectional area of the solid lower end-plug 12a take place at the depression approximated to a portion of a spherical surface in the concave portion 12f of a curved surface shape of the lower end-plug 12a. Accordingly, a stress due to applied bending load concentrates in the vicinity of the depression of the concave portion 12f of a curved surface shape, distant away from the butt joint interface 11a of the cladding tube 11 and the butt joint interface 12d of the lower end-plug 12a where the fuel cladding tube 11 and the lower end-plug 12a are joined to each other. Further, the stress concentration itself is relaxed because the depression of the concave portion 12f of a curved surface shape of the lower end-plug 12a has a shape approximated to a portion of a spherical surface. In case of cracking occurring at the uppermost portion of the interface between the metallic joint material 20 and the outer periphery surface of the connection 21 as above, a crack that propagates under a repeated stress due to the internal-external pressure difference across the nuclear fuel rod 10a propagates to the interface between the butt joint interface 12d and the metallic joint material 20, and does not penetrate the outer periphery surface of the nuclear fuel rod 10a because the butt joint interface 11a of the fuel cladding tube 11 and the butt joint interface 12d of the lower end-plug 12a are both slanted upward from the inner periphery surface side to the outer periphery surface side. Upon reaching the end portion on the inner periphery side of the butt joint interface 12d of the lower end-plug 12a, a crack that has propagated through the interface between the metallic joint material 20 and the outer periphery surface of the connection 21 propagates along the inner surface of the concave portion 12f of a curved surface shape of the lower end-plug 12a below, and the outer surface of the connection 21, and stays inside the nuclear fuel rod 10a. Here, any crack propagation into the connection 21 does not pose a problem because the crack does not penetrate the nuclear fuel rod 10a. Preferably, a silicon carbide (SiC) material is used for the fuel cladding tube 11, the lower end-plug 12a, and the connection 21. It is particularly preferable that the fuel cladding tube 11 and the lower end-plug 12a use a silicon carbide fiber reinforced silicon carbide composite material containing silicon carbide fibers in a silicon carbide matrix (hereinafter, also referred to as “SiC/SiC composite material”). Preferably, the SiC/SiC composite material used has a SiC layer formed on a part of the surface (for example, in a region corresponding to the joint surface). The method used to form the SiC layer is not particularly limited, and methods, for example, such as a chemical vapor deposition method (CVD method), and a coating and sintering method may be used. In order to shield the SiC itself from the coolant water environment inside the nuclear reactor, it is preferable to coat the fuel cladding tube 11 and the lower end-plug 12a with a Zr-, Ti-, or Cr-based alloy or compound of a thickness of about at most 100 μm. The method used to form such an environmental barrier coating is not particularly limited, and methods, for example, such as a physical vapor deposition method (PVD method), a chemical vapor deposition method (CVD method), and a coating and sintering method may be used. Preferably, the fuel cladding tube 11 has the same dimensions as traditional fuel cladding tubes of a zirconium alloy. For example, the fuel cladding tube 11 has a length of about 4 m, an outer diameter of about 11 mm, and a thickness of about 1 mm. Preferably, the lower end-plug 12a has such a shape or dimensions that no step is created on the outer surface in the vicinity of the joint made upon joining the butt joint interface 12d to the butt joint interface 11a of the fuel cladding tube 11. In order to aid insertion of the connection 21 to the fuel cladding tube 11 and to the concave portion 12f of a curved surface shape of the lower end-plug 12a, the outer diameter of the connection 21 is preferably smaller than the inner diameter of the fuel cladding tube 11 by a moderate amount of clearance (for example, about 0.02 to 0.5 mm). As illustrated in FIG. 4, the fuel cladding tube 11 and the lower end-plug 12a are supported via the connection 21, and are joined air-tight to each other by brazing and/or diffusion joining via the metallic joint material 20. The metallic joint material 20 may be preferably one selected from Si (melting point: 1,414° C.), Ti (melting point: 1,812° C.), Zr (melting point: 1,855° C.), and a Si alloy, a Ti alloy, and a Zr alloy of a composition with a solidus temperature of 1,200° C. or more. By forming a joint with the metallic joint material 20 having a melting temperature (a temperature at which a liquid phase occurs) of 1,200° C. or more, the nuclear fuel rod 10a can remain air-tight even in a rare case where the nuclear fuel rod 10a reaches a temperature as high as 1,200° C. Because the fuel cladding tube 11 and the lower end-plug 12a are joined to each other via the metallic joint material 20 in the present embodiment, it is not always possible to fully distinguish between “brazing” and “diffusion joining” on the basis of microstructure. Accordingly, the terms “brazing” and/or “diffusion joining” are used herein on the condition that the heating and joining involves the metallic joint material 20. The following describes a method for joining the fuel cladding tube 11 and the lower end-plug 12a to each other. First, for example, a coating of the metallic joint material 20 is formed on at least one of the butt joint interface 11a of the fuel cladding tube 11 and the butt joint interface 12d of the lower end-plug 12a that are to be joined to each other, and on at least one of the inner periphery surface of the fuel cladding tube 11 and the outer periphery surface of the connection 21. Preferably, the coating thickness is thick enough to close the clearance (the gap between the inner diameter of the fuel cladding tube 11 and the outer diameter of the connection 21) (for example, a thickness of about 0.01 to 0.25 mm). In this way, the lower end-plug 12a can be prevented from becoming loose or falling off when the butt joint interface 11a of the fuel cladding tube 11 is brought into contact with the butt joint interface 12d of the lower end-plug 12a, and when the connection 21 is inserted in the fuel cladding tube 11, and in the concave portion 12f of a curved surface shape of the lower end-plug 12a. The method used for the coating of the metallic joint material 20 is not particularly limited, and known methods, for example, such as vapor deposition, spraying, cold spraying, and melting may be used. The fuel cladding tube 11 and the lower end-plug 12a are then heated while being pressed against each other to join the fuel cladding tube 11, the lower end-plug 12a, and the connection 21. Here, the fuel pellets 13 have not been charged into the fuel cladding tube 11, and the fuel cladding tube 11 on the side of the upper end-plug 12b has an open end. The fuel pellets 13 are then charged into the fuel cladding tube 11, and, after the insertion of the retainer spring 15, the butt joint interface of the upper end-plug 12b is brought into contact with the butt joint interface of the fuel cladding tube 11. These are then joined to each other under heat. In joining the fuel cladding tube 11 and the lower end-plug 12a to each other without the fuel pellets 13, heat may be applied to the whole fuel cladding tube 11, including the joint with the lower end-plug 12a. In joining the upper end-plug 12b and the fuel cladding tube 11 to each other after the insertion of the fuel pellets 13 and the retainer spring 15, heat is applied locally to the joint so that the fuel pellets 13 are not heated. The heating method is not particularly limited, and known methods, for example, such as wide heating with a long heating furnace, and local heating with a laser, or a high-frequency or local heater may be used. The metallic joint material 20 used in the present embodiment has an average linear coefficient of expansion of preferably less than 10 ppm/K. The thermal stress due to temperature fluctuations (thermal expansion and thermal shrinkage) of the nuclear fuel rod 10a can be minimized, and joint damage can be prevented when the material used as the metallic joint material 20 has an average linear coefficient of expansion that does not differ greatly from the average linear coefficient of expansion (4.3 to 6.6 ppm/K) of the SiC material to be joined by the metallic joint material 20. The effect may not be obtained when the metallic joint material 20 has an average linear coefficient of expansion of 10 ppm/K or more, and the long-term reliability of the nuclear fuel rod 10a as a whole may be lost in this case. FIG. 5 is an enlarged schematic cross sectional view representing another example of the joint between the fuel cladding tube 11 and the lower end-plug 12a shown in FIG. 1. As illustrated in FIG. 5, a threaded structure 12e is provided on the inner periphery surface of the hollow cylindrical fuel cladding tube 11, the inner periphery surface of the cylindrical portion constituting the concave portion 12f of a curved surface shape of the lower end-plug 12a, and the outer periphery surface of the solid columnar portion of the connection 21. The reliability of the joint strength can be further improved by mechanically fastening the fuel cladding tube 11 and the lower end-plug 12a with the threaded structure 12e via the connection 21. Considering the thickness of the fuel cladding tube 11, the threaded structure 12e is preferably a wide threaded structure (for example, shallow thread depth, and a wide thread pitch). Such a wide threaded structure may be used as long as the connection 21 can remain screwed and attached to the fuel cladding tube 11 and the lower end-plug 12a under the frictional force between the screwed external thread and internal thread. FIG. 6 shows a side view and an elevational view of the fuel cladding tube 11 shown in FIG. 1, along with an enlarged cross sectional view of the joint shape of the fuel cladding tube 11. FIG. 7 shows a side view and an elevational view of the lower end-plug 12a shown in FIG. 1, along with an enlarged cross sectional view of the joint shape of the lower end-plug 12a. FIG. 8 shows a side view and an elevational view of the connection 21 disposed in a joint region inside the fuel cladding tube 11 and the lower end-plug 12a shown in FIGS. 6 and 7. As illustrated in FIG. 6, the butt joint interface 11a formed at the end portion of the hollow cylindrical fuel cladding tube 11 (the end portion on the left-hand side of the side view in FIG. 6) has a slanted surface that makes the outer diameter of the fuel cladding tube 11 smaller toward the tip, as shown in the enlarged cross sectional view. The butt joint interface 11a creates a slope angle θa with the inner periphery surface of the fuel cladding tube 11. Specifically, the butt joint interface 11a is slanted with a slope angle θa with respect to the axial direction of the fuel cladding tube 11. As illustrated in FIG. 7, the butt joint interface 12d formed at the end portion of the cylindrical portion constituting the concave portion 12f of a curved surface shape of the lower end-plug 12a (the end portion on the right-hand side of the side view in FIG. 7) has a slanted surface that makes the inner diameter of the cylindrical portion constituting the concave portion 12f of a curved surface shape larger toward the tip, as shown in the enlarged cross sectional view. The butt joint interface 12d creates a slope angle θb with the inner periphery surface of the cylindrical portion constituting the concave portion 12f of a curved surface shape. Specifically, the butt joint interface 12d is slanted with a slope angle θb with respect to the axial direction of the lower end-plug 12a. The slope angles θa and θb are the same, and allow contact between the butt joint interface 11a of the fuel cladding tube 11 and the butt joint interface 12d of the lower end-plug 12a. The alignment accuracy between the fuel cladding tube 11 and the lower end-plug 12a can improve with the slope angle θa provided at the butt joint interface 11a of the fuel cladding tube 11, and the slope angle θb provided at the butt joint interface 12d of the lower end-plug 12a. This also increases the joint area between the butt joint interface 11a and the butt joint interface 12d, and can improve the joint strength and air-tightness. Because the butt joint interface 11a of the fuel cladding tube 11 and the butt interface 12d of the lower end-plug 12a are slanted with the slope angles θa and θb, respectively, a crack that propagates under the repeated stress caused by the internal-external pressure difference across the nuclear fuel rod 10a in the manner described above does not penetrate the nuclear fuel rod 10a. In order to obtain these effects, the slope angles θa and θb are preferably 30 to 800, desirably 45 to 600. The alignment accuracy improving effect can be obtained with slope angles θa and θb larger than 800. However, these angles are not sufficient to reduce crack propagation to the butt joint interface 12d. Processibility suffers, and chipping tends to occur at the tips of the butt joint interfaces 11a and 12d when the slope angles θa and θb are less than 30°. Referring back to FIG. 7, the lower end-plug 12a has an outer diameter constriction 12g in a region that interdigitates with the lower tie plate of a fuel assembly (not illustrated), at a predetermined distance to the left along the lengthwise direction from the right dashed-dotted line of the side view. The outer diameter constriction 12g has such a shape that makes the outer diameter gradually smaller toward the tip of the lower end-plug 12a (toward the end portion on the left-hand side of the side view in FIG. 7). Specifically, the outer diameter constriction 12g is gradually sloped. The connection 21 is configured from a columnar portion, and a curved surface portion 21a approximated to a portion of a spherical surface, as shown in the side view of FIG. 8. FIG. 9 is a partial schematic cross sectional view of a nuclear fuel rod according to another embodiment of the present invention. As illustrated in FIG. 9, the nuclear fuel rod 10b according to the present embodiment differs from the nuclear fuel rod 10a shown in FIG. 1 in that a joint covering 14 of a coating metal having high corrosion resistance is provided over the outer periphery surface including the joint between the lower end-plug 12a and the fuel cladding tube 11, and the outer periphery surface including the joint between the upper end-plug 12b and the fuel cladding tube 11. FIG. 10 is an enlarged schematic cross sectional view representing an example of the joint between the fuel cladding tube 11 and the lower end-plug 12a shown in FIG. 9. FIG. 11 is an enlarged schematic cross sectional view representing an example of the joint between the fuel cladding tube 11 and the lower end-plug 12a shown in FIG. 9. As illustrated in FIG. 10, the joint covering 14 covers the butt joint interface 11a of the fuel cladding tube 11, and the butt joint interface 12d of the lower end-plug 12a. The lower end of the joint covering 14 is below the depression constituting the concave portion 12f of a curved surface shape of the lower end-plug 12a. The upper end of the joint covering 14 is above the upper end portion of the connection 21 disposed in the fuel cladding tube 11 and in the concave portion 12f of a curved surface shape of the lower end-plug 12a. The joint covering 14 shown in FIG. 11 also covers the butt joint interface 11a of the fuel cladding tube 11 and the butt joint interface 12d of the lower end-plug 12a, and has a lower end below the depression constituting the concave portion 12f of a curved surface shape of the lower end-plug 12a, and an upper end above the upper end portion of the connection 21 disposed in the fuel cladding tube 11 and in the concave portion 12f of a curved surface shape of the lower end-plug 12a. As described above, the nuclear fuel rod 10b of the present embodiment has the joint covering 14 having high corrosion resistance covering the outer periphery surface including the joint between the lower end-plug 12a and the fuel cladding tube 11, and the outer periphery surface including the joint between the upper end-plug 12b and the fuel cladding tube 11. This further improves the joint strength compared to the nuclear fuel rods 10a shown in FIGS. 1, 4, and 5. Fuel Assembly FIG. 12 is a schematic longitudinal sectional view of a fuel assembly according to an embodiment of the present invention. FIG. 13 is a cross sectional view of the fuel assembly of FIG. 12 at A-A. The fuel assembly 30 shown in FIGS. 12 and 13 is an example of a fuel assembly for boiling-water reactors (BWR), and includes an upper tie plate 31, a lower tie plate 32, a plurality of nuclear fuel rods 10 held to the upper tie plate 31 and the lower tie plate 32 at the both ends, water rods 33 (also referred to as water channels), a fuel support grid (spacer) 34 binding the nuclear fuel rods, and a channel box 35 attached to the upper tie plate 31 and surrounding the fuel rods bundled by the fuel support grid 34. A handle 37 is fastened to the upper tie plate 31, so that the whole fuel assembly 30 can be pulled up by lifting the handle 37. Some of the nuclear fuel rods are short part-length rods 36 of a height that does not reach the upper tie plate 31. Specifically, the short part-length rods 36 are nuclear fuel rods of a height that does not reach the upper tie plate 31, with a shorter effective fuel length than the nuclear fuel rods 10 (also called long part-length rods) inside the assembly. As illustrated in FIG. 13, the nuclear fuel rods 10 (long part-length rods), the short part-length rods 36, and the water rods 33 are bundled in a square grid pattern, and housed inside the channel box 35 having a square-shaped transverse section. In this example, two water rods 33 are disposed at substantially the center of a transverse section of the channel box 35, and each water rod 33 is disposed in a grid region that can accommodate four nuclear fuel rods 10 (long part-length rods). The water rods 33 in the fuel assembly 30 may be zirconium alloy water rods. However, considering a rare but possible incidence of loss-of-coolant accident (LOCA), it is preferable that the water rods 33 have the same configuration as the nuclear fuel rods 10, specifically a configuration with a hollow tube and end plugs made of a SiC material, and in which the hollow tube and the end plugs are joined to each other via the metallic joint material 20. The water rods 33 also may have a configuration in which the joint covering 14 covers the joint area where the hollow tube and the end plugs are joined to each other via the metallic joint material 20. In order to shield the SiC itself from the coolant water environment inside the nuclear reactor, it is preferable to cover the water contacting surfaces of the water rods 33 and the channel box 35 with a Zr-, Ti-, or Cr-based alloy or compound of a thickness of about at most 100 μm, in addition to the nuclear fuel rods 10 and the short part-length rods 36. The method used to form the environmental barrier coating is not particularly limited, and methods, for example, such as a physical vapor deposition method (PVD method), a chemical vapor deposition method (CVD method), and a coating and sintering method may be used. For improved adhesion between the environmental barrier coating and the SiC base material, it is preferable to reduce the thermal expansion difference by controlling the chemical composition or the proportion of the constituent phase. FIG. 14 is a schematic transverse sectional view representing an example of a boiling-water reactor cell. As illustrated in FIG. 14, a cell 40 of a boiling-water reactor (BWR) has four fuel assemblies 30 that are disposed in a square pattern, and control rods 41 that are arranged in a substantially crossed pattern at the center in a transverse section. With the nuclear fuel rods 10 and the fuel assemblies 30 of the present embodiment, the cell 40 can have improved safety against emergency situations (for example, a loss-of-coolant accident) while maintaining the current level of long-term reliability under a normal operating environment. FIG. 15 is a partially transparent external perspective view of a fuel assembly loaded into a pressurized-water reactor. As illustrated in FIG. 15, the fuel assembly 50 is an example of a fuel assembly for pressurized-water reactors (PWR), and includes a plurality of nuclear fuel rods 10, a plurality of control rod guide thimbles 51, an incore instrumentation guide thimble 52, a plurality of support grids (spacers) 53 that bundles and supports these components, an upper nozzle 54, and a lower nozzle 55. The upper nozzle 54 and the lower nozzle 55 are provided as frame members of the fuel assembly 50, and to locate the fuel assembly 50 in the reactor core, or to provide channels for coolant water. The incore instrumentation guide thimble 52 is provided to guide incore instrumentation devices, such as a local power range monitor (LPRM), and an average power range monitor (APRM), to the reactor core. FIG. 16 is a schematic transverse sectional view representing an example of a pressurized-water reactor cell. As illustrated in FIG. 16, four fuel assemblies 50 are directly disposed in a square pattern in the pressurized-water reactor (PWR) cell 60 because the fuel assemblies 50 have control rods therein. With the nuclear fuel rods 10 and the fuel assemblies 50 according to the present embodiment, the cell 60 also can have improved safety against emergency situations (for example, a loss-of-coolant accident) while maintaining the current level of long-term reliability under a normal operating environment. The foregoing embodiments described the nuclear fuel rods (10, 10a, and 10b) in which silicon carbide (SiC) is used as a constituent material of the fuel cladding tube 11, the lower end-plug 12a, the upper end-plug 12b, and the connection 21. However, the present invention is not limited to these embodiments. For example, the present invention is also applicable to a hollow tubular body (cladding tube) configured from common oxide ceramic materials such as alumina (Al2O3), zirconia (ZrO2), and mullite (Al6O13Si2) and having lids made of such materials, and that is sealed against high temperature and/or high pressure, and exposed to a corrosive environment. The following describes the present invention in greater detail as Examples. It is to be noted that the present invention is not limited by the following Examples. Experiment for Joining SiC Material with Metallic Joint Material A plurality of metallic joint materials 20 was prepared, and experiments were conducted by joining a SiC mock fuel cladding tube and a SiC mock end plug. The SiC mock fuel cladding tube and the SiC mock end plug were used after forming a SiC layer on the surfaces. Table 1 shows details of the metallic joint materials prepared. TABLE 1Details of metal joint materialsAverage linearHeating temperature inSoliduscoefficient ofelectric furnaceMaterialComposition (mass %)temperature (° C.)expansion (ppm/K)JointSiC2,7304.3 to 6.6materialEx. 11,450 to 1,514° C.SiC: 0.08% or less, Si: bal.1,404 to 1,4143.3Ex. 21,250 to 1,514° C.Si alloyGe: 50% or less, C: 0.08% or less,1,200 to 1,4143.5 to 5.0Si: bal.Ex. 3Mo: 5% or less, W: 20% or less,1,207 to 1,4143.5 to 4.0Fe: 40% or less, Si: bal.Ex. 41,450 to 1,514° C.Ti: 2% or less, Zr: 2% or less,1,242 to 1,4143.5 to 4.0Ta: 2% or less, Nb: 2% or less,V: 2% or less, Y: 2% or less,Cr: 2% or less, Si: bal.Ex. 51,200 to 1,400° C.TiFe: 0.3% or less, C: 0.08% or1,635 to 1,6568.6less, Ti: bal.Ex. 6Ti alloyZr: 50%, Fe: 0.3% or less,1,480 to 1,5537.5C: 0.08% or less, Ti: bal.Ex. 7ZrFe: 0.3% or less, C: 0.08% or1,740 to 1,8555.7less, Zr: bal.Ex. 8Zr alloySn: 1.2 to 1.7%, Ni: 0.03 to1,643 to 1,7446.50.08%, Fe: 0.07 to 0.2%, Cr: 0.05to 0.15%, Ti: 0.005% or less, Zr:bal.Ex. 9Sn: 1.2 to 1.7%, Fe: 0.18 to1,656 to 1,7066.50.24%, Cr: 0.07 to 0.13%, Ti:0.005% or less, Zr: bal.Ex. 10Nb: 1 to 2.5%,Ti: 0.005% or less,1,811 to 1,8536.5Zr: bal. As shown in Table 1, the metallic joint material used in Example 1 contained 0.08% or less C, and the balance Si. The metallic joint material used in Example 2 contained 50% or less Ge, 0.08% or less C, and the balance Si. The metallic joint material used in Example 3 contained 5% or less Mo, 20% or less W, 40% or less Fe, and the balance Si. The metallic joint material used in Example 4 contained 2% or less Ti, 2% or less Zr, 2% or less Ta, 2% or less Nb, 2% or less V, 2% or less Y, 2% or less Cr, and the balance Si. The metallic joint material used in Example 5 contained 0.3% or less Fe, 0.08% or less C, and the balance Ti. The metallic joint material used in Example 6 contained 50% Zr, 0.3% or less Fe, 0.08% or less C, and the balance Ti. The metallic joint material used in Example 7 contained 0.3% or less Fe, 0.08% or less C, and the balance Zr. The metallic material used in Example 8 contained 1.2 to 1.7% Sn, 0.03 to 0.08% Ni, 0.07 to 0.2% Fe, 0.05 to 0.15% Cr, 0.005% or less Ti, and the balance Zr. The metallic joint material used in Example 9 contained 1.2 to 1.7% Sn, 0.18 to 0.24% Fe, 0.07 to 0.13% Cr, 0.005 or less Ti, and the balance Zr. The metallic joint material used in Example 10 contained 1 to 2.5% Nb, 0.005% or less Ti, and the balance Zr. A SiC mock fuel cladding tube, and a SiC mock end plug were prepared that had a SiC layer formed on the surface, and the metallic joint material (thickness of about 0.2 mm) of each Example was deposited on the SiC mock fuel cladding tube and the SiC mock end plug on one of the surfaces, using a vapor deposition method. The SiC mock fuel cladding tube, and the SiC mock end plug were then butted (contacted) to each other with the deposited metallic joint material coatings facing each other, and subjected to a compression heat treatment (under a stream of argon) with an electric furnace. The heating temperature was 1,450 to 1,514° C. in Examples 1 and 4, 1,250 to 1,514° C. in Examples 2 and 3, and 1,200 to 1,400° C. in Examples 5 to 10. After forming a joint under heat, a joint cross section was polished, and the microstructure of the joint region was observed under a light microscope. Observations of the microstructure in the joint region found that Examples 1 to 4 (Si, and a Si alloy) had microstructures primarily from brazing (braze structure), and that Examples 5 to 10 (Ti, a Ti alloy, Zr, and a Zr alloy) had microstructures primarily from diffusion joining (diffusion joint structure). Cracks or communicating gas pockets were not observed in the joint region in any of the Examples. The specific descriptions of the foregoing embodiments are intended to help understand the present invention, and the present invention is not limited to having all the configurations described above. For example, a part of the configuration of a certain embodiment may be replaced with the configuration of some other embodiment, or the configuration of a certain embodiment may be added to the configuration of some other embodiment. It is also possible to delete a part of the configuration of any of the embodiments, or replace a part of the configuration with other configuration, or add other configurations. 10, 10a, and 10b: Nuclear fuel rod 11: Fuel cladding tube 11a: Butt joint interface 12a: Lower end-plug 12b: Upper end-plug 12c: Straight barrel insert 12d: Butt joint interface 12e: Threaded structure 12f: Concave portion of a curved surface shape 12g: Outer diameter constriction 13: Fuel pellet 14: Joint covering 15: Retainer spring 20: Metallic joint material 21: Connection 21a: Curved surface portion 30: Fuel assembly 31: Upper tie plate 32: Lower tie plate 33: Water rod 34: Fuel support grid (spacer) 35: Channel box 36: Short part-length rod 37: Handle 40: Cell 41: Control rod 50: Fuel assembly 51: Control rod guide thimble 52: Incore instrumentation guide thimble 53: Support grid 54: Upper nozzle 55: Lower nozzle 60: Cell |
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description | 1. Field of the Invention The present invention generally relates to the problem of excessive repair expense and increased equipment down-time due to inaccurate initial diagnosis of equipment failure. 2. Description of the Related Art The present invention generally relates to the problem of excessive repair expense and increased equipment downtime due to inaccurate initial diagnosis of equipment failure. This problem can occur when maintenance personnel do not have access to historic information regarding similar or recent failures and repairs. It can also occur when a repair technician is inexperienced on the tool he or she is trying to repair, or is still in training. The cause of an equipment failure in a factory is frequently not initially apparent. A maintenance technician will make a diagnosis and repair based on their training and experience level. With no access to historic data related to prior repairs, parts may be repaired or replaced without resolving the failure. Trial and error replacement of parts continues until the equipment is operational. Unnecessary replacement of parts results in extended equipment Mean Time To Repair (MTTR) and increased spending on components, some of which are quite expensive. This process results in additional equipment downtime if a new component is removed and returned to the spare parts inventory and the original part is reinstalled. An additional concern is that the lack of visibility to effective versus ineffective repairs can result in learning incorrect repair processes. The invention presents a computerized method, system, service, etc. for tracking equipment repair that begins by receiving an equipment identification of an item of equipment to be repaired from a user through a graphic user interface. The invention provides the user with a list of common problems for that item of equipment (and similar equipment) and a component hierarchy for the item of equipment. The invention allows the user to browse through multiple levels of the component hierarchy and select a major component, a minor component, or a subcomponent from the component hierarchy. The invention receives diagnosis input from the user optionally selecting one of the problems and/or a component from the component hierarchy and, in response, provides the user with detailed information based on prior failures for the problem and/or component selected by the user. Such detailed information comprises, for each direct subcomponent, the number of failures, the probability of failure, the mean time between failures, the occurrence of the most recent failure for each component and the next expected failure, etc. This process of providing the detailed information includes providing detailed information for similar equipment as a group, and lists detailed repair information for all successful repairs related to the selected problem and component (if any), with the most recent successful repairs being listed first. This detailed repair information can also include technician comments related to the repair and information regarding which repairs did not solve the problem. If no problem is selected by the user, the detailed repair information comprises all successful repairs for any problem and matching the component selected by the user, and if no components are selected by the user, the detailed repair information comprises solutions for repair of major components. The invention receives history input from the user (after the item of equipment is repaired) regarding repair activities and the invention maintains a database of the detailed information based on the history input from the user. The invention calculates the mean time between failures by only using successful repairs and considers repairs that were repeated within a predetermined time of the most recent failure to be unsuccessful. The invention also keeps track of which piece of equipment required the repair. Tools of a similar type are stored in a database table keyed by group name which allows real time calculation of failures for similar tools. Further, the invention calculates the probability of failure (e.g., in real time) for each major component, subcomponent, etc., by calculating how often a certain component fails, or how often a certain component is the cause of a failure. The information regarding the mean time between failures and the time since the last actual failure maintained by the database is very useful to provide guidance as to whether a certain component should be expected to fail and is likely the cause of the problem. Therefore, with the invention, historic information and calculated probability of component failure combined with even limited experience on the part of the technician will enable more accurate first time diagnosis of failures. The system provides an opportunity for cross training as technicians reference and learn from repair actions and comments entered by other technicians for past similar problems. This information is invaluable in determining which repair diagnosis and actions were successful and which were not. These, and other, aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. The present invention and the various features and advantageous details thereof are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the present invention. The examples used herein are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those of skill in the art to practice the invention. Accordingly, the examples should not be construed as limiting the scope of the invention. The invention is a computerized method that uses historic information to predict the likely cause of a current failure. The historic data is gathered when technicians enter information in the system every time a repair is completed. This includes tool ID, date/time, technician, problem, components involved, action taken and associated comments. The mean time before fail (MTBF) and next expected fail values are calculated from this information and stored for the problem and component hierarchy for the specific tool. If a problem recurs within a specified time frame, the prior fail diagnosis and repair is considered incorrect/unsuccessful and the MTBF values are recalculated with the unsuccessful repair being ignored. All comments entered at the time of the unsuccessful original repair are linked to the new repair to provide not only a history of what was useful, but also a history of what did not solve the problem, so as to allow future repairs to avoid the mistakes of the past. The invention gives maintenance personnel specific probable failure analysis and historic repair information when they encounter a new failure. In one embodiment, the invention resides in a web based system and is accessible from any terminal (e.g., a wired terminal on a manufacturing floor, or through a wireless internet connection at a remote site serviced by a field technician). FIG. 1 illustrates the database 10 that maintains the repair history. The database 10 includes data on the items of equipment (the “tool type data”) including the component hierarchy, failure descriptions, common problems and actions, and processes used to repair the components. The database 10 also includes failure data and information about the repair including the problem, the action taken, the date and time of the repair, the technicians name, the failed components, etc. The invention calculates the mean time between failures by tool based upon this information. Item 12 represents the central processing unit running the invention as software within a computerized system and items 14 represent wired or wireless terminals connected to the central processing unit 12 through any form of computerized network. In FIG. 1, item 16 represents the failure diagnosis provided to the technician by the invention. The technician inputs an identification of the tool (item of equipment), as well as optionally selecting the problem and the suspected defective components causing the problem. In response to the input provided by the technician, the invention provides the technician with data that will help solve the problem including the subcomponent failure probability (based on the history of failures with similar parameters), and the mean time before failure values by subcomponent. In addition, the invention provides the time, date, technician identification, problem identification, actions taken (successful and unsuccessful), failed components, technician's comments, etc. related to the previous repairs. This aspect of the invention can also provide troubleshooting guidelines and other similar documentation and repair instructions. Therefore, the invention receives history input from the user (after the item of equipment is repaired) regarding repair activities and the invention maintains a database 10 of the detailed information based on the history input from the user 14. The invention recalculates and stores (using CPU 12) the mean time between failures by only using successful repairs and ignoring repairs that were effected within a predetermined time prior to of the most recent failure for the same problem and component set. More specifically, the invention records when each component fails on a specific piece of equipment and the common problem defining the failure to provide a history of how long each component operates properly before failure. The invention calculates one or more statistical values, such as mean (average), mode, median, etc. relating to when the component would normally be expected to fail on the specific machine. This information can then be retrieved and processed in a variety of ways, including grouping similar tools, predicting failure of components for a given problem (or any problem), predicting failure of any level of the component hierarchy, etc. Further, the invention calculates the probability of failure for each major component, subcomponent, etc., by calculating how often a certain component fails, or how often a certain component is the cause of a failure over time. The information regarding the mean time between failures and the time since the last actual failure maintained by the database is very useful to provide guidance as to whether a certain component should be expected to fail and is likely the cause of the problem. The database 10 also keeps track of technician comments related to the repair, linking those subsequently deemed ineffective (based on recurrence of the problem in a given time period) to the most recent repair. Therefore, if a component has been in place well past its expected useful life (based on repair history in the database 10), the technician can properly be more suspicious of the older component, and consider the component to more likely be a cause of the problem (and vice versa with respect to components that have not reached their life expectancy). When this information regarding whether a component has met or exceeded its life expectancy is combined with information regarding which repair activities were successful or unsuccessful, the probability that the repair technician will perform the proper repair the first time and avoid making unnecessary repairs is substantially increased. Further, this aspect of the invention helps reduce the time it takes to diagnose a problem because the invention relies upon statistical information (mean time before failure) to help guide the technician to the correct diagnoses. The invention receives diagnosis input from the user optionally selecting one of the problems and/or a component from the component hierarchy and, in response, provides the user with detailed information regarding the problem or component selected by the user. Such detailed information comprises, for each direct subcomponent, the number of failures, the probability of failure, the mean time between failures, the occurrence of the most recent failure for each component, the next expected failure, etc. This process of providing the detailed information includes providing detailed information for similar equipment and all successful repairs related to the problem, with the most recent successful repairs being listed first. This detailed information can also include information regarding which repairs did not solve the problem. If no problem is selected by the user, the detailed information comprises all successful repairs matching the component selected by the user, and if no components are selected by the user, the detailed information comprises solutions for repair of major components. As shown in flowchart form in FIGS. 2A–2C, the technician enters a tool ID 200 and is presented with a list of common problems and the component hierarchy for tools of the same type 202. The technician can optionally select the common problem that describes the current failure 204 and/or optionally select a specific subcomponent using “drill down” through the component hierarchy if a particular area is suspect 206. The system searches the history data for fails matching the chosen problem and components 210, 214, 218, 220. More specifically, if the user identifies a problem and components 208, the invention searches for the common problems and components of the identified tool (or matching tool type) 210. If the user identifies a problem 212, the invention searches for the common problems with the identified tool (or matching tool type) 214. If the user identifies components 216, the invention searches for the components of the identified tool (or matching tool type) 218. If the user does not select a common problem or component, the invention searches historical data for failures matching the tool type and major components for all problems 220. Thus, there are several special cases which will result in a modified view of the information. If no common problem is selected, the information is presented for all successful repairs matching the selected components without regard to the problem. If no subcomponents are chosen, the information is presented for the major components defined for the tool type relating to the common problem selected. There may be an insufficient number of prior fails for a particular tool to provide guidance. In this instance, successful repair and comment information for all tools of the same type will be displayed. Information for the selected tool is listed first, followed by information for the rest of the tool type. Item 222 in FIG. 2B illustrates that the invention calculates the number of failures and probability of failure for each component, for each tool and tools of the same type. This processing can be done in response to a problem inquiry by a user or can be performed in advance with the results being stored in the database 10. In one embodiment, the probabilities of failure statistics are updated periodically, or each time a repair is made. Then, depending upon the information input by the user, the invention retrieves the mean time before failure, last failure occurrence, next expected failure, etc. for each component of the selected tool. Item 226 represents a decision block as to whether a specific tool has a statistically significant number of failures. Therefore, if a certain tool is experiencing a higher level of failure that other similar tools, the technician can be so advised. More specifically, if a certain tool does not show a statistically significant number of failures, the invention retrieves the repair information for the tool and for other similar tools including the problem, date and time of last repair, technician who made the previous repairs, action taken to resolve the problem, components involved in the failure, etc., as shown in item 228. However, if a tool has a statistically significant number of failures, the invention retrieve similar information only for the specific tool as shown in item 230. Therefore, if one individual piece of equipment tends to have a certain type of failure (that could be related to tool defect, tool usage, tool environment, etc.) that is unusual when compared to other similar tools, the technician is not provided with information regarding the other tools and is only provided information with respect to the tool in question. For example, a tool that is used within a harsh environment may suffer from repeated component failures that other similar tools used within mild environments do not suffer. Therefore, in such a situation, information regarding how other similar tools were repaired may be misleading for the tool that operates within the harsh environment. Once again, this decreases diagnostic time and increases the accuracy of the diagnoses by providing the technician with statistically relevant information. Item 232 demonstrates that the invention also retrieves comments for associated prior repairs, which can include information relating to repairs that were not successful, in order to help the technician avoid making unnecessary and ineffectual repairs. Comments for a failed repair attempt are specially marked and shown along with the comments for the ultimately successful repair. This provides the ability for the technician to see what actions resolved similar failures. Equally important, it also lets them learn which actions were ineffective. The technician then receives the following information (for each direct component for the tool) the number of fails (also for tools of the same type), the probability of failure (also for tools of the same type), MTBF, prior failure date/time, and the next expected fail date/time 234. Once a diagnosis has been made, the technician can directly access web based guides 236, 238 which contain step-by-step procedures, failure analysis guides and other documentation to complete the necessary repair. The process can then be repeated for a new tool 240, for the same tool 242, or ended. Thus, the technician may choose to select new sub components based on this information and start the search again 242. This provides the ability to drill down through the component hierarchy to find the predicted failure probability for any component. Therefore, with the invention, information for all successful prior repairs (most recent first) which match the technician's input are provided to the technician. Historic information and calculated probability of component failure combined with even limited experience on the part of the technician will enable more accurate first time diagnosis of failures. The system provides an opportunity for cross training as technicians reference and learn from repair actions and comments entered by other technicians for past similar problems. This information is invaluable in determining which repair diagnosis and actions were successful and which were not. Additionally, the invention allows the technician the ability to search the historical comment information for any combination of values. For instance, they may want to find all comments related to a particular tool, component, problem, or action taken. The invention is applicable to all forms of equipment and all types of service industries that perform repairs including, manufacturing, construction, computers, automotive, appliances, industrial, household, medical, etc. Further, the invention is useful with all systems that use some form of computerized repair tracking including stand alone computer systems, local area networks, wide area networks, worldwide networks, wired and wireless systems, etc. Other benefits of the invention include reduced tool down time, reduced problem determination time, and improved “fixed right the first time” statistics. The invention provides technicians the information they need in one place history, diagnostics and access to online repair manuals and instructions. The invention can also reduce unnecessary replacement of parts and associated costs as prior learning will show which repairs are effective and which are not. The invention also provides education of newer technicians at the time of repair using historical repair information, with less need to “consult the expert”. The invention can also be used to manage spare parts inventory using “next predicted fail” data reducing the need to carry extra inventory common with “buy “n” parts when inventory reaches “x”” or “replace as used” schemes. While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. |
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abstract | Method and apparatus for rapid monitoring of pressure in a chamber equipped with a mass spectrometer by using the primary beam current in conjunction with a conventional pressure gauge. The conventional gauge allows frequent calibration of the relationship of the beam current to the chamber pressure, preventing excessive drift in the system. An advantage of the system is that it takes advantage of instruments already present in a typical spectrometry apparatus. |
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052241459 | abstract | An X-ray beam limiting apparatus, is used for a stereoscopic X-ray tube with two focal points separated from each other by a distance of approximately 35 mm. The X-ray beam limiting apparatus includes pivotable blade means for beam-limiting inner edges of pyramid-shaped X-ray beams emitted from the first and second X-ray focal points, while pivoting around center lines of first and second pivotable shafts positionally shifted with each other; and, first slidable blade means for beam-limiting outer edges of the pyramid-shaped X-ray beams emitted from the first and second X-ray focal points, while sliding on a plane substantially perpendicular to travelling paths of the pyramid-shaped X-ray beams. |
041479386 | description | DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A spent nuclear fuel cask is generally designed to achieve at least the following goals to provide for the safe containment and transportation of spent nuclear fuel: (1) Prevention of escape of radioactive fission fragments, (2) Shielding of hazardous penetrating radiation, (3) Dissipation of thermal energy generated in radioactive decay, and (4) Assurance of the continued performance of the first three goals in spite of accidents such as collision, derailment, or fire. In FIG. 1 such a spent nuclear fuel cask 10 is seen employing the bimetallic band fire protector of this invention. Within the cask is a chamber 12 adapted for containing spent nuclear fuel. Also within the chamber there may be a heat transfer fluid for transmitting the heat generated by the fuel to the inner shell 14. This heat may be substantial, about 1 Kw per fuel pin with the surface temperature of the pin as high as 1000.degree. F. The heat transfer fluid may be a metal alloy such as lead-bismuth, sodium-potassium, or sodium; a gas such as helium or argon; a liquid such as water or organic compounds; or a heat transfer salt such as NaNO.sub.3 --NaNO.sub.2 --KNO.sub.2 ; or the like. The inner shell serves to contain the spent fuel and heat transfer fluid, provide a barrier to the spread of radioactive contamination, and provide structural strength to the cask. Surrounding the inner shell is a layer of nuclear shielding 16. The function of the nuclear shielding is to attenuate and absorb gamma and neutron radiation emitted by the spent nuclear fuel carried with the chamber 12. It may be advantageous to construct the nuclear shielding of multiple layers of different materials for attenuating the radiation and it may even be advantageous to place a portion of the shielding exterior to outer shell 18. Materials suitable for gamma shielding generally have high atomic weights and include lead, uranium, and depleted uranium. Materials suitable for neutron shielding generally have low atomic weights and include hydrogenous materials, water, metal hydrides, boron carbide, boron carbide-copper cermet, borated beachwood, hydrocarbons and the like. Suitable shielding materials also satisfactorily pass heat from the inner shell to the outer shell 18. The outer shell furnishes an additional barrier to the spread of radioactive contamination, provides additional structural strength, and supplies a convenient surface for the attachment of heat rejecting fins 20. The use of heat rejecting fins increases the surface area of the cask from which thermal energy can be rejected through the processes of radiation, conduction, or convection. In an accident environment, such as a fire, the heat rejecting fins may serve to conduct additional heat into the cask. This, of course, is undesirable insofar as it adversely affects the structural integrity of the cask or its contents. The method of the present invention utilizes a bimetallic band 22 to reduce the effective surface area of the fins during a fire and thus reducing the heat input to a cask during such as accidental occurrence. The bimetallic band, as 22a, is normally disposed between two adjacent fins and close to the outer surface of the outer shell where the band does not interfere with the rejection of heat by the fins. Should the cask be exposed to a high heat source such as a fire, the bimetallic band automatically expands outwardly, as 22b, interfering with radiation or convective heat transfer. The band may be restrained from over expanding by the use of a band retainer 24. As pictured, the band retainer may be a plurality of rods or pins positioned transverse to the fins, at the periphery of the fins. The bimetallic band may be fabricated from two strips of metal having dissimilar expansivities bent to a desired radius and affixed together along a side. It can be shown that a bimetallic strip of two dissimilar metals of equal thickness, t, will, if at an initial radius of curvature R.sub.1 expand to R.sub.2 in the temperature interval ##EQU1## The .alpha.'s and E's are the respective expansivities and elastic moduli of the component materials. The choice of materials is affected by the need for good response to a moderate rise in temperature, and the ability to withstand a high temperature. Although many such alloys will be obvious to those skilled in the art, two which may be used are type 304 stainless steel (18% Cr, 8% Ni, balance Fe) and Kovar (29% Ni, 17% Co, balance Fe). For 304SS-Kovar, .alpha..sub.a -.alpha..sub.b = 11 .times. 10.sup.-6 /.degree. C., and K = 1.34. For use in a cask with an exterior radius of 18.4 cm and a fin radius of 22.7 cm a 304SS-Kovar band with t of 0.076 cm will perform the desired expansion within a temperature change of 100.degree. C. The bimetallic band may be fabricated by forming the different metal strips to the desired radius of curvature and then affixing them together along one side with the higher expansivity metal being on the inside of the curve. It has been found that spot welding the strips at 1.8 cm intervals gives satisfactory results. The band may be fabricated such that the ends overlay in the normal position and so that full protection is afforded in the expanded position. Other materials which behave similarly to bimetallic strips may also be used. One example is the uranium-niobium alloy of U.S. Pat. No. 3,567,523 which displays thermally reversible, pseudo-plastic strain behavior. Referring now to FIG. 2, which is a fragmentary cross section of a nuclear fuel cask showing a portion of the outer shell 18 with three fins 20 attached to the outer surface, a bimetallic band 22a is shown in its normal position between two fins adjacent the surface of the outer shell. This bimetallic band is made up of two dissimilar metal strips 26 (Kovar) and 28 (304 stainless steel). The strip with the higher expansivity is located inwardly so as to cause an expansion or increase in the radius of curvature of the band upon application of heat. The band is also shown as 22b in its expanded position. It is restrained from overexpansion by band retainer 24 which may be an enlargement of the fin cross section near the periphery of the fin. As can be seen, much of the fin surface is exposed when the band is in its normal position; and much of the fin surface is hidden when the band is in its expanded position. EXAMPLE I A one-quarter scale simplified model of a spent nuclear fuel cask was constructed. The cask body was simulated by thirty-four circular steel plates 0.635 cm thick and 36.8 cm in diameter. The fin portion was simulated by seventeen circular copper plates 0.163 cm thick and 45.4 cm in diameter. These plates were stacked, alternating two steel plates with one copper plate, and bolted together to form a cylinder with radial fins. A 2.5 cm hole penetrated the center of each plate simulating a central cavity as well as affording access for chromel-alumel thermocouples. Bimetallic bands were fabricated from strips of 304 stainless steel and Kovar, each 0.076 cm thick, 1.22 cm wide, and 150 cm long. The strips were bent to the desired circular shape with the steel on the inside and then spot welded at 1.8 cm intervals. One bimetallic band was placed around the cask model and between each adjacent pair of fins. With thermocouples placed near the center and near the edge of the cask model, the model was subjected to a test fire. This test fire was simulated by a pair of butane torches, with 7 cm throats, directed at the side of the cask from a distance of 15 cm for one-half hour. Cask surface temperatures ran as high as 180.degree. C. for a band-protected cask, as opposed to as high as 295.degree. C. for an unprotected cask. Central temperatures were 115.degree. C. for a band-protected cask, as opposed to 145.degree. C. for an unprotected cask. EXAMPLE II Heat flow calculations were performed using the CINDA code (Chrysler Improved Numerical Differencing Analyzer for 3rd Generation Computers, Chrysler Corp. Space Div., New Orleans, LA). For the purposes of these calculations, the cask was assumed to be 3 meters long with an internal generation of 100 Kw of heat. With fin area equal to 15.times. cask surface area, a skin temperature of 82.degree. C. was calculated in an ambient temperature of 57.degree. C. A possible cross section of the cask was assumed to have the following radial dimensions: TABLE I ______________________________________ LAYER RADIAL DIMENSION ______________________________________ Central cavity 41 cm Inner steel shell 7 cm Uranium gamma shield 5 cm Lithium hydride neutron shield 5 cm Uranium gamma shield 6 cm Outer steel shell 6 cm Fin 16 cm ______________________________________ The assumed fire was at 802.degree. C. and lasted 0.5 hour; it was treated as a surface of unit emittance with all heat transferred by radiation. The results of the heat flow calculation are displayed in FIG. 3. Curve 1 shows the steady state temperatures with the cask surface fixed at 82.degree. C. and 100 Kw generated internally. Curve 2 shows the maximum internal temperatures due to exposure without fire protection. Curve 3 shows the maximum internal temperature with fire protection. The various features and advantages of the invention are thought to be clear from the foregoing description. However, various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims. |
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abstract | An ion beam machining and observation method relevant to a technique of cross sectional observation of an electronic component, through which a sample is machined by using an ion beam and a charged particle beam processor capable of reducing the time it takes to fill up a processed hole with a high degree of flatness at the filled area. The observation device is capable of switching the kind of gas ion beam used for machining a sample with the kind of a gas ion beam used for observing the sample. To implement the switch between the kind of a gas ion beam used for sample machining and the kind of a gas ion beam used for sample observation, at least two gas introduction systems are used, each system having a gas cylinder a gas tube, a gas volume control valve, and a stop valve. |
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abstract | A method for transporting a source pin in a Positron Emission Tomography (PET) system having a transmission ring includes aligning the transmission ring with a source pin within a storage device having a magnetic force holding the source pin in place, and moving the source pin from the storage device to the transmission ring using a magnetic force greater than the magnetic force of the storage device. |
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046722122 | claims | 1. A collimator for a beam of radiation the particles of which are selected from the group comprising high energy photons, electrons, protons, and heavy ions, which are emitted from a point type effective radiation source, comprising a protective radiation casing filled with helium gas, a frame surrounded by the casing, a plurality of pairs of opposed, elongated, curved, in cross section wedge-shaped leaves, wherein adjacent leaves are arranged side by side such that a fan-shaped configuration converging towards an apex at the effective radiation source is achieved, each wedge-shaped leaf being mounted for a combined rotational and translational movement on a support structure such that the leaves of each pair are mounted for motion towards and away from each other along a path which intersects the edge of the radiation field from the radiation source at a right angle, the inner edge surface as well as the two main surfaces of each leaf always being directed generally towards the radiation source, setting means for setting each leaf in a predetermined position along each individual path, bearing means provided between each leaf and the support structure, and read out means are provided to determine the position of the leaves by optical inspection of the leaves from a point that corresponds to the center of said radiation source. 2. A collimator in accordance with claim 1 wherein said helium gas is held at atmospheric or lower pressure. 3. A collimator in accordance with claim 1 wherein said leaves are made of a material having a high density and high atomic number, such as lead, tungsten and uranium. 4. A collimator in accordance with claim 3 wherein said setting means comprise individual motor means for setting the position of each leaf. 5. A collimator in accordance with claim 1 where in said read out means comprises TV-camera means, mirror means for viewing the radiation field from a point which corresponds to the centre of the radiation source on which the leaf collimator is focussed, the optical center of said TV-camera means being located in said point, motor means for each respective collimator leaf to set the position of said leaf, a TV-camera read out device comprising AD converting means for converting the TV-picture information into data position signals representing the position of each individual leaf, a data processor for receiving said data signals and comparing said signals with data position signals which represent the desired configuration of the radiation field and for generating, should there be any deviation between the compared data position signals, a signal to each motor in order to move the leaf to its desired position. 6. A collimator in accordance with claim 5, characterized in that said TV-camera means is arranged to establish the position of each collimator leaf by detecting light/dark transitions in predetermined lines of the TV-camera picture. 7. A collimator in accordance with claim 6, characterized in that the position of each collimator leaf is determined by the light/dark transition at a front surface of each collimator leaf with reference to stationary light bar means mounted in the collimator. 8. A collimator in accordance with claim 7, characterized in that each leaf is scanned by several TV-picture lines extending parallel to the top surface of each collimator leaf and that the light/dark transition in at least each second line is used to obtain the following data relating to the position of a leaf: (1) the actual position of said front surface of a leaf and (2) a reference position as established by said light bar means. 9. A collimator in accordance with claim 7, characterized in that data relating to the contour line of the radiation field configuration are stored, prior to the setting of the collimator leaves, in the memory of said data processor. 10. A collimator in accordance with claim 9, characterized in that data relating to the position of the radiation field are taken by the TV-camera means from a contour line drawn directly on the surface of the object to be radiated by sensing the light/dark transition of said contour line. 11. A collimator in accordance with claim 1 characterized in that the position of each collimator leaf is determined by the light/dark transition at a front surface of each collimator leaf with reference to a reflector means mounted in the collimator. 12. A collimator in accordance with claim 1, wherein said bearing means comprises for each slab; a pair of lower rollers supporting the respective slab at its lower surface and an upper roller spring biased into engagement with the upper surface of said slab. |
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046860770 | claims | 1. A nuclear reactor installation comprising a pressure vessel; a reactor core within said vessel, said core including straight vertical channel-like fuel elements for containing fissile material, vertically movable control rods between said fuel elements and absorber rods secured to said control rods between said fuel elements; a plurality of guide rods, each guide rod being disposed within and extending from a respective control rod to define an annular gap therebetween and having a tubular bottom half disposed in immobile relation to said fuel elements, each guide rod having a plurality of bores communicating an interior of said guide rod with said annular gap; conveying means for conveying a coolant from said pressure vessel into said interior of each said guide rod to move said control rods; a first annular restrictor at one end of each said control rod communicating said annular gap with the interior of said pressure vessel; and a second annular restrictor at an opposite end of each said control rod communicating said annular gap with the interior of said pressure vessel; said communicating bores and said restrictors being sized whereby said control rods move in one axial direction in response to an increasing quantity of coolant flow into said guide rod interiors and in an opposite axial direction in response to a decreasing quantity of coolant flow into said guide rod interiors. a pressure vessel; a reactor core within said vessel having at least one fuel element and a vertically movable control rod; a guide rod disposed within said control rod to define an annular gap therewith and having a tubular bottom disposed in immobile relation to said fuel element with a plurality of bores communicating an interior of said guide rod with said annular gap; conveying means for conveying a coolant from said pressure vessel into said interior of said guide rod to move said control rod relative to said guide rod and said fuel element; a first annular restrictor at one end of said control rod communication said annular gap with the interior of said pressure vessel; and a second annular restrictor at an opposite end of said control rod communicating said annular gap with the interior of said pressure vessel, said bores and said restrictors comprising means whereby said control rod moves in one axial direction in response to an increasing quantity of coolant flow into said guide rod interior and in an opposite axial direction in response to a decreasing quantity of coolant flow into said guide rod interior. 2. A nuclear reactor installation as set forth in claim 1 which further comprises a level of liquid coolant within said pressure vessel and wherein said conveying means has an intake disposed immediately below said level for conveying the coolant to said guide rods. 3. A nuclear reactor installation as set forth in claim 2 wherein said conveying means includes at least one speed-controlled pump for pumping coolant to said guide rods, a bypass line connected in parallel with said pump and a variable restrictor in said bypass line to control a flow of coolant therethrough. 4. A nuclear reactor installation as set forth in claim 1 wherein said communicating bores are distributed vertically along each said guide rod. 5. A nuclear reactor installation as set forth in claim 1 wherein each guide rod has a top half of smaller diameter than a bottom half thereof with said bores disposed in said bottom half and which further comprises a removable guide cap on a top end of each control rod to form said second restrictor with said top half for a laminar flow of coolant therethrough. 6. A nuclear reactor installation as set forth in claim 5 wherein said top half of each guide rod is of decreasing diameter in an upward direction. 7. A nuclear reactor installation as set forth in claim 5 wherein each guide rod has at least one adjustable continuous bore at a top end communicating said interior of said guide rod with the interior of said pressure vessel. 8. A nuclear reactor installation as set forth in claim 7 which further comprises at least one restrictor for controlling a supply of coolant to said continuous bore in each guide rod in response to coolant pressure whereby said restrictor opens said continuous bore in response to a shortfall of the coolant pressure. 9. A nuclear reactor installation as set forth in claim 5 which further comprises a core support plate connected to and within said pressure vessel for supporting said fuel elements and a guide lattice secured to and within said pressure vessel for guiding said top end of each guide rod. 10. A nuclear reactor installation as set forth in claim 1 wherein said communicating bores are distributed vertically along each said guide rod on an upwardly decreasing spacing. 11. A nuclear reactor installation as set forth in claim 1 wherein said communicating bores are distributed vertically along each said guide rod and which further comprises a plurality of grooves in each control rod disposed transversely thereof and with each groove in facing relation to at least one bore of a respective guide rod. 12. A nuclear reactor installation as set forth in claim 11 wherein each control rod has at least one stabilizing aperture connecting at least one of said grooves with the interior of said pressure vessel. 13. A nuclear reactor installation as set forth in claim 12 wherein each stabilizing aperture is a slot extending lengthwise of said respective control rod. 14. A nuclear reactor installation as set forth in claim 12 wherein each stabilizing aperture is a slot extending transversely of said respective control rod. 15. A nuclear reactor installation as set forth in claim 12 wherein each control rod has a stabilizing aperture connecting each of said grooves with the interior of said pressure vessel, each said aperture being of decreasing flow cross-section in an upward direction. 16. A nuclear reactor installation as set forth in claim 11 wherein said communicating bores are of decreasing flow cross-section in an upward direction. 17. A nuclear reactor installation as set forth in claim 1 wherein a top half of each guide rod has a plurality of annular grooves and each control rod has at least one annular projection facing a respective top half of a guide rod to form said second annular restrictor. 18. A nuclear reactor installation comprising 19. A nuclear reactor installation as set forth in claim 18 wherein said guide rod includes a bore extending through a top half thereof communicating said annular gap with the interior of said pressure vessel and which further comprises an adjusting cap on said guide rod for adjusting the flow cross-section of said bore in said top half. 20. A nuclear reactor installation as set forth in claim 18 wherein said restrictors are of different restrictions. |
claims | 1. A semiconductor photodiode comprising:a substrate active depletion layer fabricated from a radioisotope of a first type of conductivity material;a thick-field oxide layer formed on the substrate layer, the oxide layer having an open center region on the substrate layer; anda dopant material of a second conductivity material, different from the first conductivity material, the dopant material formed within the open center region on the substrate layer to form a photodiode junction, including an enclosure package enclosing the semiconductor diode for containing any radiation from the radioisotope such that initial emission of beta particles begins in the active depletion layer and substantially all of the emitted beta particles are contained within the enclosure package during operation. 2. The photodiode of claim 1 wherein the radioisotope is Si32. 3. The photodiode of claim 2 wherein the first conductivity type material is a p-type material and the second conductivity type is an n-type material. 4. The photodiode of claim 2 wherein the first conductivity type material is an n-type material and the second conductivity type is an p-type material. 5. The photodiode of claim 2 wherein the dopant is implanted into the open region. 6. The photodiode of claim 2 wherein the dopant is diffused into the open region. 7. A semiconductor photodiode comprising:a substrate active depletion layer fabricated from a Si32 radioisotope of a first type of conductivity material;a thick-field oxide layer formed on the substrate layer, the oxide layer having an center open region on the substrate layer;a dopant material of a second conductivity material, different from the first conductivity material, the dopant material formed within the open center region on the substrate layer to form a photodiode junction, andan enclosure package enclosing the semiconductor diode for containing any radiation from the radioisotope such that initial emission of beta particles begins in the active depletion layer and substantially all of the emitted beta particles are contained within the enclosure package during operation. |
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06132356& | summary | BACKGROUND OF THE INVENTION Field of the Invention The present invention pertains to an apparatus for the containment and suppression of hazardous material spills. More particularly, the invention pertains to a portable apparatus for quickly containing and suppressing localized hazardous material spills, including biological, chemical or radiological particulates until rigorous clean-up or other more permanent containment means can be employed. DESCRIPTION OF THE RELATED ART In the prior art, hazardous materials spills have principally been attended to by use of an absorbent device to contain the spill until clean up can be performed. However, this does not address control of vapors or off-gases originating from the hazardous material spill. Containment of military chemical agents such as nerve and mustard agents not only need liquid spill control but also require vapor or aerosol suppression. Terrorist incidents require means for quick, portable, vapor or aerosol suppression after an intentional release. Hazardous material spills may not only be in liquid form, but may also be comprised of particulate materials such as biological or radiological agents such as anthrax spores or radioactive fallout. Prior art absorbent materials would be ineffective against such materials due to the likelihood of resuspension from wind or the like. It would be desirable to provide an apparatus for the mitigation of solid, liquid and vaporous hazardous materials that can be deployed quickly. The invention provides an apparatus having a cover with rigid or inflatable sides which is light weight, inexpensive, and can quickly and easily be deployed by one person to cover a localized spill. A portable vacuum type air filtering mechanism filters the air drawn out from inside the system and maintains a negative pressure, i.e., a pressure less than atmospheric pressure, inside the system. An apron secured with grommets, rings, sandbags or weight secure the apparatus on the ground or other foundation. The apparatus has an optional sampling port for testing the encompassed hazardous material and an optional injection port for adding absorbents, foams or decontamination materials. SUMMARY OF THE INVENTION The invention provides a hazardous material containment or suppression apparatus which comprises a vapor or aerosol containment vessel comprising a cover and side walls attached around a perimeter of the cover to define an open central cavity. Each of the cover and side walls are composed of materials which resist penetration of a hazardous material therethrough. A tube extending through the vessel has a first end open at a point inside the cavity and a second end at a point outside the vessel. Means are attached to the second end of the tube for extracting and filtering hazardous material from inside the cavity to outside the vessel through the tube. The invention also provides a method of containing or suppressing a hazardous material which comprises surrounding a hazardous material with the above described hazardous material containment apparatus and then extracting and filtering the hazardous material from inside the cavity to outside the vessel through the tube. The apparatus is placed as a cover over a hazardous material spill in order to contain or suppress any off-gas or other release from the hazardous material, which may be in the form of a liquid, solid or gas. It is effective against the vaporization or aerosolization of biological, chemical and radiological hazards such as those which may be resuspended by the mechanical action of turbulent air flow. |
claims | 1. A construction method for an exhaust heat recovery boiler which generates steam by providing a plurality of heat exchanger tubes in a gas duct in which an exhaust gas flows generally horizontally, the construction method comprising:providing a heat exchanger tube bundle panel module, the heat exchanger tube bundle panel module comprising:a plurality of heat exchanger tube bundle panels positioned in a gas flow direction, the plurality of heat exchanger tube bundle panels including a plurality of heat exchanger tubes, upper and lower headers provided at opposing ends of the heat exchanger tubes, and vibration restraining supports provided at predetermined intervals to prevent contact between adjacent heat exchanger tubes in a direction transverse to the lengthwise direction of the heat exchanger tubes,a casing defining the gas duct, the casing having a thermal insulating material provided inside of the casing so as to cover an outer periphery of the gas duct, the outer casing comprising a ceiling wall, a bottom wall, and side-walls,heat exchanger tube bundle panel support beams located outside the ceiling wall of the casing, the heat exchanger tube bundle panel support beams comprising ceiling walls of the casing when installed in the exhaust heat recovery boiler,header supports which penetrate the ceiling wall of the casing and connect the upper headers to the heat exchanger tube bundle panel support beams, the header supports being configured to support a plurality of heat exchanger tube bundle panels,vertical module frames comprising vertical support members of the heat exchanger tube bundle panels located outside the side-walls of the casing, the vertical support members comprising side walls of the casing when installed in the boiler, andhorizontal module frames comprising horizontal support members of the heat exchanger tube bundle panel located outside the ceiling wall and bottom wall of the casing, the horizontal support members comprising ceiling walls and bottom walls of the casing when installed in the exhaust heat recovery boiler,the heat exchanger tube bundle panel module comprising at least one of a plurality of modules, the at least one of a plurality of modules having a size corresponding to parameters of the exhaust heat recovery boiler,wherein when transporting the heat exchanger tube bundle panel module, vibration restraining fixing members configured to prevent vibration of the heat exchange tubes are positioned between the vibration restraining supports and the casing, the heat exchanger tube bundle panel module having the vibration restraining fixing members positioned between the lower headers and the casing;providing main frames configured to support the heat exchanger tube bundle panel module, the main frames including main columns, main beams and bottom wall columns which are constructed at a construction site of the exhaust heat recovery boiler prior to installing the heat exchanger tube bundle panel module,inserting the at least one of a plurality of modules between an adjacent two main columns and setting a height of the heat exchanger tube panel support beams of the heat exchanger tube bundle panel modules to a setting, height of the main beams prior to installing the heat exchanger tube bundle panel module at the exhaust heat recovery boiler construction site,connecting and fixing the vertical module frames and the main columns to each other, connecting and fixing the horizontal module frame on the ceiling wall side and the main beam to each other, and connecting and fixing the horizontal module frame on the bottom wall side and the bottom wall columns to each other. 2. The exhaust heat recovery boiler construction method according to claim 1, further comprising:sizing each heat exchanger tube bundle panel module so as to allow at least two of the at least a plurality of modules to be positioned in a horizontal direction of a plane which is orthogonal to the gas flow of the exhaust heat recovery boiler; andproviding first aseismic braces that connect the end portion inner side of the casing which comprises the ceiling wall of the heat exchanger tube bundle panel module and the central portion inner side of the casing which comprises the side wall of the heat exchanger tube bundle panel module, the first aseismic braces being located at positions facing the heat exchanger tube bundle panels on at least one of a surface side and a back surface side in the gas flow direction, andproviding second aseismic braces that connect the end of the casing which comprises the bottom wall side of the heat exchanger tube bundle panel module and the central portion inner side of the casing which comprises the side wall of the heat exchanger tube bundle panel module, the second aseismic braces being located at positions facing the heat exchanger tube bundle panels on at least one of the surface side and the back surface side in the gas flow direction, wherein the first and second aseismic braces are not removed during transportation and installation of the heat exchanger tube bundle panel modules, the first and second aseismic braces being not removed after completion of the boiler construction. 3. The exhaust heat recovery boiler construction method according to claim 2, further comprising:providing, during transportation of heat exchanger tube bundle panel modules, transporting spacers that maintain distances between the first and second aseismic braces and the surfaces and the back surfaces in the gas flow direction of heat exchanger tube bundle panels. 4. A heat exchanger tube bundle panel module for construction of an exhaust heat recovery boiler which generates steam by providing a plurality of heat exchanger tubes inside a gas duct in which gas flows horizontally, the heat exchanger tube bundle panel module for construction of an exhaust heat recovery boiler comprising:a plurality of heat exchanger tube bundle panels positioned in a gas flow direction, each including a plurality of heat exchanger tubes, upper and lower headers provided at opposing ends of the heat exchanger tubes, and vibration restraining supports provided at predetermined intervals in a direction transverse to a lengthwise direction of the heat exchanger tubes and configured to prevent contact between adjacent heat exchanger tubes;a casing defining the gas duct, the casing having a thermal insulating material provided inside of the casing and covering the outer peripheral portion of the gas duct, the casing comprising a ceiling wall, a bottom wall, and side walls each extending along the gas flow direction of the plurality of heat exchanger tube bundle panels;heat exchanger tube bundle panel support beams located outside the ceiling wall of the casing, the heat exchanger tube bundle panel support beams comprising the ceiling wall when the heat exchanger tube bundle panel module is installed in the exhaust heat recovery boiler;header supports that penetrate the ceiling wall of the casing and connect the upper headers and the heat exchanger tube bundle panel support beams, the header supports being configured to support the heat exchanger tube bundle panel module;vertical module frames comprising vertical support members for the heat exchanger tube bundle panels located outside the casing, the vertical support frames comprising side-walls when the heat exchanger tube bundle panel module is installed in the exhaust heat recovery boiler, the vertical support frame member being provided on a casing side, the vertical support frame further comprising first aseismic braces that connect the end portion inner side of the casing which comprises the ceiling wall and the central portion inner side of the casing which comprises the side wall casing, the first aseismic braces facing the heat exchanger tube bundle panels on at least one of the surface side and the back surface side in the gas flow direction of each heat exchanger tube bundle panel module, and second aseismic braces which connect the end of the casing comprising the bottom wall side and the central portion inner side of the casing comprising the side wall side, the second aseismic braces being positioned to face the heat exchanger tube bundle panels on at least one of the surface side and the back surface side in the gas flow direction; andhorizontal module frames comprising horizontal support members for the heat exchanger tube bundle panels located outside the ceiling wall and outside the bottom wall of the casing, the horizontal module frame comprising the ceiling wall and bottom wall when the heat exchanger tube bundle panel module is installed in the exhaust heat recovery boiler, whereinthe heat exchanger tube bundle panel module is sized to allow at least two heat exchanger tube bundle panel modules to be positioned adjacent to each other in the horizontal direction of a plane orthogonal to the gas flow of the exhaust heat recovery boiler, the heat exchanger tube bundle panel module being configured to be positioned among main frames of the exhaust heat recovery boiler which are configured to support modules, the main framed comprising main columns, main beams, and bottom wall columns, the main columns and the vertical module frames, the main beams and the horizontal module frame on the ceiling wall side, and the bottom wall columns and the horizontal module frame on the bottom wall, respectively, being configured to be connected and fixed to each other. 5. The heat exchanger tube bundle panel module for construction of an exhaust heat recovery boiler according to claim 4, wherein the vertical module frames are provided with a first transporting reinforcing member that couples the end of the casing comprising the ceiling wall side and the end of the casing comprising the bottom wall side to each other, and the first transporting reinforcing member being configured to be removed after installation of the heat exchanger tube bundle panel module in the exhaust heat recovery boiler is completed, and a plurality of second transporting reinforcing members that couple the first transporting reinforcing member and the casing side-wall side to each other and are removed after installation of the heat exchanger tube bundle panel module in the exhaust heat recovery boiler is completed, the second transporting reinforcing members being positioned to face the heat exchanger tube bundle panel modules on at least one of the surface side and the back surface side in the gas flow direction of the respective heat exchanger tube bundle panels. 6. The heat exchanger tube bundle panel module for construction of an exhaust heat recovery boiler according to claim 4, wherein vibration restraining fixing members are positioned between the vibration restraining supports and the casing, and the vibration restraining fixing members are positioned between the lower headers and the casing. 7. The heat exchanger tube bundle panel module for construction of an exhaust heat recovery boiler according to claim 4, wherein baffle plates are attached to side surfaces of a plane orthogonal to the gas flow direction of the heat exchanger tube bundle panels of each heat exchanger tube bundle panel module the baffle plates being positioned between the heat exchanger tube bundle panels of two modules which are positioned adjacent to each other in the horizontal direction of a plane orthogonal to the gas flow, gas short pass preventive plates which are connected at one of the side surfaces of the baffle plates, and the gas short pass preventive plates contacting the other one of the side surfaces of the baffle plates of the other heat exchanger tube bundle panel. 8. The heat exchanger tube bundle panel module for construction of an exhaust heat recovery boiler according to claim 7, wherein the side surfaces of the gas short pass preventive plates are configured to come into contact with the baffle plates of each heat exchanger tube bundle panel, the side surfaces of the gas short pass preventive plates being bent toward a upstream side of the gas flow. |
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claims | 1. A Thorium molten salt energy system comprising:a proton beam source for producing a proton beam, wherein the proton source is adapted to vary the energy level of the produced proton beam between at least a first energy level and a second energy level, the proton beam source having a power input to receive power for driving the proton beam source,wherein the first energy level is greater than the second energy level, wherein the first energy level is such that a proton at the first energy level can interact with a Beryllium nucleus to produce a (p, n) reaction resulting in the generation of a neutron at an energy level sufficient to fission Thorium;wherein the second energy level is such that the interaction of a proton at the second energy level can interact with a Lithium nucleus to produce a (p, n) reaction resulting in the generation of a neutron at an energy level sufficient to fission uranium;a Thorium molten salt assembly comprising:a main assembly body;a tubular member positioned within the main body,a top lid coupled to the main assembly body in the form of a circular disk defining a plurality of openings passing therethrough; the plurality of openings including:a window opening defining a top window through which protons from the proton source may pass;two impeller shaft openings passing through the top lid, each defining an opening suitable for receipt of a rotating shaft;at least two heat exchanger openings passing through the top lid each heat exchanger opening being sized for receipt of either an input or an output pipe element of a primary heat exchanger;a window element positioned within the window opening; the window element being formed of a material permitting the passage of protons therethrough;a molten salt solution contained within the main assembly body, the molten salt solution containing Thorium and Lithium;a plurality of solid Thorium fuel rods positioned within the tubular member and arranged such that at least a portion of each Thorium fuel rod is below the window opening in the lid, each solid Thorium fuel rod comprising:an inner member comprising Beryllium andan outer member formed from a solid that comprises at least some solid Thorium, wherein the outer member defines an opening passing through the solid Thorium fuel rod and the inner member is located within the opening;a plurality of immersion pumps, each immersion pump including an impeller shaft having a first end extending through one impeller opening defined by the top lid and a second end extending into the molten salt assembly, wherein an impeller is coupled to the second end of each immersion pump, and wherein the length of the impeller shaft is such that the impeller of each impeller pump is located within the Thorium molten salt assembly body; anda primary heat exchange assembly comprising a first set of primary coils positioned within the main assembly body and a second set of primary coils positioned outside the main assembly body, the primary heat exchange assembly including an input pipe passing through the top lid and an output pipe passing through the top lid, the primary heat exchange assembly further including a non-Thorium containing molten salt within the primary coils and being configured such that the non-Thorium molten salt within the first set of primary coils is capable of absorbing heat generated in the main assembly body. 2. The Thorium molten salt energy system of claim 1 wherein the first energy level is above 4.4 MeV and the second energy level is between 2.4 MeV and 4.0 MeV. 3. The Thorium molten salt energy system of claim 1 wherein the proton beam source further comprises a beam focusing/defocusing instrument for varying the shape of the proton beam provided by the proton beam source, and wherein the beam focusing/defocusing instrument can be varied such that the proton beam from the proton source can take the form of a spot beam of varying diameters and patterns. 4. The Thorium molten salt energy system of claim 3 wherein the beam focusing/defocusing instrument can further be controlled to provide a proton beam having a ring-like projection pattern wherein the Thorium molten salt includes at least four Thorium fuel rods, and wherein the at least four Thorium fuel rods are arranged within the main assembly body such that the ring-like beam projection pattern from the proton beam source will result in the impingement of protons on the Beryllium cores of each of the at least four Thorium fuel rods. 5. The Thorium molten salt energy system of claim 1 wherein each of the Beryllium cores defines a central opening passing therethrough, wherein the central opening extends through at least 75% of the length of the Thorium fuel rod. 6. The Thorium molten salt energy system of claim 5 wherein a cross section of the Beryllium cores includes four inwardly projecting Beryllium members that together define four clover-leaf shaped openings passing between them. 7. The Thorium molten salt energy system of claim 1 wherein there are five Thorium fuel rods and the five Thorium fuel rods are positioned between an upper support structure and a lower support structure to form a Thorium fuel bundle assembly and wherein one of the Thorium fuel rods is surrounded by the four other Thorium fuel rods. 8. A system for producing heat comprising:a proton beam source for producing a proton beam, wherein the proton source is adapted to vary the energy level of the produced proton beam between a first energy level of at least approximately 4.5 MeV and a second energy level of at least approximately 2.4 MeV, wherein the proton source includes a power input for receiving power to drive the proton beam source;a Thorium molten salt assembly comprising:a main assembly body;a tubular member positioned within the main assembly body,a lid coupled to the main assembly body in the form of a circular disk defining a plurality of openings passing therethrough, the plurality of openings including:a first opening passing through the top lid having a diameter larger than the other openings, the first opening defining a top window opening through which protons from the proton source may pass;a window element positioned within the first opening; the window element being formed of a material permitting the passage of protons therethrough;a molten salt solution contained within the main assembly body; the molten salt solution containing Thorium and Lithium;a plurality of Thorium fuel rods positioned within the tubular member body and arranged such that the top portions of each Thorium fuel rod is below the first opening in the lid, each solid Thorium fuel rod comprising:an inner member comprising Beryllium andan outer member formed from a solid that comprises at least some solid Thorium,wherein the outer member defines an opening passing through the Thorium fuel rod and the inner member is located within the opening;a primary heat exchange assembly positioned within the main assembly body, the primary heat exchange assembly comprising:an input manifold the input manifold comprising an element defining an inlet port on the top surface of the hexahedron element of a first diameter and a plurality of openings on the bottom surface of the hexahedron element, each of the openings on the bottom surface of the hexahedron element having a diameter less than the diameter of the inlet port;an outlet manifold, the outlet manifold comprising an element defining an outlet port on the top surface of the element of a first diameter and a plurality of openings on the bottom surface of the element, each of the openings on the bottom surface of the element having a diameter less than the diameter of the outlet port; anda plurality of coiled tubular elements, each of the plurality of coiled tubular elements having a first end coupled to one of the openings on the bottom surface of the input manifold and a second end coupled to one of the openings on the bottom surface of the outlet manifold;an input pipe having a first end coupled to the inlet port of the input manifold, the input pipe passing through an opening in the top lid; andan outlet pipe having a first end coupled to the outlet port of the outlet manifold, the outlet pipe passing through an opening in the top lid;wherein the proton beam source is adapted to direct a proton beam of the first energy level such that the beam is directed to the Beryllium core of at least one Thorium fuel rod to promote the generation of fast neutrons and the fission of Thorium within the Thorium fuel rod to generate heat; andwherein the manifolds and pipes comprising the primary heat exchange assembly are adapted to circulate molten salt to remove heat from the interior of the main assembly body. 9. The system for producing heat of claim 8 wherein the window element comprises titanium. 10. The system of producing heat of claim 8 wherein the outer surface of each of the Thorium rods defines a spiral shape. 11. The system of producing heat of claim 8 wherein each Thorium fuel rod extends at least ⅔ of the way down into the main assembly body. 12. The system of producing heat of claim 8 wherein the main assembly body is rounded at the bottom. 13. The system of producing heat of claim 8 wherein the input and output manifolds of the primary heat exchange assembly are positioned above the level of the molten salt within the main body and wherein a gaseous head exists in the space above the molten salt between the input and output manifolds. |
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abstract | Apparatus for passively generating electric power during a nuclear power station blackout by utilizing the temperature difference between the hot inlet of a residual heat removal circuit and the surrounding containment environment. A heat engine, such as a thermoelectric generator, a Stirling Cycle Engine or Rankine Cycle Engine, is coupled in heat exchange relationship with an uninsulated portion of the inlet to a passive residual heat removal heat exchanger and/or passive residual heat removal heat exchanger channel head to generate the power required to operate essential equipment needed to maintain the nuclear power station in a safe condition during a loss of normal onsite and offsite power. |
