patent_number
stringlengths 0
9
| section
stringclasses 4
values | raw_text
stringlengths 0
954k
|
|---|---|---|
summary | ||
052746836 | abstract | A method for replacing a nozzle in a pressure vessel. The existing nozzle is cut approximately at the inside surface of the pressure vessel wall. The portion of the existing nozzle that extends beyond the exterior of the pressure vessel wall is removed. A weld pad is deposited on the exterior of the pressure vessel wall around the nozzle bore. The remainder of the existing nozzle is removed. A corrosion resistant thermal spray coating is applied to the nozzle bore. A replacement nozzle is installed in the nozzle bore and seal welded to the weld pad on the exterior of the pressure vessel wall. |
claims | 1. An apparatus having a reaction frame that receives reaction forces from a stage comprising: a first reaction frame portion of the reaction frame coupled to ground in a first direction by a ground rod aligned along the longitudinal side of the first reaction frame; a second reaction frame portion of the reaction frame not coupled directly to ground in the first direction; and an interconnect rod passing parallel to the plane defined by the first reaction frame portion and second reaction frame portion having a first end and a second end with a damper therebetween, wherein the first end is coupled to the first reaction frame portion and the second end is coupled to the second reaction frame portion and reaction forces in the first direction received by the second reaction frame portion are transferred to ground through the interconnect rod and the first reaction frame portion. 2. The apparatus of claim 1 further comprising: claim 1 a first drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the first reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and a slidable coupling between the fixed drive portion and the movable drive portion associated with the first drive mechanism that structurally decouples the first reaction frame portion from the stage in at least the first direction. 3. The apparatus in claim 2 wherein each slidable coupling further includes an air-bearing. claim 2 4. The apparatus of claim 1 further comprising: claim 1 a second drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the second reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and a slidable coupling between the fixed drive portion and the movable drive portion of the second drive mechanism that structurally decouples the second reaction frame portion from the stage in at least the first direction. 5. The apparatus in claim 4 wherein each slidable coupling further includes an air-bearing. claim 4 6. The apparatus of claim 1 further comprising: claim 1 a base; a first slidable coupling supporting the stage on the base that decouples the stage from the reaction frame in at least the first direction; and a second slidable coupling supporting the reaction frame on the base that decouples the reaction forces between the stage and the reaction frame. 7. The apparatus in claim 6 wherein each slidable coupling further includes an air-bearing. claim 6 8. The apparatus in claim 1 wherein the first direction is along the interconnect rod. claim 1 9. The apparatus in claim 1 wherein the reaction frame is free to move in X, Y, and Theta Z degrees of freedom with respect to the base. claim 1 10. The apparatus of claim 1 wherein the ground rod is further alligned along the center-of-gravity associated with the first reaction frame portion. claim 1 11. The apparatus of claim 1 wherein the damper is implemented using a spring-damper mechanism. claim 1 12. A stage assembly, comprising: a stage guided movably in at least a first direction; a first reaction frame portion of a reaction frame, the first reaction frame coupled to ground in the first direction by a first ground rod aligned along the longitudinal side of the first reaction frame portion; a second reaction frame portion of the reaction frame not coupled directly to ground in the first direction; and an interconnect rod passing parallel to the plane defined by the first reaction frame portion and second reaction frame portion having a first end and a second end with a damper therebetween, wherein the first end is coupled to the first reaction frame portion and the second end is coupled to the second reaction frame portion and reaction forces from the stage moving in the first direction received by the second reaction frame portion are transferred to ground through the interconnect rod and the first reaction frame portion. 13. The stage assembly of claim 12 wherein the damper is implemented using a spring-damper mechanism. claim 12 14. The stage assembly of claim 12 further comprising: claim 12 a first drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the first reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and a slidable coupling between the fixed drive portion and the movable drive portion associated with the first drive mechanism that structurally decouples the first reaction frame portion from the stage in at least the first direction. 15. The stage assembly in claim 14 wherein the reaction frame is free to move in X, Y, and Theta Z degrees of freedom with respect to the base. claim 14 16. The stage assembly of claim 14 wherein the ground rod is further alligned along the center-of-gravity associated with the first reaction frame. claim 14 17. An exposure system comprising: an illumination system that irradiates radiant energy; and the stage assembly according to claim 14 , the stage assembly carrying an object disposed on a path of the radiant energy. claim 14 18. An object on which an image has been formed by the exposure system of claim 17 . claim 17 19. The stage assembly of claim 12 further comprising: claim 12 a second drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the second reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and a slidable coupling between the fixed drive portion and the movable drive portion that structurally decouples the second reaction frame portion from the stage in at least the first direction. 20. The stage assembly in claim 19 wherein each slidable coupling further includes an air-bearing. claim 19 21. The stage assembly of claim 12 further comprising: claim 12 a base that the stage is movable thereon; a first slidable coupling supporting the stage on the base that decouples the stage from the reaction frame in at least the first direction; and a second slidable coupling supporting the reaction frame on the base that decouples the reaction forces between the stage and the reaction frame. 22. The stage assembly in claim 21 wherein each slidable coupling further includes an air-bearing. claim 21 23. The stage assembly in claim 12 wherein the first direction corresponds to the length of the interconnect rod. claim 12 24. The stage assembly in claim 23 wherein each slidable coupling further includes an air-bearing. claim 23 25. A method of processing reaction forces from a stage, comprising: providing a first reaction frame portion of a reaction frame; alligning a ground rod attached to ground and coupled along the longitudinal side of the first reaction frame; providing a second reaction frame portion of the reaction frame; and interconnecting the first reaction frame portion and second reaction frame portion together with an interconnect rod passing parallel to the plane defined by the first reaction frame portion and second reaction frame portion having a damper along the length of the interconnect rod wherein reaction forces in the first direction received by the second reaction frame portion are transferred to ground through the combination of the interconnect rod, the damper and the first reaction frame portion. 26. The method of claim 25 further comprising: claim 25 providing a first drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the first reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and structurally decoupling the first reaction frame portion from the stage in at least the first direction using a slidable coupling between the fixed drive portion and the movable drive portion associated with the first drive mechanism. 27. The method of claim 25 further comprising: claim 25 providing a second drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the second reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and structurally decoupling the first reaction frame portion from the stage in at least the first direction using a slidable coupling between the fixed drive portion and the movable drive portion associated with the second drive mechanism. 28. The method of claim 25 further comprising: claim 25 providing a base; structurally decoupling the stage from the base in at least the first direction using a slidable coupling supporting the stage on the base; and structurally decoupling the reaction forces between the reaction frame and the base in at least the first direction using a slidable coupling supporting the reaction frame on the base. 29. The method of claim 28 wherein the reaction frame is free to move in X, Y, and Theta Z degrees of freedom with respect to the base. claim 28 30. The method of claim 25 wherein the ground rod is further alligned along the center-of-gravity associated with the first reaction frame. claim 25 31. The method of claim 25 wherein the damper is implemented using a spring-damper mechanism. claim 25 32. An apparatus having a reaction frame that receives reaction forces from a stage comprising: a first reaction frame portion of the reaction frame coupled to ground in a first direction by a first ground rod aligned along the longitudinal side of the first reaction frame; a second reaction frame portion of the reaction frame not coupled directly to ground in the first direction; an interconnect rod having a first end and a second end alligned with the ground rod, wherein the first end is coupled to the first reaction frame portion and the second end is coupled to the second reaction frame portion and reaction forces in the first direction received by the second reaction frame portion are transferred to ground through the combination of the interconnect rod and the first reaction frame portion. 33. The apparatus of claim 32 further comprising: claim 32 a first drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the first reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and a slidable coupling between the fixed drive portion and the movable drive portion associated with the first drive mechanism that structurally decouples the first reaction frame portion from the stage in at least the first direction. 34. The apparatus in claim 33 wherein each slidable coupling further includes an air-bearing. claim 33 35. The apparatus of claim 32 further comprising: claim 32 a second drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the second reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and a slidable coupling between the fixed drive portion and the movable drive portion associated with the second drive mechanism that structurally decouples the second reaction frame portion from the stage in at least the first direction. 36. The apparatus in claim 35 wherein each slidable coupling further includes an air-bearing. claim 35 37. The apparatus of claim 32 further comprising: claim 32 a base; a first slidable coupling supporting the stage on the base that decouples the stage from the reaction frame in at least the first direction; and a second sidable coupling supporting the reaction frame on the base that decouples the reaction forces between the stage and the reaction frame. 38. The apparatus in claim 37 wherein each slidable coupling further includes an air-bearing. claim 37 39. The apparatus in claim 32 wherein the reaction frame is free to move in X, Y, and Theta Z degrees of freedom with respect to the base. claim 32 40. The apparatus of claim 32 wherein the ground rod is further alligned along the center-of-gravity of the first reaction frame portion. claim 32 41. A stage assembly, comprising: a stage guided movably in at least a first direction; a first reaction frame portion of the reaction frame coupled to ground in the first direction by a ground rod aligned along the longitudinal side of the first reaction frame; a second reaction frame portion of the reaction frame; and an interconnect rod having a first end and a second end alligned with the ground rod, wherein the first end is coupled to the first reaction frame portion and the second end is coupled to the second reaction frame portion and reaction forces in the first direction received by the second reaction frame portion are transferred to ground through the combination of the interconnect rod and the first reaction frame portion. 42. The stage assembly of claim 41 further comprising: claim 41 a first drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the first reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and a slidable coupling between the fixed drive portion and the movable drive portion associated with the first drive mechanism that structurally decouples the first reaction frame portion from the stage in at least the first direction. 43. The stage assembly in claim 42 wherein each slidable coupling further includes an air-bearing. claim 42 44. The stage assembly of claim 41 further comprising: claim 41 a second drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the second reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and a slidable coupling between the fixed drive portion and the movable drive portion that structurally decouples the second reaction frame portion from the stage in at least the first direction. 45. The stage assembly in claim 44 wherein each slidable coupling further includes an air-bearing. claim 44 46. The stage assembly of claim 41 further comprising: claim 41 a base that the stage is movable thereon; a first slidable coupling supporting the stage on the base that decouples the stage from the reaction frame in at least the first direction; and a second slidable coupling supporting the reaction frame on the base that decouples the reaction forces between the stage and the reaction frame. 47. The stage assembly in claim 46 wherein each slidable coupling further includes an air-bearing. claim 46 48. The apparatus in claim 41 wherein the reaction frame is free to move in X, Y, and Theta Z degrees of freedom with respect to the base. claim 41 49. An object on which an image has been formed by the exposure system of claim 48 . claim 48 50. The stage assembly of claim 41 wherein the ground rod is further alligned along the center-of-gravity of the first reaction frame. claim 41 51. An exposure system comprising: an illumination system that irradiates radiant energy; and the stage assembly according to claim 41 , the stage assembly carrying an object disposed on a path of the radiant energy. claim 41 52. A method of processing reaction forces from a stage, comprising: providing a first reaction frame portion of a reaction frame; alligning a ground rod attached to ground and coupled along the longitudinal side of the first reaction frame; providing a second reaction frame portion of the reaction frame not coupled directly to ground in the first direction; and interconnecting the first reaction frame portion and second reaction frame portion together with an interconnect rod having a first end and a second end alligned with the ground rod, wherein the first end is coupled to the first reaction frame portion and the second end is coupled to the second reaction frame portion and reaction forces in the first direction received by the second reaction frame portion are transferred to ground through the combination of the interconnect rod and the first reaction frame portion. 53. The method of claim 52 further comprising: claim 52 providing a first drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the first reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and structurally decoupling the first reaction frame portion from the stage in at least the first direction using a slidable coupling between the fixed drive portion and the movable drive portion associated with the first drive mechanism. 54. The method of claim 52 further comprising: claim 52 providing a second drive mechanism having a fixed drive portion and a movable drive portion, the fixed drive portion coupled to the second reaction frame portion and the movable drive portion coupled to the stage that moves in at least the first direction; and structurally decoupling the first reaction frame portion from the stage in at least the first direction using a slidable coupling between the fixed drive portion and the movable drive portion associated with the second drive mechanism. 55. The method of claim 52 further comprising: claim 52 providing a base; structurally decoupling the stage from the base in at least the first direction using a third slidable coupling supporting the stage on the base; and structurally decoupling the reaction forces between the reaction frame and the base in at least the first direction using a fourth slidable coupling supporting the reaction frame on the base. 56. The method of claim 55 wherein the reaction frame is free to move in X, Y, and Theta Z degrees of freedom with respect to the base. claim 55 57. The method of claim 52 wherein the ground rod is further alligned along the center-of-gravity of the first reaction frame portion. claim 52 |
|
051805472 | summary | BACKGROUND OF THE INVENTION The present invention relates to energy generation systems and, more particularly, to a natural convection boiling water reactor where the reactor can be a fission reactor. More specifically, the present invention applies to boiling water reactors which utilize a chimney for the augmentation of the coolant circulation flow, and which utilize free-surface steam separation for the extraction of the steam phase used to deliver energy from the recirculating water phase. In a boiling water reactor, heat generated by a radioactive core can be used to boil water to produce steam, which in turn can be used to drive a turbine to generate electricity. Natural convection boiling water reactors limit complexity by dispensing with the need for pumping water within the reactor vessel. The nuclear core which generates heat is immersed in water within the reactor vessel. Water circulated up through the core and a chimney above the core is at least partially converted to steam which forms a relatively low pressure head above the core. Water recirculates down a downcomer annulus between the reactor vessel and the chimney and core. The water in the downcomer is denser than the steam and water mixture in the core and chimney region. The difference in density forces circulation up through the core and chimney and down through the downcomer. The chimney directs the water/steam mixture vertically from the core. This vertical direction is best effected where the chimney includes multiple vertical sections, each of which serves as a chimney for the portion of the core directly below it. Confining the steam path in this way helps maintain a head of steam above the core, facilitating water circulation. The steam emerging from the chimney top rises through the water in the reactor vessel and exits through a steam nozzle at the vessel top. Typically, a flat annular array of dryers is disposed near the vessel top to trap any water being carried by the steam, and return trapped water to the recirculation fluid. Otherwise, water carried by the steam would limit the efficiency with which the steam can drive a turbine or other energy conversion device. Since there is a net loss of water+steam from the vessel through the exit port, means are provided to replenish the water in the vessel. This is normally accomplished by returning condensation from the turbine using a fluid handling system, including a feed pump which pumps water through a feedwater sparger which distributes subcooled return water around the downcomer. Two phenomena adversely affect the performance of a natural convection boiling water reactor. "Carryover" refers to water carried in the flow of steam from the vessel, while "carryunder" refers to steam carried in the flow of water recirculating within the vessel and through the core. Carryover can damage the turbine and adversely affects the efficiency with which a turbine can be driven. Carryunder comprises steam bubbles which have a high thermal energy per unit mass so that they can impair the subcooling provided through the feedwater sparger. The result is a higher water temperature at the core entrance, and more rapid boiling of the recirculation fluid as it flows up through the core. The more rapid boiling increases the steam voids within the core. The larger voids result in higher irreversible pressure drops through the fuel bundle than would be the case with smaller voids. This effect is amplified, since the larger voids tend to choke recirculation flow, despite a higher driving head. These irreversible head losses can be compensated in the design stage by providing greater chimney height, but this results in a bigger vessel and significantly greater reactor costs. In addition, the larger voids adversely affect core stability, as the stability-decay ratio is dependent on the proportion of two-phase pressure drop to single-phase pressure drop. This lower stability must be addressed by limiting the power production level below what might otherwise be obtainable. Furthermore, the larger voids create a negative reactivity, requiring the control rods to be withdrawn farther from the core. This reduces the opportunity to achieve long fuel burnups for a given initial core enrichment. Carryover and carryunder both result from the inadequate separation of steam and water, generally above the chimney. Given sufficient time, the different densities of steam and water would allow adequate separation. However, water is swept along with the upward steam flow and steam is swept along with the radially outward and then downward water flow too rapidly for complete separation. The time available for water and steam to separate can be increased either by reducing flow rates or by increasing flow distances. It is counterproductive to reduce flow rates. The steam flow rate directly impacts turbine output, while water flow impacts core void size and thus the efficiency with which neutrons generate heat. As an alternative, the reactor vessel can be made larger to accommodate longer flow paths within the vessel. However, enlarging the vessel not only increases the cost of the vessel, but requires geometrically larger versions of the multiple containment systems provided for a reactor vessel. Larger containment systems require more materials, more maintenance, and greater potential exposure of personnel to nuclear radiation or contaminants. What is needed is a natural convection boiling water reactor system which reduces carryunder and carryover without requiring a larger reactor vessel and without reducing the flow of steam from the vessel or water through the core. In addition, the increased efficiency provided by such a reactor system should be achieved without substantial costs in terms of size, complexity or safety. SUMMARY OF THE INVENTION A reactor system using a height-staggered chimney, preferably in conjunction with an elevation-staggered dryer system, provides for increased steam and water separation. More specifically, more central chimney sections are taller than the more peripheral chimney sections. Preferably, the stagger becomes steeper toward the periphery. The staggered chimney consumes less vessel volume due to the stagger and the volume saved is available to increase the time available for steam to separate from water flow. Likewise, the staggered dryer increases the volume and hence time available for water to separate from the flow of steam exiting the vessel. However, the advantages of staggering extend beyond these aggregate affects. The greater heat generated toward the core center is addressed by a correspondingly greater recirculation flow resulting from the staggered chimney. The recirculating fluid in the vessel flows from above each chimney section outward toward the vessel wall, downward between the vessel wall and the outsides of the chimney and core to a space below the core, and upward through the core and chimney. Since the central chimney sections are further from the vessel wall than the peripheral sections, the steam from the central section has a longer time to escape the recirculation flow than does steam from the peripheral sections. The staggered chimney lengthens the peripheral paths proportionally more than the central paths, thus adding separation time where it is needed most. By making the stagger steeper toward the periphery, this advantage is enhanced. If used with a staggered chimney, a conventional disk-shaped dryer array would leave a relatively short path over the central, tallest, chimney section. Since the central section is typically over the hottest region of the reactor core, the steam flow therethrough is typically the greatest. Hence, the conventional dryer array provides the least separation volume just where the need is the greatest. By staggering the dryer array, the steam paths can be equalized or arranged to favor the center sections to provide a more favorable carryover distribution. Furthermore, a conventional disk-shaped dryer array wastes vessel space between the dryer and the semispherical vessel top. By staggering the dryer array to conform to the vessel top, this space is reclaimed for the purpose of separating water from the steam flow. This reduces demands on the dryer array and decreases the amount of water carried to the turbine. As an additional advantage, a staggered chimney provides a better recirculation distribution through the core. The taller central chimney sections support larger steam heads which correspond to larger pressure differential, and thus faster recirculation rates. This reduces the void fraction in the core center, improving their neutron efficiency. Thus, a given aggregate circulation rate is distributed so as to enhance efficiency. The present invention thus provides that carryover and carryunder are decreased while circulation efficiency is increased. These objectives are accomplished without increasing vessel size, reducing flow rates or increasing system complexity. These and other features and advantages of the present invention are apparent from the description below with reference to the following drawings. |
048428086 | description | DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. In General Referring now to the drawings, and particular to FIG. 1, there is shown an elevational view of a nuclear fuel assembly, represented in vertically foreshortened form and being generally designated by the numeral 10. The fuel assembly 10 is the type used in a pressurized water reactor (PWR) and basically includes a lower end structure or bottom nozzle 12 for supporting the assembly on the lower core plate (not shown) in the core region of the reactor (not shown), and a number of longitudinally extending guide tubes or thimbles 14 which project upwardly from the bottom nozzle 12. The assembly 10 further includes a plurality of transverse grids 16 axially spaced along the guide thimbles 14 and an organized array of elongated nuclear fuel rods 18 transversely spaced and supported by the grids 16. Also, the assembly 10 has an instrumentation tube 20 located in the center thereof and an upper end structure or top nozzle 22 attached to the upper ends of the guide thimbles 14. With such an arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conventionally handled without damaging the assembly parts. Referring to FIG. 2, there is illustrated an axial cross-sectional view of one of the fuel rods 18 in the array thereof in the assembly 10. Each fuel rod 18 includes a plurality of nuclear fuel pellets 24 disposed in a stack in an elongated hollow cladding tube 26 having its opposite ends closed by upper and lower end plugs 28, 30 so as to hermetically seal the rod. Commonly, a plenum spring 32 is disposed within the cladding tube 26 between the upper end plug 28 and the pellets 24 to maintain the pellets in a tight, stacked relationship within the rod 18. The fuel pellets 24 preferably are of different enrichments. Pellets having common enrichments are grouped or arranged in the same zones. For example, the enrichment-zoned fuel rod 18 depicted in FIG. 2 and employed in the fuel assembly 10 of FIG. 1 contains short zones of "blanket" pellets 24A of enrichment "x" at each end of the fuel rod and three zones of pellets 24B-24D of enrichments "w", "y" and "z" between the blanket zones of pellets 24A. Pellet Collation System Turning now to FIG. 3, there is seen a system for collating nuclear fuel pellets, being generally designated 34 and constituting the preferred embodiment of the present invention. The pellet collating system 34 is operable for arranging the pellets 24A-D into rows thereof containing the above-described different enrichment zones. In its basic components, the pellet collating system 34 includes a pellet collating line 36 having pellet input, work and output stations 38-42 disposed in a serial arrangement, and a tray positioning station 44 located adjacent to the pellet collating line 36 and defining positions at which are lodged a plurality of mobile carts 46-56. The carts 46-52 each supports a plurality of pellet supply trays 58, whereas the carts 54, 56 each supports a plurality of pellet storage trays 60. Each of the trays 58, 60 has a plurality of corrugations or grooves (not shown) adapting it to support pellets 24 in multiple parallel rows thereof, for example twenty-five rows about twenty inches longs. All of the pellets 24 located on a given one of the trays has the same enrichment. However, the enrichments of pellets on some trays are different from on other trays so that all of the enrichments are represented for carrying out collating of the pellets in the different desired enrichment zones. The pellet collating system 34 also includes a tray transfer mechanism, preferably a robot 62, located between the pellet collating line and the tray positioning station. The robot 62 is preferably a commercial device marketed under the trademark PUMA by Westinghouse Electric Corporation, the assignee of the present invention. The robot 62 is operable to rotate and to transfer the supply and storage trays 58, 60 one at a time between the respective carts 46-56 at the tray positioning station 44 and the respective input and output stations 38, 42. Referring now to FIG. 4, there is illustrated pellet collating means associated with the stations of the pellet collating line 36. The collating means includes an input sweep head 64, a gripping and measuring head 66 and an output sweep head 68. All of the heads 64-68 are mounted in depending relation from a superstructure (not shown) which disposes the heads above their respective input, work and output stations 38-42. The superstructure has suitable drive mechanism which are computer-controlled and connected to the heads 64-68 for moving them individually. The input and output sweep head 64,68 and the gripping and measuring head 66 are each movable in three orthogonal directions, vertically toward and away from their respective stations 38-42 (and thus between positions adjacent the stations or retracted away therefrom as seen in FIG. 4) and horizontally in orthogonal directions along and across the respective stations. More particularly, the input sweep head 64 illustrated in detail in FIGS. 5 and 6 is substantially identical to the output sweep head 68 so a description of the former will suffice also for the latter. The input sweep head 64 (and also the output sweep head 68 not illustrated in detail) includes a vertical beam 70 having a horizontal plate 72 fixed to the lower end of the beam. The plate 72 has an elongated member 74 composed of a horizontal portion 76 and a vertical portion 78 being of right-angle configuration in cross-section. The horizontal member portion 76 is attached along one edge of the underside 80 of the plate 72 such that the vertical member portion 78 depends therefrom. A series of recesses 82 are cut out of the vertical member portion 78 to define a row of vertically-projecting fingers 84 being spaced apart by the same amount as the centers of adjacent rows of pellets 24 resting on the supply and storage trays 58, 60 are spaced apart. The fingers 78 are also aligned with such centers of the pellet rows such that movements of the input and output sweep heads 64, 68 longitudinally along the respective stations can employed to cause respective sweeping movements of the pellets in the multiple rows thereof simultaneously either from or to one supply tray 58 on the input station 38 to or from the work station 40 and from the work station 40 onto one storage tray 60 on the output station 42. As seen in FIGS. 7 and 8, the gripping and measuring head 66 includes three sensors 86-90 which detect the position of the head 66 at all times and provides information to a computer so that the position of the head 66 can be accurately controlled to carry out measurement of the lengths of pellets in the multiple rows thereof on the work station 40. The gripping and measuring head 66 also has two pairs of scissor-like gripping claws 92, 94 projecting downwardly, permitting the gripping of pellets in two adjacent rows to facilitate separation of the desired measured length of pellets in each of the two rows from the remaining pellets, if less than the total lengths of the two rows are to be measured in forming a zone of pellets of a particular enrichment from the pellets in the rows thereof. Referring again to FIG. 4 and also to FIGS. 9 and 10, the input station 38 of the pellet collating line 36 includes a platform 96 having a tray supporting region 98 defined thereon and clamping means mounted on the platform 96 adjacent the region 98. The clamping means is in the form of a pair of shafts 100 each rotatably mounted to the platform 96 along a longitudinal side of the region 98, and a plurality of hook members 102 attached to each shaft 100. The hook members 102 pivot between unclamping and clamping positions relative to the platform region 98 upon rotation of each shaft 100. An actuator 104 is mounted on the platform 96 adjacent each of shaft 100 and coupled thereto by a crank 106. Each actuator 104, being in the form of an air cylinder, is extendable and retractable for rotating the respective shaft 100 and thereby pivoting the hook members 102 attached thereto between the clamping and unclamping positions. In the unclamping positions of the hook members 102, a supply tray 58 on the input station platform 96 is unclamped relative to the platform region 98 permitting transfer of the tray from and to the region. On the other hand, in the clamping positions of the hook members 102, the supply tray 58 is clamped on the platform region 98. Also as shown in FIG. 4 and in greater detail in FIGS. 11-13, the work station 40 of the pellet collating line 36 includes a platform 108 having separate upper and lower portions 110, 112, with the upper platform portion 110 having a region 114 for supporting the pellets 24 in the multiple rows thereof. The work station 40 also includes elevating means pivotally mounted on the lower portion 112 of the platform 108 and supporting the upper portion 110 thereof above the lower platform portion 112. More particularly, the pellet supporting region 114 on the upper platform portion 110 is composed of a multiplicity of elongated generally parallel bar-like members 116 being spaced apart so as to define a multiplicity of open slots 118 between the members 116 having widths less than diameters of the pellets 24. The bar-like members 116 can be round in cross-section or have chamfered upper longitudinal edges which together with the slots 118 define channels on which to receive and support the pellets in the multiplicity of side-by-side rows thereof. The distance between the centers of adjacent channels is the same as the distance between the centers of the adjacent rows of pellets when resting on the supply tray 58 thereby permitting the pellets to slide from the corrugations of the supply tray directly onto the members 116 of the work station 40. The upper and lower platform portions 110, 112 have telescoping support members 120, 122 respectively attached at each of their four corners by which arrangement the upper platform portion 110 is mounted for vertical movement relative to the lower platform portion 112. The elevating means is provided to lower and raise the upper platform portion 110 of the work station 40 in order to properly position the work station 40 relative to the input and output stations 38, 42 to facilitate slidably moving the pellets from a supply tray 58 on the input station 38 onto the bar-like members 116 of the work station 40, and eventually from the bar-like members 116 of the work station 40 onto a storage tray 60 on the output station 42. Specifically, the elevating means includes a pair of pivotal lift arms 124 extending between the upper and lower platform portions 110, 112 at each opposite end thereof, a pair of shafts 126 each rotatably mounted on the lower platform portion 112 and extending between and attached to one of the pairs of lift arms 124, and an extendable and retractable actuator 128 coupled to one of the shafts 126 by a crank arm (not shown). Only the lift arm 124 at the right end of the work station 40 is shown in FIGS. 4 and 12. Each of the lift arms 124 has a roller 130 rotatably journaled by a stub shaft 132 to its upper end. The roller 130 is captured in a channel 134 attached to the upper platform portion 110 with an upper flange 136 of the channel 134 resting on the roller. In such manner, the upper platform portion 110 at each of its corners is movably supported on one lift arm 124. The lift arms 124 located on the same longitudinal sides of the work station 40 are pivotally interconnected at their lower ends by a connecting rod 137 so as to pivot in unison. Thus, upon extension and retraction of the actuator 128, the shafts 126 are respectively rotated clockwise and counterclockwise causing corresponding pivoting of the lift arms 124 and lowering and raising of the upper platform portion 110 relative to the stationary lower platform portion 112. In the lowered position of the work station 40, the pellet supporting region 114 on the upper platform portion 110 is located at an elevation slightly below that of the one supply tray 58 on the input station 38 for facilitating movement of the pellets 24 from the supply tray 58 onto the work station 40. On the other hand, in the raised position of the work station 40, the pellet supporting region 114 on the upper platform portion 110 is located at an elevation slightly above that of the one storage tray 60 on the output station 42 for facilitating movement of the pellets from the work station 40 onto the storage tray 60. Further, as seen in FIGS. 11-13, the work station 40 includes a pellet alignment mechanism 138 operable to align the leading pellets in the rows thereof with one another in order to provide an accurate zero position for facilitating measuring desired lengths of pellets in the rows by use of the gripping and measuring head 66. The alignment mechanism 138 includes a horizontally-slidable member 140 mounted to the underside of the upper platform portion 110 for horizontal reciprocatory sliding movement, a mast 142 mounted to the forward end of the horizontal slide member 140, a vertically-slidable member 144 mounted to the front side of the mast 142 for vertical reciprocatory sliding movement, a horizontal extendable and retractable actuator 146 connected between the horizontal slide member 140 and the upper platform portion 110 and a vertical extendable and retractable actuator 148 mounted on the mast and connected to the vertical slide member 144. At the upper end of the vertical slide member 144 is mounted a transverse member 150 having a multiplicity of upstanding spaced apart alignment elements or fingers 152 mounted thereon. By coordinated extension and retraction of the actuators 146, 148, the vertical slide member 144 can be moved toward or away from, and the horizontal slide member 140 can be moved along, the bar-like members 116 for respectively projecting the alignment fingers 152 upwardly through the respective slots 118 and above the bar-like members 116 or retracting the alignment fingers 152 downwardly through the slots 118 and below the bar-like members 116, and moving the alignment fingers 152 along the slots 118 toward and away from the pellets 24 supported by the bar-like members 116. With such degree and range of movements, the alignment fingers 152 can be placed in contact with a leading one of the pellets in each of the multiple rows thereof to establish a zero position for measuring of the desired length of the pellets, as will be described later. Referring again to FIG. 4 and also to FIGS. 14 and 15, the output station 42 of the pellet collating line 36 includes a platform 154 having separate upper and lower portions 156, 158 with the upper platform portion 156 having a region 160 for supporting one of the storage trays 60. The output station 42 also includes elevating means pivotally mounted on the lower portion 158 of the platform 154 and supporting the upper portion 156 thereof above the lower platform portion 158. Further, the output station 42 includes a weighing scales 162 disposed below the upper platform portion 156 and having a plurality of upstanding posts 162A upon and from which the storage tray 60 can be placed and removed by operation of the elevating means. More particularly, the upper and lower platform portions 156, 158 have telescoping support members 164, 166 respectively attached at each of their four corners by which arrangement the upper platform portion 156 is mounted for vertical movement relative to the lower platform portion 158. The elevating means is provided to lower and raise the upper platform portion 156 of the output station 42 in order to move the same between a lowered position in which the storage tray 60 is supported off the region 160 of the upper platform portion 156 of the output station 42 by the posts 162A of the weighing scales 162 and a raised position in which the tray 60 is supported off the scales posts 162A by the upper portion 156 of the output station platform 154. The elevating means of the output station 42 is substantially the same at that employed at the work station 40. It includes a pair of pivotal lift arms 168 extending between the upper and lower platform portions 156, 158 at each opposite end thereof, a pair of shafts 170 each rotatably mounted on the lower platform portion 158 and extending between and attached to one of the pairs of lift arms 168, and an extendable and retractable actuator 172 coupled to one of the shafts 170 by a crank arm (not shown). Only the lift arms 168 at on side of the work station 42 are illustrated, that being shown in FIGS. 4 and 14. Each of the lift arms 168 has a roller 174 rotatably journaled by a stub shaft 176 to its upper end. The roller 174 is captured in a channel 178 attached to the upper platform portion 156 with an upper flange 180 of the channel 178 resting on the roller. In such manner, the upper platform portion 156 at each of its corners is movably supported on one lift arm 168. The lift arms 168 located on the same longitudinal sides of the work station 42 are pivotally interconnected at their lower ends by a connecting rod 182 so as to pivot in unison. Thus, upon extension and retraction of the actuator 172, the shafts 170 are respectively rotated clockwise and counterclockwise causing corresponding pivoting of the lift arms 168 and lowering and raising of the upper platform portion 156 relative to the stationary lower platform portion 158. The output station 42, like the input station 38, also includes clamping means mounted on the platform 154 adjacent the region 160. The clamping means is in the form of a pair of shafts 184 each rotatably mounted to the upper platform portion 156 along a longitudinal side of the region 160, and a plurality of hook members 186 attached to each shaft 184. The hook members 186 pivot between unclamping and clamping positions relative to the platform region 160 upon rotation of each shaft 184. An actuator 188 is mounted on the upper platform portion 156 adjacent each of shaft 184 and coupled thereto by a crank arm 190. Each actuator 188, being in the form of an air cylinder, is extendable and retractable for rotating the respective shaft 184 and thereby pivoting the hook members 186 attached thereto between the clamping and unclamping positions. In the unclamping positions of the hook members 186, a storage tray 60 on the output station platform 154 is unclamped relative to the platform region 160 permitting transfer of the tray from and to the region. On the other hand, in the clamping positions of the hook members 186, the supply tray 60 is clamped on the platform region 160. Turning finally to FIGS. 16-26, there are schematically illustrated the operational steps performed on the pellet collating line 36 for collating pellets into enrichment zones of desired lengths. In FIG. 16, the respective input sweep head 64, gripping and measuring head 66 and output sweep head 68 are disposed in retracted positions relative to their respective stations 38-42. A pellet supply tray 58 having twenty-five rows of pellets 24 of a given enrichment thereof has been transferred to the tray supporting region 98 of the input station platform 96 by the transfer robot 62. FIG. 17 shows the upper portion 110 of the work station platform 108 being lowered relative to the input station platform 96 and supply tray 58 thereon. FIG. 18 shows operation of the input sweep head 64 in sweeping of the pellets 24 from the supply tray 58 on the input station platform 96 onto the bar-like members 116 of the work station upper platform portion 110. FIGS. 19 and 20 show operation of the pellet alignment mechanism 138 of FIG. 12 in projecting the alignment fingers 152 upwardly through the slots 118 between the members 116 and moving the fingers 152 toward the input station 38, for example two to three inches, to ensure that the leading pellets 24 in all of the rows are aligned at their front edges. FIGS. 21 and 22 show operation of the gripping and measuring head 66 in measuring (FIG. 21) a desired length of pellets in two adjacent rows using the front edges of the leading pellets as the zero position and then separating (FIG. 22) the measured length of pellets from the remaining pellets. The desired enrichment zone being collated might be the same length as the rows of pellets on the work station 40 or the zone might shorter or longer than the pellet rows. If the zone being collated is not equal to a multiple of the row lengths, then there will eventually be a partial row remaining on the work station after the complete zone has been collated. The measuring and separating is repeated until all rows are completed. As shown in FIG. 23, the work station upper platform portion 110 is raised relative to the input station platform 96 and the partial rows of remaining pellets are returned to the supply tray 58 on the input station 38 by operation of the output sweep head 68, although the input sweep head 64 or the gripping and measuring head 66 could alternatively be used. FIG. 24 shows the reverse operation of the output sweep head 68 in sweeping the measured length of pellets 24 from the work station 40 onto a storage tray 60 which was earlier placed by the robot 62 on the output station platform 154. Weighing of the storage tray 60 takes place both before and after the tray is filled with the measured length of pellets. The robot 62 will return the supply tray of partial pellet rows and the storage tray of pellets of measured length to the station 44 and then transfer new supply and storage trays to the respective input and output station 38, 42. The above-described operational steps are then repeated several times to collate pellets into the different enrichment zones for subsequent filling of a fuel rod. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof. |
039309398 | abstract | A gas-coolant nuclear breeder reactor includes a core enclosed by a pressure vessel having a bottom beneath the core potentially capable of burning through if the core melts due to excessive operating temperatures. A basin is positioned beneath the core, either outside or inside of the pressure vessel, to intercept the melted core. The heat of the melted core must be dissipated rapidly because the reactor is enclosed by a steel containment vessel which might be unable to resist the internal pressure that would otherwise result from the heat. Therefore, means are provided for conducting a fluid coolant cooling the metal core, in the basin, from the latter to an extended area of the inside of the steel containment vessel which, being of relatively high heat conductivity, conducts the heat from the coolant to the atmosphere outside of the containment vessel. Cooling water may be sprayed on the outside of this containment vessel to assist in the dissipation of the heat. Arrangements are provided for increasing the efficiency of the heat transfer from the melted core to the fluid coolant. |
052241459 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Basic Idea Referring now to FIG. 3, a basic idea of an X-ray beam limiting apparatus according to the present invention will now be described. As shown in FIG. 3, two sets of pivotable blades 6 and 7 are newly employed instead of the conventional horizontally movable blades 16 and 17 within a narrow triangle space V.sub.2 defined by two X-ray focal points "R.sub.2 " and "L.sub.2 " separated with each other by a predetermined distance, e.g., 35 mm, and also inner edges of pyramid-shaped X-ray beams XR.sub.10 and XR.sub.20. The pivotable blades 6 and 7 have a function to beam-limit the inner edges XR.sub.10a and XR.sub.20a of the pyramid-shaped X-ray beams "XR.sub.10 " and "XR.sub.20 " in order that a desirable common projection field "S.sub.2 " at the X-ray detecting plane "I.sub.2 " apart from the two focal points "R.sub.2 " and "L.sub.2 " by the distance of "SID", may be established by these pyramid-X-ray beams "XR.sub.10 " and XR.sub.20 ". Also, the movable blades 22 and 23 outside the above-described pivotable blades 6 and 7 have the function to beam-limit the outer edges "XR.sub.10b " and "XR.sub.20b " of these pyramid-shaped X-ray beams "XR.sub.10 " and "XR.sub.20 ". As previously described, when an X-ray tube with a shorter distance between two focal points R.sub.2 and L.sub.2 is employed, for instance, approximately 35 mm, the triangle space V.sub.2 defined by a line "RL.sub.2 " connecting these focal points "R.sub.2 ", "L.sub.2 " and also the inner edges "XR.sub.10a " and "XR.sub.20a " becomes narrower, as compared with that of the normal distance of 63 mm. Since, according to the basic idea of the present invention, the pivotable blades "6" and "7" are newly employed within the triangle space "V.sub.2 "; and are pivotable around either a common center line of first and second pivot shafts 39 and 39' (see FIG. 4), or two positionally-shafted center lines of pivot shafts 39R and 39L (see FIG. 6), the entire pivotable blade construction may be made compact and therefore may be readily arranged within such a narrower triangle space V.sub.2. Apparently, these pivotable blades 6 and 7 may be pivotable under other different pivoting conditions such that the center line of the first pivot shaft 39 intersects with the center line of the second pivot shaft 39'. CONSTRUCTION OF FIRST X-RAY BEAM LIMITING APPARATUS In FIGS. 4 and 5, there are shown a construction of an X-ray beam limiting apparatus 30 according to a first preferred embodiment of the present invention. Roughly speaking, a major feature of this first X-ray beam limiting apparatus 30 is to substitute the above-described first rectangular blades 16 and 17 which are horizontally moved, by the pivotable blades 6 and 7. As previously described, since other components (i.e., the circular limiting blade 18, compensating filter blade 19, second rectangular blades 20, 21 and third rectangular blades 22 and 23) of the conventional X-ray beam limiting apparatus 10 are similarly employed in this first X-ray beam limiting apparatus 30, no further explanation thereof is made in the following description. Accordingly, both the pivotable blades 6, 7 and a pivoting mechanism 50 will now be described more in detail. A stereoscopic X-ray tube 35 to which the first X-ray beam limiting apparatus 30 has been applied, has two sets of X-ray focal points "R.sub.2 " and "L.sub.2 " mutually separated with each other by a distance of approximately 35 mm. The pivotable blades 6 and 7 are arranged in such a manner that these blades 6 and 7 are pivotable within the triangle space "V.sub.2 " defined by the inner edges "XR.sub.10a ", "XR.sub.20a " of the pyramid X-ray beams XR.sub.10, XR.sub.20 irradiated via the X-ray focal point from this steroscopic X-ray tube 35 and the line "RL.sub.2 " connecting the two focal points "R.sub.2 " and "L.sub.2 ". It should be noted that although the pivoting mechanism 50 are symmetrically positioned for the respective pivotable blades 6 and 7, only one pivoting mechanism 50 for one pivotable blade 6 is illustrated in FIGS. 4 and 5, for the sake of simplicity. As clearly shown in FIG. 4, this pivoting mechanism 50 is constructed of a stepping motor "32L" which is fixed on a base "31L" and functions as a driving source to cause the pivotable blade 6 to be pivotable; a lead screw shaft 35La pivotably journaled to the base 31L by an L-shaped member "33L" and also mechanically coupled by a coupling member "34L" to an output shaft "32La" of this stepping motor 32L; a nut "37L" having a pin "36L" and screwed to a lead screw part "35La" of this shaft "35L"; and also a guide plate "38L" which is pivotable with respect to a center line of a first pivot shaft "39" as a pivotable center by inserting the pin 36L of the nut 37L into a slot "38La". The pivotable blade 6 is fixed at a tip portion of the guide plate 38L so that this blade 6 is pivotable around the center line of this first pivot shaft 39 in cooperation with the pivotable operation of this guide plate 38L. As represented in FIG. 5, the pivotable blade 6 has an X-ray shielding part "6La" made of, for instance, lead, and also the above-described first pivot shaft 39 fixed at a tip portion of this X-ray shielding part "6La". A size of this X-ray shielding part "6La" is so selected as to sufficiently cover an extending angle ".THETA." between the two pyramid-shaped X-ray beams "XR.sub.10 " and "XR.sub.20 " irradiated from the focal points R.sub.2 and L.sub.2 of the stereoscopic X-ray tube 35. As previously explained, a center of the first pivot shaft 39 of one pivotable blade 6 is so arranged as to be positionaly coincident with a center of a second pivot shaft 39' (shown in FIG. 5) of the other pivotable blade 7 (i.e., a common center line of the first and second pivot shafts), whereby the entire pivoting mechanism for causing both these blades 6 and 7 pivotably may be made compact. An intermediate part of the first pivot shaft 39 passes through a through hole "38Lb" of the guide plate 38L and fixed therein, whereas a ball bearing 40 for rotatably supporting the first pivot shaft 39 is arranged at a rear end part of the second pivot shaft 39'. One pivotable blade 6 limits one inner edge "XR.sub.10a " of the pyramid-shaped X-ray beam "XR.sub.10 ", whereas the other pivotable blade 7 limits the other inner edge XR.sub.20a of the pyramid-shaped X-ray beam "XR.sub.20 ". The stepping motors 32L and 32R (not shown) drive these pivotable blades 6 and 7 to pivot up to a center portion of each of these pyramid-shaped X-ray beams XR.sub.10 and XR.sub.20, as shown in FIG. 4, in such a manner that the angle extending between these pyramid-shaped X-ray beams XR.sub.10 and XR.sub.20 emitted from the stereoscopic X-ray tube 35 via the X-ray focal points R.sub.2 and L.sub.2 corresponds to the common X-ray projection field at the X-ray detecting plane I.sub.2. In other words, upon rotation of the stepping motor 32L, the nut 37L is transported via the lead screw part 35La up to a position 37' indicated by a two-dot/dash line, the guide plate 38L pivots around the first pivot shaft 39 as a center up to a position 38' also indicated by a two-dot/dash line, and thus one blade 6 many pivot up to a position 6' indicated by a two-dot/dash line. Similarly, the other pivotable blade 7 many pivot up to another position 7' represented by a two-dot/dash line by means of the stepping motor 32R (not shown), whereby this pivotable blade 7 may continuously pivot up to the symmetric position with respect to the pivoting position of the remaining pivotable blade 6. In accordance with the first X-ray beam limiting apparatus 30 with the above-described common pivotable center line for both the pivotable blades 6 and 7; these pivotable blades 6 and 7 may be arranged within the triangle space V.sub.2 defined by the inner edges XR.sub.10a and XR.sub.20a of the respective pyramid-shaped X-ray beams XR.sub.10 and XR.sub.20, and also the line RL.sub.2 for connecting the focal points R.sub.2 and L.sub.2, and may perform the X-ray beam limiting function, even if the stereoscopic X-ray tube 35 with the narrower distance between the X-ray focal points R.sub.2 and L.sub.2. As a consequence, it may provide such an X-ray beam limiting apparatus 30 capable of the enlarged type stereoscopic radiography or fluoroscopy without restricting the dimensions of SID and common projection field. CONSTRUCTION OF SECOND X-RAY BEAM LIMITING APPARATUS FIg. 6 schematically represents a construction of an X-ray beam limiting apparatus 80 according to a second preferred embodiment of the present invention. A major feature of the second X-ray beam limiting apparatus 80 is such that one pivot shaft 39L for one pivotable blade 6 is positionally shifted from the other pivot shaft 39R for the other pivot blade 7, namely a center line of the first pivot shaft 39L is not positionally coincident with another center line of the second pivot shaft 39R. As a result, an X-ray shielding part "6La" of the first pivot shaft 39L is positionally shifted with respect to the other X-ray shielding part "6Ra" of the second pivot shaft 39R, as illustrated in FIG. 6. MODIFICATIONS As apparent from the foregoing descriptions, the present invention is not limited to the above-described first and second preferred embodiments, but may be readily modified without departing from the technical scope and spirit of the present invention. For instance, as illustrated in FIG. 7, another X-ray beam limiting apparatus 90 may be realized by employing the combination of the pivotable blades 6 and 7 with the common pivot center, and furthermore only the circular fixing blade 18, the rectangular blades 22, 23 and the rectangular blades 20, 21, which are positioned in this order along the X-ray beam travelling path. As obvious from FIG. 7, a feature of this X-ray beam limiting apparatus 90 is that the compensating filter blade 19 has been omitted and the positional relationship between the rectangular blades 20;21 and 22;23 is different from that of the first and second X-ray beam limiting apparatuses 30 and 80. Moreover, although not shown in the drawings, many other X-ray beam limiting apparatuses with other blade combinations may be realized, for instance, the combination of the circular fixing blade 18, compensating filter blade 19 and rectangular blades 22, 23 with the pivotable blades 6 and 7 shown in FIG. 6. |
claims | 1. An apparatus for a nuclear fuel assembly, comprising:a top nozzle; andguide pins for aligning the top nozzle with an upper core plate of a nuclear reactor;wherein each of the guide pins has a guide hole axially formed therein,the guide holeextending from an upper end of a guide pin to an end of the guide pin located within a body of the top nozzle, andaligning with an aligning hole that extends through the body of the top nozzle and opens at a bottom surface of the top nozzle,the aligning hole, when the top nozzle is aligned with the upper core plate, being offset from a control rod assembly of the apparatus. 2. The apparatus of claim 1, wherein the aligning hole is formed at a corner of the top nozzle. 3. The apparatus of claim 1, further comprising a core instrument in the guide hole, and extending from the upper end of the guide pin through the end of the guide pin located within the body of the top nozzle into the aligning hole in the body of the top nozzle. |
|
summary | ||
059600497 | claims | 1. In a pressurized water nuclear power plant having a nuclear reactor, at least one steam generator, a plurality of feedwater pumps for supplying water to the steam generators, a first system, for controlling the power output of the reactor core by insertion of control rods into the core at a normal rate, and a second system, including means for rapidly inserting some of the control rods into the reactor core at a faster rate than said normal rate to reduce the power output from an initial level to a non-zero level upon the substantially total loss of pumping operation of a feedwater pump, the improvement for a plant having three feedwater pumps for said steam generators, comprising: switch means for manually selecting which of the three pumps are intended for pumping operation and designating which, if any, of the three pumps have been intentionally disabled from pumping operation; means for generating a pump trip signal, respectively, from each of the pumps intended for operation, when a particular pump intended for operation experiences a substantially total loss of pumping operation; means in said second system responsive to the switch means and the means for generating a pump trip signal, for generating a demand signal to rapidly insert some of the control rods, only when two pumps have been selected, and a pump trip signal is generated from only one of the selected pumps, or when three pumps have been selected, and a pump trip signal is generated from each of any two, but not all, of the selected pumps. a flip-flop circuit associated with the switch means for each pump, respectively, for generating a first signal on a first line if the pump has been selected or a second signal on a second line if the pump has been designated, an enabling AND gate electrically connected to the first line of each of the flip-flop means, respectively, and to the means for generating a pump trip signal, respectively, such that each enabling AND gate passes a logical "1" output, only upon the coincidence of a first signal and a pump trip signal, and an OR gate electrically connected to the output of each said enabling AND gates and to each said second lines, respectively. setting switch means for selecting which of the three pumps are intended for pumping operation and designating which of the three pumps, if any, are disabled from pumping operation; generating a pump trip signal from each of the pumps intended for operation, which experiences a substantially total loss of pumping operation; in response to the switch means settings and a pump trip signal, generating a demand signal for the second system to rapidly insert some of the control rods, only under the following conditions, (a) with one pump selected for operation and tripped, no demand signal is generated, (b) with two pumps selected for operation, only a trip of one selected pump generates a demand signal, and (c) with three pumps selected for operation, only a trip of two selected pumps generates a demand signal. the step of generating a demand signal is performed in a logic circuit having a pump status latch associated with each pump, respectively, each latch having a condition representative of whether or not each pump is intended to be operational, respectively, and the step of setting switch means, generates an enabling condition in a respective latch whereby a trip signal from a respective pump can pass through the logic circuit. 2. The nuclear power plant of claim 1, wherein the means responsive to the switch means and the means for generating a pump trip signal includes, 3. The nuclear power plant of claim 2, wherein the means responsive to the switch means and the means for generating a pump trip signal includes, a logical AND gate for each possible combination of two of said feedwater pumps, each logical AND gate being responsive to the output of one of said OR gates connected to the second line associated with one pump, and the output of another of said OR gates connected to the second line associated with another of said pumps. 4. In a pressurized water nuclear power plant having a nuclear reactor, at least two steam generators, three feedwater pumps for supplying water to the steam generators, a first system, for controlling the power output of the reactor core by insertion of control rods into the core at a normal rate, and a second system, including means for rapidly inserting some of the control rods into the reactor core at a rate faster than said normal rate to reduce the power output from an initial level to a non-zero level upon the substantially total loss of pumping operation of at least one feedwater pump, a method for generating a demand signal for said second system to rapidly insert some of the control rods, comprising: 5. The method of claim 4, wherein |
063242591 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scattered-ray grid, particularly for a medical X-ray device, of the type having a carrier with absorption elements, particularly in the form of lead elements, which are arranged in spaced rows, as well as to a method for determining the position of the absorption elements in a scattered-ray grid. 2. Description of the Prior Art In radiographic technology, particularly medical diagnostics, scattered-ray grids are frequently utilized to attenuate the scattered radiation which is always present with the primary radiation. The grids that are currently used most are composed of a sequence of line-like radiation absorption elements in the form of lead lamellae, which, alternately, are coated with lamellae made of a base material. X-rays that are incident in the plane of the lamellae are only insignificantly attenuated by the base material. By contrast, the lead lamellae highly absorb radiation that is obliquely incident. Since such lead lamellae generate unavoidable lines on the radiograph and since the number of lines per centimeter is limited due to manufacturing reasons, it has been suggested to use pins made of lead or another absorption material arranged in rows, the pins being spaced apart, instead of using lead lamellae in a silicon base material. Such scattered-ray grids are known from the German OS 197 26 846 and OS 197 29 596, for example. German OS 197 26 846 describes a configuration concerning the arrangement of the pins (and thus of the rows), wherein the rows extend to the center of the grid in a spoke-like manner. In this arrangement, many rows start at the same radius. The density of the absorption elements (seen in the radial direction) considerably varies as a result and grey tone discontinuities also occur, and the row spaces (seen in the tangential direction) significantly vary as well. This has a disadvantageous effect on the entire absorption behavior of the grid and therefore on the image quality. SUMMARY OF THE INVENTION An object of the present invention is to provide a scattered-ray grid, which is improved compared to known scattered-ray grids with respect to the arrangement of the absorption element rows. This object is achieved in accordance with the invention in a scattered-ray grid of the type described above wherein, inventively, the rows extend essentially radially from a center region and wherein, apart from one or more rows starting in the center point, the individual, identically structured rows of the scattered-ray grid or of the grid sectors of the scattered-ray grid proceed from starting points at respectively different radii, and wherein the origin (starting point) of each row is situated in an angle section, the angle section being determined by two points lying on a circle (or arc thereof) with a predetermined radius and which is divided in a predefined ratio for determining the position of the origin. The predetermined radius is incremented in a stepped manner to define the respective origins for all of the rows. In the inventive scattered-ray grid, the origins of the lines, which all extend in the direction of the grid center, therefore produce an asterisk-shaped configuration, the lines respectively starting at different radii with respect to the grid center, so that a scattered-ray grid results which is significantly more homogenous and radial. In one embodiment, only one row in the entire grid can have its origin at any given radius. Alternatively, the grid configuration can be sector dependent i.e. the entire grid surface is composed of a number of angle sectors, for example, four sectors each of 90.degree., with the row configuration being essentially identical in every sector, i.e. it annularly periodically repeats. In this case, a number of rows would therefore have their origins at every selected radius, but only a single row has its origin at a given radius in every sector. The position of the origin is determined on the basis of an angle section, which is determined on the basis of specific points situated at a predetermined radius. This angle section is divided in a predefined ratio p:q, is preferably with p.noteq.q. As described, an inventive scattered-ray grid can be configured by determining the row arrangement such that only one row has its origin at a circle with a fixed radius. In this case, a first row that starts at the grid center is taken as a starting basis, which represents the iteration basis. Then, the first angle section, which is to be divided in the ratio p:q, is determined on the basis of this row. In this case, the two points are defined by the first row itself, the angle section is full 360.degree. in this case. Now, this angle section is divided according to the predefined ratio for determining the position of the origin of the second row, so that the angle position of the origin of the second row is fixed at the relevant radius. Then, the position of the third row and of every further row is determined on the basis of the largest angle section, which exists between two rows that intersect the relevant circle or circle arc. The new origin is always placed in the largest angle section. Alternatively, for a sector-by-sector row configuration, at least two rows that start in the center are used as a starting basis, by means of which rows the grid is divided into the sectors, and the origin of every further row is placed between two rows that start closer to the center, these rows defining the aforementioned points on the predetermined circle and therefore the angle section and exhibit the largest possible angular spacing of all row pairs. Therefore, the origin of a new row always lies between two rows which originate closer to the center than the origin of the new row, these two rows being the rows which are spaced furthest from one another. Spiral-shaped density variations, even though slight may arise given the determination criterion of the angle section which is to be divided on the basis of the intervening angular space of the respective row pairs. This can be avoided in an embodiment of the invention wherein the row origins are determined starting with two rows that originate at the grid center, and the origin of the next row is placed between the row pair which has a maximum sum of the angular spacing between the rows and an additional angle value, this sum being allocated to the angle section. In this embodiment, the angle section to be divided in the ratio p:q is therefore not only determined on the basis of the actual angular spacing between the row pair, but is determined on the basis of the sum of the actual angular spacing between the row pair and an additional angle value. This additional angle value is determined by weighting, with a defined weighting factor, the respective angular spacings, on opposite sides of the adjacent row pair, between the adjacent row pair and the closest row thereto. For example, the sum of these two angular spacings (one from each side of the adjacent row pair) can be multiplied with the predefined factor, which can be <1 according to the invention, and this value can then be added with the angular spacing between the two adjacent rows. Then, the angle section, at which the largest of said sums is allocated, is divided corresponding to the predefined ratio. An even more homogenous distribution of rows results. Apart from the scattered-ray grid itself, the invention also relates to a method for determining the position of the absorption elements of a scattered-ray grid, which are arranged in rows and which extend essentially radially relative to a center. Apart from one or more rows that start at the grid center, the origin of each row of the scattered-ray grid, or of a grid sector of the scattered-ray grid, is placed in an angle section, which is determined on the basis of two points lying on the circle or arc of circle with the origin radius r.sub.0 +n.DELTA.r and which is divided for purposes of determining the position of the origin in a predefined ratio. Beginning with a single row that originates in the grid center as a basis, the angle section can be determined in an iterative fashion, the angle section being 360.degree. in this initial case and being defined as the start point as well as the end point by the first row. After this angle section has been divided, the origin of the second row is placed at the angle point deriving therefrom. For determining the origin of the third row, the row pair between which the largest angle section lies no matter how it is determined--is searched between the rows that are already present and is correspondingly divided. The iterative method is continued until a maximal radius is reached. In an alternative embodiment of the inventive method at least two rows that both originate at the grid center are used as a starting basis. The angle space between two adjacent rows, which rows intersect the circle or arc of circle with the predetermined radius and which define the points, is determined for determining the angle section, the angle section among all row pairs being selected that exhibits the largest angular spacing. Therefore, the angle section is immediately determined from the angular spacing in this alternative. For improving the homogeneity of the row density, the angle section is selected in each iteration that has the highest sum of the angular spacing between two adjacent rows, which intersect the origin radius and which define the points, and an additional angle value. This additional angle value is obtained by weighting the respective angular spacings to the rows on opposite sides of the aforementioned adjacent rows. The predefined factor can be <1 the ratio p:q, in which the respective angle section is divided, is preferably .noteq.1. Although the row configuration and the position of the rows can be iteratively determined (as described) for the entire scattered-ray grid by taking one single row that starts in the center as a basis, it has proven to be expedient to determine the position of the one row is only in one grid sector of the scattered-ray grid, which is composed of a number of grid sectors of equal size, and to "image" this row in the other grid sectors. The grid sectors are defined by means of the rows extending through the grid center. |
abstract | Various example embodiments are directed towards an improved control drum, as well as systems, apparatuses, and/or methods for operating a nuclear reactor with a plurality of improved control drums. The control drum includes an outer shell, an inner shell, a plurality of tubes, the plurality of tubes including at least one neutron absorbing tube and at least one neutron scattering tube, and at least one baffle plate arranged between the outer shell and the inner shell, the at least one baffle plate including a plurality of perforations, and at least one perforation of the plurality of perforations configured to support a tube of the plurality of tubes. |
|
claims | 1. A method of forming a solar absorptive coating on a surface, the method comprising:i. applying a ceramic material to the surface to form a coated surface, wherein the ceramic material comprises chromium oxide or a lanthanum-based perovskite; andii. treating the coated surface with a pulsed laser source, wherein the pulsed laser source is selected from the group consisting of a nanosecond laser and femtosecond laser, thereby forming the solar absorptive coating on the surface. 2. The method of claim 1, further comprising, before step ii, curing the ceramic material on the coated surface. 3. The method of claim 1, further comprising, after step ii, re-treating the solar absorptive coating with a pulsed laser source. 4. The method of claim 1, wherein the solar absorptive coating has a solar absorptance of greater than about 0.94 and/or is a high-temperature solar selective coating. 5. The method of claim 1, wherein the solar absorptive coating comprises a plurality of microstructures and a plurality of nanostructures. 6. The method of claim 5, wherein the microstructure comprises a trench having a width of from about 5 μm to about 30 μm and/or a spacing between trenches of from about 20 μm to about 70 μm. 7. The method of claim 1, wherein the pulsed laser source has a pulse width from about 100 fs to about 1000 ns. 8. The method of claim 7, wherein the pulse width is from about 1 ns to about 500 ns. 9. The method of claim 1, wherein the pulsed laser source has a wavelength from about 750 nm to about 1200 nm. 10. The method of claim 1, wherein the pulsed laser source has a pulse energy of more than about 1 mJ. 11. The method of claim 1, wherein the pulsed laser source has an average power of more than about 20 watts. 12. The method of claim 1, wherein the pulsed laser source has a repetition rate of between about 1 kHz to about 500 kHz. 13. The method of claim 1, wherein the pulsed energy source is a nanosecond laser. 14. The method of claim 13, wherein the nanosecond laser has a pulse duration of between about 1 ns to about 400 ns, a wavelength of about 1064 nm, an average power of more than about 20 watts, and/or a repetition rate of about 15 kHz to about 300 kHz. 15. The method of claim 1, wherein the pulsed energy source is a femtosecond laser. 16. The method of claim 15, wherein the femtosecond laser has a pulse energy of more than about 1 mJ, a repetition rate of between about 1 kHz to about 100 kHz, and/or a wavelength of about 800 nm. 17. The method of claim 1, wherein the surface is a substrate for absorption of solar energy selected from the group consisting of a concentrating solar power receiver, a solar tower, a trough, a Stirling engine, a heat absorber, and a solar collector, or a portion thereof. 18. A solar absorptive coating formed by the method of claim 1. |
|
049884735 | description | DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like are words of convenience and are not to be construed as limiting terms. Referring now to the drawings, and particularly to FIG. 1, there is shown an elevational view of a prior art fuel assembly, represented in vertically foreshortened form and being generally designated by the numeral 10. The fuel assembly 10 is the type used in a pressurized water reactor (PWR) and basically includes a lower end structure or bottom nozzle 12 for supporting the assembly on the lower core plate (not shown) in the core region of a reactor (not shown), and a number of longitudinally extending guide tubes or thimbles 14 which project upwardly from the bottom nozzle 12. The assembly 10 further includes a plurality of transverse grids 16 axially spaced along the guide thimbles 14 and an organized array of elongated fuel rods 18 transversely spaced and supported by the grids 16. Also, the assembly 10 has an instrumentation tube 20 located in the center thereof and an upper end structure or top nozzle 22 attached to the upper ends of the guide thimbles 14. With such an arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conventionally handled without damaging the assembly parts. As mentioned above, the fuel rods 18 in the array thereof in the fuel assembly 10 are held in spaced relationship with one another by the grids 16 spaced along the fuel assembly length. Each fuel rod 18 includes nuclear fuel pellets 24 and the opposite ends of the rod are closed by upper and lower end plugs 26,28 to hermetically seal the rod. Commonly, a plenum spring 30 is disposed between the upper end plug 26 and the pellets 24 to maintain the pellets in a tight, stacked relationship within the rod 18. The fuel pellets 24 composed of fissile material are responsible for creating the reactive power of the PWR. A liquid moderator/coolant such as water, or water containing boron, is pumped upwardly through the fuel assemblies of the core in order to extract some of the heat generated therein for the production of useful work. Self-Latching Reactivity-Reducing Poison Device Turning now to FIGS. 3-5, there is illustrated a self-latching reactivity-reducing device, generally designated by the numeral 32 and constructed in accordance with the present invention. The reactivity-reducing device 32 is adapted for insertion into one of the guide thimbles 14 of the fuel assembly 10, shown diagrammatically in FIG. 2, to provide the device 32 in the installed relationship with the guide thimble 14, as shown in FIG. 6. In its basic components, the reactivity-reducing device 32 includes an elongated rod 34 having leading and trailing ends 34A, 34B and a central passage 34C extending between and open at the ends, and a self-latching mechanism 36 mounted at the leading end 34A of the rod 34. Upon full insertion of the rod 34 in the guide thimble 14, the self-latching mechanism 36 automatically latches with the lower end portion 14A of the guide thimble 14 and is thereby rendered unlatchable from the guide thimble 14 without the use of an independent elongated shaft-like tool 38 (FIG. 9) inserted solely through the central passage 34C of the rod 34 from the trailing end 34B thereof. Also, the device 32 includes a closure plug 40 mounted at the trailing end 34B of the rod for closing off access to the passage 34C and thereby to the self-latching mechanism 36 by the tool 38, rendering the rod 34 non-removably installed in the guide thimble 14. More particularly, the elongated rod 34 of the reactivity-reducing device 32 includes a generally cylindrical tubular portion 42 and an upper head portion 44 attached to the tubular portion 42 at the trailing end 34B of the rod. The tubular portion 42 has an interior annular chamber 46 defined therein which contains a burnable poison or neutron absorbing material in the form of a stack of annular pellets 48. The outside diameter of the tubular portion 42 is smaller than the inside diameter of the guide thimble 14 allowing insertion of the rod tubular portion therein. Preferably, when the tubular portion 42 of the rod 34 is fully inserted in the guide thimble 14, the rod trailing end 34B is disposed adjacent to the top nozzle 22 and the guide thimble upper end portion 14B and the rod leading end 34A is disposed adjacent to the bottom nozzle 12 and the guide thimble lower end portion 14A. The upper head portion 44 of the rod 34 is a circular plate having an outside diameter larger than the inside diameter of the guide thimble 14 such that head portion 44, as seen in FIGS. 6 and 9, seats on an annular edge portion of the top nozzle 22 surrounding an opening 50 defined through the top nozzle and in which the upper end portion 14B of the guide thimble 14 is inserted. The head portion 44 of the rod 34 thus serves to suspend or support its tubular portion 42 in the guide thimble 14. The passage 34C extends centrally through the tubular portion 42 and upper head portion 44. The upper end of the passage 34C at the head portion 44 has internal threads 52 which mate with the external threads 54 on the closure plug 40 of the device 32. As seen in one exemplary embodiment of FIGS. 3-5, the self-latching mechanism 36 includes a pair of triangular-shaped latch members 56 and a pair of actuating levers 58 respectively attached to and extending inwardly of the latch members 56. The latch members 56 are disposed through a pair of opposing side slots 60 defined in the leading end 34A of the tubular portion 42 of the rod 34 such that the levers 58 extend from the latch members 56 into an enlarged diameter recess 62 in the rod leading end 34A which communicates with the central passage 34C and the slots 60. It should be understood that more than a pair of latch members 56, actuating levers 58 and slots 60 can be employed. As best seen in FIG. 5, the latch members 56 are pivotally mounted by pivot pins 64 which are mounted to the tubular portion 42 and extend across the respective slots 60, as best seen in FIG. 5. The latch members 56 are pivotally movable between displaced latching and releasing positions, as seen respectively in FIGS. 6 and 8. Biasing means in the form of twisted wire-like springs 66 encircle the pivot pins 64 and at their opposite ends engage edges on the latch members 56 and the ledges 68 in the slots 60 of the tubular portion 42 for biasing the latch members 56 toward their latching positions, as seen in FIGS. 3 and 6, and in abutment with the ledges 68. In such position, the tips 56A of the latch members 56 extend radially outward beyond the lower end portion 14A of the guide thimble 14 so as to prevent withdraw of the latch members 56 upwardly through the guide thimble 14. In order to withdraw the device 32, the actuating levers 58 must be moved in a downward direction to pivot the latch members 56 upwardly and inwardly against their biases to the releasing position of FIG. 8. Such movement of the levers 58 is accomplished by insertion of the elongated tool 38 down through the passage 34C to bring its leading end 38A into engagement with the levers 58. To insert the tool 38, the closure plug 40 must first be unthreaded and removed. Thus, several steps must be taken in order to unlatch the self-latching mechanism. For that reason, without the assistance of the tool 38, the device 32 can be characterized as non-removable from the guide thimble 14. As shown in FIG. 9, the upper head portion 44 of the rod 34 has an undercut or beveled lower peripheral edge 70 for cooperating with gripping arms 72 on an independent remover 74 for gripping the head portion 44 to permit withdrawal of the device 32 from the guide thimble 14 once the self-latching mechanism 36 has been unlatched from the guide thimble by the elongated tool 38. An annular ring (not shown) can be placed over the arms 72 to prevent them from spreading radially outward and releasing their hold on the upper head portion 44 of the device 32. To recapitulate, it is believed that the Nuclear Regulatory Commission (NRC) would consider the reactivity-reducing device 32 having such construction to be non-removable because several things must be done, involving separate independent tools, to remove it. Once installed and latched, the device 32 cannot fall out. The construction of the device 32 is rugged enough that even if the fuel assembly is damaged the device will remain in place. The reactivity-reducing device 32 will reduce fuel assembly reactivity enough so that fuel with enrichments greater by as much as 3.0 w/o than the current limit could be stored. Or they could be used to decrease the minimum burnup required for burnup credit by as much as 30,000 MWD/MTU. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof. |
summary | ||
claims | 1. An installation method of equipment, comprising:forming a pit container unit including a first frame, reinforcing steel members, a pit container, and an anchor member supporting mechanism, the forming including:disposing the first frame at a location different from an installation location of the equipment,disposing the reinforcing steel members proximate to the first frame to reinforce the first frame,placing the pit container on the first frame inside the reinforcing steel members, andattaching an anchor member supporting mechanism to the pit container, the anchor member supporting mechanism including a supporting member and a ring state reinforcing member, the supporting member supporting a ring state anchor member positioned at an outer peripheral side of the pit container, the supporting member being made up of a plurality of plate state members respectively protruding in a radial pattern from an outer peripheral portion of the pit container, the ring state reinforcing member having a center hole wherein a part of each reinforcing steel member is passed through a gap formed between the center hole and an outer peripheral portion of the pit container, the ring state reinforcing member integrally supporting the plurality of plate state members from a bottom side;placing a second frame on a base to be the installation location of the equipment;placing the pit container unit on the second frame via the first frame;embedding a portion of the pit container unit and the second frame not including the anchor member supporting mechanism, in concrete by using a primary concrete pour;disposing an anchor bolt unit including a plurality of foundation bolts for equipment installation fixed to the ring state anchor member, on the anchor member supporting mechanism after embedding the portion of the pit container unit by the primary concrete pour;correcting a positional relationship of the plurality of foundation bolts relative to the pit container by using a template member having a plurality of positioning holes into which the plurality of foundation bolts on the anchor bolt unit are individually inserted;embedding the pit container unit and the anchor bolt unit in concrete using a secondary concrete pour,wherein the secondary concrete pour does not embed the template member in concrete, andwherein the positional relationship of an opening portion of the pit container and the plurality of foundation bolts is maintained by the template member after the secondary concrete pour;removing the template member;moving the equipment into the pit container after removal of the template member; andfixing the equipment via the plurality of foundation bolts. 2. The installation method of equipment according to claim 1, wherein bottom sides of foundation bolt main bodies of the anchor bolt unit are respectively welded at predetermined positions on the ring state anchor member respectively corresponding to positions of plural installation holes bored at a casing of the equipment in advance and positions of the plural positioning holes on the template member. 3. The installation method of equipment according to claim 1, wherein correcting the positional relationship of the pit container and the plurality of foundation bolts includes:spot welding the supporting member to the ring state anchor member after the position of the foundation bolts has been corrected to fall within a tolerance range by inserting the foundation bolts into the positioning holes of the template member. 4. The installation method of equipment according to claim 1, wherein the equipment is a vertical pump. 5. The installation method of equipment according to claim 3, wherein correcting the positional relationship of the pit container and the plurality of foundation bolts includes:removing the template member and disposing additional reinforcing steel members to reinforce an upper side of the pit container unit after the supporting member and the ring state anchor member are spot welded. 6. An installation method of equipment, comprising:forming a pit container unit including a first frame, reinforcing steel members, a pit container, and an anchor member supporting mechanism, the forming includingdisposing the first frame at a location different from an installation location of the equipment,disposing the reinforcing steel members proximate to the first frame to reinforce the first frame,placing the pit container on the first frame inside the reinforcing steel members, andattaching an anchor member supporting mechanism to the pit container, the anchor member supporting mechanism including a supporting member to support a ring state anchor member positioned at an outer peripheral side of the pit container, and a ring state reinforcing member having a center hole wherein a part of each reinforcing steel member is passed through a gap formed between the center hole and an outer peripheral portion of the pit container;placing a second frame on a base to be the installation location of the equipment;placing the pit container unit on the second frame via the first frame;embedding a portion of the pit container unit and the second frame not including the anchor member supporting mechanism, in concrete by using a primary concrete pour;disposing an anchor bolt unit including a plurality of foundation bolts for equipment installation fixed to the ring state anchor member, on the anchor member supporting mechanism after embedding the portion of the pit container unit by the primary concrete pour;correcting a positional relationship of the plurality of foundation bolts relative to the pit container by using a template member having a plurality of positioning holes into which the plurality of foundation bolts on the anchor bolt unit are individually inserted;embedding the pit container unit and the anchor bolt unit in concrete using a secondary concrete pour,wherein the secondary concrete pour does not embed the template member in concrete, andwherein the positional relationship of an opening portion of the pit container and the plurality of foundation bolts is maintained by the template member after the secondary concrete pour;removing the template member;moving the equipment into the pit container after removal of the template member; andfixing the equipment via the plurality of foundation bolts,wherein bottom sides of foundation bolt main bodies of the anchor bolt unit are respectively welded at predetermined positions on the ring state anchor member respectively corresponding to positions of a plurality of installation holes bored at a casing of the equipment in advance and positions of the plurality of positioning holes on the template member. 7. The installation method of equipment according to claim 6, wherein correcting the positional relationship of the pit container and the plurality of foundation bolts includes:spot welding the supporting member to the ring state anchor member after the position of the foundation bolts has been corrected to fall within a tolerance range by inserting the foundation bolts into the positioning holes of the template member. 8. The installation method of equipment according to claim 6, wherein the equipment is a vertical pump. 9. The installation method of equipment according to claim 7, wherein correcting the positional relationship of the pit container and the plurality of foundation bolts includes:removing the template member and disposing additional reinforcing steel members to reinforce an upper side of the pit container unit after the supporting member and the ring state anchor member are spot welded. |
|
abstract | A screen panel for converting X-rays into light photons includes a rigid foam plate (2), a first layer (1) of composite material located on one face of the rigid foam plate (2) and a second layer (3) of composite material located on the other face of the rigid foam plate, parallel to the first face. The screen panel applies, for example, to medical radiology and to non-destructive testing of nuclear waste storage packages. |
|
059636106 | claims | 1. A data acquisition system for recording data associated with movement of at least one control element assembly through the nuclear reactor core of a nuclear steam supply system of the type having a plurality of control element drive mechanisms engaging a respective plurality of control element assembly shafts, each drive mechanism including a plurality of electrical coils which are powered by an electrical circuit to deliver coil-current whereby operation of the electrical circuit generates high frequency noise, said data acquisition system comprising: measuring means for producing a respective analog coil-current signal commensurate with the coil current flow through at least some of the coils of a drive mechanism; first signal conditioning means for receiving said analog coil-current signals and conditioning said signals to remove therefrom the high frequency noise generated by the electrical circuit; first digitizing means for receiving and digitizing said conditioned analog coil-current signals to produce digital coil-current signals; storage means for storing said digital coil-current signals on digital storage media; and means for displaying said digital coil-current signals received by said storage means, said means for displaying including means for automatically changing the display image when at least one of said digitized coil-current signals deviates from a predetermined value by a predetermined amount. said system further comprises: said storage means further comprises means for storing said digital position signals; and said means for displaying further comprises means for automatically changing the display image to display only one of said digital coil-current signals and one of said digital position signals when said one of said digitized coil-current signals deviates from a predetermined value by a predetermined amount. said system further comprises: said storage means further comprises means for storing said digital position signals; and said means for displaying further comprises means for automatically changing the display image to display a predetermined acceptance trace, only one of said digitized coil-current signals, and one of said digitized position signals, when said one of said digitized coil-current signals deviates from a predetermined value by a predetermined amount. said system further comprises: said storage means further comprises means for storing said digital position signals; said first signal conditioning means comprises: said second signal conditioning means further comprises means for reducing the magnitude of said conditioned analog position signals for compatibility between said analog position signals and said second digitizing means. measuring means for producing a respective analog coil-current signal commensurate with the coil current flow through at least some of the coils of a drive mechanism; means for detecting the position in the reactor core of at least one of control element assemblies to produce an analog position signal; digitizing means for receiving and digitizing said analog coil-current signals to produce digital coil-current signals and for receiving and digitizing said analog position signals to produce digital position signals; storage means for storing said digital coil-current and position signals on digital storage media; and displaying means for simultaneously displaying each of five different digital coil-current signals for one control element drive mechanism and said digital position signal for the control element assembly controlled by the control element drive mechanism associated with said digital coil-current signals also being displayed, said displaying means further comprising means for automatically changing the display image to display a predetermined acceptance trace, only one of said digitized coil-current signals, and one of said digitized position signals, when said one of said digitized coil-current signals deviates from a predetermined value by a predetermined amount. said system further comprises: said storage means further comprises means for storing said digital position signals; said first signal conditioning means comprises: said second signal conditioning means further comprises means for reducing the magnitude of said conditioned analog position signals for compatibility between said analog position signals and said second digitizing means. measuring means for producing a respective analog coil-current signal commensurate with the coil current flow through at least some of the coils of a drive mechanism; first digitizing means for receiving and digitizing said analog coil-current signals to produce digital coil-current signals; storage means for storing said digital coil-current signals on digital storage media; means for displaying said digital coil-current signals received by said storage means while said system stores said digital coil-current signals; and means for automatically changing the display image when at least one of said digitized coil-current signals deviates from a predetermined value by a predetermined amount. said system further comprises: said storage means further comprises means for storing said digital position signals; and said means for displaying further comprises means for automatically changing the display image to display only one of said digital coil-current signals and one of said digital position signals when said one of said digitized coil-current signals deviates from a predetermined value by a predetermined amount. said system further comprises: said storage means further comprises means for storing said digital position signals; and said means for displaying further comprises means for automatically changing the display image to display a predetermined acceptance trace, only one of said digitized coil-current signals, and one of said digitized position signals, when said one of said digitized coil-current signals deviates from a predetermined value by a predetermined amount. said system further comprises: said storage means further comprises means for storing said digital position signals; said first signal conditioning means comprises: said second signal conditioning means further comprises means for reducing the magnitude of said conditioned analog position signals for compatibility between said analog position signals and said second digitizing means. 2. The data acquisition system of claim 1, wherein said measuring means comprises means for simultaneously measuring the coil-current flowing through each of five coils of each of at least four control element drive mechanisms to produce an analog coil-current signal for each of the coils, and wherein said first signal conditioning means removes noise introduced by the electrical circuit from all of said analog coil-current signals prior to said signals being received by said first digitizing means. 3. The data acquisition system of claim 1, wherein 4. The data acquisition system of claim 1, wherein 5. The data acquisition system of claim 1, wherein said first signal conditioning means comprises means for calibrating said system without physically modifying said first signal conditioning means. 6. The data acquisition system of claim 1, wherein 7. A data acquisition system for recording data associated with movement of at least one control element assembly through the nuclear reactor core of a nuclear steam supply system of the type having a plurality of control element drive mechanisms engaging a respective plurality of control element assembly shafts, each drive mechanism including a plurality of electrical coils, said data acquisition system comprising: 8. The data acquisition system of claim 7, wherein said measuring means comprises means for simultaneously measuring the coil-current flowing through each of five coils of each of at least four control element drive mechanisms to produce an analog coil-current signal for each of the coils, and wherein said first signal conditioning means removes noise introduced by the electrical circuit from all of said analog coil-current signals prior to said signals being received by said first digitizing means. 9. The data acquisition system of claim 7, wherein 10. A data acquisition system for recording data associated with movement of at least one control element assembly through the nuclear reactor core of a nuclear steam supply system of the type having a plurality of control element drive mechanisms engaging a respective plurality of control element assembly shafts, each drive mechanism including a plurality of electrical coils, said data acquisition system comprising: 11. The data acquisition system of claim 10, wherein said first measuring means comprises means for simultaneously measuring the coil-current flowing through each of five coils of each of at least four control element drive mechanisms to produce an analog coil-current signal for each of the coils, and wherein said first signal conditioning means removes noise introduced by the electrical circuit from all of said analog coil-current signals prior to said signals being received by said first digitizing means. 12. The data acquisition system of claim 10, wherein 13. The data acquisition system of claim 10, wherein 14. The data acquisition system of claim 10, wherein said first signal conditioning means comprises means for calibrating said system without physically modifying said first signal conditioning means. 15. The data acquisition system of claim 10, wherein |
description | This application claims the benefit, under 35 U.S.C. § 119, of German patent application DE 10 2016 217 509.2, filed Sep. 14, 2016; the prior application is herewith incorporated by reference in its entirety. The invention relates to a method and an X-ray apparatus for generating a projective X-ray representation of an examination object using a radiator-detector system with a Talbot-Lau grating arrangement and a linear phase grating, an absorption image and a differential phase contrast image being ascertained. Such methods and projective X-ray apparatuses are generally known. Interferometric X-ray imaging (IR) is a variant of phase contrast imaging and is based on the inclusion of at least one phase grating (G1) in an X-ray imaging system. Preferably also included in the ray path of the X-ray imaging system is a source grating (G0) for generating sufficient dose rate and quasi-coherent radiation, and if applicable an analysis grating (G2) for measuring the interference pattern generated by the phase grating with a relatively coarsely segmented detector after the phase grating. By measuring the interference pattern behind the phase grating, it is possible to ascertain three image signals, namely a conventional absorption image, a dark-field image, and a differential phase contrast image. Concerning this, reference is made e.g. to the publication “Hard X-ray Dark-Field Imaging Using a Grating Interferometer”, F. Pfeiffer et al., Nature Materials 7 (2008). One problem associated with this projection-based X-ray imaging is that structures such as e.g. bones, blood vessels and organs in the radiographed examination object are often difficult to differentiate due to mutual superimposition. Tomographic methods providing sectional images that are as far as possible superimposition-free, e.g. computer tomography or tomosynthesis, represent one possible solution for reducing these structural superimpositions. However, the advantages of purely projective imaging are lost in this case, since the tomographic methods are relatively resource-intensive and also generate higher radiation exposure from one or a small number of spatial angles than a purely projective scan. The object of the invention is to find means by which it is possible to separate the information content of purely projective imaging information which was recorded using the method described in the introduction, and to create a result image of a structure of an examination object which is largely free of other structures. For example, to generate a representation of soft parts without bone superimposition and vice versa from an interferometric measurement. This object is achieved by the features in the independent claims. Advantageous developments of the invention are the subject matter of sub claims. The inventors discovered that in the lower range of diagnostically relevant energy for X-ray imaging, i.e. using X-ray spectra up to approximately 70 keV acceleration voltage, the phase signal and the absorption signal contain complementary information, since primarily photoelectric effect and Compton effect contribute to the generation of the image signal in this case. It is therefore possible by means of a weighted linear combination of both images to represent individual materials such as bones and soft parts separately without any need for exposure to different energy spectra as is required in the case of “dual-energy” imaging. Since the phase information that has been ascertained is available in differential format whereas the absorption information exists in absolute values, the phase image and the absorption image must be converted into the same representation format before any combination. This can be achieved by derivation of the absorption image, preferably perpendicular to the alignment of the grating lines of the phase grating for the phase imaging. Alternatively, an integration of at least one phase image is performed. It is also preferably possible for two phase images to be recorded with reciprocally rotated phase gratings, and both integrated perpendicular to the grating lines and amalgamated using a two-dimensional integration. This image with absolute image information can then be processed or linearly combined with the full absorption image to provide a result image. A particular advantage of the method described here is that further information can be generated from the data which is produced by a typical interferometric measurement using a single X-ray spectrum, without requiring additional measurements. Therefore the information for an absorption image and at least one phase image is obtained from one interferometric measurement using one energy range, and a result image which allows different materials to be separated is generated from these two information elements. In order to allow reciprocal processing of the image data, it is however necessary to adapt one of the images in respect of its representation format, i.e. absolute or differential, to the other by means of integration or differentiation. In accordance with this inventive idea, in a general basic variant, the inventors propose a method containing the following method steps for generating a projective X-ray representation of an examination object: a) performing an interferometric projective imaging using a radiator-detector system with a Talbot-Lau grating arrangement with a first linear phase grating with a first alignment, b) ascertaining a projective absorption image with absolute absorption values in absolute representation format, c) ascertaining a first projective differential phase contrast image with differential phase contrast values in differential representation format, d) adapting the representation format of one of the ascertained images to the other image respectively, e) generating at least one new result image by combining an unmodified image with an image which has been adapted in respect of its representation format, and f) storing and/or outputting at least one result image. It should be noted that the term combination implies a mathematical computation of image pixels of the unmodified image and of the image that has been adapted in respect of its representation format in the sense of a computing combination, at least one newly computed result image being produced. The simple adjacently disposed representation of different images in the same representation format is not considered a combination within the meaning of the invention. In a first variant, the absorption image is adapted to the phase image, wherein for the purpose of adapting the representation format of the absorption image, spatial derivatives are formed on a pixel-by-pixel basis perpendicular to the first alignment of the grating lines of the at least one phase grating, and the differential absorption image produced thereby is combined with the differential phase contrast image. In a second variant, the ascertained phase image can be adapted to the absorption image using unidimensional integration, wherein for the purpose of adapting the representation format of the differential phase contrast image, absolute values are formed by integration on a pixel-by-pixel basis perpendicular to the first alignment of the grating lines, and the absolute phase contrast image produced thereby is combined with the absolute absorption image. One problem associated with such unidimensional integrations of phase images is that linear artifacts are often produced. In order to prevent this, a second phase image is ascertained using a phase grating which is aligned in a second direction, preferably perpendicular to the alignment of the first phase grating. Accordingly, a third variant of the method proposes that provision is additionally made for ascertaining a second projective differential phase contrast image with differential phase contrast values in differential representation format using a phase grating which is aligned in a second direction. For the purpose of ascertaining the two phase images using differently oriented phase gratings, the first phase grating can normally be rotated for the second measurement, or a second phase grating having a different alignment can be used instead of the first phase grating for the purpose of ascertaining the second phase contrast image. The orientation of two phase gratings in respect of their grating lines is preferably aligned such that they run perpendicular to each other. If an absorption image with absolute image values is ascertained and two phase contrast images with differential image values are ascertained using respectively different alignments of the generating phase gratings, then: a) the two differential phase contrast images can each be converted into absolute phase contrast images by means of unidimensional integration perpendicular to the alignment of the generating phase gratings, and b) the result image can be computed from the absorption image and the absolute phase contrast images by means of pixel-by-pixel weighted combination. As an alternative to the aforementioned variant in which unidimensional integration is performed twice, it is also possible to proceed as follows: a) the differential phase contrast images can be converted into an absolute phase contrast image by means of two-dimensional integration perpendicular to the alignments of the generating phase gratings, and b) the result image can be computed from the absolute absorption image and the absolute phase contrast image by means of pixel-by-pixel combination. The invention also proposes use of a polynomial, preferably of the degree 1 to 3, for the purpose of combining the images. In this context, polynomial factors previously ascertained in the context of calibration can be used in the chosen polynomial. If the interference pattern generated by the phase grating is read out by an analysis grating with subsequent detector, this can be performed by so-called phase stepping, in which one of the gratings (preferably the analysis grating) is displaced in a step-by-step manner and a measurement is taken after each step. In total, at least three measurements per pixel must be performed in order to detect the phase shift that is present at the pixel concerned. Accordingly, it is proposed that the phase contrast measurement is performed by phase stepping one of the gratings used. As an alternative to phase stepping, it is also possible to use a high-resolution detector which is able by virtue of its high resolution directly to analyze the intensity modulation of the interference pattern generated by the phase grating. It is possible to dispense with an analysis grating in this case. Accordingly, it is proposed that the phase contrast measurement is performed by using a detector whose resolution lies in the range of grating spacings of an analysis grating. It is moreover possible to ascertain the absorption image directly by a measurement in the absence of the source grating and/or the phase grating and/or the analysis grating. However, it is preferably possible to use the measurements already available from ascertaining the phase shift, and to ascertain the absorption image from the sum of the intensity measurements of the phase contrast measurement. Furthermore, with regard to an optimized arrangement of the gratings in relation to the examination object, it is proposed to position the phase grating between the radiator and the examination object. In addition to the inventive method, the inventors also propose an X-ray apparatus for generating a projective X-ray representation of an examination object, the apparatus having at least the following features: a) a radiator-detector system for X-ray examination of the examination object arranged in a ray path, b) a Talbot-Lau grating arrangement in the ray path, with a first linear phase grating with a first alignment, c) a control and computing unit with a memory containing program code which during operation is used for the purpose of controlling the X-ray apparatus and for data processing of the signals received from the detector, wherein X-ray representations of the examination object are also generated. According to the invention, the memory of the control and computing unit also stores program code which during operation performs the method steps of one of the preceding method claims. The invention is described in greater detail below with reference to preferred exemplary embodiments and the figures, in which only those features required for an understanding of the invention are illustrated. The following reference signs and abbreviations are used here: D: detector; dx: step size in the context of “phase stepping”; F: focus; f( ) combination function; G1: phase grating; G2: system grating; G0: source grating; E1, E2: result images; E: integration; O: examination object; P: program code; R: control and computing unit; S: ray path; S1-S5: steps of the inventive method; δ: differentiation; Δφ(|): differential phase contrast image with vertical grating orientation; Δφ(−): differential phase contrast image with horizontal grating orientation; Δ(l/lo): differential absorption image; ∥φ(|): phase contrast image with absolute values with vertical grating orientation; ∥φ(−): phase contrast image with absolute values with horizontal grating orientation; ∥(l/lo): absorption image in absolute values. 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 method and X-ray apparatus for generating a projective X-ray representation of an examination object, 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 to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a schematic representation of an exemplary X-ray apparatus according to the invention, having a radiator-detector system which consists of a focus F of an X-ray tube (not shown in further detail) and a detector D for detecting the X-radiation emitted in the ray path S. The ray path S is schematically illustrated by the central ray and the two circumferential rays. In addition, three X-ray gratings corresponding to a Talbot-Lau grating arrangement are placed in the ray path S, a source grating G0 being situated directly at the focus F and generating a quasi-coherent ray bundle. This quasi-coherent ray bundle strikes the subsequent examination object O according to the formation of the ray path S, the examination object O interacting with the X-radiation. The phase grating G1 follows thereupon, and forms an interference pattern which is measured on a pixel-by-pixel basis by step-by-step displacement (phase stepping) of the analysis grating G2 and use of the subsequent detector D. Control of the radiator-detector system using the X-ray gratings in order to perform the “phase stepping”, and evaluation of the measurement results are effected by means of a control and computing unit R, which has a memory containing program code P that performs the customary projective phase contrast measurement and absorption measurement, including the imaging, during operation. In addition to this, program code P which performs the steps of the inventive method described above is also held in the X-ray apparatus. In particular, program code can also be stored and the X-ray apparatus so configured as to perform a method for projective imaging as described below with reference to FIGS. 2 to 4. If an absorption image and a phase contrast image are generated using a projective X-ray apparatus with a Talbot-Lau grating arrangement, it is inventively possible to combine, preferably linearly, the absorption image with the phase contrast image. However, since the representation format of the absorption image consists of absolute values while the representation format of the phase contrast image consists of differential values, it is necessary to adapt these representation formats to each other before combination, i.e. either to identify the derivative of the absolute values of the absorption image or to integrate the differential values of the phase contrast image. FIG. 2 shows a method flow chart, in which the standardization of the representation format is effected by linear unidimensional differentiation of the absorption image in accordance with the invention. Accordingly, in a first step S1, a scan of the examination object takes place using a single X-ray spectrum, the phase grating being adjusted to a single X-ray energy. Therefore the absolute values of an absorption image ∥(l/lo) are ascertained in the step S2a and the differential values of a phase contrast image Δφ(−) are ascertained in the step S2b. In order to adapt the representation format, in the step S3a, differential values of the absorption are formed from the absolute values of the absorption image by means of differentiation δ (forming a derivative d(l/lo)/dx) perpendicular to the alignment of the grating lines of the phase grating used for the phase contrast image) and the differential absorption image Δ(l/lo) is generated. In the step S4, provision is made for combining, preferably in a linear manner, the two differential images f(Δ(l/lo), Δφ(−)) to form at least one result image, which is then stored for further processing and/or displayed in the step S5. For the purpose of this and the other inventive methods described here, provision can additionally be made for the X-ray apparatus, supported by corresponding program code, to vary the weighting parameters of the combination function f( ) or the polynomial factors of an alternatively used polynomial function for the output of different result images. In a further variant of the method according to the invention, the standardization of the representation format can also be effected by a linear unidimensional integration of the phase contrast image. An exemplary method flow chart for this is illustrated in FIG. 3. In this case, in the step S1, a scan of the examination object is again performed using a single X-ray spectrum, the phase grating that is used being adjusted to a single X-ray energy. The absolute values of an absorption image ∥(l/lo) are identified in the step S2a and the differential values of a phase contrast image Δφ(−) are ascertained in the step S2b. In order to adapt the representation format, in the step S3b, integrals—represented by the symbol Σ—are formed perpendicular to the alignment of the grating lines of the phase grating that is used, and the absolute values of the phase contrast image ∥φ(−) are computed thus from the differential image values of the originally ascertained phase contrast image Δφ(−). Therefore both representations are available in absolute values and can be combined with each other, this occurring in the step S4. In the step S5, the at least one result image thereby produced can then be stored for further processing and/or output. The method outlined in FIG. 3 is nonetheless associated with the problem that line artifacts often occur as a result of the purely unidimensional integration. Prevention of such line artifacts can be achieved by a two-dimensional integration. According to the invention, a special variant also provides for a phase contrast image to be measured twice, wherein the alignments of the phase grating used here are preferably independent of each other, i.e. perpendicular to each other. For example, the phase grating can be rotated by 90° between the phase contrast measurements. A corresponding method flow chart for this purpose is illustrated in FIG. 4. In contrast with the method according to FIGS. 2 and 3, provision is additionally made in the step S1 for generating a further phase contrast image using a phase grating which is rotated by 90° relative to the first phase contrast image. The alignment of the source grating and the analysis grating—where present—must obviously also be rotated, such that all X-ray gratings are identically aligned. It is also possible in principle to rotate the entire radiator-detector system including the Talbot-Lau grating arrangement. Therefore an absorption image ∥(l/lo) is generated with absolute image values in the step S2a, a differential phase contrast image Δφ(−) is generated with e.g. horizontal grating orientation in the step S2b, and a further differential phase contrast image Δφ(|) is generated with e.g. vertical grating orientation in the step S2c. In the steps S3b and S3c, the differential images are integrated in a direction perpendicular to the alignment of the phase grating used in each case, and the phase contrast images ∥φ(−) and ∥φ(|) now consisting of absolute image values are obtained. Since the three available images have now been standardized in respect of their representation format to absolute values, at least one combination f(∥(l/lo), ∥φ(−), ∥φ(|)) can be computed as a result image in the step S4. The result image is then stored and/or output in the step S5. In summary, the invention proposes a method and an X-ray apparatus for generating a projective X-ray representation of an examination object, wherein two projective images obtained from a phase contrast measurement are adapted to each other in respect of their representation format and a result image is generated by combining the adapted images, the result image allowing extensive separation of different structures in the examination object that is used. Although the invention is illustrated and described in detail with reference to the preferred exemplary embodiment, the invention is not restricted by the examples disclosed herein, and other variations may be derived therefrom by a person skilled in the art without thereby departing from the scope of the invention. In particular, the invention is not restricted to the combinations of features specified below, but other combinations and partial combinations which are obvious to a person skilled in the art can also be formed from the features disclosed. |
