patent_number
stringlengths 0
9
| section
stringclasses 4
values | raw_text
stringlengths 0
954k
|
|---|---|---|
abstract | A nuclear fuel assembly is provided for a boiling water reactor. The nuclear fuel assembly includes a base, a head, and a bundle of full length fuel rods and partial length fuel rods, said bundle extending upwardly and longitudinally from the base to the head. The nuclear fuel assembly includes at least one clamp for longitudinally retaining a lower plug of a partial length fuel rod with respect to the base. The clamp is an additional part fitted to the base, the clamp is at least partially received in a housing provided in the base, and the clamp is assembled to the base by mechanical engagement of complementary assemblies. |
|
summary | ||
047284790 | claims | 1. A high pressure seal fitting with a built-in low pressure seal arrangement for sealing a space defined by an inner diameter of a pipe and a rod slidably disposed within the pipe and extending beyond an end of the pipe, said fitting comprising: a fitting body provided with an axial passage for slidably accommodating the rod and having a first and region constructed for engaging the end of the pipe for forming a high pressure seal between the pipe and said fitting body, and a second end region opposite said first end region and including an outer circumferential protrusion having the shape of a ferrule for cooperating with components utilized to form a releasable high pressure compression seal; and low pressure seal means disposed in the axial passage at said second end region of said fitting body for maintaining a low pressure seal between said fitting body and the rod when said releasable high pressure seal is disconnected, said fitting body being disposed radially intermediate said releasable high pressure compression seal and said low pressure seal means. 2. A fitting according to claim 1, wherein said fitting body has an inner surface defining the axial passage and said low pressure seal means comprises a flexible ring disposed in the axial passage at said second end region for filling a space defined by said inner surface and the rod, and compression means for compressing said flexible ring for forming the low pressure seal. 3. A fitting according to claim 2, wherein said compression means includes a seal nut, threads provided at said second end region for engaging said seal nut, and a first annular abutment provided on said inner surface at said second end region between said threads and said first end region, said first annular abutment providing a stop for said flexible ring which can be urged against said first annular abutment by appropriate rotation of said seal nut via said threads. 4. A fitting according to claim 3, wherein said first annular abutment is formed by an annular recess in said inner surface. 5. A fitting according to claim 3, wherein said low pressure seal means includes a seal washer disposed between said flexible ring and said seal nut. 6. A fitting according to claim 5, wherein said inner surface includes a second annular abutment between said first annular abutment and said threads which forms a stop for said seal washer. 7. A fitting according to claim 2, wherein said flexible ring has a U-shaped axial cross section. 8. A fitting according to claim 1, wherein the first end region of said fitting body is provided with exterior threads and an inwardly directed compression surface for cooperating with a compression nut and ferrule appropriately arranged on the pipe. 9. A fitting according to claim 1, wherein the first end region of said fitting body is adapted to be welded to the pipe. 10. A fitting according to claim 1, wherein said fitting body is comprised of first and second separate components connected together by a fluid tight joint, said first component containing said first end region and said second component containing said second end region. 11. A fitting according to claim 10, wherein said first component is provided with exterior threads and an inwardly directed compression surface for cooperating with a compression nut and ferrule appropriately arranged on the pipe. 12. A fitting according to cliam 10, wherein said first component is adapted to be welded to the pipe. 13. A fitting according to claim 10, wherein said first and second components are connected together by a welded joint. |
claims | 1. An optical storage medium, comprising stacked data storage layers each of which is readable/writeable separately from the other layers by means of a light beam striking one side of the optical storage medium, whereina recordable area of a first data storage layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which the first and second data storage layers are stacked, and said at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of the second data storage layer, and, further, whereinsaid first data storage layer is located closest to a light-striking surface of said optical storage medium, and said second data storage layer is located next to said first data storage layer, away from said light-striking surface. 2. The optical storage medium as set forth in claim 1,whereinat least one of said at least one extended area portion is a pseudo-recording area which is fully prerecorded. 3. The optical storage medium as set forth in claim 2,whereinsaid pseudo-recording area stores identification information which is unique to said optical storage medium and by which said optical storage medium is distinguished from other optical storage media. 4. The optical storage medium as set forth in claim 3,whereininformation in said pseudo-recording area is not rewriteable. 5. The optical storage medium as set forth in claim 2,whereinsaid pseudo-recording area stores encryption information by which data are encrypted before being recorded on said optical storage medium. 6. The optical storage medium as set forth in claim 5,whereininformation in said pseudo-recording area is not rewriteable. 7. The optical storage medium as set forth in claim 1,whereinsaid data storage layers exhibit a lower optical reflectance in recorded areas than in non-recorded areas. 8. The optical read/write apparatus as set forth in claim 1, whereina recordable extended area portion is provided adjacent to each end of a main recordable area portion of said first data storage layer, so as to cover more than the area directly above said recordable area of said second data storage layer in the direction in which said first and second data storage layers are stacked. 9. The optical read/write apparatus as set forth in claim 1, whereina recordable extended area portion at one or more ends of a main recordable area portion of said first data storage layer extends into one of the group consisting of an innermost part of said first data storage layer, an outermost part of said first data storage layer, or an address area on said first data storage layer. 10. The optical read/write apparatus as set forth in claim 9, whereina recordable extended area portion at one or more ends of said main recordable area portion of said first data storage layer extends into a region having a lower optical transmittance than said main recordable area portion of said first data storage layer. 11. The optical read/write apparatus as set forth in claim 9, whereina recordable extended area portion at one or more ends of said main recordable area portion of said first data storage layer extends into a region having a higher transmittance than said main recordable area portion of said first data storage layer. 12. The optical storage medium as set forth in claim 1, whereinat least one of said at least one extended area portion is assigned as a test write area. 13. An optical read/write apparatus, comprising:illumination means for supplying a read/write light beam;optical storage medium mounting means for supporting an optical storage medium such that said read/write beam from said illuminating means strikes only a light-striking side of said optical storage medium,said optical storage medium including stacked data storage layers each of which is readable/writeable separately from the other layers by means of a light beam striking said light-striking side of said optical storage medium, wherein:said optical storage medium is structured and configured such that a recordable area of a first data storage layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which the first and second data storage layers are stacked, and said at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of the second data storage layer, and, further, whereinsaid first data storage layer is located closest to said light-striking surface of said optical storage medium, and the second data storage layer is located next to the first data storage layer, away from said light-striking surface; and whereincontrolling means controls said illuminating means so that at least one of said at least one recordable extended area portion of said optical storage medium is fully recorded first. 14. The optical read/write apparatus as set forth in claim 13, whereinsaid optical storage medium exhibits a lower optical reflectance in recorded areas of said data storage layers than in non-recorded areas thereof. 15. An optical read/write apparatus comprising:illumination means for supplying a read/write light beam; andoptical storage medium mounting means for supporting an optical storage medium such that said read/write beam strikes one side of an optical storage medium, said optical storage medium including stacked data storage layers each of which is readable/writeable separately from the other layers by means of said light beam striking said one side of said optical storage medium, wherein:said optical storage medium is structured and configured such that a recordable area of a first data storage layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which said first and second data storage layers are stacked, and said at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of said second data storage layer, and, further, wherein said first data storage layer is located closest to a light-striking surface of said optical storage medium, and said second data storage layer is located next to said first data storage layer, away from said light-striking surface; and wherein controlling means controls said illuminating means so as to write test data in at least one of said at least one extended area portion. 16. The optical read/write apparatus as set forth in claim 15, whereinsaid optical storage medium exhibits a lower optical reflectance in recorded areas of said data storage layers than in non-recorded areas thereof. 17. An optical read/write method comprising the steps of:providing a read/write apparatus comprising:illumination means for supplying a read/write beam; andoptical storage medium mounting means for supporting an optical storage medium such that said read/write beam from said illumination means strikes only a light-striking side of said optical storage medium, said optical storage medium including stacked data storage layers that each are readable/writable separately from the other layers by means of a light beam striking said light-striking side of said optical storage medium, wherein said optical storage medium is structured and configured such that a recordable area of a first layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which said first and second data storage layers are stacked, and said at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of said second storage layer, and further wherein said first data storage layer is located closest to said light-striking surface of said optical storage medium, and said second data storage layer is located next to said first data storage layer away from said light-striking surface; and wherein control means controls said illuminating means so that at least one of said at least one recordable area portion of said first layer of said optical storage medium may be fully recorded first; andfully recording said at least one of said at least one extended area portion first. 18. An optical read/write method comprising the steps of:providing a read/write apparatus comprising:illumination means for supplying a read/write beam; andoptical storage medium mounting means for supporting an optical storage medium such that said read/write beam from said illumination means strikes only a light-striking side of said optical storage medium, said optical storage medium including stacked data storage layers that each are readable/writable separately from the other layers by means of a light beam striking said light-striking side of said optical storage medium, wherein said optical storage medium is structured and configured such that a recordable area of a first layer including at least one recordable extended area portion is provided above a second data storage layer in a direction in which said first and second data storage layers are stacked, and at least one recordable extended area portion extends in a radial direction of said optical storage medium past an entire recordable area of said second storage layer, and further wherein said first data storage layer is located closest to said light-striking surface of said optical storage medium, and said second data storage layer is located next to said first data storage layer away from said light-striking surface: and wherein control means controls said illuminating means so as to write test data in at least one of said at least one extrended area portion first; andwriting test data in said at least one of said at least one extended area portion first. |
|
abstract | A radiation detecting apparatus of this invention includes an arithmetic processing device which carries out arithmetic processes for drawing boundaries based on peaks of signal strengths and separating respective positions by the boundaries, and for determining, by using spatial periodicity of the peaks, the number of peaks having failed to be separated, with a plurality of peaks connecting to each other. If the separation fails with a plurality of peaks connecting to each other, the number of peaks in error is determined using spatial periodicity of the peaks. Thus, by using spatial periodicity of the peaks, the number of peaks in error can be determined and boundaries can be set easily. As a result, incident positions can also be discriminated easily, and detecting positions of radiation can be determined easily. |
|