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description | The present application is a continuation-in-part application based on U.S. Ser. No. 10/965,372, filed Oct. 14, 2004 now U.S. Pat. No. 7,139,360, entitled Use of Boron or Enriched Boron 10 in UO2. The present invention relates to a nuclear fuel assembly, to be used in a nuclear power reactor. The fuel assembly contains fuel pellets having a boron-containing compound in admixture with the nuclear fuel. In a typical nuclear reactor, such as a pressurized water (PWR), heavy water or a boiling water reactor (BWR), the reactor core includes a large number of fuel assemblies, each of which is composed of a plurality of elongated fuel elements or rods. The fuel rods each contain fissile material such as uranium dioxide (UO2) or plutonium dioxide (PuO2), or mixtures of these, usually in the form of a stack of nuclear fuel pellets, although annular or particle forms of fuel are also used. The fuel rods are grouped together in an array which is organized to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. A coolant, such as water, is pumped through the core in order to extract some of the heat generated in the core for the production of useful work. Fuel assemblies vary in size and design depending on the desired size of the core and the size of the reactor. When a new reactor starts, its core is often divided into a plurality, e.g. three or more groups of assemblies which can be distinguished by their position in the core and/or their enrichment level. For example, a first batch or region may be enriched to an isotopic content of 2.0% uranium-235. A second batch or region may be enriched to 2.5% uranium-235, and a third batch may be enriched to 3.5% uranium-235. After about 10-24 months of operation, the reactor is typically shut down and the first fuel batch is removed and replaced by a new batch, usually of a higher level of enrichment (up to a preferred maximum level of enrichment). Subsequent cycles repeat this sequence at intervals in the range of from about 8-24 months. Refueling as described above is required because the reactor can operate as a nuclear device only so long as it remains a critical mass. Thus, nuclear reactors are provided with sufficient excess reactivity at the beginning of a fuel cycle to allow operation for a specified time period, usually between about six to eighteen months. Since a reactor operates only slightly supercritical, the excess reactivity supplied at the beginning of a cycle must be counteracted. Various methods to counteract the initial excess reactivity have been devised, including insertion of control rods in the reactor core and the addition of neutron absorbing elements to the fuel. Such neutron absorbers, known in the art and referred to herein as “burnable poisons” or “burnable absorbers”, include, for example, boron, gadolinium, cadmium, samarium, erbium and europium compounds. Burnable poisons absorb the initial excess amount of neutrons while (in the best case) producing no new or additional neutrons or changing into new neutron poisons as a result of neutron absorption. During the early stages of operation of such a fuel element, excess neutrons are absorbed by the burnable poison, which preferably undergoes transformation to elements of low neutron cross section, which do not substantially affect the reactivity of the fuel element in the later period of its life when the neutron availability is lower. Sintered pellets of nuclear fuel having an admixture of a boron-containing compound or other burnable poison are known. See, for example, U.S. Pat. Nos. 3,349,152; 3,520,958; and 4,774,051. However, nuclear fuel pellets containing an admixture of a boron burnable absorber with the fuel have not been used in large land-based reactors due to concerns that boron would react with the fuel, and because the use of boron was thought to create high internal rod pressurization from the accumulation of helium in the reaction:10B+1n→11B(excited state)→4He+7Li Current practice is to coat the surface of the pellets with a boron-containing compound such as ZrB2, which avoids any potential reaction with the fuel. However, this does not solve the pressurization problem, which limits the amount of coating that can be contained within each rod. More rods with a lower 10B loading must be used, thus necessitating the handling and coating of a large number of fuel pellets, which is very expensive and results in high overhead costs. Complex manufacturing operations also result from the need to separate the coated and non-coated fuel manufacturing and assembly operations. In practice, the cost of coating the pellets limits their use, and they are used in as few rods as possible, taking into account the pressurization problem described above. Historically this was acceptable, because fuel cycles were shorter, levels of 235U enrichment were lower, and overall thermal output of a reactor was lower. Other compounds such as Gd2O3 and Er2O3 can be added directly to the pellets, but these are less preferred than boron because they leave a long-lived, high cross-section residual reactive material. Nuclear reactor core configurations having burnable poisons have been described in the art. For example, U.S. Pat. No. 5,075,075 discloses a nuclear reactor core having a first group of rods containing fissionable material and no burnable absorber and a second group of rods containing fissionable material with a burnable absorber, wherein the number of rods in the first group is larger than the number of rods in the second group. The burnable absorber comprises a combination of an erbium compound and a boron compound. U.S. Pat. No. 5,337,337 discloses a fuel assembly where fuel rods containing a burnable poison element having a smaller neutron absorption cross-section (such as boron) are placed in a region of the core having soft neutron energy and a large thermal neutron flux, while rods having a burnable poison element having a larger neutron absorption cross-section (such as gadolinium) are placed in regions of the core having average neutron energy spectrum. Neither of these prior patents disclose an arrangement of fuel rods in fuel assemblies in which a majority of fuel rods contain boron alone, as the burnable poison. Neither disclose assembly arrangements suitable for reactors producing over 500 megawatts thermal power. With the use of longer fuel cycles and higher levels of 235U enrichment, there remains a need for the development of nuclear fuels and fuel assemblies having integral burnable absorbers that are cost-effective and can extend the life of the fuel without creating additional reactive materials. The present invention solves the above need by providing a fuel assembly comprising a plurality of fuel rods, each fuel rod containing a plurality of nuclear fuel pellets, wherein at least one fuel pellet in more than 50% of the fuel rods in the fuel assembly comprises a sintered admixture of an actinide oxide, actinide carbide or actinide nitride and a boron-containing compound. Due to the fact that boron has a relatively low parasitic cross-section as compared to other burnable absorbers, it will typically be necessary to put boron-containing fuel pellets in more than 50% of the rods. It has been found, contrary to previous assumptions, that boron does not interact with the nuclear fuel, and is not the primary cause of pressure in the fuel rods, when the amount of helium produced is compared to the amounts of other fission gases released during fuel use. Preparing fuel with an admixture of boron is much less expensive. Therefore, a greater number of rods can have the boron-containing fuel pellets, providing a greater amount of boron in the core but with less boron in each rod, thus avoiding the pressurization problem. For example, with the use of coated pellets fuel rods will contain about 2 mg boron per inch, whereas with the use of boron directly in the pellet fuel rods will contain about 1-1.5 mg boron per inch, a 25-50% reduction. By adding either natural or enriched boron to at least one fuel pellet in a majority of the rods in a fuel assembly, reactivity hold-down that is equivalent or superior to that provided by current methods is provided, at much lower cost. Additionally, increasing the number of rods containing boron can reduce the internal fuel rod pressure by a factor of 2 or 3 over that found in current practice. Thus, using lower levels of a boron-containing compound, in combination with its distribution more widely among the fuel rods, provides the benefits of the present invention. As will be appreciated by one skilled in the art, these benefits are most advantageous when the thermal output of the reactor core is above 500 megawatts thermal, in the case of water-cooled reactors, or above 200 megawatts thermal in the case of gas-cooled reactors. The use of boron in boiling water reactor fuel as a substitute for the currently employed Gd2O3 and Er2O3 provides even greater benefits. In addition to simplifying manufacturing, the space that is taken up by the Gd2O3 and Er2O3 in the fuel pellets can be replaced by more UO2 (or other actinide oxide, carbide or nitride), thus allowing more fuel to be loaded in a given size core. Enrichment constraints currently applied on a rod-by-rod basis due to poor thermal conductivity of these rare-earth oxides can be completely avoided, thus yielding a significant simplification in the manufacture of nuclear fuels. Accordingly, the present invention provides a fuel assembly comprising a plurality of fuel rods, each fuel rod containing a plurality of nuclear fuel pellets, wherein at least one fuel pellet in more than 50% of said fuel rods in said fuel assembly comprises a sintered admixture of a metal oxide or metal nitride and a boron-containing compound. The boron-containing compound functions as the burnable poison in the fuel. The term “fuel pellet” is used herein to denote the individual sintered pellets of fuel that are loaded into a fuel rod. Preferably, at least one fuel pellet in more than 60% of the fuel rods in the fuel assembly contains a boron-containing compound. Even more preferably, at least one fuel pellet in more than 70-80% of the fuel rods in the fuel assembly contains a boron-containing compound. When referring to any numerical range of values herein, such ranges are understood to include each and every number and/or fraction between the stated range minimum and maximum. A range of more than 50% of the fuel rods in a fuel assembly, for example, would expressly include all intermediate values between 50 and 100%, including, by way of example only, 51%, 52%, 53%, 60%, 70%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 100%, and all other intermediate values there between. In one embodiment, at least one fuel pellet in more than 50% of the fuel rods in the fuel assembly comprises an admixture of a boron-containing compound and the nuclear fuel. In other embodiments, at least one fuel pellet in at least 60%, 70%, 80%, 90% or more of the fuel rods in the fuel assembly contain the boron compound. In the rods having at least one boron-containing fuel pellet, any number of boron-containing fuel pellets can be used, to a maximum of 100% of all the pellets in the rod. Typically, the number of fuel pellets containing boron in a rod will be greater than 50%, but the number of boron-containing pellets in a particular rod will be determined based on all aspects of fuel design, as discussed further below. Any suitable boron-containing compound can be used, so long as it is compatible with the particular nuclear fuel selected and meets fuel specifications as to density, thermal stability, physical stability, and the like. Suitable boron-containing compounds include, but are not limited to, ZrB2, TiB2, MoB2, UB2, UB3, UB4, B2O3, ThB4, UB12, B4C, PuB2, PuB4, PuB12, ThB2, BN and combinations thereof. Preferred boron-containing compounds are BN, UB12 and UB4. The boron-containing compound and actinide oxide, carbide or nitride are prepared as an admixture and then sintered to produce a fuel pellet. Such methods of preparing nuclear fuel pellets are known in the art; as described above, see U.S. Pat. Nos. 3,349,152; 3,520,958; and 4,774,051. Natural boron or boron enriched in the 10B isotope can be used, and any level of enrichment of 10B above natural levels is suitable, depending on certain factors. With the use of more enriched boron, the amount of boron-containing compound needed overall decreases, allowing a concomitant increase in fuel loading. However, enriched boron is more expensive than natural boron, and the amount of boron enrichment used will be a cost consideration balanced with other aspects of fuel design. Accordingly, the amount of boron-containing compound present in a fuel pellet will range between about 5 ppm to about 5 wt %, more preferably between about 10 ppm and 20,000 ppm, based on the total amount of fissile material in the fuel pellet, and the amount used will vary depending on the level of uranium enrichment, the level of boron enrichment, and other factors. One skilled in the art of fuel design can easily determine the desired amount of boron-containing compound to use in a fuel pellet, and how many fuel pellets with this desired amount of boron-containing compound to place in a particular number of rods in a fuel assembly. Such calculations are routinely done in design of a fuel load, which must take into account the age of the fuel, the use pattern and activity of the surrounding fuel, the level of uranium-235 in the fuel and the number of neutrons given off. By way of example only, the use of an equal amount of natural boron in all the rods of a batch (if neutronically acceptable) will require boron levels between about 66 and 7,000 ppm, while the use of 100% enriched boron would reduce the level of boron needed to between about 13 and 1200 ppm. It is recognized that the selective boration of individual rods might be preferable neutronically, similar to current poison distribution methods. Fuel rods having fuel pellets with natural boron only, enriched boron only, or a combination of pellets with natural and enriched boron, are all contemplated as being embraced by the present invention. The boron-containing compound can be used with any suitable nuclear fuel. Examples of suitable nuclear fuels include actinide oxides, actinide carbides and actinide nitrides. Exemplary fuels include, but are not limited to, UO2, PuO2, ThO2, UN, (U, P)O2, (U, P, Th)O2, and (U, Th)O2, other actinide oxides, actinide carbides and actinide nitrides, mixtures of actinide oxides, mixtures of actinide carbides, and mixtures of actinide nitrides. The above described fuel assembly is suitable and economical for use in fast breeder reactors, as well as reactors that are substantially based on thermal fission such as light or heavy water nuclear reactors, including pressurized water reactors (PWR), boiling water reactors (BWR) and pressurized heavy water reactors (PHWR or CANDU). The fuel assembly is also suitable for use in gas-cooled reactors. Preferrably, the thermal output of the reactor core of any of the above reactor types will be above 500 megawatts thermal in the case of water-cooled reactors, and above 200 megawatts thermal in the case of gas-cooled reactors. In the following description, like reference numbers designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as “forward”, “rearward”, “left”, “right”, “upwardly”, “downwardly”, and the like, are words of convenience and are not to be construed as limiting terms. Referring now to the drawings, and particularly to FIGS. 1 and 2, there is shown an embodiment of the present invention, by way of example only and one of many suitable reactor types, a pressurized water nuclear reactor (PWR), being generally designated by the numeral 10. The PWR 10 includes a reactor pressure vessel 12 which houses a nuclear reactor core 14 composed of a plurality of elongated fuel assemblies 16. The relatively few fuel assemblies 16 shown in FIG. 1 is for purposes of simplicity only. In reality, as schematically illustrated in FIG. 2, the core 14 is composed of a great number of fuel assemblies. Spaced radially inwardly from the reactor vessel 12 is a generally cylindrical core barrel 18 and within the barrel 18 is a former and baffle system, hereinafter called a baffle structure 20, which permits transition from the cylindrical barrel 18 to a squared off periphery of the reactor core 14 formed by the plurality of fuel assemblies 16 being arrayed therein. The baffle structure 20 surrounds the fuel assemblies 16 of the reactor core 14. Typically, the baffle structure 20 is made of plates 22 joined together by bolts (not shown). The reactor core 14 and the baffle structure 20 are disposed between upper and lower core plates 24, 26 which, in turn, are supported by the core barrel 18. The upper end of the reactor pressure vessel 12 is hermetically sealed by a removable closure head 28 upon which are mounted a plurality of control rod drive mechanisms 30. Again, for simplicity, only a few of the many control rod drive mechanisms 30 are shown. Each drive mechanism 30 selectively positions a rod cluster control mechanism 32 above and within some of the fuel assemblies 16. A nuclear fission process carried out in the fuel assemblies 16 of the reactor core 14 produces heat which is removed during operation of the PWR 10 by circulating a coolant fluid, such as light water with soluble boron, through the core 14. More specifically, the coolant fluid is typically pumped into the reactor pressure vessel 12 through a plurality of inlet nozzles 34 (only one of which is shown in FIG. 1). The coolant fluid passes downward through an annular region 36 defined between the reactor vessel 12 and core barrel 18 (and a thermal shield 38 on the core barrel) until it reaches the bottom of the reactor vessel 12 where it turns 180 degrees prior to following up through the lower core plate 26 and then up through the reactor core 14. On flowing upwardly through the fuel assemblies 16 of the reactor core 14, the coolant fluid is heated to reactor operating temperatures by the transfer of heat energy from the fuel assemblies 16 to the fluid. The hot coolant fluid then exits the reactor vessel 12 through a plurality of outlet nozzles 40 (only one being shown in FIG. 1) extending through the core barrel 18. Thus, heat energy which the fuel assemblies 16 impart to the coolant fluid is carried off by the fluid from the pressure vessel 12. Due to the existence of holes (not shown) in the core barrel 18, coolant fluid is also present between the barrel 18 and the baffle structure 20 and at a higher pressure than within the core 14. However, the baffle structure 20 together with the core barrel 18 do separate the coolant fluid from the fuel assemblies 16 as the fluid flows downwardly through the annular region 36 between the reactor vessel 12 and core barrel 18. As briefly mentioned above, the reactor core 14 is composed of a large number of elongated fuel assemblies 16. Turning to FIG. 3, each fuel assembly 16, being of the type used in the PWR 10, basically includes a lower end structure or bottom nozzle 42 which supports the assembly on the lower core plate 26 and a number of longitudinally extending guide tubes or thimbles 44 which project upwardly from the bottom nozzle 42. The assembly 16 further includes a plurality of transverse support grids 46 axially spaced along the lengths of the guide thimbles 44 and attached thereto. The grids 46 transversely space and support a plurality of fuel rods 48 in an organized array thereof. Also, the assembly 16 has an instrumentation tube 50 located in the center thereof and an upper end structure or top nozzle 52 attached to the upper ends of the guide thimbles 44. With such an arrangement of parts, the fuel assembly 16 forms a integral unit capable of being conveniently handled without damaging the assembly parts. As seen in FIGS. 3 and 4, each of the fuel rods 48 of the fuel assembly 16 has an identical construction insofar as each includes an elongated hollow cladding tube 54 with a top end plug 56 and a bottom end plug 58 attached to and sealing opposite ends of the tube 54 defining a sealed chamber 60 therein. A plurality of nuclear fuel pellets 62 are placed in an end-to-end abutting arrangement or stack within the chamber 60 and biased against the bottom end plug 58 by the action of a spring 64 placed in the chamber 60 between the top of the pellet stack and the top end plug 56. In the operation of a PWR, it is desirable to prolong the life of the reactor core 14 as long as feasible to better utilize the uranium fuel and thereby reduce fuel costs. To attain this objective, it is common practice to provide an excess of reactivity initially in the reactor core 14 and, at the same time, provide means to maintain the reactivity relatively constant over its lifetime. FIGS. 2, 3 and 4 illustrate a preferred embodiment of the present invention, to achieve this objective. As can be seen in FIGS. 3 and 4, a fuel rod 48 has some end-to-end arrangements, or strings, of fuel pellets 62A containing no boron compound, provided at upper and lower end sections of the fuel pellet stack of the fuel rod 48 as an axial blanket. The fuel rod 48 also has a string of the fuel pellets 62B with the boron-containing compound provided at the middle section of the stack. Referring to FIG. 2, there is shown one preferred embodiment of an arrangement in the nuclear reactor core 14 in accordance with the present invention, of assemblies with fuel rods having no boron-containing compound, denoted by an “o” in FIG. 2, and assemblies in which all the fuel rods in the assembly have at least one pellet of fuel with a boron-containing compound, denoted by an “x” in FIG. 2. By way of example only, Table 1 below provides information comparing an assembly of the present invention with prior art practice. TABLE 1Original RodsRods withWith IFBA-coatedUB4Fuel (ZrB2)(present invention)Boron loading10 mg/inch325.5 ppmPercent of all rods coated60%100%With ZrB2 or containing UB4Pellet diameter0.37 inches0.37 inchesUO2 density10.47 gm/cm310.47 gm/cm3UO2 loading18.43 gm UO2/inch18.43 gm UO2/inch10B loading108.5 ppm65.1 ppm10B level in total amount20%20%of BoronSmeared 10B loading65.1 ppm65.1 ppmTotal B loading524.5 ppm325.5 ppmUB4 loading2119 ppm UB4% of pellets with IFBA or100%100%UB4 The invention provides that any suitable boron-containing compound can be used as long as it is compatible with the particular nuclear fuel selected and further meets fuel specifications as to density, thermal stability, physical stability and the like. In a preferred embodiment, the suitable boron-containing compound is boron nitride (BN). Natural boron or boron enriched with a 10B isotope can be used in this embodiment. Any ratio of non-enriched-to-enriched boron can be used with the understanding that with the increased use of enriched boron, less boron nitride needs to be added to the fuel pellet. In the preferred embodiment, boron nitride is prepared as an admixture with an actinide nitride nuclear fuel, and then sintered to produce a fuel pellet. Preferred actinide nitrides include uranium nitride (UN), plutonium nitride (PN) and thorium nitride (ThN) or any combination thereof. By admixturing boron nitride with one or any combination of uranium nitride, plutonium nitride or thorium nitride, a unity of nitride compounds is achieved throughout the admixture. The unity of nitride compounds in the admixture gives the boron-containing compound of the invention improved compatibility with the actinide compound of the invention. Further, the combination of boron nitride with one or any combination of uranium nitride, plutonium nitride or thorium nitride does not significantly affect the properties of the actinide matrix. Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims. |
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description | This invention relates to protecting a manned spacecraft from radiation in space. Human susceptibility to the harsh space radiation environment has been identified as being a major hurdle for exploration beyond low Earth orbit (LEO). High energy protons and nuclei ions from Solar Energetic Particles (SEPs) and Galactic Cosmic Rays (GCRs) can result in radiation doses that are dangerous to astronaut health and even survivability if the astronauts are not adequately shielded. These high energy particles also cause significant amounts of secondary radiation when they impinge on spacecraft structure. The secondary neutron radiation may cause human radiogenic cancers. Hydrogen or hydrogen rich materials are ideal materials for radiation shielding because hydrogen does not easily break down and become a source for secondary radiation. When a spacecraft is positioned in LEO, the Earth's magnetic field provides some radiation protection to the spacecraft and the astronauts occupying it. Radiation protection for astronauts is critical for the future of human space flight since conventional spacecraft construction materials such as aluminum are susceptible to secondary radiation when SEPs or GCRs impinge on them. Because of the size of an aluminum nucleus, the secondary radiation produced while shielding space radiation can be just as damaging as the primary radiation and this secondary radiation contributes to the total ionizing dose received by the astronauts. Other types of hydrogen-rich materials, such as polyethylene, have been tested to determine their effectiveness at reducing the dose received from all sources of radiation. Such shielding materials do not produce the same level of damaging secondary radiation, however, the presence of carbon atoms in polyethylene means that there is less hydrogen shielding material per unit of shielding material mass than there would be if hydrogen itself is used as the shielding material. However, hydrogen is a challenging substance to store and manage and, therefore, has not been considered as a viable shielding material for spacecraft. Developing a system using cryogenic material, hydrogen, that is maintained at, for example, 10-12 K (“K” here and throughout refers to “° K” or “degrees Kelvin”), for radiation shielding presents several challenges. Thermal challenges include, for example, heat leak from the space environment into cryogenic hydrogen shielding due to, for example solar irradiation, planetary albedo, heat leak from the crew capsule that is maintained at room temperature of about 300 K, power system, propulsion, etc. into the cryogenic hydrogen shield. It is also challenging to process the cryogenic hydrogen on the ground, prior to launch, and bring it to a frozen temperature of 10 K while the hydrogen is contained in a tank that is in an ambient approximately 300 K environment. In one embodiment, a radiation shielding apparatus is provided. The radiation shielding apparatus includes a cryogenic vessel and a cryogenic hydrogen radiation shielding material capable of providing a radiation shield, the cryogenic hydrogen radiation shielding material includes hydrogen at a temperature of less than or equal to about 20 K, wherein the cryogenic hydrogen radiation shielding material is contained in the cryogenic vessel. In another embodiment, a spacecraft is provided. The spacecraft includes a radiation shielding apparatus and a crew module. The radiation shielding apparatus includes a cryogenic vessel and a cryogenic hydrogen radiation shielding material capable of providing a radiation shield, the cryogenic hydrogen radiation shielding material includes hydrogen at a temperature of less than or equal to about 20 K, wherein the cryogenic hydrogen radiation shielding material is contained in the cryogenic vessel. The crew module includes a walled enclosure with an exterior surface and a hatch to permit access and egress to an internal area within the walled enclosure, wherein the radiation shielding apparatus is disposed adjacent to the exterior surface of the crew module. In another embodiment, a spacecraft is provided. The spacecraft includes a fuselage, a radiation shielding apparatus, a crew module and a radiator system. The fuselage defines an internal volume within the spacecraft. The radiation shielding apparatus is disposed in the internal volume of the fuselage and includes a cryogenic vessel, insulation material and a cryogenic hydrogen radiation shielding material capable of providing a radiation shield, the cryogenic hydrogen radiation shielding material including solid hydrogen, subcooled solid hydrogen or a mixture thereof, wherein the cryogenic hydrogen radiation shielding material is contained in the cryogenic vessel. The crew module is disposed in the internal volume of the fuselage and includes a walled enclosure with an exterior surface and a hatch to permit access and egress to an internal area within the walled enclosure, the internal area of the crew module being substantially maintained at about room temperature. The radiator system is to remove heat emitting from the crew module. The radiation shielding apparatus is disposed between the fuselage and the exterior surface of the crew module. The radiator system is disposed between the exterior surface of the crew module and radiation shielding apparatus. Studies have shown there will be a need to protect astronauts during, for example, interplanetary missions (e.g., Mars) from deep space radiation with an annual allowable radiation dose less than 500 mSv. For a typical crew module that is 4 meter in diameter and 8 meter in length, the mass of polyethylene radiation shielding required would be more than 17,500 kg at a needed shielding a real density of approximately 140 kg/m2. By comparison, the requirement for hydrogen shielding is 70 kg/m2, much less than polyethylene shielding. Vapor hydrogen has a very low density, and the storage tank can't fit into a 5 meter payload fairing for a rocket that might launch the crew module. Liquid and solid hydrogen have much higher densities and are preferable to vapor hydrogen for the purpose of packaging the required hydrogen areal density in a reasonable volume. For example, the thickness of solid hydrogen needed to shield astronauts is about 0.43 m and the combined diameter of the crew module with shielding is about 4.86 m. However, a challenge with using either liquid or solid hydrogen as shielding material is that the hydrogen has to be stored at cryogenic temperatures. The Cryogenic Hydrogen Radiation Shielding (CHRS) requires a thermal system to prevent heat leak into cryogenic tank from the crew module (substantially maintained at room temperature, for example, about 300 K) to avoid phase change of the cryogenic hydrogen. However, even after accounting for the mass of the thermal and containment system for CHRS, CHRS may halve the mass of a radiation shield when compared to polyethylene shields. The crew module is intended to be suitably maintained in temperature and atmosphere to adequately support life and provide an environment in which astronauts could live. CHRS material includes liquid hydrogen, subcooled liquid hydrogen, solid hydrogen and subcooled solid hydrogen or a mixture thereof, preferably solid hydrogen, subcooled solid hydrogen or a mixture thereof and more preferably subcooled solid hydrogen. Liquid hydrogen at a pressure of 1 atm can be stored at a maximum temperature of about 20 K. Subcooled liquid hydrogen can be stored at a temperature from about 14 K to about 20 K. Solid hydrogen can be stored at a maximum temperature of about 14 K (the triple point of hydrogen). Subcooled solid hydrogen can be stored at a temperature of less than about 14 K, preferably from about 10 K to about 12 K. Subcooled solid hydrogen may have an advantage in that it can absorb more heat without changing phase. CHRS material has a lower mass density compared to other radiation shielding materials, such as aluminum and polyethylene. The degree of radiation shielding provided by a CHRS material depends on the mass of hydrogen per unit surface area. One embodiment includes a shielded capsule 100 including cryogenic hydrogen radiation shielding as shown in FIG. 1A and FIG. 1B. FIG. 1A and FIG. 1B include a crew module 102 defined by a circumferential side wall 104 and end walls 106 and 108 and having an inner volume 110 which the crew may inhabit. The crew module 102 is protected by an annular cryogenic vessel 112 adjacent the circumferential side wall 104 and by toroidal cryogenic vessels 114 and 116 adjacent end walls 106 and 108, respectively. When the capsule is in operation, the annular cryogenic vessel 112 and toroidal cryogenic vessels 114 and 116 contain CHRS material to provide radiation shielding to the crew module 102. A bore 118 in the middle of toroidal cryogenic tank 114 leads to hatch 120 to allow for crew access and egress from inner volume 110 of the crew module 102. Bore 118 and/or the hatch 120 can be closed with a suitable radiation shielding hatch cover in order to minimize radiation from reaching the inner area of the crew module through bore 118 and/or hatch 120. The suitable radiation shielding hatch cover may be movable and constructed of a suitable radiation shielding material, such as for example, polyethylene. Another embodiment includes a shielded capsule 200 including cryogenic hydrogen radiation shielding as shown in FIG. 2. FIG. 2 includes a crew module 202 having an inner volume 204 which the crew may inhabit, circumferential side wall 206 and end walls 208 and 210. The crew module 202 is surrounded by a cryogenic vessel 212. When the capsule is in operation, the cryogenic vessel 212 contains CHRS material, such as solid hydrogen, to provide radiation shielding to the crew module 202. The cryogenic vessel 212 includes a circumferential vessel portion 214 adjacent circumferential side wall 206 and vessel end portions 216 and 218 adjacent end walls 208 and 210, respectively. A bore 220 in the middle of vessel end portions 216 leads to hatch 222 which allows for crew access and egress from the crew module 202 of the shielded capsule 200. Bore 220 and/or the hatch 222 can be sealed with a suitable radiation shielding hatch cover 224 that may be movable and constructed of a suitable radiation shielding material, such as for example, polyethylene. A passive thermal management system, such as a 100 K thermal shield, includes end sections 228 and 230 adjacent end walls 208 and 210, respectively, and a side wall section 232 adjacent the circumferential side wall 206 and is positioned between the crew module 202 (circumferential side wall 206 and end walls 208 and 210) and the cryogenic vessel 212 (circumferential vessel portion 214 and vessel end portions 216 and 218). Conduits 225, 226 and 227 may provide a thermal link between a radiator 233 and the exemplified 100 K thermal shield insulation material. The radiator system (thermal management system end sections 228 and 230 and side wall section 232, conduits 225, 226 and 227 and radiator 233) rejects heat into deep space, the latter existing at a temperature of about 7 K. The radiator system removes heat emitting from the inner volume 204 of the crew module 202 in order to insulate and minimize heat transfer to the cryogenic vessel 212 from the inner volume 204 being maintained at about room temperature (about 300 K). Such heat transfer from inner volume 204 can affect and be problematic to the maintenance of the low temperature of the CHRS in the cryogenic vessel 212. The CHRS system components including a cryogenic tank or vessel and insulation material and their design and materials should be selected based on mechanical and fluid engineering criteria including thermal performance (e.g., insulation) and structural performance (e.g., ability to maintain integrity & internal pressure) experienced in the various rigors of space as well as in a gravitational environment, such as, on a planet (e.g., Earth). The tank or vessel may be suitably constructed of, for example, metal, such as aluminum, as well as composite or composite overwrapped tank skins. For example, the cryogenic tank or vessel that contains the CHRS material should be able to withstand some pressure increase. As a result, suitable tank or vessel specification should be determined, including, for example, proper material and wall thickness. The cryogenic system components may include various conduits to supply material to and vent material from the cryogenic system including the cryogenic tank or vessel as well as sensors to monitor the cryogenic system including the cryogenic tank or vessel. Insulation of the tank is important to maintain the temperature of the hydrogen contained therein. Such a change in temperature can be affected by various factors including convection (caused by, for example, heat flowing from the ambient atmosphere to the tank at the launch pad), conduction (caused by, for example, heat flowing from spacecraft components through the support structure to the tank) and radiation (caused by, for example, heat transmitting by solar irradiation, or planetary albedo impinging on the tank surface). The cryogenic tank or vessel (the terms “tank” or “vessel” may be used interchangeably any where herein) may include design features and components to maintain the CHRS material therein. For example, when the CHRS material includes liquid hydrogen, low or zero gravity fluid management using screen channel and/or vane systems are two possible options for the fluid management system. Such fluid management systems may be needed to provide the required fluid distribution in the cryogenic tank or vessel, and suppress the formation of large gas bubbles therein. A vane system may also be used in several locations of the cryogenic system in order to create enough surface tension force to move gas present in the cryogenic tank or vessel to a vent location or a cooler location for recondensation. The cryogenic system supplying, supporting and maintaining the cryogenic tank or vessel and the CHRS material therein may be active or passive and include a space thermal system and ground cooling system. The ground cooling system may be utilized to supply, support and maintain the cryogenic system and cryogenic tank or vessel aboard a spacecraft prior to launch, including, for example, on Earth. Such a ground cooling system may, for example, utilize a cryogenic hydrogen subcooler to cool hydrogen close to triple point temperature within a day and a helium cooler to freeze and subcool the hydrogen to 10 K. Such a ground cooling system may be included in a spacecraft or separate there from, preferably it is housed at a launch facility separate from the spacecraft and located on or close to the launch pad. In the latter preferred embodiment, the ground cooling system is connected to the spacecraft and disconnected at or before launch. The space thermal system (thermal management system) may be utilized to supply, support and maintain the cryogenic system and cryogenic tank or vessel aboard a spacecraft after launch or once a separate ground cooling system is disconnected from the spacecraft. In one embodiment, the CHRS including the solid hydrogen, the cryogen thermal and storage system would have an areal mass density of 70 kg/m2. Such a system could utilize, for example, a passive thermal control system including solar shields, load responsive multilayer insulation (LRMLI), multilayer insulation (MLI), aluminum foam (for example, 3% density), and 100 K shield cooled by a 4 meter diameter radiator. Such a design may utilize the benefit of the 7 K temperature of deep space (for example, when the spacecraft is not in planetary orbit) by pointing the radiator towards deep space. The preliminary thermal analysis results show that the heat leak from a crew module is 50 Watt, which can be easily compensated with a small heater, such as radiator 233 shown in FIG. 2. As a further example, the CHRS can absorb 1 Watt of heat in deep space from the Sun and 130 Watt of heat from the Earth and Sun over a couple of orbits in LEO. For a one year mission to Mars, for example, a spacecraft may stay in LEO for a few hours. The overall heat leak could be about 32,500 kJ for the whole mission, which could increase the temperature of, for example, solid hydrogen from 10 K to close to 14 K (the triple point of hydrogen). In this example, with CHRS, the mass of crew module with radiation shielding could be reduced from more than 26,500 kg to less than 17,800 kg. CHRS could save nearly 8,800 kg for a 4 m diameter and 8 m long cylindrical crew module and halves the required shielding mass when compared with polyethylene shields. Such could, for example, save close to 44 million dollars in launch cost, based on $5000/kg estimate for SpaceX Felcon 9. In another embodiment, the space thermal system may also include a cryocooler, for example, a 14K cryocooler, in the design to actively store the hydrogen at a desired cryogenic temperature and in, for example, solid form. Such a cryocooler, for example, a 14K cryocooler, may be beneficial on space missions lasting more than 1 year. FIG. 3 illustrates an embodiment showing a space thermal system and a ground cooling system, around a crew module. It shows half of a section view of the spacecraft, since the spacecraft is reasonably symmetric about the bottom horizontal edge of the schematic. Spacecraft 300 includes a fuselage 302 with an internal volume (area) 303, a crew module 304 and space thermal system 306. The crew module 302 includes a walled enclosure 308 with an exterior surface 309 and an internal volume (area) 310 within the walled enclosure 308. Space thermal system 306 has a tank 312 including, for example, a metal skin, for example, aluminum, and a foam insert, for example, aluminum foam, preferably about 1% to about 3% density aluminum foam, more preferably about 1% density aluminum foam. In the embodiment, tank 312 is encased with several exemplary layers of insulation materials. Encasing tank 312 is a tank integrated multilayer insulation (IMLI-a product of Quest Thermal Group) 314 composed of, for example, layers of multilayer insulation (MLI) with polymer spacers. Encasing the tank IMLI 314 is a 100 K thermal shield 316 composed of, for example, aluminum. Encasing the 100 K thermal shield 316 is a 100 K thermal shield load responsive multilayer insulation (LRMLI-a product of Quest Thermal Group) 318 composed of, for example, layers of MLI supporting a lightweight metallic vacuum shell with polymer spacers. Encasing the 100 K thermal shield LRMLI 318 is 100 K thermal shield IMLI 320 composed of, for example, layers of MLI with polymer spacers. Spacecraft 300 also includes low thermal conductivity support structure 322 (for example, T300) and thermal connections 324 and 326 that provide heat sinks for heat interception. Ground cooling system 328 includes liquid hydrogen supply cluster 330, hydrogen freezing cluster 332, hydrogen tank fill and vent cluster 334, LRMLI vent cluster 336 and liquid hydrogen ground subcooling return cluster 338. Liquid hydrogen subcooling supply cluster 330 is connected at 340 to a hydrogen subcooler and includes conduit system 342, burst disk/relief valve 344, seal-off valve 346 and thermal acoustic oscillation damper 348. Conduit system 342 is connected to tank 312 at thermal connection 350. Hydrogen freezing cluster 332 performs a freeze and subcooled freezing operation on hydrogen in tank 312 and includes an inlet and outlet for the hydrogen freezing coolant in a conduit 352 that runs from seal-off valve 354 to seal-off valve 356 through thermal connection 364, section 358 that passes through tank 312 and thermal connection 366. Hydrogen tank fill and vent cluster 334 includes conduit system 370 and burst disk/relief valve 372. Conduit system 370 is connected to a hydrogen source at 374 and provides hydrogen to tank 312 via thermal connection 376. Hydrogen tank fill and vent cluster 334 also includes conduit system 378 with pyro valve 380 connected to vent 385, seal-off valve 382 and burst disk/relief valve 383 connected to vent 386. Conduit system 378 is connected to tank 312 via thermal connection 384 to vent hydrogen from tank 312. Conduit systems 370 and 378 are connected via conduit system 387 that includes thermal acoustic oscillation damper 388. LRMLI vent cluster 336 is used to vent the LRMLI for convection insulation while the radiation shield is on the ground in an environment with an atmosphere and includes conduit system 389, burst disk/relief 390 and seal-off valve 391. Conduit system 389 is connected to tank 312 at 392 and vents through a vacuum pump at 393. Liquid hydrogen ground subcooling return cluster 338 is connected at 394 to the return side of the hydrogen subcooler and includes conduit system 395, burst disk/relief valve 396, seal-off valve 397 and thermal acoustic oscillation damper 398. Conduit system 395 is connected to tank 312 at thermal connection 399. Using the CHRS system, the crew module can be substantially maintained at about room temperature with a 50 Watt heater, while keeping the CHRS temperature at the desired low temperature, for example, below 14 K. The mass and the power requirements of the CHRS system aboard a spacecraft should be determined and incorporated into the overall spacecraft design. For example, the mass of solar panels that may be needed for the power requirement should be calculated and added to the CHRS system when liquid hydrogen is used. FIG. 4 illustrates a CHRS tank and insulation 400 embodiment including LRMLI 402 and 404, MLI or IMLI 406, 408, 410 and 412, 90-100 K shield 414, gaps 416 and 418, CHRS tank walls 420 and 422 and solid hydrogen and aluminum foam 424. A crew module is positioned in this embodiment closest to LRMLI 402. FIG. 5 illustrates comparisons on depth-effective dose estimates versus shielding thickness using the ICRP definition of quality factors for several materials. FIG. 6 illustrates comparisons on depth-effective dose estimates versus shielding thickness using the NASA Solid cancer definition of quality factors for several materials. Calculations For both FIG. 5 and FIG. 6 are for 1-year GCR exposures at solar minimum of a human behind each of the shielding materials. The shielding materials in FIG. 5 and FIG. 6 are aluminum (graphs 501 and 601, respectively), epoxy (graphs 502 and 602, respectively), water (graphs 503 and 603, respectively), polyethylene (graphs 504 and 604, respectively), and liquid hydrogen (graphs 505 and 605, respectively). The horizontal axis indicates the g/cm2 of each of the materials and the vertical axis indicates the radiation dose (exposure) in millisievert (mSv). Another benefit of an embodiment utilizing, for example, CHRS material could be used for other mission purposes, such as fuel for a final burn that could help capture the spacecraft into low Earth orbit on a return trajectory or even be used for a burn on a lunar ascent vehicle. Such a dual use could further increase the mass advantage of such embodiments. This written description uses examples as part of the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosed implementations, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. |
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063242591 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS In the form of a basic diagram, FIG. 1 shows a plan view of an inventive scattered-ray grid 1. The grid 1 is composed of a silicon carrier 2 and of a number of rows 3 of pin-shaped absorption elements 4 made of lead, which are introduced in holes that are etched into the carrier 2. Only a few of the absorption elements 4 are specifically shown; it will be understood that each row 3 is composed of a number of such elements. The etching process ensues by means of an etching mask, which can be produced by means of a photo technique with which the configuration of the row arrangement can be fixed in a simple way. The scattered-ray grid 1 can be divided into a number of grid sectors, such as six individual grid sectors I-VI, the configuration of the rows 3 being the same in all six grid sectors. For clarity, the row arrangement is only indicated in sector I. Apart from the rows 3a that respectively extend through the center Z and that border the sectors, the rows 3 start at respectively different radii and are directed toward the center Z, as can be seen from FIG. 1. FIG. 2 shows a portion of FIG. 1. The determination of the position of the origin of every row is shown in FIG. 2. Every row radially proceeds to the periphery of the carrier 2 and has its origin in the space r.sub.0 +n.DELTA.r from the center Z. Therefore, .DELTA.r, as a radial increment, determines the density of the rows; the start radius r.sub.0 optimizes the density of the rows in the center. n is an integer. A relevant space r.sub.0 +n.DELTA.r is shown in FIG. 2 as an example. A location is now to be selected within this space, at which the origin of the (next) row 3.sub.n is to be placed. The largest angular spacing between all existing adjacent rows, which intersect the circle or arc of circle with the origin radius, namely the space r.sub.0 +n.DELTA.r, is searched for this purpose. In the example, the two rows 3b are spaced from one another around the largest angle a. This angular spacing now determines the angle section, which is to be divided in a predefined ratio p:q, so that the exact position of the origin u of the new row 3.sub.n between the two rows 3b results therefrom. p and q can be rational numbers or irrational numbers. The best distribution results for p.noteq.q. In the described way, the position of each new row is determined in iterative fashion by taking the two rows 3a that start (originate) in the grid center as a basis. The described iteration condition generates an extremely homogenous radial row pattern, but it can nevertheless exhibit spiral-shaped density variations although they are almost negligible. In order to substantially avoid such density variations, a different version of the iterative method is provided, which is explained in detail in FIG. 3. In this version, for determining the position of the new row 3n, the angular spacing is also determined for each row pair that intersects the circle or arc of circle with the origin radius r.sub.0 +n.DELTA.r, as described with respect to FIG. 2. Subsequently, the angular spacings to the two rows respectively on opposite sides of the adjacent rows are determined. In the shown example, these are the angle spaces b and c respectively between the two pairs of rows 3b and 3c. The sum S=a+F (b+c) is formed on the basis of the angle spacings a, b, c, with the sum of the two angle spacings b and c being weighted with a predefined factor F, which is <1, within the sum S. The largest sum S is now selected from the cumulative values determined for each row pair at the relevant radius, and the angle section associated with this largest sub S is divided in the given ratio p:q. The width of a row is dependent on the diameter of the pin-shaped absorption elements 4 and is in the range of a few .mu.m; the start radius r.sub.0 is 30 .mu.m, for example; the individual radius step or increment .DELTA.r is 100 .mu.m, for example. In addition n is element of the natural numbers including zero. The described iterative algorithms make it possible to determine the position of the rows in a simple way, so that highly homogenous scattered-ray grids can be generated. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art. |
042971675 | summary | The invention relates to a nuclear reactor installation with a concrete cell disposed beneath the earth of a hill for enclosing activity-carrying components. Such a nuclear reactor installation is described, for example, in the German-language journal, "Atomwirtshaft", July/August 1975, pages 363 to 366. No details are given therein, however, regarding the spatial construction thereof. Furthermore, a paper with the same theme entitled "Underground Siting of Nuclear Power Reactors" has appeared which had been prepared for a Symposium in Vienna. In this paper, a nuclear reactor installation is illustrated in FIG. 1 thereof wherein not only the nuclear reactor but also the machinery building supplied thereby are disposed in the ground or earth. The construction of the machinery building is only hinted at, though. It is apparent, nevertheless, that a light structure was involved having a volume of at least the same order of magnitude as that of the concrete cell with the activity-carrying components. It is accordingly an object of the invention to provide a nuclear reactor installation of the foregoing type which is improved from the standpoint of safety engineering, at relatively low expense, over corresponding installations of the prior art. It is a further object to provide an installation of such construction, that will be less susceptible to disturbances and, in the event disturbances should occur, will be less sensitive to consequential damages. With the foregoing and other objects in view, there is provided, in accordance with the invention, a nuclear reactor installation having a concrete cell disposed beneath the earth of a hill for enclosing activity-carrying components comprising at least one additional concrete cell (auxiliary cell) disposed in the earth separated from the first-mentioned concrete cell (central cell), the additional concrete cell being one fortieth or less of the volume of the central cell, preferably one two-hundredths thereof, and being at least predominantly of shell-like construction, and including equipment of use for the nuclear reactor installation, such as secondary, emergency or auxiliary equipment, received in the additional concrete cell. This is seemingly at variance with the demand for limited expense, especially since one could believe or expect that anyway, through the underground type of construction in the earth of a hill, virtually complete protection at least against consequential damage from disturbances is provided. Actually, however, the division of secondary, emergency or auxiliary equipment into further separated concrete buildings permits first a complete exploitation of the increased security or safety connected with the underground type of construction, as explained hereinafter in clearer detail. By "separated" there is meant, in this connection, that the individual concrete buildings are "floatingly" disposed, so that they can follow movements of the earth or ground independently of one another. This can be especially ensured by means of intermediately disposed pipes or channels which are provided with movable connectors, as will be described hereinafter. Such a separation, in fact, exists also for the machinery building according to the hereinaforementioned paper prepared for the Viennese Symposium. This machinery building is not only considerably larger, however, than the auxiliary cells according to the invention. It is also constructed as a purely rectangular building with flat walls, and is in no way of shell-like construction. The conventional machinery building is therefore capable of little resistance against outer and inner pressures. This is essentially the point of the invention, as will also be explained further hereinafter. In accordance with another feature of the invention, the additional concrete cell is connected in a line through which energy is removed from the hill, and valve means are disposed in the additional concrete cell for closing off the energy removal line. In this manner, success is achieved in reliably closing off the inclusion or enclosure provided by the central concrete cell of the activity-carrying components in the sources of the line for, in contrast to an arrangement of valves within the central cell, it is impossible that valves in the auxiliary cell would be damaged or otherwise rendered inoperative due to disturbances in the central cell. The inclusion or enclosure especially reliably provided by the underground type of construction is thus, in accordance with the invention, additionlly protected through the disposition of additional auxiliary cells for the lines which extend out of the central cell. The aforementioned embodiment of the invention is especially advantageous if the central or first-mentioned cell is part of a so-called double-containment. Thus, in accordance with a further feature of the invention, the first-mentioned or central concrete cell is spaced from and surround a tight containment for enclosing activity-carrying components and defines therewith an annular space, the line extending from the containment and, in addition to the valve means in the additional or auxiliary concrete cell, further means for provided in the containment and/or in the annular space for closing off the line. The further closure means in the containment can be formed in a pressurized water reactor by the steam generating tubes which, as is generally known, separate the activated primary cooling water from the virtually activity-free secondary coolant. Additional closure valves can also be provided, however, and in fact not only inside the containment and outside the central cell, but rather, in the annular space between the containment and the central cell, so that maximal security against the liberation of activity-carriers is provided. The additional or auxiliary concrete cell, in accordance with yet another feature of the invention, has an outlet extending into the earth of the hill, the outlet having a cross section of at least 1 m.sup.2. What is achieved is that also if a rupture of the line were to occur in the auxiliary cell, no overload is conceivable which would cause a too-high pressure in the interior of the auxiliary cell and thereby cause it to burst. The outlet can be constructed as a blow-down line that is provided with a unilaterally operating closure member disposed in the interior of the auxiliary cell. By closure members there is meant not only ckeck valves but also, for example, bursting or rupture discs which, due to a bracing construction, have a lower response pressure in the one direction than in the other. The blow-down line should terminate in a gravel pile or in pipes leading to the interior of the hill. The introduction of gases and vapors which would otherwise cause excess pressure, can thereby be facilitated, because the permeability of the hill materal is limited. Furthermore, a secondary safety valve can be connected to such a blow-down line in order, for example, to attain relief when excess pressure exists in the line that is to be closed off. By means of such a blow-down line, energy, for example, in the form of steam which has been produced during emergency cooling of the nuclear reactor, can be removed. In accordance with another feature of the invention, a plurality of the additional or auxiliary concrete cells are spatially distributed around the first-mentioned or central concrete cell, the auxiliary cells being connected in respective lines thereof which energy is removed from the hill, and valve means are included which are respectively disposed in the auxiliary cells for closing off the respective energy removal lines. Preferably, the number of auxiliary cells correponds to the number of lines, it being advantageous for steam power plants to conceive of the live steam line, on the one hand, and the feedwater line, on the other hand, as one pipe system which passes through a common auxiliary cell. Besides such special auxiliary cells provided for the closure, other auxiliary cells may be provided wherein exclusively emergency equipment, for example, for emergency cooling, are accommodated, or auxiliary equipment, for example, groundwater filtering equipment, if these are to be especially safety housed independently of the central cell. In accordance with a further feature of the invention, the auxiliary cell is connected in a line extending to the central cell for removing energy from the hill, the line extending through movably sealed pipes. What is attained thereby is not only that the line per se remains free from the pressure of the earth and from movements thereof, but rather also, that accessibility for inspections is provided. Channels built with the aid of such pipes, such as concrete pipes, for example, wherein the lines run, should also, at least by creeping, be accessible for inspection personnel. The pipes are advantageously of pressure-tight construction, the pressure tightness being not only determined with respect to the weight of the earth located above the pipes, but also with respect to the conceivable inner pressure, which might be produced in the event of a line rupture. The elastic joint connectors provided at the connecting locations cannot only be obtained through the hereinaforementioned seals but also, under suitable conditions through the construction of the connecting locations per se, for example, in the form of universal or ball-and-socket joints. Through the movable sealing of the pipes, which can be effected with yieldable sealing materials, such as rubber or with impermeable coverings in the form of clay strata or also tarpaulins or sheets formed of synthetic or plastic material, assurance is provided that relative movements, at least within limits, are possible, as may be produced by settling of the earth or by earthquakes. Notwithstanding these seals, and in accordance with an added feature of the invention, the pipes and the connecting openings produced accordingly at the central and the auxiliary cells are disposed above the maximal groundwater level or water table. In accordance with an additional feature of the invention, the auxiliary cell is accessible only from the outside of the hill and not, however, from the central cell. What is achieved thereby is that the effects of disturbances in the interior of the central cell cannot have any effect upon the devices of the auxiliary cell. On the other hand, it should also not be possible that through the access to the auxiliary cell, any disturbances should be produced in the central cell which could release activity, as a result of military action or sabotage, for example. In accordance with another feature of the invention, a well extends from the auxiliary cell into groundwater in the earth, which will usually be present underneath the nuclear reactor installation. With such a well which is disposed in the auxiliary cell and protected therein uninfluenced by the activity in the central cell, the groundwater level can be influenced so as to prevent a further spread or distribution of the radioactivity. In addition, such a well can also serve for emergency and/or aftercooling. In accordance with a further feature of the invention, a plurality of redundant, spatially separated emergency cooling devices are mounted in the auxiliary concrete cells and a system of lines extending out of the central cell and associated with said emergency cooling devices. The hill serves in devices according to the invention for enclosing or at least for delaying activity which can hypothetically occur by failure (a) of the primary components of the nuclear reactor, PA1 (b) of the containment enclosing these primary components, and PA1 (c) of the concrete building of the central location. In accordance with the invention, another control is provided, however, also for this, in all probability, impossible situation, from a practical standpoint. Thus, impermeable partitions, especially formed of clay, are disposed in the hill for separating regions of varying activity in case of a disturbance, the auxiliary cells being disposed in regions of minimal activity separated by the partitions. What is attained thereby is that the auxiliary cells are still relatively well accessible even in the event of the most unlikely disturbance, so that, for example, the inclusion or enclosure of the activity in the region of the auxiliary cells, it controllable somewhat through these extending lines and is accessible for maintenance. Further in accordance with the invention, the lines extend through recesses formed in the partitions, the recesses being considerably smaller than corresponding dimensions of the auxiliary cells, so that the necessary seals for the partitions are small. In accordance with an added feature of the invention, the partitions cover connections to the auxiliary cells so as to effect an additional sealing action. For the case of a live steam line and/or a feedwater line that have already responded or been activated, a conical attachment location with a closure valve mounted thereat is provided because, with such a conical fastening location, a mechanically stable construction is able to be well united with a pressure-tight closure. For the same reasons, there is provided in accordance with an additional feature of the invention, that the line extends to the central cell and is formed as a double-wall pipe. The effect thereon is that in the event of a break in the line, the pressure released to the outside only acts upon the double-wall pipe which can be constructed so as to be adequately pressure-tight, without great expense, whereas otherwise one would have to contend with pressure increases in the concrete channel which could cause consequential damage. As noted hereinbefore, the auxiliary cells should only be accessible from the outside in order to avoid effects from the region of the central cell or into that region. For the same reason, and in accordance with yet other features of the invention, the auxiliary cells are connected only through pressure-free access means or through pressure-tightly closed sluice passages or locks. In accordance with yet a further feature of the invention, mechanically sturdy baffle plates are provided for preventing penetration of solid material into the auxiliary cells and the lines respectively connected thereto. Although the auxiliary cells with their small volume, also during unified spatial removal from the central cell, are generally covered to such a height by the earth of the hill that mechanical effects from the outside are unlikely, it can be advantageous for the earth of the hill located above the auxiliary to have a tight cover layer or stratum that is bridged by a closable outlet or discharge line. The closable discharge lines ensures pressure relief during blow-down of steam from the auxiliary cell, which is produced during a line break, because an air cushion present in the hill can be pushed out without raising the cover layer of the hill. The instant application is one of three application simultaneously filed by the applicant, related generally to the same subject matter although directed to different inventions therein. Other features which are considered as characteristics for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in nuclear reactor installation, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. |
abstract | The present invention relates to methods of predicting proximity heating of resists in electron beam lithography in real-time as the writing proceeds enabling beam compensation in current and/or dwell time to be performed during writing. A method of using a precomputed kernel capable of proximity resist temperature evaluation in real-time as beam writing proceeds by scalar product of the kernel with a graded cell size coverage map. A shifted impulse response function is shown to give the kernel values accurate to within a few percent. |
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claims | 1. A combined blade guide and exchange tool, comprising:a blade guide tool having a lower end and an upper end and a plurality of frame rails supporting a pair of collet housings at a lower end of the blade guide tool, a pair of fuel support grapple actuating rods are supported between the plurality of frame rails and having a first end engaging a pair of collets within the pair of collet housings and having a second end disposed at the upper end of the blade guide tool; anda blade exchange tool releasably mounted to the upper end of the blade guide tool and including a pair of upper collets for engaging the pair of fuel support grapple actuating rods, the blade exchange tool further including a slider and hook assembly attached to a cable guided by the blade exchange tool and adapted for engaging and lifting a control rod. 2. The combined blade guide and exchange tool according to claim 1, further comprising:a pair of air cylinders connected to respective ones of the pair of upper collets. 3. The combined blade guide and exchange tool according to claim 2, further comprising:a fuel support pin actuating rod adapted to engage a pin on a core support, the fuel support pin actuating rod is engageable by an air switch actuating assembly of the blade exchange tool, the air switch actuating assembly being engageable with an air switch of the blade exchange tool, the air switch being activated to prevent airflow to the retract side of the air cylinders of the pair of upper collets. 4. The combined blade guide and exchange tool according to claim 1, wherein the slider and hook assembly includes a hook actuator cylinder. 5. The combined blade guide and exchange tool according to claim 1, wherein the blade exchange tool includes a connecting device for releasably connecting the blade exchange tool to the blade guide tool. 6. The combined blade guide and exchange tool according to claim 1, wherein the blade guide tool includes a top plate at the upper end of the blade guide and the blade exchange tool includes a base plate that is supported on top of the top plate when the blade exchange tool is engaged with the blade guide tool. 7. The combined blade guide and exchange tool according to claim 1, wherein the pair of upper collets are each disposed within a respective upper collet housing. |
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046876278 | abstract | An improved water displacer rod includes an elongated hollow thin-walled tube with a pair of end plugs attached to opposite ends of the tube to hermetically seal the tube and a plurality of support pellets disposed in a stacked relationship within the tube. The pellets allow the thin-walled tube to be laterally flexible while still able to resist collapse due to high external pressure. Each pellet is preferably formed of a body having a hollow annular cross-sectional shape and a pair of end webs extends across and closing opposite ends of the body. The body defines a central void and the webs seal the void. Thus, when the pellets are stacked within the tube, each void is sealed individually one from the next. A double barrier is provided in the displacer rod by the hermetically sealed tube and the individually sealed pellets. Even if the tube should fail, moderator water will not flood the tube interior since the stacked pellets occupy and encapsulate substantially all of the empty space within the failed tube. As a result, the displacer rod containing the failed tube will still be able to perform its intended function. |
040574652 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Throughout the description which follows, like reference characters indicate like elements in the various figures of the drawings. Referring now more particularly to FIG. 1, a nuclear core 10, comprised of a plurality of fuel elements (not shown), which are fabricated of a fissionable material such as uranium or plutonium, is situated within a nuclear reactor pressure vessel 12. The pressure vessel 12 has coolant flow inlet means 14 and coolant flow outlet means 16 through which the primary fluid, or reactor coolant, which in the case of gas-cooled nuclear reactor may be an inert gas such as helium or argon, can enter and exit from the nuclear core 10. Connected to the inlet means 14 and the outlet means 16 is the primary coolant flow system 18, one loop of which typically includes a compressor turbine 20, a work turbine 22, heat exchange means 24 and compression means 26. During normal reactor operations, the gaseous coolant exits through the outlet means 16 of the pressure vessel 12, passes through the compressor turbine 20, and then passes through the work turbine 22. The compressor turbine 20 is mechanically connected to the compression means 26, and generally provides the powering force for operating the compression means 26. The work turbine 22 is connected to means (not shown) by which the energy generated in the work turbine 22 is used to power the load. After exiting from the work turbine 22, the coolant flows through heat exchange means 24, where it is cooled by means (not shown), exits from the heat exchange means 24 and enters the compression means 26. In the compression means 26, the coolant is compressed, passes to the pressure vessel inlet means 14, and reenters the nuclear core 10. As it passes through the core 10, the coolant receives the heat which has been generated by the core, and flows to the pressure vessel outlet means 16, where the described flow cycle is repeated. The above described primary coolant flow loop is well known in the art and is described in greater detail in, for example, U.S. Pat. No. 3,663,364. The auxiliary heat removal system, used during emergency or other conditions when the primary coolant flow system 18 is not operational, comprises a gas turbine 28, a heat exchanging means 30 such as a heat exchanger, and compression means 32, such as a compressor, for compressing the reactor coolant, conduit means 34, such as piping, for supplying the reactor coolant from the nuclear core 10 to the gas turbine 28, conduit means 26 for supplying the reactor coolant from the gas turbine 28 to the heat exchanging means 30, means such as a conduit 38 for supplying the reactor coolant from the heat exchanging means 30 to the compression means 32 and conduit means 40 such as piping, for supplying the reactor coolant from the compression means 32 to the reactor core 10 complete the flow cycle. Although the conduit means 34 for supplying the reactor coolant from the nuclear core 10 to the gas turbine 28 are shown as being connected to the pressure vessel outlet means 16, such an interconnection is not a requirement. The requirement for the conduit 34 for supplying coolant from the core 10 to the gas turbine 28 is that these conduit means 34 come into fluid communication with the gaseous reactor coolant after it has exited from the nuclear core 10 and has been heated. Likewise, the conduit means 40 for supplying coolant from the compression means 32 to the nuclear core 10 do not necessarily have to utilize the pressure vessel inlet means 14, but instead may traverse a different path so long as the conduit means 40 supply the coolant prior to its entering the nuclear core 10. The compression means 32 for compressing the reactor coolant, which may comprise a compressor, is mechanically coupled by means 42 such as the turbine shaft to the gas turbine 28. Through such a connection, the compression means 32 are driven by the gas turbine 28. Also mechanically coupled to the gas turbine 28 is a fluid pump 44 which is part of the heat exchanging means 30 for removing heat from the reactor coolant. As shown, the fluid pump 44 is connected to the gas turbine 28 by a power take-off gear box 46. The fluid pump 44 pumps a second fluid coolant, which may be a liquid such as water or a gas such as helium or air. The second fluid coolant, also part of the heat exchanging means 30 for removing heat from the first reactor coolant, passes in thermal communication with the first reactor coolant, and receives heat from the first coolant. This transfer of heat from the reactor coolant to the second fluid coolant may occur, for example, in heat exchanger 48. Means 50 for starting the gas turbine 28 are mechanically connected to the gas turbine 28. The starting means 50 may comprise a pneumatic starter 52, a starter valve 54, and a container 56 of starter fluid. Although shown as a separate element, the starter valve 54 may be incorporated integrally within the pneumatic starter 52. The starter fluid, which in this case is the same gas as the reactor coolant, is pressurized within the container 56. The starter valve 54 is connected to instrumentation (not shown) within the pressure vessel 16, the function of which will be hereinafter explained. Also included as part of the means 50 for starting the gas turbine 28 are a fluid starter pump 60, an extraction means 62 for diverting a portion of the reactor coolant exiting from the compression means 32 to the container 56 of starter fluid and conduit means 64. The starter fluid pump 60 is mechanically connected to, and driven by, the gas turbine 28 through the turbine shaft 42 and the power take-off gearbox 46. The operation of the auxiliary heat removal system is substantially as follows. Upon the occurrence of a condition which would cause the reactor to shut down, the instrumentation (not shown) which initiates the shutdown of the reactor sends a signal to the starter valve 54. The starter valve 54, upon receipt of such a signal, opens, and the starter fluid in the container 56, which is under pressure, flows to the pneumatic starter 52. This flow of starter fluid then activates the pneumatic starter 52, causing the gas turbine 28 to begin operating. The suction force created by the starting of the gas turbine 28 causes the gaseous reactor coolant to flow from the nuclear core 10 and through the supply means 34 to the turbine 28. The hot gas entering the turbine 28 is expanded through the turbine 28 causing the gas turbine 28 to rotate. The gas exits from the gas turbine 28 and flows through supply means 36 to the reactor coolant heat removal means 30. The heat in the reactor coolant is then transferred to the second fluid coolant such as in the heat exchange means 48 and the reactor coolant then flows to the compression means 32. The gas is then compressed by the compression means 32, and is reinserted, as a cool gas, into the nuclear core 10, where it will receive heat from the core 10 and begin the described flow cycle again. The work extracted by the gas turbine 28 is utilized to power the compression means 32. As such, the auxiliary heat removal system is operating as a type of closed Brayton cycle. In addition to powering the compression means 32, the gas turbine 28 also powers the fluid pump 44 which circulates the second fluid coolant. The second fluid coolant is pumped from the fluid pump 44, passes in thermal communication with the reactor coolant, receives heat from the reactor coolant, and is then either rejected or cooled. For example, if the second fluid coolant is water, the water could pass through a water turbine 56 and to a heat exchange means 68, which may be a water-to-air heat exchanger. The water would then exit from the heat exchanger 68 and be recirculated by the pump 44. The water turbine 66, which would be inserted into this means 77 for removing heat from the second fluid coolant, could be utilized to drive a means 70 for circulating air over the heat exchanger 68, which means 70 facilitates the removal of heat from the second fluid coolant. As can be seen, the entire heat removal system is independent of any external power source, but rather depends upon the heat of the reactor core 10 which is to be removed to supply the necessary power to cool the nuclear core 10. By a careful matching of the characteristics of the gas turbine 28 and the compression means 32, the gas turbine 28 and the compressor 32 will be able to circulate the reactor coolant until such time as the reactor core 10 is cooled sufficiently. However, at some point in time, the heat of the reactor coolant exiting from the core 10 will be insufficient to power the gas turbine 28. Once this occurs, the reactor coolant will no longer be circulated, and any heat being produced by nuclear core 10 will be retained within the pressure vessel 16 or the core 10 as sensible heat. After some additional time, this sensible heat may become large enough to cause structural damage, so it may be desirable to provide a means for restarting the gas turbine 28. This restarting of the gas turbine 28 is accomplished by the starter fluid pump 60 and the extraction means 62. Once the gas turbine 28 is started, the starter valve 54 closes and does not permit starter fluid to flow to the pneumatic starter 52. A small amount of reactor coolant is extracted, or "bled", by the extraction means 62. This small amount of coolant extracted, or starter fluid, is pumped by the starter fluid pump 60, which in turn is driven by the gas turbine 28 and the starter fluid is supplied to the container 56 of starter fluid. This starter fluid is continuously supplied until such time as the container 56 of starter fluid is filled and under a sufficient pressure to operate the pneumatic starter 52. Once the supply of starter fluid is sufficient, means 72 such as a valve will prohibit the introduction of any more starter fluid into the container 56. In this manner, a supply of starter fluid in the container 56 will be available to restart the gas turbine 28. As previously mentioned, once the gas turbine 28 has stopped operating, the temperature of the reactor coolant in the nuclear core 10 may rise, requiring additional circulation to cool the core 10. The starter valve 54 is responsive to the temperature of the reactor coolant in the nuclear core 10. This may be accomplished by various means, one of which may be a Bourdon tube. (A Bourdon tube, not part of this invention, is a generally semi-circular closed tube containing a fixed volume of gas. As the temperature surrounding the tube rises, the temperature causes a corresponding increase in the pressure of the gas within the tube. This increased pressure causes the semi-circular tube to begin to straighten. This straightening of the tube can then be connected to the starter valve 54 such that, upon the attainment of a predetermined movement, which corresponds to a predetermined reactor coolant temperature, the valve will open and allow the starter fluid to flow through it to the pneumatic starter 52.) Once the starter valve 54 opens, the supply of starter fluid 56 then causes the pneumatic starter 52 to operate, thereby starting the gas turbine 28, and the heat removal system functions as previously described. By providing a self-contained means for restarting the operation of the auxiliary heat removal system, the heat generated by the nuclear core 10 will be removed without the need of external controls, and the heat will not cause damage to structural components. The operation of the auxiliary heat removal system functions in an intermittent manner, and whenever the temperature in the nuclear core 10 rises above a predetermined level, cooling will occur. In addition to being utilized for land based nuclear reactor plants, the auxiliary heat removal system of this invention can be used effectively in mobile installations, such as for ship propulsion, where one of the hypothetical accidents could be the beaching or sinking of the ship. For use in, for example, a ship, the reactor system, including the auxiliary heat removal system, would be installed as heretofore described, excepting that the means 77 for removing heat from the second fluid coolant, mainly, the heat exchanger 68, the means 70 for circulating air, and the liquid turbine 66, would be located outside the containment vessel (partially illustrated and designated by the numeral 74). Upon a beaching of the ship, the auxiliary heat removal system would function as described. In the event the ship, and the reactor, would sink, the piping penetrations 76, 78 at the location where they pass through the containment vessel 74 would be sheared off by means such as explosives (not shown) which would be responsive to the increased pressure on the containment vessel 74 caused by the water. The interior of the containment vessel 74 would remain sealed except for the two openings where the piping 76, 78 passed through the vessel wall 74. Then, instead of utilizing a heat exchanger 68, the fluid pump 44 would draw water (as the second fluid coolant) in from the ocean through the piping 78, pass it in thermal communication with the reactor coolant, and after the water has received heat from the reactor coolant, the water would be rejected back into the ocean. A similar system, wherein the second fluid coolant is water, could be utilized for land based plants wherein the supply of water necessary to remove heat from the reactor coolant could be a river, lake, or similar supply of water. Additionally, in the unlikely event of an accident causing a disruption of the normal second fluid coolant flow, the piping connections 76, 78 could be sheared off, and the pump 44 could draw air from the atmosphere in, pass the air in thermal communication with the reactor coolant, and reject it out into the atmosphere thereafter. In this manner, adequate redundancy is provided to assure that the reactor coolant will at all times have a supply of coolant adequate to remove heat from it. Referring now to FIG. 2, a modification of the auxiliary heat removal system of FIG. 1, a plurality of temperature-dependent flow controllers 80 are installed, in parallel, in the means 34 for supplying the reactor coolant from the core 10 to the gas turbine 28. The flow controllers 80 are dependent upon the temperature of the reactor coolant, and regulate quantity of reactor coolant supplied to the gas turbine 28. The flow controllers 80, which may be temperature-dependent valves, operate to increase the amount of reactor coolant flowing to the gas turbine 28 when the temperature of the reactor coolant is high, and to decrease the amount of reactor coolant flowing to the gas turbine 28 when the reactor coolant temperature decreases. This may be accomplished, for example, by having each of the flow controllers 80 closed, or stop the flow of reactor coolant through it, at different temperatures. Therefore, as the reactor coolant temperature decreases, first one and then more valves will close until all the flow controllers 80 are closed when the reactor is cold. This temperature dependence could be accomplished utilizing means such as the Bourden tube utilized to operate the pneumatic starter, except that as the temperature decreased, the flow controllers 80 would stop the flow of coolant through them. By utilizing the flow controllers 80 in the means 34 for supplying coolant from the core 10 to the gas turbine 28, the necessity of extracting a quantity of coolant from the means 40 for supplying coolant from the compression means 32 to the core 10 could be eliminated. If the extraction is eliminated, the container 56 of starter fluid could be filled and pressurized prior to installation in the system, and could only be utilized once, when the emergency condition occurred. This modification, as opposed to the system shown in FIG. 1, will operate continuously until the reactor has cooled down such that the nuclear core 10 will not generate enough heat to cause any structural damage. A third modification is schematically illustrated in FIG. 3. In this modification, a second gas-powered turbine 82, herein called a supporting turbine 82, is installed in parallel with the gas turbine 28. The reactor coolant flowing through the supply means 34 would pass through, and power, both the gas turbine 28 and the supporting turbine 82. The supporting turbine 82, like the gas turbine 28, is mechanically connected to, and powers, both the fluid pump 44, through the power take-off gearbox 46, and the compression means 32. However, the supporting turbine 82 is larger than the gas turbine 28, and requires a higher temperature of reactor coolant flow through it to be able to operate than the gas turbine 28 requires. The operation of this modification then occurs with, as soon as the emergency condition occurs, both the supporting turbine 82 and gas turbine 28 are operational. As the temperature of the reactor coolant decreases, the supporting turbine 82 ceases operating prior to the ceasing operation of the gas turbine 28, and all the reactor coolant flows through the operating gas turbine 28. If the reactor coolant temperature then increases to the level wherein the supporting turbine 82 can operate, the gas turbine 28 will supply the motive force to start the larger supporting turbine 82. In this modification, the smaller gas turbine 82 will operate continuously, whereas the larger supporting turbine 82 will operate intermittently. As before, by a careful matching of the turbine 28, 82, and compressor 32 characteristics, the auxiliary heat removal system will be able to function until there is substantially no probability that the core 10 will become hot enough to cause damage. Thus, it can be seen that this invention provides a means for removing heat from a nuclear reactor during an emergency condition which does not require an external power source, and which is not dependent upon a gravitational orientation for convection flow. |
052456390 | summary | BACKGROUND OF THE INVENTION This invention relates generally to devices and techniques for plugging flow holes. More particularly, the present invention relates generally to devices and techniques for plugging the flow holes of the core support barrel of a nuclear reactor. In some nuclear installations, fuel rod wear has been directly associated with the characteristics of the flow path through the reactor core. For example, it has been established that baffle jetting causes fuel rod wear under certain conditions. In some installations, the flow characteristics can be suitably modified to alleviate the wear to the fuel rod by modifying the reactor core flow path to an upflow-type core flow path. In order to implement the flow modification, it is necessary that existing core barrel flow holes be plugged. In some reactor designs, this may require the plugging of 16 angularly spaced core barrel flow holes. Moreover, the flow holes to be plugged are typically positioned below the level of the adjacent surrounding thermal shield, and thus the thermal shield may present a significant obstacle to the hole plugging process. SUMMARY OF THE INVENTION Briefly stated, the invention in a preferred form is a plug assembly and a plugging technique for a core barrel flow hole wherein a thermal shield surrounds the barrel and is space adjacent to the flow hole. The plug assembly comprises an offset arm having first and second end portions. The first end portion includes a plug which is dimensioned to seal against the core barrel boundaries of the hole. The plug may include a circumferential sealing lip or a tapered sealing surface. The second end portion constitutes a mounting head having a pair of openings which receive bolts. The bolts are anchored in threaded bores of the core support barrel. The arm is dimensioned so that the plug is inserted into the flow hole and the bolts are positioned above the level of the thermal shield to provide headroom for completing the installation of the plug assembly. An installation method, in accordance with the invention, for plugging the flow hole of a core barrel having a thermal shield spaced from and surrounding the barrel adjacent to the hole comprises machining a threaded bore in the core barrel above the thermal shield. A plug member is positioned in the flow hole, and the plug member is staked to the threaded bore by bolts. The threaded bore is machined into the barrel. An object of the invention is to provide a new and improved plug assembly and installation technique for plugging the flow hole of a core support barrel. Another object of the invention is to provide a new and improved plug assembly which may be installed to the core barrel in an efficient process to provide a plug of high integrity. A further object of the invention is to provide a new and improved plug assembly and installation method therefor which is designed to overcome the headroom constraints presented by the thermal shield. Other objects of the invention will become apparent from the drawings and specification. |
abstract | A method for investigating transport processes in a preferably biological specimen, a laser light beam (2, 3) being guided by means of a scanning apparatus line by line over the specimen within definable specimen regions, and the light proceeding from the specimen being detected by means of a detection apparatus, is characterized, in the interest of the capability of investigating, with high accuracy, processes within the specimen that proceed on a short time scale, in that both an image production light beam (5) for the purpose of observing the specimen and a manipulation light beam (4) for the purpose of manipulating the specimen are used as the laser light beam (2, 3), the image production light beam (5) preceding the manipulation light beam (4) in such a way that pixels of the specimen not yet manipulated by the manipulation light beam (4) are illuminated with the image production light beam (5). |
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abstract | Systems and methods for process monitoring based upon X-ray emission induced by a beam of charged particles such as electrons or ions include a system and method for process monitoring that analyze a cavity before being filled and then analyze emitted X-rays from the cavity after the cavity has been filled with a conductive material. Also included are system and methods for process monitoring that apply a quantitative analysis correction technique on detected X-ray emissions. |
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abstract | An ion implanting apparatus includes an analyzer unit for analyzing ions to be implanted into a wafer from among those ions in a beam produced by an ionization, a vacuum unit for producing a vacuum in the analyzer unit, a vacuum gauge for measuring the pressure inside the analyzer unit, and a shield for preventing a magnetic field employed by the analyzer unit from affecting the vacuum gauge. The shield has a plurality of magnetic field shielding plates encircling the vacuum gauge and dielectric material inserted between the magnetic shielding plates. The shield prevents the vacuum gauge from being influenced by the magnetic field generated by the analyzer unit. Therefore, the vacuum level inside the analyzer unit can be precisely measured. |
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claims | 1. A method of operating a Boiling Water Reactor, said boiling water reactor having fuel assemblies arranged inside of channels through which coolant flows, comprising:a step of analyzing Local Power Range Monitor signals for oscillatory behavior indicative of neutron flux coupled density wave oscillations;determining if oscillatory behavior beyond a noise level is present in the signals;initiating a first reactor protective corrective action if the oscillatory behavior is determined to be present;if the Local Power Range Monitor signals analyzed in the step of analyzing Local Power Range Monitor signals are not oscillatory beyond noise level, a step of analyzing several channels of high power using a stability program on line at actual operating conditions and checking to determine if neutron flux uncoupled oscillations are possible; andinitiating a second reactor protective corrective action while the Local Power Range Monitor signals are not oscillatory beyond noise level if it is determined in the step of analyzing several channels of high power that neutron flux uncoupled oscillations are possible; andrepeating at least the step of analyzing Local Power Range Monitor signals if it is determined in the step of analyzing several channels of high power that neutron flux uncoupled oscillations are not possible. 2. The method according to claim 1, wherein at least one of the first step and the second step of initiating a reactor protective corrective action is scramming the reactor. 3. The method according to claim 1, wherein at least one of the first step and the second step of initiating a reactor protective corrective action is reducing reactor power. 4. The method according to claim 1, wherein the step of analyzing several channels of high power using a stability program on-line at actual operating conditions and checking to determine if neutron flux uncoupled oscillations are possible is performed by use of on-line computer simulations. 5. A method of operating a Boiling Water Reactor designed for power generation, said boiling water reactor having fuel assemblies arranged inside of channels through which coolant flows, said method comprising the steps of:analyzing Local Power Range Monitor signals for oscillatory behavior indicative of neutron flux coupled density wave oscillations;determining if oscillatory behavior is present in the signals;initiating a first reactor protective corrective action if the oscillatory behavior is determined to be present; and,if the Local Power Range Monitor signals analyzed in the step of analyzing Local Power Range Monitor signals are not oscillatory beyond noise levels of said Local Power Range Monitor signals, performing the further steps of:determining the identity of a plurality of channels which are operating at a relatively high power as compared to other channels;analyzing the plurality of channels which are operating at a relatively high power using a stability program on-line at actual operating conditions and checking to determine if neutron flux uncoupled oscillations are possible;initiating a second reactor protective corrective action while the Local Power Range Monitor signals are not oscillatory beyond noise levels if it is determined in the step of analyzing the plurality of channels which are operating at a relatively high power that neutron flux uncoupled oscillations are possible; andrepeating at least the step of analyzing Local Power Range Monitor signals if it is determined in the step of analyzing the plurality of channels which are operating at a relatively high power that neutron flux uncoupled oscillations are not possible. 6. The method according to claim 5, wherein at least one of the first step and the second step of initiating a reactor protective corrective action is scramming the reactor. 7. The method according to claim 5, wherein at least one of the first step and the second step of initiating a reactor protective corrective action is reducing reactor power. 8. The method according to claim 5, wherein the step of analyzing the plurality of channels which are operating at a relatively high power using a stability program on-line at actual operating conditions and checking to determine if neutron flux uncoupled oscillations are possible is performed by use of on-line computer simulations. 9. The method according to claim 5, wherein the actual operating conditions comprise a channel operating condition selected from the group consisting of: power, axial power profile, coolant flow rate, inlet flow temperature, and system pressure. 10. The method according to claim 5, wherein the actual operating conditions comprise operating power and coolant flow. 11. The method according to claim 1, wherein the actual operating conditions comprise a channel operating condition selected from the group consisting of: power, axial power profile, coolant flow rate, inlet flow temperature, and system pressure. 12. The method according to claim 1, wherein the actual operating conditions comprise operating power and coolant flow. |
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045267120 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 to 3, an embodiment of a process for treating radioactive waste according to the invention will be described hereinafter in detail. In FIG. 1, a radioactive waste such as granular ion-exchange resins 1 used for purifying mainly condensate, powder resins 2 used as filter aids for purifying reactor water, and filter sludge 3, the main component of which is cellulose used as filter aids for a radioactive waste treatment system are collected and stored in a storage tank 4. In order to pulverize the stored waste, the waste is transported to a thin film drier 6 by a feed pump 7 which can control an amount of the waste in slurry to be transported. The structure of the thin film drier 6 is shown in FIGS. 2 and 3. In FIG. 2, a shell 8 of the thin film drier 6 is cylindrical and provided with a vapour outlet 9 and a feed inlet 10 at the upper portion. The shell 8 further has a heat conduction wall 8a surrounded by a jacket 11 formed outside the shell 8. The jacket 11 is provided with an inlet 12 and an outlet 13 for heating medium such as steam. In the outside of the shell 8, a rotary shaft 14 is disposed which is rotatably supported by an upper bearing 15 and a lower bearing 16. As shown in FIG. 3, the rotary shaft 14 has a plurality of supporting arms 17 each joined to the shaft 14 and extending radially. The supporting arms 17 support rings 18. Blades 19 each are disposed between the rings 18, swingably connected to the rings 18 by pins 20, and contacted with the wall 8a of the shell 8 when the rotary shaft 14 is rotated by a driving device such as a motor 25. Over the most upper supporting ring 18, a distributor 21 is disposed for distributing the waste from the feed inlet 10 over the wall 8a of the shell 8. Over the separator 21, a mist separator 22 is disposed. The mist separator 21 defines a vapor compartment 23 thereabove in cooperation with a rid 24 secured to the shell 8. The radioactive waste in slurry state, transported from the storage tank 4 enters the thin film drier 6 at the feed inlet 10. The entered wastes are dispersed uniformly by the distributor 21 toward the wall 8a of the shell 8 which is heated to a temperature above 100.degree. C, preferably of 120.degree..about.160.degree. C. by steam entered at the inlet 12 and gone out from the outlet 13. The waste falling along the wall 8a is pressed on the wall 8a by the blades 19 on which centrifugal force is applied by the rotation of the rotary shaft 14 in a direction shown by an arrow to form thin films. The thin films receive heat from the wall 8a of the shell 8, so that the waste will be ground into powder until the waste reaches about an outlet 26. The temperature of the powder at the outlet 26 is detected by a thermometer 27 and an amount of the waste entering at the feed inlet is regulated by the feed pump 7 so that the powder will be dried substantially, preferably the temperature of the powder about the outlet 26 will be about 100.degree..about.130.degree. C. The powder in the outlet 28 has moisture content of less than about 2.about.3% and an average particle size of about 10.mu.. The thermometer 27 is used mainly for watching disorder of the apparatus in a usual operation. In order to detect the moisture content of the powder discharged from the outlet 26, a moisture detector may be used for the thermometer 27. Vapour, generated by drying the thin film waste or powder rises upward and mist mixed with the vapour is separated by the mist separator 22 so that only vapour enters the vapour compartment 23. The vapour is transferred to a condensor 28 provided out of the thin film drier 6 and condensed thereby to water. The powder formed by the thin film drier 6 is transported to a hopper 29 with a valve 30. The powder, disposed in the hopper 29 is transported to a combustion furnace 32 by air transport using a pneumatic conveyor 31, with the valve 30 being opened. The combustion furnace 32 is provided with a powder supply nozzle 33, an air nozzle 34, a first burner 35, and a second burner 36. The first and second burners 35, 36 each are connected with a propane gas tank 37 and an air tank 38 through pipes 39, 40 with valves. The burner 35 provides flames in the combustion furnace 32. The powder from the pneumatic conveyor 31, mixed with air for transport is fed into the combustion furnace 32 by the nozzle 33. The second burner 36 provides secondary combustion region in the upper portion of the combustion furnace in case where the powder does not burn completely. Where the air, mixed with the powder by the pneumatic conveyor 31 is not substantial for effecting complete combustion of the powder fed, supplemental air is supplied into the combustion furnace 32 through the nozzle 33 connected to an air supply duct 41. Combustion gas from the furnace 32 is cooled by a cooler 42, and transported to a dust collector 43 which is provided therein with celemics filters. Dusts collected by the dust collector 43, that is, mainly ashes are transported to a hopper 44 provided on a pelletizer 45 through a pipe 46 with a valve. The combustion gas passing through the dust collector 43 is further subjected to filteration by a high efficiency particle air filter 47, whereby radioactive dusts or ashes are completely removed. The combustion gas cleaned is exhausted to atmosphere from a stack 50 by a blower 48. The wastes such as the granular ion-exchange resins, powder resins, cellulose, etc. are reduced to 1/200.about.1/500 in volume by burning them. The ashes stored in the bottom of the combustion furnace 32 are collected in the hopper 44 together with the ashes from the dust collector 43, and fed into the pelletizer 45 to be formed in pellets, with binder being fed from a tank 49. In a case where the filter sludge is made into the powder, the powder corresponding to 20.about.30% of the ashes in weight may be used for the binder. The ashes can be stored as they are, however the pellets of the ashes can be stored with more safety than stored in a state of the ashes, and has a reduction ratio of 1/2 as compared with a state of the ashes. In this embodiment, for the transport of the powder made by the thin film drier 6, air is used, and the air used for the transportation is used also as burning air. Therefore, the powder and the air are mixed enough well, and spread out substantially in the combustion furnace 32. The air transport of the powder serves greatly for complete combustion of the powder. According to this embodiment of the process for treating waste, a reduction ratio in volume is very large, that is, in the case of the granular resins, the waste to be discarded is reduced to about 1/30 in volume as compared with a conventional cement-solidfying method; in the case of the powder resins, about 1/600 in volume; and in the case of the filter sludge, about 1/3000 in volume. The process can continously treat the waste with a simple apparatus and a simple operation. Various kinds of wastes can be mixed at any ratio, and treated at the same time and by the same apparatus. The waste is shaped in pellet so that their handling is easy, and the pellet can be stored stably for a prolonged period of time. Furthermore, in future, even if what type of final state of waste to be discarded will be taken, the pellets can be adapted for the final state in future. Still further, when a solidifying treatment of the pellets is done after the ashes are made into pellets, stored and subjected to falling into decay, there is advantages such that a surface does rate can be reduced, and such that after a final state in which the radioactive waste will be discarded is determined, the solidifying treatment of the pellets can be carried out. |
abstract | A control rod drive system (CRDS) for use in a nuclear reactor. In one embodiment, the system generally includes a drive rod mechanically coupled to a control rod drive mechanism (CRDM) operable to linearly raise and lower the drive rod along a vertical axis, a rod cluster control assembly (RCCA) comprising a plurality of control rods insertable into a nuclear fuel core, and a drive rod extension (DRE) releasably coupled at opposing ends to the drive rod and RCCA. The CRDM includes an electromagnet which operates to couple the CRDM to DRE. In the event of a power loss or SCRAM, the CRDM may be configured to remotely uncouple the RCCA from the DRE without releasing or dropping the drive rod which remains engaged with the CRDM and in position. |
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063242583 | summary | This invention generally relates to the production of tomographic images of an object, normally a person, according to the preamble of claim 1. Since the present invention is of importance in particular for tomographic images obtained by means of gamma radiation, the invention will hereinafter be discussed in particular for this type of radiation. It is noted with emphasis that the principle of the invention is also applicable to the production of images using other kinds of radiation. In the following, a single recording will be designated by the term "projecton image" (comparable to a photograph). Further, the term "tomography image" or "sectional image" will be used for a reconstructed image of a section of the object, obtained by combining several projection images from different directions. In principle, tomographic images can be obtained in two different ways. In the first place, it is possible to collect radiation coming from within the object itself, with a detector sensitive to such radiation (camera); such a technique is designated as emission tomography (for instance, SPECT: Single Photon Emission Computed Tomography), and the image obtained is designated as emission projection image. It can be stated in general that an emission projection image provides information about the distribution of radiation-generating matter in the object. When several emission projection images are made, in mutually different directions, it is possible to compute (reconstruct) from the obtained data the concentration distribution of that radiation-generating matter in the object; this is designated as "emission tomography image". In the second place, it is possible to generate radiation with a radiation source and to direct it towards the object, whereby the radiation that passes through the object is detected with the camera: such a technique is designated as transmission tomography, and the image obtained is designated as transmission projection image. With this technique, therefore, the object is located between the radiation source and the camera. It can be stated in general that a transmission image provides information about the distribution of radiation-attenuating or radiation-absorbing matter in the object. With this technique too, it is possible to combine different transmission projection images to provide a transmission tomography image. For different reasons it is desired to make emission images and transmission images simultaneously. By this is meant that a camera is simultaneously irradiated with emission radiation coming from the object itself, and with transmission radiation which has passed through the object, while the radiation energy from the external source can be chosen to be different from the radiation energy which is generated in the object itself. An important advantage of such combined recordings is that the transmission tomogram can be used to correct the emission tomogram for attenuation of the radiation in the object. It is desired to enable discrimination between direct radiation and scattered radiation, so as to be able to obtain better position information. To that end, use is made of a collimator placed before the camera, in combination with a predetermined spatial geometry of the radiation source. The article "Attenuation Compensation for Cardiac Single-Photon Emission Computed Tomography Imaging: Part 1. Impact of Attenuation and Methods of Estimating Attenuation Maps" by M. A. King et al in Journal of Nuclear Cardiology, volume 2, no. 6, November 1995, pp. 513-524, describes examples of this. Furthermore, the article "A Scanning Line Source for Simultaneous Emission and Transmission Measurements in SPECT" by P. Tan et al in The Journal of Nuclear Medicine, vol. 34, No. 10, October 1993, p. 1752 discloses an apparatus according to the preamble of claim 1. In this article an arrangement is disclosed wherein the line shaped irradiation pattern is moved over the camera. The object of the present invention is to provide a device which on the one hand provides an improved separation between transmission radiation and emission radiation and on the other hand provides an improved image strength in the transmission image, so that the images provided have an improved signal-to-noise ratio over the prior art. It is a general object of the present invention to provide a tomography device which enables obtaining an emission and a transmission image simultaneously, whereby a good separation between emission and transmission is achieved. It is a further object of the present invention to provide a tomography device whereby transmission and emission images can be obtained simultaneously in an efficient manner. It is a still further object of the present invention to provide a tomography device whereby the capacity of the camera is utilized in an efficient manner. These objects are met by an apparatus as defined further in the characterizing portion of claim 1. EP-A-0 526 970 and U.S. Pat. No. 5,289,008 both disclose an apparatus for making transmission recording of an object during radiation. However, the irradiation pattern is not moved over the camera as required by the present invention. |
claims | 1. A method for producing a specimen for electron microscopy, comprising:guiding at least three stationary ion beams onto a specimen surface of the specimen at predetermined angles with respect to one another such that the at least three stationary ion beams at least contact or intersect one another on the specimen surface and form a zone of incidence at the specimen surface, wherein the specimen is cut out of a solid-state material with the specimen surface fowled thereon; andtreating the specimen surface with the at least three stationary ion beams such that material of the specimen at an area of the zone of incidence is removed from the specimen surface by etching until a desired viewing surface is uncovered in the area of the zone of incidence,wherein the desired viewing surface is configured to allow viewing in a desired area of the specimen with an electron microscope, andwherein both the specimen and the at least three stationary ion beams are not moved such that the at least three stationary ion beams are operated stationarily during said treating of the specimen surface. 2. The method according to claim 1, wherein the treating of the specimen surface with the at least three stationary ion beams is in accordance with a slope etching method. 3. The method according to claim 1, wherein the treating of the specimen surface with the at least three stationary ion beams is in accordance with a wire shadow method. 4. The method according to claim 1, wherein the specimen is a standard TEM specimen having sides, wherein the treating of the specimen surface with the at least three stationary ion beams is performed such that the at least three stationary ion beams each are directed at least onto one of the sides of the TEM specimen for removal of the material of the specimen at the area of the zone of incidence. 5. The method according to claim 1, wherein the at least three stationary ion beams are guided onto the specimen surface at different incident angles, and wherein all of the at least three stationary ion beams at least contact one another in the zone of incidence. 6. The method according to claim 1, wherein positions of the at least three stationary ion beams in the zone of incidence are set such that a degree of overlapping is set for the etching. 7. The method according to claim 1, wherein at least two of the at least three stationary ion beams are generated jointly with one single ion source. 8. The method according to claim 1, wherein at least two of the at least three stationary ion beams are generated with their own respective ion source. 9. The method according to claim 1, wherein ion energy, ion current density, or a combination thereof for one of the at least three stationary ion beams is individually set, individually regulated, or a combination thereof for the treating of the specimen surface. 10. The method according to claim 1, wherein ion energy, ion current density, or a combination thereof of the at least three stationary ion beams are set to equal values or to predeterminable different values for the treating of the specimen surface. 11. The method according to claim 1, wherein a diameter of least one of the at least three stationary ion beams in the zone of incidence is set for the treating of the specimen surface. 12. The method according to claim 1, wherein, by varying at least one of ion energy, ion current, beam diameter, and a combination thereof of at least one of the at least three stationary ion beams, a predeterminable etching profile is set for the treating of the specimen surface. 13. The method according to claim 1, wherein ion energy of the at least three stationary ion beams is set in a range between 200 eV and 12 KeV for the treating of the specimen surface. 14. The method according to claim 1, wherein the specimen is at least temporarily viewed during the etching in high resolution with a viewing device. 15. The method according to claim 14, wherein the specimen is oriented prior to the etching with respect to the viewing device and is not moved any more during the etching. 16. The method according to claim 1, wherein the specimen is cooled during the etching. 17. The method according to claim 2, wherein, during the etching using the slope etching method, a mask having a plane surface is used, wherein the mask borders on the specimen surface at a distance in a range of 10 μm to 100 μm such that the plane surface and the specimen surface form a bordering line, wherein the zone of incidence of the at least three stationary ion beams lies in an area of the bordering line, wherein the at least three stationary ion beams span a plane in which the bordering line lies, wherein the plane is arranged slightly tilted with respect to the plane surface of the mask by an angle in a range between 0° and 10°, and wherein the plane surface of the mask is positioned perpendicularly to the specimen surface. 18. The method according to claim 2, wherein the at least three stationary ion beams span a circle sector having an angle which lies in a range between 10° and 180°, and wherein the at least three stationary ion beams lie in a plane of the circle sector. 19. The method according to claim 3, wherein the wire shadow method uses a wire, wherein, in the wire shadow method, the at least three stationary ion beams are guided in one plane which lies parallel to the wire, and wherein a normal to the specimen surface lies in the one plane. 20. The method according to claim 3, wherein the at least three stationary ion beams span a circle sector having a central axis, and wherein a plane of the circle sector is arranged to a normal of the specimen surface such that the central axis and the normal form an angle which lies in a range of ±20°. 21. The method according to claim 3, wherein the at least three stationary ion beams span a circle sector having an angle which lies in a range between 10° and 180°, wherein the at least three stationary ion beams lie in a plane of the circle sector, and wherein two of the at least three stationary ion beams are positioned symmetrically to surface normal during the treating of the specimen surface. 22. The method according to claim 4, wherein the at least three stationary ion beams are oriented lying on a conical circumferential surface on at least one side of the specimen, and wherein the at least three stationary ion beams are converged at a top of the cone and impinge on the zone of incidence on at least the at least one side of the specimen. 23. The method according to claim 1, wherein the at least three stationary ion beams are guided onto the specimen surface at different incident angles, and wherein all of the at least three stationary ion beams at least partially overlap one another in the zone of incidence. 24. The method according to claim 1, wherein a portion of the at least three stationary ion beams are guided onto the specimen surface at different incident angles, and wherein the portion of the at least three stationary ion beams at least contact one another in the zone of incidence. 25. The method according to claim 1, wherein a portion of the at least three stationary ion beams are guided onto the specimen surface at different incident angles, and wherein the portion of the at least three stationary ion beams at least partially overlap one another in the zone of incidence. 26. The method according to claim 1, wherein ion energy of the at least three stationary ion beams is set in a range between 500 eV and 8 KeV for the treating of the specimen surface. 27. The method according to claim 1, wherein the specimen is at least temporarily viewed during the etching in high resolution with one of a light microscope and a scanning electron microscope. 28. The method according to claim 1, wherein the at least three stationary ion beams consist of only three stationary ion beams, wherein the three stationary ion beams are guided onto the specimen surface at different incident angles, and wherein all of the three stationary ion beams at least contact one another in the zone of incidence. 29. The method according to claim 2, wherein, during the etching using the slope etching method, a mask having a plane surface is used, wherein the mask borders on the specimen surface at a distance in a range of 10 μm to 100 μm such that the plane surface and the specimen surface form a bordering line, wherein the zone of incidence of the at least three stationary ion beams lies in an area of the bordering line, wherein the at least three stationary ion beams span a plane in which the bordering line lies, wherein the plane is arranged slightly tilted with respect to the plane surface of the mask by an angle in a range between 0° and 5°, and wherein the plane surface of the mask is positioned perpendicularly to the specimen surface. 30. The method according to claim 2, wherein the at least three stationary ion beams span a circle sector having an angle which lies in a range between 30° and 140°, and wherein the at least three stationary ion beams lie in a plane of the circle sector. 31. The method according to claim 3, wherein the at least three stationary ion beams span a circle sector having a central axis, and wherein a plane of the circle sector is arranged to a normal of the specimen surface such that the central axis and the normal form an angle which lies in a range of ±10°. 32. The method according to claim 3, wherein the at least three stationary ion beams span a circle sector having an angle which lies in a range between 30° and 140°, wherein the at least three stationary ion beams lie in a plane of the circle sector, and wherein two of the at least three stationary ion beams are positioned symmetrically to surface normal during the treating of the specimen surface. |
