Split (2)

train · 33.5k rows

patent_number stringlengths 0 9	section stringclasses 4 values	raw_text stringlengths 0 954k
	summary
054596750	claims	1. A method of testing at least one of an industrial process and at least a first and second sensor for determining fault conditions therein, comprising the steps of: operating the at least first and second sensor to redundantly detect at least one physical variable of the industrial process to provide a first signal from said first sensor and a second signal from said second sensor, each said signal being characteristic of the one physical variable; obtaining a difference function characteristic of the arithmetic difference pairwise between said first signal and said second signal at each of a plurality of different times of sensing the one physical variable; obtaining a frequency domain transformation of said first difference function to procure Fourier coefficients corresponding to Fourier frequencies; generating a composite function over time domain using the Fourier coefficients; obtaining a residual function over time by determining the arithmetic difference between the difference function and the composite function, the residual function having reduced serially correlated noise; operating on the residual function using computer means for performing a statistical analysis technique to determine whether an alarm condition is present in at least one of the industrial process and the at least first and second sensor, the residual function including white noise characteristics of an uncorrelated function of reduced skewness relative to the difference function and being input to the statistical analysis technique; and said at least first and second sensor providing alarm information to an operator of the industrial process allowing modification of at least one of the industrial process and said at least first and second sensor when an alarm condition is detected. operating at least one sensor to detect at least one physical variable of the industrial process to provide a real signal from said one sensor; generating an artificial signal characteristic of the one physical variable; obtaining a difference function characteristic of the difference pairwise between said real signal and said artificial signal at each of a plurality of different times of sensing the one physical variable; obtaining a frequency domain transformation of said difference function; generating a composite function over a time domain; obtaining a residual function over time by determining the difference between the difference function and the composite function; operating on the residual function using a computer means for performing a statistical analysis technique to determine whether an alarm condition is present in at least one of the industrial process and the at lest one sensor, the residual function including white noise characteristics of an uncorrelated signal of reduced skewness relative to the difference function and being input to the statistical analysis technique; and said at least one sensor providing alarm information to an operator of the industrial process allowing modification of at least one of the industrial process and the at least one sensor when an alarm condition is detected. at least a first sensor to detect at least one physical variable of the industrial process to provide a real signal from said first sensor; first means for generating a second signal for comparison with said real signal from said first sensor; second means for determining a difference function characteristic of the arithmetic difference pairwise between said real signal and said second signal at each of a plurality of different times of sensing the one physical variable; third means for obtaining a residual function over time by means for determining the arithmetic difference between the difference function and the composite function, the residual function including white noise characteristics of an uncorrelated signal of reduced skewness; fourth means for operating on the residual function including a computer means for performing a statistical analysis technique and for determining whether an alarm condition is present in at least one of the industrial process and the at least first sensor and with said second means, said third means, and said fourth means cooperatively providing a function comprised of said white noise characteristics of uncorrelated signal of reduced skewness relative to the difference function as an input to the statistical analysis technique; and means for providing information allowing modification of at least one of the industrial process and the at least first sensor when an alarm condition is detected. operating the at least first and second sensor to redundantly detect at least one physical variable of the industrial process to provide a first signal from said first sensor and a second signal from said second sensor, each said signal being characteristic of the one physical variable; obtaining a difference function characteristic of the arithmetic difference pairwise between said first signal and said second signal at each of a plurality of different times of sensing the one physical variable; obtaining a frequency domain transformation of said first difference function to procure Fourier coefficients corresponding to Fourier frequencies; generating a composite function over time domain using the Fourier coefficients; obtaining a residual function over time by determining the arithmetic difference between the difference function and the composite function, the residual function including white noise characteristics of an uncorrelated function of reduced skewness relative to the difference function; operating on the residual function using computer means for performing a statistical analysis technique to determine whether an alarm condition is present in at least one of the industrial process and the at least first and second sensor; and said at least a first and second sensor providing alarm information to an operator of the industrial process allowing modification of at least one of the industrial process and the at least first and second sensor when an alarm condition is detected. operating the at least one sensor to detect at least one physical variable of the industrial process to provide a real signal from said at least one sensor; generating an artificial signal characteristic of the one physical variable; obtaining a difference function characteristic of the difference pairwise between said real signal and said artificial signal at each of a plurality of different times of sensing the one physical variable; obtaining a frequency domain transformation of said difference function; generating a composite function over a time domain; obtaining a residual function over time by determining the difference between the difference function and the composite function, the residual function comprising white noise characteristics of an uncorrelated signal of reduced skewness relative to the difference function; operating on the residual function using a computer means for performing a statistical analysis technique to determine whether an alarm condition is present in at least one of the industrial process and the at least one sensor; and said at least one sensor providing alarm information to an operator of the industrial process allowing modification of at least one of the industrial process and the at least one sensor when an alarm condition is detected. 2. The method described is claim 1 wherein said computer means comprises an artificial intelligence system. 3. The method as defined in claim 1 wherein the residual function further comprises reduced Markov dependent noise. 4. The method as defined in claim 1 wherein the industrial process comprises at least one of a chemical process, a mechanical process and an electrical operational process. 5. The method as defined in claim 1 wherein the step of obtaining Fourier coefficients comprise iteratively determining the minimum number of Fourier harmonics able to generate the composite function, 6. The method as defined in claim 1 further including at least one of the steps of modifying the industrial process or changing the sensor responsive to the alarm condition. 7. A method of testing at least one of an industrial process and a sensor for determining fault conditions therein, comprising the steps of: 8. The method as defined in claim 7 wherein the step of obtaining a frequency domain transformation comprises performing a Fourier transformation. 9. The method as defined in claim 7 wherein the steps of obtaining a composite function over time comprises performing an auto regressive moving average analysis. 10. The method as defined in claim 7 further including the step of determining a difference function for both the artificial signal and the real signal, as well as a separate pair of real signals. 11. The method as defined in claim 7 wherein the residual function further comprises reduced Markov dependent noise. 12. The method as defined in claim 8 wherein the step of obtaining a frequency domain transformation comprises obtaining Fourier coefficients iteratively to determine the minimum number of Fourier harmonics able to generate the composite function. 13. A system for testing at least one of an industrial process and a sensor for determining a fault condition therein, comprising: 14. The system as defined in claim 13 further including means for obtaining a frequency domain transformation of said difference function. 15. The system as defined in claim 13 wherein said computer means comprises an artificial intelligence system. 16. The system as defined in claim 13 wherein said means for generating a second signal comprises computer means for executing a computer program. 17. The system as defined in claim 16 wherein the computer program includes an autoregressive moving average procedure. 18. The system as defined in claim 13 wherein the system includes at least one pair of sensors for detecting each of the physical variables. 19. The system as defined in claim 13 wherein said computer means executes a computer program including a statistical probability ratio test on the residual function. 20. The system as defined in claim 13 further including means for changing at least one of the industrial process and substituting another sensor for a defective sensor. 21. A method of testing at least one of an industrial process and at least a first and second sensor for determining fault conditions therein, comprising the steps of: 22. A method of testing at least one of an industrial process and at least one sensor for determining fault conditions therein, comprising the steps of:
054835720	claims	1. An x-ray apparatus comprising a carrier supporting an x-ray source for producing an x-ray beam, an x-ray detector facing the x-ray source and an adjustable absorption filter which is arranged between the x-ray source and the x-ray detector, the carrier posture being variable to alter orientation of the x-ray beam path, characterized in that the x-ray examination apparatus is provided with filter-control means for accepting a posture of the carrier and furnishing a position of the absorption filter so as to control adjustment of the absorption filter in dependence upon the posture of the carrier. 2. An x-ray examination apparatus as claimed in claim 1, characterized in that the filter-control means comprises a memory device for storing pairs of position data, a pair consisting of a position data of the absorption filter and a posture of the carrier. 3. An x-ray apparatus as claimed in claim 1, characterized in that the filter-control means is arranged to furnish a translation of the absorption filter with respect to the x-ray beam path from said posture of the carrier. 4. An x-ray apparatus as claimed in claim 1, characterized in that absorption filter is rotatable and comprises an x-ray absorbing part and an x-ray transmitting part and that the filter-control means is arranged to furnish an orientation of the absorption filter with respect to an axis of rotation of the absorption filter. 5. An x-ray examination apparatus as claimed in claim 2, characterized in that the memory device is arranged to store a plurality of sets of said pairs of position data, each set corresponding to a class of objects to be examined. 6. An x-ray apparatus as claimed in claim 2, characterized in that the filter-control means is arranged to furnish a translation of the absorption filter with respect to the x-ray beam path from said posture of the carrier. 7. An x-ray apparatus as claimed in claim 5, characterized in that the filter-control means is arranged to furnish a translation of the absorption filter with respect to the x-ray beam path from said posture of the carrier. 8. An x-ray apparatus as claimed in claim 2, characterized in that absorption filter is rotatable and comprises an x-ray absorbing part and an x-ray transmitting part and that the filter-control means is arranged to furnish an orientation of the absorption filter with respect to an axis of rotation of the absorption filter. 9. An x-ray apparatus as claimed in claim 5, characterized in that absorption filter is rotatable and comprises an x-ray absorbing part and an x-ray transmitting part and that the filter-control means is arranged to furnish an orientation of the absorption filter with respect to an axis of rotation of the absorption filter.
	summary
051907216	summary	BACKGROUND OF THE INVENTION This invention relates broadly to zirconium alloys, and more specifically to corrosion resistant and ductile zirconium alloys. Improved zirconium and zirconium alloy nuclear fuel cladding tubes are disclosed in U.S. Pat. Nos. 4,200,492 and 4,372,817, incorporated herein by reference. A composite cladding tube described therein comprises a barrier layer of either high purity zirconium (such as crystal bar zirconium) or moderate purity zirconium (such as sponge zirconium) metallurgically bonded on the inside surface of a zirconium alloy tube. The composite cladding encloses the nuclear fuel material, leaving a gap between the fuel and the cladding. The barrier layer shields the alloy tube from the nuclear fuel material held in the cladding as well as shielding the alloy tube from fission products and gases. The barrier layer typically has a thickness equal to about 1 to about 30 percent of the thickness of the composite cladding. The barrier layer remains relatively soft during irradiation and minimizes localized strain inside the nuclear fuel elements, thus serving to protect the alloy tube from both stress corrosion cracking and liquid metal embrittlement. The alloy tube portion of the cladding is otherwise unchanged in design and function from previous practice for a nuclear reactor and is selected from conventional cladding material, such as zirconium alloys. It is disclosed in U.S. Pat. Nos. 4,200,492 and 4,372,817 that the high and moderate purity zirconium metal forming the metal barrier in the composite cladding, even after prolonged irradiation, is able to maintain desirable structural properties such as yield strength and hardness at levels considerably lower than those of conventional zirconium alloys. In effect, the metal barrier does not harden as much as conventional zirconium alloys when subjected to irradiation, and this together with its initially low yield strength enables the metal barrier to deform plastically and relieve pellet-induced stresses in the fuel element during transients in neutron radiation. Fuel pellet induced stresses in the fuel element can be brought about, for example, by swelling of the pellets of nuclear fuel at reactor operating temperatures (300.degree. to 350.degree. C.) so that the pellet comes into contact with the cladding. The nuclear fuel elements described in U.S. Pat. Nos. 4,200,492 and 4,372,817 provide a substantial improvement over elements which do not include internal zirconium barrier layers. However, the relatively pure zirconium barrier layers are subject to oxidation if the composite cladding is breached and water or steam enters the fuel rod during operation of the reactor. It would thus be desirable to improve the oxidation resistance in the barrier layer. It would be particularly desirable if such oxidation inhibition can be achieved without reducing the effectiveness of the zirconium barrier layer, particularly the ability of the barrier layer to deform plastically and relieve pellet-induced stresses in the fuel element during transients in radiation. U.S. Pat. No. 4,894,203, incorporated herein by reference, discloses an improved nuclear fuel cladding having an alloy layer formed as a thin layer on the inner barrier layer, the alloy layer having less than one percent by weight of one or more impurities from the group consisting of iron, chromium, copper, nitrogen, and niobium. The alloy layer can be formed by any conventional method having control over the deposition depth of the impurity elements, such as ion implantation, ion plating, or chemical vapor deposition. The alloy layer provides improved oxidation resistance to the barrier layer without substantially affecting the desired plastic properties of the barrier layer. U.S. Pat. No. 4,876,064, incorporated herein by reference, discloses corrosion resistant zirconium alloys comprised of 0.5 to 2.5 weight percent bismuth, or alternatively, 0.5 to 2.5 weight percent of a mixture of tin and bismuth, and 0.5 to 1.0 weight percent of a solute from the group consisting of niobium, molybdenum, tellurium, and mixtures thereof, and the balance zirconium. The alloys have a high resistance to both uniform and nodular corrosion as shown by laboratory high pressure steam testing that simulates the uniform and nodular corrosion that can be found on nuclear fuel rod cladding in the core of a nuclear reactor. It is an object of this invention to provide a zirconium based alloy having an improved combination of corrosion resistance and ductility. It is another object of this invention to provide a corrosion resistant zirconium alloy having ductility comparable to sponge zirconium. It is another object of this invention to provide a corrosion resistant zirconium alloy having an improved combination of corrosion resistance and ductility suitable for barrier layers in nuclear fuel cladding. BRIEF DESCRIPTION OF THE INVENTION The corrosion resistant zirconium alloys of this invention are comprised of, in weight percent, about 0.1 to less than 0.5 percent bismuth, about 0.1 to less than 0.5 percent niobium, and the balance substantially zirconium. Preferably, niobium is about 0.1 to 3 weight percent. The alloys have improved corrosion resistance as compared to the moderate-purity sponge zirconium while maintaining a ductility comparable to sponge zirconium.
	claims	1. An angular electrostatic filter comprising:a top deflection plate set to a top voltage extending from an entrance side to an exit side, wherein the top deflection plate is planar;a bottom deflection plate wherein at least a portion is substantially parallel to the top deflection plate and at least a portion is angled with respect to the top deflection plate, extending from the entrance side to the exit side, and set to a bottom voltage, wherein the bottom voltage is more negative than the top voltage, and wherein an electric field is generated between the top deflection plate and the bottom deflection plate;an entrance electrode positioned at the entrance side of the filter and set to a first focus voltage; andan exit electrode positioned at the exit side of the filter, wherein the exit electrode is set to a second focus voltage. 2. The filter of claim 1, wherein the first focus voltage and the second focus voltage are set to an average of the bottom voltage and the top voltage. 3. The filter of claim 1, wherein the electric field causes ions having a selected energy to deflect by a particular angle. 4. The filter of claim 3, further comprising an exit slit downstream of the exit electrode, wherein the ions deflected by the particular angle pass through the exit slit. 5. The filter of claim 1, wherein the entrance electrode focuses an ion beam entering through the filter and shapes the electric field near the entrance side of the filter. 6. The filter of claim 1, wherein the exit electrode focuses an ion beam exiting the filter and shapes the electric field near the exit side of the filter. 7. The filter of claim 1, wherein the top voltage is a negative value, the bottom voltage is a more negative value, and an average of the top voltage and the bottom voltage is a negative value. 8. The filter of claim 1, wherein the bottom deflection plate comprises an angled portion. 9. The filter of claim 8, further comprising a pair of edge electrodes extending from the entrance electrode to the exit electrode, set to an edge focus value, is substantially parallel to the top and bottom deflection plates, includes an angled portion and mitigates field penetration. 10. A beamline assembly comprising:an accelerator component that selectively decelerates a ribbon shaped incoming ion beam;a tube focus component that further decelerates the ion beam and focuses the ion beam in a vertical direction; andan angular electrostatic filter that removes energy contaminants from the ion beam and directs the ion beam toward a target, wherein the angular electrostatic filter comprises:a top deflection plate extending from an entrance side to an exit side, wherein the top deflection plate is planar;a bottom deflection plate having a non-angled portion substantially parallel to the top deflection plate, extending from the entrance side toward the exit side and an angled portion extending from the non-angled portion to the exit side;an entrance electrode having an aperture that permits passage of the ion beam positioned at entrance side of the filter;an exit electrode positioned having an aperture that permits passage of the ion beam positioned at the exit side of the filter;a pair of edge electrodes extending from the entrance side to the exit side, substantially parallel to the top deflection plate and positioned midway between the top deflection plate and the bottom deflection plate; andan exit slit positioned downstream of the exit electrode that blocks energy contaminants and permits passage of ions having selected energies. 11. The assembly of claim 10, wherein the tube focus voltage is negative and allows the beam to decelerate but still maintain a higher energy than a final energy while within the angular electrostatic filter. 12. The assembly of claim 10, wherein a negative bias voltage is applied across the top and bottom deflection plates that causes the ion beam to maintain a somewhat higher energy than a final energy while between the top and bottom deflection plates. 13. The assembly of claim 12, wherein the pair of edge electrodes are set to the bias voltage to mitigate edge fringe field affects. 14. The assembly of claim 13, wherein the entrance electrode is set to the bias voltage. 15. The assembly of claim 10, wherein the angled portion of the bottom deflection plate comprises about half of the bottom deflection plate near the exit side of the filter and at an angle away from the top deflection plate. 16. The assembly of claim 15, wherein the angled portion of the bottom plate is at an angle of about twice a bend angle of the beam. 17. A method of removing energy contaminants form a ribbon shaped ion beam comprising:selecting an angle of deflection for a selected energy range for the ribbon shaped ion beam;applying an entrance focus field that focuses the ion beam in a vertical direction;applying an edge field that mitigates non-uniform fields near an end of a deflection field; andapplying the deflection field according to the selected energy range at the selected angle of deflection, wherein applying the deflection field comprises applying a negative bias across a planar top deflection plate and a bottom deflection plate having an angled portion and a planar portion, wherein the ion beam travels between the top and bottom deflection plates, wherein the planar portion is parallel to the top deflection plates an is located at an entrance side of the deflection field. 18. The method of claim 17, further comprising applying an exit focus field that focuses the ion beam in a vertical direction after applying the deflection field. 19. The method of claim 17, further comprising blocking energy contaminants after applying the deflection field.
	abstract	A charged particle beam writing method includes writing a pattern on a first target object by using a charged particle beam in a writing apparatus; and conveying a second target object after having written the pattern on the first target object, wherein even though the second target object is arranged on any one of conveying paths including a carry-out port and a carry-in port of the writing apparatus, a conveying operation for the second target object is not performed during writing the pattern on the first target object.
050911392	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the environment in which this invention resides can be easily understood. A reactor vessel V having a core C generates steam. Steam S passes outwardly on a line L to a main turbine T. As is conventional, turbine T drives a generator G which generator produces electrical power. Discharge of steam occurs to a condenser cooled by coolant (not shown). A system of pumps including a feedpump take the condensate and inject it back into the reactor vessel V where the steam cycle endlessly repeats. (Also not shown) As is common in nuclear reactors, a recirculation pump R is utilized. Typically, the recirculation pump R circulates the water coolant through the core C. As is well known, such circulation is included in peripheral downcomer volumes along the sidewalls of vessel V and reverses flow to pass centrally upward through core C. The coolant has two purposes. First, it acts as a moderator. In acting as a moderator it increases or decreases power. Second, the coolant removes fuel heat and turns itself into steam S which drives turbine T. Having set forth the moderator flow path and the steam cycle in over simplified format, attention can now be directed to the reactor control. Regarding the recirculation of fluid by pump R, a master controller 20 is utilized. Master controller receives a load speed signal from generator G (by conduits not shown). Additionally, it can receive a manual input. Receiving one or both of these inputs, master controller 20 has an output to pump speed controller 22. Pump speed controller 22 acts upon a clutch 26 between a motor 28 and a generator 30. Generator 30 controls a motor 32 driving the recirculation pump R. It will be understood that the particular control used for the variable throughput of pump R can vary, and also that in another configuration multiples of pump R and motor 32 can be located directly within and below the downcomer volumes of vessel V. Likewise, the function of the control rods can be summarized in a simplified format. Typically, a group of control rods 50 are actuated by hydraulic control units (HCU) 52. These control units include precision position monitors for maintaining the rods in given positions of penetration to the core for both the shaping of the core reaction as well as its overall control. The hydraulic control units 52 are in turn activated by a rod control and information system (RCIS) 54. This rod control and information system includes inputs from the operator and outputs to the operator indicating the positions of each of the rods. Referring to FIG. 2, a section of core C is illustrated. Typically, this section includes 16 bundles 60 controlled by four control blades 62. The reader will realize that core C consists of several hundred bundles 60 with many such control rods, there being generally four control rods 62 for each group of 16 bundles. The control rods are raised into the core C and lowered from the core C by the hydraulic control unit 52, these units being below the reactor vessel V. It is this control rod movement which effects reactor operation. Simply stated, when the control rods are inserted, fission reaction is inhibited. When the control rods are withdrawn, fission reaction increases. Each group of 16 fuel bundles is monitored by 16 local power range monitors (LPRMs). Local power range monitors are typically mounted in strings in assemblies extending the vertical length of the core. In FIG. 2, four such strings 63, 64, 65, and 66 are shown. Each string includes four discrete power monitors. These power monitors are shown as A, B, C and D. It will be seen that monitors D are near the top of the core and monitors A are near the bottom of the core. Monitors B and C monitor the medial levels of the core. For the purposes of the application, it will be understood that monitoring occurs against three broad classifications of limits. First, each bundle is examined for its overall power output. It will be understood that the constant "A" which follows in this description is utilized in this function. Second, each individual fuel rod contained in any of the fuel bundles is monitored for its linear power generation. Finally, a planar averaged linear heat generation rate is monitored for each bundle at various fuel planes. For these last two considerations, it will be understood that the constant "B" which follows in this description is utilized. As will hereinafter be more fully developed, it has been found that the ratio of maximum linear heat generation rate in the fuel rods and the ratio of planar average heat generation rate at any one fuel plane of each bundle are analogous. This being the case, the constant "B" as hereinafter described can be used as a generic input to the algorithm protecting against these limits. Brief reference to FIG. 3 can be made. This reference is a schematic which sets forth the processor apparatus of this invention. Simply stated, each of the local power monitors A, B, C, and D passes its signals through a signal conditioner 70 and thereafter to a bank of optical-isolators 72. The optical-isolators input to an input/output bus 73 which bus communicates signal to the local power range monitor processing bus. Utilizing this bus, all inputs throughout the reactor in the order of 200 are scanned by the processor unit. This scanning occurs in the processing unit denominated at block 74. Thereafter, and as appropriate for each monitor block of 16 bundles, the sum and averages of the local power range monitors are computed at block 75. Once this has occurred, two microprocessor outputs are utilized. A first output at 76 goes to an algorithm microprocessor, which microprocessor processes for the so-called operating limits setpoints. A second output 78 goes to an algorithm microprocessor unit which unit is not shown and is identical to that illustrated connected at 76. This microprocessor process for so-called "safety limits" and furnishes the degree of redundancy and backup protection that this disclosure enables. Having set forth the overall architectural schematic, the specific inputs can be set forth. At 81, into a self-test unit are placed the plant parameters. Additionally, at 82 a set point result from an optional identical redundant channel is put through for cross channel comparison check. The algorithm unit receives through 84 a reference APRM which represents the reactor power level, at 85 a core simulator thermal limit output, at 86 a rod position indication. Input 87 includes applicable core flow data from recirculation pump R (see FIG. 1). The algorithm unit computes a set point. This set point is compared at comparator 93 to actual instantaneous local power range monitors based signals 92. When the reading from the actual power range monitors exceeds the set point, trip unit 94 issues a trip order. The trip order then proceeds from the automated thermal limit monitor along two conduits 96, 98. Referring back to FIG. 1, conduit 96 blocks all further rod insertions. Additionally, and as seen further in FIG. 1, conduit 98 blocks any further attempts to change core flow. As has been emphasized, it is known to have core simulator. This core simulator receives input from a neutron monitoring system 100 and constructs in a large, fast computer 102 a model of the overall reactor operation. This model of the overall reactor operation can be predicted on a time basis approaching once every two minutes by modern high speed computation equipment. This calculation result of core thermal limits is downloaded into a memory in the automated thermal limit monitor system 120. Based on these core thermal limits, the algorithm unit computes and outputs setpoints. This computation occurs to the unit in real time, in a very short calculation cycle on the order of 0.1 to 0.2 seconds. Having generalized this system, a detailed discussion of the algorithms herein utilized can now be set forth. Component Arrangement The ATLM system signal processing and logic diagram as shown in FIG. 3 can be conceptually summarized. The ATLM takes all LPRM detector readings as inputs. All LPRM signals are fed into two redundant channels of the ATLM by first passing through an analog to digital converter and sets of optical communication links. For each channel, after the LPRMs pass through the scan/process unit, they then pass through a summing and averaging circuit unit. Except for the peripheral region of the core, every square block of 16 fuel bundles are monitored by the four LPRM strings at the four corners of this block. For minimum critical power ratio (MCPR) limit monitoring, the sum of the average of each level of B, C, D, of the four LPRM strings is used to monitor the MCPR among these 16 bundles. For peripheral bundles where only three or two LPRM strings are available, specific but similar assignment methods are used. Thus, the readings of each LPRM string are used four times to provide the sum and average outputs for the four different but neighboring block regions of fuels for each of the two ATLM channels. The initial regional MCPRs of every block of 16 bundles calculated by the process computer core simulator/monitor are selected and downloaded in the algorithm unit memory in matrix form for comparison. For the power density limit (KW/FT) algorithm, the average reading of each of the four levels is used separately for monitoring local power densities in the four vertical sections of the 16 bundle block. These four vertical section correspond to the four LPRM levels, (see FIG. 2) The processed LPRM readings that cover each and every region of the core are read to both the comparator unit and the algorithm unit in matrix form. The algorithm unit takes as inputs the reference APRM value (as reactor power), the selected rod identification and its position from the RCIS, the core flow, and the regional thermal limit data from the core monitor. The algorithm unit then performs setpoint calculations for every region, separately for operating thermal limit and safety thermal limit setpoints in different sub-units. The calculated setpoint data then pass to the comparator unit where they are compared against the instantaneous LPRM data from the sum/average unit for each monitoring region. Rod block signal is issued if the instantaneous LPRM output from any one region exceeds the setpoint output of that region. A separate set of units that issues flow block signal is also included in both channels. Flow block signal will be issued if MCPR limit or KW/FT limit is approached during flow change. A separate self-test unit is included in each channel to issue test command and to perform processor calculation verification and monitor calculation verification. System Algorithm Algorithm to Prevent MCPR Limit Violation During Control Rod Withdrawal The equations that govern the relationships between the thermal limits and the processed LPRM sum outputs are as follows, for each monitoring region: ##EQU1## where: RBS.sub.o : Operating limit rod block setpoint RBS.sub.s : Safety limit rod block setpoint PA0 LPRM.sub.i : Initial sum of average of four LPRMs from B,C,D levels of the four LPRM strings that surround each 16-bundle region, (or of available LPRMs for corresponding peripheral region.) PA0 A.sub.o : Margin factor for operating limit rod block, a known function of rod pull distance. PA0 A.sub.s : Margin factor for safety limit rod block, a known function of rod pull distance. PA0 RMCPR.sub.i : Regional initial minimum CPR, i.e., the minimum CPR of the 16 bundles in the region spanned by the four LPRM strings, (less than 16 bundles for peripheral regions.) Known inputs from core simulator/monitor. PA0 OLMCPR: Operating limit MCPR in current cycles, a known function of power and flow. PA0 SLMCPR: Safety limit MCPR in current cycle, a known bounding value for all power and flow conditions. PA0 RBS.sub.s : Safety limit rod block (flow block) setpoint PA0 LPRM.sub.i : Initial sum of average of four corner LPRMs from B,C,D levels. (See System Algorithm) PA0 A.sub.o : Margin factor for operating limit rod block due to rod withdrawal, a known function of rod pull distance. Same A.sub.o as in System Algorithm. PA0 A.sub.s : Margin factor for safety limit rod block due to rod withdrawal, a known function of rod pull distance. Same A.sub.s as in System Algorithm. PA0 RMCPR.sub.i : Regional initial MCPR. See System Algorithm. PA0 OLMCPR: Same as in System Algorithm. PA0 SLMCPR: Same as in System Algorithm. PA0 A.sub.f : Margin factor for rod block due to core flow change, a known function of initial core flow and final core flow. EQU A.sub.f =1+f(W.sub.i, W.sub.f), A.sub.f =1 if W.sub.i =W.sub.f PA0 A.sub.total,o : Total margin factor that considers both rod pull and flow change for operating limit block PA0 A.sub.total,s : Total margin factor that considers both rod pull and flow change for safety limit block PA0 LPRM.sub.i (X): Initial average of the four LPRMs (level X) at the four corners of each 16 bundle fuel region. The region monitored by the X level LPRMs is the region covered up to 1.5 ft above the LPRM and 1.5 ft below the LPRM. (For peripheral region, there may be less than 4 LPRMs which cover a region with fewer bundles.) PA0 B.sub.m (X): Margin factor for MAPLHGR operating limit rod block for X level LPRMs. This factor is a function of power and rod position. PA0 M.sub.p : Off-rated power factor to consider overpower condition during worst transient at off-rated condition. This is a known function of power. PA0 MAPRAT.sub.i (X): Regional initial maximum MAPRAT for level X. i.e., the maximum MAPRAT of the 16 bundles with the 3 feet section covered by the X level LPRMs. (Less than 16 bundles for peripheral regions.) MAPRAT.sub.i is known input from the core monitor model. PA0 LPRM.sub.i (X)=Initial average of the four LPRMs (Level X) at the four corners of each 16 bundle fuel region. The region monitored by the X level LPRMs is the region covered up to 1.5 ft. above the LPRM and 1.5 ft. below the LPRM. (For peripheral region, there may be less than 4 LPRMs which cover a region with fewer bundles.) PA0 B.sub.M (X): Margin factor for MLHGR operating limit rod block for X level LPRMs. This factor is a function of power and rod position. PA0 M.sub.P : Off-rated power factor to consider over power condition during worst transient at off-rated condition. This is a known function of power. If 13.4 KW/FT is used as the operating limit for all power condition, then M.sub.P =1. PA0 KW/FT.sub.i (X): Regional initial maximum KW/FT for level X, i.e., the maximum KW/FT of the 16 bundles within the 3 feet section covered by the X level LPRMs, (less than 16 bundles for peripheral regions.) KW/FT.sub.i (X) is known input from the core monitor. The above algorithm is derived assuming no flow change. Basis of Algorithm The critical power ratio (CPR) is related to the critical quality (X.sub.c), bundle power (P) and channel flow (W) as follows: ##EQU2## For two different power conditions, ##EQU3## Assume the flow change caused by control rod withdrawal is very small. Also, if there is no adjacent rod withdrawal, assume X.sub.c change is negligible, ##EQU4## If there is axial power peaking shift caused by adjacent rod motion, then ##EQU5## where K.sub.a is the coefficient to account for axial power peaking shift. ##EQU6## (The above equation assumes no flow change.) Determination of A-factor The A-factor correlates bundle MCPR ratio to integrated LPRM ratio through combined relationships between MCPR to bundle power and bundle power to LPRM value. The construction of bundle power from LPRM readings is a major calculation task in the plant process computer model, where large amount of coefficients and data are used in lengthy calculations. In order to establish a simple relationship between measured LPRMs and "absolute" bundle power and corresponding MCPR that involves very few input data and calculations, as required by quick on-line monitoring and control purpose, an approximation method is used. This method is to construct an A-factor curve dependent only on a very few parameters, that is based on statistical interpretation of semi-empirical results from exact core physics calculations at various conditions. In order to obtain A-factor curves from rod withdrawal cases at various operating conditions, a family of operating power and flow conditions with corresponding typical rod patterns are developed in advance. These families of operating power and flow conditions are selected from spaced apart operating flow and power levels contained within the bound of the total universe of power and flow condition. This universe of power and flow conditions is illustrated in FIG. 4A. Six selected positions of power and flow specifically analyzed are shown. These are shown for core flows of 43% FIG. 4B and 70% FIG. 4C. Rod withdrawal cases with rods of higher worth are developed based on these initial conditions. Based on the highest rod worth and largest size of rod gang for rod withdrawal a family of A-factor curves are developed for various power and flow conditions and at different core cycle conditions. With the above data base, a proposed statistical A-factor curve for operating limit rod block algorithm for a typical 1100 MW reactor is shown at 200 in FIG. 4C. This is the curve of one-sided A-factor values at 95% probability at 50% confidence (best estimate) using the current data base of various A-factor data and assuming a normal distribution of the data, and with the following assumptions: a) Highest worth gang rod withdrawal cases (i.e., highest worth rods which has a gang size of eight rods) based on typical rod pattern at various power and flow conditions. b) Data included both initial core and equilibrium cycle conditions. c) Equilibrium Xenon initially and constant Xe during rod withdrawal. d) An average 15% random LPRM failure rate is included in developing the 95/50 bounding value. Based on the similar method, another set of A-factor curves is developed for any rod which is at least half way withdrawn from the core since the last core monitor update. By implementing this additional set of A-factor curves in the algorithm, the conservatism in A-factor for rods more than half withdrawn can be reduced significantly. Bounding A Factor for SLMCPR Protection The limiting rod pattern method is used to generate the A factor curve for SLMCPR protection. The highest worth rod or gang of rods is chosen as the error rod (rods) in the Rod Withdrawal Error event with a corresponding limiting rod pattern developed which would give the worst thermal limit change upon continuous rod withdrawal. This worst condition result is then used to define the rod block setpoint based on the concept that no rod withdrawal case will give a worse result; this setpoint thus prevents any SLMCPR violation under all circumstances. This same method is used here in determining the bounding A factor for SLMCPR protection. If one develops an A factor which represents the worst thermal limit change condition, then by using this A factor in MCPR protection setpoint algorithm, it will prevent any SLMCPR violation under all circumstances. (A factor is a multiplier to the setpoint itself.) The A factor curve for SLMCPR protection is calculated for a typical 1100 MW reactor and shown at 201 in FIG. 4C. Referring to FIG. 4B, typical curves relating to rod withdrawal at a selected location within the core are shown. These plots are for various power levels, at 43% core flow. Referring to FIG. 4C, a group of such curves is shown for an alternate rod location and core flow. MCPR Protection Algorithm During Core Flow Change Algorithm ##EQU7## Where: RBS.sub.o : Operating limit rod block (flow block) setpoint where EQU f(W.sub.i, W.sub.f)=1.953.times.10.sup.-2 (W.sub.f -W.sub.i)-1.722.times.10.sup.-4 (W.sub.f.sup.2 -W.sub.i.sup.2)+0.534.times.10.sup.-6 (W.sub.f.sup.3 -W.sub.i.sup.3) This algorithm shows that A.sub.f caused by flow change is uniform throughout the whole core. Overall total A factor with combination of rod pull and flow change can be obtained by multiplying the A factor due to rod pull to the A factor due to flow change. Basis of Algorithm Since core flow change is in general uniform throughout the whole core, the uniform bundle flow change will cause uniform bundle power change. The ratio of MCPR change is also uniform under specific power and flow conditions. This gives a constant A.sub.f for all core regions at specific power and flow conditions. A.sub.f value at specific power and flow conditions is proportional to the ratio of the critical power change only. This relationship is shown as follows, by definition of A.sub.f : ##EQU8## where LPRM represents the sum of the B, C, D LPRM ##EQU9## where CP represents the bundle critical power under specific flow condition (and power condition). ##EQU10## This shows that A.sub.f equals approximately the ratio between the final critical power after flow change and the initial critical power before flow change. If taking the most conservative A.sub.f value from various power conditions at a constant core flow, an A.sub.f curve as a function of core flow only can be established, which will follow the same trend as the change ratio of the bundle critical power. Since the critical power increases as flow increases. A.sub.f is always greater than 1. At lower flow A.sub.f is larger since critical power change ratio is larger: at higher flow A.sub.f is smaller since critical power change ratio is smaller. A.sub.f can be established as EQU A.sub.f =a+f(W.sub.f,W.sub.i); A.sub.f =1 if W.sub.f =W.sub.i where W.sub.f and W.sub.i are the final and initial core flow. A.sub.f due to core flow change is an independent factor that is not changed during rod withdrawal operation. A total A factor that represents a combined operation of both rod withdrawal and flow change can be obtained by multiplying the A.sub.f due to flow change by the A factor due to rod withdrawal. Determination of A.sub.f Function The exact A.sub.f value is determined based on a 10% core flow change operation (with no rod pull) performed at each typical operating point. The A.sub.f values for 10% flow change are shown in FIG. 5A, as a function of initial core flow. Based on the A.sub.f results, it shows that at any fixed core flow A.sub.f at lower power is always lower. Since lower A.sub.f represents more conservative A.sub.f (i.e., rod block setpoint is lower), the average A.sub.f values with a margin at these lowest power conditions are taken to construct an A.sub.f function which depends only on core flow. The margin used is the 95% probability and 50% confidence. This curve is shown in FIG. 5A. It is also stated as follows: ##EQU11## By integrating the above equation, one obtains EQU A.sub.f -1=1.953.times.10.sup.-2 (W.sub.f -W.sub.i)-1.772.times.10.sup.-4 (W.sub.f.sup.2 -W.sub.i.sup.2)+0.534.times.10.sup.-6 (W.sub.f.sup.3 -W.sub.i.sup.3) This relationship is included in the rod block algorithm due to core flow change to determine A.sub.f as a function of initial and final core flow. It is plotted in FIG. 5B with initial flow being 40%, 50%, and 60%. Those having skill in the art will realize that these resultant equations are capable of rapid solution in a programmed microprocessor. Algorithm to Prevent Fuel Mechanical Thermal Limit Violation During Rod Withdrawal There are two operating limits related to fuel mechanical thermal limit. One is the maximum fuel rod power density, or maximum linear heat generation rate (MLHGR), which mainly monitors the limit for prevention of cladding rupture due to pellet expansion stress. The other one is the maximum average planar linear heat generation rate, or MAPLHGR, which has to be maintained to limit cladding temperature during a loss of coolant accident (LOCA). It has been demonstrated during this study that the LPRM response to the regional maximum average planar linear heat generation rate change due to rod withdrawal is almost identical to the LPRM response to the regional MLHGR change. The MAPLHGR limit is derived from fuel rod heat flux limit with fuel rod local peaking factors taken into consideration. The MAPLHGR limit and the MLHGR limit are closely related, and are in general differed by a few percent. Due to the almost identical LPRM responses to changes of the two limits, either limit can be used in the ATLM rod block logic for fuel mechanical limit protection. With bounding conservative margins added to the B values, as to be explained later, the algorithm based on MAPLHGR or MLHGR will adequately cover both MAPLHGR and MLHGR fuel mechanical limits protection. In the core monitor model, the average planar LHGR is calculated by the model and the MAPLHGR limit is an input value being a function of fuel type and bundle exposure. The ratio of the two, called MAPRAT. is also calculated by the model and is readily obtainable through output editing. This MAPRAT value is to be used by the algorithm for rod block setpoint calculation. Also, since the overpower condition during worst transient at off-rated condition can be more severe than rated condition, a power and flow dependent multiplier factor has to be included in the MAPLHGR or MLHGR limit for off-rated condition applications. MAPLHGR Algorithm Equation The equation that governs the relationship between the MAPLHGR limit and the processed LPRM outputs are described as follows for each fuel monitoring region: ##EQU12## Where: RBS.sub.m (X): MAPLHGR operating limit rod block setpoint at LPRM level X Basis of Algorithm The average planar LHGR (APLHGR) is a calculated bundle average fuel pellet power density, expressed in term of kw/ft. The maximum APLHGR in the region monitored by the LPRM can be assumed to be proportional to the LPRM output that represents neutron flux level, or, EQU LPRM.varies.RAPLHGR where RAPLHGR is the regional maximum APLHGR. For two different power levels: ##EQU13## When a rod is being withdrawn next to a LPRM string, the true fuel power density of the fuel section around this rod next to the LPRM string are under measured. For two power conditions with one being the limiting condition, one has ##EQU14## Where B is the under-measure factor. If representing the right-hand side values in MAPRAT, i.e., dividing the RAPLHGR by MAPLHGR, one has ##EQU15## Since MAPLHGR is power and flow dependent based on over-power conditions during worst transient at off-rated conditions, an off-rated power multiplier factor for MAPLHGR (M.sub.p) has to be included in the above equation for off-rated condition setpoint calculations. Or ##EQU16## B has to be determined to cover all power and flow conditions and for all four LPRM level applications. B-Value Determination The strategy of determining the B-value is similar to the method of determining A-factor in the MCPR setpoint algorithm. For any power and flow condition, the relationship between the LPRM output and the local regional maximum APLHGR depends mainly on the withdrawal position of the adjacent control rod in this region. B-values are different for different power and flow conditions. To obtain the dependence relationship of B-values on core power, flow, and control rod position, typical power and flow conditions from the same family of operating conditions used in MCPR algorithm are selected and used. These typical cases are rod withdrawal cases with higher worth gang of rods being pulled from typical operating conditions which cover the entire power/flow operating region. Based on the above cases, a family of B-value curves are developed as a function of rod withdrawal position for the various operating conditions, for each of the four regions monitored by LPRM level A, B, C and D. The exemplary results are shown in FIGS. 6A and 6B. The results show that in general B-values vary depending on the distance between the rod position to the elevation of the concerned LPRM. For an initially deep rod. B-value tends to be close to one until the control rod is withdrawn to the vicinity of the LPRM elevation, where B-value starts to decrease. For example, for LPRM C level, the B-value drops to as low as 0.84. After the control rod is withdrawn to a position very close to the LPRM elevation, the B-value starts to increase back to near one, where the control rod is away from the LPRM. This is due to the control rod density effect described earlier. However, if the control rod initial position is very close to the LPRM or at the LPRM elevation, then the B-value no longer decreases with further rod pull. Instead, it stays close to one until the rod is completely withdrawn. Also, the results show that for higher core power conditions, the B-values stay at higher values even at rod position close to LPRM. This makes it possible to select two different set of bounding B-values for two different power ranges. Based on the bounding case results, a set of very conservative bounding margin factor B-value curves are derived for each LPRM level application. This is shown in solid line and in dashed line in FIGS. 6A and 6B. Solid line is to be applied in low power range (below 65% power); dashed line is to be applied to high power range (above 65% power). It has been demonstrated that these set of B-value margins can appropriately accommodate a random 15% probability failure of LPRMs sensors. MLHGR Algorithm Equation The equation that governs the relationship between the MLHGR limit and the processed LPRM outputs is similar to MAPLHGR algorithm equation and is described as follows for each fuel monitoring region: ##EQU17## Where: RBS.sub.M (X)=LHGR operating limit rod block setpoint at LPRM Level X Basis of Algorithm The basis of MLHGR algorithm is similar to that of the MAPLHGR algorithm. The maximum LHGR in the region monitored by the LPRM can be assumed to be proportional to the LPRM output that represents neutron flux level, or, EQU LPRM.varies.M. KW/FT Where M. KW/FT is the regional maximum KW/FT. For two different power levels: ##EQU18## When a rod is being withdrawn next to a LPRM string, the true fuel power density of the fuel section around this rod next to the LPRM string is under measured. For two power conditions with one being the limiting condition, one has ##EQU19## If an off-rated power multiplier factor for MLHGR (M.sub.P) is included, then ##EQU20## B has to be determined to cover all power and flow conditions and for all four LPRM level applications. B-Value Determination The Method of determining B value for MAPLHGR algorithm is followed to determine B value for MLHGR algorithm. Same typical cases of rod withdrawal cases are used. Based on the above cases, a family of B-value curves is developed as a function of rod withdrawal position for the various operating conditions, for each of the four regions monitored by LPRM level A, B, C, and D. The results are found to be almost identical to the results of MAPLHGR B values. MLHGR and MAPLHGR Algorithm due to Core Flow Change The B-Value to monitor KW/FT change during core flow change is evaluated. From theoretical point of view, it is concluded that the B-value during flow change is always one, for the following reasons: a) Flow change is a core-wide uniform change, the resultant power change is uniform and proportional to initial power core-wide. b) The bundle power change, or KW/FT change is uniform and proportional to the initial bundle power, independent in general of bundle location. c) The LPRM change, which monitors regional power change is proportional to the power (or KW/FT) change. This gives a B-value of one. The above conclusion is confirmed and verified by 3 dimensional core monitor model analysis. It is determined that the B-value of MLHGR algorithm due to flow change is one, regardless of power/flow conditions. Algorithm of Self Test Unit In addition to the built-in self test feature of the hardware, the self test unit has four test functions in both channels: a) Calculated versus Measured Plant Parameters Receive inputs of measured data of reactor pressure, feedwater flow, feedwater temperature, core flow, reactor power (APRM), and selected LPRMs. Compare these data with calculated data at the time when the monitor results are downloaded (including the above parameters). Issue rod block and warning if the two sets of data are different by a preset uncertainty factor. b) ATLM Algorithm Test For either channel, receive setpoint calculation result from the other channel. Compare this result with the result of own channel. Issue rod block and warning if the two do not agree by a preset error margin. c) Overall Functional Test (Manual) Upon initiation of test demand by the operator, a simulated high LPRM ratio signal is transmitted to the algorithm/comparator units to generate a trip signal. d) Setpoint Calculation Test (Manual) Upon initiating test demand, a display of a standard calculation data is available for setpoint calculation check as an ATLM functional test. System Logic a) Data Input Regional (16 bundle block or less) thermal limit data calculated by on-line monitor are downloaded to the ATLM processor memory automatically when no active rod movement is in progress. Operating limit table (a function of power and flow), safety limit MCPR value, and A-factor curves as a function of relative rod pull distance are manually entered at the beginning of cycle before startup. APRM (reference), core flow, LPRM readings, rod positions are scanned continuously and input to ATLM processor memory, MCPR, processed LPRM reading, rod position are two-dimensional matrices, (power density in KW/FT, processed LPRM reading for KW/FT monitoring are three-dimensional matrices.) B-factors tables are manually entered at the beginning of cycle before startup. Regional maximum KW/FT data or MAPRAT data (three dimensional) calculated by the on-line monitor are downloaded to the processor memory. b) Initialization Upon new monitor calculation and data download, all A-factors are initialized to one, all relative rod pull distances initialized to zero, and all rod positions are renamed as initial positions. Upon rod selection, selected rod(s) I.D., its position, and associated region(s) are identified and recorded. At beginning of first rod pull after a monitor data download, all input thermal limit and LPRM data are renamed as initial values, e.g., LPRM.sub.i, RMCPR.sub.i. The LPRM.sub.i and RMCPR.sub.i values are kept unchanged until the next monitor data update and download. A-factor is only dependent upon rod position difference between current position and initial position of the same rod(s) since the last monitor data update. All B-factor values are initialized to their designated values as a function of the initial rod position upon new monitor calculation and data download. All input KW/FT or MAPRAT data are renamed as initial values. Algorithm Calculation Time Cycle The algorithm will use the most recently scanned values of rod position and OLMCPR for calculation. The calculation will be on the order of 100 ms to 200 ms. The actual calculation (i.e., CPU) time will be much less than 100 ms, due to the simplicity of the algorithm and the current micro-processor capability. Algorithm calculation is initiated at the beginning of first rod pull and terminated a few minutes after rod motion stops. (Proposed time is 5 minutes.) With no active rod movement in progress, the algorithm calculation will still be performed periodically with a larger time cycle to monitor margin to OLMCPR and/or power density limit, caused by flow change and/or xenon variation. d) Table Look Up A-factor and OLMCPR are determined through on-line table lookup, with the former as a function of relative rod pull distance and the latter as a function of reactor power (APRM) and core flow. A-factor is applied to the algorithm based on relative rod pull distance since the last monitor update, for all control rods being pulled and for all corresponding fuel regions being affected. B-factor values and M.sub.p values are determined through on-line table lookup, with the former as a function of rod position and power, and the latter as a function of reactor power (APRM) and core flow. e) 3D Monitor Result Download Monitor calculation result is downloaded automatically upon completion of the calculation when there is no active rod movement and after completion of successful self test. The monitor calculation and download is always carried out at the end of a set of rod withdrawal motion. This will avoid any error introduced due to continuous rod motion during monitor calculation. For operating limit MCPR and KW/FT (or MAPRAT) setpoint calculation, the monitor result is automatically transferred into the algorithm input data entry memory after self test completion. For safety limit MCPR setpoint calculation, operator acknowledgement of the correctness of the monitor thermal limit data is required before this data is transferred into the algorithm input data entry memory. The SLMCPR setpoint thermal limit input update is required if the SLMCPR setpoint exceeds the operating limit MCPR setpoint. f) Rod Block If any single setpoint is exceeded by the instantaneously scanned and processed LPRM values, a rod block signal is generated by the comparator unit and sent to the RCIS for action. However, this rod block signal can be reset and cleared if a new setpoint calculation shows the setpoint is no longer exceeded. Other rod(s) then can be selected and withdrawn, either automatically through programmed rod withdrawal sequence or manually. If the number of failed LPRM detectors exceeds an allowed limit (defined in next section), a rod block signal will be issued (by RCIS). g) Rod Block Reset For rod block on SLMCPR, it cannot be reset either automatically or manually. Under this condition, operation must be transferred to manual if it is in auto. It cannot go back to auto until the OLMCPR rod block function is operational. The operator can then manually reset the block only if further setpoint calculation shows the instantaneous ATLM signal no longer exceeds this SLMCPR setpoint. For rod block on OLMCPR, it can be reset only if further setpoint calculation shows the instantaneous ATLM signal no longer exceeds the setpoint. For rod block on OLMCPR, the reset clearance can be done automatically or manually. For auto reset, the blocked rod is first to be inserted slightly (1% stroke). This logic can be programmed into the auto rod motion logic. h) Flow Block & Reset If the setpoint calculated by the flow block algorithm is exceeded by the LPRM values, a flow block signal is sent to the recirculation flow control system. It can be cleared by the operator action if subsequent ATLM readings do not exceed the setpoint. i) Self Test There are four functions in the self test unit: test of calculated versus measured plant parameters, test of ATLM algorithm performance, manual functional test, and test display check. If any one of the first two tests fails, rod block signal and warning are issued. The functional tests will always issue rod block and warning. j) 3D Monitor Calculation Frequency During constant power operation, the monitor calculation frequency can be set at every 1 to 2 hours. During power change operation, the frequency can be set at once for every 10% power change or once every 20 minutes, whichever is sooner. Monitor calculation also can be demanded by the plant's power generation and control system automatically when all rod withdrawals are temporarily inhibited by the ATLM logic due to conservatism in A-factors. A new monitor update will clear all rod blocks under this condition. It can also be demanded anytime by operator request. LPRM Failures Failure of LPRM chambers will affect the processed LPRM readings of the ATLM which in turn will affect proper rod block setpoint. Allowable failure rate thus must be established for the designed LPRM monitoring assignment. The final bounding A/B factors include a margin that cover an average 15% random LPRM failure rate. The following logic is implemented that specifies allowable failure rate for any 4 LPRM strings surrounding a 16 bundle block, if the failure number of LPRM exceeds 50% out of the designed sensor number for monitoring from these 4 strings then this region output will issue rod block. However, such rod block can be cleared with this region bypassed. During any ganged rod withdrawal operation which covers either four or eight fuel regions, up to three regions can be bypassed and still allow active rod pull in these regions with the ATLM operational. This has taken gang rod operation into consideration. Specifically, for KW/FT monitoring this means at least 2 out of 4 LPRM sensors on each level should be operational, otherwise, up to three regions can be bypassed during gang rod operation.
	abstract	A method of treating resist features comprises positioning, in a process chamber, a substrate having a set of patterned resist features on a first side of the substrate and generating a plasma in the process chamber having a plasma sheath adjacent to the first side of the substrate. The method may further comprise modifying a shape of a boundary between the plasma and the plasma sheath with a plasma sheath modifier so that a portion of the shape of the boundary is not parallel to a plane defined by a front surface of the substrate facing the plasma, wherein ions from the plasma impinge on the patterned resist features over a wide angular range during a first exposure.
	abstract	A reactor power output measurement device measuring a neutron flux with a traversing incore probe (TIP) traversing in a vertical direction in a core of a reactor, and calibrating a detection sensitivity of a local power range monitor based on a measured neutron flux distribution in the axial direction inside the reactor, which is provided with an integrated control device 9 for transmitting control data to all of TIP drive control devices 13a through 13e and performing control/monitor of all of detector drive systems 17a through 17e. An integrated unit operation/monitor device 10 for operating/monitoring the integrated control device 9, and a TIP integrated controller 8 comprising an integrated unit input/output device 11 for inputting detection signals obtained from TIP detectors 18a through 18e to the integrated control device 9 via the integrated unit input/output device 11, and which switches to the integrated unit operation/monitor device 10 when the drive unit operation/monitor devices 15a through 15e suffer from failure.
	abstract	An apparatus that transports radiopharmaceuticals and protects individuals from radioactivity that includes a first body with a first hollow core open on a first edge and a second edge. The first hollow core surrounds an insert containing a hypodermic syringe. There is a second body with a second hollow core open on a first edge and closed on a second edge. The second hollow core surrounds the insert with the hypodermic syringe. A third body with a third hollow core open on a first edge has the third hollow core fixedly communicating with a hollow stem open on a second edge. The third hollow core surrounds the insert with the hypodermic syringe. A first connection means releasably communicates the first body with the second body and a second communication means releasably communicates with the first body and third body for providing protection from the radioactive agent. A third connection means releasably communicates the third body with a dose applicator for injecting and measuring the radiopharmaceutical in the hypodermic syringe. Finally, the dose applicator is for positioning the insert and the hypodermic syringe into and out of the first and third body whereby said individuals easily measure, transport and inject the radiopharmaceutical in the hypodermic syringe.
	summary
056569025	description	DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 5 illustrates a magnetic coupler suitable for magnetically coupling one or more motors 51 and 52 from a cylindrical motor chamber 53 into a second chamber 54 that radially encircles the cylindrical motor chamber. In this embodiment, motors 53 are electric motors, but in alternate embodiments, these motors can be replaced by pneumatic motors, gas-powered motors or any other actuator that can provide rotational power. As used herein, the term motor is to have this broad meaning. A sidewall 55 defines the radial extent of motor chamber 53 and enables a pressure difference to exist between chambers 53 and 54. In this particular embodiment, chamber 53 is a robot chamber in which is contained a robot that is to transfer wafers to and from a set of reaction chambers disposed circumferentially around the robot. Selection of one of these chambers for wafer transfer is achieved by rotation of the robot. Transfer of a wafer into or out of the selected chamber is achieved by linear, radial extension of a robot arm into and out of the selected chamber. Motor 51 is bolted to a motor mount 56 that rests on a shoulder 57 of sidewall 55. Alignment pins 58 extend from mount 56 into shoulder 57 to prevent rotation of mount 56 relative to sidewall 55. Motor 52 is bolted to a motor mount 59 that has a shoulder 510 that rests on top of sidewall 55. Alignment pins 511 prevent rotation of mount 59 relative to sidewall 55. The use of shoulders and alignment pins to correctly position these motors enables quick installation or removal of these motors. The ability to access, install and remove these motors through a top opening 512 also significantly reduces down time to replace a motor and simplifies routine maintenance of these motors. Such ease of maintenance and repair are important to high average wafer throughput through the wafer processing system. Motor 51 is coupled to a reduction gear 513 to reduce the rotation speed of a typical motor to a rotation of gear output shaft 514 more appropriate for providing power to the robot. Reduction gear output shaft 514 is attached to a magnet clamp 515 that presses against a bearing 516 and that holds a set of sixteen magnets 517, each of which is closely space from sidewall 55. Magnet clamp 515 (illustrated in greater detail in FIG. 6) contains, for each of the sixteen magnets clamped to it, a pair of radial outward fingers 61 and 62 that retain that magnet laterally. Each such finger has a shoulder 63 near its base to retain the associated magnet radially. Bolted to clamp 515 vertically above and below the magnets are a pair of retainer rings that lock these magnets into position vertically. Similarly, motor 52 is connected through a reduction gear 518 and a gear output shaft 519 to a magnet clamp 520 that presses against a bearing 521 and that holds a set of sixteen magnets 522. This magnet clamp also has radial outward fingers and shoulders that retain each magnet within the plane of the magnet clamp. Bolted to this magnet clamp above and below the magnets are a pair of magnet retainer rings that prevent vertical motion of these magnets. Robot vacuum chamber 54 is enclosed by cylindrical inner wall 55, an outer wall 811 (shown in FIG. 8), top wall 523 and bottom wall 524 which are bolted to one another. In this particular embodiment, walls 524 and 811 are formed as one unitary piece. A vacuum seal of chamber 54 is created by vacuum rings 525 and 526. Within robot chamber 54 are a set of sixteen magnets 527 retained within the plane of the magnets by a magnet clamp 528 that is similar to clamps 515 and 520, except that the fingers extend radially inward. Magnet retainer rings above and below the magnets are bolted to clamp 528 to retain these magnets vertically. A similar set of magnet clamp 529 and retainer rings hold a set of 16 magnets 530. A set of bearings 531-534 enable clamps 528 and 29 to rotate about motor axis A. As illustrated in FIGS. 6 and 7, all magnets 517 have the same magnetic pole pointing in the same circumferential direction around a rotation axis A. Similarly, all magnets 530 have the same magnetic pole pointing in the same circumferential direction around rotation axis A, but this circumferential direction is opposite to that for magnets 522. Radial pole plates 64 and 65 are formed of a ferromagnetic material so that the magnetic fields from magnets 517 are concentrated into radial directions for coupling to the magnets 530. Similarly, radial pole plates 66 and 67 concentrate the magnetic fields from magnets 530 into radial directions for coupling to magnets 517. As a result of the opposite circumferential directions of magnets 517 and 530, ring 529 rotates to a position for which each South pole plate 64 is circumferentially aligned with a North pole plate 66 and each North pole plate 65 is circumferentially aligned with a South pole plate 67. The concentration of magnetic field radially between these plates 64-67 produces a strong circumferential coupling that makes them rotate together over a wide range of torque that exceeds the amount of torque that can be provided by motor 51. As a result of this, when motor 51 rotates the set of magnets 517, then magnets 530 will rotate at the same rotation rate in the same rotation direction. This is the intended magnetic coupling of power across wall 55 from magnets 517 to 530. Similarly, when motor 52 rotates the set of magnets 522, then magnets 527 will rotate at the same rotation rate in the same direction. This is the intended magnetic coupling of power across wall 55 from magnets 522 to 527. As illustrated in FIG. 7, magnets 522 each has its magnetic poles oriented circumferentially. However, in contrast to magnets 517 in FIG. 6, every second magnet around the ring has its North pole oriented clockwise about axis A and the remainder have their North pole oriented counterclockwise. This alternating pattern of orientations is also utilized for magnets 527. Radial plates 71-74 also are ferromagnetic so that they concentrate the magnetic fields radially between clamps 520 and 528. Clamp 528 rotates to a stable position at which each North pole is opposite a South pole of clamp 520. The magnetic coupling is strong enough that a clamp 528 will rotate with clamp 520 for torques ranging up to a limit that exceeds the torque from motors 51 and 51. This pattern of magnetic pole orientations is selected to reduce magnetic coupling between the magnets in sets 522 and 528 with the magnets in sets 517 and 530. This reduction can be seen as follows. If the pattern of orientations were the same in sets 527 and 530, then a minimum energy as a function of relative angular positions of clamps 528 and 529 would occur when each magnet 527 was directly over a magnet 530 because this would bring each North pole in set 530 as close as possible to a South pole in set 527 and would also bring each South pole in set 530 as close as possible to a North pole in set 527. However, when the poles are alternated circumferentially as in FIG. 7, then if a magnet 65 (in FIG. 6) is directly below a magnet 75 (in FIG. 7) such that each magnets North pole is as close as possible to a South pole in the other set, then each magnet 66 will have its North pole as close as possible to a North pole of magnet 76 and its South pole as close as possible to a South pole of magnet 76. The net repulsion and attractions will substantially cancel so that there is a significantly reduced amount of coupling between magnets 530 and 527. This also significantly reduces the coupling of magnets 530 with magnets 522 and the coupling of magnets 527 with magnets 517. FIG. 8 is a top view of a robot 80 utilizing the magnetic coupler of FIG. 5. A first strut 81 is rigidly attached to magnet clamp 528 (see FIG. 7) and a second strut 82 is rigidly attached to magnet clamp 529 (see FIG. 6). A third strut 83 (in FIG. 8) is attached by a pivot 84 to strut 81 and by a pivot 85 to a wafer blade 86. A fourth strut 87 is attached by a pivot 88 to strut 82 and by a pivot 89 to wafer blade 86. This structure of struts 81-83, 87 and pivots 84, 85, 88, 89 form a "frog leg" type connection of wafer blade 86 to magnet clamps 528 and 529. When magnet clamps 528 and 529 rotate in the same direction with the same angular velocity, then robot 80 also rotates in this same direction with the same velocity. When magnet clamps 528 and 529 rotate in opposite directions with the same absolute angular velocity, then there is no rotation of assembly 80, but instead there is a linear radial movement of wafer blade 86 to a position illustrated by dashed elements 81'-89'. To provide light-weight rigidity so that struts 81 and 82 can be moved rapidly without an undue amount of wiggle, these struts should be a four-sided box sheet metal structure as in FIG. 9 (for strut 82). In this figure, a wafer 89 is shown as being loaded on wafer blade 86 to illustrate that the wafer blade can be extended through a wafer transfer slot 810 in a wall 811 to transfer such a wafer into or out of the robot chamber. This robot can be used in place of robot 28 of FIG. 2 to provide a robot that is free of particulate generation via a rotary vacuum seal The mode in which both motors rotate in the same direction at the same speed can be used to rotate the robot from a position suitable for wafer exchange with one of chambers 23-27 to a position suitable for wafer exchange with another of these chambers. The mode in which both motors rotate with the same speed in opposite directions is then used to extend the wafer blade into one of these chambers and then extract it from that chamber. Some other combination of motor rotation can be used to extend or retract the wafer blade as the robot is being rotated about motors 51 and 52. Because side wall 55 extends between top wall 523 and bottom wall 524, when a vacuum is produced within chamber 54, there is no vertical displacement of robot blade 86 with respect to wafer rest positions within external chambers, thereby maintaining alignment of wafer blade 86 with wafer wafers external to the robot vacuum chamber for any range of internal pressures within cavity 54. FIG. 10 illustrates an alternate embodiment of providing additional support between a top wall 1001 and a bottom wall 1002 of the robot chamber 1003. This "additional" support is in addition to support by sidewall 1004. In this embodiment, the additional support is provided by a rotatable shaft 1005. In this embodiment, the robot consists of motor 1010, thrust bearings 1006 and 1007, and wafer blade 1008. This robot has the single degree of freedom to rotate a wafer 1009 to any selected angular position about shaft 1005. Thrust bearings 1006 and 1007 enable shaft 1005 to rotate even though shaft 1005 is compressed by a force equal to twice the atmospheric pressure on top wall 1001. In an alternate of this embodiment, motor 1010 is anchored to bottom wall 1002 by support 1011 and thrust bearing 1007 is located within motor 1010. To keep wafer blade 86 directed radially away from the rotation axes of motors 51 and 52, a pair of intermeshed gears 812 and 813 are included at pivots 85 and 89. These gears are loosely meshed to minimize particulate generation by these gears. To eliminate play between these two gears because of this loose mesh, a weak spring 814 extends between a point 815 on one gear to point 816 on the other gear such that the spring tension lightly rotates these two gears in opposite directions until light contact between these gears is produced. To dampen oscillations in the robot during rotation or blade extension, wall 55 should be selected to be conductive so that eddy currents therein are produced to damp such oscillations. This wall can be coated with a conductive coating to enhance these eddy currents, but preferably wall 55 is of a conductive material such as aluminum so that bulk eddy currents can be generated.
047754940	abstract	An improved method of disposing of radioactive or hazardous liquids comprises placing the liquids in a container and adding a sodium montmorillonite over intervals until the composition is substantially solid in the container.
054886449	abstract	Spring assemblies are employed in adjoining ferrules of a spacer in a nuclear fuel bundle to bias the fuel rods against stops and hence position the fuel rods in the spacer. The spring assemblies in one form include back-to-back spring bodies having central leaves with forward projections extending through rectilinear openings in adjacent ferrules to engage fuel rods to bias the rods against stops at the opposite sides of the ferrules. Outer pairs of leaves straddle the central leaf and project rearwardly and join the spring bodies one with the other whereby the central leaves, end portions of the springs connected to the central and outer leaves, and the outer leaves act as paired springs in series, providing a low spring constant. In another form, a single spring body has a central leaf with a projection extending through an aperture of a ferrule to bias the fuel rod. The outer leaves bear against the outer surface of the adjoining ferrule. In this latter form, pins may be used to compress the springs to facilitate insertion of the fuel rods into the ferrules.