046844929 | summary | The invention relates to a repair fixture for water-cooled nuclear reactors. When making repairs on the walls of a reactor pressure vessel or when replacing primary shutdown controls of water-cooled nuclear reactors, these primary shutdown controls must be evacuated beforehand. However, this is only possible if the water level in the reactor pressure vessel is lowered to the extent that it is below the level of the primary shutdown controls to be repaired or below the level of the outlets of the respective conduits, such as the feedwater distributors. The same applies when repairs on the walls of the reactor pressure vessel become necessary. In the case of boiling water reactors and pressurized water reactors, this presupposes that all of the fuel elements must first have been removed from the core barrel. This is extremely costly. Moreover, during evacuation of the core barrel and during the lowering of the water level in the reactor pressure vessel, a perceptible radiation exposure of the operating and maintenance personnel is to be expected. Lastly, the lowering of the water level in boiling water reactors requires special shielding measures to be taken for the steam separator and steam dryer. It is accordingly an object of the invention to provide a repair fixture which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, and to provide means for performing repairs on the primary shutdown controls or even on the walls of a reactor pressure vessel, which can be carried out without having to lower the water level in the reactor pressure vessel. With the foregoing and other objects in view there is provided, in accordance with the invention, a repair fixture for water-cooled nuclear reactors including an openable reactor pressure vessel having a wall, and conduits passing through the pressure vessel wall for flooding the pressure vessel, comprising a sealing box disposed in the opened, flooded pressure vessel, means connected to the sealing box for pressing the sealing box liquid-proof or tightly, abutting against the pressure vessel wall enclosing at least some of the conduits, and means connected to the sealing box for evacuating the conduits enclosed by the sealing box. A sealing box which, according to the invention, can be liquid-tightly applied against the pressure vessel wall in the flooded reactor pressure vessel in vicinity of the feedwater distributors or conduit connections, permits the evacuation of covered wall areas including the feedwater distributors and conduit connections present at that location, with the reactor pressure vessel flooded. If primary shutdown controls are placed at the same level or higher, they are then evacuated at the same time. Otherwise, they can be evacuated through the connecting conduits. In accordance with another feature of the invention, the conduits are feedwater distributors having conduit connections leading to primary shutdown controls of the pressure vessel. In accordance with a further feature of the invention, there are included means disposed in the sealing box for mounting inspection, testing and treatment equipment. In accordance with an added feature of the invention, there is provided a support ring lowerable into the pressure vessel, the sealing box being mounted on the support ring. This greatly facilitates handling of the rather bulky sealing box. Such a support ring at the same time helps to transmit to the wall of the reactor pressure vessel, the compressive forces of the sealing box exerted against the inner surface of the wall of the reactor pressure vessel. In accordance with an additional feature of the invention, there is provided a core barrel disposed in the pressure vessel below the conduits, the support ring including props engaging the core barrel when the support ring is lowered. In accordance with again another feature of the invention, the support ring has an outer periphery including lateral props engaging the inner surface of the pressure vessel wall for absorbing radial compressive forces of the sealing box. In accordance with again a further feature of the invention, there are provided setting cylinders displacing the lateral props against the inner surface of the pressure vessel wall. The very efficient bracing of the support ring on the core barrel of the nuclear reactor defines a reference height of the support ring, from which the further displacement of the sealing box relative to the support ring can occur. At the same time, a crane will be available for other jobs, such as the repositioning of fuel elements, during the running repair measures. In accordance with again an added feature of the invention, there are provided means for displacing the sealing box in radial or circumferential direction of the support ring. In accordance with again an additional feature of the invention, the support ring has an axis of symmetry, and including a guide connected to the support ring in which the sealing box is displaceable vertically and parallel to the axis of symmetry. In this way, the sealing box can by-pass or pass behind guide rods extending along and spaced from the pressure vessel wall. In accordance with yet another feature of the invention, there are provided hydraulic cylinders controlling displacements radially, circumferentially and vertically of the sealing box relative to the support ring. In accordance with yet a further feature of the invention, there are provided guide cams between the sealing box and the support ring adapted to a given reactor type for forcibly displacing the sealing box in radial direction relative to the support ring. Such cams avoid damage due to improper manipulations which are not impossible, to say the least, with universal, freely selectable hydraulic adjustment. In accordance with yet an added feature of the invention, the pressure vessel has an axis of symmetry and contains fuel elements including outer fuel elements disposed at a given distance from the axis of symmetry, and the conduits are feedwater distributors protruding into the pressure vessel, and including a support ring on which the sealing box is mounted, the sealing box having a depth in radial direction of the pressure vessel being only that which is absolutely necessary to cover the protrusion of the feedwater distributors, and the support ring and the sealing box leaving an unobstructed inside diameter of the pressure vessel being more than twice the given distance, when the sealing box is pressed against the pressure vessel wall. In accordance with yet an additional feature of the invention, the sealing box has rims to be pressed against the pressure vessel wall, and sealing lips or gaskets disposed on the rims. In accordance with still another feature of the invention, each of the gaskets is substantially L-shaped and has a longer and a shorter leg, the longer leg being pressed against the pressure vessel wall and having a narrow sealing edge and a wide sealing lip, and a shallow fillet between the sealing lip and sealing edge. In accordance with still a further feature of the invention, the evacuating means include a pump. The evacuation of the conduits or feedwater distributors covered by the sealing box can be carried out with this construction. In accordance with still an added feature of the invention, there is provided a float switch disposed in the sealing box and connected to the pump for controlling the pump. In accordance with still an additional feature of the invention, the pump is disposed in the sealing box. This simple and expedient solution causes the pump to be switched on automatically if necessary in case of leaks or other intrusions of water. In accordance with another feature of the invention, the pressure vessel has a given water level, and including an air venting hose connected to the sealing box and leading above the water level. In accordance with a further feature of the invention, the conduits are in the form of four feedwater distributors connected to the pressure vessel, and including grommets and guides being screwed to the support ring and movable for repositioning along the periphery of the support ring toward the feedwater distributors. The traverses are also needed to manipulate other core inserts, such as water separators and are guided in many nuclear reactor types for automatic coupling or for exact deposition of these core inserts in the pressure vessel area and are not rotatable at will about the axis of symmetry thereof. For this reason, this construction is especially appropriate for covering the feedwater distributors, which are usually offset relative to each other by 90.degree. or 180.degree.. In this way, the sealing box can be repositioned by 90.degree., 180.degree. or 270.degree.. In accordance with an added feature of the invention, the support ring is divided into sections. This makes the support ring easier to transport to the site where it is used and to mount it between the inserts. In accordance with an additional feature of the invention, the sealing box is at least partly transparent. In accordance with again another feature of the invention, there are provided transparent windows disposed in the sealing box. In accordance with again a further feature of the invention, there are provided means disposed in the sealing box for mounting at least one light source and a television camera. In accordance with again an added feature of the invention, the mounting means includes means for moving and adjusting a television camera along the sealing box. In accordance with a concomitant feature of the invention, the mounting means are in the form of remotely controllable carriers for eddy current testing probes having ultrasonic testing heads and means for carrying out a color penetration method. 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 repair fixture, 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. |
049833510 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a plan view, partially broken away and partially in cross-section, of a detector string 40 in accordance with the present invention; it comprises a plurality of balls 42 mounted at approximately 2-inch spacings on a wire 44 having tip pieces 46, of identical configurations, at its opposite ends. The balls 42 are of approximately 0.2 inches in diameter and are formed of stainless steel containing manganese, i.e., a manganese steel alloy, which is well known in the art and functions as a gamma emitter with a 2.6 hour half life. The 2.6 hour half life is considered sufficiently long, such that accurate compensation for decay after exposure can be made, i.e., the detected radiation level does not overly attenuate, following exposure and prior to read out, as would happen if a very short half life isotope were employed, in the alternative, as the gamma detector element. On the other hand, the half-life is short enough in time such that the radiation level of the detector string 40 will decay to a sufficiently low level of activity within 8 to 12 hours, such that it may be available for re-use following that time period. The length of the wire 44, and thus the distance between the opposite ends of tip pieces 46, is dependent on the height of the core, or lower internals, of the reactor vessel with which the instrumentation system is used and the number thereof as well is dependent on the size and power level of the vessel. As a specific example, one particular pressurized water reactor, yielding 600 megawatts of electric power and having a core design employing 145 standard Westinghouse 17.times.17 fuel assemblies, would require 48 in-core detectors 40 of the type of FIG. 1 for developing an adequate power distribution map. While the 2-inch interval spacing of the balls 42 may afford adequate axial power resolution for the in-core detectors for the exemplary and illustrative system, it is believed apparent that the spacing and number of balls, per detector, and the number of detectors may vary with the resolution requirements of a given installation. For the illustrative case, however, a total of 72 balls would be employed for a 12-foot high core, to which the height of the detector 40 would correspond. The balls 42 are 0.188 inches in diameter and are affixed to a 0.30 inch diameter stainless steel wire 44 at the indicated 2-inch spacing. The complete detector 40 for this specified installation weighs approximately 0.2 pounds, or about 3 ounces. The configuration of the tip pieces 46, comprising an arrowhead portion 46a, a reduced neck portion 46b, and an elongated, cylindrical shank portion 46c, affords high induced fluid drag, and thus movement, of the detector string 40 in response to the flow of the primary coolant fluid thereover, and also serves to span small gap spaces in the guide tubing and serves as a handling grab, all as later hereinafter described. A significant advantage afforded by the detector string 40 of the present invention is the capability of moving it through a very tight radius bend; this is afforded both by the flexibility of its structure and its configuration, especially that of the tip pieces 46 which affords sufficient flow induced drag force for moving the detector 40 through a tight radius bend. For the specific example, the calculated friction drag for the detector string 40, when moving through a 90.degree., 12-inch radius bend in its enclosing guide tube, is approximately 0.8 pounds. From this calculation, it is estimated that a minimum of 1 pound to a maximum of 2 pounds of flow induced drag force will be needed to move the detector string 40 through 0.211 inch ID tubing, which can be achieved by supplying a primary coolant flow rate of 100 to 200 pounds per hour (0.2 to 0.4 GPM). Thus, for the illustrative system, a total system primary coolant flow rate of 10 to 20 GPM will suffice to move all 48 detector strings simultaneously either into or out of the core. The velocity of the primary coolant flow and the corresponding movement of the detector string 40 resultant therefrom will be in the range of 3 to 5 feet per second. As further illustrated hereinafter, approximately 50 to 100 linear feet of each guide tube will be required, to extend between the external temporary storage chamber for the detectors 40 and the core of the reactor vessel. Correspondingly, for the indicated range of velocities, the 48 detector strings 40 will require from 15 to 30 seconds to traverse, simultaneously, the respective, 50 to 100 linear feet long guide tubes extending between the external temporary storage chamber and the core. FIG. 3 is a schematic, partially brokenaway, and generally elevational view of a pressure vessel 50 employing an instrumentation system 60 in accordance with the present invention. The vessel 50 is mounted in a containment structure 48 of reinforced concrete, formed in a conventional manner, but configured to include an open area 49a beneath the vessel 50 communicating through a horizontal passage 49b and a vertical passage 49c to an in-core instrumentation system (ICIS) read-out room 49d, the passages 49a, b and c accommodating piping 62 and other apparatus, later described, for transport of the detector strings 40 between the handling, control, and sensing apparatus of the instrumentation system 60 mounted within the ICIS read-out room 49d and the core 52 (also generally termed the "lower internals") of the vessel 50. In accordance with this first embodiment of the present invention, the tubes 62, through which the detector strings 40 pass, extend through bottom penetrations 54 which mount through the sidewall of the lower dome enclosure, or lower head, 56 of the vessel 50. As before noted, a second embodiment of the present invention, subsequently described, provides for the alternative of top head penetration, i.e., the transport tube for the detectors 40 extend through top penetrations in the sidewall of the upper dome enclosure, or upper head 58. In either instance, the interior passageways of the small diameter tubes 62 are in communication with and thus at substantially the same pressure as the primary coolant within the vessel 50. Thus, the primary coolant pressure boundary of the vessel 50 effectively is extended beyond the walls of the reactor vessel 50 and encompasses the small diameter tubes 62. Accordingly, the containment structure 48 bounds the small diameter tubes 62 and related components of the instrumentation system 60, as is illustrated in FIG. 3. A significant advantage is gained, however, in that the guide tubes inside of the reactor vessel 50, which direct the associated detector strings 40 to and from the necessary sensing positions in the core 52, do not require hermetic sealing within the internals of the vessel 50, thus