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description | This application is claiming priority based on French Patent Application No. 1200075 filed Jan. 10, 2012 and U.S. Provisional Patent Application 61/659,684 filed Jun. 14, 2012, the contents of all of which are incorporated herein by reference in their entirety. The present invention relates to a method for filtering gas effluents on industrial installations, and notably in the field of production of energy of nuclear origin. More particularly, the invention may allow selective sorting at a high flow rate of chemical and/or radioactive species in the gas state, notably by membrane separation, the goal mainly being the secured recovery of gas discharges produced on the installation under normal operating and abnormal operating situations, in particular during a serious accident. In the particular case of a nuclear installation, the impact on the environment is mainly related to the radioactive, thermal and chemical characteristics of the waste. Depending on their level of radioactivity and on their chemical composition, the radioactive elements are stored, processed and then packaged in order to form waste. Some of these radioactive elements are discharged in gaseous form into the atmosphere, of course at concentrations strictly defined by the applicable regulations. The gas discharges produced during normal operation generally stem from the purification and filtration circuits of the power plant, which collect a portion of the radioactive elements generated by the operation of the systems and equipment making up the installation. For example in France, these radioactive gas discharges produced by nuclear power plants may typically represent of the order of 1.1% of the allowed limit for rare or noble gases, 11.1% for tritium and 3.6% for iodines (both organic and inorganic). Helium, neon, argon, krypton, xenon and radon form the family of rare gases, group zero of the Periodic Table of the Chemical Elements, but the name of noble gases will be used hereafter as it is recommended by the IUPAC (International Union of Pure and Applied Chemistry) and by the “Bulletin Officiel du Ministère Français de I'Èducation nationale”. These wastes are ordinarily of low activity and the radionuclides which they contain are not very toxic and generally have a short period. It should be noted that gas discharges contain solid and liquid particles. Those having a radioactive nature form aerosols with a highly variable grain size. Fission phenomena encountered on suspended dusts produce radionuclides such as halogens, noble gases, tritium and carbon 14. The composition and the radioactivity of the thereby formed aerosols depend to a great extent on the type of reactor and on the emission routes. Ordinarily, the gas effluents of a nuclear power plant are treated before they are discharged into the atmosphere in order to extract most radioactive elements. The current practice consists of filtering the contaminated gases and the ventilation air of the premises so as to extract the radioactive particles therefrom before their discharge into the atmosphere. The air ventilation and purification systems generally include coarse pre-filters associated with absolute filters. As an indication, it will be noted that for particles with a diameter of the order of 0.3 mm, the extraction yield normally attains at least 99.9%. Radioactive iodine is extracted by means of filters with impregnated charcoal, associated with dust filters. Impregnation of the coal is required in order to retain the iodinated organic compounds. Radioactive noble gases which evolve from the fuel elements are released into the atmosphere in a deferred mode after disintegration in order to reduce the level of activity. Two methods are used for this purpose: buffer storage in special reservoirs or passage through several layers of charcoal. For storage, the noble gases and the carrier gas are therefore introduced by pumping them into sealed reservoirs where they are kept until their release is authorized into the atmosphere. The other method consists of having the effluent pass into a series of charcoal columns which delay the progress of the noble gases relatively to the carrier gases, thereby facilitating their radioactive decay. Most methods for processing and packaging waste of low and medium activity are now well developed and are used on an industrial scale. The technology is sufficiently advanced for ensuring efficient management of the waste from the power plants, but improvements are always possible and desirable. The increasing budget for this management encourages the adoption of methods and techniques with which the produced amounts may be reduced to a minimum and the study of new means for further reducing the volumes at the processing and packaging stage. As an example, let us mention the use of specific mineral sorbents for improving processing of liquid waste; the membrane technique, also for treating liquid waste; the drying of resins in beads and of muds from filters; the incineration of depleted ion exchange resins; dry cleaning of clothes and other protective textile materials for reducing the volume of laundry waters; the use of highly resistant hermetically sealed containers for packaging dried filter muds; vitrification of certain wastes of medium activity for reducing the volumes to be removed; and overcompaction of non-fuel waste. These techniques corresponding to the recent industrial state of the art will perhaps not be all universally applied to the management of waste, in particular at nuclear power plants, but this research and development effort shows the great care which the nuclear industry and power plant operators bring to the safety and to the economy of waste management, and announces enhancements. The invention relates to the use in a specific method of a membrane technique to be used for processing gas effluents generated by industrial and notably nuclear installations. In the case of a serious accident on the reactor of a nuclear power plant using the water reactor technology, i.e. about 95% of the present worldwide installed base, the atmosphere inside the reactor building changes over time and forms a mixture containing: air, steam, uncondensable gases (essentially H2, CO, CO2, fission products as aerosols, vapors and gases . . . ), the proportions of which may be variable both from a spatial and a time point of view. The increase in pressure which results from this and/or the accumulation of harmful products contained in this mixture finally lead to releases into the outer environment in order to avoid a loss of mechanical integrity consecutive to a hydrogen explosion or to the pressure exceeding the one admissible by the building. The fluid which escapes from the building may be air, radioactive gases, steam or a mixture of fluids. An object of this method is to separate during the degassing phase the radioactive and/or environmentally dangerous elements as regard discharges, to recover them for an optional particular treatment for storage or for reprocessing them with view to their possible re-use and to avoid a dangerous discharge into the environment. In the early 80s, simple means were set into place on several nuclear power plants in order to limit the consequences of accidents. One of the goals was to be able to control and filter the gas discharges by means of a specific system. Presently, these so-called <<palliative >> systems are used for causing a pressure drop in the reactor building by discharging the gases through a filtration process. Two different technologies exist on the operating worldwide nuclear installed base: a sand filtration system on which the radioactive gases are trapped without any distinction: in the case of a serious accident, the pressure inside the containment vessel of the reactor building may increase more or less rapidly. By starting the sand filtration system, it is possible to discharge in a controlled way a portion of the gas-steam mixture. This would avoid excessive pressurization of the containment vessel while considerably limiting the radioactive discharges. These sand filters mainly used in France, allow about 50% of the harmful elements contained in the gas flow to be filtered, to be retained but are inoperative on noble gases. FIG. 1 illustrates a power plant 10 equipped with a sand filter 20 and a unit for measuring waste 25 positioned upstream from the gas discharge chimney 15; a degassing system by sparging which does not allow selective degassing. In these circuits, a portion of the water circulating in the circuit escapes into the atmosphere as steam, notably when it passes into the air-cooling towers, and another portion is sent back into the environment in order to limit a too high concentration of non-vaporizable products. This system, notably used in Germany and in Sweden allows retention of about 75% of the harmful elements contained in the gas flow to be filtered, but is also inoperative on noble gases. It is very bulky (>100 m3) and difficult and therefore costly to apply and to maintain. Both of these systems are set into operation by voluntary either manually or assisted action for opening sectional valves. They require a driving pressure upstream in order to generate a flow and obtain efficient filtration. Their operation is passive up to a pressure threshold determined by the dimensioning of the filtration system and notably by its hydraulic resistance. Below this pressure threshold, actuators and therefore an electric power supply are required for extending the filtration function. Moreover, the monitoring of various parameters, notably environmental parameters, also requires a provision of electric energy. The object of the present invention is to provide a method for filtration of contaminated and/or harmful, notably radioactive, gas effluents, which does not reproduce the aforementioned drawbacks. The object of the present invention is notably to provide such a filtration method which is much more efficient, allowing substantial filtration of the totality of the harmful elements contained in the gas effluents to be processed. The object of the present invention is notably to provide a method which allows both selective separation of radioactive gases during degassing, their trapping, their discrimination, their temporary storage, their optional processing for subsequent re-use, controlled dilution and treatment of the contaminated atmosphere of the containment vessel of a nuclear power plant. The object of the present invention is also to provide a method for filtering gas effluents from a nuclear power plant, with permanent availability and able to operate continuously or intermittently depending on requirements. The object of the present invention is also to provide a method for filtering gas effluents from a nuclear power plant, which operates in the case of a serious accident. The object of the present invention is also to provide a device for filtering gas effluents from an industrial installation, said device including an improved membrane. The object of the present invention is therefore a method for filtering harmful gas effluents from an industrial installation, comprising the following steps: providing a gas effluent from an industrial installation, said gas effluent consisting of a mixture of gases, filtering the harmful, notably radioactive, elements of said gas effluent by membrane separation through a plurality of membranes, said membrane separation being achieved by sifting, sorption and/or diffusion, each membrane being adapted for filtering a specific harmful element, sorting said filtered harmful elements and storing them in separate storage reservoirs, and discharging said processed gas effluent to the atmosphere. According to a first alternative, said gas effluent to be processed consists of the fumes of an industrial installation after an accident. According to another alternative, said gas effluent to be processed consists of the fumes of an industrial installation during operation. According to another alternative, said gas effluent to be processed is extracted from a ventilation system. According to another alternative, said gas effluent to be processed comprises fumes from a fire. According to another alternative, said gas effluent to be processed comprises aerosols from fission products. Advantageously, said gas effluent to be processed has a temperature greater than the temperature of the environment outside the power plant, and notably greater than 40° C. Advantageously, said gas effluent to be processed has a processing flow rate of more than 1 kg/s, notably greater than 3.5 kg/s. Advantageously, said gas effluent to be processed has a pressure above 1 bar, notably above 10 bars. Advantageously, said storage reservoirs are gas storage reservoirs containing zeolites. Advantageously, said membranes are formed on the basis of ceramic, such as silica carbide, of tungsten or titanium, of Kevlar and/or polymer such as PEEK (polyetheretherketone) or PTFE (polytetrafluoroethylene). Advantageously, said method is of the passive type operating without provision of energy from the outside world. The method will mainly be described with reference to its application on a nuclear power plant with a containment vessel, however it also applies to nuclear power plants without any containment vessel, and more generally to any type of industrial installation. As regards pressurized water reactors of the French installed base, the containment vessel 100 has a volume of the order of 70,000 to 80,000 m3, and generally consists of a double wall 110, 120 in concrete, as illustrated in FIG. 3. The presence of fission products in the containment vessel (in the form of aerosols, vapors and gases) resulting from an accident leads to considerable β and γ dose rates in the atmosphere of the containment vessel, and in the sump where the majority of the aerosols settle. The expected dose rates in both of these phases are typically of the order of 10 kGy·h−1. Whatever the case, this value is notably dependent on the degradation condition of the fuel, on the fission products retained in the primary circuit, on the distribution of the fission products between the atmosphere and the sump in the containment vessel, itself a function of thermo-hydraulic conditions prevailing in the containment vessel and of course on the elapsed time since the accident. The temperature of the gas effluent is typically greater than the ambient temperature of the environment outside the power plant. The generally accepted temperature is typically comprised between 40° C. and 140° C. according to the scenarios and to the time scale taken into account. It should be noted that temperatures below 40° C. or above 140° C. are possible. As to the humidity rate, it may itself also vary in a range from 0 to 100%, depending on the kinetics and the contemplated type of accident. Radiolysis may lead to the formation of ozone, nitrous oxide N2O, nitrogen monoxide NO, nitrogen dioxide NO2, nitrous acid HNO2 and nitric acid HNO3. Various teams have experimentally observed the formation of O3, of NO2 and of hemipentoxide N2O5, in dry air and of O3, NO2, HNO2 and HNO3 in humid air (0.5% water mass fraction). To summarize, the radiolytic products which may be present in the containment vessel in the case of a serious accident are in majority NOx:NO2 and N2O, and of course O3. Experiments conducted by several laboratories including the IRSSN (<<Institut de Radioprotection et de Sûreté Nucléaire>>) within the scope of programs aiming at controlling the hydrogen risk in nuclear power plants and notably having dealt with the behavior of catalytic recombiners, have given the possibility of detecting physico-chemical reactions generating volatile iodine by dissociation of solid metal iodides. The table below shows an order of magnitude of the main constituents estimated for the source term (typical discharge) encountered during a serious accident on reactors of the operating French installed base. As the source term is a characteristic of a family of reactors, differences may be seen depending on the countries. Nevertheless these values may be used as a dimensioning basis for carrying out the present invention applied to a nuclear power plant: Radioiogical activityMass equivalentNoble gases1E19 BqAbout 700 kgOrganic iodine2E16 BqAbout 1 kgInorganic iodine1E15 BqA few gramsCesium1E16 BqAbout 2 kgStrontium1E15 BqAbout 35 g The significant contribution of the noble gases is to be noted both in terms of level of activity and in discharged mass equivalent. The present method may be dimensioned so as to be able to process flow rates of at least 1 kg/s, advantageously 3.5 kg/s, of humid air brought to a sufficient driving pressure for operating the system, i.e. at a pressure of at least 1 bar, advantageously at least 10 bars absolute, having an average specific gravity of 4 kg/m3 at 5 bars and capable of processing of the order of 1 kg or more of radioactive iodine over a period of several months, typically of three months. In particular, the object of the present method is to provide non-polluting treatment which takes into account the whole of the aforementioned data of a fluid to be processed for which the required purification coefficients are: For aerosols, the present method has a purification coefficient of more than a 1,000. As regards inorganic iodines (I2), the purification coefficient is greater than 1,000. As regards organic iodines (ICH3), the purification coefficient is greater than 100. The present method advantageously demonstrates a very high purification coefficient, notably of more than 1,000 on noble gases. The present method has a purification coefficient greater than 100 on ruthenium tetraoxide (RuO4). The goal of the present method is also to dilute over time the activity inside the containment vessel by treating the air containing radioactive gases. The mentioned purification coefficient is defined as the measured upstream/downstream ratio at the filtration device. The present method uses a membrane filtration method for carrying out degassing of the containment vessel: releasing as a minimum a flow rate of 3.5 to 7 kg/s under the effect of the pressure prevailing in the containment vessel, of a fluid consisting of air, steam, gases of the O3, NO2, HNO2, HNO3, N2O5 type, and of the presence of fission products in the containment vessel (in the form of aerosols, vapors and gases such as noble gases, inorganic iodines and organic iodines). The present method advantageously uses as a carrier an inert gas such as nitrogen. The fluid treated by the present method may be saturated with water and with steam. In order to avoid recombinations and the risk of oxidation of the membranes by the water, either present or not, in the fluid to be treated, the water entirely saturated with gas and pressurized by these gases is directed by a pressure difference towards several, typically four batteries of hydrophobic degassing membranes 200. The membrane separation is achieved by sifting, sorption and/or diffusion. The gases, thus carried away by a carrier gas, such as nitrogen, pass through hydrophobic membranes (a degassing method with hollow fibers), notably by diffusion and separation by osmotic pressure, and are directed towards batteries of selective gas diffusion membranes, 210, 220, 230, . . . either in a cascade or in series which allows sorting and selecting of the gases depending on the requirements and/or on the benefit. The membrane separation methods are based on the selective retention properties of membranes towards molecules to be separated. With the first gas diffusion membranes in a cascade, it is possible to take into account the whole of the aforementioned data and to recover the whole of the noble gases depending on the required purification coefficient. These are selective membranes, notably based on ceramic, (inert towards radioactivity), which notably ensure separation of xenon, krypton and argon. The membranes may also be made in other suitable materials, such as for example carbides, notably of silica, tungsten or titanium, Kevlar, polymers, notably PEEK (polyetheretherketone) or PTFE (polytetrafluoroethylene). The whole of the thereby separated gases and present in the retentate may be stored in compressed form in sealed reservoirs each comprising a single gas species. These reservoirs allow both storage, radioactivity decay of fission products, possible re-use of the trapped gases, their neutralization or even their final discharge by dilution in air. Gas diffusion and permselectivity of the membranes allow the gases to pass over specific ceramic membranes in order to trap inorganic iodines on the one hand and organic iodines on the other hand. It is also possible to provide a passage over one (or more) membrane(s) on which have been grafted crown calyx4arene molecules trapping target elements such as cesium, and then on the same principle, passage over a membrane capturing strontium (for example, including another calyxarene selected for its particular affinity for strontium). Each membrane includes a wall provided with an internal surface and an external surface. Said wall having pores P. The wall may be cylindrical or planar. Several walls may be superposed, coaxially in a cylindrical configuration or stacked in a planar configuration. FIG. 4 schematically illustrates more particularly the structure of a membrane 210 with a tubular geometry. The wall of the membrane includes pores P suitable for retaining the harmful elements of the gas effluents. Depending on the material and on the dimensions of the pores, the membrane will be dedicated to the filtration of a given element. The dimensions of the pores are variable radially, for example decreasing from the outside towards the inside, and axially, for example decreasing from right to left in the position illustrated in FIG. 4. In this example, the gas flow to be filtered flows outside the membrane in the direction of the arrow A, while the carrier gas flows in the opposite direction inside the membrane, in the direction of the arrow B. The elements to be filtered in the gas flow will separate upon crossing the wall of the membrane, from the outside towards the inside, by passing from the largest pores to the smallest pores. This separation may operate under pressure, by a pressure difference between the inside and the outside of the membrane wall, or by diffusion. The membranes are modules with calibrated hollow porous fibers. By helically winding the fibers, large exposure to flows with high degassing rates is possible with a minimum pressure drop. The pore diameters are controlled down to a few nanometers at each stage. These membranes thereby include variable porosity along the radial and longitudinal directions of the membrane surface, adapted to the molecular size to be trapped. An advantageous embodiment in ceramic material further exhibits total harmlessness of the material towards radioactivity. The selection of the carrier gas N2 allows recombination of the gases of the NO2, HNO2, HNO3, N2O5 type into nitrogen and H2O. At the outlet of the selective membranes, by measuring the gas contamination it is possible in a first phase to get a clean treated fluid discharge through a controlled solenoid valve towards the cooling and discharge chimney. This solenoid valve also gives the possibility of sending all or part of the recovered nitrogen along a return line 130 for dilution of the contamination inside the containment vessel. This may be accomplished by sending back an oxygen-rich air but free of any radioactive element through a nitrogen separation membrane. This method operates without external energy as long as the pressure in the water conditioning is greater than the lower bound value determined by the dimensioning of the system, typically 1.5 bars. Manually opening one of the inlet valves of the circuit causes automatic pressurization of the storage cylinders for storing the carrier gas (generally nitrogen) and the putting of this carrier gas into the circuit via an expansion valve. On the other hand in the case of pressure lower than the lower bound value, typically 1.5 bars, the gases are degassed from the hydrophobic membranes by means of an actuator or a pressurized external circuit for example by means of a vacuum compressor. Such an embodiment includes a vacuum pump providing suction inside an exchanger provided with an automatic purger and with a booster pump which sends back the water to the conditioning. This vacuum pump compresses the sucked-up gases in order to generate the high pressure on the side of the selective membranes. The low pressure side of the selective membranes is achieved either by the suction generated by the air-cooling towers, or by suction of the recycling air inside the containment vessel by the fan. Advantageously, the method comprises a first front filtration, notably with a metal pre-filter in order to reduce the outgoing radioactivity, a second tangential filtration for separating air, CO2, CO, steam and residual water from the effluent to be processed, a third filtration by gas diffusion for separating and storing the harmful elements, such as inorganic and organic iodines and noble gases, and discharging the remaining air, CO2 and CO towards a chimney 150, and a fourth filtration for recovering by gas permeation the carrier gas, such as nitrogen, for re-use or dilution inside the containment vessel 100 via a return line 130. With the present method it is also possible to process the radioactive environment of the containment vessel except for an accident, so as to allow faster intervention in the containment vessel during scheduled interventions. This is notably illustrated in FIG. 3, where the atmosphere contained between both walls 110 and 120 is permanently monitored. In the case of a leak in the internal wall 110, the discharges may thus be filtered continuously until the next maintenance during which the leak will be repaired. This avoids stopping the power plant as soon as such a leak appears. A particular advantage of the present method is its reliability and its particularly high efficiency. Indeed, it is possible to trap more than 99.5% of the harmful elements, and it is efficient on noble gases, unlike the existing devices. The present method uses non-dispersive technology: no risk of foam or emulsion. The filtration systems are robust and without any mobile parts unlike the absorption columns of the rotary type. The method operates regardless of the changes in pressure of the containment vessel, of the hygrometry rates or of the temperature variation. The method is easy to create on an industrial scale, notably by taking into account linear expansion scales depending on the flow rate. It is clearly more economical than existing devices. The present method resorts to the modularity principle and uses the technologies suitable for this, notably at the connections, assemblies and seals. This modularity allows increased flexibility, the number of modules being adjustable depending on the contaminating elements of the containment vessel and on their recovery rate to be obtained. The production of the modules is accomplished by assembling a few thousand to more than one million of elementary fibers, representing an accumulated length which may reach 1,000 km, for membrane surfaces of several hundred to several thousand square meters (m2). The present method comprises modules with hollow fibers with the structure of a tubular exchanger, with a high pressure (HP) circuit and a low pressure (LP) circuit, a tube side and a calender size. The present invention especially has the advantage of its compactness since the specific exchange surface area is much larger than that of a column: 2,000 to 3,000 m2/m3 instead of 30 to 300 m2/m3. The present method allows selective degassing of all radioactive gases including noble gases. The present method allows full management of gas discharges from the storage of compressed gases for possible processing or subsequent use by means of zeolites in order to transform them into solid waste. The present method mounted on the ventilation systems allows possible dilution of the contamination of the containment vessel by a system with double discharge opportunities. The present method used for processing gas discharges allows full management of noble gases. The present method used for processing the gas effluents from circuits of nuclear power plants allows full management of their radioactive gases or of those dangerous for the environment. The present method mounted on the circuits for recovering the evolved harmful gases during treatments of the injection circuits allows their recovery and their processing. The performance of a membrane separation is the combined result of the intrinsic properties of the membrane: selectivity; permeability; operating parameters, such as pressures, temperature, layout of the flows in the modules. Another important parameter for a membrane method is the pressure difference imposed on both sides of the membrane. An increase in this pressure difference (either by increasing the high pressure or decreasing the low pressure) leads to an increase in the driving force for the permeation and makes the separation easier. For applications related to gas separation, it is often the low pressure of the permeate, the pressure at which the gas is produced, which is the important parameter for optimization, the high pressure being generally imposed by the upstream processes. From the point of view of the separation performances on a membrane, it is desirable that the low pressure be as low as possible. According to another advantageous aspect, the sorting method by means of a plurality of membranes, as described above for a nuclear power plant, may also be used in other types of industrial installations, and notably chemical plants. The number and the type of membranes will be selected on the elements to be filtered and to be sorted out. Although the present invention has been described with reference to particular embodiments thereof, it is understood that it is not limited by these embodiments, but that on the contrary one skilled in the art may provide all useful modifications thereto without departing from the scope of the present invention as defined by the appended claims. |
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abstract | One embodiment relates to an apparatus for automated inspection of a semiconductor substrate. Processor-executable code is configured to control the stage electronics to move the substrate using a continuous motion in a substrate-translation direction and is configured to control the beam to scan it across the surface of the substrate and collect corresponding image data, scan lines of the scan being along a scan-line direction perpendicular to the substrate-translation direction. Processor-executable code is also configured to select from the image data two cells of the repeating pattern on the surface of the substrate, the two cells being displaced from each other by one or multiple cell heights in the scan-line direction. Finally, processor-executable code is configured to generate a difference image by subtracting image data from said two cells on a pixel-by-pixel basis. Other embodiments, aspects and features are also disclosed. |
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claims | 1. A diagnostic computer system for determining a cause of an event in a product or process, comprising:a first measurement system for indicating the event in the product or process;a display for displaying a schematic of the product or process;a processor for:selecting, from an energy function model, a first energy function from a plurality of energy functions of the product or process, the first energy function associated with a particular function describing an action designed to be performed in the operation of the product or process, wherein the first energy function describes how the particular function uses energy during operation;identifying, for the first energy function, a plurality of energy paths within the product or process;displaying, on the schematic, the first energy function and a representation of the plurality of energy paths with respect to a displayed “how” direction, an opposing “why” direction, and a perpendicular “when” direction corresponding to dependencies between the plurality of energy functions; andidentifying, based on the first energy function and the dependencies, a second measurement system for measuring a first energy to detect a contrast between how the product or process is actually performing and how the product or process is intended to perform, wherein the second measurement system is different than the first measurement system that indicated the event in the product or process;a user interface for accepting input from a user and for transmitting the input to the processor over a communications medium, wherein the processor responds to the input to select from among the plurality of energy paths, the first energy for measurement;the second measurement system comprising a sensor system operatively coupled to the processor for generating a plurality of measurements of the selected first energy; anda storage device operatively coupled to the processor for storing the plurality of generated measurements,wherein the diagnostic computer system conducts a progressive search on the contrast to identify a feature or property of the product or process responsible for causing the event. 2. The diagnostic computer system of claim 1, wherein the event comprises a malfunction event. 3. The diagnostic computer system of claim 1, wherein the display further presents graphic representations of the plurality of generated measurements. 4. The diagnostic computer system of claim 1, wherein the processor limits the schematic to the narrowest scope known to contain the root cause of the event. 5. The diagnostic computer system of claim 1, wherein the first energy function comprises a function for directing energy. 6. The diagnostic computer system of claim 1, wherein the first energy function comprises a function for transmitting energy. 7. The diagnostic computer system of claim 1, wherein the first energy function comprises a function for converting energy. 8. The diagnostic computer system of claim 1, wherein the first energy function comprises a function for containing energy. 9. The diagnostic computer system of claim 1, wherein at least one energy path of the plurality of energy paths comprises an input energy path corresponding to energy used to achieve the detected first energy function. 10. The diagnostic computer system of claim 1, wherein at least one energy path of the plurality of energy paths comprises an output energy path corresponding to the performance of useful work. 11. The diagnostic computer system of claim 1, wherein at least one energy path of the plurality of energy paths comprises a waste energy path corresponding to energy loss. 12. The diagnostic computer system of claim 1, wherein at least one energy path of the plurality of energy paths comprises an environmental energy path. 13. The diagnostic computer system of claim 1, wherein the plurality of generated measurements comprises direct measurements of the selected first energy. 14. The diagnostic computer system of claim 1, wherein the plurality of generated measurements comprises indirect measurements of the selected first energy through at least one of its component factors. 15. The diagnostic computer system of claim 1, wherein the processor selects, for measurement, a second energy from the plurality of energy paths if no contrast is detected using the plurality of measurements for the selected first energy. 16. The diagnostic computer system of claim 1, wherein the processor controls the identified feature or property to prevent a future occurrence of the event. 17. The diagnostic computer system of claim 2, wherein the processor detects the contrast between how the product or process is actually performing and how the product or process is intended to perform by generating a plurality of energy measurements for a second product or process that is not experiencing a malfunction event. 18. The diagnostic computer system of claim 2, wherein the product or process comprises a prototype product or process. 19. The diagnostic computer system of claim 18, wherein the identified feature or property corresponds to a design under consideration for which a contrast in the direct measurement of the malfunction event is not detected. 20. The diagnostic computer system of claim 1, wherein the product or process comprises a production product or process. 21. A diagnostic computer system for identifying evidence of deviation from a specification for a product or process, comprising:a first measurement system for signaling the deviation from the specification in the product or process;a display for displaying a schematic of the product or process;a processor for:selecting, from an energy function model, a first energy function from a plurality of energy functions of the product or process, the first energy function associated with a particular function describing an action designed to be performed in the operation of the product or process, wherein the first energy function describes how the particular function uses energy during operation;identifying, for the first energy function, a plurality of energy paths within the product or process;displaying, on the schematic, the first energy function and a representation of the plurality of energy paths with respect to a displayed “how” direction, an opposing “why” direction, and a perpendicular “when” direction corresponding to dependencies between the plurality of energy functions; andidentifying, based on the first energy function and the dependencies, a second measurement system for measuring a first energy to detect a contrast between how the product or process is actually performing and how the product or process is intended to perform, wherein the second measurement system is different than the first measurement system that signaled the deviation in the specification in the product or process;a user interface for accepting input from a user, wherein the processor responds to the input to select from among the plurality of energy paths, the first energy for measurement;the second measurement system comprising a sensor system operatively coupled to the processor for generating a plurality of measurements of the selected first energy; anda storage device operatively coupled to the processor for storing the plurality of generated measurements,wherein the processor compares the plurality of generated measurements to a respective target range of values and transmits, based on the comparison, a signal indicative of an alert condition for the deviation. 22. The system of claim 21, wherein the processor limits the schematic to the narrowest scope known to contain the root cause of the event. 23. The system of claim 21, wherein the product or process comprises a prototype product or process. 24. The system of claim 21, wherein the product or process comprises a production product or process. 25. A diagnostic computer system for ascertaining the reliability of a product or process by analyzing a plurality of samples of a given product or process that have been exposed to an environmental stress, comprising:a display for displaying a schematic of the product or process;a processor for:selecting, from an energy function model, a first energy function from a plurality of energy functions of the product or process, the first energy function associated with a particular function describing an action designed to be performed in the operation of the product or process, wherein the first energy function describes how the particular function uses energy during operation;identifying, for the first energy function, a plurality of energy paths within the product or process;displaying, on the schematic, the first energy function and a representation of the plurality of energy paths with respect to a displayed “how” direction, an opposing “why” direction, and a perpendicular “when” direction corresponding to dependencies between the plurality of energy functions; andidentifying, based on the first energy function and the dependencies, a measurement system for measuring a first energy to detect a contrast between how the product or process is actually performing and how the product or process is intended to perform;a user interface for accepting input from a user, wherein the processor responds to the input to select from among the plurality of energy paths, the first energy for measurement;the identified measurement system comprising a sensor system operatively coupled to the processor for generating a plurality of measurements of the selected first energy; anda storage device operatively coupled to the processor for storing the plurality of generated measurements,wherein the processor:compares the plurality of generated measurements of the plurality of exposed samples to identify the contrast;conducts a progressive search on the contrast to identify a feature or property of the plurality of samples that can be used to control the energy function that is not being achieved;compares the plurality of generated measurements to a plurality of energy measurements of an unstressed product or process; andstores, based on the comparison, a data value indicative of the useable life of a similar unstressed product or process. 26. The system of claim 25, wherein the plurality of samples are exposed to an environmental stress through a series of tests. 27. The system of claim 25, wherein the plurality of samples are exposed to an environmental stress through actual field use. 28. The system of claim 25, wherein the processor limits the schematic to the narrowest scope known to contain the root cause of the event. 29. The system of claim 25, wherein the process further selects, for measurement, a second energy from the plurality of energy paths if no contrast is detected using the plurality of measurements for the selected first energy. 30. The system of claim 25, wherein the processor controls the identified feature or property to prevent a future occurrence of the event. 31. The system of claim 25, wherein the product or process comprises a prototype product or process. 32. The system of claim 25, wherein the product or process comprises a production product or process. |
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051260980 | abstract | A method of removing bow in a nuclear fuel assembly is disclosed. The fuel assembly has top and bottom ends fittings and a plurality of longitudinally extending thimble tube members interconnecting top and bottom end fittings. At least two transverse fuel rod support grids are axially spaced along the thimble tube members. A plurality of fuel rods are transversely spaced and supported by the fuel rod support grids. In one embodiment, a weight of known magnitude is secured on the bottom end fitting and the fuel assembly is raised with the weight secured thereon so that the weight exerts a downward force on the fuel assembly for straightening the fuel assembly and eliminating compressive stresses within the fuel assembly. In another embodiment, the bottom end fitting is secured onto the upender used for transporting fuel assemblies into and out of the containment building and the fuel assembly is pulled for straightening the fuel assembly and eliminating compressive stresses within the fuel assembly. |
060312416 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Before explaining the disclosed embodiment of the present invention in detail it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. OPERATING CONDITIONS FOR A PULSED CAPILLARY DISCHARGE LAMP FOR EXTREME ULTRAVIOLET LITHOGRAPHY (EUVL) AND OTHER APPLICATIONS SUCH AS RESIST EXPOSURE TOOLS, MICROSCOPY, INTERFEROMETRY, METROLOGY, BIOLOGY AND PATHOLOGY The pulsed capillary discharge lamp sources that can be used with these operating conditions can be those described in U.S. Pat. No. 5,499,282 to Silfvast; and parent U.S. application Ser. No. 08/815,283 to Silfvast et al., which are both assigned to the same assignee as the subject invention and which are both incorporated by reference For purposes of clarification: the gaseous species excited within the capillary can be any of the following: 1. a pure, 100%, concentration of an atomic or molecular gas (which may also include vaporized atomic and/or molecular materials) in either their neutral or ionized stats: acting as the radiating species; 2. a buffered gas mixture of an atomic or molecular gas or vapor in either its neutral form or ionized form with a second atomic or molecular gas wherein the first gas or vapor serves as the radiating species and the second gas serves as the buffering species. The buffered gas interacts with the discharge, thereby promoting effective operation which might include but is not restricted to any of the following processes: generation of appropriate plasma conditions (such as temperature and density), mechanism for either cooling the electrons and/or for cooling the system, and for, in the case of a vapor emitter, preventing vapor diffusion throughout the system such that the lamp operates in either heat pipe mode or as a pure metal vapor cell. An example of a metal vapor radiator useful in the subject invention is a lithium metal vapor operating at one or both of the following wavelengths: 11.4 nm and 13.5 nm. An example of a buffered metal vapor lamp useful in the subject invention is a lithium metal vapor heat pipe as indicated in FIG. 5, buffered by helium or other gas and operating at one or both of the following wavelengths: 11.4 nm and 13.5 nm. An example of a discharge source useful in the subject invention using a pure atomic or molecular gas is an oxygen lamp which contains a 100% concentration of oxygen operating on one or more of the following wavelengths in five times ionized oxygen: 17.3 nm, 15.0 nm, 13.0 nm, and 11.6 nm, as shown in FIGS. 2A and 2B. An example of a buffered gas mixture in a lamp useful in the subject invention is a first atomic or molecular gas with a second atomic or molecular gas is in a lamp which consists of oxygen as the radiating species, (operating on one or more of the following oxygen lines: 17.3 nm, 15.0 nm, 13.0 nm, and 11.6 nm.) buffered by any second gas such as one of the noble gases(helium, neon, argon, krypton, and xenon). The subject inventors observed intense oxygen emissions at approximately 17.3, 15.0, 13.0 and 11.6 nm, wherein the peak intensity per unit wavelength of oxygen at 13.0 nm is greater than that of a tin laser produced plasma at its peak intensity per unit wavelength. The peak emission at 17.3 nm has been observed to be three times higher than at 13.0 nm. Experimental evidence we obtained in a 1 mm bore capillary discharge as shown in FIGS. 2A and 2B for oxygen, and FIGS. 1 and 4 for xenon, suggests that gaseous radiators existing in partial pressures from approximately tens of millitorr up to approximately 20 Torr can intensely emit in the EUV. The range of currents and the range of pressures for operation will now be described. (1) Current Ranges for operation A lamp with a lmm capillary using any radiating species would operate within the following current ranges, whereby the minimum current represents the smallest current at which the required flux for the selected application is obtained, and the maximum current is determined by the current at which significant bore erosion begins to occur. For aluminum nitride capillaries this is anywhere between approximately 2000 to approximately 5500 Amperes; for silicon carbide capillaries between approximately 2000 to approximately 10,000 Amperes. Larger or smaller capillary bore sizes can be used consistent with the above current densities; for aluminum nitride capillaries: approximately 250,000 to approximately 700,000 Amperes per square centimeter; for silicon carbide capillaries: approximately 250,000 to approximately 1,300,000 Amperes per square centimeter. Other ceramic capillary materials can be operated in a range of currents from a minimum current density of approximately 250,000 Amperes/cm.sup.2 and a maximum current density which is determined by that current density at which significant bore erosion occurs (as determined by debris tests indicating reduced emission from the lamp after approximately 10.sup.8 to approximately to approximately 10.sup.9 pulses or window damage). (2) Range of Pressures for Operation For a capillary discharge lamp the radiating species can exist in a partial pressure range anywhere from approximately 0.025 to approximately 20 Torr, and a total pressure (radiator plus buffer partial pressure) no greater than approximately 50 Torr. TECHNIQUES AND PROCESSES TO MITIGATE AGAINST CAPILLARY BORE EROSION, PRESSURE PULSE GENERATION, AND DEBRIS FORMATION IN CAPILLARY DISCHARGE-POWERED LAMPS OPERATING IN THE EXTREME ULTRAVIOLET (EUV) The capillary discharge lamp sources that can be used with these techniques and processes can be those described in U.S. Pat. No. 5,499,282 to Silfvast; and parent U.S. application Ser. No. 08/815,283 to Silfvast et al., which are both assigned to the same assignee as the subject invention and which are both incorporated by reference (A) Operational Ranges Erosion in ceramic capillary bores is substantially reduced if the operational current and current density are held to certain limits, and will be described in reference to FIG. 6. The range of operational currents in 1 mm capillary discharges is the following: for aluminum nitride capillaries, peak currents between approximately 2000 Amperes and approximately 5500 Amperes, and for silicon carbide capillaries, peak currents between approximately 2000 Amperes and approximately 10000 Amperes. The range of current densities for discharges in any size capillary is the following: for aluminum nitride capillaries, peak current densities between approximately 250,000 Amperes per square centimeter and approximately 700,000 Amperes per square centimeter, and for silicon carbide capillaries, peak current densities between approximately 250,000 Amperes per square centimeter and approximately 1,300,000 Amperes per square centimeter. (B) Preprocessing of the Insulator Material emissions from discharges in ceramic capillary bores is not constant over the life of the capillary and can be substantially decreased if, before the capillary is incorporated into a final lamp assembly, it is seasoned by exposure to a number of discharge current pulses, and will be described in reference to FIG. 7. From these figures, and analysis, the pre-treatment of capillary bores by passing discharge current pulses in the operational ranges described above is necessary to reduce discharge material emissions. Between approximately 1 and approximately 10,000 discharge pulses (for example 3,000 pulses using conditions in paragraph (1) for Characteristics common to all discharges . . . as described below, are required, and pulses above approximately 10,000 are not relevant to the process of emission mitigation. Pretreatment by discharge or other heat-treatment affects structural morphology of the ceramic bore. The morphological changes in the capillary bore wall are the essential causal factors resulting in material emissions decrease, and that means other than discharges can bring about the salutory changes. These other means can include, but are not limited to, laser drilling and laser heat treatment as shown in FIG. 8. (1) Characteristics Common to All Discharges in this investigation of Bore Erosion. Capacitor bank with a total capacitance of 0.18 .mu.F (microfarads) is charged to voltage and discharged across a 1 millimeter nominal diameter by 6.35 mm long capillary in ceramic, either aluminum nitride (AlN) or silicon carbide (SiC). At 5 kV discharge voltage, the total stored energy is 2.25 J. so 1-2 Joules per shot is typical across the capillary. Repetition rate is variable up to a present maximum of 60 Hz. The current-versus-time curve looks like a damped sinusoid with 460 ns full width for the first half cycle. The second half cycle peak is about -0.5 times the first half cycle peak. All discharge processing pulses were made with 10 Torr argon gas fill. (2) Bore erosion data Beginning with a virgin capillary, we fired 1000 shots at a given peak current. We microscopically analyzed the capillary bore before and after each set of shots. Microanalysis measures average bore diameter at the capillary face and also at a point slightly (estimated approximately 0.25 mm) inside the bore from the face, this for both the high-voltage-facing side and the ground-facing side of the capillary. Hence four diameter measurements are made at each peak current, which are expressed as ablated mass amounts by assuming uniform wear down the entire length of the capillary (this is not always true). In some cases the bore begins to close up at one end; this is expressed as negative ablated mass amounts. Referring to the graph in FIG. 6, fifty milligrams ablated mass corresponds to a 33% diameter increase, or a 76% increase in bore cross-sectional area. Below approximately 5 kA, aluminum nitride capillaries show very little erosion. Extended discharge runs show bore erosion at the 0 to 6% level after 100,000 shots at 4 kA. Silicon carbide capillaries do not exhibit erosion out to 10 kA peak current (1.27 MA/cm.sup.2). FIG. 6 shows the stability of SiC capillaries even at the high peak current of 7500 A. Some very slight filling in of the ground side bore aperture is evident in these data at 10,000 shots. (3) Pressure pulse data Starting with virgin capillaries, we measured the pressure impulse (time-integrated overpressure) generated by the discharge by measuring mechanical impulse delivered to a moveable detector. While we have no data on the temporal form of the pressure wave from these measurements, an assumption is typically made that its extent is roughly that of the current, i.e. about half to one microsecond. Data from AlN capillaries (FIG. 7) show that an almost two order of magnitude decrease in impulse occurs over the first few thousand discharges. We call this the "break-in" or "seasoning" curve. Systematics suggest this is caused by vaporization of more volatile components in the capillary bore inner wall. Morphology changes are seen microscopically. Early results with ultra-thin windows provided by Sandia National Labs placed approximately 10 cm from the discharge show survivability from 3.5 kA discharge pressure pulses, but failure when the current was raised to 4 kA. However, this data as taken with unseasoned capillaries (around 1600 shots at less than 3 kA before the window test was tried). So that more extensive testing with seasoned capillaries can still be done. (4) Witness plate debris data Plastic debris-collecting slides (22 mm square, approximately 160 mg each) were placed at approximately 5 and 10 cm from the discharge, with the top edge of the 5 cm plate slightly below the bore centerline and the 10 cm plate square to the bore centerline, hence partially shadowed by the 5 cm plate top edge. Weights before and after shot runs were recorded, using a scale with 100 microgram resolution and approximate 200 microgram reproducibility. Fogging observed was patterned, not uniform as would be expected for vapor diffusing. A clear shadow of the top of the 5 cm plate is seen on the 10 cm plates for all fogged sets. The as-laid transparent film which fogs after sitting on the shelf suggests oxidation of a very thin, perhaps metal, coating. No evidence of particulate deposition was seen in the fogged material when viewed microscopically, down to the resolution limit of the optical microscope (estimated at 0.5 micrometers). Atomic Force Microscope imaging can be done for future testing. ADDITIONAL MATERIALS FOR CONSTRUCTION OF CAPILLARY DISCHARGE DEVICES FOR EUVL AND RELATED APPLICATIONS Any of the previous materials combinations claimed for a lithium discharge lamp can also be used in operating lamps that use other gaseous media as described above, as well as those described in U.S. Pat. No. 5,499,282 to Silfvast; and parent U.S. application Ser. No. 08/815,283 to Silfvast et al., which are both assigned to the same assignee as the subject invention and which are both incorporated by reference. These materials can be based on the following: any combination of metallic, electrically conducting electrodes and ceramic or insulating capillaries wherein the thermal expansions of the metallic and ceramic materials are closely matched to ensure the mechanical robustness of the lamp at its operating temperature, and such that the materials are resistant to damage or corrosion by the emitting gaseous species and the buffering gaseous species (if present). These include but are not limited to molybdenum as the metallic conductor and either aluminum nitride, alumina or silicon carbide as the ceramic insulator (as described in U.S. Pat. No. 5,499,282 to Silfvast; and parent U.S. application Ser. No. 08/815,283 to Silfvast et al. for use with lithium). For an oxygen emitter/helium buffered system, the above mentioned materials combination can be used, but more conventional and economic material combinations can be used including but not limited to Kovar metallic conductor and an alumina ceramic insulator. CAPILLARY CONFIGURATIONS WITH UNIFORM DISCHARGE AND DIFFERENTIALLY PUMPED DISCHARGE FIGS. 3A and 3B show two assemblies that utilize the capillary discharge EUV source. FIG. 3A shows an arrangement which maintains a uniform constant gas pressure along the length of the capillary discharge. FIG. 3B shows a configuration which utilizes the capillary bore itself as a solid-angle limiting aperture, giving a wide divergence of emitted EUV radiation at the expense of creating a gas pressure gradient across the length of the capillary. FIG. 3A shows an arrangement for producing and detecting EUV radiation using a capillary discharge source. Electrode 300 is charged to high voltage; as well, gas is fed to the cavity region contained by this electrode. This gas will contain the EUV radiating species, and in the simplest case, will be the radiating gas itself, such as but not limited to xenon gas. A discharge 304 is initiated between electrodes 300 and 306 which flows through and is contained by the capillary bore in the insulator 302. The electrode 306 can be a separate conductor within the assembly which completes the circuit, or it can simply be the grounded body of the lamp housing as shown. A differential pumping port 308 is a plug of solid material with a long narrow bore hole, such as but not limited to 1" thick stainless steel with a 1 mm diameter hole drilled there-through. The differential pumping port interfaces to a region 310 of high vacuum (less than approximately 0.01 Torr). The impedance to gas flow caused by the long narrow hole allows the maintenance of a substantial gas pressure gradient across the differential pumping port. As a result, the gas pressure along the capillary discharge 304 is kept very nearly constant while the EUV can be propagated 312, and detected and analyzed by a spectrograph detector 314, under a vacuum condition. The gas pressure profile versus position in this assembly is plotted in 316. The base pressure P at the discharge 318, can be maintained anywhere in a useful range from approximately 0.1 to approximately 10 Torr by adjusting the gas feed rate to the electrode 300. FIG. 3B shows as less constrained sources assembly. Electrode 350 can be fed with gas and charged to high voltage, and a discharge 354 to ground electrode 356 is contained by a capillary bore in insulator 352, all as was the case in FIG. 3A for 300, 304, 306 and 302, respectively. In this assembly, however, the capillary bore itself is used as the differential pumping port and the capillary directly interfaces the high vacuum region 358. The EUV emission 360 propagates in a much wider sold angle as shown. As a consequence, the gas pressure profile 362 shows a gradient along the capillary bore. Base pressure P, 364 is here in the range of approximately 0.1 to approximately 50 Torr. FIG. 3B shows the novel lamp configuration referred to as "differentially pumped capillary geometry" which allows a lamp that uses gases (as opposed to a lamp that operates with metal vapors) to operate without a window between the gaseous region and the optics that collects the radiation emitted from the lamp in the 11 nm to 14 nm wavelength region. Because of the very strong absorption of radiation in that wavelength region by all materials, including gasses, it is necessary in an EUV lithography system, as well as other applications, to operate the imaging system within a very low pressure environment having a pressure of less than approximately 0.01 Torr. Hence, a lamp would generally need a window to separate the region of the lamp operating in the 0.1 to 50 Torr. pressure region from the low pressure region (less than approximately 0.01 Torr) of the imaging system. Our differentially pumped capillary geometry allows for the operation of the lamp containing the radiating gas without the need of such as window. In the operation of this lamp, the gas is inserted at the opposite end of the discharge capillary from that where the radiation flux in the 11 nm to 14 nm radiation is collected. The pressure at that end of the capillary would be in the range of from approximately 0.1 to approximately 50 Torr. depending upon the particular gas and the desired emission characteristics of the lamp. The gas is pumped through the capillary by having a vacuum pump accessible to the opposite end of the capillary, the end where the radiation flux between 11 nm and 14 nm is collected and used in the desired optical system such as EUV lithography. As the gas is pumped through the discharge capillary the pressure drops approximately linearly such that it is at the necessary low pressure(less than approximately 0.01 Torr.) when it emerges from the capillary. The lamp is operated just like other lamps that have a constant pressure over the length of the capillary bore region by initiating a pulsed discharge current within the capillary. We have observed that there is sufficient pressure within the capillary, even at the low pressure side, to produce the desired emission form the lamp and yet the region beyond the lamp has sufficiently low pressure to allow for transmission of the radiation between 11 nm and 14 nm. The capillary itself acts as a retarding system for the gas as it flows through the capillary so that the usage of gas is at a very low rate. The gas can also be recycled back to the high pressure side for reuse. LAMP CONFIGURATION STRUCTURES FOR LAMPS USING GASES AND FOR USING METAL VAPORS AS THE RADIATING SPECIES FIG. 5 shows a novel lamp configuration that can operate in the heat pipe mode having a wick on the front (window) side of the lamp. FIG. 5 shows a metal vapor heat pipe type lamp assembly suitable for generating EUV radiation from lithium vapor. The electrode 500 is charged to high voltage and contains in its cavity some pressure of lithium vapor 504 and a source of lithium such as a few grams of lithium metal or liquid lithium. A discharge 506 is generated between this electrode and an electrode completing the circuit, which can most simply be the grounded body of the lamp housing 510. The discharge is contained in the capillary bore 508 of the insulator 502. The plasma 508 will be ionized lithium and will radiate 522 useful narrow line emissions in the EUV. To maintain the lithium vapor pressure requires the use of a heater 514, heat sink 516, wick 512, and buffer gas 520. This is the principle of the heat pipe. Heater 514 can be a commercial high temperature resistive oven such as but not limited to a Lindberg model 50002. Heater 514 maintains an equilibrium vapor pressure between the lithium source in electrode 500 and the lithium vapor 504. Lithium vapor flowing out toward the cooler region of the assembly condenses as liquid lithium on the wick 512. Wick 512 can be a stainless steel woven wire mesh fabric with approximately 30 lines per inch or finer, which is rolled into a hollow cylinder shape and placed in contact with the inside tube walls of the heat pipe body 510. A temperature gradient across the wick is maintained by a cooling collar such as but not limited to a a few (approximately 2 to 7) turns of refrigerated fluid(such as but not limited to chilled water) flowing through a coil of copper tubing and conductively contacting the heat pipe body 510 as shown. The temperature gradient thus created along the wick causes liquid lithium which has condensed on the wick to flow back toward the hotter region, to maintain the lithium vapor pressure on the EUV output side of the capillary. A buffer gas 520, such as but not limited to helium, is necessary for the operation of the heat pipe. In unheated regions, the system-wide gas pressure equilibrium is maintained by this buffer gas. In the vicinity of the wick 512, there is a transition region 518, where there are partial pressures of both lithium vapor and buffer gas. In this region, nearer the capillary, the lithium vapor dominates, and as the temperature decreases in going outward, the partial pressure of the buffer gas progressively increases. Pressures balance so that throughout the entire lamp assembly, the total pressure (sum of lithium vapor pressure and buffer gas pressure is a constant. The region adjacent to the capillary must be maintained at a temperature equivalent to the temperature necessary to generate the desired lithium vapor density within the capillary. This will establish a lithium metal vapor in that region of the pipe. This vapor will diffuse into the capillary and rear electrode region, and will not condense there as long as these regions are maintained at a higher temperature. Thus within the capillary region is established a lithium metal vapor pressure equivalent to the saturated vapor pressure of the wick region adjacent to the capillary. A discharge is struck between the two electrodes 10, 30 such that the current passes through the ceramic capillary, exciting the lithium vapor, and generating soft x-rays. A buffer gas establishes a transition region in the pipe, on the window side, beyond which lithium vapor diffusion is sharply reduced. The heatpipe mode of FIG. 5 differ from that shown in FIG. 4 of the lithium heat pipe of U.S. Pat. No. 5,499,282 primarily in the placement of the wick. In that description, the wick is shown placed within the capillary itself and extending into the rear electrode region, opposite the window. In contrast the modified lithium heat pipe of subject invention FIG. 6 has a mesh wick 40 only on the front (window) side 90 of the lamp 1, extending up to, but not beyond the capillary 20, creating a more favorable environment for conduction through the lithium vapor within the capillary 20. The minimum capillary bore diameter will be pressure sensitive and of such a dimension so as to insure that sufficient collisions of electrons with ions occur to produce excitation of radiating states before the electrons collide with the capillary wall and are consequently de-energized. It will also be determined by the size below if it is difficult to initiate a pulsed discharge current within the capillary. Such a minimum diameter is of the order of approximately 0.5 mm. The maximum bore diameter is determined by the desire to keep the radiating flux to a minimal size so as to make it more readily adaptable to a condenser system for imaging purposes and also to keep the total current to a reasonable size and yet still provide the optimum current density desired. A reasonable maximum size would be on the order of approximately 3 mm. The minimum length of the bore should be no smaller that the capillary bore diameter. The maximum bore length should be sufficiently long to produce enough radiative flux for the selected application but not overly long so as to waste input energy to produce radiation that cannot be used because of being too far removed from the output end of the capillary. From geometrical considerations associated with radiating output flux, the bore length should be no longer than approximately ten bore diameters. Pass the 10 diameter bore length would restrict the radiation flux. PRE-PROCESSING THE CAPILLARY BORE TO MITIGATE AGAINST BORE EROSION Techniques for pre-processing the inner bore walls will now be described in reference to both FIGS. 7 and 8. FIG. 7 shows a graph of the reduction in the impulse produced on the axis of the capillary at a distance of approximately 10 cm beyond the end of the capillary as the number of pulses of discharge current are initiated within the capillary as the number of discharge current pulses are increased within the capillary. It is desirable to have this impulse minimized to prevent rupturing of a window or other optical element. This can be obtained either by subjecting the bore to a number of pre-operation pulses (3000 for the conditions shown in FIG. 8) or by heat treating the capillary bore surface with a laser or other means of heat treatment so as not to have a disruptive pressure pulse during operation that could possibly damage a window or other useful element that is located beyond the capillary region but in the path of the emitted radiation emerging from the capillary. Lasers have been used successfully for machining, heat treating, welding and the like. In the subject invention, the laser can be used to heat treat the region inside the capillary bore to make it more resistive to erosion. This treatment would occur by subjecting the surface of the capillary bore region, as shown in one embodiment in FIG. 8 to one or more pulses of high intensity laser radiation, in the intensity region of approximately 10.sup.6 to approximately 10.sup.11 W/cm.sup.2. The laser radiation would heat the entire bore region as it passes through the bore of the capillary. In some instances the lens can be adjusted along the axis to focus on different regions within the bore. FIG. 8 shows an example of preparing the capillary bore. Experimentally it has been discovered that gas pressure pulses emanating from the capillary on firing the discharge can be substantially reduced in magnitude by preliminarily firing the discharge a few thousand times. The effect is to drive all condensed volatile materials out from the capillary bore walls. Alternatively, a heat treatment using high power laser radiation can be applied to the capillary before it is mated to the lamp assembly. FIG. 8 shows a heat treatment technique. A high power pulsed laser beam 800, such as one generated from a laser such as but not limited to an excimer laser, a Nd:YAG laser, a copper vapor laser, carbon dioxide laser, and the like, sufficient to produce fluences on the order of approximately 10.sup.8 W/cm.sup.2 or higher at the capillary. Laser beam 800 will locally shock heat the capillary walls to near the melting point, is focussed by a converging lens 802 to a focal point 804 proximate and axially concentric to the capillary bore. The laser beam 800 would irradiate the bore region and produce sufficient heating to change the material structure of the bore to make it more durable and smooth than would be achieved by the process that formed the bore, such as the drilling process. Depending on the bore material used, laser pulses up to and larger than 1,000 or more can be used to achieve the required compensation change in the bore material. The concentrated light diverging just past the focus is intercepted by the capillary bore walls of the insulator 806 to be used in the EUV lamp assembly. Provided the F number of the lens is smaller than the length-to-diameter ratio of the capillary (approximately 6 or higher), most of the light will be intercepted by the bore and only a small fraction will pass through the bore. For complete coverage of the length of the capillary bore wall, the insulator can be translated axially and also flipped to present the opposite fact to the light. While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended. |
060027363 | abstract | The fuel assembly includes an arrangement for quickly fixing the guide thimble into an opening passing through the adaptor plate of a dismountable nozzle of the assembly. This arrangement includes at least two bearing stops inside the opening of the nozzle, a bearing sleeve integral with the end of the guide thimble and a locking ring which includes stops for bearing on bearing surfaces of the stops inside the opening of the nozzle and deformable elastic parts capable of being accommodated in cavities of the opening of the adaptor plate or of the bearing sleeve, in order to place the ring in a position in which the guide thimble is locked or unlocked. The sleeve includes a rim for bearing on a bearing surface of the adaptor plate at the periphery of the opening. |
044938136 | claims | 1. In a nuclear reactor fuel assembly comprising a foot and an assembly body connected to the foot having an upper part and a lower part, an upper neutron protection device comprising: a wall of substantially hollow shape and having an inner face and an outer face, said wall being fixed to said assembly body at the upper part thereof, at least one container comprising: 2. A device according to claim 1 wherein said at least one spacing plate has an outer edge, whereof at least part is substantially rectilinear and fixed to the inner face of the wall and an inner edge, whereof at least part matches the shape of the container. 3. A device according to claim 2, wherein the outer edge of said at least one spacing plate has an upper part and a lower part and has in its upper part a portion which is inclined from top to bottom towards the outside of the wall and a slot opening towards the outside of said wall and permitting the coupling of said device by a handling means. 4. A device according to claim 2, wherein the inner edge of said at least one spacing plate has an upper part and a lower part and has, in its upper part, a portion inclined from top to bottom towards the inside of the wall and a slot opening towards the inside of said wall and permitting the coupling of said device by a handling means. 5. A device according to claim 1 comprising a plurality of spacing plates which are joined to one another. 6. A device according to claim 1 wherein said at least one spacing plate has an anti-vibration system. 7. A device according to claim 6, wherein said anti-vibration system comprises at least one groove made in said at least one spacing plate. 8. A device according to claim 1 wherein said at least one spacing plate is fixed to said wall by means of nails having a head welded to said wall. 9. A device according to claim 1 wherein said at least one spacing plate is fixed to said wall by means of profiled wedges. 10. A device according to claim 1 wherein said at least one spacing plate is fixed to said wall by means of localized deformations of said wall penetrating slots made in said at least one spacing plate. 11. A device according to claim 1 wherein said at least one spacing plate is fixed to the wall by means of a flange fixed to said wall by welding. |
claims | 1. An X-ray generator for generating plasma and X-ray emitted from the plasma, said X-ray generator comprising:a unit for generating the plasma;a first reflection optical system for introducing the X-ray to a condensing point; anda second reflection optical system for introducing the X-ray to the condensing point being done without the x-ray going through said first optical system,said first and second reflection optical systems have different number of reflections. 2. An X-ray generator according to claim 1, whereinsaid first reflection optical system includes a spheroid mirror; andsaid second reflection optical system includes a spheroid mirror and a hyperboloid mirror. 3. An X-ray generator according to claim 1, whereinsaid first reflection optical system includes a spheroid mirror; andsaid second reflection optical system includes plural mirrors each having a curvature. 4. An X-ray generator according to claim 1, further comprising a debris mitigation system for preventing debris generated at a light emitting point of the X-ray from reaching one of said first and second reflection optical systems. 5. An X-ray generator according to claim 4, further including an other optical system other than said first and second the reflection optical systems that enlarges a light intensity distribution at the condensing point of the X-ray formed by the one of said first and second optical systems, with respect to an angle from an optical axis. 6. An X-ray generator according to claim 4, wherein an other optical system other than said first and second reflection optical systems includes a rotationally symmetrical mirror. 7. An X-ray generator according to claim 1, wherein said X-ray has a wavelength of 20 nm. 8. An exposure apparatus comprising:an X-ray generator according to claim 1;an illumination optical system for illuminating a reticle having a pattern with X-ray generated by said X-ray generator; anda projection optical system for projecting the pattern of the reticle illuminated by said illumination optical system, onto an object to be exposed. 9. A device manufacturing method comprising the steps of:exposing an object using an exposure apparatus according to claim 8; and developing the object exposed. |
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040242099 | abstract | A mold cavity is only partially filled with nuclear fuel particles and is closed. The volume of the cavity is then reduced until the fuel particles substantially fill the mold cavity. The mold may be heated and a fluid solidifiable binder injected into the mold cavity to fill the interstices between the fuel particles while the cavity volume is further decreased during injection of the binder to avoid formation of voids. Flow of excess binder through an upper vent passage assures complete filling of the cavity. |
047605898 | abstract | An improved radiological device comprising a grid cabinet and an X-ray cassette tray, including: means for cassette size sensing disposed in the cabinet and allowing for automatic collimation of an X-ray beam by a direct mechanical linkage of sensing components with shutter controls; means for centering a cassette including two pivotal arms pivoting about respective points positioned in two different places on the tray; ball rolling slides for all linear movements; means for actuating a grid frame being very compact and disposed in the back of the cabinet and, firstly, accelerating the grid substantially instantaneously to high speeds for very short exposure times; secondly, slowing the grid down for medium exposure times; and thirdly, reversing the grid travel direction at random points. |
043308651 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIGS. 1 to 5, the vehicle designated 1, for carrying non destructive test instrumentation, is constructed mainly of titanium enabling it to withstand the high temperature of its operational environment and comprises an elongate bridge structure 2 having two support pads 3 carried one at each end on gimbal mountings 4 each with four alignment springs 5 interposed between one support pad 3 and the bridge structure 2. Each support pad 3 has an annular seal member 6 having a series of concentric lips 7 of synthetic rubber providing a labyrinth seal and mounted on a resiliently deformable ring 8. A suction source connection 9 penetrates each pad 3 into a void bounded by the sealing member 6 and an annular series of bearing pads 10 of low friction material comprising polytetrafluoroethylene containing 15% glassfilling is disposed concentrically between the inner and outer annular lips 7. Each support pad 3 also carries three gas thrusters 11 comprising tubular ducts having gas pressure connections 13 and each thruster has a high friction elastomeric ring 12 disposed in its end face. The bridge structure 2 has four jack operated retractable stabilising feet 14 and is adapted at 15 for carrying inspection apparatus (not shown) such as a television camera and an ultrasonic probe unit. The instrumentation is arranged to be rotatable through 90.degree. and to be capable of limited lateral displacement relative to the bridge. In use to inspect a curved surface designated `S` in the drawings the vehicle can be anchored to the surface with its longitudinal axis vertical by applying suction to the pads by way of the connections 9. The resiliently deformable rings 8 urge the lips 7 of the labyrinth seals into contact with the surface, the bearing pads 10 serving to limit the deflection of the sealing lips. The gimbal mountings 4 enable the suction pads to pivot universally with the aid of the springs 5 to accommodate curvature of the surface whilst the rings 12 serve to resist sliding of the vehicle when adhering to the wall of the vessel. The stabilising feet 14 can be urged into contact with the surface to stabilise the vehicle during inspection operations. Although not shown in the drawings, the vehicle is provided with laterally disposed reaction propulsion nozzles for laterally displacing the vehicle. To displace the vehicle over the surface, gas pressure is applied to the thrusters 11 so that the friction rings 12 are caused to lift substantially clear of the surface. The resiliently deformable rings 8 extend to ensure that the lips of the labyrinth seal remain in sealing contact with the surface, any tendency for lift-off to increase due to external forces being resisted by increased depression in the void. For use in inspecting the outer surface of a primary vessel of a construction of liquid metal cooled nuclear reactor of the pool kind the suction source to each pad may be derived from jet pumps of conventional axial tubular kind which engage the connections 9. Alternatively, the jet pumps may be of the radial inducer kind as disclosed in the co-pending application entitled Suction pads for supporting loads by R. C. Farmer, H. A. Goldsmith and M. J. Proudlove and filed on the same date as the present application. As shown in FIG. 6, the bridge structure is suspended by a tie member 16 which has plurality of tubular ducts for conducting service fluid to the vehicle. A series of spaced support discs 17 shown in greater detail in FIGS. 8 and 9 is anchored to the tie member 16, the discs serving to support the tie member from adjacent surfaces are spaced at progressively shorter intervals towards the bridge structure. Each support disc 17 shown in FIGS. 8 and 9 is attached to a central hose 18 of the tie member by means of a swaged collar 19 which grips the hose and is radially located in the disc by dogs 20. A split outer ring 21 has twelve equally spaced rollers 22 for bearing on the adjacent surfaces. An inner yoke 23 is divided into four segmented spacers for supporting gas pressure hoses which pass freely through the disc by way of fair-leads 24 so that they can move relative to the central hose and thereby accommodate surface curvature. The radial loction of the disc on the swaged collar prevents twisting of the hoses. The vehicle is used for carrying television and ultrasonic apparatus for the inspection of a primary vessel designated P in FIG. 6 which is housed in the vault V. The primary vessel is generally cylindrical with a hemispherical base and the cover of the vault has twelve equally spaced access apertures designated A through which the vehicle can be threaded together with its tie member. To inspect the vessel P, the vehicle with inspection instrumentation mounted thereon is passed through a selected aperture A and suspended in the interspace between the vessel and the wall surface of the vault by the tie member 16. The vehicle is anchored to the vessel by the vacuum means whilst the surface of the vessel in the region of the vehicle is scanned. The vehicle is displaced vertically in step wise manner being intermittently anchored for scanning operation. The vehicle is capable of being anchored in any latitude on each of twelve lines of longitude of the primary vessel and by partial rotation of the television camera and ultrasonic probes the entire surface area of the vessel can be scanned. The strake welds of the primary vessel have identification marks so that the position of the vehicle can be monitored visually by means of the television camera. The support discs bear against the wall surface of the vault and the primary vessel and the progressively reduced pitching of the discs provides adequate support for the tie member in the vicinity of the pole of the hemisphere. It is envisaged that the vehicle may also be used for inspecting storage tanks or other recepticles where access is limited for any reason. In an alternative construction (not illustrated) the bridge of the vehicle comprises a triangular frame having a support pad at each corner. The frame is hinged at three axes arranged so that each support pad is capable of swinging about an axis lying parallel to the side which is opposed to the support pad. The alternative construction of vehicle would be capable of negotiating corners in a building or tank construction. |
claims | 1. A charged particle therapy apparatus comprising:a plurality of irradiation nozzles fixed to a plurality of irradiation rooms respectively and to which accelerated charged particle beams are introduced, a plurality of irradiation operation rooms, and a plurality of passages for allowing a person to move from the irradiation operation rooms to the irradiation rooms,wherein said apparatus further comprises:a first switch provided in each of said plurality of irradiation rooms for issuing an irradiation preparation request command requiring an irradiation preparation for charged particle beams; anda second switch provided in each of the irradiation operation rooms for issuing a beam irradiation command requiring irradiation of charged particle beams; andwherein said apparatus is configured such that when said beam irradiation command is issued from said second switch after said irradiation preparation request command has been issued from said first switch, charged particle beams are introduced to the corresponding irradiation nozzle. 2. The charged particle therapy apparatus according to claim 1, further comprising accelerator control means for uniquely determining an automatic operation setting file for an accelerator based on the beam request command. 3. The charged particle therapy apparatus according to claim 1, wherein the charged particle is a proton. 4. A charged particle therapy system comprising:a beam generator for generating charged particle beams;an accelerator for accelerating the charged particle beams; anda plurality of irradiation nozzles fixed to a plurality of irradiation rooms respectively and to which the accelerated charged particle beams are introduced,a plurality of irradiation operation rooms provided correspondingly to said plurality of irradiation rooms, anda plurality of passages for allowing a person to move from the irradiation operation rooms to the corresponding irradiation rooms,wherein said apparatus further comprises:a first switch provided in each of said plurality of irradiation rooms for issuing an irradiation preparation request command requiring an irradiation preparation for charged particle beams; anda second switch provided in each of the plurality of irradiation operation rooms for issuing a beam irradiation command requiring irradiation of charged particle beams; andwherein said system is configured such that when said beam irradiation command is issued from said second switch after said irradiation preparation request command has been issued from said first switch, charged particle beams are introduced to the corresponding irradiation nozzle. 5. A charged particle therapy apparatus comprising:a plurality of irradiation rooms in each of which a therapy is performed by irradiating a person to be treated with accelerated charged particle beams,wherein said apparatus is configured such that when a beam irradiation command requiring irradiation is issued after a beam request command requiring an irradiation preparation for charged particle beams has been issued, charged particle beams are applied to the person to be treated; andwherein said apparatus comprises a plurality of irradiation operation rooms provided to said plurality of irradiation rooms, and each of said plurality of irradiation rooms includes a passage for allowing an operator to move to the corresponding one of said plurality of irradiation operation rooms, and a switch for the beam request command is disposed in each of said plurality of irradiation rooms and a switch for the beam irradiation command is disposed in each of said plurality of irradiation operation rooms. 6. The charged particle therapy apparatus according to claim 5, further comprising accelerator control means for uniquely determining an automatic operation setting file for an accelerator based on the beam request command. 7. The charged particle therapy apparatus according to any one of claims 5 or 6, wherein the charged particle is a proton. 8. A charged particle therapy system comprising:a beam generator for generating charged particle beams;an accelerator for accelerating the charged particle beams; anda plurality of irradiation rooms in each of which a therapy is performed by irradiating a person to be treated with the accelerated charged particle beams,wherein said system is configured such that when a beam irradiation command requiring irradiation is issued after a beam request command requiring an irradiation preparation for charged particle beams has been issued, charged particle beams are applied to the person to be treated; andwherein said apparatus comprises a plurality of irradiation operation rooms provided to said plurality of irradiation rooms, and each of said plurality of irradiation rooms includes a passage for allowing an operator to move to the corresponding one of said plurality of irradiation operation rooms, and a switch for the beam request command is disposed in each of said plurality of irradiation rooms and a switch for the beam irradiation command is disposed in each of said plurality of irradiation operation rooms. |
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description | The invention relates to a device for producing resist profiled elements. The invention further relates to a method for producing resist profiled elements. To this is added a use of the device for producing resist profiled elements and a use of the method for producing resist profiled elements. To date, resist layers have been produced in the semiconductor industry with the help of electron-beam lithography. These structured resist layers serve as auxiliary masks for structuring the substrate lying below them. Accordingly, steep edges (perpendicular to the substrate surface) are required for the resist profiled element. Published German patent application 41 13 027.8 discloses a method and an device with which grating scales of any length may be produced, having a grating constant in the μm range. First, a master scale is imaged step-by-step continuously on a flexible metal strip coated with a photoresist. A sensor that is coupled to the imaging device detects the structures in the exposed photoresist. Alternately switched holding devices for the flexible metal strip on the imaging device and the table of the imaging device successively feed further segments of the metal strip into the imaging area via a relative displacement between the imaging device and the table. Control signals from the sensor guarantee in-phase coupling of the images of the master grating. European patent 0 648 343 discloses a Fresnel lens and a method for its production. The work is done with an electron beam, the orthogonal beam cross-section of which is changeable. Because changes are implemented quickly, a stepped Fresnel lens may be produced in this manner. Electron beam doses, which correspond to those of cylindrical lenses, are exposed one on top of the other. Any form of lens described can be produced in this manner. The finer the structures, the more problematic it becomes to produce smooth flanks on the structures with multiple exposure. The object of the invention is to create a device with which different resist profiled elements may be produced, and whereby the user is provided the means for modeling the resist profiled elements. This object is solved by a device for producing resist profiled elements comprising: an electron beam lithography system that produces an electron beam, the beam axis of which lies largely perpendicular to a resist layer in which the resist profiled element is produced, wherein the electron beam is adjustable with regard to the electron surface dose such that a resist profiled element that exhibits a non-orthogonal resist profile is produced as a result of irradiation with the electron beam. It is advantageous for the resist layer to comprise a negative resist. The resist profiled element comprises a grating structure that comprises a parallel array of depressions and elevations. The primary energy of the electron beam of the system for electron beam lithography is adjustable, whereby the lower limit of the primary energy is 1 KeV and the upper limit of the primary energy is 20 KeV. The thickness of the resist layer is between 100 nm and 500 nm. The electron surface dose depends on the primary energy of the electron beam, electron scattering in the resist layer, the probe size, and the electron dose. A further object of the invention is to create a method with which the different resist profiled elements may be produced, and whereby the user is provided the means for modeling or predetermining the resist profiled elements. This object is solved by a method for producing resist profiled elements with an electron beam lithography system, which produces the electron beam with a primary energy, the beam axis of which is largely perpendicular to a resist layer in which the resist profile is produced, comprises the steps of: determining of parameters that influence an electron surface dose, and adjusting the electron beam with regard to the electron surface dose such that a resist profiled element that exhibits a non-orthogonal resist profile is produced as a result of irradiation of the resist layer by the electron beam. It is advantageous if a device for producing resist profiled elements comprises a system for electron beam lithography that produces an electron beam. For this purpose, the beam axis is largely perpendicular to the resist layer in which the resist profiled elements is to be produced. The electron beam is adjustable with regard to electron surface dose such that a resist profiled element is produced as a result of exposure by the electron beam, which exhibits a non-orthogonal resist profile. The resist layer may be applied to a substrate. It is also conceivable that the resist layer can be used without a substrate, and that the resist profiled elements are produced in an upper region of the resist layer. The electron surface dose is defined by parameters such as the substrate type, resist type, resist thickness, design rule, and primary energy of the electron beam, and in that the electron beam is adjusted according to these parameters to produce the desired resist profiled element. The resist profiled element comprises a grating structure that consists of a parallel array of depressions and elevations. The amplitude of the primary energy of the electron beam establishes a diameter of a scattering cone in the resist layer around the site of incidence of the electron beam, whereby the diameter of the scattering cone is inversely proportional to the primary energy of the electron beam. Exploitation of the effect of the secondary electrons in combination with the negative resist enables the production of non-orthogonal resist profiled elements. The probe size is quasi-continuously adjustable. The profile in the resist layer is scribable with a single probe size, whereby the probe size is smaller than the smallest possible structure size. Further advantageous developments of the invention may be deduced from the subclaims. FIG. 1 illustrates the structure of an electron beam column 5 in which the electron beam 1 is produced by an electron cannon 7 that forms a beam source, whereby it passes through a condenser lens 9 to an objective lens 2 and consequently to a resist layer 6. Generally, the resist layer 6 is applied to a substrate 6a (see FIG. 4 to FIG. 6). Although the description below is limited to electron beams, it will be clear to a person skilled in the art that any other particle beams with charged particles may be used here. The arrangement comprises a control system 54. It is equally possible for a resist profiled element to be produced in the resist layer without a substrate. In addition, the electron beam 1 is scanned or moved over the resist layer 6 to process (electron-beam lithography) various parts the resist layer 6. For limited scanning areas, scanning can be achieved using a scanning device 11 that is controlled by a scanning control device 60. For larger movements, table control 59 ensures that the table 10, and therewith the resist layer 6, are displaced horizontally. The control system 54 is controlled by a computer (not represented). The entire device for producing resist profiled elements comprises a system consisting of the already described electron beam column and the resist layer 6. By matching the primary energy of the electron beam and the type of resist layer 6 used, one obtains an electron density distribution at a specific distance from the irradiation site. The electron beam 1, and consequently also the electron beam column 3, are adjustable with regard to the electron surface dose such that as a result of irradiation by the electron beam a resist profile 12 is producible that exhibits a non-orthogonal resist profile. As a result of the energy input of the electron beam 1 during electron beam exposure, the solubility of the exposed resist is changed in a solvent. The electron beam 1 that strikes the resist layer is scattered, and the scattering is dependent on the primary energy of the electron beam 1. FIG. 2a shows a schematic representation of scattering in the resist layer 6 of an electron beam with high primary energy. The higher the primary energy of the electron beam 1, the less the scattering of the electron beam 1 in the resist layer 6. The electron beam 1 strikes the resist layer 6 and has a probe size 1a of a certain diameter 16 on the surface 15 of the resist (see FIG. 2b). A scattering cone 18 is produced in the resist layer 6 by the scattering, such that there is a spatially expanded influence on the resist. The resist layer 6 comprises a negative resist. This means that the higher the electron energy acting upon the resist, the more the solubility of the resist is decreased by the solvent. FIG. 2c shows a schematic representation of the scattering of an electron beam 1 with low primary energy in the resist layer 6. As a result of the low primary energy of the electron beam 1, the scattering cone 18 possesses a larger diameter than that represented in FIG. 2a. As a result of the scattering of electrons in the resist layer 6, the electron beam expands more extensively in comparison to the diameter of the electron beam 1 directly on the surface 15 of the resist layer 6 (see FIG. 2d). The probe size 1a of the electron beam is represented as a circle in FIG. 2b and FIG. 2d. The representation of the probe size 1a as a circle should not be interpreted as a limitation. Other projections of the electron beam 1 on the surface 15 of the resist layer 6 are possible, and the representation of a circle as in FIG. 2b and FIG. 2c should also not be interpreted as a limitation. As represented in FIG. 2a and FIG. 2b, as a result of the scattering of the electron beam 1, areas of the resist layer are influenced by electrons that are not directly struck by the electron beam. This generally negative circumstance is known as the proximity effect. This circumstance is exploited by the invention. As already mentioned above, the size and form of the scattering cone 18 are not limited solely to a spherical form. The size and form of the scattering cone 18 within which the electrons trigger reactions in the resist layer also depend, among other things, on the primary energy of the electron beam 1. The diameter of the scattering cone 18 becomes larger as the energy of the electron beam decreases; by contrast, the number of electrons that are backscattered from the resist decreases as a result of the lower penetration depth. Electron density distribution can be adjusted within certain limits by selecting the primary energy of the electron beam 1. The probe size 1a has proved to be a further parameter for modeling resist profiled elements. In general, if a small probe size 1a is enlarged with the help of device control, this acts in the resist layer 6 like a physical integration of a multiplicity of fine adjacent probes, and therefore like a superposition of the individual scattering cones 18. Particularly in the production of diffraction gratings, this means that similar profiles can be produced for a large range of grating constants. The electron dose is a third parameter. The electron dose can be adjusted with the help of the selected current density of the electron beam and the exposure time. In the final analysis, this is where the size of the scattering cone 18 is determined, within which take place effective reactions with the resist that is sensitive to the electrons of the electron beam 1. The electron beam 1 is adjusted with regard to the electron surface dose such that a resist profiled element that exhibits a non-orthogonal resist profile is producible as a result of exposure by an electron beam. For this purpose, an energy density profile is produced in the resist layer 6 with the above-mentioned parameters. What is decisive is that one use a resist that converts this electron-density profile into a suitable solubility profile in the resist layer 6. FIG. 3 shows a resist profiled element 12 produced by an electron beam in a resist layer 6. These resist profiled elements produced according to the state-of-the-art are generally used as auxiliary masks in the semiconductor industry to structure a substrate lying thereunder. Accordingly, steep (perpendicular to the substrate surface) edges 25 are required, if possible, and therefore also produced. The edges 25 are perpendicular to the substrate surface 23. FIG. 4 to FIG. 6 disclose resist profiled elements 12 that exhibit non-orthogonal resist profiles 12. FIG. 4 shows a view of a triangular profile 22 that is producible with the present invention. The side edges of the triangular profile 22 are not perpendicular to the substrate surface 23. It is therefore important to select a resist that converts the selected electron density profile into a suitable solubility profile so that the resist profiled elements 12 shown in FIG. 4 to FIG. 6 may be produced. The resist of the resist layer 6 comprises a negative resist and possesses a linear gradation, if possible, so that the electron-density distribution in the resist layer 6 may be transformed into a solubility distribution of the resist layer 6 with gradations that are as fine as possible. Finally, the resist profile 12 consists of a great structure that comprises a parallel array of depressions 27 and elevations 26. FIG. 5 shows a sinusoidal profile 21 that is producible with the present invention. FIG. 6 shows a view of a trapezoidal profile 20 that is producible with the present invention. As is evident from FIG. 4 to FIG. 6, a structural element can typically be scribed in a single exposure step. The resist profiled element 6 comprises a grating structure 24 that consists of a parallel array of depressions 27 and elevations 26. One exposure step therefore always scribes one elevation 26. As aforementioned, the elevation is visible only after the resist layer 6 is treated with a solvent. A multiplicity of elevations 26 that are arranged parallel to each other and separated from each other comprise a grating structure 24. One element of the grating structure 24 is, for example, identified as a grating bar 35, which is producible according to the present invention in a single exposure step 30. FIG. 7 shows a representation of the production of an element 24a of the grating structure 24 with n successively undertaken exposure steps 30 to produce non-orthogonal resist structures according to the state-of-the-art. To produce a grating structure consisting of N elements 24a, N x n exposure steps are therefore necessary. The individual exposure steps 30 are chronologically exposed one after the other, and it is obvious that positional precision of the individual steps in relation to each other must be observed. To this end, t size and effect of the scattering cone 18 in the resist layer must be taken into consideration so that a certain registration overlap is observed. If the overlap precision is not observed, this may lead to a deterioration in the structural fidelity or uniformity of analogous structures. To this is added that longer processing times must be used according to this method to produce an element 24a, and therefore also to produce the entire structure. As previously described, an electron-beam lithography device 1 is needed to produce non-orthogonal structures in the resist layer 6. The electron-beam lithography device makes it possible to work with different energies of the primary electrons. In the process, such energies of the primary electrons, in particular, must be used in which the penetration depth of the primary electrons into organic resists is of the order of magnitude of typically used resist thicknesses (100 nm . . . 500 nm). The lower energy limit of the primary electrons should be at about 1 keV; an upper energy limit of the primary electrons should be adequate at 20 keV. The primary energy must be continuously changeable or at least in small steps (quasi-continuously). FIG. 8 shows a schematic representation of the production of a resist profiled element 12 having a two-dimensional design, according to the invention. For simplicity of representation, a triangular profiled 22 was selected. This should not, however, be interpreted as a limitation. The two-dimensional design of the resist profiled element 12 comprises a multiplicity of structural elements, of which each element is identified as a grating bar 35. As a result of the irradiation of the resist layer 6 by the electron beam, one obtains a laminar resist profile 12 after development of the resist layer 6. In order to produce the resist profiled element 12, the electron beam passes over the resist layer 6 in several steps. The arrow 36 defines a step by which a grating bar 35 is produced. The width of the grating bar 35 is identified by the double arrow 37. In use, electron-beam lithography devices that work either according to the point beam (Gaussian beam) principle or the form beam (variable-shaped beam) principle may be used. Two things are decisive. The probe size 1a must be quasi-continuously changeable over a certain range. The minimum probe size 1a must be smaller than or small in comparison to the minimum of the structural elements to be produced. Nanolithographical devices that work according to the point beam principle (probe size less than or equal to 5 nm) are ideal for this application, but are not absolutely necessary. The electron-beam lithography device 1 must be capable of fine dose control in the exposure regime being applied. This condition is generally met and occurs by means of exposure time (dwell time, shot rate) or the exposure speed while the substrate is being displaced. The resist being used must be a negative resist, i.e., the parts of the resist irradiated with electrons must, in comparison with the developer or solvent (at a particular temperature, particular concentration, or particular reaction time) have lower solubility than the un-irradiated resist. As a further characteristic, reference is made to the contrast curve of the resist. The contrast curve is obtained, under otherwise constant conditions like (energy of the primary electrons, development process, initial thickness d0 of the resist layer 6), one obtains a graphical representation of the residual thickness of the resist layer 6 after development as a function of the electron surface dose D used. To generalize, it is useful to switch over to a standard contrast curve in which the residual thickness of the resist layer 6 is related to the initial thickness d0 of the resist layer 6, and the electron dose used related to the maximum dose Dmax, after which there is no further erosion of the resist layer 6. The resist has a sufficiently soft gradation for the method so long as the steepness S of same does not exceed the value of 1.5 according to the curve represented in equation (1). S = ( Δ d d 0 ) / ( Δ D D max ) Equation 1 Resists, including a suitable development method that meets this condition, exist and are commercially available. The standard electron surface dose is the quotient of the electron surface dose used and the maximum electron surface dose. The maximum electron surface dose is that electron surface dose at which no erosion of the resist occurs during the development process. The following is done to determine the contrast curve for the selected resist system (substrate, resist, thickness of the resist layer 6, development rule, energy of the primary electrons). First, surfaces (of, e.g., 50 μm×100 μm) are exposed with different doses. After development, e.g., with a stylus-type instrument, the residual thickness of the resist layer 6 is measured and the contrast curve that will be needed to proceed further determined therefrom. The method is repeated for a multiplicity of potential electron energies. This applies equally to the later defined adjustment of the system that determines the scattering cone 18 and size thereof. The previously selected system is used, comprising substrate, resist, thickness of the resist layer 6, development rule, and energy of the primary electrons. Single lines are now scribed in the resist layer 6, whereby the smallest possible probe size is set on the electron-beam lithography device. At least the maximum dose Dmax is used for the purpose. As will be clear from the following, it is, however, useful to use higher values as well, and to group individual lines into groups of lines with different grating constants. After processing the substrate, same is refracted perpendicular to the lines, and the cross-section or the line profile can be determined with the help of a scanning electron microscope (not shown). One thus obtains a residual resist thickness distribution dependent on the site of incidence of the electron beam. This residual thickness distribution can be converted with the help of the contrast curve into an electron dose distribution that is effective therein. This electron dose distribution is the scattering cone 18. Overall, this yields the effective electron density for the system under consideration, dependent on the irradiation site or site of incidence of the electrons, as the case may be. Because single lines are used, this may be represented by a one-dimensional function such as, for example, in equation 2.D=D0×f(x) Equation 2 This basic function enables one, simply by superposition, to calculate the result that is yielded when the gratings are exposed. In other words, this means that the exposure of an adjacent grating bar occurs in the range at which the dose of the previously or subsequently exposed grating bar has a finite size. The gratings or wider lines, as the case may be, that are recommended by the above rule essentially serve to check the theoretical predictions experimentally. In other words, they are not absolutely necessary, although they increase the precision of the determination of D=D(x), and therefore also the significance of the prediction. For a real grating structure, one therefore obtains the electron density distribution of a grating bar by summation, as shown in equation 3.Dresult=DB×[fe(x)+fe(x−g)+fe(x+g)] Equation 3 Equation 3 applies when the grating bars are scribed with the smallest possible probe. A profile of the individual grating bar that is scribed with a probe having a width B larger than the smallest possible width b, such as for example B=(2n+1)×b is then obtained according to equation 4: D B = ( D 0 ( 2 n + 1 ) ) × ∑ i = 1 i = n [ f e ( x ) + f e ( x - i × b ) + f e ( x + i × b ) ] Equation 4 If one uses the value DB as calculated in equation 4 instead of D0 in equation 3, one can also calculate grating arrangements in which the bars are not exposed with the smallest possible probe. The electron density is then converted into a layer thickness distribution with the help of the contrast curve. By varying the parameters (D0, g, b) and selecting the energy fe(x), the particular variant can then be found that best corresponds to the desired profile. Three examples of the use of non-orthogonal resist profile elements are listed below: In these storage mediums, information is contained in so-called “pits” and “lands.” Pits and lands are arranged along the track on an alternating basis. They differ in their length. Pits are raised above their surroundings. When read, the storage medium is scanned by a focused laser beam. The diameter of the laser spot is typically about three times greater than the pits are wide. This serves to center the spots while scanning the medium. Because lasers are also used with CDs and DVDs to write the master, this means that when using a minimal spot diameter, the mediums can only be scribed three times as coarsely as is needed to read them afterwards. It is therefore obvious that one use the electron beam to produce the master in order to achieve the limit of what is optically readable. As it happens, however the signal does not originate at the raised surfaces of the pits and lands, but rather at their flanks. And the flank angle, in particular, determines amplitude and signal quality, as the case may be, and therefore also determines the reliability of the readout or of the readout speed. In other words, the desired trapezoidal form of the cross-section of the pits can be optimally set with the method described by us. In positioning systems with the highest level of precision, two methods for determining coordinates are used today, first a laser path measurement system, and then the optical scanning of precision gradations. The method described by us is helpful for the latter. When measuring, the displaced scale is irradiated by a laser, and the diffracted light is registered by sensors. The maxima and minima of the diffracted light thus registered are counted and, converted with the grating constant, yield the distance by which the system must be displaced with the firmly anchored scale. If the profile (cross-section of the grating) is then selected in the appropriate manner, the entire diffraction intensity can be directed in a single diffraction order, i.e., one achieves high signal intensity. This, in turn, means faster measuring or positioning, as the case may be, and more reliable measuring or positioning. Sinus gratings have this property, and this profile modeling can be achieved with the method described by us. Currency, credit cards, passports, etc., are increasingly being furnished with non-copyable security features. These include holograms, which are visible to the bare eye and change their color and their appearance depending on the angle of visualization. Diffractive grating structures are a physical element of such holograms. And here, too, what was said under example 2 applies: if the profile of these security features is suitable, e.g., sinusoidal, these security features become very optically luminous, pronounced, and distinctive. Further features that are based on the grating structure also result for machine evaluation, but are disclosed only with a certain hesitancy for understandable reasons. If the masters for those elements are produced with the help of an electron beam, our method is available to implement in practice the theoretically specified characteristics. |
