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046612904 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS A compacting apparatus according to the present invention will be described with reference to FIGS. 1 through 3. As shown in FIG. 1, the compacting apparatus includes a hollow cylindrical body 1 having a waste charging hopper 1a, a heating portion 1b, and a waste outlet 1c, and a rotatable shaft 4 disposed in the hollow cylindrical body 1 and having a helical screw blade 3. The hollow cylindrical body 1 is tilted downwardly toward the waste outlet 1c at an angle smaller than the angle of repose of a solid waste 2 including a plastic material in order to effectively feed, crush, grind, mix, compress the solid waste 2. The rotatable shaft 4 has its upper end connected to a prime mover 6 such as a motor through a coupling 5 with its axis radially swingable. The rotatable shaft 4 is rotatably supported by a freely movable bearing 7. Between the inner wall surface of the hollow cylindrical body 1 and the screw blade 3, there is a clearance for allowing the solid waste 2 to form a bridge between the inner wall surface of the cylindrical body 1 and the screw blade 3, the clearance being in the range of from 5 to 20 mm when the shaft 4 and the cylindrical body 1 are coaxial. As shown in FIG. 2, the screw blade 3 has its substantially half distal end portion inclined at 10 to 30 degrees toward the upper end of the rotatable shaft 4 in a region between the waste charging hopper 1a and the heating portion 1b. The screw blade 3 thus constructed can effectively stir, mix, and crush the solid waste 2. As shown in FIG. 3, the screw blade 3 has at least one recess to discharge a gas (air or water vapor) trapped when the solid waste 2 is charged or produced when the solid waste 2 is processed, so that the solid waste 2 can efficiently be fed and crushed. A waste outlet nozzle 9 is attached to the waste outlet 1c of the hollow cylindrical body 1 for compacting the solid waste 2 which has been ground and uniformized with plastic and rubber melted, into a firm solid mass or body. The waste outlet nozzle 9 may be integral with the hollow cylindrical body 1, and has substantially the same diameter as the inside diameter of the cylindrical body 1. Preferably, the nozzle 9 has a polygonal cross section such as a square or a hexagon, or a circular cross section. The nozzle 9 may have an inner wall provided with projections or a roughened surface for promoting the compression of the solid waste 2. A method of compacting the solid waste 2 by the compacting apparatus will be described with reference to FIG. 1. The solid waste 2 including a plastic material is charged into the hollow cylindrical body 1 through the hopper 1a by means of a conveyor such as a belt conveyor (not shown). The compacting apparatus has a chopper 10 for chopping the solid waste 2 as it is charged into small pieces. Therefore, the compacting apparatus can process different kinds of solid wastes, can easily control the amount of the solid waste which is charged into the cylindrical body 1, and can be small in overall size. With the chopper 10 employed, it is not necessary to convey chopped pieces to the hopper 1a and hence the solid waste 2 is prevented from being scattered around when it is conveyed toward the hopper 1a. The charged solid waste 2 is progressively fed toward the heating portion 1b by the screw blade 3 on rotation of the rotatable shaft 4. Since the cylindrical body 1 is tilted as described above, the solid waste 2 can smoothly be fed along. If the cylindrical body 1 were tilted at an angle less than 5 degrees, the solid waste 2 as melted would be subjected to an excessive resistance dependent on the type and condition of the solid waste 2, with result that an undue load would be imposed on the motor 6 and the apparatus might be broken or damaged. If the cylindrical body 1 were tilted at an angle larger than 30 degrees, the solid waste 2 would be formed into insufficient bridges, resulting in insufficient crushing, grinding and mixing of the solid waste 2, and solid masses would not be produced well. The substantially half distal end portion of the screw blade 3 is inclined in a direction opposite to the direction in which the solid waste 2 is fed, i.e., toward the upper end of the rotatable shaft 4, and the screw blade 3 has at least one recess. With this arrangement, the solid waste 2 can efficiently be fed, crushed, and ground. The length of the screw blade 3 should be selected such that when the shaft 4 rotates at a speed lower than a certain speed, the solid waste 2 is not discharged in a constant quantity. With the screw blade 3 being of a certain length, therefore, the velocity of rotation of the shaft 4 should be higher than the minimum velocity of rotation at which the solid waste 2 can be discharged in a constant quantity. The crushed and ground solid waste 2 is converted into a uniformly mixed mass in the heating portion 1b since the thermoplastic material and rubber in the solid waste 2 are melted in the heating portion 1b. The heating portion 1b is heated up to a temperature ranging from 200.degree. to 280.degree. C. by a suitable heating means 8 for applying hot air, for example. When the heating portion 1b is thus heated, the temperature within the heating portion 1b ranges from 160.degree. to 250.degree. C. In this temperature range, the plastic material and rubber are melted, but no gas is given off, and the paper is not burned. Since the solid waste 2 is moved in the closed space in the cylindrical body 1, the amount of air present therein is small, and no explosion takes place. The heating means 8 may be composed of a heating medium, an electric heater, a water vapor heater, or an induction heater, for example. The structures that the clearance is present between the inner wall surface of the hollow cylindrical body 1 and the screw blade 3 for producing a bridge of the solid waste 2 therein, and the cylindrical body 1 is inclined downwardly are not derived from the screw feeder. If a large clearance were present in the screw feeder at the time of feeding a granular or powdery material, the clearance would serve as a dead space to produce a material bridge therein, which could not be fed along. According to the present invention, the upper end of the rotatable shaft 4 is supported by the freely movable bearing 7 and coupled through the radially swingable support means or coupling 5 to the motor 6. In operation, the shaft 4 rotates while being eccentrically moved radially (i.e., the shaft 4 has not fixed axis of rotation), so that the solid waste 2 is crushed by the screw blade 3. Although the solid waste 2 forms a bridge temporarily in the clearance, it is heated due to collision and friction and hence can be crushed and ground. The heating of the solid waste 2 is an energy saver since the amount of heat applied by the heating portion 1b may be reduced. Since the waste 2 in the heating portion 1b is heated to 160.degree. through 250.degree. C. by the external heat applied thereto, the plastics and rubber of the crushed waste material 2 are melted and permeate the paper waste, heat insulation and other materials, which are uniformly mixed together and fed downwardly. The melted and mixed waste is then brought to a stop when it arrives at the lower end of the hollow cylindrical body 1, i.e., the waste outlet 1c, but is forced into the outlet nozzle 9 by the following melted and mixed waste. Inasmuch as the waste is cooled in the outlet nozzle 9, the melted plastics is solidified, and compressed due to frictional resistance between the inner wall surface of the outlet nozzle 9 and the waste, thus forming a solid mass or body. The outlet nozzle 9 should preferably be of the same diameter as that of the cylindrical body 1 as described above, but may be of a smaller inside diameter. If the diameter of the outlet nozzle 9 were too large, the melted and mixed waste would not sufficiently be compressed, and if the diameter of the outlet nozzle 9 were too small, the frictional resistance would be too large so that the screw blade 3 would be damaged or broken due to forced rotation thereof. The outlet nozzle 9 may be replaced with a plastic molding die and a cutter for producing pellets of the waste material. A method of controlling the operation of the compacting apparatus by the use of the accessory controlling facility will be described. The solid waste 2 is crushed, ground, and mixed by being jammed between the screw blade 3 and the inner wall surface of the cylindrical body 1, and the compacting apparatus is capable of continuous operation since the shaft 4 is radially displaceable. However, the screw blade 3 may be twisted or damage due to a massive jam, or the motor 6 may be subjected to an overload, so that the compacting apparatus will have to be shut off. The controlling method of the invention is effective in solving the above problems. More specifically, when the current flowing through the motor or the torque imposed on the motor exceeds a prescribed level and continues for a certain period of time, the shaft 4 is rotated in a reverse direction. When such a condition occurs, it is most likely for the solid waste 2 to be jammed between the screw blade 3 and the inner wall surface of the cylindrical body 1. If the condition continues, the motor may be subjected to a burnout or the screw blade 3 may be broken or damaged. To prevent this, when the motor current or torque reaches the preset level and continues for the given time interval, the motor 6 is reversed to release the jammed solid waste 2. When the motor 6 is rotated in the normal direction upon elapse of a certain time, therefore, the motor current or torque restores its normal level. FIG. 4 shows that the motor is reversed at points a and b upon elapse of a prescribed time (A sec) after the motor current or torque has reached a preset value and continued for a prescribed period of time, i.e., for the time short enough for the motor 6 or the screw blade 3 not to be damaged. By reversing the motor 6 in this manner, the motor 6 and the screw blade 3 are not subjected to an overload, and will not be broken or damaged. As an alternative control method, the occurrences of reversing of the shaft 4 are counted, and the shaft 4 is brought to a stop when the counted occurrences reach a prescribed count within a preset period of time. Stated otherwise, since the reversal of the shaft 4 is required under an abnormal condition in which the solid waste 2 is jammed, the apparatus should be shut off and inspected when the shaft 4 is frequently reversed. In the controlling method of the invention, the chopper 10 should also be stopped when the shaft 4 is stopped. An accessory facility for and a method for producing a solid mass or body from a solid waste material according to the present invention will be described hereinbelow. The compacted mass extruded from the compacting apparatus is shaped as it passes through the waste outlet 1c and is forced into the outlet nozzle 9 while it is gradually being cooled. If the outlet nozzle 9 were too short, the compressive force imposed on the extruded mass would be released due to the residual heat, and the extruded mass would tend to be expanded at the outlet of the outlet nozzle 9. Conversely, if the outlet nozzle 9 were too long, the apparatus would not be made compact in size, and the extruded mass would be subjected to a greater resistance in the outlet nozzle 9, thus requiring an increased amount of power from the motor 6. Since the extruded mass produced by compacting the solid waste material 2 is highly viscous, a suitable cutting means is required to cut the extruded mass off the outlet of the compacting apparatus. The cutting means may comprise a mechanical cutter or saw, which however is not preferred because of its complex construction. In the event that the waste material is radioactive, radioactive particles would be produced if the extruded mass were cut off by the mechanical cutting means. The aforesaid problems can be solved by the method and facility for producing a solid mass, associated with the compacting apparatus. The method and facility for producing a solid mass will be described with reference to FIGS. 5 through 8. As illustrated in FIGS. 5 through 7, the facility for producing a solid mass from a solid waste material includes a shaping tube 20 into which an extruded mass discharged from the compacting apparatus is forced, the shaping tube 20 having a flanged end 20a, and a tube closing assembly 21 for closing one end of the shaping tube 20 when the extruded mass is forced into the shaping tube 20 from the flanged end 20a, the tube closing assemby 21 being composed of a presser plate 21a having an outer peripheral shape substantially identical to the inner peripheral surface of the shaping tube 20, a piston 21b on which the presser plate 21a is mounted, and a fluid cylinder 21c for moving the piston 21b under a prescribed pressure. The shaping tube 20 is fixed to a belt conveyor 22 by means of attachments 23. The apparatus also includes an ejector assembly 24 composed of an ejector piston 24a and a fluid cylinder 24b for moving the ejector piston 24a. Before a solid waste material is compacted, the shaping tube 20 is disposed in place of the outlet nozzle 9 so that the flanged end 20a of the shaping tube 20 opens toward the outlet 1c of the cylindrical body 1. To prevent an extruded mass from leaking from the gap between the outlet 1c and the shaping tube 20, the flanged end 20a should firmly be attached to the outlet 1c preferably by detachable fasteners such as bolts and nuts or clamps. Since the outlet 1c is inclined downwardly at an angle smaller than the angle of repose of the solid waste material, the shaping tube 20 should also be inclined in coaxial relation to the outlet 1c. The shaping tube 20 should preferably be of a rectangular cross section to facilitate the subsequent charging of solid mass into a container. A plurality of such shaping tubes should be provided for successive production of solid masses. Then, the shaping tube 20 is closed fully across its cross section by the tube closing assembly 21. The piston 21b is movable through a stroke longer than the length of the shaping tube 20. The piston 21b can be moved through the shaping tube 20 by the fluid pressure 21c under a fluid pressure depending on the type of the solid waste (extruded mass). The presser plate 21a may be positioned anywhere in the shaping tube 20 depending on the pressure which bears the presser plate 21a. However, the presser plate 21a should preferably be positioned at the flanged end 20a of the shaping tube 20 since the presser plate 21a can be pushed back against the pressure of the fluid cylinder 21c as the extruded mass is forced into the shaping tube 20, so that the extruded mass can uniformly stuffed into the shaping tube 20. After the shaping tube 20 and the tube closing assembly 21 have been positioned, the compacting apparatus is operated to extrude a compacted solid paste by the screw blade 3 into the shaping tube 20 under a certain pressure. Where the presser plate 21a is initially positioned closely to the flanged end 20a, the presser plate 21a is gradually pushed back when the pressure of the extruded mass exceeds the pressure under which the presser plate 21a is supported by the fluid cylinder 21c. When the presser plate 21a is pushed to the end of the shaping tube 20 near the tube closing assembly 21, the compacting operation is interrupted. After the extruded mass has been charged into the shaping tube 20, the shaft 4 of the compacting apparatus is rotated in the opposite direction to cut off the extruded mass in the vicinity of the outlet 1c. The extruded mass can easily be cut off since it has a relatively high viscosity. Then, the shaping tube 20 with the extruded mass contained therein is detached from the outlet 1c, and moved over by the conveyor 22. Since the shaping tube 20 is secured to the belt conveyor 22 by the attachments 23, it does not fall off the belt conveyor 22 when it is positioned below the belt conveyor 22 as shown in FIG. 6. The belt conveyor 22 may be inclined to keep the shaping tube 20 in coaxial alignment with the inclined outlet 1c. The extruded mass filled in the shaping tube 20 is cooled while the shaping tube 20 is moved over by the belt conveyor 22. Inasmuch as the extruded mass is sufficiently cooled until the shaping tube 20 reaches the ejector assembly 24, the extruded mass in the shaping tube 20 is shrunk and solidified into a solid mass, and can hence easily be pushed off the shaping tube 20. When the shaping tube 20 reaches the ejector assembly 24, the flanged end 20a is fixed in position by a locking device 24c pivotally supported by a pivot shaft 24d. Then, the fluid cylinder 24b is actuated to push the piston 24a to eject the solid mass out of the shaping tube 20. The ejected solid mass falls onto a handling table (not shown). A certain number of such ejected solid masses are bundled on the handling table, and then closely packed in a rectangular container. Where the shaping tube 20 is of such a cross section as to allow ejected solid masses to be closely packed in the container, the solid masses 25 (FIG. 8) may directly be loaded into the container 26 in a closely packed combination. A method of processing an exhaust gas by the use of the exhaust gas processing facility for operating the compacting apparatus smoothly will hereinafter be described. The exhaust gas (primarily air containing water vapor) generated by the compacting apparatus is discharged after dust particles are removed therefrom by a filter. It is preferable from the standpoint of energy saving to employ the exhaust gas effectively. Where the induction heating coil is used as the heating means 8, coil insulation is protected by a cooling medium such as cooling water since the coil insulation is effective below a temperature of 180.degree. C. FIG. 9 shows a cooling system in which cooling water is used as a cooling medium, and FIG. 10 illustrates a cooling system in which a coolant with an antifreeze added is used as a cooling medium. In FIGS. 9 and 10, the cooling medium is circulated by a pump 11 through the induction heating coil 8 and a heat exchanger which comprises a cooling tower 13a (FIG. 9) or a fan coil 13b (FIG. 10). The fan coil 13b of FIG. 10 is cooled by a fan 14. The problems of the illustrated cooling systems are that where the cooling tower 13a is employed, the cost of installation is high, and where the fan coil 13b is used, the fan 14 should be added. These problems can be solved by the method of processing the exhaust gas according to the present invention. The method of processing the exhaust gas will be described with reference to FIG. 11. The facility shown in FIG. 11 includes an induction heating coil 8, a circulating pump 11, a filter 12, a heat exchanger 13, a circulating line 15 for passage of a cooling medium such as cooling water, an exhaust gas line 16, and an exhaust fan 17. The exhaust gas generated by the compacting apparatus is drawn from the charging hopper 1a by the exhaust fan 17 on the exhaust gas line 16 into the heat exchanger 13 through the filter 12. The filter 12 removes dust particles produced chiefly by the chopper 10. The dust particles collected by the filter 12 can subsequently be solidified by the compacting apparatus. Therefore, no secondary waste material is produced by the exhaust gas processing facility. The cooling water which has cooled the induction heating coil 8 is introduced through the line 15 into the heat exchanger 13. The exhaust gas is discharged out of the system after having cooled the cooling medium in the heat exchanger 13. The cooled cooling medium then flows through the line to cool the induction heating coil 8. The cooling medium may comprise a coolant with an antifreeze such as ethylene glycol added. A method of cleaning the compacting apparatus according to the present invention will be described. In the operation of the compacting apparatus, a solid waste material tends to be attached to or deposited in the hollow cylindrical body 1 and interferes with the compacting process in the cylindrical body 1. It is relatively difficult to discharge the remaining solid waste material out of the compacting apparatus. Known methods of cleaning the compacting apparatus include a self-cleaning process, a substitute cleaning process, and a solvent cleaning process. The self-cleaning process is characterized in that the apparatus is so constructed as to prevent the solid waste from remaining in the apparatus, but the construction of the apparatus is rendered complex. The substitute cleaning process cleans the apparatus by supplying a clean substance to replace the remaining solid waste in the apparatus, but is disadvantageous in that a secondary waste is produced. The solvent cleaning process cleans the apparatus by solving the remaining waste with an organic solvent, but is costly and complex to carry out since the organic solvent or other cleaning agent is required. The above problems can be eliminated by the cleaning method of the present invention. According to the cleaning method of the invention, a cleaning material is charged into the compacting apparatus to discharge the remaining solid waste out of the hollow cylindrical body. The cleaning material may comprise a solid waste material itself to be processed by the compacting apparatus, or sand. Where the solid waste material is to be used as the cleaning material, the solid waste material being processed is directly employed as the cleaning material, and hence the cleaning operation is simplified and no additional equipment is required for cleaning the apparatus. In the event of employing the solid waste material as the cleaning material, the remaining solid waste material should be discharged out at a temperature lower than the melting point of the plastics material contained in the solid waste material and higher than the temperature at which the solid waste material is kept in the flowing condition. If the heating temperature exceeded the melting point, then the viscosity of the remaining solid waste material would be too low to push out the remaining solid waste material. If the heating temperature were so low that the solid waste material would not be flowable, then the solid waste material would not flow and not completely be discharged out of the apparatus. The heating temperature is appropriately determined depending on the melting point of the solid waste material. If the melting point of the solid waste material is 190.degree. C., then the heating temperature should range from 150.degree. to 180.degree. C. When the solid waste material is charged into the compacting apparatus in the above temperature range, the solid waste material is crushed and ground, and is rendered flowable, but not melted. Then, it is discharged with the remaining solid waste material from the compacting apparatus. Since the temperature is lowered, the melted remaining solid waste material can easily be discharged out of the apparatus due to an increased viscosity thereof. After the charging of the solid waste material has been stopped, the screw blade 3 is rotated for a while to permit the remaining solid waste material to be completely discharged out of the compacting apparatus. In the cleaning process, the outlet nozzle 9 should be removed. The solid waste material which has been charged to discharge the remaining solid waste material will then be solidified in the normal operation of the compacting apparatus. Therefore, no secondary waste material is produced in the cleaning process, and no additional cleaning equipment is required. Where sand is used as the cleaning material, the solid waste material being compacted should be kept at the temperature to maintain the solid waste material flowable. Therefore, the apparatus can be cleaned easily under the normal temperature condition used when the apparatus is in normal operation. For example, if the melting point of the remaining solid waste material is 200.degree. C., then the temperature should range from 160.degree. to 250.degree. C. in the cleaning operation. Examples and Comparative Examples of the apparatus, facilities and methods of the present invention will hereinafter be described. EXAMPLE 1 A compacting test was conducted using the compacting apparatus of the present invention. 1 m.sup.3 of a rag, 0.7 m.sup.3 of polypropylene pipes, 0.2 m.sup.3 of wood, and 0.1 m.sup.3 of high-efficiency particulate air (HEPA) filters, having the dimensions given in the Table 1, were mixed together, and 2.2 m.sup.3 of polyethylene sheets was mixed with the above mixture. The resultant mixture was charged into the compacting apparatus shown in FIG. 1, which was operated at 16 r.p.m. and 250.degree. C. The length of a hollow cylindrical body of the compacting apparatus used in this Example was 1.8 m (the length covering a freely movable bearing 7 and waste outlet 1c in FIG. 1) and the length of a heating portion 1b in FIG. 1 was about 0.9 m. The hollow cylindrical body was made of 6 inches tube of schedule 80 (ASTM). TABLE 1 ______________________________________ Materials HEPA filter Rag Polypropylene pipe Wood ______________________________________ Dimensions 610 .times. 610 .times. 100- 30 (diameter) .times. 150 .times. before 400 200 200 (length) 150 .times. charging (mm) 150 ______________________________________ As a result, a strong and uniform solid mass was produced. The volume of the materials before being charged was 4.2 m.sup.3, and the volume of the produced solid mass was 0.285 m.sup.3. The remaining material in the compacting apparatus had a volume of 16 liters. Therefore, it was found that the ratio between the initial and compacted volumes is 1/14. EXAMPLE 2 AND COMPARATIVE EXAMPLE 1 (Comparative Example 1) A test was conducted for the method of controlling the compacting apparatus of the present invention. A piece of wood having the dimensions of 50.times.100.times.20 mm was charged into the compacting apparatus of FIG. 1 which rotated at 16.6 r.p.m., and seized by section A in FIG. 1 whereby section B of rotation shaft 4 in the same Figure was twisted. (EXAMPLE 2) The shaft 4 was replaced in the same apparatus as that used in Comparative Example 1, and the apparatus was operated under the same conditions as those of Comparative Example 1. The wood piece was seized by the screw blade, and the motor was subjected to a heavy load. This condition was confirmed by the time-dependent change of the current shown in FIG. 12. 2 seconds after the current reached 15 A or more, the motor was reversed for 10 seconds, and the current dropped to a normal level. Continued operation of the compacting apparatus according to this control method resulted no twisting of the shaft and no damage to the screw blade. EXAMPLE 3 A test was conducted for the production of a solid mass from a solid waste material, using the compacting apparatus shown in FIG. 1 and the apparatus shown in FIGS. 5 through 7 for producing solid masses from a solid waste material. The shaping tube which had a square cross section (each side being 120 mm long), a tube length of 620 mm and a tube thickness of 6 mm was detachably attached at one end thereof to the outlet of the compacting apparatus. The presser plate was mounted on the piston and inserted by the fluid cylinder into the shaping tube in the vicinity of the outlet of the compacting apparatus, there being a clearance of 2 mm between the outer peripheral edge of the presser plate and the inner wall surface of the shaping tube. Then, the waste material was charged into the compacting apparatus, and heated and kneaded for about 10 minutes. Thereafter, the pressure of the fluid cylinder was selected to be 10 kg/cm.sup.2, and the compacted extruded mass was forced into the shaping tube. When the extruded mass reached the outlet of the shaping tube closer to the fluid cylinder, the shaft of the compacting apparatus was stopped, and then reversed for about three revolutions. The shaping tube was detached from the outlet of the cylindrical body, and then was moved over toward the ejector assembly. The cooled extruded mass was ejected as a solid mass by the ejector piston. EXAMPLES 4 AND 5 The method of cleaning the compacting apparatus of the invention was tested. (EXAMPLE 4) After the compacting apparatus shown in FIG. 1 operated, 16 kg of a remaining solid waste material was left in the hollow cylindrical body of the apparatus. In order to clear away the remaining solid waste material with the solid waste material newly charged, the interior of the hollow cylindrical tube was heated up to 150.degree. C. (which is below the melting point of polyethylene). When 5 kg of a solid waste material was charged into the inlet hopper, 20.0 kg of the solid waste material was discharged from the outlet. As a consequence, it was found that 1 kg of the solid waste material was finally left in the compacting apparatus, and the percentage of the remaining material in the compacting apparatus according to the cleaning method of the invention was 6%. (EXAMPLE 5) 138 kg of a solid waste material was charged into the hollow cylindrical body while it was heated to 250.degree. C. and the shaft was rotated at 6 r.p.m., and as a result 122 kg of a solid mass was discharged. Then, 20 kg of sand was charged into the hollow cylindrical body as it was still heated in order to remove the remaining solid waste material. The remaining solid waste material and sand, totalling 35.68 kg, were discharged. Therefore, the percentage of the remaining material was 2%. Although certain preferred embodiments have been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims. The apparatus for compacting a solid waste material according to the present invention may further comprise at least one of accessory facilities respectively for controlling rotation of the rotatable shaft, producing a solid mass and processing an exhaust gas from said apparatus. |
description | The present invention relates to a steam generation system using a high temperature gas cooled reactor. For example, in the related art, a helium cooling high temperature gas cooled reactor disclosed in PTL 1 is a gas-cooled reactor that has helium gas as a coolant, in which a primary helium circuit including a nuclear reactor and a secondary helium circuit including an intermediate heat exchanger and a helium turbine are divided, heat in the primary helium circuit operates the helium turbine in the secondary helium circuit, and thus, electricity is generated. [PTL 1] Japanese Unexamined Patent Application Publication No. 8-338892 In PTL 1, helium gas is used as the coolant of a secondary cooling system. However, there is a high temperature gas cooled reactor steam generation system in which water is used as the coolant of the secondary cooling system, steam is generated by a steam generator using heat of a primary helium circuit, a steam turbine is operated by the steam, and thus, electricity is generated. In the high temperature gas cooled reactor steam generation system, in general, a steam pressure in the steam generator is set to be higher than a helium gas pressure in the nuclear reactor. Accordingly, when a heat transfer tube of the steam generator is damaged, there is a concern that high pressure water or steam supplied into the heat transfer tube may enter the nuclear reactor. In the high temperature gas cooled reactor steam generation system, a water entering suppression device is installed, and thus, water or steam entering into the nuclear reactor is prevented. However, when the water entering suppression device is not operated, graphite configuring a reactor core and water react (C+H2O→CO+H2), and there is a concern that a hydrogen explosion due to corrosion of the graphite or flammable gas may occur. The present invention is to solve the above-described problems, and an object thereof is to provide a high temperature gas cooled reactor steam generation system capable of preventing a secondary coolant in a steam generator from entering a nuclear reactor. In order to achieve the above-described object, there is provided a high temperature gas cooled reactor steam generation system including: a nuclear reactor that has helium gas as a primary coolant and heats the primary coolant by heat generated by a nuclear reaction that decelerates neutrons by a graphite block; a steam generator that has water as a secondary coolant and heats the secondary coolant by the primary coolant via the nuclear reactor to generate steam; a steam turbine that is operated by the steam from the steam generator; a generator that generates electricity according to an operation of the steam turbine; and pressure adjustment means for setting a pressure of the secondary coolant in the steam generator to be lower than a pressure of the primary coolant in the nuclear reactor. According to the high temperature gas cooled reactor steam generation system, since the pressure of the secondary coolant in the steam generator is set to be lower than the pressure of the primary coolant in the nuclear reactor by the pressure adjustment means, when a heat transfer tube of the steam generator is damaged, it is possible to prevent high pressure water or steam supplied into the heat transfer tube from entering the nuclear reactor. In addition, in the high temperature gas cooled reactor steam generation system of the present invention, the pressure adjustment means may include a primary coolant storage unit that recovers or supplies the primary coolant, and may supply the primary coolant to the primary coolant storage unit. According to the high temperature gas cooled reactor steam generation system, the pressure of the secondary coolant in the steam generator can be set to be lower than the pressure of the primary coolant in the nuclear reactor. Moreover, in the high temperature gas cooled reactor steam generation system of the present invention, the pressure adjustment means may include a secondary coolant discharging unit that discharges the secondary coolant to the steam generator, and may decrease a discharging amount of the secondary coolant in the secondary coolant discharging unit. According to the high temperature gas cooled reactor steam generation system, the pressure of the secondary coolant in the steam generator can be set to be lower than the pressure of the primary coolant in the nuclear reactor. In addition, in the high temperature gas cooled reactor steam generation system of the present invention, the pressure adjustment means may include a secondary coolant flow rate variable unit that changes a flow rate of the secondary coolant fed to the steam turbine, and may increase the flow rate of the secondary coolant fed to the steam turbine in the secondary coolant flow rate variable unit. According to the high temperature gas cooled reactor steam generation system, the pressure of the secondary coolant in the steam generator can be set to be lower than the pressure of the primary coolant in the nuclear reactor. Moreover, in the high temperature gas cooled reactor steam generation system of the present invention, the pressure adjustment means may include a secondary coolant bypass flow rate variable unit that is provided at a bypass circuit bypassing the secondary coolant to the steam turbine and changes the flow rate of the secondary coolant, and may increase the flow rate of the secondary coolant fed to the bypass circuit in the secondary coolant bypass flow rate variable unit. According to the high temperature gas cooled reactor steam generation system, the pressure of the secondary coolant in the steam generator can be set to be lower than the pressure of the primary coolant in the nuclear reactor. In addition, the high temperature gas cooled reactor steam generation system of the present invention may further include pressure control means for controlling the pressure adjustment means so that, based on a pressure difference between the pressure of the primary coolant and the pressure of the secondary coolant, the pressure difference is within a predetermined range. According to the high temperature gas cooled reactor steam generation system, based on the pressure difference between the pressure of the primary coolant and the pressure of the secondary coolant, the pressure of the secondary coolant in the steam generator can be set to be controlled to be lower than the pressure of the primary coolant in the nuclear reactor by the pressure adjustment means. Moreover, the high temperature gas cooled reactor steam generation system of the present invention may further include temperature adjustment means for increasing an outlet temperature of the secondary coolant in the steam generator according to the setting of the pressure by the pressure adjustment means. According to the high temperature gas cooled reactor steam generation system, since a steam average temperature at the time of heating is increased by increasing the temperature of the secondary coolant at an outlet of the steam generator, it is possible to improve the thermal efficiency of the high temperature gas cooled reactor steam generation system. That is, when the pressure of the secondary coolant in the steam generator is set to be lower than the pressure of the primary coolant in the nuclear reactor by the pressure adjustment means, it is possible to improve the thermal efficiency of the high temperature gas cooled reactor steam generation system that may be decreased by the setting. In addition, in the high temperature gas cooled reactor steam generation system of the present invention, the temperature adjustment means may include a secondary coolant discharging unit that discharges the secondary coolant to the steam generator, and may decrease the discharging amount of the secondary coolant in the secondary coolant discharging unit. According to the high temperature gas cooled reactor steam generation system, the outlet temperature of the secondary coolant in the steam generator can be increased according to the setting of the pressure by the pressure adjustment means. Moreover, in the high temperature gas cooled reactor steam generation system of the present invention, the temperature adjustment means may include a primary coolant temperature variable unit that changes a temperature of the primary coolant in the nuclear reactor, and may increase the temperature of the primary coolant in the primary coolant temperature variable unit. According to the high temperature gas cooled reactor steam generation system, the outlet temperature of the secondary coolant in the steam generator can be increased according to the setting of the pressure by the pressure adjustment means. In addition, the high temperature gas cooled reactor steam generation system of the present invention may further include temperature control means for controlling the temperature adjustment means so that the outlet temperature of the secondary coolant is a predetermined temperature according to the set pressure of the secondary coolant based on the outlet temperature of the secondary coolant. According to the high temperature gas cooled reactor steam generation system, based on the outlet temperature of the secondary coolant, it is possible to control the increase of the outlet temperature of the secondary coolant in the steam generator according to the setting of the pressure by the pressure adjustment means by the temperature adjustment means. According to the present invention, it is possible to prevent a secondary coolant in a steam generator from entering a nuclear reactor. Hereinafter, an embodiment according to the present invention will be described in detail with reference to the drawings. In addition, the present invention is not limited to the embodiment. Moreover, components in the embodiment described below include a component that can be replaced and can be easily obtained by a person skilled in the art, or substantially the same component. FIG. 1 is a schematic view of a high temperature gas cooled reactor steam generation system according to the present embodiment. As shown in FIG. 1, a high temperature gas cooled reactor steam generation system 1 mainly includes a nuclear reactor 2, a steam generator 3, a steam turbine 4, and a generator 5. In the nuclear reactor 2, helium gas is used as a primary coolant, and the primary coolant is heated by heat that is generated by a nuclear reaction that decelerates neutrons by a graphite block. In the steam generator 3, water is used as a secondary coolant, the secondary coolant is heated by the primary coolant via the nuclear reactor 2, and thus, steam is generated. The nuclear reactor 2 and the steam generator 3 communicate with each other by a primary cooling system circuit 2a. In the primary cooling system circuit 2a, a circulation fan (primary coolant discharging unit) 2b is provided, which discharges the primary coolant and circulates the primary coolant to the nuclear reactor 2 and the steam generator 3. That is, the primary cooling system circuit 2a discharges the primary coolant by the circulation fan 2b and circulates the primary coolant to the nuclear reactor 2 and the steam generator 3. Moreover, in the primary cooling system circuit 2a, a primary coolant storage unit 2c is provided, which recovers or supplies the primary coolant via the primary cooling system circuit 2a. Moreover, a heat transfer tube 3a is provided in the inner portion of the steam generator 3. The heat transfer tube 3a is a helical coil type, and the secondary coolant flows through the inner portion of the heat transfer tube. That is, the steam generator 3 supplies heat to the secondary coolant flowing through the heat transfer tube 3a by the primary coolant that is heated by the nuclear reactor 2, and thus, steam (overheating steam) is generated. The steam turbine 4 is operated by the steam that is supplied from the steam generator 3. The generator 5 generates electricity according to the operation of the steam turbine 4. In the present embodiment, the steam turbine 4 includes a high pressure turbine 4a and a low pressure turbine 4b, the high pressure turbine 4a is operated by the steam from the steam generator 3, and the low pressure turbine 4b is operated by the steam extracted from the high pressure turbine 4a. Moreover, the steam used in the operation of the low pressure turbine 4b is cooled to be condensed by a condenser 6, and returns to water. The returned water is discharged to a heater 8 by a condensate pump 7 that is provided at the rear step of the condenser 6. The heater 8 heats the water by the steam that is extracted from the low pressure turbine 4b. Moreover, the steam that has been used to heat the water is condensed by heat exchanging with water to become water, and the condensed water is supplied to the water of an upstream side of the heater 8. The water heated by the heater 8 is stored in a water supply tank 9. The water stored in the water supply tank 9 is discharged by a feed water pump (secondary coolant discharging unit) 10, and is supplied to the steam generator 3 via the heater 11. The heater 11 heats the water by the steam that is extracted from the high pressure turbine 4a. In addition, the steam used to heat the water is condensed by heat exchanging with water to become water, and the condensed water is supplied to the water supply tank 9. Moreover, a drain (condensed water) in the high pressure turbine 4a is also supplied to the water supply tank 9. In this way, after the steam supplied from the steam generator 3 operates the steam turbine 4, the steam is condensed to return water, and circulates a secondary cooling system circuit 12 through which the condensed water is supplied to the steam generator 3. In the secondary cooling system circuit 12, a governor valve (secondary coolant flow rate variable unit) 13, which changes a flow rate of the steam to the steam turbine 4 so that a rotational frequency of the steam turbine 4 is constant, is provided between the steam generator 3 and the steam turbine 4. Moreover, in the secondary cooling system circuit 12, a bypass circuit 14 that bypasses the steam directed to the steam turbine 4 is provided. In addition, in the bypass circuit 14, a bypass valve (secondary coolant bypass flow rate variable unit) 15 that changes the flow rate of the steam is provided. In the high temperature gas cooled reactor steam generation system 1, if a pressure of the secondary coolant in the steam generator 3 is set to be higher than a pressure of the primary coolant in the nuclear reactor 2, when the heat transfer tube 3a of the steam generator 3 is damaged, there is a concern that high pressure water or steam which is supplied into the heat transfer tube 3a may enter the nuclear reactor 2. In this case, graphite configuring a reactor core and water react (C+H2O→CO+H2), and there is a concern that a hydrogen explosion due to corrosion of the graphite or flammable gas may occur. Thus, in the high temperature gas cooled reactor steam generation system 1 of the present embodiment, the secondary coolant in the steam generator 3 is prevented from entering the nuclear reactor 2. Specifically, the high temperature gas cooled reactor steam generation system 1 of the present embodiment includes pressure adjustment means for setting the pressure of the secondary coolant in the steam generator 3 to be lower than the pressure of the primary coolant in the nuclear reactor 2. According to the high temperature gas cooled reactor steam generation system 1 of the present embodiment, since the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2 by the pressure adjustment means, when the heat transfer tube 3a of the steam generator 3 is damaged, it is possible to prevent the high pressure water or steam supplied into the heat transfer tube 3a from entering the nuclear reactor 2. Specifically, the pressure adjustment means includes at least one of the following: the primary coolant storage unit 2c, the feed water pump (secondary coolant discharging unit) 10, the governor valve (secondary coolant flow rate variable unit) 13, and the bypass valve (secondary coolant bypass flow rate variable unit) 15. Moreover, in the pressure adjustment means, the pressure of the primary coolant is increased by supplying the primary coolant to the primary coolant storage unit 2c, and thus, the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2. In addition, in the pressure adjustment means, the pressure of the secondary coolant fed to the steam generator 3 is decreased by decreasing a discharging amount of the secondary coolant in the feed water pump (secondary coolant discharging unit) 10, and thus, the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2. Moreover, in the pressure adjustment means, the pressure of the primary coolant at an outlet side of the steam generator 3 is decreased by increasing the flow rate of the secondary coolant fed to the steam turbine 4 in the governor valve (secondary coolant flow rate variable unit) 13, and thus, the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2. In addition, in the pressure adjustment means, the pressure of the primary coolant of the outlet side of the steam generator 3 is decreased by increasing the flow rate of the secondary coolant fed to the bypass circuit 14 in the bypass valve (secondary coolant bypass flow rate variable unit) 15, and thus, the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2. As shown in FIG. 1, the high temperature gas cooled reactor steam generation system 1 of the present embodiment includes pressure control means 16 for controlling the primary coolant storage unit 2c, the feed water pump (secondary coolant discharging unit) 10, the governor valve (secondary coolant flow rate variable unit) 13, and the bypass valve (secondary coolant bypass flow rate variable unit) 15. The pressure control means 16 includes a pressure difference calculation unit 17, and includes at least one of the following: a primary coolant recovery and supply setting unit 18, a secondary coolant discharging amount setting unit 19, a secondary coolant flow rate setting unit 20, and a secondary coolant bypass flow rate setting unit 21. The pressure difference calculation unit 17 inputs each pressure from a primary coolant pressure detection unit 22 that detects the pressure of the primary coolant, and a secondary coolant pressure detection unit 23 that detects the pressure of the secondary coolant flowing through the heat transfer tube 3a of the steam generator 3, and calculates a difference of the pressures. Since the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2, the primary coolant pressure detection unit 22 detects the pressure of the primary coolant that is relatively low at an inlet side of the circulation fan 2b. In addition, since the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2, the secondary coolant pressure detection unit 23 detects the pressure of the secondary coolant that is relatively high at the outlet side of the steam generator 3. The primary coolant pressure detection unit 22 detects the pressure of the primary coolant at the inlet side of the nuclear reactor 2. Moreover, the secondary coolant pressure detection unit 23 detects the pressure of the secondary coolant at the outlet side of the steam generator 3. In the primary coolant storage unit 2c, the primary coolant recovery and supply setting unit 18 recovers or supplies the primary coolant, sets a recovery pressure or a supply pressure of the primary coolant by a flow rate limitation mechanism (for example, ON-OFF valve control by pressure) such as an orifice, or sets a recovery amount or a supply amount of the primary coolant by a flow rate adjustment valve. The secondary coolant discharging amount setting unit 19 sets an increase and decrease, and an increase and decrease amount of the discharging amount of the secondary coolant in the feed water pump (secondary coolant discharging unit) 10. That is, when the discharging amount of the secondary coolant is increased, the feed water pump 10 is rotated at a high speed, the increase amount is set according to the rotational frequency, and when the discharging amount of the secondary coolant is decreased, the feed water pump 10 is rotated at a low speed, and the decrease amount is set according to the rotational frequency. The secondary coolant flow rate setting unit 20 sets an increase and decrease, and an increase and decrease amount of the flow rate of the secondary coolant in the governor valve (secondary coolant flow rate variable unit) 13. That is, when the flow rate of the secondary coolant is increased, the governor valve 13 is opened, and thus, an increase amount is set according to the opening degree, and when the flow rate of the secondary coolant is decreased, the governor valve 13 is closed, and thus, a decrease amount is set according to the opening degree. The secondary coolant bypass flow rate setting unit sets an increase and decrease, and an increase and decrease amount of the flow rate of the secondary coolant in the bypass valve (secondary coolant bypass flow rate variable unit) 15. That is, when the flow rate of the secondary coolant is increased, the bypass valve 15 is opened, and thus, an increase amount is set according to the opening degree, and when the flow rate of the secondary coolant is decreased, the bypass valve 15 is closed, and thus, a decrease amount is set according to the opening degree. The pressure control means 16 is configured of a microcomputer or the like, and a program or data for performing each setting at the primary coolant recovery and supply setting unit 18, the secondary coolant discharging amount setting unit 19, the secondary coolant flow rate setting unit 20, and the secondary coolant bypass flow rate setting unit 21 is stored in a storage unit (not shown) such as RAM or ROM so that a pressure difference is within a predetermined range based on the calculation of the pressure difference by the pressure difference calculation unit 17. Here, the predetermined range of the pressure difference may be any range as long as the pressure of the secondary coolant in the steam generator 3 is lower than the pressure of the primary coolant in the nuclear reactor 2, and the predetermined ranges are different according to various plants, for example, the pressure of the secondary coolant at the outlet side in the steam generator 3 is set to 5.8 [MPa] while the pressure of the primary coolant at the inlet side in the circulation fan 2b is set to 5.94 [MPa]. In addition, an upper limit of the pressure difference is also set according to various plants. A control of the pressure adjustment means by the pressure control means 16 will be described. FIGS. 2 to 5 are flowcharts showing a control of the high temperature gas cooled reactor steam generation system shown in FIG. 1. As shown in FIG. 2, in a control of the primary coolant storage unit 2c which is the pressure adjustment means, based on the pressure difference between the pressure of the primary coolant and the pressure of the secondary coolant obtained from the calculation by the pressure difference calculation unit 17, when the pressure difference satisfies the primary coolant pressure≤the secondary coolant pressure (Step S1: Yes), a command by which the primary coolant recovery and supply setting unit 18 supplies the primary coolant is output to the primary coolant storage unit 2c, and the primary coolant is supplied to increase the pressure of the primary coolant (Step S2). This is performed until the primary coolant pressure>the secondary coolant pressure is satisfied in Step S1 (Step S1: No). When the primary coolant pressure>the secondary coolant pressure is satisfied in Step S1 (Step S1: No), if the pressure difference is within the predetermined range (Step S3: Yes), the control ends. Moreover, in Step S3, when the pressure difference is not within the predetermined range, that is, when the pressure difference exceeds the upper limit of the pressure difference which is set for each plant and the primary coolant pressure is too high (Step S3: No), a command by which the primary coolant recover and supply setting unit 18 recovers the primary coolant is output to the primary coolant storage unit 2c, and the primary coolant is recovered to decrease the pressure of the primary coolant (Step S4). This is performed until the primary coolant pressure>the secondary coolant pressure is satisfied (in Step S1: No) in Step 1 and the pressure difference is within the predetermined range in Step S3 (Step S3: Yes). Moreover, the control is continually performed or periodically performed. As shown in FIG. 3, in a control of the feed water pump (secondary coolant discharging unit) 10 which is the pressure adjustment means, based on the pressure difference between the pressure of the primary coolant and the pressure of the secondary coolant obtained from the calculation by the pressure difference calculation unit 17, when the pressure difference satisfies the primary coolant pressure the secondary coolant pressure (Step S11: Yes), a command by which the secondary coolant discharging amount setting unit 19 decreases the discharging amount of the secondary coolant to the steam generator 3 is output to the feed water pump 10, and the discharging amount of the secondary coolant is decreased to decrease the pressure of the secondary coolant (Step S12). This is performed until the primary coolant pressure>the secondary coolant pressure is satisfied in Step S11 (Step S11: No). When the primary coolant pressure>the secondary coolant pressure is satisfied in Step S11 (Step S11: No), if the pressure difference is within the predetermined range (Step S13: Yes), the control ends. Moreover, in Step S13, when the pressure difference is not within the predetermined range, that is, when the pressure difference exceeds the upper limit of the pressure difference which is set for each plant and the secondary coolant pressure is too low (Step S13: No), a command by which the secondary coolant discharging amount setting unit 19 increases the discharging amount of the secondary coolant to the steam generator 3 is output to the feed water pump 10, and the discharging amount of the secondary coolant is increased to increase the pressure of the secondary coolant (Step S14). This is performed until the primary coolant pressure>the secondary coolant pressure is satisfied in Step S11 (Step S11: No) and the pressure difference is within the predetermined range in Step S13 (Step S13: Yes). Moreover, the control is continually performed or periodically performed. As shown in FIG. 4, in a control of the governor valve (secondary coolant flow rate variable unit) 13 which is the pressure adjustment means, based on the pressure difference between the pressure of the primary coolant and the pressure of the secondary coolant obtained from the calculation by the pressure difference calculation unit 17, when the pressure difference satisfies the primary coolant pressure≤the secondary coolant pressure (Step S21: Yes), a command by which the secondary coolant flow rate setting unit 20 increases the flow rate of the secondary coolant to the steam turbine 4 is output to the governor valve 13, and the flow rate of the secondary coolant is increased to decrease the pressure of the secondary coolant (Step S22). This is performed until the primary coolant pressure>the secondary coolant pressure is satisfied in Step S21 (Step S21: No). When the primary coolant pressure>the secondary coolant pressure is satisfied in Step S21 (Step S21: No), if the pressure difference is within the predetermined range (Step S23: Yes), the control ends. Moreover, in Step S23, when the pressure difference is not within the predetermined range, that is, when the pressure difference exceeds the upper limit of the pressure difference which is set for each plant and the secondary coolant pressure is too low (Step S23: No), a command by which the secondary coolant flow rate setting unit 20 decreases the flow rate of the secondary coolant to the steam turbine 4 is output to the governor valve 13, and the flow rate of the secondary coolant is decreased to increase the pressure of the secondary coolant (Step S24). This is performed until the primary coolant pressure>the secondary coolant pressure is satisfied in Step S21 (Step S21: No) and the pressure difference is within the predetermined range in Step S23 (Step S23: Yes). Moreover, the control is continually performed or periodically performed. As shown in FIG. 5, in a control of the bypass valve (secondary coolant bypass flow rate variable unit) 15 which is the pressure adjustment means, based on the pressure difference between the pressure of the primary coolant and the pressure of the secondary coolant obtained from the calculation by the pressure difference calculation unit 17, when the pressure difference satisfies the primary coolant pressure≤the secondary coolant pressure (Step S31: Yes), a command by which the secondary coolant bypass flow rate setting unit 21 increases the flow rate of the secondary coolant to the bypass circuit 14 is output to the bypass valve 15, and the flow rate of the secondary coolant is increased to decrease the pressure of the secondary coolant (Step S32). This is performed until the primary coolant pressure>the secondary coolant pressure is satisfied in Step S31 (Step S31: No). When the primary coolant pressure>the secondary coolant pressure is satisfied in Step S31 (Step S31: No), if the pressure difference is within the predetermined range (Step S33: Yes), the control ends. Moreover, in Step S33, when the pressure difference is not within the predetermined range, that is, when the pressure difference exceeds the upper limit of the pressure difference which is set for each plant and the secondary coolant pressure is too low (Step S33: No), a command by which the secondary coolant bypass flow rate setting unit 21 decreases the flow rate of the secondary coolant to the bypass circuit 14 is output to the bypass valve 15, and the flow rate of the secondary coolant is decreased to increase the pressure of the secondary coolant (Step S34). This is performed until the primary coolant pressure>the secondary coolant pressure is satisfied in Step S31 (Step S31: No) and the pressure difference is within the predetermined range in Step S33 (Step S33: Yes). Moreover, the control is continually performed or periodically performed. Moreover, the above-described controls of the primary coolant storage unit 2c, the feed water pump (secondary coolant discharging unit) 10, the governor valve (secondary coolant flow rate variable unit) 13, and the bypass valve (secondary coolant bypass flow rate variable unit) 15, which are the pressure adjustment means, may be performed individually or may be performed together, and are appropriately selected according to the high temperature gas cooled reactor steam generation system 1. In this way, the high temperature gas cooled reactor steam generation system 1 of the present embodiment includes at least one of the following, the primary coolant storage unit 2c, the feed water pump (secondary coolant discharging unit) 10, the governor valve (secondary coolant flow rate variable unit) 13, and the bypass valve (secondary coolant bypass flow rate variable unit) 15 which are the pressure adjustment means, and the pressure of the secondary coolant in the steam generator 3 can be set to be lower than the pressure of the primary coolant in the nuclear reactor 2 by the pressure adjustment means. Moreover, the pressure adjustment means can be appropriately selected according to the high temperature gas cooled reactor steam generation system 1. In addition, the high temperature gas cooled reactor steam generation system 1 of the present embodiment includes the pressure control means 16 for controlling the pressure adjustment means so that, based on the pressure difference between the pressure of the primary coolant and the pressure of the secondary coolant, the pressure difference is within the predetermined range, and thus, based on the pressure difference between the pressure of the primary coolant and the pressure of the secondary coolant, the pressure of the secondary coolant in the steam generator 3 can be controlled to be set to be lower than the pressure of the primary coolant in the nuclear reactor 2 by the pressure adjustment means. Then, as described above, the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2, and thus, it is possible to prevent high pressure water or steam supplied into the heat transfer tube 3a from entering the nuclear reactor 2. However, if the pressure of the secondary coolant at the outlet of the steam generator 3 is decreased, a boiling temperature of the secondary coolant is decreased, a steam average temperature is decreased when the secondary coolant is heated, and thus, thermal efficiency of the high temperature gas cooled reactor steam generation system 1 may be deteriorated. In addition, since the pressure of the primary coolant in the nuclear reactor 2 is integrally set according to the setting of the pressure by the pressure adjustment means, from the viewpoint that the pressure of the secondary coolant should be lower than the pressure of the primary coolant, as a measure for improving the thermal efficiency of the high temperature gas cooled reactor steam generation system 1, there is a limitation in an increase of the pressure of the secondary coolant at the outlet of the steam generator 3. Accordingly, the high temperature gas cooled reactor steam generation system 1 of the present embodiment includes temperature adjustment means for increasing an outlet temperature of the secondary coolant in the steam generator 3 according to the setting of the pressure by the pressure adjustment means. According to the high temperature gas cooled reactor steam generation system 1, since the steam average temperature at the time of heating is increased by increasing the temperature of the secondary coolant at the outlet of the steam generator 3, it is possible to improve the thermal efficiency of the high temperature gas cooled reactor steam generation system 1. That is, when the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2, it is possible to improve the thermal efficiency of the high temperature gas cooled reactor steam generation system 1 which may be deteriorated by the setting. FIG. 6 is a schematic diagram of a high temperature gas cooled reactor steam generation system including the temperature adjustment means in another high temperature gas cooled reactor steam generation system according to the present embodiment. Moreover, in FIG. 6, the same reference numerals are assigned to the same part as the configurations shown in FIG. 1, and the descriptions thereof can be omitted. As shown in FIG. 6, the temperature adjustment means includes at least one of the following: the feed water pump (secondary coolant discharging unit) 10, the circulation fan (primary coolant discharging unit) 2b which is a primary coolant temperature variable unit, and the nuclear reactor 2 which is the primary coolant temperature variable unit. Moreover, the temperature adjustment means decreases the generated steam amount by decreasing the discharging amount of the secondary coolant in the feed water pump (secondary coolant discharging unit) 10, and increases the outlet temperature of the secondary coolant in the steam generator 3. Moreover, the temperature adjustment means decreases the primary coolant heated by the nuclear reactor 2 by decreasing the discharging amount of the primary coolant in the circulation fan (primary coolant discharging unit) 2b, increases the outlet temperature of the primary coolant in the nuclear reactor 2, and increases the outlet temperature of the secondary coolant heated by the primary coolant. As shown in FIG. 6, the high temperature gas cooled reactor steam generation system 1 of the present embodiment includes temperature control means 25 for controlling the feed water pump (secondary coolant discharging unit) 10, the circulation fan (primary coolant discharging unit) 2b, and the nuclear reactor 2. The temperature control means 25 includes a temperature acquirement unit 26, and includes at least one of a secondary coolant discharging amount setting unit 27 and a primary coolant discharging amount setting unit 28. The temperature acquirement unit 26 inputs the outlet temperature of the secondary coolant from a secondary coolant temperature detection unit 30 which detects the outlet temperature of the secondary coolant of the steam generator 3. Moreover, since the temperature of the primary coolant having a relatively high temperature is detected at the outlet side of the nuclear reactor 2, a primary coolant temperature detection unit 31 is provided. The temperature acquirement unit 26 inputs the outlet temperature of the primary coolant from the primary coolant temperature detection unit 31. The secondary coolant discharging amount setting unit 27 sets an increase and decrease, and an increase and decrease amount of the discharging amount of the secondary coolant in the feed water pump (secondary coolant discharging unit) 10. That is, when the discharging amount of the secondary coolant is increased, the feed water pump 10 is rotated at a high speed, the increase amount is set according to the rotational frequency, and when the discharging amount of the secondary coolant is decreased, the feed water pump 10 is rotated at a low speed, and the decrease amount is set according to the rotational frequency. The primary coolant discharging amount setting unit sets an increase and decrease, and an increase and decrease amount of the discharging amount of the primary coolant in the circulation fan (primary coolant discharging unit) 2b. That is, when the discharging amount of the primary coolant is increased, the circulation fan 2b is rotated at a high speed, the increase amount is set according to the rotational frequency, and when the discharging amount of the primary coolant is decreased, the circulation fan 2b is rotated at a low speed, and the decrease amount is set according to the rotational frequency. The temperature control means 25 is configured of a microcomputer or the like, and a program or data for performing each setting at the secondary coolant discharging amount setting unit 27 and the primary coolant discharging amount setting unit 28 is stored in a storage unit (not shown) such as RAM or ROM so that the temperature is within a predetermined temperature based on the outlet temperature of the secondary coolant by the temperature acquirement unit 26. Here, the predetermined temperature is set based on the same temperature (although the predetermined temperatures are different according to various plants, for example, 550 [° C.]) as the outlet temperature of the secondary coolant before the pressure is set by the pressure adjustment means, and the range of the predetermined temperature is also set for each of the various plants. A control of the temperature adjustment means by the temperature control means 25 will be described. FIGS. 7 and 8 are flowcharts showing the control of the high temperature gas cooled reactor steam generation system shown in FIG. 6. As shown in FIG. 7, in a control of the feed water pump (secondary coolant discharging unit) 10 which is the temperature adjustment means, based on the outlet temperature of the secondary coolant which is obtained by the temperature acquirement unit 26, when the outlet temperature<the predetermined temperature is satisfied (Step S41: Yes), a command by which the secondary coolant discharging amount setting unit 27 decreases the discharging amount of the secondary coolant to the steam generator 3 is output to the feed water pump 10, and the discharging amount of the secondary coolant is decreased to increase the outlet temperature of the secondary coolant (Step S42). This is performed until the outlet temperature≥the predetermined temperature is satisfied in Step S41 (Step S41: No). When the outlet temperature the predetermined temperature is satisfied in Step S41 (Step S41: No), if the outlet temperature=the predetermined temperature is satisfied (Step S43: No), the control ends. Moreover, in Step S41, when the outlet temperature≥the predetermined temperature is satisfied (Step S41: No) and the outlet temperature>the predetermined temperature is satisfied (Step S43: Yes), that is, when the outlet temperature exceeds the predetermined temperature which is set for each plant and the outlet temperature of the secondary coolant is too high, a command by which the secondary coolant discharging amount setting unit 27 increases the discharging amount of the secondary coolant to the steam generator 3 is output to the feed water pump 10, and the discharging amount of the secondary coolant is increased to decrease the outlet temperature of the secondary coolant (Step S44). This is performed until the outlet temperature the predetermined temperature is satisfied in Step S41 (Step S41: No) and the outlet temperature=the predetermined temperature is satisfied in Step S43 (Step S43: No). Moreover, the control is continually performed or periodically performed. As shown in FIG. 8, in a control of the circulation fan (primary coolant discharging unit) 2b which is the primary coolant temperature variable unit of the temperature adjustment means, based on the outlet temperature of the secondary coolant which is obtained by the temperature acquirement unit 26, when the outlet temperature<the predetermined temperature is satisfied (Step S51: Yes), a command by which the primary coolant discharging amount setting unit 28 decreases the discharging amount of the primary coolant to the nuclear reactor 2 is output to the circulation fan 2b, and the discharging amount of the primary coolant is decreased to increase the outlet temperature of the primary coolant (Step S52). This is performed until the outlet temperature≥the predetermined temperature is satisfied in Step S51 (Step S51: No). When the outlet temperature the predetermined temperature is satisfied in Step S51 (Step S51: No), if the outlet temperature=the predetermined temperature is satisfied (Step S53: No), the control ends. Moreover, in Step S51, when the outlet temperature≥the predetermined temperature is satisfied (Step S51: No) and the outlet temperature>the predetermined temperature is satisfied (Step S53: Yes), that is, when the outlet temperature exceeds the predetermined temperature which is set for each plant and the outlet temperature of the secondary coolant is too high, a command by which the primary coolant discharging amount setting unit 28 increases the discharging amount of the primary coolant to the nuclear reactor 2 is output to the circulation fan 2b, and the discharging amount of the primary coolant is increased to increase the outlet temperature of the primary coolant (Step S54). This is performed until the outlet temperature≥the predetermined temperature is satisfied in Step S51 (Step S51: No) and the outlet temperature=the predetermined temperature is satisfied in Step S53 (Step S53: No). Moreover, the control is continually performed or periodically performed. Moreover, the above-described controls of the feed water pump (secondary coolant discharging unit) 10, the circulation fan (primary coolant discharging unit) 2b, and the nuclear reactor 2, which are the temperature adjustment means, may be performed individually or may be performed together, and are appropriately selected according to the high temperature gas cooled reactor steam generation system 1. In this way, the high temperature gas cooled reactor steam generation system 1 of the present embodiment includes at least one of the following, the feed water pump (secondary coolant discharging unit) 10, the circulation fan (primary coolant discharging unit) 2b as the primary coolant temperature variable unit, and the nuclear reactor 2 as the primary coolant temperature variable unit, which are the temperature adjustment means, and the outlet temperature of the secondary coolant in the steam generator 3 can be increased according to the setting of the pressure by the pressure adjustment means by the temperature adjustment means. Moreover, the temperature adjustment means can be appropriately selected according to the high temperature gas cooled reactor steam generation system 1. In addition, the high temperature gas cooled reactor steam generation system 1 of the present embodiment includes the temperature control means for controlling the temperature adjustment means so that the outlet temperature is within the predetermined temperature according to the set pressure of the secondary coolant based on the outlet temperature of the secondary coolant, and thus, based on the outlet temperature of the secondary coolant, it is possible to control to increase the outlet temperature of the secondary coolant in the steam generator 3 according to the setting of the pressure by the pressure adjustment means by the temperature adjustment means. Then, in the high temperature gas cooled reactor steam generation system 1, the pressure difference is set so that the primary coolant pressure<the secondary coolant pressure is satisfied until stable power output is obtained. Moreover, the setting of the pressure by the pressure adjustment means is performed after the power output is stably performed in the high temperature gas cooled reactor steam generation system 1. Accordingly, in the adjustment of the temperature by the temperature adjustment means, the temperature of the secondary coolant at the outlet of the steam generator 3 is increased to the same temperature as the temperature before the pressure is set by the pressure adjustment means. In addition, if the pressure of the secondary coolant in the steam generator 3 is set to be lower than the pressure of the primary coolant in the nuclear reactor 2, when the heat transfer tube 3a of the steam generator 3 is damaged, it is assumed that the primary coolant of the primary cooling system circuit 2a enters the heat transfer tube 3a of the steam generator 3 and reaches the secondary cooling system circuit 12. In order to solve the problems, as shown in FIGS. 1 and 6, on-off valves 33 are provided at the upstream side and the downstream side of the steam generator 3 of the secondary cooling system circuit 12, and for example, the decrease in the pressure of the secondary coolant of the steam generator 3 is detected, and thus, when it is determined that the heat transfer tube 3a of the steam generator 3 is damaged, the on-off valves 33 may be closed. 1: high temperature gas cooled reactor steam generation system 2: nuclear reactor (primary coolant temperature variable unit) 2a: primary cooling system circuit 2b: circulation fan (primary coolant discharging unit, primary coolant temperature variable unit) 2c: primary coolant storage unit 3: steam generator 3a: heat transfer tube 4: steam turbine 5: generator 10: feed water pump (secondary coolant discharging unit) 12: secondary cooling system circuit 13: governor valve (secondary coolant flow rate variable unit) 14: bypass circuit 15: bypass valve (secondary coolant bypass flow rate variable unit) 16: pressure control means 17: pressure difference calculation unit 18: primary coolant recovery and supply setting unit 19: secondary coolant discharging amount setting unit 20: secondary coolant flow rate setting unit 21: secondary coolant bypass flow rate setting unit 22: primary coolant pressure detection unit 23: secondary coolant pressure detection unit 25: temperature control means 26: temperature acquirement unit 27: secondary coolant discharging amount setting unit 28: primary coolant discharging amount setting unit 30: secondary coolant temperature detection unit 31: primary coolant temperature detection unit |
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abstract | A device and method for measuring the back pressure in chemical reactor tubes includes many automated features. Inflatable tube seals may be automatically inflated. The device may measure several tubes at once. It may transmit data electronically to a remote computer for analysis and graphic display. |
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description | As shown in FIGS. 1 and 2, the cell contains the pollution source 1 (melting pot and calciner, represented diagrammatically), and the overhead travelling-crane 2 to be protected from said pollution source 1. Said cell is filled with air. The technical problem facing the inventors was to limit significantly the contamination of hoists in such cells. The air heated and contaminated by the melting pot and the calciner 1 rises in the cell as it would in a chimney, and insofar as the air is charged with radioactive particles, it contaminates the crane 2 at the top of the cell, thereby making any maintenance operations performed on this equipment much more complex. Experience has shown that the availability of hoists present in cells containing hot pollution sources is related directly to the degree to which they are contaminated. In the context of the example, and of the entire research conducted by the Applicant, and whose results are given further on in the present text (table of the example), the cell had the following dimensions: In the prior art (FIG. 1), a ventilation system is installed for protecting said crane 2. Air is fed into the top of the cell (above the melting pot) and is extracted at the bottom of the opposite wall. Said air is injected at a temperature of 28xc2x0 C. at a flow rate of 4,300 Nm3 per hour (Nm3/h). According to the invention (FIG. 2), a confinement barrier 3 is created in a horizontal plane by maintaining a temperature difference that is large enough between the bottom portion (cold zone) 4 and the top portion (hot zone) 5 of the cell. Said temperature difference is maintained by a suitable ventilation system and must be such that the resultant of the gravitational forces that are applied to a volume of cold air penetrating into the hot zone 5 is greater than the inertial forces that are applied thereto, thereby causing the volume of cold air to fall back towards the bottom of the cell until it reaches equilibrium and thus preventing it from contaminating the crane 2 in the top portion 5 of the cell. The confinement barrier 3 is a mixing zone in whose volume the vertical temperature gradient is much steeper than the temperature gradients in either of the two volumes 4 and 5 lying outside of this zone 3 (see FIG. 3). In general, the thickness of said mixing zone must be less than 15% of the height of the cell. Said thickness is defined as a function of the geometrical characteristics of the cell, such as: the height of the cell; the height of the volume generated by the displacement of the crane; and the height occupied by the equipment included in the polluted zone. For any given level of disturbance of the zones (namely the hot zone and the cold zone), the larger the temperature difference between the zones, the smaller said thickness. The bottom volume 4 and the top volume 5 are swept by means of ventilation (the fluids involved are hot air at 60xc2x0 C. and cold air at 28xc2x0 C., see example below). The following can be specified concerning the ventilation: 1) General Principle The ventilation is designed as if it were to guarantee the desired rate of air renewal in two distinct and superposed cells (4 and 5) separated by a physical volume whose thickness is the thickness of the mixing zone 3. The two virtual cells (or zones) are fed with a flow of air that has undergone the usual treatment undergone by air for ventilating reprocessing units. The intake openings A and D are disposed such that, they produce, respectively in zone 5 and in zone 4, a continuous vertical low-speed flow (a few centimeters per second (cm/s)) whose random component needs to be as small as possible. The flow in the bottom (cold) zone 4 is directed upwards, and the flow in the top (hot) zone 5 is directed downwards. The extraction slots B and C are situated on either side of the mixing zone 3: the hot-air extraction slots B are situated just above the top interface of the said mixing zone 3; and the cold-air extraction slots C are situated just below the bottom interface of said zone 3. The extraction slots B and C stabilize the level of said mixing zone 3. This stabilization requires the ratios of the intake flow rates to the extraction flow rates of the hot air circuit and of the cold air circuit to be controlled sufficiently accurately. The simplest solution to implement for this purpose is to recycle the hot air. This also offers the advantage of saving heat energy and of reducing the size of the heater units. 2) The Physical Characteristics of the Air that Determine the Dimensioning of the Ventilation a) Air in the Hot Zone 5 Feed Flow Rate Since zone 5 does not contain any pollution source, it is necessary: on the one hand, for the flow speed (vertically downwards) through a horizontal cross-section in the vicinity of the top plane of the mixing zone 3 to be higher than the speeds of the Brownian motion and of the turbulent diffusion of the polluting particles that have penetrated into said mixing zone 3; and on the other hand, for the flow rate of hot air to be high enough to compensate for losses by convection with the walls. Thermally insulating the side walls of the top zone 5, thereby reducing the heat exchange and the stray convection currents, contributes to the stability of the mixing zone 3. Temperature The temperature in the top zone 5 must be as high as possible, and it is limited only by the constraint that the motors of the hoist must be cooled. b) Air in the Cold Zone 4 Feed Flow Rate The flow rate of the air fed into the bottom volume 4 is a function of the intensity and of the type of the pollution sources, and mainly of the total power given off by the heat sources that they contain; it being necessary for the resulting rise in the mean temperature of the air to be compensated by the flow rate of cold air. In each case, the maximum allowable value for the flow rate is determined by the constraint that it is necessary to limit the thickness of the mixing layer 3 (and thus the speed of penetration and the upward speed of the flow of air through a horizontal cross-section). Temperature Since low temperatures are a factor favorable to reducing the thickness of the mixing layer 3 and to increasing its stability (provided that it remains positive), there is no lower limit to the temperature of the air in the bottom zone. However, for reasons of simplicity and to limit investment, air at ambient temperature is generally used. The temperature taken into account for dimensioning purposes must then be the temperature corresponding to the meteorological maximum recorded on the site during a reference period of sufficient length. Level of Turbulence The turbulence is greater than in the hot zone 5 because of the presence of the heat sources and because of the way the intake openings D are disposed, and it is characterized by the maximum value of the root mean square of the random speed at the interface with the mixing zone 3, which is the parameter determining the height of said zone 3. Concerning the apparatus used to implement the ventilation, the following can be specified. 1) Feed and Design of the Ventilation Openings In order for stratification to be effective, it is essential for the intake flow rates through the ventilation openings A, D and for the extraction flow rates through the extraction slots B, C to be distributed uniformly. The feed ducts to the intake openings A, D and the extraction ducts from the extraction slots B, C must be designed as a function of this constraint (fan blading, ducts of varying section, etc.). Therefore, and because of increase in overall size that could otherwise occur, studying duct dimensions is an essential element in the design of the apparatus, it being necessary for this work to precede the work on the civil engineering of the cell. The cell may be designed with thermally-insulating double inner walls (e.g. made of expanded glass); the gap of about 0.4 m between these walls and the structural walls of the cell then being available for the ducts and apparatus for distributing the intake air. In addition, it is necessary for the speeds at the delivery sections of the intake openings A, D to be uniformly distributed. This may be obtained by lining the delivery orifice with two or three layers of perforated sheet metal having transparency of about 20%, the layers being a few millimeters apart. In general, the intake openings A, D, which are xe2x80x9cinductivexe2x80x9d (i.e. they induce internal circulation movements) must be as far as possible from the mixing zone 3, whereas the extraction slots B, C, whose induction effect on the surrounding environment is very limited in space, may be situated closer to the mixing zone 3 for which they define and stabilize the limits on the vertical walls of the cell. 2) Hot Air Intake Openings (Slots) (see FIGS. 2 and 4) a) General Configuration They must be disposed such that they make it possible to distribute the hot air flow rate across the horizontal sections in the vicinity of the mixing zone 3, so that the flow is as close as possible to laminar flow. To satisfy these conditions (while taking account of the way in which the hoist is fixed), the intake openings may be disposed in the form of narrow slots that are parallel to the longitudinal axis of the cell and that are almost continuous. Their delivery speed, which determines their minimum section as a function of the desired flow rate, must be such that the maximum speeds of impact on the elements making up the crane 2 are not more than 0.4 meters per second (m/s). This avoids any generation of turbulence which would be harmful to the stability of the mixing zone 3. b) Hot Air Flow Rate The hot air flow rate is chosen so as to guarantee a flow speed of about 0.04 m/s through the horizontal cross-sectional area of the top volume 5. In view of the intake speed and of the distribution chosen for the feed openings for feeding the top zone 5, the flow in the vicinity of the top plane of the mixing zone 3 can be considered to be a laminar flow in which turbulent diffusion is negligible, and, even for the finest polluting particles (which diffuse the fastest), the Brownian diffusion speed is much lower than 0.04 m/s. 3) Cold Air Intake Openings (Slots) (see FIGS. 2, 4, 5, and 6) a) General Configuration The cold air delivery openings D are disposed and shaped so as to make the concentration of polluted air and of hot air within the ambient environment in the bottom zone (cold zone) 4 as uniform as possible, while limiting the vertical components of the random speeds of the induced turbulence. The narrow delivery openings D (in the form of vertical slots or xe2x80x9cloopholesxe2x80x9d) are situated in the vicinity of the floor on the long sides of the cell, and are disposed in staggered manner. This layout produces interfitting jets 10 of air having vertical axial planes (see FIG. 6). By a shear effect due to the opposite speeds, these plane-jets produce eddies whose speeds have small vertical components and which cause the currents output by the various sources to mix with the ambient environment (see FIG. 5). It is observed that the eddies having horizontal axes and generating vertical random speeds are produced from an area that is very small (the area of a xe2x80x9cloopholexe2x80x9d) compared with the area of the interface between jets 10. Furthermore, it can be seen that the speed differential between the top portions of the jets 10 and the almost immobile ambient environment in the cell is half as large as the speed differential between opposite jets, thereby generating horizontal currents that predominate considerably relative to the upwardly-directed vertical currents. For these two reasons, the vertical components of the random speeds are significantly attenuated, and the phenomena of penetration into the mixing layer are thus limited; in addition, this layout tends to brake, by dilution, the upward speed of the currents output by the heat sources, this being the most important factor in any possible penetration of the pollution into the protected zone 5. b) Cold Air Flow Rate The value of the mean upward speed of the air is chosen to be about 0.04 m/s in order to limit entrainment of polluting particles by the ventilation air from the bottom zone 4 to those particles whose xe2x80x9caerodynamic diameterxe2x80x9d is smaller than 35 xcexcm. The particles having a larger diameter tend to settle in the cell, they do not adhere to the walls, and they can be removed by vacuum cleaning. This speed defines a flow rate that is a function of the horizontal cross-sectional area of the cell, and that must be high enough, in view of the feed temperature of the cold air and of the power of the heat sources 1, to maintain a sufficiently low temperature in the cold zone 4. In certain applications in which the mean heat power given off by the heat sources per unit volume of the cell is very high, a unit for cooling the feed air may then be necessary to limit its flow rate. In that particular case, the most rational solution may be to use a heat pump for raising the temperature of the hot air while lowering the temperature of the cold air. 4) Extraction Slots B, C (for Cold Air (C) and for Hot Air (B)) The cold air extraction slots C and the hot air extraction slots B are disposed in horizontal lines constituting slots that are almost continuous (gaps between the vertical sides of the suction openings as narrow as possible), the horizontal lines extending facing each other on the long sides. The top level of the cold air extraction slots C defines the bottom plane of the mixing zone 3, while the bottom level of the hot air extraction slots B defines the top plane of said mixing zone 3. The top level of the hot air extraction slots B must be situated about 1 m below the bottom level of the volume in which the hoist moves. When the crane has a vehicle deck, the top level of the hot air extraction slots must be situated below the level of the deck of said crane. With reference to FIG. 3, the following may be specified. A shallow temperature gradient is observed in the bottom volume, because of the presence of the polluting heat source. The desired steep temperature gradient is observed in the mixing zone 3 which constitutes the (virtual) confinement barrier. With reference to FIG. 4, it is specified that, for reasons of simplification, the crane 2 is not shown. The method of the invention has been implemented in the vitrification cell whose dimensions are specified above, with the apparatus described above and shown diagrammatically in accompanying FIGS. 2, and 4 to 6. The following table gives the characteristics of said method and apparatus. |
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048333344 | claims | 1. A protective box for electronic circuits hardened with respect to x-rays, said protective box comprising a molded rigid mechanical structure of composite material constituted by a fiber-reinforced resin; an x-ray protection material covering at least parts of said mechanical structure capable of being irradiated by x-rays, said x-ray protection material being potted on said mechanical structure and composed of a resin matrix containing a regularly dispersed powder consisting of at least one metal and/or at least one inorganic compound of a metal, said powder having a melting temperature at least equal to 630.degree. C., said metal and/or metal of the inorganic compound having a high atomic number at least equal to 47; and an anti-SGEMP material which at least partly covers the outer and/or inner surface of the mechanical structure. 2. A protective box according to claim 1, wherein the powder represents 25 to 50% by volume of the x-ray protection material. 3. A protective box according to claim 1, wherein the high atomic number metal is selected from the group consisting of silver, tantalum, tungsten and uranium. 4. A protective box according to claim 1, wherein the anti-SGEMP material includes at least one chemical element with a low atomic number at the most equal to 6. 5. A protective box according to claim 4, wherein the low atomic number element is selected from a group consisting of carbon, boron and beryllium. 6. A protective box according to claim 1, including an electrically conducive material covering the outer surface of the assembly composed of the mechanical structure and the x-ray protection material. 7. A protective box according to claim 1, including a material which is electrically conducive covering the inner surface of the mechanical structure. 8. A protective box according to claim 7, wherein the electricity conducting material is selected from the group consisting of silver, aluminum, beryllium and copper. 9. A protective box according to claim 1, wherein the mechanical structure is provided on its surface covered with the x-ray protection material with slots for improving the adhesion of said material to the mechanical structure. 10. A protective box according to claim 1, wherein the composite material constituting the mechanical structure is formed from a thermosetting resin. 11. A protective box according to claim 1, wherein said anti-SGEMP material has a thickness exceeding the free middle path of electrons emitted during an x-ray irradiation of said box. |
description | Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is shown how a fuel element FA of a boiling-water reactor is inspected. The lateral box has been removed such that the fuel rod bundle FB including the schematically indicated fuel rods FR is visible. The fuel rods are held at a plurality of axial positions, in each case by a spacer FS at prescribed positions distributed regularly over the fuel element cross section. Located in the middle of the fuel element is a hollow tube or cladding tube (xe2x80x9cwater tubexe2x80x9d FW), on which the foot part FF and the head part FH of the fuel element are fastened. The fuel element bundle FB with the head part and the foot part is inserted into a positioning device P, in this case the foot part FF engaging in a centering plate PC and being fixed in its position via hydraulically pressed-on lateral jaws PB. The positioning device P further contains a frame, which is constructed here as a rack PG made from guide rails for a plane table MT. The guide rails PG define the z-axis of a reference system whose center point and x-, y-axes are given by the center point and the alignment of the centering plate PC. The plane table MT is part of a measuring device M which can be displaced in the z-direction through the use of drives PD, and is positioned at the level of a spacer of the fuel rod bundle FB. Such a plane table, which can be displaced along the fuel rod bundle relative to the fuel rods and their spacers, is already used for inspection devices and generally carries a video camera VC in order to undertake optical inspection of the fuel rods and the spacers. It is usual in this case for the video camera also to move in the x- and y-directions relative to the fuel rod bundle, in order to monitor the fuel element from all sides. In the present case, a plurality of video cameras are provided at the plane table MT in order to monitor the spacer completely without having to change the relative position of the plane table MT. In FIG. 1, the spacer to be inspected, which is a part of the fuel element bundle FB, is hidden by the measuring device M. However, it is possible to see two mutually opposite arms MA of the measuring device M, which run along the left-hand and right-hand outer surface of this spacer and carry probes US which are configured as ultrasonic probes. These ultrasonic probes US are directed partly toward the left-hand or right-hand outer surface of the spacer, and partly also toward the end faces of a calibration rod CS of known length d0. These ultrasonic probes US emit ultrasonic pulses which are reflected at the outer surfaces of the spacer or the end faces of the calibration rod CS. The reflected echo is received by the ultrasonic probes US and it is therefore possible to determine the spacing of the spacer from the propagation time of the pulse echo. The calibration rod CS, disposed on the front side and the rear side of the fuel rod bundle, is mounted in each case on a further measuring arm MAxe2x80x2, which likewise carries a plurality of ultrasonic probes USxe2x80x2. It is thereby also possible to measure the outer surfaces of the spacer on the front side (visible in FIG. 1) of the fuel rod bundle and the opposite rear side. The outermost ultrasonic probes of these further measuring arms MAxe2x80x2 are directed toward the end faces of further calibration rods (covered in FIG. 1) which are located below the measuring arms MA. In the cross section through the plane IIxe2x80x94II in FIG. 1, which is shown in FIG. 2, it may be seen that the three ultrasonic probes US1, US2 and US3 at three measuring points on the left-hand outer surface FSA of the spacer FS measure the spacing of this spacer from the corresponding, left-hand measuring arm MA. The outer ultrasonic probes US4 and US5, by contrast, measure the spacing of the end faces CA or CAxe2x80x2 of the corresponding calibration rod CS or CSxe2x80x2 extending from left to right. The spacings between these end faces CA and CAxe2x80x2, on the one hand, and the measuring probes US4 and US5 differ, but are known, and so these two probes US4 and US5 supply two calibration points for the relationship between the propagation time of the ultrasonic echo and the arc covered. Corresponding probes US1B to US5B are situated opposite the probes US1 to US5 on the right-hand arm MB. In the same way, these ultrasonic probes on the opposite outer surface FSB of the spacer report three measuring points for the spacing, and two calibration points on the corresponding end faces CB, CBxe2x80x2 of the calIbration rods. Since the length do of each calibration rod CS, CSxe2x80x2 is known, this also results in an exact value for the spacing of the opposite measuring arms in this plane, or a computational correction if the measuring arms are not strictly parallel to one another. In the same way, in the plane lying therebelow, in which the ultrasonic probes USxe2x80x2 shown in FIG. 1 are situated, three measuring points and two calibration points are formed in each case for the two other mutually opposite sides of the spacer. The signals from the sensors are fed to a computer CAL with a monitor MON which is provided outside the water reservoir in which the inspection takes place. This is an electronic evaluation system which selects the sensor signals in a suitable way, calibrates them and displays them as characteristic variables of the measured spacer, as is explained with the aid of an image (FIG. 3) output on a display screen. In this FIG. 3, firstly, the geometry G of an unbowed fuel element is demonstrated; the center GC thereof would be disposed at the coordinate origin of the x-y system of the measuring device M. D1, D2, D3 illustrate the three measuring points of an outer surface, and D1xe2x80x2, D2xe2x80x2, D3xe2x80x2 illustrate the corresponding, already calibrated measuring points at the opposite outer surface, which result from the ultrasonic echoes. The most important variables for assessing the relevant spacer (here: the third spacer, xe2x80x9cspacer 3xe2x80x9d) is the maximum spacing xcex94max between opposite outer surfaces. If the fuel element is not twisted, this is the maximum value of the variables xcex94(y1), xcex94(y2), xcex94(y3), xcex94(x1), xcex94(x2), xcex94(x3), wherein xcex94(y1) is the difference between the y-coordinates on the mutually opposite points D1, D1xe2x80x2. The differences xcex94(y2) and xcex94(y3) are assigned correspondingly to the respectively mutually opposite points D2, D2xe2x80x2 and, respectively, D3, D3xe2x80x2, and the differences xcex94(x1), xcex94(x2), xcex94(x3) of the x-coordinates are assigned to the further point pairs illustrated in FIG. 3. The value xcex94max can then be specified directly-in micrometers or as a percentage with respect to the ideal fuel element. The variable xcex94d(y), which describes a convex curvature of the outer surfaces, can be determined, for example, in accordance with xcex94d(y)=xcex94(Y2)xe2x88x92(xcex94(y1)+xcex94(y3))/2. A further interesting variable is the x-coordinate C(x) or y-coordinate C(y) of the center point C (which can be determined from the two measuring points D2, D2xe2x80x2) refer to the desired center point GC (origin of coordinates). The bowing of the entire bundle can be determined thereby. In order also to detect twisting of the spacer, it is possible, for example, to determine the angle between the straight line defined by the measuring points D1xe2x80x2 and D3 and the y-axis. In the display, illustrated in FIG. 3, on the display screen of the computer CAL, a curve of second order is drawn through the points D1, D2 and D3 by computation, and the same is done for the corresponding measuring points on the other outer surfaces. These curves and their point of intersection are illustrated as contour of the measured spacer. The coordinates C(x) and C(y) for the center point of the deformed spacer describe the bowing of the fuel element and result from the point of intersection of the connecting lines which are respectively calculated from the diametrical corners of the illustrated contour, calculated from the measuring points, of the deformed spacer. The angle xcex1 describes the twisting of the fuel element and corresponds to the mean value of the angle by which in each case a diagonal of the deformed spacer is rotated relative to the corresponding diagonal of the geometry G. The connecting straight lines between two neighboring corners describe the outer contour of an undented, but twisted spacer whose deviation from the geometry G can be described by the values xcex94d(x) and xcex94d(y). The maximum width of the spacer is described by the value xcex94max. As a rule, it suffices to display these calibrated, characteristic measured values on a display or to blend them into the display screen, while the remainder of the image can be used in order to make the video images of the camera VC available to the operating staff for the optical inspection of the spacer. The walls 1 of a fuel element storage rack in the fuel element cooling pond of a nuclear power plant are visible in FIG. 4. Also illustrated are only the foot part 5a, the control rod guide tubes 5b and the spacers 5c of the fuel element 5. Mounted on the top side of this storage rack is a frame 2 which forms a workstation with a frame part 11 and a platform 3 which laterally surround the fuel element. Various apparatuses which are provided for inspecting and/or maintenance can be mounted on positioning bolts 4. A pressurized-water fuel element 5 is transported to this workstation through the use of a fuel element handling machine, only the lower end 6 of the fuel handling machine mast with the centering bolt 7 being visible in FIG. 4. It is not explicitly shown in the following figures that the centering bolts 7 can be used to position the mast 6 on the frame 2 and then to place the fuel element in a defined position relative to the frame, which defines the reference system for measuring the fuel element. Mounted on the platform 3 is a base plate 12 which bears a plane table 20 which can be displaced via an x-drive 21 and a y-drive 22 along corresponding x- and y- guide rails 21xe2x80x2, 22xe2x80x2. The face of the plane table 20 is parallel in this case to the x-y plane of a reference system whose z-axis is given by the frame 2 and the mast 6 of the handling machine. These parts therefore constitute a positioning device which can simultaneously provide a coordinate system for evaluating measured values. Via the drives 21, 22, the plane table can be moved in the plane to a desired position in the x-direction and/or y-direction. A module 8 which contains a measuring device is fastened on the plane table. This module 8 is illustrated in FIG. 5, in which the plane of a drawing is parallel to the y-z plane of the reference system described above. Also shown is a shaft 13 which is provided chiefly for fixing the fuel element to be inspected in cases in which the foot of the fuel element is not fixed in the way shown in FIG. 1, but is still suspended in the mast 6 of the handling machine. The shaft can be fastened on the plane table or, via a plane part 11, on the base plate 12 or the platform 3. It includes shaft walls 14, which support the fuel element laterally and have on three sides a transverse slot 15 through which it is possible to access the three outer surfaces of the fuel element and/or the spacer 5c thereof. Positioned at the upper edges of the shaft walls are guide planes 16, which run in obliquely, from above, onto the edges of the shaft walls and serve the purpose of facilitating the introduction of the fuel element into the shaft. The measuring device has two mutually opposite measuring arms 30 at one end of which there is a probe 31 in each case. At their other end, the measuring arms are respectively connected to the remainder of the module via a feed drive 32 operating in the y-direction. The measuring arms are provided in this case such that their longitudinal axis is parallel to the y-axis of the reference system, and that the probes can respectively be laid through the transverse slots 15 against one of the two opposite outer surfaces 35, 36 of the fuel element or spacer 5c, which are virtually parallel to the longitudinal axis of the measuring arms. The arms are advantageously fitted such that their mutual spacing can be set, in which case it is then possible to use the device for fuel elements with different widths. The device can be used, for example, to measure the boxes and the spacers in the case of boiling-water fuel elements. FIG. 6 also shows further outer surfaces 37 of the spacer 5c, which can also be inspected. Optical monitoring via a video camera is provided for the purpose of remotely controlling the positioning of the measuring arms via the x- and y-drives. The camera 40 and the associated lighting 41 are therefore fitted on the plane table itself, or are components of the module mounted on the plane table. Also to be seen in FIG. 5 is a calibration rod 50, which is illustrated more precisely in FIG. 6. This FIG. 6 shows the shaft 13 with the walls 14, and the probes 31, which grip through the transverse slots onto two opposite outer surfaces of a spacer 36, and arms 30 of the probes. The plane of the drawing in FIG. 6 is parallel to the x-y plane of the reference system. In this exemplary embodiment, the calibration rod 50 is fastened on the plane table 20 via a holder 42 which is positioned by the x- and y-drive 21, 22 on the spacer 36 until it bears resiliently with a defined pressure. To render interpolation possible during calibration, the end faces of the calibration rod 50 are configured in three steps, that is to say they have a plurality of respectively mutually opposite subareas 52, 53. The steps are configured such that the calibration rod prescribes three linear measures, of which at least one is larger, and one smaller, than the mutual spacing of opposite outer surfaces of the fuel element to be measured. It is possible in this way to use interpolation to draw a calibration curve for the relationship between probe-measured data and the expansion of the fuel element. The measuring arms 30 can be moved synchronously in the y-direction via a feed 32. They can, for example, be stiff and mounted rotatably at one end such that the deviation of the probes in the x-direction can be detected by a rotary encoder on the rotatable bearing. A hydraulic drive can also be used, for example, instead of a y-feed for the purpose of extending the telescopic arms. In the exemplary embodiment illustrated in FIG. 5, a part 34 of the arm is constructed as a spring which bears strain gauges on both sides. The resistance of the strain gauges is measured via a Wheatstone bridge circuit for the purpose of determining the position of the probes. FIG. 7 shows such a measuring arm in detail, and FIG. 8 shows a circuit diagram of the bridge circuit. FIG. 7 shows the arm 30 with the probe 63, which slides with a camber or bulge 64 along the outer surfaces of the fuel element. The arm contains an approximately triangular spring 60. A rigid part 62 of the arm with the probe 63 is attached at one corner of this spring. The rigid part 65, connected to the y-drive 32, of the arm is fastened on the opposite side of the spring. The triangular shape of the spring is favorable, because in this way the spring tension is distributed uniformly over the entire length of the spring and exhibits a virtually linear dependence on the x-deflection of the probe. The two triangular faces of the spring are coated, and each form a strain gauge. The electrical resistance of each strain gauge depends approximately linearly on the spring tension. Consequently, it is possible to use the measurement of these resistances to calculate measured values for the x-position of the probe, which can be calibrated by the measured values which are obtained on the calibration rod. The strain gauges on the faces of the spring 60 are connected via connections 66 to the bridge circuit 68 of an electronic measuring system, for example an electronic evaluation device integrated in the computer CAL. A circuit diagram of the bridge circuit 68 is shown in FIG. 8. R1 and R2 are the resistances to be measured of the two strain gauges. They are connected in a Wheatstone bridge circuit to adjustable resistors R3 and R4. To balance the bridge, the current I is controlled to zero by suitable adjustment of R3 and/or R4. The voltages which are present across R1 and R2 or R3 and R4 are then respectively of the same absolute value. If the spring with the strain gauge is in a position of rest, R1 and R2 are of the same magnitude; R3 and R4 must then likewise become equal, so that balancing comes about. If the spring is deflected, one strain gauge is stretched while the other is compressed, that is to say one of the resistances becomes larger while the other becomes smaller. The ratio of the two adjustable resistors R3 and R4 then corresponds, with the bridge balanced, to the ratio of the resistances R1 and R2 to be measured. Effects which are to be ascribed to thermal expansion are largely eliminated with this method, since R1 and R2 change in the same sense. The measurement itself is advantageously carried out using AC voltage employing the known carrier frequency principle. A connected measuring amplifier can then be calibrated such that it directly specifies the tension of the spring and/or the deflection of the probe. The invention therefore renders it possible for the geometry of the fuel element to be measured in a simple way, and for deformations to be detected. |
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056132409 | summary | BACKGROUND OF THE INVENTION This invention relates to a method for immobilizing radioactive wastes for permanent disposal. More particularly, the invention relates to a method of immobilizing mixed waste chloride salts containing radionuclides and other hazardous materials for permanent disposal. The recovery of fissionable materials such as uranium and plutonium from spent nuclear reactor fuels can be carried out by an electrorefining method using electrochemical cells of the type described in U.S. Pat. Nos. 4,596,647 and 2,951,793, as well as U.S. Pat. No. 4,880,506. It is the electrorefining method which is being developed for the reprocessing of spent nuclear fuel. In a typical electrorefining cell, an electrolyte consisting of a molten eutectic salt mixture such as KCl and LiCl is used to transport the metal or metals to be purified between electrode solutions. When used to reprocess spent nuclear reactor fuels, the salt mixture becomes contaminated with radionuclides, such as cesium.sup.-137 and strontium.sup.-90, hazardous metals such as barium and other species such as sodium and iodine.sup.-129 and eventually is no longer suitable for use in the electrorefining cell. Ideally the salt would be decontaminated by removing the heat producing radionuclides, primarily cesium and strontium, and any other metals, e.g. sodium, which could potentially interfere in the operation of the electrorefiner and the purified salt would be recycled back to the electrorefiner. However, the separation of cesium and strontium chloride from the salt is difficult, and since they are large heat producers it would be necessary to dilute them in another matrix material and/or cool them before they could be stored. It is therefore more practical to dispose of the cesium and strontium and any other radionuclides and toxic metal chlorides and iodides along with a portion of the salt matrix. The waste salt containing the cesium and strontium is a high level waste (HLW), and as such must be disposed of in the geologic repository for HLW. This requires that the waste form be leach resistant to prevent an uncontrolled release of the radionuclides and other hazardous chemicals such as barium into the groundwater. Since waste salts are chlorides and are very water soluble, a method for encapsulating and immobilizing the waste salt must be identified. One problem with developing a waste storage medium is that the waste salt consists primarily of chloride salts of the alkali metals and as such is not readily amenable to treatment using procedures and techniques developed for immobilizing the cesium and strontium in other nuclear waste streams. For instance, it has been taught that the chloride salts cannot be added directly to glass-forming compounds and processed to yield a leach-resistant glass since glasses containing halide ions are relatively water soluble, see U.S. Statutory Invention Registration H1,227, published Sep. 7, 1993. Therefore, it was thought that for immobilization in a glass matrix the waste chloride salts must be converted into oxides or other chemical forms compatible with the glass-making process. However, conversion processes are expensive and time-consuming and raise environmental concerns about the off-gases produced by the processes. A mortar matrix has also been considered as a possible waste form for the waste chloride salt. A special mortar was developed to incorporate lithium, potassium, cesium and strontium chloride salts into its structure and thereby immobilize them. However, when irradiated, the water in the mortar was radiolyzed and large quantities of hydrogen gas were generated. A new matrix for immobilizing waste chloride salts was therefore needed, and Invention Disclosure H1,227 addressed this problem by disclosing special zeolites which can be treated with molten salts. When some zeolites are treated with molten salts, salt molecules penetrate the cavities and channels of the zeolite and are then said to be occluded. Occluded molecules provide a transfer medium for ion exchange between the cations in the zeolite and those in the bulk salt. A zeolite which has a high selectivity for cesium, strontium and barium would be a promising candidate for an immobilization matrix. U.S. Pat. No. 5,340,506 which issued Aug. 23, 1994 also addressed the problem by chemically reacting mixtures of NaOH, Al.sub.2 O.sub.3, SiO.sub.2 to form a sodalite intermediate. Further processing produced a sodalite product with radionuclides and hazardous material contained in the sodalite. As stated in the '506 patent, an advantage of the process of invention registration H1,227 was in the use of certain zeolites to occlude and immobilize waste radioactive chloride salt. Contact between the zeolite (for example zeolite A or mixtures of chabazite and erionite-type zeolites or mixtures thereof) in the sodium, potassium or lithium form and the molten salt resulted in ion exchange between the radionuclides cesium and strontium and the hazardous material barium in the salt and the sodium, potassium, lithium in the zeolite and the occlusion of up to about 25% by weight of the salt within the molecular cavities of the zeolite. One of the problems inherent in the method disclosed in invention registration H1,227 is that the resultant material is not suitable for storage as a long term waste because it is not a monolithic solid. Although the use of synthetic naturally occurring minerals to store radioactive ions have been studied, as for instance in U.S. Pat. No. 4,808,318, which describes the use of a modified phlogopite to recover cesium ions from waste solutions and the advances that were set forth in the aforementioned '506 patent there is still needed a method of immobilizing mixtures of salts, particularly chloride salts containing radionuclides and other hazardous wastes so that the highly soluble salts can be safely stored for long periods of time in HLW stored facilities without presenting a hazard to the environment. SUMMARY OF THE INVENTION A method has been found by which, contrary to the teachings of the prior art, waste chloride salts containing radionuclides and other hazardous wastes can be incorporated into zeolite and combined with glass to form a leach resistant material suitable for long term storage, having a near theoretical density, resulting in a lower volume of waste material for storage than heretofore available. The method of the invention for immobilizing waste chloride salts containing radionuclides and hazardous nuclide material for permanent disposal comprises providing a substantially dry zeolite and sufficient glass to form leach resistant sodalite with occluded radionuclides and hazardous material, heating the zeolite and glass to a temperature up to about 1000.degree. K. to convert the zeolite to sodalite and thereafter maintaining the sodalite at a pressure and temperature sufficient to form a sodalite product near theoretical density. It is therefore an object of the invention to provide an effective method for disposing of waste chloride salt. It is another object of the invention to provide an improved method for stabilizing waste chloride salts containing radionuclides and other hazardous waste material. It is still another object of the invention to provide an improved method for stabilizing waste chloride salts containing radionuclides and other hazardous waste materials so that they may be safely placed in high level waste facilities for long periods of time without fear of damage to the environment. It is still another object of the invention to provide an improved matrix material for storing waste chloride salts containing radionuclides such as cesium and strontium and other hazardous waste such as barium so that they may be safely stored for long periods of time without causing damage to the environment by leaching from the matrix when contacted with water. |
claims | 1. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being placed in the at least one retention bore such that at least a portion of the at least one irradiation target is embedded inside of the tie plate attachment,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the outer structure of the tie plate attachment is further shaped with an outer perimeter that corresponds to an outer perimeter of the tie plate. 2. The structure of claim 1, wherein the at least one hole is configured to permit an end plug of a fuel rod of the nuclear fuel assembly to pass through the tie plate attachment and into the tie plate. 3. The structure of claim 2, wherein the tie plate attachment is maintainable in an axial position by a shoulder at the joining of the fuel rod and the end plug. 4. The structure of claim 1, wherein the tie plate attachment is rectangular. 5. The structure of claim 1, wherein the tie plate attachment further includes at least one cap joined to the tie plate attachment over the at least one retention bore, the cap shaped to seal and fully enclose the irradiation target within the retention bore. 6. The structure of claim 5, wherein the irradiation target substantially converts to a liquid or gaseous radioisotope when exposed to the neutron flux in the operating nuclear reactor. 7. The structure of claim 5, wherein the irradiation target is at least one of a liquid and gas. 8. The structure of claim 1, wherein the irradiation target is at least one of Iridium-191, Selenium-74, Strontium-88, and Cobalt-59. 9. The structure of claim 1, wherein a plurality of irradiation targets are placed in the retention bore, at least a first irradiation target of the plurality being a first material and at least one of a second irradiation target of the plurality being a second material. 10. The structure of claim 1, wherein the at least one retention bore does not pass entirely through the tie plate attachment such that a bottom and sides of the bore are continuously defined by the tie plate attachment. 11. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore not passing entirely through the tie plate attachment such that a bottom and sides of the bore are continuously defined by the tie plate attachment, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being inside of and retained by the at least one retention bore,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the outer structure of the tie plate attachment is further shaped with an outer perimeter that corresponds to an outer perimeter of the tie plate. 12. The structure of claim 11, wherein the tie plate attachment is rectangular. 13. The structure of claim 11, wherein the tie plate attachment further includes at least one cap joined to the tie plate attachment over the at least one retention bore, the cap shaped to seal and fully enclose the irradiation target within the retention bore. 14. The structure of claim 11, wherein a plurality of irradiation targets are placed in the retention bore, at least a first irradiation target of the plurality being a first material and at least one of a second irradiation target of the plurality being a second material. 15. The structure of claim 1, wherein the outer structure has a cross-sectional thickness sufficient to encompass only a single row of fuel rods, and the cross-sectional thickness is along a transverse cross section of the nuclear fuel assembly. 16. The structure of claim 11, wherein the outer structure has a cross-sectional thickness sufficient to encompass only a single row of fuel rods, and the cross-sectional thickness is along a transverse cross section of the nuclear fuel assembly. 17. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being placed in the at least one retention bore such that at least a portion of the at least one irradiation target is embedded inside of the tie plate attachment,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the tie plate attachment further includes at least one lateral extension configured to connect the tie plate attachment to a channel surrounding the nuclear fuel assembly, the at least one lateral extension configured to hold the tie plate attachment in a constant axial position within the fuel assembly. 18. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore not passing entirely through the tie plate attachment such that a bottom and sides of the bore are continuously defined by the tie plate attachment, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being inside of and retained by the at least one retention bore,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the tie plate attachment further includes at least one lateral extension configured to connect the tie plate attachment to a channel surrounding the nuclear fuel assembly, the at least one lateral extension configured to hold the tie plate attachment in a constant axial position within the fuel assembly. 19. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being placed in the at least one retention bore such that at least a portion of the at least one irradiation target is embedded inside of the tie plate attachment,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the tie plate attachment further defines at least one hole shaped and positioned to permit a fuel rod of the nuclear fuel assembly to pass through the tie plate attachment and into the tie plate. 20. A radioisotope production structure for use in a nuclear fuel assembly, the structure comprising:a tie plate attachment shaped to fit below a tie plate in the nuclear fuel assembly in an axial direction, the tie plate attachment defining at least one retention bore not passing entirely through the tie plate attachment such that a bottom and sides of the bore are continuously defined by the tie plate attachment, the tie plate attachment fabricated of a material that substantially maintains physical and neutronic properties when exposed to the neutron flux in an operating nuclear reactor; andat least one irradiation target configured to substantially convert to a radioisotope when exposed to a neutron flux in an operating nuclear reactor, the at least one irradiation target being inside of and retained by the at least one retention bore,wherein the tie plate attachment includes an outer structure and a hollow center, the outer structure being shaped to conform to a shape of an outer channel surrounding the nuclear fuel assembly, and a top face of the outer structure includes the at least one retention bore such that the at least one retention bore does not pass entirely through the outer structure,wherein the tie plate attachment further defines at least one hole shaped and positioned to permit a fuel rod of the nuclear fuel assembly to pass through the tie plate attachment and into the tie plate. 21. The structure of claim 19, wherein the at least one hole is shaped to seat against the fuel rod so as to lock the tie plate attachment against the tie plate. 22. The structure of claim 20, wherein the at least one hole is shaped to seat against the fuel rod so as to lock the tie plate attachment against the tie plate. |
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claims | 1. An X-ray apparatus comprising:an X-ray generator configured to emit X-rays to an object;an X-ray detector configured to detect the X-rays emitted from the X-ray generator and generate X-ray image data based on the detected X-rays;an image acquirer configured to acquire at least one object image by imaging the object;a display configured to display an X-ray image generated based on the X-ray image data; andat least one processor configured to obtain a thickness of the object based on the at least one object image and control the display to display an irradiation condition based on the thickness of the object;wherein the X-ray generator is configured to emit X-rays to the object based on the irradiation condition. 2. The X-ray apparatus of claim 1,wherein the image acquirer acquires at least two object images,wherein the at least one processor obtains the thickness of the object by comparing the at least two object images. 3. The X-ray apparatus of claim 2,wherein the at least one processor is further configured to identify a point from each of the at least two object images and obtain the thickness of the object by comparing the identified point of the each of the at least two object images. 4. The X-ray apparatus of claim 3,wherein the at least one processor obtains the thickness of the object based on a difference between a location of the identified point from each of the at least two object images. 5. The X-ray apparatus of claim 2,wherein the at least one processor controls the image acquirer to acquire first object image at first position and acquire second object image at second position by moving the image acquirer from the first position to the second position. 6. The X-ray apparatus of claim 1,wherein the at least one processor identifies a point from the at least one object image, obtains a detector distance based on a location-distance information stored in a memory, and obtains the thickness of the object based on the detector distance,wherein the location-distance information indicates a relationship between a location of the point and detector distance. 7. The X-ray apparatus of claim 1,wherein the display displays the thickness of the object. 8. A method of operating X-ray apparatus comprising:acquiring at least one object image by imaging an object;obtaining a thickness of the object based on the at least one object image;displaying an irradiation condition based on the thickness of the object;emitting X-rays to the object based on the irradiation condition;detecting the X-rays emitted from an X-ray generator;generating X-ray image data based on the detected X-rays; anddisplaying an X-ray image generated based on the X-ray image data. 9. A method of claim 8,wherein the acquiring at least one object image comprises acquiring at least two object images, andwherein the obtaining a thickness of the object comprises obtaining the thickness of the object by comparing the at least two object images. 10. A method of claim 9,wherein the obtaining the thickness of the object comprises identifying a point from each of the at least two object images and obtaining the thickness of the object by comparing the identified point of the each of the at least two object images. 11. A method of claim 10,wherein the obtaining the thickness of the object comprises obtaining the thickness of the object based on a difference between a location of the identified point from the each of the at least two object images. 12. A method of claim 9,wherein the acquiring at least one object image comprises acquiring first object image at first position and acquiring second object image at second position by moving an image acquirer from the first position to the second position. 13. A method of claim 8,wherein the obtaining the thickness of the object comprises identifying a point from the at least one object image, obtaining a detector distance based on a location-distance information stored in a memory, and obtaining the thickness of the object based on the detector distance,wherein the location-distance information indicates a relationship between a location of the point and detector distance. 14. A method of claim 8,wherein the displaying an irradiation condition comprises displaying the thickness of the object. 15. An X-ray apparatus comprising:an X-ray generator configured to emit X-rays to an object;an X-ray detector configured to detect the X-rays emitted from the X-ray generator and generate X-ray image data based on the detected X-rays;an image acquirer configured to acquire an object image by imaging an object; andat least one processor configured to obtain an object distance based on the object image and obtain a thickness of the object based on the object distance,wherein the object distance is a distance between an X-ray source and the object, and,wherein the at least one processor is further configured to determine, based on the thickness of the object, an irradiation condition, andwherein the irradiation condition comprises information related to an X-ray radiation amount and an intensity of the X-rays radiated from the X-ray source. 16. The X-ray apparatus of claim 15,wherein the X-ray apparatus further comprises an display configured to display at least one of the irradiation condition and the thickness of the object. 17. The X-ray apparatus of claim 15,wherein the at least one processor identifies a point from the object image and obtains a detector distance based on a location-distance information stored in a memory, and obtains the thickness of the object based on the detector distance,wherein the location-distance information indicates a relationship between a location of the point and detector distance. 18. A method for imaging X-ray comprising:acquiring an object image by imaging an object;obtaining an object distance based on the object imageobtaining a thickness of the object based on the object distance;determining an irradiation condition based on the thickness of the object;emitting X-rays to the object based on the irradiation condition;detecting the X-rays emitted from an X-ray generator; andgenerating X-ray image data based on the detected X-rays,wherein the object distance is a distance between an X-ray source and the object,wherein the irradiation condition comprises information related to an X-ray radiation amount and an intensity of the X-rays radiated from the X-ray source. 19. A method of claim 18, further comprising:displaying at least one of the irradiation condition and the thickness of the object. 20. A method of claim 18,wherein the obtaining the thickness of the object comprises identifying a point from the object image, obtaining a detector distance based on a location-distance information stored in a memory, and obtaining the thickness of the object based on the detector distance,wherein the location-distance information indicates a relationship between a location of the point and detector distance. |