enabling the utilization of easy-to-make, slip-fit or face-contact connections, as later described. In accordance with the invention, there is one detector string 40, of the type shown in FIG. 2, and an associated guide tube for each radial core position within the core 52 which is to be sensed and thus read-out. Approximately 50 of the detector strings 40 and associated guide tubes would be employed in a typical two or three loop plant. As is conventional and well known in the art, a two loop plant typically is in the 600 megawatt range of electric power generation, and employs two steam generators and two associated pumps with corresponding sets of two cold primary coolant inlet nozzles 51a and 51b, and tWo hot, primary coolant outlet nozzles 53a and 53b, as illustrated in FIG. 3. A three loop plant, on the other hand, has a typical power output in the range of 900 to 1,000 megawatts and includes three associated sets of components corresponding to the described sets for a two loop plant. The corresponding relationship and required number of components will be apparent, in relationship to a four loop plant which produces typically in the range of 1,000 to 1,200 (or more) megawatts of power output. Thus, it is to be understood that whereas the present invention is described with regard to an illustrative two loop plant, it is in no sense limited to any specific number of loops or power output capability, and the number of the detectors 40 and associated small diameter tubes will be selected in accordance with the size of the plant and the desired mapping resolution. Inherent in the structure of the detector string 40 of the present invention is its capability of being passed through very small diameter tubes 62 and particularly through very small, or short, bend radii of such tubes in the order of 4 to 8 inches, without inducing excessive drag and pressure drop. Actual tests have demonstrated that the detector string of the invention will flow through a bend radius of 2.6 inches; thus, bend radii in the range of 4 to 8 inches are readily achieved. This small tube bend radii facilitates either the bottom entry, or penetration, configuration as shown in FIG. 3 and mentioned above, or the top penetration through the upper dome enclosure, or head, 58 as likewise mentioned above and described in further detail hereinafter. Of particular significance to the bottom penetration configuration employed in the vessel 50 of FIG. 3 is the fact that the space beneath the lower head 56, which must be afforded within the containment structure 48, is significantly reduced. For example, as shown in FIG. 3, for a two loop system, forty-eight (48) tubes 62 are connected through a corresponding number of bottom penetrations 54 and internal tubing to the appropriate positions within the core 52. The space 49a between the lower-most extent of the lower head 56 and the containment structure 48, for accommodating the tubes 62, may be on the order of two to three feet. By contrast, the guide thimbles used in the referenced, prior art movable detector system, given the ten to twelve foot bend radii required therefor, would correspondingly require a space 7 as shown in FIG. 1 of 12 to 15 feet, and thus an additional nine feet or more greater than that required for the instrumentation system of the present invention. The present invention accordingly provides a significant advantage in terms of the reduced size and substantial savings in cost of the containment structure 48 within which the vessel 50 employing the instrumentation system 60 of the invention may be installed, compared to the prior art movable thimble detector systems. FIG. 3 also illustrates additional components, common to either of the basic, bottom and top head penetration (the latter being described subsequently) embodiments of the present invention. The forty-eight (48) tubes 62 pass through a heat exchanger 64, continuing tube portions 62' being connected to a system of solenoid valves 66, further tube portions 62'' interconnecting the valves 66 to a detector string storage chamber 68 and further tube portions 62'', interconnecting chamber 68 to a transfer device 70. As will become clear, storage chamber 68 may be simply that section of the tubes 62 extending between valves 66 and transfer device 70 and thus encompassing tube sections 62'' and 62''', and accordingly defines individual storage positions for each of the forty-eight (48) detector strings 40. As described hereafter, each detector string 40 may be individually and selectively transported into or removed from its individual storage position in the chamber 68. Transfer device 70 enables selective withdrawal of each detector string 40 from its corresponding storage position within the chamber 68 and transfer of same to a gamma counter 80 for sensing the radiation levels detected by the balls of the individual detector string 40. Following sensing, the transfer device 70 selectively directs the sensed, or monitored, detector string 40 to a suitable, further destination. For example, transfer device 70 may withdraw a selected detector string 40 from the instrumentation system 60 for disposal or, alternatively, introduce a new detector string 40 into the system and, for example, into its appropriate storage position within the chamber 68. The system is designed for automatic control by a controller (not shown in FIG. 3), typically disposed in the ICIS read-out room 49d, which provides for automatic control of the insertion, radiation, removal, read-out, and temporary storage or disposal of the detector strings 40. In that regard, the solenoid valves 66 are individually operated in accordance with the required procedure by the controller (not shown), as indicated by the bi-directional control buss 67 connected between the valves 66 and the controller (not shown). The transfer of the detector strings 40 through the associated tubes 62 and other apparatus, as before noted, is performed by directing a flow of primary coolant thereover: a circulation pump for that purpose (not shown in FIG. 3) is provided in the ICIS read-out room 49e. The primary coolant withdrawn from the vessel 50, however, is typically at 600.degree. F., a level which could produce damage or impose undesired requirements on various of the apparatus of the instrumentation system 60, such as the solenoid valves 66 and the transfer device 70. Accordingly, a heat exchanger (HX) 64 having secondary coolant inlet and outlet connections 65a and 65b is provided in the path of the tubes 62 intermediate the vessel 50 and the solenoid valve 66 for reducing the temperature of the primary coolant withdrawn from vessel 52 to, e.g., ambient. FIGS. 4A and 4B are elevational, cross-sectional views, partly schematic and partly broken away, illustrating the internal structure of a conventional pressure vessel 50; FIG. 4A, moreover, illustrates the installation therein of an instrumentation system 60 in accordance with the bottom head penetration configuration of the first embodiment of the invention, and FIG. 4B illustrates the top head penetration configuration of the second embodiment of the present invention. Attention initially is addressed to the conventional elements of the vessel 50 shown substantially identically in FIGS. 4A and 4B. The vessel 50 includes a generally cylindrical sidewall 55, through which extend an illustrative cold primary coolant inlet nozzle 51a and an illustrative hot primary coolant outlet nozzle 53a. The sidewall 55 is enclosed at its bottom by a bottom dome enclosure, or bottom head, 56 The upper end of the sidewall 55 includes an enlarged annular flange 55a further defining an internal annular ledge 55b. The upper head 58 includes a mating enlarged flange 58a which is received on the enlarged annular flange 55a of the sidewall 55 and is secured thereto by bolts 59. Within the vessel 50 there are defined an upper head region 50a, regions known as the upper and lower internals 50b and 50c, respectively, and a bottom head region 50d. The portions of the vessel 50 primarily relevant to the first embodiment of the present invention, as discussed in detail hereinafter, are the lower internals 50c and the bottom head region 50d of FIG. 4A; by comparison, those portions primarily relevant to the second embodiment are the upper head region 50a and the upper internals 50b, along with the instrumentation thimbles within the fuel rod assemblies of the lower internals 50c, of FIG. 4B. In the interests of completeness, however, the remainder of the conventional portions of the vessel 50 commonly illustrated in FIGS. 4A and 4B are also discussed at this juncture. The lower internals 50c include the core 52 comprising a large number of fuel rod assemblies 84 positioned in densely packed parallel axial relationship, mounted to and supported by lower fuel rod nozzles 85 on a lower core plate 80. The lower core plate 80 is joined, either integrally or by welding, at its outer perimeter to an outer barrel assembly 90 and particularly to the lower edge of the cylindrical sidewall 92 of the outer barrel assembly 90. The upper end of the cylindrical sidewall 92 is joined, either integrally or by welding, to an annular flange 94 which extends radially outwardly and is received on internal annular ledge 55b. The weight of the core 52 is supported through the outer barrel assembly 90 on the flange ledge 55b. Brackets 96 are affixed to the interior of the lower head 56 and project radially inwardly, so as to be received by corresponding key recesses 97 in the core plate 80 which thereby provide radially positioning, or alignment, of the lower core plate 80 and the associated elements of the lower internals assembly 50c. The upper ends of the fuel rod assemblies 84 are releasably secured by upper fuel rod nozzles 86 to the bottom surface of an upper core plate 82, the latter forming a part of the upper internals assembly 50b, later described. Pins 87, illustratively shown in association with the upper core plate 82, serve to align and secure the upper ends of the fuel rod assemblies 84 in position. Flow holes 88 in the lower core plate 80 and similar flow holes 89 in the upper core plate 82 provide for the flow of primary coolant through the core 52 and into the upper internals 50b, described in further detail hereafter. The upper internals 50b extends from the upper surface, in essence, of the upper core plate 82 to an upper internal support assembly 102, comprising a relatively thick, generally circular support plate 104 joined either integrally or by welding to a generally cylindrical sidewall 106, which in turn is joined at its upper end to an outer, annular flange 108. The annular flange 108 is received on a generally annular Bellville Spring ring 109. The head 58, when secured in position by bolts 59, bears against the flange 108, and in turn the Bellville Spring ring 109 exerts a resilient hold-down force on the ledge 55b of the lower internals assembly 50c for stabilizing the inner barrel assembly 90 within the vessel 50. Within the upper internals 50b, there are provided a plurality of upper internals support columns 14 which extend between and are rigidly secured to the bottom surface of the support plate 104 and the top surface of the upper core plate 82 and which thus provide a suspension-type support of the upper core plate 82. Radially inwardly projecting keys 100, typically four (4) in number, are received in corresponding radial recesses 82a of the upper core support plate 82, for radially positioning of the upper core plate 82, in conventional fashion. Plural rod guides 111 and 113 (only a few of each being shown) likeWise extend between and are secured at their opposite ends to the upper core support plate 82 and the upper internals support plate 104 and, in conventional fashion, telescopingly receive respective control rod clusters 110 and 112 therewithin, providing for movement thereof into and out of the core 52 in association with the fuel rod assemblies 84, in conventional fashion. The rod clusters may be of first and second, different types, known as RCC rod clusters and part length rod clusters [as shown at 110 and 112, respectively, within the upper internals region 50b] and which are supported through respective, plural drive rods 123 and 125 which extend coaxially through head extensions 118 and 120, respectively, to be engaged and controlled in position by respective drive mechanisms 122 and 124. Drive mechanism 122 may be a magnetic jack control rod guide mechanism (CRDM) and drive mechanism 124 may be a roller nut CRDM, of conventional types. The rod guides 111 and 113 serve to protect the respective rod clusters 110 and 112 from turbulent and vibrational forces imposed thereon by the primary coolant flow which passes through the upper internals 50b. As later more fully described, that flow passes in a generally axial direction from the core 52 into the upper internals 50b and within which the flow turns through a 90.degree. angle to exit from the primary coolant outlet nozzle 53a. Within the upper head region 50a, corresponding, plural upper head region rod guides 115 and 117 are mounted on the upper internal support plate 104, and serve a similar purpose of protecting the respective rod clusters 110 and 112 from turbulence and cross-flow of the primary coolant within the upper head region 50a. The head extensions 118 and 120 extend through the upper head 50a in sealed relationship therewith and the drive rods 123 and 125 correspondingly are sealed within the respective CRDM's 122 and 124. The head extensions 118 and 120 include bell-shaped cups 119 and 121 at their lower ends to facilitate alignment therewithin of the respective rod guides 123 and 125 during assembly operations. As is known, and by the structural arrangement described, the RCC rod clusters 110 and 112 are selectively movable in telescoping relationship with respect to the fuel assemblies 84, for insertion into or withdrawal from the core 52 and to selectively controlled positions therein, to alter or modulate the level of activity within the core 52 and thus the level of power generation. As is apparent, suitable openings are provided in the upper core support plate 82 and the upper internals support plate 104 to permit the full insertion into or withdrawal from the core region 52, of the respective RCC rod clusters 110 and 112. The remaining structures, not mentioned as yet but illustrated and identified by reference numerals within the upper head region 50a and the upper internals 50b, relate to the second embodiment of the invention comprising a head penetration instrumentation system and are discussed hereinafter. A significant factor in the design of an instrumentation system for a pressure vessel of the type 50 shown in FIGS. 4A and 4B is the extent of adjustment, or relocation, of its constituent components, as is required during refueling or other periodically performed maintenance operations. To better understand the significant advantages afforded by the present invention, in both of its disclosed embodiments, it is useful first to consider the principal disassembly and reassembly operations required in such refueling and maintenance operations for the vessel 50. Very generally, during a standard plant rodded refueling operation, the rod clusters 110 and 112 are fully inserted into the core 52 by the respective CRDMs 122 and 124 and the associated drive rods 123 and 125 then are released from the CRDMs 122 and 124. The top head 50a then is lifted off, the associated drive rods 123 and 125 remaining in the upper internals assembly 102. The