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claims | 1. A method for producing a neutron flux, comprising:locating a probe tip adjacent a pyroelectric crystal within a chamber;evacuating said chamber of ionizable gases;introducing a gaseous source of ions of deuterium within said chamber;changing the temperature of said pyroelectric crystal in the chamber containing the gaseous source of deuterium ions;wherein changing the temperature of said pyroelectric crystal produces an ion beam about said probe tip by field ionization of said gaseous source of deuterium ions; andpositioning a deuterated target in a trajectory of said ion beam;wherein contact between said ion beam and said deuterated target produces a neutron flux. 2. The method as recited in claim 1, further comprising cooling said pyroelectric crystal before heating the pyroelectric crystal. 3. The method as recited in claim 1, further comprising locating a plurality of probe tips adjacent to at least one pyroelectric crystal within said chamber. 4. The method as recited in claim 1, wherein said gaseous source of ions comprises tritium gas. 5. The method as recited in claim 1, wherein the target comprises a tritiated target. 6. The method as recited in claim 1, wherein said pyroelectric crystal comprises lithium tantalate. 7. A method for producing a neutron flux, comprising:locating an array of a plurality of pyroelectric crystals with adjacent probe tips within a chamber;cooling said pyroelectric crystals;evacuating said chamber;introducing a gaseous source containing deuterium ions within said chamber;heating said pyroelectric crystals in the chamber containing the gaseous source of deuterium ions;wherein heating said pyroelectric crystals produces an ion beam about said probe tips by field ionization; andpositioning a deuterated target in a trajectory of said ion beam;wherein contact between said ion beam and said deuterated target produces a neutron flux. 8. The method as recited in claim 7, wherein said gaseous source of ions comprises tritium gas. 9. The method as recited in claim 7, wherein said pyroelectric crystals comprises lithium tantalate. 10. A method for producing a neutron flux, comprising:locating an array of a plurality of pyroelectric crystals with adjacent probe tips within a chamber;cooling said pyroelectric crystals;evacuating said chamber;introducing a gaseous source of deuterium ions within said chamber;heating said pyroelectric crystals in the chamber containing the gaseous source of deuterium ions;wherein heating said pyroelectric crystals produces an ion beam about said probe tips by field ionization; andpositioning a tritiated target in a trajectory of said beam;wherein contact between said beam and said tritiated target produces a neutron Flux. |
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062434330 | summary | FIELD OF THE INVENTION This invention relates broadly to improvements in nuclear fuel elements for use in the core of nuclear fission reactors and specifically, to improved nuclear fuel elements for use in boiling water reactors having improved stress corrosion cracking resistance and improved inner surface corrosion resistance. BACKGROUND OF THE INVENTION Standard parts of nuclear reactors are the fuel elements forming the core of the reactor that contains the nuclear fuel. Although the fuel elements may assume any one of a number of geometric cross-sections, the elements are comprised of nuclear fuel enclosed by cladding. The cladding is ideally corrosion resistant, non-reactive and heat conductive. Coolant, typically demineralized water, flows in the flow channels that are formed between the fuel elements to remove heat from the core. One of the purposes of the cladding is to separate the nuclear material of the fuel from the coolant. Another purpose of the cladding is to minimize or prevent the radioactive fission products from contacting the coolant and thereby being spread throughout the primary cooling system. However, over time different cladding designs have failed by a number of failure mechanisms. In order to accomplish these and other purposes, various materials and combinations of materials have been used in the cladding. The most common cladding materials include zirconium and alloys of zirconium, stainless steel, aluminum and its alloys, niobium and other materials. Of these, zirconium and its alloys have proven to be excellent materials for such purposes in water reactors because of material properties suited for cladding, including good heat conductivity, good strength and ductility, low neutron absorptivity and good resistance to corrosion. One composite system utilizes an inner lining of stainless steel metallurgically bonded to zirconium alloy. The disadvantage of this system is that the stainless steel develops brittle phases that ultimately crack, allowing the by-products of the fission to contact the zirconium alloy cladding, initiating the deterioration of the zirconium alloy outer cladding. Furthermore, the stainless steel layer has a neutron absorption penalty of ten to fifteen times the penalty for a zirconium alloy of the same thickness. A solution to the problem of cladding failure is set forth in U.S. Pat. No. 3,969,186 which sets forth a composite consisting of refractory metals such as molybdenum, tungsten, rhenium, niobium and alloys of these materials in the form of a tube or foil of single or multiple layers or a coating on the internal surface of the cladding. Still another solution to the problem is set forth in U.S. Pat. No. 4,045,288 that teaches the use of a composite cladding of zirconium alloy substrate with a sponge zirconium liner. The concept is that the commercially pure, soft, ductile zirconium liner minimizes the localized strain that the outer cladding is subject to. However, if a breach in the outer cladding should occur, allowing water and/or steam to enter the fuel rod, the zirconium liner tends to oxidize rapidly. Yet another approach to the problem of cladding failure set forth in U.S. application Ser. No. 06/374,052 filed May 3, 1982, assigned to the assignee of the present application, and incorporated herein by reference, teaches using a composite cladding consisting of a dilute zirconium alloy inner liner metallurgically bonded to conventional cladding materials such as zirconium alloy claddings. The dilute zirconium alloy inner liner includes at least one metal alloyed with the zirconium selected from the group consisting of iron, chromium, iron plus chromium and copper. The amount of iron alloyed with the zirconium is from about 0.2% to about 0.3% by weight; the amount of chromium is from about 0.05% to about 0.3% by weight; the total amount of iron plus chromium is from about 0.15% to about 0.3% by weight and wherein the ratio of the weights of iron to chromium is in the range of from about 1:1 to about 4:1; and wherein the amount of copper is from about 0.02% to about 0.2% by weight. While advances have been made in the area of improving the performance of claddings, corrosion and brittle splitting of the cladding due to interactions of the cladding, the nuclear fuel, the fission products and the coolant continues to be a problem even with the improved systems. SUMMARY OF THE INVENTION A particularly effective nuclear fuel element is comprised of a central core of a nuclear fuel material. The nuclear material may be any radioactive materials, such as the well known radioactive materials of uranium, plutonium, thorium and mixtures thereof. The central core of nuclear fuel material is surrounded by an elongated composite cladding comprised on an inner metallic barrier and an outer metallic tubular portion. The outer portion of the cladding is unchanged in design and function from the previous practices utilized in the nuclear reactor arts. The outer metallic tubular portion remains the standard, well-known materials conventionally used in cladding, and in particular, as outer portions of composite claddings. The outer metallic portion is selected from the group consisting of zirconium and its alloys, stainless steel, aluminum and its alloys, niobium and magnesium alloys. The inner metallic barrier is zirconium in which the amount of Fe is microalloyed with the zirconium in a controlled amount of from about 850-2500 parts per million by weight (ppm). The inner metallic barrier is metallurgically bonded to the outer metallic tubular portion, but unlike the outer metallic portion when comprised of zirconium or its alloys, is alloyed only with carefully controlled amounts of iron. Trace elements in an amount so as not to affect the character and nature of the inner metallic barrier may be present. Surprisingly, by carefully controlling the amount of iron present in the zirconium, it has been discovered that the inner metallic barrier not only has greatly improved corrosion resistance over previous claddings and barriers but also improved stress corrosion cracking resistance, while the other important characteristics of the zirconium inner metallic barrier are unaffected. The barrier is ductile, compatible with the outer metallic tubular portion, but has low neutron absorptivity, yet is highly resistant to radiation hardening while maintaining good heat transfer characteristics.. It is believed that the present invention improves the ability of the fuel element to operate normally in the failed condition, that is, with the failure of the outer cladding due to primary defects developed as a result of stress corrosion or fretting, but without developing secondary long axial cracks along the inner barrier. The inner metallic barrier has sufficient corrosion resistance such that it will continue to provide an effective barrier when exposed to the nuclear fuel and the by-products of nuclear fission as well as the coolant, which may include demineralized water, steam and/or moderators. The life expectancy of the fuel element is increased, even after failure of the outer cladding, due to the ability of the inner metallic barrier to slow down the formation of corrosion products (hydrides) upon contact with coolant. Other features and advantages of the present invention will be apparent from the following description and the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. |
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039873030 | abstract | A gas analyzer is provided which is particularly suited for making transcutaneous measurement of the CO.sub.2 concentration in the blood.. In accordance with one embodiment of the invention, sample gases from the body are circulated in a cavity of the device. A rotating wheel in the cavity includes two reference cells and a sample cell which are sequentially rotated into the optical path between a source and a detector. Three signals are thereby provided which may be combined to give an output indication of the CO.sub.2 concentration in the body fluids. In a preferred embodiment, the sample cell is an "inverted cell" being in open communication with the sample gas circulating in the device so that the gas in the sample cell is a portion of the circulating gas which also surrounds the two reference cells. An output indication is thereby obtained which is insensitive to contaminants in the sample.. In accordance with another embodiment, the sample cell is isolated from the region surrounding the wheel and positioned so as to be presented in series with the reference cells in the optical detection path.. In preferred embodiments, the rotating wheel contains a number of permanent magnets which interact with a number of electromagnets driven in sequence to provide rotation of the wheel. |
abstract | A process for detecting the edges of collimator blades in digital radiography images in the first pass detects the edges of the collimator blades using original image, and the in the second pass repeats edge detection using an image enhanced by a histogram matching technique, for example. The edge detection using an enhanced image may also be repeated any number of times in cases of complex anatomy or when selected radiographic techniques does do not provide sufficient imaging data. The results of the second pass, or the collection of the results of multiple second passes, are then combined with the result from the first pass to form a list of the potential blade edge candidates. A desirable number of edges are then selected from the combined list to form a polygon which encloses the target area of the image, thereby providing the shutter area. |
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description | The invention relates to an X-ray microscope which includes a device for generating X-rays, which device is provided with: means for producing a fluid jet, means for forming a focused radiation beam whose focus is situated on the fluid jet. A device for generating soft X-rays is known from the published patent application WO 97/40650 (PCT/SE 97/00697). The means for producing a fluid jet in the known device are formed by a nozzle wherefrom a fluid such as water is ejected under a high pressure. The means for producing a focused radiation beam are formed by a combination of a pulsating laser and a focusing lens which focuses the pulsating radiation beam produced by the laser in such a manner that the focus is situated on the fluid jet. Because of the high power density of the laser pulses, the laser light thus induces a plasma in the fluid jet, thus generating said soft X-rays. The cited patent application describes how these X-rays, notably those of a wavelength of 2.3–4.4 nm, can be used for X-ray microscopy. Generating X-rays by way of pulsed laser plasma emission has a number of drawbacks. A first drawback in this respect is due to the fact that it is necessary to operate the laser in the pulsating mode in order to achieve an adequate power density of the laser. The cited patent application mentions a power density of from 1013–1015 W/cm2 ; if this power is to be generated by means of a laser in continuous operation, an extremely large laser would be required. As a result, this known X-ray source produces only X-rays of a pulsating nature. A further drawback of laser-induced plasma emission consists in the phenomenon that many particles (molecules, radicals, atoms (ionized or not), which usually have a high kinetic energy and may be very reactive chemically are present in the vicinity of the location where the X-rays are formed (the X-ray spot). The formation of these particles can be explained as follows: when energy is applied to the target (so the fluid jet) by means of laser light, as the intensity increases first the electrons of the outer shell of the target material will be ionized whereas the electrons of the inner shells, producing the X-rays, are excited only after that. The particles then formed could damage the sample to be examined by means of the X-ray microscope. In order to mitigate or prevent such damage, it is feasible to arrange an optical intermediate element (for example, a condenser lens in the form of a Fresnel zone plate) between the physical X-ray spot and the actually desired location of the X-ray spot, thus creating an adequate distance between the X-ray spot and the sample without seriously affecting the imaging properties of the X-ray microscope. Because condenser lenses are not very effective in the X-ray field, however, a considerable part of the X-ray power generated for the imaging in the X-ray microscope is thus lost. Moreover, some other types of condensers (for example, multilayer mirrors or grazing incidence mirrors) are very susceptible to damage by said high energetic particles. It is an object of the invention to avoid said drawbacks by providing an X-ray source for comparatively soft X-rays which can operate continuously while forming no or hardly any detrimental particles in the X-ray target. This object is achieved according to the invention in that the focused radiation beam consists of a beam of electrically charged particles. The above-mentioned drawbacks are avoided by irradiating the fluid jet by means of said particles. Because of the much shorter wavelength of said particles, moreover, an advantage is obtained in that the focus formed by means of said particles can be much smaller than the focus of the beam of laser light. The invention offers an additional advantage in that the energy of the electrically charged particles can be continuously controlled in a wide range by variation of the acceleration voltage of said particles; such control is realized by variation of the acceleration voltage of these particles. The beam of electrically charged particles is formed by an electron beam in a preferred embodiment of the invention. This embodiment offers the advantage that use can be made of existing apparatus such as a scanning electron microscope. Such apparatus is arranged notably to obtain a very small electron focus, that is, a focus with a diameter as small as a few nanometers. The cross-section of the fluid jet in the direction of the focused beam in a further embodiment of the invention is smaller than that in the direction transversely thereof. This embodiment is of importance in all cases where the particle beam has a width which is larger than approximately the penetration depth into the fluid jet. If a fluid jet having a circular cross-section were used in such circumstances, the X-rays generated in a comparatively thin region at the surface of the jet would be absorbed in the interior of the fluid jet again, so that a useful yield of the X-rays would be lost. This adverse effect is strongly mitigated or even avoided when a “flattened” fluid jet is used. The fluid jet in another embodiment of the invention consists mainly of liquid oxygen or nitrogen. In addition to the advantage that a fluid jet of a liquefied gas has excellent cooling properties, and hence can be exposed to heavy thermal loading, such a fluid jet also has a high degree of spectral purity, notably in the range of soft X-rays, that is, in the so-called water window (wavelength λ=2.3–4.4 nm). This wavelength range is particularly suitable for the examination of biological samples by means of an X-ray microscope, because the absorption contrast between water and carbon is maximum in this range. The means for producing a focused beam of electrically charged particles in another embodiment of the invention are formed by a standard electron gun for a cathode ray tube, the X-ray microscope also being provided with a condenser lens which is arranged between the fluid jet and the object to be imaged by means of the X-ray microscope. According to the invention a first advantage of the use of a standard electron gun of a cathode ray tube resides in the fact that such elements already are manufactured in bulk and have already proven their effectiveness for many years. Another advantage resides in fact that such electron sources are capable of delivering a comparatively large current (of the order of magnitude of 1 mA). The electron spot, however, has a dimension of the order of magnitude of 50 μm, being of the same order of magnitude as the dimensions of the object to be imaged, so that in this case a condenser lens is required which concentrates the radiation from the X-ray spot onto the sample. Even though X-ray intensity is lost due to the use of the condenser, the current in the electron beam is so large that this loss is more than compensated for. The properties that can be offered by an existing electron microscope so as to implement the invention can be used to good advantage. An electron microscope produces a focused electron beam and may be provided with a device for generating X-rays which is characterized according to the invention in that it is provided with means for producing a fluid jet and means for directing the focus of the electron beam onto the fluid jet. An X-ray microscope can thus be incorporated in the electron microscope, the device for generating X-rays then acting as an X-ray source for the X-ray microscope. Notably a scanning electron microscope is suitable for carrying out the present invention, because such a microscope can readily operate with acceleration voltages of the electron beam which are of the order of magnitude of from 1 to 10 kV; these values correspond to values necessary so as to generate soft X-rays in the water window. The FIGS. 1a to 1c show a number of configurations in which a fluid jet which is assumed to extend perpendicularly to the plane of drawing is irradiated by an electron beam. In FIG. 1a this beam originates from a spot forming objective of a scanning electron microscope (SEM); in the FIGS. 1 and b the electron beam originates from a standard electron gun for a cathode ray tube (CRT gun). In FIG. 1a the fluid jet 2, for example a jet of water, has a diameter of approximately 10 μm. The electron beam 6 focused onto the fluid jet by the objective 4 of the SEM is subject to an acceleration voltage of, for example, 10 kV and transports a current of, for example, 5 μA. An electron spot having a cross-section of 1 μm generates an X-ray spot having a dimension of approximately 2 μm with soft X-rays and a wavelength of α=2.4 nm with a weak background of Bremsstrahlung in a region 8. The surrounding water still has a monochromatizing effect and will suitably transmit the line with the wavelength of 2.4 nm, but will strongly absorb the Bremsstrahlung of a higher energy. The soft X-rays thus obtained can be used so as to irradiate an object to be imaged in an X-ray microscope. In FIG. 1b the fluid jet 2 is irradiated by an electron beam 6 which originates from a standard CRT gun (not shown). In this case the fluid jet 2 has an elliptical cross-section with a height of, for example, 20 μm and a width of, for example, 100 μm. The electron beam 6 focused onto the fluid jet by the CRT gun produces an electron spot 8 having a cross-section of approximately 50 μm. The electron beam is subject to an acceleration voltage of, for example, 30 kV and transports a current of, for example, 1 mA. As is the case in FIG. 1a, the surrounding water has a monochromatizing effect on the soft X-rays generated. When an elliptical fluid jet of the above (comparatively large) dimensions of 20×100 μm is used, it may occur that the vacuum system cannot adequately discharge the vapor produced by the jet, so that the pressure in the system could become too high for the use of an electron gun. In such cases use can be made of the configuration shown in FIG. 1c in which the fluid jet 2 is also irradiated by an electron beam 6 which originates from a standard CRT gun (not shown). The cross-section of the electron beam again amounts to 50 μm, but in this case the fluid jet 2 has a circular cross-section of the order of magnitude of, for example, 10 μm. As a result of this configuration, the X-ray spot 10 has a dimension which is not larger than the cross-section of the fluid jet, that is, 10 μm in this case. FIG. 2 shows diagrammatically the beam path in a transmission X-ray microscope according to the invention. In a transmission X-ray microscope the image is formed by irradiating the object to be imaged (the sample) more or less uniformly by means of X-rays, the object thus irradiated being imaged by means of a projecting objective lens which is in this case formed by a Fresnel zone plate. A Fresnel zone plate is a dispersive element. This could give rise to imaging defects which limit the resolution and are, of course, undesirable. Thus, it is necessary for the irradiating X-ray source to be as monochromatic as possible; this requirement is more than adequately satisfied by the X-ray source according to the invention. In the configuration shown in FIG. 2 it is assumed that the X-ray source is formed by an electron spot 8 which itself is formed in a fluid jet 2 by an electron beam 6 which originates from a SEM system, the flow direction of said fluid jet 2 extending perpendicularly to the plane of drawing. In this case the electron spot, and hence the X-ray spot, is (much) smaller than the cross-section of the fluid jet. The X-ray beam 12 originating from the electron / X-ray spot 8 more or less uniformly irradiates the object 14 to be imaged by means of the X-ray microscope. The object 14 is situated at a distance 26 of, for example, 150 μm from the X-ray spot. X-rays are scattered by the object 14 as represented by a sub-beam 16 of scattered X-rays. Each irradiated point-shaped area of the object produces such a sub-beam. The sub-beams thus formed are incident on the objective 18 which has a typical focal distance of 1 mm and a typical diameter of 100 μm. The objective images the relevant point on the image plane 22 via the sub-beam 20. When the object distance 28 is then equal to 1.001 mm and the image distance equals 1000 mm, the magnification is 1000× for the given focal distance of 1 mm. In order to prevent the X-ray spot 8 which irradiates through the object 14 from being imaged by the objective 18 in the space between the objective and the image plane 22, thus overexposing the image in the image plane, an X-ray absorbing shielding plate 24 is arranged at the center of the objective. A detector which is sensitive to the X-rays of the relevant wavelength is arranged in the image plane 22. For this purpose use can be made of an X-ray-sensitive CCD camera whose detector surface is coincident with the image plane 22. An example of such a CCD camera is a CCD camera of the so-called “back illuminated” type such as the camera type NTE/CCD-1300 EB from “Princeton Instruments”, a “Roper Scientific” company. FIG. 3 is a diagrammatic representation of the beam path in a scanning transmission X-ray microscope according to the invention. In a scanning transmission X-ray microscope the image is formed by scanning the object to be imaged in conformity with a given scanning pattern, that is, with a reduced image of the X-ray spot or not, and by detecting the X-rays scattered by the object as a function of the location on the object irradiated by the image of the X-ray spot. The image of the X-ray spot is then obtained by means of an objective lens. When this lens is formed as Fresnel zone plate, the irradiating X-ray source should again be as monochromatic as possible. For the configuration shown in FIG. 3 it is assumed again that the X-ray source is formed by an X-ray spot 8 which is formed in a fluid jet 2 by an electron beam 6 originating from a SEM system, the flow direction of said jet extending perpendicularly to the plane of drawing. The electron spot, and hence the X-ray spot, is (much) smaller than the cross-section of the fluid jet. In this case the width of the fluid jet in the direction perpendicular to the electron beam is much greater than that in the direction of the electron beam, for example, it has a width of 100 μm and a height of 20 μm. The electron beam 6 is scanned across the fluid jet in the longitudinal direction 32a, for example, by means of the standard scan coils in a SEM. As a result, the X-ray spot thus produced moves in the same way. The objective lens 34 formed by the Fresnel zone plate is arranged in such a manner that it images the X-ray spot 8 formed in the fluid jet on the object 14. Due to said displacement of the X-ray spot in the direction 32a, the image 36 thereof which is formed on the object is also displaced, that is, in the direction of the arrow 33b which opposes the direction 32a due to the lens effect of the objective 34. The X-rays 38 scattered by the object are detected again by the detector 22 and, like in the configuration shown in FIG. 2, an X-ray absorbing shielding plate 24 is arranged in the objective so as to prevent the X-ray spot 8 from coming into sight of the detector 22. FIG. 4 shows diagrammatically the beam path in a transmission X-ray microscope in which the electron source generating the X-rays is formed by a standard electron gun (not shown) for a cathode ray tube which is capable of delivering a beam current of the order of magnitude of 1 mA. The configuration shown in FIG. 4 is mainly identical to that shown in FIG. 2, except for the already mentioned difference concerning the electron source and the presence of a condenser lens 40 in FIG. 4. Because the X-ray spot 8 in this configuration has dimensions of the same order of magnitude as the object 14 (for example, from 50 to 100 μm), the condenser lens 40 is provided in the form of a Fresnel zone plate 40. The condenser lens 40 images the X-ray spot 8 on the object 14 in reduced form; the entire further imaging process is the same as already described with reference to FIG. 2. |
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claims | 1. A tomography imaging system comprising a composite objective lens assembly comprising a plurality of micro-objectives, each of the micro-objectives structured to block zero-order diffracted radiation. 2. The tomography imaging system of claim 1 wherein said micro-objectives in said composite lens are arranged in an array. claim 1 3. The tomography imaging system of claim 2 wherein said array of micro-objectives comprises a generally annular arrangement of said micro-objectives. claim 2 4. The tomography imaging system of claim 3 wherein the array of micro-objectives is substantially planar. claim 3 5. The tomography imaging system of claim 3 wherein the micro-objectives in the array of micro-objectives are mounted on a curved structure. claim 3 6. A tomography imaging system comprising: a radiation source emitting light in a desired wavelength; a collector optic positioned to collect said light and transmit or reflect it; a sample holder positioning a sample to be imaged in the path of said light from said collector optic; a composite objective lens system including an array of micro-objectives imaging said light in a desired fashion, each of the micro-objectives structured to block zero-order diffracted radiation; and an imager. 7. The tomography imaging system of claim 6 further comprising a composite aperture between said composite objective lens system and said imager. claim 6 8. The tomography imaging system of claim 6 wherein said array of micro-objectives comprises an substantially planar and generally annular array of micro-objectives. claim 6 9. The tomography imaging system of claim 6 wherein said array of micro-objectives comprises a curved and generally annular array of micro-objectives. claim 6 10. The tomography imaging system of claim 6 wherein said radiation source comprises a laser light source. claim 6 11. The tomography imaging system of claim 10 wherein said radiation source further comprises an laser plasma x-ray source in the path of light from said laser light source. claim 10 12. The tomography imaging system of claim 6 wherein said imager comprises: claim 6 an image detector detecting two dimensional images based on said imaged light from said objective lens system; an image memory storing images detected in said image detector; and a processor constructing a three dimensional image from said two dimensional images. 13. The tomography imaging system of claim 6 wherein the radiation source comprises a synchotron radiation source. claim 6 14. The tomography imaging system of claim 6 wherein the radiation source comprises an x-ray tube including an electron beam excited x-ray source. claim 6 15. The tomography imaging system of claim 6 wherein the radiation source comprises a source of energy selected from a group consisting of an electron source, a neutron source, a positron source and a photon source. claim 6 16. A method of forming an image of a sample comprising the steps of: providing x-rays; exposing said sample to said x-rays; and imaging said x-rays downstream of said sample using a composite objective lens comprising a plurality of micro-objectives, each of the micro-objectives being structured to block zero-order diffraction x-rays. 17. The method of claim 16 wherein said imaging step comprises imaging said x-ray light downstream of said sample using a substantially planar and generally hexagonal array of micro-objectives. claim 16 18. The method of claim 16 further comprising: claim 16 detecting two dimensional images based on said imaged x-rays from said objective lens system; storing images detected in said image detector; and constructing a three dimensional image from said two dimensional images. 19. A method of forming an image of a sample comprising the steps of: providing x-rays; collecting said x-rays and directing them in a desired fashion; positioning the sample in the path of said rays; imaging said x-rays downstream of said sample using a composite objective lens comprising a plurality of micro-objectives, each of the micro-objectives being structured to block zero-order diffraction x-rays; and detecting and acquiring an image using said imaged x-rays. 20. The method of claim 19 wherein said positioning step further comprises transmitting the x-rays through the sample. claim 19 21. The method of claim 19 wherein said positioning step further comprises scattering the x-rays through the sample. claim 19 22. The method of claim 19 wherein said positioning step further comprises reflecting the x-rays off the sample. claim 19 23. The method of claim 19 wherein said focusing step comprises focusing said x-ray light downstream of said sample using a substantially planar and generally hexagonal array of micro-objectives. claim 19 24. The method of claim 19 wherein said step of detecting and acquiring an image comprises: claim 19 detecting two dimensional images based on said imaged x-rays from said objective lens system; storing images detected in said image detector; and constructing a three dimensional image from said two dimensional images. 25. The tomography imaging system of claim 1 further comprising an order sorting aperture disposed downstream of the composite objective lens assembly, the order sorting aperture being structured to block all but one of odd-order diffraction radiation imaged by each of the micro-objectives. claim 1 26. The tomography imaging system of claim 6 further comprising an order sorting aperture disposed between the composite objective lens system and the imager, the order sorting aperture being structured to block all but one of odd-order diffraction radiation imaged by each of the micro-objectives. claim 6 27. The method according to claim 16 further comprising the step of: claim 16 blocking all but one of odd-order diffraction radiation imaged by the micro-objectives. 28. The method according to claim 19 further comprising the step of: claim 19 blocking all but one of odd-order diffraction radiation imaged by the micro-objectives. 29. The tomography imaging system of claim 1 wherein each of the micro-objectives is structured to block odd-order diffraction radiation other than first-order diffraction radiation. claim 1 30. The tomography imaging system of claim 6 wherein each of the micro-objectives is structured to block odd-order diffraction radiation other than first-order diffraction radiation. claim 6 31. The method according to claim 16 further comprising the step of: claim 16 adapting each of the micro-objectives to block odd-order diffraction radiation other than first-order diffraction radiation. 32. The method according to claim 19 further comprising the step of: claim 19 adapting each of the micro-objectives to block odd-order diffraction radiation other than first-order diffraction radiation. |
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abstract | The present disclosure relates to a drilling instrument for machining tubes in tube sheets of heat exchangers in a radioactive environment, comprising a transport device having clamping elements and having a drilling device with clamping fingers, which are arranged in each case on a common first side. The transport device and the drilling device are connected to a support device having a support plate on which a resting plate of the drilling device rests. In addition, the support plate is connected to the resting plate by way of at least one movable connecting element, and the resting plate is connected to the support plate in a play-free manner in a first position of the connecting element, wherein the resting plate exhibits predefinable play with regard to the carrier plate in a second position of the connecting element. |
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description | The present application is a continuation-in-part of U.S. patent application Ser. No. 12/578,413 entitled INCREASED EFFICIENCY STRAINER SYSTEM filed Oct. 13, 2009, the disclosure of which is incorporated herein by reference. Not Applicable 1. Technical Field of the Invention The present invention relates generally to strainer devices and, more particularly, to a strainer system wherein a pressure released membrane is integrated into the plenum duct at the “clean” side of multiple strainer modules. The pressure released membrane is operative to isolate one of the strainer modules of the strainer system from the remaining active strainer modules thereof, and to effectively activate the isolated strainer module when pressure across the plenum duct increases beyond a prescribed threshold as a result of a head loss increase across the originally active strainer modules attributable to precipitate formation thereon. 2. Description of the Related Art A nuclear power plant typically includes an emergency core cooling system that circulates large quantities of cooling water to critical reactor areas in the event of accidents. A boiling water reactor or BWR commonly draws water from one or more reservoirs, known as suppression pools, in the event of a loss of coolant accident. More particularly, water is pumped from the suppression pool to the reactor core and then circulated back to the suppression pool in a closed loop. A loss of coolant accident can involve the failure of reactor components that introduce large quantities of solid matter into the cooling water, which entrains the solids and carries them back to the suppression pool. For example, if a loss of coolant accident results from the rupture of a high pressure pipe, quantities of thermal insulation, concrete, paint chips and other debris can be entrained in the cooling water. In contrast to a BWR, a pressurized water reactor or PWR, after a loss of coolant accident, typically draws cooling water from a reactor water storage tank and, after a signal, shuts off the flow from the storage tank and recirculates this water through the reactor. In this regard, the pressurized water reactor has a containment area that is dry until it is flooded by the occurrence of an accident, with the emergency core cooling system using a pump connected to a sump in the containment area to circulate the water through the reactor. Nevertheless, the water that is pumped in the event of an accident will also usually contain entrained solids that typically include insulation, paint chips, and particulates. Thus, in both types of reactors (i.e., boiling water reactors and pressurized water reactors), cooling water is drawn from a reservoir and pumped to the reactor core, with entrained solids or debris potentially impairing cooling and damaging the emergency core cooling system pumps if permitted to circulate with the water. In recognition of the potential problems which can occur as a result of the presence of entrained solids or debris in the coolant water of the emergency core cooling system, it is known in the prior art to place strainers in the coolant flow path upstream of the pumps, usually by immersing them in the cooling water reservoir. It is critical that these strainers be able to remove unacceptably large solids without unduly retarding the flow of coolant. In this regard, the pressure (head) loss across the strainer must be kept to a minimum. Strainers are commonly mounted to pipes that are part of the emergency core cooling system and that extend into the suppression pool or sump, with the emergency core cooling system pumps drawing water through the strainers and introducing the water to the reactor core. There has been considerable effort expended in the prior art in relation to the design of strainers to decrease head loss across the strainer for the desired coolant flow. Existing strainers often include a series of stacked perforated hollow discs or flat perforated plates and a central core through which water is drawn by the emergency core cooling system pump. The perforated discs or plates prevent debris larger than a given size from passing the strainer perforations and reaching the pumps. As is apparent from the foregoing, large amounts of fibrous material can enter the circulating coolant water in the event of a reactor accident. This fibrous material, which often originates with reactor pipe or component insulation that is damaged and enters the emergency core cooling system coolant stream in the event of a loss of coolant accidents indicated above, typically accumulates on the strainer surfaces and captures fine particulate matter in the flow. The resulting fibrous debris bed on the strainer surfaces can quickly block the flow through the strainer, even though the trapped particulates may be small enough to pass through the strainer perforations. More particularly, the debris accumulates in a fluffy density in and on the strainer until the strainer becomes completely covered with a fiber and particulate debris bed. Once this occurs, the strainer loses its complex geometric surface advantages and becomes a simple strainer. Hours to days later, some debris typically dissolves into solution and interacts with chemicals present in the containment. At the same time, containment temperatures are trending down. This phenomenon causes certain chemical precipitates to form which eventually make their way to the strainer. Once they reach the strainer surface, the pressure drop across the strainer typically dramatically increases. The prior art has attempted to address the above-described flow blockage effect by making the strainer larger, the goal being to distribute the trapped debris over more area, reducing the velocity through the debris bed, and further reducing the head loss across the strainer as a whole. This solution, however, is often undesirable since the available space in a reactor for a suction strainer is usually limited, and further because larger strainers are typically more costly. As a result, the situation sometimes arises wherein the expected debris load after a loss of coolant accident can dictate a need for strainers that are too large for the space allotted for them in the containment area. Moreover, large strainers are often more difficult work with and thus more costly to install. In addition, prior art emergency core cooling system strainers have been constructed in ways that make them somewhat expensive to fabricate. The present invention addresses the aforementioned needs and overcomes many of the deficiencies associated with existing nuclear power plant strainer designs providing a strainer system design which is specifically suited to reduce the differential pressure experienced across the strainer in nuclear power plants with medium to high fiber loads after chemical precipitate formation. Various features and advantages of the present invention will be described in more detail below. In accordance with the present invention, there is provided an increased efficiency strainer system which is particularly suited for use in the emergency core cooling system of a nuclear power plant. In certain embodiments of the present invention, the strainer system includes one or more strainer cassettes or cartridges, with each such cassette or cartridge including a plurality of strainer pockets disposed in side-by-side relation to each other. Multiple cassettes or cartridges may be assembled together to form a strainer module of the strainer system. More particularly, in one embodiment of the present invention, each cartridge has a generally quadrangular configuration, as do the individual strainer pockets included therein. In this particular embodiment, the strainer pockets of the cartridge each define an inflow end, with the inflow ends of the strainer pockets of the cartridge facing in a common direction. Within the cartridge, or the module including multiple cartridges, the inflow ends of one or more of the strainer pockets may be enclosed by an elastic metal membrane. When in a closed position, the membrane prevents liquid flow into the corresponding strainer pocket via the inflow end thereof. The membrane remains closed when only a low pressure load is exerted thereon, but is deflected or deformed into an open position when a high pressure load is exerted thereon. The movement of the membrane to its open position effectively opens the corresponding strainer pocket, thus allowing for the flow of liquid into the interior of the strainer pocket via the inflow end thereof. In accordance with another aspect of the present invention, it is contemplated that the above-described strainer cartridge(s) included in a strainer module of the strainer system may include flat, non-perforated face plates which extend from a surface of the cartridge(s) adjacent the inflow ends of the strainer pockets thereof. The non-perforated extended face plates cause the edges of a fiber and particulate debris bed forming at the inflow ends of the strainer pockets to compress and slowly curl in from an originally flush relationship to the face plates, which results in the creation of small flow paths between the face plates and debris bed as differential pressure continues to rise, thus allowing flow into the strainer and reducing head loss. As the strainer area affected by the flow receives more debris, fiber, particulate and chemical precipitate, the head loss increases until another flow path is opened into another area of the strainer. The creation of the flow paths, as caused by the optional inclusion of the extended face plates with the strainer cartridge(s), effectively reduces the maximum differential pressure experienced across the strainer and provides a way to potentially reduce required strainer surface area necessary to satisfy a particular containment recirculation net positive suction head requirement. In accordance with another embodiment of the present invention, the strainer cassette or cartridge has a generally circular configuration, with the strainer pockets thereof being arranged in side-by-side relation to each other in a generally circular pattern. In this particular embodiment, one or more of the strainer pockets of the strainer cartridge may be outfitted with the aforementioned elastic metal membrane. Additionally, if a strainer module is constructed including multiple circularly configured strainer cartridges disposed in stacked relation to each other, it is contemplated that all of the strainer pockets of one or more of the strainer cartridges included in the module may be outfitted with an elastic metal membrane. In accordance with another embodiment of the present invention, the strainer system comprises a plurality of cylindrically configured, tubular primary strainer elements. Each of the primary strainer elements defines an inflow end, and comprises concentrically positioned inner and outer walls which are each fabricated from a perforated metal material. The inflow end is typically defined solely by the inner wall of the primary strainer element. The inflow end of one or more of the primary strainer elements included in the strainer system may be covered by a rupture disc or segmented membrane which mirrors the functionality of the above-described elastic metal membrane. In this regard, the rupture disc or segmented membrane covering the inflow end of one or more of the primary strainer elements is operative to move from a normally closed position to an open position allowing direct liquid flow into the interior of the inner wall of the primary strainer element via the inflow end defined thereby when such rupture disc or segmented membrane is subjected to a high pressure load. In this particular embodiment of the strainer system, it is also contemplated that one or more of the primary strainer elements may include a secondary strainer element concentrically positioned within the inner wall of the primary strainer element, thus creating a double cylinder strainer construction as opposed to the single cylinder strainer construction provided by a primary strainer element standing alone. The secondary strainer element, if included with a primary strainer element, has a construction mirroring that of the surrounding primary strainer element, with the inflow end defined by the inner wall of the secondary strainer element optionally being covered by the above-described rupture disc or segmented membrane. In the double cylinder strainer construction, no rupture disc or segmented membrane is provided on the inflow end defined by the inner wall of the primary strainer element due to the concentric positioning of the secondary strainer element therein. In accordance with yet another embodiment of the present invention, there is provided a strainer system comprising a plurality of strainer modules, each of which comprises multiple cassettes or cartridges assembled together in a prescribed arrangement. Each cassette or cartridge of each strainer module comprises a plurality of strainer pockets disposed in side-by-side relation to each other, each of the strainer pockets having the structural attributes described above, though none of the strainer pockets is enclosed by one of the aforementioned elastic metal membranes. In the strainer system constructed in accordance with this particular embodiment of the present invention, the “clean” sides of the strainer modules are fluidly connected to each other by a plenum duct which also has a suction pump fluidly coupled thereto. Integrated into the plenum duct is a pressure released membrane (PRM) which is positioned so as to effectively isolate one of the strainer modules from the remaining active strainer modules included in the strainer system. The pressure released membrane is uniquely configured so as to facilitate the activation of the isolated strainer module when pressure across the plenum duct increases beyond a prescribed threshold. Such pressure increase within the plenum duct typically occurs as a result of a head loss across the originally active strainer modules of the strainer system, such head loss increase being attributable to precipitate formation on such strainer modules. In the embodiment of the strainer system including the pressure released membrane in the plenum duct, the activation of the originally isolated strainer module is facilitated by the movement of the pressure released membrane from an original closed position, to an open position. When the pressure released membrane is in its closed position, it effectively blocks that portion of the plenum duct fluidly communicating with the isolated strainer module from the remainder of the plenum duct which is fluidly coupled to the originally active strainer modules and the suction pump. As indicated above, an increase in the suction pressure level within that portion of the plenum duct fluidly communicating with the originally active strainer modules beyond a prescribed threshold facilitates the movement of the pressure released membrane from its closed position to its open position, thus placing that portion of the plenum duct in fluid communication with the originally inactive strainer module into fluid communication with the remainder of the plenum duct. Such fluid communication in turn allows the operating suction pump to effectively draw fluid through the previously isolated and now active strainer module of the strainer system. The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. Common reference numerals throughout the drawings and detailed description to indicate like elements. Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same, FIGS. 1 and 2 illustrate an existing, prior art strainer cassette or cartridge 10. The cartridge 10 has a generally quadrangular configuration. When viewed from the perspective shown in FIGS. 1 and 2, the cartridge 10 includes an opposed pair of side walls 12 extending in spaced, generally parallel relation to each other, a top wall 14 extending between the top edges of the side walls 12, a bottom wall 16 extending in spaced, generally parallel relation to the top wall 14 between the bottom edges of the side walls 12, and a back wall 18 which extends between the back edges of the side walls 12 and between the back edges of the top and bottom walls 14, 16. In the strainer cartridge 10, the side, top, bottom and back walls 12, 14, 16, 18 are each fabricated from a perforated metal material. The strainer cartridge 10 further comprises a plurality of separator plates 20 which, when viewed from the perspective shown in FIGS. 1 and 2, are horizontally and vertically oriented between the side, top, bottom and back walls 12, 14, 16, 18 in a prescribed arrangement. More particularly, the separator plates 20 are arranged such that they, along with the side, top, bottom and back walls 12, 14, 16, 18, collectively define a plurality of strainer pockets 22 within the strainer cartridge 10. In the exemplary strainer cartridge 10 shown in FIGS. 1 and 2, a total of eight (8) strainer pockets 22 are included in the strainer cartridge 10, with the strainer pockets 22 being arranged in two side-by-side vertical columns of four (4) strainer pockets 22 each. Like the side, top, bottom and back walls 12, 14, 16, 18, each of the separator plates 20 is fabricated from a perforated metal material. As is most apparent from FIGS. 4 and 5, the horizontally oriented separator plates 20 included in the strainer cartridge 10 are preferably formed in a manner which imparts a generally parabolic configuration to each of the strainer pockets 22. In this regard, each of the strainer pockets 22 includes an open inflow end 24 at the front edges of the side, top, bottom and back walls 12, 14, 16, 18 and the front edges of the separator plates 20. In addition to the inflow end 24, each strainer pocket 22 includes an arcuate, concave back end 26 which is disposed proximate the back wall 18 of the strainer cartridge 10. As will be discussed in more detail below, in accordance with the present invention, the strainer cartridge 10 is provided with additional structural features which enhance the functionality thereof, and hence the functionality of a strainer module assembled to include one or more enhanced strainer cartridges. FIG. 3 depicts an exemplary strainer module 28 assembled by placing multiple strainer cartridges in side-by-side relation to each other. In the exemplary strainer module 28 shown in FIG. 3, a total of seven (7) strainer cartridges are included therein, with three (3) of the strainer cartridges being “enhanced.” For purposes of clarity, the “enhanced” strainer cartridges constructed in accordance with the present invention are labeled with the reference number “10a” in FIGS. 3 and 4 to differentiate the same from the prior art strainer cartridges 10. The remaining four (4) strainer cartridges included in the strainer module 28 are the prior art, non-enhanced strainer cartridges 10 described above. Those of ordinary skill in the art will recognize that the strainer module 28 may be assembled to include one or more enhanced strainer cartridges 10a and one or more standard strainer cartridges 10 in any combination, the aforementioned arrangement of three strainer cartridges 10a and four strainer cartridges 10 being exemplary only. When assembled to form the strainer module 28 shown in FIG. 3, the strainer cartridges 10, 10a are arranged such that the inflow ends 24 defined by the strainer pockets 22 thereof face in a common direction. When the strainer module 28 is integrated into a strainer system, a suction plenum is defined between the back wall of the strainer module 28 collectively defined by the back walls 18 of the strainer cartridges 10, 10a thereof. The suction plenum is fluidly coupled to a pump which, when activated, creates suction in the suction plenum as results in a differential pressure condition which causes liquid to be drawn into the inflow ends 24 of the strainer pockets 22 of the strainer cartridges 10, 10a, and thereafter through the strainer pockets 22 of the strainer cartridges 10, 10a into the suction plenum. As will be recognized, flow through the strainer cartridges 10, 10a of the strainer module 28 is achieved as a result of the fabrication of the strainer cartridges 10, 10a from the perforated metal material described above. FIG. 4 depicts an exemplary strainer system 30 which includes the strainer module 28 shown in FIG. 3 as paired with a second strainer module 29. The strainer module 29 is virtually identical to the strainer module 28, with the sole distinction being that is assembled with only the standard strainer cartridges 10 (i.e., a total of seven (7) of the cartridges 10 in side-by-side relation to each other). In the exemplary strainer system 30, the strainer modules 28, 29 are oriented in spaced, back-to-back relation to each other, with a suction plenum 32 being defined between the back walls of the strainer modules 28, 29. As will be recognized, in the exemplary strainer system 30, the activation of a pump fluidly coupled to the suction plenum 32 effectively draws liquid into the inflow ends 24 of the strainer pockets 22 of the strainer cartridges 10, 10a within each of the opposed strainer modules 28, 29, such liquid ultimately passing through the strainer cartridges 10, 10a and into the suction plenum 32. Again, the configuration of the strainer module 28 shown in FIG. 3 and the configuration of the strainer system 30 shown in FIG. 4 are intended to be exemplary only, with the present invention being directed in large measure toward the structural features added to the strainer cartridge 10 which facilitate the creation of the enhanced strainer cartridge 10a. These structural features or enhancements will now be described with particular regard to FIGS. 4 and 5. Referring now to FIGS. 4 and 5, in accordance with the present invention, it is contemplated that one or more of the strainer pockets 22 of each of the strainer cartridges 10a included in the exemplary strainer module 28 may be outfitted with a membrane 34 which is selectively moveable between a closed position and an open position. In the exemplary strainer system 30 shown in FIG. 4, a prescribed number of the strainer pockets 22 of the strainer module 28 included in the strainer system 30 are each outfitted with a membrane 34. Each membrane 34 is preferably fabricated from an elastic metal material and is pivotally connected to a corresponding strainer pocket 32 at a joint 36. Each membrane 34 is positioned at the inflow end 24 of the corresponding strainer pocket 22, and is sized so as to substantially cover such inflow end 24. Additionally, as is seen in FIG. 5, each strainer pocket 22 outfitted with a membrane 34 further preferably includes a membrane stopper 38 mounted thereto in opposed relation to the joint 36. In this regard, that edge of the membrane 34 disposed furthest from the joint 36 is normally abutted against the corresponding membrane stopper 38 when the membrane 34 is in its closed position. As indicated above, within one or more of the strainer cartridges 10a of the strainer module 28, the inflow end(s) 24 of one or more of the strainer pockets 22 may be enclosed by an elastic metal membrane 34. When in the closed position shown in FIGS. 4 and 5, the membrane 34 substantially prevents liquid flow into the corresponding strainer pocket 22 via the inflow end 24 thereof. The membrane 34 is normally maintained in its closed position by the abutment of one edge thereof against the corresponding membrane stopper 38, and remains in such closed position when only a low pressure load is exerted thereon. However, the exertion of a high pressure load on the membrane 34 effectively facilitates the deflection of deformation thereof into the open position in the manner shown by the phantom lines included in FIG. 5. As is apparent from FIG. 5, the level of flexion or deformation of the membrane 34 must be sufficient to cause the same to move beyond and thus be effectively disengaged from corresponding membrane stopper 38. Once the membrane 34 disengages the corresponding membrane stopper 38, such membrane 34 is free to rotate or pivot about the joint 36 to its fully open position. The movement of the membrane 34 to its open position effectively opens the corresponding strainer pocket 22, thus allowing for the flow of liquid into the interior of such strainer pocket 22 via the now unobstructed inflow end 24 thereof. Those strainer pockets 22 outfitted with the membranes 34 may be referred to as pressure controlled pockets or PCP's. Within the exemplary strainer module 28 including the strainer cartridges 10a, it is contemplated that approximately five percent (5%) of the strainer pockets 22 included in the strainer cartridges 10a will each be outfitted with a membrane 34 and thus function as a PCP. As a result, approximately ninety-five percent (95%) of the strainer pockets 22 included in the strainer cartridges 10a of the strainer module 28 will be open without membranes 34. With regard to the distribution of those strainer pockets 22 including membranes 34, it is also contemplated that such PCP's should be kept “clean” during the phase of debris coming on the strainer module 28 in the case of an accident. Accordingly, it is desirable that the strainer pockets 22 outfitted with membranes 34 be installed or located in a dead water zone of the strainer module 28 within the overall strainer system. Typically, this dead water zone may be in the middle of the strainer module 28 and/or at the opposite location of where debris typically enters into the containment. When the strainer module 28 is in use upon the occurrence of an accident, it is contemplated that the strainer pockets 22 outfitted with the membranes 34 will not open simultaneously, but rather will open sequentially as needed to cope with chemical effects in the debris laden water circulating through the strainer module 28. The sequential opening of the PCP's, as will usually occur when the pressure load exerted thereagainst by the debris field forming on the strainer module 28 exceeds the above-described high pressure threshold, facilitates an effective, controlled reduction in head loss, and further avoids any head loss “jump” due to clogging. As is further shown in FIGS. 3 and 4, the functional advantages to the exemplary strainer module 28 as a result of the inclusion of one or more PCP's in each of the strainer cartridges 10a may be further enhanced by additionally outfitting the strainer module 28 with flat, non-perforated face plates 40 which extend from prescribed surfaces of the strainer module 28 adjacent the inflow ends 24 of the strainer pockets 22 defined by the strainer cartridges 10, 10a thereof. More particularly, as is best seen in FIG. 3, the exemplary strainer module 28 includes a multiplicity of the extended face plates 40 which are attached to the front edges of corresponding ones of the top and bottom walls 14, 16 and separator plates 20 of the strainer cartridges 10, 10a included in the strainer module 28. The face plates 40 are arranged so as to define two generally quadrangular (e.g., rectangular) frames. As is seen in FIG. 3, the two quadrangular frames defined by the face plates 40 extend in spaced, generally parallel relation to each other. Since the face plates 40 are attached to the front edges of the top and bottom walls 14, 16 and separator plates 20, the frames defined thereby effectively circumvent the inflow ends 24 of a prescribed number of the strainer pockets 22, one or more of which may be outfitted with a membrane 34 so as to function as an above-described PCP. Those of ordinary skill in the art will recognize that the particular arrangement of the face plates 40 as shown in FIG. 3 is exemplary only, and that the number, size and arrangement of the face plates 40 may be selectively varied as needed to provide the functionality enhancements described below based on the particular environment or configuration of the strainer system in which the strainer module 28 outfitted with the face plates 40 is to be integrated. As indicated above, the face plates 40 extend forwardly from the strainer module 28 such that the two quadrangular frames defined by the face plates 40 effectively circumvent the inflow ends 24 of a prescribed number of the strainer pockets 22. As shown in FIG. 4, in the exemplary strainer system 30, though the strainer module 29 is not assembled to include the enhanced strainer cartridges 10a, such strainer module 29 is still outfitted with the above-described face plates 40 which are arranged on the strainer module 29 in the same pattern described above in relation to the strainer module 28. In this regard, the functional advantages attributable to the inclusion of the face plates 40 on the strainer module 28 are equally applicable to the strainer module 29, despite the absence therein of any of the PCP's. When included with the strainer module 29, the face plates 40 protrude forwardly from the strainer module 29 such that the spaced, generally parallel pair of quadrangular frames defined thereby circumvent the inflow ends 24 of a prescribed number of the strainer pockets 22 of the strainer module 29. As is further apparent from FIG. 4, the face plates 40 included with the strainer modules 28, 29 cause the edges of a fiber and particulate debris bed 42 which may form at the inflow ends of the strainer pockets 22 to compress and slowly curl in from an originally flush relationship to the inner surfaces of the face plates 40. This curling in of the debris bed 42 results in the creation of small flow paths between the inner surfaces of the face plates 40 and the debris bed 42 as differential pressure continues to rise, thus promoting liquid flow through the strainer modules 28, 29 and reducing head loss. The creation of these flow paths, as caused by the inclusion of the face plates 40 with the strainer modules 28, 29, effectively reduces the maximum differential pressure experienced across the strainer modules 28, 29. Those of ordinary skill in the art will recognize that the face plates 40 may be included on one, both or neither of the face plates 40. In this regard, the inclusion of the face plates 40 with one or both of the strainer modules 28, 29 is purely optional. Referring now to FIGS. 6-8, there is shown a strainer module 100 constructed in accordance with a second embodiment of the present invention. The strainer module 100 comprises a generally cylindrical, tubular main body section 102 which defines a section plenum 104 extending axially therethrough. Extending radially from the outer surface of the main body section 102 in spaced, generally parallel relation to each other are a plurality of circularly configured separator plates 106. Though not shown in FIG. 6, the main body section 102 includes openings formed therein which allow liquid flowing between the separator plates 106 to be drawn into the suction plenum 104 via such openings upon the creation of a pressure differential condition attributable to the activation of a pump fluidly coupled to the suction plenum 104. The strainer module 100 further comprises at least one circularly configured strainer cartridge 108 which is positioned between a prescribed adjacent pair of the separator plates 106. The strainer cartridge 108 comprises a multiplicity of wall members 110 which are arranged and attached to each other so as to collectively define a plurality of strainer pockets 112 of the strainer cartridge 108. In the strainer cartridge 108 shown in FIGS. 6 and 7, a total of ten (10) strainer pockets 112 are included in the strainer cartridge 108, with the strainer pockets 112 being arranged in a circularly configured array. The wall members 110 of the strainer cartridge 108 are each preferably fabricated from a perforated metal material. In the strainer cartridge 108 included in the strainer module 100, each of the strainer pockets 112 includes an open inflow end 114 which is defined by the peripheral edges of corresponding wall members 110. Thus, as seen in FIGS. 6 and 7, the inflow ends 114 of the strainer pockets 112 are directed or face radially outwardly relative to the suction plenum 104 defined by the main body section 102. In the strainer cartridge 108, each of the strainer pockets 112 is preferably outfitted with a membrane 116 which mimics the functionality of the above-described membrane 34. In this regard, each membrane 116 is preferably fabricated from an elastic metal material and is pivotally connected to a corresponding strainer pocket 112 at a joint 118. Each membrane 116 is positioned at the inflow end 114 of the corresponding strainer pocket 112, and is sized so as to substantially cover such inflow end 114. As is best seen in FIG. 7, each strainer pocket 112 is further outfitted with a membrane stopper 120 which is mounted thereto in opposed relation to the joint 118. In this regard, that edge of the membrane 116 disposed furthest from the joint 118 is normally abutted against the corresponding membrane stopper 120 when the membrane 116 is in its closed position. In the strainer cartridge 108, each membrane 116, when in its closed position, substantially prevents liquid flow into the corresponding strainer pocket 112 via the inflow end 114 thereof. Each membrane 116 is normally maintained in its closed position by the abutment of one edge thereof against the corresponding membrane stopper 120, and remains in such closed position when only a low pressure load is exerted thereon. However, the exertion of a high pressure load on the membrane 116 effectively facilitates the flexion or deformation thereof into the open position in the manner shown by the phantom lines included in FIG. 8. As is apparent from FIG. 8, the level of flexion or deformation of the membrane 116 must be sufficient to cause the same to move beyond and thus be effectively disengaged from the corresponding membrane stopper 120. Once the membrane 116 disengages the corresponding membrane stopper 120, such membrane 116 is free to rotate or pivot about the joint 118 to its fully open position. The movement of the membrane 116 to its open position effectively opens the corresponding strainer pocket 112, thus allowing for the flow of liquid into the interior of such strainer pocket 112 via the now unobstructed inflow end 114 thereof. Though, in FIG. 7, each of the strainer pockets 112 included in the strainer cartridge 108 is shown as being outfitted with a membrane 116, those of ordinary skill in the art will recognize that any number of the strainer pockets 112 less than the entire number thereof may be outfitted with a membrane 116 in any distribution or arrangement. Further, the strainer cartridge 108 may be assembled to include greater or fewer than ten strainer pockets 112 without departing from the spirit and scope of the present invention. Additionally, though the strainer module 100 is shown as including only one strainer cartridge 108 between one adjacent pair of the separator plates 106, those of ordinary skill in the art will also recognize that one or more additional strainer cartridges 108 may be included in the strainer module 100 between one or more other adjacent pairs of the separator plates 106. Within the strainer cartridge 108, it is contemplated that the strainer pockets 112 outfitted with the membranes 116 will not open simultaneously, but rather will open sequentially as needed to cope with chemical effects in debris laden water circulating through the strainer module 100. The sequential opening of the membranes 116 will usually occur when the pressure load exerted thereagainst by the debris field forming on the strainer module 100 exceeds a prescribed high pressure threshold as described above in relation to the strainer module 28. Referring now to FIG. 9, there is shown a strainer module 200 constructed in accordance with a third embodiment of the present invention. The sole distinction between the strainer modules 100, 200 lies in the separator plates 206 included in the strainer module 200 each having a generally quadrangular (e.g. square) configuration, as opposed to the circular configuration of the above-described separator plates 106 included in the strainer module 100. Referring now to FIGS. 10 and 11, there is shown a strainer module 400 constructed in accordance with a fourth embodiment of the present invention. The strainer module 400 comprises a main body section 402 which has a generally quadrangular cross-sectional configuration and defines a suction plenum 404. Attached to a common wall of the main body section 402 and protruding therefrom in spaced, generally parallel relation to each other are a plurality of (e.g., four) cylindrically configured, tubular primary strainer elements 406 which each fluidly communicate with the suction plenum 404. Each of the primary strainer elements 406 defines an inflow end 408, and comprises concentrically positioned outer and inner walls 410, 412. The outer and inner walls 410, 412 are each fabricated from a perforated metal, mesh-like material. The inflow end 408 is typically defined solely by the inner wall 412 of the primary strainer element 406. In the exemplary strainer module 400, the inflow end 408 of one of the primary strainer elements 406 is covered by a rupture disk or segmented membrane 414 which mirrors the functionality of the above-described membranes 34, 116. In this regard, the segmented membrane 414 is operative to move from a normally closed position (as shown in FIGS. 10 and 11) to an open position allowing direct liquid flow into the interior of the inner wall 412 of the corresponding primary strainer element 406 via the inflow end 408 defined thereby when such segmented membrane 414 is subjected to a high pressure load beyond a prescribed threshold. The segmented membrane 414 has a generally circular configuration and defines four (4) membrane quadrants which are individually movable relative to each other. In the strainer module 400 shown in FIGS. 10 and 11, it is also contemplated that one or more of the primary strainer elements 406 may include a secondary strainer element 416 concentrically positioned within the inner wall 412 of the primary strainer element 406, thus creating a double cylinder strainer construction as opposed to the single cylinder strainer construction provided by any primary strainer element 406 standing alone. The secondary strainer elements 416 defines an inflow end 418, and comprises concentrically positioned outer and inner walls 420, 422. The outer and inner walls 420, 422 are each fabricated from a perforated metal, mesh-like material. The inflow end 418 is typically defined solely by the inner wall 420 of the secondary strainer element 416. In the secondary strainer module 416, the inflow end 418 is covered by a rupture disk or segmented membrane 424 which mirrors the functionality of the above-described segmented membrane 414. In this regard, the segmented membrane 424 is operative to move from a normally closed position (as shown in FIGS. 10 and 11) to an open position allowing direct liquid flow into the interior of the inner wall 422 of the secondary strainer element 416 via the inflow end 418 defined thereby when such segmented membrane 424 is subjected to a high pressure load beyond a prescribed threshold. The segmented membrane 424 also has a generally circular configuration and defines four (4) membrane quadrants which are individually movable relative to each other. When the exemplary strainer module 400 is integrated into a strainer system, the creation of a pressure differential condition attributable to the activation of a pump fluidly coupled to the suction plenum 404 causes liquid to be drawn through the primary strainer elements 406 and the sole secondary strainer element 416 into the suction plenum 404. Within the strainer module 400, it is contemplated that the segmented membranes 414, 424 will not open simultaneously, but rather will open sequentially as needed to cope with chemical effects in debris laden water circulating through the strainer module 400. As described above in relation to the strainer module 28, the sequential opening of the segmented membranes 414, 424 will usually occur when the pressure load exerted thereagainst by a debris field forming of the strainer module 400 exceeds a prescribed high pressure threshold. Those of ordinary skill in the art will recognize that greater or fewer than four primary strainer elements 406 may be included in the strainer module 400 without departing from the spirit and scope of the present invention. Along these lines, more than one primary strainer element 406 may be outfitted with a segmented membrane 414, or with the above-described secondary strainer element 416 including its own segmented membrane 424. Further, no primary strainer module 406 need necessarily be outfitted with a secondary strainer element 416. Referring now to FIGS. 12-15C, there is shown a strainer system 500 constructed in accordance with another embodiment of the present invention. The strainer system 500 comprises a plurality of strainer modules 528 positioned in a prescribed arrangement. In the strainer system 500, each of the strainer modules 528 comprises a plurality of the above-described strainer cartridges 10 disposed in side-by-side relation to each other. More particularly, in each strainer module 528 shown in FIG. 12, a total of nine (9) strainer cartridges 10 are included therein. However, those of ordinary skill in the art will recognize that each strainer module 528 may be assembled to include more or less than nine (9) strainer cartridges 10 without departing from the spirit and scope of the present invention. In the strainer system 500, it is contemplated that none of the strainer modules 528 included therein will include any of the above-described enhanced strainer cartridges 10a. Rather, as indicated above, it is contemplated that each of the strainer modules 528 will be assembled to include only the above-described, non-enhanced strainer cartridges 10. When viewed from the perspective shown in FIGS. 12 and 15A-15C, in the strainer system 500, the strainer modules 528 are arranged in two (2) spaced, generally parallel rows of four (4), for a total of eight (8) strainer modules 528. More particularly, the back wall of each strainer module 528 in each row thereof is oriented in spaced, back-to-back relation to the back wall of a corresponding one of the strainer modules 528 included in the remaining row thereof, creating a total of four (4) opposed pairs of the strainer modules 528. In addition, the strainer modules 528 are arranged such that the inflow ends 24 of the strainer pockets 22 of the strainer cartridge 10 included in one row or set thereof face in a common first direction D1, while the inflow ends 24 of the strainer pockets 22 of the strainer cartridges 10 of the remaining row or set thereof face in a common direction D2 which is opposite or opposed to the direction D1. Though the strainer system 500 is shown as including a total of eight (8) strainer modules 528, those of ordinary skill in the art will further recognize that this total is exemplary only, and may be increased or decreased without departing from the spirit and scope of the present invention. As further seen in FIG. 12, due to the manner in which the two rows or sets of the strainer cartridges 528 are arranged within the strainer system 500, an elongate suction plenum duct 502 is partially defined by the back walls of the strainer modules 528 (which are collectively defined by the back walls 18 of the strainer cartridges 10 thereof). In addition to being partially defined by the back walls of the strainer modules 528, the plenum duct 502 is also partially defined by various segments or sections of a duct wall 506. Thus, in the strainer system 500, the back walls 18 of the strainer cartridges 10 of each of the strainer modules 528 fluidly communicate with the plenum duct 502. The plenum duct 502 is also fluidly coupled to a suction pump 504. When activated, the suction pump 504 creates suction in the plenum duct 502 as results in a differential pressure condition which causes liquid to be drawn into the inflow ends 24 of the strainer pockets 22 of the strainer cartridges 10 included in the strainer modules 528, and thereafter through the strainer pockets 22 into the plenum duct 502. As best seen in FIGS. 12-14, it is contemplated that one opposed pair of the strainer modules 528 will originally be “isolated” from the three remaining opposed pairs of the “active” strainer modules 528 included in the strainer system 500. When viewed from the perspective shown in FIGS. 12 and 15A-15C, the isolated pair of the strainer modules 528 is that pair which is disposed at the back end of the train of strainer modules 528 included in the strainer system 500. However, those of ordinary skill in the art will recognize that the isolated pair of strainer modules 528 could alternatively be that pair located at the opposite, front end of the train of strainer modules 528 included in the strainer system 500. In the strainer system 500, the isolation of one pair of strainer modules 528 from the remaining active pairs of the strainer modules 528 is facilitated by the integration of a pressure released membrane or PRM 534 within a prescribed location in the interior of the plenum duct 502. As seen in FIG. 12, the PRM 534 is positioned in that section of the plenum duct 502 located between the pair of strainer modules 528 at the back end of the train thereof and those strainer modules 528 comprising the remainder of the strainer system 500. The PRM 534 is selectively movable between a closed position (shown in solid lines in FIG. 13) and an open position (shown in phantom lines in FIG. 13). The PRM 534 is preferably fabricated from an elastic metal material, and is pivotally connected to the duct wall 506 which, as indicated above, partially defines the plenum duct 502. More particularly, the PRM 534 is pivotally connected to the duct wall 506 at a hinge joint 536. The PRM 534 is sized so as to completely span the cross-sectional area of the plenum duct 502 at the location wherein the PRM 534 is positioned therein. Thus, when the PRM 534 is in its closed position, the plenum duct 502 is effectively segregated into a first section which extends between the back walls of the active strainer modules 528 and fluidly communicates with the suction pump 504, and a second section which extends between the back walls of the isolated strainer modules 528. As further seen in FIG. 13, also attached to the duct wall 506 is a first membrane stopper bar 538 which is disposed in generally opposed relation to the joint 536. In this regard, that edge of the PRM 534 disposed furthest from the joint 536 is normally abutted against the stopper bar 538 when the PRM 534 is in its original, closed position. Thus, the stopper bar 538 is disposed in the aforementioned non-isolated first section of the plenum duct 502. Also attached to the duct wall 506 in close proximity to the stopper bar 538 is a second membrane stopper bar 539 which extends in spaced, generally parallel relation to the stopper bar 538. However, as seen in FIG. 13, the stopper bar 539 is disposed in the isolated second section of the plenum duct 502, i.e., the stopper bars 538, 539 are disposed at opposite sides of the PRM 534 when the same is in its closed position. Having thus described the structural features of the strainer system 500 of the present invention, the functionality thereof will now be described with specific reference to FIGS. 15A, 15B and 15C. Referring now to FIG. 15A, at the beginning of a postulated loss of coolant accident, fibers and particulates ladent coolant will come into contact with the strainer modules 528 of the strainer system 500. This debris, however, will only be deposited on the active strainer modules 528 of the strainer system 500. In this regard, despite the activation of the suction pump 504, no fluid will be drawn through the isolated strainer modules 528 while the PRM 534 is in its original, closed position. Stated another way, without the opening of the PRM 534, there is no flow through the isolated strainer modules 528 due to the absence of any suction pressure within the second section of the plenum duct 502 extending between the back walls thereof. Referring now to FIG. 15B, as time cools the cooling water, the above-described chemical effect begins. In this regard, if the coolant is cold enough, precipitates are formed, with such precipitates being deposited as a compact layer on the active strainer modules 528. As previously explained, these precipitate deposits lead to a significant increase in head loss across the active strainer modules 528, with the fibers and the particulates being compressed into the strainer pockets 22 of the strainer cartridges 10 of the active strainer modules 528. Referring now to FIG. 15C, as a result of the compression of fibers and particulates into the strainer pockets 22, the pressure in the non-isolated first section of the plenum duct 502 will continue to grow, and eventually reach the trigger point for the PRM 534. At this trigger point, the PRM 534 is actuated or flexed from its original closed position to its open position. As a result of the opening of the PRM 534, the previously isolated modules 528 are now free and become active. The cooling water as laden with precipitates is filtered through the previously isolated and now released strainer modules 528. Such flow causes the pressure in the plenum duct 502 to decrease rapidly to a low value due to the absence of fibers on the newly activated modules 528 with which the precipitates may react to form a dense bed. In the strainer system 500, the aforementioned first membrane stopper bar 538 is sized and configured to normally maintain the PRM 534 in the closed position and to permit the PRM 534 to flex to the open position upon the application of the prescribed suction load thereto. The second membrane stopper bar 539 is used to prevent the PRM 534 from assuming an open position as a result of a seismic event. Various potential modifications to the strainer system 500 described above are contemplated to be within the spirit and scope of the present invention. For example, any one of the strainer modules 528, whether originally active or isolated, may optionally be outfitted with one or more of the above-described enhanced strainer cartridges 10a as an alternative to the sole inclusion of the non-enhanced strainer cartridges 10 therein. Similarly, it is also contemplated that any one of the strainer modules 528, whether originally active or isolated, may optionally be outfitted with the above-described face plates 40. Moreover, though the originally isolated strainer modules 528 are shown in FIGS. 12 and 15A-15C as being disposed in relative close proximity to the originally active strainer modules 528, it is contemplated that the originally isolated strainer modules 528 may be placed a greater distance from the originally active strainer modules 528. Still further, though only one pair of the strainer modules 528 at one end of the train thereof included in the strainer system 500 is shown as being originally isolated, it is contemplated that those pairs of strainer modules 528 disposed at each of the two opposed ends of the train included in the strainer system 500 may be originally isolated, i.e., two (2) PRM's 534 would originally be integrated into the plenum duct 502 of the strainer system 500. Finally, it is contemplated that the above-described PRM 534 may be substituted with a rupture disk or segmented membrane which mirrors the functionality of the above-described segmented membrane 414. This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure. |
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abstract | The supporter supports a patient and is disposed movably along the body axis direction of said patient. The imaging part includes an X-ray-generator and an X-ray-detector. The X-ray-generator irradiates X-rays while rotating around the body axis. The X-ray-detector detects the X-rays that have permeated the patient. The collimator changes the irradiation field of the X-rays to be irradiated. The scan controller controls the movement of the supporter and the imaging part. The image-reconstructing part reconstructs image data based on the X-rays that have been detected by the X-ray detector. The movement amount-detector detects the amount of movement of the patient by the supporter. The collimator controller controls so as to change the size of the opening of the collimator based on the amount of movement. |
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047486465 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the explanation of an embodiment of this invention, a principle of synchrotron radiation will be briefly described. Synchrotron radiation beams can be obtained by bending the travelling direction of a highly energized electron with the help of a magnetic field. That is, an electron which is accelerated by a storage ring is supplied to a magnetic field of a magnet. The electron travels around the magnetic field formed by the magnet for a life of, for example, two to ten hours, so that a wide range of beams, fram ultrared-beam to an X-ray, can be obtained due to the effects of relativity, and emitted in the tangential direction. The beam thus obtained depends on the intensity of the magnetic field and the photon energy. In an X-ray lithography system, only X-rays are separated from the beams thus obtained, and used. FIG. 2 schematically illustrates an exposure system using a synchrotron radiation beam. In an X-ray generation source 11, an electron (e.sup.-) travels along a circular orbit having a diameter of, for example, 10 m. Several coil magnets 12 each having a U-shaped cross-section are arranged along the path of this circular orbit, so that path of the electron (e.sup.-) is diverted when the electron passes through the magnetic field of the magnets 12, and a radiation beam is irradiated in the tangential direction. The thus separated X-rays 14 are reflected at a mirror 15 and introduced into an exposure chamber 17 via a window 16 made of a beryllium having a high X-ray transmission property. FIG. 3 (Prior Art) is an illustration of a conventionally known X-ray exposure system, such as disclosed in J. Vac. Scl. Technol. B 1(4), Oct.-Dec. 1983, pages 1262-1266. In this system, the X-ray generation source 11 is kept in a vacuum at about 10.sup.-9 Torr, and a chamber 18 in which a scanning mirror 15 is arranged is kept in an ultrahigh vacuum at about 10.sup.-10 Torr. The surface of the mirror 15 is made of quartz or silicone carbide and finished to a roughness (smoothness) of 0.02 .mu.m. The pressure in the mirror chamber 18 is reduced to maintain the vacuum, as mentioned above, by an ion pump 19. Such an ultrahigh vacuum serves to prevent any substances from existing in the mirror chamber 18; since if such substances existed in the chamber 18, they would be adhered to the mirror surface by the X-rays. The distance from the X-ray generation source 11 to the mirror chamber 18 is about 3 m, and the distance from the mirror chamber 18 to the beryllium window 16 is about 7 m. The chamber section 20 within this distance of 7 m is kept in a vacuum at about 10.sup.-6 Torr by a plurality of turbine pumps 21. The scanning mirror 15 is inclined by 1.degree. with respect to the horizontal plane and driven by a linear motor (not shown in FIG. 3) located outside the chamber 18 and coupled to the mirror 15, so that the mirror 15 is oscillated by .+-.3 milliradian about a horizontal axis to perform a vertical scanning of the X-ray beam. In FIG. 3, 23 denotes a beam shutter; 24, a vacuum valve; 25, a flat tunnel; and 26, a mirror box. The X-ray beam thus obtained has a wide and regular distribution in the horizontal direction, but only a narrow distribution in the vertical direction, as shown in FIGS. 4A and 4B. FIG. 5 schematically illustrates the arrangement of a mask and a semiconductor wafer, in which 27 denotes a mask; 28, a mask holder; 29, a semiconductor wafer; 30, a resist coated on the surface of the wafer 29; and 31, a stage for mounting the wafer 29 thereon. FIG. 6 is a front view of the mask 27 having a size of 5 cm .times.5 cm square and provided with a pattern 32 (only a part thereof being schematically illustrated in FIG. 6). An X-ray beam having a horizontally wide but vertically short cross-section is scanned vertically on the mask 27, as shown by an arrow, while the mirror oscillates as mentioned above. Generally speaking, large sized wafers have been recently more and more in demand. Therefore, the size of the wafer must be increased accordingly, for example, from 6 inches (150 mm) to 8 inches (200 mm) in diameter. On the other hand, the verticla distribution of the X-ray beam has remained samll, for example, 5 mm. Therefore, a plurality of shots, each having an exposure area of 5 cm .times.5 cm due to the scanning limit of the mirror 15 (FIG. 3), as mentioned above, are necessary to ensure an exposure over all of the surface of the wafer 29. Therefore, the wafer 29 is mounted on the stage 31 and moved therewith at every shot by a so-called stop-and-repeat system, so that all of the surface of the wafer 29 is exposed to the X-ray beam by a plurality of shots, for example, nine shots, as seen in FIG. 9. That is, a single section, 5 cm.times.5 cm, of the surface of the wafer 29 is exposed at each shot by the scanning operation of the X-ray beam, and then the wafer 29 is moved so that the next section can be exposed, and finally, all of the surface of the wafer 29 is covered by, for example, nine shots. In the above-mentioned X-ray exposure system, the exposure chamber 17 is kept at almost atmospheric pressure (760 Torr) to facilitate the insertion and removal of wafers at the chamber 17. In addition, the gap between the mask 27 and the wafer 29 is about 50 .mu.m. The wavelength of the beam suitable for X-ray lithography is 7.ANG..+-.2.ANG.. If the wavelength of the X-ray beam is too long, the pattern exposed on the resist 30 will be dimmed by the Fresnel effects. On the other hand, if the wavelength of the X-ray beam is too short, such as 1.ANG., secondary electrons would be generated to also cause a dimming of the pattern exposed on the resist 30, since the X-ray energy will be far too high. Therefore, the X-ray beam in the range of 7.ANG..+-.2.ANG. wavelength should be used. According to experiments conducted by the inventors, the relationship between the wavelength of the X-ray beam, the thickness of the beryllium window 16, and the intensity of the X-ray beam was found to be as shown in the following Table. TABLE ______________________________________ Wavelength Thickness of Intensity of X-ray Beryllium Window of X-ray ______________________________________ 9 .ANG. 25 .mu.m .about.0 7 .ANG. " 1/2 4 .ANG. " 9/10 ______________________________________ FIG. 7 (Prior Art) illustrates an arrangement of the beryllium window 16, the mask 27, and the wafer 19 in which the distance between the beryllium window 16 and the mask 27 is 1 mm .about.2 mm, and the gap between the mask 27 and the wafer 29 is about 50 .mu.m, as mentioned above. The thickness of the beryllium window 16 is generally about 25 .mu.m .about.50 .mu.m and the diameter thereof is about 70 mm. The chamber 20 is kept at a vacuum of 10.sup.-6 Torr but, on the other hand, the mask 27 is installed in an atmospheric environment. Thus, the beryllium window 16 is subjected to a pressure as shown by arrows and, therefore, must have sufficient mechanical strength to endure the pressure exerted thereon. On the other hand, if the thickness of the beryllium window could be reduced, for example, from 25 .mu.m as in the conventional system to 10 .mu.m, the intensity of the X-ray beam transmitted by the beryllium window 16 would be increased 2.5 times. Therefore, it would be advantageous to reduce the thickness of the beryllium window. FIG. 1 is an illustration of an embodiment of an X-ray exposure system according to the present invention. As shown in FIG. 1, an X-ray beam 14 transmitted from an X-ray generation source, i.e., the storage ring 11 (FIG. 3), is transmitted through the vacuum chamber 20 by the scanning mirror 15, which is inclined by 1.degree. with respect to the horizontal plane, to a beryllium window 16. According to the present invention, the beryllium window 16 has a thickness of 10 .mu.m and a size of 5 mm (vertical).times.50 mm (horizontal), as seen in FIGS. 8 and 9. The beryllium window 16 is defined in a window holder 30 attached to an end of a flexible bellows portion 35 of the vacuum chamber 20 and defining an end wall of the vacuum chamber 20. The window holder 30 is coupled to a linear motor 33 in such a manner that the beryllium window 16 oscillates vertically as shown by an arrow B. The bellows portion 35 ensures the vertical oscillation of the window holder 30. On the other hand, the scanning mirror 15 is coupled to and driven by a linear motor 22, located outside the mirror chamber 18, so that the mirror 15 is oscillated as shown by an arrow A by .+-.3 milliradian about a horizontal axis 15a to perform a vertical scanning of the X-ray beam, in the same manner as in the system shown in FIG. 3. The linear motor 33 as well as the linear motor 22 are electrically connected to a controller 34, respectively, so that the linear motors 22 and 33 are controlled to operate synchronous with respect to each other, in such a manner that the beryllium window 16 is reciprocally shifted up and down in synchronization with the scanning operation of the X-ray beam 14, to cover the area of a single section, 5 cm.times.5 cm, with one shot. That is, the vertical stroke of the beryllium window 16 is exactly the same as the vertical scanning width of the X-ray beam 14 defined by the .+-.3 milliradian oscillation of the scanning mirror 15 at the beryllium window 16. In addition, the X-ray beam having a wide distribution in the horizontal direction, but only a narrow distribution in the vertical direction, as shown in FIGS. 4A and 4B, matches exactly the 5 mm.times.50 mm sized beryllium window 16 when penetrating therethrough and, therefore, an X-ray exposure having an area 5 mm.times.50 mm is always obtained. According to experiments canducted by the inventors, it was confirmed that the intensity of the X-ray beam transmitted through the beryllium window 16 having a thickness of, for example, 10 .mu.m, was increased 2.5 to 5.0 times, compared to that in a conventionally known X-ray lithography system as mentioned above. Any known linear motor similar to the linear motor 22 for driving the scanning mirror 15 can be used as the linear motor 33 for driving the beryllium window 16. Also, the drive coils of these two linear motors 22 and 33 can be connected to the controller 34 in a known manner to achieve a synchronous operation of these motors 22 and 33. The bellows poriton 35 also can be consturcted and attached to the end of the vacuum chamber 20 by a known technique. The other portions are the same as in a conventional system and, therefore, the present invention can be realized by a relatively simple modification of a known X-ray lithography system as illustrated in FIG. 3. |
abstract | A laser produced plasma (“LPP”) extreme ultraviolet (“EUV”) light source and method of operating same is disclosed which may comprise an EUV plasma production chamber having a chamber wall; a drive laser entrance window in the chamber wall; a drive laser entrance enclosure intermediate the entrance window and a plasma initiation site within the chamber and comprising an entrance enclosure distal end opening; at least one aperture plate intermediate the distal opening and the entrance window comprising at least one drive laser passage aperture. The at least one aperture plate may comprise at least two aperture plates comprising a first aperture plate and a second aperture plate defining an aperture plate interim space. The at least one drive laser aperture passage may comprise at least two drive laser aperture passages. The laser passage aperture may define an opening large enough to let the drive laser beam pass without attenuation and small enough to substantially reduce debris passing through the laser passage aperture in the direction of the entrance window. |