|
abstract | An apparatus for altering the radiation intensity delivered from a radiation source has a plate member for holding a plurality of radiation modulating devices. A frame member is coupled to the radiation source for holding the plate member between the radiation source and a target area. The frame member allows the plate member to rotate within the frame member so different radiation modulating devices may be positioned between the radiation source and the target area to alter the radiation intensity delivered. |
|
summary | ||
abstract | An x-ray detector panel support is disclosed that is formed with radiation absorbing material to reduce the reflection of x-rays off anything behind the scintillator, which may include the geometry of the panel support, the electronics, and the back cover of the x-ray detector. The absorbing material may take the form of a discrete layer secured to or otherwise disposed within the panel support. The radiation absorbing material may also be mixed with the base materials used to fabricate the panel support. As such, when the panel support is formed, it includes radiation absorbing components. The radiation absorbing material may include lead, barium sulfate, tungsten, as well as other materials. The panel support is constructed to inhibit the detection of backscattered x-rays without significantly increasing the size or weigh of the x-ray detector. The panel support is applicable with stationary or fixed as well as portable x-ray detectors. |
|
abstract | There are provided a leaf row in which a plurality of leaf plates are arranged in the thickness direction of the row in such a way that the respective one end faces of the leaf plates are trued up and a leaf plate drive mechanism that drives each of the plurality of leaf plates in such a way that the one end face approaches or departs from a beam axis. In each of the leaf plates, a facing side facing a leaf plate that is adjacent to that leaf plate in the thickness direction is formed of a plane including a first axis on the beam axis; the leaf plate drive mechanism drives the leaf plate along a circumferential orbit around the second axis, on the beam axis, that is perpendicular to the beam axis and the first axis. |
|
051587394 | abstract | The tubular wall (1) of the irradiated component is machined on its upper annular surface, with chips (44) being formed by the use of a metal working machine (30) bearing on this upper surface and moving in rotation about the axis (6) of the wall (1) of the component. The chips (44) formed by the metal working machine (30), e.g., a milling head, which moves in the vertical direction and downwards, are collected and cleared away continuously during the progress of the machining in the axial direction (6) of the wall (1) of the component. The device is fastened to the upper part of the tubular casing (1), arms (7a, 7b) equipped with jacks allowing the device (4) to be flanged to the wall (1) of the component, and bearing devices (12) comprising arms (13) being mounted pivotably about a horizontal axis between a low bearing position and a high withdrawal position (13'). The bearing arms (13) change from their low position to their high position at the moment when the machining tool (31) passes. |
claims | 1. A method of determining a void rate in a biphase gas/liquid medium, the void rate corresponding to a fraction of a volume of gas corresponding to gas bubbles in the gas/liquid medium to a total volume of gas and liquid in the gas/liquid medium, the method comprising:defining a size of the largest gas bubbles in the gas/liquid medium by optical measurement;deploying a bulk elastic wave resonator in contact and coupled acoustically with the biphase gas/liquid medium;measuring, by nonlinear resonant ultrasound spectroscopy of the biphase gas/liquid medium in terms of frequencies and amplitudes of acoustic excitation in a given range of frequencies based on the size of the largest gas bubbles and in a given range of amplitudes, bulk elastic waves emitted and detected at said resonator, resulting in a set of resonance curves exhibiting maxima;determining a straight line defined by the maxima of said set of resonance curves having different excitation amplitudes;determining a slope of said straight line; anddetermining the void rate based on said slope. 2. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, further comprising determining a resonant frequency of said gas bubbles. 3. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein:the gas bubbles have a radius on the order of a hundred microns,the given range of frequencies is below 33 kHz,the liquid medium is water, andthe gas bubbles are air bubbles. 4. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein the bulk elastic wave resonator is placed in said biphase gas/liquid medium, and the bulk elastic wave resonator comprises a first metallic plate connected to an emitter and a second metallic plate connected to a receiver. 5. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 4, wherein the first plate is connected to a transducer. 6. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 4, wherein the second plate is connected to a hydrophone. 7. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 4, wherein the first metallic plate is a front face of the emitter and the second metallic plate is a front face of the receiver. 8. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein the bulk elastic wave resonator is of Helmholtz type, and the biphase medium is introduced into said bulk elastic wave resonator. 9. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein the liquid is a metal in a liquid state. 10. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 9, wherein the metal is sodium. 11. A nuclear reactor configured to apply the method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1. 12. The nuclear reactor as claimed in claim 11, wherein the resonator is of plate type, and the resonator is placed within the liquid of sodium type of a primary circuit of the nuclear reactor. 13. The nuclear reactor as claimed in claim 11, wherein the resonator is of Helmholtz resonator type, and the resonator is placed branched off from a primary or secondary circuit of the nuclear reactor. 14. A fast neutron reactor configured to apply the method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1. 15. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein each resonance curve in the set of resonance curves exhibits a single maximum. 16. A method of determining a void rate in a biphase gas/liquid medium, the void rate corresponding to a fraction of a volume of gas corresponding to gas bubbles in the gas/liquid medium to a total volume of gas and liquid in the gas/liquid medium, the method comprising:deploying a bulk elastic wave resonator in the biphase gas/liquid medium, the bulk elastic wave resonator comprising a first metallic plate connected to a transducer and a second metallic plate connected to a receiver;measuring, by nonlinear resonant ultrasound spectroscopy of the biphase gas/liquid medium in terms of frequencies and amplitudes of acoustic excitation in a given range of frequencies and in a given range of amplitudes, bulk elastic waves emitted and detected at said resonator, resulting in a set of resonance curves exhibiting maxima;determining a straight line defined by the maxima of said set of resonance curves having different excitation amplitudes;determining a slope of said straight line; anddetermining the void rate based on said slope. 17. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 16, wherein the first metallic plate is a front face of the resonator and the second metallic plate is a front face of the receiver. 18. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 16, wherein the bulk elastic wave resonator is of Helmholtz type. 19. A fast neutron reactor configured to determine a void rate in a biphase gas/liquid medium, the void rate corresponding to a fraction of a volume of gas corresponding to gas bubbles in the gas/liquid medium to a total volume of gas and liquid in the gas/liquid medium, the fast neutron reactor being configured to determine the void rate in the biphase gas/liquid medium by:deploying a bulk elastic wave resonator in contact and coupled acoustically with the biphase gas/liquid medium;measuring, by nonlinear resonant ultrasound spectroscopy of the biphase gas/liquid medium in terms of frequencies and amplitudes of acoustic excitation in a given range of frequencies and in a given range of amplitudes, bulk elastic waves emitted and detected at said resonator, resulting in a set of resonance curves exhibiting maxima;determining a straight line defined by the maxima of said set of resonance curves having different excitation amplitudes;determining a slope of said straight line; anddetermining the void rate based on said slope. 20. The fast neutron reactor as claimed in claim 19, wherein the resonator is placed within a primary circuit of the fast neutron reactor. |
|
description | Embodiments of this disclosure relate to radiation devices and methods. In particular, real-time moving collimators and imaging methods using the collimators are described. Conventional x-ray collimators are typically constructed for shaping x-ray beams. Usually, conventional collimators include beam blocking leaves made of x-ray attenuating materials that have high atomic number (high-Z material). In most cases, the collimator beam blocking leaves cut out portions of the beam that are not useful for diagnostic, guidance, or therapy purposes. The collimator leaves are either manually moved or motorized with some systems allowing control over the motion of individual leaves for shrinking or expanding the x-ray field of view. However, conventional collimators have not been designed to modulate the beam quality of an x-ray beam such as the beam energy, intensity, or dose distribution. Accordingly, there is a need for a collimator device that can be used to modify the beam quality and the shape and size of a beam. There is a need for a radiation apparatus in which the operation of the x-ray source and the collimator device can be synchronized such that the modification of the beam quality, shape, or size of a beam can be substantially in real time with the generation of the beam. Various embodiments of an x-ray collimator and a method for collimating x-rays using the collimator are described. The collimator may comprise an individual leaf or leaves that can be motorized such that each leaf can be moved independently in and out of the x-ray beam. The individual leaf or leaves can be all completely attenuating or all partially attenuating of x-rays. Alternatively, the individual leaves can be a combination of partially and completely attenuating of x-rays. The leaf or leaves can be allowed to cover the entire or partial field of view of the x-rays. The movement of the individual leaf or leaves can be synchronized with the operation of the x-ray source to modify the beam on a per pulse basis. The disclosed collimator allows rapidly changing of the beam quality of x-rays from pulse to pulse, and hence the images acquired using the x-rays. A method of multi-energy imaging is described. An imaging method using x-rays of different beam qualities for a region of interest in a body portion and for the rest of the body portion is also described. Other embodiments of the disclosure are further described in the Detail Description. This Summary is provided to introduce selected embodiments in a simplified form and is not intended to identify key features or essential characteristics of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. Various embodiments of an x-ray collimator, an apparatus including the x-ray collimator, and an imaging method using the x-ray collimator are described. It is to be understood that the disclosure is not limited to the particular embodiments described as such may, of course, vary. An aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments. Further, in the following description, specific details such as examples of specific materials, dimensions, processes, etc. may be set forth in order to provide a thorough understanding of the disclosure. It will be apparent, however, to one of ordinary skill in the art that these specific details need not be employed to practice embodiments of the disclosure. In other instances, well known components or process steps may not be described in detail in order to avoid unnecessarily obscuring the embodiments of the disclosure. As used in the description and appended claims, the singular forms of “a,” “an,” and “the” may include plural references unless the context clearly dictates otherwise. As used herein, the term “collimator” refers to a device that can modify one or more parameters of an x-ray beam such as the energy, intensity, shape, size, direction, dose distribution, or other beam parameters. A collimator may include one or more leaves configured to modify one or more parameters of an x-ray beam. A collimator leaf may be partially x-ray attenuating or completely x-ray attenuating. As used herein, the term “completely x-ray attenuating” refers to complete or substantially complete block of x-rays by a collimator leaf such that the amount of x-rays passing through the collimator leaf is negligible or is not intended for any useful imaging or treatment. A collimator leaf that is completely x-ray attenuating may be referred to as a beam blocking leaf in this disclosure. As used herein, the term “partially x-ray attenuating” refers to that a portion of x-rays passes through a collimator leaf and contributes to imaging or treatment. A collimator leaf that is partially x-ray attenuating may be referred to as a beam filter in this disclosure. As used herein, the term “beam quality” refers to the energy, intensity, or dose distribution of an x-ray beam. An apparatus is provided in this disclosure. The apparatus may include an x-ray source operable to generate x-ray beams, a collimator having one or more leaves configured to modify the x-ray beams, a motorized system operable to move the one or more leaves of the collimator independently in or out of the x-ray beams, and a controller configured to synchronize operation of the x-ray source and the motorized system, allowing modification of the x-ray beams substantially in real time with generation of the x-ray beams. At least one leaf or each of the leaves of the collimator may be configured to modulate a beam quality of the x-ray beams. The x-ray source may generate x-ray beams in pulses and the motorized system may be operable to move the one or more leaves in synchrony with the operation of the x-ray source, thus allowing modification of the x-ray beams on a pulse to pulse basis. A collimator assembly is provided in this disclosure. The collimator assembly may include two or more leaves configured to modify an x-ray beam and a motorized system operable to move the two or leaves independently in or out of the x-ray beam. The two or more leaves may be configured to modify the size or shape of the x-ray beam or to modulate a beam quality of the x-ray beam. In some embodiments, at least one of the two or more leaves may be configured to modulate a beam quality of the x-ray beam. In some embodiments, each of the two or more leaves may be configured to modulate the beam quality of the x-ray beam. Each of the two or more leaves can be partially x-ray attenuating or completely x-ray attenuating. Alternatively, the two or more leaves comprise a combination of partially and completely x-ray attenuating leaves. In some embodiments, the two or more leaves can be positioned to define an aperture to allow a first portion of the x-ray beam passing through the aperture and a second portion of the x-ray beam passing through the thickness of the leaves, thereby providing a modified beam having a first beam portion that passes through the aperture and a second beam portion that passes through the thickness of the leaves. The first beam portion has a first beam quality and the second beam portion has a second beam quality. Each of the two or more leaves can be moved independently to cover an entire field of view of the x-ray beam. Therefore, the aperture defined by the two or more leaves can be located in anywhere within the field of view. In a non-limiting specific embodiment, a collimator assembly comprises four leaves each can be independently moved in or out of the x-ray beam. The four leaves can be set up in a configuration such that the adjacent two leaves can be linearly moved in directions substantially perpendicularly to each other. Each of the four leaves can be allowed to cover an entire field of view of the x-ray beam. Each of the four leaves can be made of a different partially x-ray attenuating material. Alternatively, each of the four leaves can be made of a same partially x-ray attenuating material of different thicknesses such that each leaf can modulate a beam quality of x-ray beams differently for different applications. Alternatively, each of the four leaves can be made of a same partially x-ray attenuating material or a material of a same attenuating property such that the collimator can provide a modified beam having beam portions of different beam qualities, e.g., a first beam portion passing through an aperture defined by the leaves and a second beam portion passing through the thicknesses of the leaves. Alternatively, each of the four leaves can be made of a same or different completely x-rays attenuating material such that the leaves can rapidly shape or size the x-ray beam by rapidly changing the aperture defined by the leaves and blocking the beams outside the aperture. An imaging method is provided in this disclosure. The imaging method comprises the step of directing an x-ray beam to a body portion containing a region of interest. The x-ray beam has a first beam portion directed to the region of interest and a second beam portion directed to the rest of the body portion, wherein the first beam portion has a first beam quality and the second beam portion has a second beam quality different from the first beam quality. An image is acquired including both the region of interest and the rest of the body portion. The x-ray beam having a first and a second beam portions can be provided by a collimator assembly comprising two or more leaves, wherein each of the two or more leaves comprises a same material that partially attenuates x-rays or a material of same x-ray attenuating property. The two or more leaves can be independently moved by a motorized system to define an aperture, thereby allowing the first beam portion passing through the aperture to the region of interest and the second beam portion passing through the thicknesses of the two or more leaves to the rest of the body portion. The two or more leaves of the collimator assembly can be moved in synchrony with the operation of the x-ray source such that the aperture can be defined substantially in real time with generation of the x-rays. In a non-limiting specific embodiment, the x-ray beam having a first and a second beam portions can be provided by a collimator comprising four leaves. Each of the four leaves may comprise a same material that partially attenuates x-rays or a material of same x-ray attenuating property. The four leaves can be set up in a configuration that adjacent two leaves are linearly movably in directions substantially perpendicularly to each other. The leaves can be independently moved to define an aperture, thereby allowing the first beam portion passing through the aperture to the region of interest and the second beam portion passing through the thicknesses of the leaves to the rest of the body portion. The four leaves of the collimator can be moved in synchrony with the operation the x-ray source such that the aperture can be defined substantially in real time with generation of the x-rays. A multi-energy imaging method is provided in this disclosure. In the method, a first image of a body portion may be acquired using a first pulse of x-rays having a first energy and a second image of the body portion may be acquired using a second pulse of x-rays having a second energy. The first and second images are combined to provide a third image. The first and second pulses of x-rays may be generated by an x-ray source and modulated by a collimator assembly. The collimator assembly may comprise two or more leaves each being independently moveable in synchrony with the operation of the x-ray source such that the beam quality of the first or second pulse of x-rays can be modulated by one of the two or more leaves substantially in real time with generation of the first or second pulses. In some embodiments, the beam quality of each of the first and second pulses of x-rays can be modulated by one of the two or more leaves substantially in real time with generation of the each of the first and second pulses. Exemplary embodiments will now be described with reference to the figures. It should be noted that some figures are not necessarily drawn to scale. The figures are only intended to facilitate the description of specific embodiments, and are not intended as an exhaustive description or as a limitation on the scope of the disclosure. FIG. 1 schematically shows an exemplary radiation apparatus 100 according to some embodiments of the disclosure. The radiation apparatus 100 may include a radiation source 102 operable to generate an x-ray beam 104 and a collimator 106 configured to modify the x-ray beam 104. The collimator 106 may include one or more leaves 108a, 108b, 108c, 108d each of which can be moved in and out of the x-ray beam 104, as indicated by the arrows. A motorized system 110 may include one or motion mechanisms 110a, 110b, 110c, 110d each of which may be coupled to one of the leaves 108a, 108b, 108c, 108d to independently move the leaves in and out of the x-ray beam 104. A controller 112 may be coupled to the x-ray source 102 and the motorized system 110 to synchronize the operation of the x-ray source 102 and the motorized system 110 such that the modification of the beam is substantially in real time with the generation of the x-rays. The x-ray source 102 may be an x-ray tube or accelerator supported by an arm structure which may be movable in various degrees of freedom. The x-ray source 102 may be configured to generate x-rays at any suitable energy levels such as kilovolt (keV) energy levels and/or megavolt (MV) energy levels. The x-ray source 102 may include a signal beam generator which is capable of generating x-rays at multiple energy levels. The x-ray source 102 may also include two or more generators, e.g. one for generating radiations at a keV level and one for generating radiations at an MV level. In general, an x-ray source includes a target which is configured to produce x-rays upon impingement by energetic electrons. Generation of x-rays is known in the art and its detail description is omitted herein for clarity of description of this disclosure. In some embodiments, provided is a collimator device that may be particularly useful in conjunction with an x-ray source that is configured to produce x-rays at keV energy levels for imaging. The x-ray source such as an x-ray tube may generate x-rays on a pulse by pulse basis. It will be appreciated however that the provided collimator assembly can be used in conjunction with any kind of x-ray sources. The collimator leaves 108a, 108b, 108c, 108d may be configured to modulate the beam quality of the x-ray beam 104. For example, each of the leaves 108a, 108b, 108c, 108d may be made of a partially x-ray attenuating material to modify the beam quality. The partially x-ray attenuating material can be selected such that the beam intensity or beam mean energy can be changed after the x-rays pass through the leaves. Each of the leaves 108a, 108b, 108c, 108d may be made of a same partially x-ray attenuating material. Alternatively, each of the leaves 108a, 108b, 108c, 108d may be made of a different partially x-ray attenuating material so that the beam quality can be modified differently using different leaves depending on application requirements. In some embodiments, each of the leaves 108a, 108b, 108c, 108d can be made of a same partially attenuating material but with a different thickness to modify the beam quality differently. In some embodiments, each of the leaves 108a, 108b, 108c, 108d can be made of a different partially attenuating material with a different thickness. Partially x-ray attenuating materials are typically medium to low-Z (atomic number) materials. High-Z materials with a small thickness can also be used as partially attenuating materials. By way of example, beryllium may be at the low end of Z and lead may be at the high end of Z which can be used as partially x-ray attenuating materials. Any element, an alloy or compound having a Z number between beryllium and lead can be used as partially x-ray attenuating materials. An x-ray beam emitted from an x-ray source typically has a continuous range of energies (spectrum) up to a maximal value. The maximal value depends on the peak voltage applied to the x-ray source. A partially x-ray attenuating material may have a unique attenuation spectrum or ability to stop x-ray photons at each energy level over the range of x-ray energies. Therefore, depending on the x-ray attenuating material used for the leaves, the x-ray beams emitted from an x-ray source can be modified. The resultant beam may have an average energy that is different from the original spectrum of energies. In some cases the partially attenuating material may selectively remove low energy x-rays resulting in a high average energy spectrum, while in other cases the mean energy may not be reduced significantly but the beam intensity may be reduced depending on the application requirement. FIG. 2 shows a typical x-ray spectrum generated by an x-ray source and the effect of filtration by different x-ray attenuating materials. As shown, depending on the x-ray attenuating material, the energy distribution and hence the mean energy and intensity of the spectrum changes. In FIG. 2, a same thickness (2 mm) of aluminum, copper and tin changes the beam spectrum, from the original unfiltered beam mean energy of 51.52 keV to mean energies of 55.86 keV, 82.21 keV and 97.94 keV, respectively. The thicknesses of the partially x-ray attenuating material may further define the intensity and distribution of energies of the beam. FIG. 3 shows that different thicknesses (1, 2, and 4 mm) of the same material copper modify the beam differently. Therefore, leaves made of a same partially x-ray attenuating material with different thicknesses may modulate the beam quality differently. In general, the thickness of a partially x-ray attenuating material required for a same or similar change in intensity is smaller for higher Z than for low Z material. The effect of the material and its thickness on the final spectrum is given by Beer's Law:I(E)=I0exp[−μ(E)*x]where I is the beam intensity at any energy E after attenuating the original intensity I0. The attenuation coefficient for the given energy is constant for the material and determines how much of the beam is stopped in the material of thickness x. Returning to FIG. 1, the collimator 106 may also be configured to modify the shape and/or size of the x-ray beam 104. The leaves 108a, 108b, 108c, 108d can be made of a completely x-ray attenuating material that has a high-Z or atomic number. The leaves 108a, 108b, 108c, 108d can form an aperture 114 defining a shape and/or size to allow a portion of the beam passing through and block the rest of the beam outside of the aperture 114, as will be described in greater detail below. The motorized system 110 may include one or more motion mechanisms 110a, 110b, 110c, 110d each of which may be coupled to one of the leaves 108a, 108b, 108c, 108d to independently drive the leaf in and out of the x-ray beam 104. Each of the motion mechanisms 110a, 110b, 110c, 110d may include a motor. By way of example, a motion mechanism may preferably include a servo motor and one or more feedback devices that are electrically coupled to the controller 112 operable with user interface software. A close loop control can be used to control the motion mechanisms and automatically adjust the position of the leaves in the beam. The motion mechanisms 110a, 110b, 110c, 110d may move the leaves 108a, 108b, 108c, 108d in linear directions. Alternatively, the motion mechanisms 110a, 110b, 110c, 110d may move the leaves 108a, 108b, 108c, 108d in angular directions. As shown in FIG. 1, the motion mechanisms 110a, 110b, 110c, 110d may independently move the leaves 108a, 108b, 108c, 108d in the x-ray beam 104 such that the positions of the leaves 108a, 108b, 108c, 108d in the beam 104 may define an aperture 114. As such, a portion of the x-ray beam 104 may pass through the aperture 114, providing a beam portion having a shape and size defined by the aperture 114. Outside the aperture 114, the x-rays would be either blocked or modulated depending on the attenuating properties of the leaves 108a, 108b, 108c, 108d. In embodiments where the leaves 108a, 108b, 108c, 108d are partially x-ray attenuating, the portion of x-rays outside the aperture 114 may pass through the thicknesses of the leaves 108a, 108b, 108c, 108d, providing a beam portion having a beam quality that is different from that of the beam portion passing through the aperture 114. FIG. 4A schematically shows a single image frame having two regions formed by a beam having two beam portions each beam portion having a different beam quality that can be provided by the collimator 106 described above. In embodiments where the leaves 108a, 108b, 108c, 108d are completely x-ray attenuating, the portion of x-rays outside the aperture 114 is blocked. Returning to FIG. 1, in some embodiments, one motion mechanism e.g. 110a may extend one leaf e.g. 108a in the x-ray beam 104 to cover the entire field of view, and the other motion mechanisms 110b, 110c, 110d may retract the rest of the leaves 108b, 108c, 108d out of the beam 104. As such, the x-ray beam 104 may be modulated by a single leaf 108a covering the entire field of view. Similarly, the motion mechanism 110b may extend a different leaf e.g. leaf 108b in the x-ray beam 104 to cover the entire field of view, and the other motion mechanisms 110a, 110c, 110d retract the rest of the leaves 108a, 108c, 108d out of the beam so that the x-ray beam 104 may be attenuated by the single leaf 108b having a attenuating property different from that of leaf 108a. Motion mechanisms 110c or 110d may similarly extend a single leaf 108c or 108d, which may have an attenuating property different from those of other leaves, in the beam 104 and modulate the beam 104 using the single leaf 108c or 108d to provide a modulated beam having a different beam quality. FIG. 4B schematically shows two successive image frames formed by two x-ray beams where the beam quality is uniform for each image frame but differs from frame to frame. Returning to FIG. 1, the controller 112 may be coupled to the x-ray source 102 and the motion mechanisms 110a, 110b, 110c, 110d. The controller 112 may be configured or programmed to activate and control the x-ray source 102 and the motion mechanisms 110a, 110b, 110c, 110d. The controller 112 may synchronize the operation of the x-ray source 102 and the motion mechanisms 110a, 110b, 110c, 110d such that the movement of the leaves 108a, 108b, 108c, 108d in and out of the x-ray beam 104 may be in synchrony with the generation of the x-rays. In other words, the leaves 108a, 108b, 108c, 108d may modify the beams substantially in real time with the generation of the beams by the x-ray source 102. For example, the controller 112 may be programmed to send a logic pulse signal (e.g. high/low or equivalently go/no-go) simultaneously to both the x-ray generator 102 and the motorized system 110, which activates the x-ray source 102 to generate x-ray beams and trigger the motion mechanisms 110 to control the movement of the collimator leaves 108a, 108b, 108c, 108d. Therefore, the controller 112 may allow generation of x-rays of an energy spectrum and selection of a particular leaf for modifying a beam quality of the x-rays, or allow generation of x-rays of an energy spectrum and collective movement of the leaves to define an aperture for modifying the size, shape and/or beam quality of the x-rays. The controller 112 may also be programmed to allow a sequence in generating x-ray pulses of different energies and selection of different leaves corresponding to the sequence of x-ray pulses generated. Embodiments of the collimator assembly and the apparatus including the collimator assembly can be advantageously used in multi-energy imaging. X-ray sources typically emit a continuous range of energies up to a maximum value. This maximum is dependent on the peak voltage (kVp in case of diagnostic beam) applied to the x-ray tube. Higher kVp beams are more penetrating but produce less contrast (dark to light difference) in images whereas it is the opposite for lower energy beams. Hence by combining (e.g. by using weighted logarithmic subtraction) images of the same object acquired with different energy spectra, visualization of features of interest can be greatly increased. The results improve as the mean energy separation between the spectra increases. This energy separation can be significantly improved by adding appropriate x-ray filters in the beam for each kVp used. For sequential imaging with multiple kVp, the filters would have to be changed from x-ray pulse to pulse depending on the application. Embodiments of the collimator described in this disclosure can advantageously synchronize the changing of filters with the x-ray generator so that the correct filter for each chosen kVp can be presented to the beam. Embodiments of the collimator described in this disclosure allow any possible combination of filters and kVp depending upon the application requirements. In a specific application in lung imaging for example, two successive image frames can be acquired using beams of different energies. By weighting the images appropriately and subtracting one image from another, desired features made of a certain material can be highlighted or suppressed. By fast switching of filters in image acquisition and using image processing methods, bones can be virtually “removed” to allow better visualization of the underlying soft tissue. The fast synchronized switching allows minimal shift between two successive image frames particularly in cases where motion is present such as breathing motion in case of lung imaging. This may also allow rapid synchronized multi-energy imaging in non-destructive testing particularly of large objects where the object could be slowly translated through the field of view for full coverage. FIG. 5 is a flow chart illustrating exemplary steps of a multi-energy imaging method according to embodiments of this disclosure. In the method, a first image of a body portion may be acquired using a first pulse of x-rays having a first energy (502). A second image of the body portion may be acquired using a second pulse of x-rays having a second energy (504). The first and second images may be combined to provide a third image (506). The first and second pulses of x-rays may be generated by an x-ray source and modulated by a collimator assembly. The collimator assembly may comprise two or more leaves each may be independently moveable in synchrony with the operation of the x-ray source such that the beam quality of the first or second pulse of x-rays can be modulated by one of the two or more leaves substantially in real time with the generation of the first or second pulses. In some embodiments, the beam quality of each of the first and second pulses of x-rays may be modulated by one of the two or more leaves substantially in real time with the generation of the each of the first and second pulses. Embodiments of the collimator assembly and the apparatus including the collimator assembly can be advantageously used to improve the imaging of the region of interest and reduce the exposure of x-rays to the patient in areas outside the region of interest. FIG. 6 is a flow chart illustrating exemplary steps of an imaging method according to some embodiments of this disclosure. In the imaging method, an x-ray beam having a first beam portion with a first beam quality and a second beam portion with a second beam quality different from the first beam quality is provided (602). The x-ray beam is directed to a body portion containing a region of interest, wherein the first beam portion with the first beam quality is directed to the region of interest and the second beam portion with the second beam quality is directed to the rest of the body portion (604). An image is acquired including both the region of interest and the rest of the body portion (606). The x-ray beam having a first and a second beam portions can be provided by a collimator assembly comprising two or more leaves, wherein each of the two or more leaves may comprise a same material that partially attenuates x-rays or a material of same x-ray attenuating property. The two or more leaves can be independently moved by a motorized system to define an aperture, thereby allowing the first beam portion passing through the aperture to the region of interest and the second beam portion passing through the thickness of the two or more leaves to the rest of the body portion. The two or more leaves of the collimator assembly can be moved in synchrony with the operation of the x-ray source such that the aperture can be defined substantially in real time with generation of the x-rays. In a specific embodiment, the x-ray beam having a first and a second beam portions can be provided by a collimator comprising four leaves. Each of the four leaves may comprise a same material that partially attenuates x-rays or a material of same x-ray attenuating property. The four leaves can be set up in a configuration that adjacent two leaves are linearly movably in directions perpendicularly to each other. The leaves can be independently moved to define an aperture, thereby allowing the first beam portion passing through the aperture to the region of interest and the second beam portion passing through the thicknesses of the leaves to the rest of the body portion. The four leaves of the collimator can be moved in synchrony with the operation the x-ray source such that the aperture can be defined substantially in real time with generation of the x-rays. Exemplary embodiments of a collimator apparatus and an imaging method have been described. Those skilled in the art will appreciate that various modifications may be made within the spirit and scope of the disclosure. All these or other variations and modifications are contemplated by the inventors and within the scope of the disclosure. |
|
claims | 1. A generation system comprising:a natural circulation reactor adapted to generate steam only by naturally circulating coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor;a high-pressure turbine connected to said natural circulation reactor by a main steam pipe configured to at least introduce steam generated in said natural circulation reactor to said high-pressure turbine, said main steam pipe having one end connected to said natural circulation reactor and another end connected to said high-pressure turbine;a low-pressure turbine configured to receive steam exhausted from said high-pressure turbine;a moisture separation heater installed between said high-pressure turbine and said low-pressure turbine and configured to at least receive steam exhausted from said high-pressure turbine;a first steam control valve installed in said main steam pipe at a position between the one end of the main steam pipe connected to said natural circulation reactor and the another end of said main steam pipe connected to said high-pressure turbine;an inlet pipe having a second steam control valve installed in said inlet pipe, said inlet pipe having one end of said inlet pipe connected to said main steam pipe at a position between said natural circulation reactor and said first steam control valve installed in said main steam pipe, and said inlet pipe having another end of said inlet pipe connected to said moisture separation heater, said second steam control value being installed at a position between the one end of said inlet pipe connected to said main steam pipe and the another end of said inlet pipe connected to said moisture separation heater;a control rod drive apparatus connected with a control rod configured to be inserted and withdrawn with respect to a core of said natural circulation reactor;a power control apparatus adapted to output a power adjustment demand signal and a control rod drive command signal based on a reactor power detected by a reactor power detector configured to detect reactor power;a control rod drive control apparatus adapted to control said control rod drive apparatus based on said control rod drive command signal; anda pressure control apparatus adapted to control a pressure of said natural circulation reactor;wherein said pressure control apparatus is adapted to control a degree of opening of said second steam control valve installed in said inlet pipe based on said power adjustment demand signal, and is adapted to control a degree of opening of said first steam control valve installed in said main steam pipe jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe;whereby the steam is generated in said natural circulation reactor only by the natural circulation of the coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor. 2. The generation system according to claim 1, wherein any one of said pressure control apparatus and said power control apparatus is adapted to input a load following demand signal from a center feeding chamber. 3. The generation system according to claim 2, wherein said first steam control valve installed in said main steam pipe is installed in said main steam pipe upstream of said high-pressure turbine;wherein said inlet pipe has the one end connected to said main steam pipe upstream of said first steam control valve installed in said main steam pipe; andwherein said pressure control apparatus controls a degree of opening of said steam control valve installed in said main steam pipe jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe when said load following demand signal has a narrow range and a short period. 4. The generation system according to claim 1, wherein a turbine bypass pipe is connected to said main steam pipe upstream of said high-pressure turbine and to a condenser configured to receive steam exhausted from said low-pressure turbine;wherein a turbine bypass valve is installed in said turbine bypass pipe; andwherein said pressure control apparatus is adapted to control a degree of opening of said turbine bypass valve jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe. 5. The generation system according to claim 4, wherein said pressure control apparatus has a gate portion, and controls said turbine bypass control valve to open when said power adjustment demand signal is greater than a preset threshold, and controls said second steam control valve installed in said inlet pipe to close when said power adjustment demand signal is smaller than said preset threshold. 6. The generation system according to claim 1, wherein a turbine bypass pipe is connected to said main steam pipe upstream of said first steam control valve installed in said main steam pipe and to a condenser adapted to receive steam exhausted from said low-pressure turbine;wherein a turbine bypass valve is installed in said turbine bypass pipe; andwherein said pressure control apparatus is adapted to control a degree of opening of first said steam control valve installed in said main steam pipe and a degree of opening of said turbine bypass valve jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe. 7. The generation system according to claim 6, wherein said pressure control apparatus has a gate portion, and controls said turbine bypass control valve to open when said load following demand signal is greater than a preset threshold, and controls said second steam control valve installed in said inlet pipe to close when said load following demand signal is smaller than the preset threshold. 8. The generation system according to claim 1, wherein when a variation in the reactor power of said natural circulation reactor is transient, said pressure control apparatus is adapted to control the degree of the opening of said second steam control valve installed in said inlet pipe based on said power adjustment demand signal. 9. The generation system according to claim 1, wherein said power control apparatus inputs a reactor power equivalent signal from said pressure control apparatus, and controls a control rod drive apparatus that is connected with a control rod based on said reactor power equivalent signal. 10. The generation system according to claim 1, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet pipe in inverse relation to the degree of opening of said first steam control valve installed in said main steam pipe so as to provide the joint control and said first and second steam control valves. 11. The generation system according to claim 10, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet pipe so as to decrease the degree of opening of said second steam control valve installed in said inlet pipe while jointly controlling the degree of opening of said first steam control valve installed in said main steam pipe so as to increase the degree of opening of said first steam control valve installed in said main steam pipe so that the amount of steam supplied through said inlet pipe connected to said moisture separation heater is decreased and an amount of steam introduced into said high-pressure turbine through said steam control valve installed in said main steam pipe is increased. 12. The generation system according to claim 1, wherein said inlet pipe includes a portion providing a direct connection between said second steam control valve and said moisture separation heater. 13. A method for controlling reactor power of a natural circulation reactor adapted to generate steam only by naturally circulating coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor, and having a high-pressure turbine connected to said natural circulation reactor by a main steam pipe which introduces steam generated in said natural circulation reactor at least to said high-pressure turbine, said main steam pipe having one end connected to said natural circulation reactor and another end connected to said high-pressure turbine, a low-pressure turbine to which steam exhausted from said high-pressure turbine is supplied, a moisture separation heater installed between said high-pressure turbine and said low-pressure turbine for at least receiving steam exhausted from said high-pressure turbine, a first steam control valve installed in said main steam pipe upstream of said high-pressure turbine at a position between the one end of the main steam pipe connected to said natural circulation reactor and the another end of said main steam pipe connected to said high-pressure turbine, a reactor power control apparatus which controls reactor power of said natural circulation reactor, and a pressure control apparatus which controls reactor pressure in said natural circulation reactor, said moisture separation heater being connected to said main steam pipe upstream of said first steam control valve installed in said main steam pipe by an inlet steam pipe having a second steam control valve installed in said inlet steam pipe, said inlet steam pipe having one end connected to said main steam pipe and another end connected to said moisture separation heater, said second steam control valve being installed in said inlet steam pipe at a position between the one end of said inlet steam pipe connected to said main pipe and the another end of said inlet steam pipe connected to said moisture separation heater, the method comprising the steps of:controlling a degree of opening of said first steam control valve installed in said main steam pipe jointly in accordance with control of a degree of opening of said second steam control valve installed in said inlet steam pipe based on one of a load following demand signal and a power adjustment demand signal by said pressure control apparatus; andcontrolling a control rod drive apparatus, to which a control rod is connected by said power control apparatus in order to operate said control rod when a reactor power equivalent signal is input into said power control apparatus;whereby the steam is generated in said natural circulation reactor only by the natural circulation of the coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor. 14. The method according to claim 13, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet steam pipe in inverse relation to the degree of opening of said first steam control valve installed in said main steam pipe so as to provide the joint control of said first and second steam control valves. 15. The method according to claim 14, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet steam pipe so as to decrease the degree of opening of said second steam control valve while jointly controlling the degree of opening of said first steam control valve installed in said main steam pipe so as to increase the degree of opening of said first steam control valve so that the amount of steam supplied through said inlet steam pipe connected to said moisture separation heater is decreased and an amount of steam introduced into said high-pressure turbine through said first steam control valve installed in said main steam pipe is increased. 16. The method according to claim 13, wherein said inlet steam pipe includes a portion providing a direct connection between said second steam control valve and said moisture separation heater. 17. A method for controlling reactor power of a natural circulation reactor adapted to generate steam only by naturally circulating coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor, and having a high-pressure turbine connected to said natural circulation reactor by a main steam pipe adapted to at least introduce steam generated in said natural circulation reactor to said high-pressure turbine, a low-pressure turbine adapted to receive steam exhausted from said high-pressure turbine, a moisture separation heater installed between said high-pressure turbine and said low-pressure turbine adapted to at least receive steam exhausted from said high-pressure turbine, said main steam pipe having one end connected to said natural circulation reactor and another end connected to said high-pressure turbine, a first steam control valve being installed in said main steam pipe between the one end of said main steam pipe connected to said natural circulation reactor and the another end of said main steam pipe connected to said high-pressure turbine, an inlet pipe having a second steam control valve installed in said inlet pipe, said inlet pipe having one end connected to said main steam pipe at a position between the one end of said main steam pipe connected to said natural circulation reactor and said first steam control valve installed in said main steam pipe, said inlet pipe having another end connected to said moisture separation heater, said second steam control valve being installed in said inlet pipe at a position between the one end of said inlet pipe connected to said main steam pipe and the another end of said inlet pipe connected to said moisture separation heater, a control rod drive apparatus connected with a control rod adapted to be inserted and withdrawn with respect to a core of said natural circulation reactor, a power control apparatus adapted to output a power adjustment demand signal and a control rod drive command signal based on a reactor power detected by a reactor power detector adapted to detect reactor power, a control rod drive control apparatus adapted to control said control rod drive apparatus based on said control rod drive command signal, and a pressure control apparatus configured to control a pressure of said natural circulation reactor, the method comprising the steps of:controlling with said pressure control apparatus a degree of opening of said second steam control valve installed in said inlet pipe based on said power adjustment demand signal, and controlling a degree of opening of said first steam control valve installed in said main steam pipe jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe;whereby the steam is generated in said natural circulation reactor only by the natural circulation of the coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor. 18. The method according to claim 17, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet pipe in inverse relation to the degree of opening of said first steam control valve installed in said main steam pipe so as to provide the joint control of said first and second steam control valves, said inlet pipe including a portion providing a direct connection between said second steam control valve and said moisture separation heater. 19. The method according to claim 18, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet pipe so as to decrease the degree of opening of said second steam control valve installed in said inlet pipe while jointly controlling the degree of opening of said first steam control valve installed in said main steam pipe so as to increase the degree of opening of said first steam control valve installed in said main steam pipe so that the amount of steam supplied through said inlet pipe connected to said moisture separation heater is decreased and an amount of steam introduced into said high-pressure turbine through said first steam control valve installed in said main steam pipe is increased. 20. The method according to claim 17, wherein said inlet pipe includes a portion providing a direct connection between said second steam control valve and said moisture separation heater. |
|
054406005 | abstract | A stator core for an electromagnetic pump includes a plurality of circumferentially abutting tapered laminations extending radially outwardly from a centerline axis to collectively define a radially inner bore and a radially outer circumference. Each of the laminations includes radially inner and outer edges and has a thickness increasing from the inner edge toward the outer edge to provide a substantially continuous path adjacent the circumference. |
041644794 | summary | BACKGROUND OF THE INVENTION This invention relates to a method for suppressing halide volatility during the calcination of zirconium-fluoride nuclear reprocessing waste solutions. More particularly, this invention relates to an improvement in the present method of suppressing halide volatility of adding calcium nitrate to the solution prior to calcination. The chemical reprocessing of spent nuclear reactor fuel elements to recover the unburned nuclear reactor fuel material generates large volumes of aqueous solutions containing radioactive wastes. In addition to the large volumes produced, the aqueous waste solutions are extremely corrosive and present difficult problems in their handling and storage. Since it is necessary to store these radioactive wastes for long periods of time to permit decay of the radioactive constituents in the waste, the aqueous wastes are converted to a solid form which not only occupies less volume than the corresponding liquid wastes, but is less corrosive and easier to handle and store. One method by which these aqueous radioactive wastes are converted to solid form is by calcining in a fluidized bed in the Waste Calcining Facility at the Idaho Chemical Processing Plant located at the United States Department of Energy's Idaho National Engineering Laboratory in southeastern Idaho. The aqueous radioactive waste solutions are transported through pipelines from makeup vessels to the Waste Calcining Facility where the aqueous solutions are sprayed into the fluidized bed through spray nozzles mounted in the walls to be calcined into a solid for storage. The composition of nuclear reactor fuels varies depending upon the type of reactor for which the fuel is intended. So also do the waste solutions resulting from reprocessing the fuel vary in composition, each solution presenting unique problems with regard to waste disposal. For example, it is necessary to dissolve irradiated zirconium-containing fuels in hydrofluoric acid for reprocessing. The reprocessing of these fuels results in the formation of two different waste solutions for which disposal must be provided. The one solution referred to as the first-cycle zirconium fluoride waste contains in addition a trace amount of chloride in addition to aluminum and other elements and compounds. The other solution -- second cycle waste -- contains fluoride, chloride, sodium and aluminum along with other values and is a composite waste which also includes radioactive waste from processing other fuels, operation ICPP support facilities, plant floor drains, process equipment and non-ICPP facilities located at the Idaho National Engineering Laboratory. For purposes of disposal, the first cycle waste is calcined by itself or it may be mixed with second cycle waste at a ratio of 3 to 1 by volume to form a blend. This is done to facilitate disposal of second cycle waste which, because it contains sodium nitrate, presents special disposal problems. However, calcining releases the fluorides and chlorides present in the solutions as volatile corrosive gases which, because they are highly corrosive, are very detrimental to equipment and may be damaging to the environment should they be released. It is known that adding calcium nitrate to the waste solutions before calcining the solutions will suppress the volatility of the fluoride to acceptable levels which can then be removed from the calciner off-gas by scrubbing equipment. However, the addition of calcium nitrate to the waste has little suppressive effect upon the chloride which, although present in the waste solutions in only relatively small amounts builds up in the fluidized bed of the calciner over a long period of operation, so that the quantity, in time, becomes significant. The addition of calcium nitrate to the waste solutions also results in the formation of a gelatinous solid. This solid, which is a hydrated calcium fluorozirconate, clogs transfer piping and calciner spray nozzles and generally disrupts calciner operation by increasing down-time for cleanup. The substitution of magnesium nitrate for calcium nitrate has been tried, and although it eliminates the formation of gelatinous solids while maintaining fluoride volatility suppression at acceptable levels, it has insufficient effect upon chloride volatility. When magnesium nitrate is added to first cycle waste, a calcine is produced which is very soft and breaks easily into fines during fluidized bed operation, plugging and bridging calciner off-gas and transport systems. SUMMARY OF THE INVENTION It has been found that, by adding aluminum to the waste solutions to increase the aluminum to fluoride mole ratio, before adding the calcium nitrate to the solution, the before enumerated problems are substantially reduced or eliminated. The method of the invention therefore consists of adding aluminum to the zirconium-fluoride waste solution containing zirconium, fluoride and chloride prior to adding calcium nitrate, in an amount sufficient to establish an aluminum to fluoride mole ratio of at least 0.27, whereby the quantity of gelatinous solid formed by the subsequent addition of calcium nitrate to the solution is substantially reduced and the volatility of the chloride during calcination of the waste solution is suppressed. It is further the method of the invention of adding aluminum to a blend of 3 parts zirconium-fluoride waste and 1 part second cycle waste prior to adding calcium nitrate, in an amount sufficient to establish an aluminum to fluoride mole ratio of 0.32, thereby reducing gelatinous solids formation and chloride volatility during calcination of the blend. It is therefore one object of the invention to provide an improvement in the method for calcining aqueous nuclear fuel reprocessing waste solutions containing zirconium, fluoride and chloride. It is a further object of the invention to provide an improvement in the method for suppressing the volatility of fluoride and chloride during the calcination of zirconium-fluoride nuclear fuel reprocessing wastes containing zirconium, fluoride and chloride in which calcium nitrate is added to the solution before calcination. Finally, it is the object of the invention to provide an improved method for suppressing the volatility of fluoride and chloride during the calcination of the blend nuclear fuel reprocessing wastes consisting of zirconium fluoride wastes and second cycle wastes and containing zirconium, fluoride and chloride while reducing the amount of gelatinous solids formed in the wastes by the addition of calcium nitrate to the blend before calcination. |
claims | 1. A fuel bundle for a pressurized heavy water nuclear reactor, the fuel bundle comprising:fuel elements containing fissile content of 235U, wherein each of the fuel elements of the fuel bundle has a fissile content of 235U between about 0.9 wt % 235U and 5.0 wt % 235U, and wherein at least one of the fuel elements is a poisoned low-enriched uranium fuel element further including a neutron poison in a concentration greater than about 5.0 vol %;wherein the at least one poisoned low-enriched uranium fuel element includes a mix of low-enriched uranium and at least one of: natural uranium, recycled uranium, and depleted uranium to achieve a desired fissile content of 235U. 2. The fuel bundle of claim 1, wherein the fissile content of the at least one poisoned low-enriched uranium fuel element is at least about 3.0 wt % of 235U. 3. The fuel bundle of claim 2, wherein the fissile content of the at least one poisoned low-enriched uranium fuel element is between about 3.0 wt % of 235U and about 3.5 wt % of 235U. 4. The fuel bundle of claim 1, wherein the neutron poison concentration in the at least one poisoned low-enriched uranium fuel element is between about 5.0 vol % and about 8.0 vol %. 5. The fuel bundle of claim 4, wherein the fissile content of the at least one poisoned low-enriched uranium fuel element is about 3.21 wt % of 235U and the neutron poison concentration in the at least one low-enriched uranium fuel element is about 6.82 vol %, and wherein the neutron poison is dysprosium. 6. The fuel bundle of claim 1, wherein the at least one poisoned low-enriched uranium fuel element includes a central fuel element that extends along a fuel bundle axis and a first plurality of fuel elements immediately surrounding the central fuel element, and wherein the remaining fuel elements of the fuel bundle are non-poisoned fuel elements disposed radially outside the poisoned low-enriched uranium fuel elements. 7. The fuel bundle of claim 6, wherein each of the non-poisoned fuel elements has a fissile content of 235U not exceeding the fissile content of the poisoned low-enriched uranium fuel elements, and at least some of the non-poisoned fuel elements have a fissile content of 235U that is less than the fissile content of the poisoned low-enriched uranium. 8. The fuel bundle of claim 7, wherein the non-poisoned fuel elements are arranged to include a second plurality of fuel elements immediately surrounding the first plurality of fuel elements, and a third plurality of fuel elements immediately surrounding the second plurality of fuel elements, and wherein the fuel elements of the second plurality have a higher fissile content that the fuel elements of the third plurality. 9. The fuel bundle of claim 8, wherein the fuel elements of the second plurality have a fissile content between about 3.0 wt % and about 3.5 wt % of 235U, and the fuel elements of the third plurality have a fissile content less than about 2.0 wt % of 235U. 10. The fuel bundle of claim 9, wherein the fuel elements of the second plurality have a fissile content of about 3.18 wt % of 235U, and the fuel elements of the third plurality have a fissile content of about 1.73 wt % of 235U. 11. The fuel bundle of claim 1, wherein the at least one poisoned low-enriched uranium fuel element includes a fissile content of 235U between about 0.9 wt % 235U and 5.0 wt % 235U. 12. The fuel bundle of claim 1, wherein each one of the fuel elements includes at least one of slightly-enriched uranium and low-enriched uranium mixed with at least one of: natural uranium, recycled uranium, and depleted uranium to achieve a desired predetermined fissile content of 235U. 13. The fuel bundle of claim 1, wherein the fuel bundle includes 37 total fuel elements having substantially uniform size. 14. The fuel bundle of claim 1, wherein the fuel bundle includes 43 total fuel elements, and wherein the at least one poisoned low-enriched fuel element includes 8 enlarged fuel elements positioned at the center. 15. The fuel bundle of claim 1, wherein the neutron poison includes at least one burnable neutron poison. 16. The fuel bundle of claim 15, wherein the neutron poison includes dysprosium. 17. The fuel bundle of claim 15, wherein the neutron poison includes gadolinium. 18. The fuel bundle of claim 1, wherein the neutron poison is a non-burnable neutron poison. 19. A method of operating a pressurized heavy water nuclear reactor comprising:providing a first fuel bundle made up of a plurality of fuel elements each having a fissile content of 235U between about 0.9 wt % 235U and 5.0 wt % 235U, at least one of the fuel elements being a poisoned low-enriched uranium fuel element further including a neutron poison in a concentration greater than about 5.0 vol %, wherein the at least one poisoned low-enriched uranium fuel element includes a mix of low-enriched uranium and at least one of: natural uranium, recycled uranium, and depleted uranium to achieve a desired fissile content of 235U;inserting the first fuel bundle into a pressure tube of the pressurized heavy water nuclear reactor; andoperating the pressurized heavy water nuclear reactor to burn the fuel elements, producing a power output at least as great as a fuel bundle of natural uranium while providing a negative fuel temperature coefficient (FTC), a negative power coefficient (PC), and a coolant void reactivity (CVR) that is lower than that provided by operating the pressurized heavy water nuclear reactor with natural uranium fuel. 20. The method of claim 19, wherein the first fuel bundle is inserted to replace a fuel bundle of natural uranium. 21. The method of claim 19, further comprising filling the pressure tube with 12 fuel bundles similar to the first fuel bundle. 22. The method of claim 21, further comprising refueling the pressure tube during operation of the nuclear reactor with a 4-bundle-shift. 23. The method of claim 21, further comprising refueling the pressure tube during operation of the nuclear reactor with a 2-bundle-shift. 24. The method of claim 21, further comprising refueling the pressure tube during operation of the nuclear reactor with a mixed 2-and-4-bundle-shift. 25. The method of claim 21, further comprising refueling the pressure tube during operation of the nuclear reactor with a mixed 4-and-8-bundle-shift. 26. A fuel bundle for a nuclear reactor, the fuel bundle comprising:a fuel element including a mix of low-enriched uranium and at least one of: natural uranium, recycled uranium, and depleted uranium to achieve a desired fissile content, the fuel element containing at least one fissile material selected from the group consisting of 233U, 235U, 239Pu, and 241Pu, the at least one fissile material being mixed with gadolinium and dysprosium. 27. A fuel element for a nuclear reactor, the fuel element comprising:a mix of low-enriched uranium and at least one of: natural uranium, recycled uranium, and depleted uranium to achieve a desired fissile content; andat least one fissile material selected from the group consisting of 233U, 235U, 239Pu, and 241Pu, the at least one fissile material being mixed with gadolinium and dysprosium. 28. A fuel bundle for a nuclear reactor, the fuel bundle comprising:a plurality of fuel elements including inner elements and outer elements;wherein at least one of the inner elements includes a mixture of low enriched uranium and at least one of: natural uranium, recycled uranium, and depleted uranium to achieve a desired fissile content, a first neutron poison, and a second neutron poison different from the first neutron poison. |
|
062228978 | claims | 1. A method of inspecting piping and welds of a pipe elbow in a reactor pressure vessel of a boiling water reactor using a scan apparatus, the pipe elbow including a surface and the scan apparatus including a scan head having at least one transducer probe including an ultrasonic transducer, at least one transducer arm connected to the transducer probe, a scan platform having an arcuate cutout, a connector connecting the transducer arm to the scan platform, a pivot pin, a pivot arm connecting the scan head to the pivot pin, and a motor capable of moving the scan head axially along the pipe elbow, said method comprising the steps of: positioning the scan head and the transducer probe such that the ultrasonic transducer is substantially in contact with the pipe elbow surface; moving the scan head axially along the pipe elbow in a first direction from a first axial point to a second axial point by pivoting the scan head about the pivot pin while maintaining the ultrasonic transducer in substantial contact with the pipe elbow surface; moving the connector along the arcuate cut out in the scan platform to incrementally rotate the probes circumferentially around the pipe elbow; moving the scan head axially along the pipe elbow in a second direction from the second axial point to the first axial point by pivoting the scan head about the pivot pin while maintaining the ultrasonic transducer in substantial contact with the pipe elbow surface; and inspecting the piping and the welds in the pipe elbow to detect flaws. moving the transducer probes perpendicular to the weld of the piping; and inspecting the piping and the weld as the transducer probes move substantially perpendicular to the weld. moving the scan head axially along the pipe elbow in a first direction from a first axial point to a second axial point by pivoting the scan head about the pivot pin; incrementally rotating the probes circumferentially around the pipe elbow; moving the scan head axially along the pipe elbow in a second direction from the second axial point to the first axial point by pivoting the scan head about the pivot pin; and incrementally rotating the probes circumferentially around the pipe elbow. locating the scan apparatus at the pipe elbow; adjusting the scan head to allow at least a portion of the piping to enter the scan platform cutout; positioning the ultrasonic transducers substantially in contact with the pipe elbow; moving the scan head axially along the pipe elbow in a first direction from a first axial point to a second axial point by pivoting the scan head about the pivot pin while maintaining the ultrasonic transducers in substantial contact with the pipe elbow; incrementally rotating the probes circumferentially around the pipe elbow by moving the connector along the arcuate cut out in the scan platform; and moving the scan head axially along the pipe elbow in a second direction from the second axial point to the first axial point by pivoting the scan head about the pivot pin while maintaining the ultrasonic transducer in substantial contact with the pipe elbow surface. moving the scan head axially along the pipe elbow in a first direction from a first axial point to a second axial point on the piping by pivoting the scan head about the pivot pin; circumferentially incrementing the connector along the arcuate cutout to incrementally rotate the transducer probes and the transducer arms partially about a circumference of the piping; moving the scan head axially along the pipe elbow in a second direction from the second axial point to the first axial point on the piping by pivoting the scan head about the pivot pin; and circumferentially incrementing the connector along the arcuate cutout to incrementally rotate the transducer probes and the transducer arms partially about a circumference of the piping. positioning the scan head and the transducer probe such that the ultrasonic transducer is substantially in contact with the pipe elbow surface; utilizing the motor, moving the scan head axially along the pipe elbow in a first direction from a first axial point to a second axial point by pivoting the scan head about the pivot pin while maintaining the ultrasonic transducer in substantial contact with the pipe elbow surface; circumferentially incrementing the connector along the arcuate cutout to incrementally rotate the transducer probes and the transducer arms partially about a circumference of the piping; moving the scan head axially along the pipe elbow in a second direction from the second axial point to the first axial point by pivoting the scan head about the pivot pin while maintaining the ultrasonic transducer in substantial contact with the pipe elbow surface; circumferentially incrementing the connector along the arcuate cutout to incrementally rotate the transducer probes and the transducer arms partially about a circumference of the piping; and inspecting the piping and the welds in the pipe elbow to detect flaws. 2. A method in accordance with claim 1 wherein the at least one transducer probe includes two transducer probes and wherein said step of positioning the scan head and the ultrasonic transducer probe further comprises the step of positioning two transducer probes in contact with the surface of the pipe elbow approximately 180 degrees apart. 3. A method in accordance with claim 2 wherein the motor is connected to the pivot arm, and wherein the step of moving the scan head further comprises the step of pivoting the ultrasonic transducers, utilizing the motor, substantially about the pivot pin which allows the transducer probes to travel axially along the pipe elbow. 4. A method in accordance with claim 3 wherein the step of moving the scan head further comprises: 5. A method in accordance with claim 3 wherein the scan platform includes an arcuate cutout and wherein the step of moving the scan head further comprises moving the connector incrementally along the arcuate cutout to rotate the transducer probes and the transducer arms partially about a circumference of the piping. 6. A method in accordance with claim 1 wherein the step of moving the scan head further comprises the steps of: 7. A method in accordance with claim 6 further comprising repeating the method steps of claim 6 until the entire pipe elbow surface has been inspected. 8. A method in accordance with claim 3 wherein the step of moving the scan head further comprises pivoting the scan head up to about 90 degrees to accommodate a bend in the pipe elbow and to enable the scan head to access an upper side of the pipe elbow. 9. A method of positioning ultrasonic transducer probes to examine piping and welds of a pipe elbow in a reactor pressure vessel of a boiling water reactor using a scan apparatus, the scan apparatus including a motor connected to a scan head having at least two ultrasonic transducer probes each including an ultrasonic transducer, a transducer arm connected to each transducer probe, a scan platform having an arcuate cutout, a connector connecting each transducer arm to the scan platform, a pivot pin, and a pivot arm connecting the scan head to the pivot pin, said method comprising the steps of: 10. A method in accordance with claim 9 wherein the motor is connected to the pivot arm, and wherein the step of moving the scan head further comprises the step of pivoting the ultrasonic transducers, utilizing the motor, substantially about the pivot pin which allows the transducer probes to travel axially along the pipe elbow. 11. A method in accordance with claim 10 wherein the step of moving the scan head further comprises the steps of: 12. A method in accordance with claim 11 further comprising repeating the method steps of claim 11 until the entire pipe elbow surface has been inspected. 13. A method of inspecting piping and welds of a pipe elbow in a reactor pressure vessel of a boiling water reactor using a scan apparatus, the pipe elbow including a surface and the scan apparatus including a scan head having at least two transducer probes including an ultrasonic transducer, a transducer arm connected to each transducer probe, a scan platform having an arcuate cutout, a connector connecting each transducer arm to the scan platform, a pivot pin, a pivot arm connecting the scan head to the pivot pin and a motor coupled to the scan platform and the pivot arm, said method comprising the steps of: 14. A method in accordance with claim 13 further comprising repeating the method steps of claim 13 until the entire pipe elbow surface has been inspected. |
047864621 | claims | 1. In a nuclear reactor having a nuclear reactor vessel, a support structure comprising: (a) a basemat and an unitary reinforced concrete core having exterior walls and containing an open vertical void for placement of a nuclear reactor vessel, said void extending from the top of basemat to the top surface of the unitary reinforced concrete core, said concrete core providing structural support to the reactor vessel at the upper end of said reactor vessel and upper end of said core and said core providing shielding for radiation from the reactor vessel; (b) said reinforced concrete core having concrete ligaments in said unitary reinforced concrete core between said void and the edge of said concrete core, said ligaments extending from the top of said core to the basemat where said core is integrally connected to said basemat and said ligaments being large enough to assure that the deformation of support structure is shear controlled and (c) said unitary reinforced concrete core and basemat having a distribution of mass and stiffness which provides a fundamental horizontal natural frequency of vibration greater than 10 Hertz for said unitary concrete core and basemat and greater than the fundamental natural frequency of the supported reactor vessel. (a) a reinforced concrete basemat: (b) a unitary reinforced core; (c) said reinforced core containing a central vertical void for housing a nuclear reactor vessel said core having exterior walls; a plurality of vertical voids for satellite tanks that include heat exchanger means and pump means; and (d) at least two horizontal voids between the central vertical void in said central core and the voids for said satellite tanks, said horizontal voids connecting the central vertical void to vertical voids for satellite tanks that are sized to accomodate upper and lower liquid metal conduits between said nuclear reactor vessel and said satellite tanks; (e) said reinforced concrete core having concrete ligaments in said unitary reinforced concrete core between said vertical voids and the edge of said concrete core, said ligaments extending from the top of said core to said basemat where said core is integrally connected to said basemat and said ligaments being large enough to assure that deformation of the support structure is shear controlled, and (f) said reinforced concrete core and basemat having a distribution of mass and stiffness which provides a fundamental horizontal natural frequency greater than 10 Hertz and greater than the natural frequency of the supported components. 2. A support structure for a nuclear reactor as defined in claim 1 wherein said reinforced concrete core has a fundamental frequency of vibration sufficiently above 10 Hertz and above the major components fundamental natural frequencies so that seismic coupling effects do not result in significant amplification of ground level seismic forces to the supported components. 3. A support structure for a nuclear reactor as defined in claim 1 wherein the exterior walls of said unitary core are flat. 4. A support structure for a nuclear reactor as defined in claim 1 wherein the exterior walls of said unitary core are circular. 5. A support structure for a nuclear reactor as defined in claim 1 further comprising passages for heat removal means and inspection means. 6. A support structure for a nuclear reactor as defined in claim 5 which is made of prestressed concrete. 7. A support structure for a nuclear reactor as defined in claim 5 further comprising a plurality of openings in said core for permitting inspection access to said nuclear reactor and said heat removal means. 8. A support structure for a nuclear reactor as defined in claim 7 further comprises a plurality of exterior compartments adjacent to said unitary reinforced concrete core. 9. A support structure for a nuclear reactor as defined in claim 8 which further comprises an exterior compartment adjacent to said unitary reinforced concrete core which contains steam generation means that is connected to said heat removal means. 10. A support structure as defined in claim 1 further comprising a plurality of open vertical voids for placement of vessels other than the reactor vessel. 11. A support structure as defined in claim 1 further comprising a void for supporting a steam generator. 12. A support structure as defined in claim 1 further comprising a void for supporting a fuel storage cell. 13. In a nuclear reactor having a nuclear reactor vessel, means for exchanging heat, means for generating steam and means for pumping a coolant, a support structure comprising: 14. A support structure as defined in claim 13 further comprising of a void for supporting a steam generator. 15. A support structure as defined in claim 13 further comprising of a void for supporting a fuel storage vessel. 16. A support structure as defined in claim 11 further comprising at least one horizontal void. 17. A support structure as defined in claim 11 further comprising at least two horizontal voids. |
summary | ||
claims | 1. A module for forming a nuclear fuel assembly comprising:a casing extending in a longitudinal direction,a bundle of fuel rods encased in and supported by the casing anda connector provided on the casing for removably connecting the casing side-by-side to an other casing of at least one other module to obtain, when assembled, a nuclear fuel assembly having a channel box defined by the casing of the assembled module and the other casing of the at least one other module, the channel box being of a larger cross-section than that of the casing of each of the assembled modules and the other modules and a bundle of fuel rods of larger cross-section than that of each of the assembled modules and other modules, each module being movable as a single individual unit independent of the other modules. 2. The module according to claim 1 wherein the casing has a cross-section of polygonal shape with one bevelled corner for delimiting a space for a water channel between the casings of assembled modules. 3. The module according to claim 1 wherein the casing has a cross-section of a regular polygonal shape with the exception of one bevelled corner. 4. The module according to claim 2 wherein the bevelled corner is opened or is closed by a bevel wall of the casing. 5. The module according to claim 2 wherein the connector is provided on longitudinal edges of the casing edging the bevelled corner. 6. The module according to claim 2 wherein the connector comprises at least one sleeve aligned in the longitudinal direction with a missing edge of the polygonal cross-section of the casing. 7. The module according to claim 1 wherein the casing comprises at least one first side wall adapted to separate two sub-channels in the channel box defined by the casings of assembled modules. 8. The module according to claim 7 wherein each first side wall comprises at least one groove on an outer face of the first side wall. 9. The module according to claim 7 wherein each first side wall is adapted to define with first side walls of other modules assembled to the module a cross-shaped partition in the channel box defined by the casings of the assembled modules. 10. A nuclear fuel assembly comprising the module according to claim 1 assembled together side-by-side with the at least one other module. 11. The nuclear fuel assembly according to claim 10 comprising a water channel delimited by bevel walls of casings of the modules each closing a bevelled corner of a respective casing exhibiting a polygonal cross-section with the bevelled corner. 12. The nuclear fuel assembly according to claim 11 comprising the water channel delimited by a tube inserted in a spaced formed by the bevelled corners of the casings of the modules exhibiting a polygonal cross-section with the bevelled corner. 13. The nuclear fuel assembly according to claim 10 comprising a channel box defined by the casings of the assembled modules and a partition of cross-shaped cross-section dividing the channel box in sub-channels receiving a sub-bundle of fuel rods. 14. The nuclear fuel assembly according to claim 10 comprising an outer tubular housing having a section corresponding to that of the channel box defined by the modules assembled side-by-side. 15. The module as recited in claim 3 wherein the casing has a cross-section of the beveled corner and four other sides. |
|
045487839 | description | DESCRIPTION OF SPECIFIC EMBODIMENTS Referring to FIG. 1, there is shown a typical boiling water reactor 10 in which an apparatus according to this invention may be used. The boiling water reactor 10 comprises a pressure vessel 12 having a vessel head 14 here shown in an open position for maintenance. The vessel 12 has a steam outlet conduit 16, a feed water inlet conduit 18 and a recirculation loop 20. Nuclear fuel resides in a core 22 below steam separators 24 and steam dryers 26 within a shroud 28. Cooling fluid flows in a toroidal pattern about the core shroud impelled by jet pump assemblies 30 ringing the shroud at a radius between the shroud 28 and the vessel wall 32. The recirculation loop 20 comprises an outlet nozzle 34 coupled to an outlet conduit 36 which in turn is coupled to a first valve 38. The outlet of the first valve 38 is coupled to a recirculating pump 40 which in turn is coupled to a second valve 42 to an inlet conduit 44 which in turn is coupled to an inlet nozzle 46. The inlet nozzle 46 is coupled to a jet pump nozzle assembly 48 forming a portion of the jet pump assembly 30. According to the invention, an apparatus in the form of a plug assembly 50 is provided which can be lowered into the reactor vessel 12 and positioned to seal off the recirculation loop outlet nozzle 34. Referring now to FIGS. 2 and 3 in connection with FIG. 1, the plug assembly 50 is illustrated in its collapsed position (FIG. 2) and extended position (FIGS. 1 and 3). The plug assembly 50 is suspended by two cables 52, 54 from an elevated location through the open vessel 12. The plug assembly 50 is completely removable from the reactor vessel 12 when not needed. Turning to FIG. 2, the plug assembly 50 includes a plug member 56 having frusto-conical shape to provide a tapered outer or male face generally conforming with a countersunk or beveled inner seat 60 of the nozzle 34, a jack 62 at one end attached to the plug member 56 and at the other end attached to a jack pad 64, and a hydraulic piston 66 for extending and retracting the jack 62. The hydraulic piston 66 may be a two-way retractable and extendable device normally pivotally mounted at one end in a cavity 68 on the back of the plug member 56 and at the other end pivotally mounted to an arm 70 of a scissor assembly forming the jack 62. The plug assembly 50 may be maneuvered by the two cables 52, 54 into a position facing the nozzle 34 between the outer wall 32 of the pressure vessel 12 and the jet pump assemblies 30. In an extended position, the plug member 56 of the plug assembly 50 abuts to the seat 60 of the nozzle 34 and is held in place by the jack pad 64 pressing against the core shroud 28. Since a scissor type jack has a relatively low retracted length for a given extended length (as compared, for example, to a hydraulic type of jack), the scissor portion of jack 62 easily fits through the narrow space between the jet pump assemblies 30, and the jack pad 64 is sufficiently narrow to also fit through the space between adjacent jet pump assemblies 30. The seat 60 of the nozzle 34 has a surface whose roughness is generally unknown. It may be irregular due to corrosion, for example. Means must be provided to assure a reliable seal between the seat 60 and the face 58 of the plug member 56. To this end, gasket means comprising first and second O-rings 72, 74 are provided concentrically around the face 58. The O-rings 72, 74 are highly compliant in order to adapt to the abutting surface of the seat 60. Specifically, the O-rings 72, 74 are remotely inflatable. In a collapsed, noninflated condition (FIG. 2) the O-rings 72, 74 are retained in parallel grooves in the face 58 of the plug portion 56. In the inflated condition (FIG. 3), the O-rings 72, 74 expand and seal against the seat 60. Two rings are disposed adjacent the margins of the face 58 to assure that the seal will be adequate in the event of a mismatch in the taper of the face 58 and seat 60 or in the event of irregularities such as a seam or cavity in the seat 60. The plug assembly 50 is remotely controllable through a hydraulic control panel 76 (FIG. 2) external to the reactor vessel 12. The control panel 76 is coupled to hydraulic lines 78 through which pressure is communicated to inflate and deflate the O-rings 72, 74 and to extend and retract the jack 62. The plug assembly 50 is preferably buoyant in the cooling fluid, so that it may be more easily handled. To this end, the plug portion 56 may have a hollow chamber 79 to increase displacement of the plug assembly 50 without increasing weight. The chamber 79 may be filled with closed-cell, rigid polyurethane foam arranged in two locations on either side of the cavity 68 into which the jack 62 retracts. The chamber 79 contributes to proper balance of the plug in both the retracted and extended positions, and it minimizes the weight relative to displacement. In the hydraulic system, the working fluid is preferably demineralized water, although other working fluids may be used. An air-driven hydraulic pump is the power source for the hydraulic system. It may be housed in the control console 76 to which is attached a pneumatic source. In operation, the plug assembly 50 is lowered into position confronting the nozzle 34, the jack 62 is extended to press the plug portion 56 in facing abutment to the seat 60, and then the O-rings 72, 74 are inflated to seal the seat 60. The recirculation loop 20 can then be drained through an outlet conduit 36 (FIG. 1) connected to the outlet nozzle 34. When the fluid is drained from the recirculation loop, the static pressure of fluid in the reactor vessel 12 helps to hold the plug member 56 in place against the countersunk seat 60 thereby assuring a secure seal. The first valve 38 may then be removed and serviced in the recirculation loop 20 without loss of fluid in the reactor vessel. The invention has now been explained with reference to the specific embodiments. Other embodiments will be apparent to those of ordinary skill in the art. It is therefore not intended that this invention be limited except as indicated by the appended claims. |
description | The present application is a continuation of International Patent Application No. PCT/EP2003/008413, filed Jul. 30, 2003, which claims priority of German Patent Application No. 102 39 732.5, filed Aug. 26, 2002, the content of which is herein incorporated by reference. 1. Field of the Invention The invention relates to an attenuator for attenuating wavelengths unequal to a used wavelength. The used wavelength is preferably a wavelength in the wavelength region of ≦100 nm, and especially preferably in the wavelength region which can be used for EUV lithography, i.e. in the region of 11 to 14 nm, especially 13.5 nm. 2. Description of the Related Art In order to enable a further reduction in the structural widths of electronic components, and in particular in the submicron range, it is necessary to reduce the wavelengths of the light used for microlithography. It is possible to use light with wavelengths of less than 100 nm, e.g. lithography with soft X-rays, i.e. the so-called EUV lithography. EUV lithography is one of the most promising future lithographic techniques. Currently, wavelengths in the region of 11 to 14 nm, and in particular 13.5 nm, at a numeric aperture of 0.2 to 0.3 are discussed as wavelengths for lithography. The image quality in EUV lithography is determined on the one hand by the projection lens and on the other hand by the illumination system. The illumination system should provide a uniform illumination of the field plane as far as possible in which the structure-bearing mask (i.e. the so-called reticle) is disposed. The projection lens images the field plane in a image plane (the so-called focal or wafer plane) in which a light-sensitive lens is disposed. Projection exposure systems for EUV lithography are equipped with reflective optical elements. The form of the field in the focal plane of an EUV projection exposure system is typically that of a ring field with a high aspect ratio of 2 mm (width)×22 to 26 mm (arc length). The projection systems are usually operated in scanning mode. Reference is hereby made to the following publications concerning EUV projection exposure systems: W. Ulrich, S. Beiersdörfer, H. J. Mann, “Trends in Optical Design of Projection Lenses for UV and EUV-Lithography” in Soft-X-Ray and EUV Imaging Systems, W. M. Kaiser, R. H. Stulen (Publishers), Proceedings of SPIE, Vol. 4146 (2000), p. 13-24 and M. Antoni, W. Singer, J. Schultz, J. Wangler, I. Escudero-Sanz, B. Kruizinga, “Illiumination Optics Design for EUV-Lithography” in Soft X Ray and and EUV Imaging Systems, W. M. Kaiser, R. H. Stulen (Publishers), Proceedings of SPIE, Vol. 4146 (2000), p. 25-34 whose scope of disclosure is hereby fully included in the present application. In the case of illumination systems for wavelengths ≦100 nm there is the problem that the light source of such illumination systems emits radiation which can lead to an undesired exposure of the light-sensitive object in the wafer plane of the projection exposure system and moreover the optical components of the exposure system such as the multi-layer mirrors are heated thereby. In EUV systems at wavelengths of 13.5 nm for example multi-layer mirrors are used which perform a spectral filtering in the region about the EUV wavelengths, but reflect the incident radiation again with higher reflectivities from 130 nm for example. The radiation in the DUV wavelength region in particular, i.e. wavelengths in the region of 130 nm-330 nm, leads to such exposures of the light-sensitive object in the wafer plane. Radiation in the close UV region, in the visible or infrared region, i.e. wavelengths above 330 nm, lead to a heating of the mirrors. For filtering out or attenuating this undesired radiation transmission filters made of zirconium for example are used in illumination systems for wavelengths ≦100 nm. Such filters or attenuators have the disadvantage of high losses of light. Moreover, they can easily be destroyed by heat loads. As an alternative, it is possible to provide the filtering with grating elements according to the concept of conventional spectral filtering. In such a method, the grating period of the grating element is chosen in such a way that the radiation of the used wavelength is diffracted in the first order. With the help of a diaphragm downstream of the grating element in the beam path it is then possible to filter out especially the light of the 0th diffraction order which comprises a considerable amount of radiation with wavelengths which do not correspond to the used wavelength by blocking radiation of the 0th diffraction order. The radiation of the used wavelength of 13.5 nm for example is then diffracted substantially completely in the 1st order and allowed to pass completely to the following illumination system by the diaphragm downstream in the beam path. The advantage of such a spectral filter is that is at least a theoretical possibility to completely surpress or block undesirable wavelengths. As a result of such an arrangement it is possible to block substantially complete the undesired DUV radiation which designates radiation in the wavelength region of 130 nm to 330 nm. Such a filter element in an EUV illumination system is shown in EP-A-1 202 291 and copending U.S. patent application US 2002/0186811 A1, whose scope of disclosure is hereby fully included in the present application. The grating elements which are described in EP-A-1 202 291 and copending U.S. patent application Ser. No. 2002/0186811 A1 particularly provided as echelle gratings have the disadvantage that they show a total efficiency of less than 60% and place high demands on the production of the grating. As a result, the grating must have an optical functionality, for example must have optical power, so that the formation of the 1st diffraction order can occur to a certain extent in an aberration-free way at the used wavelength. The behaviour in diffraction gratings as are known from EP-A-1 202 291 and copending U.S. patent application US 2002/0186811 A1 are described by the grating equation n λ p = sin α i - sin β ( 1 ) with the grating period p, the diffraction order n, the angle of incidence al relating to the surface normal of the grating, the angle β of the diffraction ray relating to the surface normal of the grating and the wavelength λ. The grating element as described in EP-A-1 202 291 and copending U.S. patent application US 2002/0186811 Al are suitable in an illumination system for wavelengths ≦200 nm for spectral filtering in the case that the individual diffraction orders and the wavelengths are clearly separated from each other. This is achieved by a sufficiently large diffraction angle between the 0th order and a 1st order, e.g. with a diffraction angle γ=β−αi>2°. The diffraction at a wavelength of 13.5 nm for example by a larger diffraction angle γ of γ>2° for example is achieved in such a way that the grating grooves are aligned virtually perpendicular to the plane of incidence of the radiation and the grating is used under grazing incidence, i.e. the angle of incidence ax is larger than 70° relative to the surface normal of the surface. Grating periods of 500 l/mm to 1000 l/mm are thus sufficient for example. The plane of incidence is defined as the plane which is defined by the incidence vector and the normal vector of the grating surface where the incident beam pierces the grating surface. The grating vector which is situated perpendicular to the grating grooves in the tangential plane at the grating surface therefore nearly lies in the plane of incidence. If the grating vector is situated in the plane of incidence, the vector equation of the grating diffraction can be reduced to the above equation (1). A disadvantage of the known spectral filters or attenuators is that in the case of thin films they can be destroyed by the thermal load and show only a very low efficiency in transmission. If gratings as described in EP-A-1 202 291 are used as filters or attenuators, it is possible that the DUV radiation can be blocked in particular. There is a disadvantage however that there is a very low efficiency in the region of EUV wavelengths. The maximum achievable efficiency of such gratings in the region of EUV wavelengths is only 35% to 50%. It is thus the object of the present invention to overcome the disadvantages of the state of the art and to provide an attenuator or spectral filter in particular which can suppress the undesirable radiation, but which shows a substantially higher efficiency than previously known solutions in order to enable lower power requirements for the employed light source. This object is solved in accordance with the invention in that an attenuator is provided which comprises at least one grating element, with the grating comprising grating grooves producing at least one grating periodicity and the grating periodicity being much larger than the used wavelength, i.e. in the case of EUV radiation very much larger than the used wavelength of 13.5 nm. The inventors have recognized surprisingly that in order to avoid damage to the optical components, and the mirrors in particular, and in order to avoid undesirable exposure to the light-sensitive substrate by wrong wavelengths in the DUV region for example, it is not necessary to completely suppress undesirable wavelengths in the region of DUV radiation and/or infrared radiation, but that it is sufficient to attenuate this radiation in relationship to the radiation of the used wavelength. Depending on the spectral characteristics of the light source, an attenuation of certain wavelength regions by 20% relative to the used wavelength can be sufficient for example. The filtering or attenuation of the undesirable wavelengths in the DUV or IR region with the attenuator in accordance with the invention is achieved in such a way that the 0th diffraction order is used instead of in a 1st diffraction order for example of a grating element as disclosed in EP-A-1 202 291 in an illumination system in which an attenuator in accordance with the invention is used and the undesirable long-wave radiation is diffracted away to orders other than the 0th order due to the grating period of the grating element which is much larger than the wavelength of the used light. If a diaphragm with a diameter of slightly larger than the 0th diffraction order is attached near the 0th order, all higher diffraction orders which contain radiation with longer wavelengths can be blocked. Preferably, the attenuator in accordance with the invention is used in an illumination system, e.g. a EUV illumination system, with a used wavelength of 13.5 nm for example. The diaphragm around the 0th order is disposed in such an illumination system preferably in a beam focus, for example in a first image of the source. It is also possible to deflect the undesired radiation in the illumination system in such a way that the higher diffraction orders come to lie next to the field to be illuminated. The undesired radiation can be blocked in such a case by a field diaphragm. A field diaphragm consists of one or several diaphragms in or close to the field plane which only allow the radiation to pass to the illuminated field. The edge of the mirror per se can act as a diaphragm that blocks undesired radiation because the edge of the mirror can preferably be designed in such a way as is required for a complete illumination of the field to be illuminated. Due to the fact that the undesired long-wave radiation can be diffracted away at least partially into diffraction orders other than the 0th diffraction order, radiation in the DUV and/or infrared region can be attenuated substantially in an illumination system by blocking the diffracted radiation by means of a diaphragm for example. Preferably, the grating periodicity of the grating in accordance with the invention is more than 150 times the used wavelength, especially preferably more than 200 times the used wavelength. Moreover, the attenuator in accordance with the invention can be operated both under grazing incidence as well as under normal incidence. In this application grazing incidence is understood in such a way that the rays of a beam bundle which impinges on the grating have an incidence angle αi>70° relative to the normal of the surface of the grating. In the case of grazing incidence the grating vector of a grating preferably stands virtually perpendicular to the incidence plane of the grating, with the incidence plane being defined by the incident ray and the normal of the surface. Normal incidence is understood in such a way that the rays of a beam bundle which impinges on the grating have an incidence angle αi<30° relative to the normal of the surface of the grating. The diffraction angle γ=β−αi can be calculated in an approximate manner by equation (2) both in the case of gratings whose grating vector lies virtually perpendicular to the incidence plane as well as when using gratings under virtually perpendicular incidence, i.e. incidence angles of αi<30° relative to the normal of the surface and at small diffraction angles: sin ( γ ) ≈ λ p ( 2 ) Equation (2) is for grazing incidence an approximation because one is situated in the zone of the so-called conical diffraction for a grating with a grating vector which stands perpendicular to the incidence plane, which means that the grating grooves are oriented parallel to the incident ray. The diffraction orders then lie on a conical surface. Since the used light is not diffracted away in the attenuator or grating element in accordance with the invention but uses the same in the 0th order, the grating element does not have any optical effect on the used wavelength. This is because in the 0th order of the grating element the optical properties of the carrier surface to which the grating element is applied do not change substantially. As a result, the grating can be applied without any disadvantages to a curved surface. As a result of the low-frequency grating of the attenuator in accordance with the invention, the used wavelength is deflected according to equation (2) at a period p of approx. 4 μm into the +/−1st order by only γ(13.5 nm)≈0.2° with respect to γ(130 nm)≈2° for the disturbing wavelength of 130 nm. In a further example the deflection occurs into the 1st order for example only by approx. 0.2 mrad at 13.5 nm, but by approx. 2 mrad at 130 nm. As a result of the ray that is diffracted away in the first example by approx. 2° or in the second example by 2mrad into the +/−1st order, it is possible, by introducing a diaphragm in the path of rays downstream of the attenuator for example, to attenuate the undesirable radiation at 130nm in an illumination system for example. The operation of an attenuator with at least one grating element in the 0th diffraction order for the used wavelength further has advantages in production. For example it is therefore irrelevant whether the grating is made from one piece or is made in segments. Moreover, the grating can comprise conically tapered grating grooves in the case that the grating is used in a converging path of rays of an illumination system. This arrangement can be chosen optionally and has an influence merely on the position and blurring of the diffraction orders in which the disturbing light is diffracted. This is virtually without any relevance whatsoever for the light in the 0th diffraction order which also contains the light for the used wavelength. The grating element in accordance with the invention is thus very insensitive to production faults. The grating in accordance with the invention is especially preferably designed as a so-called binary grating which has only two different heights, e.g. a first height H1=0 relating to the local coordinate system and a second height H2=h. The zones of different height can be chosen equally wide for example and thus half as wide as the grating period p. The ratio of the two widths of the differently high zones is also known as aspect ratio. In the case of binary gratings with equally wide structures of different height there is thus an aspect ratio of 1. It is also possible to choose the widths differently, so that the period is obtained in the sum total of the widths of the two differently high zones with the heights H1 and H2. The diffraction efficiency can be influenced in the different diffraction orders through the variation of the structural widths, i.e. the aspect ratio. One advantage of binary gratings is the edge steepness. Due to the steepness of the edges, the shadings are low in a binary grating when it has a periodicity perpendicular to the incidence plane. Perpendicular to the incidence plane means in this case that the grating vector stands virtually perpendicular to the incidence plane. As a result of this arrangement of the grating grooves parallel in the direction of the incident ray, i.e. in the incidence plane, it is possible to achieve especially under grazing incidence at relatively high grating structures that the shadings and thus the light loss for the used wavelength is low. The grating is then substantially invisible for the used wavelength. The diffraction efficiency of such a binary grating element will attain a maximum when the following applies for the depth of the grating: h n λ = ( 2 n + 1 2 ) · λ 2 cos α i n = 0 , 1 , 2 , 3 … ( 3 ) with hλn being the grating depth for maximum diffraction efficiency at wavelength λ and the incidence angle αi relating to the normal of the surface and n an integer number. If in a preferred embodiment the grating element is designed as a binary grating with only two heights, namely a first height and a second height, the diffracted light distributes substantially between 0th and +/−1st diffraction order. If h=hλ1n according to equation (3), approx. 80% of the light is diffracted into the the+/−1st diffraction order for wavelength λ1, e.g. λ1=130 nm. Accordingly, only an amount of light intensity of this wavelength λ1 of less than 20% remains in the 0th diffraction order. In order to consider the relative attenuation with respect to the EUV radiation, it is necessary to consider the reflectivity of the attenuator for the EUV radiation at 13.5 nm for example. Under grazing incidence for example at an incidence angle αi of 76° relative to the normal of the surface with a ruthenium coating, reflectivities of over 80% are achieved, i.e. the desired EUV radiation is also attenuated by 20%. If this is taken into account, it is possible to achieve for the wavelength λ1 an attenuation by 80% (DUV, i.e. 130 nm) to 20% (at EVU, i.e. 13.5 nm), i.e. of 75% relative to the λ=13.5 nm. Through equation (3) the depth of the grating can be chosen in such a way that certain wavelengths are substantially diffracted out of the beam. Advantageously the depth hn is chosen in such a way that in the 0th order undesirable DUV and IR wavelengths are diffracted into the the +/−1st order. It is understood that the condition (3) will possibly also be fulfilled for the used wavelength λ=13.5 nm. However, the diffraction angle is very low at 13.5 nm in higher orders, e.g. the ±1st order for a grating which is constructed to be efficient and thus diffracts light with wavelengths in the DUV region. Such a grating comprises a periodicity p=4 μm and a grating depth of 210 nm for example. For such gratings light of the used wavelength of 13.5 nm which is diffracted into the the ±1st order comes to lie so close to the 0th order that this has an effect merely as a slight blurring of the 0th order. On the other hand, the grating with the depth hn has another effect at another wavelength and at depths h m ′ = m · λ 2 cos α i m = 0 , 1 , 2 , 3 … ( 4 ) there is virtually no diffraction any more, i.e. the entire light with wavelengths which fulfill this condition cannot be diffracted into another diffraction order and moves to the 0th diffraction order and thus to the specular reflex. Generally, the diffraction efficiency η can be expressed by a simple formula depending on the depth of a binary grating and the wavelength: η ( h , λ ) = c m · sin 2 ( 2 π λ h cos α i ) ( 5 ) with h being the depth of the grating and cm the maximum diffraction efficiency in the desired diffraction order, i.e. approx. c−1≈40% for the−1st diffraction order and c1≈40% for the+1st diffraction order, in total for both diffraction orders approx. c−1+c1≈2c1≈80%. The diffraction efficiency can be dependent on the material properties and additionally depend on the wavelength or the reflectivity of the used grating material at the respective wavelengths. As will become clear from the above discussion, the grating element in accordance with the invention can be used to diffract various wavelengths only to certain amount out of the 0th order. On the average only approx. 50% of the maximum diffraction efficiency 2c1 can be reached over a specific spectral region, i.e. approx. only 40% of the disturbing radiation can be filtered out. Through a proper choice of the depth it is possible to achieve an optimal suppression of especially strongly occurring disturbing wavelengths. As shown above, the attenuator in accordance with the invention can filter out at most 80% of the intensity of a undesirable DUV radiation at certain wavelengths. At other wavelengths the grating does not work for example. The grating is therefore preferably designed in such a way that in the DUV region several strongly occurring and disturbing wavelengths are filtered out virtually completely. In order to achieve this, the grating depth h is provided in an advantageous embodiment in such a way that the condition (3) is fulfilled for the highest possible number of wavelengths. In a further, particularly advantageous embodiment the grating depth h is chosen in such a way that the mean diffraction efficiency assumes a maximum in the desired spectral region. On the average over all DUV wavelengths it is possible to achieve a mean diffraction efficiency of approx. 40% and thus an attenuation of this undesirable radiation by the same amount. On the other hand, the reflectivity for the used wavelength of e.g. λ=13.5 nm is approx. 80% when in a preferred embodiment a ruthenium coating is used and the grating is used under grazing incidence, i.e. the rays of the beam bundle impinge under an angle of <20° relative to the surface tangent or an angle of αi>70° relative to the normal of the surface. With such a grating element as an attenuator it is possible to reduce the amount of undesired DUV-wavelengths by 25% for example. In a particularly advantageous embodiment a mean diffraction efficiency of approx. 68% is achieved by a optimisation of the depth to approx. 210 nm at an angle of incidence of 76° relative to the normal of the surface for wavelengths of the DUV spectral region of 130 nm to 330 nm. This corresponds to an attenuation of the amount of undesired radiation in the DUV-wavelengths-region by 60%. Since the diffraction efficiency is substantially independent of the grating period, this applies to several grating periods and can be used in an analogous way for attenuator in accordance with the invention which are used under normal incidence angles. Such modifications are obvious to a person skilled in the art. In order to achieve a even higher suppression of radiation in the DUV-wavelengths-region, the principle of the invention can be used several times successively in a preferred embodiment, e.g. under multiple reflection under grazing incidence or even on normal incidence mirrors, which are mirrors on which the rays of the beam or rays impinge under an angle of of αi>20° relative to the surface tangent or of <70° relative to the normal of the surface. Preferably, the grating grooves are designed in a conical way (i.e. in a tapered manner) in the converging path of the rays and under grazing incidence. At small aperture angles this is not mandatorily required. The complete grating can also be designed as a single large binary grating with the same period if smaller shadings are acceptable. Instead of grating grooves that taper, the grating can also be realized by individual segments which are oriented in a respective fashion with respect to the local angle of incidence of the converging beam bundle. The grating periods of the individual segments can differ in addition. In a converging path of rays the angle of incidence a, changes over the grating. As a result, the wavelength also changes via the grating for which equation (1) achieves the highest diffraction efficiency. In an especially advantageous embodiment, the grating depth can also vary over the grating instead of individual grating elements with different grating depths which are arranged several times behind one another, e.g. by segmentation or by a production method with which the course can be set. FIG. 1 shows an EUV projection exposure system with a grating element in accordance with the invention. The EUV projection exposure system comprises a light source 1, a focusing optical component, a so-called collector 3 which is arranged as a nested collector according to German patent application DE 101 38 313 A1 and the copending U.S. patent application Ser. No. 2003-0043455 A1 as filed on Jan. 23, 2002 with the United States Patent Office for the applicant, the scope of disclosure of which is hereby fully included in the present application. The collector 3 projects the light source 1 situated in the object plane of the illumination system to a picture of the light source 5 or a so called secondary light source in or close to a diaphragm plane 7. In the present case, the light source 1, which can be either a laser-plasma source or a plasma-discharge source, is situated in the object plane 2 of the illumination system. The picture of the primary light source 1 comes to lie in or close to the diaphragm plane 7 of the illumination system 10. The picture of the primary light source is also designated as secondary light source 5. An additional diaphragm 24 is arranged between the attenuator 20 in accordance with the invention with at least one grating element and the physical diaphragm 22 in the diaphragm plane 7. In accordance with the invention, the focus of the 0th order comes to lie in the plane 7 of the diaphragm 22, i.e. the light source is projected by the collector and the attenuator in the 0th diffraction order in a virtually stigmatic way to the plane of the diaphragm and leads to the secondary light source 5 there. All other diffraction orders such as +1st or −1st diffraction order are blocked by the diaphragms 22 and 24 for light of longer wavelength, e.g. light or radiation of longer wavelengths. Due to the low deflection angle of the used radiation in higher diffraction orders, e.g. in the ±1st diffraction order, this light is generally not blocked by the diaphragm. Instead, a blurring of light of the used wavelength occurs close to the 0th diffraction order. The deflection to other diffraction orders is not shown in FIG. 1. In this respect, reference is made to FIG. 3. The illumination system of the projection system further comprises an optical system 50 for shaping and illuminating the field plane 100 with a ring-shaped field, as described in the U.S. Pat. No. 6,438,199 B1, whose scope of disclosure is hereby fully included in the present application. The local x,y,z coordinate system is depicted in the field plane 100. The optical system 50 comprises two faceted mirrors, which are in refractive systems also called fly eye's lenses, 54, 56 as a mixing unit 52 for the homogeneous illumination of the field in the field plane 100. Furthermore the illumination system comprises a projection lens 58 with two projecting mirrors 62, 64 in addition to the mixing unit 52 and a field-forming grazing-incidence mirror 70. Additional diaphragms 82, 84, 86, 88 for suppressing spill light are arranged in the optical system. The first faceted mirror 54, the so-called field facet mirror, produces a plurality of secondary light sources in or close to the second faceted mirror 56, the so-called pupil facet mirror. The following projection lens 58 projects the pupil facet mirror to the exit pupil of the illumination system which comes to lie in the entrance pupil 200 of the projection lens 202. The entrance pupil of the projection lens 200 is given by the point of intersection of the main beam CR with the optical axis HA of the projection lens 202. The angle of inclination of the individual facets of the first facet mirror 54 and the second facet mirror 56 are designed in such a way that the images of the individual field facets of the first facet mirror substantially overlap in the field plane 100 of the illumination system and thus a substantially homogenized illumination of the structure-bearing mask which comes to lie in this field plane is enabled. The segment of the ring field is formed via the field-forming grazing-incidence mirror 70 which is operated under the grazing incidence. The structure-bearing mask which is disposed in the field plane 100 and is also designated as reticle is projected by a projection lens 202 into the image plane 204 of the field plane 100. The projection lens is a six-mirror projection lens as filed with the U.S. application Ser. No. 60/255214 on 13 Dec. 2000 with the US Patent Office on behalf of the applicant or as disclosed in U.S. Pat. No. 6,353,470, the scope of disclosure of which is hereby fully included in the present application. The object to be exposed such as a wafer is disposed in the image plane 204 of the projection lens. FIG. 2 shows a sectional view in the x-z direction through an attenuator in accordance with the invention with at least one grating element. A three-dimensional schematic view of such an attenuator is shown in FIG. 3. The sectional view is perpendicular to the direction of incidence of the rays of a beam bundle impinging on the grating element. The periodic height profile H(z) of the grating element is shown. The attenuator in accordance with the invention comprises a binary grating element as a grating element which comprises a first height H1 and a second height H2. The difference between the first height H1=0 and the second height H2=H is the groove depth. In the present case the groove depth is h=H−0=H as shown in FIG. 3. The periodicity of the grating element arising from the course of the height in the x direction is designated with p. The width of the structure with height H1=0 being designated with b1 and the width of the structure with height H2=H with b2. The period is obtained from the sum total of b1+b2=p. In the present illustrated case b1=b2. Then the aspect ratio is b1/b2=1. Other aspect ratios are also possible. If for example the light in the DUV wavelength region of 130 nm is to be diffracted by γ=2° in a +1st or −1st order, one requires a grating period p of approx. 3.7 μm. EUV radiation which is also diffracted by such a grating into higher orders, e. g. into the ±1st order is diffracted by only and therefore 0.2° —as explained above—only leads to a slight blurring of the secondary light source 5 in the plane 7. FIG. 3 shows an attenuator in accordance with the invention in a three-dimensional representation. The local x, y, z coordinate system is also shown. The grating grooves are oriented in the y direction, i.e. parallel to the direction of the impinging rays of a beam bundle. The grating vector 308 which is situated in the tangential plane to the grating stands perpendicular to the grating grooves and therefore faces in the x direction. From the plurality of rays of a beam bundle impinging the grating a representative beam 300, e.g. the principle or the chief ray of a beam bundle is shown which impinges upon the grating surface. The ray 300 impinges on the grating element under an incidence angle αi relative to the normal line of the surface 302. The incidence angle αi is larger than 70°. The normal line 302 of the surface coincides with the z direction. The impinging ray 300 and the normal line 302 define the local incidence plane which in the present case coincides with the y-z plane. The ray of the beam bundle deflected into the 0th order is designated with 302, the rays diffracted into the +1st and −1st order with 304 and 306. When using such a grating in which the grating vector stands perpendicularly to the incidence plane, the diffracted rays do not lie in the incidence plane. Merely the 0th order which corresponds to the reflected ray comes to lie in the incidence plane. The other diffraction orders are deflected in the direction towards the grating vector and in the height. In this case one speaks of conical grating diffraction. FIG. 4 shows the shape of the diffraction efficiency η(h,λ) for one of the two 1st diffraction orders according to equation (5) over the wavelength λ for four different grating depths of 135 nm, 210 nm, 340 nm and 500 nm at an incidence angle of αi=76°. Binary gratings are assumed. The following reference numerals are used: for a grating depth of 135 nm reference numeral 350, for a grating depth of 210 nm reference numeral 352, for a grating depth of 340 nm reference numeral 354, for a grating depth of 500 nm reference numeral 356. At a low grating depth of h=210 nm (curve 352) for example only one diffraction maximum is situated at approx. λ≈200 nm in the DUV spectral region. If a larger grating depth of h=340 nm (curve 354) for example is chosen, the maximum diffraction efficiency is achieved according to equation (5) for the wavelengths λ≈110 nm and λ≈330 nm. For the wavelength λ≈330 nm and a number of shorter wavelengths, e.g. a third of said wavelength at λ≈110 nm, a maximum diffraction efficiency of approx.≈40% is achieved in the two 1st diffraction orders, i.e. for said wavelengths approx. 80% are diffracted out of the 0th order and thus filtered out. For the wavelengths between said ideal wavelengths a sin2-like shape of the diffraction efficiencies is obtained approximately, i.e. for other wavelengths the intensity of the DUV radiation located in the 0th order is only attenuated or the grating will not have any effect at all, e.g. for the depth of h=340 nm at the wavelength λ≈165 nm. The amount and the wavelength of the suppressed or transmitted DUV-radiation can be thus determined by depth of the grating. If sources provide a evenly distributed DUV spectrum or a unknown spectral distribution of radiation the grating depth h is best chosen in such a way that over a spectral region to be suppressed a maximum for the diffraction efficiency according to equation (5) or FIG. 4 as averaged over said spectral region is provided. FIG. 5 shows the mean diffraction efficiency ηmittel over two spectral regions, namely for the DUV spectral region from 130 nm to 330 nm (reference numeral 360) and for a broader wavelength region from 130 nm to 600 nm (reference numeral 362), depending on the grating depth at an incidence angle of αi=76°. The shape of the curve is obtained by averaging the diffraction efficiencies according to equation (5), i.e. η mittel = ∫ λ min λ max η ( h , λ ) P ( λ ) ⅆ λ ∫ λ min λ max P ( λ ) ⅆ λ ( 6 ) with η(h,λ) representing the diffraction efficiency according to equation (5), h the grating depth, λmin the shortest wavelength and λmax the longest wavelength of the wavelength region to be averaged, and P(λ) the spectral distribution which impinges on the attenuator. In the present simplified example P(λ) is set constant to equal 1 without any limitation to the generality thereof. The shape η(h,λ) is shown in FIG. 4 for four examples over the considered spectral region. When examining the spectral region, the maximum mean diffraction efficiency according to equation (6) of FIG. 5 can be found at a grating depth of approx. 210 nm. The averaged diffraction efficiency is in this case≈34%. In both 1st diffraction orders 68% of the radiation is diffracted out with a wavelength between 130 nm and 330 nm. A maximum of 32% of the undesired radiation then remains in the 0th order. If this is compared with the reflectivity of ruthenium of at least 80% for the used wavelength of 13.5 nm, one obtains a transmission of the undesired DUV radiation of 32%: 80%≈40%, i.e. a relative suppression of 60% of the undesired radiation. For the broader spectral region of 130 nm to 600 nm an ideal groove depth is found at approx. h≈420 nm. The mean diffraction efficiency is then approx. ≈29%, which leads to a suppression of the respective spectral region by more than approx. ≈47%. FIG. 6a shows the arrangement of the grating grooves 450 for a beam bundle impinging in a converging manner on the attenuator in accordance with the invention under a grazing incidence of e.g. of αi=76°. The grating grooves are always aligned ideally parallel to the local plane of incidence. As is shown above, the local plane of incidence is defined by the respective impinging ray of the beam bundle and the normal vector of the surface. The normal vector of the surface stands perpendicular to the grating plane. The focal point of the converging beam lies in this case to the right of the grating. All grating grooves 450 point to said focal point. For the functionality of the attenuator in accordance with the invention it is not absolutely necessary that the grating consists of conically tapered grating grooves. Especially in the case of small apertures of up to NA≈0.2 the grating can also be composed of virtually parallel grating grooves, as is shown in FIG. 3. This is simpler from a production viewpoint. As is shown in FIG. 6b, the grating can also be composed of segments 460.1, 460.2 of the same grating period. FIG. 7 schematically shows the detailed arrangement of an attenuator in accordance with the invention in an x-z sectional view on the basis of a grating element. A stop layer 502 is applied at first onto a substrate 500. The substrate 500 can be made of silicon for example. A material 504 is applied onto the stop layer 502. The material is then structured, e.g. by known etching techniques. The stop layer 502 is used for the purpose that the etching process comes to an end and does not move forward to the substrate 500. In order to increase the reflectivity in the EUV region the etched structure is provided with a coating 506 which reflects a high amount of the EUV radiation. Such a coating can be ruthenium or a multi-layer made of molybdenum and silicon for example. Both the stop layer as well as the material applied onto the stop layer have the advantage that they can be processed with a very high surface quality. In order to ensure a high reflectivity under grazing incidence for example of αi>70° the grating must show a very low roughness around rms ˜0.6 nm. The following method is therefore recommended for production: At first a plane substrate 500 with the stop layer 502 is polished. Then the substrate is coated with a layer 504. The layer 504 is an etchable layer of a certain thickness. A certain layer thickness can be provided by finishing, e.g. lapping of the surface. This etchable layer can be structured by means of photolithographical techniques. Since both the etchable layer as well as the substrate can be polished very well, a small roughness can be achieved. The etchable layer can be removed right up to the substrate by directional etching, e.g. by means of ion beaming of the etchable layer at the places not protected by resistant or protective layers. A grating with a well-controlled depth of the grating grooves can then be produced. FIG. 8a shows a further embodiment of a projection exposure system with an attenuator in accordance with the invention in a schematic representation. The attenuator in this embodiment is attached to the mirrors which are operated under small incidence angles. In this case the attenuator is attached to pupil facets 656 of the illumination system. The illumination system comprises a collector 603 which projects the light source 601 to a first image of the light source 605. The path of rays between collector 603 and the image of the light source 605 is guided via a plane mirror 620 which may comprise a first attenuator in accordance with the invention. A diaphragm 622 is arranged for this purpose in the plane of the first image of the light source 605. The illumination system of the projection exposure system further comprises an optical system 650 for shaping and illuminating the field plane 700 with a ring-like field 690.1. The optical system 650 comprises two facet mirrors 654, 656 as a mixing unit for the homogeneous illumination of the field and a projection lens 658 with two projecting mirrors 662, 664 and a field-forming grazing-incidence mirror 670. Additional diaphragms 684, 688.1 and 688.2 for suppressing spill light are arranged in the optical system. The first faceted mirror 654, the so-called field facet mirror, produces a plurality of secondary light sources in or close to the second faceted mirror 656, the so-called pupil facet mirror. The following projection lens consisting of the mirrors 662, 664 and 670 projects the pupil facet mirror into the exit pupil of the illumination system. The exit pupil of the illumination system coincidence in this case with the entrance pupil of the projection lens (not shown here). The angle of inclination of the individual facets of the first facet mirror 654 and the second facet mirror 656 are designed in such a way that the images of the individual field facets of the first facet mirror substantially overlap in the field plane 700 of the illumination system and thus a substantially homogenized illumination of the structure-bearing mask which comes to lie in this field plane is enabled. The segment of the ring field is formed via the field-forming grazing-incidence mirror 670 which is operated under the grazing incidence. If a grating in accordance with the invention for attenuating undesired radiation is situated on each pupil facet, virtual double images of the field are produced in the field plane 700 next to the field to be illuminated. The path of rays via a pupil facet 656.1 is shown as an example for this case. Pupil facet 656.1 projects the associated field facet 654.1 into the field 690.1. The impinging radiation is diffracted by the grating on the pupil facet 656.1, so that next to the field illumination 690.1 two further field illuminations 690.2 and 690.3 are produced according to the 1st diffraction order. They are blocked by the additional diaphragms 684, 688.1 and 688.2 in such a way that the associated radiation cannot lead to an exposure of the light-sensitive substrate in the focal plane of the projection lens (not shown). In this embodiment the gratings on the facet mirrors for example are designed in such a way that the diffraction orders come to lie virtually in the incidence plane, i.e. the grating vector lies in the incidence plane. To ensure that the 1st diffraction orders 690.2 and 690.3 cannot overlap with the desired field 690.1 and thus can be separated completely, the diffraction angle must be chosen large enough. This can be calculated as follows: the distance between the pupil facet 656.1 and the associated field facet 654.1 is in this case approx. 1 m. The height of the field facet in the y direction is approx. 3 mm in this plane. The aperture of the radiation at the pupil facet is then 3 mrad. In order to separate the diffraction orders completely it is sufficient to choose the diffraction angle larger than the radiation aperture at the location of the pupil facet 656.1. The diffraction angle in the present case is therefore >3 mrad. If an incidence angle of 4 mrad is chosen for example for radiation higher than 130 nm, one obtains a required grating period of ≈32 μm. At an incidence angle of αi≈5° an ideal grating depth of h ≈51 nm can be determined for this case from equation (5) in order to suppress radiation of the wavelengths between 130 nm and 330 nm. If the attenuator in accordance with the invention is used in the exemplary pupil facet mirrors 656 in combination with the attenuator on the plane mirror 620, another depth of e.g. h ≈90 nm can be advantageous in order to obtain the highest possible attenuation of the undesirable radiation over the spectrum of 130 nm to 330 nm. FIG. 8b schematically shows the grating on the pupil facet mirror 656.1. The arrangement is preferably made in this case too by a binary grating, which is shown schematically by a number of grating grooves 655. It is understood that the attenuator in accordance with the invention can be applied in similar form also onto the field facets 654 or the further mirrors of the illumination system, including the collector 603. The invention presents for the first time an optical attenuator for EUV lithography in particular which is characterized by high efficiency and is easy to produce. It should be understood by a person skilled in the art that the disclosure content of this application comprises all possible combinations of any element(s) of any claims with any element(s) of any other claim, as well as combinations of all claims amongst each other. |