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053923219 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also, in the following description, it is to be understood that such terms as "forward," "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 FIG. 1, there is shown a typical nuclear power reactor vessel, generally referred to as 10, for producing heat by a controlled fission of a fissionable material (not shown). The reactor vessel 10 is disposed in a reactor cavity 12 defined by a containment building 14. The reactor vessel 10 includes a cylindrical shaped bottom 20 open at its top end and having a plurality of inlet nozzles 30 and outlet nozzles 40 attached to the upper portion thereof (only one of each nozzle is shown). A flanged, hemispherical shaped reactor vessel closure head 50, which may be carbon steel, is mounted atop the bottom 20 and is sealingly attached to the open top end of the bottom 20 so that the closure head 50 sealingly caps the bottom 20. Capping the bottom 20 in this manner allows for suitable pressurization of the coolant (not shown) circulating through the bottom 20 as the reactor vessel 10 operates. The coolant may be borated demineralized water maintained at a relatively high pressure sure of approximately 2500 psia and a temperature of approximately 650 degrees Fahrenheit. A reactor core 55 is disposed in the interior of the reactor vessel 10. The reactor core 55 comprises a plurality of nuclear fuel assemblies 57 containing the fissionable material. The fuel assemblies 57 include a plurality of vertically extending fuel rods (not shown) structurally bound together. A plurality of vertically extending thimble tubes (not shown) are selectively positioned within each fuel assembly 57 for receiving a control rod which functions to control the fissionable process. The thimble tubes are structurally bound together by a spider assembly forming a movable control rod cluster (not shown in FIG. 1). A plurality of closure head openings 60 are formed through the top of closure head 50 for respectively receiving a plurality of generally tubular shaped control rod drive mechanism (CRDM) penetration tubes 70. Each penetration tube 70 is affixed to the closure head 50 by weldments 77. Each CRDM penetration tube 70 houses a control rod drive shaft (not shown) extending therethrough; the drive shaft engaging at least one movable control rod cluster. A control rod drive mechanism (CRDM) 90 is connected to the penetration tube 70 for axially moving a drive rod 80 and thus the control rod cluster connected thereto. The CRDM comprises a generally tubular pressure housing 100, which may be type 304 stainless steel. An electromagnetic coil stack assembly 110 is attached to the pressure housing 100 for electromagnetically and axially moving the drive rod 80 as the coil stack assembly 110 is electrically energized. When the coil stack assemblies 110 are energized, the control rods are fully withdrawn from the core 55. When the coil stack assemblies 110 are de-energized, the control rods are fully inserted into the core 55. A rod position indicator (RPI) 120 is attached to the coil stack assembly 110 for monitoring the position of the control rods, as is well known in the art. AS the reactor vessel 10 operates, the coolant enters the bottom 20 and circulates therethrough generally in the direction of the arrows. As the coolant circulates through the bottom 20, it also circulates over the fuel assemblies 57 for assisting in the fission process and for removing the heat produced by fission of the fissionable material contained in the fuel assemblies 57. The coil stack assemblies 110 axially move the control rod clusters in and out of fuel assemblies 57 to suitably control the fission process therein. The heat, generated by the fuel assemblies 57, is ultimately transferred to a turbine-generator set for producing electricity in a manner well known in the art. FIG. 2 illustrates a rod position indicator 120 of the linear voltage type with which the method and device of the present invention are particularly useful for compensating its output for variations due to magnetic coupling and temperature compensation. It should be understood that the present method is not restricted with application to the linear voltage transformer indicator but rather may be used with other types of rod position indicators, including the one described below which employs a single long winding, the resistance of which varies as a function of rod position. The indicator 120 includes a plurality of annular, layered-wound primary coils P which are electrically connected in series to form a primary winding, and a plurality of annular, layered-wound secondary coils S which are electrically connected in series to form a secondary winding. The coils P and S are stacked in tandem and are mounted on a coil form 130 having end plates 140 and 150. The coil form 130 includes a thin nonmagnetic stainless steel tubular substructure that is slid over a nonmagnetic rod travel housing 160 which encloses the drive rod 80. The secondary coils S are alternatively interleaved and inductively coupled with the primary coils P, with a secondary coil S located at the top of the coil stack and a primary coil located at the bottom of the coil stack. A sinusoidal current source 170 is connected to the primary for exciting a current in the primary winding which induces a voltage across terminals of the secondary winding. In one illustrative configuration, the coil form 130 is approximately 393.7 cm long with a combined primary and secondary active coil length of approximately 384.81 cm. The active coil includes layered-wound coils, half of which are primary coils P with the other half being secondary coils S alternatively interleaved as discussed above. Each coil is 13.72 cm in diameter and approximately 5.08 cm high. The primary coils P are essentially identical while the secondary coils S preferably have progressively more turns near the bottom of the detector. A space of approximately 7.62 cm exists between the lowest primary coil P and the bottom end plate 150 of the coil form 130. The drive rod 80 is made of a metal having magnetic properties. As may be appreciated, as the drive rod 80 moves up through its housing, the coupling between the primary and secondary windings increases which causes a proportional increase in the magnitude of the voltage induced in the secondary winding. The secondary voltage thus also corresponds to the position of the control rod as it is withdrawn from the core 55 of the reactor vessel 10. While in theory the relationship between the secondary voltage and rod position should be linear, in fact there are a number of variables which introduce error into the output of the secondary winding. One such error is electromagnetic linkage between the primary and secondary of one indicator 120 and the primary and secondary of a plurality of indicators 120 located nearby. The system of the present invention includes a method and device for compensating the rod position indication system for such linkage. FIG. 3 illustrates a circuit of the present invention for compensating for electromagnetic linkage. Two sinusoidal current sources 170a and 170b are respectively connected to the primaries of two adjacent indicators 120a and 120b for activating and inducing a voltage on its respective secondary. Although adjacent indicators are used in this embodiment, any two indicators 120 having electromagnetic linkage could be used. The current sources 170a and 170b are turned on and off by electronic circuitry located in a control room (not shown), each respectively via cabling 180 and 190. A termination 200 and 210 of the secondary of each detector is tied together via a cable 220 for connecting the two secondaries in series, and two differential amplifiers 230 and 240 are then connected in parallel via the unconnected terminations 250 and 260 of each secondary. With this parallel connection, each differential amplifier 230 and 240 produces an output representative of the difference of the two secondary outputs. It is instructive to note that the termination 250 is connected to the positive terminal of the differential amplifier 230 and to the negative terminal of the differential amplifier 240, and the termination 260 is, likewise, connected to terminals of different polarities on each differential amplifier 230 and 240. With this configuration, the output of each amplifier 230 and 240 produces a positive output during operation, as will be described later in detail. Although two differential amplifiers 230 and 240 are used in this embodiment, it can be appreciated by those skilled in the art that one differential amplifier may also be used in lieu of two differential amplifiers. However, with one differential amplifier, the output of the differential amplifier varies from positive to negative. To operate the circuit for magnetic coupling compensation of the indicator 120a, the current source 170a is turned on, and the other current source 170b is turned off. With the indicator 120a activated, the secondary output of the activated indicator 120a includes the actual voltage representative of the drive rod 80 position plus a voltage induced from electromagnetic fields of other indicators (not shown) located nearby, which is hereinafter referred to as noise. This noise will be substantially equally induced on both secondaries, and the de-activated indicator 120b will, therefore, only have a voltage representative sentative of the noise on its secondary. The voltage induced across the terminals of the differential amplifier 230, to which the secondaries are connected, is equal to the difference of the two secondary voltages, the magnetic coupling compensation voltage of the indicator 120a. In effect, the noise induced on one secondary cancels out the noise induced on the other secondary. The above may be represented by the following equation: EQU V.sub.compensated =V.sub.secondary 1 -V.sub.secondary 2 V.sub.compensated =(V.sub.actual position +V.sub.noise)-(V.sub.noise)V.sub.compensated =V.sub.actual position The polarity connection arrangement of the secondaries to the differential amplifier 230, as described above, ensures that the output of the differential amplifier 230 is a positive number. The differential amplifier 240 is not operated during the compensation of the indicator 120a. To operate the circuit for compensation of the indicator 120b, its current source 170b is turned on, and the other current source 170a is turned off. The compensated voltage is measured across the terminals of the differential amplifier 240 in the same manner as stated above; similarly, the differential amplifier 230 is inactive during the compensation of the indicator 120b. The above compensation steps may be repeated for all indicators by pairing two indicators together and repeating the above described process. FIG. 4 illustrates an alternative embodiment of the present invention and depicts a device for temperature compensating indicators 120a and 120b immediately subsequent to the magnetic coupling compensation. Through extensive evaluation, it has been found that a major source of system error is introduced by variation in the temperature of the drive rod 80 which is caused by changes in coolant temperature. The reason for this is that the permeability and resistivity of the drive rod 80 are temperature dependent so that as the temperature of the drive rod 80 changes, its permeability and resistivity also change which, of course, directly affects the coupling between the primary and secondary windings of the indicator. Obviously, either the secondary voltage of the indicator has to be recalibrated each time the temperature of the coolant (and hence of the drive rod) changes, or some form of compensation for the errors caused by temperature has to be made. A measurement which is directly responsive to the temperature of the drive rod 80 for purposes of temperature compensation of the secondary voltage of the indicator would thus be preferred to any indirect temperature measurement. This is accomplished in accordance with the embodiment of FIG. 4 for measuring the resistance of both secondaries. The description below will be further appreciated by noting that the resistance of both secondaries varies generally linearly from 50 to 80 ohms over the operating temperature (70 F. to 650 F.) of the reactor vessel (see FIG. 1). Therefore, there is a direct correlation between temperature and resistance of the secondaries. In this regard, two switches 270 and 280 are connected respectively to the two terminations 250 and 260 of each secondary for switching the device to the temperature compensation mode immediately after magnetic compensation. A negative terminal of a third differential amplifier 290 is connected to both switches 260 and 270, and a positive terminal of the third differential amplifier 290 is tied to the series connection between the secondaries forming a termination 300. A third switch 310 is attached between the termination 300 and the positive terminal, and is in the on position (indicated by the dashed line) only when temperature compensation takes place. During magnetic coupling compensation, the switch 310 is in the off position (indicated by the solid line) for eliminating any current flow to the third differential amplifier 290. A direct current (DC) source 320 is connected between leads 330 and 340 extending from the terminals of the differential amplifier 290 for providing direct current during temperature compensation. To temperature compensate the indicators 120a and 120b, all three switches 270, 280, and 310 are placed in the position indicated by the dashed lines, which temporarily terminates the magnetic coupling compensation. With this configuration, DC flows from the DC source 320, through both secondaries, and returns to the third differential amplifier 290. In effect, this measures the resistance of the secondaries. The third differential amplifier 290 obtains the results of the resistance and passes it along to process instrumentation for further processing. A system and method for using the resistance values for temperature compensation are disclosed in U.S. Pat. No. 4,714,926 which is assigned to the assignee of the present invention and is herein incorporated by reference. After temperature compensation, the switches 270, 280, and 310 are switched to the off position for continuing magnetic coupling compensation. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described merely a preferred or exemplary embodiment thereof. |
claims | 1. A microirradiator, comprising:a non-radioactive conducting electrode;an insulating sheath disposed about at least a portion of the non-radioactive conducting electrode along a longitudinal axis of the non-radioactive conducting electrode; anda radioactive source in electrical communication with the non-radioactive conducting electrode, wherein the radioactive source is positioned at a terminus of a first longitudinal end of the non-radioactive conducting electrode via electroplating;wherein the insulating sheath is disposed about at least a portion of the radioactive source along a longitudinal axis of the radioactive source. 2. The microirradiator of claim 1, wherein a terminus of the insulating sheath is level with a terminus of the radioactive source. 3. The microirradiator of claim 1, wherein a terminus of the insulating sheath extends beyond a terminus of the radioactive source to define a channel within the insulating sheath. 4. The microirradiator of claim 1, further comprising a contact electrode in electrical communication with the non-radioactive conducting electrode. 5. The microirradiator of claim 4, wherein the contact electrode is electrically coupled to the non-radioactive conducting electrode within the insulating sheath. 6. The microirradiator of claim 1, wherein the average thickness of the electroplated radioactive source along the longitudinal axis is less than or equal to about 50 micrometers. 7. The microirradiator of claim 1, wherein the microirradiator produces an absolute radiation of less than or equal to about 1000 Becquerels and a radiation flux density of greater than or equal to about 104 Becquerels per square centimeter. 8. The microirradiator of claim 1, wherein the non-radioactive conducting electrode is an inert metal, the insulating sheath is a glass capillary tube, and the radioactive source is an elemental radioisotope. 9. The microirradiator of claim 1, wherein a target of radiation has an average longest cross-sectional dimension of less than or equal to about 30 micrometers. 10. A microirradiator, comprising:a non-radioactive conducting electrode;an insulating sheath disposed about at least a portion of the non-radioactive conducting electrode along a longitudinal axis of the non-radioactive conducting electrode, wherein a terminus of a first longitudinal end of the non-radioactive conducting electrode extends beyond the insulating sheath to define a probe; anda radioactive source in electrical communication with the non-radioactive conducting electrode, wherein the radioactive source is electroplated on the probe. 11. The microirradiator of claim 10, further comprising a contact electrode in electrical communication with the non-radioactive conducting electrode. 12. The microirradiator of claim 11, wherein the contact electrode is electrically coupled to the non-radioactive conducting electrode within the insulating sheath. 13. The microirradiator of claim 10, wherein the average thickness of the electroplated radioactive source on the probe is less than or equal to about 50 micrometers. 14. The microirradiator of claim 10, wherein the microirradiator produces an absolute radiation of less than or equal to about 1000 Becquerels and a radiation flux density of greater than or equal to about 104 Becquerels per square centimeter. 15. The microirradiator of claim 10, wherein the non-radioactive conducting electrode is an inert metal, the insulating sheath is a glass capillary tube, and the radioactive source is an elemental radioisotope. 16. The microirradiator of claim 10, wherein the microirradiator is configured to be inserted into a target of radiation. 17. The microirradiator of claim 16, wherein the target of radiation has an average longest cross-sectional dimension of less than or equal to about 30 micrometers. 18. A method for making a microirradiator, the method comprising:disposing an insulating sheath about at least a portion of a non-radioactive conducting electrode; andelectroplating a radioactive source at or about a terminus of a first longitudinal end of the non-radioactive conducting electrode. 19. The method for making a microirradiator of claim 18, wherein the disposing comprises inserting the non-radioactive conducting electrode into the insulating sheath. 20. The method for making a microirradiator of claim 18, further comprising electrically coupling a contact electrode to the non-radioactive conducting electrode. |
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claims | 1. A method for counting neutrons, comprising:collecting neutrons in a multi-detector array;generating a plurality of digital words by feeding pulses from said multidetector array in parallel to a plurality of separate inputs, wherein each input of said plurality of inputs is tied to an individual bit in a digital word of the plurality of digital words;reading each said digital word at regular intervals to produce a plurality of read and digitized words, wherein all bits are read simultaneously to minimize latency; andstoring each read and digitized word of said plurality of read and digitized words, wherein each read and digitized word is stored in a number of storage locations for subsequent processing, thereby reducing front-end pulse pileup. 2. A method of event counting, comprising:collecting neutron data as input signals in parallel input circuits;counting the collected neutron data in one or more summing intervals created by a clock;controlling a minimum summing interval for counting said data;summing said data in said summing interval to produce a data sum;storing said sum in multiple arrays; andbuilding data structures by constructing summed sections from each said array of said multiple arrays. 3. The method of claim 2, wherein said input signals are edge triggered. 4. The method of claim 2, wherein said minimum summing interval is controlled with a clock. 5. The method of claim 2, wherein said data structures comprise data selected from the group consisting of multiple superset interval sizes, interval sizing after an external trigger, event totals in a fixed interval, event totals in a fixed interval after an external trigger, time intervals between events, time intervals between events after an external trigger, and arrival time of certain clump sizes after an external trigger. 6. The method of claim 2, wherein said data structures comprise multiple superset interval sizes, interval sizing after an external trigger, event totals in a fixed interval, event totals in a fixed interval after an external trigger, time intervals between events, time intervals between events after an external trigger, and arrival time of certain clump sizes after an external trigger. 7. A method of neutron event counting, comprising:inputting edge triggered input signals into parallel input circuits observing each neutron event to be counted;counting each neutron event in one or more summing intervals created by a clock;controlling a minimum summing interval for counting each neutron event, for use by a parallel set of means for adding, wherein each input circuit of said input circuits is operatively connected to multiple independent means for adding of said parallel set;reading a sum in each said means for adding during said minimum summing interval to produce a sum read;zeroing each said means for adding at the end of the minimum summing interval;storing said sum read into multiple arrays; andconstructing summed sections from said array to build data structures comprising multiple superset interval sizes, interval sizing after an external trigger, event totals in a fixed interval, event totals in a fixed interval after an external trigger, time intervals between events, time intervals between events after an external trigger, and arrival time of certain clump sizes after an external trigger. |
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053234405 | summary | FIELD OF THE INVENTION AND RELATED ART This invention relates to an exposure apparatus for the manufacture of semiconductor devices such as ICs, LSIs, etc. More particularly, the invention is concerned with an X-ray exposure apparatus which uses radiation light as exposure light (printing light). In another aspect, the invention is concerned with a mask which is usable in such an X-ray exposure apparatus. As for the exposure light source in the exposure apparatus, in many cases a light source which produces visible light or ultraviolet light is used. In the exposure process using such a light source, the possibility of damaging a mask is very small. However, in the exposure process which uses synchrotron radiation light as a light source, having recently been proposed in an attempt to allow printing of very fine patterns, it has been reported that there is a possibility of a change in the characteristics of a mask ("Radiation Damage Effects in Boron Nitride Mask Membranes Subjected to X-ray Exposures" by W. A. Johnson, R. A. Levy, D. J. Resnick, T. E. Sanders, A. W. Yanof, H. Betz, H. Hunber and H. Oertel, "Journal of Vacuum Science & Technology", B. Vol. 5, No. 1, Jan/Feb 1987). This generates a necessity of replacing an over-exposed mask and, in order to properly determine the timing of replacement, it is necessary to accurately detect the dose of each mask. However, conventional exposure apparatuses are not equipped with such a function. SUMMARY OF THE INVENTION Since conventional exposure apparatuses are not equipped with the function of detecting the dose of each mask, there is a possibility that during exposure the dose of the mask goes beyond the limit of an allowable dose, resulting in failure of correct exposure. Since the manufacture of ICs, LSIs, etc. based on radiation light involves several tens of repetitions of an exposure process and the exposure time itself should be controlled very strictly, if correct exposure ends in failure, all the preceding exposure processes are wasted. This is a heavy loss. It is accordingly a primary object of the present invention to provide an exposure apparatus with which the dose of each mask can be detected accurately. It is another object of the present invention to provide a mask suitably usable in such an exposure apparatus. In accordance with an aspect of the present invention, an X-ray exposure apparatus which uses radiation light as exposure light includes display means; detecting means for detecting in each exposure the amount of exposure absorbed by a mask during the exposure; storing means for memorizing an accumulated dose of the mask; and control means for causing said display means to display a dose of the mask, wherein the does to be displayed corresponds to the sum of the accumulated dose memorized in said storing means and the amount of exposure detected by said detecting means. Each mask may be equipped with such a storing means. The control means may be arranged to compare the sum of the accumulated dose and the detected exposure amount, with a predetermined allowable dose and to cause the display means to display the result of the comparison. Mask replacing means may be provided such that, when the control means discriminates an excess of the sum of the accumulated dose and the detected exposure amount beyond the predetermined allowable dose, the mask replacing means operates to replace the mask by another. Since in an exposure of a mask, the exposure amount (dose) of the mask in that exposure is detected by the detecting means and the exposure amount converted into an accumulated dose memorized in the storing means is displayed in the display means, it is possible to obtain an accurate dose of each mask. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. |
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051986809 | abstract | A method for manufacturing a single focus collimator in a high precision without increasing a cost for manufacturing. In this method, grooves are on a bulk block member first, and a metallic material having sufficient .gamma. ray shielding property such as lead is casted into the grooves formed on the bulk block member, and then the bulk block member with the metallic material casted into the grooves is immersed into a solvent capable of dissolving the bulk block member but not the metallic material, such that a collimator body formed by the metallic material in a shape of the grooves is obtained as the bulk block member is dissolved by the solvent. The sensitivity of the single focus collimator can be made substantially uniform over the entire effective view field by forming the grooves with such intervals that holes formed on the collimator body have larger size toward a center of the collimator body. |
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claims | 1. A calibrated radioactive source, comprising a flexible sheath of a container material, and a labeled material labeled by at least one radionuclide, wherein:the labeled material is contained in the flexible sheath;at least part of the container material is transparent to radiation emitted by the at least one radionuclide; andat least part of the labeled material is a self-hardening polymer chemically inert relative to the container material. 2. The calibrated radioactive source according to claim 1, wherein the flexible sheath is a hollow cylinder of essentially constant diameter. 3. The calibrated radioactive source according to claim 1, wherein the container material is a polymer material. 4. The calibrated radioactive source according to claim 3, wherein the polymer material is a silicone elastomer. 5. The calibrated radioactive source according to claim 1, wherein the self-hardening polymer of the labelled material is an epoxy type resin. 6. The calibrated radioactive source according to claim 5, wherein the self-hardening polymer comprises 53±1% of epoxy resin, 32±1% of hardener, and 15±1% of liquefier. 7. The calibrated radioactive source according to claim 1, wherein the labelled material comprises cobalt 57. 8. An assembly comprising a brick of a tissue-equivalent phantom and at least one calibrated source according to claim 1, wherein:the brick is a polymer block, one face of which comprises a hole intended to receive the calibrated radioactive source;the calibrated radioactive source has at least one curvature along its length, whereby a distance between a highest part and a lowest part of the calibrated radioactive source along its width is equal to a largest internal diameter of the hole; andthe calibrated radioactive source is in contact with a wall of the hole in at least two contact points and exerts a force on the wall on level with the at least two contact points. 9. An assembly according to claim 8, wherein the hole is a cylindrical and rectilinear hole of essentially constant diameter. 10. A method for placing a calibrated radioactive source according to claim 1 in a hole on one face of a block, wherein the calibrated radioactive source has at least one curvature along its length, the method comprising:deforming the calibrated radioactive source until a distance between a highest part and a lowest part of the calibrated radioactive source along its width is less than a smallest diameter of the hole of the block;inserting the calibrated radioactive source into the hole; andblocking the calibrated radioactive source in the hole by returning the calibrated radioactive source to its non-deformed state, wherein the distance between the highest part and the lowest part of the source along its width in a non-deformed state is greater than the smallest diameter of the hole. 11. The method for placing a calibrated radioactive source in a hole of one face of a block according to claim 10, wherein the block is a brick of a tissue-equivalent phantom of polymer. |
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claims | 1. A method, comprising:loading a patient onto a treatment couch having a tabletop and a lower-torso assembly;adjusting the patient along a longitudinal direction relative to a shoulder line of the tabletop using the lower-torso assembly while the lower-torso assembly remains outside a radiolucent region of the tabletop; andconverting the lower-torso assembly between a bolster seat and a flat tabletop. 2. The method of claim 1, wherein adjusting the patient along the longitudinal direction comprises manually adjusting the position of the lower-torso assembly to adjust the patient along the longitudinal direction relative to the shoulder line. 3. The method of claim 1, wherein adjusting the patient comprises adjusting an upper half of the patient relative to the shoulder line of the tabletop. 4. The method of claim 1, wherein adjusting the patient comprises positioning the shoulders of the patient at the shoulder line regardless of the height of the patient. 5. The method of claim 4, wherein positioning the shoulders comprises:moving the lower-torso assembly in a translational direction that is substantially perpendicular to the shoulder line; andlocking the lower-torso assembly to the tabletop when the shoulders of the patient are at the shoulder line. 6. The method of claim 1, wherein converting the lower-torso assembly comprises:configuring the lower-torso assembly to be substantially flat with respect to a plane of the top surface of the tabletop; andconfiguring an upper section of the lower-torso assembly to be at an angle with respect to the plane of the top surface of the tabletop. 7. The method of claim 1, wherein converting the lower-torso assembly comprises:moving a first slide bar, coupled to a first hinge, along a slot of the tabletop; andmoving a second slide bar, coupled to a second hinge, along a slot of the first slide bar, wherein moving the first and second slide bars comprises moving a link member, coupled to the first and second hinges, between a flat configuration and a seat configuration. 8. The method of claim 7, wherein converting the lower-torso assembly further comprises locking relative positions of the first slide bar and the second slide bar, and wherein the relative positions configure the lower-torso assembly to be in at least one of a seat configuration, a flat configuration, or an intermediate configuration between the seat configuration and the flat configuration. 9. The method of claim 7, wherein converting the lower-torso assembly further comprises:moving hinge centers of the first and second hinges towards one another to form the bolster seat with the link member; andmoving hinge centers of the first and second hinges away from one another to configure the link member to be substantially flat with respect to a top surface of the tabletop to form the flat tabletop. 10. The method of claim 9, wherein converting the lower-torso assembly further comprises locking the positions of the first and second hinges, and wherein the relative positions configure the lower-torso assembly to be in at least one of a seat configuration, a flat configuration, or an intermediate configuration between the seat configuration and the flat configuration. 11. The method of claim 1, wherein the lower-torso assembly is converted before loading the patient onto the treatment couch. 12. The method of claim 1, wherein the lower-torso assembly is converted after loading the patient onto the treatment couch. 13. A method, comprising:loading a patient onto a treatment couch having a tabletop and a lower-torso assembly;adjusting the patient along a longitudinal direction relative to a shoulder line of the tabletop using the lower-torso assembly while the lower-torso assembly remains outside a radiolucent region of the tabletop; andconverting the lower-torso assembly between a seat configuration and a flat configuration, wherein a top surface of the lower-torso assembly is configured to be flat along the substantially same plane as a top surface of the tabletop in the flat configuration, and wherein a top surface of an upper section of the lower-torso assembly is positioned to be at an angle with respect to the plane of the top surface of the tabletop in the seat configuration. 14. An apparatus, comprising:a tabletop having a radiolucent region; anda lower-torso assembly coupled to the tabletop, wherein the lower-torso assembly comprises:a first slide member coupled to a slot of the tabletop;a second slide member coupled to a slot of the first slide member; anda link member coupled to the first slide member and the second slide member, wherein the first slide member, second slide member, and link member are disposed outside the radiolucent region of the tabletop. 15. The apparatus of claim 14, further comprising a locking mechanism coupled to the first slide member and the tabletop, wherein the first slide member is configured to slide along the slot of the tabletop when the first locking mechanism is disengaged to adjust a patient along a longitudinal direction relative to a shoulder line of the tabletop while the lower-torso assembly remains outside the radiolucent region of the tabletop. 16. The apparatus of claim 14, wherein the link member comprises an upper section and a lower section, wherein top surfaces of the upper and lower sections of the link member are configured to be flat with respect to a top surface of the tabletop in a first configuration, and wherein the top surface of the upper section of the link member is configured to be at an angle with respect to the top surface of the tabletop in a second configuration. 17. The apparatus of claim 14, wherein the first slide member is a first slide bar, wherein the second slide member is a second slide bar, and wherein the apparatus further comprises:a first hinge coupled to the first slider bar; anda second hinge coupled to the second slide bar; wherein the link member is coupled to the first hinge and the second hinge. 18. The apparatus of claim 14, further comprising a first locking mechanism coupled to the first slide bar, wherein the first locking mechanism is configured to lock relative positions of the first slide bar and the second slide bar. 19. The apparatus of claim 18, wherein the relative positions comprises at least one of a seat configuration, a flat configuration, or an intermediate configuration between the seat configuration and the flat configuration. 20. The apparatus of claim 19, wherein at the flat configuration the first slide bar and the second slide bar are locked with their hinge centers at a distance substantially equal to the length of the link member, and wherein at the seat configuration the first and second slide bars are locked with their hinge centers at a distance less than the length of the link member. 21. The apparatus of claim 20, wherein the first locking mechanism is configured to allow the first slide bar and the second slide bar to slide the hinge centers of the first and second hinges relative to one another when the first locking mechanism is disengaged, and to prevent the first slide bar and the second slide bar to slide the hinge centers of the first and second hinges relative to one another when the first locking mechanism is engaged. 22. The apparatus of claim 18, wherein the first locking mechanism is a pin. 23. The apparatus of claim 22, wherein the pin is a spring pin. 24. The apparatus of claim 18, further comprising a second locking mechanism coupled to the first slide bar and the tabletop, wherein the second locking mechanism is configured to lock the relative position of the first slide bar and the tabletop, and wherein the lower-torso assembly is configured to move along the longitudinal direction of the tabletop when the second locking mechanism is disengaged from the tabletop. 25. The apparatus of claim 24, wherein the patient load is carried in shear by the second locking mechanism on the first slide bar and in moment by the boundaries of the slot of the tabletop. 26. The apparatus of claim 24, wherein the tabletop comprises a plurality of height positions at which the second locking mechanism locks the first slide member to the tabletop. 27. The apparatus of claim 26, wherein the plurality of height positions comprise at least a first height position and a second height position, wherein the first height position is configured to position a female having the one percentile female height to the shoulder line of the tabletop, and wherein the second height position is configured to position a male having the 99th percentile male height to the shoulder line of the tabletop. 28. The apparatus of claim 24, wherein the second locking mechanism is a spring pin. 29. The apparatus of claim 28, wherein the pin is a spring pin. 30. The apparatus of claim 17, wherein the link member comprises one or more rigid links. 31. The apparatus of claim 17, wherein the link member comprises:a first rigid link coupled to the first hinge; anda second rigid link coupled to the second hinge and to the first rigid link using a third hinge, wherein the first and second rigid links are configured to rotate relative to each other while being fixed in the other direction at the first and second hinges, respectively. 32. The apparatus of claim 17, wherein the link member comprises:a first rigid link coupled to the first hinge;a second rigid link coupled to the first rigid link using a third hinge; anda third rigid link coupled to the second hinge and the second rigid link using a fourth hinge, wherein the first, second, and third rigid links are configured to rotate relative to each other. 33. The apparatus of claim 32, wherein the rotation of the first, second, and third rigid links are restricted. 34. The apparatus of claim 14, wherein the first slide member is a seat positioning bar, wherein the second slide member is a bolster bar, wherein the link member comprises a seat pan and a lower-leg support member, and wherein the apparatus further comprises:a first hinge coupled to the seat positioning bar and the seat pan;a second hinge coupled to the bolster bar and the lower-leg support member; anda third hinge coupled to the seat pan and the lower-leg support member. 35. The apparatus of claim 34, further comprising a foot extension coupled to the lower-leg support member, wherein the foot extension is configured to provide support beyond the surface area of the lower-leg support member. 36. The apparatus of claim 34, wherein the seat pan comprises one or more patient handles. 37. The apparatus of claim 34, wherein the radiolucent region of the tabletop is substantially from a head end of the tabletop to substantially the first hinge. 38. The apparatus of claim 34, wherein the radiolucent region of the tabletop is substantially from a head end of the tabletop to substantially the seat pan. 39. The apparatus of claim 34, wherein all components of the lower-torso assembly are disposed outside the radiolucent region of the tabletop. 40. The apparatus of claim 14, wherein the lower-torso assembly is metal, and wherein substantially all of the metal of the lower-torso assembly is outside of the radiolucent region of the tabletop. 41. The apparatus of claim 14, when the lower-torso assembly is configured to be a bolster seat on the tabletop in a first configuration, and wherein the bolster seat is configured to be positioned at a plurality of positions along a longitudinal direction relative to a shoulder line of the tabletop when in the first configuration. 42. The apparatus of claim 41, wherein the bolster seat is configured to have a seat pan of approximately 120 degrees between a top surface of the seat pan and a top surface of the tabletop. 43. The apparatus of claim 41, wherein the bolster seat is configured to have a seat pan of approximately 135 degrees between a top surface of the seat pan and a top surface of the tabletop. 44. The apparatus of claim 14, when the lower-torso assembly is configured to be a flat tabletop on the tabletop in a second configuration. 45. The apparatus of claim 14, wherein the tabletop and the lower-torso assembly are configured to provide a support assembly that has a flat surface upon which the patient is disposed in a first configuration, and wherein the tabletop and the lower-torso assembly are configured to provide a support assembly having a seat to support a lower-torso area of the patient in a second configuration. 46. The apparatus of claim 14, wherein the first slide member is an upper-seat bracket, wherein the second slide member is a lower-seat bracket, and wherein the upper-seat bracket and the lower-seat bracket are configured to move relative to one another in along the longitudinal direction relative to the shoulder line of the tabletop when a first locking mechanism is disengaged, and to move together along the longitudinal direction relative to the shoulder line of the tabletop when a second locking mechanism is disengaged. 47. The apparatus of claim 46, wherein the link section comprises:a seat pan coupled to the upper-seat bracket by a first hinge; anda lower-leg support coupled to the lower-seat bracket by a second hinge, and wherein the seat pan and the lower-leg support are coupled together by a third hinge. 48. The apparatus of claim 47, wherein the seat pan comprises one or more patient handles. 49. The apparatus of claim 47, wherein the lower-torso assembly comprises a foot extension coupled to the lower-leg support, and wherein the foot extension is configured to support a lower portion of the legs of the patient when the legs of the patient go beyond the lower-leg support. 50. The apparatus of claim 46, wherein the first locking mechanism is a seat creation handle, wherein the seat creation handle is configured to allow the lower-torso assembly to convert between a bolster seat on the tabletop and a flat tabletop when disengaged, wherein the second locking mechanism is a seat motion handle, and wherein the seat motion handle is configured to allow the lower-torso assembly to move along the longitudinal direction relative to the shoulder line of the tabletop when disengaged. 51. An apparatus, comprising:a tabletop; andmeans for positioning patients of various heights at a shoulder line on the tabletop while the means for positioning patients remain outside a radiolucent region of the tabletop, and wherein the radiolucent region is above the lowest point of the rear pelvic area of the human body, wherein the means for positioning patients comprises:means for moving a patient in the longitudinal direction relative to the shoulder line of the tabletop, wherein the means for moving the patient remain outside the radiolucent region of the tabletop; andmeans for converting the positioning means between a flat configuration and a bolster seat configuration. 52. The apparatus of claim 51, wherein the means for positioning patients increases an available workspace of a radiation source of a radiation treatment system. 53. The apparatus of claim 51, wherein the means for positioning patients remain outside an imaging zone of the patient for the patients of various heights. 54. The apparatus of claim 51, wherein the means for positioning patients comprises means for not entering the radiolucent region of the tabletop. 55. The apparatus of claim 51, wherein the means for positioning patients comprises means for not obstructing an imaging zone of the patient for the patients of various heights, and wherein the imaging zone is above at least the highest point of the leg posterior to the hip of the human body. 56. The apparatus of claim 51, wherein the means for positioning patients comprises means for supporting a patient load up to approximately 500 pounds (lbs). 57. A system, comprising:a radiation treatment system comprising a radiation source; anda treatment couch upon which a patient is disposed, wherein the treatment couch comprises:a tabletop having a radiolucent region; anda lower-torso assembly coupled to the tabletop, wherein the lower-torso assembly comprises:a first slide member coupled to a slot of the tabletop;a second slide member coupled to a slot of the first slide member; anda link member coupled to the first slide member and the second slide member, wherein the slots of the tabletop and the slot of the first slide member are disposed outside the radiolucent region of the tabletop. 58. The system of claim 57, wherein the lower-torso assembly further comprises a locking mechanism coupled to the first slide member and the tabletop, wherein the first slide member is configured to slide along the slot of the tabletop when the first locking mechanism is disengaged to adjust a patient along a longitudinal direction relative to a shoulder line of the tabletop while the lower-torso assembly remains outside the radiolucent region of the tabletop. 59. The system of claim 57, wherein the radiation treatment system is at least one of a gantry-based radiation treatment system or a robot-based linear accelerator system. 60. The system of claim 57, further comprising a patient positioning system to position the patient with respect to the radiation source of the radiation treatment system, wherein the patient positioning system comprises a robotic arm coupled to the treatment couch, and wherein the robotic arm is configured to move the treatment couch along one or more degrees of freedom. 61. The system of claim 60, wherein the robotic arm is configured to move the treatment couch along at least three degrees of freedom. 62. The system of claim 60, wherein the robotic arm is configured to move the treatment couch along five degrees of freedom. 63. A system, comprising:a computed tomography (CT) scanner; anda treatment couch upon which a patient is disposed, wherein the treatment couch comprises:a tabletop having a radiolucent region; anda lower-torso assembly coupled to the tabletop, wherein the lower-torso assembly comprises:a first slide member coupled to a slot of the tabletop;a second slide member coupled to a slot of the first slide member; anda link member coupled to the first slide member and the second slide member, wherein the slots of the tabletop and the slot of the first slide member are disposed outside the radiolucent region of the tabletop. 64. The system of claim 63, wherein the lower-torso assembly further comprises a locking mechanism coupled to the first slide member and the tabletop, wherein the first slide member is configured to slide along the slot of the tabletop when the first locking mechanism is disengaged to adjust a patient along a longitudinal direction relative to a shoulder line of the tabletop while the lower-torso assembly remains outside the radiolucent region of the tabletop. 65. The system of claim 63, further comprising a patient positioning system to position the patient with respect to the CT scanner, wherein the patient positioning system comprises a robotic arm coupled to the treatment couch, and wherein the robotic arm is configured to move the treatment couch along one or more degrees of freedom. 66. The system of claim 65, wherein the robotic arm is configured to move the treatment couch along at least three degrees of freedom. 67. The system of claim 65, wherein the robotic arm is configured to move the treatment couch along five degrees of freedom. 68. An apparatus, comprising:a treatment couch, to load a patient thereon, having a tabletop and a lower-torso assembly, wherein the lower-torso assembly is configured to:adjust the patient along a longitudinal direction relative to a shoulder line of the tabletop while the lower-torso assembly remains outside a radiolucent region of the tabletop; andconvert the lower-torso assembly between a bolster seat and a flat tabletop. |
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052971767 | summary | BACKGROUND OF THE INVENTION This invention relates to replacement fuel assembly alignment pins for installation in the upper core plate of a nuclear reactor, working exclusively from the bottom side of the upper core plate. The invention provides a replacement pin structure and method for mounting the replacement pin from below the core plate, which captures the remnants of the existing fuel alignment pin and nut, thus eliminating the risk of internal damage as well as the cost associated with accessing the top of the upper core plate when replacing alignment pins. Pressurized water nuclear reactors have fuel assemblies supported in the reactor core between upper and lower core plates. The lower core plate is supported by a core barrel, which surrounds the reactor core between the upper and lower core plates. A number of fuel assemblies reside between the upper and lower core plates. Each fuel assembly has an upper end structure known as the top nozzle, and a lower end structure or bottom nozzle. The upper nozzle comprises an upper hold-down plate and a lower adapter plate, rigidly coupled by sidewalls forming a top enclosure on the fuel assembly. The upper and lower nozzles are arranged parallel to one another and parallel to intermediate grid plates, the grid plates having openings through which a plurality of spaced parallel fuel rods extend between the nozzles. Extending between the nozzles and through the grid plates, and perpendicular thereto, are guide tubes or thimbles which support movable control rods. The nozzles, thimbles and grid plates form an integral fuel assembly unit for carrying, for example, about three hundred fuel rods as a unitary structure, and a plurality of such assemblies are placed in close proximity between the upper and lower core plates of the reactor core. The control rods are moved axially into the fuel assembly to damp the nuclear flux, and out of the fuel assembly to increase nuclear flux, namely by either absorbing or allowing passage of the products of nuclear fission passing between the fuel rods. In this manner, it is possible to control the generation of heat in the reactor core, which is submerged in a heat transfer fluid, i.e., pressurized water. The control rods are controllably lowered vertically through the upper core plate into thimbles of the fuel assemblies. Therefore, it is important that the fuel assemblies be accurately aligned relative to the core plates in order to allow accurate and free passage of the control rods in the fuel assembly thimbles. The control rods are mounted relative to the bottom flange of a guide structure which includes a guide tube support pin engaging in the upper surface of the core plate and thus referencing the control rods to the core plate. For likewise referencing the fuel assembly to the core plate, the core plate has protruding alignment pins oriented parallel to the axes of the fuel rods, control rods and thimbles. The alignment pins attached to the core plates mate with openings in the nozzles of the fuel assemblies, thereby fixing the relative positions of the fuel assembly thimbles and the control rods. The fuel assemblies must be serviced periodically, for example for replacement of the fuel rods, and can be removed from engagement with the core plates for this purpose, and thereafter replaced. The alignment pins are sometimes damaged in such operations. The failure of particular alignment pins can adversely affect the ability to control the reactor core, due to resulting misalignment of the control rods and the thimbles for receiving them. Therefore, the alignment pins are routinely checked, and sometimes replaced. The attachment of the alignment pins to the core plate is also necessarily durable and rigid, to keep the alignment pins accurately fixed in position as well as to minimize damage. In U.S. Pat. No. 4,820,479--Hornak et al, an alignment pin is disclosed with a conical nose for engaging a fuel assembly, a shoulder resting against the lower surface of the upper core plate, and a shaft protruding through the upper core plate. The shaft of the alignment pin is threaded to receive a nut, for clamping the alignment pin to the upper core plate between the shoulder and the nut. The shaft also has a transverse opening which resides above the clamping nut when tightened down. A deformable locking cup is placed on the shaft of the alignment pin over the clamping nut, engaged to the clamping nut preferably by welding, and crimped to engage in the transverse opening in the shaft of the alignment pin. The locking cup thus cannot turn relative to the shaft and likewise prevents rotation of the clamping nut. It is also known in such an arrangement to weld the clamping nut directly to the top surface of the upper core plate and thereby prevent the clamping nut from loosening. The Hornak alignment pin mounting is considered advantageous because it is more readily replaceable. To remove an alignment pin, the deformable locking cup is forced out of engagement with the transverse opening in the shaft of the pin, and the clamping nut can be loosened. However, this requires access to the top surface of the upper core plate to loosen and remove the clamping nut, and access to the bottom surface of the upper core plate to hold and/or retrieve the alignment pin. Other forms of clamping nuts on the top surface of the upper core plate are also known. The clamping nut can be disposed in a counterbore in the upper core plate, fixed to the core plate by various forms of locking pins, screws or keys, etc. A more permanent and secure coupling of the clamping nut to the upper core plate is desirable to obtain a durable mounting for the alignment pin. A more durable mounting is of course more difficult to remove than a less durable one, and in either case, removing the mounting requires access to the top of the upper core plate. Alignment pins are replaced using a remotely controlled and/or at least partly robotic techniques, monitored by video, to avoid exposure of plant personnel to the radioactive core elements. A certain amount of space is needed to accommodate the tools and viewers needed to conduct pin replacement operations. Typically, part of the upper internals of the reactor, in the region over the upper core plate, must be removed to gain access to the clamping nuts of the alignment pins. Removal of such structures, operations in this region, and replacement of the structures, are time consuming and may cause damage to the structures in the region. For all these reasons, it is desirable to enable a pin replacement technique which is conducted entirely from below the upper core plate. SUMMARY OF THE INVENTION It is an object of the invention to provide an alignment pin replacement structure which is secure and relatively permanent, and which can be installed working exclusively from the underside of the upper core plate. It is another object of the invention to provide a replacement alignment pin design which captures an existing fuel alignment pin clamping nut structure for obtaining a secure engagement with the core plate. These and other objects of the invention are accomplished by a replacing the guide pin aligning a top nozzle of a nuclear fuel assembly to an upper core plate of a nuclear reactor, with the replacement guide pin of the invention, working exclusively from below the upper core plate. The replacement guide pin has a shaft portion engaged with the upper core plate and the clamping nut which held the original guide pin, by threadable connection and/or by an expansion fitting. A shoulder on the pin bears against a lower surface of the upper core plate, and a nose of the pin is received in the upper nozzle of the fuel assembly. A preferred expansion fitting has a bushing with ridges on its outer surface and a conical inside surface, and is inserted into the bored out original guide pin shaft. A threaded conical plug is pulled axially with rotation of the replacement pin to expand the bushing. The ridges form a series of axially spaced concentric rings and grooves, that rigidly lock the replacement pin between the shoulder and the clamping nut. |
description | The present application claims priority from Japanese patent applications JP2008-139473 filed on May 28, 2008, and, JP2009-103490 filed on Apr. 22, 2009, the content of which is hereby incorporated by reference into this application. 1. Field of the Invention The present invention relates to a charged particle beam apparatus, such as an electron microscope, an electron beam writer, a focused ion beam system, etc. and in particular, to an evacuating technology that can achieve extremely high degree of vacuum of an electron gun or an ion gun. 2. Description of the Related Art A scanning electron microscope (SEM) or an electron beam writer (EB) according to the related art accelerates electron beams emitted from an electron gun including a cold cathode field emission type electron source or a thermal field emitter electron source, which are changed into fine electron beams using an electron lens, and scans them as primary electron beams on a sample by using a scanning deflector. In the case of SEM, images are obtained by detecting secondary electrons or reflected electrons and in the case of EB, patterns previously registered on a resist film that is applied on the sample are written. As a material for the field emission type electron source, tungsten has been used in the case of a multi-purpose SEM. Further, in the case of the EB, LaB6 may be used. The cold cathode field emission type electron gun is a field emission type electron gun that uses a needle-shaped tungsten tip at normal temperature. The electrons are emitted by a tunnel effect that is generated by applying high field to a point of the tip. Brightness is ˜108, which is better than that of the thermal field (emission) type. An energy band of the emission electron is narrower than that of the thermal field type (˜0.4 eV) and high energy resolution can be obtained. A smaller probe compared with that of the thermal field type can be manufactured, but the total amount of emission current is smaller than that of the thermal field type. Meanwhile, the thermal field type (generally referred to as Schottky electron gun) is an electron gun according to a scheme that heats the needle-shaped tungsten tip under field and emits electrons. The thermal field emitter electron gun heats a tip to ˜1800 K and emits electrons using a Schottky effect, wherein the tungsten tip is coated with zirconia and a potential barrier of the tip is lowered (˜2.7 eV). The energy band of the emission electron is 0.7 eV, which is slightly wider than that of the cold cathode type, but since the tip is heated all time, stable emission current (variation ratio ˜1%) can be obtained without absorbing residual gases on a surface of the tip. Brightness is about 107 to 108. In order to emit good electron beams from the electron source over a long period of time, there is a need to keep the surrounding area of the electron source at high vacuum (10−8 to 10−9 Pa). To this end, the related art has used a method that forcibly evacuates the surrounding area of the electron gun by an ion pump. Further, there is a charged particle beam apparatus that has a non-evaporable getter pump therein to achieve a higher degree of vacuum (For example, see U.S. Pat. No. 4,833,362 and Japanese Patent Application Laid-Open No. 2006-294481). This is particularly an effective method for the cold cathode field emission type electron source or the thermal field emitter electron source (Schottky electron source). When a pumping speed is about 20 L/s, generally, the ion pump has a size of 15 cm to 20 cm, which is a pump including a high voltage electrode and a magnet. However, it is difficult to build the ion pump in the vicinity of the electron source. Therefore, the ion pump that is adhered to a side of a barrel (column) configured of the electron gun including the electron source and an electron optical system is usually used. The non-evaporable getter pump is a pump that chemically absorbs and fixes gas molecules to a special alloy surface and if the surface of the pump is activated by being heated once, it can continue a pumping function without needing any energy. Because the alloy surface is covered with the gas molecules, the pumping speed is reduced, but if the surface of the pump is reactivated by being heated, the gas molecules absorbed on the surface are diffused into the alloy and permanently fixed thereto, such that the non-evaporable pump has a characteristic when a pure surface is exposed, the surface returns to a state capable of absorbing gases again. Moreover, there is a charged particle beam apparatus including an electron source using a photo-cathode that is different from the field emission type electron source as described in Japanese Unexamined Patent Application Publication No. 2002-500809. If the electron source makes gallium, arsenic, etc., which are special materials, into a thin film and intensively irradiates a laser beam to the rear of the thin film, it also excites an irradiated the thin film to emit electrons. The electron source is suitable for applications for which the time-divided pulse-shaped electron beams are necessary. However, since a size of a light source is large or it is difficult to continuously emit electrons, the electron source is not suitable for observing high resolution which is an object of the present invention. In addition, it can be said that an electron emission mechanism of the photo-cathode uses different physics, and is a totally different technology. However, the electron source kept in a ultra high degree of vacuum is installed in a narrow region surrounded by the electrode to generate field for extracting and if a small amount of gas is emitted in the vicinity of the electron source, the degree of vacuum inside the electron gun chamber is maintained but the pressure in the vicinity of the electrode of the electron source is suddenly increased, such that an adverse effect may occur. As the gas emission source, in the case of SEM, it is considered that the gas emitted from the observation sample rises from the sample chamber or the electron-stimulated-desorbed gas from the electrode that located in the vicinity of the electron source and is irradiated by electron beams. Such atoms adhered to the surface are excited and emitted again. In particular, in the case of thermal field emitter electron source (Schottky electron source), as described in Journal of Vacuum Science Technology, Vol. 12, No. 6, 1975; L. W. Swanson; “Comparative study of the zirconiated and built-up W thermal-field cathode,” it has been known to cause an adverse effect of decreasing the emission current when there is a very small amount of oxygen. In the case where only the ion pump is used for the vacuum evacuation, since there are an electrode, a magnetic shield, etc. between the electron source and the ion pump and the conductance is lowered, there is a problem in that it is difficult to effectively achieve evacuation in the vicinity of the electron source. On the other hand, in the case of using the non-evaporable getter pump, there are other problems. The non-evaporable getter pump as described above is an alloy made of zirconium and vanadium system. As described in U.S. Pat. No. 4,833,362, it is preferable to install the alloy while providing a heater for heating somewhere in the vicinity of the electron source. However, in order for the non-evaporable getter alloy to have effective pumping speed like the vacuum pump, the alloy surface area should be practicably widened to have a microscopic concave-convex shape from about 1 μm to about 100 μm so as to be molded. For microscopic concave-convex shape, there is a high probability that the point becomes fragile and drops out. Since the non-evaporable getter alloy has conductive property, if it falls into the electron optical system where there are electrodes applied with a high voltage, it causes problems such as discharge, a short, etc. Another problem in using the non-evaporable getter pump is that there is a relationship between a temperature (activation temperature) to activate the non-evaporable getter alloy and a baking temperature to heat the vacuum vessel when the vacuum starts. In order to effectively operate the non-evaporable getter pump, there is a need to keep the activation temperature for a predetermined time under pressure of about 10−4 Pa. By doing so, the gas molecules, which adhere to the non-evaporable getter alloy surface, are diffused into the alloy and the pure surface is exposed, such that the gas molecules can be absorbed again. Since this phenomenon is continued even when the temperature of the non-evaporable getter alloy falls to room temperature, then it is considered that any energy to continue the evacuation is not needed. If the activation temperature selected lower than baking temperature or less in the evacuation procedure, the activation is progressed during the baking and a massive amount of gas generated by the baking is absorbed during the baking, which causes a problem in that the pumping speed decreases or the lifetime of the pump is shortened. Therefore, it is an object of the present invention to provide a charged particle beam apparatus that keeps the degree of vacuum in the vicinity of the electron source to be ultra-high vacuum such as 10−8 to 10−9 Pa even in the state when the electron beams are emitted using the non-evaporable getter pump and are not affected by the dropout foreign particles. In order to achieve the above object, the present invention includes a vacuum vessel in which a field emission type charged particle source (electron source, ion source, etc.) is disposed and a non-evaporable getter pump disposed at a position that faces the field effect type charged particle source on an electrode surface for extracting as a subsidiary vacuum pump and does not directly face charged particle beams and includes a structure that makes the non-evaporable getter pump upward with respect to a horizontal direction to drop out foreign particles into a bottom in a groove or is covered with a shield means, so that the particles dropped out from the non-evaporable getter pump do not face an electron optical system. Or, the present invention includes a means that the non-evaporable getter pump's position is located where the electron beams are not seen vertically from the surface of the non-evaporable getter pump, and has a concave structure capable of trapping the dropout particles on a lower portion of the non-evaporable getter pump. Hereinafter, a characteristic configuration example of the present invention will be enumerated. (1) A charged particle beam apparatus of the present invention includes a charged particle optical system that enters charged particle beams emitted from a field emission type charged particle source on a sample, a vacuum evacuating means that evacuates the charged particle optical system and a non-evaporable getter pump as a subsidiary vacuum pump that evacuates the inside of a vacuum chamber evacuated by the vacuum evacuating means, wherein the non-evaporable getter pump is disposed at a position where an optical axis of the charged particle beam emitted from the field emission type charged particle source does not exist on a portion vertical to the surface of the non-evaporable getter pump. (2) In the charged particle beam apparatus configured as above, the field emission type charged particle source is disposed so that the charged particle beams are emitted in a gravity direction, the non-evaporable getter pumps are provided in concave parts of grooves formed around an aperture through which the charged particle beams on the electrode surface existing immediately below the field emission type charged particle source, and a heater is provided on a rear of the electrode. (3) The charged particle beam apparatus configured as above includes the shield means that covers a portion of the non-evaporable getter pump so that the charged particle beams emitted from the field emission type charged particle source are not irradiated to the non-evaporable getter pump. (4) In the charged particle beam apparatus configured as above, the shape of the electrode is a cup shape and the cylindrical heater is provided on an outer side of the cup-shaped electrode, the non-evaporable getter pumps are provided at outer circumference of the cylindrical heater, and the outer circumference of the non-evaporable getter pump provided in the cylindrical shape is surrounded by a magnetic shield means. (5) In the charged particle beam apparatus configured as above, the non-evaporable getter pumps are provided at inner circumference of the vacuum vessel including the field emission type charged particle source, the heater is provided between a wall surface of the vacuum vessel and the non-evaporable getter pump at an atmospheric side of the vacuum vessel, and the non-evaporable getter pump is surrounded by the wall surface of the vacuum vessel and the magnetic shield means. (6) In the charged particle beam apparatus configured as above, the activation temperature of the non-evaporable getter pumps disposed around the electrode is 500° C. and the activation temperature of the non-evaporable getter pump disposed at the inner wall of the vacuum vessel is 350° C. (7) A vacuum evacuation method according to the present invention includes a process of baking at about 250° C. or less using a heater provided at an atmospheric side while performing rough pumping; a process of baking at about 450° C. or less using a heater provided at an electrode in addition to the condition of the process; a process of activating a non-evaporable getter pump at about 350° C. or more using the heater provided at the atmospheric side; and a process of activating the non-evaporable getter pump at about 500° C. or more using the heater provided at the electrode. Further, it is to be noted that when an electron gun is called a field emission electron gun, it includes both a cold cathode field emission type electron gun and a thermal field emitter electron gun (generally referred to as Schottky electron gun) and when a charged particle source is called a field emission type charged particle source, it further includes a field emission type ion source. The field emission type ion source is an ion source that can attract gas molecules polarized by field, such as helium, hydrogen, to a point of a needle-shaped metal having a point diameter of 0.1 μm or less cooled at an ultracold temperature to attract ion particles, which are ionized electrolytically at the point of the tip, by field and then radiated to be polarized in one direction. With the present invention, the degree of vacuum in the vicinity of the charged particle source can be kept to the ultra-high vacuum such as 10−8 to 10−9 Pa and thus the charged particle beam apparatus without problems due to foreign particles and the vacuum starting method can be provided. Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Further, although the following description describes a charged particle beam generator using a field emission type electron gun as a field emission type charged particle source, it can be applied to a charged particle beam generator using a field emission type ion source as the field emission type charged particle source. FIG. 1 shows a configuration of a charged particle beam generator according to a first embodiment using an electron gun. Hereinafter, the electron gun according to the first embodiment will be described in detail. A vacuum chamber, which is a vacuum vessel, includes an electron source 2 to emit electrons downward. The emitted electron beam passes through an aperture 14 and enters into a sample via an electron optical system installed below the aperture 14. The inside of the electron gun has a differential pumping system from which the aperture is separated and includes vacuum pumps, respectively, to evacuate each chamber. In the first embodiment, the charged particle beam generator, that is, the electron gun means a configuration that the electron gun is positioned at a higher portion than a movable valve 10. The vacuum chamber in which the electron source 2 is disposed is coupled with a vacuum pump 8, a valve 9, and a rough pumping port (rough pumping hole) 12 via a vacuum pipe 15. As the vacuum pump 8, for example, an ion pump may be used. A rear of the vacuum pump 8 is provided with a heater 17 for baking. The other vacuum chamber connected to be separated from the vacuum chamber and the aperture 14 is coupled with a vacuum pump 11, a valve 13, and a rough pumping port 12 via a vacuum pipe 16. A rear of the vacuum pump 11 is provided with a heater 18 for baking. The aperture that separates a lower vacuum chamber from the vacuum chamber can be opened and closed by the movable valve 10 and can separate vacuum and atmospheric pressure. Therefore, even when the vacuum is deteriorated due to problems, the valve 10 is closed, thereby making it possible to prevent the increase in pressure inside the electron gun chamber that is the charged particle beam generator. Next, non-evaporable getter pumps disposed in each chamber will be described in detail. The non-evaporable getter pump is a kind of gas-molecule-absorbable-alloy and is a pump that when it is activated by being heated at a predetermined temperature under vacuum, performs pumping by diffusing gas molecules adhered to the alloy surface into the alloy, forming an active surface on the surface, and absorbing the gas molecules drifted to the circumference. As the alloy, an alloy of zirconium and vanadium system has been used well and marketed. Assume that the temperature necessary for activation is referred to as activation temperature. The activation temperature can be selected depending on a percentage of metal to be included in the alloy. In the first embodiment, a method capable of keeping an efficient pumping speed over a long time by changing the activation temperature according to an installation place is provided. The detailed contents thereof will be described when a vacuum starting method to be described below is described. Well, although there is a sheet-type non-evaporable getter pump 1 on an inner wall surface of the vacuum chamber in which the electron source 2 is disposed, in the sheet-type non-evaporable getter pump 1, the alloy is deposited only on one side of the sheet. In the sheet-type non-evaporable getter pump 1, the alloy surface becomes a vacuum side of the vacuum chamber and a rear side of the sheet is fixed to contact the inner wall surface. By the above configuration, since it can prevent members from directly contacting the non-evaporable getter alloy surface, reducing the amount of foreign particles dropped out from the non-evaporable getter alloy can be achieved. The heater 7 for heating is provided at an atmospheric side separated from the wall surface of the vacuum vessel of the non-evaporable getter pump 1. The heater 7 is also used for baking when the evacuation and the activation of the non-evaporable getter pump 1 that is performed later. The method used thereof will be described below in detail. There is an electrode 4 immediately below the electron source 2 and at a position facing the electron source 2. There is the aperture 14 at the center of the electrode 4, wherein electron beams (not shown) emitted from the electron source 2 pass through the aperture 14. An overhead view and a cross-sectional view of the structure of the electrode 4 are shown in FIGS. 2A and 2B, respectively. The shape of the electrode 4 is a disc shape, a surface facing the electron source 2 is formed with a doughnut-shaped groove 4′, and the non-evaporable getter pump 6 is fixed in the groove 4′ while facing the non-evaporable getter alloy surface up. The non-evaporable getter pump 6 is also a sheet type similar to the above-mentioned non-evaporable getter pump 1. In other words, the optical axis of the electron beam is disposed at a position that does not exist on a portion vertical to the surface of the non-evaporable getter pump 6. More preferably, the non-evaporable getter pump 6 is disposed at a position where the electron beams emitted from the electron source 2 are not irradiated. The rear of the electrode 4 is provided with a heater 5 for heating, which can heat the electrode 4 and the non-evaporable getter pump 6. Further, for convenience of explanation, it is to be noted that there is a case where the non-evaporable getter pump 6 and the non-evaporable getter pump 1 is referred to as the first and second non-evaporable getter pumps, respectively. Next, a method of evacuating the electron gun, which is the charged particle beam generator, to ultra-high vacuum from the atmosphere will be described. First, the valves 9 and 13 for rough pumping are opened and the vacuum evacuation starts by the vacuum evacuating means (not shown) that exists at a lower side of the rough pumping port 12. The time is estimated in order to make the internal degree of vacuum become about 10−4 Pa and the following baking process is performed. The degree of vacuum is a level that can be sufficiently achieved in about one hour from the rough pumping starting in a general electron gun. In the following baking process, in addition to the vacuum evacuation of the previous process, each heater 7, 17, and 18 is conducted to heat the whole vacuum vessel to about 150 to 200° C. The process is performed to suppress gas emission from the vacuum inner wall surface. The longer the time, the more the gas emission decreases, but in actuality, the gas is sufficiently emitted in about 10 hours. The baking of the electrode 4 is performed following the baking process. The electrode 4 is a part that is irradiated by the electron beams emitted from the electron source 2 and since the gas emission is excited by the incidence of electrons, there is a need to reduce the gas molecules before the other portions. Then, gas absorbed on the surface, hydrogen existing in the inside of the electrode, etc. are emitted by heating the electrode 4 to about 400° C. The gas emitted from each heater is evacuated through the rough pumping port 12, but if the wall surface temperature of the circumference is low, an effect of re-adhesion decreases. Then, the re-adhesion of the gas molecule is avoided by further heating the electrode 4 to a state heated by the previous process. Even with this process, about 10 hours are standard. At this time, the vacuum pump 8 and the other vacuum pump 11 are operated. Next, in addition to the baking of the electrode 4, the activation of the non-evaporable getter pump is performed. In the step of the process, the non-evaporable getter pump 1 is heated to 150 to 200° C. and the other non-evaporable getter pump 6 is heated to about 400° C. Herein, the activation temperature of the non-evaporable getter pump 1 is 350° C. and the activation temperature of the other non-evaporable getter pump 6 is 500° C. As such, it is important to make the activation temperature higher than the baking temperature throughout all the processes. By doing so, the activation can be prevented during the baking. Since massive amounts of gas generated during the baking is not absorbed, the non-evaporable getter pump can be used without reducing the pumping speed or lifetime thereof. In the first embodiment, the activation temperature of the non-evaporable getter pump 1 is 350° C. and the activation temperature of the other non-evaporable getter pump 6 is 500° C. In the present process, it is preferable that the voltage conducting the heater 7 at the atmospheric side and the heater 5 at the rear of the electrode 4 rises to set the activation temperature so as to exceed the baking temperature. In the first embodiment, the activation temperature of the non-evaporable getter pump 1 rises to 400° C. and the activation temperature of the other non-evaporable getter pump 6 rises to 600° C., such that they are activated. This activation is performed by keeping the activation temperature to about one hour. Further, when the non-evaporable pump is activated, a large amount of gas and hydrogen are generated and emitted according to heating. If overload is applied to the vacuum pumps 8 and 11 by the gas generation, it is preferable to turn-off the vacuum pump during the activation process. When the activation of the non-evaporable getter pump ends, as the following process, conduction to each heater stops and the heaters are cooled down to room temperature. If the vacuum pump 8 is turned-off in the previous process, it is preferable to wait for the increase of the degree of vacuum by turning-on the vacuum pump and closing the valves 9 and 13 of the rough pumping port. By the above process, the degree of vacuum in the vicinity of the electron source 2 inside the electron gun can be achieved to a level higher than 10−9 Pa. Thus, in the electron gun achieving the ultra-high vacuum, if the electron beams are emitted from the electron source 2, the emitted electron beam faces the electrode 4 while diffusing into a cone shape as shown in FIGS. 2A and 2B. Generally, as a well-known phenomenon, the excited gas molecules are emitted from the surface to which the electron beams are irradiated. In the electron gun, it is not preferable that a new gas emission source is generated in the vicinity of the electron source necessary for the ultra-high vacuum. In the configuration of the related art, since the vacuum pump 8 or the non-evaporable getter pump 1 are disposed at a position separated from the electron source 2, there is a problem in that the influence by the gas due to the irradiation of the electron beams or the gas entered from the lower side of the electron gun is not prevented. However, in the first embodiment, a large effect capable of performing effective evacuation can be obtained by providing the non-evaporable getter pump 6 at a position facing the electron source 2 in the vicinity of the electron source 2. In addition, the groove 4′ is formed in the electrode 4 and the non-evaporable getter pump is disposed in the groove 4′ upward, such that an adverse effect due to the dispersion of foreign particles generated by dropping out chipped pieces of the non-evaporable getter alloy can be also prevented. Other effects according to the first embodiment will be described. As shown in FIGS. 2A and 2B, the first non-evaporable getter pump 6 provided on the electrode 4 is disposed at a position where the electron beams are not irradiated. This is to avoid gas emission by the irradiation of the electron beam as described above. The surface of the non-evaporable getter pump 6 has a microscopic concave-convex shape to increase the pumping speed and since the surface area is widened, if the electron beams are irradiated, there is a high possibility that a large amount of gas can be emitted, which is particularly important. Herein, there is a case where the non-evaporable getter pump 6 is installed in order to increase the limitation of the used electron source or electron optical system to the irradiation region of the electron beams. At this time, as a modified example of the first embodiment, an overhead view and a cross-sectional view of a configuration as shown in FIGS. 3A and 3B are effective. There is a structure where a shield plate 19 is provided on the irradiation portion of the electron beams of the upper portion of the electrode 4. By the above-mentioned structure, the non-evaporable getter pump 6 can be effectively provided while suppressing the lowering of gas emission due to the irradiation of the electron beams. Next, the structure of another modified example, which changes the configuration of the electron gun, will be described with reference to FIG. 4. In the modified example, there is a case where the shape of the electrode 4 according to the previous embodiment is an electrode 20 changed from the disc shape to the cup shape. By this structure, since the wall surface in the vicinity of the electron source 2 can be baked at a high temperature by the internal heater, it is effective in reducing the degassing amount. Since another structure of the cup-shaped electrode 20 is similar to the previous embodiment, the cup-shape electrode 20 will be described herein. There is a cylindrical heater 24 on the side of the cup-shaped electrode 20, such that the electrode 20 can be heated. The non-evaporable getter pump 21 is wound around the cylindrical heater 24, such that it can be also heated by the heater 24. FIG. 5 is a perspective view of the cup-shaped electrode 20. The non-evaporable getter pumps 22 and 23 disposed upward are disposed in the middle of the groove similar to the non-evaporable getter pump 6 shown in FIG. 1 of the previous embodiment, making it possible to prevent the dispersion of foreign particles. Moreover, the non-evaporable getter pump 21 wound around the cylindrical heater 24 is covered with the magnetic shield 25 and has a structure where even if the foreign particles occur, the foreign particles are supplemented with the magnetic shield cover and the dropout dispersion does not occur in the region through which the electron beams pass. As can be clearly appreciated from FIG. 5, holes are disposed on the side of the magnetic shield 25 so that the pumping conductance of the non-evaporable getter pump 21 becomes large. Also, for convenience of explanation, there is a case where the non-evaporable getter pump 21 is referred to as a third non-evaporable getter pump. The vacuum evacuating method of the electron gun having the present structure is basically similar to the disc-shaped electrode 4 according to the previous embodiment. The difference is the activation temperature of the non-evaporable getter pumps 21, 22, and 23 provided around the cup-shaped electrode 20. In the electron gun, the activation temperature of the non-evaporable getter pump 21 is 500° C. and the non-evaporable getter pumps 22 and 23 are 400° C. Herein, at the baking sequence, the temperature of the non-evaporable getter pump 21 is 400° C., and that of the non-evaporable getter pumps 22 and 23 is 300° C. In a second embodiment, a case where the electron gun described in the first embodiment is applied to the scanning electron microscope will be described. FIG. 6 is a schematic configuration diagram of the scanning electron microscope (SEM). The electron gun as the charged particle beam generator shown in FIG. 1 is mounted on the top. An electron optical system 28, an objective lens 31, and a sample chamber 35 are disposed on the lower portion of the electron gun in series and are separated each other by the aperture for passing through the electron beam 36. The vacuum evacuation of the electron optical system chamber 28 includes a dedicated vacuum pump 26 similar to the electron gun. For the vacuum evacuation from the atmosphere, each chamber is connected to the rough pumping port 12 and can be opened and closed by the valve 30 for rough pumping. The rough pumping port 12 is connected to the sample chamber 35 and the vacuum evacuation of the sample chamber 35 is performed by a turbo molecular pump 33. Next, the vacuum starting method according to the second embodiment will be described. In the case of the vacuum evacuating from the atmosphere, the turbo molecular pump 33 as the vacuum evacuating means connected to the sample chamber 35 is driven to perform the rough pumping of the entire apparatus. At this time, all the valves 9, 13, and 30 for rough pumping are opened. If the entire degree of vacuum achieves to the order of 10−5 Pa, the baking of the apparatus is ready to operate. The preset temperature is controlled in a range of 150 to 200° C. The baking time may be about 8 to 10 hours. From the above description, it may be considered that the previous processes are basically similar to the processes described in the first embodiment. The difference is the closing time of the valve 30 for rough pumping at the lower side than the electron gun. It is preferable to close the valve 30 for rough pumping before the baking ends and also before the activation of the non-evaporable getter pump. By operating as described above, the ultra-high vacuum can be obtained with each of the individually provided ion pumps without being affected by a large amount of gas emission generated at the time of activation. In the case of observing the SEM image, the movable valve 10, which passes through the electron beam 36 emitted from the electron source 2, is driven by a valve driving means 29 to open the aperture. The electron beam which passes through the aperture is intensively focused and scanned on the observation plane of the sample 34 by the electron optical system 28 and the objective lens 31, thereby generating secondary electrons 37. The secondary electrons are detected by a detector 32 and formed as image signals by a controller (not shown). It is preferable that the image signals are displayed on an image display means (not shown). With the second embodiment, the degree of vacuum in the vicinity of the electron source 2 is kept to the ultra-high vacuum, such that the stable image can be obtained without changing the current of the electron beams used for the SEM image observation. A configuration of a third embodiment where the charged particle beam generator having a separate configuration is applied to the scanning electron microscope apparatus will be described with reference to FIG. 7. An electron gun according to the third embodiment has a structure including a non-evaporable getter pump 36 having a high pumping speed in addition to the vacuum pump 11 that evacuates the vacuum chamber 39 that is located lower side of the vacuum chamber 38 in which the electron source 2 exists. Theses two chambers are separated each other by the aperture. In the scanning electron microscope, in the case of observing the images as shown in FIG. 7, since the scanning electron microscope is connected to the sample chamber having the lowest degree of vacuum by the aperture through which the electron beams passes, there is a problem. The problem is an increased possibility that the gas in the sample chamber could blow up in the vicinity of the electron source 2. For this problem, there is an effective solution by introducing the vacuum pump that has higher pumping speed at the lower side than the chamber in which the electron source is set. For the non-evaporable getter pump 36 having the high pumping speed of FIG. 7, a cartridge-type non-evaporable getter pump shown in FIG. 8 is effective. In other words, the cartridge-type non-evaporable getter pump is a cartridge-type non-evaporable getter pump 36 that is formed by welding a pipe to a vacuum flange and winding and fixing the sheet-type non-evaporable getter pump 42 tied in an accordion-fold shape around a pipe being a part 40 into which the heater 41 can be inserted from the atmospheric side. The cartridge-type non-evaporable getter pump 36 is used installing the port of the vacuum chamber 39 of FIG. 7. Further, for convenience's sake, it is to be noted that there is a case where the non-evaporable getter pump 36 is referred to as a fourth non-evaporable getter pump. The vacuum evacuating method is approximately equal to the second embodiment. After baking, when the non-evaporable getter pump is activated, it is preferable to heat and activate the non-evaporable getter pump 42 inside the vacuum by switching on the heater 41 of the cartridge-type non-evaporable getter pump 36. Other processes may be the same as the method shown in the second embodiment. As described above, although the preferred embodiments of the present invention describes the scanning electron microscope (SEM) using the electron source, it is clear that the present invention used the ion source instead of the electron source, for example, can be similarly applied to a focused ion beam (FIB) system. In this case, as the field emission type charged particle source, the field emission type ion source can be used. Next, a fourth embodiment to be described below relates to one configuration example of a case where the scanning electron microscope to which the cold cathode field emission electron gun is applied. The cold cathode field emission type electron gun is a field emission type electron gun that uses a needle-shaped tip made of tungsten at a room temperature. The electrons are emitted by a tunnel effect generated by applying high field to a point of the tip. Brightness is high, which is better than that of the thermal field (emission) type. The energy bandwidth of the emission electron is narrower (˜0.4 eV) than that of the thermal field type and high energy resolution can be obtained, such that the scanning electron microscope having the cold cathode field emission type electron gun is frequently used as a multi-purpose microscope necessary for high resolution observation. In order for the cold cathode field emission type electron gun to emit electrons well, there is a need to remove materials such as extra gas molecules, etc. that covers the surface of the tungsten tip before the emission. To this end, an operation called flashing is performed. The flashing heats the tungsten tip, which is fixed to a filament, by flowing current into the tungsten tip for a short time to remove the extra materials adhered to the surface of the tungsten tip. Therefore, there is a need to keep the gas molecules to be extremely small in the vicinity of the tungsten tip. In the fourth embodiment, an apparatus configuration and a method of operating the same when the non-evaporable getter pump is disposed in the vicinity of the tungsten tip will be described. In the above configuration, it is important to do not suppress the generation of the field emission electrons caused by the adhesion of gas molecules to the surface of the tungsten tip at the time of heating when the non-evaporating getter pump is activated, and also important to evacuate the gas molecules generated from the surface of the tungsten tip at the time of the flashing by using the non-evaporable getter pump. Next, the contents of the fourth embodiment will be described in detail with reference to the accompanying drawings. FIG. 9 schematically shows the whole configuration of the field emission type electron gun according to the fourth embodiment. A column 51 in which an electron source 54 is disposed includes an ion pump 56. Further, a non-evaporable getter pump 53 sintered by a metal sheet is disposed around the electrode source 54 along an inner wall surface of a cylindrical ceramic heater 52 and is disposed to surround the circumference of the electron source 54. Next, the vacuum evacuating around the electron gun according to the fourth embodiment will be described. The evacuation from the atmosphere is made to high vacuum of about 10−5 Pa by using a turbo molecular pump (not shown) from a rough pumping port (not shown). Thereafter, the heater (not shown) is conducted to heat the electron gun column 51 and keeps it to 200 to 250° C. for 10 hours so as to perform baking. In the end of the baking, the non-evaporable getter pump 53 is activated by using a constant current generator 50 in a state where the electron gun column 51 is still high temperature. By doing so, the re-adhesion of a large amount of gas generated at the time of the activation to the inner wall surface of the electron gun column 51 can be prevented and the achieved degree of vacuum when the temperature falls to a room temperature becomes high. Further, the activation time of the non-evaporable getter pump, which depends on its specification, is 10 minutes at 800° C. in the fourth embodiment. In the fourth embodiment, when being conducted to the non-evaporable getter pump 53 and heating it, the electron source 54 is conducted and heated at the same time, such that a large amount of gas generated from the non-evaporable getter pump 53 is not re-adhered to the surface of the electron source 54. As described above, the field emission type electron gun cannot obtain excellent emission current if the pure surface of tungsten is not exposed. Consequently, as described in the fourth embodiment, if the non-evaporable getter pump is disposed in the vicinity of the electron source 54, the surface of the tungsten tip is contaminated due to degassing from the non-evaporable getter pump such that there is a disadvantage in that excellent emission current cannot be obtained, but if the fourth embodiment is applied, there is no contamination and the activation one can keep the high degree of vacuum around the electron source. Next, the conducting and heating circuit according to the fourth embodiment will be described. One of the output terminals of the constant current generator 50 shown in FIG. 9 is connected to a switch 55, which can switch over three terminals (A, B, and C). When the switch 55 is connected to terminal A, the heating circuit is switched off. If the switch 55 is connected to terminal B, a current flows in the ceramic heater 52 holding the non-evaporable getter pump 53, thereby heating the non-evaporable getter pump 53. Thereafter, current is conducted from the terminal of the electron source 54 and the electron source 54 is also heated at the same time. At last, the current output from the constant current generator 50 returns to the constant current generator 50 from the other terminal of the electron source 54, such that a series circuit is formed. Finally, if the switch 55 is connected to terminal C, a current is conducted only to the electron source 54, making it possible to perform the flashing of the electron source. FIG. 10 shows an equivalent circuit of the conducting and heating circuit. A resistance of the ceramic heater 52 and a resistance of the electron source 54 are shown as a square. Three, that is, A: non-conduct, B: conduct the non-evaporable getter pump 53 and the electron source 54 in series, C: conduct only to the electron source, can be selected by switching over the switch. The current supplied by the constant current generator 50 is an unambiguously determined value together with the temperature heating the electron source 54. In the fourth embodiment, the current is used in the range of 2 to 8 A by the heating temperature. The ceramic heater 52 is assumed to have a resistance specification of about 30Ω at a room temperature. When activating the non-evaporable getter pump 53, the switch 55 is assumed to be terminal B and conducts 2.5 A. The current is one corresponding to heating the non-evaporable getter pump to a temperature of 800° C. and the electron source 54 to a temperature of 1500° C. It is confirmed that the achieved vacuum pressure in the vicinity of the electron source 54 obtains ultra-high vacuum pressure of 10−9 Pa or less by performing the vacuum evacuating method of the electron gun as described above. In the fourth embodiment, the non-evaporable getter pump 53 is disposed to surround the electron source 54, but the configuration thereof is not limited thereto. For example, as in the configuration of the first embodiment shown in FIG. 1, the non-evaporable getter pump 6 may be disposed so that the electron source 2 is disposed thereon. At this time, the conducting and heating circuit may be equivalent to one shown in FIG. 10 and can be configured without specially change. In addition to this, although some arrangement and configuration may be considered, if the electron source is configured to be able to be heated when the non-evaporable getter pump is activated, it is apparent that the same effect can be obtained. The foregoing present invention is useful as the evacuating technology to achieve extremely high degree of vacuum of the charged particle beam apparatus, such as the electron microscope, the electron beam writer, the focused ion beam system, etc. and in particular, the electron gun or the ion gun. |
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claims | 1. An extreme ultraviolet light generation system, comprising:a laser device configured to emit pulse laser light;an EUV light concentrating mirror configured to reflect and concentrate extreme ultraviolet light generated by irradiating a target with the pulse laser light; anda processor configured to receive a first energy parameter of the extreme ultraviolet light and control an irradiation frequency of the pulse laser light with which the target is irradiated so that change in a second energy parameter related to energy per unit time of the extreme ultraviolet light reflected by the EUV light concentrating mirror is suppressed,wherein the first energy parameter includes a combination of one of EUV pulse energy and EUV power and one of EUV light concentration size and EUV emission size, and the second energy parameter includes one of EUV power, EUV power density, and EUV radiation brightness. 2. The extreme ultraviolet light generation system according to claim 1,wherein the processor is connected to an EUV light utilization apparatus that receives the extreme ultraviolet light generated in the extreme ultraviolet light generation system and is configured to receive the first energy parameter from the EUV light utilization apparatus. 3. The extreme ultraviolet light generation system according to claim 1,wherein the processor calculates the second energy parameter based on the first energy parameter. 4. The extreme ultraviolet light generation system according to claim 1,wherein the processor receives the second energy parameter as the first energy parameter. 5. The extreme ultraviolet light generation system according to claim 1,wherein the processor increases the irradiation frequency by increasing an emission frequency of the pulse laser light from the laser device. 6. The extreme ultraviolet light generation system according to claim 1,further comprising a target supply unit configured to sequentially generate and supply a plurality of droplets as the target to an optical path of the pulse laser light,wherein the processor increases the irradiation frequency by increasing both a generation frequency of the plurality of droplets from the target supply unit and the emission frequency of the pulse laser light from the laser device. 7. The extreme ultraviolet light generation system according to claim 1,wherein the target includes a plurality of droplets that are sequentially generated and supplied to an optical path of the pulse laser light,the plurality of droplets includes a droplet not to be irradiated with the pulse laser light and a droplet to be irradiated with the pulse laser light, andthe processor increases the irradiation frequency by increasing a ratio of the number of the droplets to be irradiated with the pulse laser light to the number of the plurality of droplets. 8. The extreme ultraviolet light generation system according to claim 1,further comprising a target supply unit configured to sequentially generate and supply a plurality of droplets as the target to an optical path of the pulse laser light,wherein the processor controls the irradiation frequency by setting relationship between a generation frequency FD of the plurality of droplets from the target supply unit and an emission frequency FL of the pulse laser light from the laser device to FL=FD/N1, where N1 is an integer of 2 or larger, and thereafter, increases the irradiation frequency by setting the relationship to FL=FD/N2, where N2 is an integer of 1 or larger and smaller than N1. 9. The extreme ultraviolet light generation system according to claim 1,wherein the processor increases the irradiation frequency when the second energy parameter is lower than a threshold value. 10. The extreme ultraviolet light generation system according to claim 1,wherein the processor increases the irradiation frequency when operation time of the extreme ultraviolet light generation system reaches a predetermined value. 11. The extreme ultraviolet light generation system according to claim 1,wherein the processor increases the irradiation frequency when the number of output pulses of the extreme ultraviolet light reaches a predetermined value. 12. An extreme ultraviolet light generation system, comprising:a laser device configured to emit pulse laser light;an EUV light concentrating mirror configured to reflect and concentrate extreme ultraviolet light generated by irradiating a target with the pulse laser light; anda processor configured to receive a first energy parameter of the extreme ultraviolet light and control an irradiation frequency of the pulse laser light with which the target is irradiated so that change in a second energy parameter related to energy per unit time of the extreme ultraviolet light reflected by the EUV light concentrating mirror is suppressed,wherein the processor performs first processing of controlling pulse energy of the pulse laser light so as to suppress change in the second energy parameter and second processing of increasing the irradiation frequency and decreasing the pulse energy of the pulse laser light. 13. The extreme ultraviolet light generation system according to claim 12,wherein, in the first processing, the processor increases target pulse energy of the pulse laser light when the second energy parameter is lower than a target value. 14. The extreme ultraviolet light generation system according to claim 12,wherein the processor performs the second processing when target pulse energy of the pulse laser light is higher than a threshold value. 15. The extreme ultraviolet light generation system according to claim 12,wherein the target includes a plurality of droplets that are sequentially generated and supplied to an optical path of the pulse laser light,the plurality of droplets includes a droplet not to be irradiated with the pulse laser light and a droplet to be irradiated with the pulse laser light, andin the second processing, the processor increases the irradiation frequency by increasing a ratio of the number of the droplets to be irradiated with the pulse laser light to the number of the plurality of droplets. 16. The extreme ultraviolet light generation system according to claim 12,further comprising a target supply unit configured to sequentially generate and supply a plurality of droplets as the target to an optical path of the pulse laser light,wherein the processor controls the irradiation frequency by setting relationship between a generation frequency FD of the plurality of droplets from the target supply unit and an emission frequency FL of the pulse laser light from the laser device to FL=FD/N1, where N1 is an integer of 2 or larger, and thereafter in the second processing, increases the irradiation frequency by setting the relationship to FL=FD/N2, where N2 is an integer of 1 or larger and smaller than N1. 17. An electronic device manufacturing method, comprising:generating extreme laser light in an extreme ultraviolet light generation system;emitting the extreme ultraviolet light to an exposure apparatus; andexposing a photosensitive substrate to the extreme ultraviolet light in the exposure apparatus to manufacture an electronic device,the extreme ultraviolet light generation system including a laser device configured to emit pulse laser light, an EUV light concentrating mirror configured to reflect and concentrate the extreme ultraviolet light generated by irradiating a target with the pulse laser light, and a processor configured to receive a first energy parameter of the extreme ultraviolet light and control an irradiation frequency of the pulse laser light with which the target is irradiated so that change in a second energy parameter related to energy per unit time of the extreme ultraviolet light reflected by the EUV light concentrating mirror is suppressed,wherein the first energy parameter includes a combination of one of EUV pulse energy and EUV power and one of EUV light concentration size and EUV emission size, and the second energy parameter includes one of EUV power, EUV power density, and EUV radiation brightness. 18. A method of manufacturing an electronic device, comprising:inspecting a defect of a mask by irradiating the mask with extreme ultraviolet light generated in an extreme ultraviolet light generation system;selecting a mask using a result of the inspection; andexposing and transferring a pattern formed on the selected mask onto a photosensitive substrate,the extreme ultraviolet light generation system including a laser device configured to emit pulse laser light, an EUV light concentrating mirror configured to reflect and concentrate the extreme ultraviolet light generated by irradiating a target with the pulse laser light, and a processor configured to receive a first energy parameter of the extreme ultraviolet light and control an irradiation frequency of the pulse laser light with which the target is irradiated so that change in a second energy parameter related to energy per unit time of the extreme ultraviolet light reflected by the EUV light concentrating mirror is suppressed,wherein the first energy parameter includes a combination of one of EUV pulse energy and EUV power and one of EUV light concentration size and EUV emission size, and the second energy parameter includes one of EUV power, EUV power density, and EUV radiation brightness. |
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046363637 | abstract | Apparatus for the conditioning of radioactive wastes capable of ultimate storage, using a multicomponent binding agent, with a continuous-flow mixer, a filling station for the ultimate storage barrels, a receiver tank for liquid waste materials, a silo for a component of the binding agent, and several conveyors. A premixer for the one binding agent component and for flowable waste materials is provided. The premixer is connected via throughput measuring devices to the silo and to a container for flowable wastes. The premixer is connected via a dosing conveyor device to one end of the continuous-flow mixer. Thereafter, the receiver tank is connected to the continuous-flow mixer. A discharge conveyor device which feeds the ultimate storage barrels is mounted at the other end of the continuous-flow mixer. |
description | The present invention relates to x-ray optical systems. Researchers have long employed focusing x-ray optics in x-ray diffraction experiments to increase the flux incident on the sample and to thereby increase the signal to noise ratio. A focusing optic increases the flux by directing a large number of photons through the sample. Moreover, by positioning a detector near or at the focus of the optic, resolution of the system can be greatly improved. However, the focusing nature of a focusing multilayer optic limits its applicability, since for each application, a different convergence angle, and thus a different optic, is often needed. Thus, a plurality of optics with different focal lengths are used to accommodate the needs of different applications. However, changing the optical elements is costly and time consuming. Another issue with the focusing optic is that beam intensity is not uniform since the portion of the optic far from the source corresponds to a smaller capture angle. By varying the focal position of the optic, one can design an optic that delivers a uniform beam at a specific location, such as sample location or detector location. Traditional bending total reflection mirrors have been used to adjust the focal distance to adapt the optic for different applications. However, the alignment and adjustment of bending total reflection mirrors is time consuming and difficult to perform, and any imperfection in the alignment or adjustment of the optic degrades the overall system performance. Further, this approach cannot be used for multilayer optics because of its inability to satisfy both Bragg and geometric conditions. In overcoming the above mentioned and other drawbacks, the present invention provides an x-ray optical device that delivers an x-ray beam with variable convergence. The convergence or the divergence of the x-ray beams varies over different parts of the reflector. The device may include an adjustable aperture to further select the convergence or divergence. The adjustable aperture selects the convergence angle by selectively occluding a portion of the x-ray beams. In a general aspect of the invention, an x-ray optical device includes an x-ray source and a reflective element with variable focal points. The variable focal points relate to varying convergence or divergence of an output beam from the x-ray system. The convergence or divergence varies from a near end of the reflective element to a far end of the reflective element. The near end and the far end are defined by the respective positions of the ends relative to the x-ray source. In certain embodiments, the reflective element has a curved surface and the portion of the beam with the lowest convergence or divergence is delivered from the far end of the reflective element. Alternatively, the portion of the beam with the lowest convergence or divergence is delivered from the near end of the reflective element. Accordingly, the optical device may produce a uniform beam of x-rays toward a sample or a detector. The optical device may include an adjustable aperture for selecting a portion of the beam, which optimizes the convergence or divergence and flux of the beam. In certain implementations, the surface of the reflective elements varies according to a pre-defined function to provide the varying divergence. For example, the convergence or divergence may vary according to a linear function. The optical device may include a second reflective element arranged relative to the first reflective element to provide a two-dimensional conditioned beam. Or the reflective element may be a two-dimensional curved surface which provides a two-dimensional conditioned beam. Further features and advantages of the invention will be apparent from the drawings, detailed discussion, and claims. The present invention provides an x-ray optical device with a reflective element having varying focal points, that is, varying focal distances relative to the reflective element. Thus, a focal point of the x-ray device can be selected for a particular measurement. Hence, the flux and resolution of the device can be easily altered for the needs of different applications or measurements, thereby improving the usability of the overall optical system. In accordance with an embodiment of the invention, FIG. 1 illustrates an x-ray optical device 10 including an x-ray source 12, an x-ray reflective optic 14, a top blade 16 and a bottom blade 18. The x-ray source 12 can be a laboratory source, such as a high brilliance rotating anode x-ray generator or a microfocusing source, and the x-ray reflective optic 14 can be a focusing multilayer optic with one or two reflective planes, a total reflection optic, or an x-ray reflective crystal. In operation, the source 12 emits an x-ray field of beam toward the reflective optic 14, which in turn reflects the beam through an aperture 21 defined by the blades 16 and 18 toward a sample S; after the beam passes the sample, the beam, which can be either a direct beam or a diffracted beam is captured by a detector 22. The x-ray field reflected by the optic 14 generally includes a top portion 24 reflected by a far end 19 of the optic 14 and a bottom portion 26 reflected by a near end 20. An aperture with a fixed size, for example, either with a square profile or a round profile, can be used to replace the adjustable aperture 21. The selection of the beam in such an arrangement case is realized by moving the aperture. The optic 14 can have various surface designs depending on the requirements of the particular application. In some implementations, the reflective surface of the optic 14 is designed so that the reflected beams from the optic 14 from the far end 19 to the near end 20 are projected towards the detector 22 uniformly. In other implementations, the convergence/divergence across the reflective surface varies according to a pre-defined function. As shown in FIG. 2, the optic 14 may have different focal points from different parts of the optic 14 as indicated by the intersection of the rays 21 at different positions relative to the optic 14. The function can be determined by the beam uniformity at a predefined position, such as the position of the detector 22. The function can be linear; that is, the intersection of the rays across a base line vary uniformly. In the particular embodiment shown in FIG. 1, the optic 14 is a focusing optic with a convergence angle that is large enough for a particular set of applications, such as for protein crystallography with typical unit cells ranging from about 80 angstroms to about 500 angstroms. With a sample of small unit cell, the portion of the beam with larger convergent angle should be selected to increase the flux; with a sample of large unit cell, the portion of the beam with smaller convergence should be selected to improve the beam resolution. An optic with varying focal distance can be easily achieved as shown in FIG. 3, where the rays from a portion of the optic cross the rays from the portion of the optic nearer to source at an increasing distance from the source. That is, the x-rays delivered by the far end of the optic has less convergence and the x-rays from the near end of the optic has higher convergence. A portion of the beam with suitable divergence can be selected for a specific application (or a particular sample of the same application). The x-ray device 10 is particularly well suited for delivering a uniform beam toward the sample position or detector position, such as a biological sample or protein molecule. A uniform beam at the sample position or the detector position may be needed for easy modeling. For a reflective optic, the capture angle density is smaller at the far end 19 of the optic 14. Thus, the beam delivered by the far end 19 of the optic to the detector 22 typically has a lower density than that delivered by the near end of an elliptic mirror. Hence, by employing an optic with a variable focal lens, that is, a lens that includes a far end with higher convergent angle and shorter focal length and a near end with lower convergent angle with longer focal length, the beam can be designed to be uniform at a selected location, such as the sample position or the detector position. As mentioned above, the optic 14 can be designed to provide varying divergence (or convergence). For example, as shown in FIG. 4, the x-ray optical device 10 is well suited for providing varying divergence. In this arrangement, the lower portion 26 of the beam delivered from the near end 20 has the lowest convergence (or divergence after the focal point), such that the convergence of the beam from the optic 14 increases from the near end 20 to the far end 19. Accordingly, the top blade 16 is positioned as shown in FIG. 4 where the beam has the highest divergence. It should be noted that the loss of flux attributed to obtain the low divergence in the arrangement shown in FIG. 4 is less than that associated with the arrangement shown in FIG. 3. Turning now to FIG. 5, there is shown an x-ray optical device 31 with an integrated adjustable aperture 42 in accordance with another embodiment of the present invention. A set of Cartesian axes is also provided in the figure to better illustrate the operation of the x-ray optical device 31. To vary the convergence of an x-ray beam in two dimensions, the x-ray optical device 31 includes a confocal optic 40 to which the adjustable aperture 42 is attached. Note that the adjustable aperture 42 can be located in close proximity to the confocal optic 40 and therefore does not have to be attached to the confocal optic 40. The confocal optic 40 includes a first optical element 32a lying in the y-z plane and a second optical element 32b lying in the x-z plane. The first and second optical elements 32a, 32b define a first reflective surface 33a and a second reflective surface 33b, respectively. In certain arrangements, the near or proximal portion 41a of the confocal optic 40 is located closest to an x-ray source, and therefore the far or distal portion 41b is located farther from the x-ray source. When the confocal optic 40 is in use, x-rays propagate along an optical axis, which are substantially parallel to the z-axis. In some implementations, the first and second optical elements 32a, 32b, as well as the optic 14 described earlier, are multilayer reflectors with graded d-spacing. Specifically, the first and second optical elements 32a, 32b may have either laterally graded d-spacing or depth graded d-spacing. Depending on the type of measurements performed with the x-ray optical device 31, both the first reflective surface 33a and the second reflective surface 33b may have either a focusing or collimating shape or the reflective surfaces 33a and 33b may have different geometries. For example, one surface can have an elliptic shape and the other can have a surface with variable focal length. The design of the surfaces 33a and 33b may be similar to that of the optic 14 described earlier. That is, the surfaces 33a and 33b can be designed so that the optical device 31 provides varying focal points and varying divergence or convergence. Accordingly, various embodiments of the present invention are directed to an x-ray optical device varying focal points. In particular, the optic has a varying divergence or convergence to optimize the beam divergence or convergence, as well as the flux incident on a sample. In one application, the divergence delivered by the optic varies from a low divergence at the far end of the optic relative to the x-ray source to a higher divergence at the near end of the optic. In another application, the divergence delivered varies form a low divergence at the near end to a higher divergence at the far end of the optic. This arrangement provides for lower loss of flux associated with the lower divergence. Although various implementations of the invention have been described above, other implementations are also within the scope of the following claims. For example, the aperture can be formed from four individual blades or from two angles blades. Alternatively, the aperture can be a round pinhole, such that selecting a portion of the beam involves a position change of the pinhole. The optical device of claim may include a second reflective element arranged relative to the first reflective element to provide a two-dimensional conditioned beam. Alternatively, the reflective element may be a two-dimensional curved surface which provides a two-dimensional conditioned beam. |
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summary | ||
claims | 1. A method comprising the step of: administering radiation in a neurodegeneration-inhibiting amount to a head or eye area of a subject to thereby protectively inhibit the eye of the subject against neurodegeneration caused by glaucoma, prior to the onset of glaucoma,wherein the subject has the potential to develop an age-related form of hereditary glaucoma that causes optic nerve damage. 2. The method of claim 1, wherein the radiation is therapeutically targeted to the posterior portion of the eye. 3. The method of claim 2, wherein the radiation is therapeutically targeted to tissue in the retina. 4. The method of claim 2, wherein the radiation is therapeutically targeted to tissue in the optical disk. 5. The method of claim 2, wherein the radiation is therapeutically targeted to tissue in the optic nerve. 6. The method of claim 1, wherein the radiation is gamma radiation. 7. The method of claim 6, wherein the gamma radiation is applied to the eye and penetrates the eye to at least the retina to therapeutically interact with tissue in the retina. 8. The method of claim 6, wherein the gamma radiation is applied to the eye and penetrates the eye to at least the retina to therapeutically interact with tissue in the optic disk. 9. The method of claim 6, wherein the gamma radiation is applied to the eye and penetrates the eye to at least the retina to therapeutically interact with tissue in the optic nerve. 10. The method of claim 6, wherein the gamma radiation dose is in the range of about 8 Gray (Gy) to about 15 Gray (Gy). 11. The method of claim 6, wherein the gamma radiation is below 2.5 Grays (Gy). 12. The method of claim 6, wherein the gamma radiation dose is in the range of about 1.0 Gray (Gy) to about 5.0 Gray (Gy). 13. The method of claim 6, wherein the gamma radiation dose is about 2.5 Gray (Gy). 14. The method of claim 1, wherein the radiation is x-ray radiation. 15. The method of claim 14, wherein the x-ray radiation is applied to the eye and penetrates the eye to at least the retina to therapeutically interact with tissue in the retina. 16. The method of claim 14, wherein the x-ray radiation is applied to the eye and penetrates the eye to at least the retina to therapeutically interact with tissue in the optic disk. 17. The method of claim 14, wherein the x-ray radiation is applied to the eye and penetrates the eye to at least the retina to therapeutically interact with tissue in the optic nerve. 18. The method of claim 14, wherein the x-ray radiation dose is in the range of about 8 Gray (Gy) to about 15 Gray (Gy). 19. The method of claim 14, wherein the x-ray radiation dose is in the range of about 1.0 Gray (Gy) to about 5.0 Gray (Gy). 20. The method of claim 14, wherein the x-ray radiation dose is about 2.5 Gray (Gy). 21. The method of claim 1, wherein the radiation dose is in the range of about 8 Gray (Gy) to about 15 Gray (Gy). 22. The method of claim 1, wherein the radiation dose is in the range of about 1.0 Gray (Gy) to about 5.0 Gray (Gy). 23. The method of claim 1, wherein the radiation dose is about 2.5 Gray (Gy). 24. The method of claim 1, wherein the form of glaucoma is an age-related hereditary form of glaucoma. 25. The method of claim 1, wherein the radiation is administered as two or more approximately equal radiation doses. 26. The method of claim 1, wherein the neurodegeneration-inhibiting amount of x-ray radiation administered provides a delivery area to the head or eye area of the subject having a diameter of at least 10 microns. 27. The method of claim 1, wherein the neurodegeneration-inhibiting amount of x-ray radiation administered provides a delivery area having a diameter of at least 50 microns. 28. The method of claim 1, wherein the subject has an intraocular pressure (IOP) less than or equal to 21 mm Hg. 29. The method of claim 1, wherein the subject has a genetic precursor for developing neurodegeneration. 30. The method of claim 29, wherein the precursor is selected from the group consisting of GLC1A (1q24), GLC1B (2-cen-q13), GLC1C (3q21-q24), GLC1D (8q23), GLC1E (10p14-p15), GLC1F (7q35-q36), GLC3A (2p21 Cytochrome), P4501B1 (CYP1B1), GLC3B (1p36.2-36.1), Tyrp1 and Gpnmb. 31. The method of claim 1, wherein a cup to disc ratio of the subject is less than 0.5. 32. A method comprising the step of: administering radiation in a neurodegeneration-inhibiting amount to a head or eye area of a subject to thereby protectively inhibit the eye of the subject against neurodegeneration caused by glaucoma, prior to the onset of glaucoma manifestations,wherein the subject is a suspect of developing glaucoma manifestations because the subject exhibits one or more risks factors for glaucoma, and wherein the risks factors are for an age-related form of glaucoma that causes optic nerve damage. 33. The method of claim 32, wherein the radiation interacts with the posterior portion of the eye. 34. The method of claim 33, wherein the radiation interacts with tissue in the retina. 35. The method of claim 33, wherein the radiation interacts with tissue in the optical disk. 36. The method of claim 33, wherein the radiation interacts with tissue in the optic nerve. 37. The method of claim 32, wherein the radiation is gamma radiation. 38. The method of claim 37, wherein the gamma radiation is applied to the eye and penetrates the eye to at least the retina to interact with tissue in the retina. 39. The method of claim 37, wherein the gamma radiation is applied to the eye and penetrates the eye to at least the retina to interact with tissue in the optic disk. 40. The method of claim 37, wherein the gamma radiation is applied to the eye and penetrates the eye to at least the retina to interact with tissue in the optic nerve. 41. The method of claim 37, wherein the gamma radiation dose is in the range of about 8 Grays (Gy) to about 15 Grays (Gy). 42. The method of claim 37, wherein the gamma radiation dose is in the range of about 1.0 Grays (Gy) to about 5.0 Grays (Gy). 43. The method of claim 37, wherein the gamma radiation dose is about 2.5 Grays (Gy). 44. The method of claim 32, wherein the radiation is x-ray radiation. 45. The method of claim 44, wherein the x-ray radiation is applied to the eye and penetrates the eye to at least the retina to interact with tissue in the retina. 46. The method of claim 44, wherein the x-ray radiation is applied to the eye and penetrates the eye to at least the retina to interact with tissue in the optic disk. 47. The method of claim 44, wherein the x-ray radiation is applied to the eye and penetrates the eye to at least the retina to interact with tissue in the optic nerve. 48. The method of claim 44, wherein the x-ray radiation dose is in the range of about 8 Grays (Gy) to about 15 Grays (Gy). 49. The method of claim 44, wherein the x-ray radiation dose is in the range of about 1.0 Grays (Gy) to about 5.0 Grays (Gy). 50. The method of claim 44, wherein the x-ray radiation dose is about 2.5 Gy. 51. The method of claim 32, wherein the radiation dose is in the range of about 8 Grays (Gy) to about 15 Grays (Gy). 52. The method of claim 32, wherein the radiation dose is in the range of about 1.0 Grays (Gy) to about 5.0 Grays (Gy). 53. The method of claim 32, wherein the radiation dose is about 2.5 Grays (Gy). 54. The method of claim 32, wherein the form of glaucoma is an age-related hereditary form of glaucoma. 55. The method of claim 32, wherein the radiation is administered as two or more approximately equal radiation doses. 56. The method of claim 32, wherein the neurodegeneration-inhibiting amount of x-ray radiation administered provides a delivery area to the head or eye area of the subject having a diameter of at least 10 microns. 57. The method of claim 32, wherein the neurodegeneration-inhibiting amount of x-ray radiation administered provides a delivery area having a diameter of at least 50 microns. 58. The method of claim 32, wherein the subject has an intraocular pressure (IOP) less than or equal to 16 mm Hg. 59. The method of claim 32, wherein the subject has a genetic precursor for developing neurodegeneration. 60. The method of claim 59, wherein the precursor is selected from the group consisting of GLC1A (1q24), GLC1B (2-cen-q13), GLC1C (3q21-q24), GLC1D (8q23), GLC1E (10p14-p15), GLC1F (7q35-q36), GLC3A (2p21 Cytochrome), P4501B1 (CYP1B1), GLC3B (1p36.2-36.1), Tyrp1 and Gpnmb. 61. The method of claim 32, wherein a cup to disc ratio of the subject is less than 0.5. |
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055815863 | claims | 1. A drive device for control rod drive mechanisms for driving control rods of an atomic power plant, each drive mechanism including an electric motor drive, the drive mechanisms being divided into a plurality of groups, the device comprising: a control rod changeover device provided for each group of control rod drive mechanisms; an inverter power source, associated with each said control rod changeover device, to provide a drive power source for said electric motor drives; an inverter controller, for each said inverter power source, to output control signals for controlling said inverter power source; a control device coupled to receive control rod position signals from each of said control rod drive mechanisms and to output control signals to each said control rod changeover device and inverter controller; and a man-machine device to interface with an operator, the man-machine device for outputting control rod drive information to said control device. wherein the man-machine device includes means for providing a selected mode signal to cause ganged mode operation; the control device including: the control rod selection unit responsive to the selected mode signal to provide a control rod changeover device signal to said inverter power source selection unit and a selected one of said control rod changeover devices associated with the selected control rod drive mechanism. 2. A drive device for control rod drive mechanisms according to claim 1, wherein in a ganged mode of operation, a selected control rod drive mechanism in each of the plurality of groups is operated; 3. A drive device for control rod drive mechanisms according to claim 1, wherein on full insertion of all the control rods, in the plurality of groups of control rod drive mechanisms, the control rod changeover device for each of these plurality of groups selectively couples the associated inverter power source to successive single control rod drive mechanisms. 4. A drive device for control rod drive mechanisms according to claim 1, wherein said control rods are separated from said electric motor drives and the control rods are inserted by water pressure, when reacter scram occurs. 5. A drive device for control rod drive mechanisms according to claim 1, wherein the control device includes means for operating the control rod drive mechanisms to a fully inserted position when a reactor scram occurs. 6. A drive device for control rod drive mechanisms according to claim 1, wherein said control rod changeover device is provided for each group of the control rod drive mechanisms. 7. A drive device for control rod drive mechanisms according to claim 1, wherein said control device comprises a drive control rod selection means to output control signals to said control rod changeover device. 8. A drive device for control rod drive mechanisms according to claim 1, wherein said control device comprises an inverter power source selection means to output control signals to said inverter controller. 9. A drive device for control rod drive mechanisms according to claim 8, wherein said control device comprises a control rod drive mechanism information evaluation means to output control signals to said inverter power source selection means. 10. A drive device for control rod drive mechanisms according to claim 7, wherein said man-machine device includes means to output control signals to said drive control rod selection means. 11. A drive device for control rod drive mechanisms according to claim 9, wherein said man-machine device includes means to output control signals to said control rod drive mechanism information evaluation means. 12. A drive device for control rod drive mechanisms according to claim 1, wherein said inverter power source is coupled to one of a conventional power source and a stand-by power source. 13. A drive device for control rod drive mechanisms according to claim 1, wherein said man-machine device is operated to select one of a control rod selection mode, a control rod drive mode, and a control rod insertion/withdrawal mode. |
claims | 1. A method of reducing the volume of an elongated boiling water reactor fuel assembly fuel channel having a plurality of sides, with each side connected along the elongated dimension to two other sides, for storage, comprising, substantially in the following order, performed under water, the steps of:enclosing the fuel channel with the plurality of sides connected, in an outer sleeve that extends over the entire elongated dimension of the fuel channel, and is malleable, wherein a portion of the outer sleeve is perforated to allow the water to escape and the perforations have traps to prevent debris from escaping with the water;inserting an inner sleeve within the fuel channel with the inner sleeve extending over the elongated dimension around an inside surface of the fuel channel;attaching a top of the outer sleeve to a top of the inner sleeve and a bottom of the outer sleeve to a bottom of the inner sleeve around an entire circumference of the fuel channel; andlaterally compacting the fuel channel within the outer sleeve over the entire length of the outer sleeve at the same time. 2. The method of claim 1 wherein the outer sleeve is constructed from a material selected from a group of metals comprising aluminum and copper. 3. The method of claim 1 including the step of laterally segmenting the fuel channel in the outer sleeve into segmented pieces of a desired length, after the laterally compacting step. 4. The method of claim 3 including the step of packaging the segmented pieces for storage. 5. The method of claim 3 wherein the step of laterally segmenting the fuel channel includes the step of shearing the outer sleeve and fuel channel. |
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056299630 | claims | 1. A storage tank for radioactive fissile material solutions, said tank (11) comprising at least one cell for containing a radioactive solution (12) and solid neutron absorbing material (14) for avoiding the risks of criticality, said radioactive solution (12) being separated from said solid neutron absorbing material (14) by metal walls (12', 13'), which tank is characterized in that an array of substantially vertical tubes (13) containing solid neutron absorbing material (14) is arranged within said cell, said tubes (13) having metal walls (13') and being located in compartments which are themselves delimited by metal walls (12') and distributed throughout said radioactive solution (12). 2. A tank according to claim 1, characterized in that the volumes (20) between said tubes (13) and said walls (12') of said compartments are used for the circulation of a cooling fluid. 3. A tank according to claim 2, characterized in that said volumes (20) communicate with orifices (22) created at the base of the tank (11). 4. A tank according to claim 3, characterized in that said tank (11) is raised and in that said orifices (22) are open to the ambient air. 5. A tank according to claim 1, characterized in that it also comprises means for homogenizing said radioactive solution (12). 6. A tank according to any claim 1, characterized in that it also comprises cooling means within said radioactive solution (12). 7. A tank according to any claim 1, characterized in that it is an annular tank within whose central space there is at least one cell containing said array of tubes (13). |