051606950	claims	1. Apparatus of enhancing nuclear fusion reactions comprising: a) a plasma, made up of ions and electrons, contained with a core region having a core radius; b) means for directing said ions and electrons of said plasma to converge toward said core region which includes one of (1) a central axis of a cylindrical system and (2) a center of a generally spherical system; c) means for recirculation said plasma in generally radial motion outwards from said core region and returning thereto by the action of the directing means on the ions and electrons of the plasma, and; d) means for enhancing the density of said plasma in the core region so as to increase nuclear fusion reactions by generating ion-acoustic electrostatic waves therein, said ion-acoustic electrostatic waves reducing the collisional mean free path of said ions to dimensions set by the wavelength of the said ion-acoustic electrostatic waves creater therein, thus enhancing density by collision-diffusion trapping of said ions to thereby enhance nuclear fusion reactions. a first, inner electrode structure and a second outer electrode structure spaced apart form one another; said first and second electrode structures being permeable to ions and electrons and being generally spherical and centered about said center of said generally spherical system, and means for providing a potential difference between said first and second electrode structures so as to accelerate positive ions located outside said first electrode structure inwardly, through said first electrode structure and toward said center. a first, inner electrode structure and a second outer electrode structure spaced apart form one another; said first and second electrode structures being permeable to ions and electrons and being generally cylindrical about said central axis of said cylindrical system; means for providing a potential difference between said first and second electrode structures so as to accelerate positive ions located outside said first electrode structure inwardly, through said first electrode structure and toward said central axis. a) forming a plasma, made up of ions and electrons, with a core region; b) directing ions and electrons of said plasma to converge toward one of (1) a central axis of a cylindrical system and (2) a center of a generally spherical system; c) recirculation said plasma in generally radial motion outwards from said core region and returning thereto by the action of the directing means on the ions and electrons of the plasma, and; enhancing the density of said plasma in the core region so as to increase fusion reactions by generating ion-acoustic electrostatic waves therein, said ion-acoustic electrostatic waves reducing the collisonal means free path of said ions to dimensions set by the wavelength of the said ion-acoustic electrostatic waves created therein, thus enhancing density by collision-diffusion trapping of said ions to thereby enhance nuclear fusion reactions. (a) generating a spherically symmetric electrostatic field in a spherical system having a center or a cylindrically symmetric electrostatic field in a cylindrical system having a central axis, (b) producing a plasma of ions and electrons in said spherically symmetric or cylindrically symmetric electrostatic field for accelerating said ions in a radial direction toward the center of said spherical system or the central axis of said cylindrical system, (c) accelerating said ions along said radial paths with a speed and flux density such as to produce ion acoustic waves at a core radius r.sub.c wherein the wavelength of said ion acoustic waves is less than r.sub.c and such that the ratio of change of the ion acoustic wavelengths with change in radial position of the ions is directly proportional to the ion radial position. increasing the density of said ions within said core by injecting ions or a neutral gas within or near said core and by confining said ions utilizing said collisional interactions. (a) generating a spherically symmetric electrostatic field in a spherical system having a center or a cylindrically symmetric electrostatic field in a cylindrical system having a central axis, (b) producing a plasma of ions and electrons in said spherically symmetric or cylindrically symmetric electrostatic field for accelerating said ions in a radial direction toward the center of said spherical system or the central axis of said cylindrical system, (c) accelerating ions along said radial paths such that their density within said core and their injection power are related such as to fall within the region 1000 of FIG. 7. (a) generating a spherically symmetric electrostatic field in a spherical system having a center or a cylindrically symmetric electrostatic field in a cylindrical system having a central axis, (b) producing a plasma of ions and electrons in said spherically symmetric or cylindrically symmetric electrostatic field for accelerating said ions in a radial direction toward the center of said spherical system or the central axis of said cylindrical system so as to circulate through a core region having a core radius, (c) accelerating ions along said radial paths such that their density within said core region and their injection power are related such as to satisfy the following two relationships: EQU n.sub.c >(2.pi.E.sub.w /Z.sup.2 e.sup.2 r.sub.c.sup.2)(a.sub.ij) (1) EQU P.sub.inj .gtoreq.5.21E-3(a.sub.ij)(E.sub.w.sup.2.5 /Z.sup.2 G.sub.j) (watts) (2) n.sub.c is the ion density at the core radius; E.sub.w is the energy of the ions at the core radius; r.sub.c is the critical radius at which ion-acoustic waves are generated; a.sub.ij is 1 for ion/ion acoustic waves and (m.sub.c /m.sub.i).sup.0.5 for ion/electron acoustic waves wherein m.sub.c and m.sub.j are the mass of the electron and ion respectively; P.sub.inj is the ion injection power; G.sub.j is the electron recirculation ratio; and Z is the ionic charge in units of electronic charge e. E.sub.w is the energy of the ions at the core radius; a.sub.ij is 1 for ion/ion acoustic waves and m.sub.c /m.sub.i).sup.0.5 for ion/electron acoustic waves wherein m.sub.c and m.sub.i are the mass of the electron and ion respectively; P.sub.inj is the ion injection power; and G.sub.j is the electron recirculation ratio. n.sub.c is the ion density at the core radius; r.sub.c is the critical radius at which ion-acoustic waves are generated; and Z is the ionic charge in units of electronic charge e. 2. Apparatus as recited in claim 1 wherein said directing means comprises: 3. Apparatus as recited in claim 2 wherein said first and second electrode structures are enclosed in an electron reflective boundary wall. 4. Apparatus as recited in claim 2 wherein said first and second electrode structures comprise sets of grid wires. 5. Apparatus as recited in claim 2 wherein said first and second electrode structures comprise sheet conductors. 6. Apparatus as recited in claim 2 wherein said first and second electrode structures comprise point or button-like electrodes. 7. Apparatus as recited in claim 1, wherein said directing means comprises: 8. Apparatus as recited in claim 7 wherein said first and second electrode structures are enclosed in an electron reflective boundary wall. 9. Apparatus as recited in claim 7 wherein said first and second electrode structures comprise sets of grid wires. 10. Apparatus as recited in claim 7 wherein said first and second electrode structures comprise sheet conductors. 11. Apparatus as recited in claim 7 wherein said first and second electrode structures comprise point or button-like electrodes. 12. Apparatus as recited in claim 1, wherein said directing means comprises two concentric spherical arrays of conducting electrodes having electrode elements thereon, said elements of each array positioned with spherical angular coordinates so as to generally correspond to those of one another and energized to electric potentials so as to accelerate ions inwardly with energies in the range of 5 keV to 150 keV for the collisional-compression of ions of deuterium (D) with ions of D and/or tritium (T) and/or helium-3 (.sup.3 He), and to 35 keV to 700 keV for the collisional compression of ions of hydrogen (protons, p) with ions of lithium-6,7 (.sup.6 Li, .sup.7 Li), beryllium-9 (.sup.9 Be), boron-11 (.sup.11 B), or other suitable combinations capable of undergoing nuclear fusion reactions. 13. Apparatus as recited in claim 1 wherein said directing means comprises wires or sheet strip conductors oriented so that their small dimension (thickness) is arranged to be circumferential and their large dimension (width) is arranged to be radial, said conductors arranged in a spherical geometric pattern to lie in centrally-fixed planes containing the edges of any regular or irregular polyhedron. 14. Apparatus as recited in claim 1 wherein said directing means comprises wires or sheet strip conductors oriented so that their small dimension (thickness) is arranged to be circumferential and their large dimension (width) is arranged to be radial, said conductors arranged in a spherical geometric pattern to lie along the path of any curvilinear winding that circumscribes a sphere with approximately equal areas between adjacent elements of the geometric pattern. 15. Apparatus as recited in claim 14, wherein said spherical geometric pattern is selected from the group of a curvilinear cube, tetrahedron, octahedron, dodecahedron, or "tennis ball seam" winding. 16. Apparatus as recited in claim 1 wherein said directing means comprises conductors arranged in a spherical geometric pattern to lie in centrally-fixed planes containing the edges of any regular or irregular polyhedron figure, said conductors in the form of a "button", point or rod electrodes placed at the vertices of said polyhedral figures. 17. Apparatus as recited in claim 2, wherein said first and second electrode structures include means for minimizing magnetic fields due to current flow within said electrode structures, thus avoiding magnetic influences on ion/electron motion within said region, and thus allowing the electric fields resulting from said potential difference to effect and control the motion and collisional-compression of ions within the spherical system. 18. Apparatus as recited in claim 17 wherein said minimizing means includes means for passing current through said first electrode structure in pairs of opposing current paths so as to null effects of any magnetic field resulting from current flowing in a single current path, and further includes means in said second electrode structure for passing current through said second electrode structure in pairs of opposing current paths so as to null effects of any magnetic field resulting from current flowing in a single current path. 19. Apparatus as recited in claim 7, wherein said first and second electrode structures include means for minimizing magnetic fields due to current flow within said electrode structures, thus avoiding magnetic influences on ion/electron motion within said region, and thus allowing the electric fields resulting from said potential difference to effect and control the motion and collisional-compression of ions within the cylindrical system. 20. Apparatus as recited in claim 19 wherein said minimizing means includes means for passing current through said first electrode structure in pairs of opposing current paths so as to null effects of any magnetic field resulting from current flowing in a single current path, and further includes means in said second electrode structure for passing current through said second electrode structure in pairs of opposing current paths so as to null effects of any magnetic field resulting from current flowing in a single current path. 21. Apparatus as recited in claim 1 wherein said means for directing comprises an inner grid array (g1) whose radius (rg1) is in the range of 20 cm rg1<200 cm, and an outer concentric grid array (g2) larger than and separated from the inner grid array by a radial spacing (.delta.r12) in a range limited by electrical arc breakdown between the concentric grid arrays. 22. Apparatus as recited in claim 21 wherein the minimum practical arc-breakdown-limited radial spacing (in cm) is given by the formula .delta.r12.gtoreq.E.sub.g /20, where E.sub.g is the electric potential difference between the inner grid array (g1) and its surrounding outer grid array (g2), in thousands of volts (kilovolts, kV). 23. Apparatus as recited in claim 22 wherein said potential difference E.sub.g is in the range of 5 kV <E.sub.g <600 kV. 24. Apparatus as reoited in claim 23 wherein E.sub.g =400 kV corresponding to a grid spacing of .delta.r12 .gtoreq.20 cm, and wherein said potential difference is selected to be greater than the desired mean ion energy E.sub.w of said ions at said grid array (gl). 25. Apparatus as recited in claim 21 wherein said directing means further includes an additional grid array placed outside the inner and outer grid arrays, and means for supplying an alternating electric potential to said additional grid array outside the region of the inner and outer grid arrays in order to control the motion of electrons between said outer and additional grid arrays. 26. Apparatus as recited in claim 25 wherein said additional grid array is disposed spherically symmetrically around the inner and outer grid arrays, conforms to the shape and angular position of the outer grid array and is energized oppositely to the voltage difference between said inner and outer grid arrays so that electrons accelerated in an outward direction between grids g1 and g2 will be decelerated and returned inward in the region between g2 and g3. 27. Apparatus as recited in claim 1 wherein said means for directing comprises an inner grid array (g1) having a radius (rg1), and an outer concentric grid array (g2) larger than and separated from the inner grid array by a radial spacing (.delta.r12), and an additional grid array placed outside the inner and outer grid arrays, and means for supplying an alternating electric potential to said additional grid array outside the region of the inner and outer grid arrays in order to control the motion of electrons between said outer and additional grid arrays. 28. Apparatus as recited in claim 27 wherein said additional grid array is disposed spherically symmetrically around the inner and outer grid arrays, conforms to the shape and angular position of the outer grid array and is energized oppositely to the voltage difference between said inner and outer grid arrays so that electrons accelerated in an outward direction between grids g1 and g2 will be decelerated and returned inward in the region between g2 and g3. 29. Apparatus as recited in claim 27 wherein said additional grid array is formed of a plurality of conducting wires arranged in a rectangular pattern to form rectangular cells, as in a wire mesh screen, and wherein each wire carries current in such a manner that each rectangular cell is surrounded by a loop of current producing a central magnetic field within the cell such that each adjacent cell is of opposite magnetic polarity, said central magnetic fields reflecting outgoing electrons at the radial position of the additional grid array and returning them on inwardly directed trajectories. 30. A method of enhancing nuclear fusion reactions comprising the steps of: 31. A method as recited in claim 30 wherein the step of directing includes providing an inner grid array (g1) having a radius (rg1), and an outer concentric grid array (g2) larger than and separated from the inner grid array by a radial spacing (.delta.r12). 32. A method as recited in claim 31 including the step of providing a potential difference between said inner and outer grid arrays such that ions in the space between grid arrays g1 and g2 will be accelerated with nearly pure radial motion towards the system center at energies E.sub.i that are in the range E.sub.i .ltoreq.E.sub.g, resulting in an increase in ion density as the system center is approached more closely, where E.sub.g represents the ion maximum energy at the center. 33. A method as recited in claim 32 further comprising the step of decelerating said inward-moving ions, inside grid array g1, by converting ion kinetic energy of radial motion into electrostatic energy of repulsion due to the buildup of positive ion density at the system center, and into increasing kinetic energy of transverse (angular) motion with decreasing radial distance from the center, whereby a virtual anode is formed around the system center. 34. A method as recited in claim 33 further including the step of attracting electrons from the grid array g1 and from the space within g1, toward the system center, following said ions, said electrons tending to neutralize the buildup of repulsive positive charge of said ions near the system center, thus permitting the ions to continue their radial inward motion, with continuing increase in ion density. 35. A method as recited in claim 34 wherein the ratio of ion current to electron current in the region of the system center is controlled to fall in the range of 0.5 to 0.02. 36. A method as recited in claim 32 further including the step of selecting the initial density of ions of said plasma in the region between g1 and g2 such that the mean free path for electron/atom ionization collisions in this region, under the influence of the potential difference is E.sub.g is comparable to or less than the spacing between said inner and outer grid arrays. 37. A method as recited in claim 33 further including the step of ceasing radial inward motion of said ions at a momentum-convergence-limited radius r.sub.o, given by r.sub.o .apprxeq.(E.sub.t /E.sub.w).sup.0.5, where E.sub.t is the transverse energy of the ion at the position of grid array g1 and E.sub.w is the mean energy of the ions at the position of grid array (gl). 38. A method as recited in claim 36 further including the step of ceasing radial inward motion of said ions at a momentum-convergence-limited radius r.sub.o, given by r.sub.o .apprxeq.(E.sub.t /E.sub.w).sup.0.5, where E.sub.t is the transverse energy of the ion at the position of grid array g1, and E.sub.w is the energy of the ions at the position of grid array (gl). 39. A method as recited in claim 38 further including the step of applying a grid potential difference [E.sub.i ] E.sub.g .gtoreq.E.sub.w and increasing ion density towards and within the central core near to and inside of r.sub.o, by adjusting ion density within the region between the inner and outer grid arrays to sufficiently large values that the total current density in the core region within said inner grid array exceeds a critical value for the given ion energy such that the converging ion current will initiate and resonantly maintain ion acoustic waves those wavelength is small compared to the momentum-limited convergence radius, r.sub.o, at a critical core radius r.sub.c comparable to r.sub.o. 40. A method as recited in claim 31 further including the step of generating ion acoustic waves within the region interior to said critical core radius r.sub.c and tapping incoming ions within said critical core region by reflecting and scattering said ions from the boundaries of said ion acoustic waves, whereby said ions move diffusively through and within the said critical core region with mean free paths between such reflections and scatterings that are much smaller than the dimensions of said critical core region. 41. A method as recited in claim 40 wherein the step of generating ion acoustic waves includes injecting said ions with an injection power greater than 10-100 kw, with rg1 between 50-100 cm, with ion current recirculation ratios of 10-30, and with a potential difference between said inner and outer grid arrays between 10-400 keV. 42. A method as recited in claim 41 wherein injection power is in the range 100-500 kw with radius g1 at 40-80 cm, ion recirculation ratio of 10-20 and potential difference energy of 15-30 keV for use with DT fuels. 43. A method of enhancing nuclear fusion reactions comprising the steps of: 44. The method as recited in claim 43 wherein said accelerating step includes adjusting the ion density and ion flow such that the ion acoustic wavelength is at least approximately an integer divisor of the circumference of the sphere having said core radius r.sub.c. 45. The method as recited in claim 44 maintaining said ion acoustic waves so as to cause collisional interactions of said ions with said ion acoustic waves, said collisional interactions occurring on the scale of said ion acoustic wavelength and within said core radius r.sub.c, and 46. A method of enhancing nuclear fusion reactions comprising the steps of: 47. The method as recited in claim 46 wherein said accelerating step includes accelerating said ions such that their density and injection power are related such as to fall within the region 1000 of FIG. 7 excluding the region 1010. 48. The method as recited in claim 46 wherein r.sub.c is in the range of 0.1-2 cm, and E.sub.w is in the range of 10.sup.4 -10.sup.5 eV. 49. A method of enhancing nuclear fusion reactions comprising the steps of: 50. Apparatus as recited in claim 1, wherein said enhancing means comprises means for injecting said ions into said core region so that ion injection power, P.sub.inj satisfies at least one of the following relationships: EQU P.sub.inj .gtoreq.5.21E-3(a.sub.inj)(E.sub.w.sup.2.5 /Z.sup.2 G.sub.j) (watts) (1) EQU P.sub.inj .gtoreq.5.9E-3(a.sub.inj)(E.sub.w.sup.2.5 /Z.sup.2 G.sub.j) (watts) (2) 51. Apparatus as recited in claim 50 wherein the density within the core radius satisfies the following relationship: EQU n.sub.c >(2.pi.E.sub.w /Z.sup.2 e.sup.2 r.sub.c.sup.2)(a.sub.ij)
047175311	description	DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 1 thereof, there is shown a railroad-type transport car, generally designated by the reference character 10, which is employed in a conventional manner within the nuclear reactor fuel assembly transfer system of the present invention. The transport car 10 comprises a primary, longitudinally extending, central support beam member 12 to which are fixedly secured, such as, for example, by welding or the like, at least two, longitudinally spaced, transversely extending secondary crossbeam members 14 and 16. For the purposes of this discussion, forward movement of the transport car 10, as designated by the arrow A, is considered to be in the direction leading from the reactor containment handling pool, not shown, to the spent fuel storage pool, also not shown. In this context, it is seen that the forward crossbeam 14 is fixedly secured to the upper surface of the central beam member 12 at an axial position intermediate the ends of beam 12, while the rearward crossbeam 16 is fixedly secured to the undersurface of the central beam member 12 at the trailing end thereof. Forward crossbeam 14 has upstanding, square-shaped plates 18 fixedly secured to the opposite ends thereof, while rearward crossbeam 16 has rearwardly extending, elongated plates 20 similarly fixedly secured to the opposite ends thereof. Each of the plates 18 serves as a mounting frame for a railroad-type wheel 22, while each of the substantially rectangularly shaped plates 20 serves as a mounting frame for a plurality of longitudinally spaced wheels 22. In this manner, transportation of car 10 along rails or tracks, not shown, disposed within the plant transfer tube or conduit, the reactor containment handling pool, and the spent fuel storage pool, all of which is also not shown but conventionally well-known, is facilitated. An upwardly extending, arch-shaped tie beam 24 is also provided to connect the rear ends of the car plates 20 together in order to provide the rear end of the car with the requisite amount of lateral structural rigidity. A fuel container 26, having a configuration of a substantially rectangular parallelopiped which is square in transverse cross-section, is pivotably mounted upon the transport car 10 by means of trunnions 28. The trunnions 28 are fixedly secured atop the side car plates 20 at an axial position interposed between the forwardmost set of wheels 22 mounted upon plates 20 and the rear sets of wheels 22 plates 20. In this manner, the fuel container 26 is able to be pivotably moved between its vertical or upended position at the extreme ends of its transportation travel path, and its horizontal position characteristic of its transportation through the plant transfer tube or conduit, not shown. It is noted that when the fuel container 26, which of course will contain either spent or fresh fuel assemblies during a transportation mode through the plant transfer tube or conduit between the reactor containment handling pool and the spent fuel storage pool, is disposed in its horizontal mode or disposition, the forward end of the container 26 is effectively laterally confined by means of a cradle defined by means of the forward crossbeam 14 and the upstanding wheel frames 18. In addition, a suitable latch mechanism 30 may be secured upon the forward end of central support beam 12 for retaining the fuel container 26 in its horizontal transport mode, however, for the purpose of this patent application and the present invention embodied herein, this latch mechanism 30 forms no part of the present invention. Lastly, it will be appreciated that, as viewed in FIG. 1, the lower end of the fuel container 26 is of course closed in order to retain the fuel assemblies, therein not shown, when the fuel assemblies are loaded into the fuel container 26 through means of the open upper end of the container by suitable crane or elevator apparatus, also not shown. When the fuel container 26 is then pivotably moved to its horizontal mode for transportation through the plant transfer tube or conduit, it is desired to effectively close the upper or forward end of the container 26 so as to prevent any inadvertent or undesired axial movement of the fuel assemblies out of the fuel container 26 in response to any axial loads which may possibly be impressed upon the fuel container-fuel assemblies assemblage during the horizontal transfer mode. In this regard, an upstanding fuel assembly retainer plate 32 is fixedly secured to the forward end of the transport car central beam 12 so as to effectively cover the open forward end of the fuel container 26 as the same is pivotably moved downwardly from its vertical upended, fuel load-unload mode to its horizontal transportation mode. In accordance with the present invention, there are provided upending mechanisms disposed within the reactor containment handling and spent fuel storage pools for automatically pivoting the fuel container 26 and its associated fuel assemblies between the aforenoted vertical loading-unloading and horizontal transport modes in response to the translational movement of the fuel container-fuel assemblies-transport car assemblage. With particular reference now being made to FIG. 2 of the drawings, the upending mechanism and system disposed within the spent fuel storage pool is shown as including an upender arm 34. Arm 34 is pivotably mounted upon a pivot rod 36 which is fixedly secured within the spent fuel storage pool by suitable means, not shown. A counterweight 38 is fixedly mounted upon a counterweight arm 40 which is integrally secured to the arm 34 so as to define an acute angle therewith, the counterweight 38 being disposed forwardly of the upender arm 34 as viewed in the forward direction of travel of the fuel container as designated by the arrow A. A horizontally disposed stop plate 42 is fixedly secured within the storage pool at a location rearwardly of upender arm 34, and consequently, under the weighted action of counterweight 38, upender arm 34 is normally vertically disposed against stop plate 42. Upender arm 34 extends downwardly beneath the level of stop plate 42, and the lower end of upender arm 34 is provided with a transversely extending bar 44 such that its ends project laterally outwardly from the plane of upender arm 34. The upender mechanism is disposed at an elevational level above the plane of horizontal travel of the fuel container 26 when the same is disposed within its horizontal transportation mode or orientation. A pair of brackets 46 are fixedly secured to the upper surface 48 of fuel container 26 at an axial or longitudinal location which is forwardly of the trunnions 28. Each of the brackets 46 is provided with a forwardly extending open slot 50 which is disposed at an elevational level matching that of the upender bar 44. In this manner, as the fuel container emerges from the plant transfer tube or conduit and is transported into the spent fuel storage pool, the fuel container slotted brackets 46 will engage the ends of upender arm bar 44 and be caused to automatically pivot upwardly from its horizontal transport mode to its vertical unload-load mode. This last-mentioned operational sequence may be appreciated with reference being made to FIG. 3 of the drawings wherein such movement of the fuel container 26, as caused by the upending system of the present invention, is schematically illustrated. As the fuel container proceeds from the reactor containment handling pool toward the spent fuel storage pool in its horizontal transportation mode, and in the direction of movement as designated by the arrow A, the fuel container will emerge from the plant transfer tube or conduit and approach the upender mechanism disposed within the spent fuel storage pool. In FIG. 3, the upender mechanism is schematically illustrated as including the upender pivot rod 36 and upender pick-up bar 44. The fuel container 26 is illustrated in various positions relative to the upender mechanism as exemplified, for example, by its approach position B wherein the fuel container trunnions are noted as 28'. When the fuel container is at such relative position, the fuel container upender brackets 46' are still upstream of the upender pick-up bar 44. As the fuel container 26 continues to approach the upender mechanism and the pick-up bar 44, engagement is made between the fuel container brackets 46 and the pick-up bar 44 when the fuel container trunnions are at station or position C. Continued horizontal translational movement of the railroad transport car 10 causes the corresponding translational movement of the fuel container 26 in the direction of arrow A and as illustrated by the illustrative location of the fuel container trunnions 28" at station or position D, however, as a result of the engagement of the fuel container brackets 46 with the upender pick-up bar 44, the upender arm 34, upender pick-up bar 44, fuel container 26, and fuel container brackets 46 are automatically caused to move to their upended positions denoted respectively at 34", 44", 26", and 46". In effect, then, by means of the present invention upending system, the fuel container is automatically caused to move, by means of the single translational movement of the railroad transport car 10, simultaneously through both translational and pivotable movements at the end of its travel path within the spent fuel storage pool. A horizontally disposed stop plate 54, similar to stop plate 42, is located within the lower depths of the spent fuel storage pool so as to arrest the pivotable movement of the trailing end of the fuel container 26" and thereby orient the same in its vertical mode whereby the container 26" is now made ready for its spent fuel unloading-fresh fuel loading operations by means of the suitable elevator or crane apparatus, not shown. Suitable stop means, also not shown, are provided immediately downstream of the end of the railroad rails or tracks for similarly arresting the translational movement of the transport car at the position or station D of trunnions 28". It is of course to be appreciated that the upending mechanism of the present invention is located within the spent fuel storage pool at a sufficient distance downstream from the end of the plant transfer tube or conduit extending into the spent fuel storage pool so as to in fact permit the clearance of the fuel container 26 beyond the transfer tube terminal end whereby the pivotable upending movement of the fuel container 26 may in fact be achieved. Furthermore, it is to be noted that the counterweight mechanism 38 serves the additionally desired function of maintaining engagement between the upender pick-up bar 44 and the fuel container brackets 46. If it is found in practice that this counterweighted force is required to be supplemented, suitable spring mechanisms, not shown, may be incorporated within the upender arm system so as to tend to bias the same still further toward its normally vertical mode as illustrated within FIG. 2. Another feature to be appreciated from the present invention system is that the trunnions 28 of the fuel container 26 are disposed rearwardly of the center of the fuel container as viewed along the axial length thereof. In this manner, the center of gravity is disposed to the right, or downstream, of the trunnions 28 of the fuel container as viewed, for example, in FIG. 3. As a result of this particular mounting of the fuel container upon the transport car 10, the fuel container 26 will tend to assume its horizontal transportation mode. This enhances the stability of the system, and acts in conjunction with the counterweight forces impressed upon the upending mechanism by means of counterweight 38. These forces become particularly active when the fuel container is caused to move from its vertical mode illustrated at 26" in FIG. 3 to its horizontal transport mode 26 upon completion of a fresh-fuel loading operation, and the commencement of a transport mode from the spent fuel storage pool toward the reactor containment handling pool. During the initial movement of the fuel container from its vertical mode 26" to its horizontal transport mode 26, it will of course be appreciated that the upending system of the present invention operates in precisely the same manner as described hereinabove, except in reverse, with disengagement of the upender pick-up bar 44 and the fuel container brackets 46 being achieved when the fuel container trunnions are located at station C. As has been briefly alluded to hereinbefore in connection with the general operation of the fuel transfer system characteristic of a nuclear plant, upending means must likewise be provided within the reactor containment handling pool of the plant, and in accordance with the present invention, such means is illustrated within FIG. 4. This system is operationally similar, but somewhat reversed, with respect to the upending system employed within the spent fuel storage pool, and is seen to include a pair of brackets 146 fixedly secured to the underside of fuel container 26. The brackets 146 are disposed forwardly of the fuel container trunnions 28, as considered in view of the relative direction of travel of the fuel container from the spent fuel storage pool to the reactor containment handling pool as designated by the arrow E, and include forwardly open slots 150. An upending mechanism is disposed within the reactor containment handling pool, and is seen to comprise an upender arm 134 pivotably mounted upon a pivot rod 136 which is fixedly secured within the reactor containment handling pool by suitable means, not shown. A counterweight 138 is fixedly mounted upon a counterweight arm 140 which is integrally formed with upender arm 134 so as to define therewith an obtuse angle such that the counterweight 138 is disposed below and rearwardly of upender arm 134. A horizontally disposed stop plate 142 is fixedly secured within the reactor containment handling pool at a location rearwardly of upender arm 134, and consequently, under the force of counterweight 138, the upender arm 134 is normally disposed vertically against stop plate 142. The upender arm 134 extends vertically above stop plate 142, and the upper end of arm 134 is provided with a transversely extending bar 144 such that its ends project laterally outwardly from the plane of arm 134. The upender mechanism is disposed at an elevational level below the plane of horizontal translational movement of the fuel container 26 so as not to interfere with the transportation thereof into the reactor containment handling pool, however, the upender pick-up bar 144 is disposed at an elevational level which matches that of the bracket slots 150 so as to operationally engage the same. In this manner, as the fuel container 26 emerges from the plant transfer tube or conduit into the reactor containment handling pool, the upending mechanism within the containment pool will automatically cause the leading end of the fuel container 26 to be pivoted downwardly whereby the fuel container 26 is ultimately re-oriented to its vertical fresh fuel unloading mode. This last-mentioned operational sequence may be appreciated from reference being made to FIG. 5 of the drawings wherein such movement of the fuel container 26, and the interaction with the upending mechanism within the reactor containment pool, is schematically illustrated. As the fuel container proceeds in its horizontal transport mode through the plant transfer tube or conduit and emerges from the same, the container 26 will enter the containment pool and approach the upending mechanism illustrated within FIG. 4. In FIG. 5, the upending mechanism of FIG. 4 is schematically illustrated as including the upender pivot rod 136 and the upender pick-up bar 144. The fuel container 26 is illustrated in various positions relative to the upender mechanism as exemplified, for example, by its approach position F wherein the fuel container trunnions are noted as 28'. When the fuel container 26' is at such relative position, the fuel container upender brackets 146' are still upstream of the upender pick-up bar 144. As the fuel container 26 continues to approach the upender mechanism and the pick-up bar 144, engagement is made between the fuel container brackets 146 and the pick-up bar 144 when the fuel container trunnions 28 are disposed at station or position C. Continued horizontal translational movement of the railroad transport car 10 causes the corresponding translational movement of the fuel container 26 in the direction of arrow E and as illustrated by the location of the fuel container trunnions 28" at station or position D. However, as a result of the engagement of the fuel container brackets 146 with the upender pick-up bar 144, the upender arm 134, upender pick-up bar 144, fuel container 26, and fuel container brackets 146 are automatically caused to be pivoted downwardly so as to achieve their upended positions 134", 144" , 26", and 146", respectively. A horizontally disposed stop plate 154 is located within the lower depths of the reactor containment handling pool so as to arrest the downwardly pivotable movement of the leading end of the fuel container 26" and thereby orient the same in its vertical mode whereby the container 26" is now made ready for its fresh fuel unloading-spent fuel loading by means of suitable elevator or crane apparatus, not shown. Suitable stop means, also not shown, is also provided immediately downstream of the end of the railroad rails or tracks within the containment pool for similarly arresting the translational movement of the transport car corresponding to the position or station D of trunnions 28". It is to be noted at this juncture that the aforenoted relative disposition of the trunnions 28 and the center of gravity of the fuel container likewise enhances the operational stability of the system within the reactor containment handling pool as such was characteristic of the operational modes within the spent fuel storage pool. Referring now to FIG. 6 of the drawings, a second, modified arrangement of the upending system of the present invention is disclosed. While the system of FIG. 6 is similar to that of FIG. 2 so as to be employed within the spent fuel storage pool of the fuel handling building, another system similar to that of FIG. 6 yet modified in accordance with the operational orientation of the system of FIG. 4, may likewise be provided so as to be capable of being employed within the reactor containment pool. As seen in FIG. 6, in lieu of the single dependent upender arm 34 of the embodiment of FIG. 2, the system of FIG. 6 employs a pair of laterally spaced dependent upender arms 234. In addition, in lieu of the single laterally outwardly projecting pick-up bar 44 of the system of FIG. 2, each arm 234 is provided at its lower end with a laterally inwardly projecting pick-up bar 244. The arms 234 are pivotally supported by suitable pivot rods, not shown, and are connected together by means of a transversely extending support bar 252. A pair of counterweights 238 are respectively operatively associated with each upender arm 234 through means of counterweight arms 240 integrally formed with the upender arms 234. Another modification of the system of FIG. 2 as embodied within the system of FIG. 6 resides in the disposition of the upender fuel container brackets 246 upon the sidewalls of the fuel container 226 as opposed to the same being disposed upon the upper and lower surfaces of the container. The brackets 246 are of course still provided with forwardly open slots 250 whereby the brackets 246 can operatively engage the upender pick-up bars 244. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.
042253900	abstract	Ion exchangers which reversibly store borate ions in a temperature dependent process are combined with evaporative boric acid recovery apparatus to provide a boron control system for controlling the reactivity of nuclear power plants. A plurality of ion exchangers are operated sequentially to provide varying amounts of boric acid to a nuclear reactor for load follow operations. Evaporative boric acid recovery apparatus is utilized for major changes in the boron concentration within the nuclear reactor.
	abstract	A passive cooling system for a reactor core of a large-scale pressurized water reactor nuclear power plant includes a shield building having an outer wall and a through air inlet arranged on an upper part of the outer wall, a water tank arranged at an upper part of the shield building, a cooling water distribution plate arranged above a top of a containment within the shield building, a spray pipe arranged at an inside of the top of the shield building and having a water inlet end and a water outlet end, wherein the water inlet end is connected to a bottom of the water tank and the water outlet end is extended to be above the cooling water distribution plate, and an air deflector arranged between the shield building and the containment and having an upper end connected to an inside of the top of the shield building.
	description	The present invention relates generally to ion detection, and more particularly to a method and device for detecting positively charged ionized particles, as well as negatively charged ionized particles. Mass spectrometry has proven to be an effective analytical technique for identifying unknown compounds and for determining the precise mass of known compounds. Advantageously, compounds can be detected or analysed in minute quantities allowing compounds to be identified at very low concentrations in chemically complex mixtures. Not surprisingly, mass spectrometry has found practical application in medicine, pharmacology, food sciences, semi-conductor manufacturing, environmental sciences, security, and many other fields. A typical mass spectrometer includes an ion source that ionizes particles of interest. The ions are passed to an analyser region, where they are separated according to their mass (m)-to-charge (z) ratios (m/z). The separated ions are detected at a detector. A signal from the detector may be sent to a computing or similar device where the m/z ratios may be stored together with their relative abundance for presentation in the format of a m/z spectrum. Typical ion sources are detailed in “Ionization Methods in Organic Mass Spectrometry”, Alison E. Ashcroft, The Royal Society of Chemistry, UK, 1997; and the references cited therein. Conventional ion sources may create ions by atmospheric pressure chemical ionisation (APCI); chemical ionisation (CI); electron impact (EI); electrospray ionisation (ESI); fast atom bombardment (FAB); field desorption/field ionisation (FD/FI); matrix assisted laser desorption ionisation (MALDI); or thermospray ionization (TSP). Ionized particles may be separated by quadrupoles, time-of-flight (TOF) analysers, magnetic sectors, and Fourier transform and quadrupole ion traps. Most ion sources are capable of producing ionized particles of positive or negative in polarity. For example, ESI transfers ions that are created in an acidic or basic solution directly into the gas phase. These ions are typically products of acid base reactions, such as protonated molecular adducts that tend to have basic sites, or negatively charged ions that are slightly acidic. APCI creates negative or positive ions in the gas phase, through chemical reactions. The ion detector in a mass spectrometer typically amplifies the ion signal striking a detection surface in order to provide sufficient signal-to-noise to measure intensity as a function of mass. Typical ion detectors include discrete electrodes with a resistive chain or a continuous channel with a resistive surface. Ions strike the first electrode, causing secondary electrons to be emitted from the surface and undergo a cascade of amplification as they are accelerated down the tube. The electron acceleration potential is the difference between the voltage on the first electrode and the last electrode. The emission of secondary electrons is velocity dependent, with higher velocity ions producing more emission. Ions of different mass-to-charge ratios are accelerated to the same energy (for the same charge state), and since E=1/2 mv2 the velocities and therefore the detection efficiency is mass dependent. Two common approaches to detection are used: pulse counting and analog current detection. In pulse counting detection, individual ion pulses are amplified, typically with a gain between 1×106 and 100×106, and detected as a current pulse. In analog current detection, the individual ion pulses are amplified with a gain between 1,000 and 10,000 and measured as a DC current. In some applications such as pharmaceutical drug discovery and drug development, it is desirable to investigate both positive and negative ions generated by one or more ion sources at approximately the same time. Therefore the mass analyser and ion detector must be able to rapidly switch from a mode that samples one polarity (e.g. negative ions) to another (e.g. positive ions). Such switching typically requires reversal of polarity of large applied voltages. To do so, a power supply having a high voltage range that is capable of quick switching is required. Moreover, extreme care must be taken to limit the noise resulting from power supply switching, and to ensure the output signal is not distorted, and that the detector is not damaged. Typically, providing a suitable supply and integrating it in an ion detector is costly, and complex. At least one ion detector that may be used to simultaneously detect both positively and negatively charged ions uses two conversion electrodes (also referred to as dynodes). Incoming positive ions strike one conversion electrode, held at high negative voltage, causing ejection of electrons. Incoming negative ions are attracted to, and strike the second conversion electrode, held at high positive voltage, causing ejection of a positive ion. Positive ions, and electrons emitted by the conversion electrodes are attracted to, and strike the inlet of a glass or similar electron multiplier, that is kept at a voltage above that of the conversion electrodes. Incident ions and electrons cause the emission of electrons, within the multiplier. Measurement of emitted electrons and associated energies allows for detection of ions incident on the conversion electrodes. By design, emitted electrons are detected at ground potential, and may thus be detected by an analog detector. Not surprisingly, conversion of ions to electrons at electrodes is dependent on the mass of the ions. Unfortunately, conversion of negative to positive ions at a conversion electrode is not well understood and may exhibit poor sensitivity for certain compounds. Thus, negative ion detection in such a detector is mass and compound dependent. Further, as positive ions are heavier than electrons, the electrons are accelerated more quickly to the multiplier, than positive ions. The relatively slow speed of the positive ion can impede high speed operation of the detector. Accordingly, there is a need for an improved ion detector, and method capable of quickly and efficiently detecting both positively and negatively charged ionized particles. In accordance with an aspect of the present invention, an ion detector includes collision surfaces for converting both positively and negatively charged ions into electrons. The collision surfaces may be formed as conversion electrodes. Emitted secondary electrons may be detected using an electron detector that may, for example, include an electron multiplier. Conveniently, secondary electrons (or electrons emitted by the multiplier) may be detected using an electron pulse counter. In accordance with an embodiment of the present invention, a method of detecting charged particles, comprises guiding the charged particles toward first and second electrodes; biasing the first and second electrodes, at potentials with the first electrode biased to attract positive ones of the charged particles, and the second electrode biased to attract negatively charged ones of the charged particles. Secondary electrons are emitted by the first and second electrodes. The secondary electrons are attracted to an electron multiplier, and cause the electron multiplier to emit electrons. Electrons emitted by the electron multiplier, are detected at a detection surface biased at a potential above the first and second electrodes, to detect the electrons emitted by the electron multiplier, and thereby the charged particles. In accordance with a further embodiment, an ion detector comprises first and second electrodes that emit secondary electrons when collided by a charged ion. An electron detector having a detection surface detects emitted secondary electrons. At least one voltage source biases the first electrode at a potential above ground, the second electrode at a potential below ground, and the detection surface of the detector at a potential above the first electrode. In a further embodiment, a charged particle detector comprises first and second conversion electrodes that emit electrons when collided by charged particles. An electron multiplying detector multiplies the emitted electrons. The multiplying detector has a detection surface. At least one voltage source biases the first electrode at a potential above ground, the second electrode at a potential below ground, and the detection surface of the electron multiplier at a potential above the first and second electrodes. In accordance with yet a further embodiment, a method of detecting charged particles, comprises guiding the charged particles toward first and second collision surfaces; biasing the first and second collision surfaces, at potentials with the first collision surface biased to attract positive ones of the charged particles, and the second collision surface biased to attract negatively charged ones of the charged particles; wherein the first and second collision surfaces each emit secondary electrons in response to collisions by ones of the charged particles; and detecting emission of the electrons by the collision surfaces to detect the charged particles. In accordance with yet another embodiment, a method of detecting charged particles, comprises biasing first and second collision surfaces, at potentials with the first collision surface biased to attract positive ones of the charged particles, and the second collision surface biased to attract negatively charged ones of the charged particles; wherein the first and second collision surfaces each emit secondary electrons in response to collisions by ones of the charged particles; guiding charged particles of a single first polarity toward first and second collision surfaces; detecting emission of the electrons by the collision surfaces to detect the charged particles of the first polarity; after the detecting, guiding charged particles of a second, opposite, polarity toward first and second collision surfaces; detecting emission of the electrons by the collision surfaces to detect the charged particles of the second polarity. Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. FIG. 1 schematically illustrates an ion detector 100, exemplary of an embodiment of the present invention. Ion detector 100 typically forms part of a mass spectrometer. Ions enter detector 100, from an upstream stage (typically referred to as a mass analyser) of the mass spectrometer. The mass analyser (not shown) may take the form of a sector, time of flight, quadrupole, quadrupole ion trap, fourier transform, orbitrap, or other mass analyser, known to those of ordinary skill. As illustrated, ion detector 100 includes two conversion electrodes 102, 104. Conversion electrodes 102 and 104 provide collision surfaces that emit electrons in response to collisions by particles, such as molecules, ions, electrons and the like. The number of emitted electrons will be dependent on the energies of incident particles. Example conversion electrodes 102, 104 may, for example, be dynodes formed of metal or semi-conductor material. For example, conversion electrodes 102, 104 may be formed of stainless steel bars. Alternatively, conversion electrodes may be formed of alloys, or coated materials. Optional heating device may be in thermal communication with electrodes 102 and 104, to heat these to as suitable temperature to further facilitate the emission of electrons. A suitable temperature may, for example, be between 200° C. and 800° C. An electron detector 110 is positioned downstream of conversion electrodes 102 and 104 that detects the emission of secondary electrons by electrodes 102 and 104. In the depicted embodiment, electron detector 110 includes an electron multiplier 112, having an inlet 108 and an outlet 120 connecting a channel 122 that provides electrons to a detection surface 114. Typically, a capacitor 116, transmits electron pulses emitted by electron multiplier 112 to a pulse counter, such as pulse amplifier/discriminator/counter 124. Capacitor 116 isolates the high voltage of detection surface 114 from the (usually) ground potential of the amplifier/discriminator/counter 124. Of course, electron detector 110 could be embodied as any suitable electron detector. Electron detector 110 could, for example, accelerate the electrons (perhaps after several stages of amplification) into a photo-emissive detection surface which provides resulting photons into a photomultiplier or avalanche photodiode. Other suitable electron detectors will be apparent to those of ordinary skill. In any event, detection surface 114 is typically a conductive or semi-conductive surface on which receives electrons to be detected. Surface 114 may, for example, be stainless steel. Pulse amplifier/discriminator/counter 124 is an example of any suitable high sensitivity electron pulse counting apparatus. An example pulse amplifier/discriminator/counter 124 is available from ORTEC of Oak Ridge, Tenn., under model number Model Number 9302. Other suitable electron pulse counting devices will be apparent to those of ordinary skill. Electron multiplier 112 may be a channel electron multiplier, and as such, channel 122 may be a ceramic channel, a semi-conductor channel, a glass channel, or the like. Again, the channel may be coated, with a material that facilitates emission of electrons. Alternatively, electron multiplier 112 may be a discrete dynode electron multiplier, a multi-channel plate multiplier, or any other suitable electron multiplier, known to those of ordinary skill. Electric power supplies 118a, 118d apply DC voltages to the conversion electrodes 102 and 104, respectively. Similarly, supplies 118b and 118c apply front and rear potentials to regions proximate inlet 108 and outlet 120 of electron multiplier 112. Supply 118e provides a DC voltage to plate 114. Supplies 118a, 118b, 118c, 118d and 118e may be conventional DC supplies. Multiple ones of supplies 118a, 118b, 118c, 118d and 118e may be combined. For example, one or two physical DC power supplies and suitable resistor network may be used to provide voltages of supplies 118a, 118b, 118c, 118d and 118e. In operation, positive and negative ions are sequentially produced by a suitable ion source upstream of detector 100. Ions (positive or negative) enter a region proximate conversion dynodes 102, 104. Positively charged ions are attracted to conversion electrode 102, at a negative voltage, and collide therewith. Conversion electrode 102 emits secondary electrons, at energies close to the voltage of power supply 118d. As the inlet 108 of electron multiplier is at a more positive potential than electrode 102, secondary electrons are accelerated to inlet 108 of electron multiplier 112. Negative ions are similarly attracted by conversion electrode 104. Upon impact, these negative ions cause the emission of secondary electrons by conversion electrode 104. The secondary electrons, emitted by conversion electrode 104 are similarly attracted to inlet 108 of multiplier 112, which is also at a higher potential than conversion electrode 104. Supplies 118a and 118d provide DC biases to attract incident ions. In the depicted embodiment, supplies 118a and 118d apply DC apply biases of +4 kV and −6 kV to conversion electrodes 104 and 102, respectively. Supply 118b applies a fixed voltage of +6 kV to inlet 108. As such, secondary electrons emitted by conversion electrodes 104 and 102 are respectively accelerated through potentials of 2 kV and 12 kV to inlet 108 of electron multiplier 112. Of course, other voltages could be applied to conversion electrodes 104, 102 and electron multiplier 112. For example, suitable voltages in the range of about +3 kV and +10 kV above the energies of ions to be detected, could be applied to conversion electrode 104. Similarly, voltages in the range of about −2 kV and −10 kV below the energies of ions to be detected could be applied to conversion electrode 102, depending upon the maximum mass detected. Corresponding voltages above that applied to conversion electrode 104 could be applied proximate the inlet 108 of electron multiplier 112. In the depicted embodiment, supplies 118a-118e provide the indicated voltages relative to ground. Of course, voltages would typically be provided relative to the potentials at which the ions are introduced into detector 100. For example, ions typically leave the upstream mass analyser at an elevated potential of, for example, between about 150V and −150V. Supplies 118a-118e may be biased accordingly, above the potential of the output of the mass analyser. Power supply 118c applies a voltage higher than that proximate inlet 108. As such, secondary electrons, from both conversion electrode 102 and 104, at inlet 108, are accelerated to outlet 120 at a higher potential than inlet 108. The emission electrons, incident at inlet 108 further cause the emission of a cascade of tertiary electrons by electron multiplier 112 resulting in the electrons at output 120. Electrons at outlet 120 are incident on detection surface 114. In order to attract electrons, detection surface 114 is maintained at a voltage higher than outlet 120. Surface 114 is maintained more positive than electrode 104 (e.g. at least +100V more positive than electrode 104, and in the depicted embodiment about +200V more positive than outlet 120), by supply 118e. Pulse detector 124, in turn, detects the output electrons. In the depicted embodiment, electron detector 110 takes the form of a pulse counting detector. As such, it may provide its output to a computing device (not shown), that in turn may tabulate counted pulses, and their masses and display measured results. Conveniently, although the output of multiplier 112 and detection surface 114 are maintained at positive voltages, above ground, pulses may be easily detected by a pulse counting detector. Alternatively, current could be measured directly. However, high speed, sub-picoamp current detection at about the potential of outlet 120, is difficult and costly. Conveniently, ion detector 100 allows for the detection of both positively charged and negatively charged ions. No switching of power supplies 118 is required and the sensitivity is not compromised. Moreover, ion to electron conversion efficiencies of both conversion electrodes 102, 104 (and electron multiplier 112) are not dependent on the particular structure of incident molecules. After ions of one polarity have been detected, ions of the opposite polarity may be introduced to detector 100, and detected. As will be appreciated, applied voltages on electrodes 102, 104 and electron multiplier 112 (and surface 114) may be adjusted by a small amount in dependence on the polarity of ions to be detected, to aid in the formation, extraction and focusing of electrons, and remain within the scope of the invention. For example, for negative ions the voltage of electrode 104 may be made more positive by between 0 to 25% from the voltage applied for positive ions, and the voltage applied to electrode 102 may be made more negative by between 0 to 25%. For positive ions, the voltages applied to electrodes 102, 104 may again be respectively raised for electrode 104 and lowered for electrode 102. In an alternate mode of operation, positive and negative ions may be detected concurrently by detector 100. For example, both positive and negative ions may be introduced to detector 100, as described above. Both types (i.e. positive and negative) may be detected as described above: they are attracted to one of conversion electrodes 102, 104 causing emission of secondary electrons that are attracted to and detected by electron detector 110. Discriminating detection of positive ions from negative ions may, however, not be possible as both positive and negative ions result in the detection of electrons at detection surface 114. As will now be appreciated, conversion electrode 104 of detector 100 could actually be integrated with electron multiplier 112. In this way, detector 100 may be modified to form an alternate detector 100′ depicted in FIG. 2. Unmodified elements of detector 100 forming detector 100′ are identified using numerals identical used in FIG. 1. As illustrated in FIG. 2, inlet 108′ of electron multiplier 112′ acts as conversion electrode 104′. In operation, incident negatively charged ions would impact inlet 108′ directly, causing emission of secondary (and tertiary electrons) within channel 122, as described above. Power supply 118a may be eliminated. Positively charged ions may be detected as in detector 100 (FIG. 1) In further embodiments, an ion detector 100″ illustrated in FIG. 3, may be formed with electrodes 102″, 104″ identical to electrodes 102, 104 but tilted, so that collision surfaces of electrodes 102″ and 104″ are at an angle α relative to an axis 140 parallel to the central axis approximately normal to a plane of inlet 108 of electron multiplier 112. In the depicted embodiment, the planes of the collision surfaces 102″ and 104″ are at an angle of between about 30° and 90° relative to axis 140. In yet a further embodiment, an ion detector 100′″ illustrated in FIG. 4, includes electrodes 102′″, 104′″ having non-planar collision surfaces 142 and 144, respectively. As illustrated, electrodes 102′″, 104′″ may have non-planar collision surfaces 142, 144 to aid in the formation, extraction and focusing of electrons including concave surfaces, as illustrated, or convex surfaces, ridged, or corrugated surfaces are possible. Again, detectors 102′″ and 104′″ may be formed of metal or semiconductor, or other suitable material. Detectors 100′, 100″, and 100′″ of FIGS. 2-4 may be operated to sequentially or concurrently to detect positive and negative ions, in much the same way as these may be detected using detector 100. A person of ordinary skill will now appreciate that detectors 100, 100′, 100″, and 100′″ may be used to detect particles other than ions. For example, positrons, or other charged particles could be detected. Of course, the above described embodiments are intended to be illustrative only and in no way limiting. The described embodiments of carrying out the invention are susceptible to many modifications of form, arrangement of parts, details and order of operation. The invention, rather, is intended to encompass all such modification within its scope, as defined by the claims.
	summary
044118597	abstract	A gamma sensor is supported coaxially in a bore, extending through the core of a nuclear reactor, by centering means which span the annular space between the gamma sensor and the bore. Said centering means also acts as a thermal bridge so that the portion of the gamma sensor contacted by the centering means will assume a thermal temperature close to that of the bore. Since poor thermal contact between the gamma sensor and the bore is thereby avoided, the accuracy of sensor readings is improved.
	description	The invention relates to the field of collimation, and more specifically to a collimator for providing constant collimation effect over a plurality of beam angles, combined with simplicity of design. Collimators are used in many applications in order to define the shape and alignment of radiation (which may be electromagnetic waves or beams of particles). For example it is possible to create two-dimensional fan-shaped beams of radiation or one-dimensional pencil beams of radiation using collimators. In particular applications of collimation, such as those using electromagnetic radiation in the visible or near visible spectrum, mirrors and lenses can be used to produce collimated beams. However for electromagnetic radiation with significantly shorter wavelengths and therefore higher energy (such as X-rays and Gamma-rays) or for radiation in the form of beams of particles, a collimator that acts as a filter to the radiation is required, such that only radiation travelling in desired directions is able to pass through the collimator unhindered. Collimation is a necessity in many areas of physics and medicine where it is desirable to confine a divergent source of radiation into a useful, well-defined beam. Use of collimated beams of radiation enable a number of different analysis techniques to be performed and leads to improved resolution in some imaging applications, by minimising the amount of radiation that interacts with material that is not under test. Example applications where collimated beams of radiation may be required include X-ray and Gamma-ray radiography, radiation therapy and neutron imaging. Collimators may also be used to filter radiation from a scene, such that only radiation from a specific direction is allowed to pass through to, for instance, a detector. Further example applications where the ability to detect radiation from specific directions may be useful are Gamma-ray observations of space, and in the analysis of radioactive material. Typically, a collimator for high energy electromagnetic radiation is made from a material of high atomic number such as tungsten or lead, and defines a number of apertures through which radiation can travel towards a target or detector. Radiation that is incident upon the body of the collimator is attenuated, so that only rays aligned with the apertures pass through unhindered. A common problem with collimation techniques is that the flux at the target is greatly reduced as most of the source waves are blocked by the body of the collimator. This hinders imaging and analysis techniques by reducing performance and image clarity or by increasing the power of the source needed to attain the same image clarity at equal penetration. Furthermore, inconsistency in collimation effect (for instance with different beam angles) can further complicate imaging and analysis techniques. Certain imaging applications such as x-ray backscatter, require the use of a scanning beam of radiation to build up a two-dimensional image of an object or field of view. A scanning beam can be achieved by introducing relative movement between the radiation source and the collimator in one dimension to produce a strip of image. If such one-dimensional scanning is combined with relative movement between the object and the source in an orthogonal direction, multiple one-dimensional strip images can be combined to form a two-dimensional image. It is known that to create a scanning pencil beam, a radiation source can be placed at the centre of a collimator in the form of a large rotating disc provided with radial apertures. As the disc rotates, a beam is emitted through each aperture and scanned across the field of view. However, such a disc is necessarily large and heavy. This affects the weight and portability of the whole equipment, requires significant power to maintain the correct rate of rotation and requires multiple moving parts, all of which increase the risk of equipment failure through breakage. An alternative collimator design, disclosed in U.S.2014/0010351 (Rommel), utilises two parallel plates separated by a distance d. Each plate comprises a slot with the slots being arranged in a crossed arrangement to form an “X” or “+” shape. For radiation approaching from a given angle there is only a single compound aperture which passes through both slots, however as relative movement between the source and the collimator is introduced in one dimension, the single compound aperture “moves” in a lateral dimension. Therefore, by moving either the source or the collimator up and down, a laterally scanning beam can be created. In the parallel plate collimator example, the path length through the compound aperture varies with displacement along the length of the apertures. This leads to a variation in the collimation effect and a variation in the size and shape of the beam exiting from the collimator, both of which have a negative impact on the quality of the final image. This latter problem is addressed in U.S.2014/0010351 (Rommel) by manipulating the shape of the slots. By increasing the width of the slots towards the edges of the block it is possible to maintain a constant beam cross-section area independent of the beam angle. However, the variance in path lengths remains, affecting the quality of collimation. A further design of collimator is the solid cuboid twisted slit collimator. Such a collimator is illustrated in EP2124231 (BAM). For this collimator the path length through the compound aperture varies with displacement along the length of the slit, thereby resulting in variable collimation effect. Furthermore, in applications where a scanning beam of radiation is required, the solid cuboid twisted slit collimator needs to be rotated back-and-forth, rather than spun continuously, thus limiting achievable scanning speeds. Therefore it is an aim of the invention to provide a collimator for providing constant collimation effect over a plurality of beam angles, combined with simplicity of design. According to a first aspect of the invention there is provided a collimator for providing collimation of radiation from at least one radiation source, the collimator comprising radiation attenuating material and featuring a twisted slit comprising radiation transmissive material, wherein the twisted slit comprises first and second apertures configured to provide a series of compound apertures from a radiation entry point in one aperture to a radiation exit point in the other aperture, wherein the collimator substantially takes the form of a prolate spheroid body having a major axis that passes through its longest dimension, the first aperture extending at least partially around the body in a plane orthogonal to the major axis and the second aperture extending at least partially around the body in a spiral form relative to the major axis such that all direct pathways from an entry point to an exit point and passing through the major axis at a predetermined angle, are of constant length in order to provide constant collimation effect. In accordance with a second aspect of the invention there is provided, a method of generating a scanning beam of radiation, the method comprising the steps of: Providing a collimator in accordance with the first aspect of the invention; Providing at least one divergent radiation source fixed stationary relative to the collimator and substantially positioned within the first aperture; and Rotating the collimator about the major axis such that the compound aperture through the collimator from the position of the at least one divergent radiation source, changes, thereby generating a scanning beam. The term “radiation” is used in a broad sense to include energy in the form of waves or subatomic particles and is not limited to electromagnetic radiation. In some embodiments of the invention the collimator is used, to collimate radiation from a single divergent radiation source. In other embodiments of the invention the collimator is used to collimate radiation from a spatial source comprising, or approximated by, multiple divergent radiation sources. The term “prolate spheroid” is used to describe a tri-axial ellipsoid with two equal semi-diameters (semi-axis a and semi-axis b). As a result the prolate spheroid has a circular cross section in any plane that is parallel to both semi-diameters. The third semi-axis of the prolate spheroid is longer than the two equal semi-diameters and is referred to as semi-axis c. The major axis in the context of the invention is the axis that passes through the longest dimension of the prolate spheroid (along semi-axis c). A particular example of a prolate spheroid is provided by the intersection between two overlapping equal sized circles being rotated about the axis passing through the points of intersection. A more particular example is provided when those equal sized circles each dissect the centre of the other. The invention provides a collimator substantially taking the form of a prolate spheroid. In some embodiments of the invention the collimator takes the form of a whole prolate spheroid. In other embodiments of the invention the collimator takes the form of part of a prolate spheroid, for example where the collimator must conform to a particular form factor. The radiation attenuating material acts to reduce the energy of radiation incident upon it, or travelling through it. The attenuating material may be attenuating to specific forms of radiation. The attenuating material may be completely opaque to specific forms of radiation. As radiation passes into and through the attenuating material, energy may be lost such that the radiation does not pass completely through the material, or emerges from the material with sufficiently minimal energy such that it may be disregarded. The radiation attenuating material may comprise tungsten, for example. Radiation that is incident upon radiation transmissive material is able to pass into and through the material unhindered. Unhindered is used to mean the radiation either does not interact with the radiation transmissive material, or interacts to a minimal degree such that the interaction can be ignored for the purposes of the invention. The radiation transmissive material may be air, or may comprise other suitable materials. The twisted slit can be described as a pseudo-helix or spiral of a series of holes bored through a prolate spheroid structure. The holes each start at the circumference of the prolate spheroid—the circumference being the edge of the circular cross-section of the prolate spheroid in the plane containing ‘semi-axis a’ and ‘semi-axis b’ (also referred to as the xy plane). The holes boring though at some angle ϕ to the horizontal xy plane with some angle θ about the vertical axis in the horizontal xy plane—an angle relative to the direction of the first hole. The first hole has angles ϕ0=+ϕmax and θ0=0; each successive hole has angles: ϕn=ϕn−1+dϕ to the limit of ϕn=−ϕmax and θn=θn−1+dθ to the limit of θn=2π−dθ. In accordance with the invention the collimator comprises radiation attenuating material and features a twisted slit. The term ‘first aperture’ refers to the gap in the radiation attenuating material produced at the circumference as a result of the holes bored through the prolate spheroid. The term ‘second aperture’ refers to the gap in the radiation attenuating material that spirals around the prolate spheroid about the major axis, produced as a result of the holes bored through the radiation attenuating material at predetermined angles, exiting the prolate spheroid. The first and second apertures extend substantially around the prolate spheroid. In some embodiments the apertures do not extend completely around the prolate spheroid for structural stability reasons. In embodiments where the radiation transmissive material filling the twisted slit comprises a solid material, the apertures may extend completely around the prolate spheroid. The term compound aperture is used to describe an aperture through the collimator provided as a result of the arrangement of the first and second apertures forming the twisted slit. For each point in the first aperture, there is a direct pathway through the major axis of the prolate spheroid, at a predetermined angle, to a point in the second aperture, thereby creating a compound aperture. The direct paths transit through the radiation transmissive material. By ensuring that all path lengths through the collimator—from an entry point in the first aperture to an exit point in the second aperture—are the same length, it is possible to form a collimated beam having constant cross-section, and constant collimation effect, irrespective of the compound aperture through which radiation has transited. This is not achieved by cuboid, cylindrical or spherical collimators. The collimator may be configured to rotate about at least the major axis. The rotation may be continuous at fixed or variable rates. In an embodiment of the invention, one divergent radiation source is provided and fixed stationary relative to the collimator, such that when the collimator is rotated about the major axis, the compound aperture for radiation from the divergent source, moves, and a continuously scanning beam of radiation is generated. This is advantageous over back-and-forth rotation because the mechanism required to maintain constant speed can be less complex and higher speeds can be achieved. Alternatively, in embodiments where it is necessary to steer a beam of radiation in a non-continuous fashion, the collimator may be configured to rotate to specific positions and dwell at those positions. Furthermore, the collimator may be configured such that it can be rotated about a secondary axis. The secondary axis may be orthogonal to the major axis such that combinations of rotations about both axes will allow a beam of radiation to be steered or scanned in two dimensions. In an embodiment of the invention, the collimator is rotated such that the projection of the compound aperture is steered or scanned across a spatial radiation source. In this embodiment only radiation originating from a particular position on the spatial source is able to pass through each projection of the compound aperture. The radiation passing through the compound aperture may then be detected. The collimator may incorporate within the first aperture a recess which completely circumnavigates the body, suitable for confining at least one radiation source or detector. The recess may continue beyond the extent of the aperture itself. It may be particularly desirable for the radiation source to sit within the outer surface of the collimator if it is a divergent source, to enable the divergent radiation to pass directly through the apertures at all angles from the lowest aperture angle, −ϕmax, to the highest aperture angle, +ϕmax. Further, the more enclosed source requires less additional shielding to prevent unwanted radiation leakage. In practical applications such as X-ray backscatter imaging, the radiation source may be an anode target upon which electrons are incident, and from which X-rays are generated and are subsequently collimated. In a similar manner it may be desirable for the detector to sit within the outer surface of the collimator in embodiments where the collimator is being used to scan a scene across a plurality of angles for radiation. In an embodiment of the invention, in particular one in which a divergent radiation source is mounted in a fixed position relative to the collimator and located within the recess of the first aperture, and one in which the collimator is rotated at a constant speed, a beam of radiation can be scanned across a field of view in a direction parallel to the axis of rotation. The solid angle scanned by the collimator can be up to 120° and the spot size and shape are maintained constant through the entire angular range. The drawings are for illustrative purposes only and are not to scale. FIG. 1 illustrates a parallel plate collimator 10 in accordance with U.S.2014/0010351 (Rommel). Plates 11, 12 are arranged parallel to each other and separated by a distance d. The plates 11, 12 are made from a material which is opaque to the radiation to be collimated and are provided with elongate apertures 13, 14 which are transparent to the radiation to be collimated. The apertures 13, 14 are arranged in the form of an “X” such that for radiation approaching from a given angle there is only a single compound aperture 15 which allows radiation to pass through both plates 11, 12. Therefore, a single collimated beam of radiation passes through the collimator 10. As the collimator 10 is rotated up and down about a horizontal axis ‘A’ the position of the compound aperture 15 moves from side to side relative to a fixed source of radiation (not shown). The effect is that a collimated beam of radiation is scanned laterally across a field of view. The same effect is achieved by moving the radiation source up and down relative to a fixed collimator. FIG. 2 illustrates a solid cuboid collimator 20 in accordance with EP2124231 (BAM). The body of the collimator 21 is made from a material which is opaque to the radiation to be collimated and is provided with elongate apertures 23, 24 which are transparent to the radiation to be collimated. The apertures 23, 24 are arranged in the form of an “X” such that for radiation approaching from a given angle there is only a single compound aperture 25 which allows radiation to pass through the collimator 20. The apertures 23, 24 are joined by two hyperbolic paraboloid surfaces which pass through the collimator and define the volume to which radiation is confined by the collimator. This is referred to as the twisted slit. Examples of solid cuboid collimators that would operate at visible wavelengths were modeled by the inventor and 3D printed as optical proxies for x-ray collimators. Four versions were tested using the experimental setup shown in FIG. 3. A tri-axis “Zaber Motorised Stage” 31 was used to move a light source (LED) 32 sequentially about a volume behind the collimator 33, whilst a webcam 34 recorded and collated images of the emitted light at each point, as viewed on a paper image screen 35 protected by light shields 36, 37. The collimators which gave largest fields of view were those where the angle between the first and second aperture were greatest. The concept of the solid cuboid twisted slit collimators being used to steer a beam in one axis by rotating about an opposing axis has been proven to work by the inventor. However, they have limitations in that the path length—and thus the collimation effect—varies with the displacement along the length of the slit. This causes a change in the size and shape of the beam which would have a negative impact on the final image. Another issue with the cuboid collimator is its inability to be spun continuously and keep the spot “flying;”. The collimator would need to be spun back-and-forth in order to achieve this effect, reducing the speed it could be rotated at and further limiting its use as, for instance, a replacement for current X-ray back-scatter fly-wheel designs. A solution to both of these issues is to curve the apertures around the surface of a specially formed prolate spheroid, where the first aperture is orthogonal to the axis of rotation (in this example the major axis) and the second aperture (the one which emits the collimated beam) extends partially around the body in a spiral form such that all direct path lengths through a compound aperture of the first and second apertures (from an entry point in the first aperture, passing through the major axis at a predetermined angle, to an exit point in the second aperture), are of constant length. FIG. 4 illustrates a prolate spheroid adaptation 40 of the solid cuboid twisted slit collimator 20, having a first aperture 43 and a second aperture 44. The primary objective was to define the form of the twisted slit and hence the apertures 43, 44 relative to the axis of rotation B (the major axis), with the external body shape 41 being consequential rather than the driving factor. Whilst the first aperture 43, in this embodiment, does not extend all the way around the collimator body, in order to maintain the integrity of the solid body, a relatively shallow recess 46 is provided between the ends of the aperture 43 to provide a continuous recess which circumnavigates the body. This allows for the collimator 40 to be continuously rotated about major axis B whilst a radiation source (not shown) is fixedly positioned within the confines of the recess 46. To create the body shape in FIG. 4, first the twisted slit was developed relative to an axis of rotation (in this example, the major axis). The twisted slit was created in MATLAB® as a set of lines with start and end points of (0, y) and (+nx, y) respectively, where y goes in incremental steps between −ny and +ny. These lines were rotated about the y-axis, to define the angle of rotation as a function of the line's position along the y-axis. This ensured the paths were kept at the same length, correcting the issue of relying upon the surface of the outer shape (cuboid or sphere) to dictate this length. These equal paths which would run around the undefined surface of the structure were then translated so their start points were at the origin; rotated about the z-axis using spherical polar matrix operations to wrap them around a circular circumference; before being translated again to a separation of the initial path length. FIG. 5a and FIG. 5b show the basic surface structure created from these transformed and translated paths from two different views and illustrates how the twisted slit can be described as a pseudo-helix of an infinite number of holes bored through a solid prolate spheroid structure. The holes each start at the circumference of the prolate spheroid 51 in the plane containing the two equal semi-diameters, boring though at some angle ϕ to the horizontal xy plane with some angle θ about their start points in the horizontal xy plane—an angle relative to the direction of the first hole. The first hole has angles ϕ0=+ϕmax and θ0=0; each successive hole has angles: ϕn=ϕn−1+dϕ to the limit of ϕn=−ϕmax and θn=θn−1+dθ to the limit of θn=2π−dθ, where dθ and dϕ are infinitesimal angle steps. The equations governing the cartesian (x,y,z) end-points 52 of the slit are detailed in Equations 1-3. These are joined to respective points on the circumference in the x-y plane, given by a simple circle equation in x and y.x(ρ, ϕ, θ)=ρ sin ϕ cos θ [Equ. 1]y(ρ, ϕ, θ)=ρ sin ϕ sin θ [Equ. 2]z(ρ, θ)=ρ cos θ [Equ. 3] Where: ρ = length ⁢ ⁢ of ⁢ ⁢ hole ϕ = [ π 6 ⁢ : ⁢ n ⁢ : ⁢ 5 ⁢ π 6 ] θ = [ 0 ⁢ : ⁢ n ⁢ : ⁢ 2 ⁢ π ] The code, produced in MATLAB®, gave the start and end points of a series of beam-lines passing through a solid body defined by joining these same points; expanding these to have radii as well as length gave a simplified representation of the solid surface which could be used to produce the 3-D computer aided design (CAD) model. The resultant start and end points form two distinct apertures on the surface of a prolate spheroid. The radii of each beam line, which gives rise to the width of the final twisted slit, can be varied to suit the degree of collimation required. The inventor has determined that in an embodiment of the invention, the collimator may be used to scan a collimated beam of radiation over a solid angle of 120°; full parameter details can be found in Table 1. pathLengthOpeningFilename - SBC(mm)numberOfPathsnumberOfSpheroidRingsgreatestBeamAngleDiameterCompletedSpheroidColimator_2.0.stl10060153010 Table 1: A table giving the initial parameters for a collimator, as used in the MATLAB® code, which generated the start and end points for the model. Parameters in the table are: pathLength, which is the diameter of the prolate spheroid from each point on the circumference to the opposite point on the surface ie the width of material radiation is collimated through; numberOfPaths which is the number of start and end points for (ultimately) the cylindrical holes; numberOfSpheroidRings defined how many points were used to create the body surface, although the final surface was significantly decimated to reduce computational time; greatestBeamAngle was used to define the maximum and minimum angle from the x-y plane of the paths; whilst Opening Diameter is the diameter of the paths through the solid. The same experimental setup shown in FIG. 3 was used to determine the FoV for a scanning beam embodiment of the collimator except that in this case the collimator 33 was placed on a rotational stage with the LED 32 being fixed. The FoV given by the scanning beam embodiment of the collimator at ˜170 mm from the vertical axis of the collimator was (500+/−10)mm, an image of which can be seen in FIG. 6. This is an order of magnitude larger than the equivalent FoV for the solid cuboid twisted slit collimators. The dark patch 60 is an artefact of the experimental setup chosen for testing an embodiment of the collimator. FIG. 7 shows a set of superimposed still images illustrating that the size and shape of the spot produced by the scanning beam collimator is a constant, differing only slightly from the maximum angle to the minimum angle. This is beneficial to imaging applications such as X-ray back scatter since it would give a more uniform illumination across the image, reducing the distortion. The two spots of light which can be seen in FIGS. 6 and 7 either side of the main beam FoV are from the light passing round the edges of the inner surface at the circumference. The spots are in a constant position so could be removed in a final system either through image processing or with small additional collimation. Whilst an optical collimator has been described it will be apparent to the skilled person that a collimator for use with other types of radiation would be manufactured from other materials and by other manufacturing techniques. For example the 3-D model could be used to create a plastic mould into which a powdered tungsten alloy could be cast, removing the need for the complex machining of expensive, solid tungsten blocks. The prolate spheroid shape can be scaled as required to suit the application. By way of an example, assuming a circumference diameter of 50 mm, the moment of inertia for a tungsten scanning beam collimator rotating in front of the source is a factor of ˜100 less than a copper fly-wheel spinning around the source. This would reduce the torque needed and hence reduce power consumption by ˜16%. The calculations don't take into account resistive angular momentum of the spinning disk which could improve this power-reduction further.
	description	This application claims priority to U.S. provisional patent application No. 62/914,158 filed Oct. 11, 2019, the disclosure of which is incorporated by reference herein. The presently-disclosed invention relates generally to systems and methods of use thereof for detecting fuel leaks in nuclear reactors and, more specifically, to systems and methods of use thereof for detecting fuel leaks in heavy water-moderated fission-type nuclear reactors. Known systems and methods for detecting fluid leaks from failed fuel bundles in heavy water moderated nuclear fission reactors (such as a CANDU (CANada Deuterium Uranium) reactor shown in FIGS. 1A through 1C) tend to be inefficient, time consuming, and costly (for example, a few reactors have a delayed neutron system whereby each outlet endfitting has a small sample tube, all of which congregate in a sampling room where neutron detectors measure the presence of fission products from each sample tube). As shown in FIGS. 1A through 1C, in an example reactor 100, each fuel bundle is inserted into a pressure tube of a corresponding fuel channel 102 on the primary fluid side of the reactor 100 with an existing fueling machine 106 of the reactor. As shown in FIG. 1C, the fueling machine 106 includes a charge machine 108 and an accept machine 109, each of which is configured to interact with a corresponding set of fuel channel end fittings 103a and 103b, respectively, that are disposed on opposing ends of the plurality of fuel channel pressure tubes. As shown in FIG. 1C, the charge machine 108 is disposed on the upstream side of the reactor core 101 (meaning primary coolant flows through the reactor core from left to right (arrow 107)) and accesses each fuel channel pressure tube 102 by way of a corresponding fuel channel end fitting 103a, whereas the accept machine 109 is disposed on the downstream side of the reactor core 101 and accesses the desired fuel channel pressure tube 102 through the corresponding fuel channel end fitting 103b. Note, however, in other embodiments of reactors, the charge machine 108 may be disposed on the downstream side of the reactor core 101, whereas the accept machine 109 is disposed on the upstream side of the reactor core 101 (in short, the reactor may either be set up as “fuel with flow” or as “fuel against flow”). The presence of gaseous fission products in the primary fluid indicates that there are one or more failed fuel bundles. One known method of determining the location of a failed fuel bundle includes drawing primary samples from the main headers. However, there are only two headers, each one receiving flow from its designated half of the fuel channels 102. As such, the detection of gaseous fission products in one of the headers merely narrows the location of the failed bundle to any of the one-hundred and twenty-two. Note, various CANDU reactors have different numbers of fuel channels. As such, the number of fuel channels associated with each header may vary. In yet another method, the primary fluid flow is monitored for neutrons that are present when particles are leaked from a fuel bundle. In neutron monitoring systems, a bleeder line may be connected to each individual fuel channel 102 and utilized for sampling primary fluid flow out of that fuel channel 102. The water from each fuel channel 102 may be sampled via its bleed line which terminates at a detector matrix. This system is complicated based on the sheer number of fuel channels, each one having a designated bleeder line, and also very expensive (leading some reactor designs to omit the system). As well, the ability to retrofit an existing reactor with a neutron monitoring bleed line system is limited based on the excessive amount of down time that is required for its installation. Lastly, feeder scanning includes passing a detector through a network of existing feeder pipes that are collecting water exiting the fuel channel into a header manifold pipe. By correlating a position of the scanner with the feeder pipe, the source location may often be deduced. This process can also be very time consuming and can only be used when a reactor has been shut down, as in a planned outage. Typical fuel bundles last approximately a year during normal operations. Most fuel bundle failures occur when the fuel bundles have been moved from a high radiation area within the reactor to a lower radiation area over the useful life of the fuel bundle or vice versa. The flux along the reactor channel is lower at the two ends so a shift can be into or out of the more intense central regions, also the shift in fuel in one channel will perturb adjacent channels where a developing failure may be aggravated. The changes in operating temperatures that are related to moving the fuel bundles may cause them to flex and expand, causing potential failure. As well, if the changes in temperature are not the main cause of a failure, they can be a stressor that completes an already developing crack. If the undetected leak rate becomes too high, or has persisted too long to accumulate unacceptable emissions, and cannot be located, it may be necessary to “de-rate” the reactor until the one or more failed fuel bundles can be located. As would be expected, reduced operating power limitations on the reactor lead to increased operating costs and inability to meet the desired reactor power output. Another reason for finding the bundle sooner is that extended degradation of the bundle often hides the original defect cause and prevents preventive action on fuel manufacturing or reactor operations. There at least remains a need, therefore, for systems and methods for detecting fuel leaks in fission-type nuclear reactors in a timely manner. One embodiment of the present invention provides a defective fuel bundle location system for use with a heavy water moderated nuclear fission reactor having a fueling machine, the system including a test tool defining an internal volume, the test tool being configured to be received within both the fueling machine and a corresponding fuel channel of the reactor, and a test container defining an internal volume, wherein the test container is configured to be received within the internal volume of the test tool and the internal volume of the test container is configured to receive primary fluid from the reactor when the test tool is disposed within the corresponding fuel channel of the reactor. Another embodiment of the present invention includes a method of detecting fuel leaks in a heavy water moderated nuclear fission reactor having a plurality of fuel channels and a fueling machine, including the steps of providing a test container defining an internal volume, disposing the test container within the fueling machine, engaging the fueling machine with a corresponding one of the fuel channels, inserting the test container within the corresponding fuel channel, drawing primary fluid from the corresponding fuel channel into the internal volume of the test container, and withdrawing the test container from the fuel channel. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention. Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention according to the disclosure. Reference will now be made to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. The present disclosure is related to systems and procedures to facilitate locating a fuel channel within a CANDU reactor that contains a defective fuel bundle while the reactor remains on-power, i.e., producing power under normal operating conditions, and the fuel strings are not disturbed. As well, the presently disclosed systems and procedures may also be utilized when a reactor has been shut down or during an outage. Referring now to FIG. 2, to initiate sampling of the primary fluid, the accept machine 109 of the reactor's fueling machine 106 is positioned at the reactor's ancillary port 110 and locked on. As previously noted, whether the reactor is “fuel with flow” or “fuel against flow” will determine whether the accept machine or the charge machine is on the downstream side of the reactor 101. The ancillary port fuel carrier 112 is installed as well as the shield plug trough 114. After ensuring that an empty magazine position is available in the charge machine 108, the ancillary port shield plug is removed. Next, a test tool 120, which is preferably sized similarly to a regular fuel bundle, including a test container 122 disposed therein, is placed on the trough 114 while ensuring that the test tool 120 is properly orientated. Preferably, the ram of the charge machine 108 is used to activate the test container 122 once the test container 122 is in the desired fuel channel, as discussed in greater detail below, meaning that the desired end of the test tool 120 must be positioned adjacent the ram 111 so it can make contact with the ram 111 for activation when desired. Next, the charge tube/ram 111 of the charge machine 108 is engaged and locked onto the test tool 120. The charge tube/ram 111 of the charge machine 108 is withdrawn so that the test tool 120 will be stored in an empty position of the charge machine's magazine. The charge tube/ram 111 releases the test tool in the magazine, retracts further and allows the magazine to rotate to the next empty position. In the present example, up to eight test tools 120 may be loaded into the magazine of the charge machine 108 dependent upon the number of fuel channel samples that are to be taken. Note, however, in other embodiments the magazine may contain fewer or more than eight test tools. After the ancillary port shield plug is replaced and the charge machine 108 is disengaged, the charge machine 108 is moved to the desired fuel channel 102 to be tested. Referring now to FIGS. 3A through 3E, the charge machine 108 is positioned adjacent the target fuel channel 102 and locked onto the corresponding fuel channel end fitting 103 (FIG. 3A). After the fuel channel closure 130 and the shield plug 132 are removed and stored in magazine locations, the magazine rotates to a test tool location, the charge tube/ram 111 is engaged with the test tool 120 and the test tool 120 is installed into the fuel channel 102 in the same manner as a fuel bundle carrier would be (FIG. 3B). Next, the charge tube/ram 111 of the charge machine 108 is utilized to activate the test container 122 in order to obtain the sample of primary fluid from the target fluid channel 102 (FIG. 3C). The ingestion of primary fluid commences only after activation by relative movement of the ram and or charge tube. Primary liquid then enters until the interior volume equalizes with the fuel channel pressure. The lower pressure can be a pre-pressurized gas, atmospheric air or a vacuum. Once equalized with the fuel channel, release or relative movement of the charge tube/ram 111 returns the test container 122 to the sealed configuration. The test container 122 sample volume can be provided by a means of increasing the internal volume, e.g., a contracted or squeezed bellows/accordion can be released to or made to expand when in channel conditions by relative movements of the charge tube/ram 111 or by their action releasing a trigger. The test container 122 sample volume can be: increased by the charge tube/ram 111 action releasing a trigger of a sprung piston causing an retraction of the piston and ingestion of water; provided by a means of positive displacement wherein the charge tube/ram 111 movement grips a piston extension and draws water into a syringe type canister; and a porous media that once a valve is opened or membrane perforated, liquid would be wicked/absorbed. The test container 122 is also preferably self-sealing after obtaining the primary fluid sample. With the sample obtained, the charge tube/ram 111 of the charge machine 108 are retracted so that the test tool 120 and corresponding test container 122 are stored in the desired position within the magazine of the charge machine 108 (FIG. 3D). After installation of the shield plug 132 and channel closure 130, the charge machine 108 is undocked from the fuel channel outlet end fitting 103. The above steps are repeated at each target fuel channel 102 until the desired number of primary fluid samples are obtained, the magazine of the charge machine 108 being able to hold up to eight test tools 120 and their corresponding test containers 122 (FIG. 3E). Referring now to FIG. 4, after the desired number of primary fluid samples have been taken, the charge machine 108 is returned to the ancillary port 110 and locked on to the port. As before, the ancillary port fuel carrier 112 is installed along with the shield plug trough 114 prior to removing the ancillary port shield plug. The tool carriers 120 are advanced onto the trough 114 in the same manner that ancillary tooling would be retrieved. Next, each test container 122 is removed from the corresponding test tool 120 until each previously activated test container 122 has been unloaded. If additional samples are to be taken, non-activated, empty test containers 122a may be loaded into the test tools 120 and loaded into the charge machine 108 as previously discussed. Once the unloading operation is complete, the ancillary port shield plug is installed and the ancillary port trough 114 removed. Lastly, the charge machine 108 is disengaged from the ancillary port 110 and may continue with further testing for fueling procedures as desired. After being removed from the corresponding test tools 120, the activated test container 122 are placed into a transport case 140 for transfer to an analysis facility. As shown in FIG. 5, the primary fluid samples within the activated test containers 122 are moved to a lab for analysis by a detection device 150. Note, the primary samples may be analyzed at both on and off-site facilities. For example, if measurement equipment allows, the sample could be analyzed close to the port. After analysis, the test containers 122 may be emptied and readied for future use. The above described fuel leak detection system and methods offer various advantages over known testing systems and methodologies. For example, the first results of fluid testing may be obtained within 4 to 6 hours of the beginning of the operation, and up to 16 fuel channels may be tested in one fuel machine trip. The described method is non-disruptive in that it may be utilized when the reactor is online at full power, with no piping modifications, and no modifications to the present CANDU fueling machines. The ability to determine the location of leaks faster than previous methods allows for maximum operation of the reactor and provides less risk of reactor power production de-rating, or outages. Early detection of defective fuel bundles also allows the potential cause of the fuel leak to be more discernable as less corrosion will have taken place over the life of the fuel leak. The present system causes no fuel physics perturbations in that the fuel bundles within the fuel channels are not manipulated during the testing process and premature fueling (new in/not-fully utilized out) has not been performed as a means to cause deductive shifts in detection from the feeder header monitor style. A current method uses deductive logic reviewing the change in leak rate indications after selective shifts in fuel to change the fuel bundle temperatures in that vicinity via moving a one channel's bundles to different flux/temperature positions. A leaking bundle in the vicinity of the shift will raise or lower its emission of leaking fission products. Multiple pushes are usually required to deduce which channel contains the leak. One channel or a zone of channels cannot be ‘over-fueled’ in a short period of time as the accumulation of fresh fuel in one area will create excessive power in surrounding channels or reactor zones. This method often must be done in batches separated by sufficient time for new bundles to decay; a major reason this method protracts the residence time of the bundle, increases the released emissions, risks defect aggravation and risks reactor de-rating. Notably, because the above described system includes test tools and test containers that are integrated with existing CANDU fueling machines and systems, the described system is transferable to any CANDU reactor site without requiring modifications thereto. While one or more preferred embodiments of the invention are described above, it should be appreciated by those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For example, at some reactors, the ancillary port is a preferred embodiment, or a tool path entering through the new fuel machine/port and exiting through the spent fuel port may be utilized. The spent fuel port in the spent fuel bay could be a means to retrieve the canisters and keep them shielded until flasked for transport. At some reactors, a fueling machine tooling or maintenance port could be used as the ancillary port is described. Alternatively the new fuel port and spent fuel tunnel path could be used to retrieve the canisters and tool from the spent fuel bay. Once the canister is retrieved, the preferred embodiment would be to flask the canister and move it to an existing neutron detector. Alternatively a local detector could be made available at/on the ancillary port or near the spent fuel bay to avoid shipping. The resetting of a tool with empty canister could be performed by replacing the canister in a tool that is presented and returned to the FM. It could be done by ensuring a stock pile of refurbished tool and canister are on hand. With refurbishment and return to stores locally or offsite. Measured canisters would have their contents returned to a heavy water recovery/cleansing path existing at site or provided offsite. It is intended that the present invention cover such modifications and variations as come within the scope and spirit of the appended claims and their equivalents.