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claims | 1. A nuclear powered quantum dot light source, comprising:quantum dots; anda radionuclide. 2. The nuclear powered quantum dot light source of claim 1, further comprising a material into which the quantum dots and the radionuclide are located. 3. The nuclear powered quantum dot light source of claim 2, wherein the material is radiolucent. 4. The nuclear powered quantum dot light source of claim 2, wherein the material comprises one or more of a radiolucent solid, a radiolucent liquid, a radiolucent gel, and/or a sol-gel hybrid. 5. The nuclear powered quantum dot light source of claim 2, wherein the material comprises one or more of a thermal sol-gel hybrid, a UV sol-gel hybrid, a plastic resin, polycarbonate, polystyrene, polymethylmethacrylate), and/or polyethylene. 6. The nuclear powered quantum dot light source of claim 1, further comprising a holder into which the quantum dots and radionuclide are placed, the holder comprising at least a portion that is radiolucent. 7. The nuclear powered quantum dot light source of claim 6, wherein the holder comprises radiolucent side walls. 8. The nuclear powered quantum dot light source of claim 1, wherein the quantum dots are selected to give off light at a single, predetermined wavelength when energized by the radionuclide. 9. The nuclear powered quantum dot light source of claim 8, wherein the single, predetermined wavelength can be in or out of the visible light spectrum. 10. The nuclear powered quantum dot light source of claim 1, wherein the quantum dots comprise a plurality of different types of quantum dots that are selected to give off light at a plurality of predetermined wavelengths when energized by the radionuclide. 11. The nuclear powered quantum dot light source of claim 10, wherein the plurality of predetermined wavelength can be selected to be in and/or out of the visible light spectrum. 12. The nuclear powered quantum dot light source of claim 1, wherein the radionuclide is a single type of a radionuclide that emits either alpha or beta particles. 13. The nuclear powered quantum dot light source of claim 1, wherein the radionuclide comprises a plurality of different types of radionuclides. 14. The nuclear powered quantum dot light source of claim 1, wherein the radionuclide is selected from the group consisting of hydrogen 3 (3H), carbon 14 (14C), silicon 32 (32Si), nickel 63 (63Ni), thallium 204 (204Tl), polonium 210 (210Po), americium 241 (241Am) and thorium 232 (232Th). 15. The nuclear powered quantum dot light source of claim 13, wherein the radionuclides comprise a plurality of different radionuclides selected from the group consisting of hydrogen 3 (3H), carbon 14 (14C), silicon 32 (32Si), nickel 63 (63Ni), thallium 204 (204Tl), polonium 210 (210Po), americium 241 (241Am) and thorium 232 (232Th). 16. The nuclear powered quantum dot light source of claim 1, wherein the quantum dots comprises CdSe and are coated with ZnS as a protective layer. 17. A nuclear powered quantum dot light source, comprising:a holder having at least a portion that is a radiolucent;a mixture comprising quantum dots, a radionuclide, and a radiolucent material into which the quantum dots and radionuclide are located. 18. The nuclear powered quantum dot light source of claim 17, wherein the radiolucent material comprises a radiolucent solid, a radiolucent liquid, a radiolucent gel, and/or a sol-gel hybrid. 19. The nuclear powered quantum dot light source of claim 17, wherein the radiolucent material comprises one or more of a thermal sol-gel hybrid, a UV sol-gel hybrid, a plastic resin, polycarbonate, polystyrene, polymethylmethacrylate), and/or polyethylene. 20. The nuclear powered quantum dot light source of claim 17, wherein the quantum dots are selected to give off light at a single, predetermined wavelength when energized by the radionuclide. 21. The nuclear powered quantum dot light source of claim 20, wherein the single, predetermined wavelength can be in or out of the visible light spectrum. 22. The nuclear powered quantum dot light source of claim 16, wherein the quantum dots comprise a plurality of different types of quantum dots that are selected to give off light at a plurality of predetermined wavelengths when energized by the radionuclide. 23. The nuclear powered quantum dot light source of claim 22, wherein the plurality of predetermined wavelength can be selected to be and/or out of the visible light spectrum. 24. The nuclear powered quantum dot light source of claim 17, wherein the radionuclide is a single type of a radionuclide that emits either alpha or beta particles. 25. The nuclear powered quantum dot light source of claim 17, wherein the radionuclide comprises a plurality of different types of radionuclides. 26. The nuclear powered quantum dot light source of claim 17, wherein the radionuclide is selected from the group consisting of hydrogen 3 (3H), carbon 14 (14C), silicon 32 (32Si), nickel 63 (63Ni), thallium 204 (204Tl), polonium 210 (210Po), americium 241 (241Am) and thorium 232 (232Th). 27. The nuclear powered quantum dot light source of claim 25, wherein the radionuclides comprises a plurality of different radionuclides selected from the group consisting of hydrogen 3 (3H), carbon 14 (14C), silicon 32 (32Si), nickel 63 (63 Ni), thallium 204 (204Tl), polonium 210 (210Po), americium 241 (241Am) and thorium 232 (232Th). 28. A nuclear powered quantum dot light source, comprising:a holder comprising a radiolucent outer wall;a radionuclide that is either of a single type or a plurality of types, the single radionuclide or plurality of types of radionuclides emitting alpha and/or beta particles;quantum dots that are selected to give off light at a single, predetermined wavelength or a plurality of wavelengths when energized by the radionuclide;a radiolucent material in which the radionuclide and quantum dots are mixed, the mixture of the radiolucent material, radionuclide and quantum dots being placed in the holder,wherein the radionuclide energizes the quantum dots to cause them to give off light at the desired predetermined wavelength or a plurality of wavelengths. 29. The nuclear powered quantum dot light source of claim 28, wherein the radiolucent material comprises a radiolucent solid, a radiolucent liquid, a radiolucent gel, and/or a sol-gel hybrid. 30. The nuclear powered quantum dot light source of claim 28, wherein the radiolucent material comprises a radiolucent resin. 31. The nuclear powered quantum dot light source of claim 28, wherein the emitted light can be in or out of the visible light spectrum. 32. The nuclear powered quantum dot light source of claim 28, wherein the radionuclide is selected from the group consisting of hydrogen 3 (3H), carbon 14 (14C), silicon 32 (32Si), nickel 63 (63Ni), thallium 204 (204Tl), polonium 210 (210Po), americium 241 (241Am) and thorium 232 (232 Th). 33. The nuclear powered quantum dot light source of claim 28, wherein the quantum dots comprises CdSe and are coated with ZnS as a protective layer. |
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description | For purposes of the USPTO extra-statutory requirements, the present application constitutes a division of U.S. patent application Ser. No. 11/605,848, entitled METHOD AND SYSTEM FOR PROVIDING FUEL IN A NUCLEAR REACTOR, naming Roderick A. Hyde, Muriel Y. Ishikawa, Nathan P. Myhrvold, and Lowell L. Wood, Jr., as inventors, filed 28 Nov. 2006, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. The present application is related to and claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Related Applications”) (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Related Application(s)). All subject matter of the Related Applications and of any and all parent, grandparent, great-grandparent, etc. applications of the Related Applications is incorporated herein by reference to the extent such subject matter is not inconsistent herewith. The United States Patent Office (USPTO) has published a notice to the effect that the USPTO's computer programs require that patent applicants reference both a serial number and indicate whether an application is a continuation or continuation-in-part. Stephen G. Kunin, Benefit of Prior-Filed Application, USPTO Official Gazette Mar. 18, 2003, available at http://www.uspto.gov/web/offices/com/sol/og/2003/week11/patbene.htm. The present Applicant Entity (hereinafter “Applicant”) has provided above a specific reference to the application(s) from which priority is being claimed as recited by statute. Applicant understands that the statute is unambiguous in its specific reference language and does not require either a serial number or any characterization, such as “continuation” or “continuation-in-part,” for claiming priority to U.S. patent applications. Notwithstanding the foregoing, Applicant understands that the USPTO's computer programs have certain data entry requirements, and hence Applicant is designating the present application as a continuation-in-part of its parent applications as set forth above, but expressly points out that such designations are not to be construed in any way as any type of commentary and/or admission as to whether or not the present application contains any new matter in addition to the matter of its parent application(s). The present application relates to nuclear reactors, and systems, applications, and apparatuses related thereto. The following embodiments and aspects thereof are described and illustrated in conjunction with systems and methods which are meant to be exemplary and illustrative, not limiting in scope. Exemplary embodiments provide automated nuclear fission reactors and methods for their operation. Exemplary embodiments and aspects include, without limitation, re-use of nuclear fission fuel, alternate fuels and fuel geometries, modular fuel cores, fast fluid cooling, variable burn-up, programmable nuclear thermostats, fast flux irradiation, temperature-driven neutron absorption, low coolant temperature cores, refueling, and the like. In addition to the exemplary embodiments and aspects described above, further embodiments and aspects will become apparent by reference to the drawings and by study of the following detailed description. By way of overview, embodiments provide automated nuclear fission reactors and methods for their operation. Details of an exemplary reactor, exemplary core nucleonics, and operations, all given by way of non-limiting example, will be set forth first. Then, details will be set forth regarding several exemplary embodiments and aspects, such as without limitation re-use of nuclear fission fuel, alternate fuels and fuel geometries, modular fuel cores, fast fluid cooling, variable burn-up, programmable nuclear thermostats, fast flux irradiation, temperature-driven neutron absorption, low coolant temperature cores, refueling, and the like. Referring now to FIG. 1A, a nuclear fission reactor 10, given by way of example and not of limitation, acts as an exemplary host environment for embodiments and aspects described herein. While many embodiments of the reactor 10 are contemplated, a common feature among many contemplated embodiments of the reactor 10 is origination and propagation of a nuclear fission deflagration wave, or “burnfront”. Considerations Before discussing details of the reactor 10, some considerations behind embodiments of the reactor 10 will be given by way of overview but are not to be interpreted as limitations. Some embodiments of the reactor 10 reflect attainment of all of the considerations discussed below. On the other hand, some other embodiments of the reactor 10 reflect attainment of selected considerations, and need not accommodate all of the considerations discussed below. Portions of the following discussion includes information excerpted from a paper entitled “Completely Automated Nuclear Power Reactors For Long-Term Operation: III. Enabling Technology For Large-Scale, Low-Risk, Affordable Nuclear Electricity” by Edward Teller, Muriel Ishikawa, Lowell Wood, Roderick Hyde, and John Nuckolls, “PRESENTED AT the July 2003 Workshop of the Aspen Global Change Institute”, University of California Lawrence Livermore National Laboratory publication UCRL-JRNL-122708 (2003). (This paper was prepared for submittal to Energy, The International Journal, 30 Nov. 2003.) the entire contents of which are hereby incorporated by reference. Nuclear fission fuels envisioned for use in embodiments of the reactor 10 are typically widely available, such as without limitation uranium (natural, depleted, or enriched), thorium, plutonium, or even previously-burned nuclear fission fuel assemblies. Other, less widely available nuclear fission fuels, such as without limitation other actinide elements or isotopes thereof may be used in embodiments of the reactor 10. While embodiments of the reactor 10 contemplate long-term operation at full power on the order of around ⅓ century to around ½ century or longer, an aspect of some embodiments of the reactor 10 does not contemplate nuclear refueling (but instead contemplate burial in-place at ends-of-life) while some aspects of embodiments of the reactor 10 contemplate nuclear refueling—with some nuclear refueling occurring during shutdown and some nuclear refueling occurring during operation at power. It is also contemplated that nuclear fission fuel reprocessing may be avoided, thereby mitigating possibilities for diversion to military uses and other issues. Other considerations behind embodiments of the reactor 10 include disposing in a manifestly safe manner long-lived radioactivity generated in the course of operation. It is envisioned that the reactor 10 may be able to mitigate damage due to operator error, casualties such as a loss of coolant accident (LOCA), or the like. In some aspects decommissioning may be effected in low-risk and inexpensive manner. As a result, some embodiments of the reactor 10 may entail underground siting, thereby addressing large, abrupt releases and small, steady-state releases of radioactivity into the biosphere. Some embodiments of the reactor 10 may entail minimizing operator controls, thereby automating those embodiments as much as practicable. In some embodiments, a life-cycle-oriented design is contemplated, wherein those embodiments of the reactor 10 can operate from startup to shutdown at end-of-life in as fully-automatic manner as practicable. Some embodiments of the reactor 10 lend themselves to modularized construction. Finally, some embodiments of the reactor 10 may be designed according to high power density. Some features of various embodiments of the reactor 10 result from some of the above considerations. For example, simultaneously accommodating desires to achieve ⅓-½ century (or longer) of operations at full power without nuclear refueling and to avoid nuclear fission fuel reprocessing entails use of a fast neutron spectrum. As another example, in some embodiments a negative temperature coefficient of reactivity (αT) is engineered-in to the reactor 10, such as via negative feedback on local reactivity implemented with strong absorbers of fast neutrons. As a further example, in some embodiments of the reactor 10 a distributed thermostat enables a propagating nuclear fission deflagration wave mode of nuclear fission fuel burn. This mode simultaneously permits a high average burn-up of non-enriched actinide fuels, such as natural uranium or thorium, and use of a comparatively small “nuclear fission igniter” region of moderate isotopic enrichment of nuclear fissionable materials in the core's fuel charge. As another example, in some embodiments of the reactor 10, multiple redundancy is provided in primary and secondary core cooling. Exemplary Embodiment of Nuclear Fission Reactor Now that some of the considerations behind some of the embodiments of the reactor 10 have been set forth, further details regarding an exemplary embodiment of the reactor 10 will be explained. It is emphasized that the following description of an exemplary embodiment of the reactor 10 is given by way of non-limiting example only and not by way of limitation. As mentioned above, several embodiments of the reactor 10 are contemplated, as well as further aspects of the reactor 10. After details regarding an exemplary embodiment of the reactor 10 are discussed, other embodiments and aspects will also be discussed. Still referring to FIG. 1A, an exemplary embodiment of the reactor 10 includes a nuclear fission reactor core assembly 100 that is disposed within a reactor pressure vessel 12. Several embodiments and aspects of the nuclear fission reactor core assembly 100 are contemplated that will be discussed later. Some of the features that will be discussed later in detail regarding the nuclear fission reactor core assembly 100 include nuclear fission fuel materials and their respective nucleonics, fuel assemblies, fuel geometries, and initiation and propagation of nuclear fission deflagration waves. The reactor pressure vessel 12 suitably is any acceptable pressure vessel known in the art and may be made from any materials acceptable for use in reactor pressure vessels, such as without limitation stainless steel. Within the reactor pressure vessel 12, a neutron reflector (not shown) and a radiation shield (not shown) surround the nuclear fission reactor core assembly 100. In some embodiments, the reactor pressure vessel 12 is sited underground. In such cases, the reactor pressure vessel 12 can also function as a burial cask for the nuclear fission reactor core assembly 100. In these embodiments, the reactor pressure vessel 12 suitably is surrounded by a region (not shown) of isolation material, such as dry sand, for long-term environmental isolation. The region (not shown) of isolation material may have a size of around 100 m in diameter or so. However, in other embodiments, the reactor pressure vessel 12 is sited on or toward the Earth's surface. Reactor coolant loops 14 transfer heat from nuclear fission in the nuclear fission reactor core assembly 100 to application heat exchangers 16. The reactor coolant may be selected as desired for a particular application. In some embodiments, the reactor coolant suitably is helium (He) gas. In other embodiments, the reactor coolant suitably may be other pressurized inert gases, such as neon, argon, krypton, xenon, or other fluids such as water or gaseous or superfluidic carbon dioxide, or liquid metals, such as sodium or lead, or metal alloys, such as Pb—Bi, or organic coolants, such as polyphenyls, or fluorocarbons. The reactor coolant loops suitably may be made from tantalum (Ta), tungsten (W), aluminum (Al), steel or other ferrous or non-iron groups alloys or titanium or zirconium-based alloys, or from other metals and alloys, or from other structural materials or composites, as desired. In some embodiments, the application heat exchangers 16 may be steam generators that generate steam that is provided as a prime mover for rotating machinery, such as electrical turbine-generators 18 within an electrical generating station 20. In such a case, the nuclear fission reactor core assembly 100 suitably operates at a high operating pressure and temperature, such as above 1,000K or so and the steam generated in the steam generator may be superheated steam. In other embodiments, the application heat exchanger 16 may be any steam generator that generates steam at lower pressures and temperatures (that is, need not be not superheated steam) and the nuclear fission reactor core assembly 100 operates at temperatures less than around 550K. In these cases, the application heat exchangers 16 may provide process heat for applications such as desalination plants for seawater or for processing biomass by distillation into ethanol, or the like. Optional reactor coolant pumps 22 circulate reactor coolant through the nuclear fission reactor core assembly 100 and the application heat exchangers 16. Note that although the illustrative embodiment shows pumps and gravitationally driven circulation, other approaches may not utilize pumps, or circulatory structures or be otherwise similarly geometrically limited. The reactor coolant pumps 22 suitably are provided when the nuclear fission reactor core assembly 100 is sited approximately vertically coplanar with the application heat exchangers 16, such that thermal driving head is not generated. The reactor coolant pumps 22 may also be provided when the nuclear fission reactor core assembly 100 is sited underground. However, when the nuclear fission reactor core assembly 100 is sited underground or in any fashion so the nuclear fission reactor core assembly 100 is vertically spaced below the application heat exchangers 16, thermal driving head may be developed between the reactor coolant exiting the reactor pressure vessel 12 and the reactor coolant exiting the application heat exchangers 16 at a lower temperature than the reactor coolant exiting the reactor pressure vessel 12. When sufficient thermal driving head exists, the reactor coolant pumps 22 need not be provided in order to provide sufficient circulation of reactor coolant through the nuclear fission reactor core assembly 100 to remove heat from fission during operation at power. In some embodiments more than one reactor coolant loop 14 may be provided, thereby providing redundancy in the event of a casualty, such as a loss of coolant accident (LOCA) or a loss of flow accident (LOFA) or a primary-to-secondary leak or the like, to any one of the other reactor coolant loops 14. Each reactor coolant loop 14 is typically rated for full-power operation, though some applications may remove this constraint. In some embodiments, one-time closures 24, such as reactor coolant shutoff valves, are provided in lines of the reactor coolant system 14. In each reactor coolant loop 14 provided, a closure 24 is provided in an outlet line from the reactor pressure vessel 12 and in a return line to the reactor pressure vessel 12 from an outlet of the application heat exchanger 16. The one-time closures 24 are fast-acting closures that shut quickly under emergency conditions, such as detection of significant fission-product entrainment in reactor coolant). The one-time closures 24 are provided in addition to a redundant system of automatically-actuated conventional valves (not shown). Heat-dump heat exchangers 26 are provided for removal of after-life heat (decay heat). The heat-dump heat exchanger 26 includes a primary loop that is configured to circulate decay heat removal coolant through the nuclear fission reactor core assembly 100. The heat-dump heat exchanger 26 includes a secondary loop that is coupled to an engineered heat-dump heat pipe network (not shown). In some situations, for example, for redundancy purposes, more than one the heat-dump heat exchanger 26 may be provided. Each of the heat-dump heat exchangers 26 provided may be sited at a vertical distance above the nuclear fission reactor core assembly 100 so sufficient thermal driving head is provided to enable natural flow of decay heat removal coolant without need for decay heat removal coolant pumps. However, in some embodiments decay heat removal pumps (not shown) may be provided or, if provided, the reactor coolant pumps may be used for decay heat removal, where appropriate. Now that an overview of an exemplary embodiment of the reactor 10 has been given, other embodiments and aspects will be discussed. First, embodiments and aspects of the nuclear fission reactor core assembly 100 will be discussed. An overview of the nuclear fission reactor core assembly 100 and its nucleonics and propagation of a nuclear fission deflagration wave will be set forth first, followed by descriptions of exemplary embodiments and other aspects of the nuclear fission reactor core assembly 100. Given by way of overview and in general terms, structural components of the reactor core assembly 100 may be made of tantalum (Ta), tungsten (W), rhenium (Re), or carbon composite, ceramics, or the like. These materials are suitable because of the high temperatures at which the nuclear fission reactor core assembly 100 operates, and because of their creep resistance over the envisioned lifetime of full power operation, mechanical workability, and corrosion resistance. Structural components can be made from single materials, or from combinations of materials (e.g., coatings, alloys, multilayers, composites, and the like). In some embodiments, the reactor core assembly 100 operates at sufficiently lower temperatures so that other materials, such as aluminum (Al), steel, titanium (Ti) or the like can be used, alone or in combinations, for structural components. The nuclear fission reactor core assembly 100 includes a small nuclear fission igniter and a larger nuclear fission deflagration burn-wave-propagating region. The nuclear fission deflagration burn-wave-propagating region suitably contains thorium or uranium fuel, and functions on the general principle of fast neutron spectrum fission breeding. In some embodiments, uniform temperature throughout the nuclear fission reactor core assembly 100 is maintained by thermostating modules, described in detail later, which regulate local neutron flux and thereby control local power production. The nuclear fission reactor core assembly 100 suitably is a breeder for reasons of efficient nuclear fission fuel utilization and of minimization of requirements for isotopic enrichment. Further, and referring now to FIGS. 1B and 1C, the nuclear fission reactor core assembly 100 suitably utilizes a fast neutron spectrum because the high absorption cross-section of fission products for thermal neutrons does not permit utilization of more than about 1% of thorium or of the more abundant uranium isotope, U238, in uranium-fueled embodiments, without removal of fission products. In FIG. 1B, cross-sections for the dominant neutron-driven nuclear reactions of interest for the Th232-fueled embodiments are plotted over the neutron energy range 10−3-107 eV. It can be seen that losses to radiative capture on fission product nuclei dominate neutron economies at near-thermal (˜0.1 eV) energies, but are comparatively negligible above the resonance capture region (between ˜3-300 eV). Thus, operating with a fast neutron spectrum when attempting to realize a high-gain fertile-to-fissile breeder can help to preclude fuel recycling (that is, periodic or continuous removal of fission products). The radiative capture cross-sections for fission products shown are those for intermediate-Z nuclei resulting from fast neutron-induced fission that have undergone subsequent beta-decay to negligible extents. Those in the central portions of the burn-waves of embodiments of the nuclear fission reactor core assembly 100 will have undergone some decay and thus will have somewhat higher neutron avidity. However, parameter studies have indicated that core fuel-burning results may be insensitive to the precise degree of such decay. In FIG. 1C, cross-sections for the dominant neutron-driven nuclear reactions of primary interest for the Th232-fueled embodiments are plotted over the most interesting portion of the neutron energy range, between >104 and <106.5 eV, in the upper portion of FIG. 1C. The neutron spectrum of embodiments of the reactor 10 peaks in the ≧105 eV neutron energy region. The lower portion of FIG. 1C contains the ratio of these cross-sections vs. neutron energy to the cross-section for neutron radiative capture on Th232, the fertile-to-fissile breeding step (as the resulting Th233 swiftly beta-decays to Pa233, which then relatively slowly beta-decays to U233, analogously to the U239-Np239-Pu239 beta decay-chain upon neutron capture by U238). It can be seen that losses to radiative capture on fission products are comparatively negligible over the neutron energy range of interest, and furthermore that atom-fractions of a few tens of percent of high-performance structural material, such as Ta, will impose tolerable loads on the neutron economy in the nuclear fission reactor core assembly 100. These data also suggest that core-averaged fuel burn-up in excess of 50% can be realizable, and that fission product-to-fissile atom-ratios behind the nuclear fission deflagration wave when reactivity is finally driven negative by fission-product accumulation will be approximately 10:1. Origination and Propagation of Nuclear Fission Deflagration wave Burnfront The nuclear fission deflagration wave within the nuclear fission reactor core assembly 100 will now be explained. Propagation of deflagration burning-waves through combustible materials can release power at a predictable level. Moreover, if the material configuration has the requisite time-invariant features, the ensuing power production may be at a steady level. Finally, if deflagration wave propagation-speed may be externally modulated in a practical manner, the energy release-rate and thus power production may be controlled as desired. For several reasons, steady-state nuclear fission detonation waves are not generally appropriate for power production, such as for electrical power generation and the like. Further, nuclear fission deflagration waves are rare in nature, due to having to prevent the initial nuclear fission fuel configuration from disassembling as a hydrodynamic consequence of energy release during the earliest phases of wave propagation. However, in embodiments of the nuclear fission reactor core assembly 100 a nuclear fission deflagration wave can be initiated and propagated in a sub-sonic manner in fissionable fuel whose pressure is substantially independent of its temperature, so that its hydrodynamics is substantially ‘clamped’. The nuclear fission deflagration wave's propagation speed within the nuclear fission reactor core assembly 100 can be controlled in a manner conducive to large-scale civilian power generation, such as in an electricity-producing reactor system like embodiments of the reactor 10. Nucleonics of the nuclear fission deflagration wave are explained below. Inducing nuclear fission of selected isotopes of the actinide elements—the fissile ones—by capture of neutrons of any energy permits the release of nuclear binding energy at any material temperature, including arbitrarily low ones. Release of more than a single neutron per neutron captured, on the average, by nuclear fission of substantially any actinide isotope admits the possibility-in-principle of a diverging neutron-mediated nuclear-fission chain reaction in such materials. Release of more than two neutrons for every neutron which is captured (over certain neutron-energy ranges, on the average) by nuclear fission by some actinide isotopes admits the possibility-in-principle of first converting an atom of a non-fissile isotope to a fissile one (via neutron capture and subsequent beta-decay) by an initial neutron capture, and then of neutron-fissioning the nucleus of the newly-created fissile isotope in the course of a second neutron capture. Most really high-Z (Z≧90) nuclear species can be combusted if, on the average, one neutron from a given nuclear fission event can be radiatively captured on a non-fissile-but-‘fertile’ nucleus which will then convert (such as via beta-decay) into a fissile nucleus and a second neutron from the same fission event can be captured on a fissile nucleus and, thereby, induce fission. In particular, if either of these arrangements is steady-state, then sufficient conditions for propagating a nuclear fission deflagration wave in the given material can be satisfied. Due to beta-decay in the process of converting a fertile nucleus to a fissile nucleus, the characteristic speed of wave advance is of the order of the ratio of the distance traveled by a neutron from its fission-birth to its radiative capture on a fertile nucleus to the half-life of the (longest-lived nucleus in the chain of) beta-decay leading from the fertile nucleus to the fissile one. Since such a characteristic fission neutron-transport distance in normal-density actinides is approximately 10 cm and the beta-decay half-life is 105-106 seconds for most cases of interest, the characteristic wave-speed is 10−4-10−7 cm sec−1, or 10−13-10−14 of that of a nuclear detonation wave. Such a “glacial” speed-of-advance makes clear that the wave is that of a deflagration wave, not of a detonation wave. The deflagration wave propagates not only very slowly but very stably. If such a wave attempts to accelerate, its leading-edge counters ever-more-pure fertile material (which is quite lossy in a neutronic sense), for the concentration of fissile nuclei well ahead of the center of the wave becomes exponentially low, and thus the wave's leading-edge (referred to herein as a “burnfront”) stalls. Conversely, if the wave slows, however, the local concentration of fissile nuclei arising from continuing beta-decay increases, the local rates of fission and neutron production rise, and the wave's leading-edge, that is the burnfront, accelerates. Finally, if the heat associated with nuclear fission is removed sufficiently rapidly from all portions of the configuration of initially fertile matter in which the wave is propagating, the propagation may take place at an arbitrarily low material temperature—although the temperatures of both the neutrons and the fissioning nuclei may be around 1 MeV. Such conditions for initiating and propagating a nuclear fission deflagration wave can be realized with readily available materials. While fissile isotopes of actinide elements are rare terrestrially, both absolutely and relative to fertile isotopes of these elements, fissile isotopes can be concentrated, enriched and synthesized. The use of both naturally-occurring and man-made ones, such as U235 and Pu239, respectively, in initiating and propagating nuclear fission detonation waves is well-known. Consideration of pertinent neutron cross-sections (shown in FIGS. 1B and 1C) suggests that a nuclear fission deflagration wave can burn a large fraction of a core of naturally-occurring actinides, such as Th232 or U238, if the neutron spectrum in the wave is a ‘hard’ or ‘fast’ one. That is, if the neutrons which carry the chain reaction in the wave have energies which are not very small compared to the approximately 1 MeV at which they are evaporated from nascent fission fragments, then relatively large losses to the spacetime-local neutron economy can be avoided when the local mass-fraction of fission products becomes comparable to that of the fertile material (recalling that a single mole of fissile material fission-converts to two moles of fission-product nuclei). Even neutronic losses to typical neutron-reactor structural materials, such as Ta, which has desirable high-temperature properties, may become substantial at neutron energies ≦0.1 MeV. Another consideration is the (comparatively small) variation with incident neutron energy of the neutron multiplicity of fission, v, and the fraction of all neutron capture events which result in fission (rather than merely γ-ray emission). The algebraic sign of the function α(v−2) constitutes a necessary condition for the feasibility of nuclear fission deflagration wave propagation in fertile material compared with the overall fissile isotopic mass budget, in the absence of neutron leakage from the core or parasitic absorptions (such as on fission products) within its body, for each of the fissile isotopes of the nuclear fission reactor core assembly 100. The algebraic sign is generally positive for all fissile isotopes of interest, from fission neutron-energies of approximately 1 MeV down into the resonance capture region. The quantity α(v−2)/v upper-bounds the fraction of total fission-born neutrons which may be lost to leakage, parasitic absorption, or geometric divergence during deflagration wave propagation. It is noted that this fraction is 0.15-0.30 for the major fissile isotopes over the range of neutron energies which prevails in all effectively unmoderated actinide isotopic configurations of practical interest (approximately 0.1-1.5 MeV). In contrast to the situation prevailing for neutrons of (epi-) thermal energy (see FIG. 1C), in which the parasitic losses due to fission products dominate those of fertile-to-fissile conversion by 1-1.5 decimal orders-of-magnitude, fissile element generation by capture on fertile isotopes is favored over fission-product capture by 0.7-1.5 orders-of-magnitude over the neutron energy range 0.1-1.5 MeV. The former suggests that fertile-to-fissile conversion will be feasible only to the extent of 1.5-5% percent at-or-near thermal neutron energies, while the latter indicates that conversions in excess of 50% may be expected for near-fission energy neutron spectra. In considering conditions for propagation of a nuclear fission deflagration wave, neutron leakage may be effectively ignored for very large, “self-reflected” actinide configurations. Referring to FIG. 1C and analytic estimates of the extent of neutron moderation-by-scattering entirely on actinide nuclei, it will be appreciated that deflagration wave propagation can be established in sufficiently large configurations of the two types of actinides that are relatively abundant terrestrially: Th232 and U238, the exclusive and the principal (that is, longest-lived) isotopic components of naturally-occurring thorium and uranium, respectively. Specifically, transport of fission neutrons in these actinide isotopes will likely result in either capture on a fertile isotopic nucleus or fission of a fissile one before neutron energy has decreased significantly below 0.1 MeV (and thereupon becomes susceptible with non-negligible likelihood to capture on a fission-product nucleus). Referring to FIG. 1B, it will be appreciated that fission product nuclei concentrations must significantly exceed fertile ones and fissile nuclear concentrations may be an order-of-magnitude less than the lesser of fission-product or fertile ones before it becomes quantitatively questionable. Consideration of pertinent neutron scattering cross-sections suggests that right circular cylindrical configurations of actinides which are sufficiently extensive to be effectively infinitely thick—that is, self-reflecting—to fission neutrons in their radial dimension will have density-radius products >>200 gm/cm2—that is, they will have radii >>10-20 cm of solid-density U238-Th232. As an example, studies have indicated that circular cylinders of solid-density Th232 of 25 cm radius, overcoated with an annular shell of 15 cm of C12 (as graphite), may propagate nuclear fission deflagration waves with ≧70% burn-up of the Th232 initially present. Moreover, studies have indicated that replacing the Th232 with half-density U238 may yield similar results—albeit fertile isotope burn-up of ≧80% is realized (as would be expected from inspection of FIG. 1C). A basic condition on the ‘local’ geometry of the breeding-and-burning wave is that the flux history of neutrons excess to the local fissioning process in the core of the burn wave be quantitatively sufficient to at-least-reproduce the fissile atom density 1-2 mean-free-paths into the yet-unburned fuel, in a self-consistent sense. The ‘ash’ behind the burn-wave's peak is substantially ‘neutronically neutral’ in such an accounting scheme, since the neutronic reactivity of its fissile fraction is just balanced by the parasitic absorptions of structure and fission product inventories on top of leakage. If the fissile atom inventory in the wave's center and just in advance of it is time-stationary as the wave propagates, then it's doing so stably; if less, then the wave is ‘dying’, while if more, the wave may be said to be ‘accelerating.’ Thus, a nuclear fission deflagration wave may be propagated and maintained in substantially steady-state conditions for long time intervals in configurations of naturally-occurring actinide isotopes. The above discussion has considered, by way of non-limiting example, circular cylinders of natural uranium or thorium metal of less than a meter or so diameter—and that may be substantially smaller in diameter if efficient neutron reflectors are employed—that may stably propagate nuclear fission deflagration waves for arbitrarily great axial distances. However, propagation of nuclear fission deflagration waves is not to be construed to be limited to circular cylinders, to symmetric geometries, or to singly-connected geometries. To that end, additional embodiments of alternate geometries of the nuclear fission reactor core 100 will be described later. Propagation of a nuclear fission deflagration wave has implications for embodiments of the nuclear fission reactor 10. As a first example, local material temperature feedback can be imposed on the local nuclear reaction rate at an acceptable expense in the deflagration wave's neutron economy. Such a large negative temperature coefficient of neutronic reactivity confers an ability to control the speed-of-advance of the deflagration wave. If very little thermal power is extracted from the burning fuel, its temperature rises and the temperature-dependent reactivity falls, and the nuclear fission rate at wave-center becomes correspondingly small and the wave's equation-of-time reflects only a very small axial rate-of-advance. Similarly, if the thermal power removal rate is large, the material temperature decreases and the neutronic reactivity rises, the intra-wave neutron economy becomes relatively undamped, and the wave advances axially relatively rapidly. Details regarding exemplary implementations of temperature feedback within embodiments of the nuclear fission reactor core assembly 100 will be discussed later. As a second example of implications of propagation of a nuclear fission deflagration wave on embodiments of the nuclear fission reactor 10, less than all of the total fission neutron production in the nuclear fission reactor 10 may be utilized. For example, the local material-temperature thermostating modules may use around 5-10% of the total fission neutron production in the nuclear fission reactor 10. Another ≦10% of the total fission neutron production in the nuclear fission reactor 10 may be lost to parasitic absorption in the relatively large quantities of high-performance, high temperature, structure materials (such as Ta, W, or Re) employed in structural components of the nuclear fission reactor 10. This loss occurs in order to realize ≧60% thermodynamic efficiency in conversion to electricity and to gain high system safety figures-of-merit. The Zs of these materials, such as Ta, W and Re, are approximately 80% of that of the actinides, and thus their radiative capture cross-sections for high-energy neutrons are not particularly small compared to those of the actinides, as is indicated for Ta in FIGS. 1B and 1C. A final 5-10% of the total fission neutron production in the nuclear fission reactor 10 may be lost to parasitic absorption in fission products. As noted above, the neutron economy characteristically is sufficiently rich that approximately 0.7 of total fission neutron production is sufficient to sustain deflagration wave-propagation in the absence of leakage and rapid geometric divergence. This is in sharp contrast with (epi) thermal-neutron power reactors employing low-enrichment fuel, for which neutron-economy discipline in design and operation must be strict. As a third example of implications of propagation of a nuclear fission deflagration wave on embodiments of the nuclear fission reactor 10, high burn-ups (on the order of around 50% to around 80%) of initial actinide fuel-inventories which are characteristic of the nuclear fission deflagration waves permit high-efficiency utilization of as-mined fuel—moreover without a requirement for reprocessing. Referring now to FIGS. 1D-1H, features of the fuel-charge of embodiments of the nuclear fission reactor core assembly 100 are depicted at four equi-spaced times during the operational life of the reactor after origination of the nuclear fission deflagration wave (sometimes referred to herein as “nuclear fission ignition”) in a scenario in which full reactor power is continuously demanded over a ⅓ century time-interval. In the embodiment shown, two nuclear fission deflagration wavefronts propagate from an origination point 28 (near the center of the nuclear fission reactor core assembly 100) toward ends of the nuclear fission reactor core assembly 100. Corresponding positions of the leading edge of the nuclear fission deflagration wave-pair at various time-points after full ignition of the fuel-charge of the nuclear fission reactor core assembly 100 are indicated in FIG. 1D. FIGS. 1E, 1F, 1G, and 1G illustrate masses (in kg of total mass per cm of axial core-length) of various isotopic components in a set of representative near-axial zones and fuel specific power (in W/g) at the indicated axial position as ordinate-values versus axial position along an exemplary, non-limiting 10-meter-length of the fuel-charge as an abscissal value at approximate times after nuclear fission ignition of approximately 7.5 years, 15 years, 22.5 years, and 30 years, respectively. The central perturbation is due to the presence of the nuclear fission igniter module indicated by the origination point 28 (FIG. 1D). It will be noted that the neutron flux from the most intensely burning region behind the burnfront breeds a fissile isotope-rich region at the burnfront's leading-edge, thereby serving to advance the nuclear fission deflagration wave. After the nuclear fission deflagration wave's burnfront has swept over a given mass of fuel, the fissile atom concentration continues to rise for as long as radiative capture of neutrons on available fertile nuclei is considerably more likely than on fission product nuclei, while ongoing fission generates an ever-greater mass of fission products. Nuclear power-production density peaks in this region of the fuel-charge, at any given moment. It will also be noted that in the illustrated embodiments, differing actions of two slightly different types of thermostating units on the left and the right sides of the igniter module account for the corresponding slightly differing power production levels. Still referring to FIGS. 1D-1H, it can be seen that well behind the nuclear fission deflagration wave's advancing burnfront, the concentration ratio of fission product nuclei (whose mass closely averages half that of a fissile nucleus) to fissile ones climbs to a value comparable to the ratio of the fissile fission to the fission product radiative capture cross-sections (FIG. 1B), the “local neutronic reactivity” thereupon goes slightly negative, and both burning and breeding effectively cease—as will be appreciated from comparing FIGS. 1E, 1F, 1G, and 1H with each other, far behind the nuclear fission deflagration wave burnfront. In some embodiments of the nuclear fission reactor 10, all the nuclear fission fuel ever used in the reactor is installed during manufacture of the nuclear fission reactor core assembly 100, and no spent fuel is ever removed from the nuclear fission reactor core assembly 100, which is never accessed after nuclear fission ignition. However, in some other embodiments of the nuclear fission reactor 10, additional nuclear fission fuel is added to the nuclear fission reactor core assembly 100 after nuclear fission ignition. However, in some other embodiments of the nuclear fission reactor 10, spent fuel is removed from the reactor core assembly (and, in some embodiments, removal of spent fuel from the nuclear fission reactor core assembly 100 may be performed while the nuclear fission reactor 10 is operating at power). Regardless of whether or not spent fuel is removed, pre-expansion of the as-loaded fuel permits higher-density actinides to be replaced with lower-density fission products without any overall volume changes in fuel elements, as the nuclear fission deflagration wave sweeps over any given axial element of actinide ‘fuel,’ converting it into fission-product ‘ash.’ Launching of nuclear fission deflagration waves into Th232 or U238 fuel-charges is readily accomplished with ‘nuclear fission igniter modules’ enriched in fissile isotopes. Higher enrichments result in more compact modules, and minimum mass modules may employ moderator concentration gradients. In addition, nuclear fission igniter module design may be determined in part by non-technical considerations, such as resistance to materials diversion for military purposes in various scenarios. Such modules may employ U235 in U238, in sufficiently low concentration as to be effectively non-detonatable in any quantity or configuration—such as ≦20%—in contrast, for example, to technically more optimal Pu239 in Th232. Quantities of U235 already excess to military stockpiles suffice for ≧104 such nuclear fission igniter modules, corresponding to a total inventory of nuclear fission power reactors sufficient to supply 10 billion people with kilowatt-per-capita electricity. While the illustrative nuclear fission igniter of the previously described embodiments included nuclear fission material configured to initiate propagation of the burning wavefront, in other approaches, the nuclear fission igniter may include other types of reactivity sources in addition to or in place of those previously described. For example, nuclear fission igniters may include “burning embers”, e.g., nuclear fission fuel enriched in fissile isotopes via exposure to neutrons within a propagating nuclear fission deflagration wave reactor. Such “burning embers” may function as nuclear fission igniters, despite the presence of various amounts of fission products “ash”. For example, nuclear fission igniters may include neutron sources using electrically driven sources of high energy ions (such as protons, deuterons, alpha particles, or the like) or electrons that may in turn produce neutrons. In one illustrative approach, a particle accelerator, such as a linear accelerator may be positioned to provide high energy protons to an intermediate material that may in turn provide such neutrons (e.g., through spallation). In another illustrative approach, a particle accelerator, such as a linear accelerator may be positioned to provide high energy electrons to an intermediate material that may in turn provide such neutrons (e.g., by electro-fission and/or photofission of high-Z elements). Alternatively, other known neutron emissive processes and structures, such as electrically induced fusion approaches, may provide neutrons (e.g., 14 Mev neutrons from D-T fusion) that may thereby initiate the propagating fission wave. Now that nucleonics of the fuel charge and the nuclear fission deflagration wave have been discussed, further details regarding “nuclear fission ignition” and maintenance of the nuclear fission deflagration wave will be discussed. A centrally-positioned nuclear fission igniter moderately enriched in fissionable material, such as U235, has a neutron-absorbing material (such as a borohydride) removed from it (such as by operator-commanded electrical heating), and the nuclear fission igniter becomes neutronically critical. Local fuel temperature rises to a design set-point and is regulated thereafter by the local thermostating modules (discussed in detail later). Neutrons from the fast fission of U235 are mostly captured at first on local U238 or Th232. It will be appreciated that uranium enrichment of the nuclear fission igniter may be reduced to levels not much greater than that of light water reactor (LWR) fuel by introduction into the nuclear fission igniter and the fuel region immediately surrounding it of a radial density gradient of a refractory moderator, such as graphite. High moderator density enables low-enrichment fuel to burn satisfactorily, while decreasing moderator density permits efficient fissile breeding to occur. Thus, optimum nuclear fission igniter design may involve trade-offs between proliferation robustness and the minimum latency from initial criticality to the availability of full-rated-power from the fully-ignited fuel-charge of the core. Lower nuclear fission igniter enrichments entail more breeding generations and thus impose longer latencies. The maximum (unregulated) reactivity of the nuclear fission reactor core assembly 100 slowly decreases in the first phase of the nuclear fission ignition process because, although the total fissile isotope inventory is increasing monotonically, this total inventory is becoming more spatially dispersed. As a result of choice of initial fuel geometry, fuel enrichment versus position, and fuel density, it may be arranged for the maximum reactivity to still be slightly positive at the time-point at which its minimum value is attained. Soon thereafter, the maximum reactivity begins to increase rapidly toward its greatest value, corresponding to the fissile isotope inventory in the region of breeding substantially exceeding that remaining in the nuclear fission igniter. A quasi-spherical annular shell then provides maximum specific power production. At this point, the fuel-charge of the nuclear fission reactor core assembly 100 is referred to as “ignited.” Now that the fuel-charge of the nuclear fission reactor core assembly 100 has been “ignited”, propagation of the nuclear fission deflagration wave, also referred to herein as “nuclear fission burning”, will now be discussed. The spherically-diverging shell of maximum specific nuclear power production continues to advance radially from the nuclear fission igniter toward the outer surface of the fuel charge. When it reaches this surface, it naturally breaks into two spherical zonal surfaces, with one surface propagating in each of the two opposite directions along the axis of the cylinder. At this time-point, the full thermal power production potential of the core has been developed. This epoch is characterized as that of the launching of the two axially-propagating nuclear fission deflagration wave burnfronts. In some embodiments the center of the core's fuel-charge is ignited, thus generating two oppositely-propagating waves. This arrangement doubles the mass and volume of the core in which power production occurs at any given time, and thus decreases by two-fold the core's peak specific power generation, thereby quantitatively minimizing thermal transport challenges. However, in other embodiments, the core's fuel charge is ignited at one end, as desired for a particular application. In other embodiments, the core's fuel charge may be ignited in multiple sites. In yet other embodiments, the core's fuel charge is ignited at any 3-D location within the core as desired for a particular application. In some embodiments, two propagating nuclear fission deflagration waves will be initiated and propagate away from a nuclear fission ignition site, however, depending upon geometry, nuclear fission fuel composition, the action of neutron modifying control structures or other considerations, different numbers (e.g., one, three, or more) of nuclear fission deflagration waves may be initiated and propagated. However, for sake of understanding, the discussion herein refers, without limitation, to propagation of two nuclear fission deflagration wave burnfronts. From this time forward through the break-out of the two waves when they reach the two opposite ends, the physics of nuclear power generation is effectively time-stationary in the frame of either wave, as illustrated in FIGS. 1E-1H. The speed of wave advance through the fuel is proportional to the local neutron flux, which in turn is linearly dependent on the thermal power demanded from the nuclear fission reactor core assembly 100 via the collective action on the nuclear fission deflagration wave's neutron budget of the thermostating modules (not shown). When more power is demanded from the reactor via lower-temperature coolant flowing into the core, the temperature of the two ends of the core (which in some embodiments are closest to the coolant inlets) decreases slightly below the thermostating modules' design set-point, a neutron absorber is thereby withdrawn from the corresponding sub-population of the core's thermostating modules, and the local neutron flux is permitted thereby to increase to bring the local thermal power production to the level which drives the local material temperature up to the set-point of the local thermostating modules. However, in the two burnfront embodiment this process is not effective in heating the coolant significantly until its two divided flows move into the two nuclear burn-fronts. These two portions of the core's fuel-charge—which are capable of producing significant levels of nuclear power when not suppressed by the neutron absorbers of the thermostating modules—then act to heat the coolant to the temperature specified by the design set-point of their modules, provided that the nuclear fission fuel temperature does not become excessive (and regardless of the temperature at which the coolant arrived in the core). The two coolant flows then move through the two sections of already-burned fuel centerward of the two burnfronts, removing residual nuclear fission and afterheat thermal power from them, both exiting the fuel-charge at its center. This arrangement encourages the propagation of the two burnfronts toward the two ends of the fuel-charge by “trimming” excess neutrons primarily from the trailing edge of each front, as illustrated in FIGS. 1E-1H. Thus, the core's neutronics may be considered to be substantially self-regulated. For example, for cylindrical core embodiments, the core's nucleonics may be considered to be substantially self-regulating when the fuel density-radius product of the cylindrical core is ≧200 gm/cm2 (that is, 1-2 mean free paths for neutron-induced fission in a core of typical composition, for a reasonably fast neutron spectrum). The primary function of the neutron reflector in such core designs is to drastically reduce the fast neutron fluence seen by the outer portions of the reactor, such as its radiation shield, structural supports, thermostating modules and outermost shell. Its incidental influence on the performance of the core is to improve the breeding efficiency and the specific power in the outermost portions of the fuel, though the value of this is primarily an enhancement of the reactor's economic efficiency. Outlying portions of the fuel-charge are not used at low overall energetic efficiency, but have isotopic burn-up levels comparable to those at the center of the fuel-charge. Final, irreversible negation of the core's neutronic reactivity may be performed at any time by injection of neutronic poison into the coolant stream, via either the primary loops which extend to the application heat exchangers 16 (FIG. 1A) or the afterheat-dumping loops connecting the nuclear fission reactor 10 (FIG. 1A) to the heat dump heat exchangers 26 (FIG. 1A). For example, lightly loading the coolant stream with a material such as BF3, possibly accompanied by a volatile reducing agent such as H2 if desired, may deposit metallic boron substantially uniformly over the inner walls of the coolant-tubes threading through the reactor's core, via exponential acceleration of the otherwise slow chemical reaction 2BF3+3H2→2B+6HF by the high temperatures found therein. Boron, in turn, is a highly refractory metalloid, and will not migrate from its site of deposition. Substantially uniform presence of boron in the core in <100 kg quantities may negate the core's neutronic reactivity for indefinitely prolonged intervals without involving the use of powered mechanisms in the vicinity of the reactor. Exemplary Embodiments and Aspects of Reactor Core Assemblies Exemplary embodiments and aspects of the nuclear fission reactor core assembly 100 and exemplary nuclear fission fuel charges disposed therein will now be discussed. Referring now to FIG. 1I, the nuclear fission reactor core assembly 100 is suitable for use with a fast neutron spectrum nuclear fission reactor. It will be appreciated that the nuclear fission reactor core assembly 100 is shown schematically in FIG. 1I. As such, no geometric limitations are intended regarding shape of the nuclear fission reactor core assembly 100. As mentioned above, details were discussed for circular cylinders of natural uranium or thorium metal that may stably propagate nuclear fission deflagration waves for arbitrarily great axial distances. However, it is again emphasized that propagation of nuclear fission deflagration waves is not to be construed to be limited to circular cylinders or to metallic nuclear fission fuels, or to pure uranium or thorium nuclear fission fuel materials. To that end, additional embodiments of alternate geometries of the nuclear fission reactor core assembly 100 and fuel charges disposed therein will be described later. A neutron reflector/radiation shield 120 surrounds nuclear fission fuel 130. The nuclear fission fuel 130 is fissionable material, that is material appropriate for undergoing fission in a nuclear fission reactor, examples of which are actinide or transuranic elements. As discussed above, the fissionable material for the nuclear fission fuel 130 may include without limitation Th232 or U238. However, in other embodiments discussed below, other fissionable material may be used in the nuclear fission fuel 130. In some embodiments, the nuclear fission fuel 130 is contiguous. In other embodiments, the nuclear fission fuel 130 is non-contiguous. A nuclear fission igniter 110 acts within the nuclear fission fuel 130 for initiating a nuclear fission deflagration wave burnfront (not shown). The nuclear fission igniter 110 is made and operates according to principles and details discussed above. Therefore, details of construction and operation of the nuclear fission igniter 110 need not be repeated for sake of brevity. Referring now to FIG. 1J, after the nuclear fission fuel 130 (FIG. 1I) has been ignited by the nuclear fission igniter 110 (in a manner as discussed above), a propagating burnfront 140 (that is, a propagating nuclear fission deflagration wave burnfront, as discussed above) is initiated and propagates throughout the nuclear fission fuel 130 (FIG. 1I) a direction shown by an arrow 144. As discussed above, a region 150 of maximum reactivity is established around the propagating burnfront 140. The propagating burnfront 140 propagates through unburnt nuclear fission fuel 154 in the direction indicated by the arrow 144, leaving behind the propagating burnfront 140 burnt nuclear fission fuel 160 that includes fission products 164, such as isotopes of iodine, cesium, strontium, xenon, and/or barium (and referred to in the discussion above as “fission product ash”). In the context of burnt nuclear fission fuel and unburnt nuclear fission fuel, the term “burning” (as applied to nuclear fission fuel) means that at least some components of the nuclear fission fuel undergo neutron-mediated nuclear fission. In the context of propagating nuclear fission deflagration wave burnfronts, the terms “burning” and “burnt” also mean that at least some components of the nuclear fission fuel undergo “breeding”, whereby neutron absorption is followed by multi-second half-life beta-decay transmutation into one or more fissile isotopes, which then may or may not undergo neutron-mediated nuclear fission. Thus, the unburnt nuclear fission fuel 154 may be considered a first neutron environment having a first set of neutron environment parameters. Similarly, the burnt nuclear fission fuel 160 may be considered a second neutron environment having a second set of neutron environment parameters that are different than the first set of neutron environment parameters. The term “neutron environment” refers to the detailed neutron distribution, including its variation with respect to time, space, direction, and energy. The neutron environment includes the aggregate of multiple individual neutrons, each of which may occupy different locations at different times, and each of which may have different directions of motion and different energies. In some circumstances, a nuclear environment may be characterized by a reduced subset of these detailed properties. In one example, a reduced subset may include an aggregation of all neutrons within given space, time, direction, and energy ranges of specified time, space, direction, and energy values. In another example, some or all of the time, space, direction, or energy aggregations may incorporate value-dependent weighting functions. In another example, a reduced subset may include weighted aggregation over the full range of direction and energy values. In another example, the aggregation over energies may involve energy-dependent weighting by a specified energy function. Examples of such weighting functions include material and energy-dependent cross-sections, such as those for neutron absorption or fission. In some embodiments, only the propagating burnfront 140 is originated and propagated through the unburnt nuclear fission fuel 154. In such embodiments, the nuclear fission igniter 110 may be located as desired. For example, the nuclear fission igniter 110 may be located toward the center of the nuclear fission fuel 130 (FIG. 1I). In other embodiments (not shown) the nuclear fission igniter 110 may be located toward an end of the nuclear fission fuel 130. In other embodiments, in addition to the propagating burnfront 140, a propagating burnfront 141 is originated and propagated through the other fuel 154 along a direction indicated by an arrow 145. A region 151 of maximum reactivity is established around the obligating burnfront 141. The propagating burnfront 141 leaves behind it the burnt nuclear fission fuel 160 and the fission products 164. Principles and details of origination and propagation of the propagating burnfront 141 are the same as that previously discussed for the propagating burnfront 140. Therefore, details of origination and propagation of the propagating burnfront 141 need not be provided for sake of brevity. Referring now to FIG. 2A, a nuclear fission reactor 200, such as a fast neutron spectrum nuclear fission reactor, includes nuclear fission fuel assemblies 210 disposed therein. The following discussion includes details of exemplary nuclear fission fuel assemblies 210 that may be used in the nuclear fission reactor 200. Other details regarding the nuclear fission reactor 200, including origination and propagation of a nuclear fission deflagration wave burnfront (that is, “burning” the nuclear fission fuel) are similar to those of the nuclear fission reactor 10 (FIG. 1A), and need not be repeated for sake of brevity. Referring now to FIG. 2B and given by way of non-limiting example, in one embodiment the nuclear fission fuel assembly 210 suitably includes a previously burnt nuclear fission fuel assembly 220. The previously burnt nuclear fission fuel assembly 220 is clad with cladding 224. The cladding 224 is the “original” cladding in which the previously burned nuclear fission fuel assembly 220 was clad. The term “previously burnt” means that at least some components of the nuclear fission fuel assembly have undergone neutron-mediated nuclear fission and that the isotopic composition of the nuclear fission fuel has been modified. That is, the nuclear fission fuel assembly has been put in a neutron spectrum or flux (either fast or slow), at least some components have undergone neutron-mediated nuclear fission and, as result, the isotopic composition of the nuclear fission fuel has been changed. Thus, a burnt nuclear fission fuel assembly 220 may have been previously burnt in any reactor, such as without limitation a light water reactor. It is intended that the previously burnt nuclear fission fuel assembly 220 can include without limitation any type of nuclear fissionable material whatsoever appropriate for undergoing fission in a nuclear fission reactor, such as actinide or transuranic elements like natural thorium, natural uranium, enriched uranium, or the like. In some other embodiments, the previously burnt nuclear fission fuel assembly 220 may not be clad with “original” cladding 224, but in these embodiments, the previously burnt nuclear fission fuel assembly 220 is chemically untreated subsequent to its previous burning in the nuclear fission reactor 200. Referring now to FIG. 2C, the previously burnt nuclear fission fuel assembly 220 and its “original” cladding 224 is clad with cladding 230. Thus, the previously burnt nuclear fission fuel assembly 220 is retained in its original cladding 224, and the cladding 230 is disposed around an exterior of the cladding 224. The cladding 230 can accommodate swelling. For example, when the previously burnt nuclear fission fuel assembly 220 was burnt in a light water reactor, the cladding 224 was sufficient to contain swelling at approximately 3% burn-up of the previously burnt nuclear fission fuel assembly 220. In one nonlimiting example, the cladding 230 contacts the cladding 224 at azimuthally, symmetric, cylindrical faces around the cladding 224. Such an arrangement enables removal of heat through the contacting faces while allowing at least one half of the cladding 224 to expand into void spaces between the cladding 224 and the cladding 230. In some embodiments, the cladding 230 is made up of cladding sections (not shown) that are configured to help accommodate swelling into the void spaces, as described above. In other embodiments, the cladding 230 may be provided as a barrier, such as a tube, provided between an exterior of the cladding 224 and reactor coolant (not shown). In some other embodiments, the previously burned nuclear fission fuel assembly 220 is burnt in the nuclear fission reactor 200 as the nuclear fission fuel assembly 210. That is, the previously burnt nuclear fission fuel assembly 220 may not be clad with the cladding 230. This embodiment envisions burning the previously burnt nuclear fission fuel assembly 220, such as one that was burnt in a light water reactor, or in a fast neutron spectrum nuclear fission reactor, or in any other form of nuclear fission reactor and either (a) tolerating or planning to accept possible failure of the cladding 224 due to swell or, (b) burning the previously burnt nuclear fission fuel assembly 220 in the fast neutron spectrum nuclear fission reactor 200 to levels significantly less than isotopic depletion (in which case swelling may be of acceptable magnitude). Referring now to FIGS. 3A, 3B, 3C, and 3D, alternate nuclear fission fuel geometries of nuclear fission fuel structures 310, 320, 330, and 340, respectively, are discussed. Each of the nuclear fission fuel structures 310, 320, 330, and 340 includes a nuclear fission igniter 300, and a propagating nuclear fission deflagration wave 302 is propagated in a direction indicated by an arrow 304. In a spherical nuclear fission fuel structure 310 (FIG. 3A), the nuclear fission igniter 300 is disposed toward a center of the spherical nuclear fission fuel structure 310. The propagating burnfront 302 propagates radially outward from the nuclear fission igniter 300, as indicated by the arrows 304. In a parallelepiped nuclear fission fuel structure 320, the nuclear fission igniter 300 is disposed as desired. As discussed above, two propagating burnfronts 302 may be originated and propagated toward ends of the parallelepiped nuclear fission fuel structure 320 along directions indicated by the arrows 304. Alternately, the nuclear fission igniter 300 may be disposed toward an end of the parallelepiped nuclear fission fuel structure 320, in which case one propagating burnfront 302 is originated and propagates toward the other end of the parallelepiped nuclear fission fuel structure 320 along the direction indicated by the arrow 304. In a toroidal nuclear fission fuel structure 330 (FIG. 3C), the nuclear fission igniter 300 is disposed as desired. Two propagating burnfronts 302 may be originated and propagated away from the nuclear fission igniter 300 and toward each other along directions indicated by the arrows 304. In such a case, the toroidal nuclear fission fuel structure 330 may be considered to be “burnt” when the propagating burnfronts 302 meet, and propagation of the propagating burnfront 302 may stop. Alternately, only one propagating burnfront 302 is originated and propagates around the toroidal nuclear fission fuel structure 330 along the direction indicated by the arrow 304. In such a case, the toroidal nuclear fission fuel structure 330 may be considered to be “burnt” when the propagating burnfront 302 returns to the site of the nuclear fission igniter 300, and propagation of the propagating burnfront 302 may stop or may be re-started. In another embodiment, the propagating burnfront 302 is “restarted” due to the removal or decay of fission products during the burnfront's propagation around the toroid. In another embodiment, the propagating burnfront 302 is “restarted” due to control of neutron modifying structures, as discussed later. In another embodiment, the toroidal nuclear fission fuel structure 330 is not a “geometric” toroid, but a “logical” toroid, with a more general reentrant structure. As mentioned above, nuclear fission deflagration propagating wave burnfronts can be initiated and propagated in nuclear fission fuels having any shape as desired. For example, in an irregularly-shaped nuclear fission fuel structure 340, the nuclear fission igniter 300 can be located as desired. Propagating burnfronts 302 are initiated and propagate along directions indicated by the arrows 304 as desired for a particular application. In one approach, thermal management may be adjusted to provide thermal control appropriate for any changes in operational parameters, such as revised neutronic action of the previously burnt or modified nuclear fission fuel or other parameter changes, that may result from removal of ash, addition of fuels, or from other parameters of re-burning. In these exemplary geometries, the nuclear fission ignitor 300 may be any of the varieties of nuclear fission ignitor previously discussed. The indicated nuclear fission ignitor 300 is the site at which nuclear fission ignition occurs, but for some embodiments (e.g., electrical neutron sources) additional components of the nuclear fission ignitor may exist, and may reside in different physical locations. Referring now to FIG. 4, a nuclear fission fuel structure 400 includes a nuclear fission igniter 410 and non-contiguous segments 420 of nuclear fission fuel material. The behavior of a nuclear fission deflagration wave with non-contiguous segments 420 of nuclear fission fuel material is similar to that previously discussed for contiguous nuclear fission fuel material; it is crucial only that the non-continguous segments 420 be in “neutronic” contact, not physical contact. Referring now to FIG. 5, a modular nuclear fission fuel core 500 includes a neutron reflector/radiation shield 510 and modular nuclear fission fuel assemblies 520. The modular nuclear fission fuel assemblies 520 are placed as desired within the fuel assembly receptacles 530. The modular nuclear fission fuel core 500 may be operated in any number of ways. For example, all of the fuel assembly receptacles 530 in the modular nuclear fission fuel core 500 may be fully populated with modular nuclear fission fuel assemblies 520 prior to initial operation (e.g., prior to initial origination and propagation of a nuclear fission deflagration propagating wave burnfront within and through the modular nuclear fission fuel assemblies 520). As another example, after a nuclear fission deflagration wave burnfront has completely propagated through modular nuclear fission fuel assemblies 520, such “burnt” modular nuclear fission fuel assemblies 520 may be removed from their respective fuel assembly receptacles 530 and replaced with unused modular nuclear fission fuel assemblies 540, as desired; this emplacement is indicated by the arrow 544. A nuclear fission deflagration wave burnfront can be initiated in the unused modular nuclear fission fuel assemblies 540, thereby enabling continued or extended operation of the modular nuclear fission fuel core 500 as desired. As another example, the modular nuclear fission fuel core 500 need not be fully populated with modular nuclear fission fuel assemblies 520 prior to initial operation. For example, less than all of the fuel assembly receptacles 530 can be populated with modular nuclear fission fuel assemblies 520. In such a case, the number of modular nuclear fission fuel assemblies 520 that are placed within the modular nuclear fission fuel core 500 can be determined based upon power demand, such as electrical loading in watts, that will be placed upon the modular nuclear fission fuel core 500. A nuclear fission deflagration wave burnfront is originated and propagated through the modular nuclear fission fuel assemblies 520 as previously described. In one approach, thermal management may be adjusted to provide thermal control appropriate to maintain the inserted fuel assembly receptacles 530 at appropriate temperatures. As another example, the modular nuclear fission fuel core 500 again need not be fully populated with modular nuclear fission fuel assemblies 520 prior to initial operation. The number of modular nuclear fission fuel assemblies 520 provided may be determined based upon a number of modular nuclear fission fuel assemblies 520 that are available or for other reasons. A nuclear fission deflagration wave burnfront is originated and propagates through the modular nuclear fission fuel assemblies 520. As the nuclear fission deflagration wave burnfront approaches unpopulated fuel assembly receptacles 530, the unpopulated fuel assembly receptacles 530 can be populated with modular nuclear fission fuel assemblies 520, such as on a “just-in-time” basis; this emplacement is indicated by the arrow 544. Thus, continued or extended operation of the modular nuclear fission fuel core 500 can be enabled without initially fueling the entire modular nuclear fission fuel core 500 with modular nuclear fission fuel assemblies 520. It will be appreciated that the concept of modularity can be extended. For example, in other embodiments, a modular nuclear fission reactor can be populated with any number of nuclear fission reactor cores in the same manner that the modular nuclear fission fuel core 500 can be populated with any number of modular nuclear fission fuel assemblies 520. To that end, the modular nuclear fission reactor can be analogized to the modular nuclear fission fuel core 500 and nuclear fission reactor cores can be analogized to the modular nuclear fission fuel assemblies 520. The several contemplated modes of operation discussed above for the modular nuclear fission fuel core 500 thus apply by analogy to a modular nuclear fission reactor. Applications of modular designs are shown in FIGS. 6A-6C. Referring to FIG. 6A, a nuclear fission facility 600 includes a fast neutron spectrum nuclear fission core assembly 610 that is operationally coupled to an operational sub system 620 (such as without limitation an electrical power generating facility) via a core-subsystem coupling 630 (such as without limitation a reactor coolant system such as a primary loop and, if desired, a secondary loop including a steam generator). Referring now to FIG. 6B, another fast neutron spectrum nuclear fission core assembly 610 may be emplaced within the nuclear fission facility 600. The additional fast neutron spectrum nuclear fission core assembly 610 is operationally coupled to another operational sub system 620 by another core-subsystem coupling 630. The operational sub system's 620 are coupled to each other via a subsystem-subsystem coupling 640. A subsystem-subsystem coupling 640 can provide prime mover or other energy transfer medium between the operational sub systems 620. To that end, energy produced by any one of the nuclear core assemblies 610 can be transferred to any operational sub system 620 as desired. Referring now to FIG. 6C, a third fast neutron spectrum nuclear fission core assembly 610, and associated operational sub system 620, and core-subsystem coupling 630 have been placed in the nuclear fission facility 600. Again, as described above, energy produced by any one of the fast neutron spectrum nuclear fission core assemblies 610 can be transferred to any operational sub system 620 as desired. In other embodiments, this linking process can be more general than discussed above, so that, the nuclear fission facility 600 may consist of a number N of fast neutron spectrum nuclear fission core assemblies 610, and a same or different number M of operational subsystems 620. It will be appreciated, that the individual nuclear fast neutron spectrum nuclear fission core assemblies 610 need not be identical to each other, nor need the operational sub systems 620 be identical to each other. Similarly, the core-subsystem couplings 630 need not be identical to each other, nor do the subsystem-subsystem couplings 640 need be identical to each other. In addition to the operational sub system 620 embodiment discussed above, other embodiments of operational sub system 620 include, without limitation, reactor coolant systems, electrical nuclear fission ignitors, afterlife heat-dumps, reactor site facilities (such as basing and security), and the like. Referring now to FIG. 7, heat energy can be extracted from a nuclear fission reactor core according to another embodiment. In a nuclear fission reactor 700, a nuclear fission deflagration wave burnfront is initiated and propagated in a burning wavefront heat generating region 720, in a manner as described above. Heat absorbing material 710, such as a condensed phase density fluid (e.g., water, liquid metals, terphenyls, polyphenyls, fluorocarbons, FLIBE (2LiF—BeF2) and the like) flows through the region 720 as indicated by an arrow 750, and heat is transferred from the propagating burnfront fission to the heat absorbing material 710. In some fast fission spectrum nuclear reactors, the heat absorbing material 710 is chosen to be a nuclear inert material (such as He4) so as to minimally perturb the neutron spectrum. In some embodiments of the nuclear fission reactor 700, the neutron content is sufficiently robust, so that a non-nuclear-inert heat absorbing material 710 may be acceptably utilized. The heat absorbing material 710 flows to a heat extraction region 730 that is substantially out of thermal contact with the burning wavefront heat generating region 720. The energy 740 is extracted from the heat absorbing material 710 at the heat extraction region 730. The heat absorbing material 710 can reside in either a liquid state, a multiphase state, or a substantially gaseous state upon extraction of the heat energy 740 in the heat extraction region 730. Referring now to FIG. 8, in some embodiments a nuclear fission deflagration wave burnfront can be driven into areas of nuclear fission fuel as desired, thereby enabling a variable nuclear fission fuel burn-up. In a propagating burnfront nuclear fission reactor 800, a nuclear fission deflagration wave burnfront 810 is initiated and propagated as described above. Actively controllable neutron modifying structures 830 can direct or move the burnfront 810 in directions indicated by areas 820. In one embodiment, the actively controllable neutron modifying structures 830 insert neutron absorbers, such as without limitation Li6, B10, or Gd, into nuclear fission fuel behind the burnfront 810, thereby driving down or lowering neutronic reactivity of fuel that is presently being burned by the burnfront 810 relative to neutronic reactivity of fuel ahead of the burnfront 810, thereby speeding up the propagation rate of the nuclear fission deflagration wave. In another embodiment, the actively controllable neutron modifying structures 830 insert neutron absorbers into nuclear fission fuel ahead of the burnfront 810, thereby slowing down the propagation of the nuclear fission deflagration wave. In other embodiments the actively controllable neutron modifying structures 830 insert neutron absorbers into nuclear fission fuel within or to the side of the burnfront 810, thereby changing the effective size of the burnfront 810. In another embodiment, the actively controllable neutron modifying structures 830 insert neutron moderators, such as without limitation hydrocarbons or Li7, thereby modifying the neutron energy spectrum, and thereby changing the neutronic reactivity of nuclear fission fuel that is presently being burned by the burnfront 810 relative to neutronic reactivity of nuclear fission fuel ahead of or behind the burnfront 810. In some situations, an effect of the neutron moderators is associated with detailed changes in the neutron energy spectrum (e.g., hitting or missing cross-section resonances), while in other cases the effects are associated with lowering the mean neutron energy of the neutron environment (e.g., downshifting from “fast” neutron energies to epithermal or thermal neutron energies). In yet other situations, an effect of the neutron moderators is to deflect neutrons to or away from selected locations. In some embodiments, one of the aforementioned effects of neutron moderators is of primary importance, while in other embodiments, multiple effects are of comparable design significance. In another embodiment, the actively controllable neutron modifying structures 830 contain both neutron absorbers and neutron moderators; in one nonlimiting example, the location of neutron absorbing material relative to that of neutron moderating material is changed to affect control (e.g., by masking or unmasking absorbers, or by spectral-shifting to increase or decrease the absorption of absorbers), in another nonlimiting example, control is affected by changing the amounts of neutron absorbing material and/or neutron moderating material. The burnfront 810 can be directed as desired according to selected propagation parameters. For example, propagation parameters can include a propagation direction or orientation of the burnfront 810, a propagation rate of the burnfront 810, power demand parameters such the heat generation density, cross-sectional dimensions of a burning region through which the burnfront 810 is to the propagated (such as an axial or lateral dimension of the burning region relative to an axis of propagation of the burnfront 810), or the like. For example, the propagation parameters may be selected so as to control the spatial or temporal location of the burnfront 810, so as to avoid failed or malfunctioning control elements (e.g., neutron modifying structures or thermostats), or the like. Referring now to FIGS. 9A and 9B, a nuclear fission reactor can be controlled with programmable thermostats, thereby enabling the temperature of the reactor's fuel-charge to be varied over time responsive to changes in operating parameters. Temperature profiles 940 are determined as a function of position through a fuel-charge of a nuclear fission reactor 900. An operating temperature profile 942 of operating temperatures throughout the nuclear fission reactor 900 is established responsive to a first set of operating parameters, such as predicted power draw, thermal creep of structural materials, etc. At other times, or in other circumstances, the operating parameters may be revised. To that end, a revised operating temperature profile 944 of revised operating temperatures throughout the nuclear fission reactor 900 is established. The nuclear fission reactor 900 includes programmable temperature responsive neutron modifying structures 930. The programmable temperature responsive neutron modifying structures 930 (an example of which is described in detail later) introduce and remove neutron absorbing or neutron moderating material into and from the fuel-charge of a nuclear fission reactor 900. A nuclear fission deflagration wave burnfront 910 is initiated and propagated in a fuel-charge of the nuclear fission reactor 900. Responsive to the revised operating temperature profile 944, the programmable temperature responsive neutron modifying structures 930 introduce neutron absorbing or moderating material into the fuel-charge of the nuclear fission reactor 900 to lower operating temperature in the nuclear fission reactor 900 or remove neutron absorbing or moderating material from the fuel-charge of the nuclear fission reactor 900 in order to raise operating temperature of the nuclear fission reactor 900. It will be appreciated, that operating temperature profiles are only one example of control parameters which can be used to determine the control settings of programmable temperature responsive neutron modifying structures 930, which are in such cases responsive to the selected control parameters, not necessarily to the temperature. Nonlimiting examples of other control parameters which can be used to determine the control settings of programmable temperature responsive neutron modifying structures 930 include power levels, neutron levels, neutron spectrum, neutron absorption, fuel burnup levels, and the like. In one example, the neutron modifying structures 930 are used to control fuel burnup levels to relatively low (e.g., <50%) levels in order to achieve high-rate “breeding” of nuclear fission fuel for use in other nuclear fission reactors, or to enhance suitability of the burnt nuclear fission fuel for subsequent re-propagation of a nuclear fission deflagration wave in a propagating nuclear fission deflagration wave reactor. Different control parameters can be used at different times, or in different portions of the reactor. It will be appreciated that the various neutron modifying methods discussed previously in the context of neutron modifying structures can also be utilized in programmable temperature responsive neutron modifying structures 930, including without limitation, the use of neutron absorbers, neutron moderators, combinations of neutron absorbers and/or neutron moderators, variable geometry neutron modifiers, and the like. According to other embodiments and referring now to FIGS. 10A and 10B, material can be nuclearly processed. As shown in FIG. 10A, nuclearly processable material 1020 (that has a set of non-irradiated properties) is placed in a propagating nuclear fission deflagration wave reactor 1000. A nuclear fission deflagration wave propagating burnfront 1030 is originated and propagated along a direction indicated by arrows 1040 as described above. The material 1020 is placed in neutronic coupling with a region of maximized reactivity 1010, that is the material is neutron irradiated, as the nuclear fission deflagration wave propagating burnfront 1030 propagates through or in the vicinity of the material 1020, thereby irradiating the material 1020 and conferring upon the material 1020 a desired set of modified properties. In one embodiment, the neutron irradiation of material 1020 may be controlled by the duration and/or extent of the nuclear fission deflagration wave propagating burnfront 1030. In another embodiment, the neutron irradiation of material 1020 may be controlled by control of the neutron environment (e.g., the neutron energy spectrum for Np237 processing) via neutron modifying structures. In another embodiment, the propagating nuclear fission deflagration wave reactor 1000 may be operated in a “safe” sub-critical manner, relying upon an external source of neutrons to sustain the propagating burnfront 1030, while using a portion of the fission-generated neutrons for nuclear processing of the material 1020. In some embodiments, the material 1020 may be present before nuclear fission ignition occurs within the propagating nuclear fission deflagration wave reactor 1000, while in other embodiments the material 1020 may be added after nuclear fission ignition. In some embodiments, the material 1020 is removed from the propagating nuclear fission deflagration wave reactor 1000, while in other embodiments it remains in place. Alternately and as shown in FIG. 10B, a nuclear fission deflagration wave propagating burnfront 1030 is initiated and propagated in a propagating nuclear fission deflagration wave reactor 1000 along a direction indicated by arrows 1040. Material 1050 having a set of non-irradiated properties is loaded into the propagating nuclear fission deflagration wave reactor 1000. As indicated generally at 1052, the material 1050 in transported into physical proximity and neutronic coupling with a region of maximized reactivity as the nuclear fission deflagration wave propagating burnfront 1030 passes through the material 1050. The material 1050 remains in neutronic coupling for a sufficient time interval to convert the material 1050 into material 1056 having a desired set of modified properties. Upon the material 1050 having thus been converted into the material 1056, the material 1056 may be physically transported out of the reactor 1000 as generally indicated at 1054. The removal 1054 can take place either during operation of the propagating nuclear fission deflagration wave reactor 1000 or afterward it has been “shut-off”, and can be performed in either a continuous, sequential, or batch process. In one example, the nuclearly processed material 1056 may be subsequently used as nuclear fission fuel in another nuclear fission reactor, such as without limitation LWRs or propagating nuclear fission deflagration wave reactors. In another nonlimiting example, the nuclearly processed material 1056 may be subsequently used within the nuclear fission ignitor of a propagating nuclear fission deflagration wave reactor. In one approach, thermal management may be adjusted to provide thermal control appropriate for any changes in operational parameters, as appropriate for the revised materials or structures. According to further embodiments, temperature-driven neutron absorption can be used to control a nuclear fission reactor, thereby “engineering-in” an inherently-stable negative temperature coefficient of reactivity (αT). Referring now to FIG. 11A, a nuclear fission reactor 1100 is instrumented with temperature detectors 1110, such as without limitation thermocouples. In this embodiment the nuclear fission reactor 1100 suitably can be any type of fission reactor whatsoever. To that end, the nuclear fission reactor 1100 can be a thermal neutron spectrum nuclear fission reactor or a fast neutron spectrum nuclear fission reactor, as desired for a particular application. The temperature detectors detect local temperature in the nuclear fission reactor 1100 and generate a signal 1114 indicative of a detected local temperature. The signal 1114 is transmitted to a control system 1120 in any acceptable manner, such as without limitation, fluid coupling, electrical coupling, optical coupling, radiofrequency transmission, acoustic coupling, magnetic coupling, or the like. Responsive to the signal 1114 indicative of the detected local temperature, the control system 1120 determines an appropriate correction (positive or negative) to local neutronic reactivity in the nuclear fission reactor 1100 to return the nuclear fission reactor 1100 to desired operating parameters (such as desired local temperatures for full reactor power). To that end, the control system 1120 generates a control signal 1124 indicative of a desired correction to local neutronic reactivity. The control signal 1124 is transmitted to a dispenser 1130 of neutron absorbing material. The signal 1124 suitably is transmitted in the same manner as the signal 1114. The neutron absorbing material suitably is any neutron absorbing material as desired for a particular application, such as without limitation Li6, B10, or Gd. The dispenser 1130 suitably is any reservoir and dispensing mechanism acceptable for a desired application, and may, for example, have the reservoir located remotely (e.g., outside the neutron reflector of the nuclear fission reactor 1100) from the dispensing mechanism 1130. The dispenser 1130 dispenses the neutron absorbing material within the nuclear fission reactor core responsive to the control signal 1124, thereby altering the local neutronic reactivity. Referring now to FIG. 11B and given by way of non-limiting example, exemplary thermal control may be established with a neutron absorbing fluid. A thermally coupled fluid containing structure 1140 contains a fluid in thermal communication with a local region of the nuclear fission reactor 1100. The fluid in the structure 1140 expands or contracts responsive to local temperature fluctuations. Expansion and/or contraction of the fluid is operatively communicated to a force coupling structure 1150, such as without limitation a piston, located external to the nuclear fission reactor 1100. A resultant force communicated by the force coupling structure 1150 is exerted on neutron absorbing fluid in a neutron absorbing fluid containing structure 1160. The neutron absorbing fluid is dispensed accordingly from the structure 1160, thereby altering the local neutronic reactivity. In another example, a neutron moderating fluid may be used instead of, or in addition to, the neutron absorbing fluid. The neutron moderating fluid changes the neutron energy spectrum and lowers the mean neutron energy of the local neutron environment, thereby driving down or lowering neutronic reactivity of nuclear fission fuel within the nuclear fission reactor 1100. In another example, the neutron absorbing fluid and/or the neutron modifying fluid may have a multiple phase composition (e.g., solid pellets within a liquid). FIG. 11C illustrates details of an exemplary implementation of the arrangement shown in FIG. 11B. Referring now to FIG. 11C, fuel power density in a nuclear fission reactor 1100′ is continuously regulated by the collective action of a distributed set of independently-acting thermostating modules, over very large variations in neutron flux, significant variations in neutron spectrum, large changes in fuel composition and order-of-magnitude changes in power demand on the reactor. This action provides a large negative temperature coefficient of reactivity just above the design-temperature of the nuclear fission reactor 1100′. Located throughout the fuel-charge in the nuclear fission reactor 1100′ in a 3-D lattice (which can form either a uniform or a non-uniform array) whose local spacing is roughly a mean free path of a median-energy-for-fission neutron (or may be reduced for redundancy purposes), each of these modules includes a pair of compartments 1140′ and 1160′, each one of which is fed by a capillary tube. The small thermostat-bulb compartment 1160′ located in the nuclear fission fuel contains a thermally sensitive material, such as without limitation, Li7, whose neutron absorption cross-section may be low for neutron energies of interest, while the relatively large compartment 1140′ positioned in a different location (e.g., on the wall of a coolant tube) may contain variable amounts of a neutron absorbing material, such as without limitation, Li6, which has a comparatively large neutron absorption cross-section. Lithium melts at 453 K and 1-bar-boils at 1615 K, and therefore is a liquid across typical operating temperature ranges of the nuclear fission reactor 1100′. As the fuel temperature rises, the thermally sensitive material contained in the thermostat-bulb 1160′ expands, and a small fraction of it is expelled (approximately 10−3, for a 100K temperature change in Li7), potentially under kilobar pressure, into the capillary tube which terminates on the bottom of a cylinder-and-piston assembly 1150′ located remotely (e.g., outside of the radiation shield) and physically lower than the neutron absorbing material's intra-core compartment 1140′ (in the event that gravitational forces are to be utilized). There the modest volume of high-pressure thermally sensitive material drives a swept-volume-multiplying piston in the assembly 1150′ which pushes a potentially three order-of-magnitude larger volume of neutron absorbing material through a core-threading capillary tube into an intra-core compartment proximate to the thermostat-bulb which is driving the flow. There the neutron absorbing material, whose spatial configuration is immaterial as long as its smallest dimension is less than a neutron mean free path, acts to absorptively depress the local neutron flux, thereby reducing the local fuel power density. When the local fuel temperature drops, neutron absorbing material returns to the cylinder-and-piston assembly 1150′ (e.g., under action of a gravitational pressure-head), thereby returning the thermally sensitive material to the thermostat-bulb 1160′ whose now-lower thermomechanical pressure permits it to be received. It will be appreciated that operation of thermostating modules does not rely upon the specific fluids (Li6 and Li7) discussed in the above exemplary implementation. In one exemplary embodiment, the thermally sensitive material may be chemically, not just isotopically, different from the neutron absorbing material. In another exemplary embodiment, the thermally sensitive material may be isotopically the same as the neutron absorbing material, with the differential neutron absorbing properties due to a difference in volume of neutronically exposed material, not a difference in material composition. Referring now to FIG. 12, in another embodiment a propagating nuclear fission deflagration wave reactor 1200 operates at core temperatures significantly lower than core temperatures of nuclear fission reactors of other embodiments. While nuclear fission reactors of other embodiments may operate at core temperatures in the order of around 1,000K or so, (e.g., to enhance electrical power conversion efficiency) the propagating nuclear fission deflagration wave reactor 1200 operates at core temperatures of less than around 550K, and some embodiments operate at core temperatures of between around 400K and around 500K. Reactor coolant 1210 transfers heat from nuclear fission in the propagating nuclear fission deflagration wave reactor 1200. In turn thermal energy 1220 is transferred from the reactor coolant 1210 to a thermally driven application. Given by way of non-limiting examples, exemplary thermally driven applications include desalinating seawater, processing biomass into ethanol, space-heating, and the like. In another embodiment, a propagating nuclear fission deflagration wave reactor 1200 may operate at core temperatures above 550K, and utilize thermal energy 1220 from the reactor coolant 1210 for thermally driven applications instead of or in addition to, electrical power generation applications. Given by way of non-limiting examples, exemplary thermally driven applications include thermolysis of water, thermal hydrocarbon processing, and the like. Referring now to FIG. 13, in another embodiment nuclear fission fuel can be removed after it has been burned. A nuclear fission deflagration wave propagating burnfront 1310 is initiated and propagated in a modular nuclear fission reactor core 1300 along a direction indicated by arrows 1320 toward modules 1340 of nuclear fission fuel material, thereby establishing a region 1330 of maximized reactivity as discussed above. As discussed above, the modules 1340 of nuclear fission fuel material may be considered “burnt” after the propagating burnfront 1310 has propagated the region 1330 of maximized reactivity through the module 1340 of nuclear fission fuel material. That is, the modules 1340 of nuclear fission fuel material “behind” the region 1330 of maximized reactivity may be considered “burnt”. Any desired number of the “burnt” modules 1340 of nuclear fission fuel material (behind the region 1330 of maximized reactivity) are removed, as generally indicated at 1350. As generally indicated at 1360, nuclear fission fuel material has been removed from the nuclear fission reactor core 1300. Referring now to FIGS. 14A and 14B, according to other embodiments nuclear fission fuel can be re-burned in place without reprocessing. As shown in FIG. 14A, a propagating nuclear fission deflagration wave reactor 1400 includes regions 1410 and 1420. A nuclear fission deflagration wave burnfront 1430 is initiated and propagated through the region 1410 toward the region 1420. The nuclear fission deflagration wave burnfront 1430 propagates through the region 1420 as a nuclear fission deflagration wave burnfront 1440. After the nuclear fission deflagration wave burnfront 1440 propagates into region 1420, and either before or after it reaches an end of the propagating nuclear fission deflagration wave reactor 1400, the nuclear fission deflagration wave burnfront 1440 is redirected or re-initiated and retraces a path of propagation away from the end of the propagating nuclear fission deflagration wave reactor 1400 back toward the region 1410. The nuclear fission deflagration wave burnfront 1440 propagates through the region 1410 as a nuclear fission deflagration wave burnfront 1450 away from the region 1420 toward an end of the propagating nuclear fission deflagration wave reactor 1400. The nuclear fission fuel in regions 1410 and 1420 is different during the repropagation of nuclear fission deflagration wave burnfronts 1440 and 1450 than it was during the previous propagation of nuclear fission deflagration wave burnfronts 1430 and 1440, due to changes in the amounts of fissile isotopes and the amounts of fission product “ash”. The neutron environment may differ during propagation and repropagation due to the above differences in the nuclear fission fuel, as well as other factors, such as without limitation, possible changes in the control of neutron modifying structures, thermal heat extraction levels, or the like. As shown in FIG. 14B (and as briefly mentioned in reference to FIG. 3C), the geometry of an embodiment of the propagating nuclear fission deflagration wave reactor 1400 forms a closed loop, such as an approximately toroidal shape. In this exemplary embodiment, the propagating nuclear fission deflagration wave reactor 1400 includes the regions 1410 and 1420 and a third region 1460 different from the regions 1410 and 1420. The nuclear fission deflagration wave burnfront 1430 is initiated and propagated through the region 1410 toward the region 1420. The nuclear fission deflagration wave burnfront 1430 propagates through the region 1420 as the nuclear fission deflagration wave burnfront 1440. The nuclear fission deflagration wave burnfront 1440 propagates through the region 1460 as a nuclear fission deflagration wave burnfront 1470. When the nuclear fission deflagration wave burnfronts 1430, 1440, and 1470 have propagated completely through the regions 1410, 1420, and 1460, respectively, nuclear fission fuel material in the regions 1410, 1420, and 1460 can be considered “burnt”. After the nuclear fission fuel material has been burnt, the nuclear fission deflagration wave burnfront 1430 is re-initiated and propagates through the region 1410 as a nuclear fission deflagration wave burnfront 1450. The re-initiation in region 1410 may occur without limitation, through the action of a nuclear fission igniter, such as discussed earlier, or may occur as a result of the decay and/or removal of nuclear fission products from the nuclear fission fuel material in region 1410, or may occur as the result of other sources of neutrons or fissile material, or may occur due to control of neutron modifying structures, as discussed previously. In another exemplary embodiment, the nuclear fission deflagration wave may potentially propagate in a plurality of directions. One or more propagation paths may be established, and may thereafter split into one or more separate propagation paths. The splitting of propagation paths may be accomplished without limitation by such methods as the configuration of the nuclear fission fuel material, the action of neutron modifying structures as discussed earlier, or the like. Propagation paths may be distinct, or may be reentrant. Nuclear fission fuel material may be burnt once, never, or multiple times. Repropagation of a nuclear fission deflagration wave multiple times through a region of nuclear fission fuel material may involve either the same or a different propagation direction. While some of the embodiments described previously illustrate nuclear fission fuel cores of substantially constant chemical and/or isotropic materials, in some approaches nuclear fission fuel cores of nonuniform material may be used. For example, in some approaches nuclear fission fuel cores may include regions having different percentages of uranium and thorium. In other approaches, nuclear fission fuel cores may include regions of different actinide or transuranic isotopes, such as without limitation different isotopes of thorium or different isotopes of uranium. In addition, mixtures of such different combinations may also be appropriate. For example, mixtures of thorium and of different uranium isotope ratios may provide different burning rates, temperatures, propagation features, localization, or other features. In other approaches, the nuclear fission fuel cores may include mixtures of “breedable” isotopes (such as Th232 or U238) along with other fissionable actinide or transuranic elements, such as without limitation, uranium, plutonium, americium, or the like. Additionally, such variations in chemicals, isotopes, cross sections, densities, or other aspects of the fuel or may vary radially, axially or in a variety of other spatial manners. For example, such variations may be defined according to anticipated variations in energy demand, aging, or other anticipated variations. In one aspect, where growth of energy demand in a region would be reasonably anticipated, it may be useful to define the fuel or materials to correlate to an expected increased demand of the region. In still another aspect, such variations may be implemented according to other approaches described herein. For example, the variations may be defined after initiation of burning using the modular approach is described herein or the multipath approaches described herein. In other approaches, movement of portions of the material may produce the appropriate material concentrations, positioning, ratios, or other characteristics. While the embodiments above have illustrated propagating nuclear fission deflagration wavefronts in fixed or variable fuel cores, in one aspect, propagating nuclear fission deflagration wavefronts may remain substantially spatially fixed while the fuel core or portions of the fuel core move relative to the wavefront. In one such approach, movement of the nuclear fission fuel core to maintain substantially localized positioning of the propagating nuclear fission deflagration wavefront can stabilize, optimize, or otherwise control thermal coupling to a cooling or heat transfer system. Or, in another aspect, controlled positioning of the propagating nuclear fission deflagration wavefront by physically displacing the nuclear fission fuel can simplify or reduce constraints upon other aspects of the nuclear fission reactor, such as the cooling system, neutron shielding, or other aspects of neutron density control. While a number of exemplary embodiments and aspects have been illustrated and discussed above, those of skill in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, and sub-combinations as are within their true spirit and scope. |