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053012127 | description | DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 shows the vessel 1 of a pressurized-water nuclear reactor, mounted inside a vessel well 2 made within a concrete structure 3 constituting part of the reactor building of the nuclear power station. The vessel 1, which is of generally cylindrical shape, is arranged in the vessel well 2 with its axis vertical, and has its lower part closed by a domed bottom and its upper part by a cover 1a, likewise of domed shape. Above the cover 1a of the vessel is arranged the set 4 of mechanisms for controlling the bars adjusting the reactivity of the core of the reactor, which consists of juxtaposed fuel assemblies placed inside the vessel 1. The vessel 1 is connected by means of connection pieces 5 to the pipelines 6 of the various loops of the primary circuit of the reactor, in which circulates the pressurized water coming into contact with the core assemblies within the vessel 1 and ensuring the heating and evaporation of feed water inside the steam generators of the power station. The concrete structure 3 forms, above the vessel well 2, a pool 8 which can be filled with water up to the vicinity of its upper level 8a, to make it possible to execute handling and maintenance operations on the inside of the vessel of the nuclear reactor during reactor shutdowns and after removal of the control set 4 and of the cover 1a of the vessel. The pool 8 comprises a part 9 which is placed laterally of the actual reactor pool located vertically in line with the vessel and in which the internal equipment of the reactor vessel can be arranged in order to carry out underwater maintenance or repair operations. The bottom of the vessel 1 has passing through it instrumentation conduits 10 which are connected to an instrumentation room located laterally of the vessel well 2. FIG. 2 illustrates the vessel 1 of a pressurized-water nuclear reactor during a dismantling operation executed by the use of the process according to the invention. The process according to the invention is put into practice after a permanent shutdown of the nuclear reactor and after unloading of the core assemblies and of the internal equipment of the nuclear reactor. After the shutdown and cooling of the nuclear reactor, the pool 8 is filled with water and the vessel cover is removed. The unloading of the core assemblies and the dismounting and disposal of the internal equipment of the vessel are then carried out under water. The fuel assemblies can be placed in containers to ensure their transport and disposal towards a reprocessing factory. The generally highly-irradiated internal equipment can be stored temporarily, before being dismantled under water and disposed of in transport containers. It is also possible at least partially to carry out the underwater dismantling of the internal equipment of the vessel on the inside of the latter. After the unloading of the vessel, the disposal of the internal equipment and the emptying of the pool, there is installed above the upper level 8a of the reactor pool a supporting structure 11 which consists of beams and on which rests the upper part of a lifting device 12, comprising particularly a mast of great length 13 which is arranged vertically along the axis of the vessel and whose lower part is connected to the bottom of the vessel 1. The mast 13 is arranged within a tubular structure 14 placed vertically along the axis of the vessel 1 and having its upper part connected to the supporting structure 11. Arms 15 for centering and retaining the device 12 on the inside of the vessel, each having a jack 16 at its end, are fastened to the lower part of the tubular structure 14 and are arranged in the form of a star around this tubular structure. The jacks 16, which come to bear with their end part on the inner surface of the vessel 1, make it possible to carry out the centering and retention of the vessel 1 in relation to the tubular structure 14 and to the mast 13. The mast 13 comprises a toothing 13a over a substantial part of its length, the toothing 13a interacting with pawls 18 of a vessel-lifting mechanism 20 resting on the supporting structure 11 by means of a rotary thrust bearing 19. The rotating part of the bearing 19 can be driven in rotation about the vertical axis common to the vessel well 2 and to the vessel 1 by means of a motor 21. The lower part of supporting structure 11 carries a circular rail 22 on which are mounted movably in terms of rotation about the axis of the vessel well, by means of carriages, two monorails 23 and 23', shown in FIG. 5, allowing the displacement of hoists 24 in the entire zone located above the upper edge of the vessel 1 and in the storage pool 9 for the internal equipment as a result of the presence of fixed rails 25 and 25', in the extension of which the rotationally movable rails 23 and 23' can be placed As will be explained later, the cutting of blocks 26 of irradiated material from the wall of the vessel is carried out substantially level with the bottom 9a of the pool 9 for the internal equipment, i.e., at the upper level of the vessel well. When a block 26 has been cut from the wall of the vessel 1, a hoist 24 can ensure that this block is picked up in any position and the block 26 transported into the pool 9 for the internal equipment, in which is arranged a container 27 for the storage and transport of the blocks 26 of irradiated material. The hoist 24 makes it possible to transport the blocks 26 between their cutting zone and their storage zone within the container 27. Zone containment walls 28 are placed at the upper level of the pool, below the supporting structure 11, in order to isolate the zone in which the cutting of the blocks 26 is carried out during the dismantling of the vessel 1, from the zone located above the pool, from which the control of the various operations put into effect for the dismantling is executed. Likewise, walls 29 make it possible to separate the pool for storing the internal equipment of the reactor from the zone 8 located vertically in line with the vessel, although passages are provided for the hoists 24 for transporting the blocks 26. Finally, the inner volume of the vessel 1 is isolated from the reactor pool 8 by means of walls 30, in order to limit the radiation in the zone located above the vessel well 2. FIGS. 3 and 4 illustrate the lower part of the mast 13 of the lifting device 12 for the vessel 1. This lower part consists of a platen 32 which can be fastened to the lower part of the mast 13 in its axial direction by means of a threaded part 32a engaged in an internally-threaded hole at the end of the mast 13. The platen 32 comprises four orifices 33 and a centering stud 34 intended for ensuring the fastening and positioning of the end of the mast 13 on the bottom of the vessel 1. After unloading of the vessel, the connection pieces joining this vessel to the primary circuit and all the auxiliary pipework as well as the instrumentation tubes 10 of the vessel bottom are severed and then closed off. Four passage holes through the vessel bottom are machined or remachined in arrangements corresponding to the arrangements of the passage holes 33 of the platen 32 of the mast 13. It is also possible to fasten the vessel to the mast 13 by the use of a number of passage holes through the vessel bottom and a number larger than four of ties fastened in these holes, so as to employ ties and to machine holes of smaller diameter. The mast 13 can be installed by introducing the centering stud 34 into an instrumentation passage hole and by bringing the holes 33 into coincidence with the orifices of the vessel bottom which have been machined or remachined. All the passage orifices of the instrumentation tubes, with the exception of the orifices which have been remachined as appropriate, are closed off, and the fastening of the mast 13 is ensured by means of threaded rods 37 fastened to the platen 32 by nuts 35. A fastening plate 36 (see FIG. 2) having orifices in positions corresponding to the orifices 33 of the platen 32 is placed under the vessel bottom in such a way that the threaded rods 37 engage into the orifices of this fastening plate 36. The fastening of the mast 13 is completed by nuts engaged on the rods 37 and coming to bear with a clamping effect against the lower face of the plate 36. The vessel 1 is thus firmly fixed at the end of the mast 13 which is mounted movably in the vertical direction along the axis of the tubular structure 14 and on the inside of this structure. Devices for wedging in the radial directions are also interposed between the tubular structure 14 and the mast 13, so as to ensure the guidance and retention of the mast 13 during its displacements in the vertical direction. Inflatable gaskets are likewise interposed between the mast 13 and the structure 14, so as to ensure the isolation or containment of the inner volume of the vessel 1 during the dismantling operations. Finally, as mentioned above, the vessel is retained by the arms 15 and jacks 16 in a position such that its axis is aligned with the axis of the mast 13 and of the tubular structure 14. As can be seen in FIG. 5, the supporting structure 11 comprises two parallel main beams 11a and 11b and four lateral beams 11c, 11d, 11e and 11f arranged in the form of a star around the axis of the vessel well of the reactor. The ends of the beams 11a to 11f rest on the concrete structure of the reactor, for example on the bearing surfaces of the anti-missile slab arranged vertically in line with the vessel well and at the upper level 8a of the reactor pool. FIG. 6 illustrates the entire apparatus for dismantling the vessel during an operation for cutting the wall of the vessel. The corresponding elements in FIGS. 2 and 6 bear the same references, the apparatus, as illustrated in FIG. 6, comprising, in addition to the means for lifting the vessel and for handling the cut blocks 26, a horizontal cutting unit 40 and a vertical cutting unit 70 which are mounted on the tubular structure 14. The horizontal cutting unit 40 consists of a band saw 41 mounted on a support 42 fastened to the tubular structure 14 by means of a pivot bearing 43. The saw support 42 can be displaced, for the purpose of executing the cutting of the wall of the vessel, in the way which will be described in detail hereinbelow. The vertical cutting unit 70 consisting of a second band saw 71 makes it possible to separate the segment of the vessel wall cut by the saw of substantially horizontal displacement into blocks of irradiated materials 26, which are transported by the hoists 24 into the storage pool 9 for the internal equipment and deposited in a storage and disposal container 27. The cutting of the wall of the vessel over a particular height is carried out after the vessel 1 has been raised some distance in the vertical direction by means of the mast 13 and the lifting unit 20. The lifting unit 20 consists of a pawl device which will be described below. An appliance 46 for the suction and filtration of the gases in the storage pool 9 for the internal equipment is arranged in an isolated zone of this pool, in order to clear away the gases contaminated by radioactive materials present in the dismantling zone and in the storage zone for the irradiated material. An access orifice making it possible to dispose of the container 27 containing the blocks of irradiated material is provided in the biological containment wall 28, this orifice being closed during the dismantling operations by a slab 48 of radiation-absorbing material. As can be seen in FIG. 7, the pawl-type lifting device 20 comprises a support 50 resting on the supporting structure 11 by means of the pivoting bearing 19, the axis of which is the axis of the mast 13 coinciding with the axis of the vessel well 2 and the axis of the vessel 1. The bearing 19 is a roller bearing, the rollers 51 of which are inclined inwards and downwards so as to ensure perfect alignment of the axis of the mast 13 with the axis of the vessel well. The support 50 of the lifting device 20 has an annular shape and carries four fixed pawls, such as the pawl 18a, arranged at 90.degree. relative to one another about the axis of the mast 13, and mounted pivotably on the support 50 about horizontal axes, such as the axis 52a. The upper part of the support 50 constitutes a jack body 54 which is level with each of the fixed pawls 18a and in which is mounted a jack rod 55 of large cross-section, carrying at its upper end a support 56 in which a movable pawl 18b is mounted pivotably about a horizontal axis 52b. The pawls 18a and 18b comprise a profiled end part, the shape of which corresponds to the shape of the space delimited between two successive teeth of the toothing 13a of the mast 13. The pawls 18a and 18b are capable of pivoting through a particular angle of low amplitude between their position shown in solid lines in FIG. 7 and their position shown in broken lines. In the position shown in solid lines, the pawls are in engagement with the toothing 13a of the mast 13, and in their position shown in broken lines, they are in a position disengaged from the toothing 13a. FIGS. 8A to 8F show schematically the pawls 18a and 18b, the mast 13 and the actuating jack 54 of the movable pawls 18b in successive positions during a displacement phase in the vertical direction and towards the top of the mast 13, to the lower part of which the vessel 1 is fastened. In FIG. 8A, the mast 13 bears on the fixed pawl 18a in its engagement position within the toothing 13a. The jack rod 55 is in the low position. To execute the lifting of the mast 13 and of the vessel 1, the chamber of the jack 54 is fed in such a way as to displace the piston 55 and the support 56 upwards, as shown in FIG. 8B. The bearing pawl 18a, which has a ramp corresponding to the slope of the toothing 13a, comes into the disengaged position as a result of the sliding of its ramp on the toothing. The mast 13 rests on the movable pawl 18b which ensures that it is lifted by means of the jack 54. During the lifting of the mast 13, as shown in FIGS. 8C and 8D, the fixed pawl 18a disengages completely from the toothing as a result of an upward pivoting, and then escapes at the tip of the tooth with which it was in contact, when the tip of the tooth comes level with the end of the pawl 18a. The pawl 18a is then released and falls by pivoting back into the space located below the tip of the tooth, its inclined surface coming into contact with the slope of the toothing 13a. As illustrated in FIG. 8E, the double-action jack 54 is fed in such a way as to cause the descent of the rod 55 and of the movable pawl 18b which disengages from the toothing 13a, the mast 13 coming to rest on the fixed pawl 18a. As can be seen in FIG. 8F, the pawl 18b comes into position again in a space between two teeth located below the space in which this pawl 18b was engaged before the displacement of the mast 13, as shown in FIG. 8A. The pawls 18a and 18b are in identical positions in FIGS. 8A and 8F, the mast 13 having been displaced by one pitch of the rack 13a. The displacement of the jack 55 is equal to the pitch of the rack plus some play necessary for bringing about the engagement and disengagement of the pawls 18a and 18b. To carry out the lifting of a vessel of a pressurized-water nuclear reactor, four sets of pawls 18a and 18b and four jacks arranged at 90.degree. relative to one another about the axis of the mast 13 have been used. Each of the jacks has a lifting force of 100 tons, so that the total lifting capacity is 400 tons. The jacks have a stroke of 60 mm and the pitch of the toothing 13a of the mast 13 is 50 mm. The progressive raising of the mast 13 and of the vessel 1 is carried out in complete safety by means of the pawls, with which are associated devices for monitoring the correct engagement of the pawls in the toothing 13a. The lifting of the vessel is executed over a vertical distance corresponding to a particular number of displacement pitches of the rack, so as to provide above the level of the bottom of the pool for the internal equipment some wall height of the vessel 1, on which the cutting of blocks of material is carried out in a manner to be described below. FIGS. 9 and 10 illustrate in more detail the cutting machine 40 which consists of a band saw shown in FIG. 6. The band 41 of the saw is mounted on pulleys 44a and 44b driven in rotation by a motor means. The cutting of the wall of the vessel 1 is performed at a level located just above the level of the bottom 9a of the pool for the internal equipment. A guiding and centering device 60 is placed on the upper rim of the vessel well 2, level with the bottom 9a of the storage pool 9 for the internal equipment. The device 60 comprises bearing abutments 61 making it possible to carry out the centering of the vessel 1 and the alignment of its axis with the axis common to the well 2 and to the tubular structure 14, to which the cutting device 40 is fastened by means of the bearing 43. The guiding device 60 comprises a helical groove 62 the axis of which corresponds to the axis of the vessel well 2. The cutting machine 40-has a guide roller 64 which moves along within the groove 62 during the cutting of the vessel. The groove 62 has an angular amplitude determining the rotational displacement of the saw blade 41 about the axis of the vessel, of the order of 30.degree.. The support 42 of the cutting machine, which is mounted rotatably on the tubular structure 14 by means of the pivot bearing 43, is displaced in rotation about the axis of the tubular structure 14 coinciding with the axis of the vessel, so as to describe an angle of 30.degree. about this axis, at the same time making a cut in part of the wall of the vessel 1 along a helix, the shape of which is homothetic with the helix formed by the guide groove 62. During this displacement, the support 42 of the cutting machine is also capable of pivoting in a vertical direction as a result of the construction of the bearing 43 in the form of a ball joint. The saw blade 41 taking the form of a band is driven in rotation by a drive motor. After the wall of the vessel 1 has been cut along a cylindrical sector of an amplitude of 30.degree. and along a helix the axis of which is the axis of the vessel, the cutting machine 40 is returned to its initial position, and the vessel is rotated oppositely to the cutting direction by means of the device 21 for setting the mast 13 in rotation, while at the same time it is raised over a height corresponding to one displacement pitch of the mast 13, so as to return the cutting blade 41 to the end of the helical incision previously made. A new cut of an amplitude of 30.degree. and of helical shape is made in the wall of the vessel as a result of the rotational displacement of the cutting machine 40 about the axis of the vessel. A cut of helical shape can thus be made over all or part of the periphery of the vessel by means of successive rotational displacements of the cutting machine 40 and translational and rotational displacements of the vessel 1. The total height H of the segment of the wall cut in the course of a complete revolution of the cutting machine is equal to the displacement pitch P of the mast 13 multiplied by the number of rotational displacements of the machine in the direction in which cutting is being carried out. For a rotational displacement of the machine of 30.degree., the number of displacements in the course of one revolution is 12, hence H=12P where the pitch P is 50 mm and the height H cut during each revolution is 600 mm. FIG. 13 shows a developed view of the helical cuts 65a, 65b, 65c, slightly inclined relative to the horizontal plane, which are made in the wall of the vessel 1 by the cutting machine illustrated in FIGS. 9 and 10. FIGS. 11 and 12 show the cutting machine 70 allowing straight cuts to be made in a direction forming a small angle relative to the vertical, so as to execute a sectioning of the vessel wall, in which one or more cuts, such as the cuts 65a, 65b, 65c shown in FIG. 13, have been made in a substantially horizontal direction. The cutting machine 70 illustrated in FIGS. 11 and 12 allows successive cuts 66 (FIG. 13) to be made in the wall of the vessel 1, in order to form blocks 26 of irradiated material which are delimited by the horizontal and vertical cuts. As explained above, the blocks 26 are picked up by a hoist 24 which makes it possible to transport these blocks into a storage container 27 arranged in the pool for the internal equipment. The machine 70 for cutting in the vertical direction comprises a support 72 mounted pivotably about a horizontal axis 73 on a second support 74 itself fixed to the rotating part 75 of a bearing mounted rotatably about the tubular structure 14. An actuating jack 76, of which the body is fixed to the tubular structure 14 and the rod is connected to the support 72 of the cutting machine 70, makes it possible to pivot the support 72 about the axis 73. FIG. 11 illustrates a first position, shown in solid lines, of the support 72 and two positions 72' and 72", shown in broken lines, which are obtained during the upward pivoting of the support 72 from its low position shown in solid lines. The actual cutting tool consists of a band saw mounted on the lower part of the support 72. The tensioning and driving of the band 71 of the saw are ensured by two pulleys 77a and 77b mounted loosely on the support 72, and by a driving pulley 78. The pivoting axis 73 of the support 72 in relation to the support 74 can be inclined slightly relative to the horizontal plane, so that the pivoting of the support 72 and of the saw band 71 under the effect of the jack 76 takes place in a plane slightly inclined relative to the vertical. This provides cuts, such as the cuts 66, inclined slightly in relation to the vertical direction. By rotating the support 72 about the axis of the vessel by means of the bearing 75, the cutting tool 70 can be placed in such successive positions that the band 71 executes the cutting of blocks 26 in the wall of the vessel 1, after horizontal cuts, such as the cuts 65a, 65b, 65c shown in FIG. 13, have been made. The centering of the vessel 1 and the alignment of its axis with the axis of the tubular structure 14 are ensured by the centering arms 15 and the jacks 16 and by the external centering devices 61. As can be seen in FIG. 13, the first cut 65a in the circumferential direction of the vessel, inclined slightly in relation to the horizontal plane, allows the horizontal cutting saw to penetrate into the metal of the vessel wall at a small angle and permits a progressive advance in the axial direction of the vessel. The first ring of metal delimited by a helical cut is sectioned by the vertical cutting saw according to the cuts 66, in order to form a first series of blocks 26 which can be disposed of and stored in a container placed in the pool for the internal equipment. The succeeding rings delimited by helical cuts and of substantially constant height are likewise sectioned by the vertical cutting saw, to form blocks 26 of substantially rectangular or square shape which are disposed of in sequence. The dismantling of the vessel is effected by a successive execution of substantially horizontal cuts and of substantially vertical cuts delimiting blocks 26 which are disposed of in sequence. During the cutting of the blocks for the purpose of dismantling of the vessel, the vessel can be filled with water up to a level below the part which is being cut or, if appropriate, can be empty of water. The water level in the vessel can be lowered during the progress of the cutting in the direction of the vessel bottom, before each operation of lifting the vessel between two successive series of cutting operations. The cutting operations are conducted at a substantially constant level located slightly above the upper level of the vessel well. This avoids the need to carry out the cutting on the inside of the vessel well and from the inner surface of the vessel, thus limiting the pollution of the concrete structures delimiting the vessel well by radioactive products. Moreover, the tools used for cutting are more easily accessible and it likewise becomes easier to control and guide them. FIGS. 14 and 15 and FIGS. 16 and 17 illustrate alternative embodiments of the horizontal cutting device and of the vertical cutting device making it possible to dismantle the vessel 1 by cutting blocks from its wall. The horizontal cutting device 80 illustrated in FIGS. 14 and 15 and the vertical cutting device 90 illustrated in FIGS. 16 and 17 consist of a respective circular saw 81 and 91 mounted movably in a radial direction in relation to the vessel 1, on a respective gantry 82 and 92 placed in a transverse direction above the vessel well. Where the device 80 for cutting in a horizontal direction is concerned, the disk 83 of the circular saw 81 is placed in a horizontal plane and mounted rotatably about a vertical axis. The advancing movement of the circular saw 81 in the direction of the arrow 84 allows a horizontal cut to be made in the wall of the vessel 1 and over its entire thickness, slightly above the vessel well and the bottom 9a of the pool for the internal equipment. If a cutting device comprising a circular saw is used, it is possible to make a perfectly horizontal cut, the penetration into the metal of the vessel wall being effected from inside the vessel and in a cross-sectional plane thereof. The circular saw for vertical cutting 91 comprises a saw disk 93 arranged in a vertical plane and mounted rotatably about a horizontal axis. The penetration into the metal of the vessel wall is effected from inside the vessel and in an axial plane. The cuts can be perfectly vertical and perpendicular to the horizontal cuts made previously. This provides blocks 26 of irradiated material of rectangular or square shape, delimited by the horizontal cuts and the vertical cuts. The cutting of the vessel wall is executed by rotating the vessel through a particular angle between two cutting operations involving successively the device 80 for cutting in the horizontal direction and the device 90 for cutting in the vertical direction. The cutting tools are controlled remotely, and the cutting operations are in all cases carried out in a zone making it possible to avoid major contamination of the reactor structures by radioactive products. FIG. 18 shows a vessel 101 of a water-cooled nuclear reactor during a preparatory phase prior to its dismantling. The vessel 101 is arranged inside a vessel well 102 within the concrete structure 103 of the nuclear reactor. The vessel well 102 opens out in its upper part into the pool 104 of the reactor. To dismantle the components of the reactor and particularly the vessel 101, the reactor is cooled after its permanent shutdown and the pool 104 is filled with water. The cover of the vessel is then dismounted and the core assemblies and of the internal equipment arranged in the vessel are unloaded underwater. The pool of the reactor is subsequently emptied and the vessel decontaminated, for example by the circulation of a chemical reagent in contact with its inner surface. The vessel is emptied and a device for the containment of the vessel well is installed. A scaffolding 107 is erected in the extension of the vessel well, underneath the hemispherical vessel bottom 101a. Cutting tool equipment is introduced into the vessel well so as to carry out the cutting of the pipework connecting the vessel to the reactor circuit, in the region of the connection pieces 105, 105' and 106, 106'. The cutting of the guide tubes or instrumentation tubes 108 passing through the bottom 101a of the vessel is also executed. This operation is conducted from the upper part of the scaffolding 107. A support 110, which can be seen particularly in FIG. 19, is put in place under the bottom 1a of the vessel. The support 110 comprises a bearing plate 10a which is fastened under the vessel bottom by means of rods 111 engaged in guide tubes or instrumentation tubes passing through the vessel bottom 101a, depending on the type of nuclear-reactor vessel for which the dismantling process according to the invention is used. The rods 111 have a threaded end which is engaged into an orifice passing through the plate 110a and onto which a nut is screwed. The nuts screwed onto the threaded end parts of the rods 111 make it possible to ensure the fastening of the plate 110a which carries abutments 112 coming to bear on the vessel bottom 101a during the tightening of the nuts. Before the displacement of the vessel 101 in successive steps in the vertical direction is executed to allow it to be cut in a zone located in the vicinity of the upper part of the vessel well 102, on the inside of the reactor pool 104, there are installed around the upper part of the vessel 101 an inflatable gasket 113 for closing the upper part of the vessel well 102 and guide jacks 114 for centering and guidance of the vessel 101 during its displacements in the vertical direction. Likewise installed in the pool 104 and in a room 104' arranged laterally of pool 4 are cutting and handling means which can be similar to the means described above and which enable cutting of blocks from the wall of the vessel 101 and the disposal of the cut blocks in storage containers. The reactor vessel 101 for which the dismantling process according to the invention is used rest by means of supporting feet 116 on a supporting ring 115 fastened to the concrete structure 103 of the reactor at the upper level of the vessel well 102. In FIG. 21, the supporting ring 115 has been shown in a plan view, the upper surface of the ring 115 comprising eighteen successive zones 117 in the circumferential direction, the angular amplitude of each of these zones being 20.degree.. Fifteen zones 117 are intended for receiving the bearing surface of a supporting foot 116 of the vessel 101. The three remaining zones 117a, 117b and 117c, which are arranged vertically in line with the connection pieces joining the vessel to the reactor circuit, such as the connection pieces 105 and 105', do not receive supporting feet of the vessel 101 coming to bear on the ring 115. As can be seen in FIGS. 19 and 20, an initial lifting of the vessel can be carried out by means of jacks 120 which are interposed between the supporting ring 115 and some of the supporting feet 116. The jacks 120 are arranged within cutouts 121 of the supporting ring 115 and are brought to bear on wedging pieces 122. The height of the cutouts 121 is sufficient to ensure that a jack 120 bearing on the wedges 122 can be placed underneath a supporting foot 116 at the initial moment of prior lifting of the vessel 101. As can be seen in FIG. 21, the cutouts 121 are made in three zones distributed at 120.degree. around the ring 115 and corresponding to two successive zones 117 allowing the bearing of a supporting foot 116. Three sets of two jacks 120 are placed in the cutouts 121, each made in two successive zones 117 of the ring 115. The vessel is lifted in passes by the simultaneous action of three jacks 120, each arranged in one of the three cutouts 121 distributed over the periphery of the vessel. After the vessel has been lifted over the height of a pass by the use of three jacks each located in a cutout 121, a wedging piece of a height corresponding to the height of the pass is placed underneath each of the jacks which have not been used for the lifting and which are arranged in the vicinity of the jacks which have executed the lifting, in the same cutout 121 of the ring 115. The next lifting pass is executed by using the jacks, the wedging of which has just been carried out, thus making it possible to raise the vessel an additional step. The wedging of the first set of three jacks which executed the lifting of the vessel is then carried out. This ensures the lifting of the vessel in successive passes by the placing of the wedging elements 23 (see FIG. 20) under each of the jacks 120. During the successive steps of the lifting of the vessel, wedging pieces are placed under all or some of the supporting feet 116 of the vessel which are not being used for lifting of the vessel as a result of interaction with a jack 120. At the end of the operation for the initial lifting of the vessel, there are placed underneath the supporting feet, in two zones 125 and 125', wedging pieces of sufficient height to maintain the vessel in the high position reached at the end of the initial lifting. The supporting ring 115 of the vessel is then cut in four zones aligned two by two, to allow the passage of two parallel sections or girders 127, 127' intended for constituting part of the stationary support of the vessel during its subsequent displacement in successive steps in the vertical direction. The sections 127, 127' have the same height as the ring 115 and come to rest on the concrete structure 103 of the reactor in a lateral orifice 131, as can be seen in FIG. 19. The wedging pieces 128 make it possible to ensure good stability of the sections 127 and 127' which, together with the ring 115, constitute a stationary support on which the vessel rests during its lifting in successive steps and its cutting. As can be seen in FIGS. 22 and 23, at the end of the operation for the initial lifting of the vessel by the use of the jacks 120 and the wedging pieces 123, the vessel bottom 101a and the support 110 are at a particular height above the upper surface of the stationary support consisting of the ring 115 and of the sections 127. The vertical spacing present between the upper surface of the sections 127 and the lower bearing surface of the support 110 makes it possible to introduce between these elements a lifting module 130 which will be described below. The lifting module 130 is introduced through the lateral orifice 131 made in the concrete structure of the reactor, at a level located in the vicinity of the vessel bottom 101a. The rails 127 and 127' are arranged over the length of the orifice 131 and form a transfer track for the modular lifting element 130 when it is being put in place underneath the support 110 fixed to the vessel bottom 101a. The lifting element 130, which will now be described with reference to FIGS. 22, 23 and 24, comprises a raising device 24. The lifting element 130 comprises a raising device 132 and a modular supporting element 133 which are assembled together by means of keys 134. The raising device 132 takes the form of a frame comprising two parallel uprights 135a and 135b assembled together by means of spacers 136. The uprights and the spacers consist of metal plates assembled by welding. Fastened to the ends of the uprights 135a and 135b are jack boxes, such as 137a and 137b, inside each of which is placed a hydraulic jack, the body of which bears on the bottom of the corresponding jack box. As can be seen in FIG. 24, when the lifting element 130 is in vertical alignment with the vessel bottom 101a, as shown in FIGS. 22 and 23, the jack boxes 137a and 137b of the raising device 132 are in vertical alignment with the supporting ring 115. The rods of the jacks 138a and 138b (FIG. 23) arranged inside the jack boxes 137a and 137b come to bear on the upper surface of the supporting ring 115. By feeding the jacks, such as 138a and 138b, of the raising device 132 in the direction bringing about the extension of the jack rods, the frame of the device 132 is raised in a direction perpendicular to the frame by means of the jack body coming to bear on the bottom walls of the corresponding jack boxes. By means of the frame of the raising device 132, the modular supporting element 133 fastened to the frame of the raising device 132 by means of the keys 134 is raised. The modular supporting element 133 takes the form of a frame of square cross-section, the faces 139 of which are connected at each of their ends to columns 140 in the region of the corners of the frame. The columns 140 are diametrically penetrated by orifices allowing the passage of the assembly keys 134 and having male or female frustoconical ends allowing a stable stacking of identical modular elements. The dimensions of the modular supporting element 133 are such that this modular element can come into place within the frame of the raising device 132 delimited by the uprights 135a and 135b and the spacers 136. In FIG. 24, the raising device 132 and the modular supporting element 133 are shown in their assembly position, the uprights 135a and 135b having through-orifices in alignment with the orifices of the columns 140 of the modular supporting element 133. In this position, the keys 134 can be introduced into the aligned orifices of the uprights 135a and 135b and of the columns 140. The columns 140 of the modular element 133 are arranged vertically in line with the supporting sections 127 and 127' when the lifting module 130 is in its operating position beneath the vessel bottom 101a. Feeding the jacks, such as 138a and 138b of the raising device 132 causes, by the extraction of the jack rods, the frame of the device 132 and of the modular supporting element 133 which is fastened thereto to to be raised. The upper part of the modular supporting element 133 taking the form of a turntable 141 (see FIG. 22) comes into contact with the lower surface of the plate 110a of the support 110 fixed to the vessel bottom 101a. The vessel 1 resting by means of the support 110 on the modular supporting element 133 can thereby be raised over a particular height corresponding to the amount of vertical displacement of the raising device 132. As can be seen in FIG. 25, when the lifting element 130 is in the high position obtained as a result of the extension of the jacks, such as 138a and 138b, a second modular supporting element 133' identical to the element 133 can be introduced underneath the element 133 raised by the device 132. The element 133 is displaced by transfer along the track consisting of the sections 127 and 127'. The amount of raising of the device 132 corresponds to the height of a modular lifting element, such as 133 or 133', plus a clearance allowing the passage of the element 133' underneath the frame of the device 132 and the modular supporting element 133 fastened within the frame of the device 132. The device 133' is arranged so as to be in exact vertical alignment with the modular element 133. The jacks, such as 138a and 138b of the raising device 132, are fed oppositely to the raising direction, in such a way that the element 133 comes to rest on the element 133', itself bearing on the sections 127 and 127', by means of frustoconical bearing surfaces of the columns 140. The assembly keys 134 making the connection between the frame of the raising device 132 and the modular supporting element 133 are then removed. The descending movement of the device 132 is then continued by feeding the jacks in the desired direction, up to the moment when the frame of the device 132 has returned to its initial position. The modular supporting element 133' is then in the position of the modular element 133 shown in FIG. 24. The modular supporting element 133' and the raising device 132 can be assembled by introducing keys 134 into the aligned orifices of the uprights of the device 132 and of the columns of the modular supporting element 133'. A lifting element identical to the lifting element 130 and consisting of the raising device 132 to which the modular supporting element 133' is fastened is then placed underneath the modular supporting element 133 on which the vessel rests by means of the support 110. The vessel 101 is raised inside the well 102, in such a way that its upper part, consisting particularly of the vessel flange 101b, can be cut on the inside of the reactor pool 104 and in the vicinity of the upper part of the vessel well 102. It should be noted that, during the cutting at the end of the vertical displacement of the vessel by the agency of the raising device 132, the vessel 101, while it is being raised, rests by means of its bottom 101a, the support 110 and the modular supporting elements 133 and 133' on the rails 127 and 127' constituting elements of the stationary support of the vessel 101. The vessel 101 is therefore not suspended inside the vessel well 102 but rests, during the cutting operations, by means of its bottom on supporting elements bearing on the fixed structure of the reactor. The operations of cutting and handling the blocks cut from the wall of the vessel 101 can be conducted in the way described above. At the end of the cutting operation conducted on the part of the vessel located above the upper level of the vessel well after the vertical displacement of the vessel by means of the displacement device 132, the latter can execute a new vertical displacement of the vessel 101 which rests on the element 133', assembled together with the frame of the raising device 132, by means of the support 110 and the modular element 133. The vessel is raised by an amount slightly greater than the height of a modular supporting element, such as 133 and 133'. A third modular supporting element 133" identical to the modular supporting elements 133 and 133' is displaced by shifting on the sections 127 and 127' and is vertically aligned with the element 133' fixed to the frame of the raising device 132 and placed in the high position by this raising device. The jacks of the raising device 132 are subsequently fed oppositely to the raising direction, in such a way as to bring the element 133', on which the vessel rests by means of the element 133 and the support 110, to rest on the modular supporting element 133". The vessel 101 is now in a new lifting position in the vertical direction which allows a new segment of the vessel wall to be cut on the inside of the pool 104 above the upper level of the vessel well 102. The cutting of the vessel wall is thus executed in successive segments after each of the unit lifts of the vessel making it possible to place a new modular supporting element underneath the element, which is raised by means of the device 132, and to bring the vessel to rest, by means of the stacked modular elements, on this new element resting on the stationary support of the vessel formed by the rails 127. As can be seen in FIG. 26, the raising of the vessel in successive steps makes it possible to execute its cutting as far as the level of the domed bottom 101a. Successive supporting elements 133, 133', 133", . . . 133n have been interposed between the support 110 fixed to the vessel bottom and the stationary support of the vessel formed by the rails 127 and 127'. It is thus also possible to cut the vessel bottom 101a in the vicinity of the upper level of the vessel well 102 by the use of a specially adapted cutting tool outfit. It has been possible to execute the cutting of the vessel in the course of successive operations, during each of which the vessel rests, by means of a stack of modular supporting elements, on a stationary structure, itself bearing on the vessel bottom. The successive lifts of the vessel are of identical amount and are obtained from the same raising device which interacts successively with each of the modular supporting elements bearing on the stationary support. The process and apparatus according to the embodiment just described make it possible to obtain a vertical displacement of the vessel in successive steps, simply and in such a way that the vessel has a stable bearing during each of the cutting operations following a displacement in the vertical direction. The lifting of the vessel can be executed by a pull or a push on the vessel bottom by the use of means different from those described. Where the vessel is lifted by a push on the bottom, the initial displacement of the vessel in the vertical direction, making it possible to install the lifting element underneath the vessel bottom, can be effected by any means allowing the vessel to be raised by a push on its lower part. The raising device and the modular supporting element of the lifting unit employed for executing a unit lift of the vessel can have forms and structures different from those described. The push on the lower bottom of the vessel or, more generally, of the component being dismantled can be exerted by means of an intermediate support, as described, or directly on one or more push surfaces formed on the lower part of the component. The tools for cutting sections of irradiated material from the wall of the vessel can be different from a band saw or a circular saw. These cutting means can be non-mechanical, for example, an oxygen cutting torch, although thermal cutting processes give rise to the formation of vapor and of fine particles containing radioactive products, the trapping and filtration of which can be difficult to carry out. The cutting tools can comprise means for displacement and guidance over a complete revolution about the axis of the vessel. In this case, the dismantling of the vessel can be executed without the need to rotate the vessel about its axis. The disposal and storage of the sections of irradiated material can be carried out by means different from those described. The sections disposed of can be processed on the site of the reactor before their storage at a deactivation site or, on the contrary, transported to a processing factory and conditioned there for long-term storage. The cutting of the domed bottom of the vessel can be carried out by using the tools for cutting the cylindrical wall of the vessel as a result of accessory means for handling the domed bottom or, on the contrary, by using special tool outfits. Finally, the process according to the invention can be used for dismantling the vessel of any water-cooled nuclear reactor of the PWR or BWR type or for dismantling the internal equipment of such vessels. More generally, the process according to the invention can be used for carrying out the dismantling of any irradiated component of a nuclear reactor comprising at least one part of tubular shape arranged with its axis vertical. |
051046113 | abstract | A nuclear steam generator 10 with economizer 32 adjacent secondary side feedwater inlets 38a and 38b includes a secondary side divider plate 36 and handholes 40 at opposing 180.degree. locations in alignment with the ends of the plate 36. Notches 42 in the ends of the plate 36 adjacent the aligned handholes 40 facilitate inspection and maintenance access on the secondary side above tubesheet 22. To prevent bypass flow from one side of the divider plate 36 to the other, a novel flow blocker 50 of cylindrical shape is provided for mounting in handholes 40 and notches 42. The flow blocker 50 is defined by telescopically assembled member 52 and 62 which are biased in opposite directions by pre-loaded spring 64 therein to insure stability against vibration and flow induced loads. The flow blocker 50 fits sungly in notch 42 and handhole 40 and is bolted to the inside of closure plate 74 of handhole 40. |
052001393 | abstract | A temperature regulation system of a pressurized water nuclear reactor is inhibited when a combination of the nuclear and the axial power difference exceeds a predetermined inhibit threshold. |
054901863 | abstract | A shipping container is provided for a hexagonal nuclear fuel assembly including a top nozzle having a top end, an outer barrel, an external shoulder, and an inner barrel; a plurality of grids which support fuel rods; and a bottom nozzle having an internal shoulder within a recess, a spherical taper, and a bottom end. The container may include a housing, a support for the fuel assembly, a top nozzle holder secured to the support, plural grid supports secured to the support, plural clamping frames for clamping the grids, plural guide plates for guiding the fuel assembly between adjacent grid supports, and a bottom nozzle holder secured to the support. The top nozzle holder may include a shoulder holder for holding the external shoulder, an end holder for enclosing and holding the top end, and a shoulder clamp for clamping the shoulder holder to the support. The shoulder holder may include a resilient split ring for positioning around the inner barrel and a resilient split support for encasing the resilient split ring. The grid supports may each include two wedges for supporting two sides of the grid, a base plate for fixedly supporting the two wedges thereto, a bearing pad fixedly mounted to the support for slidably supporting the base plate, and shoulder screws for limiting a sliding motion of the base plate on the bearing pad. The guide plates may have a guide side and two surfaces for guiding the two sides of the grids. The guide plates may further have an absorbing side having a coating of gadolinium oxide. The bottom nozzle holder may include a recess holder for holding the internal shoulder. The recess holder may include a wedge mechanism for wedging against the bottom nozzle within the recess and a moving mechanism for moving the wedge mechanism within the recess. The recess holder may also include plural grippers for gripping the internal shoulder and a cam mechanism for moving the grippers. |
summary | ||
description | The present application claims the benefit of U.S. Provisional Application No. 62/729,482 filed Sep. 11, 2018, which is incorporated herein by reference in its entirety. The present invention relates generally to ventilated dry storage modules used to store and/or transport heat-emitting spent nuclear fuel (“SNF”) from nuclear power generating plants or other facilities. In the operation of nuclear reactors, the nuclear energy source is typically in the form of a plurality of hollow Zircaloy tubes each filled with enriched uranium pellets, which are collectively arranged in assemblages referred to as fuel assemblies. When the energy in the fuel assembly has been depleted to a certain predetermined level, the fuel assembly is removed from the nuclear reactor and referred to as used or spent nuclear fuel (“SNF”). The standard structure used to package used or spent fuel assemblies discharged from light water reactors for off-site shipment or on-site dry storage is known as the fuel basket. The fuel basket is essentially an assemblage of prismatic storage cells each of which is sized to store one fuel assembly each of which in turn comprises a plurality of individual spent nuclear fuel rods. The fuel basket is arranged inside a metallic storage canister, which in turn is placed inside a ventilated outer overpack or module for safe transport and/or storage of the multiple spent fuel assemblies within the inner fuel basket. In addition to emitting dangerous ionizing neutron and gamma photons (i.e. neutron and gamma radiation) requiring protective shielding, the highly radioactive SNF in the fuel assemblies still produces considerable heat which must be dissipated to avoid damage to the fuel assemblies. Cooling of conventional ventilated modules suffers from several drawbacks. The cooling air inlets are typically close to the support pad and susceptible to blockage by snow, debris, or runoff and floor waters at outdoor flood prone sites. In unsheltered locations, the variability in wind direction with respect to the location of cooling air inlet and outlet duct locations may adversely impact the air flow rate and cooling of the fuel assemblies. At sunny sites, the support pad absorbs solar radiation which heats the pad, thereby in turn heating the incoming air as it passes over the pad since the air inlets are close to the pad. This adversely affects cooling performance and efficiency resulting in inadequate cooling of the fuel assemblies held inside the outer storage module. A need exists for improved nuclear fuel storage modules. The present application is directed to an improved ventilated dry storage system for passively cooling spent nuclear fuel using available ambient cooling air. An outer ventilated storage cask or module for dry storage of SNF. The module has an elongated body which comprises an internal cavity configured for holding a single SNF canister containing a plurality of heat-emitting nuclear fuel assemblies. The module may be vertically oriented in one embodiment and rests on a concrete support pad. A plurality of radially oriented cooling air inlet ducts spaced circumferentially around the module body fluidly connects the internal cavity with ambient cooling air outside the module. The inlet ducts each draw cooling air radially inwards into the cavity via natural circulation and distributes the air around the canister which emits heat produced by the SNF. The cooling air flows alongside the canister and upwards in the cavity due to the natural chimney effect as it is heated by the heat emitted by the SNF inside the canister and exits the top of the cavity via one or a plurality of air outlet ducts. The outlet ducts may be radially oriented in one embodiment. No blower or fans are used to supply pressurized cooling air to the canister. In one embodiment, the air inlet ducts may each have a recurving configuration to draw cooling air radially inwards and initially upwards into each air inlet duct, and then redirect the cooling air downwards in the air inlet duct into the lowermost part of the internal cavity of the module. The inlet ducts may have a multi-angled configuration such that no straight line of sight exists between the inlet and outlet end openings of the air inlet ducts to prevent neutron streaming from the canister to ambient atmosphere. In some embodiments, radiation attenuation shielding comprising steel or other radiation attenuation inserts or shields may be incorporated into the ducts to enhance radiation blocking. The present cooling air inlet ducts may each have an inlet end opening located at a different preferably higher elevation than the outlet end opening which opens into the cavity of the storage module. The inlet end openings may be sufficiently elevated above the concrete support pad and bottom of the module to prevent flood waters from entering the module particularly in flood prone SNF storage sites. In addition, this advantageously elevates the inlet end openings of each duct above the pad or ground surrounding the fuel storage module by a distance sufficient to minimize heating the cooling air entering the ducts by the concrete support pads encountered by the foregoing conventional SNF fuel storage module duct arrangements previously described above. The inlet openings are arranged to draw air radially directly inward into the internal cavity of the module from the ambient environment surrounding the lower portion of the storage module. In one embodiment, the inlet end openings of each cooling air inlet duct preferably may be below the vertical midline of module. This also avoids thermal interference between the air inlet ducts and outlet ducts near the top of the module to avoid heating the cooling air drawn into the module cavity with the already heated air leaving the outlet ducts. In some arrangements, the inlet end openings have a vertically staggered arrangement in which the elevation of the inlet end opening of each air inlet duct is at a different elevation than the inlet end opening of each adjacent inlet air duct to maximize the supply of available cool ambient air to each inlet duct in the event air temperature stratification surrounding the storage module is present when the air is calm. The present disclosure also provides an improved module lid comprised of a metallic shell filled with concrete for radiation shielding. The lid is configured such that an interface between the top end of the SNF storage module and the lid forms a circumferentially-extending vertical annular gap which defines radial air outlet ducts for ejecting cooling air heated by the canister in the module cavity to atmosphere. In lieu of a multitude of individual discrete air outlet ducts which increases resistance to airflow, the present air outlet ducts are radially open to atmosphere for substantially a full 360 degrees around the circumference of the lid-to-module interface to minimize airflow resistance and maximize ejection of heated cooling air by discharging the air around the entire circumference of the module. This provides essentially radially symmetric outflow of heated air from the module. The present module lid also comprises a pair of lifting beams in the form of vertical plates embedded in the concrete liner of the lid. The lifting beans may be arranged in an interlocked X-shaped configuration in one embodiment. The beam plates each have an exposed downwardly extending lower portion which may be stepped in configuration and is insertable into the open top of the SNF storage module to create neutron scatter and enhance radiation attenuation. In addition, this unique configuration provides a wind-resistant feature which divides the radial cooling air outlet duct into four discrete sectors or quadrants beneath the lid at the interface to the module body to block. This advantageously mitigates the adverse impacts of wind working directly against the discharge flow of heated cooling air radially outwards form the air outlet ducts of the module. Accordingly, because the wind typically blows from one direction at a time, only heated cooling air discharged from primarily one cooling air outlet quadrant might be adversely affected since the downwardly extending lower portion of the lifting beam plates shields or shrouds the other remaining air outlet quadrants from the wind. It further bears noting that discharging heated cooling air from entire sectors or quadrants at the top end of module beneath the lid creates a larger air outlet flow area and concomitantly less resistance to flow than individual smaller ducts. This advantageously maximizes the outflow of heated air and heat removal from the SNF canister in the module. In one aspect, a passively cooled storage module for spent nuclear fuel comprises: an elongated module body defining a top end, a bottom end, a sidewall, and an internal cavity extending between the ends along a longitudinal axis, the internal cavity being configured for holding a fuel storage canister; a plurality of cooling air inlet ducts spaced circumferentially apart around the body, the inlet ducts each forming a radially oriented air inlet passageway fluidly connecting ambient atmosphere with the internal cavity; each air inlet duct having an inlet end opening at an exterior surface of the sidewall and an outlet end opening at an interior surface of the sidewall adjoining the cavity; wherein the air inlet ducts each have a recurving configuration to draw cooling air radially inwards and initially upwards from ambient atmosphere, and then redirect the cooling air downwards through the air inlet duct into a lower part of the internal cavity of the module. In another aspect, a ventilated dry storage system for passive cooling of spent nuclear fuel comprises: an elongated module defining a top end, a bottom end, and a sidewall extending between the ends defining an internal cavity extending along a longitudinal axis; the sidewall including an inner shell, an outer shell, a radiation shielding fill material disposed between the shells; a plurality of radially oriented interconnector plates embedded in the fill material and welded to the inner and outer shells to rigidly couple shells together; a base plate sealingly affixed to the bottom end of the module; a removable lid detachably coupled to the top end of the module; a fuel storage canister disposed in the internal cavity and containing heat-emitting spent nuclear fuel; a plurality of cooling air inlet ducts each forming a radially oriented air inlet passageway through the sidewall of the module configured to fluidly connect ambient atmosphere with the internal cavity; the air inlet ducts each having an inlet end opening at an exterior surface of the sidewall which is at a higher elevation than at an outlet end opening of each air inlet duct at an interior surface of sidewall adjacent to the internal cavity; wherein cooling air is drawn into the internal cavity through each air inlet duct, flows upwards alongside the canister thereby heating the cooling air, and the heated cooling air is discharged back to atmosphere through a plurality of air outlet ducts. In another aspect, a passively cooled storage module for spent nuclear fuel comprises: an elongated module body defining a top end, a bottom end, a sidewall, and an internal cavity extending between the ends along a longitudinal axis, the internal cavity being configured for holding a fuel storage canister; a baseplate attached to the bottom end of the module body; a plurality of cooling air inlet ducts fluidly connecting ambient atmosphere with the internal cavity; a lid detachably coupled to a top end of the module body to access the internal cavity; the lid comprising a metallic shell filled with concrete and a first lifting beam embedded in the concrete; wherein the first lifting beam includes a lower portion which protrudes downwards through and beneath a bottom cover of the lid into a top end of the cavity. In another aspect, a passively cooled storage module for spent nuclear fuel comprises: an elongated module body defining a top end, a bottom end, a sidewall, and an internal cavity extending between the ends along a longitudinal axis, the internal cavity being configured for holding a fuel storage canister; a plurality of cooling air inlet ducts spaced circumferentially apart around the body, the inlet ducts each forming a radially oriented air inlet passageway through the sidewall fluidly connecting ambient atmosphere with the internal cavity; the air inlet ducts each having an inlet end opening at an exterior surface of the sidewall which is at a higher elevation than at an outlet end opening of each air inlet duct at an interior surface of sidewall adjoining the internal cavity; the air inlet ducts each comprising an upper roof wall and a lower floor wall; wherein a highest point of the roof wall of each air inlet duct is at an elevation higher than a top of the inlet end opening of the air inlet duct. In another aspect, a passively cooled storage module for spent nuclear fuel comprises: an elongated module body defining a top end, a bottom end, a sidewall, and an internal cavity extending between the ends along a longitudinal axis, the internal cavity being configured for holding a fuel storage canister; a plurality of cooling air inlet ducts spaced circumferentially apart around the body, the inlet ducts each forming a radially oriented air inlet passageway through the sidewall fluidly connecting ambient atmosphere with the internal cavity; the air inlet ducts each having an exterior inlet end opening and an interior outlet end opening adjoining the cavity; wherein the inlet end openings are vertically staggered in arrangement in which the elevation of the inlet end opening of each air inlet duct is at a different elevation than the inlet end opening of each adjacent inlet air duct. In another aspect, a passively cooled storage module for spent nuclear fuel comprises: an elongated module body defining a top end, a bottom end, a sidewall, and an internal cavity extending between the ends along a longitudinal axis, the internal cavity being configured for holding a fuel storage canister; a plurality of cooling air inlet ducts spaced circumferentially apart around the body, the inlet ducts each forming a radially oriented air inlet passageway through the sidewall fluidly connecting ambient atmosphere with the internal cavity; the air inlet ducts each having a radiation attenuation shield member attached to an exterior surface thereof. In another aspect, a ventilated dry storage system for passive cooling of spent nuclear fuel comprises: an elongated module defining a top end, a bottom end, and a sidewall extending between the ends defining an internal cavity extending along a longitudinal axis; the sidewall including an inner shell, an outer shell, a radiation shielding fill material disposed between the shells, and a plurality of radially oriented interconnector plates embedded in the fill material and rigidly coupling the inner and outer shells together; a base plate sealingly affixed to the bottom end of the module; a removable lid detachably coupled to the top end of the module; a fuel storage canister disposed in the internal cavity and containing heat-emitting spent nuclear fuel; a plurality of cooling air inlet ducts each forming a radially oriented air inlet passageway through the sidewall of the module configured to fluidly connect ambient atmosphere with the internal cavity; the air inlet ducts each having an inlet end opening at an exterior surface of the sidewall which is at a higher elevation than at an outlet end opening of each air inlet duct at an interior surface of sidewall adjacent to the internal cavity; wherein cooling air is drawn into the internal cavity through each air inlet duct, flows upwards alongside the canister thereby heating the cooling air, and the heated cooling air is discharged back to atmosphere through the air outlet ducts. In another aspect, a passively cooled storage module for spent nuclear fuel comprises: an elongated module body defining a top end, a bottom end, a sidewall, and an internal cavity extending between the ends along a longitudinal axis, the internal cavity being configured for holding a fuel storage canister; a baseplate attached to the bottom end of the module body; a plurality of cooling air inlet ducts fluidly connecting ambient atmosphere with the internal cavity; a lid detachably coupled to a top end of the module body to access the internal cavity; the lid comprising a metallic shell filled with concrete and a first lifting beam embedded in the concrete; wherein the first lifting beam includes a lower portion which protrudes downwards beneath a bottom cover of the lid into a top end of the cavity. In another aspect, a ventilated dry storage system for passive cooling of spent nuclear fuel comprises: an elongated module defining a top end, a bottom end, and a sidewall extending between the ends defining an internal cavity extending along a longitudinal axis; the sidewall including an inner shell, an outer shell, a radiation shielding fill material disposed between the shells; a plurality of radially oriented interconnector plates embedded in the fill material and welded to the inner and outer shells to rigidly couple shells together; a base plate sealingly affixed to the bottom end of the module; a removable lid detachably coupled to the top end of the module; a fuel storage canister disposed in the internal cavity and containing heat-emitting spent nuclear fuel; a plurality of cooling air inlet ducts each forming a radially oriented air inlet passageway through the fill material of the module and configured to fluidly connect ambient atmosphere with the internal cavity; wherein each of the interconnector plates are disposed between adjacent ones of the air inlet ducts. In another aspect, a passively cooled storage module for spent nuclear fuel comprises: an elongated module body defining a top end, a bottom end, a sidewall, and an internal cavity extending between the ends along a longitudinal axis, the internal cavity being configured for holding a fuel storage canister; a baseplate attached to the bottom end of the module body; a plurality of cooling air inlet ducts fluidly connecting ambient atmosphere with the internal cavity; a lid detachably coupled to a top end of the module body to access the internal cavity; the lid comprising a metallic shell filled with concrete and a first lifting beam embedded in the concrete; wherein the first lifting beam includes a lower portion which protrudes downwards through and beneath a bottom cover of the lid into a top end of the cavity. In another aspect, a passively cooled storage module for spent nuclear fuel comprises: an elongated module body defining a top end, a bottom end, a sidewall, and an internal cavity extending between the ends along a longitudinal axis, the internal cavity being configured for holding a fuel storage canister; a plurality of cooling air inlet ducts fluidly connecting ambient atmosphere with the internal cavity; a lid detachably coupled to a top end of the module body to access the internal cavity; the lid comprising a pair of lifting beams each including a downwardly extending lower portion which protrudes below the top end of the module into the cavity; wherein the lower portions of the lifting beams divides the interface into quadrant-shaped cooling air outlet ducts for radially discharging the cooling air from the cavity to atmosphere. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. All drawings are schematic and not necessarily to scale. Features shown numbered in certain figures are the same features which may appear un-numbered in other figures unless noted otherwise herein. The features and benefits of the invention are illustrated and described herein by reference to exemplary embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. Accordingly, the disclosure expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. As used throughout, any ranges disclosed herein are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. In addition, all references cited herein are hereby incorporated by reference in their entireties. In the event of a conflict in a definition in the present disclosure and that of a cited reference, the present disclosure controls. FIGS. 1-5 depict a nuclear fuel storage system comprising a passively cooled and ventilated outer storage module 20 configured to hold a single fuel canister loaded with spent nuclear fuel (SNF) assemblies emitting radioactive decay heat. Module 20 may be a double-walled vessel in one embodiment having an elongated module body 28 including cylindrical outer shell 24, inner shell 23, and radiation shielding which may comprise a concrete mass or liner 72 in one exemplary construction which is disposed in an annular space therebetween for radiation blocking. Other shielding materials may be used in addition to or instead of concrete including lead for radiation shielding, including for example boron containing materials (e.g. Metamic® or others), steel, lead, and others typically used for such purposed in the art. Inner shell 23 defines an interior surface 76 and outer shell 24 defines an exterior surface 77 of the module. Surfaces 76, 77 may be cylindrical and arcuately curved in one embodiment. The passively cooled storage module 20 may be vertically elongated and oriented as shown in the illustrated embodiment; however, other orientations such as horizontal may be used with the same features described herein. The inner and outer shells 23, 24 may be formed of a suitable metallic material, such as without limitation steel (e.g. carbon or stainless) which may be epoxy painted/coated in one embodiment for corrosion protection. Shells 23, 24 may each have representative thickness of about ¾ inches as one non-limiting example. A vertically-extending central cavity 26 extends along a centerline or longitudinal axis LA defined by the vertically elongated module body 28. Cavity 26 may be of cylindrical configuration in one embodiment; however, other shaped cavities may be used including polygonal shapes and other non-polygonal shapes (e.g. rectilinear, hexagon, octagonal, etc.). A metal baseplate 27 seal welded to the bottom end 24 of the module 20 closes the bottom of the cavity. Baseplate 27 is configured for placement on a preferably flat concrete support pad which provides radiation shielding in the vertical downwards direction. Baseplate 27 may be made of a similar material to the shells 23, 24. In one embodiment, baseplate may be about 3 inches thick. Cavity 26 of module 20 has a configuration and height suitable for holding a single SNF canister 29 therein (represented by dashed lines in FIG. 3). The diameter of cavity 26 is intentionally larger than the diameter of the fuel canister 29 by a smaller amount to form a ventilation annulus 31 between the canister and inner shell 23 of the module. The width of annulus 31 preferably is sufficient to draw heat generated by the SNF within the canister away from the canister as the cooling air flows upwards alongside the canister. A typical airflow annulus may be in the range of about and including 2-6 inches in width as a non-limiting example depending the estimated heat load of the fuel canister 29. The annulus 31 extends vertically for the full height of the canister which may terminate at top adjacent to the top ends of guide tubes 29-1 (see, e.g. FIG. 3). Accordingly the canister 29 has a height approaching the height of the cavity 26, and at least greater than ¾th the height of the cavity as shown. A plurality of radially and vertically extending support brackets 30 are disposed at the bottom of cavity 26 which are configured to engage and center the canister 29 to maintain the ventilation annulus 31. Brackets 30 are interspersed between some the air inlet ducts 50 and configured to elevate the bottom of the canister above the top surface 27-1 of baseplate 27. This allows ambient cooling air to circulate beneath the canister. Support brackets 30 may be L-shaped in one embodiment as shown and preferably are made of steel (e.g. carbon or stainless). Brackets 30 may have a typical thickness of about ¾ inches in one embodiment and are integrally attached to the baseplate 27 and preferably also inner shell 23 as well such as via welding. Brackets 30 each have a horizontal portion 31 which extends radially inwards from the inner shell 23 towards centerline longitudinal axis LA of module 20 and a vertical portion 32 which extends vertically upwards from the baseplate along the interior surface 76 of inner shell 23 and parallel to the longitudinal axis. Horizontal portions 31 may be about 5 inches high in one non-limiting embodiment. The vertical portions 32 of brackets 30 may have a height suitable to effective center the canister 29 when inserted in cavity 26 and maintain the ventilation annulus 31 between the canister and inner shell 23 (e.g. about 2 feet or less in some embodiments). The top ends of the vertical portions 32 of brackets 30 may be angled or chamfered to create a lead-in which facilitates guiding and centering the canister 29 when through the open top end 21 of the module in cavity 26 via a crane or hoist. The baseplate equipped with the steel support brackets 30 advantageously serves to stiffen the baseplate 27 and support the fuel-bearing canister 29 in a manner that minimizes the bending stress in the baseplate since a portion of the dead weight of the canister is carried by the inner shell 23. The vertical portions of each bracket 30 further restrains the canister from moving laterally when the storage module 28 is being lifted and carried by a crane and/or cask handling crawler, or during a seismic even which rattles the module 20. The top of the canister 29 may be centered in module cavity 26 by plural circumferentially spaced apart guide tubes 29-1 rigidly attached to the interior surface 76 of the inner shell 23 proximate to its top end such as via welding. Guide tubes 29-1 are provided around the entire inner shell for full 360 degree coverage. The inward sides guide tubes are configured to abuttingly engage and prevent the canister from excessively moving laterally or rattling if vibrated during a seismic event or when lifted by a crane or hoist. Module 20 further includes a top end 21, bottom end 22, and longitudinally-extending sidewall 77 extending between the ends. A baseplate 27 is seal welded to bottom end 22 of the module to prevent the ingress of water into the cavity 26. Baseplate 27 may be circular and flat in configuration in one embodiment and defines an upward facing flat top surface 27-1 exposed to cavity 26. The flat bottom surface 27-2 of the baseplate is intended for placement on a concrete support pad CP. Baseplate 27 may be formed a suitable metal compatible for welding to the bottom ends of the inner and outer shells 23, 24, such as steel (e.g. carbon or stainless). Referring to FIGS. 3 and 7-11, a removable lid 40 is detachably coupled to the module top end 21 which closes the normally upwardly open cavity 26 when in place. Lid 40 may be a hollow circular structural shell filled with a radiation shielding material such as a concrete plug or liner 41. Other shielding materials may be used in addition to or instead of concrete. Lid 40 provides radiation shielding in the vertical direction, whereas the concrete liner 72 disposed in the sidewall 77 of the module provides radiation shielding in the lateral or horizontal direction. In one embodiment, lid 40 may have a generally circular structure including an outer shell comprising a top cover 43, bottom cover 45, and a circumferentially-extending peripheral ring wall 48. Concrete liner 41 is encased inside the top and bottom covers and the ring wall which are welded together to form a permanently joined assembly, such as via seal welding in one embodiment. The opposing top and bottom major surfaces of each of the covers 43, 45 may be parallel to each other and flat as shown. A pair of lifting ribs or beams 49 are at least partially embedded in the concrete liner 41 of the shell. The lifting beams 49 may each have an interlocked X-shaped arrangement oriented perpendicularly to each other. Each beam may be a strong flat vertically oriented metallic plate (e.g. steel) arranged perpendicularly to each other as shown. The beams 49 are interlocked to each other via mating vertical slots 49-2 as shown and welded together. One slot opens upwardly and the other downwardly such that the bottom edges of the beams 49 lie in the same horizontal reference plane when the beam assembly is completed. The lifting beam 49 plates extend laterally/horizontal for the full diameter of the lid and may abut the inner surface of the peripheral ring wall 48. The lifting beam plates extend vertically from the bottom surface of the top cover 43 downwards through the bottom cover 45 via an X-shaped slot 45-1 formed in the bottom cover. The slot is complementary configured to the lifting beam plates (best shown in FIG. 12). The lower portions 49-3 of the lifting beams 49 thus are exposed and protrude vertically below the bottom major surface of the lid's bottom cover 45. In one embodiment, the exposed lower portions of beams 49 may have a multi-stepped configuration and project downward farther than the annular outlet vent screen 46. One purpose is to protect the screen from damage when the lid is placed on a flat surface during the canister loading operations. According to a notable aspect of the lid 40, the central-most and vertically deepest/highest part of the exposed beam lower portions 49-3 may further project downwards into the cavity below the top end 21 of the module body 28 when the lid 40 is seated on top of the module. This feature, along with the vertically shallower/shorter outer peripheral portions of the exposed stepped lower portions 49-3 of lifting beams 49, advantageously provide enhanced radiation attenuation and shielding to minimize block radiation escape through the cooling air outlet vents 70 (see, e.g. FIG. 15). This downward projection of the lifting beam lower portion 49-3 causes neutron scatter and interferes with the radial streaming and scattering of radiation out of the air outlet vents 70. Beneficially, use of the metallic lifting beams plates to block neutron stream instead of a solid concrete plug used in some lid designs make the present lid 40 lighter in weight, easier to handle, and eliminates the need for complexly configured air venting arrangements formed through lid which adds to fabrication costs. Additionally, the stepped lower portions 49-3 of lifting beams 49 also as act as shear support under side impact forces or lateral vibrations induced by seismic events. This keeps the lid 40 centered on the module 20 and reduces shearing forces on the closure fasteners 42. Another unique aspect of the downwardly protruding exposed lower portion 49-3 of the lifting beam 49 plates is that it divides the circumferentially-extending radial cooling air outlet 70 into four quadrants beneath the lid at the lid-to-module body interface. The quadrant-shaped air outlet ducts 70 act as wind breaks or shields to block and mitigate the adverse impacts of wind blowing against on the radial discharge direction of heated cooling air emitted from the module. Accordingly, because the wind typically blows from one direction, only heated cooling air flow discharged from the windward single or pair of air outlet quadrant might be impeded due to the increased backpressure caused by the wind since the lower portion of the lifting beam plates generally shields the other remaining leeward quadrants from the wind to maintain their normal discharge airflow rate. It further bears noting that the quadrant-shaped air outlet ducts 70 further provide a greater air discharge flow area with full 360 degree outflow from the module 20 than multiple individual smaller ducts which create a greater resistance to air flow that impedes heat removal from the SNF canister in the module cavity 26. The cavity is thus fully open to the underside of the lid without requiring the heated cooling air to be funneled into smaller diameter or sized outlet ducts with concomitant reduction in discharge of heat air from the module. When the lid 40 is emplaced on the storage module 20, it bears noting that the shallower outer peripheral portions of the exposed stepped lower portions 49-3 of lifting beams 49 are configured to engage the top end 21 of the module body 28 which supports the weight of the lid. This engagement also eliminates annular gaps between the stepped lower portion 49-3 and module to enhance radiation shielding and wind blocking. Accordingly, it is apparent to one skilled in the art that the unique lifting beams 49 configuration disclosed herein provides a multitude of benefits beyond simply providing a lifting structure for the lid. Each lifting beam 49 further includes a pair of upwardly protruding lifting lug 49-1 which extend upwards through slots 43-1 in the top cover 43. Each lifting lug includes a hole for coupling rigging thereto to raise and lower the lid with a crane or hoist. The lifting beams 49 and lid have a sufficiently robust structure and thicknesses to allow the entire storage module 20 with loaded SNF canister 29 therein to be lifted via the lifting beams. The X-shaped lifting beam arrangement ensures that the weight of the lid 40 is carried evenly to prevent distortion when lifted. To secure the lid to the module body 28 in a manner which allows the module to be lifted via the lid 40 and lifting beams 49, the lid 40 may be bolted to the top end 21 of the module body via a plurality of threaded closure fasteners 42 (see, e.g. FIG. 2). Four fasteners may be used in one representative construction. The fasteners 42 may be one piece or comprise an assemblage of a threaded stud and heavy hex nut. The module body 28 includes internally threaded mounting sleeves 42-1 rigidly mounted in its top end 21 which threadably engage the fasteners 42. In one embodiment, the mounting sleeves 42-1 may be welded to metallic upper radial shell interconnector plates 73 rigidly affixed to the inner and outer shells 23, 24 of the module 20 (further described below). The interconnector plates 73 form part of the module's superstructure. Upwardly open mounting slots 73-1 may be formed in plates 73 which receive the sleeves for welding thereto. To maintain a vertical opening through lid 40 for the bolting, a plurality of tubular collars 44 may be rigidly mounted via welding to the top and/or bottom covers 43, 45 of the lid to form passages through the concrete liner for the closure fasteners 42. The collars 44 may protrude slightly above the top surface of the lid's top cover 43. In the unlikely event that the nuclear fuel storage module 20 might tip over on the concrete support pad CP when being maneuvered via the crane, the collars would take the brunt of the force from the fall and transfer it to the robust body of the module to prevent or minimize structural damage to the lid. In various embodiments, the lid 40 may also be seal welded to the module 20 in addition to bolting or instead of bolting; however, the module may be lifted with reliance on the bolting assembly alone for support and strength. The top end 21 of storage module 20 may further include a top plate ring 47 which partially closes the top end of the module body 28 and sidewall 77. Top plate ring 47 has a circular horizontally flattened body with flat top and bottom surfaces and a height substantially less than a width. Plate ring 47 may be secured to the outer shell 24 via welding, and optionally the tops of the upper interconnector plates 73 thereby forming an integral part of the module body structure. A plurality of annular lid spacers 42-2 are provided; one spacer 42-2 for each closure fastener 42. The fasteners extend completely through the spacers which are interspersed between the bottom cover 45 of the lid 40 and the top end 21 of the module. Each spacer 42-2 nests partially inside a semi-circular cutout 47-1 in the top plate ring 47 of the module 20 which helps locate the spacers on the module. The spacers 42-2 form and maintain a vertical air gap G at the interface between the bottom cover 45 of the lid 40 and the top end 21 of the module 20 to form the radial cooling air outlet ducts 70. Gap G may be about 3 inches as one representative non-limiting example. The gap G is closed at its periphery by a perimetrically and circumferentially extending annular outlet vent screen 46. The screen 46 may be comprise a metallic plate ring (e.g. steel) which includes a plurality of radial through perforations or holes forming open area for venting heated cooling air radially outwards between the bottom of lid 40 and top end 21 of the module body 28 from gap G. This defines the cooling air outlet ducts 70. The annular outlet screen 46 may be welded to the bottom cover 45 of lid 40 and protrudes downwardly therefrom for a distance co-extensive in height to and enclosing otherwise radially open gap G. With exception of the concrete liner, the foregoing lid-related components are preferably all formed of a metal such as without limitation steel (e.g. carbon or stainless). The vertical nuclear fuel storage module 20 includes a natural circulation cooling air ventilation system. Referring generally to FIGS. 1-14 as applicable, the ventilation provisions include a plurality of cooling air inlet ducts 50 to introduce ambient cooling air into the module cavity 26, and cooling air outlet ducts 70 to expel the air heated from the cavity (which flows vertically upwards alongside the sidewall of the heat-emitting fuel canister 29) back to atmosphere. Both the air inlet and outlet ducts may generally be radially oriented as shown in the illustrated embodiment. In a one non-limiting preferred embodiment, the air inlet ducts 50 are disposed in the lower portion of module 20 proximate to the bottom end 22 of the module and cavity 26, and the air outlet ducts 70 are disposed proximate to the top end 21 of the module and cavity. Each air inlet duct 50 extends completely through the sidewall 77 of module 20 from the outer shell 24 to the inner shell 23. The ducts 50 define an air inlet passageway which places the lower portion of the module cavity 26 in fluid communication with ambient atmosphere and cooling air. In one embodiment, the air inlet ducts 50 may have a multi-angled circuitous configuration designed to both advantageously prevent the ingress of rain or standing water into the cavity and to prevent straight line neutron streaming to the ambient environment. Each duct 50 includes an exterior inlet end opening 54 forming an opening penetrating the outer shell 24 and an interior outlet end opening 55 forming an opening penetrating the inner shell 23 into the module cavity 26. The outlet end openings of each air inlet duct 50 are arranged to introduce ambient cooling air directly into the bottom of the ventilation annulus 31 between the canister 29 and inner shell 23, and preferably adjacent to the top surface of the baseplate 27. The inlet end opening includes a top 102 and opposing bottom 103. The outlet end opening includes a top 104 and opposing bottom 105. No portion of the air inlet ducts 50 extend below the baseplate, but instead extend only through the sidewalls in the described embodiments. Referring to FIGS. 3-5, the air inlet ducts 50 in one non-limiting embodiment includes an inlet section 51 adjacent to the inlet end opening 54, an outlet section 52 adjacent the outlet end opening 55, and an intermediate section 53 extending radially between the inlet and outlet sections. In one embodiment, the air inlet ducts 50 may have a rectilinear transverse cross-sectional configuration such as rectangular (best shown in FIG. 4). Ducts 50 may be horizontally elongated having a greater width than height to produce a slim profile. Each duct 50 includes a roof wall 100, opposing floor wall 101, and pair of lateral sidewalls 106 extending therebetween. Each wall or sidewall is perpendicularly oriented to its adjoining walls or sidewalls. Ducts 50 may be embedded in the concrete liner 72 of the sidewall 77 of the module body. In fabrication, the inlet end opening 55 of each duct 50 is seal welded to the outer shell 24 and the outlet end opening 54 is seal welded to the inner shell 23 of the module. This not only seals the ducts to shell interfaces, but also supports the ducts 50 in position until the concrete liner is poured around the ducts to complete the embedment. The inlet section 51 of duct 50 penetrates the module outer shell 24 to form the flow inlet end opening 54. Inlet section 51 may be obliquely angled upwards relative to the longitudinal axis LA of the module and baseplate 27 such that the innermost end of inlet section 51 at the joint to intermediate section 53 of duct 50 is higher than its outermost end. This defines the highest point HP1 of the roof wall 100 of the air inlet duct 50, which preferably is higher in elevation than the top 102 of the inlet end opening 54. Such an arrangement advantageously resists the ingress of rainwater into the duct 50 from the ambient environment. To prevent choking off the cooling air flow through the duct 50 to the canister in cavity 26 of the module 20 as the surround water level rises during a flood event, the highest point HP2 of the floor wall 101 of duct 50 preferably is lower in elevation than the top 102 of the air inlet end opening 54. This maintains a flowpath for the cooling air to flow through the air inlet duct 50 to the canister in the module to continue air cooling until the water level rises above the top end 102 of the inlet air opening 54. In that case, water will enter the duct 50 and module cavity 26 to water cool the canister and prevent overheating and degradation of the SNF stored inside and its fuel shielding. Intermediate section 53 of the cooling air inlet duct 50 may be obliquely angled downwards relative to the longitudinal axis LA such that the innermost end of intermediate section 53 is lower than its outermost end adjoining the inlet section of the duct 50 at the joint. The intermediate section may be longer in length than the inlet and/or outlet sections 51, 52. The upwardly angled inlet section 51 advantageously prevents ingress of rainwater into the inlet duct 50. Outlet section 52 may be horizontal and perpendicularly oriented relative to longitudinal axis LA in one embodiment as illustrated. The outlet section 52 penetrates the module inner shell 23 to form a flow outlet opening. Obliquely angled joints 50-1 may be formed between the duct sections 51, 52, and 53 as shown. In some possible constructions, the outlet section may be omitted and the intermediate section 53 may be directly seal welded to and penetrates the inner shell 23 of module 20 to form the outlet opening. To prevent standing water or particularly floodwater from entering the cooling air inlet ducts 50 at flood prone nuclear fuel storage sites, the inlet end openings 54 of the ducts in the outer shell 24 are preferably spaced by a sufficient preselected vertical distance D1 above the bottom of the baseplate 27 which rests on the concrete support pad CP. Distance D1 is measured to the bottom 103 of inlet end openings 51 of air inlet ducts 50 from the bottom of the baseplate 27 (see, e.g. FIG. 3). Some representative non-limiting examples of a minimum value of D1 is at least 1 foot, and preferably at least 3 feet in some flood resistant embodiments. Distance D1 may be selected and adjusted as needed based on the prevailing or historic flood levels anticipated at the nuclear fuel storage site. In one embodiment, the inlet end openings 54 of the cooling air inlet ducts 50 are located at a higher elevation than the outlet end openings 55. The inlet end openings are located on a lower half or portion of the module below the module vertical midline ML defined at half a height of the module (measured from top end 21 to bottom of the baseplate 27 integrally attached to the bottom end 22 of the shells 23, 24). In one embodiment, the inlet end openings 54 are located on the lower portion of the module at 25 percent or less than the height of the module below the midline ML. The air inlet ducts 50 are configured to draw cooling air radially inwards into each duct through the inlet end openings 54 and direct the cooling air then downwards in the air inlet duct to its respective outlet end opening 55 and into cavity 26. Cooling air is therefore radially discharged into the internal cavity of the module from the outlet end openings of each air inlet duct 50. It bears noting that the inlet end openings 54 of the air inlet ducts are radially open directly to ambient atmosphere without any additional extension piping or ducting which adversely increases resistance to flow and decreases the cooling air flow into the module cavity 26. In one embodiment, the inlet end openings 54 of the air inlet ducts 50 may have a vertically staggered arrangement in which the elevation of the inlet end of each inlet air duct is at a different elevation and distance D1 above concrete support pad CP than the inlets end of each adjacent inlet air duct on either side as shown. This staggered arrangement advantageously prevents each inlet duct 50 from drawing ambient cooling air from the same elevation to maximize cooling effectiveness and eliminate potential temperature stratification of available cooling air surrounding the storage module 20. It bears noting that the lowest inlet end openings 54 of the air inlet ducts 50 in the staggered arrangement if used may meet the foregoing elevation criteria previously described herein for placement in accordance with vertical spacing distance D1 above the baseplate 27 and concrete support pad CP to prevent the ingress of standing water or floodwater. In other possible embodiments shown in FIGS. 7 and 12, however, the inlet end openings 54 of the air inlet ducts may be at the same elevation and spacing D1 above the concrete support pad CP. The outlet end openings 55 of the cooling air inlet ducts 50 are preferably located in the inner shell 23 adjacent to the top surface 27-1 of baseplate 27. This introduces cooling air radially into the lowermost part of the module cavity 26 and ventilation annulus 31 to maximize cooling efficiency and heat removal from the canister 29. In one non-limiting embodiment as illustrated, the air inlet ducts 50 may have a mitered construction formed of sections of ducting seal welded together at joints formed between the inlet, outlet, and intermediate sections 51-53 of the ducts. The ducts may be formed a suitable metal such as steel (e.g. carbon or stainless) in one embodiment. The inlet ducts 50 emulate the shape of a periscope with the angles of the mitered sections selected as needed for installation and neutron streaming blocking. It bears noting that the seal welding mentioned herein refers to continuous welds that form hermetically sealed joints that are water and gas/air tight. The welded mitered joints of the mitered duct 50 allows radiation attenuation shields 50-1 to be placed transversely in the ducts to the air flow direction at the joints to enhance neutron streaming blocking (see, e.g. FIGS. 3 and 5). In one embodiment, perforated steel plates 56 may be used for shields 50-1 at least at the mitered joint between the inlet and intermediate sections 51, 53 of each mitered joint. In other embodiments, a shield 50-1 may be also be disposed at the joint between the intermediate and outlet sections 53, 52 of the ducts 50 (e.g. two total at the joints between the intermediate section 53 and adjoining inlet and outlet sections 51, 52). The perforations allow cooling air to flow through neutron blocking plates, but reduces neutron streaming. In other embodiments, external radiation shields 80 may also be attached to the exterior of the inlet air ducts 50 (see, e.g. FIG. 5) which are further described herein. In other constructions contemplated, the inlet ducts 50 may have the same design described above but can be formed by a single monolithic unitary tube of rectilinear cross-sectional shape hot bent to shape with curvilinear bends formed between the intermediate section 53 and adjoining inlet and outlet sections 51, 52. In such a case only the inlet and outlet end openings 54, 55 of each duct 50 is seal welded to the outer and inner shells 24, 23, respectively. In such a construction, the external radiation attenuation shields 80 may be used with the ducts. FIGS. 14-17 depict an alternative configuration of a mitered and welded cooling air inlet duct 50″. In this embodiment, the upwardly angled inlet section 51 described above is eliminated. Air inlet duct 50″ includes obliquely/downwardly angled intermediate section 53″ and obliquely/downwardly angled outlet section 52″. Outlet section 52″ is oriented at a different oblique angle to longitudinal axis LA and baseplate 27 of module 20 than intermediate section 53″. As one non-limiting illustrative example, outlet section 52″ may be disposed at an oblique angle of about 30 degrees to the horizontal baseplate 27 and intermediate section 53″ may be oriented at an oblique angle of 45 degrees or greater, such as about 70 degrees in one configuration. Other oblique angles may be sued. Because previous inlet section 51 shown in FIGS. 3 and 5 previously described herein is eliminated, intermediate section 53″ may be considered to serve as the inlet section of the alternative duct 50″. The outer end of intermediate duct section 53″ defines the exterior inlet end opening 54″ and the inner end of outlet duct section 52″ defines the interior outlet end openings 55″ of the duct. Duct 50″ may similarly be formed of steel or another metal. Both mitered inlet air ducts 50″ (FIGS. 14-17) and 50 (see, e.g. FIG. 3) may further each include a radiation attenuation shield 80 which is attached to the exterior of each of the ducts, such as via welding, fasteners, or other methods. The shield members may be attached to the top surface of the roof wall of the ducts in one embodiment as illustrated. Radiation shields 80 are complementary configured to ducts 50/50″ and include two obliquely orientated sections as shown to match the angled sections of the mitered ducts. The shields 80 have a multi-angled plate-like body which extends radially through module sidewall 77 from proximate to the outer shell 24 adjacent to inlet vent shield covers 54-1 to the inner shell 23 thereby shielding and covering substantially the entirety of the top of each inlet duct 50/50″. The shields may have a lateral width approximately as wide as the ducts 50/50″ and length substantially coextensive with the radial length of the ducts. In one embodiment, shields 80 may be formed of steel plate; however other metallic materials including boron-containing materials may be used. The inlet end openings 54″ of each mitered duct 50″ or 50 may be fitted with a perforated radiation attenuating inlet vent shield cover 54-1 which is attached to the outer shell 24 of module 20 at each air inlet opening. Welding or fasteners may be used to secure the covers to the shell 24. The shield covers 54-1 have a configuration and sufficient thickness to a serve as both effective attenuation of radiation emitted through the ducts and to minimize the ingress of ambient rainwater while allowing cooling air to enter the ducts. Each cover 54-1 is thus a relatively thick structure in one (e.g. about 2 inches thick) which includes a plurality of through bores or perforations 54-2. In one embodiment, the covers 54-1 may be made of steel; however, other metallic materials including those containing boron may be used. The perforations are obliquely angled in orientation relative to longitudinal axis LA of module 20 such that their outer ends are lower than their inner ends to preclude the entrance of rain and to eliminate any straight line of sight through the perforations from end to end to prevent neutron streaming. In yet other possible constructions, alternative cooling air inlet ducts 50′ shown in FIG. 6 may be provided which are formed instead of circular flow conduits. Alternative circular ducts 50′ may be formed from standardly available sections of metal piping (e.g. steel) of circular cross section which are seal welded together to emulate the same general periscopic shape as inlet air ducts 50 previously described herein. For example, inlet section 51′ may be formed by a 60 degree long radius elbow, outlet section 52′ may be formed by a 45 degree long radius elbow, and intermediate section 53′ be formed by a straight pipe section. The same angular orientations of these different sections may be the same as their counterparts in rectilinear air inlet duct 50 previously described herein. In some variations, the piping air inlet duct 50′ may be formed from three straight sections of circular piping which are cut to form miter joints between the different sections 51′, 52′, and 53′. In yet another variation, the piping air inlet duct 50′ may instead be formed by a single monolithic unitary section of piping of circular cross-sectional shape hot bent to shape with curvilinear bends between the intermediate section 53′ and adjoining inlet and outlet sections 51′, 52′. The arrangement of any of the foregoing piping structures in relation to the lower section of storage module 20 may be the same as rectilinear air inlet duct 50 previously described herein (see, e.g. FIG. 3). Accordingly, the air inlet and outlet end openings 54′, 55′ of the duct 50′ may be at identical locations to the inlet and outlet end openings of the rectilinear air inlet duct 50. In operation, ambient cooling flows generally inwards 360 degrees around module 20 in all directions into the inlet ducts. The cooling air then flows in a generally downward direction in each air inlet duct 50 traversing the full radial extent or thickness of the cask's sidewall 77 before entering module cavity 26 near the bottom of the ventilation annulus 31. Thus, while the cooing air enters the module 20 well above its bottom to prevent the ingress of floodwater via the outer inlet end openings 54 of the inlet ducts 50 through the outer shell 24, the full benefit of the maximum vertical distance available within the cavity 26 between the top and bottom vents for cooling the nuclear fuel-bearing canister 29 is advantageously maintained. After the cooling air enters the bottom of the ventilation annulus 31 inside module 20, the air is heated by the canister 29 and flows vertically upwards in the annulus from the air inlet ducts 50 to the air outlet ducts 70 at the top of cavity 26. The heated cooling air is then discharge radially outwards from the module 20 in all directions 360 degrees around the module. It bears noting that an advantageous aspect of any of the foregoing inlet air ducts having a majority of their radial length obliquely angled in a downward direction toward the cavity 26 of the storage module 20 will act to drain any water or rain entering module into the bottom of the cavity. At this location in the cavity, the water will be exposed to the heat emitted from the canister and evaporated. The present obliquely angled duct arrangements thus effectively eliminate any horizontal portions of ducting of any substantially length where water might accumulate and accelerate corrosion of the ducting. According to another aspect of the invention, the inner and outer shells 23, 24 of the main body of the module 20 may be structurally tied and joined together via a pair of welded rigid radial shell interconnector plates 73, 74. Upper interconnector plates 73 are located at the top end 21 of the module. Lower interconnector plates 74 are located at the bottom end 22 of the module. The two interconnector plates in turn are spaced vertically apart from each other as shown. The interconnector plates 73, 74 extend radially from the inner shell 23 to the outer shell 24 of module 20 and are welded at each of their ends to each shell. Each interconnector plate 73, 74 has opposing inner and outer vertical edges welded to the inner and outer shells 23, 24, respectively. The interconnector plates 73, 74 each have a height less than the height of the module, and preferably less than half the height of the module (see, e.g. FIGS. 3 and 8). In one embodiment, the radial interconnector plates may each have a flat, vertically oriented body which is perpendicularly and radially oriented relative to the inner and outer shells 23, 24. In other embodiments, the radial interconnector plates can be slightly oblique in angular orientation to the shells if desired. Four interconnector plates 73, 74 evenly spaced circumferentially apart may be provided in one embodiment as shown; however, other embodiments may have more or less plates. The interconnector plates 73, 74 may be formed of steel (e.g. carbon or stainless) in one embodiment. A representative thickness of plates 73, 74 is about 1 inch in one non-limiting embodiment. The upper interconnector plates 73 serve dual important functions. First, similarly to lower interconnector plates 74, the upper interconnector plates 73 rigidly reinforce the module structure. Secondly, the upper interconnector plates further function as the lifting points for the module to transfer the weight of the entire module (with SNF canister inside) to the closure fasteners 42 and lifting beams 49 in the lid 40 to the crane or hoist. The dead load of the module is thus transferred through the skeleton of the module 20 formed by the weldment of the metallic inner and outer shells 23, 24, lower interconnectors 74, and baseplate 27 to the upper interconnector plates 73 where it is picked up by the bolting. The combination of the weld joined shells 23, 24, interconnector plates 73, 74 and a thick rigid baseplate 27 provide a strong rigid structural weldment which support as dense a concrete fill or liner 72 (serving as radiation shielding material) in the sidewall 77 of module 20 particularly when lifted as a unit. Concrete fill weighing as much as 250 pcf (pounds per cubic foot) density are typically employed to maximize blockage of radiation. This rigid structural shell assembly ensures that the base plate 27 which bears the entire dead load of the concrete liner, shells, and lid 40 does not deform when lifted off the concrete support pad CP by a hoist or crawler crane. While the foregoing description and drawings represent some example systems, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope and range of equivalents of the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. In addition, numerous variations in the methods/processes described herein may be made. One skilled in the art will further appreciate that the invention may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims and equivalents thereof, and not limited to the foregoing description or embodiments. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention. |
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abstract | An apparatus for passively cooling and retaining molten core material discharged from a damaged reactor vessel during a severe accident in the nuclear plant including: a molten core material retention tank to retain molten core material; a compressed gas tank storing high-pressure inert gas; a cooling water storage tank being installed higher than the molten core material retention tank; and a mixing means. The molten core material retention tank includes an outer retention vessel having at least one coolant hole, a porous protection vessel formed at an inside of the outer retention vessel, and a gravel layer formed between the outer retention vessel and the porous protection vessel. The apparatus can be installed in a reactor cavity without changing the compartment structure of a containment building, and makes it possible to prevent a steam explosion during the cooling process for the ultrahigh-temperature molten core material and to secure the reliability of the cooling process. |
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claims | 1. A liquid metal ion gun comprising:a liquid metal member that is made of a first metal material;a liquid metal ion source that includes a reservoir and a emitter, the reservoir being made of a second metal material and holding the liquid metal member, the emitter being made of the second metal material; anda beam limiting aperture that is formed with a liquid metal member made of the first metal material placed on a base made of the second metal material, has an opening enabling an ion beam extracted from the liquid metal ion source to pass therethrough, and limits the diameter of the ion beam,wherein the beam limiting aperture has a structure that causes the liquid metal member to gather into a region located around the opening,the base has a recessed portion that is provided so as to include the opening, anda distance between the opening and an outer circumference of the recessed portion is smaller than a capillary length of the liquid metal member made of the first metal material. 2. The liquid metal ion gun according to claim 1,wherein the base has a groove structure that is provided on an inner side of the recessed portion and surrounds the opening. 3. The liquid metal ion gun according to claim 1,wherein the base includes a groove structure that is provided so as to surround the opening, andwherein an annular member is placed so as to surround the groove structure, and forms a recessed portion that includes the opening. 4. The liquid metal ion gun according to claim 1, further comprising:an annular member that is provided so as to surround the opening, and forms a recessed portion that includes the opening,wherein the annular member is made of a metal material whose wettability with the liquid metal member made of the first metal material is lower than at least wettability with the second metal material. 5. The liquid metal ion gun according to claim 4, further comprising:a groove structure that is provided on an inner side of the recessed portion so as to surround the opening. 6. The liquid metal ion gun according to claim 5,wherein at least a part of the groove structure is located in a region extending from an outer circumference of the recessed portion to a bottom surface of the recessed portion. 7. The liquid metal ion gun according to claim 1,wherein the first metal material is gallium, and the second metal material is tungsten. 8. The liquid metal ion gun according to claim 7,wherein a surface of the beam limiting aperture is wetted with molten gallium and the gallium is then solidified, so that the surface of the beam limiting aperture is formed. 9. An ion beam device comprising:a vacuum container;a liquid metal ion gun that is located inside the vacuum container and includes a liquid metal ion source and a beam limiting aperture; andan acceleration electrode,wherein the liquid metal ion source includes:a liquid metal member that is made of a first metal material;a reservoir that is made of a second metal material and holds the liquid metal member; andan emitter that is made of the second metal material,wherein the beam limiting aperture is formed with a liquid metal member made of the first metal material placed on a base made of the second metal material, has an opening enabling an ion beam extracted from the liquid metal ion source to pass therethrough, and limits the diameter of the ion beam, the base of the beam limiting aperture has a recessed portion that is provided so as to include the opening as a having a structure that causes the liquid metal member to gather into a region located around the opening, and a distance between the opening and an outer circumference of the recessed portion is smaller than a capillary length of the liquid metal member made of the first metal material, andwherein the acceleration electrode is located inside the vacuum container and accelerates the ion beam that has passed through the opening. |
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062663925 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soller slit used in an X-ray device, etc., for collimating diverging X-rays to parallel X-rays and a manufacturing method of the same soller slit. 2. Description of the Related Art In general, a soller slit is constructed by piling up a plurality of thin metal foils with interposing a spacer therebetween and is used in an X-ray optical system to restrict vertical and/or horizontal divergence of X-rays. The metal foils of the conventional soller slit may be formed from rolled stainless steal or brass (Cu-Zn) and the like. However, since such rolled metal foil has a mirror-surfaces, incident X-rays R1 are totally reflected thereby as shown in FIG. 7, so that it is impossible to obtain parallel X-ray beams having required precision to thereby obtain an aimed resolution in an X-ray measurement. Particularly, in a case where the aimed resolution is not more than the critical angle for wavelength of incident X-rays at which total reflection occur, a divergence of X-rays due to total reflection becomes substantially equal to or more than the resolution, causing a big problem. In order to restrict the total reflection, it has been usual, for example, to rough the surfaces of the metal foils by emery papers, to etch them with using acid, and to plate them. However, in any of the conventional roughing techniques, satisfactory high precision parallel X-ray beams, and thus, high resolution has not been obtained. SUMMARY OF THE INVENTION The present invention was made in view of the above mentioned state of art and has an object to provide a soller slit capable of forming parallel X-ray beams with high precision and improving resolution in an X-ray measurement. According to the present invention, the above object can be achieved by a soller slit that is featured by the following matters: (1) A soller slit comprising a plurality of metal foils stacked with a constant interval between adjacent foils and having a function to restrict divergence of X-rays when arranged on an X-ray optical path, is featured by that each metal foil is formed by sintering a metal material such that surfaces of the metal foil have high harmonic surface roughness. In this specification, the term "high harmonic surface roughness" means the roughness of surface having a repetition of irregularity at short period, like high frequency vibration. In detail, the surface of the metal foil is smoother than a surface having a repetition of irregularity at long period like a surface roughed by emery finishing, by etching with acid etc., and is rougher than a super smooth surface such as a glass surface. In more detail, it is the surface roughness enough to prevent total reflection of X-rays from occurring. The term "sintering" has the usual meaning. That is, a metal foil prepared by sintering a material can reliably provide high harmonic surface roughness within the required roughness range. The sintering is a still developing technology and it has been known that the surface roughness of a metal foil prepared by sintering a metal material with using the conventional sintering technology is considerable and it is difficult to provide the high harmonic surface required in the present invention. Recently, however, it becomes possible to provide such surface roughness as required in the present invention, by the sintering technology. In view of the recent development of the sintering technology, it may be possible to form an ultra smooth surface condition close to a mirror surface having space period not larger than several tens .mu.m and root mean square (RMS) value not larger than several tens nm(nanometer) by a sintering processing. In such case, however, a resultant ultra smooth surface might be outside the high harmonic surface condition required in the present invention. In the soller slit according to the present invention, it is possible to prevent X-rays incident to the soller slit from being totally reflected on metal foils since metal foils have a high harmonic surface roughness. Thus, high precise parallel X-ray beams can be obtained, to thereby improve resolution in the X-ray measurement. (2) Surface roughness of the metal foil and the like can be generally defined by the space period of X-rays and the RMS value (that is, mean amplitude of X-rays). A relatively rough surface obtainable by emery finishing and the like usually has a surface roughness defined by space period of 0..about.1 mm and by RMS value of 0.1.about.1 .mu.m. Also, an ultra smooth surface of a product such as a silicon substrate or a plate glass usually have a roughness defined by space period not larger than 25 .mu.m and by RMS value of about 0.2 nm. The high harmonic surface roughness in the present invention corresponds to surface roughness having space period of, for example not larger than 50 .mu.m, preferably 20.about.50 .mu.m and RMS value of, for example 20 nm.about.1 .mu.m, preferably 20.about.50 nm, with which total reflection of X-rays can be prevented. Particularly, in order to obtain the effect expected in the present invention, it is considered as necessary to set RMS value within the above mentioned range. (3) In the above-mentioned construction, the material forming the metal foil is not limited to any specific material. However, it may be preferably tungsten or molybdenum and the like. (4) Another soller slit according to the present invention, which includes a plurality of metal foils stacked with a constant interval between adjacent foils and functions to restrict divergence of X-rays when the soller slit is arranged on an X-ray optical path, is featured by that each metal foil has oxide material formed on surface thereof by an oxidation processing and having high harmonic surface roughness. Since the metal foils of the soller slit have high harmonic surface roughness, it is possible to restrict total reflection of X-rays incident on the soller slit, so that it becomes possible to form high precision parallel X-ray beams, to thereby improve resolution in the X-ray measurement. Further, since the compound that is lighter in mass than the metal foil exists on the surfaces of the metal foil, another effect of reducing the critical angle for total reflection can be obtained. Incidentally, the term "oxidation processing" means a processing for forming oxides on the surfaces of the metal foil, which is different from the etching processing for etching the surfaces of the metal foil. Etching processing cannot produce high harmonic surface roughness required in the present invention. (5) In the construction of the soller slit mentioned in the paragraph (4), high harmonic surface roughness preferably has RMS value of 20 nm.about.1 .mu.m, more preferably 20 nm.about.50 nm. (6) In the construction of the soller slit mentioned in the paragraph (4), the material of the metal foil is not limited to any specific metal. For example, it may be brass or stainless steal, etc. In a case where brass is used as the material of the metal foil, using dense nitric acid or permanganate and the like can perform the oxidation processing. Also, in a case of employing a stainless steal, the oxidation processing using nitric acid may be difficult, since an oxide layer is formed on the surface of the metal foil and prevents further oxidation from occurring. (7) A first method according to the present invention for manufacturing a soller slit including a plurality of metal foils stacked with a constant interval between adjacent ones of the metal foils, said soller slit being arranged on an X-ray optical path to restrict divergence of X-rays, wherein the metal foils are prepared by sintering a metal material such that surfaces thereof have high harmonic surface roughness. According to this method, it is possible to collimate diverging X-rays to high precision parallel X-ray beams by preventing X-rays incident on the surfaces from being reflected totally to thereby improve resolution in the X-ray measurement. (8) A second method according to the present invention for manufacturing a soller slit including a plurality of metal foils stacked with a constant interval between adjacent ones of the metal foils, said soller slit being arranged on an X-ray optical path to restrict divergence of X-rays, wherein oxide material is formed on both surface of each said metal foil by oxidizing said metal foil and said oxide material has high harmonic surface roughness. According to the second method, it is also possible to form high precision parallel X-ray beams by preventing X-rays incident on the surfaces from being reflected totally to thereby improve resolution in the X-ray measurement. |
062114247 | claims | 1. A module for vitrification of waste comprising: a disposable canister; and, frit loaded inside the canister wherein the frit is in the form of one or more solid sections creating one or more regions in the canister for receiving waste, wherein each section is continuous to the approximate width or the height of the canister, and wherein the sections have a combined unmelted density in the canister of about 100%. a. loading frit into a canister wherein the frit is in the form of one or more solid sections creating one or more regions in the canister for receiving waste, wherein each section is continuous to the approximate width or the height of the canister, and wherein the sections have a combined unmelted density in the canister of about 100%; b. loading waste into said region or regions; c. heating the waste and frit inside the canister until a melted mixture is obtained; and d. cooling said melted mixture to form a vitrified product. 2. A module according to claim 1 further comprising an inner container disposed inside the canister; and a thermal insulator disposed between the canister and the inner container. 3. A module according to claim 1 wherein said frit comprises a plurality of vertical rectangular plates. 4. A module according to claim 1 wherein said frit has a cross-shaped cross section. 5. A module according to claim 1 wherein said frit has a honeycomb cross section. 6. A module according claim 1 wherein said frit comprises a plurality of angled horizontal plates. 7. A module according to claim 1 wherein said frit has a star-plate cross section. 8. A module according to claim 1 wherein said frit comprises a plurality of cylindrical rods. 9. A module according to claim 1 wherein said frit comprises a plurality of hollow cylindrical rods. 10. A method for vitrifying waste comprising the steps of: 11. The method according to claim 10 wherein said canister is a module having an inner container, an outer container and a thermally insulating material between said inner container and outer container. 12. The method according to claim 10 wherein said frit is one or more vertical rectangular plates. 13. The method according to claim 10 wherein said frit has a cross-shaped cross section. 14. The method according to claim 10 wherein said frit has a star-plate cross section. 15. The method according to claim 10 wherein said frit has a honeycomb cross section. 16. The method according to claim 10 wherein said frit has an angled horizontal plate cross section. |
abstract | Contamination control apparatus and methods for the removal of particulate contamination on EUV mirrors and reflective masks are provided. Embodiments in accordance with the present invention involve providing a charge to the particles and moving them away from the reflective surface by electrostatic elements. An electron source and one or more electrostatic elements are positioned adjacent the reflective surface of the reflective component. The electron source is adapted to shower electrons onto the particles in an area above the reflective surface and on the reflective surface to provide a negative charge to the particles. The electrostatic elements are adapted to provide an attractive electrostatic charge to attract the negatively charged particles on and near the reflective surface. |
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claims | 1. Use of a transponder (2) during a disconnection process which is performed in the course of maintenance, serving and/or repair work on a component and/or a commercial installation, wherein the disconnection process comprises the steps of creating a disconnection plan, of performing the disconnection and of reconnection or normalization, and wherein the transponder (2) has a reception element (7), a transmission element (8), a visual display unit (6) and a memory unit (10) for storing at least one state/operational information unit and also a control element (9) which is operatively connected to these, in a commercial installation in an arrangement or positioning on or in proximity to the component or at a switching or measuring point associated with said component for the purpose of visually displaying an operating state for the component or the switching or measuring point associated therewith using the visual display unit (6) of the transponder (2), wherein the visual display unit (6) visually displays the number of stored state/operational information units and a warning signal is shown on the visual display unit (6) by means of the control element (9) when the number of stored state/operational information units is greater than zero. 2. Use of a transponder (2) according to claim 1 for producing a communication system comprising a read/write unit (3). 3. Use of a transponder (2) according to claim 1 for producing an information system comprising an electronic data processing (EDP) system. 4. Use of a transponder (2) according to claim 1, characterized by a fixed arrangement for the transponder (2) on the component. 5. Use of a transponder (2) according to claim 1, characterized in that the memory element (10) permanently stores a transponder identification information unit and is used to store at least one state/operational information unit which relates to a component associated with the transponder (2), wherein the transponder identification information unit and the at least one state/operational information unit are read from the memory element (10) via the transmission element (8), and the at least one state/operational information unit is supplied to the memory element (10) via the reception element (7), and wherein the transponder (2) is designed such that at least one portion of the information contained in the state/operational information units is displayed on the visual display unit (6). 6. Use of a transponder (2) according to claim 1, characterized in that the visual display unit (6) not visually displays the state/operational information unit itself. 7. Use of a transponder (2) according to claim 1, characterized in that the state/operational information units which can be stored in the memory element (10) each comprise a piece of information regarding a connection or disconnection state of the component and/or recently performed servicing on the component and/or a recently performed official examination of the component and/or recently performed measured value recording for the component. 8. Use of a transponder (2) according to claim 1, characterized in that the visual display unit (6) is a display based on electronic ink with bistable display elements and/or the transponder (2) is an RFID transponder. 9. Use of a transponder (2) according to claim 2, characterized in that the read/write unit (3) stores at least one state/operational information unit and at least one identification information unit, wherein each identification information unit has at least one associated state/operational information unit, the read/write unit (3) can read a transponder identification information unit from the memory element (10) of the transponder (2), and the read/write unit (3) takes the read transponder identification information unit as a basis for transmitting at least one state/operational information unit from the read/write unit (3) to the transponder (2). 10. Use of a transponder (2) according to claim 9, characterized in that the content of at the least one state/operational information unit which is stored in the read/write unit (3) can be altered by a user of the read/write unit (3) prior to the transmission to the transponder (2) and/or in that the read/write unit (3) is designed to compare the transponder identification information unit read from the transponder (2) with the at least one identification information unit stored in the read/write unit (3). 11. Use of a transponder (2) according to claim 9, characterized in that if the content of the transponder identification information unit and of an identification information unit matches then the read/write unit (3) reads state/operational information units stored in the transponder (2) and/or transmits a state/operational information unit which is associated with at least the identification information unit and which is stored in the read/write unit (3) from the read/write unit (3) to the transponder (2) and/or in that if the content of the transponder identification information unit and of an identification information unit matches then the read/write unit (3) sends a control signal to the transponder (2), which control signal prompts the control element (9) to erase a state/operational information unit stored in the memory element (10). 12. Use of a transponder (2) according to claim 3, characterized in that at least one of the state/operational information units stored in a read/write unit (3) is read from the read/write unit (3) by the central EDP system (4), and state/operational information units which are to be stored in the read/write unit (3) are transmitted from the central EDP system (4) to the read/write unit (3). 13. Use of a transponder (2) according to claim 12, characterized in that the central EDP system (4) is designed to process state/operational information units read by the read/write unit (3), particularly to compare them with state/operational information units stored in the EDP system (4). 14. Method for performing maintenance, servicing and/or repair work on a component and/or on a switching or measuring point associated with said component in a commercial installation wherein a transponder (2), which has a reception element (7), a transmission element (8), a visual display unit (6) and a memory element (10) for storing at least one state/operational information unit and also a control element (9) which is operatively connected to these, is arranged on or in proximity to the component or at the switching or measuring point associated with said component during a disconnection process which is performed in the course of the maintenance, serving and/or repair work on the component and/or the commercial installation, wherein the disconnection process comprises the steps of creating a disconnection plan, of performing the disconnection and of reconnection or normalization, and wherein the visual display unit (6) of the transponder (2) is used to visually display an operating state for the component or the switching or measuring point associated therewith on said visual display unit, wherein the visual display unit (6) visually display the number of stored state/operation information units and a warning signal is shown on the visual display unit (6) by means of the control element (9) when the number of stored state/operational information units is greater than zero. 15. Method according to claim 14, characterized in that use of the transponder (2) according to claim 2 is performed. 16. Commercial installation characterized in that it is equipped with a transponder (2) used in accordance with claim 1. 17. Use of a transponder according to claim 1, wherein the commercial installation is a power plant. 18. Method according to claim 14, wherein the commercial installation is a power plant. 19. Commercial installation according to claim 16, wherein the commercial installation is a power plant. |
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abstract | A radiotherapy apparatus incorporating multi-source focusing therapy and conformal and intensity-modulated therapy is disclosed. The radiotherapy apparatus includes a base, a movable couch, a gantry, at least one therapeutic head, and a counterweight. The therapeutic head includes a shielding part, a source carrier received in the shielding part, provided with a focusing radioactive source for focused therapy and a conformal radioactive source for conformal and intensity-modulated radiotherapy, a switch part configured for controlling on/off the source, a shielding door configured for controllably shielding the radiation beams of the radioactive sources; and a collimator assembly. By using this apparatus, accurate multi-source focused therapy and conformal therapy can be implemented in a single current Gamma Knife device. |
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049869531 | summary | The invention relates to a device for the support and positioning of means for checking and tools for working on fuel assemblies of a water nuclear reactor which are immersed in a pool. After a certain time of operation in the reactor, the fuel assemblies constituting the core of a reactor require examinations and checks in order to ensure that these assemblies have not suffered damage preventing their subsequent use in the core of the reactor. Dimensional checks may be performed in order to confirm the characteristics of an assembly after irradiation. If certain defects have been detected, it may be possible to perform certain repairs or certain work operations which make it possible to reuse the fuel assembly for refuelling the core of the reactor. These checking operations using visual means or a probe as well as the implementation of tools for working on the fuel assembly must be performed under a certain depth of water in the region of the minimum biological protection requirement of 3 metres, or slightly more, of water. These operations are performed in a pool where the assembly, whose height is in the region of 4 metres, is placed in a vertical position. These checks or work operations may thus be performed, in certain cases, under a depth of water which is far greater than 3 metres and in any position according to the height of the assembly. Among the work operations envisaged or in respect of which tools have already been designed, it is possible to mention the removal of foreign bodies or particles inside the fuel assembly, the straightening of the fins of the grids of fuel assemblies, the checking of the sliding of the fuel pencils in their structure and the removal of pieces of peripheral rods in the assembly which have suffered a breakage. In all cases, it is necessary to set in place visual checking means and a tool for working at a very precise location situated in the vicinity of the fuel assembly. It must also be possible to adjust, remotely and accurately and using a simple and rapid procedure, the positioning and the orientation of the work tool. No device was known hitherto which made it possible to perform the installation and accurate positioning of means for checking and tools for working on fuel assemblies immersed in a storage pool. The invention thus aims to propose a device for the support and positioning of means for checking and tools for working on fuel assemblies of a water nuclear reactor which are immersed in a pool under a certain depth of water, it being possible for this device to be implemented simply and rapidly, making it possible to obtain an extremely precise positioning of the means for checking and the work tools. To this end, the device according to the invention comprises: a control station having a support fixed on the edge of the pool, a rod of great length connected to the support of the control station at its upper end and disposed in a substantially vertical position inside the pool so as to present a part located opposite at least one fuel assembly disposed inside the pool, means for adjusting the inclination of the rod relative to the vertical direction and for immobilizing the rod in at least one inclined position, which means are fixed on the support of the control station, a carriage mounted so as to be movable along the length of the rod interacting with guide means carried by the rod, means for displacing the carriage which are controlled from the control station, at least one tool support intended to receive at least one means for checking and at least one work tool, an assembly for displacing the tool support in two different directions perpendicular to the axis of the rod, carried by the carriage, means for controlling the displacements of the tool support which can be activated from the control station, and means for controlling the work tool and the means for checking from the control station. |