|
description | The invention was made with government support under grant # DE-NE0000566 awarded by the Department of Energy. The government has certain rights in the invention. The invention relates to methods of manufacturing a zirconium alloy cladding having a ceramic-containing coating formed thereon including an oxidation resistant layer for use in a nuclear water reactor and, in particular, an improved capability for the zirconium alloy cladding to withstand normal and accident conditions to which it is exposed in the nuclear water reactor. In a typical nuclear water reactor, such as a pressurized water reactor (PWR), heavy water reactor (e.g., a CANDU) or a boiling water reactor (BWR), the reactor core includes a large number of fuel assemblies, each of which is composed of a plurality of elongated fuel elements or fuel rods. Fuel assemblies vary in size and design depending on the desired size of the core and the size of the reactor. The fuel rods each contain nuclear fuel fissile material, such as at least one of uranium dioxide (UO2), plutonium dioxide (PuO2), thorium dioxide (ThO2), uranium nitride (UN) and uranium silicide (U3Si2) and mixtures thereof. At least a portion of the fuel rods can also include neutron absorbing material, such as, boron or boron compounds, gadolinium or gadolinium compounds, erbium or erbium compounds and the like. The neutron absorbing material may be present on or in pellets in the form of a stack of nuclear fuel pellets. Annular or particle forms of fuel also can be used. Each of the fuel rods has a cladding that acts as containment to hold the fissile material. The fuel rods are grouped together in an array which is organized to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and thus, the release of a large amount of energy in the form of heat. A coolant, such as water, is pumped through the reactor core to extract the heat generated in the reactor core for the production of useful work such as electricity. The cladding on the fuel rods may be composed of zirconium (Zr) and may include as much as about two percent by weight of other metals, such as niobium (Nb), tin (Sn), iron (Fe) and chromium (Cr). Recent developments in the art have provided fuel rod cladding composed of a ceramic-containing material, such as silicon carbide (SiC). SiC has been shown to exhibit desirable properties in beyond design basis accidents, e.g., a temperature of greater than 1200° C. and therefore, may be considered a suitable material of construction for nuclear fuel rod claddings. However, maintaining fission gas impermeability during flexing induced by handling or accidents or natural phenomena, such as earthquakes, is difficult due to the natural inelasticity of ceramic materials generally. Fastening end plugs on SiC tubes in a high throughput, economic manner yielding a hermetic seal at temperatures beyond 1200° C. is also difficult. The use of an inner sleeve composed of a Zr alloy wrapped with SiC fibers has been attempted but has failed due to excessive corrosion encountered during chemical vapor infiltration (CVI) when SiC is deposited within and on the SiC fibers to hold them together. Thus, issues relating to nuclear fuel rod cladding remained, including corrosion of the Zr tube at temperatures associated with a nuclear water reactor core, e.g., about 800 to about 1200° C., and the chemical conditions, e.g., gas containing H2, Cl2 and HCl, encountered during the CVI process. It has also been attempted to make the SiC winding separately, subject it to CVI, and then fit it over the Zr tube. However, there are issues with this approach as well. For example, the space between the Zr tube and the SiC composite matrix forms an additional heat transfer barrier within the cladding layer, which could cause fuel centerline melt at the very high linear heat generation rates encountered by nuclear fuel (normally greater than 5 kw/ft). Because the ends of the tube are not covered, there is a potential for the Zr tube to slip from the SiC composite sleeve and provide a pathway for high temperature steam and other gases to infiltrate below the SiC composite and attack the Zr alloy tube. Each of the fuel rods/cladding has a plug or cap positioned at each end. Further, a hold down device, such as a metal spring, is provided in the fuel rod/cladding to maintain the configuration of the stack of nuclear fuel pellets. FIG. 1 illustrates a prior art design which shows a stack of fuel pellets 10, a zirconium-based cladding 12, a spring hold down device 14, and end plugs 16. One of the end plugs, i.e., the one positioned closest to the hold down device 14, is typically referred to as the top end plug. It is necessary to seal the end plugs of the cladding to isolate the fuel contained therein from the reactor core environment. There are known sealing technologies that employ various materials such as Ti-based or Al—Si based compositions as well as brazing and other conventional methods to seal SiC cladding and end plugs. It is an object of this invention to provide methods for manufacturing a SiC reinforced Zr alloy nuclear fuel cladding using an intermediate coating layer which contains an oxidation and corrosion resistant material, such as but not limited to, Al2O3, Cr2O3 and mixtures thereof, in order to protect the underlaying zirconium tube from oxidation or corrosion during the CVI process. In order for the fuel to maintain its geometry and to resist a loss of fuel from the core through melting, a covering or coating that is capable of withstanding high temperature needs to be formed on at least a portion of the exterior surface of a nuclear fuel rod cladding composed of zirconium alloy. In one aspect, the invention provides a method of coating a ceramic-containing nuclear fuel rod cladding for a nuclear water reactor. The cladding includes a tubular wall having an interior surface and an exterior surface, the tubular wall forming a cavity therein and having a first open end and a second open end. The method further includes providing a first end plug, inserting and sealing the first end plug into the first open end of the cladding, filling the fuel rod cladding with nuclear fuel and a hold down device, inserting and sealing the second end plug into the second open end of the cladding, pressurizing the cavity, providing a first composition including an oxidation resistant material, providing a second composition including silicon carbide, applying the first composition to at least a portion of the exterior surface of the cladding to form a first exterior coating, and applying the second composition to at least a portion of the first exterior coating to form a second exterior coating. The second exterior coating includes depositing SiC reinforced fibers having voids formed between at least a portion of the SiC reinforced fibers; and depositing a SiC material to at least partially fill the voids formed between at least a portion of the SiC reinforced fibers. The second exterior coating substantially encapsulates the exterior surface of the cladding. In certain embodiments, the method further includes applying the first composition on the interior surface of the cladding to form a first interior coating thereon. The applying of the first interior coating and the first exterior coating may be conducted by atomic layer deposition. The first interior coating and the first exterior coating can have a thickness from 10 nanometers to 10 microns. An end plug can be positioned within each of the first end and the second end of the cladding. The depositing of the first interior coating can occur when neither or one of the first end plug and the second end plug is positioned within the first open end or the second open end of the cladding. The depositing of the SiC reinforced fibers in the second exterior coating can be conducted by winding or braiding. The second exterior coating can have a thickness from 10 mils to 40 mils. In certain embodiments, the second exterior coating has a density of about 3.22 grams/cm3. The first composition can include Al2O3, Cr2O3 and mixtures thereof. In certain embodiments, depositing of the second exterior coating includes coating an exposed surface of each of the first and second end plugs positioned within the first and second ends of the cladding. In another aspect, the invention provides a composite for coating a ceramic-containing nuclear fuel rod cladding for a nuclear water reactor. The composite includes a ceramic-containing cladding. The cladding includes a tubular wall having an interior surface and an exterior surface, a cavity formed by the tubular wall, the cavity having nuclear fuel disposed therein, a first open end, and a second open end, a first end plug and a second end plug, the first open end sealed with the first end plug and the second open end sealed with the second end plug. In certain embodiments, each of the first and second end plugs is a metal plug. The first composition is deposited on at least a portion of at least the exterior surface of the cladding to form a first exterior coating. The first composition includes an oxidation resistant material. A second composition is deposited on at least a portion of the first exterior coating to form a second exterior coating. The second coating composition includes a plurality of SiC reinforced fibers deposited on at least a portion of the first exterior coating to form a fiber layer. The fibers have voids formed therebetween. Further, the second coating composition includes a SiC material at least partially applied to the fiber layer to at least partially fill the voids. The present invention relates generally to fuel rod cladding, depositing a composition on an exterior surface of the cladding to form a coating thereon, and methods of manufacturing a zirconium alloy nuclear fuel cladding that has the capability to withstand normal and accident conditions in a nuclear water reactor. In certain embodiments, the cladding manufactured in accordance with the invention is able to withstand temperatures in a range from about 800° C. to about 1200° C. Further, the cladding is capable to withstand beyond design basis accidents in a nuclear water reactor. Generally, the invention includes depositing an oxidation resistant material on, e.g., directly on, the interior surface and/or the exterior surface of the cladding to form a first interior coating and/or a first exterior coating, respectively, and subsequently depositing a SiC composition, e.g., composite, on the first exterior coating to form a second exterior coating thereon. The cladding may be composed and constructed of a variety of conventional materials known in the art. As previously described herein, it is known to construct fuel rod cladding for a nuclear water reactor from zirconium alloy containing a majority amount of zirconium and a minority amount, e.g., up to about 2% by weight based on total weight of the composition, of other metals. Further, it is known in the art for cladding to be composed of ceramic. Due to the known brittleness associated with ceramic, the cladding material is typically a combination of ceramic and another material, e.g., a ceramic-containing materials, such as but not limited to, silicon carbide (SiC). Non-limiting examples of suitable cladding materials for use in the invention include silicon carbide (SiC) fiber reinforced composites. These composites may have two or three layers. The two-layer composite includes a cladding of high purity beta or alpha phase stoichiometric SiC at least partially covered by a layer of continuous beta phase stoichiometric SiC fibers infiltrated with beta phase SiC. The three-layer composite includes an additional outer protective layer of fine grained beta phase SiC. In certain instances, it is typical to pre-stress the fiber component forming the fibers into tows and tow reverse winding overlapping, where the fibers are coated with less than one micrometer of carbon or graphite or boron nitride to provide a weak interface allowing fiber slippage. This process may be conducted to improve crack propagation resistance. United States Patent Publication No. 2006/0039524 A1 to Feinroth et al. which is herein incorporated by reference, describes such nuclear fuel tubes and matrix densification using well known processes of chemical vapor infiltration (CVI) or polymer impregnation and pyrolysis (PIP). The invention is applicable to a wide variety of cladding compositions and designs known in the art, such as but not limited to monolithic, duplex with monolithic SiC on the inside and a composite made with SiC fibers and SiC matrix on the outside, or duplex with a composite made with SiC fibers and SiC matrix on the inside and with a monolith on the outside. The fuel rod cladding is typically in the shape of an elongated tube having a cavity formed therein and two opposing open ends. The thickness of the tube wall can vary. In certain embodiments, the tube wall thickness is from about 100 to about 1000 microns or from about 200 to 400 microns. The cavity has fuel pellets contained therein and typically a hold down device, such as a spring, to maintain the configuration, e.g., a stack, of the fuel pellets. An end cap or plug is positioned at or in each open end of the cladding to provide a seal and prevent reactor coolant circulating in the core from entering the cavity of fuel rod cladding. The fuel rod cladding is positioned in the core of a nuclear water reactor. In certain embodiments of the invention, the end plugs are constructed of the same or different material/composition as the cladding. Each of the two end plugs may be inserted into the opposing open ends of the cladding at the same time or one end plug may be inserted prior to the other. Each of the end plugs has a top surface and a bottom surface. When each of the end plugs is inserted into an open end of the cladding, the bottom surface is positioned within the cavity and the top surface forms a closed end of the cladding. In a conventional fuel loading process, one end plug is inserted and attached to an open end of the cladding such as to seal the one end, the fuel pellets and stack hold down spring are then loaded into the cavity of the cladding and following loading, the other end plug is inserted and attached to the other open end of the cladding. As an alternative, the fuel pellets and stack hold down may be loaded into the cladding and subsequently, both of the end plugs may be inserted and attached to the open ends of the cladding. The end plugs may be attached or sealed to the open ends of the cladding using a variety of compositions, e.g., joining material, and methods. Suitable examples are disclosed in U.S. patent application Ser. No. 14/205,823 which is incorporated herein by reference. Metal end plugs may also be welded onto the ends of the zirconium alloy tube, either singly or together at the same time. In the invention, the oxidation resistant material can include a wide variety of such compounds known in the art. Non-limiting examples for use in the invention include Al2O3, Cr2O3 and mixtures thereof. In certain embodiments, the oxidation resistant material is deposited on at least a portion of the interior and/or exterior surfaces of the cladding, e.g., a Zr alloy cladding, to form a first interior coating and/or a first exterior coating. Thus, in alternate embodiments, the oxidation resistant material can be deposited on the exterior surface only or on both the interior and exterior surfaces of the cladding. It is contemplated that coating of the interior surface allows the Zr alloy material to be resistant to corrosive attack on the inside of the tube in the event of a tube rupture. Preferably, the tube is loaded with fuel pellets and a hold down spring, and end plugs are attached. The exterior surface is at least substantially covered or completely covered with the oxidation resistant material. The oxidation resistant material may be deposited using conventional apparatus and methods known in the art. In certain embodiments, the oxidation resistant material is deposited using atomic layer deposition. The coating or layer formed by deposition of the oxidation resistant material is typically in the form of a nanolayer having a thickness from about 10 nanometers to about 10 microns or from about 50 nanometers to about 1 micron. In certain embodiments, wherein the oxidation resistant material is deposited on the interior surface of the cladding tube to form a first interior coating, such deposition is conducted prior to loading of the fuel and hold down device in the cavity, and insertion of the end plugs in the open ends of the cladding. In certain other embodiments, wherein the oxidation resistant material is deposited on the exterior surface of the cladding tube to form a first exterior coating, such deposition may be conducted prior to or following loading of the fuel and hold down device in the cavity, and insertion of the end plugs in the open ends of the cladding. A first end plug may be inserted and secured, e.g., welded or joined, into or onto a first end of the cladding tube. A joining material may be selected such that it has sufficient strength and high-temperature capability to ensure the joint integrity during a CVI or CVD process that is subsequently conducted in forming the second coating. Further, the joining material may or may not be capable of exhibiting sufficient corrosion resistance in a nuclear reactor environment. The joining material may be deposited on at least a portion of the external surface of the first end plug to form a coating thereon and the coated first end plug inserted into the first open end of the cladding tube to form a seal between the first end plug and the interior surface and/or end face of the cladding tube. The fuel, e.g., stack of pellets, and the hold down device, e.g., spring, can then be inserted and positioned within the cavity of the tubular cladding. Subsequently, the cladding tube may be pressurized with an inert gas, such as helium (He), as in conventional designs or other backfill gas, e.g., gas having similar or improved thermal conductivity, such as hydrogen. That is, the cavity of the tubular cladding is filled with the gas to a desired pressure. The pressure can vary and in certain embodiments, is from 5 to 50 atmospheres or from 10 to 20 atmospheres. Following loading of the fuel and pressurizing of the tube, the second end plug can then be inserted and secured into the second open end of the cladding tube, in accordance with the method described above for the first end plug. Alternatively, a central hole or opening may be formed in the second end plug to allow entry of the gas therethrough to pressurize the rod. Afterwards, the hole or opening may be at least partially filled and sealed with the joining material as described above. In alternate embodiments, the fuel and hold down device may be positioned within the cavity of the tubular cladding prior to inserting and securing either of the first and second end plugs. The invention includes a dual or two-layer matrix, composite or coating on the exterior surface of the fuel rod cladding which is applied by a two-step method. Further, a single layer or coating of oxidation resistant material may be deposited on the interior surface of the cladding tube. The first step in the two-step method includes deposition of the oxidation resistant material on, e.g., directly on, the interior and/or exterior surfaces of the cladding to form the first interior coating and/or first exterior coating as described above, and the second step includes deposition of a SiC composition, e.g., composite, on the first exterior coating which is deposited on the exterior surface of the cladding to form the second exterior coating on the cladding. The second exterior coating includes a first component and a second component. The first component includes SiC fibers. Thus, following welding or joining of the first and second end plugs to seal the cladding tube, the closed tube is wound or braided with SiC fibers. The winding or braiding typically is conducted such that the process is initiated at the first end plug of the cladding tube and is completed at the opposing second end plug of the cladding tube. The thickness of the deposited SiC fibers may vary and in certain embodiments, the SiC fibers are deposited to form a layer that is from about 100 microns to about 1000 microns thick or from about 200 microns to about 600 microns thick. Typically, there are voids that exist between individual or groups of SiC fibers. Following this winding or braiding step, the second component is applied. The second component includes a SiC material which is effective to at least partially fill the voids formed between the SiC fibers in the first component. The second component is deposited or applied by employing chemical vapor infiltration (CVI) or chemical vapor deposition (CVD) technology. In certain embodiments, CVI or CVD application forms a second component layer or coating on the first component layer or coating. As used herein and the claims, CVI refers to depositing ceramic matrix material in pores using decomposed gaseous ceramic matrix precursors and CVD refers to depositing ceramic matrix material on surfaces using decomposed gaseous ceramic matrix precursors. The density of the second exterior coating can vary and in certain embodiments, is from about 50% to about 100% of the theoretical SiC density of about 3.22 grams/cm3, or from about 75% to about 95% theoretical density. Further, as a result of filling the voids between the fibers with the CVI or CVD process, the second exterior coating can at least substantially and preferably, completely, encase the Zr alloy tubular cladding structure including the first and second end plugs. In certain embodiments, the Zr alloy cladding structure is at least 99% encased in the second exterior coating. In certain embodiments, CVI is conducted at temperatures from about 300° C. to about 1100° C. depending on the particular CVI process and apparatus employed. Traditional decomposition-based CVI occurs from about 900° C. to about 1100° C. In certain embodiments, atomic layer deposition-based SiC deposition is carried out at temperatures from about 300° C. to about 500° C. The second component, e.g., SiC material, in the second exterior coating which is applied by CVI or CVD to fill the voids, may include a variety of compositions. Suitable examples are disclosed in U.S. patent application Ser. No. 14/205,799 which is incorporated herein by reference. The overall tube wall thickness of a Zr alloy cladding with coating in accordance with the invention is significantly less than the thickness of a 100% SiC tube exhibiting the same or similar hermeticity and strength in the absence of a coating. The coated cladding of the invention provides a SiC protective layer that is capable of holding together the cladding tube including end plugs and keeping the temperature rise due to corrosion-generated self-heating to a minimum to temperatures greater than 1800° C., which is significantly higher than the temperatures at which corrosion of other metal alloys and, in particular, significantly higher than Zr alloys alone, i.e., in the absence of the SiC protective layer begin to increase. Furthermore, the overall neutron cross-section of the cladding tube manufactured in accordance with the invention may be less than that of a conventional Zr alloy tube alone since the wall thickness is supported by a SiC layer. Thus, a significantly thicker wall can be used since the SiC has a cross-section only 25% of that of Zr alloys. FIG. 2 illustrates a fuel rod cladding 22 in accordance with certain embodiments of the invention. The cladding 22 includes an elongated tube wall 21 having an interior surface 23, an exterior surface 25, and forming a cavity 27. An oxidation resistant coating composition is deposited on the interior surface 23 and/or exterior surface 25 of the cladding 22 to form a first coating 29 on the interior surface 23 and/or a first coating 33 on the exterior surface 25. FIG. 3 illustrates a fuel rod cladding 22 in accordance with certain embodiments of the invention. FIG. 3 includes the elongated tube wall 21, interior surface 23, exterior surface 25, and cavity 27, as shown in FIG. 2. In addition, FIG. 3 shows a stack of fuel pellets 20 and a hold down device 24 positioned within the cavity 27, and a first end 31a and a second end 31b. A first end plug 26a is positioned and secured in the first end 31a and a second end plug 26b is positioned and secured in the second end 31b. The mechanism of securing the first and second end plugs 26a,b may include a seal which includes a joint of brazing material 30. In certain embodiments, the seal can be formed by a weld of the end plugs 26a,b to the ends 31a,b. As shown in FIG. 3, an oxidation resistant composition is deposited on the exterior surfaces 25 of the cladding tube 22 to form a first coating 33. As described herein, it is contemplated that a first coating can be deposited on both the interior surface 23 (e.g., coating 29 as shown in FIG. 2) and the exterior surface 25 (e.g., coating 33 as shown in FIG. 3). FIG. 3 also shows a second coating 51 formed on an outer surface of the first coating 33 on the exterior surface 25 of the cladding tube 22 and the surfaces of the first and second end plugs 26a,b. The second coating 51 is effective to completely enclose or encapsulate the cladding tube 22 including the end plugs 26a,b. As shown in FIG. 4, the second coating 51 (shown in FIG. 3) includes a layer 60 of SiC reinforcement fibers 62 deposited on the outer surface of the first coating 33 (shown in FIGS. 2 and 3). Between the fibers 62 are shown voids 64. A SiC coating 66 is applied by CVI or CVD to the layer 60 of SiC reinforcement fibers 62 to fill the voids 64. FIG. 5 shows a substrate 65 which is representative of a coated fuel rod cladding surface. As shown in FIG. 5, substrate 65 includes the elongated tube wall 21 and, its interior and exterior surfaces 23,25. The first coating 29 is optionally deposited on the interior surface 23 and the first coating 33 is deposited on the exterior surface 25. The second coating 51 is deposited on the first coating 33. The second coating 51 includes the SiC fiber layer 60 and the SiC coating 66. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
|
059582340 | abstract | A suction strainer includes a hollow internal core tube and an external filtering surface built around the internal core tube. A plurality of openings are defined through the side wall of the internal core tube core. In some cases the openings through the side wall are constructed and arranged such that there is somewhat less open area near the downstream end than the upstream end of the internal core tube, and the amount of open area tapers between the upstream end and the downstream end. As a result, when liquid is drawn into the internal core tube through the plurality of openings, a substantially uniform inflow distribution may be defined along substantially the entire length of the internal core tube. The internal core tube functions as a rigid structural support for the external filtering surface, enabling the apparatus to withstand post-LOCA hydrodynamic forces. The size of the filtering surface is enlarged by virtue of the fact that the filtering surface defines a plurality of filtering disk assemblies that are connected to and extend radially from the internal core tube. A separation distance is defined between neighboring disk assemblies, and filtering inner walls connect between neighboring disk assemblies and extend around the internal core tube at a radius less than the outermost radius of the disk assemblies. The total flow surface area is increased within a limited geometric profile. This serves to maximize surface area while minimizing post-LOCA reactive forces on attachment ECCS piping in a BWR suppression pool. |
summary | ||
summary | ||
summary | ||
044217161 | claims | 1. For use in a nuclear reactor power plant, including a reactor vessel having a reactor core, said power plant having a number of first subsystems utilized for operating said plant during normal operating conditions, a number of second subsystems utilized for operating said plant during abnormal and accident operating conditions, and a control panel for displaying plant parameters relating to plant operation, said first and second subsystems including subsystems that add water to said reactor vessel, and subsystems that take water away from said reactor vessel, a transient interpreter comprising: A. means (36) connected to said first and second subsystems for receiving signals representing the values of various ones of said plant parameters; B. interpreter logic means (22) responsive to said receiving means (36) for analyzing said ones of said plant parameters, said interpreter logic means including: means for determining the instantaneous water inventory of said reactor vessel by monitoring the parameters of those of said first and second subsystems that add water to said reactor vessel, and those of said first and second subsystems that take water away, to provide first data corresponding to the net inflow or outflow of water to said reactor vessel as indicated by directly measured process instrumentation level meters; means for converting said first data to measured water level data relative to the top of said reactor core; back-up system means for calculating reactor vessel water level based upon an analytical model of said reactor vessel and said core, said analytical model being based upon the integration of the inflow and outflow of water to said reactor vessel, reactor power, reactor pressure, and reactor water mass, to thereby provide calculated water level data as an alternate to said measured water level data; means for setting said calculated water level data to be equal to said measured water level data, so that said calculated water level is consistent with said measured water level data as indicated by said directly measured process instrumentation level meters, said means for setting being operative periodically only during normal operation of said plant; C. first means (14) responsive to said interpreter logic means (22) for generating for display, a primary display, said primary display comprised of information corresponding to primary parameters, said primary parameters comprising a first subset of said plant parameters, said first subset of said plant parameters relating to said first subsystems utilized for operating said plant during normal operating conditions; D. second means (18, 20) responsive to said interpreter logic means (22) for generating for display, a plurality of secondary displays, each of said secondary displays comprised of information corresponding to secondary parameters, said secondary parameters comprising a second subset of said plant parameters relating to said second subsystems utilized for operating said plant during abnormal and accident operating conditions, said second means including third means (310) responsive to said determining means within said interpreter logic means (22) for generating a first one of said plurality of secondary displays, said first one secondary display comprised of said calculated water level data; and, E. fourth means (16, 32, 34) connected to said first means (14) and to said second means (18, 20), said fourth means being selectively operable by an operator, for selecting for display any one of said secondary displays, including said first one of said secondary displays, from said plurality of secondary displays. fifth means for determining the instantaneous power level; and, sixth means for determining whether or not the reactor is reaching the containment pressure limit that will rupture said containment vessel; said first means (14) further including seventh means responsive to said determining means within said interpreter logic means (22), and to said fifth, and sixth means, for generating for display, a primary display, said primary display comprised of information corresponding to said instantaneous water inventory of said reactor vessel, said instantaneous power level, and information as to whether or not the reactor is reaching the containment pressure limit that will rupture the containment vessel. means (22) for logically combining critical ones of said plant parameters to thereby provide data as to normal, abnormal and accident plant conditions; first means (14), responsive to said combining means (22), for generating a primary output display comprised of primary output display (POD) data, said POD data containing information in summary form of selected ones of said critical plant parameters, said selected ones of said critical plant parameters comprising a first subset of said plant parameters, said first subset of said plant parameters relating to said first subsystems utilized for operating said plant during normal operating conditions said POD data including measured data corresponding to the net inflow or outflow of water to said reactor vessel as indicated by directly measured process instrumentation level meters; displaying means (9, 10, 11) for displaying data inputted thereto; second means (26) connected to said first means (14) and to said displaying means (9, 10, 11) for gating said primary output display, selectively under control of a first selection input (17), to said displaying means (9, 10, 11); third means (18) responsive to said combining means (22) for generating a plurality of secondary output displays (19), said third means including means for calculating reactor vessel water level based upon an analytical model of said reactor vessel and said core, said analytical model being based upon the integration of the inflow and outflow of water to said reactor vessel, reactor power, reactor pressure, and reactor water mass, to thereby provide calculated water level data, said secondary output displays (19) comprised of secondary output display (SOD) data, said SOD data comprising a second subset of said plant parameters relating to said second subsystems utilized for operating said plant during abnormal and accident operating conditions, said SOD data containing information in summary form of said second subset of said plant parameters, said SOD data including said calculated water level data which provides an operator with a secondary display during abnormal and accident operating conditions which is an alternative to said measured data available on said primary output display; fourth means (34) connected to said third means (18) and to said displaying means (9, 10, 11) for gating one of said secondary output displays (19), selectively under control of a corresponding one of said second selection inputs (28), to said displaying means; and, fifth means (16) operable by an operator, for selectively energizing and deenergizing said second selection inputs (28) and said first selection input (17) to thereby provide said operator with a display of only selected ones of said second subset of said plant parameters. A. generating primary information as to whether the core is covered and likely to remain covered, including information as to the status of those of said first and second subsystems needed to provide water to cool the core and maintain core integrity; said step of generating primary information including the steps of: determining the instantaneous water inventory of said reactor vessel by monitoring the parameters of those of said first and second subsystems that add water to said reactor vessel, and those of said first and second subsystems that take water away, to provide first data corresponding to the net inflow or outflow of water to said reactor vessel as indicated by directly measured process instrumentation level meters; converting said first data to measured water level data relative to the top of said reactor core; and, generating for display, a primary display, said primary display comprised of information corresponding to said instantaneous water inventory of said reactor vessel; B. generating secondary information which provides a secondary display comprised of information as to reactor vessel water inflow and outflow in ranked order which can be viewed selectively for more detailed information when an abnormal condition occurs; said step of generating secondary information including the steps of: calculating reactor vessel water level based upon an analytical model of said reactor vessel and said core, said analytical model being based upon the integration of the inflow and outflow of water to said reactor vessel, reactor power, reactor pressure, and reactor water mass, to thereby provide calculated water level data as an alternate to said measured water level data; setting said calculated water level data to be equal to said measured water level data periodically only during normal operation of said plant, so that said calculated water level is consistent with said measured water level data as indicated by said directly measured process instrumentation level meters; and, C. displaying with said primary information, a prompt message indicating that said secondary display should be selected for viewing. 2. The combination in accordance with claim 1 wherein said interpreter logic means further comprises: 3. For use in a nuclear reactor power plant, including a reactor vessel, said power plant having a number of first subsystems utilized for operating said plant during normal operating conditions, a number of second subsystems utilized for operating said plant during abnormal and accident operating conditions, and a control panel for displaying plant parameters relating to plant operation, a transient interpreter comprising: 4. The combination in accordance with claim 3, wherein said fifth means (16) operable by an operator, for selectively energizing and deenergizing said second selection inputs (28) includes a number of pushbuttons, each of said number of pushbuttons being associated with a corresponding one of said second selection inputs (28), and said POD data includes at least one prompt message for display to thereby inform an operator as to which of said number of pushbuttons to press in order to call up the corresponding one of said secondary displays for viewing. 5. For use in a nuclear reactor power plant, including a reactor vessel, said power plant having a number of first subsystems utilized for operating said plant during normal operating conditions, a number of second subsystems utilized for operating said plant during abnormal and accident operating conditions, and a control panel for displaying plant parameters relating to plant operation, said plant including a water-cooled reactor core in a reactor vessel, the method comprising the steps of: 6. The method in accordance with claim 5 wherein said step B of generating secondary information includes the further step of performing a thermal-hydraulic analysis in order to generate secondary information for display as to whether the water level is rising or dropping, and how much time remains before the core will become uncovered if the water level continues to drop at its current rate. |
description | 1. Field of the Invention The present invention relates to the correction of beam current fluctuations in electron beam inspection tools and other similar apparatus. 2. Description of the Background Art In electron beam inspection systems, defects are often detected by comparing the signals from corresponding image pixels in a chip (die) being tested and a reference standard. The reference standard may be an electronic database (for die-to-database inspection) or a reference die (for die-to-die inspection). A defect is typically detected when the signals between the die and reference differ by more than a threshold amount. Beam current fluctuations may cause errors in such defect detection. These beam current fluctuations may be caused, for example, by emission noise from cold field or Schottky electron emission sources, or from other causes. A conventional technique for correcting beam current fluctuations uses a circuit connected to the beam-limiting aperture to measure an electrical current from the aperture. This electrical current is due to the electrons being absorbed by the aperture. From the current measured, a beam current may be inferred. Changes in the current measured are used to infer changes in the beam current. One embodiment of the invention relates to an electron beam imaging apparatus. An electron source is configured to generate an electron beam, and a beam-limiting aperture is configured to block a portion of the electron beam and to allow transmission of another portion of the electron beam through the aperture. A first detector is configured to detect scattered electrons emitted by the aperture due to the blocked portion of the electron beam. The imaging apparatus may also include a second detector configured to detect scattered electrons emitted by the sample due to impingement of the transmitted portion of the electron beam. A gain control device may also be included to adjust a gain of a detected signal derived from the second detector using a control signal derived from the first detector. Another embodiment of the invention relates to an electron beam lithography apparatus. The lithography apparatus may adjust a pixel dwell time based on a control signal derived from the scattered electrons emitted by the aperture. As discussed above, a conventional technique measures an electrical current due to electrons being absorbed by an aperture to infer a beam current. Unfortunately, this conventional technique is suitable to detect fluctuations only within a limited bandwidth of frequencies. In particular, detecting high-frequency (for example, above a few kilohertz) fluctuations is problematic. Hence, the conventional technique does not allow for correction of higher-frequency variations in the beam current. This bandwidth limitation appears to be due to the low current levels and high stray capacitance in the conventional technique. The present invention relates to an improved technique to correct for beam fluctuations in charge-particle metrology equipment, lithography equipment, or inspection equipment, or other similar tools. Instead of measuring an electrical current due to electrons being absorbed by the aperture, an embodiment of the present invention uses a detector mounted above the aperture to collect and measure secondary and/or backscattered electrons. The secondary and/or backscattered electrons are emitted due to the impingement of part of the primary beam (the part being blocked) onto the aperture. In a preferred embodiment, the detector is mounted just above the beam-limiting aperture, and the detector comprises a high-speed electron detector. High-speed electron detectors include, for example, Everhart-Thornley detectors, PIN diode based detectors, and microchannel plate detectors. The detector collects the secondary and/or the backscattered signal from that part of the beam being blocked by the aperture. The collected signal is converted into a voltage signal that is proportional to the (nearly) instantaneous current being blocked by the aperture. Assuming that the fluctuations in the beam current are not spatially correlated at the aperture plane, this signal is a reasonably accurate proxy for the actual beam current. An embodiment of the invention is described in relation to the cross-sectional diagram of FIG. 1 and the flow chart of FIG. 2. The diagram of FIG. 1 shows an apparatus for beam current fluctuation correction, while the flow chart of FIG. 2 depicts a method of beam current fluctuation correction. In accordance with an embodiment of the invention, the apparatus comprises an electron beam column 101. An electron gun 102 near the top portion of the column 101 generates 202 a primary electron beam. The primary electron beam is aperture limited 204 by a beam-limiting aperture 104. In other words, a portion of the primary beam is blocked by the electron-opaque portion of the aperture 104, and a portion of the primary beam goes through the opening of the aperture 104. The portion going through the opening of the aperture 104 is focused by an objective lens 105 onto the sample or specimen 106. The apparatus includes at least two detectors. The first detector is a sample scattered electron (SE) detector 108. The sample SE detector 108 may comprise a detector configured to detect 210 secondary electrons and/or backscattered electrons that are emitted due to impingement 206 of the primary beam onto the sample 106. The second detector is an aperture SE detector 110. The aperture SE detector 110 may comprise a detector configured to detect 208 secondary and/or backscattered electrons that are emitted due to blocking of the primary beam by the opaque portion of the aperture. While the sample SE detector 108 may be found in a conventional apparatus, the aperture SE detector 110 is advantageously included in accordance with an embodiment of the invention. The aperture SE detector 110 preferably comprises a high-speed electron detector, such as an Everhart-Thornley detector, a PIN diode based detector, or a microchannel plate detector. An alternative implementation would use an annular-shaped detector in the region between the beam-limiting aperture and the electron source. Such an annular detector would be oriented to directly detect part of the beam current coming from the gun that would otherwise be intercepted by the beam-limiting aperture. Another embodiment of the invention may use an annular-shaped detector in the aperture plane. The annular-shaped detector would be configured so that the incident beam is transmitted through the opening of the detector. Such a detector in the aperture plane would detect primary electrons from the electron gun that impinge upon the annular-shaped detector. In accordance with an embodiment of the invention, the apparatus further includes an auto-gain circuit 116. The detected signal from the sample SE detector 108 is fed through an amplifier circuit 112 to a first input of the auto-gain circuit 116. The detected signal from the aperture SE detector 110 is fed through an amplifier circuit 114 to a second input of the auto-gain circuit 116. The auto-gain circuit 116 may include a variable gain amplifier configured to amplify the sample SE signal. The aperture SE signal may be used 212 as a control input to the auto-gain circuit 116 so as to control the variable gain applied 214 to the sample SE signal. The auto-gain circuit 116 outputs 216 the gain corrected sample SE signal 118. This corrected output 118 may then be used to generate an image of the sample area for metrology or inspection purposes. The image so generated being corrected for nearly instantaneous brightness variations in the primary beam. The above-described embodiment utilizes a variable gain amplifier circuit. Another embodiment of the invention is described in relation to the cross-sectional diagram of FIG. 3. The apparatus of FIG. 3 is similar to the apparatus of FIG. 1, with a few differences. The apparatus of FIG. 3 includes an analog-to-digital converter (ADC) circuit 302 to convert the sample SE signal from analog to digital form. In digital form, the magnitude of the sample SE signal is represented using digital bits. Furthermore, the auto-gain circuit 304 is configured with a multiplying DAC. The multiplying DAC is configured to receive as input the digitized sample SE signal and to multiply that signal by an amount proportional to the aperture SE signal. The output is the gain corrected sample SE signal 306 (in analog form). This corrected output 306 may then be used to generate image data of the sample area for metrology or inspection purposes. The image data so generated being corrected for nearly instantaneous brightness variations in the primary beam. An alternative embodiment may not use such an auto-gain circuit. Instead, the gain correction may be done in the digital domain during processing of the image data. In this digital domain embodiment, digital image data would be processed so as to effectively adjust the gain of the sample SE image data based on the amplitude of the aperture SE signal at the corresponding time. Another embodiment of the invention utilizes an aperture SE detector in a lithography system. While traditional lithographic processes utilize electromagnetic energy in the form of ultraviolet light (or x-rays) for selective exposure of the resist, charged particle beams have also been used for high resolution lithographic resist exposure. In particular, electron beams have been used since the low mass of electrons allows relatively accurate control of an electron beam at relatively low power and relatively high speed. Electron beam lithographic systems may be categorized as electron-beam direct write (EBDW) lithography systems and electron beam projection lithography systems. In EBDW lithography, the substrate is sequentially exposed by means of a focused electron beam. The focused beam writes the desired structure on the substrate (by controlled blanking or in a vector scan method). In electron beam projection lithography, analogously to optical lithography, a mask or portion thereof is illuminated and is imaged on a reduced scale on a wafer by means of projection optics. In accordance with an embodiment of the invention, an EBDW or an electron beam projection lithography apparatus may be configured with an aperture SE detector above a beam-limiting aperture in the apparatus. In an electron beam projection lithography apparatus, the aperture SE detector may alternatively be positioned above the mask. FIG. 4 is a cross-sectional diagram of an electron beam lithography apparatus including beam current fluctuation correction in accordance with an embodiment of the invention. The signal from the detector 110 may be fed back to the lithography controller 402 and used to adjust a pixel dwell time of the beam. A brighter beam would cause the pixel dwell time to be adjusted to a proportionally shorter time. A dimmer beam would cause the pixel dwell time to be adjusted to a proportionally longer time. As discussed above, an embodiment of the invention advantageously allows for correction of image brightness or dose variation due to beam current fluctuations. The correction may be done at a high-speed (at a rate approaching or exceeding the pixel speed of the system) due to the use of a high-speed aperture SE detector (instead of measuring current from the aperture). As a result, lower-noise images may be obtained in a shorter period of time for imaging systems, or more precise linewidth control may be obtained in lithographic systems. Another embodiment of the invention utilizes the output of the aperture detector as basis for feedback to adjust the beam current of an electron beam apparatus. In other words, the beam current may be adjusted by feedback to a electron gun controller of a signal based on the detected scattered electrons emitted by the aperture. This embodiment may be used in metrology, inspection, and lithography applications. Prior gun control systems have used feedback from an electrical current measured from the aperture, but not feedback from electrons scattered from the aperture. In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation. |
|
abstract | Embodiments of systems and methods for compressing plasma are disclosed in which plasma can be compressed by impact of a projectile on a magnetized plasma in a liquid metal cavity. The projectile can melt in the liquid metal cavity, and liquid metal may be recycled to form new projectiles. |
|
description | Network service providers may own and operate networks and may sell virtual channels (e.g., virtual networks) as a service to customers. For example, a business customer may rent a virtual channel from a network service provider in order to connect two remote offices for the exchange of data between the two offices. The network service provider may guarantee a level of performance for the virtual channel to the customer. The level of performance may be measured by latency, packet loss, and/or jitter, among other things. In addition, the customer may agree not to exceed, and the service provider may agree to provide, a certain data rate (e.g., measured in bits per second) over the virtual channel. The level of performance guaranteed by the service provider and the data rate requirements may be documented in a service level agreement (SLA) between the service provider and the customer. The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. One or more embodiments disclosed herein may allow for the automatic determination of when a virtual channel in a transport network does not meet one or more performance criteria. One or more embodiments disclosed herein may also determine whether transport network equipment (e.g., a service provider) or end-point equipment (e.g., a customer) is at fault for the lack of performance of the virtual channel in the transport network. FIG. 1 is a block diagram of an exemplary network 100 in which systems and methods, consistent with exemplary embodiments, may be implemented. As illustrated, network 100 may include a first piece of customer premise equipment (CPE) 102-1 and a second piece of CPE 102-2 (collectively “CPE 102”), a transport network 104, and a virtual channel (VC) 106. As shown in FIG. 1, CPE 102-1 may communicate with CPE 102-2 through transport network 104 using VC 106, for example. In one exemplary embodiment, a network service provider may own and operate transport network 104 and may sell VC 106 as a service to a customer, such as a customer that owns CPE 102. In this example, CPE 102-1 may be in the customer's home office and CPE 102-2 may be in the customer's remote office. The customer may user VC 106 for communications between these two offices. In alternative embodiments, transport network 104 and CPE 102 may be owned and operated by the same entity. The network service provider may guarantee a level of performance for VC 106 to the customer. The level of performance may be measured by latency, packet loss, and/or jitter, among other things. In addition, the customer may agree not to exceed, and the service provider may agree to provide, a certain data rate for data passing through VC 106. The level of performance guaranteed by the service provider and the data rate requirements may be documented in a service level agreement (SLA). If the level of performance is not met, the service provider and the customer may want to know the reason, which could be the fault of equipment in transport network 104 (e.g., the service provider) or the fault of CPE 102 (e.g., the customer). Embodiments disclosed herein may automatically detect when the level of performance of a virtual channel is not met and, when it is not met, may determine whether transport network 104 (e.g., the service provider) or CPE 102 (e.g., the customer) is at fault. CPE 102 may include any device or combination of devices that may communicate over VC 106. For example, CPE 102 may include any combination of personal computers, laptops, or another type of computation or communication device. CPE 102 may also include a network device, such as a router and/or switch, which routes the data traffic (e.g., packets) for transmission over VC 106. CPE 102 may include one or more computer systems for hosting programs, databases, and/or applications. Transport network 104 may represent a network used to route customer data traffic to/from various devices in network 100, such as CPE 102-1 and CPE 102-2. Transport network 104 may include devices, systems, and/or protocols that provide switching and/or routing of packets. For example, transport network 104 may include Multi-Protocol Label Switching (MPLS) devices, systems, and protocols. Protocols other than MPLS are possible. Transport network 104 may include virtual channels, such as VC 106, or virtual private networks. Transport network 104 may include one or more sub-networks of any type, including a Local-Area Network (LAN), a Wide-Area Network (WAN), a satellite network, a Metropolitan-Area Network (MAN), a telephone network, such as the Public-Switched Telephone Network (PSTN) or a Public Land Mobile Network (PLMN), an ad hoc network, an intranet, the Internet, or a combination of networks. The PLMN(s) may further include a packet-switched sub-network, such as, for example, General Packet Radio Service (GPRS), Cellular Digital Packet Data (CDPD), or Mobile IP sub-network. Transport network 104 may include a high-speed fiber optic network, such as Verizon's FiOS™ network. FIG. 2 is a more detailed block diagram of exemplary network 100 in which embodiments described herein may be implemented. As shown in FIG. 2, network 100 may include a network management system (NMS) 212, a VC monitor 210, and a report server 214. In addition, transport network 104 may include network devices 202-1 through 202-4 (collectively “network devices 202,” individually “network device 202-x”) and access circuits 204-1 and 204-2 (collectively “access circuits 204”). Network devices 202 may accept packets (e.g., on one interface) and may route packets (e.g., on another interface) toward destination devices. As used herein, the term “packet” may include any type of data unit, including a packet, cell, or datagram; a fragment of a packet, cell, or datagram; a group of packets, cells, or datagrams; or other types or arrangements of data. Network devices 202 may include switches and/or routers. Network devices 202 may also include logic circuitry and/or software to measure and/or monitor packet losses (e.g., the number of dropped packets) on interfaces. Access circuits 204 may provide interfaces for the entry and/or exit of packets to and from transport network 104. For example, access circuits 204 may, in one embodiment, convert a packet that enters transport network 104 from a native packet into an MPLS packet by adding an MPLS header. Access circuits 204 may also convert a packet that leaves transport network 104 from an MPLS packet to a native packet, e.g., a non-MPLS packet, by stripping away its MPLS header. In one embodiment, network device 202-1 may include access circuit 204-1 and network device 202-4 may include access circuit 204-2. As shown in FIG. 2, VC 106 may pass through network devices 202-1, 202-2, and 202-4. That is, in one direction, network device 202-1 may receive packets from access circuit 204-1 and route the packets to network device 202-2; network device 202-2 may receive packets from network device 202-1 and route the packets to network device 202-4; network device 202-4 may receive packets from network device 202-2 and route the packets to access circuit 204-2. In the other direction, network device 202-4 may receive packets from access circuit 204-2 and route the packets to network device 202-2; network device 202-2 may receive packets from network device 202-4 and route the packets to network device 202-1; network device 202-1 may receive packets from network device 202-2 and route the packets to access circuit 204-1. VC monitor 210 may include one or more computer systems for hosting programs, databases, and/or applications. VC monitor 210 may monitor and/or measure the performance of virtual channels, such as VC 106. In one embodiment, VC monitor 210 may inject packets into a virtual channel, e.g., VC 106, to measure the performance. VC monitor 210 may measure the performance by measuring latency, packet loss, and/or jitter of the virtual channel, among other things. Latency may include the time it takes a packet to travel from a source end-point to the destination end-point of a virtual channel. Jitter may include the variation of the latency in the virtual channel over a period of time. Packet loss may include the number or percentage of packets sent from one end-point that do not arrive at the other end-point of the virtual circuit during a period of time. In one embodiment, VC monitor 210 may communicate with network devices, such as network devices 202, at or near the end-points of virtual channels. For example, VC monitor 210 may communicate over communication path 218 with network device 202-1 (near one end point of VC 106) and network device 202-4 (near the other end-point of VC 106). VC monitor 210 may measure and/or monitor the performance of a virtual channel periodically, such as every 30 minutes, every 20 minutes, every 15 minutes, every 10 minutes, every 5 minutes, every 1 minute, every 30 seconds, every 10 seconds, every second, or every fraction of a second. VC monitor 210 may store the measured and/or monitored performance for analysis. In one exemplary embodiment, because VC monitor 210 may send packets in-band, VC monitor 210 may measure and/or monitor the performance no more frequently than every 10 minutes to minimize overhead in-band data traffic (e.g., packets). NMS 212 may include one or more computer systems for hosting programs, databases, and/or applications. NMS 212 may measure and/or monitor the performance of network devices, such as network devices 202. In one embodiment, NMS 212 may measure and/or monitor packet losses on the different interfaces of network devices 202. In another embodiment, NMS 212 may measure and/or monitor additional or different performance characteristics, such as jitter and/or latency. As shown in FIG. 2, NMS 212 may communicate with network devices 202 through a communication path 216 to gather the performance information with respect to the interfaces of network devices 202. NMS 212 may measure and/or monitor the performance periodically, such as every 30 minutes, every 20 minutes, every 15 minutes, every 10 minutes, every 5 minutes, every 1 minute, every 30 seconds, every 10 seconds, every second, or every fraction of a second. NMS 212 may store the reported performance for analysis. NMS 212 may, for example, monitor packet losses on “internal interfaces” and/or “ingress interfaces.” An ingress interface is an interface of network device 202-x that receives packets into transport network 104. For example, the interface 252 of network device 202-1 that receives packets from access circuit 204-1 for VC 106 may be considered an ingress interface. The interface 254 of network device 202-4 that receives packets from access circuit 204-2 for VC 106 may also be considered an ingress interface. An internal interface is an interface of network device 202-x that forwards or receives packets to or from another network device in transport network 104. For example, the interface 256 of network device 202-2 that receives packets from network device 202-1 may be considered an internal interface. The interface 258 of network device 202-4 that receives packets from network device 202-2 may also be considered an internal interface. In another embodiment, NMS 212 may communicate with access circuits 204 to monitor and/or measure the performance of interfaces in access circuits 204. Report server 214 may include one or more computer systems for hosting programs, databases, and/or applications. Report server 214 may communicate with NMS 212 and/or VC monitor 210 to combine or aggregate the performance data recorded by VC monitor 210 and/or NMS 212. Report server 214 may also analyze the recorded performance data to determine fault, for example, for a poorly performing virtual channel. Report server 214 may determine that customer equipment (e.g., CPE 102 attached or coupled to an end-point of VC 106) is generating too much data traffic (e.g., packets), which may result in the poor performance of VC 106. On the other hand, report server 214 may determine that one or more network devices 202 in transport network 104 are dropping packets, which may result in the poor performance of VC 106. In one exemplary embodiment, CPE 102 may be owned and/or operated by a customer and be located on the customer's premises. In this exemplary embodiment, transport network 104 may be owned and operated by a service provider. In another embodiment, CPE 102 and/or transport network 104 may be owned and operated by another party or may both be owned by the same party. In other embodiments, network 100 may include more, fewer, or different components. For example, network 100 may include additional CPE 102 or additional network devices 202. Moreover, one or more components shown in network 100 (e.g., components 102-106 and 202-214) may perform one or more functions described as being performed by another component of network 100. For example, NMS 212, VC monitor 210, and report server 214 may be combined into a single server. In addition, the functions of measuring and/or monitoring of interfaces in network devices 202 may be shared among NMS 212 and network devices 202. Although FIG. 2 shows components 102-106 and 202-214 coupled in a particular configuration, components 102-106 and 202-214 may also be coupled in other configurations. Furthermore, one or more of components 102-106 and 202-214 may be remotely located from each other. FIG. 3 is a block diagram of exemplary components of a computing module 300. CPE 102, access circuits 104, network devices 202, NMS 212, VC monitor 210, and report server 214 may each include one or more (e.g., a rack of) computing modules, such as module 300. Module 300 may include a bus 310, processing logic 320, a communication interface 350, and a memory 360. Module 300 may include other components (not shown) that aid in receiving, transmitting, and/or processing data. Moreover, other configurations of components in module 300 are possible. Bus 310 may include a path that permits communication among the components of module 300. Processing logic 320 may include any type of processor or microprocessor (or groups of processors or microprocessors) that interprets and executes instructions. In other embodiments, processing logic 320 may include an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or the like. Communication interface 350 may include any transceiver-like mechanism that enables module 300 to communicate with other devices and/or systems. Communications interface 350 may include a network interface card, e.g., Ethernet card, for wired communications or a WiFi card for wireless communications. Communication interface 350 may include a transmitter that may convert baseband signals from processing logic 320 to radio frequency (RF) signals and/or a receiver that may convert RF signals to baseband signals. Memory 360 may include a random access memory (RAM) or another type of dynamic or static storage device that may store information and instructions, e.g., an application, for execution by processing logic 320; a read-only memory (ROM) device or another type of static storage device that may store static information and instructions for use by processing logic 320; and/or some other type of magnetic or optical recording medium and its corresponding drive, e.g., a hard disk drive (HDD), for storing information and/or instructions. Memory 360 may include one or more applications 362 and one or more data tables 364. In the case of NMS 212, applications 362 may include, for example, an application for NMS 212 to measure, monitor, and record performance characteristics, such as packet loss, for the interfaces of network devices 202 for a group of time periods. In this case, data tables 364 may include, for example, a data table that stores the performance measurements, such as packet loss, for the interfaces of network devices 202. In the case of VC monitor 210, applications 362 may include, for example, an application for VC monitor 210 to measure, monitor, and record performance characteristics, such as latency, packet loss, and/or jitter, for virtual channels for a group of time periods. In this case, data tables 364 may include a table that stores the performance measurements, such as latency, packet loss, and/or jitter for virtual channels for the time periods. In the case of report server 214, applications 362 may include, for example, an application for report server 214 to combine and analyze the performance measurements stored in VC monitor 210 and/or NMS 212. In this case, data tables 364 may include a table that stores the combined performance measurements. Module 300 may perform certain operations, as described below. Module 300 may perform these operations in response to processing logic 320 executing software instructions (e.g., one or more applications 362) stored in a computer-readable medium, such as memory 360. A computer-readable medium may be defined as a physical or logical memory device. The software instructions may be read into memory 360 from another computer-readable medium or from another device via communication interface 350. The software instructions contained in memory 360 may cause processing logic 320 to perform processes that are described below. FIG. 4 is a block diagram of an exemplary VC performance table 400. VC performance table 400 may store the performance measurements taken by VC monitor 210. As such, VC performance table 400 may be stored in VC monitor 210 (e.g., in memory 360 as data table 364). In another embodiment, VC performance table 400 may be stored in another component of network 100, such as NMS 212 and/or report server 214. VC performance table 400 may include a VC field 402, a time period field 404, a latency field 406, a packet loss field 408, and a jitter field 410. VC performance table 400 may include additional, different, or fewer fields than illustrated in FIG. 4. VC field 402 may store information identifying a virtual channel for which the data in fields 404-410 correspond. In exemplary VC performance table 400, VC field 402 indicates that the data in fields 404-410 all correspond to VC 106. Other virtual channels are possible. Time period field 404 may store information identifying a time period for which the performance measurements in fields 406-410 correspond. As shown in VC performance table 400, four time periods are listed, e.g., periods T1 through T4. In the exemplary embodiment descried below, time periods T1 through T4 may be different periods of time of any duration. In another embodiment, time periods T1 through T4 may be consecutive time periods. In yet another embodiment, time periods T1 through T4 may not be consecutive (e.g., there may be time gaps between the time periods). Time period field 404 may store a start and an end time (e.g., month, day, year, time of day) of the time period. Latency field 406 may store the measured latency during the time period identified in field 404 for the virtual channel identified in field 402. As shown in FIG. 4, four latency measurements L1 through L4 correspond to the four time periods T1 through T4, respectively. Latency may be measured and stored in milliseconds, for example. Packet loss field 408 may store the measured packet loss during the time period identified in field 404 for the virtual channel identified in field 402. As shown in FIG. 4, four packet loss measurements PL1 through PL4 correspond to the four time periods T1 through T4, respectively. Packet loss may be measured and stored as the number of packets lost per hundred packets sent, for example, or as a percentage. Jitter field 410 may store the measured jitter during the time period identified in field 404 for the virtual channel identified in field 402. As shown in FIG. 4, four jitter measurements J1 through J4 correspond to the four time periods T1 through T4, respectively. Jitter may be measured and stored in milliseconds, for example. For simplicity, the latency measurements in VC performance table 400 are shown with labels L1 through L4; the packet loss measurements are shown with labels PL1 through PL4; the jitter measurements are shown with labels J1 through J4; and the time periods are shown with labels T1 through T4. In other implementations, the raw values may be stored in VC performance table 400. FIG. 5 is a block diagram of an exemplary ingress interface (IF) performance table 500. Ingress IF performance table 500 may store the performance measurements taken by NMS 212. As such, ingress IF performance table 500 may be stored in NMS 212 (e.g., in memory 360 as data table 364). In another embodiment, ingress IF performance table 500 may be stored in another component of network 100, such as VC monitor 210 and/or report server 214. Ingress IF performance table 500 may include a VC field 502, a time period field 504, a first ingress IF packet loss field 506, and a second ingress IF packet loss field 508. VC field 502 may store information identifying a virtual channel for which the data in fields 504-508 correspond. As shown in ingress IF performance table 500, VC field 502 indicates that the data in fields 504-508 all correspond to VC 106. Other virtual channels are possible. Time period field 504 may store information identifying a time period for which the performance measurements in field 506 and 508 correspond. As shown in FIG. 5, four time periods are listed, e.g., periods T1 through T4. The time periods (e.g., T1 through T4) stored in ingress IF performance table 500, thus, may correspond to the time periods stored in VC performance table 400. In one embodiment, time period field 404 may store a start and an end time (e.g., month, day, year, time of day) of the time period. First ingress IF packet loss field 506 may store the measured packet loss for a first ingress interface during the time period identified in field 504 for the virtual channel identified in field 502. For example, two ingress interfaces may carry packets through VC 106—one for each direction through transport network 104. In the example of FIG. 2, a first ingress interface (e.g., in network device 202-1) may receive packets from access circuit 204-1 from CPE 102-1 for VC 106. As shown in FIG. 5, four packet loss measurements PLA1 through PLA4 may correspond to the four time periods T1 through T4, respectively. Packet loss in field 506 may be measured and stored as the number of packets lost per hundred packets sent, for example, or as a percentage. Second ingress IF packet loss field 508 may store the measured packet loss for a second ingress interface during the time period identified in field 504 for the virtual channel identified in field 502. In the example of FIG. 2, a second ingress interface (e.g., in network device 202-4) may receive packets from access circuit 204-2 from CPE 102-2 for VC 106. As shown in FIG. 5, four packet loss measurements PLB1 through PLB4 correspond to the four time periods T1 through T4, respectively. Packet loss in field 508 may be measured and stored as the number of packets lost per hundred packets sent, for example, or as a percentage. Ingress IF performance table 500 may include additional, different, or fewer fields than illustrated in FIG. 5. For example, ingress IF performance table 500 may include additional ingress packet loss fields when a virtual channel includes more than two ingress interfaces, e.g., when the virtual channel is multi-point to multi-point. In one embodiment, ingress IF performance table 500 may include only one ingress packet loss field for a unidirectional virtual channel. For simplicity, the packet loss measurements of a first ingress interface in ingress IF performance table 500 are shown with labels PLA1 through PLA4, the packet loss measurements of a second ingress interface are shown with labels PLB1 through PLB4, and the time periods are shown with labels T1 through T4. In other implementations, the raw values may be stored in ingress IF performance table 500. FIG. 6 is a block diagram of an exemplary internal IF performance table 600. Internal IF performance table 600 may store the performance measurements taken by NMS 212. As such, internal IF performance table 600 may be stored in NMS 212 (e.g., in memory 360 as data table 364). In another embodiment, internal IF performance table 600 may be stored in another component of network 100, such as VC monitor 210 and/or report server 214. Internal IF performance table 600 may include a VC field 602 and a time period field 604. Internal IF performance table 600 may also include a first internal IF packet loss field 606 through an Nth internal IF packet loss field 608, where N is a positive integer. In other words, there may be many (e.g., N) packet loss fields, one field corresponding to each of the internal interfaces carrying packets for a virtual channel through transport network 104. Internal IF performance table 600 may include additional, different, or fewer fields than illustrated in FIG. 6. VC field 602 may store information identifying a virtual channel for which the data in fields 604-608 correspond. As shown in internal IF performance table 600, VC field 602 indicates that the data in fields 604-608 all correspond to VC 106. Other virtual channels are possible. Time period field 604 may store information identifying a time period for which the performance measurements correspond. As shown in FIG. 6, four time periods are listed, e.g., periods T1 through T4. The time periods (e.g., T1 through T4) stored in internal IF performance table 600, thus, may correspond to the time periods stored in VC performance table 400 and ingress IF performance table 500. In one embodiment, time period field 604 may store a start and an end time (e.g., month, day, year, time of day) of the time period. First internal IF packet loss field 606 may store the measured packet loss for a first internal interface during the time period identified in field 604 for the virtual channel identified in field 602. For example, many internal interfaces (e.g., N) may carry VC 106 through transport network 104. In the example of FIG. 2, a first internal interface (e.g., in network device 202-2) may receive packets from network device 202-1 for VC 106. As shown in FIG. 6, four packet loss measurements PL11 through PL14 correspond to the four time periods T1 through T4, respectively. Packet loss in field 606 may be measured and stored as the number of packets lost per hundred packets sent, for example, or as a percentage. Nth internal IF packet loss field 608 may store the measured packet loss for the Nth internal interface during the time period identified in field 604 for the virtual channel identified in field 602. In the example of FIG. 2, an Nth internal interface (e.g., in network device 202-4) may receive packets from network device 202-2 for VC 106. As shown in FIG. 6, four packet loss measurements PLN1 through PLN4 correspond to the four time periods T1 through T4, respectively. Packet loss in field 608 may be measured and stored as the number of packets lost per hundred packets sent, for example, or as a percentage. For simplicity, the packet loss measurements of a first internal interface in internal IF performance table 600 are shown with labels PL11 through PL14; the packet loss measurements of an Nth internal interface are shown with labels PLN1 through PLN4, and the time periods are shown with labels T1 through T4. In other implementations, the raw measurement values may be stored in internal IF performance table 600. FIG. 7 is a block diagram of an exemplary combined performance table 700. Combined performance table 700 may store the performance measurements stored in VC performance table 400, ingress IF performance table 500, and internal IF performance table 600. Combined performance table 700 may be stored in report server 214 (e.g., in memory 360 as data table 364). In another embodiment, internal IF performance table 600 may be stored in another component of network 100, such as VC monitor 210 and/or NMS 212. Combined performance table 700 may include a VC field 702, a time period field 704, a VC performance field 706, an ingress IF performance field 708, and an internal IF performance field 710. VC field 702 may store information identifying a virtual channel for which the data in fields 704-708 correspond. As shown in combined performance table 700, VC field 702 indicates that the data in fields 604-608 all correspond to VC 106. Other virtual channels are possible. Time period field 704 may store information identifying a time period for which the performance measurements correspond. As shown in FIG. 7, four time periods are listed, e.g., periods T1 through T4. The time periods (e.g., T1 through T4) stored in combined performance table 700, thus, may correspond to the time periods stored in VC performance table 400, ingress IF performance table 500, and ingress IF performance table 600. In one embodiment, time period field 704 may store a start and an end time (e.g., month, day, year, time of day) of the time period. VC performance field 706 may include the performance measurements from fields 406 through 410 of VC performance table 400 that correspond to the time period stored in field 704 and the virtual channel stored in field 702. Ingress IF performance field 708 may include the performance measurements from fields 506 and 508 of ingress IF performance table 500 that correspond to the time period stored in field 704 and the virtual channel stored in field 702. Internal IF performance field 710 may include the performance measurements from fields 606 and 608 of internal IF performance table 600 that correspond to the time period stored in field 704 and the virtual channel stored in field 702. As shown in FIG. 7, exemplary combined performance table 700 may include the data stored in VC performance table 400, ingress IF performance table 500, and internal IF performance table 600. Combined performance table 700 may include additional, different, or fewer fields than illustrated in FIG. 7. For example, VC performance field 706 may include separate fields similar to fields 406 through 410 of VC performance table 400; ingress interface performance fields 708 may include separate fields similar to fields 506 and 508 of ingress IF performance table 500; and internal IF performance field 710 may include separate fields similar to fields 606 and 608 in internal IF performance table 600. FIG. 8 is a block diagram of an exemplary performance criteria (e.g., standard) table 800. Performance criteria table 800 may store the performance criteria that a virtual channel and a transport network should meet. In other words, the measured performances stored in combined performance table 700 may be compared to the criteria in performance criteria table 800 to determine, for example, whether a virtual channel is meeting performance requirements. Performance criteria table 800 may be stored in report server 214 (e.g., in memory 360 as data table 364). In another embodiment, internal performance criteria table 800 may be stored in another component of network 100, such as VC monitor 210 and/or NMS 212. Performance criteria table 800 may include a VC field 802, a VC performance criteria field 806, an ingress IF performance field criteria 808, and an internal IF performance criteria field 810. VC field 802 may store information identifying a virtual channel for which the criteria in fields 806 through 810 correspond. As shown in performance criteria table 800, VC field 802 indicates that the criteria stored in fields 806-810 are for two virtual channels, e.g., VC 106 and VC X. Other virtual channels are possible. VC performance criteria field 806 may include the performance criteria, from the perspective of VC monitor 210, that the virtual channel identified in VC field 802 may be required to meet. The criteria stored in VC performance criteria field 806 may, in one embodiment, be derived from an SLA negotiated between a customer and a service provider. For example, an SLA may require that a virtual channel, such as VC 106, be able to deliver packets with a latency less than L′, a packet loss less than PL′, and a jitter less than J′. As such, L′, PL′, and J′ may be recorded in performance criteria table 800 as the maximum latency, the maximum packet loss, and the maximum jitter in field 806 for VC 106. The criteria in VC performance criteria field 806 may be compared, for example, to the measured performance stored in VC performance field 706 of combined performance table 700. Ingress IF performance criteria field 808 may include the performance criteria, from the perspective of NMS 212, that the ingress interfaces for the virtual channel identified in VC field 802 may be required to meet. The criteria stored in ingress IF performance criteria field 806 may, in one embodiment, be derived from an SLA negotiated between a customer and a service provider. For example, an SLA may require that the virtual channel, such as VC 106, be able to transport packets at a rate of R mega bits per second (mbps), e.g., 10 mbps, in each direction. As such, the maximum rate R may correspond to a maximum packet loss of PLA′ and PLB′ at ingress interfaces for VC 106 and PLA′ and PLB′ may be recorded in ingress IF performance criteria field 808 for VC 106. The criteria in field 808 may be compared, for example, to the measured performance stored in field 708 of combined performance table 700. Internal IF performance criteria field 810 may include the performance criteria, from the perspective of NMS 212, that the interfaces carrying the virtual channel identified in VC field 802 may be required to meet. The criteria stored in internal IF performance criteria field 810 may be derived from the known maximum capacity of the network devices, such as network devices 202. For example, it may be known that the N internal interfaces for VC 106 should not experience a packet loss of greater than PL1′ through PLN′. As such the packet losses PL1′ through PLN′ may be recorded in internal IF performance criteria field 810 for VC 106. The criteria in field 810 may be compared, for example, to the measured performance stored in field 710 of combined performance table 700. Performance criteria table 800 may include additional, different, or fewer fields than illustrated in FIG. 8. For example, VC performance criteria field 806 may include separate criteria fields corresponding to fields 406 through 410 of VC performance table 400; ingress IF performance criteria fields 808 may include separate criteria fields similar to fields 506 and 508 of ingress IF performance table 500; and internal IF performance criteria field 810 may include separate criteria fields similar to fields 606 and 608 in internal IF performance table 600. FIG. 9 is a flowchart of an exemplary process 900 for identifying virtual channel performance violations and assigning fault for virtual channel performance violations. Process 900 may be executed in another component in network 100, such as in VC monitor 210, NMS 212, and/or report server 214, for example, alone or in a distributed manner. The performance of a virtual channel may be measured (block 903). For example, VC monitor 210 may measure the performance of VC 106 through transport network 104. The measurements may include measurements of latency, packet loss, and/or jitter, for example, among other things. VC monitor 210 may record the measurements in VC performance table 400 for a group of time periods (e.g., T1 to T4) for each virtual channel being monitored, such as VC 106. In one embodiment descried below, time periods T1 through T4 may be different periods of time of any duration. In another embodiment, time periods T1 through T4 may be consecutive time periods. In yet another embodiment, time periods T1 through T4 may not be consecutive (e.g., there may be time gaps between the time periods). The performance of one or more ingress interfaces may be measured (block 905). For example, NMS 212 may measure and/or monitor the performance of ingress interfaces to transport network 104 that carry packets for VC 106. In this example, NMS 212 may measure the performance of the interface of network device 202-1 that receives packets from access circuit 204-1 for VC 106. NMS 212 may also measure the performance of the interface of network device 202-4 that receives packets from access circuit 204-2 for VC 106. The measurements may include measurements of packet loss, among other things, for example. NMS 212 may record the measurements in ingress IF performance table 500 for time periods (e.g., T1 to T4) for each virtual channel being monitored, such as VC 106. The performance of one or more internal interfaces may be measured (block 907). For example, NMS 212 may measure and/or monitor the performance of internal interfaces in transport network 104 that carry packets for VC 106. In this example, NMS 212 may measure and/or monitor the performance of the interface in network device 202-2 that receives packets from network device 202-1 for VC 106. NMS 212 may also measure the performance of the interface in network device 202-4 that may receive packets from network device 202-2 for VC 106. The measurements may include measurements of packet loss, among other things, for example. NMS 212 may record the measurements in internal IF performance table 600 for time periods (e.g., T1 through T4) for each virtual channel being monitored, such as VC 106. The performance measurements may be combined (block 909). Report server 214 may receive a VC performance table from VC monitor 210, and an ingress IF performance table and an internal IF performance table from NMS 212. Report server 214 may combine the different performance tables into a combined performance table, such as combined performance table 700. Report server 214 may store data in combined performance table 700 by virtual channel and by time period, such that report server 214 may analyze a “snapshot” of any virtual channel (e.g., VC 106) at any period of time (e.g., T1, T2, T3, or T4). Virtual channel performance violations may be determined (block 911). Report server 214 may identify instances where a virtual channel did not meet performance criteria set for that virtual channel. To identify these instances, report server 214 may compare the measured performance stored in VC performance field 706 of combined performance table 700 with the performance criteria stored in VC performance criteria field 806 of performance criteria table 800. Although a virtual channel may not meet performance criteria, the virtual channel may still function, but not up to the performance criteria. Examples of the identification of violations are illustrated in FIG. 10. FIG. 10 is a block diagram of the exemplary combined performance table 700 with virtual channel performance violations highlighted (e.g., circled). As shown in FIG. 10, packet loss measurement PL2 for VC 106 at time period T2 did not meet performance criteria. In addition, packet loss measurement PL3 for VC 106 at time period T3 did not meet performance criteria, and the packet loss measurement PL4 for VC 106 at time period T4 did not meet performance criteria. In these three instances, packet loss measurements PL2, PL3, and PL4 may have been greater than the criterion PL′ stored in performance criteria table 800 (e.g., in VC performance criteria field 806). Because the performance criteria stored in VC performance criteria field 806 may be derived from an SLA, the virtual channel performance violations may also be referred to as virtual channel “SLA violations.” Thus, as shown in FIG. 10, there were virtual channel SLA violations at time T2, T3, and T4. The remaining blocks described below may attribute fault of the SLA violations to CPE 102 or transport network 104, for example. The ingress interface performance violations corresponding to the virtual channel performance violations may be identified (block 913). Report server 214 may identify instances where an ingress interface did not meet performance criteria set for that ingress interface. Report server 214 may identify ingress interface performance violations by comparing ingress IF performance field 708 of combined performance table 700 to ingress IF performance criteria field 808 of performance criteria table 800. As shown in FIG. 10, packet loss measurement PLB2 for VC 106 at time period T2 did not meet performance criteria. In addition, packet loss measurement PLA4 for VC 106 at time period T4 did not meet performance criteria. In these two instances, packet loss measurements PLB2 and PLA4 may have been greater than the criteria PLB′ and PLA′ stored in performance criteria table 800 (e.g., in ingress IF performance criteria field 808). The ingress interface violations may be a result of CPE 102 attempting to transmit at a higher data rate than provisioned for VC 106, the provisioning of which may have been derived from an SLA. Thus, as shown in FIG. 10, at times T2 and T4, CPE 102 may have been attempting to transmit at a data rate greater than that provisioned for VC 106. VC 106 not meeting the performance criteria at time T2 (measurement PL2) corresponds with an ingress interface not meeting performance criteria (measurement PLB2). Thus, the SLA violation at time period T2 may have been caused by the customer equipment, such as CPE 102-2, transmitting too much data traffic (e.g., packets) over an ingress interface (e.g., the second ingress interface) at that time. In addition, VC 106 not meeting the performance criteria at time T4 (measurement PL4) corresponds with an ingress interface not meeting performance criteria (measurement PLA4). Thus, the SLA violation at time period T2 may have been caused by the customer equipment, such as CPE 102-1, transmitting too much data traffic (e.g., packets) over an ingress interface (e.g., first ingress interface) at that time. The internal interface performance violations corresponding to the virtual channel performance violations may be identified (block 915). Report server 214 may identify instances where an internal interface did not meet performance criteria set for that ingress interface. Report server 214 may identify internal interface performance violations by comparing internal IF performance field 710 of combined performance table 700 to internal IF performance criteria field 810 of performance criteria table 800. As shown in FIG. 10, packet loss measurement PL13 for VC 106 at time period T3 did not meet performance criteria. In addition, packet loss measurement PLN4 for VC 106 at time period T4 did not meet performance criteria. In these two instances, packet loss measurements PL13 and PLN4 may have been greater than the criteria PL1′ and PLN′ stored in performance criteria table 800. Because the performance criteria stored in internal IF performance criteria field 810 may be derived from the known characteristics of network devices 202, the internal interface violations may be a result network devices 202, for example, being overloaded. Thus, as shown in FIG. 10, network devices 202 may have been overloaded, for example, at times T3 and T4. VC 106 not meeting performance criteria at time T3 (measurement PL3) corresponds with the an internal interface not meeting performance criteria (measurement PL13). Thus, VC 106 not meeting performance criteria at time period T3 may have been caused by a network device, such as network device 202-2, handling too much data traffic (e.g., packets). In addition, VC 106 not meeting performance criteria at time T4 (measurement PL4) corresponds with the Nth internal interface not meeting performance criteria (measurement PLN4). Thus, VC 106 not meeting its performance criteria at time period T4 may have been caused by a network device, such as network device 202-4, handling too much data traffic (e.g., packets). As shown, the violation of performance of VC 106 at time T4 may have been caused by either the customer equipment (e.g., CPE 102) or the service provider (e.g., transport network 104) because the violation at time period T4 corresponds with a violation of an ingress interface performance (measurement PLA4) and a violation of an internal interface performance (measurement PLN4). On the other hand, the violation of performance criteria of VC 106 at time T2 appears to have been caused by excess data traffic (e.g., packets) from CPE 102 (e.g., measurement PLB2). Further, the violation of performance criteria of VC 106 at time T3 appears to have been caused by the overload of network devices 202 in transport network 104 (e.g., measurement PL13) and not CPE 102. Reports may be generated (block 915). Report server 214 may generate reports indicating when one or more virtual channels, such as VC 106, do not meet performance criteria. In other words, report server 214 may generate reports indicating when a virtual channel SLA was violated. Report server 214 may also generate reports indicating when the virtual channel SLA violation was likely caused by customer equipment (e.g., CPE 102 transmitting too much data traffic). Report server 214 may also generate reports indicating when the virtual channel SLA violation was likely caused by the service provider equipment (e.g., network devices 202 in transport network 104, not CPE 102). FIGS. 11A, 11B, and 11C are block diagrams of exemplary performance reports 1100A, 1100B, and 1100C, respectively. Performance report 1100A lists virtual channel SLA violations likely caused by end-point equipment (e.g., the violation at time period T2 likely caused by CPE 102). Performance report 1100B lists virtual channel SLA violations likely caused by transport network 104 (e.g., the service provider). Performance report 1100C lists virtual channel SLA violations where the equipment at fault may not be immediately identified, but may require further analysis (e.g., the violation at time period T4). In one embodiment, report server 214 may automatically and continuously combine performance reports from NMS 212 and VC monitor 210 and generate reports identifying virtual channel SLA violations and the party at fault, for example. While a series of blocks has been described above, such as with respect to FIG. 9, the order of the blocks may differ in other implementations. Moreover, non-dependent blocks may be implemented in parallel. For example, blocks 903, 905, and 907 may be implemented in parallel, as many of the measurements by VC monitor 210 and NMS 212 may take place during the same time periods (e.g., time period T1, T2, T3, or T4). In the preceding specification, various embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense. It will be apparent that aspects of the embodiments, as described above, may be implemented in many different forms of software, firmware, and hardware in the implementations illustrated in the figures. The actual software code or specialized control hardware used to implement these embodiments is not limiting of the invention. Thus, the operation and behavior of the embodiments of the invention were described without reference to the specific software code—it being understood that software and control hardware may be designed to the embodiments based on the description herein. Further, certain portions of the invention may be implemented as “logic” that performs one or more functions. This logic may include hardware, such as an application specific integrated circuit, a field programmable gate array, a processor, or a microprocessor, or a combination of hardware and software. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one” or similar language is used. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. |
|
063174774 | abstract | A seal assembly for sealing a space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal to provide a temporary water barrier during refueling operations. The seal assembly includes an annular closure plate having an outer portion secured to the surrounding ledge and an inner portion supporting a first sealing surface. A second sealing surface opposing the first sealing surface is formed on or secured to the annular flange of the reactor vessel. An annular space between the first and second sealing surfaces provides a ventilation path from the reactor cavity during normal plant operation. The annular space is sealed by an inflatable seal during refueling operations to provide a water barrier between the refueling canal and the reactor vessel. The inflatable seal is secured to and supported by an annular support structure that straddles the annular space. The annular support structure provides a structure for handling the inflatable seal during installation and removal. The annular support structure also provides a leak limiting function in the event the inflatable seal is pulled or pushed through the annular space or otherwise fails to seal the annular space. The inflatable seal is secured to the annular support structure in a manner that allows independent movement of the seal to conform to irregularities in the sealing surfaces. The closure plate has a plurality of normally closed access ports that permit access to the external core detectors and the reactor vessel cavity. |
abstract | A method of forming a water resistant boundary on a fissile material for use in a water cooled nuclear reactor is described. The method comprises mixing a powdered fissile material selected from the group consisting of UN and U3Si2 with an additive selected from oxidation resistant materials having a melting or softening point lower than the sintering temperature of the fissile material, pressing the mixed fissile and additive materials into a pellet, sintering the pellet to a temperature greater than the melting point of the additive. Alternatively, if the melting point of the oxidation resistant particles is greater than the sintering temperature of UN or U3Si2, then the oxidation resistant particles can have a particle size distribution less than that of the UN or U3Si2. |
|
summary | ||