drive rods 123 and 125 are uncoupled from the respective rod clusters 110 and 112 and then the upper internals assembly 102, including the retained drive rods and comprising both the upper internals support plate 104 and the upper core plate 82 connected thereto by the upper internals support columns 114, is withdrawn. The fuel rod assemblies 84 thereby are rendered accessible, for performing conventional refueling functions. When required, for maintenance or other purposes, the core 52 may be removed by raising the lower internals assembly 90 by engaging the upper end of the barrel 92. Significant to the instrumentation provisions, it will be appreciated that various mechanical interfaces exist within the vessel 50 with regard to the elements (e.g., hollow tube guide structures, or thimbles) which define the path for movement into and withdrawal from the core region 52 of detector elements, whether in accordance with the present invention or the prior art systems. Directing attention first to a bottom head penetration instrumentation system as disclosed in the Figures thus far described, the detector guide structures and tubes, or guide path defining elements, must extend through the bottom head 54 and the lower core plate 80 and into the core 52 throughout its full axial height, and be uniformly distributed throughout the cross-sectional area thereof. Typically, in the prior art systems hereinabove described, a removable thimble is inserted through the described path and through an interior channel provided therefor within each fuel rod assembly 84. Prior art thimbles, which are hermetically sealed from the primary coolant within the vessel 50 and thus within the core 52, thus must have sufficient structural integrity to withstand the substantial pressure (2,250 psi) within the vessel 50--leading to the relative rigidity of such prior art thimbles and the relatively large bend radii before referenced. Moreover, because of the need to remove and/or rearrange the fuel assemblies 84 on a periodic basis, the interface of the fuel rod assemblies 84 at their lower nozzles 85 with the lower core support plate 80 presents a critical operating impediment. Specifically, the thimbles must be withdrawn from within the fuel rod assemblies 84 and positioned below the lower core plate 80, to permit removal of the corresponding fuel rod assemblies 84 for rearrangement, or for replacement with fresh fuel rod assemblies 84, after which the thimbles must be reinserted. In addition to the alignment problems thus imposed, considerable care must be exercised so as not to abrade or rupture the sidewalls of the thimbles in these withdrawal and reinsertion operations. As will also be apparent, complex seals must be provided which can withstand the pressure within the vessel 52, yet also permit the telescoping or sliding movement of the thimbles in these insertion and withdrawal operations. Aside from the potential of and/or actual mechanical wear and damage presented, the thimble withdrawal and reinsertion operations impose substantial additional down time and power outage during these necessary, periodic refueling and other maintenance operations. The manner by which the instrumentation system of the present invention overcomes these difficult problems of prior art such systems will be better understood by reference to the following Figures. As will become clear, a significant advantage of the hydro-ball instrumentation system of the present invention is that the interior passageways defined by the instrumentation thimbles and associated guide structures are maintained at the interior pressure of the reactor vessel. As a result, the necessary interfaces in the guide paths structure to accommodate the disassembly and reassembly operations may be simple face-contact joints, such as ball and cone joints, which may be simply moved axially into or out of face-contact engagement, at all interface positions within the vessel 50. Significantly, in the bottom head penetration configuration of the first embodiment (i.e., FIG. 4A), no disconnection and/or no movement of any guide path elements is required during refueling and maintenance operations, thereby avoiding both any related down time and, significantly, any radiation exposure to operating personal. FIGS. 5A and 5B are elevational and cross-sectional views, partly schematic and broken-away, of the bottom head penetration and associated guide structures, FIG. 5B being an enlargement of the upper portion of FIG. 5A. Bottom head penetration 54 is of generally cylindrical configuration and has a central axial bore or passageway 54' therethrough in sealed communication with the hollow interior 62' of the tube 62, the latter being secured to the lower end 54a of penetration 54 by weld bead 63. The central enlarged collar 54b rests on the interior surface 56b of the lower head 56, the juncture being sealed by weld bead 56c. The upper end 54c of the penetration 54 terminates in a male cone end 54d. An extension assembly 130 is supported within the lower head 50d and provides for removably and resiliently interconnecting the bottom head penetration 54 with an instrumentation thimble 150 mounted axially within and extending the full height of the fuel rod assembly 84, thereby to define a transport path for a detector string 40 from the penetration 54 into the instrumentation thimble 150. Wall guard tube 131 is of generally cylindrical configuration and includes an intermediate annular collar 132 which is attached to a stiffener plate 134 (of which several may be provided) which interconnects and thus secures a plurality of such wall guard tubes 131 in the desired, axially aligned positions. Particularly, the lower end 131a of the tube 131 extends through a corresponding aperture 134' in the plate 134. The upper end 131b of the tube 131 includes an annular collar 136 which abuts and is attached to the lower surface 80a of the lower core plate 80; preferably, lower core plate 80 further has a counterbore 80b which receives the protruding end 130c of the tube 130 for axially aligning the tube 130 with the bore, or passageway, 80c. Bolts 138 and 139 threadingly secure the collars 132 and 136, respectively, to the stiffener plate 134 and the lower core support plate 80. The wall guard tube 131 protects the interior portion of the extension assembly 130 from the turbulent effects of the primary coolant flowing through the lower head 50d, as previously described. Guide tube extension head 140 includes a female cone seat 140a on its lower end which is received on the male cone upper end 54d of the bottom penetration 54, which together form a loosely sealed, detachable ball and cone joint 141 which, moreover, automatically aligns the interior bore 141' of the guide tube extension piece 140 with the interior bore 54' of the bottom penetration 54 during assembly. The upper end 140b of the guide tube extension piece 140 defines a slip joint 142 with a bellows expansion joint 144, which connect to and support a male cone extension 146. More particularly, the male cone extension 146 includes a cylindrical lower extension 146a, the lower end of which is received within an interior counterbore 140c in the upper end 140b of the guide tube extension piece 140 and is free for limited axial movement therein, and a male cone head 146b at its upper end. Bellows 145 is formed of metal and is welded at its lower end to the upper end 140b of guide tube extension piece 140, as indicated by weld line 148, and at its upper end to the upper exterior circumference of the tubular extension 146a, as indicated by weld bead 149. As will be appreciated, the bellows expansion joint 144 in conjunction with the slip joint 142 affords an axially extensible or contractible, substantially continuous interior passageway through the interior 146' of the male cone head 146 which is of the same diameter as the interior passageway through the interior 140' of guide tube extension piece 140. The fuel bottom nozzle 85 is designed to minimize the effects of turbulence and impact of the primary coolant flow in the lower intervals 50c, on the final connection between the extension assembly 130 and the instrumentation thimble 150. Particularly, the fuel bottom nozzle 85 includes a downward extension 85a received in a hole 81 of similar geometry in the upper surface of lower core plate 80, the extension 85a being counterbored from its bottom edge to define an internal ledge 85b which rests on the mating surface of the lower core support plate 80, interiorly of the hole 81. The solid end portion 85c of the bottom nozzle 85 furthermore includes a central bore 85d which receives and has secured therein the lower end of instrumentation thimble 150. Finally, cylindrical extension piece 152 includes an annular protrusion 152a at its upper end which is received in the aperture 85d, abutting the lower end of the thimble 150, and a female cone seat 152a at its lower end which receives the male cone head 146b, these surfaces, under the upward resilient biasing of the metal bellows 145, affording a loosely sealed, disconnectable ball and cone joint 154. As is apparent, the interior surfaces 152' and 150' of the extension piece 152 and intermediate thimble 150 are of a common diameter and are axially aligned with the interior surfaces 146' and 141' thereby providing a passageway which is substantially continuous and sealed, at least sufficiently to prevent any significant cross-current of primary coolant flow within the passageway. By virtue of the foregoing construction of the extension assembly 130, including particularly the slip-fit connection 142 with the associated bellows expansion joint 144, and the disconnectable ball and cone joint 154, the associated fuel rod assembly 84 and instrumentation thimble 150 readily may be removed from the lower core plate 80 without requiring the withdrawal or relocation of the elements defining the detector string passageway. Moreover, since the interior of the referenced passageway is maintained at substantially the same pressure as the interior of the pressure vessel 50 (e.g., 2250 psia), there is no substantial tendency of primary coolant to flow through any of the loosely sealed disconnectable joints. The structure furthermore permits removal of the lower internals package, including the core plate 80, without requiring any disassembly of the instrumentation components. Particularly, the core plate 80 and extension assembly 130 with the stiffening plates 134 secured thereto simply are removed as a complete assemblage. In this regard, the extension pieces 140 are effectively captured and removed by and with the core plate 80, as is afforded by the ball and cone, detachable connection joint 141. More specifically, the aperture 80c through the lower core plate 80 includes a reduced diameter annular collar 80d at its lower extent, which is brought into engagement with the outer annular collar 140d of the associated guide tube extension plate 140 as the plate 80 is raised, such that the extension plate 140 is withdrawn with the core plate 80 when the latter is raised vertically for removal. For reassembly, the core plate 80 simply is lowered with the guide tube extension pieces 140 suspended therefrom and extending coaxially with their respectively associated wall guard tubes 131, such that the detachable connections 141 are completed, or reconnected , upon the lower core plate 80 reaching its intended, rest position. This arrangement also permits removing the extension pieces 140 (i.e., assuming the corresponding fuel rod assembly 84 is previously removed), simply by raising same vertically from within the bore 80c and correspondingly replacing same by lowering an extension piece 140 through the bore 80c--again, as permitted by the capability of using a simple, surface contact detachable connection joint 141. The installation of each fuel rod assembly 84 in its proper aligned position within the recess 81 in the core plate 80 is assured by the beveled interior end surface 85d, of the extension 85a. Moreover, as the fuel rod assembly 84 is lowered into its rest position, the cylindrical extension piece 151 is axially aligned with and comes into engagement with the male cone extension 146, which is biased resiliently upwardly by the bellows expansion joint 144, for reassembly of the joint 154. FIG. 6 is an elevational and fragmentary cross-sectional view of an upper portion of the fuel rod assembly 84 and the corresponding top end segment of the instrumentation thimble 150 and its associated upper nozzle 86. The upper nozzle 86 may have substantially the same configuration as the lower fuel nozzle 85 and thus may include an upwardly projecting cylindrical extension for being received in a corresponding annular channel in the lower surface of the upper core support plate 82. The thimble 150 includes a neck portion 150b, which extends above the surface of the fuel rod assembly 84 and is of a gradually increasing diameter, and which joins a relatively larger diameter, cylindrical upper end portion 150c. A spring loaded retainer latch 160 is disposed coaxially within the cylindrical upper end portion 150c and includes a socket portion 162, secured to the top end of the upper end portion 150c of the thimble 150 by rolled seams 163, and latch spring fingers 160a, 160b, . . . depending downwardly therefrom at angularly spaced relationship about the common axis and thus in a segmented, annular configuration. Protrusions 161a, 161b, . . . extend radially inwardly at the lower ends of the spring fingers 160a, 160b, . . . , respectively, and define a spring loaded cylindrical passageway 165 therebetween having an interior passageway slightly larger than the neck portion 46b of the tip piece 46 of a detector string 40 (FIG. 2). The spring fingers are sufficiently resilient so as to be urged outwardly by the arrowhead portion 46a, as it is impelled axially upwardly by the driving force of the fluid flow during insertion of a detector string 40 into the thimble 150, and thus to latch the tip point 46 therein. A plug 166 is received within and extends through the interior bore 162' of the socket portion 162; it is secured in position by peening over the normally upstanding, integral flange 162a of the socket portion 162. The plug 166 includes a reduced diameter cylindrical portion 166a extending coaxially downwardly within the upper end portion 150 C of thimble 150, to a position about midway of the length of the spring fingers 160a, 160b, . . . and serves as a stop for the arrowhead 46a of an upwardly moving detector string 46. Flow holes 168 are provided at the upper ends of the spring fingers 160a, 160b, and flow holes 169 are provided in the sidewall of the upper end portion 150c of the thimble 150, to permit the primary coolant fluid to flow through the thimble 150 and thereby move the detector string 40 upwardly through the thimble 150 and into its fully inserted portion, engaged by the latch 164. These same flow holes 168 and 169 permit the opposite direction of the flow of the coolant for withdrawing a detector string 40 from the latched position and driving same downwardly through the thimble 150, as later discussed. FIG. 7A is a schematic block diagram of the fluid handling system 170 which generates the flow of primary coolant for selectively moving the detector strings for insertion into and withdrawal from the vessel 50 and for the handling, or transport, functions associated with the ICIS read-out room 49c as shown in FIG. 3. Components of FIG. 7A identical to those of FIG. 3 are identified by identical numerals. Thus, in FIG. 7A, tubes 62 pass through the head exchanger (HX) 64, tube portions 62' connect the latter to respectively associated valve systems 66, and tube portions 62'''connect the latter to respective storage positions in the chamber 68, and tube portions 62''' connect the latter to corresponding connection positions of the transfer device 70; as before noted, chamber 68 effectively comprises continuous tube segments extending between valves 66 and device 70, and thus encompasses the tube portions 62'' and 62'''. Transfer device 70 includes a number of connection positions corresponding to the number of storage positions in chamber 68 and at least two additional positions. Position 70-1 is connected to the detector loading tube 180-1 and position 70-2 is connected to the spent detector string discharge tube 180-11, which in turn is coupled through the indicated valves and joints to the spent detector storage vessel 174. For the illustrative two (2) loop plant, device 70 further includes forty-eight (48) connection positions (i.e., 70-3 to 70-50) corresponding to tubes 62''' and may include a null position. As subsequently described in connection with FIG. 8, the transfer device 70 selectively connects each of the selectable connection positions 70-1, . . . 