description | The present application claims the benefit of U.S. Provisional Application Ser. No. 61/768,495, filed Feb. 24, 2013, U.S. Provisional Application Ser. No. 61/755,661, filed Jan. 23, 2013, and U.S. Provisional Application Ser. No. 61/714,588, filed Oct. 16, 2012, all of which are hereby incorporated by reference herein in their entirety, including any figures, tables, or drawings. Embodiments of the subject invention pertain to detection of radiation related to, for example, nuclear nonproliferation activities. The Office of Nuclear Nonproliferation Research and Development has been focused on enabling the development of next generation technical capabilities for radiation detection of nuclear materials. Recently, the Special Nuclear Material (SNM) Movement Detection Program created an evolving technology roadmap that identified the following fundamental objectives: 1. detect shielded highly enriched Uranium; 2. detect SNM at standoff distances; and 3. detect shielded weapon-grade plutonium. General features of an advanced detection system able to meet the above objectives may include, but are not limited to the following: 1. a large area detector, e.g., at least several square meters; 2. capable of efficiently detecting and distinguishing fast neutrons, with gamma discrimination of at least 10,000:1 and preferably 100,000:1; 3. capable of efficiently detecting and distinguishing thermal neutrons, with gamma discrimination of at least 100,000:1 and preferably at least 1,000,000:1; 4. a nanosecond time resolution capability for neutron time of flight measurement, multiplicity measurements, as well as coincidence counting for active interrogation; 5. a segmented detector; 6. robust, moderate price, stable, safe, and easily field deployable. There has been a major effort towards making a large area, efficient, fast neutron detector with good gamma discrimination. A recent review of methods of neutron detection is provided by Runkle R. C. et al., Journal of Applied Physics 108. 111101. (2010). There are many methods under investigation, yet none have appeared to come very close to meeting the challenging requirements. Organic crystals, liquid scintillator, and specially designed plastic scintillator have been studied, (PCT Patent Application PCT/US2012/045094, published Jan. 3, 2013 under publication number WO 2013/003802, and “Plastic Scintillators with Efficient Neutron/Gamma Pulse Shape Discrimination”, N. Zaitseva et al., Nuclear Instruments and Methods in Physics Research A 668(2012) 88-93). The different materials have been studied in small volume detectors and their gamma ray discrimination abilities are similar. The gamma ray discrimination is measured by the difference in scintillation pulse shape of interactions of neutron and gamma ray. This technique is known as Pulse Shape Discrimination (PSD). These types of material have been shown to have Figures of Merit (FOM) of 2.5 to 3.5, corresponding to gamma ray discrimination factors of about 1,000:1. In these small volume detector studies, the scintillation material has an efficient optical coupling to a Photo Multiplier Tube (PMT). In large area detectors, it is almost inevitable that loss of some scintillation light will result in a reduced gamma discrimination factor. Accordingly, it appears the gamma ray discrimination of these detectors is inadequate for effective detection of SNM. In general, the PSD method suffers from an inherent disadvantage; the pulse shape discrimination is effective only after a time delay, at which point the pulse height has fallen by at least an order of magnitude. As a result, there is a major loss of quantum statistical information when using PSD, which limits the ability to provide powerful gamma ray discrimination in large detectors. Pacific Northwest National Laboratory (PNNL-15214) has evaluated the performance of a large area (0.7 m2) twin sheet plastic scintillator time of flight (TOF) system for direct detection of fast neutrons. The TOF method yielded a gamma ray discrimination of at least 10,000:1, but only when the fast neutron intrinsic detection efficiency was limited to less than 4%. That detection efficiency is comparable to traditional moderator-based fast neutron detection systems (which have an intrinsic detection efficiency of 5 to 10% depending on the number of thermal neutron detectors), such as presently deployed in Radiation Portal Monitors (RPMs). This implies the TOF method would likely offer no improvement in the gross neutron counting sensitivity beyond that of existing RPMs. In addition, the intrinsic detection efficiency of up to 4% is inadequate to perform fast neutron multiplicity measurements, which are powerful indicators of SNM material. With the fast neutron multiplicity measurement technique, the measured count rate of two simultaneous fission neutrons is proportional to the square of the intrinsic detection efficiency. Thus, there is a premium on having intrinsic detection efficiency much higher than 4%. There is, therefore, a continuing need for fast neutron detection with both high intrinsic detection efficiency (>4%) and high gamma ray discrimination factor (>10,000:1 and preferably >100,000:1). Similarly, there is a continuing need for thermal neutron detection with both high intrinsic detection efficiency (e.g., >5% and preferably >10%) and high gamma ray discrimination factor (e.g., >100,000:1 and preferably >1,000,000:1). To achieve high detection efficiency it is preferred to have a high concentration of a suitable isotope, such as Li-6 dissolved in the material. However, lithium forms polar compounds that are very poorly soluable (about (0.01% wt/wt) in non-polar scintillating plastics, such as polystyrene (PS) and polyvinyltoluene (PVT). Accordingly, a highly efficient, thermal neutron plastic scintillation detector has not yet been achieved. Therefore, despite major efforts by Federal Agencies, National Laboratories and many researchers, there has been less progress than desired in meeting the fundamental objectives of improved neutron detection for the SNM Movement Detection Program. Accordingly, there is a need for a large area, fast and thermal neutron detector with high intrinsic efficiency and acceptable gamma discrimination. Embodiments relate to an advanced fast and thermal neutron detector material composition with the properties useful for Special Nuclear Material (SNM) detection. Specific embodiments of the material composition result in two excimer scintillation light production mechanisms that provide two corresponding independent techniques for gamma discrimination; namely Pulse Shape Discrimination and Pulse Height Discrimination. A dual discrimination method, Pulse Shape and Pulse Height Discrimination (PSHD), can be implemented relying on both pulse height discrimination and pulse shape discrimination, and can allow the operation of large area, fast and thermal neutron detectors. In specific embodiments, the estimated fast neutron intrinsic detection efficiency is >20%, >25%, and/or >30%, and the gamma discrimination factor is >10,000:1, >50,000:1, >90,000:1, and/or >100,000:1. In specific embodiments, the estimated thermal neutron intrinsic detection efficiency is >10, >20, and/or >30%, and the gamma discrimination factor is >100,000:1, and/or >1,000,000:1. Embodiments can incorporate dyes as excimer fluorescent sources of scintillation light. In specific embodiments, polycyclic aromatic fluors can be used. The selection of the dyes as excimer fluorescent sources of scintillation can be selected based on the properties of the polycyclic aromatic fluor's solubility, propensity to form dimers, absorption spectrum, excimer fluorescence spectrum, and monomer and dimer scintillation intensity and decay times. Embodiments can incorporate dyes as singlet state sources of scintillation light. Standard primary scintillation dyes can be selected based on their solubility, absorption spectrum, fluorescence spectrum, scintillation intensity, degree of Stokes shift and decay times. Such dyes can be selected based on performances when they are dissolved in polystyrene (PS), polyvinyltoluene (PVT), polymethylmethacrylate (PMMA), and other amorphous polymers. A Bismuth electron source and Polonium alpha particle source can be used to initially evaluate such dyes. Such dyes can serve to provide a conventional measure of the energy loss in the plastic. Embodiments of the subject plastic scintillators can be fabricated of a polymer that contains: a) 0.2, 0.4, 0.6, 0.8 and >1.0 mol/L of the selected dimer fluor; and b) 0.25, 0.5, 1.0, 2.0, 3.0 and >4.0% wt/wt of the primary dye. The plastic scintillators can be bombarded with electrons and alpha particles, and pulse height and pulse shape measurements taken by sampling the scintillation pulses at 2 ns intervals over a total time of 200 ns. Embodiments of the plastic scintillators can also be placed in a flux of fast neutrons from, for example, an Americium source and a Cesium gamma ray source, and pulse height and pulse shape measurements taken by sampling the scintillation pulses at 2 ns intervals over a total time of 200 ns. Values of gamma discrimination can be utilized in the selection of material composition. Various combinations of polymer and dimer fluor, and various concentrations of dimer fluor can be utilized. Further specific embodiments can be at least 8 inch by at least 1 inch in cross-section and at least 48 inches long. Two Photo-Physical Mechanisms for Obtaining Two Independent Measurements of Gamma Discrimination Table 1 describes four developments with respect to the photo-physical mechanisms used in organic scintillators. Specific embodiments of the subject scintillation material can incorporate two photo-physical mechanisms for obtaining two independent measurements of gamma discrimination. TABLE 1The Four Milestones in Organic Scintillator Development.PhysicalPulse HeightMechanismPusle ShapeDiscriminationfor PromptDiscrimination(PHD) fromType ofScintillation(PSD) fromnormalizedFast NeutronOrganicLightDelayedintra-dimerGammaItemScintillatorProductionEmissionTTADiscrimination1ConventionalMolecular———PlasticSinglet StateScintillator/DecayPilot Chem.Co. (1950)2ConventionalMolecularDiffustion—≈103:1LiquidSinglet StateControlled TTA***Good for SmallScintillator/DecayBetween MoleculesDetector(1949)3PSD* PlasticMolecularInter Molecular—≈103:1Scintillator/Singlet StateTTA*** by DirectGood for SmallNanoptics,DecayEnergy Transfer viaDetectorInc. (2010)Electron ExchangeLLNL (2010)4PSHD**ExcimerInter Dimer TTA***Intra DimerObjectivePlasticSinglet Stateby Direct EnergyTTA*** by≧105:1Scintillator/DecayTransfer via ElectronContactGood for LargeNanoptics,ExchangeAnnihilationDetectorInc. (2012)*PSD—Pulse Shape Discrimination**PSHD—Pulse Shape and Height Discrimination***TTA—Triplet-Triplet AnnihilationItem 1. Conventional plastic scintillators rely on harvesting the fluorescent radiation from the plastic and exciting a primary dye at a concentration of about 1% wt/wt into an excited singlet state. That state decays via prompt Forster fluorescence and produces scintillation light via a secondary dye. Any triplet states that are produced are immobile in the solid and slowly lose their energy by non-radiative transitions.Item 2. Conventional liquid scintillators rely on producing the prompt scintillation light by the same singlet mechanism as described in item 1 above. The production rate of triplets depends on the ionization density along the track of the incident radiation. The triplet states diffuse through the liquid until they annihilate one another according to the process: The Triplet-Triplet Annihilation (TTA) rate is controlled by the diffusion constant of the Triplet states in the liquid. In this way, delayed scintillation light is produced with intensity dependent on the nature of the incident particle. This is the physical basis of Pulse Shape Discrimination in a liquid. In the measurement of recoil protons from fast neutrons, the measured gamma ray discrimination factor is about 103:1. Item 3. In 2010, a material composition of solid plastic scintillator was made to give PSD with about the same discrimination as liquid scintillator. The physical mechanism was found by Nanoptics, Inc. to be Direct Energy Transfer via Electron Exchange (DETEE) between immobile triplet states in the solid material. The mechanism was used to design a scintillation material composition for the desired pulse shape structure. A group at Lawrence Liveintore National Laboratory (LLNL) has shown that the gamma discrimination is comparable to the 103:1 found for liquid scintillator in Item 2, or in many organic crystals.Item 4. In 2012, Nanoptics, Inc. taught the use of a solid plastic composition that employs the self-assembly of dyes into dimers. This material composition produces excimer scintillation light. Most importantly, there are two mechanisms that can provide independent measurements of Pulse Height Discrimination and Pulse Shape Discrimination. The two photo-physical mechanisms are 1) intra-dimer light production from excimer decay and TTA and 2) inter-dimer TTA. An advantage of this technique is having two independent measurements of gamma discrimination. Because the inter-dimer TTA mechanism to produce PSD is the same mechanism, namely DETEE, as used in Item 3, embodiments can provide a similar gamma discrimination factor, namely about 103:1. The intra-dimer mechanism to produce PHD can, in specific embodiments, provide a gamma discrimination of >100:1 and >1000:1. The combination of gamma discrimination factors from these two independent mechanisms can, in specific embodiments, provide a total gamma discrimination of >105:1 and >106:1. This powerful discrimination allows the scintillating material of specific embodiments of the subject detector to operate reliably as a large area detector. When the polymeric material is made to contain elements with large thermal neutron capture cross-sections, the nuclear fragments resulting from capture can be detected by their scintillation. Importantly, the high ionization density of these fragments can be detected by the same PSHD physical mechanism as described above for the recoil protons from neutron scattering. Material COmposition and Photo-Physics Specific embodiments can have high concentration of a polycyclic aromatic fluorescent compound, such as pyrene, dissolved in a monomer and the solution can then be polymerized. Plastics such as polystyrene and polyvinyltoluene (Tymianski and Walker, U.S. Pat. No. 5,606,638) have been taught and the identification and description of such plastics, which can be utilized in various embodiments of the subject invention, is hereby incorporated by reference in its entirety. The fluor utilized with specific embodiments is selected to self-assemble into dimers at concentrations greater than about 0.2 mol/L. A dimer is a pair of fluors that form a weakly bound co-planar state in which the two rigid planar molecules are parallel to each other. Their separation is typically 3 to 4 Angstroms. Intra-Dimer Light Production There are two processes which produce intra-dimer light. Process One Various embodiments can utilize the first process for intra-dimer light production. A low energy proton recoiling from a neutron scatter, nuclear fragments from a capture event, or an electron recoiling from a gamma ray scatter all have different probabilities to excite or ionize one pyrene molecule in the dimer. That process can result in the dimer being in an excited singlet state, termed an excimer. Excimer decay produces prompt excimer radiation with a large Stokes shifted scintillation pulse of maximum intensity at 480 nm and decay time of 40 to 65 nanoseconds. This prompt emission is the first source of excimer scintillation light and it is produced by protons, nuclear fragments, and electrons. Process Two Various embodiments can utilize a second process, either in conjunction with the first process described above or alone. The second process for intra-dimer light production involves excimer scintillation light from a single dimer. This process is primarily activated by highly ionizing particles. The ionizing density can be calculated using a modified Bethe formula (Radiation Detection and Measurement, P32, by Glenn F. Noll, Wiley) using the ESTAR program available from NIST. The result is shown in FIG. 1. In the relevant energy range 0.3 to 3 MeV, the proton (nuclear fragments) has a 100 (>100) higher specific ionization (dE/dx) compared to the electron. This much higher energy loss per unit distance provides the proton (nuclear fragments), compared to an electron, more than 10,000 times higher probability of ionizing both pyrene molecules in the dimer. It can be seen in FIG. 1 that the average ionization energy loss by the proton (nuclear fragment) along a distance characterized by the dimension (10 A) of a dimer is >twice the ionization energy, 7 eV, of pyrene. A horizontal line is plotted at 14 eV in FIG. 1, which is the minimum necessary energy loss to ionize both pyrene molecules in the dimer. However, electrons will essentially never ionize both pyrene molecules in the dimer. An ionized pyrene molecule will rapidly attract a free electron from the plastic matrix environment, and the molecule will cascade down to the lowest energy level, singlet or triplet. For statistical reasons, a large fraction of ionization interactions will result in a pair of triplet states being formed in the dimer. Due to the physical intimacy of the triplets, the Triplet-Triplet Annihilation (TTA) process occurs with a large rate constant and results in a TTA process within 1 ns. That process leads to an excited singlet state pyrene (an excimer) and a ground state pyrene: T1+T1→S1+S0. The excimer decays by scintillation light emission as described above. This excimer emission through the process of TTA is termed delayed emission. However, the delay in this instance is very short, 1 ns, and is therefore virtually indistinguishable from the prompt emission described above in process one. From an operational point of view, both the prompt emission and this form of delayed emission occur nearly simultaneously. For this reason we refer to this light as “prompt” emission. This second source of excimer scintillation light is efficiently produced by protons and nuclear fragments, and essentially not at all by electrons. Accordingly, for intra-dimer scintillation light, recoil protons and nuclear fragments have two routes to producing excimer scintillation as compared to only one route for electrons. The light has a characteristic 40 to 65 ns decay time. This effect appears to have been observed before. J. B. Birks (Chemical Physics Letters Vol. 4, No. 10, 1970) described a dramatic increase in the prompt excimer scintillation light from dimers of several aromatic compounds relative to monomer emission as the density of ionization was increased. A variable intensity electron beam was employed to increase the ionization density. That result is most simply, if not uniquely, interpreted as due to the ionization dependent intra-dimer TTA mechanism. This is the fundamental photo-physical basis for the PHD mechanism. Method to Normalize the Intra-Dimer Scintillation Light Intensities To take account of the different possible energy depositions by each particle, the excimer scintillation pulse height from the subject plastic material composition can be normalized. An independent scintillation fluor mechanism, which is not based on the dimer/excimer process, can be used to measure the conventional scintillation intensity with a 2 nanosecond decay time constant. This conventional excited singlet state scintillation mechanism is designed to minimally exchange energy with the excimer light production process. A primary dye at a conventional concentration of, for example, 1% wt/wt, will receive energy from the PVT via the Forster process and emit scintillation light through singlet decay. The primary dye can be selected to have a large enough Stokes shift that no secondary dye is required. For this reason, little of this light will be diverted into the excimer process. This independent light production can be referred to as “Normal Scintillation Light” (NSL), as distinct from the “Excimer Scintillation Light” (ESL). The time dependent pulse shapes are shown schematically in FIG. 2 for specific embodiments. The scintillation pulse for each event is normalized to a fixed height of the NSL pulse as shown in FIG. 2. In this context, it is to be understood that the height of the NSL pulse is defined as the height of the measured NSL pulse after subtraction of the average height of the Excimer pulse under the NSL pulse. The difference in normalized excimer scintillation pulse height is used to distinguish interactions produced by neutrons from those produced by gamma rays. The amount of extra scintillation light for protons (nuclear fragments) compared to electrons is a function of the proton (nuclear fragment) energy. However, in specific embodiments, there is at least a factor of 2 more excimer light from heavily ionizing particles compared to electrons after the normalization process has been made. This form of discrimination against gamma rays is referred to as Pulse Height Discrimination (PHD). Discrimination can be quantitatively obtained by on-line analysis or off-line analysis as described later. Inter-Dimer Light Production Beyond the intra-dimer triplet-triplet annihilation process discussed above, inter-dimer triplet-triplet annihilation will occur because of the high pyrene concentrations employed in the material incorporated in specific embodiments. In specific embodiments, the mean distance between dimers is in the range 10 to 15 Angstroms. At large transverse distance from the proton (nuclear fragment) track, the ionization density will reduce and no longer be adequate to ionize both pyrene molecules in a dimer. At that radius, most recoil protons (nuclear fragments) will produce excimers that contain only one ionized pyrene molecule. Three times out of four these states will be triplets. These triplet states will only rarely give rise to scintillation light via spin forbidden intersystem crossing transitions to the ground state. However, these triplet states can give rise to delayed excimer scintillation light via inter-dimer triplet-triplet annihilation (TTA). In the solid polymer matrix, this process occurs by Direct Energy Transfer by Electron Exchange (DETEE) as described, and demonstrated experimentally with alpha particles, U.S. Patent Application Pub. No.: US 2012/0241630 and PCT Patent Application No.: PCT/US2012/045094, published Jan. 3, 2013 under publication number WO 2013/003802, all of which are hereby incorporated herein by reference in their entirety. Also, this mechanism was experimentally demonstrated using neutrons and gamma rays by N. Zaitseva et al., Nuclear Instruments and Methods in Physics Research A 668 (2012) 88-93; and International Application No.: PCT/US2012/033449, which are hereby incorporated herein by reference. The net effect of the inter-dimer DETEE physical mechanism is to produce delayed scintillation light. The decay time of the delayed light is calculable and controllable by the dimer concentration as described by the DETEE mechanism. The results are similar to the diffusion controlled process underlying PSD in liquid scintillator. The expected scintillation pulse shape for heavily ionizing recoil protons (nuclear fragments) is illustrated in FIG. 3. FIG. 3 illustrates the difference in pulse shapes of recoil protons (nuclear fragments) and electrons. Summary of the PSHD Photo-Physical Mechanisms in Plastic Scintillators Embodiments of the subject method utilize both PSD and PHD for achieving superior gamma discrimination, which can be referred to as the “PSHD” method. The two major results of considering both photo-physical mechanisms associated with the use of dimers in the PSHD method are: 1. Increased proton (nuclear fragment) pulse height at all decay times from the intra-dimer TTA mechanism. This light is unique to the use of dimers in the plastic. This is the basis for the PHD mechanism. 2. The increased delayed scintillation intensity from the inter-dimer TTA mechanism; which is the basis for the PSD mechanism. An advantage of the PSHD method is the use of two independent mechanisms, rather than the current approach of using the single PSD mechanism of measuring TTA. In specific embodiments, this is achieved by the use of two dye molecules that self-assemble in the form of dimers and create the intra-dimer TTA process. In one embodiment of the invention the polymeric matrix can be cross-linked. This process confers greater mechanical and thermal integrity to the scintillating plastic product. Fast Neutron Scatter Detection and Gamma Discrimination Embodiments of the subject PSHD method can use the discrimination present in the large pulse heights in the short time region due to the PHD mechanism as well as the increased intensity in the delayed pulse tail region due to the PSD mechanism. Preferably, specific embodiments will provide a gamma discrimination using the PHD mechanism of at least 50:1, at least 100:1, at least 200:1, and/or at least 300:1 and provide a gamma discrimination using the PSD mechanism of at least 50:1, at least 100:1, at least 200:1, and/or at least 300:1. In a specific embodiment utilizing the independent photo-physical mechanisms (PHD and PSD) with a scintillating plastic material, such as a scintillating plastic material described herein, can provide a total gamma discrimination of at least 1000:1, at least 10,000:1 and at least 100,000:1. Various embodiments of the invention can utilize a variety of dyes as excimer fluorescent sources of scintillation light. In the 1960s and 1970s it was found that self assembly of dimers and excimer formation occurs in a wide variety of condensed polycyclic hydrocarbons. Dyes which can be utilized in embodiments of the subject detector include, but are not limited to: 1) Anthracene and its alkyl derivatives 2) Pyrene and its derivatives 3) 1,2-benzanthracene and its derivatives 4) Tetracene 5) 3,4-benzophenanthrene and its derivatives and 6) Triphenylene. Specific PAH compounds can be selected based on their solubility, propensity to form dimers, absorption spectrum, excimer fluorescence spectrum, and monomer and dimer fluorescence or scintillation intensity and decay times, when they are dissolved in organic solvents, such as polystyrene (PS), polyvinyltoluene (PVT), or other amorphous polymers. In addition, commercial availability, price, and ease of purification are among other factors that can be taken into account. Scintillation development work with pyrene was taught in U.S. Pat. No. 5,606,638, and is incorporated herein in its entirety. Pulse height and shape information can be obtained using a commercial 500 MHz sampling pulse information system, such as the Acquiris system from Agilent. Electronics and data analysis system can also be used to collect the needed data. Various embodiments can utilize dyes as singlet state sources of scintillation light for the purposes of determining normalization (NSL) of the excimer pulse heights. Standard primary scintillation dyes can be selected based on their solubility, absorption spectrum, fluorescence spectrum, large Stokes shift, scintillation intensity, and decay times when they are dissolved in polystyrene and polyvinyltoluene. Dyes that can be used include the class of compounds described in “Organic Scintillators with Unusually Large Stokes' Shifts”, Gusten, H. and W. Seitz, J. Phys. Chem. 82:459-463 (1978), which is hereby incorporated by reference in its entirety. Two of these dyes are shown in Table 2. Such dyes have decay times in the range 1 to 2 ns. TABLE 2Three Large Stokes’ Shift Primary DiesLight Yield *MolarMaxima *(arbitrary unitsPrimaryMass gAbsorptionEmissionrelative to eachDyemol−1nmnmother)PMP-420264302414100PMP-440296307428973-HF23833852820* These spectral properties and light output have been measured in polystyrene. The light yield is seen to be much higher than with the conventional large Stokes' shift dye, 3-HF. The absorption and emission spectra for PMP-420 are shown in FIG. 4. The large Stokes shift of the PMP dyes is acquired by steric hindrance produced by two methyl groups. The quantum efficiency of the PMP-420 dye is 0.9. Importantly, the emission spectra peak of polystyrene and polyvinyltoluene are at 332 nm and 312 respectively and have good overlap with the absorption spectrum of PMP-420. Scintillating plastic fibers with the single dye PMP-420 have been successfully used at the Large Hadron Collider, CERN, Geneva for several years and performed well in a high radiation environment “Particle Tracking with Scintillating Fibers”, D'Ambrosio, C. et al., IEEE Transactions on Nuclear Science, Vol. 43, No. 3, June 1996. Thus, the use of a single dye for producing stable, bright scintillation light with little reabsorption has been well established. This scintillation mechanism is based on singlet state decay of the PMP-420. In some embodiments of the invention, there is little spectral overlap of the scintillation emission from the excimer and NSL light sources. In this case, two separate photo-sensitive detectors with different and appropriate spectral sensitivities can be used to readout the two sources of scintillation light. This technique obviates the necessity of high bandwidth waveform electronic digitizers. In a specific embodiment, where a non-aromatic polymer such as PMMA is used, PMP-420 can be used at higher concentration to produce adequate scintillation light intensity. For this purpose, concentrations of 2% to 6% wt/wt may be used. There is a very small concentration quenching of the emitted light due to the large Stokes shift. In specific embodiments, it is important that the emission spectrum of the PMP does not overlap with the absorption spectrum of Pyrene. The latter spectrum has been measured in polymethylmethacrylate at high concentrations of at least 1 mol/L. The absorption spectrum is shown in FIG. 5. The dye spectra are dependent on the polarity of the matrix polymer. However, these differences are quite small compared to the effects of interest in this application. It can be seen that the pyrene absorption is essentially zero at wavelengths above 350 nm. Since the PMP emission starts at 360 nm, this demonstrates that there is negligible transfer of energy from the PMP-420 singlet emission into the pyrene system. Conversely, the pyrene excimer emission starts at 400 nm and peaks at 480 nm. Therefore, no light from the pyrene can be absorbed by the PMP-420 dye whose absorption is zero above 370 nm. Thermal Neutron Detection Using a Plastic Scintillator Employing PSHD In another embodiment of the invention, the plastic scintillator described supra, that provides PSHD can be used to detect thermal neutrons with gamma discrimination factor of at least 100,000:1 and preferably >1,000,000:1. The thermal neutron may be generated by a fast neutron incident on the plastic that suffers multiple scatters in the plastic, each of which degrades the energy of the fast neutron. Such an event can be detected by what appears to be a single recoil proton event (due to the short time between two or more scatters) by employing PSHD, followed by a neutron capture event occurring usually at least a few hundred nanoseconds later. Alternatively, the thermal neutrons may have been thermalized external to the plastic and subsequently incident on the plastic where it is captured. The neutron capture process in the plastic can employ the well-known use of 10B or 6Li in the plastic. These two nuclei have large cross-sections for absorption of thermal neutrons with the production of highly ionizing nuclear fragments such as an alpha particle, a lithium nucleus, or a triton. The specific ionization of these particles is greater than that of a recoil proton, as can be seen in FIG. 1. As a result, the use of PSHD is even more effective for providing large gamma discrimination for identifying thermal neutrons than it is for identifying fast neutrons. The use of covalently bonded boron compounds dissolved in polymers is well known, and there are commercial plastic scintillators available from ELJEN and BICRON. Because these plastics do not provide significant gamma discrimination, they have found very limited applicability. However, the use of several percent wt/wt of boron in a plastic, in accordance with specific embodiments of the subject invention, can offer very effective PSHD and create an excellent thermal neutron detector. Such plastic can be formed into fiber and can be used as a high spatial resolution thermal neutron detector with high gamma discrimination. The use of lithium compounds, such as lithium chloride and lithium nitrate, in plastic is difficult due to the highly polar nature of lithium compounds. The compounds can exist in ionic form and are rather insoluble in a non-polar matrix. In the non-polar plastics such as PS and PVT it is possible to achieve lithium ion concentrations of up to about 0.01% wt/wt. This low concentration of lithium can severely limit the sensitivity of thermal neutron capture by lithium in these plastics. However, if 10 cm or more thickness of plastic scintillator is required to detect fast neutrons, the plastic can contain enough 6Li to offer acceptable thermal neutron detection in some embodiments of the invention. Embodiments of the invention utilize amorphous polar polymers that are transparent and can dissolve polar compounds to a significant concentration. These polymers include, for example, PMMA, and polyvinylpyrrolidone. Embodiments using moderately polar PMMA as the plastic matrix can achieve concentration of lithium compound greater than 0.01% wt/wt, greater than 0.05% wt/wt, in the range of 0.01% wt/wt to 0.05% wt/wt in the range 0.05 to 0.1% wt/wt, and/or greater than 0.1% wt/wt and preferably, also achieved up to 15% wt/wt of pyrene, and up to 3% wt/wt of PMP-420 providing normalization information. In addition, an aromatic solvent, such as pseudocumene, can be dissolved to increase the light output. To provide adequate structural integriy the material is preferably cross-linked. Embodiments utilizing such a plastic scintillator can provide a good thermal neutron detector. A plastic scintillator with such a composition can offer good fast neutron detection coupled with effective thermal neutron capture. Embodiments utilizing PSHD for the fast neutron detection event and PSHD for the delayed neutron capture event can provide a gamma discrimination of at least one billion to one. This type of neutron detection is referred to “neutron capture gated”. Further embodiments of the invention utilize a soluble, non-polar aggregate of organolithium compounds. Such compounds include n-butyl lithium, hexyllithium, lithium phenoxide, and hundreds of other such compounds. These compounds self-assemble in solution as dimers, trimmers, tetramers, and oligomers. T. S. De Vries, et al., Journal of the ACS, 2009, 131, 13142-13154. By forming these higher order species, the overall polarity of the entity is drastically reduced and they become soluble in the non-polar monomer solvent. Remaining insoluble salt crystallites precipitate, and can be removed by filtering. Lithium solubility in solution can be determined by conventional NMR spectroscopy. In the case of n-butyl lithium, solubility was achieved such that the lithium concentration was at least 0.1% wt/wt. Another embodiment of the invention utilizes a organolithium compound being dissolved in a polar solvent. In order to achieve higher lithium solubility, a solvent, such as tetrahydrofuran (THF), dimethoxyethane (DME) and tetramethylethylenediamine (TMEDA), can be used as an initial solvent for the organolithium compound. A molecule of the solvent can occupy one or more of the coordination sites of lithium, thus reducing the degree of nuclearity of the aggregate, as shown in FIG. 6. The solvent is removed and the reformed solid is lightly dried to ensure retention of the donor solvent molecules. That non-polar solid is then easily dissolved in the non-polar styrene and can provide at least, and/or greater than, 0.1% wt/wt of lithium in the final polymerized plastic scintillator. Another embodiment of the invention utilizes the principles of self-assembling soluble dimer, trimer, and tetramer lithium species of simple lithium salts of the form LiX, including but not limited to, LiOH, LiCl, LiF, and LiClO4. These salts are not soluble in styrene and result in sub-micron crystallites. In this case, the extended inorganic polymeric salt is converted into discrete molecular units, as shown in FIG. 7, by dissolving the salt in a polar solvent, such as THF. The donor molecule satisfies the coordination sphere of the lithium ion and the counter-ion is separated from the lithium ion. There is a resulting large drop in polarity, which allows the entity to be soluble in styrene. In practice, the compound LiX is dissolved in a polar solvent, such as THF, DME, or TMEDA, and discrete species of aggregates form, as shown in FIG. 7. The solvent is removed to reform a solid that is not dried excessively. In this case, the coordinated solvent is retained and the solid, shown on the right hand side of FIG. 7, is found to be soluble to at least 3.6% wt/wt in styrene. This solubility provides a lithium concentration of at least 0.1% wt/wt in the scintillating plastic after polymerization. Fast Neutron Detection Using a Liquid Scintillator Employing PSHD In another embodiment of the invention, fast neutrons are detected using a liquid solvent scintillation matrix. A polycyclic aromatic dye can be used to provide self-assembled dimers as described supra in plastic materials. The normalization of the energy loss can be performed, as with a solid scintillator, using a dye such as PMP-420. The effectiveness of PSHD in liquid and solid polymers is similar. Consequently, similar neutron detection sensitivity and gamma discrimination can be obtained in a liquid matrix as in a solid plastic matrix. Thermal Neutron Detection Using a Liquid Scintillator Employing PSHD In another embodiment of the invention, thermal neutrons are detected using a liquid solvent scintillation matrix. The thermal neutron capture process in the liquid can use, for example, 10B or 6Li in the liquid. A polycyclic aromatic dye is used to provide self-assembled dimers as described supra in plastic materials. The normalization of the energy loss is performed, as with a solid scintillator, using a dye such as PMP-420. The effectiveness of PSHD for gamma discrimination in liquid and solid polymer is similar. Consequently, similar gamma discrimination can be obtained in a liquid matrix as in a solid plastic matrix. In the case of the use of highly polar liquids, which include, but are not limited to, N-Methylpyrrolidone, Dimethylsulphoxide, and 1,3-Dimethyl 2-Imidazolidone, we have achieved concentrations of 6Li up to 1% wt/wt. Relatively short mean free paths (e.g., in the range of 1 to 2 cm) for thermal neutrons can be obtained. These liquids can be made into a gel by using 5 to 20% wt/wt of a very high molecular weight of the corresponding polymer such as polyvinylpyrrolidone in N-Methylpyrrolidone. When such a polymer is lightly cross-linked it can form a solid gel which retains shape and cannot be poured. In some embodiments of the invention, this is an important safety feature of the detection system. Method and Measurements of Pulse Shape and Height Discrimination (PSHD) In an embodiment of the subject invention, the combination of these unique pulse shape and pulse height characteristics are measured in-line by a high bandwidth waveform digitizer. The data is sent to a processor and analyzed on-line with algorithms to provide optimum discrimination against gamma ray interaction in the scintillating material composition. The results from the data analysis can permit distinguishing a fast neutron scatter or neutron capture process in the material from a gamma ray interaction. Gamma discrimination ratios of greater than 100,000 to 1 can be achieved. In another embodiment of the invention, the integrated charge within a small number of time windows during the pulse can be measured and compared with one another on-line. This is a more economical approach to performing PSHD and is appropriate in some embodiments of the invention. Aspects of the invention, such as measuring the data for the PHD and PSD, may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that the invention may be practiced with a variety of computer-system configurations, including multiprocessor systems, microprocessor-based or programmable-consumer electronics, minicomputers, mainframe computers, and the like. Any number of computer-systems and computer networks are acceptable for use with the present invention. Specific hardware devices, programming languages, components, processes, protocols, and numerous details including operating environments and the like are set forth to provide a thorough understanding of the present invention. In other instances, structures, devices, and processes are shown in block-diagram form, rather than in detail, to avoid obscuring the present invention. But an ordinary-skilled artisan would understand that the present invention may be practiced without these specific details. Computer systems, servers, work stations, and other machines may be connected to one another across a communication medium including, for example, a network or networks. As one skilled in the art will appreciate, embodiments of the present invention may be embodied as, among other things: a method, system, or computer-program product. Accordingly, the embodiments may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware. In an embodiment, the present invention takes the form of a computer-program product that includes computer-useable instructions embodied on one or more computer-readable media. Computer-readable media include both volatile and nonvolatile media, transient and non-transient, removable and non-removable media, and contemplate media readable by a database, a switch, and various other network devices. By way of example, and not limitation, computer-readable media comprise media implemented in any method or technology for storing information. Examples of stored information include computer-useable instructions, data structures, program modules, and other data representations. Media examples include, but are not limited to, information-delivery media, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD), holographic media or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage, and other magnetic storage devices. These technologies can store data momentarily, temporarily, or permanently. The invention may be practiced in distributed-computing environments where tasks are performed by remote-processing devices that are linked through a communications network. In a distributed-computing environment, program modules may be located in both local and remote computer-storage media including memory storage devices. The computer-useable instructions form an interface to allow a computer to react according to a source of input. The instructions cooperate with other code segments to initiate a variety of tasks in response to data received in conjunction with the source of the received data. The present invention may be practiced in a network environment such as a communications network. Such networks are widely used to connect various types of network elements, such as routers, servers, gateways, and so forth. Further, the invention may be practiced in a multi-network environment having various, connected public and/or private networks. Communication between network elements may be wireless or wireline (wired). As will be appreciated by those skilled in the art, communication networks may take several different forms and may use several different communication protocols. And the present invention is not limited by the forms and communication protocols described herein. All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification. It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application. |
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claims | 1. A radiation treatment table comprising:a generally flat patient support surface, the surface comprising an opening to allow a woman's breast to hang downwardly through the opening and below said patient support surface to receive radiation when a woman is placed on said patient support surface in a prone position;a platform support connected to the patient support surface, the platform support comprising at least one vertical support, the at least one vertical support having an upper end coupled to the patient support surface and having a lower end adapted to be secured to a linear accelerator table; anda head positioning device attachable to the patient support surface. 2. The radiation treatment table of claim 1, wherein the head positioning device is moveable along the patient support surface. 3. The radiation treatment table of claim 1, wherein the head positioning device is fixably attached to the patient support surface. 4. The radiation treatment table of claim 1, wherein the head positioning device is constructed of molded plastic. 5. The radiation treatment table of claim 1, wherein the head positioning device is constructed of memory foam. 6. The radiation treatment table of claim 1, wherein the head positioning device further includes a cushion for a patient's head. 7. The radiation treatment table of claim 1, wherein the patient support surface further includes a padded upper surface. 8. The radiation treatment table of claim 1, wherein the patient support surface further comprises at least two generally flat support surfaces moveable relative to one another. 9. The radiation treatment table of claim 8, wherein the opening is formed between the at least two generally flat support surfaces. 10. The radiation treatment table of claim 1, wherein the opening is adjustable so as to accommodate different sized breasts. 11. The radiation treatment table of claim 1, wherein said opening is formed as part of a hinged opening plate. 12. The radiation treatment table of claim 1, wherein said opening is formed as part of a removable plate having a generally circular opening. 13. A method for reproducibly positioning a patient to receive radiation of the breast comprising the steps of:positioning a patient in a prone position upon a positioning platform, the positioning platform including a patient support surface elevated above a linear accelerator table, the patient support surface having at least one opening through which a breast may hang downwardly toward the linear accelerator table, the positioning platform further including a platform support having at least one vertical support having a lower end adapted to be secured to the linear accelerator table and having an upper end secured to the patient support surface, and a head positioning device;placing the patient's head in the head positioning device such that at least one of the patient's breasts is positioned to hang downwardly through the opening and below said patient support surface to receive radiation;positioning a radiation source relative to the patient's breast; andirradiating the breast. 14. The method of claim 13, further comprising the step of positioning the opening to allow the at least one breast to hang freely through the opening. |
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claims | 1. Device for removing flammable gases produced by radiolysis in a closed chamber which is a receptacle, tank or container, suitable for transporting and/or storing radioactive matters, said closed chamber containing radioactive matters comprising solid or liquid organic compounds and possibly water, or radioactive matters in the presence of solid or liquid organic compounds and possibly water, comprising:a) a first catalyst of at least one reaction for oxidizing the flammable gases by oxygen contained in the chamber atmosphere, supported by a hygroscopic, microporous, inert solid support, andb) a second catalyst of at least the reaction for oxidizing CO to CO2. 2. The device according to claim 1, wherein the first catalyst is a catalyst of at least the reaction for oxidizing hydrogen to water. 3. The device according to claim 1, wherein the first catalyst is a rare earth metal, selected from the lanthanide group. 4. The device according to claim 1, wherein the first catalyst is a precious metal selected form the group consisting of platinum, palladium, and rhodium. 5. The device according to claim 4, wherein the inner solid support of the first catalyst supports less than 0.1% by weight of precious metal. 6. The device according to claim 1, wherein the inert solid support is selected from molecular sieves, possibly activated. 7. The device according to claim 6, wherein the molecular sieve comprises a material selected from aluminas and activated aluminas. 8. The device according to claim 1, wherein the inert solid support has a specific surface area of at least 200 m2/g. 9. The device according to claim 1, wherein the second catalyst comprises a mixture of manganese dioxide (MnO2) and copper oxide (CuO). 10. The device according to claim 1, wherein the mass ratio of second catalyst to first catalyst is from 1:1 to 1:10. 11. The device according to claim 1, further comprising an oxygen source. 12. The device according to claim 11, wherein the oxygen source is selected from solid peroxides. 13. A closed chamber, which is a receptacle, tank or container, suitable for transporting and/or storing radioactive matters, said closed chamber being capable of containing radioactive matters comprising solid or liquid organic compounds and possibly water, or radioactive matters in the presence of solid or liquid organic compounds and possibly water, capable of producing flammable gases, by radiolysis, said chamber further containing at least one device for removing inflammable gases as defined in claim 1. 14. The device according to claim 1, wherein the microporous, inert solid support is sufficiently hygroscopic that it can absorb about 30% of its mass of water. 15. Device for removing flammable gases produced by radiolysis in a closed chamber which is a receptacle, tank or container, suitable for transporting and/or storing radioactive matters, said closed chamber containing radioactive matters comprising solid or liquid organic compounds and possibly water, or radioactive matters in the presence of solid or liquid organic compounds and possibly water, comprising:a) a first catalyst of at least one reaction for oxidizing the flammable gases by oxygen contained in the chamber atmosphere, supported by an inert solid support, andb) a second catalyst of at least the reaction for oxidizing CO to CO2;andc) a hygroscopic microporous support within the chamber. 16. The device according to claim 15, wherein the inert solid support is hygroscopic and microporous, and wherein the inert solid support supporting the first catalyst, the second catalyst, and the hygroscopic microporous support are fractionated into discrete elements. 17. The device according to claim 16, wherein the discrete elements have an envelope diameter of between about 2 mm and about 20 mm. 18. The device according to claim 17, further comprising an oxygen source, wherein at least one of the first catalyst, the second catalyst, the oxygen source, and the hygroscopic microporous support is placed, mixed or separately, in at least one receptacle that is at least partially permeable. 19. The device according to claim 15, wherein the hygroscopic microporous support is capable of absorbing between about 15% and about 30% of its mass of water. 20. A closed chamber, which is a receptacle, tank or container, suitable for transporting and/or storing radioactive matters, said closed chamber being capable of containing radioactive matters comprising solid or liquid organic compounds and possibly water, or radioactive matters in the presence of solid or liquid organic compounds and possibly water, capable of producing flammable gases, by radiolysis, said chamber further containing at least one device for removing inflammable gases as defined in claim 15. |
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044329334 | summary | BACKGROUND OF THE INVENTION Minute quantities of nuclear fuel such as deuterium, tritium, and mixtures thereof are used in various devices to produce a burst of high energy gamma radiation, X-rays, fast neutrons, other forms of radiation, and fusion reactions. Examples of such devices are neutron generators, magnetic confinement devices, electrom beam fusion devices, and laser driven fusion devices. The fast neutrons and various forms of radiation produced from fusion fuel by such devices are useful in producing tritium, simulation studies of nuclear weapons, the testing and radiation hardening of materials, the testing of electronic systems such as those used in antiballistic missiles to determine their susceptibility to malfunctioning by being subjected to such radiation, sterlization of insects such as fruit flies, and medical research and treatment of tumors and various cancers. The minute quantities of fusion fuel used in neutron generators and various fusion reactor devices are usually hydrogen isotopes in the form of solid slabs, cubes, or droplets. While these simple geometries have been adequate for some experimental tests, it is desirable to provide other fuel configurations in large quantities for use in such devices and when available, commercial fusion reactor operations. To increase the yield of fast neutrons, high energy radiation, X-rays, and energy from fusion fuel when irradiated with laser energy, it is believed to be desirable to have the minute quantity of fusion fuel in the form of a small sphere of gas and preferably in the form of a solid hollow sphere. Such spherical configurations of fusion fuel, which can be referred to as a pellet, may have a diameter which varies all the way from 1/16 of a millimeter (mm) to approximately 2 mm or larger, but is preferably in the range of 1/8 to 1 mm. Such configurations of fusion fuel and methods and apparatus for utilizing laser energy to irradiate fusion fuel in such configurations to obtain a burst of high energy gamma radiation, X-rays, fast neutrons and a fusion reaction are disclosed in the copending U.S. application of Keith A. Brueckner, Ser. No. 337,094, filed Mar. 2, 1973 as a continuation-in-part of application, Ser. No. 12,624, filed Feb. 20, 1970, and copending U.S. application of Keith A. Brueckner, Ser. No. 377,508, filed July 10, 1973 as a continuation-in-part of application, Ser. No. 116,707, filed Jan. 29, 1971, which are incorporated herein by reference. All of these Brueckner patent applications are assigned to the assignee hereof. Thus, the problems before the art are to provide spherical fuel pellets which can be accurately regulated in dimension and thus are more efficient in producing fast neutrons, high energy gamma radiation, X-rays, and other forms of radiation and more efficient in the ultimate fusion process, and also to provide fuel pellets with a spherical configuration which lends itself to an efficient fusion implosion by the input of laser energy and thus a higher yield of fast neutrons, high energy gamma radiation, X-rays, other forms of radiation, and energy. OBJECTS OF THE INVENTION It is, therefore, an object of the present invention to disclose a thermonuclear fuel pellet configuration which conforms to the prescribed requirements of the nuclear physics involved as set forth in the aforementioned Brueckner patent applications incorporated herein by reference, and also to disclose a method for manufacturing these fuel pellets which can be easily regulated and which permits manufacturing at low cost with uniform results under circumstances which are conducive to commercialization and production. Other objects and features of the invention relating to details of the process, the materials used, and the construction will be apparent in the following description and claims in which the principles of operation, together with the best mode presently contemplated for the invention, are disclosed. |
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039379698 | claims | 1. A gamma ray camera system for imaging an in vivo distribution of a radioactive material which emits gamma rays comprising: a gamma ray detector, including a transducer sensitive to gamma rays, of the type producing output signals delineating spatial coordinates of interaction of gamma rays with said transducer; and a gamma ray collimator adapted to be mounted adjacent said transducer comprising a plurality of straight strips of lead foil no greater than about 0.01 inches in thickness and a plurality of strips of lead foil no greater than about 0.01 inches in thickness and having corrugations therein arranged with each corrugated strip mounted between successive straight strips to produce an array of collimating channels. a gamma ray detector, including a transducer sensitive to gamma rays, of the type producing output signals delineating spatial coordinates of interaction of gamma rays with said transducer; and a gamma ray collimator adapted to be mounted adjacent said transducer comprising a plurality of straight strips of lead foil no greater than about 0.01 inches in thickness and a plurality of corrugated strips of lead foil no greater than about 0.01 inches in thickness, said corrugated strips each having corrugations which focus substantially to a common point and are generally wider and deeper on the side more remote from said common point such that said straight strips and corrugated strips provide a collimator with multiple channels focused substantially to a common focus. 2. Apparatus as claimed in claim 1, wherein said corrugated strips have regular, parallel corrugations and said collimator is thereby a parallel multi-channel collimator. 3. Apparatus as claimed in claim 1, wherein said corrugated strips have corrugations which focus substantially to a common point and are generally wider and deeper on the side more remote from said common point and said collimator is thereby a focused multi-channel collimator which may be employed as an image-minifying or image-magnifying collimator. 4. A gamma ray camera system for imaging an in vivo distribution of a radioactive material which emits gamma rays comprising: 5. A collimator for a gamma ray imaging system comprising a plurality of strips of lead foil no greater than about 0.01 inches in thickness at least some of which contain a repetitively occurring pattern of corrugations and alternating ones of said strips have surfaces extending laterally relative to said corrugations and lying in contact with and sealed to adjacent corrugations, thereby forming a multiplicity of collimating channels aligned with the areas of contact between said laterally extending surfaces and said corrugations. 6. A lead collimator for use in gamma ray imaging comprising a plurality of strips of lead foil no greater than about 0.01 inches in thickness at least some of which are deformed into a pattern of recurring corrugations having contiguous sides which form intersecting planes and at least some of said strips have laterally expansive planar surfaces lying in contact with and sealed to adjacent corrugations of another strip so that contiguous sides of each corrugation and a laterally expansive surface of an adjacent strip intersect in a single straight line extending the coextensive width of adjacent strips, thereby defining a multiplicity of collimating channels aligned with straight lines formed as aforesaid. |
description | This application claims the benefit of priority based on U.S. Provisional Patent Application No. 61/426,910, filed Dec. 23, 2010, and Netherlands Patent Application No. 2005904, filed Dec. 22, 2010, which are all incorporated herein by reference. The present disclosure relates generally to a mobile X-ray unit. The present disclosure further relates to a method of visualization of an X-ray beam. The incidence rate of skin cancer has substantially increased in the last decade of the 20th century. It is appreciated that over 1.3 million new skin cancers are diagnosed annually, which is increasing at a rate of about 5% per year. Increased exposure to the sun without skin protection and a decreased ozone layer are regarded as the main causes of this increase—a problem estimated to be costing over 1 billion Euros in annual medical treatment expenses. Over 80% of skin cancers occur in the head and neck regions with 50% occurring in patients over 60 years of age. It is expected that a portion of the senior population will double in year 2025 compared to the present demographics. Because of the growing incidence of skin cancer and increasing share of the senior population in the overall demographics, much focus has been placed on cancer treatments and cancer treatment logistics. Non-proliferative cancers, which are defined by substantially superficial lesions, may be treated in different ways. In one example, non-proliferative cancers may be treated surgically. Surgery, may, however, have certain drawbacks, such as, for example, long waiting lists, complications related to post-treatment care, and risk of infection. Alternatively, patients may undergo irradiation using electrons of soft X-rays. Irradiation may have an advantage of being non-invasive and of a short duration (a treatment session may be as short as 2 to 4 minutes). It will be appreciated that usually the integral treatments using radiotherapeutic techniques may require a number of sessions. Recently, the use of a mobile and portable X-ray unit has been suggested, which may be used inside a hospital radiotherapy department. An embodiment of such portable unit is described in U.S. 2007/0076851. Existing X-ray units include an X-ray source and a filtering device having a plurality of filters rotatably arranged with respect to a focal point of the X-ray tube for changing filtering characteristics on demand. The plurality of filters are arranged in a filtering device, which is transversely arranged with respect to a longitudinal axis of the X-ray tube. These units, while effective, may have certain drawbacks. For example, it may be difficult to delineate the X-ray beam emitted from the X-ray applicator and a treated region on the patient. It is an object of the present disclosure to provide a mobile X-ray unit configured to delineate between at least a portion of the actual X-ray beam emitted from the X-ray applicator and a target region on the patient. It is a further object of the present disclosure to provide a mobile X-ray unit that has visual information regarding the full geometry of the X-ray beam emitted from an exit surface of the X-ray tube. To this end, the mobile X-ray unit, according to the present disclosure, includes an indicator configured to delineate at least a portion of the X-ray beam emitted from the exit surface of an X-ray tube. It will be appreciated that the terms ‘mobile’ and ‘portable’ in the context of the present application may be interchangeable as these terms equally relate to an easily moved or transported device, such as, for example, a device which may be moved or transported by a single individual. Treatment efficacy may be substantially improved when an indicator is provided for delineating at least a portion of the generated X-ray beam, like a central axis thereof, and/or a partial or a full beam geometry. In an exemplary embodiment, the indicator is a light source. The light source may be arranged to provide a shadow-like indication of a two-dimensional area irradiated by the X-ray beam (full or partial). In other embodiments, the light source may be advantageously arranged to provide a light beam which illuminates either partially or wholly an area of the surface irradiated by the X-ray beam. In this manner, the target region on the skin and the X-ray beam may be properly aligned. The light source may be arranged in the X-ray applicator or, alternatively, the light source may be arranged around an outer surface of the X-ray applicator. When the light source is arranged in the X-ray applicator, the light source may be configured to delineate the central axis of the X-ray beam and/or the full beam geometry. When the light source is arranged around the outer surface of the X-ray applicator, the light source may be arranged to delineate a central axis of the X-ray beam, preferably at a pre-determined distance from the X-ray applicator. This may be advantageous when the X-ray applicator is used at a standard distance from the patient's skin. However, it will be appreciated that the light source arranged around the X-ray applicator may be adjusted so as to indicate the central axis of the X-ray beam at a variety of axial distances from the X-ray applicator. It will be appreciated that the light source may be arranged to provide a contrast image of at least a portion of the X-ray beam. For example, the light source may be arranged to generate a light image of a portion of the X-ray beam. The light image may be surrounded by a darker background. Alternatively, the light source may be arranged to generate a shadow image. The darker image of the portion of the X-ray beam may be surrounded by a lighter background. In both cases, the contrast edge of the image may be used for suitably aligning the X-ray applicator and the target region. In various embodiments, the indicator includes an array of light sources concentrically arranged around the X-ray applicator. Although it may be sufficient to provide a single light source that generates a narrow beam for indicating the central axis of the X-ray beam, it may be advantageous to provide a plurality of light sources each of which generates a narrow light beam. These light beams may intersect at a given distance from the lower surface of the X-ray applicator. In this manner, the X-ray applicator may be positioned at a prescribed distance from the skin. In order to ensure a correct coverage of the target region by the X-ray beam, the X-ray applicator may be positioned so that the indicated center of the X-ray beam is positioned substantially at a center of the target region. It will be appreciated that these embodiments function particularly well for regular shaped X-ray beams, for example, when a circular, a square, an elliptic, or a triangular collimator is used for shaping the X-ray beam. In various embodiments, the light source may be disposed inside the X-ray applicator for generating a light beam configured to be intercepted by the collimator for providing a light image of the X-ray field emitted from the exit surface. This embodiment may be advantageous when the full shape of the X-ray beam is to be delineated such as, for example, in situations when an irregular beam shape is used. In such cases, the light source may be provided near the target region or, via a mirror, off-axis, for generating a light beam configured to be intercepted by the collimator. It will be appreciated that a direction of propagation of the light beam must essentially conform to a direction of propagation of the X-ray beam. In one embodiment, when a mirror is used, the light source may advantageously be positioned off-axis minimizing its radiation damage. In various embodiments, the indicator includes a light source and an optical fiber configured to deliver light from the light source for interception by the collimator. The light source may be positioned outside the X-ray applicator so as to minimize the size of the X-ray applicator. For example, the light source may be arranged in the base of the X-ray unit and the optical fibers may run from the base to the X-ray applicator for illuminating the collimator and for obtaining an image of the generated X-ray beam. The indicator may include a plurality of optical fibers distributed in the X-ray applicator in an area above the collimator for illuminating a collimator opening and for causing the collimator opening to intercept the resulting light field. This embodiment may be advantageous for obtaining a light field having a substantial intensity. In various embodiments, the light source may emit a narrow light beam arranged inside the applicator for delineating the longitudinal axis of the X-ray beam. In some embodiments, a miniature laser source may be used. In various embodiments, the collimator may be provided with automatic identification devices configured to generate a signal in the control unit representative of collimator characteristics. It may be advantageous to automatically identify when the collimator has been inserted in the X-ray tube so as to minimize or eliminate human errors in defining the field geometry. For example, the collimator may be positioned in a receptacle having a resistive path whose resistivity may be changed. The collimator may be arranged with projections adapted to cooperate with the resistive path of the receptacle for changing the resistivity of the receptacle, and thus, generating a signal indicating that the collimator has been inserted into the receptacle. In some embodiments, the signal may be transmitted to the control unit of the mobile X-ray unit for independent verification. It is contemplated that the mobile X-ray unit includes a set of collimators each having identification devices. In various embodiments of the present disclosure, the mobile X-ray unit may include a signaling device configured to indicate that an X-ray beam has been generated. It may be advantageous to provide a signaling device that indicates the operational state of the X-ray beam. For example, the signaling device may be a light on the X-ray applicator. One or more light emitting diodes may be used for this purpose. It may be possible to provide a plurality of signaling devices that indicate the energy of the generated X-ray beam. For example, for the X-ray beam of a lower portion of the spectrum (about 50 kV), a first indicator may be used, such as, for example, a first light color. For an intermediate portion of the spectrum (about 60-65 kV), a second indicator may be used, such as, for example, a second light color. Finally, for the higher portion of the spectrum (66-75 kV, preferably 66-70 kV), a third indicator may be used, such as, for example, a third light color. It will be appreciated that a plurality of possibilities exist for indicating different spectra, including but not limited to a progressive illumination of a plurality of indicators upon hardening of the delivered X-ray beam. It will be further appreciated that such indication of the kV range may be disposed in the device, in a user interface, or in a supplementary unit. It will be further appreciated that the named kV ranges may be scaled with, for example the factors 1:1; 1:2; 1:3; 1:4; 1:5. Preferably, the signaling devices comprise a light indicator arranged on an outer housing. The arrangement of the signaling devices is advantageous as the patient is made aware about the starting point and the termination of irradiation so that the patient may retain a static position during the course of treatment. It will be appreciated that the signal device that indicates that the X-ray beam is on is separate from the indicator configured to delineate the X-ray beam discussed above. In various embodiments of the present disclosure, the mobile X-ray unit may include a cooler arranged with piping to provide a cooling medium in a vicinity of the X-ray tube. The piping may run in a space between the X-ray tube and a shielding wall associated with the X-ray tube. It may be advantageous to provide a space between the outer surface of the X-ray tube and the inner surface of the X-ray tube, that is at least partially filled with a coolant. In some embodiments, it may be advantageous to provide circulated water as a cooling agent due to high specific heat capacity, offering improved heat transfer of water with respect to a gas. However, pressurized gas may also be used as a suitable coolant. In some embodiments, a temperature sensor may be arranged on the outer housing of the X-ray applicator for measuring actual temperature of the outer housing. The temperature sensor may be connected to the control unit for controlling the cooler and/or for controlling the high voltage supply. Should the temperature rise above a pre-determined shut-off value, the control unit may be arranged to disable the high voltage supply and/or to intensify the cooling mode, for example, by increasing a pumping capacity of the coolant. In various embodiments of the present disclosure, a radiation detector may be provided inside the outer housing for detecting the X-ray beam. It may be advantageous to provide an independent radiation detector for detecting the presence of the generated X-ray beam. In some embodiments, the mobile X-ray unit includes a primary timer which sets a time for the high voltage supply for delivering a predetermined radiation dose. The radiation sensor accommodated inside the outer housing of the X-ray applicator may be part of a secondary timer circuit adapted to shut down the high voltage supply after the predetermined radiation dose is delivered. In this way radiation safety control may be improved. In various embodiments of the present disclosure, the X-ray applicator may include an exit surface directed towards a patient. The surface may be covered by an applicator cap. It may be advantageous to provide an applicator cap, which may have many functions in use. In one example, the applicator cap may be used for protecting the exit surface of the X-ray applicator from intra-patient contamination. In another example, the thickness of the cap in a direction of the beam propagation may be sufficient for substantially eliminating electron contamination from the X-ray beam. In some embodiments, the applicator cap may be manufactured from PVDF (Polyvinylidene fluoride) and may have a thickness of about 0.4-0.7 mm, preferably 0.6 mm, across the window portion. The applicator cap may have a density of about 1.75-1.8, and preferably 1.78. In other embodiments, the applicator cap may have a thickness of 0.3-0.6 mm, and preferably 0.5 mm, across the window portion. In these embodiments, the applicator cap may have a density of 1.30-1.45, and preferably 1.39, and may be manufactured from PPSU (polyphenylsulfone). It is found that these materials may be particularly suitable as they as stable under influence of the X-rays and are suitable for different types of sterilization procedures, such as chemical sterilization, or sterilization under elevated temperatures. It will be appreciated that those skilled in the art will readily appreciate the relationship between the energy of the secondary electrons emanating from the X-ray tube and a required thickness of a given material, such as, for example plastic, glass, ceramics, sufficient for fully intercepting these electrons. In some embodiments, the applicator cap may be disposable. In yet another example, the applicator cap may function as a heat absorber to dissipate the elevated temperature of the X-ray applicator. As a result the patient will feel the applicator contacting the skin as a slightly warm object. It will be appreciated that the indicator configured to delineate the X-ray beam may be configured to have sufficient intensity to provide a field image through the applicator cap. Lasers may be particularly suited for this purpose. Alternatively, light emitting diodes may be used. In another embodiment, an arrangement of one or more light sources generating a narrow beam outside the X-ray applicator may be advantageous. In that embodiment, one or more sources may be arranged on respective support arm such that the respective narrow light beams are not intercepted by the applicator cap. In various embodiments, the X-ray applicator may be connected to the base using a displaceable panel. The flexible cabling may run substantially in the displaceable panel. It may be advantageous to provide an intermediate mechanical unit connecting the base of the mobile X-ray unit and the X-ray applicator, and for housing the flexible cables so as to prevent the cables from entangling. The displaceable panel may be arranged with a pre-defined travel distance with respect to a lowest achievable stand position and a highest achievable stand position. This may be advantageous for increasing durability of the cables tubes and wiring of the mobile X-ray unit, and especially of the tubes accommodating the coolant. It may be advantageous to provide the remote light source as is discussed above in the displaceable panel as this may reduce the required length of the optical fibers. In various embodiments, the displaceable panel may include a user interface for controlling the X-ray unit. In some embodiments, the user interface may be a display. For example, the display may be implemented as a touch screen arranged for enabling data input. Alternatively, the display may be arranged for echoing data. In this embodiment, the display may include buttons or other suitable means for entering input data into the mobile X-ray unit. Another embodiment of the present disclosure is directed a method for visually delineating an X-ray beam emitted from a mobile X-ray unit. The mobile X-ray unit may include a base having a control unit and a power supply. The mobile X-ray unit may further include an articulated arm coupled to an X-ray applicator having an X-ray tube. The X-ray tube may include a target, a collimator, and an exit surface through which the X-ray beam may pass. The method may include generating an X-ray beam and shaping the X-ray beam. The method may further include providing a visual indication of at least a portion of the X-ray beam emitted from the exit surface. In some embodiments, the target and the collimator are accommodated in a substantially cylindrically shaped outer housing, and a direction of propagation of the generated X-ray beam may be substantially parallel to the longitudinal axis. Additional objects and advantages of the invention will be set forth in part 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 will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. Reference will now be made in detail to the present exemplary embodiments of the invention, an examples of which is are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. FIG. 1a presents a partial perspective view of a mobile X-ray unit according to the invention. The mobile X-ray unit 10 comprises a base 2 having at least a high voltage supply unit, a cooling system, and a control unit (FIG. 2) for controlling an operation of an X-ray applicator 4. The X-ray applicator 4 includes an X-ray tube (FIG. 3) disposed in an outer housing of the X-ray applicator 4. The X-ray applicator 4 may be connected to the base 2 using flexible cables 3, which may be at least partially disposed in a displaceable panel 5. The X-ray applicator 4 may be coupled to an articulated arm 4a, which may include a pivot for varying the position of the X-ray applicator 4 in space. In some embodiments, the articulated arm 4a includes a brake (not shown) for holding the X-ray applicator 4 in a particular position in space. In one embodiment, the brake may be manually controlled and may be used for simultaneously switching on a light source used for aligning the X-ray applicator 4 with respect to a target region on a patient P. The X-ray applicator 4 may include a longitudinal axis and an exit window 8 through which the generated X-ray beam exits the X-ray applicator 4. In some embodiments, the X-ray applicator 4 and the X-ray tube (not shown) are coaxial. In this manner, the X-ray beam 8a may propagate from the exit window 8 and may have a beam axis (not shown) that substantially corresponds to the longitudinal axis of the X-ray tube. The X-ray applicator 4 may include an indicator. The indicator may provide a visual indication of at least a portion of the X-ray beam 8a on the patient P, when the X-ray applicator 4 is being positioned relative to the patient P. In an exemplary embodiment, the indicator may be a light source 8c. In some embodiments, the light source 8c may be disposed either inside the X-ray applicator 4 or around the X-ray applicator 4. In other embodiments, the light source 8c may be remotely positioned, for example in the base 2. In the latter case, light from the light source 8c may be conducted towards the X-ray applicator 4 using one or more optical fibers. The articulated arm 4a may be mechanically connected to the displaceable panel 5. The displaceable panel 5 may be configured to move relative to the base 2 to alter a vertical position of the X-ray applicator 4. In some embodiments, the displaceable panel 5 may be provided with a handle 6 enabling easy manipulation thereof. The displaceable panel 5 may be guided along suitable rails for enabling a substantially smooth and shock-free displacement thereof. The displaceable panel 5 may include a display 7, which may function as a suitable user interface 7a. For example, patient data, such as, for example, a photo of the patient and/or a photo of a lesion, may be provided in window 7b, whereby relevant patient information, such as the date of birth, gender, dose prescription and dose delivery protocol and so on may be displayed in window 7c. Inputs 7d may also be provided. Alternatively and/or additionally, suitable hardware switches or buttons may be provided as well. The display panel 7 may also include a button, switch, or other structure to activate the light indicator. Alternatively, the light source 8c may always be on when the X-ray unit is switched on. FIG. 1b presents a partial perspective view of the mobile X-ray unit illustrating movement of the displaceable panel. In this enlarged view 10a, specific elements of the displaceable panel 5 are depicted. A handle 6 may be implemented as a mechanical item for pulling or pushing the displaceable panel 5. Alternatively, the handle 6 may be arranged as an electrical actuator for triggering motors (not shown) for displacing the displaceable panel 5. For example, when the handle 6 is pulled the motors may be activated for causing the panel 5 to displace in a direction A. Pushing of the handle 6 may cause lowering of the panel 5 in a direction B. In some embodiments, the mobile X-ray unit 10 includes stops, limits, or other known structures for limiting the movement of the displaceable panel 5. This may be advantageous for ensuring mechanical stability of the mobile X-ray unit 10 (limitation of the upper level) and may also be beneficial for preventing cable damage (limitation of the lower level). In some embodiments, the displaceable panel 5 may travel along built-in rails whose length may be chosen for limiting the displacement range of the panel 5 in a desirable way. In one exemplary embodiment, a light source 8c′ configured to delineate at least a portion of the X-ray beam, may be positioned inside the displaceable panel 5. Suitable optical fibers (not shown) may be used for conducting light from the light source 8c′ towards the X-ray applicator. More details on suitable light source arrangements, although not limitative, are discussed with reference to FIGS. 3a-3c. FIG. 1c illustrates the displacement of the X-ray applicator 4 of the X-ray unit 10. It will be understood that the mobile X-ray unit 10 may be configured so as to support a broad range of translational and rotational movements of the X-ray applicator 4. In view 11, the X-ray applicator 4 is in its retracted position. It will be appreciated that cabling is not depicted for clarity reasons. The retracted position may be suitable for transport of the mobile X-ray unit 10 towards a booth and/or for maneuvering the X-ray unit 10 around the patient. In order to retract the X-ray applicator 4 as close as possible to the base 2, the articulated arm 4a may be positioned under the outer portion 5a of the displaceable panel 5. For ensuring stability of the mobile X-ray unit 10 during maneuvering thereof, a load block 2a may be provided for lowering the point of gravity of the X-ray unit 10. In view 12, the X-ray applicator 4 may be in an extended position having an X-ray exit surface 8 oriented towards a patient P. In order to suitably position the X-ray applicator 4 with respect to the patient P, the displaceable panel 5 may be moved to an intermediate position located between the lowest position and the highest position of the displaceable panel 5. The articulated arm 4a may be used for suitably rotating the X-ray applicator 4 about a rotation axis. Preferably, a rotation axis is selected to coincide with a direction of emanation of the X-ray beam from the exit surface 8 for a vertically oriented X-ray applicator 4. In view 13, the X-ray applicator 4 may be in a lowered position. For this purpose the displaceable panel 5 may be in its lowest position and the arm 4a may be used for orienting the X-ray applicator 4 in a desirable way. FIG. 2 is a diagrammatic representation of the mobile X-ray unit 10 according to the invention. The mobile X-ray unit 10 according to the invention comprises a high voltage supply, preferably adapted to generate 50-75 kV X-rays in a suitable X-ray tube, a cooling system for cooling the X-ray tube during use, and a control system for controlling electronic and electric parameters of sub-units of the X-ray unit during use. View 20 diagrammatically depicts main units of the control system 21 and of the X-ray applicator 22. The control system 21 includes a hard wired user interface 21a for enabling switching on and switching off of the high voltage supply 21b. In some embodiments, the high voltage supply 21b comprises a high voltage generator 21c with improved ramp-up and ramp-down characteristics. The high voltage supply is preferably operable for delivering power of about 200 W in use. In some embodiments, the ramp-up time may be of the order of 100 ms. The hard wired interface 21a, may also be arranged to automatically switch on the cooling system 21d when the high voltage generator is switched on. In addition, the control system 21 may include a primary controller 21e arranged for controlling the dose delivery from the X-ray applicator 22 in use. The primary controller 21e may be provided with a primary counter adapted to register time lapsed after the X-ray radiation is initiated. The primary counter may then automatically switch off the high voltage supply to the X-ray tube 22a in the event a pre-determined dose is reached. It will be appreciated that the pre-determined dose is at least dependent on the energy of the X-rays and the dose rate, which may be calibrated in advance. Where calibrated data is made available to the primary controller, adequate primary dose delivery control may be achieved. In some embodiments, a secondary controller 21f may be provided for enabling an independent loop of dose delivery control. The secondary controller 21f may be connected to a dose meter accommodated inside the X-ray applicator 22 in the X-ray field before the collimator 22d. Accordingly, the dose meter may provide real-time data on actual dose delivery taking into account dose variation during ramp up and ramp down of the high voltage source. Still preferably, the control system 21 may include a safety controller 21g adapted to compare readings from the primary controller 21e and the secondary controller 21g for switching off the high voltage generator 21c after a desired dose is delivered. Additionally and/or alternatively, the safety controller 21g may be wired to guard emergency stop, door interlock and a generator interlock. The control system 21 may further include an indicator controller 21h for controlling source light source configured to delineate at least a portion of an X-ray beam. The indicator controller 21h may be linked to a power supply unit 21b for switching on the light source once the system 21 is on. In some embodiments, the light source may be switched on demand. Accordingly, the indicator control 21h may be arranged to provide electrical power to the light source when triggered by the user. The user may provide trigger signal via a user interface, or, for example, using a dedicated hardware switch. In an exemplary embodiment, the X-ray applicator 22 may include an X-ray tube 22a housed in an outer housing (shielding) 22k. The X-ray tube 22a may have a target-collimator distance of between 4 and 10 cm, and preferably 5 and 6 cm. The X-ray applicator 22 may further comprise a beam hardening filter 22b selected to intercept low-energy radiation and a beam flattening filter 22c, designed to intercept portions of X-ray radiation for generating a substantially flat beam profile near the exit surface of the X-ray applicator 22. Further, the X-ray applicator 22 may comprise one or more collimators 22d arranged to define treatment beam geometry. Preferably a set of collimators 22d may be used having, for example, diameters of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 cm. It will be appreciated that although circular collimators are discussed, collimators of any shape, such as square, elliptic or custom made collimators are possible. It may be advantageous to have an X-ray applicator 22 with automatic collimator detection means 22f adapted to automatically signal which collimator is being used. In some embodiments, resistive sensing may be used to identify which collimator 22d is being used. In particular, each collimator may be provided with at least a couple of projections for bridging a resistive path provided in a collimator receptacle. The resulting electrical resistance of the receptacle constitutes a signal representative of a collimator being used. The X-ray applicator 22 may also include a built-in temperature sensor 22g adapted to signal temperature of the X-ray tube 22a and/or its shielding 22k. The signal from the temperature sensor 22g may be received by the control system 21 which may carry out the analysis thereof. Should the measured temperature be elevated beyond an allowable level, an alarm signal may be generated. Optionally, a shut-off signal to the high voltage generator may be provided. The X-ray applicator 22 may further comprises a radiation sensor 22h arranged inside the outer housing 22k for detecting X-ray radiation which may be delivered by the X-ray tube 22a. Preferably, for safety reasons the X-ray applicator 22 may include a non-volatile data storage 22i arranged for recording operational parameters at least of the X-ray tube 22a. Further, to enhance radiation safety, the X-ray applicator 22 may be provided with a radiation indicator 22j arranged for providing a visual and/or an audio output to the user and/or the patient regarding ON/OFF condition of the X-ray tube 22a. It will be appreciated that the radiation indicator 22j may comprise a plurality of signaling devices. In one embodiment, at least one signaling device, for example a light emitting diode (LED), is associated with the X-ray applicator 22 and provided on the X-ray applicator 22. It is understood, however, that the signaling devices may be positioned at any other location on the mobile X-ray unit. FIG. 3a presents a cross-section of an X-ray applicator of the mobile X-ray unit having an indicator in accordance with a first embodiment of the present disclosure. The X-ray applicator 30 includes an outer housing 36 and an X-ray tube 35 disposed in the outer housing 36. The X-ray tube 35 may have an external shielding 35a, a target (not shown), and a collimator 33. In one embodiment, the indicator may be light source 48a. The light source 48 may cooperating with a mirror 48 for emitting a light beam indicative of a two-dimensional beam of X-rays produced by the X-ray tube 35. In some embodiments, X-rays have a propagation axis 45a which coincides with a longitudinal axis of the X-ray tube 35. The light source 48a and the mirror 48 may be arranged so that the light beam may substantially propagate along the longitudinal axis of the X-ray tube 45a. When the light beam is intercepted by the collimator 33 a visual indication and simulation of the two-dimensional X-ray beam is created so as to facilitate alignment of the X-ray applicator and the target region of the patient P. In one embodiment, the distance between a target of the anode (not shown) and the collimator 33 is in the range of 4 to 10 cm, preferably about 5 to 6 cm. Such relatively short target-collimator distance may generate an X-ray beam having a substantially narrow penumbra (1.5-1.8 mm for 20/80% lines) and good beam flatness due to a relatively small focal size. It will be appreciated that while the anode has a longitudinal axis arranged substantially parallel to the longitudinal axis 45a of the X-ray tube 35, the target may be a substantially flat plate which extends substantially perpendicular to the axis 45a. The X-ray applicator 30 further include a filter 39 for hardening the X-ray beam emanating from the target, a beam flattening filter 40 for flattening out a beam profile, and a collimator receptacle 41 for receiving collimator 33. A cooling system 34 may be provided so as to prevent overheating of the X-ray tube 35. In one embodiment, the cooling system 34 may be arranged in the space between the X-ray tube 35 and the shielding 35a in contact with the surface of the X-ray tube 35. A suitable coolant may be provided using a pipe 31. It is contemplated that the coolant may be water, a pressurized gas, or even a special oil. The X-ray applicator 30 may further comprise a temperature sensor 37. The X-ray assembly 30 may further include a suitable radiation detector 38 connected to a radiation indicator 43. Data collected by the radiation detector 38 may be stored in a data storage unit 44. In order to protect an X-ray exit surface of the X-ray applicator 30 from intra-patient contamination, an applicator cap 42 may be provided to cover at least the exit surface of the X-ray applicator 30. In some embodiments, the applicator cap 42 is thick enough to fully intercept secondary electrons emanating from the X-ray applicator. The applicator cap 32 may be manufactured from PVDF (polyvinylidene fluoride) and may be about 0.4-0.7 mm, and preferably 0.6 mm thick across the window portion. The applicator cap may have density of about 1.75-1.8, and preferably 1.78. Alternatively the applicator cap 42 may be 0.3-0.6 mm thick, and preferably 0.5 mm thick across the window portion. In those embodiments, the applicator cap 32 may have a density of 1.30-1.45, and preferably 1.39. Further, the applicator cap 42 may be manufactured from PPSU (polyphenylsulfone). These materials may be particularly suitable as they as stable under influence of the X-rays and are suitable for different types of sterilization procedures, such as chemical sterilization, or sterilization under elevated temperatures. FIG. 3b presents a cross-section of an X-ray applicator of the mobile X-ray unit having an indicator in accordance with a second embodiment of the present disclosure. In this exemplary embodiment, the indicator includes at least one optical fiber 47a connected to a light source that may be positioned remotely in, for example, base 2 (FIG. 1a). An anode 45 may have a longitudinal axis coaxially arranged with respect to a longitudinal axis 45a of the X-ray applicator 30. Accordingly, a central axis of the X-ray beam emitted by the anode 45 substantially coincides with the longitudinal axis 45a of the X-ray applicator 30. Optical fiber 47a may be provided in the collimator receptacle 41 above the collimator 33. The optical fiber 47a may be configured to generate a light field that is substantially centered about the collimator opening 33 for creating a two-dimensional cross-section of an X-ray beam emitted from the collimator 33. In this embodiment, optical fiber 47a may be configured to emit a substantially narrow beam having a divergence representative with expected divergence of the X-ray beam. Alternatively, it may be possible to use the optical fiber 47a for visualizing a central axis 45a of the X-ray beam in addition to visualizing of the two-dimensional area of the X-ray beam. In this case the optical fiber is advantageously arranged to emit a narrow beam light producing a miniature light spot on a surface of the patient. In one embodiment, a dimension of the light spot is less than 5 mm2, and more preferably a dimension of the light spot is about 1 mm2. A suitable light emitting diode or a laser may be used for generating light emitted from the fiber 47a. In one embodiment, the light emitting diode and the laser are remotely arranged with respect to the X-ray applicator 30. It will be appreciated that an alternative configuration may be used such as for example, having one or more light sources that may be electrically connected to one or more optical fibers. FIG. 3b presents a cross-section of an X-ray applicator 30 of the mobile X-ray unit having an indicator in accordance with a second embodiment of the present disclosure. In this exemplary embodiment, the indicator may be disposed externally of the X-ray applicator 30 and may be one or more light sources 52. As illustrated in FIG. 3b, the X-ray applicator 30 may include an anode 45 provided with a target for generating an X-ray beam 45c having the longitudinal X-ray axis 45a. The one or more light source 52 may be configured to illuminate the longitudinal axis 45a of the X-ray beam 45c at a pre-determined distance D from the lower surface 49 of the X-ray applicator 30. It will be appreciated that the lower surface 49 may relate to the exit window as discussed with reference to FIG. 1a, or it may relate to the applicator cap, as will be discussed with reference to FIG. 4. The one or more light sources 52a, 52b may be disposed on support arms 54a, 54b. Light sources 52a, 52b may generate narrow light beams 53a, 53b that may be directed towards the axis 45a and intersect at a pre-determined distance D from the lower surface 49 of the X-ray applicator 30. Preferably, the distance D is selected to be between 0.5 and 2 cm. The support arms 54a, 54b may be arranged so that light beams 53a, 53b do not intersect the X-ray applicator 30. In use, a user may position the X-ray applicator 30 with respect to the patient P in such a way that the beams 53a, 53b intersect at the surface of the patient. However, should the treatment regime require the use of a dose build-up material, the beams 53a, 53b may cross on a surface of the dose build-up material. In some embodiments, the support arms 54a, 54b may be adjustable to indicate the central axis 45a at different distances from the lower surface 49 of the X-ray applicator 30. In order to calibrate adjustment of the support arms, a transparent calibration phantom may be used, wherein the central axis and depth are marked. It will be appreciated that although FIGS. 3a-3c disclose separate embodiments of the indicator, combination of such embodiments is contemplated as well. For example, embodiments directed to indicating the central axis may be combined with embodiments directed to indicating the complete field. In addition, internal and external indicators may be combined. FIG. 4 presents a partial perspective view of the X-ray applicator provided with an applicator cap. The applicator cap 42 may be manufactured from transparent glass, transparent plastic, or from ceramics as well as from PVDF and PPSU. Applicator cap 42 may also be manufactured from a metal. In the latter case, the applicator cap may be sterilized, otherwise, the applicator cap 42 may be a disposable applicator cap. In view 50 of FIG. 4, it is seen that an outer dimension of the X-ray applicator 51 may be larger than the outer dimension of an exit portion covered by the applicator cap 42. Although such embodiment is preferable for minimizing total weight of the X-ray applicator 51, it may be possible that the exit portion has the same dimension as the body of the X-ray applicator 51. FIG. 5 presents a perspective view of a collimator with identification devices. The collimator 63 may be provided with a central opening 64 for defining a shape and dimension of the resulting X-ray beam emitted from the X-ray applicator 30 as is discussed with reference to FIGS. 3a-3c. The collimator 63 may be adapted to be fittingly received in a collimator receptacle 61. In order to enable automatic collimator identification, the collimator 63 may be provided with two projections 65a, 65b, adapted to interact with a resistive path 62 in the collimator receptacle 61. When the projections 65a, 65b come into contact with the path 62 a net resistance of the collimator receptacle 61 may be changed. The change in the resistance of the collimator receptacle 61 may be used to indicate when the collimator has been inserted in the collimator receptacle 61. It will be appreciated that for a set of collimators, each collimator may be provided with a unique pair of projections leading to a distinguishable change in the net resistivity of the collimator receptacle 61. Those skilled in the art will readily appreciate that a plurality of pairs 65a, 65b may be positioned at different locations on a surface of the collimator 63. Alternatively, it is possible to provide each collimator 63 with an electronic identification device such as, for example, a chip cooperating with a plug. When the plug is plugged-in the collimator receptacle 61 (provided with a cooperating socket), a signal may be transferred to the control unit of the mobile X-ray unit 10. FIG. 6 presents a schematic view of the indicator, in accordance with another embodiment of the present disclosure. In this embodiment, the indicator may be a light source 126 provided at a side surface of the X-ray tube 35. The light source may be an LED or any other suitable light source. Light emitted from the light source 126 may impinge on a reflective surface of the X-ray collimator 132. The light beam may then be reflected from a further reflective surface 134 and directed as respective beams B1 and B2 towards the central axis X of the X-ray tube 35. It will be appreciated that the X-ray tube 35 may be suitably shaped and manufactured for providing a reflective body 134. The reflective body 134 may be a concentric reflective ring attached in a corresponding recess of the X-ray tube 35. It will be further appreciated that the reflective surfaces 132 may be advantageously provided on a collimator surface facing away from the patient towards the X-ray source (not shown), positioned on the axis X. Those skilled in the art will readily appreciate how to arrange the collimator 134, and the X-ray tube 135, shown in FIG. 3 for enabling the geometry discussed in FIG. 6. A light spot generated by the light source 126 in the manner described above may be used for accurately positioning the X-ray tube 35 with respect to the patient P. It will be further appreciated that the spatial position of the intersection between the beams B1 and B2 may be chosen to provide a minimum spot at a pre-determined distance from an outer surface of the X-ray applicator (not shown) accommodating the X-ray tube 35. For example, the pre-determined distance may be selected at 1, 2, 3, 4, or 5 cm from the outer surface of the X-ray applicator. In this way the alignment between the target region on the patient P and the central axis of the X-ray beam may be controlled and maintained. It may be advantageous to select the pre-determined distance at about 2-3 cm from the outer surface of the X-ray applicator for enabling maneuverability of the X-ray applicator without contacting the patient. When the X-ray applicator is set with respect to the patient P, using the articulated arm 4a, shown in FIG. 1a and the light source 126, may be positioned using fine mechanics. An embodiment of suitable fine mechanics is discussed with reference to FIG. 7. It will be further appreciated that while the indicator (i.e., light sources) and the reflective bodies are explained with reference to the X-ray tube 35, it may be possible to implement a similar configuration attaching the light sources 126 to an outer surface of the X-ray applicator 4a, depicted in FIG. 1. In this case instead of using collimators for implementing a reflective purpose, a dedicated reflector may be used. FIG. 7a presents a partial perspective view of a mechanism for finely adjusting an axial position of the X-ray applicator 4. In one embodiment, the X-ray applicator 4 may be provided in a sleeve 9 having a rotating portion 9a. The rotating portion 9a includes suitable mechanics engaged with the X-ray applicator 4 for enabling its axial translation. In use, X-ray applicator 4 may positioned using the articulated arm 4a. In particular, articulated arm 4a may have a rotational joint 6a that coupled to the base 2 (FIG. 1a) of the mobile X-ray unit 10, and a ball joint 6b, coupled to the X-ray applicator 4. The position of the X-ray applicator 4 may be determined using the indicators discussed above, and may be fixed using built-in brakes (not shown) provided in the joints 6a, 6b. After this, the rotating portion 9a may be moved for allowing an axial displacement of the X-ray tube. In this way the X-ray applicator 4 may be gradually brought closer to the target region. In one embodiment, the rotating portion 9a may be adapted to move about 1-4 cm. FIG. 7b presents an exploded view of the mechanism of FIG. 7a. In this figure, it is shown that the X-ray applicator 4 may be disposed within the axial displacement mechanism, which may include a rotating body 9a, an adapter 19a for engaging the X-ray applicator 4, a screw mechanics 19, and a holder 9 connected to the articulated arm 4a. It will be appreciated, however, that other mechanisms for axially translating the X-ray applicator may be contemplated, including, but not limited to, telescopic mechanisms. FIGS. 8, 8E-E, and 8F-F, illustrate various views of the X-ray tube. The X-ray tube 100 may have a body 102 enclosing at one end an end window 104 through which the X-rays pass. See FIG. 8, cross-section E-E. The end window 104 may be made from a thin sheet of Beryllium metal. An applicator cap 106 may be positioned over the end window 104 so as to covering the end window 104 and protect end window 104. Applicator cap 106 may be made from a plastic material. The applicator cap may be manufactured from PVDF (polyvinylidene fluoride) and has a thickness of about 0.4-0.7 mm, and preferably 0.6 mm, across the window portion. Alternatively, the applicator cap 106 may be manufactured from PPSU (polyphenylsulfone) and have a thickness of about 0.3-0.6 mm, and preferably 0.5 mm, across the window portion. In the tube body 102, a target 108 may be located at a range between 4 and 10 cm from the collimator 130, and preferably between 4 and 5 cm from the collimator 130 (see FIG. 7, cross-section F-F). It will be appreciated that this distance is measured between the outer surface of the target 108 and a midplane of the collimator 130. The target 108 may be made from Tungsten metal to provide the desired X-ray spectrum. The tungsten tip of the target 108 may be mounted on a large anode assembly 110 which also serves to dissipate the heat created from the generation of the X-rays in the target 108. Most of the anode assembly 110 is made from copper. The cathode 112 (see FIG. 7, cross-section F-F) may be located slightly off—axis near the end window 104. Electrons emitted from the cathode are accelerated across the gap by the potential difference between the cathode and anode, in this case set at about 70 kV, to the target 108 where the impact causes the generation of X-rays in a known manner. X-rays emitted from the target 108 pass through a beam hardening filter 122 before passing through a collimator 130 and an exit surface 124 on an applicator cap 106. The collimator 130 may be housed in a suitable collimator receptacle 128. The anode assembly 110 may be mounted in the body 102 and electrically insulated. One of a number of known techniques and materials may be used to provide the desired level of insulation between the anode assembly 110 and the body 102. As is well known in the art, the production of X-rays generates large amounts of waste heat. Accordingly, it may be necessary to cool the X-ray tube 100 in order to maintain it at a safe temperature. Various cooling mechanisms are known and used in the art. In one embodiment, the X-ray tube 100 may be cooled by cooled water forced around the anode region. Cooled water enters the back of the tube by a first conduit 116 and leaves by a second conduit 118 (see FIG. 7, cross-section F-F). The water cooling circuit is a closed loop circuit, with the water leaving the tube assembly 105 to be cooled by a remote cooler (not shown) before returning to the X-ray tube 100. It is contemplated that oil or another liquid may be used as the cooling medium. It is also known that a pressurized gas may be used as an effective coolant in some applications. As is known in the art, X-rays are generated and emitted in all directions, however the body 102 of the X-ray tube 100 and other internal components will tend to reduce the amount of radiation emitted from the body 102 of the X-ray tube 100 to a minimum, with most of the radiation emitted from the end window 104. The thickness of the shielding provided by the body 102 may be designed so that it provides at least the minimum level of shielding required for safe use by the operator. A high voltage cable assembly 120 may be connected to the anode assembly 110. The high voltage cable assembly 120 may be connected to flexible cable means (not shown) which in turn may be connected to a high voltage power supply. A radiation detector 114 may be placed outside the path of the X-ray beam emitted from the target 108 and passing through the end window 104. This detector can be any known form of radiation detector. In one embodiment, the radiation detector may be a hardened semi-conductor connected to an amplifier. The radiation detector 114 may detect when the tube 102 is working and emitting X-ray energy. Output from the detector 114 may connected to a control unit, and the output signals from the detector 114 may be used to provide an optical indication to a user of whether the tube is operating or not. By this means an X-ray detector 114 may be provided which may be used to detect if the X-ray tube is on or off. With further calibration of the radiation detector 114, it may be possible to determine and calculate the X-ray dose administered to the patient during the treatment. By this means it may be possible to have a real time dosimetry measurement system, in which the precise amount of radiation dose administered can be determined. Once the dose rate is known, a treatment plan can be modified during treatment. This may be advantageous because it may enable a very accurate and carefully controlled dose of X-rays to be administered. In order to enable the X-ray tube 100 to be placed accurately over a tumour, a tumour illumination device may be is used. The tumour illumination device may include a plurality of lights 126 placed around the circumference of the X-ray tube 100 near the end window 104. When in use, the lights shine onto the skin of the patient. Since the lights 126 are positioned around the circumference of the tube body 102, at a short distance from the end of the X-ray tube 100, they create a circle of light with a sharp cut off of the inner part of the circle. In this way, the position of the lights on the tube body 102 may create a shadow. This shadow circle may be used to indicate the region which will be subject to irradiation when the X-ray tube 100 is turned on. It should be appreciated the area within the circle may not be completely dark; the ambient light may be able to enter the shadow region. In some embodiments, the lights 126 are white LEDs which can be bright enough to clearly illuminate the target region but do not generate large amounts of heat and have very long lives. The lack of heat generation is important because the lights will be in close proximity to the skin of the patient, and so it is important to minimise the risk of burning or other damage to the skin. Other colours of LEDs may be used. Alternatively, other light sources could be used, such as known filament lamps or even a remote light source connected to the ring by fibre optic cables. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. |
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abstract | The present invention relates to an electromagnetically-countered system including at least one wave source irradiating harmful electromagnetic waves and at least one counter unit emitting counter electromagnetic waves for countering the harmful waves by such counter waves. More particularly, the present invention relates to generic counter units of electromagnetically-countered systems and to various mechanisms for countering the harmful waves by the counter units such as, e.g., by matching configurations of the counter units with those of the wave sources, matching shapes of such counter waves with shapes of the harmful waves, and the like. The present invention also relates to various methods of countering the harmful waves with the counter waves by such source matching or wave matching and various methods of providing the counter units as well as counter waves. The present invention further relates to various processes for providing such systems, such counter units thereof, and the like. The present invention relates to various electric and/or magnetic shields which may be used alone or in conjunction with such counter units to minimize irradiation of the harmful waves from the system. |
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047073250 | summary | BACKGROUND OF THE INVENTION The present invention relates to a gauge plate for determining and measuring the actual locations of the guide pins for the lower internal structure in a nuclear reactor vessel for use in customizing a replacement upper internals structural package, and to a method of using this gauge plate. More particularly, the present invention relates to a gauge plate, and a method of using same, whereby the actual position and dimensions of the existing guide pins in the barrel of a nuclear reactor vessel for the lower internal structure can be determined so that the conventional inserts for the upper core plate which mate with these guide pins can be customized to the required close tolerances when the upper internals structural package for an existing nuclear reactor is replaced. In a liquid cooled nuclear reactor, the internal structure of the core barrel generally includes, in addition to the core itself, an upper internals structural package, which is installed and can be removed as a unit, and a lower internals structure which is axially aligned with the upper internals structural package. To ensure that the upper and lower internals structures are correctly oriented and aligned with one another, the inner surface of the core barrel is provided with a plurality, usually four, symmetrically disposed guide pins which are fixedly aligned with the lower internal structure and which extend radially inwardly from the inner wall of the core barrel and engage in respective slots formed in the peripheral surface of the upper core plate, which, in turn, forms the lower most portion of the upper internals structural package. In view of the relatively close tolerances required for the orientation of the upper and lower internal structures, it is customary to machine the surfaces of the peripheral slots in the upper core plate to general relatively large tolerances relative to the guide pins, and then to customize the upper core plate to the actual position and size of the guide pins by providing each of the perpheral slots of the upper core plate with an insert which has been finely machined to provide the desired small clearances, e.g. 0.013 cm (0.005 in.), based on actual clearance measurements. In order to make these measurements when the reactor is initially being built at the factory, the upper internals structural package or unit, or at least the portion of same necessary to properly position the upper core plate, is placed in the core barrel and properly aligned with the lower internal structure including the baffle plate arrangement which surrounds the area in which the core is located. Thereafter, the various clearances between the surfaces of the peripheral slots in the upper core plate and the adjacent surfaces of the respective guide pins are actually measured by an individual, and then the upper internals structural package is removed from the core barrel. Thereafter, the actual measurements taken are used to machine the relatively small inserts which are then positioned and fastened in the respective perpheral slots of the upper core plate so as to customize the core plate to the actual positions of the lower internal structure. Although the above technique is satisfactory when a new reactor is being built, a number of significant problems are presented when it is necessary to replace the upper internals structural package of a reactor which has been in use for some time. Initially, since the reactor vessel, including the core barrel with its guide pins and the fixed portions of lower internal structure, e.g., the baffle plate arrangement, are no longer located at the situs of the factory, it would be extremely difficult, time consuming and expensive, particularly in view of the large size and weight of even the upper core plate, which for example is in the order of 13-1400 kg (3000 lbs.) for a typical reactor, to ship the upper core plate, or a sufficient portion of the upper internals structural package, to the situs of the reactor, to take the necessary measurements, return the upper core plate to the factory for customizing, and then return the completed package to the reactor for ultimate installation. Moreover, since the reactor vessel of a previously operating reactor is somewhat radioactive and accordingly is conventionally flooded with water during the replacement or refitting period, it would be very difficult and extremely dangerous for an individual to take the necessary measurements in order to customize the new upper core plate to the existing guide pins in the core barrel. SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide an apparatus for taking the measurements necessary for the customization of a replacement upper core plate, and in particular the upper core plate inserts for the peripheral guide slots, without requiring the use of the actual upper core plate for such measurements, as well as to provide a method of using the apparatus to take the measurements which overcomes the above problems. The above object is initially achieved according to the invention by a gauge plate for use in customizing replacement upper core plate inserts of a nuclear reactor of the type including a pressure vessel, a core barrel disposed within the pressure vessel, a lower internal structure disposed in the core barrel and including a baffle plate arrangement, and an upper internals structural package having an upper core plate at its lower end, with the upper core plate being provided with a plurality of peripheral grooves, each including an insert machined to close tolerances, for engaging respective approximately rectangular shaped guide pins extending radially inwardly from the inner surface of the core barrel for aligning the upper internal structural package relative to the lower internal structure; wherein the gauge plate comprises a circular metal plate of a known diameter corresponding substantially to that of the upper core plate of the nuclear reactor to be gauged; a plurality of U-shaped gauging slots formed in the peripheral surface of the gauge plate and extending between its major surfaces, with the gauging slots being formed at locations corresponding to the respective locations of the guide pins of the reactor vessel to be gauged and being of a known size sufficient to receive the respective guide pins with clearance on all sides; first means for positioning the gauge plate within the core barrel of the nuclear reactor vessel to be gauged, while it contains the baffle plate arrangement but not the upper internals structural package, at the normal elevation of the upper core plate inserts and the guide pins; second means, disposed on the gauge plate, for positioning the gauge plate relative to the baffle plate arrangement of the reactor to be gauged; gauge means for the gauge plate for determining the actual position of the gauge plate relative to the baffle plate arrangement; and, remotely controlled measuring means, disposed on the gauge plate, for measuring the respective clearances between each of the U-shaped gauging slots and the adjacent surfaces of a respective guide pin and the clearance between the peripheral surface of the gauge plate and the inner surface of the core barrel adjacent each gauging slot, and for providing an indication of the measured clearances at a remote location. Preferably, the gauge plate has a thickness substantially less than that of the upper core plate for the reactor, and is provided with cutouts in its interior portion in order to reduce its weight and to permit it to be more easily lowered through the flooding water. According to the preferred embodiment of the gauge plate according to the invention, the first means comprises a plurality of support pads disposed on one major surface of the gauge plate and positioned so as to be able to rest on the upper end of the baffle plates of the baffle plate arrangement of the reactor in which said gauge plate is to be used, with the support plates being of the thickness so as to position the gauge plate at the elevation of the interface of the upper core plate inserts and the guide pins when the pads are resting on the upper ends of the baffle plates, and the second means comprises a plurality of positioning pins extending from the above mentioned major surface of the gauge plate, with the positioning pins being located on the gauge plate at respective positions corresponding to the outer most positions of the fuel assembly top nozzles of the reactor, and with each positioning pin being of a length so that it can extend into the area enclosed by the baffle plate arrangement when the gauge plate is resting on the upper ends of the baffle plates. Moreover, in the preferred embodiment of the gauge plate according to the invention, the gauging means includes a plurality of gauging holes extending through the gauge plate for receiving gauge pins, with the gauging holes being located at positions corresponding to the expected positions of respective baffle plates of the reactor in which the gauge plate is to be used. According to the method of the invention the actual dimensions of the lower internals guide pin locations of a nuclear reactor vessel are measured by positioning a gauge plate of the type described above in a nuclear reactor vessel core barrel containing a baffle plate arrangement, but with the upper internals structural package removed, so that the gauge plate rests on the upper end of the baffle plate arrangement with the lower internal structure guide pins of the reactor vessel extending into the gauging slots of the gauge plate and with the positioning pins of the gauge plate being properly positioned relative to the baffle plate arrangement; at each of the gauging slots and with the gauge plate in the same position, (a) measuring the difference between the peripheral surface of the gauging plate and the inner surface of the reactor barrel, and (b) measuring the clearance between each of the three sides of the U-shaped gauging slot and the adjacent sides of the associated guide pin; and, with said gauge plate in the same position, determining the actual position of the gauge plate relative to the existing baffle plates by inserting gauging means into each of the gauging holes. According to the preferred embodiment of the method wherein the gauging plate utilized includes at least three gauging holes with two of the gauging holes being located at positions corresponding to the positions of two adjacent baffle plates and the third gauging hole being located at a position corresponding to a baffle plate diametrically opposite one of the two adjacent baffle plates, and with the center line of each of the gauging holes being displaced by a common given dimension from the expected position of the upper edge of the respective baffle plate in a direction perpendicular to the inner surface of the respective baffle plate, the actual position of the gauge plate relative to the baffle plates is determined by inserting gauge pins of known size into the gauging holes until the inner surface of the respective baffle plate is located. Preferably, gauge pins of known different size are successively inserted into one of the gauge holes to determine the largest diameter gauge pin which can be inserted, and then, with this largest diameter gauge pin inserted in its respective gauge hole, the sequence of successively inserting gauge pins is carried out for each of the other gauge holes. Finally, according to a preferred feature of the invention, the step of determining the actual position of the gauge plate relative to the baffle plates is carried out before the measurements are taken at the respective gauging slots. |
046876170 | abstract | The inductively formed spheromak plasma can be maintained in a highly stable and controlled fashion. Steady-state operation is obtained by forming the plasma in the linked mode, then oscillating the poloidal and toroidal fields such that they have different phases. Preferably, the poloidal and magnetic fields are 90.degree. out of phase. |
claims | 1. A passive residual heat removal system, comprising:a plate type heat exchanger configured to exchange heat between secondary system fluid and cooling fluid, wherein the secondary system fluid has received sensible heat in a reactor coolant system and residual heat in a core, and wherein the cooling fluid is introduced from an inside or outside of a containment;a circulation line configured to connect a steam generator to the plate type heat exchanger to form a circulation flow path of the secondary system fluid, wherein the steam generator is disposed at a boundary between a primary system and a secondary system;an emergency cooling water storage section formed to store the cooling fluid therewithin and installed at an outside of the containment; anda plurality of the plate type heat exchangers installed within the emergency cooling water storage section,wherein the plurality of the plate type heat exchangers are all connected to the circulation line to receive the secondary system fluid through the circulation line, andthe circulation line is first branched into a plurality of lines in a position facing a plate type heat exchanger located at the center of the plurality of the plate type heat exchangers and the branched lines are connected to the plurality of plate type heat exchangers, respectively,wherein a lower part of each of the plate type heat exchangers is immersed into the cooling fluid within the emergency cooling water storage section to allow the cooling fluid within the emergency cooling water storage section and atmosphere outside the containment to pass through a plurality of first channels which are provided within each of the plate type heat exchangers, and an upper part of each of the plate type heat exchangers is protruded to an upper portion of the emergency cooling water storage section through the emergency cooling water storage section to discharge the cooling fluid and fluid evaporated by heat transfer with the secondary system fluid in the atmosphere to an outside. 2. The passive residual heat removal system of claim 1, wherein each of the plate type heat exchangers comprise at least one of:a printed circuit type heat exchanger provided with channels formed by diffusion bonding and densely formed by a photochemical etching technique; anda plate type heat exchanger configured to extrude a plate to form channels, and formed to couple the plates using at least one of a gasket, a welding, and a brazing welding methods. 3. The passive residual heat removal system of claim 1,wherein each of the plate type heat exchangers comprise a plurality of channels for exchanging heat while maintaining a pressure boundary to the cooling fluid with the secondary system fluid supplied through the circulation line, andwherein the plurality of channels comprises:the plurality of first channels arranged to be separated from one another to allow the cooling fluid to pass therethrough; anda plurality of second channels formed to allow the secondary system fluid to pass therethrough, and alternately arranged with the first channels to exchange heat while maintaining a pressure boundary to the cooling fluid. 4. The passive residual heat removal system of claim 3, wherein the passive residual heat removal system further comprises:a first inlet header formed at an inlet of the plurality of first channels to distribute the cooling fluid to each first channel;a first outlet header formed at an outlet of the plurality of the first channels to collect the cooling fluid that has passed through each first channel;a second inlet header formed at an inlet of the plurality of second channels to distribute the secondary system fluid to each second channel; anda second outlet header formed at an outlet of the plurality of the second channels to collect the secondary system fluid that has passed through each second channel. 5. The passive residual heat removal system of claim 3, wherein the circulation line comprises:a steam line branched from a main steam line and connected to an inlet of each of the second channels to receive the secondary system fluid from the main steam line extended from an outlet of the steam generator; anda feedwater line branched from a main feedwater line extended to an inlet of the steam generator and connected to an outlet of each of the second channels to transfer heat to the cooling fluid and recirculate the cooled secondary system fluid to the steam generator. 6. The passive residual heat removal system of claim 5, wherein the plate type heat exchanger is installed in an inner space of the containment, and communicates with an outside of the containment by a connection line in which an inlet and an outlet of the first channel pass through the containment to allow atmosphere outside the containment to pass through the first channel. 7. The passive residual heat removal system of claim 5, wherein each of the plate type heat exchangers is installed outside of the containment, and the steam line and the feedwater line are connected to the main steam line and main feedwater line from an outside of the containment. 8. The passive residual heat removal system of claim 5, wherein the emergency cooling water storage section is provided with an opening portion at an upper portion thereof to dissipate heat transferred by evaporating the cooling fluid stored therewithin during a temperature increase due to heat transferred from the secondary system fluid to the cooling fluid. 9. The passive residual heat removal system of claim 8, wherein each of the plate type heat exchangers is installed in an inner space of the containment, and an inlet and outlet of each of the first channels are connected to the emergency cooling water storage section by a connection line passing through the containment to allow cooling fluid within the emergency cooling water storage section to pass through each of the first channels. 10. The passive residual heat removal system of claim 8, wherein at least part of each of the plate type heat exchangers is installed within the emergency cooling water storage section to allow at least part thereof to be immersed into the cooling fluid. 11. The passive residual heat removal system of claim 3, wherein the circulation line comprises:a steam line at least part of which is connected to the reactor coolant system and an inlet of the second channel to receive the primary system fluid from the reactor coolant system to transfer said fluid to each of the plate type heat exchangers; andan injection line at least part of which is connected to an outlet of each of the second channels and the reactor coolant system to reinject the primary system fluid cooled by transferring heat to the cooling fluid to the reactor coolant system. 12. The passive residual heat removal system of claim 1, wherein each of the plate type heat exchangers further comprise:a casing formed to surround at least part of each of the plate type heat exchangers; anda cooling fin formed to surround at least part of the casing to expand a heat transfer area. |
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description | This application is a continuation application of U.S. application Ser. No. 12/190,883, filed Aug. 13, 2008, now U.S. Pat. No. 7,929,656, the entirety of which is incorporated herein by reference. 1. Field of the Invention The present invention relates to inspection apparatuses for inspecting a weld zone between a reactor pressure vessel and a structure inside a nuclear reactor. For example, the invention relates to an inspection apparatus for inspecting weld zones in a reactor pressure vessel, the inspection apparatus being capable of detecting a crack of a weld zone between a control rod drive housing and a reactor pressure vessel, which are located on the bottom of a boiling water reactor. 2. Description of the Related Art In a pressure vessel of a nuclear reactor, it is necessary to check its soundness; in particular, weld zones and the like in the nuclear reactor need to be inspected. In most cases, visual inspection is performed periodically. If it is judged that further inspection is necessary as a result of the visual inspection, situational tests of the surface and inside of the material are carried out (the size of a crack is measured). Well known methods for the above inspection include ultrasonic testing and eddy current testing. In addition, inspection areas often exist in narrow portions; therefore, as a method for improving such inspection efficiency, there is disclosed an inspection method in which a lower head of a pressure vessel of the nuclear reactor is inspected by use of a scanning cart that travels while adhering to the lower head (for example, refers to JP-A-6-11595). A reactor pressure vessel is equipped with a control rod drive housing, an in-core monitor housing, a shroud support, and the like. The control rod drive housing, which is located in a nuclear reactor, is a tube for storing a mechanism for driving a control rod that is used for the output control of the nuclear reactor. The control rod drive housing is mounted onto the reactor pressure vessel by welding in such a manner that the control rod drive housing penetrates the bottom of the reactor pressure vessel. In addition, the in-core monitor housing is a tube for storing a monitor that is used to monitor neutrons generated by nuclear fission in the nuclear reactor. The in-core monitor housing is mounted onto a build-up weld inside the reactor pressure vessel by welding in such a manner that the in-core monitor housing penetrates the bottom of the reactor pressure vessel. Moreover, the shroud support is provided in order that structures inside the nuclear reactor are supported. The shroud support is mounted onto the inner surface of the reactor pressure vessel by welding. The weld zone is located inside the reactor pressure vessel that is a pressure boundary, or the weld zone itself is a withstand pressure boundary. The inner bottom surface of the reactor pressure vessel is subjected to cladding processing by welding. The weld zone and the build-up weld are attached to this cladding portion. The weld zones of the reactor pressure vessel are located in areas where devices inside the reactor pressure vessel are closely placed; their spaces are narrow, and their shapes are complex. Accordingly, the accessibility of the inspection apparatus within the reactor pressure vessel is limited. Presently, when some form of abnormality is found by visual inspection, a situational test is conducted on the surface of and the inside of the weld material by placing a sensor (probe) against or close to those complex and narrow areas. Since inspection areas are thus complex and narrow, a certain level of skill has been required to have the inspection apparatus and the probe approach those areas. Furthermore, since weld materials to be inspected change in three-dimensional shape, inspection needs to be preformed with their curvatures and surface states in mind especially when the ultrasonic testing is to be applied. Also, because of largeness and poor ultrasonic propagation properties of the weld portions, the ultrasonic testing occasionally involves difficulty when it is performed toward a deeper region from the inner surface of the reactor pressure vessel. The present invention has been made on the basis of the foregoing facts and circumstances, and an object of the present invention is to provide an inspection apparatus for inspecting weld zones in a reactor pressure vessel, the inspection apparatus being capable of easily approaching three-dimensionally shape-changing weld zones present at complex and narrow portions and of accurately performing inspection. In order to achieve the above object, in a first aspect of the present invention, the invention is an inspection apparatus for inspecting weld zones in a reactor pressure vessel, the inspection apparatus inspecting a weld zone of a control rod drive housing and an area in proximity to the weld zone, the control rod drive housing being placed from the bottom of the reactor pressure vessel to the inside thereof, the inspection apparatus comprising: a probe for emitting an ultrasonic wave; a probe holding unit for holding the probe such that an ultrasonic wave transmitting surface of the probe is kept in direct contact with or at a constant distance from the outer surface of the reactor pressure vessel; a pressing unit for pressing the probe holding unit parallel to the central axis of the control rod drive housing against the reactor pressure vessel; and a rotator for rotating the probe holding unit and the pressing unit around the central axis of the control rod drive housing. In addition, in a second aspect of the present invention, the invention is the inspection apparatus according to the first aspect, wherein the longer side of the ultrasonic wave transmitting surface of the probe if said surface is rectangular-shaped or the major axis of said surface if said surface is oval-shaped or circular-shaped is set to a value selected from 35 mm to 120 mm. In addition, in a third aspect of the present invention, the invention is the inspection apparatus according to the second aspect, wherein the reactor pressure vessel and an area to be inspected inside the reactor pressure vessel are provided by the probe with an ultrasonic field within a range of −6 db with respect to a focus of the ultrasonic wave or the echo intensity of the focus. In addition, in a fourth aspect of the present invention, the invention is the inspection apparatus according to the first aspect, the inspection apparatus further comprising an elevator for moving up and down the probe, the probe holding unit, the pressing unit, and the rotator along the control rod drive housing. In addition, in a fifth aspect of the present invention, the invention is the inspection apparatus according to the fourth aspect, wherein the longer side of the ultrasonic wave transmitting surface of the probe if said surface is rectangular-shaped or the major axis of said surface if said surface is oval-shaped or circular-shaped is set to a value selected from 35 mm to 120 mm. Moreover, in a sixth aspect of the present invention, the invention is the inspection apparatus according to the fifth aspect, wherein the reactor pressure vessel and an area to be inspected inside the reactor pressure vessel are provided by the probe with an ultrasonic field within a range of −6 db with respect to a focus of the ultrasonic wave or the echo intensity of the focus. Furthermore, in a seventh aspect of the present invention, the invention is the inspection apparatus according to the first or second aspect, wherein the probe can inspect a weld zone between the reactor pressure vessel and a structure inside an nuclear reactor, a built-up weld, and an inner-surface cladding portion of the reactor pressure vessel. According to the present invention, the ultrasonic probe can easily approach three-dimensionally shape-changing weld zones present at complex and narrow portions and perform the inspection accurately. An embodiment of an inspection apparatus for inspecting weld zones in a reactor pressure vessel according to the present invention will be described below with reference to the accompanying drawings. FIGS. 1 and 2 are diagrams illustrating an inspection apparatus for inspecting weld zones in a reactor pressure vessel according to one embodiment of the present invention. To be more specific, FIG. 1 is a front view illustrating an example in which the present invention is applied to the inspection of weld zones of a control rod drive stub tube that is mounted onto a reactor pressure vessel; and FIG. 2 is a plan view as viewed from the direction of the arrow II-II in FIG. 1. First of all, as one embodiment of the inspection apparatus for inspecting weld zones in the reactor pressure vessel according to the present invention, how the control rod drive stub tube, mounted onto the reactor pressure vessel, and weld zones of the control rod drive stub tubes are configured will be described with reference to FIG. 1. A control rod drive stub tube 2 is secured to the inside of a reactor pressure vessel 1 by a weld zone 3. A control rod drive housing 8 is inserted into and secured to the control rod drive stub tube 2. In order to inspect the weld zone 3 of the control rod drive stub tube 2 that is mounted onto the reactor pressure vessel 1, an ultrasonic probe 6 is placed on the outer surface side of the reactor pressure vessel 1 so that the ultrasonic probe 6 emits an ultrasonic wave toward the inner surface side of the reactor pressure vessel 1. The incident ultrasonic wave reaches the inside of the weld zone 3 of the control rod drive stub tube 2 or reaches an inner-surface cladding portion 200. If a crack exists there, the reflection of the ultrasonic wave from the position of the crack is detected. The depth of the crack inside the weld zone 3 can be evaluated by identifying the position at which the ultrasonic wave is reflected. The size of the ultrasonic probe 6 needs to be set in consideration of the accessibility of the ultrasonic probe 6 to a narrow portion, the thickness of the reactor pressure vessel 1, and the like. This point described in detail, the reactor pressure vessel 1 has a thickness of about 150 mm or more. If the end face of the weld zone 3 is included, the reactor pressure vessel 1 is about 200-mm thick. In order to detect a crack existing in the weld zone 3 by use of an ultrasonic wave, it is necessary to emit the ultrasonic wave to the area whose thickness ranges from about 150 mm to 200 mm. In addition, in order to acquire a sufficiently strong signal from the reflection source of a flaw such as a crack, it is necessary to properly converge the ultrasonic wave on the above area so as to perform inspection. The criterion for selecting a proper focus area of the ultrasonic wave when inspection is performed from the outer surface of the reactor pressure vessel 1 is now explained with reference to FIG. 3. In FIG. 3, the horizontal axis indicates the size of the transducer of the ultrasonic probe (sensor); the vertical axis indicates the distance from the sensor (more specifically, the distance in the thickness direction in which inspection is performed). The size of the sensor is expressed as the size of the long side of the sensor or the size of the long axis of the sensor because it is known that the focus settable area of an ultrasonic wave generated by the sensor depends on the size of the long side if the sensor has a rectangular shape including a square and depends on the size of the long axis if the sensor has an oval shape including a circle. In FIG. 3, the solid line indicates maximum sound pressure characteristics; the dotted line indicates sound pressure characteristics obtained when a forward shift from the maximum sound pressure is made by −6 dB; and the alternate long and short dash line indicates sound pressure characteristics obtained when a backward shift from the maximum sound pressure is made by −6 dB. When the ultrasonic probe 6 is placed on the outer surface of the reactor pressure vessel 1, the size of the sensor can be set at a value ranging from 35 mm to 120 mm, as shown in FIG. 3, in order that an effective focus area (within a range of −6 dB from the maximum sound pressure height) reaches an area to be inspected ranging from 150 mm to 200 mm. In particular, when a narrow portion is to be inspected, the size of the sensor can be set at 35 mm at minimum; it is desirable that the size of the sensor be 45 mm. Next, one embodiment of the inspection apparatus using the ultrasonic probe 6 whose size has been set as above will be described with reference to FIGS. 1 and 2 again. In one embodiment of the inspection apparatus according to the present invention, because the weld zone 3 exists 360 degrees around the control rod drive stub tube 2, the inspection apparatus also rotates 360 degrees so as to inspect the whole target area. In addition, in order to locate the position of the ultrasonic probe 6 or an ultrasonic wave inspection position, the inspection apparatus has the function of setting the position at which the main body of the inspection apparatus is placed. Moreover, because the lower surface of the reactor pressure vessel 1 has a spherical shape and because the tilt of the surface accessed by the ultrasonic probe 6 becomes larger as the ultrasonic probe 6 moves from the center of the nuclear reactor toward its outside, the inspection apparatus has the function of adjusting the posture of the ultrasonic probe 6 to the shape of an inspection area. For the purpose of achieving the above-described functions, the inspection apparatus according to one embodiment of the present invention is configured such that the main body of the access device is placed and secured around the control rod drive housing 8. The inspection apparatus includes an elevator 30 for moving up and down the whole inspection apparatus along the control rod drive housing 8; a rotator 40 for rotating the ultrasonic probe 6 360 degrees around the control rod drive housing 8; a height adjustment unit (pressing mechanism) 50 for adjusting the height-directional distance between the reactor pressure vessel 1 and the whole inspection apparatus; and a probe holding unit 60 including a probe-posture adjustment mechanism 21 for adjusting the posture of the ultrasonic probe 6 to the surface of the reactor pressure vessel 1. Besides the method in which the inspection apparatus is secured around the control rod drive housing 8 as shown in this embodiment, an alternatively possible method is one in which the position of the inspection apparatus is set by measuring the reference distance between the inspection apparatus and the control rod drive housing 8 by use of, for example, an ultrasonic wave range finder or a laser range finder while keeping the distance constant. As a function of the probe holding unit 60, if the ultrasonic probe 6 is pressed against a wall surface of the reactor pressure vessel 1, the ultrasonic probe 6 rotates around a pin 22 attached to the probe-posture adjustment mechanism 21 that functions as a gimbal. This makes it possible to arbitrarily change the angle of the ultrasonic probe 6 in response to the slant of the reactor pressure vessel 1. As a result, the ultrasonic probe 6 can stably move along the surface of the reactor pressure vessel 1. When inspection is performed, besides the method in which the ultrasonic probe 6 is kept in direct contact with the outer surface of the reactor pressure vessel 1, the ultrasonic probe 6 may also be provided with a spacer or the like on the sound-wave-generating-surface side of the ultrasonic probe 6 so that the distance between the ultrasonic probe 6 and the reactor pressure vessel is kept constant. The probe holding unit 60 is attached to the height adjustment unit 50. The height adjustment unit 50 is mounted onto the rotator 40. The height adjustment unit 50 includes a fixed frame 18 that is secured to the rotator 40; a guide 20 guided by this fixed frame 18, the upper end of which is connected to the probe holding unit 60; and a spring 19 that is disposed between the fixed frame 18 and the probe holding unit 60. Even when the whole inspection apparatus is further lifted after the ultrasonic probe 6 is brought into contact with the reactor pressure vessel 1, the ultrasonic probe 6 can be kept in contact with the reactor pressure vessel 1 by the contraction of the spring 19. The rotator 40 is disposed on the top surface of a base 14 whereas the elevator 30 is disposed on the bottom surface of the base 14. The elevator 30 includes a fixed stand 13 that is located on the lower surface side of the base 14; an elevator wheel 12 provided on the fixed stand 13; an elevator motor 10 also mounted onto the fixed stand 13; and a gear 11 for transferring the rotational force of the elevator motor 10 to the elevator wheel 12. Driving of the elevator motor 10 rotates the elevator wheel 12, which moves up or down the whole inspection apparatus along the control rod drive housing 8. The rotator 40 includes a rotator table 17 located on the upper surface side of the base 14; a rotator motor 15 that is mounted on the upper surface side of the base 14; and a gear 16 for transferring the rotational force of the rotator motor 15 to the rotator table 17. The rotation of the rotator motor 15 causes the rotator table 17 to rotate around the control rod drive housing 8. The rotation of the rotator table 17 causes the ultrasonic probe 6 to rotate 360 degrees around the axis of the control rod drive housing 8. The position of the ultrasonic probe 6 or an ultrasonic wave inspection position can be identified by a sensor detecting the rotational angle of the rotator table 17 or detecting the distance traveled by the inspection apparatus around the control rod drive housing, which distance can be converted from the rotational angle. The base 14 of the rotator 40 is provided with a positioning pad 24 through an arm 23. As shown in FIG. 2, placed against the side surface of a control rod drive housing 9 adjacent to the control rod drive housing 8 to which the inspection apparatus is attached, the positioning pad 24 determines the position of the whole inspection apparatus in its rotational direction. In place of the mechanical positioning method using the arm 23 and the positioning pad 24, an ultrasonic-wave or laser range finder can be used; with the use of such a device, each distance from one or more adjacent control rod drive housings 9 to the control rod drive housing 8 can be measured to compute the current position of the inspection apparatus and thereby to locate the position of the ultrasonic probe 6 or of an ultrasonic wave inspection. Next, the operation of the above-described inspection apparatus according to one embodiment of the present invention in which weld zones of the control rod drive stub tube are inspected will be described with reference to FIGS. 4 through 6. FIG. 4 is a diagram illustrating, as the initial access state of an inspection apparatus according to one embodiment of the present invention, the state in which the inspection apparatus is located at a surface of the bottom side in the reactor pressure vessel 1 of the control rod drive housing 8. First of all, the ultrasonic probe 6 is mounted onto the inspection apparatus (step 600 in FIG. 6). Focus position settings for the ultrasonic probe 6 are then performed (step 601 in FIG. 6). After that, the inspection apparatus is attached to the control rod drive housing 8 (step 602 in FIG. 6). Next, the ultrasonic probe 6 is pressed against the reactor pressure vessel 1 by the elevator 30 (step 603 in FIG. 6) so that the spring 19 of the height adjustment unit 50 is brought into the most contracted state (step 604 in FIG. 6). Proper pressing of the ultrasonic probe 6 is checked by emitting an ultrasonic wave toward the reactor pressure vessel 1 to judge whether or not the ultrasonic wave reflected at its inner bottom surface can be externally acquired through its inner surface. Next, the rotator 40 rotates the ultrasonic probe 6 around the control rod drive housing 8 to a position at which inspection is required (step 605 in FIG. 6), and the inspection is then performed (step 606 in FIG. 6). FIG. 5 is a diagram illustrating the state in which the inspection apparatus is positioned at a surface of the upper side in the reactor pressure vessel 1 of the control rod drive housing 8. In this case, the expansion of the spring 19 continuously presses the ultrasonic probe 6 against the reactor pressure vessel 1, and the probe-posture adjustment mechanism 21 adjusts the posture of the probe 6. Thus, sufficient adjustability of the probe 6 to the outer surface of the reactor pressure vessel 1 can be ensured. After the completion of the inspection (step 607 in FIG. 6), the elevator 30 lowers the ultrasonic probe 6 to a lower portion of the reactor pressure vessel 1 (step 608 in FIG. 6). The inspection apparatus is then removed from the control rod drive housing 8 (step 609 in FIG. 6), and this completes the operation (step 610 in FIG. 6). The above-described operation control enables the ultrasonic probe 6 to access an arbitrary region around the control rod drive housing 8. Moreover, inspection with high accuracy can be performed by use of the probe holding unit 60 which stably adjusts the posture of the ultrasonic probe 6 and the positioning mechanism 24 of the inspection apparatus. The above embodiment describes the example in which the inspection apparatus according to the present invention is applied to the inspection of the weld zone 3 of the control rod drive stub tube 2. Not limited to this, the inspection apparatus according to the present invention can also be applied to a case where a weld zone 5 of an in-core monitor housing 4, a weld zone 101 of a shroud support 100, and an inner-surface cladding portion 200, which are shown in FIG. 7, are inspected from the outer surface of the reactor pressure vessel 1 by the ultrasonic inspection. In addition, in the above embodiment, the spring 19 is used to stably adjust the posture of the ultrasonic probe 6 to the wall surface shape of the reactor pressure vessel 1. However, instead of using the spring 9, a cylinder mechanism can also be used. According to the above embodiment of the present invention, after the inspection apparatus is correctly positioned, inspection can be performed with the posture of the ultrasonic probe 6 stably adjusted to the wall surface of the reactor pressure vessel 1. Therefore, the probe 6 can easily approach three-dimensionally shape-changing weld zones present at complex and narrow portions and perform inspection accurately there. Moreover, the size of a crack present in a weld zone of a structure inside the nuclear reactor can be simply and easily measured without employing underwater remote control for access to a complex and narrow region. Furthermore, deep areas of weld zones, which was conventionally difficult to inspect by an ultrasonic wave because of its attenuation caused by a material and the shape of the material, can also be easily subjected to the ultrasonic wave inspection by external access of the ultrasonic probe to the reactor pressure vessel, contrary to the conventional method. |