description | This application: is a continuation-in-part of U.S. patent application Ser. No. 12/425,683 filed Apr. 17, 2009, now U.S. Pat. No. 7,939,809 which claims the benefit of: U.S. provisional patent application No. 61/055,395 filed May 22, 2008; U.S. provisional patent application No. 61/137,574 filed Aug. 1, 2008; U.S. provisional patent application No. 61/192,245 filed Sep. 17, 2008; U.S. provisional patent application No. 61/055,409 filed May 22, 2008; U.S. provisional patent application No. 61/203,308 filed Dec. 22, 2008; U.S. provisional patent application No. 61/188,407 filed Aug. 11, 2008; U.S. provisional patent application No. 61/188,406 filed Aug. 11, 2008; U.S. provisional patent application No. 61/189,815 filed Aug. 25, 2008; U.S. provisional patent application No. 61/201,731 filed Dec. 15, 2008; U.S. provisional patent application No. 61/205,362 filed Jan. 21, 2009; U.S. provisional patent application No. 61/134,717 filed Jul. 14, 2008; U.S. provisional patent application No. 61/134,707 filed Jul. 14, 2008; U.S. provisional patent application No. 61/201,732 filed Dec. 15, 2008; U.S. provisional patent application No. 61/198,509 filed Nov. 7, 2008; U.S. provisional patent application No. 61/134,718 filed Jul. 14, 2008; U.S. provisional patent application No. 61/190,613 filed Sep. 2, 2008; U.S. provisional patent application No. 61/191,043 filed Sep. 8, 2008; U.S. provisional patent application No. 61/192,237 filed Sep. 17, 2008; U.S. provisional patent application No. 61/201,728 filed Dec. 15, 2008; U.S. provisional patent application No. 61/190,546 filed Sep. 2, 2008; U.S. provisional patent application No. 61/189,017 filed Aug. 15, 2008; U.S. provisional patent application No. 61/198,248 filed Nov. 5, 2008; U.S. provisional patent application No. 61/198,508 filed Nov. 7, 2008; U.S. provisional patent application No. 61/197,971 filed Nov. 3, 2008; U.S. provisional patent application No. 61/199,405 filed Nov. 17, 2008; U.S. provisional patent application No. 61/199,403 filed Nov. 17, 2008; and U.S. provisional patent application No. 61/199,404 filed Nov. 17, 2008; claims the benefit of U.S. provisional patent application No. 61/209,529 filed Mar. 9, 2009; claims the benefit of U.S. provisional patent application No. 61/208,182 filed Feb. 23, 2009; claims the benefit of U.S. provisional patent application No. 61/208,971 filed Mar. 3, 2009; claims the benefit of U.S. provisional patent application No. 61/270,298 filed Jul. 7, 2009; and claims priority to PCT patent application serial No.: PCT/RU2009/00015, filed Mar. 4, 2009, all of which are incorporated herein in their entirety by this reference thereto. 1. Field of the Invention This invention relates generally to treatment of solid cancers. More particularly, the invention relates to magnetic field control elements used in conjunction with charged particle cancer therapy beam acceleration, extraction, and/or targeting methods and apparatus. 2. Discussion of the Prior Art Cancer A tumor is an abnormal mass of tissue. Tumors are either benign or malignant. A benign tumor grows locally, but does not spread to other parts of the body. Benign tumors cause problems because of their spread, as they press and displace normal tissues. Benign tumors are dangerous in confined places such as the skull. A malignant tumor is capable of invading other regions of the body. Metastasis is cancer spreading by invading normal tissue and spreading to distant tissues. Cancer Treatment Several forms of radiation therapy exist for cancer treatment including: brachytherapy, traditional electromagnetic X-ray therapy, and proton therapy. Each are further described, infra. Brachytherapy is radiation therapy using radioactive sources implanted inside the body. In this treatment, an oncologist implants radioactive material directly into the tumor or very close to it. Radioactive sources are also placed within body cavities, such as the uterine cervix. The second form of traditional cancer treatment using electromagnetic radiation includes treatment using X-rays and gamma rays. An X-ray is high-energy, ionizing, electromagnetic radiation that is used at low doses to diagnose disease or at high doses to treat cancer. An X-ray or Röntgen ray is a form of electromagnetic radiation with a wavelength in the range of 10 to 0.01 nanometers (nm), corresponding to frequencies in the range of 30 PHz to 30 EHz. X-rays are longer than gamma rays and shorter than ultraviolet rays. X-rays are primarily used for diagnostic radiography. X-rays are a form of ionizing radiation and as such can be dangerous. Gamma rays are also a form of electromagnetic radiation and are at frequencies produced by sub-atomic particle interactions, such as electron-positron annihilation or radioactive decay. In the electromagnetic spectrum, gamma rays are generally characterized as electromagnetic radiation having the highest frequency, as having highest energy, and having the shortest wavelength, such as below about 10 picometers. Gamma rays consist of high energy photons with energies above about 100 keV. X-rays are commonly used to treat cancerous tumors. However, X-rays are not optimal for treatment of cancerous tissue as X-rays deposit their highest does of radiation near the surface of the targeted tissue and delivery exponentially less radiation as they penetrate into the tissue. This results in large amounts of radiation being delivered outside of the tumor. Gamma rays have similar limitations. The third form of cancer treatment uses protons. Proton therapy systems typically include: a beam generator, an accelerator, and a beam transport system to move the resulting accelerated protons to a plurality of treatment rooms where the protons are delivered to a tumor in a patient's body. Proton therapy works by aiming energetic ionizing particles, such as protons accelerated with a particle accelerator, onto a target tumor. These particles damage the DNA of cells, ultimately causing their death. Cancerous cells, because of their high rate of division and their reduced ability to repair damaged DNA, are particularly vulnerable to attack on their DNA. Due to their relatively enormous size, protons scatter less easily in the tissue and there is very little lateral dispersion. Hence, the proton beam stays focused on the tumor shape without much lateral damage to surrounding tissue. All protons of a given energy have a certain range, defined by the Bragg peak, and the dosage delivery to tissue ratio is maximum over just the last few millimeters of the particle's range. The penetration depth depends on the energy of the particles, which is directly related to the speed to which the particles were accelerated by the proton accelerator. The speed of the proton is adjustable to the maximum rating of the accelerator. It is therefore possible to focus the cell damage due to the proton beam at the very depth in the tissues where the tumor is situated. Tissues situated before the Bragg peak receive some reduced dose and tissues situated after the peak receive none. Synchrotrons Patents related to the current invention are summarized here. Proton Beam Therapy System F. Cole, et. al. of Loma Linda University Medical Center “Multi-Station Proton Beam Therapy System”, U.S. Pat. No. 4,870,287 (Sep. 26, 1989) describe a proton beam therapy system for selectively generating and transporting proton beams from a single proton source and accelerator to a selected treatment room of a plurality of patient treatment rooms. Injection K. Hiramoto, et. al. “Accelerator System”, U.S. Pat. No. 4,870,287 (Sep. 26, 1989) describes an accelerator system having a selector electromagnet for introducing an ion beam accelerated by pre-accelerators into either a radioisotope producing unit or a synchrotron. K. Hiramoto, et. al. “Circular Accelerator, Method of Injection of Charged Particle Thereof, and Apparatus for Injection of Charged Particle Thereof”, U.S. Pat. No. 5,789,875 (Aug. 4, 1998) and K. Hiramoto, et. al. “Circular Accelerator, Method of Injection of Charged Particle Thereof, and Apparatus for Injection of Charged Particle Thereof”, U.S. Pat. No. 5,600,213 (Feb. 4, 1997) both describe a method and apparatus for injecting a large number of charged particles into a vacuum duct where the beam of injection has a height and width relative to a geometrical center of the duct. Accelerator/Synchrotron H. Tanaka, et. al. “Charged Particle Accelerator”, U.S. Pat. No. 7,259,529 (Aug. 21, 2007) describe a charged particle accelerator having a two period acceleration process with a fixed magnetic field applied in the first period and a timed second acceleration period to provide compact and high power acceleration of the charged particles. T. Haberer, et. al. “Ion Beam Therapy System and a Method for Operating the System”, U.S. Pat. No. 6,683,318 (Jan. 27, 2004) describe an ion beam therapy system and method for operating the system. The ion beam system uses a gantry that has vertical deflection system and a horizontal deflection system positioned before a last bending magnet that result in a parallel scanning mode resulting from an edge focusing effect. V. Kulish, et. al. “Inductional Undulative EH-Accelerator”, U.S. Pat. No. 6,433,494 (Aug. 13, 2002) describe an inductive undulative EH-accelerator for acceleration of beams of charged particles. The device consists of an electromagnet undulation system, whose driving system for electromagnets is made in the form of a radio-frequency (RF) oscillator operating in the frequency range from about 100 KHz to 10 GHz. K. Saito, et. al. “Radio-Frequency Accelerating System and Ring Type Accelerator Provided with the Same”, U.S. Pat. No. 5,917,293 (Jun. 29, 1999) describe a radio-frequency accelerating system having a loop antenna coupled to a magnetic core group and impedance adjusting means connected to the loop antenna. A relatively low voltage is applied to the impedance adjusting means allowing small construction of the adjusting means. J. Hirota, et. al. “Ion Beam Accelerating Device Having Separately Excited Magnetic Cores”, U.S. Pat. No. 5,661,366 (Aug. 26, 1997) describe an ion beam accelerating device having a plurality of high frequency magnetic field inducing units and magnetic cores. J. Hirota, et. al. “Acceleration Device for Charged Particles”, U.S. Pat. No. 5,168,241 (Dec. 1, 1992) describe an acceleration cavity having a high frequency power source and a looped conductor operating under a control that combine to control a coupling constant and/or de-tuning allowing transmission of power more efficiently to the particles. Vacuum Chamber T. Kobari, et. al. “Apparatus For Treating the Inner Surface of Vacuum Chamber”, U.S. Pat. No. 5,820,320 (Oct. 13, 1998) and T. Kobari, et. al. “Process and Apparatus for Treating Inner Surface Treatment of Chamber and Vacuum Chamber”, U.S. Pat. No. 5,626,682 (May 6, 1997) both describe an apparatus for treating an inner surface of a vacuum chamber including means for supplying an inert gas or nitrogen to a surface of the vacuum chamber with a broach. Alternatively, the broach is used for supplying a lower alcohol to the vacuum chamber for dissolving contaminants on the surface of the vacuum chamber. Magnet Shape M. Tadokoro, et. al. “Electromagnetic and Magnetic Field Generating Apparatus”, U.S. Pat. No. 6,365,894 (Apr. 2, 2002) and M. Tadokoro, et. al. “Electromagnetic and Magnetic Field Generating Apparatus”, U.S. Pat. No. 6,236,043 (May 22, 2001) each describe a pair of magnetic poles, a return yoke, and exciting coils. The interior of the magnetic poles each have a plurality of air gap spacers to increase magnetic field strength. Extraction T. Nakanishi, et. al. “Charged-Particle Beam Accelerator, Particle Beam Radiation Therapy System Using the Charged-Particle Beam Accelerator, and Method of Operating the Particle Beam Radiation Therapy System”, U.S. Pat. No. 7,122,978 (Oct. 17, 2006) describe a charged particle beam accelerator having an RF-KO unit for increasing amplitude of betatron oscillation of a charged particle beam within a stable region of resonance and an extraction quadrupole electromagnet unit for varying a stable region of resonance. The RF-KO unit is operated within a frequency range in which the circulating beam does not go beyond a boundary of stable region of resonance and the extraction quadrupole electromagnet is operated with timing required for beam extraction. T. Haberer, et. al. “Method and Device for Controlling a Beam Extraction Raster Scan Irradiation Device for Heavy Ions or Protons”, U.S. Pat. No. 7,091,478 (Aug. 15, 2006) describe a method for controlling beam extraction irradiation in terms of beam energy, beam focusing, and beam intensity for every accelerator cycle. K. Hiramoto, et. al. “Accelerator and Medical System and Operating Method of the Same”, U.S. Pat. No. 6,472,834 (Oct. 29, 2002) describe a cyclic type accelerator having a deflection electromagnet and four-pole electromagnets for making a charged particle beam circulate, a multi-pole electromagnet for generating a stability limit of resonance of betatron oscillation, and a high frequency source for applying a high frequency electromagnetic field to the beam to move the beam to the outside of the stability limit. The high frequency source generates a sum signal of a plurality of alternating current (AC) signals of which the instantaneous frequencies change with respect to time, and of which the average values of the instantaneous frequencies with respect to time are different. The system applies the sum signal via electrodes to the beam. K. Hiramoto, et. al. “Synchrotron Type Accelerator and Medical Treatment System Employing the Same”, U.S. Pat. No. 6,087,670 (Jul. 11, 2000) and K. Hiramoto, et. al. “Synchrotron Type Accelerator and Medical Treatment System Employing the Same”, U.S. Pat. No. 6,008,499 (Dec. 28, 1999) describe a synchrotron accelerator having a high frequency applying unit arranged on a circulating orbit for applying a high frequency electromagnetic field to a charged particle beam circulating and for increasing amplitude of betatron oscillation of the particle beam to a level above a stability limit of resonance. Additionally, for beam ejection, four-pole divergence electromagnets are arranged: (1) downstream with respect to a first deflector; (2) upstream with respect to a deflecting electromagnet; (3) downstream with respect to the deflecting electromagnet; and (4) and upstream with respect to a second deflector. K. Hiramoto, et. al. “Circular Accelerator and Method and Apparatus for Extracting Charged-Particle Beam in Circular Accelerator”, U.S. Pat. No. 5,363,008 (Nov. 8, 1994) describe a circular accelerator for extracting a charged-particle beam that is arranged to: (1) increase displacement of a beam by the effect of betatron oscillation resonance; (2) to increase the betatron oscillation amplitude of the particles, which have an initial betatron oscillation within a stability limit for resonance; and (3) to exceed the resonance stability limit thereby extracting the particles exceeding the stability limit of the resonance. K. Hiramoto, et. al. “Method of Extracting Charged Particles from Accelerator, and Accelerator Capable Carrying Out the Method, by Shifting Particle Orbit”, U.S. Pat. No. 5,285,166 (Feb. 8, 1994) describe a method of extracting a charged particle beam. An equilibrium orbit of charged particles maintained by a bending magnet and magnets having multipole components greater than sextuple components is shifted by a constituent element of the accelerator other than these magnets to change the tune of the charged particles. Transport/Scanning Control K. Matsuda, et. al. “Particle Beam Irradiation Apparatus, Treatment Planning Unit, and Particle Beam Irradiation Method”, U.S. Pat. No. 7,227,161 (Jun. 5, 2007); K. Matsuda, et. al. “Particle Beam Irradiation Treatment Planning Unit, and Particle Beam Irradiation Method”, U.S. Pat. No. 7,122,811 (Oct. 17, 2006); and K. Matsuda, et. al. “Particle Beam Irradiation Apparatus, Treatment Planning Unit, and Particle Beam Irradiation Method” (Sep. 5, 2006) describe a particle beam irradiation apparatus have a scanning controller that stops output of an ion beam, changes irradiation position via control of scanning electromagnets, and reinitiates treatment based on treatment planning information. T. Norimine, et. al. “Particle Therapy System Apparatus”, U.S. Pat. No. 7,060,997 (Jun. 13, 2006); T. Norimine, et. al. “Particle Therapy System Apparatus”, U.S. Pat. No. 6,936,832 (Aug. 30, 2005); and T. Norimine, et. al. “Particle Therapy System Apparatus”, U.S. Pat. No. 6,774,383 (Aug. 10, 2004) each describe a particle therapy system having a first steering magnet and a second steering magnet disposed in a charged particle beam path after a synchrotron that are controlled by first and second beam position monitors. K. Moriyama, et. al. “Particle Beam Therapy System”, U.S. Pat. No. 7,012,267 (Mar. 14, 2006) describe a manual input to a ready signal indicating preparations are completed for transport of the ion beam to a patient. H. Harada, et. al. “Irradiation Apparatus and Irradiation Method”, U.S. Pat. No. 6,984,835 (Jan. 10, 2006) describe an irradiation method having a large irradiation filed capable of uniform dose distribution, without strengthening performance of an irradiation field device, using a position controller having overlapping area formed by a plurality of irradiations using a multileaf collimator. The system provides flat and uniform dose distribution over an entire surface of a target. H. Akiyama, et. al. “Charged Particle Beam Irradiation Equipment Having Scanning Electromagnet Power Supplies”, U.S. Pat. No. 6,903,351 (Jun. 7, 2005); H. Akiyama, et. al. “Charged Particle Beam Irradiation Equipment Having Scanning Electromagnet Power Supplies”, U.S. Pat. No. 6,900,436 (May 31, 2005); and H. Akiyama, et. al. “Charged Particle Beam Irradiation Equipment Having Scanning Electromagnet Power Supplies”, U.S. Pat. No. 6,881,970 (Apr. 19, 2005) all describe a power supply for applying a voltage to a scanning electromagnet for deflecting a charged particle beam and a second power supply without a pulsating component to control the scanning electromagnet more precisely allowing for uniform irradiation of the irradiation object. K. Amemiya, et. al. “Accelerator System and Medical Accelerator Facility”, U.S. Pat. No. 6,800,866 (Oct. 5, 2004) describe an accelerator system having a wide ion beam control current range capable of operating with low power consumption and having a long maintenance interval. A. Dolinskii, et. al. “Gantry with an Ion-Optical System”, U.S. Pat. No. 6,476,403 (Nov. 5, 2002) describe a gantry for an ion-optical system comprising an ion source and three bending magnets for deflecting an ion beam about an axis of rotation. A plurality of quadrupoles are also provided along the beam path to create a fully achromatic beam transport and an ion beam with difference emittances in the horizontal and vertical planes. Further, two scanning magnets are provided between the second and third bending magnets to direct the beam. H. Akiyama, et. al. “Charged Particle Beam Irradiation Apparatus”, U.S. Pat. No. 6,218,675 (Apr. 17, 2001) describe a charged particle beam irradiation apparatus for irradiating a target with a charged particle beam that include a plurality of scanning electromagnets and a quadrupole electromagnet between two of the plurality of scanning electromagnets. K. Matsuda, et. al. “Charged Particle Beam Irradiation System and Method Thereof”, U.S. Pat. No. 6,087,672 (Jul. 11, 2000) describe a charged particle beam irradiation system having a ridge filter with shielding elements to shield a part of the charged particle beam in an area corresponding to a thin region in said target. P. Young, et. al. “Raster Scan Control System for a Charged-Particle Beam”, U.S. Pat. No. 5,017,789 (May 21, 1991) describe a raster scan control system for use with a charged-particle beam delivery system that includes a nozzle through which a charged particle beam passes. The nozzle includes a programmable raster generator and both fast and slow sweep scan electromagnets that cooperate to generate a sweeping magnetic field that steers the beam along a desired raster scan pattern at a target. Beam Shape Control M. Yanagisawa, et. al. “Particle Beam Irradiation System and Method of Adjusting Irradiation Field Forming Apparatus”, U.S. Pat. No. 7,154,107 (Dec. 26, 2006) and M. Yanagisawa, et. al. “Particle Beam Irradiation System and Method of Adjusting Irradiation Field Forming Apparatus”, U.S. Pat. No. 7,049,613 (May 23, 2006) describe a particle therapy system having a scattering compensator and a range modulation wheel. Movement of the scattering compensator and the range modulation wheel adjusts a size of the ion beam and scattering intensity resulting in penumbra control and a more uniform dose distribution to a diseased body part. T. Haberer, et. al. “Device and Method for Adapting the Size of an Ion Beam Spot in the Domain of Tumor Irradiation”, U.S. Pat. No. 6,859,741 (Feb. 22, 2005) describe a method and apparatus for adapting the size of an ion beam in tumor irradiation. Quadrupole magnets determining the size of the ion beam spot are arranged directly in front of raster scanning magnets determining the size of the ion beam spot. The apparatus contains a control loop for obtaining current correction values to further control the ion beam spot size. K. Matsuda, et. al. “Charged Particle Irradiation Apparatus and an Operating Method Thereof”, U.S. Pat. No. 5,986,274 (Nov. 16, 1999) describe a charged particle irradiation apparatus capable of decreasing a lateral dose falloff at boundaries of an irradiation field of a charged particle beam using controlling magnet fields of quadrupole electromagnets and deflection electromagnets to control the center of the charged particle beam passing through the center of a scatterer irrespective of direction and intensity of a magnetic field generated by scanning electromagnets. K. Hiramoto, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 5,969,367 (Oct. 19, 1999) describe a charged particle beam apparatus where a the charged particle beam is enlarged by a scatterer resulting in a Gaussian distribution that allows overlapping of irradiation doses applied to varying spot positions. M. Moyers, et. al. “Charged Particle Beam Scattering System”, U.S. Pat. No. 5,440,133 (Aug. 8, 1995) describe a radiation treatment apparatus for producing a particle beam and a scattering foil for changing the diameter of the charged particle beam. C. Nunan “Multileaf Collimator for Radiotherapy Machines”, U.S. Pat. No. 4,868,844 (Sep. 19, 1989) describes a radiation therapy machine having a multileaf collimator formed of a plurality of heavy metal leaf bars movable to form a rectangular irradiation field. R. Maughan, et. al. “Variable Radiation Collimator”, U.S. Pat. No. 4,754,147 (Jun. 28, 1988) describe a variable collimator for shaping a cross-section of a radiation beam that relies on rods, which are positioned around a beam axis. The rods are shaped by a shaping member cut to a shape of an area of a patient go be irradiated. Beam Energy/Intensity M. Yanagisawa, et. al. “Charged Particle Therapy System, Range Modulation Wheel Device, and Method of Installing Range Modulation Wheel Device”, U.S. Pat. No. 7,355,189 (Apr. 8, 2008) and Yanagisawa, et. al. “Charged Particle Therapy System, Range Modulation Wheel Device, and Method of Installing Range Modulation Wheel Device”, U.S. Pat. No. 7,053,389 (May 30, 2008) both describe a particle therapy system having a range modulation wheel. The ion beam passes through the range modulation wheel resulting in a plurality of energy levels corresponding to a plurality of stepped thicknesses of the range modulation wheel. M. Yanagisawa, et. al. “Particle Beam Irradiation System and Method of Adjusting Irradiation Apparatus”, U.S. Pat. No. 7,297,967 (Nov. 20, 2007); M. Yanagisawa, et. al. “Particle Beam Irradiation System and Method of Adjusting Irradiation Apparatus”, U.S. Pat. No. 7,071,479 (Jul. 4, 2006); M. Yanagisawa, et. al. “Particle Beam Irradiation System and Method of Adjusting Irradiation Apparatus”, U.S. Pat. No. 7,026,636 (Apr. 11, 2006); and M. Yanagisawa, et. al. “Particle Beam Irradiation System and Method of Adjusting Irradiation Apparatus”, U.S. Pat. No. 6,777,700 (Aug. 17, 2004) all describe a scattering device, a range adjustment device, and a peak spreading device. The scattering device and range adjustment device are combined together and are moved along a beam axis. The spreading device is independently moved along the axis to adjust the degree of ion beam scattering. Combined, the devise increases the degree of uniformity of radiation dose distribution to a diseased tissue. A. Sliski, et. al. “Programmable Particle Scatterer for Radiation Therapy Beam Formation”, U.S. Pat. No. 7,208,748 (Apr. 24, 2007) describe a programmable pathlength of a fluid disposed into a particle beam to modulate scattering angle and beam range in a predetermined manner. The charged particle beam scatterer/range modulator comprises a fluid reservoir having opposing walls in a particle beam path and a drive to adjust the distance between the walls of the fluid reservoir under control of a programmable controller to create a predetermined spread out Bragg peak at a predetermined depth in a tissue. The beam scattering and modulation is continuously and dynamically adjusted during treatment of a tumor to deposit a dose in a targeted predetermined three dimensional volume. M. Tadokoro, et. al. “Particle Therapy System”, U.S. Pat. No. 7,247,869 (Jul. 24, 2007) and U.S. Pat. No. 7,154,108 (Dec. 26, 2006) each describe a particle therapy system capable of measuring energy of a charged particle beam during irradiation during use. The system includes a beam passage between a pair of collimators, an energy detector mounted, and a signal processing unit. G. Kraft, et. al. “Ion Beam Scanner System and Operating Method”, U.S. Pat. No. 6,891,177 (May 10, 2005) describe an ion beam scanning system having a mechanical alignment system for the target volume to be scanned and allowing for depth modulation of the ion beam by means of a linear motor and transverse displacement of energy absorption means resulting in depth-staggered scanning of volume elements of a target volume. G. Hartmann, et. al. “Method for Operating an Ion Beam Therapy System by Monitoring the Distribution of the Radiation Dose”, U.S. Pat. No. 6,736,831 (May 18, 2004) describe a method for operation of an ion beam therapy system having a grid scanner and irradiates and scans an area surrounding an isocentre. Both the depth dose distribution and the transverse dose distribution of the grid scanner device at various positions in the region of the isocentre are measured and evaluated. Y. Jongen “Method for Treating a Target Volume with a Particle Beam and Device Implementing Same”, U.S. Pat. No. 6,717,162 (Apr. 6, 2004) describes a method of producing from a particle beam a narrow spot directed towards a target volume, characterized in that the spot sweeping speed and particle beam intensity are simultaneously varied. G. Kraft, et. al. “Device for Irradiating a Tumor Tissue”, U.S. Pat. No. 6,710,362 (Mar. 23, 2004) describe a method and apparatus of irradiating a tumor tissue, where the apparatus has an electromagnetically driven ion-braking device in the proton beam path for depth-wise adaptation of the proton beam that adjusts both the ion beam direction and ion beam range. K. Matsuda, et. al. “Charged Particle Beam Irradiation Apparatus”, U.S. Pat. No. 6,617,598 (Sep. 9, 2003) describe a charged particle beam irradiation apparatus that increased the width in a depth direction of a Bragg peak by passing the Bragg peak through an enlarging device containing three ion beam components having different energies produced according to the difference between passed positions of each of the filter elements. H. Stelzer, et. al. “Ionization Chamber for Ion Beams and Method for Monitoring the Intensity of an Ion Beam”, U.S. Pat. No. 6,437,513 (Aug. 20, 2002) describe an ionization chamber for ion beams and a method of monitoring the intensity of an ion therapy beam. The ionization chamber includes a chamber housing, a beam inlet window, a beam outlet window, a beam outlet window, and a chamber volume filled with counting gas. H. Akiyama, et. al. “Charged-Particle Beam Irradiation Method and System”, U.S. Pat. No. 6,433,349 (Aug. 13, 2002) and H. Akiyama, et. al. “Charged-Particle Beam Irradiation Method and System”, U.S. Pat. No. 6,265,837 (Jul. 24, 2001) both describe a charged particle beam irradiation system that includes a changer for changing energy of the particle and an intensity controller for controlling an intensity of the charged-particle beam. Y. Pu “Charged Particle Beam Irradiation Apparatus and Method of Irradiation with Charged Particle Beam”, U.S. Pat. No. 6,034,377 (Mar. 7, 2000) describes a charged particle beam irradiation apparatus having an energy degrader comprising: (1) a cylindrical member having a length; and (2) a distribution of wall thickness in a circumferential direction around an axis of rotation, where thickness of the wall determines energy degradation of the irradiation beam. Dosage K. Matsuda, et. al. “Particle Beam Irradiation System”, U.S. Pat. No. 7,372,053 (Nov. 27, 2007) describe a particle beam irradiation system ensuring a more uniform dose distribution at an irradiation object through use of a stop signal, which stops the output of the ion beam from the irradiation device. H. Sakamoto, et. al. “Radiation Treatment Plan Making System and Method”, U.S. Pat. No. 7,054,801 (May 30, 2006) describe a radiation exposure system that divides an exposure region into a plurality of exposure regions and uses a radiation simulation to plan radiation treatment conditions to obtain flat radiation exposure to the desired region. G. Hartmann, et. al. “Method For Verifying the Calculated Radiation Dose of an Ion Beam Therapy System”, U.S. Pat. No. 6,799,068 (Sep. 28, 2004) describe a method for the verification of the calculated dose of an ion beam therapy system that comprises a phantom and a discrepancy between the calculated radiation dose and the phantom. H. Brand, et. al. “Method for Monitoring the Irradiation Control of an Ion Beam Therapy System”, U.S. Pat. No. 6,614,038 (Sep. 2, 2003) describe a method of checking a calculated irradiation control unit of an ion beam therapy system, where scan data sets, control computer parameters, measuring sensor parameters, and desired current values of scanner magnets are permanently stored. T. Kan, et. al. “Water Phantom Type Dose Distribution Determining Apparatus”, U.S. Pat. No. 6,207,952 (Mar. 27, 2001) describe a water phantom type dose distribution apparatus that includes a closed water tank, filled with water to the brim, having an inserted sensor that is used to determine an actual dose distribution of radiation prior to radiation therapy. Starting/Stopping Irradiation K. Hiramoto, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 6,316,776 (Nov. 13, 2001) describe a charged particle beam apparatus where a charged particle beam is positioned, started, stopped, and repositioned repetitively. Residual particles are used in the accelerator without supplying new particles if sufficient charge is available. K. Matsuda, et. al. “Method and Apparatus for Controlling Circular Accelerator”, U.S. Pat. No. 6,462,490 (Oct. 8, 2002) describe a control method and apparatus for a circular accelerator for adjusting timing of emitted charged particles. The clock pulse is suspended after delivery of a charged particle stream and is resumed on the basis of state of an object to be irradiated. Movable Patient N. Rigney, et. al. “Patient Alignment System with External Measurement and Object Coordination for Radiation Therapy System”, U.S. Pat. No. 7,199,382 (Apr. 3, 2007) describe a patient alignment system for a radiation therapy system that includes multiple external measurement devices that obtain position measurements of movable components of the radiation therapy system. The alignment system uses the external measurements to provide corrective positioning feedback to more precisely register the patient to the radiation beam. Y. Muramatsu, et. al. “Medical Particle Irradiation Apparatus”, U.S. Pat. No. 7,030,396 (Apr. 18, 2006); Y. Muramatsu, et. al. “Medical Particle Irradiation Apparatus”, U.S. Pat. No. 6,903,356 (Jun. 7, 2005); and Y. Muramatsu, et. al. “Medical Particle Irradiation Apparatus”, U.S. Pat. No. 6,803,591 (Oct. 12, 2004) all describe a medical particle irradiation apparatus having a rotating gantry, an annular frame located within the gantry such that is can rotate relative to the rotating gantry, an anti-correlation mechanism to keep the frame from rotating with the gantry, and a flexible moving floor engaged with the frame is such a manner to move freely with a substantially level bottom while the gantry rotates. H. Nonaka, et. al. “Rotating Radiation Chamber for Radiation Therapy”, U.S. Pat. No. 5,993,373 (Nov. 30, 1999) describe a horizontal movable floor composed of a series of multiple plates that are connected in a free and flexible manner, where the movable floor is moved in synchrony with rotation of a radiation beam irradiation section. Respiration K. Matsuda “Radioactive Beam Irradiation Method and Apparatus Taking Movement of the Irradiation Area Into Consideration”, U.S. Pat. No. 5,538,494 (Jul. 23, 1996) describes a method and apparatus that enables irradiation even in the case of a diseased part changing position due to physical activity, such as breathing and heart beat. Initially, a position change of a diseased body part and physical activity of the patient are measured concurrently and a relationship therebetween is defined as a function. Radiation therapy is performed in accordance to the function. Patient Positioning Y. Nagamine, et. al. “Patient Positioning Device and Patient Positioning Method”, U.S. Pat. Nos. 7,212,609 and 7,212,608 (May 1, 2007) describe a patient positioning system that compares a comparison area of a reference X-ray image and a current X-ray image of a current patient location using pattern matching. D. Miller, et. al. “Modular Patient Support System”, U.S. Pat. No. 7,173,265 (Feb. 6, 2007) describe a radiation treatment system having a patient support system that includes a modularly expandable patient pod and at least one immobilization device, such as a moldable foam cradle. K. Kato, et. al. “Multi-Leaf Collimator and Medical System Including Accelerator”, U.S. Pat. No. 6,931,100 (Aug. 16, 2005); K. Kato, et. al. “Multi-Leaf Collimator and Medical System Including Accelerator”, U.S. Pat. No. 6,823,045 (Nov. 23, 2004); K. Kato, et. al. “Multi-Leaf Collimator and Medical System Including Accelerator”, U.S. Pat. No. 6,819,743 (Nov. 16, 2004); and K. Kato, et. al. “Multi-Leaf Collimator and Medical System Including Accelerator”, U.S. Pat. No. 6,792,078 (Sep. 14, 2004) all describe a system of leaf plates used to shorten positioning time of a patient for irradiation therapy. Motor driving force is transmitted to a plurality of leaf plates at the same time through a pinion gear. The system also uses upper and lower air cylinders and upper and lower guides to position a patient. Imaging P. Adamee, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 7,274,018 (Sep. 25, 2007) and P. Adamee, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 7,045,781 (May 16, 2006) describe a charged particle beam apparatus configured for serial and/or parallel imaging of an object. K. Hiramoto, et. al. “Ion Beam Therapy System and its Couch Positioning System”, U.S. Pat. No. 7,193,227 (Mar. 20, 2007) describe a ion beam therapy system having an X-ray imaging system moving in conjunction with a rotating gantry. C. Maurer, et. al. “Apparatus and Method for Registration of Images to Physical Space Using a Weighted Combination of Points and Surfaces”, U.S. Pat. No. 6,560,354 (May 6, 2003) described a process of X-ray computed tomography registered to physical measurements taken on the patient's body, where different body parts are given different weights. Weights are used in an iterative registration process to determine a rigid body transformation process, where the transformation function is used to assist surgical or stereotactic procedures. M. Blair, et. al. “Proton Beam Digital Imaging System”, U.S. Pat. No. 5,825,845 (Oct. 20, 1998) describe a proton beam digital imaging system having an X-ray source that is movable into the treatment beam line that can produce an X-ray beam through a region of the body. By comparison of the relative positions of the center of the beam in the patient orientation image and the isocentre in the master prescription image with respect to selected monuments, the amount and direction of movement of the patient to make the best beam center correspond to the target isocentre is determined. S. Nishihara, et. al. “Therapeutic Apparatus”, U.S. Pat. No. 5,039,867 (Aug. 13, 1991) describe a method and apparatus for positioning a therapeutic beam in which a first distance is determined on the basis of a first image, a second distance is determined on the basis of a second image, and the patient is moved to a therapy beam irradiation position on the basis of the first and second distances. Problem There exists in the art of particle beam treatment of cancerous tumors in the body a need for efficient control of magnetic fields used in the control of charged particles in a synchrotron of a charged particle cancer therapy system. Further, there exists in the art of particle beam therapy of cancerous tumors a need for reduced power supply requirements, reduced construction costs, and reduced size of the synchrotron. Further, there exists a need in the art to control the charged particle cancer therapy system in terms of specified energy, intensity, and/or timing of charged particle delivery. Still further, there exists a need for efficient, precise, and/or accurate noninvasive, in-vivo treatment of a solid cancerous tumor with minimization of damage to surrounding healthy tissue in a patient. 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. This invention relates generally to treatment of solid cancers. More particularly, the invention relates to intensity control of a charged particle stream in a particle accelerator. Magnetic field control elements and intensity control are used in conjunction with charged particle cancer therapy beam acceleration, extraction, and/or targeting methods and apparatus. Novel design features of a synchrotron are described. Particularly, 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 is described. More particularly, intensity control 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. Cyclotron/Synchrotron A cyclotron uses a constant magnetic field and a constant-frequency applied electric field. One of the two fields is varied in a synchrocyclotron. Both of these fields are varied in a synchrotron. Thus, a synchrotron is a particular type of cyclic particle accelerator in which a magnetic field is used to turn the particles so they circulate and an electric field is used to accelerate the particles. The synchroton carefully synchronizes the applied fields with the travelling particle beam. By increasing the fields appropriately as the particles gain energy, the charged particles path can be held constant as they are accelerated. This allows the vacuum container for the particles to be a large thin torus. In practice it is easier to use some straight sections between the bending magnets and some turning sections giving the torus the shape of a round-cornered polygon. A path of large effective radius is thus constructed using simple straight and curved pipe segments, unlike the disc-shaped chamber of the cyclotron type devices. The shape also allows and requires the use of multiple magnets to bend the particle beam. The maximum energy that a cyclic accelerator can impart is typically limited by the strength of the magnetic fields and the minimum radius/maximum curvature, of the particle path. In a cyclotron the maximum radius is quite limited as the particles start at the center and spiral outward, thus this entire path must be a self-supporting disc-shaped evacuated chamber. Since the radius is limited, the power of the machine becomes limited by the strength of the magnetic field. In the case of an ordinary electromagnet, the field strength is limited by the saturation of the core because when all magnetic domains are aligned the field may not be further increased to any practical extent. The arrangement of the single pair of magnets also limits the economic size of the device. Synchrotrons overcome these limitations, using a narrow beam pipe surrounded by much smaller and more tightly focusing magnets. The ability of this device to accelerate particles is limited by the fact that the particles must be charged to be accelerated at all, but charged particles under acceleration emit photons, thereby losing energy. The limiting beam energy is reached when the energy lost to the lateral acceleration required to maintain the beam path in a circle equals the energy added each cycle. More powerful accelerators are built by using large radius paths and by using more numerous and more powerful microwave cavities to accelerate the particle beam between corners. Lighter particles, such as electrons, lose a larger fraction of their energy when turning. Practically speaking, the energy of electron/positron accelerators is limited by this radiation loss, while it does not play a significant role in the dynamics of proton or ion accelerators. The energy of those is limited strictly by the strength of magnets and by the cost. Charged Particle Beam Therapy Throughout this document, a charged particle beam therapy system, such as a proton beam, hydrogen ion beam, or carbon ion beam, is described. Herein, the charged particle beam therapy system is described using a proton beam. However, the aspects taught and described in terms of a proton beam are not intended to be limiting to that of a proton beam and are illustrative of a charged particle beam system. Any charged particle beam system is equally applicable to the techniques described herein. Referring now to FIG. 1, a charged particle beam system 100 is illustrated. The charged particle beam preferably comprises a number of subsystems including any of: a main controller 110; an injection system 120; a synchrotron 130 that typically includes: (1) an accelerator system 132 and (2) an extraction system 134; a targeting/delivery system 140; a patient interface module 150; a display system 160; and/or an imaging system 170. An exemplary method of use of the charged particle beam system 100 is provided. The main controller 110 controls one or more of the subsystems to accurately and precisely deliver protons to a tumor of a patient. For example, the main controller 110 obtains an image, such as a portion of a body and/or of a tumor, from the imaging system 170. The main controller 110 also obtains position and/or timing information from the patient interface module 150. The main controller 110 then optionally controls the injection system 120 to inject a proton into a synchrotron 130. The synchrotron typically contains at least an accelerator system 132 and an extraction system 134. The main controller preferably controls the proton beam within the accelerator system, such as by controlling speed, trajectory, and timing of the proton beam. The main controller then controls extraction of a proton beam from the accelerator through the extraction system 134. For example, the controller controls timing, energy, and/or intensity of the extracted beam. The controller 110 also preferably controls targeting of the proton beam through the targeting/delivery system 140 to the patient interface module 150. One or more components of the patient interface module 150 are preferably controlled by the main controller 110. Further, display elements of the display system 160 are preferably controlled via the main controller 110. Displays, such as display screens, are typically provided to one or more operators and/or to one or more patients. In one embodiment, the main controller 110 times the delivery of the proton beam from all systems, such that protons are delivered in an optimal therapeutic manner to the patient. Herein, the main controller 110 refers to a single system controlling the charged particle beam system 100, to a single controller controlling a plurality of subsystems controlling the charged particle beam system 100, or to a plurality of individual controllers controlling one or more sub-systems of the charged particle beam system 100. Synchrotron Herein, the term synchrotron is used to refer to a system maintaining the charged particle beam in a circulating path; however, cyclotrons are alternatively used, albeit with their inherent limitations of energy, intensity, and extraction control. Further, the charged particle beam is referred to herein as circulating along a circulating path about a central point of the synchrotron. The circulating path is alternatively referred to as an orbiting path; however, the orbiting path does not refer a perfect circle or ellipse, rather it refers to cycling of the protons around a central point or region. Referring now to FIG. 2, an illustrative exemplary embodiment of one version of the charged particle beam system 100 is provided. The number, position, and described type of components is illustrative and non-limiting in nature. In the illustrated embodiment, the injection system 120 or ion source or charged particle beam source generates protons. The protons are delivered into a vacuum tube that runs into, through, and out of the synchrotron. The generated protons are delivered along an initial path 262. Focusing magnets 230, such as quadrupole magnets or injection quadrupole magnets, are used to focus the proton beam path. A quadrupole magnet is a focusing magnet. An injector bending magnet 232 bends the proton beam toward the plane of the synchrotron 130. The focused protons having an initial energy are introduced into an injector magnet 240, which is preferably an injection Lamberson magnet. Typically, the initial beam path 262 is along an axis off of, such as above, a circulating plane of the synchrotron 130. The injector bending magnet 232 and injector magnet 240 combine to move the protons into the synchrotron 130. Main bending or turning magnets, dipole magnets, or circulating magnets 250 are used to turn the protons along a circulating beam path 264. A dipole magnet is a bending magnet. The main bending magnets 250 bend the initial beam path 262 into a circulating beam path 264. In this example, the main bending magnets 250 or circulating magnets are represented as four sets of four magnets to maintain the circulating beam path 264 into a stable circulating beam path. However, any number of magnets or sets of magnets are optionally used to move the protons around a single orbit in the circulation process. The protons pass through an accelerator 270. The accelerator accelerates the protons in the circulating beam path 264. As the protons are accelerated, the fields applied by the magnets 250 are increased. Particularly, the speed of the protons achieved by the accelerator 270 are synchronized with magnetic fields of the main bending magnets 250 or circulating magnets to maintain stable circulation of the protons about a central point or region 280 of the synchrotron. At separate points in time the accelerator 270/main bending magnet 250 combination is used to accelerate and/or decelerate the circulating protons while maintaining the protons in the circulating path or orbit. An extraction element of the inflector/deflector system 290 is used in combination with a Lamberson extraction magnet 292 to remove protons from their circulating beam path 264 within the synchrotron 130. One example of a deflector component is a Lamberson magnet. Typically the deflector moves the protons from the circulating plane to an axis off of the circulating plane, such as above the circulating plane. Extracted protons are preferably directed and/or focused using an extraction bending magnet 237 and extraction focusing magnets 235, such as quadrupole magnets along a transport path 268 into the scanning/targeting/delivery system 140. Two components of a scanning system 140 or targeting system typically include a first axis control 142, such as a vertical control, and a second axis control 144, such as a horizontal control. In one embodiment, the first axis control 142 allows for about 100 mm of vertical or y-axis scanning of the proton beam 268 and the second axis control 144 allows for about 700 mm of horizontal or x-axis scanning of the proton beam 268. A nozzle system is optionally used for imaging the proton beam and/or as a vacuum barrier between the low pressure beam path of the synchrotron and the atmosphere. Protons are delivered with control to the patient interface module 150 and to a tumor of a patient. All of the above listed elements are optional and may be used in various permutations and combinations. Use of the above listed elements is further described, infra. Protons are delivered with control to the patient interface module 170 and to a tumor of a patient. In one example, the charged particle irradiation includes a synchrotron having: a center, straight sections, and turning sections. The charged particle beam path runs about the center, through the straight sections, and through the turning sections, where each of the turning sections comprises a plurality of bending magnets. Preferably, the circulation beam path comprises a length of less than sixty meters, and the number of straight sections equals the number of turning sections. Preferably no quadrupoles are used in or around the circulating path of the synchrotron. Circulating System A synchrotron 130 preferably comprises a combination of straight sections 310 and ion beam turning sections 320. Hence, the circulating path of the protons is not circular in a synchrotron, but is rather a polygon with rounded corners. In one illustrative embodiment, the synchrotron 130, which is also referred to as an accelerator system, has four straight elements and four turning sections. Examples of straight sections 310 include the: inflector 240, accelerator 270, extraction system 290, and deflector 292. Along with the four straight sections are four ion beam turning sections 320, which are also referred to as magnet sections or turning sections. Turning sections are further described, infra. Referring now to FIG. 3, an exemplary synchrotron is illustrated. In this example, protons delivered along the initial path 262 are inflected into the circulating beam path with the inflector 240 and after acceleration are extracted via a deflector 292 to a beam transport path 268. In this example, the synchrotron 130 comprises four straight sections 310 and four turning sections 320 where each of the four turning sections use one or more magnets to turn the proton beam about ninety degrees. As is further described, infra, the ability to closely space the turning sections and efficiently turn the proton beam results in shorter straight sections. Shorter straight sections allows for a synchrotron design without the use of focusing quadrupoles in the circulating beam path of the synchrotron. The removal of the focusing quadrupoles from the circulating proton beam path results in a more compact design. In this example, the illustrated synchrotron has about a five meter diameter versus eight meter and larger cross-sectional diameters for systems using a quadrupole focusing magnet in the circulating proton beam path. Referring now to FIG. 4, additional description of the first turning section 320 is provided. Each of the turning sections preferably comprises multiple magnets, such as about 2, 4, 6, 8, 10, or 12 magnets. In this example, four turning magnets 410, 420, 430, 440 in the first turning section 320 are used to illustrate key principles, which are the same regardless of the number of magnets in a turning section 320. A turning magnet 410 is a particular type of circulating magnet 250. In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. The Lorentz force is given by the equation 1 in terms of magnetic fields with the election field terms not included.F=q(v×B) eq. 1 In equation 1, F is the force in newtons; B is the magnetic field in Teslas; and v is the instantaneous velocity of the particles in meters per second. Referring now to FIG. 5, an example of a single magnet turning section 410 is expanded. The turning section includes a gap 510. The gap is preferably a flat gap, allowing for a magnetic field across the gap that is more uniform, even, and intense. A magnetic field enters the gap through a magnetic field incident surface and exits the gap through a magnetic field exiting surface. The gap 510 runs in a vacuum tube between two magnet halves. The gap is controlled by at least two parameters: (1) the gap 510 is kept as large as possible to minimize loss of protons and (2) the gap 510 is kept as small as possible to minimize magnet sizes and the associated size and power requirements of the magnet power supplies. The flat nature of the gap 510 allows for a compressed and more uniform magnetic field across the gap. One example of a gap dimension is to accommodate a vertical proton beam size of about 2 cm with a horizontal beam size of about 5 to 6 cm. As described, supra, a larger gap size requires a larger power supply. For instance, if the gap size doubles in vertical size, then the power supply requirements increase by about a factor of four. The flatness of the gap is also important. For example, the flat nature of the gap allows for an increase in energy of the extracted protons from about 250 to about 330 MeV. More particularly, if the gap 510 has an extremely flat surface, then the limits of a magnetic field of an iron magnet are reachable. An exemplary precision of the flat surface of the gap 510 is a polish of less than about five microns and preferably with a polish of about one to three microns. Unevenness in the surface results in imperfections in the applied magnetic field. The polished flat surface spreads unevenness of the applied magnetic field. Still referring to FIG. 5, the charged particle beam moves through the gap with an instantaneous velocity, v. A first magnetic coil 520 and a second magnetic coil 530 run above and below the gap 510, respectively. Current running through the coils 520, 530 results in a magnetic field, B, running through the single magnet turning section 410. In this example, the magnetic field, B, runs upward, which results in a force, F, pushing the charged particle beam inward toward a central point of the synchrotron, which turns the charged particle beam in an arc. Still referring to FIG. 5, a portion of an optional second magnet turning section 420 is illustrated. The coils 520, 530 typically have return elements or turns at the end of one magnet, such as at the end of the first magnet turning section 410. The return elements take space. The space reduces the percentage of the path about one orbit of the synchrotron that is covered by the turning magnets. This leads to portions of the circulating path where the protons are not turned and/or focused and allows for portions of the circulating path where the proton path defocuses. Thus, the space results in a larger synchrotron. Therefore, the space between magnet turning sections 560 is preferably minimized. The second turning magnet is used to illustrate that the coils 520, 530 optionally run along a plurality of magnets, such as 2, 3, 4, 5, 6, or more magnets. Coils 520, 530 running across turning section magnets allows for two turning section magnets to be spatially positioned closer to each other due to the removal of the steric constraint of the turns, which reduces and/or minimizes the space 560 between two turning section magnets. Referring now to FIGS. 6 and 7, two illustrative 90 degree rotated cross-sections of single magnet turning sections 410 are presented. The magnet assembly has a first magnet 610 and a second magnet 620. A magnetic field induced by coils, described infra, runs between the first magnet 610 to the second magnet 620 across the gap 510. Return magnetic fields run through a first yoke 612 and second yoke 622. The charged particles run through the vacuum tube in the gap. As illustrated, protons run into FIG. 6 through the gap 510 and the magnetic field, illustrated as vector B, applies a force F to the protons pushing the protons towards the center of the synchrotron, which is off page to the right in FIG. 6. The magnetic field is created using windings. A first coil of wire is wound around the magnet to yield a first winding coil 650. The second coil of wire is wound to around the second magnet to yield a second winding coil 660. Isolating gaps 630, 640, such as air gaps, isolate the iron based yokes 612, 622 from the gap 510. The gap is approximately flat to yield a uniform magnetic field across the gap, as described supra. Referring again to FIG. 7, the ends of a single turning magnet are preferably beveled. Nearly perpendicular or right angle edges of a turning magnet 410 are represented by a dashed lines 674, 684. Preferably, the edge of the turning magnet is beveled at angles alpha, α, and beta, β, which is the off perpendicular angle between the right angles 674, 684 and beveled edges 672, 682. The angle alpha is used to describe the effect and the description of angle alpha applies to angle beta, but angle alpha is optionally different from angle beta. The angle alpha provides an edge focusing effect. Beveling the edge of the turning magnet 410 at angle alpha focuses the proton beam. Multiple turning magnets provide multiple magnet edges that each have edge focusing effects in the synchrotron 310. If only one turning magnet is used, then the beam is only focused once for angle alpha or twice for angle alpha and angle beta. However, by using smaller turning magnets, more turning magnets fit into the turning sections 320 of the synchrotron 310. For example, if four magnets are used in a turning section 320 of the synchrotron, then there are eight possible edge focusing effect surfaces, two edges per magnet. The eight focusing surfaces yield a smaller cross-sectional beam size. This allows the use of a smaller gap 510. The use of multiple edge focusing effects in the turning magnets results in not only a smaller gap, but also the use of smaller magnets and smaller power supplies. For a synchrotron 310 having four turning sections 320 where each turning sections has four turning magnets and each turning magnet has two focusing edges, a total of thirty-two focusing edges exist for each orbit of the protons in the circulating path of the synchrotron 310. Similarly, if 2, 6, or 8 magnets are used in a given turning section, or if 2, 3, 5, or 6 turning sections are used, then the number of edge focusing surfaces expands or contracts according to equation 2. TFE = NTS ⋆ M NTS ⋆ FE M eq . 2 where TFE is the number of total focusing edges, NTS is the number of turning section, M is the number of magnets, and FE is the number of focusing edges. Naturally, not all magnets are necessarily beveled and some magnets are optionally beveled on only one edge. The inventors have determined that multiple smaller magnets have benefits over fewer larger magnets. For example, the use of 16 small magnets yields 32 focusing edges whereas the use of 4 larger magnets yields only 8 focusing edges. The use of a synchrotron having more focusing edges results in a circulating path of the synchrotron built without the use of focusing quadrupoles magnets. All prior art synchrotrons use quadrupoles in the circulating path of the synchrotron. Further, the use of quadrupoles in the circulating path necessitates additional straight sections in the circulating path of the synchrotron. Thus, the use of quadrupoles in the circulating path of a synchrotron results in synchrotrons having larger diameters or larger circumferences. In various embodiments of the system described herein, the synchrotron has: at least 4 and preferably 6, 8, 10, or more edge focusing edges per 90 degrees of turn of the charged particle beam in a synchrotron having four turning sections; at least about 16 and preferably about 24, 32, or more edge focusing edges per orbit of the charged particle beam in the synchrotron; only 4 turning sections where each of the turning sections includes at least 4 and preferably 8 edge focusing edges; an equal number of straight sections and turning sections; exactly 4 turning sections; at least 4 edge focusing edges per turning section; no quadrupoles in the circulating path of the synchrotron; a rounded corner rectangular polygon configuration; a circumference of less than 60 meters; a circumference of less than 60 meters and 32 edge focusing surfaces; and/or any of about 8, 16, 24, or 32 non-quadrupole magnets per circulating path of the synchrotron, where the non-quadrupole magnets include edge focusing edges. Referring now to FIG. 6, the incident magnetic field surface 670 of the first magnet 610 is further described. FIG. 6 is not to scale and is illustrative in nature. Local imperfections or unevenness in quality of the finish of the incident surface 670 results in inhomogeneities or imperfections in the magnetic field applied to the gap 510. Preferably, the incident surface 670 is flat, such as to within about a zero to three micron finish polish, or less preferably to about a ten micron finish polish. Referring now to FIG. 8, additional magnet elements, of the magnet cross-section illustratively represented in FIG. 6, are described. The first magnet 610 preferably contains an initial cross-sectional distance 810 of the iron based core. The contours of the magnetic field are shaped by the magnets 610, 620 and the yokes 612, 622. The iron based core tapers to a second cross-sectional distance 820. The magnetic field in the magnet preferentially stays in the iron based core as opposed to the gaps 630, 640. As the cross-sectional distance decreases from the initial cross-sectional distance 810 to the final cross-sectional distance 820, the magnetic field concentrates. The change in shape of the magnet from the longer distance 810 to the smaller distance 820 acts as an amplifier. The concentration of the magnetic field is illustrated by representing an initial density of magnetic field vectors 830 in the initial cross-section 810 to a concentrated density of magnetic field vectors 840 in the final cross-section 820. The concentration of the magnetic field due to the geometry of the turning magnets results in fewer winding coils 650, 660 being required and also a smaller power supply to the coils being required. In one example, the initial cross-section distance 810 is about fifteen centimeters and the final cross-section distance 820 is about ten centimeters. Using the provided numbers, the concentration of the magnetic field is about 15/10 or 1.5 times at the incident surface 670 of the gap 510, though the relationship is not linear. The taper 860 has a slope, such as about 20 to 60 degrees. The concentration of the magnetic field, such as by 1.5 times, leads to a corresponding decrease in power consumption requirements to the magnets. Referring now to FIG. 9, an additional example of geometry of the magnet used to concentrate the magnetic field is illustrated. As illustrated in FIG. 8, the first magnet 610 preferably contains an initial cross-sectional distance 810 of the iron based core. The contours of the magnetic field are shaped by the magnets 610, 620 and the yokes 612, 622. In this example, the core tapers to a second cross-sectional distance 820 with a smaller angle theta, θ. As described, supra, the magnetic field in the magnet preferentially stays in the iron based core as opposed to the gaps 630, 640. As the cross-sectional distance decreases from the initial cross-sectional distance 810 to the final cross-sectional distance 820, the magnetic field concentrates. The smaller angle, theta, results in a greater amplification of the magnetic field in going from the longer distance 810 to the smaller distance 820. The concentration of the magnetic field is illustrated by representing an initial density of magnetic field vectors 830 in the initial cross-section 810 to a concentrated density of magnetic field vectors 840 in the final cross-section 820. The concentration of the magnetic field due to the geometry of the turning magnets results in fewer winding coils 650, 660 being required and also a smaller power supply to the winding coils 650, 660 being required. Still referring to FIG. 9, optional correction coils 910, 920 are illustrated that are used to correct the strength of one or more turning magnets. The correction coils 920, 930 supplement the winding coils 650, 660. The correction coils 910, 920 have correction coil power supplies that are separate from winding coil power supplies used with the winding coils 650, 660. The correction coil power supplies typically operate at a fraction of the power required compared to the winding coil power supplies, such as about 1, 2, 3, 5, 7, or 10 percent of the power and more preferably about 1 or 2 percent of the power used with the winding coils 650, 660. The smaller operating power applied to the correction coils 920, 920 allows for more accurate and/or precise control of the correction coils. The correction coils are used to adjust for imperfection in the turning magnets 410, 420, 430, 440. Referring now to FIG. 10, an example of winding coils and correction coils about a plurality of turning magnets in an ion beam turning section is illustrated. The winding coils preferably cover 1, 2, or 4 turning magnets. In the illustrated example, a winding coil 1030 winds around two turning magnets 410, 420 generating a magnetic field. Correction coils are used to correct the magnetic field strength of one or more turning or bending magnets. In the illustrated example, a first correction coil 1010 corrects a single turning magnet. Combined in the illustration, but separately implemented, a second correction coil 1020 corrects two turning magnets 410, 420. The correction coils supplement the winding coils. The correction coils have correction coil power supplies that are separate from winding coil power supplies used with the winding coils. The correction coil power supplies typically operate at a fraction of the power required compared to the winding coil power supplies, such as about 1, 2, 3, 5, 7, or 10 percent of the power and more preferably about 1 or 2 percent of the power used with the winding coils. The smaller operating power applied to the correction coils allows for more accurate and/or precise control of the correction coils. More particularly, a magnetic field produced by the first correction coil 1010 is used to adjust for imperfection in a magnetic filed produced by the turning magnet 410 or the second correction coil 1020 is used to adjust for imperfection in the turning magnet sections 610, 620. Optionally, separate correction coils are used for each turning magnet allowing individual tuning of the magnetic field for each turning magnet, which eases quality requirements in the manufacture of each turning magnet. Correction coils are preferably used in combination with magnetic field concentration magnets to stabilize a magnetic field in a synchrotron. For example, high precision magnetic field sensors 1050 are used to sense a magnetic field created in one or more turning magnets using winding elements. The sensed magnetic field is sent via a feedback loop to a magnetic field controller that adjusts power supplied to correction coils. The correction coils, operating at a lower power, are capable of rapid adjustment to a new power level. Hence, via the feedback loop, the total magnetic field applied by the turning magnets and correction coils is rapidly adjusted to a new strength, allowing continuous adjustment of the energy of the proton beam. In further combination, a novel extraction system allows the continuously adjustable energy level of the proton beam to be extracted from the synchrotron. For example, one or more high precision magnetic field sensors 1050 are placed into the synchrotron and are used to measure the magnetic field at or near the proton beam path. For example, the magnetic sensors are optionally placed between turning magnets and/or within a turning magnet, such as at or near the gap 510 or at or near the magnet core or yoke. The sensors are part of a feedback system to the correction coils, which is optionally run by the main controller 110. The feedback system is controlled by the main controller 110 or a subunit or sub-function of the main controller 110. Thus, the system preferably stabilizes the magnetic field in the synchrotron elements rather than stabilizing the current applied to the magnets. Stabilization of the magnetic field allows the synchrotron to come to a new energy level quickly. Optionally, the one or more high precision magnetic field sensors are used to coordinate synchrotron beam energy and timing with patient respiration. Stabilization of the magnetic field allows the synchrotron to come to a new energy level quickly. This allows the system to be controlled to an operator or algorithm selected energy level with each pulse of the synchrotron and/or with each breath of the patient. The winding and/or correction coils correct 1, 2, 3, or 4 turning magnets, and preferably correct a magnetic field generated by two turning magnets. A winding or correction coil covering multiple magnets reduces space between magnets as fewer winding or correction coil ends are required, which occupy space. Referring now to FIG. 11, an example is used to clarify the magnetic field control using a feedback loop 1100 to change delivery times and/or periods of proton pulse delivery. In one case, a respiratory sensor 1110 senses the breathing cycle of the subject. The respiratory sensor sends the information to an algorithm in a magnetic field controller 1120, typically via the patient interface module 150 and/or via the main controller 110 or a subcomponent thereof. The algorithm predicts and/or measures when the subject is at a particular point in the breathing cycle, such as at the bottom of a breath. Magnetic field sensors 1130, such as the high precision magnetic field sensors 1050, are used as input to the magnetic field controller, which controls a magnet power supply 1140 for a given magnetic field 1150, such as within a first turning magnet 410 of a synchrotron 130. The control feedback loop is thus used to dial the synchrotron to a selected energy level and deliver protons with the desired energy at a selected point in time, such as at the bottom of the breath. More particularly, the synchrotron accelerates the protons and the control feedback loop keeps the protons in the circulating path by synchronously adjusting the magnetic field strength of the turning magnets. Intensity of the proton beam is also selectable at this stage. The feedback control to the correction coils allows rapid selection of energy levels of the synchrotron that are tied to the patient's breathing cycle. This system is in stark contrast to a system where the current is stabilized and the synchrotron deliver pulses with a period, such as 10 or 20 cycles second with a fixed period. The feedback or the magnetic field design coupled with the correction coils allows for the extraction cycle to match the varying respiratory rate of the patient. Traditional extraction systems do not allow this control as magnets have memories in terms of both magnitude and amplitude of a sine wave. Hence, in a traditional system, in order to change frequency, slow changes in current must be used. However, with the use of the feedback loop using the magnetic field sensors, the frequency and energy level of the synchrotron are rapidly adjustable. Further aiding this process is the use of a novel extraction system that allows for acceleration of the protons during the extraction process, described infra. Referring again to FIG. 10, an example of a winding coil 1030 that covers two turning magnets 410, 420 is provided. As described, supra, this system reduces space between turning section allowing more magnetic field to be applied per radian of turn. A first correction coil 1010 is illustrated that is used to correct the magnetic field for the first turning magnet 410. Individual correction coils for each turning magnet are preferred and individual correction coils yield the most precise and/or accurate magnetic field in each turning section. Particularly, the individual correction coil 1010 is used to compensate for imperfections in the individual magnet of a given turning section. Hence, with a series of magnetic field sensors, corresponding magnetic fields are individually adjustable in a series of feedback loops, via a magnetic field monitoring system 1030, as an independent coil is used for each turning section magnet. Alternatively, a multiple magnet correction coil 1020 is used to correct the magnetic field for a plurality of turning section magnets. Flat Gap Surface While the gap surface is described in terms of the first turning magnet 410, the discussion applies to each of the turning magnets in the synchrotron. Similarly, while the gap 510 surface is described in terms of the magnetic field incident surface 670, the discussion additionally optionally applies to the magnetic field exiting surface 680. The magnetic field incident surface 670 of the first magnet 610 is preferably about flat, such as to within about a zero to three micron finish polish or less preferably to about a ten micron finish polish. By being very flat, the polished surface spreads the unevenness of the applied magnetic field across the gap 510. The very flat surface, such as about 0, 1, 2, 4, 6, 8, 10, 15, or 20 micron finish, allows for a smaller gap size, a smaller applied magnetic field, smaller power supplies, and tighter control of the proton beam cross-sectional area. Proton Beam Extraction Referring now to FIG. 12, an exemplary proton extraction process from the synchrotron 130 is illustrated. For clarity, FIG. 12 removes elements represented in FIG. 2, such as the turning magnets, which allows for greater clarity of presentation of the proton beam path as a function of time. Generally, protons are extracted from the synchrotron 130 by slowing the protons. As described, supra, the protons were initially accelerated in a circulating path 264, which is maintained with a plurality of turning magnets 250. The circulating path is referred to herein as an original central beamline 264. The protons repeatedly cycle around a central point in the synchrotron 280. The proton path traverses through an RF cavity system 1210. To initiate extraction, an RF field is applied across a first blade 1212 and a second blade 1214, in the RF cavity system 1210. The first blade 1212 and second blade 1214 are referred to herein as a first pair of blades. In the proton extraction process, a radio-frequency (RF) voltage is applied across the first pair of blades, where the first blade 1212 of the first pair of blades is on one side of the circulating proton beam path 264 and the second blade 1214 of the first pair of blades is on an opposite side of the circulating proton beam path 264. The applied RF field applies energy to the circulating charged-particle beam. The applied RF field alters the orbiting or circulating beam path slightly of the protons from the original central beamline 264 to an altered circulating beam path 265. Upon a second pass of the protons through the RF cavity system, the RF field further moves the protons off of the original proton beamline 264. For example, if the original beamline is considered as a circular path, then the altered beamline is slightly elliptical. The applied RF field is timed to apply outward or inward movement to a given band of protons circulating in the synchrotron accelerator. Each orbit of the protons is slightly more off axis compared to the original circulating beam path 264. Successive passes of the protons through the RF cavity system are forced further and further from the original central beamline 264 by altering the direction and/or intensity of the RF field with each successive pass of the proton beam through the RF field. The RF voltage is frequency modulated at a frequency about equal to the period of one proton cycling around the synchrotron for one revolution or at a frequency than is an integral multiplier of the period of one proton cycling about the synchrotron. The applied RF frequency modulated voltage excites a betatron oscillation. For example, the oscillation is a sine wave motion of the protons. The process of timing the RF field to a given proton beam within the RF cavity system is repeated thousands of times with successive passes of the protons being moved approximately one micrometer further off of the original central beamline 264. For clarity, the effect of the approximately 1000 changing beam paths with each successive path of a given band of protons through the RF field are illustrated as the altered beam path 265. With a sufficient sine wave betatron amplitude, the altered circulating beam path 265 touches a material 1230, such as a foil or a sheet of foil. The foil is preferably a lightweight material, such as beryllium, a lithium hydride, a carbon sheet, or a material of low nuclear charge. A material of low nuclear charge is a material composed of atoms consisting essentially of atoms having six or fewer protons. The foil is preferably about 10 to 150 microns thick, is more preferably 30 to 100 microns thick, and is still more preferably 40-60 microns thick. In one example, the foil is beryllium with a thickness of about 50 microns. When the protons traverse through the foil, energy of the protons is lost and the speed of the protons is reduced. Typically, a current is also generated, described infra. Protons moving at a slower speed travel in the synchrotron with a reduced radius of curvature 266 compared to either the original central beamline 264 or the altered circulating path 265. The reduced radius of curvature 266 path is also referred to herein as a path having a smaller diameter of trajectory or a path having protons with reduced energy. The reduced radius of curvature 266 is typically about two millimeters less than a radius of curvature of the last pass of the protons along the altered proton beam path 265. The thickness of the material 1230 is optionally adjusted to created a change in the radius of curvature, such as about ½, 1, 2, 3, or 4 mm less than the last pass of the protons 265 or original radius of curvature 264. Protons moving with the smaller radius of curvature travel between a second pair of blades. In one case, the second pair of blades is physically distinct and/or are separated from the first pair of blades. In a second case, one of the first pair of blades is also a member of the second pair of blades. For example, the second pair of blades is the second blade 1214 and a third blade 1216 in the RF cavity system 1210. A high voltage DC signal, such as about 1 to 5 kV, is then applied across the second pair of blades, which directs the protons out of the synchrotron through a deflector 292, such as a Lamberson magnet, into a transport path 268. Control of acceleration of the charged particle beam path in the synchrotron with the accelerator and/or applied fields of the turning magnets in combination with the above described extraction system allows for control of the intensity of the extracted proton beam, where intensity is a proton flux per unit time or the number of protons extracted as a function of time. For example, when a current is measured beyond a threshold, the RF field modulation in the RF cavity system is terminated or reinitiated to establish a subsequent cycle of proton beam extraction. This process is repeated to yield many cycles of proton beam extraction from the synchrotron accelerator. Because the extraction system does not depend on any change any change in magnetic field properties, it allows the synchrotron to continue to operate in acceleration or deceleration mode during the extraction process. Stated differently, the extraction process does not interfere with synchrotron. In stark contrast, traditional extraction systems introduce a new magnetic field, such as via a hexapole, during the extraction process. More particularly, traditional synchrotrons have a magnet, such as a hexapole magnet, that is off during an acceleration stage. During the extraction phase, the hexapole magnetic field is introduced to the circulating path of the synchrotron. The introduction of the magnetic field necessitates two distinct modes, an acceleration mode and an extraction mode, which are mutually exclusive in time. Charged Particle Beam Intensity Control Control of applied field, such as a radio-frequency (RF) field, frequency and magnitude in the RF cavity system 1210 allows for intensity control of the extracted proton beam, where intensity is extracted proton flux per unit time or the number of protons extracted as a function of time. Referring still to FIG. 12, when protons in the proton beam hit the material 1230 electrons are given off resulting in a current. The resulting current is converted to a voltage and is used as part of a ion beam intensity monitoring system or as part of an ion beam feedback loop for controlling beam intensity. The voltage is optionally measured and sent to the main controller 110 or to a controller subsystem 1240. More particularly, when protons in the charged particle beam path pass through the material 1230, some of the protons lose a small fraction of their energy, such as about one-tenth of a percent, which results in a secondary electron. That is, protons in the charged particle beam push some electrons when passing through material 1230 giving the electrons enough energy to cause secondary emission. The resulting electron flow results in a current or signal that is proportional to the number of protons going through the target material 1230. The resulting current is preferably converted to voltage and amplified. The resulting signal is referred to as a measured intensity signal. The amplified signal or measured intensity signal resulting from the protons passing through the material 1230 is preferably used in controlling the intensity of the extracted protons. For example, the measured intensity signal is compared to a target signal or goal signal, which is predetermined in an irradiation of the tumor plan. The difference between the measured intensity signal and the planned for goal signal is calculated. The difference is used as a control to the RF generator. Hence, the measured flow of current resulting from the protons passing through the material 1230 is used as a control in the RF generator to increase or decrease the number of protons undergoing betatron oscillation and striking the material 1230. Hence, the voltage determined off of the material 1230 is used as a measure of the orbital path and is used as a feedback control to control the RF cavity system. Alternatively, the measured intensity signal is not used in the feedback control and is just used as a monitor of the intensity of the extracted protons. As described, supra, the photons striking the material 1230 is a step in the extraction of the protons from the synchrotron 130. Hence, the measured intensity signal is used to change the number of protons per unit time being extracted, which is referred to as intensity of the proton beam. The intensity of the proton beam is thus under algorithm control. Further, the intensity of the proton beam is controlled separately from the velocity of the protons in the synchrotron 130. Hence, intensity of the protons extracted and the energy of the protons extracted are independently variable. For example, protons initially move at an equilibrium trajectory in the synchrotron 130. An RF field is used to excite the protons into a betatron oscillation. In one case, the frequency of the protons orbit is about 10 MHz. In one example, in about one millisecond or after about 10,000 orbits, the first protons hit an outer edge of the target material 130. The specific frequency is dependent upon the period of the orbit. Upon hitting the material 130, the protons push electrons through the foil to produce a current. The current is converted to voltage and amplified to yield a measured intensity signal. The measured intensity signal is used as a feedback input to control the applied RF magnitude, RF frequency, or RF field. Preferably, the measured intensity signal is compared to a target signal and a measure of the difference between the measured intensity signal and target signal is used to adjust the applied RF field in the RF cavity system 1210 in the extraction system to control the intensity of the protons in the extraction step. Stated again, the signal resulting from the protons striking and/or passing through the material 130 is used as an input in RF field modulation. An increase in the magnitude of the RF modulation results in protons hitting the foil or material 130 sooner. By increasing the RF, more protons are pushed into the foil, which results in an increased intensity, or more protons per unit time, of protons extracted from the synchrotron 130. In another example, a detector external to the synchrotron 130 is used to determine the flux of protons extracted from the synchrotron and a signal from the external detector is used to alter the RF field or RF modulation in the RF cavity system 1210. Here the external detector generates an external signal, which is used in a manner similar to the measured intensity signal, described in the preceding paragraphs. In yet another example, when a current from material 130 resulting from protons passing through or hitting material is measured beyond a threshold, the RF field modulation in the RF cavity system is terminated or reinitiated to establish a subsequent cycle of proton beam extraction. This process is repeated to yield many cycles of proton beam extraction from the synchrotron accelerator. In still yet another embodiment, intensity modulation of the extracted proton beam is controlled by the main controller 110. The main controller 110 optionally and/or additionally controls timing of extraction of the charged particle beam and energy of the extracted proton beam. In yet still another embodiment, a method or apparatus for controlling intensity of charged particles extracted from a circulating charged particle beam path in a synchrotron includes: a radio-frequency field generator, where during use said radio-frequency generator applies a radio-frequency field to the circulating charged particles yielding betatron oscillating charged particles; an extraction material, where at least a portion of the betatron oscillating charged particles pass through the extraction material resulting in a secondary emission electron flow; an intensity sensor for determining a measure of the electron flow; and a feedback control loop providing the measure of electron flow as a feedback to the radio-frequency generator. Preferably, the target signal calculates a difference between the measure of the electron flow and the target signal, where the intensity controller alters amplitude of the radio-frequency field based upon said difference, which results in control of intensity of the extracted charged particles. In yet still an additional embodiment, a method or apparatus for extracting intensity controlled charged particles from charged particles circulating in a synchrotron of a charged particle cancer therapy system, includes: oscillation blades with a radio-frequency voltage across the for inducing oscillating charged particles from the charged particles circulating in the synchrotron; an extraction material where the oscillating charged particles traverse the extraction material during use generating both reduced energy charged particles and secondary emission electrons or a current; and extraction blades used in extracting the energy controlled and intensity controlled charged particles from the synchrotron. Preferably, the system includes a feedback intensity controller that generates a measure of the secondary emission electrons, compares the measure and a target signal, such as an irradiation plan signal 1260 for each beam position striking the tumor 1101, and having the intensity controller adjusts amplitude of the radio-frequency voltage based on the comparison yielding intensity controlled and energy controlled extracted charged particles. The benefits of the system include a multi-dimensional scanning system. Particularly, the system allows independence in: (1) energy of the protons extracted and (2) intensity of the protons extracted. That is, energy of the protons extracted is controlled by an energy control system and an intensity control system controls the intensity of the extracted protons. The energy control system and intensity control system are optionally independently controlled. Preferably, the main controller 110 controls the energy control system and the main controller simultaneously controls the intensity control system to yield an extracted proton beam with controlled energy and controlled intensity where the controlled energy and controlled intensity are independently variable. Thus the irradiation spot hitting the tumor is under independent control of: time; energy; intensity; x-axis position, where the x-axis represents horizontal movement of the proton beam relative to the patient, and y-axis position, where the y-axis represents vertical movement of the proton beam relative to the patient. In addition, the patient is optionally independently rotated relative to a translational axis of the proton beam at the same time. Proton Beam Position Control Referring now to FIG. 13, a beam delivery and tissue volume scanning system is illustrated. Presently, the worldwide radiotherapy community uses a method of dose field forming using a pencil beam scanning system. In stark contrast, FIG. 13 illustrates a spot scanning system or tissue volume scanning system. In the tissue volume scanning system, the proton beam is controlled, in terms of transportation and distribution, using an inexpensive and precise scanning system. The scanning system is an active system, where the beam is focused into a spot focal point of about one-half, one, two, or three millimeters in diameter. The focal point is translated along two axes while simultaneously altering the applied energy of the proton beam, which effectively changes the third dimension of the focal point. For example, in the illustrated system in FIG. 13, the spot is translated up a vertical axis, is moved horizontally, and is then translated down a vertical axis. In this example, current is used to control a vertical scanning system having at least one magnet. The applied current alters the magnetic field of the vertical scanning system to control the vertical deflection of the proton beam. Similarly, a horizontal scanning magnet system controls the horizontal deflection of the proton beam. The degree of transport along each axes is controlled to conform to the tumor cross-section at the given depth. The depth is controlled by changing the energy of the proton beam. For example, the proton beam energy is decreased, so as to define a new penetration depth, and the scanning process is repeated along the horizontal and vertical axes covering a new cross-sectional area of the tumor. Combined, the three axes of control allow scanning or movement of the proton beam focal point over the entire volume of the cancerous tumor. The time at each spot and the direction into the body for each spot is controlled to yield the desired radiation does at each sub-volume of the cancerous volume while distributing energy hitting outside of the tumor. The focused beam spot volume dimension is preferably tightly controlled to a diameter of about 0.5, 1, or 2 millimeters, but is alternatively several centimeters in diameter. Preferred design controls allow scanning in two directions with: (1) a vertical amplitude of about 100 mm amplitude and frequency up to 200 Hz; and (2) a horizontal amplitude of about 700 mm amplitude and frequency up to 1 Hz. More or less amplitude in each axis is possible by altering the scanning magnet systems. In FIG. 13, the proton beam goes along a z-axis controlled by the beam energy, the horizontal movement is along an x-axis, and the vertical direction is along a y-axis. The distance the protons move along the z-axis into the tissue, in this example, is controlled by the kinetic energy of the proton. This coordinate system is arbitrary and exemplary. The actual control of the proton beam is controlled in 3-dimensional space using two scanning magnet systems and by controlling the kinetic energy of the proton beam. The use of the extraction system, described supra, allows for different scanning patterns. Particularly, the system allows simultaneous adjustment of the x-, y-, and z-axes in the irradiation of the solid tumor. Stated again, instead of scanning along an x,y-plane and then adjusting energy of the protons, such as with a range modulation wheel, the system allows for moving along the z-axes while simultaneously adjusting the x- and or y-axes. Hence, rather than irradiating slices of the tumor, the tumor is optionally irradiated in three simultaneous dimensions. For example, the tumor is irradiated around an outer edge of the tumor in three dimensions. Then the tumor is irradiated around an outer edge of an internal section of the tumor. This process is repeated until the entire tumor is irradiated. The outer edge irradiation is preferably coupled with simultaneous rotation of the subject, such as about a vertical y-axis. This system allows for maximum efficiency of deposition of protons to the tumor, as defined using the Bragg peak, to the tumor itself with minimal delivery of proton energy to surrounding healthy tissue. Combined, the system allows for multi-axes control of the charged particle beam system in a small space with low power supply. For example, the system uses multiple magnets where each magnet has at least one edge focusing effect in each turning section of the synchrotron and/or multiple magnets having concentrating magnetic field geometry, as described supra. The multiple edge focusing effects in the circulating beam path of the synchrotron combined with the concentration geometry of the magnets and described extraction system yields a synchrotron having: a small circumference system, such as less than about 50 meters; a vertical proton beam size gap of about 2 cm; corresponding reduced power supply requirements associated with the reduced gap size; an extraction system not requiring a newly introduced magnetic field; acceleration or deceleration of the protons during extraction; control z-axis energy during extraction; and simultaneous variation of z-axis energy during extraction. The result is a 3-dimensional scanning system, x-, y-, and z-axes control, where the z-axes control resides in the synchrotron and where the z-axes energy is variably controlled during the extraction process inside the synchrotron. Referring now to FIG. 14, an example of a targeting system 140 used to direct the protons to the tumor with 4-dimensional scanning control is provided, where the 4-dimensional scanning control is along the x-, y-, and z-axes along with intensity control, as described supra. Typically, charged particles traveling along the transport path 268 are directed through a first axis control element 142, such as a vertical control, and a second axis control element 144, such as a horizontal control and into a tumor 1101. As described, supra, the extraction system also allows for simultaneous variation in the z-axis. Further, as describe, supra, the intensity or dose of the extracted beam is optionally simultaneously and independently controlled and varied. Thus instead of irradiating a slice of the tumor, as in FIG. 13, all four dimensions defining the targeting spot of the proton delivery in the tumor are simultaneously variable. The simultaneous variation of the proton delivery spot is illustrated in FIG. 14 by the spot delivery path 269. In the illustrated case, the protons are initially directed around an outer edge of the tumor and are then directed around an inner radius of the tumor. Combined with rotation of the subject about a vertical axis, a multi-field illumination process is used where a not yet irradiated portion of the tumor is preferably irradiated at the further distance of the tumor from the proton entry point into the body. This yields the greatest percentage of the proton delivery, as defined by the Bragg peak, into the tumor and minimizes damage to peripheral healthy tissue. Proton Beam Therapy Synchronization with Breathing In another embodiment, delivery of a proton beam dosage is synchronized with a breathing pattern of a subject. When a subject, also referred to herein as a patient, is breathing many portions of the body move with each breath. For example, when a subject breathes the lungs move as do relative positions of organs within the body, such as the stomach, kidneys, liver, chest muscles, skin, heart, and lungs. Generally, most or all parts of the torso move with each breath. Indeed, the inventors have recognized that in addition to motion of the torso with each breath, various motion also exists in the head and limbs with each breath. Motion is to be considered in delivery of a proton dose to the body as the protons are preferentially delivered to the tumor and not to surrounding tissue. Motion thus results in an ambiguity in where the tumor resides relative to the beam path. To partially overcome this concern, protons are preferentially delivered at the same point in a breathing cycle. Initially a rhythmic pattern of breathing of a subject is determined. The cycle is observed or measured. For example, a proton beam operator can observe when a subject is breathing or is between breaths and can time the delivery of the protons to a given period of each breath. Alternatively, the subject is told to inhale, exhale, and/or hold their breath and the protons are delivered during the commanded time period. Preferably, one or more sensors are used to determine the breathing cycle of the individual. For example, a breath monitoring sensor senses air flow by or through the mouth or nose. Another optional sensor is a chest motion sensor attached or affixed to a torso of the subject. Once the rhythmic pattern of the subject's breathing is determined, a signal is optionally delivered to the subject to more precisely control the breathing frequency. For example, a display screen is placed in front of the subject directing the subject when to hold their breath and when to breath. Typically, a breathing control module uses input from one or more of the breathing sensors. For example, the input is used to determine when the next breath exhale is to complete. At the bottom of the breath, the control module displays a hold breath signal to the subject, such as on a monitor, via an oral signal, digitized and automatically generated voice command, or via a visual control signal. Preferably, a display monitor is positioned in front of the subject and the display monitor displays at least breathing commands to the subject. Typically, the subject is directed to hold their breath for a short period of time, such as about one-half, one, two, or three seconds. The period of time the subject is asked to hold their breath is less than about ten seconds as the period of time the breath is held is synchronized to the delivery time of the proton beam to the tumor, which is about one-half, one, two, or three seconds. While delivery of the protons at the bottom of the breath is preferred, protons are optionally delivered at any point in the breathing cycle, such as upon full inhalation. Delivery at the top of the breath or when the patient is directed to inhale deeply and hold their breath by the breathing control module is optionally performed as at the top of the breath the chest cavity is largest and for some tumors the distance between the tumor and surrounding tissue is maximized or the surrounding tissue is rarefied as a result of the increased volume. Hence, protons hitting surrounding tissue is minimized. Optionally, the display screen tells the subject when they are about to be asked to hold their breath, such as with a 3, 2, 1, second countdown so that the subject is aware of the task they are about to be asked to perform. A proton delivery control algorithm is used to synchronize delivery of the protons to the tumor within a given period of each breath, such as at the bottom of a breath when the subject is holding their breath. The proton delivery control algorithm is preferably integrated with the breathing control module. Thus, the proton delivery control algorithm knows when the subject is breathing, where in the breath cycle the subject is, and/or when the subject is holding their breath. The proton delivery control algorithm controls when protons are injected and/or inflected into the synchrotron, when an RF signal is applied to induce an oscillation, as described supra, and when a DC voltage is applied to extract protons from the synchrotron, as described supra. Typically, the proton delivery control algorithm initiates proton inflection and subsequent RF induced oscillation before the subject is directed to hold their breath or before the identified period of the breathing cycle selected for a proton delivery time. In this manner, the proton delivery control algorithm can deliver protons at a selected period of the breathing cycle by simultaneously or near simultaneously delivering the high DC voltage to the second pair of plates, described supra, that results in extraction of the protons from the synchrotron and subsequent delivery to the subject at the selected time point. Since the period of acceleration of protons in the synchrotron is constant, the proton delivery control algorithm is used to set an AC RF signal that matches the breathing cycle or directed breathing cycle of the subject. Multi-Field Illumination The 3-dimensional scanning system of the proton spot focal point, described supra, is preferably combined with a rotation/raster method. The method includes layer wise tumor irradiation from many directions. During a given irradiation slice, the proton beam energy is continuously changed according to the tissue's density in front of the tumor to result in the beam stopping point, defined by the Bragg peak, to always be inside the tumor and inside the irradiated slice. The novel method allows for irradiation from many directions, referred to herein as multi-field irradiation, to achieve the maximal effective dose at the tumor level while simultaneously significantly reducing possible side-effects on the surrounding healthy tissues in comparison with existing methods. Essentially, the multi-field irradiation system distributes dose-distribution at tissue depths not yet reaching the tumor. Although the invention has been described herein with reference to certain preferred embodiments, one skilled in the art will readily appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the present invention. Accordingly, the invention should only be limited by the Claims included below. |
|
043137946 | claims | 1. A self-actuating, self-locking flow cutoff valve particularly adapted for use in a nuclear reactor of the type which utilizes a plurality of fluid supported neutron absorber elements to provide for the safe shutdown of the reactor, said flow cutoff valve comprising: a substantially vertical elongated housing having opposite ends for the flow of said fluid therethrough; an apertured plate located in said housing, the apertures providing for fluid flow from one end of said housing to the other end; a substantially vertical elongated nozzle member having top and bottom ends located in said housing, and fixed to said housing, an opening in the bottom end of said nozzle member for receiving said fluid and apertures adjacent the top end for discharging said fluid, and two sealing means comprising radially outwardly and downwardly extending sealing surfaces, one located above and the other below said apertures; an elongated flow cutoff sleeve located in said housing and having walls surrounding said nozzle, a fluid flow opening adjacent an upper end of said sleeve, two sealing means comprising radially inwardly and upwardly extending sealing surfaces affixed to said sleeve, one below said flow opening and one adjacent a lower end of said sleeve, said sleeve being movable between an upper open position wherein said apertures in said nozzle member are substantially unobstructed for the flow of fluid therethrough, and a closed position wherein said sleeve and said nozzle sealing surfaces are mated, the mated sealing surfaces and the walls of said sleeve obstruct the flow of said fluid through said apertures, said nozzle and sleeve sealing means cooperatively acting together to further provide for the exposure of a greater area for fluid pressure to exert a force in a downward direction than is exposed for fluid pressure to exert force in an upward direction whereby once said valve is in a closed position an increase in fluid pressure will act to maintain said valve in a closed position; and a balance member located above and attached to said flow cutoff sleeve, said balance member contacting said apertured plate when said sleeve is in an open position and obstructing the flow of fluid through a predetermined flow area of the apertures in said apertured plate for producing a pressure drop across the apertured plate and said balance member, said pressure drop being just sufficient to support said balance member and flow cutoff sleeve at a predetermined minimum fluid flow whereby, when said fluid flow drops below the predetermined flow, the pressure drop across said balance member will be insufficient to maintain said flow cutoff sleeve in the open position and it will move under the influence of gravity to a closed position. a self-actuating, self-locking flow cutoff valve, said valve including: a substantially vertical elongated housing having opposite ends for the flow of said fluid therethrough; an apertured plate located in said housing, the apertures providing fluid flow from one end of said housing to the other end; a substantially vertical elongated nozzle member having top and bottom ends located in said housing and fixed to said housing, an opening in the bottom end of said nozzle member for receiving said fluid, apertures adjacent the top end for discharging said fluid, and two sealing means comprising radially outwardly and downwardly extending sealing surfaces, one located above and the other below said apertures; an elongated flow cutoff sleeve located in said housing having walls surrounding said nozzle, a fluid flow opening adjacent an upper end of said sleeve, two sealing means comprising radially inwardly and upwardly extending sealing surfaces affixed to said sleeve, one below said flow opening and one adjacent a lower end of said sleeve, said sleeve being moveable between an upper open position wherein the apertures in said nozzle member are substantially unobstructed for the flow of fluid therethrough and a closed position wherein said sleeve and nozzle sealing surfaces are mated, the mated sealing surfaces and the wall of said sleeve obstruct the flow of said fluid through said apertures, and said nozzle and sleeve sealing means cooperatively acting together to further provide for the exposure of a greater area for fluid pressure to exert force in a downward direction than is exposed for fluid pressure to exert force in an upward direction whereby once said valve is in a closed position, an increase in fluid pressure will act to maintain said valve in a closed position; and a balance member located above and attached to said flow cutoff sleeve, said balance member contacting said apertured plate when said sleeve is in an open position and obstructing the flow of fluid through a predetermined flow area of the apertures in said apertured plate for producing a pressure drop across the apertured plate and said balance member, said pressure drop being just sufficient to support said balance member and flow cutoff sleeve at a predetermined minimum fluid flow whereby, when said fluid flow drops below the predetermined flow, the pressure drop across the balance member will be insufficient to maintain said flow cutoff sleeve in the open position and it will move under the influence of gravity to a closed position. 2. The flow cutoff valve of claim 1 further comprising a piston member extending upwardly from the top end of the nozzle member into said flow cutoff sleeve a sufficient distance such that when said sleeve moves from an open to a closed position, the uppermost portion of said piston member moves past said flow opening in said flow cutoff sleeve and provides a dampening force on the closure of said flow cutoff sleeve. 3. The flow cutoff valve of claim 1 further comprising means for moving said flow cutoff sleeve between an open and closed position. 4. In a nuclear reactor of the type which includes a plurality of laterally displaced vertical neutron absorber column assemblies located in and extending out of the reactor core, each of the column assemblies containing a plurality of neutron absorbing elements which, during normal operation of the reactor, are hydraulically supported outside of the core of the reactor, the improvement comprising: 5. The flow cutoff valve of claim 4 further including a piston member extending upwardly from the top end of the nozzle member into said flow cutoff sleeve a sufficient distance such that when said sleeve moves from an open to a closed position, the uppermost portion of said piston member moves past said flow opening in said flow cutoff sleeve and provides a dampening force on the closure of said flow cutoff sleeve. 6. The flow cutoff valve of claim 5 further including means for moving said flow cutoff sleeve between an open and closed position. 7. The flow cutoff valve of claim 6 wherein said means comprises an elongated rod releasably attached to a weighted member, having sufficient weight to move said flow cutoff sleeve to a closed position. 8. The flow cutoff valve of claim 7 wherein said rod is releasably connected to said weighted member by at least one magnet. 9. The flow cutoff valve of claim 8 wherein said magnet comprises a curie point alloy. 10. The flow cutoff valve of claim 8 wherein said rod is releasably connected to said weighted member by two magnets, one of said magnets comprising a curie point alloy magnet and the other comprising an electromagnet. |
summary | ||
abstract | A method, computer readable medium, and system for optimizing utilization of one or more assets includes obtaining at least one of operational data and condition data for one or more elements of at least one of the assets. At least one of historical maintenance data and life-cycle data for the one or more elements of the at least one of the assets is retrieved. One or more diagnostics on the one or more elements of the at least one of the assets is conducted based on the obtained at least one of the operational data and the condition data. One or more prognostics on the one or more elements of the at least one of the assets is conducted based on the at least one of the obtained operational data and condition data and on the retrieved at least one of the historical maintenance data and the life-cycle data. One or more optimization instructions for the at least one asset are determined based on the conducted diagnostics and prognostics and the determined one or more optimization instructions are displayed. |
|
051924919 | claims | 1. In a boiling water reactor having a control element disposed in a water pond, an apparatus for the neutron-radiography testing of the control element, comprising a film cassette having a recording area, a water-free hood fitting over the control element, said hood having an open bottom and a wall facing said film cassette, said wall having an opening formed therein with a cross section corresponding to said for receiving said film cassette, said holding device having a downwardly open side extended below said opening through which said film cassette is to be introduced into said holding device, a neutron source, and a collimator, said neutron source, said collimator and said film cassette lying in one measurement plane. 2. The apparatus according to claim 1, wherein said holding device has a skimmer past which a surface of said film cassette adjacent to said hood can be fed. 3. The apparatus according to claim 1, including a coupling piece projecting from said film cassette, a coupling rod, and a detachable coupling link interconnecting said coupling piece and said coupling rod. 4. The apparatus according to claim 1, wherein said holding device has a guide surface with an upper end, a stop for said film cassette adjoining said upper end, and a locking device holding said film cassette in a test position. |
summary | ||
046648801 | claims | 1. In a fuel assembly for a nuclear reactor including a plurality of nuclear fuel rods, at least one grid supporting said fuel rods in an organized array, an end nozzle having a central transverse adapter plate disposed adjacent said grid and a lower end of said fuel rods with a series of coolant flow holes defined therethrough which allow liquid coolant flow through said end nozzle and into said fuel assembly, a trap for capturing and retaining debris carried by said coolant flow to prevent entry of debris into said fuel assembly, said debris trap comprising: (a) a hollow enclosure disposed across said end nozzle adjacent to said transverse adapter plate and on an opposite side thereof from said grid, said enclosure being composed of material formed into a wire mesh screen which is permeable to the liquid coolant but impermeable to debris carried by the coolant; (b) said hollow enclosure having upper and lower walls extending across said end nozzle, spaced apart and interconnected at their peripheries so as to define a debris capturing and retaining chamber within said enclosure, one of said upper and lower walls being disposed adjacent to said adapter plate and the other of said walls being disposed away from said adapter plate; and (c) means on said hollow enclosure defining at least one opening into said chamber of said enclosure through said other of said upper and lower walls disposed away from said adapter plate, said opening defining means being disposed in a predetermined positional relationship with respect to the direction of coolant flow such that debris carried by said liquid coolant flow which enters said chamber of said enclosure through said opening will be substantially detered from exiting through said opening; (d) said opening defining means on said other wall including a wall section which is connected to said other wall, disposed at an angle to said other wall and the direction of coolant flow and is displaced at an inner edge from said other wall, so as to define said opening between its inner edge and said other wall in a plane extending generally parallel to the direction of coolant flow through said hollow enclosure and so as to define a path along which the debris must move in order to enter said chamber through said opening in a direction substantially transverse to the direction of coolant flow through said hollow enclosure. said partially severed wall section has multiple edge portions; and said opening defined between said multiple edge portions of said partially severed wall section and said adjacent portions of said remainder of said other wall lies in multiple planes extending generally parallel to the direction of coolant flow through said hollow enclosure. (a) a hollow enclosure disposed between said bottom nozzle adapter plate and said lower core plate and in a path of coolant flow from said openings in said core plate and to said holes in said adapter plate, said hollow enclosure being composed of material formed into wire mesh screen which is permeable to the liquid coolant but impermeable to debris carried by the coolant; (b) said hollow enclosure having an upper wall disposed adjacent said adapter plate, a lower wall located away from said adapter plate and a side wall which interconnects said upper and lower walls at their respective peripheries and spaces said upper and lower walls apart so as to define a debris capturing and retaining chamber within said enclosure, said upper and lower walls extending between said legs of said bottom nozzle; and (c) a plurality of wall sections on said lower wall being connected to adjacent portions of said lower wall and displaced at inner edges of said wall sections within said chamber inwardly toward said upper wall and away from said adjacent portions of said lower wall so as to define a plurality of openings into said hollow enclosure through said lower wall being matched in number and alignment with said plurality of coolant flow openings in said lower core plate, said each wall section also being disposed at an angle to the direction of coolant flow through said enclosure such that said opening defined between said inner edge of said each wall section and adjacent portions of said lower wall lies in a plane extending generally parallel to the direction of coolant flow through said hollow enclosure and such that debris carried by said coolant flow which enters said chamber of said enclosure through said opening will be substantially detered from exiting through said opening. 2. The debris trap as recited in claim 1, wherein opening defining means includes a plurality of said wall sections defining a plurality of said openings into said chamber of said hollow enclosure. 3. The debris trap as recited in claim 1, wherein said wall section is a portion of said other wall which has been partially severed from the remainder of said other wall and bent inwardly to extend at said angle to said remainder of said other wall. 4. The debris trap as recited in claim 3, wherein: 5. The debris trap as recited in claim 1, wherein said hollow enclosure has cross-sectional dimensions sized to fit said enclosure within said end nozzle, and said trap further includes means on said enclosure for releasably locking it within said end nozzle such that said trap will be retained with said end nozzle when moved with said fuel assembly. 6. The debris trap as recited in claim 5, wherein said locking means is in the form of a pair of leaf springs disposed on opposite sides of said enclosure and engagable with said end nozzle upon installation of said enclosure in said end nozzle. 7. The debris trap as recited in claim 1, further including a central annular sleeve mounted between said upper and lower walls of said hollow enclosure for bolstering the structural integrity of said hollow enclosure. 8. In a liquid cooled nuclear reactor having a plurality of fuel assemblies supported on a lower core plate, each of said fuel assemblies and said lower core plate being constructed to allow coolant flow therethrough, said fuel assembly including a plurality of nuclear fuel rods, a plurality of grids axially disposed along and supporting said fuel rods in an organized array, a bottom nozzle having a central adapter plate disposed adjacent a lowermost one of said grids and a lower end of said fuel rods, said adapter plate having a series of coolant flow holes defined therethrough and a plurality of transversely-displaced legs extending downwardly from the periphery of said adapter plate for supporting said fuel assembly on said lower core plate of said reactor and in alignment with a plurality of coolant flow openings in said lower core plate, and liquid coolant flowing from said openings in said lower core plate and through said holes in said bottom nozzle adapter plate, a trap for capturing and retaining debris carried by said flowing coolant to prevent entry of debris into said fuel assembly, said debris trap comprising: 9. The debris trap as recited in claim 8, wherein each of said wall sections is a portion of said lower wall which has been partially severed from the remainder of said lower wall and bent inwardly to extend at said angle to said remainder of said lower wall. 10. The debris trap as recited in claim 8, further comprising means on said enclosure for releasably locking it within said bottom nozzle such that said enclosure will be retained with said bottom nozzle when moved with said fuel asembly, said locking means being in the form of a pair of leaf springs disposed on opposite sides of said enclosure and engagable with at least two of said bottom nozzle legs upon installation of said enclosure in said bottom nozzle. 11. The debris trap as recited in claim 8, further including a central annular sleeve mounted between said upper and lower walls of said hollow enclosure for bolstering the structural integrity of said hollow enclosure. |
048062782 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus proposed by the invention and capable of carrying out the method of segregating radioactive iodine isotopes (FIG. 1) comprises a sampling unit MV interconnected with a pipeline transporting a fluid medium containing among others radioactive iodine isotopes. Such pipeline can be the primary liquid coolant circuit of a pressurized water reactor serving as heat energy source of a water-water-type nuclear power plant. The sampling unit MV continuously takes samples of suitable pressure and temperature and passes them into a degassing vessel G having an inlet for introducing gas as nitrogen (N.sub.2). The nitrogen bubbles ensure agitation of the treated sample and permit to control the liquid level in the vessel. The degassing vessel G is connected through a piping to a transfer pump P1 and thereby to a cock CS receiving appropriate reagent from a container R by means of a pump P2. The fluid sample mixed with the reagent in the cock CS is transported to a bubble removing cell BC wherefrom the mixture is transferred to a segregation column K containing a filling made of amorphous zirconium phosphate. The segregation column K is connected--again through a piping--to a continuously operating flow-type energy-selective gamma radiation detecting system GD and a signal processing and recording unit JR. Instead of nitrogen it is possible to apply other appropriate inert gas. The degassing vessel G serves for expelling the gases dissolved in the sample (among them the radioactive isotopes of the noble gases). The pH-value of the samples taken is adjusted always to a neutral or alkaline level if necessary by means of the appropriate reagent placed in the container R. The samples treated in the required manner (having e.g. the required pH-value adjusted, being free of bubble and noble gases) are transported into the segregation column K with a speed ensuring full contact time generally from at least about 5 minutes to about 15 minutes. The active filling of the column containing high specific surface absorbent as zirconium phosphate is capable of binding the cations, fluoride anions and different colloid-state corrosion products from the sample. Before detecting the sample treated it flows about 20 minutes in order to premits the decay of the very short and short half-period radioactive isotopes remaining in the effluent in spite of the previous segregation steps and capable of disturbing the measurements related to iodine. The samples are introduced into the radiation detecting system GD for detecting gamma radiation of different energy levels. In the fluid carrier medium they contain in considerable percentage the radioactive iodine isotopes only. The detection system includes calibrated counters operated in gated mode and adjusted according to the different gamma-energy levels of the different radioactive iodine isotopes in order to determine their radiation level. With reference to FIG. 2 the following non-limiting example should be helpful in better understanding the essence of the invention. EXAMPLE A laboratory model was constructed for carrying out the method proposed by the invention. This model takes into account the specific conditions of the water-water-type nuclear power plant built-up in Paks (Hungary) operating with pressurized water nuclear reactors. The method should serve for measuring the radiation levels of the radioactive iodine isotopes in the primary coolant circuit of the Paks plant and it was realised in an arrangement shown in FIG. 2. The measurement was carried out as described here below. The sample is cooled after taking and the cooled sample is led into a 1000 cm.sup.3 glass bubbling vessel 2 at a flow rate of about 3 cm.sup.3 /min. At a flow rate of at least 10 dam.sup.3 /min, air is passed across a glass filter arranged at the bottom of the vessel 2. The surplus of the air/liquid mixture leaves the vessel at its top and enters a degassing unit, from where the part of the water sample is recycled into the primary circuit. From the noble-gas-free and bubble-free part of the solution collecting under the filter, the sample is pumped into a delay pipe section 3 by a peristaltic pump 4 at a flow rate of about 1 cm.sup.3 /min. By another peristaltic pump 5 connected to an Y-pipe 7, suitable reagents can be fed from a reagent storage tank 6 into the sample, e.g. for adjusting its pH-value. Before segregation, a portion of the sample can be picked up in a sampling vessel 9 through a two-way cock 8 for the purpose of reference measurements. By setting the two-way cock 8 into its other position, the sample is led into a column 10 of 6 mm inner diameter, with the spaces between quartz wad filter beds being previously filled up with 10 g of amorphous zirconium phosphate. The effluent is led through a hollow NaI(T1) scintillation detector 11 consisting of a teflon tube of 2 millimeter inner diameter and provided with a spirally arranged flow cell. From said detector the effluent gets through a shut-off cock 12 into a sampling vessel 13. The scintillation detector 11 obtains its supply voltage from an analyser 14. The energy selective signals of the scintillation detector 11 are led in a differential gated mode into counters or ratemeters 15, 16, 17 adjusted to the characteristic gamma lines of the iodine isotopes 131.sub.I, 132.sub.I and 135.sub.I, then the signals of the counters or the analogue signals of the ratemeters are plotted in the function of time by recorders 18, 19 and 20. The segregation of iodine isotopes by means of the method and apparatus proposed by the invention is in several aspects more advantageous than other methods known so far. After segregation--having determined its efficiency through checking measurements using semi-conductor detectors--the sample solution containing iodine is--within the sensitivity limits of the measurement--free of N, O, Na and K matrix components, i.e. of cationoc radioactive components in general, and its content of noble gases and fluoride ions belonging to the matrix components is low enough to leave the sensitivity of the measurement uneffected even in reactor shut-down periods associated with very low radioactive iodine concentrations. The method leads itself to continuous and parallel measurement of preferably at least three iodine isotopes, and by inserting a required number of signal processing units (and respective circuit elements), simultaneous measurement of all occurring iodine isotopes is feasible. Also, the apparatus for implementing the method can be arranged to contain two segregating columns connected parallel, filled up with charges of identical composition, permitting regeneration of exhausted charge without interrupting continuity of measurement and continuous supervision of operation. The metod is economical, it is characterized by low demand on time and work, it is based on exclusively inexpensive and simple pieces of equipment, resulting in low installation and operating costs. |
claims | 1. An ion beam generator comprising:a discharge tank for generating plasma that includes ions;a lead-out electrode, having an annular grid portion provided with openings for leading out the ions generated in the discharge tank, while accelerating the generated ions as an annular ion beam, which is led out of the lead-out electrode; anda deflecting electrode for deflecting the annular ion beam, led out of the lead-out electrode, in an annular center direction, the deflecting electrode comprising a first electrode tube and a second electrode tube, the first electrode tube and the second electrode tube being in a circular truncated cone shape having respective openings in an upper surface portion and a bottom surface portion thereof, a diameter of an opening of the second electrode tube being smaller than a diameter of an opening of the first electrode tube,wherein the ion beam led out from the lead-out electrode enters the deflecting electrode between the first electrode tube and the second electrode tube, and is deflected. 2. The ion beam generator according to claim 1, wherein the annular grid portion of the lead-out electrode is a grid portion having one of a substantially circular ring shape and a substantially regular polygonal shape. 3. The ion beam generator according to claim 1, further comprising a drive mechanism for moving the deflecting electrode in a direction to face the lead-out electrode. 4. The ion beam generator according to claim 3, wherein the drive mechanism moves the deflecting electrode reciprocally. 5. The ion beam generator according to claim 1, wherein the openings of the annular grid portion are linear holes. 6. An ion beam etching apparatus comprising:a neutralizer for irradiating electrons;a substrate holder for holding a substrate; andan ion beam generator disposed to face the substrate held by the substrate holder,wherein the ion beam generator is one according to any one of claims 1 to 5. 7. The ion beam etching apparatus according to claim 6, wherein, in the ion beam generator, the grid is arranged parallel to the substrate held by the substrate holder, and the deflecting electrode deflects the ion beam led out by the grid portion, so that the ion beam is caused to enter the substrate held by the substrate holder at an angle that is inclined relative to the substrate. |
|
claims | 1. An X-ray CT apparatus comprising:X-ray generating means for generating X-rays;X-ray detecting means arranged opposite to the X-ray generating means for two-dimensionally detecting a dose of X-rays passing through an object to be examined;means for holding the X-ray generating means and the X-ray detecting means so that the object is located therebetween;means for adjusting a distance between the X-ray generating means and the X-ray detectinci means on the holdinci means;rotation driving means for driving the holding means to rotate around the object;image processing means for producing a tomogram of the object based on the X-ray dose detected by the X-ray detecting means;display means for displaying the tomogram; andmeans for changing an FOV size of the X-ray detecting means so as to reduce the FOV size of the X-ray detecting means to less than a maximum FOV size of the X-ray detecting means in accordance with a detected portion of the object displayed by the display means;wherein the FOV size changing means includes X-ray converting means for converting the X-rays into visible light; light receiving means for converting the visible light converted by the X-ray converting means into electrical signals; and means for changing a portion of the visible light converted by the X-ray converting means necessary for creating the tomogram. 2. An X-ray CT apparatus according to claim 1, wherein the FOV size changing means includes means for inputting a desired FOV size by moving a cursor of a pointing device onto an FOV size changing switch displayed on the display means and control means for changing an FOV size to the size input by the inputting means. 3. An X-ray CT apparatus according to claim 1, wherein the adjusting means adjusts a size of the tomogram displayed by the display means. 4. An X-ray CT apparatus according to claim 3, further including means for expanding the tomogram obtained with the FOV size changed by the FOV size changing means. 5. An X-ray CT apparatus according to claim 1, wherein the adjusting means adjusts the distance between the X-ray generating means and the X-ray detecting means by extending and retracting a part of the holding means. 6. An X-ray CT apparatus according to claim 1, wherein the holding means is a U-shaped arm which is adjustable by the adjusting means and is provided with the X-ray generating means and the X-ray detecting means respectively on the ends, and the rotation driving means rotates the holding means around an intermediate portion of the U-shaped arm being the center. 7. An X-ray CT apparatus according to claim 1, further comprising means for determining a position of the object so that an arbitrary portion of the object is located on the rotation center of the X-ray generating means and the X-ray detecting means. 8. An X-ray CT apparatus according to claim 1, wherein the maximum FOV size is based upon the detection of actual data and the FOV size changing means reduces the FOV size to less than the maximum FOV size based upon detection of actual data. 9. An X-ray CT apparatus according to claim 1, wherein the FOV range changing means reduces the FOV size to less than the maximum FOV size while maintaining the same resolution as obtained with the maximum FOV size. 10. An x-ray CT apparatus according to claim 9, wherein the FOV size changing means maintains substantially the same contrast when the FOV size is reduced as obtained with the maximum FOV size of the X-ray detection means. 11. An X-ray CT apparatus comprising:X-ray generating means for generating X-rays;X-ray detecting means arranged opposite to the X-ray generating means for two-dimensionally detecting a dose of X-rays passing through an object to be examined;means for holding the X-ray generating means and the X-ray detecting means so that the object is located therebetween;means for adjusting a distance between the X-ray generating means and the X-ray detecting means on the holding means;rotation driving means for driving the holding means to rotate around the object;image processing means for producing a tomogram of the object based on the X-ray dose detected by the X-ray detecting means;display means for displaying the tomogram; andmeans for changing an FOV size of the X-ray detecting means so as to reduce the FOV size of the X-ray detecting means to less than a maximum FOV size of the X-ray detecting means in accordance with a detected portion of the object displayed by the display means;wherein the X-ray detecting means is a two-dimensional X-ray flat sensor for converting X-rays into electrical signals, and the FOV size changing means includes means for changing a portion of the electrical signals converted by the two-dimensional X-ray flat sensor necessary for creating the tomogram. 12. An X-ray CT apparatus according to claim 3, wherein the adjusting means adjusts a size of the tomogram displayed by the display means. 13. An X-ray CT apparatus according to claim 3, wherein the adjusting means adjusts the distance between the X-ray generating means and the X-ray detecting means by extending and retracting a part of the holding means. 14. An X-ray CT apparatus comprising:X-ray generating means for generating X-rays;X-ray detecting means arranged opposite to the X-ray generating means for two-dimensionally detecting a dose of X-rays passing through an object to be examined;means for holding the X-ray generating means and the X-ray detecting means so that the object is located therebetween;means for adjusting a distance between the X-ray generating means and the X-ray detecting means on the holding means;rotation driving means for driving the holding means to rotate around the object;image processing means for producing a tomogram of the object based on the X-ray dose detected by the X-ray detecting means;display means for displaying the tomogram,means for changing an FOV size of the X-ray detecting means in accordance with a detected portion of the object displayed by the display means; andmeans for controlling conditions of X-ray generation of the X-ray generating means in accordance with the FOV size changed by the FOV size changing means. 15. An X-ray CT apparatus according to claim 14, wherein the means for controlling conditions of X-ray generation of the X-ray generating means controls conditions of an X-ray generator of the X-ray generating means in accordance with the FOV size as changed by the FOV size changing means so that each of images obtained in a different FOV size has the same contrast. 16. An X-ray CT apparatus according to claim 15, wherein the means for controlling conditions of X-ray generation of the X-ray generating means controls conditions of the X-ray generator so that an image obtained at an imaging portion of interest has the same resolution as that of an image at a portion relating to the imaging portion. 17. An X-ray CT apparatus according to claim 14, wherein the means for controlling conditions of X-ray generation of the X-ray generating means controls conditions of an X-ray generator of the X-ray generating means so that an image obtained at an imaging portion of interest has the same contrast as that of an image at a portion related to the imaging portion. 18. An X-ray CT apparatus according to claim 5, wherein the adjusting means adjusts a size of the tomogram displayed by the display means. 19. An X-ray CT apparatus according to claim 5, wherein the adjusting means adjusts the distance between the X-ray generating means and the X-ray detecting means by extending and retracting a part of the holding means. |
|