	summary
062193996	summary	BACKGROUND OF THE INVENTION The present invention relates to a maintenance method in a nuclear power plant, and more particularly, to a maintenance method for maintaining a suppression chamber and a spent fuel storage pool provided in a nuclear reactor building in a nuclear power plant. The reactor building of a nuclear power plant is provided with a reactor primary containment vessel (called containment vessel hereinlater) to enclose radioactive materials leaking from a reactor core within a nuclear reactor primary system and to prevent leakage of radiation in the event of a reactor failure accident in the primary system. All of the containment vessels provided in boiling-water reactors (BWR), including advanced boiling-water reactors (ABWR), are pressure-suppression type vessels, which are generally constructed to be provided with a dry well and a suppression chamber. FIG. 10 is a schematic cross-sectional view showing one example of such a containment vessel in the boiling-water reactor mentioned above. A primary containment vessel 1 is provided with a dry well 2 and a suppression chamber 3, and a reactor pressure vessel 5 is arranged at the central portion of the interior of the dry well 2 and supported by a reactor pressure vessel pedestal 4. A suppression pool 6 is provided in the suppression chamber 3 and is always filled with water. The dry well 2 and the suppression chamber 3 communicate with each other through a vent pipe 7. The vent pipe 7 is connected to a downcomer 8 within the suppression chamber 3. The downcomer 8 is opened at a tip end portion to the water of the suppression pool 6. FIG. 11 is a schematic cross-sectional view showing a primary containment vessel in a boiling-water reactor different in type from that of FIG. 10. As in the case of FIG. 10, the containment vessel of FIG. 11 is provided with a dry well 2 and a suppression chamber 3. A reactor pressure vessel 5 is provided at the central portion of the interior of the dry well 2 and is supported by a reactor pressure vessel pedestal 4. A suppression pool 6 is provided in the suppression chamber 3 and is always filled with water. The dry well 2 and the suppression chamber 3 communicate with each other through a vent pipe 7. The vent pipe 7 has openings at forked tip end portions into the water of the suppression pool 6 in the suppression chamber 3. The suppression chambers 3 shown in FIGS. 10 and 11 are formed by using steel plates. Since the steel plate does not have a corrosion allowance, the surface thereof is coated in viewpoints of corrosion resistance, water resistance and decontamination. Therefore, on the basis of the idea of preventive maintenance that the suppression chamber 3 is repaired before the life of a coated film applied onto the steel plate of the suppression chamber is over, the coated film of the suppression chamber 3 must be repaired almost at ten years intervals. In the case of performing such repair coating operation, the state of the coated film on the inner surface of a suppression pool wall 6a is conventionally inspected throughout the pool by using a remote-controlled underwater camera or the like provided within the suppression chamber 3 in advance. Based on the inspection result, re-coating timing and re-coating areas must be determined. In the re-coating operation, first, the suppression chamber 3 is drained off, and the suppression pool 6 is made vacant by draining off the chamber 3. In this state, although the re-coating operation is conducted. In the air, unlike in the water, radiation shielding effect is reduced or lost. For this reason, it is required to carry out the decontamination for removing radioactive materials present in the suppression chamber 3 before the re-coating operation. Since the radioactive materials involve substances or matters floating in the water of the suppression pool or those deposited on the bottom thereof which exist as residues or sludges, the inner surface of the suppression pool wall 6a is washed or the floating substances and/or sludges are removed through the remote control operation as the decontamination operation. After the decontamination is over, a scaffold is mounted, operators go downs along the suppression chamber wall 6a through the scaffold, carries out substrate treatment for the target coated film to be repaired and then starts re-coating. After all of the repair target surfaces are re-coated, the scaffold is dismounted and the suppression pool is filled up with water again, thereby completing the operation. Further, as shown in FIG. 12, a spent fuel storage pool 10 is provided in the nuclear reactor building 9 for storing the spent fuel, which was burnt in the reactor of the containment vessel 1 and which life has expired. Since the interior of the spent fuel storage pool 10 is normally lined with a stainless steel, it is not necessary to apply coating. However, in view of the deterioration of the lining and a generation of other various deposits, an internal inspection is desired. Conventionally, when inspecting and decontaminating the spent fuel storage pool 10, the pool is drained off. However, it takes considerable workload, time and cost to drain off the suppression chamber 3 and the spent fuel storage pool 10 and to perform decontamination following the above-stated internal inspection and repair coating operation. Further, if the decontamination operation is performed while the suppression chamber 3 and the spent fuel storage pool 10 are being drained off, i.e., in the air, it requires more operators due to the fact that radiation dose in the air becomes larger than that in the water, which also requires far more facility, considerable labor, time and cost. Moreover, if the repair coating operation is conducted for the local deterioration of the coated film within the suppression chamber 3, it is required to entirely drain off the suppression pool 6. It takes, therefore, considerable workload, time and cost to perform such a local repair. SUMMARY OF THE INVENTION An object of the present invention is to almost eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a maintenance method in a nuclear power plant capable of eliminating much workload, working time, cost and the like which have been conventionally required for the maintenance of a suppression pool and a spent fuel storage pool of a nuclear power plant due to the necessity for draining off the pools and capable of performing the repairing operation relatively easily for a short time and at low cost. This and other objects can be achieved according to the present invention by providing, in one aspect, a maintenance method in a nuclear power plant including a reactor primary containment vessel provided with a suppression pool of a suppression chamber, comprising the steps of: improving clearness of a water in the suppression pool and decontaminating an interior of the suppression pool; and PA1 inspecting a coated film applied on an inner surface of a wall portion of the suppression pool, wherein the improving, decontaminating and inspecting steps are performed while maintaining a water level in the suppression pool. PA1 improving clearness of a water in the spent fuel storage pool and decontaminating an interior of the spent fuel storage pool; PA1 inspecting a surface condition of an inner surface of a wall portion of the spent fuel storage pool, PA1 wherein the improving, decontaminating and inspecting steps are performed while maintaining a water level in the spent fuel storage pool. In preferred embodiments, a repair coating is further carried out to the coated film -through the underwater operation in the suppression pool after inspecting the coated film applied on the inner surface of the suppression pool wall. The clearness and the decontamination of the water in the suppression pool are performed by collecting substances or matters floating in the water of the suppression pool, such as chalk river unclassified deposit or substance, and removing and collecting substances deposited as sludges on an inner bottom surface of the suppression pool wall. The substances floating in the water of the suppression pool is sucked up together with the surrounding water out of the suppression pool by suction means movable in or above the water. The floating substances and the surrounding water sucked up in the suppression pool are subjected to solid-liquid separation on an outside the suppression pool. The suction means includes a rotating brush and a suction port arranged around the rotating brush so as to suck up the substances deposited as sludges on the inner bottom surface of the suppression pool together with the surrounding water therein. The decontamination of the interior of the suppression pool includes removing of sludges and/or deteriorated substances on the inner surface of the suppression pool wall. The sludges and/or deteriorated substances, called hereunder merely as sludge or sludges, on the inner surface of the suppression pool wall are removed through a sucking step by using a suction means comprising a rotating brush and a suction port arranged around the rotating brush so as to suck up the sludges together with the surrounding water in the suppression pool. The sludges and the surrounding water sucked up in the suppression pool are subjected to solid-liquid separation on an outside the suppression pool. The inspecting step of the coated film applied on the inner surface of the suppression pool wall is performed by visually observing an surface condition of the coated film by using an underwater camera, which may include at least one of a fixed camera disposed in the suppression chamber and a camera movable in the water of the suppression pool. The underwater camera may include a fixed camera disposed in the suppression chamber and a camera movable in the water of the suppression pool, the fixed camera being used to set a general inspection position in the suppression pool and the movable camera including a first movable camera used to set a fine position approaching the inspection point and a second movable camera used to observe a state of the coated film while approaching the inspection position more closely than the first movable camera. An information obtained by the underwater camera is displayed on a monitor television disposed outside the suppression pool to thereby allow observation in the air. A repair coating is carried out to the coated film through the underwater operation in the suppression pool after inspecting the coated film applied on the inner surface of the suppression pool wall. The repair coating step to the coated film on the inner surface of the suppression pool wall is carried out by peeling off a deteriorated or deformed coated film at a portion to be repaired by using one of a disc sander and a grinder provided with a suction means and a substrate treatment is carried out by sucking up the surrounding water out of the suppression pool. The repair coating step of the coated film on the inner surface of the suppression pool wall is carried out by applying an underwater coating to the inner surface of the suppression pool wall by using one of a brush having suction means arranged around the brush, a roller and other coating means and a coating splashed during the underwater coating applying step is sucked up outside the suppression pool together with the surrounding water. The maintenance method may further include the step of measuring a thickness of the coated film on the inner surface of the suppression pool wall by using a film thickness measuring device in the suppression pool. The maintenance method may further include the step of preparing an underwater plate thickness measuring device into the suppression pool and measuring a plate thickness of a plate constituting the suppression pool wall by using the plate thickness measuring device. The maintenance method may further include the steps of closing a strainer provided on the inner surface of the suppression pool wall in an underwater operation and inspecting a valve of a piping communicating with the outside of the suppression pool through the strainer. The maintenance method may further include the step of welding defect portions and portions to be repaired of the suppression poll wall, inner structure of the suppression pool, ducts, machineries and duct supports in an underwater operation in the suppression pool, and the welded portions are subjected to a nondestructive test in an underwater operation. The maintenance method may further include the step of carrying out a cutting working for repairing an inner structure of the suppression pool, ducts, machineries and duct supports in an underwater operation in the suppression pool. In another aspect of the present invention, there is provided a maintenance method in a nuclear power plant including a reactor primary containment vessel provided with a spent fuel storage pool, comprising the steps of: In this aspect, preferred embodiments similar to those mentioned above with respect to the maintenance method performed in the suppression pool water will be applicable. According to the present invention of the aspects mentioned above, the maintenance workings such as cleaning, decontaminating, inspecting workings to the inner wall surface of the suppression pool and the spent fuel storage pool in the reactor primary containment vessel can be carried out in the underwater therein without draining off the pools. Such draining working involves much labour, time and cost as in the conventional maintenance method. The maintenance method according to the present invention can be easily performed for short time and with low cost. The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.
	description	This application claims the priority, under 35 U.S.C. §119, of Austrian application AT GM 830/2005, filed Dec. 6, 2005; the prior application is herewith incorporated by reference in its entirety. The invention relates to a first-wall component of a fusion reactor. The component has at least one heat shield of a graphitic material and a cooling tube of copper or a copper alloy. The heat shield has a closed or open passage. A typical example of the use of such first-wall components is that of diverters and limiters, which are exposed to extremely high thermal loads in excess of 10 MW/m2. First-wall components usually comprise a heat shield and a heat dissipating region. The material of the heat shield must be compatible with the plasma, have a high resistance to physical and chemical sputtering, a high melting point/sublimation point and be as resistant as possible to thermal shock. In addition, it must also have a high thermal conductivity, low neutron activation and adequate strength/fracture toughness, along with good availability and acceptable costs. Apart from refractory metals, such as tungsten for example, graphitic materials best meet this diverse and to some extent conflicting set of requirements. Since the energy flows from the plasma act on these components over a long period of time, such first-wall components are typically actively cooled. The heat removal is assisted by heat sinks, for example of copper or copper alloys, which are usually connected to the heat shield by a material bond. The copper has the function of ensuring the heat removal. In addition, it may also perform the function of stress reduction, as is the case when graphite is connected to a high-strength copper alloy via an intermediate layer of pure copper (for example Cu—Cr—Zr). The copper layer thereby usually has a thickness of 0.5 to 3 mm. Apart from the regions of graphite and one or more copper materials, such first-wall components may also have further regions, for example of steel or a tungsten alloy. The joining region between the graphite and the copper in this case represents the weak point of such material composites. A method for producing cooling devices with improved strength in the joining region is described in European patent No. EP 0 663 670 B1. There, the metal of the cooling device in the molten state is brought into contact with a heat-resistant material, elements of one or more metals of the IVth and/or Vth subgroups of the periodic system being provided in the joining region during the connecting operation. Material composites produced in such a way have a much improved strength. First-wall components can be made in different designs. A distinction is drawn here between flat tile, saddle and monobloc designs. If a heat shield with a planar connecting area is connected to the heat sink through which coolant flows, this is referred to as a flat tile design. In the case of the saddle design, a heat shield with a semicircular recess is connected to a heat sink of a tubular form. The heat sink has in each case the function of establishing the thermal contact between the heat input side and the cooling medium and is thereby exposed to cyclical, thermally induced loads caused by the temperature gradient and the different coefficients of expansion of the elements joined together. In the case of the monobloc design, the first-wall component comprises a heat shield with a concentric passage. The heat shield is connected by means of this concentric passage to a cooling tube. Owing to the geometrical conditions, the stress reduction brought about by plastic deformation of the copper intermediate layer takes place more effectively in the case of the flat tile design than in the case of the monobloc design, where there is a triaxial state of stress, which suppresses plastic deformation to the greatest extent. On account of this restricted stress reduction, cracks can therefore occur in the graphitic material. First-wall components not only have to withstand thermally induced mechanical stresses but also mechanical stresses that additionally occur. Such additional mechanical loads may be produced by electromagnetically induced currents which flow in the components and interact with the surrounding magnetic field. This may involve the occurrence of high-frequency acceleration forces, which have to be transferred by the heat shield. However, graphitic materials have a low mechanical strength and fracture toughness. In addition, neutron embrittlement occurs during use, leading to a further increase in the sensitivity of these materials to crack initiation. Fiber reinforced graphite (CFC, carbon fiber-reinforced carbon) is usually used as the graphitic material. The fiber enforcement is in this case three-dimensionally and linearly arranged. The architecture of the fibers provides the material with different properties, depending on the spatial direction. CFC is usually reinforced in one spatial direction by ex-pitch fibers, which have both the greatest strength and thermal conductivity. The two other spatial directions are reinforced by ex-PAN fibers (PAN, polyacrylonitrile), one direction typically only being needled. Therefore, while CFC has a linear material architecture, the heat shield/cooling tube connection geometry in the case of the monobloc design is circular. On account of the different coefficients of thermal expansion of the materials used, a build-up of stresses occurs during the production process and may lead to cracks in the CFC. On account of the geometrical conditions and the combination of materials used, these cracks can only be detected with very complex methods, if at all. Against the background of a nuclear environment for such components, this gives rise to corresponding problems, in particular also because cracks/detachments can be regarded as possible triggers of a more major incident. In spite of many years of laborious development work in the field of first-wall components, the structural elements so far available do not optimally meet the set of requirements. The object of the invention is therefore to provide a first-wall component of a monobloc design which meets the requirements resulting from mechanical and physical stresses in a suitable way. With these and other objects in view there is provided, in accordance with the invention, a first-wall component of a fusion reactor, comprising: at least one heat shield of a graphitic material formed with a closed or open passage; a cooling tube of copper or a copper alloy; a tube segment disposed between said heat shield and said cooling tube; and copper-containing layers connecting said tube segment at least in certain regions to said heat shield and to said cooling tube. In other words, the first-wall component in this case comprises at least one heat shield of a graphitic material and a cooling tube of copper or a copper alloy, the heat shield having a closed or open passage and a tube segment being arranged between the heat shield and the cooling tube. The tube segment is respectively connected to the heat shield and the cooling tube via ductile copper layers. The tube segment has the effect that the internal stresses in the heat shield, which result from the different coefficients of expansion, are reduced. In order to achieve this in an optimum way, it is advantageous if the coefficients of expansion of the heat shield and of the tube segment are similar and the tube segment has an adequate thickness of at least 0.2 mm, and a thermal conductivity and strength that are as high as possible. With smaller thicknesses, adequate reduction of the stresses is not accomplished. An upper limit of approximately 1.5 mm is attributable to geometrical conditions. The mechanical/physical requirements on the tube segment are best met by materials from the group comprising molybdenum, molybdenum alloys, tungsten and tungsten alloys. To be noted in particular are the pseudoalloys in the tungsten-copper system and in the molybdenum-copper system. In the case of tungsten-copper, the preferred copper content is 5 to 25% by weight, in the case of molybdenum-copper it is 15 to 40% by weight. The tube segment has with preference an opening angle α of from 20° to 180°, preferably from 50° to 130°. With larger opening angles, the reduction of the stresses is not adequate. With smaller opening angles, the heat flux is hindered. It also proves to be favorable if the angle bisector of the opening angle α is perpendicular to the surface of the heat shield that is exposed to the plasma. The heat shield is connected to the tube segment via a copper-containing layer, the tube segment in turn likewise being connected to the cooling tube via a copper-containing layer. These layers likewise serve for stress reduction. The opening region of the tube segment is likewise filled with copper or a copper alloy, so that in this region the heat shield is connected to the cooling tube via this copper-containing region. As a result, in this region the heat flux is not impaired by the tube segment. The passage through the heat shield is preferably closed and formed as a bore, the wall of which is structured by means of a laser, the wall being metallically and/or carbidically activated. To produce the first-wall component according to the invention, firstly a passage, preferably a bore, is introduced into a block of a graphitic material, preferably CFC. The surface of the passage is structured, in a preferred way by means of a laser, and subsequently metallically and/or carbidically activated in such a way that the activated surface can be wetted by liquid copper. In the passage pretreated in such a way, the tube segment is subsequently inserted. The preferred thickness of the tube segment is in this case 0.2 to about 1.5 mm. The gap between the tube segment and the wall of the activated passage is approximately 0.2 to 0.8 mm. A sleeve of pure copper is introduced into this gap. A sleeve of pure copper is also positioned against the inside diameter of the tube segment. The construction produced in this way is heated under a vacuum or inert gas to a temperature above the melting point of copper. In order to ensure replenishment of copper, in particular in the gap between the CFC and the tube segment and in the opening region of the tube segment, a corresponding copper depot is provided. This produces a composite with the following radial construction (from outside to inside): CFC/activation layer/copper/molybdenum-copper or tungsten-copper/copper. A cooling tube of a copper alloy, preferably copper-chromium-zirconium, can be materially bonded to the inner copper layer by usual standard methods, such as soldering/brazing or HIP. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in first-wall component with tube segment, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. For the production of a first-wall element 1, a CFC (carbon fiber-reinforced carbon) heat shield 2 with dimensions of 45 mm×30 mm×25 mm was used. The CFC heat shield 2 had a 3D fiber structure, different properties being obtained depending on the direction. The fibers with the highest thermal conductivity lay parallel to the outer dimension of 45 mm. The fiber bundles with the average thermal conductivity lay parallel to the outer dimension of 30 mm. The through-bore 4 with a diameter of 18 mm was introduced normal to the 30 mm×45 mm area, at its center of symmetry. This bore, 25 mm deep, was subsequently structured by way of a laser, achieving an increase in the surface area of over 100%. The conical laser bores had a depth of approximately 1000 μm, the opening width at the surface being approximately 200 μm. The sequence of laser pulses was in this case chosen such that the individual bores lay as close together as possible. The surface treated in this way was activated, so that a carbidically bonded surface wetted by liquid copper was created on the CFC material 2. This was achieved by titanium being applied to the surface. After that, the part was heated to a temperature above the melting point of titanium, the molten titanium penetrating into the CFC as a result of the capillary forces acting, thereby forming titanium carbide. Titanium carbide on the one hand adheres to the CFC by a very good chemical bond and on the other hand makes the heat shield 2 wettable for the liquid copper. A pure copper foil with a thickness of 0.4 mm was then positioned in the activated bore 4 in such a way as to form a cylinder, which lay against the inner side of the bore in the heat shield 2. Subsequently, a tube segment 5 of W with 10% by weight Cu of a height of 25 mm, an outside diameter of 17 mm, a wall thickness of 0.5 mm and an opening angle α of 90° was introduced into the bore. The angle bisector of the opening angle α in this case lay perpendicular to the 45 mm×25 mm area. This area 9 is exposed to the plasma during use. A copper core with an outside diameter of 15.8 mm was positioned in the inner region of the tube segment 5, this core having a head with a diameter of 20 mm. This head performed the function of the melt depot. This assembly was subsequently installed in a vacuum furnace and heated under a vacuum for approximately 10 minutes to 1100° C., before the cooling phase was initiated. In this way, the heat shield 2 was connected to the tube segment 5 via the copper layer 6. The opening region 8 of the tube segment 5 was likewise filled with copper. Subsequently, the monobloc produced in this way was worked on all sides. The original outer dimensions were thereby reduced by 1 mm in each case, whereby the monobloc had, before further processing, outer dimensions of 44 mm×29 mm×24 mm. The copper-filled passage 4 was drilled out to a diameter of 15 mm. The inside diameter in this case had a continuous copper layer 7. A copper-chromium-zirconium tube 3 with an outside diameter of 14.8 mm was then positioned in the passage 4. The cooling tube 3 and the monobloc were subsequently materially bonded by means of an HIP process, so that an actively coolable first-wall component 1 was obtained.
	summary
	summary
	summary
	summary
	claims	1. A charged particle beam apparatus that emits charged particle beams onto a specimen and utilizes generated secondary charged particle beams, comprising:a charged particle beam generator that generates a plurality of charged particle beams;a primary optics system including at least one lens that makes the plurality of charged particle beams irradiate the specimen and a deflector that deflects the plurality of charged particle beams to scan the specimen;signal detectors that individually detect a plurality of secondary charged particle beams generated from a plurality of locations on the specimen by the irradiation of the plurality of charged particle beams;a secondary optics system that makes the plurality of secondary charged particle beams incident on the signal detectors;a stage onto which the specimen is loaded and which can carry the specimen;a display that displays images based upon outputs of the signal detectors; anda first adjuster that adjusts positions on a surface of the specimen which the plurality of charged particle beams irradiate,wherein a layout of a plurality of reference marks, each of which is corresponding to each of the plurality of charged particle beams, are provided on the stage; andthe first adjuster adjusts a position on the specimen, which each of the plurality of charged particle beams irradiates, based upon an image of each of the plurality of reference marks on the stage displayed on the display at a standstill during calibration, and measures a layout of the plurality of charged particle beams on the specimen, and carries out calibration of the plurality of charged particle beams at the same time. 2. The charged particle beam apparatus according to claim 1, further comprising:a memory that stores an operating condition of at least one of the primary optics system, the signal detectors and the stage, determined based upon characteristics of the specimen,wherein the first adjuster adjusts positions on the specimen which the plurality of charged particle beams irradiate, referring to the stored operating condition. 3. The charged particle beam apparatus according to claim 1,wherein the operating condition is a move rate of the stage. 4. The charged particle beam apparatus according to claim 1,wherein the charged particle beam generator that generates the plurality of charged particle beams includes at least two charged particle beam selectors having at least each two apertures for passing each charged particle beam and a mechanical operation control unit that mechanically rotates the charged particle beam selector. 5. The charged particle beam apparatus according to claim 1,wherein the charged particle beam generator that generates the plurality of charged particle beams is provided with at least two charged particle beam selectors for passing each charged particle beam and further, a temperature control unit that is arranged in contact with the charged particle beam selector, configured by a member different in a thermal expansion coefficient from the charged particle beam selector and controls the temperature of the charged particle beam generator. 6. The charged particle beam apparatus according to claim 1, comprising:a second adjuster for adjusting positions on the signal detectors which the plurality of secondary charged particle beams irradiate. 7. The charged particle beam apparatus according to claim 6,wherein the second adjuster is an electromagnetic lens. 8. The charged particle beam apparatus according to claim 6, further comprising:a memory that stores an operating condition of at least one of the primary optics system, the signal detectors and the stage, determined based upon characteristics of the specimen,wherein the first adjuster adjusts positions on the specimen which the plurality of charged particle beams irradiate, referring to the stored operating conditions. 9. A charged particle beam apparatus that emits charged particle beams onto a specimen and utilizes generated secondary charged particle beams, comprising:a charged particle beam generator that generates a plurality of charged particle beams;a primary optics system including one or more lens that makes the plurality of charged particle beams irradiate the specimen and a deflector that deflects the plurality of charged particle beams to scan the specimen;signal detectors that individually detect a plurality of secondary charged particle beams generated from a plurality of locations on the specimen by the irradiation of the plurality of charged particle beams;a secondary optics system that makes the plurality of secondary charged particle beams incident on the signal detectors;a stage onto which the specimen is loaded and which can carry the specimen;a display that displays images based upon outputs of the signal detectors; anda second adjuster that adjusts positions on the signal detectors which the plurality of secondary charged particle beams irradiate in order to maximize a secondary electron current detected by each of the signal detectors,wherein each of the signal detectors reaches a position coincides with a position of the signal detector for obtaining the maximum of the secondary electron current. 10. The charged particle beam apparatus according to claim 9,wherein the second adjuster is an electromagnetic lens. 11. A specimen inspection method of emitting charged particle beams onto a specimen on a movable stage and inspecting the specimen utilizing generated secondary charged particle beams, comprising the steps of:generating a plurality of charged particle beams;irradiating the stage by the plurality of charged particle beams using a primary optics system;making a plurality of secondary charged particle beams generated from a plurality of locations on the specimen reach signal detectors using a secondary optics system and individually detecting the plurality of secondary charged particle beams;displaying acquired images acquired by processing detection signals of the detected plurality of secondary charged particle beams on a display;measuring respective positions on the stage which the plurality of charged particle beams irradiate using the displayed acquired images;adjusting the primary optics system based upon the measured irradiated positions;forming a plurality of reference marks corresponding to each of the plurality of charged particle beams on the stage; and emitting each of the plurality of charged particle beams onto the corresponding plurality of reference marks, measuring a position which each of the plurality of charged particle beams irradiates using the acquired images of the plurality of reference marks and adjusting the primary optics system based upon each of the measured irradiated positions at a standstill during calibration;measuring a layout of the plurality of charged particle beams on the specimen; andcarrying out calibration of each of the plurality of charged particle beams at the same time. 12. The specimen inspection method according to claim 11, comprising the steps of:determining inspecting conditions of at least one of the primary optics system, the signal detectors and the stage based upon characteristics of the inspected specimen. 13. The specimen inspection method according to claim 12,wherein the inspecting conditions include a move rate of the stage. 14. The specimen inspection method according to claim 12, comprising the steps of:storing inspecting conditions determined based upon characteristics of the specimen on at least one of the primary optics system, the signal detectors and the stage; andadjusting the primary optics system based upon the stored inspecting conditions. 15. The specimen inspection method according to claim 14, comprising the steps of:measuring positions on the signal detectors which the plurality of secondary charged particle beams irradiate; andadjusting the positions on the signal detectors which the secondary charged particle beams irradiate based upon the measured results. 16. A charged particle beam apparatus that emits charged particle beams onto a specimen and utilizes generated secondary charged particle beams, comprising:a charged particle beam generator that generates a plurality of charged particle beams;a primary optics system including at least one lens that makes the plurality of charged particle beams irradiate the specimen and a deflector that deflects the plurality of charged particle beams to scan the specimen;signal detectors that individually detect a plurality of secondary charged particle beams generated from a plurality of locations on the specimen by the irradiation of the plurality of charged particle beams;a secondary optics system that makes the plurality of secondary charged particle beams incident on the signal detectors;a stage onto which the specimen is loaded and which can carry the specimen; anda display that displays images based upon outputs of the signal detectors,wherein when the number of the charged particle beams is set to n and a deflection width deflected by the deflector per charged particle beam is set to S, the specimen can be scanned by the plurality of charged particle beams in a state in which width F of a field-of-view acquired by the plurality of charged particle beams meets a condition of (2 n−1)SF(2 n+1)S. 17. The charged particle beam apparatus according to claim 16,wherein the condition is (n−1)S≦F≦(n+1)S.
	claims	1. A method for diagnosing a failure in a computer system, comprising:testing the computer system using a sequence of tests, wherein a given test includes a given load associated with a pre-determined failure mechanism for a given failure condition;obtaining results during the given test, wherein the results include telemetry signals that are monitored within the computer system; andif the results indicate the given failure condition, ceasing the testing and indicating that the computer system has the given failure condition, and otherwise continuing the sequence of tests until the sequence is completed, at which point, if no fault has been detected, indicating that a no-trouble-found (NTF) condition exists;wherein the sequence of tests includes one or more stress tests, and wherein after the one or more stress tests, the method further comprises applying one or more sinusoidal perturbations in computer-load or physical variables to the computer system to obtain a dynamic input-output characterization of the computer system in the frequency domain. 2. The method of claim 1, wherein the given load includes an application. 3. The method of claim 2, wherein the application is configured to stress a portion of the computer system. 4. The method of claim 3, wherein the portion of the computer system includes one or more of the following: a processor, memory, an application-specific integrated circuit, an input/output interface, or a disk drive. 5. The method of claim 1, wherein different sequences of tests are used for different types of computer systems. 6. The method of claim 1, wherein the telemetry signals include information associated with thermal dynamics of the computer system. 7. The method of claim 1, wherein the telemetry signals include temperature samples measured at different locations in the computer system. 8. The method of claim 1, wherein an order of the sequence of tests is selected to increase a probability of inducing the given failure condition in a given time interval. 9. The method of claim 1, further comprising determining if the computer system successfully powers up prior to performing the sequence of tests. 10. The method of claim 9, wherein, after determining that the computer system powers up, the sequence of tests includes one or more stress tests. 11. The method of claim 10, wherein, after the one or more stress tests, the sequence of tests includes applying the one or more sinusoidal perturbations in computer-load or physical variables to the computer system. 12. The method of claim 11, wherein, after applying the one or more sinusoidal perturbations, the sequence of tests includes determining an effect of temperature variation in the computer system. 13. The method of claim 12, wherein the temperature variation is induced by varying a flow of a coolant through the computer system while the computer system is operating. 14. The method of claim 12, wherein, after applying the one or more sinusoidal perturbations, the sequence of tests includes comparing a characteristic of the computer system with a pre-determined value associated with a computer-system type to which the computer system belongs; andwherein the pre-determined value is associated with the absence of the given failure condition. 15. The method of claim 14, wherein, after applying the one or more sinusoidal perturbations and determining the effect of temperature variation in the computer system, the method further includes analyzing telemetry signals obtained during these tests to determine one or more frequencies in the frequency domain that are associated with one or more temperature signals. 16. The method of claim 15, wherein the presence of the given failure condition is determined based on the one or more frequencies. 17. The method of claim 15, wherein, after analyzing the telemetry signals, the sequence of tests includes characterizing vibrations of the computer system based on vibrations internal to the computer system. 18. The method of claim 17, wherein the vibrations are inferred from throughput to one or more disk drives in the computer system. 19. A computer-program product for use in conjunction with a computer system, the computer program product comprising a computer-readable storage medium and a computer-program mechanism embedded therein for diagnosing a failure in a computer system, the computer-program mechanism including:instructions for testing the computer system using a sequence of tests, wherein a given test includes a given load associated with a pre-determined failure mechanism for a given failure condition;instructions for obtaining results during the given test, wherein the results include telemetry signals that are monitored within the computer system; andif the results indicate the given failure condition, instructions for ceasing the testing and indicating that the computer system has the given failure condition, and otherwise instructions for continuing the sequence of tests until the sequence is completed, at which point, if no fault has been detected, instructions for indicating that a no-trouble-found (NTF) condition exists;wherein the sequence of tests includes one or more stress tests, and wherein the instructions for testing the computer system include instructions for applying, after the one or more stress tests, one or more sinusoidal perturbations in computer-load or physical variables to the computer system to obtain a dynamic input-output characterization of the computer system in the frequency domain. 20. An apparatus, comprising:a processor;memory; anda program module, wherein the program module is stored in the memory and configured to be executed by the processor, the program module for diagnosing a failure in a computer system, wherein the program module includes:instructions for testing the computer system using a sequence of tests, wherein a given test includes a given load that characterizes a pre-determined failure mechanism for a given failure condition;instructions for obtaining results during the given test, wherein the results include telemetry signals that are monitored within the computer system; andif the results indicate the given failure condition, instructions for ceasing the testing and indicating that the computer system has the given failure condition, and otherwise instructions for continuing the sequence of tests until the sequence is completed, at which point, if no fault has been detected instructions for indicating that a no-trouble-found (NTF) condition exists;wherein the sequence of tests includes one or more stress tests, and wherein the instructions for testing the computer system include instructions for applying, after the one or more stress tests, one or more sinusoidal perturbations in computer-load or physical variables to the computer system to obtain a dynamic input-output characterization of the computer system in the frequency domain.
	summary
040617009	claims	1. A process for sintering a body of nuclear fuel material comprising the steps of a. admixing the nuclear fuel material in a particulate form with a binder having a particle size less than 400 mesh so as to achieve a uniform dispersal of said binder in the nuclear fuel material so that said binder and said nuclear fuel material undergo adhesion, said binder being comprised of ammonium bicarbonate, ammonium bicarbonate carbamate, ammonium sesquicarbonate, ammonium carbamate and mixtures thereof, b. forming the resulting mixture by pressing into a green body having a density ranging from about 30% to about 70% of theoretical density, c. heating said green body at a temperature sufficient to decompose substantially all of the binder into gases that enter an atmosphere maintained over said green body, d. heating the body at a temperature sufficient to produce a sintered body and further decompose any binder residues that enter the atmosphere maintained over said body, and e. cooling the sintered body in the atmosphere maintained over said body. 2. A process according to claim 1 in which the admixing step is conducted to give from about 0.5 to about 7.0 weight percent binder in the mixture with the nuclear fuel material. 3. A process according to claim 1 in which the nuclear fuel material is comprised of uranium dioxide and plutonium dioxide. 4. A process according to claim 1 in which the nuclear fuel material is uranium dioxide. 5. A process according to claim 1 in which the binder is ammonium bicarbonate. 6. A process according to claim 1 in which the binder is ammonium bicarbonate carbamate. 7. A process according to claim 1 in which the nuclear fuel material is uranium oxide. 8. A process according to claim 1 in which the binder is ammonium sesquicarbonate. 9. A process according to claim 1 in which the binder is ammonium carbamate.
	abstract	A scintillator material is made of a zinc-oxide single crystal grown on a +C surface or a −C surface of a plate-shaped seed crystal of zinc oxide including a C surface as a main surface. The zinc-oxide single crystal contains In and Li. In response to an incident radiation, the scintillator material emits fluorescence of less than 20-ps fluorescence lifetime.
039403106	description	DETAILED DESCRIPTION Referring to FIG. 1, the reactor pressure vessel is designated generally by the numeral 1 and is moderated by ordinary water, so-called "light water" (H.sub.2 O), as a coolant under pressure. The primary coolant circuit 2 for the reactor vessel 1 includes a heat exchanger 3, a main coolant pump 4 and a pressure stabilizer 5. The core 7 in the reactor vessel 1 contains guide tubes 8, 9 and 10 which are located in the region of the fuel elements which are not shown in FIG. 1. Guide tubes 9 and 10 contain control rods 12 and 13, one control rod being disposed longitudinally within each guide tube. The lower end of guide tubes 9 and 10 are connected to guide tube 8 by means of ducts 14. Guide tube 8 is connected to a pressure line 15 carrying coolant fluid under pressure from outside the reactor vessel 1. The pressure line 15 branches into two separate lines outside reactor vessel 1. One branch line is connected to high pressure control valve 16 and then to the high pressure side of a pump 17. The low pressure side of pump 17 is connected to a suction line 18 which, in turn, is connected to the reactor vessel 1. The second branch of pressure line 15 leads to low pressure control valve 20 and then to low pressure volume tank 21. The upper end of guide tubes 9 and 10 are connected with the interior of the reactor vessel 1 by means of nozzleshaped constrictions 23 and 24. When high pressure control valve is open, the flow of coolant, as the result of the action of pump 17, is down through guide tube 8 as indicated by the arrow in guide tube 8, then through ducts 14 and up through guide tubes 9 and 10 as indicated by the arrows in guide tubes 9 and 10. This flow of coolant under pressure in guide tubes 9 and 10 supports control rods 12 and 13 in the upper region of guide tubes 9 and 10, that is, in the position of control rods 12 and 13 shown in FIG. 1. The canals 27 and 28 shown in FIG. 1 are part of an apparatus which is designed to indicate the position of the control rods 12 and 13 within guide tubes 9 and 10. The canals 27 and 28 run parallel to the upper end position of the control rods 12 and 13. The canals 27 and 28 are connected with metal bellows 29 shown in FIG. 2. The metal bellows 29 are variable in length depending upon the pressure prevailing in the upper part of the guide tubes 9 and 10 shown in FIG. 1 and thereby indicate the position of the control rods 12 and 13 with guide tubes 9 and 10. Returning to FIG. 1, the guide tubes 8, 9 and 10 comprise part of the pressure line carrying coolant fluid within reactor vessel 1. The pressure line carrying coolant fluid has a substantially U-shaped configuration in the area where it carries coolant to the lower end of guide tubes 8, 9 and 10. The pressure which is generated by means of pump 17 located outside the reactor vessel 1 is transmitted in the coolant to the lower end of guide tubes 9 and 10 and then to control rods 12 and 13. A high pressure control valve 16 located outside of the reactor vessel 1 and arranged in the pressure line 15 carrying coolant fluid controls the movement of the control rods 12 and 13. The control rods 12 and 13 are movable hydraulically within guide tubes 9 and 10 by means of the pressure generated by pump 17 which moves the control rods 12 and 13 out of guide tubes 9 and 10 and away from core 7. In the event of an accident resulting in a break in the pressure line and a loss of pressure, the control rods 12 and 13 are inserted further into guide tubes 9 and 10 and thus into core 7. In the event of danger, such insertion of the control rods 12 and 13 can be accelerated by opening low pressure control valve 20, thereby switching into the pressure line a low pressure volume tank 21 for producing low pressure. A break in the suction line 18, which runs between the reactor vessel 1 and the pump 17, likewise, can only result in a release of pressure and, therefore, in the further insertion of the control rods 12 and 13 within guide tubes 9 and 10. It has been found advantageous to arrange the control rods 12 and 13 symmetrically with respect to the fuel elements, and preferably with rotational symmetry with respect to the fuel elements, thereby facilitating the reaction of the fuel elements. The high pressure control valve 16 is responsive to increased pressure in pressure line 15 and the high pressure control valve 16 will close when the pressure line 15 becomes too high. After the pressure line 15 enters reactor vessel 1 it branches into a plurality of feed lines, not shown in FIG. 1, which will be explained in greater detail subsequently. Additional means may be disposed in the feed lines to open as a function of pressure. Such means include rupture discs and valves. Referring to FIG. 2, a flow control connector referred to generally by the numeral 33 is disposed outside of the reactor vessel 1 (shown in FIG. 1). The flow control connector 33 is connected to the pressure line 15 (shown in FIG. 1) carrying coolant fluid from pump 17 to the guide tubes 8, 9 and 10 (shown in FIG. 1) within reactor vessel 1 (shown in FIG. 1). The flow control connector 33 protrudes through the lid of the reactor vessel 1 (shown in FIG. 1). The flow control connector 33 is positioned in reference to the reactor vessel 1 at the point where pressure line 15 shown in FIG. 1 enters the reactor vessel 1. In the embodiment shown in FIG. 2, the flow control connector 33 has been designed for use with three control rods of three fuel elements. Other embodiments of the flow control connector may be designed for use with the control rods of a greater or lesser number of control rods and fuel elements. Since the flow control connector 33 has been designed for the control rods of three fuel elements, three magnetically operated valves 35, 36 and 37 have been arranged as a valve unit on the flow control connector 33 outside the lid of the reactor vessel 1. The valves 35, 36 and 37 may be distributed uniformly around the circumference of the flow control connector 33 in one plane outside of the lid of reactor vessel 1. In the alternative the valves 35, 36 and 37 may be arranged in several planes. Also, the valves 35, 36 and 37 may be resiliently mounted on flow control connector 33. The magnetically operated valves, such as valve 36 shown in FIG. 2, control the flow of coolant from connections 38 which leads to pump 17 (shown in FIG. 1) to ducts 39 in the interior of flow control connector 33. The valve unit consisting of valves 35, 36 and 37 corresponds to high pressure control valve 16 shown in FIG. 1. The valve unit, consisting of valves 35, 36 and 37, operates in conjunction with metal bellows 29 which are disposed in the flow control connector and are provided in triplicate. The metal bellows 29 in conjunction with cores 31 control the inductance of indicator coil 30. As previously explained in reference to FIG. 1, the metal bellows 29 shown in FIG. 2 are variable in length depending upon the pressure prevailing in the upper part of guide tubes 9 and 10 as shown in FIG. 1. Thus, the position of the metal bellows depends upon the pressure in canals 27 and 28 (shown in FIG. 1) and the change in length of metal bellows 29 is sensed electrically by means of an electrical sensing device, indicator coils 30, for sensing the change in length of the metal bellows 29 and for delivering an electrical signal responsive to the changes in length of metal bellows 29. As a result, indicator coils 30 indicate the position of control rods 12 and 13 within guide tubes 9 and 10 within the reactor vessel 1 (shown in FIG. 1). Since the embodiments shown in FIGS. 2 and 3 are designed for three control rods of three fuel elements, a third canal has been provided for the third control rod, but this third canal and the third control rod are not shown in the drawings. Referring to FIG. 4, a guide adapter 34 is disposed within the reactor vessel (shown in FIG. 1) and above the fuel elements. Feed line 25 shown in FIG. 4 represents one of the feed lines which have branched off from pressure line 15 (shown in FIG. 1) after the pressure line 15 has entered reactor vessel 1. Referring to FIG. 4, feed line 25 is connected to guide tube 9, provided for control rod 12 (shown in FIG. 1) by cross pieces 40 and mounting flange 41. Mounting flange 41 closes off openings 43 which are provided for the guide adapter 34 in cover plate 42 positioned above core 7 (shown in FIG. 1). The canal 28, which is used for providing an indication as to the position of the control rod 12 within guide tube 9, runs next to guide tube 9 with opening 23 at the upper end of guide tube 9. Feed line 25 in guide adapter 34 is connected to a feed line in the fuel element (not shown). There are the same number of feed lines in the guide adapter 34 and in the fuel element 53 (FIG. 8). The feed lines from several fuel elements, after passing through guide adapters 34, lead into one flow control connector 33 (FIG. 2) and from there into pressure line 15 (FIG. 1). FIG. 5 shows the coupling of the guide adapter 34 to the guide tubes 8 and 9 of the fuel elements in the core 7. The space above the grid plate 45 denotes the upper limit of the fuel elements. Metal bellows 47 provide a flexible coupling in all directions. Instead of the metal bellows 47 shown in FIG. 5, the fitting 49 loaded by a spring 48, shown in FIG. 6, may be used. Returning to FIG. 5, guide pin 50 and hole 51 in cross piece 40 insure an aligned lateral positioning of the feed lines 25 that are to be connected to each other. FIG. 7 illustrates an alternate embodiment relating to the coupling between the guide adapter 34 and guide tube 9 which has control rod 12. The predetermined spacing, indicated by the letter A, is provided at the joint between guide adapter 34 and guide tube 9 containing control rod 12. This spacing A provides tolerance for thermal expansion. However, the flow in guide tube 9 is influenced by this arrangement and, as a result, a different kind of position indication is necessary. Referring to FIG. 8, base plate 54 of fuel element 53, which is indicated by dash-dot lines, is used to form duct 55 and connection openings which connect the feed line 25 with guide tube 9 in a U-shaped configuration. The guide tubes 8 and 9 are fastened to base plate 54 by screws 56 and nuts 57. Spring 59 prevents shock to control rod 12 when it reaches the lower end position of guide tube 9. Although not clearly visible in the drawings, the cross sections of the feed lines 25, particularly in the region of valves 35, 36 and 37, are smaller than the clearance between the control rods 12 and 13 and the guide tubes 9 and 10 which surround the control rods. The cross section ratio is preferably 1:2 to 1:5. If, in spite of this, excessive pressure should develop, such as through evaporation of the coolant, the elastic couplings shown in FIGS. 5 and 6 will open. In addition, as already mentioned, special rupture discs or other means can also be provided. Thus, in event of malfunction or accident, the upwardly directed pressure force acting upon the control rods is smaller than the weight of the control rods. Referring to FIG. 9, a sealing ring 62, which is at least radially resilient, is disposed at the lower end of the control rod within guide tube 9. A spring 61 is disposed beneath the sealing ring 62 within guide tube 9. The reference to the lower end of the control rod 12 refers to the end of the control rod 12 nearer the core 7. When the control rod 12 reaches its upper position, the sealing ring 62 is at a constriction within guide tube 9. The result is that the flow of coolant under pressure is largely shut off.
	abstract	A fuel transfer system is used for transporting spent fuel from a first room to a second room. The system includes a carriage configured for travel between the first room and the second room, and a boom assembly that extends and retracts between the first room and the second room, wherein the boom assembly facilitates travel of the carriage. The system also includes a hoist system positioned in the first room. The hoist system includes at least one boom cable interconnected with the boom assembly to extend and retract the boom assembly. The hoist system also includes at least one carriage cable interconnected with the carriage to move the carriage.
056065892	abstract	Air cross grids, for absorbing scattered secondary radiation and improving X-ray imaging in general radiography and in mammography, are provided with a large plurality of open air passages extending through each grid panel. These passages are defined by two large pluralities of substantially parallel partition walls, respectively extending transverse to each other. Each grid panel is made by laminating a plurality of thin metal foil sheets photo-etched to create through openings defined by partition segments. The etched sheets are aligned and bonded to form the laminated grid panel, which is moved edgewise during the X-ray exposure to pass primary radiation through the air passages while absorbing scattered secondary radiation arriving along slanted paths.
052992438	claims	1. Glove holder unit for a confinement enclosure (1), said enclosure having at least one access opening (9) on which is fixed a glove disk (10), the glove holder unit having a sleeve (11) for protecting the arm and forearm fixed to said glove disk (10) and a working glove (15) protecting the hand and provided with means (17) for the detachable assembly with said protective sleeve (11), wherein the protective sleeve (11) comprises at least two parts, a first part (12) provided with bellows and a second part (13) made from a flexible material, the latter part (13) being able to bend within the first part (12), the glove holder unit further comprising means (49) for locking the assembly means (17) of the glove (15) and the protective sleeve (11), said locking means (49) being mobile between a locked position in which it maintains the assembly means (17) and the glove (15) outside the enclosure (1) and an unlocked position in which it allows the passage of the glove (15) and its assembly means (17) between the interior and exterior of the enclosure. 2. Glove holder unit according to claim 1, wherein the assembly means (17) of the glove (15) and the protective sleeve (11) comprises a glove holder bracelet provided at the end of said sleeve and is able to cooperate with an O-ring (22) provided on said glove and in that the locking means (49) incorporates at least two elements (51, 53) which can be assembled with one another about a glove disk (10) of the enclosure, each of these elements (51, 53) having a circular arc-shaped shoulder (65) able to receive at least one part of said glove holder bracelet (17) and lock the latter when the elements (51, 53) are assembled in the locked position. 3. Glove holder unit according to claim 2, wherein the locking means (49) comprises at least one return-preventing strip (69) which prevents the return of the glove (15) to the interior of the enclosure (1) when positioned outside the same. 4. Glove holder unit according to claim 2, wherein the glove holder bracelet (17) is externally provided with two substantially parallel, annular grooves (19, 21) able to receive the O-ring (22) provided on the glove (15). 5. Glove holder unit according to claim 2, wherein the glove disk (10) comprises a lateral flange (31) and the locking means (49) comprises at least two elements (51, 53) shaped like a semicircularly curved channel, each channel being positioned astride at least one part of the lateral flange (31). 6. Glove holder unit according to any one of the preceding claims, further comprising means (39) for sealing the first part of the sleeve (12), said sealing means (39) making it possible to insulate said first part from the interior of the enclosure (4) and maintain the second part (13) of the sleeve within said first part. 7. Glove holder unit according to claim 6, wherein the sealing means (39) comprises a ring located on the protective sleeve (11) at a junction between the first bellows-equipped part (12) and the second flexible part (13) and a sealing plug (41) provided with means for fixing said sealing plug to said ring. 8. Glove holder unit according to claim 7, wherein the fixing means comprises a tap and the outer surface of the ring (39) is threaded to mate with said tap. 9. Glove holder unit according to claim 7, wherein the sealing plug (41) is provided with an aerating grid (45). 10. Glove holder unit according to claim 7, wherein the bottom of the sealing plug (41) is provided with a gripping handle (47). 11. Glove holder unit according to claim 1, wherein the first, bellows-equipped part (12) of the protective sleeve protects the arm and the second part of said sleeve (13), made from flexible material, protects the user's forearm and elbow. 12. Glove holder unit according to claim 1, wherein the first part of the protective sleeve (12) is made from rigid, synthetic rubber. 13. Glove holder unit according to claim 1, wherein the second part (13) of the protective sleeve is made from vinyl. 14. Glove holder unit according to claim 1, wherein the protective sleeve (11) is detachably fixed to said glove disk (10). 15. Glove holder unit according to claim 9, wherein the bottom of the sealing plug (41) is provided with a gripping handle (47).
049869582	abstract	A fuel assembly for use in a boiling water reactor has a multiplicity of fuel rods. In the fuel assembly, among the fuel rods located in the periphery (for example, the outermost periphery) of the cross section of the fuel assembly, the proportion of fuel rods whose enrichment in their respective lower regions are greater than the average enrichment in the lower region of the fuel assembly is less than the proportion of fuel rods whose enrichment in their respective upper regions are greater than the average enrichment in the upper region of the fuel assembly.
	abstract	The invention pertains to a diagnostic device for a fluidic device (11, 12, 23), in particular for a valve array and or a maintenance unit. Furthermore, the invention pertains to a fluidic device (11, 12, 23) equipped with said diagnostic device. The diagnostic device preferably can be locally attached to the fluidic device (11, 12, 23). It features a diagnostic module (34) to determine at least one wear parameter (38b-40b,44) causing wear on the fluidic device (11,12,23) and for reporting of at least one wear status ascertained on the basis of the at least one wear parameter (38b-40b,44).
	claims	1. A neutron source comprising a composite, said composite comprising crystals comprising BeO and AmBe13, and an excess of beryllium, wherein:a) the crystals have an average size of less than 2 microns;b) the size distribution of the crystals is less than 2 microns; andc) the beryllium is present in a 7-fold to a 75-fold excess by weight of the amount of AmBe13. 2. The neutron source of claim 1, wherein the crystals have an average size of from about 0.01 micron to about 2 microns. 3. The neutron source of claim 1, wherein the composite is enclosed in a sealed capsule. 4. The neutron source of claim 3, wherein the sealed capsule comprises Ta, W, Zircaloy, or Pt30% Rh. 5. The neutron source of claim 4, wherein the sealed capsule is comprised of Ta. 6. A neutron source comprising a composite, said composite comprising crystals comprising BeO and AmBe13 and an excess of beryllium, wherein the beryllium is present in a 7-fold to a 75-fold excess by weight of the amount of AmBe13, and wherein the composite has a tensile strength of greater than 20,000 psi. 7. The neutron source of claim 6, wherein the crystals have an average size of from about 0.01 micron to about 2 microns. 8. The neutron source of claim 6, wherein the composite is enclosed in a sealed capsule. 9. The neutron source of claim 8, wherein the sealed capsule comprises Ta, W, Zircaloy, or Pt30% Rh. 10. The neutron source of claim 9, wherein the sealed capsule is comprised of Ta. 11. A method of producing a composite, said composite comprising crystals comprising BeO and AmBe13 and an excess of beryllium, comprising:a) providing AmO2 powder and Be metal powder in a sealed capsule, wherein the weight ratio of the Be metal to the AmO2 powder is from about 10:1 to about 100:1;b) heating the mixed AmO2 powder and Be metal powder in an induction furnace to a temperature of from about 1400° C. to about 1600° C. for a period of about 5 minutes; andc) lowering the temperature below the freezing point of the composite within about 5 minutes. 12. The method of claim 11, wherein the sealed capsule comprises Ta, W, Zircaloy, or Pt30% Rh. 13. The neutron source of claim 12, wherein the sealed capsule is comprised of Ta. 14. The method of claim 11, wherein the AmO2 powder and the Be metal are intimately mixed prior to heating.
046577327	summary	This invention relates generally to the art of nuclear reactor designs, and more particularly, to high temperature reactors. Specifically, the invention concerns improvements in safety barrier designs for such reactors, in which the need for separate reactor containment buildings is eliminated, without comprising reactor safety. BACKGROUND OF THE INVENTION In the known structural configurations of nuclear reactors, the pressurized enclosure of the primary loop performs a pressure-containing function and a sealing function, such that the release of fission products to the environment in normal operation and in design base events is limited to values below maximum permissible limits. In certain types of nuclear reactors, both the pressure-containing function and the sealing function for the primary loop are performed by a single wall steel pressure vessel. The loss of the pressure containment function, such as in a catastrophic failure of the pressure vessel, is prevented by redundant measures, for example, design for basis safety, quality control and operational surveillance. As it is assumed that leakage will precede fracturing, a safety container surrounding the steel pressure vessel is required as a redundant barrier against the release of fission products. In this manner, the pressurized containment of the primary loop is secured against failure even in relation to the sealing function. A safety container as a redundant barrier against the loss of the sealing function is required primarily because the reactor coolant has a high radioactivity content. Nuclear reactors of this type are described, for example, in German Auslegeschrift No. 23 15 318 and German Offenlegungsschrift No. 23 15 319. In the case of a high temperature reactor with spherical fuel elements, the fissionable material is coated to form the spherical elements, which are then embedded in a graphite matrix. The coating and the graphite matrix form a first barrier and a second barrier, respectively, against release of fission products. In addition, two further barriers are provided against the release of fission products. These are formed by the reactor pressure vessel (with a sealing function and a failure-safe pressure containment function) and the protective reactor housing (with a sealing and a pressure containment function). The reactor pressure vessel may be made of steel or prestressed concrete and the protective reactor housing of steel or concrete. A nuclear reactor of this structural type is known for example from German Offenlegungsschrift No. 32 12 322 which corresponds to United States Application Ser. No. 718,193, in continuation of Ser. No. 481,749. In such an installation, construction costs are very high, because the protective reactor housing must function not only as a safety container for the primary loop, but must also act as a structural enclosure for the reactor pressure vessel and the operating installations of the reactor, that is, it must function as the protective barrier against effects from the external environment. In a high temperature reactor with a prestressed concrete pressure vessel, all of the components of the primary loop are located in a cavity (or several cavities) of the prestressed concrete pressure vessel, which, for installation and disassembly and to receive the components, comprises a plurality of large passages. Tight enclosure of the primary loop is effected in the area of these passages by means of closure devices, which close off the passages in a pressurized and gas-tight manner. A nuclear reactor with a prestressed concrete pressure vessel comprising such passages and closure devices is described in German Offenlegungsschrift No. 31 41 734. The closure devices consist in each case of a double steel cover set into the passage involved. The inner cover represents the seal for the primary gas. In this installation, again, a tight protective reactor building must be present. German Offenlegungsschrift No. 15 14 783 also discloses the principle of using double covers as a safety closure for nuclear reactor pressure vessels. SUMMARY OF THE INVENTION It is an object of the invention to reduce the construction requirements for multiple barriers against release of fission products in a high temperature reactor of the above-mentioned type, for reasons of economy and technical reliability, without compromising the sealing function of the pressurized enclosure of the primary loop. According to the invention, this object is attained by utilizing the concrete body of the prestressed concrete pressure vessel and the liner of the vessel as the fourth and the third barriers, respectively, against the release of fission products. In the area of the passages through the pressure vessel, the sealing function of the third and fourth barrier is performed by known closure devices made of double steel covers arranged in the passages, with the inner cover forming the seal of the primary gas. The spaces between the outer and the inner covers are, in each case, connected to a pipeline, which conducts leakages of the primary gas into an exhaust stack through a filter system for the retention of the fission products. Further objects, features and advantages of the present application will become apparent from the detailed description of preferred embodiments, which follows, when considered together with the attached figure.