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description | Field of the Invention The present invention relates to an X-ray topography apparatus that uses X-rays to form a two-dimensional image in correspondence with a crystal defect structure present in a single crystal sample. Description of the Related Art There is a known conventional X-ray topography apparatus disclosed, for example, in Patent Citation 1 (Japanese Patent Laid-Open Publication H08-124983). Patent Citation 1 discloses that a single and individual X-ray topographic image is captured. Patent Citation 1, however, does not disclose that a plurality of X-ray topographic images are acquired from a single sample. Patent Citation 2 (Japanese Patent Laid-Open Publication 2006-284210) describes that a plurality of section topographic images (that is, two-dimensional cross-sectional images) are acquired by using X-rays and then caused to undergo multiple exposure. Patent Citation 2, however, provides no detailed description about the multiple exposure. According to typical interpretation, the multiple exposure is believed to mean exposure of a plurality of images superimposed on a single two-dimensional detector by using a large amount of step movement of the sample. Patent Citation 3 (WO2008/052287A1) discloses that an X-ray source as small as 10 to 50 μm is used to output X-rays, that the width of the X-rays is limited with a slit, and that a sample is moved stepwise for acquisition of a plurality of diffraction images. Patent Citation 3, however, does not mention the intensity of the X-rays with which the sample is irradiated. When the X-ray source is small and the width of the X-rays is limited with a slit, the intensity of the X-rays that reach the sample is significantly attenuated, which means that the sample needs to undergo very long exposure, for example, for several hours to ten hours in order to provide a single desired X-ray image. No one has therefore considered acquisition of a large number of X-ray images or as many as several hundreds of X-ray images. Non-Patent Citation 1 (http://cheiron2010.Spring8.or.Jp/text/bl/11_BL19B2.pdf, (file stamp date: 30 Sep. 2010), “beam line BL19B2 at Spring-8, synchrotron radiation facility”) discloses that a sample is moved stepwise with respect to synchrotron radiation for acquisition of section topographs of the sample irradiated with the synchrotron radiation in each step position and that the section topographs are superimposed on each other to provide a 3D (three-dimensional) image. Synchrotron radiation, which inherently contains high-intensity X-rays, allows acquisition of a plurality of section topographs in a relatively short period. The period required to acquire a plurality of section topographic images can therefore be greatly shortened. It is, however, impossible to use a synchrotron radiation facility in typical corporate research or manufacturing situations. Non-Patent Citation 1 does not mention at all use of a laboratory-level X-ray source. Since a laboratory-level X-ray source outputs low-intensity X-rays, acquisition of a plurality of section topographs within a practically acceptable period of time by using the X-ray source is not worth consideration. Non-Patent Citation 2 is the “Report on current status of X-ray topography research group” (Spring-8 User's Information/Vol. 13 No. 1 Jan. 2008/Research Group Report Spring-8 Users Society//Faculty of Science, University of Toyama, Satoshi IIDA, Graduate School of Engineering, Osaka University, Takayoshi SHIMURA, Japan Synchrotron Radiation Research Institute, Industrial Application Division, Kentaro KAJIWARA). Non-Patent Citation 2 discloses that a sample is scanned with synchrotron radiation and cross-sectional images of several portions of the sample irradiated with the synchrotron radiation are captured, and that the images are superimposed on each other in a computer for estimation of a three-dimensional distribution of in-crystal lattice distortion. Non-Patent Citation 2 does not describe at all use of a laboratory-level X-ray source, too. Since a laboratory-level X-ray source outputs low-intensity X-rays, acquisition of a plurality of section topographic images within a practically acceptable period of time by using the X-ray source is not worth consideration. Patent Citation 4 (Japanese Patent Laid-Open Publication 2007-240510) discloses an X-ray topography apparatus in which a zone plate or any other X-ray collection means is used to collect X-rays and a sample is irradiated with the collected X-rays. Patent Citation 4 does not mention technologies for outputting X-rays from a minute focal spot, converting X-rays into monochromatic X-rays, collimating X-rays into a collimated beam, or increasing the intensity of X-rays. The apparatus described in Patent Citation 4 cannot therefore acquire a large number of section topographic images in a short period. The present invention has been made in view of the problems with the conventional X-ray topography apparatus described above, and an object of the present invention is to acquire a large number of section topographic images or as many as several hundreds of section topographic images by using a laboratory-level X-ray source in a practically acceptable short period, for example, one hour to a dozen of hours. An X-ray topography apparatus according to the present invention is an X-ray topography apparatus that uses X-rays to form two-dimensional images in correspondence with a crystal defect structure present in a single crystal sample, the apparatus including an X-ray source that produces X-rays with which the sample is irradiated, a multilayer film mirror provided in a position between the sample and the X-ray source, a slit member provided in a position between the sample and the X-ray source and including a slit that limits the width of the X-rays, two-dimensional X-ray detection means for two-dimensionally detecting X-rays having exited out of the sample, and sample moving means for achieving stepwise movement of the sample and the X-rays with which the sample are irradiated relative to each other to sequentially move the sample to a plurality of step positions. The X-ray source produces the X-rays from a minute focal spot. The multilayer film mirror converts the X-rays emitted from the X-ray source into monochromatic, collimated, high-intensity X-rays. The direction in which the multilayer film mirror collimates the X-rays coincides with the width direction of the slit of the slit member. The width of the slit is sufficiently narrower than the thickness of the sample. The step size by which the sample moving means moves the sample is smaller than the width of the slit. The combination of the size of the minute focal spot, the width of the slit, and the intensity of the X-rays that exit out of the multilayer film mirror allows the contrast of an X-ray image produced when the two-dimensional X-ray detection means receives the X-rays for a predetermined period of 1 minute or shorter to be high enough for observation of the X-ray image. The X-ray topography apparatus allows generation of a large number of two-dimensional cross-sectional images or as many as several-hundred images without a huge X-ray source used in a synchrotron radiation facility but with a laboratory-level X-ray source within a period acceptable in research and manufacturing processes in the industries (within one hour to a dozen of hours, for example). Subsequent observation of the large number of two-dimensional cross-sectional images can provide knowledge of the structure of the sample crystal. In the configuration described above, even when the X-ray source is a minute focal spot source or the width of the X-rays with which the sample is irradiated is narrowed with the slit, the intensity of the X-rays is high enough to produce an X-ray image having sufficiently high contrast within a predetermined period of one minute or shorter. The intensity of the X-rays described above can be stably achieved by using the multilayer film monochromator. The reason why the imaging period is limited to one minute or shorter is that an imaging period of one minute or longer requires an impractically very long period for acquisition of several hundreds of two-dimensional cross-sectional images. In the configuration described above, the X-ray source formed of a minute focal spot, the monochromatic, collimated X-rays, and the narrow slit are requirements for acquisition of high-resolution, clear two-dimensional cross-sectional images. The multilayer film mirror is an element for forming monochromatic, collimated, high-intensity X-rays. Using the multilayer film mirror to increase the intensity of the X-rays allows the X-ray source to be a minute focal spot, and even when the X-rays emitted from the minute focal spot are caused to pass through the narrow slit, the increased intensity X-rays allows an X-ray image having sufficient contrast to be produced within a practically acceptable short predetermined period. In general, sufficient contrast in the field of X-ray analysis means that a signal (S0) is sufficiently greater than noise (N) in FIG. 4. The noise (N) is typically three times greater than the standard deviation in background. The sufficient signal (S0) is typically at least 1.5 times greater than the noise (N), that is,S0≧1.5N. FIGS. 5 and 6 show examples of the contrast of measured data. In the examples shown in FIGS. 5 and 6, contrast high enough for observation is achieved. In both examples, dislocation is clearly extracted. In the images shown in FIGS. 5 and 6, dislocation is expressed with black dots. The profile along each of the lines shown in FIGS. 5 and 6 shows peaks corresponding to the black dots in the image. The S/N ratio changes with peak intensity. Since the noise level is assumed to be about 100, the S/N ratio is about 4 at a low peak in FIG. 5. The S/N ratio is greater than 10 at a high peak in FIG. 6. The period of the measurement made to achieve the results shown in FIGS. 5 and 6 is 60 seconds per image. Based on X-ray photon statistics, which shows that the S/N ratio is improved by a factor of ½ power of a measurement period of time, even when the measurement period of 60 seconds is shortened by a factor of ¼ to 15 seconds, an S/N ratio of 2 can be theoretically ensured at the low peak in FIG. 5. The multilayer film monochromator 50 is a monochromator formed by alternately stacking a heavy element layer 51 and a light element layer 52 multiple times on a substrate 53 having a smooth surface, as labelled with reference character 50 in FIG. 2. The heavy element layer 51 and the light element layer 52, each having an appropriate thickness, are alternately and periodically stacked on each other in an appropriate film formation method, for example, a sputtering process. The multilayer film periodic structure provided by repeatedly forming the stacked structure formed of the heavy element layer 51 and the light element layer 52 periodically multiple times allows efficient diffraction of characteristic X-rays, for example, CuKa rays. As a result, high-intensity diffracted X-rays R2 can be produced on the exiting side of the multilayer film monochromator 50. A surface P1 of the multilayer film monochromator 50 can be formed to be parabolic. The entire parabolic surface P1 allows X-rays R1 incident thereon to be diffracted in parallel to each other. Further, the interplanar spacing of lattice planes in the multilayer film monochromator 50 is so differentiated from each other location-to-location that the X-rays R1 incident at different angles of incidence are reflected off the entire surface P1 of the multilayer film monochromator 50. Specifically, the interplanar spacing of lattice planes on the X-ray incident side, where the angle of incidence is large, are small, whereas the interplanar spacing of lattice planes on the X-ray exiting side, where the angle of incidence is small, are large, with the interplanar spacing of lattice planes in between the two sides continuously changing. As described above, when the surface P1 of the multilayer film monochromator 50 is a parabolic surface and the interplanar spacing of lattice planes in each position in the parabolic surface is appropriately adjusted, the multilayer film monochromator 50 outputs the high intensity, collimated x-rays. Further, when the total thickness of a pair of the heavy element layer 51 and the light element layer 52, that is, a stacked thickness T2 corresponding to one cycle on the X-ray exiting side is greater than a stacked thickness T1 on the X-ray incident side, the intensity of the X-rays R2 outputted from the multilayer film monochromator 50 and applied through the slit to the sample can be higher than the intensity of the X-rays in a case where no multilayer film monochromator 50 mirror is used. Conceivable examples of the heavy element may include W (tungsten), Mo (molybdenum), and Ni (nickel). Conceivable examples of the light element may include Si (silicon), C (carbon), and B4C. Conceivable examples of the stacked structure may include a two-layer structure using two types of element and a multilayer structure using at least three types of element. Further, the number of stacked heavy element layer 51 and light element layer 52 can, for example, be about 200. Moreover, the one-cycle thickness of the layer formed of a single heavy element layer 51 and a single light element layer 52 can be set at a value ranging, for example, from 20 to 120 angstroms. In the X-ray topography apparatus according to the present invention, irradiating the sample with the X-rays in each of the plurality of step positions for the predetermined period and detecting X-rays having exited out of the sample irradiated with the X-rays with the two-dimensional X-ray detection means allow acquisition of a two-dimensional cross-sectional image associated with each of the step positions, formation of a three-dimensional image by arranging the plurality of two-dimensional cross-sectional images, and acquisition of a second two-dimensional image by extracting data along a flat plane different from the measurement planes associated with the three-dimensional image. In the X-ray topography apparatus according to the present invention, dislocation density can be calculated based on the second two-dimensional image. In the X-ray topography apparatus according to the present invention, the minute focal spot can be a focal spot so sized that it falls within a circle having a diameter of 100 μm, and the width of the slit can be set at a value ranging from 10 to 50 μm. The X-ray topography apparatus according to the present invention allows generation of a large number of two-dimensional cross-sectional images or as many as several hundreds of two-dimensional cross-sectional images without a huge X-ray source used in a synchrotron radiation facility but with a laboratory-level X-ray source within a period acceptable in research and manufacturing processes in the industries (within one hour to a dozen of hours, for example). Subsequent observation of the large number of two-dimensional cross-sectional images allows knowledge of a crystal defect structure in the sample. An X-ray topography apparatus according to the present invention will be described below based on an embodiment. The present invention is not, of course, limited to the embodiment. In the drawings accompanying the present specifications, each component is drawn in some cases in a ratio different from an actual ratio for ease of illustration of a characteristic portion of the component. FIG. 1 shows an embodiment of the X-ray topography apparatus 1 according to the present invention. An X-ray topography apparatus 1 shown in FIG. 1 includes a measurement system 2 and a control system 3. The measurement system 2 includes an incident optical system 4, a sample stage 5, and a reception optical system 6. (Incident Optical System) The incident optical system 4 includes an X-ray tube 11, a multilayer film mirror 12, and a slit member 13. The X-ray tube 11 has a filament 14, which is a cathode, and a target 15, which is an anode. When the filament 14 is energized (that is, when current is caused to flow through filament 14), electrons are discharged from the filament 14. An area of the surf ace of the target 15 on which the discharged electrons are incident is an X-ray focal spot F. Xrays are radiated from the X-ray focal spot F. The X-ray focal spot F functions as an X-ray source. The radiated X-rays are extracted as point-focused X-rays through an X-ray window 16. The X-ray focal spot F of the thus extracted X-rays is a minute focal spot having a size that falls within a circle having a diameter of 100 μm. A distance D1 from the X-ray focal spot F to a sample S is 800 mm. The multilayer film mirror 12 is formed of the multilayer film monochromator 50 shown in FIG. 2. The multilayer film mirror 12 converts the X-rays emitted from the X-ray tube 11 into monochromatic, collimated, higher-intensity X-rays. The collimation is performed in the direction along a width direction H of a slit 13a of the slit member 13. The monochromatic, collimated, higher-intensity X-rays produced by the multilayer film mirror 12 allow generation of a large number of segment topographic images (that is, partial two-dimensional cross-sectional images) or as many as 400 images within a short period, as will be described later. The width of the slit 13a is a predetermined width ranging, for example, from 10 to 50 μm. A width of the slit 13a smaller than 10 μm attenuates the intensity of the X-rays so much that clear segment topographic images may not be produced. On the other hand, a width of the slit 13a greater than 50 μm may not produce sharp (that is, clear) segment topographic images. (Sample Stage) The sample crystal (hereinafter also simply referred to as sample) S, which is an object under measurement, is placed on the sample stage 5. The sample stage 5 is not drawn in accordance with an actual shape but is diagrammatically drawn. The thickness d1 of the sample S ranges, for example, from 0.2 to 2 mm. The sample S extends in the direction passing through the plane of view of FIG. 1. Each of a plurality of crystal lattice planes k present in the sample S extends roughly along the direction of the thickness d1 of the sample S. Further, the crystal lattice planes k are arranged at equal intervals in parallel to each other along a direction roughly perpendicular to the direction of the thickness d1 of the sample S. The sample stage 5 is provided with a sample moving device 20. The sample moving device 20 can linearly move the sample stage 5 intermittently or stepwise in the direction indicated by the arrow A. The sample moving device 20 can further linearly move the sample stage 5 in a returning direction indicated by the arrow A′. The directions A-A′ are parallel to the surface of the sample S. The sample moving device 20 is formed of an arbitrary linearly driving mechanism. The linearly driving mechanism can be formed, for example, of a mechanism using a feed screw shaft driven by a pulse motor or any other power source. A pulse motor is a motor capable of controlling the angle of rotation of an output shaft thereof. X-rays R3-1 having passed through the slit 13a of the slit member 13 penetrates the sample S in the width direction (direction of the thickness d1 of the sample S) thereof. When the sample stage 5 moves in the direction A by a predetermined step width and the sample S moves in the direction A by the same step width accordingly, X-rays R3-2 are incident on the next step position on the sample S. Thereafter, whenever the sample S moves by the fixed step width, subsequent X-rays are incident on the respective step positions on the sample S. A step width Sd of the step movement (that is, intermittent movement) of the sample S is smaller than the width of the slit 13a of the slit member 13. As a result, among a plurality of section topographic images (that is, two-dimensional cross-sectional images) formed by the X-rays R3-1, X-rays R3-2, etc., adjacent section topographic images are not separated with a gap therebetween but can be seamlessly connected to each other. (Reception Optical System) The reception optical system 6 includes a two-dimensional X-ray detector 21. The two-dimensional X-ray detector 21 extends in the direction passing through the plane of view of FIG. 1 and receives the X-rays having exited out of the sample S, that is, diffracted X-rays R4 in a planar manner, that is, in a two-dimensional manner. The two-dimensional X-ray detector 21 can, for example, be formed of a photon-counting-type pixel two-dimensional X-ray detector (that is, pulse-counting-type pixel array two-dimensional detector) or a two-dimensional CCD and/or CMOS detector. The photon-counting-type pixel two-dimensional X-ray detector is an X-ray detector having a plurality of two-dimensionally arranged pixels each of which directly converts a photon into an electric signal. The two-dimensional detector is an X-ray detector having a plurality of charge coupled device (CCD) elements arranged in a planar manner. (Control System) The control system 3 is formed of a computer in the present embodiment. Specifically, the control system 3 includes a CPU 24, a read only memory (ROM) 25, a random access memory (RAM) 26, a memory 27, and a bus 28, which connects the components described above to each other. The memory 27 is formed, for example, of a hard disk drive or any other mechanical memory or a semiconductor memory. A printer 29, which is an example of image display means, and a display 30, which is another example of the image display means, are connected to the bus 28. The X-ray tube 11, the two-dimensional X-ray detector 21, and the sample moving device 20, which are components of the measurement system 2, are connected to the bus 28 via an interface 31. In the memory 27 are installed topography achieving software 34, which is function achieving means for driving the measurement system 2 to achieve desired topographic measurement, and dislocation density analysis software 35, which is software for analyzing measured data. Further, in the memory 27 is provided a data file 36, which is an area where measured data and analyzed data are stored. (Operation) The operation of the X-ray topography apparatus 1 shown in FIG. 1 will next be described with reference to the flowchart shown in FIG. 3. First, in step S1, initial adjustment is made to locate each element in FIG. 1 in a predetermined initial position. Measurement is then initiated in a case where an operator has instructed initiation of the measurement (YES in step S2). Specifically, in step S3, the X-ray tube 11 in FIG. 1 is operated to radiate X-rays. The radiated X-rays are converted by the multilayer film mirror 12 into monochromatic, collimated, higher-intensity X-rays. The X-rays having undergone the processes carried out by the multilayer film mirror 12 are then narrowed in terms of width by the slit 13a of the slit member 13 and incident on the sample S. Reference character R3-1 denotes the incident X-rays in FIG. 1. The X-ray irradiation continues for a predetermined period, for example, one minute or shorter. At this point, when a diffraction condition is satisfied between the incident X-rays R3-1 and the crystal lattice planes k, the diffracted X-rays R4 are produced. The X-rays R4 are detected with the two-dimensional X-ray detector 21 (step S4). FIG. 7 shows an example of two-dimensional cross-sectional images (what is called section topographic images) detected with the two-dimensional X-ray detector 21 in FIG. 1. In FIG. 7, an elongated rectangular image labelled with reference character G1 represents a two-dimensional cross-sectional images produced by the incident X-rays R3-1 in FIG. 1. When a lattice defect D is present in a path along which the incident X-rays R3-1 travels in FIG. 1, high-intensity diffracted X-rays R4-1 corresponding to the defect are produced in the portion where the defect is present, and the high-intensity diffracted X-rays produce a black dot in the two-dimensional cross-sectional image G1. That is, it is shown that a lattice defect is present in a position in the sample S that corresponds to the position where the black dot is formed in the two-dimensional cross-sectional image G1. In FIG. 7, the direction indicated by the arrows B corresponds to the direction in which the X-rays R3-1 in FIG. 1 travel (that is, thickness direction of sample S). The width L1 of the two-dimensional cross-sectional image G1 in FIG. 7 corresponds to the path along which the incident X-rays R3-1 pass through the sample S in FIG. 1. The direction indicated by the arrow C in FIG. 7 corresponds to the scan direction C in FIG. 1. The direction labelled with reference character E in FIG. 7 is the direction passing through the plane of view of FIG. 1 (that is, direction perpendicular to scan direction C along which sample S is scanned). The predetermined period described above for which the sample S is irradiated with the incident X-rays R3-1 is a period that allows sufficient contrast, that is, a sufficient S/N ratio between the background and the black dots in the two-dimensional cross-sectional image G1 produced by the two-dimensional X-ray detector 21. In the present embodiment, since the multilayer film mirror 12 is provided in the X-ray optical path in the incident optical system 4 to increase the intensity of the X-rays, the X-ray irradiation period can be significantly shortened as compared with a conventional apparatus using no multilayer film mirror. Specifically, it takes several tens of minutes for a conventional X-ray topography apparatus to produce the single two-dimensional cross-sectional image G1, whereas in the present embodiment, the characteristics of the X-ray source 11 and the multilayer film mirror 12 are so optimized that sufficient contrast is achieved in a predetermined period of one minute or shorter, preferably 10 to 20 seconds, more preferably 10 seconds. After the predetermined period for X-ray exposure has elapsed as described above (YES in step S5 in FIG. 3), the CPU 24 (FIG. 1) extracts an X-ray intensity signal from the two-dimensional X-ray detector 21 (step S6 in FIG. 3), data carried by the signal (that is, data corresponding to two-dimensional cross-sectional image G1 in FIG. 7) is stored in the data file 36 in the memory 27 (step S7 in FIG. 3). When imaging using the incident X-rays R3-1 in a single position on the sample S is completed, the CPU 24 instructs the sample moving device 20 to move the sample stage 5 and hence the sample S by the predetermined step width Sd in the direction indicated by the arrow A and stop the sample stage 5 and hence the sample S in the post-movement position (NO in step S8, step 9 in FIG. 3). The step width Sd is, for example, 10 μm. The step width Sd is set to a value smaller than the width of the slit 13a of the slit member 13. As a result, a state in which the incident X-rays R3-2 are incident on an adjacent step position separated by the step width Sd is achieved. In this state, steps S3 to S7 in FIG. 3 are repeated, and a two-dimensional cross-sectional image G2 in FIG. 7 is produced in the form of data in the X-ray intensity signal and stored. When a lattice defect D is present in the path along which the incident X-rays R3-2 travel, high-intensity diffracted X-rays R4-2 corresponding to the defect are produced, and the diffracted X-rays produce a black dot in the two-dimensional cross-sectional image G2. Thereafter, the step movement of the sample S and the X-ray measurement are repeatedly performed until a predetermined large number of two-dimensional cross-sectional images G1, G2, . . . Gn, for example, 400 two-dimensional cross-sectional images are produced (NO in step S8, step S9 in FIG. 3). As a result, a large number of two-dimensional cross-sectional images G1, G2, . . . Gn associated with the step positions on the sample S are stored, as shown in FIG. 7. After the measurement is made for the predetermined number of images (YES in step S8), and when an operator instructs analysis (YES in step S10), the CPU 24 produces, in step S11 in FIG. 3, a three-dimensional image J diagrammatically shown in FIG. 8 and stores the three-dimensional image J in the memory. The three-dimensional image J is formed by arranging the large number of (400 in the present embodiment) two-dimensional cross-sectional images G1, G2, G3, . . . Gn associated with the respective step positions on the sample S in such a way that the images are superimposed on each other in a three-dimensional coordinate system Z. The three-dimensional coordinate system Z has a horizontal axis representing a movement distance X, a vertical axis representing a direction E perpendicular to the sample scan direction, and a height axis representing the direction in which the X-rays travel (or direction of sample thickness d1). The CPU 24 then produces a second two-dimensional image in step S12 and stores them in the memory. Specifically, the three-dimensional image J is sectioned along a flat plane different from the plane where the measurement was made, and data on dislocation images (i.e., black dots) in the flat plane are gathered and stored in the memory. For example, in FIG. 8, data that belong to a surface P2 of the three-dimensional image J are gathered and stored, and data that belong to a flat plane P3 separated from the surface by a distance d2 are gathered and stored. The resulting second two-dimensional image is displayed, for example, in the form of the left photograph in FIG. 9. The photograph is a displayed image formed by measuring an SiC wafer as the sample S in FIG. 1 to produce a three-dimensional image J, such as that shown in FIG. 8, and gathering dislocation data in the surface P2 or a surface in the vicinity thereof. The measurement conditions were as follows: Step movement intervals: 10 μm The number of acquired two-dimensional cross-sectional images (section topographic images): 400 Measurement period spent to acquire single two-dimensional cross-sectional image: 50 seconds Field of view: 4 mm×6 mm In the photograph, the long lines show that dislocation extends in the flat plane, and the dots show that the dislocation extends in the thickness direction of the sample. The right photograph in FIG. 9 is presented for comparison purposes and is a two-dimensional image produced by measuring the same place of the sample using a traverse transmission topography technique, which is a conventional topography measurement technique. In the traverse topography technique, in which data in cross sections are integrated in a two-dimensional X-ray detector, all dislocation sites present in the sample are superimposed on each other, and the operator views the superimposed image. Dislocation information at a certain depth in the sample cannot therefore be accurately reflected in the image. In contrast, in the present embodiment a result of which is shown in the left portion of FIG. 9, dislocation information in the flat plane at the certain depth is accurately reflected. It is therefore clearly shown that the present embodiment allows accurate discrimination between and identification of basal plane dislocation, threading screw dislocation, and threading edge dislocation. The CPU next calculates dislocation density in step S13 in FIG. 3. That is, dislocation density (number of dislocation sites/cm2) is calculated based on dislocation images in the flat plane that are produced in the form of the left photograph in FIG. 9. Thereafter, image display using the display 30 is performed as required (steps S14, S15), and image printing using the printer 29 is further performed as required (steps S16, S17). As described above, the present embodiment allows measurement of a high-contrast image of dislocation present in a cross section along an incident X-ray beam. A large number of X-ray measurement are made while a cross section irradiated with X-rays is slightly shifted whenever single X-ray measurement is made for acquisition of a large number of section topographic images, and analysis of the section topographic images provides a three-dimensional structure of dislocation in a wafer. Cutting the resultant three-dimensional image in a direction parallel to the surface of the sample provides an image of dislocation present in a plane at a fixed depth. The present embodiment allows observation of dislocation present in a position in the vicinity of a surface and observation of only dislocation present at a fixed depth from the surface. Comparison of the present embodiment with reflective X-ray topography measurement using synchrotron radiation has proved that threading edge dislocation is observable. Further, the present embodiment can provide clear knowledge of the path along which dislocation extends. For example, it can be determined whether dislocation is parallel to a surface, extends from rear to front, or extend from front to rear and is redirected back toward the front. It can further be evaluated that the surface of a sample has many dots representing threading dislocation or the interior of the sample has may lines representing basal plane dislocation. The present invention has been described with reference the preferable embodiment, but the invention is not limited thereto and a variety of changes can be made thereto within the scope of the invention set forth in the claims. For example, the multilayer film mirror 12 in FIG. 1 is not limited to a multilayer film mirror shaped as shown in FIG. 2 and can be arbitrarily shaped as required. Further, the control procedure shown in FIG. 3 is an example and can be modified as required. A crystal formed by growing an SiC epitaxial film on an SiC substrate to a thickness of about 10 μm, that is, a homoepitaxial crystal, which is grown under the condition that the substrate and the film are made of the same crystal, was measured as a sample by using the X-ray topography apparatus in FIG. 1. As a result, a second two-dimensional image of a plane in the vicinity of the surface of the epitaxial film was produced as shown in FIG. 10. Further, a second two-dimensional image of a plane at an interface between the epitaxial film and the substrate was produced as shown in FIG. 11. Moreover, a second two-dimensional image of a plane at another interface between the epitaxial film and the substrate was produced as shown in FIG. 12. Further, a second two-dimensional image of a plane at a location in the substrate was produced as shown in FIG. 13. Moreover, a second two-dimensional image of a plane at another location in the substrate was produced as shown in FIG. 14. Further, a second two-dimensional image of a plane on rear side of the substrate was produced as shown in FIG. 15. 1. X-ray topography apparatus, 2. Measurement system, 3. Control system, 4. Incident optical system, 5. Sample stage, 6. Reception optical system, 11. X-ray tube, 12. Multilayer film mirror, 13. Slit member, 13a. Slit, 14. Filament (cathode), 15. Target (anode), 16. X-ray window, 20. Sample moving device, 21. Two-dimensional X-ray detector, 27. Memory, 28. Bus, 29. Printer (image display means), 30. Display (image display means), 31. Interface, 34. Topography achieving software, 35. Dislocation density analysis software, 36. Data file, 50. Multilayer film monochromator, 51. Heavy element layer, 52. Light element layer, 53. Substrate, B. Direction along thickness of sample, C. Direction in which sample is scanned by X-rays, D. Lattice defect, D1. Distance from X-ray focal spot to sample, d1. Thickness of sample, d2. Separated planes distance, E. Direction perpendicular to scanning direction, F. X-ray focal spot (X-ray source), G1, G2, G3, . . . Gn. Two-dimensional cross-sectional image, H. Direction of slit width, J. Three-dimensional image, k. Crystal lattice planes, L1. Width of two-dimensional cross-sectional images, P1. Surface, P2,P3. Planes for sectioning three-dimensional image, R1: Incident X-rays, R2: Diffracted X-rays, R3-1,R3-2: Incident X-rays, R4-1,R4-2: Diffracted X-rays, S: Sample crystal, Sd: Step width, T1: Stacked layer thickness on X-ray incident side, T2: Stacked layer thickness on X-ray exiting side, X: Horizontal axis representing sample moving distance, Z: Three-dimensional coordinate system, |
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047327057 | description | (a) Cement Solidification of Untreated Resin Particles 60 parts by weight of the untreated resin particle mixture with 50% water content, i.e. fully swelled, were mixed with 100 parts by weight of synthetic Portland cement with high silicate content, designation CPA 55 HTS, produced by Ciments Lafarge France, F-92214 St. Cloud (corresponding to the French norm NF P 15301, December 1978, and the American norm ASTM as type V, quality "low alkali cement"), PA1 40 parts by weight of hydraulic Nettetal trass according to DIN 51043, produced by Trass-Werke Meurin, Andernach/Rhine, FRG, Kruft plant, PA1 10 parts by weight of calcium hydroxide, Ca(OH).sub.2 PA1 4.2 parts by weight of super liquified (naphthaline-formaldehyde condensate), designation Sikament, produced by Sika AG, CH-8048 Zurich, and PA1 30.8 parts by weight of water. PA1 36.0 parts by weight of BaS.sub.4 solution with 72.4% by weight water content (solid matter dry 27.6% by weight) and PA1 43.35 parts by weight of Ba(OH).sub.2.8H.sub.2 O. PA1 100 parts by weight of synthetic Portland cement of the same quality as described in section (a), and PA1 40 parts by weight of hydraulic Nettetal trass of the same quality as described in section (a) PA1 2.5 parts by weight of cement additive for improving the cement density and solidity, designation Sperrbarra Plus OL, supplied by Meynadier & Cie AG, CH-8048 Zurich. The mixture according to the above prescription was left to harden with a water coating. The thus resulting solid matrix provided the values as shown in table II. (b) Pretreatment of the Resin Particles 63.65 parts by weight of the resin particle mixture with 16.4% by weight water content (solid matter dry 83.6% by weight) were mixed to a thin gruel with the following additives: Thereby the cation resin was charged with Ba.sup.++ and the anion resin with S.sub.4.sup.--. The borate which was split off from the anion resin was precipitated with more Ba.sup.++ as insoluble barium-metaborate. This reaction, resulting from the mixing, caused heat to be released, which had the effect that the mixture heated itself from room temperature to about 50.degree. C. Then, the mixture was kept for several hours at 50.degree. C. The cement solidification took place about 24 hours after the described pretreatment. In the meantime, the mixture was stirred further, in order to prevent a settling of the solid matter and the formation of larger crystals. A water loss by evaporation during this time was compensated for by more water. The thus pretreated resin particles provided the values cited in table I under no. 89. (c) Cement Solidification of the Pretreated Resin Particles A previously prepared mixture, consisting of was added to the mixture described in section (b) with the pretreated ion exchange resin particles. At the beginning, only enough of the above mixture was added and homogenically stirred in until there was a thick gruel which ran together by itself. Then followed the addition of With the addition of this cement additive, the gruel became obviously more liquid. It was then possible to add the remaining Portland cement/trass mixture with constant stirring. The final gruel had a just pumpable consistency and was homogenically mixed for another 10 minutes. The mixed in air bubbles were removed by vibration. After about 2 hours, the mixture was gelled sufficiently thixotrope so that it could be coated with water for hardening. The hardening by setting of the cement started after 5 to 6 hours, which could be recognized by a rise in temperature. The finally resulting matrix showed the values as listed in table II. (d) Comparison of the Properties of the Hardened Matrix with Untreated or Treated Ion Exchange Resin Particles Compared in table II are the corresponding values of the hardened matrix produced according to section (a) (state of the art) and the matrix produced according to sections (b) and (c). It can be clearly seen from table II that by the described pretreatment of the ion exchange resin particles, according to the invention, for reduction of the swelling factor has two essential advantages as compared to the state of the art. The main advantage can be seen in the fact that the water resistance of the hardened matrix is guaranteed, even when the matrix is dried to a weight constant at 20% relative humidity and is then stored again in water, whereby the water resistance in the matrix according to the state of the art is only guaranteed as long as there is no intermediate drying. The other advantage is that at a given matrix volume, e.g. 100 liter, a considerably greater amount of resin particles, 35.1 kg as compared to 22 kg dry substance of the original resin particles can be enclosed. This can effectively ease the disposal and final storage for radioactive waste ion exchange resins. It has to be stated as another advantage of the new process that the other properties of the solid matrix, especially the compressive strength and sulfate resistance, are not impaired by the pretreatment of the ion exchange resin particles according to the invention. It is clear that for the pretreatment of the ion exchange resin particles to be solidified it is possible to use a large number of other substances besides those listed in table I and that the prescription stated as example for the cement solidification can be modified. The ion exchange resin particles with reduced swelling factor, pretreated according to the invention, are not only suitable for cement solidification, but can be solidified also, with equally good results, using bitumen or plastics. TABLE I __________________________________________________________________________ Lewatit (%) S M comp. vol. swell No. 100 500 treated with: wet dry factor __________________________________________________________________________ (l/kg) 1 100 -- none 2.50 1.19 2.10 2 -- 100 none 3.23 1.44 2.24 3 50 50 none 2.86 1.28 2.23 4 100 -- cocosamine acetate 2.61 1.89 1.38 5 100 -- dibutylamine 2.59 2.28 1.14 6 100 -- tributylamine 2.67 2.28 1.17 7 100 -- dibutylamine nitrate 2.42 1.94 1.25 8 100 -- tributylamine nitrate 2.51 2.04 1.23 9 100 -- vinyl imidazole 2.56 1.79 1.43 10 100 -- vinyl imidazole nitrate 2.44 1.51 1.62 11 100 -- benzylcocodimethyl- 2.60 1.45 1.79 ammonium chloride 12 100 -- suetalkyltrimethyl- 2.73 1.56 1.75 ammonium chloride 13 100 -- disuetalkyldimethyl- 2.68 1.45 1.85 ammonium chloride 14 100 -- dioctyldimethylammonium 2.57 1.79 1.44 chloride 15 100 -- didecyldimethylammonium 2.61 1.66 1.57 chloride 16 100 -- tetraethylammonium 3.08 2.32 1.33 hydroxide 17 100 -- tetrapropylammonium 3.01 2.43 1.24 hydroxide 18 100 -- tetrabutylammonium 2.85 2.48 1.15 hydroxide 19 100 -- tributylmethylammonium 3.08 2.75 1.12 hydroxide 20 100 -- benzyltrimethylammonium 2.73 2.23 1.22 hydroxide 21 100 -- trimethylammoniumethyl- 2.53 1.59 1.59 methacrylate metho- sulfate 22 100 -- as in 21 then polymerized 2.40 1.84 1.30 with ammonium peroxi- disulfate 23 100 -- ethylenediamine 2.35 1.42 1.65 24 100 -- ethylenediamine carbonate 2.30 1.37 1.68 25 100 -- 1,2 propylenediamine 2.46 1.57 1.57 26 100 -- 1,2 propylenediamine 2.54 1.58 1.61 carbonate 27 100 -- 1,4 phenylenediamine 2.34 1.94 1.21 28 100 -- 1,4 phenylenediamine 2.43 1.86 1.31 carbonate 29 100 -- piperazine 2.52 1.59 1.58 30 100 -- piperazinecarbonate 2.70 1.70 1.59 31 100 -- semicarbazide hydro- 2.19 1.27 1.72 chloride 32 100 -- guanidine carbonate 2.28 1.65 1.38 33 100 -- aminoguanidine carbonate 2.25 1.57 1.43 34 100 -- S--methylisothiourea 2.11 1.66 1.27 hydroxide 35 100 -- S--benzylisothiourea 2.20 1.88 1.17 hydroxide 36 100 -- acethydrazide-trimethyl 2.24 1.37 1.64 ammonium chloride 37 100 -- pentane-1,5-bi-trimethyl 1.81 1.21 1.50 ammonium iodite 38 100 -- decane-1,10-bi-trimethyl 2.01 1.43 1.41 ammonium iodite 39 100 -- hydrazine hydrate 2.26 1.27 1.78 40 100 -- heptamethylguanidine 2.50 1.78 1.40 hydroxide 41 100 -- propane-1,3-bi-trimethyl 2.10 1.45 1.45 ammonium hydroxide 42 100 -- tetrabutylphosphonium 2.58 2.20 1.17 hydroxide 43 100 -- methyltriphenylphospho- 2.32 1.76 1.32 nium hydroxide 44 100 -- trimethylsulphonium 2.51 1.60 1.57 hydroxide 45 100 -- thallium nitrate 2.09 1.19 1.76 46 100 -- magnesium chloride 2.40 1.19 2.02 47 100 -- calcium chloride 2.36 1.20 1.97 48 100 -- barium chloride 2.06 1.21 1.70 49 100 -- barium hydroxide 2.05 1.31 1.56 50 100 -- cadmium chloride 2.45 1.27 1.93 51 100 -- copper chloride 2.47 1.20 2.06 52 100 -- manganese-2-chloride 2.40 1.30 1.85 53 100 -- cobalt chloride 2.48 1.23 2.02 54 100 -- nickel chloride 2.49 1.27 1.96 55 100 -- iron-3-chloride 2.44 1.16 2.10 (1 kg) 56 100 -- iron-2-sulfate 2.21 1.37 1.61 57 100 -- chromium chloride 2.59 1.28 2.02 58 100 -- aluminum chloride 2.45 1.24 1.98 59 100 -- titanium-3-chloride 2.57 1.28 2.01 60 100 -- zinc acetate 2.55 1.18 2.16 61 100 -- tin chloride 2.38 1.17 2.03 62 -- 100 ammonium stearate 3.23 2.53 1.28 63 -- 100 acrylic acid 2.89 1.73 1.67 64 -- 100 dimethylacrylic acid 2.86 1.73 1.65 65 -- 100 diammonium sebacate 2.80 1.69 1.66 66 -- 100 sylvatac 140, dimerized 1.98 1.44 1.38 liquid rosin, SZ 134, (Sylvachem Corp., USA) H.sub.2 O soluble w/10% NaOH 67 -- 100 resin B 106, colophonium 2.68 1.80 1.49 pentester SZ 204 (Hercules Inc. USA) H.sub.2 O soluble w/ 6.25% NH.sub.3 68 -- 100 Vinsol resin, pine root 2.72 1.80 1.51 resin SZ 95 (Hercules Inc. USA) H.sub.2 O soluble w/7% NaOH 69 -- 100 ammonium lauryl sulfate 2.84 1.74 1.63 70 -- 100 vinylpentasulphonate-Na 2.83 1.78 1.59 71 -- 100 monobutylphosphoric acid 2.88 1.83 1.57 ester (l/kg) 72 -- 100 mono and dibutylphosphoric 2.98 2.08 1.43 acid ester, 50% each 73 -- 100 monostearylphosphoric 4.09 3.25 1.26 acid ester 74 -- 100 mono + di-nonyletraethoxi- 3.30 2.57 1.28 phenolphosphoric acid ester 75 -- 100 potassium polysulfide 2.61 1.57 1.66 at 20.degree. C. 76 -- 100 potassium polysulfide 2.49 1.51 1.65 at 50.degree. C. 77 -- 100 calcium polysulfide 2.14 1.53 1.40 at 20.degree. C. 78 -- 100 calcium polysulfide 1.55 1.51 1.03 at 50.degree. C. 79 -- 100 as 77 + 10% potassium 1.75 1.70 1.03 ethylxanthogenate (rel. to resin dry) 80 -- 100 barium polysulfide 2.11 1.69 1.25 at 20.degree. C. 81 -- 100 barium polysulfide 1.77 1.71 1.04 at 50.degree. C. 82 -- 100 as 80 + 10% potassium 2.11 1.83 1.15 ethylxanthogenate (rel. to resin dry) 83 -- 100 complete thermolysis at 1.01 1.01 1.00 150.degree. C. in air stream 84 50 50 as 83 1.80 1.10 1.64 85 50 50 tetrabutylammonium hydroxide 1.94 1.86 1.04 then thermolysis at 160.degree. C. in air stream 86 50 50 guanidine carbonate, 1.57 1.28 1.23 then thermolysis at 160.degree. C. in air stream 87 50 50 aminoguanidinehydrogen 1.57 1.31 1.20 carbonate, then thermo- lysis at 160.degree. C. in air stream 88 50 50 tetrabutylammonium hydrox- 2.14 1.89 1.13 ide, then calcium poly- sulfide 89 50 50 barium polysulfide a/50.degree. C. 1.91 1.51 1.26 90 50 50 as 89 + 10% K--ethyl- 2.08 1.57 1.32 xanthogenate a/20.degree. C. 91 50 50 ethylenediamine polysulfide 1.90 1.44 1.32 92 50 50 as 91 + heat treatment at 1.62 1.38 1.17 160.degree. C. 93 50 50 propylenediamine poly- 1.80 1.38 1.30 sulfide 94 50 50 as 93 + heat treatment at 1.57 1.36 1.15 160.degree. C. 95 50 50 piperazine polysulfide 1.96 1.39 1.41 96 50 50 as 95 + heat treatment 1.62 1.37 1.18 160.degree. C. 97 50 50 guanidine polysulfide 1.93 1.51 1.28 98 50 50 as 97 + heat treatment 1.57 1.33 1.18 160.degree. C. 99 50 50 aminoguanidine poly- 1.98 1.57 1.26 sulfide 100 50 50 as 99 + heat treatment 1.75 1.45 1.21 160.degree. C. 101 50 50 tetramethylguanidine 1.97 1.47 1.34 polysulfide 102 50 50 as 101 + heat treatment 1.67 1.59 1.05 160.degree. C. 103 50 50 dicyandiamide + heat 1.89 1.55 1.22 treatment 160.degree. C. __________________________________________________________________________ TABLE II ______________________________________ Cement solidification of Cement solidification of Properties untreated ion exchange pretreated ion exchange of matrix resin particles resin particles ______________________________________ volume 1.8 t/m.sup.3 (water content 1.8 t/m.sup.3 (water content weight acc.to recipe) acc.to recipe) resin 22 kg dry substance 35.1 kg dry substance content in 100 liter matrix without treatment, in 100 liter matrix compressive 22 N/mm.sup.2 after more 21 N/mm.sup.2 after more strength than 20 weeks of than 20 weeks of (acc. SIA hardening hardening 215) sulfate is assured is assured resist. water is assured as long as is assured even when resistance the matrix has not the matrix has been been dried before dried before wetting wetting leach rates in distilled water: values not yet obtained RL 730 10.sup.-4 to 10.sup.-5 for Based on recipe Cs-137 about the same results 10.sup.-6 to 10.sup.-7 for are expected. Co-60 10.sup.-3 to 10.sup.-4 for Sr-90 (in water saturated with gypsum, smaller by 1 or 2 orders of magnitude) ______________________________________ |
052805077 | claims | 1. The method of sensing obstructions in a tubular nuclear fuel rod or the like, and comprising the steps of providing a nozzle having high and low gas pressure sourced connected thereto, and providing a gas flow balance circuit directly communicating with the nozzle, said gas flow balance circuit including an outlet having a variable restriction, calibrating the balance circuit and including positioning the nozzle in sealed relationship with one end of a fuel rod known to be free of internal obstructions, flowing a low pressure gas from the low pressure gas source through the nozzle and into and through the fuel rod, sensing the pressure of the flowing gas at a location in the nozzle so as to define a standardized pressure, flowing a balance circuit gas through the balance circuit while sensing the pressure of the gas within the balance circuit, and adjusting the variable restriction of the balance circuit so that the sensed pressure within the balance circuit equals the standardized pressure, positioning the nozzle in sealed relationship with one end of a fuel rod to be tested, flowing a low pressure gas from the low pressure gas source through the nozzle and then into and through the fuel rod to be tested, flowing a balance circuit gas through the balance circuit to produce the standardized pressure, sensing the pressure of the flowing low pressure gas in the nozzle, and comparing the sensed pressure of the flowing low pressure gas with the standardized pressure of the balance circuit flowing gas and such that a difference between the sensed pressure of the low pressure gas flowing in the nozzle from the low pressure gas source and the standardized pressure of the balance circuit is indicative of an obstruction in the fuel rod being tested. a nozzle adapted to engage one end of a fuel rod in an air tight sealed relationship, means connected to said nozzle for flowing an initial high pressure gas flow through said nozzle and into a fuel rod positioned in an air tight sealed relationship with said nozzle so as to blow any obstructions from the interior of fuel rod, means connected to said nozzle for flowing a low pressure ga flow through said nozzle and into a fuel rod positioned in an air tight sealed relationship with the nozzle, means for sensing the pressure of the flowing low pressure gas in the nozzle when the low pressure gas is flowing through the nozzle, a gas flow balance circuit directly communicating with the nozzle, said gas flow balance circuit including an outlet having a variable restriction, means for flowing a balance circuit gas through the balance circuit, and means for sensing the balance circuit gas flow and such that the pressure of the balance circuit gas flow equals a standardized pressure, and means for comparing the sensed pressure of the flowing low pressure gas with the standardized pressure of the balance circuit gas flow, and such that a difference between the sensed pressure and the standardized pressure is indicative of an obstruction in the fuel rod. 2. An apparatus for sensing obstructions in a tubular nuclear fuel rod or the like, and comprising 3. The method as defined in claim 1 wherein the fuel rod and the outlet of the balance circuit both vent to the atmosphere, and so as to render the method insensitive to changes in atmospheric pressure. 4. The method as defined in claim 1 comprising the further step of generating a visible or audible alarm signal when the difference between the sensed pressure and the standardized pressure is greater than a predetermined value. 5. The method as defined in claim 1 comprising the further step of passing an initial high pressure gas from the high pressure gas source through the nozzle and into and through the fuel rod prior to the step of flowing the low pressure gas therethrough, and so as to blow any obstructions from the interior of the fuel rod. 6. The apparatus as defined in claim 2 wherein the fuel rod and the outlet of said balance circuit both vent to the atmosphere, and so as to render the apparatus insensitive to changes in atmospheric pressure. 7. The apparatus as defined in claim 2 wherein said comparing means includes means for generating a visible or audible alarm signal when the difference between the sensed pressure and the standardized pressure is greater than a predetermined value. |
abstract | An improved process for the preparation of high purity rare metal compounds such as oxides utilizing TBP (Tri-Butyl Phosphate)-nitrate solvent extraction technique adapted to manufacture nuclear grade rare metal compounds such as zirconium oxide wherein the said process substantially aids in reducing the specific generation of ammonium nitrate effluent volume thereby increasing its concentration when the said effluent comprising ammonium nitrate and ammonium sulphate are utilized for stripping of the said rare metal compound from the organic solvent in the said process of production of high purity rare metal oxide powder. |
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description | This is a continuation application of U.S. patent application Ser. No. 11/812,353, filed Jun. 18, 2007, now abandoned which is a continuation application of U.S. application Ser. No. 09/960,703, filed Sep. 24, 2001, now abandoned both of which are herein incorporated by reference in their entireties. 1. Field of the Invention The present invention relates to methods for sterilizing biological materials to reduce the level of one or more active biological contaminants or pathogens therein, such as viruses, bacteria (including inter- and intracellular bacteria, such as mycoplasmas, ureaplasmas, nanobacteria, chlamydia, rickettsias), yeasts, molds, fungi, prions or similar agents responsible, alone or in combination, for TSEs and/or single or multicellular parasites. The present invention particularly relates to methods of sterilizing biological materials containing one or more non-aqueous solvents with irradiation. 2. Background of the Related Art Many biological materials that are prepared for human, veterinary, diagnostic and/or experimental use may contain unwanted and potentially dangerous biological contaminants or pathogens, such as viruses, bacteria (including inter- and intracellular bacteria, such as mycoplasmas, ureaplasmas, nanobacteria, chlamydia, rickettsias), yeasts, molds, fungi, prions or similar agents responsible, alone or in combination, for TSEs and/or single or multicellular parasites. Consequently, it is of utmost importance that any biological contaminant or pathogen in the biological material be inactivated before the product is used. This is especially critical when the material is to be administered directly to a patient, for example in blood transfusions, blood factor replacement therapy, organ transplants and other forms of human therapy corrected or treated by intravenous, intramuscular or other forms of injection or introduction. This is also critical for the various biological materials that are prepared in media or via culture of cells or recombinant cells which contain various types of plasma and/or plasma derivatives or other biologic materials and which may be subject to mycoplasma, prion, bacterial, viral and other biological contaminants or pathogens. Most procedures for producing biological materials have involved methods that screen or test the biological materials for one or more particular biological contaminants or pathogens rather than removal or inactivation of the contaminant(s) or pathogen(s) from the material. Materials that test positive for a biological contaminant or pathogen are merely not used. Examples of screening procedures include the testing for a particular virus in human blood from blood donors. Such procedures, however, are not always reliable and are not able to detect the presence of certain viruses, particularly in very low numbers. This reduces the value or certainty of the test in view of the consequences associated with a false negative result. False negative results can be life threatening in certain cases, for example in the case of Acquired Immune Deficiency Syndrome (AIDS). Furthermore, in some instances it can take weeks, if not months, to determine whether or not the material is contaminated. Moreover, to date, there is no reliable test or assay for identifying prions within a biological material that is suitable for screening out potential donors or infected material. This serves to heighten the need for an effective means of destroying prions within a biological material, while still retaining the desired activity of that material. Therefore, it would be desirable to apply techniques that would kill or inactivate contaminants or pathogens during and/or after manufacturing the biological material. The importance of these techniques is apparent regardless of the source of the biological material. All living cells and multi-cellular organisms can be infected with viruses and other pathogens. Thus the products of unicellular natural or recombinant organisms or tissues carry a risk of pathogen contamination. In addition to the risk that the producing cells or cell cultures may be infected, the processing of these and other biological materials creates opportunities for environmental contamination. The risks of infection are more apparent for multicellular natural and recombinant organisms, such as transgenic animals. Interestingly, even products from species as different from humans as transgenic plants carry risks, both due to processing contamination as described above, and from environmental contamination in the growing facilities, which may be contaminated by pathogens from the environment or infected organisms that co-inhabit the facility along with the desired plants. For example, a crop of transgenic corn grown out of doors, could be expected to be exposed to rodents such as mice during the growing season. Mice can harbour serious human pathogens such as the frequently fatal Hanta virus. Since these animals would be undetectable in the growing crop, viruses shed by the animals could be carried into the transgenic material at harvest. Indeed, such rodents are notoriously difficult to control, and may gain access to a crop during sowing, growth, harvest or storage. Likewise, contamination from overflying or perching birds has to potential to transmit such serious pathogens as the causative agent for psittacosis. Thus any biological material, regardless of its source, may harbour serious pathogens that must be removed or inactivated prior to the administration of the material to a recipient. In conducting experiments to determine the ability of technologies to inactivate viruses, the actual viruses of concern are seldom utilized. This is a result of safety concerns for the workers conducting the tests, and the difficulty and expense associated with the containment facilities and waste disposal. In their place, model viruses of the same family and class are used. In general, it is acknowledged that the most difficult viruses to inactivate are those with an outer shell made up of proteins, and that among these, the most difficult to inactivate are those of the smallest size. This has been shown to be true for gamma irradiation and most other forms of radiation as these viruses' diminutive size is associated with a small genome. The magnitude of direct effects of radiation upon a molecule are directly proportional to the size of the molecule, that is the larger the target molecule, the greater the effect. As a corollary, it has been shown for gamma-irradiation that the smaller the viral genome, the higher the radiation dose required to inactive it. Among the viruses of concern for both human and animal-derived biological materials, the smallest, and thus most difficult to inactivate, belong to the family of Parvoviruses and the slightly larger protein-coated Hepatitis virus. In humans, the Parvovirus B19, and Hepatitis A are the agents of concern. In porcine-derived materials, the smallest corresponding virus is Porcine Parvovirus. Since this virus is harmless to humans, it is frequently chosen as a model virus for the human B19 Parvovirus. The demonstration of inactivation of this model parvovirus is considered adequate proof that the method employed will kill human B19 virus and Hepatitis A, and by extension, that it will also kill the larger and less hardy viruses such as HIV, CMV, Hepatitis B and C and others. More recent efforts have focussed on methods to remove or inactivate contaminants in the products. Such methods include heat treating, filtration and the addition of chemical inactivants or sensitizers to the product. According to current standards of the U.S. Food and Drug Administration, heat treatment of biological materials may require healing to approximately 60° C. for a minimum of 10 hours, which can be damaging to sensitive biological materials. Indeed, heat inactivation can destroy 50% or more of the biological activity of certain biological materials. Filtration involves filtering the product in order to physically remove contaminants. Unfortunately, this method may also remove products that have a high molecular weight. Further, in certain cases, small viruses may not be removed by the filter. The procedure of chemical sensitization involves the addition of noxious agents which bind to the DNA/RNA of the virus and which are activated either by UV or other radiation. This radiation produces reactive intermediates and/or free radicals which bind to the DNA/RNA of the virus, break the chemical bonds in the backbone of the DNA/RNA, and/or cross-link or complex it in such a way that the virus can no longer replicate. This procedure requires that unbound sensitizer is washed from products since the sensitizers are toxic, if not mutagenic or carcinogenic, and cannot be administered to a patient. Irradiating a product with gamma radiation is another method of sterilizing a product. Gamma radiation is effective in destroying viruses and bacteria when given in high total doses (Keathly et al., “Is There Life After Irradiation? Part 2,” BioPharm July-August, 1993, and Leitman, “Use of Blood Cell Irradiation in the Prevention of Post Transfusion Graft-vs-HostDisease,” Transfusion Science 10:219-239 (1989)). The published literature in this area, however, teaches that gamma radiation can be damaging to radiation sensitive products, such as blood, blood products, protein and protein-containing products. In particular, it has been shown that high radiation doses are injurious to red cells, platelets and granulocytes (Leitman). U.S. Pat. No. 4,620,908 discloses that protein products must be frozen prior to irradiation in order to maintain the viability of the protein product. This patent concludes that “[i]f the gamma irradiation were applied while the protein material was at, for example, ambient temperature, the material would be also completely destroyed, that is the activity of the material would be rendered so low as to be virtually ineffective”. Unfortunately, many sensitive biological materials, such as monoclonal antibodies (Mab), may lose viability and activity if subjected to freezing for irradiation purposes and then thawing prior to administration to a patient. In view of the difficulties discussed above, there remains a need for methods of sterilizing biological materials that are effective for reducing the level of active biological contaminants or pathogens without an adverse effect on the material. The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background. An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. Accordingly, it is an object of the present invention to provide methods of sterilizing biological materials by reducing the level of active biological contaminants or pathogens without adversely effecting the material. Other objects, features and advantages of the present invention will be set forth in the detailed description of preferred embodiments that follows, and in part will be apparent from the description or may be learned by practice of the invention. These objects and advantages of the invention will be realized and attained by the compositions and methods particularly pointed out in the written description and claims hereof. In accordance with these and other objects, a first embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising irradiating the biological material with radiation for a time effective to sterilize the material at a rate effective to sterilize the material and to protect the material from radiation. Another embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) adding to a biological material at least one stabilizer in an amount effective to protect the biological material from radiation; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the material. Another embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) reducing the residual solvent content of a biological material to a level effective to protect the biological material from radiation; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the biological material. Another embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) reducing the temperature of a biological material to a level effective to protect the biological material from radiation; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the biological material. Another embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) applying to the biological material a stabilizing process selected from the group consisting of: (a) reducing the residual solvent content of a biological material, (b) adding to the biological material at least one stabilizer, and (c) reducing the temperature of the biological material; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the biological material, wherein the stabilizing process and the rate of irradiation are together effective to protect the biological material from radiation. Another embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) applying to the biological material at least two stabilizing processes selected from the group consisting of: (a) reducing the residual solvent content of a biological material, (b) adding to the biological material at least one stabilizer, and (c) reducing the temperature of the biological material; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the biological material, wherein the stabilizing processes may be performed in any order and are together effective to protect the biological material from radiation. The invention also provides a composition comprising a biological material and a non-aqueous solvent in an amount effective to preserve the preparation for its intended use following sterilization with radiation. The invention also provides a composition comprising at least one biological material, a least one non-aqueous solvent and at least one stabilizer, wherein the non-aqueous solvent and stabilizer are together present in an amount effective to preserve the material for its intended use following sterilization with radiation. Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. A. Definitions Unless defined otherwise, all technical and scientific terms used herein are intended to have the same meaning as is commonly understood by one of ordinary skill in the relevant art. As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. As used herein, the term “sterilize” is intended to mean a reduction in the level of at least one active biological contaminant or pathogen found in the biological material being treated according to the present invention. As used herein, the term “biological material” is intended to mean any substance derived or obtained from a living organism. Illustrative examples of biological materials include, but are not limited to, the following: cells; tissues; blood or blood components; proteins, including recombinant and transgenic proteins, and proteinaceous materials; enzymes, including digestive enzymes, such as trypsin, chymotrypsin, alpha-galactosidase and iduronodate-2-sulfatase; immunoglobulins, including mono and polyimmunoglobulins; botanicals; food and the like. Preferred examples of biological materials include, but are not limited to, the following: ligaments; tendons; nerves; bone, including demineralized bone matrix, grafts, joints, femurs, femoral heads, etc.; teeth; skin grafts; bone marrow, including bone marrow cell suspensions, whole or processed; heart valves; cartilage; corneas; arteries and veins; organs, including organs for transplantation, such as hearts, livers, lungs, kidneys, intestines, pancreas, limbs and digits; lipids; carbohydrates; collagen, including native, afibrillar, atelomeric, soluble and insoluble, recombinant and transgenic, both native sequence and modified; chitin and its derivatives, including NO-carboxy chitosan (NOCC); stem cells, islet of Langerhans cells and other cells for transplantation, including genetically altered cells; red blood cells; white blood cells, including monocytes; and platelets. As used herein, the term “non-aqueous solvent” is intended to mean any liquid other than water in which a biological material may be dissolved or suspended and includes both inorganic solvents and, more preferably, organic solvents. Illustrative examples of suitable non-aqueous solvents include, but are not limited to, the following: alkanes and cycloalkanes, such as pentane, 2-methylbutane (isopentane), heptane, hexane, cyclopentane and cyclohexane; alcohols, such as methanol, ethanol, 2-methoxyethanol, isopropanol, n-butanol, t-butyl alcohol, and octanol; esters, such as ethyl acetate, 2-methoxyethyl acetate, butyl acetate and benzyl benzoate; aromatics, such as benzene, toluene, pyridine, xylene; ethers, such as diethyl ether, 2-ethoxyethyl ether, ethylene glycol dimethyl ether and methyl t-butyl ether; aldehydes, such as formaldehyde and glutaraldehyde; ketones, such as acetone and 3-pentanone (diethyl ketone); glycols, including both monomeric glycols, such as ethylene glycol and propylene glycol, and polymeric glycols, such as polyethylene glycol (PEG) and polypropylene glycol (PPG), e.g., PPG 400, PPG 1200 and PPG 2000; acids and acid anhydrides, such as formic acid, acetic acid, trifluoroacetic acid, phosphoric acid and acetic anhydride; oils, such as cottonseed oil, peanut oil, culture media, polyethylene glycol, poppyseed oil, safflower oil, sesame oil, soybean oil and vegetable oil; amines and amides, such as piperidine, N,N-dimethylacetamide and N,N-dimethylformamide; dimethylsulfoxide (DMSO); nitriles, such as benzonitrile and acetonitrile; hydrazine; detergents, such as polyoxyethylenesorbitan monolaurate (Tween 20) and monooleate (Tween 80), Triton and sodium dodecyl sulfate; carbon disulfide; halogenated solvents, such as dichloromethane, chloroform, carbon tetrachloride, 1,2-dichlorobenzene, 1,2-dichloroethane, tetrachloroethylene and 1-chlorobutane; furans, such as tetrahydrofuran; oxanes, such as 1,4-dioxane; and glycerin/glycerol. Particularly preferred examples of suitable non-aqueous solvents include non-aqueous solvents which also function as stabilizers, such as ethanol and acetone. As used herein, the term “biological contaminant or pathogen” is intended to mean a biological contaminant or pathogen that, upon direct or indirect contact with a biological material, may have a deleterious effect on the biological material or upon a recipient thereof. Such other biological contaminants or pathogens include the various viruses, bacteria (including inter- and intracellular bacteria, such as mycoplasmas, ureaplasmas, nanobacteria, chlamydia, rickettsias), yeasts, molds, fungi, prions or similar agents responsible, alone or in combination, for TSEs and/or single or multicellular parasites known to those of skill in the art to generally be found in or infect biological materials. Examples of other biological contaminants or pathogens include, but are not limited to, the following: viruses, such as human immunodeficiency viruses and other retroviruses, herpes viruses, filoviruses, circoviruses, paramyxoviruses, cytomegaloviruses, hepatitis viruses (including hepatitis A, B and C and variants thereof), pox viruses, toga viruses, Ebstein-Barr viruses and parvoviruses; bacteria, such as Escherichia, Bacillus, Campylobacter, Streptococcus and Staphatococcus; nanobacteria; parasites, such as Trypanosoma and malarial parasites, including Plasmodium species; yeasts; molds; fungi; mycoplasmas and ureaplasmas; chlamydia; rickettsias, such as Coxiella burnetii; and prions and similar agents responsible, alone or in combination, for one or more of the disease states known as transmissible spongiform encephalopathies (TSEs) in mammals, such as scrapie, transmissible mink encephalopathy, chronic wasting disease (generally observed in mule deer and elk), feline spongiform encephalopathy, bovine spongiform encephalopathy (mad cow disease), Creutzfeld-Jakob disease (including variant CJD), Fatal Familial Insomnia, Gerstmann-Straeussler-Scheinker syndrome, kuru and Alpers syndrome. As used herein, the term “active biological contaminant or pathogen” is intended to mean a biological contaminant or pathogen that is capable of causing a deleterious effect, either alone or in combination with another factor, such as a second biological contaminant or pathogen or a native protein (wild-type or mutant) or antibody, in the biological material and/or a recipient thereof. As used herein, the term “blood components” is intended to mean one or more of the components that may be separated from whole blood and include, but are not limited to, the following: cellular blood components, such as red blood cells, white blood cells and platelets; blood proteins, such as blood clotting factors, enzymes, albumin, plasminogen, fibrinogen and immunoglobulins; and liquid blood components, such as plasma, plasma protein fraction (PPF), cryoprecipitate, plasma fractions and plasma-containing compositions. As used herein, the term “cellular blood component” is intended to mean one or more of the components of whole blood that comprises cells, such as red blood cells, white blood cells, stem cells and platelets. As used herein, the term “blood protein” is intended to mean one or more of the proteins that are normally found in whole blood. Illustrative examples of blood proteins found in mammals, including humans, include, but are not limited to, the following: coagulation proteins, both vitamin K-dependent, such as Factor VII and Factor IX, and non-vitamin K-dependent, such as Factor VIII and von Willebrands factor; albumin; lipoproteins, including high density lipoproteins and low density lipoproteins; complement proteins; globulins, such as immunoglobulins IgA, IgM, IgG and IgE; and the like. A preferred group of blood proteins includes Factor I (fibrinogen), Factor II (prothrombin), Factor III (tissue factor), Factor V (proaccelerin), Factor VI (accelerin), Factor VII (proconvertin, serum prothrombin conversion), Factor VIII (antihemophiliac factor A), Factor IX (antihemophiliac factor B), Factor X (Stuart-Prower factor), Factor XI (plasma thromboplastin antecedent), Factor XII (Hageman factor), Factor XIII (protransglutamidase), von Willebrands factor (vWF), Factor Ia, Factor IIa, Factor IIIa, Factor Va, Factor VIa, Factor VIIa, Factor VIIIa, Factor IXa, Factor Xa, Factor XIa, Factor XIIa and Factor XIIIa. Another preferred group of blood proteins includes proteins found inside red blood cells, such as hemoglobin and various growth factors, and derivatives of these proteins. Yet another preferred group of blood proteins include proteins found in commercially available plasma protein fraction products, such as Plasma-Plex® (Centeon/Aventis Behring). Protenate® (Baxter Laboratories), Plasmanate® (Bayer Biological) and Plasmatein® (Alpha Therapeutic). As used herein, the term “liquid blood component” is intended to mean one or more of the fluid, non-cellular components of whole blood, such as plasma (the fluid, non-cellular portion of the whole blood of humans or animals as found prior to coagulation) and serum (the fluid, non-cellular portion of the whole blood of humans or animals as found after coagulation). As used herein, the term “a biologically compatible solution” is intended to mean a solution to which a biological material may be exposed, such as by being suspended or dissolved therein, and remain viable, i.e., retain its essential biological and physiological characteristics. As used herein, the term “a biologically compatible buffered solution” is intended to mean a biologically compatible solution having a pH and osmotic properties (e.g., tonicity, osmolality and/or oncotic pressure) suitable for maintaining the integrity of the material(s) therein. Suitable biologically compatible buffered solutions typically have a pH between 4 and 8.5 and are isotonic or only moderately hypotonic or hypertonic. Biologically compatible buffered solutions are known and readily available to those of skill in the art. As used herein, the term “stabilizer” is intended to mean a compound or material that reduces damage to the biological material being irradiated to a level that is insufficient to preclude the safe and effective use of the material. Illustrative examples of stabilizers include, but are not limited to, the following: antioxidants; free radical scavengers, including spin traps, such as tert-butyl-nitrosobutane (tNB), α-phenyl-tert-butylnitrone (PBN), 5,5-dimethylpyrroline-N-oxide (DMPO), tert-butylnitrosobenzene (BNB), α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) and 3,5-dibromo-4-nitroso-benzenesulphonic acid (DBNBS); combination stabilizers, i.e., stabilizers which are effective at quenching both Type I and Type II photodynamic reactions; and ligands, such as heparin, that stabilize the molecules to which they bind. Preferred examples of stabilizers include, but are not limited to, the following: ethanol; acetone; fatty acids, including 6,8-dimercapto-octanoic acid (lipoic acid) and its derivatives and analogues (alpha, beta, dihydro, bisno and tetranor lipoic acid), thioctic acid, 6,8-dimercapto-octanoic acid, dihydrolopoate (DL-6,8-dithioloctanoic acid methyl ester), lipoamide, bisonor methyl ester and tatranor-dihydrolipoic acid, furan fatty acids, oleic and linoleic and palmitic acids and their salts and derivatives; flavonoids, phenylpropanoids, and flavenols, such as quercetin, rutin and its derivatives, apigenin, aminoflavone, catechin, hesperidin and, naringin; carotenes, including beta-carotene; Co-Q10; xanthophylls; polyhydric alcohols, such as glycerol, mannitol; sugars, such as xylose, glucose, ribose, mannose, fructose and trehalose; amino acids and derivatives thereof, such as histidine, N-acetylcysteine (NAC), glutamic acid, tryptophan, sodium caprylate, N-acetyl tryptophan and methionine; azides, such as sodium azide; enzymes, such as Superoxide Dismutase (SOD) and Catalase; uric acid and its derivatives, such as 1,3-dimethyluric acid and dimethylthiourea; allopurinol; thiols, such as glutathione and reduced glutathione and cysteine; trace elements, such as selenium; vitamins, such as vitamin A, vitamin C (including its derivatives and salts such as sodium ascorbate and palmitoyl ascorbic acid) and vitamin E (and its derivatives and salts such as tocopherol acetate and alpha-tocotrienol); chromanol-alpha-C6; 6-hydroxy-2,5,7,8-tetramethylchroma-2 carboxylic acid (Trolox) and derivatives; extraneous proteins, such as gelatin and albumin: tris-3-methyl-1-phenyl-2-pyrazolin-5-one (MCI-186); citiolone; puercetin; chrysin; dimethyl sulfoxide (DMSO); piperazine diethanesulfonic acid (PIPES); imidazole; methoxypsoralen (MOPS); 1,2-dithiane-4,5-diol; reducing substances, such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT); cholesterol; probucol; indole derivatives; thimerosal; lazaroid and tirilazad mesylate; proanthenols; proanthocyanidins; ammonium sulfate; Pegorgotein (PEG-SOD); N-tert-butyl-alpha-phenylnitrone (PBN); 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (Tempol); mixtures of ascorbate, urate and Trolox C (Asc/urate/Trolox C); proteins and peptides, such as glycylglycine and carnosine, in which each amino acid may be in its D or L form; diosmin; pupurogalin; gallic acid and its derivatives including but not limited to propyl gallate, sodium formaldehyde sulfoxylate and silymarin. Particularly preferred examples include single stabilizers or combinations of stabilizers that are effective at quenching both Type I and Type II photodynamic reactions and volatile stabilizers, which can be applied as a gas and/or easily removed by evaporation, low pressure and similar methods. Such individual or combinations of stabilizers are referred to herein as “combination stabilizers”. As used herein, the term “residual solvent content” is intended to mean the amount or proportion of freely-available liquid in the biological material. Freely-available liquid means the liquid, such as water or an organic solvent (e.g., ethanol, isopropanol, acetone, polyethylene glycol, etc.), present in the biological material being sterilized that is not bound to or complexed with one or more of the non-liquid components of the material. Freely-available liquid includes intracellular water. The residual solvent contents related as water referenced herein refer to levels determined by the FDA approved, modified Karl Fischer method (Meyer and Boyd, Analytical Chem., 31:215-219, 1959; May, et al., J. Biol. Standardization, 10:249-259, 1982; Centers for Biologics Evaluation and Research, FDA, Docket No. 89D-0140, 83-93; 1990) or by near infrared spectroscopy. Quantitation of the residual levels of other solvents may be determined by means well known in the art, depending upon which solvent is employed. The proportion of residual solvent to solute may also be considered to be a reflection of the concentration of the solute within the solvent. When so considered, the greater the concentration of the solute, the lower the amount of residual solvent. As used herein, the term “sensitizer” is intended to mean a substance that selectively targets viral, bacterial, prion and/or parasitic contaminants, rendering them more sensitive to inactivation by radiation, therefore permitting the use of a lower rate or dose of radiation and/or a shorter time of irradiation than in the absence of the sensitizer. Illustrative examples of suitable sensitizers include, but are not limited to, the following: psoralen and its derivatives and analogs (including 3-carboethoxy psoralens); inactines and their derivatives and analogs; angelicins, khellins and coumarins which contain a halogen substituent and a water solubilization moiety, such as quaternary ammonium ion or phosphonium ion; nucleic acid binding compounds; brominated hematoporphyrin; phthalocyanines; purpurins; porphorins; halogenated or metal atom-substituted derivatives of dihematoporphyrin esters, hematoporphyrin derivatives, benzoporphyrin derivatives, hydrodibenzoporphyrin dimaleimade, hydrodibenzoporphyrin, dicyano disulfone, tetracarbethoxy hydrodibenzoporphyrin, and tetracarbethoxy hydrodibenzoporphyrin dipropionamide; doxorubicin and daunomycin, which may be modified with halogens or metal atoms; netropsin; BD peptide, S2 peptide; S-303 (ALE compound); dyes, such as hypericin, methylene blue, eosin, fluoresceins (and their derivatives), flavins, merocyanine 540; photoactive compounds, such as bergapten; and SE peptide. In addition, atoms which bind to prions, and thereby increase their sensitivity to inactivation by radiation, may also be used. An illustrative example of such an atom would be the Copper ion, which binds to the prior protein and, with a Z number higher than the other atoms in the protein, increases the probability that the prion protein will absorb energy during irradiation, particularly gamma irradiation. As used herein, the term “proteinaceous material” is intended to mean any material derived or obtained from a living organism that comprises at least one protein or peptide. A proteinaceous material may be a naturally occurring material, either in its native state or following processing/purification and/or derivatization, or an artificially produced material, produced by chemical synthesis or recombinant/transgenic technology and, optionally, process/purified and/or derivatized. Illustrative examples of proteinaceous materials include, but are not limited to, the following: proteins and peptides produced from cell culture; milk and other dairy products; ascites; hormones; growth factors; materials, including pharmaceuticals, extracted or isolated from animal tissue, such as heparin and insulin, or plant matter; plasma, including fresh, frozen and freeze-dried, and plasma protein fraction; fibrinogen and derivatives thereof, fibrin, fibrin I, fibrin II, soluble fibrin and fibrin monomer, and/or fibrin sealant products; whole blood; protein C; protein S; alpha-1 anti-trypsin (alpha-1 protease inhibitor); butyl-cholinesterase; anticoagulants, such as coumarin drugs (warfarin); streptokinase; tissue plasminogen activator (tPA); erythropoietin (EPO); urokinase; neupogen; anti-thrombin-3; alpha-glucosidase: (fetal) bovine serum/horse serum; meat; immunoglobulins, including anti-sera, monoclonal antibodies, polyclonal antibodies and genetically engineered or produced antibodies; albumin; alpha-globulins; beta-globulins; gamma-globulins; coagulation proteins; complement proteins; and interferons. As used herein, the term “radiation” is intended to mean radiation of sufficient energy to sterilize at least some component of the irradiated biological material. Types of radiation include, but are not limited to, the following: (i) corpuscular (streams of subatomic particles such as neutrons, electrons, and/or protons); (ii) electromagnetic (originating in a varying electromagnetic field, such as radio waves, visible (both mono and polychromatic) and invisible light, infrared, ultraviolet radiation, x-radiation, and gamma rays and mixtures thereof); and (iii) sound and pressure waves. Such radiation is often described as either ionizing (capable of producing ions in irradiated materials) radiation, such as gamma rays, and non-ionizing radiation, such as visible light. The sources of such radiation may vary and, in general, the selection of a specific source of radiation is not critical provided that sufficient radiation is given in an appropriate time and at an appropriate rate to effect sterilization. In practice, gamma radiation is usually produced by isotopes of Cobalt or Cesium, while UV and X-rays are produced by machines that emit UV and X-radiation, respectively, and electrons are often used to sterilize materials in a method known as “E-beam” irradiation that involves their production via a machine. Visible light, both mono- and polychromatic, is produced by machines and may, in practice, be combined with invisible light, such as infrared and UV, that is produced by the same machine or a different machine. As used herein, the term “to protect” is intended to mean to reduce any damage to the biological material being irradiated, that would otherwise result from the irradiation of that material, to a level that is insufficient to preclude the safe and effective use of the material following irradiation. In other words, a substance or process “protects” a biological material from radiation if the presence of that substance or carrying out that process results in less damage to the material from irradiation than in the absence of that substance or process. Thus, biological material may be used safely and effectively after irradiation in the presence of a substance or following performance of a process that “protects” the material, but could not be used safely and effectively after irradiation under identical conditions but in the absence of that substance or the performance of that process. As used herein, an “acceptable level” of damage may vary depending upon certain features of the particular method(s) of the present invention being employed, such as the nature and characteristics of the particular biological material and/or non-aqueous solvent(s) being used, and/or the intended use of the biological material being irradiated, and can be determined empirically by one skilled in the art. An “unacceptable level” of damage would therefore be a level of damage that would preclude the safe and effective use of the biological material being sterilized. The particular level of damage in a given biological material may be determined using any of the methods and techniques known to one skilled in the art. B. Particularly Preferred Embodiments A first preferred embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising irradiating the biological material with radiation for a time effective to sterilize the material at a rate effective to sterilize the material and to protect the material from radiation. Another preferred embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) adding to a biological material at least one stabilizer in an amount effective to protect the biological material from radiation; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the material. Another preferred embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) reducing the residual solvent content of a biological material to a level effective to protect the biological material from radiation; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the biological material. Another preferred embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) reducing the temperature of a biological material to a level effective to protect the biological material from radiation; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the biological material. Another preferred embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) applying to the biological material a stabilizing process selected from the group consisting of: (a) reducing the residual solvent content of a biological material, (b) adding to the biological material at least one stabilizer, and (c) reducing the temperature of the biological material; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the biological material, wherein the stabilizing process and the rate of irradiation are together effective to protect the biological material from radiation. Another preferred embodiment of the present invention is directed to a method for sterilizing a biological material that is sensitive to radiation and contains a non-aqueous solvent comprising: (i) applying to the biological material at least two stabilizing processes selected from the group consisting of: (a) reducing the residual solvent content of a biological material, (b) adding to the biological material at least one stabilizer, and (c) reducing the temperature of the biological material; and (ii) irradiating the biological material with radiation at an effective rate for a time effective to sterilize the biological material, wherein the stabilizing processes may be performed in any order and are together effective to protect the biological material from radiation. Another preferred embodiment of the present invention is directed to a composition comprising a biological material and a non-aqueous solvent in an amount effective to preserve the preparation during sterilization with radiation, such that it remains suitable and effective for its intended use. Another preferred embodiment of the present invention is directed to a composition comprising at least one biological material, a least one non-aqueous solvent and at least one stabilizer, wherein the non-aqueous solvent and stabilizer are together present in an amount effective to preserve the material for its intended use following sterilization with radiation. The non-aqueous solvent is preferably a non-aqueous solvent that is not prone to the formation of free-radicals upon irradiation, and more preferably a non-aqueous solvent that is not prone to the formation of free-radicals upon irradiation and that has little or no dissolved oxygen or other gas(es) that is (are) prone to the formation of free-radicals upon irradiation. Volatile non-aqueous solvents are particularly preferred, even more particularly preferred are non-aqueous solvents that are stabilizers, such as ethanol and acetone. According to certain embodiments of the present invention, the biological material may contain a mixture of water and a non-aqueous solvent, such as ethanol and/or acetone. In such embodiments, the non-aqueous solvent(s) is preferably a non-aqueous solvent that is not prone to the formation of free-radicals upon irradiation, and most preferably a non-aqueous solvent that is not prone to the formation of free-radicals upon irradiation and that has little or no dissolved oxygen or other gas(es) that is (are) prone to the formation of free-radicals upon irradiation. Volatile non-aqueous solvents are particularly preferred, even more particularly preferred are non-aqueous solvents that are stabilizers, such as ethanol and acetone. According to certain methods of the present invention, a stabilizer is added prior to irradiation of the biological material which contains a non-aqueous solvent with radiation. This stabilizer is preferably added to the biological material which contains a non-aqueous solvent in an amount that is effective to protect the biological material from the radiation. Alternatively, the stabilizer is added to the biological material which contains a non-aqueous solvent in an amount that, together with the non-aqueous solvent, is effective to protect the biological material from the radiation. Suitable amounts of stabilizer may vary depending upon certain features of the particular method(s) of the present invention being employed, such as the particular stabilizer being used and/or the nature and characteristics of the particular biological material which contains a non-aqueous solvent being irradiated and/or its intended use, and can be determined empirically by one skilled in the art. According to certain methods of the present invention, the residual solvent content of the biological material which contains a non-aqueous solvent is reduced prior to irradiation of the biological material with radiation. The residual solvent content is preferably reduced to a level that is effective to protect the biological material from the radiation. Suitable levels of residual solvent content may vary depending upon certain features of the particular method(s) of the present invention being employed, such as the nature and characteristics of the particular biological material which contains a non-aqueous solvent being irradiated and/or its intended use, and can be determined empirically by one skilled in the art. There may be biological materials for which it is desirable to maintain the residual solvent content to within a particular range, rather than a specific value. According to certain embodiments of the present invention, when the biological material which contains a non-aqueous solvent also contains water, the residual solvent (water) content of a biological material may be reduced by dissolving or suspending the biological material which contains a non-aqueous solvent in a non-aqueous solvent that is capable of dissolving water. When the biological material is in liquid phase, the same result may also be achieved by the dilution of the residual solvent (water) by the addition of liquid non-aqueous solvent. Preferably, such a second non-aqueous solvent is not prone to the formation of free-radicals upon irradiation and has little or no dissolved oxygen or other gas(es) that is (are) prone to the formation of free-radicals upon irradiation. When the biological material which contains a non-aqueous solvent is in a liquid phase, reducing the residual solvent content may be accomplished by any of a number of means, such as by increasing the solute concentration. In this manner, the concentration of protein in the biological material which contains a non-aqueous solvent dissolved within the solvent may be increased to generally at least about 0.5%, typically at least about 1%, usually at least about 5%, preferably at least about 10%, more preferably at least about 15%, even more preferably at least about 20%, still even more preferably at least about 25%, and most preferably at least about 50%. In certain embodiments of the present invention, the residual solvent content of a particular biological material which contains a non-aqueous solvent may be found to lie within a range, rather than at a specific point. Such a range for the preferred residual solvent content of a particular biological material which contains a non-aqueous solvent may be determined empirically by one skilled in the art. While not wishing to be bound by any theory of operability, it is believed that the reduction in residual solvent content reduces the degrees of freedom of the biological material which contains a non-aqueous solvent, reduces the number of targets for free radical generation and may restrict the solubility of these free radicals. Similar results might therefore be achieved by lowering the temperature of the biological material which contains a non-aqueous solvent below its eutectic point or below its freezing point, or by vitrification to likewise reduce the degrees of freedom of the biological material. These results may permit the use of a higher rate and/or dose of radiation than might otherwise be acceptable. Thus, the methods described herein may be performed at any temperature that doesn't result in unacceptable damage to the biological material which contains a non-aqueous solvent, i.e., damage that would preclude the safe and effective use of the biological material. Preferably, the methods described herein are performed at ambient temperature or below ambient temperature, such as below the eutectic point or freezing point of the biological material which contains a non-aqueous solvent being irradiated. The residual solvent content of the biological material which contains a non-aqueous solvent may be reduced by any of the methods and techniques known to those skilled in the art for reducing solvent from a biological material which contains a non-aqueous solvent without producing an unacceptable level of damage to the biological material. Such methods include, but are not limited to, addition of solute, evaporation, concentration, centrifugal concentration, vitrification and spray-drying. A particularly preferred method for reducing the residual solvent content of a biological material which contains a non-aqueous solvent is lyophilization. Another particularly preferred method for reducing the residual solvent content of a biological material which contains a non-aqueous solvent is the addition of solute. Another particularly preferred method for reducing the residual solvent content of a biological material which contains a non-aqueous solvent is spray-drying. Another particularly preferred method for reducing the residual solvent content of a biological material which contains a non-aqueous solvent is vitrification, which may be accomplished by any of the methods and techniques known to those skilled in the art, including the addition of solute and or additional solutes, such as sucrose, to raise the eutectic point of the biological material which contains a non-aqueous solvent, followed by a gradual application of reduced pressure to the biological material which contains a non-aqueous solvent in order to remove the residual solvent. The resulting glassy material will then have a reduced residual solvent content. According to certain methods of the present invention, the biological material which contains a non-aqueous solvent to be sterilized may be immobilized upon a solid surface by any means known and available to one skilled in the art. For example, the biological material which contains a non-aqueous solvent to be sterilized may be present as a coating or surface on a biological or non-biological substrate. The radiation employed, in the methods of the present invention may be any radiation effective for the sterilization of the biological material which contains a non-aqueous solvent being treated. The radiation may be corpuscular, including E-beam radiation. Preferably the radiation is electromagnetic radiation, including x-rays, infrared, visible light, UV light and mixtures of various wavelengths of electromagnetic radiation. A particularly preferred form of radiation is gamma radiation. According to the methods of the present invention, the biological material which contains a non-aqueous solvent is irradiated with the radiation at a rate effective for the sterilization of the biological material, while not producing an unacceptable level of damage to that material. Suitable rates of irradiation may vary depending upon certain features of the methods of the present invention being employed, such as the nature and characteristics of the particular biological material, which may contain a non-aqueous solvent, being irradiated, the particular form of radiation involved and/or the particular biological contaminants or pathogens being inactivated. Suitable rates of irradiation can be determined empirically by one skilled in the art. Preferably, the rate of irradiation is constant for the duration of the sterilization procedure. When this is impractical or otherwise not desired, a variable or discontinuous irradiation may be utilized. According to the methods of the present invention, the rate of irradiation may be optimized to produce the most advantageous combination of product recovery and time required to complete the operation. Both low (≦3 kGy/hour) and high (>3 kGy/hour) rates may be utilized in the methods described herein to achieve such results. The rate of irradiation is preferably selected to optimize the recovery of the biological material which contains a non-aqueous solvent while still sterilizing the biological material which contains a non-aqueous solvent. Although reducing the rate of irradiation may serve to decrease damage to the biological material which contains a non-aqueous solvent, it will also result in longer irradiation times being required to achieve a particular desired total dose. A higher dose rate may therefore be preferred in certain circumstances, such as to minimize logistical issues and costs, and may be possible when used in accordance with the methods described herein for protecting a biological material which contains a non-aqueous solvent from irradiation. According to a particularly preferred embodiment of the present invention, the rate of irradiation is not more than about 3.0 kGy/hour, more preferably between about 0.1 kGy/hr and 3.0 kGy/hr, even more preferably between about 0.25 kGy/hr and 2.0 kGy/hour, still even more preferably between about 0.5 kGy/hr and 1.5 kGy/hr and most preferably between about 0.5 kGy/hr and 1.0 kGy/hr. According to another particularly preferred embodiment of the present invention, the rate of irradiation is at least about 3.0 kGy/hr, more preferably at least about 6 kGy/hr, even more preferably at least about 16 kGy/hr, and even more preferably at least about 30 kGy/hr and most preferably at least about 45 kGy/hr or greater. According to the methods of the present invention, the biological material which contains a non-aqueous solvent to be sterilized is irradiated with the radiation for a time effective for the sterilization of the biological material. Combined with irradiation rate, the appropriate irradiation time results in the appropriate dose of irradiation being applied to the biological material which contains a non-aqueous solvent. Suitable irradiation times may vary depending upon the particular form and rate of radiation involved and/or the nature and characteristics of the particular biological material which contains a non-aqueous solvent being irradiated. Suitable irradiation times can be determined empirically by one skilled in the art. According to the methods of the present invention, the biological material which contains a non-aqueous solvent to be sterilized is irradiated with radiation up to a total dose effective for the sterilization of the biological material, while not producing an unacceptable level of damage to that material. Suitable total doses of radiation may vary depending upon certain features of the methods of the present invention being employed, such as the nature and characteristics of the particular biological material which contains a non-aqueous solvent being irradiated, the particular form of radiation involved and/or the particular biological contaminants or pathogens being inactivated. Suitable total doses of radiation can be determined empirically by one skilled in the art. Preferably, the total dose of radiation is at least 25 kGy, more preferably at least 45 kGy, even more preferably at least 75 kGy, and still more preferably at least 100 kGy or greater, such as 150 kGy or 200 kGy or greater. The particular geometry of the biological material which contains a non-aqueous solvent being irradiated, such as the thickness and distance from the source of radiation, may be determined empirically by one skilled in the art. A preferred embodiment is a geometry that provides for an even rate of irradiation throughout the preparation. A particularly preferred embodiment is a geometry that results in a short path length for the radiation through the preparation, thus minimizing the differences in radiation dose between the front and back of the preparation. This may be further minimized in some preferred geometries, particularly those wherein the preparation has a constant radius about its axis that is perpendicular to the radiation source, by the utilization of a means of rotating the preparation about said axis. Similarly, according to certain methods of the present invention, an effective package for containing the preparation during irradiation is one which combines stability under the influence of irradiation, and which minimizes the interactions between the package and the radiation. Preferred packages maintain a seal against the external environment before, during and post-irradiation, and are not reactive with the preparation within, nor do they produce chemicals that may interact with the preparation within. Particularly preferred examples include but are not limited to containers that comprise glasses stable when irradiated, stoppered with stoppers made of rubber that is relatively stable during radiation and liberates a minimal amount of compounds from within, and sealed with metal crimp seals of aluminum or other suitable materials with relatively low Z numbers. Suitable materials can be determined by measuring their physical performance, and the amount and type of reactive leachable compounds post-irradiation and by examining other characteristics known to be important to the containment of biological materials empirically by one skilled in the art. According to certain methods of the present invention, an effective amount of at least one sensitizing compound may optionally be added to the biological material which contains a non-aqueous solvent prior to irradiation, for example to enhance the effect of the irradiation on the biological contaminant(s) or pathogen(s) therein, while employing the methods described herein to minimize the deleterious effects of irradiation upon the biological material. Suitable sensitizers are known to those skilled in the art, and include psoralens and their derivatives and inactines and their derivatives. According to the methods of the present invention, the irradiation of the biological material which contains a non-aqueous solvent may occur at any temperature that is not deleterious to the biological material being sterilized. According to one preferred embodiment, the biological material which contains a non-aqueous solvent is irradiated at ambient temperature. According to an alternate preferred embodiment, the biological material which contains a non-aqueous solvent is irradiated at reduced temperature, i.e., a temperature below ambient temperature, such as 0° C., −20° C., −40° C., −60° C., −78° C. or −196° C. According to this embodiment of the present invention, the biological material which contains a non-aqueous solvent is preferably irradiated at or below the freezing or eutectic point of the biological material. According to another alternate preferred embodiment, the biological material which contains a non-aqueous solvent is irradiated at elevated temperature, i.e., a temperature above ambient temperature, such as 37° C., 60° C., 72° C. or 80° C. While not wishing to be bound by any theory, the use of elevated temperature may enhance the effect of irradiation on the biological contaminant(s) or pathogen(s) and therefore allow the use of a lower total dose of radiation. Most preferably, the irradiation of the biological material which contains a non-aqueous solvent occurs at a temperature that protects the preparation from radiation. Suitable temperatures can be determined empirically by one skilled in the art. In certain embodiments of the present invention, the temperature at which irradiation is performed may be found to lie within a range, rather than at a specific point. Such a range for the preferred temperature for the irradiation of a particular biological material which contains a non-aqueous solvent may be determined empirically by one skilled in the art. According to the methods of the present invention, the irradiation of the biological material which contains a non-aqueous solvent may occur at any pressure which is not deleterious to the biological material which contains a non-aqueous solvent being sterilized. According to one preferred embodiment, the biological material which contains a non-aqueous solvent is irradiated at elevated pressure. More preferably, the biological material which contains a non-aqueous solvent is irradiated at elevated pressure due to the application of sound waves or the use of a volatile. While not wishing to be bound by any theory, the use of elevated pressure may enhance the effect of irradiation on the biological contaminant(s) or pathogen(s) and/or enhance the protection afforded by one or more stabilizers, and therefore allow the use of a lower total dose of radiation. Suitable pressures can be determined empirically by one skilled in the art. Generally, according to the methods of the present invention, the pH of the biological material which contains a non-aqueous solvent undergoing sterilization is about 7. In some embodiments of the present invention, however, the biological material which contains a non-aqueous solvent may have a pH of less than 7, preferably less than or equal to 6, more preferably less than or equal to 5, even more preferably less than or equal to 4, and most preferably less than or equal to 3. In alternative embodiments of the present invention, the biological material which contains a non-aqueous solvent may have a pH of greater than 7, preferably greater than or equal to 8, more preferably greater than or equal to 9, even more preferably greater than or equal to 10, and most preferably greater than or equal to 11. According to certain embodiments of the present invention, the pH of the preparation undergoing sterilization is at or near the isoelectric point of one of the components of the biological material. Suitable pH levels can be determined empirically by one skilled in the art. Similarly, according to the methods of the present invention, the irradiation of the biological material which contains a non-aqueous solvent may occur under any atmosphere that is not deleterious to the biological material being treated. According to one preferred embodiment, the biological material which contains a non-aqueous solvent is held in a low oxygen atmosphere or an inert atmosphere. When an inert atmosphere is employed, the atmosphere is preferably composed of a noble gas, such as helium or argon, more preferably a higher molecular weight noble gas, and most preferably argon. According to another preferred embodiment, the biological material which contains a non-aqueous solvent is held under vacuum while being irradiated. According to a particularly preferred embodiment of the present invention, a biological material which contains a non-aqueous solvent (lyophilized, liquid or frozen) is stored under vacuum or an inert atmosphere (preferably a noble gas, such as helium or argon, more preferably a higher molecular weight noble gas, and most preferably argon) prior to irradiation. According to an alternative preferred embodiment of the present invention, a liquid biological material which contains a non-aqueous solvent is held under low pressure, to decrease the amount of gas, particularly oxygen, dissolved in the liquid, prior to irradiation, either with or without a prior step of solvent reduction, such as lyophilization. Such degassing may be performed using any of the methods known to one skilled in the art. In another preferred embodiment, where the biological material which contains a non-aqueous solvent contains oxygen or other gases dissolved within or associated with it, the amount of these gases within or associated with the preparation may be reduced by any of the methods and techniques known and available to those skilled in the art, such as the controlled reduction of pressure within a container (rigid or flexible) holding the preparation to be treated or by placing the preparation in a container of approximately equal volume. In certain embodiments of the present invention, when the biological material which contains a non-aqueous solvent to be treated is a tissue, at least one stabilizer is introduced according to any of the methods and techniques known and available to one skilled in the art, including soaking the tissue in a solution containing the stabilizer(s), preferably under pressure, at elevated temperature and/or in the presence of a penetration enhancer, such as dimethylsulfoxide. Other methods of introducing at least one stabilizer into a tissue include, but are not limited to, applying a gas containing the stabilizer(s), preferably under pressure and/or at elevated temperature, injection of the stabilizer(s) or a solution containing the stabilizer(s) directly into the tissue, placing the tissue under reduced pressure and then introducing a gas or solution containing the stabilizer(s) and combinations of two or more of these methods. One or more sensitizers may also be introduced into a tissue according to such methods. It will be appreciated that the combination of one or more of the features described herein may be employed to further minimize undesirable effects upon the biological material which contains a non-aqueous solvent caused by irradiation, while maintaining adequate effectiveness of the irradiation process on the biological contaminant(s) or pathogen(s). For example, in addition to the use of a stabilizer, a particular biological material which contains a non-aqueous solvent may also be lyophilized, held at a reduced temperature and kept under vacuum prior to irradiation to further minimize undesirable effects. The sensitivity of a particular biological contaminant or pathogen to radiation is commonly calculated by determining the dose necessary to inactivate or kill all but 37% of the agent in a sample, which is known as the D37 value. The desirable components of a biological material may also be considered to have a D37 value equal to the dose of radiation required to eliminate all but 37% of their desirable biological and physiological characteristics. In accordance with certain preferred methods of the present invention, the sterilization of a biological material which contains a non-aqueous solvent is conducted under conditions that result in a decrease in the D37 value of the biological contaminant or pathogen without a concomitant decrease in the D37 value of the biological material. In accordance with other preferred methods of the present invention, the sterilization of a biological material which contains a non-aqueous solvent is conducted under conditions that result in an increase in the D37 value of the material. In accordance with the most preferred methods of the present invention, the sterilization of a biological material which contains a non-aqueous solvent is conducted under conditions that result in a decrease in the D37 value of the biological contaminant or pathogen and a concomitant increase in the D37 value of the biological material. The following examples are illustrative, but not limiting, of the present invention. Other suitable modifications and adaptations are of the variety normally encountered by those skilled in the art and are fully within the spirit and scope of the present invention. Unless otherwise noted, all irradiation was accomplished using a 60Co source. In this experiment, the effect of gamma radiation on dried urokinase suspended in polypropylene glycol (PPG) 400 or phosphate buffered saline (PBS) was determined. Method Six 1.5 ml polypropylene microfuge tubes containing urokinase and PPG400 (tubes 2 and 5), PBS (tubes 3 and 6) or dry urokinase alone (tubes 1 and 4) were prepared as indicated in the table below. Tubes 4-6 were gamma irradiated at 45 kGy (1.9 kGy/hr) at 4° C. Tubes 1-3 were controls (4° C.). weightof dryvolumeurokinasePPG400volumeTubeSample(mg)(ul)PBS (ul)1dry urokinase alone3.2002urokinase suspended in PPG4003.1612603urokinase suspended in PBS3.0801234dry urokinase alone3.38005urokinase suspended in PPG4003.313206urokinase suspended in PBS3.520141 After irradiation, the samples were centrifuged at room temperature for 5 minutes at 14 k RPM. PPG400 solvent was removed from tubes 2 and 5 and 120 μl PBS were added to those two tubes. 128 μl and 135 μl PBS were added to tubes 1 and 4, respectively (urokinase concentration of 40,000 IU/ml). All samples were then diluted 50-fold with PBS and absorbance at 280 nm was determined. 50 μl of each diluted sample were then added to a 96-well microtiter plate, followed by 50 μl of 3 mM substrate in 2× assay buffer. The plates were incubated at 37° C. with shaking and absorption read at both 405 and 620 nm every 20 minutes beginning 5 minutes after substrate addition. The absorption at 630 nm (background) was subtracted from the value at 405 nm to obtain a corrected absorption value. The final concentration of urokinase was 1000 IU/ml. Materials Urokinase—Sigma cat. # U-5004, lot 29H1054; 2.5 mg=4000 IU Urokinase. PPG400—Fluka cat. # 81350. Substrate—urokinase substrate 1, colormetric—Calbiochem. cat. # 672157, lot B23901, 5 mg vials, final concentration 1.5 mM. 2× Assay Buffer—100 mM Tris (pH 8.8), 100 mM NaCl, 0.2% PEG8000. Results Urokinase suspended in PPG400 and then gamma irradiated to a total dose of 45 kGy maintained the same percent activity as gamma irradiated dry powder urokinase (80%). In contrast, urokinase suspended in PBS subjected to the same gamma irradiation maintained only 6% activity. The results of this experiment are presented in FIG. 1. In this experiment, the activity (as shown by the ability to bind antigen) of immobilized anti-insulin monoclonal antibody was determined after irradiation in the presence of various forms of polypropylene glycol (molecular weights of 400, 1200 and 2000). Method In two 96-well microliter plates (falcon plates—ProBind polystyrene cat. # 353915), the wells were washed four times with full volume PBS (pH 7.4). Once the two plates were prepared as described above, they were coated with 100 μl/well of freshly prepared 2 μg/ml anti-insulin in coating buffer and left overnight at 4° C. The plates were then washed briefly three times with PBS (pH 7.4) and 100 μl of PPG400, PPG1200 or PPG2000 were added to specific wells. Each solution was prepared in a 11, i.e., 2-fold, dilution series with PBS. Both plates were covered tightly with a cap mat (Greiner cap mat cat. # 381070 (USA Scientific)) and irradiated at either 0 kGy/hr or 45 kGy (1.92 kGy/hr), both at 4° C. Following irradiation, approximately 380 μl full volume blocking buffer were then added to all wells and the plates were incubated for two hours at 37° C. The plates were washed four times with TBST and 100 μl of 50 ng/ml biotin-labelled insulin in binding buffer were added to each well. The plates were covered with a plate sealer (Dynatech acetate plate sealers) and incubated at 37° C. with shaking (LabLine Titer Plate Shaker set at 3) for 1.5 hours. The plates were washed four times with TBST and 100 μl of 0.5 μg/ml phosphatase-labelled streptavidin in binding buffer were added to each well. The plates were covered with a plate sealer and incubated at 37° C. for one hour with shaking. The plates were then washed four times with TBST and 100 μl of 1 mg/ml phosphatase substrate in DEA buffer were added to each well and the plates were incubated at 37° C. with shaking. Absorption was read at both 405 and 620 nm at 5 minute intervals as needed. The absorption at 630 nm (background) was subtracted from the value at 405 nm to obtain a corrected absorption value. Materials Blocking buffer—2% BSA/PBS (pH 7.4). TBST—Tris Buffered Saline (pH 7.4) with 0.05% Tween 20. Biotin-Labelled Insulin—from bovine pancreas—Sigma 1-2258 lot 110H8065, 5 mg insulin, 1.2 mol. FITC per mol, insulin, reconstituted in 5 ml sterile water at 1.0 mg/ml stored at 4° C. Binding Buffer—0.25% BSA/PBS (pH 7.4). Phosphatase-Labelled Streptavidin—KPL cat. # 15-30-00; 05 mg/ml in 50% glycerol/H2O (stock diluted 1:1000). DEA Buffer—per 1 L-97 ml diethanolamine (Sigma D-8885), 0.1 g MgCl2.6H2O, 0.02% sodium azide, stored at 4° C. Phosphatase Substrate—p-nitrophenyl phosphate—Sigma 104-105, 5 mg/tablet. The phosphatase substrate was prepared fresh as a 1 mg/ml solution in phosphatase substrate buffer, i.e., DEA buffer. The solution is light sensitive so it had to be stored in the dark until ready to dispense. Monoclonal IgG1 anti-Human Insulin—Biodesign Int. cat. # E86102M, lot 8J2877. Coating Buffer—carbonate/bicarbonate (pH 9.4). Polypropylene glycol P400—Fluka cat. # 81350. Polypropylene glycol P1200—Fluka cat. # 81370. Polypropylene glycol P2000—Fluka cat. # 81380. Results Irradiated samples containing PPG exhibited approximately 50-63% of binding activity of unirradiated control. In contrast, irradiated samples containing PBS exhibited no binding activity. The results are presented in FIG. 2. In this experiment, liquid thrombin containing 50% glycerol and spiked with porcine parvovirus (PPV) was irradiated to varying total doses of radiation. Method 1. Add 100 μl 100% glycerol, 20 μl thrombin (100 U/ml thrombin) spiked with 50 μl PPV and optionally 20 μl (200 mM) sodium ascorbate as a stabilizer (adjusted to a total volume of 1 ml with H2O) to Wheaton 3 ml tubes (in duplicate), and irradiate to a total dose of 10, 30 or 45 kGy at 1.8 kGy/hr at 4° C. 2. Label and seed 96-well cell culture plates to allow at least 4 well per dilution (seeding to be done one day before inoculation). Add 200 μl of cell suspension per well at a concentration of 4×104/ml. The same cell culture medium is used for cell growth and maintenance after virus inoculation. 3. Perform virus inoculation when the cells sheets are 70-90% confluent. In this experiment 800 μl PK-13 growth media was added to 200 μl samples first. 4. Make appropriate dilution (1:5) of samples with PK-13 growth media, then filter sterilize each sample using low-protein-binding disc filters. 5. Add 50 μl of the pre-diluted sample to column 1 of a 96-well plate. In column 1 mix the medium and the sample together by pipetting up and down 4-5 times. With fresh tips transfer the necessary amount (50 μl) to the next column and repeat the mixing process. Empty all the liquid out of the tips and using the same set of tips, transfer the sample to the next column. Repeat this process in each column until column 12 is reached. When the sample in column 12 is mixed, empty the liquid out of the tips, withdraw the sample amount and dispose of this extra liquid in a waste bottle. This gives you 12 samples dilutions. 6. Return plates to the incubator at 37° C. 7. Observe microscopically and record the cytopathic effect in inoculated cultures on day 4-5 and day 7. The TCID50 is calculated from CPE reading according to the method of Kärber. 8. Positive controls were done by adding 50 μl PPV infecting stock, and negative controls were done by adding 50 μl PK-13 growth media followed by serial 1:5 dilutions.Materials Wheaton tubes—glass serum vials, Wheaton # 223684, lot # 1154132-02. Thrombin—bovine origin, 5000 US Units (5000 U/ml stock). Sodium Ascorbate—Aldrich Chem. Co. cat. # 26,855-0 (Milw, Wis. 53201). Porcine Parvovirus (PPV)—ATCC # VR-742; PPV infecting stock was prepared by PEG8000 preparation wherein ⅕ volume of PEG8000 (20% in 2.5 M NaCl) was added to PPV and incubated at refrigerated temperatures for 24 hours after which, PPV was pelleted by 15,000 rpm for 45 minutes in a Beckman SW-28 rotor, and resuspended in 1/10 volume of PEG buffer. PPV titer of porcine parvovirus was determined by TCID50 and was about 9.0 log/ml (032301 stock). PPV spike ratio was 1:4 (50 μl PPV stock mixed with 150 μl protein solution) into liquid thrombin. PEG Buffer—0.1 M NaCl, 0.01 M Tris (pH 7.4), 1 mM EDTA. Siliconized stoppers were used in the experiment obtained from American Stemli (Princeton, N.J.), 6720GC rubber formulation, lot # G009/7202. Cells—PK-13 (ATCC # CRL-6489), passage # 14. Cells are maintained in PK-13 growth medium (Dulbecco's modified Eagle medium supplemented with 10% FBS and 1× pencillin/streptomycin/L-glutamine). Results TCID50 TiterSampleper 0.05 mlLog Reduction0 kGy/+200 mM sodium ascorbate6.290 kGy/no stabilier6.37510 kGy/+200 mM sodium ascorbate4.971.3210 kGy/no stabilizer2.973.40530 kGy/+200 mM sodium ascorbate3.053.2430 kGy/no stabilizer2.354.02545 kGy/+200 mM sodium ascorbate3.053.2445 kGy/no stabilizer3.053.325 With a 10 kGy total dose, there was a 1.32 log and a 3.405 log reduction in PPV levels in the presence and absence of sodium ascorbate, respectively. Similarly, with a 30 kGy total dose, there was a 3.24 log and a 4.025 log reduction in PPV levels in the presence or absence, respectively, of sodium ascorbate. With a 45 kGy total dose, there was a 3.24 log and a 3.325 log reduction in PPV levels with or without ascorbate, respectively. This experiment demonstrates that inactivation of even small non-enveloped viruses is effective in the presence of a non-aqueous solvent both with and without an effective stabilizer. In this experiment, trypsin suspended in polypropylene glycol 400 was subjected to gamma irradiation at varying levels of residual solvent (water) content. Method Trypsin was suspended in polypropylene glycol 400 at a concentration of about 20,000 U/ml and divided into multiple samples. A fixed amount of water (0%, 1%, 2.4%, 4.8%, 7%, 9%, 10%, 20%, 33%) was added to each sample; a 100% water sample was also prepared which contained no PPG 400. Samples were irradiated to a total dose of 45 kGy at a rate of 1.9 kGy/hr and a temperature of 4° C. Following irradiation, each sample was centrifuged to pellet the undissolved trypsin. The PPG/water soluble fraction was removed and the pellets resuspended in water alone for activity testing. Assay conditions: 5 U/well trypsin (50 U/ml)+BAPNA substrate (0.5 mg/ml) was serially diluted 3-fold down a 96-well plate. The assay was set up in two 96-well plates and absorption read at both 405 and 620 nm at 5 and 20 minutes. The absorption at 630 nm (background) was subtracted from the value at 405 nm to obtain a corrected absorption value. The change in this value over time between 5 and 15 minutes of reaction time was plotted and Vmax and Km determined in Sigma Plot using the hyperbolic rectangular equation). Results The irradiated samples containing a mixture of polypropylene glycol (PPG 400) and water (up to 33% water) retained about 80% of the activity of an unirradiated trypsin control and activity equal to that of a dry (lyophilized) trypsin control irradiated under identical conditions. No activity was detected in the 100% water sample irradiated to 45 kGy. The results of this experiment are shown graphically in FIG. 3. In this experiment, porcine heart valves were gamma irradiated in the presence of polypropylene glycol 400 (PPG400) and, optionally, a scavenger, to a total dose of 30 kGy (1.584 kGy/hr at −20° C.). Materials: Tissue—Porcine Pulmonary Valve (PV) Heart valves were harvested prior to use and stored. Tissue Preparation Reagents— Polypropylene Glycol 400. Fluka, cat# 81350 lot# 386716/1 Trolox C. Aldrich, cat# 23,881-3 lot#02507TS Coumaric Acid. Sigma, cat# C-9008 lot# 49H3600 n-Propyl Gallate. Sigma, cat# P-3130 lot# 117H0526 α-Lipoic Acid. CalBiochem, cat# 437692 lot#B34484 Dulbecco's PBS. Gibco BRL cat# 14190-144 lot# 1095027 2.0 ml Screw Cap tubes. VWR Scientific Products, cat# 20170-221 lot# 0359Tissue Hydrolysis Reagents— Nerl H2O, NERL Diagnostics cat# 9800-5 lot# 03055151 Acetone. EM Science cat# AX0125-5, lot# 37059711 6 N constant boiling HCl. Pierce cat# 24309, lot# BA42184 Int-Pyd (Acetylated Pyridinoline) HPLC Internal Standard. Metra Biosystems Inc. cat# 8006, lot# 9 Hydrochloric Acid. VWR Scientific cat# VW3110-3, lot# n/a Heptafluorobutyric Acid (HFBA) Sigma cat# H-7133, lot# 20K3482 FW 214.0 store at 2-8° C. SP-Sephadex C-25 resin. Pharmacia cat# 17-0230-01, lot# 247249 (was charged with NaCl as per manufacturer suggestion)Hydrolysis vials—10 mm×100 mm vacuum hydrolysis tubes. Pierce cat# 29560, lot #BB627281Heating module—Pierce, Reacti-therm. Model# 18870, S/N 1125000320176Savant—Savant Speed Vac System: 1. Speed Vac Model SC110, model # SC110-120, serial # SC110-SD171002-1H a. Refrigerated Vapor Trap Model RVT100, model # RVT100-120V, serial # RVT100-58010538-1B b. Vacuum pump, VP 100 Two Stage Pump Model VP100, serial # 93024Column—Phenomenex, Luna 5μ C18(2) 100 Å, 4.6×250 mm. Part # 00G-4252-E0, S/N#68740-25, B/N# 5291-29HPLC System: Shimadzu System Controller SCL-10A Shimadzu Automatic Sample Injector SIL-10A (50 μl loop) Shimadzu Spectrofluorometric Detector RF-10A Shimadzu Pumps LC-10AD Software—Class-VP version 4.1Low-binding tubes—MiniSorp 100×15 Nunc-Immunotube. Batch # 042950, cat# 468608Methods:A. Preparation of Stabilizer Solutions:Trolox C: MW=250; therefore, want 250 mg/ml for 1M or 125 mg/ml for 0.5 M actual weight=250.9 mg 250÷125 mg/ml=2.0 mlNot soluble; therefore an additional 2 ml of PPG was added. After water bath sonication and time, Trolox C is soluble at 125 mM.Coumaric Acid: MW=164; therefore, 164 mg/ml for 1 M actual weight=164.8 mg 164.8 mg÷164 mg/ml=1.0 mlWater bath sonicated for approximately 15 minutes—not 100% soluble. An additional 1 ml PPG was added and further water bath sonicated.n-Propyl Gallate: MW=212.2; therefore, 212 mg/ml for 1M or 106 mg/ml for 0.5 M actual weight=211.9 mg 211.9 mg÷106 mg/ml=2.0 mlSoluble after a 20-30 minute water bath sonication.1 M α-Lipoic Acid: MW=206; therefore, 206 mg/ml actual weight=412 mg 412 mg÷206 mg/ml=2.0 mlVery soluble after 10 minute water bath sonication. Final Stocks of Scavengers: 125 mM Trolox C—4 ml 1 M Lipoic Acid—2 ml 0.5 M Coumaric acid—2 ml 0.5 M n-Propyl Gallate—2 mlB. Treatment of Valves Prior to Gamma-Irradiation. 1. PV heart valves were thawed on wet ice. 2. Cusps were dissected out from each valve and pooled into 50 ml conical tubes containing cold Dulbecco's PBS. 3. Cusps were washed in PBS at 4° C. for approximately 1.5 hrs; changing PBS during that time a total of 6×. 4. 2 cusps were placed in each 2 ml screw cap tubes. 5. 1.2 ml of the following were added to two tubes (for 0 and 30 kGy): PPG 125 mM Trolox C in PPGSCb stabilizer mixture—comprising of 1.5 ml 125 mM Trolox C, 300 μl 1 M Lipoic Acid, 600 μl 0.5 M Coumaric Acid and 600 μl 0.5 M n-Propyl Gallate. (Final concentrations: 62.5 mM, 100 mM, 100 mM and 100 mM respectively.) 6. Tubes were incubated at 4° C., with rocking. 7. Stabilizer solutions and cusps were transferred into 2 ml glass vials for gamma-irradiation. 8. All vials were frozen on dry ice. 9. Control samples were kept in-house at −20° C. C. Gamma-Irradiation of Tissue. Samples were irradiated at a rate of 1.584 kGy/hr at −20° C. to a total dose of 30 kGy. D. Processing Tissue for Hydrolysis/Extraction. 1. Since PPG is viscous, PBS was added to allow for easier transfer of material. 2. Each pair of cusps (2 per condition) were placed into a 50 ml Falcon tube filled with cold PBS and incubated on ice-inverting tubes periodically. 3. After one hour PBS was decanted from the tubes containing cusps in PPG/0 and 30 and replenished with fresh cold PBS. For the PPG samples containing Trolox C or stabilizer cocktail, fresh 50 ml Falcon tubes filled with cold PBS were set-up and the cusps transferred. 4. An additional 3 washes were done. 5. One cusp was transferred into a 2 ml Eppendorf tube filled with cold PBS for extraction. The other cusp was set-up for hydrolysis. E. Hydrolysis of Tissue. Hydrolysis of tissue: 1. Each cusp was washed 6× with acetone in an Eppendorf tube (approximately 1.5 ml/wash). 2. Each cusp was subjected to SpeedVac (with no heat) for approximately 15 minutes or until dry. 3. Samples were weighed, transferred to hydrolysis vials and 6 N HCl added at a volume of 20 mg tissue/ml HCl: Sample IDDry Weight (mg)μl 6 N HCl1. PPG/06.493252. PPG/307.263633. PPG T/05.802904. PPG T/308.204105. PPG SCb/06.413216. PPG SCb/308.60430 4. Samples were hydrolyzed at 110° C. for approximately 23 hours. 5. Hydrolysates were transferred into Eppendorf tubes and centrifuged @ 12,000 rpm for 5 min. 6. Supernatent was then transferred into a clean Eppendorf. 7. 50 μl of hydrolysate was diluted in 8 ml Nerl H2O (diluting HCl to approximately 38 mM). 8. Spiked in 200 μl of 2×int-pyd. Mixed by inversion. (For 1600 μl 2×int-pyd:160 μl 20×int-pyd+1440 μl Nerl H2O.) 9. Samples were loaded onto SP-Sephadex C25 column (approximately 1×1 cm packed bed volume) that had been equilibrated in water. (Column was pre-charged with NaCl) 10. Loaded flow through once again over column. 11. Washed with 20 ml 150 mM HQ. 12. Eluted crosslinks with 5 ml 2 N HCl into a low binding tube. 13. Dried entire sample in Savant. F. Analysis of Hydrolysates. Set-up the following: Sampleμlμl H2Oμl HFBA1. PPG/0 kGy1818022. PPG/30 kGy5913923. PPG T/0 kGy6717124. PPG T/30 kGy6413425. PPG SCb/0 kGy1018826. PPG SCb/30 kGy321662Results: The HPLC results are shown in FIGS. 4A-4C. In the presence of PPG 400, the results were nearly identical whether the heart valve had been irradiated or not. The addition of a single stabilizer (trolox C) or a stabilizer mixture produced even more effective results. The gel analysis, shown in FIG. 4D, confirmed the effectiveness of the protection provided by these conditions. In this experiment, the effects of gamma irradiation were determined on porcine heart valve cusps in the presence of 50% DMSO and, optionally, a stabilizer, and in the presence of polypropylene glycol 400 (PPG400). Preparation of Tissue for Irradiation: 1. 5 vials of PV and 3 vials of atrial valves (AV) were thawed on ice. 2. Thaw media was removed and valves rinsed in beaker filled with PBS. 3. Transferred each valve to 50 ml conical containing PBS. Washed by inversion and removed. 4. Repeated wash 3×. 5. Dissected out the 3 cusps (valves). 6. Stored in PBS in 2 ml screw top Eppendorf Vials (Eppendorfs) and kept on ice. Preparation of Stabilizers: All stabilizers were prepared so that the final concentration of DMSO is 50%. 1 M Ascorbate in 50% DMSO: Aldrich cat# 26,855-0 lot# 10801HU 200 mg dissolved in 300 μl H2O. Add 500 μl DMSO. The volumn was adjusted to 1 ml with H2O Final pH is ≈8.0 1 M Coumaric Acid: Sigma cat# C-9008 lot# 49H3600. MW 164.2 Dissolve 34.7 mg in 106 μl DMSO, pH=≈3.0 138 μl H2O was added. Sample crashed out. Coumaric went back into solution once pH was adjusted to 7.5 with 1 N NaOH. 1 M n-Propyl Gallate: Sigma cat# P-3130 lot# 117H0526. MW 212.2 Dissolve 58.2 mg in 138 μl DMSO. Add 138 μl H2O. Final pH is 6.5 or slightly lower. Stabilizer Mixture: 1.0 ml 500 mM Ascorbate 500 μl 1 M Coumaric Acid 300 μl 1 M n-propyl gallate 1.2 ml 50% DMSO 3.0 ml Method: 1.6 ml of a solution (stabilizer mixture or PPG400) was added to each sample and then the sample was incubated at 4° C. for 25 days. Valves and 1 ml of the solution in which they were incubated were then transferred into 2 ml irradiation vials. Each sample was irradiated with gamma irradiation at a rate of 1.723 kGy/hr at 3.6° C. to a total dose of 25 kGy. Hydrolysis of Tissue: 1. Washed each cusp 6× with acetone in a 2 ml Eppendorf Vial. 2. After final acetone wash, dried sample in Savant (without heat) for approximately 10-15 minutes or until dry. 3. Weighed the samples, transferred them to hydrolysis vials and then added 6 N HCl at a volume of 20 mg tissue/ml HCl: Sample IDDry Weight (mg)μl 6 N HCl1. PBS/0 kGy11.45702. PBS/25 kGy6.03003. DMSO/0 kGy6.423214. DMSO/25 kGy8.144075. DMSO/SC-a/0 kGy8.74356. DMSO/SC-a/25 kGy8.154087. PPG/0 kGy13.096558. PPG/25 kGy10.88544 5. Samples were hydrolyzed at 110° C. for approximately 23 hours. 6. Hydrolysates were transferred into eppendorf vials and centrifuged at 12,000 rpm for 5 min. 7. Supernatent was transferred into a clean eppendorf vial. 8. 50 μl hydrolysate was diluted in 8 ml Nerl H2O (diluting HCl to approximately 37 mM). 9. Spiked in 200 μl of 2×int-pyd. Mixed by inversion. (For 2000 μl 2×int-pyd: 200 μl 20×int-pyd+1.8 ml Nerl H2O.) 10. Samples were loaded onto SP-Sephadex C25 column (approximately 1×1 cm packed bed volume) that had been equilibrated in water. (Column was pre-charged with NaCl) 11. Loaded flow through once again over column. 12. Washed with 20 ml 150 mM HCl. 13. Eluted crosslinks with 5 ml 2 N HCl into a low binding tube. 50 ml 2 N HCl: 8.6 ml concentrated HCl adjusted to a volume of 50 ml with Nerl H2O. 14. Dried entire sample in Savant. Guanidine HCl Extraction and DEAE-Sepharose Purification of Proteoglycans: 4M Guanidine HCl Extraction: 1. Removed all three cusps from gamma irradiation vial and transferred to separate 50 ml conical tube. 2. Washed cusps five times with 50 ml dPBS (at 4° C. over approx. 5 hours) and determined wet weight of one cusp after damping on Kimwipe. 3. Transferred one cusp from each group to 1.5 ml microfuge tube and added appropriate volume of 4M guanidine HCl/150 mM sodium acetate buffer pH 5.8 with 2 μg/ml protease inhibitors (aprotinin, leupeptin, pepstatin A) to have volume to tissue ratio of 15 (see Methods in Enzymology Vol. 144 p. 321—for optimal yield use ratio of 15 to 20). 4. Diced cusps into small pieces with scissors. 5. Nutated at 4° C. for ˜48 hours. 6. Centrifuged at 16,500 RPM on Hermle Z-252M, 4° C.×10 min. 7. Collected guanidine soluble fraction and dialyze against PBS in 10K MWCO Slide-A-Lyzer overnight against 5 L PBS (3 slide-a-lyzers with one 5 L and 5 slide-a-lyzers in another 5 L) to remove guanidine. 8. Changed PBS and dialyzed for additional 9 hours at 4° C. with stirring. 9. Collected the dialysate and store at 4° C. 10. Centrifuged at 16,500 RPM on Hermle Z-252M, 4° C.×5 min 11. Removed PBS soluble fraction for DEAE-Sepharose chromatography. DEAE-Sepharose Chromatography 1. Increase the NaCl concentration of 500 μl of PBS soluble guanidine extract to 300 mM NaCl (Assumed PBS soluble fractions were already at ˜150 mM NaCl, so added 15 μl 5M NaCl stock to each 500 μl sample). 2. Equilibrated ˜1 ml of packed DEAE-Sepharose (previously washed with 1M NaCl/PB pH 7.2) into 300 mM NaCl/PB pH 7.2 (Note: To make 300 mM NaCl/PB pH7.2—added 3 ml of 5M NaCl stock to 100 ml PBS). 3. Added 200 μl of 1:μl slurry of resin to 515 μL of GuHCl extracts (both at 300 mM NaCl). 4. Nutated at ambient temperature for ˜one hour. 5. Centrifuged gently to pellet resin. 6. Removed “unbound” sample and stored at −20° C. 7. Washed resin 5 times with ˜1.5 ml of 300 mM NaCl/PBS pH7.2. 8. After last wash, removed all extra buffer using a 100 μl Hamilton syringe. 9. Eluted at ambient temperature with three 100 μl volumes of 1M NaCl/PB pH 7.2. Stored at −20° C. SDS-PAGE: 5-20% gradient gels for analysis of PBS soluble Guanidine HCl extracts and DEAE-Sepharose chromatography. 1. Gel#1: GuHCl extracts/PBS soluble fractions—Toluidine blue and then Coomassie blue stained. 2. Gel#2: DEAE-Sepharose Eluant Fraction#1—Toluidine Blue stained then Coomassie Blue stained. Quantification of Collagen Crosslinks by HPLC: 1. Prepare 100-200 μl 1× solution in 1% heptafluorobutyric acid (HFBA). 2. Inject 50 μl on C18 HPLC column equilibrated with mobile phase. 3. Spectrofluorometer is set for excitation at 295 nm and emission at 395 nm. 4. Calculate the integrated fluorescence of Internal-Pyridinoline (Int-Pyd) per 1 μl of 1× solution of Int-Pyd.Results: The HPLC results are shown in FIGS. 5A-D. The major peak represents the Internal-Pyridinoline (int-Pyd) peak. Irradiation in an aqueous environment (PBS) produced pronounced decreases in the smaller peaks (FIG. 5A). Reduction of the water content by the addition of a non-aqueous solvent (PPG 400) produced a nearly superimposable curve (FIG. 5B). DMSO was less effective (FIG. 5C), while DMSO plus a mixture of stabilizers (FIG. 5D) was more effective at preserving the major peak although some minor peaks increased somewhat. The area under the pyd peak for each sample was calculated as shown in the table below. These results confirm the above conclusions and show that the amino acid crosslinks (pyd) found in mature collagen are effectively conserved in the samples containing PPG and DMSO with a scavenger mixture. Gel analysis is shown in FIG. 5E and reflects the major conclusions from the HPLC analysis, with significant loss of bands seen in PBS and retention of the major bands in the presence of non-aqueous solvents. SampleArea of Pyd PeakPBS/0 kGy94346PBS/25 kGy60324DMSO/0 kGy87880DMSO/25 kGy49030DMSO/SCa/0 kGy75515DMSO/SCa/25 kGy88714PPG/0 kGy99002PPG/25 kGy110182 In this experiment, frozen porcine AV heart valves soaked in various solvents were gamma irradiated to a total dose of 30 kGy at 1.584 kGy/hr at −20° C. Materials: 1. Porcine heart valve cusps were obtained and stored at −80° C. in a cryopreservative solution (Containing Fetal calf serum, Penicillin-Streptomycin, M199 media, and approximately 20% DMSO). 2. Dulbecco's Phosphate Buffered Saline: Gibco BRL cat#14190-144 lot 1095027 3. 2 ml screw cap vials: VWR cat# 20170-221 lot #0359 4. 2 ml glass vials: Wheaton cat# 223583 lot#370000-01 5. 13 mm stoppers: Stelmi 6720GC lot#G006/5511 6. DMSO: JT Baker cat# 9224-01 lot# H406307. Sodium ascorbate: Aldrich cat#26,855-0 lot 10801HU; prepared as a 2M stock in Nerl water. 8. Fetal calf serum 9. Penicillin-Streptomycin 10. M199 media 11. DMSO Methods: Cryopreservative Procedure: Preparation of Solutions: Freeze Medium: Fetal calf serum (FCS) (10%)=50 ml Penicillin-Streptomycin=2.5 ml M199=QS500 ml 2M DMSO DMSO=15.62 g Freeze Medium=QS 100 ml 3M DMSO DMSO=23.44 g Freeze Medium=QS 100 ml 1. Place dissected heart valves (with a small amount of conduit/muscle attached) into glass freezing tubes (label with pencil). 2. Add 2 ml of freeze medium. 3. At 21° C., add 1 ml 2M DMSO solution. 4. At 5 minutes, add 1 ml 2M DMSO solution. 5. At 30 minutes, add 4 ml 3M DMSO solution. 6. At 45 minutes and 4° C., place freezing tubes on ice. 7. At 50 minutes and −7.2° C., seed bath. 8. At 55 minutes and −7.2° C., nucleate. 9. At 70 minutes, cool to −40° C. at 1° C./minute. Remove from bath and place in canister of LN2, and store in cryogenic storage vessel.Procedure for Irradiation of Heart Valves: 1. Thawed AV heart valve cusps on wet ice. 2. Pooled cusps into 50 ml tubes. 3. Washed cusps with ˜50 ml dPBS at 4° C. while nutating. Changed PBS 5× over the course of 5 hrs. 4. Transferred cusps into 2 ml screw cap tubes (2 cusps/tube). 5. Added 1.0 ml of the following to two of each of two tubes: dPBS, 50% DMSO and 50% DMSO with 200 mM sodium ascorbate (2M sodium ascorbate stock was diluted as follows: 400 μl (2M)+1.6 ml water+2 ml 100% DMSO). 6. Incubated tubes at 4° C. with nutating for ˜46 hours. 7. Transferred solutions and cusps to glass 2 ml vials, stoppered and capped. 8. All vials were frozen on dry ice. 9. Frozen samples were then irradiated at −20° C. at a rate of 1.584 kGy/hr to a total dose of 30 kGy. Results: The results of the HPLC analysis are shown in FIGS. 6A-6D. Irradiation in an aqueous environment (PBS) produced decreases in the smaller peaks (FIG. 6A). Reduction of the water content by the addition of a non-aqueous solvent (20% DMSO) reproduced these peaks more faithfully (FIG. 6B). Increasing the DMSO concentration to 50% was slightly more effective (FIG. 6C), while DMSO plus a mixture of stabilizers (FIG. 6D) was very effective at preserving both the major and minor peaks (the additional new peaks are due to the stabilizers themselves). Gel analysis is shown in FIG. 6E and reflects the major conclusions from the HPLC analysis, with significant loss of bands seen in PBS and retention of the major bands in the presence of non-aqueous solvents with and without stabilizers. In this experiment, frozen porcine AV heart valves soaked in various solvents were gamma irradiated to a total dose of 45 kGy at approximately 6 kGy/hr at −70° C. Materials: 1. Porcine heart valve cusps were obtained and stored at −80° C. in a cryopreservative solution (Same solution as that in Example 7). 2. Dulbecco's Phosphate Buffered Saline: Gibco BRL cat#14190-144 lot 1095027 3. 2 ml screw cap vials: VWR cat# 20170-221 lot #0359 4. 2 ml glass vials: Wheaton cat# 223583 lot#370000-01 5. 13 mm stoppers: Stelmi 6720GC lot#G006/5511 6. DMSO: JT Baker cat# 9224-01 lot# H40630 7. Sodium ascorbate: Aldrich cat# 26,855-0 lot 10801HU; prepared as a 2M stock in Nerl water. 8. Polypropylene glycol 400 (PPG400): Fluka cat#81350 lot#386716/1Methods: Cryopreservative Procedure is the Same as that Shown in Example 7. 1. Thawed AV heart valve cusps on wet ice. Dissected out cusps and washed the pooled cusps 6× with cold PBS. 2. Dried each cusp and transferred cusps into 2 ml screw cap tubes (2 cusps/tube). 3. Added 1.2 ml of the following to two of each of two tubes: dPBS, dPBS with 200 mM sodium ascorbate, PPG400, PPG400 for rehydration, 50% DMSO and 50% DMSO with 200 mM sodium ascorbate (2M sodium ascorbate stock was diluted as follows: 400 μl (2M)+1.6 ml water+2 ml 100% DMSO). 4. Incubated tubes at 4° C. with nutating for ˜46 hours. 5. Replaced all solutions with fresh (with the following exception: for one PPG400 set, PPG400 was removed, the cusp washed with PBS+200 mM ascorbate, which was then removed and replaced with fresh PBS+200 mM ascorbate). 6. Incubated tubes at 4° C. with nutating for ˜46 hours. 7. Changed the solution on the PPG400 dehyd./PBS+ascorbate rehydration cusps prepared in step 5). 8. Incubated tubes at 4° C. with nutating for ˜6 hours. 9. Transferred solutions and cusps to glass 2 ml vials, stoppered and capped. 10. All vials were frozen on dry ice. 11. Frozen samples were then irradiated at −70° C. at a rate of 6 kGy/hr to a total dose of 45 kGy. Results: The results of the HPLC analysis are shown in FIGS. 7A-7F. Irradiation in an aqueous environment (PBS) resulted in changes in the minor peaks and a right shift in the major peak. The inclusion of various non-aqueous solvents, reduction in residual water, and the addition of stabilizers produced profiles that more closely matched those of the corresponding controls. The gel analysis is shown in FIGS. 7G-7H and shows a significant loss of bands in PBS, while the other groups demonstrated a significant retention of these lost bands. When comparing the results from Example 8 to the results from Examples 5, 6, and 7, it becomes apparent that lowering the temperature for the gamma irradiation usually results in a decrease in the amount of modification or damage to the collagen crosslinks. One illustration of this temperature dependence is the sample containing 50% DMSO and ascorbate, in which the additional peaks are markedly decreased as the temperature is lowered from −20° C. to −80° C. Having now fully described this invention, it will be understood to those of ordinary skill in the art that the methods of the present invention can be carried out with a wide and equivalent range of conditions, formulations and other parameters without departing from the scope of the invention or any embodiments thereof. All patents and publications cited herein are hereby fully incorporated by reference in their entirety. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that such publication is prior art or that the present invention is not entitled to antedate such publication by virtue of prior invention. The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. |