description | This invention relates to one-dimensional magnetic scanning or switching of a charged particle beam. The invention can be extended to two dimensions at the cost of added complexity. The distinctions between scanning and switching are that a scanned beam is used while its position is changing, whereas a switched beam is used while its position is stationary, and in a scanning application, a single beam species is usually used, whereas in some switching applications it is desired to switch between different beam species, for example between different isotopes in a mass spectrometer. For a scanned beam the velocity with which the beam is translated is critical, whereas for a switched beam it is the accuracy and stability with which position can be maintained between changes in position that is important. The apparatus is essentially the same in each case, and only the waveform is different. The stored magnetic energy U in any ion beam-deflecting magnet is related to the magnetic rigidity of the ion beam, the cross section of the beam, the scan angle xcex8, and the length of the magnet as follows: U = 1 2 ∫ B . H ⅆ v ≈ 2 kr 2 1 · 2 MqV μ υ q 2 ϑ 2 1 2 = 4 kMVr ϑ 2 μ 0 q1 ( equation xe2x80x83 1 ) where M is the highest ion mass, qV its highest ion energy, q the charge of the ions, r the radius of the ion beam (including clearance for vacuum chamber walls, etc), xcexc0 the permittivity of vacuum, l the length of the scanner magnet, and k is a numerical factor from the integration covering fringe fields, whose value is 2 to 2.5. This relationship assumes the scan angle is small, and that l less than r/xcex8 but reveals the scaling law. The stored energy is related to the inductance, and to the reactive power required to scan the beam. If the scanning current waveform is an approximately triangular function of time, the reactive power required must exceed four times (4xc3x97) the peak-stored energy in the magnetic field. The stored energy may be 100 Joules in a compact system. At a frequency of 100 Hz this means a power of 40 kVA; at 2.5 kHz it means 1 MVA. Typically, ion beam switching or scanning magnets are placed within a vacuum, since the changing magnetic field is strongly attenuated by metal vacuum walls. Instead the illustrative embodiment of the present invention uses glass, quartz, or other insulating material as a vacuum wall within the poles, along with disks of conductive material grounded through a relatively high resistance to shield the insulating walls from charged particles. The method of construction keeps the magnetic losses low and the construction inexpensive. The innovation here is laminated beam baffles. In addition, a low inductance is desired, which is proportional to the square of the peak flux, while beam deflection is proportional only to the flux. Hence, a low flux density is economic. The construction of the magnet is optimized if laminated steel separated by laminated dielectric sheets are used. For a field of 0.3 Tesla, 0.014xe2x80x3 laminations of steel separated by 0.040xe2x80x3 of dielectric may be used. The power supply must deliver a voltage V=LdI/dt+IR. The reactive power requirement may be many tens of kVA. We address only those applications where dI/dt varies by only a few percent from a nominal value, or else is zero within a few percent. Under these conditions we can separate the power supplies required to meet the real (V=IR) and reactive (V+LdI/dt) parts of the load voltage requirement. The real part is supplied by a power amplifier. The reactive part is provided by a capacitor charged to the required voltage (V=|dI/dt|) which is either disconnected from the load or connected in either polarity in series with the load by a commutator. It may be necessary to provide a low-power high voltage supply to maintain the correct charge on this capacitor, as discussed in detail below. FIG. 4 illustrates a beam scanning apparatus 20, which happens to be bipolar (since this reduces the total energy), while FIG. 5 illustrates a beam switching apparatus 22, which is monopolar. The beam switching apparatus 22 is illustrated in FIG. 11 in more detail. The corrector magnet 10 depicted in FIG. 4 can be shaped to control the relationship between deflection angle in a scanner magnet and beam position in an object plane, such as an implant location. It is possible to simultaneously correct the trajectories to be parallel and to achieve a linear relationship between scan angle and position. However, it is often necessary to minimize the need for a non-linear scan waveform by the correct design of the shape of the corrector magnet 10, but nonetheless to retain the capability of programming the scanner with a non-linear waveform so that correction of residual errors or unforeseen systematic errors is possible. For more detail involving the operation and construction of the corrector magnet 10 we hereby incorporate by reference U.S. Pat. No. 5,834,786 of White et al. and U.S. Pat. No. 5,350,926 of White et al. The scanning waveform is generated by a computer or sequencer through a digital-to-analog converter (DAC). The scanning waveform is related to the desired position of the beam as a function of time at a reference plane. Historically, in dosing applications, the average current at different locations has been measured, and the scan waveform his been iteratively corrected until this is uniform. Advantageously, the illustrative embodiment of the present invention provides a direct method of setting up the desired waveform, which is described below in more detail. First, we note that the relationship between deflection angle and beam position will not be perfectly linear. If no optics intervene between scanner and reference plane, then the beam position is related to tan xcex8, where xcex8 is the deflection angle. Then we note that the deflection angle may not be perfectly linearly related to the field in the magnet. Finally we note that the placement of a xe2x80x9ccorrectorxe2x80x9d magnet 10, or other optics (not shown) between the scanner and the reference plane will tend to introduce even-ordered aberrations. In summary the relationship between beam position, x, in the reference plane and the current, I, in the scanner is of the form I=a98 +a1x+a2x2+a3x3+a4x4+a5x5+xe2x80x83xe2x80x83(equation 2) where at least the coefficients through third-order should be non-zero. Note that the dose rate from a scanned beam is inversely proportional to dx/dt, hence to first-order is proportional to V/L, and that it is imperative that V be almost constant and smoothly varying during periods when uniform doping is desired. The commutator must not switch until the beam is scanned beyond the implanted target. As FIG. 4 illustrates, an aperture plate 12 is placed in the path of the beam at the reference plane. Apertures are placed at known values of x. The scanner power supply is operated to determine the current I required to place the beam centroid over each of the apertures, by maximizing the transmitted current. This can be done using a scanned beam and fast automated data acquisition, or a dc beam and manual data acquisition. Provided the number of apertures equals or exceeds the number of coefficients to be determined, we can solve the equation for the coefficients. If we desire that the scan position varies uniformly in time, we can create a table of scan digital to analog converter (DAC) values at uniform increments in x by substituting in equation 2. The magnet is then scanned by sequentially sending each value in the table to the DAC at equal time intervals. If it is desired that the relationship between x and time is other than linear, we simply substitute the desired x-position at each linear time increment into equation 2 to calculate the DAC values. The required non-linear scan profile with then be generated. To generate a quasi-triangular waveform, the values in the scan table are programmed sequentially, and on reaching the end point, the sequence is reversed. In the implant plane, an aperture plate 12 can be placed in the path of the beam. The aperture plate 50 has a hole at a reference position at its center, and additional holes at 25.0 mm increments on either side, in the scanning direction. Behind its aperture plate 12 is a Faraday cup 14, which is sized to accept 100% of the beam that is scanned with a +/xe2x88x92110 mm path. In operation, an ion beam is passed through the system 20 with the scanner magnet 74 programmed to zero, and the corrector magnet 10 is adjusted from zero until the beam is centered on the central aperture, as determined by maximizing the beam current on the fifth major peak encountered (the others having been caused by the beam traversing the first four holes). If the scanner magnet 74 is now energized by programming triangular waveform (whose amplitude in amps can be estimated from the setting of the corrector magnet in direct proportion), there is a brief period during which the capacitor 36 of the driver circuit 50 which is discussed below in more detail, charges to a quiescent value, after which the beam is stably scanned across all nine apertures in the aperture plate 12. The capacitor 36 may charge to a voltage, which is either too high or too low, if the phase relationship is incorrect. The xe2x80x9ccorrectxe2x80x9d voltage is one that causes the excursion of the amplifier 40 to be minimized, and it is therefore possible to create an error signal based upon the average amplifier voltage or to current or both which are used to adjust the phase of the commutator 36, either as a dynamic readback adjustment or as a preset adjustment. A shift of 1 degree in phase can be sufficient to prevent correct operation of the driver circuit 50. It is necessary to measure the exact programming voltage Vprog to the scanner power supply associated with maximum transmission through each of the nine apertures in the aperture plate 12. This measurement must be performed to a precision of about 0.1 amps, and can be accomplished automatically as the beam is scanned, or manually using a dc current to the scanner magnet 74. As the illustrative table 1 indicates, one beam pass is designed to occupy 10 mS. The return pass would be a reverse of the table. The scanning frequency would thus be 50 Hz, and the total scan amplitude 250 mm, which would cleanly scan a beam of up to 50 mm diameter off the edge of a 200 mm wafer. The actual table used to drive a DAC to drive the scanner requires many more points. If the sampling frequency is 20 kHz, for example, the table requires 201 points. These points must lie along a smoothly varying curve, and linear interpolation of the points in the measured table is insufficiently smooth, so the data should be fitted to a polynomial: Vprog=a0+a1t+a2t2+a3t3+xe2x80x83xe2x80x83(equation 3) from which the full table can be evaluated by substitution. Once the table is generated, the scan waveform is programmed by indexing up and down the table in equal time increments of 100 microseconds, and programming the scan amplifier 40 with the resulting values of Vprog. Implants are performed by traversing wafers at uniform velocity through the scanned beam. Typically five terms retained in equation 3 should be sufficient to cover known aberrations of sufficient magnitude to adversely affect the uniformity of the dose rate achieved by the scan system although fewer terms or additional terms can be utilized. To provide smooth scanning, a much larger table with finer time increments can be created. In practice a table of up to 500 points at time increments of 20 microseconds is considered sufficient. The waveform can be modified slightly at the turning points to splice in a smooth curve. This results in a waveform which can be followed with greater fidelity. For most applications, it is desired to hold the scanner current at a constant value for part of the time. This may be at asynchronous or synchronous moments. For example, in isotope switching applications, the desired scanned waveform can be as shown in FIG. 6a, whereas in ion implantation applications such as those described in U.S. Pat. No. 4,922,106, the desired switched waveform can be as shown in FIG. 6b. When the slew rate is desired to be high, the capacitor 36 of the driver circuit 50 or 60, which are described below in more detail, is switched in series with the scan amplifier 40 in the appropriate polarity. When it is desired to be low or zero, the capacitor is switched out and the terminals shorted (S1 and S2 both in position A). In this mode, the xe2x80x9cDCxe2x80x9d mode, the magnet current can be changed slowly to any desired value. The driver circuit 50 illustrated in FIG. 8a operates in the following manner. The inductance L is the scanner magnet 30. The losses of the scanner magnet 30 are lumped with all other losses, including the sense resistor 32 (Rs), into a resistor 34 (R). If the laminated magnet is well-designed, most of the losses are ohmic, so R is a close representation of the DC resistance of the circuit. The amplifier 40 has an output Vamp, which has a maximum value Vmax and minimum value Vmin. The storage capacitor 36 in the commutator 38 has a capacitance C that should exceed L/f2, where f is the operating frequency. The amplifier 40 delivers a current I proportional to a programming signal Vprog unless there is insufficient voltage drive to overcome the reactance of the scanner magnet 30. To compensate for non-linearity in the behavior of the laminated steel core, i.e. between the current I and the total flux, "PHgr", a sense coil (not shown) could be wound on the inductor, and its output could be integrated and combined with the signal from the dc current sense resistor 32 for use as a feedback signal in the amplifier 40. In this manner, the amplifier 40 operates to control the rate of change of flux in the scanner magnet 30. However, the amplifier 40 is incapable of producing a sufficient output voltage to support the required dI/dt, as discussed above without going into saturation. The commutator 38 has three states, characterized by the symbol Kcom, which can take the value +1, 0 or xe2x88x921. K=+1 represents the state where switch S1 is in position B, and switch S2 is in position A. K=0 represents the state where S1 and S2 are both in position A. K=xe2x88x921 represents the state where S1 is in position A and S2 is in position B. The switches may be solid-state half-bridge elements utilizing insulated gate bipolar transistors (IGBT). The switches S1 and S2 need to be break-before-make switches with overvoltage protection and freewheeling bypass diodes that operate in a time interval of a few microseconds maximum. Typically, switches S1 and S2 are configured to be a pair of IGBT""s or alternatively a pair of field effect transistors (FET). The electromagnetic field (EMF), E, in the driver circuit 50, is the algebraic sum of Kcom*Q*Cxe2x88x92IR+Vamp, and this can be equated to LdI/dt. The programming signal for the current is electronically differentiated to give a signal Vdiff. Assuming Vdiff to run from xe2x88x925 to +5V, the commutation signal can be generated from it by defining: K=+1 for Vdiff greater than 0.5V, K=0 for xe2x88x920.5 less than Vdiff less than 0.5V, and K=xe2x88x921 for Vdiff less than xe2x88x920.5V. This satisfactory provides Vmax greater than 0.1*L*(dI/dt)max in a system where the expected range of amplitude does not exceed a factor of xcx9c5. The phase of the signal so derived needs to have a provision for fine adjustment by +/xe2x88x921 degree in order to ensure that the net current to the capacitor C is zero on average when it has the optimum voltage. FIG. 9a graphically depicts the results when the driver circuit 50 is started from a state where all voltages and currents are zero. With a frequency of about 50 Hz, the waveform, a pure triangular wave, the inductance is 16 mH, the capacitance is 5,000 xcexcF, and Vmax is 75V. For the first eight cycles the output current is way below the desired value, and the amplifier 40 saturates while trying to deliver the required voltage. But in the process, charge is injected into the capacitor 38, whose voltage increases so that by the end of the 10th cycle the amplifier 40 is substantially out of saturation and the error in current is small, recovering to be within 0.5% of the setpoint for 90% of the cycle. If the amplitude of the programming signal, or more particularly the value of dI/dt, should be reduced, a lower voltage is required on the capacitor 36 and the driver circuit 50 functions in an analogous fashion to reduce the voltage over ten or so cycles. The energy must be given up to the amplifier 40, which must be provided with energy-absorbing capabilities. For various reasons, this is likely to be a switching pulse width modulation (PWM) amplifier such as those manufactured for driving large DC motors, and having a useful bandwidth above 1 kHz. Typically, these amplifiers are efficient, and have suitable energy-shedding capabilities. Reactive power levels are tens of kVA. When the apparatus is used to uniformly scan a beam across a workpiece in order to dope it, a more-or-less triangular wave is used. Commutation occurs at the turning points, but not while the beam is traversing the region where doping is to be uniform. Again, note that the dose rate from a scanned beam is inversely proportional to dx/dt, hence to first-order is inversely proportional to V/L, and that it is imperative that V be almost constant and smoothly varying during periods when uniform doping is desired. Note, however, that if the amplifier 40 is a pulse width modulated amplifier, or under other circumstances described blow, there may be switching noise superimposed on this waveform, requiring a high-order filter to be used to smooth V before judging its shape. The average voltage on the capacitor 36 remains constant at a desired value if the average current is zero. Because of the use of the commutator 38 this condition is not necessarily met if the average current in the inductor is zero. Also, it is possible to meet this condition even when the average current in the inductor is non-zero. This is determined by the timing of the commutation with respect to the state of the amplifier 46, and the precise timing with respect to the turning points when dI/dt reverses has a large effect on whether the capacitor 36 receives a net charging current or a net discharging current. It will be appreciated that the amplifier 40 must supply the power dissipated in the ohmic and other losses in the system. An alternative approach, dispenses with the amplifier 40 and utilizes a higher voltage DC power supply of equivalent power rating, which maintains the charge on the capacitor 36 directly. In this alternative approach, the DC voltage exceeds the highest voltage required to achieve the desired rate of current change. Since there is now no low-voltage amplifier 40 to correct errors in the current waveform, errors in its current waveform must be corrected in an alternative manner. The commutator 38 can be operated in a pulse-width-modulated mode at a high frequency, typically in the range of 10 to 30 kHz. Such systems are commercially available, and use a pulse-width-modulated amplifier switching at 20 kHz. A suitable system is manufactured by Glentek Incorporated of El Segundo, Calif. However, since these systems are primarily designed to deliver large amounts of real power to electric motors, they are not optimized for this application. One of the limitations of such a system is that the bandwidth is automatically limited. Under the Nyquist theorem, the bandwidth of a 20 kHz pwm amplifier cannot exceed 10 kHz. In practice it is limited to about 5 kHz by stability criteria. This limits the fidelity with which a 100 Hz waveform can be followed. A second limitation is that as the varying load current transitions through zero, the emf driving dI/dt falls by the forward voltage drop in the IGBTs that are performing the pwm switching. As a result, dI/dt also undergoes a change. The feedback loop controlling the pulse width modulator cannot respond within 200 microseconds, as mentioned above, resulting in a significant and asymmetric crossover distortion. As FIG. 8b illustrates, the system need not operate at a fixed switching frequency. Instead, when the error between the desired and the actual current in the inductive load exceeds a certain threshold, the commutator 37 is switched on in the appropriate direction for an undetermined amount of time until the error is reduced below a lower threshold, such as zero. The error signal described above is used to switch the commutator 38 into the Kcom=+1, 0 or xe2x88x921 modes in such a manner as to reduce the error, whenever the error exceeds a certain preset threshold. Referring to FIG. 8b, comparators 51 and 52 will change their output to a logic xe2x80x9c1xe2x80x9d level if the positive input value exceeds the negative input value by an amount DV, and will change from a logic xe2x80x9c1xe2x80x9d level to a logic xe2x80x9c0xe2x80x9d level if the negative input value exceeds the positive input value by an amount DV. Thus comparators 51 and 52 each have a total hysteresis of 2DV. Threshold T1 may be set to xe2x88x92DV, and threshold T2 may be set to +DV. The circuit 60 functions in the following manner. If the coil current through the coil 62 is less the desired value, the error signal from the current comparator 53 will be positive with respect to the ground mode 100. The ratio of the error signal to the error in coil current is determined by the values of resistors Rs, R1 and R2. If the error signal is positive by more than an amount 2DV, then comparator 51 switches the commutator 37 into state Kcom=+1, by placing switch S1 in state B. This applies the voltage across capacitor 35 so as to increase the current in the coil L in the positive direction. When the error falls to zero, the commutator 37 is again placed in state 0 by returning S1 to A. Conversely, if the error signal from the current comparator 53 falls below the threshold T2, comparator 52 places switch S2 in state B, which places the commutator 37 instate Kcom=xe2x88x921, which tends to drive the current negative, again until the error is reduced in magnitude to zero. One skilled in the art will recognize that additional components may be added to ensure clean switching without oscillation, and that the selection of thresholds may be slightly different in each application. In this mode the frequency of switching is proportional to a) the error between the desired dI/dt and the instantaneous value obtained when the commutator 37 is conducting, and b) the reciprocal of the hysteresis in comparators 51 and 52. Nevertheless, those of ordinary skill in the art will recognize that issues of isolation and grounding need to be on a per application basis. To illustrate the above described operation, if DV=0.5V, Rs=0.01 ohms, and the desired current varies from +100A to xe2x88x92100A at frequencies between 10 and 100 Hz, with a required precision of +/xe2x88x920.1A, then comparator 53 requires a gain of xcx9c1000, which can be achieved by setting R1=100 ohms, and R2=100 kohms. The gain of the comparator 53 can be such that the maximum tolerable error in current generates an error signal of magnitude 0.5V at the output of the comparator 53. The highest switching frequency is estimated to be 100/0.1*100 Hz=100 kHz. However, the switching frequency is much lower if the waveform frequency or the peak current is reduced. Typically, the commercially available pwm amplifier is limited to a frequency response of xcx9c5 kHz by the combination of the Nyquist criterion and feedback loop stability, whereas the circuit 60 responds in a time interval on the order of five microseconds, which happen to be the minimum on and off times of the commutator switches 51 and 52. Under normal conditions, the circuit 60 switches at a far lower frequency because dI/dt is lower. However, the maximum error in I would not be exceeded. Furthermore there is no clock frequency, so no possibility of beat frequencies or alias frequencies can cause unexpected variations in dI/dt exists. A further refinement of the circuit 60 is to adjust the magnitude of both the hysteresis and the voltage on the capacitor 36 downward when the waveform frequency is reduced, so as to keep the commutation frequency relatively high and improve the fidelity of the output current waveform. FIG. 9b graphically illustrates a comparison of the desired and resultant waveforms from the driver circuit 60. Preferred Embodiment 1 for an Ion Implanter. The following description is for equipment capable of scanning a 1 MeV123Sb+ beam across a 200 mm wafer, or any other beam of similar or lower magnetic rigidity. The beam is assumed to have a radius of 22 mm at the scanner magnet 74. As FIG. 7 illustrates, a set of annular disks 70 of tantalum surround the beam as it passes through a quartz tube 72 through the scanner magnet 74. The annular disks 70 prevent the beam from striking the interior walls of the quartz tube 72, thereby preventing forward sputtering by the ion beam of contaminants, and they provide a reference potential in spite of the presence of quartz walls. The annular disks 70 are connected as shown in FIG. 7 to prevent the creation of conductive loops, which would dissipate power as a result of the changing magnetic flux. The overall radius of the quartz tube 72 is about 35 mm. The scan angle desired is +/xe2x88x922.5 degrees. Substituting these values into equation 1 gives a stored energy of 45 J multiplied by a geometry factor k. Detailed modeling has shown that k has a value in this instance of approximately 2, and the stored energy is xe2x88x9285J. The scanner magnet 74 is constructed from a stack of 8xe2x80x3 thick E-shaped transformer laminations 76 and 78, each 0.014xe2x80x3 thick, from which a piece has been cut. The laminations 76 and 78 are 12xe2x80x3xc3x978xe2x80x3 with 2xe2x80x3 slots for the coil windings 80 and 82. FIG. 10 illustrates a cross-section of the scanner magnet 74. The pole gap 84 is about 70 mm. The two coil windings 80 and 82 each consist of about seventy turns of square #4 wire. The coil windings 80 and 82 are water-cooled by means of a non-shorted {fraction (3/16)}xe2x80x3 diameter copper tube passing cooling water that art built into the coil structure. Inductance is 16 mH and the operating maximum current is about over 100A. The power amplifier 40 consists of a bipolar amplifier sold commercially for the purpose of driving a dc electric motor, and rated at up to +/xe2x88x9275V and 100A. The capacitor 36 is switched by commercial half-bridge IGBT-based switches, with logic to prevent short-circuiting. The capacitor can charge to xcx9c400V during operation. Overvoltage protection is provided built-in reverse-voltage clamps that keep the maximum IGBT voltage a few volts over the capacitor voltage by virtue of the bridge connections. Scan correction is accomplished by a 35 degree 1T magnet with entrance and exit pole angles of 40 and xe2x88x9223 degrees, optimized by the computer programs TRANSPORT and TOSCA. The following coordinate definitions, typical of such applications, are used: x, y and z are beam-centered curvilinear coordinates, where the beam is traveling in the positive z-direction. The magnets deflect the beam in the x-z plane, i.e. the dominant magnetic field component is in the y-direction (positive or negative). The angles xxe2x80x2 and yxe2x80x2 are angles to the reference trajectory in the x-z and y-z planes. The scanner varies xxe2x80x2 between xe2x88x922.5 and +2.5 degrees. The suffixes 1 and 2 refer to input and output conditions, specifically to the centroid of the scanner field and the implant location respectively. The first-order condition is that xxe2x80x22/xxe2x80x21=0, for a parallel scanned output beam. The xxe2x80x22/xxe2x80x212 aberration has been reduced to an insignificant level to control scan linearity, and the coefficients xxe2x80x22/xxe2x80x212 and xxe2x80x22/yxe2x80x212 have been reduced to a sufficiently low level to keep the parallelism of the beam within +/xe2x88x920.5 degrees. These refinements are accomplished by means of the curvatures of the entrance and exit pole faces, and by controlling the non-uniformity of the field, as is well known to practitioners of the art. In the implant plane, an aperture 50 can be placed in the path of the beam. It has a hole at a reference position at its center, and additional holes at 25.0 mm increments on either side, in the scanning direction. Behind this aperture array is a Faraday cup which is sized to accept 100% of the beam which is scanned with a +/xe2x88x92110 mm path. The ion beam is passed through the system with the scanning magnet programmed to zero, and the corrector magnet is adjusted from zero until the beam is centered on the central aperture, as determined by maximizing the beam current on the fifth major peak encountered (the others having been caused by the beam traversing the first four holes). If the scanner is now energized by programming triangular waveform (whose amplitude in amps can be estimated from the setting of the corrector magnet in direct proportion), there will be a brief period during which the capacitor charges to a quiescent value, after which the beam is stable scanned across all nine apertures in the plate. The capacitor may charge to a voltage which is either too high or too low if the phase relationship is incorrect. The xe2x80x9ccorrectxe2x80x9d voltage is one which causes the excursion of the amplifier to be minimized, and it is therefore possible to create an error signal based upon the average amplifier voltage and/or current which is used to adjust the phase of the commutation, either as a dynamic readback adjustment or as a preset adjustment. A shift of 1 degree in phase can be sufficient to prevent correct operation of the circuit. It is necessary to measure the exact programming voltage Vprog to the scanner power supply associated with maximum transmission through each of the nine apertures in the plate. This measurement must be performed to a precision of less than xcx9c0.1 amp, and can be accomplished automatically as the beam is scanned, or manually using a dc current to the scan magnet. A table, of which the following is illustrative is constructed: According to Table 2, one beam pass is designed to occupy 10 mS. The return pass would be a reverse of the table. The scanning frequency would thus be 50 Hz, and the total scan amplitude 250 mm, which would cleanly scan a beam of up to 50 mm diameter off the edge of a 200 mm wafer. The actual table used to drive a DAC to drive the scanner requires many more points. If the sampling frequency is 20 kHz, for example, the table requires 201 points. These points must lie along a smoothly varying curve, and linear interpolation of the points in the measured table is insufficiently smooth, so the data should be fitted to a polynomial: Vprog=a0+a1t+a2t2+a3t3+xe2x80x83xe2x80x83(equation 3) from which the full table can be evaluated by substitution. Once the full table is generated, the scan waveform is programmed by indexing up and down the table in equal time increments of 100 microseconds, and programming the scan amplifier with the resulting values of Vprog. Implants are performed by traversing wafers at uniform velocity through the scanned beam. Experience should determine the number of terms to be retained in equation 3, but 5 terms should be sufficient to cover known aberrations of sufficient magnitude to adversely affect the uniformity of the dose rate achieved by the scan system. To provide smooth scanning, a much larger table with finer time increments can be created. We have used a table of 500 points at time increments of 20 microseconds. The waveform can be modified slightly at the turning points to splice in a smooth curve. This results in a waveform which can be followed with greater fidelity. The commutator consists of a bridge of four FETs or four IGBTs. In general IGBTs handle higher power levels than FETs; other devices may be substituted as they become available. IGBTs are available in modules of two, in a package which contains the driving logic. Therefore Bridge 30 in FIG. 8a or 8b can comprise two such IGBT packages, one represented by switch S1, and one represented by switch S2. In a practical embodiment, ancillary components such as isolated power supplies, and opto-isolated signals, must be provided. Suitable electronic devices for switching high voltages and currents are constantly being invented, and any new embodiments of the bridge structure shown are intended to fall within the scope of this invention. Preferred Embodiment 2 for an Ion Implanter The same beam and scanner apparatus is used as for the first embodiment, but an alternative power supply is used as illustration FIG. 8b. The source of power in this embodiment is a high voltage power supply of 300 to 600V, which need not be well regulated but is attached to a large capacitance of 1000 microfarads. For convenience this is full-wave rectified three-phase power. The combination is placed within the commutator 37. A sense resistor Rs produces a signal proportional to the current in the scanner magnet 74. A comparator 53 compares this current with the desired current programming signal. Those skilled in the art will recognize that the comparison can also be performed in a digital manner. When the error exceeds a threshold for a certain time (e.g. 0.1A for 2 microseconds) one of the commutator switches 51 or 52 is operated so as to apply the voltage on the capacitor 35 to the coil L in the direction which would reduce the error. The commutator 37 is switched off when the error falls below a second threshold for a certain time (e.g. 0.00A for 1 microsecond). There is a defined deadband and a minimum deadtime between changes in state of the commutator 37. The deadband and deadtime are related to the frequency of switching, and also affect the amount of heating of the power devices in the commutator 37. The maximum required frequency is about 100 kHz. Preferred Embodiment 3 for a Beam Switcher FIG. 11 illustrates the construction of an illustrative switching magnet 86. Construction of the switching magnet 86 is in the same E-core steel lamination 76 and 78 of the scanner magnet 74, but the center leg is trimmed at a slight angle, to create a slight gradient in the magnetic field. Each lamination 88 and 89 are clamped and glued to lie on an arc whose radius approximates the intended trajectory of a central ion of a selected species, at 300 mm. The switching magnet 86 is designed to bend a selected species through 90 degrees, and to provide simultaneous focussing in x- and y-coordinates, as is inclined at 45 degrees to the beam axis, and this requires a field index n of approximately xe2x88x920.29, where n is defined to be n=r/B dB/dr, where r=300 mm is the radius of the trajectory, and B is the magnetic field strength seen by the reference trajectory. In operation, it is desired to switch rapidly between certain magnetic field settings, for example between those for 20 keV beams of 12Cxe2x88x92, 13Cxe2x88x92, and 14Cxe2x88x92, which would require fields of 0.23, 0.24, and 0.250 T respectively. Switching time is typically around 5 msec. Each beam is identically focussed when its respective field is produced. Systematic differences in the ion-optical conditions encountered by each beam consist only of variations in the stability of the field at each value. This depends on timing of the commutation to ensure that the current is within required limits at the moment the capacitor 36 is removed from the circuit 50. That is, the capacitor 36 is in use only during transitions from one deflection to the next. The power amplifier 40 is in this instance a standard commercial programmable DC switching power supply, to which over- and under-voltage protection devices have been added. Other variants of the invention should be apparent to those skilled in the art. For example, the optics of the magnets may be modified to achieve different beam position/divergence objectives, or obtain the same objectives by other pole profiles than those described herein. The invention may also be applied to higher and lower magnetic rigidity beams, and to applications requiring non-uniform beam scanning patterns, for example spinning disk batch processors. |
|
047818840 | description | PREFERRED EMBODIMENTS OF THE INVENTION The numeral 10 generally designates a fuel assembly unit. The fuel assembly 10 includes an upper end fitting 12, a lower end fitting 14, spacer grids 16 supporting fuel rods 17, and a skirt portion 18 shown partially broken away in FIG. 1 to illustrate a debris catching strainer grid constructed accordingly to the principles of the invention, generally designated by the numeral 20. Behind the skirt 18, within the compartments defined by the debris catching strainer grid 20 and at the ends of fuel rods 17, are solid fuel rod end caps 22. Each fuel rod end cap 22 is located in an end cap compartment of the type illustrated in perspective in FIG. 2. The end cap compartment is defined by pairs of first intersecting and slottedly interlocked grid forming strips 24 known as top grid strips because of their lower slots 27. Strips 24 are for assembly with a second pair of intersecting grid forming strips 26, which are known as bottom grid strips because their slots 27 for slottedly interlocking with the grid forming strips 24 are located and along their upper margin. When assembled, the strips 24 in the area of intersection are above the strips 26. The pairs of first and second intersecting and slottedly interlocked grid forming strips 24 and 26 are attached to the perimeter strip 28 shown in detail in FIGS. 10, 11 and 12. The end cap compartments, as can be seen in FIG. 2, include vertical rows of integral leaves 30 intermediate their intersection of the pairs of first and second intersecting and slottedly interlocked strips 24 and 26. Each of the leaves 30 of a vertical row have a distance of projection out of the plane of its respective strip 24 or 26 different from the others of its row with the lower leaf 30 projecting out of the plane of its strip the most, while each successive leaf in the row as flow proceeds upwardly past it, projects a lesser amount. Collectively, these rows act as a strainer to prevent debris from leaving the inactive region of the fuel assembly in the area of skirt 18 and fuel rod end caps 22 and proceeding along the fuel rods 17 into the active region of the fuel assembly 10 along the sides of the cladding of fuel rods 17. The rods 17 are hollow and filled with fuel material in the active region as opposed to being solid in the fuel end cap region. As seen, for example, in FIG. 2, each of the leaves 30 in a vertical row is spaced from its adjacent leaves 30 in the row by an amount equal to the width of a leaf 30a in a row on the opposite side of the strip of which it is integral. For convenience, the designation 30 has been made for leaves which extend outwardly from the compartment illustrated in FIGS. 2 through 4 and the designation 30a is given to leaves which extend inwardly into the compartment illustrated in FIGS. 2, 3 and 4. FIGS. 5 through 9 show the details of the strips utilized in making up the embodiment of the strainer grid 20 of which the compartment shown in perspective in FIG. 2 is a part. The fragmentary strips 24 and 26 illustrated in FIGS. 5 though 9 include weld material tabs 32 to provide material for nugget welds when the strips 24 and 26 are in assembled grid-like condition. FIGS. 10 through 12 show the perimeter member 28 with its equivalent structure to that of strips 24 and 26 to the extent necessary to make complete compartments on the outside margins on the grid 20. Obviously, only leaves 30a which are inwardly directed toward the compartment are required. In the illustrated embodiment of FIGS. 2 through 12, all of the leaves 30 and 30a are constructed by bending them out of the plane at angles which are multiples of 15.degree.. Thus, the lowermost outwardly extending leaf 30 leaves the plane of the strips 24, for example, at 45.degree. and the next leaf 30 up, at 30.degree.. The lowermost leaf 30a leaves the plane of the strip 24 at 60.degree. and the next uppermost leaf 30a of the innervertical row leaves the plane of the strip 24 at 30.degree.. This is the same for the leaves 30a of all of the strips 24, 26 and includes perimeter strip 28. It will be seen that an effective strainer grid structure is shown by the embodiment of FIGS. 2 through 12, in the form of a grid which is attached, for example, by welding to the upper surface of the lower end fitting 14. The grid is oriented such that the solid fuel rod end caps 22 have the leaves 30 and 30a between them such over a flow hole 34 in the lower end fitting 14. Accordingly, the reactor coolant flow is directly presented to the grid device 20 in a manner in which the grid is likely to collect and retain debris in the reactor coolant flowing through flow hole 34 and upward along and between the solid fuel rod end caps 22. In the embodiment shown in FIGS. 13 through 19, parts analogous to the parts of the embodiment of FIGS. 2 through 12 are designated with the numeral 1 preceding the other digits of the designating number. Thus, top grid strips 124 and bottom grid strips 126 are utilized as the pairs of intersecting and slottedly interlocking strips in the embodiment of FIGS. 13 to 19 except the strips 124 and 126 are in reality, blanks which are half of a strip in order that double intersections, as shown in FIG. 19, can be produced. To accommodate these double blank intersecting strips, double slots 127a and 127b are provided in the lower margin of blank strip 124 in the upper margin of blank strip 126. A suitable perimeter strip 128 is provided, as shown in FIGS. 17 and 18 into which welding tabs 132 are inserted through holes 132a. In the case of the embodiment of FIGS. 13 through 19, leaves 130 c and 130d are provided on the blank strips 124 and 126. In this embodiment there are no vertical rows and the leaves 130c and 130d are mirror images of each other designed to coact with the contour of the fuel rod end caps 22. They are of asymmetric shape with the portions of their greatest distance of projection out of the plane of the strips 124 and 126 remote from the midpoint of the strips between their intersections. Since the leaves are in rather close proximity to the contour of the end caps 22, they provide a means for trapping debris against the end caps 22. The end caps 22 are of solid material and are therefore capable of accepting a great deal of wear without penetration of the fuel barrier. While the illustrated embodiments show only a limited number of leaves per strip, more are possible. The grid strip thicknesses relate to the number of leaves but they may be as thin as 12 mils to minimize the overall fuel assembly pressure drop. Accordingly, it will be seen that a novel debris catching strainer grid for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of the fuel assembly and creates fuel rod cladding damage is provided. |
abstract | A charged particle beam apparatus has a charged particle beam column configured to irradiate a charged particle beam, and a controller configured to control the charged particle beam column to irradiate the charged particle beam at a first pixel interval for a first region and to irradiate the charged particle beam at a second pixel interval different from the first pixel interval for a second region included in the first region. The first and second regions include plural first and second pixels each including first and second sub-pixels which are irradiated by the charged particle beam to generate secondary electrons. First and second sub-pixel images are formed based on the detected secondary electrons, and the first and second sub-pixel images are synthesized to form first and second images. |
|
abstract | A method of investigating a sample using Scanning Electron Microscopy (SEM), comprising the following steps: Irradiating a surface (S) of the sample using a probing electron beam in a plurality (N) of measurement sessions, each measurement session having an associated beam parameter (P) value that is chosen from a range of such values and that differs between measurement sessions; Detecting stimulated radiation emitted by the sample during each measurement session, associating a measurand (M) therewith and noting the value of this measurand for each measurement session, thus allowing compilation of a data set (D) of data pairs (Pi, Mi), where 1≦i≦N,wherein: A statistical Blind Source Separation (BSS) technique is employed to automatically process the data set (D) and spatially resolve it into a result set (R) of imaging pairs (Qk, Lk), in which an imaging quantity (Q) having value Qk is associated with a discrete depth level Lk referenced to the surface S. |
|
claims | 1. A nuclear fuel assembly comprising:a top nozzle;a bottom nozzle;a plurality of grids arranged in between the top nozzle and the bottom nozzle at spaced axial elevations between the top nozzle and bottom nozzle, the plurality of grids including a bottom grid disposed closest to the bottom nozzle among the plurality of grids; anda plurality of control rod guide assemblies, at least one of the control rod guide assemblies including:a guide tube having an axial dimension, the guide tube being supported by the plurality of grids and extending axially between the top nozzle and the bottom nozzle, the guide tube having an upper portion having a first external radius, a lower portion having a second external radius less than the first external radius, and a transition portion disposed between the upper portion and the lower portion, wherein the guide tube linearly transitions between the first external radius and the second external radius in the transition portion, and wherein the guide tube is monolithic through the first portion, the second portion and the transition portion; andan external dashpot tube disposed around a portion of the lower portion of the guide tube in an area beginning at the bottom grid and extending toward the top nozzle,wherein the guide tube includes at least one bulge and the external dashpot tube includes at least one bulge corresponding to the at least one bulge in the guide tube. 2. The nuclear fuel assembly of claim 1, wherein the external dashpot tube includes at least one weep hole formed therein. 3. The nuclear fuel assembly of claim 2, wherein the at least one weep hole includes a first weep hole and a second weep hole, and wherein the first weep hole is formed in an upper half of the external dashpot tube and the second weep hole is formed in a lower half of the external dashpot tube. 4. The nuclear fuel assembly of claim 1, wherein the guide tube includes a first bulge formed in its upper half and a second bulge in its lower half and the external dashpot tube includes first and second bulges corresponding to the first and second bulges of the guide tube. 5. The nuclear fuel assembly of claim 4, wherein the external dashpot tube includes at least one weep hole formed therein, and wherein the at least one weep hole is formed between the first and second bulges in the external dashpot tube. 6. The nuclear fuel assembly of claim 1, wherein the lower portion of the guide tube is substantially cylindrical and the external dashpot tube is substantially cylindrical. 7. The nuclear fuel assembly of claim 1, wherein the grids include a lower middle grid disposed second closest to the bottom nozzle among the plurality of grids, and wherein the external dashpot tube begins at the bottom grid and ends before reaching the lower middle grid. |
|
claims | 1. Process for generation of a fog composed of droplets of a liquid, comprising: the nozzle opening up into an area in which the pressure is equal to or less than 10 xe2x88x922 Pa and thus generates a fog of liquid droplets with sizes of an order of 10 xcexcm to 30 xcexcm at an area at an exit from the nozzle, an average fog density being greater than or equal to 10 20 molecules/cm 3 , the fog being strongly confined on a center line of the nozzle. pressurizing the liquid at a pressure of an order of 5xc3x9710 5 Pa to 10 7 Pa; and injecting the liquid thus pressurized into a nozzle with a diameter of between 20 xcexcm and 1 mm, 2. Process according to claim 1 , wherein the nozzle is heated. claim 1 3. Process according to claim 1 , further comprising focusing a laser beam on the fog, the laser beam configured to interact with the fog to generate light in an extreme ultraviolet range. claim 1 4. Process according to claim 3 , wherein the laser beam is focused on the fog at a distance of an order of 1 mm to 10 mm from the nozzle. claim 3 5. Process to claim 3 , wherein the light generated in the extreme ultraviolet range is used for insolation of a substrate on which a photoresist layer is deposited. claim 3 6. Device for generating a fog composed of droplets of a liquid, the device comprising: to thus generate a fog of liquid droplets in the vacuum chamber at an exit from the nozzle, with sizes of an order of 10 xcexcm to 30 xcexcm, an average fog density being greater than or equal to 10 20 molecules/cm 3 , the fog being strongly confined on a center line of the nozzle. a reservoir configured to contain the liquid; means for pressurizing the liquid contained in the reservoir, by subjecting the liquid to a pressure of an order of 5xc3x9710 5 Pa to 10 7 Pa; a nozzle having a diameter between 20 xcexcm and 1 mm and connected to the reservoir; a vacuum chamber containing the nozzle; and pumping means for setting up a pressure less than or equal to about 10 xe2x88x922 Pa in the vacuum chamber, 7. Device according to claim 6 , further comprising means for heating the nozzle. claim 6 8. Device according to claim 6 , wherein the means for pressurizing includes means for injecting a pressurized gas into the reservoir. claim 6 9. Device according to claim 6 , wherein the nozzle includes a pulsing means for producing the fog in pulsed form. claim 6 10. Device according to claim 6 , wherein the liquid is water. claim 6 11. Light source in an extreme ultraviolet range, comprising: the device according to claim 6 , claim 6 means for generating a laser beam configured to interact with the fog generated using the device; and means for focusing the laser beam on the fog. 12. Lithography apparatus for semiconducting substrates, comprising: wherein the light source in this apparatus is according to claim 11 . claim 11 means for supporting a semiconducting substrate on which a photoresist layer is deposited that will be insulated according to a determined pattern; a mask comprising the determined pattern in enlarged form; a light source in an extreme ultraviolet range; optical means for transmitting light to the mask, the mask supplying an image of the pattern in enlarged form; and optical means for reducing the image and projecting the reduced image on the photoresist layer, |
|
description | The present application is a continuation of, and claims benefit under 35 USC 120 to, international application PCT/EP2017/070056, filed Aug. 8, 2017, which claims benefit under 35 USC 119 of German Application No. 10 2016 214 785.4, filed Aug. 9, 2016. The entire disclosure of these applications are incorporated by reference herein. The present disclosure relates to an optical module, in particular a facet mirror with a number of components, the collision of which during operation is to be prevented by an anticollision device. The disclosure also relates to a corresponding component for such an optical module, to an optical imaging device with such an optical module, to a method for supporting a component of such an optical module and also to a corresponding optical imaging method. The disclosure can be used in conjunction with any desired optical imaging methods. It can be used particularly advantageously in the production or the inspection of microelectronic circuits and the optical components used for this purpose (for example optical masks). Optical modules, in particular facet mirrors, are used in semiconductor lithography at operating wavelengths in the UV range (for example in the range of 193 nm), but also in the so-called extreme UV range (EUV) with operating wavelengths of between 5 nm and 20 nm (typically in the range of 13 nm), for the production of microstructured or nanostructured components. The optical modules serve in such cases for ensuring that a mask plane or reticle plane is illuminated as homogeneously as possible. The optical modules are also used for obtaining different illumination settings (illumination angle distributions) in the region of the mask plane or reticle plane. The arrangement and the functioning of optical modules of the type in question here, in particular facet mirrors, in a projection exposure apparatus are described for example in DE 100 53 587 A1 and DE 10 2010 003 169 A1, the entire disclosure of which is hereby respectively incorporated by reference. Such facet mirrors generally include a plurality of facet elements with one or more reflective optical surfaces. The facet elements are supported by a supporting structure and are usually arranged in a number of facet groups. The tilting angle of the individual facet elements or their optical surfaces can be set alone or in groups by a corresponding actuator system of the supporting structure, in order to achieve, in each case, desired intensity distributions across the illumination light beam or different illumination settings, respectively. The supporting structure supporting the respective facet element in this case prescribes the path of movement of the individual facet element. In the case of the facet mirrors described above, as also in the case of other known facet mirrors with individually supported facet elements, the fundamental problem exists that, on the one hand, the supporting structure is in fact generally designed to be sufficiently stiff to keep the respective facet element in its respective position and/or orientation during normal undisturbed operation (without the effect of unusual internal or external mechanical disturbances, such as for example shocks or vibrations) and avoid collisions with adjacent facet elements or adjacent components of the imaging device (for example adjacent components of the supporting structure). However, if there are unusual mechanical disturbances, or the energy of such disturbances exceeds certain limit values, undesired collisions between the respective facet element and adjacent components, for example further facet elements or components of the supporting structure, can occur. This can cause, in particular, undesired damage to the optical surfaces, deformation of the facet elements or the like. It would in fact be possible in principle to design the supporting structure of the individual facet elements to be even stiffer in order to avoid such collisions. But there are limits to this, not least because of the desired properties typically imposed on the adjustability of the facet elements (in particular the dynamics of the adjusting movement) and the overall space available. It is known in principle from GB 1 556 473 A to use magnetic fields for contactlessly positioning an optical element in the form of a mirror, or keeping it in a predefined position, consequently therefore preventing a collision of the mirror with the adjacent supporting structure. However, it is problematic here that the magnetic fields used in this case are constantly active, so that, when making adjustments, their force effect on the mirror has to be overcome by the actuators, or the magnetic fields have to be varied in a complex way, respectively. Both lead to increased apparatus-wise expense for the imaging device. The disclosure seeks to provide an optical module, an optical component, an optical imaging device, a method for supporting an optical component and also an imaging method that do not have the aforementioned disadvantages, or at least to a lesser extent, and, in particular, to avoid a collision of components of such an optical module that is caused by defined mechanical disturbances, or of reducing the risk of such collisions, in a simple way. The disclosure is based on the technical teaching that, in the case of an optical module of the type mentioned at the beginning, a collision of components of such an optical module that is caused by defined mechanical disturbances can be avoided, or the risk of such collisions can be reduced, in a simple way by using an anticollision device that acts contactlessly by mutually assigned fields assigned, in the case of which at least one of the fields of the mutually assigned anticollision units is modified by superimposition of partial fields of a plurality of anticollision elements of the anticollision units in such a way that the field line density decreases more sharply with increasing distance from the anticollision unit than the respective field line density of the individual partial fields. The decrease of the field line density is preferably exponential. This achieves the effect that an appreciable counter-force that counteracts the collision is only achieved over a comparatively small range or only when the two components approach each other beyond the maximum approach resulting from normal adjusting movements between the components. On the other hand, no appreciable counter-force is produced during normal operation, in which there is no disturbance or there are only disturbances of such an energy that cannot lead to the components approaching each other that closely or lead to the components colliding. Accordingly, no appreciable counter-force has to be overcome for eventual normal adjusting movements of the components concerned (in the case of which no critical approach of the two components occurs). Hence, the actuator system used for this can be of a correspondingly simple design. A further advantage of such a sharply decreasing field line density is that the counter-force preferably increases correspondingly sharply when the components approach one another closely or more closely than the intended normal amount, in order to achieve a timely slowing of the relative movement of the components before the collision, and thereby avoid such a collision. It goes without saying in this respect that the fields of the anticollision units and the maximum counter-force achievable thereby are designed for a certain predefined energy of the mechanical disturbance to be expected as a maximum. A distinction can be made in this case between different disturbance scenarios. In particular, a distinction can be made between disturbances of different types and/or directions of effect that result in different relative movements of the two components. If it is expected that there will be such different disturbances which produce different relative movements of the two components and which can result, in particular, in collisions at different locations, a number of pairs of anticollision units may eventually be provided. These pairs of anticollision units may in principle be identically constructed, possibly only differing with regard to the counter-force produced, or being adapted to the respective disturbance scenario, respectively. According to one aspect, the disclosure therefore relates to an optical module, in particular a facet mirror, with a first component, a second component, a supporting structure, and an anticollision device. The first component is supported by the supporting structure and is arranged adjacent to the second component. Furthermore, the first component is arranged at a distance from the second component to form a gap. The supporting structure defines a path of relative movement of the first component, on which the first component moves along a direction of approach in relation to the second component under the influence of a defined mechanical disturbance, in particular a shock, wherein a collision between a first collision region of the first component and a second collision region of the second component occurs if the anticollision device is absent or inactive. The anticollision device includes a first anticollision unit, which is arranged on the first component and produces a first field. Furthermore, the anticollision device includes a second anticollision unit, which is arranged on the second component, is assigned to the first anticollision unit and produces a second field. The first anticollision unit and the second anticollision unit are designed in such a way that, as the first component and the second component increasingly approach each other along the path of relative movement, the first field and the second field produce an increasing counter-force on the first component that counteracts the approach. The first anticollision unit and/or the second anticollision unit includes a plurality of anticollision elements producing partial fields, the anticollision elements being assigned to one another in such a way that the superimposition of their partial fields produces a field of the anticollision unit with a field line density that decreases more sharply with increasing distance from the anticollision unit along the path of relative movement than a field line density of one of the partial fields. In other words, the concentration of the field lines described above is achieved in the vicinity of the anticollision unit, and consequently therefore the described sharp decrease of the field line density or sharper decrease in comparison with the partial fields with increasing distance from the anticollision unit is achieved by the superimposition of the partial fields. The decrease of the field line density resulting from the superimposition of the partial fields of the anticollision elements can in principle be chosen to be as sharp as desired in order to achieve the above-described effects of a late start of an appreciable counter-force effect and least-possible or negligible hindrance of normal adjusting movements, respectively. With preference, the anticollision elements of at least one of the anticollision units are therefore assigned to one another in such a way that the superimposition of partial fields produces a field of the anticollision unit with a field line density that varies in dependence on a distance from the anticollision unit along the path of relative movement. In this case, the field line density preferably decreases exponentially with the distance from the anticollision unit. In addition or as an alternative, it may be provided that the field line density decreases with the distance from the anticollision unit by a power of 5 to a power of 21, preferably a power of 7 to a power of 21, more preferably by a power of 9 to a power of 21. In the case of certain variants, the superimposed partial fields of the anticollision unit produce an real field which, in interaction with a predefined counter-field, produces a predefined counter-force on the first component only at a distance between the first collision region and the second collision region which si smaller than in a theoretical reference state, for which the theoretical partial forces that are obtained in the direction of approach from the respective partial field without the superimposition of the partial fields are added together. For the reference state, a theoretical situation is assumed for each anticollision element of the anticollision unit concerned, in which the other anticollision elements of the anticollision unit are absent (consequently therefore no superimposition with their partial fields takes place). For this theoretical situation, the theoretical partial counter-force is then determined from the partial field in dependence on the distance between the components. Subsequently, the theoretical counter-force is calculated by adding the respective amount of the partial counter-forces of all the anticollision elements. It goes without saying that such superimposition of the partial fields of anticollision elements may in principle also be provided only for one of the two anticollision units of such a pair of mutually assigned anticollision units. With preference, such a superimposition of partial fields of a number of anticollision elements is provided for both anticollision units of such a pair, since the short-rangedness of both fields can be achieved thereby and it can in this way be ensured that an appreciable counter-force effect only occurs when the two components approach each other closely, while normal adjusting movements between the two are not hindered by such a counter-force effect. The number of anticollision elements of the respective anticollision unit may in principle be chosen as desired, wherein it is adapted to the desired properties of the respective application, in particular to the decrease of the field line density that is to be achieved. In this case, the degree of the decrease of the field line density generally increases with the number of anticollision elements. In the case of certain variants of the disclosure, the first anticollision unit includes N first anticollision elements, while the second anticollision unit includes M second anticollision elements. Here, the two anticollision units of the pairing may have different numbers of anticollision elements. A particularly simple match is obtained, however, if the anticollision units of a pairing have the same number of anticollision elements, consequently therefore N is equal to M. Particularly advantageous setups with regard to the superimposition of the partial fields and the resultant counter-force effect are obtained if N and/or M is an even number, since a particularly uniform or advantageous field line distribution can be achieved thereby. The respective partial fields of the anticollision elements can in principle have any desired, possibly different strength and/or field line distribution. In the case of variants of a particularly simple design, the respective partial fields of the anticollision elements have a substantially identical strength and/or field line distribution. It may also be provided that an asymmetric field line distribution of the real fields is achieved by the number of anticollision elements and/or their respective partial field strength and/or the field line distribution of the respective partial field, in order to achieve a counter-force effect that is adapted to the approaching movement between the components. This may be of advantage in particular if the approach does not take place on a linear path of relative movement. In principle, any desired number of anticollision elements may be used for the respective anticollision unit. Particularly advantageous setups with a counter-force effect that starts sufficiently late but in time before a collision are obtained if N equals 2 to 20, preferably N equals 4 to 16, more preferably N equals 4 to 12. The same applies if, in addition or as an alternative, M equals 2 to 20, preferably M equals 4 to 16, more preferably M equals 4 to 12. It should be noted here that, depending on their arrangement, the field line density in the case of N (or M, respectively) anticollision elements generally decreases with the distance from the anticollision unit approximately by a power of N+1 (or by a power of M+1, respectively). Because of the advantageously sharp decrease of the field line density, typically higher numbers of anticollision elements are preferred, as long as it is compatible with the geometrical boundary conditions and the tolerances that are to be maintained. In order to achieve the above-described sharp decrease of the field line density of the respective field (with increasing distance from the respective anticollision unit), consequently the desired concentration of the field lines in the vicinity of the anticollision unit, the anticollision elements may in principle be arranged in any desired suitable way, in particular the partial fields of the individual anticollision elements may in principle be aligned in any desired suitable way. In this case, the anticollision elements of at least one of the anticollision units define, in their interior, an inner field direction of the partial field with an inner polarity. Particularly advantageous setups, in particular, particularly advantageous field line distributions, can be achieved if the anticollision elements of the at least one anticollision unit are arranged in a substantially annular arrangement in a plane extending transversely, in particular perpendicularly, to the counter-force. Similar applies if the anticollision elements of the at least one anticollision unit are arranged in a substantially annular arrangement in a plane perpendicular to the inner field direction of one of the anticollision elements. In this case, it is of advantage if at least two anticollision elements of the at least one anticollision unit are arranged along a circumferential direction of the annular arrangement in such a way that they have substantially opposed inner polarities. In particular, one or more groups of anticollision elements with a first polarity and one or more groups with an opposed second polarity may be provided along the circumferential direction. In this case, each of these groups may include one or more anticollision elements. In particular, the above-described setups with an asymmetric field distribution can be achieved thereby. In the case of further variants of the disclosure, the anticollision elements of the at least one anticollision unit, at least section-wise along a circumferential direction of the annular arrangement, are arranged with alternating polarity of the inner field direction. By this approach, it is possible to achieve the uniform field distribution as described above in a particularly simple way. The alignment of the inner field directions may in principle be chosen as desired here. In particular, the alignment of the inner field directions may be adapted to the desired field distribution. In the case of certain variants, the inner field directions of at least two anticollision elements, in particular all the anticollision elements, of the at least one anticollision unit are substantially parallel. As a result, it may be possible for a uniform field distribution to be achieved in a particularly simple way. In the case of certain variants, it is provided that, in a state of rest without any influence of the mechanical disturbance, the first collision region and the second collision region are at an at-rest distance along the direction of approach, in the case of which the first anticollision unit and the second anticollision unit produce a negligible first counter-force on the first component. Furthermore, for the first collision region and the second collision region, a minimum distance along the direction of approach is predefined, below which, under the effect of the mechanical disturbance, the approach must not go and at which the first anticollision unit and the second anticollision unit produce a second counter-force on the first component. For the first collision region and the second collision region there is then an intermediate distance along the direction of approach, which is achieved under the effect of the mechanical disturbance, which lies between the at-rest distance and the minimum distance, and at which the first anticollision unit and the second anticollision unit produce a third counter-force on the first component that is not negligible and has a magnitude between the first counter-force and the second counter-force. In the case of certain advantageous variants, the minimum distance is 3% to 20%, preferably 4% to 10%, more preferably 4% to 6%, of the at-rest distance. In addition or as an alternative, the intermediate distance may be 20% to 70%, preferably 30% to 50%, more preferably 30% to 40%, of the at-rest distance. Particularly advantageous configurations in which a sufficiently late but timely start of an appreciable counter-force effect is achieved can be realized in this way. The at-rest distance, the minimum distance and the intermediate distance may, in principle, be chosen as desired to correspond to the desired properties of the respective imaging device. In the case of certain variants, the at-rest distance is 0.2 mm to 1.0 mm, preferably 0.3 mm to 0.8 mm, more preferably 0.4 mm to 0.6 mm. In addition or as an alternative, the minimum distance may be 0.015 mm to 0.1 mm, preferably 0.02 mm to 0.08 mm, more preferably 0.02 mm to 0.04 mm. In addition or as an alternative, the intermediate distance may be 0.2 mm to 0.02 mm, preferably 0.15 mm to 0.04 mm, more preferably 0.1 mm to 0.06 mm. With these values, particularly advantageous designs can be achieved, in particular for applications in microlithography. The value of the respective counter-force may in principle be chosen as desired and be adapted to the respective application. In the case of certain advantageous variants with a late start of the counter-force effect, the first counter-force is less than 3% to 20%, preferably less than 4% to 10%, more preferably less than 4% to 6%, of the second counter-force. In addition or as an alternative, the third counter-force may be less than 20% to 70%, preferably less than 30% to 50%, more preferably less than 30% to 40%, of the second counter-force, consequently therefore a sufficiently late start of the counter-force effect can be achieved. For the same reason, in addition or as an alternative, finally the third counter-force may be 350% to 750%, preferably 500% to 750%, more preferably 650% to 750%, of the first counter-force. A timely start of a sufficient counter-force effect can be achieved in principle in any desired way in dependence on the respective application, in particular the mass inertia of the moved components. In the case of certain variants, the path of relative movement defines at every point a distance between the first collision region and the second collision region along the direction of approach, wherein a minimum distance of the first collision region and the second collision region in the direction of approach, below which the approach must not go under the effect of the mechanical disturbance, is predefined for the first component and the second component. The first anticollision unit and the second anticollision unit are designed here in such a way that the counter-force produced by them on the first component, which counteracts the approach caused by the mechanical disturbance, has reduced a relative speed between the first collision region and the second collision region along the direction of approach to a value of zero at the latest when the minimum distance is reached. A timely slowing of the relative movement between the two components can be achieved thereby. The arrangement of the respective anticollision unit on the respective component may in principle be realized in any desired suitable way, as long as it is ensured that the counter-force effect achieved with them starts in time to prevent a collision in the event of the respective maximum disturbance to be expected. It is not necessarily required that the anticollision units are arranged in the vicinity of the collision regions of the two components. Rather, they may in principle be provided at a distance as great as desired from these collision regions, as long as a collision is reliably prevented by their force effect in the event of the maximum disturbance to be expected. In the case of certain variants, the first anticollision unit is arranged in the region of the first collision region, in particular directly in the first collision region, of the first component. In addition or as an alternative, the second anticollision unit may be arranged in the region of the second collision region, in particular directly in the second collision region, of the second component. Both variants allow a particularly simple design of the anticollision units. As already mentioned at the beginning, in principle a single pairing of two anticollision units may suffice to avoid a collision between the components in all cases of disturbance to be expected. Depending on the type of disturbance to be expected, or the path of relative movement predefined by the supporting device, it may however be desirable to provide a number of such pairings of anticollision units. In the case of certain variants, the anticollision device therefore includes a third anticollision unit, which is at a distance from the first anticollision unit, is arranged on the first component and produces a third field. Furthermore, the anticollision device includes a fourth anticollision unit, which is at a distance from the second anticollision unit, is arranged on the second component, is assigned to the third anticollision unit and produces a fourth field. If the anticollision device is absent or inactive, a collision between a third collision region of the first component and a fourth collision region of the second component occurs here under the influence of the mechanical disturbance and/or a further mechanical disturbance. The third anticollision unit and the fourth anticollision unit are in turn designed in such a way that, with an increasing approach of the third collision region and the fourth collision region along the path of relative movement or along a further path of relative movement, the third field and the fourth field produce a further counter-force on the first component that increases and counteracts the approach. It goes without saying that the pairing including the third and fourth anticollision units can in principle be designed and arranged in the same way as described above for the pairing including the first and second anticollision units. In particular, here too, the measures described above can be used to achieve a sufficiently late but timely start of the counter-force effect that prevents a collision of the third and fourth collision regions in case of the maximum disturbance to be expected. To this extent, initially, reference is expressly made in this respect to the statements made above. In the case of certain variants, it is therefore provided in turn that the third anticollision unit and/or the fourth anticollision unit includes a plurality of further anticollision elements producing further partial fields. Here too, the further anticollision elements are assigned to one another in such a way that the superimposition of the further partial fields produce a further field of the anticollision unit with a field line density that decreases more sharply with increasing distance from the anticollision unit along the path of relative movement than a field line density of one of the further partial fields. In other words, here too, the concentration of the field lines described above in the vicinity of the respective anticollision unit, or the previously described sharp decrease of the field line density with increasing distance from the respective anticollision unit, is advantageously achieved, respectively. Here too, it is preferably provided, in turn, that the third anticollision unit is arranged in the region of the third collision region, in particular directly in the third collision region, of the first component, while the fourth anticollision unit is preferably arranged in the region of the fourth collision region, in particular directly in the fourth collision region, of the second component. As already mentioned above, it may suffice that a design is created which is tailored to a given maximum disturbance to be expected. This may be the case, in particular, whenever all other disturbances to be expected do not lead to a collision. Here, without the counter-force effect of the anticollision units along the path of relative movement, the same maximum disturbance to be expected may lead both to collisions in the region of the first and second collision regions and in the region of the third and fourth collision regions. The collisions may in this case occur simultaneously or sequentially. In the case of certain variants, however, different disturbances, in particular disturbances of different directions, may also lead to different paths of relative movement. In this case, one of the disturbances may lead to a collision in the region of the first and second collision regions, while the other may lead to a collision in the region of the third and fourth collision regions. In the case of certain variants, the further mechanical disturbance is therefore different at least in its direction of effect from that of the mechanical disturbance and the supporting structure defines the further path of relative movement of the first component, which is different from the path of relative movement and on which the first component moves along a further direction of approach in relation to the second component under the influence of the further mechanical disturbance, in particular a further shock. In principle, any desired suitable fields may be used to achieve the counter-force effect. Preferably, however, magnetic or electric fields are respectively used, alone or in combination. In the case of certain variants, at least one of the anticollision elements, in particular each of the anticollision elements of at least one of the anticollision units, is therefore designed so as to produce a magnetic partial field and/or an electric partial field. The magnetic or electric field may be produced in any desired suitable way. Thus, for example, a corresponding, possibly actively adjustable field can be produced by a corresponding active device of the respective anticollision element. Particularly variable or adaptive anticollision units can be obtained in this way. In addition or as an alternative, at least one of the anticollision elements, in particular each of the anticollision elements of at least one of the anticollision units, may include a permanent magnet. Particularly simple and robust configurations can be achieved in this way. The first component may be any desired component of the optical module. It is preferably an optical component with an optical surface. For example, the first component may be a facet element of a facet mirror. The second component may be a further optical component of the optical module, which has a further optical surface and is possibly supported in the same way as the first component by the supporting structure. For example, this may also be a further facet element of the facet mirror. However, it is similarly also possible that the second component is a different component of the optical module. In particular, it may be a component of the supporting structure that is adjacent to the first component. It also goes without saying that the anticollision units may be formed in such a way that the counter-force effect is available or can come into effect, respectively, at any desired times during operation but also during transportation of the optical module. In particular, the advantages take effect particularly well when transporting the optical module (alone or for example installed in an illumination device or a projection device, respectively), when there is a higher risk of unintentional disturbances in the form of shocks or the like. But also during operation of the optical module, for example, in an optical imaging device, the advantages of the disclosure can take effect particularly well in the event of disturbances, such as in particular earth tremors. The present disclosure also relates to a component for an optical module, in particular a facet element, which is formed as the first component or the second component of an optical module according to the disclosure, as described in detail above. To this extent, reference is expressly made to the statements made above with regard to the features and advantages of this component. Accordingly, the component again includes an anticollision unit with a plurality of anticollision elements producing partial fields, which are assigned to one another in such a way that the superimposition of partial fields produce the real field described above. This makes it possible to achieve the variants and advantages described above in the context of the optical module according to the disclosure to the same extent, and so reference is made to the explanations given above in this respect. The present disclosure also relates to an optical imaging device, in particular for microlithography, including an illumination device with a first optical element group, an object device for receiving an object, a projection device with a second optical element group and an image device, the illumination device being configured for illuminating the object and the projection device being configured for projecting an image of the object onto the image device. The illumination device and/or the projection device includes at least one optical module according to the disclosure. This also makes it possible to achieve the variants and advantages described above in the context of the optical module according to the disclosure to the same extent, and so reference is made to the explanations given above in this respect. The present disclosure also relates to a method for supporting a first component of an optical module, in particular a facet element of a facet mirror, wherein the first component is supported by a supporting structure and is arranged adjacent to a second component, the first component being arranged at a distance from the second component to form a gap. The supporting structure defines a path of relative movement of the first component, on which the first component moves along a direction of approach in relation to the second component under the influence of a defined mechanical disturbance, in particular a shock, wherein a collision between a first collision region of the first component and a second collision region of the second component occurs if the anticollision device is absent or inactive. A first anticollision unit of an anticollision device is arranged on the first component and produces a first field, while a second anticollision unit of the anticollision device is arranged on the second component, is assigned to the first anticollision unit and produces a second field. As the first component and the second component increasingly approach each other along the path of relative movement, the first field and the second field produce a counter-force on the first component that increases and counteracts the approach. The first anticollision unit and/or the second anticollision unit includes a plurality of anticollision elements producing partial fields, wherein the anticollision elements are assigned to one another in such a way that a superimposition of the partial fields produces a field of the anticollision unit with a field line density that decreases more sharply with increasing distance from the anticollision unit along the path of relative movement than a field line density of one of the partial fields. This also makes it possible to achieve the variants and advantages described above in the context of the optical module according to the disclosure to the same extent, and so reference is made to the explanations given above in this respect. The present disclosure also relates to an optical imaging method, in particular for microlithography, in which an object is illuminated by way of an illumination device with a first optical element group and an image of the object is produced on an image device via a projection device with a second optical element group. A method according to the disclosure is used for supporting a first component of an optical module in the illumination device and/or the projection device, in particular while producing the image. This also makes it possible to achieve the variants and advantages described above in the context of the optical module according to the disclosure to the same extent, and so reference is made to the explanations given above in this respect. Further aspects and embodiments of the disclosure become apparent from the dependent claims and the following description of preferred embodiments, which relates to the accompanying figures. All combinations of the disclosed features, irrespective of whether or not they are the subject of a claim, lie within the scope of protection of the disclosure. A preferred embodiment of a projection exposure apparatus 101 according to the disclosure, which includes a preferred embodiment of an optical module according to the disclosure, is described below with reference to FIGS. 1 to 8. To simplify the following explanations, an x, y, z coordinate system is indicated in the drawings, the z direction corresponding to the direction of the gravitational force. It goes without saying that it is possible in further designs to choose any desired other orientations of an x, y, z coordinate system. FIG. 1 is a schematic, not-to-scale representation of the projection exposure apparatus 101, which is used in a microlithographic process for producing semiconductor components. The projection exposure apparatus 101 includes an illumination device 102 and a projection device 103. The projection device 103 is designed to transfer, in an exposure process, an image of a structure of a mask 104.1, which is arranged in a mask unit 104, onto a substrate 105.1, which is arranged in a substrate unit 105. For this purpose, the illumination device 102 illuminates the mask 104.1. The optical projection device 103 receives the light from the mask 104.1 and projects the image of the mask structure of the mask 104.1 onto the substrate 105.1, such as for example a wafer or the like. The illumination device 102 includes an optical element group 106, which has an optical module 106.1 according to the disclosure. As explained in more detail below, the optical module 106.1 is designed in the form of a field facet mirror. The projection device 103 also includes an optical element group 107, which includes the optical module 107.1. The optical modules 106.1, 107.1 of the optical element groups 106, 107 are arranged along a folded optical axis 101.1 of the projection exposure apparatus 101. Each of the optical element groups 106, 107 may include a multiplicity of optical modules 106.1, 107.1. In the present embodiment, the projection exposure apparatus 101 operates with light in the EUV range (extreme ultraviolet radiation), with wavelengths of between 5 nm and 20 nm, in particular with a wavelength of 13 nm. The optical modules 106.1, 107.1 of the illumination device 102 and the projection device 103 are therefore exclusively reflective optical elements. In further configurations of the disclosure, it is of course also possible (in particular in dependence on the wavelength of the illumination light) to use any type of optical elements (refractive, reflective, diffractive) alone or in any desired combination. In particular, the illumination device 102 and/or the projection device 103 may include one or more optical modules 106.1 according to the disclosure. FIG. 2 shows an embodiment of an optical module 106.1 according to the disclosure. The latter is a field facet mirror, which serves, in particular, in interaction with a pupil facet mirror for producing secondary light sources in an illumination beam path, in order to achieve an illumination of the mask 104.1 that is as homogeneous as possible in the regions to be illuminated, and, in particular, to obtain different illumination distributions or illumination settings, respectively. In the present example, the incidence of light on the facet mirror 106.1 represented takes place substantially along the z direction. However, any other desired direction of illumination, inclined in relation to the z direction, may also be provided. The facet mirror 106.1 according to FIG. 2 includes a plurality of optical elements 108 to 110, which are designed as field facet elements. On their upper side, which during operation is facing the incident light, the facet elements 108 to 110 respectively have in the present example one or more optically effective surfaces in the form of mirror surfaces 111. In the present example, the facet elements 108 to 110 of the facet mirror 106.1 are arranged in facet groups 106.2. The facet groups 106.2 of the facet mirror 106.1 in this case respectively define reference planes 106.3, which in the present example are arranged at different angles of inclination in relation to the plane of main extension (xy plane) defined by the x and y directions. In FIG. 2, the individual facet elements 108 to 110 are merely represented for one facet group 106.2. The other facet groups 106.2 likewise include facet elements 108 to 110 arranged over the extent of the respective reference planes 106.3. It goes without saying, however, that in the case of other variants of the disclosure any other desired arrangement and/or grouping of the facet elements may also be chosen. FIG. 3 shows a schematic plan view of the detail III of the optical module 106.1 from FIG. 3, while FIG. 4 shows a schematic sectional view of the optical module 106.1 along the line IV-IV from FIG. 3. As can be seen, in particular, from FIGS. 2 to 4, the optical module 106.1 includes as a first component a first facet element 108, as a second component a second facet element 109 and a third facet element 110, which are all supported by a supporting structure 112. Here, the first facet element 108 is supported by a first supporting unit 112.1 of the supporting structure 112, while the second facet element 109 is supported by a second supporting unit 112.2 of the supporting structure 112. Equally, the third facet element 110 is supported by a third supporting unit 112.3 of the supporting structure 112. The respective supporting unit 112.1 to 112.3 in this case each includes an actuator unit 113, by which the position and/or orientation of the optical surface 111 of the respective facet element 108 110 can be actively set in one or more (up to all six) degrees of freedom in space. It goes without saying, however, that in the case of other variants such an active setting possibility may also be absent, consequently therefore purely passive support may be provided. Similarly, any desired combination of active and passive support is of course also possible. The first facet element 108 is in this case arranged adjacent to the second facet element 109, the two being spaced apart from one another in such a way that a gap is formed between them, hence, they do not touch. The same applies to the second facet element 109 and the third facet element 110. The third facet element 110 is finally arranged adjacent to a component 112.4 of the supporting structure 112, the two being spaced apart from one another in such a way that a gap is formed between them, hence, they do not touch. In each case, the supporting structure 112 defines a path of relative movement RBi between the facet elements 108 to 110 and the supporting structure 112, respectively, on which they move in relation to one another under the influence of a defined mechanical disturbance MSi, for example, a shock, along a direction of approach ARi. Depending on the magnitude of the disturbance MSi, in each case, a collision may occur between the two components located adjacent to one another. As described below by way of example on the basis of the facet elements 108 and 109, an anticollision device 114, which counteracts such collisions and avoids such collisions for the disturbances MSi to be expected during operation or transportation of the components of the projection exposure apparatus 101, respectively, is therefore provided. As can be seen, in particular, from FIGS. 3 and 6, for example under the influence of a defined first mechanical disturbance MS1 (for example a shock along the y direction), the first facet element 108 and the second facet element 109 approach each other along a path of relative movement RB1 in a direction of approach AR1. If the anticollision device 114 were absent or inactive, there would in this case be a collision between a first collision region 108.1 of the first facet element 108 and a second collision region 109.1 of the second facet element 109, as becomes apparent from the dashed contours in FIG. 3. In order to avoid such collisions, the anticollision device 114 includes a first anticollision unit 114.1, which is arranged on the first facet element 108 and produces a first field F1, and also a second anticollision unit 114.2, which is arranged on the second facet element 109, is (spatially and functionally) assigned to the first anticollision unit 114.1 and produces a second field F2. The first anticollision unit 114.1 and the second anticollision unit 114.2 are configured in such a way that, as the first facet element 108 and the second facet element 109 increasingly approach each other along the path of relative movement RB1, the first field F1 and the second field F2 contactlessly produce an increasing counter-force CF1 on the first facet element 108 that counteracts the approach. A corresponding reaction force CF2 is also exerted on the second facet element 109 by the reaction of the fields F1 and F2. In principle, any desired suitable fields F1 and F2 may be used to achieve the counter-force effect. Preferably, however, magnetic or electric fields are respectively used for this, alone or in any desired combination. In the present example, the anticollision elements 115.1, 115.2 are designed as permanent magnets, which in each case produce a magnetic partial field TF1 and TF2, respectively. It goes without saying, however, that in the case of other variants the respective partial field TF1 or TF2 may also be produced in any other desired suitable way. Thus, for example, a corresponding, possibly actively adjustable partial field TF1 or TF2 may be produced by a corresponding active device of the respective anticollision element 115.1 or 115.2. Particularly variable or adaptive anticollision units 114.1 to 114.4 can be respectively obtained in this way. As can be seen in particular from FIGS. 4 to 6, the first anticollision unit 114.1 and the second anticollision unit 114.2 respectively include a plurality of anticollision elements 115.1, 115.2, which in each case produce substantially equally strong partial fields TF1, TF2 with the same field line distribution and the same pattern of the field line density, respectively. In the present example, N=4 anticollision elements 115.1, 115.2, more precisely, two anticollision elements 115.1 and two anticollision elements 115.2, are provided for the first anticollision unit 114.1. The same applies to the second anticollision unit 114.2 with M=4 anticollision elements 115.1, 115.2, more precisely, two anticollision elements 115.1 and two anticollision elements 115.2. The anticollision elements 115.1 115.2 are respectively arranged in a so-called quadrupole configuration and in each case produce a partial field TF1 or TF2, respectively (as is represented in FIG. 7). The anticollision elements 115.1, 115.2 are assigned to one another in such a way that the superimposition of their partial fields TF1 and TF2 produces the real field F1 and F2, respectively. For this purpose, the anticollision elements 115.1, 115.2 in each case, in their interior, define an inner field direction IFR1 or IFR2 of the partial field TF1 and TF2, respectively, with an inner polarity IP1 and IP2, respectively. As can be seen in particular from FIGS. 4, 5 and 8, the anticollision elements 115.1, 115.2 of the anticollision units 114.1 and 114.2 are arranged in a substantially annular arrangement in a plane (here: xy plane) extending perpendicularly to the counter-force CF1 or CF2 and perpendicularly to the inner field direction IFR1 or IFR2, respectively. Here, the anticollision elements 115.1, 115.2 of the anticollision units 114.1 to 114.4 are arranged along a circumferential direction U of the annular arrangement in such a way that they alternately have substantially opposed inner polarites IP1, IP2 with substantially parallel inner field directions IFR1, IFR2. Consequently, the anticollision elements 115.1 115.2 are therefore arranged with alternating polarities IP1, IP2 of the inner field directions IFR1, IFR2. In the case of FIGS. 5 and 8, therefore, an anticollision element 115.1 with a magnetic north pole (on the surface facing the anticollision unit 114.1) is respectively followed along the circumferential direction U by an anticollision element 115.2 with a magnetic south pole (on the surface facing the anticollision unit 114.1), and vice versa. Here, FIG. 8 shows the pattern and the direction, respectively, of the field lines at certain points in a plane parallel to the xz plane. It goes without saying that, in the case of other variants, the alignment of the inner field directions IFR1, IFR2 can in principle be chosen as desired. In particular, the alignment of the inner field directions IFR1, IFR2 may be adapted to the desired field distribution of the fields F1, F2. Furthermore, one or more groups G1 of anticollision elements 115.1 with the first polarity IP1 and one or more groups G2 of anticollision elements 115.2 with an opposed second polarity IP2 may be provided along the circumferential direction U. In this case, each of these groups G1 or G2 may include one or more anticollision elements 115.1 or 115.2, respectively. Herewith, in particular, the above-described setups with an asymmetric field distribution can be achieved. As becomes apparent from FIGS. 6 and 7, the assignment of the anticollision elements 115.1, 115.2 is performed in such a way that a predefined counter-force CF1 is produced on the first facet element 108 when there is a distance Dreal between the first collision region 108.1 and the second collision region 109.1. This distance Dreal is smaller than a reference distance Dref between the first collision region 108.1 and the second collision region 109.1, in the case of which this predefined counter-force CF1 is achieved for a theoretical reference state (see FIG. 7). For this theoretical reference state, the amounts of the four theoretical individual partial forces TCF1 and TCF2 along the direction of approach AR1 are added together, which are obtained from the respective partial field TF1 or TF2 of the respective anticollision element 115.1, 115.2 of the first anticollision unit 114.1 (without the respective superimposition of the partial fields of the other anticollision elements 115.1, 115.2 of the anticollision unit 114.1) in interaction with the second anticollision unit 114.2. Consequently, the respective partial force TCF1 or TCF2 is therefore obtained from the interaction between the partial field TF1 or TF2 of the anticollision element 115.1 or 115.2, respectively, of the first anticollision unit 114.1 and the field F2 of the second anticollision unit 114.2. In other words, for the reference state, a theoretical situation is assumed for each anticollision element 115.1 or 115.2 of the anticollision unit 114.1 or 114.2, respectively, in which the other anticollision elements 115.1 or 115.2 of the anticollision unit 114.1 or 114.2, concerned are absent (consequently therefore no superimposition of their partial fields TF1 or TF2 takes place). For this theoretical situation, the theoretical partial counter-force TCF1 or TCF2 is then determined from the partial field TF1 or TF2 in dependence on the distance D between the components. Subsequently, the theoretical counter-force is calculated by adding the respective amounts of the theoretical partial counter-forces TCF1, TCF2 of all the anticollision elements 115.1, 115.2 of the anticollision unit 114.1 or 114.2 concerned in the direction of approach. As can be seen, in particular, from FIG. 6, in other words, by the superimposition of the partial fields TF1 and TF2, a concentration of the field lines of the fields F1 or F2 is achieved in the vicinity of the anticollision unit 114.1 or 114.2. This therefore brings about the above-described decrease of the field line density with increasing distance from the anticollision unit 114.1 or 114.2 that is sharper than the decrease of the field line density of the individual partial fields TF1 and TF2. With the anticollision device 114, the fields F1 and F2 of the anticollision units 114.1 and 114.2 assigned to one another are consequently therefore modified by the superimposition of partial fields TF1, TF2 of the anticollision elements 115.1, 115.2 in such a way that the field line density decreases sharply with increasing distance from the anticollision unit 114.1 and 114.2, respectively, along the direction of approach AR1. In the present example, in particular, an advantageous exponential decrease of the field line density is achieved. By this approach, the effect is achieved that an appreciable counter-force CF1 or CF2 that counteracts the collision is only achieved over a comparatively small range and only when the two facet elements 108 and 109 reach an approach (i.e. a distance) Dlim towards each other along the direction of approach AR1 which is closer (i.e. of a smaller amount) than the maximum approach (i.e. the distance) Dstell,max which results from normal (i.e. intended during normal operation) adjusting movements between the facet elements 108 and 109 (i.e., it holds: Dstell, max>Dlim). On the other hand, no appreciable counter-force CF1 or CF2 is produced during normal operation, in which there is no disturbance MSi or in which there are only disturbances MSi of such an energy that cannot lead to the components approaching each other that closely or the facet elements 108 and 109 colliding. Accordingly, no appreciable counter-force CF1 or CF2 has to be overcome for normal adjusting movements that may be desired at the facet elements 108 and 109 (in the case of which no critical approach of the two facet elements 108 and 109 occurs). Hence, the actuator system 113 provided for this purpose can be of a correspondingly simple design. A further advantage of the exponentially decreasing field line density of the fields F1 and F2 is that the counter-force CF1 or CF2 increases correspondingly sharply when the facet elements 108 and 109 approach one another closely or more closely than the intended normal amount, in order to achieve a timely slowing of the relative movement of the facet elements 108 and 109 before the collision, and thereby prevent such a collision. It also goes without saying that the fields F1 and F2 of the anticollision units 114.1 and 114.2 and the maximum counter-force CF1 or CF2 achievable thereby are configured for a certain predefined energy EMSi of the mechanical disturbance MSi to be expected as a maximum. A distinction can be made here between different disturbance scenarios. In particular, a distinction can be made between disturbances MSi of different types and/or directions of effect that result in different relative movements of the two facet elements 108 and 109. In the present example, such different disturbances MSi which produce different relative movements of the two facet elements 108 and 109 and which can result in collisions at different locations can be expected. Accordingly, along with the pair of anticollision units 114.1 and 114.2, a further pair of anticollision units 114.3 and 114.4 is provided for the facet elements 108 and 109. The anticollision units 114.3 and 114.4 are in this case provided at the other end (in the x direction) of the facet elements 108 and 109 and are, in principle, designed identically to the anticollision units 114.1 and 114.2. In the present example, the superimposition of the partial fields TF1, TF2 of the anticollision elements is provided for both anticollision units 114.1, 114.2 and 114.3, 114.4, respectively, of the respective pair, since the desired short-rangedness of the two fields F1 and F2 can be achieved thereby and, by this approach, it can be ensured that an appreciable counter-force effect CF1 or CF2 only occurs when the two facet elements 108 and 109 approach each other highly closely, while normal adjusting movements between the two facet elements 108 and 109 are not hindered by such a counter-force effect. It goes without saying, however, that the described superimposition of the partial fields TF1, TF2 of the anticollision elements 115.1, 115.2 may in principle also be provided only for one of the two anticollision units 114.1 or 114.2 and 114.3 or 114.4, respectively, of such pairs of anticollision units 114.1, 114.2 and 114.3, 114.4, respectively, that are assigned to one another. The decrease of the field line density resulting from the superimposition of the partial fields TF1, TF2 of the anticollision elements 115.1, 115.2 can in principle be chosen to be as sharp as desired in order to achieve the above-described effects of a late start of an appreciable counter-force effect CF1, CF2, and least-possible or negligible hindrance of normal adjusting movements, respectively. In the present example, the anticollision elements 115.1, 115.2 of the two anticollision units 114.1, 114.2 and 114.3, 114.4 are assigned to one another in such a way that the superimposition of the partial fields TF1, TF2 produces a field F1 or F2 with a field line density that, in dependence on a distance from the anticollision unit 114.1, 114.2 or 114.3, 114.4, respectively, along the path of relative movement Ri in the direction of approach ARi, decreases exponentially with the distance from the anticollision unit 114.1, 114.2 and 114.3, 114.4, respectively. To be more precise, the four anticollision elements 115.1, 115.2 of each of the two anticollision units 114.1, 114.2 and 114.3, 114.4, respectively, are arranged in a so-called quadrupole configuration, in which the field line density of the fields F1 or F2 decreases along the direction of approach ARi with the distance from the anticollision unit 114.1, 114.2, 114.3, 114.4 approximately by a power of 5. It goes without saying, however, that in the case of other variants of the disclosure a different decrease of the field line density of the fields F1 or F2 may also be obtained. Thus, the field line density may decrease with the distance from the anticollision unit 114.1, 114.2, 114.3, 114.4 by a power of 5 to a power of 21, preferably a power of 7 to a power of 21, more preferably by a power of 9 to a power of 21. It goes without saying that the number N or M, respectively, of anticollision elements 115.1, 115.2 of the respective anticollision unit 114.1, 114.2, 114.3, 114.4 may in principle be chosen as desired, wherein in it is adapted to the desired properties of the respective application, in particular to the decrease of the field line density that is to be achieved. In this case, the degree of the decrease of the field line density generally increases with the number of anticollision elements 115.1, 115.2. With some variants, both anticollision units 114.1, 114.2 and 114.3, 114.4, respectively, of the respective pairing may have different numbers of anticollision elements (i.e. it holds: N is not equal to M). Thus, an asymmetric field distribution of the fields F1, F2 can be achieved by the number of anticollision elements 115.1, 115.2 and/or their respective partial field strength TF1, TF2, in order to achieve a counter-force effect CF1, CF2 that is adapted to the approaching movement between the facet elements 108 and 109. This may be of advantage, in particular, if the approach does not take place on a linear path of relative movement Ri. In principle, any desired number of anticollision elements 115.1, 115.2 may be used for the respective anticollision unit 114.1, 114.2, 114.3, 114.4. Particularly advantageous setups with a counter-force effect that starts sufficiently late but in time before a collision are obtained if N equals 2 to 20, preferably N equals 4 to 16, more preferably N equals 4 to 12. The same applies if, in addition or as an alternative, M equals 2 to 20, preferably M equals 4 to 16, more preferably M equals 4 to 12. In the present example, in a state of rest without any influence of the mechanical disturbance MS1, the first collision region 108.1 and the second collision region 109.1 are at an at-rest distance DRuhe along the direction of approach AR1, in the case of which the first anticollision unit 114.1 and the second anticollision unit 114.2 produce a negligible first counter-force CF1 on the first facet element 108. For the first collision region 108.1 and the second collision region 109.1 there is also predefined a minimum distance Dmin along the direction of approach AR1, below which the approach must not go under the effect of the mechanical disturbance MS1 and at which the first anticollision unit 114.1 and the second anticollision unit 114.2 produce a second counter-force CF12 on the first facet element 108. For the first collision region 108.1 and the second collision region 109.1 there is also predefined an intermediate distance Dzwi along the direction of approach AR1 which is achieved under the effect of the mechanical disturbance MS1, lies between the at-rest distance DRuhe and the minimum distance Dmin and at which the first anticollision unit 114.1 and the second anticollision unit 114.2 produce a third counter-force CF13 on the first facet element 108 that is not negligible and lies between the first counter-force CF11 and the second counter-force CF12. In the present example, the minimum distance Dmin is approximately 5% of the at-rest distance DRuhe. In the case of advantageous variants, the minimum distance Dmin is 3% to 20%, preferably 4% to 10%, more preferably 4% to 6%, of the at-rest distance DRuhe. In the present example, the intermediate distance Dzwi is approximately 30% of the at-rest distance DRuhe. In the case of advantageous variants, the intermediate distance Dzwi is 20% to 70%, preferably 30% to 50%, more preferably 30% to 40%, of the at-rest distance DRuhe. Particularly advantageous configurations in which a sufficiently late but timely start of an appreciable counter-force effect CF1 is achieved can be achieved in this way. The at-rest distance DRuhe, the minimum distance Dzwi and the intermediate distance Dzwi may, in principle, be chosen as desired to correspond to the desired properties of the respective imaging device 101. With certain variants, the at-rest distance DRuhe, is 0.2 mm to 1.0 mm, preferably 0.3 mm to 0.8 mm, more preferably 0.4 mm to 0.6 mm. In addition or as an alternative, the minimum distance Dmin may be 0.015 mm to 0.1 mm, preferably 0.02 mm to 0.08 mm, more preferably 0.02 mm to 0.04 mm. In addition or as an alternative, the intermediate distance Dzwi may be 0.2 mm to 0.02 mm, preferably 0.15 mm to 0.04 mm, more preferably 0.1 mm to 0.06 mm. With these values, particularly advantageous designs can be achieved, in particular for applications in microlithography. The value of the respective counter-force CF1 may in principle be chosen as desired and be adapted to the respective application. In the case of certain advantageous variants with a late start of the counter-force effect CF1, the first counter-force CF11 is less than 3% to 20%, preferably less than 4% to 10%, more preferably less than 4% to 6%, of the second counter-force CF12. In addition or as an alternative, the third counter-force CF13 may be less than 20% to 70%, preferably less than 30% to 50%, more preferably less than 30% to 40%, of the second counter-force CF12, consequently therefore a sufficiently late start of the counter-force effect CF1 can be achieved. For the same reason, in addition or as an alternative, finally the third counter-force CF13 may be 350% to 750%, preferably 500% to 750%, more preferably 650% to 750%, of the first counter-force CF11. The timely start of a sufficient counter-force effect CF1 is achieved in the present example in dependence on the respective application, in particular, dependent on the mass inertia of the moved facet elements 108 to 110. The first anticollision unit 114.1 and the second anticollision unit 114.2 are formed, here, in such a way that the counter-force CF1 produced by them on the first facet element 108 has reduced a relative speed (caused by the mechanical disturbance MS1) between the first collision region 108.1 and the second collision region 109.1 along the direction of approach AR1 to a value of zero at the latest when the minimum distance Dmin is reached. A timely slowing of the relative movement between the two facet elements 108 and 109 can be achieved thereby. The arrangement of the respective anticollision unit 114.1 to 114.4 on the respective facet element 108 to 110 may, in principle, be chosen in any desired suitable way, as long as it is ensured that the counter-force effect CF1, CF2 achieved with them starts in time to prevent a collision in the event of the maximum disturbance MSi to be expected. It is not absolutely necessary here that the anticollision units 114.1 to 114.4 are arranged in the vicinity of the collision regions 108.1, 109.1 of the two facet elements 108 and 109. Rather, they may in principle be provided at a distance as great as desired from these collision regions 108.1, 109.1, as long as a collision is reliably prevented by their force effect CF1, CF2 in the event of the maximum disturbance MSi to be expected. In the present example, the first anticollision unit 114.1 is however arranged directly in the first collision region 108.1. In addition, the second anticollision unit 114.2 is arranged directly in the second collision region 109.2. Both variants allow a particularly simple design of the anticollision units 114.1, 114.2. As already mentioned at the beginning, in principle, a single pairing of two anticollision units 114.1, 114.2 may suffice to avoid a collision between the facet elements 108, 109 in all cases of disturbance MSi to be expected. Depending on the type of disturbance MSi to be expected or the path of relative movement Ri predefined by the supporting device 112, respectively, it may however be desirable, as in the present example, to provide a number of such pairings of anticollision units 114.1, 114.2 and 114.3, 114.4, respectively, spaced apart from one another. The third anticollision unit 114.3 and the fourth anticollision unit 114.4 are again designed in such a way that, with an increasing approach of the third collision region 108.2 and the fourth collision region 109.2 along the path of relative movement R1 or along a further path R2 of relative movement, the third field F3 of the third anticollision unit 114.3 and the fourth field F4 of the fourth anticollision unit 114.4 produce an increasing further counter-force CF3 on the first facet element 108 that counteracts the approach. In the present example, the pairing including the third anticollision unit 114.3 and the fourth anticollision unit 114.4 can be designed and arranged in the same way as described above for the pairing including the first anticollision unit 114.1 and the second anticollision unit 114.2. In particular, here too, the measures described above can be used to achieve a sufficiently late but timely start of the counter-force effect CF3, CF4 that prevents a collision of the third collision region 108.2 and the fourth collision region 109.2 for the maximum disturbance MSi to be expected. To this extent, initially, reference is expressly made in this respect to the statements made above. In the present example, the third anticollision unit 114.3 and the fourth anticollision unit 114.4 therefore, again, include a plurality of anticollision elements 115.1 115.2 producing partial fields TF1, TF2. Here too, the further anticollision elements 115.1, 115.2 are assigned to one another in such a way that the superimposition of further partial fields TF1, TF2 produce a further field F3 and F4, respectively, of the anticollision unit 114.3, 114.4, respectively, with a field line density that decreases more sharply with increasing distance from the anticollision unit 114.3 and 114.4, respectively, along the path of relative movement Ri than a field line density of one of the further partial fields TF1, TF2. Thus, here too, the concentration of the field lines described above in the vicinity of the respective anticollision unit 114.3, 114.4, and the previously described sharp decrease of the field line density with increasing distance from the respective anticollision unit 114.3, 114.4, respectively, is advantageously achieved. Here too, the third anticollision unit 114.3 is arranged directly in the third collision region 108.2, while the fourth anticollision unit 114.4 is arranged directly in the fourth collision region 109.2. As already mentioned above, it may suffice that a design is created for a certain maximum disturbance MS1 to be expected. This may be the case, in particular, whenever all other disturbances to be expected do not lead to a collision. Here, without the counter-force effect of the anticollision units 114.1 to 114.4 along the path of relative movement R1, the same disturbance MS1 to be expected as a maximum may lead both to collisions in the region of the first collision region 108.1 and the second collision region 109.1 and in the region of the third collision region 108.2 and the fourth collision region 109.2. The collisions may occur simultaneously or sequentially. In the present example, however, different disturbances MS1 and MS2, in particular disturbances MS1 and MS2 in different directions, may also lead to different paths of relative movement R1 and R2. In this case, one of the disturbances MS1 may lead to a collision in the region of the first collision region 108.1 and the second collision region 109.1, while the other disturbance MS2 may lead to a collision in the region of the third collision region 108.2 and the fourth collision region 109.2. In the present example, the further mechanical disturbance MS2 is therefore different at least in its direction of effect from the first mechanical disturbance MS1 and the supporting structure defines the further, second path of relative movement R2 of the first facet element 108, which is different from the first path of relative movement R1 and on which the first facet element 108 moves along a further direction of approach AR2 in relation to the second facet element 109 under the influence of the further mechanical disturbance MS2 (in particular a further shock). The relative movement and the avoidance of collisions between the facet elements 108 and 109 has been described above. Similarly or identically designed pairs of anticollision units 114.1, 114.2 and 114.3, 114.4, respectively, may be provided between all or a number of the facet elements of the facet mirror 106.1, as can be seen in particular in FIG. 3. The second component may, however, also be another component of the optical module 106.1, in particular a component 112.4 of the supporting structure 112 that is located adjacent to a facet element, as is shown in FIG. 3 for the facet element 110 and the component 112.4 of the supporting structure 112. Similarly or identically designed pairs of anticollision units 114.1, 114.2 and 114.3, 114.4, respectively, are likewise provided between the facet element 110 and the component 112.4. It also goes without saying that the counter-force effect of the anticollision units 114.1 to 114.4 is available or comes into effect at any desired times during operation but also during transportation of the optical module 106.1. The advantages take effect particularly well, in particular, when transporting the facet mirror 106.1 (alone or, for example, installed in the illumination device 102 or the projection device 103), when there is a higher risk of unintentional disturbances MSi in the form of shocks or the like. But also during operation of the facet mirror 106.1 in the imaging device 101 the advantages of the disclosure can advantageously take effect in the event of disturbances, such as, in particular, earth tremors. A further preferred embodiment of the optical module 206.1 according to the disclosure, which can be used instead of the optical module 106.1 in the imaging device 101, is described below with reference to FIGS. 1 to 9. The optical module 206.1, in its basic design and the way in which it functions, corresponds to the optical module from FIGS. 2 to 8, and so only the differences are to be discussed here. In particular, identical components are provided with identical reference numerals, while similar components are provided with reference numerals increased by the value 100. Unless otherwise stated below, reference is made to the statements made above in the context of the first embodiment with regard to the features, functions and advantages of these components. The only difference with respect to the optical module 106.1 is that, with the optical module 206.1, instead of the anticollision units 114.1 to 114.4, anticollision units, such as they are represented in FIG. 9 by way of the example of the anticollision unit 214.2, are respectively used for the anticollision device 214. As can be seen from FIG. 9, the anticollision unit 214.2 again is an annular arrangement of a plurality of anticollision elements 115.1, 115.2 producing partial fields TF1, TF2. In the present example, N=6 anticollision elements 115.1, 115.2, more precisely, three anticollision elements 115.1 and three anticollision elements 115.2, are provided for the first anticollision unit (not represented). The same applies to the second anticollision unit 214.2 with M=6 anticollision elements 115.1, 115.2, more precisely, three anticollision elements 115.1 and three anticollision elements 115.2. The anticollision elements 115.1, 115.2 are respectively arranged in a so-called hexapole configuration and, in each case, produce a partial field TF1 or TF2, respectively (as explained above on the basis of FIG. 7). The anticollision elements 115.1, 115.2 are assigned to one another in such a way that the superimposition of their partial fields TF1 and TF2 produces the real field F1 and F2, respectively. Here, the anticollision elements 115.1, 115.2 of the anticollision unit 214.2 are arranged along a circumferential direction U of the annular arrangement in such a way that they alternately have substantially opposed inner polarites IP1, IP2 with substantially parallel inner field directions IFR1, IFR2. Consequently, here too, the anticollision elements 115.1, 115.2 are arranged with alternating polarities IP1, IP2 of the inner field directions IFR1, IFR2. In the view of FIG. 9, therefore, an anticollision element 115.1 with a magnetic north pole (on the surface facing the first anticollision unit) is respectively followed, along the circumferential direction U, by an anticollision element 115.2 with a magnetic south pole (on the surface facing the first anticollision unit), and vice versa. Here too, the superimposition of the partial fields TF1, TF2 of the anticollision elements 115.1, 115.2 can have the effect of achieving the desired short-rangedness of the two fields F1 and F2 and it can in this way be ensured that an appreciable counter-force effect CF1 or CF2 only occurs when the two facet elements 108 and 109 approach each other highly closely, while normal adjusting movements between the two facet elements 108 and 109 are not hindered by such a counter-force effect. More precisely, with the six anticollision elements 115.1, 115.2 of the anticollision unit 214.2 the hexapole configuration provides a field line density of the fields F1 and F2, respectively, that decreases along the direction of approach ARi with the distance from the anticollision unit 214.2 approximately by a power of 7. The decrease of the field line density is therefore sharper here than in the case of the previous embodiment with the quadrupole configuration, and so the range of the fields F1 and F2 is even smaller. A further preferred embodiment of the optical module 306.1 according to the disclosure, which can be used instead of the optical module 106.1 in the imaging device 101, is described below with reference to FIGS. 1 to 8 and 10. The optical module 306.1, in its basic design and the way in which it functions, corresponds to the optical module from FIGS. 2 to 8, and so only the differences are to be discussed here. In particular, identical components are provided with identical reference numerals, while similar components are provided with reference numerals increased by the value 200. Unless otherwise stated below, reference is made to the statements made above in the context of the first embodiment with regard to the features, functions and advantages of these components. The only difference with respect to the optical module 106.1 is that, in the case of the optical module 306.1, instead of the anticollision units 114.1 to 114.4, anticollision units, such as they are represented in FIG. 10 by way of the example of the anticollision unit 314.2, are respectively used for the anticollision device 314. As can be seen from FIG. 10, the anticollision unit 314.2 again is an annular arrangement of a plurality of anticollision elements 115.1, 115.2 producing partial fields TF1, TF2. In the present example, N=8 anticollision elements 115.1, 115.2, more precisely four anticollision elements 115.1 and four anticollision elements 115.2, are provided for the first anticollision unit (not represented). The same applies to the second anticollision unit 214.2 with M=8 anticollision elements 115.1, 115.2, more precisely four anticollision elements 115.1 and four anticollision elements 115.2. FIG. 10 shows the pattern and the direction of the field lines, respectively, at certain points in a plane parallel to the xz plane. The anticollision elements 115.1, 115.2 are respectively arranged in a so-called octupole configuration and in each case produce a partial field TF1 and TF2, respectively (as explained above on the basis of FIG. 7). The anticollision elements 115.1, 115.2 are assigned to one another in such a way that the superimposition of their partial fields TF1 and TF2 produces the real field F1 and F2, respectively. Here, the anticollision elements 115.1, 115.2 of the anticollision unit 314.2 are arranged along the circumferential direction U of the annular arrangement in such a way that they alternately have substantially opposed inner polarites IP1, IP2 with substantially parallel inner field directions IFR1, IFR2. Consequently, here too, the anticollision elements 115.1, 115.2 are arranged with alternating polarities IP1, IP2 of the inner field directions IFR1, IFR2. In the view of FIG. 10, therefore, an anticollision element 115.1 with a magnetic north pole (on the surface facing the first anticollision unit) is respectively followed along the circumferential direction U by an anticollision element 115.2 with a magnetic south pole (on the surface facing the first anticollision unit), and vice versa. Here too, the superimposition of the partial fields TF1, TF2 of the anticollision elements 115.1, 115.2 can have the effect of achieving the desired short-rangedness of the two fields F1 and F2 and it can herewith be ensured that an appreciable counter-force effect CF1 or CF2 only occurs when the two facet elements 108 and 109 approach each other highly closely, while normal adjusting movements between the two facet elements 108 and 109 are not hindered by such a counter-force effect. More precisely, with the eight anticollision elements 115.1, 115.2 of the anticollision unit 214.2 the octupole configuration provides a field line density of the fields F1 and F2, respectively, that decreases along the direction of approach ARi with the distance from the anticollision unit 214.2 approximately by a power of 9. The decrease of the field line density is therefore even sharper here than in the case of the two previous embodiments with the quadrupole configuration (FIG. 8) and the hexapole configuration (FIG. 9), and so the range of the fields F1 and F2 is even smaller. The present disclosure was described above exclusively on the basis of an example from the area of microlithography. However, it goes without saying that the disclosure can also be used in connection with any other desired optical applications, in particular imaging methods at other wavelengths. The disclosure can also be used in connection with the inspection of objects, such as for example so-called mask inspection, in which the masks used for microlithography are inspected for their integrity, etc. In FIG. 1, a sensor unit for example, which senses the imaging of the projection pattern of the mask 104.1 (for further processing), then takes the place of the substrate 105.1. This mask inspection may then take place both substantially at the same wavelength as is used in the later microlithographic process. However, it is likewise also possible to use any desired wavelengths deviating therefrom for the inspection. Finally, the present disclosure was described above on the basis of a specific embodiment, which shows specific combinations of the features defined in the following patent claims. It is explicitly noted at this point that the subject matter of the present disclosure is not restricted to these combinations of features but that the subject matter of the present disclosure also includes all other combinations of features, as they emerge from the subsequent patent claims. |