043127088	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The closure head assembly of a nuclear reactor is secured to the reactor vessel by a large number, for example, 54 studs which extend about the perimeter of the closure head assembly and extend through the assembly into the wall of the reactor vessel. A typical stud is seven inches in diameter. In order to remove the closure member, each stud must be removed and the stud hole completely plugged so that when the reactor vessel is flooded the flooding liquid, normally boric acid, does not get into the stud holes and cause corrosion which would then prevent proper reassembly of the closure head assembly onto the reactor vessel. The sectional view of FIG. 1 illustrates my stud hole plug unit, generally designated 10, in place within a wall opening 18 of a reactor wall 14. The portion of the reactor, generally designated 12, illustrated includes a portion of the reactor head 16 having an opening 20 therethrough. The reactor head 16 is resting on the reactor wall 14 and the opening 20 through the reactor head 16 is in registry with the opening 18 in the reactor wall 14. The opening 18 in the reactor wall 14 includes internal threads 22 spaced downwardly of the top of wall 14. As illustrated, the stud (not shown) has already been removed from the threads 22 and the plug unit 10 has been installed through the head opening 20 and into opening 18 so that it rests on the top of the reactor wall 14. The components of my plug hole unit 10 include the compression plate 24, the mandrel 26, the seal ring 32 and the nut 30. The compression plate 24 is circular and includes an upper (outer) surface 34, a lower (inner) surface 36 and a central axial opening 38 therethrough. Extending outward from the lower surface 36 is an annular rim 40. Annular rim 40 is spaced inwardly from the periphery of the compression plate 24 so as to define a small ledge 42 which rests on the opening 18 in the reactor wall 14 as the rim 40 extends into the opening to be plugged. The mandrel 26 includes an upper cylindrical section 44, a lower cylindrical section 48 of larger diameter than the upper cylindrical section 44 and a frustoconical connecting section 46. The mandrel 26 also includes a central opening 54 into which is inserted a stud 28. Stud 28 extends only partially through the mandrel opening 54 so as to form a recess 68 between the bottom of the stud 28 and the mandrel bottom surface 52. The stud 28 is welded to the mandrel 26 so as to become an integral part thereof. The weld 70 is generally within the recess 68. The particular unit 10 illustrated is for a seven inch stud hole and, therefore, the stud 28 and mandrel 26 were made separately and connected by the weld 70. In smaller diameter units, it may be practical to machine the stud and mandrel from the same blank so that welding is not necessary. The stud 28 extends through the opening 38 in the compression plate and is held in assembled relationship thereto by means of nut 30 threaded on the external threads 56 of stud 28. The seal is ring shaped and rectangular in cross section, FIG. 3. This rectangular cross section provides a more controlled flow as compared to a simple O-ring. The seal ring 32 is dimensioned so that its inner diameter tightly fits around the upper cylindrical section 44 of mandrel 26. In the uncompressed state, the seal ring 32 extends above the upper surface 50 of the mandrel 26. Seal 32 has an upper surface 60 which engages the rim 40 of the compression plate 24 in aligned relationship. In the uncompressed state, the bottom surface 62 of the seal ring 32 is positioned at the interface of the upper cylindrical section 44 and the frustoconical section 46. In the uncompressed state with the compression plate 24 just resting on the seal ring 32, the lower surface 36 of the compression plate 24 is spaced from the upper surface 50 of the mandrel 26 by a distance designated A which is equal to the distance between the bottom surface of the seal 62 and the bottom surface 52 of the mandrel 26, said distance being designated B. As will be described hereinafter, the seal ring is dimensioned so that it deforms the axial extent B in the compressed state. The unit 10 in FIG. 1 illustrates a stud 28 having an internal tap 58 whose threads (left handed) are the reverse of the external threads 56 (right handed) on the stud 28. The reason for this is to permit installation since the reactor head 16 is quite thick and a special tool must be employed to set the plug unit 10 in place, compress the seal and allow removal of the tool from the installed unit. The particular tool (not shown) includes a long outer pipe terminating in a socket which fits nut 30 and a round bar threaded at one end and having a handle at the other end and which is positioned concentrically within the pipe so as to engage the left handed thread 58 of the stud hole. To install the stud hole plug unit 10, the round bar is threaded to the stud 58 and the unit 10 is lowered through the reactor head 16 and into the stud hole 18 until the compression plate 24 rests on the top of the reactor wall 14. Then while the inner round bar is held stationary the outer pipe engages the nut and is turned clockwise. The turning of the nut 30 causes the mandrel 26 to advance linearly toward the compression plate 24. As this occurs, the seal ring 32 is forced down the frustoconical section 46. The mandrel 26 is moved upward until it engages the lower surface 36 of the compression plate 24, it being noted that the upper cylindrical section 44 is dimensioned to just fit within the diameter of the rim 40 of the compression plate 24. In the fully compressed state, FIG. 2, the seal ring 32 has been caused to flow into the confined space between the reactor wall 14 and the perimetric surface of the mandrel 26. The seal ring is so dimensioned that in the compressed state, it will extend downward to a point substantially planar or in line with the bottom surface 52 of the mandrel 26. In a typical application the flooding liquid (not shown) exerts a force or head of approximately 20 psi in the direction of the arrow H. The particular stud 28 shown in the compressed state, FIG. 2, includes a clear through vent 66 which then permits the cavity being plugged to be pressurized, if desired. A typical stud hole plug is machined from series 400 stainless steel and is then subjected to bright hardening, a process which gives the material substantial resistance to etching and corrosion. The ring 32, which provides a mechanical seal, is made of a halogen free Buna-N elastomer, thus providing an effective means of sealing off the stud cavity. Representative dimensions for a stud hole plug used in a seven inch stud hole having an upper unthreaded section of 7.03 inches are as follows: Compression plate I.D.=7.25 inches PA0 Lip I.D.=6.30 inches PA0 Lip O.D.=6.96 inches PA0 Lip thickness=0.20 inch PA0 Mandrel upper cylindrical section O.D.=6.25 inches PA0 Mandrel lower cylindrical section O.D.=6.75 inches PA0 Depth of recess for stud weld=1/4 inch PA0 cone angle=45.degree. PA0 Seal thickness=3/8 inch PA0 Seal height=5/8 inch PA0 Distance of seal above mandrel top (uncompressed)=1/4 inch PA0 Distances "A" and "B" (FIG. 1)=1/4-3/8 inch Stud hole plug units for reactors have been tested to determine their ability to withstand pressures created by a head wall of boric acid solution. The plug hole units have been subjected to hydrostatic pressures in excess of 200 psi without failure of the components and without any leakage of the seal. 9n
	description	The invention is described below in the context of multiple representative embodiments. However, it will be understood that the invention is not limited to those embodiments. First Representative Embodiment A plan view of a hollow-beam aperture according to this embodiment is shown in FIG. 1. The FIG. 1 embodiment is substantially planar in configuration and includes a first member 1 and multiple second members 2a, 2b. The first member 1 is attached to the second planar members 2a, 2b by respective flexible members 3a, 3b. The first planar member 1 includes opposing triangular portions 12 of which the respective apices are connected together by a narrow bridge 13. In the middle of the bridge 13 is a circular portion 11. The triangular portions 12 each have opposing edges 14a, 14b, and the second members 2a, 2b each have opposing edges 22a, 22b, respectively. The respective distal ends 15a, 15b of the second members 2a, 2b define respective semicircular cutouts 21a, 21b. Each of the semicircular cutouts 21a, 21b has a radius slightly larger (by approximately 20 xcexcm) than the radius of the circular portion 11. The edges 22a, 22b are configured to engage the edges 14a, 14b, respectively, in a conformable manner. In such a configuration, the bridge 13 and triangular portions 12 support the circular portion 11. The first member 1, second members 2a, 2b, and the flexible members 3a, 3b desirably are formed as a single unit as shown. Alternatively, these members can be separate from each other. Also, the flexible members 3a, 3b are not required. However, they are desirable because they simplify engagement of the second members 2a, 2b with the first member 1 (which occurs whenever the edges 14a, 14b engage the respective edges 22a, 22b). The flexible members 3a, 3b desirably are sufficiently thin to allow flexible expansion and contraction of the members. A unified structure (including the members 1, 2a-2b, and 3a-3b) can be manufactured (e.g., by EDM) from a 0.5-mm thick sheet of heat-resistant material (e.g., W, Mo, or sintered graphite). For use as a hollow-beam aperture, the FIG. 1 structure is configured further, as shown in FIGS. 2(a)-2(b), to include a support base 4, respective movable members 5a, 5b, nuts 6a, 6b, and screws 7a, 7b. FIG. 2(a) is a plan view, and FIG. 2(b) is an elevational section through the midline of FIG. 2(a). The first member 1 is mounted to the support base 4. The support base 4 defines a centrally located through-hole 8. The movable members 5a, 5b are affixed to the respective second members 2a, 2b, and the nuts 6a, 6b are attached to opposite ends of the first member 1. A respective screw 7a, 7b is attached rotatably to each movable member 5a, 5b is threaded through the respective nut 6a, 6b. By rotating the screws 7a, 7b, the respective second members 2a, 2b can be moved closer together or farther apart. Such movements of the second members 2a, 2b are opposed by a respective force produced by the respective flexible member 3a, 3b. As the second members 2a, 2b move toward each other, the edges 14a, 14b eventually contact the edges 22a, 22b, respectively. After such contact, further turning of the screws 7a, 7b causes the respective second members to move further together relative to the triangular portions 12 until the respective distal edges 15a, 15b contact the lateral edges of the bridge 13. The first member 1 and second members 2a, 2b are shaped such that, whenever the second members 2a, 2b are moved maximally together in this manner, no gaps exist between the distal edges 15a, 15b and the bridge 13 or between the edges 14a, 22a and 14b, 22b. Also, whenever the second members 2a, 2b are moved maximally together in this manner, the circular portion 11 is concentric with the semicircular cutouts 21a, 21b. Thus, during use, the circular portion 11 serves as a beam-absorbing body, and the space between the circular portion 11 and the semicircular cutouts 21a, 21b defines a substantially annular beam aperture (i.e., the aperture is contiguously ring-shaped except where interrupted by the bridge 13) surrounding the circular portion 11. The annular aperture is transmissive to the charged particle beam (which also passes through the through-hole 8), while the circular portion 11 and structure surrounding the annular aperture absorb charged particles of the beam incident on such structure. In the foregoing description, the circular portion 11 and cutouts 21a, 21b are emphasized by making them appear disproportionately large in FIGS. 1 and 2(a)-2(b). However, it will be understood that the cutouts 21a, 21b actually are no more than 100 xcexcm in diameter, whereas the second members 2a, 2b and first member 1 are relatively quite large (a few millimeters and a few tens of millimeters wide, respectively). Second Representative Embodiment A hollow-beam aperture according to this embodiment is depicted in FIGS. 3(a)-3(b), and comprises a first member 31 and a second member 35 intended to be mounted together as shown in FIG. 3(b). The first member 31 comprises a central body 32a (desirably cylindrical in shape), a planar portion 32b surrounding the central body 32a, and radial supports 33 connecting the central body 32a to the planar portion 32b. The planar portion 32b defines fastening holes 34. The second member 35 defines fastening holes 36 and a beam-transmitting opening 37. Appropriate fasteners (e.g., screws, not shown) are inserted through respective fastening holes 34, 36 to mount the second member 35 to the first member 31. The first member 31 defines a substantially circular through hole 38 in which the central body 32a is disposed centrally and coaxially, supported by the supports 33 (e.g., three supports 33 as shown). The first member 31 desirably is made of a heat-resistant material such as W, Mo, or sintered graphite, formed desirably by EDM as a single unit shaped as shown. The central body 32a is structured so that it extends above the plane of the first member 31 by at least the thickness of the second member 35. The second member 35 desirably is made from an approximately 0.5-mm-thick sheet of W, Mo, or sintered graphite. In an assembled hollow-beam aperture according to this embodiment, the central body 32a functions as a beam-absorbing body. The central body 32a also can be used during fabrication of the hollow-beam aperture as an EDM electrode for cutting the opening 37 in the second member 35. The opening 37 desirably has a radius that is approximately 20 xcexcm larger than the radius of the central body 32a. To assemble the hollow-beam aperture, the respective fastening holes 34, 36 in each comer are aligned with each other (FIG. 3(b)) and secured with screws or the like. Certain aspects of a top plan view of the assembled hollow-beam aperture according to this embodiment are shown in FIG. 4. In this figure, the annular gap between the central body 32a and the edge of the opening 37 readily can be seen. During EDM as described above, the outer edge of the opening 37 is formed due to the existence of a spark gap between the central body 32a and the second member 35 as the central body 32a is passed through the graphite sheet of the second member 35. In FIGS. 3(a)-3(b) and 4 the central body 32a and opening 37 are emphasized by making them appear disproportionately large. Actually, the opening 37 typically is less than 100 xcexcm in diameter, as in the first representative embodiment. The sizes of the first and second members, on the other hand, is arbitrary. Third Representative Embodiment A hollow-beam aperture according to this embodiment is shown in FIGS. 5(a)-5(b), and the results of certain steps in the manufacture of this embodiment are depicted in FIGS. 6(a)-6(d), respectively. Each of FIGS. 5(a)-5(b) is an isometric view, wherein FIG. 5(a) is an upper oblique view and FIG. 5(b) is a lower oblique view. The hollow-beam aperture comprises a main body 52 machined to have structural elements including a beam-absorbing body 51 and a support bar 53. The main body 52 also defines openings 54, 56 and spaces 55 that are best understood from a description of how the hollow-beam aperture of this embodiment is manufactured. Finally, when viewed axially (FIG. 6(d)), the hollow-beam aperture defines a substantially annular aperture 57 surrounding the beam-absorbing body 51. Fabrication of the hollow-beam aperture is described with reference to FIGS. 6(a)-6(d). To make these figures easier to understand, the dimensions of the beam-absorbing body 51 and the annular aperture 57 are depicted larger than actual, compared to other structural features. In reality, the annular aperture 57 has an outer diameter of 100 xcexcm or less, whereas the main body 52 has a width on each side of several millimeters. Fabrication begins with a block 61 of a suitable rigid, beam-absorbing material such as W, Mo, or sintered carbon. The block 61 desirably has a rectangular parallelopiped shape. Turning the block 61 about an axis A allows a cylindrical portion 62 (rotationally symmetric about the axis A, destined to be the beam-transmission axis, and relatively thick in the axial direction) to be cut (FIG. 6(a)). The cylindrical portion 62 is destined to become the beam-absorbing body 51, and has a diameter D1 and a xe2x80x9cheightxe2x80x9d (along the axis A) of H1. Thus, the remaining block 61 has a thickness H2. Similarly, turning the block 61 about the axis A allows a cylindrical void 63 to be cut (rotationally symmetrical about the axis A; FIG. 6(b)). The void 63 essentially forms the circular opening 56, and has a diameter D3 (wherein D1 less than D3) and a xe2x80x9cheightxe2x80x9d H3. Thus, of the original block 61, a rotationally symmetric shoulder 64 (having a xe2x80x9cheightxe2x80x9d of H2-H3, and being relatively thin in the axial direction, i.e., (H2-H3) less than H1)) and a portion 65 (that is relatively thick in the axial direction) are left. Two cylindrical voids 66a, 66b are formed (e.g., by drilling) along respective axes that are perpendicular to the axis A (see FIG. 6(c), showing the full circumference of each void). The radius of each void 66a, 66b is selected such that, when the finished hollow-beam aperture is viewed from a direction along the axis A (FIG. 6(d)), the substantially annular aperture 57 is formed that is bisected by the support bar 53 and flanked by lateral bars 67. The three manufacturing steps described above and shown in FIGS. 6(a)-6(c), respectively, can be performed in any order. In this embodiment, the cylindrical portion 62 has a diameter equal to the intended inner diameter of the annular aperture 57. The cylindrical void 63 desirably has a diameter equal to the intended outer diameter of the annular aperture 57. Thus, a structure is formed that, when viewed along the axis A, is rotationally symmetric (FIG. 6(d)). Along the axial direction, the cylindrical portion 62 is relatively thick, the shoulder 64 is relatively thin, and the lateral bars 67 are relatively thick. As noted above, the voids 66a, 66b can be formed by drilling from a lateral direction perpendicular to the axis A, but such that the voids flank the axis A (FIG. 6(c)). Thus, the voids 66a, 66b remove part of the shoulder 64 that is relatively thin in the axial direction. (Compare FIG. 6(c) with FIG. 6(b); also, as shown in FIG. 5(a), the only remaining portion of the shoulder 64 defines the support bar 53.) The items shown in FIGS. 5(a)-5(b) and 6(a)-6(d) are related as follows when manufacture is complete: the cylindrical portion 62 is the beam-absorbing body 51, which is relatively thick in the axial direction; the wall 65 corresponds to the main body 52, which is relatively thick in the axial direction; portions remaining after machining of the rotationally symmetrical shoulder 64 correspond to the support bar 53, which is relatively thin in the axial direction; and the cylindrical void 63 corresponds to the opening 56. As shown in FIG. 5(a), the individual openings 54 are somewhat crescent-shaped especially when viewed from a non-orthogonal direction. However, when viewed orthogonally from above, as shown in FIG. 6(d), with the beam-absorbing body 51 centrally situated over the opening 56, the openings 54 collectively appear as a complete ring (except for the support bars 53). Fourth Representative Embodiment A hollow-beam aperture according to this embodiment is shown in FIGS. 7(a)-7(b). FIG. 7(a) depicts a step in the manufacture of the subject hollow-beam aperture. Two steps in the manufacture of this embodiment are the same as shown in FIGS. 6(a)-6(B), respectively, and described above in connection with the third representative embodiment. I.e., fabrication begins with a block of a suitable rigid, beam-absorbing material such as tungsten, molybdenum, or sintered carbon. Turning the block about the axis A allows the cylindrical portion 62 (rotationally symmetric about the axis A and relatively thick in the axial direction) to be cut. The cylindrical portion 62 is destined to become the beam-absorbing body 51. Similarly, turning the block about the axis A allows the cylindrical void 63 to be cut (rotationally symmetrical about the axis A). The diameter of the void 63 is destined to become the outer diameter of the annular aperture. Thus, of the original block, the cylindrical portion 62 (that is relatively thick in the axial direction), a rotationally symmetric shoulder 64 (that is relatively thin in the axial direction), and a portion 65 (that is relatively thick in the axial direction) are left (see FIG. 6(b)). In FIG. 7(a), in contrast with FIG. 6(c), machining in a direction perpendicular to the axis A is performed using a suitable rectangular EDM electrode 68 tilted at an angle a relative to the axis A and urged (arrows) obliquely toward the axis A. Each resulting cut 70 has a rectangular transverse profile as shown in FIG. 7(a) and produces a respective sloping surface 69 flanked by a lateral bar 67 (FIG. 7(b)). Other features of this embodiment are similar to corresponding features of the third representative embodiment and have the same respective reference numerals. After completion of the machining described above (in which the individual machining steps can be performed in any order), the resulting hollow-beam aperture has a substantially annular aperture 57 that is ring-shaped except for support bars 53 supporting the beam-absorbing body 51. In this embodiment the annular aperture 57 has an inner diameter that is established by the diameter of the cylindrical portion 62, an outer diameter that is established by the diameter of the cylindrical void 63, and a radial width equal to the difference in these two diameters. Hence, the radial width of the annular aperture 57 can be made extremely small. Also, the annular aperture 57 is flanked by the sloped surfaces 69. Portions of an incident charged particle beam striking a sloped surface 69 are reflected diagonally, which prevents disturbance of the incident beam from stray particles generated by multi-path reflections. An advantage of this embodiment over the third representative embodiment is that this embodiment requires less complex machining than the third representative embodiment, and thus can be made in less time. I.e., in the third representative embodiment the openings 16 are formed by drilling through the entire width (several millimeters) of the body 51, whereas the cuts 70 of the fourth representative embodiment are formed readily (typically about 100 xcexcm wide) by EDM at respective locations flanking the ring-shaped opening 17. Also, the hollow-beam aperture of the fourth representative embodiment has greater mechanical strength than the third representative embodiment. Fifth Representative Embodiment A hollow-beam aperture according to this embodiment is depicted in FIGS. 9(a)-9(b), and FIGS. 8(a)-8(d) depict the results of certain respective steps in the manufacture of a hollow-beam aperture according to this embodiment. The hollow-beam aperture is formed from a main body 71 having a center axis 72 (which will be the beam axis). The main body 71 defines a ring-shaped groove 73 having a triangular sectional profile as shown in FIG. 8(a), truncated pyramidal openings 74, a peripheral frame portion 75, a beam-absorbing body 76, a support bar 77, sloping surfaces 78, a planar surface 79, and a substantially ring-shaped opening 80. To form the hollow-beam aperture of this embodiment, reference is made to FIGS. 8(a)-8(d). As shown in FIG. 8(a), the ring-shaped groove 73 (with triangular sectional profile) is machined into a bottom (in the figure) surface of the main body 71, about the axis 72. Cutting the groove 73 can be performed either by holding the main block 71 stationary and rotating a cutting tool about the axis 72, or holding the cutting tool stationary and rotating the main block 71 about the axis 72. This machining step can be performed using a lathe or by EDM. As shown in FIG. 8(b), the truncated pyramidal openings 74 are cut into the top (in the figure) surface of the main block 71 using complementary-shaped EDM electrodes (profiled by dash-dot lines) engaged perpendicularly (arrows) to the top surface. Each electrode has sloping sides. EDM machining is performed at bilaterally symmetrical positions relative to the center axis 72. EDM machining depths are set such that the width of the resulting ring-shaped opening 80 extending through the main block 71 after machining from above and below will be equal to the prescribed diameter of the hollow beam to be formed by the hollow-beam aperture of this embodiment. Sectional and plan views of the resulting hollow-beam aperture produced by the foregoing machining steps are shown in FIGS. 8(c) and 8(d), respectively. Isometric views of the hollow-beam aperture as seen from above and below are shown in FIGS. 9(a) and 9(b), respectively. These figures show the peripheral frame portion 75 and centrally located beam-absorbing body 76 supported relative to the frame portion 75 by the support bars 77. The beam-absorbing body 76 is surrounded by the substantially ring-shaped opening 80 and is coaxial with the center axis 72. The planar surface 79 is oriented perpendicularly to the center axis 72. The radial gap between the diameter of the base of the cone-shaped beam-absorbing body 76 and the outer diameter of the substantially ring-shaped opening 80 is configured to the prescribed value by using appropriate specifications for the downward-machining step (FIG. 8(b)), in view of the specifications used for the upward-machining step (FIG. 8(a)). Also, multi-path reflection problems are avoided by making the planar surfaces 79 as small as possible. Because the beam-absorbing body 76 is made cone-shaped in this embodiment, it has a sharp edge residing in a plane perpendicular to the center axis 72 (i.e., the same plane as that of the planar surface 79). This configuration provides an ideal trimming of the beam regardless of the angle of incidence of the beam to the hollow-beam aperture. Also, the inner and outer circumferences of the substantially ring-shaped opening 80 can be made perfectly concentric because they are both defined by the same groove 73. The sides of the support bars 77 desirably are sloped as shown. This allows the support bars 77 to be made as thin as possible, thereby minimizing possible adverse effects from the support bars 77 interfering with an inclined beam. In each of representative embodiments three, four, and five, the beam-transmitting portion of the respective hollow-beam aperture was formed by machining voids in two locations. Alternatively, it will be understood that this machining could have been performed in three or more locations. Whenever the machining in performed in three locations, the beam-absorbing body is supported by three support bars. Also, in any of the third, fourth, and fifth representative embodiments, machining for forming the beam-transmitting portion desirably is performed at rotationally symmetric locations about the center of the aperture. In so doing, the formation of a ring-shaped beam having anisotropic characteristics can be avoided. Sixth Representative Embodiment A hollow-beam aperture according to this embodiment is shown in FIGS. 10(a)-10(c), in which item 81 is a main block, items 82 and 83 are respective truncated conical openings, item 84 is a beam-absorbing body, item 85 is a support bar, and item 86 is a substantially ring-shaped opening. The truncated conical opening 82 is formed in the main block 81 by machining from above (FIG. 10(a)). The opening 82 is formed with its axis A being perpendicular to the top (in the figure) surface of the main block 81. The axis A of the opening 82 will become the center axis of the beam-absorbing body 84. Four truncated conical openings 83 are machined with their respective axes B being perpendicular to the bottom (in the figure) surface of the main block 81. The respective axes B of the conical openings 83 are equidistant from, and rotationally-symmetric about, the axis A of the opening 82. Machining is performed such that portions of the opening 82 are situated over the openings 83 below it. The respective sizes, positions, and depths of the openings 82, 83 are such that a xe2x80x9cpassagexe2x80x9d (comprising openings 86) is formed through the structure. Plan and isometric views of a structure machined in this manner are provided in FIGS. 10(b) and 10(c), respectively. In the center of the structure is the beam-absorbing body 84, which is supported in the main block 81 (as the equivalent of a first member) by four supports 85. Formed around the beam-absorbing body 84 is a substantially ring-shaped opening comprising four segments 86. The outer diameter of the beam-absorbing body 84 (i.e., the diameter of a circle inscribed in the beam-absorbing body 84) and the outer diameter of the substantially ring-shaped opening 86 (i.e., the diameter of a circle circumscribing the segments 86) are established by using the proper respective values for the size, location, and depth of the openings 82 and 83 above and below it, respectively. Hence, a substantially ring-shaped aperture, having a prescribed width and thickness, is provided in this representative embodiment. In this embodiment, the side wall of the truncated conical opening 82 desirably is sloped. Such a configuration reflects an incident beam at an angle that prevents multi-path reflection problems. Also, because the substantially ring-shaped opening 86 is formed in a plane that is perpendicular to the center axis A of the beam-absorbing body 84, the ring-shaped opening can achieve an ideal trimming of the beam, regardless of the angle of incidence of the beam to the hollow-beam aperture. In addition, because the substantially ring-shaped (annular) opening 86 is rotationally symmetric about the axis A, anisotropism of a beam passing through the annular aperture can be eliminated. Seventh Representative Embodiment A hollow-beam aperture according to this embodiment is shown in FIGS. 11(a)-11(b), and 12. In a conventional hollow-beam aperture as shown in FIG. 17, the thickness in the axial direction is relatively thin. Consequently, the hollow-beam aperture has a correspondingly low rigidity, which can result in distortion or fracture of the hollow-beam aperture. On the other hand, if the axial thickness of the hollow-beam aperture of FIG. 17 were to be increased to reduce distortion, then manufacture of the hollow-beam aperture would be made correspondingly more difficult; also, propagation of the beam through the substantially annular aperture may be impaired due to collision of particles of the beam with side walls of the openings. Since a beam incident in a normal manner to such a hollow-beam aperture typically can have an inclination (relative to the axis) of, for example, 8 mrad, a hollow-beam aperture configured as shown in FIG. 17 exhibits a significant absorption and scattering of incident charged particles in the beam. Reference now is made to FIGS. 11(a)-11(b), wherein FIG. 11(a) is an elevational section along the line A-Axe2x80x2 of FIG. 11(b). The hollow-beam aperture according to this embodiment comprises three portions 101, 103, 104 that can be made as three separate respective items laminated together, or as a single integrated unit. The portion 101 is a xe2x80x9ccharged-particlexe2x80x9d (xe2x80x9cCPxe2x80x9d) stop member, the portion 103 is a support member, and the portion 104 is an optional reinforcing member. The CP-stop member 101 defines an annular-shaped cutout 107 that serves to define a beam-absorbing member 102. The support member 103 defines multiple (e.g., four) openings 105 each being, for example, desirably circular with a diameter of 170 xcexcm. The reinforcing member 104 is optional; if a combination of the CP-stop member 101 and support member 103 provides sufficient rigidity to prevent distortion of the CP-stop member, then the reinforcing member 104 can be deleted. If present, the reinforcing member 104 defines an opening 108 that desirably is circular with a diameter of, e.g., 300 xcexcm and that is concentric with the substantially annular opening 107. A representative thickness of the reinforcing member 104 is 300 xcexcm. The support member 103 supports the CP-stop member 101. Hence, the CP-stop member 101 can be thin with low rigidity. (However, the CP-stop member 101 desirably is sufficiently thick to absorb incident charged particles; a representative thickness is 50 xcexcm.). A representative thickness of the support member is 150 xcexcm. In the configuration of FIGS. 11(a)-11(b), the support member 103 defines four circular openings 105 equiangularly and equi-radially spaced about the axis A. The portions of the support member 103 extending between the openings 105 serve as support bars 109 for a region 106 of the support member 103 that support the beam-absorbing member 102. Each opening 105 can have a relatively small diameter (e.g., 170 xcexcm). But, if the support member 103 is sufficiently thick to maintain requisite rigidity of the hollow-beam aperture, then portions of an incident beam divergently propagating through the substantially annular aperture 107 may be blocked by collision with a wall of an opening 105. In such a case, the diameter of the openings 105 can be increased as appropriate and the reinforcing member 104 be included to maintain adequate rigidity of the hollow-beam aperture. If the reinforcing member 104 is included, then the opening 108 desirably has a relatively large diameter (e.g., 300 xcexcm) to prevent the beam colliding with a wall of the opening 108 during passage of the beam through the hollow-beam aperture. FIG. 12 shows representative positional relationships of the various openings 105, 107, 108 of this embodiment. In the configuration of FIG. 5, the center of each opening 105 is coincident at a respective apex A, B, C, D of a square 110. The square 110 has sides each having a length xe2x80x9csxe2x80x9d. The square 110 is tangent to a circle 11 having a radius xe2x80x9crxe2x80x9d that is the midline of the substantially annular aperture 107. Each support bar 109 has a width xe2x80x9cwxe2x80x9d, wherein d=sxe2x88x92w. An alternative configuration of a hollow-beam aperture according to this embodiment is shown in FIGS. 13(a)-13(b), wherein FIG. 13(a) is an elevational section along the line C-Cxe2x80x2 of FIG. 13(b), and components that are similar to components shown in FIGS. 11(a)-11(b) have the same respective reference numerals. The configuration of FIGS. 13(a)-13(b) includes only two openings 105xe2x80x2 (analogous to the openings 105 in the configuration of FIG. 11(b)). Each opening 105xe2x80x2 has a profile that is extended from circular (i.e., each opening 105xe2x80x2 is an elongated slot with full-radius ends). Such a configuration exhibits reduced beam blocking, compared to the configuration of FIGS. 11(a)-11(b). However, the circular openings 105 in the configuration of FIGS. 11(a)-11(b) generally are easier to make than the openings 105xe2x80x2. The material used to manufacture a hollow-beam aperture according to this embodiment desirably is tantalum, molybdenum, or graphite. Graphite has the lowest cost. The openings desirably are formed by EDM or mechanical machining. In any of the embodiments described herein, the member situated at the center of the hollow-beam aperture has been referred to as a xe2x80x9cbeam-absorbing memberxe2x80x9d that blocks propagation of the incident beam through it. The center member alternatively can be a xe2x80x9cbeam-scattering memberxe2x80x9d that transmits the beam (while scattering the beam). In the alternative situation, a scattering aperture desirably is situated axially downstream to block propagation of the particles scattered by the center member (see item 47 in FIG. 17, discussed below). Eighth Representative Embodiment This embodiment of a charged-particle-beam (CPB) microlithography apparatus is shown in FIG. 14. The apparatus comprises a CPB source 41, illumination lenses 42, a hollow-beam aperture 43 such as any of the embodiments described above, a first aperture stop 44, a reticle 45, projection lenses 46, a second aperture stop (xe2x80x9cscattering aperturexe2x80x9d) 47, and a substrate (wafer) 48. As in a conventional CPB microlithography apparatus, the illumination lenses 42 cause the reticle 45 to be illuminated uniformly by a charged particle beam emitted from the CPB source 41. A pattern defined by the reticle 45 is imaged on the substrate 48 by the projection lenses, which form a latent image in a layer of resist on the wafer 48. The aperture stops 44, 47 are provided to shield the wafer 48 from scattered charged particles. As noted above, the FIG. 14 embodiment includes a hollow-beam aperture 43 desirably situated at a beam crossover (an axial location where the charged particle beam converges). Placing the hollow-beam aperture 43 at a crossover provides maximal effectiveness of the hollow-beam aperture 43 in preventing Coulomb effects. Although a hollow-beam aperture 43 placed at a crossover normally experiences heating to an extremely high temperature by absorption of particles of the charged particle beam, a hollow-beam aperture according to the present invention withstands such high temperatures extremely well. This is because, inter alia, the hollow-beam aperture is made of a material that can withstand high temperatures, such as sintered graphite, tantalum, or molybdenum, and constructed as described above. Another problem with placing the hollow-beam aperture at a crossover is that the beam is very small in transverse profile at such a location. Consequently, an annular aperture must have an extremely narrow radial width to make the hollow center of the beam large enough while achieving the desired reduction in Coulomb effects. Hollow-beam apertures according to the invention provide, for the first time, annular apertures that are sufficiently narrow in radial width (e.g., 20 xcexcm) to be effective at the crossover. Ninth Representative Embodiment FIG. 15 is a flowchart of an exemplary microelectronic-device fabrication method to which apparatus and methods according to the invention readily can be applied. The fabrication method generally comprises the main steps of wafer production (wafer fabrication and preparation), wafer processing, device (chip) assembly (including dicing, lead connections, and chip packaging), and device inspection. Each step usually comprises several sub-steps. Among the main steps, wafer (substrate) processing is key to achieving the smallest feature sizes (critical dimensions) and best inter-layer registration. In the wafer-processing step, multiple circuit patterns are layered successively atop one another on the wafer, wherein the formation of each layer typically involves multiple sub-steps. Usually, many operative microelectronic devices (e.g., memory chips or CPUs) are produced on each wafer. Typical wafer-processing steps include: (1) thin-film layer formation involving formation of a dielectric layer for electrical insulation or a metal layer for forming interconnects and electrodes; (2) oxidation of the thin-film layer or wafer substrate; (3) microlithography to form a resist pattern, for selective processing of the thin film or the substrate itself, according to a reticle; (4) etching or analogous step to etch the thin film or substrate according to the resist pattern; (5) impurity doping or implantation (e.g., by ion bombardment or diffusion) as required to implant ions or impurities into the thin film or substrate according to the resist pattern; (6) resist stripping to remove the resist from the wafer; and (7) wafer inspection. Wafer processing is repeated as required (typically many times) to fabricate the desired microelectronic device(s) on the wafer. FIG. 16 provides a flowchart of typical steps performed in microlithography, which is a principal step in wafer (substrate) processing. The microlithography step typically includes: (1) resist-coating step, wherein a suitable resist is coated on the wafer or wafer substrate (which can include a circuit element formed in a previous wafer-processing step; (2) exposure step, to expose the resist with the desired pattern; (3) development step, to develop the exposed resist; and (4) optional resist-annealing step, to enhance the durability of the resist pattern. Details of the microelectronic-device manufacturing process outlined above are well known by persons of ordinary skill in the art, and hence do not require elaboration here. Whereas the invention has been described in connection with multiple representative embodiments, it will be apparent that the invention is not limited to those embodiments. On the contrary, the invention is intended to encompass all modifications, alternatives, and equivalents as may be included within the spirit and scope of the invention, as defined by the appended claims.
	claims	1. A control device which evaluates an examination result sent from at least one user terminal, comprising:a receiver configured to receive, from a user terminal via a network, an examination result of a quality control sample assayed by at least one analyzing unit of a plurality of analyzing units, each analyzing unit configured to analyze a biological sample and a quality control substance using a particular assay mode;a processor configured to statistically evaluate the received examination result against stored quality control sample data for the quality control substance and the particular assay mode and prepare a quality control report,wherein the processor tallies examination results for each analyzing unit and for each quality control substance and each assay mode; anda notifying section comprising a WWW server which is accessible from the user terminal, wherein the notifying section is configured to notify the quality control report to the user terminal via the network by putting up the quality control report on the WWW server. 2. The control device of claim 1, wherein the quality control report comprises a graphic display showing a history of examination results of the quality control sample assayed by the at least one analyzing unit. 3. The control device of claim 2, wherein the graphic display further shows a history of an average of the examination results of the quality control sample assayed by the at least one analyzing unit. 4. A quality control method implemented in a control device which evaluates an examination result sent from at least one user terminal, the method comprising:from a user terminal via a network, receiving an examination result of a quality control sample assayed by at least one analyzing unit of a plurality of analyzing units, each analyzing unit configured to analyze a biological sample and a quality control substance using a particular assay mode;statistically evaluating the received examination result against stored quality control sample data for different kinds of quality control substances and for different assay modes, wherein the processor tallies examination results for each analyzing unit and for each quality control substance and for each assay mode and preparing a Web page including a quality control report based on the evaluation of the received examination result; andnotifying the quality control report to the user terminal via the network by putting up the Web page on a WWW server which is accessible from the user terminal. 5. The control device of claim 1, wherein the receiver receives the examination result accompanied with at least one of a lot number of the quality control sample, a type of the quality control sample, an assay mode where the quality control sample was assayed, and an identification of the at least one analyzing unit which assayed the quality control sample. 6. The control device of claim 1, wherein the quality control report comprises an external quality control report which statistically compares an examination result of the quality control sample assayed by one analyzing unit against examination results of the quality control sample received by the control device. 7. The control device of claim 1, wherein the receiver receives an e-mail containing the examination result. 8. The quality control method of claim 4, wherein receiving an examination result comprises receiving an examination result accompanied with at least one of a lot number of the quality control sample, a type of the quality control sample, an assay mode where the quality control sample was assayed, and an identification of the at least one analyzing unit which assayed the quality control sample. 9. The quality control method of claim 4, wherein the quality control report comprises an external quality control report which statistically compares an examination result of the quality control sample assayed by one analyzing unit against examination results of the quality control sample received by the control device. 10. The quality control method of claim 4, wherein receiving an examination result comprises receiving an e-mail containing the examination result. 11. A control device which evaluates an examination result sent from at least one user terminal, the control device comprising:a receiver configured to receive, from a user terminal via a network, an examination result of a quality control sample assayed by at least one analyzing unit of a plurality of analyzing units, each analyzing unit configured to analyze biological samples and a quality control substance, wherein the receiver receives the examination result accompanied with at least one of a lot number of the quality control sample, a type of the quality control sample, an assay mode where the quality control sample was assayed, and an identification of the at least one analyzing unit which assayed the quality control sample;a processor configured to statistically evaluate the received examination result against stored quality control sample data, wherein the processor tallies examination results for each analyzing unit and for each quality control sample and for each assay mode and prepares a quality control report based on the evaluation of the received examination result; anda notifying section configured to notify the quality control report to the user terminal via the network. 12. The control device of claim 11, wherein the quality control report comprises a graphic display showing a history of examination results of the quality control sample assayed by the at least one analyzing unit. 13. The control device of claim 12, wherein the graphic display further shows a history of an average of the examination results of the quality control sample assayed by the at least one analyzing unit. 14. The control device of claim 11, wherein the quality control report comprises an external quality control report which statistically compares an examination result of the quality control sample assayed by one analyzing unit against examination results of the quality control sample received by the control device. 15. The control device of claim 11, wherein the receiver receives an e-mail containing the examination result. 16. A quality control method implemented in a control device which evaluates an examination result sent from at least one user terminal, comprising:from a user terminal via a network, receiving an examination result of a quality control sample assayed by at least one analyzing unit of a plurality of analyzing units, each analyzing unit configured to analyze biological samples and a quality control substance, wherein the result of examination is accompanied with at least one of a lot number of the quality control sample, a type of the quality control sample, an assay mode where the quality control sample was assayed, and an identification of the at least one analyzing unit which assayed the quality control sample;statistically evaluating the received examination result against stored quality control sample data by tallying examination results for each analyzing unit and for each quality control sample and for each assay mode and preparing a quality control report based on the evaluation of the received examination result; andnotifying the quality control report to the user terminal via the network. 17. The quality control method of claim 16, wherein the quality control report comprises an external quality control report which statistically compares an examination result of the quality control sample assayed by one analyzing unit against examination results of the quality control sample received by the quality control device. 18. The quality control method of claim 16, wherein receiving an examination result comprises receiving an e-mail containing the examination result. 19. A control device which evaluates an examination result sent from at least one user terminal, comprising:a receiver configured to receive, from a user terminal via a network, an examination result of a quality control sample assayed by at least one analyzing unit of a plurality of analyzing units, each analyzing unit configured to analyze a biological sample and a quality control substance using a particular assay mode;a processor configured to statistically evaluate the received examination result against stored quality control sample data for the quality control substance and for the particular assay mode, wherein the processor tallies examination results for each analyzing unit and for each quality control sample and for each assay mode and prepare a quality control report based on the evaluation of the received examination result; anda notifying section configured to notify the quality control report to the user terminal via the network,wherein the quality control report comprises an external quality control report which statistically compares an examination result of the quality control sample assayed by one analyzing unit against examination results of the quality control sample received by the control device. 20. The control device of claim 19, wherein the quality control report comprises a graphic display showing a history of examination results of the quality control sample assayed by the at least one analyzing unit. 21. The control device of claim 20, wherein the graphic display further shows a history of an average of the examination results of the quality control sample assayed by the at least one analyzing unit. 22. The control device of claim 19, wherein the receiver receives an e-mail containing the examination result. 23. A quality control method implemented in a control device which evaluates an examination result sent from at least one user terminal, comprising:from a user terminal via a network, receiving an examination result of a quality control sample assayed by at least one analyzing unit of a plurality of analyzing units, each analyzing unit configured to analyze biological samples and a quality control substance using a particular assay mode from different kinds of quality control substances and for different assay modes;statistically evaluating the received examination result against stored quality control sample data by tallying the examination results for each analyzing unit and for each kind of quality control substance and for each assay mode and preparing a quality control report based on the evaluation of the received the examination result; andnotifying the quality control report to the user terminal via the network,wherein the quality control report comprises an external quality control report which statistically compares an examination result of the quality control sample assayed by one analyzing unit against examination results of the quality control sample received by the control device. 24. The quality control method of claim 23, wherein receiving an examination result comprises receiving an e-mail containing the examination result. 25. A control device which evaluates a result of examination sent from at least one user terminal, comprising:a receiver configured to receive, from a user terminal via a network, an examination result of a quality control sample assayed by at least one analyzing unit of a plurality of analyzing units, each analyzing unit configured to analyze a biological sample and a quality control substance using a particular assay mode, wherein the receiver receives an e-mail containing the examination result;a processor configured to statistically evaluate the received examination result against stored quality control sample data from the quality control substance and for the particular assay mode and prepare a quality control report based on the evaluation of the received examination result, wherein the processor tallies examination results for each analyzing unit and for each kind of quality control substance and for each assay mode; anda notifying section configured to notify the quality control report to the user terminal via the network. 26. The control device of claim 25, wherein the quality control report comprises a graphic display showing a history of examination results of the quality control sample assayed by the at least one analyzing unit. 27. The control device of claim 26, wherein the graphic display further shows a history of an average of the examination results of quality control sample assayed by the at least one analyzing unit. 28. A quality control method implemented in a control device which evaluates an examination result sent from at least one user terminal, comprising:from a user terminal via a network, receiving an examination result of a quality control sample assayed by at least one analyzing unit of a plurality of analyzing units, each analyzing unit configured to analyze biological samples and a quality control substance, wherein the receiver receives an e-mail containing the examination result;statistically evaluating the received examination result against stored quality control sample data by tallying examination results for each analyzing unit and for each kind of quality control sample and for each assay mode and preparing a quality control report based on the evaluation of the received examination result; andnotifying the quality control report to the user terminal via the network.
	description	The storage device shown in FIG. 1, hereinafter also referred to as a cask and designated by 10, is only an example of the type of storage container which is useful for storing nuclear fuel in accordance with the invention, namely a storage container that includes a concrete body and at least one fuel receptacle or receiver embedded in the concrete body and serving to hold the nuclear fuel during storage. The nuclear fuel to be stored may take various forms, but the embodiment of the storage container or cask 10 shown in FIG. 1 is especially useful for the storage of fuel in the form of fuel assemblies or bundles of fuel rods. This also is true of the cask shown in FIG. 3. Broadly, the cask 10 is in the shape of a straight cylindrical body having an axial through cylindrical central passage 11 of circular cross-section. The main part of the space accommodated by the cylinder is occupied by a concrete body 12, which is of the same general shape as the entire cask. The cylindrical outer surface of the concrete body 12 is covered by a cylindrical shell 13, and its central passage is lined with a cylindrical centre tube 14 forming the major part of the central passage 11. The shell 13 and the centre tube 14 are permanent parts of the formwork in which the concrete body 12 is cast, i.e. they remain parts of the cask 10 in use. The ends of the concrete body 12 are covered by a circular lower end cover 15 and a similar upper end cover 16. As will be seen from the following detailed description, the end covers 15 and 16 are made of sheet steel and like the shell 13 and the centre tube 14 they are permanent formwork parts. Embedded in the concrete body 12 is a pre-stressed reinforcement, generally designated by 17, which is anchored in the end covers 15 and 16 and pre-stresses the concrete body three-dimensionally, that is axially and in all radial directions. The reinforcement 17 is positioned adjacent the cylindrical outer surface of the concrete body 12. A fuel receiver including a number of closed circular cylindrical receiver sections or storage vessels, generally designated by 18 is embedded in the concrete body 12 such that there are no joints in the concrete contacting the storage vessels. The storage vessels are hermetically sealed and form distributed storage compartments (fuel compartments) for holding the stored fuel units. In the illustrated embodiment, the storage vessels 18 are eight in number and positioned with their axes on an imaginary cylindrical surface which is concentric with the concrete body 12 and the central passage 11. As is apparent from the figures, see especially FIGS. 1 and 3, the distance separating the storage vessels 18 from the centre tube 14 is much smaller than the distance separating the storage vessels 18 and the shell 13. The storage compartments formed by the storage vessels 18 are filled with a fluid coolant, such as water. In each storage vessel 18 the coolant circulates through natural convection (thermosiphon circulation) in a closed coolant circuit including a tube 19, the ends of which communicate with the interior of the storage vessel 18 at the upper and lower ends of the vessel and which is positioned mainly in the radially outer part of the concrete body 12. Thus, the coolant carries part of the heat produced in the storage vessel 18 outwardly to that part of the concrete body, and from that part the heat can dissipate into the ambient air or water. Additional heat is carried away inwardly into the central passage 11 from which it can be dissipated convectively into the ambient medium by air or water flowing upwardly through the passage. That part of the coolant circuit which is located outside the storage vessel 18 also includes an expansion vessel 20 adjacent the upper end of the storage vessel. The end covers 15 and 16 are substantially identical, and in the following description they are primarily represented by the upper end cover 16. Both end covers 15, 16 serve as end walls of the permanent formwork in which the concrete body 12 is cast, as anchoring members for the reinforcement 17 of the concrete body, and as protective members of the ends of the concrete body in the completed cask 10. Additionally, the upper end cover 16 can serve as a work platform during stressing of the reinforcement and any future removal of the contents of the storage vessels 18. Such removal includes working off the concrete directly above the storage vessels 18, so that the upper ends of the storage vessels can be reopened. As is apparent from the drawing figures, the end cover 16 consists mainly of an upper or outer plate 21 and a lower or inner plate 22. In the finished cask 10 the plates 21, 22 are joined together in a suitable manner, e.g. by welding, and the space between them is partly or completely filled with concrete. Advantageously, the space between the plates may also accommodate equipment which is accessible from the exterior of the cask 10 and used e.g. for monitoring and signalling purposes, such as equipment for temperature and activity measurements, leakage detection and communication with monitoring stations. Both plates 21, 22 are circular and have a central opening of approximately the same diameter as the centre tube 14. At their inner edge and their outer edge the plates are provided with downwardly directed circular cylindrical rims 23 and 24 on the outer plate 21, and 25 and 26 on the inner plate 22. The rims 23 and 24 on the outer plate 21 extend over the rims 25 and 26 on the inner plate 22. The upper end of the shell 13 extends into the gap between the outer rims 23 and 25, and in a corresponding manner the upper end of the centre tube 14 extends into the gap between the inner rims 24 and 26. On the radially outer part of the inner plate 24 an annular steel rail 27 is supported which serves as an anchoring member for two groups of circumferentially uniformly spaced anchoring members (rods, cables or wires) 28, 29 of the reinforcement 17, and as a means for introducing the pre-stressing forces into the concrete body 12. Additionally, the rail 27 serves as an anchoring member for a plurality of circumferentially spaced devices (not shown) for attaching lifting devices used for lifting the entire cask 10. The central portion of the outer plate 21 is depressed and provided with a number of openings 31, one such opening being directly above each storage vessel 18. In the inner plate 22 a corresponding opening 32 is provided. These openings are sized such that the fuel units can readily be introduced into the open upper ends of the storage vessels 18 before the concrete body 12 is formed by placement of the concrete. Preferably, the diameter of the openings 31, 32 is at least as large as the diameter of the storage vessels 18. Adjacent the openings 32 the upper plate 21 also is provided with auxiliary means, symbolically represented by dots 33, for the positioning and attachment of suitable tools for working off the concrete beneath the openings when the contents of the storage vessels 18 are to be made accessible a shorter or longer storage time after the cask 10 has been completed, such as when the stored fuel units are to be extracted to be subjected to inspection or reprocessing or other treatment. In the upper end cover 16 a ring of openings 34 are formed for the passage of concrete placing tubes (not shown) through which concrete is introduced into the space defined between the shell 13, the centre tube 14 and the end covers 15, 16. Moreover, there is a ring of openings 35 through which anchoring devices for the reinforcing members 27, 28 are accessible for manipulation. The lower end cover 15 may be substantially identical with the upper end cover 16 but may also be modified at least such that it does not have openings corresponding to the openings 31, 32 and 34 of the upper end cover 16. FIG. 2 shows the steel reinforcement 17 in greater detail. A characteristic feature of the reinforcement 17 is the disposition of each of the reinforcing members 28, 29 of the two groups along a spiral line, namely a cylindrical helical line, between the end covers 15 and 16. In one of the two groups the reinforcing members 28 are disposed along an imaginary cylindrical surface slightly closer to the shell 13 than the reinforcing members 29 of the other group, which are also disposed on an imaginary cylindrical surface and the hand of which is opposite to the hand of the reinforcing members of the first group. The two imaginary cylindrical surfaces are concentric with the shell 13 and the centre tube 14. Suitably, the helix angle of all reinforcing members is about 45xc2x0, and at least at some of their intersections the reinforcing members suitably are interconnected by wire bindings or other suitable interconnecting members (not shown). For reasons which will become apparent, each reinforcing member 28, 29 suitably is enclosed in a tubular sheath (not shown in the drawings). The storage device 40 shown in FIG. 3, which is hereinafter also designated as a cask, is primarily intended for interim or other relatively short-term storage of nuclear fuel, especially during shipping or transfer of nuclear fuel units, e.g. when moving nuclear fuel units from storage pools to a long-term storage site. The cask 40 differs from the cask 10 of FIGS. 1, 2 in that it only has a single fuel receiver or storage vessel 41, which is centrally positioned and not intended to be completely surrounded by the concrete. Instead, the storage vessel 41 is sealed by means of a separate non-permanent or reopenable closure device 41, which is only diagrammatically shown in FIG. 3 because it may be of any suitable conventional design. FIG. 3 also shows a fuel unit B held in a centered position in the storage space defined by the storage vessel 41, resting on a pedestal 43 therein. Another difference is that the cask 40 has no separate cooling arrangement. Because the storage is of a short-term nature, the heat produced by the fuel unit can be absorbed by the concrete body without undue heating of the cask. However, if the cask should require separate cooling means, it may be provided with a number of through axial passages which are disposed in a ring about the storage vessel 41 and extend axially through the cask. Air or water can flow upwardly through the passages by natural convection to carry away heat conducted outwardly from the storage vessel 41. An additional difference is that the outer side of the concrete body 44 is provided with a metal jacket 45 which extends over and past, upwardly and downwardly, the section of the storage vessel 41 that accommodates the nuclear fuel unit B. This jacket, which is suitably made of steel, has a considerable wall thickness, e.g. 10 cm. It adds to the radiation protection afforded by the section of the concrete body 44 it encloses. The diameter of the concrete body 44 can therefore be substantially smaller than in the case where the concrete body alone provides the radiation protection. The reinforcement 46 is essentially identical with the reinforcement 17 in FIG. 1. However, the end covers 47 and 48 are slightly different from those shown in FIG. 1. In this case the rail 27 is positioned on the outer side of the outer plate 47A, 48A in an annular groove the bottom wall of which engages the outer side of the inner end cover plate 47B, 48B. Suitably, the design of the end covers shown in FIG. 3 can also be used for the storage container shown in FIG. 1. It is advantageous in that the reinforcing members 46A, 46B are more easily accessible for tensioning and anchoring tha in the design shown in FIG. 1. The installation or system shown in FIG. 4 for the manufacture of the sealed storage containers 10 with the nuclear fuel contained therein may suitably be located near the site where the storage containers are to be kept during storage, regardless of whether that site is an ultimate storage site or an interim storage site. For example, the storage site may be near a nuclear power plant or at some other place where spent nuclear fuel is stored. In the present case, the nuclear fuel is presumed to be temporarily kept under water in a pool which is dedicated to such short-term storage and from which it is transferred to the system according to the invention. In FIG. 4 this pool is designated by 50 and comprises three individual pool sections. From the pool 50 the nuclear fuel is transferred in shipping or interim storage containers 51 of the kind shown in FIG. 3, for example, to a different pool or pool system 52 having three pool sections 53, 54, 55 which can be selectively placed in communication with one another, suitably through water locks (only diagrammatically indicated at L in FIG. 4). In FIG. 4, the transfer of the containers 51 is symbolised by arrows A which also symbolises the facilities required for the transfer, such as hoisting or conveying machinery and any other necessary load-handling and control equipment etc. Pool section 53, which is dedicated to receiving the interim storage containers 51 coming from the pool 50, is filled with water to a depth which is at least equal to and preferably at least 2-3 m greater than the sum of the height of the transport storage containers 51 and the height of the fuel units held in the containers 51. Thus, when the containers 51 rest on the bottom of the pool section 53, the fuel units B can be lifted from the containers 51 and then shifted horizontally without penetrating the water surface. Preferably, the fuel units should newer come closer to the water surface than 2-3 m. Alternatively, the fuel units can be taken out of the interim storage containers by the side of the pool section and put down into racks or other suitable holders in the pool. In the adjacent pool section 54 the fuel units removed from the transport containers 51 are introduced into the storage vessels 18 mounted in the formwork which has been prepared for the manufacture of the casks 10 and immersed in the body of water held in the pool section 54. The fuel units are taken from the pool section 53 and moved under water to the pool section 54 where they are put down into the storage vessels 18 in the formwork; throughout this operation the fuel units are completely immersed in the water. To this end, the depth of the body of water in the pool section 54 is at least equal to the height of the formwork and the height of the fuel units, and preferably several metres greater. In FIG. 4, the transfer of the fuel units kept in the containers 51 into the storage vessels 18 is symbolised by an arrow B which also symbolises the facilities required for the transfer, such as hoisting or conveying machinery and any other necessary load-handling and control equipment etc. The formwork is assembled in an assembly station 56 by the side of the pool 52 and then lifted and moved to the pool section 54 and placed on the pool bottom. Assembly can be carried out using pre-assembled units which are transported to the assembly station where the formwork is assembled from these units. This is diagrammatically shown in FIG. 4 where the assembly station 56 comprises three sections designated by 57, 58 and 59. In the first section 57 the lower end cover 15 is assembled and the shell 13 and the centre tube 14 are mounted on the lower end cover. The unit 60 so formed is then moved to the section 59 where the group of storage vessels 18 forming the fuel receiver is added to the unit and secured in position therein by means of suitable supporting and anchoring means. This step, which can also be carried out in the section 57, is symbolised by an arrow C which also symbolises the facilities required for carrying out the step, such as hoisting or conveying machinery and any other necessary load-handling and control equipment etc. In section 58 of the assembly station 56 the upper end cover 16 and the reinforcement 17 are joined to form a unit 61 which is then lifted and moved to the section 59 and combined with the unit 60 to form the completed formwork 62. This step is symbolised by an arrow D which also symbolises the facilities required for carrying out the step, such as hoisting or conveying machinery and any other necessary load-handling and control equipment etc. The unit formed by the formwork 62 is then lifted and moved to the pool section 54 and put down on the bottom of that pool section and filled with water. Prior to that, the storage vessels 18 have been filled with the coolant, such as pure water. This step is symbolised by an arrow E which also symbolises the facilities required for carrying out the step, such as hoisting or conveying machinery and any other necessary load-handling and control equipment etc. Now the fuel units are transferred from pool section 53 into the storage vessels 18 in the formwork 62 (arrow B). Naturally, the fuel units then displace some of the pure water in the vessels 18. Because of the pre-filling of the storage vessels with the pure water coolant, contamination of the coolant is avoided. The depth of the water in pool section 54 of course should be great enough to ensure that the fuel units need not come closer to the water surface than 2 to 3 m. Then the storage vessels 18 are sealed, whereupon the formwork 62 is transferred to the pool section 55. The depth of the water body therein in great enough to ensure that the formwork will be completely immersed. Preferably, the depth of the water is such that the top of the formwork is at least 2 to 3 m below the water surface. The transfer of the formwork to the pool section is symbolised by an arrow F which also symbolises the facilities required for carrying out the transfer step, such as hoisting or conveying machinery and any other necessary load-handling and control equipment etc. In the pool section 55 the formwork 62 is filled with concrete taken from a nearby concrete station 63. Preferably, the placement of the concrete in the formwork is carried out by means of one or more so-called tremie tubes, that is, placing tubes used for underwater placement of concrete, which are passed through the openings 34, 35 in the upper end cover 16 down to near the lower end cover 15. As the upper surface of the concrete being fed into the formwork raises, the placing tube or tubes is/are raised such that the lower tube end is constantly slightly below that surface. The concrete may be vibrated during the placement. The concrete placement step described in the preceding paragraph is symbolised by an arrow G which also symbolises the facilities required for carrying out the this step, such as hoisting or conveying machinery and any other necessary load-handling and control equipment, the tremie or placing tubes, etc. When the concrete has set and hardened to some extent, but not reached its ultimate strength, such as after one or two days, the reinforcement 17 is tensioned to some degree, working from the upper end cover 16. The completed cask 10 can then be taken out of the pool section 55. After some additional time, the reinforcement 17 is further tensioned in one or more steps, until it has reached its final pre-tension. This aftertensioning is suitably carried out from both end covers 15, 16. Containment of the reinforcing members in tubular sheaths, which may be filled with a lubricant, ensures transmission of the tensioning force all the way between the end covers. When the tensioning is completed, concrete may be injected into the sheaths and the cavities at the rails 27 in the end covers. After any required monitoring and signalling equipment has been added to the cask 10, the completed cask is transported to a storage site, designated by 64 in FIG. 4. At this site the casks 10 may be stacked, e.g. with three casks in each stack, leaving an open space between the stacks so that air, or water if the storage site is in water, can flow freely between the stacks. The stacks are suitably placed on a support which allows air or water to flow into and upwardly through the shafts formed by the aligned central passages 11 in the casks 10. If desired or required, this shaft may be extended upwardly by means of an extension tube for enhancing the chimney draught or thermosiphon flow that the shaft produces as a result of the heating of the air or water caused by the heat generated by the nuclear fuel in the casks 10 and conducted to the shaft. The removal of the formwork 62 with the concrete body formed therein, the operations carried out on the completed cask 10 after the removal, including the transfer to the storage site 62 as described in the two preceding paragraphs is symbolised by an arrow H. This arrow also symbolises the facilities required for carrying out the this step, such as hoisting or conveying machinery and any other necessary load-handling and control equipment, etc. Adjacent to the pool section 55 a purifying system 65 is provided, through which the water in that pool section is circulated to be purified. The manufacturing system or plant shown in FIGS. 5 to 7 largely embodies the principles of the system shown in FIG. 4 but is somewhat different in respect of the construction of the pool 52, that is, the part of the system in which the fuel units are introduced into the storage vessels mounted in the formwork and concrete is placed in the formwork. Parts in FIGS. 5-7 for which there are corresponding parts in FIG. 4 have the same reference numerals as the parts in FIG. 4. The pool 52 in FIGS. 5-7 differs from the pool in FIG. 4 mainly by being in the shape of a circular, silo-like construction, in which the formwork 62 is moved along an arcuate path. The outermost part of the pool 52 is formed by an outer wall 52A, which is a truss-like circular cylindrical shell construction with an outer shell 52B, an inner shell 52C and a number of walls 52C interconnecting the outer and inner shells. The open spaces between the outer and inner shells may be used as storage rooms for equipment and materials used in the production of casks. Inside the outer wall 52A and concentric with it there is a circular cylindrical inner wall 52F. The space between the outer wall 52A and the inner wall 52F, and also the space inside the inner wall are filled with water. The last-mentioned space forms the pool section 53 where the shipping storage containers 51 and the fuel units B are placed before the fuel units are transferred to the storage vessels 18 in the formwork 62. In the annular space between the outer wall 52A and the inner wall 52F additional pool sections 54A, 54B, 55A, 55B and 55C are provided. Of these pool sections, pool section 54 may be regarded as corresponding to a part of the pool section 54 of FIG. 4, while the pool sections 55A and 55B may be regarded as corresponding respectively to the rest of the pool section 54 and the pool section 55 of FIG. 4. Pool sections 54A and 55C have no direct counterparts in FIG. 4. From the assembly station 56 the assembled formwork 62 with the storage vessels 18 mounted therein are transferred, e.g. lifted over to pool section 53 in which they are placed on a carriage 70 that is movable on a track 71. This track runs along a circular line or path through all pool sections except pool section 55C and may be slightly inclined in the direction of movement of the carriages 70 to facilitate the movement. On the track, which of course may be constructed in any other suitable way, the formwork 62 may be moved from pool section 554 to the following pool sections 54A, 55A, 55B and 55C. In order that this movement may take place without intermixing the water contained in the various sections too much, the delimitations between pool sections 54A/54B, 54B/55A and 55A/55C are formed by water locks represented by the radial walls shown in the figures. Alternatively, the formwork 62 may be moved within and between the pool section by means of hoisting machinery. Pool 55C is used in a manner described below to hold casks 10 to be opened for removal of the stored nuclear fuel. The manufacture of the casks 10 and the containment of the nuclear fuel in them are carried out in substantially the same way as in the system shown in FIG. 4. The formwork 62 assembled in the assembly station 56 and the storage vessels mounted in the formwork to serve as a fuel receiver are lifted over to pool section 54A using suitable hoisting machinery. In the illustrated embodiment, pool section 54A can hold formwork 62 for two casks at a time, but it may also be dimensioned and designed to hold formwork for either a single cask or more than two casks. When the formwork 62 for a cask 10 is to be charged with fuel units B from pool section 53, that formwork in the pool section 54A which is closest to the next pool section 54B is moved over to that pool section through the intervening water lock. The fuel units B are moved from the central pool section 53 to the storage vessels 18 in the formwork 62 moved over to pool section 62, and the storage vessels 18 are then sealed in the manner described above. The thus charged formwork 62 is then moved from pool section 54B to pool section 55A through the intervening water lock. In pool section 55A the casting of the concrete body of the cask is carried out in the manner described with reference to FIG. 4. Pool section 55A can hold formwork 62 for two casks at a time, but it may also be made to hold formwork for a single cask or formwork for more than two casks. If it is made to hold formwork for two or more casks, is may also serve as a buffer space, so that formwork for a cask that has already been cast can be left in pool section 55A until space is free in pool section 55B without the placement of concrete in the formwork for the next cask is obstructed. After placement of the concrete, which is supplied from a concrete station corresponding to that shown in FIG. 4, the formwork 62 with the placed concrete therein is moved to pool section 55B where the concrete is allowed to set and harden and supplemental work on the now more or less completed cask 10 may be carried out, such as initial tensioning and/or aftertensioning of the reinforcement members. When the concrete in the cask 10 has hardened sufficiently, the cask is lifted from pool section 55B to be moved to a storage site corresponding to the storage site 64 shown in FIG. 4, if required after additional supplemental work on the casks has been carried out by the side of the pool 52. Pool section 55C is used if for some reason a cask 10 containing nuclear fuel needs to be reopened for removal or inspection of the nuclear fuel. This may be necessary if the fuel is to be reprocessed or otherwise has to be removed from the cask. In such case the cask 10 is immersed in pool section 55C and opened. If the cask is made in accordance with FIGS. 1 to 3, the opening is carried out by working off the concrete above the storage vessels, so that the stored fuel units can be lifted and transferred to the central pool section 53 and placed in shipping casks 51 without having in any phase of the process to be raised to the water surface in the pool section or even come close to it. In a modification of the method according to the invention the formwork 62 is not provided with storage vessels corresponding to the storage vessels 18 shown in FIG. 1 before the formwork is placed in pool section 54. Instead, storage vessels in the form of special fuel containers are used, in which the nuclear fuel is loaded while the fuel containers are in a separate pool or pool section or in pool section 53. In this modification, the part which corresponds to the formwork 62 is prepared so that it can receive the fuel containers after it has been placed in the pool section 54. For example, that part of the formwork which corresponds to the formwork unit 60 may be provided with suitable guides and supports enabling positioning of the fuel containers correctly in the formwork prior to the placement of the concrete. That part of the formwork which corresponds to the formwork unit 60 may first be placed in pool section 54, in which the fuel containers are the positioned in that part, whereupon the part corresponding to the formwork unit 61 is mounted. It is to be understood that the illustrated and described systems and facilities for the production of casks are only examples of the implementation of the invention and that the practical details may be varied widely within the scope of the invention. For ease of illustration and explanation of the invention, the hoisting and other material handling facilities needed for the manipulation and transfer of components and materials are omitted or illustrated only symbolically, e.g. by arrows. The construction of such facilities and their mode of operation form no part of this invention and may be entirely conventional.
050646036	summary	BACKGROUND OF THE INVENTION This invention relates to a nuclear reactor sensing system; and more particularly to a hydroball string sensing system that determines the location and velocity of a hydroball string. To control the operation of a nuclear reactor the neurron flux within the reactor core region is monitored. To monitor this neutron flux, numerous tubes are positioned within the core. These tubes house strings called hydroball strings that include stainless steel beads on a flexible stainless steel cable. Each of the stainless beads includes a material such as manganese that absorbs neutrons while the stainless steel bead is in the core region. After the strings have been in the core for several minutes, the strings are removed from the core region and the decay time of the activated manganese in each bead is measured. This measurement indicates the neutron flux to which each bead was subjected while within the reactor core region. The hydroball strings are moved into and out of the reactor core region by pumping water through the tubes in the direction of desired hydroball string movement. With this technique for approximating the neutron flux in a reactor core region, it is critical: (1) to know how long the hydroball string spends in the reactor core region, (2) to know how much time elapses between the string leaving the core region and the start of measuring the radiation emitted from each hydroball, and (3) to confirm the location of the hydroball string at various times as it is moved into and out of the reactor core region. Because the hydroball string is housed within a thick walled stainless steel tube that contains reactor core fluid at the same pressure as within the reactor core, it is difficult to achieve these critical objectives. SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydroball string sensing system which can accurately determine the time spent by a hydroball string within a reactor core region. It is another object of the present invention to provide a hydroball string sensing system capable of operating on tubes which are maintained at 600.degree. F. or above. It is a further object invention to provide a hydroball string sensing system which can accurately locate a hydroball string. It is still another object of the present invention to provide a hydroball string sensing system that can accurately determine the amount of time that the radiation from a particular hydroball is sensed. It is still a further object of the present invention to provide a hydroball string sensing system capable of detecting and controlling the velocity of a hydroball string within a tube. To achieve the above and other objects, the present invention provides a hydroball string sensing system for a nuclear reactor having a core containing a fluid at a fluid pressure, the system comprises: a tube connectable to the nuclear reactor core so that the fluid can flow within the tube at a fluid pressure that is substantially the same as the fluid pressure of the nuclear reactor core; a hydroball string including a string member having objects positioned thereon with a specified spacing, the objects include a plurality of hydroballs and bullet members positioned at opposing ends of the string member; and a first sensor means positioned outside of a first segment of the tube, for sensing one of the objects being positioned within the first segment, and for providing a sensing signal responsive to the sensing of the first sensing means. The present invention also provides a hydroball string sensing system for a nuclear reactor having a core containing a fluid at a fluid pressure, the system comprises: a tube connectable to the nuclear reactor so that the fluid can flow within the tube at a fluid pressure that is substantially the same as the fluid pressure of the nuclear reactor core; a hydroball string including--a string member having objects positioned therealong with a specified spacing, the objects including a plurality of hydroballs, and bullet members positioned at opposing ends of the string member; first ultrasonic transducer sensor means, positioned outside a first segment of the tube, for sensing one of the objects being positioned within the first segment, and for providing a sensing signal responsive to the sensing of the first sensor means; second ultrasonic transducer sensor means, positioned outside a second segment of the tube being spaced a given distance along the tube from the first segment, for sensing one of the objects being positioned within the second segment, and for providing a sensing signal responsive to the sensing of said second sensor means; timing means for determining an amount of time between the first sensor means sensing the one of the objects within the first segment and the first sensor means sensing another one of the objects within the first segment; means for determining a velocity of the objects based upon the specified spacing and the determined amount of time; means for adjusting the rate of the fluid flow so as to make the determined velocity substantially equal to a desired velocity; and detector means, positioned outside of the tube and between the first and second segments for counting gamma rays emitted from one of the objects while the object is between the first and second sensor means.
053316762	abstract	Nuclear fuel rod tubes of zirconium alloy are heat treated in an induction furnace to produce a protective oxide coating two to fifteen microns in thickness. The furnace is only slightly larger than the tubes and receives the endmost eight inches of the tube. The furnace is controllable in zones along the tube. To calibrate the furnace to produce the desired temperature profile, typically a flat profile at a temperature between 650.degree. and 750.degree. C..+-.1.5.degree. C., a temperature calibration probe is provided with spaced thermocouples for sensing the temperature developed in the probe at each of the zones when heated. The probe is made of inconel 600 stainless or the like, and is dimensioned and shaped to correspond closely to the dimensions of the fuel rod tubes, including having a closed chamfered end. At the opposite end the probe protrudes from the furnace, where the thermocouple leads are terminated. The leads pass through a potting compound in the probe, such as magnesium oxide. Whereas the probe conductive structures are substantially identical to the tube, the probe responds to the electromagnetic field in the induction furnace substantially the same as does the end of the tube, permitting calibration of the induction furnace zones for a desired temperature profile, e.g., flat along the length of the tube, notwithstanding differences in induced currents that would otherwise occur due to the end of the tube or the adjacent tube material.
	description	The present invention relates to handling of nuclear fuel assemblies. More specifically, the present invention provides a fuel assembly and a lifting support for a fuel assembly to aid in the lifting of a boiling water reactor nuclear fuel assembly. Lifting of heavy objects, such as fuel assemblies, is a necessary activity performed for safe and continuous operation of nuclear power plants. Lifting of such nuclear fuel assemblies is often strictly regulated with varying precautions being undertaken prior to actual load lift. Typical precautions include, for example, ascertaining the weight of the assembly, determination of a path that the assembly will take during the lift, identification of critical and/or safety sensitive nuclear related components which may be jeopardized during the lift, and evaluation of potential damage in the event of a load drop. Fuel assemblies provided for boiling water nuclear reactors are composed of a plurality of fuel rods which are supported at a lower end by a lower nozzle or end fitting. A top nozzle or end fitting is located above the plurality of rods. Water rods are interspersed in the plurality of fuel rods to help channel coolant flow and moderate the nuclear reaction. Between the upper and lower nozzles or end fittings, a plurality of spacer grids are positioned at intervals to provide lateral support and prevent potentially destructive side to side movement of individual fuel rods. The fuel assembly top nozzle and bottom nozzle may be configured to aid in channeling coolant flow through the assembly during operation, the bottom nozzle accepting coolant flow and the top nozzle discharging coolant from the assembly in the case of a conventional boiling water reactor fuel assembly. In this typical configuration, the weight of the fuel rods is supported by structures such as an internal water channel, the water rods, inert rods or tie rods during fuel assembly load lift. Certain areas in a nuclear power plant are more safety sensitive and require extremely thorough procedures to ensure continued health and safety of the public at large. Such safety sensitive areas include, among other areas, the nuclear reactor itself and the fuel pool. The presence of potentially large amounts of radioactive materials in these areas, as well as vital cooling systems, requires the utmost care when lifting is performed. The resulting required safety in these areas necessitates additional checks before load lift. A typical check usually involves, for example, inspecting the structural components of the polar crane or a fuel handling crane. In addition to inspecting the crane, the actual load lifted (i.e. the fuel assembly itself) is inspected and evaluated. Nuclear plant operating experience indicates that when typical materials used in nuclear reactors are exposed to radiation over 62 Mwd/kgU, these materials may start to degrade. Specific experience shows a potential for stress corrosion cracking, hydrogen embrittlement and irradiation hardening which may challenge the structural integrity of both tie rods and water rods as well as other components used in lifting a fuel assembly with current designs. Currently, structural members used for a load lift of boiling water reactor fuel assemblies may be composed of a zirconium alloy with a thickness of less than 0.03 inches. Although weight reduction is achieved, the minimal corrosion allowance provided for these members from corrosion is a serious potential problem during load lift. As a typical potential problem, water rods, which may also be used to carry the fuel assembly load, are normally exposed to coolant on both inner and outer surfaces, which in turn increases the possibility of corrosion on these surfaces. Additionally, as a result of this exposure, hydrogen embrittlement of the water rod may occur. The water rod hydrogen concentration may approach 500 to 700 ppm, thereby requiring a reduction in load carrying capability for the assembly components. If these problems occur, current practices in the nuclear industry require costly and time consuming alterations to fuel assemblies which are exposed to radiation at or near this level of radiation, which are mechanically damaged, or for fuel assemblies which may have hydrogen embrittlement. To correct these problems, complete disassembly of the fuel assembly and reconstitution of the fuel assembly may be needed with new parts installed in the fuel assembly. New (unirradiated) fuel assemblies also present other load lift difficulties. New fuel assemblies must be lifted by a special lifting device to allow for sufficient structural lift capacity over critical plant/safety sensitive areas. These special lift devices often provide complicated structures which may include connecting bolts, bayonet mounts, compression springs and washers to transfer the weight of the assembly from the fuel assembly to the crane. There is a need to provide a lifting support for a boiling water nuclear fuel assembly to eliminate complicated structural support mechanisms currently used in existing nuclear fuel assembly configurations. There is a further need to provide a lifting support for a fuel assembly for new (unirradiated) fuel handling operations. There is a still further need to provide a configuration that will allow repair of fuel assemblies which exhibit stress corrosion cracking problems, hydrogen embrittlement, irradiation hardening or other similar load path defects without incurring costly and time consuming alterations to the fuel assembly. It is an object of the present invention to provide a lifting support for a boiling water nuclear fuel assembly to eliminate current complicated structural support mechanisms. It is a further object of the present invention to provide a lifting support for a fuel assembly for initial (new) fuel handling operations. It is a further object of the present invention to provide a repair to fuel assemblies which exhibit stress corrosion cracking problems, hydrogen embrittlement, irradiation hardening or other similar load path defects without incurring costly and time consuming alterations. The invention comprises a lifting support for a boiling water reactor nuclear fuel assembly comprising a grappling head configured to allow attachment of a lifting device, a body with an upper end and a lower end, the upper end connected to the grappling head, the body configured to be inserted into a water channel of a boiling water reactor nuclear fuel assembly, and an end connected to the lower end, the end configured to be accepted by the water channel of the nuclear fuel assembly. The invention also provides a fuel assembly. The fuel assembly for a boiling water reactor comprises a fuel channel configured to define a volume, the channel having a lower end and an upper end, the lower and the upper ends open, a plurality of rods with a lower end and an upper end placed within the volume, the plurality of rods containing fissile material to produce a nuclear reaction, a lower tie plate configured to support the plurality of rods, the lower tie plate configured to join with the fuel channel lower end to allow flow of coolant from the lower tie plate through the channel and the plurality of rods, a removable upper tie plate configured to be attached to the fuel channel, a water channel placed within the volume and connected to the lower tie plate, the water channel configured to channel coolant flow from the lower tie plate, the water channel further configured with an attachment end, a removable reinforcement configured with a grappling head to allow attachment to a lifting device, a body with an upper end and a lower end, the upper end connected to the grappling head, the body configured to be inserted into the water channel of the boiling water reactor nuclear fuel assembly, and an end connected to the lower end, the end configured to be accepted by the water channel attachment end, a plurality of spacers positioned between the lower tie plate and the removable upper tie plate, the plurality of spacers configured to maintain individual fuel rod positions of the plurality of rods, and a lower nozzle, the lower nozzle configured to channel fluid to the lower tie plate and the water channel, the nozzle connected to the fuel channel. Referring to FIG. 1, a lifting support 10 is illustrated. The lifting support 10 allows a fuel assembly 36 to be lifted by a lifting device such that the fuel assembly 36 is transported in one piece. The lifting support 10 may be configured from metal or other material such that the lifting support 10 has sufficient load carrying capacity for expected service. Typical service may include a capacity to lift ten times the load of the attached fuel assembly 36, as an example. Other capacities, either higher or lower, may be used. Typical materials which may be used include stainless steel or other non-corroding material. Types 304 and 18-8 stainless steel may be used as an example. Design loadings for the lifting support 10 may include dead weight of the fuel assembly, dead weight of the lifting support 10, impact loading, anticipated seismic loadings for vertical and horizontal planes, impulse loading and other loading. The lifting support 10 may also be configured to perform lifting capabilities over an extended period of time, therefore deformation from creep and cyclical loading may also be considered. The lifting support 10 is configured with a grappling head 12. The grappling head 12 is configured with an inner open diameter 14 to allow attachment of a hook, slings or other lifting device thereby allowing lifting of the fuel assembly 36. The inner open diameter 14 may be configured of any size, such that it is sufficient for attachment of the lifting device. Typical sizes may include 12 inches, but the size may be varied according to the application needs. The grappling head 12 may be configured such that anticipated sheer, tension and bending forces may be transferred through the head 12 without significant deformation or structural weakening. The grappling head 12 may also have any desired configuration, including circular, square or other geometric shape to allow necessary access by the lifting device. A body 16 is attached to the grappling head 12 at an upper end 122. The body 16 may be configured of the same material as the grappling head 12 or may be a different material. If a differing material is used, then a connection between the body 16 and the head 12 shall allow load transfer between the body 16 and the head 12. The body 16 may be configured in a cylinder (rod) shape out of stock material or may be configured with all-thread stock or similar material. As with the grappling head 12, the body 16 may be configured for all anticipated design loads from the fuel assembly 36 such that proper load transfer is accomplished as well as to fit into a water channel 18. A water channel 18 positioned in the interior of a fuel assembly 36 allows water entering the lower nozzle 38 to be channeled up through the fuel assembly 36 thereby cooling the fuel rods 28. The water channel 18 is configured with an attachment end 104 which is configured to allow connection of the lifting support 10. The water channel 18 may be configured with an upper end 40 with differing configurations to allow differing flow conditions for the fuel assembly 36. The fuel rods 28, as illustrated in the current example, may be full length fuel rods, however other configurations may be used, wherein part length fuel rods, or mixtures of part length fuel rods and full length fuel rods are possible. The fuel rods 28 provide a fissile material, typically in the form of pellets, to allow a nuclear chain reaction. The fuel rods 28 have a cladding around the fissile material to protect the fissile material from coolant flow and mechanical damage. Typical cladding materials may include zirconium alloys, thereby providing sufficient corrosion protection while providing a relatively small neutron capture cross-section. The fuel rods 28 are supported by the lower tie plate 26 to provide a desired spacing between individual rods 28. The water channel 18 is configured with a bottom end 20, which in the example embodiment illustrated, rests on a lower nozzle 38, however, other configurations are possible. The water channel 18 may be constructed such that an attachment between the channel 18 and the nozzle 38 may be through a screw fitting or other mechanism. The water channel 18 may be configured with an opening 42 which is adapted to receive the body 16 of the lifting support 10. The channel 18 may also be threaded at several positions for instance when all-thread material is used for the body 16. If the water channel 18 is configured with an opening 42 which is of lesser diameter than the outside diameter 34 of the body 16, the opening 42 may be widened to a diameter such that the outside diameter 34 allows engagement. A lower nozzle 38 allows coolant to be accepted into the fuel assembly 36 and transported to the water channel 18 and the lower tie plate 26. Spacer grids 30 are positioned between the upper tie plate and the lower tie plate 26. The spacer grids 30 are configured to maintain relative positions of individual fuel rods 28 within the volume defined by the fuel channel 32. The spacer grids 30 may be provided with vanes to provide a mixing of coolant circulating within the fuel assembly 36. The spacer grids 30 may be positioned to maximize critical power within the fuel assembly and to provide sufficient safety margin with respect to departure from nucleate boiling. An end 22 is attached to a lower end 120 of the body 16. The end 22 may be configured with threads 24 so that the end 22 may be accepted and/or attached to the water channel 18 which may have a corresponding matching thread surface. The number of threads used on the end 22 and the channel 18 may be varied such that either a coarser or finer screw engagement is established. The material used to engage the surface of the end 22 may be chosen such that it provides a relatively softer contact surface, thereby protecting the fuel assembly 36 from damage during installation and removal of the lifting support 10. Engagement of the end 22 to the channel 18 may be by rotating the lifting hook or device such that a desired engagement is established. In an alternative exemplary embodiment, the body 16 of the lifting support 10 may be configured with an actuator 50. The actuator 50 may be a spring-loaded push button actuator or a remotely controlled actuator. In this embodiment, the body 16 of the lifting support 10 is configured to define an interior volume such that it is hollow with an inner rod 48 which has a first end 108 and a second end 110. The inner rod 48 connects the actuator 50 to a ball-lock end 46. Upon actuation, the actuator 50 moves the inner rod 48, thereby causing the ball lock end 46 to project from the extension 44 of the lifting support 10. The extension 44 may be configured such that it extends a sufficient amount to allow the ball-lock end 46 to be actuated. The ball lock end 46 may be configured to provide a load lifting capacity appropriate for necessary design considerations, such as dead weight, and seismic loading for the fuel assembly 36 through connection to the lower tie plate or water channel for examples, through a sheer connection as a further example. The inner rod 48 may also be configured to support the entire weight of the fuel assembly 36, thereby allowing full load transfer from the ball-lock end 46 through the inner rod 48 to the grappling head 12. In any embodiment, a spacer 130 may be attached to the body 16 of the lifting support 10 to limit unintended contact between the fuel assembly 36 and the lifting support 10. The spacer 130 may be configured from a material that is softer than materials of the fuel assembly thereby preventing marring of fuel assembly surfaces. As an example, the spacer 130 may be manufactured from a plastic suitable for high temperature and anticipated radiation dose levels. The spacer 130 may be removable from the body 16. FIG. 1A illustrates the inner rod 48, the actuator 50, including the connection to the actuator 50, the ball lock end 46 and the connection of the ball lock end 46 to the inner rod 48. Referring to FIG. 2, an upper end of the fuel assembly 36 is illustrated. A bolt 52 is inserted into a slot A 54 through to a slot B 58 in the fuel channel of the fuel assembly 36. The bolt 52 is inserted into slot A 54 and slot B 58 in such a way that the bolt 52 is positioned through a removable upper tie plate 70 not shown in FIG. 1 for clarity. The bolt 52 may be sized such that the external diameter of the bolt 52 fits into an interior diameter of slot A 54 and slot B 58 of fuel channel 32 and through upper tie plate 70. The bolt 52 has an attached bolt head 64 which is configured such that placement of the bolt 52 into slot A 54 will be stopped by impact of the bolt head 64 on the fuel channel 32 of the fuel assembly 36. The bolt 52 may be manufactured of any material, including non-corrosive metals, to allow proper load transfer and sheer capacity for expected service ranges. The bolt 52 consequently may be manufactured from stainless steel type 304 or other appropriate material. The bolt 52 is configured with a hole 124 with a machined surface, such as screw threads. A screw 60 with matching screw threads to the bolt 52 mechanical surface maybe inserted through a top plate 62 into the bolt 52 to establish a connection between the bolt 52 and the screw 60. The screw 60 may be configured with match markings to allow easy identification of bolt size and material type, as well as relative positioning with respect to the bolt 52. Both the bolt 52 and the screw 60 may additionally be manufactured with an additional hole to allow connection of a retaining arrangement to allow retention of the bolt 52 or screw 60 such that the bolt 52 or screw 60 do not become dislodged and potentially lost in the reactor or fuel pool thereby eliminating foreign material exclusion concerns. As an alternative, the screw 60 may be manufactured such that is will not become dislodged from the top plate 62, thereby reducing foreign material exclusion concerns. The top plate 62 is attached to the fuel assembly 36 through the fuel channel 32. The fuel channel 32 may be configured of metal or other appropriate material to limit bending of the fuel rods of the fuel assembly 94. The fuel channel 32 defines a volume for the fuel rods and allows the fuel assembly 94 to be handled without damage occurring to the fuel rods. Although illustrated as a relatively thin box like member, other configurations to provide structural rigidity are possible. In a typical installation, the fuel channel 32 wall thickness is three to four times the thickness of either the tie rods or water rod wall thickness. The overall fuel channel size 32 also results in a much larger overall cross-sectional area as compared to tie rod configurations. The larger overall cross-sectional area thereby results in a decreased overall stress during load lifts. The fuel channel 32 is configured with an open top and bottom, wherein the top allows insertion and removable of the removable upper tie plate 70 and the bottom is configured to join to the lower nozzle 38. A member 66 may be attached to the fuel channel 32 by an attachment 68. The member 66 allows transfer of load from the fuel assembly 36 through the fuel channel 32 to a lifting device. The attachment 68 is therefore configured with sufficient sheer, tension and bending capacity to allow load transfer. The attachment 68 may be configured as a welded attachment or bolted attachment as an example. The member 66 may be configured with a safety factor of 10 to 1 of load lifted to ultimate capacity or other appropriate load capacity according to the load to be lifted. The top plate 62 is connected to the fuel channel 32 through a connection type such as welding or bolting. The screw 60 may be configured such that the screw threads match the corresponding hole 124 in the bolt 52 allowing for completion of the connection. Although illustrated as a hexagonal head screw 60, other configurations are possible and that the embodiment illustrated is merely exemplary. In FIG. 3, a side cross-sectional view of FIG. 2 is illustrated. The screw 60 attaches to the bolt 52 through hole 124 thereby providing a connection between the fuel channel 32 and the fuel assembly 36. A structure 96 is provided around the placement of the screw 60 to allow load transferred from the bolt 52 to be transferred to the channel 32 with minimal bending. The structure 96 may be increased or decreased in size according to the amount of load transferred along the bolt 52, the desired resistance to deflection, and sheer forces expected. The screw 60 and the bolt 52 may have markings located on their respective heads to allow identification of material type, length, relative positioning, thread length, and numbers of threads per unit length. In FIGS. 4, 5 and 6, a second embodiment of a connection between a alternate fuel channel 72 and a removable upper tie plate 98 of a fuel assembly 36 is illustrated. FIG. 4 illustrates a top end of a fuel channel 72. The top end of the fuel channel 72 is configured with a slot A 74, a slot B 78 and a slot C 76. The purpose of the slots 74, 76 and 78 is to allow attachment of the removable upper tie plate 98 (illustrated in FIG. 5) to the fuel channel 72. As illustrated in FIG. 5, the removable upper tie plate 98 has two lugs 80, 82 that engage slot A 74 and slot B 78 of the fuel channel 72. Slot C 76 is engaged by a third lug C 90. Installation of the removable upper tie plate 98 is accomplished by tilting the tie plate 98 grid and sliding lugs A and B 80,82 into corresponding slots A and B 74, 78 of the fuel channel 72. The corner at lug C is then lowered until the underside of the screw 84 rests on a wedged block 100 illustrated in FIG. 6. The tie plate 98 is then locked by tightening the screw 84. When tightened, the wedged block 100 is drawn upwards and into slot C 76, thereby locking the removable upper tie plate 98. Load transfer from the screw 84 to the fuel channel 72 occurs through a top plate 86 which connects the lugs 80, 82, 90 to the channel 72. The lugs 80, 82 and 90 may be configured such that shear, tension and bending loads from the assembly are transferred along the lugs 80, 82, 90 without significant structural deterioration. A bail 88 is attached to lugs 80, 82 to provide an attachment point for a lifting device. The bail 88 may be configured with a sufficient opening to allow a hook, sling or other device to be attached, allowing load lift. Although described as a screw 84, other configurations are possible such as a bolt and the exemplary embodiment illustrated should not be considered limiting. The screw 84 may be configured with identification markings on the head to allow determination of material type, thread length, number of threads per inch, and relative positioning. The present invention provides many improvements over prior configurations. The present invention allows elimination of the connecting bolt, bayonet bolt, compression spring, washer and locking device used in other configurations. The present invention provides a less complex design while providing heavy load lift functionality. The present invention may be configured to provide lifting capability for fuel assemblies from differing manufacturers. The present invention uses fewer overall quantity of materials, thereby decreasing eventual final storage and disposal of radioactive material. The present invention is configured to permit easy installation and removal of the lifting support in both a manufacturing facility and a “field” location at a nuclear reactor site. The body of the lifting support may be sized to fit into existing water channels limiting expensive alterations to current fuel assembly designs. The present invention also provides superiority over other configurations as the simple, easily understood configuration allows manipulation by mechanics skilled in the nuclear maintenance field. Less overall mechanical parts decreases the possibility of inadvertent error in design and maintenance activities. In the case of a repair to a used boiling water reactor nuclear fuel assembly, the current invention also allows workers to repair the assembly underwater or from a shielded environment, thereby protecting workers from radiation exposure. Repairs employing the lifting support, due to their simple construction, involve a shorter repair period also protecting workers from inadvertent radiation exposure. Operationally, a fuel assembly with attached lifting support is delivered to a nuclear reactor refueling floor or other refueling area. In this example embodiment, the fuel assembly is delivered in a shipping crate to protect the assembly during transit. The shipping crate is positioned such that the fuel assembly stands on end, head up, similar to the configuration of the typical assembly installed in a nuclear reactor. The shipping crate is opened and a crane, such as an overhead polar crane, is connected to the grappling head of the lifting support. The fuel assembly is then lifted and placed in a fuel assembly stand, where it may be inspected prior to incorporation into the reactor according to the operating procedures of the reactor. After inspection, a fuel channel is then lifted over the top of the fuel assembly and slid into position around the periphery of the entire fuel assembly, thereby providing additional structural support for the fuel assembly. The lifting support is then unscrewed from the attachment point to the water channel while being supported by the crane. Next, the removable upper tie plate is positioned at the top of the fuel rods at the top end of the assembly. An upper bolt then passes through slot (A) and through horizontal hole(s) in the tie plate cast member(s) and protrudes through slot (B) of the fuel channel. A channel fastener screw is then installed such that it engages the upper bolt, thereby completing the structural attachment of the fuel channel to the upper tie plate. The fuel assembly may then be incorporated into the nuclear reactor through the polar crane or other lifting device. In the foregoing specification, the invention has been described with reference to specific exemplary embodiments, thereof. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.