70-50, thereof to its common connection 70b, to enable selectively transporting each individual detector string 40 through tube 80'to and from the gamma counter 80. Device 70 also permits simultaneous transport of all detector strings, selectively from the chamber 68 to the vessel 50 and in reverse, for return to the chamber 68, as well as other functions, later explained. Details of the transfer device 70 and of the gamma counter 80 are shown in FIGS. 8 to 11, subsequently described. Further components of the system of FIG. 7A include a detector string loading funnel 172, a vessel 174 for spent detector strings, a detector circulating pump 176 and a second heat exchanger (HX) 178 having secondary coolant inlet and outlet connections 178a and 178b, respectively. The components of the system 170 are connected by a series of internal tubes 180, specific ones thereof identified by the reference numerals 180-1, 180-2, . . . and several valves, as to which the following designations are adopted: "SV" designates remotely controlled solenoid actuated valves; "MD" designates manual valves; and "DC" designates disconnect joints. Controller 182 provides appropriate outputs for operation of the components of the system 170, under automated control from a programmed computer 184, in accordance with the required operations of the system 170 as now described. To load a new detector string 40 (FIG. 2), MV1 is opened and the new detector string is inserted through the loading funnel 172 and into the loading tube 180-1. MV1 then is closed. Transfer device 70 is set to its corresponding position 70-1. (MV1 optionally could be a remotely controlled solenoid actuated valve "38".) SV1, SV2, SV3 and SV4 then are opened to permit pump 176 to produce a flow through tubes 180-2, 180-1, the transfer device 70, the counter 80, tube 180-3 and the return tube 180-4, thus completing the flow path back to pump 176. The new detector string is impelled, by the fluid flow, into counter 80 and comes to rest with its leading end at stop 81. Transfer device 70 then is moved to its connection position corresponding to the position for the new detector string in chamber 68. Valve systems 66 are controlled so as to afford a bypass path for the flow of coolant while blocking progress of the detector strings out of the chamber 68 and toward the vessel 50, and thus for retaining the detector strings in the chamber 68. Particularly, vales SV14 are opened to provide the bypass path while valves SV13 are closed to block passage of the detectors 40. Valves SV15 are isolated valves, connected in line with the solenoid valves SV13, and are normally opened, to complete the fluid passage to vessel 50. Accordingly, valves SV1, SV2, and SV4 are closed and valves SV5, SV6 and SV7 are opened. (Valve SV7 optionally may be manually operated since it serves to provide isolation of system 170 from vessel 50. As shown, SV7 connects through tube 180-5 to the vessel 50 and permits bi-directional primary coolant flow between the vessel 50 and system 170. SV7 accordingly is normally open, during all transport operations of system 170.) SV6, when opened and with SV8 closed, permits a feed flow from vessel 50 through tube 180-5 to system 170, and particularly into the return line tube 180-4 to pump 176. (Conversely, SV8, when opened and with SV6 closed, connects the flow output of pump 176 through tube 180-6 to produce the opposite flow of coolant, i.e., from system 170 through tube 180-6 to vessel 50 and return to system 170.) Accordingly, to transport the new detector string from counter 80 to its storage position in chamber 68, valves SV1, SV2 and SV4 are closed, SV3 remains open, and valves SV5 and SV6 are opened to permit a flow of coolant from vessel 50 through tube 180-5 and the return line 180-4 to the pump 176 and then through tubes 180-2, 180-7 and 180-7a to the counter 80. The fluid propels the detector string out of counter 80 and through transfer device 70 to the storage position in chamber 68. As noted, the corresponding valve system 66 is in the bypass/ blocking position, to complete the flow through the associated tubes 62'', 62', and 62 back to vessel 50, while retaining the detector string in its position in chamber 68. When the detector storage chamber 68 is fully loaded with the requisite number of detector strings, they are transported simultaneously from chamber 68 through tubes 62'' and the valve systems 66, as now adjusted to their open, non-blocking positions, and thus through lines 62' and 62 to the vessel 50. To perform this function, valve SV6 is opened to supply primary coolant from vessel 50 through tubes 180-5 and 180-5 to the pump 176 and valve SV9 is opened to connect tube 180-7 through motive flow line tube 180-8 to transfer device 70. The motive flow is communicated within device 70 in parallel to all of the forty-eight (48) connection positions associated with the storage positions of the detector storage chamber 68, and simultaneously projects the detector strings through the tubes before-noted to the vessel 50. (In this operation, valve SV10, connected between the motive flow line tube 180-8 and a return tube 180-9, is closed as is valve SV11, which is connected to the spent detector string discharge tube 180-11). To withdraw the detector strings simultaneously and in parallel from vessel 50 and return them to system 170, valve systems 66 remain in their open, non-blocking positions, valve SV9 is closed and valve SV10 is opened to connect the motive flow line 180-8 through the return tubes 180-9 and 180-4 to the pump 176. Moreover, SV6 is closed and SV8 is opened for connecting the output of pump 176 through the exhaust flow tubes 180-6 and 180-5 to the vessel 50. Accordingly, the fluid flow from the vessel 50 passes in parallel through all of the tubes 62, 62' and 62'' and simultaneously transports the detector strings back into their positions in chamber 68. In this operation, transfer device 70 is placed in a null position, before-noted and later described in detail, which permits fluid flow through the guide tubes 62'' in parallel into the transfer device 70 and return tubes 180-9 and 180-4, but mechanically blocks the detector strings 40 at the positions 70-3 to 70-50. In this regard, it will be understood that the chamber 68 effectively extends to and includes the connections positions 70-2 through 70-50 of transfer device 70 and thus encompasses, as well, the tubes 62'''. A further detector string transport operation of system 170 permits discharging spent detector tubes into the spent detector storage vessel 174. Disconnect joints DC1 and DC2 permit disconnecting the vessel 174 from system 170 when it is desired to remove spent detector strings therefrom and manual valves MV1 and MV2 permit sealing off the flow inlet 174-1 and flow output 174-2 of vessel 174. During normal operations, of course, vessel 174 is connected at joints DC1 and DC2 in the flow path and MV1 and MV2 are normally open. SV12 connects the outlet 174-2 of vessel 174 through return line tubes 180-12 and 180-4 to pump 176. To perform the spent detector discharge operation, transfer device 70 is positioned at the connection position corresponding to the position of the spent detector string in chamber 68. SV3, SV4 and SV8 are opened thereby permitting pump 176 to produce a flow of coolant from the vessel 50 and through the associated position of chamber 68, device 70 and counter 80, and through SV4, tubes 180-3 and 180-4, the pump 176, the exhaust tube 180-6 and tube 180-5 to the vessel 50. The spent detector string accordingly moves into counter 80, advancing to stop 81. Transfer device 70 is then positioned at connection 70-2 to the spent detector discharge tube 180-11. Valve SV3 remains open valve SV4 is closed and valves SV5, SV11 and SV12 are opened, thereby completing a flow path through tubes 180-2 and 180-7a, counter 80, transfer device 70, and discharge tube 180-9 for transporting the spent detector string into vessel 174. The flow path is completed through outlet 174-2 of vessel 174, SV12, tube 180-12 and the return line tube 180-4 to pump 176. (Vessel 174 is filled fully with coolant and thus permits this closed loop operation.) As noted in the above, the valve systems 66, associated with the detector storage positions of chamber 68 through the tubes 62'', are selectively operable to retain the detectors in the storage positions in chamber 68, or to provide for transport of all the detector strings simultaneously between the chamber 68 and the vessel 50. Valve systems 66 may be operated individually, moreover, to open a selected in-line valve SV13 (and close the corresponding by-pass valve SV14), to transport an individual detector string to and from chamber 68 and vessel 50. As before noted, each valve system 66 includes an in-line valve SV13 and a bypass valve SV14, as more readily seen in FIG. 7B. Valve SV15 is in-line and functions as an isolation valve (i.e., as is SV7), and thus may be a manually operated valve ("MV") instead. Accordingly, valve SV15 is normally open during operation of system 170 and the control functions are afforded by valves SV11 and SV12. Transport of a detector through a valve system 66 and thus between tubes 62' and 62'', in either direction, requires that SV13 be open and SV14 be closed. Conversely, where a detector string is to be retained in chamber 68 but a fluid flow through chamber 68 to the vessel 50 is required, in-line valve SV13 is closed and bypass valve SV14 is opened. As readily visualized from FIG. 7B, the closed valve SV13 provides a mechanical stop for retaining of the detector string while the necessary fluid flow passes through the bypass path of valve SV14. (It thus will be understood that chamber 68 effectively extends to the valves SV14 and the tubes 62'' are within chamber 68.) Heat exchanger 178 provides for cooling the supply flow from vessel 50 passing through tube 180-5 and then through SV6 and return line tube 180-4 to pump 176, and etc., as explained earlier with regard to heat exchanger 64. Orifice 186 interconnects tubes 180-4 and 180-6 to provide a minimum pump flow bypass in the event that all flow paths within system 170 are closed, thus avoiding potentially harmful "shut-off" pump operations. MV15 and MV16 are selectively operable to connect tubes 180-6 and 180-4 to a coolant purification system 188; the purification system 188, as is known and conventional, insures that proper reactor grade water coolant chemistry is maintained, thereby to avoid injection of impurities into the reactor vessel 50. Suitable filters, demineralizers, and pumps of the purification system 188 are employed for this purpose. The water chemistry of system 170 is established before a run and cleaned up after a run, as well, by the system 188. During actual operations of system 170, however, valves MV 15 and MV 16 are closed, to cutoff the bypass connection. Programmed computer 184 provides for the necessary coordinated actuation of the SV valves through controller 182 which provides corresponding outputs to those valves. In this regard, each of the forty-eight (48) valve systems 66 is provided with its respectively responding outputs SV13' and SV14'. The same is true as to valves SV15, if they are solenoid actuated rather than manually actuated. Controller 182 also provides for actuation of transfer device 70 and for driving the counter 80 in its sensing operations, both as later described, and for driving the circulating pump 176, as indicated by outputs 70', 80' and 176'. FIG. 8 is an elevational and cross-sectional, partially broken-away and schematic, view of the transfer device 70 including its connection positions to tubes 62''', and its common connection through tube 180' to valve SV3, as seen in FIG. 7A. Casing 190 is formed of two major components, a cone 192 having an annular flange 193 and a cap 194 of generally cylindrical configuration having a solid end wall 194a, a cylindrical sidewall 194b, and an annular flange 195. The flanges 193 and 195 are appropriately bored and threaded for being secured together by a plurality of bolts 196 about their mating peripheries, one such bolt 196 being shown in FIG. 8. O rings 198 received in corresponding grooved recesses 195 in the flat surface of flange 193 provide a pressure seal with respect to the interior chamber 190' of the casing 190. Rotor 200 includes an elongated shaft 202 which may be of any desired cross-sectional configuration, e.g., either a hollow cylinder or two or more elongated support rods, and interconnects a pair of pistons 204 and 206 at its opposite ends. Bearings 196 and 198 are mounted in axially aligned relationship in the forward end of cone 192 and the central portion of the solid end wall 194a of cap 194, respectively, within which the respective pistons 204 and 206 are received. Piston rings 205 and 207 seal against the bearings 196 and 198, respectively, yet permit both axial reciprocating and rotary movement of the pistons 204 and 206. Pistons 204 and 206 and their associated bearings 196 and 198, define corresponding chambers 197 and 199 which respectively communicate through passageways 197a and 199a to external hydraulic fittings 197b and 199b, respectively. Hydraulic lines 197c and 199c are connected to a hydraulic pressure source 72 which receives the control signal 70' from the controller 182 (FIG. 7A). The control signal 70' causes the hydraulic pressure source 72 to direct pressurized hydraulic fluid into a selected one of the chambers 197 and 199 and simultaneously to vent the other chamber, thereby to drive the rotor 200 in corresponding and oppositely directed, or reciprocating, axial directions relative to the casing 190. A rotation ratchet 210 mounted on an internal annular flange 192a of the cone 192 engages a toothed surface 212 of the collar 214, which is formed integrally with and extends radially from the shaft 202 adjacent the piston 204, whereby each cycle of the reciprocating axial movement of the rotor 200 (see arrow "RAX") causes the rotor to step through a predetermined annular displacement in a fixed direction of rotation (see arrow "ROT"). The solid end wall 194a of the cap 194 includes a number of sockets 216 corresponding to the number of connection positions for tubes 62''', the detector string loading tube 180-1 and the detector