|
abstract | A beam modifier shapes the distribution of a dose delivered to a target by a radiation beam emitted from a beam emitter of a radiotherapy device, particularly a beam that delivers a high radiation dose within a single, short period of time (e.g., less than a second). Elements of the beam modifier (e.g., rods) include material that can block or attenuate the beam. The elements can be dynamically and quickly configured to form an opening or transparent area through which a portion of the beam can pass unimpeded and to present different thicknesses of material to block or attenuate other portions of the beam, in this manner shaping the dose distribution at the target while protecting surrounding tissue. |
|
abstract | An autonomous self-powered system for cooling radioactive materials comprising: a pool of liquid; a closed-loop fluid circuit comprising a working fluid having a boiling temperature that is less than a boiling temperature of the liquid of the pool, the closed-loop fluid circuit comprising, in operable fluid coupling, an evaporative heat exchanger at least partially immersed in the liquid of the pool, a turbogenerator, and a condenser; one or more forced flow units operably coupled to the closed-loop fluid circuit to induce flow of the working fluid through the closed-loop fluid circuit; and the closed-loop fluid circuit converting thermal energy extracted from the liquid of the pool into electrical energy in accordance with the Rankine Cycle, the electrical energy powering the one or more forced flow units. |
|
claims | 1. An X-ray detection system configured to provide for increased penetration of an object, comprising:an X-ray source for generating an X-ray beam in an inspection volume;a conveyor for moving the object through the inspection volume;a collimator positioned between the X-ray source and the object, wherein the collimator is configured to receive the X-ray beam and comprises a plurality of controlled fast actuators coupled with beam attenuators to shape the X-ray beam, thus producing one or more fanlets from the X-ray beam, and wherein each fanlet comprises a vertically moving fan beam having an angular range greater than 1 degree but smaller than the angular coverage of the object;a detector array opposing said X-ray source and positioned within the inspection volume for detecting the one or more fanlets projected on the object;a controller configured to synchronize the X-ray source and the collimator and collect image slices from the detector array corresponding to each of the one more fanlets and control the conveyor such that a total time for the one or more fanlets multiplied by a rate of speed of the conveyor is equal to or less than a width of a detector in the detector array; anda processing unit for combining the image slices collected into a composite image. 2. The system of claim 1 wherein the X-ray source is a pulsed X-ray source. 3. The system of claim 2 wherein the X-ray source is configured to produce dual-energy beams. 4. The system of claim 3 wherein the dual-energy beams are interlaced. 5. The system of claim 2 wherein the X-ray source is configured to produce X-ray pulses comprising low and high energy X-ray beams separated in time. 6. The system of claim 1 wherein the collimator is configured to generate an overlap between the one or more fanlets of approximately 1 degree. 7. The system of claim 1 wherein the X-ray source is a CW X-ray source. 8. The system of claim 1 wherein the collimator comprises a beam chopper. 9. The system of claim 1 wherein the collimator comprises a rotating wheel with slits designed to produce the vertically moving one or more fanlets. 10. An X-ray detection method comprising:irradiating an object with more than one X-ray fanlet, wherein each X-ray fanlet comprises a vertically moving fan beam having an angular range greater than 1 degree but smaller than the angular coverage of the object and wherein each X-ray fanlet is produced by using a collimator for collimating an X-ray beam generated by an X-ray source;synchronizing the X-ray beam and the more than one X-ray fanlet;detecting the more than one X-ray fanlet irradiating the object;adjusting a beam intensity and energy of each of the more than one X-ray fanlet based on signals detected from a previous X-ray fanlet at a same vertical position with respect to the object to generate a control output;collecting image slices from the detector array corresponding to a complete scan cycle of the more than one X-ray fanlet; andprocessing the image slices and combining the image slices into a composite image. 11. The method of claim 10 wherein the X-ray source is a pulsed X-ray source. 12. The method of claim 10 wherein the X-ray source is configured to produces dual-energy beams. 13. The method of claim 10 wherein the dual-energy beams are interlaced. 14. The method of claim 10 wherein the X-ray source is configured to produces X-ray pulses comprising low and high energy X-ray beams separated in time. 15. The method of claim 10 wherein the collimator is configured to generate an overlap between the one or more X-ray fanlets at every position with respect to a surface area of the object. 16. The method of claim 10 wherein the collimator comprises a spinning cylinder with a helical aperture. 17. The method of claim 10 wherein the collimator comprises a plurality of controlled fast actuators coupled with beam attenuators to shape the X-ray beam. 18. The method of claim 10 wherein adjusting the beam intensity and the energy of each of the more than one X-ray fanlet based on signals detected from the previous X-ray fanlet at the same vertical position causes every vertical position to be subject to interlaced dual-energy scanning. 19. The method of claim 10 wherein the X-ray source is a CW X-ray source. |
|
048658014 | abstract | A shielding device is disclosed for use in the under-vessel area from radiation emanating above the lower terminus of a control rod drive of a power generating nuclear reactor of the boiling water type. The device may be comprised of a plurality of individually mountable shell-like housings which are joined in mating contiguous relation to surround the lower terminus of a control rod drive. In the preferred embodiment, each such device is provided with an intergrated access door which will allow access to and removal of any connectors and cables such as those of a position indicating probe. g |
description | In FIG. 1 shows a part of a cladding tube 1. The tube is arranged in a light water reactor and nuclear fuel is provided therein as fuel pellets 2. On its outer surface 3, the cladding tube 1 presents a coating 4 according to the invention. The cladding tube 1 also presents a liner layer 6 on its inner surface 5, on which layer a coating 7 according to the invention is provided. The coating 7 may be deposited by means of CVD-technique. By use in a light water reactor the coating 4 on the outer surface 3 of the cladding tube 1 is in contact with a primary cooling circuit that comprises water, water steam or a combination thereof. The coating 4 on the outer surface 3 of the cladding tube 1 has as its task to protect the outer surface 3 of the cladding tube against attacks, preferably caused by oxidation, due to the presence of the water, water steam or the combination thereof, or wear due to the contact with other components in the light water reactor. The coating 4 thus presents a good resistance against oxidation and wear. If, despite this, the coating 4 will get a damage extending through the total thickness of the coating 4, an area of the outer surface 3 of the cladding tube 1 will be exposed to the water, water steam or the combination thereof, whereby this area will oxidate until a damage extending through the total thickness of the cladding tube 1 finally will be created. If the oxidation continues, a damage extending through the total thickness of the liner layer 6 will finally be created. Thereby, a damage extending through the total thickness of the coating 4, the cladding tube 1, the liner layer 6 and the coating 7, a so called primary damage, is formed. In such cases the water, water steam or the combination thereof will penetrate through the primary damage to an inner space 8 between the coating 7 and the fuel pellets 2. Thereby, the water, water steam or the combination thereof will fill the inner space 8 and attack the coating 7. These attacks may occur at long distances from the primary damage and be caused by hydration. Thanks to the coating 7 of the invention having a high resistance against hydration mostly no damages extending through the total thickness of the coating 7 are formed. The coating 7 and the combination of the coating 7 and the liner layer 6 thereby significantly reduce the risk of secondary damages being formed on the cladding tube 1 in comparison with uncoated cladding tubes. It also possible to exclude the liner layer 6 and still obtain a good protection against hydration at the inner surface 5 of the cladding tube 1. In FIG. 2 shows a part of a cladding tube 1 according to prior art. The tube being arranged in a light water reactor and nuclear fuel is arranged therein as fuel pellets. By use in a light water reactor, an outer surface 3 of the cladding tube 1 is in contact with a primary cooling circuit comprising water, water steam or a combination thereof. Water, water steam or a combination thereof has an oxidating effect on the outer surface 3 of the cladding tube 1. The outer surface 3 of the cladding tube 1 is also subjected to wear from other components present in the light water reactor. The material of the cladding tube 1 has not a sufficient resistance against wear and oxidation to prevent the creation of damages by these attacks. When such a damage is well initiated on the outer surface 3 of the cladding tube 1, through the action of oxidation or wear, the oxidation progresses at the location of this damage. Finally, the result thereof is a damage extending through the total thickness of the cladding tube 1. By such a primary damage the nuclear fuel in the fuel pellets 2 may leak through the damage to the primary cooling circuit and thus spread radioactivity to the circuit. The damage extending through the total thickness of the cladding tube 1 also implies that the water, water steam or the combination thereof from the primary cooling circuit penetrates through the damage into the cladding tube to an inner space 8 located between the fuel pellets 2 and an inner surface 5 of the cladding tube 1. The water, water steam or the combination thereof is spread in the inner space 8 and has a hydrating effect on the inner surface 5 of the cladding tube 1. The material of the cladding tube 1 has not a sufficient resistance against this hydration, and damages will therefore be created on the inner surface 5 of the cladding tube 1. These damages may occur at long distances from the primary damage due to the fact that the water, water steam or the combination thereof causing the damage is spread over so large areas in the inner space 8. The damage created on the inner surface 5 of the cladding tube 1 then grows until, finally, a damage extending through the total thickness of the cladding tube is formed. The nuclear fuel from the fuel pellets 2 may leak out through such secondary damages and further spread radioactivity to the primary cooling circuit. An uncoated cladding tube for nuclear fuel with a liner layer provided on an inner surface of the cladding tube was subjected to a final annealing in order to produce a coating according to the invention on an inner surface onto the liner layer as well as an outer surface of the cladding tube. This final annealing was performed at atmospheric pressure by treating the cladding tube for 90 minutes at a temperature of 565xc2x0 C. under the action of a gas mixture comprising oxygen, argon and water steam. This treatment resulted in a coating of zirconium dioxide (ZrO2) on an inner surface on the liner layer as well as on an outer surface of the cladding tube. This coating presented a good resistance against hydration, oxidation and wear. The final annealing was executed in the same way as in example 1 with the only exception that the gas mixture contained nitrogen instead of oxygen. The result thereof was a coating comprised by zirconium nitride (ZrN) on an inner surface, upon the liner layer, and on an outer surface of the cladding tube. This coating had a good resistance against hydration, oxidation and wear. The thickness of the coating according to the invention may vary from at least 1 xcexcm or at least 3 xcexcm to at most 10 xcexcm or at most 25 xcexcm in order to obtain a good resistance against hydration, oxidation and wear. Generally, the method comprises the provision of a coating of zirconium oxide or zirconium nitride on the inside of a cladding tube by subjecting said tube to an environment that comprises a controlled gas mixture that comprises metal organic compounds and also one or more other gases, such as oxygen gas, carbon dioxide, methane and/or nitrogen gas. By controlling the temperature, reaction amounts, pressure and gas content of said environment, an even coating which is very dense and resistant to hydration may be provided. The thickness thereof is preferably between 1 and 10 xcexcm. |
|
039740277 | abstract | A pressurized-water reactor installation comprises a metal pressure vessel surrounded by a concrete wall forming an annular space around the vessel so that the vessel's side wall can be inspected by instrumentation lowered within the space. To provide the vessel with rupture protection, its side wall is encircled by cylindrical segments of pressure-resistant, heat-insulating material, the segments being themselves encircled by high-tensile strength elements. These parts are proportioned so that when the reactor vessel thermally expands, the segments are placed in compression under the restraint of the high-tensile encircling elements which remain cooler than the vessel, and when the vessel is at room temperature, the segments are free from compression and can be removed to clear the annular space around the vessel's side wall and permit use of the instrumentation for the side wall inspection. |
claims | 1. An inspection apparatus for inspecting welds in a nuclear reactor jet pump, the jet pump comprising an inlet mixer and a diffuser, the nuclear reactor comprising a reactor pressure vessel having a top flange, said inspection apparatus comprising: a frame structure configured to attach to a top flange of a reactor pressure vessel; a motor mounted to said frame structure; a flexible drive cable operatively coupled to said first motor; a tool head coupled to said flexible cable, said tool head comprising a probe subassembly, said probe subassembly rotatable around a longitudinal axis of said tool head, said probe subassembly comprising a probe housing and a plurality of probe arms, each said probe arm having a first end and a second end, each said probe arm pivotably coupled to said housing at said first end of said probe arm, each said probe arm comprising a sensor coupled to said second said sensor comprising an ultrasonic transducer probe or an eddy current transducer probe, end of said probe arm, said probe arms said sensor comprising an ultrasonic transducer probe or an eddy current transducer probe, pivotably movable between a first position and a second position, in said first position, said probe arms are parallel to a longitudinal axis of said probe subassembly, in said second position said probe arms are at an angle to said longitudinal axis of said probe subassembly; and an insertion subassembly configured to couple to a jet pump suction inlet, said insertion subassembly sized to receive said tool head and said flexible drive cable and guide said tool head and flexible drive cable into the jet pump suction inlet, said insertion subassembly comprising an elongate tube portion having a first end and a second end, a location cone attached to said first end of said tube portion, and an attachment clamp configured to clamp to the jet pump suction inlet. 2. An inspection apparatus in accordance with claim 1 wherein said frame structure comprises: claim 1 an elongate frame member having a first end portion and a second end portion; an attachment frame member extending from said first end portion of said elongate frame member, said attachment frame member configured to attach to the top flange of the reactor; and a support wheel coupled to said second end portion of said elongate frame member. 3. An inspection apparatus in accordance with claim 2 wherein said frame structure further comprises: claim 2 an elongate track attached to said elongate frame member; and a trolley movably coupled to said track, said motor mounted on said trolley, said motor capable of rotating said drive cable around the longitudinal axis of said drive cable, said axial rotation of said drive cable causing said probe subassembly to rotate around the longitudinal axis of said tool head. 4. An inspection apparatus in accordance with claim 1 wherein said tool head further comprises a first portion coupled to a second portion by a first flexible U-joint, said second portion coupled to said probe subassembly by a second flexible U-joint. claim 1 5. An inspection apparatus in accordance with claim 1 wherein said probe subassembly comprises three probe arms. claim 1 6. An inspection apparatus in accordance with claim 1 wherein said attachment clamp comprises a plate coupled to said second end of said tube portion, said plate comprising a notch sized to receive an end of the jet pump suction inlet. claim 1 7. An inspection apparatus in accordance with claim 6 wherein said attachment clamp further comprises an engagement arm pivotably coupled to said plate and a ratchet assembly coupled to said engagement arm, said engagement arm movable into engagement with the jet pump suction inlet by tightening said ratchet assembly. claim 6 8. An inspection apparatus for inspecting welds in a nuclear reactor jet pump, the jet pump comprising an inlet mixer and a diffuser, the nuclear reactor comprising a reactor pressure vessel having a top flange, said inspection apparatus comprising: a frame structure configured to attach to a top flange of a reactor pressure vessel; a motor mounted to said frame structure; a flexible drive cable operatively coupled to said first motor; a tool head coupled to said flexible cable, said tool head comprising a probe subassembly rotatable around a longitudinal axis of said tool head, said probe subassembly comprising: a probe housing; and three probe arms, each said probe arm having a first end and a second end, each said probe arm pivotably coupled to said housing at said first end of said probe arm, each said probe arm comprising a sensor coupled to said second end of said probe arm, said probe arms said sensor comprising an ultrasonic transducer probe or an eddy current transducer probe, pivotably movable between a first position and a second position, in said first position, said probe arms are parallel to a longitudinal axis of said probe subassembly, in said second position said probe arms are at an angle to said longitudinal axis of said probe subassembly; and an insertion subassembly configured to couple to a jet pump suction inlet, said insertion subassembly sized to receive said tool head and said flexible drive cable and guide said tool head and flexible drive cable into the jet pump suction inlet said insertion subassembly comprising an elongate tube portion having a first end and a second end, a location cone attached to said first end of said tube portion, and an attachment clamp configured to clamp to the jet pump suction inlet. 9. An inspection apparatus in accordance with claim 8 wherein said frame structure comprises: claim 8 an elongate frame member having a first end portion and a second end portion; an attachment frame member extending from said first end portion of said elongate frame member, said attachment frame member configured to attach to the top flange of the reactor; and a support wheel coupled to said second end portion of said elongate frame member. 10. An inspection apparatus in accordance with claim 9 wherein said frame structure further comprises: claim 9 an elongate track attached to said elongate frame member; and a trolley movably coupled to said track, said motor mounted on said trolley, said motor capable of rotating said drive cable around the longitudinal axis of said drive cable, said axial rotation of said drive cable causing said probe subassembly to rotate around the longitudinal axis of said tool head. 11. An inspection apparatus in accordance with claim 8 wherein said tool head further comprises a first portion coupled to a second portion by a first flexible U-joint, said second portion coupled to said probe subassembly by a second flexible U-joint. claim 8 12. An inspection apparatus in accordance with claim 8 wherein said attachment clamp comprises a plate coupled to said second end of said tube portion, said plate comprising a notch sized to receive an end of the jet pump suction inlet. claim 8 13. An inspection apparatus in accordance with claim 12 wherein said attachment clamp further comprises an engagement arm pivotably coupled to said plate and a ratchet assembly coupled to said engagement arm, said engagement arm movable into engagement with the jet pump suction inlet by tightening said ratchet assembly. claim 12 |
|
042630967 | abstract | In a plasma device having a toroidal plasma containment vessel, a toroidal field-generating coil system includes fixed linking coils each formed of first and second sections with the first section passing through a central opening through the containment vessel and the second section completing the linking coil to link the containment vessel. A plurality of removable unlinked coils are each formed of first and second C-shaped sections joined to each other at their open ends with their bights spaced apart. The second C-shaped section of each movable coil is removably mounted adjacent the second section of a linking coil, with the containment vessel disposed between the open ends of the first and second C-shaped sections. Electric current is passed through the linking and removable coils in opposite sense in the respective adjacent second sections to produce a net toroidal field. |
description | If an Application Data Sheet (ADS) has been filed on the filing date of this application, it is incorporated by reference herein. Any applications claimed on the ADS for priority under 35 U.S.C. §§119, 120, 121, or 365(c), and any and all parent, grandparent, great-grandparent, etc. applications of such applications, are also incorporated by reference, including any priority claims made in those applications and any material incorporated by reference, to the extent such subject matter is not inconsistent herewith. The present application is related to and/or claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Priority Applications”), if any, listed below (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Priority Application(s)). In addition, the present application is related to the “Related Applications,” if any, listed below. For purposes of the USPTO extra-statutory requirements, the present application claims benefit of priority of U.S. Provisional Patent Application No. 61/629,430, entitled ENHANCED NEUTRONICS SYSTEMS, naming Jesse R. Cheatham III, Robert C. Petroski, Nicholas W. Touran, Charles Whitmer as inventors, filed 18, Nov., 2011, which was filed within the twelve months preceding the filing date of the present application or is an application of which a currently co-pending application is entitled to the benefit of the filing date. None The United States Patent Office (USPTO) has published a notice to the effect that the USPTO's computer programs require that patent applicants reference both a serial number and indicate whether an application is a continuation, continuation-in-part, or divisional of a parent application. Stephen G. Kunin, Benefit of Prior-Filed Application, USPTO Official Gazette Mar. 18, 2003. The USPTO further has provided forms for the Application Data Sheet which allow automatic loading of bibliographic data but which require identification of each application as a continuation, continuation-in-part, or divisional of a parent application. The present Applicant Entity (hereinafter “Applicant”) has provided above a specific reference to the application(s) from which priority is being claimed as recited by statute. Applicant understands that the statute is unambiguous in its specific reference language and does not require either a serial number or any characterization, such as “continuation” or “continuation-in-part,” for claiming priority to U.S. patent applications. Notwithstanding the foregoing, Applicant understands that the USPTO's computer programs have certain data entry requirements, and hence Applicant has provided designation(s) of a relationship between the present application and its parent application(s) as set forth above and in any ADS filed in this application, but expressly points out that such designation(s) are not to be construed in any way as any type of commentary and/or admission as to whether or not the present application contains any new matter in addition to the matter of its parent application(s). If the listings of applications provided above are inconsistent with the listings provided via an ADS, it is the intent of the Applicant to claim priority to each application that appears in the Priority Applications section of the ADS and to each application that appears in the Priority Applications section of this application. All subject matter of the Priority Applications and the Related Applications and of any and all parent, grandparent, great-grandparent, etc. applications of the Priority Applications and the Related Applications, including any priority claims, is incorporated herein by reference to the extent such subject matter is not inconsistent herewith. The present application relates to nuclear fission reactors, and systems, applications, and apparatuses related thereto. Illustrative embodiments provide for operation of nuclear fission reactors and interfaces therewith that include simulation. Illustrative embodiments and aspects include, without limitation, a nuclear reactor modeling interface and modeling system configured to simulate operation of a variety of nuclear fission reactors and reactor modules, including modular nuclear fission reactors and reactor modules, nuclear fission deflagration wave reactors and reactor modules, modular nuclear fission deflagration wave reactors and modules, methods of operating nuclear reactors and modules including the aforementioned, methods of simulating operating nuclear reactors and modules including the aforementioned, and the like. The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. The disclosed embodiments will now be described with reference to the accompanying drawings. In the drawings, like reference numbers may indicate identical or similar elements. Additionally, the left-most digit(s) of a reference number may identify the drawing in which the reference number first appears. Introduction In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, generally similar symbols identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments and, thus, are not intended to limit the claimed subject matter and the appended claims in any way. While specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the pertinent art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the claimed subject matter. It will be apparent to a person skilled in the pertinent art that the claimed subject matter can also be used in a variety of other applications. The scope of the claimed subject matter is not limited to the disclosed embodiments. The claimed subject matter is defined by the claims appended hereto. References to “one embodiment,” “an embodiment,” “this embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment might not necessarily include the particular feature, structure or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such a feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. In some instances, one or more components may be referred to herein as “configured to,” “configurable to,” “operable/operative to,” “adapted/adaptable,” “able to,” “conformable/conformed to,” etc. Those skilled in the art will recognize that such terms (e.g. “configured to”) can generally encompass active-state components and/or inactive-state components and/or standby-state components, unless context requires otherwise. Those having skill in the art will recognize that the state of the art has progressed to the point where there is little distinction left between hardware, software, and/or firmware implementations of aspects of systems; the use of hardware, software, and/or firmware is generally (but not always, in that in certain contexts the choice between hardware and software can become significant) a design choice representing cost vs. efficiency tradeoffs. Those having skill in the art will appreciate that there are various vehicles by which processes and/or systems and/or other technologies described herein can be effected (e.g., hardware, software, and/or firmware), and that the preferred vehicle will vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle; alternatively, if flexibility is paramount, the implementer may opt for a mainly software implementation; or, yet again alternatively, the implementer may opt for some combination of hardware, software, and/or firmware. Hence, there are several possible vehicles by which the processes and/or devices and/or other technologies described herein may be effected, none of which is inherently superior to the other in that any vehicle to be utilized is a choice dependent upon the context in which the vehicle will be deployed and the specific concerns (e.g., speed, flexibility, or predictability) of the implementer, any of which may vary. Those skilled in the art will recognize that optical aspects of implementations will typically employ optically-oriented hardware, software, and or firmware. The foregoing detailed description has set forth various embodiments of devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In an embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, can be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., transmitter, receiver, transmission logic, reception logic, etc.), etc.). By way of overview, illustrative embodiments provide nuclear fission reactors, and apparatuses and methods for their operation and simulation. Illustrative embodiments and aspects include, without limitation, nuclear fission reactors and reactor modules, including modular nuclear fission reactors and reactor modules, nuclear fission deflagration wave reactors and reactor modules, modular nuclear fission deflagration wave reactors and modules, methods of operating nuclear reactors and modules including the aforementioned, methods of simulating operating nuclear reactors and modules including the aforementioned, and the like. Still by way of overview and referring to FIG. 1A, an illustrative nuclear fission reactor 10 will be discussed by way of illustration and not limitation. Nuclear fission reactor 10 may be, but is not limited to, a fission deflagration wave reactor. The reactor 10 suitably includes a nuclear reactor core 100 disposed within a reactor vessel 12 and a reactor coolant system having one or more reactor coolant loops 14. A reactor may be a modular design including one or more nuclear reactor modules—see, e.g., an exemplary modular reactor 50 illustrated in FIG. 1B. Each reactor module 12 may be operatively coupled in fluid communication to at least one heat sink 58 via a reactor coolant system 56. Thus, each of the nuclear reactor modules may be considered a complete, stand-alone nuclear reactor system by itself. A nuclear reactor module may be neutronically coupled to at least one other adjacent reactor module. Thus, adjacent nuclear reactor modules can be neutronically integrated yet physically separate from each other. In order to provide an understanding of the control and simulation of reactors such as reactor 10 and reactor 50, illustrative core nucleonics, given by way of non-limiting examples, will be set forth first. While many reactor embodiments are contemplated, several of these non-limiting examples are illustrated in U.S. patent application Ser. No. 12/069,907 entitled MODULAR NUCLEAR FISSION REACTOR, naming AHLFELD, CHARLES E., GILLELAND, JOHN ROGERS, HYDE, RODERICK A., ISHIKAWA, MURIEL Y., MCALEES, DAVID G., MYHRVOLD, NATHAN P., WHITMER, CHARLES, and WOOD, LOWELL L. as inventors, filed 12 Feb. 2008, U.S. patent application Ser. No. 11/605,943, entitled AUTOMATED NUCLEAR POWER REACTOR FOR LONG-TERM OPERATION, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006, U.S. patent application Ser. No. 11/605,848, entitled METHOD AND SYSTEM FOR PROVIDING FUEL IN A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006, and U.S. patent application Ser. No. 11/605,933, entitled CONTROLLABLE LONG TERM OPERATION OF A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006, the entire contents of which are hereby incorporated by reference in their entireties. Then, details will be set forth regarding several illustrative embodiments and aspects of reactors. Considerations Before discussing details of the reactors such as reactor 10 and reactor 50, some considerations behind reactor embodiments will be given by way of overview but are not to be interpreted as limitations. Some reactor embodiments address many of the considerations discussed below. On the other hand, some other reactor embodiments may address one or a select few of these considerations, and need not accommodate all of the considerations discussed below. Certain of the nuclear fission fuels envisioned for use in reactor embodiments are typically widely available, such as without limitation uranium (natural, depleted, or enriched), thorium, plutonium, or even previously-burned nuclear fission fuel assemblies. Other, less widely available nuclear fission fuels, such as without limitation other actinide elements or isotopes thereof may be used in embodiments of the reactor. While some reactor embodiments contemplate long-term operation at full power, or some portion thereof, on the order of around ⅓ century to around ½ century or longer, an aspect of some reactor embodiments does not contemplate nuclear refueling. Other reactor embodiments contemplate nuclear refueling, however. In some cases, embodiments may contemplate burial in-place at end-of-life. Nuclear refueling may occur during shutdown periods and/or operation at power. It is also contemplated that nuclear fission fuel reprocessing may be avoided in some cases, thereby mitigating possibilities for diversion to military uses and other issues. Some reactor embodiments may be sited underground, thereby addressing large, abrupt releases and small, steady-state releases of radioactivity into the biosphere. Some embodiments may entail minimizing operator controls, thereby automating those embodiments as much as practicable. In some embodiments, a life-cycle-oriented design is contemplated, wherein those embodiments can operate from startup to shutdown at end-of-life. In some life-cycle oriented designs, the embodiments may operate in a substantially fully-automatic manner. Some embodiments lend themselves to modularized construction. Finally, some embodiments may be designed according to high power density or to selected power densities corresponding to a variety of design considerations, such as burn-up criteria, power demand, neutronic flux considerations, and other parameters. During operation, the materials (e.g., elements and isotopes of elements) in a reactor, especially a reactor core region, change over time. For example, fuel atoms fission into fission products. Atoms of fuel, structural materials, neutron absorbing materials (fission product poisons or neutron absorbing materials intentionally inserted into the reactor), and so forth may absorb neutrons and become other isotopes or elements. These changes may be accounted for by design and reactor control in both the short term and the long term. An ability to move materials throughout the core may increase a reactor's effective lifetime. Some features of various reactor embodiments result from some of the above considerations. For example, simultaneously accommodating desires to achieve ⅓-½ century (or longer) of operations at full power without shutdown for nuclear refueling and to avoid nuclear fission fuel reprocessing may entail use of a fast neutron spectrum. As another example, in some embodiments a negative temperature coefficient of reactivity (αT) is engineered-in to the reactor, such as via negative feedback on local reactivity implemented with strong absorbers of neutrons or other approaches to reactivity control. In the alternative or in addition, some embodiments are configured to control the fission process in whole or in part by achieving a spectral shift in a neutron flux using spectral control methods such as displacing and/or inserting a neutron moderator for some time period. As a further example, in some modular deflagration wave embodiments, a distributed thermostat enables a propagating nuclear fission deflagration wave mode of nuclear fission fuel burn. This mode simultaneously permits a high average burn-up of non-enriched actinide fuels, such as natural uranium or thorium, and use of a comparatively small “nuclear fission igniter” region of moderate isotopic enrichment of nuclear fissionable materials in the core's fuel charge. As another example, in some embodiments, multiple redundancy is provided in primary and secondary core cooling. Exemplary Embodiments of Nuclear Fission Reactors Now that some of the considerations behind some of the reactor embodiments have been set forth, further details regarding an exemplary embodiment of nuclear fission reactors will be explained. This information is provided to enhance the understanding of the considerations taken into account when modeling and simulaitng nuclear reactor performance. It is emphasized that the following description of exemplary nuclear reactor embodiments is given by way of non-limiting examples only and not by way of limitation. As mentioned above, several embodiments of nuclear reactors and their simulation are contemplated, as well as further aspects of reactor 10. After details regarding an exemplary embodiment of reactor 10 are discussed, other embodiments and aspects will also be discussed. Still referring to FIG. 1A, an exemplary embodiment of reactor 10 includes a reactor core assembly 100 that is disposed within a reactor pressure vessel 12. Several embodiments and aspects of reactor core assembly 100 are contemplated that will be discussed later. Some of the features that will be discussed later in detail include nuclear fission fuel materials and their respective nucleonics, fuel assemblies, fuel geometries, and the operation and simulation of reactor core assembly 100 in a complete reactor system. The reactor pressure vessel 12 suitably is any acceptable pressure vessel known in the art and may be made from any appropriate form of materials acceptable for use in reactor pressure vessels, such as without limitation stainless steel. Within the reactor pressure vessel 12, a neutron reflector (not shown) and a radiation shield (not shown) surround reactor core assembly 100. In some embodiments, the reactor pressure vessel 12 is sited underground. In such cases, the reactor pressure vessel 12 can also function as a burial cask for reactor core assembly 100. In these embodiments, the reactor pressure vessel 12 suitably is surrounded by a region (not shown) of isolation material, such as dry sand, for long-term environmental isolation. The region (not shown) of isolation material may have a size of around 100 meters in diameter or so. However, in other embodiments, the reactor pressure vessel 12 is sited on or toward the Earth's surface. Reactor coolant loops 14 transfer heat from nuclear fission in reactor core assembly 100 to application heat exchangers 16. The reactor coolant may be selected as desired for a particular application. In some embodiments, the reactor coolant suitably is helium (He) gas. In other embodiments, the reactor coolant suitably may be other pressurized inert gases, such as neon, argon, krypton, xenon, or other fluids such as water or gaseous or superfluidic carbon dioxide, or liquid metals, such as sodium or lead, or metal alloys, such as Pb—Bi, or organic coolants, such as polyphenyls, or fluorocarbons. The reactor coolant loops suitably may be made from tantalum (Ta), tungsten (W), aluminum (Al), steel or other ferrous or non-iron groups alloys or titanium or zirconium-based alloys, or from other metals and alloys, or from other structural materials or composites, as desired. In some embodiments, the application heat exchangers 16 may be steam generators that generate steam that is provided as a prime mover for rotating machinery, such as electrical turbine-generators 18 within an electrical generating station 20. In such a case, reactor core assembly 100 suitably operates at a high operating pressure and temperature, such as above 1,000K or so and the steam generated in the steam generator may be superheated steam. In other embodiments, the application heat exchanger 16 may be any steam generator that generates steam at lower pressures and temperatures (that is, need not be superheated steam) and reactor core assembly 100 operates at temperatures less than around 550K. In these cases, the application heat exchangers 16 may provide process heat for applications such as desalination plants for seawater or for processing biomass by distillation into ethanol, or the like. Optional reactor coolant pumps 22 circulate reactor coolant through reactor core assembly 100 and the application heat exchangers 16. Note that although the illustrative embodiment shows pumps and gravitationally driven circulation, other approaches may not utilize pumps, or circulatory structures or be otherwise similarly geometrically limited. The reactor coolant pumps 22 suitably may be provided when reactor core assembly 100 is sited approximately vertically coplanar with the application heat exchangers 16, such that thermal driving head is not generated. The reactor coolant pumps 22 may also be provided when reactor core assembly 100 is sited underground. However, when reactor core assembly 100 is sited underground or in any fashion so reactor core assembly 100 is vertically spaced below the application heat exchangers 16, thermal driving head may be developed between the reactor coolant exiting the reactor pressure vessel 12 and the reactor coolant exiting the application heat exchangers 16 at a lower temperature than the reactor coolant exiting the reactor pressure vessel 12. When sufficient thermal driving head exists, reactor coolant pumps 22 need not be provided to provide sufficient circulation of reactor coolant through reactor core assembly 100 to remove heat from fission during operation at power. In some embodiments more than one reactor coolant loop 14 may be provided, thereby providing redundancy in the event of a casualty, such as a loss of coolant accident, a loss of flow accident, a primary-to-secondary leak or the like, to any one of the other reactor coolant loops 14. Each reactor coolant loop 14 may be rated for full-power operation, though some applications may remove this constraint. In some embodiments, closures 24, such as reactor coolant shutoff valves, are provided in lines of the reactor coolant system 14. In each reactor coolant loop 14, a closure 24 may be provided in an outlet line from the reactor pressure vessel 12 and in a return line to the reactor pressure vessel 12 from an outlet of the application heat exchanger 16. Closures 24 may be fast-acting closures that shut quickly under emergency conditions, such as detection of significant fission-product entrainment in reactor coolant. Closures 24 may be provided in addition to a redundant system of automatically-actuated valves (not shown). One or more heat-dump heat exchangers 26 are provided for removal of after-life heat (decay heat). Heat-dump heat exchanger 26 includes a primary loop that is configured to circulate decay heat removal coolant through reactor core assembly 100. Heat-dump heat exchanger 26 includes a secondary loop that is coupled to an engineered heat-dump heat pipe network (not shown). In some situations, for example, for redundancy purposes, more than one heat-dump heat exchanger 26 may be provided. Heat-dump heat exchanger 26 may be sited at a vertical distance above reactor core assembly 100 so sufficient thermal driving head is provided to enable natural flow of decay heat removal coolant without need for decay heat removal coolant pumps. However, in some embodiments decay heat removal pumps (not shown) may be provided. Reactor coolant pumps may be used for decay heat removal, where appropriate. Now that an overview of an exemplary embodiment of the reactor 10 has been given, other embodiments and aspects will be discussed. First, embodiments and aspects of reactor core assembly 100 will be discussed. An overview of reactor core assembly 100 and its nucleonics will be set forth first, followed by descriptions of exemplary embodiments and other aspects of reactor core assembly 100. Again, this information enhances the understanding and considerations taken into account when modeling or simulating nuclear reactor performance. Given by way of overview and in general terms, structural components of reactor core assembly 100 may be made of tantalum (Ta), tungsten (W), rhenium (Re), various alloys including but not limited to steels such as martensitic stainless steels (e.g., HT9), austenitic stainless steels (e.g., Type 316), or carbon composite, ceramics, or the like. These materials are suitable because of the high temperatures at which reactor core assembly 100 operates, and because of their creep resistance over the envisioned lifetime of full power operation, mechanical workability, and corrosion resistance. Structural components can be made from single materials, or from combinations of materials (e.g., coatings, alloys, multilayers, composites, and the like). In some embodiments, reactor core assembly 100 operates at sufficiently lower temperatures so that other materials, such as aluminum (Al), steel, titanium (Ti) or the like can be used, alone or in combinations, for structural components. In deflagration wave embodiments, reactor core assembly 100 may include a small nuclear fission igniter and a larger nuclear fission deflagration burn-wave-propagating region. The nuclear fission deflagration burn-wave-propagating region suitably contains thorium or uranium fuel, and functions on the general principle of fast neutron spectrum fission breeding. In some deflagration wave embodiments, uniform temperature throughout reactor core assembly 100 is maintained by thermostating modules which regulate local neutron flux and thereby control local power production. Some example deflagration wave embodiments are further discussed in the aforementioned U.S. patent application Ser. No. 11/605,933, entitled CONTROLLABLE LONG TERM OPERATION OF A NUCLEAR REACTOR (“the '933 application”), which is herein incorporated by reference in its entirety. Nuclear reactors may be modular. Referring now to FIG. 1B, an illustrative modular reactor 50 is shown. It is emphasized that the following description of an exemplary embodiment of reactor 50 is given by way of non-limiting example only and not by way of limitation. As mentioned above, several embodiments of reactors such as reactors 10 and 50, are contemplated, as well as further aspects of reactors. Features illustrated in reactors 10 and 50 may be implemented separately or in any suitable combination. After details regarding an exemplary embodiment of reactor 50 are discussed, other embodiments and aspects will also be discussed. Modular reactor 50 is shown by way of illustration and does not limit modular reactors to a toroidal arrangement or any other arrangement of reactor modules 52. It will be understood that no limitation to such a geometric arrangement or to any geometric arrangement of any type whatsoever is intended. To that end, additional arrangements of reactor modules 52 will be discussed further below. In the interest of brevity, the description of additional arrangements of reactor modules 52 is limited to those illustrated herein. However, it will be appreciated that reactor modules 52 may be arranged in any manner whatsoever as desired and may accommodates neutronic coupling of adjacent nuclear fission deflagration wave reactor modules 52. As discussed above, the exemplary modular reactor 50 suitably includes reactor modules 52. Each reactor module 52 may suitably include a reactor core 54 and a reactor coolant system 56. Each nuclear fission deflagration wave reactor module 52 may be operatively coupled in fluid communication to at least one heat sink 58 via one or more associated reactor coolant systems 56. That is, each reactor modules 52 suitably may be considered a complete, stand-alone nuclear reactor by itself. A reactor module 52 may be neutronically coupled to at least one adjacent reactor module 52. While many embodiments of the modular reactor 50 are contemplated, a common feature among many contemplated embodiments of modular reactor 50 is neutronic coupling of adjacent reactor modules 52 via origination of a nuclear fission deflagration wave, or “burnfront” as further discussed in the aforementioned U.S. patent application Ser. No. 12/069,907 entitled MODULAR NUCLEAR FISSION REACTOR (the '907 application”), which is herein incorporated by reference in its entirety. Referring now to FIG. 1C, heat energy can be extracted from a nuclear fission reactor core according to another embodiment. In a nuclear fission reactor 110, nuclear fission occurs in a heat generating region 120 (e.g., throughout the fuel-bearing core or propagated in a burning wavefront, for example). Heat absorbing material 160, such as a condensed phase density fluid (e.g., water, liquid metals, terphenyls, polyphenyls, fluorocarbons, FLIBE (2LiF—BeF2) and the like) flows through the region 120 as indicated by an arrow 150, and heat is transferred from the heat generating region 120 to heat absorbing material 160. In some embodiments, e.g., fast fission spectrum nuclear reactors, heat absorbing material 160 is chosen to be a nuclear inert material (such as He4) so as to minimally perturb the neutron spectrum. In other embodiments of nuclear fission reactor 110, the neutron content is sufficiently robust, so that a non-nuclear-inert heat absorbing material 160 may be acceptably utilized. Heat absorbing material 160 flows (e.g., by natural convection or by forced movement) to a heat extraction region 130 that is substantially out of thermal contact with heat generating region 120. Heat energy 140 is extracted from heat absorbing material 160 at heat extraction region 130. Heat absorbing material 110 can reside in either a liquid state, a multiphase state, or a substantially gaseous state upon extraction of the heat energy 140 in the heat extraction region 130. Exemplary Movements of Nuclear Reactor Materials Fuel materials include not only fuel materials, but also structural materials (e.g., cladding). Referring now to FIG. 2A, a reactor 200, which may include any type of fission reactor including those described elsewhere herein, may include nuclear fission fuel assemblies 210 disposed therein. The following discussion includes details of exemplary nuclear fission fuel assemblies 210 that may be used in reactor 200. Referring now to FIG. 2B and given by way of non-limiting example, in an embodiment the nuclear fission fuel assembly 210 suitably includes a nuclear fission fuel assembly 220. In an embodiment, nuclear fission fuel assembly 220 has been “previously burnt.” The term “previously burnt” means that at least some components of the nuclear fission fuel assembly have undergone neutron-mediated nuclear fission and that the isotopic composition of the nuclear fission fuel has been modified. That is, the nuclear fission fuel assembly has been put in a neutron spectrum or flux (either fast or slow), at least some components have undergone neutron-mediated nuclear fission and, as result, the isotopic composition of the nuclear fission fuel has been changed. Thus, a previously burnt nuclear fission fuel assembly 220 may have been previously burnt in any reactor including reactor 200, such as without limitation a light water reactor. Previously burnt fission fuel (e.g., in a previously burnt nuclear fission fuel assembly 220) may be chemically untreated subsequent to its previous burning. It is intended that nuclear fission fuel assembly 220 can include without limitation any type of nuclear fissionable material whatsoever appropriate for undergoing fission in a nuclear fission reactor, such as actinide or transuranic elements like natural thorium, natural uranium, enriched uranium, or the like. Nuclear fission fuel assembly 220 is clad with cladding 224. If nuclear fission fuel assembly has been previously burnt, the cladding 224 may be the “original” cladding in which the nuclear fission fuel assembly 220 was clad before it was burnt. In some other embodiments, a previously burnt nuclear fission fuel assembly 220 may not be clad with “original” cladding 224. For example, a previously burnt nuclear fission fuel assembly 220 may be retained in its original cladding 224, and a new cladding (not shown) may be disposed around an exterior of cladding 224. In some embodiments, the new cladding is made up of cladding sections (not shown) that are configured to help accommodate swelling into the void spaces. In other embodiments, the new cladding may be provided as a barrier, such as a tube, provided between an exterior of the cladding 224 and reactor coolant (not shown). Referring now to FIG. 3, an exemplary nuclear fission fuel structure 300 includes non-contiguous segments 320 of nuclear fission fuel material. Non-contiguous segments 320 may be in “neutronic” contact without being in physical contact. Nuclear fission fuel structure 300 may also include an optional nuclear fission igniter 310. As described in the aforementioned '933 application, nuclear fission igniter 310 may be used in deflagration propagating wave-type nuclear reactors. Referring now to FIG. 4, a modular nuclear fission fuel core 400 may include an optional neutron reflector/radiation shield 410 and modular assemblies 420. Modular assemblies 420 may be modular fuel assemblies having some fuel material content. Modular assemblies may also be modular neutron absorbing assemblies (having some neutron absorbing material content), modular structural assemblies (serving a primarily structural purpose), modular payload assemblies (designed to carry a payload of, for example, a material to be subjected to a neutron flux), modular blank assemblies (serving as a mere placeholder, for example, to reduce the nucleonic, flow, structural, and thermal perturbations induced by a void or void filled with coolant and/or moderator), or any combination of the above. Modular assemblies 420 are placed as desired within the assembly receptacles 430. Modular nuclear fission fuel core 400 may be operated in any number of ways. For example, all of the assembly receptacles 430 in the modular nuclear fission fuel core 400 may be fully populated with modular fuel assemblies 420 prior to initial operation. For example, in deflagration propagating wave-type nuclear reactor embodiments, prior to initial operation means prior to origination and propagation of a nuclear fission deflagration propagating wave burnfront within and through the modular fuel assemblies 420. In other reactor embodiments, prior to initial operation means prior to initial criticality or prior to a modular nuclear fission fuel core being exposed to a neutron flux. As another example, modular assemblies 420 may be removed from their respective assembly receptacles 430 and replaced with other modular assemblies 440 (of the same or different type), as desired; this emplacement is indicated by the arrow 444. For example, “burnt” fuel assemblies may be replaced with “unburnt” fuel assemblies, neutron absorbing assemblies may be replaced with fuel assemblies, and so forth. The other modular nuclear assemblies 440 may be unused or may have previously been used. For example, in deflagration propagating wave-type nuclear reactor embodiments, modular fission fuel assemblies 420 may be removed and replaced with other modular nuclear fission fuel assemblies 440 after a nuclear fission deflagration wave burnfront has completely propagated through modular nuclear fission fuel assemblies 420. In other embodiments, modular assemblies 420 may be removed and replaced with other modular assemblies 440 for any reason (e.g., testing or experimental uses, redistribution of fuel or neutron absorbing materials, etc.). Such replacement strategies may be used to extend operation of modular nuclear fission fuel core 400 as desired. As another example, the modular nuclear fission fuel core 400 need not be fully populated with modular assemblies 420 prior to initial operation. For example, less than all of the assembly receptacles 430 can be populated with modular assemblies 420. In such a case, the number of modular fuel assemblies that are placed within the modular nuclear fission fuel core 400 can be determined based upon many reasons, such as a number of modular fuel assemblies that are available, power demand (e.g., electrical loading in watts), that will be ultimately be placed upon the modular nuclear fission fuel core 400, etc. Thus, continued or extended operation of the modular nuclear fission fuel core 400 can be enabled without initially fueling the entire modular nuclear fission fuel core 400 with modular fuel assemblies. It will be appreciated that the concept of modularity can be extended. For example, in other embodiments, a modular nuclear fission reactor can be populated with any number of nuclear fission reactor cores in the same manner that the modular nuclear fission fuel core 400 can be populated with any number of modular assemblies 420. To that end, the modular nuclear fission reactor can be analogized to the modular nuclear fission fuel core 400 and nuclear fission reactor cores can be analogized to the modular nuclear fission fuel assemblies 420. The several contemplated modes of operation discussed above for the modular nuclear fission fuel core 400 thus apply by analogy to a modular nuclear fission reactor. Core materials not in a modular assembly may also be moved in a reactor core. It is well known in the art to control reactivity (and thus core average temperature in an operating reactor having a negative coefficient of reactivity) using control rods or other devices. In addition, other neutron modifying structures are contemplated in embodiments. For example, referring now to FIGS. 5A and 5B, neutron modifying structures 530 can position neutron modifying (e.g., absorbing, reflecting, moderating, etc.) substances in a reactor 500, including a propagating burnfront nuclear fission reactor 550, for a variety of purposes. In an embodiment, neutron modifying structures 530 insert neutron absorbers, such as without limitation Li-6, B-10, or Gd, into nuclear fission fuel. In another embodiment, neutron modifying structures 530 insert neutron moderators, such as without limitation hydrocarbons or Li-7, thereby modifying the neutron energy spectrum, and thereby changing the neutronic reactivity of nuclear fission fuel in the local region. In some situations in a reactor 500 (including a propagating burnfront nuclear fission reactor 550) an effect of the neutron moderators is associated with detailed changes in the neutron energy spectrum (e.g., hitting or missing cross-section resonances), while in other cases the effects are associated with lowering the mean neutron energy of the neutron environment (e.g., downshifting from “fast” neutron energies to epithermal or thermal neutron energies). In yet other situations, an effect of the neutron moderators is to deflect neutrons to or away from selected locations. In some embodiments, one of the aforementioned effects of neutron moderators is of primary importance, while in other embodiments, multiple effects are of comparable or lesser design significance. In another embodiment, neutron modifying structures 530 contain both neutron absorbers and neutron moderators; in one nonlimiting example, the location of neutron absorbing material relative to that of neutron moderating material is changed to affect control (e.g., by masking or unmasking absorbers, or by spectral-shifting to increase or decrease the absorption of absorbers), in another nonlimiting example, control is affected by changing the amounts of neutron absorbing material and/or neutron moderating material. In embodiments such as propagating burnfront nuclear fission reactor 550, a nuclear fission deflagration wave burnfront can be driven into areas of nuclear fission fuel as desired, thereby enabling a variable nuclear fission fuel burn-up. In propagating burnfront nuclear fission reactor 550, a nuclear fission deflagration wave burnfront 510 is initiated and propagated. Neutron modifying structures 530 can direct or move the burnfront 510 in directions indicated by arrows 520. In an embodiment, neutron modifying structures 530 insert neutron absorbers behind burnfront 510, thereby driving down or lowering neutronic reactivity of fuel that is presently being burned by burnfront 510 relative to neutronic reactivity of fuel ahead of burnfront 510, thereby speeding up the propagation rate of the nuclear fission deflagration wave. In another embodiment, neutron modifying structures 530 insert neutron absorbers into nuclear fission fuel ahead of burnfront 510, thereby slowing down the propagation of the nuclear fission deflagration wave. In other embodiments, neutron modifying structures 530 insert neutron absorbers into nuclear fission fuel within or to the side of the burnfront 510, thereby changing the effective size of the burnfront 510. In another embodiment, neutron modifying structures 530 insert neutron moderators, thereby modifying the neutron energy spectrum, and thereby changing the neutronic reactivity of nuclear fission fuel that is presently being burned by the burnfront 510 relative to neutronic reactivity of nuclear fission fuel ahead of or behind the burnfront 510. Thus, local neutronic reactivity in reactor 500, and burnfront 510 in propagating burnfront nuclear fission reactor 550, can be directed as desired according to selected local reaction rate or propagation parameters. For example, local reaction rate parameters can include fission rate, a heat generation density, cross-section dimensions of power density, or the like. In burnfront nuclear fission reactor 550, propagation parameters can include a propagation direction or orientation of the burnfront 510, a propagation rate of the burnfront 510, power demand parameters such the heat generation density, cross-sectional dimensions of a burning region through which the burnfront 510 is to the propagated (such as an axial or lateral dimension of the burning region relative to an axis of propagation of the burnfront 510), or the like. For example, the propagation parameters may be selected so as to control the spatial or temporal location of the burnfront 510, so as to avoid failed or malfunctioning control elements (e.g., neutron modifying structures or thermostats), or the like. Neutron modifying structures 530 may be actively controlled and/or passively controlled (e.g., programmable). Actively controlled neutron modifying structures are actively controlled by an operator and/or an external control system. Passively controlled neutron modifying structures are responsive to conditions at one or more locations in the core. For example, programmable temperature responsive neutron modifying structures (examples of which are discussed in detail in the aforementioned '933 application) introduce and remove neutron absorbing or neutron moderating material into and from the fuel-charge of a reactor 500 (including embodiments such as propagating burnfront nuclear fission reactor 550). Responsive to an operating temperature profile, programmable temperature responsive neutron modifying structures introduce neutron absorbing or moderating material into the fuel-charge of the nuclear fission reactor to lower operating temperature in the nuclear fission reactor or remove neutron absorbing or moderating material from the fuel-charge of the nuclear fission reactor in order to raise operating temperature of the nuclear fission reactor. It will be appreciated that temperatures are only one example of control parameters which can be used to determine the control settings of passively controlled or programmable neutron modifying structures. Nonlimiting examples of other control parameters which can be used to determine the control settings of programmable neutron modifying structures include power levels, neutron levels, neutron spectrum, neutron absorption, fuel burnup levels, and the like. In one example, the neutron modifying structures are used to control fuel burnup levels to relatively low (e.g., <50%) levels in order to achieve high-rate “breeding” of nuclear fission fuel for use in other nuclear fission reactors, or to enhance suitability of the burnt nuclear fission fuel for subsequent re-propagation of a nuclear fission deflagration wave in a propagating nuclear fission deflagration wave reactor. Different control parameters can be used at different times, or in different portions of the reactor. It will be appreciated that the various neutron modifying methods discussed previously in the context of neutron modifying structures can also be utilized in programmable temperature responsive neutron modifying structures, including without limitation, the use of neutron absorbers, neutron moderators, combinations of neutron absorbers and/or neutron moderators, variable geometry neutron modifiers, and the like. A material may be subjected to a neutron flux in a reactor. It should be appreciated that the neutron irradiation of material in a reactor may be controlled by the duration and/or extent of duration and local power level. In another embodiment, the neutron irradiation of material may be controlled by control of the neutron environment (e.g., the neutron energy spectrum for Np-237 processing) via neutron modifying structures. Referring to FIGS. 6A and 6B, for example, a material 610 inserted into a reactor 600, as indicated generally with arrow 602, will be subject to a neutron flux dependent upon, inter alia, local power level, duration, neutron modifying structures, and/or neutron spectrum modifying features. In an embodiment where the reactor is a propagating nuclear fission deflagration wave reactor, such as reactor 650, material 610 may be inserted into reactor 650 as indicated generally with arrow 652. In another embodiment, propagating nuclear fission deflagration wave reactor 650 may be operated in a “safe” sub-critical manner, relying upon an external source of neutrons to sustain the propagating burnfront, while using a portion of the fission-generated neutrons for nuclear processing of core materials. It should be appreciated that the movement of material 610 to a location within reactor 600 (or 650) may be from a location external to the reactor (as shown) or from another location within the reactor (not shown). In some embodiments, a material 610 may be present in a location within the reactor before nuclear fission ignition occurs within a reactor, while in other embodiments the material may be added (i.e., moved to the location) after nuclear fission occurs or occurs in that locale. In some embodiments, material is removed from the reactor, while in other embodiments it remains in place. Alternately, a material having a set of non-irradiated properties is loaded into a reactor. The material is transported (e.g., as indicated generally by arrows 652 and 602) into physical proximity and neutronic coupling with a region of maximized reactivity—in the case of propagating nuclear fission deflagration wave reactor 650, as the nuclear fission deflagration wave propagating burnfront (e.g., burnfront 670) passes through the material. The material 610 remains in neutronic coupling for a sufficient time interval to convert the material 610 into a second material 606 having a desired set of modified properties. Upon the material 610 having thus been converted into the material 606, the material 606 may be physically transported out of reactor 600 (or reactor 650) as generally indicated by arrow 604 (or 654). The removal can take place either during operation of reactor 600 (or 650) or after shutdown. The removal can be performed as a continuous, sequential, or batch process. In one example, nuclearly processed material 606 may be subsequently used as nuclear fission fuel in another nuclear fission reactor, such as without limitation LWRs or propagating nuclear fission deflagration wave reactors. In another nonlimiting example, nuclearly processed material 606 may be subsequently used within the nuclear fission igniter of a propagating nuclear fission deflagration wave reactor. In one approach, thermal management may be adjusted to provide thermal control appropriate for any changes in operational parameters, as appropriate for the revised materials or structures. According to further embodiments, temperature-driven neutron absorption can be used to control a nuclear fission reactor, thereby “engineering-in” an inherently-stable negative temperature coefficient of reactivity (αT). Referring now to FIG. 7A, a nuclear reactor 700 is instrumented with temperature detectors 710, such as without limitation thermocouples. In this embodiment, the nuclear fission reactor 700 suitably can be any type of fission reactor whatsoever. To that end, the nuclear fission reactor 700 can be a thermal neutron spectrum nuclear fission reactor or a fast neutron spectrum nuclear fission reactor, as desired for a particular application. For example, temperature detectors detect local temperature in reactor 700 and generate a signal 714 indicative of a detected local temperature. The signal 714 is transmitted to a control system 720 in any acceptable manner, such as without limitation, fluid coupling, electrical coupling, optical coupling, radiofrequency transmission, acoustic coupling, magnetic coupling, or the like. Responsive to signal 714 indicative of the detected local temperature, control system 720 determines an appropriate correction (positive or negative) to a local neutronic reactivity of reactor 700 (e.g., to return reactor 700 to a desired operating parameter, such as desired local temperatures during reactor operations at power). To that end, control system 720 generates a control signal 724 indicative of a desired correction to local neutronic reactivity. Control signal 724 is transmitted to a dispenser 730 of neutron absorbing material. Control signal 724 suitably may be transmitted in the same manner or a different manner as signal 714. The neutron absorbing material suitably may be any neutron absorbing material as desired for a particular application, such as without limitation Li-6, B-10, or Gd. Dispenser 730 suitably is dispensing mechanism acceptable for a desired application. A reservoir (not shown) may be located locally to dispenser 730 or may be located remotely from the dispensing mechanism 730 (e.g., outside a neutron reflector of reactor 700). Dispenser 730 dispenses the neutron absorbing material within the nuclear fission reactor core responsive to the control signal 1124, thereby altering the local neutronic reactivity. Referring now to FIG. 7B and given by way of non-limiting example, exemplary thermal control may be established with a neutron absorbing fluid. A thermally coupled fluid containing structure 740 contains a fluid in thermal communication with a local region of reactor 700. The fluid in the structure 740 expands or contracts responsive to local temperature fluctuations. Expansion and/or contraction of the fluid is operatively communicated to a force coupling structure 750, such as without limitation a piston, located external to the nuclear fission reactor 700. A resultant force communicated by the force coupling structure 750 is exerted on neutron absorbing fluid, such as Li-6, in a neutron absorbing fluid containing structure 760. The neutron absorbing fluid is dispensed accordingly from the structure 760, thereby altering the local neutronic reactivity. In another example, a neutron moderating fluid may be used instead of, or in addition to, the neutron absorbing fluid. The neutron moderating fluid changes the neutron energy spectrum and lowers the mean neutron energy of the local neutron environment, thereby driving down or lowering neutronic reactivity of nuclear fission fuel within the nuclear fission reactor 700. In another example, the neutron absorbing fluid and/or the neutron modifying fluid may have a multiple phase composition (e.g., solid pellets within a liquid). FIG. 7C illustrates details of an exemplary implementation of the arrangement shown in FIG. 7B. Referring now to FIG. 7C, fuel power density in a nuclear fission reactor 701 is continuously regulated by the collective action of a distributed set of independently-acting thermostating modules, over very large variations in neutron flux, significant variations in neutron spectrum, large changes in fuel composition and order-of-magnitude changes in power demand on the reactor. This action provides a large negative temperature coefficient of reactivity just above the design-temperature of reactor 701. Located throughout the fuel-charge in the nuclear fission reactor 701 in a 3-D lattice (which can form either a uniform or a non-uniform array) whose local spacing may be roughly a mean free path of a median-energy-for-fission neutron (it may be reduced for redundancy purposes), each of these modules includes a pair of compartments, each one of which is fed by a capillary tube. A small thermostat-bulb compartment 761 located in the nuclear fission fuel contains a thermally sensitive material, such as without limitation, Li-7, whose neutron absorption cross-section may be low for neutron energies of interest, while the relatively large compartment 741 is positioned in a different location (e.g., on the wall of a coolant tube) and may contain variable amounts of a neutron absorbing material, such as without limitation, Li-6, which has a comparatively large neutron absorption cross-section. At a pressure of 1 bar, lithium melts at 453K and boils at 1615K, and therefore is a liquid across typical operating temperature ranges of reactor 701. As fuel temperature rises, the thermally sensitive material contained in the thermostat-bulb 761 expands, and a small fraction of it is expelled (e.g., approximately 10−3, for a 100K temperature change in Li-7), potentially under kilobar pressure, into the capillary tube which terminates on the bottom of a cylinder-and-piston assembly 751 located remotely (e.g., outside of the radiation shield) and physically lower than the neutron absorbing material's intra-core compartment 741 (in the event that gravitational forces are to be utilized). There the modest volume of high-pressure thermally sensitive material drives a swept-volume-multiplying piston in the assembly 751 which pushes a larger (e.g., potentially three order-of-magnitude larger) volume of neutron absorbing material through a core-threading capillary tube into an intra-core compartment proximate to the thermostat-bulb which is driving the flow. There the neutron absorbing material, whose spatial configuration is immaterial as long as its smallest dimension is less than a neutron mean free path, acts to absorptively depress the local neutron flux, thereby reducing the local fuel power density. When the local fuel temperature drops, neutron absorbing material returns to the cylinder-and-piston assembly 751 (e.g., under action of a gravitational pressure-head), thereby returning the thermally sensitive material to the thermostat-bulb 761 whose now-lower thermomechanical pressure permits it to be received. It will be appreciated that operation of thermostating modules does not rely upon the specific fluids (Li-6 and Li-7) discussed in the above exemplary implementation. In one exemplary embodiment, the thermally sensitive material may be chemically, not just isotopically, different from the neutron absorbing material. In another exemplary embodiment, the thermally sensitive material may be isotopically the same as the neutron absorbing material, with the differential neutron absorbing properties due to a difference in volume of neutronically exposed material, not a difference in material composition. Reactor Control and Simulation The aforementioned examples thus demonstrate that fuel, neutron absorbing material, and other materials may be moved throughout a reactor core by several mechanisms with or without moving complete assemblies. Such movements may complicate calculations of nuclide concentrations (i.e., numbers of atoms and isotopes and nuclear isomers of atoms per unit volume) in the core. In general, the calculation of nuclide concentrations in the core or an operating reactor or simulation thereof may be broken into two interrelated parts: neutron transport and transmutation. Neutron transport calculations may determine neutron populations (e.g., flux and flux spectrum), while transmutation calculations determine the populations of nuclides given a starting population and a neutron flux. Neutron transport calculations can be done, for example, using deterministic methods (e.g., a discrete ordinates method), using stochastic methods such as a Monte Carlo method, or by using a hybrid of the two (e.g., using deterministic methods to calculate certain aspects in an otherwise Monte Carlo implementation). Deterministic methods typically solve transport equations using average particle behavior. A discrete method typically divides the phase space into many small volumes. Neutrons moving between adjacent volumes take a small amount of time to move a small distance. Thus, calculation approaches the integro-differential transport equation (having space and time derivatives) as time, volume, and distance are made smaller, i.e., approach 0. Monte Carlo methods, on the other hand, obtain answers by simulating individual particles and recording some aspects of their average behavior. Monte Carlo methods are often used when it is difficult to determine an example result using a deterministic method. As applied to neutron transport, a Monte Carlo method may simulate the individual probabilistic events, thus following neutrons through their lifecycle from birth to death (e.g., absorption, escape, etc.). The associated probability distributions (e.g., represented by continuous and/or discrete probability density functions) are randomly sampled to determine the outcome (e.g., scatter, fission, neutron capture, leakage) at each time step. Collisions may be modeled using physics equations and cross sectional data. The frequency of collisions, and thus neutron induced reactions such as fission and loss due to absorption by neutron absorbing materials are, of course, dependent on the concentration of fissile isotopes and neutron absorbing materials respectively in the volume of interest. Cross-sectional data for an atom represents the effective cross sectional area that an atom presents to a particle for an interaction, e.g., for a neutron, for interactions such as the various scattering and absorption types. Cross sections typically vary by the atom, the particle, and the energy of the particle. Thus, a cross section may be used to express the likelihood of a particular interaction of an atom with an incident particle having a certain energy. Microscopic properties, such as a microscopic cross section for a reaction (e.g., scatter, radiative capture, absorption, fission), are intrinsic properties of a type of nuclei (i.e., of a specific material's nuclei). Macroscopic properties, such as a macroscopic cross section for a reaction, is a property of a volume of the material having a concentration or density (e.g., in number of atoms per unit volume) of the material. Microscopic cross section is typically expressed in units of area (e.g., cm2 or “barns”—a barn is 10−28 m2). Macroscopic cross sections are proportional to the microscopic cross section multiplied by the density, or equivalently 1/(mean free path length) and thus are expressed in units of 1/length (e.g., m−1). Cross sectional data is typically determined by empirical means. Thus, especially for short-lived isotopes, cross sectional data for a large spectrum of neutron energies is simply not available yet. Therefore, performing accurate Monte Carlo calculations on volumes having a population of isotopes not having completely known or well-characterized properties such as neutron cross-sections can be difficult. Additionally, even if all the cross sectional data for each and every material was well characterized, the computational burden would be significant. Methods which may help reduce these difficulties and/or computational burdens are described in detail elsewhere herein. Transmutation calculations determine the inventory or concentration of each nuclide as it varies, for example, under a neutron flux. In general, transmutation calculations may be thought of as determining a new population of a material based on the loss rate and the production rate of the material subject to a given neutron flux. A given atom of a material may, for example, fission and produce two fission products; while another atom of the material might be converted to an isotope of a larger atomic mass number (A) after capturing a neutron. Yet another atom of the material might beta or alpha decay to another element, and so forth. Thus, the rate of change of an amount of a material in an operating reactor is typically the sum of the loss rate due to decay, gain rate due to decay, loss due to neutron-induced reactions, and gain due to neutron-induced reactions. It is to be appreciated that transmutation calculations for materials depend upon the current neutron flux, and neutron flux calculations depend upon the current concentration of materials such as fissile isotopes and neutron absorbing materials. These calculations may be linked together in various ways, including but not limited to such iterative numerical analysis tools such as the Runge-Kutta methods. A complete description of Runge-Kutta is not necessary, as it is well known in the art. In general, however, explicit Runge-Kutta methods, “solve” the initial value problemy′=f(t,y),y(t0)=y0 using the equations y n + 1 = y n + h ∑ i = 1 s b i k i where k 1 = f ( t n , y n ) , k 2 = f ( t n + c 2 h , y n + a 21 hk 1 ) , k 3 = f ( t n + c 3 h , y n + a 31 hk 1 + a 32 hk 2 ) , k s = f ( t n + c s h , y n + a s 1 hk 1 + a s 2 hk 2 + … + a s , s - 1 hk s - 1 ) To specify a specific Runge Kutta method, one may supply an integer, s, and a set of coefficients aij, bij, and ci, The Runge Kutta method is consistent if the coefficients are such that: ∑ j = 1 i - 1 a ij = c i for i = 2 , … , s . Thus, for example, a consistent fourth order Runge Kutta is:yn+1=yn+⅙h(k1+k2+k3+k4),tn+1=tn+h wherek1=f(tn,yn),k2=f(tn+½h,yn+½hk1),k3=f(tn+½h,yn+½hk2), andk4=f(tn+h,yn+hk3). Thus, the next value, yn+1, is determined by the present value, yn, plus the product of the size of the interval and an estimated slope. The slope is a weighted average of slopes: k1 is the slope at the beginning of the interval, k2 is the slope at the midpoint of the interval using slope k1 to determine the value of y at the point tn+h/2 using Euler's method; k3 is again the slope at the midpoint, but now using the slope k2 to determine the y-value; and k4 is the slope at the end of the interval, with its y-value determined using k3. The Euler method is a one stage Runge Kutta method. The Euler method essentially estimates the slope and advances a small step using that slope. Examples of second order Runge Kutta methods include the midpoint method and Heun's method. Thus, an updated amount (e.g., inventory or concentration) of a material in a reactor core or volume of interest (inside or outside the reactor core) may be determined by determining an average rate of change of the amount of the material based on the previous amount of the material and a neutron flux. This may be performed individually or simultaneously for all of the materials in the reactor core or the volume of interest. The neutron flux, in turn, may be determined by determining an average rate of change of flux based on the amount of the materials in the core. Accuracy of the calculations may be enhanced if subvolumes of a reactor are considered rather than a reactor core in gross. For example, gross calculations may be performed on a homogenous model of a reactor core—the core is simulated to have an even distribution of all materials. Higher resolution may be obtained by representing the core as a volume comprised of many homogeneous cells, each cell being allowed to have different concentrations of materials. Although cells need not be homogenous, homogenous cells are typically preferred to simplify calculations. If the resolution is high enough, the core may be represented with very good precision. For example, a three-dimensional geometry of cells, each having a defined geometry and concentrations of materials may be used. Cells may be defined in many ways, including but not limited to by their bounding surfaces such as equations of surfaces and intersections and unions of regions of space. Transport calculations typically determine for each cell the number of reactions and boundary crossings to each neighboring cell. As illustrated in FIG. 8A, a structure 800 may be formed by cells having complicated shapes. For the sake of simplicity, only two dimensions are shown (i.e., a cross section), but it is understood that cells are typically three dimensional. Moreover, in this non-limiting example, the locations and shapes are relatively uniform. For example, exemplary cell 802 may be a sphere. Exemplary cell 804 may be a larger sphere excluding the volume defined by cell 802. Exemplary cell 806 may be a cube, excluding the volume circumscribed by the outer spherical surface of cell 804. Alternatively, cell 802 could be a cylinder extending some distance into the figure, cell 804 could be the volume determined by a larger cylinder excluding the volume of cell 802, and cell 806 could be a rectangular prism excluding the volume within the cylinder defined by cell 804's outer surface. In any case, cell 802 may include one composition of fuel materials, neutron absorbing materials, and structural materials. Cell 804 may have a second composition of fuel materials, neutron absorbing materials, and structural materials. Cell 806 may be a third composition of structural materials only (e.g., cladding). As illustrated in FIG. 8B, cells may be combined to form larger structures. For example, structure 800 may represent a rectangular prism-shaped fuel assembly. Structure 830 includes many structures 800. For example, structure 830 may define a fuel module of six fuel pins by four fuel pins and fifty fuel pins deep. Thus, even larger structures may be formed. For example, as illustrated by FIG. 8C, exemplary structure 860 may represent a reactor core having an arrangement of nineteen structures 830 (e.g., fuel modules) each including many structures 800 (fuel assemblies). Thus, specific physical locations in space of an actual operating reactor or a detailed reactor design may be represented by a cell. Calculations may be performed using a detailed model representing an actual reactor during operation. The results may be used to make decisions regarding reactor control. Similarly, calculations may be performed on a representation of a proposed reactor to test operating procedures or to test proposed fuel and neutron absorbing material loading. Transmutation and transport calculations may be performed for each cell. For a complex model, this can result in a large computational burden due in part to the large number of cells. The computational burden is also increased by the number of materials which may be present in each cell. Prior to operation, a reactor already contains a large number of materials (e.g., various fuel isotopes, installed neutron absorbing material, structural isotopes, moderator, reflectors, etc.). Immediately upon operation, however, the number of materials (e.g., isotopes) in the reactor increases significantly due to neutron capture and especially neutron-induced fission. The distribution of fission products from a fission of a given isotope induced by a neutron of a given energy may be described by a fission product yield curve. FIG. 9 illustrates an exemplary fission product yield curve 900. It should be appreciated that the graph illustrates the total fission yield in percent of fission products having each mass number (A). More than one isotope may have a given mass number. Thus, fission products having a mass number of, for example, 140, fall under the point on the curve defined by mass number=140. In this example, the fission products produced by the thermal fission of U-235 is illustrated on fission product yield curve 900. Curves for fissions of U-235 induced by fast neutrons will have a similar but different shape. Neutron energies may be classified in more detail than “fast” or “thermal.” Also, fission yield curves for other fissile isotopes will have a similar but different shape. In general, however, fission yield curves follow this “M” shape having two peaked “humps.” Thus, the curve may be divided into two portions, left curve portion 912 which includes a left peak 922, and right curve portion 914 which includes a right peak 924. Thus area 902 falls under left peak 922 and left curve portion 912 and area 904 falls under right peak 924 and right curve portion 914. As a reactor operates, the level of fission products tends to increase due to fission (i.e., have a production rate due to fission), but tends to decrease due to decay and neutron capture or “burnout” (i.e., have loss rates due to decay and capture). Transmutation calculations may be used to determine or approximate these levels during reactor operation. As discussed elsewhere herein, reactor control systems, such as control system 720, may determine appropriate corrections (positive or negative) to a local neutronic reactivity of reactor 700 (e.g., to return reactor 700 to a desired operating parameter, such as desired local temperatures during reactor operations at power). To that end, control systems may generate a control signal (e.g., control signal 724) indicative of a desired correction to local neutronic reactivity. Reactor control systems and control signals are not limited to the embodiments such as control system 720 and control signal 724. Reactor Control Systems may also control other neutron affecting or absorbing features such as control rods, to control and/or shut down the reactor as desired, which is well known in the art. Reactor Control Systems may also generate control signals to order changes in various flows, e.g., the flow of heat absorbing material (e.g., coolant) through the reactor or portions of the reactor by ordering changes in reactor coolant pump (e.g., reactor coolant pumps 22) operation and/or various valve positions in the reactor system, including but not limited to reactor closures (e.g., closures 24) or reactor coolant shutoff valves, steam shutoff valves, etc. Reactor Control Systems may also order changes in breaker positions (e.g., reactor coolant pump power supply breakers, steam turbine-generator output breakers, etc.). As is well known in the art, Reactor Control Systems may have temperature inputs (e.g., control system 720 receiving input from temperature detectors 710) in addition to neutron detectors (e.g., to sense neutron flux to determine reactor power or local reactor power at a portion of the core), and flow and position detectors (e.g., venturi-type flow detectors, valve position indicators, breaker position indicators). Thus, Reactor Control Systems may control the flow of heat absorbing material (e.g., coolant) through the reactor and/or portions of the reactor to control overall temperatures and local temperatures in response to overall reactor thermal power and/or local reactor thermal power. Reactor Control Systems may also provide operator indications and accept operator inputs. Thus, a Reactor Control System monitors reactor operations, may provide some automatic control features (such as changing flow rates and moving control rods or otherwise positioning neutron affecting or absorbing materials, which are described in more detail elsewhere herein), displays operational parameters, and accepts and executes operator inputs for manual control actions. Example Computer System Some aspects and/or features of the disclosed subject matter can be implemented by software, firmware, hardware, or a combination thereof. Calculations may be approximated using table look-ups. Hardware implementations of individual components are not limited to digital implementations and may be analog electrical circuits. Additionally, embodiments may be realized in a centralized fashion in at least one communication system, or in a distributed fashion where different elements may be spread across several interconnected communication systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein may be suited. FIG. 10 illustrates an example computer system 1000 in which the present subject matter, or portions thereof, can be implemented as computer-readable code. Various embodiments are described in terms of this example computer system 1000. After reading this description, it will become apparent to a person skilled in the relevant art how to implement the disclosed subject matter using other computer systems and/or computer architectures. Computer system 1000 includes one or more processors, such as processor 1004. Processor 1004 can be a special purpose or a general purpose processor. Processor 1004 is connected to a communication infrastructure 1006 (for example, a bus or network). Computer system 1000 also includes a main memory 1008, preferably random access memory (RAM), and may also include a secondary memory 1010. Secondary memory 1010 may include, for example, a hard disk drive 1012, a removable storage drive 1014, any type of non-volatile memory, and/or a memory stick. Removable storage drive 1014 may comprise a floppy disk drive, a magnetic tape drive, an optical disk drive, a flash memory, or the like. The removable storage drive 1014 reads from and/or writes to a removable storage unit 1018 in a well known manner. Removable storage unit 1018 may comprise a floppy disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive 1014. As will be appreciated by persons skilled in the relevant art(s), removable storage unit 1018 includes a computer usable storage medium having stored therein computer software and/or data. In alternative implementations, secondary memory 1010 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 1000. Such means may include, for example, a removable storage unit 1022 and an interface 1020. Examples of such means may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, and other removable storage units 1022 and interfaces 1020 which allow software and data to be transferred from the removable storage unit 1022 to computer system 1000. Computer system 1000 may also include a communications interface 1024. Communications interface 1024 allows software and data to be transferred between computer system 1000 and external devices. Communications interface 1024 may include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, or the like. Software and data transferred via communications interface 1024 are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface 1024. These signals are provided to communications interface 1024 via a communications path 1026. Communications path 1026 carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link or other communications channels. Computer system 1000 may also be coupled to a Reactor Control system 1030. Reactor Control System 1030 may be directly interfaced to the communications infrastructure 1006 as shown in the figure. Reactor Control System may also be interfaced via communications interface 1024 or communications interface 1024 and communications path 1026. In this document, the terms “computer program medium” and “computer usable medium” are used to generally refer to media such as removable storage unit 1018, removable storage unit 1022, and a hard disk installed in hard disk drive 1012. Signals stored elsewhere and carried over communications path 1026 can also embody the logic described herein. Computer program medium and computer usable medium can also refer to memories, such as main memory 1008 and secondary memory 1010, which can be memory semiconductors (e.g. DRAMs, etc.). These computer program products are means for providing software to computer system 1000. Computer programs (also called computer control logic) are stored in main memory 1008 and/or secondary memory 1010. Computer programs may also be received via communications interface 1024. Such computer programs, when executed, enable computer system 1000 to implement the present subject matter as discussed herein. In particular, the computer programs, when executed, enable processor 1004 to be used in the performance of processes of the present subject matter, such as the methods illustrated by the flowcharts described elsewhere herein. Accordingly, such computer programs represent controllers of the computer system 1000. Where the disclosed subject matter is implemented using software, the software may be stored in a computer program product and loaded into computer system 1000 using removable storage drive 1014, interface 1020, hard drive 1012 or communications interface 1024. The present subject matter is also directed to computer program products comprising software stored on any computer useable medium. Computer programs or software in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form. Such software, when executed in one or more data processing device, causes a data processing device(s) to operate as described herein. Embodiments employ any computer useable or readable medium, known now or in the future. Examples of computer useable mediums include, but are not limited to, primary storage devices (e.g., any type of random access memory), secondary storage devices (e.g., hard drives, floppy disks, CD ROMS, ZIP disks, tapes, magnetic storage devices, optical storage devices, MEMS, nanotechnological storage device, etc.), and communication mediums (e.g., wired and wireless communications networks, local area networks, wide area networks, intranets, etc.). Methods for Mapping Reactor Materials Now that illustrative embodiments of nuclear reactors and reactor control and simulation have been discussed, illustrative methods associated therewith will now be discussed. Following are a series of flowcharts depicting implementations of processes. For ease of understanding, the flowcharts are organized such that the initial flowcharts present implementations via an overall “big picture” viewpoint and thereafter the following flowcharts present alternate implementations and/or expansions of the “big picture” flowcharts as either sub-steps or additional steps building on one or more earlier-presented flowcharts. Those having skill in the art will appreciate that the style of presentation utilized herein (e.g., beginning with a presentation of a flowchart(s) presenting an overall view and thereafter providing additions to and/or further details in subsequent flowcharts) generally allows for a rapid and easy understanding of the various process implementations. In addition, those skilled in the art will further appreciate that the style of presentation used herein also lends itself well to modular design paradigms. The blocks may be performed in any order or concurrently unless specified otherwise. Some embodiments do not require the performance of each and every block, regardless whether the block or blocks is/are explicitly labeled or described as optional. Other embodiments require the repetition of one or more blocks, regardless whether the block is labeled or described as repeated. Referring now to FIG. 11, an illustrative method 1100 is provided for simulating and/or controlling a nuclear reactor. The method 1100 starts at a block 1105. At block 1105, a flux in a first cell is determined based on the amount(s) of at least one material in at least the first cell. The flux determination may be further based on the amounts of more than one material in the first cell and/or a previous flux in the first cell. Also, the flux determination may be further based on the amounts one or more materials in one or more other cells. For example, a flux may be determined by a transport calculation (e.g., solving neutron transport equations). A “flux” may be any flux (e.g., photon, alpha, beta, etc.), but is typically a neutron flux. The flux may be determined by numerical analysis methods using an average rate of change of the flux. The average rate of change of the flux may be a weighted average (e.g., as determined by a Runge Kutta method or any other method). The flux may be dependent upon the amount(s) of one or more materials in the first cell. The flux may be further dependent upon the amount(s) of one or more materials in one or more additional cells. An “amount” may be a mass or a number (e.g., number of atoms) or may be a density/concentration (e.g., mass or number of particles per unit volume). A cell represents a physical location or region in a nuclear reactor. The reactor may be, for example, real or simulated, currently operating, or under design. The reactor may be any type or sub-type of reactor, including light water reactor, heavy water reactor, pressurized water reactor, boiling water reactor, propagating nuclear fission deflagration wave reactor, etc. The reactor is typically represented by many homogeneous cells, but heterogeneous cells may be used. Each cell may have the same or different shape or volume as any other cell. A material may be one or more of any element, molecule, family of elements, family of molecules, isotope, family of isotopes, isomers of isotopes, fertile isotope(s), fission product(s), fission product poisons, etc. Materials are typically elements and isotopes of elements. Thus, U-235 and U-238 are thus typically two different materials. At block 1110, the average rate(s) of change of the one or more amount(s) of one or more material(s) in the first cell is determined based on previous amount(s) of the material(s) and a flux in the first cell. For example, average rates of change may be determined by a transmutation rate calculation. The average rate of change of the amount of one or more materials may be determined by numerical analysis methods using an average rate of change of the amount. The average rate of change of the flux may be a weighted average (e.g., as determined by a Runge Kutta method or any other method). The amount may be dependent upon the flux in the first cell. The average rates of change for the one or more materials may be solved individually or simultaneously (such as when coupled through transmutation equations). At block 1115, updated amount(s) in the first cell for the material(s) are determined based on the average rate(s) of change. For example, updated amounts may be determined by performing transmutation calculations. The updated amounts for the one or more materials may be solved individually or simultaneously (such as when coupled through transmutation equations). At block 1120, at least one move quantity is determined. A move quantity may be any quantity of one or more materials such as a quantity of a material that is desired to be moved into or out of a cell. In this block one or more move quantities may each apply to one or more materials in the first cell. A move quantity may be determined in response to one or more reactor parameters such as a flux or a fluence, a power level (local or overall), a temperature, etc. A reactor parameter may be compared to a threshold or set point for that parameter. This block may be repeated as suitable, e.g., for each of one or more materials in the first cell. At block 1125, the updated amount(s) in the first cell is (are) adjusted by the move quantity(-ies). One or more move quantities are each applied to the amounts of one or more materials in the first cell, thus increasing or decreasing each affected amount. A move amount of zero may be used to signify no change. In an embodiment, a material may be moved outside the reactor. In this case, blocks 1130 through 1145 may be skipped. At block 1130, a flux in a second cell is determined based on amount(s) of at least one material in the second cell. As discussed above, the flux determination may be further based on the amounts of more than one material in the second cell. Also, the flux determination may be further based on the amounts one or more materials in one or more other cells. At block 1135, average rate(s) of change of the amount(s) of the material(s) in the second cell based on previous amount(s) of the material(s) and a flux in the second cell is determined. At block 1140, updated amount(s) in the second cell for the material(s) is (are) determined based on the average rate(s) of change in the second cell. At block 1145, the updated amount(s) in the second cell is (are) adjusted by the move quantity(-ies). At block 1150, a control action for a nuclear reactor is determined. A control action may be a change (positive or negative) to a local neutronic reactivity of a reactor using any neutron affecting or absorbing features such as movement of neutron absorbing materials or fluids, control rods, etc.; a change in one or more various flows, e.g., the flow of heat absorbing material (e.g., coolant) through the reactor by ordering changes in reactor coolant pump operation and/or various valve positions in the reactor system, including but not limited to reactor closures or reactor coolant shutoff valves, steam shutoff valves, etc.; a change in one or more breaker positions (e.g., reactor coolant pump power supply breakers, steam turbine-generator output breakers, etc.); or the like. The determined control action may be displayed to a user. In an embodiment, this block is optional. At block 1155, a control action for the nuclear reactor is performed. This performance may be automatic or manual. In an embodiment, this block is optional. At block 1160, approximately the move quantity(-ies) of the material(s) is/are transferred to/from the first cell location in a reactor. In this block, an actual of amount of at least one substance corresponding to one or more of the at least one material is transferred from or to one location (i.e., from the first cell location or to the first cell location). This block may be performed in conjunction with block 1155 or separately. The transferred amount of a substance (i.e., approximately the move quantity of the corresponding material or materials) may, but is not required, to be associated with a component in the location represented by the cell (e.g., an assembly including fuel, neutron absorbing material, structural components, or any combination of these). In an embodiment such as a simulation or evaluation of a reactor design, this step is optional. The method stops at block 1160, but may continue to point A as indicated in other methods in other figures. Referring now to FIG. 12, an illustrative method 1200 is provided for simulating and/or controlling a nuclear reactor. The method 1200 starts at a block 1210. As illustrated by point A, method 1200 may be preceded by method 1100. At block 1210, approximately the move quantity(-ies) of the material(s) is/are transferred from/to a second cell. In this block, an actual amount of at least one substance corresponding to one or more of the at least one material is transferred from or to the location of the second (i.e., from the second cell location or to the second cell location). For example, in conjunction with block 1160 of method 1100, a quantity of a substance, approximately equal to the determined move quantity or quantities of the corresponding materials, may be transferred from the first cell to the second cell or vice versa. The method stops at block 1210. Referring now to FIG. 13, an illustrative method 1300 is provided for simulating and/or controlling a nuclear reactor. The method 1300 starts at a block 1305. As illustrated by point A, method 1300 may be preceded by method 1100. Illustrative method 1300 provides an exemplary method of moving matter in a four-cell loop through the reactor. At each cell in the loop, the amount and type of matter moved need not be identical. A person of skill in the art would understand that the four-cell loop may be expanded or contracted as suitable (i.e., include fewer or more cells). At block 1305, approximately the move quantity(-ies) of material(s) is/are transferred to a second cell. For example, in conjunction with block 1160 of method 1100, a quantity of a substance, approximately equal to the determined move quantity or quantities of the corresponding materials, may be transferred from the first cell to the second cell. At block 1310, second move quantity(-ies) is (are) determined. The second move quantity or quantities may be calculated in any way as described above. At block 1315, amount(s) in the second cell is (are) adjusted by the second move quantity(-ies). At block 1320, approximately the second move quantity(-ies) of material(s) are transferred from the second cell to a third cell. At block 1325, third move quantity(-ies) is (are) determined. At block 1330, amount(s) in the third cell is (are) adjusted by the third move quantity(-ies). At block 1335, approximately the third move quantity(-ies) of material(s) is (are) transferred from the third cell to a fourth cell. At block 1340, fourth move quantity(-ies) is (are) determined. At block 1345, amount(s) in the fourth cell is (are) adjusted by the fourth move quantity(-ies). At block 1350, approximately the fourth move quantity(-ies) of material(s) is (are) transferred from the fourth cell to a first cell The method stops at block 1350. Referring now to FIG. 14, an illustrative method 1400 is provided for simulating and/or controlling a nuclear reactor. The method 1400 starts at a block 1405. As illustrated by point A, method 1400 may be preceded by method 1100. Illustrative method 1400 illustrates, inter alia, mixing quantities of one or materials from a first cell and a third cell, and transferring at least a portion of the mixture back to the first cell. One or more additional iterations of neutron flux and transmutation calculations may optionally occur. A person of skill in the art would understand that this illustrative method could be expanded or contracted to include various mixing methods using fewer or more cells. At block 1405, approximately the move quantity(-ies) of materials is (are) transferred to a second cell. At block 1410, second move quantity(-ies) is (are) determined. At block 1415, amount(s) in the second and third cells is (are) adjusted by the second move quantity(-ies). At block 1420, approximately the second move quantity(-ies) are transferred to/from a third cell and from/to the second cell. At block 1425, a new average rate(s) of change of the amount(s) of the material(s) in the first cell based on current amount(s) of the material(s) and an updated flux in the first cell is (are) determined. At block 1430, new updated amount(s) in the first cell for the material(s) is (are) determined based on the new average rate(s) of change. At block 1435, third move quantity (-ies) is (are) determined. At block 1440, amount(s) in the second and first cell is (are) adjusted by the third move quantity(-ies). At block 1445, approximately the third move quantity (-ies) is (are) transferred from the second cell to the first cell. The method stops at block 1445. Referring now to FIG. 15, an illustrative method 1500 is provided for simulating and/or controlling a nuclear reactor. As illustrated by point A, method 1500 may be preceded by method 1100. Illustrative method 1500 provides an exemplary method of, inter alia, transferring quantities of one or more materials to a cell location for holding (e.g., a holding tank or reservoir, etc.). While the material is in the holding cell location, one or more additional iterations of neutron flux and transmutation calculations may optionally occur. Material may also be transferred out of the holding cell (e.g., to a location that is not represented by the first cell). A person of skill in the art would understand that this illustrative method could be expanded or contracted to include various holding methods using fewer or more cells. The method 1500 starts at a block 1505. At block 1505, approximately the move quantity(-ies) of material(s) is (are) transferred to a second cell. At block 1510, second move quantity(-ies) is (are) determined. At block 1515, amount(s) in the second cell is (are) adjusted by the second move quantity(-ies). At block 1520, approximately the second move quantity(-ies) of material(s) is (are) transferred from the second cell. At block 1525, new average rate(s) of change of the amount(s) of the material(s) in the first cell is (are) determined based on current amount(s) of the material(s) and an updated flux in the first cell. At block 1530, new updated amount(s) in the first cell for the material(s) is (are) determined based on the new average rate(s) of change. At block 1535, an average rate(s) of change of the amount(s) of the material(s) in the second cell is (are) determined based on current amount(s) of the material(s) and a flux in the second cell. At block 1540, updated amount(s) in the second cell for the material(s) is (are) determined based on the average rate of change in the second cell. At block 1545, third move quantity(-ies) is (are) determined. At block 1550, amount(s) in the first and second cells is (are) adjusted by the third move quantity(-ies). At block 1555, approximately the third move quantity(-ies) of material(s) is (are) transferred from the second cell to the first cell. The method stops at block 1555. Referring now to FIG. 16, an illustrative method 1600 is provided for simulating and/or controlling a nuclear reactor. Illustrative method 1600 differs from illustrative method 1110, but some steps may be similar. For example, illustrative method 1600 provides an example of a continuous move of material(s) rather than discrete moves. The method 1600 starts at a block 1605. At block 1605, a flux in a first cell is determined based on amount(s) of at least one material in the first cell. As discussed above, the flux determination may be further based on the amounts of more than one material in the first cell. Also, the flux determination may be further based on the amounts one or more materials in one or more other cells. This block is similar to block 1105. At block 1610, average rate(s) of change of the amount(s) of the material(s) in the first cell is (are) determined based on previous amount(s) of the material(s) and a flux in the first cell. This block is similar to block 1110. At block 1615, at least one move rate for the material(s) in the first cell is (are) determined. A move rate may be any rate of movement of one or more materials such as a quantity of a material that is desired to be moved into or out of a cell. In this block one or more move rates may each apply to one or more materials in the first cell. A move rate may be determined in response to one or more reactor parameters such as a flux or a fluence, a power level (local or overall), a temperature, etc. A reactor parameter may be compared to a threshold or set point for that parameter. This block may be repeated as suitable, e.g., for each of one or more materials in the first cell. At block 1620, the average rate(s) of change in the first cell is (are) adjusted based on the move rate(s) for the material(s) in the first cell. For example, an average rate of change of a material in the first cell may be adjusted (increased or decreased) based on a determined move rate. The adjustment may be made to a single average rate of change or to individual rates of change which are averaged (e.g., in a straight average or a weighted average). The average rates of change for more than one material may be solved individually or simultaneously (such as when coupled through transmutation equations). At block 1625, updated amount(s) in the first cell is (are) determined based on the adjusted average rate(s) of change. In an embodiment, a material may be moved outside the reactor. In this case, blocks 1630 through 1645 may be skipped. At block 1630, a flux in a second cell is determined based on amount(s) of at least one material in the second cell. As discussed above, the flux determination may be further based on the amounts of more than one material in the first cell. Also, the flux determination may be further based on the amounts one or more materials in one or more other cells. At block 1635, average rate(s) of change of the amount(s) of the material(s) in the second cell is (are) determined based on previous amount(s) of the material(s) and a flux in the second cell. At block 1640, the average rate(s) of change in the second cell is (are) determined based on move rate(s) of at least one material. At block 1645, updated amount(s) in the second cell is (are) based on the adjusted average rate(s) of change. At block 1650, a control action for a nuclear reactor is determined. In an embodiment, this block is optional. At block 1655, a control action for nuclear reactor is performed. In an embodiment, this block is optional. At block 1660, material(s) is (are) transferred to/from the first cell at a transfer rate approximately equivalent to the move rate(s) of the material(s). As with block 1160, an actual amount of at least one substance is transferred, but the transfer is at a transfer rate equivalent to the appropriate move rate. In an embodiment such as a simulation or evaluation of a reactor design, this step is optional. The method stops at block 1660, but may continue to point B as indicated in other methods in other figures. Referring now to FIG. 17, an illustrative method 1700 is provided for simulating and/or controlling a nuclear reactor. The method 1700 starts at a block 1705. As illustrated by point B, method 1700 may be preceded by method 1600. At block 1705, material(s) is (are) transferred from/to a second cell at the transfer rate(s) approximately equivalent to the move rate(s) of the materials. In this block, an actual of amount of at least one substance corresponding to one or more of the at least one material is transferred from or to the location of the second (i.e., from the second cell location or to the second cell location) at the move rate(s). For example, in conjunction with block 1660 of method 1600, a quantity of a substance, approximately equal to the determined move quantity or quantities of the corresponding materials, may be transferred from the first cell to the second cell or vice versa at the appropriate move rate(s). The method stops at block 1705. Referring now to FIG. 18, an illustrative method 1800 is provided for simulating and/or controlling a nuclear reactor. The method 1800 starts at a block 1805. As illustrated by point B, method 1800 may be preceded by method 1600. Illustrative method 1800 provides an exemplary method of moving matter at various rates in a four-cell loop through the reactor. At each cell in the loop, the rate and type of matter moved need not be identical. A person of skill in the art would understand that the four-cell loop may be expanded or contracted as suitable (i.e., include fewer or more cells). At block 1805, material(s) is (are) transferred to the second cell at transfer rate(s) approximately equivalent to the move rate(s) of the materials. At block 1810, a second (set of) move rate(s) for material(s) in the second cell is (are) determined. At block 1815, further adjustment(s) to average rate(s) of change in the second cell is (are) made based on the second (set of) move rate(s) of the material(s). At block 1820, material(s) is (are) transferred from the second cell to a third cell at approximately the second (set of) move rate(s). At block 1825, move rate(s) for material(s) in the third cell is (are) determined. At block 1830, average rate(s) of change for material(s) in the third cell is (are) adjusted by the second (set of) move rates for the second cell and/or the determined move rates of the third cell. At block 1835, material(s) is (are) transferred from the third cell to a fourth cell at approximately the determined move rate(s) of the third cell. At block 1840, move rate(s) for material(s) in the fourth cell is (are) determined. At block 1845, average rate(s) of change for material(s) in the fourth cell is (are) adjusted by the determined move rate(s) of the third cell and/or the determined move rates of the fourth cell. At block 1850, material(s) is (are) transferred from the fourth cell to the first cell at approximately the determined move rates of the fourth cell. The method stops at block 1850. Referring now to FIG. 19, an illustrative method 1900 is provided for simulating and/or controlling a nuclear reactor. Illustrative method 1900 illustrates, inter alia, mixing quantities of one or materials from a first cell and a third cell, and transferring at least a portion of the mixture back to the first cell. The transfers occur at various rates. One or more additional iterations of neutron flux and transmutation calculations may optionally occur during the transfer. A person of skill in the art would understand that this illustrative method could be expanded or contracted to include various mixing methods using fewer or more cells. The method 1900 starts at a block 1905. As illustrated by point B, method 1900 may be preceded by method 1600. At block 1905, material(s) is (are) transferred to the second cell at transfer rate(s) approximately equivalent to the move rate(s) of the materials. At block 1910, a second (set of) move rate(s) for material(s) of the second cell is (are) determined. At block 1915, further adjustments are made to average rate(s) of change in the second cell and to the average rate(s) of change in a third cell based on the second (set of) move rate(s) of the material(s). At block 1920, material(s) is (are) transferred at approximately the second (set of) move rate(s) to/from a third cell from/to the second cell. At block 1925, new average rate(s) of change of the amount(s) of the material(s) in the first cell is (are) determined based on current amount(s) of the material(s) and an updated flux in the first cell. At block 1930, new updated amount(s) in the first cell for the material(s) is (are) determined based on the new average rate(s) of change. At block 1935, a third (set of) move rate(s) is determined for material(s) of the second cell. At block 1940, average rate(s) of change of material(s) in the first and second cells is (are) adjusted using the third (set of) move rate(s). At block 1945, material(s) is (are) are transferred at approximately the third (set of) move rate(s) from the second cell to the first cell. The method stops at block 1945. Referring now to FIG. 20, an illustrative method 2000 is provided for simulating and/or controlling a nuclear reactor. Illustrative method 2000 provides an exemplary method of, inter alia, transferring quantities of one or more materials to a cell location for holding (e.g., a holding tank or reservoir, etc.) at various rates. While the material is being transferred to/from the holding cell location, one or more additional iterations of neutron flux and transmutation calculations may optionally occur. Material may also be transferred out of the holding cell (e.g., to a location that is not represented by the first cell). The method 2000 starts at a block 2005. As illustrated by point B, method 2000 may be preceded by method 1600. At block 2005, material(s) is (are) transferred to the second cell at transfer rate(s) approximately equivalent to the move rate(s) of the materials. At block 2010, a second (set of) move rate(s) for material(s) of the second cell is determined. At block 2015, further adjustment(s) is (are) made to average rate(s) of change in the second cell based on the second (set of) move rate(s) of the material(s). At block 2020, material(s) is (are) transferred at approximately the