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046438661 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As illustrated in FIG. 1, the present invention includes fuel rod cladding 10, which may be any cladding material usable in a nuclear reactor, which typically is a Zircaloy tube having an inside diameter in a range from about 0.25 inches to about 0.55 inches, depending on the manufacturer. A Zircaloy-4 cladding tube having an inside diameter of 0.38 inches can be used as a waveguide in the electromagnetic microwave frequency range above about 16 GHz, as can be calculated from mathematical equations well known to those skilled in the art. Fuel rod cladding 10 has a preferred length of about 6 inches, but may be on the order of from about 3.5 inches to about 12 inches in length. A plurality of individual fuel pellets 12 comprises fuel column 14 within cladding 10. Fuel pellets 12 may be made of any fissionable material suitable for use as fuel in the core of a nuclear reactor, such as uranium dioxide. Cooling jacket 16, comprising a thermostatically controlled substantially cylindrical water jacket in a preferred embodiment, encloses fuel rod cladding 10, except ends 18, 19 of fuel rod cladding 10. Cooling jacket 16 includes water inlet 20 and water outlet 22. Cooling jacket 16 can dissipate the full power of gyrotons 24, 26 to permit temperature control in the event of 100% susceptance by the target, fuel column 14. In a preferred embodiment, illustrated in FIG. 1, gyrotrons 24, 26 generate microwave radiation which is conducted through waveguides 28, 30, through windows 32, 34 respectively, which may be of ceramic or other material which is substantially transparent to microwaves, but which permit fuel rod cladding 10 to be substantially sealed at each end 18, 19, thereby enabling the experimenter to control the initial atmosphere within fuel rod cladding 10. Helium is a preferred atmosphere, but this can be changed to simulate changes in the atmosphere inside fuel rod cladding 10 that occur during use. Loads 36, 38, well known in the art, provide a safety valve to absorb and dissipate the full microwave power generated by gyrotrons 24, 26 if target material, i.e., usually fuel column 14 fails to suscept. Waveguides 28, 30 are conventional and well known in the art. Sensors 40, 42 may comprise thermocouples, in which case they must be located outside fuel rod cladding 10 to prevent impingement by microwaves, which would cause false temperature readings. Preferably, sensors 40, 42 are infrared spectrometer sensors, which require ports through cooling jacket 16, or optical pyrometry sensors, which provide the preferred means for measuring temperature. Sensors 40, 42 may desirably be located at any point along the length of fuel rod cladding 10, although perhaps the point of most nearly uniform volumetric heating is located at the midpoint of the length of fuel rod cladding 10. The departure from uniform volumetric heating throughout fuel rod cladding 10 and fuel column 14, however, is relatively slight since heating is caused by a standing wave in fuel rod cladding 10 and only the extra heat leakage at end 18 and end 19 normally causes departure from uniform volumetric heating. Other sensors for measuring, e.g., heat flux, stress, strain or other parameters of interest may of course be employed. For example, a Youngs Modulus ultrasonic test device can provide data which permit calculation of pellet creep. As illustrated in FIG. 2, an alternative preferred embodiment contemplated as the best mode of practicing the invention, employs a single gyrotron 24 which generates microwaves that are conducted through waveguides 28 and window 32 into fuel column 14. In this embodiment, Reflector 35 is the last element on end 19 of fuel rod cladding 10. Reflector 35 reflects microwaves that penetrate fuel column 14 back into fuel column 14, and establishes a standing wave in fuel column 14, thereby providing nearly uniform volumetric heating throughout fuel rod cladding 10 and fuel column 14. Reflector 35 is mounted on adjustment mechanism 37, which may be a threaded screw adjustment mechanism or other adjustment means for adjusting the distance between end 18 and reflector 35 to promote development of a standing wave within fuel rod cladding 10 and vary the deposition of power therein. Reflector 35, which may be made of any conductive metal, is preferably made of copper. The adjustment of reflector 35 is on the order of about 0-1.75 inches. Reflector 35 must also maintain the fluid tight seal of end 19 throughout all stages of adjustment. Construction of such a sealed adjustable reflector is known in the art. In the alternative embodiment illustrated in FIG. 3, the microwave output of a single gyrotron 24 is split into two separate beams by beam splitter 31 by well known technique and is conducted via separate waveguides 28, 30, and through windows 32, 34 respectively into respective ends 18, 19 of fuel rod cladding 10. In all other respects, the embodiment of FIG. 3 conforms to the basic configuration of FIG. 1. In operation, the microwave radiation of gyrotrons 24, 26 produces a substantially uniform volumetric heating in fuel column 14, particularly near the midpoint of fuel column 14 because there are only nominal barriers to penetration of fuel pellets 12 by microwaves, which do not rely on conduction to heat fuel pellets 12 but rather upon the natural susceptance of uranium dioxide to microwave radiation. The microwave heating tends to produce a homogeneous temperature throughout the area of uniform volumetric heating. Fuel rod cladding 10 and water in cooling jacket 16, however, cool fuel column 14 by conduction from fuel pellets 12 to cladding 10 to the water. This cooling sequence leads to the relative temperature profile illustrated by steady state curve 50 of FIG. 4. (FIGS. 4, 5, and 6 are graphs having relative temperature on the vertical axis and relative distance from the center of the fuel rod on the horizontal axis. FIG. 7 helps clarify orientation of FIGS. 4, 5, and 6.) As illustrated by steady state curve 50, the temperature profile through a fuel pellet decreases in essentially parabolic fashion through small gap 52 (not shown in FIGS. 1, 2, and 3) between fuel pellet 12 and cladding 10, and becomes more nearly flat through cladding 10 and cooling water 54. Steady state curve 50 closely resembles reactor core steady state curve 56 of FIG. 6, which illustrates the temperature profile of a typcial fuel rod in an operating nuclear reactor. By controlling the flow rate, flow volume, temperature, and pressure of cooling water 54 in cooling jacket 16, and the heat produced in fuel column 14 by the microwave radiation, any desired realistic temperature profile can be produced in fuel column 14 and fuel cladding 10. In the core of an operating nuclear reactor, nuclear fission tends to heat each fuel rod uniformly because nuclear fission has only nominal barriers and consequently fission tends to proceed uniformly throughout the fuel (ignoring the regulating effect of burnable poison rods). Cooling water 54 used for heat transfer, cools the fuel rods primarily through conduction with the fuel rod cladding. Thus the distribution of heating and heat transfer mechanisms of the test apparatus of the present invention and an operating nuclear reactor core are substantially similar. In contrast, as illustrated in FIG. 5, in the conventional test apparatus axial electrical heater 58, disposed along the longitudinal axis of test cladding 60 through a central longitudinal bore in test fuel pellets (not shown) generates the highest temperature at its surface and the fuel pellets themselves must be heated by conduction from their centers to their perimeters leading to a downwardly convex steady state pellet temperature profile 62 of FIG. 5, which is nearly opposite in shape from steady state curve 50. As illustrated by transient curve 64 of FIG. 4 and electrical transient curve 66, the contrast between temperature profiles produced by the present invention and the prior art test apparatus are even greater when sudden high temperature transients are induced into the fuel column, a condition of great interest which cannot be tested in an operating reactor. Thus, the temperature profile from the inside of a fuel pellet to the outside of a fuel pellet in an operating nuclear reactor can be substantially duplicated in the test apparatus of the present invention. While the invention has been described with respect to certain preferred embodiments, changes and variations in the embodiments disclosed may occur to those skilled in the art. It is not intended that the invention be limited to the precise embodiments disclosed; rather the scope of the invention should be measured by the claims that follow. |
claims | 1. A fuel assembly for a boiling water reactor adapted during operation of the reactor to allow coolant to flow upwards through the fuel assembly while absorbing heat from a plurality of fuel rods to transform a portion of the water into steam, said fuel assembly comprising: a first steam pipe arranged with a longitudinal axis parallel to a longitudinal axis of the fuel assembly, wherein the first steam pipe comprises an inlet for the steam arranged in a first end of the first steam pipe, and an outlet for the steam arranged at a second end of the first steam pipe; a second steam pipe arranged above and spaced from the first steam pipe along the longitudinal direction of the fuel assembly such that an opening is formed between the first and second steam pipes, wherein the outlet of the first steam pipe has an outlet diameter which is larger than an inlet diameter of the inlet of the second steam pipe, wherein fuel rods are arranged laterally with respect to said first and second steam pipes in said fuel assembly, wherein a second end of the second steam pipe comprises means for collecting water on an inside of the second steam pipe and conducting the collected water towards the outlet of the second steam pipe. 2. A fuel assembly according to claim 1 , further comprising a third steam pipe arranged above and spaced from the second steam pipe such that an opening is formed between the second and third steam pipes, claim 1 wherein an outlet of the second steam pipe has a diameter which is larger than a diameter of an inlet of the third steam pipe. 3. A fuel assembly according to claim 1 , wherein the second end of the first steam pipe is arranged tapering towards the outlet of the first steam pipe and the first end of the second steam pipe is arranged tapering towards the inlet of the second steam pipe for achieving a venturi effect. claim 1 4. A fuel assembly according to claim 1 , wherein a distance between the outlet of the first steam pipe and the inlet of the second steam pipe is less than half a diameter of the inlet of the second steam pipe. claim 1 5. A fuel assembly according to claim 1 , wherein the second end of the first steam pipe comprises means for collecting water on an inside of the first steam pipe and conducting the collected water towards the outlet of the first steam pipe. claim 1 6. A fuel assembly according to claim 5 , wherein said means for collecting water comprise a plurality of elongated grooves on the inside of the first steam pipe. claim 5 7. A fuel assembly for a boiling water reactor adapted during operation of the reactor to allow coolant to flow upwards through the fuel assembly while absorbing heat from a plurality of fuel rods to transform a portion of the water into steam, said fuel assembly comprising: a first steam pipe arranged with a longitudinal axis parallel to a longitudinal axis of the fuel assembly, wherein the first steam. pipe comprises an inlet for the steam arranged in a first end of the first steam pipe, and an outlet for the steam arranged at a second end of the first steam pipe; a second steam pipe arranged above and spaced from the fist steam pipe along the longitudinal direction of the fuel assembly such that an opening is formed between the first and second steam pipes, wherein the outlet of the first steam pipe has an outlet diameter which is larger than an inlet diameter of the inlet of the second steam pipe, wherein fuel rods are arranged laterally with respect to said first and second steam pipes in said fuel assembly, wherein the second end of the first steam pipe comprises means for collecting water on an inside of the first steam pipe and conducting the collected water towards the outlet of the first steam pipe, wherein said means for collecting water comprise a plurality of lugs arranged around the outlet of the first steam pipe. 8. A fuel assembly according to claim 1 , wherein the fuel assembly comprises at least two fuel units stacked on top of each other, claim 1 each fuel unit comprising a top tie plate, a bottom tie plate, a plurality of fuel rods extending between the top tie plate and the bottom tie plate, and one of said first and second steam pipes. 9. A fuel assembly according to claim 8 , wherein the first end of the first steam pipe is attached to the bottom tie plate and the second end of the first steam pipe is attached to the top tie plate. claim 8 10. A fuel assembly for a boiling water reactor adapted during operation of the reactor to allow coolant to flow upwards through the fuel assembly while absorbing heat from a plurality of fuel rods to transform a portion of the water into steam, said fuel assembly comprising: a first steam pipe arranged with a longitudinal axis parallel to a longitudinal axis of the fuel assembly, wherein the first steam pipe comprises an inlet for the steam arranged in a first end of the first steam pipe, and an outlet for the steam arranged at a second end of the first steam pipe; a second steam pipe arranged above and spaced from the first steam pipe along the longitudinal direction of the fuel assembly such that an opening is formed between the first and second steam pipes, wherein the outlet of the first steam pipe has an outlet diameter which is larger than an inlet diameter of the inlet of the second steam pipe, wherein fuel rods are arranged laterally with respect to said first and second steam pipes in said fuel assembly, wherein the second end of the first steam pipe comprises means for collecting water on an inside of the first steam pipe and conducting the collected water towards the outlet of the first steam pipe, wherein a second end of the second steam pipe comprises means for collecting water on an inside of the second steam pipe and conducting the collected water towards the outlet of the second steam pipe. |
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claims | 1. A spent nuclear fuel pool emergency cooling system comprising:an evaporator/heat exchanger having an internal fluid path that extends in a generally planar direction, the evaporator/heat exchanger being supported substantially vertically from a wall of a spent fuel pool;a hinged support connecting a first side portion of the evaporator/heat exchanger to the wall of the spent fuel pool, the hinged support configured to rotate the evaporator/heat exchanger away from the wall and outward into a coolant within the spent fuel pool with a second side portion of the evaporator/heat exchanger, which is opposed from the first side portion, laterally spaced from the wall of the spent fuel pool;a fusible link actuator that connects the wall and the second side portion of the evaporator/heat exchanger to maintain the evaporator/heat exchanger in the substantially vertical position, the fusible link actuator being responsive to a preselected change in an element of an environment of the spent fuel pool, to a pre-established level, to transfer the evaporator/heat exchanger to a position wherein the second side portion of the evaporator/heat exchanger is laterally spaced from the wall of the spent fuel pool;a supply of a cryogenic fluid fluidly connected to the internal fluid path;a cryogenic storage vessel for storing the supply of the cryogenic fluid; anda passively actuated valve for preventing the flow of the cryogenic fluid from the cryogenic storage vessel to the internal fluid path until the second side portion of the evaporator/heat exchanger is laterally spaced by a preselected extent from the wall of the spent fuel pool. 2. The spent nuclear fuel pool emergency cooling system of claim 1 wherein the position wherein the second side portion of the evaporator/heat exchanger is laterally spaced from the wall of the spent fuel pool places the evaporator/heat exchanger in a substantially horizontal position, to insure the evaporator/heat exchanger is submerged in the coolant of the spent fuel pool. 3. The spent nuclear fuel pool emergency cooling system of claim 1 wherein when the second side portion of the evaporator/heat exchanger is laterally spaced by the preselected extent from the wall of the spent fuel pool, the passively actuated valve opens to expand the cryogenic fluid through the internal fluid path wherein the cryogenic fluid captures heat and exits the internal fluid path as a pressurized gas. 4. The spent nuclear fuel pool emergency cooling system of claim 3 wherein the pressurized gas is connected to a gas driven mechanical pump. 5. The spent nuclear fuel pool emergency cooling system of claim 4 wherein the gas driven mechanical pump supplies makeup water to the spent fuel pool. 6. The spent nuclear fuel pool emergency cooling system of claim 4 wherein the gas driven mechanical pump is an air operated double diaphragm pump. 7. The spent nuclear fuel pool emergency cooling system of claim 6 wherein the air operated double diaphragm pump is connected to a pulse dampener. 8. The spent nuclear fuel pool emergency cooling system of claim 3 wherein the pressurized gas is connected to a compressed gas turbo generator. 9. The spent nuclear fuel pool emergency cooling system of claim 8 wherein the compressed gas turbo generator drives an air cooling system. 10. The spent nuclear fuel pool emergency cooling system of claim 8 wherein the compressed gas turbo generator provides power to an electrical pump. 11. The spent nuclear fuel pool emergency cooling system of claim 10 wherein the electrical pump supplies make-up water to the spent fuel pool. 12. The spent nuclear fuel pool emergency cooling system of claim 9 wherein the pressurized gas exiting the internal fluid path is conducted through a gas to air heat exchanger after driving the compressed gas turbo generator. 13. The spent nuclear fuel pool emergency cooling system of claim 3 including a check valve in fluid communication with an inlet to the evaporator/heat exchanger to prevent the pressurized gas from flowing back into the cryogenic storage vessel. 14. The spent nuclear fuel pool emergency cooling system of claim 3 wherein the internal fluid path is in fluid communication with a pressure regulating valve to control pressure of the gas in the internal fluid path. 15. The spent nuclear fuel pool emergency cooling system of claim 1 wherein aside from the evaporator/heat exchanger, a plurality of components and instrumentation necessary for implementing the emergency cooling system can be supported on a transportable skid that can be back fitted into existing nuclear power plants. 16. The spent nuclear fuel pool emergency cooling system of claim 1 wherein the evaporator/heat exchanger has an inlet and an outlet to the internal fluid path and the internal fluid path extends in a serpentine pattern between the inlet and the outlet. 17. The spent nuclear fuel pool emergency cooling system of claim 1 wherein the internal fluid path extends substantially through a single plane. 18. The spent nuclear fuel pool emergency cooling system of claim 1 wherein the evaporator/heat exchanger is supported substantially vertically upward from the wall of the spent fuel pool. 19. The spent nuclear fuel pool emergency cooling system of claim 1 wherein the cryogenic fluid is nitrogen or mixtures of nitrogen. 20. The spent nuclear fuel pool emergency cooling system of claim 3 wherein the pressurized gas is air. |
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claims | 1. A nuclear reactor comprising:an elongated reactor vessel having a lower portion sealed at a lower end and having an open upper end on which an annular flange is formed and a central axis extending along an elongated dimension;a reactor vessel head having an annular portion on an underside of the head that is machined to form a sealing surface;a removable annular seal ring, sized to seat on the reactor vessel flange between the flange and the sealing surface on the underside of the reactor vessel head, the seal ring being interposed between the sealing surface on the underside of the vessel head and the flange on the reactor vessel lower portion and having a thickness sized to sealably accommodate radial passages through which utility conduits pass from outside of the reactor vessel to an interior thereof to transport one or more utilities comprising hydraulic fluid for hydraulic mechanisms, instrumentation signals or power for electrical mechanisms, the removable annular seal ring including one or more of such radial passages;a reactor internals assembly comprising a lower internals which includes a reactive core and an upper internals situated above the core, the internals assembly being seated within the reactor vessel, wherein the removable annular seal ring is attached to the reactor internals assembly; anda substantially annular passage between an interior wall of the reactor vessel lower portion and the internals assembly for a downward flow of relatively cool reactor coolant to access an underside of the reactive core, wherein at least a portion of the removable annular seal ring extends over the annular passage where it is attached to the reactor internals assembly, wherein the portion of the removable annular seal ring that extends over the annular passage includes axially extending openings for the passage of reactor coolant. 2. The nuclear reactor of claim wherein the axially extending openings are circumferentially spaced from the radial passages. 3. The nuclear reactor of claim wherein the removable annular seal ring is attached to the upper internals. 4. The nuclear reactor of claim 3 wherein the removable annular seal ring is removable from the reactor vessel with removal of the upper internals. 5. The nuclear reactor of claim 4 wherein at least one or more of the utility conduits are an integral part of the upper internals and include a utility disconnect outside of the reactor vessel. 6. The nuclear reactor of claim 1 wherein the annular seal ring has an upper and a lower double o-ring seals on opposite sides that mate with the reactor vessel flange on one of the opposite sides and the annular portion of the reactor vessel head on another of the opposite sides, the annular seal ring having a hole extending between the upper and lower double o-ring seals allowing leakage to be detected through both sets of seals via one reactor vessel flange leak-off line. 7. The nuclear reactor of claim 6 including one reactor vessel flange leak-off line extending from the lower double o-ring seal. 8. The nuclear reactor of claim 1 wherein the removable annular seal ring is forged from a metal having substantially the same thermal expansion properties as the reactor vessel. 9. The nuclear reactor of claim 8 wherein the removable annular seal ring is forged from either (i) carbon steel in which the surfaces in contact with reactor coolant are clad with stainless steel or (ii) Alloy 690. 10. The nuclear reactor of claim 1 including a plurality of holes axially through the annular seal ring in line with openings in the reactor vessel head and the reactor vessel flange through which studs pass that anchor the head to the flange with the seal ring captured therebetween. 11. The nuclear reactor of claim 10 wherein one or more of the radial passages extend in between two adjacent ones of the holes. 12. The nuclear reactor of claim 1 wherein the utility conduits are sealed to the radial passages on the inner diameter of the seal ring. |
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description | 1. Field of the Invention The present invention relates, in general, to instrumented capsules for nuclear fuel irradiation tests in research reactors and, more particularly, to an instrumented capsule for nuclear fuel irradiation tests in research reactors, which is used to measure in real time the properties of nuclear fuels irradiated in a research reactor during a nuclear fuel irradiation test, thus providing nuclear fuel irradiation test data required for the design of nuclear fuels and the determination of in-pile performance and structural integrity of nuclear fuels. 2. Description of the Related Art In the related art, nuclear fuel irradiation tests and material irradiation tests in research reactors have been actively executed using irradiation testing facilities, such as capsules or loops. Of the irradiation testing facilities, the capsules which are in-pile testing facilities used in research reactors to execute nuclear fuel irradiation tests are classified into instrumented capsules and non-instrumented capsules. The instrumented capsules are testing facilities in which a variety of measuring instruments are installed in the shell of a capsule to measure the properties of irradiated nuclear fuel, such as the temperature of the irradiated nuclear fuel and the inner pressure and strain of irradiated nuclear fuel rods, and determine in-capsule irradiation test data, such as the quantity of neutron radiation and the temperature, flow quantity and flow rate of coolant. In the meantime, the non-instrumented capsules are testing facilities, the shells of which are not provided with such measuring instruments. In recent years, the irradiation tests for nuclear reactor materials, nuclear fuels and other nuclear materials by the use of research reactors have been actively studied and executed. Particularly, the requirements for irradiation tests using research reactors have rapidly increased to provide: in-pile irradiation test data for pressure vessels and in-core materials of nuclear reactors in an effort to lengthen the life spans of commercial reactors; in-pile irradiation test data for in-core materials and pressure pipe materials of heavy water reactors in an effort to develop advanced materials for the reactors; and in-pile irradiation test data required for the development of advanced nuclear fuels for pressurized light water reactors, proliferation-resistant oxide nuclear fuels, nuclear fuels for next generation reactors and advanced sheath materials. Thus, a variety of irradiation test facilities which are thermohydraulically and mechanically compatible with in-core irradiation holes of research reactors and agreeable with irradiation test properties of materials have been developed and utilized. In addition, to provide further improved irradiation test facilities, many improvements to the facilities have been attempted. To provide in-pile test data for design and performance qualification of nuclear fuels for commercial nuclear power plants and in-pile test data for qualifying in-pile performance and structural integrity of nuclear fuels to develop advanced nuclear fuels suitable for a variety of nuclear reactors, such as next generation reactors, irradiation tests using research reactors must be carried out. To execute the irradiation tests in the research reactors, the non-instrumented capsules and instrumented capsules for the irradiation tests are installed in the irradiation holes of the research reactors to qualify in real time the properties of a variety of nuclear fuels, such as metal fuels and ceramic fuels, during the irradiation tests. In such a case, the capsules must be designed to be thermohydraulically and mechanically compatible with the irradiation holes. Furthermore, the capsules must be prevented from causing mechanical damage to the inner surfaces of the irradiation holes due to in-pile liquid vibration despite being installed in the irradiation holes for lengthy periods. In addition, the capsules must exhibit desired structural integrity and operational reliability thereof even though the capsules are irradiated in the research reactors for lengthy periods. Furthermore, the capsules must be constructed to allow the in-capsule instruments, nuclear fuel rods, fuel rod assemblies, and capsule shells to be easily assembled and disassembled through remote controls from hot cells. An example of conventional non-instrumented capsules for nuclear fuel irradiation tests may be referred to Korean Patent Registration No. 296946, entitled “Remote-controlled Non-instrumented Capsule for Nuclear Fuel Irradiation Tests”. The above-mentioned non-instrumented capsule can be used in a nuclear fuel irradiation test for a short period, three months to six months, while testing three kinds of sintered nuclear fuels at the same time. However, the use of the non-instrumented capsule of No. 296946 is limited to an irradiation test for one nuclear fuel rod assembly having three irradiation test fuel rods. Furthermore, the non-instrumented capsule is problematic in that the capsule has a weak welded structure so that some welded parts thereof, such as a collar welded to a rod tip provided at a lower portion of the capsule, may be broken if excessive force is imposed on the welded parts during a process of assembling the capsule. In addition, the capsule is not able to resist wear or breakage induced by in-pile liquid vibration, and furthermore, may damage the inner wall of the irradiation hole caused by the wear. Furthermore, the above-mentioned non-instrumented capsule is unable to accommodate irradiation growth of structural materials of nuclear fuels, such as sheath materials of fuel rods, induced by lengthy period neutron irradiation, so that the capsule is limited in terms of structural integrity and safety thereof in the irradiation hole when the capsule is used in a nuclear fuel irradiation test for a lengthy period, six months to three years. Another example of conventional non-instrumented capsules for nuclear fuel irradiation tests may be referred to Korean Patent Application No. 2001-81880, entitled “Non-instrumented Capsule for Nuclear Fuel Irradiation Tests in Irradiation Holes of Research Reactors”. This non-instrumented capsule was developed to solve the problems experienced in the capsule of No. 296946, and has many advantages as follows. That is, the non-instrumented capsule of No. 2001-81880 enhances its structural integrity and safety, thus solving the conventional problems in that the capsule may be easily worn or broken due to external force imposed thereon during the process of assembling the capsule or due to the in-pile liquid vibration. Furthermore, the capsule of No. 2001-81880 has a structure capable of accommodating irradiation growth of fuel rods, thus being effectively used in a lengthy irradiation test. In addition, the capsule includes a thermo-neutron absorption tube capable of allowing for control of linear power density of the nuclear fuel in the irradiation hole. However, the non-instrumented capsule of No. 2001-81880 having the above-mentioned advantages is problematic in that the capsule does not allow for real time measurement of the properties of the nuclear fuels irradiated in the irradiation hole during an irradiation test. Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an instrumented capsule for nuclear fuel irradiation tests in research reactors which allows for easy assembling and disassembling of the in-capsule instruments, nuclear fuel rod assemblies and elements of the capsule, enhances the mechanical integrity and safety of elements of both the capsule and the nuclear fuel assemblies irradiated in the irradiation hole of a research reactor, accommodates dimensional changes of irradiation test fuel rods induced by irradiation growth during neutron irradiation, and measures and determines the properties of the nuclear fuels during the irradiation test. In order to accomplish the above object, the present invention provides an instrumented capsule for nuclear fuel irradiation tests in research reactors, including a capsule part comprising: an outer shell with a predetermined length and opposite open ends; one or more nuclear fuel rod assemblies loaded in the outer shell and each having a plurality of irradiation test fuel rods each containing a sintered nuclear fuel body therein; a plurality of support tubes inserted into the outer shell to support the plurality of fuel rod assemblies in a predetermined place in the outer shell; an upper end plate and a lower end plate mounted to an upper end and a lower end of the outer shell, respectively, with a plurality of coolant flow channels formed in each of the upper and lower end plates; and a rod tip assembly comprising: a rod tip inserted into the lower end plate; a support spring supported by both the lower end plate and the rod tip to support the weight of the instrumented capsule; and a rod tip support ring coupled to an upper end of the rod tip which passes upwards through the lower end plate; a plurality of in-capsule instruments including: a thermocouple installed in the sintered nuclear fuel body of each of the fuel rod assemblies, with an instrument control cable extending from the thermocouple to an outside of the capsule part; and a self-powered neutron detector (SPND) placed in a housing support rod of each of the fuel rod assemblies, with an instrument control cable extending from the SPND to the outside of the capsule part; a protective tube connected to a top of the upper end plate by means of an upper end plate connector, and protecting the instrument control cables extending from the in-capsule instruments to the outside of the capsule part; a junction tree connected to an upper end of the protective tube and having both a vertical extension part and an inclined extension part, with a cable connection adapter provided at an upper end of the inclined extension part to hold the instrument control cables; a guide pipe connected to the inclined extension part through the cable connection adapter and guiding the instrument control cables to a control unit provided outside the research reactor; and a grapple head assembly connected to an upper end of the vertical extension part to be coupled to a capsule treatment system. The in-capsule instruments may further include a combination of a linear variable differential transformer (LVDT) and a bellows-shaped pressure gauge to measure variation in an inner pressure of each of the irradiation test fuel rods, or a combination of a linear variable differential transformer (LVDT) and a strain gauge to measure variation in length of the sintered nuclear fuel body of each of the irradiation test fuel rods. The instrumented capsule may further comprise: an upper end cap provided around an upper end of an outer surface of the upper end plate; a lower end cap provided around an outer surface of a junction of the outer shell and the lower end plate; a lower stopper provided around an outer surface of the protective tube at a predetermined position corresponding to an upper portion of an irradiation hole in a reflector of the research reactor, thus being in contact with the upper portion of the irradiation hole, the lower stopper having a plurality of coolant flow channels; and an upper stopper provided around the outer surface of the protective tube at a predetermined position at which the upper stopper is locked to a locking clamp provided at an upper portion of a chimney of the research reactor. In the instrumented capsule, each of the upper end cap and the lower end cap may be made of aluminum or an aluminum alloy which is softer than in-core materials of the research reactor to protect the reactor from damage. The instrumented capsule may further comprise a cable guide tube for guiding the instrument control cables in the capsule part. The cable guide tube is supported at a lower end thereof by the center of the upper surface of the upper housing of the fuel rod assemblies and at an upper end thereof by the lower surface of the upper end plate. In the meantime, each of the fuel rod assemblies comprises: a cooling block placed between a lower housing and an upper housing which support the irradiation test fuel rods and housing support rods; a cooling block support tube longitudinally passing through the cooling block and locked to the lower housing at a lower end thereof and to the upper housing at an upper end thereof, thus supporting the cooling block; three irradiation test fuel rods each containing sintered nuclear fuel bodies therein and placed in the cooling block such that the lower ends of the fuel rods are locked to fuel rod installation holes of the lower housing, while the upper ends of the fuel rods are locked to fuel rod locking slots of the upper housing; a plurality of hold-down springs fitted over the lower ends of the fuel rods and supported on the upper surface of the lower housing so that the hold-down springs accommodate dimensional changes of the fuel rods induced by irradiation growth during neutron irradiation; three housing support rods passing through the cooling block so that upper ends of the housing support rods are locked to the support rod locking slots of the upper housing, while lower ends of the housing support rods pass through support rod installation holes of the lower housing so as to protrude downwards from the lower end of the lower housing; and a plurality of housing nuts with washers tightened to the lower ends of the housing support rods which protrude downwards from the lower end of the lower housing, so that the irradiation test fuel rods are securely installed in each of the fuel rod assemblies. Each of the irradiation test fuel rods comprises: a sheath tube; a lower end plug which closes the lower end of the sheath tube; an upper end connector mounted to the upper end of the sheath tube; lower alumina spacers placed in a lower portion of the sheath tube; sintered nuclear fuel bodies placed in the sheath tube at positions above the lower alumina spacers; upper alumina spacers having thermocouple installation holes to support thermocouples therein and placed above the sintered nuclear fuel bodies; a plenum spring installed in the sheath tube at a position between the upper end connector and the upper alumina spacers; and an end connector sealing nut tightened to the upper end connector. The sintered nuclear fuel bodies loaded in each of the irradiation test fuel rods comprise first and second sintered fuel bodies each having a hole to receive the thermocouple therein, and a third sintered fuel body without having any hole. In each of the irradiation test fuel rods, the end of the thermocouple is placed in the sintered nuclear fuel bodies. Each of the housing support rods comprises an SPND installation hole of a predetermined depth which is formed downwards from the center of the upper surface of each housing support rod. When the thermocouple is installed in the irradiation test fuel rod through a thermocouple insert hole, the end connector sealing nut is tightened to the upper end of the upper end connector with a sealing tube provided around a thermocouple control cable which is placed at the upper end of the upper end connector, so that the thermocouple insert hole of the upper end connector is sealed. Furthermore, a thermo-neutron absorption tube may be placed between the upper housing and the lower housing of the nuclear fuel rod assemblies. The thermo-neutron absorption tube provides flexibility allowing for controlling the linear power density of the nuclear fuels in the irradiation hole according to in-core properties of the research reactor. Reference should now be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. The instrumented capsule for nuclear fuel irradiation tests in research reactors 1 according to the present invention comprises a capsule part which houses therein a plurality of nuclear fuel rods which are subjected to an irradiation test, a plurality of in-capsule instruments which is installed in the capsule part and connected to a control unit 7 provided outside a research reactor 1 to measure in real time the properties of irradiated nuclear fuels of the fuel rods during the irradiation test, and a connection/treatment part which guides a plurality of instrument control cables extending from the in-capsule instruments of the capsule part to the control unit provided outside the research reactor 1 while protecting the instrument control cables, and allows an operator to easily manipulate the capsule outside the reactor. As shown in FIG. 1, a research reactor 1 comprises a chimney of reactor 3 in which is installed an instrumented capsule. A lower stopper 120 and an upper stopper 140 are mounted at predetermined lower and upper position in the chimney of reactor 3. A locking clamp 5 is provided at upper position of the chimney of reactor 3 to lock the chimney of reactor 3. A control unit 7 and a capsule treatment system 9 are installed outside the research reactor 1. As shown in FIGS. 2 through 5, the capsule part comprises an outer shell 10 with a predetermined length and opposite open ends. One or more nuclear fuel rod assemblies 50, each of which has three irradiation test fuel rods 30 each containing sintered nuclear fuel bodies therein, are loaded in the outer shell 10. An upper support tube 13 and a lower support tube 11 are inserted into upper and lower ends of the outer shell 10 to support the fuel rod assemblies 50 in desired places in the shell 10. An upper end plate 60 and a lower end plate 70 are mounted to the upper and lower ends of the shell 10, respectively, with a plurality of coolant flow channels 63, 73 formed around a center through hole 61, 71 in each of the upper and lower end plates 60 and 70 to minimize impact induced by coolant flow in the shell 10. The capsule part further includes a rod tip assembly that comprises a rod tip 80, a support spring 85, and a rod tip support ring 87. The rod tip 80 is inserted into the center through hole 71 of the lower end plate 70 to move upwards and downwards, with a spring stop ring 81 provided around the rod tip 80 to limit vertical movement of the rod tip 80 relative to the lower end plate 70. The support spring 85 is fitted over the rod tip 80 to support the weight of the capsule. The rod tip support ring 87 is coupled to an upper end of the rod tip 80 which passes upwards through the center through hole 71 of the lower end plate 70. When the rod tip assembly is completely assembled to the lower end plate 70, the support spring 85 which is fitted over the rod tip 80 is stopped at both ends thereof by the spring stop ring 81 of the rod tip 80 and the lower surface of the lower end plate 70 as shown in FIG. 5a. During an irradiation test of the capsule installed in the irradiation hole of the research reactor, impact may be applied to the capsule. However, in the capsule of the present invention, such impact is absorbed by the rod tip 80 placed in contact with a bayonet provided on the bottom of the irradiation hole. Thus, the structure of the capsule is protected from impact. As shown in FIG. 5b, the in-capsule instruments housed in the outer shell 10 of the capsule part include three thermocouples 100 which are installed in the sintered nuclear fuel bodies of the fuel rod assemblies 50, with a plurality of instrument control cables extending from the thermocouples 100 to the outside of the capsule part so as to measure the temperatures of the irradiated nuclear fuel bodies. The in-capsule instruments also include three self-powered neutron detectors (SPND) 110 which are placed in housing support rods 250 of the fuel rod assemblies 50, with an instrument control cable extending from each SPND 110 to the outside of the capsule part. When necessary, the in-capsule instruments may further include a combination of a linear variable differential transformer (LVDT) 103 and a bellows-shaped pressure gauge 107 which may be installed on the sheath tube 305 of each fuel rod 30 to measure in real time variation in the inner pressure of each fuel rod 30, and/or a combination of a linear variable differential transformer (LVDT) 103 and a strain gauge which is not shown in the accompanying drawings but may be installed on the sheath tube 305 of each fuel rod 30 to measure in real time variations in the lengths of the sintered nuclear fuel bodies of each fuel rod 30. As shown in FIG. 5c, the connection/treatment part of the non-instrumented capsule of the present invention comprises a protective tube 130, a junction tree 150, a guide pipe 180 and a grapple head assembly 190. The protective tube 130 is connected to the top of the upper end plate 60 by means of an upper end plate connector 69, and protects the instrument control cables extending from the in-capsule instruments, such as the thermocouples 100 and the SPNDs 110, to the outside of the capsule part. The junction tree 150 is connected to the upper end of the protective tube 130 and has two branch extension parts which are a vertical extension part 153 and an inclined extension part 157, with a cable connection adapter 160 provided at the upper end of the inclined extension part 157 to hold the plurality of instrument control cables. The guide pipe 180 is connected to the inclined extension part 157 through the cable connection adapter 160 and guides the instrument control cables extending from the capsule to the control unit provided outside the research reactor. The grapple head assembly 190 is connected to the upper end of the vertical extension part 153 to be coupled to a capsule treatment system 9 (See FIG. 1) such as an overhead crane positioned above a reactor pool. The capsule part preferably includes one or two nuclear fuel rod assemblies 50, and is limited in the number and lengths of the support tubes thereof according to the number of fuel rod assemblies 50. In other words, when one nuclear fuel rod assembly 50 is loaded in the outer shell 10 of the capsule part, two support tubes, including the upper support tube 13 and the lower support tube 11 with lengths controlled according to the position of the fuel rod assembly 50 in the outer shell 10, are installed in the outer shell 10 above and under the fuel rod assembly 50, respectively, as shown in FIG. 2. The lengths of the support tubes 13 and 11 may be controlled such that the fuel irradiation positions can be changed along a vertical direction in the reactor according to linear power densities of the fuel rods. Thus, it is possible to adjust the irradiation positions for the fuel rod assemblies 50 in an effort to accomplish desired linear power densities and desired combustion degrees of the nuclear fuels. The capsule part also has cable guide tubes 90 and 93 for guiding instrument control cables. As shown in FIG. 7, each of the cable guide tubes 90 and 93 includes a plurality of longitudinal side openings 91. Thus, the instrument control cables extending from the fuel rod assemblies 50 pass through the openings 91 of the cable guide tubes 90 and 93, and thereafter, pass through the center through hole 61 of the upper end plate 60, thus being lead to the outside of the capsule part. Due to the cable guide tubes 90 and 93, the instrument control cables are effectively lead to the outside of the capsule part without failure even though many instruments are installed in the capsule part. The nuclear fuel rod assemblies 50 installed in the capsule of the present invention will be described herein below with reference to FIGS. 5a, 5b, 5c, 8, 9a, 9b and 9c. As shown in the drawings, each of the fuel rod assemblies 50 comprises a lower housing 205, an upper housing 215, a cooling block 235, a cooling block support tube 239, three irradiation test fuel rods 30, three hold-down springs 245, three housing support rods 250, and a plurality of washers 265 and housing nuts 275. As best seen in FIG. 9a, the lower housing 205 comprises three support rod installation holes 213, three fuel rod installation holes 217 and six coolant flow channels 219 which are formed around a center hole 211 of the lower housing 205 while being spaced out at regular intervals. As best seen in FIG. 9b, the upper housing 215 comprises three support rod locking slots 223, three fuel rod locking slots 227 and six coolant flow channels 229 which are formed around a center hole 221 of the upper housing 215 while being spaced out at regular intervals. As shown in FIG. 8, the cooling block 235 is placed between the lower housing 205 and the upper housing 215. The cooling block support tube 239 longitudinally passes through the cooling block 235 and is locked to the lower housing 205 at a lower end thereof and to the upper housing 215 at an upper end thereof, thus supporting the cooling block 235 as shown in FIGS. 5b and 9b. The three irradiation test fuel rods 30, each containing sintered nuclear fuel bodies therein, are placed in the cooling block 235 such that the lower ends of the three fuel rods 30 are locked to the three fuel rod installation holes 217 of the lower housing 205, while the upper ends of the three fuel rods 30 are locked to the three fuel rod locking slots 227 of the upper housing 215. The hold-down springs 245 are fitted over the lower ends of the three fuel rods 30 and are supported on the upper surface of the lower housing 205 so that the hold-down springs 245 accommodate dimensional changes of the fuel rods 30 induced by irradiation growth during neutron irradiation. The three housing support rods 250 pass through the cooling block 235 so that upper ends of the housing support rods 250 are locked to the support rod locking slots 223 of the upper housing 215, while lower ends of the housing support rods 250 pass through the support rod installation holes 213 of the lower housing 205 so as to protrude downwards from the lower end of the lower housing 205. The housing nuts 275 with the washers 265 are tightened to the lower ends of the housing support rods 250 which protrude downwards from the lower end of the lower housing 205, so that the irradiation test fuel rods 30 are securely installed in each of the fuel rod assemblies. As shown in FIG. 10, each of the irradiation test fuel rods 30 comprises a sheath tube 305, a lower end plug 315 which closes the lower end of the sheath tube 305, and an upper end connector 325 mounted to the upper end of the sheath tube 305. Lower alumina spacers 335 are placed in a lower portion of the sheath tube 305, while sintered nuclear fuel bodies 405, 415 and 425 are placed in the sheath tube 305 at positions above the lower alumina spacers 335. One or more upper alumina spacers 345, each having a thermocouple installation hole 341 to support a thermocouple 100 therein, are placed above the sintered nuclear fuel bodies 405, 415 and 425. A plenum spring 355 is installed in the sheath tube 305 at a position between the upper end connector 325 and the upper alumina spacers 345. Each of the irradiation test fuel rods 30 further includes an end connector sealing nut 365 which has a sealing tube coupling hole 361 and is tightened to an upper end of the upper end connector 325. The sintered nuclear fuel bodies loaded in each of the irradiation test fuel rods 30 must be specifically shaped to install the thermocouple 100 therein. In other words, the sintered nuclear fuel bodies of each irradiation test fuel rod 30 comprise a first sintered fuel body 405, a second sintered fuel body 415 and a third sintered fuel body 425. The first sintered fuel body 405 has a hole of a predetermined depth which is formed downwards from the center of the upper surface of the fuel body 405. The second sintered fuel body 415, which has a center through hole 411 to allow the thermocouple 100 to pass through, is placed above the first fuel body 405, while the third sintered fuel body 425 which is a simple fuel body without having any hole is placed under the first fuel body 405. The irradiation test fuel rods 30 having the above-mentioned construction can be controlled in the lengths of the sintered fuel bodies 405, 415 and 425, the length of the sheath tube 305, and the length of the upper end connector 325 according to an object of the irradiation test. When it is required to change the lengths of the sintered fuel bodies 405, 415 and 425, the sheath tube 305 and the upper end connector 325 as described above, the lengths of the cooling block 235, the cooling block support tube 239 and the housing support rods 250 must be changed. Furthermore, an SPND installation hole 251 of a predetermined depth is formed downwards from the center of the upper surface of each of the housing support rods 250 as shown in FIG. 11, with an inlet slot 253 longitudinally formed along a sidewall of each of the housing support rods 250 at a position around the SPND installation hole 251. Thus, an SPND 110 can be installed in the SPND installation hole 251 through the inlet slot 253. After the SPND 110 is installed in the SPND installation hole 251, the inlet slot 253 is closed by a slot cover 257 and sealed through a caulking process. As shown in FIG. 10, a thermocouple 100 is inserted into each of the irradiation test fuel rods 30 through a thermocouple insert hole 321 of the upper end connector 325 so that a lower end of the thermocouple 100 is placed at a predetermined position in the fuel rod 30. After the thermocouple 100 is inserted into the irradiation test fuel rod 30 through the thermocouple insert hole 321, the end connector sealing nut 365 is tightened to the upper end of the upper end connector 325 with a sealing tube 105 provided around a thermocouple control cable which is placed at the upper end of the upper end connector 325. Thus, the thermocouple insert hole 321 of the upper end connector 325 is sealed. If desired to provide flexibility allowing for controlling the linear power density of the nuclear fuels in the irradiation hole according to in-core properties of the research reactor, a thermo-neutron absorption tube 95 having an inner diameter corresponding to the outer diameter of the cooling block 235 may be placed between the upper housing 215 and the lower housing 205 of the nuclear fuel rod assemblies 50 as shown in FIG. 9c. An upper end cap 65, made of aluminum or an aluminum alloy, is fitted around the upper end of the outer surface of the upper end plate 60 as shown in FIGS. 3c and 5c. To prevent the upper end cap 65 from being undesirably removed from the upper end plate 60, a cap locking ring 67 is forcibly inserted into a gap between the upper end plate 60 and the upper end cap 65. In the same manner, a lower end cap 75, made of aluminum or an aluminum alloy, is fitted around the outer surface of a junction of the shell 10 and the lower end plate 70 as shown in FIGS. 3a and 5a. To prevent the lower end cap 75 from being undesirably removed from a designated position, a cap stopper 77 is forcibly fitted around the lower end of the outer surface of the lower end plate 70. As described above, the instrumented capsule of the present invention is provided with both the upper end cap 65 and the lower end cap 75 which are made of aluminum or aluminum alloy and placed to come into direct contact with the inner wall of the irradiation hole. Due to the upper and lower end caps 65 and 75, the upper end plate 60 and the lower end plate 70 are not brought into direct contact with the inner wall of the irradiation hole regardless of in-pile liquid vibration. Furthermore, as both the upper end cap 65 and the lower end cap 75 are made of aluminum or aluminum alloy, the end caps 65 and 75 may minimize damage to the inner wall of the irradiation hole even though the end caps 65 and 75 come into contact with the inner wall of the irradiation hole. Thus, the instrumented capsule of the present invention can be used in an irradiation test for a lengthy period while ensuring desired structural integrity and safety of both the capsule and the research reactor. Furthermore, a lower stopper 120 is securely provided around the outer surface of the protective tube 130 at a position corresponding to an upper portion of the irradiation hole in a reflector of the research reactor as shown in FIG. 5c such that the lower stopper 120 is in contact with the reflector. An upper stopper 140 is securely provided around the outer surface of the protective tube 130 at a predetermined position at which the upper stopper 140 is locked to a locking clamp 5 provided at an upper portion of a chimney of the reactor 3. The lower stopper 120 is provided with a plurality of coolant flow channels 121 to minimize impact induced by the flow of the coolant as shown in FIGS. 3d and 12. An upper stopper fixing guide tube 145 having a plurality of locking holes is welded to the outer surface of the protective tube 130, while the upper stopper 140 is fitted over the fixing guide tube 145 and locked thereto by a plurality of locking screws 147. To use the instrumented capsule of the present invention for a nuclear fuel irradiation test in a research reactor, the capsule is transported to the research reactor through a designated procedure for irradiation tests, and is installed in the in-core irradiation hole of the reactor as shown in FIG. 1. Thereafter, the instrument control cables guided by the guide pipe 180 are connected to the control unit provided outside the research reactor. The nuclear fuel irradiation test is, thereafter, executed through the designated procedure for irradiation tests. When the instrumented capsule is completely installed in the in-core irradiation hole, the capsule is supported in the irradiation hole by the lower end cap and the upper end cap which have outer diameters larger than the diameter of the outer shell of the capsule and are in contact with an inner wall of the irradiation hole. Furthermore, a rod tip of the instrumented capsule is placed in contact with a bayonet provided on the bottom of the irradiation hole so that impact which may be applied to the capsule in an axial direction can be effectively absorbed by a support spring fitted over the rod tip. Furthermore, a lower stopper 120 and an upper stopper 140, which are mounted around the outer surface of a protective tube at predetermined lower and upper positions, are locked to an upper portion of the irradiation hole in a reflector of the research reactor and locked to a locking clamp provided at an upper portion of a chimney of the reactor, respectively, thus stably supporting the capsule. Therefore, the instrumented capsule of the present invention can be used in the nuclear fuel irradiation test for a lengthy period while securing the desired structural integrity and safety of both the capsule and the research reactor. As described above, the present invention provides an instrumented capsule for nuclear fuel irradiation tests in research reactors. The instrumented capsule of the present invention is used to measure in real time the properties of nuclear fuels irradiated in a research reactor during a nuclear fuel irradiation test which must be executed to provide nuclear fuel irradiation test data required for the design and development of nuclear fuels. Thus, the instrumented capsule of the present invention provides a variety of irradiation test data which are required along with data obtained from post-irradiation tests in designing nuclear fuels and determining in-pile performance and structural integrity of nuclear fuels. The instrumented capsule of the present invention can be used for irradiation tests of a variety of nuclear fuels, such as metal fuels and ceramic fuels, at the same time, and furthermore, can be used for irradiation tests of a large amount of nuclear fuels at the same time because the capsule contains a maximum of six fuel rods therein. In addition, as the capsule has improved structural integrity and improved operational reliability, the capsule can be used for a lengthy nuclear fuel irradiation test. The capsule further minimizes damage to the inner wall of the irradiation hole of the research reactor caused by mechanical vibration of the capsule induced by in-pile liquid vibration even though the capsule is irradiated in the irradiation hole for a lengthy period. Thus, the instrumented capsule of the present inventions ensures desired operational safety of the research reactor. Furthermore, in the instrumented capsule of the present invention, a thermo-neutron absorption tube can be installed in a nuclear fuel rod assembly, thus allowing control of linear power density of the nuclear fuel in the irradiation hole. This allows the positions of the fuel rods in the irradiation hole to be controlled as desired. Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. |
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description | 1. Field of the Invention The present invention relates to a decay heat removal system of a liquid metal reactor, and introduces a new heat exchange system which integrates a decay heat removal heat exchanger or decay heat exchanger (DHX) and an intermediate heat exchanger (IHX). The new heat exchange system makes it possible for effective decay heat removal to start immediately after an occurrence of an accident while maintaining the complete passivity of the decay heat removal operation. By this invention, passive, proper and stable cooling of the nuclear core can be achieved from the initial stage of an accident. 2. Description of the Related Art Liquid Metal Reactor A liquid metal reactor (LMR) generates heat using fast neutrons from nuclear fission, and simultaneously converts a non-fissile material U238 into a fissile material Pu239, thereby serving as a breeding reactor by producing more fissile material than the fuel it consumes. Further, the liquid metal reactor is a reactor which can burn radioactive nuclides produced from other type reactors such as water-cooled reactors, and thus can reduce substantially the storage load of high level radioactive wastes generated from other type reactors. The above liquid metal reactors are divided into loop type reactors and pool type reactors. The loop type reactor has a structure such that heat transfer devices of its primary heat transport system are installed outside a reactor vessel, and is advantageous in that the heat transfer devices are easily maintained and repaired and the reactor vessel has a simple structure. On the other hand, the pool type reactor has a structure such that its primary heat transport system including the equipment such as intermediate heat exchangers (IHXs) and pumps are installed in a reactor vessel, and is advantageous in that the leakage of the coolant due to the breakage of a pipeline of the primary system is prevented and a large amount of the coolant is contained in the primary system, thus having a high thermal inertia that makes the system transient speed slow and provides a long grace time in an accident. The liquid metal reactor uses liquid metal as coolant, and preferably uses sodium (Na) having an excellent heat removal capacity as coolant. Decay Heat Removal Type Conventional liquid metal reactors use various types of decay heat removal systems for removing decay heat from the nuclear core in an accident. Hereinafter, a pool type reactor will be exemplarily described. FIG. 1 is a longitudinal-sectional view of a conventional active decay heat removal system. In FIG. 1, a nuclear core 11 installed in a reactor 10 heats sodium (Na) 17 and feeds the heated sodium 17 into a hot pool 18, which is positioned in the upper part of the reactor 10. The reactor includes conventional pumps 12 for circulating the liquid sodium. The sodium 17 in the hot pool 18 transfers its heat to intermediate heat exchangers (IHXs) 13, thus being cooled. The cooled sodium 17 is fed into the cold pool 19, which is positioned in the lower part of the reactor 10, and again enters the core 11. The IHXs 13 transfers heat thereof to a steam generation system (not shown), and the steam generation system generates steam, and then generates electricity. A decay heat exchanger 14 is installed separately from the IHXs 13 in the hot pool 18 of the reactor 10, and a valve 15 is installed in the pipeline connected to the decay heat exchanger 14. The valve 15 serves to prevent heat loss to the outside through the decay heat exchanger 14 when the reactor 10 operates normally. That is, the valve 15 is closed when the reactor 10 operates normally, and is opened in an accident. In the active decay heat removal system shown in FIG. 1, the switch valve 15 installed in the pipeline connected to the decay heat exchanger 14 needs to be opened in an accident in order to activate heat exchange with the external atmosphere. It means that an active decay heat removal system has weak safety features of requiring the operation of active devices such as a motor and valve 15 and also the supply of electric power from the outside for the operation of the valve 15. Accordingly, instead of the above active decay heat removal system, there is required a passive decay heat removal system, in which removal of decay heat is automatically activated without relying on active devices. FIG. 2 illustrates a conventional passive decay heat removal system. The structure of the passive decay heat removal system of FIG. 2 is the same as that of the active decay heat removal system of FIG. 1 in that a nuclear core 21, which is installed in a reactor 20, heats sodium (Na) 27 and feeds via pumps 22 the heated sodium 27 into a hot pool 28, which is positioned in the upper part of the reactor 20, and the sodium (Na) is cooled by exchanging heat in IHXs 23. In an accident, the normal heat transfer path of the core-IHX-steam generation system is not credited and the sodium in the reactor is heated since the normal heat transfer path is no longer available, and the sodium expands. Consequently, the sodium level X1 in the hot pool 28 rises, and the sodium in the reactor 20 flows over the overflow slot 30. The overflowed sodium 27 directly contacts the wall 31 of a reactor vessel 30, thus transferring its heat to the wall 31 of the reactor vessel 30. The heat transferred to the wall 31 of the reactor vessel 30 is transferred to the air route 26 outside the reactor vessel 30 by radiation and convection heat transfer, and is then transferred to the air flowing in the air route 26 divided by an air separator 24. The air, to which the heat is transferred, continuously flows out to the atmosphere by virtue of the difference in its density along its path, that is, by the natural convection. Cold external air is introduced into the reactor vessel 30 through the air path 26. The arrow 25 in the air path 26 represents the flow path of the air. The above-described passive decay heat removal system is operated completely by the natural phenomena without relying on any operator action or any active device operation at an accident, thus being advantageous in that the reliability of the system operation is very high. However, it takes several hours for the sodium to overflow, that is, it takes several hours for the decay heat removal system to become fully functional and be able to remove the decay heat properly. During this period of time before the system becomes functional, proper heat removal from the reactor pool is not made and it is difficult for the natural circulation flow head to be built up. The flow head is the driving force of the natural circulation in the pool which cools the core. Consequently, the core cooling capability becomes low and the temperature of the nuclear fuel in the core can rise excessively high. Summarizing the description, in a conventional passive decay heat removal system, the volume of the fluid in the reactor needs to be expanded substantially for the system to be able to remove decay heat properly, and the expansion of the fluid volume requires time and a rise of the pool temperature, and this feature results in weak safety features that the core cooling capability is not certain during, the time period of the volume expansion and the temperature in the reactor may become unnecessarily high. Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a decay heat removal system which can passively and effectively remove the decay heat immediately after the initiation of an accident without relying on any external support such as an operator action or power supply. To achieve the object, the system is designed so that the natural circulation flow head can be properly built and maintained during an accident from the moment immediately after an accident. According to an aspect of the present invention, the above and other objects of the present invention can be accomplished by the provision of a decay heat removal system for a liquid metal reactor comprising: a reactor vessel including a hot pool for containing a high-temperature fluid discharged from a reactor core and a cold pool which is separated from the hot pool by a partition and contains a low-temperature fluid; an intermediate heat exchanger (IHX) transferring heat from the hot pool to an external steam generation system and positioned in the hot pool, the IHX having a bottom portion connected to the cold pool and discharging the fluid from the hot pool into the cold pool; a decay heat exchanger (DHX) separated from the IHX by a designated distance for transferring reactor core decay heat to the external air; a cylinder surrounding the IHX and the DHX, and having an opened top portion protruding out of the level of the fluid in the hot pool, a bottom portion connected to the cold pool and a guide pipe for allowing the passage of the fluid from the hot pool into the IHX; and a pump for pumping the fluid from the cold pool to the reactor core, whereby the level of the fluid in the cylinder is maintained lower than the level of the fluid in the hot pool during its operation. According to another aspect of the present invention, there is provided a modified decay heat removal system for a liquid metal reactor comprising: a reactor vessel including a hot pool for containing a high-temperature fluid discharged from a reactor core and a cold pool which is separated from the hot pool by a partition and contains a low-temperature fluid; an intermediate heat exchanger (IHX) transferring heat from the hot pool to an external steam generation system and positioned in the hot pool, the IHX having a bottom portion connected to the cold pool and discharging the fluid from the hot pool into the cold pool; a decay heat exchanger (DHX) separated from the IHX by a designated distance for transferring reactor core decay heat to the external air; a cylinder surrounding the IHX and the DHX, and having an opened top portion protruding out of the level of the fluid in the hot pool, a bottom portion connected to the cold pool and a guide pipe for allowing the passage of the fluid from the hot pool into the IHX; a switch valve installed on the outer wall of the guide pipe in the cylinder and having a buoy floatable on the fluid by buoyancy to switch the flow path from the guide pipe into the cylinder; and a pump for pumping the fluid from the cold pool to the reactor core, whereby the level of the fluid in the cylinder is maintained lower than the level of the fluid in the hot pool during its operation. Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings. Hereinafter, although the following discussion will present a decay heat removal system for a pool type reactor, this may be also applied to a loop type reactor (through modification more or less or even omission of an element). Structure of Decay Heat Removal System FIG. 3 is a longitudinal-sectional view of a decay heat removal system for a pool type reactor in accordance with the first embodiment of the present invention; FIG. 4 is a perspective view illustrating the installation of an intermediate heat exchanger (IHX), a decay heat exchanger (DHX) and a cylinder; FIG. 5 is a cross-sectional view taken along the line A-A of FIG. 4; and FIG. 6 is a cross-sectional view taken along the line B-B of FIG. 4. A pool type reactor 50 has intermediate heat exchangers (IHXs) 70 and pumps 53 installed in a reactor vessel 51, which is filled with coolant. As shown in FIG. 3, a hot pool 56 is formed in the reactor vessel 51 of the pool type reactor 50 to contain a hot fluid discharged from a reactor core 52. Further, a cold pool 55 is divided from the hot pool 55 by a partition 54 to contain cooled fluid formed from the hot fluid in the hot pool 55 by heat transfer. When the heat generated by nuclear fission in the reactor core 52 is transferred to the fluid in the reactor core 52, the heated fluid moves to the hot pool 56, and into the IHXs 70 positioned in the hot pool 56 transferring heat to operating fluid in the IHXs 70. The IHXs 70 serve to transfer the heat of the hot pool fluid to the intermediate heat transport system (IHTS) (not shown). It means that each of the IHXs 70 is also a part of an intermediate heat transport system (IHTS) that includes a steam generator, a pipeline and a pump, which are positioned outside the reactor vessel 51. The coolant filling the hot pool 56 and the cold pool 55 of the reactor vessel 51 is made of sodium (Na) having an excellent heat removing capacity. The IHX 70 has an opening at the bottom communicating with the cold pool 55 so that the IHX 70 discharges the fluid from the hot pool 56 into the cold pool 55 while exchanging heat with the fluid flowing inside the heat transfer tubes 71. That is, as shown in FIG. 4, the fluid from the hot pool 56 is flown along outer surfaces of heat transfer tubes 71 of the IHX 70 to perform heat transfer through convection. Then, the fluid cooled by the heat transfer is discharged into the cold pool through the bottom opening of the IHX 70. As shown in FIGS. 3 and 4, the decay heat exchanger (DHX) 80 is installed around the IHX 70. That is, as shown in FIGS. 3 and 4, the DHX 80 has heat transfer tubes that are coiled around the IHX 70, spaced at a designated distance from the IHX 70. The DHX 80 consists of the cylinder, heat transfer tubes and the outer wall of the IHX 70 and comes to have the shape of an annular cylinder. The decay heat removal system includes the DHX 80, an external heat exchanger, piping connecting the DHX to the external heat exchanger, in which only the decay heat removal exchanger 80 is installed inside the reactor vessel 51. The external heat exchanger finally discharges the transferred core decay heat to the atmosphere. As in the reactor 50, sodium (Na) is used as operating fluid contained within flow channels of the external heat exchanger and the DHX since it has an excellent heat conductivity. The external heat exchanger installed outside the reactor is located at a higher level than the DHX in order to generate natural convection and can be operated without using a pump. The heat transfer tubes of the DHX 80 are arranged adjacent to the IHX 70. The IHX 70 and the heat transfer tubes of the DHX 80 are primarily separated from the fluid in the hot pool 56 by the cylinder 61. The cylinder 61 surrounds the IHX 70 and the DHX 80. The top portion of the cylinder 61 is open and protrudes from the upper surface of the level X1 of the fluid in the hot pool 56. Further, the bottom portion of the cylinder 61 extends to the cold pool 55. As shown in FIG. 4, the cylinder 61 has an overall cylindrical shape. The IHX 70 and the heat transfer tubes of the DHX 80 are arranged inside the cylinder 61, and a guide pipe 63 is connected to the IHX 70 so that the fluid can flow from the hot pool 56 into the IHX 70. As shown in FIG. 4, the guide pipe 63 has a cylindrical tubular shape, and is so designed that the fluid flows only into the IHX 70 through the pipe 63. The bottom portion of the cylinder 61 is connected to the cold pool 55 through the peripheral holes 62 so that the fluid can flow between the cylinder 61 and the cold pool 55. That is, the bottom portion of the cylinder 61 has a central through hole 72 formed in the center thereof, to which the lower end of the IHX 70 is installed. The IHX, the heat transfer tubes of the DHX and the cylinder are constituted into one unit of the heat exchanger system, and a plurality of such heat exchanger systems are arranged in the reactor vessel. Pumps 53 are installed in the cold pool 55 of the reactor vessel 51 to circulate the fluid from the cold pool 55 into the reactor core 52. While the pumps 53 pump the fluid from the cold pool 55 into the reactor core 52 during normal operation, the fluid flow automatically maintains the level X2 of the fluid in the cylinders 61 lower than the level X1 of the fluid in the hot pool 56 and prevents undesirable heat loss through DHX during normal reactor operation. This feature will be explained later in details. FIG. 11 is a schematic view illustrating the principle of forming different levels of the fluid in the cylinder 61 and the hot pool 55 of the present invention during the operation of the pump. The following discussion explains the vertical pressure distribution between a point □ and a free surface, in which the point □ is positioned at the bottom portion of the annular space in which the heat transfer tubes of the DHX 80 are arranged, as well as the bottom portion of the IHX 70. The pressure at the point □ can be described by Equations 1 and 2 below:P2a=P1+ρgΔHa−(ρva2)/2 Equation 1, andP2b=P3+ρgΔHb−(ρvb2)/2 Equation 2, wherein P2a is obtained by the integral path from the point □ on the hot pool free surface to the point □ along the IHX path, and P2b is obtained by an integral path from the point □ on the free surface to the point □ along the annular space path, in which the heat transfer tubes of the DHX 80 therein are arranged. When the pump 53 is operated, the velocity va of the fluid flowing in the IHX is considerably high, but the velocity vb of the fluid flowing in the space, in which the heat transfer tube of the DHX 80 therein is arranged, is practically zero. Accordingly, Equation 2 above is expressed as Equation 3 below:P2b=P3+ρgΔHb Equation 3. Since P2a and P2b denote the pressure at the same point, they need to be the same, and thus are expressed as Equation 4 below:P1+ρgΔHa−(ρva2)/2=P3+ρgΔHb Equation 4. Since the pressures at the point □ and the point □ are pressures on the free surface exposed to the gas inside the reactor, P1=P3 and thus Equation 5 below is obtained:ΔHb=ΔHa−(va2)/2g Equation 5. When the pump 53 is operated, the relation of ΔHa□ΔHb is obtained due to the velocity of the fluid. Accordingly, the fluid level X2 in the cylinder becomes much lower than the fluid level X1 in the hot pool. However, when the pumps 53 are not operated such as during an accident, the velocity of the fluid flowing the IHX 70 reaches approximately zero, and thus ΔHa and ΔHb become nearly the same (ΔHb□ΔHa). This means that the fluid in the cylinder 61 rises to the level X1 of the fluid in the hot pool when the pump 53 is stopped. Accordingly, when the pump 53 is operated, during normal reactor operation, the level X2 of the fluid in the cylinder 61 is maintained much lower than the level X1 of the fluid in the hot pool 56 so that the heat transfer tubes of the DHX 80 do not contact the fluid in the reactor 50. When the pump 53 is stopped, the level X2 of the fluid in the cylinder 61 rises to the level X1 of the fluid in the hot pool 56 so that the heat transfer tubes of the DHX 80 contact the fluid in the reactor 50. Operation of Decay Heat Removal System As described above, the decay heat removal system of the present invention comprises the IHXs installed in the reactor vessel and the DHXs surrounding the IHXs. Both of the IHXs and DHXs are arranged within the same cylinders. Here, the operation of the decay heat removal system of the present invention will be described in detail with reference to FIGS. 7a and 7b. FIGS. 7a and 7b illustrate the operation of the decay heat removal system of FIG. 3, and more particularly, FIG. 7a illustrates the decay heat removal system during normal operation in a pool type reactor, and FIG. 7b illustrates the decay heat removal system during an accident in a pool type reactor. It is necessary to design the DHX 80 so that the heat transfer rate by the DHX during normal reactor operation, that is, the heat loss during normal operation is minimum but is sufficiently large to achieve sufficient reactor core cooling during an accident. For this purpose, the DHX 80 is placed within the cylinder 61 isolating its heat transfer tubes from the fluid in the hot pool 56 and also its heat transfer tubes are separated from the IHX 70 by a designated distance in a radial direction in order to avoid direct contact with the IHX 70. In a vertical direction, the DHX 80 is isolated from the fluid in the reactor 50 based upon the different fluid levels formed by the operation of the pump 53 as above. That is, as shown in FIG. 7a, the level X2 of the fluid in the cylinder 61 from the cold pool 55 is lower than the level X1 of the fluid in the hot pool 56 during normal reactor operation. Accordingly, the heat transfer tubes of the DHX 80 are placed in gas filled in the reactor 50 without contacting the fluid in the cold pool. In this case, the cylinder 61 is filled with inert gas such as helium, nitrogen, argon and etc. The inert gas prevents direct contact of the fluid in the pool such as sodium with air to avoid chemical reaction. Also, the inert gas can achieve thermal shielding since it has poor heat transfer characteristics. In normal operation of the reactor 50, the fluid is fed from the hot pool 56 into the IHX 70 through the guide pipe 63, discharges its heat in the IHX 70, and is then fed to the cold pool 55. Because the DHX 80 does not contact the fluid in the hot pool 56 or in the cold pool 55 as shown in FIG. 7a, the heat transfer in the DHX 80 is made only by the very inefficient gas convection or radiation. As a consequence, the entire quantity of the heat transfer made in the DHX 80, that is, the heat loss during normal operation of the reactor 50 becomes negligibly small. In an abnormal state, i.e., in an accident of the reactor 50, the pumps 53 are stopped by a reactor protection system (not shown), and the level X2 of the fluid in the cylinder 61 becomes approximately the same as the level X1 of the fluid in the hot pool 56. It means the cylinder 61 is filled with the fluid from the cold pool 55 and the heat transfer tubes of the DHX 80 come to have direct contact with the fluid of the cold pool 55 so that heat transfer can be effectively made. The fluid level elevation in the cylinder 61 as above is immediately formed when the pump 53 is stopped in an accident. Since the normal heat transfer path of a plant, that is, reactor core-IHX-IHTS-steam generator-condenser-atmosphere is for normal reactor operation, its design is made with much emphasis on plant economics while less emphasis is given on safety. Consequently the normal heat transfer path is not formally credited for assessing the plant safety at an accident and a nuclear plant should be able to remove the core decay heat only by the system dedicated for the decay heat removal, such as the decay heat removal system of this invention, without using the normal heat transfer path. In an accident, the decay heat will be removed as follows. When the reactor has an accident, the pumps 53 are stopped by a reactor protection system (not shown). Then, the level of fluid in the annular space of the DHX 80 is raised so that the heat transfer tube of the DHX 80 is submerged into the fluid in the reactor 50. The hot fluid in the hot pool 56 from the reactor core 52 flows into the IHX 70 via natural. Heat of the fluid entered the IHX 70 is transferred to the fluid filled in the cylinder 61 through the wall of the IHX 70, and then to the heat transfer tubes of the DHX 80. Here, since the fluid is made of liquid metal such as sodium having a high heat transfer coefficient, it can efficiently transfer heat to the DHX 80. The heated fluid inside the heat transfer tubes of the DHX 80 flows to an external heat exchanger (not shown) placed outside the reactor 50, and after being cooled by the air of the external heat exchanger, is circulated again into the DHX 80 inside the reactor 50 by the natural circulation, thereby forming a natural and continuous heat transfer cycle. Also explaining the fluid in the reactor side, after being cooled through the heat exchange with the DHX 80, the fluid flows from the IHX 70 into the cold pool 55, and into the reactor core 52 and then is heated by the decay heat, and then is circulated into the hot pool 56 and the IHX 70. The above fluid circulation has two flow segments, i.e., a high-temperature segment from the reactor core 52 through the hot pool 56 to the DHX 70 and a low-temperature segment from the DHX 70 through the cold pool 55 to the reactor core 52. At the two segments there are definite and stable heating and cooling, respectively, and thereby stable and passive natural convection cooling of the core can be achieved. Also the initiation of the decay heat removal by the DHX 80 of the present invention is made purely passively without relying on any operator action or external power supply. Further, the decay heat removal system of the present invention performs the decay heat removal function immediately after the reactor has an accident. In the conventional decay heat removal system shown in FIG. 2, the heat transfer for removing decay heat is performed only after the temperature rises to the extent that the fluid in the hot pool 28 expands and floods into the cold pool 29 to form a decay heat removal circuit. This requires a long time before initializing the decay heat removal system, and thus has a difficulty in immediately coping with an accident. However, in the decay heat removal system of the present invention, the level of the fluid in the cylinder rises immediately after the stoppage of the pumps, and contacts the DHX, thereby forming an efficient decay heat removal circuit. Accordingly, the decay heat removal system of the present invention immediately copes with an accident of the reactor. In addition to the immediate removal of the decay heat in the reactor, the decay heat removal system of the present invention further has several advantages, as follows. 1) Stable Cooling of Reactor Core In the conventional system as described above, the decay heat removal is not effectively made until the fluid temperature increases to the extent of expansion so that the flow over the overflow slot is formed. Accordingly, a cooling source is not clear during that period of the expansion, and the formation of the natural convection head required for cooling the reactor core is unreliable. Thereby, the local temperature in the reactor core can exceed a limit value even though the mean temperature of the fluid in the reactor remains under the limit value. However, the decay heat removal system of the present invention performs decay heat removal immediately after the accident of the reactor and presents a cooling source clear, thereby reliably forming a route for natural convection through the reactor core. Accordingly, the decay heat removal system of the present invention overcomes the unreliability of the conventional system in order to stably cool the reactor core. 2) Prevention of Exposure of Internal Structure of Reactor to High Temperature In the conventional system, the decay heat removal is performed only after the fluid in the reactor is heated to a designated temperature or more. However, the decay heat removal system of the present invention operates immediately after the occurrence of an accident without waiting for the fluid temperature increase to a designated value or more. This can limit the maximum temperature of an internal structure of the reactor remarkably below a limit temperature as well as remarkably shorten the exposure time of the internal structure to high temperature and reduce heat load to the internal structure, thereby improving the mechanical integrity of the internal structure. In an accident, the fluid passing through the IHX in the conventional system does not remove the decay heat from the reactor, but merely connects the hot pool with the cold pool. This reduces the temperature difference between a high-temperature region and a low-temperature region in the reactor, making it difficult to build up a fluid head for natural convection required to cool the reactor core in an accident and deteriorating a cooling capacity. However, the present invention allows the fluid passing through the IHX to be cooled also via the heat transfer to the DHX. The reactor protection system is designed to automatically trip the pumps when there is an accident to prevent the heat input from the pumps to the system. In the case of an extremely unlikely event of multiple failures, in which the reactor protection system is not enabled either, the decay heat removal system of the present invention operates similar to the conventional decay heat removal system. That is, when the fluid in the hot pool 56 of the reactor 50 expands according to temperature growth to the extent of flowing over the top of the cylinder 61, the hot fluid from the hot pool 56 directly contacts the heat transfer tube of the DHX 80, thereby to efficiently remove decay heat. In this case, since the pumps 53 are operated, the fluid is fed at a sufficient flow rate to the reactor core 52, thereby to prevent the above-described problem in that the reactor core is of locally overheated. That is, the decay heat removal system of the present invention stably cools the reactor core 52 in any type of accidents including the exceptional multiple failures. The decay heat removal system in accordance with the first embodiment of the present invention has been described. Hereinafter, a decay heat removal system in accordance with a second embodiment of the present invention will be described in detail. In addition to the structure of the decay heat removal system of the first embodiment, the decay heat removal system of the second embodiment further comprises a switch valve, which is operated based on the action of the pumps, in order to enhance the cooling function. Operation of Switch Valve of Decay Heat Removal System FIG. 8 is a perspective view of a decay heat removal system for a pool type reactor in accordance with the second embodiment of the present invention, FIG. 9 is a cross-sectional view of the switch valve of FIG. 8 during normal operation, and FIG. 10 is a cross-sectional view of the switch valve of FIG. 8 in an accident. The decay heat removal system of the second embodiment of the present invention comprises a switch valve for allowing the fluid in the hot pool to circulate directly into the cylinder. The reactor vessel, the IHX 70, the DHX 80 and the pump of the decay heat removal system in this embodiment have the same structures as those in the first embodiment. The components in this embodiment shown in FIG. 8, which are substantially the same as those in the first embodiment, are denoted by the same reference numerals even though they are depicted in different drawings. A switch valve 91 is installed on the outer wall of the guide pipe 64 in the cylinder 61. A through hole 94 is formed through the guide pipe 64 of the cylinder 61 so that the fluid flowing from the hot pool to the IHX 70 is introduced into the cylinder 61 therethrough. When the switch valve 91 is opened from the through hole 94, the fluid in the hot pool flows through the through hole 94 into the cylinder 61, in which the DHX 80 is installed, thereby forming a flow path from the hot pool to the cylinder 61. Here, the through hole 94 is formed in an inclined surface of an inlet 92 protruded from the outer circumference of the cylinder 61. The inlet 92 is protruded from the guide pipe 64 such that the lower surface of the inlet 92 has the longest length and the upper surface of the inlet 92 has the shortest length, thereby obtaining the inclined surface, which is closed by the switch valve 91. The above inclination of the inclined surface of the inlet 92 allows the switch valve 91 to steadily close the inlet 92 by means of the weight load of the valve and the buoy 93 which is described below. The switch valve 91 hinged to the upper part of the inlet 92. A buoy 93 is attached to the switch valve 91 to be floated on the fluid by buoyancy. The buoy 93 is designed heavy enough to withstand the pressure of the fluid in the guide pipe 64 so that the inlet 92 is closed by the switch valve 91 during normal operation. That is, as shown in FIG. 9, the force for closing the switch valve 91 by means of a moment of the buoy 93 is larger than the force for opening the switch valve 91 by means of the pressure of the fluid acting inside the switch valve 91. This prevents the fluid from flowing into the decay heat removal system in normal operation. Also, the switch valve 91 is designed to be automatically opened by the buoyancy acting on the buoy 93 as shown in FIG. 10 when the cylinder 61 is filled with the fluid in an accident of the reactor. The buoy 93 has a volume sufficient to automatically open the switch valve 91 by the buoyancy. That is, the buoy 93 has a structure of a balloon containing a weight, with a weight sufficient to maintain the closed position of the switch valve 91 against the pressure of the fluid in the guide pipe 64 if surrounded by gas, and a volume sufficient to completely open the switch valve 91 by means of the buoyancy if floated on the fluid in the cylinder 61. Here, the volume of the buoy 93 sufficient to completely open the switch valve 91 means that the mean density of the buoy 93 is much lower than the density of the fluid. Operation of Switch Valve of Decay Heat Removal System In the decay heat removal system of this embodiment of the present invention, the switch valve 91 is closed when the reactor operates normally. When the reactor operates normally, the level X2 of the fluid in the cylinder 61 is much lower than the level X1 of the fluid in the hot pool 56 as shown in FIG. 7a, and the heat transfer tubes of the DHX 80 lose contact with the fluid of the pool but are exposed to gas. Accordingly, as described above, the efficient heat transfer in the DHX cannot be made and the heat loss during normal operation becomes negligible. This means that the switch valve 91 is closed as shown in FIG. 9. In gas, the weight of the buoy 93 generates a clockwise moment which closes the switch valve 91 larger than the counterclockwise moment from the pressure of the fluid in the guide pipe 64 which opens the switch valve 91, in order to maintain the closed position of the switch valve 91. When the reactor has an accident, the level X2 of the fluid in the cylinder 61 rises up to the level X1 of the fluid in the hot pool as shown in FIG. 7b. This means that the inside of the cylinder 61 is filled with the fluid and the switch valve 91 is affected by the fluid. When the buoy 93 of the switch valve 91 rises by the buoyancy of the fluid, the switch valve 91 is opened as shown in FIG. 10 so that the fluid flows from the hot pool into the cylinder 61. When the fluid in the hot pool flows into the cylinder 61 through the switch valve 91, a flow path from the hot pool into the cold pool is formed, and the fluid from the hot pool directly contacts the heat transfer tubes of the DHX 80, thereby forming an efficient heat transfer path for removing decay heat. Such a heat transfer path is used together in parallel with the heat transfer path between the fluid passing through the IHX and the heat transfer tubes of the DHX as described in the above first embodiment. Accordingly, the decay heat removal system of the second embodiment can have enhanced decay heat removal capability while maintaining those advantages of the decay heat removal system of the first embodiment. As apparent from the above description, the present invention provides a decay heat removal system which works on the natural convection and completely passively without relying on any operator action or external support in an accident. Further, the decay heat removal system of the present invention is designed to operate immediately after an accident without losing the complete passivity by utilizing the natural level rise at the trip of the pump. Accordingly, the decay heat removal system of the present invention eliminates the uncertainty in cooling the reactor core at an early stage of an accident, thus improving the plant safety, and shortens the time of an internal structure of the reactor exposed to high temperature and lowers the maximum temperature of the internal structure, thus improving the mechanical integrity of the internal structure. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. |
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claims | 1. A method of operating a scanning probe microscope having a cantilever having a minute probe at one end thereof and a reflective surface portion, a laser beam radiating device for radiating laser beans onto the reflective surface portion of the cantilever, an optical position sensor for detecting positions of laser beams reflected by the reflective surface portion, specimen moving means for moving a specimen relative to the probe, and cantilever oscillating means for periodically oscillating the cantilever at a predetermined amplitude, the method comprising the steps of: performing a first operation in which the specimen is moved relative to the probe and uneven surface data of the specimen surface is obtained when the optical position sensor detects a reduced amplitude of the cantilever smaller than the predetermined amplitude during the relative movement when the probe comes into contact with the specimen, the uneven surface data being obtained by controlling the specimen moving means to move the specimen relative to the probe in upward or downward directions in order to maintain the reduced amplitude constant; and performing a second operation in which physical action force data of the specimen is obtained by causing relative movement of the specimen and the probe while keeping the probe spaced by a predetermined distance from the specimen on the basis of the uneven surface data obtained in the first operation; wherein, in the first operation, the uneven surface data is obtained by controlling the oscillating means so that the cantilever is oscillated outside a frequency band defined by one-half the value of a dependent curve of the cantilever oscillating frequency and amplitude and, in the second operation, the cantilever is oscillated with a frequency near a resonant point of the dependent curve of the cantilever oscillating frequency and amplitude. 2. A method of operating a scanning probe microscope having a cantilever having a minute aperture at one end thereof and a reflective surface portion, a laser beam radiating device for radiating laser beams onto the reflective surface portion of the cantilever, an optical position sensor for detecting positions of laser beams reflected by the reflective surface portion, specimen moving means for moving a specimen relative to the probe, and cantilever oscillating means for periodically oscillating the cantilever at a predetermined amplitude, the method comprising the steps of: performing a first operation in which the specimen is moved relative to the probe and uneven surface data of the specimen is obtained when the optical position sensor detects a reduced amplitude of the cantilever smaller than the predetermined amplitude during the relative movement when the probe of the cantilever comes into contact with the specimen, the uneven surface state data being obtained by controlling the specimen moving means to move the specimen relative to the probe in upward or downward directions in order to maintain the reduced amplitude constant; and performing a second operation in which physical action force data of the specimen is obtained by causing relative movement of the specimen and the probe while keeping the probe spaced by a predetermined distance from the specimen on the basis of the uneven surface state data obtained by the first operation; wherein, in the first operation, the uneven surface data is obtained by oscillating the cantilever with an oscillation frequency outside a frequency band which is defined by one-halt the value of a dependent curve of the cantilever oscillating frequency and amplitude and, in the second operation, flexibility of the cantilever is measured by moderately oscillating the cantilever while causing relative movement of the specimen and the probe. 3. A method of operating a scanning probe microscope according to claim 1 ; further comprising the steps of using p phase sensor to detect a signal generated in response to a time delay in oscillations of the cantilever caused by interactions of the specimen surface and the probe; and measuring a difference in at least one physical property of the specimen surf ace selected from a magnetic field, an electric field or a physical action force on the basis of the detected signal. claim 1 4. A method of operating a scanning probe microscope according to claim 1 ; further comprising the steps of using a phase sensor to detect a signal generated in response to a time delay in oscillations of the cantilever caused by interactions of the specimen surface and the probe; and measuring a difference in at least one physical property of the specimen surface selected from a magnetic field, an electric field or a physical action force on the basis of a signal which is generated in accordance with a shift amount of a resonance frequency of the cantilever and is detected by the phase sensor. claim 1 5. A method of operating a scanning probe microscope according to claim 1 ; wherein the first and second operations are performed at each of a plurality of measurement points on the specimen surface. claim 1 6. A method of operating a scanning probe microscope according to claim 1 ; wherein the first and second operations are performed at each of a plurality of measurement lines along the specimen surface. claim 1 7. A method of operating a scanning probe microscope according to claim 1 ; wherein the first and second operations are performed by causing relative scanning movement of the probe relative to the specimen surface throughout each of a plurality of frames of the specimen surface. claim 1 8. A method of operating a scanning probe microscope according to claim 1 ; wherein the first and second operations are performed with the specimen exposed to air. claim 1 9. A method of operating a scanning probe microscope according to claim 1 ; further comprising the steps of providing a cell containing therein a solution, placing the specimen in the solution, and performing the first and second operations with the specimen placed in the solution. claim 1 10. A method of operating a scanning probe microscope according to claim 1 ; further comprising the steps of providing a vacuum container and vacuum pumping means, and performing the first and second operations with the specimen located in the vacuum container under a vacuum produced by the vacuum pumping means. claim 1 11. A method of operating a scanning probe microscope according to claim 1 ; further comprising the steps of providing a vacuum container, placing the specimen in the vacuum container, evacuating the vacuum container, and then filling the vacuum container with a gas, and performing the first and second operations with the specimen placed in the gas. claim 1 12. A method of operating a scanning probe microscope according to claim 8 ; further comprising the step of providing means f or heating or cooling the specimen, and performing the first and second operations with the specimen being in a heated or cooled state. claim 8 13. A method of operating a scanning probe microscope according to claim 8 ; further comprising the steps of providing means for applying a magnetic field to the specimen, and performing the first and second operations with the specimen disposed in a magnetic field. claim 8 14. A method of operating a scanning probe microscope according to claim 8 ; further comprising the steps of providing means for applying an electric field to the specimen, and performing the first and second operations during the application of the electric field. claim 8 15. A method of operating a scanning probe microscope having a cantilever with a probe at one end thereof, the method comprising the steps of: performing a data acquisition process by oscillating the cantilever at a frequency offset from a resonant frequency thereof, causing the probe to undergo relative scanning movement with respect to a specimen so that the cantilever undergoes oscillation at a reduced amplitude when the probe comes into contact with the specimen, maintaining the reduced amplitude constant by causing the cantilever to nova toward or away from the specimen, and obtaining surface state data of the specimen on the basis of movement of the cantilever toward or away from the specimen; and performing a measurement process by oscillating the cantilever near a resonant frequency thereof, causing the probe to undergo relative scanning movement with respect to the specimen, and obtaining physical data of the specimen by maintaining the probe at a predetermined distance from the specimen on the basis of the surface state data. 16. A method of operating a scanning probe microscope according to claim 15 ; wherein the step of performing the data acquisition process includes the step of oscillating the cantilever at a frequency outside a frequency band which is defined by one-half the value of a dependent curve of the cantilever oscillating frequency versus amplitude, and the step of performing the measurement process includes the step of oscillating the cantilever at a frequency near a resonant point of the dependent curve of the cantilever oscillating frequency versus amplitude. claim 15 17. A method of operating a scanning probe microscope according to claim 15 ; further comprising the steps of using a phase sensor to produce a phase signal in response to a time delay in oscillation of the cantilever caused by interaction of the specimen surface and the probe; and measuring a physical property of the specimen surface on the basis of the phase signal. claim 15 18. A method of operating a scanning probe microscope according to claim 15 ; wherein the data acquisition process and the measurement process are performed with the specimen exposed to air. claim 15 19. A method of operating a scanning probe microscope according to claim 15 ; wherein the data acquisition process and the measurement process are performed with The specimen maintained in a vacuum. claim 15 20. A method of operating a scanning probe microscope according to claim 15 ; wherein the data acquisition process and the measurement process are performed with the specimen placed in a solution. claim 15 |
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claims | 1. An optical element, comprising:a substrate having first and second sides;a first coating supported by the first side of the substrate; anda second coating supported by the second side of the substrate,wherein:the substrate comprises a glass;the first coating reflects EUV radiation;the second coating transmits radiation at a first wavelength;the second coating comprises a member selected from the group consisting of an absorbing layer that absorbs radiation having a second wavelength and a transmitting layer that transmits radiation having the second wavelength;the first wavelength is in a range selected from the group consisting of the visible range and the infrared range;the second wavelength is in a range selected from the group consisting of the visible range and the infrared range;the second wavelength is different from the first wavelength; andthe optical element is an EUV mirror. 2. The optical element of claim 1, wherein the second coating further comprises an anti-reflecting layer that suppresses reflection of radiation at the second wavelength, and the absorbing layer is between the substrate and the anti-reflection layer. 3. The optical element of claim 2, wherein a maximum absorbance of the absorbing layer is at wavelengths of more than 1500 nm. 4. The optical element of claim 3, wherein a maximum suppression of the anti-reflection layer is at wavelengths of more than 1500 nm. 5. The optical element of claim 2, wherein a maximum suppression of the anti-reflection layer is at wavelengths of more than 1500 nm. 6. The optical element of claim 1, wherein the absorbing layer has a maximum transmission at wavelengths less than 1500 nm. 7. The optical element of claim 1, wherein the substrate comprises a material that is at least partially absorbent for radiation at the second wavelength. 8. The optical element of claim 7, wherein the substrate comprises a material that is at least partially transparent for radiation at the first wavelength. 9. The optical element of claim 1, wherein the substrate comprises a material that is at least partially transparent for radiation at the first wavelength. 10. The optical element of claim 1, wherein the second coating further comprises an anti-reflecting layer that suppresses reflection of radiation at the first wavelength and at the second wavelength, and the transmitting layer is between the substrate and the anti-reflection layer. 11. The optical element of claim 1, wherein the glass comprises a silicate glass. 12. The optical element of claim 1, wherein the glass comprises a quartz glass. 13. The optical element of claim 1, wherein the glass comprises a TiO2-doped quartz glass. 14. The optical element of claim 1, wherein the glass comprises a glass ceramic. 15. The optical element of claim 1, wherein the second coating comprises an absorbing layer that absorbs radiation having the second wavelength. 16. The optical element of claim 1, wherein the second coating comprises a transmitting layer that transmits radiation having the second wavelength. 17. An arrangement, comprising:an optical element according to claim 1; anda light source configured to generate radiation at a wavelength in a range selected from the group consisting of visible radiation and infrared radiation,wherein the second coating is between the light source and the substrate. 18. The arrangement of claim 17, wherein:the arrangement comprises a plurality of light sources in a grid-type arrangement; andfor each light source, the second coating is between the light source and the substrate. 19. The arrangement of claim 18, wherein the arrangement is an EUV lithography apparatus. 20. The arrangement of claim 17, wherein the arrangement is an EUV lithography apparatus. |
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046363521 | description | DETAILED DESCRIPTION The present invention provides a nuclear fuel rod which incorporates a pellet-clad interaction fix with a burnable poison concept. As illustrated in FIG. 1, a nuclear fuel rod 1, comprises a metallic tubular cladding 3, which may be formed from known metal cladding materials such as zircaloy, the tube being closed at both ends, as is conventional, by closure means, not shown. Positioned within the metallic tubular cladding 3, are a plurality of nuclear fuel pellets 5. The nuclear fuel pellets generally comprise sintered pellets of uranium dioxide that is enriched in the U-235 isotope. In place of the use of enriched uranium dioxide, a mixture of uranium-plutonium dioxide may be used. These fuel pellets are generally formed by enriching the uranium dioxide and either alone or in a mixture with plutonium dioxide, compacting the material to a desired size and shape and sintering the same to produce dense pellets for use in the nuclear fuel rod. The nuclear fuel pellets will normally be of a length on the order of 0.4-0.6 inch, and have a length to diameter ratio of less than 1.7:1, and preferably of about 1.2:1. As formed, the nuclear fuel pellts have concavities 7, therein, to provide concave faces on the confronting faces of the pellets arranged in the tubular cladding in an axial relationship. During the operation of a reactor containing the nuclear fuel, volatile fission products are released. Because such a release is generally temperature dependent, it has been found that the greatest release of such volatile fission products occurs at the concave faces of the fuel pellets, as indicated by the arrows shown in the drawing. Normally only a small amount of such volatile fission products are released from the sides of the fuel pellets directly confronting the wall of the metallic cladding. Thus, the present invention substantially reduces or eliminates attack on the cladding which could cause a pellet-clad interaction failure by freezing out the fission products released from the concave faces of the fuel pellets. In order to freeze out the volatile fission products, and to also assist in controlling the power shaping of the reactor system, a plurality of ceramic wafers 9, are each axially disposed between a major portion of adjacent fuel pellets, the wafers being formed from gadolinium oxide and natural or depleted uranium dioxide. The uranium dioxide used in the formation of the ceramic wafers 9 have no more uranium-235 isotope than is present in natural uranium dioxide. Generally, natural uranium dioxide will contain on the order of 0.71 percent by weight of the uranium-235 isotope. In the production of enriched uranium dioxide for use as a nuclear fuel, the same is processed so as to increase the uranium-235 isotope content. The scaling or residue from such processing is depleted uranium which contains an amount of uranium-235 isotope lower than that of the natural uranium, and can be essentially devoid of that isotope. It is this depleted uranium dioxide, or natural uranium dioxide which is usable in the formation of the ceramic wafers of the present invention. The natural or depleted uranium dioxide has added thereto gadolinium oxide, and the mixture is sintered to form the ceramic wafers. The amount of gadolinium oxide added to the natural or depleted uranium dioxide is between about 1-8 percent by weight of the mixture. The ceramic wafers 9 so formed should have a diameter substantially the same as the diameter of the fuel pellets 5, as indicated in the drawings but will be of a much smaller length. The length of the wafers should be between about 10-100 mils. Wafers of less than 10 mils in thickness would be difficult to produce and could not retain an integral structure during handling and use, while wafers of a thickness of more than 100 mils would space the fuel pellets so far apart as to tend to cause problems relative to power peaking. It is not necessary that a ceramic wafer 9 be disposed between all of the adjacent fuel pellets 5, but a major portion of the adjacent fuel pellets should have a wafer disposed therebetween. By varying the number of ceramic wafers present in the fuel rods, flexibility in the power shaping of the system is achieved. For example, a ceramic wafer could be disposed between each of adjacent fuel pellets in the zone of high power generation, generally the middle region of the rod, while adjacent fuel pellets at the end regions of the rods, or other areas of low power generation, would not have a ceramic wafer therebetween. Also, as an aid to power shaping of the system, particular wafers throughout the rod could vary in the amount of gadolinium oxide present, in the range of 1-8 percent by weight. The use of the present fuel rods, in addition to reducing or eliminating pellet-clad interaction failures, can thus eliminate the need for a burnable poison in the fuel pellets and eliminate the need for use of separate burnable poison rods in the reactor system. In the present fuel rod, containing the ceramic wafers of natural or depleted uranium dioxide and gadolinium oxide, power generation from the ceramic wafers is very low and the wafers freeze out volatile fission products and prevent such fission products from reaching the cladding and causing pellet-clad interaction failures. After the gadolinium oxide has burned out, the natural or depleted uranium dioxide in the wafer is still low in power production, and will act to freeze out the harmful fission products. |
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062427474 | abstract | A method and apparatus is provided for controlling the operational parameters of a radio frequency (RF) linear accelerator (linac) (23) in an ion implanter (1). An operator or a higher level computer enters into an input device (10) the desired type of ions, the ionic valence value of ions, the extraction voltage of ion source (21), and the final energy value that is needed. Using internally stored numeric value calculation codes in parameter storage device (18), a control calculation device (11) simulates the ion beam acceleration or deceleration, and the anticipated dispersion of the ion beam, and calculates the RF linac operational parameters of amplitude, frequency and phase for obtaining an optimum transport efficiency. The parameter related to the amplitude is sent from control calculation device (11) to amplitude control device (12) which adjusts the amplitude of the output of RF power supply (15). The parameter related to the phase is sent to phase control device (13), which adjusts the phase of the output of RF power supply (15). The parameter related to the frequency is sent to frequency control device (14). Frequency control device (14) controls the output frequency of RF power supply (15) while it also controls the resonance frequency of RF resonator (23-1) of RF linac (23). |
summary | ||