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description | The present invention relates generally to a measurement system and more particularly to a system for a measurement system with thickness calculation. The rapidly growing market for portable electronic devices, e.g. cellular phones, laptop computers, and tablet computers, is an integral facet of modern life. The multitude of portable devices represents one of the largest potential market opportunities for next generation manufacturing. These devices have unique attributes that have significant impacts on manufacturing integration, in that they must be generally small, lightweight, and rich in functionality and they must be produced in high volumes at relatively low cost. As an extension of the semiconductor industry, the electronics manufacturing industry has witnessed ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace. Manufacturing, materials engineering, and development are at the very core of these next generation electronics insertion strategies outlined in road maps for development of next generation products. Future electronic systems will be more intelligent, have higher density, use less power, operate at higher speed, and include mixed technology devices and assembly structures at lower cost than today. There have been many approaches to addressing the advanced manufacturing requirements of microprocessors and portable electronics with successive generations of semiconductors. Many industry road maps have identified significant gaps between the current semiconductor capability and the available supporting electronic manufacturing technologies. The limitations and issues with current technologies include increasing clock rates, electromagnetic interference, thermal loads, second level assembly reliability stresses, and cost. As these manufacturing systems evolve to incorporate more components with varied environmental needs, the pressure to push the technological envelope becomes increasingly challenging. More significantly, with the ever-increasing complexity, the potential risk of error increases greatly during manufacture unless monitoring during the fabrication process is performed. Thin films are an essential part of fabricating electronics. Thickness measurements for thin films are normally done by optical or X-ray based techniques in a fast and non-destructive fashion. The X-ray or optical techniques can include Ellipsometry, X-Ray Reflectivity (XRR), or X-Ray Fluorescence (XRF). The common inherent disadvantage of such techniques is the big measurement spots, the sizes of which are usually from several millimeters to several tens of microns. Therefore, for the purpose of tuning and monitoring of the thin film deposition processes, such measurements are usually performed either on blank substrates (e.g., silicon wafer) or on specially designed monitor pads on patterned wafers. Since the behavior of the thin film deposition processes on small patterned structures is often different from their behavior on the large monitor areas, the thickness results obtained cannot be used directly to assess the thickness on the small patterned structures. Due to such a limitation of the above mentioned thickness measurement techniques, scanning electron microscopy or transmission electron microscopy (TEM) imaging coupled with focus ion beam (FIB) or manual cross section, is often used to directly measure the thickness of the thin films on the small patterned structures. The cross section imaging is performed either on finished devices or on specially designed sacrificial patterns on patterned wafers. Either solution can be very expensive. Another disadvantage of the cross section imaging is that it is extremely slow. The whole process of cross section imaging of even one sampling spot often takes several hours to finish; therefore, it cannot achieve the statistical precision that can be achieved by the optical and X-ray based metrology techniques. An additional metrology challenge is measurement close to a substrate edge. As the integrated circuit (IC) manufactures strive to utilize more of the usable area of the wafer, film uniformity close to the very edge of the wafer is required and consequently measurements with two millimeters (mm) or even one-millimeter edge exclusion are demanded. The optical and X-ray based metrology tools have difficulty fulfilling such requirement because of their large spot sizes and the requirement of a flat substrate at the very edge of the wafer. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems. Thus, a need remains for thickness measurements of thin films on patterned wafers and especially those on the small patterned structures. Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art. The present invention provides a method of operation of a measurement system including: providing a specimen having a film; controlling a beam generator to direct a charged particle beam into the specimen; detecting a reference signal emitted from the specimen; normalizing the reference signal to create a film L-ratio; and determining a thickness of the film by correlating the film L-ratio to a calibration curve. The present invention provides a measurement system, including: a control module for providing a specimen having a film; a beam generator, coupled to the control module, for directing a charged particle beam into the specimen; a detector, coupled to the beam generator, for detecting an reference signal emitted from the specimen; and an analysis unit, coupled to the detector, for normalizing the reference signal to create a film L-ratio and determining a thickness of the film by correlating the film L-ratio to a calibration curve. Certain embodiments of the invention have other steps or elements in addition to or in place of those mentioned above. The steps or elements will become apparent to those skilled in the art from a reading of the following detailed description when taken with reference to the accompanying drawings. The following embodiments are described in sufficient detail to enable those skilled in the art to make and use the invention. It is to be understood that other embodiments would be evident based on the present disclosure, and that system, process, or mechanical changes can be made without departing from the scope of the present invention. In the following description, numerous specific details are given to provide a thorough understanding of the invention. However, it will be apparent that the invention can be practiced without these specific details. In order to avoid obscuring the present invention, some well-known circuits, system configurations, and process steps are not disclosed in detail. The drawings showing embodiments of the system are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing FIGs. Similarly, although the views in the drawings for ease of description generally show similar orientations, this depiction in the FIGs. is arbitrary for the most part. Generally, the invention can be operated in any orientation. In addition, where multiple embodiments are disclosed and described having some features in common, for clarity and ease of illustration, description, and comprehension thereof, similar and like features one to another will ordinarily be described with similar reference numerals. For expository purposes, the term “horizontal” as used herein is defined as a plane parallel to a top surface of the substrate, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms, such as “above”, “below”, “bottom”, “top”, “side” (as in “sidewall”), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane, as shown in the figures. The term “on” means that there is direct contact between elements without having any intervening material. The term “module” referred to herein can include software, hardware, or a combination thereof in the present invention in accordance with the context in which the term is used. For example, the software can be machine code, firmware, embedded code, and application software. Also for example, the hardware can be circuitry, processor, computer, integrated circuit, integrated circuit cores, a microelectromechanical system (MEMS), passive devices, environmental sensors including temperature sensors, or a combination thereof. Referring now to FIG. 1, therein is shown a cross-sectional view of a measurement system 100 in an embodiment of the present invention. The measurement system 100 can include techniques including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and wavelength dispersive spectroscopy (WDS) for film thickness and non-uniformity measurement on patterned or blank film. The measurement system 100 can use SEM-, EDS-, or WDS-based technique for thickness measurements of thin films on patterned wafers and especially those on the small patterned structures. The same technique can be suitable for the thickness measurements on blanket wafers with zero edge-exclusion requirements. The measurement system 100 can use a SEM together with an energy dispersive X-ray detector (EDX), a wavelength λ-ray detector (WDX), or a combination thereof to detect characteristic X-rays from a thin film and silicon (Si) substrate from areas of interest on the wafer. The measurement system 100 is shown having a beam generator 102, which directs a charged particle beam 104 toward a specimen 106. The beam generator 102 produces the charged particle beam 104 as an electron beam. The beam generator 102 can be a scanning electron microscope or an electron emitter such as a thermionic emitter, a photocathode emitter, a cold emission emitter, or a plasmas source emitter. The charged particle beam 104 can be directed toward the specimen 106. The specimen 106 can be a substrate 108 having a film 110 formed thereon. The substrate 108 is defined as a structure capable of providing structural support for components or the film 110 formed there over. The substrate 108 can be a support structure including a silicon substrate, gallium arsenide substrate, carbon substrate, or ceramic substrate. The charged particle beam 104 can impact the specimen 106 with enough energy to penetrate the film 110 and the substrate 108. The charged particle beam 104 can impact the specimen 106 in a diameter of less than 10 micrometers (μm); however, the size of the charged particle beam 104 impact can range between 1-100 μm in diameter. It has been discovered that utilizing the beam generator 102 impinging the specimen 106 with the charged particle beam 104 allows for small measurement spots down to 1 μm. The small measurement spots enable measurements of the film 110 on the substrate 108 of wafers with a zero-edge exclusion requirement. The zero-edge exclusion requirement allows the film 110 to be formed at edges of the substrate 108 such that edges of the film 110 and the substrate 108 substantially aligned with each other resulting in peripheral areas at the edges of the substrate 108 completely utilized with the film 110 directly formed thereon. The film 110 can be formed above the substrate 108 to cover the substrate 108. The substrate 108 and the film 110 can be processed to include a pattern 112. The pattern 112 is a complex geometric pattern with multi-sided structures formed in the substrate 108 and the film 110. For example, the pattern 112 can be a line and trench pattern or other geometric patterns. The film 110 can be a metallic or oxide film such as copper (Cu), aluminum, or silicon oxide. The charged particle beam 104 can bombard the specimen 106 and interact with the substrate 108 and the film 110 to emit reference signals 114. The reference signals 114 can include energies in a range of 100 (102) electron volts (eV) to 105 electron volts (eV) or frequencies in a range of 3×1016 hertz (Hz) to 3×1029 hertz (Hz). For example, the reference signals 114 can be a frequency of an electromagnetic radiation including X-rays, Auger electrons, or any other energy sources. The charged particle beam 104 can be deflected in an elastic scattering event or absorbed by the specimen 106 in an inelastic scattering event that changes the energy of the charged particle beam 104 after impact. When the charged particle beam 104 interacts in an inelastic way with the specimen 106, the charged particle beam 104 excites electrons within inner orbitals of atoms (not shown) within the specimen 106. These electrons can be ejected from the inner orbitals leaving an electron hole. When a higher energy electron from the atom fills the hole, the electron emits electromagnetic radiation in the form of the reference signals 114. The film 110 and the substrate 108 can have unique atomic structures (not shown). When the charged particle beam 104 interacts in an inelastic way with the film 110 or the substrate 108 to produce the reference signals 114, the frequency signal or energy of the reference signals 114 will be different for the substrate 108 and for the film 110 because of the unique atomic structures. The reference signals 114 can be detected by detectors 116 positioned above the specimen 106. The detectors 116 can be dispersive spectrometers such as energy-dispersive spectrometers, wavelength-dispersive spectrometers, electron dispersive X-ray spectroscopy, wavelength dispersive X-ray spectroscopy, or a combination thereof. The detectors 116 can detect the reference signals 114 resulting from inelastic interaction between the charged particle beam 104 and the specimen 106. For example, the detectors 116 can be electromagnetic radiation detectors including X-ray receivers with counters. The detectors 116 can be coupled to an analysis unit 118. The analysis unit 118 is configured to analyze the reference signals 114 collected by the detectors 116. The analysis unit 118 can be a processing system or computing system such as a personal computer or a workstation. The analysis unit 118 can include a calculation module 120. The calculation module 120 is a structure that provides part of a class of computational algorithms that rely on repeated random sampling to compute a property. The calculation module 120 can be applied with the analysis unit 118 as a computer simulation of an electron-atom interaction and associated events including generation of the reference signals 114 by the inelastic interaction of the charged particle beam 104 with the film 110 or the substrate 108. For example, the calculation module 120 can be implemented using a computational algorithm including a Monte Carlo method. The analysis unit 118 utilizes the calculation module 120 to determine how thick the film 110 is over the substrate 108 based on the random interaction of the charged particle beam 104 with the film 110 and the substrate 108. Examples of the Monte Carlo method are the National Institute of Standards and Technology Desktop Spectrum Analyzer II (DTSA-II) and the Cambridge quantum Monte Carlo code CASINO. Referring now to FIG. 2, therein is shown a magnified cross-sectional view of section A of FIG. 1. Section A shows the substrate 108 and the film 110 in greater detail. The substrate 108 and the film 110 are shown having the pattern 112 formed therein. The film 110 is shown covering the substrate 108 and having the pattern 112 formed therein. The film 110 is also shown having a thickness 202. The thickness can vary over the substrate 108 and within the pattern 112. The charged particle beam 104 is shown scanning across the pattern 112 and is shown impacting the film 110 and the substrate 108 generating the reference signals 114. The charged particle beam 104 can scan over the pattern 112 with a raster (side to side then incrementing ninety degrees) motion, with a highly localized pinpoint sampling motion or defocused point over several repeat units of the pattern 112 at different locations on the substrate 108. The charged particle beam 104 can impact the pattern 112 of the film 110 and the substrate 108 randomly with elastic or inelastic interactions. The reference signals 114 can be substrate signals 204 or film signals 206. The film signals 206 are the reference signals 114 that are emitted from the interaction between the charged particle beam 104 and the film 110. The substrate signals 204 are the reference signals 114 that are emitted from the interaction between the charged particle beam 104 and the substrate 108. Referring now to FIG. 3, therein is shown a control flow of the measurement system 100. The measurement system 100 is shown having a calibration module 302. The calibration module 302 stores signals measured by the detectors 116 of FIG. 1 for various predetermined references including elements from the film 110 of FIG. 1 and the substrate 108 of FIG. 1. For example, the predetermined references can be known standards that are used as references for comparison or calculation purposes. The calibration module 302 can determine or detect a film-only peak 304 and a substrate-only peak 306. The film-only peak 304 is a peak intensity of the reference signals 114 of FIG. 1 when the charged particle beam 104 of FIG. 1 interacts only with a bulk predetermined reference including the same element(s) as in the film 110. The substrate-only peak 306 is a peak intensity of the reference signals 114 when the charged particle beam 104 interacts only with a bulk predetermined reference including the same element(s) as in the substrate 108. The term “bulk” refers to a reference or a material into which the charged particle beam 104 penetrates into but cannot go through it. Depending on the structure to be analyzed, one signal in the calibration module 302 can be used as film-only reference or substrate-only reference. All the signals stored in the calibration module 302 are measured under the same conditions. For example, in case of EDS, it would be the same configuration setup as in FIG. 1 and the same electron beam energy and dose (current×time). For example, other materials different from copper can be used for the film 110 in semiconductor processing. As a specific example, the other materials can include Tantalum, Hafnium, Tungsten, Titanium, Aluminum, Germanium, Cobalt, and their compounds including oxides and nitrides. Also for example, a table of data or information can be generated using Monte Carlo simulation results for K-ratios and L-ratios for various thicknesses of the film 110 for each of the other materials and different structures. The calibration module 302 can obtain the film-only peak 304 and the substrate-only peak 306 whenever the configuration of the beam generator 102 of FIG. 1 or the detectors 116 has changed. The calibration module 302 can be implemented using the beam generator 102 and the detectors 116. The calibration module 302 can further process the reference signals 114 within the analysis unit 118 of FIG. 1 to identify the film-only peak 304 and the substrate-only peak 306. The calibration module 302 can be coupled to a control module 308. The control module 308 provides the introduction of the specimen 106 of FIG. 1 to be tested. Once the specimen 106 is positioned properly below the beam generator 102, the control module 308 invokes an emittance module 310 coupled to the control module 308. The emittance module 310 controls the beam generator 102 and directs the charged particle beam 104 toward the specimen 106. When the charged particle beam 104 impacts the specimen 106, a detection module 312, coupled to the emittance module 310, can be invoked. The detection module 312 returns a detection spectrum 314 from the analysis unit 118 based on the reference signals 114 detected by the detectors 116. The detection spectrum 314 can be a frequency spectrum including an X-ray spectrum obtained from energy dispersive spectroscopy or from wavelength dispersive spectroscopy. The detection spectrum 314 for the specimen 106 can be most conveniently obtained by the calculation module 120 of FIG. 1. As an example, a particular thin film or thin film stack with defined thickness, composition and stack structure, and pattern geometry (including the simplest case of no pattern) can be obtained by the calculation module 120. The calculation module 120 has been proven to accurately simulate the detection spectrum 314 including an EDS spectrum. Therefore, the calculation module 120 can be set up for a series of different conditions corresponding to the variables of interest, e.g. thickness, and generate a curve for calibration, which can be used for the EDS from real acquisition. The calculation module 120 can model the detection spectrum 314 having a film peak 316 and a substrate peak 318 based on the film signals 206 of FIG. 2 and the substrate signals 204 of FIG. 2, respectively. The film peak 316 and the substrate peak 318 are peak intensities of the reference signals 114 detected by the detectors 116 and analyzed using the calculation module 120 by the analysis unit 118. The film signals 206 and the substrate signals 204 can be used in the calculation module 120 as variables of corresponding to the thickness 202 of FIG. 2. The film peak 316 is a signal intensity collected from the film 110 as a sample to be measured. For example, the sample to be measured can be a thin film on a patterned substrate. The substrate peak 318 is a signal intensity collected from the substrate 108 as a sample to be measured. The film peak 316 and the substrate peak 318 are measured at the same conditions. For example, in case of EDS, all the signals can be collected simultaneously by the detectors 116 resulting in no extra requirements. The film peak 316 and the substrate peak 318 can be output from the detection module 312 to a first normalization module 320. The term normalize is defined as conforming data to those data stored in the first normalization module 320 to eliminate energy function differences of the detectors 116 as used in different systems and simulations. K-prime ratios (K′-ratios) can be obtained for elements from both the film 110 and the substrate 108. K-prime denotes a difference compared to a predetermined K-ratio, where the dose of charged particles are to be the same for both spectra, which is not required here for the K-prime ratios. The K-prime ratios become the predetermined K-ratio when the doses are the same. Film K-prime ratios 322 of the film 110 can be calculated by Equation 1: K ′ ( A ) = Intensity film Element A Intensity standard Element A , ( Equation 1 ) where IntensityfilmElementA denotes an intensity from the detection module 312 associated film with a film element A characterized or identified by the film peak 316 and IntensitystandardElementA denotes an intensity from the detection module 312 associated with the film element A from a predetermined reference having element A characterized or identified by the film-only peak 304. Substrate K-prime ratios 324 can be calculated by Equation 2: K ′ ( B ) = Intensity film Element B Intensity standard Element B , ( Equation 2 ) where IntensitysubstrateElementB denotes an intensity from the detection module 312 associated with the substrate 108 characterized or identified by the substrate peak 318 and IntensitystandardElementB denotes an intensity from the detection module 312 associated with the substrate 108 characterized or identified by the substrate-only peak 306. The film K-prime ratios 322 and the substrate K-prime ratios 324 eliminate influences from the detectors 116. It has been discovered that the film K-prime ratios 322 and the substrate K-prime ratios 324 allow measurement of the specimen 106 having complex geometry directly without the need for blank substrate measurement, specially designed monitor pads, or cross-section imaging. This has been shown to increase process control allowing tighter quality standards during fabrication. It has further been discovered that utilizing the film K-prime ratios 322 and the substrate K-prime ratios 324 allow the faster tool maintenance and qualification by removing irregularities in the configuration of the beam generator 102 and the detectors 116 thus reducing expense and eliminating measurement variability resulting in improved accuracy. The film K-prime ratios 322 and the substrate K-prime ratios 324 outputs from the first normalization module 320 can be input into a second normalization module 326 coupled to the first normalization module 320. The second normalization module 326 generates film L-ratios 328 to normalize the film K-prime ratios 322 for intensity. The film L-ratios 328 can be calculated by Equation 3: L ( film ) = K ′ ( film ) K ′ ( film ) + K ′ ( substrate ) , ( Equation 3 ) The second normalization module 326 generates substrate L-ratios 330 to normalize the substrate K-prime ratios 324 for intensity. The substrate L-ratios 330 can be calculated by Equation 4: L ( substrate ) = K ′ ( substrate ) K ′ ( film ) + K ′ ( substrate ) , ( Equation 4 ) where K′(film) denotes the film K-prime ratios 322 and K′(substrate) denotes the substrate K-prime ratios 324. L-ratios of either the film 110 or the substrate 108 can be used. The film L-ratios 328 and the substrate L-ratios 330 eliminate influences from control of the dose of the charged particle beam 104 and energy function of the detectors 116. It has been discovered that the film L-ratios 328 and the substrate L-ratios 330 have the special property of being constant regardless of current changes in the charged particle beam 104 thereby allowing increased capacity and reduced measurement time because detection and calculation of the thickness 202 based on the film L-ratios 328 and the substrate L-ratios 330 does not need extremely refined control over current and exposure time of the charged particle beam 104. The second normalization module 326 can be implemented in the analysis unit 118. The output of the second normalization module 326 can be input into a match module 332 coupled to the second normalization module 326 and implemented on the analysis unit 118. The match module 332 matches the film L-ratios 328 of the second normalization module 326 to a calibration curve 334 generated by the calibration module 302. The calibration curve 334 has been discovered and shown as a graph correlating the film L-ratios 328 to the thickness 202 of the film 110 providing improved method for calculation of the thickness 202. The calibration curve 334 can be established by using the detection spectrum 314 to calculate the film L-ratios 328 to a series of the film 110 that has been prepared with a predetermined value of the thickness 202. The calibration curve 334 can also be established using Monte Carlo simulation to simulate the spectra for a pattern structure of the film 110 with a series of the thickness 202 of the film 110 and simulate the spectra of same standard or reference as in the calibration module 302 to construct the film L-ratios 328. As an example, the thickness 202 of a copper film, film K-ratios 336 of the copper film, substrate K-ratios 338 of a silicon substrate, and the film L-ratios 328 can be represented in Table 1 as: TABLE 1Cu ThicknessK-RatioL-Ratio(nm)CuSiCu/(Cu + Si)001050.0790.8870.082100.1640.7570.178150.2510.6470.279200.3570.5380.399250.4430.4330.506300.5380.3440.610350.6270.2650.703400.6960.2080.770450.7420.1600.823500.8260.1060.8861000.9950.0040.996 Table 1 can be generated based on Monte Carlo simulation results for the film K-ratios 336, the substrate K-ratios 338, and the film L-ratios 328 for various thicknesses of the film 110 of copper on the substrate 108 of silicon. The simulation is based on the assumptions of the film 110 having a certain density, the film 110 having the pattern 112 of FIG. 1 with a certain geometry, the charged particle beam 104 running at 5 kilo-electron volts (keV) energy and at normal incidence, and the detectors 116 having a 35-degree take-off angle. The calibration curve 334 can be generated by graphing the film L-ratios 328 and the thickness 202 of the film 110 in Table 1. The thickness 202 of the film 110 is shown in nanometers (nm). When the thickness 202 of the film 110 decreases, the film K-ratios 336 can be closer to zero indicating a large difference between the film-only peak 304 and the film signals 206. As the thickness 202 increases near 100 nm, the film peak 316 converges with the film-only peak 304 and the film K-ratios 336 become closer to one. This indicates that the film signals 206 detected by the detectors 116 from the charged particle beam 104 interactions with the pattern 112 differ less, from the film-only peak 304, as the thickness 202 increases. Conversely, the substrate K-ratios 338 are closest to one when the thickness 202 is small and move toward zero when the thickness 202 increases. This indicates that the substrate signals 204 are closer to the substrate-only peak 306 when the thickness 202 is low but diverge from the substrate-only peak 306 as the thickness 202 increases. A different beam voltage (energy) can be set up to accommodate film thicknesses. Table 1 shows the film L-ratios 328 become 1 (maximum) for the thickness 202 of the film 110 larger than 100 nm. To measure thicker films, larger beam voltage (e.g., 10 kV or more) can be used. Either the film L-ratios 328 of the film 110 or the substrate L-ratios 330 of the substrate 108 can be used. Referring now to FIG. 4, therein is shown an example graph of the calibration curve 334. The calibration curve 334 is shown having the film L-ratios 328 of Table 1 plotted against the thickness 202 of Table 1. The thickness 202 is shown in nanometers. The film L-ratios 328 show a positive correlation with the thickness 202. The film L-ratios 328 can increase as the thickness 202 increases. The rate of the film L-ratios 328 can decrease slightly as the thickness 202 increases. Correlating the film L-ratios 328 with the thickness 202 has the advantage that only the voltage not the current of the beam generator 102 of FIG. 1 must be controlled to compute the thickness 202 of the film 110 of FIG. 1; thus decreasing measurement time and increasing throughput. Referring now to FIG. 5, therein is shown an example graph of the detection spectrum 314. The detection spectrum 314 is shown with the film peak 316 next to the substrate peak 318 generated from the film 110 of FIG. 1 and the substrate 108 of FIG. 1, respectively. The film peak 316 can be plotted based on the film signals 206 of FIG. 2 analyzed by the calculation module 120 of FIG. 1. Intensity 506 of the film peak 316 is shown along the left side of the graph. An energy range 508 of the film peak 316 is shown along a bottom side of the graph and measured in electron volts. The composition of the film 110 can be determined by the energy range 508 of the film peak 316. The film peak 316 can, for example, indicate the reference signals 114 of FIG. 1 generated by the charged particle beam 104 of FIG. 1 running at 5 kV interacting with the film 110 of copper and a small pattern structure. The substrate peak 318 can be plotted based on the substrate signals 204 of FIG. 2 analyzed by the calculation module 120. The intensity 506 of the substrate peak 318 is shown along the left side of the graph. The energy range 508 of the substrate peak 318 is shown along the bottom side of the graph measured in electron volts. The substrate peak 318 can, for example, indicate the reference signals 114 generated by the charged particle beam 104 running at 5 kV interacting with the substrate 108 of silicon. As an example, the detection spectrum 314 measured from 8 different locations on the specimen 106 of FIG. 1 can be used to calculate the thickness 202 of FIG. 2 by matching the film L-ratios 328 of FIG. 3 with the calibration curve 334 of FIG. 3 using Table 1 or FIG. 4. TABLE 2LocationL-RatioThickness (nm)10.61930.48920.59729.37530.59129.09040.61130.07850.58328.69460.63031.05270.61530.28580.54626.962 Table 2 can exemplify the thickness 202 extracted with the film L-ratios 328 from the calibration curve 334. Table 2 shows the thickness 202 with an average value of 29.5 nm and a standard deviation of 4.1%. Referring now to FIG. 6, therein is shown an example graph of a response function of the detectors 116 of FIG. 1. The graph depicts an efficiency 602 as a function of an energy 604 of the reference signals 114 of FIG. 1. The efficiency 602 is defined as a response of how the detectors 116 respond to captured signals. The efficiency 602 can approach 100% when the energy 604 is greater than 20,000 electron volts (eV). For example, the graph can represent an imaginary detector efficiency function. The substrate signals 204 of FIG. 2 and the film signals 206 of FIG. 2 including electromagnetic radiation such as X-rays can be excited. The substrate signals 204 and the film signals 206 excited from electrons interaction with a sample can be a characteristic of materials of the sample. The substrate signals 204 and the film signals 206 can be described in energy in electron volts (eV). For example, all elements in the materials (except Hydrogen and Helium) can excite their characteristic (group) of X-rays. The energy 604 of the substrate signals 204 and the film signals 206 can be element dependent. For example, Oxygen (O) excites an X-ray of 525 eV, Fluorine (F) excites an X-ray of 677 eV, and Iron (Fe) excites a group at 6404 eV, 6391 eV, 7057 eV, 705 eV, and 719 eV. From the substrate signals 204 and the film signals 206 detected, constituents of materials in the substrate 108 of FIG. 1 and the film 110 of FIG. 1, respectively, can be determined. The response function (or detector function) of the detectors 116 can indicate how the detectors 116 respond to captured signals as well as converting and recording them. One of the most important responses can include the efficiency 602 or yield to different energies of the substrate signals 204 and the film signals 206. For example, the efficiency 602 indicates that the detectors 116 can be able to capture 75% of the substrate signals 204 or the film signals 206 of 500 eV energy or 25% of the substrate signals 204 or the film signals 206 for 250 eV energy. Referring now to FIG. 7, therein is shown an example graph of an energy count 702 of the film signals 206 of FIG. 2. The graph depicts the energy count 702 associated with the energy 604. The energy count 702 indicates how many of the substrate signals 204 of FIG. 2 or the film signals 206 at the energy 604. A total energy can be determined as an integral of the energy count 702 as a function of the energy 604. The graph depicts the total energy as an area, shown with a hatch pattern, under the energy count 702. For example, the graph can represent an EDS spectrum of a pure bulk copper from a 15-kV electron beam. For example, the graph can represent the energy count 702 of the film 110 of FIG. 1 including a pure bulk copper. Also for example, the graph depicts the film peak 316 of approximately 430,000 counts, 40,000 counts, and 10,000 counts of the film signals 206 at 1 keV, 8 keV, and 9 keV, respectively. Each of the substrate signals 204 and the film signals 206 is a single energy. When multiple of the substrate signals 204 or the film signals 206 that are the same are captured by the detectors 116 of FIG. 1, they are displayed as the film peak 316 or the substrate peak 318 of FIG. 3, respectively, from a low background. Depending on the mechanism of the detectors 116, the film peak 316 or the substrate peak 318 is not a single line on the energy 604 as shown in the graph. How fine the detectors 116 can present the substrate signals 204 and the film signals 206 is called a resolution. The response function therefore can also be based on the resolution. For example, wavelength dispersive spectrometer (WDS) can include at least 10 times better energy resolution than energy dispersive spectrometer (EDS). The substrate signals 204 and the film signals 206 can depend on materials and structures of the sample, energy of source electrons, direction of the source electrons traveling to the sample, and amount of the source electrons. The latter can be directly proportional to a number of controllable and measurable values including current and exposure time of the source electrons of sample exposure to electron beam. A (small) portion of the substrate signals 204 and the film signals 206 can be captured by the detectors 116. The portion can depend on the sample, locations of the detectors 116 including a take-off angle or an angle of the detectors 116 to a sample surface and a beam impinging point, a solid angle of the detectors 116, and the response function of the detectors 116. Therefore, detection of the substrate signals 204 and the film signals 206 can be based on a combination of factors described in two paragraphs above. Each of the film K-prime ratios 322 of FIG. 3 and the substrate K-prime ratios 324 of FIG. 3 is a ratio of intensity of the same peak between the spectra from an unknown and a reference acquired with the same conditions. The film K-prime ratios 322 and the substrate K-prime ratios 324 cancel out the response function of the detectors 116. For example, the same peak can be a peak of an X-ray at 525 eV for Oxygen. Therefore, the film K-prime ratios 322 and the substrate K-prime ratios 324 of a sample or a sample-reference combination can be the same for different detectors. There can be multiple elements from a sample to be analyzed. Therefore, multiple references can be used. For example, during a semiconductor process, monitoring of thousands of measurements, using the film K-prime ratios 322 and the substrate K-prime ratios 324 would be based on the same current and time control/measurement for all measurements. Using the film L-ratios 328 of FIG. 3 and the substrate L-ratios 330 of FIG. 3 would ease the monitoring with the references measured under the same condition of electron current×exposure time, and for each same the X-ray is detected under the same condition of electron current×exposure time. For the former, there can be only a few of the references to be measured for one time only. This information can be stored for subsequent measurements. For the latter, in EDS, the detectors 116 can detect all X-ray simultaneously, and therefore it is automatically fulfilled. In case of WDS and other techniques, during the short period of single sample measurement, the beam current variation can be negligible, so only timing control can be required. The calibration curve 334 of FIG. 3 of the film L-ratios 328 or the substrate L-ratios 330 versus the thickness 202 of FIG. 2 can be stored. The calibration curve 334 can be generated from either Monte Carlo simulation or direct measurement from sample structures of the references and measured intensity from several of the references, to measure the thickness 202 if density of the film 110 is known. The thickness 202 can be determined by a) calculating the film L-ratios 328 and the substrate L-ratios 330 by using the spectra from the sample and the references and then b) comparing the film L-ratios 328 and the substrate L-ratios 330 to the calibration curve 334. Uniformity of the thickness 202 or a percentage of the thickness 202 variation over multiple locations would not require the exact knowledge of the density of the film 110, hence is easier and more accurate. Therefore, the uniformity of the thickness 202 of the film 110 can be measured from different patterns including narrow versus thick lines, which is of vast importance. The measurement system 100 of FIG. 1 is not limited to the film 110 on the substrate 108 of FIG. 1 but multiple of the film 110 having different materials and structures on the substrate 108 can also work in the same fashion. Referring now to FIG. 8, therein is shown a flow chart of a method 800 of operation of the measurement system 100 of FIG. 1 in a further embodiment of the present invention. The method 800 includes: providing a specimen having a film in a block 802; controlling a beam generator to direct a charged particle beam into the specimen in a block 804; detecting a reference signal emitted from the specimen in a block 806; normalizing the reference signal to create a film L-ratio in a block 808; and determining a thickness of the film by correlating the film L-ratio to a calibration curve in a block 810. Thus, it has been discovered that the measurement system of the present invention furnishes important and heretofore unknown and unavailable solutions, capabilities, and functional aspects for a measurement system with thickness calculation. The resulting processes and configurations are straightforward, cost-effective, uncomplicated, highly versatile, accurate, sensitive, and effective, and can be implemented by adapting known components for ready, efficient, and economical manufacturing, application, and utilization. Another important aspect of the present invention is that it valuably supports and services the historical trend of reducing costs, simplifying systems, and increasing performance. These and other valuable aspects of the present invention consequently further the state of the technology to at least the next level. While the invention has been described in conjunction with a specific best mode, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the scope of the included claims. All matters hithertofore set forth herein or shown in the accompanying drawings are to be interpreted in an illustrative and non-limiting sense. |
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044712260 | claims | 1. A safety housing for portable radiation applicators comprising: an applicator assembly including a radiation source, cable means furnishing power and control connections to the radiation source and a radiation port located on a first surface of the applicator assembly, through which radiation is directed to a surface to be irradiated; and a locator plate which is positioned between the surface to be irradiated and the radiation port and which supports the applicator on the surface to be irradiated, said plate being a means into which the applicator assembly fits with close clearances, said plate containing radiation sealing means to prevent peripheral leakage of radiation and including an opening which aligns with the radiation port on the applicator assembly when the applicator assembly is positioned within the locator plate with the radiation port directed at the surface to be irradiated. 2. The safety housing of claim 1 further comprising a force actuated switch means, located on the first surface of the applicator assembly and electrically interconnected with the radiation source, to prevent operation of the radiation source unless the applicator is properly fit in the locator plate and the force actuated switch means is forced against a surface of the locator plate to be activated. 3. The safety housing of claim 2 further comprising a mechanical lock-out mechanism spring loaded to interfere with the action of the force actuated switch, unless a positive action is performed to release the force actuated switch. 4. The safety housing of claim 1 further including a magnetic switch located adjacent to a surface of the applicator assembly and electrically interconnected with the radiation source; and a magnet attached to the locator plate at a location which aligns with the magnetically activated switch when the applicator assembly is properly positioned within the locator plate. 5. The safety housing of claim 1 further including a gas supply means within the applicator assembly directing gas to the region of the radiation port to blanket a work area exposed to radiation with a gas. 6. The safety housing of claim 1 wherein the radiation source comprises a means to generate ultraviolet radiation. 7. The safety housing of claim 1 further including a gas supply means within the applicator assembly directing gas to the region of the radiation source to cool the radiation source. |
description | This application claims priority to U.S. Provisional Patent Application No. 62/021,627 filed on Jul. 7, 2014, the contents of which are herein incorporated by reference. This invention was made with Government support under Contract No. DE-NE0000633 awarded by the Department of Energy. The Government has certain rights in this invention. In a nuclear reactor, a core of nuclear material may be confined to a relatively small volume internal to the reactor so that a reaction may occur. A controlled nuclear reaction may persist for an extended period of time, which may include several years, before refueling of the reactor core is required. Accordingly, when used as a source of heat for converting water into steam, a properly designed nuclear reactor may provide a carbon-free, stable, and highly reliable source of energy. During operation of a nuclear reactor, it may be useful to monitor the temperatures, pressures, and/or flow rates of the coolant within the reactor to ensure that all aspects of the reactor's internal operation are maintained within acceptable limits. For example, in the event that the flow of coolant is too low, components within the reactor may undergo excessive heating, which may result in the failure of one or more reactor components. In the event that the flow of coolant is too high, the reactor core may experience an undue level of cooling, which may result in undesirable fluctuations of reactor output power levels. Temperatures and potentially corrosive characteristics of primary coolant located near the reactor core may cause sensors, gauges, and/or other types of measurement devices to fail over a period of time. Additionally, shutting down the reactor to replace and/or repair the failed measurement devices may result in significant operational costs and ultimately a less efficient and less reliable source of energy. Coolant located within a volume, such as a reactor vessel, may experience temperature, pressure, and/or flow rate differentials according to the position and/or operational mode of the reactor at which the measurement is being made. For example, coolant flowing in a relatively straight direction may have a different flow rate as compared to coolant flowing around a corner or around an obstacle within the volume. Similarly, coolant flow during a reactor start-up may experience turbulence and/or surges due to uneven temperature distributions throughout the coolant. This application addresses these and other problems. A method of measuring the flow rate of a fluid located in a volume is disclosed herein. The method may comprise computing a first change in flow rate from a quiescent propagation time of a first acoustic signal transmitted through a first portion of a volume, and computing a second change in the flow rate from a quiescent propagation time of a second acoustic signal transmitted through a second portion of the volume. The flow rate of the fluid through the volume may be measured and/or estimated by, at least in part, aggregating the first change in flow rate and the second change in flow rate. In some examples, the flow rate may be measured within an annular volume located outside of a riser of a reactor vessel. A system for measuring the flow rate of a fluid located in a volume is disclosed herein. The system may comprise at least one emitter positioned at a first elevation on a surface of a vessel containing the volume, and at least one receiver positioned at a second elevation on the surface of the vessel. Additionally, the system may comprise a signal processor coupled to the at least one emitter and the at least one receiver. The signal processor may be configured to compute and/or estimate the flow rate of the fluid through the volume. In some examples, the system may be configured to measure the flow rate of a coolant located within a reactor vessel of a nuclear reactor module. The flow rate of the coolant may be the result of natural circulation within a reactor vessel that is achieved without any pumps. A method for measuring flow rate within a volume is disclosed herein. The method may comprise transmitting, by a transmission device, a first signal through fluid contained within the volume. The volume may be bounded, at least in part, by an interior surface of an outer structure and an object at least partially located within the outer structure. The transmission device may be located at a first location on the outer structure. In some example, the transmission device may be located on an exterior surface of the outer structure. A first time of flight of the first signal may be measured from the first location to a second location on the outer structure. Additionally, the method may comprise propagating a second signal through the fluid from the second location to a third location on the outer structure, and measuring a second time of flight of the second signal. The flow rate of the fluid within the volume may be determined based, at least in part, on both the first time of flight and the second time of flight. A system for measuring flow rate within a volume is disclosed herein. The system may comprise a first transmission device configured to transmit a first signal through fluid contained within the volume. The volume may be bounded, at least in part, by an interior surface of an outer structure and by an object at least partially contained within the outer structure. The first transmission device may be located at a first location on an exterior surface of the outer structure so as to transmit the first signal while avoiding the object. A processing device may be configured to measure a first time of flight of the first signal from the first location to a second location on the exterior surface of the outer structure. Additionally, a second transmission device located at the second location may be configured to transmit a second signal through the fluid from the second location to a third location on the exterior surface of the outer structure while avoiding the object. The processing device may further be configured to measure a second time of flight for the second signal. The flow rate of the fluid within the volume may be determined based, at least in part, on both the first time of flight and the second time of flight. Methods, apparatuses, and systems for measuring, calculating, estimating, or otherwise determining a flow rate through a fluid-filled volume, such as an annular volume, are described herein. As described in greater detail herein, one or more example systems may comprise various nuclear reactor technologies. Thus, some example systems may comprise and/or be used in conjunction with nuclear reactors that employ uranium oxides, uranium hydrides, uranium nitrides, uranium carbides, mixed oxides, and/or other types of fuel. It should be noted that the examples described herein may comprise and/or also be used with a variety of different types of reactor designs, reactor cooling mechanisms, and/or cooling systems. Various examples disclosed and/or referred to herein may be operated consistent with, or in conjunction with, one or more features found in U.S. Pat. No. 8,687,759, entitled Internal Dry Containment Vessel for a Nuclear Reactor, U.S. Pat. No. 8,588,360, entitled Evacuated Containment Vessel for a Nuclear Reactor, U.S. application Ser. No. 14/712,507, entitled Transportable Monitoring System, and/or U.S. Provisional Application No. 62/021,627, entitled Flow Rate Measurement in a Volume, the contents of which are incorporated by reference herein. FIG. 1 illustrates a diagram of an example nuclear reactor module 75 employing a system for measuring flow rate. A reactor core 5 is positioned at a bottom portion of a cylinder-shaped or capsule-shaped reactor vessel 20. Reactor core 5 may comprise a quantity of fissile material that generates a controlled reaction that may occur over a period of perhaps several years. In some examples, one or more control rods may be employed to control the rate of fission within reactor core 5. The control rods may comprise silver, indium, cadmium, boron, cobalt, hafnium, dysprosium, gadolinium, samarium, erbium, europium, other types of materials, and any combination thereof, including alloys and compounds. In some examples and/or modes of operation of the reactor module 75, a cylinder-shaped or capsule-shaped containment vessel 10 that surrounds reactor vessel 20 may be partially or completely submerged within a pool of water or other fluid. The volume between reactor vessel 20 and containment vessel 10 may be partially or completely evacuated to reduce heat transfer from reactor vessel 20 to the external environment. However, in other examples and/or modes of operation of the reactor module 75, the volume between reactor vessel 20 and containment vessel 10 may be at least partially filled with a gas and/or a fluid that increases heat transfer between the reactor and the containment vessels. Reactor core 5 is illustrated as being partially or completely submerged within a coolant or fluid, such as water, which may include boron or other additives. The coolant, rises after making contact with a surface of the reactor core. The upward motion of heated coolant is represented by arrow 15 above reactor core 5. The coolant travels upward through riser 30 and over the top of heat exchangers 40 and 42 and is pulled downward by way of convection along the inner walls of reactor vessel 20, thus allowing the coolant to impart heat to heat exchangers 40. After reaching a bottom portion of the reactor vessel, contact with reactor core 5 results in heating the coolant as symbolized by arrow 15. Although heat exchangers 40 and 42 are illustrated as comprising distinct elements in FIG. 1, heat exchangers 40 and 42 may represent a number of helical coils that wrap around an upper portion of riser 30. Additionally, other helical coils may wrap around an upper portion of riser 30 in an opposite direction, in which, for example, a first helical coil wraps helically in a counterclockwise direction, while a second helical coil wraps helically in a clockwise direction. Further, although a water line 70 is shown as being positioned some distance above heat exchangers 40 and 42, in other examples, reactor vessel 20 may include a lesser or a greater amount of water, fluid, and/or other type of coolant than illustrated by water line 70. During normal operation of the nuclear reactor module 75, heated coolant rises through a channel defined by riser 30 and makes contact with heat exchangers 40 and 42. After contacting heat exchangers 40 and 42, the coolant sinks towards the bottom of reactor vessel 20 in a manner that induces a thermal siphoning process as shown by arrows 25. In some examples, coolant within reactor vessel 20 remains at a pressure above atmospheric pressure, thus allowing the coolant to maintain a high temperature without vaporizing (i.e. boiling). As coolant within heat exchangers 40 and 42 increases in temperature, the coolant may begin to boil. As boiling commences, vaporized coolant may be routed from a top portion of heat exchangers 40 and 42 to drive one or more of turbines 80 and 82. Turbines 80 and 82 may be configured to convert the thermal potential energy of steam into electrical energy. After condensing, coolant is returned to a bottom portion of heat exchangers 40 and 42. An emitter 50 may be positioned at an external surface of reactor vessel 20 at a first elevation, such as relative to a bottom portion of reactor vessel 20. Additionally, a receiver 60 may also be positioned on an external surface of reactor vessel 20 at an elevation that is below the elevation of emitter 50. As will be explained in greater detail with reference to subsequent figures, due to the component of the acoustic signal propagating in the same direction as coolant from heat exchangers 40 and 42, the acoustic signal from emitter 50 to receiver 60 may be accelerated as the signal propagates through the portion of the fluid-filled annular volume. In a similar manner, a second acoustic signal from emitter 52 may be accelerated as the second signal propagates from emitter 52 towards receiver 62. FIG. 1A illustrates an example system 100 for measuring flow rate through a volume 175. A coolant flows downward through volume 175 as indicated by arrows 125. In some examples, volume 175 may comprise an annular volume. A first emitter 150, located at an elevation h4, may be configured to transmit, retransmit, convey, and/or propagate a first signal at least partially in the direction of the coolant flow through a first portion of volume 175. The first signal may be received at a first receiver 160 at an elevation h3. A second emitter 152, located at an elevation h3, may be configured to transmit, retransmit, convey, and/or propagate a second signal at least partially in the direction of the coolant flow through a second portion of volume 175. Second emitter 152 may be located adjacent to, next to, and/or co-located with, first receiver 160. In some examples, the second signal may be transmitted, retransmitted, and/or propagated by second emitter 152 in response to first receiver 160 having received the first signal. The second signal may be received by a second receiver 162 at an elevation h2. A third emitter 154, located at elevation h2, may be configured to transmit, retransmit, convey and/or propagate a third signal from emitter 154, located adjacent or next to second receiver 162, at least partially in the direction of the coolant flow through a third portion of volume 175. Third emitter 154 may be located adjacent to, next to, and/or co-located with, second receiver 162. In some examples, the third signal may be transmitted, retransmitted, and/or propagated by third emitter 154 in response to second receiver 162 having received the second signal. The third signal may be received by a third receiver 164 located at the reverse (back) side of volume 175 at an elevation h1. A fourth emitter 156, located at elevation h1, may be configured to transmit, retransmit, convey, and/or propagate a fourth signal at least partially in the direction of the coolant flow through a fourth portion of volume 175. Fourth emitter 156 may be located adjacent to, next to, and/or co-located with, third receiver 164. In some examples, the fourth signal may be transmitted, retransmitted, and/or propagated by fourth emitter 156 in response to third receiver 164 having received the third signal. The fourth signal may be received by a fourth receiver 166 at an elevation h0. The coolant indicated by arrows 125 may comprise a fluid, such as water, a gas, such as air, or a mixture of fluid and gas, such as steam. Additionally, the coolant may comprise one or more types of fluids, gases, two-phase mixtures, other types of mediums, or any combination thereof. FIG. 2 illustrates a top view of an example system 200 for measuring flow rate through an annular volume 275. An internal surface 215 may represent an inner volume 225 having, for example, two-thirds the radius of the annular volume 275 bounded by external surface 205. An emitter 250 is located at an elevation h4 and may be in line with receiver 266 located an elevation h0. Receiver 260 may be approximately collocated with emitter 252, emitter 254 may be approximately collocated with receiver 262 at elevation h2, and emitter 256 may be approximately collocated with receiver 264 at elevation h1. Distances L1, L2, L3, and L4 represent line-of-sight paths and/or signal paths between an emitter and a corresponding receiver located at a different, such as lower, elevation than the emitter. In examples in which internal surface 215 may comprise an inner volume 225 having a larger radius in comparison to the radius of the annular volume 275 bounded by external surface 205, additional emitter and receiver pairs may be used to provide a line-of-sight path between each emitter and receiver. In some examples, an emitter and a corresponding receiver are located at different elevations. The plurality of emitters 250, 252, 254, 256 may be externally located to a surface of a reactor vessel 220 of a nuclear reactor module. Each emitter of the group may be positioned at a unique elevation along a flow path of fluid coolant that exits a heat exchanger and travels downward between an inward facing portion of the reactor vessel 220 and an outward facing portion of a riser 210 located internal to the reactor vessel 220. In some examples, one or more of the plurality of emitters 250, 252, 254, 256 may be configured to transmit, retransmit, convey and/or propagate an acoustic signal. The plurality of emitters 250, 252, 254, 256 may be mounted to and/or located on the external surface 205 of reactor vessel 220 without requiring any physical penetrations through external surface 205. Additionally, by locating the emitters and/or receivers on the external surface 205, they do not impede the flow of coolant within the reactor vessel 220. The acoustic signal may comprise an ultrasonic signal having a frequency of between 20.0 kHz and 2.5 MHz, a sonic signal having a frequency of between 20 Hz and 20.0 kHz, an infrasound signal having a frequency of less than 20.0 kHz, other frequency ranges, or any combination thereof. In other examples, one or more of the plurality of emitters 250, 252, 254, 256 may be configured to transmit, retransmit, convey and/or propagate vibratory signals, light signals, ultraviolet signals, microwave signals, x-ray signals, electrical signals, infrared signals, other types of signals, or any combination thereof. Additionally, one or more of the signals may be transmitted, retransmitted, conveyed and/or propagated through an intervening rigid medium, such as an external surface of the reactor vessel 220, and through at least a portion of a fluid located within the annular volume 275 located internal to the reactor vessel 220. By positioning two, three, four, or another number of emitters at different elevations along the external surface of a reactor vessel 220, a longer effective signal path may be created. The effective signal path may comprise a plurality of signal paths as between one or more pairs of emitters and receivers. For example, the effective signal path may comprise signal paths associated with distances L1, L2, L3, and L4. Similarly, the length of the effective signal path may comprise a summation of the distances L1, L2, L3, and L4. In some examples, a receiver, such as fourth receiver 266, may be configured to receive a response signal in response an emitter, such as first emitter 250, having transmitted an initial signal into the fluid located within annular volume 275. The initial signal may be transmitted by first emitter 250 to first receiver 260. In response to first receiver having received the initial signal, second transmitter 252 may be configured to transmit, retransmit, convey and/or propagate an intermediate signal to second receiver 262. The receipt of the initial signal may act as a trigger to transmit the intermediate signal. Similarly, additional intermediate signals may be transmitted, retransmitted, conveyed and/or propagated between other pairs of emitters and receivers located around the reactor vessel 205 until the response signal is received by fourth receiver 266. In some examples, the pairs of emitters and receiver may be configured as signal repeaters, in which a signal is repeated, reflected, and/or bounced along the perimeter of reactor vessel 220, forming a signal loop of up to 360 degrees or more. The effective signal path may be initiated at a first rotational angle, and may conclude at a second rotational angle. In some examples, the second rotational angle approximately equals the first rotational angle, such that the effective signal path may completely surround internal surface 215. If annular volume 275 is bounded by an inner surface having approximately one-half the radius of an outer surface, three pairs of emitters and receivers may be sufficient to provide a continuous line-of-sight path through the entire annular volume 275. In other examples, in which annular volume 275 is bounded by an inner surface of greater than one-half the radius of an outer surface, a larger number of emitter and receiver pairs may be employed, such as four or more pairs, to provide a line-of-sight path through the annular volume 275. FIG. 3 illustrates an example system 300 comprising an emitter and receiver pair configured to measure flow rate through a volume 375. A signal transmitted at t0 from emitter 350 may be conveyed through an intervening rigid medium 325 that encloses the volume 375, such as, for example, stainless steel. The signal may be conveyed at least partially in the direction of flow and received by receiver 360 at a time tai, as given by the following equation:td1=L/(c+v*cos θ) (1) In the right side expression shown in equation (1), “c” represents the speed of the signal in the fluid volume, “v” represents coolant velocity, “L” represents the distance between emitter 350 and receiver 360, and 0 represents an angle between “L” and elevation indicator (h) of emitter 350. Thus, as the velocity of the coolant flow through the volume increases, the propagation time of the signal conveyed in the direction of the flow decreases. Further, as the velocity of flow decreases to zero, the time at which the signal is received at receiver 360 reduces to:td2=L/c (2)in which equation (2) may be referred to as a quiescent propagation time of a signal propagating between emitter 350 and receiver 360. Equation (1) may also be used to determine a change from a quiescent propagation time that results, at least in part, from the velocity of a fluid flowing through the volume. In some examples, the change, such as the time delay, from a quiescent propagation time to a propagation in which the fluid may be flowing at a velocity “v” may be determined by:td1−td2=L/(c+v*cos θ)−L/c (3) Additionally, timing measurements resulting from a signal propagating in a first direction, such as from emitter 350 to receiver 360, may be complemented by timing measurements resulting from the signal propagating in a direction opposite the first direction, such as from receiver 360 to emitter 350. Such time delay measurement may be performed using the equation (3) below in which +v is replaced with −vtd1−td2=L/(c−v*cos θ)−L/c (3a) As can be seen from equation (3a), as the velocity of the coolant flow through the volume is opposite the direction of propagation of the signal, the propagation time of the signal increases from a quiescent propagation time. FIG. 4 illustrates an example system 400 for measuring flow rate comprising multiple pairs of emitters and receivers. A first signal may be introduced by a first emitter 450 through an intervening rigid medium and into a fluid-carrying volume wherein the fluid travels at a velocity “V1” may be signal may be received by a first receiver 460 located a distance “L1” from first emitter 450. At a time that may be approximately equal to the time that the signal is received at receiver 460, a second emitter 452 may be configured to introduce a second signal through a second portion of the fluid-carrying volume wherein the fluid travels at a velocity “V2” to a second receiver 462 located at a distance “L2” from second emitter 452. In some examples, one or more emitter/receiver pairs, such as emitter 350 and receiver 360 (FIG. 3), first emitter 450 and first receiver 460, and second emitter 452 and second receiver 462, may be configured to couple acoustic energy to and from the fluid carried within the volume through an intervening rigid medium 425, such as stainless steel. In some examples, changes (i.e. time delays) from quiescent propagation times of signals conveyed through the first and second portions of the volume may be aggregated, at least in part, by way of receivers 460 and 462. The aggregation may be determined by:Time Delay(aggregated)=L1/(c+v1*cos θ1)−L1/c+L2/(c+v2*cos θ2)−L2/c (4),wherein, as mentioned previously, L1 represents a distance between first emitter 450 and first receiver 460, and L2 represents a distance between second emitter 452 and second receiver 462; “c” represents the speed of the signal through a quiescent volume of fluid; V1 and V2 represent fluid velocities through the first and second portions of the volume, respectively; and θ1 and θ2 represent the angles that L1 and L2 make with elevation indicators h1 and h2. In some examples, “c” may represent the speed of an acoustic wave through the volume. First emitter 450 may make use of a signal having different characteristics than second emitter 452. This may, for example, result in less interference between signals transmitted from first emitter 450 and, for example, signals transmitted from second emitter 452. Thus, in one example, first emitter 450 may be configured to emit a signal having a first frequency, such as 20 kHz, to be received by first receiver 460. Second emitter 452 may be configured to emit a signal having a second frequency, such as 22 kHz, to be received by second receiver 462. In other examples, emitters 450 and 452 may employ non-interfering digital codes using a similar acoustic frequency band. In still other examples, emitters 450 and 452 may make use of non-identical pulse widths or other techniques to reduce crosstalk between emitters and unintended receivers. By identifying signals with different characteristics, a receiver may be able to distinguish between two signals that it receives from two different emitters. In some examples, the receiver may be configured to ignore a signal that it has inadvertently received from an emitter associated with a different emitter and receiver pair. One or more of emitters 450, 452 and/or receivers 460, 462 may be configured to measure, calculate, estimate, or otherwise determine a temperature associated with a fluid volume. For example, a first temperature may be determined for a fluid volume associated with first fluid velocity V1, and a second temperature may be determined for a fluid volume associated with second fluid velocity second V2. The temperature may affect the speed at which the signal propagates through the fluid volume. A time delay associated with a signal received by first receiver 460 and/or second receiver 462 may be calibrated or otherwise adjusted to compensate for the temperature of the corresponding fluid volume. In some examples, a difference in temperature from a nominal operating temperature may be determined to adjust the time delay. The temperature of the fluid may be measured directly in some examples, or via the external surface of the container 425, e.g., as a result of conduction of heat through the container wall. In some examples, a temperature and/or difference in temperature between one or more fluid volumes may be inferred based, at least in part, on the time delays measured by system 400. A first time delay may be associated with a first temperature of a fluid volume, and a second time delay may be associated with a second temperature of a fluid volume. The differences in time delays and/or differences in temperatures of the fluid volumes may be used to determine if there is a relatively cold slug of fluid that is passing through the container 425. Similarly, the differences in time delays and/or differences in temperatures of the fluid volumes may be used to determine if there is an air bubble or a steam bubble that is being propagated through the container 425. Additionally, the time delay may be used to determine if the fluid comprises a homogenous mixture of two or more mediums. For example, the level of concentration of a secondary medium within a primary medium may affect the time delay of a signal propagated through the primary medium. System 400 may be configured to determine when the secondary medium has been fully incorporated into or mixed with the primary medium. In still other examples, the time delay associated with a received signal may be used to determine if a level of turbidity and/or turbulence of the fluid within container 425. The flow rates within different regions of the container 425 may be mapped out based on the temperatures and/or time delays. In some examples, system 400 may be configured to monitor the different regions and determine when there is a uniform flow of coolant throughout the entire container. Similarly, system 400 may be configured to determine when there is a uniform temperature distribution of fluid within the container 425. Additionally, system 400 may be configured to determine when there is a uniform mixture and/or concentration of two or more fluids within the container 425. The uniform flow, temperature, mixture, and/or concentration of the fluid may be determined based, as least in part, on a comparison of the time delay(s) of the signals propagated through the fluid. In a nuclear reactor module, such as illustrated in FIG. 1, a reactor start-up system may be configured to initiate a reactor core start-up based, at least in part, on information provided by system 400. For example, the reactor start-up system may be configured to remove one or more control rods after system 400 determines that there is a uniform flow and/or uniform temperature of coolant circulating through the reactor core. FIG. 5 illustrates a top view of a further example system 500 for measuring flow rate through an annular volume 575. An emitter 550, located at an elevation h3, may be configured to emit a signal for reception by receiver 560, located a distance L1 from emitter 550 and at an elevation h2. Emitter 552, which may be approximately co-located with receiver 560, may be configured to emit a signal for reception by receiver 562 located a distance L2 from emitter 552 at an elevation h1. Emitter 554, which may be approximately co-located with receiver 562, may be configured to emit a signal for reception by receiver 564 located a distance L3 from emitter 554 at an elevation h0. The effective length of the signal path may be increased by aggregating or combining one or more signals associated with distances L1, L2, and L3. Internal surface 315 may represent an inner volume 525 having, for example, approximately one-half the radius of the annular volume 575 bounded by external surface 305. Inner volume 525 may comprise a cylindrically shaped object approximately centrally located within the annular volume 575. In some examples, internal surface 315 may represent an inner volume 525 having a smaller radius in comparison to the radius of the annular volume 575 bounded by external surface 305. Accordingly, a relatively smaller number of emitter and receiver pairs may be used as compared to an inner volume having a larger radius. The number of pairs of emitter and receivers may be selected so that a line of sight path exists between each emitter and receiver. In one example, in which an internal surface represents an inner volume having radius of perhaps one-fifth or one-sixth the radius of the annular volume 575 bounded by an external surface, an emitter may convey a first signal to an receiver located almost completely to the opposite side of annular volume 575, such as receiver 162 of FIG. 1A. An emitter, perhaps co-located approximately with receiver 162, may then convey a second signal to a receiver located almost completely to the opposite side of emitter 154 such as, for example, a location proximate with receiver 166. In some examples, one or more of the emitters, such as emitter 550, may be configured to transmit, re-transmit, convey, and/or propagate a signal along a reflective path L0. For example, a signal transmitted from transmitter 550 may be configured to reflect against the internal surface 315 and be received by receiver 564. The reflective path L0 is therefore approximately equal to, or slightly greater than, twice the distance between internal surface 315 and external surface 305. The length of reflective path L0 between internal surface 315 and external surface 305 may vary according to the change in elevation, or longitudinal distance, between transmitted 50 and receiver 564 along the length of external surface 305. In some examples, reflective path L0 may be less than distances L1, L2, and L3, either individually or collectively. The diameter, location, and/or curvature of internal surface 315 may change as a result of thermal stress induced by the heated coolant within volume 575. Similarly, the diameter. location, and/or curvature of external surface 305 may change as a result of thermal stress. Accordingly, the receiver 564 may be located and/or sized to accommodate the changes in surface conditions of one or both of internal surface 315 and external surface 305. By locating the plurality of emitters and receivers along external surface 305 and transmitting the one or more signals along the paths associated with distances L1, L2, and L3, the effects of thermal expansion and/or retraction may be further minimized. FIG. 6 illustrates a block diagram of an example system 600 for measuring flow rate through a volume. A first emitter 650 may be coupled to an external surface of the volume and may convey a first signal through an intervening rigid medium and through a first fluid-filled portion of the volume to a first receiver 660. System 600 may comprise other emitters, such as emitter 658, which may also be coupled to an external surface of the volume and may convey one or more additional signals through an intervening rigid medium into a fluid filled portion of the volume to one or more additional receivers, such as receiver 668. A number of additional emitter and receiver pairs may be used to convey acoustic signals through additional portions of the volume to a corresponding receiver. A signal processor 670 may include a memory and a logic unit, such as a microprocessor, programmable logic circuit, or other logic unit, for aggregating signals from receivers, such as receiver 660 and 668. In an example, such aggregation may include arithmetically summing timing signals from each receiver by way of an operation that accords with expression (4). Signal processor 670 may then compute an estimated flow rate through the entire volume based on such aggregation. In still other examples, signal processor 670 may be configured to calculate an average of the timing signals, in order to determine an average flow rate through the volume. The average flow rate may be used to factor in and/or offset variations in flow in different regions of the volume. The average of the timing signals may be determined from an aggregated sum of a plurality of timing signals associated with multiple emitter and receiver pairs. In some examples, the plurality of timing signals which are averaged may be sequentially transmitted, and in other embodiments, the plurality of timing signals may be transmitted substantially at the same time or concurrently. An emitter and receiver pair may be positioned so as to maximize the distance that the signal travels through the volume. Maximizing the distance that the signal and/or signals are propagated may provide for a more accurate reading of the flow rate of the entire volume. The distance between an emitter and its associated receiver may be limited by line-of-sight, such that the distance that the signal travels may only comprise a small portion of the volume in which the flow is being measured. By adding multiple pairs of emitters and receivers, and similarly by aggregating information associated with their respective signals, a longer effective signal path length may be obtained. In some examples, the effective signal path length may circumnavigate an obstacle located within the volume. For example, with reference to FIG. 3, an effective path of the multiple pairs of emitters and receivers may comprise the combined distances L1, L2, and L3, such that the effective signal path surrounds the internal surface within the surrounding volume. The plurality of signals may be sequentially transmitted along the effective signal path. A second signal may be transmitted after a first signal, a third signal may be transmitted after the second signal, etc. In some examples, the signals may be sequentially transmitted in response to receiving the prior signal, as a type of chain-reaction. In still other examples, the signal may be reflected and/or re-transmitted by each pair of emitters and receivers to the next pair of emitters and receivers. The multiple pairs of emitters and receivers may form an effective signal path comprising a plurality of signal paths that commence at an initial transmitter and conclude at a terminal receiver. Signal processor 670 may aggregate signals from receivers, such as receivers 660 and 668, using weighting factors so that timing signals from a first portion of a volume, such as an annular volume, are given more importance than timing signals from a second portion of the volume. In some examples, signals may be weighted according to a relative position of the associated emitter and/or receiver. For example, signals propagated through coolant flowing in a relatively straight direction may have a first weighting factor, and signals propagated through coolant flowing around a corner or around an obstacle within the volume may be associated with a second weighting factor. Similarly, signals propagated through coolant flow during a reactor start-up, during power surges, and/or when uneven temperature distributions are detected throughout the coolant, may also be weighted to account for variations in flow in different regions of the volume. Signal processor 670 may be configured to compute a change, such as a time delay, of the acoustic signal from a quiescent value. Based, at least in part, on the change, the flow rate of fluid through the portion of the volume may be computed. Additionally, signal processor 670 may be configured to aggregate changes in time delays of acoustic signals conveyed through other portions of the annular volume to estimate the flow rate of fluid through the total volume, such as the total annular volume. FIG. 7 illustrates an example process 700 of measuring flow rate in a volume. At operation 710, a first change from a quiescent propagation time of a first acoustic signal transmitted through a first portion of an annular volume may be calculated. In some examples, said computing may comprise coupling a portion of a first acoustic signal from a first portion of the annular volume through an intervening rigid material to an acoustic receiver. At operation 720 a second change from a quiescent propagation time of a second acoustic signal transmitted through a second portion of the annular volume may be calculated. The first and second changes may be transmitted by a plurality of emitters, located at a corresponding first plurality of locations external to an annular volume. Additionally, a plurality of receivers may be configured to receive time-delayed acoustic signals from the fluid at a second plurality of locations. In some examples, the acoustic signals may be transmitted at a frequency of between 3.0 kHz and 2.5 MHz A sufficient number of emitters may be configured and/or arranged to provide a line of sight between each emitter and at least one receiver. In some examples, each of the plurality of receivers may be approximately collocated with an emitter. Each of the plurality of emitters may be positioned at a unique elevation on an intervening rigid medium that encloses the annular volume. A first emitter positioned at a first elevation may be configured to emit an acoustic signal in a first direction. In some examples, a second emitter, positioned proximate with a receiver, may be configured to emit an acoustic signal in a second direction approximately opposite the first direction. A signal processor may be configured to compute a time delay of the acoustic signals in both the first direction and the second direction to estimate the flow rate. In still other examples, three or more emitters may be located at three or more locations around the annular volume. An inner radius of the annular volume may be approximately one half an outer radius of the annular volume. Additionally, each of the three locations may be positioned at a unique elevation on an intervening rigid medium that encloses the annular volume. At operation 730, the first change and the second change may be aggregated. A processor may be configured to estimate, measure, and/or otherwise determine the flow rate through the annular volume at least in part by aggregating representations of the time-delayed acoustic signals. In some examples, the flow rate may be estimated by adding a correction factor to the aggregation of the first change and the second change. At operation 740, a flow rate of a fluid through the annular volume may be estimated by, at least in part, aggregating the first change and the second change. In some examples, said estimating may comprise adding a correction factor to the aggregation of the first change and the second change. At operation 750, a third change from a quiescent propagation time of a third acoustic signal transmitted through a third portion of the annular volume may be calculated. In some examples, the first acoustic signal may be transmitted in a first direction through a first portion of the annular volume, and the third acoustic signal may be transmitted in direction opposite to the first direction through the first portion of the annular volume. Additionally, the second acoustic signal may be transmitted in a second direction through a second portion of the annular volume, and the third acoustic signal may be transmitted in a direction opposite to the second direction through the second portion of the annular volume. At operation 760, the first change, the second change, and the third change may be aggregated. At operation 770, a flow rate of a fluid through the annular volume may be estimated, at least in part, by aggregating the third change with the first and the second change. One or more signals may be transmitted at varying intervals according to a particular system operating condition. For example, during normal system operation, signals may be transmitted at regular intervals, e.g., once per second, to monitor the status of the flow rate. At other operations, such as during a reactor startup, the intervals may be shortened to a number of milliseconds to provide more immediate response time to any change or variation in flow rate and/or temperature of the fluid. FIG. 8 illustrates a side view of another example system 800 for measuring flow rate through a volume 875. Volume 875 may be located between a containment vessel 850 and an internal object 825 located at least partially within containment vessel 850. In some examples, internal object 825 may be approximately centrally located within containment vessel 850. Additionally, internal object 825 may be substantially surrounded by liquid 840 within volume 875. Fluid 840 may be configured to flow between containment vessel 850 and internal object 825 in a general longitudinal direction. In some examples, system 800 may be configured such that fluid 840 flows from a first end of containment vessel 850 to a second end of containment vessel 850, such as through a pipe or conduit. In other examples, system 800 may be configured such that fluid circulates in a first direction outside of internal object 825, and in a second direction inside of internal object 825, e.g., through an internal passageway of internal object 825. One or more sets of signal transponders and/or processing devices may be configured to measure, calculate, estimate, or otherwise determine a flow rate of fluid 840 through volume 875. For example, a first set of signal transponders comprising a first transmitter 810 and a first emitter 815 may be configured to transmit and receive, respectively, a signal along a first reflective signal path 812. Similarly, a second set of signal transponders comprising a second transmitter 820 and a second emitter 825 may be configured to transmit and received, respectively, a signal along a second reflective signal path 822. First reflective signal path 812 and second reflective signal path 822 may reflect off different portions of object 825. In some examples, the distance of first reflective signal path 812 may be approximately equal to the distance of second reflective signal path 822 A signal propagation time associated with first reflective signal path 812 may be used to evaluate a flow rate of fluid 840 within a first portion of volume 875. Additionally, a signal propagation time associated with second reflective signal path 822 may be used to evaluate a flow rate of fluid 840 within a second portion of volume 875. The first and second portions may correspond to different elevations or longitudinal positions within containment vessel 850. In other examples, the first and second portions may correspond to different circumferential positions within volume 875 around internal object 825. Signal propagation times for a plurality of signals transmitted by two or more transmitters and reflected off internal object 825 may be compared to evaluate any variation in flow rate and/or temperature of fluid 840 within volume 875. In some examples, the plurality of signal propagation times may be averaged to determine an average flow rate of fluid 840 through volume 875. In still other examples, one or more of the plurality of signal propagation times may be calibrated or adjusted to compensate for any thermal expansion or retraction of internal object 825 during operation of system 800, and for the associated change in distance of first reflective signal path 812 and/or second reflective signal path 822 as a result of the thermal expansion or retraction. In some examples, one or both of first transmitter 810 and second transmitter 820 may be configured to both transmit and receive a signal. Similarly, one or both of first emitter 815 and second emitter 825 may be configured to both transmit and receive a signal. A first propagation time associated with a signal transmitted from first transmitter 810 to first emitter 815 may be analyzed in relation with, or otherwise compared to, a second propagation time associated with a signal transmitted in the opposite direction from first emitter 815 to first transmitter 810. The comparison between first and second propagations times may be used to verify, corroborate, and/or calibrate one of both of first transmitter 810 and first emitter 815. FIG. 9 illustrates a top view of yet another example system 900 for measuring flow rate through a volume 975. Volume 975 may be located between a fluid container 950 and an internal object 925. In some examples, volume 975 may comprise a concentric or annular shaped region between fluid container 950 and internal object 925, such as when internal object 925 and/or fluid container 950 are cylindrical in shape. In other examples, volume 975 may comprise non-concentric or non-circular annular region, such as when internal object 925 and/or fluid container 950 are non-cylindrical in shape. A transponder 920 may be configured to transmit a signal along a signal path 922 associated with two or more devices such as propagation devices 930, 940, 960, positioned about a perimeter of fluid container 950. One or more of the propagation devices may comprise a reflective surface. For example, a first propagation device 930 may comprise a reflective surface configured to reflect the signal received from transponder 920 such that the signal is propagated and/or reflected to a second propagation device 940. Similarly, second propagation device 940 may be configured to propagate and/or reflect the signal to a third propagation device 960. Ultimately, the signal path may terminate at a receiving device 925. Receiving device 925 and/or a processing device communicatively coupled to receiving device 925 may be configured to determine a time of flight of the signal along signal path 922. In some examples, receiving device 925 may be located at a different elevation than transponder 920 on fluid container 950. Similarly, some or all of propagation devices 930, 940, 960 may be located at different or unique elevations. In some examples, one or more of the propagation devices 930, 940, 960 may be mounted or otherwise located internal to fluid container 950. In other examples, one or more of the propagation devices 930, 940, 960 may be mounted or otherwise located external to fluid container 950. Some or all of the various devices of system 900 may be located internal or external to fluid container 950 without requiring any physical penetrations through the wall of fluid container 950. Rather, at least a portion of signal path 922 may pass through the wall of fluid container 950 at one or more points. FIG. 10 illustrates an example process 1000 of measuring flow rate in a volume. At operation 1010, a first signal is transmitted through fluid contained within the volume. The volume may be bounded, at least in part, by an interior surface of an outer structure and an object at least partially located within the outer structure. The transmission device may be located at a first location on the outer structure. In some examples, the first signal may travel through the fluid along a substantially linear path that passes between the object and the interior surface of the outer structure before arriving at the second location. The object may comprise a cylindrically shaped surface. Additionally, the volume may comprise an annular region formed between the cylindrically shaped surface of the object and the interior surface of the outer structure. In other examples, the object may be non-cylindrical in shape, such as having a cross-section which is substantially rectangular, oval, or otherwise non-circular in cross-section. Accordingly, the volume may comprise a non-circular or non-concentric annular region. At operation 1020, a first time of flight of the first signal may be measured from the first location to a second location on the outer structure. At operation 1030, a second signal is propagated through the fluid from the second location to a third location on the outer structure. In some examples, the second signal may travel through the fluid along a substantially linear path that passes between the object and the interior surface of the outer structure before arriving at the third location. At operation 1040, a second time of flight of the second signal may be measured. At operation 1050, the flow rate of the fluid within the volume may be determined based, at least in part, on both the first time of flight and the second time of flight. In other examples, a temperature of the fluid may be determined based, at least in part, on the first time of flight and the second time of flight. Determining the flow rate and/or temperature of the fluid within the volume may comprise taking an average of the first time of flight and the second time of flight. In other examples, determining the flow rate and/or temperature of the fluid within the volume may comprise taking a weighted average of the first time of flight and the second time of flight to account for structural interference to the flow of the fluid within the volume. One or more additional signals may be transmitted through the fluid by one or more additional transponder devices, along substantially linear paths. A plurality of the linear paths may be aggregated as a combined signal path that passes around the internal object. In some examples, the combined signal path may pass completely around the internal object. The first time of flight of the first signal may be compared with the second time of flight of the second signal to identify irregularities in flow rate and/or temperature of the fluid within the volume. For example, a cold slug of the fluid within the volume may be identified based, at least in part, the comparison of the first time of flight with the second time of flight. Additionally, a location associated with the cold slug may be determined according to which transponder is associated with the signal that identifies the change in temperature and/or the change in flow rate of the fluid. One or more or all of the systems described herein may be used to measure not only fluid flow rates at one or more locations within the volume, but also any temperature changes or variously at the one or more locations within the volume. By locating the one or more described receivers, emitters, propagation devices, transponders, or other devices at various positions and/or locations with respect to the volume being monitored, fluid characteristics (such as flow rate and temperature) may be mapped or tracked by various of the systems in localized regions or throughout substantially the entire volume. Although the examples provided herein have primarily described a pressurized water reactor and/or a light water reactor, it should be apparent to one skilled in the art that the examples may be applied to other types of power systems. For example, the examples or variations thereof may also be made operable with a boiling water reactor, sodium liquid metal reactor, gas cooled reactor, pebble-bed reactor, and/or other types of reactor designs. Although certain examples have described the use of acoustic signals to measure, calculate, estimate, or otherwise determine a fluid flow rate, other types of signals are also contemplated herein. Similarly, although some of the examples describe locating the emitters and/or receivers on an external surface of a container, other locations for locating the emitters and/or receivers, such as on an internal surface of the container, are also contemplated herein. It should be noted that examples are not limited to any particular type of reactor cooling mechanism, nor to any particular type of fuel employed to produce heat within or associated with a nuclear reaction. Any rates and values described herein are provided by way of example only. Other rates and values may be determined through experimentation such as by construction of full scale or scaled models of a nuclear reactor system. Having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail. We claim all modifications and variations coming within the spirit and scope of the following claims. |
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summary | ||