second (set of) move rate(s) from the second cell. At block 2025, new average rate(s) of change of the amount(s) of the material(s) in the first cell is (are) determined based on current amount(s) of the material(s) and an updated flux in the first cell. At block 2030, new updated amount(s) in the first cell is (are) determined for the material(s) based on the new average rate(s) of change. At block 2035, new average rate(s) of change of the amount(s) of the material(s) in the second cell is (are) determined based on current amount(s) of the material(s) and a flux in the second cell. At block 2040, a third (set of) move rate(s) for materials in the second cell is determined. At block 2045, the average rate(s) of change of the amount(s) of material(s) in the first cell is (are) determined based on the third (set of) move rate(s) for materials in the second cell. At block 2050, the average rate(s) of change of the amount(s) of material(s) in the second cell is (are) determined based on the third (set of) move rate(s) for materials in the second cell. At block 2055, material(s) is (are) transferred at approximately the third (set of) move rate(s) from the second cell to the first cell. The method stops at block 2055. Referring now to FIG. 21, an illustrative method 2100 is provided for simulating and/or controlling a nuclear reactor. As discussed elsewhere herein, neutron transport equations may use cross sectional data for some or all of the materials in the reactor. Method 2100 illustrates a non-limiting example method that may have one or more of the following benefit. It may reduce the computational burden, reduce the need for exhaustive cross sectional data for each reaction for each target particle across a spectrum of incident particle energies, and/or improve accuracy of current methods. The method 2100 starts at a block 2105. At block 2105, a neighbor to a principal material in a first cell is selected. A principal material is a material of one or more materials in a reactor or reactor cell that may be represented by an agent material. In an embodiment, principal materials may be fission products (elements, isotopes, and/or isomers of isotopes). A principal material might not be well-characterized with respect to a microscopic property such as microscopic cross sectional data. For example, some of the cross sections for scattering, radiative capture, fission, etc. reactions with neutrons of various energies may not be known. Also, the principal's information may be well-known, but for other reasons (such as reducing computational burden), the principal material may be represented by a neighbor material which will act as an agent. The neighbor may be selected from a plurality of agent materials. In an embodiment, multiple neighbors may be selected from the plurality of agent materials to represent the principal material as agents for more than one property. Agent materials are typically well-characterized with regard to pertinent microscopic cross sectional data. In an embodiment, agent materials are actual materials (e.g, isotopes) with empirically determined microscopic quantities. In a further embodiment, agent materials include one or more fictional materials. A fictional material is essentially a collection of fictional values for various cross sections and optionally other properties. A neighbor may be chosen to act as the agent for the principal on one or more of many criteria. Typically, a neighbor has microscopic properties such that a certain density of the neighbor will have similar macroscopic properties as the existing density of the principal. Thus, a neighbor may be selected to act as an agent for the principal based on a comparison of microscopic properties of the principal to the microscopic properties of each of the neighbors. Microscopic properties may be approximated having one or more discrete values with respect to incident particle (e.g., neutron) energy, or may be evaluated as a function of incident particle energy. In an embodiment, the selection of a neighbor or neighbors is limited to a selection from one or more agent materials that are also fission products of the fissions of one or more fissile materials. The fission products may further be limited to fissions induced by neutrons and/or neutrons of certain energy levels. In an embodiment further limiting the selection, potential neighbors may be chosen from agent materials under the same “hump” as the principal material of a fission yield curve (e.g., left curve portion 912 or right curve portion 914 of fission yield curve 900 illustrated in FIG. 9). In an embodiment, the number of potential principal materials is larger than the number of agent materials. For example, the known fission product isotopes number in the thousands. In a further embodiment, the number of agent materials is limited to a relatively small number (e.g., under 100, 50, 30, or 20). In an embodiment, the number of agent materials is limited to 12. In an embodiment, this block is performed by exemplary method 2200 described below. At block 2110, a proxy amount of the selected neighbor or neighbors is determined. As discussed above, a neighbor might have microscopic properties such that a certain density of the neighbor will have similar macroscopic properties as the existing density of the principal. The proxy amount is the amount or density (e.g., concentration) of the neighbor that will serve to represent the principal in a given concentration. As with microscopic properties, macroscopic properties may be approximated as one or more discrete values or as a function of incident particle energy. At block 2115, blocks 2105 and 2110 are repeated for each of a plurality of principal materials in the first cell. In this block, a neighbor or neighbors is/are selected to act as an agent(s) for each of the plurality of principal materials (which may or may not make up all of the materials in the cell). A given agent material may be selected as a neighbor for more than one principal material. Other agent materials may not be selected to be any principal's neighbor. Proxy amounts of each agent are determined for each principal to which the agent is a neighbor. At block 2120, a summed proxy amount for each agent material is determined. In this block, a total proxy amount of each agent is determined based on the proxy amounts for each neighbor of the agent material. For example, suppose an agent material was selected to be the neighbor of three different principal materials. After performance of the previous blocks, the agent may have three proxy amounts (one for each principal). In this block, a summed proxy amount is determined based on the three proxy amounts (e.g., by summing them). At block 2125, a flux in the first cell is determined based on the summed proxy amounts of each agent material the first cell. As described elsewhere herein, for example, a flux may be determined by a transport calculation (e.g., solving neutron transport equations to determine a neutron flux) and may be further based on the summed proxy amounts of each agent material in one or more other cells. The flux may be approximated by one or more discrete values, or may be a continuous function, thus describing a flux spectrum. The flux may be space and/or energy dependent. The flux may be determined by numerical analysis methods including Monte Carlo methods. The average rate of change of the flux may be a weighted average (e.g., as determined by a Runge Kutta method or any other method). The flux may be dependent upon the amount of each of one or more materials in the first cell. Instead of using the actual amounts (e.g., concentrations) of each material in the cell, the calculation instead uses the summed proxy amounts of each agent material. Thus, the cross sectional data and concentrations of the principal materials are accounted for in a flux determination (e.g., neutron transport calculations) by agents having proxy concentrations. In embodiments where the number of agents is relatively small, the computational burden may be reduced significantly. At block 2130, an updated amount of one or more materials (principal or agent) is determined based on the previous amount of the materials and the flux (e.g., the estimated average flux) in the first cell. The one or more materials may be a subset of the materials in the cell. For example, updated amounts may be determined by a transmutation calculation, which may take into account production rates (e.g., based on reactions rates such as fission rates) and decay rates (e.g., using decay constants). The updated amounts for the one or more materials may be solved individually or simultaneously (such as when coupled through transmutation equations). The calculation may include calculating the updated amount based on a specified length of time. At block 2135, a control action for a nuclear reactor is determined. As described above, the control action may be a change (positive or negative) to a local neutronic reactivity of a reactor using any neutron affecting or absorbing features such as movement of neutron absorbing materials or fluids, control rods, etc.; a change in one or more various flow rates for any reason including but not limited to localized or overall reactor power, e.g., the flow of heat absorbing material (e.g., coolant) through the reactor or portions of the reactor by ordering changes in reactor coolant pump operation and/or various valve positions in the reactor system, including but not limited to reactor closures or reactor coolant shutoff valves, steam shutoff valves, etc.; a change in one or more breaker positions (e.g., reactor coolant pump power supply breakers, steam turbine-generator output breakers, etc.); or the like. Other control actions will be apparent to persons skilled in the art based on the teachings herein. The determined control action may be displayed to a user. At block 2140, a control action for the nuclear reactor is performed. As described above, this performance may be automatic or manual. The method stops at block 2140. Referring now to FIG. 22, an illustrative method 2200 is provided for simulating and/or controlling a nuclear reactor. In an embodiment, method 2200 is used to perform block 2105 above. The method 2200 starts at a block 2205. At block 2205, a plurality of potential neighbors is identified. Continuing the description of block 2205, potential neighbors may be limited to materials that are fission products of certain isotopes, perhaps induced by incident particles of a certain energy. In an embodiment, potential neighbors for a given principal may be limited to fission products under the same “hump” of a fission yield curve or curves as the principal. The fission yield curve of interest might be, for example, the curve of one particular fissile material's fission reaction or the curves of multiple fission reactions in any combination of incident particle energy and fissile material. Potential neighbors may also be limited to materials which are characterized to the extent necessary to be suitable as agent materials. In an embodiment, the plurality of potential neighbors for a given principal is chosen by identifying some number (e.g., three) of agent materials having atomic mass numbers (A) “most similar” to that of the principal material. The “most similar” decision may be restricted to agent materials having larger (or smaller) atomic mass numbers. Also, the “most similar” decision may be forced to take at least one smaller and one larger (in atomic mass number) agent material. Potential neighbors having a microscopic cross section of zero or close to zero may be ruled out in some embodiments. At block 2210, a neighbor is selected from the plurality of potential neighbors. Once a plurality of potential neighbors is identified, one or more neighbors may be selected from the plurality. In an embodiment, neighbors may be selected by comparing one or more microscopic properties such as a cross section. Thus, the number of comparisons needed to select a neighbor is limited by the number of materials determined to be potential neighbors in block 2205. The method stops at block 2210. In an embodiment, potential neighbors may be identified by comparing one or more microscopic properties such as a cross section. Potential neighbors having a microscopic cross section of zero or close to zero may be ruled out in some embodiments. Enhanced Neutronics Modeling Now that illustrative embodiments of nuclear reactors and reactor control and simulation have been discussed, including movement and mapping of materials in nuclear reactors, illustrative systems and methods associated with enhanced neutronics modeling will now be discussed. There are a wide variety of conventional codes in use for simulation and modeling of nuclear reactor performance. Fast reactor cross section processing codes include, for example, ETOE-2, MC2-2, SDX. Diffusion and transport theory codes include, for example, DIF3D, DIF3DK, VARIANT, and VIM. Fuel cycle/depletion codes include, for example, REBUS-3, RCT and ORIGEN-RA. Perturbation theory codes include, for example, VARI3D. Thermal-hydraulic codes include, for example, SE2-ANL (SUPERENERGY2). Reactor dynamics and safety analysis codes include, for example, SAS4A, SASSYS-1 and SAS-DIF3DK. Surveillance and diagnostics codes include, for example, MSET and PRODIAG. Stochastic, Monte-Carlo based neutronics modeling codes include, for example, KENO, MONK and various versions of MCNP. The enhanced neutronics modeling in the embodiments described below allows for the creation, maintenance and storage of a standardized set of data describing the state of a nuclear reactor under input conditions established by an operator. The state of the reactor is stored as an abstract nuclear reactor model (ANRM). The abstract nuclear reactor model can be created and maintained regardless of the particular mode of simulation employed by the enhanced neutronics modeling scheme. Maintenance of an abstract nuclear reactor model allows for a number of improvements over conventional, and typically proprietary, neutronics modeling schemes. For example, standardized data reflecting the state of the nuclear reactor allows the information to be easily accessed in format understandable to programmers, modelers, and reactor operators. Importantly, maintenance of an abstract nuclear reactor model characterized with standardized data sets also allows the ability to transform the data into a variety of data structures useable in other, different neutronics modeling schemes for verification. Enabling simple verification of neutronics simulation results across multiple modeling programs greatly improves reliability—an important feature, for instance, when attempting to secure funding for a multi-billion dollar nuclear reactor project. Conventional analysis typically does not allow the raw input data from one particular modeling program to be readily used in another. Such verification analysis has previously been hampered by a lack of a standardized data format. As illustrated, a wide variety of codes currently exist for nuclear reactor simulation and modeling. It is also not uncommon for known code to form the basis for multiple, subsequent, proprietary versions. The result is a plethora of nuclear reactor simulation and modeling programs. They are often proprietary, and they have little or no known interoperability or standardization. Further, the front end of conventional modeling programs (i.e., the means by which the simulation input conditions are described and generated) are typically cumbersome and are within the capability of only the most experienced users. Still further, verification of nuclear reactor simulations, which requires substantially similar results using different programs, is expensive, time consuming, and (at worst) unreliable. This may be unacceptable when billion-dollar investments hang in the balance. There is a need, therefore, for a modeling interface capable of creating standardized data sets that can be used in creating and maintaining an abstract nuclear reactor model. One novel simulation and modeling interface will be described supporting deterministic-type modeling. A Deterministic Modeling Interface One exemplary enhanced neutronics modeling scheme employs a modeling interface for deterministic neutronics modeling. As noted above, an exemplary deterministic modeling program is REBUS-3. REBUS-3 is a system of codes designed for the analysis of reactor fuel cycles. Two basic types of problems are typically solved by REBUS-3: 1) the infinite-time, or equilibrium, conditions of a nuclear reactor operating under a fixed fuel management scheme; or, 2) the explicit cycle-by-cycle, or nonequilibrium operation of a reactor under a specified periodic or non-periodic fuel management program. For the equilibrium type problems, the code uses specified external fuel supplies to load the reactor. Optionally, reprocessing may be included in the specification of the external fuel cycle and discharged fuel may be recycled back into the reactor. For non-equilibrium cases, the initial composition of the reactor core may be explicitly specified or the core may be loaded from external feeds and discharged fuel may be recycled back into the reactor as in equilibrium problems. A novel modeling interface is described that analyzes received reactor modeling data and nuclear reactor simulation data to create and maintain an abstract nuclear reactor model (ANRM). By way of illustration, FIG. 23 shows a nuclear reactor modeling system 2300 comprising of a modeling interface 2310, nuclear reactor modeling data 2320, simulation data 2340, and a database 2360. The modeling data 2320 further includes a plurality of data types 2330-1 to 2330-n. For example, the modeling data 2320 may include nuclear reactor material data 2330-1, geometry data 2330-2 of a portion of the nuclear reactor model or nuclear reactor performance data 2330-n or some portion thereof. In an embodiment, the nuclear reactor material data 2330-1 may include fuel data, structural data, shielding data, coolant data, isotope data, moderator data, and cycle load data. In an embodiment, the nuclear reactor performance data 2330-n may relate to fuel cell swelling, fuel depletion, fission product removal, coolant expulsion and fission gas removal for all, or a portion, of the nuclear reactor under simulation. The simulation data 2340 is generated by one or more simulators 2350-1 to 2350-n. For example, the simulators could include a neutronics simulator 2350-1, a fuel burn simulator 2350-2, or a thermal hydraulic simulator 2350-n. The simulation data 2340 may also be generated by a material performance simulator, a thermal simulator or an atomistic simulator. In an embodiment, the neutronics simulator 2350-1 is a stochastic simulation tool. In a further embodiment, the stochastic simulation tool is based on a Monte Carlo N-Particle transport code (MCNP) simulation tool. In an embodiment, the neutronics simulator 2350-1 may also be a deterministic simulation tool. For example, the deterministic simulation tool is a REBUS simulation tool. In an embodiment, the neutronics simulator 2350-1 interacts with the fuel burn simulator 2350-2 to iteratively produce time dependent nuclear reactor simulation data. The modeling interface 2310 receives the modeling data 2320 as input, sends the modeling data 2320 to any number of simulators 2350-1 to 2350-n, and receives the output simulation data 2340. In an embodiment, the modeling interface 2310 builds an abstract nuclear reactor model (ANRM) 2362 from analyzing both the modeling data 2320 and the simulation data 2340. In an embodiment, the simulation data 2340 may include embedded metadata added by the simulators 2350-1 to 2350-n to determine an additional state of the ANRM 2362. The ANRM 2362 is made up of homogenized assemblies which are made up of axial blocks as will be discussed in further detail. The ANRM 2362 is stored in database 2360 for either subsequent analysis or viewing by the user. In an embodiment, the modeling interface 2310 standardizes the data representing the ANRM 2362 defining structural, behavioral or creational patterns in an object orientated program environment that are sufficient to describe a certain state of the ANRM 2362 as will be discussed in further detail. In an embodiment, once the ANRM 2362 has been created, the modeling interface 2310 may run subsequent cycles, perform safety coefficient generation, run other coupled physics codes (such as thermal hydraulics or fuel performance) and/or produce succinct summaries. As previously mentioned, the modeling interface 2310 uses an object orientated programming environment to build the ANRM 2362 based on inputted data. In an example, object orientated programs include data structures or classes wherein each instance of the class is an object. Various functions can be called upon to retrieve, modify, or add data to each object. Examples of commonly used object orientated programs include C++, Python, and Java. By way of illustration, FIG. 24A shows the fundamental class structure 2400 of the modeling interface 2410. The class structure 2400 comprises: a main operator 2410, a nuclear reactor data structure 2420, an assembly level 2430 comprising of individual assembly structures 2440, and a block level 2450 comprising of individual block structures 2460. Referring to FIG. 24B, in an embodiment, each block structure 2460 is geometrically arranged within an assembly structure 2440. In an embodiment, each block structure 2460 includes one or more material variables. For example, the material variables can include density, flux, power, temperature, and flow. Referring to FIG. 24C, in an embodiment, a single block structure 2460 may include a plurality of locations 2470 for which material variables are stored. The main operator 2410 reads all inputs and builds the ANRM 2362 which is the nuclear reactor data structure 2420 in a certain state. In an embodiment, the main operator 2410 may modify the input by adding metadata for use in determining a first or additional state of the ANRM 2362. In an embodiment, the main operator 2410 further controls and processes typical multi-cycle coupled simulations, fuel performance lookups, history tracking, summary making, fuel management, database interaction and restarts. The nuclear reactor data structure 2420 contains the state of the reactor at any given time. The nuclear reactor data structure 2420 comprises, for example, one or more assembly structures 2440. Data regarding the state of the reactor at any time can be stored in the database 2360. In an embodiment, the nuclear reactor data structure 2420 could further comprise a spent fuel pool structure (not shown). In an embodiment, the nuclear reactor data structure 2420 could further comprise a fuel handling machine structure (not shown). An assembly structure 2440 comprises one or more block structures 2460. The history of an assembly structure 2440 is produced at the end of the building of the ANRM 2362. The history summary may be Lagrangian in nature, following a specific assembly through its path. In an embodiment, an assembly structure 2440 can act like a list and be iterated over or indexed. A block structure 2460 contains the majority of the simulation data and material variables. The histories of both the block structure 2460 and each location 2470 within the block structure 2460 are produced at the end of the building of the ANRM 2362. The history summary of the block structure 2460 may also be Lagrangian in nature while the history summary of the location 2470 within the block structure 2460 may be Eulerian, which is focused on a specific spatial location as assemblies pass through it. Referring now to FIG. 25, an example of a file 2500 to be received by the modeling interface 2310 as input modeling data 2320 is displayed. In an embodiment, the file contains geometry descriptions and locations of each assembly and specifies composition labels of the assemblies that correspond to nuclide-level loading labels. For example, file 2500 shows a reactor 2510 that includes three exemplary assemblies, P0001, E0002, and E0003. Each assembly is shown to further include exemplary composition and geometry data for each block within the assembly. In an embodiment, the file is written in an XML format. Other textual data formats may be used to input modeling data, for example, XHTML, RSS, Atom, and KML. Referring now to FIG. 26, an example of an input graphical user interface (GUI) 2600 used to input modeling data 2320 to the modeling interface 2310 is displayed. In an embodiment, the input GUI 2600 further allows the user to choose which simulators to use and the parameters for each simulation. In an embodiment, the input GUI 2600 includes a plurality of tabs which allow the user to input various parameters. For example, the tabs may include a simulation parameter tab 2610, a reactor parameter tab 2620, a safety calculation tab 2630, a REBUS settings tab 2640, an MCNP tab 2650, a fuel management tab 2670, and a tab for other settings 2660. In an example, the fuel management tab 2670 may include parameter fields regarding how to move and organize the fuel rods around at each cycle. A new job designed to create the ANRM 2362 may be executed from the exemplified input GUI 2600. The code that makes up the entirety of the modeling interface 2310 can be divided into subgroups of functions. For example, the subgroups may include components, modules, and external code interfaces. Table 1 below displays a listing of at least some of the exemplary components included in the code of the modeling interface 2310. In an embodiment, the components contain the basic ANRM 2362 which include the block structures 2660 and the assembly structures 2640. The bulk of the modeling interface code is included in the components. TABLE 1Exemplary listing of modeling interface componentsNameDescriptionassemblies.pyContains Assembly class and many subclasses that deal with Assembly level methods.assemblyLists.pyContains AssemblyList classes that are useful for tracking assemblies that change or discharge from the core.blocks.pyContains Block class and all its methods.database.pyContains Database and Database borg objects that interface with the SQL database for data persistence.fuelHandlers.pyContains FuelHandler object and code relevant to moving fuel around the reactor.operatorFactory.pyContains compositions of the overall main classes. This is where to import from to run a full modeling interface case.historyTracker.py Contains Historylnterface that tracks block and assembly parameters for requested blocks and assemblies. Produces reports of these objects as they move through the core.interfaces.pyContains the base class for all Interfaces.library.pyContains code that can read ISOTXS binary libraries and other such things like SPECTR, etc.locations.pyLocation object code and subclasses. Location objects tell assemblies and blocks where they are in terms of rows/positions, coordinates, indices, etc. Can also find symmetric identicals.armiLog.pyPerforms logging operation to print to the standard output.nucDirectory.pyContains nuclide data like atomic mass, density, Z number, etc.operators.pyContains the main loop and main operators that coordinate most of the modeling interface code.paramSearch.pyContains code that allows many similar cases with a few parameters to be submitted sequentially for parameter search studies.reactors.pyContains the Reactor class, defining the main object that holds the assembly objectssettings.pyContains the case settings object that travels around with all the global settings like power level, etc.skeletallnputs.pyContains large amounts of input that are copied directly or slightly modified into MC**2/REBUS inputs such as burn chains and fission product yields.sodiumRemoval.py Controls sodium bond removal fuel performance coupling.submitter.pyThe GUI modeling interface Submission Control Program. Click this to start a modeling interface run.summarizer.pyAn interface that produces useful summaries during a run.twr_shuffle.pyHandles input parameters and instantiates the proper operator.Utils.pyContains some basic utilities like file cleaningand list searching Table 2 below displays a table with a listing of at least some of the exemplary modules included in the modeling interface code. In an embodiment, the modules contain code that adds physics to the modeling interface 2310 using internal codes. In an example, the thermo module adds temperatures and flow rates to a model that already has power and flux. In another example, the safety coefficient generator module runs the modeling interface in a manner that produces reactivity coefficients. TABLE 2Exemplary listing of modeling interface modulesNameDescriptionerWorth.pyContains code with specialized operator that inserts control rods and produces control rod worth curves.reprocessing.pyContains code that can modify assemblies as a reprocessing plant would, flipping them, refining them, etc.safetyCoefficients.pyThe safety coefficient generator.waveBuilder.pyContains logic that, given an equilibrium case, will try to build enrichment distribution that matches it, building the wave in place, if you will.thermo.pyThermal-hydraulic model that adds flow orificing and temperature distributions to the modeling interface state after power has been computed. Table 3 below displays a listing of at least some of the exemplary external code interfaces included in the modeling interface code. In an embodiment, the external code interfaces are the links between the modeling interface 2310 and the simulators 2350-1 to 2350-n. Examples of simulator programs include, but are not limited to, REBUS, SASSYS, SUPERENERGY, and FEAST. In an embodiment, the external code interfaces may be called upon by the main operator 2610. TABLE 3Exemplary listing of modeling interface external code interfacesNameDescriptioneqRebusInterface.pyInterfaces with the REBUS using fast equilibrium search capabilities built into REBUS. Can get equilibrium state much faster than running many explicit cycles.feastExtract.pyExtracts FEAST relevant fuel performance information from MCNPXT r files.feastInterface.pyInteracts with modeling interface to extract fluxes, powers, etc, and builds FEAST input files for selected assembles. Can also run FEAST.mcnpInterface.pyAllows modeling interface to create MCNP/MCNPXT inputs with shuffling. This contains ability to make homogenized hexes/triangles and pin-detail models.povRayInterface.pyInteracts with POVRay ray tracer to produce high-quality 3-D plots of the core.rebusInterface.pyContains subclasses of Operator and Reactor, etc. that has specific functionality tied to REBUS and MC**2. This produces the inputs, runs the codes, and calls the output-reading classes.rebusOutputs.pyContains the classes that can read and abstract REBUS related output files.sassysInterface.py Contains an interface and Input Writers/Output Readers for SASSYS transient analysis code.superEnergyInterface.pyInteracts with SuperEnergy to produce more detailed thermal hydraulic information. Referring now to FIG. 27, an example of an output GUI 2700 is displayed for multi-dimensional visualization of the current state of the ANRM 2362 stored in the database 2360. In an embodiment, the exemplary GUI 2700 can be used to read the material variables from any block structure 2660 stored in the database 2360 in an explorable manner. In an embodiment, the exemplary GUI can be used to interact in real time with the abstract nuclear reactor model by either modifying/receiving the modeling data 2320 or directing the analysis of the modeling data 2320 and the simulation data 2340. For example, a block level view 2710 is displayed whereby a user may obtain data from each location 2720 within the block structure 2660. It can be appreciated that more than one level within the ANRM 2362 can be viewed simultaneously as exemplified by the multiple view windows depicted in FIG. 27. Referring now to FIG. 28, an illustrative method 2800 is provided for maintaining and standardizing an abstract data model. The method 2800 starts at block 2810. At block 2810, modeling data which represents a first part of a system is received. For example, the modeling data may include nuclear reactor material data, geometry data of a portion of the nuclear reactor model or nuclear reactor performance data or some portion thereof, as fully described above. In an example, the modeling data may be received by a file. The exemplary file can contain geometry descriptions and locations of each assembly and specify composition labels of the assemblies that correspond to nuclide-level loading labels, as fully described above. In an embodiment, each assembly can be shown to further include exemplary composition and geometry data for each block within the assembly. In embodiments, the file may written in an XML format. As previously noted, other textual data formats may be used to input modeling data, for example, XHTML, RSS, Atom, and KML. In another example the modeling data can be received through a GUI. In an embodiment, the GUI can include a plurality of tabs which allow the user to input various parameters. At block 2820, simulation data from a simulator capable of simulating a first part of the system from a first set of simulation parameters is received. As described above, examples of simulators can include a neutronics simulator, a fuel burn simulator, a thermal hydraulic simulator, a material performance simulator, a thermal simulator or an atomistic simulator. At block 2830, the modeling data and the simulation data are analyzed. In an embodiment, the analysis is performed by the modeling interface. At block 2840, intermediate data is generated representing a second part of the system. In an embodiment, the intermediate data is generated by the modeling interface. In an embodiment, the intermediate data represents a state of a nuclear reactor determined by the analysis of the modeling data and simulation data collected by the modeling interface. At block 2850, an abstract data model representing a certain system state and characterized by the modeling data, simulation data, and intermediate data is maintained. In an embodiment, the abstract data model is stored in a nuclear reactor data structure, as previously discussed, further comprising of assembly structures and block structures. At block 2860, the data representing the system state is standardized. In an embodiment, the standardized data contains defined structural, behavioral or creational patterns in an object orientated program environment that are sufficient to describe a certain state of the abstract data model. At block 2870, the data is exported to a database. In an embodiment, the data can be maintained for subsequent system analysis once it has been exported to the database. In an example, the subsequent system analysis may include running subsequent cycles, performing safety coefficient generation, running other coupled physics codes (such as thermal hydraulics or fuel performance) and/or producing succinct summaries. In another embodiment, the data may be viewed by the user as previously discussed. Referring now to FIG. 29, an illustrative method 2900 is provided for controlling a nuclear fission reactor. It will be appreciated that the nuclear fission reactor controlled by the method 2900 may be any nuclear fission reactor as desired, such as without limitation any of the illustrative nuclear fission reactors described above. Referring additionally to FIG. 10, it will also be appreciated that the method 2900 suitably may implemented as computer-readable code executed on a suitable computer, such as the computer system 1000. In this embodiment, the computer system 1000 is coupled to the Reactor Control System 1030. As discussed above, the Reactor Control System 1030 may be directly interfaced to the communications infrastructure 1006 as shown in the figure, or the Reactor Control System 1030 may also be interfaced via communications interface 1024 or communications interface 1024 and communications path 1026, as desired for a particular application. Details of the Reactor Control System 1030 are discussed above and need not be repeated for an understanding. The method 2900 starts at block 2910. At block 2910, modeling data which represents a first part of a system is received. For example, the modeling data may include nuclear reactor material data, geometry data of a portion of the nuclear reactor model or nuclear reactor performance data or some portion thereof, as fully described above. In an example, the modeling data may be received by a file. The exemplary file can contain geometry descriptions and locations of each assembly and specify composition labels of the assemblies that correspond to nuclide-level loading labels, as fully described above. In an embodiment, each assembly can be shown to further include exemplary composition and geometry data for each block within the assembly. In embodiments, the file may written in an XML format. As previously noted, other textual data formats may be used to input modeling data, for example, XHTML, RSS, Atom, and KML. In another example the modeling data can be received through a GUI. In an embodiment, the GUI can include a plurality of tabs which allow the user to input various parameters. At block 2920, simulation data from a simulator capable of simulating a first part of the system from a first set of simulation parameters is received. As described above, examples of simulators can include a neutronics simulator, a fuel burn simulator, a thermal hydraulic simulator, a material performance simulator, a thermal simulator or an atomistic simulator. At block 2930, the modeling data and the simulation data are analyzed. In an embodiment, the analysis is performed by the modeling interface. At block 2940, intermediate data is generated representing a second part of the system. In an embodiment, the intermediate data is generated by the modeling interface. In an embodiment, the intermediate data represents a state of a nuclear reactor determined by the analysis of the modeling data and simulation data collected by the modeling interface. At block 2950, an abstract data model representing a certain system state and characterized by the modeling data, simulation data, and intermediate data is maintained. In an embodiment, the abstract data model is stored in a nuclear reactor data structure, as previously discussed, further comprising of assembly structures and block structures. At block 2960, the data representing the system state is standardized. In an embodiment, the standardized data contains defined structural, behavioral or creational patterns in an object orientated program environment that are sufficient to describe a certain state of the abstract data model. At block 2970, the data is exported to a database. In an embodiment, the data can be maintained for subsequent system analysis once it has been exported to the database. In an example, the subsequent system analysis may include running subsequent cycles, performing safety coefficient generation, running other coupled physics codes (such as thermal hydraulics or fuel performance) and/or producing succinct summaries. In another embodiment, the data may be viewed by the user as previously discussed. At a block 2980, the data is provided to a reactor control system, such as the Reactor Control System 1030. For example, as described above, in an embodiment, the Reactor Control System 1030 may be directly interfaced to the computer system 1000 via the communications infrastructure 1006 as shown in FIG. 10, or the Reactor Control System 1030 may also be interfaced via communications interface 1024 or communications interface 1024 and communications path 1026, as desired for a particular application. It will be appreciated that, regardless of how the interface between the Reactor Control System 1030 and the computer system 1000 is implemented, the result is that the standardized data is provided from the database 2360 (FIG. 23) to the Reactor Control System 1030. The Reactor Control System 1030 may use the provided data to control parameters of the controlled nuclear fission reactor (not shown) as desired, dependent upon the system state of the reactor described in the standardized data and the actual state of the controlled nuclear fission reactor (not shown). For example, in an embodiment the Reactor Control System 1030 may be implemented as the control system 720 (FIG. 7A) and may determine appropriate corrections (positive or negative) to a local neutronic reactivity of the controlled nuclear fission reactor (e.g., to return the controlled nuclear fission reactor to a desired operating parameter, such as desired local temperatures during reactor operations at power) in response to the provided data. To that end, the Reactor Control System 1030 may generate a control signal (e.g., control signal 724) indicative of a desired correction to local neutronic reactivity. In another embodiment, the Reactor Control System 1030 may also control other neutron affecting or absorbing features, such as control rods and/or safety rods, to control and/or shut down the controlled nuclear fission reactor as desired, in response to the provided data. In another embodiment, in response to the provided data the Reactor Control System 1030 may also generate control signals to order changes in various flows, e.g., the flow of heat absorbing material (e.g., coolant) through the reactor or portions of the controlled nuclear fission reactor by ordering changes in reactor coolant pump operation and/or various valve positions in the reactor system, including but not limited to reactor closures or reactor coolant shutoff valves, steam shutoff valves, etc. In an embodiment, the Reactor Control System 1030 may also order changes in breaker positions (e.g., reactor coolant pump power supply breakers, steam turbine-generator output breakers, etc.). In some embodiments, the Reactor Control System 1030 may have temperature inputs (e.g., control system 720 receiving input from temperature detectors 710) in addition to neutron detectors (e.g., to sense neutron flux to determine reactor power or local reactor power at a portion of the core), and flow and position detectors (e.g., venturi-type flow detectors, valve position indicators, breaker position indicators). In such embodiments, in response to the provided data the Reactor Control System 1030 may control the flow of heat absorbing material (e.g., coolant) through the reactor and/or portions of the reactor to control overall temperatures and local temperatures in response to overall reactor thermal power and/or local reactor thermal power. In some embodiments the Reactor Control System 1030 may also provide operator indications and accept operator inputs. In such embodiments, the Reactor Control System 1030 receives the provided data, monitors reactor operations, may provide some automatic control features (such as changing flow rates and moving control rods or otherwise positioning neutron affecting or absorbing materials, which are described in more detail elsewhere herein), displays operational parameters, accepts and executes operator inputs for manual control actions, and/or provides to an operator information indicative of actions (either taken automatically or recommended for manual execution by the operator) based upon operational data from the controlled nuclear fission reactor and the data received from the computer system 1000. With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations are not expressly set forth herein for sake of clarity. While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. Furthermore, it is to be understood that the claimed subject matter is defined by the appended claims. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. With respect to context, even terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise. The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, “operatively coupled,” or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components, and/or wirelessly interactable, and/or wirelessly interacting components, and/or logically interacting, and/or logically interactable components. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. |
|
abstract | The present invention provides a method of operating a Boiling Water Reactor, having the steps of analyzing LPRM signals for oscilliatory behavior indicative of neutron-flux-coupled density wave oscillations, determining if oscilliatory behavior is present in the signals; initiating a reactor protective corrective action if the oscilliatory behavior is determined, and in addition, initiating corrective actions if neutron uncoupled oscillations are possible. Detecting the later is performed through analytically determined exclusion zone on the power flow map or by on-line stability calculations for several high power channels. |
|
description | This application is based on and claims priority from European Patent Application 01309445.3 filed on Nov. 7, 2001, the contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to a piezoelectric actuator and to a lithographic projection apparatus. 2. Description of Related Art The term “patterning structure” as here employed should be broadly interpreted as referring to a structure that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term “light valve” can also be used in this context. Generally, the said pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning structure includes: A mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired. A programmable mirror array. An example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the said undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using a suitable electronic structure. More information on such mirror arrays can be gleaned, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference. In the case of a programmable mirror array, the said support structure may be embodied as a frame or table, for example, which may be fixed or movable as required. A programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required. For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table; however, the general principles discussed in such instances should be seen in the broader context of the patterning structure as hereabove set forth. A lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning structure may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion in one go; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus—commonly referred to as a step-and-scan apparatus—each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the “scanning” direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally <1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference. In a manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book “Microchip Fabrication: A Practical Guide to Semiconductor Processing”, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4, incorporated herein by reference. For the sake of simplicity, the projection system may hereinafter be referred to as the “lens”; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a “lens”. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such “multiple stage” devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Twin stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, incorporated herein by reference. To reduce the size of features that can be imaged, it is desirable to reduce the wavelength of the projection beam of radiation. It has been proposed to use wavelengths of less than about 200 nm, for example 193 nm, 157 nm or 126 nm. Further reductions in the wavelength to the range of EUV (extreme ultra-violet radiation, e.g. having a wavelength in the range of 5–20 nm) are envisaged. EUV radiation in particular is more conveniently focused and controlled by reflective optics, such as mirrors. However, mirrors in lithography apparatus must be positioned to especially high accuracy, as compared to refractive elements, because any rotational orientation errors are magnified by the total downstream optical path length. In any apparatus using very short wavelength radiation, the optical path length may be of the order of 2 m or more. For example, to have a good overlay performance, it can be necessary to keep the position of an image of an irradiated portion of the mask stable at a given position at substrate level with an error (e) of less than about 1 nm in particular when EUV is used. If the distance between the mirror and the substrate is 2 m the maximum permissible rotational error of the reflected beam, to keep the system within specification, is 28×10−9 degrees (1×10−9 m/2 m=tan(28×10−9 degrees)), if e=1 nm. Since, for a mirror, the angle of reflection equals the angle of incidence, a rotational error in the position of the mirror will give rise to twice as large an error in the direction of the reflected beam. Thus, the mirror must be positioned with an accuracy of 14×10−9 degrees or better. If the mirror has a width of order 0.1 m and a rotating point at one side, that rotating point must be positioned to within 0.024 nm (tan 14×10−9×0.1=2.4×10−11). Clearly, the accuracy with which such a mirror must be orientated is extremely high and will only increase as the specification for image accuracy increases. The accuracy requirements for position in X, Y and Z are less demanding, as such errors are magnified less at substrate level, but still remain high. A projection system for a scanning EUV lithographic projection apparatus may include six mirrors, for example, for reflecting and thereby projecting the patterned beam onto a target portion of the substrate. In this case, the mirrors are to be positioned relative to each other with an accuracy of about 0.1 nm. It has been proposed before to use a plurality of one dimensional actuators for adjusting the position and/or orientation of a reflective optical element. For example, a corresponding arrangement is described in EP 1107068 A2. This document describes the use of position sensors to maintain the reflective element stationary in spite of vibrations that might occur. In particular, the actuators or other components of the lithographic projection apparatus, such as a gravity compensator, might cause such vibrations. A reflective or refractive optical member has six independent degrees of freedom (DOF)—three transitional and three rotational. One possibility to adjust the optical member with respect to more than one DOF is to use a plurality of actuators. The actuators may be piezoelectric, electro-resistive or magneto-resistive and act, for example, perpendicularly to a surface of the optical member which extends transversely to the beam of radiation incident at the optical member. In the past a plurality of one degree of freedom inch-worms have been used to position the reflective or refractive optical member. In a typical one-dimensional inch-worm actuator four piezoelectric stacks (two opposed pairs) surround a central cylinder which is connected to an actuation rod comprising decoupling portions. Each piezo stack comprises 2 layers of which one is capable of expanding/contracting and the other is capable of shearing in one direction. The central cylinder and the actuation rod which is connected to e.g. a central pin (which in turn is connected to the optical member) can be moved only in the axial direction. These one-dimensional actuators themselves may surround a central pin in opposed pairs to make the arrangement more robust. Breakage of a decoupling portion in one of the one-dimensional actuators leads to failure of the whole actuator. The reason that each one-dimensional actuator must be opposed by another one-dimensional actuator is that a non-symmetric arrangement can lead to over-burdening of a single decoupling portion in an actuator. This requirement makes the whole actuator quite large. In order to provide the optical member with the necessary six degrees of freedom, twelve one-dimensional inch-worm actuators are used in a hexapod arrangement. This results in an eccentric construction that takes up considerable space within the lithographic apparatus. It is an aspect of the present invention to provide a piezoelectric actuator which is compact and multi functional. This and other aspects are achieved according to the invention in a piezoelectric actuator including two outer plates, an inner plate positioned between the two outer plates, and at least two piezoelectric stacks positioned on at least one side of the inner plate between the inner plate and one of the two outer plates. The outer and inner plates are substantially parallel and the outer plates are biased towards each other by a compression structure. Such an actuator has the advantage of being compact and is capable of positioning an object in two substantially orthogonal directions. It further requires fewer piezoelectric stacks than four one-dimensional actuators of the prior art. This results in a more compact design. Additionally, if a membrane-like portion extending from the inner plate to a central pin is provided, the design is more robust than conventional designs because it does not require as many decoupling portions as the actuators of the prior art. According to a preferred embodiment, the at least one piezoelectric actuator is an inch-worm actuator. An inch-worm actuator is an actuator which has a plurality of piezoelectric stacks each comprising at least two layers. One of the layers is for contracting/expanding and another one is for shear. If further layers are present, they can be orientated for shear in different directions to those already present. An inch-worm actuator positioned between two plates and attached to one of those plates makes it possible to move the other of those plates relative to the one with a stepping motion of the inch-worm resulting in a relatively large displacement. The inch-worm actuator also enables relatively small displacements (in sub-nm range) just by shearing one of the layers in each piezo stack, while the stacks are still in contact with both plates. It is also an aspect of the present invention to provide a lithographic projection apparatus in which the structure for moving the optical member is compact. This and other aspects are achieved according to the invention in a lithographic apparatus that includes a radiation system for supplying a projection beam of radiation; a support structure for supporting a patterning structure, the pattern structure serving to pattern the projection beam according to a desired pattern; a substrate table for holding a substrate; and a projection system for projecting the patterned beam onto a target portion of the substrate. At least one of the radiation system and the projection system includes at least one optical member and a piezoelectric actuator for positioning the optical member. The piezoelectric actuator is constructed and arranged to position the optical member in two substantially orthogonal directions. A two-dimensional piezoelectric actuator has layers of piezoelectric material orientated in at least three different directions. Preferably those three different directions are substantially orthogonal. The layers of piezoelectric material of the two-dimensional actuator are generally stacked two or three on top of each other and those stacks may be positioned in a plane. The optical member is, for example, a mirror or a lens. The at least one piezoelectric actuator serves to position the optical member relative to the projection beam or the pattern beam with an accuracy of up to 0.03 nm or better. Preferably the optical member is supported by a mounting frame, the frame extending in a plane transverse to a path for radiation to or from the optical member and the frame thereby enclosing, within said plane, the optical member, wherein the optical member is connected to the frame and the frame is connected to said at least one piezoelectric actuator. Thus, by attaching at least three piezoelectric actuators to the frame member it is possible to achieve the desired six degrees of freedom (three transverse and three rotational). According to a further aspect of the invention there is provided a device manufacturing method including providing a substrate that is at least partially covered by a layer of radiation-sensitive material; providing a projection beam of radiation using a radiation system; using patterning structure to endow the projection beam with a pattern in its cross-section, projecting the patterned beam of radiation onto a target portion of the layer of radiation-sensitive material; using at least one optical member for at least one of reflecting and refracting the projection beam of radiation or the patterned beam; and positioning said optical member in a plane by using at least one piezoelectric actuator which is constructed and arranged to position the optical member in two substantially orthogonal directions. In a preferred embodiment, the method includes adjusting the propagation direction of the propagation beam of radiation or the patterned beam by adjusting at least one of the position and the orientation of the optical member. Although specific reference may be made in this text to the use of the apparatus according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle”, “wafer” or “die” in this text should be considered as being replaced by the more general terms “mask”, “substrate” and “target portion”, respectively. In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g. having a wavelength in the range 5–20 nm) as well as particle beams, such as ion beams or electron beams. In the Figures, corresponding reference symbols indicate corresponding parts. Embodiment 1 FIG. 1 schematically depicts a lithographic projection apparatus 1 according to a particular embodiment of the invention. The apparatus 1 includes a radiation system Ex, IL, for supplying a projection beam PB of radiation (e.g. EUV radiation), which in this particular case also comprises a radiation source LA; a first object table (mask table) MT provided with a mask holder for holding a mask MA (e.g. a reticle), and connected to a first positioning structure PM for accurately positioning the mask with respect to item PL; a second object table (substrate table) WT provided with a substrate holder for holding a substrate W (e.g. a resist-coated silicon wafer), and connected to a second positioning structure PW for accurately positioning the substrate with respect to item PL; and a projection system (“lens”) PL (e.g. a refractive or catadioptric system or a reflective system) for imaging an irradiated portion of the mask MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. As here depicted, the apparatus 1 is of a reflective type (i.e. has a reflective mask). However, in general, it may also be of a transmissive type, for example (with a transmissive mask). Alternatively, the apparatus 1 may employ another kind of patterning structure, such as a programmable mirror array of a type as referred to above. The source LA (e.g. an undulator or wiggler provided around the path of an electron beam in a storage ring or synchrotron, or a mercury lamp) produces a beam of radiation. This beam is fed into an illumination system (illuminator) IL, either directly or after having a traversed conditioning structure, such as a beam expander Ex, for example. The illuminator IL may comprise an adjusting structure AM for setting the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the beam. In addition, it will generally comprise various other components, such as an integrator IN and a condenser CO. In this way, the beam PB impinging on the mask MA has a desired uniformity and intensity distribution in its cross-section. It should be noted with regard to FIG. 1 that the source LA may be within the housing of the lithographic projection apparatus 1 (as is often the case when the source LA is a mercury lamp, for example), but that it may also be remote from the lithographic projection apparatus 1, the radiation beam which it produces being led into the apparatus 1 (e.g. with the aid of suitable directing mirrors); this latter scenario is often the case when the source LA is an excimer laser. The current invention encompasses both of these scenarios. The beam PB subsequently intercepts the mask MA, which is held on a 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 portion C of the substrate W. With the aid of the second positioning structure PW (and an interferometric measuring structure IF), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the beam PB. Similarly, the first positioning structure PM can be used to accurately position the mask MA with respect to the path of the beam PB, e.g. after mechanical retrieval of the mask MA from a mask library, or during a scan. 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. 1. However, in the case of a wafer stepper (as opposed to a step-and-scan apparatus) the mask table MT may just be connected to a short stroke actuator, or may be fixed. The depicted apparatus 1 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 “flash”) onto a target portion C. The substrate table WT is then shifted in the x and/or y directions so that a different target portion C can be irradiated by the beam PB. 2. In scan mode, essentially the same scenario applies, except that a given target portion C is not exposed in a single “flash”. Instead, the mask table MT is movable in a given direction (the so-called “scan direction”, 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=¼ or ⅕). In this manner, a relatively large target portion C can be exposed, without having to compromise on resolution. FIG. 2 shows a (two-dimensional) piezoelectric actuator 10 for moving an optical member, in particular a mirror, for refracting and/or reflecting radiation that is incident on the circular surface of the optical member. The two-dimensional piezoelectric actuator 10 comprises a first outer plate 20 and a second outer plate 25. The outer plates 20, 25 may be part of another component of the lithographic projection apparatus 1. An inner plate 30, is positioned between and substantially parallel to the first and second outer plates 20, 25. A compression structure, in the illustrated embodiment in the form of springs 35 connected between the outer plates 20, 25 at each corner, pulls the outer plates 20, 25 together. Four piezoelectric stacks 40 (so called “inch-worms”) are positioned on each side of the inner plate 30 between the inner plate 30 and an outer plate 20, 25. This is the preferred arrangement. However, it is possible to provide four piezoelectric stacks 40 on one side of the inner plate 30 and not on the other side. On the side without piezoelectric stacks, a guide structure is provided which allow low friction movement between the inner plate 30 and the respective outer plate 20, 25. This low friction movement may be provided by the guide structure such as grease or ball-bearings. Furthermore, the inner plate 30 may be much larger than illustrated in FIG. 2. For example, the inner plate 30 may be part of a force frame. The four piezoelectric stacks 40 are positioned along the edges of the plates 20, 25, 30. Each piezoelectric stack 40 is comprised of three layers of piezoelectric material. Each layer of piezoelectric material is orientated such that it is capable of expanding or contracting in only one direction, that direction being orthogonal to the direction in which the other two layers of the piezoelectric material in the stack can shear. The directions are indicated by arrows 42, 43 and 44 in the enlarged section of the view. Thus, on electric stimulation, each of those layers accommodates movement in a different direction. In the preferred embodiment, two of the directions are in the same plane as the plates 20, 25, 30. A central pin 50 is attached to the inner plate 30. This necessitates a cut-out 55 in the first outer plate 20 through which the central pin 50 extends. The central pin 50 is attached to the optical member whereas the second outer plate 25 is attached to components of the lithographic apparatus 1. This embodiment requires only eight piezoelectric stacks 40 and the three plate configuration is more compact than a two-dimensional actuator using four one-dimensional actuators as described in the introduction. It is preferred that a cut-out 60 is provided in the center of the inner plate 30. In the cut-out, a membrane 17 is inserted and firmly connected at its outer circumference to the rim of the cut-out area. The membrane 17 can be sheet-like, but a configuration of members 18 shown in FIG. 2 is preferred. The membrane 17 comprises a plurality of spokes 18 which extend between the rim of the cut-out area and the central pin 50. The number and dimension of the spokes 18 may vary, and can, in particular, be adjusted to adjust the de-coupling properties of the membrane 17. Generally, de-coupling means that the optical member is de-coupled from adverse mechanical conditions which may apply to the two-dimensional piezoelectric actuator, such as vibrations or undesired forces that act on the two-dimensional piezoelectric actuator. Furthermore, the shape of the spoked membrane can be different, for example, the spokes 18 may be connected to a ring-like portion of the membrane at the outer and/or inner circumference of the membrane. By providing spokes 18, forces in the four remaining degrees of freedom are decoupled, thereby reducing the quantity of parasitic forces by a factor of about 5 relative to a two-dimensional actuator comprising four one-dimensional actuators as described in the introduction. Moreover, the spokes 18 have an additional advantage that the membrane 17 will still work when one (or a few) spokes are broken. The inner plate 30 and the membrane 17 may be a single part, for example made of a block of the same material. However, it is preferred that at least the membrane 17 is manufactured separately from the inner plate 30 and are connected in a later manufacturing step to the inner plate 30. A second embodiment of two-dimensional actuator is illustrated in FIG. 3. In the embodiment illustrated in FIG. 3 the central pin 50 of the first embodiment illustrated in FIG. 2 is not required. This is because a further inner plate 300 with a central cut out 600, is supported by a membrane 17 extending between the outer periphery of the inner plate 30 and the inner peripheral surface of the central cut out 600. Four piezoelectric stacks 40 are positioned between the inner plate 30 and the outer plate 20. Tensioning by springs 35 between the outer plates 20, 25 is accomplished by leaving gaps in the membrane 17 such that the springs may pass through central cut out 600. In this way, movement of the inner plate 30 relative to the outer plates 20, 25 is transferred to the further inner plate 300 via decoupling membrane 17. Movement of the inner plate relative to the outer plates for embodiments illustrated in FIGS. 2 and 3 will now be described with reference to FIG. 4. FIG. 4 is schematic in that it is an unwound cross-sectional view of the actuator illustrated in FIG. 2 so that the stacks 40 are more clearly illustrated in a row rather than partly/wholly obscured by one another. Each of the piezoelectric stacks 40 are attached, preferably by gluing, to their corresponding outer plate 20, 25. The individual layers 42, 43, 44 of each piezoelectric stack 40 are also adhered to one another, preferably by gluing. The piezoelectric stacks 40 are not adhered to the inner plate 30. FIG. 4A illustrates the equilibrium position in which all piezoelectric stacks 40 are in contact with both the inner plate 30 and their respective outer plate 20, 25. In order to move the inner plate 30 to the right, two piezoelectric stacks 40 on each side of the inner plate 30 are shortened by actuation of the piezoelectric layer which is orientated in such a direction that contraction/expansion occurs perpendicular to the plane of the plates 20, 25, 30. This is achieved by energizing layers 42 of the second and fourth stacks from the left such that those layers contract (FIG. 4B). Only two piezoelectric stacks 40 on each side of the inner plate 30 are actuated in this way such that the unactuated stacks maintain the distance d between the first and second outer plates 20, 25 constant. FIG. 4C illustrates the next stage. The piezoelectric layer 43 (which is orientated in such a direction that it expands/contracts to the left or right) of the already contracted stacks 40 (i.e. the second and fourth from the left) is actuated. This results in a displacement of the bottom layer 42 of the second and fourth stacks 40 to the left. After this stage, the second and fourth stacks from the left are brought back into contact with the inner plate 30 by deactivating the layer 42 which is orientated in a direction of expansion/contraction perpendicular to the plane of the plates 20, 25, 30. This is illustrated in FIG. 4D. In FIG. 4E the next stage is illustrated in which the first and third stacks from the left have their lower layer 42 actuated such that they no longer contact the inner plate 30. The final movement is illustrated in FIG. 4F where the middle layer of the second and fourth stacks 40 from the left is deactivated such that it returns to its original shape. Because the inner plate 30 is gripped between the second and fourth stacks 40 from the left on both sides, when the piezoelectric layer 43 of those stacks is deactivated the inner plate 30 moves to the right with respect to plates 20, 25. Each step can result in a movement of the inner plate 30 relative to the outer plates 20, 25 of between 1 to 4 μm. If further movement to the right is needed this can either be accomplished by activating the middle layer 43 of the first and third stacks and proceeding through the stages illustrated in FIGS. 4D and E except for performing those acts illustrated on the second and fourth stacks on the first and third stacks and visa versa. Alternatively, the piezoelectric layer 42 of the first and third stacks from FIG. 4F can be deactivated such that further movement is achieved by taking stages illustrated in FIGS. 4A to F once again. It will be appreciated that if the other layer 44 which is orientated in a direction of expansion/contraction parallel to the plane of the plates 20, 25, 30 is actuated, movement in/out of the page can be achieved. Of course composite movement can also be achieved. The above described stepping motion with reference to FIG. 4 results in a relatively coarse adjustment of position. Fine adjustment of position is possible by shearing individual layers of the piezoelectric stacks by an amount effective to bring around the desired movement whilst those stacks are kept in contact with the relevant plate 20, 25, 30. FIG. 5 illustrates a third embodiment of two-dimensional actuator. In the embodiment illustrated in FIG. 5, the structure of the outer plates 20, 25 and inner plate 30 as well as of central pin 50 is the same as that of the first embodiment. The difference lies in the piezoelectric stacks 40. In the embodiment illustrated in FIG. 5 there are only four piezoelectric stacks 400, 401. All four of those stacks only comprise two piezoelectric layers. All four stacks have one piezoelectric layer which expands/contracts to bring the piezoelectric stack into and out of contact with the inner (or outer) plate 20, 25, 30. The second layer of each of the stacks 400, 401 is orientated for shear. Two of the stacks 400 have layers orientated for shear in the X direction and the other two of the stacks 401 have layers orientated for shear in the Y direction which is perpendicular to the X direction. The piezoelectric stacks 400, 401 are preferably positioned on both sides of the inner plate 30, but the stacks can also be positioned merely on one side of the inner plate. In such cases, on the other side of the inner plate 30 a bearing structure between the inner plate 30 and the outer plate 20, 25 is provided to keep those plates a constant distance apart such as grease or ball-bearings. Coarse movement in the X and Y direction can only be performed separately. For example, for coarse movement in the X direction whilst the inner plate 30 is supported by the Y stacks 401, one layer of the X stacks 400 contracts and the other layer shears. On expansion of that expansion/contraction layer, the X stacks 400 re-engage with the inner plate 30. On contraction of the expansion/contraction layer of the Y stacks 401 and shear of the shear layers in the X stack 410, the plate 30 will move in the X direction. Repetition of these steps results in a stepping of the inner plate 30 in the X direction. Movement in the Y direction is accomplished in a similar manner. Fine movement of the actuator illustrated in FIG. 5 is possible in one of two ways: the first way for movement in the Y direction is for the X piezoelectric stacks 400 to have the expansion/contraction layer contracted such that they no longer contact the inner plate 30. Fine movement in the Y direction is then performed by analogue adjustment of the shear of the shear layer in the Y stacks 401. The alternative method for fine adjustment is to leave all four stacks 400, 401 in contact with the inner plate 30 and shear the shear layers of the Y stacks. In this case, the friction of the X stacks must be overcome by the shear layers of the Y stacks 401. In this way, the piezoelectric stacks are generally under strain during fine movement. In all of the embodiments illustrated in FIGS. 2, 3 and 5, the piezoelectric stacks are placed symmetrically around the membrane 17. This arrangement is most preferred but is not in fact essential and the piezoelectric stacks may be arranged asymmetrically. In fact, with the appropriate bearing structure on each side of the inner plate 30 to maintain a constant plate separation, it can be seen that the two-dimensional actuator could comprise only two, three layer piezoelectric stacks. FIG. 6 illustrates a mounting frame 11 having a triangular frame structure. An optical member 13 e.g. a multi layer mirror for EUV radiation, is connected in the center of the mounting frame 11. The mounting frame 11 comprises three corner blocks 15 that are positioned at the three corners of the triangular structure. Each corner block 15 is connected to a central pin 50 of a two-dimensional piezoelectric actuator 10. Each of the two-dimensional piezoelectric actuators 10 are positioned such that their plane of movement is perpendicular to the page as illustrated in FIG. 6. This arrangement allows translation of the optical member 13 in two dimensions in the plane of the page as well as rotation in the plane of the page. This is accomplished by translation of the central pins 50 of the two-dimensional piezoelectric actuators 10 in the plane of the page. Movement of the central pins 50 perpendicularly to the page allows height adjustment of the optical member 13 in one dimension and further allows rotation of the optical member 13 in two further dimensions. Thus, with the mounting frame 11 arranged as illustrated in FIG. 6, the optical member 13 may be accurately positioned with six degrees of freedom. In the illustrated embodiment, the central pins 50 are shown oversized. In order to maintain high stiffness, the central pin 50 must be kept as short as possible so that the distance between the membrane of the piezoelectric actuator and the mounting frame 11 is as small as possible. Alternatively, the mounting frame 11 is connected to one of the outer plates, whereby the central pin 50 extends in a direction away from the mounting frame 11 and is connected to another part of the apparatus. In the preferred embodiment, the position or the corner of the mounting frame coincides with the center of the membrane. Whilst specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The description is not intended to limit the invention. |
|
claims | 1. A fuel assembly for a boiling water reactor, comprising:a fuel assembly foot formed of a sieve plate with an opening passing therethrough and a frame part surrounding said sieve plate;a water channel having a lower end carrying a stopper formed with a bore and being attached to said fuel assembly foot;a skirt integrally formed on an underside of said stopper, surrounding said bore and extending into said opening in said sieve plate;a bush having a first and a second longitudinal section, said second longitudinal section projecting into said opening in a rotationally-fixed manner, said bush having a radial shoulder disposed between said first and second longitudinal sections and bearing directly against the underside of said sieve plate; anda threaded bolt of a screw passing through said bush and engaging in a thread of said bore of said stopper. 2. The fuel assembly according to claim 1, wherein said skirt has a polygonal contour and a region of said opening in said sieve plate, which surrounds said skirt, has a cross-sectional area complementary said polygonal contour. 3. The fuel assembly according to claim 1, wherein mutually facing end faces of said second longitudinal section of said bush and of said skirt bear against one another, and wherein said bush and said skirt have respective lengths so as to define a gap between an underside of said stopper and an upper side of said sieve plate. 4. The fuel assembly according to claim 1, wherein said bush is mounted in said opening in a rotationally-fixed manner and said screw is connected to said bush in a rotationally-fixed manner. 5. The fuel assembly according to claim 4, wherein said second longitudinal section of said bush has a polygonal contour and a region of said opening in said sieve plate, which surrounds said bush, has a cross-sectional area complementary thereto, and wherein a circumferential region of said first longitudinal section has a radially inwardly facing plastic deformation interacting with a head of said screw in a torque-locking manner. 6. The fuel assembly according to claim 5, wherein said threaded bolt has a thread-free collar extending away from said head and bears against an inner face of said first longitudinal section of said bush by an outer circumferential face thereof. 7. The fuel assembly according to claim 1, wherein said skirt extends into said opening and said skirt has a skirt contour and a region of said opening in said sieve plate, which surrounds said skirt, has a mating contour for said skirt contour to rotational fix said stopper. 8. The fuel assembly according to claim 1, wherein said underside of said stopper presses against an upper side of said sieve plate. |
|
049960210 | abstract | A pressurized water reactor fuel assembly (10) has a fastener or bolt (40) of stainless steel with a longitudinal groove (48) attaching zircaloy guide tubes (16) to stainless steel lower end fitting (14). The guide tubes have internally threaded zircaloy plugs (52) for mating with the threads (46) of bolt (40) with points (50) created in the threads (46) by groove (48) providing increased friction. The groove (48) acts to accommodate stresses set up by differential thermal expansion of zircaloy and stainless steel. Apertured stainless steel cups (60) receive the plugged ends of guide tubes (16) to capture them and provide connections to lower grid (22) of stainless steel. |
description | The present invention relates to a nuclear fuel assembly body and a nuclear fuel assembly with such a body. Power stations which produce energy from nuclear fission reactions use fuel elements in which fission reactions occur which release caloric power. This power is extracted from the elements by heat exchange with a heat transfer fluid which cools them. The fuel elements are in the form of fuel pins collected into bundles, where these bundles are housed in a body, and where the entire unit forms a fuel assembly. Different types of assembly exist, depending on the operational and performance conditions of the reactors. As part of the development of new-design reactors, known as IVth generation reactors, fast neutron reactors cooled either by a heat transfer gas, RNR-G (Gas Heat Transfer Reactor), or by sodium, RNR-Na. An assembly of a known type for a sodium-cooled fast neutron reactor core comprises, from base to top: a cylindrical foot of circular section used for positioning and holding the assembly in a pillar of the diagrid used as the core's cold sodium feed manifold. All the core's assemblies rest on the diagrid, and are positioned next to one another, a monolithic body consisting of a cylindrical tube of regular hexagonal section extending between the foot and the upper neutron protection which will be described below. The body contains a bundle of sheathed pins enclosing a fissile and/or fertile material, where the pins are generally kept regularly spaced, a cylindrical solid block of regular hexagonal section consisting of one or more materials preventing neutron leaks in the upper part of the core, where the end of this block also forms a gripper head for gripping the entire assembly. In addition, a channel traverses this block from base to top to drain off through the head the sodium flow cooling the assembly. This unit is called an upper neutron protection or PNS. Each assembly can be removed individually, and can be removed from or installed on the diagrid according to the reactor's operational requirements, notably for operations to reload it. In position on the diagrid, the assemblies are traversed in the core by the liquid sodium; the sodium penetrates into each assembly through the apertures designed for this purpose around the foot, and flows from base to top from the foot, and exits through the upper neutron protection whilst cooling the bundle of fuel pins or fertile pins as it passes through the body. The current embodiments of sodium-cooled fast neutron reactors in the world have fuel assemblies with a body comprising a metal monolithic hexagonal tube, usually made of austenitic, ferritic or ferritic/martensitic stainless steel. The body accomplishes two main functions guaranteeing the satisfactory operation of the assemblies and of the core. Firstly, the body mechanically connects the foot to the upper neutron protection. It is thus responsible for the integrity of the assembly when it is gripped by the upper neutron protection. It also gives rigidity to the unit, enabling it to be held when the foot is assembled in the diagrid. Secondly, the tube guides the flow of cooling fluid required to cool the fuel bundles and/or fertile bundles from base to top, and controls the hydraulic diameters in each section of the assembly. Indeed, maintenance of the hydraulic diameters is an important condition to guarantee stability of operation. The tube's diametrical deformation must therefore be limited. It is designed so as to form a pressure tube. The body also accomplishes secondary functions the aim of which is to make the functions of the other constituents more robust, and to raise globally the level of operational safety of the assemblies and of the core. Since the body forms an integral part of the core, the material of which it is made is chosen so as to be a material which is neutronically compatible with obtaining a fast flow and with the volume power density sought in the core. In addition, it provides a protective mechanical confinement of the fuel elements constituting the assembly, protecting them from all risks of damage during the lifetime of the assemblies, such as during manufacture, transport and handling, and during reactor operation and during the cycle outside the reactor as a used fuel assembly. The hexagonal section of the tube enables a hexagonal compact network to be produced, and a high geometrical compactness of the components and, by this means, a critical mass to be obtained with a high volume density of fissile nuclei. In addition, a material to construct the body is chosen which minimises the presence of materials which are unfavourable for neutron reactions. Materials with satisfactory mechanical properties are thus chosen, and among these those which have the least impact on the neutron reactions. In the case of bodies of sodium-cooled fast neutron reactor assemblies, the steels chosen are stainless steels of austenitic, ferritic or ferritic/martensitic grades. As for the pressure tube function, the thickness of steel is chosen which is appropriate for the internal pressure. Consequently, the current assembly bodies consist of a monolithic tube with a hexagonal section, the material of which is the least unfavourable for the neutron balance, and the thickness of which is able to withstand the internal pressure. In the case of fourth-generation reactors, an improvement of performance and an improvement of core safety are sought, notably during accidental sequences. It is sought, notably, to produce assembly bodies with increased resistance to thermal creep and to the effects of high, fast fluence (E>0.1 MeV). The effect of fast fluence is to degrade the mechanical properties and to cause deformations, for example a radiation creep and swelling. The stainless steels used currently are suitable for the operating temperature range 380° C.-700° C., which is the temperature range of RNR-na reactors. Outside this normal operating temperature range, the mechanical properties of steel rapidly degrade around 850° C.-900° C., which are temperatures which can be attained by RNR-gas reactors, which greatly degrades the capacity of the body to maintain its mechanical functions. The melting point of steel is around 1400° C., i.e. well below that of the fuel. Refractory materials exist which are capable of withstanding these temperature levels; however they are incompatible from a neutron standpoint. It is, consequently, one aim of the present invention to provide a nuclear fuel assembly, and more specifically an assembly body, capable of meeting the mechanical conditions at temperatures higher than those of the operating temperatures, and in which there is minimal presence of materials which are unfavourable to neutron reactions in the reactor core. The aim set out above is attained by a composite assembly body comprising end elements connected by a metal structure with slots, and a central cylinder made from a ceramic material, the negative influence of which on the neutron reactions is reduced, and where this material can even have a positive influence. In other words, the assembly body comprises two metal end sleeves, an external metal structure which is perforated over the fissile height, and an internal structure made from a ceramic material constituting the hydraulic channel over the fissile height. By producing a composite body, it is possible to achieve a functional optimisation of each sub-assembly. Through use of the present invention, it is possible to optimise the choice of the constituent materials in order to improve the neutron balance of the fissile volume of the core through its atomic composition by reducing the presence of species negatively influencing the balance, and by increasing more favourable species, with a positive influence, or at least a less negative influence. Indeed, by producing an openwork frame which has only a mechanical role, it is possible substantially to reduce the volume fraction of materials having a negative influence on the neutron balance. By means of this structure with ceramic sleeves, the flow of fluid cooling the bundle of fuel elements is confined, whilst at the same time the hydraulic sections are controlled in the top part of the bundle. In addition, the tubular geometry produced in this fashion forms a continuous or near-continuous wall around the bundle, guaranteeing that the axial flow is contained in the bundle. In the case of a near-continuous wall, a certain acceptable rate of radial leaks can appear close to the inter-assembly zones. Advantageously, the shape of the joint planes between the ceramic segments, and their positioning facing non-perforated sections of the frame are such that they enable the radial leaks to be regulated. The subject-matter of the present invention is then mainly a nuclear fuel assembly body intended to contain nuclear fuel pins, where said body of lengthways axis comprises a first tubular sleeve and a second tubular sleeve made from a metal material form the lengthways ends of the assembly body, where a frame made from a metal material connects the first and second sleeves, where the frame is openworked, and where a ceramic tubular internal structure is positioned between the first and second sleeve inside the frame. In an example embodiment, the internal structure prevents any leakage of the cooling fluid intended to pass along it. In another example embodiment, the internal structure comprises calibrated leakage zones. For example, the internal structure comprises segments which are superimposed lengthways, where the two segments positioned at both ends of the internal structure partially penetrate into the first and second sleeves. Advantageously, the segments are socketed into one another. The lengthways ends of the socketed segments may have, in the case of one, a groove and, in the case of the other, a rib of a matching shape. The frame is formed, for example, by the assembly of struts defining windows. The frame can comprise axial and crossways struts. Advantageously, the crossways struts cover zones where the segments are connected. The frame can be attached to the sleeves by welding and/or a mechanical assembly, where the latter is, for example, of the dovetail type. The frame according to the present invention can be formed by a tube perforated with drill holes forming circular or oblong slots. In a variant the internal structure can be formed from plates attached on to the frame so as to block the windows of said frame. The assembly body according to the present invention advantageously comprises a device for compensating for an axial gap between the end of the end section and the second sleeve intended to be located in the upper part of the assembly. The latter is, for example, formed from a washer with undulations of amplitude 5 mm inserted between the end section and the second upper sleeve. Advantageously, the assembly body has a regular hexagonal transverse section. The internal structure is, for example, made of SiC, fibre-reinforced SiC or MAX-phases of the Ti3SiC2 type. In the case of an assembly body for a sodium-cooled fast neutron reactor, the sleeves and the frame can be made of austenitic, ferritic or ferritic/martensitic stainless steel. As a variant, the sleeves can be made of 316 Ti standard austenitic steel, and the frame of EM10. In the case of an assembly body for a gas-cooled fast neutron reactor, the sleeves and the frame can be made from refractory metals. Another subject-matter of the present invention is an assembly comprising a foot, an assembly body according to the present invention, nuclear fuel pins positioned in the assembly body and an upper neutron protection, where the body is attached to the foot and to the upper neutron protection in the area of the first and second sleeves respectively, for example by welding. In FIG. 1 an assembly body 2 according to the present invention can be seen intended to receive within it nuclear fuel pins to form an assembly. In FIG. 8, the complete assembly according to the present invention can be seen; the pins are not visible. The assembly body is designed to be positioned vertically when it is in the core. Assembly body 2 according to the present invention with lengthways axis X has a first sleeve 4 of axis X intended to form the lower end of body 2, a second sleeve 6 of axis X intended to form the upper end of body 2, a frame 8 of axis X connecting first sleeve 4 and second sleeve 6, and an internal structure between first sleeve 4 and second sleeve 6 and positioned inside frame 8. In the assembly, first sleeve 4 is mechanically connected to the foot of assembly 11 intended to be housed in the reactor's diagrid, and second sleeve 6 is connected to upper neutron protection 13. The assembly is cooled by circulation of a fluid from base to top, for example gas in the case of an RNR-G reactor or sodium in the case of an RNR-Na reactor. The cooling fluid enters through the foot, traverses first sleeve 4, internal structure 10 and second sleeve 6, and exits from the assembly through the upper neutron protection. The height of internal structure 10 is such that the structure extends over the entire fissile height, i.e. the zone receiving the fuel pins. Frame 8 also extends over the entire fissile height. In the represented example, and advantageously, body 2 has a regular hexagonal section, enabling a high volume density of fissile nuclei to be obtained. However, a body having a transverse section of another shape does not fall outside the scope of the present invention, for example one of circular section. According to the invention, the frame is positioned outside the body and forms an external framework mechanically holding the body. The frame provides the mechanical connection between the foot of the assembly via first sleeve 4 and the upper neutron protection via second section 6. Frame 8 withstands the bending moments to ensure beam resistance of the assembly, the torsional moments to maintain the alignment of tubular segments over the height of the assembly, and the axial forces due to the weight of the structures, under traction and compression when the assembly is handled. FIG. 3 shows frame 8 which comprises lengthways struts 11 and transverse struts 12, where these struts 11 and 12 define windows 13. FIG. 9 shows frame 8 which comprises lengthways struts 111 and transverse struts 112, where these struts 111 and 112 define windows. In the represented example, the six faces of frame 8 each comprise four rectangular-shaped windows. Other window shapes are conceivable, such as holes, for example, distributed according to the mechanical stresses to which the frame is subject. The frame represents a very small volume of the body, which minimises its volume fraction in the fissile volume of the core. In addition, as we shall see below, it enables the cooling fluid to pass into the inter-assembly zones. Advantageously, to construct frame 8 a material is used which has mechanical properties such that plasticity and in thermal creep ductilities are greater than or equal to 0.2% and such that the toughness KIC is greater than or equal to 20 MPa·m1, 2. The material of the frame is chosen such that these mechanical properties are present taking account of the exposure to the maximum fluence of the core and of the operating temperature conditions. The frame is made from a metal material, for example stainless steel. The steel is chosen such that it does not expand, or expands only slightly, with the core fluence, such as stainless steel of a ferritic/martensitic grade, EM10 for example. The atomic composition of the materials used for the frame is preferably favourable to the neutron balance, both during normal operation and in accidental situations, and for the post-use cycles from the standpoint of the excitation level. The frame is made, for example, by welding rods one to another, by making windows in a sheet metal which is then shaped into a tube, or by making windows directly in a tube. The sleeves are made of metal materials and are welded on to the ends of the frame. Sleeves 4, 6 are roughly identical. Sleeves 4, 6 have a section which is roughly identical to that of frame 8, and make an internal passage for the flow of the cooling fluid. Sleeves 4, 6 are positioned respectively below and above the fissile zone; they are not therefore greatly exposed to the neutron flow of the fuel pins. Consequently, the material or materials constituting them need merely be resistant to moderate radiation conditions. Indeed, the local fluence to which they are subject is less than half the core's maximum fluence. The sleeves are made from a metal material, for example stainless steel. The same materials can be chosen as for the frame; however, as was mentioned above, since the sleeves are subject to lesser neutron flows, their properties can then be adjusted to these conditions. End sleeves 4, 6 are attached to the ends of frame 8. In the example represented in FIGS. 1 and 4, the sleeves and the frame are assembled by a dovetail joint connection and a welding step is undertaken to make the connection even more robust. To this end, the transverse edges of windows 13 located at the ends of the frame are not closed, since a transverse strut is missing; ends 18 of the axial struts are then free, and have flaring shapes 20 which fit into recesses 22 of corresponding shapes made in the ridges of sleeves 4, 6. A weld is then made. It is clearly understood that any other type of assembly is conceivable. The welds between the frame and the sleeves are located outside the fissile zone. They are not therefore greatly exposed to the neutron flow, which would probably degrade their mechanical resistance. It is clearly understood that an assembly body in which the frame and the sleeves are secured only by welding or by a mechanical assembly does not fall outside the scope of the present invention. In FIG. 6 a section view in plane A-A of the dovetail assembly can be seen. The internal structure of the body is made from a ceramic material defining a channel, in which the pins are positioned, and in which the cooling fluid flows from base to top. In the example represented in FIG. 2, internal structure 10 consists of tubular segments 10.1 of hexagonal section, for example four such (10.1a, 10.1b, 10.1c, 10.1d), positioned one on top of the other along axis X within the frame. This segment-based structure is more specifically adapted to RNR-Na reactors, in which the sodium pressure is relatively high, since the segments are more capable of withstanding these pressure levels. Segments 10.1 are advantageously socketed into one another; to this end the axial ends of the segments are advantageously configured to allow such socketing. In FIG. 7 an example of such socketing can be seen. For example, each segment 10.1 comprises a lengthways end 24 fitted with an annular groove 26 of hexagonal shape and a lengthways end 28 fitted with an annular rib 30 the shape of which matches that of groove 26. Advantageously, rib 30 has a triangular transverse section, facilitating socketing and centring of the segments. In addition, this shape restricts the leakage of the cooling fluid outside the assembly by forming a baffle for the fluid; the flow of the fluid between the segments is therefore impeded. It is clearly understood that segments 10.1 comprising flat or bevelled axial ends do not fall outside the scope of the present invention. In addition, the end portions of internal structure 10 penetrate into sleeves 4, 6, as can be seen in FIG. 6. It is possible either to make an assembly of segments 10.1 forming a duct which prevents any leakage of the cooling fluid, or a duct which prevents most leakage, where the fluid flows towards the inter-assembly zones. The presence of a certain flow in the inter-assemblies spaces can be beneficial for the overall cooling thermal hydraulics of the core, in normal operation and/or in accidental situations. In the represented example shown in FIGS. 1, 13A, 13B, 15A, and 15B, the connection zones 31 between segments 10.1 are covered by transverse struts 12 of frame 8; the effect of this covering is to restrict the leaks of cooling fluid, as we shall see below. Transverse struts 12 could also be staggered axially relative to the connection zones 31 as shown in FIGS. 14A, 14B, 16A, and 16C. Advantageously, the inner faces of the adjacent walls of the segments are connected by a fillet, the diameter of which is roughly equal to that of the pins of the bundle, so as to define a hydraulic channel of roughly constant section between the inner face of the segment and the pins located on the outside of the bundles. The external ridges also have a radius of curvature, as can be seen in FIGS. 5 and 6. The outer faces of the segments are advantageously recessed relative to the external surface of the assembly body, which reduces the risks of impact for the ceramic segments whilst it is transported and handled. Segments 10.1 define a channel for the cooling fluid. The junction between segments 10.1 does not necessarily prevent all leakage, as indicated above. However, in the event of a leak, it is sought to obtain calibrated leaks through calibrated leakage zones 33 between the segments 10.1, 110.1, in order to control the cooling flow. These leaks from the interior of the assembly to the exterior cause fluid to flow between the assemblies. The leakage flow is comprised in the calculation of the flow at the inlet of the assembly, in order to control the hydraulic cooling flow. The appearance of leaks in the form of erosive jets is prevented by producing shapes such as those described above, which are capable of causing a laminar leak, preventing damage to the connection zones 31 between the segments. In addition, due to this possibility of the fluid flowing between the segments, in the case of a plug in the lower portion of the assembly preventing the cooling fluid from penetrating into the assembly, the fluid can penetrate into the assembly between two segments and cool the pins in degraded fashion. In addition, due to the structure a dynamic form of leak prevention is obtained. Indeed, in operation, and more specifically while the pressurised cooling fluid is flowing, the segments tend to expand under the effect of the pressure of the cooling fluid, and are pressed against frame 8, the frame being such that its struts cover the connection zones 31 of segments 10.1, as explained above. The entire unit then forms a pressure-seal gasket. This production of a modular assembly body then enables the choice of materials of each module to be optimised. Segments 10.1 of the internal structure are made of a ceramic material, which has a very high melting temperature, close to the melting temperature of the fuel. In addition, the ceramic material is relatively rigid; its expansion under the effect of the pressure of the cooling fluid is then limited, enabling the flow rate within the assembly to be better controlled. Segments 10.1 can be made from SiC—SiCf or from MAX-phases of the Ti3SiC2 type. MAX-phases materials are nano-lamellar ceramics combining some properties of ceramic materials and some properties of metals. SiC has a melting temperature of the order of 2000° C., which is higher than that of steel. In addition, it has a moderating effect within the core, enabling core runaway to be limited. Advantageously, the segments are made from fibre-reinforced SiC (SiCf), which is even more resistant to the internal pressure applied by the cooling fluid. The internal structure made from segments is able to resist the internal high pressure required to establish the bundle cooling flow, which is of the order of 3 to 5 bar for a RNR-Na reactor, and of the order of 1 to 1.5 bar for a RNR gas reactor. In addition, the ceramic materials of the internal structure retain sufficient mechanical resistance at high temperatures to resist the internal high pressure of the cooling fluid. The internal structure according to the present invention maintains the confinement of the fissile bundle cooling flow in the field of the high temperatures which can be reached in accidental situations, which range from the operating temperature to the melting temperature of the fuel. In addition, in an accidental situation, the internal structure is the first structure in contact with the fuel elements. Due to the high melting temperature of the ceramic materials, by maintaining its integrity it provides a certain mitigation of the accident by limiting the possibilities of fuel displacement, notably radially in the events of local melting of a bundle. SiC/SiCf and Ti3SiC2 type MAX-phases composites have suitable mechanical properties in terms of resistance and toughness, and ensure mechanical fuel bundle confinement up to some 2000° C. In addition, from the neutron standpoint, these materials lead to a more favourable neutron balance the than a metal in normal operation. Furthermore, in addition to its neutral “transparency”, SiC/SiCf provides a flow-moderating effect which improves the Doppler coefficient which comes into play in accidental transients. In terms of variation of potential core reactivity in an accidental melt situation, the replacement of a portion of the assembly body made of steel by SiC/SiCf significantly reduces the variation of reactivity caused by draining the molten steel. In assemblies of the state of the art, the volume fraction of the steel in the fissile zone consists of the sheaths of the fuel elements and of the assembly body. By means of the invention, production of a portion of the assembly body using SiC/SiCf reduces the volume fraction of steel, and therefore the associated draining effect. The assembly body according to the present invention is assembled as follows: segments 10.1 installed in frame 8, end sleeves 4 and 6 socketed in the lengthways ends of frame 8, using a clip-on system, and welding at the sockets. It may also be conceived to produce the internal structure in the form of plates blocking the windows of frame 8; such an embodiment is more specifically suitable for a RNR gas reactor: since the gas pressure is lower, the plates can be less thick. Referring to FIG. 10, each of segments 110.1a, 110.1b, 110.1c, and 110.1d may be made-up of plates. For example, 110.1a is made-up of 110.1a1, 110.1a2, 110.1a3, 110.1a4, 110.1a5, 110.1a6. The other segments 110.1b, 110.1c, and 110.1d, are likewise made-up of plates. However, for convenience, only the reference numerals for segment 110.1a are shown in FIG. 10. For example, these plates are assembled in runners in the frame. For example the plates are made from SiC, and the frame and the sleeves from vanadium. We shall now describe an example embodiment which is more specifically suitable for a fourth-generation sodium-cooled fast neutron reactor. The dimensioning was calculated on the basis of the following conditions: a pitch of the fuel assemblies network or inter-assembly gap of 210.8 mm, a distance between flats internal to the assembly body, in the case of a tube with a hexagonal section, which is defined by the size of the fuel bundles of 197.3 mm, a fissile height of the core of 1000 mm, an internal sodium high pressure in the assembly body of 0.34 MPa, a sodium temperature of 395° C. when entering the core, and of 550° C. when leaving the core, a maximum fluence (E>111 keV) of 3.3.1027 n·m2. The internal distance between flats is the distance separating two parallel faces of the internal surface of a hexagon, and the external distance between flats is the distance separating two parallel faces of the external surface of a hexagon. On the basis of these dimensional and operational conditions, the characteristics of the various elements of the assembly body according to the present invention can be as follows: first sleeve 4 and second sleeve 6 are made from a 316 Ti standard austenitic steel having an external distance between flats of 207.8 mm and an internal distance between flats of 197.3 mm, i.e. a thickness of 5.25 mm, frame 8 is made of EM10 steel, with an external distance between flats of 207.8 mm and an internal distance between flats of 205.8 mm, i.e. a thickness of 1 mm. The frame is openworked. The dimensions of the windows are 230 mm×99 mm. the internal structure is made from a fibre-reinforced SiC—SiC composite ceramic material, formed from four segments extending over the fissile height, having an external distance between flats of 204.8 mm, and an internal distance between flats of 198.3 mm, i.e. a thickness of 3.25 mm. Advantageously, to control the geometry of the assembly body during manufacture, whilst complying with the functional tolerance intervals, the body can be made in the form of segments 250 mm in height. The above dimensions were determined taking account of the various properties of the materials under the operating conditions in the core. Indeed, the metals used for frame 8 and first and second sleeves 4 and 6 expand more than SiC—SiCf. The expansion coefficient of SiC—SiCf is 4.10−6 and that of EM10 steels and of the sheathing of the fuel pins is between 12.10−6 and 14.10−6. To accommodate these differential expansions between the fuel bundle and the internal structure made of SiC, the distance between flats of segments 10.1 is 198.3 mm, i.e. 1 mm greater than that of the distance between flats of first and second sleeves 4, 6. The segments are fitted into the sleeves which have a machined socketing bore suitable for the external dimension of the segments, allowing for an assembly gap. For example, the internal dimension of the bore is 205.8 mm and the external dimension of the segments is 204.8 mm. The gap between the pin bundle and the assembly body is therefore increased by 1 mm facing the internal wall of the segments to prevent interaction at the operating temperature. In addition, the material of the frame and that of the segments have different expansions when subject to flows: at the sought fluence EM10 will expand only at the end of its lifetime. Conversely, SiC—SiCf expands from the moment when it is first irradiated, for example when for the first time a fast fluence of the order of 0.34.1025 n/m2 is reached. SiC—SiCf very quickly reaches its saturation volume expansion value which is of the order of 1% to 1.5% at the operating temperature between 400° C. and 550° C. To accommodate this expansion of the SiC at the start of the lifetime without a strong interaction with frame 8 made of EM10 there is a gap between the external surface of the segments and the internal surface of frame 8. For example, an initial gap of 1 mm is allowed, with an internal distance between flats of the EM10 frame of 205.8 mm and an external distance between flats of the SiC segments of 204.8 mm. In addition, an axial gap is advantageously allowed in the bore where the end of the segment is socketed into the second sleeve. The latter has, for example, a depth such that it makes an axial gap of 5 mm when the unit is assembled. Advantageously, an axial gap compensation device is comprised between the end of the segment and the second sleeve, to hold the segments in a contiguous position before the assemblies are installed in the reactor, notably during the transport and handling operations. For example, the compensation device can take the form of a thin washer having undulations of amplitude 5 mm inserted between the axial stack of the segments and the upper second sleeve. At the start of operation the washer is crushed when the segments are subject to axial expansion. For example, the thickness of the segments is of the order of 3.5, enabling the stress level in the segments to be minimised under the effect of the internal pressure. In addition, the connection fillets in the area of the internal ridges of the segments can measure 5 mm to prevent stress concentrations, and to regulate the hydraulic diameter of the cooling channel of the corner pin of the bundle. The assembly body according to the present invention, with the elements having the dimensions given above, therefore has the following dimensions: an external distance between flats of 207.8 mm, an internal distance between flats of 197.3 mm with 198.3 mm locally in the upper part of the SiC TH, a clearance in the network pitch of 3 mm. The dimensions of a metal monolithic assembly body made of EM10 of the state of the art suitable for this same core are given below: an external distance between flats of 206.3 mm, an internal distance between flats of 197.3 mm, a clearance in the network pitch (inter-assemblies clearance): 4.5 mm. On the basis of these dimensions, the volume fractions of materials in the fissile volume of the core of a monolithic assembly body made of steel of the state of the art and an assembly body according to the present invention were calculated and are presented in the table below: VOLUME FRACTION IN THE FISSILE ZONEMetalSodiumSiC—SiCfMonolithic assembly8.17%4.22% 0%bodyMetal/SiC SiCf0.44%6.05%5.9%assembly body It can therefore be seen that, by means of the present invention, the volume fraction of metal is greatly reduced, since it is 0.44% instead of 8.17% in the case of the assembly body of the state of the art, which is mainly attributable to the contribution of a significant volume fraction of the SiC—SiCf material having improved neutron properties, i.e. improved neutron “transparency” and a moderating effect. The presence of sodium in the recesses of frame 8 slightly increases by 1.8% the volume fraction of sodium of the inter-assemblies space. A neutron evaluation of the effects of this modification of the volume fractions of the materials constituting the assembly body, in comparison with a metal monolithic assembly body, shows for the core for a given staying time: a gain for the sodium draining coefficient of 0.3%, a gain for the Doppler coefficient of 10%, a slight gain for regeneration gain and for Pu investment, a comparable rate of damage for the sheaths of the fuel elements, a rate of damage for the SiC of 186 dpa-SiC, compared to 145 dpa for the reference metal TH. Regeneration Gain, GR, is the ratio between the final number of fissile atoms and the initial number of fissile atoms; when GR is >1, breeding is said to occur; more fissile matter is produced than is consumed. This is, for example, the case of an RNR reactor with production of Pu239 from the fertile U238 with, at the end of the process, more Pu239 than at the start. Dpa or displacement per atom expresses the radiation damage incurred by a material subject to a fast neutron flow; it quantifies statistically the number of times that an atom of the material is subject to a displacement under the impact of a fast neutron (of energy greater than 0.1 MeV). In addition, the substantial reduction of the volume fraction of metal also has effects in an accidental melting situation since when the molten steel is drained in the case of melting the variation of the reactivity caused by this drainage is significantly reduced. The assembly body according to the present invention, whilst satisfying the specifications of existing assembly bodies, therefore enables the core's neutron operation parameters during normal operation, or incidental operation, which qualifies operational incidents occurring more frequently than 10−2/year, and accidental operation, to be improved significantly. It also contributes elements which mitigate accidents which may lead to the melting of the fuel, by strengthening the overall degree of refractoriness of the core structure materials, and by reducing their reactivity influence while the accident is occurring. The assembly body according to the present invention can easily be adapted to gas-cooled fast neutron reactors, for example by making the sleeves and the frame from refractory metals such as NbZrC, or semi-refractory metals such as vanadium, for example. It may be decided to make the frame and the sleeves from the same metal, satisfying the most severe conditions applied to the frame; however, for reasons of cost different materials are preferably chosen, the properties of which are adjusted to the conditions of use, since the material of the sleeves have lesser properties in terms of neutron flow resistance. In the case of an assembly body intended to be used in an RNR-Na reactor for which the operating temperatures are within the range 350° C.-700° C., the metal parts such as the frame and the sleeves are made from austenitic, ferritic and ferritic/martensitic stainless steels, and the ceramic internal structure can be made from SiC—SiCf or MAX-phases of the Ti3SiC type. In the case of an assembly body intended to be used in an RNR-gas reactor for which the operating temperatures are within the range 350° C.-900° C., the metal parts such as the frame and the sleeves can be made from refractory metals, and the ceramic internal structure can be made from SiC—SiCf or MAX-phases of the Ti3SiC2 type. Except for the internal ceramic structure, the present invention has the advantage that there is no requirement to develop new materials, but that existing materials may be used, the properties of which have previously been tested in reactor assemblies. |
|
041558073 | abstract | A core and a transition fuel assembly for a nuclear reactor having a first fuel assembly including structure for laterally spacing parallel and coextending fuel rods positioned at preselected core elevations and also having a second fuel assembly including lateral spacing structure at preselected core elevations, at least one of which is different than the elevations of the spacing structure of the first fuel assembly. The transition fuel assembly is positioned between the first and second assemblies and includes lateral spacing structure positioned at each core elevation where the first and second fuel assemblies have a spacing structure. The transition fuel assembly ensures that contact among the fuel assemblies of the core is through the spacing structures. |
summary | ||
abstract | A separate type safety injection tank comprises: a coolant injection unit connected to a reactor coolant system by a safety injection pipe such that coolant stored therein is injected into the reactor coolant system by a pressure difference from the reactor coolant system when a loss-of-coolant-accident (LOCA) occurs; a gas injection unit connected to the coolant injection unit, and configured to pressurize the coolant injected into the reactor coolant system, by introducing gas stored therein to an upper part of the coolant injection unit in the loss-of-coolant-accident; and a choking device disposed between the coolant injection unit and the gas injection unit, and configured to contract a flow cross-sectional area of the gas introduced to the coolant injection unit, and configured to maintain a flow velocity and a flow rate of the gas introduced to the coolant injection unit as a critical flow velocity and a critical flow rate when a pressure difference between the coolant injection unit and the gas injection unit is more than a critical value. |
|
claims | 1. A nuclear steam supply system with natural gravity-driven coolant circulation, the system comprising:a vertically-oriented reactor vessel comprising an elongated cylindrical shell forming an internal cavity configured for containing primary coolant and a nuclear reactor fuel core;a vertically-oriented steam generating vessel comprising an elongated cylindrical shell defining an internal cavity configured for containing secondary coolant, a top tubesheet, and a bottom tubesheet;a plurality of heat transfer tubes extending vertically between the top and bottom tubesheets, the tubes including a lower preheater section, an intermediate steam generator section, and an upper superheater section, wherein secondary coolant in a liquid state enters a shell side of the preheater section at a bottom of the steam generating vessel and flows upward to the steam generator section where a portion of the secondary coolant boils to produce steam which in turn flows upward into the superheater section at a top of the steam generating vessel;a vertical riser pipe extending vertically between the top and bottom tubesheets, the riser pipe fluidly connected to the reactor vessel;a fluid coupling forming a flow conduit for exchanging primary coolant between the steam generating vessel and reactor vessel; anda tubular recirculation shroud surrounding the tubes in the steam generator section, the shroud configured to recirculate a portion of the liquid secondary coolant in the steam generator section back to the preheater section;wherein primary coolant flows upward through the riser pipe and downward through the tubes on the tube side of the steam generating vessel to heat the secondary coolant. 2. The system according to claim 1, wherein the primary coolant flows in a parallel counter flow arrangement to the secondary coolant through the steam generating vessel. 3. The system according to claim 1, wherein a water level of secondary coolant is formed in the steam generating vessel above a top of the recirculation shroud, the water level defining a liquid-steam interface in which the recirculation shroud is submerged in the liquid secondary coolant. 4. The system according to claim 3, wherein the recirculation shroud forms an annular downcomer between the shroud and the shell of the steam generating vessel for recirculating the liquid secondary coolant, the liquid secondary coolant flowing downwards in the annular downcomer to the preheater section, reverses direction around a bottom of the recirculation shroud, and flows upwards inside the recirculation shroud back to the top of recirculation shroud to complete a recirculation flow loop. 5. The system according to claim 1, wherein the preheater section includes a plurality of horizontally oriented flow baffles configured to form a combination perpendicular cross-flow and parallel counter-flow pattern of secondary coolant flowing through the preheater. 6. The system according to claim 5, wherein the flows baffles include a first configuration of circular baffles attached to the shell of the steam generating vessel and a second configuration of circular baffles attached to the riser pipe. 7. The system according to claim 6, wherein the first and second configurations of baffles are arranged in an alternating pattern in a vertical direction to create a staggered shell-side fluid flow path through the preheater section. 8. The system according to claim 4, further comprising an interface plate forming a horizontally oriented demarcation between the preheater section from the steam generator section, the interface plate comprising a plurality of holes which receives the tubes which pass through interface plate. 9. The system according to claim 8, wherein the interface plate has a convex top surface to sweep debris to an outer periphery of the steam generating vessel. 10. The system according to claim 8, wherein the recirculation shroud terminates at a point spaced above and proximate to the interface plate. 11. A steam generator for a nuclear steam supply system, the steam generator comprising:a vertically-oriented steam generating vessel comprising an elongated cylindrical shell defining an internal cavity configured for containing secondary coolant, a top tubesheet, a secondary coolant outlet nozzle proximate to the top tubesheet, a bottom tubesheet, and a secondary coolant inlet nozzle proximate to the bottom tubesheet;a plurality of heat transfer tubes extending vertically between the top and bottom tubesheets, the tubes including a preheater section, a steam generator section, and a superheater section, wherein secondary coolant in a liquid state enters a shell side of the preheater section via the inlet nozzle and flows upward to the steam generator section where a portion of the secondary coolant boils to produce steam which in turn flows upward into the superheater section and exits the steam generating vessel through the outlet nozzle; anda vertical riser pipe extending vertically between the top and bottom tubesheets, the riser pipe in fluid communication with the tubes and configured for fluid coupling to a reactor vessel containing primary coolant;a double-walled fluid coupling forming a flow conduit for exchanging primary coolant between the steam generating vessel and reactor vessel, the fluid coupling configured so that primary coolant from the reactor vessel flows through the fluid coupling into the steam generator riser pipe and returns from the steam generating vessel to the reactor vessel through the fluid coupling;a bottom collection plenum formed below the bottom tubesheet by the fluid coupling and configured for fluid coupling to the reactor vessel, the collection plenum in fluid communication with the tubes;a top distribution plenum formed above the top tubesheet, the distribution plenum in fluid communication with the riser pipe and tubes; anda tubular recirculation shroud surrounding the tubes in the steam generator section, the shroud configured to recirculate a portion of the liquid secondary coolant in the steam generator section back to the preheater section. 12. The steam generator according to claim 11, wherein the steam generating vessel is configured so that primary coolant flows upward through the riser pipe and downward through the tubes on a tube side of the steam generating vessel to heat the secondary coolant which flows upward on the shell side inside the recirculation shroud. 13. The steam generator according to claim 11, wherein a water level of secondary coolant is formed in the steam generating vessel above a top of the recirculation shroud, the water level defining a liquid-steam interface. 14. The system according to claim 12, wherein the recirculation shroud forms an annular downcomer between the shroud and the shell of the steam generating vessel for recirculating the liquid secondary coolant, the liquid secondary coolant flowing downwards in the annular downcomer to the preheater section, reverses direction around a bottom of the recirculation shroud, combines with the liquid secondary coolant exiting the preheater section, and the combined liquid secondary coolant flow flows upwards inside the recirculation shroud back to the top of recirculation shroud to complete a recirculation flow loop. 15. The system according to claim 14, further comprising a horizontally oriented interface plate forming a demarcation between the preheater section from the steam generator section, wherein the recirculation shroud terminates at a point spaced above and proximate to the interface plate which precludes the liquid secondary coolant flow from the annular downcomer from re-entering the preheater section. 16. The steam generator according to claim 11, wherein the preheater section includes a plurality of horizontally oriented flow baffles configured to form a combination perpendicular cross-flow and parallel counter-flow pattern of secondary coolant flowing through the preheater. 17. The steam generator according to claim 16, wherein the flows baffles include a first configuration of circular baffles attached to the shell of the steam generating vessel and a second configuration of circular baffles attached to the riser pipe. 18. The steam generator according to claim 17, wherein the first and second configurations of baffles are arranged in an alternating pattern in a vertical direction to create a staggered flow of liquid secondary coolant through the preheater section. 19. The steam generator according to claim 16, wherein the steam generator section does not include horizontal oriented flow baffles. 20. The steam generator according to claim 11, wherein the bottom tubesheet has a convexly rounded top surface. |
|