	description	The following relates to the nuclear reactor arts, nuclear power generation arts, nuclear safety arts, and related arts. A conventional pressurized water reactor (PWR) includes a cylindrical pressure vessel containing a nuclear reactor core comprising a fissile material. The reactor core is located near the bottom of the pressure vessel, which is filled with primary coolant water. During operation, the reactor core heats the primary coolant water and the heated water tends to rise. A cylindrical central riser located above the reactor core and coaxially inside the pressure vessel conveys the rising heated water to near the top of the pressure vessel where the heated water discharges and flows back down through a “downcomer” annulus defined between the central riser and the inside wall of the cylindrical pressure vessel to complete the primary coolant flow circuit. This primary coolant circulation can occur naturally (i.e., natural circulation) driven by the heat generated by the reactor core. Additionally or alternatively, a set of reactor coolant pumps can be provided to assist or drive the primary coolant circulation. In a conventional PWR the primary coolant is piped out of the pressure vessel and into an external steam generator. This steam generator is a heat exchanger in which the piped primary coolant serves as the heat source for heating secondary coolant water flowing through a secondary coolant flow path within the steam generator. Typically, two or more external steam generators are operated in parallel, so as to provide a level of redundancy. An integral PWR is a design variant in which the steam generator is located inside the pressure vessel. Typically, the steam generator is annular (or a set of steam generators form an annular assembly) that is disposed in the downcomer annulus. The primary coolant flowing downward through the downcomer annulus serves as the heat source, and secondary coolant is flowed into the pressure vessel and upward through the steam generator to remove the thermal energy. The steam generator typically has a tube-and-shell configuration in which an assembly of tubes is surrounded by a shell. In some such configurations, the primary coolant flows downward through the tubes (i.e., tube-side) and the secondary coolant flows upward through the shell (i.e., shell-side). Alternatively, the downward primary coolant flow may be shell-side while the upward secondary coolant flow may be tube-side. The tubes may have various geometries, such as straight vertical tubes, or helical tubes winding around the central riser, or so forth. Integral PWR designs employing helical steam generator tubes are described in Thome et al., “Integral Helical-Coil Pressurized Water Nuclear Reactor”, U.S. Pub. No. 2010/0316181 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. In some integral PWR designs, the steam generator outputs dry single-phase steam directly suitable to drive a turbine or other steam-driven machinery. Alternatively, if the steam generator outputs wet steam or a steam-water mix, then it can be dried in an external steam drum. See, e.g. Shulyak, “Westinghouse Small Modular Reactor Development Overview”, presented at the Interregional Workshop on Advanced Nuclear Reactor Technology for Near Term Deployment, International Atomic Energy Agency (IAEA), Vienna, Austria, Jul. 4-8, 2011. In one aspect of the disclosure, a pressurized water reactor (PWR) includes: a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum interposed between the upper plenum and the lower plenum and containing secondary coolant; a nuclear reactor core comprising fissile material disposed in the lower plenum; one or more risers arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum; and a plurality of tubes passing through the steam generator plenum and arranged to convey primary coolant downward from the upper plenum to the lower plenum. A steam separator is operatively connected with the steam generator plenum to separate secondary coolant in the steam phase from secondary coolant in the water phase. In another aspect of the disclosure, a pressurized water reactor (PWR) includes: a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum interposed between the upper plenum and the lower plenum and containing secondary coolant; a nuclear reactor core comprising fissile material disposed in the lower plenum; one or more risers arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum; and a plurality of tubes passing through the steam generator plenum and arranged to convey primary coolant downward from the upper plenum to the lower plenum. A steam separator is operatively connected with the steam generator plenum to separate secondary coolant in the steam phase from secondary coolant in the water phase. There is there is no pump configured to actively circulate secondary coolant between the steam generator plenum and the steam separator. In another aspect of the disclosure, a pressurized water reactor (PWR) includes: a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum interposed between the upper plenum and the lower plenum and containing secondary coolant; a nuclear reactor core comprising fissile material disposed in the lower plenum; one or more risers arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum; and a plurality of tubes passing through the steam generator plenum and arranged to convey primary coolant downward from the upper plenum to the lower plenum. A steam separator is operatively connected with the steam generator plenum to separate secondary coolant in the steam phase from secondary coolant in the water phase. The steam generator plenum does not include or contain piping arranged to convey secondary coolant along a defined flow path. For example, the steam generator plenum does not include or contain a shell-and-tube steam generator in which one of primary coolant and secondary coolant flows in a one direction in tubes of the shell-and-tube steam generator and the other of primary coolant and secondary coolant flows in an opposite direction in the shell of the shell-and-tube steam generator. In another aspect of the disclosure, a pressurized water reactor (PWR) includes: a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum interposed between the upper plenum and the lower plenum and containing secondary coolant; a nuclear reactor core comprising fissile material disposed in the lower plenum; a plurality of riser tubes passing through an inboard cylindrical region of the steam generator plenum and arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum; and a plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum wherein the tubes pass through an outboard annular region of the steam generator plenum that surrounds the inboard cylindrical region of the steam generator plenum. A steam separator is operatively connected with the steam generator plenum to separate secondary coolant in the steam phase from secondary coolant in the water phase. With reference to FIG. 1, an illustrative nuclear reactor of the pressurized water reactor (PWR) type 10 includes a pressure vessel 12, which in the illustrative embodiment is a cylindrical vertically mounted vessel. (Note that the term “cylindrical” as used herein does not require a mathematically precise cylinder, but rather allows for deviations such as changes in diameter along the length of the cylinder axis, inclusion of vessel penetrations or other localized features, or so forth). A nuclear reactor core 14 is disposed in a lower portion of the pressure vessel 12. The reactor core 14 includes a mass of fissile material, such as a material containing uranium oxide (UO2) that is enriched in the fissile 235U isotope, in a suitable matrix material. In a typical configuration, the fissile material is arranged as “fuel rods” arranged in a core basket. The pressure vessel 12 contains primary coolant water (typically light water, that is, H2O, although heavy water, that is, D2O, is also contemplated) in a subcooled state. A hollow cylindrical central riser 16 is disposed concentrically within the cylindrical pressure vessel 12 to funnel primary coolant heated by the radioactive reactor core 14 generally upward. The illustrative PWR 10 includes an internal pressurizer volume 20 defined by a top portion of the pressure vessel 12 and a baffle plate 22. The baffle plate 22 provides a restricted fluid communication between the pressurizer volume 20 above the baffle plate 22 and the remainder of the volume of the pressure vessel 12 disposed below the baffle plate 22. In a suitable embodiment, the baffle plate 22 is a steel plate spanning the diameter of the pressure vessel 12, and the restricted fluid communication is provided by constricted passages such as a surge line 24 and vent pipes 26. During normal operation of the PWR 10, the pressurizer volume 20 contains a steam bubble filling some but not all of the volume 20, and the pressure of this steam bubble is adjusted by pressure control devices (not shown) such as heaters (to heat the bubble so as to increase pressure) and spargers (to inject cooler steam or water into the bubble so as to reduce pressure). The controlled pressure of the steam bubble transfers to the lower (operational) volume of the pressure vessel 12 below the baffle plate 22 via the passages 24, 26. Instead of an integral pressurize as illustrated, it is contemplated to employ a separate external pressurizer that is connected with the pressure vessel 12 via suitable piping. The PWR 10 includes other components known in the art that are not shown, such as a “basket” or other structure supporting the reactor core 14 in the pressure vessel 12, neutron-absorbing control rods selectively inserted into the reactor core 14 by a control rod drive mechanism (CRDM) to control the nuclear chain reaction, various thermal and/or radiative shielding, or so forth. These various components may be variously disposed inside or outside the pressure vessel. For example, the CRDM may be external, as is conventionally the case, or may be located internally inside the pressure vessel as described in Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, U.S. Pub. No. 2010/0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety; and Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, Intl Pub. WO 2010/144563 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. The pressure vessel 12 is divided into an upper plenum 30 containing primary coolant and a lower plenum 32 containing primary coolant and the nuclear reactor core 14. The upper plenum 30 is located below the baffle plate 22 such that the baffle plate 22 delineates the boundary between the pressurizer volume 20 and the upper plenum 30. The hollow cylindrical central riser 16 is arranged to convey primary coolant upward from the nuclear reactor core 14 in the lower plenum 32 to the upper plenum 30. Additionally, a steam generator plenum 34 is interposed between the upper plenum 30 and the lower plenum 32. In the embodiment of FIG. 1 the steam generator plenum 34 is a steam generator annulus 34 that encircles or surrounds the hollow cylindrical central riser 16. The steam generator plenum 34 contains secondary coolant (diagrammatically indicated by cross-hatching in FIG. 1). The primary coolant circuit is completed by a plurality of tubes 36 passing through the steam generator annulus 34. The tubes 36 are arranged to convey primary coolant downward from the upper plenum 30 to the lower plenum 32. In a suitable arrangement, an upper annular tube sheet 40 connects with upper ends of the tubes 36 and defines the boundary between the upper plenum 30 and the steam generator plenum 34, and a lower annular tube sheet 42 connects with lower ends of the tubes 36 and defines the boundary between the lower plenum 32 and the steam generator plenum 34. Thus, starting at the reactor core 14 the primary coolant flows upward through the hollow cylindrical central riser 16 discharging at the top into the upper plenum 30, enters the upper tube sheet 40 and flows downward through the tubes 36 discharging out of the lower tube sheet 42 back into the lower plenum 32, where it re-enters the reactor core 14 from below. The primary coolant flow may be driven by natural circulation, that is, convective flow driven by heat generated by the reactor core 14. Additionally or alternatively, reactor coolant pumps (not shown) may be provided to actively assist or drive the primary coolant circulation. If provided, such reactor coolant pumps may couple at substantially any point of the primary coolant circuit, and may be wholly internal pumps (that is, internal to the pressure vessel 12), or canned pumps having a motor stator external to the pressure vessel 12 and an impeller disposed inside the pressure vessel 12 to engage the primary coolant. Designs of the latter type may employ either a wet rotor or a dry rotor. A steam generator operates as follows: secondary coolant in the steam generator plenum 34 is heated by primary coolant flowing downward through the tubes 36 such that the steam generator plenum 34 contains secondary coolant as a steam/water mixture. The steam has lower density and naturally tends to rise toward the top of the steam generator plenum 34. A steam outlet 44 (which in some embodiments is an outlet annulus encircling the pressure vessel 12) and steam piping 46 conveys “wet” steam (that is, a mixture of steam and water) to a steam separator 50 (also sometimes referred to in the art as a “steam drum”) that separates dry steam from the water phase. The steam separator 50 can employ substantially any type of steam/water phase separation mechanism, such as a combination of cyclone separators and steam dryers (not shown). The resulting dry steam is output as a useful steam output 52, which may by way of illustrative example be input to a turbine of a nuclear electrical power plant. The phase-separated water (i.e., the liquid phase) is returned by drainage piping 54 and a feedwater inlet 56 (which in some embodiments is an inlet annulus encircling the pressure vessel 12) to the steam generator plenum 34. Additionally, the steam output 52 is recondensed and returned into the drainage piping 54 (or, alternatively, directly into the steam generator plenum 34) at a make-up water return 58. Typically, the make-up water comprises recondensed steam as well as some added water to compensate for any water mass that is lost in the turbine or elsewhere in the secondary coolant circuit running from the steam output 52 to the make-up return 58. The disclosed steam generator differs from a conventional shell-and-tube steam generator which is usually employed as the internal steam generator of an integral PWR. In a shell-and-tube steam generator, primary coolant flows in a first direction (downward) in tubes of the shell-and-tube steam generator and secondary coolant flows in an opposite second direction (upward) in the shell of the shell-and-tube steam generator. (Alternatively, secondary coolant may flows upward in tubes of the shell-and-tube steam generator and primary coolant downward in the shell of the shell-and-tube steam generator). The conventional shell-and-tube steam generator relies upon there being a defined tube-side or shell-side flow path for the secondary coolant, and toward this end requires active pumping to drive the secondary coolant flow through the tubes or shell. In contrast, the steam generator of FIG. 1 suitably operates in a natural circulation mode with the circulation being driven by elevation of the steam separator 50 respective to the steam generator plenum 34 in conjunction with the buoyancy of (wet) steam compared with water. In this case there is there is no pump configured to actively circulate secondary coolant between the steam generator plenum and the steam separator. (Although the secondary coolant circulation can occur naturally, it is contemplated to enhance the circulation through the use of secondary coolant pumps 60 indicated diagrammatically in phantom in FIG. 1). The steam generator plenum 34 does not include or contain piping arranged to convey secondary coolant along a defined flow path. (In contrast, the shell-and-tube steam generator employs either the tubes or the shell to convey the secondary coolant along a defined flow path which is typically a counter-flow to the primary coolant flow). The steam generator plenum 34 does not define a secondary coolant flow path. Instead, the secondary coolant is merely constrained to reside within the steam generator plenum 34, and any flow pattern of the secondary coolant is driven by convection due to temperature variations rather than by any piping or other defined flow path. In some embodiments, the steam generator plenum 34 comprises an unsectioned single annulus. Alternatively, the steam generator plenum 34 may be sectioned into two or more sections. For example, FIG. 1 shows two steam separators 50—in such the steam generator plenum 34 may optionally be sectioned into two sections each comprising a half-annulus and each connected with a corresponding one of the two steam separators 50. (Alternatively, both steam separators 50 can be connected with a single full annular steam generator plenum 34 that has no sectioning). Any sectioning of the steam generator plenum 34 should be limited so that individual sections do not become so small as to define narrow flow paths that affect the natural circulation of the secondary coolant. For example, in some embodiments, the steam generator plenum is either (1) a single volume that is not divided into sections or (2) divided into N sections where N is an integer between 2 and 6 inclusive. (Six sections would still have each section encompassing a sizable 60° arc of the steam generator annulus 34, assuming uniform sectioning). In embodiments in which the steam generator annulus 34 is sectioned, each section should be operatively connected with at least one steam separator. With reference to FIG. 2, a variant illustrative nuclear reactor of the pressurized water reactor (PWR) type 100 includes most of the components of the PWR 10 of FIG. 1. These components are indicated in FIG. 2 using the same reference numbers as in FIG. 1, and their description is not reiterated here. The PWR 100 of FIG. 2 differs from the PWR 10 of FIG. 1 in that the single hollow cylindrical central riser 16 of FIG. 1 is replaced by a plurality of riser tubes 116 in the embodiment of FIG. 2. With the omission of the central riser 16 the steam generator plenum 34 comprising an annular volume, i.e. annulus, becomes a steam generator plenum 134 comprising a cylindrical volume. The riser tubes 116 pass through an inboard cylindrical region of the steam generator plenum 134 and are arranged to convey primary coolant upward from the nuclear reactor core 14 to the upper plenum 30 (thus performing the same primary coolant flow function as the single hollow cylindrical central riser 16 of the embodiment of FIG. 1). The tubes 36 are arranged to convey primary coolant downward from the upper plenum 30 to the lower plenum 32 as in the embodiment of FIG. 1. The tubes 36 pass through an outboard annular region of the steam generator plenum 134 that surrounds the inboard cylindrical region of the steam generator plenum 134. Put another way, the steam generator plenum 136 comprises a single connected volume through which passes both the riser tubes 116 and the tubes 36 arranged to convey primary coolant downward from the upper plenum to the lower plenum. In some embodiments the annular tube sheets 40, 42 of the embodiment of FIG. 1 become circular tube sheets 140, 142. The upper tube sheet 140 connects with upper ends of the tubes 36 and with upper ends of the riser tubes 116, and the upper tube sheet 140 defines the boundary between the upper plenum 30 and the steam generator plenum 134. The lower tube sheet 142 connects with lower ends of the tubes 36 and with lower ends of the riser tubes 116, and the lower tube sheet 142 defines the boundary between the lower plenum 32 and the steam generator plenum 134. Note that the upper tube sheet 140 serves as the inlet to the tubes 36 but serves as the discharge for the riser tubes 116. Similarly, the lower tube sheet 142 serves as the discharge for the tubes 36 but as the inlet for the riser tubes 116. In some embodiments the riser tubes 116 and the tubes 36 both have the same cross-section, and in some embodiments the tubes 36 and the riser tubes 116 are substantially the same (i.e., same inner diameter, same outer diameter, same material, et cetera). However, the riser tubes 116 carry the “hot leg” of the primary coolant circuit while the tubes 36 carry the “cold leg” of the primary coolant circuit. While the temperature difference between the hot leg and the cold leg is relatively small, the difference can be large enough to generate a potentially problematic difference in thermal expansion at the operating temperature. To compensate, in some embodiments at 25° C. (i.e., about room temperature) the tension in the riser tubes 116 is greater than the tension in the tubes 36. This room temperature tension difference is chosen such that at operating temperature the tension in the riser tubes 116 and in the tubes 36 is about the same. Operation of the steam generator of FIG. 2 is substantially similar to operation of the steam generator of FIG. 1. Secondary coolant in the steam generator plenum 134 is heated by primary coolant flowing downward through the tubes 36. In the embodiment of FIG. 2, heating is also provided by primary coolant flowing upward through the riser tubes 116. Because of this heating, the steam generator plenum 134 contains secondary coolant as a steam/water mixture. The steam tends to rise toward the top of the steam generator plenum 134, and the annular steam outlet 44 and steam piping 46 conveys wet steam to the steam separator 50 which generates useful steam output 52, and returns phase-separated water to the steam generator plenum 134 via drainage piping 54 and the annular feedwater inlet 56. Additionally, the steam output 52 is recondensed and returned as make-up water 58. The steam generator of the embodiment of FIG. 2 is expected to be more efficient than the steam generator of FIG. 1 due to additional heating provided by the riser tubes 116. The secondary coolant circulation can be natural circulation controlled by the elevation of the steam separator 50 respective to the steam generator plenum 134. However, it is also again contemplated to include assistive active pumps 60 (shown in phantom). The primary coolant flow circuit in the embodiment of FIG. 2 is substantially similar to the primary coolant flow circuit in the embodiment of FIG. 1, except that the hot leg passes through riser tubes 116 in FIG. 2 rather than through the single central riser 16 in FIG. 1. In the upper plenum 30 a suitable flow guide 150 is optionally included to ensure separation of the openings of the upper tube sheet 140 that operate as discharge for the riser tubes 116 from the openings that operate as inlets for the tubes 36. Similarly, a shroud 152 ensures separation of the openings of the lower tube sheet 142 that operate as inlets for the riser tubes 116 from the openings that operate as discharge for the tubes 36. In illustrative FIG. 2, the shroud 152 has a hollow annular configuration and also surrounds the reactor core 14. Not illustrated are remaining components of a nuclear reactor such as the containment structure configured to contain radioactive steam escaping from the pressure vessel in the event of an accident, an external turbine (in the case of a nuclear power electrical plant), or so forth. Typically, the containment structure will contain both the pressure vessel 12 and the steam separator 50. The disclosed integral PWR systems as described with reference to illustrative embodiments 10, 110 have certain advantages over more conventional systems that employ conventional a shell-and-tube steam generator disposed in the downcomer annulus between the central riser and the inner wall of the cylindrical pressure vessel. The steam generators disclosed herein are expected to reduce tube mass by 40-50% due to elimination of piping defining secondary coolant flow paths. This reduces cost and has ancillary benefits such as reduced mass to be moved during refueling (and hence simplified refueling), a higher secondary coolant inventor (since the entire steam generator plenum 34, 134 is substantially filled with secondary coolant, rather than filling only the tubes or shell of a shell-and-tube steam generator), and so forth. Additionally, if the steam separator 50 is located inside the containment structure than by valving off the steam outlet 52 and the return 58 a natural circulation emergency core cooling system (EGOS) component is defined. (In other words, the closed natural circulation steam generator system can be used to assist removal of residual heat). The embodiment of FIG. 2 may also reduce manufacturing cost by eliminating the large hollow cylindrical central riser 16 and enhancing component interchangeability by using the same tubing for both the riser tubes 116 and the tubes 36. The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
	summary
046541730	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A number of large cations, including Tl.sup.+, AG.sup.+, Ca.sup.+, nitron [4,5-dihydro-2,4-diphenyl-5-(phenylimino)-1,2,4-triazole] and (C.sub.6 H.sub.5).sub.4 As.sup.+, form precipitates with pertechnetate anion that are insoluble, or only slightly soluble, in aqueous solution. But solubility correlations, based on a common anion, between compounds comprising different cations are notoriously erratic. Accordingly it cannot be predicted a priori whether a given cation complex with the pertechnetate anion will be sufficiently insoluble to be useful in a process for removing technetium as described above, particularly when technetium is present in concentrations typical of the Savannah River Plant salt solution, i.e., in the range of about 2.5.times.10.sup.-5 to 1.times.10.sup.-4 M (average of about 6.times.10.sup.-5 M) or approximately 35-200 mCi per liter of waste solution. It was surprising, therefore, to discover that tetraphenylphosphonium ion (TPP.sup.+) not only forms a pertechnetate salt which is essentially insoluble in aqueous solution, but also that precipitation of the pertechnetate-phosphonium complex could be effected even under conditions of high pH and/or low Tc-99 content that are characteristic of a waste salt solution like that produced by the Savannah River Plant. More specifically, in simulated waste solutions containing 3.times.10.sup.-5 M pertechnetate (see Table 1), the addition of 4.2.times.10.sup.-4 M tetraphenylphosphonium chloride (TPPCl) resulted in the precipitation of approximately 96% of the pertechnetate, providing a decontamination factor (DP) of 30, where DF is defined as the ratio of technetium activity measured before precipitation to that measured after precipitation. TABLE 1 ______________________________________ COMPOSITION OF SIMULATED SALT SOLUTION Concentration Component (molar) ______________________________________ Na.sup.+ 5.6 K.sup.+ .015 NO.sub.3.sup.- 2.3 NO.sub.2.sup.- .70 OH.sup.- (free) 1.3 CO.sub.3.sup.2- .20 AlO.sub.2.sup.- .38 SO.sub.4.sup.2- .17 F.sup.- .017 Cl.sup.- .025 SiO.sub.3.sup.2- .0045 CrO.sub.4.sup.2- .0039 MoO.sub.4.sup.2- .00051 C.sub.2 O.sub.4.sup.2- (oxalate) .029 PO.sub.4.sup.3- .012 TPB.sup.- (tetraphenylborate) .001 TcO.sub.4.sup.- 3.0 .times. 10.sup.-5 ______________________________________ It was found that the DF for the simulated waste solutions was directly dependent on the amount of TPPCl added. A DF of 10, for example, required 0.053 grams of TPPCl per liter of waste solution. As described below, the DF values obtained with actual waste solutions (see Table 2) were somewhat lower than those achived with simulated solutions. Thus, to obtain a 90% removal of technetium required the addition of 0.29 grams of TPPCl per liter of actual waste solution. TABLE 2 ______________________________________ AVERAGE COMPOSITION OF DECONTAMINATED SALT SOLUTION Major Non-Radioactive Major Components Radioactive Components Concentration Concentration Component (molar) Radionuclide (mCi/l) ______________________________________ Na.sup.+ 5.0 Tc-99 50 NO.sub.3.sup.- 2.0 Ru-106 50 OH.sup.- 1.2 Cs-137 25 NO.sub.2.sup.- .62 Sr-90 .9 AlO.sub.2.sup.- .34 I-129 .25 CO.sub.3.sup.2- .15 SO.sub.4.sup.2- .023 F.sup.- .015 PO.sub.4.sup.3- .011 TPB.sup.- .002 (tetraphenyl- borate) ______________________________________ Preferably, technetium precipitation by addition of TPP.sup.+ in accordance with the present invention is accomplished in a batch process. An exemplary arrangement for batch processing of a waste stream to remove Tc-99 using the present invention is shown schematically in FIG. 1. Typically, waste solution from which cesium-137 and strontium-90 has been removed via the process disclosed by Lee et al is pumped from a storage tank 1, first to one of two or more precipitation tanks 2 and then, alternatively, to the other tank(s). For a system comprising two precipitation tanks, as shown in FIG. 1, the cycle of alternatively filling the tanks could extend, for example, over about eight hours. After the first tank has been filled, and while filling of the second tank is in progress, a batch precipitation of Tc-99 is carried out by addition of a water soluble tetraphenylphosphonium salt, such as a soluble TPP halide salt (e.g., TPP chloride, TPP bromide and TPP fluoride) or TPP hydroxide, to the solution in the first tank. The resulting slurry of pertechnetate precipitate is then separated for further processing, as elaborated below, and the procedure repeated in the other tank(s) in succession. A precipitation process within the present invention is now described in greater detail, with reference to a batch processing setup as shown in FIG. 1; (1) Actual waste solution, preferably partially decontaminated by the removal of cesium and strontium, is fed into a precipitation tank (2) which could contain, for example, some 7,200 gallons of solution based on an instantaneous processing rate of 15 gallons per minute. (The "instantaneous processing rate" corresponds to the maximum rate achieveable at any given time; the average processing rate, which includes downtime, might be the range of about 10 gallons per minute over an entire year.) (2) A water soluble potassium salt is then optionally added to precipitate tetraphenylborate (TPB) ion present by virtue of a prior addition of sodium tetraphenylborate in accordance with Lee et al. A 45% KOH solution (11 molar) is suitable for this purpose, with about two gallons of the 11M solution required per 720 gallons of the waste solution shown in Table 2. When the KOH and waste solutions are thoroughly mixed over a period of about one-half hour, precipitation of potassium tetraphenylborate (KTPB) is rapid and no additional time for ripening of the crystals comprising the precipitate is required to obtain crystals of a size amenable to easy filtering. (3) TPP.sup.+ is then added in the form of an aqueous concentrate of a water soluble tetraphenylphosphonium compound. TPPCl is preferred in this regard, but other soluble TPP compounds, such as tetraphenylphosphonium hydroxide, can be used, for example, if elimination of chloride is necessary to ameliorate corrosion. After addition of TPP.sup.+ to a concentration preferably in the range of about 7.times.10.sup.-4 M to 2.times.10.sup.-3 M, the batch solution is agitated for about one-half hour or more in the tank to assure complete mixing of the solution and precipitation of the phosphonium complex. The batch can be sampled at this stage and analyzed for technetium content. If the DF value thus determined is too low, more TPP.sup.+ -contributing precipitating agent can be added. For the above-mentioned preferred range of TPP.sup.+ concentration, the corresponding range for DF is between about 10 and 130. If preliminary decontamination in accordance with Lee et al is not carried out, and precipitation (2) of TPB ion therefore not effected, somewhat smaller phosphonium crystals may be obtained. If TPB ion is present, filtration of the resulting KTPB precipitate formed in step (2) is not required, as the presence of KTPB actually enhances technetium recovery in the present invention, presumably by aiding in the filtration of tetraphenylphosphonium pertechnetate (TPPTcO.sub.4). For reasons not fully understood, the efficiency of technetium removal is also improved if the concentration of the initial salt solution, as reflected by sodium ion content, is adjusted (e.g., by allowing water to evaporate during storage) to a level higher than 5.6M sodium ion, preferably up to about 7M sodium. In addition, the volume of the TPPTcO.sub.4 precipitate obtained is reduced by up to 40% or more by carrying out step (3) at the higher salt concentration. The pertechnetate precipitate, which forms as a slurry at the bottom of the precipitation tank, can be removed and concentrated for easier storage. Preferably, concentration of the precipitate is accomplished by cross-flow filtration, as disclosed by Martin et al, "In-tank Precipitation Process for Decontamination of Water Soluble Radioactive Waste" in 1 Waste Management '84 291 (Univ. Arizona 1984), the contents of which are incorporated herein by reference. In the setup shown in FIG. 1, cross-flow filtration is carried out by pumping the pertechnetate slurry through a sintered metal pipe (3), such that filtered waste solution "weeps" through the sintered metal and leaves the slurry behind. The dewatered slurry is returned to the tank and recycled back through the pipe until the slurry is concentrated to about 10-15% solids (approximately 35 to 50 gallons for a 7200-gallon batch). From the original waste solution to a concentrated slurry of about 10% solids, the overall concentration factor for technetium, using cross-filtration, is about 155:1. Higher concentrations are possible with other methods, such as bed filtration or centrifugation, that allow for greater removal of water. But cross-flow filtration requires no moving parts aside from the pump components, and hence offers the advantages of operational simplicity and reliability. After the pertechnetate slurry has been sufficiently concentrated, it can be retained in a slurry storage tank 4, from which the slurry is transferred periodically to another facility for incorporation into glass or for further recovery processing. The filtered waste solution is collected from the sintered metal pipe 3 and retained in a holding tank 5; it can be transferred from there to a saltstone disposal facility. As noted above, both simulated and actual waste solutions were processed, in accordance with the present invention, to remove Tc-99 by the addition of TPP.sup.+. More specifically, 10 ml aliquots of waste solution, simulated or actual, were each placed in 25 ml polyethylene containers. To each container, a sufficient amount (approximately 0.1 ml) of 0.32M KOH solution was added to precipitate TPB ion after thorough agitation over several seconds. About 0.05 ml of TPPCl solution (0.088M) was then added to each container; the containers were capped and shaken for one hour. The resulting slurry in each container was filtered through a cellulose filter (0.2 micron nominal pore size), and the filtrate was analyzed for technetium by a standard scintillation counting method. The observed DF values for Tc-99 at differing TPP.sup.+ concentrations are shown, for both simulated and actual waste solutions, in FIG. 2. The present invention permits the high efficiency precipitation, from relatively Tc-poor, caustic waste streams, of technetium in a form that is non-toxic and easily stored.
048872822	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles of the present invention are particularly useful when utilized in the apparatus schematically illustrated in FIG. 1. As illustrated in FIG. 1, the apparatus includes a radiation source Q, a mask M carrying the desired structure, an adjustment unit J, which mounts a semiconductor wafer W covered by a radiation-sensitive layer S. The semiconductor wafer W is positioned at a prescribed distance P from the mask M with the assistance of the mounting or holding means H, and the wafer W is aligned relative to the mask. Storage rings or storage accelerators particularly come into consideration as a radiation source Q for x-ray lithography. Synchroton radiation RS, which is emitted tangentially relative to an orbital path by a highly relativistic electrons being coupled out from the path via a vacuum-tight window in the wall of the accelerator ring, are supplied to the apparatus. The wavelength of the synchroton radiation RS can, therefore, be continuously varied over a great range, for example, 0.1.ltoreq..tau..sub.s .ltoreq.1.00 nm, by a suitable selection of the machine parameters, such as electron energy, radius of curvature, etc.. Thus, the pattern of the mask M at a distance of several meters from the radiation guide tube of the accelerator can be imaged onto a semiconductor wafer W with a nearly exact, parallel projection as a result of the high degree of collimation of the x-ray radiation RS that is coupled out of the source Q. A further advantage of the synchroton radiation is its high intensity, which enables extremely short exposure times of only a few seconds. As a consequence of limited homogenity of the radiation in the direction perpendicular to the orbital plane of the electrons, however, one is forced to limit the beam cross section to a band shape. The synchroton beam RS, coming from the source Q, is shaped by a diaphragm system B and is usually brought to the lithographic equipment in an evacuated beam tube to impinge on the mask M, which is fashioned in a known way inside of the chamber that is not illustrated in FIG. 1. Examples of this type of equipment are disclosed in an article by H. Luethje, entitled "X-ray Lithography For VLSI", Philips Techn. Rev. Vol. 41, 1983/84, No. 5, pp.150-163. The mask M is usually composed of a radiation-impermeable holding membrane having reinforced edging and of a radiation-permeable metal layer, which is structured according to a mask pattern to be transferred onto the semiconductor wafer W. Adjustment marks are also situated on the masks, and these adjustment marks are optically read during the alignment and are capable of being brought into the desired rated position with the assistance of a control unit ST by displacing the mask M relative to the semiconductor waver W. As a consequence of the high degree of collimation of the synchroton radiation, the methods known from the area of lithography with punctiform x-ray sources modifying the imaging scale cannot be utilized in the arrangement shown in FIG. 1. It is therefore proposed, in accordance with the invention, that the semiconductor wafer W be deformed, at least in the region to be exposed and that the radius R of curvature produced at the respective surface points by deformation be kept constant during the irradiation. On the basis of a spherical deformation of the semiconductor wafer W, one thus achieves a magnification of the surface lying opposite the mask M in two orthogonal directions relative to one another. This leads to a corresponding scale modification .epsilon. in these directions. The quantity .epsilon. is, thereby, defined by the quotient .epsilon.=.DELTA.L/L, wherein L is a characteristic length and .DELTA. L is the change in this lenght produced by imaging. The scale modification is based on a projection effect (imaging of the planar mask structure onto a curved surface), and on a stretching of the semiconductor material supplying the smaller quantity. A cylindrical warping of the object to be exposed requires less of a force exertion and is, technically, simpler to obtain, particularly for semiconductor wafers. In this case, a scale modification occurs in the direction x, as illustrated in FIG. 1, which is perpendicular to the symmetry axis ZA of the cylinder and amounts to .epsilon.x=d/2R, wherein d is the thickness of the semiconductor wafer W, and R is the radius of curvature produced by deformation. Given a thickness of d=0.6 mm, and given a scale modification of .epsilon.=10.sup.-5, usually required in a conventional arrangement, a radius of curvature of R=30 m, which can be technically obtained without trouble, is required. Given the exemplary embodiment of the arrangement of the invention for modifying the imaging scale as shown in FIG. 1, the deformation of the surface region to be structure occurs with the assistance of a holder H arranged between the semiconductor wafer W and the adjustment unit J. The surface of this holder H at a side facing toward the mask M has a spherical or cylindrical curvature with a radius of curvature R. One or more annular grooves N are formed in the face of the holder and are connected to a vacuum pump VP via channels AK. Thus, the desired surface deformation is automatically set by suctioning the semiconductor wafer W onto the surface of the holder H. A cylindrical deformation of the semiconductor wafer can also be achieved by a force F which is preferably generated with the assistance of the arrangement illustrated in FIG. 2. In this arrangement, the semiconductor wafer W is held on its edges and a force F is applied to a back surface of the wafer W to cause a bending of the wafer. As illustrated, the force is created by a piezo-electric element PE and is positioned at the center. In order to guarantee a cylindrical deformation over a large surface area, the semiconductor wafer W comprising the planar surface on the side facing toward the mask M and having a convex surface at the side facing away from the mask M is preferably utilized. Thus, the wafer thickness steadily increases from the edge towards the center. In accordance with the further feature of the invention, the semiconductor wafer can also be held by a holding device having elastic walls. In this arrangement, the wafer is held on its periphery and is deformed by changing the inside pressure of the container with the elastic walls. Given cylindrical deformation of the semiconductor wafer W, the imaging scale or, respectively, the magnification changes is in only one spatial direction. For example, as illustrated in FIG. 1, in the x direction, with .epsilon..sub.x =d/2R. In order to also produce a scale modification in the direction of symmetry axis ZA of the cylinder, which would be the y direction in FIG. 1, it is proposed to sweep the synchroton beam RS, which has been gated out nearly line-shaped, across the mask M in the direction of the cylindrical axis ZA with a constant speed v.sub.S. This is executed, for example, with the assistance of a rotatably mounted mirror. Instead of this deflection, the mask M and the semiconductor wafer W can also be drawn through the stationary beam in common and the width b measured in the deflection direction or, respectively, displacement direction, is smaller than the height h. Thus, for example, h is approximately 30 nm, while b is approximately 3 mm. When the mask M is also displaced with a speed v.sub.M relative to the semiconductor wafer W in the direction of the cylindrical axis ZA, then this leads to a change in the magnification .epsilon..sub.y =v.sub.M /v.sub.S and, thus, leads to a modification of the imaging scale in this direction, whereby v.sub.S =v.sub.S .multidot.e.sub.y, which refers to the relative speed of the synchroton beam RS relative to the mask M and v.sub.M =v.sub.M .multidot.e.sub.y, which is the relative speed of the mask relative to the semiconductor wafer W. A finite width b for the synchroton beam leads to a resolution limit a =.epsilon.y.multidot.b, which lies at a =30 nm for typical values of b=3 mm and .epsilon..sub.y =10.sup.-5. The described method of the cylindrical deformation in combination with the scale modification on the basis of relative motion has the advantage over the spherical warping because the scale can be set in orthogonal directions independent of one another. The orthogonal error of the mask M can also be corrected with the method of the invention when the mask M is also additionally displaced with constant speed relative to the semiconductor wafer W in that direction, for example, the x-direction of FIG. 1, which is perpendicular to the cylindrical axis ZA. The invention, of course, can also be employed in a synchroton stepper in which large semiconductor wafers having a diameter of up to 20 cm are structured with the assistance of a step and repeat method. This method is known from lithography with electron beams. In this method, the semiconductor wafer W is successively exposed in sub-regions BF arranged perpendicular relative to one another, and the size of these regions BF is prescribed by the mask field, for example, 4.times.4 cm. In order to also guarantee a scale variation which is constant over the entire surface of the semiconductor wafer W and is dependent on the radius R of curvature and on the wafer thickness d in the synchroton steppers, the sub-regions BF1, BF2, to be respectively exposed, must be positioned immediately under the mask M by three-dimensional displacement of the semiconductor wafer W, as illustrated in FIG. 3. Care must, therefore, be exercised to see that when using spherical deformation that the center or, when using cylindrical deformation, the points lying on a straight line proceeding through the center of the respective sub-regions, BF1 and BF2, and exhibit the smallest distance P from the mask M. The displacement executed with the assistance of the adjustment unit J then corresponds to the virtual rotation of the semiconductor wafer W around the center of the sphere or, respectively, the rotation around the symmetrical axis ZA of the cylinder. Although various minor modifications may be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent granted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.
	summary
053923235	description	As shown in FIG. 1, a cylindrical reactor pressure vessel 1 of a nuclear reactor plant is provided with a pipe socket 2, which is welded in a known manner into the vessel wall 1'. The left-hand end of the pipe socket 2 in FIG. 1 is connected to a feed-water supply line 3, e.g. by a weld 3', whereby the internal and external diameters of the line 3 and of the end of the pipe socket 2 are substantially the same. Outside the region of this connection the pipe socket 2 is widened slightly on its inside and then passes into a cylindrical face 4, which the outer end of a protective sleeve 5 slidably abuts, which sleeve extends through the pipe socket 2 towards the interior of the vessel. During the operation of the reactor pressure vessel 1, the protective sleeve 5 is subject to temperature changes, and for this reason the term "thermal sleeve" is also used for the protective sleeve. Towards the interior of the vessel next to the cylindrical face 4 in the pipe socket 2 there is also a widened portion, which then passes into a cylindrical face 4, so that an annular gap 6 remains between the protective sleeve 5 and the pipe socket 2. The end of the protective sleeve 5 protruding into the interior of the vessel passes into a feed-water distributing ring 7 (not shown in further detail), which in the vessel 1 extends along the vessel perimeter. Close to the inner end of the pipe socket 2 the outer side of the protective sleeve 5 is provided with cams 8, which extend through the annular gap 6 and centre the protective sleeve in the socket bore. During the operation of the reactor pressure vessel 1, cold feed-water is supplied via the feed-water supply line 3 and the protective sleeve 5 to the distributing ring 7, from which the feed-water overflows into the interior of the pressure vessel. The interior of the pressure vessel is otherwise filled with hot reactor water, which is also situated in the annular gap 6. As the narrow gap between the outer end of the protective sleeve 5 and the cylindrical face 4 is not tight, cold feed-water also enters the annular gap 6. Thermal stresses, which can result in cracks in the material of the pipe socket, may occur in the pipe socket 2 by the meeting of cold and hot water in the annular gap 6. As shown in FIG. 2, between the outer end of the pipe socket 2 and the feed-water supply line 3 is inserted a pipe section 10, which is widened in its central part 10' in comparison with the internal and external diameters of line 3 and the socket end. The two ends of this widened part 10' pass into a hollow conical part 11 and 11', which are tightly connected to the line 3 and the end of the pipe socket 2 respectively, e.g. by welds 13 and 14. For reasons relating to production technology, a weld joint seam 12 is also provided between the hollow conical part 11 and the central part 10'. In the widened part 10' are disposed bellows 15, which at their left-hand end in FIG. 2 comprise a cylindrical pipe section 16, the diameter of which roughly corresponds to the internal diameter of the bellows. The left-hand end in FIG. 2 of the pipe section 16 is tightly connected to a ring 17, which is welded into the central part 10' and bridges the space between pipe section 16 and the internal diameter of the central part 10'. A pipe section 18 corresponding to the cylindrical pipe section 16 is provided at the right-hand end in FIG. 2 of the bellows 15, which extend over the pipe section 10 into the protective sleeve 5. The pipe section 18 is tightly connected on its inside to the protective sleeve 5, e.g. by welding. In this manner it is possible that the protective sleeve 5--as before--can expand in the pipe socket 2 under the affect of temperature changes and that at the same time cold feed-water is prevented from overflowing into the annular gap 6, because the bellows 15 also experience the thermal expansion, but are tightly connected to the pipe section 10 and the protective sleeve 5. For reasons relating to flow technology, in the bellows 15 is disposed a pipe 20, the external diameter of which corresponds to the internal diameter of the hollow conical part 11 in the region of the weld 13. The pipe 20 is tightly connected to the hollow conical part 11 at its tapered end and extends to the end of the cylindrical pipe section 18 of the bellows 15 situated in the protective sleeve 5. The right-hand end of the pipe 20 in FIG. 2 abuts the pipe section 18 and is connected thereto in a nonsecure manner. Thus the pipe 20 can freely expand, and therefore is also a thermal sleeve. Deviating from the described exemplified embodiment shown in FIG. 2, the pipe section 10 may have the same diameter measurements as the feed-water line 3 and pipe socket 2. In such a case the bellows 15 protrude slightly into the cross section of flow. The pipe 20, which is provided in appropriate circumstances, could then be expanded at its left-hand end in FIG. 2.
	description	The present invention relates to a charged particle beam application apparatus such as an electron microscope, an ion-beam machining/observation apparatus or the like. In recent years, the integration densities of semiconductor products have been more and more enhanced, and higher definition of the circuit patterns is demanded. In the specimens on which circuit patterns are formed, typified by semiconductor wafers, various kinds of inspection means are used for the purpose of quality control and enhancement of yield. There are cited, for example, a scanning electron microscope (hereinafter, called a length measuring SEM) which irradiates charged particle beam to measure the dimensional accuracy of a circuit pattern, a scanning electron microscope (hereinafter, called a review SEM) which also irradiates charged particle beam to evaluate a defect of a circuit pattern or attached extraneous matters, and the like. In the observation of a specimen typified by a wafer by using charged particle beam, the electric field distribution of the periphery of the specimen edge changes, and therefore, the image quality degradation such as distortion, or blur of the observation image of the above described periphery occurs. As the influence of this phenomenon, various problems are caused such as occurrence of an error to a measurement dimensional value, erroneous detection of a defect, and inability to obtain a clear image. As the means for solving the problems, there is proposed a method for controlling the electric field of the periphery of the edge to be uniform by adding a ring-shaped conductor element capable of applying a voltage to the specimen holding means in the vicinity of the specimen edge (see JP-A-2004-235149). Further, as another means, there is proposed a method for making the distribution of an electric field gentle by narrowing the height gap of the edge and the specimen holding means which has conventionally existed by surrounding the specimen by a specimen positioning component with substantially the same height as the specimen (see JP-A-2004-79516). Depending on the specimen holding state, the observed image significantly differs. As an example of mechanical specimen holding, there is a method in which two reference pins are provided at the outer periphery of a specimen, and the specimen is held by the pressing force by a movable pin from the opposing direction. In this method, the holding force which increases the pressing force for the specimen increases, and a deviation of the specimen due to vibration can be reduced. However, the specimen is distorted on one hand, and observation with favorable accuracy becomes difficult. Further, since the wafer is thin, and the flatness is low (parallelism of the single body is favorable), the specimen tends to be held in the form of a concave shape or a convex shape. In such a state, the height significantly varies with the movement of the specimen (about 100 μm at the maximum), and therefore, the depth of focus or focus movable length of the electron-optical system has to be set to be large. This becomes a large constraint to the electronic lens design, and it becomes difficult to increase the resolution which leads to improvement in image quality. Thus, by using an electrostatic chuck for the specimen holding means, flattening of the specimen surface and reinforcement of the holding force can be achieved at the same time. An electrostatic chuck is very effective as the specimen holding means in a vacuum, but is generally made of ceramics and its manufacture cost is high. Accordingly, it leads to substantial increase in prime cost to prepare a holder attachable and detachable to and from a stage as the specimen holding means for each specimen size. Further, when the electrostatic chuck is fixed to the stage, if the specimen size is switched to a small specimen size, the surface to which the specimen is not sucked appears, which is highly likely to suck foreign matters, and when the specimen size is switched to a large specimen size, there is the fear that the specimen catches the foreign matters, and the specimen surface distorts. On the other hand, in the conventional means for uniformalizing the electric field of the specimen edge, each of the aforementioned means is the proposal intended for a different holder for each specimen size, and as many electrostatic chucks as holders are required. As a result, substantial increase in prime cost is inevitable. The present invention is contrived to solve the above described problems, and an object of the present invention is to provide an apparatus which makes it possible to suck specimens of different sizes electrostatically and improves image quality by uniformalizing an electric field of a specimen edge portion, while suppressing increase in prime cost. In a charged particle beam application apparatus including a stage which moves a specimen, and specimen holding means which is included on the stage and holds the specimen, and treats specimens of at least two kinds of sizes, the specimen holding means is an electrostatic chuck, a master flat plane part which surrounds a specimen of a largest size of the specimen sizes, and an opening which surrounds the specimen size other than the largest specimen size are included at an outer circumferential portion of the electrostatic chuck, a dummy specimen attachable to and detachable from the electrostatic chuck is included, and at a time of switching the specimen size, the dummy specimen is selected (the dummy specimen may be prevented from being used). The height of the master flat plane part is desired to be substantially the same as a specimen height of the largest specimen size. The thickness of the dummy specimen is desired to be substantially the same as a specimen thickness corresponding to a dimension of the opening. The dummy specimen is desired to be of the same material as the specimen. The dummy specimen is desired to be in contact with an earth intended for static dissipation. The dummy specimen and the specimen are desired to have transport mechanisms which are respectively attachable to and detachable from the stage individually. The electrostatic chuck is desired to be provided with a groove portion or a non-suction portion in the vicinity of the specimen size except for the largest specimen size. It is desirable to include positioning means which positions the specimen and dummy specimen on the stage. Further, a stocker capable of storing at least one dummy specimen or more is included, and transport means which is capable of selecting a dummy specimen in accordance with a size and a material of the specimen to be treated is included. According to the present invention, an apparatus capable of significantly enhancing throughput as compared with the conventional apparatus by reducing or eliminating a stage setting time while securing image precision can be provided. Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. The present invention will be described with reference to FIGS. 1 to 3, by taking a scanning electron microscope as an example as a charged particle beam application apparatus to which the present invention is applied. First, the apparatus constitution shown in FIG. 1 will be described. A mount 4 which damps a floor vibration is mounted on a pedestal 6 installed on a floor, and the mount 4 further supports a specimen chamber 2. The specimen chamber 2 is mounted with a column 1 which generates and controls electronic beam, and a load lock 3 containing a transport robot 31 which transports a specimen. The specimen chamber is always evacuated by a vacuum pump 5, and the inside of the column 1 is also kept at a high vacuum degree by a vacuum pump not illustrated. Meanwhile, the load lock 3 is mounted with an atmosphere side gate valve 33 which isolates the load lock 3 from atmosphere, and a vacuum side gate valve 32 which isolates the load lock 3 from the specimen chamber 2. Here, the transport route for a specimen will be briefly described. The atmosphere side gate valve 33 is opened, and a specimen 10 is introduced into the load lock 3 from the atmosphere side by the transport robot 31. The atmosphere side gate valve 33 is closed, and the inside of the load lock 3 is evacuated by a vacuum pump not illustrated. When the vacuum degree becomes about the same as the inside of the specimen chamber 2, the vacuum side gate valve 32 is opened, and the specimen 10 is transported onto a stage 21 which is contained in the specimen chamber 2, by the transport robot 31. After the specimen 10 is treated, the specimen passes through the load lock 3 in the reverse order and is returned to the atmosphere. The specimen 10 is electrostatically sucked by an electrostatic chuck 24 mounted on the stage 21, and is firmly held on the stage 21. A bar mirror 22 is also mounted on the stage 21, and by performing laser measurement of relative distance change to an interferometer 23 mounted on the specimen chamber 2, the specimen position on the stage can be controlled. The positional information of the stage is generated in a position control section 71, and thereafter, is transmitted to a stage control section 72 which drives the stage. In the stage control section 72, feedback control is performed so that the deviation between the present positional information and target coordinates is eliminated. As for the feedback control, the control which is performed by only simple position feedback, the PID control which enhances the response speed and positioning accuracy by adding the speed information of the stage and the integral information of the stage position deviation, and the like are conceivable. Meanwhile, electron beam 12 which is generated by an electron gun 11 in the column 1 passes through an electron lens 13 having a convergent action and an electron lens 16, and is deflected to a desired track by a deflector 14, and thereafter, is irradiated to the specimen 10. A reflection electron or a secondary electron generated by irradiation of the electron beam is detected by a detector 15, and is transmitted to an image control section 73 together with the control information of the deflector 14. Here, an image is generated based on the control information of the deflector and the obtained information from the detector, and the image is projected on a monitor 74. An optical type Z sensor 25 which detects the height of a specimen is mounted at the upper side of the specimen chamber 2, and is capable of always monitoring the height of the specimen, and the obtained signal is subjected to positional conversion in the position control section 71, and thereafter, is transmitted to the column control section. By the information, the optical conditions of the electron lens are changed in the column control section, and the electron lens is treated so that the focus does not shift even if the height of the specimen changes. Next, with reference to FIGS. 2 and 3, details of the specimen holding state will be described. FIG. 2 shows specimen holding means corresponding to different specimen sizes. FIG. 3 shows a section taken along the line III-III in FIG. 2. Here, for the sake of clarity, explanation will be made on the assumption that the corresponding specimen sizes are two kinds, that is, a wafer of φ300 mm and a wafer of φ200 mm. In FIG. 2, a wafer 10A of 200 mm is sucked on the electrostatic chuck, and a dummy specimen 40 is similarly chucked on an electrostatic chuck 24. Here, it should be noted that the electric path is set so that a master flat plane part 26A, the wafer 10A of 200 mm and the dummy specimen 40 are at an equal potential. A gap G1 exists between the dummy specimen 40 and the wafer 10A of 200 mm, and the distribution state of the surface potential changes depending on its size. Accordingly, it is desirable to make G1 as small as possible and uniform over the entire circumference. Further, for the purpose of removing the wafer 10A of 200 mm and the dummy specimen 40 from the electrostatic chuck 24 respectively, a specimen arm 41 and a dummy arm 42 vertically movable are provided and respectively connected to an actuator not illustrated. Thereby, in the case of continuously treating the wafer of 200 mm, only the wafer of 200 mm can be transported while the dummy specimen is left on the electrostatic chuck. FIG. 4 shows the state in which the specimen size is switched to a wafer 10B of φ300 mm. When the dummy specimen 40 is removed and the wafer 10B of φ300 mm is mounted, a gap G2 occurs between the master flat plane part 26A and the edge portion of the wafer 10B of φ300 mm. By making G2 small and by making the entire circumference uniform similarly to the aforementioned wafer of φ200 mm, the potential gradient becomes smaller and favorable image quality can be also obtained in the wafer peripheral portion. Here, in the present invention, by providing the positioning means as shown in FIGS. 5 and 6, the above described gap can be controlled. The dummy specimen 40 is provided with a positioning projection 40A for a notch and a positioning projection 40B for an outer periphery, and a run-off portion of a movable pin 40D for a wafer of φ200 mm is provided at the position which is substantially equiangular from them. After the wafer 10A of φ200 mm which is transported with a certain degree of gap (up to about 1 mm) from these projections and the movable pin 40D for φ200 mm is mounted on the electrostatic chuck 24, the positioning accuracy is ensured by pressing the wafer against the above described two projections by the movable pin 40D for 200 mm. Thereafter, the wafer 10A of φ200 mm is completely fixed by electrostatic suction, and pressing of the movable pin 40D for 200 mm is released. The movable pin 40D for φ200 mm completely escapes downward from the surface of the electrostatic chuck 24 when the movable pin 40D is released, and thereby, it does not interfere with mounting of the wafer 10B of φ300 mm. The sequence will be summarized as follows. 1) The wafer 10A of φ200 mm is mounted on the electrostatic chuck 24 while a certain degree of gap is kept between the positioning projection 40A for the notch and the positioning projection 40B for the outer periphery. 2) The movable pin 40D for φ200 mm is operated, and the wafer 10A of φ200 mm is pressed against the above described two projections. 3) Electrostatic suction is performed, and the wafer is completely fixed. 4) The movable pin 40D for φ200 mm is retreated. For the contact portions of the aforementioned positioning projection 40A for the notch, positioning projection 40B for the outer periphery and the movable pin 40D for 200 mm with the wafer 10A of φ200 mm, the material or the surface treatment in which a foreign matter hardly occurs is effective. For example, a resin with high abrasion resistance, excellent conductivity and small emission gas in vacuum is effective. Next, for positioning of the dummy specimen 40, the positioning means for the wafer of φ300 mm is utilized. Therefore, a notch 40C is formed at the outer periphery of the dummy specimen 40 as in the wafer to be a reference point in the rotational direction. A reference pin 50 for a notch and a reference pin 51 for an outer periphery are mounted on a top table 26, and the dummy specimen 40 is positioned by a movable pin 52 for φ300 mm. The mounting procedure of the dummy specimen 40 (the same for the wafer of φ300 mm) will be shown as follows. 1) The dummy specimen 40 is mounted on the electrostatic chuck 24 while a certain degree of gap is kept from the reference pin 50 for the notch and the reference pin 51 for the outer periphery. 2) The movable pin 52 for φ300 mm is operated, and the dummy specimen 40 is pressed against the two reference pins. 3) Electrostatic suction is performed, and the wafer is completely fixed. 4) The movable pin 52 for φ300 mm is retreated. Further, by providing an ordinary pattern (for example, a line pattern and a dot pattern) at the dummy specimen, various kinds of information can be collected. By measuring the distance of two selected patterns in time series, for example, the state of thermal expansion by temperature is known, and therefore, the temperature of the electrostatic chuck can be calculated from the result conversely. Alternatively, the transport accuracy of the dummy specimen can be calculated based on the pattern observation and the stage position information at this time. Further, while treating the specimen, contamination to the pattern due to quality of vacuum and adherence of a foreign matter can be tested for a long time. Further, by setting a certain pattern to be the reference of the size or the positional coordinates, as the standard pattern, the pattern can be also used for confirmation and correction of deformation of the stage, a beam drift and the like, and can be said to be very effective means. When the dummy specimen is irradiated with charged particle and observed, the dummy specimen surface is charged, and the phenomenon that the image blurs or distorts occurs. As the countermeasure against this, an earth projection 40E is provided at the outer periphery of the dummy specimen 40 so as to contact an earth mechanism 43 mounted on the top table 26 by performing suction action to allow charges to escape. Here, “earth” means that the dummy specimen 40 is grounded to a voltage level at which the dummy specimen 40 should originally be, and does not indicate 0 V unconditionally. As the shape of the contact portion of the earth mechanism 43, a needle-shaped projection, and an edge shape in a knife form are conceivable, and the contact portion is pressed against the dummy specimen with a constant force by a compressing spring. The earth mechanism 43 brings about a state which is hardly chargeable, and observation with favorable image quality becomes possible for a long time. The surface of the electrostatic chuck which is described so far is assumed to be in a uniform state, but a suction force occurs even in a small gap between the specimen and the dummy specimen, and therefore, the gap attracts a foreign matter. As the countermeasure against this, the present invention proposes an electrostatic chuck shown in FIGS. 7 and 8. In the vicinity of the gap between the dummy specimen 40 and the wafer 10A of φ200 mm in the electrostatic chuck 24 shown in FIG. 7, the suction surface is covered with a mask member 24A, and the suction force is removed. FIG. 7 shows the state in which the wafer 10A of φ200 mm and the dummy specimen 40 are sucked by the electrostatic chuck 24. Here, the width of the mask member 24A is designed to be larger than the gap between the wafer 10A of φ200 mm and the dummy specimen 40, and thereby, suction of a foreign matter can be reliably removed. Meanwhile, in the vicinity of the gap between the dummy specimen 40 and the wafer 10A of φ200 mm in the electrostatic chuck 24 shown in FIG. 8, a groove portion 24B is formed. Therefore, even if a foreign matter is sucked and the wafer of φ300 mm is sucked, the wafer is not deformed. The width of the groove portion 24B is designed to be larger than the gap between the wafer 10A of φ200 mm and the dummy specimen 40, and thereby, suction of the foreign substance can be reliably removed. Next, the transport mechanism of the present invention will be described with reference to FIG. 9. The vacuum robot 31 is contained in the load lock 3 to transport the specimen 10 and the dummy specimen 40. The load lock 3 is mounted with a stoker 60 capable of storing at least one dummy specimen 40 or more, so that a dummy specimen for each specimen size or each material, or a spare dummy specimen can be on standby. Thereby, switch of the specimen size, and replacement with a spare dummy specimen can be carried out quickly, and therefore, reduction in availability of the apparatus can be suppressed. It goes without saying that in the description above, the specimen size is applicable to the other wafers than the wafer of φ200 mm and the wafer of φ300 mm which are cited as examples. According to the present invention described so far, the image quality can be improved by making it possible to suck specimens of different sizes electrostatically, and uniformalizing an electric field of a specimen edge portion, while suppressing increase in prime cost. It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
	description	This is a National Phase Application in the United States of International Patent Application No. PCT/JP03/07002 filed Jun. 3, 2003, which claims priority on Japanese Patent Application No. 162365/2002, filed Jun. 4, 2002. The entire disclosures of the above patent applications are hereby incorporated by reference. 1. Field of the Invention The present invention relates to a neutron beam controlling apparatus that performs converging and diverging of a neutron beam, and a method for manufacturing the same. 2. Description of the Related Art A neutron beam is different from an X ray or a photon, and has the following characteristics. (1) The neutron beam strongly interferes with an atomic nucleus. (2) Energy and a wavelength of the neutron beam have the same degree as motion and a structure in a level of an atom. (3) The neutron beam has a magnetic moment. (4) The neutron beam has strong penetration power. By taking advantage of such characteristics of the neutron beam, in a case of research of position itself of an atomic nucleus, for example, in a case of obtaining position information of a hydrogen atom in an organic material, a scattering experiment that uses a neutron beam is inevitable because it is extremely difficult to obtain such position information by X-ray scattering. Furthermore, since a neutron has a ½ spin and a magnetic moment, the neutron beam is useful for examining a magnetic structure of a material. Further, in a case where research of an inside of a large object such as an industrial product is performed by using radiation, the neutron beam having strong penetration power enables fluoroscoping of the large object. However, it is not easy to generate a neutron beam, so that a place where the neutron beam can be available is limited to a nuclear reactor, an accelerator facility and the like. For this reason, in order that the neutron beam is efficiently introduced from the neutron source to an apparatus using the neutron beam, and a minute sample is irradiated with the high-density neutron beam, a beam controlling technique for raising a degree of parallelization of the neutron beams and focusing the neutron beams is inevitable. Recently, attention has been paid to above-described analyzing that uses the neutron beam, and the applicant of present patent application has already proposed a device for converging and diverging of the neutron beams (refer to “Japanese Laid-Open Patent Publication No. 2001-062691). Hereinbelow, this device is referred to as a “neutron lens”). FIG. 1 shows a principle of a refraction of a neutron beam by a substance. Almost interaction between a neutron and a substance is caused by interaction between the neutron and an atomic nucleus in the substance. Because of this interaction, when the incident neutron enters the inside of the substance, the neutron loses a part of its energy, so that the neutron is decelerated in the direction perpendicular to the boundary surface of the substance. Thereby, the neutron beam that obliquely enters the boundary surface of the substance is refracted such that a refractive index becomes a value smaller than 1 as shown in FIG. 1. A material that has a refractive index of less than 1 for a neutron beam includes oxygen O, carbon C, beryllium Be and fluorine F among those having naturally occurring isotopic concentrations, and deuterium D among enriched isotopes. FIG. 2 shows a principle of a neutron lens, and shows a way in which a neutron beam 16 enters one plate member 11. Linear projections 12 each including an almost vertical surface 15 and an inclining surface 15 are formed on the plate member 11. The neutron beam 16 that enters the inclining surface 15 of the linear projection 12 is refracted such that a refractive index becomes lower than 1 similarly to FIG. 1. However, a refracted angle δ by this one refraction is minute. For example, when the plate member 11 is made of polytetrafluoroethylene (PTFE), and the inclining surface 15 of the linear projection 12 is inclined from a surface plane of the plate member 11 by an angle α of 45 degrees, an refracted angle of a neutron beam 16 that has a wavelength of 14 angstroms (Å) and vertically enters the plate member 11 is only 0.14 mrad. FIG. 3 is a perspective view showing a neutron lens that has a function of focusing a neutron beam. FIG. 4 is a sectional view taken along the line A-A of FIG. 3. This neutron lens includes a body part 20, and upper and lower annular outer frames 21 and 22 that fix the body part 20. The body part 20 is sandwiched between the upper and lower annular outer frames 21 and 22, and the outer frames 21 and 22 are fixed on pins 23 arranged between the outer frames 21 and 22 by screws 24 so that the neutron lens can be assembled. FIGS. 5A and 5B show a structure of a plate member 25 that constitutes the body part 20. To assemble the body part 20, many plate members 25 that each have a hole 32 at the center thereof are multi-layered. The plate member at the higher position has the larger hole at the center thereof, and the plate member at the bottom position does not have the hole at the center thereof. Accordingly, the body part 20 has cone-shaped hollow at the center. In the example of FIG. 4, the body part 20 is constituted by 33 plate members 25 that are multi-layered. The reference numerals 33a through 33d designate holes for pins 23. In FIGS. 5A and 5B, annular protrusions 31 of which sections are triangle-shaped are formed successively on a thin plate in the radial direction of the thin plate to configure the plate member 25. An inclining surface 31a of the annular protrusion 31 has a triangle-shaped section, provides an incident surface inclined with respect to a beam axis of the incident neutron beam, and faces the inside of the concentric circles, that is, the center axis of the neutron lens. The neutron beam that enters the neutron lens shown in FIGS. 4, 5A and 5B in parallel with the axis of the neutron lens obliquely enters the inclining surface of the annular protrusion 31 formed on the plate member. For this reason, the neutron beam is deflected toward the center axis of the neutron lens. A part of the neutron beam that enters the center part of the neutron lens penetrates through the relatively small number of the annular protrusions to be deflected by a small angle. On the other hand, a part of the neutron beam that enters the peripheral part of the neutron lens penetrates through the relatively large number of the annular protrusions to be deflected by a large angle. As a result, the neutron lens performs a function similar to that of a convex lens in an optical system, and thus, can focus the neutron beam on a minute region. Contrary to the example of FIG. 5, if the inclining surfaces 31a of the annular protrusions 31 are formed to face the outer side of the concentric circles, the neutron lens can perform a function similar to that of a concave lens, and can force the neutron beam to diverge with the same configuration as that of FIG. 4. As described above, the plate member 25 need be made of a material that has a refraction index of less than 1 for a neutron beam. This material includes oxygen O, carbon C, beryllium Be and fluorine F among those having naturally occurring isotopic concentrations, and deuterium D among enriched isotopes. Specifically, the material of the plate member 25 is polytetrafluoroethylene. (PTFE), quartz, MgF2, lead glass, glassy carbon, polyethylene deuteride formed by replacing hydrogen of polyethylene with deuterium, or the like. Among these materials, quartz, MgF2, lead glass, and glassy carbon (hereinbelow, simply referred to as carbon) are relatively easily available, and desirably, the plate member is formed from the carbon plate. However, the carbon is hard and fragile, so that the edge part of the annular protrusion is broken by usual machining such as cutting. For this reason, there is a problem in that the material cannot be machined to have a desired shape. In other words, since it is necessary to form the neutron lens by multi-layering many plate members 25, the thinner plate member 25 is better to downsize the neutron lens. For example, desirably, the plate member 25 is about 1 mm in thickness. However, if carbon plate is made thin, the carbon plate is broken by a slight machining resistance. Furthermore, to accurately deflect the neutron beam, it is necessary to raise accuracy of the inclining surface 31a of the annular protrusion 31. In addition, to increase penetration efficiency of the neutron beam while suppressing diffused reflection of the neutron beam on the surface of the neutron lens, the inclining surface 31a need be finished to have a surface roughness near a mirror surface. In order to solve the above problems, the inventor of the present invention et al devised a method for machining a neutron lens and filed a patent application of this method (refer to Japanese Laid-Open Patent Publication No. 2001-062691). According to this method, as schematically shown in FIG. 6, one or more tapered surfaces 33a of a grinding wheel makes with each other an angle that is sharper than an angle of a V-shaped groove formed on the surface of the neutron lens member 32. The grinding wheel 33 is positioned by a grinding wheel driving machine 34 such that the axis of the grinding wheel 33 is tilted from the rotational axis of the neutron lens member 32. At this position, the tilting angle of the axis of the grinding wheel is changed such that the grinding wheel slightly swings. However, in this machining method, it is difficult to avoid change of a sectional shape of the tool caused by frictional wear. As a result, sectional shapes of the minute grooves are changed, and thereby, it also becomes difficult to control a surface roughness of the optical surface of the device. Consequently, neutron beam controlling performance of the device is lowered, a cost for correcting the changed shape of the tool is required, and machining efficiency is deteriorated. In order to solve the above problems, the present invention was made. It is an object of the present invention to provide a neutron beam controlling apparatus that can efficiently perform converging and diverging of a neutron beam, wherein the neutron beam controlling apparatus is made of a material (for example, hard and fragile glassy carbon) having a refractive index of less than 1 for a neutron beam. It is also an object of the present invention to provide a method for manufacturing the neutron beam controlling apparatus. According to the present invention, there is provided an apparatus for controlling a neutron beam, comprising a plurality of columnar prisms (1) that are made of a material having a refractive index of less than 1 for a neutron beam, and are arranged so as to be multi-layered. Thereby, the columnar prisms can be machined so as to have the sectional surfaces and the surface roughness of the respective columnar prisms with high accuracy and/or high quality. It is possible, therefore, to configure the neutron lens that does not have a rounded part and a broken part at an end portion and an acute-angled portion of the neutron lens. According to a preferred embodiment of the present invention, the columnar prisms 1 each have an approximately right-triangle-shaped section, and are three-dimensionally multi-layered such that respective surfaces (1a, 1b, 1c) of the columnar prisms are in parallel to one another. Thereby, it is possible to deflect the neutron beam that passes through two surfaces (1a, 1b) of each columnar prism (1). Accordingly, a plurality of the multi-layered columnar prisms can repeatedly deflect the neutron beam. As a result, the neutron beam can be largely deflected. Preferably, oblique surfaces of the multi-layered columnar prisms are in parallel to one another, and face in the same direction so as to approximately form a triangular prism as a whole. Thereby, a part of the neutron beam that enters a low-height part of the triangular prism (2) passes through the relatively small number of the columnar prisms (1) so as to be deflected by a small angle. On the other hand, a part of the neutron beam that enters a high-height part of the triangular prism (2) passes through the relatively large number of the columnar prisms (1) so as to be deflected by a large angle. In this manner, the triangular prism (2) performs a function similar to that of a convex lens in an optical system, and thus, can focus the neutron beam on a minute region. Furthermore, the apparatus for controlling the neutron beam preferably comprises a plurality of the above-mentioned triangular prisms arranged such that oblique surfaces respectively constituting the triangular prisms cross each other. Thereby, a plurality of the triangular prisms can focus the neutron beam on a minute region so as to multiply intensity of the neutron beam. Preferably, the columnar prisms 1 each have an approximately right-triangle-shaped section, the apparatus for controlling the neutron beam comprises a plurality of horizontal prism plates (3) each of which includes the columnar prisms horizontally arranged such that respective surfaces (1a, 1b, 1c) of the columnar prisms are in parallel to one another, and the plurality of horizontal prism plates are vertically multi-layered so as to be horizontally turned alternately by 90 degrees. Thereby, it is possible to deflect the neutron beam alternately in the different directions that differ by 90 degrees. As a result, it is possible to focus the neutron beam on one point as a whole. Further, the apparatus for controlling the neutron beam preferably comprises a positioning member that sets the plurality of columnar prisms at predetermined positions, respectively. By the positioning member (4), it is possible to easily set a plurality of the columnar prisms at predetermined positions, respectively. According to the present invention, there is also provided a method for manufacturing a neutron beam controlling apparatus, comprising: forming a plurality of columnar prisms that are made of a material having a refractive index of less than 1 for a neutron beam, and each have an approximately right-triangle-shaped section; and three-dimensionally multi-layering the plurality of columnar prisms such that respective surfaces of the columnar prisms are in parallel to one another. According to a preferred embodiment of the present invention, the forming of the plurality of columnar prisms is performed by any of molding, extruding, cutting, grinding, whetting or any combination thereof. Thereby, the columnar prisms can be machined so as to have the sectional surfaces and the surface roughness of the respective columnar prisms with high accuracy and/or high quality. It is possible, therefore, to configure the neutron lens that does not have a rounded part and a broken part at an end portion and an acute-angled portion of the neutron lens. In addition, forming the plurality of prisms preferably comprises: making stick-shaped members (5) of the above-mentioned material; setting the stick-shaped members (5) in a plurality of grooves formed on a jig (6), the grooves having the same shape; and flattening upper surfaces of the grooves at the same time. Preferably, the flattening of the upper surfaces of the grooves is performed by ELID grinding. By this flattening process, it is possible to efficiently form the columnar prisms (1) that have the same shape and do not have a rounded part and a broken part. Furthermore, preferably, the flattening of the upper surfaces of the grooves is performed by a straight grinding wheel, a cup grinding wheel or a lap. By the application of the ELID grinding, it is possible to form the columnar prisms (1) of which surfaces have a surface roughness of a high quality near that of a mirror surface. Other object and advantageous features of the present invention will become apparent from the following description with reference to the attached drawings. In the following, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numeral is attached to the common part or element, and the overlapping description is omitted. FIGS. 7A, 7B, 7C and 7D show a principle of an apparatus for controlling a neutron beam according to the present invention. FIG. 7A shows the entire configuration of the apparatus, FIG. 7B is the operational illustration, FIG. 7C is the single operational illustration, and FIG. 7D shows the effect. As shown in these drawings, the neutron beam controlling apparatus includes a plurality of columnar prisms 1 (neutron prisms in the drawings). The columnar prism 1 is made of a material having a refractive index of less than 1 for a neutron beam. The material of the columnar prism 1 includes oxygen O, carbon C, beryllium Be and fluorine F among those having naturally occurring isotopic concentrations, and deuterium D among enriched isotopes. Specifically, the material of the columnar prism 1 includes polytetrafluoroethylene (PTFE), quartz, MgF2, lead glass, glassy carbon, and polyethylene deuteride formed by replacing hydrogen of polyethylene with deuterium. Hereinbelow, the material having a refractive index of less than 1 for the neutron beam is referred to as “neutron deflecting material”. The section of the columnar prism 1 is approximately right-triangle-shaped. The columnar prisms 1 are three-dimensionally multi-layered such that sides 1a, 1b and 1c of the triangles of the prisms 1 are respectively in parallel to one another. An angle β that the oblique surface (or side) 1a makes with the bottom surface (or side) 1c is arbitrary. The angle β enables the neutron beam to be deflected toward the oblique surface 1a as shown in FIG. 7C. This deflection angle (θ′−θ is slight, but a large number of layers of prisms 1 (“n” number of layers in the drawings) are multi-layered so that a large deflection angle δ as a whole can be obtained as shown in FIGS. 7A and 7B. Further, horizontal arranging of the columnar prisms 1 achieves the deflecting performance equal to that of a single large prism as shown in FIG. 7D, and an amount of neutrons absorbed by the material can be reduced. FIGS. 8A and 8B schematically show one example of a manner of shaping columnar prisms according to the present invention. FIGS. 9A, 9B and 9C schematically show one example of a manner of multi-layering columnar prisms according to the present invention. As shown in FIGS. 8A, 8B, 9A, 9B and 9C, a method for manufacturing the neutron beam controlling apparatus according to the present invention includes a shaping step of shaping a plurality of columnar prisms 1 that are made of the neutron deflecting material and have an approximately right-triangle-shaped section. Further, the method for manufacturing the neutron beam controlling apparatus includes a multi-layering step of three-dimensionally multi-layering columnar prisms 1 such that the surfaces of the columnar prisms are respectively in parallel to one another. In the shaping step, stick-shaped members 5 are made of the neutron deflecting material. To make the stick-shaped members 5 of the neutron deflecting material, any of molding, extruding, cutting, grinding and whetting or any combination thereof may be performed. Next, as shown in FIG. 8A, the stick-shaped members 5 are respectively set in a plurality of grooves 6a that have the same shape and are formed on a jig 6. At this time, if necessary, an adhesive agent or the like may be used. Thereafter, as shown in FIG. 8B, flattening is simultaneously performed on upper surfaces (parts) of the respective grooves 6a. In FIG. 8B, the reference numeral 7 designates an ELID grinding wheel, and the reference numeral 8 designates an ELID electrode. In other words, in this example, to form oblique surfaces la of the columnar prisms 1, electrolytic in-process dressing grinding (ELID grinding) is performed by applying an electrolyzing voltage between the grinding wheel 7 and the electrode 8 while supplying conductive grinding liquid between the grinding wheel 7 and the electrode 8. The ELID grinding is also performed for the other surfaces 1b and 1c by using other jigs 6. Thereby, the ELID grinding wheel 7 always having an optimum toothed state can be used even when the ELID grinding wheel 7 includes ultra-minute grinding particles. Furthermore, by the ELID grinding, the machining can be performed at a low machining resistance, at high efficiency, with high accuracy, and it is possible to achieve mirror surfaces having fine surface roughness. The grinding wheel 7 in FIG. 8B is not limited to a straight grinding wheel, and may be a cup grinding wheel. Further, instead of machining by the grinding wheel 7, lapping may be performed by using a lap. The shaping step is not limited to the ELID grinding, and may be any of molding, extruding cutting, grinding and whetting, or any combination thereof for forming the columnar prisms 1 from the neutron deflecting material. Next, in the multi-layering step, by using a positioning member 4 shown in FIG. 9B, the respective columnar prisms 1 are set at predetermined positions. A material (for example, aluminum) having high permeability for a neutron is used as a material of the positioning member 4. After the respective columnar prisms 1 are set in each positioning member 4, the positioning members 4 are multi-layered so that the columnar prisms 1 can be three-dimensionally multi-layered as shown in FIG. 9C. The positioning member 4 is not inevitable, and the multi-layering of the columnar prisms 1 may be performed without using the positioning member 4 in accordance with a necessity. FIG. 10 shows a first embodiment of the neutron beam controlling apparatus according to the present invention. In FIG. 10, the section of each columnar prism 1 is approximately right-triangle-shaped. The columnar prisms 1 are horizontally and vertically multi-layered such that the surfaces 1a, 1b and 1c of the prisms 1 are respectively in parallel to one another. In this manner, an entire cubic block is formed. There are gaps between the columnar prisms 1, and if necessary, the gaps may be filled with inert gas, or be held in a vacuumized state. Alternatively, the gaps may be filled with a material that does not absorb a neutron beam to fix the columnar prisms 1. With this configuration, by a plurality of columnar prisms 1, a neutron beam that passes through the surfaces 1a and 1b of the columnar prisms 1 can be repeatedly deflected. As a result, it is possible to largely deflect the neutron beam. FIG. 11 shows a second embodiment of the neutron beam controlling apparatus according to the present invention. In FIG. 11, the columnar prisms 1 are multi-layered such that the oblique surfaces 1a of the right triangles of the columnar prisms 1 are in parallel to one another, and face in the same direction. In this manner, the columnar prism 1 constitutes an entire triangular prism 2. In this example, the neutron beam controlling apparatus includes two triangular prisms 2 that are arranged such that oblique surfaces of the triangular prisms 2 constituted by the oblique surfaces 1a of the prisms 1 crosses each other. With this configuration, the triangular prisms 2 can focus the neutron beam on a minute region to multiply intensity of the neutron beam. FIG. 12 shows a third embodiment of the neutron beam controlling apparatus according to the present invention. In FIG. 12, the neutron beam controlling apparatus includes four triangular prisms 3 similar to or same as that of FIG. 11. Two triangular prisms 3 at the lower side of FIG. 12 are arranged such that the oblique surfaces of the triangular prisms 3 constituted by the oblique surfaces 1a of the prisms 1 cross each other. The triangular prisms 3 at the upper side are arranged so as to be turned by 90 degrees from the triangular prisms 2 at the lower side. With this configuration, the neutron beam can be deflected alternately in the different directions that differ by 90 degrees. In this manner, the entire neutron beam controlling apparatus can focus the neutron beam on one point. As described above, the present invention has the following advantages. (1) The machining of the columnar prisms can be performed such that the sectional surfaces and the surface roughness of the columnar prisms have high accuracy and/or high quality. It is possible, therefore, to configure the neutron lens that does not have a rounded part and a broken part at the end portion and an acute-angled bottom portion of the neuron lens. (2) The multi-layered columnar prisms 1 can perform the same function as that of a convex lens in an optical system so as to focus the neutron lens on a minute region. It is possible, therefore, to multiply the intensity of the neutron beam, and to further focus the neutron beam on one point. (4) Use of the positioning member 4 enables a plurality of columnar prisms to be easily set at predetermined positions. (5) The machining of the columnar prisms 1 can be relatively easily machined at high efficiency such that the sectional shape and the surface roughness of each columnar prism 1 have high accuracy and/or high quality. It is possible, therefore, to configure the neutron lens that does not have a rounded part and a broken part at the end portion and the acute-angled bottom portion of the neuron lens. Thus, according to the neutron beam controlling apparatus and the method for manufacturing the same, the neutron beam controlling apparatus is configured by a material having a refractive index of less than 1 for a neutron beam. An example of the material is hard and fragile glassy carbon. Thereby, the neutron beam controlling apparatus has an excellent advantage to efficiently perform converging or diverging of the neutron beam. The present invention is described in the above by the several preferred embodiments. However, it can be understood that the scope of the present invention is not limited to these embodiments. Thus, the scope of the present invention includes all improvements, modifications and equivalents that do not depart from the scope of claims.