042077230 | description | Referring now to the drawings, and in particular to FIGS. 1-3, a system for canning and inspection of fuel and reflector elements of a nuclear reactor while transferring the elements from a fuel transfer cask to a storage area is indicated generally at 10. The system 10, which may alternatively be termed a fuel canning system for a nuclear reactor, is adapted for remote control and facilitates transfer and canning of fuel and reflector elements while maintaining the elements in a gaseous environment sealed against egress of radioactive contaminants and ingress of air. As will become more apparent hereinbelow, the system 10 overcomes the problems heretofore associated with maintaining a large gas-filled facility for handling fuel and reflector elements of a nuclear reactor, and more particularly the problems associated with maintaining gas purity in a cell containing quantities of cooling water separated from a gaseous environment by dynamic seals. The system of the present invention is adapted to isolate the gaseous environment to those areas surrounding the radioactive fuel and reflector elements. The nuclear reactor fuel and reflector elements with which the present invention relates are of known design and may have hexagonal external configurations with longitudinal control rod and coolant flow passages therein. For purposes of the present description, only the term fuel element will be used, it being understood that this term is to encompass both fuel and reflector elements. Very generally, the illustrated system 10 includes a pair of parallel transfer chutes 12 housed within a suitable reinforced concrete building or housing 14 which defines an internal maintenance chamber or cell 16, an internal fuel transfer hoist chamber 18, an internal conveyor chamber 20 and an internal fuel storage chamber 22, the various chambers having suitable radioactive shielding and the conveyor chamber and fuel storage chamber being in generally underlying relation to the maintenance chamber 16 and fuel transfer hoist chamber 18, as best seen in FIG. 1. An inspection area 26 is formed in the housing 14 so as to preferably extend about at least three sides of the conveyor chamber 20 at an elevation suitable to facilitate inspection of fuel elements during canning and transfer thereof to and from the storage chamber 22. The transfer chutes 12 extend from adjacent an upper surface 28 of the housing 14 downwardly through the maintenance chamber 16 and into the conveyor chamber 20 where the transfer chutes terminate in environmental chambers, each of which is indicated generally at 30. Each transfer chute 12 is adapted to receive radioactive fuel elements from an associated fuel transfer cask of known design, a portion of one being indicated at 32 in FIG. 1, and transfer the fuel elements downwardly through the environmental chamber 30 to corresponding conveyor means 34 housed within the conveyor chamber 20. Each conveyor means 34 includes a plurality of watertight chambers 36a, b, c, d, etc. which, for cooling purposes, are submerged in water 38 for the greater part of their lengths. As will become more apparent hereinbelow, the watertight conveyor chambers 36a, b, c, etc. define conveyor stations selected ones of which further define fuel element receptacles in the form of shipping containers having releasable sealing lids, and others of which define inspection tables for the fuel and reflector elements. The conveyor chambers are selectively movable along the endless paths of the conveyors to positions underlying the corresponding environmental chambers 30, associated canning machines, indicated generally at 40 in FIGS. 2 and 3, and inspection areas to be described. The conveyor means 34 are also operative to move the conveyor chambers 36a, b, c, etc. to positions underlying corresponding fuel transfer tubes 42 (FIG. 1) formed in the housing 14 and through which a lift hoist 44 is operative to remove sealed fuel containers from the conveyor chambers and transfer the containers through corresponding passages 46 to the fuel storage chamber 22 which is also water filled. A container of the type carried within selected ones of the container chambers 36 on the conveyor means 34 is partially illustrated at 48 in FIGS. 5, 9 and 11. The containers 48 comprise watertight cylindrical tubular containers having open upper ends and peripheral upper lid mounting flanges 48a. A container cover lid 49 is releasably mounted on the upper end of each container 48 through a plurality of fasteners in the form of circumferentially spaced screws 51 preferably having hexagonal shaped heads to facilitate removal and tightening by a canning machine 40 as will be described more fully hereinbelow. The screws 51 are held captive in the associated container lids 49 through threaded connection therewith and are adapted for threaded engagement with the mounting flanges 48a on the containers. TRANSFER CHUTE AND ENVIRONMENTAL CHAMBER Turning now to a more detailed description of the system 10, and particularly to one of transfer chutes 12 and its corresponding environmental chamber 30, and having reference to FIGS. 1-6, the major length of the transfer chute 12 is defined by a cylindrical tubular guide sleeve 50 having an orientation rib or key 52 secured to its inner surface so as to extend longitudinally of the guide sleeve. The tubular guide sleeve 50 terminates at its upper end in a floor valve 54 (FIG. 1) of known design adapted to be remotely operated to selectively open and close the upper end of the sleeve 50 so as to effect a fluid-type seal therewith when in closed position. The floor valve 54 is mounted within a recess 56 in the housing 14 so that a fuel transfer cask 32 may be moved to a position overlying the floor valve 54. The fuel element transfer cask 32 is of known design and includes internal hoist or grapple means (not shown) adapted to be lowered through the bottom of the transfer cask to facilitate loading of fuel and reflector elements into the transfer cask at the location of a reactor core, and thereafter individually lower the fuel and reflector elements into the transfer chute 12 through the floor valve 54 after movement of the transfer cask to overlie chute 12. The guide sleeve portion 50 of each transfer chute 12 terminates at its lower end in its corresponding environmental chamber 30. Each environmental chamber 30 includes an upper tubular wall 58 mounted internally of an annular mounting sleeve 60 secured within a wall 14a of the concrete housing 14. An upper hexagonal shaped guide sleeve 62 is fixedly supported within the tubular wall 58 so as to axially underlie the upper tubular guide sleeve 50, and is adapted to receive and guide fuel elements downwardly therethrough when lowered by the grapple of the fuel transfer cask 32. A lower hexagonal shaped guide sleeve 64 is mounted within the environmental chamber 30 for axial sliding movement on a pair of parallel upstanding support rods 66a and 66b fixed at their lower ends to a horizontal floor plate 68 and secured at their upper ends to the tubular wall 58. An electric guide sleeve drive motor 70 is mounted within the maintenance area 16 on an upper end plate 72 of the environmental chamber 30 and is operable to rotate a ball screw shaft 74 having connection at 76 with the movable guide sleeve 64 to facilitate movement of the lower guide sleeve between an upper position axially abutting the lower end of the upper guide sleeve 62 and a lower position projecting downwardly through a circular opening 78 in the floor plate 68 axially aligned with the tubular wall 58. A pair of parallel guide bars 80a and 80b are mounted on the lower guide sleeve 64 and cooperate with the upper guide sleeve 62 to effect axial registration therewith. The upper and lower sleeves also carry orientation ribs 52a (FIG. 5) for registration with the transfer cask grapple when lowering or raising a fuel element through the environmental chamber 30. As best seen in FIGS. 4-6, a grapple mechanism means, indicated generally at 84, is supported within the environmental chamber 30 and is operable to handle container lids 49 for containers 48 disposed within selected ones of the conveyor chambers 36. The grapple means 84 includes a tubular spline shaft 86 mounted at its upper end to the end plate 72 and connected to an electric control motor 88 through a spline and worm gear arrangement (not shown) to facilitate selective rotation of the spline shaft 84 about its longitudinal axis. A radial tubular arm 92 is mounted on the lower end of the tubular spline shaft 86 through a right angle bevel gear housing 94. A second right angle bevel gear housing 96 is secured to the outer end of the radial arm 92 and supports a vertical tubular arm 98 having a grapple head 100 mounted on its lower end. The grapple head 100 and associated support arms 98 and 92 are located within an enlarged area of the environmental chamber 30 defined internally of a cylindrical housing 102 secured eccentrically to and communicating with the lower end of the tubular wall 58. The grapple head 100 and associated support arms 98 and 92 are adapted for rotation about the axis of the spline shaft 86 to effect movement of the grapple head to a position axially overlying the circular access opening 78 in the bottom end plate 68, or to a position overlying either one of two container lid storage chambers 104 and 106 formed in the end plate 68. The chambers 104 or 106 may be employed to temporarily store the container lids 49 for the containers 48, or may store new container lids and receive damaged lids, as will become more apparent hereinbelow. To effect raising and lowering of the grapple means 84 relative to the lower end 68 of the environmental chamber 30, the upper end of the spline shaft 84 carries a ball screw housing 106 which has cooperative relation with a helically grooved ball screw shaft 108 rotatable through an electric elevator drive motor 110 supported on the upper end plate 72 within the maintenance chamber 16. Energizing the drive motor 110 effects rotation of the screw shaft 108 to raise the spline shaft 84 and thus the grapple head 100 relative to the floor plate 68 of the environmental chamber. The circular access opening 78 in the environmental chamber 30 is defined by an annular housing 114 secured at its upper end to the floor plate 68. The housing 114 supports an annular ring seal 116 through a pair of concentric metallic bellows 118a and 118b. The metallic bellows 118a, b are normally maintained in compressed conditions holding the annular seal ring 116 raised clear of the underlying conveyor means 34 and associated chambers 36. When it is desired to effect a sealing relation between the environmental chamber 30 and an underlying conveyor chamber 36, pressure is applied to the interspace between the bellows 118a, b to extend the bellows and press the sealing ring 116 into contact with an upper surface 120 on an axially underlying chamber 36, the sealing ring preferably having a pair of suitable concentric sealing rings 122a, b mounted thereon for this purpose. Preferably, a gas line 124 has communication with the surface of the sealing ring 116 in which the ring seals 122a, b are disposed, and is operative to flush the upper surface 120 of an underlying chamber 36 with a suitable gas so as to clean the same as the sealing ring is brought into sealing engagement therewith. The gas ejected to flush the surface 120 also serves to provide a buffer within the area underlying the grapple head so as to prevent ingress of air. The grapple head 100 is operative to remove container lids 49 from their associated containers 48 when axially underlying the access opening 78, and thereafter replace the container lids after removing and/or inserting a fuel element into the underlying container. To effect manipulation of the container lids 49, the grapple head 100 includes a circular housing plate 130 which is suitably fixed to the lower end of the tubular support arm 98, as best seen in FIG. 5. The housing plate 130 is adapted to engage an annular surface 132 on an underlying lid 49, either during pickup of a lid from one of the storage chambers 104 or 106, or when moving the grapple head into position to remove a container lid from its associated container 48. A grapple plate 134 is carried on the lower end of a grapple control shaft 136 through a bearing 138 and cooperates with the housing plate 130 to support a plurality of radially reciprocal latch members 140 which are movable between inner positions disposed between the plates 130 and 134 and outer positions wherein outer ends 140a of the latch members engage an annular groove 142 formed in each of the container lids 49. Radial movement of the latch members 140 is effected by a cam plate 144 having a helical cam groove or slot 144a in its lower surface which receives a roller 146 mounted on the upper surface of each of the latch members 140. The cam plate 144 is fixed on the grapple control shaft 136 so that rotation of the grapple control shaft is operative to rotate the cam plate and, because of the helical shape of the cam groove 144a, effect radial outward or inward movement of the associated latch members 140 depending upon the direction of rotation of the cam plate. The control shaft 136 is connected through suitable right-angle bevel gear connections within the gear housings 96 and 94 to an upper grapple control shaft 136a the upper end of which extends coaxially upwardly through the screw shaft 108 and is connected to an electric grapple drive motor 146 mounted on the upper end plate 172 within the maintenance chamber 16. Preferably, one or more grapple keys, such as shown at 148 in FIG. 5, are carried by the grapple housing plate 130 and are adapted to be received within suitable radial slots 150 formed in the container lids 49 to prevent rotation of the container lid during manipulation by the grapple head 100. Microswitches (not shown) are provided in suitable locations to indicate contact of the grapple housing 130 with a container lid 49 and for indicating engaged or disengaged positions of the latch members 140. It is desirable that the access opening 78 in the bottom end plate 68 of the environmental chamber 30 be sealed closed when the sealing ring 116 is in its upper position disconnected from an underlying conveyor chamber 36 so that a gaseous atmosphere (or a vacuum) may be maintained in the environmental chamber 30. To this end, the grapple head 100 carries a floating flange 154 on the tubular arm 98 through circumferentially spaced guide rollers, one of which is shown at 156 in FIG. 5. The floating flange 154 is recessed within its lower surface so as to nest with the grapple housing plate 130 and is urged against the grapple housing plate by a coil compression spring 158. A metallic bellows seal 160 is mounted concentrically of the tubular arm 98 within the compression spring 158, and has its upper end sealingly secured to a radial flange 162 on the gear housing 96. The lower end of the bellows seal 160 is sealingly secured to the floating flange 154. An annular sealing plate 166 is carried by the floating flange 154 and has a pair of suitable annular seals 168 mounted thereon for engagement with an annular shoulder surface 170 formed on the housing 114 when the grapple head is moved downwardly through the access opening 78 to lace a container lid 49 on an underlying container 48, or when removing a container lid therefrom. During sealing engagement of the sealing plate 166 with the shoulder surface 170 on the housing 114, the interior of the environmental chamber 30 is sealed against both egress of gas, such as helium, therefrom and ingress of air or other undesirable gas into the environmental chamber. A gas line 172 has connection between a source of suitable gas and the sealing surface of the seal housing 166 to facilitate cleaning of the sealing surface 170 prior to contact therewith. Such gas also provides a buffer media when the closure is made. Four equidistantly circumferentially spaced power rams, one of which is shown at 174 in FIG. 5, are mounted on the lower surface of the sealing plate 166 and are adapted to engage an underlying container lid 49 for securing the lid against the associated container mounting flange 48a during actuation of the latch members 140. To facilitate observation within the environmental chambers 30, and particularly the grapple heads 100 and associated support structures, a suitable telescope and lighting device 180 is interconnected to each enlarged environmental chamber housing 102 so as to extend outwardly into the inspection area 26. Each device 180 has an outer control end 180a which permits manipulation for viewing within its associated environmental chamber. CONVEYOR Taking one of the conveyor means 34 as representative of the two conveyors in the illustrated embodiment of the system 10, and with particular reference to FIGS. 7-9 taken in conjunction with FIGS. 1-3, each conveyor means 34 includes a pair of parallel over-shaped frame members 184 and 186 supported within the conveyor chamber 20 to define an endless path through which the chambers 36 may be moved to effect underlying axial alignment of the axis of each chamber with the access opening 78 in the environmental chamber 30. The frame members 184 and 186 support mutually facing C-shaped tracks 188 and 190, respectively, which cooperate to define a track along which the conveyor chambers 36 are conveyed. The conveyor means 34 preferably supports a number of watertight chambers 36 sufficient to provide storage for one refueling zone inventory of a reactor core, the watertight chambers 36 being interconnected for articulated movement so as to readily traverse the oval guide path. The chambers 36 are formed in pairs of two parallel spaced chambers interconnected through a housing link 192 formed integral with or otherwise secured to the associated pair of spaced chambers. Each housing link 192 is supported by a pair of guide rollers 194a and 194b which are received within and guided along the tracks 188 and 190, respectively. The juxtaposed chambers 36 which are not fixedly connected through a housing link 192 are interconnected for articulated movement therebetween through housing links or connecting frames 198 which are also supported by pairs of guide rollers 194a and 194b received within the tracks 188 and 190. The housing links 192 and 198 maintain fixed spacing between the chambers 36 as they are conveyed along the guide path defined by the tracks 188 and 190. To effect movement of the chambers 36 along the guide tracks, the housing links 192 and 198 each rotatably support a drive roller 200 adapted for cooperation with an annular drive sprocket 202. The drive sprocket has a plurality of equidistantly circumferentially spaced recesses 204 formed therein to receive successive ones of the drive rollers 200 during rotation of the drive sprocket. Rotation of the drive sprocket is effected by a drive pinion 206 secured to the lower end of a conveyor drive shaft 208 and having mating engagement with an internal ring gear 210 mounted on the sprocket 202. The conveyor drive shaft 208 is connected at its upper end to a suitable electrical drive motor 212 supported within the maintenance chamber 16, as shown in FIG. 1. A normally engaged pneumatically releasable locking latch (not shown) is operable to prevent movement of the conveyor chambers 36 when the environmental chamber seal ring 116 is engaged with one of the chambers 36 or when the canning machine, to be described hereinafter, is engaged with a container carried within one of the chambers 36. The locking latch is preferably provided with suitable interlocks (not shown) which prevent withdrawal of the locking latch until safety signals indicate safe conditions for moving the conveyor. Referring particularly to FIG. 9, each chamber 36 has stepped diameters at its upper end and supports a plurality of transfer balls 216 on an annular surface 218 within the chamber. The transfer balls 216 underlie and support a self-centering support ring 220 on which the annular flange 48a of a container 48 may be supported internally of the watertight chamber 36. The support ring 220 compensates for possible misalignment when a container 48 is moved to a position underlying the access opening 78 in the environmental chamber 30, or when a container is moved to a position axially underlying the canning machine 40 or the lifting hoist 44. Preferably, a plurality of latches 222 are pivotally mounted on an annular support ring 224 circumferentially of the upper end of the watertight chamber 36 and are operative through pneumatic actuating means (not shown) to engage the upper surface of a container lid 49 and maintain the lid in normally sealed relation with its underlying container 48. An annular plate 226 is mounted on the upper end of the chamber 36 to maintain the latch support ring 224 and self-centering ring 220 in assembled relation within the upper end of the chamber. INSPECTION TABLE At least one station on each of the conveyors 34 includes inspection table means, indicated generally at 232, on which fuel and reflector elements can be placed for both mechanical and visual inspection. With particular reference to FIGS. 10 and 10a, taken in conjunction with FIG. 7, the inspection table means 232 includes a watertight cylindrical tubular casing 234 supported by housing links 192 and 198 in a manner similar to the watertight chambers 36 for movement along the guide path defined between the tracks 188 and 190. The upper end of the casing 234 has rollers 236 mounted thereon in generally diametrically opposed relation for centering engagement with the mutually facing upper edges of the guide tracks 188 and 190 during movement along the conveyor path. The inspection table means 232 includes an upper circular support table or platform 238 mounted on the upper end of a cylindrical tubular wall 240 which has a circular gear housing 242 secured to its lower end. The support table 238 and associated cylindrical wall 240 are rotatable within a sleeve 246 having an annular bearing support plate 248 secured to its lower end. The sleeve 246 is adapted for axial telescoping movement relative to the outer casing 234 through rollers 250 secured in circumferentially spaced relation to the sleeve 246 for rolling engagement with the internal surface of the outer wall 234. Axial movement of the support table 238 and associated wall 240 is effected by a double acting pneumatic cylinder or ram 252 the upper end of which is secured to the bearing support plate 248. The double acting cylinder 252 has a first piston (not shown) extendible from its lower end to effect axial movement of the gear housing 242, support plate 248 and support table 238 between upper positions, as shown in FIG. 10, and lowered positions retracted within the outer casing 234 to lower a fuel or reflector element, a portion of which is shown in phantom at 256 in FIG. 10, below the upper surface of the associated conveyor 234 so that the fuel element clears the environmental chamber 30 during movement of the inspection table along the path of the conveyor 34. When it is desired to inspect a fuel element, the inspection table means 232 is advanced to a position axially underlying the access opening 78 in the environmental chamber 30 by operation of the conveyor drive motor 212. With the grapple head 100 moved to a position clear of the opening 78, a fuel element may be transferred downwardly through the transfer chute 12 and positioned on the underlying support table 238. Thereafter, the support table may be lowered through the double acting cylinder 252 and the inspection station advanced to a position generally adjacent a viewing window 258 mounted within the housing 14, as best seen in FIGS. 2 and 3. Alternatively, a periscope or closed-circuit TV may be mounted within the housing 14 or internally of the conveyor chamber 20 to facilitate inspection of the fuel elements. A pair of locating dowels 260 are mounted on the support table 238 for registration with correspondingly located recesses in the lower surfaces of fuel elements to effect desired registration of the fuel elements on the support table 238. When the inspection table means 234 has been moved to a desired inspection position, the actuating cylinder 252 is pressurized to raise the support table 238 and associated fuel element to a position generally level with the upper surface of the conveyor 34 for visual inspection. With the fuel element in a raised position, the support table may be rotated through a pneumatic motor 264 having a drive pinion 266 thereon engaging a ring gear 268 on the gear housing 242. The gear housing 242 is interconnected to the upper end of the cylinder 252 and to the bearing support plate 248 through suitable bearings. The fuel and reflector elements 256 conventionally have cooling channels extending longitudinally therethrough which may become obstructed so as to adversely effect cooling of the fuel and reflector elements during operation within a reactor core. To facilitate mechanical inspection of the cooling channels within a fuel or reflector element, the inspection table means 232 includes a plurality of elongated parallel probes 270 mounted in upstanding relation on a circular base plate 272 and extending through corresponding axially aligned openings 238a formed in the inspection table 238. The base plate 272 is mounted on the upper end of an extendible piston rod 274 adapted for outward extension from the upper end of the double acting cylinder 252 so as to extend the probes 270 upwardly through the support table 238 and into the cooling channels within the fuel or reflector element supported on the support table. As best seen in FIG. 10a, each of the inspection probes 270 is axially slidable within a bore 272a in the base plate 272 and is retained therein by a bolt 273 against the upward bias of a compression spring 275. The probes 270 are thus downwardly movable relative to the base plate 272 in the event any of the probes encounters an obstruction within its corresponding cooling channel in the fuel element being inspected. Such downward movement of a probe 270 serves to effect engagement of its corresponding bolt 273 with a guide plate 276 supported by the mounting plate 272 so as to move the guide plate downwardly to actuate a limit switch 278 mounted on a plate 280 which is also fixed on the upper end of the piston 274. The limit switch 278 is connected in circuit to provide a signal to the operator that an obstruction has been encountered and may also be operative to deenergize the cylinder 252. A guide rod 282 is secured to the lower surface of the plate 280 and extends through a suitable opening in the gear housing 242 to prevent rotation of the inspection probes 270 about the axis of the piston rod 274. Suitable instrumentation (not shown) may be provided to indicate to the operator the vertical positions of the support table 238 and inspection probes 270 during an inspection operation. When retracted below the upper surface of the conveyor 34, the support table 238 may be employed to store container lids 49 in addition to those stored in the storage chambers 104 and 106 in the environmental chamber 30. It will be appreciated that if the fuel and reflector elements have different coolant channel patterns, more than one inspection table means 232 should be provided on each conveyor 34. CANNING MACHINE As aforedescribed, container lids 49 are normally secured on the upper ends of the containers 48 by screws or bolts 51 having threaded connection to the container mounting flanges 48a. To facilitate loosening and removal of the screws 51 of a container lid from its associated container preparatory to removing the lid, and to facilitate subsequent remounting of the container lid on the container, the system 10 includes a canning machine 40 overlying each of the conveyors 34. With reference to FIG. 11, taken in conjunction with FIGS. 2 and 3, a canning machine 40 is mounted within the housing 14 generally adjacent each environmental chamber 30 to facilitate removal of the hold-down screws or bolts 51 on a container lid 49 from the associated container flange 48a just prior to advancing the container to a position underlying the access opening 78 in the environmental chamber. Each canning machine 40 is supported within a vertical penetration 284 in the housing 14, as shown in FIG. 11, and is removable from its penetration for servicing. Each canning machine 40 includes an outer annular member 286 having an upper radial flange 286a which supports the member 286 within and facilitates attachment to the penetration 284. A cylindrical tubular housing 288 is mounted interiorly of the annular member 286 for axial sliding movement therewithin, and has a lower annular flange 290 which carries a plurality of parallel discrete stub shafts 292 each of which has a bolt-head receiving socket 294 on its lower end. The stub shafts 292 are adapted to be rotated about their longitudinal axes within the flange 290 by corresponding torque rods 296 which extend upwardly through the annular member 286 and have connection to individual pneumatically operated bolt setters 298 of known design mounted within the maintenance chamber 16. The stub shafts 292 are mounted within the flange 290 so as to have a degree of vertical freedom and thereby accommodate varying rates of bolt displacement. Axial movement of the inner tubular housing 288 and associated bolt sockets 294 is effected by a pneumatic cylinder or ram 300 having an extendible piston 302 connected to a counterweight 304 secured within the tubular housing 288 such that extension and retraction of the piston 302 effects a corresponding axial movement of the bolt sockets 294. An annular counterbalance weight 306 is disposed about the upper end of the inner tubular housing 288 and is connected to the counterweight 304 through cables 308a and 308b which are reeved over pulleys 310a and 310b, respectively, mounted within a suitable housing 312 secured to the upper end of the canning machine. A lift lug 314 is mounted on the housing 312 to facilitate removal of the canning machine 40 from its associated penetration 284. With a container 48 and associated lid 49 clamped within a conveyor chamber 36 by the aforedescribed latches 222 and moved to a position axially underlying a canning machine 40, the pneumatic ram 300 may be energized to move the tubular body 288 to a downward position wherein a lower chamfered end 288a on the tubular housing 288 seats within the underlying container lid 49 as the housing 288 moves downwardly to engage the underlying container. At least one, and preferably three, locating keys 316 are mounted on the lower end of the housing 288 for registration with corresponding underlying slots 150 formed in the container lids in similar fashion to the operation of the aforedescribed grapple keys 148. The keys 316 assure proper orientation of the bolt sockets 294 with the bolts 51 in the container lid so that bolts may be removed from or run down into the threaded receiving bores in the container flange by the pneumatic bolt setters 298. Indicator switches (not shown) are provided to indicate when the housing member 288 is fully seated within an underlying container lid 49. Indicator switches (not shown) are also preferably provided to indicate when each bolt 51 is engaged and seated. A system for torque sensing the preload on each bolt 51 is also preferably provided. SUMMARY OF OPERATION Having thus described the various elements of the system 10 in accordance with the present invention, its general operation will now be described. For purposes of example, the operation will be described in the transfer of a fuel element from the fuel transfer cask 32 to the storage area 22. Assuming that the bolts 51 securing a container lid 49 to its associated container 48 have been removed by a canning machine 40 in a manner as aforedescribed, and that the container lid is retained on the container through the latches 222 mounted on the associated watertight chamber 36 which has been moved to a position axially underlying the access opening 78 in the environmental chamber 30, and assuming further that the corresponding grapple head 100 is disposed in a position wherein its floating flange 154 has sealing relation with the annular housing 114, the sealing ring 116 is then moved downwardly to engage the underlying surface 120 on the chamber 36 in sealed relation therewith. As the sealing ring 116 and the floating flange 154 are moved into sealing engagement, respectively, with the underlying chamber 36 and annular housing 114, a suitable gas such as helium may be ejected at the sealing surfaces to clean the mating surfaces and establish a gaseous barrier preventing ingress of air. The space internally of the bellows 118b, sealed grapple head 100 and underlying chamber 36 may then be purged with a suitable gas such as helium. After purging the area immediately surrounding the container 48 underlying the environmental chamber 30, the elevation motor 110 is energized to move the grapple means 84 downwardly to lower the grapple housing 130 until the grapple plate 134 is seated within the upper recessed surface of the underlying container lid 49. The grapple drive motor 146 is then energized to effect rotation of the cam plate 144 in a direction to move the latch members 140 radially into engagement with the annular groove 142 in the container lid. The elevation motor 110 is then reversed to raise the grapple head 100 and container lid 49 into the environmental chamber 30 whereupon the azimuth drive motor 88 is energized to move the grapple head to a position overlying either of the recesses 104 or 106. If the container lid is damaged or otherwise needs replacement, it is deposited within one of the recesses 104 or 106 and the grapple head is then moved to the other of the recesses to pick up a new container lid. With the grapple head 100 removed from the access opening 78, the lower guide sleeve 64 is moved downwardly through the opening 78 to a position adjacent the underlying open ended container 48. The floor valve 54 is then opened and a fuel or reflector element is lowered into a transfer chute 12 from the transfer cask 32 which has previously been moved to a position overlying the floor valve 54. The fuel or reflector element is lowered from the transfer cask by the transfer cask hoist downwardly through the upper and lower guide sleeves 62 and 64 into the underlying container 48. After loading a fuel or reflector element into a container 48, the floor valve 54 is again closed and the lower guide sleeve 64 is retracted to its upper position within the environmental chamber 30. The grapple head 100 is then moved to a position overlying the access opening 78 by energizing the motor 88, and the motors 110 and 146 are again energized in sequence to lower the grapple head 100, which has retained the previously removed lid or has picked up a new replacement lid, and placed the container lid on the underlying container after which the grapple head 100 is released from the container lid and the latches 222 are again actuated to clamp the container lid firmly in place. After the container lid 49 is placed on the container 48 and the latch members 140 retracted, the grapple housing 130 is raised to a position nesting with the floating sealing flange 154 to clear the conveyor 34. The conveyor chamber 36 and associated container 48 underlying the environmental chamber opening 78 are now moved to a position axially underlying the associated canning machine 40 whereupon the screws or bolts 51 carried by the container lid are run down into the underlying container flange 48a to firmly secure the lid in sealed relation to its underlying container in a manner as aforedescribed. From the canning machine 40, the sealed container and internal fuel or reflector element may be advanced to a position underlying the transfer tube 42 whereupon the lifting hoist 44 may be moved downwardly to remove the sealed container from its associated chamber 36, raise the sealed container upwardly within the transfer hoist chamber 18 and move it to a position overlying the passage 46 whereupon the hoist 44 can lower the sealed container down into the fuel storage chamber 22 which is filled with water to a height sufficient to totally cover the fuel element containers. Movement of the fuel element containers 48 from the storage chamber 22 to a conveyor 34 from which the container is moved to underlie the environmental chamber 30 and the fuel or reflector element transferred upwardly to the fuel transfer cask is effected in a reverse procedure to that just described. When it is desired to inspect a fuel or reflector element, an inspection table means 232 on the conveyor 34 is moved to a position axially underlying the access opening 78 in the environmental chamber. The support table 238 is raised to the level of the upper surface of the associated conveyor 34 and sealing is effected with the sealing ring 116 in a similar manner to sealing with a chamber 36 as aforedescribed. A fuel or reflector element may then be lowered from the transfer cask to the support table 238 whereupon the support table is lowered through actuation of the double acting cylinder 252 to lower the fuel element sufficiently to allow movement to an inspection station. The support table 238 may then be raised to raise the associated fuel element, and the pneumatic motor 264 energized to rotate the fuel element for visual inspection thereof. The inspection probes 270 may then be raised through the double acting cylinder 254 for mechanically inspecting the cooling channels within the fuel or reflector element. Upon completing inspection, the fuel or reflector element may be lowered and again returned to a position underlying the environmental chamber 30 whereupon the fuel element may be moved back into the fuel transfer casks 32 or temporarily raised into the environmental chamber and then lowered into a container 48 which has been moved to a position underlying the environmental chamber through selective movement of the conveyor 34. Having thus described the system 10 in accordance with the present invention, it is seen that a remotely controllable system for the transfer of fuel and reflector elements between a reactor vessel and a storage area is provided having capability to maintain the element in a gaseous environment sealed against egress of radioactive contaminants and ingress of air. The system is operative to effect canning of the fuel and reflector elements while maintaining the elements in a desired gaseous environment. This is accomplished by the environmental chamber 30, the grapple means 84, the underlying conveyor 34, and an associated canning machine 40. The associated environmental chambers, conveyors, and canning machines together remove and replace the closures of containers in which the fuel elements are sealed, and permit visual and mechanical inspection of the elements by operators located in remote shielded areas, while maintaining a predetermined gaseous atmosphere in the containers. While a preferred embodiment of the system in accordance with the present invention has been illustrated and described, it will be understood to those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects. Various features of the invention are defined in the following claims. |
description | Systems are now being adopted for sterilizing various types of articles including food products by radiating the food products. When the food products are relatively narrow, electron beams are now generally being used. The electron beams have especial utility when the articles being irradiated have a thickness within particular limits. For example, electron beams are used to irradiate flat hamburger patties weighing one-quarter of a pound (xc2xc lb) or one-half of a pound (xc2xd lb). Electron beams are generally not effective in irradiating articles having a relatively great width. This results from the fact that the electron beams have weight. This weight causes the electron beams to become decelerated as they pass through the article being irradiated. Thus, the interior of the articles is not irradiated. This is true even when the electron beams enter into the article from two (2) opposite sides of the articles in two (2) successive movements of the article past the radiator. For articles of considerable thicknesses, x-rays are often used to irradiate the articles. X-rays are advantageous because they constitute electromagnetic waves which do not have any mass. As a result, the x-rays are not slowed as they pass through the articles being sterilized. A disadvantage is that a considerable amount of the x-ray energy is not utilized in sterilizing articles when the thickness of the articles is (a) above the range where the articles can be sterilized by electron beams (b) but below the range where the full intensity of the radiation from the x-rays can be efficiently utilized in sterilizing the articles. The preferred embodiment of this invention provides for an efficient use of the full intensities of x-rays in sterilizing relatively thick articles. This efficient use is provided by subjecting the articles initially to the full intensity of the x-ray radiation from an accelerator and subsequently to the reduced intensity remaining after the initial radiation of the articles. The initial and subsequent radiations are provided in a way so that the number of articles radiated per unit of time is not reduced relative to the number of units which are radiated per the unit of time when only the initial radiations are provided. In a preferred embodiment of the invention, a beam of radiation, preferably x-rays, is provided by accelerators generally indicated at 10. The x-rays may be formed in a conventional manner well known in the art. For example, the x-rays may be formed by impinging electrons in an electron beam on a Brehm stalling member such as a member made from titanium. This is well known in the prior art. The beam of x-rays is directed to articles 12 which are transferred from a loading area generally indicated at 14. The articles 12 may have a thickness which is greater than the maximum thickness at which the articles can be irradiated by an electron beam. The articles 12 may be stacked in a queue 16 at a position between the loading area 14 and the position at which the articles are irradiated by the accelerators 10. The release of successive ones of the articles 12 from the queue 16 may be controlled by a microprocessor 18. The loading area 14, the queue 16 and the microprocessor 18 may be constructed in a conventional manner well known to persons of ordinary skill in the art. The articles 12 may be moved by a conveyor system, generally indicated at 20, from the loading area 14 to the position at which the articles are irradiated by the radiation, preferably xrays, from the accelerator 10. The irradiation of the articles 12 is preferably provided within a closed chamber 22. The chamber 20 may be made from a suitable material such as concrete or steel to insulate the space outside of the chamber from the radiation within the chamber. The articles 12 on the conveyor system 20 are transferred to a conveyor system, generally indicated at 24, which is preferably disposed in the form of a loop within the chamber 22. Preferably the conveyor system 24 may be constructed in a conventional manner and is preferably provided in the form of a closed loop. The articles 12 are moved on the conveyor system 24 past the accelerators 10 which direct the radiation from the accelerator against a first side of the articles. The articles 12 are then moved on the conveyor system 24 to apparatus 26 which rotates the articles in a conventional manner through an angle of substantially 180xc2x0. In this way, radiation from the accelerators 10 will be directed against a second side of the articles opposite the first side when the articles are directed by the conveyor system 24 for a second time past the radiation from the accelerators 10. A switch 25 is provided with first and second states of operation. In the first state of operation, the switch 25 provides for a transfer of the loading article 12 in the queue 16 to the conveyor system 24. In the second state of operation, the switch 25 provides for the movement of the article on the conveyor system 24 past the accelerators 10 in a second pass to obtain an irradiation of the x-ray beam through the second side of the article 12 after the article has been rotated through an angle of substantially 180xc2x0. The operation at each instant of the switch 25 in the respective one of the first and second states is controlled by the microprocessor 18. As will be appreciated, the switch 25 operates in the first state for each article 12 to provide for a transfer of the article from the conveyor system 20 to the conveyor system 24. The switch 25 subsequently operates in the second state to provide for the movement of the article 12 a second time past the accelerators 10 to obtain an irradiation of the second side of the article. The times for the operation of the switch 25 in the first and second states are controlled by the microprocessor 18. A switch 28 is provided on the conveyor system 24. The switch 28 may be provided with first and second states of operation under the control of the microprocessor 18. In the first state of operation, the switch 28 provides for the movement of the articles 12 past the apparatus 26 for rotating the articles through the angle of 180xc2x0. In the second state of operation, the switch 28 provides for the transfer of the articles 12 from the conveyor system 24 to a conveyor system, generally indicated at 30. The operation of the switch 28 in the first and second states may be controlled by the microprocessor 18. The switch 28 is initially operated in the first state for each of the articles 12 under the control of the microprocessor 18 and is subsequently operated in the second state for each of the articles 12 under the control of the microprocessor. By providing the switch 28 in the first state of operation and rotating the article 12 through the angle of substantially 180xc2x0, the article 12 on the conveyor system 24 is irradiated from the second side of the article. This causes the cumulative irradiation at the different positions in the article 12 to be, for every position in the article, between maximum and minimum limits. The minimum limit of irradiation intensity is selected to insure that the cumulative irradiation at every position in the article 12 is at least at a level of intensity where harmful bacteria such as E col are destroyed. The maximum limit of irradiation intensity is selected so that beneficial bacteria in the article will not be destroyed. The thickness of the article 12 may sometimes be above a value where the cumulative intensity of the radiation of the article at some positions in the article will be above the maximum intensity of the article irradiation for optimal results even though the intensity of the irradiation of the article at other positions is between the maximum and minimum limits. Under such circumstances, a member may be positioned between the accelerator 10 and the article 12 to absorb some of the radiation intensity from the accelerator at the positions in the article where the intensity of the radiation is above the maximum limit. In this way, the cumulative intensity of the radiation at every position in the articles is between the minimum and maximum optimal values. A system for adjusting the intensity of the irradiation in the article 12 to intensities between the minimum and maximum values is disclosed and claimed in U.S. patent application listing Gary K. Loda and Richard C. Miller as joint inventors and relating to a SYSTEM FOR, AND METHOD OF, IRRADIATING AN OBJECT WITH AN OPTIMAL AMOUNT OF RADIATION. Patent application Ser. No. 09/710,930 is assigned of record to the assignee of record of this patent application. Since x-rays can penetrate the article 12 through relatively great thicknesses, the x-rays can often pass from one side of the article through the article and emerge from the opposite side of the article with a significant intensity. Until now, such x-ray energy has been lost since no use has been made of such energy. This application provides a system for, and method of, utilizing the significant amount of energy passing through each of the articles 12 so as to irradiate the article with this significant amount of energy. In this way, substantially all of the x-ray energy in the radiation beam from the accelerators 10 is used to irradiate the article 12. In irradiating the article 12 twice in this manner, the intensity of the radiation beam from the accelerator 10 can be reduced, thereby minimizing the cost of the accelerator and the cost of providing radiation from the accelerator, when the irradiations of the articles 12 on the conveyor systems 24 and 30 are cumulatively at the desired intensity. To utilize the x-ray energy passing through the article 12 on the conveyor system 30, the switch 28 is operated in the second state after the article has been rotated through an angle of substantially 180xc2x0 by the apparatus 26 and the second side of the article has been irradiated by the x-ray beam from the accelerators 10. In the second state of operation, the switch 28 passes the article 12 to the second conveyor system 30. The second conveyor system 30 is disposed in the thick amber 22. The second conveyor system 30 may be disposed in a loop, preferably closed, similar to the configuration of the conveyor system 24. However, as shown at 29 in the single FIGURE, the article 12 may have to travel through a portion of a loop after it has been transferred from the conveyor 24 and before it reaches the conveyor system 30. At substantially the same time that the article 12 on the first conveyor system 24 is transferred to the second conveyor system 30, an article 12 in the loading area 14 is transferred to the queue 16. At substantially the same time, the leading article 12 in the queue 16 is transferred to the conveyor system 24. The movement of the article 12 from the first conveyor system 24 to the position on the second conveyor system 30 for receiving the x-ray beam passing from the accelerators 10 through the article on the first conveyor system 24 is synchronized with the movement of the article from the queue 16 to the position on the first conveyor system for receiving the x-ray beams from the accelerators 10. This synchronization is provided by the operation of a queue 32 on the second conveyor system. The queue 32 stores articles transferred from the first conveyor system 24 and releases the leading article in the queue for movement to the position for receiving the x-ray beam passing from the accelerators 10 through the article on the first conveyor system. The microprocessor 18 synchronizes the movement of the article 12 from the queue 32 to the position for receiving the x-ray beam passing from the accelerator 10 through the article on the first conveyor system 24. The microprocessor 18 also synchronizes the movement of the article from the queue 16 in the first conveyor system 24 to the position for receiving the radiation from the accelerators 10. In this way, the x-ray beam from the accelerators 10 passes through the article 12 on the first conveyor system 24 and then through the article on the second conveyor system 30. The synchronization by the microprocessor 18 between the movement of each article on the first conveyor system 24 and the article on the second conveyor system 30 is even more sophisticated than indicated in the previous paragraph. This even more sophisticated synchronization is provided by the microprocessor 18. Under the control of the microprocessor 18, the first side of the article 12 on the conveyor system 24 moves past the radiation from the accelerators 10 at the same time that the first side of the article on the conveyor system 30 moves past the radiation passing from the accelerators through the article on the conveyor system 24. In like manner, the second side of the article 12 on the conveyor system 24 moves past the radiation from the accelerators 12 at the same time that the second side of the article on the conveyor system 30 moves past the radiation passing from the accelerators through the article on the conveyor system 24. The synchronous movement of the second sides of the articles 12 on the conveyor systems 24 and 30 past the radiation from the accelerators 10 may be facilitated by providing queues 35 and 37 respectively on the conveyor systems 24 and 30 and by having the microprocessor 18 synchronize the release of the articles from the queues. An apparatus 33 is provided for rotating each article 12 on the conveyor system 30 through an angle of 180xc2x0 after the article has moved a first time past the position for receiving irradiation on the first side of each article on the conveyor system 30 from the accelerators 10 and before the article has moved a second time past the position for receiving irradiation on the second side of the article on the conveyor system 30 from the accelerators 10. The operation of the apparatus 33 in rotating each article 12 through an angle of 180xc2x0 is controlled by the microprocessor 18. A switch 34 having first and second states of operation is provided on the conveyor system 30 at a position past the position where each article 12 on the conveyor system is irradiated with the radiation passing through the article on the conveyor system 24 from the accelerators 10. In the first state, the switch 34 provides for the movement of each article 12 on the conveyor system 30 past the position where the radiation from the accelerator 10 passes through the articles on the conveyor system 24. In the second state, the switch 34 provides for the passage of the articles on the conveyor system 30 to a conveyor system generally indicated at 36. The conveyor system 36 moves the articles 12 to an unloading area generally indicated at 38. The articles 12 are removed from the conveyor system 36 at the unloading area 38. The operation of the switch 34 in the first and second state is controlled by the microprocessor 18. The switch 34 initially operates in the first state to move each article 12 on the conveyor system 30 past the position for irradiating the article with radiation passing through the article on the conveyor system 24 from the accelerator 10. The switch 34 operates in the first state twice so that the article 12 can move twice past the position for receiving radiation from the accelerators 10, the first time for receiving radiation on the first side of the article 10 and the second time for receiving radiation on the second side of the article. The switch 34 subsequently operates in the second state for transferring each article 12 from the conveyor system 30 to the conveyor system 36 and then to the unloading area 38 after the first and second sides of the article on the conveyor system 30 have been irradiated. Radiation shielding material is disposed within the chamber 22 in a strategic relationship to shield the articles 12 from radiation, except at the positions where they receive radiation from the accelerators 10, as the articles move through the chamber 22. For example, the chamber 22 may be defined by radiation shielding material 40. The shielding material 40 may be made from concrete. A radiation shielding member 42 made from a suitable material such as concrete may be disposed within the conveyor system 24 to prevent radiation from the accelerator 10 from passing to the conveyor systems 20 and 36, the loading area 14 and the unloading area 38. The radiation shielding member 42 also prevents radiation from the accelerator 10 from passing to the articles on the conveyor system 30 other than in the area where the radiation from the accelerator 10 passes directly to such articles. The radiation shielding member 42 may extend integrally from the radiation on shielding materials 40. A radiation shielding member 44 made from a suitable material such as concrete may be disposed within the conveyor system 30 to shield the articles on the conveyor system from radiation except where the articles move past the position where the articles receive the radiation passing through the articles on the conveyor system 24 from the accelerators 10. A radiation shielding member 46 made from a suitable material such as concrete may be disposed within the conveyor system 30 to shield the articles 12 as they move on the conveyor system except in the portion of the conveyor system where the articles move past the accelerators 10. Although this invention has been disclosed and illustrated with reference to particular preferred embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to persons of ordinary skill in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims. |
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claims | 1. A device for the creation and containment of plasma comprising:a chamber defining a volume;a first and second cathode positioned in the center of the chamber, the cathodes comprising electrode ends and cathode tip ends, wherein each of the first and second cathodes are positioned vertically within the chamber on a single yertical axis such that the cathode tip ends and the electrode ends of the cathodes are positioned on the vertical axis and the cathode tip end of the first cathode and the cathode tip end of the second cathode are aligned and facing one another, the cathode tip ends spaced from one another by a vertical gap, the gap centered about a gap point on the vertical axis;an anode formed as an elongate anode with a narrow widthwise end positioned outside of the gap and facing the gap, the widthwise anode end horizontally-positioned in the chamber at a height of the gap point and spaced a horizontal distance away from the gap point;a fuel source in communication with the chamber; andwherein a distance between the first cathode tip end and second cathode tip end is adjustable during operation based on an input from a sensor;wherein, the cathode electrode ends and anode end are in communication with an electricity source upon application of a voltage from the electricity source to the first and second cathode and anode, the positioning of the first and second cathode tips form a virtual point charge at the gap point, the voltage causing an ionization of fuel from the fuel source into a plasma, the charged plasma held in orbit about the virtual point charge and containing the plasma. 2. The device of claim 1, wherein the cathode tip ends comprise an exposed portion of metal. 3. The device of claim 2, wherein the metal is tungsten. 4. The device of claim 3, wherein the cathodes are insulated between the electrode end and the cathode tip end with an insulator. 5. The device of claim 4, wherein the insulator is aluminum oxide ceramic. 6. The device of claim 1, further comprising a current controller in communication with the electricity source, the current controller configured to oscillate a current to the anode and to the cathodes. 7. The device of claim 6, further comprising a voltage controller in communication with the electricity source, the voltage controller configured to oscillate a voltage to the cathodes. 8. The device of claim 7, further comprising a gap controller, the gap controller configured to move the cathodes along the vertical axis to modify a size of the gap. 9. The device of claim 8, further comprising a computerized controller, the computerized controller in communication with the gap controller, the voltage controller, and the current controller, and further in communication with at least one sensor, the sensor sensing a condition within the volume of the chamber, and wherein the computerized controller is configured to activate at least one of the gap controller, the voltage controller, and the current controller in response to the sensed condition within the chamber. 10. A method of operating the device of claim 1, the method comprising: drawing a vacuum in the chamber; injecting a fuel from the fuel source into the chamber; applying a current to the anode and to the cathodes by operating the electricity source. 11. The method of claim 10, wherein at least one wall of the chamber is used as a second anode. 12. The method of claim 11, wherein the fuel selected from the group consisting of hydrogen, deuterium, and tritium. 13. The method of claim 11, wherein the fuel contains positively charged ions. 14. The method of claim 13, wherein applying a current to the cathodes creates a virtual point charge that attracts the positively charged ions. 15. The method of claim 14, wherein the positively charged ions pass through the gap. 16. The method of claim 15, wherein the positively charged ions enter an orbit around and between the cathodes. |
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047180765 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 and 2, an example of an X-ray imaging apparatus according to the present invention comprises: an X-ray generator 21; a collimator or slit plate 23 separated by a certain distance from the X-ray generator 21 and having slits through which X-rays from the X-ray generator are allowed to pass; an X-ray image intensifier (or X-ray I.I.) 25 arranged facing the slit plate 23 with the subject or object 24 to be imaged interposed between them; a camera tube 28 for picking up the image through an optical lens system 27, said image then appears on an output screen 26 of the X-ray I.I. 25; and a signal processing means 30 for processing signals from the image obtained by the camera tube 28 and for applying these signals to reproduce the image on either a display means 29 and/or a recording means (not shown). The X-ray I.I. 25, lens system 27 and camera tube 28 form an X-ray image detector which serves to convert the X-ray image to electrical signals. The X-ray generator 21 includes a cylindrical anode target 32 housed in a vacuum container 31 which is rotated by a drive motor 33, an electron gun 34 arranged facing the cylindrical target 32 to generate an electron beam, and an electromagnetic deflection coil means 35 for deflecting the electron beam of the electron gun 34 in such a way that the electron beam (focused by an focusing device, not shown) scan the cylindrical target 32 while remaining substantially parallel with its rotating shaft. The vacuum container 31 is provided with an elongated X-ray irradiating window 36 extending in the longitudinal direction of the target 32, and is positioned between the target 32 and the slit plate 23. The X-ray beam is irradiated from that portion of the cylindrical target 32 in which the electron beam is irradiated from the electron gun 34, thus passing through the X-ray irradiating window 36. The X-ray generator 21 receives power and is energized by a power source 37 through a high tension cable 38. Deflection power is also supplied from the power source 37 to the deflection coil 35. The position of the X-ray focal point or X-ray emitting point (F) which corresponds to the irradiated point of the electron beam on the target 32 is supplied, in the form of electrical signals, to the signal processing means 30. The slit plate 23 is a thin plate made of heavy metal such as lead, for example, and is provided with a slit 22. The slit 22 may be made by partially cutting away the slit plate 23, or by covering the slit 22 thus formed with a metal, such as aluminium or beryllium, through which X-rays can pass with ease. The slit plate 23 is arranged so that its slit 22 is perpendicular to the direction in which the X-ra focal point (F) is moved. The X-ray I.I. 25 serves to convert an incoming X-ray image to an amplified optical image and has an input screen (P) which can sufficiently cover that part of the subject to be imaged. The X-ray I.I. 25 receives the X-ray beam which has passed through the slit 22 on its input screen (P), and displays on its output screen 26 the amplified optical image which corresponds to the X-ray beam received. The camera tube 28 is provided with a light conductive target, and is preferably energized by the current already supplied. The image signal reading position of the camera tube 28 is commanded by a signal applied from the signal processing means 30 so that the camera tube 28 can read image signals from this commanded position. Read image signals, as well as the commanded position information, are supplied to the signal processing means 30 through a signal electrode from the camera tube 28. The signal processing means 30 receives signals which show the X-ray focal positions of the X-ray generator 21, receives signals picked up by the camera tube 28, and receives signals which show the reading positions of the picked up signals. The signal processing means 30 then causes a spatial filter (which will be described later) to eliminate degraded components which are caused by scattered X-rays in the object. The signal processing means 30 also generates signals which correspond to the X-ray image and applies them to a cathode ray tube display means 29 which displays the received signals as an X-ray image. The signals may be applied to and recorded by a recording means (not shown) instead of being displayed by the display means 29. The signal processing means 30 also has the function of controlling the scanning area by the camera tube 28 according to the position of the X-ray focal point (F). The cylindrical target 32 in the X-ray generator 21 is rotated by the drive motor 33. The electron beam emitted from the electron gun 34 is deflected by the deflection coil means 35 to move relative to the target 32 in a direction substantially parallel to the axis of the target 32. X-rays are emitted from that point of the target on which the electron beam is irradiated. Since the electron beam moves, as described above, on the target 32 in a direction parallel to its axis, the X-ray focal point (F) also moves in a same direction. Referring to FIG. 2, when a human body whose chest is, for example, about 40 cm wide is to be imaged, the distance (S) which the X-ray focal point (F) moves on the cylindrical target 32 is 30 cm; the electron beam draws on the target 32 an oval having a shorter diameter of 0.5mm and a longer diameter of 2.5 mm; and the effective X-ray focal point (F) draws a circle having a diameter of 0.5 mm when viewed from the slit 22. If the width (G) of the slit 22 is 0.34 mm and its length is 17 cm, the effective diameter of the input screen of the X-ray I.I. 25 is about 57 cm. The distance (L1) between the moving line of the X-ray emitting point at the section of the X-ray generator 21, and the slit plate 23 is about 65 cm. The distance (L2) between the slit plate 23 and the X-ray II 25 is about 87 cm. The number of horizontal scanning lines on the camera tube 28 and on the display means 29 is about 1,024. When the moving line of the X-ray focal point is electrically scanned one time, image signals for each frame of the image relating to the human body are obtained. The size and shape of the X-ray focal point (F) at the section of the X-ray generator 21 are not limited to the above. For example, the electron beam irradiated on the target 32 may draw a prolate ellipsoid having a shorter diameter 0.5 mm and a longer diameter of 12.5 mm; the effective X-ray focal point may draw an oval having a shorter diameter of 0.5 mm and a longer diameter of 2.5 mm when viewed from the slit 22; and the shorter diameter formed by the X-ray focal point may be directed in the longitudinal direction of the slit 22. X-rays having a larger output can be obtained in this case. Image signals thus obtained contain a blur component because of the scattered X-rays generated in the subject to be imaged and because of the veiling glares generated in the X-ray I.I. 25 by the scattered rays and the discharging of undesired floating electrons. Referring to FIGS. 3A through 3D, FIG. 3A shows an X-ray image (Q) when an X-ray beam is irradiated onto an optional area (V0) of the entire region (P) to be imaged. The pickup signal level relating to the X-ray image (Q) in the vertical scanning direction of the electron beam of the camera tube 28 is shown in FIG. 3B. In FIG. 3B, the signal level of the picked-up X-ray image is plotted on the abscissa and position (V) in the scanning direction of the region to be picked up is plotted on the ordinate. As shown in FIG. 3B, the picked-up signal is highest at the area position (V0), and has skirting portions on both sides of its peak value. These skirting portions represent a blur component contained in the pick-up signal which is caused by scattered X-rays and the like. The blur component must be eliminated to obtain a high accuracy image. Specifically, for the purpose of obtaining such a highly accurate image display, therefore, the blur component must be eliminated from the image signal picked up by the camera tube 28. In the case of this embodiment, the noise component or blur components is removed by the signal processing means 30 which is adapted to also serve as a spatial filter. More specifically, because the signal processing means 30 functions as a spatial filter having the filter characteristic shown in FIG. 3C, it can filter the picked-up signal. The abscissa represents the filter functions and the coordinate positions in the scanning direction in FIG. 3C. This signal filtering is made possible by the digital operational process in the signal processing means. Thanks to this signal filtering, an image signal from which the blur component has been completely removed in the moving direction of the X-ray focal point (F). Therefore, only components containing no blur components can be picked up. Consequently, a high resolution and a high contrast can be obtained, as seen in FIG. 3D. The blur components are referred to as "further components" in claims 29-30. The components containing no blur components are referred to as "fundamental components" in claim 25. The abscissa represents various levels of the image signal and the coordinate positions in the scanning direction in FIG. 3D. This process is successively repeated for the entire region to be picked up. X-ray images obtained by scanning the moving line of the X-ray focal point (F) once are re-composed, thereby enabling a highly resolved and high contrast image to be displayed on the display 29. The filter function characteristic shown in FIG. 3C can be found by previously storing in the signal processing means 30 data regarding the amount of scattered X-rays and the amount of veiling glares of the X-ray I.I., expected based on the properties of the subject to be imaged and the imaging conditions, and by carrying out a predetermined operation in the signal processing means 30 on the basis of the stored data. Generally speaking, one scan using the X-ray focal point (F) can be finished in less than 0.5 seconds, for example. One frame area may be scanned twice at a high speed (0.1 second/30 cm, for example), and the image information thus obtained may be used to reproduce an image. As apparent from the above, X-ray imaging can be done quickly at a high speed, and an excellent image having high resolution and contrast can be obtained. Since the cylindrical target 32 is made rotatable and since the electron beam is electrically deflected to perform scanning, a large amount of X-rays can be obtained, thereby enabling high speed and an excellent S/N ratio. In the above-described embodiment, image signals are obtained by repeating the scanning of the signal reading electron beam of the camera tube 28 on the whole of the frame in its vertical direction (V). However, it is not limited to this embodiment. It may also be arranged that image signals are picked up (for every position of the X-ray focal point) only at a specific position and its adjacent area on the frame which correspond to the position of the X-ray focal point. This system of picking up image signals only for a specific position and its adjacent area will be described referring to FIGS. 4AI through 4DI, and FIGS. 4AII through 4DII, in which the abscissa represents the levels of an X-ray signal and the coordinate positions in the scanning direction. As shown in FIG. 4AI, it is assumed that the X-ray focal point is in a position which corresponds to a position (V1) on the frame. An area (Q) onto which the X-ray beam is being projected and its adjacent area are horizontally and vertically scanned by the camera tube 28 to read out such an image signal as shown in FIG. 4AII. The image signal is processed using the above-described spatial filter function of the signal processing means 30. In the case where the X-ray focal point then moves to a position (V2), an area (Q) onto which the X-ray beam is being projected and its adjacent area are horizontally and vertically scanned in a way that is similar to that of position (V1), as shown in FIG. 4BI. The image signal shown in FIG. 4BII is obtained and filtered through the spatial filter. Thereafter, every time the position of the X-ray focal point moves to V3, V4 . . . as shown in FIGS. 4CI, 4CII, 4DI and 4DII, the same process is repeated. The image is reconstructed on the basis of the image signals thus obtained, and is displayed on the display means 29. Symbol H in FIG. 4AI represents the scanning lines of the reading-out electron beam. As will be understood, in this embodiment, area Q on which the X-rays are irradiated is scanned along a plurality of scanning lines so that the fundamental components are obtained. The signal processing which uses the spatial filter may be carried out in such a way that signals read out by the X-ray detector are temporarily stored in the signal processing means before being subjected to the filtering process. According to the system which has been described referring to FIGS. 4AI through 4DII, read-out beam scanning may be applied for every X-ray emission to only a part of the vertically scanned region. Therefore, a sufficiently faster read-out scanning can be achieved, as compared with the moving speed of the X-ray focal point. More specifically, scanning by the read-out electron beam of the camera tube 28 is carried out at a speed sufficiently faster than the moving speed of the X-ray focal point (F) and at a position on the subject which corresponds to the X-ray focal position and on its adjacent area. The area to be scanned by the electron beam can be changed to correspond to a change in the position of the X-ray focal point. If this happens, the time necessary for taking the image can be further shortened, the amount of information relating to the image signals can be increased, and thus an X-ray image whose resolution has been further enhanced can be reproduced. During the processing of the X-ray image, X-ray image signals may be read out only at the area onto which the slit 22 of the slit plate 23 has been projected from the X-ray focal point, thereby reproducing an image. As an example of this system, wherein the X-ray image detector is provided with a camera tube, image signals may be selectively read out only when the scanning line of the read-out electron beam of the camera tube 28 is present on an area which corresponds to the X-ray beam which has projected the slit. The X-ray image detector is not limited to a combination of the X-ray I.I. and the camera tube as in the above-described embodiment. It may also be an X-ray I.I. which contains an output circuit for converting the output image directly to an electrical signal. Or it may be arranged that a fluorescent screen for storing energy which corresponds to the X-ray image may be used to energize image information on the screen which is read out by laser or the like and which is then converted to electrical signals. The X-ray generator 21 will be described more concretely with reference to FIGS. 5 and 6. The vacuum container 31 is similar in shape to a slightly flatter television cathode ray tube. The vacuum container 31 includes an enlarged portion 41 in which the cylindrical target 32 is housed. An electron emitting cathode electrode 42 which forms the electron gun 34 is also housed in the vacuum glass container 43. A cone portion 44, an air-tight connector portion 45, a ceramic or thin metal cylindrical portion 46, a bellows portion 47 and a cylindrical acceleration electrode portion 48 of the electron gun 34 are all air-tightly and successively connected with one another between the enlarged portion 41 and the container portion 43. The air-tight connector portion 45 includes a contact member arranged on the side of the cone portion 44 and another contact member arranged on the side of the cylindrical portion 46. The contact members are detachably connected, with each other by bolts 50, with an air-tight conductive packing 49 interposed between them. They are detachably arranged, as described above, for assembly, disassembly, or reassembly. Electromagnetic deflection coils 35 for deflecting electron beams are arranged outside the cylindrical portion 46. The inner face of the cylinder 46 is covered with a thin conductive film such as carbon so as to cause almost no eddy-current loss because of deflected magnetic field. The bellows portion 47 is intended to achieve micro-adjustment between the central axis of the electron gun 34 and the axis of the enlarged portion 41. An electromagnetic focusing coil 51 for the electron beam is fitted onto the acceleration electrode portion 48. An assembly including the coils 35 and 51 is covered with a cylindrical metal cover 52 and is connected to the ground. An insulating oil container 53 is arranged around the glass container 43 and is fixed to a flange of the vacuum container by bolts 55. An insulating cylindrical receptacle 56 is plugged in one end of the insulating oil container 53 to connect a high voltage cable (which corresponds to the one represented by numeral 38 in FIG. 1) thereto. Lead lines extending to a cathode 42 are connected to connecting terminals 57 arranged in the receptacle 56. The cathode 42 applies a high negative potential to the grounded vacuum container. The container 53 is filled with insulating oil, and is connected to an external cooler (not shown) through a pipe, thereby enabling the oil to be circulated into the container 53 through the cooler. An ion pump 59 is connected to the cone portion 44 of the vacuum container. A discharging pipe 61 which is connected to a discharge means 60 shown by a broken line is branched from the duct which extends to the ion pump 59. The cylindrical anode target 32 is a column made of a heavy metal such as tungsten (W) having a high melting point. Both ends of the target 32 ar rotatably supported in the enlarged portion 41 of the vacuum container 31 by means of support arms 62, 63 and bearings 64, 68. The upper bearing 64 is arranged in an air-tight vacuum cap 65 having a bolt-screwed flange 66, and is supported by two ball bearings 67. The other lower bearing 68 is supported by a magnetic seal 69 which has ball bearings 70 arranged on the outside, as shown in FIG. 7. The magnetic seal 69 includes a permanent magnet 71, magnetic poles 72, 73 each made of a ferromagnetic material, and a ferromagnetic cylinder 74 fixed onto the support arm. Magnetic liquid is present in a micro-clearance between these magnetic poles 72, 73 and the cylinder 74, thereby providing vacuum air-tightness. The ball bearings 70 are arranged outside or on the atmospheric side of the magnetic seal 69 to become integral with the magnetic seal 69. The angular-contact bearing is employed as the ball bearing 70 because it must mechanically support the heavy and large cylindrical target 32. As apparent from the above, vacuum air-tightness can be held by the inner magnetic seal 69 while the weight of the cylindrical target 32 can be supported by the ball bearings 70 arranged on the atmospheric side. These bearings are forcedly cooled from the outside by cooling pipes 75 and are mechanically fixed to the vacuum container 31 through a flange 76. That portion of the support arm 63 around which the bearings are arranged is made hollow so as to allow a cooling medium circulating pipe 77 to be inserted thereinto. The cooling medium is introduced and discharged, as shown by arrows, to circulate through the pipe 77, thereby preventing the magnetic seal 69 from being overheated while enabling heat from the target 32 to be discharged outside. The cooling medium passes through that portion of the pipe 77 which corresponds to the magnetic seal 69 and then through the portion which corresponds to the target 32 before being discharged. A gear 78 is connected to the support arm via a drive motor 33 to rotatably drive the support arm. The motor 33 is mechanically fixed to the vacuum container 31 through a support frame 79 and a fixing flange 80. Numeral 82 represents a jacket for the cooling medium. An elongated X-ray irradiating window 36 is arranged adjacent to the cylindrical target 32 in the vacuum container 31. The X-ray irradiating window 36 is formed by a thin plate of beryllium or titanium and is held air-tightly by a window frame 81. The cylindrical target 32 is rotated at a predetermined speed by means of a motor and receives the impact of the deflected scanning electron beam (E) to shoot X-rays. The electron beam (E) is irradiated through the deflection coil to a position on the cylindrical target 32 which is slightly separated from the center axis (O) of the target 32, and X-rays are shot from this focal point. The reason why the electron beam (E) is irradiated to that position on the cylindrical target 32 which is slightly separated from the center axis thereof is so that the projected electron beam can draw a true circle when the target 32 is viewed from the X-ray irradiating window or from the slit plate 23 at the time when the electron beam (E) strikes the target 32. Therefore, the electron beam (E) is irradiated on the cylindrical target 32 in such a way that its projected shape becomes a true circle when viewed from the X-ray irradiating window 36, thereby enabling a small X-ray focal point (F) to be formed with a sufficiently intense electron beam. According to the X-ray generator 21 having such an arrangement as described above, the electron beam scans the rotating cylindrical target 32, but remains parallel with the axis of the target to shoot X-rays. Accordingly, a sufficiently large amount of X-rays can be obtained, and the X-ray focal point (F) can be moved at high speed. In addition, the integral combination of the inner magnetic seal 69 and the outer ball bearings 70, which is used to support the cylindrical target 32, enables a sufficient amount of air-tightness to be held so that large and heavy targets can be supported stably while being rotated at high speed. Further, the inside of the vacuum container can be held to a pressure less than 1.times.10.sup.-7 torr thanks to the magnetic seal 69. Furthermore, the ball bearings 70 can be used on the atmospheric side, with lubricating agent being supplied, so that a large and heavy target can be operated at high speed over a long period of time. Heat generated from the target 32 is discharged to the outside as it is irradiated to the wall of the vacuum container. For the purpose of increasing this heat irradiation, the inner wall of the vacuum container may be colored black, or heat radiating fins or cooling pipes may be arranged around the vacuum container to forcefully cool it. As shown in FIG. 5, the X-ray generator 21 having the arrangement described above is well suited for the bearings 68 and 64, where the bearing 68 which is an integral combination of the magnetic seal and the ball bearings is located on the underside, and where the ball bearing 64 which is arranged in the vacuum inside the air-tight cap 65 is located on the top. More specifically, the bearing located on the underside serves to support the weight of the target by means of the ball bearings arranged in the atmosphere while keeping the vacuum in the container air-tight by means of the magnetic seal. On the other hand, the other bearing located on the top is similar to those used in the conventional X-ray tube of rotary anode type since it serves only to prevent the support arm from being deflected. The integral combination of the magnetic seal and the ball bearings may be used as the bearing located on the top. Therefore, a relatively large and heavy cylindrical target can be rotated at high speed, the X-ray focusing point can be moved to achieve scanning at a desired speed, and high speed X-ray photography can be carried out. Another X-ray generator 21 shown in FIG. 9 has a cylindrical target 32 comprising a plurality of spacers 91 which are piled one upon the other around the support arm or shaft 63. A heavy metal target layer 32a is coated over the outer surface of the piled spacers 91. The cylindrical target 32 is therefore allowed to have a larger diameter without increasing its weight. Some of the heat is transmitted from the target layer to the support shaft 63 through the spacers 91, while the remaining heat is transmitted to the vacuum container due to radiation, thereby balancing the distribution of heat over the whole of the X-ray generator. The bearing 68 which is similar to the one shown in FIG. 7 and which is an integral combination of the magnetic seal 69 and the ball bearings 70 is used at both ends of the support shaft 63. The support shaft 63 is hollow and is divided at its center by a partition plate 92. The cooling medium circulating pipe 77 is inserted into each of these hollow portions so as to circulate a cooling medium through the pipe as shown by the arrows. The rive motor 33 is connected to one end of the support shaft 63 through the gear 78. The cooling medium introduced from outside cools the magnetic seal portion 69 at first, enters into the target to absorb heat, and is finally discharged to the outside from the jacket 82 through the pipe 77. The temperature of the magnetic seal 69 is usually kept low due to the flow of this cooling medium, thereby enabling the vacuum and air-tight condition to be kept reliably. In addition, this cooling system also serves to cool the cylindrical target 32 so that the entire X-ray generator can be simplified in construction. The pair of upper and lower bearings 68, 68 is fitted into an opening of the vacuum container 31 at its flange portion and is air-tightly welded and fixed thereto at its arc welded portions 85, 85. The electron gun 34 comprises a cathode 42, a plurality of cylindrical electrodes 93, 94, and an acceleration electrode 95 arranged before the cathode 42 to form an electrostatic focus lens. These cathode and electrodes are arranged inside a ceramic insulating container 96. Numeral 97 represents a corona discharge preventing ring. This X-ray generator 21 has the same functions as that of the already-described first example of an X-ray generator, with the additional function that it allows the weight of the target to be reduced. In addition, the bearing, which is an integral combination of the magnetic seal 69 and the ball bearings 70 arranged outside the magnetic seal 69, is used at both ends of the target 32. Therefore, the X-ray generator 21 can be settled both in the vertical and horizontal directions thus making its vacuum and air-tightness as well as its mechanical support to remain stable. FIG. 10 shows another embodiment of the present invention. This embodiment is similar to the first one except that a slit plate 123 provided with a plurality of parallel slits 22a, 22b, 22c . . . is employed instead of the slit plate 23 provided with only one slit 22. The same parts as those in the first embodiment will be represented by the same reference numerals, but a description of these parts will be omitted. The anode target 32 may be of a rotating type as in the first embodiment or of a stationary type. When it is of a rotating type, it is made to be cylindrical, but when it is of a stationary type, it may serve only to irradiate the X-ray beam in a certain direction at the time when electron beam is moving. The target 32 may be a disc because the moving distance of the X-ray focal position may be small. As in the first embodiment, the slit plate 123 has slits 22a, 22b, 22c . . . perpendicular to the direction in which the X-ray focal point (F) is moved on the target 32. The slit plate 123 is a flat plate of heavy metal such as lead, 2 mm thick, for example, and the slit width (G) and the pitch distance (P) of these slits 22a, 22b, 22c . . . are 0.2 mm and 2 mm, respectively. A hundred slits, for example, can be formed in the slit plate 123. In FIG. 11A, however, only six slits 22a, 22b, 22c, 22d, 22e and 22f are formed for the sake of clarifying the drawing. Similar to the case of the first embodiment, each of the slits 22a, 22b, 22c . . . may be made either as a through-hole, or as a through-hole which has been filled with a metal, such as aluminium or beryllium, which has a high X-ray transmittance. When it is assumed that the X-ray focal position (F) is located at the top of an X-ray focal distance (S) on the rotating target 32, those X-rays which have passed through the slits 22a, 22b . . . after being emitted toward the slit plate 123, further pass through the subject 24 to be imaged, and enter the image intensifier 25 after being modulated by the subject 24. The image intensifier 25 converts the entered X-ray image to an intensified optical image. The converted optical image is detected by the detector (which is similar to the one 22 shown in FIG. 1). The optical images obtained by the X-ray I.I. 25 correspond to electrical signal images obtained by the detector which includes the X-ray I.I. 25, the lens system 27, and the camera tube 28 of FIG. 1. In the following description which will be made referring to FIGS. 10 and 11A, therefore, optical images A11, A12, A13, A14, A21, A22, A23, A24 . . . obtained by the X-ray I.I. 25 will be used as electrical signal images obtained by the detector. When a human body whose chest is, for example about 40 cm wide is to be imaged, the distance (S) which the X-ray focal point (F) moves on the cylindrical target 32 is 4 mm; the electron beam draws on the target 32 an oval having a shorter diameter of 0.4 mm and a longer diameter of 2.5 mm, and the effective X-ray focal point (F) draws a circle having a diameter of 0.4 mm when viewed from the slits 22a, 22b, 22c . . . A hundred slits 22a, 22b, 22c . . . are formed in the slit plate 123. The slits 22a, 22b, 22c . . . are parallel one another. The width (G) of the slits 22a, 22b, 22c . . . is 0.2 mm, the thickness is 2 mm and the pitch is 2 mm the effective diameter of the input screen of the X-ray I.I. 25 is about 57 cm. The distance (L1) between the moving line of the X-ray focal point at the section of the X-ray generator 21, and the slit plate 123 is about 1 m. The distance (L2) between the slit plate 123 and the X-ray I.I. 25 is about 1 m. X-ray image signals, obtained by the detector in the case where the X-ray focal position (F) is located at the top of an X-ray focal line, are as shown in FIG. 12A. FIG. 12A shows the level of the image signal or the strength at each of the positions on the to-be-detected surface in the vertical direction thereof, in which the abscissa represents the image signal levels and the coordinate times. Signal All at a position Y1 in FIG. 12A corresponds to an X-ray signal at a position Y1 on the X-ray I.I. 25 shown in FIG. 11A. Similarly, signals A12, A13 and A14 at positions Y2, Y3 and Y4 in FIG. 12A correspond to X-ray image signals at positions Y2, Y3 and Y4, respectively, on the X-ray I.I. 25 shown in FIG. 11A. Low level signal components appearing at each of the positions Y1, Y2, Y3 and Y4 in FIG. 12A represent blurs caused by scattered X-rays generated in the subject to be imaged, and by veiling glares generated in the X-ray I.I 25 by undesired floating electrons and the like. As previously mentioned, in the claims, the blur components are referred to as "further components", and the components containing no blur components are referred to as "fundamental components". For the purpose of gaining a highly accurate image, it is necessary to eliminate these blur component and to pick up only those signals at the positions Y1, Y2, Y3, Y4 . . . This can be satisfied when the signals which represent the positions of the X-ray focal point of the X-ray generator 21 are coordinated with those signals which represent the positions on the to-be-detected surface onto which the X-rays are irradiated from the positions of the X-ray focal point. This signal processing can be achieved according to the conventionally well-known manner. In a case where the detector means, which is a combination of the X-ray I.I. 25 and the camera tube 28, is used as in the first embodiment, it may be arranged that X-ray images obtained by X-ray emission at every X-ray focal point are stored on the target of the camera tube 28, that the entire of the region to be picked up is scanned at least once or at least for one frame both in the horizontal an vertical direction by the read-out electron beam of the camera tube 28, and that image signals which correspond to the positions Y1, Y2 . . . are extracted from the pickup signals obtained. The blur component caused by scattered X-ray generated in the subject to be imaged, and veiling glares and the like can be eliminated substantially by this process, thereby enabling a highly resolved and contrasty image to be obtained. Image signals B11, B12, B13 and B14 shown in FIG. 12B represent the signals obtained after this signal processing. When the X-ray focal point (F) is shifted slightly downward, X-ray signals obtained by the detector are accordingly obtained at positions Y1, Y2 . . . which are slightly shifted, as apparent from FIG. 12C where they are shown as A21, A22, A23 and A24. The X-ray signals shown in FIG. 12C are also processed like those shown in FIG. 11A to remove the blur component, so that only the image signal components B21, B22, B23 and B24 can be extracted as shown in FIG. 12D. The X-ray focal point (F) is successively moved on the scanning line (S) to the lowermost position thereof and the signal processing is repeated at every position of the X-ray focal point (F) to obtain the image signals B11 . . . B14, B21 . . . B24 . . . The image signals obtained at every position of the X-ray focal point (F) on the scanning line are stored in the signal processing means 30 and then are processed to reproduce a X-ray image of the entire subject. This reproduced image signal is applied to the display means and is displayed on it. In FIG. 11A, the projected lines of the X-ray beam are shown by broken lines Xn in the case where the X-ray focal point (F) is at the lowermost position on the moving line. When the X-ray focal point (F) moves from the top to the lowermost position on the moving line (S), the image area on which the X-ray which has passed through the slit 22a is projected is limited to an area (Ya) in FIG. 11B. Similarly, it is limited to an area (Yb) in the case of the slit 22b, and an area (Yc) in the case of the slit 22c. Some adjacent areas overlap with each other. Speaking of signals at this overlapped area, it may be arranged that only signals obtained from the X-ray beam passing through one of the adjacent slits, that is, signals at that portion of one area which is overlapped with its adjacent area are picked up, or that signals at those portions of both adjacent areas which are overlapped with each other are composed to obtain an average value. When the arrangement of the apparatus components, and the shape and relative position of the slits are determined to partially overlap the projected image areas, as described above, all X-ray beams passing through the entire region (Q) where the object 24 is located can be irradiated on the detection surface to thereby obtain a highly accurate image. A more accurate signal processing can be achieved when the image pickup is done once beforehand (or for more than one frame) with no object located therein. The relation between the positions of the X-ray emitting point and the signal positions which correspond to the point positions, as well as reference level values, are gained on the basis of signals obtained by the image pickup. This information is stored in the signal processing means 30. The X-ray focal point (F) may be moved continuously or in a stepped manner with a microinterval interposed. When the moving distance of the X-ray focal point (F) is made short, the time during which an image is reproduced can be shortened accordingly. In addition, the moving distance (S) of the X-ray focal point (F) can be shortened when the number of slits is increased. Further, when the ratio (L1/L2) between distance (L1) from the X-ray focal point to the slit plate 123, and between distance (L2) from the slit plate 123 to the detection surface is made smaller, the moving distance (S) of the X-ray focal point (F) can be shortened accordingly. When the pitch interval (P) between adjacent slits is made shorter, however, blur component because of scattered X-rays generated in the object increases thereby lowering image accuracy. When the ratio (P/S) between the pitch interval (P) of the adjacent slits and the moving distance (S) of the X-ray focal point is made larger, the region (Q) where the object can be located becomes narrow. Therefore, the moving distance (S) of the X-ray focal point, distances (L1) and (L2), the pitch interval (P) between adjacent slits, and the like are appropriately determined considering the above-mentioned matters. Input power applied to this X-ray generator 21 has a voltage of 120 KV and a beam current of 50 mA, thereby enabling power consumption to be reduced to 600 KW. Accordingly, the target 32 employed can be relatively small in heat capacity. The time which is needed to finish imaging one frame can be made less than 30 msec. The image display means 29 has a thousand horizontally scanning lines which serve as a television screen which can produce sufficient resolution and sufficient S/N. When a slit plate having a hundred slits, for example, is used, and imaging is carried out in sucn a way that a slit-projected X-ray image (A), obtained at every position following the movement of the X-ray focal point, is formed ten times between the adjacent beam positions or between positions (Y1) and (Y2), for example, so that an image on one frame can be reproduced by the hundred horizontally scanning lines. In short, image reproduction can be achieved using a large amount of image information, thereby enabling the accuracy of the image to be enhanced. FIG. 13 shows a further slit plate 123 wherein each of slits 22a, 22b . . . is directed to become coaxial with a line which connects the slits to the target. In the case of the slit plate shown in FIG. 13, therefore, the slope of the slits directed to the target 32 becomes deeper as they come nearer to the outer edge of the slit plate. FIG. 14 shows a still another slit plate 123 wherein the width (G) of each of the slits increases as they come nearer to the outer edge of the slit plate, and whereby the width of X-rays which have passed through any one of the slits is made to be substantially equal to that of the slits. FIG. 15 shows a still further slit plate 123 wherein the whole of the slit plate 123 is bent like an arch, taking the target as its center, or using the distance from the target 28 to the slit plate 123 as its radius, and whereby the slits are directed radially, taking the target 32 as their center. The strength of X-rays which have passed through any one of the slits can be therefore made substantially equal throughout the picked-up area thereby enhancing the accuracy of the reproduced images. FIG. 16 shows roughly the construction of the X-ray generator 21 employed in the embodiment shown in FIG. 10. This X-ray generator 21 is similar in construction to the one employed in the other embodiment shown in FIGS. 1 and 2. A portion of the deflection device is shown in detail in FIG. 16. It is preferable that the electron density of the electron beam irradiated on the target 32 at a unit area thereof is as small as possible in order to reduce the temperature rise of the surface of the target. When a focusing lens system is formed, it is also preferable that the sectional shape of the electron beam emitted from the electron gun 34 be circular. In the case of this embodiment, therefore, an electron beam (E) having a circular or a1 m ost circular section is emitted from the electron gun 34. Arranged between the electron gun 34 and the target 32 are a first electrostatic deflection electrode 131 for deflecting the emitted electron beam (E) in a direction parallel to the axis of the target 32, and a second electrostatic deflection coil 133 for deflecting the emitted electron beam (E) in a direction perpendicular to the axis of the target 32. The deflection electrodes 131 and 133 form the deflection means 35. A deflection current having sawtooth waveform and a frequency of f1, for example, is applied from a deflection power source 132 to the first deflection coil 131, while a deflection current having a sawtooth waveform or sine-waveform and a frequency of f2, for example, is applied from a power source 134 to the second deflection electrode 133. The power sources 132 and 134 form the power source means 37. The frequency f2 of the deflection current is set at 3 KHz, for example, to be sufficiently higher than the frequency f1 of the deflection current which is set at 30 Hz, for example. Accordingly, as shown in FIG. 17 the circular electron beam (E) is reciprocated in the direction (X) at a high speed which corresponds to the high frequency f2, while moving continuously or in stepped manner in the direction (Y) at a low speed which is determined by the low frequency f1 . X-ray beam is emitted from that portion of the target 32 on which the electron beam is irradiated. Since the electron beam (E) is deflected as described above, the shape of the electron beam (E) on the target 32 at an optional instant becomes practically the same as an elongated beam shape extending in the longitudinal direction of each of the slits in the slit plate, that is, in a direction perpendicular to the axis of the target 32, as shown in FIG. 18. This means practically that the elongated beam (E') moves along the direction (Y). X-rays generated when the target 32 is irradiated by the beam (E') are brought in a direction in which the beam (E') is viewed like a circle, or in a direction Xo (to which the slits 22a, 22b . . . of the slit plate 123 are directed perpendicularly) as in FIG. 16. Therefore, the electron beam density per unit time and area can be lowered. As deflection scanning in the direction (X) is enough to only cover a distance of 3-5 mm, it is unnecessary to use a large amount of deflection power thus enhancing the practicability of the apparatus. Further, the blur of the X-ray images obtained can be reduced. The deflection means is not limited to those of the electrostatic deflection type, but may be of the electromagnetic deflection type or a combination of these two types. With the two embodiments as have been described, the X-ray focal point (F) is moved on the target while the slit plate is stationary. However, in the embodiment shown in FIG. 10 in which the slit plate is provided with a plurality of slits, the X-ray focal point (F) may be fixed while the slit plate may be moved along a direction perpendicular to the direction in which the plurality of slits extend. In this case, an ordinal X-ray tube of a rotating anode type may be used instead of the X-ray tube in which the electron beam is deflected, and the slit plate may be moved by 1.5 times the pitch distance (P) of the slits. In this case, a short exposure time is required for obtaining one frame of the image. Although two embodiments have been described, they are quite similar except that the target 32 is of a rotating type and that the slit plate 32 has a single slit in the case of the embodiment shown in FIGS. 1 and 2, and that the target 32 may be either of the rotating or stationary type and that the slit plate 132 has a plurality of slits 22a, 22b, 22c . . . in the case of the other embodiment shown in FIGS. 10 and 11A. Therefore, the description which has been made above can be applied to any of these embodiments commonly, except as it applies to the above-mentioned differences. As apparent from the above, there can be provided an X-ray imaging apparatus wherein a high speed operation can be achieved and wherein the influence of scattered X-rays can be reduced to produce a highly resolved and contrasty image of high S/N. |
claims | 1. An apparatus for carrying out a process for purifying Mo-99, the apparatus comprising:a column or vessel containing an adsorbent comprising a zirconium oxide, zirconium hydroxide, zirconium alkoxide, zirconium halide and/or zirconium oxide halide; a source of a solution of a strong base, the source of strong base solution being arranged in fluid communication at an inlet of the column or vessel containing the adsorbent;a column or vessel containing an anion exchange material on which Mo-99 can be quantitatively adsorbed and arranged in downstream fluid communication with the column or vessel containing the adsorbent;a source of a solution of an acid, the source of acid solution being arranged in fluid communication at an inlet of the column or vessel containing the anion exchange material; anda column or vessel containing MnO2 material and arranged in downstream fluid communication with the column or vessel containing the anion exchange material;a source of a solution of sulfuric acid containing thiocyanide ions and a reducing agent, the source of sulfuric acid solution containing thiocyanide ions and a reducing agent being arranged in fluid communication at an inlet of the column or vessel containing the MnO2 material;and a column or vessel containing an ion exchange material comprising iminodiacetate groups and arranged in downstream fluid communication with the column or vessel containing the MnO2 material. 2. An apparatus of claim 1, wherein the adsorbent further comprises a titanium oxide and/or silicon oxide. 3. An apparatus of claim 1, wherein the zirconium compound is present at a concentration of from 5 to 70 mol % of the adsorbent. 4. An apparatus of claim 1, wherein the adsorbent is in the form of pellets. |
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claims | 1. An X-ray fluorescence analyzer, comprising:an X-ray tube for emitting incident X-rays in the direction of a first optical axis,a slurry handling unit configured to maintain a constant distance between a sample of slurry and said X-ray tube,a first crystal diffractor located in a first direction from said slurry handling unit, said first crystal diffractor being configured to separate a predefined first wavelength range from fluorescent X-rays that propagate into said first direction, and configured to direct the fluorescent X-rays in the separated predefined first wavelength range to a first radiation detector, wherein:the first crystal diffractor comprises a pyrolytic graphite crystal that has a diffractive surface, andsaid first radiation detector is a solid-state semiconductor detector;characterized in thatthe diffractive surface of said pyrolytic graphite crystal is a simply connected surface; andthe crystal is the wavelength-dispersive component of the crystal diffractor. 2. The X-ray fluorescence analyzer according to claim 1, wherein the diffractive surface of said pyrolytic graphite crystal is curved in one direction only. 3. The X-ray fluorescence analyzer according to claim 1, wherein the first crystal diffractor comprises a substrate to which said pyrolytic graphite crystal is attached, and wherein a three-dimensional geometrical shape of the entity constituted by said pyrolytic graphite crystal and said substrate is that of a prism, one side face of which is cut away by the curved diffractive surface. 4. The X-ray fluorescence analyzer according to claim 1, wherein said first radiation detector is one of: a PIN di-ode detector, a silicon drift detector, a germanium detector, a germanium drift detector. 5. The X-ray fluorescence analyzer according to claim 1, wherein the first crystal diffractor comprises:a first slit on a first optical path between said slurry handling unit and said pyrolytic graphite crystal, anda second optical path between said pyrolytic graphite crystal and said first radiation detector. 6. The X-ray fluorescence analyzer according to claim 5, wherein:the diffractive surface of said pyrolytic graphite crystal is curved in one direction only, with a radius of curvature in a plane defined by said first and second optical paths, andsaid first slit is a linear slit oriented perpendicular against said plane. 7. The X-ray fluorescence analyzer according to claim 5, wherein:the diffractive surface of said pyrolytic graphite crystal is curved in two directions, forming a part of a toroidal surface, andsaid first slit is a curved slit with a first radius of curvature oriented perpendicular against said first optical path. 8. The X-ray fluorescence analyzer according to claim 5, wherein:the diffractive surface of said pyrolytic graphite crystal is curved in two directions, forming a part of a rotationally symmetric surface, the rotational axis of which is in the plane defined by said first and second optical paths, andsaid first slit is point-like. 9. The X-ray fluorescence analyzer according to claim 6, wherein:the first crystal diffractor comprises a second slit on said second optical path between said pyrolytic graphite crystal and said first radiation detector,a center point of said diffractive surface, said first slit, and said second slit are located on a Rowland circle the radius of which is R,a radius of curvature of said diffractive surface in the plane defined by said first and second optical paths is 2R, anda radius of curvature of reticular planes in said crystal is 2R; so that the first crystal diffractor has a Johann geometry. 10. The X-ray fluorescence analyzer according to claim 6, wherein:the first crystal diffractor comprises a second slit on said second optical path between said pyrolytic graphite crystal and said first radiation detector,a center point of said diffractive surface, said first slit, and said second slit are located on a Rowland circle the radius of which is R,a radius of curvature of said diffractive surface in the plane defined by said first and second optical paths is R, andthe radius of curvature of reticular planes in said crystal is 2R; so that the first crystal diffractor has a Johansson geometry. 11. The X-ray fluorescence analyzer according to claim 9, wherein R is at most 40 centimeters. 12. The X-ray fluorescence analyzer according to claim 6, wherein:said first crystal diffractor is enclosed in a casing delimited by a first planar surface and a second planar surface that is parallel to said first planar surface. 13. The X-ray fluorescence analyzer according to claim 6, comprising a plurality of other crystal diffractors in addition to said first crystal diffractor, each of said first and other crystal diffractors being located at a respective rotation angle around said first optical axis and each of said first and other crystal diffractors being configured to separate a predefined wavelength range from fluorescent X-rays that propagate into the respective direction, and configured to direct the fluorescent X-rays in the respective separated predefined wavelength range to a respective radiation detector. 14. The X-ray fluorescence analyzer according to claim 13, wherein:said plurality of other crystal diffractors comprises a second crystal diffractor comprising a second crystal, configured to direct the fluorescent X-rays in the respective separated second predefined wavelength range to a respective second radiation detector,said second crystal is of a material other than pyrolytic graphite, andsaid first and second crystal diffractors are con-figured to direct to their respective radiation detectors characteristic fluorescent radiation of a same element. 15. The X-ray fluorescence analyzer according to claim 14, wherein said second crystal is one of: a silicon dioxide crystal, a lithium fluoride crystal, an ammonium dihydrogen phosphate crystal, a potassium hydrogen phthalate crystal. 16. The X-ray fluorescence analyzer according to claim 14, wherein said second radiation detector is a gas-filled proportional counter. 17. The X-ray fluorescence analyzer according to claim 14, wherein said element is gold. 18. The X-ray fluorescence analyzer according to claim 14, wherein:said slurry handling unit is configured to maintain a planar surface of said sample of slurry on a side facing said X-ray tube,said first optical axis is at an oblique angle against said planar surface,said first crystal diffractor is located at that rotational angle around said first optical axis at which said planar surface of said sample covers the largest portion of a field of view of the first crystal diffractor, andsaid second crystal diffractor is located at another rotational angle around said first optical axis. 19. The X-ray fluorescence analyzer according to claim 6, wherein an energy resolution of said first radiation detector is better than 300 eV at a reference energy of 5.9 keV. 20. The X-ray fluorescence analyzer according to claim 6, wherein the in-put power rating of said X-ray tube is at least 400 watts. 21. The X-ray fluorescence analyzer according to claim 20, wherein the input power rating of said X-ray tube is at least 1 kilowatt, preferably at least 2 kilowatts, and more preferably at least 4 kilowatts. 22. The X-ray fluorescence analyzer according to claim 6, wherein the optical path between said X-ray tube and said slurry handling unit is direct with no diffractor therebetween. 23. The X-ray fluorescence analyzer according to claim 6, whereinthe X-ray tube comprises an anode for generating said incident X-rays, andsaid slurry handling unit is configured to maintain a shortest linear distance that is shorter than 50 mm, preferably shorter than 40 mm, and more preferably shorter than 30 mm between said sample of slurry and said anode. 24. The X-ray fluorescence analyzer according to claim 23, wherein said X-ray tube is an X-ray tube of the end window type. 25. The X-ray fluorescence analyzer according to claim 6, further comprising:an analyzer body,a front wall of said analyzer body,an opening in said front wall, anda holder for removably holding said slurry handling unit against an outer side of said front wall and aligned with said opening in said front wall. 26. The X-ray fluorescence analyzer according to claim 25, wherein said X-ray tube and said first crystal diffractor are both inside said analyzer body, on the same side of said front wall. 27. The X-ray fluorescence analyzer according to claim 6, comprising a filter plate on the optical path between said X-ray tube and said slurry handling unit. 28. The X-ray fluorescence analyzer according to claim 27, wherein said filter plate is located closer to said X-ray tube than to said slurry handling unit. 29. The X-ray fluorescence analyzer according to claim 6, comprising a calibrator plate and an actuator configured to controllably move said calibrator plate between at least two positions, of which a first position is not on the path of the incident X-rays and a second position is on the path of the incident X-rays and in a field of view of the first crystal diffractor. |