discharge tube 180-12, a null position, and any other required positions. The sockets 216 are displaced at equiangular positions at a fixed radius about the axis of rotor 200, corresponding to the angular segment stepping function of the rotation ratchet 210. Tubes 62''', 180-1, 180-12 are received in respective sockets 216 and secured in position as indicated by weld lines 217. Bored passageways 218 extend in parallel axial relation from each socket 216 to the interior, generally flat surface 194c of the cap 194. Female cone connectors 219 are formed in the surface 194c by counter boring that surface in alignment with the respective, bored passageways 218. Annular plate 208 of the rotor 200 includes a single male cone connector 209 which is received in loosely sealed engagement by the female cone connector 219 at each angular stepped position of the rotor 200. The reciprocating axial movement of rotor 200 withdraws the male cone connector 209 from a given female cone connector 219, prior to the angular step rotation of the rotor 200 into aligned position with the next successive female cone seat 219. Tube 220, which may be similar to the tubes 62''', is affixed to the plate 208, as indicated by weld line 221, and is in communication with a passageway extending through the plate 208 and the male cone connector 209. Tube 220 extends through a gently curved path, passing through an opening 203 in the shaft 202 of rotor 200 and a central axial bore 204a in the end wall of piston 204 and is secured thereto as indicated by weld line 204b. The remaining, free end of tube 220 is encased in a rotary seal 220 received within a central bore 192a in the cone 192, and the base 192a is sealed by an external connector seal 192b, the latter together comprising the common connection 70b. Tube 180' is joined by the external seal 192b to the common connection 70b of transfer device 70 and to valve SV3 which in turn is connected to a sealed internal passageway of the counter 80, to be described. Finally, the motive flow tube 180-8 is connected by an external connector seal 222 to and through radial passageway 224 to the interior 190' of the casing 190. As will be appreciated, the rotor 200 is stepped through the successive angular displacements by the successive cycles of reciprocating axial movements to thus come into selective and successive sealed communication with each of the tubes connected to the cap 194. Further, when rotor 20 is stepped to position the male cone connector 209 at a null position, or at least to a position unassociated with any of the tubes 62''', all of the corresponding female cone connectors 219 are exposed to the interior chamber 190' of the casing 190. When primary coolant is introduced into that interior chamber 190' through the motive flow line tube 180-8, or withdrawn therefrom through that same tube 180-8, the detector strings simultaneously are transported from the detector string storage positions of chamber 68 to the instrumentation thimbles 150 of the vessel 50, or in the reverse direction, respectively. The gamma counter 80 of FIG. 3 is shown in FIGS. 9, 10 and 11, FIG. 9 being a simplified and plan view, FIG. 10 being a simplified and cross-sectional elevational view, and FIG. 11 being an enlarged and fragmentary, elevational and cross-sectional view, each of FIGS. 10 and 11 being taken in a plane along the line 10,11 - 10,11 in FIG. 9. The gamma counter 80 is of a generally circular configuration and comprises an annular base 230 and an annular cover 232 having an underlying annular recess by which it is received over the base 230 and supported thereon for relative rotational movement by a bearing race 234. The base 230 is secured to a support 236 on which is mounted a motor 238. The motor shaft 239 extends coaxially relative to the annular base 230 and cover 232 and carries a drive arm 240 connected at its opposite ends to the rotary cover 232, as shown by bolt 241. A gamma counter 242 is mounted on the annular cover 232 such that its detector crystal 246 is disposed over a slit window 248 in cover 232. The slit window 248 aligns with an annular slit channel 250 in the annular base 230, at the lower end of which is received a high pressure tube 180'' which in turn is connected to the internal tubing 180 of the control system 170, as before described. A detector string 40 is moved into the gamma detector 80 as described in connection with FIG. 7A and, in relation to FIGS. 9, 10 and 11, will be understood to form into an arcuate segment comprising approximately 270.degree. of a circle, the leading end abutting the detector stop 81. Motor 238 then is energized to drive the gamma counter 242 through the 270.degree. and derive the required measurements by reading of the detector balls by the crystal sensor 246, a small segment at a time, through the slit 248. The cable 243 connects the gamma counter to appropriate circuitry for processing the sensed outputs. If desired, plural detectors and corresponding slits may be employed. It will be understood that the base and cover 230 and 232 are appropriately shielded to prevent any radiation exposure and reduce the background radiation to which the counter is subjected, and which would degrade readout accuracy. From the foregoing, it will be appreciated that the hydro-ball in-core instrumentation system of the present invention in accordance with the first embodiment thereof hereinabove disclosed affords numerous advantages over the prior art, significantly complying with the specified characteristics of an ideal such system. Substantially all operating functions may be remotely controlled thus affording minimum potential exposure of personnel to radiation. Significant size reductions are achieved, providing both reductions in costs for the instrumentation system and an even more significant reduction in the size and thus cost of the containment structure for a given pressure vessel, afforded primarily due to the high degree of flexibility of the detector strings. The capability of simultaneous insertion and withdrawal of the detector strings moreover contributes to improved accuracy of the data sensing and thus of the resultant mapping. Significantly, by virtue of the bottom penetration configuration, neither disconnection nor movement of the instrumentation thimbles 150 is required during refueling and maintenance operations. A highly significant feature is that the tubing and related structures defining internal passageways for the detector strings are maintained at the same pressure as the primary coolant within the vessel; as a result, simple slip fit or face contact connections suffice, enabling substantial simplification of the disassembly and/or reassembly of the components defining the detector string passageways within the vessel and thus minimizing the time and effort required for performing maintenance and refueling operations. Thus, both the down time during power outages and the extend and duration of potential exposure of personnel to radiation are minimized. The second embodiment of the instrumentation system of the invention, shown generally in FIG. 4B, employs top head penetration of the pressure vessel and thus permits complete elimination of the need for any spacing below the bottom of the pressure vessel, for example the space 49a shown in FIG. 3. This enables a further reduction in the corresponding size requirements of the containment structure 48. The elimination of the bottom penetrations moreover reduces the consequences and recovery problems of a core melt-down and bottom penetration LOCA's. As will be seen in the following detailed description, the top head penetration embodiment does not require a detector string positioning latch inside the fuel assembly instrument thimble. On the other hand, the top head penetration increases the complexity of the vessel head package and does require disconnection of several guide tube jumper bundles which run between the vessel head instrumentation columns and the refueling cavity wall. While additional complexity is introduced in the head region and upper internals because of the head penetration, the common feature of both embodiments that the detector string passageways are maintained throughout at the internal pressure of the vessel again permits use of simple slit fit or face contact connections, affording similar simplification of the assembly and disassembly operations of the instrumentation components in conjunction with performing refueling and other maintenance operations within the vessel. A single head penetration assembly 300 is illustrated in FIG. 4B, which accommodates twelve (12) passageways for a corresponding twelve (12) detectors of the type 40 of FIG. 2. For the same illustrative example of a two loop plant, requiring forty-eight (48) detectors, there would thus be four head penetration assemblies 300 equiangularly disposed about the head 58 to provide for an efficient disbursement of the individual guide tubes 304 within the upper head region 50a, as more fully explained hereinafter. For the illustrated head penetration assembly 300 of FIG. 4B, there are thus, illustratively, twelve (12) guide tubes 304 grouped within the detector head column 306. The head column 306 is supported at its lower end by a bracket 308 mounted on the upper support plate 104 and passes upwardly through a head penetration 310, the upper end 306a of the head column 306 protruding above the upper end of the head penetration 310 and being joined by a flanged disconnect joint 312 to the jumper bundle 302. A second flanged disconnect joint 314 is mounted on a support wall 48 and serves to join the individual tubes within the bundle 302 to the respective tubes 62a which are shown, schematically, to extend from the flanged disconnect 314 and through the wall 48. In an actual installation, as schematically illustrated in FIG. 3, the tubes 62a would extend through the containment wall 48 which separates the vessel 50 from the ICIS readout room 49d at the height relative to the vessel head 58 as indicated in FIG. 4B, and through a similarly relocated heat exchanger (affording the function of HX64 in FIG. 3) to the solenoid valve systems 66 and the storage chamber 68 substantially as shown in FIG. 3. The remainder of the in-core instrumentation system of this second embodiment may be identical to that of the first embodiment as described above. FIG. 12 is an elevational, cross-sectional view, partially broken-away and partially schematic, of an upper extremity of the head penetration 310 also shown in FIG. 4B, and of a coupling assembly 316 which joins the head column 306 containing the twelve (12) tubes 304 to the flanged disconnect joint 312. More specifically, as seen in FIG. 12, coupling assembly 316 includes lower and upper sections 317 and 318 which are interconnected by a selectively releasable clamp joint 318, so as to be relatively rotatable. The enlarged diameter and interiorly threaded lower end 317a of the lower section 317 is received in threaded engagement on the exteriorly threaded upper end 310a of the head penetration 310. The flanged upper end 317b of the lower section 317 preferably is machined to define stepped grooves which mate with corresponding stepped grooves in the flanged lower end 318a of the upper section 318, thus permitting relative rotation while maintaining axial alignment thereof. A seal (not shown) is received between the abutted and mating, grooved surfaces. Ring clamp 319 is fitted about the flanges 318a and 381b and tightly secured by bolts 320, schematically illustrated in FIG. 12, to secure the upper and lower parts 317 and 318 of the coupling assembly 316 against relative axial or rotational movement. As better seen in FIG. 13, a cross-sectional view taken in a plane along the line 13--13 and transverse to the axis of the coupling assembly 316, ring clamp 319 may comprise three (3) roughly 60.degree. angled sections 319a, 319b and 319c having corresponding radial flanges which are suitably apertured and threaded to receive respective bolts 320. The upper end 306a of the head column 306 is secured (as late detailed in reference to FIG. 14) to the lower end of a face contact plug 321, a component of the joint 312. The upper end 318b of the upper section 318 includes a reduced diameter collar 318c which is received about a mating, reduced diameter neck portion 321a of the plug 321 and sealed thereto by ring seal 321b. The seal is maintained by a jack-type ring clamp 347 which, as seen in the cross-sectional view of FIG. 12, includes an internal, annular groove 347a which receives a split lock ring 348, the latter seated in an annular groove 321a in the plug 321. Screws 349, typically three (3) in number (but only one of which is seen in FIG. 12), are received in threaded engagement through the ring clamp 347 and bear against the flat, upper end 318b of the upper part 318 of the coupling assembly 316. By tightening the screw(s) 349, the ring clamp 347 imposes an upward axial force on the plug 321, compressing the ring seal 321a and thus completing the fluid-tight connection of the coupling assembly 316 and particularly between the plug 321 and associated head column 306 and the head penetration 310. Flanged disconnect joint 312 comprises face contact plugs 321 and 326. Plug 321 includes an annular collar 322 which is received over a split lock ring 323, in turn received in a mating annular recess 324 adjacent the upper end of the plug 321. Plug 326 has an integral annular collar 327. Plural bolts 328, of which one is shown in FIG. 12, are inserted through suitable apertures in the collar 327 and received in threaded engagement in corresponding threaded holes in the annular collar 322, to secure the flanged disconnect joint 312. FIG. 14 is a fragmentary and more detailed cross-sectional view of the interface portion of the components of the flanged disconnect joint 312. The upper end 306a (shown in fragmentary section) is suitably joined to the lower end of plug 321, about its outer circumference. Plug 321 includes an interior bore 330 which is counterbored at 331 to receive an end of a tube 304, the latter secured thereto such as by weld bead or brazed joint 305, for each of the twelve (12) tubes 304 (see FIG. 9). As will be appreciated from the broken-away illustration of plug 321 in FIG. 14, the plug 321 is of substantial axial length, extending from its bottom end within the upper part 318 of the coupling assembly 316 of the interface with plug 326 of the common joint 312, as seen in FIG. 12. The upper plug 326 includes bore 340, axially aligned with the bores 330 of the lower plug 321, to which corresponding tubes of the bundle 302 are secured, in like fashion as the tubes 304 and plug 321. The mating ends of the bores 330 and 340 preferably are counterbored as shown at 330a and 340a to assure that an adequate interface defining the required passage therethrough is afforded. Proper axial engagement of the plugs 321 and 326 is assured by the cylindrical socket 332 of plug 330 which receives annular ring 342 of plug 326. Bore 326' extends through plug 326 and by rotation of plug 326 is brought into alignment with bore 321' in plug 321, alignment pin 326a being inserted through the aligned bores 321' and 326' to establish proper rotary alignment of the plugs 321 and 326. An annular seal 344 is received in a corresponding annular recess 334 of plug 321, and may be either a metal "O" ring or a flexitallic gasket. It is significant to the invention that the flanged disconnect 312 may be so constructed, in the sense that the individual passageways defined