050248057	abstract	Metal surfaces having an oxide coating containing radioactive substances, such as the primary system of a pressurized water reactor, are decontaminated by passage thereover of a decontamination solution containing a weak chelating agent, such as nitrilotriacetic acid, and a ferrous salt, such as ferrous glutonate. The weak chelating agent is present in an aqueous solution in an amount of 0.1 to 2.0 percent by weight and the ferrous salt in an amount to provide 50 to 500 parts per million iron based on the weight of the solution. The solution, after contact with the metal surfaces is regenerated by an ion exchange resin or, preferably, by electrolysis.
	claims	1. A epoxy resin composition which, when cured, provides a transparent product having a high neutron shielding capability, said epoxy resin composition comprising a 4,4xe2x80x2-isopropylidenecyclohexanol type epoxy resin, without any non-transparent inorganic substance, and a hardener, said epoxy resin composition having a viscosity at ambient temperatures of less than 7000 mPaxc2x7s and being curable at said temperatures. 2. The epoxy resin composition of claim 1 , wherein said hardener is selected from the group consisting of aliphatic amine, alicyclic amine, heterocyclic amine, heterocyclic diamine and modified products thereof. claim 1 3. A transparent neutron shield material produced from the epoxy resin composition which, when cured, provides a transparent product having a high neutron shielding capability, said epoxy resin composition comprising a 4,4xe2x80x2-isopropylidenecyclohexanol type epoxy resin, without any non-transparent inorganic sustance, and a hardener, said epoxy resin composition having a viscosity at ambient temperatures of less than 7000 mPaxc2x7s and being curable at said temperatures. 4. The transparent neutron shield material of claim 3 , wherein said hardener is selected from the group consisting of aliphatic amine, alicyclic amine, heterocyclic amine, heterocyclic diamine and modified products thereof. claim 3 5. The transparent neutron shield material of claim 3 comprising a single body comprising a transparent mold and said epoxy resin composition. claim 3
	abstract	The invention comprises intensity control of a charged particle beam acceleration, extraction, and/or targeting method and apparatus used in conjunction with charged particle beam radiation therapy of cancerous tumors. Particularly, intensity of a charged particle stream of a synchrotron is described. Intensity control is described in combination with turning magnets, edge focusing magnets, concentrating magnetic field magnets, winding and control coils, and extraction elements of the synchrotron. The system reduces the overall size of the synchrotron, provides a tightly controlled proton beam, directly reduces the size of required magnetic fields, directly reduces required operating power, and allows continual acceleration of protons in a synchrotron even during a process of extracting protons from the synchrotron.
050230484	abstract	The fuel rod comprises a sheath having an inner tubular layer and an outer surface layer composed of zirconium alloys which differ from each other. The surface layer, whose thickness is between 10 to 25% of the total thickness of the wall of the sheath, is constituted by a zirconium-base alloy containing by weight 0.35 to 0.65% tin, 0.20 to 0.65% iron, 0.09 to 0.16% oxygen and niobium in a proportion of 0.35 to 0.65% or vanadium in a proportion of 0.25 to 0.35%. The inner layer may be constituted by an alloy such as Zircaloy 4 or a zirconium-niobium alloy.
055442137	claims	1. A method of holding a mask on a mask, chuck, said method comprising: providing a mask in which V-shaped linear groove portions are disposed at not less than three positions on a holding surface of the mask; providing a mask chuck in which projecting portions are disposed at not less than three positions on a holding plane of the mask chuck; aligning the V-shaped linear groove portions of the mask with the projecting portions of the mask chuck; and engaging the V-shaped linear groove portions of the mask with corresponding projecting portions of the mask chuck to hold the mask on the mask chuck. providing a mask in which projecting portions are disposed at not less than three positions on a holding surface of the mask; providing a mask chuck in which V-shaped linear groove portions are disposed at not less than three positions on a holding plane of the mask chuck; aligning the projecting portions of the mask with the V-shaped linear groove portions of the mask chuck; and engaging the projecting portions of the mask with corresponding V-shaped linear groove portions of the mask chuck to hold the mask on the mask chuck. a transfer pattern; and a mask support frame having a holding surface, said mask support frame comprising one of V-shaped linear groove portions and projecting portions disposed at not less than three positions on the holding surface, wherein one of the V-shaped linear groove portions and the projecting portions at the three positions on said mask support frame respectively engage with corresponding ones of projecting portions and V-shaped linear groove portions, respectively, disposed at not less than three positions on a holding plane of a mask chuck when said mask is held on the mask chuck. a holding plane for holding the mask; means for attracting the mask to said holding plane; and one of projecting portions and V-shaped linear groove portions disposed at not less than three positions on said holding plane, wherein one of the projecting portions and the V-shaped linear groove portions disposed at the three positions on said holding plane respectively engage with corresponding ones of V-shaped linear groove portions and projecting portions, respectively, disposed at not less than three positions on the mask when the mask is held on said holding plane. a mask chuck for holding a mask, said mask chuck including a mask chuck holding plane having one of projecting portions and V-shaped linear groove portions disposed at not less than three positions thereon; a mask including a mask holding plane having one of V-shaped linear groove portions and projecting portions, respectively corresponding to the projecting portions and the V-shaped linear groove portions of said mask chuck being disposed at not less than three positions on the mask holding plane, wherein corresponding portions of said mask chuck engage with those of said mask when said mask is held on said mask chuck; and exposure means for transferring a pattern of said mask held on said mask chuck onto a wafer by exposure. 2. A mask holding method according to claim 1, wherein the mask is an X-ray mask. 3. A mask holding method according to claim 1, wherein the positions on the holding surface of the mask are equidistant and the positions on the holding plane of the mask chuck are equidistant. 4. A method of holding a mask on a mask chuck, said method comprising: 5. A mask holding method according to claim 4, wherein the mask is an X-ray mask. 6. A mask holding method according to claim 4, wherein the positions on the holding surface of the mask are equidistant and the positions on the holding plane of the mask chuck are equidistant. 7. A mask, comprising: 8. A mask according to claim 7, wherein said mask is an X-ray mask. 9. A mask according to claim 7, wherein the positions on the holding surface of the mask are equidistant and the positions on the holding plane of the mask chuck are equidistant. 10. A mask chuck for holding a mask, comprising: 11. A mask chuck according to claim 10, wherein the mask is an X-ray mask. 12. A mask chuck according to claim 10, wherein the positions on the holding surface of the mask are equidistant and the positions on the holding plane of the mask chuck are equidistant. 13. An exposure apparatus, comprising: 14. An exposure apparatus according to claim 13, wherein said exposure means performs exposure transfer by using X-rays. 15. An exposure apparatus according to claim 13, wherein the positions on the holding surface of the mask are equidistant and the positions on the holding plane of the mask chuck are equidistant.
059178752	summary	The present invention relates to apparatus for inspecting nuclear fuel assemblies and, in particular with apparatus which will rectify the tendency of a fuel assembly to incline from the perpendicular. Typically, a nuclear fuel assembly comprises a plurality of fuel rods and control rod guide thimbles held in parallel relationship by spacer grids arranged at spaced locations along the fuel rods and secured to the guide thimbles. Attached to opposite ends of the guide thimbles are top and bottom nozzles. When installed in the core of a nuclear reactor, the fuel assemblies are arranged in close proximity to one another between upper and lower core plates. Since the fuel assemblies in the reactor core are closely spaced, it is essential that each fuel assembly upon completion satisfies stringent quality control procedures, particularly with regard to dimensional accuracy. It is particularly important to ensure that the fuel assembly stands truly perpendicular when the bottom nozzle of an assembly is supported by a horizontal surface. A known technique for ensuring perpendicularity of a fuel assembly involves measuring the out of alignment of the assembly from the perpendicular using a theodilite or similar instrument and assessing how much material requires to be removed from the lower surfaces of the bottom nozzle. The fuel assembly is then placed in a vertical position and the required amount of material is removed by grinding one or more of the bottom nozzle surfaces. After the grinding operation, the fuel assembly is placed on a horizontal surface and remeasured. If necessary, further material is ground from the bottom nozzle until the desired verticality of the fuel assembly is attained. This technique for rectifying the tilt of a fuel assembly is not satisfactory in that it involves several time-consuming mechanical handling operations to move the assembly between the measuring and grinding positions. According to the invention there is provided apparatus for rectifying the tendency of a nuclear fuel assembly to incline from the perpendicular, the fuel assembly having interconnected upper and lower support members, the apparatus comprising an upper locating means for locating the upper support member and a base assembly adapted to support said lower support member whereby the fuel assembly extends perpendicularly between the upper locating means and said base assembly, elevating means incorporated in said base assembly, the elevating means being operable to engage the lower support member and raise the fuel assembly, the base assembly further including material removal means operable to remove material from a lower surface of the lower support member when raised by the elevating means whereby said lower surface is made to lie in a horizontal plane. Preferably the base assembly includes a support surface on which the lower surface of the lower support member rests, the elevating means being operable to raise the lower surface above the support surface. Advantageously the elevating means moves along an axis coaxial with a longitudinal central axis of the fuel assembly. The lower support surface may comprise a plurality of lower surfaces, the material removal means being operable to remove material from each of the lower surfaces, whereby each of the lower surfaces is made to lie in said horizontal plane. The elevating means preferably comprises a gimbal mounting arrangement which includes a gimbal member movably supported on a gimbal mount and arranged to engage the lower support member. Preferably the gimbal member has a spherically-shaped female bearing portion which receives a spherically-shaped male bearing portion provided on the gimbal mount. In a preferred embodiment the material removal means comprises a grinding wheel, the grinding wheel being mounted on a rotor member arranged for rotation about the axis along which the elevating means moves. Advantageously the grinding wheel is radially spaced from the axis about which the rotor member rotates, whereby the grinding wheel is able to remove material from each of the lower surfaces during one revolution of the rotor member. Preferably the base assembly includes a vertical post, the rotor member being arranged to rotate about the post, and wherein pressurised air bearings are provided between the post and the rotor member. The base assembly may include a stationary gear wheel arranged coaxially with respect to the axis along with the elevating means moves, the gear wheel having gear teeth provided around the periphery thereof, and a drive motor mounted on said rotor member, the drive motor having an output gear wheel arranged to mesh with the stationary gear wheel. Drive means are preferably provided for moving the grinding wheel along its axis of rotation. The drive means for moving the grinding wheel along its axis of rotation may comprise a stepper motor which moves the grinding wheel along said axis of rotation in incremental steps. Preferably the base assembly includes at least one locating pin and actuator means for extending and retracting the locating pin along a vertical axis, whereby the locating pin can be inserted into or retracted from a locating hole provided in said lower support member. The upper locating means preferably includes at least one upper locating pin and further actuating means for extending and retracting said upper locating pin along a vertical axis, whereby the upper locating pin can be inserted into or retracted from an upper locating hole provided in the upper support member. The upper locating pin may comprise a larger diameter portion of substantially the same diameter as that of the upper locating hole and a reduced diameter end portion, the further actuator means being operable to insert the larger diameter portion or the reduced diameter end portion into the upper locating hole. Advantageously the base assembly includes measuring means for determining the weight of the fuel assembly. The measuring means preferably comprises a load cell located beneath the elevating means.
	claims	1. A portable radiographic imaging apparatus for fluoroscopy comprising:a wheeled transport frame;a C-shaped support arm mounted on the frame;radiation sources attached to a fixed end of the support arm;a radiation detector attached to a retractable end of the support arm when the retractable end is extended outward from the support arm, the retractable end opposite the fixed end, wherein the radiation sources comprise two or more radiation sources that are individually energizable to emit a radiation beam toward the retractable end, the imaging detector is removable from the retractable end for free-standing operation, and wherein the retractable end is configured to retract into an interior space of the support arm;a rotatable switching actuator that is configured to replace one of the radiation sources by simultaneously rotating into position a new radiation source while rotating out of position said replaced one of the radiation sources and to align the radiation beams from each of the new and replaced radiation sources along the same optical path;a temperature sensor that provides a signal indicative of a temperature near an energized radiation source; anda processor configured to monitor the signal from the temperature sensor, and to control energization of the two or more radiation sources according to the monitored signal. 2. The portable radiographic imaging apparatus for fluoroscopy according to claim 1, further comprising a collimator, wherein the processor is configured to detect an orientation of the radiation detector relative to one of the radiation sources and to adjust an aperture of the collimator to shape the radiation beam for incidence on a predetermined area of the radiation detector. 3. The portable radiographic imaging apparatus of claim 1, further comprising a collimator having an aperture to shape an x-ray beam emitted by the radiation sources, the collimator including a plurality of collimator blades to define a non-rectangular shape of the aperture. 4. The portable radiographic imaging apparatus of claim 1, wherein the radiation detector is configured to capture radiographic images at a rate greater than one image per second. 5. The portable radiographic imaging apparatus of claim 1, wherein the processor is further configured to wirelessly communicate with the radiation detector, and wherein the radiation detector comprises a wireless transmitter to transmit radiographic images to the processor. 6. The portable radiographic imaging apparatus of claim 1, wherein the retractable end comprises jointed sections that telescope inward and outward, and wherein the detector and radiation source cooperate to expose and acquire radiographic image data according to a synchronization signal. 7. The portable radiographic imaging apparatus of claim 1, wherein the retractable end is configured to retract automatically when the radiation detector is removed therefrom. 8. A portable radiographic imaging apparatus comprising:a transport frame having wheels to rollably transport the portable radiographic imaging apparatus;a C-shaped support arm mounted on the transport frame;radiation sources attached to a fixed end of the support arm;a radiation detector attached to a retractable end of the support arm, the retractable end of the support arm opposite the fixed end of the support arm; anda rotatable actuator attached to the fixed end of the support arm, the rotatable actuator configured to replace one of the radiation sources by simultaneously rotating into an imaging position a new radiation source while rotating out of the imaging position the replaced one of the radiation sources, and to align the radiation beams emitted from each of the new and replaced radiation sources along the same optical path when in the imaging position. 9. The portable radiographic imaging apparatus of claim 8, wherein the radiation sources comprise two or more radiation sources that are individually energizable to emit a radiation beam toward the retractable end. 10. The portable radiographic imaging apparatus of claim 8, wherein the imaging detector is removable from the retractable end for free-standing operation. 11. The portable radiographic imaging apparatus of claim 10, wherein the retractable end is configured to retract into an interior space of the support arm. 12. The portable radiographic imaging apparatus of claim 8, further comprising a temperature sensor configured to provide a signal indicative of a temperature near an energized radiation source. 13. The portable radiographic imaging apparatus of claim 12, further comprising a processor configured to monitor the signal from the temperature sensor, and to control activation of the radiation sources in response to the monitored signal. 14. The portable radiographic imaging apparatus of claim 8, further comprising a collimator having an adjustable aperture to shape the radiation beams emitted from the radiation sources for incidence on a predetermined area of the radiation detector. 15. The portable radiographic imaging apparatus of claim 14, wherein the collimator comprises individual collimator blades configured to define a non-rectangular shape of the adjustable aperture. 16. The portable radiographic imaging apparatus of claim 8, wherein the radiation detector is configured to capture radiographic images at a rate greater than one image per second. 17. The portable radiographic imaging apparatus of claim 16, wherein the radiation detector comprises a wireless transmitter to transmit the captured radiographic images wirelessly during free-standing operation. 18. The portable radiographic imaging apparatus of claim 8, wherein the retractable end of the support arm comprises telescoping extendable and retractable sections that extend inward and outward. 19. A method of operating a portable radiographic imaging apparatus, the method comprising:attaching an adjustable support arm to the portable radiographic imaging apparatus;attaching radiation sources to a first end of the support arm;transporting the portable radiographic imaging apparatus to a position adjacent a patient in a bed using wheels attached to the portable radiographic imaging apparatus;positioning a radiation detector on one side of the patient;adjusting an imaging position of a first one of the radiation sources to align a central axis of a radiation beam emitted by the first one of the radiation sources toward the detector; andsimultaneously rotating into the imaging position a second one of the radiation sources while rotating out of the imaging position the first one of the radiation sources, and aligning a central axis of a radiation beam emitted by the second one of the radiation sources with the central axis of the radiation beam emitted by the first one of the radiation sources, wherein the first and second radiation sources are rotated about a common axis. 20. The method of claim 19, further comprising attaching the radiation detector to a second end of the support arm opposite the first end of the support arm before the step of positioning the radiation detector.
045086770	abstract	A self-contained modular nuclear reactor which can be prefabricated at a factory location, nuclear-certified at the factory, transported to a field location for final assembly and connection to a large-scale electric-power generating facility. The modular reactor includes a prefabricated nuclear heat supply module and a plurality of shell segments which can be assembled about the heat supply module and which provide a form for the pouring and curing of a cementatious biological shield about the heat supply module. The modular reactor includes passive shutdown heat removal systems sufficient to render the reactor safe in an emergency. A large-scale power plant arrangement is disclosed which incorporates a plurality of the modular reactors.
050154362	description	DESCRIPTION OF THE PREFERRED EMBODIMENT Embodiment 1 In FIG. 1, steam generated in a reactor 10 actuates a turbine 1 and is then condensed in a condenser 2; when condensed water including corrosion products is passed from the condenser 2 through condensed water pre-filter 4 and condensed water desalter 5 by means of condensed water pump 3, most portion of the corrosion products are removed. The purified water is flowed through feed water pump 6, low pressure feed water heater 7, pressurizing pump 8 and high pressure feed water heater 9 into nuclear reactor pressure vessel 10. Corrosion products carried into pressure vessel 10 were composed of corrosion product which had not been removed in condensed water desalter 5 and, in addition, Ni or the like which was mainly generated due to corrosion of high pressure feed water heater 9. The amount of the corrosion products carried into pressure vessel was measured by analysing a specimen picked through a sampling line 11 by means of a concentration measuring means 12. The sampling of specimen and the measuring of iron concentration existing in the specimen were effected in the manner explained below. A specimen holder having a sheet of millipore filter of 0.45 .mu.m in pore size and two or three sheets of positive iron-exchanging papers was attached to a sampling line 11. Then, in order to catch iron clad contained in the reactor-cooling water, the cooling water was made to flow through the specimen holder disposed in the sampling line 11 at a flow rate of about 100 ml so that an accumulation flow amount of the cooling water flowing therethrough was in a range of 100 to 150 litters. The iron clad caught by the millipore filter was dissolved in a heated hydrochloric acid of 200 ml in volume and 6N in concentration and then distilled water was added thereto to provide a constant volume. The positive ion-exchanging paper for catching iron ion was immersed in hydrochloric acid of 15 ml in volume and 2N in concentration for a period of not less than 5 minutes, this treatment being repeated two or three times, and finally an iron ion-containing solution of a constant volume was prepared by use of hydrochloric acid of 2N in concentration. The resultant specimen solution having been thus prepared was measured by use of a usually used atomic absorption spectro photometer to thereby obtain an iron concentration, the specific process of the atomic absorption spectro photometry being prescribed in JIS K 0121. In the present invention, the measured iron concentration was converted into iron accumulation rate on fuel rod through calculator 13 while referring to plant parameters stored in a data memory 14 by use of the following equation. ##EQU1## where, .alpha.: iron accumulation rate on fuel rod (mg/m.sup.2 /hr) C: iron concentration in feed water (ppb) PA1 F: nominal feed water flow rate (t/hr) PA1 S: fuel rod surface area (m.sup.2) PA1 P: plant output power at measurement time (MW) PA1 P.sub.max : rated output power (MW) When iron accumulation rate .alpha. is smaller than 0.5, the iron concentration in cooling water should be increased correspondingly to the amount (0.5-.alpha.), namely, iron concentration to be added was calculated by the following equation 2: ##EQU2## where, .delta.C: lower limit of iron concentration in feed water to be added Iron amount to be injected from an iron-injecting means 15 correspondingly to the above lower limit value .delta.C was obtained as .delta.C.times.F. However, actually, the iron amount to be poured is required to be further added by an iron amount which compensates the iron adhering to structures and tubings of reactor. Since experiences in the past showed that 80-90% of iron carried into reactor adhered to fuel rod, the lower limit of the iron amount to be further added may be determined as 10-20% of (C+.delta.C). A suitable amount of iron was injected from iron pouring means 15 under control of flow rate control valve 16. The ion-injecting device 15 was provided with a device for generating electrolytic iron disclosed in Japanese Utility Model Unexamined Publication No. 63-135200. The construction of the electrolytic iron-generating device used in the embodiment is shown in FIG. 8, which device comprises a water tank 21 operating as a source of water containing carbonic ion, an electrolytic cell 22 provided with an iron sheet electrode 25 operatively connected to the water tank 21 so as to receive the CO.sub.2 gas, and a device 23 for discharging cabonic ion contained in iron ion-including water generated in the electrolytic cell 22. By using the electrolytic iron-generating device, water containing iron ion of about 100 ppm was obtained under such conditions that CO.sub.2 gas was fed to the water reservoir 21 through a nozzle 24 at a rate of 50 litter/hour to generate the carbonic ion in water, N.sub.2 gas being fed to the electrolytic iron-generating device 23 at a rate of 100 litter/hour through a nozzle 26 for agitating water in the vicinity of the iron sheet electrode, N.sub.2 gas being fed in the carbonic ion-removing device 23 at a rate of 200 litter/hour through a nozzle 27 so as to remove carbonic ion contained in the iron ion-including water, electrolytic current being 20 A at 100 V, degased pure water being fed to the water reservoir 21 at a rate of 60 litter/hour. By controlling the flow rate of the resultant ion ion-including water through a flow control valve, it was possible to increase ion concentration in feed water by 0.3 to 1.0 ppb in a case of a nuclear power plant of 1100 MWe and 6400 t/h in feed water flow rate. On the other hand, when iron accumulation rate .alpha. obtained from equation (1) is greater than 3, preferably greater than 2 (mg/m.sup.2 /hr), iron concentration in cooling water should be decreased correspondingly to the value (.alpha.-2.0), namely as follows: ##EQU3## where, .delta.C': iron concentration to be decreased in feed water (ppb) The iron accumulation rate on fuel rod can be controlled smaller than 2.0 (mg/m.sup.2 /hr) by decreasing the iron amount to be poured by an amount (.delta.C'.times.F) corresponding to the above .delta.C' by means of flow rate control valve 16, or by stopping the iron injection. In a case of injecting water containing iron ion of 100 ppm in concentration in a nuclear power plant of 1100 MWe class, amount of change in feed flow rate corresponding to .delta.C'.times.F becomes 64 .delta.C' (l/h) (, that is, .delta.C'.times.6400/100). By changing the flow rate by this value, the value of .alpha. becomes in a preferred range of not more than 2.0. However, in a case of relatively high iron concentration, there occurs such unfavorable phenomenon as radioactivity increases due to the increment of iron concentration in feed water. Thus, after the lapse of operating time of 5000 hours, it is preferred to control the injecting rate of the iron ion-containing water so that the .alpha. value may be in a range of 0.5 to 1.0. But, if concentration of iron ion contained in the feed water exceeds a value corresponding to 0.5 regarding the .alpha. value even in a case where the injecting rate of the iron ion-containing water fed into the feed water is zero, it is unnecessary to effect the injecting of the iron ion-containing water into the feed water. Since in this case it becomes impossible to effect the control of ion concentration in the feed water, it is preferred to improve the ability of condensate-purification means. By controlling the iron concentration in feed water between 0.5 and 2.0 (mg/m.sup.2 /hr) as described above, the increase rate of .sup.60 Co concentration can be maintained at a low level. Although the output value (P) of the plant at the time of measuring iron concentration is used for calculating iron accumulation rate .alpha. in equations (1), (2) and (3), it can be replaced by feed water flow rate at the measuring time, as follows: ##EQU4## wherein F' is a feed water flow rate at measuring time (t/hr). MODIFIED EXAMPLE For the above-mentioned embodiment, a modification is possible as described below. In an initial operational stage of first cycle of a new nuclear power plant, the probability of contacting of iron with nickel or with cobalt on fuel rod surface is considered low, because corrosion product is still of a small quantity. Considering this matter, it may be preferable to set the lower limit of iron accumulation rate on fuel rod to be not less than 0.5 until corrosion product is adhered on the whole surface of fuel rod in the initial operational stage of the first cycle. It is effective for maintaining dose rate of primary system at a low level to positively form an iron adhesion layer on fuel rod surface at an early stage of operation, which iron adhesion layer reduces the concentration of radioactive corrosion product in reactor water in a period of time when a rather great quantity of radioactive corrosion product is being adhered to structures or tubings of plant. EMBODIMENT 2 In the nuclear power plant of the second embodiment of the invention in which the accumuration rate of iron accumurated on fuel rods is to be controlled, a relation between a concentration of iron contained in feed water and an accumuration rate of iron on the fuel rod was previously obtained in accordance with parameters inherent in the power plant. Then, as shown in FIG. 4, there was determined a target value for controlling the iron concentration of the feed water with respect to the operating time of the nuclear power plant. In compliance with the target value, an actual iron concentration of the feed water was controlled during the operation of the plant so that the accumulation rate or iron accumulated on the fuel rods was not less than 0.5 mg/m.sup.2 /hr. Specific example is explained below with respect to a nuclear power plant of 1100 MWe. The parameters of the plant were a rated heat output (P.sub.max) of 3300 MWt, a feed water flow rate of 6400 t/h, and a fuel rod surface area of 7000 m.sup.2. Under an assumption of the rated output operating, the control target lower values of .alpha. was determined to be 0.7 till 5000 hours from the commencement of the operating of the plant and to be 0.5 after the lapse of 5000 hours therefrom. Thus, an iron concentration of the feed water was 0.77 ppb till 5000 hours from the commencement of the operating of the plant by calculating from the formula (1) and was 0.55 ppb after 5000 hours therefrom, as shown in FIG. 4. In FIG. 9 there is shown a result of analysis of a simulation with respect to .sup.60 Co ion concentration of feed water in a case of effecting an operating of the plant in accordance with the iron concentration-controlling pattern of FIG. 4. For comparison, in a case where the iron concentration was made to be a constant value of 0.3 ppb during the whole operating period with the result that the iron accumulation rate of the fuel rod (.alpha.) was a constant value of 0.27, there was also effected another simulation to thereby obtain an analysis result shown in FIG. 10. In comparing the results shown in FIGS. 9 and 10, it was found that in the second embodiment of the invention the .sup.60 Co concentration of the feed water was reduced by 20% to 40% in comparison with the case of FIG. 10 where no control of iron concentration was effected. Thus, it was deemed that, after the lapse of 10000 hours from the commencement of the operating of the plant shown above, a dose rate of the surface of piping was about 25 mR/h, while the dose rate was about 35 mR/h in the case of FIG. 10 (, that is, the dose rate in the case of FIG. 10 is higher by about 20% than the case of FIG. 9 of the invention). This difference further increases in a case where iron concentration in the feed water is less than the case of FIG. 10. In a case where a pattern for controlling the concentration of iron contained in the feed water is previously determined, it is unnecessary to calculate the accumulation rate of iron accumurated on the fuel rod after measuring the iron concentration of the feed water, so that the control thereof can be effected in a simple manner while control in response to variation in output can not be effected. As shown in FIG. 4, the iron concentration of the feed water is made to be in a high level during an initial period of the operating cycle of the plant while the iron concentration is made to be in a low level after the lapse of the initial period thereof, so that the fuel rod surface is covered by iron in an early stage in the initial period of the operating cycle to thereby adhere nickel and cobalt (both contained in the feed water) on the fuel rod while changing the nickel and cobalt into chemically stable states such as NiFe.sub.2 O.sub.4 and CoFeO.sub.4. EMBODIMENT 3 Although in the first and second embodiments, a rather rough estimation for .sup.60 Co concentration increase rate is used for controlling the iron concentration in feed water, the relation between iron accumulation rate on fuel rod and .sup.60 Co concentration increase rate in reactor water shown in FIG. 3 has actually a wide variation range. Therefore, in the third embodiment, control method of which is shown in FIG. 5, .sup.60 Co concentration in reactor water, feed water flow rate, operation date as well as iron concentration in feed water are input into the calculator and stored in the memory, and then iron accumulation rate on fuel rod and .sup.60 Co concentration increase rate in reactor water are calculated based on the above data. When the .sup.60 Co concentration increase rate is lower than a predetermined value, the newestly measured iron accumulation rate is registered as a new lower limit of the suitable iron accumulation rate. On the other hand, when the .sup.60 Co concentration increase rate is higher than the predetermined value, iron accumulation rate greater than the newestly measured iron concentration rate by 10-20% is registered as a new lower limit of the suitable iron accumulation rate. Thus, by varying the range of the optimum iron accumulation rate, the control of iron accumulation rate can be made the most optimum one for a peculiar plant and for a peculiar date. When the lower limit has been defined, other processes are identical to those in the first embodiment. MODIFIED EMBODIMENT Here, .sup.60 Co concentration in reactor water and .sup.54 Mn concentration in reactor water are used as control indexes for controlling iron concentration in feed water. As shown in FIG. 6, when .sup.60 Co concentration in reactor water become higher, iron concentration in feed water is controlled at a higher level, while when .sup.52 Mn concentration in reactor water become higher, iron concentration in feed water is controlled at a lower level. In this case, since the radioactive corrosion products to be decreased are directly designated as control indexes, the control method is easy to understand, and can be carried out even if the detail of the reaction behavior is not clearly known. However, this method is not so optimum, because there is a considerable time delay regarding both the phenomenon of the activation and a time when numerical data showing the effective control by use of iron concentration is obtained. EMBODIMENT 4 In a plant where nickel is so rich that Fe/Ni ratio is smaller than 2, nickel concentration measured in the feed water is required to be incorporated into control indexes for calculating iron accumulation rate, even if iron concentration rate is maintained to be not less than 0.5 (mg/m.sup.2 /hr). Nickel accumulation rate on fuel rod can be calculated through equation (1) by replacing iron concentration in the equation (1) by nickel concentration. Then, iron concentration in the feed water is controlled so that the ratio of iron accumulation rate to nickel accumulation rate become greater than 2. By virtue of this control method, nickel or cobalt adheres on fuel rod in a chemically stable state (NiFe.sub.2 O.sub.4, CoFe.sub.2 O.sub.4, etc.), thereby minimizing dissolution of radioactive cobalt. It should be noticed that the amount of nickel dissolved in the feed water from plant structures is not negligible for calculating nickel accumulation rate differently from iron case, and that only 60-70% of this nickel adheres to fuel rod surface, which value is small in comparison with iron case. For dealing with this matter in a simple manner, the nickel generation in reactor may be neglected by estimating the accumulation rate on fuel rod to be somewhat higher. This simplification causes little error. Further, in an operation suffering great output power variation such as in a starting test, the above-mentioned processes are not necessarily required, because, in a state of output power variation, corrosion products are liable to separate from fuel rod, and a sufficient control effect can not be expected. In the invention, Fe/Ni ratio is preferred to be in a range of 2-5. EMBODIMENT 5 In the embodiment 1 the device for measuring the concentration of iron contained in the feed water was disposed between the high pressure feed-water heater and the pressure vessel of the nuclear reactor as shown in FIG. 1. In the embodiment 5, two devices for measuring the concentration of iron of the feed water were provided, the first device thereof being disposed with the same position as in the embodiment 1 and the second device was disposed at a position which was downstream side of the ion-injecting point and was at upstream side of the feed-water pump as shown in FIG. 7. By comparing two values measured through these upstream and downstream devices, it was possible to detect a loss of injected iron which loss occurred due to the adhesion of the iron to the feed-water heater and piping position between these two devices. In a case where this loss is varied in a large degree, it is deemed that a chemical stage of the injected iron is changed, with the result that it becomes possible to detect an abnormality of the iron ion-injecting device. According to the present invention, .sup.60 Co concentration increase rate in reactor water can be maintained at a low level through whole period of operation substantially without increasing the concentration of radioactive corrosion product in reactor water which product adheres to plant structure such as piping. By virtue of the lowered .sup.60 Co concentration in reactor water, .sup.60 Co amount adhering to tubings of primary system of plant is decreased, thereby decreasing dose rate of the primary system which dose rate must be taken into consideration at the time of periodic inspections.
062051962	abstract	A boiling water type nuclear reactor core, in which a plurality of fuel assemblies, each enclosed in a channel box, are loaded and a plurality of control rods, each having control blades, are arranged between the channel boxes. Latitudinal long blade control rods, each having control rod blades which extend latitudinally in four directions, are arranged between channel boxes on diagonals of square bundle regions each formed by a plurality of fuel assemblies, and latitudinal short blade control rods, each having control rod blades which extend latitudinally in four directions with each control rod blade having a latitudinal length of about half of the width of one of the square bundle regions, are arranged between the channel boxes in the center of each of the square bundle regions. The long blade control rods have a latitudinal blade length which is about twice as long as the latitudinal blade length of the short blade control rods.
	abstract	A method of producing [18F]F2 from [18F] fluoride through a plasma induced scrambling procedure is provided. The present invention also provides an apparatus for preparing [18F]F2 from [18F] fluoride in a plasma induced scrambling procedure. Kit claims for preparing [18F]F2 from [18F] fluoride in a plasma induced scrambling procedure as well as method of use and use of claims for preparing [18F]F2 from [18F] fluoride through a plasma induced scrambling procedure are also provided.
048184764	description	DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, FIGS. 1 and 2 show one design of a typical nuclear reactor pressure vessel 10 having a removable closure head 13, the closure head 13 being sealingly engaged with the pressure vessel 10 by means of a plurality of stud bolts 16 (see FIG. 3). Each bolt 16 has a lower end 19 which is threadingly received in a portion of the reactor vessel flange 22. An upper end 25 of the bolt 16, which also has a threaded section, passes through a corresponding aperture in the vessel head 13 and projects thereabove. The upper end 25 is threadingly engaged with a nut 28 and washer 31 to compress vessel head closure seals 34 disposed between the vessel head 13 and the flange 22 to thereby sealingly engage the closure head 13 with the pressure vessel 10. In this configuration, the upper most end of the top threaded section 25 remains exposed to the environment. To prevent damage to the top threaded section 25 or the nut 28, which would prevent the nut 28 from being easily removed from the stud bolt 16, a reactor vessel stud thread protector 40 (see FIG. 4) of the present invention is utilized. The stud thread protector or cap 40 is comprised of a tubular or generally cylindrical wall portion 43 disposed over a single stud bolt which is opened at its lower end 46 and substantially closed at its upper end 49, the upper end 49 having a hole therethrough to allow passage of a closure or hold down screw 52 which is threadingly engaged with an internally threaded section 55 of vertical bore 58 within the stud bolt 16. On the lower end 46 of the wall portion 43 is a seal 61 to prevent coolant, typically water, from passing under the protector 40 into contact with the stud 16, nut 28, or washer 31. Preferably, this seal 61 is constructed of nuclear grade neoprene and is in the form of a replaceable O-ring or gasket. To prevent damage to the stud bolt 16, the hold down screw 52, which may also have a seal associated therewith, is sufficiently torqued within the reactor vessel stud bolt 16 to sufficiently compress the seal 61. In the embodiment shown in FIG. 4, the reactor vessel stud thread protector 40 further includes a drip pan 64 associated therewith; the drip pan 64 being radially inwardly disposed with respect to the outer periphery of the vessel head 13 whereby the drip pan 64 collects any fluid which may be emitted from the reactor vessel 10. This drip pan 64, at one end 67 thereof, is form fitting with the top surface 70 of the vessel head 13 to further prevent any damage by borated fluid to the stud bolts 16. If necessary, coolant may be removed from around the bolts 16 by a typical water vacuum system prior to removal of the reactor vessel head 13. With the inclusion of the drip pan 64 any possible accidental corrosive leakage from mechanical seals of the control rod drive mechanism housings or instrumentation ports 73 on top of the reactor vessel 16 can be controlled. The drip pan 64 can be an integral part of the protector 40, or a separate member which is placed upon the protector prior to the hold down screw 52 being threadedly engaged therein. A further advantage of the reactor vessel stud thread protector 40, in addition to protecting the threaded section 25 of the stud bolt 16 from accidental corrosive leakage impingement, is that the reactor vessel stud thread protector provides protection from inadvertent deformation due to operator maintenance around adjacent studs. Preferably the stud thread protector 40 is made of a strong material, such as stainless steel, the walls 43 being from 1/16 to 1/8 inch thick. By providing a seal 61, a close fit between the protector 40 and the elements of the stud 16 and nut 28 is not required. Thus, no problem arises with the protector 40 becoming stuck on the stud bolt 16 and thereby causing delay in removal of the head of refueling operations. In a second embodiment shown in FIG. 5, the reactor vessel stud protector 40 is designed to cover several studs with one device in the shape of a curved box having a generally rectangular cross-section. For example, five such studs 16 could be covered by one protector 40. In this manner, it is necessary only to engage a holddown screw 52 with alternating stud bolts 16 (see FIG. 5). Since there is essentially no vibration of the reactor vessel 10, the minimal force required to seal the protector 40 against the vessel head 13 with hold down screws 52, i.e., to compress the seal 61 which in this embodiment is oval-shaped in conformity with the multiple stud protector, is therefore readily provided for by such a configuration. In this design drip pans 64 of adjacent protectors 40 have overlapping sections such that, as a whole, said drip pans 64 combine to form a continuous channel around the circumference of the vessel head 13. Alternatively, if the drip pan 64 is a separate member apart from the protector 40, it can be constructed of a continuous, one-piece ring-like element which is positioned over the stud protector 40 and the vessel head 13. This configuration lends itself to even greater speed in removing the reactor vessel head 13, in that a substantially less number of hold down screws 52 need be removed from the stud bolts 16, prior to removal of the nuts 28 and washers 31 to remove the vessel head 13. Once the hold down or closure screws 52 have been removed from every other stud 16, the stud thread protectors 40 can easily be removed by engaging a lifting eye (not shown) on the protector 40 to lift it out of engagement with the vessel head 13. Since the risk of damage to the exposed upper threaded section 25 of the stud bolt 16 by either the inadvertent corrosive leakage impingement or accidental deformation is virtually eliminated, removal of the nuts 28 is greatly facilitated. Hence, the vast number of stud bolts 16 can be more quickly and easily removed thereby reducing man-rem exposure to maintenance personnel within a potentially hazardous environment, as well the amount of time necessary for refueling operations. 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 alterations would be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting to the scope of the invention which is to be given the full breadth of the appended claims and in any and all equivalents thereof.
046860894	claims	1. A sieve-plate column for the liquid-liquid counterflow extraction of two phases which are of different weights and not soluble one in the other, the sieve-plate column defining a longitudinal axis and comprising: a plurality of sieve plates arranged transversely to said axis; and, a static mixing element connected directly between two mutually adjacent ones of said sieve plates for cross mixing the two phases as the latter pass therethrough, the static mixing element including a plurality of channels one adjacent the other arranged over the entire cross-section of said element, said channels communicating with apertures in said sieve plates and being inclined with respect to the direction of flow so as to cause the upper opening thereof to be radially displaced from the lower opening thereof and being arranged so as to cause a radial displacement of flow paths that are formed. a plurality of sieve plates arranged transversely to said axis; and, a static mixing element connected directly between two mutually adjacent ones of said sieve plates for cross mixing the two phases as the latter pass therethrough, the static mixing element including a plurality of channels one adjacent the other arranged over the entire cross-section of said element, said channels communicating with apertures in said sieve plates and being inclined with respect to the direction of flow so as to cause the upper opening thereof to be radially displaced from lower opening thereof and being arranged so as to cause a radial displacement of the flow paths that are formed. 2. The sieve-plate column of claim 1, said sieve-plate column having an upper portion and four of the sieve plates of said plurality of sieve plates being disposed in said upper portion one above the other, each two mutually adjacent ones of said four plates conjointly defining an intermediate space, and, said sieve-plate column comprising three of said static mixing elements disposed in corresponding ones of said intermediate spaces. 3. The sieve-plate column of claim 2, each two successive ones of said static mixing elements being rotated 90.degree. with respect to each other. 4. The sieve-plate column of claim 1, one of said phases being a delivering phase and the other one of said phases being a receiving phase, said phases being metered to said column so as to move therethrough in mutually opposite directions, said sieve-plate column comprising a plurality of said static mixing elements mounted in the first third of said sieve-plate column when viewed in the direction in which said delivery phase is metered to said column. 5. The sieve-plate column of claim 1, each two mutually adjacent ones of said sieve plates conjointly defining an intermediate space, said sieve-plate column further comprising a plurality of said static mixing elements mounted in corresponding ones of the intermediate spaces defined by said sieve plates. 6. The sieve-plate column of claim 1, said static mixing element being configured as an electrode. 7. The sieve-plate column of claim 1, said static mixing element being made of neutron-absorbing material. 8. The sieve-plate column of claim 1, said static mixing element being itself self-supporting and stable and being mounted so as to rest on one of said two sieve plates. 9. A sieve-plate column for the liquid-liquid counterflow extraction of two phases in a nuclear facility for reprocessing irradiated nuclear fuels, the two phases being of different weights and not soluble one in the other, the sieve-plate column defining a longitudinal axis and comprising:
	summary
	description	This is a continuation application, under 35 U.S.C. § 120, of copending International Application PCT/EP2015/055532, filed Mar. 17, 2015, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2014 205 085.5, filed Mar. 19, 2014; the prior applications are herewith incorporated by reference in their entirety. The invention relates to a nuclear facility having a cooling element for cooling a cooling liquid in a fuel element pool in which a fuel element rack for receiving fuel elements is disposed. The cooling element, which includes a heat exchanger, is constructed for connection to a cooling circuit in a system for cooling the cooling liquid in the fuel element pool. Two technically different systems are currently predominantly used in order to cool fuel element pools. The first system provides direct cooling of the pool water. For that purpose, the water is removed from the pool by using a pump, cooled in an external cooling unit and then fed back into the pool. If a leak occurs in the cooling circuit in the process, there is a risk of the fill level of the pool lowering. A second conventional system is based on the use of suspension coolers. In that case, the pool water is cooled by using an intermediate cooling circuit. By contrast with the previously mentioned method, in that system, there is no risk of pool leakage, since firstly no penetrations of the pool are required, and secondly the pool water remains in the pool. However, due to the required heat transfer surfaces, such a system requires a significant amount of installation space in the storage pool. German Patent Application DE 102 17 969 A1, corresponding to Canadian Patent CA 2 483 182C, discloses an intermediate storage system for fuel elements of a nuclear facility including a passive single-phase cooling circuit. The internal space of a wet storage pool is cooled by using a heat exchanger suspended in the wet storage pool. German Patent Application DE 29 44 962 A1 discloses a storage pool for fuel elements of nuclear reactors, in which heat exchangers are immersed in the pool water and suspended without a permanent connection to the pool wall. U.S. Patent Application US 2012/0051484 A1 describes a storage pool for fuel elements, in which heat exchangers are attached to the edge of the pool, including a two-phase cooling circuit, in which the cooling medium in the heat exchangers conducts a phase transition. The retrofits of redundant and diversitary pool coolings required as part of the “post Fukushima” measures, which are predominantly based on the second outlined variant, frequently face the problem that the necessary installation space in the existing pools is too small for a corresponding quantity of suspension coolers to be accommodated. The only alternative is often that of rearranging the storage space for the fuel elements, which is costly and complicated in terms of gaining authorization. In addition, attaching suspension coolers in a manner which is safe in terms of earthquakes is problematic, since there is a reluctance to modify the existing pool structures by welding or drilling. It is accordingly an object of the invention to provide a nuclear facility, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known facilities of this general type and which provides a cooling element that can be integrated in a space-efficient manner in an already existing fuel cooling pool in a corresponding system for cooling a cooling liquid. With respect to the cooling element, the above-mentioned problem is solved in that the cooling element is sized and configured in such a way that it can be disposed and/or attached in a free position for a fuel element in the fuel element rack. Other advantageous embodiments of the invention are described below. The invention is based on the consideration that, due to current safety requirements for nuclear facilities, the need for cooling systems which are reliable, can be replaced in a modular manner and are redundant or can be used in a supplementary manner, has drastically increased. Known systems are usually very complex in terms of construction, and uncertainties also may arise with respect to the safety of the new structure and thus also to the reauthorization. For these reasons, a technical system would thus be desirable which can be implemented with no or only minor modifications to the configurations of the cooling pool and the cooling systems. As has now been recognized, a technical system of this type for cooling the pool water can be implemented by using existing installation spaces or spaces which have previously been used to place other components for the accommodation of the cooling elements. As has additionally been recognized, free slots or compartments in the fuel element rack are particularly suited to this purpose. For this purpose, the cooling elements must be sized accordingly, i.e. adapted to the specified dimensions in terms of the diameter or cross section thereof, and optionally also in terms of the length thereof. In addition, they should be configured in such a way that they can be safely inserted and removed again and can be disposed in a sturdy manner. In some circumstances, each cooling element can also be longer than the fuel element which it replaces, so that it can project, for example, upwards out of the case or compartment which is assigned thereto in the fuel element rack. A type of funnel which conducts the pool water can also be attached at the upper end as a type of intake. Advantageously, each cooling element in principle thus has the typical dimensions of a fuel element. Purely by way of example, as a rough guideline for the typical dimensioning, it is mentioned in this regard that a typical fuel element of a pressurized-water reactor contains 15×15 fuel rods and has a length of approximately 4500 mm and a square cross section having an edge length of 250 mm. A fuel element of a pressurized-water reactor of the EPR type has, for example, 18×18 fuel rods and accordingly a greater edge length and fuel elements for boiling-water reactors have for example 8×8 fuel rods and accordingly a smaller edge length. However, there are also, for example, fuel elements having a hexagonal cross section or yet another shape. Furthermore, the cooling element can deviate from the typical dimensions if the fuel element rack, which is also referred to as a fuel element case, has special dimensions which are produced specifically for this application. Preferably, the cooling element is in the form of a suspension cooling element for suspension in the fuel element rack. Preferably, after mounting, the cooling element is then disposed in one of the free positions for a fuel element. Alternatively, the cooling element is disposed next to the fuel element cases or outside the outer wall of the fuel element rack. A fuel element compartment is then used to receive a holder which fixes the cooling element. In this variant, the spatial dimensions of the cooling element are not limited by the size of the compartment. In one possible embodiment, the heat exchanger includes a coolant channel for the passage of a coolant which is conducted in the associated cooling circuit, the cooling element including at least one coolant supply connection and at least one coolant discharge connection for connection to and integration in the cooling circuit. A cooling element of this type is suitable, in particular, for a single-phase cooling circuit in which the coolant absorbs heat in the heat exchanger, but in so doing, does not change physical state. In a preferred embodiment, however, the cooling element is constructed for integration in a two-phase cooling circuit, wherein at least one condensate channel is provided for feeding the coolant into a condensate collector, wherein the heat exchanger includes at least one vaporizer channel for guiding the vaporized coolant into a vapor collector, and wherein the cooling element further includes a supply line and a return line for connection to the cooling circuit. Two-phase cooling circuits or heat transportation circuits, in which the circulating coolant changes physical state in the vaporizer from the liquid to gaseous state and subsequently changes back again in a condenser, which is located outside the fuel element pool, allow generally increased rates of heat transportation by comparison with single-phase cooling circuits. In terms of construction, each cooling element or the cooler thus preferably includes a plurality of tubular coolant channels for the coolant circulating in the cooling circuit, which, in the installation position, are oriented preferably in parallel with the longitudinal direction of the compartments in the fuel element rack. Of these, preferably a comparatively small proportion is used for supplying condensate to the lower condensate collector (in a downstream flow), and the greater proportion is used for vaporizing the condensate and for guiding the vapor/liquid mixture produced in this way to the upper vapor collector (in an upstream flow). Instead of or in addition to the pipes, the cooler may also include plates through which a flow passes. The pool water flows between the pipes or plates, preferably from top to bottom, through corresponding cavities or channels, and is cooled by heat being emitted to the coolant in the cooling circuit, which coolant is preferably brought to boiling point thereby. Firstly, the vapor or condensate collector interconnects the pipes which are connected in parallel in terms of flow, and secondly, it should be ensured by using suitable recesses or the like that the pool water can flow through the collector. The interpretation as to what proportion of the cross-sectional area of the cooling element is used for the pipes/plates conducting the coolant in the cooling circuit and what proportion is used for the downstream flow of the pool water is determined in each case according to the given thermodynamic constraints. Optionally, the functions of a plurality of cooling elements of this type can also be combined, for example by a common vapor collector in the case of a corresponding connection of the pipe or connection lines. In the various embodiments, the lines through which the cooling element is connected to the cooling system can be constructed to be rigid or flexible. In any case, they should be constructed to be pressure-resistant. With respect to the system, the above-mentioned problem is solved by a fuel element rack and at least one cooling element of the type described which can be inserted or is inserted therein. With respect to the fuel element pool, the above-mentioned problem is solved in that the fuel element pool is filled with a cooling liquid, in particular water (pool water), and in that a system of the type described above is disposed therein. The fuel element pool is preferably a storage pool for fuel elements, in particular a wet storage pool, a cooling pool, an intermediate storage pool or permanent disposal pool. With respect to the nuclear facility, the above-mentioned problem is solved by a fuel element pool of this type. The nuclear facility preferably further includes a cooling system which is configured in the manner of a circuit, including at least one recirculating cooler for connection to each cooling element. The cooling system can be configured to be active or passive according to requirements. The advantages of the invention lie, in particular, in the fact that, by using the cooling elements, a relatively simple and robust cooling of fuel element storage pools is achieved. As a result, it is possible to modify or supplement pool-cooling systems in a simple manner. Through the use of the modular construction, various approaches are possible, which include both redundant and diversitary cooling options. In addition, it is possible to carry out temporary cooling in the case of a fully loaded core. Since in the future, unprecedented burn-ups may be produced, a cooling system of this type can be used in a very variable manner. It is also possible to react effectively to a reduction in the thermal load by using cooling processes. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a nuclear facility, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Referring now in detail to the figures of the drawings, in which like parts are provided with the same reference numerals, and first, particularly, to FIG. 1 thereof, there is seen a cooling element 2 which includes a cooling element body 8 that has a number of condensate channels 20 and vaporization channels 56 extending in the longitudinal direction 14 of the cooling element 2. The channels are in the form of pipes which are oriented in parallel. Instead of a plurality of pipes, a single pipe, preferably having a correspondingly large cross section, can also be used (or also plates). The cooling element 2 is connected to a condenser (not indicated therein) of a cooling circuit or is connected into the cooling circuit through at least one supply line 32 which is connected to the cooling element in a head region 26. Condensate, i.e. coolant in liquid form, is fed through the supply line 32 to the cooling element 2 in a supply direction indicated by an arrow 34. The condensate flows in the condensate channels 20 along a gravitational vector 38 towards a condensate collector 50 which is disposed in a base region 44 of the cooling element 2. The gravitational vector 38 points in the direction of the gravitational acceleration or gravitational force acting on the surface of the earth. From there, the fluid or coolant which, despite being preheated in the condensate collector 50, is still in the form of a liquid, rises through the tubular vaporizer channels 56, which are disposed in the cooling element 2. The fluid or coolant rises in the opposite direction to the gravitational vector 38 into a vapor collector 62 which is disposed at the head region 26. The vaporizer channels 56 thus form a heat exchanger 64 which acts as a coolant vaporizer. Through the use of the vaporization process, during the rise and vaporization of the coolant, thermal energy is absorbed from the pool water, which cools down as a result. A two-phase cooling system is thus achieved, in which the coolant circulating in the cooling circuit during the passage through the cooling element 2 changes phase state from the liquid to gaseous state. The vapor is fed from the vapor collector 62 through at least one return line 68, preferably in the form of a rising pipe, to the condenser (not shown in FIG. 1) which is provided for cooling down the coolant in a return direction indicated by an arrow 70, and condensed there. The condensate is supplied back to the cooling element 2 through the supply line 32, which is preferably in the form of a downpipe, so that the cycle ends. The mass flow inside the cooling circuit can be achieved either by using an active mechanical device (pumps, etc.) or in a passive manner (in accordance with the principle of natural convection or free convection). Through the use of the described cooling, a density gradient is produced on the pool side, so that a flow of the pool water in the direction of the gravitational vector 38 is induced. The downstream flow is part of a so-called convection roll in which the other part is achieved in adjacent fuel elements 98 by using a corresponding upstream flow. The pool water enters intermediate spaces 130, which are disposed between the vaporizer channels 56 and extend in the longitudinal direction, at the head region 26 of the cooling element 2, as is indicated by arrows 74. The pool water then flows through the cooling element 2 in the direction of the gravitational vector 38 and the water emits the heat thereof to the coolant rising in the vaporizer channels 56. It exits the cooling element 2 again at the base region or foot end 44, as is indicated by arrows 80. If the cooling element 2 projects upwards slightly out of a fuel element rack 92, then the pool water does not have to flow through corresponding recesses in the vapor collector 62, but rather can flow laterally. The cooling element 2 is strengthened, with respect to the spatial dimensions thereof, in order to be inserted or integrated in a fuel element storage rack, or fuel element rack 92 for short as is shown in FIG. 2, in the direction of the gravitational vector 38, i.e. substantially from above. For this purpose, the cooling element 2 is in the form of a suspension cooler. In order to provide for suspension in the fuel element rack 92, the element has a suitable shape and optionally suitable projections or retaining elements. The cooling element 2 can, however, also rest on the base of the fuel element rack 92. In FIG. 2, the fuel element rack 92 including inserted fuel elements 98 is shown in a plan view from above. The fuel element rack 92 is constructed, in terms of the cross section thereof when viewed in a plan view, as a two-dimensional grid. A plurality of fuel elements 98 are inserted in the fuel element rack 92. In this case, the fuel element rack 92 has a free position 106. In the present embodiment, the fuel element rack 92 includes 25 integration or insertion spaces or compartments 104 (slots) for fuel elements 98. In two of the insertion spaces, cooling elements 2 are inserted instead of fuel elements 98. In extreme cases, all of the insertion spaces can be occupied by cooling elements 2. In this case, the cooling elements 2 have a length l in the longitudinal direction 14 thereof, which length substantially corresponds to that of the fuel elements 98. However, the length l can also be selected so as to be slightly greater, so that each cooling element 2 then projects upwards out of the fuel element rack 92, and the pool water can also flow in laterally (see above). In this case, each cooling element 2 has a substantially constant square cross section over the entire length thereof. The width b of each cooling element 2 substantially corresponds to the clear span of the compartment 104 which is provided to receive the fuel element. Due to these dimensions, each cooling element 2 fits into a compartment 104 in a similar manner to a fuel element 98. In a variant which is not shown in greater detail, cooling elements 2 can be disposed outside the fuel element rack 92. However, the fixing takes place on the fuel element rack 92 and more specifically preferably by using a holder which engages in an empty compartment 104 and is attached therein. The fuel element rack 92 and the cooling elements 2 which are disposed therein or thereon form a system 110 for cooling the cooling liquid in a fuel element pool. FIG. 3 is a diagrammatic view of a fuel element pool 115, in this case, for example, in the case of an external storage facility (for intermediate storage), including a fuel element rack 92 disposed therein, which receives cooling elements 2 in at least some of the positions which were originally provided for fuel elements 98. The cooling elements 2 are each connected individually or bundled into groups in cooling circuits 120. The cooling circuits 120 can be operated both actively (by using corresponding pumps 134) and passively. In order to cool down the coolant heated in the cooling elements 2, corresponding recirculating coolers 136 are disposed inside or outside the building surrounding the fuel element pool 115 and thermally coupled to a suitable heat sink. In the case of a two-phase cooling circuit 120, which is preferably used, the cooling elements 2 act as vaporizers, and the recirculating coolers 136 act as condensers for the coolant conducted in the circuit. The same applies analogously to the nuclear power plant shown by way of example in FIG. 4, which includes a fuel element pool 115 (cooling pool) that is located in a reactor building, next to a reactor cavity containing a reactor pressure vessel 138.
	claims	1. A clamp assembly for connecting a diffuser adapter or lower ring to a diffuser tail pipe of a jet pump diffuser in a boiling water nuclear reactor, the clamp assembly comprising:at least two clamp segments shaped generally corresponding to an exterior circumference of the diffuser;a swivel link affixed at each end of each of the clamp segments; andat least two connecting bands pivotably secured to the swivel links between the ends of the clamp segments,wherein the clamp segments each comprises a clamp body and a locking assembly cooperable with the clamp body and engageable with the diffuser adapter or lower ring and the diffuser tail pipe, the locking assembly including radially oriented pins directly engageable with corresponding holes formed in the diffuser adapter or lower ring and the diffuser tail pipe. 2. A clamp assembly according to claim 1, wherein each of the locking assemblies includes an upper pin insert and a lower pin insert secured to its respective clamp body, the upper and lower pin inserts including the pins directly engageable with the corresponding holes formed in the diffuser adapter or lower ring and the diffuser tail pipe. 3. A clamp assembly according to claim 2, wherein the clamp bodies comprise two circumferential channels on an inside surface thereof, the circumferential channels being sized to receive the upper and lower pin inserts. 4. A clamp assembly according to claim 2, wherein the pins on the upper and lower pin inserts are conical, and wherein the holes formed in the diffuser adapter or lower ring and the diffuser tail pipe are correspondingly tapered. 5. A clamp assembly according to claim 2, wherein the upper pin insert engageable with the diffuser tail pipe is formed of a first material having a coefficient of thermal expansion substantially matching that of the diffuser tail pipe, and wherein the lower pin insert engageable with the diffuser adapter or lower ring is formed of a second material having a coefficient of thermal expansion substantially matching that of the diffuser adapter or lower ring. 6. A clamp assembly according to claim 5, wherein the first material is type 316 austenitic stainless steel, and wherein the second material is inconel alloy 600. 7. A clamp assembly according to claim 2, wherein the clamp body is formed of a material having a coefficient of thermal expansion that is intermediate between a coefficient of thermal expansion of the diffuser tail pipe and a coefficient of thermal expansion of the diffuser adapter or lower ring. 8. A clamp assembly according to claim 7, wherein the material of the clamp body is type XM-19 austenitic stainless steel (nitronic 50). 9. A clamp assembly according to claim 1, wherein each of the clamp segments comprises a bolt collar at each end thereof, the bolt collars including at least one aperture for receiving a bolt engageable with a corresponding one of the swivel links. 10. A clamp assembly for connecting a diffuser adapter or lower ring to a diffuser tail pipe of a jet pump diffuser in a boiling water nuclear reactor, the clamp assembly comprising:two clamp segments shaped generally corresponding to an exterior circumference of the diffuser, each clamp segment including a clamp body housing an upper pin insert and a lower pin insert, the upper and lower pin inserts including radially oriented pins directly engageable with corresponding holes formed in the diffuser adapter or lower ring and the diffuser tail pipe;a swivel link affixed at each end of each of the clamp segments; andat least two connecting bands pivotably secured to the swivel links between the ends of the clamp segments. 11. A clamp assembly for connecting a diffuser adapter or lower ring to a diffuser tail pipe of a jet pump diffuser in a boiling water nuclear reactor, the clamp assembly comprising:at least two clamp segments shaped generally corresponding to an exterior circumference of the diffuser;a swivel link affixed at each end of each of the clamp segments; andat least two connecting bands pivotably secured to the swivel links between the ends of the clamp segments,wherein the clamp segments each comprises a clamp body and a locking assembly cooperable with the clamp body and engageable with the diffuser adapter or lower ring and the diffuser tail pipe, the clamp body including two circumferential channels on an inside surface thereof, and wherein the locking assembly is disposed in the circumferential channels facing the diffuser adapter or lower ring and the diffuser tail pipe.
	claims	1. An X-ray fluoroscopic imaging system, comprising:an inspection passage (3) through which an inspected object (8) is passed;an electron accelerator (1) comprising an electron accelerating unit (102), an electron emitting unit (101) and a target (103), an electron beam (E) coming from the electron emitting unit and accelerated by the electron accelerating unit bombarding the target to generate an X-ray, wherein the X-ray has different energy distributions at different azimuth angles relative to the target (103);a shielding collimator apparatus (2) comprising a shielding structure (201), and a first collimator (202a) for extracting a low energy planar sector X-ray beam and a second collimator (202b) for extracting a high energy planar sector X-ray beam which are disposed within the shielding structure;a low energy detector array (4) for receiving the X-ray beam from the first collimator;a high energy detector array (5) for receiving the X-ray beam from the second collimator;wherein the shielding structure surrounds the target;wherein the first collimator, the low energy detector array and a target point (O) bombarded by the electron beam are located in a first plane; andwherein the second collimator, the high energy detector array and the target point bombarded by the electron beam are located in a second plane. 2. The X-ray fluoroscopic imaging system according to claim 1, wherein the angles between the directions in which the first and/or second collimators are disposed and the electron beam bombarding the target are 30° to 150°. 3. The X-ray fluoroscopic imaging system according to claim 1, wherein the angle between the axis of the electron accelerator and the inspection passage is less than 60°. 4. The X-ray fluoroscopic imaging system according to claim 1, wherein the first and second collimators are located on the same side of the axis (L) of the electron beam. 5. The X-ray fluoroscopic imaging system according to claim 1, wherein the axis of the electron accelerator is parallel to the inspection passage. 6. The X-ray fluoroscopic imaging system according to claim 1, wherein the angle between the central symmetric line of the first and second collimators and the inspection passage is larger than 45°. 7. The X-ray fluoroscopic imaging system according to claim 1, wherein the central symmetric line of the first and second collimators is perpendicular to the inspection passage. 8. The X-ray fluoroscopic imaging system according to claim 1, wherein the low and high energy detector arrays are in a linear type arrangement, a segmented linear arrangement, a standard L type arrangement or a C type arrangement, and are constituted by a plurality of low and high energy detectors respectively. 9. The X-ray fluoroscopic imaging system according to claim 1, wherein the low and high energy detector arrays are a plurality of detectors arranged in one row or a plurality of rows respectively. 10. The X-ray fluoroscopic imaging system according to claim 1, further comprising:a signal analyzing and image processing subsystem (7) for receiving signals from the low and high energy detector arrays and generating a fluoroscopic image finally by computation and analysis; anda power supply and control subsystem (6) for providing power and control to the operation of the X-ray fluoroscopic imaging system. 11. The X-ray fluoroscopic imaging system according to claim 1, further comprising:a detector arm support (9) for the mounting and fixation of detectors, the detector arm support being formed into an arrangement structure of linear type, segmented linear type, standard L type or C type. 12. The X-ray fluoroscopic imaging system according to claim 11, further comprising:an adjustable fixing apparatus (11) for fixing the detector arm support on the ground independently. 13. The X-ray fluoroscopic imaging system according to claim 1, further comprising any combination of the followings:a conveying apparatus (10) for dragging the inspected object to pass through the inspection passage at a given speed;a scatter shielding structure (12) disposed on one side or both sides of the inspection passage;an equipment room (13) for the mounting and fixation of apparatuses such as the electron accelerator and the like;a control room (14) for providing an equipment operation and working place to the working staffs of the system; anda ramp (24) for increasing the height of the inspected object. 14. The X-ray fluoroscopic imaging system according to claim 1, comprising a plurality of collimators and a plurality of corresponding detector arrays. 15. The X-ray fluoroscopic imaging system according to claim 1, wherein the electron accelerator is a single energy accelerator, a double energy accelerator or a multiple energy accelerator, and the detector arrays are single energy detector arrays, double energy detector arrays or multiple energy detector arrays correspondingly. 16. A combined and fixed type X-ray fluoroscopic imaging system, comprising:the X-ray fluoroscopic imaging system according to claim 1;an equipment room (13) fixed to the ground on one side of the inspection passage and having the electron accelerator and the shielding collimator apparatus mounted therein, the first and second collimators facing the inspection passage at different angles;a conveying apparatus (10) mounted in the inspection passage;a first and second detector arm supports (9) disposed on the other side of the inspection passage, fixed to the ground by an adjustable fixing apparatus, and having the low and high energy detector arrays mounted therein respectively;a scatter shielding structure (12) disposed between the equipment room and the inspection passage; anda control room (14) fixed to the ground, having the signal analyzing and image processing subsystem as well as the power supply and control subsystem mounted therein, and controlling the combined and fixed type X-ray fluoroscopic imaging system. 17. A track moving type X-ray fluoroscopic imaging system, comprising:the X-ray fluoroscopic imaging system according to claim 1;a plurality of tracks (20) disposed in parallel, the inspection passage being disposed between two adjacent tracks;a moving apparatus (21) disposed on the tracks;an equipment room (13) disposed on the tracks on one side of the inspection passage via the moving apparatus and having the electron accelerator and the shielding collimator apparatus mounted therein, the first and second collimators facing the inspection passage at different angles;two L type detector arm supports (9), a vertical segment bottoms thereof being disposed on the tracks on the other side of the inspection passage via the moving apparatus, the other ends being connected and fixed to the top of the equipment room, and the low and high energy detector arrays being mounted therein respectively; anda control room (14) fixed to the ground, having the signal analyzing and image processing subsystem as well as the power supply and control subsystem mounted therein, and controlling the track moving type X-ray fluoroscopic imaging system. 18. A vehicle-mounted moving type X-ray fluoroscopic imaging system, comprising:the X-ray fluoroscopic imaging system according to claim 1; anda chassis vehicle (30), and an X-ray source cabin (32), an equipment cabin (33), a working cabin (34), a low energy detector arm support system and a high energy detector arm support system mounted on the chassis vehicle;wherein the electron accelerator and the shielding collimator apparatus are mounted in the X-ray source cabin, and low and high energy X-ray beams are extracted to one side of the chassis vehicle at different angles through the first and second collimators respectively;wherein the low energy detector arm support system has the low energy detector array mounted therein, and in a working state, the low energy detector arm support system is opened on one side of the chassis vehicle, forms a “gate” type structure with the chassis vehicle, and makes the low energy detector array locate in the first plane in which the first collimator situates, and in a non-working state, the low energy detector arm support system is folded and stored on the top of the chassis vehicle;wherein the high energy detector arm support system has the high energy detector array mounted therein, and in a working state, the high energy detector arm support system is opened on one side of the chassis vehicle, forms a “gate” type structure with the chassis vehicle, and makes the high energy detector array locate in the second plane in which the second collimator situates, and in a non-working state, the high energy detector arm support system is folded and stored on the top of the chassis vehicle;wherein the low and high energy detector arm support systems are located on the same side of the chassis vehicle and form two “gate” type structures one after another with the chassis vehicle, and an internal passage formed by the two “gate” type structures becomes the inspection passage;wherein the equipment cabin has the power supply and control subsystem as well as the signal analyzing and image processing subsystem mounted therein; andwherein the working cabin has system operation and office equipments mounted therein and controls the vehicle-mounted moving type X-ray fluoroscopic imaging system.