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description | 1. Field of the Invention The present invention relates to an X-ray optical apparatus that radiates an X-ray onto an object, and particularly, to an X-ray optical apparatus that parallelizes and emits the X-ray which travels in a divergence manner. 2. Related Background Art An X-ray optical apparatus that one-dimensionally parallelizes an X-ray has been known. An example of such an X-ray optical apparatus is a solar slit in which metal flat panels are laminated with a regular interval. In the solar slit, a non-parallel component of the X-ray is absorbed by the metal flat panel and only a predetermined range of a parallel component of the X-ray passes through. If the X-ray is reflected from the metal flat panel, the non-parallel component of the X-ray that passes the solar slit is increased and a degree of parallelization is lowered. Japanese Patent Application Laid-Open No. 2000-137098 discloses that a surface of a metal foil is formed to have a surface roughness to prevent the reflection and only a predetermined parallel component of the X-ray passes the solar slit to form a parallel X-ray beam with high precision. Japanese Patent Application Laid-Open No. 2004-89445 discloses that a collimator, in which a plurality of minute capillaries is two-dimensionally arranged, is combined with multiple X-ray sources, which are arranged in a two-dimensional matrix, to parallelize an X-ray which is emitted from the capillary. Further, Japanese Patent Application Publication (Translation of PCT Application) No. H10-508947 discloses that a divergence X-ray, which is diverged from a small spotlight type of an X-ray source, is efficiently captured in a monolithic optical device, which includes a plurality of hollow glass capillaries, to form a quasi-parallel beam. In the technology disclosed in Japanese Patent Application Laid-Open No. 2000-137098, there is a problem in that since only a parallel component of the X-ray is taken, only a very small part of generated X-ray is used and the usage efficiency is low. Further, a power, which is supplied to the X-ray source, has a limitation due to the influence of the heat generation of the X-ray source, so that an amount of irradiated X-ray is also limited. Therefore, it is difficult to improve an illuminance of the X-ray. In the technology disclosed in Japanese Patent Application Laid-Open No. 2004-89445, it is difficult to form uniform capillaries in the collimator. It is also difficult to two-dimensionally arrange the X-ray sources with high density. In the technology disclosed in Japanese Patent Application Publication (Translation of PCT Application) No. H10-508947, the hollow glass capillaries are fused together and plastically shaped. Therefore, it is difficult to form uniform capillaries. It is an object of the invention to provide an X-ray optical apparatus which is capable of efficiently parallelizing the generated X-ray to be emitted with a simple configuration. According to the present invention there is an X-ray optical apparatus including an X-ray reflective structure in which at least three reflective substrates are laminated so as to match both edges with an interval and an X-ray which is incident into an X-ray passage formed by a space, both sides of the passage being put between the reflective substrates, is reflected from the reflective substrate at both sides of the X-ray passage and then emitted from the X-ray passage. The at least three reflective substrates have a constant and equal thickness. When an edge of the X-ray reflective structure is an inlet of the X-ray and the other edge is an outlet of the X-ray, a pitch of the reflective substrates at the outlet is larger than a pitch of the reflective substrates at the inlet. According to the present invention, it is possible to efficiently parallelize the generated X-ray with a simple structure. Further, since a shape precision of the X-ray reflective substrate is loose or not strict, it is easy to assemble the X-ray reflective structure or adjust a position of the X-ray reflective structure. Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. The present invention relates to an X-ray optical apparatus that includes an X-ray reflective structure (hereinafter, referred to as a “slit lens”) to parallelize an X-ray diverged from an X-ray source and may be applied to an X-ray imaging apparatus such as an X-ray CT. (1) Slit Lens As illustrated in FIG. 1A, a slit lens 3 has a structure in which at least three X-ray reflective substrates (hereinafter, referred to as reflective substrate) 11 are laminated so as to match both edges with an interval. Preferably, each of the reflective substrates has a constant thickness and the at least three reflective substrate have the same thickness. As illustrated in FIGS. 8A and 8B, spacers 18 having different heights are disposed between the adjacent reflective substrates. By the spacers 18, intervals between the reflective substrates 11 are formed so that an interval at an outlet b side, which is an edge of the slit lens 3, is larger than an interval at an inlet a side of the X-ray which is the other edge of the slit lens 3. The interval between the reflective substrates 11 is gradually increased from the inlet of the X-ray to the outlet of the X-ray. The spacers 18 have a pillar shape (for example, a quadrangular prism) and are disposed between the reflective substrates with a predetermined interval. Further, the spacers 18 are disposed at the same position on the different layers of reflective substrates 11 (disposed at the overlapping position). The spacers 18 are disposed so as to be bonded with the reflective substrates 11. However, the reflective substrates 11 and the spacers 18 may be integrally formed by etching a glass substrate. Further, in FIG. 8A, even though the reflective substrates 11 are illustrated as a flat substrate, actually, the reflective substrates 11 are laminated so as to be curved with a predetermined curvature as illustrated in FIG. 8B. X-rays 2, which are incident into a plurality of passages (hereinafter, referred to as an “X-ray passage”) formed by a space whose both sides are put between the reflective substrates 11, are reflected from the reflective substrate 11 at both sides of the X-ray passage to be parallelized and emitted from the X-ray passages. The “parallelization” in the present invention refers that an X-ray component in a laminated direction (y direction) of the reflective substrate 11 is reduced and the emission direction of the X-ray becomes parallel (collimates) to a plane (xz plane) perpendicular to the y direction. (2) Resolving Power In an X-ray imaging apparatus to which the present invention is applied, a penumbra amount (resolution) will be described below, which is generated when an X-ray, which is incident into the X-ray passage of the slit lens 3 from the X-ray source 1 and passes the X-ray passage, is irradiated onto a sample to project a transmission image onto an X-ray detector 4. FIG. 1A is a schematic diagram of a system illustrating a concept of the present invention and FIG. 1B is a cross-sectional view of an YZ plane that passes through the X-ray source 1 of the system. When there is an infinitely small object A at the outlet of the slit lens 3 and a defocused state of an image that transmits the object A is defined as a penumbra amount Δp of the image, the penumbra amount Δp is represented by Equation 1 using a divergence angle θout of the X-ray at the outlet of the slit lens 3 and a distance L3 between the outlet of the slit lens 3 and the X-ray detector 4 in an opposite direction.Δp=L3×θout (Equation 1) Equation 1 is established for the X-ray which is emitted from the X-ray passage. A resolving power of an X-ray imaging apparatus is lowered as the penumbra amount Δp is increased. Therefore, in order to increase the resolving power, if the distance L3 is constant, it is important to lower the divergence angle θout. In other words, it is important to increase the degree of parallelization of the X-ray which is emitted from the X-ray passages in the slit lens 3. The resolving power of the X-ray imaging apparatus is determined by not only the half shade amount Δp but also larger one of the penumbra amount Δp and a pixel size Δd of the X-ray detector 4 (for example, flat panel detector (FPD)). If the pixel size Δd is small, the X-ray detector 4 becomes expensive and it takes time to perform data transfer processing. In the meantime, for lowering the penumbra amount Δp, for example, a size of the optical source of the X-ray source is required to be reduced, so that a load applied to an optical system is increased as described below. Therefore, it is important to keep a balance between the pixel size Δd and the penumbra amount Δp. If an acceptable range of a ratio of the pixel size Δd and the penumbra amount Δp is two, the following Equation 2 is established.0.5<Δp/Δd<2 (Equation 2) (3) Parallelization Principle A principle (parallelization principle) of parallelizing the X-ray, which is emitted from the X-ray passages in the slit lens 3, will be described. FIG. 2 is an enlarged view of a range enclosed by a two-dot chain line in the system illustrated in FIG. 1B. Hereinafter, a case where a thin glass plate is used as the reflective substrate 11 will be described. However, the reflective substrate 11 may be metal. The X-ray 2 which is emitted from the X-ray source 1 is divergence light and is radiated in all directions. An X-ray source illustrated in FIG. 3 may be used as the X-ray source 1. The slit lens 3 is disposed so as to be separated by a distance L1 from the X-ray source in the opposite direction of the X-ray source 1. The slit lens 3 is arranged such that the thin glass plates having a gentle curvature are arranged with predetermined pitch and a pitch at the outlet of the X-ray is larger than a pitch at the inlet of the X-ray. Here, the pitch refers to a distance between top surfaces or bottom surfaces of the adjacent reflective substrates. 10 to 1000 sheets of the thin glass plates each having a thickness of 1 μm to 100 μm are laminated and the X-ray may be reflected from both surfaces of the thin glass plate. An X-ray 2, which is incident into the X-ray passage (air) between the thin glass plates 11a and 11b, travels while being reflected from both the thin glass plates 11a and 11b and then is emitted from the X-ray passage. Similarly, in the X-ray passage between the thin glass plate 11b and the thin glass plate 11c, the incident X-ray 2 travels while being reflected from both the thin glass plates 11b and 11c and then is emitted from the X-ray passage, which is similar in the X-ray passage between other adjacent thin glass plates. As described above, as the X-ray travels in the X-ray passage in the slit lens 3, an X-ray whose traveling direction is not a parallel direction is reflected multiple times from the thin glass plate and the traveling direction gradually becomes parallel. Therefore, the X-ray is parallelized and emitted from the X-ray passage. Further, an X-ray which travels in a parallel direction is emitted from the X-ray passage as it is. Accordingly, it is possible to efficiently parallelize the X-ray to be emitted with a simple structure. By doing this, the penumbra amount Δp, which is formed on the X-ray detector 4, also becomes lower. Here, a virtual plane 5 is set in a position which is separated from both the thin glass plates of the X-ray passages with the same distance and a tangential plane 6 of the virtual plane 5 at the inlet of the slit lens 3 is considered. If X-ray sources 1 are disposed on tangential planes of the plurality of virtual planes 5 at the inlet side, more X-rays may be incident into the X-ray passages. In case of the X-ray source 1 illustrated in FIG. 3, it is preferred that an X-ray generating unit which generates an X-ray with a light source size s be disposed on the tangential planes of the plurality of virtual planes 5 at the inlet side. If all the tangential planes 6 of the plurality of virtual planes 5, which are set between the adjacent thin glass plates, at the inlet side intersect on a common straight line and the X-ray source 1 is disposed on the straight line, a size of the X-ray source 1 may be smaller. Further, if the thin glass plate at the outlet of the slit lens 3 is parallel, in other words, if the tangential planes 6 of the plurality of virtual planes 5 at the outlet side are approximately parallel, the degree of parallelization of the X-rays emitted from the X-ray passages may be increased. FIG. 4 illustrates an X-ray reflectance of a quartz substrate with respect to an X-ray having a wavelength of 0.071 nm. A horizontal axis is a glancing angle θg at which the X-ray is incident onto the X-ray passage and a vertical axis is a reflectance of the X-ray. When the glancing angle θg is 0.5 mrad, the reflectance of the X-ray is 99.8% or higher. Therefore, it can be understood that 90% or more of the X-ray passes the slit lens 3 even if the X-ray is reflected 50 times. In the meantime, when the glancing angle θg is 1.8 mrad, the reflectance of the X-ray is rapidly attenuated. In this case, the glancing angle θg is referred to as a critical angle and denoted by θc. When the X-ray source 1 is disposed on the tangential planes 6 of the plurality of virtual planes 5 at the inlet side, if the angular variation of the tangential planes 6 is increased, a variation in an angle at which each of the thin glass plates brings to the X-ray source into view is generated. Then, the X-ray 2 which is emitted from the X-ray source 1 will not be reflected on a position where the glancing angle θg is larger than the critical angle θc in the thin glass plate. Accordingly, when a distance between the X-ray source 1 and the inlet of the slit lens 3a in the opposite direction is L1 and a critical angle of the glancing angle θg at which the X-ray is incident onto the X-ray passage is θc, the distance Δs between the X-ray source 1 and the X-ray passage in a direction perpendicular to the opposite direction is required to satisfy the following Equation 3.Δs<L1×θc (Equation 3) Therefore, it is required to determine a relative position of the slit lens 3 and the X-ray source 1, that is, a relative position of the thin glass plate and the X-ray source 1 so as to satisfy Equation 3. Here, a slit lens 3 will be described, in which the interval between adjacent thin glass plates is constant and thicknesses of all thin glass plates are formed such that a thickness at the outlet side is larger than a thickness at the inlet side as illustrated in FIG. 1B. Such a slit lens 3 may be manufactured by laminating thin glass plates having a wedge shaped thickness. Then, a maximum glancing angle θgmax, at which the X-ray being incident onto the X-ray passage is reflected from the thin glass plate, is represented by Equation 4.θgmax=(s+g)/2L1 (Equation 4) Here, s indicates a size of the X-ray source 1 (diameter of the light source) and is 2σ when an intensity distribution of the light source may be approximated by a Gaussian distribution. g is an interval between adjacent thin glass plates. However, θgmax needs to be smaller than the critical angle θc. If the thin glass plates are parallel to each other at the outlet of the slit lens 3, the divergence angle θout of the X-ray, which is emitted from each of the X-ray passages in the slit lens 3, is represented by Equation 5.θout=2×θgmax (Equation 5) In this case, the penumbra amount Δp is represented by Equation 6 based on Equations 1, 4 and 5.Δp=L3×(s+g)/L1 (Equation 6) Further, Equation 7 is established based on Equations 2 and 6.0.5×Δd<L3×(s+g)/L1<2×Δd (Equation 7) If the degree of parallelization of the thin glass plate is lowered, the X-ray does not reach a pixel of the X-ray detector 4 that detects an intensity of the X-ray or a pixel having an extremely weak X-ray intensity is generated. In order to remove such troubles, the parallelism Δout of all the thin glass plates is required to satisfy larger one of an acceptable value Δout-a in Equation 8a and an acceptable value Δout-b in Equation 8b. Here, Δd indicates a pixel size of the X-ray detector 4.Aout-a<(s+g)/L1 (Equation 8a)Aout-b<Δd/L3 (Equation 8b) Next, a slit lens 3 will be described, in which thicknesses of all thin glass plates are constant and an interval between adjacent thin glass planes at the outlet side is larger than an interval at the inlet side as illustrated in FIG. 5. In order to simplify the description, a straight guide is considered, in which the thin glass plates 11a and 11b form an angle θa as illustrated in FIG. 6. If an angle between the virtual plane 5 and the X-ray 2 is referred to as a half divergence angle, an X-ray, which is incident into the X-ray passage between the thin glass plates 11a and 11b with the half divergence angle θ0 (0.5×θa<θ0<θc), is reflected at a point P0 of the thin glass plate 11b and then reflected at a point P1 of the thin glass plate 11a. A half divergence angle θ1 after the first reflection is represented by Equation 9.θ1=θ0−θa (Equation 9) Therefore, the angle θn after n-th reflection is represented by Equation 10 in a range of “θ0−n×θa>0”.θn=θ0−n×θa (Equation 10) If θn<0.5×θa, the X-ray 2 does not reach the thin glass plate, so that the half divergence angle is not varied. Further, if an interval between the adjacent thin glass plates at the outlet side is gout, an interval between the adjacent thin glass plates at the inlet side is gin and a length of the thin glass plate is L2, Equation 11 is established.θa=(gout−gin)/L2 (Equation 11) In this case, since θa<θout, the penumbra amount Δp is represented by Equation 12 based on Equations 1 and 11.(gout−gin)×L3/L2<Δp (Equation 12) Further, Equation 13 is established based on Equations 2 and 12.0.5×Δd<L3×(gout−gin)/L2<2×Δd (Equation 13) For the same reason as the above mentioned reason with respect to the slit lens 3 having the structure illustrated in FIG. 1B, even in a slit lens 3 having a structure illustrated in FIG. 5, it is preferred that the thin glass plates at the outlet of the slit lens 3 be parallel to each other. Therefore, the parallelism Δout of all the thin glass plates is required to satisfy larger one of an acceptable value Δout-a in Equation 14a and an acceptable value Δout-b in Equation 14b. Here, Δd indicates a pixel size of the X-ray detector 4.Δout-a<(gout−gin)/L2 (Equation 14a)Δout-b<Δd/L3 (Equation 14b) In the meantime, a penumbra amount Δx in a dimension where the thin glass plate does not have curvature, that is, direction (x-direction) perpendicular to both an opposite direction between the X-ray source 1 and the inlet of the slit lens 3 and a direction perpendicular to the opposite direction between the X-ray source 1 and the X-ray passage is represented by Equation 15.Δx=s×L3/(L2+L1) (Equation 15) Therefore the penumbra amount Δx is determined by the relative position of the slit lens 3, the X-ray source 1 and the X-ray detector 4. Further, a slit lens 3, where the X-ray source 1 is disposed on the tangential planes of the plurality of virtual planes 5 at the inlet side and the tangential planes 16 of the plurality of virtual planes at the outlet sides intersect on a common straight line 17, may also be applied to the X-ray optical apparatus in accordance with the present invention (see FIG. 7). Such a structure also exerts the effect of the present invention. As illustrated in FIG. 7, if all tangential planes 6 of the plurality of virtual planes 5 at the inlet side intersect on the common straight line and the X-ray source 1 is disposed on the straight line, it is advantageous in that the size of the X-ray source 1 may be reduced. In this case, the common straight line intersecting at the inlet side is a different straight line from the common straight line 17 intersecting at the outlet side. [First Exemplary Embodiment] As illustrated in FIG. 1B, the exemplary embodiment includes a slit lens 3 where an interval g between the adjacent thin glass plates is constantly 10 μm, and a thickness of all thin glass plates is 20 μm at the outlet side and 10 μm at the inlet side. An X-ray 2 radiated from the X-ray source 1 is incident into an X-ray passage between thin glass plates 11a and 11b and travels while being reflected from both the thin glass plates 11a and 11b, which is similar in the X-ray passage between other adjacent thin glass plates. A solid angle Ω1 of the X-ray which is incident into one X-ray passage is proportional to the interval g. However, since the plurality of thin glass plates are arranged so as to be spaced apart from each other with the interval g, even though the interval g is small, the amount of entire X-ray which can be incident into the X-ray passage is proportional to a divergence angle θm and an aperture ratio. Here, the “aperture ratio” refers to a ratio of the gap which occupies in the inlet of the slit lens 3 and the aperture ratio is 50% (=10 μm/(10 μm+10 μm)) in this exemplary embodiment. 50% of X-ray 2, which is radiated from the X-ray source 1 with the divergence angle θm or smaller, is incident into the X-ray passage and travels while being reflected from the thin glass plates and is radiated from the X-ray passage with the divergence angle θout. An image of the object, which is disposed between the outlet of the slit lens 3 and the FPD, is projected onto the FPD by the radiated X-ray. In this case, a penumbra amount Δp of the image of the object is formed on the FPD in accordance with Equation 1, so that the resolution is lowered. A method for restricting the lowering of resolution in a predetermined range will be described. Since the penumbra amount Δp is represented by Equation 6, a size s of the X-ray source 1 is represented by Equation 16 based on Equations 2 and 6.0.5×L1/L3×Δd−g≦s≦2×L1/L3×Δd−g (Equation 16) When a distance L1 between the X-ray source 1 and the inlet of the slit lens 3 in the opposite direction is 100 mm, a distance L3 between the outlet of the slit lens 3 and the FPD in the opposite direction is 200 mm, and a pixel size Δd of the FPD is 100 μm, an acceptable range of the size s of the light source is “15 μm≦s≦90 μm”. It is required to adjust the size s of the light source within the acceptable range. In the transmissive X-ray source 1 illustrated in FIG. 3, an electron beam 13 radiated from an electron beam source 12 is converged by an electron lens 14 for converging an electron to be focused on a target 15. A size of the electron beam 13 may be easily varied by changing a power of the electron lens 14. In this way, it is possible to adjust the size s of the X-ray source 1. In the meantime, when the length L2 of the slit lens 3 is 100 mm and the size s of the light source is 90 πam, the penumbra amount Δx is 90 μm in accordance with Equation 15, which is almost equal to the pixel size Δd of the FPD. As described above, the resolution in a direction perpendicular to both the opposite direction between the X-ray source 1 and the inlet of the slit lens 3 and a direction perpendicular to the opposite direction between the X-ray source 1 and the X-ray passage is also similar to the resolution in the opposite direction between the X-ray source 1 and the inlet of the slit lens 3. Therefore, it is possible to efficiently parallelize the X-ray to be emitted and restrict the lowering of the resolution within a predetermined range with a simple structure. [Second Exemplary Embodiment] As illustrated in FIG. 5, the exemplary embodiment includes a slit lens 3 where a thickness of all thin glass plates is constant and an interval between the adjacent thin glass plates is 50 μm at the outlet side gout and 10 μm at the inlet side gin. Similarly to the first exemplary embodiment, an X-ray 2 radiated from an X-ray source 1 is incident into an X-ray passage, travels while being reflected from thin glass plates, and is radiated from the X-ray passage with a divergence angle θout so that an image of an object is projected onto an FPD. In this case, the resolution is lowered in accordance with Equation 1. If a length L2 of the slit lens is 100 mm, an angle θa formed by adjacent thin glass plates is 0.4 mrad. If an X-ray, which is incident with a glancing angle θg of 1.8 mrad which is a critical angle θa, is reflected four times, a relationship of “θn<0.5×θa” is satisfied and the divergence angle θout is 0.4 mrad or less. If a distance L3 between the outlet of the slit lens 3 and the FPD in the opposite direction is 200 mm, the penumbra amount Δp is 80 μm. Further, if the pixel size Δd is 100 V, Equation 2 is satisfied. Therefore, it is possible to efficiently parallelize the X-ray to be emitted and restrict the lowering of the resolution within a predetermined range with a simple structure. Further, if the size s of the light source is large, when the X-ray is incident onto the slit lens 3 at an angle which is larger than the critical angle θc, the first reflection does not occur, so that the resolution is not lowered. However, an X-ray which is incident at an angle which is larger than the critical angle θc is absorbed by the thin glass plate, so that the X-ray may not pass through the slit lens 3. Accordingly, in order to efficiently use the X-ray radiated from the X-ray source 1, the size s of the light source is required to be adjusted so as to satisfy Equation 17.s<L1×2θc (Equation 17) [Third Exemplary Embodiment] As illustrated in FIG. 7, this exemplary embodiment includes a slit lens 3 where if a virtual plane is set in a position which is separated from adjacent thin glass plates with the same distance, an X-ray source is disposed on tangential planes of a plurality of virtual planes at an inlet side and the tangential planes 16 of the plurality of virtual planes at the outlet side intersect on a common straight line 17. Even in accordance with this exemplary embodiment, it is also possible to efficiently parallelize the X-ray to be emitted and restrict the lowering of the resolution within a predetermined range with a simple structure. While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. This application claims the benefit of Japanese Patent Application No. 2012-053617, filed on Mar. 9, 2012, which is hereby incorporated by reference herein in its entirety. |
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abstract | Target assemblies are provided that can include a uranium-comprising annulus. The assemblies can include target material consisting essentially of non-uranium material within the volume of the annulus. Reactors are disclosed that can include one or more discrete zones configured to receive target material. At least one uranium-comprising annulus can be within one or more of the zones. Methods for producing isotopes within target material are also disclosed, with the methods including providing neutrons to target material within a uranium-comprising annulus. Methods for modifying materials within target material are disclosed as well as are methods for characterizing material within a target material. |
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claims | 1. An intra-oral x-ray sensor, comprising:an x-ray image component configured to acquire intra-oral x-ray image information associated with a patient; andan intra-oral radiation shield structure configured to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%, wherein a portion of the intra-oral radiation shield structure is flexible or jointed so as to conform to a portion of an oral cavity. 2. The intra-oral x-ray sensor of claim 1, wherein the intra-oral radiation shield structure includes one or more high atomic number (high-Z) materials in an amount sufficient to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. 3. The intra-oral x-ray sensor of claim 1, wherein the intra-oral radiation shield structure includes one or more materials having a K-edge greater than 15 kiloelectron volts in an amount sufficient to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. 4. The intra-oral x-ray sensor of claim 1, wherein the intra-oral radiation shield structure includes one or more materials having an L-edge greater than 10 kiloelectron volts in an amount sufficient to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. 5. The intra-oral x-ray sensor of claim 1, wherein the intra-oral radiation shield structure includes a laminate structure having at least a first layer and a second layer, the second layer having an x-ray attenuation profile different from the first layer. 6. The intra-oral x-ray sensor of claim 1, wherein at least a portion of the intra-oral radiation shield structure is mounted behind an x-ray image detector on the intra-oral x-ray sensor. 7. The intra-oral x-ray sensor of claim 1, wherein at least a portion of the intra-oral radiation shield structure is formed from at least one x-ray attenuating material, x-ray radio-opaque material, or x-ray attenuating ceramic material. 8. The intra-oral x-ray sensor of claim 1, wherein the intra-oral radiation shield structure is removably attachable. 9. The intra-oral x-ray sensor of claim 1, wherein at least a portion of the intra-oral radiation shield structure is composed of at least a first x-ray shielding material and a second x-ray shielding material, the second x-ray shielding material having one or more absorption edges different from the first x-ray shielding material. 10. The intra-oral x-ray sensor of claim 9, wherein at least one of the first x-ray shielding material or the second x-ray shielding material includes at least one material that absorbs x-rays at one or more frequencies and fluoresces x-rays at one or more lower frequencies. 11. The intra-oral x-ray sensor of claim 9, wherein at least a portion of the second x-ray shielding material is interlayered with at least a portion of the first x-ray shielding material. 12. The intra-oral x-ray sensor of claim 9, wherein the second x-ray shielding material includes one or more K-edges, or one or more L-edges, different from the first x-ray shielding material. 13. The intra-oral x-ray sensor of claim 9, wherein the second x-ray shielding material includes an x-ray mass attenuation coefficient different from the first x-ray shielding material. 14. An intra-oral x-ray sensor, comprising:an x-ray image component configured to acquire intra-oral x-ray image information associated with a patient; andan intra-oral radiation shield structure configured to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%, wherein the intra-oral radiation shield structure includes a composition having a carrier fluid and a plurality of x-ray shielding particles each having at least a first x-ray shielding agent and a second x-ray shielding agent, the second x-ray shielding agent having one or more absorption edges different from the first x-ray shielding agent. 15. The intra-oral x-ray sensor of claim 1, wherein a portion of the intra-oral radiation shield structure has an x-ray shielding lead equivalence of about 0.25 millimeters to about 0.5 millimeters. 16. The intra-oral x-ray sensor of claim 1, wherein a portion of the intra-oral radiation shield structure extends outwardly beyond a terminal border of an x-ray image detector forming part of the intra-oral x-ray sensor. 17. An intra-oral x-ray sensor, comprising:an x-ray image component configured to acquire intra-oral x-ray image information associated with a patient;an intra-oral radiation shield structure configured to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%; andan x-ray backscatter component operably coupled to the x-ray image component;wherein the x-ray image component is configured to detect backscattering, and the x-ray backscatter component is configured to modify the intra-oral x-ray image information responsive to one or more inputs from the x-ray image component indicative of the presence of backscatter. 18. The intra-oral x-ray sensor of claim 1, further comprising:an embedded orientation detection component configured to generate information associated with at least one of an intra-oral x-ray sensor orientation, an intra-oral x-ray sensor position, an intra-oral x-ray sensor dimension, or an intra-oral x-ray sensor centroid position. 19. The intra-oral x-ray sensor of claim 18, wherein the embedded orientation detection component is operably coupled to one or more orientation sensors. 20. The intra-oral x-ray sensor of claim 18, wherein the embedded orientation detection component is operably coupled to one or more local positioning system based sensors. 21. The intra-oral x-ray sensor of claim 18, wherein the embedded orientation detection component is operably coupled to at least two acceleration sensors in a substantially perpendicularly arrangement. 22. The intra-oral x-ray sensor of claim 18, wherein the embedded orientation detection component is operably coupled to at least one electrolytic fluid based sensor. 23. The intra-oral x-ray sensor of claim 18, wherein the embedded orientation detection component is operably coupled to a two-axis tilt sensor configured to detect an intra-oral x-ray sensor pitch angle and an intra-oral x-ray sensor roll angle. 24. The intra-oral x-ray sensor of claim 18, wherein the embedded orientation detection component is operably coupled to one or more acoustic transducers. 25. The intra-oral x-ray sensor of claim 1, wherein the x-ray image component is operably coupled to one or more charge-coupled devices. 26. The intra-oral x-ray sensor of claim 1, wherein the x-ray image component is operably coupled to one or more complementary metal-oxide-semiconductor sensors. 27. The intra-oral x-ray sensor of claim 1, further comprising:one or more active optic devices configured to generate an output indicative of an intra-oral x-ray sensor border position. 28. The intra-oral x-ray sensor of claim 1, further comprising:one or more passive optics devices configured to indicate an intra-oral x-ray sensor border position. 29. The intra-oral x-ray sensor of claim 1, further comprising:a beacon component configured to convey information associated with at least one of a sensor position or a sensor orientation. 30. The intra-oral x-ray sensor of claim 29, wherein the beacon component is operably coupled to a transducer configured to generate an output indicative of an intra-oral x-ray sensor border position. |
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043427219 | claims | 1. A fast neutron nuclear reactor comprising a vesel having a vertical axis and containing a reactor core, a volume of liquid metal for cooling the core, at least one main heat exchanger and at least one auxiliary heat exchanger, said reactor vessel being closed at the top by a reactor vault roof, said auxiliary heat exchanger being constituted by a plurality of vertical heat-exchanger modules, each of said modules comprising a circuit for the flow of coolant fluid, said reactor vault roof being pierced by a single orifice in vertical alignment with the vertical axis of said auxiliary heat exchanger, the dimension of said orifice in horizontal cross-section being larger than that of each one of said heat-exchanger modules but smaller than the overall dimension of the auxiliary heat exchanger in horizontal cross-section, and a removable shield plug closing said orifice, said shield plug having a depending axial extension penetrating into said reactor vessel with said modules disposed around said extension, the fluid circuit of each module communicating with an inlet tube and with an outlet tube for admission and discharge of the coolant fluid, said inlet and oulet tubes of each module extending in a direction parallel to the shield plug and the axial extension thereof within a respective recess formed in the inner surface of one of said orifice and said shield plug, whereby any of said modules of said auxiliary heat exchanger can be individually introduced into and taken out of said reactor in any order through said orifice after removal of said shield plug. 2. A nuclear reactor according to claim 1, wherein the fluid circuit of each module is constituted by a heat-transfer tube connected at the ends thereof respectively to said inlet tube and to said outlet tube for admission and discharge of the coolant fluid. 3. A nuclear reactor according to claim 2, wherein said heat-transfer tube has the shape of a tube coil. 4. A nuclear reactor according to claim 2, wherein said heat-transfer tube has the shape of a series of reversed hairpins. 5. A nuclear reactor according to claim 1, wherein the fluid circuit of each module is constituted by a plurality of U-tubes connected to an inlet header and an outlet header, said headers communicating respectively with said inlet tube and with said outlet tube for admission and discharge of the coolant fluid. 6. A nuclear reactor according to claim 1, wherein said fluid circuit of each heat-exchange module is constituted by a plurality of straight tubes connected at the ends thereof to an inlet header and to an outlet header, said header communicating respectively with said inlet tube and with said outlet tube for admission and discharge of the coolant fluid. 7. A nuclear reactor according to claim 2, wherein the inlet tubes of the modules are connected to an annular inlet manifold and the outlet tubes of the modules are connected to an annular discharge manifold communicating with means for pumping the coolant fluid, said annular manifolds being located externally of the reactor vessel and above the reactor vault roof and said pumping means being located externally of the reactor vessel. 8. A nuclear reactor according to claim 7, wherein the coolant fluid is liquid sodium and wherein the pumping means are constituted by an electromagnetic pump. 9. A nuclear reactor according to claim 1, wherein the modules constituting said auxiliary heat exchanger are surrounded externally by a cylindrical guide shell provided with open portions. 10. A nuclear reactor according to claim 1, wherein each heat-exchange module is provided at the lower end with a centering pin engaged in a bore provided in a support structure which is mounted within the reactor vessel and rigidly fixed thereto. |
description | This patent application claims priority to U.S. Provisional Patent Application No. 61/416,371 which was filed on Nov. 23, 2010. 1. Field of the Invention This invention relates generally to light water nuclear reactors and more particularly, to automated computational systems and methods for performing safety analyses in pressurized water reactors (PWRs) in conformance with 10 CFR 50.46, such as, postulated Loss of Coolant (LOCA) accidents. 2. Background of the Invention In general, safety analysis data is used in assessing and managing various issues relating to the operation of light water nuclear reactors at commercial nuclear plants. Various systems and methods are known in the art to perform safety analyses in PWRs in conformance with 10 CFR 50.46. For example, there are known systems and methods for analyzing postulated Large Break and Small Break Loss of Coolant (LOCA) accidents. In compliance with 10 CFR 50.46, postulated large break and small break LOCA accidents are analyzed to show that the Emergency Core Cooling System (ECCS) of PWRs satisfy the general design acceptance criteria. In the nuclear industry, particularly, in the United States, these types of safety analyses are performed using different evaluation models. For example, a conservative, deterministic approach is used to analyze Small Break LOCA and a Best-Estimate Plus Uncertainty (BEPU) method is used to analyze Large Break LOCAs. It is typical not to analyze intermediate breaks because they are considered not to be limiting based on simplistic engineering arguments of analysis. It is desired in the art to develop automated computational systems and methods which are capable to perform safety analyses in PWRs of LOCAs for a full spectrum of break types and sizes including small breaks, intermediate breaks and large breaks. These needs and others are satisfied by the present invention, which is directed to a computation system and method for performing a safety analysis of a Loss of Coolant Accident in a nuclear reactor. In one aspect, the present invention provides a computational system for performing a safety analysis of a postulated Loss of Coolant Accident in a nuclear reactor. The computational system includes an input model which includes noding for a full spectrum of break sizes of the postulated Loss of Coolant Accident, the input model includes an input deck which identifies parameters of the nuclear reactor selected from the group consisting of reactor geometry, initial conditions and boundary conditions, the parameters include constant values and uncertainty values; an uncertainty database including a set of uncertainty values for specific parameters identifying phenomena expected to occur during the postulated Loss of Coolant Accident; an input processor to extract uncertainty values from the uncertainty data base, generate an input deck for each of the uncertainty values and execute a Loss of Coolant Accident simulation for each of the uncertainty values, the uncertainty values encompassing a spectrum of break sizes for the postulated Loss of Coolant Accident ranging from small break to large break; and a code to compute a response of the nuclear reactor to the Loss of Coolant Accident simulation for each of the uncertainty values. In another aspect, the present invention provides a computational method for safety analysis of a postulated Loss of Coolant Accident in a nuclear reactor. The computational method includes developing an evaluation model; creating an input template comprising plant-specific data of the nuclear reactor including constant values and variables, one of the variables being break size of the postulated Loss of Coolant accident; entering the input template into the evaluation model; employing a random sampling procedure to assign numerical values to the variables, the variables encompassing a spectrum of break sizes for the postulated Loss of Coolant Accident ranging from small break to large break; transforming the input template into N input models, wherein N represents a number of variations; executing the N input models in parallel; obtaining results for each of the N input models; post-processing the results; and obtaining statistical merits to demonstrate compliance with design acceptance criteria. In still another aspect, the present invention provides a computational method for safety analysis of a postulated Loss of Coolant Accident in a nuclear reactor. The computational method includes developing an evaluation model; creating an input template to load into the evaluation model, the input template comprising plant-specific data of the nuclear reactor including constant values and uncertainty values, one of the uncertainty values being break size of the postulated Loss of Coolant Accident; employing a random sampling approach to generate model parameters and assign numerical values to the uncertainty values, the uncertainty values encompassing a spectrum of break sizes for the postulated Loss of Coolant Accident ranging from small break to large break; generating variations of the input template to represent different values for the uncertainty values; executing a plurality of transient simulations to encompass a spectrum of break sizes for the postulate d Loss of Coolant Accident; computing a response of the nuclear reactor for the spectrum of break sizes for the postulated Loss of Coolant Accident; and post-processing the results to obtain statistical figure of merits to demonstrate compliance with design acceptance criteria. The computational systems and methods of the present invention include a software tool designed to model and analyze postulated loss of coolant accidents (LOCAs) in compliance with 10 CFR 50.46. The present invention allows the application of a Best-Estimate Plus Uncertainty approach to an entire spectrum of break sizes including various small, intermediate and large breaks for postulated LOCAs in a PWR. Further, modeling and analyzing postulated small break, intermediate break and large break LOCAs with a single computer code and a single input model properly validated against relevant experimental data is provided. Input and physical model uncertainties are combined following a random sampling procedure, e.g., a direct Monte Carlo approach (ASTRUM-FS) and advanced statistical procedures are utilized to show compliance with 10 CFR 50.46 criteria. A postulated LOCA scenario is initiated by an instantaneous rupture of a reactor coolant system (RCS) pipe. The break type considered is either (i) a double-ended guillotine defined as complete severance of the pipe resulting in unimpeded flow from either end or (ii) a split break defined as a partial tear. The break size considered in this invention includes any break size such that break flow is beyond the capacity of the normal charging pumps up to and including a double ended guillotine rupture with a break flow area two times the pipe area. Thus, the computational systems and methods described are capable to model and analyze a spectrum of break sizes, such as intermediate break sizes, which are typically not analyzed in known evaluation models. Plant-specific data, such as the geometry of the reactor model, the power history, and the materials properties, are used as inputs to solve various calculations. These inputs are unique to a particular nuclear reactor being analyzed. This invention is applicable to light water nuclear reactors, such as, pressurized water reactors (“PWRs”) and boiling water reactors (“BWRs”), and is fully customizable to various light water nuclear reactor designs and not limited based on a particular nuclear reactor design. A full-spectrum LOCA evaluation model (FSLOCA EM) has been developed in accordance with and adherence to Nuclear Regulatory Guide 1.203, Evaluation Model Development and Assessment Process. In general, regulatory guides describe processes which the Nuclear Regulatory Commission (NRC) consider acceptable for use in developing and assessing evaluation models that may be used to analyze transient and accident behavior that is within the design basis of a nuclear power plant. The process for developing an evaluation model typically is initiated by identifying the functional requirements of the evaluation model that satisfy its intended purpose. To provide the appropriate focus and balance to the development process, a Phenomena Identification and Ranking Table (PIRT) may be employed. The PIRT identifies and classifies important phenomena to be simulated in the evaluation model. Use of the PIRT is based on expert opinion and engineering judgment about the scenario that needs is being modeled. The evaluation model is incorporated into a computational system or code and the code is validated against Separate Effect Tests (SETs) and Integral Effect Tests (IETs) which simulate relevant LOCA phenomena. The purposes of assessing the code against SET and IET include: 1) to confirm the adequacy of the evaluation model capabilities in modeling the scenario for which it is designed and 2) to assess bias and uncertainties of key model parameters to allow quantification of total uncertainty for performing a best-estimate plus uncertainty analysis. The second purpose is accomplished by characterizing the bias and uncertainty associated with parameters controlling the important phenomena and obtaining the probability density functions (PDFs) associated with such parameters. However, for some evaluation models, a conservative bias may be used to reduce licensing risks. PDFs or cumulative distribution functions (CDFs) are generated by comparing code predictions of SET against the data. In one embodiment, a procedure is utilized to determine bias and uncertainty (and CDF) for a critical flow model. The assessment of the break flow model includes a large number of data points from various geometries which are used to determine bias and uncertainty associated with the critical flow model prediction used in the code. The ratio between the measured value and the predicted value is obtained. This ratio is referred to as the discharge coefficient (CD). The CD is the correction (or multiplier) that is applied to the code results to correct for the bias observed in a specific data point relative to the measured value. The application of the discharge coefficient is accomplished by modifying the break flow area. Two uncertainty parameters are considered in the code: i) the uncertainty during the single-phase sub-cooled period, i.e., CD1 and ii) the uncertainty during the two-phase saturated and single-phase vapor period, i.e., CD2. The break type and break area are selected, and the uncertainty on the break flow model is treated by independently sampling a value for CD1 and CD2 from their respective distributions (PDFs). In one embodiment, the distributions for CD1 and CD2 are characterized by the following bias and standard deviation. BiasStandard DeviationCD1 (−0.043 ≦ Quality ≦ 0)9.2%19.6%CD2 (0 < Quality ≦ 1.0)26.8%31.1%. FIGS. 1 and 2 show the histograms (or PDFs) for CD1 and CD2. As shown in FIGS. 1 and 2, the Anderson-Darling Normality Test failed to prove that the distribution was normal for either CD1 or CD2. Thus, the actual distribution that results from the assessment of the evaluation model is used. The empirical CDFs for the multipliers will be used where the multiplicative factor applied to the break flow model is CD=1+Error. The CDFs corresponding to FIGS. 1 and 2 are shown in FIGS. 3 and 4, respectively. A similar procedure is developed for other uncertainty attributes (e.g., core heat transfer). The details may be different and can depend on the specific parameter, what is extracted from the data and the simulation results of the corresponding tests generating the data. The general purpose is to obtain the distribution of the correction factor that once applied to the code solution. In one embodiment, there are more than 40 uncertainty attributes. The number of attributes can depend on the specific application and the specific design of the nuclear reactor. In an embodiment, the model can miss-predict the data to a moderate extent. For example, the mean error or bias of the model is different when considering the single-phase sub-cooled region as compared to the two-phase saturated region. As previously shown, the bias is relatively small (e.g., −9.2%) in the sub-cooled region and is larger (e.g., −26.8%) in the two-phase saturated region. For the purpose of the uncertainty analysis, these biases are represented individually. The single-phase sub-cooled region predicts the initial blowdown and depressurization during a LOCA until two-phase flow is established in the loop. For smaller breaks, the two-phase discharge is significant during later stages of the LOCA when the venting rate of the steam impacts the energy release from the Reactor Coolant System (RCS) and therefore, the system pressure over a longer period of time. The timing of events such as the loop seal clearance, the depressurization rate during the boil-off period and the accumulator discharge are, for example, impacted by the break flow in the two-phase saturate region. Larger breaks are characterized by a very rapid initial blowdown and very short period of sub-cooled discharge. Fluid upstream of the break reaches saturated conditions very quickly. During most of a large break LOCA transient (until the flow becomes sub-critical) the two-phase critical flow is dominant. The uncertainty in both input (plant parameters) and the code's physical models are ranged and combined following a random sampling approach. In one embodiment, a Monte Carlo procedure considers the computer code as a black box or transfer function between a random set for the uncertainty parameter X and the figure of merits of the analysis, for example, the peak clad temperature (PCT) and maximum local oxidation (MLO) as shown below. { PCT MLO } i = 1 , … , N = C ( t ) { X 1 X 2 … X h } i = 1 , … , N wherein N represents the sample size. An automated process is developed that spins off, for example, several hundred simulations, N, which are executed in parallel on a cluster of processors. The results are analyzed with non-parametric order statistics procedures to obtain the upper tolerance limit of estimated quantities. In one embodiment, a full spectrum LOCA is modeled and analyzed in accordance with the flow chart as shown in FIG. 5. A single input model (e.g., template) is developed for a light water nuclear power plant to be analyzed. The template contains the input deck which describes the plant-specific geometry and, initial and boundary conditions. This information can be obtained from detailed design drawings, plant-specific design data, and operation parameters. The initial and boundary conditions can include, for example, core design parameters, RCS and ECCS parameters, RCS pressure and temperature, accumulator volume, temperature and pressure, technical specifications and the like. A geometrical model can be rendered using available geometry modeling tools known in the art. The input data that is supplied by the user can be entered using a variety of user-friendly mechanisms known in the art. The noding or mesh identified for the input model is designed to be applicable to the full spectrum of LOCA scenarios. Nodalization and model options are prescribed in procedures which are developed with the intent of providing consistency between the plant model and the models used to describe the SETs and IETs for the verification and validation (V&V) of the evaluation model. For example, prototypical fuel bundle tests to assess core heat transfer are modeled with the criterion of two hydraulic mesh between two spacer grid. The same criterion is applied for modeling of the assemblies in the reactor core of a PWR. Most of the values in the template are constant, however, there is a small subset of uncertainty variables. Model and input parameters for which there is an uncertainty are input as variables to be set by an automated process. An input processor generates multiple copies of input decks for downstream execution of multiple sensitivity cases. Input and model uncertainties are randomly sampled following a direct Monte Carlo approach and advanced statistical procedures are utilized to develop an uncertainty statement that satisfies compliance with 10 CFR 50.46 criteria (automated Statistical Treatment of Uncertainty for the Full Spectrum—ASTRUM-FS). The input processor assigns a random value to variables following the Monte Carlo process. A direct Monte Carlo sampling of the uncertainties is performed and a database of uncertainty attributes is generated. The range of uncertainty parameters covers the full spectrum of LOCA scenarios from small break LOCA to large break LOCA. The uncertainty attributes correspond to break size, break type, plant initial and boundary conditions, global modeling, and local uncertainty variables. The input processor extracts the parameters from the uncertainty database, assigns a numerical value to the uncertainty parameters in the input template, calibrates the steady states and launches the execution of transient simulations. Numerous cases (“N”), such as but not limited to, several hundred, are performed in parallel on a cluster of processors. A computer code, such as but not limited to WCOBRA/TRAC-TF2, is used to compute the plant's response to a LOCA event for each of the cases. As a result, a sample of the LOCA population is obtained. The sample size is extended such that variability in the predictor is minimized to the extent practical. See FIG. 6. The variability of the estimator is estimated by monitoring the confidence interval around a specific quantile of the population. In one embodiment, the variability of the estimator is estimated by monitoring the confidence interval around the estimated 95th quantile of the population, i.e., the difference between the (95/5) and the (95/95). The rank for the order statistics of such estimators is a function of the sample size N as shown in Tables 1 and 2. As indicated, break size and break type are random variables. The break size spectrum is divided into two regions (Region I and Region II) to achieve a well-balanced coverage (break size spectrum frequency) of all break sizes and types and corresponding scenarios. In known evaluation models, a uniform break area sampling is assumed within each region. However, different and more realistic break area and break type distribution can be considered. For each Regions I and II, the relevant figure of merits are ranked from the highest to the lowest value. In one embodiment, Peak Clad Temperature (PCT) and Maximum Local Oxidation (MLO) are the selected figure of merits. Using a non-parametric statistical procedure, the desired quantile (e.g., the 95th percentile of the PCT and MLO population) is bounded with the desired confidence level (typically at least 95% joint-probability or confidence is required by regulations). For each of Regions I and II, compliance with 10 CFR 50.46 criteria is demonstrated by comparing the upper tolerance limit figures against limits prescribed by the rule. The subdivision in Regions I and II is suggested for the purpose of obtaining a sample which provides coverage of the break spectrum consistent with current 10 CFR 50.46 rule (as of November 2010). However, a more realistic break area and break type distribution may be considered. The statistical procedure used above is an extension of the upper tolerance limit procedure discussed by Guba and Makai (Guba, et al., 2003). The derivation is based on the non-parametric multivariate tolerance limits formulation first proved by Wald (1943) and more recently adapted by Guba-Makai (Guba, et al., 2003) to the problem of making safety inferences based on the output of models of complex systems. Accordingly to Guba-Makai the one sided confidence level using the highest rank as estimator is given by: β = 1 - I ( γ , N - p + 1 , p ) = ∑ j = 0 N - p ( N j ) γ j ( 1 - γ ) N - j ( 1 ) In one embodiment, two output variables: PCT and MLO are considered. If β=0.95 and γ=0.95 are specified, the number of samples N can be calculated as 93. The statistical interpretation of this result is that if we observe a random sample of size N=93, then there is a β=95% probability that the proportion of the population for the two considered output variables (PCT and MLO for the specific application presented herein) having a value below the maximum calculated values among the 93 sampled cases, γ, is 95%. The extension considered in ASTRM-FS is the use of lower ranks which tend to be more stable. If instead of the extreme case (rank k=1), a given rank k is chosen as a predictor for the one sided confidence level then: β = 1 - I ( γ , N - p - k + 2 , p + k - 1 ) = ∑ j = 0 N - p - k + 1 ( N j ) γ j ( 1 - γ ) N - j ( 2 ) This expression is obtained by considering (r1=r2= . . . =rp=0) and sp=N−p−k+2 in the derivation provided in the paper (Guba et. al. 2003). If: ( N j ) = N ! j ! ( N - j ) ! ( 3 ) Then, this can be expanded as follows: ( N j ) = N ( N - 1 ) … ( N - j + 1 ) j ( j - 1 ) … 1 = ∏ l = 1 j N - l + 1 1 ( 4 ) Equation 2 can then be expressed as follows: β = 1 - I ( γ , N - p - k + 2 , p + k - 1 ) = ( 1 - γ ) N + ∑ j = 0 N - p - k + 1 ( ∏ l = 1 j N - l + 1 1 γ j ( 1 - γ ) N - j ) ( 5 ) Table 1 lists the different k-th estimator/rank (estimation of the 95th quantile) and the corresponding required sample size to achieve the 95% confidence level using Equation 5. By increasing the sample size, N, to infinity, the estimator will be simply k=N/20 (=0.05*N). As the sample size is increased for a given quantile and confidence level, a lower rank order statistic can be used with the advantage of reducing the predictor variability. A measure of the variance can be extracted by examining for a given sample size the ranks kL and kU for the lower and upper tolerance limit respectively for a given quantile. These values can be calculated from Equation 5, and are shown in Table 2 for β=0.95 and 0.05. The tolerance interval (from <5% to >95%) is a measure of the Q95/95 predictor variability. As the sample size increases the tolerance interval is expected to decrease in magnitude. Whereas particular embodiments of the invention have been described herein for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details may be made without departing from the invention as set forth in the appended claims. TABLE 1Required Sample Sizes for Different k-th Maximum as Estimate of0.95 Quantile at 95% Confidence LevelRequired95/95 Estimator95/95 Estimator Sample95/95 Estimator withwith p = 2with p = 3Size Np = 1 k-th Predictork-th Predictork-th Predictor 59k = 1—— 93k = 2k = 1—124k = 3k = 2k = 1153k = 4k = 3k = 2181k = 5k = 4k = 3208k = 6k = 5k = 4234k = 7k = 6k = 5260k = 8k = 7k = 6286k = 9k = 8k = 7311k = 10k = 9k = 8336k = 11k = 10k = 9361k = 12k = 11k = 10386k = 13k = 12k = 11410k = 14k = 13k = 12434k = 15k = 14k = 13458k = 16k = 15k = 14482k = 17k = 16k = 15506k = 18k = 17k = 16. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .Infinityk = N/20k = N/20k = N/20 TABLE 2Ranks kL and kU Corresponding to Lower (<5% Tolerance Interval) andUpper (>95% Tolerance Interval) Bounds for Different Sample Sizes forp = 2RequiredSampleSize N95/5 Estimator k-th Predictor95/95 Estimator k-th Predictor 59—— 93k = 8k = 1124k = 10k = 2153k = 12k = 3181k = 14k = 4208k = 16k = 5234k = 17k = 6260k = 19k = 7286k = 21k = 8311k = 22k = 9336k = 24k = 10361k = 25k = 11386k = 27k = 12410k = 28k = 13434k = 29k = 14458k = 31k = 15482k = 32k = 16506k = 34k = 17. . .. . .. . .. . .. . .. . .. . .. . .. . .Infinityk = N/20k = N/20 |
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description | The present invention relates to a method of detecting concealed fissile or fissionable special nuclear material in an article, such as a shipping container. More particularly, the present invention relates to a method of detecting special nuclear material in an article, employing fast neutrons. Several non-intrusive inspection systems, including X-ray scanning systems and neutron interrogation systems, have been developed and deployed for the detection of conventional explosives or narcotics. However, these systems are not adequate for the detection of the fissile material of a nuclear weapon hidden in a typical cargo container. X-ray techniques cannot easily differentiate the fissile material from innocuous heavy metals such as lead, tungsten and bismuth. The most common neutron-based technique employed to detect fissile material is differential die-away (DDA). In this method, the item to be inspected is placed in a chamber or enclosure containing a pulsed source of energetic, or fast, neutrons. The fast neutrons slow down to thermal energies, and then die away over a period of microseconds to milliseconds, depending on the thermal neutron capture properties of the environment. If fissile material is present in the item, then fission events induced by thermal neutrons will perturb the die-away characteristics of the thermal neutron fluence rate due to the addition of fission neutrons. Consequently, by monitoring the thermal neutron fluence rate die-away time with a thermal neutron detector between fast neutron pulses, the presence of fissile material in an item can be detected. The DDA technique suffers from the fact that the thermal neutron detectors typically employed for DDA cannot process very high event rates, and a significant waiting period after the pulse is needed before counting can begin in order to allow the detectors to recover from saturation effects due to the pulse. This time delay results in a significant reduction in detection sensitivity. Furthermore, DDA can be circumvented by placing a thermal neutron absorber, such as boron, lithium or cadmium, around the fissile material. Simple gamma spectroscopy can also be employed to detect and identify fissile or fissionable material. This method relies on the detection of the decay radiation emitted from fissile or fissionable radionuclides by a high resolution gamma ray detector. However, the most prominent radiation emitted from fissile nuclides is typically low energy gamma rays, especially in the cases of uranium 235 and plutonium 239, and can therefore be absorbed with a modest amount of gamma shielding placed around the fissile device. Thus, a system relying solely on decay gamma detection can easily be circumvented. Previous work in this area has been limited by a lack of sensitivity of detector electronics. For work employing pulsed neutron generators and gamma-ray detection, the short pulse durations (1–5 microseconds) were characterized by extremely high instantaneous neutron emission rates, and the resulting gamma ray flux was so large that the gamma-ray detector electronics were paralyzed. In addition, all systems—whether using electronic or isotopic neutron sources—were hampered by relatively poor signal-to-background noise ratios for peaks from trace constituents in a sample. To enhance homeland security protection, new and/or improved technologies are needed to prevent and deter the smuggling of materials that can be employed for catastrophic terrorist attacks. These materials include constituents of nuclear, conventional (i.e., explosive), chemical and radioactive weapons. Detection of illicit attempts to transport these threat materials past points of entry, such as airports, ports and borders is a key component of the fight to protect the security of U.S. and allied countries. The current non-intrusive inspection methods for the detection of fissile material are either inadequate or can readily be circumvented. The present invention provides a non-intrusive inspection method which overcomes many of the problems with prior technologies. In one aspect, the present invention provides a method of detecting fissile material in an article comprising: providing at least one fast neutron detector and at least one source of neutrons characterized by a particle intensity, source strength, pulse width and pulse frequency; irradiating the article with the at least one neutron source to effect emission of fast neutron radiation from the fissile material, if present; acquiring fast neutron data indicative of the number of fast neutrons emitted from the fissile material during a predetermined time period; and analyzing the data to determine the presence or absence of the fissile material. The method, referred to as Prompt Neutron Neutron Activation Analysis (PNNAA), can detect concealed fissile or fissionable material in a container with high precision and is not affected by gamma shielding. As used herein, the term “fissile material” will be defined to include fissile material, fissionable material and special nuclear material, as those terms are understood in the art, and will be used to refer to nuclear materials characterized as having nuclei which are capable of undergoing fission. Examples of such materials include, but are not limited to, isotopes of thorium, uranium, neptunium, plutonium, americium, and elements of higher atomic number. Isotopes of principal interest in common application include 233U, 235U, 239Pu and 241Pu. Any isotope or mix of isotopes which undergoes nuclear fission induced by incident neutrons will produce energetic fission neutrons which the disclosed method is capable of employing for detection. PNNAA relies on the detection of prompt fast fission neutrons emitted by fissile or fissionable nuclides during the time interval between pulses of fast source neutrons. As used herein, “fast neutrons” refers to neutrons having an energy greater than about 100 keV. Because the fast source neutrons die away within less than a microsecond after the end of a pulse, the fast neutron background between pulses is insignificant if the period is of the order of microseconds and the detector counting is set to start after the end of a pulse and set to stop before the start of the next pulse. If fissile material is present in the container, then fast fission neutrons will be emitted between pulses through fission events induced by both fast and thermal neutrons, and their detection will provide an unambiguous indication of the presence of fissile material. Unlike DDA, PNNAA relies on the direct measurement of fast (i.e., energetic) neutrons produced by fission, and is therefore less subject to interference than DDA. In an additional aspect, the present invention provides an apparatus for detecting fissile material in an article comprising: a neutron source for generating neutrons characterized by a particle energy, source strength, pulse width and pulse frequency; at least one fast neutron detector for detecting the fast neutron radiation emitted from the article; source electronics means associated with the neutron source for controlling the pulse width of neutrons generated by the neutron source; detector electronics means associated with the at least one fast neutron detector for amplifying and digitalizing signals generated by the at least one fast neutron detector and storing data representing the digitalized signals; spectral analysis means for analyzing the data and determining the presence or absence of fast neutron emission from the article; and an acquisition interface module (AIM) for controlling the timing of the source and detector electronics such that the neutron source generates neutrons in a burst of a prescribed pulse width and the detectors and detector electronics means detect fast neutrons during the time interval between bursts and acquire data indicative of the number of fast neutrons emitted in the time interval between successive bursts. PNNAA relies on a neutron detector that can detect and discriminate fast neutrons in the presence of thermal neutrons and gamma radiation. The detector is able to process high count rates and is resistant to radiation damage, and is preferably a solid state neutron detector comprised of silicon carbide. This type of detector has excellent resistance to radiation damage and has a fast charge-collection time, which enables it to process very high count rates. The silicon carbide detectors are highly insensitive to both thermal neutrons and gamma rays. It is an aspect of the present invention, therefore, to provide a method of detecting fissile material in an article, such as a shipping container, by detecting fast neutron emission from the fissile material. It is an additional aspect of the invention to provide a method of detecting fissile material in an article by detecting fast neutron emission from the fissile material with a solid-state neutron detector. In an additional aspect, the present invention provides an apparatus for the detection of fissile material in an article such as a shipping container, by detecting fast neutron emission from the fissile material. These and other aspects of the present invention will become more readily apparent from the following drawings, detailed description and appended claims. The present invention provides a method of detecting fissile material in an article by providing at least one fast neutron detector and a source of neutrons characterized by a particle energy, a source strength (number of neutrons per unit time), a pulse width and a pulse frequency. As used herein, the term “article” refers to any container which can be used to conceal fissile material. Exemplary articles include, but are not limited to, shipping containers, packages, luggage and the like. The method of the present invention can be used to scan any article to determine the presence or absence of fissile material. The article is irradiated with the neutron source to effect emission of fast neutron radiation from the article. Fast neutron data indicative of the number of fast fission neutrons emitted from the fissile material during a predetermined time interval is collected and analyzed to determine the presence or absence of fissile material. In order to produce pulses of neutrons on a time scale which can be employed in the disclosed method, the most commonly used neutron sources are electronic neutron generator tubes of the type developed for oil well logging applications. These tubes contain a compact accelerator which propels deuterons into tritium or deuterium at an incident kinetic energy of 100–200 keV. This produces fusion reactions, with a resulting neutron yield. The D+T reactions produce 14 MeV neutrons and the D+D reactions produce 2–3 MeV neutrons. It may be desirable to use a combination of neutron sources to penetrate the article or container at different depths, thus ensuring complete evaluation of the article. Other systems (e.g., the proton linear accelerator approach, the RFQ system or other accelerator-based systems which provide up to 25 MeV neutrons) capable of providing a controllable, regular pattern of neutron bursts can also be used. At least one neutron source is used, and in one embodiment, a plurality of sources can be used. Therefore, in one aspect the method includes generating neutrons with energies of approximately 25 MeV, 14 MeV, 2.5 MeV, and 0.025 eV. While these energies are conveniently available, other energies are also available and useful for various applications, e.g., 750 keV neutrons can be produced using a proton linear accelerator and a lithium target. As the initially energetic neutrons migrate through the materials contained within the inspected article, natural collision processes will slow the neutrons, until they eventually reach a kinetic energy of approximately 0.025 eV, which is the average kinetic energy of the atoms of a substance at room temperature. At this point, the neutrons are said to be in thermal equilibrium with the environment, and are termed “thermal neutrons”. Depending on the isotope, fission reactions can be induced copiously by these “thermal” neutrons, whereas for some of the isotopes of interest fission reactions can only be induced by the neutrons while they are still quite energetic (kinetic energy on the order of 1 MeV). Hence, the selection and placement of neutron sources is based on considering requirements of neutron energy and penetration of the sample. This selection is typically based on computer calculations modeling a diverse sampling of such articles, which can be readily performed by one skilled in the art. PNNAA relies on detection of the fast fission neutrons produced by (n, fission) reactions to indicate if fissile material is present in a container. A pulsed neutron source is employed to provide energetic source neutrons that can penetrate into the container and produce fission neutrons in any fissile material present. The key to PNNAA is to discriminate fission neutrons from source neutrons. This discrimination is achieved by using time-sequenced neutron measurements with fast-response SiC neutron detectors. See, e.g., “Development of a Silicon Carbide Radiation Detector”, F. H. Ruddy, A. R. Dulloo, J. G. Seidel, S. Seshadri, and L. B. Rowland, IEEE Transactions on Nuclear Science NS-45, 536 (1998); “The Thermal Neutron Response of Miniature Silicon Carbide Semiconductor Detectors”, A. R. Dulloo, F. H. Ruddy, J. G. Seidel, J. M. Adams, J. S. Nico, and D. M. Gilliam, Nuclear Instruments and Methods A, 498, 415 (2003); “Simultaneous Measurement of Neutron and Gamma-Ray Radiation Levels from a TRIGA Reactor Core Using Silicon Carbide Semiconductor Detectors”, A. R. Dulloo, F. H. Ruddy, J. G. Seidel, C. Davison, T. Flinchbaugh, and T. Daubenspeck, IEEE Transactions on Nuclear Science 46, 275 (1999). These detectors have charge collection times of less than 5 nanoseconds, which allows processing of very high count rates. Previous work has shown that SiC detectors can detect high-energy neutrons in the presence of a thermal neutron field and a high gamma-ray background through the nuclear reactions of these neutrons with Si and C nuclei of the detector. See, e.g. “Monitoring of D-T Accelerator Neutron Output in a PGNAA System Using Silicon Carbide Detectors”, A. R. Dulloo, F. H. Ruddy, J. G. Seidel, and B. Petrovic, Applications of Accelerators in Research and Industry—Sixteenth International Conference, AIP CP576 (2001); “Fast Neutron Spectrometry Using Silicon Carbide Detectors”, F. H. Ruddy, A. R. Dulloo, B. Petrovic, and J. G. Seidel, in Reactor Dosimetry in the 21st Century, J. Wagemans, H. A. Abderrahim, P. D'hondt, and C. De Raedt (Eds.), World Scientific, London (2003) pp 347–355. As used herein, the term “pulse width” refers to the time duration of the neutron pulse, e.g., the time interval during which the source is emitting neutrons. Typically, the pulse width of the neutron beam emanating from the source will be between about 4 nanoseconds to 200 microseconds. The pulse frequency will be between about 100 to 10,000,000 Hz, which translates into an interval between pulses of about 10 milliseconds to 100 nanoseconds. FIG. 1 illustrates a set of neutron reaction time scales. Neutron reactions occur over time periods of less than 10−15 s, which is instantaneous for detection/counting purposes. However, the time scale for observation of neutron-induced reactions is controlled by other factors, including neutron time-of-flight and capture rates. Neutrons in the 1–14 MeV range will travel 1–5 cm per nanosecond and the time scale for observation of reactions induced by these neutrons will be dominated by time-of-flight considerations, such as, the distance of the fissile material from the neutron source and the detector. The reaction time scale of lower-energy neutrons, e.g., 1 eV, is controlled primarily by neutron lifetime before capture. Fast neutrons are generally thermalized within a microsecond. The prior Prompt Gamma Neutron Activation Analysis (PGNAA) work of the inventors has shown that thermal neutron capture reaction rates decrease by a factor of two in time periods in the 200–400 microsecond range, depending on the thermal neutron capture properties of the surroundings. See, e.g., “Neutron Fluence Rate Measurements in a PGNAA 208-Liter Drum Assay System Using Silicon Carbide Detectors,” A, R. Dulloo, F. H. Ruddy, J. G. Seidel, S. Lee, B. Petrovic, and M. E. Mcllwain, Nuclear Instruments and Methods B 213 (2003) pp 400–405. Consider a time interval starting one microsecond after the end of one pulse and ending before the start of the next pulse. In this interval, fast source neutrons have already thermalized or escaped from the system. If fissile material is present, the thermal neutrons will induce fission reactions, which in turn release fast fission neutrons. Consequently, fast neutrons detected during this interval can be correlated with the presence of fissile material. PNNAA with SiC detector technology has excellent sensitivity for fissile material detection because of the near-zero fast-neutron background in this interval. In addition, the rapid response of SiC detectors eliminates any detector saturation concern and allows counting throughout this period. Bench scale laboratory tests were conducted using a single 6-mm diameter-equivalent SiC neutron detector and a 14-MeV pulsed neutron source. A PNNAA run was performed with a 5.2-gram sample of 93.16%-enriched U-235. Detector counts were recorded in the time interval between pulses. For comparison, a PNNAA run without the U-235 sample was also performed. The measured count rates were 0.237±0.013 (±5.5%) counts s−1 with the U-235 sample and 0.024±0.005 (±21%) counts s−1 without the U-235 sample present. This PNNAA test, involving a very small amount of fissile material (<0.05% of the amount needed for a bomb), demonstrates unambiguously that PNNAA can detect fissile material with high sensitivity, since the count rate in the presence of U-235 is almost ten times the background count rate. Fissile material-detection techniques that rely solely on thermal-neutron reactions in the material can be circumvented by reducing the thermal neutron flux with a thermal neutron absorber (e.g., boron, cadmium, lithium). These absorbers are less effective at preventing fast or even epithermal neutron-induced reactions in the material. Consequently, PNNAA can potentially overcome such masking attempts through detection of neutrons emitted by energetic (non-thermal) neutron-induced fission. A fast-response detector, such as SiC, is needed to take advantage of energetic neutron-induced reactions due to the time scale involved (see FIG. 1). Further, neutron source pulses should preferably be about 10-ns wide or less. Finally, due to potential interference from (n, xn) reactions in surrounding materials, the source neutron energy should preferably be less than the energy threshold of these reactions. As used herein, the term “source strength” refers to the number of neutrons per second emitted by the neutron source. The neutron source should be able to provide about 107 to 1012 neutrons per second. As a preliminary investigation of fissile material detection based on energetic-neutron reactions, calculations using the MCNP-4b Code were performed with a simple configuration consisting of a 100-cm3 U-235 sphere placed at a distance of 50 cm from a 6.5-MeV neutron source (energy chosen to minimize interference from [n, xn] reactions). See, e.g., J. F. Briesmeister, Ed., “MCNP—A General Monte Carlo N-Particle Transport Code, Version 4B,” LA-12625-M, Los Alamos National Laboratory, March, 1997. The neutron flux was studied as a function of time from the end of a pulse at a 50-cm distance from the sphere. Calculations with bare U-235 and with boric acid (an easily-acquired thermal-neutron absorber) and lead (a common high-Z material) present around the U-235 were performed. The results from these cases are shown in FIG. 2. Results from a calculation done with steel substituted for U-235 are also shown to provide a baseline where no fissile material is present in the system. The data in FIG. 2 indicate that: (a) the presence of U-235 significantly prolongs the die-away of both the E>0.5 eV and E>1 MeV neutron flux in the 0.1 to 1 microsecond range; (b) lead has very little impact on this effect; and (c) boric acid appears to enhance the effect in both flux cases and extends the time scale to greater than 100 microseconds in the E>0.5 eV flux case. This enhancement is thought to be due to the extra moderation provided by the hydrogen, boron and oxygen nuclides of the boric acid. Neutron moderation in this energy regime more than offsets neutron capture by the boron-10 nuclide, and, consequently, more fission events occur in the U-235. Thus, fast- and epithermal-neutron fission die-away measurements overcome a major weakness of existing neutron-based interrogation systems. Finally, in pulsed neutron systems, the delayed fission neutron flux is expected to reach an equilibrium value during the interrogation period. Hence, delayed fission neutrons will make a small and time-independent contribution to the PNNAA signal if fissile material is present. The fast neutron detector employed in this method is preferably a solid state neutron detector. A particularly preferred, radiation resistant, neutron detector employs a semiconductor active region fabricated from silicon carbide (SiC). Use of suitable semiconductors having active regions comprised of other materials such as silicon, cadmium zinc telluride (CZT), cadmium telluride, gallium arsenide or diamond, is also contemplated and within the scope of the present invention. Referring to FIG. 3, an exemplary PNNAA system 1 includes a suitable neutron detector 2; a suitable high speed, high throughput count rate preamplifier (PREAMP) 3; a high count rate, high speed spectroscopy amplifier (AMP) 4; a detector high voltage supply 5; a high speed analog-to-digital converter (ADC) 6; an Acquisition Interface Module (AIM) 7; a special neutron generator timing module 8; and a pulsed neutron source or generator 9. The timing module 8 provides for time-correlated data acquisition to coordinate firing of the neutron generator 9 with fast neutron emission data acquisition. Such time-correlated data acquisition techniques are known in the art. The system 1 also includes a suitable computer 10, such as a high speed minicomputer, and multi-channel analyzer software 11, which is typically integrated with or loaded on the computer 10, along with spectral analysis algorithms 16. See, for example, Dulloo, A. R. et al., Nuclear Technology, “Detection Limits of a Laboratory Pulsed Gamma Neutron Activation Analysis System for the Nondestructive Assay of Mercury, Cadmium and Lead”, A. R. Dulloo, F. H. Ruddy, T. V. Congedo, J. G. Seidel, and R. J. Gehrke, Nuclear Technology 123, 103 (1998); and U.S. Pat. No. 5,539,788. The AIM is a commercially available product made by Canberra Industries of Meriden, Conn. It will be appreciated that, while reference has been made to the exemplary computer 10, a wide range of other processors such as, for example, mainframe computers, workstations, personal computers (e.g., network or standalone), microcomputers, and other microprocessor-based computers may be employed. In an additional aspect, the present invention provides an apparatus for detecting fissile or fissionable material in an article. The apparatus comprises a neutron source for generating neutrons of a predetermined energy; at least one fast neutron detector for detecting the fast neutron radiation emitted from the article; source electronics means associated with the neutron source for controlling pulse width, pulse frequency and source strength of neutrons generated by the neutron source; detector electronics means associated with the fast neutron detectors for amplifying and digitalizing signals generated by the fast neutron detectors and storing data representing the digitalized signals; spectral analysis means for analyzing the data and determining the presence or absence of fast neutron emission from the article; and an acquisition interface module (AIM) for controlling the timing of the source and detector electronics such that the neutron source generates neutrons in a burst of a prescribed pulse width and the detectors and detector electronics means detect fast neutrons during the time interval (referred to herein as the pulse interval) between the bursts and acquire data, indicative of the number of fast neutrons emitted during the time interval between bursts. The PNNAA system can be enhanced in many ways. In one embodiment, through integration with an X-ray screening system, PNNAA can verify whether a high density region in a container detected by the X-ray system is special nuclear material or not. In an additional embodiment, it can be integrated with a gamma-ray detector, and the capability to detect explosives and chemical warfare agents through prompt gamma neutron activation analysis can be implemented. The PNNAA system can be used directly on individual packages identified as suspicious by previous data or intelligence. For the examination of large cargo containers, coupling of the system with a known form of high reliability primary scanning will provide maximum efficiency and economy. In such a case, a suitable primary scan by an X-ray or other methods could isolate a region of a shipping container containing a suspicious item of cargo. For fissile material, this would probably correspond to an agglomeration of high density material in a transmission X-ray image or tomographic reconstruction. This could be either the fissile material itself or heavy metals such as lead, tungsten or bismuth, used to shield gamma rays from detection by the passive methods described above. FIG. 4 presents a diagram of a preferred embodiment in which a conveyor-based system is used for PNNAA scanning of a cargo container. In this embodiment, the apparatus further comprises a protective enclosure 20 having a wall made of a neutron-reflecting material and a conveyor 22 for supporting the article 24 in the protective enclosure. The protective enclosure 20 is designed to provide partial thermalization (slowing down) of neutrons, and to provide radiation protection. A plurality of detectors 26 are used, wired into distinct individual chains, to ensure high sensitivity and to provide coarse spatial resolution. One or more neutron sources 28, 30 are used to irradiate the article. Conveyor systems have already been successfully deployed for high energy X-ray investigation of cargo containers at Japanese ports by BIR Inc. (Bio-Imaging Research, Inc., 425 Barclay Boulevard, Lincolnshire, Ill. 60069), in cooperation with the Japanese government. Beginning with such a platform, the inclusion of a conveyor segment dedicated to PNNAA would simply constitute an extension of the mechanical system already deployed. Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appending claims. |
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summary | ||
abstract | Provided herein is a radiation powered device comprising a semiconductor comprising a diamond material. |
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abstract | The disclosed apparatus is a surface illuminator i.e. surface light source typically used in lighting for liquid crystal displays (LCDs). The surface illuminator using point light source may comprise a first light guide member for a surface lighting having a first light exiting surface and a first light entering surface; a second light guide member for a light distribution having a second light exiting surface and a second light entering surface; at least one point light source (LED) optically communicated with the second light entering surface; a channel light guide member having a fiber optic channel array having a plurality of light guiding portions optically isolated one another; and wherein the channel light guide member is disposed between the first light guide member and the second light guide member. The second light guide member may be an elongated light guide member having a linear or nonlinear elongated member. |
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052767248 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for exposing a substrate like a semiconductor wafer to X-rays in the lithographic process in the manufacture of semiconductor devices, and more particularly, to an X-ray transmitting window which forms a partitioning wall of two vessels having a relative pressure difference and which transmits X-rays so as to allow X-rays to be transferred between the vessels. 2. Description of the Related Art There is an increasing demand for fine circuit patterns in order to provide high-density and high-performance semiconductor integrated circuits. The possibility of formation of fine patterns on the order of 0.1 .mu.m or less is the primary reason for developing X-ray lithography. A promising high-output X-ray source employed in such an X-ray lithography is SOR (synchrotron orbital radiation). In X-ray lithography which employs SOR, X-rays generated under a high vacuum of about 10.sup.-10 Torr are irradiated onto a sample, such as a semiconductor wafer, generally placed in an atmosphere having 1 atm. To achieve this, an X-ray transmitting window made of a material having a high X-ray transmittance, such as beryllium (Be), is provided between the SOR source and the sample chamber. For the reason mentioned above, a pressure difference substantially equal to 1 atm is applied to the X-ray transmitting window. In the case of an X-ray transmitting window made of a Be plate and having an opening area of, for example, 30 mm.times.30 mm, such a pressure difference can be resisted if the thickness is about 0.2 mm. However, such a Be X-ray transmitting window has the following drawbacks. (1) 10 .ANG. X-rays which pass through Be are attenuated at about 0.2 dB/.mu.m. This attenuation rate increases as the wavelength increases. Thus, the use of X-rays of short wavelengths in x-ray lithography is advantageous from the viewpoint of transmittance. However, X-ray absorber (which may be a gold film) on the exposure mask readily transmits X-rays of short wavelengths. Consequently, in X-ray lithography, the contrast of the X-ray absorber patterns is reduced, making exposure of fine patterns difficult. Thus, the use of a Be X-ray transmitting window which is as thin as possible and of X-rays of long wavelengths is desired. To achieve these objectives, it is necessary for the thickness of the Be X-ray transmitting window to be reduced to 1/10th or less of that of the conventional window. (2) To achieve a high throughput in X-ray lithography, it is desired to increase the opening area of the X-ray transmitting window to about several tens of millimeters x several tens of millimeters. Currently, it is very difficult to provide a Be X-ray transmitting window which satisfies the aforementioned requirements. SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray transmitting window which exhibits a high transmittance to X-rays having long wavelengths of 10 .ANG. or above, which has an opening area whose side dimension is several tens of millimeters, and which can withstand a pressure difference of about 1 atm. Another object of the present invention is to provide an X-ray exposure apparatus having two vessels which are connected to each other through the partitioning wall formed of the abovementioned window, so that, in a source connected to one of the vessels, an SOR is generated, and in another vessel, a sample like a silicon wafer coated with a resist film is exposed to an X-ray of the SOR transmitted through the window. To achieve the above object, an X-ray transmitting window according to the present invention is a plate-like member formed by joining a large number of juxtaposed capillary tubes, each having an inner diameter of about several tens of .mu.m, parallel to each other. The smaller the inner diameter of each of the capillary tubes and the larger the length thereof, the greater the pressure difference obtained at the two sides of the window. That is, it is possible to produce a vacuum at one side of the window and an atmospheric pressure at the other side thereof. However, a decrease in the inner diameter of the thin tubes and an increase in the length thereof reduces the transmittance of the window. Thus, the inner diameter and length (the thickness of the window) of the capillary tubes are determined with the practical pressure difference and transmittance taken into consideration. The size of the window is determined such that the window withstands that pressure difference. |
claims | 1. A method of moving nuclear fuel from a fuel pool with a graphical user interface, the method comprising:inputting at least one fuel attribute into the graphical user interface;graphically populating, by the graphical user interface, a graphical loading map with graphical fuel bundles,the graphical fuel bundles representing fuel bundles in at least one fuel pool,the graphical user interface populating the graphical loading map according to the input at least one fuel attribute and at least one corresponding attribute of the nuclear fuel bundles represented by the graphical fuel bundles,the graphical user interface including one or more loading tools configured to graphically select, sort, filter, or move the graphical fuel bundles into the graphical loading map based on the at least one corresponding attribute of the fuel bundles represented by the graphical fuel bundles;graphically filtering, by the graphical user interface, the graphical fuel bundles in the graphical loading map, the graphical filtering based on the input of at least one fuel attribute; andphysically placing the fuel bundles into a reactor core according to the populated graphical loading map. 2. The method of claim 1, wherein the graphical user interface further includes at least one fuel pool table and a reload table, and wherein the graphically populating includes graphically selecting, sorting, filtering, or moving the graphical fuel bundles within or among the graphical loading map, the at least one fuel pool table, and the reload table via the one or more loading tools, the selecting, sorting, filtering, and moving being based on the one or more fuel attributes of the fuel bundles represented by the graphical fuel bundles. 3. The method of claim 2, further comprising:storing at least one fuel pool database, the fuel pool database including a fuel pool list of at least one of the fuel bundles residing in the fuel pool; andgraphically populating the at least one fuel pool table with a graphical representation of at least one of the fuel bundles on the fuel pool list. 4. The method of claim 2, wherein the graphical user interface further includes a fresh fuel table, and wherein the graphically populating includes graphically selecting, sorting, filtering, or moving the graphical fuel bundles within or among the loading map, the at least one fuel pool table, the reload table, and the fresh fuel table via the one or more loading tools, the selecting, sorting, filtering, and moving being based on the one or more fuel attributes of the fuel bundles represented by the graphical fuel bundles. 5. The method of claim 4, further comprising:storing at least one fresh fuel database, the fresh fuel database including a fresh fuel list of at least one of the fresh fuel bundles; andgraphically populating the at least one fresh fuel table with a graphical representation of at least one of the fuel bundles on the fresh fuel list. 6. The method of claim 1, further comprising:analyzing the populated graphical loading map by simulating reactor performance with the populated graphical loading map, the analyzing performed before the physically placing the fuel bundles into the reactor core according to the populated graphical loading map. 7. The method of claim 1, wherein the one or more fuel attributes include at least one of exposure, a previous cycle in which the fuel bundle was used, k infinity, bundle product line, initial uranium loading, initial gadolinium loading, number of axial zones, historical fuel cycle numbers previous to a most recent for which the fuel bundle was used, a corresponding reactor core in which the fuel bundle was resident for each of the historical fuel cycles, accumulated residence time, and fuel bundle pedigree, which is a parameter that reflects usability of the fuel bundle for continued reactor operation. 8. A method of moving nuclear fuel from a fuel pool, the method comprising:inputting at least one fuel attribute into the graphical user interface;providing the graphical user interface including a graphical loading map graphically representing fuel bundles in a reactor core;graphically sorting, filtering and moving, with one or more loading tools within the graphical user interface, graphical bundles into the graphical loading map, the sorting, filtering, and moving based on at least one fuel attribute of the fuel bundles represented by the graphical fuel bundles, at least one of the graphical fuel bundles representing a fuel bundle in a fuel pool; andphysically placing the fuel bundles into the reactor core according to the populated loading map. 9. The method of claim 8, wherein the graphical user interface further includes at least one fuel pool table graphically representing bundles in a fuel pool and a reload table, and wherein the method further comprises:graphically selecting, sorting, filtering, or moving the graphical fuel bundles based on the one or more fuel attributes of the fuel bundles represented by the graphical fuel bundles within or among the fuel pool table and the reload table, wherein the graphically populating the loading map includes graphically populating the loading map with graphical fuel bundles moved into the reload table. 10. The method of claim 9, further comprising:storing at least one fuel pool database, the fuel pool database including a fuel pool list of at least one of the fuel bundles residing in the fuel pool; andgraphically populating the at least one fuel pool table with a graphical representation of at least one of the fuel bundles on the fuel pool list. 11. The method of claim 9, wherein the graphical user interface further includes a fresh fuel table, and wherein the graphically populating includes graphically selecting, sorting, filtering, or moving the graphical fuel bundles within or among the graphical loading map, the at least one fuel pool table, the reload table, and the fresh fuel table via the one or more loading tools, the selecting, sorting, filtering, and moving being based on the one or more fuel attributes of the fuel bundles represented by the graphical fuel bundles. 12. The method of claim 10, further comprising:storing at least one fresh fuel database, the fresh fuel database including a fresh fuel list of at least a portion of available fresh fuel bundles; andgraphically populating the at least one fresh fuel table with a graphical representation of at least one of the fresh fuel bundles on the fresh fuel list. 13. The method of claim 8, further comprising:analyzing the populated graphical loading map by simulating reactor performance with the populated graphical loading map, the analyzing performed before the physically placing the fuel bundles into the reactor core according to the populated graphical loading map. 14. The method of claim 8, wherein the one or more fuel attributes include at least one of exposure, a previous cycle in which the fuel bundle was used, k infinity, bundle product line, initial uranium loading, initial gadolinium loading, number of axial zones, historical fuel cycle numbers previous to a most recent for which the fuel bundle was used, a corresponding reactor core in which the fuel bundle was resident for each of the historical fuel cycles, accumulated residence time, and fuel bundle pedigree, which is a parameter that reflects usability of the fuel bundle for continued reactor operation. |
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062263463 | abstract | Optical systems compatible with extreme ultraviolet radiation comprising four reflective elements for projecting a mask image onto a substrate are described. The four optical elements comprise, in order from object to image, convex, concave, convex and concave mirrors. The optical systems are particularly suited for step and scan lithography methods. The invention enables the use of larger slit dimensions associated with ring field scanning optics, improves wafer throughput, and allows higher semiconductor device density. The inventive optical systems are characterized by reduced dynamic distortion because the static distortion is balanced across the slit width. |
abstract | A multi-leaf collimator includes a first carriage, a second carriage, a drive device, a first set of leaves disposed on the first carriage, and a second set of leaves disposed on the second carriage, wherein the first set of leaves and the second set of leaves are disposed oppositely to each other, and each leaf in each of the sets of leaves is movable relative to each respective carriage; and the drive device is configured to drive the first carriage and the second carriage to move in the same direction synchronously. |
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claims | 1. An anti-scatter collimator, comprising:a first anti-scatter structure defining a retaining member comprising:a first protruding member having a top surface defining a first plane;a second protruding member having a second top surface defining a second plane, the second protruding member spaced apart from the first protruding member to define a groove; anda support member extending between the first protruding member and the second protruding member, wherein:the support member defines a bottom surface of the groove, andthe bottom surface of the support member is spaced a distance apart from the first plane and the second plane; anda second anti-scatter structure comprising a septum disposed within the groove, wherein the first protruding member, the second protruding member, and the support member maintain a position of the septum relative to the first anti-scatter structure. 2. The anti-scatter collimator of claim 1, wherein:the first anti-scatter structure has a second attenuation coefficient; andthe septum has a third attenuation coefficient that is substantially similar to the second attenuation coefficient. 3. The anti-scatter collimator of claim 1, comprising a first layer defining a first retaining member at a first surface of the first layer, wherein the first layer has a first attenuation coefficient. 4. The anti-scatter collimator of claim 3, wherein:the first anti-scatter structure has a second attenuation coefficient,the septum has a third attenuation coefficient, andthe first attenuation coefficient is less than the second attenuation coefficient and the third attenuation coefficient. 5. The anti-scatter collimator of claim 1, wherein the first protruding member and the support member at least partially define an opening that passes through the first anti-scatter structure between a first side and a second side of the first anti-scatter structure. 6. The anti-scatter collimator of claim 1, wherein the support member defines a top support surface that is co-planar with the first plane of the first protruding member and the second plane of the second protruding member. 7. The anti-scatter collimator of claim 6, wherein the top support surface and the bottom surface of the support member extend along a length of the support member. 8. The anti-scatter collimator of claim 1, wherein the septum is in contact with the bottom surface of the support member, the septum extending substantially parallel to the support member and substantially perpendicular to the first protruding member and the second protruding member. 9. An anti-scatter collimator, comprising:a first anti-scatter structure defining a retaining member comprising:a first protruding member;a second protruding member spaced apart from the first protruding member to define a groove; anda support member extending between the first protruding member and the second protruding member, wherein the support member defines a bottom surface of the groove,wherein the first protruding member and the support member at least partially define an opening that passes through the first anti-scatter structure between a first side and a second side of the first anti-scatter structure; anda second anti-scatter structure comprising a septum disposed within the groove, wherein the first protruding member, the second protruding member, and the support member maintain a position of the septum relative to the first anti-scatter structure. 10. The anti-scatter collimator of claim 9, comprising a second support member extending substantially parallel to and spaced apart from the support member. 11. The anti-scatter collimator of claim 10, comprising a third protruding member extending substantially parallel to and spaced apart from the first protruding member, wherein the first protruding member, the third protruding member, the support member, and the second support member define the opening. 12. The anti-scatter collimator of claim 11, comprising a fourth protruding member extending substantially parallel to and spaced apart from the second protruding member, the fourth protruding member spaced apart from the third protruding member to define a second groove. 13. The anti-scatter collimator of claim 12, wherein the support member defines a bottom surface of the second groove, the septum disposed within the second groove. 14. The anti-scatter collimator of claim 9, wherein:the septum has a septum thickness;the groove has a groove thickness between the first protruding member and the second protruding member; andwherein the septum thickness is less than or equal to the groove thickness. 15. The anti-scatter collimator of claim 14, wherein the support member has a support member thickness that is greater than the septum thickness and the groove thickness. 16. The anti-scatter collimator of claim 9, wherein the septum and the support member are co-planar. 17. An anti-scatter collimator, comprising:a first layer defining a first retaining member at a first surface of the first layer, wherein the first layer has a first attenuation coefficient,a first anti-scatter structure defining a second retaining member at a first surface of the first anti-scatter structure, wherein:the first surface of the first anti-scatter structure faces the first surface of the first layer, andthe first anti-scatter structure has a second attenuation coefficient that is greater than the first attenuation coefficient; anda second anti-scatter structure comprising a septum disposed between the first layer and the first anti-scatter structure and physically contacting the first retaining member and the second retaining member, wherein:the first retaining member and the second retaining member maintain a position of the septum relative to the first layer and the first anti-scatter structure, andthe septum has a third attenuation coefficient that is greater than the first attenuation coefficient. 18. The anti-scatter collimator of claim 17, wherein the third attenuation coefficient is substantially similar to the second attenuation coefficient. 19. The anti-scatter collimator of claim 17, wherein the second retaining member defines a groove within which the septum is disposed. 20. The anti-scatter collimator of claim 17, wherein the first anti-scatter structure defines at least one opening that passes through the first anti-scatter structure between a first side and a second side of the first anti-scatter structure. |
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056298722 | claims | 1. A method of testing at least one of a process and a sensor for determining a particular condition therein, comprising the steps of: operating at least a first and second sensor to redundantly detect at least one variable of the process to provide a first signal from said first sensor and a second signal from said second sensor, each said signal being characteristic of the one variable; obtaining a difference function characteristic of the difference pairwise between said first signal and said second signal at each of a plurality of different times of sensing the one variable; obtaining a frequency domain transformation of said first difference function to procure Fourier coefficients corresponding to Fourier frequencies; generating a composite function over time domain using the Fourier coefficients; obtaining a residual function over time by determining the difference between the difference function and the composite function, the residual function being substantially free of serially correlated noise; operating on the residual function using computer means for performing a statistical analysis technique to determine whether a particular condition is present in at least one of the process and the sensor, the residual function having substantially white noise characteristics input to the statistical analysis technique; and said sensor system providing alarm information to a user of the process allowing changing of at least one of the process and the at least first and second sensor when the particular condition is detected. operating at least one sensor of the system to detect at least one variable of the process to provide a real signal from said one sensor; generating an artificial signal characteristic of the one variable; obtaining a difference function characteristic of the difference pairwise between said real signal and said artificial signal at each of a plurality of different times of sensing the one physical variable; obtaining a frequency domain transformation of said difference function; generating a composite function over a time domain; obtaining a residual function over time by determining the difference between the difference function and the composite function; operating on the residual function using a computer for performing a statistical analysis technique to determine whether an alarm condition is present in at least one of the process and the at least one sensor, the residual function including white noise characteristics of an uncorrelated signal of reduced skewness relative to the difference function and being input to the statistical analysis technique; and said at least one sensor providing a signal to said system allowing modification of at least one of the process and the at least one sensor when an alarm condition is detected. at least a first data source to collect data of at least one variable of the process to provide a signal from said first data source; a second data source to collect data for comparison with said real signal from said first data source; means for determining a difference function characteristic of the arithmetic difference pairwise between said signals from said first and second data source at each of a plurality of different times of sensing the one variable; means for generating a composite function; means for obtaining a residual function over time by means for determining the arithmetic difference between the difference function and the composite function, the residual function including white noise characteristics of an uncorrelated signal of reduced skewness; means for operating on the residual function including computer means for performing a statistical analysis technique and for determining whether an alarm condition is present in at least one of the process and the at least first and second data source, said means for obtaining a residual function and said means for operating on the residual function cooperatively providing a function comprised of said white noise characteristics of uncorrelated signal of reduced skewness relative to the difference function as an input to the statistical analysis technique; and means for providing information allowing modification of at least one of the process and the at least first data source when an alarm condition is detected. accumulating data from the at least first and second data source of the system to redundantly detect at least one variable of the process to provide a first signal from said first data source and a second signal from said second data source, each said signal being characteristic of the one variable; obtaining a difference function characteristic of the arithmetic difference pairwise between said first signal and said second signal at each of a plurality of different times of sensing the one variable; obtaining a frequency domain transformation of said first difference function to procure Fourier coefficients corresponding to Fourier frequencies; generating a composite function over time domain using the Fourier coefficients; obtaining a residual function over time by determining the arithmetic difference between the difference function and the composite function, the residual function including white noise characteristics of an uncorrelated function of reduced skewness relative to the difference function; operating on the residual function using computer means for performing a statistical analysis technique to determine whether an alarm condition is present in at least one of the process and the at least first and second data source; and said at least first and second data source providing a signal to the system which produces alarm information allowing modification of at least one of the process and the at least first and second data source when the alarm condition is detected by the system. using the at least one data source of the system to detect at least one variable of the process to provide a real signal from said at least one data source of the system; generating an artificial signal characteristic of the one variable using the system; obtaining a difference function characteristic of the difference pairwise between said real signal and said artificial signal at each of a plurality of different times of sensing the one variable; obtaining a frequency domain transformation of said difference function; generating a composite function over a time domain; obtaining a residual function over time by determining the difference between the difference function and the composite function, the residual function comprising white noise characteristics of an uncorrelated signal of reduced skewness relative to the difference function; operating on the residual function using computer means for performing a statistical analysis technique to determine whether an alarm condition is present in at least one of the process and the at least one data source; and said at least one data source providing a signal to the system for generating alarm information to a user of the process allowing modification of at least one of the process and the at least one data source when the alarm condition is detected. 2. The method described in claim 1 wherein said computer means comprises an artificial intelligence system. 3. The method as defined in claim 1 wherein the residual function futher comprises reduced Markov dependent noise. 4. The method as defined in claim 1, wherein the process comprises at least one of a chemical process, a mechanical process and an electrical operational process. 5. The method as defined in claim 1 wherein the step of obtaining Fourier coefficients comprises iteratively determining the minimum number of Fourier harmonics able to generate the composite function. 6. The method as defined in claim 1 further including at least one of the steps of modifying the process or changing the sensor responsive to the alarm condition. 7. The method as defined in claim 6 wherein the step of modifying the process or changing the sensor comprises ceasing its operation. 8. A method of operating a system to test at least one of a process and a sensor for determinining fault conditions therein, comprising the steps of: 9. The method as defined in claim 8 wherein the step of obtaining a frequency domain transformation comprises performing a Fourier transformation. 10. The method as defined in claim 8 wherein the steps of obtaining a composite function over time comprises performing an auto regressive moving average analysis. 11. The method as defined in claim 8 further including the step of determining a difference function for both the artificial signal and the real signal. 12. The method as defined in claim 8 wherein the residual function futher comprises reduced Markov dependent noise. 13. The method as defined in claim 9 wherein the step of obtaining a frequency domain transformation comprises obtaining Fourier coefficients iteratively to determine the minimum number of Fourier harmonics able to generate the composite function. 14. A system for testing at least one of a process and a data source for determining a fault condition therein, comprising: 15. The system as defined in claim 14 futher including means for obtaining a frequency domain transformation of said difference function. 16. The system as defined in claim 14 wherein said computer means comprises an artificial intelligence system. 17. The system as defined in claim 14 wherein said means for generating a second data source comprises computer means for executing a computer program. 18. The system as defined in claim 17 wherein the computer program includes an autoregressive moving average procedure. 19. The system as defined in claim 14 wherein said computer means executes a computer program including a statistical probability ratio test on the residual function. 20. The system as defined in claim 14 further including means for changing at least one of the process and substituting another data source for a defective data source. 21. A method of using a system for testing at least one of a process and at least a first and second data source for determining fault conditions therein, comprising the steps of: 22. A method of operating a system for testing at least one of a process and at least one data source for determining fault conditions therein, comprising the steps of: |
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