by the twelve (12) pairs of respective, aligned bores 330 and 340 need not be more critically sealed and instead that only the perimeter of the flanged disconnect joint 312 need be sealed against the full primary coolant pressure. Specifically, pressure differentials between the guide tubes and thus between the aligned sets of bores 330, 340 are very small, some cross-leakage is tolerable, and the seal afforded by the finished metal, face contact surfaces of plugs 321 and 326 with the matched, aligned holes are adequate. Joint 314 (FIG. 4B) may be identical to joint 312. It thus will be understood that the flanged disconnect joint 312, and joint 314 which may be identical thereto, permit easy disconnection and removal of the jumper bundle 302 during maintenance and refueling operations, and subsequent, easy reconnection during reassembly. Disassembly then proceeds by disconnecting joint 312 and removing split ring 323 and collar 322. The jack-type ring clamp 347 then is released by loosening screw(s) 349, and the split ring 348 and ring clamp 347 then are removed. The head 58 now may be raised, with the head penetration 310 sliding in telescoping or coaxial relationship along the head column 306, which remains supported by bracket 308 on the support plate 104. The latter arrangement will be understood more clearly from FIG. 15, now described. FIG. 15 is a fragmentary and cross-sectional elevational view, on an enlarged scale, of the head column 306, support plate 104 and associated structures within the head region 50a. Particularly, head column 306 extends downwardly from the head penetration 310, the lower end of which terminates in a bell shaped end connector 311 to facilitate aligning the column 306 therein during reassembly of the head. As seen in FIG. 15, bracket 308 may comprise an upstanding cylindrical sleeve 308a which receives a lower end 306b of the generally cylindrical column 306, a bore through a common diameter thereof receiving a bolt 350 and the bolt 350 and a nut 351 securing the same together. The lower end of sleeve 308a may be welded to a base plate 308b which in turn may be bolted (not shown) to the support plate 104. As before described, the detector guide tubes 304 exit through an opening in the sidewall of the column 306 and are dispersed to appropriate positions from which they pass through very small radius bends, as illustrated for the tube 304', to turn to a vertical axial orientation in alignment with an instrumentation thimble in an associated fuel assembly, as now described. Concurrent reference is now had to FIGS. 15, 16 and 17; FIG. 16 is a partially broken-away cross-sectional elevational view of a portion of the upper and lower internals 50b and 50c of the vessel 50 of FIG. 4B, and FIG. 17 is a fragmentary portion of FIG. 16, on an enlarged scale. An upper internal support column 114 extends between the upper support plate 104 (FIG. 15) and the upper core plate 82 (FIG. 16) and defines an internal passage 114'. The column 114 further includes an annular collar 114a which abuts the lower surface of the upper support plate 104 and an upper end portion 104a which extends through an aperture 104' in plate 104 and protrudes above the upper surface of plate 104. The protruding portion is threaded on its outer surface for receiving a nut 114c which secures it to the support plate 104. Column guide tube 356 extends coaxially through the interior 114' of the column 114 and extends vertically above the upper support plate 104 for connection to the guide tube 304' by a swage-lock fitting 358. Collar 360 is affixed to the column tube 356 and is received for sliding movement within the enlarged bore 114'' in the upper end of the support column 114. Coil spring 362 is received in the enlarged bore 114' and extends between the collar 360 and a cap 364 which is threadingly received on the uppermost end of the column 114. Coil spring 362 thus resiliently biases the column tube 356 in a downward direction, urging collar 360 against the lower extremity of the bore 114'', for a reason to be explained. With reference to FIG. 16, the lower end 114d of the column 114 is conical in shape, or tapered, facilitating its alignment into and insertion through a correspondingly configured central opening 366' in a lower support bracket 366 which comprises radial legs 366a, 366b, . . . which are welded to the column 114 and supported on and affixed to the upper core plate 82, such as by bolts (not shown). The open-leg configuration facilitates passage of coolant flow through the associated opening 82' in the upper core plate 82. The fuel rod assembly 84 (FIG. 16) is mounted by nozzles 85 and 86 at its lower and upper ends to the lower and upper core plates 80 and 82, respectively, as before described. Instrumentation thimble 350 extends axially and centrally, substantially throughout the full height of the fuel element assembly 84; it is secured within the upper bracket 86 by a stub 352 which forms, at its upper end, the female portion of a ball and cone seal affording a detachable connection 354 (which may be identical to the connection 141, before described). As better seen in FIG. 17, the upper end 350a of the instrumentation thimble 350 extends through a suitable opening in the upper fuel assembly nozzle 86 and within a corresponding counterbore 352'' of the stub 352 and is secured thereto as indicated by weld bead 353a or other means such as brazing or roll expansion. The stub 352 is secured to the nozzle 86 in like fashion, as shown at 353b. The interior 352' of the stub 352 again corresponds in diameter to that of the interior 350' of the thimble 350 and the interior 356' of the column tube 356. The female cone seat at the upper end 352a of stub 352, which receives the male ball end 356a of the column tube 356, likewise is more readily seen in FIG. 17. Thimble 350 includes flow holes 351 at its lower end providing for coolant flow either into or out of the interior passageway 350' of the thimble 350, which flow provides for the detector string movement as described previously. It now will be appreciated that the upper internals 50b comprises, in normally assembled relationship, the upper core plate 104, the plural upper internals support columns 114 with the respective support brackets 366 bolted to the upper core plate 82 and thus the upper core plate 82 as well, to the column guide tubes 356 therein (FIGS. 15 and 16) as well as the head penetration columns 306 and the respective detector guide tubes 304 of each thereof. In the reassembly of the vessel 50, such as following refueling or other normal maintenance operations, this normally assembled package of the upper internals 50b is lowered, maintaining the upper internals support columns 114 aligned with the corresponding fuel element assemblies 84. As the upper core plate 82 reaches its rest position, the ball and cone detachable connections 354 are completed, as shown in FIGS. 16 and 17, the coil spring 362 (FIG. 15) affording a resilient force for that purpose. Head 58, with the head penetrations 310 aligned with the respective head columns 306, then is lowered, the bell shaped ends 311 of the head penetrations 310 facilitating alignment of the upper ends of the head penetration columns 306 such that they pass through the respective head penetrations 310 and achieve the assembled relationship shown in FIG. 4B. The guide tube jumper bundle 302 then is installed, through use of the flanged connect joints 312 and 314, to complete the assembly operations relating to the instrumentation system. It thus will be apparent that an extremely simplified assembly and disassembly operation is afforded by the head penetration embodiment of the present invention. Again, the feature that the detector string interior passageways are maintained at the internal pressure of the vessel 50 enables the use of relatively loosely-sealed joint structures at all interface connections of the detector string interior passageways within the interior of the assembly and disassembly operations. FIG. 18 is a schematic of a fluid handling system 170' comprising an alternative embodiment of the system 170 of FIG. 7A, identical parts being identified by identical numerals. Advantages afforded by the system 170' of FIG. 18 are that a substantial number of valves are eliminated and that the amount of reactor coolant which actually enters the system 170' is substantially reduced, thus reducing a major source of contamination and clogging of the narrow passageways in the detector string handling devices and tubes of the system, relative to that of FIG. 7A. Particularly, a propulsion flow header 370 is employed in the system 170' in lieu of the bypass solenoid valves SV4 of the forty-eight (48) valve systems 66 of FIG. 7A. In FIG. 18, manual isolation valves MVa are connected in the respective tubes 62' and serve the corresponding isolation purposes as the valves SV15 in the system of FIG. 7A; the valves MVa accordingly may be either manual, as shown, or solenoid controlled ("SV"). The flow header 70 is discussed with concurrent reference to FIGS. 18 and 19, FIG. 19 being a schematic representation thereof. Header 370 has a single input 372 which connects through parallel paths 370-1 through 370-48 to the forty-eight (48) tubes 62'' of chamber 68 and the forty-eight (48) in-line valves SV13. Tube 180a connects tube 180-7 through valve SVa to the bi-directional flow tube 180b, and the latter is connected for the reverse or return flow condition through valve SVb, when opened, and tube 180c to the return tube 180-4. Thus, use of the header 370 and the two valves SVa and SVb permits elimination of the forty-eight (48) bypass valves SV14 of the valve systems 66 in FIG. 7A. Further, the system 170' functions in a closed loop for all internal detector string transport operations, using solely the coolant existing within the lines, vessels and devices which in fact are common to both system 170 and system 170'. Accordingly, it will be understood that the forty-eight (48) valves SV13 are closed during these internal operations, both to act as stops relative to transfer of detector strings into the chamber 68 and to isolate the internal system 170' from the tubes extending to the vessel 50. It follows as well that the valves SV6 and SV8 are closed during these internal transport operations. By opening valve SVa and closing SVb, coolant existent within the system 170' is directed into the header 370 to transport any selected detector string, in accordance with the position of transfer device 70, into the gamma counter 80, SV4 being opened to complete the fluid flow circuit to pump 176 and SV5 being closed. The reverse flow for transporting a detector string from the gamma counter 80 back to its assigned position within the chamber 68 is achieved by the opposite, opened and closed conditions of SVa, SVb, SV4 and SV5. The closed state of valves SV13 throughout these operations both isolates the reactor coolant and assures the proper flow direction in the header 370 while additionally serving as a mechanical stop for the detector strings during the return from counter 80 to the chamber 68. Loading of a new detector string is the same as that performed by the system of FIG. 7A, through the step of locating the detector string in the gamma counter 80. Thereafter, with SV4 closed, SV5 is opened, as before, but now the flow proceeds through flow header 370, with SVa closed and SVb open and thus through tube 180c and return tube 180-4, for completing the flow circuit to the pump 176, thereby transporting the new detector string out of counter 80 and through device 70 into the proper position in chamber 68. Discharging a spent detector string again involves the use of header 370. SVa is opened and SVb is closed to produce a flow from pump 176 through tubes 180-7 and 180-7a and bi-directional tube 180b to the header 370 and from header 370 through chamber 68, counter 80, and open valve SV4 (with valve SV5 closed) and the return tubes 183 and 184 to complete the fluid circuit to the pump. With the device 70 appropriately positioned, the spent detector string is transported from chamber 68 into counter 80. The path for driving the detector string from counter 80 into the spent detector storage vessel 174 includes tube 180-2, 180-7 and 180-7a , opened valve SV5 (with SVr closed) SV3 opened, transfer device 70 positioned at connection 70-2, discharge tube 180-11 and opened valves SV11 and SV12, the return path being completed through tubes 180-12 and 180-4 to pump 176. Thus, since no flow of primary coolant to or from the reactor vessel is required in these internal transport operations, substantial contamination and clogging problems which that flow may produce is avoided. In the transport of the detector strings, either simultaneously as to all or selectively as to one or more individual detector strings from the chamber 68 to the reactor vessel 50 and return, the appropriate valve or valves SV13 is/are opened, SVa and SVb are both closed (as a result of which header 370 serves no function), and valves SV6 and SV8 along with valves SV9 and SV10 are operated as in the case of the system of FIG. 7A to provide the appropriate motive flow through tube 180-8 to or from transfer device 70. It will be recognized by those of skill in the art that numerous modifications and adaptations may be made to the various structures and the systems disclosed herein and in the method of operation thereof and thus it is intended by the appended claims to encompass all such modifications which fall within the true spirit and scope of the invention. |