049842587	claims	1. An apparatus for slit radiography, which comprises: an X-ray source: an X-ray detector for collecting radiation passing through a body to be radiographed; a slit diaphragm positioned between said X-ray source and said body for forming a substantially planar X-ray beam; means for scanning said body with said planar X-ray beam; a plurality of attenuating elements positioned along said slit diaphragm, each of said attenuating elements having a free end extendable into and thereby attenuating said planar X-ray beam; control means for extending said free ends of said attenuating elements into and out of said planar X-ray beam during scanning of said body with said planar X-ray beam; and a dampening assembly affixed to each of said attenuating elements to prevent oscillation of each of said attenuating elements as a result of extension into and out of said planar X-ray beam during scanning of said body with said X-ray beam. 2. The apparatus as defined in claim 1 wherein said dampening assembly includes a piston disposed in a fluid-filled cylinder. 3. The apparatus as defined in claim 1 wherein said dampening assembly is a vane extending into a vessel containing liquid. 4. An apparatus according to claim 3, characterized in that the vane is corrugated. 5. An apparatus according to claim 3, characterized in that the vessel comprises partitions forming juxtaposed compartments, a vane of an attenuation element extending into each compartment. 6. An apparatus according to claim 5, characterized in that each vane is provided on at least one side at least partly with electrically conductive material and that means are provided for generating an inhomogeneous magnetic field oriented transversely to the vanes. 7. An apparatus according to claim 6, characterized in that the vanes are made of electrically conductive material and that means are provided for generating an inhomogeneous magnetic field oriented transversely to the vanes. 8. The apparatus as defined in claim 1 wherein each attenuation element comprises a vane of electrically non-conductive material provided on at least one side thereof with a layer of electrically conductive material and that means are provided for generating an inhomogeneous magnetic field oriented transversely to said vanes. 9. The apparatus as defined in claim 1 wherein each attenuation element comprises a vane of electrically conductive material and means are provided for generating an inhomogeneous magnetic field oriented transversely to said vanes.
	abstract	A boiling water reactor includes a reactor pressure vessel; a steam pipe for transporting steam generated in the reactor pressure vessel out from a steam dome positioned at an upper part of the reactor pressure vessel; a high pressure turbine connected to the steam pipe and driven by the steam; a feedwater heater which heats feedwater supplied to the reactor pressure vessel using bleed steam flowing from the high pressure turbine to the feedwater heater; a bleeding valve which adjusts a flow rate of the bleed steam; and a pressure sensor provided in a main steam line including the steam dome and the steam pipe. The boiling water reactor further includes a monitor and control system which controls an opening degree of the bleeding valve based on a magnitude of fluctuating pressure in the main steam line that is detected by the pressure sensor.
	description	The invention relates to a system and a method for applying an intensity-modulated proton therapy on a predetermined tumor volume within the body of the patient. The number of new hospital-based facilities for charged particles therapy is growing quickly, especially in Japan and in the USA. Proton therapy is becoming a realistic therapeutic possibility for treating well-selected cancer types in centralized large hospitals. All new commercial systems are based on the passive scattering technique. The compact gantry for proton therapy at the Swiss Paul Scherrer Institute (PSI) is still the only facility in the world using a dynamic beam delivery technique based on the active scanning of a small proton pencil beam. Only at the German GSI facility (GSI=Gesellschaft fur Schwerionenforschung, Darmstadt) is a similar beam delivery technique used, with carbon ions in a horizontal beam line. By using this modern approach to radiation therapy the conformal shaping of the dose is achieved just by computer control without the need of field specific hardware. This approach to proton therapy is attracting more and more the interest from industry and hospitals internationally, because this method is now being recognized as the preferred method for providing intensity-modulated radiation therapy (IMRT) using proton beams, a technique now known in the community as intensity-modulated-proton therapy (IMPT). This technique (based on the modulation of the totally delivered beam fluence) should not be confused with the active dynamic control of the beam intensity (the instantaneous dose rate) described later below. In contrast to photon-IMRT, with proton beam scanning one can control independently the flux, the range, the position and direction of each proton pencil beam, making use of all available degrees of freedom including the depth of penetration of the proton beam into the patient. With this method similar results can be obtained as with IMRT but with improved conformity and with a significant reduction (by a factor of two or three) of the dose burden on the healthy tissues surrounding the tumor. The practical feasibility of IMPT was demonstrated recently at PSI by applying this new technique to a few of the clinical cases treated on the PSI Gantry 1. Subsequently, the main features of the existing PSI Gantry 1 are described to recall the strengths and the weak points of the present system. The PSI Gantry 1 is operational since 1997. By the end of 2003 166 patients have been treated with this system, with tumors located mainly in the skull, spinal cord and in the low pelvis. Currently up to 17 patients are treated per day. The preliminary clinical results obtained by using the new beam scanning technique are very encouraging. The positive aspects achieved with the present system, PSI Gantry 1, are: a) the possibility to apply conformal therapy with variable modulation of the range delivered “all by computer” without the need to use field specific beam shaping devices like collimators and compensators; b) the capability to apply multiple fields without the personnel entering the treatment room; and c) the capability to deliver IMPT (presently only on well immobilized targets). The concepts for this system are now more than 13 years old, the system was built with limited resources, only for the goal of showing the feasibility of scanning. For a better understanding of the technical improvements introduced by the inventions for the PSI Gantry 2 the main technical features of the PSI Gantry 1 are briefly given below: The patient table is mounted eccentrically on the PSI Gantry 1 and rotates with the gantry. A counter-rotation maintains the patient table horizontal at any time. This choice was dictated by the limited amount of space available for the gantry. Without pushing the compactness of the system down to only 4 m diameter it would not have been possible to build such a Gantry 1 system at PSI. The eccentric mounting of the patient is now the most often criticized point, since the patient table moves away from the floor and the patient couch is not accessible to the personnel when the proton beam is applied from below. The beam delivery used on Gantry 1 is a “discrete” spot scanning method (a “step-and-shoot” method), based on maximum simplicity. A proton pencil beam with a Gaussian profile of 7-8 mm FWHM is used and the beam is scanned in steps of 5 mm. The beam flux is measured with parallel plate ionization monitors in front of the patient. The beam is switched off during the displacement of the beam in-between spots with a kicker magnet. The most often used scan motion is done with a sweeper magnet installed upstream of the last 90° bending magnet. The beam optics is designed such that the action of the sweeper results in a parallel displacement of the swept beam in the patient. The magnetic scanning is applied on Gantry 1 only in one lateral direction, in the dispersive plane of the gantry (the direction U along the gantry axis). A range shifter system is used in front of the patient for providing fast changes of the penetration depth of the beam (second direction S of scanning, in depth). The range shifter consists of a stack of 5 mm-thick polyethylene plates, which are moved sequentially into the beam by pneumatic valves. The motion of the patient table is used as the third axis of scanning. This is the slowest and most seldom used motion, which is applied in the transverse non-dispersive direction T. The whole is a Cartesian beam scanning system. The points to be improved on an inventive system and an inventive method in comparison to the present system are: The unsatisfactory access to the patient table when the beam is applied from below. The slow speed of scanning, due to the chosen sequence of the scanning devices, magnetic 1st, range 2nd and table 3rd. The use of two mechanical systems makes the scan too slow for applying repeatedly target repainting. The scanning on Gantry 1 is therefore quite sensitive to organ movements. Further, a system for an intensity-modulated proton therapy of a predetermined volume within an object is known in the prior art, comprising: a) a proton source in order to generate a proton beam being adjustable with respect to the beam intensity; b) a degrader being optionally disposed in the proton beam in order to attenuate the energy of the protons in the proton beam to a desired proton energy in the proton beam; c) a number of proton beam bending and/or focusing units constituting the beam line for the transport of the beam, where a section of the beam line can be rotated around the patient table (the actual proton gantry); d) a beam nozzle on the gantry having an outlet for the proton beam to penetrate the predetermined volume of the object; e) a beam bending magnet being disposed upstream of the nozzle; and f) a couple of sweeper magnets being disposed upstream of said beam bending magnet in order to sweep in a parallel fashion the proton beam in both lateral direction at the exit of the last beam bending magnet. The method to deliver the dose by a double magnetic scanning and by changing the beam energy is known. However, the innovations, which are protected by this application, are related to particular aspects of the system and of the beam delivery method described in the cited publication. The innovations can be summarized in the following list: The first part of the invention regards the optimized system design. An inventive system for an intensity-modulated proton therapy of a predetermined volume within an object comprises: a) a proton source in order to generate a proton beam (B) being adjustable with respect to the beam intensity; b) a degrader being optionally disposable in the proton beam (B) in order to attenuate the energy of the protons in the proton beam (B) to a desired proton energy in the proton beam (B); c) a number of proton beam bending and/or focusing units; d) a beam nozzle (N) having an outlet for the proton beam (B) to penetrate the predetermined volume (T) of the object (M); e) a beam bending magnet (A3) being disposed upstream of the nozzle (N); and f) a couple of sweeper magnets (WT, WU) being disposed upstream of said beam bending magnet (A3) in order to sweep the proton beam (B) in both lateral directions (T, U) before the proton beam (B) enters into the beam bending magnet (A3),characterized in that g) said beam nozzle (N) is defining a cross-sectional scanning area (SF) substantially perpendicular to the proton beam (B) in the range of 10 to 30 cm2, and h) said sweeper magnets (WT, WU) and said beam bending magnet (A3) are controlled in order to guarantee a parallel beam orientation over the complete cross-sectional scanning area (SF). The use of a reduced range of magnetic scanning—on a small compact nozzle and a small air gap to the patient allow to design a very compact gantry which brings an almost unscattered (due to the short distance) proton beam into the target volume. The use of the two-dimensional parallelism of scanning—for the field size extension using the patient table on the basis of a “geometrical” field patching—which opens up the option to use a slow continuous table motion during multiple target rescannings in order to compensate the comparably small cross-sectional scanning area at the nozzle. The possibility, by virtue of the design of the beam optics, to scan the beam in two dimensions while keeping the direction and the shape of the beam unchanged (parallel beam scanning) is a major characteristics of the PSI Gantry 2. Strong emphasis is given on the utilization of this important feature. The parallelism of scanning can be used for extending the range of beam scanning beyond the given magnetic scanning range, by combining it with the patient table motion in a simple procedure, which is independent of treatment planning (“geometrical” field patching). While using a geometrical field patching technique the patient table can be moved very slowly and continuously, by compensating the displacement of the table motion with an offset applied to the sweepers (field patching applied with continuous table motion). This approach is very attractive especially in the context of multiple target repaintings, which are needed in the presence of organ motion (slow table motion during multiple target repaintings). The geometric field patching method allows overcoming the problems posed by a limited range of magnetic scanning. This feature can then be used for designing a nozzle which is small in size in both transverse directions to the beam (slim very compact nozzle) as given by the defined size of the cross-sectional scanning area. The use of a slim nozzle is the preferred solution for placing the patient very close to a pre-absorber system and to the beam monitors, both enclosed in the nozzle (small air gap to the patient), without colliding with patient shoulders, to avoid the broadening of the beam due MCS in the air gap to the patient. According to the inventive process for an intensity-modulated proton therapy of a predetermined volume within an object (M); the following steps are comprised: a) dividing the predetermined volume (T) into a number of iso-energy layers (L) each corresponding to a determined energy of the proton beam (B); b) determining a final target dose distribution for each iso-energy layer (L); and c) applying the final target dose distribution or at least a predetermined part of this final target dose distribution by parallel beam scanning under controlling the respective beam sweepers (WT, WU), thereby scanning one iso-energy layer (L) after the other using an intensity-modulated proton beam (B) while scanning a predetermined iso-energy layer (L). Therefore, it is now possible to perform the magnetic scan (at each iso-energy layer) along the target contour (at that proton depth) and on similar equidistant contours in the interior of the target (contoured double magnetic scanning). The concentric contours are scanned with close-to-maximum speed by shaping the dose using the beam intensity modulation controlled at the ion source of the accelerator. By this method scanning speed is gained and thus a large amount of target repaintings can be applied. Additionally, the best possible quality of the lateral fall-off of the dose distribution at the edge of the field can be obtained and the dynamics for the beam intensity variations can be kept low, while working with maximum speed of scanning. By virtue of the 1:1 imaging of the beam optics of Gantry 2 from the coupling point of the gantry to the isocenter, an imaged (virtual) collimation on the scanned beam spots can be applied by using a (real) collimator block (moving radially and azimuthally) at the coupling point of the gantry (contoured double magnetic scanning with imaged collimation applied to a scanned broad beams). All these points are explained in more details below. FIG. 1 shows a schematic diagram of the depth dose distribution of protons (graph 2) in comparison to the depth dose distribution of photons (graph 4) in human tissue equivalent material. The advantage of proton therapy is given by its superior physical selectivity, which allows to design a plateau SOBP (the so-called spread out Bragg peak) for the dose in a distinct depth of the target volume which is located within the patient. Protons have a well-defined penetration range in biological tissue and they deposit the maximum of their energy in the region where they stop. This gives rise to the so-called Bragg peak, which is shown in FIG. 1 as the dose deposition of a mono-energetic proton beam as a function of depth. This must be compared with clinical photons, which have a characteristic exponential fall-off of the dose (graph 4). Due to their electric charge protons offer the possibility to localize the dose not only in the lateral directions by the magnetic scanning technique but also as a function of the depth. Compared to photons, with protons a remarkably reduction of the integral dose outside of the target volume is achieved, i.e. by a factor of 2 to 5 depending on the specific case (savings on insane tissue treatment being indicated by the hatched areas in FIG. 1). FIG. 1 depicts also how a spread out Bragg peak SOBP can be obtained through the stacking of pencil proton beams having different ranges and intensities. A homogenous dose distribution in depth can be thus constructed from a single beam direction (with photons one needs several beam directions). One can easily imagine that this technique allows to design rather complicated three-dimensional target volume dose distributions which can be achieved by magnetic scanning of the proton beam in both lateral directions and by energy scanning in depth. FIG. 2 is a schematic top view on the cross section of a gantry G for the illustration of its mechanical layout. A proton beam B is generated in a non-illustrated accelerator, such as a cyclotron (but synchrotron, linear accelerator or others are possible as well), which is adjustable with respect to the intensity of the beam B. For directing the beam B to an object, such as a patient or a biological probe volume, a beam transport system BT is installed within a support frame SF. The support frame SF is pivoted with a front roll FR and a back roll BR. The beam transport system BT is supposed to rotate only on one side of the gantry G by ±95°. Therefore, a patient table PT is mounted independently from the gantry G and is accessible from one side of the treatment room TR which enables the medical personal to access to the patient at any time through a permanent fixed floor. Further, medical equipment favorable to the medical therapy, like CT, anesthesia devices etc. can be disposed at any time very close the patient table PT. A nozzle N located utterly downstream of the beam transport system BT can be located very close to the patient, too, achieving remarkably benefits to the sharpness of the proton beam B in the target volume. From the patient table PT, the patient experiences the treatment room TR more or less as a room having normal dimensions with a small rotating nozzle N with a sliding cover extending inside this treatment room TR. The patient sees only the nozzle N rotating along a slit in the half cylindrical internal wall of the treatment room TR. With this design the need of a moving floor (except for the slit of the nozzle N) is canceled. The treatment room TR has for example a length of 6 to 7 m, depth of 5 to 6 m and a height of 2.2 to 2.4 m. These dimensions of the treatment room TR even facilitates the horizontal rotation of the patient table PT along its horizontal axis. The beam transport system BT used for the application of the proton beam B to the target volume within a patient is schematically shown in FIG. 3. This beam transport system BT comprises a system of three dipoles A1, A2, A3 and seven quadrupols Q1 to Q7. Other elements are steering magnets Sx/y (some of those elements are embedded as separate windings in the sextupoles H), optional slits or fixed collimators K, beam diagnostic elements M and vacuum pumps P. The main dynamic elements for the scanning are the two sweeper magnets WU and WT and a dynamic quadrupole corrector QC. The beam optics calculations were performed for a nominal beam energy of 230 MeV (other energies are obtained by scaling the electric current in the magnetic elements of the beam line according to the momentum of the beam). The bending radius applied to the beam B is chosen to 1.5 m. The nominal field is B=1.5 Tesla. The radial parallel displacement of the beam line from the rotation axis is about 3.2 m. The distance of the exit field boundary of the 90° bending magnet to the isocenter is approx. 1.7 m. This space available in this embodiment is sufficient for keeping the bulk of the 90° bending magnet A3 during rotation to stay outside of the treatment room TR at a distance of about 1.2 m from the isocenter, in order to keep the ceiling of the treatment room TR at least 2.4 m high (normal room height) which is a significant improvement for the mental well-being of the patient. The shape of the beam line is derived from these settings, by using the minimal space necessary to place all beam transport elements needed to fulfill the beam optics requirements inside the most minimal space of the support frame SF. This beam transport system BT offers therefore the full parallelism of the beam B during painting, a true size imaging from the starting point of the rotating beam line (gantry coupling point) to the isocenter (the end point where the beam is scanned in the patient). Further, beam achromatism and beam focus invariance during double sweeping in U- and T-direction is achieved. The beam delivery elements disposed upstream of the beam transport system BT are not shown. A cyclotron delivers a continuous beam being adjustable with respect to its intensity. The change of the energy will be preferentially done by changing dynamically the setting of a degrader and the tune in the beam line ahead and on the gantry G. Between the cyclotron and the degrader a fast kicker magnet is mounted for the switching ON and OFF of the proton beam B with a reaction time of only 50 μs. FIG. 4 shows the main difference of the PSI solution compared to the more usual solution to place the scanning magnets after the last bending magnet. The most usual approach is to place in the layout of the beam line of the gantry, the sweeper magnets (or scattering devices) after the last bending magnet (solution A, adopted for all proton gantries proposed or realized so far, except for the Gantry 1 of PSI). In this case, a long drift space (throw) is required between the sweeper magnets and the isocenter, in order for the lateral spread of the beam to take place. The drift space is thus added to the radius of the gantry. The beam impinges in the patient with varying divergence. The shorter the throw, the stronger is the bending power needed for the sweeper magnets and the stronger is the divergence of the beam. Usually, one chooses a distance of 1.5-2 m and for the lateral extent of the scan a maximum width of the scanned region of typically 30 cm×40 cm. By placing the sweepers before the last bending magnet the radius of the gantry (to 7.5 m for an iso-centric layout like the new Gantry 2 of PSI) can be tremendously reduced since the drift space is included in the path of the beam in the last bending magnet (solution B, left side of FIG. 4). Thus, a significantly more compact gantry system is achieved. The only “drawback” in this last solution is that the range of scanning is limited by the gap and the width of the poles of the last bending magnet A3, which must be wide enough to contain the scanned beam to the exit of this beam element. This implies that the applicable range of scanning is somewhat reduced and that the power consumption for the last bending magnet A3 is higher as for a solution of the type A. If the geometrical shape and the magnetic field of the last bending magnet A3 is designed very carefully, the beam can be scanned in a parallel fashion in two dimensions (to keep the apparent source of the protons at the infinite) at the given cross-sectional area. The idea to provide the parallelism of the scanned beam in both directions is well known in the field, since it was realized at least in one dimension already on the PSI Gantry 1. New is however the proof through detailed beam optics calculations (as shown in the proposal for Gantry 2), that this method is indeed possible also for a two-dimensional scan. The advantages of having a parallel scanned beam are summarized in the following: With solution B we simplify treatment planning, since the calculation is applied on a simple Cartesian grid. The verification dosimetry is also simpler and less prone to errors. We are not sensitive to the longitudinal positioning of the dosimetric equipment and of the patient along the beam direction (the distance d of the object to the apparent source of the protons produces otherwise, in a divergent system, a “one over d-squared” dependent effect on the dose, an effect well-known from conventional therapy). Additionally, with a parallel scan less skin dose outside of the target volume is applied. If one uses collimators (as optional devices in addition to scanning), one can machine the edges of the collimators with simple normal cuts. With solution A one needs to apply a conical cut on the internal face of the collimator hole to compensate for the divergence of the beam, another problem known from conventional therapy). A major advantage often not recognized in the proton therapy field (mainly because only PSI has up to now some practical experience of using scanning on a gantry) is however the potential for applying patching field techniques, for extending “on line” the range of magnetic scanning. The parallelism of scanning makes the patching of dose fields very easy. One can keep the range of magnetic scanning quite small (typically in the range of 150 to 300 cm2, i.e. of only 20 cm×10 cm). The delivery of the dose is however calculated in treatment planning as if the range of magnetic scanning would be unlimited. Since the beam is maintained parallel to its nominal beam direction we don't need to decide in the dose calculation, where the beam and the patient table will be exactly positioned in practice during treatment; magnetic parallel scanning and table motions are in principle freely interchangeable. The dose depends only on the final position of the beam with respect to the patient body, we can thus postpone the decision on how to move the patient table in combination with the sweepers magnets to the last instant during beam delivery (the patient table is used here as a device for extending “on-line” the range of scanning). The same is not true for a system with an inherent divergence. With a scattered (necessarily divergent) beam it is not possible to combine dose fields delivered at different table positions without destroying the homogeneity of the resulting dose distribution (with unavoidable dose errors in the overlapping region of the fields). With a divergent scanning system one can in principle combine several fields applied at different table positions into a homogenous dose, since one has all the degrees of freedom to modify the dosage of each single beam spot. This must however be implemented already in the optimization procedure in the dose calculations during the phase of treatment planning (the field patching must be part of the actual planning). This is probably one of the reasons, why the range of magnetic scanning for the systems of the type A is usually chosen to be very large, enough to cover all possible target sizes. The puzzling question with those systems is however: which may be in practice the maximum target size that can reasonably be considered? With a parallel scanned beam, we gain in principle the freedom to simply extend the range of scanning beyond the chosen magnetic range, and to treat virtually any target size, just be shifting the patient table, independently of therapy planning. One important advantage of the present invention is the idea to take the maximum advantage from the possibility to use a parallel scanned beam. The combined use of magnetic scanning and table motion permits to extend the range of scanning beyond any practical limits (to treat for example medulloblastoma cases, which are cranio-axial spinal irradiation of children extending over a range of up to 80 to 90 cm length, just in one go). The basic patching technique is performed in its simpler form as following: a) if a large target volume is bigger than the range of scanning, the matrix of beam spots will be separated in partially overlapping sub-volumes (concept of “patched” dose fields, addition of constituent dose fields) b) each subvolume is chosen small enough to be covered by the (limited) range of magnetic scanning c) the dose is delivered on each subvolumes at different body positions by moving the patient table d) each subvolume is usually irradiated including energy changes, i.e. as a fully painted dose volume e) in the overlapping region between sub-volumes the constituent dose fields are applied with opposed smooth dose transitions (a gradual dose fall-off of field 1 compensated by the corresponding rising of the dose of field 2) in order for the method to be less sensitive to organ motion errors. The manipulation of the fall-off is very simple since it is realized by a linear reduction (in the overlapping region) of the required dosage of each spot. The gantry solution B allows a fast double magnetic scanning on a more compact gantry. This compact gantry having diameters in the range of 4 m (eccentric) to 7.5 m (isocentric) must keep reasonably small the pole size and the air gap, the weight and power consumption of the last beam bending magnet A3. This yields on the other hand in a lower power consumption for the sweepers WU, WT, delivering a comparably faster speed of scanning. The fast speed of scanning is accessible due to the chosen sequence of the scanning devices now double magnetic 1st and 2nd with range or energy 3rd, and with the additional movement of the table for treating large fields. The use of a fast double magnetic scanning system makes the scan fast for applying repeatedly target repainting (typically 10 times) and facilitates the scanning even under quite sensitive organ movements. Option to move the table continuously for treating large fields with multiple repainted volumes In the context of repeatedly applied volumetric target rescannings, the table can be moved very slowly in a continuous fashion during beam delivery. Since the direction and the dose characteristics of each pencil beam are all maintained invariant, any ongoing small table movement can be equivalently corrected with a similar sweeper motion in the opposite direction. While the beam is delivered as a partial volume in a grid we can freely move the table. The effectively displaced position of the patient due to the movement of the table is known at any instance and can be immediately corrected as an offset applied to the sweepers. Under the assumption of repainting the dose several times (i.e. 10 times) the position of the patient table PT can be changed in smaller steps between repainted fields as shown in FIG. 5. By changing the position of the patient table PT very slowly the patient does not recognize its motion. The dose gradient of the cumulated in the interior of the field can be kept very low (about 50% of the dose per 8 cm≈6% per cm). The delivery of each partial-dose partial-volume field is done while moving slowly the patient table PT across the resulting large field. Pictorially, the dose distribution grows like in a moving sand dune. The gradients are so shallow that there does not occur any practical difference between this technique and the situation where the scan range in T- and U-direction is large enough to cover any assumed very large target volume. FIG. 5 now depicts schematically this patching of fields for volumes larger than those directly accessible by only T- and U-sweeping with the second method of multiple target repaintings. Instead of delivering the same dose 8-times at the same position of the patient table PT the patient table is shifted continuously between the delivery of partial volumes. The volumes are painted (using the T-sweeper, the U-sweeper and the energy) according to a trapezoidal filter function applied to the T-sweeper motion to the required intensity of the beams spots (painted lines in FIG. 5). The dose filters are cumulated in connection with the slow movement of the patient table PT, which is moved once from the left to the right and back to the left. The control unit of the T-sweeper steers the beam B in a way that the motion of patient table is considered as an offset of the T-sweeper but offering “new” sub-volumes for painting on the leading edge of the patient table and loosing “old” sub-volumes on the trailing edge of the patient table PT as seen in the direction of the movement of the patient table PT. Very often the predetermined target volume is located close to the skin of a patient what requires a low range of the proton beam in the tissue. Unfortunately, low ranges of the protons may imply low beam energies, which have several drawbacks. At low energy most of the beam is lost in the degrader, the intensity of the beam becomes rapidly prohibitively low, even if one try to compensate for this by increasing the current extracted from the accelerator (this applies to using a cyclotron). A major drawback is the difficulty of designing a dose plateau in depth with the beam, since the beam becomes very sharp in depth at lower energy (the behavior is shown in FIG. 6). The task to deliver of a homogeneous Spread out Bragg peak (SOBP) using a reasonably small number of energy steps becomes prohibitively difficult. This problem is shown in FIG. 6, where several Bragg peaks are plotted at different beam energy (using a momentum band of the transmitted beam which is representative for the state of this technique). The lower the energy of the beam is, the sharper is the width of the Bragg peak. In order to avoid these drawbacks, a pre-absorber body may be optionally disposed between the outlet of the nozzle and the patient. Preferably, the pre-absorber body may comprise absorbing materials of low atomic number, to keep the broadening of the pencil beam due to Coulomb multiple scattering (MCS) in this material as low as possible. Through the use of such a pre-absorber the proton energy in the proton beam can be used within a rather high beam energy bandwidth enhancing also the stability of the proton beam. In addition, a dose plateau (according to spread out Bragg peak) can be designed starting closely under the skin in comparably lower depths. The impact of a pre-absorber PA (FIG. 7) is setting a depth off-set. Therefore, the use of very low energy proton beams is avoided which in addition are both difficult to handle stable and show a very sharp Bragg peak making the low energy beams very sensitive to organ motion errors. The use of a pre-absorber is a necessity for working with low proton ranges (if we disregard the use of complex moulds applied directly onto the patient skin), when we want to stop the beam at low ranges under the patient skin. When such a pre-absorber block is inserted in the beam, this represents a significant amount of material in the beam, which inevitably scatters the protons through the physical process called Coulomb multiple scattering (MCS). This effect results in an unwanted broadening of the pencil beam width due to the use of the pre-absorber. The beam width increases linearly with the distance between pre-absorber and patient (linear propagation of MCS of the block in the air gap before the patient). The best strategy is therefore to keep the air gap as small as possible, preferably zeroed. The larger the air gap is, the bigger is the pencil beam width, the less precise is the lateral fall-off of the dose distribution and the more unsatisfactory is the quality of the treatment. The major point to be considered in the design of the nozzle, is therefore to be able to place the patient as close as possible to the exit of the nozzle (near the pre-absorber). This must be possible for all considered beam directions. This is a major point acquired from the experience of using Gantry 1, a point, which is now most optimally realized on Gantry 2. The patient shoulders pose a severe problem in this respect, especially when the patient is lying supine and the beam must be delivered horizontally on the left or right side of the head (as shown FIG. 4). The smaller is the space occupied by the nozzle, the better we can bring the patient head close to the pre-absorber. We therefore aim of using a possibly small slim nozzle design. In FIG. 7 a) to c) the system design with respect to the pre-absorber PA is schematically illustrated. The pre-absorber PA is used to mimic human tissue in order to establish a spread out Bragg peak also very close under the skin of a patient without being forced to use comparably lower energies to shorten the beam range. Therefore, the drawbacks inherited from too small energies, namely weak beam stability, too low intensity and difficulties to design a spread out Bragg peak, are avoided. The pre-absorber body PA shifts the proton range back to the patient skin while using dynamic energies above 120 MeV. Additionally, the pre-absorber body PA may be machined with an embedded ridge filter to increase the width of the Bragg peak for a better homogeneity of the spread-out Bragg peak. While incorporating the pre-absorber body PA within the nozzle N, the principle layout of the nozzle N though having a rather smaller scan field region area SF in both directions T and U enroles now its main advantages because the patient can be placed very close to the outlet of the nozzle N. For that reason, the lateral broadening of the beam B due to multiple Coulomb scattering can be almost completely suppressed and the beam B maintains its sharpness thereby adjusting the true dose delivery close to the calculated dose gained from theoretical dose simulations. The area scanned by the parallel beam should ideally correspond to only the lateral cross section of the nozzle. This problem is depicted in the FIG. 4, option B. In principle, one can argue that in theory one can position the head close to the edge of the nozzle N also with a bulky nozzle of a long throw gantry. This implies however that we are delivering the beam with the most tilted incidence on the patient. The pre-absorber block is depicted in FIG. 4 for the two gantry types A (prior art) and B (inventive solution). If we have a long throw gantry A we are using a large preabsorber block PAA of the size of about 40 cm×50 cm with a weight of 20 kilograms. Since in most cases we want to deliver the proton beam—with and without block—in one and the same fraction, this block should be designed to be removable by motors from the beam. At PSI, we have decided to accept a compromise, by using a rather limited range of magnetic scanning (10 cm×20 cm) since this allows the design of a very slim (permanently installed) small simple nozzle. The pre-absorber block PAB is then of the size of about 25 cm×15 cm, i.e. of only 4 kilograms. For the compactness of Gantry 2 (of the solution B type) we suggest to just tilt in and out the pre-absorber PAB plate in the beam by rotating it along its longer side. The space in the longitudinal beam direction occupied by the rotation is the short side of the block PAB, which is only 15 cm. If we would rotate in and out the 50 cm×40 cm pre-absorber block PAA for a long throw gantry in the same way we have to place the monitors at a larger distance from the patient. We would then have a less good knowledge from the monitors on the position of the beam impinging in the patient and we would increase the broadening of the beam due to the MCS in the monitors. If we would move the pre-absorber out laterally out of the beam we would increase the cross section of the nozzle, making it even more bulky. A small nozzle appears to us for these practical reasons and for the comfort of the patient to be a better solution than a bulky nozzle. Innovative is here the compact arrangement for the motion of the pre-absorber block to keep the size of the nozzle small in all three dimensions. By accepting a rather reduced range of magnetic scanning and by compensating this limitation with the geometrical patching technique described above, we can afford to use a nozzle having a very small cross section transverse to the beam. This is a more friendly solution to the patient for positioning him very close to the pre-absorber. In this way we can satisfy all given therapy conditions in the most optimal way. We now describe in more details the scanning methods. For the therapy of the target volume within a patient, two general known methods can be applied. A first method provides a “step and shot”-method while painting the total dose in one plane in depth (one energy step) by sweeping the beam B in both lateral directions T and U. The shifting of the Bragg peak in depth is performed in this method as the last frequent motion. Under the assumption of a target volume of 1 liter (10 cm×10 cm×10 cm) and a 7 mm FWHM on a 5 mm grid, approximately 21×21×21≈10,000 shots having an average duration of 10 ms have to be applied to the target volume that leads to approximately 100 seconds beam on time. Further, under the consideration of a given reaction time of the kicker of 50 μs, a dead time between the spots of about 2 ms and a dead time of either the U- or the T-sweeper of 1 s per plane and a dead time of the motion degrader of about 3 s (150 ms per plane times 21) the total dead time lays in the range of about 24 second per 10,000 shots allowing a scanning speed of 5,000 to 10,000 spots per minute. The patient table PT will be only used for patching fields and/or for the correction of the positioning of the patient. The second method is prosecuted by a continuous scanning with beam intensity modulation (a television-like mode). This method requires that the target volume is divided into isorange-layers of planes each having lines in the lateral U-or T-direction. These lines can be painted with continuous speed in the respective direction without switching off the beam B. The shape to the dose is thereby given by using the modulation of the intensity of the beam at the ion source within the cyclotron. The scanning in depth (the change from one isorange-layer to the other) is thereby again done by changing the energy of the proton beam B dynamically with the degrader. In this method, a liter of the target volume can be painted about 9 times per minute under the assumption that a line can be painted within 5 ms plus 3 ms for the step motion of the respective other sweeper. One plane having again a line structure with a grid of 5 mm leading to 21 line each requiring 8 ms to be painted. One plane therefore requires 168 ms plus 150 ms for the change of energy for the next plane which results at 318 ms for painting and, changing a plane. According to the 5 mm grid structure 21 energy steps are required that leads to 318 ms times 21=6.7 second for painting the complete target volume of 10 cm×10 cm×10 cm=1 liter volume. It can be summarized that the time needed for changing the energy is comparable to the time needed for painting a plane of dose. The time required for painting the target volume once lays in the range of the respiration cycle of a person in idle status. Therefore, dose errors caused by organ motion can be middled out due to the possibility of multiple target painting within a comparably low period of time. Therefore, the required dose in each sub-volume of the target volume can be as well divided into sub-doses, which will be applied step by step within the repainting procedure of the target volume. Additionally, the scan strategy might further be optimized for example by less rescanning on the most proximal slices and more on the most distal layers, those which require most of the dose. With this method the same quality of the dose distribution as with the first method can be achieved but with a factor 8 to 10 faster target repaintings. With this method it is possible to apply IMPT (intensity modulated proton therapy) also to moving targets by scanning the small pencil beam without the need to use collimators and compensators while maintaining the advantage of the small size of the nozzle N with the afore-mentioned features. A very fast scan procedures provides a painting strategy with painting the two dimensional array line by line, whereby the intensity of the proton beam is modulated according to the desired target doses or partial target doses along the line. Therefore, the proton beam can be applied to the two-dimensional arrays comparable to the function of an electron beam of a cathode ray tube. The dead times of the proton beam per two-dimensional array of sub-volumes are therefore limited to only switching off the proton beam when changing the line. Additional dead time only occur when changing the range of the proton beam in order to paint the subsequent two-dimensional array of sub-volumes. In total, this procedure enables the facility to be best suited for multiple three-dimensional target volume repainting within a time period comparable to the human idle respiration cycle. This performance supports tremendously the elimination of organ motion errors. Of course, the proton beam can be applied discontinuously within each line, which involves unfortunately on the other side longer dead time in-between the spots. The method to adapt the dose by slowing down the beam motion of the sweeper magnets instead of changing dynamically the intensity is another easier but slower alternative method. As a new method is the procedure to scan the volume following the target contours and on equidistant contour at the interior of the target. Option 1: Contoured Painting with Optional use of Beam Intensity Modulation This mode of scanning has the following approaches: a.) Painting of the treatment volume in iso-energy layers (the Bragg peak covers with dose a layer at a depth equivalent to the range of the protons for the given beam energy). Such a layer is very efficiently conformally painted by double magnetic scanning. b.) Change of energy in between layers with beam off, by changing the setting of the degrader and the setting of the beam line elements in the section from the degrader to the patient. c.) Optionally, magnetic painting of a layer by scanning the beam along concentric target contours. d.) Optionally, control of the dose delivery during a contour painting by changing dynamically the beam intensity directly in the proton source. FIG. 8 shows the principle. The method is based on the idea to scan the volume in energy layers L and lines as this is done on a television-like mode, but where the lines are painted along the beam-eye-view (BEV) contour of the target T at the depth corresponding to the given energy-layer and on similar equidistant contours in the inside of the target T. The beam shall be moved with close-to-maximum velocity and the painting of the dose will be achieved through modulation of the beam intensity using the deflector plate of the accelerator. To understand the difference to the previous scanning mode, we have to understand the factors affecting the lateral fall-off of the dose. We assume that the beam spot that we use is the one minimally available in the beam line to obtain the sharpest possible fall-off. FIG. 9 shows the difference in the lateral fall-off obtained through the addition of Gaussian beam spots for two typical cases. In the case a) the beam spot profiles are added at separately spaced sparse discrete positions. Through the optimization algorithm in the dose calculation, by selecting the dosage of each contribution individually, one can obtain a good homogeneity of the dose on the inside of the target, while keeping the dose lateral fall-off to be essentially governed by the fall-off of a single constituent Gaussian. If one deposit the same beam in a continuous mode (integrating it along a beam off-on-off rectangle) one obtains curve b). The relative difference in the fall-off of the curves a) and b) is in the limiting case the difference between a Gauss function and the error-function (which is the folding of the original Gaussian with a step function). The difference in slope at the 50% level is 48%. From this we conclude that it is more convenient from the point of view of the precision of the dose distribution to place isolated beam spots in the direction perpendicular (surface normal) to the target contour. If one uses the approach to scan along parallel beam lines (the television mode described above), the dose optimization algorithm will thus try to construct an intensity modulation profile which simulates as much as possible isolated sparse spots at the edge of the field. The intensity modulation will thus try to produce intensity patterns with very sharp dose peaks at the edge of the contour. The optimization will thus try to deliver a very high dose in a very short time. The system will thus be very demanding on the maximum dose rate and on the speed of changing the intensity (i.e. a very high beam intensity dynamics). This behavior will be much relaxed if we pay the effort to scan both magnets along isocentric contour lines. The method to follow contours shall provide the same amount of rescanning as with a television-like mode, but we expect with this method two possible major advantages: 1. By moving the beam tangentially along the contour we keep the lateral fall-off as sharply as possible as given by the original Gaussian shape of the beam, while needing a much lower dynamics of the beam intensity as compared with the mentioned television-mode. To achieve an edge enhancement effect as described above, we need to deliver almost separated single spots at the edge of the target if the beam is crossing the target contour. This would require the delivery of very high doses (at very high dose rate) in a very short time (high beam intensity dynamics). With the new contoured mode we are now able to obtain the same precision but with a much lower dynamics. 2. We expect that along the contours the required optimized dose will vary less rapidly as when we move the beam perpendicular to the edges of the field. The internal contours will probably require less dose than the one on the target boundary. We could therefore repeat the volumetric repainting more often on the external contours and less often in the inside of the target (i.e. to work with a more equalized beam intensity bandwidth in general).Option 2: Broad Beam Contoured Scanning with “Imaged Collimation” For this option we will use the same approach as above, but we will scan the beam at a somewhat slower speed and we will paint the dose with a much larger beam spot. The next idea is to have a collimator mounted at the coupling point of the gantry (the point on axis of the entrance into the rotating beam line). The collimator can be moved under motor control radially in-out and azimuthally around the beam axis as shown schematically on the left side of FIG. 10. The collimation effect applied to the beam at the entrance to the gantry (the beam optics source) is then imaged 1:1 on the scanned beam spot. We can therefore apply scanning with a large beam spot, while keeping the lateral fall-off very sharp (the spot gets clipped at the boundary to the target). The method is in principle available in view of the proposed beam optics, which is a 1:1 image from the coupling point of the gantry to the isocenter. While the beam follows the target contour, the collimator at the coupling point will be moved into the beam and will be rotated for the cut to remain tangential to the virtually imaged target contour. In this way it is possible to obtain a sharp lateral fall-of the dose while scanning an inherently broad beam. FIG. 10 shows on the right the result of a Monte Carlo simulation applied for a proof of principle to a circle as the target. The beam spot images at the isocenter show the effect of the collimator imaged from the coupling point to the gantry. The use of a remotely controlled collimator could be thus used to produce sharp dose edge boundaries while using large beams, i.e. to obtain the same effect as by using an individually shaped collimator placed just before the patient. By scanning with a broad beam we will avoid depositing sharp dose gradients at the interior of the target. This method is therefore quite robust against organ motion problems. By using a broad beam we can gain in capability of repainting (coarser grid—shorter path—more repainting), especially at the interior of the target, where can run with a higher speed (when the collimator is radially fully retracted). The result should be quite similar as a beam delivery with a passive scattering technique, but with the advantage that there is no need to fabricate individually shaped apertures and no need to mount additional equipment on the nozzle for each field. The new method could however suffer from MCS in the monitors, spoiling the quality of the lateral fall-off of the dose especially at low energy. The design of an overall beam delivery system for proton therapy capable of satisfying different clinical requirements all at once is a difficult optimization exercise. One has to provide: automated conformal fast dose delivery to apply multiple fields in a sequence, with good homogeneity of the dose and with a sharp lateral and distal fall-off, dose delivery to any depth in the body and to any possible target size, freedom in a 4π solid angle for the use of multiple beam directions applied on the immobilized supine patient, small air gap, short treatment time, multiple target repaintings to cope with organ motion, possibly small compact gantry design. These contradictory requirements are in our opinion conceptually well satisfied in our design all at once, which is a significant achievement. The availability of both modes, fast contoured scanning with a small beam or slower contoured scanning with imaged collimated varying (small or large) beams, should bring the scanning technique close to its maximum possible performance, to the maximum benefit to the patients. These advanced beam scanning techniques applied on the optimized nozzle design described in the first part, should provide one of the most performing systems of the world.
	abstract	An apparatus for filtering an x-ray beam emitted by an x-ray source comprises a filter, adjustable from a parked position (P) outside of a path of the x-ray beam into a filtering position (F) in the x-ray beam path. A corresponding first sensor device detects when the filter in the filtering position (F), and a corresponding second sensor device detects when the filter in the parked position (P). Further, sensor signals are communicated by the first and second corresponding sensors to an evaluation device. The evaluation device generates a report if the filter is not in at least one of the parked position (P) and the filtering position (F).
	abstract	A device and a method for the multispectral correction of radiation hardening in computer tomography with variable tube voltage is described. In particular, a water correction and a post-reconstructive hardening correction is disclosed. To perform the water correction, project image data is corrected, in that correction values are obtained from a previously determined correction table, by means of which a correction of the projection image data can be performed. By means of an image reconstruction, this produces a corrected volumetric image.
	description	1. Field Example embodiments generally relate to fuel structures and radioisotopes produced therein in nuclear power plants. 2. Description of Related Art Generally, nuclear power plants include a reactor core having fuel arranged therein to produce power by nuclear fission. A common design in U.S. nuclear power plants is to arrange fuel in a plurality of fuel rods bound together as a fuel assembly, or fuel assembly, placed within the reactor core. These fuel rods typically include several elements joining the fuel rods to assembly components at various axial locations throughout the assembly. As shown in FIG. 1, a conventional fuel assembly 10 of a nuclear reactor, such as a BWR, may include an outer channel 12 surrounding an upper tie plate 14 and a lower tie plate 16. A plurality of full-length fuel rods 18 and/or part length fuel rods 19 may be arranged in a matrix within the fuel assembly 10 and pass through a plurality of spacers 20. Fuel rods 18 and 19 generally originate and terminate at upper and lower tie plates 14 and 16, continuously running the length of the fuel assembly 10, with the exception of part length rods 19, which all terminate at a lower vertical position from the full length rods 18. As shown in FIG. 2, fuel elements 25 may be shaped in pellet-form and placed within the fuel rods 18 or 19. These fuel elements 25 may be “stacked” within the fuel rod continuously to provide fuel through the length of the fuel rod 18 or 19. The stacking of fuel elements 25 may permit expansion or other deformation of the fuel elements 25 during the operation cycle of the reactor core. Further, a gap 21 between the elements 25 and an inner wall 23 of the fuel rod 18 or 19 may accommodate gaseous fission products produced from the fuel elements 25 during operation of the reactor. Spring 24 at ends, typically at least an upper end, of the fuel element stack in the fuel rod may be present to further allow fission product accumulation and fuel element 25 deformation. Example embodiments and methods are directed to irradiation target retention devices and systems that may be inserted into conventional nuclear fuel rods and assemblies. Example embodiment devices may hold several irradiation targets for irradiation during operation of a nuclear core containing the assemblies and fuel rods having example embodiment irradiation target retention devices. Irradiation targets may substantially convert to useful radioisotopes upon exposure to neutron flux in the operating nuclear core and be removed and harvested from fuel rods 18/19 after operation. An example embodiment irradiation target retention device may include one or more irradiation targets that may be inserted and held in retaining bores in the device during operation. Bores may be sealed by a cap or by other retention devices so as to provide multiple levels of containment to the irradiation targets and radioisotopes produced therein. In other example embodiments, irradiation targets may be removed from example embodiment retention devices by aligning exit spaces within the devices and removing irradiation targets therefrom. Detailed illustrative embodiments of example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only example embodiments set forth herein. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” or “fixed” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the language explicitly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. FIG. 3A illustrates an example embodiment irradiation target retention device 125 that may makeup an irradiation target retention system. Irradiation target retention device 125 has dimensions that enable it to be inserted into conventional fuel rods (cladding tubes) used in conventional fuel assemblies. For example, irradiation target retention device 125 may have a maximum width of an inch or less and a maximum length of several feet. Although irradiation target retention device 125 is shown as cylindrical, a variety of properly-dimensioned shapes, including hexahedrons, cones, and/or prismatic shapes may be used for irradiation target retention device 125. Example embodiment irradiation target retention device 125 includes one or more axial bores 130 that extend partially downward into device 125 in an axial direction from a top end/top face 128. Axial bores 130 may be arranged in any pattern and number, so long as the structural integrity of example embodiment irradiation target retention devices is preserved. Axial bores 130 may have a variety of dimensions and shapes. For example, axial bores 130 may taper with distance from top face 128 and/or may have rounded bottoms and edges. Irradiation targets 140 may be inserted into one or more axial bores 130 in any desired number and/or pattern. Irradiation targets 140 may be in a variety of shapes and physical forms. For example, irradiation targets 140 may be small filings, rounded pellets, wires, liquids, and/or gasses. Irradiation targets 140 are dimensioned to fit within axial bores 130, and/or axial bores 130 are shaped and dimensioned to contain irradiation targets 140. Irradiation targets 140 may be fabricated of a variety of materials that substantially convert into radioisotopes when exposed to a neutron flux encountered in example embodiment irradiation target retention devices 125. For example, irradiation targets 140 may include Iridium-191, which may convert to Iridium-192 when exposed to neutron flux encountered in an operating nuclear reactor, and/or Cobalt-59, which may convert to Cobalt-60 when exposed to neutron flux encountered in an operating nuclear reactor, etc. Irradiation targets 140 may further be sealed containers of a material designed to substantially maintain physical and neutronic properties when exposed to neutron flux within an operating reactor. The containers may contain a solid, liquid, and/or gaseous irradiation target and/or produced radioisotope so as to provide a third layer of containment (other containments discussed below) within irradiation targets 140. A cap 138 may attach to top end/face 128 and seal irradiation targets 140 into axial bores 130. Cap 138 may attach to top end 128 in several known ways. For example, cap 138 may be directly welded to top face 128. Or, for example, as shown in FIG. 3B, cap 138 may screw onto top end 128 via threads 129 on example retention device 125 and cap 138. Or, for example, cap 138 may attach to an top end 128 via a lock-and-key mechanism on cap 138 and device 125. In any of these attachments, cap 138 may retain irradiation targets 140 within an axial bore 130 and allow easy removal of cap 138 for harvesting of irradiated irradiation targets 140. Cap 138 may further have a flat face that seats against each axial bore 130 on top face 128 so as to prevent irradiation targets 140 or solid, liquid, or gaseous radioisotopes produced by irradiation targets 140 from intermingling with other irradiation targets 140 and/or escaping from axial bores 130. Example embodiment irradiation target retention device 125 is fabricated from a material designed to substantially retain its neutronic and physical properties when exposed to a neutron flux encountered in an operating nuclear reactor. Thus example embodiment irradiation target retention device 125 may not substantially interfere with neutron flux reaching irradiation targets 140 and may not chemically react with irradiation targets 140 or radioisotope produced therefrom. Example embodiment irradiation target retention device may be fabricated from, for example, a zirconium alloy, stainless steel, aluminum, a nickel alloy, Inconel, etc. As shown in FIG. 4, example embodiment irradiation retention device 125 may be inserted into conventional nuclear fuel rods 18 and/or 19 (FIGS. 1 & 2) in the same manner as conventional fuel pellets may be inserted into fuel rods 18/19 and sealed therein. Example embodiment irradiation retention device 125 may substantially fill the nuclear fuel rod 18/19, or alternatively, may not substantially fill nuclear fuel rod 18/19 and allow for empty space and/or nuclear fuel pellets to fill the remaining space of nuclear fuel rod 18/19. A spring 24 may be positioned axially with example embodiment irradiation retention device 125 so as to maintain a constant position of device 125 while permitting minor expansion and/or shifting due to variable conditions encountered in an operating nuclear reactor. A nuclear reactor including a fuel assembly with a fuel rod having an example embodiment irradiation target retention device 125 may be operated at normal power operation such that example embodiment irradiation target retention device 125 and irradiation targets 140 therein are irradiated by neutron flux present in the operating reactor. Because flux levels in the reactor are known, and depth of bores 130 (shown in FIG. 3) and placement and composition of irradiation targets 140 therein may be known, it is possible for one skilled in the art to calculate the specific activity of radioisotopes produced from irradiation targets 140. Conversely, a person skilled in the art may calculate a bore 130 depth in order to affect optimal radioisotope production knowing operating flux levels and irradiation target 140 makeup. Once irradiated and substantially converted into useful radioisotopes, irradiation targets 140 and example embodiment irradiation target retention device 125 may be removed from the nuclear reactor, for example, during reactor shut down. Example embodiment irradiation retention device 125 may be removed from irradiated fuel assemblies and fuel rods 18/19 and disassembled by removing cap 138 in order to harvest the irradiated irradiation targets 140 therein. Rod 18/19 and example embodiment device 125 being capped and sealed provide at least a double containment for irradiation targets 140. This provides insurance against irradiation target escape in the event of fretting of cladding of fuel rod 18/19 containing example embodiment irradiation target retention device 125. Depending on placement of axial bores 140, additional containment may be provided by the radial thickness of example embodiment irradiation target retention devices 125. As shown in FIG. 5, an alternative example embodiment irradiation target retention device 225 may be in a fuel element shape/cylindrical pellet-type configuration, although other shapes are useable for example embodiments. Example embodiment device 225 may be dimensioned so as to fit within a conventional nuclear fuel rod 18/19, had have a maximum length such that several example embodiment irradiation target retention devices 225 may fit within a fuel rod 18/19. For example, irradiation target retention device may have a length of a few centimeters or less. Example embodiment irradiation target retention device 225 may otherwise share several characteristics with previously-discussed example embodiments, redundant portions of which are omitted. Example embodiment device 225 defines one or more bores 230 that extend into but not through example embodiment device 225. Bores 230 may be filled with a desired irradiation target 240 that substantially converts to a radioisotope when exposed to neutron flux passing through example embodiment device 225. Ingot-type example embodiment devices may further include a cap as described above with regard to previous example embodiments to contain irradiation targets 240 in bores 230 therein. Alternatively, as shown in FIG. 6, instead of having a cap to retain irradiation targets 240 within bores 230, example embodiment irradiation target retention device 225 may be sealed and/or contained by an empty device 225 and/or a slug 226. Example target retention devices 225 may be tightly stacked with other example target retention devices 225 within a conventional nuclear fuel rod 18/19. A gap 21 may further be present between example devices 225/slug 226 and wall 23 of the fuel rod 18/19. A spring 24 or other holding device may supply resistive pressure against a stack of example embodiment devices 225 in order to hold them substantially flush against one another in the fuel rod 18/19. Because bores 230 may not pass entirely through example devices 225, the bottom surface of each device may be largely flat so as to facilitate a containing seal against another example device 225 stacked immediately below. A slug 226 may be placed between the spring 24 or other preloading device and the stack of example embodiment irradiation retention devices 225 in order to provide the same sealing structure for the topmost device 225 in the stack. Slug 226 may be substantially similar to example embodiment devices 225, except it does not contain any irradiation targets so as to not leak targets onto spring 24 or any other tensioning device within rod 18/19. Example embodiment irradiation target retention devices 225 may permit several different types and phases of irradiation targets 240 to be placed in each device 225 and each bore 230 thereof. Because several example devices 225 may be placed at precise axial levels within the fuel rod 18/19, it may be possible to provide a more exact amount/type of irradiation target 240 at a particular axial level within fuel rod 18/19. Because the axial flux profile may be known in the operating reactor, this may provide for more precise generation and measurement of useful radioisotopes in irradiation targets 240 placed within example embodiment irradiation target retention devices 225. As shown in FIG. 7, yet a further example embodiment irradiation target retention device 325 may be substantially similar to ingot-type example embodiment retention devices 225. However, example embodiment devices 325 may have one or more bores 330 that share a radial position about a central axis 380 of example embodiment devices 325. Example embodiment devices 325 further include a hole 385 in the shared radial position that passes completely through example embodiment irradiation target retention device 325, unlike bores 330. Irradiation targets may not be placed in hole 385. Example embodiment irradiation target retention devices may further include a keyed slit 395 or other aperture positioned at central axis 380. Keyed slit 395 may be shaped to permit a correspondingly shaped shaft to pass through example embodiment device 395 and rotate example embodiment device 395 about central axis 380. The keyed slit 395 may be oriented in the same position with respect to the hole 385 in each example embodiment irradiation target retention devices 325. As shown in FIG. 8, because bores 330 and hole 385 may share the same radial position about a central axis 380 in example embodiment irradiation target retention devices 325, if example devices 325 are stacked along axis 380 in fuel rod 18/19, all holes 385 may be aligned at a single angular position so as to form an exit shaft 390 through the stack of example embodiment devices 325. Further, because keyed slits 395 may also align and share a common orientation with holes 385 if example devices 325 are stacked, a tool having a keyed end corresponding to slit shape 395 may be passed into and through the stack of irradiation target retention devices 325. As shown in FIG. 9, in order to harvest radioisotopes produced by example embodiment irradiation target retention devices 325 after irradiation thereof in an operating nuclear core, the stack of example embodiment devices 325 may be oriented with bores 330 facing downward such that irradiation targets 340 may fall out of bores 330 by gravitational action alone. Selected example embodiment devices 325 stacked within fuel rod 18/19 may then be rotated about central axis 380 until all holes 385, and thus exit shaft 390, align with a desired bore 330 of an unrotated device 325 within the stack. Irradiation targets 340 and radioisotopes present therein may fall from bore 330 through exit shaft 390 for harvesting. Stacked example embodiment devices 325 may be rotated by a keyed tool 396 moved into keyed slit 395 at a desired axial distance. Thus the particular irradiation target retention device emptied through exit shaft 390 may be selected by the axial distance the keyed tool 396 is moved into keyed slits 395. Because all keyed slits 395 may be oriented similarly with respect to holes 385, exit shaft 390 may be rotated consistently to a bore 330 to be emptied. Further, a bottom-most (after turning the stack downward) example irradiation target retention device 325 may lack any irradiation targets 340 such that irradiation targets 340 will not fall from the bottom-most device 325 while emptying a stack of example embodiment devices 325. Example embodiment irradiation target retention devices may be rotated by other mechanisms and lack a central keyed slit 395. For example, external sleeves may rotate individual retention devices 325 in a stack to desired angular positions to drain irradiated irradiation targets from exit shaft 385. Similarly, holes 385 need not contemporaneously align in a stack of example embodiment retention devices 325; an irradiation target may fall into an unaligned hole 385 that is later aligned with a lower hole 385, such that irradiation target 340 may fall in increments through a stack of example embodiment devices until harvested. Although example embodiment retention devices may be inserted into BWR-type fuel rods and fuel assemblies in example embodiments, it is understood that other types of fuel and power plants may be useable with example embodiment retention devices. For example, PWR, CANDU, RBMK, ESBWR, etc. type reactors may include fuel rods that can accommodate example embodiment retention devices in order to irradiate irradiation targets therein. Example embodiments thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied through routine experimentation and without further inventive activity. For example, the word “assembly” is used throughout to denote a collection of fuel rods in example embodiments, but terms like “bundle” may also be used interchangeably, and example embodiments may be useable with fuel bundles lacking all components typically found in a finished fuel assembly. Or, for example, other fuel types, shapes, and configurations may be used in conjunction with example embodiment irradiation target systems. Variations are not to be regarded as departure from the spirit and scope of the exemplary embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
	abstract	An electrical system having an underlying structure resembling the double helix most commonly associated with DNA may be used to produce useful electromagnetic fields for various application.
055442110	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear fuel assembly for use in a boiling water nuclear reactor (referred tonn as "BWR" hereinafter) and a BWR having a core loaded with such a nuclear fuel assembly. 2. Description of the Related Art Improvement in nuclear power station economy can effectively be achieved by a reduction in the fuel cycle cost through enhancement of the fuel exposure. It would be possible to enhance the exposure simply by increasing enrichment of conventional fuel. The increase in the enrichment, however, causes hardening of neutron spectrum, resulting in occurrence of phenomena such as (a) increase in the absolute value of the void coefficient, (b) increase in the reactivity in the core in cold state, (c) reduction in ability to control the reaction by burnable poison such as gadolinia. Such phenomenon may undesirably lead to reduction in thermal margin and shut-down margin of the nuclear reactor. Enhancement of exposure merely by increase in the enrichment is inevitably accompanied by increase in the cost of natural uranium per fuel, as well as in the cost incurred in the course of enriching of the fuel, so that the effect in reducing the fuel cycle cost achieved through fuel enrichment is diminished. This problem is dealt with in BWRs by softening neutron spectrum through increasing water-to-fuel ratio. More specifically, it is effective to increase the water region of water rods in a fuel assembly. Increase in the water region of water rod in the center of a fuel assembly having fuel rods arranged in 8 rows and 8 columns (referred to as "8.times.8 fuel assembly" hereinafter) can be realized only at the cost of decrease in the fuel rods, resulting in a reduced thermal margin. Furthermore, degree of freedom in the nuclear design is disadvantageously reduced due to, for example, restriction in the arrangement design of gadolinia-containing fuel, because the number of fuel rods per assembly is decreased. Fuel assemblies improved to achieve higher fuel economy have been proposed in, for example, Japanese Patent Publication No. 3-78954 and U.S. Pat. No. 5,198,186. These fuel assemblies employ water rods of different cross-sectional shapes, but has a common feature in that each fuel rod has upper and lower end regions of natural uranium, and an enriched uranium region between these natural uranium regions, the enriched uranium region having upper, middle and lower sections, the upper and lower sections having average enrichments across horizontal cross-section which are equal to each other and lower than that of the middle section, the content of burnable poison per unit axial length being lower in the upper section than in other sections of the enriched uranium region. For instance, U.S. Pat. No. 5,198,186 discloses a fuel assembly in which an area where four fuel rods can be disposed is occupied by a single water rod of an increased diameter. The fuel assembly disclosed in U.S. Pat. No. 5,198,186 exhibits an average discharge exposure of 38 GWd/t. An attempt to further enhance the exposure through increase in the average enrichment in this fuel assembly is encountered with a problem in that the thermal margin is reduced due to increase in the area of the water region of the water rod at the center of the nuclear fuel assembly. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fuel assembly, as well as a nuclear reactor incorporating the same, which can enhance fuel exposure by a comparatively low increase in the average enrichment. To this end, according to the present invention, this is provided a nuclear fuel assembly having a plurality of fuel rods charged with a nuclear fuel material, and at least one water rod surrounded by the fuel rods, comprising: a fuel-charged zone including axially upper and lower end regions charge with natural uranium, and enriched uranium region between the upper and lower end regions, the enriched uranium region having an upper section, a middle section and a lower section of different levels of enrichment; the middle section having average enrichment of a level higher than those of the upper and lower sections; the difference in the average enrichment level between the middle section and the lower section being smaller than that between the middle section and the upper section; the burnable poison content per unit axial length in the upper section being smaller than those in other sections of the enriched uranium region. According to the invention, axial power distribution is rendered uniform by virtue of the fact that the average enrichment is greater in the middle section than in the lower section of the enriched uranium region. It is to be understood, however, that the peak of axial power distribution appears rather at a lower portion where the neutron moderation effect is large, due to the fact that the difference in the average enrichment between the middle section and the lower section is smaller than that between the middle section and the upper section. This leads to improvement in the neutron utilization factor in the lower section to provide an enhanced reactivity in this section, so as to suppress deterioration in the performance of the reactor core. It is impossible to enhance the exposure without requiring substantial increase in the average enrichment. The above and other objects, features and advantages of the present invention will become clear from the following description when the same is read in conjunction with the accompanying drawings.
	summary
	summary
045368821	description	DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a cross-sectional view of an X-ray lithography mask known in the art. In FIG. 1, a suitable support ring 10 such as quartz or other suitable material is provided. A thin supporting membrane 11 is stretched cross support structure 10 and bonded thereto in a suitable manner. Membrane 11 may be formed of any suitable material substantially transparent to X-rays such as thin metals, covalently bonded materials, polymers or the like. Patterned absorber layer 12 is disposed on the surface of supporting membrane 11. Pattern 12, which is substantially opaque to soft X-rays, may be achieved by initially placing the layer of opaque material on membrane 11 and then patterning this material using a lithography step or an etching step. As noted above, it is clear that the prior art mask includes a patterned absorber layer 12 which protrudes above the surface of membrane 11 therein subjecting the absorber layer to both excessive wear and the possibility of trapping contaminants therebetween wherein the mask becomes less useful and less accurate. Moreover, by producing the mask in the standard manner, membrane 11 is usually subjected to non-uniform stresses as a result of the operation of the lithographic and/or etching step which patterns the absorber layer to form elements 12. Referring now to FIGS. 2a through 2e, there is shown and described a method of forming a mask and the mask produced by the method. In FIG. 2a there is shown composite 20 which includes a polished planar substrate 21 which serves to act as a temporary support for a mask membrane during fabrication. Typically, substrate 21 may be formed of polished glass, silicon or any other suitable material to serve as a substrate as will become evident hereinafter. In the embodiment shown in FIG. 2a, layer 22 is formed on the planar surface of substrate 21. Layer 22 can be either a parting compound or an etch stop as will appear hereinafter. Typically the parting compound may be a sugar film or a suitable highly soluble salt such as NaCl, CsI, BaCl.sub.2, or the like. Alternatively, the parting compound may be a soap or detergent film or soluble organic film as is known in the art. Conversely, if layer 22 is an etch stop layer, a substance which is not soluble in the etchant to be used on the substrate 21 may be used. The material of the etch stop layer and the substrate as well as the etchant will be mutually defined. The etch stop layer 22 should be substantially pinhole-free to prevent etching of capping layer 23, adhesion layer 24 or 26, or absorber layer 25, as noted hereinafter. Absorber layer 25 is a layer which is utilized to absorb the X-rays and to form a pattern. Layer 25 is typically 0.2-1.0 .mu.m thick and formed of a heavy metal such as gold, tungsten, platinum or the like which is substantially opaque to X-ray radiation. Typically, layer 25 may be deposited by suitable vacuum depositon or other plating process either directly on the substrate 21, on etch step or parting layer 22, on capping layer 23, on an adhesion layer 24 which may be desirable to promote adhesion of the absorber pattern. Use of layers 22, 23, and 24 is optional--one layer may perform the function of two or more. Alternatively one or more of these intermediate layers may be omitted. Referring now to FIG. 2b, absorber layer 25 is shown as having been patterned. Patterning of layer 25 is typically performed by a lithography step and by a wet or dry etching step as is known in the art. Conversely, the patterning layer could be produced by plating through a lithography mask or by a lift-off method or any combination of the above. These steps are typically known in the art. Moreover as noted above, each of these steps tends to produce strained distortions in the supporting substrate 21. In composite shown in FIG. 2b, the stress variations produced by the patterning of layer 25 produce strain distributed through substrate 21 which is, typically, over 100 times as thick as the X-ray mask membrane such as membrane 11 in FIG. 1. Consequently, little or no strain is produced and patterning is maintained in a high fidelity and resolution. Referring to FIG. 2c, the supporting membrane 27 is deposited. Membrane 27 can be deposited by means of spinning a polymide film or the like onto the patterned surface of the composite. Of course, other techniques such as vacuum evaporation, plasma deposition, low vacuum condensation and the like can be utilized. Suitable materials for substrate 27 have high transparency or transmissivity for soft X-rays and can be formed of materials such as Be, B.sub.4 C, organic polymers or the like. Incidentally, in some cases it may be desirable to include thin layer 26 of a material to promote adhesion between the absorber 25 and the membrane. The adhesion promoting layer 26 can be of any suitable material such as titanium and can be applied in any typical fashion known in the art. It should be noted that membrane 27 is provided only subsequent to the patterning of layer 25 wherein no non-uniform stresses or strains are applied to this membrane. Referring now to FIG. 2d, there is shown one alternative of the final mask structure. In FIG. 2d, a separate supporting peripheral ring 28 is provided and is bonded to membrane 27 in any suitable fashion. After support ring 28 is in place, supporting substrate 21 may be etched away in a suitable fashion. Alternatively, in the event that the layer 22 was formed of a parting compound, layer 22 may be dissolved in a suitable manner wherein the mask comes free from the supporting substrate 21 thereby leaving a mask with a planar surface and X-ray absorbing pattern embedded therein. Referring to FIG. 2e, there is shown an alternative mask structure wherein a portion of support substrate 21 is etched away thereby leaving a peripheral support ring 21A. In this structure, layer 22 is an etch stop layer which controls etching through support substrate 21a to prevent etching of membrane 25. Thus, the various relationships between membrane 27, support substrate 21, etch stop layer 22 and the etchant are determined as noted above. At the time of separation of the mask from support substrate 21, the stress of the patterned absorber 25 is freed to distort the thin mask membrane which now consists of a composite of layers 23, 24, 26, and 27. If, however, care is taken to deposit a stress-free absorber layer 25, or to match the tension of the absorber 25 and the membrane film 27, the resultant mask will exhibit uniform tension and be free of pattern related strains. Also, non-planar layers can be added to both sides of the mask membrane composite to adjust the composite membrane tension. FIGS. 2d and 2e show a totally encapsulated mask structure, wherein frequently the capping layer 23 and membrane 27 are of the same material. It has already been indicated that many of the layers used might be eliminated by using a single layer with several functions (e.g. a "capping layer" that also functions as an etch stop). In fact, useful "partially embedded" masks can be made without layers 22, 23, 24, or 26. For example, in FIG. 2b, metal absorber pattern 25 can be disposed directly on a suitable substrate 21 such as glass, silicon or the like. In FIG. 2c, the pattern 25 is coated directly with a suitable membrane material 27. After removal of the substrate 21 by an etchant which does not attack absorber pattern 25 or mask membrane 27, the finished "partially embedded" mask similar to the devices seen in FIGS. 2d or 2e is produced (without layers 23, 24 and 26). In FIG. 2d, support frame 28 is attached to membrane 27 and the substrate 21 completely removed. In FIG. 2 e, a portion of substrate 21a is retained for mechanical support. Thus, there has been shown and described a method of forming an X-ray mask wherein a patterned X-ray absorber layer is embedded in the mask substrate. No stress or strain are imposed upon the mask supporting membrane during the patterning process related to the absorber layer. The planar mask layer provides both mechanical and contamination free advantages. Moreover, the technique described herein produces masks which are relatively distortionless as a result of the patterning process of the X-ray absorber layer. The distortionless mask permits high resolution of microcircuits and the ready replication thereof. While certain specific materials have been recited in the description, other materials can be utilized in a satisfactory manner. The description is intended to define the best mode of the invention known to date and is not intended to limit the scope of the invention. The scope of this invention is limited by the claims appended hereto.