059237163 | summary | FIELD OF INVENTION The present invention relates to reactors that confine plasma within magnetic fields at temperatures and pressures conducive to establishing nuclear fusion reactions and methods related to establishing such conditions. BACKGROUND OF THE INVENTION Magnetic fusion reactions, such as between deuterium and tritium combined in a hot plasma, have the potential to provide energy with minimal production of long-lived radioisotopes. It is well known that such reactions take place under very high temperatures conditions at which particle momentum is sufficient to overcome the mutual electrostatic repulsion of the reacting nuclei. Physical walls are not feasible for containing the reactions at the required temperatures, because the walls will cool the reactants, thereby quenching the reaction. As such, devices or apparatuses have been pursued that use non-physical means to containing the fusion reactions. These non-physical means of containment have used inertia, magnetism and electrostatic forces as the means for containing the reactions. Because the present invention is in the class of devices that use magnetic forces, the following will be confined to a discussion of this class of device. Hot plasma is an electrically conductive fluid that will flow with little resistance along magnetic field lines, but diffuse slowly across field lines because it is retarded by the magnetic reaction forces resulting from currents induced in the plasma. For this reason, an objective in designing a magnetic containment system is to suspend the plasma in a field with lines which form closed paths within the plasma confinement volume, and therefore do not provide direct escape paths along field lines. Closed current loops in the conductive plasma form closed magnetic flux loops within the plasma. A simple current loop, for example, forms poloidal flux loops that enclose a toroidal volume which surrounds the current loop. Three magnetic confinement schemes using such internal magnetic currents to generate at least a portion of the confining field are tokamaks, spheromaks and theta pinch systems. Spheromaks are formed by two interlinked plasma current loops generated by inductive and/or coaxial gun conductive means, resulting in a near-spherical toroidal confinement volume with field components in both the poloidal and toroidal directions. Tokamaks are toroidal confinement volumes formed by toroidal field components from an external set of poloidal coils and poloidal field components from a toroidal current loop induced by a time-changing external field. Theta pinch systems are toroidal confinement volumes formed by a single plasma current loop induced by a time-changing external field, with field components primarily in the poloidal direction. Reference also should be made to U.S. Pat. No. 4,436,691; Thomas R. Jarboe, "Review of Spheromak Research", Plasma Physics and Controlled Fusion, Vol. 36, pp. 945-990 (1994); Kenro Miyamoto, Plasma Physics for Nuclear Fusion (Revised Edition), pp. 530-552, The MIT Press, Cambridge, Mass. (1987); and M. Tuszewski, "Field Reversed Configurations", Nuclear Fusion, Vol. 28, No. 11, pp. 2033-2092 (1988). There are a number of known processes for forming currents in the plasma as briefly discussed below. In one process, an inductive transformer action induces transient current loops in a stationary plasma, using time-changing external fields. This process is simple and does not require conductive electrodes to contact with the plasma. However, it is by nature transient, not steady-state. This principle is used in the tokamak and theta pinch approaches In another process, a conductive current transfer forms a plasma current between two electrodes, and then the plasma is moved away from the electrodes. The movement causes the current to detach from the electrodes and reconnect as a closed loop. The process may be repeated rapidly to form a sequence of current loops which merge with and sustain a preexisting current loop. See also Y. Ono, A. Morita, M. Katsurai and M. Yamada, "Experimental Investigation of Three-Dimensional Magnetic Reconnection by Use of Two Colliding Spheromaks," Phys. Fluids B, Vol. 5, pp 3691- to 3701 (1993). This principle is used in the coaxial gun spheromak formation approaches referenced above. In yet another process, an inductive current transfer forms a plasma current in a plasma volume, and then the plasma is moved away from the formation area. The movement causes a process in which magnetic reconnection results in a closed current loop that is no longer inductively linked with the original formation field. As with the conductive current transfer process, this process may be repeated rapidly to form a sequence of current loops which merge with and sustain a preexisting current loop. This principle is used in the inductive and conical theta pinch spheromak formation approaches referenced above. Particle beams or traveling waves may be used to differentially move the plasma electrons relative to the positive nuclei and create a steady-state current within the plasma. This method is discussed in the tokamak confinement scheme referenced above. It is also used in the rotamak, confinement scheme, a variation of the spheromak. See also P. M. Bellan, "Particle Confinement in Realistic 3D Rotamak Equilibria", Physical Review Letters, Vol. 62, No. 21 pp 2464-2467 (1989). Radial diffusion of plasma through the poloidal field lines of a tokamak has been observed to generate a toroidal "bootstrap" current which supplements or replaces the inductively generated current (See Kenro Miyamoto, Plasma Physics for Nuclear Fusion (Revised Edition), pp. 225 and 552, The MIT Press, Cambridge, Mass. (1987)). This is a first order electromagnetic dynamo process, and is potentially steady-state, assuming a sustained flow of fresh plasma into the confinement volume. It has the further advantage of being driven by the temperature and pressure differences between the central fusion reaction zone and the outside of the containment volume, and therefore does not consume external electric power. Magnetic mirror plasma confinement devices generate open solenoidal magnetic fields with stronger mirror fields at the ends to reflect plasma particles back toward the center of the containment volume. Experiments were carried out on various means of inserting plasma into these devices, including shooting high velocity pulses of plasma axially through the mirrors, e.g., see B. W. Johnson and J. G. Siambis, "Injection of a Streaming Plasma Into a Mirror Machine," Plasma Physics, Vol. 15, pp 369 to 374 (1973). The experimental data include the finding that the peak transient plasma density in the inlet throat of the mirror is about 6 times higher than the peak plasma density achieved at the midplane of the device. The authors interpret this high inlet density as the result of a shock wave, and treat it as a problem to be overcome in achieving efficient plasma injection into the mirror machine. The above described systems, have not progressed to the stage where conditions conducive to fusion reactions have been continuously maintained so that energy can be reliably produced for consumption. As such, there is still need for devices, systems and methods for confining plasmas under conditions conducive to fusion reactions and more particularly a system/method where a steady-state current is formed internal to the plasma. SUMMARY OF THE INVENTION The present invention features a system, a plasma extrusion dynamo, and method for generating conditions conducive to fusion reactions and which confine the fusion reactions using a novel magnetic confinement scheme. In the method and system of the present invention, a magnetic field, preferably a conical magnetic field, is generated that defines an inlet region or nozzle and an outlet region. A pressure driven flow of conductive plasma is flowed towards the nozzle of the magnetic field. The flow conditions established are such that the inlet region is at a higher pressure than in the outlet region. Further, the inlet region pressure conditions are established so the conductive plasma continuously crosses the radial components of the magnetic field and generates a circularly polarized voltage and current loop around the axis of the nozzle. More particularly, the method that establishes conditions conducive for fusion reactions includes generating a converging magnetic field, preferably a conical converging magnetic, that has a nozzle region and an exit region and generating a conductive plasma using any of a number of means known to those skilled in the art. The pressurized flow of the conductive plasma is directed towards the nozzle region so the plasma crosses radial components of the magnetic field being generated. The crossing of the field lines by the plasma establishes an annular ring of current in the plasma in the nozzle region thereby creating poloidal magnetic fields thereabout. The magnitude of the magnetic field being generated and the flow of the plasma are selected so as to create conditions within the poloidal magnetic fields conducive to fusion reactions. The plasma current loop being established generates a set of closed poloidal magnetic flux loops that encloses a toroidal volume which contains the plasma current loop. The interaction of the plasma current loop with its own poloidal field compresses the plasma toward the toroid section axis through the pinch effect. This pinched plasma is contained far from any physical wall, thereby sustaining nuclear fusion reaction conditions. Also featured are two fusion reactor embodiments that utilize at least one plasma extrusion dynamo of the present invention to create conditions conducive to fusion reactions and to generate sustained fusion reactions so as to produce energy for consumption. In a first embodiment, such a fusion reactor includes a plasma extrusion dynamo, an impermeable housing, a means for generating a source of high pressure conductive plasma for the fusion reaction and a means for exhausting the impermeable housing to remove or scavenge the reaction by-products and unreacted fuel. Preferably, the exhausting means also establishes the low pressure conditions required for proper system operation. In a specific embodiment, the means for supplying or generating the high pressure conductive plasma is a high velocity plasma jet that converts neutral fuel into a conductive plasma and propels it towards the nozzle region of the extrusion dynamo. Preferably, the jet also establishes a stagnation pressure zone that drives the plasma extrusion dynamo and forms the toroidal plasma structure and associated current loop. The fusion reactor also includes means for collecting the energy produced by the fusion reactions and converting the excess energy into available power (e.g., electricity) for use. In a second embodiment, a fusion reactor according to the instant invention includes two plasma extrusion dynamos. The two dynamos are in a nozzle-to-nozzle relationship along a common axis with shared magnetic field lines so as to form an enclosed plasma pressure chamber between the nozzles. Neutral fuel is injected into the enclosed plasma chamber and it is ionized and heated to form the relatively high temperature low pressure plasma. The ionization and heating energy may be supplied by external means such as microwaves or neutral beams. Preferably, the fuel is ionized and heated by radiant energy from fusion reactions taking place in the two nozzle throats. The plasma then expands through each nozzle and drives the plasma extrusion dynamos, forming two toroidal plasma structures. In a specific embodiment, a separating coil is positioned on the plane of symmetry between the nozzles. Additionally, the separating coil is energized with a current that prevents the coalescence or merger of the two toroidal plasma structures in the nozzle regions of the plasma extrusion dynamos. The separator coil also preferably clamps the current loops of the respective plasma extrusion dynamos to reduce the tendency of the loops to rotate about an axis perpendicular to the dynamos' common axis. |
description | This application is a 371 of PCT/FR2010/050532, filed on Mar. 24, 2010, which is incorporated herein by reference. The present invention relates to a process for packaging radioactive wastes, in which radioactive wastes are melted and after cooling a monolith of mineral, glassy or vitrocrystalline rock is obtained in which are included said radioactive wastes. The present invention more particularly relates to a method for treating a particularly category of radioactive wastes, i.e. radioactive wastes so-called WA/MA (i.e. weakly active or moderately active) radioactive waste, intended to be stored at the surface. These are radioactive wastes, the residual radioactivity of which after 300 years should have decreased so as not to form any longer a health risk after this period. Among these wastes, are essentially distinguished: so-called “homogeneous” wastes of small grain size, notably of less than 1 mm, such as earths, sludges, ashes, sands, dusts or powders, filter dusts, and so-called “heterogeneous” wastes of larger grain size, notably greater than 1 cm, preferably from 1 to 5 cm, such as stones, concrete rubble, scrap iron, plastics, glass, . . . The method according to the invention in practice essentially tackles homogeneous waste, but also concerns certain heterogeneous wastes such as concrete rubble, as explained hereafter. The method according to the present invention more particularly relates to the treatment of material essentially consisting of limestone (CaCO3), silica (SiO2) and trivalent oxides, such as alumina (Al2O3) or hematite (Fe2O3) and, optionally boric anhydride (B2O3). This type of material is again found in: a—limestone soils based on aluminosilicate, calcium carbonate and silica, contaminated as a result of radioactive leaks outside a nuclear plant. About 5,000 m3 in volume of contaminated soil to be treated in France are evaluated. b—sludges produced by nuclear facilities, including nuclear power stations, including residues consisting of a mixture of metal oxides, of concrete dust from the building, organic products and water stemming from the process. The volume of dry extracts of these contaminated sludges to be treated represents at least 100 m3/year. c—concretes from infrastructures of nuclear facilities, including old shutdown power reactors, at the end of their lifetime, to be dismantled. This third source represents at least 10,000 m3 of WA/MA concrete. In the processes presently used for packaging WA/MA waste targeted by the method according to the invention, the main technique applied today consists of mixing them with a grout of mortar so as to form after drying a concrete block containing the initial waste and its radioactivity. The major drawback of this technique is that the incorporation rates, i.e. the volume of the initial waste divided by the volume of the final concrete are very low, i.e. between 0.2 and 0.5 depending on the treated waste. In other words, the volume of the final concrete is very large relatively to the volume of initial waste, which involves high storage costs since storage costs are related to the stored volume. On the other hand, industrial amounts of non-radioactive cement and concrete are transformed into radioactive waste. Development of other methods has been attempted in order to increase the incorporation rate of the waste, as an alternative to immobilization in a matrix of hydraulic binders, such as mortar. In particular, in FR 2 741 552, a method is described for packaging toxic waste consisting in immobilizing the wastes in a glassy matrix, i.e. leading to obtaining a monolith having the composition of the lower melting temperature ternary eutectic point in the ternary phase diagram at thermodynamic equilibrium for CAS (lime/alumina/silica), i.e. at a theoretical thermodynamic melting temperature of less than 1,300° C. To do this, the composition of the radioactive wastes to be packaged is adjusted with limestone, silica and/or alumina compounds, so as to obtain after melting, a final target composition around the relevant ternary eutectic, with: 10 to 16% by weight of Al2O3, and 59 to 65% by weight of SiO2, and 22 to 28% by weight of CaO. In the materials of radioactive wastes targeted by the method according to the invention, water evaporates from 100° C. onwards, organic materials burn between 300 and 500° C. and calcium carbonate dissociates around 900° C. in order to become lime (CaO) while degassing CO2. Other products which may enter the composition of the radioactive wastes to be treated, or even the composition of the additives, decompose at high temperature and become oxides, such as nitrates, sulfates. Because of the evaporation of water, of the combustion of organic products and of calcinations, the wastes intended to be treated lose mass by heating at high temperature. The ignition loss rate, i.e. the mass lost divided by the initial mass, may be from 25 to 40%, which, with the densification effect when passing from a divided solid to a monolith, explains the possibility of reducing the volume of wastes with a significant incorporation rate. However, this method has a certain number of the following drawbacks which prevents it from being applied to industrial manufacturing: The strong silica content of the obtained glass (59 to 65% by weight of SiO2) has the consequence of strong viscosity of the melt, especially at low temperature (less than 1,300° C.), which makes it difficult to homogenize the melt when the latter represents a large volume. Now, degassings still occur beyond 1,000° C., which generates bubbles in the melt. These bubbles cannot escape from the melt considering its strong viscosity, so that the incorporation rate of radioactive wastes into the final monolith is thereby decreased. Considering these risks of breaking up the glass, patent FR 2 741 552 imposes the application of a step for annealing the monolith at a temperature above 700° C. before the cooling step. The recommended cooling rate for glass blocks of industrial size is 1° C./h from an annealing temperature of 750° C. This imposes a one month period for cooling the monolith before reaching room temperature. For an industrial plant treating 1,000 tons a year, a cooling oven should be able to contain up to 400 glass blocks immobilized for one month. Moreover, the composition of the glass, in its ternary eutectic composition, is quite far from that of most radioactive wastes based on limestone soil and/or concrete, requiring consequently an adjustment of the composition leading to doubling of the initial mass of the waste in order to obtain the target composition. In practice, the obtained incorporation rate in FR 2 741 552 does not exceed 2. Finally, taking into account the inhomogeneity of the product to be melted, it is necessary to apply a melting temperature much higher than the theoretical thermodynamic melting temperature, as explained hereafter. For all these reasons, the method described in FR 2 741 552 was never applied industrially. Methods are also known, as described in FR 2 502 999, consisting of making an artificial rock, i.e. a solid including crystalline phases and glassy phases, by immersing electrodes in the radioactive wastes to be confined, and of then having a current pass through them until the environment of the electrodes is melted. In WO 03/038361, this treatment is directly applied to wastes packaged in containers. This method is not applicable as such to the treatment of radioactive wastes consisting in limestone soils and/or concrete rubble or sludges from nuclear power stations, since the limestone which they contain, produces lime which violently reacts with water and is extremely soluble, which is incompatible with the packaging of radioactive waste. Further, the limestone is transformed into lime at 900° C. with emission of CO2, but lime (CaO) melts at more than 2,500° C. At this temperature, most radioactive elements (cesium, ruthenium, plutonium) are volatile. Finally the metal or concrete container of the waste would not withstand these temperatures. The object of the present invention is to provide a method for confinement-packaging of radioactive waste, with which a high incorporation rate greater than 2 notably from 2 to 4, may be attained under industrial application conditions. Another object of the present invention is to provide a final waste confined as a more or less crystallized monolith of the glassy or polycrystalline type with grain boundaries (artificial rock) which meets the solid block's properties of strength to compression of at least 8 MPa and of insolubility which makes it capable of being stored in surface storage centers. The compression strength criterion means that the final waste block should be sufficiently solid so as not to break up into small pieces, during the cooling or subsequently. The insolubility criterion means that the final waste should not be soluble and especially it should not react with water. Finally, another object of the present invention is to provide a confinement method which allows industrial application with reduced cooling time, of course without having the thermal cooling stresses breaking up the block, and a melting temperature compatible with retaining at least 50% of the volatile radioactive elements in the melt. The method according to the invention consists of heating wastes after adjustment of their composition, by adding additives or by mixing wastes, so as to melt them and to pour them into a container in which they are packaged as artificial rock or glass monoliths. More specifically, the present invention provides a method for packaging radioactive waste, wherein the following successive steps are accomplished: a/ radioactive wastes are treated, for which the composition of the dry extract after calcination at 950° C., called the starting composition hereafter, comprises at least 90% of compounds selected from CaO, Fe2O3, SiO2, Al2O3 and B2O3, and the composition of said wastes is supplemented so as to attain a target composition of said supplemented wastes after calcination, and b/ said supplemented radioactive wastes are melted and c/ said melt is cast into a container, so as to obtain after cooling a product comprising a synthetic, glassy or vitro-crystalline rock, having said target composition, characterized in that said starting composition and said target composition meet the following definitions, in a ternary system CaO, SiO2 et X2O3, wherein X2O3 is a trivalent oxide or a mixture of trivalent oxides selected from Al2O3, Fe2O3 et B2O3: for said starting composition: PC and PX are less than 90%, and PS is less than 75%, and for said target composition: PC is from 35 to 60%, preferably from 40 to 50%, and PS is from 10 to 45%, preferably from 20 to 40%, with in both cases: PC+PS+PX=100%, and PX=PA+PH+PB, with PC=[MC/(MC+MS+MA+0.28MH+2MB)]×100%, and PS=[MS/(MC+MS+MA+0.28MH+2MB)]×100%, and PA=[MA/(MC+MS+MA+0.28MH+2MB)]×100%, and PH=[0.28MH/(MC+MS+MA+0.28MH+2MB)]×100%, and PB=[2MB/(MC+MS+MA+0.28MH+2MB)]×100%, and Pi and Mi, with i=C, S, A, H or B, are the mass percentages (Pi) and the masses (Mi), of CaO (i=C), SiO2 (i=S), Al2O3 (i=A), Fe2O3 (i=H) and B2O3 (i=B), respectively. It is understood that in step a/, the composition of said radioactive waste is supplemented so as to attain a said target composition, which is also the composition of the monolith obtained at the end of step c/. By “starting composition” is meant here the composition of non-supplemented radioactive wastes, the latter however being calculated according to what it would be after calcination. In the starting composition, the mass percentage is based on the mass of CaO and not of CaCO3, and/or Ca(OH)2, if necessary, since CaCO3 and Ca(OH)2 after calcination at 950° C. are transformed into CaO. Also, as regards alumina, silica and boron oxide, the starting radioactive wastes generally rather comprise pre-cursors, such as hydrates, silicate, sulfate, nitrate salts, of acids, notably boric acid H3BO3, and/or hydroxides of these molecules giving, after calcination, alumina, silica and boron oxide. It is thus possible to locate the starting composition and the target composition in the same ternary CaO, SiO2, X2O3 diagram. This target composition is particularly advantageous since with it, as this will be explained hereafter, a melt may be obtained which is relatively fluid and therefore more homogeneous, whence the result that it is possible to obtain glassy or crystalline monoliths having advantageous mechanical properties without requiring any annealing and with reduced cooling times. This is in particular due to the fact that in this relatively reduced domain of the target composition the ternary lime/alumina/silica, lime/hematite/silica and lime/boric anhydride/silica ternary diagrams have similarities in every case with an eutectic valley substantially at the centre of the thereby defined parallelograms, as explained hereafter and illustrated in FIG. 1. The parallelogram is voluntarily defined so that the eutectic valley is excentered because of the dissymmetry of the valley having an abrupt left flank (the melting temperature increases very rapidly upon moving away from the eutectic) and a straight flank with a gentle slope. A monolith of a target composition, as defined above, gives the possibility of attaining incorporation rates (initial waste volume/waste volume packaged as a monolith) of greater than 2 for wastes for which said starting composition consists of at least 90% of compounds selected from CaO, SiO2, Al2O3, Fe2O3 and B2O3, on the one hand, and which meet the following mass percentages, after calcination, in a (CaO, SiO2, X2O3) ternary system as defined above: PS<75%, PC<90%, and PX<90%. In particular, it is observed that incorporation rates comprised between 2.4 and 8.1 are obtained according to the composition of the starting wastes. Another advantage of this target composition of the monoliths including the immobilized radioactive wastes in a more or less crystallized solid block in the form of glass or preferably in the form of an artificial rock of polycrystalline solids with grain boundaries, is that it observes regulatory specifications in terms of the solid block's compressive strength of at least 8 MPa, and of resistance to solubilization. Moreover, this method is particularly of interest in an industrial application since with it: it is possible to cast large blocks of said monoliths, notably of at least 200 L, or even up to 500 L, within a reasonable cooling time, notably not more than two weeks or even not more than a week and for most of the time within less than 24 hours, without of course having the thermal stresses break up the block into small pieces during cooling, and at least 50% of the volatile radioactive elements such as cesium or plutonium are retained in the melted pool and then in the solid monolith block. The composition, in the (CaO, SiO2, X2O3) ternary system corresponds to a crystalline phase domain in the different ternary diagrams (CaO, SiO2, Al2O3), (CaO, SiO2, Fe2O3) and (CaO, SiO2, Be2O3) corresponding to the region of eutectic valleys, i.e.: for the CAS (lime/alumina/silica) diagram (FIG. 1), the eutectic valley separating larnite (Ca2SiO4) and gehlenite (Ca2Al2SiO7) on the one hand, and the eutectic valleys between larnite and rankinite (3CaO.2SiO2) and pseudo-wollastonite (CaO.SiO2) on the other hand and, the eutectic value separating pseudo-wollastonite and gehlenite with a triple pseudo-wollastonite/gehlenite/anorthite (CaO.Al2O3.2SiO2) eutectic, and finally at the bottom of the diagram, the 2 valleys between 3CaO.Al2O3, 5CaO.3Al2O3 and CaO.Al2O3. for the lime/hematite/silica ternary diagram (FIG. 4), this target composition corresponds to the regions of the eutectic valleys between larnite and hematite, larnite and rankinite, rankinite and pseudo-wollastonite, and at the bottom of the diagram the whole of the valleys between 2CaO.Fe2O3, CaO.Fe2O3, CaO.2Fe2O3 and hematite. for the lime/boric anhydride/silica diagram (FIG. 5), this target composition corresponds to the regions of the eutectic valleys between larnite (2CaO.SiO2, indicated as “C2S” in the diagram) and pseudo-wollastonite (CaO.SiO2), and then lower down, between the compounds 3CaO.B2O3 et 2CaO.B2O3. Initially, the inventors tested wastes based on limestone soil by adding thereto alumina, and various other wastes based on CaCO3, SiO2 and Al2O3 by adding alumina thereto. In this way, they defined a target composition domain as defined above in the ternary CAS diagram. Next, they empirically noticed that by replacing alumina with other trivalent oxides, i.e. boric anhydride B2O3, notably present in a large amount in evaporator concentrates of nuclear power stations, and hematite Fe2O3, present in a large amount in the sludges of nuclear power plants, hematite Fe2O3 and boric anhydride B2O3 may be assimilated to alumina in the CAS (lime/alumina/silica) diagram, insofar that coefficients of 0.28 and 2, respectively described above are ascribed to the considered masses of hematite and boric anhydride. In other words, a total mass of trivalent oxide is taken into account, equivalent to alumina, i.e. the addition of the actual alumina mass+0.28 time the hematite mass+2 times the boric anhydride mass. In this case, the target composition corresponds to compositions contained in a theoretical diagram CXS, X representing X2O3, i.e. a mixture of Al2O3, Fe2O3 et B2O3, and corresponding to the parallelogram A of FIG. 1 in the CAS diagram. The equivalent coefficients of 0.28 and 2 mentioned above do not simply result from an empiric observation but are corroborated from the comparison of the lime/alumina/silica, lime/hematite/silica and lime/boric anhydride/silica ternary diagrams, as explained later on with reference to FIG. 8, and resulting from that: a relatively rectilinear set of eutectic valleys joins the point M of the CaO—SiO2 to a point of the line CaO—X2O3 in the three triangles of the three ternary diagrams, and the position of the point M does not depend on the nature of the trivalent oxide and is located in the domain of rankinite. On the other hand, the positions of point P, for the diagrams of the various trivalent oxides, allow determination of these equivalence coefficients. Further it will be noted that in the three diagrams, if the composition is unbalanced so as to have it deviate from the eutectic, the melting temperature increases relatively rapidly on the left of the valley (lime excess) and relatively more slowly on the right of the valley (lime shortage). According to the present invention, the fact that the regions of the target composition are around binary eutectic valleys rather than around a ternary eutectic as in FR 2 741 552, is much better adapted to the treatment of waste. Indeed, the composition of a waste is naturally variable and a valley extending around one substantially rectilinear line in a ternary diagram, provides a much larger range of target compositions, which allows this target composition to be obtained by applying, if required, reduced amounts of additives as compared with those required for a monolith with a composition around a ternary point, such as in the prior patent FR 2 741 552. Finally, another advantage of the target composition according to the present invention lies in that the silica contents are comparatively reduced with respect to those of the composition of the ternary eutectic of the prior patent FR 2 741 552, which corresponds to a comparatively reduced viscosity. The result of this is a reduced gap between the actual melting temperature and the theoretical thermodynamic melting temperature. Indeed, the melting temperatures indicated in the ternary diagrams, such as the CAS diagrams, are temperatures of thermodynamic equilibrium, in the sense that they were obtained by first melting the mixture at a higher temperature so as to perfectly homogenize the pool, and then by slowly reducing the temperature and by measuring the crystallization temperature. However, in practice, the heterogeneity of the mixture imposes heating far beyond the thermodynamic temperature in order to obtain melting of the different constituents of SiO2, CaCO3 and X2O3 aggregates. Indeed, even with an intimate mixture, for example soil with alumina powder, a grain of alumina and a grain of earth will have to be melted in order to obtain a mixture on a molecular scale, i.e. homogenization of the chemical composition. Thus, the tests show that the selected eutectic according to the present invention has interesting characteristics for melting wastes since the actual melting temperature does not exceed the thermodynamic temperature by more than 100° C. or even 70° C., for treating earth supplemented with alumina, 270° C. for treating concrete supplemented with alumina, while, for a glass around the ternary eutectic composition according to patent FR 2 741 752, the deviation may exceed 500° C., which strongly decreases the benefit of working around the ternary eutectic point of the CAS diagram at a theoretical thermodynamic temperature of 1,170° C., but which, for reasons of homogenization of the chemical composition, actually requires melting temperatures substantially identical with those obtained according to the present invention. Moreover, finally, low viscosity limits the continued presence of gas bubbles in the final product, which would have a negative effect on the incorporation rate on the one hand but also on the mechanical resistance to breaking up on the other hand, it being understood that as mentioned earlier, within the scope of treatment of radioactive wastes, the goal is to obtain a solid block resisting to cracking and breaking up. Target compositions are preferred, which have a silica content PS of less than 40%, so as to reduce the viscosity of the melt and, thus facilitate homogenization thereof and reduce the melting temperature. More particularly, a method according to the present invention has the following characteristics: in step b/, the radioactive wastes are heated in a crucible and are melted to a temperature from 1,250 to 1,650° C., and in step c/, said melt is cast into a container, preferably with a capacity of at least 200 L, still preferably with a capacity of at least 500 L, so as to form said monoliths and said melt packaged in this way is cooled, without annealing, down to room temperature, within a period of less than 15 days, preferably less than a week, still preferably less than 24 hours. For monoliths with a reduced weight of less than or equal to 2 kg, cooling may even be obtained within less than 2 hours. It is understood that in step b/, the melting temperature represents the temperature at which the melt mixture is homogenized as regards chemical composition. The presence of hematite (Fe2O3) and/or of boric anhydride (B2O3) in the place of and/or as a supplement to alumina (Al2O3) in said target composition has the effect of significantly lowering the melting temperature values, especially in the presence of boric anhydride. In practice, target monoliths as described above are obtained from these initial products with melting temperatures comprised between 1,550 and 1,620° C., most often between 1,500 and 1,600° C., in the absence of boron oxide or boric anhydride in the target composition. In a preferred embodiment, in step c/, a cooling step is carried out in two steps, namely: c.1/ the cooling rate of said container filled with said melt is limited in the cooling phase between 1,250 and 1,000° C., to a cooling rate comprised between 50° C./h and 250° C./h, preferably by burying it in a bed of refractory material particles, such as alumina particles, and by letting it cool naturally in room temperature premises and still preferably by sweeping said container with an airflow at room temperature, at a rate from 0.1 to 1 m/s, and then c.2/ the cooling of said container from 1,000° C. down to room temperature is finished without limiting the cooling rate, preferably by placing said container in open air or by quenching it in cold water until its temperature decreases down to room temperature. In step c.1/ above, the rate is decreased so as to allow crystallization of the monolith, while retaining a minimum cooling rate, so that said container does not melt. More particularly, said radioactive wastes comprise of limestone soil, concrete rubble, sludges from nuclear power plants, concentrates from evaporators of nuclear power plants, sand, and/or ashes from incinerated radioactive wastes. Still more particularly, said starting radioactive wastes have an starting composition meeting the following definition in the CaO/SiO2/X2O3 ternary system, wherein X2O3 and PI have the meanings given earlier: Pc and PX are less than 75% and Ps is less than 60%. In a preferred embodiment, said target composition corresponds to the following mass percentages: PC is comprised between 40 and 50%, and PS is comprised between 20 and 40%. With this target composition domain, a polycrystalline material may be obtained by aiming at a composition close to but different from the eutectic, it being understood that obtaining a polycrystalline material is more favorable than obtaining a glass. Indeed, the polycrystalline material generally resists better than glass with generated internal stresses during the cooling, even if the latter is very fast, for less than 24 hours, and therefore does not risk any breaking up under the effect of these stresses. Crystallization is promoted through two effects: by deviating from the eutectic or by reducing the cooling rate around the crystallization temperature (between 1,250° C. and 1,000° C. in our case). When deviating from the eutectic, it is better to aim the domain of gehlenite where the melting temperatures increase very little above that of the eutectic, rather than that of larnite, where the melting temperatures increase very rapidly. Still more particularly, in a method according to the invention, steps are performed with according to which: a.1/ a limestone soil and/or concrete rubble is treated, for which the starting composition meets the following definition in a ternary CaO/SiO2/X2O system, wherein X2O3 and PI have the meanings given above: PC is comprised between 30 and 80%, and PX is less than 20%. a.2/ 5 to 50% of X2O3, selected from Al2O3, Fe2O3 et B2O3 are added. Still more particularly, in step a.2/, it is proceeded with addition of less than 10% of B2O3, preferably less than 5% of the mass of the radioactive wastes to be treated and/or PB is less than 15%, preferably less than 7% in said target composition of the obtained monolith. Boric anhydride has the property of reducing the melting temperature of our mixture. Thus, by adding 10% of boric anhydride based on the mass of radioactive wastes to be treated, one manages to lower the melting temperature to 1,250° C. for treatment of limestone soil, concrete rubble and/or sludges from nuclear power stations. However, boric anhydride has the drawback of melting at a very low temperature, i.e. from 300° C., so that in the presence of boron oxide or molten boric anhydride, the gas evolvements generated by calcination of the carbonates, which occurs around 900° C., produces a foam, the result being that an extremely porous material is obtained. This is why preferably addition of boron oxide or boric anhydride is limited to 5%, which is sufficient for lowering the melting temperature by about 100° C. for treating radioactive wastes consisting of limestone soil and/or concrete rubble and/or sludges from nuclear power stations. Still preferably, in step a.2/: the addition of B2O3 is less than 5% of the mass of radioactive wastes to be treated in step a.1/ and/or PB is less than 7% in said target composition of the obtained monolith, and addition of Al2O3 and Fe2O3 is greater than 10%, preferably greater than 20% of the mass of radioactive wastes to be treated in step a.1/, and/or PX is greater than 15%, preferably greater than 30% in said target composition of the obtained monolith. Insofar that is often difficult to accurately measure the composition of the starting radioactive wastes and/or of the additions, taking into account their inhomogeneity, it seems relevant to also characterize them according to the sought target composition. This is why the addition of boron oxide was characterized above by giving the value of PB in said target composition of the monolith. It is possible to trace back the composition of the addition by a computation, by subtracting the starting composition and by taking into account the mass loss by melting or loss on ignition. According to an advantageous alternative embodiment of the invention, the mixing of the radioactive wastes of different compositions is carried out in order to obtain said target composition, without adding any non-radioactive trivalent oxide(s) selected from Al2O3, Fe2O3 et B2O3. Treatment of the starting products may thus be contemplated, i.e. of the radioactive wastes, outside the general definition of the composition of radioactive wastes as given above, i.e. Pc and PX less than 75% and PS less than 60%, insofar that the mixing directly results in said target composition. Further, incorporation rates greater than 3 are obtained. Still more particularly, it is proceeded with the mixing of: 1/ a so-called limestone soil and/or said concrete rubble of said following starting compositions: PC comprised between 50 and 80%, and 2/ a sludge of radioactive wastes, preferably a sludge from a nuclear power plant, of said following starting composition: PX comprised between 10 and 70%, preferably from 15 to 40% and PC less than 50%, preferably less than 35%, notably from 30 to 40%. In both composition domains of radioactive earth and sludge respectively, in each type of soil composition, there exists at least one suitable sludge composition for directly obtaining the target composition by mixing both wastes in a relative mass percent proportion from 30/70 to 70/30, preferably from 40/60 to 60/40. More particularly, in a method according to the invention, in step a/, the following steps are performed wherein: a.1/ limestone soil and/or concrete rubble are treated, said starting composition of which meets the following definition, in the ternary CaO/SiO3/X2O3 system: PC is comprised between 50 and 80%, and PS is comprised between 20 and 50%, and PX is less than or equal to 20%, preferably comprised between 4 and 10%, X2O3 being a trivalent oxide or a mixture of trivalent oxides selected from Al2O3 and Fe2O3, and PB=0, and a.2/ the additive containing X2O3 is added so as to reach said following monolith target composition in the ternary CaO/SiO3/X2O3 system: PC is comprised between 35 and 55%, and PS is comprised between 15 and 40%, and PX is comprised between 10 and 45%. In an advantageous embodiment, the big stones are extracted from the limestone soils so as to approach said starting composition of said target composition. More particularly, big particles with a size of more than 1 cm, preferably more than 5 cm are extracted from the limestone soils so that the composition of the fine portion approaches said target composition, preferably so that it attains said target composition. Still more particularly, big particles are extracted from limestone soils, with a grain size cut-off threshold with which 20 to 80% of the initial soil mass may be eliminated. Depending on the grain size distribution of the soil, this threshold will be greater than 1 cm, preferably greater than 5 cm. The grain size separation of stones, notably upon treating a limestone soil, has two benefits: when the contamination is of exogenous origin, which is most often the case, the small or large grains are contaminated at the surface but not in the bulk. Accordingly, the small grains have a higher radioactive mass activity than those of the big ones, and the stones essentially consist of limestone with a clay gangue, which is more concentrated in alumina than the crude soil, so that separation of the large size stones gives the possibility of decreasing the amount of alumina to be added to the wastes in order to obtain the target composition. Thus, grain size sorting of the radioactive soil to be treated may even allow modification of said starting composition so that it enters the definition of said target composition, by extracting the big stones, which may then be transformed into VWA wastes by simple washing. In a particular embodiment, in step b/, heating of the wastes and then of the pool is accomplished by radiation from an electric arc produced above the wastes. In another particular embodiment, in step b/, heating is started by radiation from an electric arc above the wastes, and then when the wastes begin to melt, the electrodes are immersed into the pool in order to complete the heating. In this particular embodiment, when the electrodes are in graphite, in the presence of the graphite of the electrodes, the iron oxide present in the wastes to be treated are reduced into metal iron, according to the same chemical reactions as those occurring in a blast furnace when iron ore is heated in the presence of coal. The melt then separates into two phases, one consisting of the synthetic rock having said target composition according to the invention, the other consisting of cast iron (iron plus carbon) After solidification, the iron is again found in the form of small metal inclusions in the synthetic rock, said small inclusions being of a size of less than 2 cm, in practice of the order of 0.5 to 2 cm. These inclusions were observed for small amounts of iron and/or iron oxide, i.e. less than 20% of the mass depending on the operating conditions. In the presence of larger amounts of iron and/or iron oxide, the bottom of the block consists of cast iron, the top of the block consists of synthetic rock and small inclusions are incorporated into the synthetic rock at the interface with the cast iron. In a particular embodiment, the method therefore comprises the following characteristics: in step b/, said additional radioactive wastes are melted by Joule effect heating, with graphite electrodes immersed in the radioactive waste material to be treated, and in step c/, a bi-phasic product is contained, comprising a synthetic rock matrix having said target composition in which X2O3 is selected from Al2O3 and B2O3, said matrix incorporating cast iron inclusions. It is understood that the total mass of cast iron inclusions is in relationship with the mass of iron or iron oxide initially contained in the starting compositions, preferably less than 20%. Preferably, said radioactive waste material is placed in a cooled crucible consisting of joined steel pipes, in which a liquid is circulated such as water, so as to maintain the crucible at a temperature below the melting temperature of the steel entering its composition. In a known way, these crucibles consist of steel pipes through which water flows, so as to maintain the temperature of the steel at a temperature below the melting temperature of steel, i.e. about 1,550° C. According to other advantages features of a method according to the invention: before introducing said radioactive wastes into said crucible, it is proceeded with the milling of said radioactive wastes, preferably in order to obtain a grain size of less than 5 cm, still preferably less than 1 cm, of at least one portion of the particles which it contains, and the fumes evolved during the melting of the radioactive wastes are cooled to less than 200° C. and gaseous radio-elements such as cesium, which they contain, are trapped in a particle filter. The treated wastes (limestone soil, concrete, sludge) in Examples 1 to 9 hereafter, essentially consist of calcium carbonate (CaCO3), silica (SiO2), alumina (Al2O3) and hematite (Fe2O3). In the following tables, the average compositions of the wastes are indicated in a first table, and then in a second table the mass percentages of the wastes PC, PS and PX, in a CaO/SiO2/X2O3 ternary diagram system, as defined earlier, after calcination and application, if necessary, of a hematite/alumina equivalence coefficient explained later on. 1/ Soil ComponentsHumidityOtherandCaCO3SiO2Al2O3Fe2O3mineralsorganicsSoil mass %67.5174.51.31.78CaOSiO2X2O3Pc = 63.3%PS = 28.6%PX = 8.1% 2/ Concrete ComponentsHumidityOtherandCaOAl2O3Fe2O3SiO2mineralsorganicsConcrete58.930.430.11.66mass %CaOSiO2X2O3PC = 53.9%PS = 41.7%PX = 4.4% 3/ Mud ComponentsCaCO3SiO2Al2O3Fe2O3Mud mass %3533626CaOSiO2X2O3Pc = 30%PS = 50%PX = 20% B.1—Effect of Calcination Let a waste originally consist of: ComponentHumidityOtherandCaCO3SiO2Al2O3mineralsorganicsMassP′CP′SP′AP′XP′OPercentage By definition: P′C+P′S+P′A+P′X+P′O=100 The calcination has the effects of vaporizing humidity, burning the organic materials, and transforming carbonates (CaCO3) into lime (CaO):CaCO3→CaO+CO2 If an initial sample of 100 g is considered, the P′C grams of CaCO3 become P′c/1.78 gram of lime (1.78=ratio of the molar mass of the carbonate to that of the lime), and the P′O grams of humidity and of organics will have disappeared. Molar masses of CaO, SiO2, Al2O3, B2O3 et Fe2O3 are the following: 1 mole of CaO=56.1 g, 1 mole of SiO2=60.1 g, 1 mole of Al2O3=102 g, 1 mole of B2O3=69.6 g and 1 mole of Fe2O3=159.7 g. The mass of the calcined sample, M1, is therefore written as: M 1 = P C ′ 1.78 + P S ′ + P A ′ + P X ′ . And the mass percentages of the constituents of the calcined waste are written as: HumidityOtherandComponentsCaOSiO2Al2O3mineralsorganicsMass percentage P C 1 = 100 · P C ′ 1.78 · M 1 P S 1 = 100 · P S ′ M 1 P A 1 = 100 · P A ′ M 1 P X 1 = 100 · P X ′ M 1 0 In this way, we have:PC1+PS1+PA1+PX1=100 The quick lime (CaO) may also be obtained by calcination of gypsum (CaSO4(H2O)2) or of slaked lime (Ca(OH)2). The molecular mass ratios are then of 3.07 and 1.32 respectively, rather than 1.78 for carbonate. B.2—Percentages of the CAS Diagram In order to locate the composition of the waste in the CAS diagram, the calcined waste is considered and only lime, alumina and silica are taken into account. In the M1 grams of calcined waste from paragraph B.1—, only a portion M2 is taken into account, written as: M 2 = P C ′ 1.78 + P S ′ + P A ′ And the mass percentages in the CAS diagram are written as: ComponentCaOSiO2Al2O3Mass percentage P C = 100 · P C 1.78 · M 2 P S = 100 · P S M 2 P A = 100 · P A M 2 In this way, one has:PC+PS+PA=100 B.3—Examples of Calculations of the Proportions The mass percentage proportions for the soil, used in the examples, are the following: ComponentHumidityOtherandCaCO3/CaOSiO2Al2O3mineralsorganicsCrude soil67.5174.538compositionAfter60.727.37.24.80calcinationCAS63.828.67.6——percentages The mass percentage proportions for concrete, other than the one used in the examples but which was tested, were the following: ComponentHumidityOtherandCaCO3/CaOSiO2Al2O3mineralsorganicsCrude80.715.11.82.40concretecompositionAfter70.123.42.83.70calcinationCAS72.824.32.9——percentages B.4—Alumina Equivalence Coefficient for Hematite and Boron Oxide Initially, the soil and the concrete were treated by exclusively adding alumina alone. Then, the replacement of alumina with other trivalent oxides, i.e. Fe2O3 and B2O3, was tested. It was seen that the alumina may be totally or partly substituted with hematite or boric anhydride or with precursors which transform into these molecules during calcination, so as to retain a similarity between the properties of the different oxides used, by recording in the final mixture, a total alumina mass equal to the actual alumina mass to which is added 0.28 time the mass of hematite and 2 times the mass of boric anhydride. These equivalence coefficients, 0.28 and 2 do not simply result from an empirical observation, but were determined from the comparison of lime/hematite/silica and lime/boric anhydride/silica ternary diagrams with the CAS diagram. On the three diagrams, it is actually observed that a relatively rectilinear set of eutectic valleys (A (FIG. 1) and 9-10 (FIGS. 4-5)) joins the point M of the CaO—SiO2 line to a point P of the CaO—X2O3 (wherein X2O3 is the trivalent oxide), as schematized in FIG. 8. The position of the point M does not depend on the nature of the trivalent oxide, and is located in the domain of rankinite. A comparison of the positions of the point P for the different trivalent oxides allows determination of these equivalence coefficients. As for the case of alumina, if the composition is unbalanced so as to deviate from the eutectic, the melting temperature rapidly increases on the left of the valley (excess lime) and gently on the right of the valley (lime shortage). The position of the point P defines px, pX being the X2O3 mass percentage in a binary mixture CaO—X2O3. These px values were determined graphically on ternary diagrams, by taking an approximate middle point when the eutectic valleys branch towards the CaO/X2O3 line (case of X═Fe et X═Al): Trivalent oxideAl2O3Fe2O3B2O3% px538036 The equivalence coefficients are defined in such a way that by recording, in a binary or ternary mixture, the mass of X2O3 by the actual mass multiplied by this equivalence coefficient, the point P of the CXS diagram is superposed to the point P of the CAS diagram. In the following: px is the actual mass proportion of the trivalent oxide X2O3 in the CaO/X2O3 mixture corresponding to the position of point P in the CXS diagram, pA is the actual mass proportion of Al2O3 in the CaO/Al2O3 mixture corresponding to the position of point P in the CAS diagram, kx is the equivalent coefficient. 1 gram of binary mixture, corresponding to P, contains px grams of X2O3 et (1−px) grams of CaO. By applying the equivalence coefficient, this mixture is supposed to be equivalent to a mixture of k·px grams of Al2O3 and (1−px) grams of CaO. The proportions in this equivalent mixture are k · p x k · p x + 1 - p x of Al2O3 and 1 - p x k · p x + 1 - p x of CaO. k is sought in such a way that the proportion of Al2O3 is equal to pA: k · p x k · p x + 1 - p x = p A ⇔ k = p A · ( 1 - p X ) p X · ( 1 - p A ) The thereby determined equivalence coefficients are 2 for B2O3 and 0.28 for Fe2O3. The experimental data have validated these equivalence coefficients. The method for packaging toxic waste in an artificial rock, a glass or a vitrocrystalline solid comprised the successive steps of: analyzing the waste(s), adjusting the composition by adding additives, so that the final composition is in the target domain, if necessary, mixing the wastes so as to enter the starting domain as defined above, when the final composition comprises more than 10% of boric acid, separately calcining the components which may decompose at a temperature above 300° C., melting the whole at a temperature comprised between 1,250 and 1,650° C. (temperatures below 1,550° C. being obtained with boron oxide concentrations of more than 3%) casting the molten liquid in a lost or reusable ingot mold, obtaining a monolith after cooling without annealing, within a few hours to 15 days, depending on the size of the monolith. For the laboratory tests of Examples 1 to 9, the wastes to be treated were heated in a sacrificial crucible in alumina, placed in an oven, this crucible allowing automatic adjustment of the composition of the final waste. On the other hand, for the industrial tests of Examples 10 to 12, heating was carried out by the Joule effect, with graphite electrodes immersed in a crucible based on graphite. A crucible in any other refractory material and inert towards the produced lavas may be used. This heating technique via the Joule effect is preferred to the heating technique with the plasma torch since a significant amount of wastes has to be melted, with an industrial objective of robustness and throughput. In the diagram of FIGS. 6A to 6D, the graphite electrodes 30 (FIG. 6A) (usually 3 in number) heat the solid material 32 by radiation from an arc 31 between the electrodes, and are then immersed in the pool 34 (FIG. 6B) in order to sustain the melting via the Joule effect. Depending on the material forming the initial waste, it is also possible to begin heating by immersing the electrodes in the load. The electrodes are motorized so that they be raised or lowered. As the Joule effect is more efficient than radiative heating, it is interesting to operate semi-continuously with a pool of a larger volume than that of the ingot 26 (FIG. 7), so as to always keep a melt in the crucible 33. The cooled crucible 33 consists of joined pipes 33a which delimit a cavity. Water is circulated in the pipes so that the outermost layer of the waste solidifies. The thereby generated solid layer 35 protects the crucible from corrosion. The electrodes 30 are gradually consumed. This consumption represents at most 1% of the mass of the treated waste, and therefore does not significantly reduce the incorporation rate. This oven principle is used industrially for melting metals and for producing ceramics. The principle of heating with an arc and with the Joule effect is also known. In FIG. 7, an installation is illustrated with upstream equipment and downstream equipment of the oven 15. Before injecting the wastes 10 into the oven 15, it is necessary: to dry them 14, if need be, to mill them 11, if required, in order to obtain a grain size of less than 5 cm, typically. In certain cases, notably that of contaminated soil, it may be economically of interest to separate the big pieces in order to discharge them as a VWA (very weakly active) waste, a category below WA/MA, and less expensive, to carry out the mixing with the adjuvants 12. The upstream equipment comprises ingot molds 26 and premises 27 for the cooling. The premises 27 should be dimensioned depending on the flow of treated waste and on the cooling time, a maximum of one week. The preferred final packaging method is the metal barrel as a “lost” ingot mold. The melt is directly cast into the barrel. The barrel is buried in alumina sand in order to limit the cooling rate. After cooling, the loading of the barrel is completed by mortar 28 if necessary, the barrel is painted and closed and then evacuated. The most active wastes are conditioned in other packages such as concrete boxes or shells. In this case, the melt is cast into ingot molds with suitable dimensions and shapes for the final packaging, so as not to leave any voids. The ingots 26 are removed from the mold a few minutes after the casting, and like the barrels, they are buried in alumina sand for cooling. Depending on the nature of the waste, the fumes 17 contain, in addition to nitrogen and oxygen, water, CO2, CO, VOCs (volatile organic compounds), SOx, NOx and dusts. The radioactivity, except for very particular cases, (tritium and 14C), is borne by the dust and partly in the form of a gas (iodine, cesium and ruthenium isotopes). A strong VOC and CO content (from a strong content of organic products in the waste) would require post-combustion (not illustrated in the diagram). The following step is cooling 18 of the fumes to less than 200° C., so that the gaseous radio-elements (cesium, ruthenium) again pass into a particulate form, and are trapped in the particle filter 19. In the absence of particular radio-elements (tritium, 14C, iodines), the gas after filtration 19 may be considered as non-radioactive. It undergoes washing with water 22 in a washing column 20 to destroy the NOx and the SOx. The gas 21 is monitored and then discharged into the atmosphere. Full destruction of the NO requires a particular device, as a supplement, known in the industry, in which these NO gases are reduced to dinitrogen by ammonia. When the gas washing solution is saturated, it is evaporated and crystallized. The steam 22 is condensed so as to be reused as a washing solution. The salts 23 25 (nitrates, sulfates, carbonates) form a waste material which, according to the regulations and to the nature of the radioactivity of the incoming waste, will be considered as special industrial waste or a VWA radioactive waste. For practical reasons, certain conducted tests were made in a sacrificial crucible in alumina, the melt then incorporates the alumina of the crucible, until it finds equilibrium at the temperature which is imposed to it. Moreover, crude products (earth and concrete) are very heterogeneous, which makes the determination of their composition difficult. Therefore, additionally, analyses of the calcined products were also conducted, by checking the independently determined ignition loss factors, by thermo-gravimetric analysis. The tests of Examples 1 to 9 were conducted at a small scale (100 g), the samples having been finely milled (a grain size of less than 1 cm). Other tests on Examples 1 to 9 were conducted on a larger scale (2 kg), with a grain size attaining 1 cm. The tests of Examples 10 to 12 were carried out at an industrial scale (200 kg per casting). At this scale, a grain size which may attain 5 cm or even 10 cm, may be tolerated. In Examples 1 to 9, the target was a target domain defined around the eutectic valley separating gehlanite (Ca2Al2SiO7) from larnite (Ca2SiO4) in the CAS diagram, with: 50%>PC>35%, and 40%>PS>20%. The thermodynamic melting temperatures in this valley range from a little less than 1,400° C. to a little more than 1,500° C. in the CAS diagram. In the tables of the following Examples 1 to 12, the compositions of the crude starting products and of the products after calcination are in mass percentages, with: (1)=CaCO3 for the crude soil, CaO for the calcined product (2)=Al2O3 for lines 1 and 3 of the tables (3)=X2O3 (Al2O3 equivalent proportion) for the last line “CXS proportions” in a ternary system PC+PS+PX=100% In the tables of the following Examples 1 to 9, in the “CXS proportions” line, the values of PC, PX, PS, are given in the CaCO3/CaO, Al2O3/X2O3, Fe2O3 and SiO2 columns, respectively, as defined above with: PC+PS+PX=100%, and PX=PA+PB+PH. The incorporation rate of a given waste material is the volume of the obtained monolith divided by the volume of said material. In the last column of the tables, the term of “orga” means “organic compounds”. 50% of soil + 50% of sludge (simulated sludge)ComponentH2OCaCO3Al2O3 (2)OtherandCaO (1)X2O3 (3)Fe2O3SiO2mineralsorga.Crude soil67.54.51.317.11.48.2composition(%)Addition3562633(crudesludgemass %)Calcined39.27.118.634.11.0—mixturecomposition(%)Calcined45.714.539.8——mixtureCXSproportions(%)Melting temperature (° C., observed)1400Soil incorporation rate1.7Incorporation rate of soil + sludge3.5 The composition of crude soil is shown in reference 6, FIG. 3 and that of crude sludge in reference 7, FIG. 3. It is seen that the composition of the 50/50 sludge and calcined soil mixture (reference 8, FIG. 3) enters the target domain defined above. Concrete + 10% of alumina (reference 2, FIG. 2)ComponentH2OAl2O3 (2)OtherandCaO (1)X2O3 (3)Fe2O3SiO2mineralsorga.Crude58.93.00.430.11.66.0concretecomposition(%)Addition10(crude mass%)Calcined46.315.50.535.81.9—concretecomposition(%)Calcined47.416.036.6——concreteCXSproportions(%)Melting temperature (° C., observed)1620Incorporation rate of the soil (the added alumina is a fresh4.0product)Incorporation rate of soil + Al2O3 (the added alumina is4.3from a radioactive waste)(1): as regards crude concrete, this is in fact a mixture of more or less hydrated lime (CaO(H2O)n) and of carbonate (CaCO3). The composition of the crude concrete (reference 1, FIG. 2) is close to the domain of rankinite. The composition of the calcined concrete (reference 2, FIG. 2) is close to the intersection between the four domains: rankinite, pseudo-wollastonite, gehlenite, larnite. Soil + 20% of alumina + 20% of hematiteComponentH2OCaCO3Al2O3 (2)OtherandCaO (1)X2O3 (3)Fe2O3SiO2mineralsorga.Crude soil67.54.51.317.11.48.2composition(%)Addition2020(crude mass%)Calcined soil37.124.020.916.71.4—composition(%)Calcined soil44.335.720.0——CXSproportions(%)Melting temperature (° C., observed)1550Incorporation rate of soil (the added alumina and2.4hematite are fresh products)Incorporation rate of soil + Fe2O3 (the added alumina2.7is a fresh product)Incorporation rate of soil + Al2O3 (the additions are3.2from radioactive wastes) Soil + 10% of alumina + 30% of hematiteComponentH2OCaCO3Al2O3 (2)OtherandCaO (1)X2O3 (3)Fe2O3SiO2mineralsorga.Crude soil67.54.51.317.11.48.2composition(%)Addition1030(crude mass%)Calcined soil37.114.230.716.71.4—composition(%)Calcined soil48.429.821.8——CXSproportions(%)Melting temperature (° C., observed)1510Incorporation rate of soil (the added alumina and2.4hematite are fresh products)Incorporation rate of soil + Fe2O3 (the added alumina is2.8a fresh product)Incorporation rate of soil + Al2O3 + Fe2O3 (the additions3.1stem from radioactive wastes) Soil + 15% of alumina + 2.5% boric anhydrideComponentH2OCaCO3Al2O3 (2)OtherandCaO (1)X2O3 (3)Fe2O3B2O3SiO2mineralsorga.Crude soil67.54.51.317.11.48.2composition(%)Additional152.5(crude mass%)Calcined soil47.524.51.73.121.51.8—composition(%)Calcined soil47.431.121.4——CXSproportions(%)Melting temperature (° C., observed)1550Incorporation rate of soil (the added alumina and3.1hematite are fresh products)Incorporation rate of soil + B2O3 (the added alumina is3.2a fresh product)Incorporation rate of the earth + Al2O3 + B2O3 (the3.7additions stem from radioactive wastes) Soil + 10% boric anhydrideComponentH2OCaCO3Al2O3 (2)OtherandCaO (1)X2O3 (3)Fe2O3B2O3SiO2mineralsorga.Crude soil67.54.51.317.11.48.2composition(%)Addition10(crudemass %)Calcined52.56.21.813.923.71.9—soilcomposition(%)Calcined47.431.221.4——soilCXSproportions(%)Melting temperature (° C., observed)1250Incorporation rate of soil (the added B2O3 is a fresh3.4product)Incorporation rate of soil + B2O3 (B2O3 stems from a3.8radioactive waste) The very low melting temperature will be noted. This mixture is the most concentrated in boron, which does not produce any foam. The incorporation of boron oxide being in amounts above 5%, in order to avoid or reduce the production of foam, the carbonates have to be calcined before incorporating boron oxide, either sequentially in a single oven, or by using an oven dedicated to calcinations (around 950° C.). Fine fraction of the soil: grain size ofless than 1 cm (50% of the initial mass)ComponentH2OCaCO3Al2O3 (2)OtherandCaO (1)X2O3 (3)Fe2O3SiO2mineralsorga.Crude soil67.54.51.317.11.48.2composition(%)Addition−41.7−1.3−0.4−5.9−0.7(crude soilmass %)Composition47.710.33.136.82.4—of thecalcinedmixture (%)Calcined49.811.738.5——mixtureCXSproportions(%)Melting temperature (° C., observed)1530Incorporation rate8.1 The “additions” are negative because a portion of the initial material was removed. The very high incorporation rate (8.1) results from the fact that large particles assumed to be VWA particles, represent a negligible waste cost relatively to the final WA product. The CXS proportions of the final product are very close to those corresponding to concrete+10% Al (reference 2, FIG. 2) and to the calcined 50/50 soil/sludge mixture (reference 8, FIG. 3). The above tests show that the concerted addition of alumina in order to reach the eutectic valley separating gehlenite (Ca2Al2SiO7) from larnite (Ca2SiO4) in the CAS (lime, alumina, silica) ternary diagram, reduces both the melting temperature and the corrosivity of the melt. The conducted tests show that the regions of the selected eutectic valleys have interesting characteristics for melting the wastes: an actual reasonable melting temperature (below 1,650° C.) and low viscosity of the pool. The low viscosity is ascribed to the strong proportion of lime. This low viscosity reduces the difference between the actual melting temperature and the thermodynamic melting temperature. The difference observed on soil+alumina is 70° C., the one observed on concrete+alumina (a lower lime content) is 270° C. As a comparison, for a glass E (FIG. 1) as targeted in FR 2 741 552, the difference may exceed 500° C., which strongly reduces the benefit of working around the low point of the CAS diagram (1,170° C.). The tests have demonstrated that 50% of the cesium initially present in the waste remains captured in the monolith obtained according to the present invention, even with melting temperatures of 1,650° C. Moreover, the low viscosity allows rapid homogenization of the molten glass, which facilitates cooling of the monolith. According to the present invention, monolithic blocks of several kilograms are obtained with cooling for a few hours, without any crack, or, a fortiori any breaking up. Tests were conducted at an industrial scale (a monolith of 500 kg), with a cooling period of only 24 hours. A polycrystalline solid rather than a glass is preferably obtained. A polycrystalline solid or artificial rock is more likely not to crack in spite of rapid cooling. The conditions for obtaining such a condition of the final product are a composition slightly away from the eutectic, preferably in the domain of gehlenite, and a controlled cooling rate down to 1,000° C. Indeed, in order to obtain a polycrystalline material, a close composition must be targeted on the one hand, but different from the eutectic, the cooling rate must be reduced around the crystallization temperature on the other hand. It is easier to place the target in the domain of gehlenite (an excess of alumina in the earth) than in that of larnite (lack of alumina in the earth). Indeed, the melting temperature increases very rapidly when moving away from the eutectic in order to enter the domain of larnite, while it increases very slowly in the domain of gehlenite. A glass is less favorable than a polycrystalline solid, but it may also be contemplated taking into account the good homogeneity of the pool. The cooling time then has to be increased (one week). The tests have shown that a poorly balanced melt i.e. the composition of which is too far away from an eutectic, is highly in need for alumina. Coupled with low viscosity, this characteristic allows self-adjustment of the composition. It is sufficient to use a sacrificial crucible or alumina blocks in the pool so that the composition adjusts by itself to that of the closest eutectic valley, within a few minutes, by the composition of the crucible. It was observed that the crystallization of the target material occurs during cooling between 1,250 and 1,000° C. A relatively low cooling rate down to 1,000° C. (of the order of one hour) triggers crystallization. Once crystallized the material withstands highly rapid cooling (within less than 24 hours) down to room temperature, without developing any cracks. The desired cooling profile is obtained by burying the freshly cast ingot into a bed of powdered alumina (or another refractory material having similar heat conductivity) and by letting the assembly cool naturally in premises at room temperature for a few hours. Below 1,000° C., the cooling may be accelerated by extracting the ingot from its alumina bed (air quenching), or even by quenching it in water. A glass should be left in its alumina bed during the whole cooling period. The addition of non-radioactive alumina purchased commercially, with the purpose of adjusting the composition, degrades the incorporation rate. It is therefore preferable to adjust the composition by mixing radioactive wastes, notably radioactive alumina, sewage sludges from effluents of nuclear power plants, the incorporation rate then being maximum. The melting temperatures of the ternary diagrams with hematite and boric anhydride are significantly lower, which is favorable and corroborated by experimental results, especially in the presence of boric anhydride. As regards the investigated wastes, (soil and concrete) the compositions of the larnite/gehlenite eutectic valley are much closer to those of the initial waste than to the eutectic E: this valley is attained by adding 20% by mass of alumina to the soil, while 25% of alumina and 129% of silica would have to be added in order to attain the eutectic E. For an initial waste with an apparent density of 1.1, the incorporation rate is then 3.0 in the valley, instead of 1.6 for the eutectic E. The conducted tests have shown that soil, the stones of which have been extracted beforehand (a grain size greater than 1 cm, representing 50% of the initial mass), melts at 1,530° C., without any addition of alumina. By grain size sorting, if necessary, completed by washing with water, it is possible to declassify the stones of the WA (weakly active), VWA (very weakly active) category. The latter waste category requires less strict packaging than the WA wastes (putting into a big-bag, without any immobilization) and the handling cost is lower. Grain size separation of the stones, notably during the treatment of a limestone soil, not only allows reduction in the volume of waste to be treated, but also a favorable composition adjustment may be achieved. Boric anhydride, considered previously as a substitute for alumina, may also be considered as a flux agent (with the purpose of reducing the melting temperature). As a flux agent, additions will practically be limited to less than 10%. Beyond, foam problems occur. Soda is also a known flux agent agent. In equal proportion, its effect is not as strong as that of boric anhydride. With the silica enrichment, other eutectic valleys may be attained (larnite/rankinite, rankinite/pseudo-wollastonite, pseudo-wollastonite/gehlenite, pseudo-wollastonite/gehlenite/anorthite triple point) as quickly as with enrichment in alumina, the valley between gehlenite and larnite may be attained. The silica-depleted eutectic valleys around the compounds 3CaO.Al2O3, 5CaO.3Al2O3, CaO.Al2O3, CaO.2Al2O3 concern binary composition wastes (CaO and Al2O3), while the present invention concerns ternary compositions. But the behavior of the mixture is probably close to that of the investigated mixtures. Heating of the waste by the Joule effect was carried out by immersing graphite electrodes into the wastes, as described earlier. From the examples hereafter, it emerges that in the presence of the graphite of the electrodes, the iron oxides are reduced into metal iron, according to the same chemical reactions as those produced in a blast furnace, when iron ore is heated in the presence of coal. The melt then separates into 2 phases, one consisting of the synthetic rock with the target composition according to the invention in which X2O3 is Al2O3, the other one consisting of cast iron (iron+carbon); after solidification the iron is again found in the form of small metal inclusions with a size of less than 2 cm in the synthetic rock. The cooled block nonetheless forms a packaged waste material, acceptable by a center for surface storage of radioactive waste. For the tested wastes (with less than 5% of iron oxides, as in Example 11) the consumption of graphite electrodes which results from this, is negligible (less than 1% of the treated mass). For wastes which are more loaded with iron (cf. Example 12) or iron oxide (cf. Example 10), it may be interesting to promote this biphasic behavior, notably by adding carbon (carbon black, powdered graphite, coal) in a stoichiometric proportion with iron oxide, so as to avoid or reduce the consumption of electrodes. The final waste is more compact, because the reduction of the oxide into a metal releases mass in the form of CO2 gas but especially because the cast iron is denser than the synthetic rock (7,000 kg/m3 versus 2,700 kg/m3). The relevant wastes are in particular sludges (cf. Example 10), concretes with scrap iron (cf. Example 12). However, if the intention is to avoid reduction of iron oxides by the graphite of the electrodes, it is sufficient to operate the oven with an arc, i.e. without immersing the electrodes in the melt, (electrodes above the pool). In this case, it is possible to avoid segregation of metal cast iron and retain involvement of the iron oxides in said target composition. There remains the fact that the electrodes are nonetheless consumed by emission of CO2, even if they do not modify the redox characteristics of the melt. In Examples 11 and 12, the target composition was included in the domain of larnite (2CaO.SiO2), with a lime content close to 60%. It is found that melting occurs around 1,600° C., well before the theoretical temperature (>1,900° C.), that the solid formed contains a high proportion of gehlenite, and that, consequently, resistance to leaching is acceptable. Moreover, the mechanical characteristics are good, and especially the density is remarkably high (greater than 3), which allows reduction in the volume of final waste. The following starting compositions were applied (in mass %): ComponentHumidityOtherandCaCO3SiO2Al2O3Fe2O3mineralsorganicsSoil (%)67.517.14.51.31.48.2Mud (%)12.311.52.19.165 These compositions are identical with those mentioned earlier, illustrated in references 6 for the soil and 7 for the sludge in FIG. 2, except that the sludge contains 65% of water. A soil-sludge-alumina (adjuvant) mixture in proportions of 50%-45%-5% melts around 1,600° C. and a biphasic product is obtained comprising a synthetic rock incorporating small cast iron inclusions, of the following composition: ComponentsCastOtherCaOSiO2Al2O3ironmineralsMass %44.329.117.47.81.4 The phase of the synthetic rock is shown in FIG. 3, with reference 9-1, in the gehlenite domain. The initial volume of 100 kg of waste (sludge+soil, except alumina) is of 86.9 L, the final volume is 17.2 L: the volume reduction factor is 5.1. This very favorable reduction factor is due to: the water content of the sludge to the soil-sludge mixture limiting the required additions to the separation of the cast iron as an inclusion, and to the density of these inclusions. The synthetic rock block includes cast iron inclusions, with a total mass of 3.6 kg and a total volume of 0.54 L for 100 kg of initial waste. Density values: sludge: 1.2 kg/L soil: 1.1 kg/L synthetic rock: 2.7 kg/L cast iron: 7 kg/L. With the soil composition of Example 10, and addition of only 4% of alumina (96% of soil for 4% of alumina), the mixture melts around 1,600° C. (because of impurities outside CAS of the soil) and a biphasic product is obtained, comprising a synthetic rock including cast iron inclusions of the following composition: ComponentCastOtherCaOSiO2Al2O3ironmineralMass %57.525.913.11.42.1 The target composition of the synthetic rock is illustrated in reference 9-2 in FIG. 3, in the larnite domain. The initial volume of 100 kg of waste (sludge+soil, except alumina) is 90.9 L, the final volume is 21.8 L: the volume reduction factor is 4.2, this very favorable reduction factor is due to the smallness of addition of alumina (smallness authorized by the proximity of the starting composition of the soil and of the target composition), and to the strong density of the synthetic rock (3 kg/L). A crude concrete without any scrap iron was applied, with the following composition (mass %): ComponentCaCO3OtherCa(OH)2SiO2Al2O3Fe2O3mineralsWaterConcrete58.930.13.00.41.66(%) This composition of crude concrete is identical with the one used earlier. The concrete composition was supplemented with 20% by mass of scrap iron. It is interesting to mix this concrete with lime in order to enrich it in calcium. Certain concretes are originally richer in calcium. A concrete with a scrap iron-lime-alumina (adjuvant) mixture in proportions of 75%-17%-8% melts around 1,600° C. and a biphasic product of a synthetic rock incorporating cast iron inclusions of the following composition, similar to the one of Example 11 is obtained, but with a larger proportion of cast iron: ComponentCastOtherCaOSiO2Al2O3ironmineralsMass %47.821.411.618.01.1 The target composition of the synthetic rock is illustrated in reference 9-2 in FIG. 3, in the larnite domain, like for Example 11. The initial volume of 100 kg of waste (only concrete with scrap iron) is 100 L (the scrap iron concrete as rubble is denser than concrete without scrap iron), the final volume is 18.9 L: the volume reduction factor is 5.3 which is very favorable, is due to: the strong density of the synthetic rock (3 kg/L, excluding cast iron inclusions) the separation of the inclusions' cast iron, and to the density of these inclusions. The synthetic rock block includes cast iron inclusions, with a total mass of 10.5 kg and a total volume of 1.7 L for 100 kg of initial waste. |
|
abstract | A device and method for inspecting and measuring weld defects in a cylindrical wall of a cylindrical conduit. The device can include an inspection head forming a probe having a proximal end and a distal end along its longitudinal axis, and of which a first side called “inner side” is provided with at least one ultrasound wave transducer. The inspection head can include a second side, called “outer side” opposite the first side that has a curved surface in the form of a cylinder fraction, and wherein the curved surface of the second side has outward facing convexity. The wave transducer can be formed of a series of juxtaposed elements, each element being both a transmitter and receiver, wherein a surface of the series is curved and in the form of a cylinder fraction, and wherein the surface of the series has outward facing concavity. |
|
048184721 | summary | The invention relates to a method and an apparatus for the wet dismantling or disintegration of radioactively contaminated or activated components of nuclear reactor plants, wherein the component is provided with a sheathing having a thickness permitting it to perform the supporting function of a receptacle container for at least a part of the component after dismantling or disintegrating the component into individual pieces, the component is flooded with water for shielding radiation, the component is at least partly dismantled into individual pieces by a material-removing tooling or machining method, and the individual pieces are removed. Dismantling and crushing of a reactor pressure vessel in nuclear power plants is made more difficult by the contamination and activation resulting from neutron bombardment. The resultant radiation load on the operating staff can be kept at a low level by providing short staff exposure times, good shielding against radiation and remote control operation of the equipment. When radioactive components are disassembled, all of these three criteria are accordingly combined. The disassembly and crushing of a reactor pressure vessel can either be performed dry, i.e., in air, or under water. During remote-controlled dry dismantling or disintegration, which is performed under suitably shielding conditions using thick shielding plates, poor accessibility causes difficulties in extracting the radioactive elements. Moreover, if trouble is encountered during dismantling, the poor accessibility presents even further difficulties. During wet dismantling or disintegration, the good shielding effect of the water is exploited. It is known from the journal Electrical World, Feb. 15, 1978, page 47/48, to dismantle a demonstration reactor by filling both the safety vessel that surrounds the reactor vessel having the cooling system and the pool for spent and new fuel assemblies with water for shielding against radioactive radiation and by crushing the reactor vessel into small fragments. The fragments are first moved to a storage pool with a crane and are then delivered to a final storage location. With this conventional method, great quantities of radioactive waste are produced and the final storage thereof entails high costs. FIG. 1 of U.S. Pat. No. 3,158,546 discloses a nuclear power plant having a reactor pressure vessel disposed in a concrete pit, which is lined on the inside with a separate vessel to approximately 2/3 the height of the reactor pressure vessel. This vessel extends only up to a predetermined height of the concrete pit, not up to the height of the reactor pressure vessel, so that the reactor pressure vessel cannot be placed completely under water from the outside. If a reactor pit of this kind or such a pit that is not lined with an additional vessel were to be flooded for dismantling the reactor pressure vessel, leaks in the concrete and in the liner, if a liner is used, could lead to problems. After many years in operation, fissures in the concrete or in the biological shield which are in fact possible, result in a spreading of the contamination and hence in a greatly increased amount of radioactive waste. It is accordingly an object of the invention to provide a method and apparatus for the wet dismantling or disintegration of radioactively contaminated or activated components of nuclear reactor plants, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type, and which enables dismantling to be performed with simple means, while avoiding the spread of contamination into the biological shield even when the biological shield surrounding the component is not lined in advance with a water-tight vessel. With the foregoing and other objects in view there is provided, in accordance with the invention, a method for the wet dismantling of radioactively contaminated or activated components of nuclear reactor plants, which comprises enclosing the component with a jacket at the end of the service life of the component, providing a sheathing between the component and the jacket having a thickness sufficient to support at least part of the component after dismantling the component into individual pieces, flooding the component with water for radiation shielding, at least partly dismantling the component into individual pieces through a material removing method, and removing the individual pieces. With the objects of the invention in view there is also provided an apparatus for the wet dismantling of radioactively contaminated or activated components of nuclear reactor plants, comprising a jacket enclosing the component, and a sheathing in the form of shielding material disposed between the component and the jacket, the sheathing having a thickness sufficient to support at least a part of the component after dismantling the component into individual pieces. With the objects of the invention in view there is additionally provided a method for the wet dismantling of a radioactively contaminated or activated reactor pressure vessel disposed inside a reactor pit and spaced from a concrete biological shield defining a gap between the pressure vessel and the shield, which comprises severing coolant lines and closing connector stumps of the reactor pressure vessel, subsequently filling the gap between the pressure vessel and the shield by casting or injection molding forming a sheathing having a thickness sufficient to support at least part of the component after dismantling the component into individual pieces, flooding the component with water for radiation shielding, at least partly dismantling the component into individual pieces through a material removing method, and removing the individual pieces. With the objects of the invention in view there is furthermore provided an apparatus for the wet dismantling of a radioactively contaminated or activated reactor pressure vessel disposed inside a reactor pit and spaced from a concrete biological shield defining a gap between the pressure vessel and the shield, comprising a sheathing filling the gap between the reactor pressure vessel and the shield by casting or injection molding after severing coolant lines and closing connector stumps of the reactor pressure vessel, the sheathing having a thickness sufficient to support at least part of the component after dismantling the component into individual pieces. With the objects of the invention in view there is also provided a method for the wet dismantling of a radioactively contaminated or activated pressure vessel of a nuclear reactor plant, which comprises placing a bottom plate with a given diameter below the reactor pressure vessel, enclosing the pressure vessel with an enclosure tube having a lower end with the given diameter, tightly joining the lower end of the tube to the bottom plate, flooding the pressure vessel with water for radiation shielding, at least partly dismantling the pressure vessel into individual pieces through a material removing method, and removing the individual pieces. With the objects of the invention in view there is additionally provided an apparatus for the wet dismantling of a radioactively contaminated or activated pressure vessel of a nuclear reactor plant, comprising a bottom plate with a given diameter disposed below the reactor pressure vessel, and an enclosure tube enclosing the pressure vessel, the tube having a lower end with the given diameter tightly joined to the bottom plate. With the objects of the invention in view there is furthermore provided an apparatus for the wet dismantling of a radioactively contaminated or activated pressure vessel of a nuclear reactor plant having a bottom with a given diameter, comprising an enclosure tube enclosing the pressure vessel, the tube having a lower end with the given diameter tightly joined to the bottom of the pressure vessel. The advantages attainable with the invention are above all that it can be adapted to the most varied conditions in a reactor building and is therefore highly flexible. Typically, the thermal insulation formed of individual modules which is secured to the inner periphery of the biological shield and correspondingly the thermal insulation elements disposed on the bottom, are removed prior to the disposition of the sheathing. The dismantling or disintegration can be performed successively and the individual pieces can be removed from the sheathing and deposited in a spent fuel cooling pool or in a barrel for final storage. Prior to the disposition of the sheathing by integral casting or extrusion coating, in order to reinforce the sheathing and make it stronger, it may be suitable to provide the component with a framework or a skeleton of a reinforcement, which is suitably formed of annular members and jacket members, so that the result is a reinforcement network that covers the entire outer surface of the component. This network is then joined to or cast integral with the casting compound of the sheathing. When an enclosure tube is used, the outer diameter thereof is preferably dimensioned in such a way as to leave the smallest possible air gap between the tube and the reactor pit. 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 method and apparatus for wet dismantling or disintegration of radioactively contaminated or activated components of nuclear reactor plants, 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. |
claims | 1. A process for removal of radon from indoor air comprising the step of contacting said indoor air with adsorbent, said adsorbent comprising a silver-exchanged zeolite. 2. The process of claim 1 wherein the radon level within said indoor air is at least 2 pCi/l. 3. The process of claim 1 wherein the radon level within said indoor air is at least 4 pCi/l. 4. The process of claim 1 further comprising the step of removing moisture from said indoor air prior to said contacting step. 5. The process of claim 1 wherein the zeolite is selected from the group consisting of zeolite A, zeolite X, zeolite LSX, zeolite Y, mordenite, chabazite, clinoptilite, erionite, ferrierite, zeolite L and offretite. 6. The process of claim 1 wherein the silver-exchanged zeolite is also exchanged with lithium. 7. The process of claim 1 wherein the silver-exchanged zeolite is silver/lithium-exchanged zeolite having an ion exchange composition of the form LixAgyMz where 0.85≦x+y≦1, 0.2≦y≦0.7, and 0≦z≦0.15 with M representing one or more cations, and x, y, and z representing fractions of total exchangeable sites in the zeolite. 8. The process of claim 7 wherein M is a cationic form of one or more elements selected from the group consisting of Na, K, Cs, Mg, La, Ce, Ca, Al, and Zn. 9. The process of claim 7 wherein the zeolite is zeolite X. 10. The process of claim 4 wherein said step of removing said moisture from said indoor air is performed by contacting said indoor air with adsorbent. 11. The process of claim 10 wherein said adsorbent for said removing step is alumina, silica gel, zeolite or mixtures thereof. 12. A process for the removal of impurities from indoor air contaminated with radon within a building comprising the steps of;contacting the indoor air steam with porous material which releases silver ions upon contact with water for removing bacteria and molds;contacting the indoor air with desiccant under conditions for removing moisture; and,contacting the indoor air with silver exchanged zeolite capable of removing radon. 13. The process of claim 12 further comprising the step of contacting the indoor air with adsorbent capable of removing ozone after said contacting with said dessicant step. 14. The process of claim 13 further comprising the step of contacting the indoor air with adsorbent capable of removing volatile organics or carbon oxides prior to said contacting step for removing radon. 15. The process of claim 14, wherein the silver exchanged zeolite for removing radon is selected from the group consisting of zeolite A, zeolite X, zeolite LSX, zeolite Y, mordenite, chabazite, clinoptilite, erionite, ferrierite, zeolite L, and offretite. 16. The process of claim 14 wherein the silver exchanged zeolite for removing radon is also exchanged with lithium. 17. The process of claim 1 further comprising the step of contacting said air with adsorbent capable of removing hydrocarbons from said air prior to said contacting said silver-exchanged zeolite. 18. The process of claim 1 further comprising the step of contacting said air with adsorbent capable of removing ozone from said air prior to said contacting said silver-exchanged zeolite. 19. The process of claim 1 further comprising prior to said contacting of said silver-exchanged zeolite step, the steps of:contacting said air with adsorbent capable of removing moisture from said air, contacting said air with adsorbent capable of removing hydrocarbons from said air, and contacting said air with adsorbent capable of removing ozone from said air. 20. The process of claim 1 further comprising prior to said contacting of said silver-exchanged zeolite step, the steps of:contacting said air with adsorbent for removing moisture from said air comprising a material selected from the group consisting of alumina, silica gel, zeolite and mixtures thereof;contacting said air with adsorbent for removing hydrocarbons from said air comprising a material selected from the group consisting of activated carbon, silica gel, alumina and high Si/Al ratio zeolites; andcontacting said air with adsorbent comprising a material selected from the group consisting of hopcalite (CuO/MnO mixture), noble metal catalysts, activated carbon, zeolites, silica gel, hydrotalcite, clays and alumina for removing ozone from said air. 21. The process of claim 20 further wherein the silver-exchanged zeolite for removal of said radon is silver/lithium-exchanged zeolite having an ion exchange composition of the form LixAgyMz where 0.85≦x+y≦1, 0.2≦y≦0.7, and 0≦z≦0.15 with M representing one or more cations, and x, y, and z representing fractions of total exchangeable sites in the zeolite. |
|
048184730 | summary | BACKGROUND OF THE INVENTION This invention relates to nuclear reactors and has particular relationship to fuel bundles or fuel assemblies. To aid those skilled in the art in practicing this invention by the description of this invention in this application of a concrete structure, this application deals in detail with a fuel assembly of a boiling-water reactor (BWR). To the extent that this invention may be embodied in reactors of other types, such as pressurized-water reactors (PWR), it is understood that such embodiments are within the scope of equivalents of this invention. A fuel bundle includes a top plate and a bottom plate between which fuel rods are mounted. The fuel rods are held together by axially spaced straps or spacers. In accordance with teachings of the prior art, each bundle is provided with tie rods which are screwed into, or bolted to, the bottom plate. Each prior art bundle also has spacer-capture rods which are secured to the bottom plate by pins to suppress rotation about their axes and have axially spaced tabs to prevent axial displacement of the spacers. Removal of the tie rods during reconstitution, particularly complete reconstruction, of a fuel bundle presents formidable difficulties because it demands access to the bottom plate, usually in a radioactive environment, to unscrew or unbolt the tie rods and to disengage the spacer-capture rods. It is an object of this invention to overcome the above-described drawbacks and disadvantages and to provide a fuel bundle which may be readily completely reconstituted by removal of tie rods without access to the bottom plate. It is another object of this invention to provide a fuel bundle in which the spacer-capture rods shall be dispensed with. SUMMARY OF THE INVENTION In accordance with this invention there is provided a fuel bundle having one or more tie rods each secured to the bottom plate by a key by means of which the tie rod can be locked to, and unlocked from, the bottom plate without direct access to the bottom plate. Each tie rod is also secured to the top plate by means for preventing rotation of the tie rod. Specifically, the tie rod has at the bottom a flat key which passes through a slot in the bottom plate. The tie rod may be locked to the bottom plate by turning the rod so that the key is at an angle to the slot under the bottom plate. At the top the tie rod has a flattened plug whose transverser cross-section resembles a race track. The plug has a thread on its rounded sides. A nut is threaded onto the thread on the plug and engages the top plate. The plug passes through a slot in the top plate. The nut has a crimping lip which is crimped to the plug. To disassemble the bundle the crimp for each tie rod is broken by turning the nut. The nut and top plate can then be removed and the tie rod turned to unlock the key and removed by access to the top of the bundle. The plug has a flat tip which may be engaged to prevent rotation of a tie rod when the crimp is broken and the nut unscrewed by turning the nut. Since the tie rods of this invention are not rotatable they may carry the tabs which prevent displacement of the straps and the spacer-capture rods may be dispensed with. |
summary | ||
049816160 | summary | BACKGROUND OF THE INVENTION This invention relates to a method of treating spent fuel utilizable in a spent nuclear fuel retreatment process, scrap nuclear fuel wet reclamation process, etc. Ordinarily, in spent nuclear fuel re-treatment and scrap nuclear fuel wet reclamation processes, organic solvent used in an extraction process is degraded by the effects of acidity and radiation. Consequently, the degraded products are removed from the organic solvent by a solution of sodium hydroxide or sodium carbonate, after which the solvent is reused. Certain shortcomings, however, exist in such conventional methods. These are as follows: (1) Reclamation of organic solvent in which there is advanced deterioration is impossible, and the solvent becomes a liquid radioactive waste that is difficult to treat. (2) A solution containing sodium is mixed with radioactive liquid waste of the nitrate family, after which the resulting solution is reduced in volume and solidified in glass or asphalt. However, owing to the large amount of sodium contained, the reduction in volume has its limitations. This also accounts for complicated solidification treatments. In view of the foregoing, there is a need to develop a process which minimizes the use of sodium as well as a solvent reclamation process. Further, though evaporation cans are used to concentrate radioactive material in treatment of liquid radioactive wastes, these are disadvantageous because decontamination is inefficient and the cans are subject to considerable corrosion. It is desired, therefore, that a treatment process with a higher decontaminating efficiency and less corrosion be developed. SUMMARY OF THE INVENTION This invention has been devised to solve the foregoing problems and its object is to provide a method of treating spent fuel in which a salt-free process is capable of being employed. Another object of the invention is to provide a method of treating spent fuel in which, by using a freeze-vacuum drying process, material corrosion is eliminated by operation at low temperatures, safety is enhanced by eliminating the danger of fire, explosion and the like, and use of organic substances containing sodium is minimized to enable reduction and simplification of equipment for asphalt and glass solidification. Still another object of the invention is to provide a method of treating spent fuel in which recovered solution can be reutilized and liquid radioactive waste reduced in volume. A further object of the invention is to provide a method of treating spent fuel in which solvent can be reutilized and liquid radioactive waste reduced in volume by employing a vacuum distillation process, which has a high decomtamination efficiency, in the recovery of the solvent. The invention provides a method of treating spent fuel in a spent nuclear fuel retreatment process and scrap nuclear fuel wet reclamation process, characterized by separating a spent solvent of a solvent cleansing process into tri-n-butyl phosphate (hereinafter referred to as TBP), n-dodecan and dibutyl phosphate (hereinafter referred to as DBP) by using a freeze-vacuum drying process and vacuum distillation process. Further, the invention provides a method of treating spent fuel in a spent nuclear fuel retreatment process and scrap nuclear fuel wet reclamation process, characterized by separating a liquid radioactive waste into liquid and residue by using a freeze-vacuum drying process in treatment of the liquid radioactive waste. Further, the invention provides a method of treating spent fuel in a spent nuclear fuel retreatment process and scrap nuclear fuel wet reclamation process, characterized by obtaining a nitrate by powdering a plutonium solution and a uranium solution using a freeze-vacuum drying process, denitrifying the nitrate and subjecting the same to roasting reduction to obtain an oxide powder. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawing. |
summary | ||
summary | ||
054694817 | claims | 1. A method of making a cladding tube having an outer substrate, an intermediate zirconium barrier layer, and a zirconium-based inner liner having alloying elements, the substrate, barrier layer, and inner liner each having interior and exterior circumferential surfaces, the method comprising the following steps: (a) bonding the zirconium barrier layer exterior circumferential surface to the substrate interior circumferential surface; (b) bonding the inner liner outer circumferential surface to the zirconium barrier layer inner circumferential surface; and (c) conducting a diffusion anneal after steps (a) and (b) at a time and temperature sufficient to cause the alloying elements from the inner liner to diffuse into the barrier layer to form a diffusion layer containing a concentration of alloying elements that decreases from the interior circumferential surface of the barrier layer to a location interior to the barrier layer where there is substantially no alloying elements, wherein the alloying elements in the diffusion layer impart corrosion resistance to the barrier layer. (a) bonding the zirconium barrier layer exterior circumferential surface to the substrate interior circumferential surface; (b) bonding the inner liner outer circumferential surface to the zirconium barrier layer inner circumferential surface; and (c) conducting a diffusion anneal after steps (a) and (b) at a time and temperature sufficient to cause the alloying elements from the inner liner to diffuse into the barrier layer to form a diffusion layer containing a concentration of alloying elements that decreases from the interior circumferential surface of the barrier layer to a location interior to the barrier layer where there is substantially no alloying elements, wherein the alloying elements in the diffusion layer impart corrosion resistance to the barrier layer. (a) bonding the zirconium barrier layer exterior circumferential surface to the substrate interior circumferential surface and bonding the inner liner outer circumferential surface to the zirconium barrier layer inner circumferential surface to form a tubeshell; (b) conducting a diffusion anneal at a time and temperature sufficient to cause the alloying elements from the inner liner to diffuse into the barrier layer to form a diffusion layer containing a concentration of alloying elements that decreases from the interior circumferential surface of the barrier layer to a location interior to the barrier layer where there is substantially no alloying elements; (c) performing two or more cold work steps, each followed by a stress relief or recrystallization anneal; and (d) heating at most about the outer 33% of the outer substrate into the alpha plus beta or beta phase and then cooling to produce a distribution of fine precipitates in the outer region of the substrate, wherein the alloying elements in the diffusion layer impart corrosion resistance to the barrier layer. 2. The method of claim 1 wherein the step of conducting a diffusion anneal is performed at a temperature and a time of between about 650.degree. and 1000.degree. C. for between about 1 minute and 20 hours. 3. The method of claim 1 wherein the step of conducting a diffusion anneal is performed after formation of a tubeshell. 4. The method of claim 3 wherein the step of conducting a diffusion anneal is performed at a temperature of between about 650.degree. and 825.degree. C. for between about 4-20 hours. 5. The method of claim 1 wherein the step of conducting a diffusion anneal is performed after a final pass cold work step. 6. The method of claim 5 wherein the step of conducting a diffusion anneal is performed at a temperature of between about 650.degree. and 825.degree. C. for between about 5 minutes and 10 hours. 7. The method of claim 1 wherein steps (a) and (b) are conducted as a single step. 8. The method of claim 1 further comprising a step of removing the inner liner by a surface conditioning process. 9. A cladding tube having an outer substrate, an intermediate zirconium barrier layer, and a zirconium-based inner liner having alloying elements, the substrate, barrier layer, and inner liner each having interior and exterior circumferential surfaces, the cladding tube being made by a process comprising the following steps: 10. The cladding tube of claim 1 wherein the step of conducting a diffusion anneal is performed at a temperature and a time of between about 650.degree. and 1000.degree. C. for between about 5 minutes and 20 hours. 11. The cladding tube of claim 1 wherein the step of conducting a diffusion anneal is performed after formation of a tubeshell. 12. The cladding tube of claim 1 wherein the step of conducting a diffusion anneal is performed after a final pass cold work step. 13. A method of making a cladding tube having an outer substrate, an intermediate zirconium barrier layer, and an inner liner having alloying elements, the substrate, barrier layer, and inner liner each having interior and exterior circumferential surfaces, the method comprising the following steps: 14. The method of claim 13 wherein the step of conducting a diffusion anneal is performed at a temperature and a time of between about between about 650.degree. and 825.degree. C. for between about 4 hours and 20 hours. 15. The method of claim 14 wherein the step of conducting a diffusion anneal is performed at a temperature and a time of between about between about 800.degree. and 825.degree. C. for between about 4 hours and 6 hours. 16. The method of claim 13 further comprising a step of removing the inner liner by a surface conditioning process. 17. The method of claim 16 wherein the surface conditioning process is a chemical etch. |
abstract | A container for storing and transporting device containing radioactive materials used for medical procedures is disclosed. Such devices may include a radioactive shielding material which contains a portion of the radioactivity emitted by the radioactive material. The container has an upper portion and a lower portion, and at least one of the portions includes a radiation shielding material, such as lead, steel or other appropriate shielding materials. Devices containing radioactive material are placed within the container. The container secures the devices against lateral movement within the container. The radiation shielding material of the lower portion of the container may cooperate with the radiation shielding material of the device to contain more of the emitted radiation than is contained by the device alone. The container and the holder may be sterilizable to allow such devices to be transported and sterilized for medical use. |
|
062630385 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One conventional type of nuclear reactor in which the MOX fuel can be utilized is the pressurized water reactor (PWR). This type of reactor typically combusts a uranium oxide (UO.sub.2) fuel to produce steam. These NSSS (nuclear steam supply systems) traditionally include two-loop arrangement with two steam generators, two hot legs, and four cold legs each with a reactor coolant pump. One specific example of a PWR in which the embodiments of the invention can be implemented is ABB Combustion Engineering' s'System 80.RTM. reactor which loads 241 fuel assemblies. Each assembly, as seen in FIG. 1, is mechanically identical to the others and consists of a 16.times.16 fuel rod array 20 with five large structural guide tubes 21 that each occupy 2.times.2 fuel lattice locations. The four outer guide tubes are for control element assembly (CEA) fingers, while the center guide tube is used for in-core instrumentation. The in-core instruments are bottom-entry, and therefore do not interfere with the upper internal design for CEA guidance. Each fuel assembly contains 236 fuel rods 22. As seen in FIG. 2, the CEA's have either 4 or 12 element arrangements. The 12 element CEA has the unique characteristic of inserting into five adjacent fuel assemblies, as shown in FIG. 3. This characteristic is made possible by the unique upper guide structure design of the reactor internals, which provide continuous guidance for each individual CEA element into the fuel assembly guide tube. This upper guide structure, shown in FIG. 4, is a rugged, all-welded structure, and protects each individual CEA element from flow forces and dynamic loads. In this UO.sub.2 core design, burnable absorber pins which contain erbia (Er.sub.2 O.sub.3) admixed with enriched UO.sub.2 are used in the fuel assemblies. These burnable fuel rods are located in predetermined locations to provide reactivity hold down and control power peaking. Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. FIGS. 5A to 14A show ten different 16.times.16 fuel assembly designs containing MOX fuel which were developed for use in the equilibrium cycle core designs of the above mentioned type of nuclear reactor. According to the invention, it is possible to select a number (e.g. 241) of one or more of the these fuel assembly designs and to compile the core in a manner which will enable a particular set of combustion characteristics, such as produced by using only conventional uranium fuel, to be replicated. Burnable absorber rods containing erbia are incorporated into these MOX fuel assembly designs to provide reactivity hold down and control power peaking. These are fuel-bearing burnable absorbers, but do not contain MOX in accordance with the above mentioned ground rules/restraints which have been imposed. Instead, the burnable absorber rods employed in these MOX assemblies are, in the disclosed embodiments, an admixture of erbia and enriched UO.sub.2, and are functionally identical to the burnable absorber pins described earlier in the discussion of the traditional UO.sub.2 core design. The fuel assembly designs in FIGS. 5 to 14 are differentiated by the number of MOX fuel rods and the number of urania-erbia (UO.sub.2 --Er.sub.2 O.sub.3) rods within each assembly as well as by the specific arrangement of these rods. In FIGS. 5 to 14, "M" represents a MOX fuel rod and "E" represents an urania-erbia fuel rod. The number of urania-erbia rods in the fuel assembly designs in the arrangements shown in FIGS. 5 to 14 ranges from 24 to 88. Within each fuel assembly design, the locations of the burnable absorber (urania-erbia) rods and the MOX fuel rods are fixed. Both the UO.sub.2 enrichment in the urania-erbia rods and the plutonium enrichment (wt % of Pu-239) in the MOX fuel rods can be varied during the core design process. Typically, there are 5 to 8 different plutonium enrichments in the MOX fuel rods within any given fuel assembly. For the urania-erbia rods, the UO.sub.2 enrichment is the same in all of the rods within a particular fuel assembly. Each of the fuel assembly designs in FIGS. 5A to 14A were developed on an octant basis and are octant-symmetric. Each of FIGS. 5B to 14B and 5C to 14C depict, for an assembly octant, the specific Pu-239 enrichment of each MOX fuel rod and the resulting normalized intra-assembly power distribution. Since the enrichment of the burnable absorber rods is fixed within any one of these fuel assembly designs, the respective octant maps in FIGS. 5B to 14B and 5C to 14C identify them within each assembly with the letter "E". Actually, two such octant maps are depicted for each assembly design, representing data for a low enrichment case in FIGS. 5B to 14B and a high enrichment case in FIGS. 5C to 14C, respectively. Between these two cases, each fuel pin's enrichment differs by exactly 1.0 wt. %. For the MOX pins, the Pu-239 enrichment is as shown. For the erbia pins, a fixed UO.sub.2 enrichment of 4.0 wt. % is selected for the low enrichment case and a fixed UO.sub.2 enrichment of 5.0 wt. % is selected for the high enrichment case. Each MOX assembly is designed to provide optimal performance over this range of enrichments represented by the low enrichment case and the high enrichment case. Detailed neutronics, generated for both cases, indicates that the neutronics behavior is characterized as a function of fuel enrichment. This design approach makes it possible to consider the effects of varying assembly enrichments during an equilibrium cycle core design phase without the need of re-generating any additional assembly data. By using different fuel rod enrichments within each MOX fuel assembly as described herein and as shown in the corresponding figures, it is possible to both optimize the intra-assembly power peaking, which enhances the performance of the fuel assemblies during operation, and to maximize the throughput of weapons-grade plutonium in each core. The burner absorber rod characteristics for the MOX assembly designs are also arranged to optimize the intra-assembly power peaking and have the secondary benefit of enhancing the throughput of weapons-grade plutonium in each core. FIG. 5A shows the MOX fuel assembly design of a first embodiment of the instant invention having a 16.times.16 fuel rod array including 24 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 5B shows a low enrichment octant map and FIG. 5C shows a high enrichment octant map of this embodiment. Each of these maps depicts one octant of the 236 rod arrangement shown in FIG. 5A. As will be noted, in the case of the low enrichment, while most of the MOX rods have a Pu-239 enrichment of 4.8 wt %, a number of the rods, which are in proximity of the guide tubes 21, have lower values which are as low as 3.3 wt %. The corresponding MOX rods according to the high enrichment schedule are, as mentioned above, 1% richer. FIG. 6A shows the MOX fuel assembly design according to a second embodiment of the instant invention and which has a 16.times.16 fuel rod array including 32 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 6B shows a low enrichment octant map and FIG. 6C shows a high enrichment octant map of this embodiment. FIG. 7A shows the MOX fuel assembly design of a third embodiment of the instant invention having a 16.times.16 fuel rod array including 40 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 7B shows a low enrichment octant map and FIG. 7C shows a high enrichment octant map of this embodiment. FIG. 8A shows the MOX fuel assembly design of a fourth embodiment of the instant invention having a 16.times.16 fuel rod array including 48 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 8B shows a low enrichment octant map and FIG. 8C shows a high enrichment octant map of this embodiment. FIG. 9A shows the MOX fuel assembly design of a fifth embodiment of the instant invention having a 16.times.16 fuel rod array including 56 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 9B shows a low enrichment octant map and FIG. 9C shows a high enrichment octant map of this embodiment. FIG. 10A shows the MOX fuel assembly design of a sixth embodiment of the instant invention having a 16.times.16 fuel rod array including 60 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 10B shows a low enrichment octant map and FIG. 10C shows a high enrichment octant map of this embodiment. FIG. 11A shows the MOX fuel assembly design of a seventh embodiment of the instant invention having a 16.times.16 fuel rod array including 64 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 11B shows a low enrichment octant map and FIG. 11C shows a high enrichment octant map of this embodiment. FIG. 12A shows the MOX fuel assembly design of an eighth embodiment of the instant invention having a 16.times.16 fuel rod array including 72 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 12B shows a low enrichment octant map and FIG. 12C shows a high enrichment octant map of this embodiment. FIG. 13A shows the MOX fuel assembly design of a ninth embodiment of the instant invention having a 16.times.16 fuel rod array including 80 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 13B shows a low enrichment octant map and FIG. 13C shows a high enrichment octant map of this embodiment. FIG. 14A shows the MOX fuel assembly design of a tenth embodiment of the instant invention having a 16.times.16 fuel rod array including 88 erbium (UO.sub.2 --Er.sub.2 O.sub.3) rods. FIG. 14B shows a low enrichment octant map and FIG. 14C shows a high enrichment octant map of this embodiment. In accordance with the invention, equilibrium cycle core designs using MOX fuel can be developed using a subset consisting of any combination (e.g. up to three) of the ten fuel assembly designs shown in FIGS. 5A to 14A. FIGS. 15 and 16 show examples of two different equilibrium cycle core loading patterns having a feed batch size of 81 fuel assemblies (i.e. 81 new fuel assemblies). FIG. 17 shows an equilibrium cycle core loading pattern having a feed batch size of 88 fuel assemblies. In FIGS. 15 to 17, "X" represents a fresh assembly, "Y" represents a once-burned assembly and "Z" represents a twice-burned assembly, "O" represents an assembly sub-type with 24 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods, "3" represents an assembly sub-type with 48 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods, "4" represents an assembly sub-type with 56 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods, "5" represents an assembly sub-type with 60 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods and "7" represents an assembly sub-type with 72 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods. FIG. 15 shows a feed batch having 25 assemblies with 24 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods and 56 assemblies with 56 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods. The average enrichment of MOX fuel rods in this feed batch is 5.16 wt % Pu-239. FIG. 16 shows a second feed batch arrangement having 17 assemblies with 24 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods, 36 assemblies with 56 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods and 28 assemblies with 72 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods. The average enrichment of MOX fuel rods in this feed batch is 5.01 wt % Pu-239. FIG. 17 shows a third feed batch arrangement having 64 assemblies with 48 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods, 12 assemblies with 56 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods and 12 assemblies with 60 UO.sub.2 --Er.sub.2 O.sub.3 fuel rods. The average enrichment of MOX fuel rods in this feed batch is 4.67 wt % Pu-239. A summary of some important design parameters for the equilibrium cycle for a MOX core design and a typical UO.sub.2 core design is shown in Table 1 set forth at the end of this disclosure. These equilibrium cycle core designs using MOX fuel were evaluated to assess their performance characteristics relative to a typical UO.sub.2 equilibrium cycle core design. As will be appreciated, the invention enabled the MOX core to perform in a manner which closely corresponds to the power level--average coolant temperature series of parameters produced with a UO.sub.2 core. Table 2, which is also set forth at the end of this disclosure, shows a comparison of some important core performance characteristics for the 88 feed batch assembly MOX core design shown in FIG. 17 and a typical 18-month cycle UO.sub.2 core design. The core average burn-up for the MOX-based 18-month cycle core design (17,000 MWd/MTHM) is consistent with that for a similar UO.sub.2 -based cycle (17,500 MWd/MTHM). The maximum fuel rod burn-up is within the licensed limit of 60,000 MWD/MT. The discharge burn-up (46,000 MWd/MTHM) is consistent with discharge burn-ups (45,000 MWd/MTHM) for comparable UO.sub.2 -based fuel cycles. The hot full power (HFP) all-rods-out (ARO) BOC critical boron concentration (CBC) for the MOX-based core design is 1990 ppm, compared to 1250 ppm for a UO.sub.2 -based core design. Although larger than the value for a typical UO.sub.2 core, the HFP BOC CBC for the MOX core is less than the maximum allowable value of 2000 ppm necessary to remain within the existing analysis envelope for existing plants. The power distributions for the MOX-based core design are similar to those for a comparable UO.sub.2 -based core design. The maximum expected peaking factors for the MOX core are slightly higher than those for the UO.sub.2 core, but within the allowable limits (less than or equal to 1.72 for Fr, 2.00 for Fz, for HFP ARO conditions) necessary to remain within the existing analysis envelope. The MOX-based equilibrium cycle core designs developed in the instant invention achieve a throughput of approximately 1.5 MT (Metric Tons) of weapons-grade plutonium per 18 month cycle. As a result, the disposal of 50 MT of weapons-grade plutonium could be accomplished in three System 80.RTM. reactors in approximately 17 years of plant operation. This includes the transition from a conventional, low enrichment UO.sub.2 core to a MOX core. Numerous 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 invention may be practiced otherwise than as specifically described herein. For example, as will be self-evident from the above disclosure, if a fuel qualification for MOX fuel wherein the use of erbia in the MOX rods was permitted, a substantial increase in the throughput of plutonium would be enabled with an attendant reduction in the time needed to dispose of any given quantity of weapons grade plutonium. TABLE 1 Core Design Parameters UO.sub.2 Core MOX Core Power Level 3876 Mwth 3876 Mwth Nominal Cycle Length 18 Months 18 Months .about.460 EFPD 463.5 EFPD 17.500 GWd/MTHM 17,000 GWd/MTHM Fuel Assemblies 241 241 Fuel Assembly Configuration 16 .times. 16 16 .times. 16 Fuel Rod Locations/Assembly 236 236 Active Core Height (inches) 150 150 Fuel Loading (MTHM) 102.3 102.3 Fuel Type Enriched U-235 Enriched WG Pu.sub.2 O.sub.3 in Tails UO.sub.2, Burnable Absorber Type Er.sub.2 O.sub.3 in Enriched UO.sub.2 Er.sub.2 O.sub.3 in Enriched UO.sub.2 Fuel Management 3-batch, mixed central zone 3-batch, mixed central zone Erbia Loading (integral) <2.5 wt % (integral) <2.5 wt % Feed Batch Size Assemblies 72-104 81-88 Feed Fuel Enrichment <4.5 wt % U-235 .about.4.5-5.0 wt % Pu-239.sup.(1) Soluble Burnable Absorber Natural B.sub.10 Natural B.sub.10 Control Element Assemblies Standard Configuration 76 Full-Length, Full Strength 76 Full-Length, Full Strength or 13 Part-Length, Part Strength 13 Part-Length, Part Strength Enhanced Configuration 89 Full-Length, Full Strength Average Heat Generation Rate 5.45 KW/FT 5.45 KW/FT Average Coolant Temperature 585.degree. F. 585.degree. F. .sup.(1) Average for MOX pins only TABLE 2 Core Performance Characteristics System 80 .RTM. Equilibrium Cycle Core Design UO.sub.2 Core MOX Core BOC EOC BOC EOC Burnup Data, MWd/MTHM Core Average 13,700 31,200 17,000 34,000 Maximum Fuel Rod -- 51,600 -- 57,400 Discharge Batch Average -- 45,000 -- 46,400 Critical Boron Data, PPM HFP, ARO 1250 1 1990 90 Inverse Boron Worth, PPM/% .DELTA.p Hot Full Power -130 -107 -227 -169 Maximum Peaking Factors Fr (HFP, ARO) 1.51 1.64 Fq (HFP, ARO) 1.83 1.96 Moderator Temperature Coefficient (MTC), 10.sup.-4 .DELTA.p/.degree.F. Hot Zero Power +0.17 -- -1.62 -- Hot Full Power -0.72 -2.89 -1.80 -3.91 Standard CEA Standard CEA Enhanced CEA Configuration Configuration Configuration CEA Worths, % .DELTA.p.sup.(1) Total Net Total Net Total Net BOC, HZP 12.6 10.0 11.0 8.7 11.9 9.9 EOC, HZP 15.1 11.3 13.3 10.2 14.4 11.3 EOC, Cold (68.degree. F.) 11.1 7.5 10.2 6.7 11.1 7.7 .sup.(1) The CEA worths are raw values, with no biases or uncertainties, for comparison purposes only. |
summary | ||
abstract | The invention relates to x-ray filters in a collimator for controlling the energy of an x-ray beam along a projection axis in computed tomography systems. According to the invention, the filter assembly comprises a filter element for attenuating the x-ray beam, and at least a support plate which fixes the filter element. The filter element and the support plate are notch-shaped in the center part of the filter assembly along a direction perpendicular to the projection axis. The design may free space to be used by other collimator parts and further allows use of more than one filter element in a filter assembly for backup purposes. This simplifies replacement of a defective x-ray filter in the field. |
|
abstract | An exemplary embodiment is a method and system for performing an automated independent technical review. The method includes receiving an assay result of a radioactive waste container, determining whether the assay result is within a predetermined parameter, determining whether a review is required if the assay result is not within the predetermined parameter and rejecting the assay result if the review is not required and the assay result is not within the predetermined parameter. |
|
summary |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.