052672867 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described hereunder with reference to FIGS. 1 to 7. In this embodiment, a fuel assembly 10 is composed of four small fuel bundles 30, fuel assembly upper portion tie members 12b, channel boxes 17, a water cross 50 and fuel assembly lower nozzles 18. The water cross 50 is integrally welded to the channel box 17 to divide the inside of the channel box 17 into four coolant flow passages. The four small fuel bundles 30 are respectively provided with upper tie plates 12a and lower tie plates 13a and arranged in flow passages surrounded by the central water cross 50 and the channel boxes 17 with the lower tie plates 13a being mounted on the fuel assembly lower nozzles 18. The upper and lower end portions of the fuel rods 11 are supported by the upper and lower tie plates 12a and 13a. A plurality of spacers 16 are arranged along the axial direction of the fuel bundles 30 to properly keep the gaps between the mutually adjoining fuel rods 11. The fuel spacers 16 are supported in their axial directions by fuel rods provided with tabs, not shown. The channel boxes 17 are fastened to the fuel assembly lower nozzles 18 with fastening screws 22 to thereby surround the outer peripheries of the four fuel bundles 30, respectively, thus constituting one fuel assembly unit. The lower tie plate 13a mounted on the lower nozzle 18 has, at its upper end, a fuel rod support 14a which is provided with, a coolant inlet from space 15. As shown in FIG. 7, each of the fuel rod 11 is composed of a cladding tube 45 into which a plurality of fuel pellets 48 are charged and upper and lower ends of the cladding tube 45 are plugged with plugs 46 and 47. A gas plenum 49 is formed to the inner upper portion of the cladding tube 45. FIGS. 3 and 4 represent detailed structure of the water cross 50 providing one feature of the present invention. Referring to FIGS. 3 and 4, the water cross 50 is constituted by four plate members 51 each in substantially L-shape, the channel box 17 and, coolant rising and lowering passages 53 and 54 both surrounded by the L-shaped plate members 51 and the channel box 17. FIG. 4 is an illustration of sectional view taken along the line IV--IV of FIG. 3, and referring to FIG. 4, the upper and lower end portions of the cross water 50 are closed by upper and lower cover members 55 and 56, and partition plates acting as flow passage sectioning spacers 52 are arranged to keep gaps between the L-shaped plate members 51 to thereby form the coolant rising and lowering passages 53 and 54. A guide tube 24 for guiding a control element is fitted in the central portion of the water cross 50 and supported by the L-shaped plate members 51. The guide tube 24 penetrates the upper cover member 55 at its upper end. The upper end of the guide tube 24 is opened upward. The lower end of the guide tube 24 penetrates the lower cover member 56 and extends downward into a through hole 62, shown in FIG. 5E, of a fuel assembly lower nozzle 18. The flow passage sectioning spacers 52 are disposed at blade (or wing) portions of the water cross 50 and divides the flow passage of this blade portions into the coolant rising passages 53 and the coolant lowering passages 54. In the illustrated structure, the flow passage adjoining the control element guide tube 24 is referred to as the coolant lowering passage 54. The flow passage sectioning spacer 52 has a conjunction port 57 positioned below the upper cover member 55 to connect the coolant rising passage 53 with the coolant lowering passage 54. The sectioning spacer 52 extends towards the lower cover member 56 to divide the coolant passages. The lower portions of the blade portions of the water cross 50 are closed by the lower cover member 56 positioned below the fuel rod support portion 14a of the lower tie plate 13a. The coolant rising passage 53 has a coolant inlet 42a positioned above the fuel rod support portion 14a. The coolant lowering passage has a drain port 43a towards the control element guide tube at a portion near the lower end thereof. The details of the lower nozzle or nozzles 18 and its associated members are described hereunder with reference to FIGS. 5A to 5D. A fuel assembly weight is applied to the upper portion of the fuel assembly lower nozzle 18 because the lower tie plate 13a of the fuel bundle 30 is mounted on the fuel support seat 61. The lower end of the water cross 50 is inserted into grooves 64 formed to the fuel support seat 61 to thereby separate the coolant flow passages of the fuel bundle 30 so as not to be connected between them. Namely, as shown in FIG. 5A, the grooves 64 are also have a cross shape as a whole. A control element guide tube support tube 68 is arranged at the central portion of the grooves 64 to form a through hole 62 to be inserted by the control element guide tube 24. Extended portions 65 constituting the grooves 64 extend to the lower portion of the lower nozzle 18 to thereby divide into sections four lower nozzle flow passages 63. Orifice plates 23 are disposed at the lower portions of the lower nozzle flow passages 63, respectively, to form orifices 67. The lower end portion of the control element guide tube 24 is connected to the control element guide tube 24a secured to a fuel support fitting 20. The fuel support 20 is fitted into an upper opening of the control rod guide tube 71 and is provided with an opening 25 at its central portion so as to act as a guide for the insertion of the cruciform control rod blade into the water gap between the fuel assemblies 10 as shown in FIG. 1. Surrounding the cross shaped through hole 25, there are arranged four openings 73 for receiving the fuel assembly lower nozzles 18, respectively, to form a coolant flow passage of the fuel support 20. One such coolant flow passage is formed to one fuel assembly surrounding the cruciform control rod blade. In the central portion of the opening 73, the control element guide tube 24a is disposed. The guide tube 24a is connected to the control element guide tube 24, penetrating the fuel support 20, having a control element insertion hole 26 at the bottom of the support 20 and then supported by a support plate 69. The support plate 69 has an opening 27 through which the coolant passes. The fuel support 20 is provided with a lower side surface to which orifices 21 for the coolant flow passage conjunction with the openings 73 are formed at a portion facing the openings 72 of the control rod guide tube 71. FIG. 6 shows an appearance of the control rod 6 utilized in combination with the fuel assembly according to the present invention. The control rod 6 corresponds to that shown in FIG. 23 but additionally provided with columnar control elements 7 and mainly composed of sheaths 117 control rod blade provided inside with poison tubes 118 and the control elements 7. The control element 7 may be composed of a hollow tube made of SUS into which neutron absorbing poison such as B.sub.4 C, Hf is packed, or composed of mere a hollow tube or SUS rod. Further, in the illustrated example, a speed limiter and a control rod connection-separation handle of conventional structure are not located. The operation and function of the fuel assembly of the present embodiment will be described hereunder by assuming that the fuel assembly is charged in the core of the BWR. As shown in FIG. 1, the coolant is guided into the coolant flow passage between the fuel rods 11 of the fuel bundle 30 through the opening 72 of the control rod guide tube 71, the coolant passing orifice 21 of the fuel support 20, the opening 67 of the lower nozzle 18 of the fuel assembly, and the through hole formed to the fuel rod support member 14a of the lower tie plate 13a. One part of the coolant flown in the coolant guide port 15 of the lower tie plate 13a flows towards a bypass flow passage, which is outside a channel flow passage, through a leak hole formed to the lower nozzle 18. One part of the coolant flown in the upper portion of the fuel rod support member 14a is flown, as shown in FIGS. 3 and 4, into the coolant rising passage 53 through the coolant inlet 42a of the water cross 50, and then drained inside the control element guide tube 24 through the conjunction port 57, a flow lowering passage 54 and the drain port 43a at a portion near the lower end of the flow passage of the water cross. In a case where the front (upper) end of the control element 7 is positioned below the drain port 43a, the coolant flown through the coolant drain port 43a becomes the liquid phase and/or steam phase in accordance with the flow rate of the coolant flown through the coolant inlet port 42a in response to the core flow rate (refer to curve A in FIG. 8). In the present embodiment, the coolant inlet port 42a is disposed slightly above the fuel rod support member 14a for the reason that the pressure in the control element guide tube 24 is equal to that in the bypass flow passage, and accordingly, the coolant inlet port 42a is disposed above the fuel rod support member 14a for preventing the coolant from excessively flowing. This further has advantage for easily designing the openings diameter of 42a and 43a. So, depending on desighs, the coolant inlet port 42a is disposed under the fuel rod support member 14a. In a case where the front end of the control element 7 is positioned above the drain port 43a, there causes a large flow resistance because the drain port 43a is closed by the control element 7. A steam void is caused in the inside of the water cross 50 by the heating and heat transfer due to neutron and .gamma.-rays, which results in the increasing of the pressure drop at portions of the drain port 43a, the coolant rising passage 53 and the coolant lowering passage 54. Accordingly, the water levels of the coolant rising and lowering passages 53 and 54 fall until the time when the pressure difference between the coolant inlet 42a and the drain port 43a is balanced to the water head and pressure drop in the water cross 50, thus the steam being filled up in the water cross 50. Furthermore, since the coolant is less supplied in the control element guide tube 24, the steam void is also caused and the inside of the water cross is hence almost filled up with the steam (refer to the curve C in FIG. 8). In a case where the control rod 6a is inserted into the upper portion, the control element 7 is also inserted into the upper portion of the control element guide tube arranged centrally in the water cross 50. In this case, the upper end of the flow passage 58 is opened, and hence, the coolant is discharged through the upper end opening without increasing its pressure. According to such structure, the control rod can be easily inserted, thus preventing the fuel assembly from jumping at the control rod insertion operation. In a case where the control rod is withdrawn downward, the pressure in the control element guide tube is reduced, but since the steam occupies the inside of the control rod guide tube during power operation state and its steam is expanded, the degree of such pressure reduction is small. In the shut-down state, since non-boiling water occupies the inside of the control element guide tube, the flow resistance becomes small and the non-boiling water is counterflown through the upper end opening, thus easily withdrawing the control rod. The function of the fuel assembly 10 of the present invention charged in the BWR will be described hereunder. An example is taken to a case where 100% rated power is kept between the core flow rate of 80 to 115%. The core flow rate is kept to 80% during the almost period (about 70 to 80%) of the operating cycle, thereby compensating against the reactivity change due to the burning of the fuel by adjusting the reactivity by means of the control rod. In the fuel assembly with the control rod being drawn out, the axial direction of the control rod is set so as to position the upper end of the control element 7 to a position above the coolant drain port 43a of the water cross 50 and below the fuel active region of the fuel assembly. The number of the fuel assemblies, in which the upper ends of the control elements 7 are set to portions below the drain port 43a by further drawing downward the control rods from the time when the rated power cannot be kept even by entirely drawing out the all control rods from the core fuel active regions, is increased in response to the reduction of the reactivity. Furthermore, the core flow rate is finally increased so as to obtain the core maximum flow rate of 115% at the end of the operating cycle, whereby the core reactivity at the end of the cycle is increased and the cycle life can thus be expanded. When the pressure difference (between the inlet and outlet ports of the water cross of the present invention)--the void factor characteristic is set to the curve A in FIG. 8 with respect to a case where the upper end of the control element 7 is positioned below the drain port 43a, the inside of the water cross is kept with the void factor less than 10% in a core flow rate range (in this example, 80 to 115% rated core flow rate) utilized in the rated power operation period. Accordingly, there causes no dispersion of the void fraction inside the water rod between the fuel assembly due to the power distribution (curve B in FIG. 8) caused by the water rod of the conventional design of the fuel assembly. Further, in a case where the upper end of the control element 7 is positioned above the drain port 43a, the void fraction inside the water cross is kept more than 80%, as shown by the curve C in FIG. 8, in the core flow rate range operated with the rated power. Accordingly, at the power operation period, for the control rods except for those inserted into the fuel active region of the fuel assemblies for controlling the excessive reactivity and the core power distribution, the void fraction inside the water cross can be kept more than 80% by setting the control rods at axial portions at which the upper ends of the control elements 7 are positioned just above the drain ports 43a and below the fuel active region in the core flow rate range which is utilized at the rated power without lowering the power at the lower portions of the fuel assemblies. As this result, according to the present invention, the steam void can be caused inside the water cross 50 by the axial position control of the control rod without being influenced with the core flow rate, and the power level and the axial power distribution of the fuel assembly throughout the almost operation period of cycle with the core flow rate being less than 100%, whereby the production of the plutonium 239 can be facilitated under the suppression of the neutron moderating. Furthermore, in a case where the core flow rate is largely reduced at the reactor starting period or shutdown operation period, for example, at the time of less than 65% rated core flow rate, the void fraction inside the water cross can be kept high regardless of the position of the control rods, so that the inclination of the curve, representing the reactor core flow rate--power curve, become large and the core power control can be hence easily done, which is the same merit as that in the conventional design of the fuel assembly with the water rod 9. Still furthermore, since the void fraction in the water cross can be precisely controlled by the control rods, the evaluation accuracy of the thermal limitation, the power distribution, the exposure distribution and the reactivity can be remarkably improved, with the three dimensional nuclear-thermal-hydraulic simulation code, as well as the improvement in the monitoring of the core performance. In addition, since the control elements can be inserted into the inside of the central control element guide tube of the water cross of the fuel assembly, the core shut-down margin can be increased in comparison with the fuel assembly of the conventional structure. Other embodiments according to the present invention will be described hereunder with reference to FIGS. 10 to 20. First, referring to FIG. 10 representing a second embodiment of the fuel assembly according to the present invention, the L-shaped plate members 51 constituting the water cross are press bent and welded to form coolant flow sections. In the first embodiment, the flow passage sectioning spacers of the water cross are utilized for forming the coolant rising passage and the coolant lowering passage. According to the structure of this second embodiment, the spacers 52 of the first embodiment can be eliminated for forming the coolant rising and lowering passages 75 and 76, thus simplifying the structure. Next, FIG. 11 represents a third embodiment according to the present invention, in which a hollow tube 52b is arranged as flow passage sectioning member at an outside of the control element guide tube 24 concentrically therewith and in which the blade portions of the water cross are formed as coolant rising passages 77 and an annular portion is formed as coolant lowering passage 78. In this embodiment, a plurality of support spacers are arranged in a hollow tube 52b along the axial direction of the fuel assembly and support the control element guide tube 42, not shown in FIG. 11, having structure capable of passing the coolant through the annular portion. According to this structure of the fuel assembly, the control element guide tube and the water cross can be made simple, thus being easily manufactured. In the fuel assembly of FIG. 11, when the water cross has thin thickness, the hollow tube of the central control element guide tube is made too slender and, hence, only small contribution is achieved to the increasing of the control rod worth, a countermeasure is such that the outer diameter of the control element guide tube may be made large by removing the fuel rods adjoining the central portion of the water cross to increase the control rod reactivity. As described above, such improved structure may be utilized in combination with the water cross of the structure shown in FIG. 2 or 10. FIGS. 12 and 13 further represent a fourth embodiment according to the present invention, in which a plurality of control element guide tubes 24 are arranged in the water cross 50. In this structure, the fuel bundle 30 has a lattice structure larger than that, i.e. 4.times.4 lattice structure, of the embodiment shown in FIG. 2. For example, this structure may be preferably adapted for the large-sized fuel assembly 78 having a water cross constituted by fuel bundles each in 6.times.6 lattice structure. By increasing the number of the control element guide tubes in this manner, the control rod reactivity can be increased and the reduction of the reactor shut-down margin in the enlargement of the fuel assembly can be improved. Furthermore, since the control elements 7 are inserted into the control element guide tubes disposed in the water cross, the number of the fuel rods per one fuel assembly is not reduced and the fuel packing amount in the fuel pellet is not reduced, thus being advantageous in the fuel economy. Furthermore, in such large-sized fuel assembly, since it is intended that the thermal neutron flux at the central portion of the fuel bundle is increased to make flat the power distribution, the water rod 5 of the conventional structure shown in FIG. 21 or the water rod 9 capable of having spectrum shift of the conventional structure shown in FIG. 25 may be utilized in combination. FIGS. 14 and 15 represent a fuel assembly of a fifth embodiment as a modification of the first embodiment, in which a further coolant inlet 42b is formed to the lower portion of the control element guide tube 24, and an opening is formed to a corresponding position of the hollow tube 68, shown in FIG. 5B, disposed at the central portion of the flow passage sectioning member 65 of the lower nozzle 18, so that the coolant passing the flow passage 63 can be taken inside the control element guide tube 24 through the inlet opening 42b. In this fifth embodiment, the coolant inlet opening 42b is formed above the orifice 23 acting as the flow passage resisting means in a view point of reducing the pressure difference between the openings 42b and 32 shown in FIG. 15 and preventing the extremely large coolant flow rate. As shown in FIGS. 14 and 15, in a case where the upper end of the control rod element 7 is positioned below the inlet opening 42b, the coolant through the lower nozzle 18 flows in the control element guide tube through the opening 42b and then flows out through the upper opening 32 in the upper plenum. As this result, non-boiling water flows inside the control element guide tube. This fact increases the amount of the moderator at the end of cycle and the area of the control element guide tube is occupied with the non-boiling water like the case of the water cross when it is required to facilitate the moderation of the neutron, thus increasing the moderating effect. In a case where the upper end of the control element 7 is positioned above the drain opening 43a, the opening 43a is closed by the control element 7 and the flow resistance at the drain port becomes large, so that the coolant flow amount flown out is reduced, whereby the steam void is caused in the water cross as described hereinbefore due to the heating and the heat transfer by the neutron and .gamma.-rays and the liquid surfaces of the flow passages 53 and 54 are depressed. In thus manner, the liquid levels in the flow passages 53 and 54 are depressed downward until the time when the pressure difference between the inlet port 42a and the drain port 43a has been balanced to the pressure drop and water head in the flow passage in the water cross. As this result, the inside of the water cross is filled up with the steam. Further, a large amount of the steam void is also caused in the control element guide tube because of the reduced coolant flow rate through the openings 42b and 43a. When the upper end of the control element 7 is moved downward below the coolant inlet port 42b by the downward withdrawal of the control element 7, the coolant flows into the control element guide tube through the coolant inlet 42b and rises upward, and at this time, the steam flow is sucked through the drain port 43a. Accordingly, the flow mode change, i.e. transformation from steam filling state to liquid single phase flow state, in the water cross is accelerated, and the power increasing of the reactor can be speedily changed in comparison with the case of locating no coolant inlet port 42b. FIGS. 16 to 18 represent a sixth embodiment of the fuel assembly 80 of the present invention, which is different from the embodiment of FIGS. 1 and 2 in which the control element guide tube is incorporated in the water cross. Namely, in the sixth embodiment, the fuel assembly 80 is provided with a water rod 19 in which a control element guide tube is incorporated, and FIG. 16 shows an example in which one polygonal, substantially square in illustrated cross section, water rod 19 is centrally disposed in the fuel assembly 80, but it may be possible to dispose, in alternation, a circular cylindrical water rod or a plurality of water rods. Furthermore, the water rod 5 of the conventional structure or the water rod 9 having the spectrum shift function may be utilized in combination. The water rod 19 is composed, as shown in FIGS. 17 and 18, of an inner tube 35, an outer tube 36, spacers 37 and a control element guide tube 24. The inner tube 35 and the control element guide tube 24 are supported by the spacers 37, and the upper end openings of the inner tube 35 and the outer tube 36 are closed by an annular end plug 38a. The control element guide tube 24 is connected with a control element guide tube 24a, having an upper portion extending beyond the end plug 38a and inserted into the upper tie plate 12 and supported thereby with an upper end opening 32 being opened above the upper tie plate 12. The inner tube 35 is provided with a conjunction hole 34 positioned below the end plug 38a so as to connect an annular flow passage 41 (coolant lowering passage), between the inner tube 35 and the control element guide tube 24, with an annular coolant rising passage 40, between the outer tube 36 and the inner tube 35. Each of the spacers 37 has an opening for ensuring the spaces for the coolant rising and lowering passages 40 and 41. The lower ends of the inner and outer tubes 35 and 36 are closed by an annular end plug 39a positioned above the fuel rod support member 14, and the end plug 39a is provided with a coolant inlet opening 42a connecting with the annular coolant flow passage 40. The control element guide tube 24 has a drain port 43a positioned above the annular plug 39a and the lower end portion of the guide tube 24 penetrates the fuel rod support member 14 and is supported by a guide tube support plate 23a. The lowermost end of the guide tube 24 is formed as a control element insertion opening 26 opened at the lower end portion of the lower tie plate 13. The fuel support 20 is fitted to the upper end opening of the control rod guide tube 71 and is provided, at its lower side surface, with coolant inlet ports 21 facing the openings 72 of the control rod guide tube 71 as shown in FIG. 16. The coolant inlet port 21 is formed to each of the four fuel bundles. The control element guide tube 24a is secured to the fuel support fitting 20 by means of a guide tube support plate 69 and the bottom portion of the fuel support 20. The upper end portion of the control element guide tube 24a is engaged with the lower end portion of the control element guide tube 24 of the water rod 19 in this embodiment. To the central portion of the fuel support 20 is formed a cross shaped opening into which the cross shaped control blades are guided and inserted so that the control blades are positioned at the central portion of the four fuel assemblies such as shown in FIG. 2. The coolant is guided, as shown in FIG. 16, to the coolant passage between the fuel rods 11 of the respective fuel rod bundles through the opening 72 formed to the side surface of the control element guide tube 71 and the coolant inlet orifice 21 formed to the side surface of the fuel support 20 and then through the through hole, not shown in FIG. 16, formed to the fuel rod support member 14 of the lower tie plate 13 of the fuel assembly. One part of the coolant flown in the coolant guide inlet 15 of the lower tie plate 13 flows into the bypass flow passage, which is outside the channel flow passage, through the leak hole, not shown in FIG. 16, formed to the lower tie plate 13. As shown in FIG. 18, the coolant flows into the coolant rising passage 40 through the coolant inlet 42a of the water rod 19 and then is drained into the inside 58 of the control element guide tube 24 through the conjunction hole 34, the coolant lowering passage 41 and finally the drain port 43a positioned near the lower end portion of the water rod 19. In a case where the front (upper) end of the control element 7 is positioned below the drain port 43a, the coolant flown through the drain port 43a is becomes the liquid phase or steam phase in accordance with the flow rate of the coolant flown through the coolant inlet 42a in accordance with the core flow rate (refer to the curve A in FIG. 8). In a case where the upper end of the control element 7 is positioned above the drain port 43a, the drain port 43a is closed by the control element 7 and the drain port resistance is hence increased. The steam void is caused in the inside of the water rod 19 due to the heating and heat transfer by the neutron and .gamma.-rays, whereby the pressure drop is increased at the drain port 43a and in the coolant rising and lowering passages 40 and 41, and the water levels in the passages 40 and 41 are lowered until the time when the pressure difference between the coolant inlet 42a and the drain port 43a is balanced to the pressure drop and the water head in the water rod passage. As this result, the inside of the water rod 19 is filled up with the steam, and furthermore, since the coolant is less supplied into the inside 58 of the control element guide tube 24, the void is caused in the inside 58 of the guide tube 24 and the steam is hence filled up therein (refer to the curve C in FIG. 8). When the control rod 6a is inserted into the upper portion, the control element 7 is also inserted into the upper portion of the central control element guide tube of the water rod 19. In this case, since the upper end of the inside passage 58 is opened, the inner pressure does not increase and the coolant is then discharged through this upper end opening. As this result, the control rod is smoothly inserted without jumping the fuel assembly at the control rod insertion time. On the contrary, when the control rod is drawn downwardly outward, the inner pressure in the control element guide tube 24 is reduced. However, the steam occupies the inside of the control element guide tube during the power operation state and is expanded therein, so that the degree of this pressure reduction is small. At the reactor shut-down state, the non-boiling water occupies its inside to thereby make small the flow resistance and counterflows through the upper end opening, thus smoothly drawing downward the control rod. Accordingly, the void fraction can be surely controlled by the control elements 7, as described with respect to the first embodiment, in the fuel assembly provided with the water rod 19. Furthermore, according to the structure in which the opening is formed to the lower portion of the control element guide tube 24 at a portion below the fuel rod support member 14 to thereby guide the coolant into the inside of the control element guide tube 24, substantially the same functions as those attained by the fourth embodiment of FIGS. 14 and 15 can be attained as well as the controlling of the axial position of the upper end of the control element 7. It may be better to secure the water rod 19 integrated with the control element guide tube 24 to the lower tie plate 13 to prevent the water rod from vertically shifting at the control rod insertion or withdrawal time. In FIG. 17 there is the water rod in one fuel assembly, but a plurality of water rods design case is considered also. FIGS. 19 and 20 represent a seventh embodiment as a modification of the first embodiment, in which four fuel assemblies 10 are combined to form a large fuel assembly unit 81. In such fuel assembly unit 81, the lower nozzles of the fuel assemblies 10 and the fuel support are integrated and a channel box 17a is directly fastened to the fuel support by means of screws. According to the provision of such large-sized fuel assembly unit, the four fuel assemblies surrounding the control rod are integrated, so that the control elements 7 and their guide tube 24 can be stably mounted at their combined portions, thus being advantageous. It is to be understood that four fuel assemblies of the other embodiments can be combined into a fuel assembly unit in the like manner to thereby achieve substantially the same advantages. In a case where an abnormal transition phenomenon or accident be caused during the reactor power operating state, the control rod should be rapidly inserted to rapidly change the reactor to a subcritical state or low power operating state to thereby protect the nuclear reactor or power plant. In such case, it is better for a scram control rod, i.e. rapidly inserting control rod, to have a weight as light as possible and insertion resistance as small as possible. In this meaning, it is better for the scram control rod to have a conventional cross shape (such as structure shown in FIG. 6 but not provided with the control element 7). In such case, there causes a coolant flow directing from the coolant inlets 42a and 42b, towards the control element insertion inlet or towards the upper end opening 32 of the control element guide tube, and the coolant flow rate cooling the fuel rods 11 is reduced, so that it is better to insert, from the lower portion of the guide tube 24, and then attach thereto an inserting member, as a flow rate limiter, having a shape corresponding to a upper end of the control element at a portion below the opening 43a so as to close the opening 42b. In such case, the spectrum shift function can be also realized by the control of the core flow rate. Furthermore, this can be realized by the number of the scram control rods less than one fourth of the number of the total control rods in the core, so that the effects attained by the spectral shift operation is less lowered. In the foregoing embodiments, the cross shaped control rod has a B.sub.4 C poison tube, but it may be possible to provide a control rod formed by Hf rods or Hf plates in shape of cross form to attain substantially the same effects. Furthermore, the water rod of the structure shown in FIG. 18 integrated with the control element guide tube may be utilized in a fuel assembly used in combination of a cluster type control rod also to attain substantially the same effects described above. |
summary | ||
abstract | A fuel assembly may include a channel nosepiece; a lower tie plate positioned above the channel nosepiece; and at least one bundle retention clip connected to the channel nosepiece and the lower tie plate and configured to resist movement of the lower tie plate away from the channel nosepiece. |
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044951418 | claims | 1. A tagging gas releasing element for insertion within a nuclear fuel rod, said tagging gas releasing element consisting essentially of an inorganic solid material having a tagging gas composed of at least one rare gas selected from the group consisting of helium, xenon, neon and krypton adsorbed on the surface region thereof so as to detect failure in a nuclear fuel rod, said tagging gas being released from said element and into the interior of said fuel rod by means of desorption under the high temperature operation conditions of a nuclear reactor so as to tag each fuel rod and detect failure of the fuel rod when the tagging gas leaks therefrom, said inorganic solid material containing the tagging gas being the sole source of the tagging gas. 2. A tagging gas releasing element according to claim 1, wherein the inorganic solid material is a metal containing a tagging gas injected and entrained into the surface region thereof. 3. A tagging gas releasing element according to claim 2, wherein the metal is in the form of a thin film. 4. A tagging gas releasing element according to claim 3, wherein the thin metal film is formed on the surface of a solid carrier. 5. A tagging gas releasing element according to claim 3, wherein a number of thin metal films into which the tagging gas is injected and entrained into the surface region thereof are closely laminated to one another to form a multi-layer structure. 6. A tagging gas releasing element according to claim 3, wherein the thin metal film into which the tagging gas is injected forms a coating on the surface of a nuclear fuel pellet. 7. A tagging gas releasing element according to claim 3, wherein the thin metal film, in the outer surface of which the tagging gas is injected, is wrapped around the peripheral face of a nuclear fuel pellet. 8. A tagging gas releasing element according to claim 2, wherein the metal is selected from the group consisting of titanium, aluminum, zirconium, nickel, stainless steel and alloys thereof. 9. A tagging gas releasing element according to claim 1, wherein the inorganic solid material is a heat-resistant porous material in which the tagging gas is adsorbed. 10. A tagging gas releasing element according to claim 9, wherein the heat-resistant material is a heat-resistant porous granular material and the tagging gas is adsorbed in said porous granular material. 11. A tagging gas releasing element according to claim 10, wherein the tagging gas-adsorbed porous granular material is filled in a capsule comprising a cylinder composed of a hardly fusible metal and porous walls of the same metal disposed on both ends of said cylinder. 12. A tagging gas releasing element according to claim 1, wherein the tagging gas is a mixture of stable isotopes of at least one member selected from a group consisting of xenon and krypton. 13. A tagging gas releasing element according to claims 2 or 5 in which the tagging gas is injected and entrained onto the surface of said inorganic solid material by the ion injection method. 14. In a nuclear fuel rod composed of a cladding tube containing nuclear fuel pellets and a tagging gas composed of at least one rare gas selected from the group consisting of helium, xenon, neon and krypton, the improvement in which the tagging gas is entirely adsorbed onto the surface region of the tagging gas release element inserted into the cladding tube, said element composed of an inorganic solid material such that the tagging gas is released from said element by desorption under the high temperature operation conditions of a nuclear reactor to tag each fuel rod and detect failure of the fuel rod when the tagging gas leaks from the fuel rod. 15. The improvement according to claim 14 in which the inorganic solid material is a metal containing the tagging gas injected into the surface region of said metal. 16. The improvement according to claim 15 wherein the inorganic solid material is composed of a number of thin metal films formed on the surface of a solid carrier and in which a plurality of carrier and film combinations are closely laminated to one another to form a multi-layer structure. 17. The improvement according to claims 15 or 16 in which the tagging gas is injected into the surface of said metal or metal films by the ion injection method. 18. A fuel rod comprising a cladding tube and a fuel pellet material loaded in the cladding tube, characterized in that a metal foil having a tag gas injected therein for detecting breakage of the cladding tube is further loaded in the cladding tube, the metal foil being loaded in the cladding tube on the end portion in the form of circular foils, said foils each having a diameter smaller than the inner diameter of the cladding tube. 19. The fuel rod according to claim 18, wherein the metal foil is formed of a metal selected from the group consisting of aluminum, an aluminum alloy, zirconium, a zirconium alloy and stainless steel. 20. The fuel rod according to claim 18, wherein said tag gas is injected into a surface region of the metal foil. 21. The fuel rod according to claim 18, wherein said tag gas-injected metal foil is loaded in a plenum of the cladding tube. 22. A nuclear fuel rod, which comprises: a cladding tube, filled with a tag gas and sealed at both ends; and a plurality of nuclear fuel pellets piled one atop another in the cladding tube, wherein an adsorbent carrying a tag gas for detecting a nuclear fuel rod failure is received in the inner space of the cladding tube above the nuclear fuel pellet pile whereby said gas is released from said adsorbent when the temperature thereof increases. 23. The nuclear rod according to claim 22, wherein the adsorbent is active carbon. 24. The nuclear rod according to claim 22, wherein the adsorbent is received in a container. 25. The nuclear rod according to claim 24, wherein the container is formed of a hardly fusible metal container which is perforated at the top. 26. The nuclear rod according to claim 22 wherein the tag gas is at least one member selected from the group consisting of helium, xenon and krypton. 27. The fuel rod according to claim 19, wherein said tag gas-injected metal foil is loaded in a plenum of the cladding tube. 28. The fuel rod according to claim 20, wherein said tag gas-injected metal foil is loaded in a plenum of the cladding tube. |
description | This application claims priority to U.S. Provisional Patent Application Ser. No. 62/353,223, filed Jun. 22, 2016 entitled NUCLEAR FUEL ROD. This invention relates in general to nuclear fuel rods and, more particularly, to nuclear fuel rods that have a cladding constructed from a material that cannot be welded or brazed to an end plug. The primary side of nuclear reactor power generating systems which are cooled with water under pressure comprises a closed circuit which is isolated and in heat exchange relationship with a secondary side for the production of useful energy. The primary side comprises the reactor vessel enclosing a core internal structure that supports a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are connected to the vessel to form a loop of the primary side. For the purpose of illustration, FIG. 1 shows a simplified nuclear reactor primary system, including a generally cylindrical reactor pressure vessel 10 having a closure head 12 enclosing a nuclear core 14. A liquid reactor coolant, such as water is pumped into the vessel 10 by pump 16 through the core 14 where heat energy is absorbed and is discharged to a heat exchanger 18, typically referred to as a steam generator in which heat is transferred to a utilization circuit (not shown), such as a steam driven turbine generator. The reactor coolant is then returned to the pump 16, completing the primary loop. Typically, a plurality of the above described loops are connected to a single reactor vessel 10 by reactor coolant piping 20. An exemplary reactor design is shown in more detail in FIG. 2. In addition to the core 14 comprised of a plurality of parallel, vertical, co-extending fuel assemblies 22, for purposes of this description, the other vessel internal structures can be divided into the lower internals 24 and the upper internals 26. In conventional designs, the lower internals' function is to support, align and guide core components and instrumentation as well as direct flow within the vessel. The upper internals restrain or provide a secondary restraint for the fuel assemblies 22 (only two of which are shown for simplicity in this figure), and support and guide instrumentation and components, such as control rods 28. In the exemplary reactor shown in FIG. 2, coolant enters the reactor vessel 10 through one or more inlet nozzles 30, flows down through an annulus between the vessel and the core barrel 32, is turned 180 degrees in a lower plenum 34, passes upwardly through a lower support plate 37 and a lower core plate 36 upon which the fuel assemblies 22 are seated and through and about the assemblies. In some designs, the lower support plate 37 and the lower core plate 36 are replaced by a single structure, the lower core support plate, at the same elevation as 37. The coolant flow through the core and surrounding area 38 is typically large on the order of 400,000 gallons per minute at a velocity of approximately 20 feet per second. The resulting pressure drop and frictional forces tend to cause the fuel assemblies to rise, which movement is restrained by the upper internals, including a circular upper core plate 40. Coolant exiting the core 14 flows along the underside of the upper core plate 40 and upwardly through a plurality of perforations 42. The coolant then flows upwardly and radially to one or more outlet nozzles 44. The upper internals 26 can be supported from the vessel or the vessel head and include an upper support assembly 46. Loads are transmitted between the upper support assembly 46 and the upper core plate 40, primarily by a plurality of support columns 48. A support column is aligned above a selected fuel assembly 22 and perforations 42 in the upper core plate 40. The rectilinearly moveable control rods 28 typically include a drive shaft 50 and a spider assembly 52 of neutron poison rods that are guided through the upper internals 26 and into aligned fuel assemblies 22 by control rod guide tubes 54. The guide tubes are fixedly joined to the upper support assembly 46 and connected by a split pin 56 force fit into the top of the upper core plate 40. The pin configuration provides for ease of guide tube assembly and replacement if ever necessary and assures that the core loads, particularly under seismic or other high loading accident conditions, are taken primarily by the support columns 48 and not the guide tubes 54. This support column arrangement assists in retarding guide tube deformation under accident conditions which could detrimentally affect control rod insertion capability. FIG. 3 is an elevational view, represented in vertically shortened form, of a fuel assembly being generally designated by reference character 22. The fuel assembly 22 is the type used in a pressurized water reactor and has a structural skeleton which, at its lower end, includes a bottom nozzle 58. The bottom nozzle 58 supports the fuel assembly 22 on a lower core support plate 60 in the core region of the nuclear reactor (the lower core support plate 60 is represented by reference character 36 in FIG. 2). In addition to the bottom nozzle 58, the structural skeleton of the fuel assembly 22 also includes a top nozzle 62 at its upper end and a number of guide tubes or thimbles 54, which extend longitudinally between the bottom and top nozzles 58 and 62 and at opposite ends are rigidly attached thereto. The fuel assembly 22 further includes a plurality of transverse grids 64 axially spaced along and mounted to the guide thimbles 54 (also referred to as guide tubes) and an organized array of elongated fuel rods 66 transversely spaced and supported by the grids 64. Although it cannot be seen in FIG. 3, the grids 64 are conventionally formed from orthogonal straps that are interleafed in an egg-crate pattern with the adjacent interface of four straps defining approximately square support cells through which the fuel rods 66 are supported in transversely spaced relationship with each other. In many conventional designs springs and dimples are stamped into the opposing walls of the straps that form the support cells. The springs and dimples extend radially into the support cells and capture the fuel rods therebetween, exerting pressure on the fuel rod cladding to hold the rods in position. Also, the fuel assembly 22 has an instrument tube 68 located in the center thereof that extends between and is mounted to the bottom and top nozzles 58 and 62. With such an arrangement of parts, fuel assembly 22 forms an integral unit capable of being conveniently handled without damaging the assembly of parts. As mentioned above, the traditional fuel rods 66 in the array thereof in the fuel assembly 22 are held in spaced relationship with one another by the grids 64 spaced along the fuel assembly length. Each fuel rod 66 includes a plurality of nuclear fuel pellets 70 and is closed at its opposite ends by upper and lower end plugs 72 and 74. The pellets 70 are maintained in a stack by a plenum spring 76 disposed between the upper end plug 72 and the top of the pellet stack. The fuel pellets 70, composed of fissile material, are responsible for creating the reactive power of the reactor. The cladding which surrounds the pellets functions as a barrier to prevent the fission by-products from entering the coolant and further contaminating the reactor system. The power output of a reactor is limited by the highest temperatures the materials within the core can tolerate without compromising their integrity. In the case of pressurized water reactors the fuel rod cladding, which is typically constructed from a Zirconium alloy, is the limiting material. Zirconium is generally chosen for the fuel rod cladding for its excellent neutronic properties. Alternatively, silicon carbide (SiC) has excellent neutronic and high temperature properties making it a possible candidate for accident tolerant fuel (ATF). However, sealing silicon carbide fuel tubes has been a difficult problem and no entirely satisfactory solution has been found. SiC cannot be welded, and seals that involve metal bonding have had only limited success. Silicon carbide has a low coefficient of expansion, and an elongation before break value of less than 1%. Thermal cycling puts high stresses on the bond, causing failures. Deposition of SiC bonding material has been used to avoid thermal mismatch problems and achieve good hermeticity, but this approach to bonding is expensive and has not been successful in reactor testing at MIT. Accordingly, a new end plug seal is desired for SiC fuel rods that will overcome these difficulties. This invention overcomes the foregoing shortcomings by providing a nuclear fuel rod comprising a tubular cladding constructed from a material that cannot be welded or brazed, that surrounds an interior volume. A first closure seals off one end of the tubular cladding, with a nuclear fuel occupying a portion of the interior volume, and a gland seal end plug seals off a second end of the tubular cladding. In one embodiment the gland seal end plug comprises a flexible material that is supported between a wall of the tubular cladding and a force generator that is configured to exert a radially outward force on the flexible material to pressure the flexible material against a wall of an interior of the tubular cladding and seal off the second end of the tubular cladding. In the latter embodiment, the force generator may comprise a ram that extends into an interior of the tubular cladding from an end stopper that closes off the second end of the tubular cladding. The ram is configured to support and exert the radially outward force on the flexible material. Preferably, the ram expands the flexible material against the wall of the interior of the tubular cladding and a seat on an interior of the end stopper. In the latter embodiment the ram may also include a stem that extends through the end stopper from an interior of the tubular cladding to an exterior thereof, with an exterior of the stem being threaded. The stem includes a nut, coupled to the exterior thread that is configured to draw the stem through the end stopper to pressure the flexible material against the wall of the interior of the tubular cladding. In the latter embodiment the flexible material is pressured between an interior end of the ram, the stem, the interior wall of the tubular cladding and the seat. Preferably, a spring washer is included that is structured to be compressed long with the flexible material and maintains a force on the flexible material even if there is themral expansion of the stem or relaxation of the flexible material. Desirably, the spring washer comprises an alloy such as X-750 or 718. Alternately, the spring washer may comprise a high temperature ceramic such as silicon carbide or a partially stabilized Zirconium Oxide. In the case where the spring washer comprises a ceramic material, the spring washer may include a stack of ceramic spring washers. Preferably, the end stopper is configured to prevent the flexible material from expanding through an interface between the interior of the tubular cladding and the end stopper. In one such embodiment, the tubular cladding is silicon carbide and the flexible material comprises graphite. Desirably, the flexible material comprises pure graphite, preferably in the form of a mixture of graphite fibers and expanded graphite. Preferably, the end stopper and/or the ram comprises Zircaloy 4. In such an embodiment one or more of the seat, ram and nut comprise silicon carbide and, preferably, the end stopper is coated with silicon carbide. In still another embodiment the seat is constructed in two layers including a gasket between the two layers of the seat that form a seal between the seat and the stem and the seat and the wall of the hollow tubular member. Preferably, the gasket comprises a plurality of O-ring gaskets. The O-ring gaskets may take the shape of a traditional simple circular design or may be shaped as C-rings, U-rings, V-rings or W-rings or the like. Thus, this invention provides a Gland Seal End Plug closure for a fuel rod cladding composed of silicon carbide or other materials that cannot be welded. The sealant is, preferably, made from one or more forms of pure graphite and the ram, seat and other components are formed from high temperature metallic or ceramic materials. This invention overcomes the foregoing difficulties by providing a Gland Seal End Plug for Accident Tolerant Fuel (ATF) that uses a soft graphite packing material to achieve a hermetic seal for SiC cladding that can function at pressures expected in a PWR or BWR, even in accident situations. The design is capable of maintaining a seal under high rod internal pressures and high reactor coolant system pressures. A conceptual drawing of the Gland Seal End Plug for ATF is shown in FIG. 4. The plug (76) is composed of five basic components. The sealant (78) is a flexible material that expands against the inside diameter of the silicon carbide tube (80) as it is compressed between the gland seal ram (82) and the gland seal seat (84). The sealant (78) engages with the rough surface of the silicon carbide tube (80) inside diameter, such that once the sealant (78) is fully expanded, the plug (76) cannot be pulled from the tube (80) or forced further into the tube. A nut (86) that is threaded onto the gland seal ram stem or shaft (88) is used to draw the gland seal ram (82) toward the gland seal seat (84) to compress the sealant (78). A spring washer (90) is compressed along with the sealant (78), and maintains the force on the sealant even if there is thermal expansion of the gland seal ram (82), or a long term relaxation of the sealant (78). The Allen Socket (92) allows the nut (86) to be tightened without spinning the ram (82). The plug (76) is designed with dimensions such that it can be pushed into the silicon carbide tube (80) with little or no force before it is expanded. The outside diameter of the plug (76) is sized such that neither the ram (82) nor the seat (84) will apply force to the inside diameter of the silicon carbide tube due to radiation induced swelling and/or thermal expansion. The preferred material for the sealant (78) is pure graphite. Graphite packing has been used for high temperature valves and is known to be able to withstand temperatures up to 3000° F. (1649° C.). The ideal packing would be a mix of graphite fiber and expanded graphite. The fiber holds the expanded graphite flakes in place and prevents the sealant from being extruded through gaps such as between the tube wall inside diameter and the ram. Expanded graphite sealants maintain their resilience for long periods and at high temperatures, so the spring washer does not need to exert force over a large distance. A variety of different materials could be used for the other plug components. Zirconium alloys, such as Zircaloy 4, would make a suitable ram, seal seat, and nut material due to proven performance in water cooled reactors, low coefficient of thermal expansion, and high melting point. Zircaloy 4 can be easily welded which would allow several other features to be added to the plug. A hole could be located in the ram for filling the rod with helium and for pressure testing, and afterwards the hole could be welded closed. A tack weld between the nut and the ram could be used to assure that the nut did not loosen during operation. Another favorable material for the seat, ram, and nut would be silicon carbide. This would give the plug the same thermal expansion as the cladding and the same high temperature performance. Being the same material as the cladding would allow bonding schemes that would otherwise not be possible. For instance, the plug region could be coated with a thin layer of Chemical Vapor Deposition (CVD) silicon carbide which would serve to provide an additional gas barrier, but the layer would not have to have mechanical strength. The spring washer could be a high temperature metal such as Alloy X-750 or Alloy 718. These materials are known to be corrosion resistant and resistant to stress relaxation during normal operation. The fuel end plugs would not heat up to the same extent as more central core locations during an accident, so these alloys would likely not limit ATF performance. However, if it is determined that for a particular fuel design and core that the spring washer would limit performance, they could also be manufactured from a tough, high temperature ceramic such as silicon carbide or a partially stabilized Zirconium Oxide. If a ceramic material is used for the spring washer, a stack of ceramic spring washers would be required to compensate for growth of the ram and sealant relaxation. A second embodiment of the invention is shown in FIG. 5. A set of high temperature O-rings (94) has been added to provide a back-up sealing capability. The inside of the tube has been machined to produce a smooth surface for sealing. The top of the seat (84) is now constructed of two segments (96, 98), with one of the two segments (96) containing O-ring grooves. The grooves are constructed such that the O-ring expands to contact both the ram stem (88) and the cladding (80) when the Gland Seal End Plug assembly (76) is fully compressed with the nut (86). Besides providing a sealing function themselves, the O-rings (94) also transmit pressure to the graphite sealant (78), assisting the spring washer (90) in compensating for ram (82) growth or sealant (78) compression during operation. In a preferred embodiment of the secondary O-ring seal, the O-rings (94) are composed of a high-temperature alloy such as X-750 or 718, coated with a soft metallic coating such as platinum or nickel. The invention does not limit the shape of the sealing ring to a simple circular design, but it also includes C-ring, U-rings, V-rings and W-ring, as well as designs that have a more nearly square cross section. Multiple sealing ring segments may be stacked to afford additional reliability. This is shown in FIG. 6. This embodiment, where two sets of C-rings (94) are stacked with the C-ring facing in opposite directions, is particularly favorable due to the fact that the sealing force will increase with pressure, and sealing is equally effective for excluding coolant from the interior of the fuel rod and preventing gasses within the fuel rod from escaping. More than one sealing segment can be used as well as more than one sealing ring. This is shown in FIG. 7, where two different packing segments (100, 102) are connected by a packing spacer (104). Note that in this embodiment of the invention, the seat (84), the ram (82), and the spacer (104) have all been shaped to transmit more of the pressure from sealant compression toward the sealing surfaces along the tube (80) and the ram stem (88). Such shaping can be employed whether or not multiple flexible sealants are used. Note that in this embodiment, the end of the tube does not contact the seat, so that system pressurization can more effectively apply sealing pressure to the flexible sealant. Accordingly, this invention provides a nuclear fuel rod cladding (80) formed from a material such as a ceramic that cannot be welded with a flexible gland seal closure. Preferably, the gland sealant (78) is formed from a material such as pure graphite. A screw ram (82) and a wedge-shaped seat (84) are used to compact and radially expand the sealant (78) and the seat (84), ram (82), and nut (86) are preferably composed of high temperature metallic materials such as Zircaloy 4. In an alternated embodiment of the device all components, except the graphite sealant, are composed of tough ceramic materials such as silicon carbide or partially stabilized zirconium oxide. A spring washer (90) or stack of spring washers are used to maintain compressive force on the sealant to compensate for sealant shrinkage or ram thermal or radiation induced expansion. In another alternate embodiment of the device, resilient metal sealing O-rings (94) provide a secondary seal and also apply force to the sealant to compensate for sealant shrinkage or ram thermal or radiation induced expansion. Multiple sets of sealing rings may be used. The resilient metal seal rings may be O, C, V, U or W shaped and the rings may be coated with a soft metallic material such as nickel or platinum so the soft metal and the resilient base metal do not corrode or otherwise degrade below 1200° F. (649° C.) in a primary water or steam environment. In still another embodiment, the ram (82) has a sealable passage through which helium can be added to the rod and the seal pressure tested. Where seal rings are employed, the end of the fuel rod inside diameter being sealed is machined to a flatness and ovality such that sealing rings will function. The ram and seat are shaped to optimally transmit compressive forces in a radial direction to the sealing surfaces. Multiple sealing rings and/or flexible sealants may be used. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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summary | ||
abstract | A betavoltaic power source for mobile devices and mobile applications includes a stacked configuration of isotope layers and energy conversion layers. The isotope layers have a half-life of between about 0.5 years and about 5 years and generate radiation with energy in the range from about 15 keV to about 200 keV. The betavoltaic power source is configured to provide sufficient power to operate the mobile device over its useful lifetime. |
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abstract | A method for investigating a cause of decrease in frequency of abnormality detections for a certain device mounted on a vehicle, wherein when a plurality of abnormality detection conditions are satisfied, the abnormality detection for the certain device is performed to determine if the certain device is in failure, the method includes (i) when the frequency of the abnormality detections is below a predetermined value, disabling one of the abnormality detection conditions; (ii) when the abnormality detection conditions except the disabled abnormality detection condition are satisfied, performing an abnormality detection for the certain device; (iii) repeating the step (ii) a plurality of times; and (iv) determining if the disabled abnormality detection condition at that time is the cause of the decrease in the frequency of the abnormality detections, based on frequency of the abnormality detections in the step (iii). |
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051125676 | abstract | The shutoff device consists of a housing (14) inserted in the conduit, in which a movable shutter (32) is mounted for oscillation about a horizontal axis (33) in the housing (14) and comprising a closing member (35) returned into a position of closing a channel (28) by a counterweight (36). A manometer (43) enables the pressure inside the housing (14) to be measured. The shutoff device, wholly passive in operation, can be employed in particular in a conduit for guiding a measurement probe employed in a pressurized water nuclear reactor. |
abstract | Systems and methods for providing and using molten salt reactors are described. While the systems can include any suitable component, in some cases, they include a graphite reactor core defining an internal space that houses one or more fuel wedges, where each wedge defines one or more fuel channels that extend from a first end to a second end of the wedge. In some cases, one or more of the fuel wedges comprise multiple wedge sections that are coupled together end to end and/or in any other suitable manner. In some cases, one or more alignment pins also extend between two sections of a fuel wedge to align the sections. In some cases, one or more seals are also disposed between two sections of a fuel wedge. Thus, in some cases, the reactor core can be relatively long (e.g., to be a pipeline reactor). Other implementations are also described. |
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description | This application claims priority to and any other benefit of U.S. Provisional Application Ser. No. 60/822,134, filed Aug. 11, 2006, the entirety of which is incorporated by reference herein. This application is related to the application entitled PATTERNING NON-PLANAR SURFACES, U.S. Provisional Application Ser. No. 60/822,216, filed Aug. 11, 2006, the entirety of which is incorporated herein. Patterning methods and applications have become increasingly complex. For example, it may be desirable to pattern complex surfaces using patterning processes. Such complex surfaces include, but are not limited to, curved radomes that house instruments and provide frequency selective surfaces on moving vehicles or land based installations and three-dimensional printed circuit boards. These complex surfaces present special difficulties because complex shaped masks are difficult to fabricate. Additionally, such masks can be expensive, difficult to use and/or reuse, and prone to patterning errors. For example, rigid shells having patterns of electromagnetic radiation blocking material and formed in the complex shape of the part have been used. However, this rigid shell can be expensive and difficult to fabricate. Additionally, this rigid shell may introduce patterning errors if good contact is not established between the shell and the surface to be patterned. Thus, there remains a need in the art for additional methods, compositions, and masks for use in patterning surfaces. In various embodiments of the invention, masks are provided. The masks can comprise an electromagnetic radiation sensitive mask material. The electromagnetic radiation sensitive mask material can be selected such that a first percentage of electromagnetic radiation at a first wavelength is transmitted through the electromagnetic radiation sensitive mask material prior to the exposure of the electromagnetic radiation sensitive mask material to electromagnetic radiation at a second wavelength; a second percentage of electromagnetic radiation at the first wavelength is transmitted through at least a portion of the electromagnetic radiation sensitive mask material after the at least a portion of the electromagnetic radiation sensitive mask material is exposed to electromagnetic radiation at the second wavelength; and the electromagnetic radiation sensitive mask material is suitable to define features on a substrate at the first wavelength after the exposure of the at least a portion of the electromagnetic radiation sensitive mask material to electromagnetic radiation at the second wavelength to form patterns defining the features in the electromagnetic radiation sensitive mask material. In various additional embodiments, methods are provided. The methods can comprise exposing at least one selected portion of a mask comprising an electromagnetic radiation sensitive mask material having at least one electromagnetic radiation sensitive portion to electromagnetic radiation at a patterning wavelength to cause a reaction of the at least one electromagnetic radiation sensitive portion such that a pattern is formed in the mask; and subsequently exposing a substrate to electromagnetic radiation at an exposure wavelength through the mask such that the pattern is formed on the substrate, wherein the substrate is sensitive to electromagnetic radiation at the exposure wavelength. In yet other various embodiments, compositions for producing masks are provided. The compositions can comprise a polymer and at least one electromagnetic radiation sensitive additive. Upon processing of the polymer, an electromagnetic radiation sensitive mask material is formed. The electromagnetic radiation sensitive mask material transmits a smaller percentage of electromagnetic radiation at a first wavelength after exposure of the electromagnetic radiation sensitive mask material to electromagnetic radiation at a second wavelength than the electromagnetic radiation sensitive mask material transmits at the first wavelength prior to exposure of the electromagnetic radiation sensitive additive to electromagnetic radiation at the second wavelength. In other various embodiments, compositions for producing a masks are provided. The compositions can comprise at least one electromagnetic sensitive polymer and at least one acid sensitive additive. Upon processing of the polymer, an electromagnetic radiation sensitive mask material is formed. The electromagnetic radiation sensitive mask material transmits a smaller percentage of electromagnetic radiation at a first wavelength after exposure of the electromagnetic radiation sensitive mask material to electromagnetic radiation at a second wavelength than the electromagnetic radiation sensitive mask material transmits at the first wavelength prior to exposure of the electromagnetic radiation sensitive compound to electromagnetic radiation at the second wavelength. In yet further various embodiments, systems are provided. The systems can comprise a source for a first and a second electromagnetic radiation, a mask sensitive to the second electromagnetic radiation, a substrate sensitive to the first electromagnetic radiation, and a device in conjunction with the source for the first and second electromagnetic radiations. The device is capable of exposing the mask to the second electromagnetic radiation such that regions that are selectively opaque to the first electromagnetic radiation are formed in the mask, and the device is capable of subsequently exposing the substrate to the first electromagnetic radiation through the selectively opaque mask such that portions of the substrate are selectively exposed to the first electromagnetic radiation. It will be understood that the various embodiments described above are exemplary embodiments only, and that this invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. The present invention will now be described with occasional reference to the specific embodiments of the invention. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. Unless otherwise indicated, all numbers expressing quantities, properties, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless otherwise indicated, the numerical properties set forth in the following specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values to the extent that such are set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from error found in their respective measurements. Except as otherwise specifically defined herein, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only, and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless otherwise indicated, all numbers expressing quantities, properties, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless otherwise indicated, the numerical properties set forth in the following specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values to the extent that such are set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from error found in their respective measurements. A complete understanding of the invention will be obtained from the following description when taken in connection with the accompanying drawing figures wherein like reference characters identify like parts throughout. For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “front”, “back” and derivatives thereof shall relate to the invention as it is oriented in the drawing figures. However, it is to be understood that the invention may assume various alternative variations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments disclosed herein are not to be considered as limiting. The present invention relates to compositions, masks, systems and patterning methods that may be used to produce a variety of patterned substrates. The compositions, masks, systems and patterning methods may be scalable and useful for patterning substrates that have complex shapes. In accordance with embodiments of the invention, masks are provided. Referring to FIG. 1, a mask 10 is illustrated. The mask 10 comprises a electromagnetic radiation sensitive mask material 12. For purposes of defining and describing the present invention, the term “electromagnetic radiation sensitive mask material” shall be understood as referring to a material that exhibits a change in transmittance in areas exposed to electromagnetic radiation of a desired wavelength and that has a contrast ratio between unexposed areas and exposed areas suitable to pattern the mask material and use the mask material to define features on a substrate sensitive to electromagnetic radiation of a desired wavelength. For purposes of describing and defining this invention, “wavelength” shall be understood as referring to range of wavelengths emitted by a particular electromagnetic radiation source and as delivered through filters, including, but not limited to, high-pass, low-pass, and band-pass, to the material. The electromagnetic radiation sensitive mask material is selected such that a first percentage of electromagnetic radiation at a first wavelength is transmitted through the electromagnetic radiation sensitive mask material prior to the exposure of the electromagnetic radiation sensitive mask material to electromagnetic radiation at a second wavelength. Additionally, the electromagnetic radiation sensitive mask material is selected such that a second percentage of electromagnetic radiation at the first wavelength is transmitted through at least a portion of the electromagnetic radiation sensitive mask material after at least a portion of the electromagnetic radiation sensitive mask material is exposed to electromagnetic radiation at the second wavelength. The electromagnetic radiation sensitive mask material is suitable to define features on a substrate to electromagnetic radiation at the first wavelength after the exposure of the at least a portion of the electromagnetic radiation sensitive mask material to electromagnetic radiation at the second wavelength to form patterns defining the features in the electromagnetic radiation sensitive mask material. It will be understood that the mask can be used to pattern a substrate sensitive to electromagnetic radiation at a first wavelength in any suitable manner. For example, a substrate having a photoresist that is sensitive to electromagnetic radiation at a first wavelength thereon may be provided. The mask can be used to photolithographically pattern such a substrate. In other examples, the substrate can comprise a electromagnetic radiation sensitive mask material of the present invention. In yet another alternative, the substrate may be provided with a layer in which a change in the surface charge is produced upon exposure to electromagnetic radiation at a first wavelength. A toner and cure can be subsequently provided to fix the features on the substrate. Any other suitable substrate that is electromagnetic radiation sensitive may be used. For example, the masks can be used in photoimaging of the substrate. It will be further understood that the mask itself may be the substrate. For example, a photoresist that is sensitive to electromagnetic radiation at a first wavelength may be provided on at least a portion of the mask, and the resist may be exposed through the mask. In some examples, the first percentage of electromagnetic radiation may be greater than the second percentage of electromagnetic radiation. In other examples, the first percentage of electromagnetic radiation may be less than the second percentage of electromagnetic radiation. In yet other examples, the second percentage of electromagnetic radiation may be a gradient of electromagnetic radiation. For example, there may be a gradient of percentages of the second electromagnetic radiation from one face of the mask to another face of the mask, and such a mask may be exposed from either side. It will be understood that the relationship between the first percentage and the second percentage of electromagnetic radiation can be controlled by selecting the electromagnetic radiation sensitive mask material as further discussed herein. For example, the electromagnetic radiation sensitive mask material can have a contrast ratio between the area of the electromagnetic radiation sensitive mask material that is not exposed to electromagnetic radiation at the second wavelength and an area of the electromagnetic radiation sensitive mask material that is exposed to electromagnetic radiation at the second wavelength of about 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1 25:1, or up to 100:1 or more. It will be understood that the contrast ratio can be a range of about x to about y, where x and y are selected from the contrast ratios listed above. In general, the contrast ratio will be determined by the sensitivity of the substrate sensitive to electromagnetic radiation of a first wavelength to be patterned with the mask or the level of optical clarity of the mask, or both. For example, referring to FIG. 2, the electromagnetic radiation sensitive mask material 12 can have a pattern 14 formed therein upon exposure of the electromagnetic radiation sensitive mask material 12 to electromagnetic radiation at a second wavelength. It will be understood that the pattern 14 is defined by areas 16 of the electromagnetic radiation sensitive mask material 12 that transmit a different percentage of electromagnetic radiation at a first wavelength than areas 18 that have not been exposed to electromagnetic radiation at the second wavelength. It will be further understood that the areas 16 may exhibit a color change that is apparent under visible electromagnetic radiation. Alternatively, the areas 16 may not exhibit any color change under visible electromagnetic radiation. In some examples, some areas 16 may exhibit a color change that is apparent under visible electromagnetic radiation, and other areas 16 may not exhibit any color change under visible electromagnetic radiation. In some examples, the first wavelength and the second wavelength may be the same wavelength. For example, the electromagnetic radiation sensitive mask material may be exposed to electromagnetic radiation of a first wavelength at a first total exposure energy and the substrate may be subsequently patterned by exposure through the mask to electromagnetic radiation of a first wavelength at a second total exposure energy. For example, the first total exposure energy may be much greater than the second total exposure energy, and the electromagnetic radiation sensitive mask material would transmit a different percentage of electromagnetic radiation only after exposure to the first total exposure energy, because the second total exposure energy may be too small to cause the electromagnetic radiation sensitive mask material to react. In another example, the electromagnetic radiation sensitive mask material may be selected such that the transmissivity of a particular electromagnetic radiation through the mask material is changed only after the absorption of two or more photons. The substrate could be subsequently processed with electromagnetic radiation that does not cause the absorption of two or more photons. For example, the substrate could be exposed to electromagnetic radiation having less total energy than the electromagnetic radiation used to expose the electromagnetic radiation sensitive mask material. In other examples, the first wavelength and the second wavelength are different. For example, at least a portion of the electromagnetic radiation sensitive mask material may be exposed to electromagnetic radiation in the UV or deep UV range such that the portions of the electromagnetic radiation sensitive mask material that are exposed to this electromagnetic radiation exhibit reduced transmission of electromagnetic radiation in the visible range. In other examples, the electromagnetic radiation sensitive mask material may be exposed to electromagnetic radiation in the visible or x-ray range. It will be understood that the electromagnetic radiation sensitive mask material can be selected to perform as desired at desired first and second wavelengths. The mask may be of any suitable dimensions and thickness. For example, the mask may be from less than about two inches in diameter to greater than about ten feet in diameter. In some examples, the mask may be from about 1 μm to about 200 μm thick. In yet other examples, the mask may be from about 0.025 mm to about 1 mm thick. It will be understood that the particular dimensions and thickness of the mask may be selected or controlled with the selection of appropriate electromagnetic radiation sensitive mask materials. The electromagnetic radiation sensitive mask material can comprise any suitable electromagnetic radiation sensitive material. In some embodiments, the electromagnetic radiation sensitive mask material comprises an electromagnetic radiation transparent material having at least one electromagnetic radiation sensitive additive. The electromagnetic radiation transparent material can be any suitable material allows an effective amount of electromagnetic radiation through the material. Compositions for producing the electromagnetic radiation sensitive mask material are additionally provided. These compositions comprise at least one polymer, at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both. The compositions comprise at least one electromagnetic sensitive portion. Upon processing of the polymer, an electromagnetic radiation sensitive mask material is formed. It will be understood that the processing of the polymer can comprise processing a polymer having at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both dispersed therein such that a polymer matrix is formed having the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both dispersed in the matrix. In other examples, processing of the polymer can comprise processing a polymer such that a polymer matrix is formed and subsequently applying the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both to the polymer matrix in any suitable manner as will be discussed further herein. In yet other examples, processing of the polymer can comprise processing a polymer such that a polymer matrix is formed and subsequently infusing the at least one electromagnetic sensitive additive, acid sensitive additive, or both into the polymer matrix as will be discussed further herein. In some embodiments, the electromagnetic radiation transparent material can comprise a cured polymer matrix. These cured polymer matrices can be provided in any suitable manner, and compositions for producing a mask are additionally provided. The compositions comprise an uncured polymer and at least one electromagnetic radiation sensitive additive, acid sensitive, or both. The compositions comprise at least one electromagnetic radiation sensitive portion. According to some embodiments, the uncured polymer is processed to form an electromagnetic radiation transparent layer. For example, the uncured polymer may processed by curing. Upon curing of the polymer, the electromagnetic radiation sensitive mask material is formed. This electromagnetic radiation sensitive mask material performs as discussed above. In some examples, the electromagnetic radiation sensitive additive, the acid sensitive additive, or both is dispersed in the cured polymer matrix. For example, the electromagnetic radiation sensitive additive, the acid sensitive additive, or both, the uncured polymer, and a suitable solvent can be mixed to disperse the electromagnetic radiation sensitive additive, acid sensitive additive, or both in the matrix. Subsequently, the uncured polymer can be cured to form the electromagnetic radiation sensitive mask material. In other examples, the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be provided in a layer proximate to the cured polymer matrix. In this example, the polymer matrix may be cured, and the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be provided in contact with one or more surfaces of the cured polymer matrix. In yet other examples, the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be infused into the cured polymer matrix. In other embodiments, the electromagnetic radiation transparent material can comprise a thermoplastic polymer matrix. These thermoplastic polymer matrices can be provided in any suitable manner, and compositions for producing a mask are also provided. The compositions comprise a thermoplastic polymer and at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both. The compositions comprise at least one electromagnetic sensitive portion. The thermoplastic polymer is processed to form the electromagnetic radiation transparent layer. For example, the thermoplastic polymer can be processed by compounding or solution casting. This electromagnetic radiation sensitive mask material performs as discussed above. In some examples, the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both is dispersed in the thermoplastic polymer matrix. For example, the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both and the thermoplastic polymer can be mixed at a temperature above the melting point of the thermoplastic polymer. Subsequently, the thermoplastic polymer can be formed into a film by suitable techniques to form the electromagnetic radiation sensitive mask material. In other examples, the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be provided in a layer proximate to the thermoplastic polymer matrix. In this example, the polymer matrix may be already formed into a film and the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be provided in contact with one or more surfaces of the thermoplastic polymer matrix. In yet further examples, the at least electromagnetic radiation sensitive additive, acid sensitive additive, or both may be infused into the thermoplastic polymer matrix. In yet other embodiments, the electromagnetic radiation transparent material can comprise a soluble polymer matrix. These soluble polymer matrices can be provided in any suitable manner, and compositions for producing a mask are provided. The compositions comprise a soluble polymer and at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both. The compositions comprise at least one electromagnetic sensitive portion. The soluble polymer is processed to form the electromagnetic radiation sensitive mask material. For example, the soluble polymer can be processed by evaporating a solvent to form a soluble polymer matrix. This electromagnetic radiation sensitive mask material performs as discussed above. In some examples, the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both is dispersed in the soluble polymer matrix. For example, the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both and the soluble polymer can be mixed in a solvent. Subsequently, the soluble polymer can be formed into a film by suitable techniques to form the electromagnetic radiation sensitive mask material. In other examples, the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be provided in a layer proximate to the soluble polymer matrix. In this example, the polymer matrix may be already formed into a film and the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be provided in contact with one or more surfaces of the soluble polymer matrix. In yet other examples, the polymer matrix may be formed into a film, and the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be infused into the polymer matrix. In some embodiments, the curable, thermoplastic, or soluble polymers that form the matrix do not react to electromagnetic radiation. In other embodiments, the curable, thermoplastic, or soluble polymers that form the matrix may react to electromagnetic radiation. For example, modified polymers that contain at least one electromagnetic radiation sensitive portion may be provided. In this example, the electromagnetic radiation sensitive mask material can comprise the polymer alone. Alternatively, additional electromagnetic radiation sensitive additives, additional acid sensitive additives, or both may be provided. In other embodiments, the curable, thermoplastic, or soluble polymer may be a polymer that produces an acidic species upon exposure to electromagnetic radiation. For example, the composition can comprise at least one acid sensitive additive that may cause a change in transmittance of the electromagnetic sensitive material, as will be discussed further herein. Such polymers include, but are not limited to, chlorine containing polymers such as polyvinyl chloride (PVC), polyvinylidine chloride (PVDC), or ethylene chlorotrifluorethylene (ECTFE). These polymers may be exposed to electromagnetic radiation and this exposure can cause elimination of hydrochloric acid (HCl) from the polymer backbone through a dehydrochlorination reaction. Examples of additional suitable curable, thermoplastic, and soluble polymer matrices include, but are not limited to styrene and ethylene/butylene linear block copolymers, such as Kraton G1652, styrene and ethylene/butylene linear block copolymers having maleic anhydride, such as Kraton FG1901, and aliphatic polyurethanes such as Clearflex Polyurethane 50A or 90A. Other electromagnetic radiation transparent polymer matrices include, but are not limited to, polyolefins, such as oriented polypropylene (OPP); cycloolefins, such as Topas, Surlyn (ionomer); polyesters; polyethers; polyimides; isoprene polymers and copolymers; amorphous polymers like polymethyl methacrylate (PMMA), polycarbonate (PC), styrene acrylonitrile (SAN), polystyrene (PS); as well as fluoropolymers, such as Teflon AF, ethylene trifluoroethylene (ETFE), and fluorinated ethylene propylene (FEP). It will be understood that any suitable combinations of the polymer matrix materials can also be used. The selection of polymer can depend on a number of factors, such as flexibility, processability, and any other desired properties. It will be understood that any suitable configuration of the electromagnetic radiation sensitive mask material may be utilized. For example, as shown in FIG. 3, the electromagnetic radiation sensitive mask material 12 can comprise an electromagnetic radiation transparent layer 20 and a layer having at least one electromagnetic radiation sensitive additive or acid sensitive additive 22 disposed on the electromagnetic radiation transparent layer 20. In other examples, at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be disposed between two or more electromagnetic radiation transparent layers (not shown). In yet further examples, at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both may be disposed on two or more electromagnetic radiation transparent layers (not shown). Alternatively, as discussed above, the electromagnetic radiation sensitive mask material can comprise a single layer, as shown in FIG. 1, wherein the at least one electromagnetic radiation sensitive additive, acid sensitive additive, or both is dispersed within the electromagnetic radiation transparent layer. It will be understood that the electromagnetic radiation transparent layers may be formed in any suitable manner. For example, the electromagnetic radiation transparent layer, the electromagnetic radiation sensitive additive or additives, acid sensitive additive or additives, or both and a suitable solvent may be mixed to provide a solution that may be cast, spin coated, molded, or formed in any other suitable manner and processed to provide the electromagnetic radiation sensitive mask material. It will be understood that the conditions under which the electromagnetic radiation sensitive mask material are formed and processed may be selected as suitable for each particular configuration. For example, suitable solvents for the polymers identified above include, but are not limited to, toluene, chloroform, methyl ethyl ketone, xylene and mixtures thereof. In some examples, the solids content of the solution is from about 10 percent to about 40 percent by weight. In other examples, the solids content of the solution is about 25 percent by weight, or about 20 percent by weight, or about 15 percent by weight. In other examples, at least one electromagnetic radiation transparent layer may be formed in a suitable manner and the electromagnetic radiation sensitive additive or additives, acid sensitive additive or additives, or both may be infused into the at least one electromagnetic radiation transparent layer. For example, the electromagnetic radiation sensitive additive or additives, acid sensitive additive or additives, or both may be dissolved in a solvent that does not act as a solvent for the at least one electromagnetic radiation transparent layer. Subsequently, the solution may be spray coated onto the at least one electromagnetic radiation transparent layer and allowed to infuse into the electromagnetic radiation transparent layer. It will be understood that the electromagnetic radiation sensitive additive or additives, acid sensitive additive or additives, or both may be infused into the at least one electromagnetic radiation transparent layer in any suitable manner. The electromagnetic radiation sensitive mask material can be formed as a single component film or sheet. Alternatively, a layer or layers having at least one electromagnetic radiation sensitive additive can be integrated on or into a multilayer structure that may contain additional layers comprising electromagnetic radiation transparent polymer matrices. For example, the electromagnetic radiation sensitive additive can be deposited as a coating on a preformed polymer matrix film. Alternatively, a polymer film having at least one electromagnetic radiation sensitive additive can be laminated with a preformed polymer film or coextruded to form a multilayer structure. In this way, large area parts can be produced readily using a wide variety of base polymer films that satisfy the requirements of electromagnetic transparency in the wavelength range of interest and mechanical/physical properties e.g. tensile strength and percent elongation. The layers can be formed from the same or different polymers, depending on properties such as interfacial adhesion, refractive index matching, and stress-strain elongation behavior of the composite. The layers can be of different thickness, for example a thin electromagnetic radiation sensitive layer can be combined with one or more thicker electromagnetic radiation transparent layers. In one example, the electromagnetic radiation sensitive additives may be included in a styrene-copolymer resin (SEBS) and deposited on a commercial styrene-copolymer film (Diamant Film, Inc.). In another example, the same formulation may be coated on a commercial polyvinylidine chloride-polyvinyl chloride (PVDC/PVC) copolymer film such as Saran Wrap®. Such multilayer structures may have advantages in cost, durability and handling compared to the single layer films. It will be understood that the electromagnetic radiation sensitive mask material can be provided in any suitable manner. For example, the electromagnetic radiation sensitive mask material can be provided as perforated or unperforated sheets. In another example, the electromagnetic radiation sensitive mask material can be provided as perforated or unperforated rolls of material. Such rolls can be used in accordance with any suitable system to provide in-line exposure of the mask and patterning of a part. In some examples, the polymer matrix is chosen to provide desired properties. For example, the matrix may be chosen to be deformable such that the electromagnetic radiation sensitive mask material is deformable. In some cases the electromagnetic radiation sensitive mask material can deform by about 30 percent to about 100 percent or by about 100 percent to about 500 percent. This deformability may be useful when using the masks for contact patterning on complex surfaces, such as curved surfaces and surfaces having features. In other examples, the electromagnetic radiation sensitive mask material can deform at a temperature of less than about 50° C., and this may be useful when the substrate to be patterned can not be exposed to elevated temperatures. In other examples, the polymer matrix can be chosen to have a desired tensile strength, hardness, and/or viscosity. In further examples, the electromagnetic radiation transparent layer can be rigid. An electromagnetic radiation sensitive additive may be any suitable additive that is sensitive to electromagnetic radiation at a desired wavelength. The electromagnetic radiation sensitive additive may be chosen to undergo a particular chemical reaction at the second wavelength such that the transmissivity of electromagnetic radiation at the first wavelength through an area containing the electromagnetic radiation sensitive additive is changed after exposure of the electromagnetic radiation sensitive additive to the second wavelength. This electromagnetic radiation sensitive additive allows the electromagnetic radiation sensitive mask material to be patterned as discussed herein and used as a mask. For example, suitable compound that undergoes a chemical reaction upon exposure to electromagnetic radiation may be used. An acid sensitive additive may be any suitable additive that is sensitive to the presence of an acidic species. In some cases, the acid sensitive additive itself may cause a change such that the transmissivity of electromagnetic radiation at the first wavelength through an area containing the acid sensitive additive is changed after the exposure of the electromagnetic radiation sensitive material to the second wavelength. For example, the electromagnetic radiation sensitive mask material may have an electromagnetic sensitive additive or an electromagnetic sensitive polymer that produces an acidic species upon exposure to electromagnetic radiation of the second wavelength. According to some examples, the mask material also has an acid sensitive additive. The presence of the acidic species causes the acid sensitive additive to undergo a chemical reaction. This chemical reaction is chosen such that the transmissivity of the mask material to electromagnetic radiation at the first wavelength is different after exposure of the material to electromagnetic radiation at the second wavelength. It will be understood that the acid sensitive additive may be sensitive to electromagnetic radiation at a wavelength different from an electromagnetic radiation sensitive additive that is also present. Thus, in some cases, the electromagnetic radiation exposure wavelength can be chosen to either produce an acidic species from the electromagnetic radiation sensitive additive to activate the acid sensitive additive or the wavelength could be chosen to directly activate the acid sensitive additive. In one example, electromagnetic radiation sensitive additives that undergo photo elimination reactions may be used. For example, leuco dyes, such as fluoran leuco dyes that undergo alkyl elimination upon exposure to electromagnetic radiation of a particular wavelength, may be used. In some examples, the leuco dyes are chosen to exhibit a permanent change after exposure to a particular electromagnetic radiation source. In another example, compounds that undergo photo-oxidation upon exposure to electromagnetic radiation may be used. For example, a different type of leuco dye based on triarylmethanes e.g. Leuco Malachite Green or 4,4′-Benzylidenebis(N,N-Dimethyl Aniline) may be used. Upon exposure to electromagnetic radiation of particular wavelength range, this compound undergoes photo-oxidation as shown in FIG. 4D. Other triaryl and diaryl methane compounds can also be used. In further examples, an electromagnetic sensitive photo acid generator may be used in conjunction with an acid sensitive additive, to achieve discrete color formation. Suitable acid sensitive additives include, but are not limited to, leuco dyes and acid indicators such as phenolphthalein. FIG. 5 shows the reaction scheme by which a colored form of a leuco dye can be achieved. Generally, the photo acid generator is selected to produce an acidic species at a desired wavelength. The production of the acidic species at the desired wavelength of electromagnetic radiation causes the leuco dye to change from the colorless to the colored state. The use of a photo acid generator can allow the portion of the electromagnetic radiation sensitive mask material exposed to electromagnetic radiation at the second wavelength to exhibit a visible color change. This visible color change may be useful in allowing a user to properly align the mask. Suitable leuco dyes include, but are not limited to, Pergascript Green I-2GN (FIG. 4A) available from Ciba-Geigy, Black XV (FIG. 4B) available from ESCO, and ODB-250 (FIG. 4C) available from ESCO. For example, Black XV can be used with a photo acid generator that produces H+ at about 320 nm to cause the Black XV to become colored. Suitable photo acid generators include, but are not limited to the Irgacure series available from Ciba Geigy for example Irgacure 203. The leuco dye and/or the photo acid generator may be used in any suitable amount. For example, from about 0.5 percent by weight to about 10 percent by weight of the leuco dye may be used. In other examples, about 0.5 percent by weight or about 2 percent by weight of the leuco dye may be used. In a further example, about 0.5 percent by weight to about 10 percent by weight of the photo acid generator may be used. In a further example, about 0.5 percent by weight to about 2 percent by weight of the photo acid generator may be used. In yet further examples, the compositions can comprise a polymer that is electromagnetic radiation sensitive such that an acidic species is produced and an acid sensitive additive. Examples of suitable polymers useful according to such examples, include, but are not limited to, chlorine containing polymers such as polyvinyl chloride (PVC), polyvinylidine chloride (PVDC), or ethylene chlorotrifluorethylene (ECTFE). Examples of suitable acid sensitive additives include, but are not limited to, acid sensitive Leuco Dye such as but not limited to the Fluoran leuco dyes Black XV (ESCO) and Pergascript Green I-2GN (Ciba-Geigy). Upon exposure of the mask material to electromagnetic radiation of a wavelength suitable to cause the polymer to produce an acid sensitive species, an open zwitterion form of the dye may occur that causes a color change. In other examples, the mask material may be exposed to electromagnetic radiation of a wavelength suitable to cause a reaction of the dye. In this case, an alkyl elimination product that produces a different color change may occur. Other examples of suitable electromagnetic radiation sensitive additives include compounds that undergo a photo rearrangement reaction. For example, compounds that undergo a photo-fries rearrangement may be used. One such photo-fries rearrangement of bisphenol-A diacetate is shown in FIG. 6. The photo-fries rearrangement occurs predominantly at a specific wavelength region, and this wavelength is generally chosen to be the second wavelength of electromagnetic radiation to which the electromagnetic radiation sensitive mask material is exposed. Once the compound is exposed to the second wavelength, the molecular structure is rearranged, and the rearranged molecular structure may transmit a different amount of electromagnetic radiation at the first wavelength. Thus, these electromagnetic radiation sensitive additives may be used to provide patternable masks. Examples of compounds that undergo photo-fries rearrangement, include, but are not limited to phenolic derivates such as aromatic esters like bisphenol-A diacetate and catechol diacetate. For example, bisphenol-A diacetate in the electromagnetic radiation sensitive mask material can be exposed to electromagnetic radiation at about 254 nm to cause the rearrangement. Subsequently, electromagnetic radiation at a first wavelength of about 340 nm can be used for patterning of a substrate. Similarly, catechol diacetate in the electromagnetic radiation sensitive mask material can be exposed to electromagnetic radiation at about 254 nm to cause the rearrangement, and the first wavelength can be about 320 nm. The compounds that undergo photo-fries rearrangement may be used in any suitable amount. For example, from about 0.5 percent by weight to about 10 percent by weight of the compounds may be used. For example, about 0.5 percent by weight to about 2 percent by weight of the compound may be used. Further examples of suitable electromagnetic radiation sensitive additives include compounds that generate photo-fries products. These electromagnetic radiation sensitive additives include, but are not limited to, aromatic isocyanate urethane, urea, and carbamate derivatives. The mechanism by which photo-fries products may be generated is shown in FIG. 7. For example, polyurethane or polyurea dimers, trimers, or oligomers such as diethylamine-diphenlymethane diisocyanate di-urea may be used. Alternatively, carbamates such as ethyl phenylcarbamate may be used as shown in FIG. 8. These urethane, urea, or carbamate groups may be present in the side-chains of backbones of polymers. These photo-fries generated compounds generally will transmit electromagnetic radiation at the first wavelength at a different percentage than the unreacted electromagnetic radiation sensitive additives. The compounds that undergo photo-fries generation of products may be used in any suitable amount. For example, from about 0.5 percent by weight to about 10 percent by weight of the compounds may be used. In a further example, about 0.5 percent by weight to about 2 percent by weight may be used. It will be understood that any other suitable electromagnetic radiation sensitive additives, acid sensitive additives, electromagnetic radiation sensitive additive systems, acid sensitive additive systems, or combinations thereof may be employed. Generally, the electromagnetic radiation sensitive additives, acid sensitive additives, or both are selected such that the first wavelength is a wavelength compatible with a particular treated or untreated substrate in the patterning system being employed. It will be further understood that in examples when a electromagnetic radiation sensitive additive, acid sensitive additive, or both is dispersed or infused in a polymer matrix, the mobility of the additive within the matrix may be of concern. Having an additive that is too mobile for a particular system may degrade the useful life of the mask after the electromagnetic radiation sensitive mask material is exposed to the electromagnetic radiation of the second wavelength. The mobility of an additive depends on several factors including the mean free path, the size of the molecule, and the temperature to which the electromagnetic radiation sensitive mask material is exposed. Thus, the additive will be chosen for a particular application. Additionally, the concentration and processing temperatures can be controlled to control the mobility of the molecule. Additionally, it will be understood that the electromagnetic radiation at the second wavelength can have any suitable intensity and can be provided for any suitable length of time. For example, the areas of electromagnetic radiation sensitive mask material for patterning can be exposed to the electromagnetic radiation of the second wavelength for from a few seconds to a few minutes or less at high intensity to about 300 minutes or more at very low intensity. The amount of time for the exposure and the intensity can be selected depending on the particular electromagnetic radiation sensitive additive used for the electromagnetic radiation sensitive mask material. In accordance with embodiments of the present invention, patterning methods employing the masks described herein are provided. The methods comprise exposing at least one selected portion of a mask comprising a electromagnetic radiation sensitive mask material having at least one electromagnetic radiation sensitive additive to electromagnetic radiation at a patterning wavelength to cause a reaction of the at least one electromagnetic radiation sensitive additive such that a pattern is formed in the mask and subsequently exposing a substrate electromagnetic radiation at an exposure wavelength through the mask. The substrate is sensitive to electromagnetic radiation at an exposure wavelength. For purposes of defining and describing the present invention, the term “pattern” shall be understood as referring to areas of the mask that have been exposed to electromagnetic radiation of the patterning wavelength and through which electromagnetic radiation at an exposure wavelength is transmitted to a greater or lesser extent than through areas of the mask that have not been exposed to electromagnetic radiation of the patterning wavelength. Additionally, it will be understood that a pattern “in” the electromagnetic radiation sensitive mask material may be a pattern formed on top of or inside the material, or a combination thereof. It will be understood that the patterning wavelength is the second wavelength as discussed herein. It will be further understood the exposure wavelength is the first wavelength as discussed herein. The patterning and exposure wavelength may be the same or different. The substrate may be made sensitive to electromagnetic radiation at an exposure wavelength in any suitable manner. For example, a photoresist may be provided on the substrate and developed after the pattern has been formed thereon. Alternatively, the substrate may be made sensitive to the radiation such that a surface charge is provided on an exposed area of the substrate. The substrate may be subsequently processed in any suitable manner, for example by using a toner and curing. In other examples, the substrate may comprise a mask of the present invention. In other cases, substrates amenable to photo-imaging may be provided. The electromagnetic radiation sensitive mask material may be exposed to the electromagnetic radiation at the patterning wavelength in any suitable manner. For example, a traditional mask having a particular pattern may be placed in contact with the mask and the mask can be exposed to the electromagnetic radiation of the patterning wavelength for the desired period of time. This exposure causes the selected reaction of the electromagnetic radiation sensitive additive or additives such that the exposed areas of the mask transmit a different percentage of electromagnetic radiation at the exposure wavelength than the unexposed areas. In this manner, a mask that does not require extensive wet chemistry can be formed. In other examples, direct write systems may be used to expose the mask to electromagnetic radiation of a patterning wavelength. The present invention can be used to form features of any suitable dimension. For example, features of from about 1 μm to about 300 μm or more can be resolved using the masks of the present invention. In other examples, features of less than 10 μm can be resolved. In cases where a photoresist is used on the substrate, the photoresist may be any suitable photoresist. It will be understood that particular photoresists may be chosen depending on the substrate being patterned and the desired exposure wavelength. The photoresist can be developed in accordance with any suitable methods. Additionally, the substrate may be any suitable substrate that can be used in the patterning processes. It will be further understood that dark field masks and light field masks may be produced in accordance with the present invention. The patterning and exposure wavelengths may be any suitable wavelength. In some examples, the exposure wavelength comprises about 365 nm. The masks of the present invention can be used for contact patterning. Thus, the masks can be placed in contact with the substrate prior to exposing the substrate through the mask. When flexible, deformable electromagnetic radiation sensitive mask materials are used, as discussed above, the mask can be deformed to contact a substrate having a non-planar shape. For example, the mask may be deformed to contact a domed, conical, rectangular, or circular shape. In some examples, the mask may be heated to assist in deforming the mask to the non-planar substrate. It will be understood that the masks of the present invention can be used in conjunction with any suitable patterning system. For example, a system may apply a differential pressure such that the mask substantially deforms in a manner corresponding to at least a portion of the surface of a non-planar part to be patterned. In some examples, the masks may be reused to expose a plurality of substrates after the step of exposing at least one selected portion of the electromagnetic radiation sensitive mask material to electromagnetic radiation at the patterning wavelength. Thus, the masks may be reusable, and flexible, reusable masks may be provided in embodiments of the present invention. In accordance with further embodiments, systems are provided. These systems provide integrated patterning of the mask and exposure of at least one substrate through the patterned mask. The system comprises a source for a first and a second electromagnetic radiation; a mask sensitive to the second electromagnetic radiation; a substrate sensitive to the first electromagnetic radiation; and a device in conjunction with the source for the first and second electromagnetic radiation. The device is capable of exposing the mask to the second electromagnetic radiation such that regions that are selectively opaque to the first electromagnetic radiation are formed in the mask. The device is capable of subsequently exposing the substrate to the first electromagnetic radiation through the selectively opaque mask such that portions of the substrate are selectively exposed to the first electromagnetic radiation. In some examples, at least one additional substrate is exposed to the first electromagnetic radiation through the selectively opaque mask subsequent to the exposure of the substrate sensitive to the first electromagnetic radiation. The device may have more than one source for the first and second electromagnetic radiation. In addition, the device may have a master mask for exposure of the mask to the second electromagnetic radiation. In other examples, the device may have a direct write system that employs the second electromagnetic radiation to pattern the mask. It will be understood that any suitable device capable of patterning the mask using the second electromagnetic radiation may be used. Transparent urethane rubber films were prepared using the following procedure. Clear Flex 50 and Clear Flex 90 (Smooth-On Inc.), are two-component water white clear aliphatic urethane liquid rubber compounds that have high clarity and resistance to sunlight. The procedure provides about 1% loading. Into a suitable container were placed: 0.3 parts electromagnetic radiation sensitive additive, 2 parts suitable solvent (e.g. chloroform or toluene). The mixture was stirred till dissolved. Next 10 parts Clearflex 50 Part A were added and the mixture was again stirred till dissolved. To this container, 20 parts Clearflex 50 Part B were added and stirred for ˜two minutes. The mixture was then degassed briefly to remove any entrained bubbles in a vacuum oven. Film Preparation: Electromagnetic radiation transparent films were prepared by casting into molds, or depending on the thickness desired, prepared using conventional drawdown bars (Gardner) onto flat substrates. The films were then placed into an oven at ˜60 C until curing was complete. Thermoplastic elastomers, such as those based on hydrocarbon rubbers such as styrene-butadiene-ethylene-styrene (SEBS) block copolymers (e.g. Kraton G 1652, Kraton Polymers), maleic anhydride modified SEBS (Kraton 1901x), and other hydrocarbon rubbers such as polyisoprene, were found to form good films for this application. They can be prepared by thermoplastic compounding methods or solution film casting methods. In a typical solution casting experiment (@1% loading) the following general procedure was followed. Into a suitable container were placed 0.125 parts UV electromagnetic radiation sensitive additive (e.g. Bisphenol Diacetate (Aldrich) BPDA), 5 parts suitable solvent (e.g. toluene) and the mixture stirred till dissolved. Next 50 parts of a 25 wt % SEBS dissolved in toluene (=12.5 parts SEBS) was added to the container and stirred till mixed thoroughly. The mixture was then degassed either by allowing the entrained air bubbles to escape gradually, or if to be used immediately-degassed using a vacuum oven. Film Preparation: Films were prepared by the cast film or drawdown film methods described in Example 1 or by a spin coating procedure. In a typical draw-down film formation procedure, a large glass plate (˜10″×12″) was treated with a small amount of mold release (e.g. Ren RP79-2). Next a 8″ wide Universal Blade Applicator (Paul Gardner Co.) with adjustable thickness control was positioned on the glass substrate, and set to the required thickness to provide final films of target thickness, based on the percent solids of the formulation. Next a sufficient aliquot of the polymer resin solution was poured onto the glass plate and the applicator drawn-down to level the film. Next the film on glass was placed in a ˜60 C oven to cure, and evaporate the solvent. Finally the film was removed from the glass plate and subjected to optical characterization, mask generation, photostability testing, and other physical property testing. Free-standing thin films were prepared using a Specialty Coating Systems SGS/G3-8 Spin Coater (Cookson Electronics). Spin coating parameters were dependent on the viscosity and the desired sample thickness. Representative parameters were: Acceleration time: 10-20 seconds; Spin time: 300-600 seconds; Spin Speed: 400-1000 rpm; Deceleration Time 10-20 seconds. In a typical spin coating cast film preparation an aliquot of the UV sensitive additive polymer solution was deposited on a 4″-6″ diameter Silicon wafer under the conditions described above. Then the film-coated substrate was briefly placed into a oven (˜60-90 C) to remove any residual solvent, then removed an allowed to cool, The free-standing flexible transparent polymer film was then readily peeled off the Silicon wafer substrate and subjected to optical characterization, mask generation and photostability testing. Examples 1 and 2 described methods used to prepare single-layer free standing films containing UV electromagnetic radiation sensitive additives. An extension of this approach is to prepare multilayer films, laminates, or coated flexible substrates. For example, a thin electromagnetic sensitive layer can be deposited on or coextruded on or in between transparent carrier films. The carrier film can be the same or different composition as the UV electromagnetic radiation sensitive layer film. By way of demonstration two-layer films were prepared using the electromagnetic radiation transparent thermoplastic elastomer resin (Example 2) on two commercial films: one styrene-copolymer based (Diamant Film Inc.) and one based on polyvinylidine chloride-polyvinylchloride (PVDC/PVC) copolymer (Saran, Dow Corp.). For the examples shown in FIGS. 26A-34: into a suitable container were placed 0.10 parts Leuco Malachite Green (LMG, Aldrich), 1 part toluene, and the mixture stirred till dissolved. Then, 10 parts of 25 wt % SEBS (Kraton G 1652) in toluene (=2.5 parts polymer) were added to the container and stirred till dissolved. Finally, the resin mixture was coated onto corresponding styrene copolymer (SEBS) or PVDC/PVC copolymer film (˜0.5-0.7 mil thick) substrates, using in this case, a spin coating method. The final bilayer films (˜2-3 mil thick) were removed and subjected to optical characterization, and mask generation procedures. Mask generation was accomplished by the following general procedure: First the freestanding films produced by the methods outlined in Examples 1-3 were taken and sections were mounted onto ˜2″×4″ thin film substrate holders with ˜1″×1″ apertures for UV-vis spectral characterization. The initial baseline spectra of the films were determined using a Cary 5000 UV-vis Spectrophotometer. Mask generation was initially performed by irradiating the substrate mounted film samples with a low power UV-lamp (Cole Palmer A-97609-20) at either 254 nm, 302 nm, or 365 nm depending on the electromagnetic radiation sensitive additive involved at a distance of ˜3″ (or ˜1.7 mW/cm2), for selected exposure times. After each exposure time, the sample spectrum was reacquired and then the exposure continued until the sequence was completed. This procedure permitted the determination of the early stage mask generation, as well as the photostability of the final mask at the wavelength used for eventual photolithography (e.g. the Hg i-line 365 nm), since photoresist exposure energy requirements are typically only ˜100 mJ/cm2 (<1 minute @˜2 mW/cm2). Higher contrast ratio mask samples were prepared by irradiating these initial samples with a higher power UV-lamp (EFOS Ultracure 100ss Plus) equipped with a ˜100 watt Hg/Xe arc lamp, an optical filter (˜320-500 nm), and a flexible light guide which delivered a total source energy of about 100 mW/cm2 as measured using the photometer sensor (˜300-500 nm range) at about 2″ distance from the substrate. Typically, the samples were irradiated for about 10 seconds to about 1 minute intervals using a pulsed sequence, and the mask spectrum was reacquired. Contrast ratios were determined as the ratio of the initial percent transmittance divided by the final percent transmittance (To/T). A representative compound of this type is a phenolic ester e.g. Bisphenol Diacetate (BPDA). The films depicted in FIGS. 9-15 were prepared at 0.5 wt % BPDA (Aldrich) in a maleic anhydride (MA) modified SEBS resin (Kraton 1901x) using the procedures described in Example 2. Mask generation was conducted @254 nm using the procedures described in Example 4. FIGS. 9-15 illustrate various absorbance measures relating to the masks. In addition to aromatic esters and related compounds, good results have been obtained with aromatic isocyanate based urethanes, ureas, and carbamates. To illustrate this class, a model compound adduct was prepared by endcapping 4,4′-Diphenylmethane diisocyanate (MDI, 125.13 g/eq.) with Diethylamine ((DEA, Aldrich, 73.14 g/eq.): Into a suitable container was placed 14 parts MDI and 150 parts toluene and stirred to mix. Next, 7 parts DEA was added drop wise while stirring, forming a white precipitate. Then, 600 parts chloroform was added to form a clear solution at ˜2.7% product. This stock solution was used to prepare films in SEBS copolymers as described in Example 2. Mask generation was conducted using the procedure described in Example 4. FIGS. 16-17 show various absorbance measurements of the masks. Leuco dyestuffs, such as fluoran leuco dyes, as represented by Black XV (ESCO) and Pergascript Green I-2GN (Ciba-Geigy) are used in carbonless paper and other applications. Compounds of this type can undergo photo-elimination reactions (e.g. N-ethyl groups) to produce colored products. In a representative example (see FIGS. 20 and 21), mask films containing a relatively high loading (10 wt %) Pergascript Green I-2GN were prepared in Kraton G 1652 (SEBS) using the procedures outline in Example 2. The films remained optically transparent and mask generation was conducted at >300 nm as described in Example 4 using both the low and high power UV lamp sources. FIGS. 20A-22 illustrate percent transmission and contrast ration of masks prepared by this method. An alternative electromagnetic radiation sensitive reaction for mask generation uses a combination of a photoacid generator (PAG) specific for the mid-deep-UV (˜254 nm-˜320 nm) and an acid sensitive Leuco Dye such as but not limited to the Fluoran leuco dyes of Example 6. In this case, the final photoproduct is primarily that of the corresponding open zwitterion form of the leuco dye (e.g. black for Black XV) rather than the Alkyl elimination product (yellow) rate. The rate and degree of color formation at a given mask generation wavelength depends on the particular PAG, and the relative loading of the components. In a representative example, mask films were prepared in SEBS using Black XV (1.0 wt %) and Irgacure PAG 203 (1.0 wt %) (aka CGI-263, Ciba-Geigy) a mid-deep-UV selective (˜254 nm-˜320 nm) photoacid generator using procedures as described in Example 2. The films remained optically transparent and mask generation was conducted at about 320 nm as described in Example 4. Additional samples with higher contrast ratio were prepared using loadings up to 2 wt % Black XV and up to 4 wt % Irgacure PAG 203. Samples of this film were subjected to photostability testing at 365 nm and produced no color formation at this wavelength. Samples prepared with corresponding near-UV (˜365 nm) photoacid generators, such as Irgacure PAG 121 substituted in the formulation produced marked color change (as expected) when tested at 365 nm. FIGS. 18-19 illustrate absorbance of masks produced by this method. Useful masks can also be produced using a different class of leuco dyes based on triaryl methane such as Leuco Malachite Green (LMG), and Leuco Crystal Violet. In this case the photoreaction involves a hydrogen elimination (oxidation) (see FIG. 4D). By way of illustration mask film samples were prepared at up to 10 wt % loading LMG in SEBS (Kraton G 1652) as described in Example 2. The films were subjected to mask generation at ˜300-500 nm using the procedures described in Example 4. FIGS. 23A-25 illustrate the percent transmission and contrast ratios of mask prepared in this way. Further examples of this type were prepared at 4 wt % loading in the same base polymer and deposited on both styrene-copolymer (Diamant) and PVDC/PVC copolymer (Saran Wrap®) using procedures as described in Example 3 (see FIGS. 26-33), producing multilayer films with high optical transmittance and good contrast ratio at both 340 nm and 365 nm wavelength regions. Comparative examples prepared using a related compound Crystal Violet Lactone, produced no color change under the same conditions. FIGS. 26A and 26B illustrate the absorbance of Diamant and Saran Wrap®. FIGS. 27-34 illustrate percent transmission and contrast ratios of masks prepared in accordance with this procedure. Yet further examples of this type, an alternative mid-UV sensitive photo-acid generator may be used. An alternative electromagnetic radiation sensitive composition with higher EMR mask generation sensitivity comprises substitution of Irgacure PAG 203 (see FIG. 36A.) with a mid-UV sensitive photo-acid generator such as Ciba CGI 725 (see FIG. 36B). This composition exhibits high thermal stability (Td ˜210 C), high sensitivity (˜270 nm-˜370 nm, insensitive >˜370 nm) and good compatibility in mask polymer films. In this example, compositions containing ˜1.0 wt % CGI 725 with ˜1.0 wt % Black XV were prepared using procedures as described in Example 8. Films prepared in this way were tested for EMR mask generation by irradiation in the ˜320 nm-500 nm range as described previously. Contrast ratios of greater than 100:1 (T0/T) were achieved at total exposure energies of <12 J/cm2 as compared to a contrast ratio of ˜7.5:1 for the films of Example 8 at the same thickness and exposure energy. Contrast ratios of ˜10:1 required only ˜1 J/cm2. Results for this example are presented in FIGS. 37-40. Exposing chlorine containing polymers such as polyvinyl chloride (PVC), polyvinylidine chloride (PVDC), or ethylene chlorotrifluorethylene (ECTFE) to heat (above 100 C), ultraviolet light, or gamma radiation, can cause elimination of hydrochloric acid (HCl) from the polymer backbone through a dehydrochlorination reaction. As such, an alternative electromagnetic radiation sensitive reaction for mask generation uses a combination of an acid generating electromagnetic radiation sensitive polymer and an acid sensitive Leuco Dye such as but not limited to the Fluoran leuco dyes of Example 7. In this case, depending on the wavelength of the electromagnetic radiation 254 nm or 302 nm, the final photoproduct is primarily that of the corresponding open zwitterion form of the leuco dye (e.g. green for Pergascript I-2GN) rather than the Alkyl elimination product (red), respectively. The rate and degree of color formation at a given mask generation wavelength depends on the particular polymer, and the relative loading of the components. In a representative example, mask films were prepared in polyvinyl chloride (PVC) using Pergascript I-2GN (5 wt %). using procedures as described in Example 2. The films remained optically transparent and mask generation was conducted at 254 nm and 302 nm as described in Example 4 (see FIG. 35). The present invention should not be considered limited to the specific examples described above, but rather should be understood to cover all aspects of the invention. Various modifications, equivalent processes, as well as numerous structures and devices to which the present invention may be applicable will be readily apparent to those of skill in the art. It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention, which is not to be considered limited to what is described in the specification. |
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claims | 1. A preventive maintenance/repair device for use in maintaining and repairing a cylindrical structure of a cylindrical shape among reactor internal structures installed in a reactor pressure vessel, the preventive maintenance/repair device comprising:a device body;a holding mechanism connected to the device body, the holding mechanism being configured to hold the device body on an outer circumferential surface of the cylindrical structure;a traveling and driving part disposed on the device body, the traveling and driving part being configured to be circumferentially movable along the outer circumferential surface of the cylindrical structure; anda maintenance/repair mechanism disposed on the holding mechanism, the maintenance/repair mechanism being configured to maintain and repair the cylindrical structure,wherein the cylindrical structure is a jet pump,the device body is provided with an access device configured to bring the device body to the cylindrical structure and to detachably hold the device body,the access device includes:an access-device holding part engageable with the device body and holding the device body;an operation pole extending to an operation floor; anda rotating and driving part interposed between the access-device holding part and the operation pole, the rotating and driving part being configured to rotate the access-device holding part with respect to the operation pole around an axis disposed substantially perpendicular to a longitudinal axis of the cylindrical structure, andthe access device is configured to hold the device body in substantially a same direction as a longitudinal axis of the operation pole or a direction substantially perpendicular to the longitudinal axis of the operation pole. 2. The preventive maintenance/repair device according to claim 1, whereinthe holding mechanism includes: a pair of arms each having a shape along the outer circumferential surface of the cylindrical structure; guide rollers respectively disposed on distal ends of the pair of arms; arm cylinders configured to respectively drive the pair of arms; and links connected between the arms and the arm cylinders, the links being configured to transmit drives of the arm cylinders to the arms. 3. The preventive maintenance/repair device according to claim 2, whereineach of the arms of the holding mechanism is separable into a proximal arm body and a distal arm end, andin order to hold the device body on an outer circumferential surface of another cylindrical structure of a different outer diameter, the arm end is configured to be replaced with another arm end of a different length with respect to the arm body. 4. The preventive maintenance/repair device according to claim 2, whereineach of the arms of the holding mechanism is separable into a proximal arm body and a distal arm end, andin order to hold the device body on an outer circumferential surface of another cylindrical structure of a different outer diameter, the arm body is configured to be replaced with another arm body of a different length with respect to the device body. 5. The preventive maintenance/repair device according to claim 1, whereina distance sensor is disposed on an outer surface of the device body on a side opposed to a surrounding structure. 6. The preventive maintenance/repair device according to claim 1, whereinthe maintenance/repair mechanism includes an equipment configured to maintain and repair the cylindrical structure, and an equipment cylinder configured to drive the equipment in a direction parallel to the longitudinal axis of the cylindrical structure. 7. The preventive maintenance/repair device according to claim 1, wherein the rotating and driving part comprises a frame rotatably connected to the access-device holding part and a rotational cylinder, the rotational cylinder having a shaft configured to expand and contract such that the access-device holding part rotates with respect to the operation pole around the axis disposed substantially perpendicular to the longitudinal axis of the cylindrical structure. 8. A preventive maintenance/repair method using a preventive maintenance/repair device for use in maintaining and repairing a cylindrical structure of a cylindrical shape among reactor internal structures installed in a reactor pressure vessel, the preventive maintenance/repair device comprising:a device body;a holding mechanism connected to the device body, the holding mechanism being configured to hold the device body on an outer circumferential surface of the cylindrical structure;a traveling and driving part disposed on the device body, the traveling and driving part being configured to be circumferentially movable along the outer circumferential surface of the cylindrical structure; anda maintenance/repair mechanism disposed on the holding mechanism, the maintenance/repair mechanism being configured to maintain and repair the cylindrical structure;wherein the device body is provided with an access device configured to bring the device body closer to the cylindrical structure so as to attach the device body to the outer circumferential surface of the cylindrical structure and to detach therefrom the device body,an operation pole is connected to the access device, andthe access device includes a rotating and driving part,the preventive maintenance/repair method comprising the steps of:mounting the access device and the operation pole on the device body;sending the device body into the reactor pressure vessel in a hanging manner through the operation pole and bringing the device body closer to the cylindrical structure using the rotating and driving part, the rotating and driving part being configured to rotate the access device with respect to the operation pole around an axis disposed substantially perpendicular to a longitudinal axis of the cylindrical structure;holding the device body on the outer circumferential surface of the cylindrical structure by the holding mechanism;removing the access device from the device body, after the device body has been held on the cylindrical structure by the holding mechanism; andperforming a maintenance/repair operation to the cylindrical structure by the maintenance/repair mechanism. 9. The preventive maintenance/repair method according to claim 8, wherein the rotating and driving part comprises a frame rotatably connected to an access-device holding part of the access device and a rotational cylinder, and bringing the device body closer to the cylindrical structure using the rotating and driving part comprises expanding and contracting a shaft of the rotational cylinder such that the access device rotates with respect to the operation pole around the axis disposed substantially perpendicular to the longitudinal axis of the cylindrical structure. 10. An access device for a preventive maintenance/repair device for use in maintaining and repairing a jet pump of a cylindrical shape among reactor internal structures installed in a reactor pressure vessel, the access device being configured to bring the preventive maintenance/repair device to the jet pump and to detachably hold the preventive maintenance/repair device,the access device comprising:an access-device holding part engageable with the preventive maintenance/repair device and holding said preventive maintenance/repair device;an operation pole extending to an operation floor; anda rotating and driving part interposed between the access-device holding part and the operation pole, the rotating and driving part being configured to rotate the access-device holding part with respect to the operation pole around an axis disposed substantially perpendicular to a longitudinal axis of the cylindrical structure, andwherein the access device is configured to hold the preventive maintenance/repair device in substantially a same direction as a longitudinal axis of the operation pole or a direction substantially perpendicular to the longitudinal axis of the operation pole. 11. The access device according to claim 10, wherein the rotating and driving part comprises a frame rotatably connected to the access-device holding part and a rotational cylinder, the rotational cylinder having a shaft configured to expand and contract such that the access-device holding part rotates with respect to the operation pole around the axis disposed substantially perpendicular to the longitudinal axis of the cylindrical structure. |
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abstract | A lithographic projection apparatus, in which movement of a substrate table in a plane is accomplished by a planar magnetic positioning device, has a mechanical limiter that limits rotation of the substrate table about a direction orthogonal to the plane. |