053496175	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates in general terms to pressurized water nuclear reactors and more specifically relates to the problem of the need of removing the residual power or after-power from the core in the case of a programmed or accidental reactor shutdown. 2. Brief Description of Related Art Firstly the term residual power will be defined. On shutting down a reactor by introducing a high antireactivity into the core, the number of fissions in the latter becomes very rapidly negligible after a few seconds. However, the radioactivity of the fission products developed in the core during the normal reactor operating period continues to release a significant power, which can represent approximately 7% of the operating power at the time of reactor shutdown. Therefore, no matter why the shutdown has taken place and in particular when it occurs as a result of a depressurization incident with respect to the primary circuit, it is necessary to have means for removing said residual power or after-power from the core without the heating leading to catastrophic conditions and which could even bring about core meltdown. Conventionally three means have been used up to now for removing the residual power from pressurized water reactors. They are constituted by the steam generator, the system for cooling the reactor on shutdown and the safety injection device for accidental situations. The steam generator, whose normal function is to absorb heat, can obviously continue to serve a heat exchange function with the primary water following reactor shutdown. This process, which can last several hours, becomes inoperative when the pressure and temperature respectively drop to approximately 30 bars and 180.degree. C. Thus, the steam generators and secondary circuit are not designed for removing heat at low temperature and low pressure. As from this time it is the system for cooling the reactor on shutdown which comes into action by injecting cold water into the primary circuit. Thus, within about 15 hours it is possible to bring the core to a temperature below about 100.degree. C. The safety injection circuit ensures the emergency cooling of the core and the rapid insertion of antireactivity into it in all cases where there is an accidental depressurization of the primary circuit and which can even lead to a complete break in said circuit. It fulfils its function by as rapidly as possible injecting boric acid cooling solution into the reactor core. These various means, whose operation is satisfactory unfortunately suffer from a number of deficiencies, which will be given hereinafter. The distance between the cold air source and the core can lead to an inadequate operation of these means. Thus, the more equipment existing between the core and the cold source, the greater the failure risk (pipe breaks, poor operation of a valve, motor, etc.). The design of the steam generator only enable it to operate at high pressures and temperatures. At low pressures and temperatures, the shutdown reactor cooling system is used for removing the residual power. Generally, the operational overlap range of the two systems is narrow and requires a special procedure. During intervention on the steam generator, the water level in the primary circuit is at mid-height in the hot and cold pipes and the shutdown reactor cooling system openings are just below this level. Special precautions relative to the operation of the shutdown reactor cooling system have to be taken, so as to avoid any air entrainment risk and the formation of vortexes leading to the disappearance of the residual power removal function. Following a primary coolant loss incident, the steam generators and shutdown reactor cooling system can become completely unavailable, even on a long term basis. The only way to remove the residual power is the safety injection device, which is an active system. However, in this hypothesis, a possible disappearance of electric sources leads to a stoppage to the removal of the residual power. As has been shown, existing systems may be defective and this may lead to serious consequences for the reactor and its environment. Various solutions have already been proposed for improving the safety of the nuclear reactor residual power removal apparatus. Virtually all the solutions proposed consist of introducing an auxiliary heat exchanger into the reactor vessel. Reference can be made in this connection to the CEA FR-A-8,103,632, which recommends the introduction of an exchanger into the reactor vessel for extracting the heat from the heat transfer fluid without using loops. However, in order for such a system to be effective, it is necessary for the heat transfer fluid to be able to flow between the core and the exchanger. This arrangement within the actual vessel is not described and the vessel design proposed is completely different from that of presently used vessels. Other documents, such as the article "A water level initiated decay energy cooling system" by Charles W. Forsberg, Oak Ridge National Laboratory, pp. 229 ff, Nuclear Technology, Vol. 96, November 1991, also describe water reactors with integrated exchangers for removing residual power. These are astute "heat switch" systems controlling the heat exchange between the primary circuit and the exchanger. However, these systems are cumbersome, are not compatible with existing pressurized water reactors and are really intended for other reactor types. SUMMARY OF THE INVENTION The present invention relates to an apparatus for removing the residual power from the core of a reactor making it possible, by using as in the prior art apparatus an auxiliary exchanger within the vessel, to solve the aforementioned problems in all cases where the vessel remains filled with primary water. This apparatus for removing the residual power from the core of a pressurized water nuclear reactor, having a primary water circulation in accordance with a hairpin path in the reactor vessel and for this purpose having two concentric ferrules defining an external annular compartment, in which the cold primary water describes a downward path and a central cylindrical compartment containing the actual core, in which the primary water flows from bottom to top, accompanied by heating, through the core, is characterized in that it comprises a third ferrule defining a complementary annular space between the two preceding compartments, said annular space being linked in its lower part by a first orifice issuing into the external annular compartment with the cold water of the primary circuit and in its upper part and by a second orifice issuing into the central compartment with the hot water of the primary circuit and an auxiliary heat exchanger located in said complementary annular space, said auxiliary exchanger being supplied autonomously by a second heat transfer fluid, which is independent of the primary cooling water of the reactor core. The presence of a third ferrule and a complementary annular space between the core and the periphery of the vessel consequently makes it possible to create an area in which there is a flow of primary water, either by the vacuum or pressure drop effect when the primary circuit is still operating, or by a thermosiphon effect if the latter flow is interrupted. The auxiliary heat exchanger located in the complementary annular space formed in this way is supplied independently of said primary circuit by a second heat transfer fluid able to issue to the outside of the reactor on any cold source such as a condenser, air cooler, etc., so that the apparatus according to the invention in all circumstances ensures a good removal of the residual core power, even following reactor shutdown. According to an important feature of the present invention, following the closure of the first orifice, the removal apparatus comprises means for increasing the vacuum effect in the vicinity of the bottom of the complementary annular space. It is sometimes necessary to use these means when the pressure drop of the primary liquid through the core becomes excessive and would compromise the primary fluid flow in the complementary annular space housing the auxiliary heat exchanger. Two particularly interesting embodiments are envisaged within the scope of the present invention for obtaining these vacuum effect increasing means. In a first embodiment, said means for increasing the vacuum effect incorporate means for closing the first orifice and a series of radial, cylindrical pipes extending, in the vicinity of the base of the core, in the external annular compartment, said cylindrical, radial pipes issuing onto openings provided for this purpose every so often on the periphery of the lower portion of the intermediate ferrule in the complementary annular space and being provided on their wall with longitudinal slots for linking with the external annular compartment. In this first embodiment, it is the flow of the primary water around the longitudinal slots of the cylindrical pipes, which creates a greater pressure reducing or vacuum effect than could be obtained with the first orifice of the overall apparatus. In this connection, the best results are obtained when there are two such longitudinal slots for communicating with the external annular compartment on each pipe and when their azimuth position on the surface of the cylindrical pipes forms an angle .phi. close to 80.degree. in the main downward flow direction in the external annular compartment. In the second embodiment of the means for increasing the vacuum effect, the apparatus has in the external annular compartment below the auxiliary heat exchanger, an annular chamber linked by a series of openings with the complementary annular space and by an annular slot with the external annular compartment, said annular chamber having an extension in the radial direction of the vessel much that it creates in the external annular compartment, a constriction or narrowing which brings about an increase, at the location of the preceding slot, of the flow rate of the downward primary fluid in said external annullar compartment of the auxiliary heat exchanger. In this embodiment, the physical principle applied is similar to the previous one to the extent that the increase of the vacuum effect is simultaneously obtained by the positioning of the slot in an area where the flow of fluid brings about a vacuum and by a restriction of the channel offered in the external annular compartment to the primary water flow.
	abstract	A method for focusing a charged particle beam, the method including: (a) altering a focal point of a charged particle beam according to a first focal pattern while scanning a first area of a sample and collecting a first set of detection signals; (b) altering a focal point of a charged particle beam according to a second focal pattern while scanning a second area that is ideally identical to the first area and collecting a second set of detection signals; and (c) processing the first and second set of detection signals to determine a focal characteristic; wherein the first focal pattern and the second focal pattern differ by the location of an optimal focal point.
	summary
	description	FIG. 1 shows a plasma focus discharge source 210 according to a first embodiment of the present invention. The plasma focus discharge source 210 comprises a generally cylindrical cathode 211 surrounding an elongate anode 212 with an annular space therebetween. A voltage source 214 applies a high voltage between the anode and cathode sufficient to cause ionization of the gas in the annular space so that a discharge current I begins to flow radially from anode to cathode. The discharge current I generates a circular magnetic field B in the annular space between anode and cathode. The ions of the discharge current are driven by their interaction with the magnetic field B along the anode 212, as indicated by arrows 216. The anode 212 is shorter than the cathode 211 and has a hollow tip so that the plasma is driven over the end of the anode 212 and converges to form a very hot plasma in pinch volume 218. According to the invention, the plasma is formed in a driver gas which fills the annular space between anode 212 and cathode 211 between each discharge. The driver gas is chosen according its magneto-hydrodynamic properties to effectively form a conducting medium, guiding the current from anode to cathode, and, induced by the thus generated magnetic field, comprising the enclosed volume around and onto the axis. To provide EUV radiation of the desired wavelength, a working (primary) substance, e.g. gas, vapor, clusters or liquid, is provided into the enclosed volume and is heated by the converging plasma to emit EUV radiation. The working substance is chosen for its efficiency in emitting EUV radiation at the desired wavelength, e.g. about 9 to 16 nm, preferably 11 or 13 nm, and may be Li, Xe or water. The working substance is preferably emitted into the region of the pinch volume 218 of the converging plasma as a jet, e.g. a cluster jet or a droplet-like jet, appropriately timed to the discharge voltage that is derived from an appropriately pulsed source 214. The working substance can be supplied from a source 215 via a bore 213 in the anode 212 to form a jet 217 in the hollow tip of the anode 212. The source 215 comprises a reservoir of the working substance as well as necessary pumps, valves, etc to control the jet. A second embodiment of the invention, which may be the same as the first embodiment of the invention save as described below, comprises a so-called Z-pinch plasma discharge source. The Z-pinch plasma discharge source 220 is shown in FIG. 2. It comprises an annular cathode 221 and annular anode 222 provided at opposite ends of a cylindrical chamber 223 having insulating walls. A quantity of driver (secondary) gas is injected from source 225 through an annular opening close to the outer wall of the cylindrical chamber 223 and pre-ionized. Voltage source 224 then applies a high voltage between anode 222 and cathode 221 causing a cylindrical discharge starting on the insulating walls of the chamber 223 which generates an azimuthal magnetic field. The magnetic field causes the discharge to contract into a thin axial thread, or pinch volume, 229 at high pressure and temperature. Ceramic plug 226 defines the aperture through which the extreme ultraviolet radiation to form projection beam PB is emitted. To enhance the emission of EUV, according to the invention, a working substance is jetted into the region of the pinch volume 229 in chamber 223 from source 227 at an appropriate time to be entrained with and compressed by the plasma discharge. As in the first embodiment, the driver gas can be chosen for its effectiveness in generating a high-temperature plasma and the working substance for its efficiency in emitting EUV radiation of the desired wavelength. A third embodiment, which may be the same as the first embodiment, save as described below, comprises a capillary discharge plasma source. FIG. 3 shows the capillary discharge source 230, which has a cathode 231 and anode 232 forming the end plates of a small chamber 233. The anode 232 has a small central through-hole aligned with a narrow capillary 236 formed in an insulator 235 which covers the side of the anode 232 which faces the cathode 231 and the side walls of the chamber 233. A discharge will be formed in the capillary 236, which, as in the previous embodiments, will compress on the axis of the capillary into a pinch volume to create a highly-ionised, high-density plasma having a high temperature. The emission aperture is defined by aperture plate 237. According to the invention, a working (primary) substance is jetted into capillary 236 from source 238. As in the previous embodiments, a driver gas can be chosen for its effectiveness in generating a high-temperature plasma and the working substance for its efficiency in emitting EUV radiation of the desired wavelength. In the third embodiment, and also the first and second embodiments, the driver gas can be injected into the chamber for each discharge (shot) of the source. The working and driver gasses can be ejected, e.g., by a two part annular nozzle, as will be described in the seventh and eight embodiment. This provides for a decreased divergence of the jet of working fluid ejected and for a shielding gas around the pinch volume to increase the efficiency of the source. The primary jet nozzle preferably provides for a supersonic jet to have a sharply-peaked density distribution of the working gas on-axis of the ejection from the jet nozzle. FIG. 4 shows a fourth embodiment of a radiation source according to the invention, which is a variant of the first embodiment described above. The Figure shows the configuration of anode 110 and cathode 120, which are kept separated by an electrical insulator 130 and which are connected to a capacitor bank 140. A central part of the radiation source has cylindrical symmetry around central axis A. FIG. 8 further shows an annular cathode aperture 121 and an annular cathode cavity 122 around central axis A. A driver gas or vapor is supplied to cavity 122 via an inlet 125 so as to provide a low pressure within the cavity. In the present embodiment, argon (Ar) is taken as the driver gas, but basically any gas, such as for instance helium (He), neon (Ne) and hydrogen (H2), is suitable. Hydrogen may be specially preferred since it shows a low absorption of radiation in the EUV range. The driver gas inside cavity 122 is used as a source of electrons to start a discharge between anode and cathode. The cathode cavity 122 surrounds a (primary) working gas or vapor source 160, which ejects a working gas or vapor in the anode-cathode gap in a region around central axis A. The working gas or vapor is chosen for its spectral emission characteristics as a plasma. The present embodiment uses lithium (Li) for its very strong emission line at approximately 13.5 nm. Xenon (Xe) may also be used, which has a broad emission spectrum in the XUV (and EUV) region of the electromagnetic radiation spectrum. The Li source 160 shown comprises a heater 161 below a container 162 containing solid lithium. Vaporized Li reaches the anode-cathode gap through a supersonic (Laval) nozzle 163, however other types of nozzle may also be used. A trigger electrode 150 is inserted in cathode cavity 122. Electrode 150 is connected to appropriate electrical circuitry (not shown in FIG. 8) for applying a voltage pulse to the electrode to start the discharge described below. Initially, the radiation source is close to auto-triggering. A voltage pulse applied to trigger electrode 150 causes a disturbance of the electrical field within cathode cavity 122, which will cause triggering of the hollow cathode and the formation of a breakdown channel and subsequently a discharge between cathode 120 and anode 110. An initial discharge may take place at low initial pressure (p less than 0.5 Torr) and high voltage (V less than 10 kV) conditions, for which the electron mean free path is large compared to the dimension of the anode-cathode gap, so that Townsend ionization is ineffective. Those conditions are characterized by a large electrical field strength over gas or vapor density ratio, E/N. This stage shows rather equally spaced equipotential lines having a fixed potential difference. The ionization growth is initially dominated by events inside the hollow cathode that operates at considerable lower E/N, resulting in a smaller mean free path for the electrons. Electrons e from hollow cathode 120, and derived from a driver gas or vapor within cavity 122, are injected into the anode-cathode gap, a virtual anode being created with ongoing ionization, which virtual anode propagates from anode 110 towards hollow cathode 120, bringing the full anode potential close to the cathode. The electric field inside the hollow cavity 122 of cathode 120 is now significantly enhanced. In the next phase, the ionization continues, leading to a rapid development of a region with high ion density inside the hollow cathode, immediately behind the cathode aperture 121. Finally, injection of an intense beam of electrons 126 from this region into the anode-cathode gap, forms the final breakdown channel. The configuration provides for a uniform pre-ionization and breakdown in the discharge volume. When a working gas or vapor has been ejected from source 160 and a discharge has been initiated, a partially ionized, low-density and relatively cold plasma of the working gas or vapor is created in the anode-cathode gap above aperture 121. An electrical current will be flowing within the plasma from cathode 120 to anode 110, which current will induce an azimuthal magnetic field, having magnetic field strength H, around the radiation source. The azimuthal magnetic field causes the partially ionized plasma above cathode aperture 121 to compress toward central axis A. Dynamic compression of the plasma will take place, because the pressure of the azimuthal magnetic field is much larger than the thermal plasma pressure: H2/8xcfx80 greater than greater than nkT, in which n represents plasma particle density, k the Boltzmann constant and T the absolute temperature of the plasma. Electrical energy stored in capacitor bank 140 connected to anode 110 and cathode 120 will most efficiently be converted into energy of the kinetic implosion during the full time of the plasma compression. A homogeneously filled pinch volume with a high spatial stability is created. At the final stage of plasma compression, i.e. plasma stagnation in the pinch volume on central axis A, the kinetic energy of the plasma is converted into thermal energy of the plasma and finally into electromagnetic radiation having a very large contribution in the XUV range. Radiation emitted from a collapsed plasma will pass through an opening 111 in the anode 110 into a vacuum chamber 170 that is evacuated through opening 171 in a wall of the vacuum chamber. Plasma and debris particles may also escape through opening 111. A flywheel shutter 180 is present to block these particles when no XUV radiation pulse is emitted for preventing them to reach any optical elements in the radiation path of the XUV radiation to the projection system PL. FIG. 5 depicts a fifth embodiment of the invention, which is a variation of the fourth embodiment and further shields the aperture region of cathode 120 from plasma collapse at central axis A. Both anode 110 and cathode 120 have a xe2x80x9chat-likexe2x80x9d structure. Annular cathode cavity 122 and aperture 121 are located at the bottom side of the hat. A partially ionized, low-density and relatively cold plasma created by a discharge at aperture 121 will compress upwards and xe2x80x9caround the cornerxe2x80x9d towards central axis A. Further, the positions of anode 110 and cathode 120 have been interchanged. Cathode 120 is located on the outside of the configuration and comprises aperture 123 for passing XUV radiation to vacuum chamber 170. However, the density of the working gas or vapor, also Li vapor in the present embodiment, may be too low at annular aperture 121 of cathode 120 for creating a discharge and a plasma. In embodiment 6, the radiation source is configured so as to yield a sufficiently high pressure of the driver gas or vapor, Ar in the present embodiment, within the anode-cathode gap in the region at the annular aperture 121 for creating a discharge in the driver gas. The resulting plasma of the driver gas will start to compress towards central axis A and at some point encounter a sufficiently high pressure of the working gas or vapor to create a plasma of the working gas or vapor, which will then further compress until stagnation into a pinch volume on central axis A. The plasma of the driver gas or vapor may even first have to go xe2x80x9caround the cornerxe2x80x9d to reach a sufficiently high pressure of the working gas or vapor. A radiation source according to a sixth embodiment of the invention is shown schematically in FIG. 6 and 7 and comprises primary and secondary jet nozzles 10 and 20 and a supply of primary and secondary gases 11, 21 to the primary and secondary jet nozzles, respectively. In this embodiment, both jet nozzles are pulsed jet nozzles, in which both supply lines 11, 21 comprise valves which are opened at certain instants in time to supply a pulse of primary and secondary gases to the respective jet nozzles. FIG. 6 shows a longitudinal section through the jet nozzle source for the primary and secondary gases. FIG. 7 shows a front view of the nozzle source. The primary and secondary jet nozzles are arranged co-axial, the secondary jet nozzle 20 enclosing the primary jet nozzle 10. The primary jet nozzle 10 has a circular outlet 13 and the secondary nozzle 20 has a annular outlet 23. Plungers 12 and 22 are arranged in the supply of the primary and secondary gases 11 and 21, respectively, and may be independently operated to close off their respective supply by abutting against a tapered end of the supply. In this way valves are obtained for opening and closing the respective supplies to yield a pulsed outflow of the primary and secondary gasses. However, pulsed nozzles may be obtained in various other configurations. The plungers 12, 22 are operated by means which are not shown in the drawings. Further, the use of continuous nozzles is also possible. When a pulse of primary gas and no pulse of secondary gas is ejected from the nozzle source, the outflow of the primary gas 15 from the jet nozzle outlet 13 will be strongly divergent. Ejecting a pulse of secondary gas 25 as well results in a less divergent or even parallel or convergent outflow of the primary gas 15. An optimum outflow of the primary gas for the radiation source can be reached by varying one or more of several parameters. One of these parameters is the supply rate of secondary gas to the secondary jet nozzle 20 with respect to the supply rate of primary gas to the primary jet nozzle 10. Another parameter is the timing of the pulse of secondary gas with respect to the timing of the pulse of primary gas. It appears that an appropriately delayed pulse of primary gas with respect to the pulse of secondary gas results in a less divergent beam if the secondary gas is a lighter gas than the primary gas as compared to a non-delayed pulse at the same flow rates of primary and secondary gasses. Other relevant parameters are the backing pressures of the gases in the nozzle source and the jet geometry. The optimum parameters will depend on the gases or liquids used and on the specific geometry of the primary and secondary jet nozzles. The primary gas of the sixth embodiment of the radiation source comprises krypton or xenon, which may be supplied pure or in a mixture with other (inert) gases. A xenon plasma, for instance, has been shown to emit a large contribution of extreme ultraviolet radiation. In an alternative embodiment water droplets or cryogenic liquids, such as liquid xenon, in a carrier gas may be used as a primary liquid. The secondary gas may be selected from the group comprising helium, neon, argon, krypton, methane, silane and hydrogen. In the preferred embodiment the secondary gas is hydrogen, because hydrogen hardly absorbs extreme ultraviolet radiation. Since hydrogen has favorable absorption characteristics with respect to extreme ultraviolet radiation, a very large outflow of hydrogen from the secondary nozzle can be employed, resulting in a high local density in the outflow. A lighter secondary gas is expected to provide worse confinement of xenon as a primary gas with respect to a heavier secondary gas due to the smaller momentum transfer in a collision. The much larger outflow and higher pressure of hydrogen which can be employed in the radiation source according to the invention overcompensates for the smaller mass of hydrogen with respect other secondary gasses, due to the considerably larger local pressures which can be tolerated. With the above jet nozzles a less divergent, confined or an approximate parallel outflow of the working (primary) gas from the primary jet nozzle 10 may be obtained to receive the ejected working gas in a rather confined region at the pinch volume, which is preferably located at some distance from the nozzle source outlet to not produce debris from the jet nozzle by interaction of the plasma with the nozzle. A continued ejection of secondary fluid from the annular secondary jet nozzle will provide for a gas shield around the compressed high-temperature plasma in the pinch volume to block or slow down and neutralize any fast particulates that will be emitted from the hot plasma. Parts of the source, and possibly also optical elements comprised in the illuminator of a lithographic projection apparatus, are thus protected from damage by such fast particulates or from deposition of those particulates. Further, the flushing gas shield of secondary gas also provides for an environment around the pinch volume, which is highly transparent for the generated XUV radiation when an appropriate secondary fluid is chosen. Heavy (metal) particles, for instance, eroded from the electrodes or primary Xenon (working) gas that might be present around the high-temperature plasma in the pinch volume would cause a large absorption of the XUV radiation generated. FIG. 8 schematically shows a front view of a nozzle source used in a variant of the radiation source according to the sixth embodiment of the invention. The variant differs from the basic arrangement of the sixth embodiment in that the secondary nozzle is positioned at one side of the primary nozzle. The Figure shows the outlets 13 and 23 of the primary and secondary jet nozzles, respectively. The divergence of the outflow from the primary nozzle may for this embodiment only controlled at this one side, which may be convenient in some applications. An embodiment in which the secondary jet nozzle partly encloses the primary jet nozzle, or having, for instance, outlets of the secondary jet nozzle on opposite sides of or all around the outlet of the primary jet nozzle may also be envisaged. FIG. 9 schematically depicts a lithographic projection apparatus 1 in which the radiation sources according to the invention may be used. The apparatus comprises: a radiation system LA, IL for supplying a projection beam PB of EUV radiation; a first object table (mask table) MT provided with a first object (mask) holder for holding a mask MA (e.g. a reticle), and connected to first positioning means PM for accurately positioning the mask with respect to item PL; a second object table (substrate table) WT provided with a second object (substrate) holder for holding a substrate W (e.g. a resist-coated silicon wafer), and connected to second positioning means PW for accurately positioning the substrate with respect to item PL; a projection system (xe2x80x9clensxe2x80x9d) PL (e.g. a refractive, catadioptric or reflective system) for imaging an irradiated portion of the mask MA onto a target portion C (die) of the substrate W. As here depicted, the apparatus is of a reflective type (i.e. has a reflective mask). However, in general, it may also be of a transmissive type, for example. The radiation system comprises a source LA which may be any of the radiation sources described above and which produces a beam of extreme ultraviolet (EUV) radiation. This beam is passed along various optical components included in illumination system (xe2x80x9clensxe2x80x9d) IL so that the resultant beam PB is collected in such a way as to give illumination of the desired shape and intensity distribution at the entrance pupil of the projection system and the mask. The beam PB subsequently impinges upon the mask MA which is held in the mask holder on the mask table MT. Having been selectively reflected by the mask MA, the beam PB passes through the lens PL, which focuses the beam PB onto a target area C of the substrate W. With the aid of the interferometric displacement measuring means IF and positioning means PW, the substrate table WT can be moved accurately, e.g. so as to position different target areas C in the path of the beam PB. Similarly, the positioning means PM and interferometric displacement measuring means IF can be used to accurately position the mask MA with respect to the path of the beam PB. In general, movement of the object tables MT, WT will be realized with the aid of a long stroke module (course positioning) and a short stroke module (fine positioning), which are not explicitly depicted in FIG. 9. The depicted apparatus can be used in two different modes: 1. In step mode, the mask table MT is kept essentially stationary, and an entire mask image is projected in one go (i.e. a single xe2x80x9cflashxe2x80x9d) onto a target area C. The substrate table WT is then shifted in the X and/or Y directions so that a different target area C can be irradiated by the beam PB; 2. In scan mode, essentially the same scenario applies, except that a given target area C is not exposed in a single xe2x80x9cflashxe2x80x9d. Instead, the mask table MT is movable in a given direction (the so-called xe2x80x9cscan directionxe2x80x9d, e.g. the Y direction) with a speed v, so that the projection beam PB is caused to scan over a mask image; concurrently, the substrate table WT is simultaneously moved in the same or opposite direction at a speed V=Mv, in which M is the magnification of the lens PL (typically, M=xc2xc or ⅕). In this manner, a relatively large target area C can be exposed, without having to compromise on resolution.
	abstract	The invention discloses a multibeam modulator which generates a plurality of individual beams from a particle beam. The particle beam illuminates the multibeam modulator at least partially over its surface. The multibeam modulator comprises a plurality of aperture groups composed of aperture row groups. The totality of all aperture rows defines a matrix of m×n cells, where m cells form a row, and k openings are formed in each row. The density of openings within a row is inhomogeneously distributed.
	summary
	summary
059237163	claims	1. A method for forming a closed current loop in a conductive fluid comprising the steps of: establishing a converging magnetic field; and flowing the conductive fluid through the converging magnetic field in the direction of contraction. establishing two converging magnetic fields; and flowing the conductive fluid through each of the converging magnetic fields in the direction of contraction for each. 2. The method for forming a closed current loop of claim 1, wherein the conductive fluid is a conductive plasma suitable for nuclear fusion reactions. 3. The method for forming a closed current loop of claim 1, wherein said step of flowing includes establishing a high to low pressure gradient in the direction of flow. 4. The method for forming a closed current loop of claim 1, wherein said step of flowing includes flowing the conductive fluid in the direction of contraction so the flowing conductive fluid crosses radial components of the field lines of the converging magnetic field being established. 5. The method for forming a closed current loop of claim 4, further comprising the step of establishing poloidal magnetic fields about the formed current loop. 6. The method for forming a closed current loop of claim 1, wherein the converging magnetic field being established has a cross sectional configuration in the direction of flow of one of circular, oval, elliptical and polygonal. 7. The method for forming a closed current loop of claim 1, wherein the converging magnetic field being established has a circular cross section in the direction of flow and wherein the current loop being formed is an annular ring of current. 8. The method for forming a closed current loop of claim 5, wherein the conductive fluid is a conductive plasma suitable for nuclear fusion reactions and wherein said method further comprises the step of selecting a magnitude for the converging magnetic field being established and a flow for the flowing plasma so as to create conditions within the poloidal magnetic field conducive to fusion reactions. 9. The method for forming a closed current loop of claim 8, further comprising the steps of exhausting fusion reaction by-products and unreacted plasma from within the poloidal magnetic fields and replacing therewith fresh unreacted plasma so as to continuously maintain the conditions conducive for fusion reactions. 10. The method for forming a closed current loop of claim 1, further comprising the step of interacting the flowing conductive fluid and field lines of the converging magnetic field. 11. A method for forming two closed current loops in a conductive fluid comprising the steps of: 12. The method for forming two closed current loops of claim 11, wherein said step of flowing includes establishing a high to low pressure gradient in the direction of flow for each converging magnetic field. 13. The method for forming two closed current loops of claim 11, wherein each converging magnetic field includes an inlet region and wherein said method further comprises the step of arranging the two converging magnetic fields so the inlet regions are in back to back relationship and so a long axis of each converging magnetic field is in common. 14. The method for forming two closed current loops of claim 13, further comprising the step of establishing poloidal magnetic fields about each of the formed current loops. 15. The method for forming two closed current loops of claim 14, wherein the conductive fluid is a conductive plasmas suitable for nuclear fusion reactions and wherein said method further comprises the step of selecting a magnetic field magnitude for each of the converging magnetic fields and a flow for the flowing plasma through each converging magnetic field so as to create conditions within each poloidal magnetic field conducive to fusion reactions. 16. The method for forming two closed current loops of claim 15, further comprising the steps of exhausting fusion reaction by-products and unreacted plasma from within each poloidal magnetic field and replacing therewith fresh unreacted plasma so as to continuously maintain the conditions conducive for fusion reactions in each poloidal magnetic field. 17. The method for forming two closed current loops of claim 11, further comprising the step of interacting the flowing conductive fluid flowing through each converging magnetic field and field lines therefor.
	summary
048333344	summary	BACKGROUND OF THE INVENTION The present invention relates to a protective box for electronic circuits hardened with respect to X-rays. It more especially applies to protecting high performance electronic circuits used in the aeronautical and space fields against X-rays. High-performance electronic circuits, both from the processing speed and the capacity standpoints, are very sensitive to the effects of X-rays. These effects can even lead to the destruction of the active components of the electronic circuits involving latch up phenomena. Apart from the X-radiation dose or quantity received, a particularly important parameter is that of the time during which said quantity is supplied. The dose associated with its application time is called the dose rate. The behavior or resistance of the active components of the electronic circuits with respect to said parameters (dose, dose rate) and the energy spectrum of said radiation is essentially linked with the production technology thereof. In most cases, it is necessary to reduce the dose levels and rates in order to permit the electronic circuits to retain their functional integrity. One of the most widely used methods for reducing doses and dose rates received by electronic circuits consists of enclosing them in an envelope made from a pure metal with a high atomic number. The metal and thickness of the metal sheet are chosen and adapted as a function of the energy of the X-radiation in question and the desired filtering rate. This metal sheet effectively protects against high X-ray doses and dose rates. As a function of the circuits and/or technology of the electronic components, the need for protection can be felt as from 1 to 10 Krad and 10.sup.5 to 10.sup.7 rad.s. Generally, the metal sheet covers a metal structure, particularly of light alloy, enclosing the electronic circuits, said structure providing the necessary mechanical strength and protection. The metal sheet is mechanically fixed over the entire outer surface of the metal structure. Unfortunately the realization of the most interesting metals for this type of protection is difficult and costly. Moreover, the requirements with respect to said protection materials and the guarantee that they will not deteriorate under various ionizing, mechanical and climatic surrounding conditions means that the weight breakdown of the electronic circuits is highly increased, compared with circuits which are not protected against X-rays. In most cases, the metal sheet for protecting against X-rays cannot be engaged directly over the entire outer surfaces of the metal structure of the encapsulating box due to the often complex profile thereof. This profile complexity is often imposed by heat dissipation constraints. Therefore the volume defined by the metal protection sheet is greater than the volume of the mechanical structure to be protected. This leads to an increase in the weight and overall dimensions of the mechanical structure, which is further increased by the mechanical devices required for maintaining the metal sheet in place on the mechanical structure (spacers, angle brackets, screws, bolts, etc.). In addition, these maintenance devices must be made from the same metal as the metal protection sheet, so as not to create "holes" in the protection against X-rays. Furthermore, as the mechanical structure is made from a metal or alloy, this further increases the total weight of the box for encapsulating the electronic circuits. It is clear that these disadvantages as regards the overall dimensions and weight of the encapsulating boxes are particularly prejudicial with respect to the use of electronic circuits on-board aircraft. Another method consists of directly depositing the X-ray protection metal on the mechanical structure to be protected either by impregnating the latter in a liquid bath, or by electrolysis. However, these deposition processes are not possible for all the metals usable for providing protection against X-rays. Moreover, in this case it is also necessary to examine the corrosion compatibilities of the metals present. In addition, the thicknesses which can be deposited for the metals lending themselves to this procedure are limited, otherwise the deposit adhesion quality may be prejudiced. Moreover, the obtaining of a homogeneous deposit makes it necessary to proceed in successive stages with further machining between the deposits so that, in certain cases, the dimensions of the encapsulating box are respected in the final stage. Thus, these deposition methods are limited and lead to a high cost of the X-ray protection encapsulating boxes. Another approach consists of envisaging a specific protection for each on-board electronic component, which constitutes a different and more advance solution compared with those referred to hereinbefore. This specific protection described in FR-A-2 547 113, filed on 3 June 1983, consists of using several stacked layers of different materials having different atomic numbers (Z). Materials with a high atomic number are dielectric ceramics, such as barium or neodymium titanate, titanium oxide or a complex lead-based ceramic. Materials having a low atomic number are carbon, aluminium, silicon, alumina and silica. As a function of the applications and number of components involved, the number of individual protections can be more disadvantageous from the weight standpoint than an overall protection of all the electronic components. Moreover, the technology for producing the different materials forming the piles or stacks is based on processes used for the production of capacitors and in particular fritting processes. In particular, the process described does not make it possible to obtain an X-ray protection material with a complex shape. Within the framework of protecting persons working in the presence of X-rays, the materials mainly comprise a charge such as lead, dispersed in an organic binder. Such protection materials are in particular described in FR-A-2 190 717, filed in the name of the Giken Company, FR-A-2 482 761, filed in the name of A. Maurin and US-A-3 622 432 of H. K. Porter Company. These lead-based materials can only be used as X-ray protection materials for radiation with a low flow rate associated with relatively long dose distribution times. Another known electronic circuit encapsulating box is described in FR-A-2 490 917, filed on 2 September 1980. This box is made from a moulded plastic material, such as an epoxy resin, in which the electronic circuits are embedded. This box is extremely thin and does not make it possible to effectively mechanically protect the electronic circuits. Moreover, there is no X-ray protection. The present invention relates to a box for protecting electronic circuits hardened with respect to X-rays and making it possible to obviate the various disadvantages referred to hereinbefore. Compared with the use of a heavy metal sheet covering a metal structure, this protective box in particular leads to an important weight and overall dimension gain, whilst effectively protecting against radiation with a high dose rate and in particular exceeding those referred to hereinbefore. Moreover, this protective box causes no major manufacturing problem and can be manufactured in a much shorter time than that necessary for manufacturing prior art encapsulating boxes. Moreover, compared with FR-A-2 547 113, the invention makes it possible to bring about a development of the X-ray protection levels without any detrimental affect on the definition of the electronic circuits contained in the box. SUMMARY OF THE INVENTION The present invention specifically relates to a protective box for electronic circuits hardened with respect to X-rays, wherein it comprises at least one element formed from a rigid mechanical structure made from a composite material, constituted by a fibre-reinforced resin, and an X-ray protection material at least partly covering the mechanical structure and which is formed from a resin matrix containing, in the form of a regularly dispersed powder, at least one metal and/or at least one inorganic compound of a metal, the powder only melting at a temperature at least equal to 630.degree. C. and the metal having a high atomic number at least equal to 47. In particular, the powder can be constituted by a metal and an inorganic compound of said same metal or another metal. This metal and this inorganic compound has a melting temperature equal to or above 630.degree. C. The term element of the box is understood to mean any part used in the formation of the box, such as the cover or the base on which the cover is fixed, as well as part of the cover or base (case of a cover or base in several parts). The X-ray protection must be associated with all the visible faces of the box, bearing in mind the random direction of X-rays. The use of materials with high melting points makes it possible to avoid undesirable effects due to heat shocks caused within the material during X-radiation, such as the surface melting of the powder grains which can lead to the destruction of the protective material. Moreover, the use of a metal with a high atomic number equal to or greater than 47 permits an effective X-ray filtering. For an equal material quantity, the use of powder regularly distributed in a resin matrix leads to an efficiency loss compared with pure sheet metal, all other conditions being the same. As this efficiency loss is essentially a function of the grain size of the powder and the powder quanitity in the organic binder, preference is given to a powder having a grain size between 0.5 and 25 .mu.m and e.g. between 1.6 and 10 .mu.m. In the same way the powder quantity in the binder can range between 25 and 50% by volume of the finished X-ray protection material. The doping quantity of the organic binder in this range is a function of the sought X-ray protection efficiency. This also applies with respect to the thickness of the X-ray protection material. The resin used for forming the matrix of protective material can be a thermoplastic or thermosetting resin, whose heat expansion coefficient is compatible with that of the composite material forming the mechanical structure and whose polymerization catalyst is compatible with the resin of said composite material. As a resin entering into the composition of the X-ray protection material, examples are polyamides, polyethers, polyesters, phenoplastics, polyolefines, epoxydes, polyimides, silicones, furans, etc. The metal powder embedded in the organic matrix of the X-ray protection material can be a silver, antimony, barium, rare earth, tantalum, tungsten, rhenium, iridium, platinum, gold, uranium or hafnium powder or a powder formed from a mixture of these metals. Preference is given to the use of silver, tantalum, tungsten or uranium. When the powder is formed by an inorganic component, the latter can be an oxide, a nitride or a carbide of a heavy metal, such as those referred to hereinbefore. In particular, the inorganic compound is an oxide, nitride or carbide of silver, tantalum, tungsten or uranium when said compound effectively exists. In order to optimize the protection against X-rays over a very broad energy spectrum, it is possible to use one or more metals and/or one or more inorganic compounds of a metal. The rigid mechanical structure is constituted by a material able to withstand the mechanical stresses which the final protective box is exposed. It can be formed from a thermoplastic or thermosetting resin reinforced by fibres. However, in order to ensure an excellent mechanical strength, preference is given to the use of thermosetting resins, such as epoxy, phenolic, polyester, polyimide and furan resins. The reinforcing fibres can be short or long and can be made from an organic or inorganic material, such as glass, carbon, boron, kevlar or metal. This composite material (resin + fibres) has a density between 1.2 and 1.8 instead of 2.8 for aluminium. The weight gain of a rigid structure according to the invention is consequently significant. The mechanical structure has a shape and size corresponding to the needs for fixing and housing the electronic circuits to be located there. It is obtained by moulding by injection, by compression or by a hybrid method called "compressiontransfer moulding", described in French patent application No. 85 18769 filed by the present Application on 18 December 1985. On the thus obtained rigid structure is effected a potting of the X-ray protection material either by injection, or by compression. In order to ensure a good adhesion of the X-ray protection material to the mechanical structure, the latter can be previously heated and/or can be subject to a surface preparation. In order to obtain a good distribution of the powder in the organic binder forming the X-ray protection material for bringing about homogeneity of the opacity, prior to potting premixing takes place of the powder and binder. This premixing is performed either by mixing the powder with melted grains of resin and then forming mixture granules by extrusion, or by simply mixing the powders, or by mixing the powder in an organic liquid binder. This premix is then introduced in the mould to be polymerized on the mechanical structure. The production of the X-ray protection material by potting makes it possible to ensure a continuous, homogeneous adhesion of the material on the rigid mechanical structure. This makes it possible to reduce the overall dimensions of the encapsulating box compared with the prior art solutions. In order to improve the attachment of the X-ray protection material to the rigid mechanical structure, the latter can have slots formed during the moulding of the structure. These slots are filled with X-ray protection material during the potting thereof, thus ensuring a sought supplementary attachment effect. In order to prevent the emission of electrons by the walls or elements of the protection box during X-ray irradiation and in particular by the metal powder, the box element can be covered with a material formed from at least one element having a low atomic number, at the most equal to 6, at least partly constituting the outer or inner surface of said box element. This material has a thickness exceeding the mean free travel of the electrons emitted by the walls of the box protected against X-rays during X-ray irradiation. It always forms the final layer with respect to the surrounding atmosphere. The element with a low atomic number can be carbon, boron or beryllium. The material for preventing the emissivity effects of the protective box walls is generally known under the name anti-SGEMP material (System Generating ElectroMagnetic Pulse). It can be in the form of a paint containing particles of the element with an atomic number at the most equal to 6 and is e.g. of Astral type Pyroflex 7D 713. Advantageously, the considered element of the protective box is equipped with a material which is a good electricity conductor which serves to filter the electromagnetic waves other than the X-rays, whereby said material covers the outer surface of the assembly formed by the mechanical structure and the X-ray protection material and/or the inner surface of said mechanical structure. This good electricity conducting material constitutes a Faraday cage protecting the electronic circuits located in the protective box and will hereinafter be called a faradization material. The faradization material can be nickel, silver, pure aluminium, copper and beryllium. Beryllium has the advantage of being able to serve both as an anti-SGEMP material and as a Faraday cage, due to its low atomic number and its good electrical conductivity.
043812805	summary	BACKGROUND OF THE INVENTION It is well known to those skilled in the art that the main ingredients of a nuclear fusion process are the nuclei of Hydrogen. In particular, its isotopes, deuterium and tritium (D-T). A fusion reaction consist of these light nuclei coalescing to form heavier elements with the release of energy. In order to coalesce or react these isotopes, referred to as the fuel, must be ionized to form a plasma. In the plasma state they have a net positive charge and normally repel one another. Therefore, before a fusion reaction can occur the repulsion force between the nuclei must be overcome by energetic collisions. However, even in energetic collisions there is a greater probability that the colliding nuclei will not fuse but will, instead, rebound elastically. Thus, the plasma must be confined in a region where they will approach each other and collide many times until fusion eventually takes place. The temperature required for the collisions to be energetic enough for the fusion reaction to produce more energy than the plasma loses by radiation is of the order of 10.sup.8 .degree. K. This temperature is a threshold value or initiation temperature; and because of the energy losses such as radiation and particle losses due to instabilities which occur concurrently with the additions of heat energy, the critical temperature for sustaining the reaction has to be even higher than that required to initiate fusion. The critical temperature requirment and the need for confining the plasma for a long enough time for an appreciable fraction of the fuel to burn precludes the use of material walls. Thus, for relatively low density plasmas, all feasible methods of containing the plasma rely on some form of magnetic confinement means. These low density plasmas require quite long confinement times because it is agreed by those skilled in the art that the product of density and confinement time must exceed a certain value before the reaction can be sustained. However, the longer the confinement time, the greater the energy losses due to the leakage of particles, to other instabilities, and to radiation which is greatly aggravated by the presence of any contaminates. For many years the research effort on controlled thermonuclear fusion was dominated by problems associated with magnetic confinement. However, all attempts to achieve useful controlled fusion energy release by these methods have been unsuccessful. Therefore, recently, there have been attempts to solve the controlled thermonuclear fusion problem by producing a microsize nuclear explosion. To accomplish this it is necessary to use a small fuel target and to produce a small clean energetic trigger which is capable of producing the very high temperatures required to ignite a very small thermonuclear explosion in the small volume of dense D-T mixture within a very short time. This time is determined by the time required for the plasma to cool. An ideal trigger would produce the necessary energy in a very short pulse which could be readily guided to the target and focused into the small volume of the target. The energy should be in a form such that it is totally absorbed by the small amount of target material. Preferably in a manner so that the nuclear fuel is heated uniformly. Thus, because of the ease with which short pulse length, high power laser beams can be guided to targets and focused into small volumes, they have been considered as a trigger. The basic idea of a laser-driven fusion device is to heat a small pellet or target containing a deuterium-tritium (D-T) mixture to ignition temperatures by the absorption of laser light in a time short compared to the time, T.sub.d, of its disassembly at the speed of sound in the material at the ignition temperature. Of course, the D-T reaction time, T.sub.r, must be short compared to T.sub.d and the range of the 3.5 MeV alpha particles which are produced should be less than the radius of the target. These conditions cannot be met at solid D-T densities with lasers which can be expected to be developed in the foreseeable future. Therefore, the targets are designed so that the D-T fuel is compressed by a factor of 10.sup.3 to 10.sup.4 above its solid density by a compressive pressure which is the reaction to the outward momentum of an ablating outer region of heavy material about the target. Pressures of the order of 10.sup.12 atmospheric are estimated to occur during the ablation-implosion process in laser fusion concepts. However, to achieve these pressures the laser pulse or pulses must have a special form, that is, they must be tailored according to the target requirements and the target must be spherically radiated. Multiple laser beams can be produced and guided to targets so that the targets are spherically radiated. Special care must be taken so that the beam from each laser arrives at the target at the same time. Laser beams have been used to generate high temperature dense plasma from which a few (10.sup.4) neutrons have been obtained. However, the energy limit of currently available lasers imposes severe restrictions on their use for this purpose. Numerous articles have been published which disclose the limitations of lasers for this purpose. A typical article is "LASER FUSION", Practical Power Plant May be Unattainable--Panel" Nuclear News, pages 79-80, May 1975. State of the art laser technology is noted as being inadequate for laser fusion. Relativistic electron beams possess energies which are several orders of magnitude larger than the best laser beams. Because of this, they are receiving attention as a means of achieving substantial thermonuclear yields by compression and heating of small masses of D-T fuel. This, of course, is the electron beam analogue of the inertial confinement schemes that employ lasers. However, difficulties associated with the use of high energy electron beams stem from the requirements for focusing and guiding them to small targets; from their relatively long pulse lengths (tens of nanoseconds); and from their long energy deposition lengths in dense mixtures of T-D fuels. To overcome these problems, several prior art methods have been proposed which require the use of multiple electron beams and specially designed targets. For example, U.S. Pat. Nos. 3,892,970; 3,899,681 and T. G. Roberts et al, "An Electron Beam Initiated Fusion Neutron Generator," IEEE TPS, Vol. PS-2, pp. 257-260, December 1974, teach that the electron beams are to be delivered to the target simultaneously so that the target is radiated properly and hydrodynamic instabilities do not develop. Consideration of hydrodynamic stability requirements impose severe restriction on the design of electron beam imploded fusion targets. Thus, when several beams are used, a high degree of simultaneity is required to insure a sufficiently uniform implosion. SUMMARY OF THE INVENTION The nuclear fusion device produces a multiple high energy electron beam trigger for a "controlled" thermonuclear explosion (reaction) wherein two or more electron beams arrive at the target with a high degree of simultaneity. The beams arrive at the target within 10.sup.-11 seconds of each other. The targets used are either targets which allow only for one dimensional expansion for confinement of both the beam at the target and the instantaneous direction of expansion, when two electron beams are used, or a spherical target of hydrogen isotope fuel where more than two electron beams are used. The method and device for triggering nuclear fusion reactions satisfies the requirements for use of high energy electron beams to initiate a thermonuclear plasma. In addition it removes the target sufficiently far from the electron beam generator to allow protection of the generator or device from the explosion which is produced. This trigger is used to produce a high temperature high density D-T plasma which is contained for times long enough for the copious production of neutrons and for the release of thermonuclear energy in excess of that required to produce the trigger. The confinement time is determined by the rate of energy loss by radiation which is low enough to allow the use of currently produced electron beams. The confinement time may also be determined by the ultimate disassembly of the target. A unique feature of this trigger device is the ability to deliver the separate high energy electron beams to the target at exactly the same time. The target is symmeterically radiated. Delivery of the electron beams at exactly the same time actually means that the pulses of high energy electrons arrive at the target within at least 10.sup.-11 seconds of each other. That is nearly simultaneously. The electron beams are produced in the electrode space of a conventional pulsed electron accelerator which utilizes a cathode for producing multiple electron beams. These electron beams exit the accelerator through thin film transparent apertures in the anode of the accelerator. Each electron beam is injected into a separate conventional linear pinch discharge. The high energy electron beams follow the pinch discharge and are delivered to the target. Each pinched discharge is curved so that each electron beam approaches the target from a different direction, thus irradiating the target symmeterically to produce a symmeterical implosion.
	description	This is a continuation application of U.S. patent application Ser. No. 12/871,079, filed Aug. 30, 2010, entitled, OPTIMIZED FLOWER TUBES AND OPTIMIZED ADVANCED GRID CONFIGURATIONS, which application is a continuation-in-part application claiming priority under 35 USC. § 119(e) to U.S. patent application Ser. No. 11/033,434, filed Jan. 11, 2005, entitled to HELICALLY FLUTED TUBULAR FUEL ROD SUPPORT. Field of the Invention The present invention relates to nuclear reactor fuel assemblies and more particularly to an array for supporting fuel rods wherein the array, or support assembly, consists of a matrix of substantially flat members forming a grid-like frame assembly and a plurality of helically fluted tubular members wherein the helical portions may have a variable pitch. Background Information In a typical pressurized water reactor (PWR), the reactor core is comprised of a large number of generally vertically, elongated fuel assemblies. The fuel assemblies include a support grid structured to support a plurality of fuel rods. The fuel assembly includes a top nozzle, a bottom nozzle, a plurality of the support grids and intermediate flow mixing grids, and a plurality of thimble tubes. The support grids are attached to the plurality of elongated thimble tubes which extend vertically between the top and bottom nozzles. The thimble tubes typically receive control rods, plugging devices, or instrumentation therein. A fuel rod includes a nuclear fuel typically clad in a cylindrical metal tube. Generally, water enters the fuel assembly through the bottom nozzle and passes vertically upward through the fuel assembly. As the water passes over the fuel rods, the water is heated until the water exits the top nozzle at a very elevated temperature. The support grids are used to position the fuel rods in the reactor core, resist fuel rod vibration, provide lateral support for the fuel rods and, to some extent, vertically restrain the fuel rods against longitudinal movement. One type of conventional support grid design includes a plurality of interleaved straps that together forum an egg-crate configuration having a plurality of roughly square cells which individually accept the fuel rods therein. Depending upon the configuration of the thimble tubes, the thimble tubes can either be received in cells that are sized the same as those that receive fuel rods therein, or can be received in relatively larger thimble cells defined in the interleaved straps. The straps are generally flat, elongated members having a plurality of relatively compliant springs and relatively rigid dimples extending perpendicularly from either side of the flat member. Slots in the straps are utilized to effect an interlocking engagement with adjacent straps, thereby creating a grid of “vertical” and “horizontal” straps which form generally square cells. The location of the springs and dimples are configured such that each cell typically has a spring on each of two adjacent sides. On each of the sides of the cell opposite the springs there are, typically, two dimples. The springs must be disposed opposite the dimples so that the fuel rod is biased against the dimples by the springs. The springs and dimples of each cell engage the respective fuel rod extending through the cell thereby supporting the fuel rod at six points (two springs and four dimples) in each cell. Preferably, each spring and/or dimple includes an arcuate, concave platform having a radius generally the same as a fuel rod. This concave platform helps distribute the radial load on the sides of the fuel rods. The perimeter straps have either springs or dimples extending from one side and peripherally enclose the inner straps of the grid to impart strength and rigidity to the grid. During assembly, the straps must be assembled in as specific configuration to ensure that each cell has the springs and dimples in the proper position. As such, assembly of the prior art frame assembly is a time consuming process. It would be advantageous to have a support assembly that is more easily constructed. The straps may include one or more mixing vanes formed thereon that facilitate mixing of the water within the reactor to promote convective heat exchange between the fuel, rods and the water. This motion, along with the elevated temperatures, pressures, and other fluid velocities within the reactor core tend to cause vibrations between the grids and the fuel rods. As with the proper positioning of the straps, care must be used to ensure that the mixing vanes are disposed at the proper locations. Additionally, the action of the water flow impinging on the mixing vanes cause both a pressure drop in the pressure vessel and creates torque in the frame assembly, neither of which are desired. Since the grids support the fuel rods within the fuel cell, such vibrations therebetween can result in fretting of the fuel rods. Such fretting, if sufficiently severe, can result in breach of the fuel rod cladding with resultant nuclear contamination of the water within the reactor. It is desired to provide an improved grid designed to minimize fretting wear between the grids and the fuel rods while maintaining a mixed flow of water through the reactor core. It is also desired to have a support assembly that is easily assembled. These needs, and others, are met by the present invention which provides a support grid for a nuclear fuel assembly, wherein the fuel rod is a generally cylindrical fuel rod with a diameter, and the support grid includes a frame assembly having a plurality of generally uniform cells, each cell having at least one sidewall and a width, and at least one generally cylindrical tubular member or a helical frame member. The tubular member/helical frame member has a cell contact portion with a greater diameter and at least one fluted helical fuel rod contact portion with a lesser diameter. As used herein, a “fuel rod contact portion” is typically, but is not limited to, an arcuate line extending at least partly around the cylinder that is a fuel rod. The cell contact portion and the fuel rod contact portion are joined by a transition portion. The greater diameter is generally equivalent to the cell width, and the lesser diameter is generally equivalent to the fuel rod diameter. In this configuration, a fuel rod disposed in the tubular member would engage the inner diameter. The tabular member is disposed in one cell of the plurality of generally square cells so that the cell contact portion engages the at least one cell sidewall. In this manner, the fuel rod is held by the helical fuel rod contact portion and the tubular member is held by the frame assembly. In a preferred embodiment, the tubular member has a wall of uniform thickness so that the helical fuel rod contact portion defines a passage with a helical shape on both the side adjacent to the fuel rod and the side adjacent to the cell wall. These helical shaped passages act to mix the water so that mixing vanes are not required. There are at least two advantages to using the helical shaped passages; first, the water flow does not impinge on the shaped passage, so there is a minimal pressure drop created by the mixing structure. Second, by reversing the direction of the helical passage in selected cells, the amount of torque exerted on the frame assembly may be controlled. The helical fuel rod contact portion may be formed in various configurations. For example, there may be a single for multiple) helical fuel rod contact portion having an angular displacement of 360 degrees, that is, extending 360 degrees around the tubular member. However, given the relatively short height of a typical cell, the pitch (radial distance/height) of the helical fuel rod contact portion may be too great thereby restricting the flow of water through the helical portion of the passage. Alternatively, there may be at least two helical fuel rod contact portions each extending 180 degrees around the tubular member. However, in a preferred embodiment, there are four helical fuel rod contact portions each extending 90 degrees around the tubular member. While these examples have used a number (N) of helical fuel rod contact portions and an angular displacement (A) that equals 360 (N*A=360), this is not required. That is, virtually any number of helical fuel rod contact portion(s) may be used with any angular displacement. It is further noted that, while a symmetrical helical contact portion is preferred, a helical contact portion may be an asymmetrical helix; that is the pitch may be variable along the tubular member. For example, the tubular member, or helical frame member, may have a first axial portion and a second axial portion. The helical contact portion extends over both axial portions. The helical contact portion may have a first pitch at the first axial portion and a second pitch at the second axial portion. The tubular members, preferably, have a smooth transition between the cell contact portion and the helical fuel rod contact portion. Where there are four helical fuel rod contact portions, the shape of the tubular member is similar to the perimeter of a flower with four petals. Alternatively, the tubular member may include extended platform sections structured to engage either the wall of the frame assembly and/or the fuel rod. Where there is a platform, the transition section will typically be a sharp curve. In another embodiment, the greater portion of the length of the transition portion is generally flat and the ends are sharply angled. The frame assembly includes a plurality of cells typically structured to contain a nuclear fuel rod. As noted above, some cells are adapted to enclose a thimble rod or other device. However, the non-fuel rod cells are not relevant to this invention and, while noted, will not be discussed hereinafter. In the preferred embodiment, the frame assembly is made from a plurality of substantially flat, elongated snap members disposed in two interlocked sets, a “vertical” set and a “horizontal” set. The vertical set of strap members is disposed generally perpendicular to the horizontal strap members. Also, the strap members in each set are generally evenly spaced. In this configuration, the cells are generally square. In an alternate embodiment, the frame assembly is made from the helical frame members that have been welded together, preferably at 90 degree intervals. As used herein, directional terms, such as, but not limited to, “upper” and “lower” relate to the components as shown in the Figures and are not limiting upon the claims. As shown in FIG. 1, there is a fuel assembly 20 for a nuclear reactor. The fuel assembly 20 is disposed in a water vessel (not shown) having an inlet at the bottom and an outlet at the top. The fuel assembly 20 comprises a lower end structure or bottom nozzle 22 for supporting the fuel assembly 20 on the lower core plate (not shown) in the core region of a reactor (not shown); a number of longitudinally extending control rod guide tubes, or thimbles 24, projecting upwardly from the bottom nozzle 22; a plurality of transverse support grids 26 axially spaced along the guide thimbles 24; an organized array of elongated fuel rods 28 transversely spaced and supported by the grids 26; an instrumentation tube 30 located in the center of the assembly; and an upper end structure or top nozzle 32 attached to the upper ends of the guide thimbles 24, in a conventional manner, to frill an integral assembly capable of being conventionally handled without damaging the assembly components. The bottom nozzle 22 and the top nozzle 32 have end plates (not shown) with flow openings (not shown) for the upward longitudinal flow of a fluid coolant, such as water, to pass up and along the various fuel rods 28 to receive the thermal energy therefrom. To promote mixing of the coolant among the fuel rods 28, a mixing vane grid structure, generally designated by the numeral 34, is disposed between a pair of support grids 26 and mounted on the guide thimbles 24. The top nozzle 32 includes a transversely extending adapter plate (not shown) having upstanding sidewalls secured to the peripheral edges thereof in defining an enclosure or housing. An annular flange (not shown) is secured to the top of the sidewalls. Suitably clamped to this flange are leaf springs 36 (only one of which being shown in FIG. 1) which cooperate with the upper core plate (not shown) in a conventional manner to prevent hydraulic lifting of the fuel assembly caused by upward coolant flow while allowing for changes in fuel assembly length due to core induced thermal expansion and the like. Disposed within the opening defined by the sidewalls of the top nozzle 32 is a conventional rod cluster control assembly 38 having radially extending flukes, being connected to the upper end of the control rods, for vertically moving the control rods in the control rod guide thimbles 24 in a well known manner. To form the fuel assembly 20, support grids 26 and a mixing vane grid structure 34 are attached to the longitudinally extending guide thimbles 24 at predetermined axially spaced locations. The bottom nozzle 22 is suitably attached to the lower ends of the guide thimbles 24 and then the top nozzle 32 is attached to the upper ends of guide thimbles 24. Fuel rods 28 are then inserted through the grids 26 and grid structure 34. The fuel rods 28 are generally elongated cylinders having a diameter. For a more detailed description of the fuel assembly 20, reference should be made to U.S. Pat. No. 4,061,536. The fuel assembly 20 depicted in the drawings is of the type having a square array of fuel rods 28 with the control rod guide thimbles 24 being strategically arranged within the fuel rod array. Further, the bottom nozzle 22, the top nozzle 32, and likewise the support grids 26 are generally square in cross section. In that the specific fuel assembly 20 represented in the drawings is for illustrational purposes only, it is to be understood that neither the shape of the nozzles or the grids, or the number and configuration of the fuel rods 28 and guide thimbles 24 are to be limiting, and the invention is equally applicable to different shapes, configurations, and arrangements than the ones specifically shown. For example, as shown in FIGS. 2 and 4, the support grid 26 includes a frame assembly 40 and at least one fuel rod support 51 that is a generally cylindrical tubular member 50. The frame assembly 40 includes a plurality of cells 42 defined by cell walls 43. Each cell 42 has a width as indicated by the letter “w.” In one embodiment, the cells 42 and cell walls 43 are formed from a plurality of substantially flat, elongated strap members 44 disposed in two interlocked sets, a vertical set 46 and a horizontal set 48. The strap members 44 in the vertical and horizontal sets 48 of strap members 44 are generally perpendicular to each other. Additionally, the strap members 44 in each set are generally evenly spaced. In this configuration, the strap members 44 form generally square cells 42A. Thus, each cell 42A has two diagonal axes “d1” and “d2,” which are perpendicular to each other and extend through the corners of the cell 42A, as well as two normal axes “n1” and “n2,” which are perpendicular to each other and extend through the center of the cell 42A and which intersect perpendicularly with the cell walls 43. The points on the cell wall 43 that the two normal axes pass through are the closest point, “cp.” between the cell wall 43 and the center of the cell 42. As shown in FIG. 3, the frame assembly 40 also has a height, indicated by the letter “h,” wherein the height is substantially less than the width or length of the frame assembly 40. Further, the frame assembly 40 has a top side 47 and a bottom side 49. It is notable that the strap members 44 of the present invention do not include protuberances, such as springs and dimples, as did strap members of the prior art. The lack of additional support structures make the construction of the frame assembly 40 very easy. The tubular member 50 of the support grid 26 is shown in FIGS. 4 and 5. The tubular member 50 includes at least one helical fluted portion or fuel rod contact portion 52, a cell contact portion 54, and a transition portion 56 disposed therebetween. As shown in FIGS. 4-6, the tubular member 50 has four fuel rod contact portions 52, which is the preferred embodiment. Other configurations are discussed below. The cell contact portion 54 has a greater diameter being generally equivalent to said cell width and is structured to snugly engage the cell 42. The fuel rod contact portion 52 has a lesser diameter, being generally equivalent to said fuel rod 28 diameter. Thus, the tubular member 50 may be disposed in a cell 42 and a fuel rod 28 may be disposed in the tubular member 50. In a preferred embodiment, the tubular member 50 is made from a material having a uniform thickness. Thus, the helical fuel rod contact portion 52 defines an outer passage 60 between the outer side of the tubular member 50 and the cell wall 43. Additionally, the cell contact portion 54, which is spaced from the fuel rod 28, defines an inner passage 62. Water which flows through either the outer or inner passages 60, 62 is influenced by the shape of the helical fuel rod contact portion 52 resulting in the water being mixed. The tubular member 50 may be constructed with any number of helical fuel rod contact portions 52 which may have any degree of pitch. For example, as shown in FIG. 7, a tubular member 50 has a single helical fuel rod contact portion 52 that extends 360 degrees about the tubular member 50. As shown in FIG. 8, a tubular member 50 has a two helical fuel rod contact portions 52 that each extend 180 degrees about the tubular member 50. As shown in FIG. 9, a tubular member 50 has a two helical fuel rod contact portions 52 that each extend 360 degrees about the tubular member 50. As noted above, FIG. 5 shows a tubular member 50 having a four helical fuel rod contact portions 52 that each extend 90 degrees about the tubular member 50. Preferably, the helical fuel rod contact portions 52 are spaced evenly about the tubular member 50, but this is not required. The pitch is, preferably, between 0.001 and 20.0. These examples have used a number (N) of helical fuel rod contact portions 52 and an angular displacement (A) that equals 360 degrees or a multiple of 360 degrees. This configuration is especially adapted for use in a square cell 42A. That is, the cell contact portion 54 will only contact the cell wall 43 at the closest point on the cell wall 43. At other points, e.g., the corner of the cell 42A, the tubular member 50 greater diameter, that is the cell contact portion 54, will not contact a cell wall 43. Thus, as shown best in FIG. 6, where there are four evenly spaced, helical fuel rod contact portions 52 that each extend 90 degrees about the tubular member 50, there are four corresponding cell contact portions 54, each disposed between to helical fuel rod contact portions 52. To ensure the greatest amount of surface area contact between the tubular member 50 and the cell wall 43, the tubular member 50 is disposed with each helical, fuel rod contact portion 52 generally aligned with a diagonal axis at the top side 47 of the cell and aligned with a different diagonal axis at the bottom side 49 of the cell. In this orientation, the cell contact portion 54 is aligned with a cell wall 43 closest point at the top side 47 and at the bottom side 49. A similar configuration may be made with cells 42 of any shape. That is, the number (N) of helical fuel rod contact portions 52 is preferably equal to the number of sides (S) to the cell 42, and the angular displacement (A) is preferably 360 degrees/S. Thus, the tubular member may be positioned with each helical fuel rod contact portion 52 generally aligned with an axis passing through the corner of the cell 42 at the top side 47 of the cell and aligned with a different axis passing through the corner of the cell 42 at the bottom side 49 of the cell. Thus, the cell contact portion 54 is aligned with the cell wall 43 closest point at the top side 47 and at the bottom side 49. In another embodiment, the frame assembly 40 includes a plurality of cylindrical cells 42B defined by a plurality of connected tubular frame members 70. As shown in FIG. 10, the frame assembly 40 may have a plurality of densely packed tubular frame members 70, however, as shown in FIG. 11, a pattern of aligned tubular frame members 70 is preferred. That is, the tubular frame members 70 are coupled to each other at 90 degree intervals about the perimeter of each tubular frame member 70. The tubular member 50 is disposed within the cylindrical cells 42B. As shown in FIG. 12, the combination of the tubular member 50 and the cylindrical cell 42B again creates an inner passage 62 between the fuel rod 28 and the tubular member 50 and an outer passage 60 between the tubular member 50 and the tubular frame member 70. The cylindrical cell 42B of the tubular frame member 70 has the additional advantage that the entire cell contact portion 54 abuts the cell wall 43. That is, the diameter of the cylindrical cell 42B is the same as the cell width, which is also the same as the closest point, and, as such, the cell contact portion 54 will engage the cell wall 43 along the entire height of the cell wall 43. This is unlike a square cell 42A wherein the cell contact portion 54 does not contact the cell wall 43 at the corners. In another embodiment, shown in FIG. 13, the functions of the tubular member 50 and the tubular frame member 70 have been combined in a helical frame member 80. That is, the frame assembly 40 includes a plurality of helical frame members 81 disposed in a matrix pattern. The helical frame member 80, like the tubular member 50, includes at least one helical fuel rod contact portion 52, however, instead of a cell contact portion 54, the outer side of the helical frame member 80 is a contact portion 55 structured to be directly coupled to the contact portion 55 of an adjacent helical frame member 80. As with the tubular frame member 70 embodiment of the frame assembly 40, the helical frame members 80 are coupled to each other at 90 degree intervals about the perimeter of each helical frame member 80. Additionally, in this embodiment the frame assembly 30 preferably includes a plurality of outer straps 82 structured to extend about the perimeter of the plurality of helical frame members 81. The outer straps 82 are coupled to the contact portion 55 of the helical frame members 80 disposed at the outer edge of the plurality of helical frame members 81. A fuel rod 28 is disposed through at least one helical frame member 80. As shown best in FIG. 12, as viewed as a cross-section, the tubular member 50 components, i.e., the helical fuel rod contact portion 52, the cell contact portion 54, and the transition portion 56, preferably, are shaped as smooth curves. This configuration gives the tubular member 50 a compressible, spring-like quality. However, as shown in FIG. 14, the cell contact portion 54 may include an extended planar length or platform 90. The platform 90 is structured to provide a greater surface area which engages the cell wall 43. The greater length of the platform 90 will necessitate the transition portion 56 having a sharp curve. Similarly, as shown in FIG. 15, the helical fuel rod contact portion 52 may include a concave platform 92 adapted to extend radially about the fuel rod 28. As before, greater length of the concave platform 92 will necessitate the transition portion 56 having a sharp curve. A tubular member 50 may also include both a platform 90 at the cell contact portion 54 and a concave platform 92 at the helical fuel rod contact portion 52. Finally, the tubular member 50 may also be constructed with a generally flat transition portion 56 with angled ends 94. As shown in FIG. 16, in this embodiment the transition portion 56 is generally planar in a cross-sectional top view. It is understood that, due to the helical nature of the fuel rod contact portion 52, the transition portion 56 is not flat in the direction of the height of the frame assembly 40. As noted above, pitch of the helical contact portion 52 may be variable along the tubular member 50. For example, the helical contact portion 52 at a tubular member 50, and/or tubular frame member 70, lower edge 100 (discussed below) may have a first pitch and the same helical contact portion 52 may have a different pitch at the tubular member 50, and/or tubular frame member 70, upper edge 102 (discussed below). As shown in FIG. 17, which is a schematic having the helical contact portion 52 shown as a line for clarity, each tubular member 50, and/or each tubular frame member 70, has a leading edge, with respect to the flow of water, which is a lower edge 100. Similarly, each tubular member 50, and/or each tubular frame member has a trailing edge, with respect to the flow of water, which is an upper edge 102. When a tubular member 50, and/or tubular frame member 70, is disposed in a frame assembly 20, the tubular member lower edge 100 is disposed closer to the frame assembly bottom side 49 than the top side 47. Conversely, the tubular member upper edge 102 is disposed closer to the frame assembly top side 47 than the bottom side 49. It is further noted that each tubular member 50, and/or each tubular frame member 70 has a height. Thus, the at least one helical contact portion 52 may have a first pitch at the tubular member lower edge 100 and change to a second pitch at the tubular member upper edge 102. In one embodiment (not shown), the change is gradual. In this configuration, the at least one helical contact portion 52, essentially, has a different pitch at each elevation over the height of the tubular member 50. In a preferred embodiment, however, the tubular member 50, and/or the tubular frame member 70, has two or more portions 106, 108, each portion being an axial portion, wherein the helical contact portion 52 has a different pitch. That is, the tubular member 50 has a cylinder axis 110 which, when the tubular member is positioned in a fuel assembly 20 in a nuclear reactor, extends generally vertically. As shown, the first axial portion 106 is the lower, upstream portion of the tubular member 50. The two or more axial portions, hereinafter the first and second axial portions 106, 108, are located on either side of an imaginary plane or line 112 extending generally perpendicular to the tubular member cylinder axis 110. The at least one helical fuel rod contact portion 52 extends over, i.e. travels over, both the first axial portion 106 and the second axial portion 108. The at least one helical fuel rod contact portion 52 on the first axial portion 106 has a first pitch and the at least one helical fuel rod contact portion 52 on the second axial portion 108 has a second pitch. Preferably, the pitch of the at least one helical fuel rod contact portion 52 on the first axial portion 106 is smooth (relative to the now path or the water. i.e. generally vertical), or, may be described as having a lower, helical gradient. Conversely, the pitch of the at least one helical fuel rod contact portion 52 on the second axial portion 108 has sharper pitch, or, a higher helical gradient. As shown in FIG. 17, the pitch of the at least one helical fuel rod contact portion 52 is exaggerated for clarity. As noted above, the helical fuel rod contact portions 52 may be spaced evenly about the tubular member 50, but this is not required. That is, when the at least one helical fuel rod contact portion 52 is a plurality of helical fuel rod contact portions 53, the points where the helical fuel rod contact portions 52 begin and end, at the tubular member lower edge 1110 and the tubular member upper edge 102, respectively, are equally spaced about the perimeter of the tubular member 50. This may also be described as each helical fuel rod contact portion 52 in the plurality of helical fuel rod contact portions 53 being disposed “equally angularly” about the tubular member 50. For example, two helical fuel rod contact portions 52 may be spaced 180 degrees apart, three helical fuel rod contact portions 52 may be spaced 120 degrees apart, four helical fuel rod contact portions 52 may be spaced 90 degrees apart, five helical fuel rod contact portions 52 may be spaced 72 degrees apart, six helical fuel rod contact portions 52 may be spaced 60 degrees apart, eight helical fuel rod contact portions 52 may be spaced 45 degrees apart, as shown in FIG. 21, and so forth. It is again noted that while equal spacing of the helical fuel rod contact portions 52 is preferred, it is not required. For example, a tubular member 50 may have two helical fuel rod contact portions 52 disposed 90 degrees apart and each extending 180 degrees over the axial length, i.e. height, of the tubular member 50. In this configuration, one quarter (an arc extending about 90 degrees around the perimeter) of the tubular member would be generally smooth from the tubular member lower edge 100 to the tubular member upper edge 102. As noted above, the frame assembly 40 has a height. Put another way, each strap member 44 has a height. Typically, the height of each strap member 44 is the same, however, the outer straps 82 may have an increased height relative to the inner strap members 44. The tubular members 50 (and/or a tubular frame member 70) may have an axial length, or height, that is substantially similar to the frame assembly 40, strap members 44, and/or outer straps 82. In another embodiment, shown in FIG. 18, the tubular member 50 (and/or a tubular frame member 70) has a height that is different than the frame assembly 40. For example, the tubular member 50 may be taller than the frame assembly 40 and a portion of the tubular member 50 extends above and/or below the frame assembly 40 (not shown). In a preferred embodiment, the tubular member 50 has height that is less than the frame assembly 40 height, shown in FIG. 18. In this configuration, the tubular member upper edge 102 is preferably about parallel with the frame assembly top side 47. As noted above, by reversing, the direction of the helical passages 60, 62 in selected cells 42, the amount of torque exerted on the frame assembly 41) may be controlled. That is, when viewed axially, the tubular members (and/or a tubular frame member 70) have a twist. The twist may be clockwise or counterclockwise as shown, in FIG. 19. When tubular members (and/or a tubular frame members 70) with different twists are disposed in a frame assembly 40, the amount of torque exerted on the frame assembly 40 may be controlled. A number of variations of tubular members 50 and frame assemblies 40 have been described above. In one embodiment, all the tubular members (and/or a tubular frame members 70) in a frame assembly 40 are substantially similar tubular members 50 (and/or a tubular frame members 70). That is, all the tubular members 50 (and/or a tubular frame members 70) have substantially the same characteristics. In another embodiment, selected tubular members 50 (and/or a tubular frame members 70) disposed in a single frame assembly 40 or support grid 26 have different characteristics. As noted above, tubular members 50 (and/or a tubular frame members 70) with different twists may be disposed in a single frame assembly 40. Further, as an example only, in one support grid it may be desirable to have a selected number of tubular members 50 with four helical fuel rod contact portions 52 while the remaining tubular members 50 have eight helical fuel rod contact portions 52. Alternatively, as another example only, in one support grid it may be desirable to have a selected number of tubular members 50 with helical fuel rod contact portions 52 with a variable pitch while the remaining tubular members 50 have helical fuel rod contact portions 52 with a constant pitch. As yet another example, the support grid 26 may have a combination of frame assemblies 40. That is, as shown in FIG. 20, the frame assembly 40 may include outer straps 82 and a limited number of inner strap members 44, i.e. less than enough strap members 44 to form a complete and uniform grid. When a frame assembly 40 has a limited number of strap members 44, only a limited number of cells 42 may be formed. In such a configuration the strap members 44 are not equally spaced and are, preferably, disposed relatively adjacent to the outer straps 82. In this configuration, the medial portion of the frame assembly 40 is empty. The tubular frame members 70 described above may be installed in such an open medial portion. Thus, a support grid 26 may include both tubular members 50 disposed in cells 42 as well as tubular frame members 70 disposed in an open area 120, which is larger than a cell 42, between the strap members 44. It is understood that any combination of the variations described above are possible. Accordingly, to describe a support grid 26 having elements with a mix of characteristics (e.g. number of contact portions 52, height, variable pitches of the contact portions 52, etc.) it may be said that “at least one of the tubular members 50,” or, “at least one of the helical frame members 70” has the specified characteristic(s). Such a description means that the other tubular members 50 and/or a tubular frame members 70 may, or may not, have the same specified characteristic(s). For example, a support grid 26 may be described as having “at least one of the plurality of helical frame member 81 with a cylinder axis 110 and at least a first axial portion 106 and a second axial portion 108.” This means that the other tubular members 50 and/or a tubular frame members 70 may, or may not, have a “first axial portion 106 and a second axial portion 108.” As a further example, a support grid 26 may be described as having at least one tubular member 50 with a clockwise twist and at least one tubular member 50 with a counterclockwise twist. Thus, in a support grid 26 of one hundred tubular members 50, there could be (1) fifty tubular members 50 with a clockwise twist and fifty tubular members 50 with a counterclockwise twist, or, (2) one tubular member 50 with a clockwise twist and ninety-nine tubular members 50 with a counterclockwise twist, or any other combination thereof. 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 arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
	abstract	A method treats a flow gas that is guided via a catalytic adsorber module to oxidize contaminants carried in the flow gas. The method reliably purifies the flow gas using equipment that is held to a comparatively low level of complexity. To this end, the flow gas is guided in a first purification step via a first catalytic adsorber module to oxidize contaminants carried along therewith, during which molecular or atomic oxygen is added to the flow gas, and the flow gas mixed with the added oxygen is guided in a second purification step via an oxidation catalyst. The flow gas flowing away from the oxidation catalyst is guided in a third purification step via a second catalytic adsorber module to reduce excessive oxygen.

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.