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description | This application is based upon and claims the benefit of priorities from prior Japanese Patent Application No. 2010-097161 filed on Apr. 20, 2010 in Japan, and from prior Japanese Patent Application No. 2010-097162 filed on Apr. 20, 2010 in Japan, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method and, for example, relates to a technique to determine the dose of an electron beam to improve uniformity in line width in electron beam writing. 2. Related Art A lithography technique, which leads development of micropatterning of a semiconductor device, is a very important process for exclusively generating a pattern in semiconductor manufacturing processes. In recent years, with an increase in integration density of an LSI, a circuit line width required for semiconductor devices is getting smaller year by year. In order to form a desired circuit pattern on such semiconductor devices, a high-precision original pattern (also called a reticle or a mask) is necessary. In this case, an electron beam writing technique has an essentially excellent resolution, and is used in production of high-precision original patterns. FIG. 20 is a conceptual diagram for describing an operation of a variable-shaped electron beam writing apparatus. The variable-shaped electron beam (EB) writing apparatus operates as described below. An oblong, for example, rectangular opening 411 to shape an electron beam 330 is formed in a first aperture plate 410. A variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired oblong shape is formed in a second aperture plate 420. The electron beam 330 irradiated from a charged particle source 430 and having passed through the opening 411 of the first aperture plate 410 is deflected by a deflector, passes through a part of the variable-shaped opening 421 of the second aperture plate 420, and is shone on a target object 340 placed on a stage continuously moving in one predetermined direction (for example, an X direction). That is, an oblong shape which can pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is written in a write region of the target object 340 placed on the stage continuously moving in the X direction. A scheme which causes an electron beam to pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 to form an arbitrary shape is called a variable-shaping scheme (VSB scheme). In the electron beam writing described above, more precise uniformity in line width in a target object plane, for example, a mask plane is demanded. In such electron beam writing, if a mask coated with a resist is irradiated with an electron beam to write a circuit pattern, a phenomenon called a proximity effect caused by back scattering of the electron beam that passes through the resist layer to reach a layer below the resist layer and then reenters the resist layer occurs. Dimensional fluctuations in which lines are written in dimensions deviating from desired dimensions when lines are written are thereby caused. On the other hand, dimensional fluctuations called a loading effect resulting from the density of circuit patterns are caused also when the development or etching is performed after writing. The dose of an electron beam is calculated as a product of, for example, a base dose Dbase and a proximity effect-corrected dose Dp(η,U) depending on a proximity effect correction coefficient η to correct the proximity effect and a pattern area density ρ or a proximity effect density U. The proximity effect correction coefficient η that fits the proximity effect correction well is present for each base dose Dbase. Dimensions of a resist image increase with an increasing base dose Dbase. Thus, a first technique that also corrects dimensional fluctuations caused by the loading effect while maintaining the proximity effect correction by changing the set of the base dose Dbase and the proximity effect correction coefficient η for each position of a substrate is known (see Japanese Patent Application Laid-Open No. 2007-150243, for example). In recent years, the user is required to create set data of a base dose Dbase map and a proximity effect correction coefficient η map for each cause of dimensional fluctuations such as the loading effect and to write using such a plurality of set data on the writing device side. However, the base dose Dbase and the proximity effect correction coefficient η cannot simply be combined and thus, it is difficult to use a plurality of set data for writing on the writing apparatus side. In doses obtained by the first technique, the same dimensional variation is obtained regardless of the proximity effect density U. That is, a dimensional correction is made such that the proximity effect correction is not shifted. Such a dimensional correction is appropriate for correction of the loading effect caused during etching of a light-shielding film after writing. On the other hand, a second technique that makes correction by changing the base dose Dbase in accordance with the dimension to be corrected and the dose latitude without changing the proximity effect correction coefficient η is also known. According to the second technique, a different amount of dimensional correction is obtained for each proximity effect density. The technique is appropriate for correction when the embedded dose adjusted by the proximity effect correction deviates from a threshold at the time of developing a resist. Therefore, the second technique is appropriate for correction of the loading effect resulting from non-uniformity of the development threshold caused by irregularities in density of a developing solution. An error in pattern dimensions caused by the loading effect when a mask is actually produced has the loading effect during development and the loading effect during etching as described above merged therein. That is, both effects may be mixed in the same position. Thus, the correction by one of the above techniques may not be enough. Therefore, a third technique by which the former is corrected by the first technique and the latter by the second technique is discussed. However, it is necessary for the user to separate dimensional errors that actually occur into components for the first technique and components for the second technique to make corrections by the third technique and it is very difficult to do this. Moreover, the above third technique cannot be applied if it becomes necessary to change the proximity effect correction coefficient η used for correction between the loading effect during development and the loading effect during etching. As described above, the user is required to create set data of a base dose Dbase map and a proximity effect correction coefficient η map for each cause of dimensional fluctuations such as the loading effect and to write using such a plurality of set data on the writing device side. However, there is a problem that even if the plurality of set data is input from the writing device side, it is difficult to write by combining the plurality of set data. Moreover, both of the above techniques have a problem that it is difficult to make adequate corrections of both of dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching while correcting the proximity effect. A charged particle beam writing apparatus according to an embodiment, includes a storage unit configured to input and store a plurality of set data including a set of a proximity effect correction coefficient map and a base dose map of a beam; a first dose calculating unit configured to read each the set data and to calculate a first dose map for each set; a dimension map creation unit configured to create a dimension map of a pattern by using the first dose map calculated for each set; an adder configured to add dimensions of all sets for each position of the dimension map by using the dimension map of each set; a set map creation unit configured to create a set of a proximity effect correction coefficient map and a base dose map by using an added dimension map after addition; a second dose calculating unit configured to calculate a second dose map by using a created set of the proximity effect correction coefficient map and the base dose map; and a writing unit configured to write the pattern to a target object by using a charged particle beam of a dose defined in the second dose map. A charged particle beam writing apparatus according to an embodiment, includes a storage unit configured to input and store a plurality of set data including a set of a proximity effect correction coefficient map and a base dose map of a beam; a first dose calculating unit configured to read each the set data and to calculates a first dose map for each set; a dimension map creation unit configured to create a dimension map of a pattern for each of a plurality of proximity effect densities by using the first dose map calculated for each set; an adder configured to add dimensions of all sets for each position of the dimension map for each proximity effect density by using a plurality of dimension maps for mutually different proximity effect densities of each set; a selection unit configured to select a set of a proximity effect correction coefficient and a base dose with which dimensional errors of the pattern are corrected for a part of the proximity effect densities and correction residues of dimensional errors of the pattern are generated for a remaining proximity effect densities by using a plurality of added dimension maps for the mutually different proximity effect densities after addition; a correction term calculating unit configured to calculate a correction term to correct the correction residues depending on the proximity effect density for each position of the map; a second dose calculating unit configured to calculate a second dose map by using a selected set of the proximity effect correction coefficient and the base dose and the correction term in each position of the map; and a writing unit configured to write the pattern to a target object by using a charged particle beam of a dose defined in the second dose map. A charged particle beam writing apparatus according to an embodiment, includes a storage unit configured to input and store a correlation information among a pattern area ratio, a proximity effect correction coefficient, and a base dose for each of a plurality of phenomena causing dimensional fluctuations in a mask plane when mask fabricating; a first set map creation unit configured to read each of the correlation information and to create a first set of a proximity effect correction coefficient map and a base dose map to correct the phenomenon for each phenomenon; a first dose calculating unit configured to calculate a first dose map by using a corresponding proximity effect correction coefficient map and a base dose map for each set of the first sets; a dimension map creation unit configured to create a dimension map of a pattern by using the first dose map calculated for each set of the first sets; an adder configured to add dimensions of all sets for each position of the dimension map by using the dimension map of each set of the first sets; a set map creation unit configured to create a second set of a proximity effect correction coefficient map and a base dose map by using an added dimension map after addition; a second dose calculating unit configured to calculate a second dose map by using the second set of the proximity effect correction coefficient map and the base dose map; and a writing unit configured to write the pattern to a target object by using a charged particle beam of a dose defined in the second dose map. A charged particle beam writing apparatus according to an embodiment, includes a storage device configured to input and store a plurality of pattern dimension map data for mutually different proximity effect densities indicating a distribution of a pattern dimension formed on a substrate when a pattern is written to the substrate by making the proximity effect density variable; a selection unit configured to select a set of a proximity effect correction coefficient and a base dose with which dimensional errors of the pattern dimension are corrected for a part of the proximity effect densities and correction residues of dimensional errors of the pattern dimension are generated for a remaining proximity effect densities when a writing position corresponding to a map position is written to with a dose obtained by a dose function correcting dimensional errors calculated by using the proximity effect correction coefficient and the base dose for each map position; a correction term calculating unit configured to calculate a correction term to correct the correction residues depending on the proximity effect density for each map position; a dose calculating unit configured to calculate a dose by using a selected set of the proximity effect correction coefficient and the base dose and the correction term for each map position; and a writing unit configured to write a desired pattern to the substrate by using a charged particle beam of the dose calculated for each map position. A charged particle beam writing method according to an embodiment, includes reading each of set data from a storage device storing a plurality of set data including a set of a proximity effect correction coefficient map and a base dose map and calculating a first dose map for each set; creating a dimension map of a pattern by using a calculated first dose map for each set; adding dimensions of all sets for each position of the dimension map by using the dimension map of each set; creating a set of a proximity effect correction coefficient map and a base dose map by using an added dimension map after addition; calculating a second dose map by using a created set of the proximity effect correction coefficient map and the base dose map; and writing the pattern to a target object by using a charged particle beam of a dose defined in the second dose map. A charged particle beam writing method according to an embodiment, includes reading each piece of set data from a storage device storing a plurality of set data including a set of a proximity effect correction coefficient map and a base dose map and calculating a first dose map for each set; creating a plurality of dimension maps of a pattern for a plurality of proximity effect densities by using a calculated first dose map for each set; adding dimensions of all sets in each position of the dimension map for each proximity effect density by using a plurality of dimension maps for mutually different proximity effect densities of each set; selecting a set of a proximity effect correction coefficient and a base dose with which dimensional errors of the pattern are corrected for a part of the proximity effect densities and correction residues of dimensional errors of the pattern are generated for a remaining proximity effect densities by using a plurality of added dimension maps for the mutually different proximity effect densities after addition; calculating a correction term to correct the correction residues depending on the proximity effect density for each position of the map; calculating a second dose map by using a selected set of the proximity effect correction coefficient and the base dose and the correction term in each position of the map; and writing the pattern to a target object by using a charged particle beam of a dose defined in the second dose map. A charged particle beam writing method according to an embodiment, includes reading a plurality of pattern dimension map data from a storage device storing the plurality of pieces of pattern dimension map data, for mutually different proximity effect densities, indicating a distribution of a pattern dimension formed on a substrate when a pattern is written to the substrate by making the proximity effect density variable; selecting a set of a proximity effect correction coefficient and a base dose with which dimensional errors of the pattern dimension are corrected for a part of the proximity effect densities and correction residues of dimensional errors of the pattern dimension are generated for a remaining proximity effect densities when a writing position corresponding to a map position is written to with a dose obtained by a dose function correcting dimensional errors calculated by using the proximity effect correction coefficient and the base dose for each map position; calculating a correction term to correct the correction residues depending on the proximity effect density for each map position; calculating a dose by using a selected set of the proximity effect correction coefficient and the base dose and the correction term for each map position; and writing the desired pattern to the substrate by using a charged particle beam of the dose calculated for each map position. In the following embodiments, a configuration which uses an electron beam as an example of a charged particle beam will be described. The charged particle beam is not limited to an electron beam, and a beam using charged particles such as an ion beam may be used. In the following embodiments, a variable-shaped writing apparatus as an example of the charged particle beam writing apparatus will be described. In the first embodiment, an apparatus capable of calculating a dose by using a plurality of set data after the plurality of set data of the base dose Dbase map and the proximity effect correction coefficient η map created on the user side is input and a method therefor will be described below. FIG. 1 is a conceptual diagram showing a configuration of a writing apparatus according to the first embodiment. In FIG. 1, a writing apparatus 100 includes a pattern writing unit 150 and a control unit 160. The writing apparatus 100 is an example of the charged particle beam writing apparatus. Particularly, the writing apparatus 100 is an example of the variable-shaped (VSB type) writing apparatus. The pattern writing unit 150 includes an electron lens barrel 102 and a pattern writing chamber 103. In the electron lens barrel 102, an electron gun assembly 201, an illumination lens 202, a blanking deflector (blanker) 212, a blanking aperture plate 214, a first shaping aperture plate 203, a projection lens 204, a deflector 205, a second shaping aperture plate 206, an objective lens 207, and a deflector 208 are arranged. In the pattern writing chamber 103, an X-Y stage 105 capable of moving at least in the XY directions is arranged. On the X-Y stage 105, a target object 101 to be written to is placed. The target object 101 includes, for example, a mask for exposure and a silicon wafer to produce a semiconductor device. The mask includes mask blanks. The control unit 160 includes a control computer 110, a memory 112, a deflection control circuit 120, a DAC (digital-analog converter) amplification unit 130 (deflection amplifier), and storage devices 140, 142, 144 such as magnetic disk drives. The control computer 110, the memory 112, the deflection control circuit 120, and the storage devices 140, 142 such as magnetic disk drives are connected to each other by a bus (not shown). The DAC amplification unit 130 is connected to the deflection control circuit 120. The DAC amplification unit 130 is connected to the deflector 212. A digital signal for blanking control is output from the deflection control circuit 120 to the DAC amplification unit 130. Then, the DAC amplification unit 130 converts the digital signal into an analog signal and amplifies the analog signal, which is then applied to the deflector 212 as a deflection voltage. An electron beam 200 is deflected by the deflection voltage to form a beam for each shot. In the control computer 110, a dose calculating unit 50 or “dose operation unit 50”, a dimension map creation unit 52, an adder 54, a proximity effect correction coefficient η/base dose Dbase map creation unit 12, a dose calculating unit 18 or “dose operation unit 18”, a beam irradiation time calculating unit 20, a write data processing unit 22, and a density calculation unit 24 are arranged. Each function of the dose calculating unit 50, the dimension map creation unit 52, the adder 54, the proximity effect correction coefficient η/base dose Dbase map creation unit 12, the dose calculating unit 18, the beam irradiation time calculating unit 20, the write data processing unit 22, and the density calculation unit 24 may be configured by software such as a program. Alternatively, such functions may be configured by hardware such as an electronic circuit. In addition to the above alternatives, these alternatives may be combined. Input data necessary for the control computer 110 or a calculation result, or “operation result” is stored each time in the memory 112. Similarly, the deflection control circuit 120 may be configured as a computer operated by software such as a program or by hardware such as an electronic circuit. Alternatively, these alternatives may be combined. Here, in FIG. 1, only the configuration needed to explain the first embodiment is shown. The writing apparatus 100 may generally include other necessary configurations. For example, it is needless to say that each DAC amplification unit for the deflector 205 and the deflector 208 is included. FIG. 2 is a flowchart showing principal portion processes of a writing method according to the first embodiment. In FIG. 2, the writing method according to the first embodiment executes a series of processes including a dose calculating process (S100), a dimension map creation process (S102), an addition process (S104), a proximity effect correction coefficient η/base dose Dbase map creation process (S106), a dose calculating process (S112), a beam irradiation time calculating process (S114), and a writing process (S116). First, a plurality of set data in which a set includes a base dose Dbase map and a proximity effect correction coefficient η map created on the user side and depending on the position is input from outside the writing apparatus 100 and stored in the storage device 142. The plurality of set data contains set data to correct dimensional fluctuations (or, deviations) of patterns caused by the loading effect when the target object 101 is developed and set data to correct dimensional fluctuations of patterns caused by the loading effect when a light-shielding film of chrome (Cr) or the like is etched after the development of the target object 101. In the writing apparatus 100, the write data processing unit 22 reads write data input from outside and stored in the storage device 140 from the storage device 140 and performs data conversion processing in a plurality of stages. Then, the write data processing unit 22 generates shot data specific to the writing apparatus by the data conversion processing in the plurality of stages. Then, writing processing is performed according to the shot data. The density calculation unit 24 reads the write data, calculates a pattern area density in each position, and further calculates a proximity effect density U(x) in each position. The proximity effect density U(x) is defined as a value obtained by convolution of a pattern area density ρ(x) in a proximity effect mesh with a distribution function g(x) over a range beyond the range of influence of the proximity effect. The proximity effect mesh is suitably of size of, for example, 1/10 of the range of influence of the proximity effect and the size of, for example, about 1 μm is suitable. The proximity effect density U(x) is defined by Formula (1) shown below. x is a vector indicating the position.U(x)=∫ρ(x′)g(x−x′)dx′ (1) As the dose calculating process (S100), the dose calculating unit 50 (first dose calculating unit) reads each piece of set data from the storage device 142 to calculate a dose map (first dose map) for each set. A dose D is defined by Formula (2) (dose function) shown below.D(x,U)=Dbase(x)Dp(η(x),U(x)) (2) As shown in Formula (2), the dose D(x, U) can be defined as a product of the base dose Dbase (x) and the proximity effect-corrected dose Dp(η(x), U(x)) depending on a proximity effect correction coefficient η(x) and the proximity effect density U(x). Next, as the dimension map creation process (S102), the dimension map creation unit 52 creates a dimension map of pattern for each set by using the calculated first dose map. FIG. 3 is a graph showing an example of correlation data between a pattern dimension CD and a dose D in the first embodiment. The vertical axis of the graph represents the pattern dimension CD and the horizontal axis represents the dose D logarithmically. Here, the correlation data is determined by experiments for each case of the proximity effect density U(x)=0 (0%), 0.5 (50%), and 1 (100%). The proximity effect density U(x)=0 means that there is actually no pattern and thus, the correlation data can approximately be determined by writing, for example, one line pattern for measurement in a state in which there is nothing therearound. Conversely, the proximity effect density U(x)=1 means that the entire mesh including the surroundings is filled with patterns and dimensions cannot be measured and thus, the correlation data can approximately be determined by writing, for example, one line pattern for measurement in a state in which the entire surroundings are filled with patterns. If a 1:1 line and space pattern is written by assuming the density of, for example, 50%, one mesh may contain only a line pattern and an adjacent mesh may contain only a space pattern because the mesh size is small. In such a case, the pattern area density ρ(x) becomes a density inside a mesh regardless of the surroundings thereof. By using the proximity effect density U(x), by contrast, the density of each mesh can be calculated to be 50%. The proximity effect density U(x) to be set is not limited to cases of 0%, 50%, and 100%. For example, three values of 10% or less, 50%, and 90% or more may suitably be used as the proximity effect density U(x). The number of cases of the proximity effect density U(x) is not limited to three and any other number of cases of the proximity effect density U(x) may be used for measurement. For example, four cases of the proximity effect density U(x) or more may be used for measurement. Correlation data between the pattern dimension CD and the dose D is stored in the storage device 144 as a correction parameter. FIG. 4 is a graph showing an example of the correlation data between the proximity effect correction coefficient η and the base dose Dbase according to the first embodiment. The vertical axis of the graph represents the base dose Dbase and the horizontal axis represents the proximity effect correction coefficient η. Here, for example, the proximity effect density U(x) of 50% is set as the reference proximity effect density and correlation data between the proximity effect correction coefficient η and the base dose Dbase with which the pattern dimension CD becomes constant in the reference proximity effect density is shown. The proximity effect correction coefficient η that fits the proximity effect correction well is present for each base dose Dbase. The pattern dimension is made variable in advance to calculate correlation data for each pattern dimension before writing. Correlation data between the proximity effect correction coefficient η and the base dose Dbase is stored in the storage device 144 as a correction parameter. Alternatively, the correlation data may be calculated from correlation data between the pattern dimension CD and the dose D by the dimension map creation unit 52. The dimension map creation unit 52 calculates the dimension of pattern corresponding to the dose in each calculated position by referring to the correlation data between the pattern dimension CD and the dose D. Then, the dimension map creation unit 52 creates a dimension map of pattern for each set. Here, one of a plurality of proximity effect densities U(x) is set as the reference proximity effect density to calculate the dimension of pattern corresponding to the dose in the reference proximity effect density. As the reference proximity effect density, for example, the proximity effect density U(x)=0.5 is used. A plurality of dimension maps 1, 2 corresponding to the plurality of set data can be created by the processes described above. FIG. 5 is a conceptual diagram for explaining an calculating method of a pattern dimension in the first embodiment. If the proximity effect correction coefficient η and the base dose Dbase are decided, as described above, the dose D can be calculated by using Formula (2). Then, if the dose D is determined, the pattern dimension can be determined from the correlation data between the pattern dimension CD and the dose D shown in FIG. 3. FIG. 6 is a conceptual diagram for explaining a dimension map in the first embodiment. A dimension map 40 has the pattern dimension corresponding to the position of each mesh by dividing a write region into mesh regions of a predetermined size. The mesh size of the dimension map 40 is suitably of size of, for example, 1/10 of the range of influence of the loading effect to be used for correcting the loading effect. For example, the mesh is suitably a mesh of 1 mm per side. As the addition process (S104), the adder 54 adds dimensions of all sets for each position of the dimension map by using the dimension map of each set. While it is difficult to simply combine the proximity effect correction coefficients η or the base doses of the beam Dbase, such parameters are converted into dimensions in the first embodiment and when set data of the base dose Dbase map and the proximity effect correction coefficient η map individually set for each of a plurality of phenomena is input, such converted dimensions can be combined. As the proximity effect correction coefficient η/base dose Dbase map creation process (S106), the proximity effect correction coefficient η/base dose Dbase map creation unit 12 creates a set of the proximity effect correction coefficient map and base dose map by using the added dimension maps obtained by addition. The proximity effect correction coefficient η/base dose Dbase map creation unit 12 is an example of a set map creation unit. Here, the proximity effect correction coefficient η/base dose Dbase map creation unit 12 creates both of the proximity effect correction coefficient map and base dose map, but is not limited to this. It is needless to say that the proximity effect correction coefficient η/base dose Dbase map creation unit 12 may function by being divided into a proximity effect correction coefficient map creation unit and a base dose map creation unit. Here, a set of the proximity effect correction coefficient η producing the corresponding dose and the base dose Dbase is calculated as a pattern dimension in the reference proximity effect density (U(x)=0.5) for each position of the map. As the dose calculating process (S112), the dose calculating unit 18 (second dose calculating unit) calculates a dose map (second dose map) in each position in the proximity effect density U(x) obtained from write data by using a set of a proximity effect correction coefficient map and a base dose map created after dimensions are combined. The dose D may be calculated by using the above Formula (2). The dose calculating unit 18 may calculate a value obtained by further multiplying each value of the dose map calculated by using the created set of the proximity effect correction coefficient map and the base dose map by a correction coefficient of the fogging effect defined for each map position as the dose map (second dose map) here. By calculating the dose D as described above, entire dimensional fluctuations based on a plurality of phenomena such as dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching can be corrected without distinguishing the phenomena while also correcting the proximity effect. As the beam irradiation time calculating process (S114), the beam irradiation time calculating unit 20 calculates a beam irradiation time T of the electron beam 200 in each position of the write region. The dose D can be defined as a product of the beam irradiation time T and a current density J and thus, the beam irradiation time T can be determined by dividing the dose D by the current density J. The calculated beam irradiation time is output to the deflection control circuit 120. As the writing process (S116), the pattern writing unit 150 writes a desired pattern on the target object 101 by using the electron beam 200 of the dose defined in the dose map (second dose map). A more concrete operation will be described below. The deflection control circuit 120 outputs a digital signal to control the beam irradiation time for each shot to the DAC amplification unit 130. Then, the DAC amplification unit 130 converts the digital signal into an analog signal and amplifies the analog signal, which is then applied to the blanking deflector 212 as a deflection voltage. The electron beam 200 emitted from the electron gun assembly 201 (discharge unit) is controlled to pass through the blanking aperture plate 214 by the blanking deflector 212 when passing through the blanking deflector 212 in a beam ON state and controlled to be deflected so that the whole beam is blocked by the blanking aperture plate 214 in a beam OFF state. The electron beam 200 having passed through the blanking aperture plate 214 during a time from the beam OFF state to the beam ON state and back to the beam OFF state becomes an electron beam for one shot. The blanking deflector 212 alternately generates the beam ON state and the beam OFF state by controlling the orientation of the passing electron beam 200. For example, no voltage may be applied for the beam ON state and a voltage may be applied to the blanking deflector 212 for the beam OFF state. The dose of the electron beam 200 per shot shone on the target object 101 is adjusted by the beam irradiation time T of each of such shots. The electron beam 200 of each shot generated by being passed through the blanking deflector 212 and the blanking aperture plate 214 illuminates the whole first shaping aperture plate 203 having an oblong, for example, rectangular hole through the illumination lens 202. Here, the electron beam 200 is first formed into an oblong, for example, a rectangular shape. Then, the electron beam 200 of a first aperture image having passed through the first shaping aperture plate 203 is projected onto the second shaping aperture plate 206 through the projection lens 204. The first aperture image is controlled to deflect by the deflector 205 on the second shaping aperture plate 206 so that the beam shape and dimensions thereof can be changed (variably shaped). Such variable shaping is performed for each shot and a different beam shape and dimensions are formed for each normal shot. Then, the electron beam 200 of a second aperture image having passed through the second shaping aperture plate 206 is focused by the objective lens 207 and deflected by the deflector 208 before being shone onto a desired position of the target object arranged on the continuously moving XY stage 105. Thus, a plurality of shots of the electron beam 200 is successively deflected onto the target object 101 to be a substrate by each deflector. According to the first embodiment, as described above, even if a plurality of set data of the proximity effect correction coefficient map and the base doses of the beam map is input, such data can be combined in the apparatus. Then, according to the first embodiment, even if dimensional fluctuations based on a plurality of phenomena are input as set data of the proximity effect correction coefficient η map and the base dose Dbase map that makes a correction for each phenomenon, the data can be converted into the proximity effect correction coefficient η map and the base dose Dbase map capable of correcting dimensional fluctuations based on the plurality of phenomena together. Therefore, even if set data of a plurality of set data of the base dose Dbase map and the proximity effect correction coefficient η map created on the user side is input, the dose can be calculated by using the plurality of set data. In the first embodiment, a dimension conversion is made in the reference proximity effect density (U(x)=0.5) by assuming that similar dimensions are obtained also when the proximity effect density is other than the reference proximity effect density (U(x)=0.5) and after combination, the base dose Dbase map and the proximity effect correction coefficient η map are created in the reference proximity effect density (U(x)=0.5). However, the present invention is not limited to this. In the second embodiment, dimension conversions are made in a plurality of proximity effect densities U(x) to improve precision and after combination, the base dose Dbase map and the proximity effect correction coefficient η map are created. FIG. 7 is a conceptual diagram showing the configuration of the writing apparatus according to the second embodiment. FIG. 7 is the same as FIG. 1 except that a selection unit 10, a correction residue fitting processing unit 14, and a correction term calculation unit 16 are further added to the control computer. Each function of the correction residue fitting processing unit 14 and the correction term calculation unit 16 may be configured by software such as a program. Alternatively, such functions may be configured by hardware such as an electronic circuit. In addition to the above alternatives, these alternatives may be combined. The second embodiment is the same as the first embodiment except for content specifically described below. FIG. 8 is a flowchart showing principal portion processes of the writing method according to the second embodiment. In FIG. 8, the writing method according to the second embodiment is the same as in FIG. 2 except that the dimension map created in the dimension map creation process (S102) and the dimension map created after addition in the addition process (S104) are different, a proximity effect correction coefficient η/base dose Dbase selection process (S105) is added between the addition process (S104) and the proximity effect correction coefficient η/base dose Dbase map creation process (S106), and further a correction residue fitting process (S108) and a correction term calculation process (S110) are added between the proximity effect correction coefficient η/base dose Dbase map creation process (S106) and the dose calculating process (S112). The dose calculating process (S100) is the same as in the first embodiment. As the dimension map creation process (S102), the dimension map creation unit 52 creates dimension maps of pattern in a plurality of proximity effect densities for each set by using the calculated dose map (first dose map). That is, for example, in addition to the dimension map in the proximity effect density U(x)=0.5, a dimension map in the proximity effect density U(x)=0 and a dimension map in the proximity effect density U(x)=1 are created for each set. The dimension map creation unit 52 calculates the dimension of pattern corresponding to the dose in each calculated position by referring to the correlation data between the pattern dimension CD and the dose D shown in FIG. 3. Then, the dimension map creation unit 52 creates dimension maps of pattern for each set. A plurality of dimension maps 1, 2 corresponding to the plurality of set data and depending on the proximity effect density U(x) can be created by the processes described above. As the addition process (S104), the adder 54 adds dimensions of all sets for each position of the dimension map for each proximity effect density U(x) by using the plurality of dimension maps having different proximity effect densities U(x) of each set. According to the second embodiment, higher precision can be achieved than in the first embodiment by converting such parameters into dimensions for each proximity effect density U(x). As the proximity effect correction coefficient η/base dose Dbase selection process (S105), the selection unit 10 selects a set of the proximity effect correction coefficient η and the base dose Dbase with which dimensional errors of pattern are corrected for a part of proximity effect densities and correction residues of dimensional errors of pattern are generated for the remaining proximity effect densities by using a plurality of added dimensional maps after being added and having mutually different proximity effect densities U(x). The selection unit 10 selects a set of the proximity effect correction coefficient η and the base dose Dbase with which dimensional errors of pattern are corrected for a part of proximity effect densities U(x) and dimensional fluctuation amounts δ0, δ100 to be correction residues of dimensional errors of pattern are generated for the remaining proximity effect densities U(x) when each map position of the pattern dimension map 40 is written to with the dose D correcting dimensional errors calculated by using the proximity effect correction coefficient η and the base dose Dbase and obtained by a dose function. FIG. 9 is a graph showing an example of the correlation data between the pattern dimension CD and the proximity effect correction coefficient η in the second embodiment. The vertical axis of the graph represents the pattern dimension CD and the horizontal axis represents the proximity effect correction coefficient η. Here, the proximity effect density U(x) of 50% is set as the reference proximity effect density and the correlation between the proximity effect correction coefficient η and the base dose Dbase is such that the pattern dimension CD becomes constant in the reference proximity effect density and thus, the pattern dimension CD is constant when the proximity effect density U(x)=0.5. Here, correlation data of the pattern dimension CD depending on the proximity effect correction coefficient η is further calculated for the remaining proximity effect densities U(x). As shown in FIG. 9, the pattern dimension CD depending on the proximity effect correction coefficient η changes in the proximity effect density U(x) other than 50%, which is set as the reference proximity effect density. In FIG. 9, a dimensional fluctuation amount δ of the pattern dimension CD depending on the proximity effect correction coefficient η in the proximity effect density other than the reference proximity effect density is shown and δ0 is the dimensional fluctuation amount when the proximity effect density U(x)=0 and δ100 is the dimensional fluctuation amount when the proximity effect density U(x)=1. Next, correction parameters below are created by using the above correlation data. FIG. 10 is a diagram showing an example of the correlation data among the base dose, the proximity effect correction coefficient, the pattern dimension when U(x)=0.5, and a dimensional fluctuation amount when U(x) is other than 0.5 in the second embodiment. As described above, one of the plurality of proximity effect densities U(x) is set as the reference proximity effect density and the set of the proximity effect correction coefficient η and the base dose Dbase is correlated so that a desired pattern dimension is obtained in the reference proximity effect density. FIG. 10 shows correction parameters 30 to be correlation data among a plurality of sets of the proximity effect correction coefficient η and the base dose Dbase, the pattern dimensions CD obtained for the plurality of sets when the proximity effect density U(x)=0.5, and the dimensional fluctuation amounts δ0, δ100 for the plurality of sets in the remaining proximity effect densities. In the correction parameters 30 shown in FIG. 10, for example, the set of the proximity effect correction coefficient η and the base dose Dbase is made variable for each pattern dimension CD to show the dimensional fluctuation amounts δ0, δ100 in each case. Such correction parameters are also stored in the storage device 144. As shown in FIG. 9, sets of the proximity effect correction coefficient η and the base dose Dbase are configured so that the pattern dimension CD becomes constant when the proximity effect density U(x)=0.5. Thus, unless one proximity effect correction coefficient η that generates the desired pattern dimension CD for all proximity effect densities U(x) is selected, a correction residue of the proximity effect correction will be generated under conditions of no loading effect when the proximity effect density U(x) is other than 0.5. In the second embodiment, one proximity effect correction coefficient η that generates the desired pattern dimension CD for all proximity effect densities U(x) is consciously not selected and instead, the proximity effect correction coefficient η is selected by shifting the coefficient η. As a result, if the proximity effect density U(x)=0.5, the desired dimension is obtained when the relevant distribution position is written to with the dose D obtained from the dose function by canceling out the loading effect to correct a dimensional error of the pattern dimension. If the proximity effect densities U(x)=0, 100, by contrast, when the relevant distribution position is written to with the dose D obtained from the dose function, a correction residue may be generated in the dimensional error of the pattern dimension. Next, the selection technique will be described more specifically. FIGS. 11A and 11B are conceptual diagrams for explaining a technique to select a set of the proximity effect correction coefficient and the base dose in the first embodiment. The pattern dimension CD in each proximity effect density U(x) is read for each position of the pattern dimension map 40. First, as shown in FIG. 11A, a set of the proximity effect correction coefficient η and the base dose Dbase that generates the pattern dimension CD in the proximity effect density U(x)=0.5 to be the reference proximity effect density is assumed. Next, an absolute value Δ0 of a difference between a dimensional error ΔCD0 of the pattern dimension defined in the pattern dimension map 40 when the proximity effect density U(x)=0 from the pattern dimension when U(x)=0.5 and a pattern dimension fluctuation amount δ0 when written with the dose D obtained for the relevant set when the proximity effect density U(x)=0 is calculated. The absolute value Δ0 becomes a correction residue when the proximity effect density U(x)=0. Similarly, an absolute value Δ100 of a difference between a dimensional error ΔCD100 of the pattern dimension defined in the pattern dimension map 40 when the proximity effect density U(x)=1 from the pattern dimension when U(x)=0.5 and a pattern dimension fluctuation amount δ100 when written with the dose D obtained for the relevant set when the proximity effect density U(x)=1 is calculated. The absolute value Δ100 becomes a correction residue when the proximity effect density U(x)=1. Then, as shown in Formula (3) below, both terms are added.Δerr=|CD0(η)−δ0|+|CD100(η)−δ100| (3) Then, as shown in FIG. 11B, the selection unit 10 selects a set of the proximity effect correction coefficient η and the base dose Dbase that minimizes Δerr shown in Formula (3) for each distribution position of the pattern dimension map 40 by referring to the correction parameters 30. In other words, the selection unit 10 selects a set of the proximity effect correction coefficient η and the base dose Dbase that makes a correction residue smaller. Then, as the proximity effect correction coefficient η/base dose Dbase map creation process (S106), the proximity effect correction coefficient η/base dose Dbase map creation unit 12 creates a proximity effect correction coefficient η map and a base dose Dbase map depending on each writing position corresponding to map positions (each distribution position of the pattern dimension map 40) by using the set of the proximity effect correction coefficient η and a base dose Dbase selected for each position. Here, the proximity effect correction coefficient η/base dose Dbase map creation unit 12 creates both of the proximity effect correction coefficient map and base dose map, but the creation function may be divided into a proximity effect correction coefficient η map creation unit and a base dose Dbase map creation unit. With the above configuration, the proximity effect correction coefficient η map and the base dose Dbase map capable of correcting entire dimensional fluctuations based on a plurality of phenomena such as dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching without distinguishing the phenomena can be created from the pattern dimension map for each proximity effect density U(x). Then, the proximity effect can also be corrected at the same time for the proximity effect density U(x)=0.5. However, the correction residue remains for the proximity effect density U(x) other than 0.5 and thus, a correction term is provided as described below. FIGS. 12A and 12B are conceptual diagrams for explaining the technique to calculate a correction term in the second embodiment. In FIG. 12A, the vertical axis of the graph represents a correction residue Δ and the horizontal axis represents the proximity effect density U(x). In FIG. 12B, the vertical axis of the graph represents a correction term Dcorr and the horizontal axis represents the proximity effect density U(x). First, as the correction residue fitting process (S108), as shown in FIG. 12A, the correction residue fitting processing unit 14 calculates an approximate expression by fitting the correction residue Δ for each proximity effect density U(x) using a predetermined function. Then, as the correction term calculation process (S110), the correction term calculation unit 16 calculates the correction term Dcorr that corrects the correction residue Δ depending on the proximity effect density U(x) for each map position. Here, the function of the correction term Dcorr may be set so that the correction residue Δ depending on the proximity effect density U(x) obtained from the approximate expression created in the correction residue fitting process (S108) is corrected. As the dose calculating process (S112), the dose calculating unit 18 calculates the dose D by using the selected set of the proximity effect correction coefficient η and the base dose Dbase and the correction term Dcorr for each map position. The dose calculating unit 18 calculates a dose map (second dose map) in each position in the proximity effect density U(x) obtained from write data by using the created set of the proximity effect correction coefficient map and the base dose map. The dose D is defined by Formula (4) (dose function) below.D(X,U)=Dbase(x)Dp(η(x),U(x))Dcorr(x,U(x)) (4) As shown in Formula (4), the dose D(x, U) in the second embodiment can be defined by a formula that multiplies a product of the base dose Dbase (x) and the proximity effect-corrected dose Dp (η(x), U(x)) depending on the proximity effect correction coefficient η(x) and the proximity effect density U(x) further by the correction term Dcorr(x, U(x)) depending on the position x and the proximity effect density U(x). By calculating the dose D as described above, entire dimensional fluctuations based on a plurality of phenomena such as dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching can be corrected without distinguishing the phenomena while also correcting the proximity effect. Moreover, by increasing conditions of the proximity effect density U(x), precision of the dimension map and the set of the proximity effect correction coefficient η and the base dose Dbase can further be improved. A case where it is necessary to correct η such as changing η for each of a plurality of phenomena according to a conventional method can also be handled. Furthermore, correction precision can be improved by introducing the correction term depending on the proximity effect density. The dose calculating unit 18 may calculate a value obtained by further multiplying each value of the dose map calculated by using the created set of the proximity effect correction coefficient map and the base dose map and the correction term Dcorr by a correction coefficient of the fogging effect defined for each map position as the dose map (second dose map) here. The beam irradiation time calculating process (S114) and the subsequent process are the same as those in the first embodiment. FIGS. 13A to 13C are diagrams showing an example of the dose correction in the second embodiment. FIG. 13A shows a case where the dimensional error ΔCD0 of the pattern dimension defined in the pattern dimension map 40 when the proximity effect density U(x)=0, 1 from the pattern dimension when U(x)=0.5 is, for example, 1 nm and ΔCD100 is, for example, −1 nm. FIG. 13C shows an example in such a case of the correlation between the pattern dimension CD and the proximity effect correction coefficient η. In the example of the correlation in FIG. 10C, the proximity effect correction coefficient η that generates δ0=1 and δ100=−1 is present. In this example, as shown in FIG. 13B, dimensional errors can be corrected without generating any correction residue by selecting the above proximity effect correction coefficient η. Thus, the correction term Dcorr=1 can be set. FIGS. 14A to 14C are diagrams showing another example of the dose correction in the second embodiment. FIG. 14A shows a case where the dimensional error ΔCD0 of the pattern dimension defined in the pattern dimension map 40 when the proximity effect density U(x)=0, 1 from the pattern dimension when U(x)=0.5 is, for example, 1 nm and ΔCD100 is, for example, 0 nm. In such a case, the proximity effect correction coefficient η that generates δ0=1 and δ100=0 is not present in the example of the correlation in FIG. 14C. Thus, as shown in FIG. 14B, for example, the proximity effect correction coefficient η that generates the correction residue of −0.5 nm for both is selected. By making such a selection, a respective correction to some extent can be made, though not complete, when the proximity effect density U(x)=0, 1. In the second embodiment, the correction residue can also be corrected by using the correction term Dcorr. FIGS. 15A and 15B are diagrams showing still another example of the dose correction in the second embodiment. FIG. 15A shows a case where the dimensional error ΔCD0 of the pattern dimension defined in the pattern dimension map 40 when the proximity effect density U(x)=0, 1 from the pattern dimension when U(x)=0.5 is, for example, 1 nm and ΔCD100 is, for example, 1 nm. In such a case, the proximity effect correction coefficient η that generates δ0=1 and δ100=1 is not present in the example of the correlation in FIG. 15B. Dimensional fluctuations when the proximity effect density U(x)=0, 1 act in the direction of the opposite side and thus, it is difficult to correct both at the same time according to a conventional method. According to the second embodiment, by contrast, corrections can be made also in such a case by using the correction term Dcorr. According to the first and second embodiments, a plurality of set data including a set of a proximity effect correction coefficient η map and a base dose Dbase map is input into the writing apparatus 100 from the user side, but the present invention is not limited to this. In the third embodiment, further a case where data in a stage before creating a proximity effect correction coefficient η map and a base dose Dbase map is used as input data will be described. Some users may be assumed to create set data including correlation data between a pattern area density ρL and the proximity effect correction coefficient η and correlation data between the pattern area density ρL and the base dose Dbase. Thus, in the third embodiment, a configuration enabling the writing apparatus 100 to handle even when the user creates the above set data for each of phenomena of dimensional fluctuations and inputs the set data to the writing apparatus 100. FIG. 16 is a conceptual diagram showing the configuration of the writing apparatus according to the third embodiment. FIG. 16 is the same as FIG. 1 except that a proximity effect correction coefficient η/base dose Dbase map creation unit 56 is further added to the control computer and input data stored in the storage device 142 is a plurality of set data correlated by the pattern area density ρL, the proximity effect correction coefficient η, and the base dose Dbase. The function of the proximity effect correction coefficient η/base dose Dbase map creation unit 56 may be configured by software such as a program. Alternatively, such a function may be configured by hardware such as an electronic circuit. In addition to the above alternatives, these alternatives may be combined. The third embodiment is the same as the first embodiment except for content specifically described below. First, correlation information among the pattern area density (area ratio) ρL, the proximity effect correction coefficient η, and the base dose Dbase is created for each of a plurality of phenomena causing dimensional fluctuations in a mask plane when fabricating a mask. Then, a plurality of set data created on the user side and correlated by the pattern area density ρL, the proximity effect correction coefficient η, and the base dose Dbase is input from outside the writing apparatus 100 and stored in the storage device 142. The plurality of set data includes a set data to correct dimensional fluctuations of patterns caused by the loading effect when the target object 101 is developed and a set data to correct dimensional fluctuations of patterns caused by the loading effect when a light-shielding film of chrome (Cr) or the like is etched after the development of the target object 101. Correlation information among the pattern area ratio, the proximity effect correction coefficient, and the base dose is input for each of a plurality of phenomena causing dimensional fluctuations in a mask plane during mask writing and stored. The density calculation unit 24 divides a write region into mesh regions and calculates the pattern area density ρL in each mesh by referring to write data. The mesh size is suitably of size of about 1/10 of the range of influence of the loading effect to be used for correcting the loading effect. For example, the mesh is suitably a mesh of 1 mm per side. As the proximity effect correction coefficient η/base dose Dbase map creation process, the proximity effect correction coefficient η/base dose Dbase map creation unit 56 (first set map creation unit) reads each piece of correlation information to create a set of the proximity effect correction coefficient map and the base dose map for each phenomenon to correct the phenomenon. Here, the corresponding proximity effect correction coefficient η and base dose Dbase are determined from the pattern area density ρL in each position obtained from write data to be actually written by the writing apparatus 100 by referring to correlation data among the pattern area density ρL, the proximity effect correction coefficient η, and the base dose Dbase created on the user side. Then, as the dose calculating process (S100), the dose calculating unit 50 (first dose calculating unit) calculates a dose map (first dose map) for each set. Each subsequent process is the same as that in the first embodiment. According to the third embodiment, as described above, even if correlation information among the pattern area ratio, proximity effect correction coefficient, and base dose is input for each phenomenon, such information can be combined in the apparatus. Then, even if content of input data is different from phenomenon to phenomenon, the input data can be combined in the writing apparatus 100 to calculate the appropriate dose D. In the fourth embodiment, an apparatus and a method capable of correcting both of dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching while correcting the proximity effect will be described. FIG. 17 is a conceptual diagram showing the configuration of the writing apparatus according to the fourth embodiment. In FIG. 17, the writing apparatus 100 includes the pattern writing unit 150 and the control unit 160. The writing apparatus 100 is an example of the charged particle beam writing apparatus. Particularly, the writing apparatus 100 is an example of the variable-shaped (VSB type) writing apparatus. The pattern writing unit 150 includes the electron lens barrel 102 and the pattern writing chamber 103. In the electron lens barrel 102, the electron gun assembly 201, the illumination lens 202, the blanking deflector (blanker) 212, the blanking aperture plate 214, the first shaping aperture plate 203, the projection lens 204, the deflector 205, the second shaping aperture plate 206, the objective lens 207, and the deflector 208 are arranged. In the pattern writing chamber 103, the X-Y stage 105 capable of moving at least in the XY directions is arranged. On the X-Y stage 105, the target object 101 to be written to is placed. The target object 101 includes, for example, a mask for exposure and a silicon wafer to produce a semiconductor device. The mask includes mask blanks. The control unit 160 includes the control computer 110, the memory 112, the deflection control circuit 120, the DAC (digital-analog converter) amplification unit 130 (deflection amplifier), and the storage devices 140, 142 such as magnetic disk drives. The control computer 110, the memory 112, the deflection control circuit 120, and the storage devices 140, 142 such as magnetic disk drives are connected to each other by a bus (not shown). The DAC amplification unit 130 is connected to the deflection control circuit 120. The DAC amplification unit 130 is connected to the blanking deflector 212. A digital signal for blanking control is output from the deflection control circuit 120 to the DAC amplification unit 130. Then, the DAC amplification unit 130 converts the digital signal into an analog signal and amplifies the analog signal, which is then applied to the blanking deflector 212 as a deflection voltage. The electron beam 200 is deflected by the deflection voltage to form a beam for each shot. In the control computer 110, a selection unit 910, a proximity effect correction coefficient η/base dose Dbase map creation unit 912, a correction residue fitting processing unit 914, a correction term calculation unit 916, a dose calculating unit 918, a beam irradiation time calculating unit 920, and a write data processing unit 922 are arranged. Each function of the selection unit 910, the proximity effect correction coefficient η/base dose Dbase map creation unit 912, the correction residue fitting processing unit 914, the correction term calculation unit 916, the dose calculating unit 918, the beam irradiation time calculating unit 920, and the write data processing unit 922 may be configured by software such as a program. Alternatively, such functions may be configured by hardware such as an electronic circuit. In addition to the above alternatives, these alternatives may be combined. Input data necessary for the control computer 110 or a calculating result is stored each time in the memory 112. Similarly, the deflection control circuit 120 may be configured as a computer operated by software such as a program or by hardware such as an electronic circuit. In addition to the above alternatives, these alternatives may be combined. Here, in FIG. 17, only the configuration needed to explain the fourth embodiment is shown. The writing apparatus 100 may generally include other necessary configurations as a matter of course. For example, it is needless to say that each DAC amplification unit for the deflector 205 and the deflector 208 are included. FIG. 18 is a flowchart showing principal portion processes of the writing method according to the fourth embodiment. In FIG. 18, as processes to be executed in advance before input into the writing apparatus 100, an acquisition process of correlation data between the pattern dimension CD and the dose D (S9102), an acquisition process of correlation data between the proximity effect correction coefficient η and the base dose Dbase (S9104), an acquisition process of correlation data between the pattern dimension CD and the proximity effect correction coefficient η (S9106), and a correction parameter creation process (S9108) are performed. Further, a dimension map creation process (S9110) is executed as a process to be executed in advance. Then, the writing method executed in the writing apparatus 100 according to the fourth embodiment executes a series of processes including a proximity effect correction coefficient η/base dose Dbase selection process (S9120), a proximity effect correction coefficient η/base dose Dbase map creation process (S9122), a correction residue fitting process (S9124), a correction term calculation process (S9126), a dose calculating process (S9128), a beam irradiation time calculating process (S9130), and a writing process (S9132). First, as the acquisition process of correlation data between the pattern dimension CD and the dose D (S9102), correlation data between the pattern dimension CD and the dose D is acquired through experiment for each proximity effect density U. The proximity effect density U(x) is defined as a value obtained by integrating a convolution of the pattern area density ρ(x) in a proximity effect mesh with a distribution function g(x) over a range beyond the range of influence of the proximity effect. The proximity effect mesh is suitably of size of, for example, 1/10 of the range of influence of the proximity effect and the size of, for example, about 1 μm is suitable. The proximity effect density U(x) is defined by Formula (1) shown above. x is a vector indicating the position. A graph showing an example of correlation data between the pattern dimension CD and the dose D in the fourth embodiment is like in FIG. 3. The vertical axis of the graph represents the pattern dimension CD and the horizontal axis represents the dose D logarithmically. Here, the correlation data is determined by experiments for each case of the proximity effect density U(x)=0 (0%), 0.5 (50%), and 1 (100%). The proximity effect density U(x)=0 means that there is actually no pattern and thus, the correlation data can approximately be determined by writing, for example, one line pattern for measurement in a state in which there is nothing therearound. Conversely, the proximity effect density U(x)=1 means that the entire mesh including the surroundings is filled with patterns and dimensions cannot be measured and thus, the correlation data can approximately be determined by writing, for example, one line pattern for measurement in a state in which the entire surroundings are filled with patterns. If a 1:1 line and space pattern is written by assuming the density of, for example, 50%, one mesh may contain only a line pattern and an adjacent mesh may contain only a space pattern because the mesh size is small. In such a case, the pattern area density ρ(x) becomes a density inside a mesh regardless of the surroundings thereof. By using the proximity effect density U(x), by contrast, the density of each mesh can be calculated to be 50%. The proximity effect density U(x) to be set is not limited to cases of 0%, 50%, and 100%. For example, three values of 10% or less, 50%, and 90% or more may suitably be used as the proximity effect density U(x). The number of cases of the proximity effect density U(x) is not limited to three and any other number of cases of the proximity effect density U(x) may be used for measurement. For example, four cases of the proximity effect density U(x) or more may be used for measurement. Next, as the acquisition process of correlation data between the proximity effect correction coefficient η and the base dose Dbase (S9104), correlation data between the proximity effect correction coefficient η and the base dose Dbase is calculated by using the correlation data between CD and the dose D obtained by experiments. A graph showing an example of correlation data between the proximity effect correction coefficient η and the base dose Dbase in the fourth embodiment is like in FIG. 4. The vertical axis of the graph represents the base dose Dbase and the horizontal axis represents the proximity effect correction coefficient η. Here, for example, the proximity effect density U(x) of 50% is set as the reference proximity effect density and correlation data between the proximity effect correction coefficient η and the base dose Dbase with which the pattern dimension CD becomes constant in the reference proximity effect density is calculated. The proximity effect correction coefficient η that fits the proximity effect correction well is present for each base dose Dbase. The pattern dimension is made variable in advance to calculate correlation data for each pattern dimension. Next, as the acquisition process of correlation data between the pattern dimension CD and the proximity effect correction coefficient η (S9106), correlation data between the pattern dimension CD and the proximity effect correction coefficient η is calculated by using the correlation data between the proximity effect correction coefficient η and the base dose Dbase obtained for each pattern dimension. A graph showing an example of correlation data between the pattern dimension CD and the proximity effect correction coefficient η in the fourth embodiment is like in FIG. 9. The vertical axis of the graph represents the pattern dimension CD and the horizontal axis represents the proximity effect correction coefficient η. Here, correlation data of the pattern dimension CD depending on the proximity effect correction coefficient η is further calculated for the remaining proximity effect densities U(x). As shown in FIG. 5, the pattern dimension CD depending on the proximity effect correction coefficient η changes in the proximity effect density U(x) other than 50%, which is set as the reference proximity effect density. In FIG. 9, the dimensional fluctuation amount δ of the pattern dimension CD depending on the proximity effect correction coefficient η in the proximity effect density other than the reference proximity effect density is shown and δ0 is the dimensional fluctuation amount when the proximity effect density U(x)=0 and δ100 is the dimensional fluctuation amount when the proximity effect density U(x)=1. Next, as the correction parameter creation process (S9108), correction parameters are created by using the above correlation data. A diagram showing an example of the correlation data among the base dose, the proximity effect correction coefficient, the pattern dimension when U(x)=0.5, and the dimensional fluctuation amount when U(x) is other than 0.5 in the fourth embodiment is like in FIG. 10. As described above, one of the plurality of proximity effect densities U(x) is set as the reference proximity effect density and the set of the proximity effect correction coefficient η and the base dose Dbase is correlated so that a desired pattern dimension is obtained in the reference proximity effect density. FIG. 10 shows correction parameters 930 to be correlation data among a plurality of sets of the proximity effect correction coefficient η and the base dose Dbase, the pattern dimensions CD obtained for the plurality of sets when the proximity effect density U(x)=0.5, and the dimensional fluctuation amounts δ0, δ100 for the plurality of sets in the remaining proximity effect densities. In the correction parameters 930 shown in FIG. 6, for example, the set of the proximity effect correction coefficient and the base dose Dbase is made variable for each pattern dimension CD to show the dimensional fluctuation amounts δ0, δ100 in each case. Next, as the dimension map creation process (S9110), a dimension map depending on the position of the target object 101 is created for each proximity effect density U(x). FIGS. 19A and 19B are conceptual diagrams for explaining the creation method of a dimension map in the fourth embodiment. In FIG. 19A, evaluation patterns 9302 are regularly formed on an evaluation substrate 9300 so that the evaluation patterns 9302 are distributed substantially over an entire surface of the evaluation substrate 9300. In each of the evaluation patterns 9302, patterns to be the proximity effect density U(x)=0.0.5, and 1 are arranged. After the evaluation patterns 9302 are written to the entire surface of the evaluation substrate 9300 coated with a resist by using the writing apparatus 100, the resist is developed and a chrome (Cr) film, for example, to be a light-shielding film of the groundwork is etched and further ashed. Then, the pattern dimension of each light-shielding film formed on the evaluation substrate 9300 is measured. Then, as shown in FIG. 19B, the pattern dimension map 40 defined by the measured pattern dimension being made depending on the position is created for each proximity effect density U(x). In this manner, data of a plurality of pattern dimension maps 940 of mutually different proximity effect densities showing the distribution of the pattern dimensions CD formed on the evaluation substrate 9300 when patterns are written to the evaluation substrate 9300 by making the proximity effect density U(x) variable is created. The measured pattern dimension contains both of dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching. The mesh size of the pattern dimension map 940 is suitably of size of about 1/10 of the range of influence of the loading effect to be used for correcting the loading effect. For example, the mesh is suitably a mesh of 1 mm per side. The correction parameters 930 and the pattern dimension map 940 for each proximity effect density U(x) are created as described above before starting to write by the writing apparatus 100. Each piece of data of the correction parameters 930 and the pattern dimension map 940 for each proximity effect density U(x) is input into the writing apparatus 100 from outside the writing apparatus 100 and stored in the storage device 142. Thus, the storage device 142 stores correlation data showing a plurality of sets of the proximity effect correction coefficient and base dose, pattern dimensions obtained for each of the plurality of sets in the reference proximity effect density, and dimensional fluctuation amounts for the plurality of sets in the remaining proximity effect densities. The correlation data is stored in one unit of the storage device 142 here, but the present embodiment is not limited to this and the correlation data may be divided and stored in a plurality of storage devices. Then, the data is used to write patterns by the writing apparatus 100. In the writing apparatus 100, the write data processing unit 922 reads write data input from outside and stored in the storage device 140 from the storage device 140 and performs data conversion processing in a plurality of stages. Then, the write data processing unit 922 generates shot data specific to the writing apparatus by the data conversion processing in the plurality of stages. Then, writing processing is performed according to the shot data. The write data processing unit 922 reads the write data, calculates the pattern area density in each position, and further calculates the proximity effect density U(x) in each position. As the proximity effect correction coefficient η/base dose Dbase selection process (S9120), the selection unit 910 selects a set of the proximity effect correction coefficient η and the base dose Dbase with which dimensional errors of pattern are corrected for a part of proximity effect densities U(x) and dimensional fluctuation amounts δ0, δ100 to be correction residues of dimensional errors of pattern are generated for the remaining proximity effect densities U(x) when each map position of the pattern dimension map 940 is written to with the dose D correcting dimensional errors calculated by using the proximity effect correction coefficient η and the base dose Dbase and obtained by a dose function. The dose function can be defined by the above Formula (2). As shown in Formula (2), the dose D(x, U) can be defined as a product of the base dose Dbase (x) and the proximity effect-corrected dose Dp(η(x), U(x)) depending on the proximity effect correction coefficient η(x) and the proximity effect density U(x). As shown in FIG. 9, sets of the proximity effect correction coefficient η and the base dose Dbase are configured so that the pattern dimension CD becomes constant when the proximity effect density U(x)=0.5. Thus, unless one proximity effect correction coefficient η that generates the desired pattern dimension CD for all proximity effect densities U(x) is selected, a correction residue of the proximity effect correction will be generated under conditions of no loading effect when the proximity effect density U(x) is other than 0.5. In the fourth embodiment, one proximity effect correction coefficient η that generates the desired pattern dimension CD for all proximity effect densities U(x) is consciously not selected and instead, the proximity effect correction coefficient η is selected by shifting the coefficient η. As a result, if the proximity effect density U(x)=0.5, the desired dimension is obtained when the relevant distribution position is written to with the dose D obtained from the dose function by canceling out the loading effect to correct a dimensional error of the pattern dimension. If the proximity effect densities U(x)=0, 1, by contrast, when the relevant distribution position is written to with the dose D obtained from the dose function, a correction residue will be generated in the dimensional error of the pattern dimension. Next, the selection technique will be described more specifically. A conceptual diagram for explaining the technique to select a set of the proximity effect correction coefficient and the base dose in the fourth embodiment is like in FIGS. 11A and 11B. The pattern dimension CD in each proximity effect density U(x) is read for each position of the pattern dimension map 940. First, as shown in FIG. 11A, a set of the proximity effect correction coefficient η and the base dose Dbase that generates the pattern dimension CD in the proximity effect density U(x)=0.5 to be the reference proximity effect density is assumed. Next, the absolute value Δ0 of a difference between the dimensional error ΔCD0 of the pattern dimension defined in the pattern dimension map 940 when the proximity effect density U(x)=0 from the pattern dimension when U(x)=0.5 and the pattern dimension fluctuation amount δ0 when written with the dose D obtained for the relevant set when the proximity effect density U(x)=0 is calculated. The absolute value Δ0 becomes a correction residue when the proximity effect density U(x)=0. Similarly, the absolute value Δ100 of a difference between the dimensional error ΔCD100 of the pattern dimension defined in the pattern dimension map 940 when the proximity effect density U(x)=1 from the pattern dimension when U(x)=0.5 and the pattern dimension fluctuation amount δ100 when written with the dose D obtained for the relevant set when the proximity effect density U(x)=1 is calculated. The absolute value Δ100 becomes a correction residue when the proximity effect density U(x)=1. Then, as shown in Formula (3) above, both terms are added. Then, as shown in FIG. 11B, the selection unit 910 selects a set of the proximity effect correction coefficient η and the base dose Dbase that minimizes Δerr shown in Formula (3) for each distribution position of the pattern dimension map 940 by referring to the correction parameters 930. In other words, the selection unit 910 selects a set of the proximity effect correction coefficient η and the base dose Dbase that makes a correction residue smaller. Then, as the proximity effect correction coefficient η/base dose Dbase map creation process (S9122), the proximity effect correction coefficient η/base dose Dbase map creation unit 912 creates a proximity effect correction coefficient η map and a base dose Dbase map depending on each distribution position of the pattern dimension map 940 by using the set of the proximity effect correction coefficient η and a base dose Dbase selected for each position. Here, the proximity effect correction coefficient η/base dose Dbase map creation unit 912 creates both of the proximity effect correction coefficient map and base dose map, but the creation function may be divided into a proximity effect correction coefficient η map creation unit and a base dose Dbase map creation unit. With the above configuration, the proximity effect correction coefficient η map and the base dose Dbase map capable of correcting entire dimensional fluctuations based on a plurality of phenomena such as dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching without distinguishing the phenomena can be created from the pattern dimension map for each proximity effect density U(x). Then, the proximity effect can also be corrected at the same time for the proximity effect density U(x)=0.5. However, the correction residue remains for the proximity effect density U(x) other than 0.5 and thus, a correction term is provided as described below. A conceptual diagram for explaining the technique to calculate a correction term in the fourth embodiment is like in FIGS. 12A and 12B. In FIG. 12A, the vertical axis of the graph represents the correction residue Δ and the horizontal axis represents the proximity effect density U(x). In FIG. 12B, the vertical axis of the graph represents the correction term Dcorr and the horizontal axis represents the proximity effect density U(x). First, as the correction residue fitting process (S9124), as shown in FIG. 12A, the correction residue fitting processing unit 914 calculates an approximate expression by fitting the correction residue Δ for each proximity effect density U(x) using a predetermined function. Then, as the correction term calculation process (S9126), the correction term calculation unit 916 calculates the correction term Dcorr that corrects the correction residue Δ depending on the proximity effect density U(x) for each map position. Here, the function of the correction term Dcorr may be set so that the correction residue Δ depending on the proximity effect density U(x) obtained from the approximate expression created in the correction residue fitting process (S9124) is corrected. As the dose calculating process (S9128), the dose calculating unit 918 calculates the dose D by using the selected set of the proximity effect correction coefficient η and the base dose Dbase and the correction term Dcorr for each map position. The dose D is defined by the above Formula (4). As shown in Formula (4), the dose D(x, U) in the fourth embodiment can be defined by a formula that multiplies a product of the base dose Dbase (x) and the proximity effect-corrected dose Dp(η(x), U(x)) depending on the proximity effect correction coefficient η(x) and the proximity effect density U(x) further by the correction term Dcorr(x, U(x)) depending on the position x and the proximity effect density U(x). By calculating the dose D as described above, entire dimensional fluctuations based on a plurality of phenomena such as dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching can be corrected without distinguishing the phenomena while also correcting the proximity effect. The dose calculating unit 918 can suitably calculate a value obtained by further multiplying the dose D(x, U) calculated by using the selected set of the proximity effect correction coefficient η (x) and the base dose Dbase and the correction term Dcorr by a correction coefficient of the fogging effect defined for each map position to use the result thereof as the dose D(x, U). As the beam irradiation time calculating process (S9130), the beam irradiation time calculating unit 920 calculates the beam irradiation time T of the electron beam 200 in each position of the write region. The dose D can be defined as a product of the beam irradiation time T and the current density J and thus, the beam irradiation time T can be determined by dividing the dose D by the current density J. The calculated beam irradiation time is output to the deflection control circuit 120. As the writing process (S9132), the pattern writing unit 150 writes a desired pattern on the target object 101 by using the electron beam 200 of the dose obtained for each map position. A more concrete operation will be described below. The deflection control circuit 120 outputs a digital signal to control the beam irradiation time for each shot to the DAC amplification unit 130. Then, the DAC amplification unit 130 converts the digital signal into an analog signal and amplifies the analog signal, which is then applied to the blanking deflector 212 as a deflection voltage. The electron beam 200 emitted from the electron gun assembly 201 (discharge unit) is controlled to pass through the blanking aperture plate 214 by the blanking deflector 212 when passing through the blanking deflector 212 in a beam ON state and controlled to be deflected so that the whole beam is blocked by the blanking aperture plate 214 in a beam OFF state. The electron beam 200 having passed through the blanking aperture plate 214 during a time from the beam OFF state to the beam ON state and back to the beam OFF state becomes an electron beam for one shot. The blanking deflector 212 alternately generates the beam ON state and the beam OFF state by controlling the orientation of the passing electron beam 200. For example, no voltage may be applied for the beam ON state and a voltage may be applied to the blanking deflector 212 for the beam OFF state. The dose of the electron beam 200 per shot shone on the target object 101 is adjusted by the beam irradiation time T of each of such shots. The electron beam 200 of each shot generated by being passed through the blanking deflector 212 and the blanking aperture plate 214 illuminates the whole first shaping aperture plate 203 having an oblong, for example, rectangular hole through the illumination lens 202. Here, the electron beam 200 is first formed into an oblong, for example, a rectangular shape. Then, the electron beam 200 of a first aperture image having passed through the first shaping aperture plate 203 is projected onto the second shaping aperture plate 206 through the projection lens 204. The first aperture image is controlled to deflect by the deflector 205 on the second shaping aperture plate 206 so that the beam shape and dimensions thereof can be changed (variably shaped). Such variable shaping is performed for each shot and a different beam shape and dimensions are formed for each normal shot. Then, the electron beam 200 of a second aperture image having passed through the second shaping aperture plate 206 is focused by the objective lens 207 and deflected by the deflector 208 before being shone onto a desired position of the target object arranged on the continuously moving XY stage 105. Thus, a plurality of shots of the electron beam 200 is successively deflected onto the target object 101 to be a substrate by each deflector. According to the fourth embodiment, as described above, dimensional fluctuations based on a plurality of phenomena can be corrected together. The dimension map for each proximity effect density is directly input for processing and thus, it is not necessary to, like in a conventional method, assign the correction width for each phenomenon from the user side. A case where it is necessary to correct η such as changing η for each of a plurality of phenomena according to a conventional method can also be handled. Furthermore, correction precision can be improved by introducing the correction term depending on the proximity effect density. According to the fourth embodiment, as described above, the proximity effect correction coefficient and the base dose can be selected without being bound by proximity effect correction conditions. Then, dimension corrections can be made regardless of phenomena of dimensional fluctuations. According to the fourth embodiment, as described above, entire dimensional fluctuations based on a plurality of phenomena such as dimensional fluctuations caused by the loading effect during development and dimensional fluctuations caused by the loading effect during etching can be corrected without distinguishing the phenomena while also correcting the proximity effect. A diagram showing an example of the dose correction in the fourth embodiment is like in FIGS. 13A to 13C. FIG. 13A shows a case where the dimensional error ΔCD0 of the pattern dimension defined in the pattern dimension map 940 when the proximity effect density U(x)=0, 1 from the pattern dimension when U(x)=0.5 is, for example, 1 nm and ΔCD100 is, for example, −1 nm. FIG. 13C shows an example in such a case of the correlation between the pattern dimension CD and the proximity effect correction coefficient η. In the example of the correlation in FIG. 13C, the proximity effect correction coefficient η that generates δ0=1 and δ100=−1 is present. In this example, as shown in FIG. 13B, dimensional errors can be corrected without generating any correction residue by selecting the above proximity effect correction coefficient η. Thus, the correction term Dcorr=1 can be set. A diagram showing another example of the dose correction in the fourth embodiment is like in FIGS. 14A to 14C. FIG. 14A shows a case where the dimensional error ΔCD0 of the pattern dimension defined in the pattern dimension map 940 when the proximity effect density U(x)=0, 1 from the pattern dimension when U(x)=0.5 is, for example, 1 nm and ΔCD100 is, for example, 0 nm. In such a case, the proximity effect correction coefficient η that generates δ0=1 and δ100=0 is not present in the example of the correlation in FIG. 14C. Thus, as shown in FIG. 14B, for example, the proximity effect correction coefficient η that generates the correction residue of −0.5 nm for both is selected. By making such selection, a respective correction to some extent can be made, though not complete, when the proximity effect density U(x)=0, 1. In the fourth embodiment, the correction residue can also be corrected by using the correction term Dcorr. A diagram showing still another example of the dose correction in the fourth embodiment is like in FIGS. 15A and 15B. FIG. 15A shows a case where the dimensional error ΔCD0 of the pattern dimension defined in the pattern dimension map 940 when the proximity effect density U(x)=0, 1 from the pattern dimension when U(x)=0.5 is, for example, 1 nm and ΔCD100 is, for example, 1 nm. In such a case, the proximity effect correction coefficient η that generates δ0=1 and δ100=1 is not present in the example of the correlation in FIG. 15B. Dimensional fluctuations when the proximity effect density U(x)=0, 1 act in the direction of the opposite side and thus, it is difficult to correct both at the same time according to a conventional method. According to the fourth embodiment, by contrast, corrections can be made also in such a case by using the correction term Dcorr. In the foregoing, the embodiments have been described with reference to concrete examples. However, the present invention is not limited to such concrete examples. Although parts such as an apparatus configuration and a control method which are not directly required for the explanation of the present invention have not been described, a required apparatus configuration or a required control method can be appropriately selected and used. For example, although the configuration of a control unit which controls the writing apparatus 100 has not been described, a required control unit configuration can be appropriately selected and used as a matter of course. In addition, all charged particle beam writing apparatuses and writing methods which include the elements of the present invention and can be attained by appropriate change in design by a person skilled in the art are included in the spirit and scope of the invention. Additional advantages and modification 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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054066050 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Described herein is an existing analytical tag design approach which is employed in carrying out a portion of the method for designing gas tag compositions of the present invention. The first step of the design procedure is to compute a set of geometric cosines, .mu..sub.i, with the equation ##EQU1## Equation (1) is derived from angular quadrature relationships used in discrete-ordinates approximations to the neutron transport equation..sup.1 Here, N.sub.I, the number of cosines in the positive .mu. direction, is the subscript of the commonly used S.sub.n discrete-ordinates scheme. Use of Eq. (1) ensures that the resulting system of tag nodes will possess complete symmetry with respect to the origin, and that the distances between each node and all of its closest neighbors are equalized as nearly as possible. FNT B. G. CARLSON and K. D. LATHROP, in Computing Methods in Reactor Physics, p. 171, H. GREENSPAN, C. N. KELBER, and D. OKRENT, Eds., Gordon and Breach, Science Publishers, Inc., New York (1968). Using the set of .mu..sub.i generated by Eq. (1), the locations of the tag nodes for the inner sphere are determined from ##EQU2## where (X.sup.n, Y.sup.n, Z.sup.n).sub.I are the coordinates of tag node n on the surface of the inner sphere, and R.sub.I is the radius of the inner sphere. Note that as indices i and j vary from 1 to N.sub.I and from 1 to (N.sub.I -i+1), respectively, n varies from 1 to M.sub.I, where M.sub.I, the total number of nodes on the inner sphere, is equal to 4N.sub.I (N.sub.I +1). After M.sub.I nodes are specified for the inner sphere, M.sub.0 node locations are computed with the same equation for the outer sphere. The geometry of the resulting node arrangement is illustrated graphically in FIG. 1, which depicts a few nodes from the positive octants of each sphere. The relationship between the radii of the inner and outer spheres is given by ##EQU3## Use of Eq. 3 together with Eqs. (1) and (2) will minimize the overall cost of the system of tags. In general, the more spread out the system of tags becomes in tag-ratio space, the greater the enrichment requirements and, hence, the greater the overall costs for the noble gases used to create the tags. Use of Eq. (3) ensures that the system of tags will be packed as efficiently as possible into a given volume of ratio space. The last independent variable, R.sub.I, is determined by expanding the system of nodes isotropically about the (common) origin of the two spheres until the closest distance between any two nodes is greater than a minimum separation distance, .tau., thereby ensuring the ability to unambiguously identify single-element failures. The value of .tau. is left as an input variable and can be adjusted to allow for experimental uncertainties in the mass-spectrometer system used for the isotopic analyses, uncertainties associated with blending the tags, and, depending on the gases used, uncertainties in neutron burnout of the constituent isotopes..sup.2 FNT .sup.2 Recent isotopic burnout correlations used at EBR-II are described in J. D. B. LAMBERT, B. Y. C. SO, F. S. KIRN,J. R. ARMSTRONG; E. R. EBERSOLE, and M. T. LAUG, "Recent Improvements in Identifying Fission Product Sources in the Experimental Breeder Reactor II," Nucl. Technol., 39, 275 (1978). The final step of the node-design procedure is systematic elimination of certain points that violate either of the following analytical constraints: 1. No four nodes in the system may lie in the same plane unless that plane is parallel to one of the three coordinate planes. PA1 2. No tag node on the inner sphere can fall on a straight line connecting any two other tag nodes. Constraint 1 ensures that the system of tags is amenable to a recently devised multiple-failure-analysis technique..sup.3 Constraint 2 ensures that single-assembly failures cannot be confused with double-assembly failures. FNT .sup.3 K. C. GROSS, C. PASSERELLO, and A. SHAPIRO, "Barycentric Coordinates Technique for Resolution of Multiple Fuel Failures with Gas Tagging," Trans. Am. Nucl. Soc., 27,685 (1977). If the number of tags remaining after elimination is less than the total number of tags required for the given reactor, then N.sub.I and/or N.sub.0 are increased, and the procedure is repeated. When the required number of tag nodes is obtained, the entire system is translated rectilinearly to the positive octant of the Cartesian ratio space. The values of the component compositions for each node are then normalized appropriately so that the maximum value in each direction is spaced sufficiently far away from the corresponding background isotopic compositions. Unfortunately, the locations of the tag nodes specified with an analytical design such as this concentric sphere design are not precise points in composition space as discussed above. This "movement" arises from experimental variations in the tag cylinder filling process and may result in erroneous failed assembly identification and removal from the reactor's core of the wrong fuel assemblies. Although it is impossible to totally eliminate the source of all inaccuracies in the tag blending procedure, the present invention provides a method for designing gas tag compositions which substantially reduces the possibility of misidentification of leaking fuel assemblies particularly in the case of multiple leaking fuel assemblies. In accordance with the present invention, the present method for designing gas tag compositions solves the problem endemic to prior art approaches not by eliminating experimental uncertainties, but by accepting and accommodating these uncertainties with an iterative genetic algorithm approach that is run during the blending procedure. In prior art approaches, the node-design method (such as the concentric sphere method described above) would produce a table of all the target compositions for every required tag node. These target compositions would then be used to guide the gas blending operation. Unavoidable experimental uncertainties would result in small discrepancies between the target compositions and the measured final compositions. The inventive method disclosed herein starts with a table of target compositions as in earlier approaches and uses the first target composition to blend the first canister of tag gas. When that canister of tag gas is produced, its final composition is measured accurately with a mass spectrometer. This measured composition is now used as the "true" location of node #1, and nodes 2, 3 . . . , NTAG (where NTAG is the total number of tags in the system) are adjusted using a genetic algorithm approach described in the following paragraphs. Genetic algorithms are used in the analysis of complex phenomena and are derived from a simple heuristic assumption: that optimal solutions are located in regions of the search space containing relatively high numbers of good solutions, and that these solutions can be found by judicious sampling of the space. Genetic algorithms are further based upon two key axioms: (1) that non-biological structures may be described by simple bit strings and (2) that these structures may be improved by the application of simple transformations to these strings. A genetic algorithm controls the representation and alteration of such strings in order to evolve well-adapted solutions to the optimization problem under consideration. The basic approach undertaken in and operation of genetic algorithms is described in Advances in Nuclear Science and Technology, Vol. 21, J. Lewins and M. Becker (editors), Plenum Press, New York, New York (1990). Referring to FIG. 4, there is shown a flow chart illustrating the sequence of steps in carrying out the method for designing gas tag compositions of the present invention. In FIG. 4, an oval symbol indicates the start of an operational sequence, a rectangle indicates an instruction or set of instructions resulting in the performance of a control function, and a hexagon indicates a decision based upon the comparison of binary signals within a microprocessor controller which is described below. At step 76, the operation of a program stored in a microprocessor controller for designing gas tag compositions is initiated. At step 78, the microprocessor controller is initialized by resetting its control flags to an initial set of conditions whereupon the microprocessor controller is ready for controlling apparatus for manufacturing gas tags, which apparatus is described in detail below. At step 80, the program in the microprocessor controller perturbs all node positions on the inner and outer tag spheres described above in a random direction. The random direction selected is constrained in that the node does not leave the surface of the sphere on which it resides. The program next, at step 82, then computes a distance parameter, d(I), for each node on the inner sphere, where d(I) is the minimum distance to any tie-line connecting other nodes in the system. The distance d(I) is the shortest distance between a node and a tie line connecting any two other nodes, with the goal being to maximize the distance parameter at a later step in the process. At step 84, the program computes a control parameter D by taking the root-mean-square of all d(I)'s, where ##EQU4## The overall objective of the inventive method is to maximize the magnitude of the control parameter D, while adhering to the analytical constraint that the target tag nodes do not leave the surfaces of their respective spheres. The program at step 86 then selects M nodes from the population of remaining nodes that give the highest, or best, values of d(I). The selected M nodes can be on either of the concentric spheres, with d(I) connecting nodes on the inner and outer spheres. Those M nodes which give the highest values of d(I) are termed "parent" nodes and retain their positions in the subsequent generation, or during subsequent steps in the process. The program at step 88 then selects N nodes from the population of remaining nodes that give the lowest, or poorest, values of d(I) and these N node positions are marked for "death" and may be disqualified during the subsequent generation. Those nodes are designated as "children nodes". In one embodiment, M=N which simplifies calculations in carrying out the inventive method. The program then proceeds to step 90 to determine if there are any remaining nodes. If there are no remaining nodes, the program proceeds to step 92 and ends. If, at step 90, it is determined that there are remaining nodes present, the program proceeds to step 94 and holds the parent nodes fixed, while producing "mutated" children nodes by perturbing all non-parent node positions and reevaluating the new d(I) values. The new d(I) values for the mutated children nodes are recomputed at step 96 with the value of the first (J=1) remaining node determined at step 98. From step 98, the program proceeds to step 100 to determine if the J node has been marked for death. If the J node has not been marked for death, the program branches to step 84 and again computes the control parameter D of all d(I)'s. If at step 100 it is determined that the J node has been marked for death, the program, at step 102, determines whether the position of the node has improved compared to its position two generations ago. If at step 100 it is determined that the node's position has not improved as compared to its position two generations ago, the program branches to step 104 and returns the node to its original position it had two generations ago, followed by an incrementing by one of the value of J to the next node at step 106. The program then determines, at step 108, if J+1 is equal to the number of nodes remaining, or to the number of nodes which have not yet been fixed in position. If J+1 equals the number of remaining nodes, the program branches to step 84 for again computing the control parameter D for all nodes. If at step 108 it is determined that J+1 does not equal the number of nodes remaining, the program branches to step 100 to determine if the J+1 node has been marked for death. If at step 102 it is determined that the J+1 node's position has improved compared to its position two generations ago, the program branches to step 110 and fixes the position of the node at its new location. The program then increments J by one at step 112 and at step 114 determines whether the J+1 node is equal to the number of remaining nodes. If J+1 is equal to the number of remaining nodes, the program branches to step 84 and again computes the control parameter D for all nodes. If at step 114 it is determined that J+1 is not equal to the number of nodes remaining, the program branches to step 100 and determines whether the J+1 node has been marked for death. The program then proceeds as previously described. Referring to FIG. 5, there is shown a simplified schematic and block diagram of a tag gas blending system 30 for designing gas tag compositions in accordance with the method of the present invention. The present invention is not limited to use with the gas tag blending system 30 of FIG. 5, but can be used with virtually any conventional gas tag blending system. The gas tag blending system 30 of FIG. 5 is disclosed and claimed in co-pending application, Ser. No. 08/174,146, filed Dec. 28, 1993, and assigned to the assignee of the present application, the disclosure of which is hereby incorporated by reference in the present application. Tag gas blending system 30 includes a tag blending manifold 32, a vacuum system 34 and a microprocessor-based controller 36. Tag blending manifold 32 includes a stainless steel manifold 42 to which are coupled a plurality of filling gas cylinders, or canisters, 40. Each of the filling gas cylinders 40 is coupled to the tag blending manifold 32 by means of a respective microprocessor-controlled valve 38. Each of the valves 38 is coupled to and controlled by microprocessor controller 36 for opening and closing each of the individual valves and connecting its associated gas cylinder 40 to manifold 42. Microprocessor controller 36 is coupled to the tag blending manifold 32 by means of a first control/communication bus 54 by means of which control signals are provided from the microprocessor controller to each of the valves 38 and also by means of which status signals relating to each of the valves is provided to the microprocessor controller. Each of the filling gas cylinders 40 contains a feed gas having a specified composition. Manifold 32 couples each of the filling gas cylinders 40 to a blended tag canister 46 for filling the blended tag canister with metered quantities of each of the feed gases in the filling gas cylinders 40. The metering is accomplished by means of microprocessor controller 36 which also is coupled to a tag gas canister valve 52 to allow for introduction into the blended tag gas canister 46 of the required feed gases to provide a tag gas having a designated composition. Vacuum system 34 is coupled by means of a vacuum line 48 to manifold 42 within the tag blending manifold 32. A first pressure transducer 44 is coupled to manifold 42 in the tag blending manifold 32, while a second pressure transducer 50 is coupled to vacuum line 48 within vacuum system 34. Vacuum system 34 is further coupled to controller 36 by means of a second control/communication bus 56. Microprocessor controller 36 controls the operation of vacuum system 34 in forming a vacuum within manifold 42 for drawing various of the feed gases within the filling gas cylinders 40 into the blended tag canister 46. Two pumps 34a and 34b are shown in the vacuum system 34 for drawing feed gases from the filling gas cylinders 40 into the blended tag canister 46 via manifold 42. In a typical tag gas blending system, X tag isotopes for Y distinct feed gas mixtures commercially available from an enriched gas supplier are used to fill blended tag canister 46 with a tag gas having a designated composition. The procedure typically involves opening one of the valves connected to one of the filling gas cylinders, drawing off a predetermined amount of feed gas, closing the valve to the filling gas cylinder as well as the valve to the blended tag canister, and purging the gas line before introducing another feed gas to the blended tag canister in forming the tag gas blend. Microprocessor controller 36 includes a ROM 60, a clock 64, an accumulator (ACC) 68, a controller 62 and an arithmetic and logic unit (ALU) 66. Microprocessor controller 36 stores instructions and data, periodically updates the stored data, compares both stored and real-time data and makes decisions based upon these comparisons by means of logic instructions in providing control for the tag gas blending system 30. An oscillator circuit 70 external to the microprocessor controller 36 provides timing signals to clock 64 for controlling the timing of operations carried out by the microprocessor controller. Program instructions and data and the sequence of steps carried out under the control of microprocessor controller 36 are illustrated in FIG. 4 and described in detail above. There has thus been shown an improved method for designing gas tagging compositions for use in identification of failed fuel assemblies in a nuclear reactor. The inventive method employs an analytical approach wherein the final composition of a first canister of tag gas as measured by a spectrometer is designated as node #1. Lattice locations of tag nodes in multi-dimensional space are then used in calculating the compositions of a node #2 and each subsequent node so as to maximize the distance of each node from any combination of tag components which might be indistinguishable from another tag composition in a reactor fuel assembly. This is accomplished by employing a genetic algorithm which improves the gene pool with time as undesirable mutated children nodes are eliminated from consideration. The method employs a sequential approach wherein the measured compositions of tag gas numbers 1 and 2 are used to fix the locations of nodes 1 and 2, with the locations of nodes 3-N then calculated for optimum tag gas composition. The geometric space representing inter-nodal spacing is in the form of one or more concentric spheres defining lattice locations of the tag nodes. While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art. |
abstract | A method for measuring the drop time of a rod in nuclear reactor with the rod position indication system coils remaining energized. The signal generated at the coils includes both the rod drop trace and the coil power. A filter is applied to separate the rod drop trace from the coil power. The drop time of all rods in a reactor can be measured simultaneously in a single test. Furthermore, the test data results are plotted automatically with plot overlay capability to compare rod drop traces to the results of previous tests or to compare an individual rod to another within the same test. |
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claims | 1. A charged particle system, comprising:a charged particle column for focusing a primary charged particle beam onto the surface of a target, wherein the impact of the charged particle beam with the target induces emission of secondary particles from the target;a charged particle detector assembly including:a detector for producing an electrical signal corresponding to the number of charged particles impacting the detector;at least one grid, positioned between the charged particle detector and the surface of the target for causing charged particles to move from the target to the detector; anda source of a field that deflects the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector by spreading the impinging particles more evenly over the detector, thereby prolonging the useful life of the charged particle detector. 2. The charged particle system of claim 1 wherein:the at least one grid comprises at least two grids; andthe source of the field that deflects the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector comprises different potentials on the different ones of the at least two grids. 3. The charged particle system of claim 1 wherein:the at least one grid comprises at least one resistive grid; andthe source of the field that deflects the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector comprises different potentials on the different parts of the at least one resistive grid. 4. The charged particle system of claim 1 wherein the source of the field that deflects the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector comprises deflector electrodes positioned between the at least one grid and the target. 5. The charged particle system of claim 1 wherein the source of the field that deflects the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector comprises a source of a field that deflects the secondary charged particles away from the axis of the charged particle column. 6. The charged particle system of claim 1 wherein the charged particle detector comprises a multichannel plate and a collection anode; a PIN diode; or a scintillator-photomultiplier with a light optical coupling means positioned between the scintillator and the photomultiplier, configured to transmit light emitted by the scintillator into the photomultiplier. 7. The charged particle system of claim 1 wherein the charged particle beam is an electron beam or a focused ion beam, and wherein the voltages on the at least one grid and the voltages on the charged particle detector are configured to collect secondary electrons. 8. The charged particle system of claim 1 wherein the charged particle beam is a focused ion beam, and wherein the voltages on the at least one grid and the voltages on the charged particle detector are configured to collect secondary ions. 9. The charged particle system of claim 1 wherein the charged particle beam is a focused ion beam, and wherein the source of the field that deflects the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector is configured to collect secondary ions. 10. The charged particle system of claim 1 in which the source of the field that deflects the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector deflects the secondary particles in a manner that maintains the relative positions of the secondary particles from the optical axis of the column. 11. A method of reducing the rate of damage or contamination in a secondary particle detector in a charged particle system, comprising:providing a charged particle column to focus a charged particle beam onto the surface of a target, wherein the impact of the charged particle beam with the target induces the emission of secondary particles from the target;providing a secondary particle detector to collect a portion of the secondary particles emitted from the target;providing a field to deflect the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector by spreading the impinging particles more evenly over the detector, thereby prolonging the useful life of the charged particle detector. 12. The method of claim 11 further comprising providing at least one grid to accelerate secondary particles from the surface toward the secondary particle detector. 13. The method of claim 12, wherein providing at least one grid includes providing a resistive grid, and further comprising a first voltage to one portion of the resistive grid and a second voltage to a second portion of the resistive grid, wherein the first and second voltages are unequal. 14. The method of claim 12 wherein:providing at least one grid includes providing two grids; andproviding a field to deflect the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector comprises providing different potentials on the different ones of the at least two grids. 15. The method of claim 12 wherein:providing at least one grid includes providing at least one resistive grid; andproviding a field to deflect the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector comprises providing different potentials on the different parts of the at least one resistive grid. 16. The method of claim 12 wherein providing a field to deflect the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector comprises providing deflector electrodes positioned between the at least one grid and the target. 17. The method of claim 11 further in which providing a secondary particle detector includes providing a secondary particle detector between the column and the target. 18. The method of claim 11 wherein providing a field to deflect the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector comprises providing a field that deflects the secondary particles away from the axis of the charged particle column. 19. The method of claim 11 wherein providing a secondary charged particle detector comprises providing a multichannel plate and a collection anode; a PIN diode; or a scintillator-photomultiplier with a light optical coupling means positioned between the scintillator and the photomultiplier, configured to transmit light emitted by the scintillator into the photomultiplier. 20. The method of claim 11 wherein providing a charged particle column includes providing an electron beam or a focused ion beam, and wherein the secondary particle collector collects secondary electrons. 21. The method of claim 11 wherein providing a charged particle column includes providing a focused ion beam, and wherein the secondary particle collector collects secondary ions. 22. A charged particle system, comprising:a charged particle column for focusing a primary charged particle beam onto the surface of a target;a charged particle detector assembly including:a detector for producing an electrical signal corresponding to the number of charged particles impacting the detector;at least one grid, positioned between the charged particle detector and the surface of the target for causing charged particles to move from the target to the detector;a source of a field that deflects the secondary charged particles to reduce the maximum current density of the charged particles impinging on the charged particle detector by spreading the impinging particles more evenly over the detector, thereby prolonging the useful life of the charged particle detector. |
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description | This application claims benefit of U.S. Provisional Application Ser. No. 60/635,639 filed Dec. 13, 2004, incorporated by reference herein. This invention was made with U.S. Government support under Contract No. F04611-03-M-3014 awarded by the Office of the Secretary of Defense (OSD). The Government may have certain rights in the subject invention. This invention relates generally to a Hall thrusters and more particularly to an improved Hall thruster with a shared magnetic structure. Hall Thrusters are typically used in rockets, satellites, spacecraft, and the like. In a typical Hall Thruster the working fluid is plasma and the means of acceleration is an electric field. A Hall thruster typically includes a plasma accelerator that includes a propellant, a gas distributor, and an anode located at one end of a channel. An electric circuit provides an electric potential that is applied between the anode and a floating externally located cathode that emits electrons. A magnetic circuit structure typically includes an outer pole, an inner pole, and a plurality of outer magnetic field sources, e.g., electromagnetic coils or permanent magnets, for the outer pole and an inner magnetic field source for the inner pole. The magnetic circuit structure establishes a transverse magnetic field between the outer pole and the inner pole that presents an impedance to electrons attracted to the anode. As a result, the electrons spend most of their time drifting azimuthally (orthogonally) due to the transverse magnetic field. This allows the electrons time to collide with and ionize the neutral atoms. The collisions create positively charged ions that are accelerated by the electric field to create thrust. See e.g., U.S. Pat. Nos. 6,150,764; 6,078,321; 6,834,492 by one or more common inventors hereof, all incorporated in their entity by reference herein. When a plurality of conventional Hall thrusters are arranged in close proximity to each other to power a spacecraft or similar vehicle, each plasma accelerator of each thruster requires its own magnetic circuit structure that typically includes a plurality of outer magnetic field sources for the outer pole and an inner magnetic field source for the inner pole. Each thruster also includes its own power processing unit (PPU) that provides power for the magnetic circuit structure and the electric circuit. Such a design suffers from excessive weight, volume and power, is complex, expensive, and inefficient. It is therefore an object of this invention to provide an improved Hall thruster with a shared magnetic structure. It is a further object of this invention to provide such a Hall thruster which can share one or more magnetic circuit structures with a plurality of plasma accelerators. It is a further object of this invention to provide such a Hall thruster which reduces the number of magnetic field sources needed for a plurality of plasma accelerators. It is a further object of this invention to provide such a Hall thruster which reduces the weight. It is a further object of this invention to provide such a Hall thruster which can share a single power processing unit with a plurality of plasma accelerators. It is a further object of this invention to provide such a Hall thruster which reduces the volume. It is a further object of this invention to provide such a Hall thruster which saves power. It is a further object of this invention to provide such a Hall thruster which provides for steering of the Hall thruster. It is a further object of this invention to provide such a provides for attitude control of the Hall thruster. It is a further object of this invention to provide such a Hall thruster which provides for throttle adjustment of the Hall thruster. It is a further object of this invention to provide such a Hall thruster is less complex. It is a further object of this invention to provide such a Hall thruster which is less expensive. It is a further object of this invention to provide such a Hall thruster which is more efficient. The invention results from the realization that an improved Hall thruster that can share one or more magnetic circuit structures with a plurality of plasmas accelerators to reduce the weight, volume, and power requirements of the Hall thruster and also provide for steering, attitude control and throttle adjustment is effected with a plurality of plasma accelerators that each include an anode and a discharge chamber to provide plasma discharge, an electrical circuit that includes at least one cathode connected to the plurality of plasma accelerators that emit electrons that are attracted to the anode in each of the plasma accelerators, and a shared magnetic circuit structure that establishes a transverse magnetic field in each of the plasma accelerators which presents an impedance to the flow of electrons towards the anode in each of the plurality of plasma accelerators and enables ionization of a gas moving through one or more of the plurality of plasma accelerators and which creates an axial electric field in each of the plurality of plasma accelerators for accelerating ionized gas through one or more of the plurality of accelerators to create thrust. The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. This invention features a Hall thruster with a shared magnetic structure including a plurality of plasma accelerators each including an anode and a discharge zone for plasma discharge occurs in the presence of imposed electric and magnetic field. An electrical circuit having one or more cathodes connected to the plurality of plasma accelerators that emit electrons that are attracted to the anode in each of the plasma accelerators. A shared magnetic circuit structure establishes a transverse magnetic field in each of the plurality of plasma accelerators that creates an impedance to the flow of electrons toward the anode in each of the plurality of plasma accelerators and enables ionization of a gas moving through one or more of the plurality of plasma accelerators. The impedance localizes an axial electric field in the plurality of plasma accelerators for accelerating ionized gas through the one or more of the plurality of plasma accelerators to create thrust. In one embodiment, the shared magnetic circuit structure may include at least one magnetic field source for creating the transverse magnetic field in each of the plurality of plasma accelerators. The at least one magnetic field source may include a magnetic field source chosen from the group consisting of an electromagnetic coil and a permanent magnet. The shared magnetic circuit structure may include a selected combination of the at least one magnetic field source. The shared magnetic circuit structure may include an outer pole and an inner pole for each of the plurality of plasma accelerators. The shared magnetic circuit structure may include a magnetic material interconnecting the outer pole and the inner pole. The shared magnetic circuit structure may include at least one shared magnetic path for establishing the transverse magnetic field in each of the plurality of plasma accelerators. The shared magnetic circuit structure may carry magnetic flux between the inner pole and the shared outer pole and through the magnetic material and the shared magnetic path. The shared magnetic path may include at least one magnetic field source chosen from the group consisting of an electromagnetic coil and a permanent magnet. The shared magnetic path may include a selected combination of the at least one magnetic field source. The Hall thruster may further include a plurality of shared magnetic paths for establishing the transverse magnetic field in each of the plurality of plasma accelerators. The plurality of shared magnetic cores each may include one or more magnetic field sources chosen from the group consisting of an electromagnetic coil and a permanent magnet. The plurality of magnetic paths may include a selected combination of the one or more magnetic field sources. The Hall thruster may further include a plurality of cathodes. The plurality of plasma accelerators may be selectively enabled for steering and attitude control of the Hall thruster. The shared magnetic path may reduce the number of the one or more magnetic sources required to achieve a predetermined transverse magnetic field in each of the plurality of plasma accelerators. The reduced number of the one or more magnetic field sources may decrease the weight and volume of the Hall thruster. The plurality of plasma accelerators may include one or more inner plasma accelerators and one or more outer plasma accelerators arranged concentrically. The shared magnetic path may provide an outer pole for the one or more inner plasma accelerators and an inner pole for the one or more outer plasma accelerators that establish the transverse magnetic field in each of the concentrically arranged plasma accelerators. The inner pole may be racetrack shaped. The inner pole and the outer pole may define a racetrack shaped plasma gap. The inner pole and the outer pole may be linearly shaped to define at least one linearly shaped plasma gap. The shared magnetic path may include a plurality of branches that provide the inner pole for each of the plurality of plasma accelerators. The plurality of branches may be arranged relative to each other in a configuration chosen from the group consisting of: an orthogonal configuration, an angle configuration, a parallel configuration, and an opposite configuration. The plurality of plasma accelerators may be arranged relative to each other in a configuration chosen from the group consisting of an orthogonal configuration, an angle configuration, a parallel configuration, and an opposite configuration. At least one of the plurality of plasma accelerators may be selectively enabled for steering and attitude control of the Hall thruster. The Hall thruster may further include one or more shared power processing units for providing power to the electrical circuit and the shared magnetic circuit structure. The gas may be selectively provided to at least one of the plurality of plasma accelerators to create the thrust. Selectively providing the gas to the one or more of the plurality of plasma accelerators may be used for throttling, steering, and attitude control of the Hall thruster. This invention also features a Hall thruster with shared magnetic structure including a plurality of plasma accelerators that each provide a plasma discharge. A magnetic circuit structure including a shared magnetic core establishes a transverse magnetic field in each of the plurality of plasma accelerators to control the plasma discharge from each of the plurality of plasma accelerators. A plasma discharge circuit in each of the plurality of plasma accelerators creates a plasma and accelerating the plasma to produce thrust. This invention also features a Hall thruster cluster with shared magnetic structure including a plurality of plasma accelerators that each provide a plasma discharge, a magnetic circuit structure including a shared outer pole and an inner pole for each of the plurality of plasma accelerators and a shared magnetic core for establishing a transverse magnetic field in each of the plurality of plasma accelerators to control the plasma discharge from each of the plurality of plasma accelerators, and a plasma discharge circuit in each of the plurality of plasma accelerators for creating a plasma and accelerating the plasma to produce thrust. Although specific features of this invention are shown in some drawings and not others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. A typical conventional Hall effect thruster 20, FIG. 1, includes plasma accelerator 21 with discharge chamber 24, anode 30 and propellant distributor 31 in discharge chamber 24 with transverse magnetic field 36 and axial electric field 38. Propellant 22, e.g., xenon or similar gas, is introduced through propellant distributor 31 into discharge chamber 24. Thruster 20 also typically includes externally located cathode 26 which emits electrons 28, 29, and 31. Anode 30 located within the discharge chamber 24, attracts the electrons 28-31 emitted from cathode 26. Electric circuit 32 creates the axial electric field 38 and magnetic field source 33, e.g., an electromagnetic coil attached to magnetic structure 34 creates transverse magnetic field 36. Transverse magnetic field 36 provides an impedance to the flow of electrons 28-31 toward anode 30 which forces the electrons to travel in a helical fashion about the magnetic field lines associated with magnetic field 36, as shown at 42, FIG. 2. When the electrons trapped by magnetic field 36 collide with propellant atoms, e.g., atom 23, they create positively charged ions. The positively charged ions are rapidly expelled from discharge chamber 24 due to axial electric field 38, indicated at 46, to generate thrust. For example, when electron 33 on magnetic field line 36 collides with propellant or gas atom 23, indicated at 35, the collision strips one of the electrons, e.g., electron 44 from propellant atom 23, to create positively charged ion 45 which is expelled from discharge chamber 24 by axial electric field 38 to generate thrust. Conventional Hall thruster 60, FIG. 3, includes a plasma accelerator 62 with anode/discharge chamber 63. Cathode 64 emits electrons 80 that are attracted to anode/discharge chamber 63. Thruster 60 also includes magnetic circuit structure 66 including inner pole 68 and outer pole 69. Outer magnetic field sources 70, 72, 74 and 76, and inner magnetic field source 77, e.g., electromagnetic coils or permanent magnets, create transverse magnetic field 78 between inner pole 68 and outer pole 69 that creates an impedance to the flow of electrons 80 emitted from cathode 64 towards anode/discharge chamber 63, similar to that described above. When a plurality of conventional Hall thrusters are arranged in close proximity to each other, each plasma accelerator requires its own magnetic circuit structure having an inner pole and an outer pole, a plurality of outer magnetic field sources for the outer pole, and a magnetic field source for the inner pole. For example, one plasma accelerator would require magnetic circuit structure 66a, FIG. 4, with inner pole 68a and outer pole 69a, outer magnetic field source locations 70a, 72a, 74a and 76a, and inner magnetic field source location 77a. Similarly, the remaining plasma accelerators would each require a magnetic circuit structure, e.g., magnetic circuit structure 66b includes inner pole 68b and outer pole 69b, outer magnetic field sources 70b, 72b, 74b and 76b and inner magnetic field source 77b; and magnetic circuit structure 66c includes inner pole 68c and outer pole 69c, outer magnetic field sources 70c, 72c, 74c and 76c, and inner magnetic field source 77c, and magnetic circuit structure 66d includes inner pole 68d and outer pole 69d, outer magnetic field sources 70d, 72d, 74d and 76d, and inner magnetic field source 77d. Such a design suffers from excessive weight, volume and power requirements of a spacecraft or satellite that utilizes a plurality of Hall thrusters arranged in close proximity. In contrast, Hall thruster 100, FIG. 5, with a shared magnetic circuit structure 120 according to this invention, preferably includes a shared magnetic path, e.g., a magnetic core, that establishes a transverse magnetic field between the inner pole and the outer pole of a plurality of plasma accelerators, e.g., plasma accelerators 102, 104, 106 and 108. The shared magnetic path or core reduces the weight, volume, complexity and power requirements of Hall thruster 100, as discussed below. Hall thruster 100 typically includes plasma accelerators 102, 104, 106 and 108 that provide plasma discharge. Plasma accelerators 102, 104, 106 and 108 each include an anode and a discharge zone, e.g., anode/discharge chambers 112, 114, 116, and 118, respectively. Electric circuit 99 includes one or more cathodes, e.g., cathode 110 connected to plurality of plasma accelerators 102-108 that emit electrons 113 that are attracted to anode/discharge chambers 112-118. Shared magnetic circuit structure 120 establishes transverse magnetic fields 122, 124, 126 and 128 in plasma accelerators 102, 104, 106, 108, respectively. That creates an impedance to the flow of electrons 113 towards anode/discharge chambers 112-118 and enables ionization of a gas moving through plasma accelerators 102-108. This creates axial electric fields 119, 121, 123, 125 in plasma accelerators 102-108, respectively, for accelerating the ionized gas through one or more of plasma accelerators 102-108 to create thrust, as described above with reference to FIGS. 1 and 2. Shared magnetic circuit structure 120, FIG. 5, preferably includes a shared outer pole and an inner pole for each of plasma accelerators 102-108. For example, shared magnetic circuit structure 120 includes outer pole 140 and inner pole 130 for plasma accelerator 102, and outer pole 142 and inner pole 132 for plasma accelerator 104, outer pole 144 and inner pole 134 for plasma accelerator 106, and outer pole 146 and inner pole 136 for plasma accelerator 108. Shared magnetic circuit structure 120 also includes a magnetic material, e.g., front plate 150, that includes outer poles 140-146 and back plate 152 that interconnects inner poles 130-136. Shared magnetic circuit structure 120 also includes outer magnetic field sources 131, 133, 135, and 137, e.g., a permanent magnet, electromagnetic coil, or superconducting electromagnetic coil, associated with inner poles 130-136 of plasma accelerators 102-108, respectively. Shared magnetic circuit structure 120 also preferably includes shared magnetic path 160, e.g., a magnetic core that is shared by plasma accelerators 102-108. Shared circuit structure 120 with shared magnetic path 160 and magnetic field sources 131-137 establish transverse magnetic fields 122-126 in each of plasma accelerators 102-108. Shared magnetic path 160 is typically configured as a magnetic core made of a magnetic material. Shared magnetic path 160 may also include magnetic field source 162, e.g., an electromagnetic coil, superconducting electromagnetic coil. In other designs, shared magnetic path 160 may be configured as a permanent magnet, such as an Alnico type magnet that includes aluminum, nickel and cobalt, a hard ferrite magnet, a sintered neodymium-iron-boron (NdFeB) magnet, a samarium cobalt (SmCo) magnet, or any similar type magnet. Shared magnetic path 160 may also include any combination of an electromagnetic coil and a permanent magnet. Similarly, magnetic field sources 131-137 may be configured as a permanent magnet as discussed above, an electromagnetic coil, or any combination thereof. Shared magnetic circuit structure 120 carries magnetic flux between inner poles 130-136 and outer poles 140-146 of plasma accelerators 102-108, respectively, through the magnetic material (e.g., front plate 150 and back plate 152) and shared magnetic path 160. For example, shared magnetic circuit structure 120 carries magnetic flux between inner pole 130 and outer pole 140 of plasma accelerator 102 through front plate 150, through shared magnetic path 160, through back plate 152, to inner pole 130, as shown by loop 180. In other examples, shared magnetic circuit structure 120 may carry magnetic flux in a direction opposite to loop 180. The result is that Hall thruster 100 with shared magnetic circuit structure 120 and shared magnetic path 160 significantly reduce the number of magnetic field sources required to create the transverse magnetic fields 122-126 in plasma accelerators 102-108, respectively. For example, as shown in FIG. 4, a typical conventional Hall thruster design that includes four close proximity Hall thrusters with four plasma accelerators and the associated magnetic circuit structures 66a-66d requires at least sixteen (16) outer magnetic field sources, e.g., magnetic field sources 70a-76d, 70b-76d, 70c-76d, and 70d-76d associated with outer poles 69a, 69b, 69c, and 69d, respectively, and four (4) inner magnetic field sources 77a, 77b, 77c, and 77d associated with inner poles 68a, 68b, 68c and 68d, e.g., to create the transverse magnetic fields between inner poles 68a-68d and outer poles 69a-69d, respectively. In contrast, Hall thruster 100, FIG. 5, of this invention, with shared magnetic circuit structure 120 and shared magnetic path 160 requires only four outer magnetic field sources for inner poles 130-136, e.g., magnetic field sources 131, 133, 135, and 137, and one magnetic field source for shared magnetic path 160, e.g., shared magnetic path 160 includes a magnetic field source, e.g., a permanent magnet or electromagnet coil, to establish transverse magnetic fields 122-126 in each of plasma accelerators 102-108. The result is a significant reduction in weight, volume, complexity, power, thermal requirements, and cost of Hall thruster 100. Although as described above with reference to FIG. 5, Hall thruster 100 includes four plasma accelerators and the associate components therewith, this is not a necessary limitation of this invention, as Hall thruster 100 may have any number of plasma accelerators. In other designs, Hall thruster 100 may include a shared magnetic circuit structure 120a, FIG. 6, that includes a plurality of shared magnetic paths 160a, 200, 202, 204, 206, 208, 210 and 212 magnetic shared paths 160a and 200-212 may be a core made of a magnetic material, or a magnetic field sources such as, e.g., permanent magnets or electromagnetic coils as described above. In this example, shared magnetic paths or cores 160a and 200-212 reduce the number of outer magnetic field sources needed to establish the transverse magnetic fields between the inner poles and shared outer poles, e.g., from a total of sixteen as shown in FIG. 4, to a total of nine, as shown in FIG. 6. The result is a significant reduction in weight and volume of shared magnetic circuit structure 120. Hall thruster 100a, FIG. 7, where like parts have been given like numbers, includes shared magnetic circuit structure 120 described above with front plate 150, back plate 152, and assembly 190 made of a magnetic material that interconnects front plate 150 and back plate 152. In this design, Hall thruster 100a includes four cathodes 192, 194, 196 and 198 that emit electrons that are attracted to anode/discharge chambers 112-118 as described above. Any of plasma accelerators 102-108 of Hall thruster 100a may be selectively enabled or disabled for steering and providing attitude control for Hall thruster 100a by selectively enabling gas to any of plasma accelerators 102-108, (discussed below) or selectively powering plasma accelerators 102-108. In other embodiments of this invention, the Hall thruster with a shared magnetic circuit structure may include one or more inner plasma accelerators and one or more outer plasma accelerators concentrically arranged. For example, Hall thruster 100b, FIG. 8, includes inner plasma accelerator 220 and outer plasma accelerator 223. Shared magnetic circuit structure 120a includes shared magnetic path or core 209 that includes outer pole 208 for inner plasma accelerator 220 and inner pole 210 for outer plasma accelerator 222. Inner plasma accelerator 220 includes inner pole 212 and outer plasma accelerator 222 includes outer pole 213. Similar as described above, shared magnetic circuit structure 120a establishes a transverse magnetic field between inner pole 212 and outer pole 208 of plasma accelerator 220 and between inner pole 210 and outer pole 213 of plasma accelerator 223. Although as shown in FIG. 8, Hall thruster 100b includes two plasma accelerators concentrically arranged, this is not a necessary limitation of this invention as Hall thruster 100b may include any number of plasma accelerators concentrically arranged. Any of plasma accelerators 102-108 of Hall thrusters 100, 100a and 100b, FIGS. 5, 7, and 8 discussed above may include a racetrack shaped inner pole and an outer pole that define a racetrack shaped plasma gap. FIG. 9 shows one example of racetrack shaped inner pole 250 and outer pole 252 that define racetrack shaped plasma gap 254. The racetrack shaped plasma accelerator offers scaling advantages. The shared magnetic circuit structure may include an outer pole and inner poles that define slit shaped plasma gaps. For example, shared magnetic circuit structure 120c, FIG. 10 includes inner pole 270 and outer poles 272 and 274 that define slit shaped plasma gaps 276 and 278. Hall thruster 100c, FIG. 11, of this invention with shared magnetic circuit structure 120d includes shared magnetic path 160b, e.g., a magnetic core made of a magnetic material as described above, that includes branches 269, 271 and 273 that provide inner poles 270, 272, and 274 for plasma accelerators 278, 280, and 282, respectively. Shared magnetic circuit structure 120d includes magnetic structure 284 that provides outer pole 286 for plasma accelerator 278, outer pole 290 for plasma accelerator 280, and outer pole 294 for plasma accelerator 282. Similar as described above, plasma accelerator 278 includes anode/discharge chamber 288, plasma accelerator 280 includes anode/discharge chamber 292 and plasma accelerator 282 includes anode/discharge chamber 296. In this example, shared magnetic path 160b includes magnetic field source 300, e.g., an electromagnetic coil 300 that creates transverse magnetic field 301 between inner pole 270 and outer pole 286, transverse magnetic field 302 between inner pole 272 and outer pole 290, and transverse magnetic field 304 between inner pole 274 and outer pole 294. Transverse magnetic fields 301-304 present an impedance to electrons 299 emitted from cathode 303 which is used to create thrust, as described above. In this design, branched shared magnetic path 160b includes poles 270, 272, and 274 that are arranged in a parallel configuration. Shared magnetic path 160b may also be configured as a permanent magnet or a combination of an electromagnetic coil and a permanent magnet. In other embodiments of this invention, Hall thruster 100d, FIG. 12, where like parts have been given like numbers, includes shared magnetic path 160c with inner poles 270, 272 and 274 that are arranged at an angle, e.g., orthogonal, to each other. Plasma accelerators 278a, 280a, and 282a are similarly arranged orthogonal to each other. In this example, magnetic structure 284 is configured as a housing about plasma accelerators 278a-282a. Similar as described above, magnetic circuit structure 120e and shared magnetic path 160c with electromagnetic coil 300 establishes transverse magnetic fields 301, 302, and 304 for plasma accelerators 278a, 280a and 282a, respectively. In operation various plasma accelerators 278a-282a may be selectively enabled for steering and attitude control of thruster 100d. An example of electromagnetic coil 300 is shown in FIG. 13, where like parts have been given like numbers. Hall thruster 100d may also include a shared power processing unit 301, FIG. 14, where like parts have been given like numbers, that provides power to electromagnetic coil 300 and plasma accelerators 278a-282a, as well as the shared magnetic circuit structure and magnetic field sources associated therewith, as described above. Shared power processing unit 301 eliminates the need for a separate power processing unit for each of the plasma accelerators and therefore saves weight and volume and reduces cost. Gas lines 350, 352 and 354, FIG. 13 provide gas to the anode/discharge chambers described above. In operation, the gas provided to any of plasma accelerators 278a-282a can be selectively controlled for throttling and steering Hall thruster 100d. FIG. 15 shows an example of Hall thruster 100d with plasma accelerators 178a-282a that includes and shared cathode 350. Hall thruster 100e, FIG. 16 shows an example in which branched shared magnetic path 160c provides for oppositely oriented plasma accelerators 290, 292, 294 and 296. Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims. In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended. |
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abstract | An improved biomarker generator and a method suitable for efficiently producing short lived radiopharmaceuticals in quantities on the order of a unit dose. The improved biomarker generator includes a particle accelerator and a radiopharmaceutical micro-synthesis system. The micro-accelerator of the improved biomarker generator is optimized for producing radioisotopes useful in synthesizing radiopharmaceuticals in quantities on the order of one unit dose allowing for significant reductions in size, power requirements, and weight when compared to conventional radiopharmaceutical cyclotrons. The radiopharmaceutical micro-synthesis system of the improved biomarker generator is a small volume chemical synthesis system comprising a microreactor and/or a microfluidic chip and optimized for synthesizing the radiopharmaceutical in quantities on the order of one unit dose allowing for significant reductions in the quantity of radioisotope required and the processing time when compared to conventional radiopharmaceutical processing systems. |
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040385531 | summary | BACKGROUND OF THE INVENTION 1. The Field of the Invention This invention relates to apparatus utilized in the construction of enclosures, such as rooms, whose walls preclude the passage of harmful electromagnetic radiation, such as X-rays. 2. Description of the Prior Art The prior art abounds with apparatus useful in the construction of walls impervious to the transmission of X-rays therethrough. U.S. Pat. No. 2,720,105 issued on Oct. 11, 1955 to J. O. Billups teaches a wall construction utilizing lead-filled bricks or blocks interlocked to each other utilizing dovetail marginal edges. Such a construction results in a heavy wall cross-section which requires exterior and interior finished wall board surfaces to provide a finished pleasing construction. The cost of such walls is excessive and frequently requires external vertical support columns to maintain the wall in vertical alignment. U.S. Pat. No. 1,815,922 issued on July 28, 1931 to S. Lapof discloses a composite of a lead layer adhered to one side of a wall covering board, overcoming the need to fasten such layers together in the field. A strip of lead material is utilized as a lath extending along the length of each stud's facing area and horizontally between studs, so as to overlap joints formed by adjacent sheets of lead covered wallboard. Nails, protruding through the wallboard and the lath-like stud facings, secure the composite wallboard to the studs. This invention requires the handling of heavy composite wallboard sheets and does not preclude occasional leakage paths piercing the lead covering of the wallboard or the lead lathing strips. The present invention permits lead sheeting to be installed on the surface of studs without creating a plurality of holes therein, thereby permitting the erection of a lightweight radiation-proof wall. SUMMARY OF THE INVENTION A primary object of the present invention is to provide a lead sheet supporting apparatus which does not require the use of nails or other piercing type fasteners to form openings in the lead sheet. Another object of the present invention is to provide a metallic jacket which when combined with a lead sheet abutting thereto, substantially encapsulates a wooden stud. Still another object of the present invention is to provide a lead sheet stud facing portion which can effectively bridge an abutting or overlapping joint in the lead sheets affixed to the stud there-behind. Present day hospital X-ray rooms or X-ray rooms utilized in laboratories, physicians' and dentists' offices are frequently constructed utilizing thin lead sheets disposed against the studs along the innermost marginal edges of the walls comprising an X-ray radiation-proof room. The low cost and relatively lightweight of the lead sheeting has resulted in its increased popularlity. However, great care must be exercised in the erection of the sheet so as to prevent cracks or openings to be formed therein. The piercing of the sheet by nails, utilized to support it to the studs forming the wall oftentimes results in protrusions, caused by the heads of the fastening nails, to extend inwardly into the rooms, interfering with the installation of a wallboard covering such as plasterboard or wood panelling to be affixed thereto. Should the nails, used to support the wallboard material contact the nails used to support the lead sheeting, a tearing action may occur in areas of the lead sheeting adjacent the heads of the nails fastening it to the studs, requiring expensive repairs or, if the installer is unaware of such a tearing action, resulting in a leakage path for X-ray radiation generated within the room. The present invention overcomes these objections by providing a stud capturing portion having a pair of inwardly turned edges disposed against the surface of the stud destined to support the lead sheeting. The lead sheeting is placed against the inwardly turned edges and clamped thereto by a stud facing portion, which in turn is bolted to the stud capturing portion. Wallboard is fastened to the exterior face of the stud facing portion, utilizing any convenient fastening means therefor. Ceiling panels having radiation-proof properties may be supported in conventional fashion so as to protect the ceiling area from the transmission of harmful X-ray radiation. These objects, as well as other objects of the present invention, will become more readily apparent after reading the following description of the accompanying drawings. |
055263860 | abstract | A method and apparatus for improving the efficiency and performance of a nuclear electrical generation system that comprises the addition of steam handling equipment to an existing plant that results in a surprising increase in plant performance. More particularly, a gas turbine electrical generation system with heat recovery boiler is installed along with a micro-jet high pressure and a low pressure mixer superheater. Depending upon plant characteristics, the existing moisture separator reheater (MSR) can be either augmented or done away with. The instant invention enables a reduction in T.sub.hot without a derating of the reactor unit, and improves efficiency of the plant's electrical conversion cycle. Coupled with this advantage is a possible extension of the plant's fuel cycle length due to an increased electrical conversion efficiency. The reduction in T.sub.hot further allows for a surprising extension of steam generator life. An additional advantage is the reduction in erosion/corrosion of secondary system components including turbine blades and diaphragms. The gas turbine generator used in the instant invention can also replace or augment existing peak or emergency power needs. Another benefit of the instant invention is the extension of plant life and the reduction of downtime due to refueling. |
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