047626739 | summary | BACKGROUND OF THE INVENTION This present invention relates to burnable poison rods for use in a nuclear reactor and to a fuel assembly of a nuclear reactor containing such rods. It is well-known that the process of nuclear fission involves the disintegration of the fissionable nuclear fuel material into two or more fission products of lower mass number. Among other things the process also includes a net increase in the number of available free neutrons which are the basis for a self-sustaining reaction. When a reactor has operated over a period of time the fuel assembly with fissionable material must ultimately be replaced due to depletion. Inasmuch as the process of replacement is time consuming and costly, it is desirable to extend the life of a given fuel assembly as long as practically feasible. For that reason, deliberate additions to the reactor fuel of parasitic neutron-capturing elements in calculated small amounts may lead to highly beneficial effects on a thermal reactor. Such neutron-capturing elements are usually designated as "burnable poisons" or "burnable absorbers" if they have a high probability (or cross section) for absorbing neutrons while producing no new or additional neutrons or changing into new absorbers as a result of neutron absorption. During reactor operation the burnable absorbers are progressively reduced in amount so that there is a compensation made with respect to the concomitant reduction in the fissionable material. The life of a fuel assembly may be extended by combining an initially larger amount of fissionable material as well as a calculated amount of burnable absorber. During the early stages of operation of such a fuel assembly, excessive neutrons are absorbed by the burnable absorber which undergoes transformation to elements of low neutron cross section which do not substantially affect the reactivity of the fuel assembly in the latter period of its life when the availability of fissionable material is lower. The burnable absorber compensates for the larger amount of fissionable material during the early life of the fuel assembly, but progressively less absorber captures neutrons during the latter life of the fuel assembly, so that a long life at relatively constant fission level is assured for the fuel assembly. Accordingly, with a fuel assembly containing both fuel and burnable absorber in carefully proportioned quantity, an extended fuel assembly life can be achieved with relatively constant neutron production and reactivity. Burnable absorbers which may be used include boron, gadolinium, samarium, europium, and the like, which upon the absorption of neutrons result in isotopes of sufficiently low neutron capture cross section so as to be substantially transparent to neutrons. The incorporation of burnable absorber in fuel assemblies has been recognized in the nuclear fuel as an effective means of increasing fuel capacity and thereby extending core life. Burnable absorbers are used either uniformly mixed with the fuel (i.e., distributed aborber) or are placed discretely as separate elements in the reactor, so arranged that they burn out or are depleted at about the same rate as the fuel. Thus, the net reactivity of the core is maintained relatively constant over the active life of the core. When the burnable absorbers are placed as discretely separate elements in the reactor, the same are normally contained in a burnable poison rod, and the rods inserted into empty control rod guide thimbles in the fuel assembly. Control rods are not required in all guide thimbles of all fuel assemblies, thus allowing for the use of burnable poison rods. In U.S. Pat. No. 4,342,722, there is described prior art burnable poison rods and a specific rod is disclosed which contains sections of boron glass. That rod contains a plurality of sections of boron glass tubes, and provides for the joints between the tube sections to be outside the zone of maximum flux density. The rod described is, however, of a full length design, such rods being on the order of 8-14 feet in length. Situations arise where a part length burnable poison rod is desirable. In such part length rods, the neutron absorber must be reduced in amount and the absorber must be repositioned near the center of the core height. One proposed design of a part length burnable poison rod is a shortened version of a full length burnable poison rod containing a shortened length of burnable absorber. This design, due to its shorter length, however, is not compatible with present handling equipment. If costly handling equipment modifications are to be avoided, a part length burnable poison rod is needed which has the dimensions of conventional full length burnable poision rods. SUMMARY OF THE INVENTION A burnable poison rod for use in a nuclear reactor comprises a tubular metallic cladding and upper and lower closure means. A neutron absorber, or burnable absorber, is positioned within the tubular cladding and is spaced from the lower closure means by use of a neutron moderating spacing means. The neutron moderating spacing means can comprise a solid mass of a neutron moderating material, or the spacing means can comprise a lower section of the rod in which water or other liquid coolant acts as the moderator, and an intermediate sealing plug provided to seal the neutron absorber from the neutron moderator. Preferably, the neutron absorber comprises a borosilicate glass tube that is held in spaced relation to the bottom closure means of the cladding by the neutron moderating spacing means. |
abstract | A neutron multi-detector array feeds pulses in parallel to individual inputs that are tied to individual bits in a digital word. Data is collected by loading a word at the individual bit level in parallel. The word is read at regular intervals, all bits simultaneously, to minimize latency. The electronics then pass the word to a number of storage locations for subsequent processing, thereby removing the front-end problem of pulse pileup. |
|
abstract | Systems and methods for digital X-ray imaging are disclosed. An example portable X-ray scanner includes: an X-ray detector configured to generate digital images based on incident X-ray radiation; an X-ray tube configured to output X-ray radiation; a computing device configured to control the X-ray tube, receive the digital images from the X-ray detector, and output the digital images to a display device; a power supply configured to provide power to the X-ray tube, the X-ray detector, and the computing device; and a frame configured to: hold the X-ray detector, the computing device, and the power supply; and hold the X-ray tube such that the X-ray tube directs the X-ray radiation to the X-ray detector. |
|
049922327 | claims | 1. An improved method of utilizing hydrogen water chemistry in a boiling water reactor nuclear power plant, the plant including a reactor which boils water to produce a liquid phase and a steam phase, a turbine for extracting power from the steam phase, a condenser for condensing steam from which power has been extracted, and a feed water system returning the condensed steam as boiler feed water to the reactor, wherein the process of injecting hydrogen into the boiler feed water is utilized to reduce stress corrosion, the improvement comprising the step of reducing the transfer of radioactive gaseous nitrogen compounds from the liquid phase to the steam by inhibiting the formation of said nitrogen compounds in the liquid phase. 2. The process of claim 1, wherein said inhibiting step comprises chemically inhibiting the formation of volatile N-16 species in the liquid phase. 3. The process of claim 2, wherein said inhibiting step includes adding at least one free-radical scavenger to the boiler feedwater, whereby the evolution of gaseous nitrogen compounds is inhibited. 4. The method of claim 3, wherein said scavenger is selected from the group consisting of nitrous oxide, copper, zinc, low molecular weight alcohols and ketones, carbon dioxide, nitrite and nitrate. 5. The process of claim 1, wherein said inhibiting step comprises adjusting the pH of said water to a basic level in the range from about 7 to 8.6, whereby the evolution of volatile nitrogen compounds is inhibited. 6. The process of claim 1, wherein said inhibiting step comprises the use of reduced sparging in a core of said reactor. 7. The process of claim 1, wherein said inhibiting step comprises increasing the recirculation rate of water flow. 8. The process of claim 1, wherein said inhibiting step comprises adjusting a control rod pattern. 9. The process of claim 1, wherein said inhibiting step comprises raising the reactor water level. 10. The process of claim 1, wherein said inhibiting step comprises injecting said hydrogen into a preselected region in the recirculation system, said region having been selected to allow for reduced hydrogen utilization, whereby less radioactive volatile nitrogen is evolved. 11. The process of claim 10, wherein hydrogen is injected into a region below a jet pump inlet in the recirculation system. 12. The process of claim 11, wherein hydrogen is injected into a bypass region in a core inlet. 13. The process of claim 1, wherein the transfer of radioactive volatile nitrogen compounds is inhibited by use of a selective adsorbent to increase the hold-up time of the nitrogen compounds to allow for further decay. 14. The process of claim 1, wherein the transfer of radioactive volatile nitrogen compounds is inhibited by increasing the hold-up time in steam lines from the reactor. 15. The process of claim 1, wherein the transfer of radioactive volatile nitrogen compounds is inhibited by the use of surface catalysis to improve hydrogen utilization, whereby the evolution of gaseous nitrogen is decreased. 16. The process of claim 1, wherein the transfer of radioactive volatile nitrogen compounds is inhibited by the use of increased radiation to enhance hydrogen-oxygen recombination. 17. The process of claim 1, wherein the transfer of radioactive volatile nitrogen compounds is inhibited by operating at a more positive electropotential allowing less hydrogen addition. 18. An improved method of utilizing hydrogen water chemistry in a boiling water reactor nuclear power plant, the plant including a reactor which boils water to produce a liquid phase and a steam phase, the improvement comprising the step of adding a free-radical scavenger to the liquid phase to inhibit the transfer of gaseous nitrogen compounds from the liquid phase to the steam phase. 19. The method of claim 18, wherein said scavenger is selected from the group consisting of nitrous oxide, copper, zinc, low molecular weight alcohols and ketones, carbon dioxide, nitrite and nitrate. |
claims | 1. A method for removing heat from a molten fuel nuclear reactor having a reactor core containing high temperature liquid nuclear fuel, the method comprising:delivering lower temperature nuclear fuel into the reactor core, therebydisplacing some high temperature nuclear fuel from the reactor core upward into a first heat exchanger anddisplacing some nuclear fuel downward in a second heat exchanger,wherein the first heat exchanger is arranged above and in fluid communication with the reactor core to receive nuclear fuel from the reactor core,wherein the second heat exchanger is arranged above the reactor core and in fluid communication with both the first heat exchanger and the reactor core to receive nuclear fuel from the first heat exchanger and to deliver nuclear fuel to the reactor core,wherein the first heat exchanger comprises a shell-and-tube heat exchanger and the second heat exchanger comprises a separate shell-and-tube heat exchanger; androuting coolant through the first and second heat exchangers, therebytransferring heat from the high temperature nuclear fuel to the coolant andconverting the displaced high temperature nuclear fuel into the lower temperature nuclear fuel. 2. The method of claim 1, wherein delivering the lower temperature nuclear fuel into the reactor core includes passing the lower temperature nuclear fuel from the second heat exchanger into the reactor core. 3. The method of claim 1, wherein delivering the lower temperature nuclear fuel includes operating at least one impeller to drive flow of the nuclear fuel through the first and second heat exchangers. 4. The method of claim 1 further comprising:neutronically shielding the first and second heat exchangers from neutrons generated in the reactor core. 5. The method of claim 1, wherein routing the coolant includes delivering coolant at a temperature less than that of the high temperature nuclear fuel to the second heat exchanger. 6. The method of claim 1, wherein routing coolant includes pumping coolant first through the second heat exchanger and then through the first heat exchanger. 7. The method of claim 1, wherein the first and second heat exchangers are vertically-oriented shell-and-tube heat exchangers located above the reactor core. |
|
055641059 | claims | 1. A method of treating a contaminated aqueous solution, characterized by the steps of: pumping a borated aqueous solution out of a reactor coolant system, the solution containing ionic complexes comprised of a ferrous cation contaminant and an organic complexing agent; adding an oxidizing agent to the borated aqueous solution to oxidize the complexing agent and thereby to destroy the complex and precipitate the contaminant to produce a borated aqueous solution contaminated with less than 1 ppm ferrous cation; separating the precipitated contaminant from the solution; and then reusing the borated aqueous solution. 2. The method of claim 1, wherein the complexing agent is a dicarboxylic acid or a salt thereof. 3. The method of claim 2, wherein the complexing agent is selected from the group consisting of oxalic acid, citric acid, picolinic acid, nitrilotriacetic acid, ethylenediaminetetraaceticacid, hydroethylenediaminetetraacetic acid and salts thereof. 4. The method of claim 1, wherein the complexing agent is vanadous formate or formic acid. 5. The method of claim 1, wherein the complexing agent is a soap or a detergent. 6. The method of claim 1, wherein the oxidizing agent is selected from the group consisting of O.sub.3, and H.sub.2 O.sub.2. 7. The method of claim 1, wherein the oxidizing agent is H.sub.2 O.sub.2, and wherein the oxidizing agent is added to the contaminated aqueous solution to reduce its Total Organic Carbon from about 360 ppm to less than about 50 ppm in no more than 50 minutes. 8. The method of claim 1, wherein the oxidizing agent is continuously added to the borated aqueous solution. |
claims | 1. An assembly part for a manufacturing system, comprising: a body on which a unit is assembled in a vacuum column; a first insulating film provided on the body; a wiring arranged on the first insulating film; a wiring terminal provided at the wiring in a position for direct connection to another assembly part; and a second insulating film covering the wiring except for the wiring terminals. 2. The assembly part of claim 1 , wherein either the first or second insulating film is an electro-deposited polyimide film. claim 1 3. The assembly part of claim 2 , wherein either the first or second insulating film has a resistance of 10 12 xcexa9cm to 10 13 xcexa9cm. claim 2 4. The assembly part of claim 3 , wherein either the first or second insulating film is 15 xcexcm to 25 xcexcm thick. claim 3 5. The assembly part of claim 1 , wherein the first insulating film is larger than the second insulating film. claim 1 6. The assembly part of claim 1 , wherein the wiring terminal is provided on the body at a position for connection to a wiring terminal of another assembly part. claim 1 7. The assembly part of claim 1 , wherein the wiring terminal is integral with at least one end of the wiring. claim 1 8. The assembly part of claim 7 , wherein the wiring and the wiring terminal are made of copper, copper alloy, aluminum, aluminum alloy or gold. claim 7 9. The assembly part of claim 1 , wherein the body is made of metal. claim 1 10. The assembly part of claim 1 , wherein the body is provided with bolt holes or bolt-screw holes for assembling. claim 1 11. The assembly part of claim 6 , wherein the wiring extends over one surface or at least two surfaces of the body. claim 6 12. The assembly part of claim 1 , wherein the first insulating film is formed on the body via an adhesive film, and the second insulating film is covered by a protective film. claim 1 13. A semiconductor manufacturing system comprising: a vacuum column and a unit constituted by an assembly part assembled in the vacuum column, wherein the assembly part includes: a body; a first insulating film provided on the body; a wiring provided on the first insulating film; a wiring terminal provided at the wiring in a position for direct connection to another assembly part; and a second insulating film covering the wiring except for the wiring terminal. 14. The semiconductor manufacturing system of claim 13 , wherein at least the first or second insulating film is an electro-deposited polyimide film. claim 13 15. The semiconductor manufacturing system of claim 14 , further comprising a conductive cable which is constituted by a core, a third insulating film covering the core, a shield film covering the third insulating film and a fourth insulating film covering the shield film, and is electrically connected to the wiring terminal. claim 14 16. The semiconductor manufacturing system of claims 15 , wherein at least the third or fourth insulating film is an electro-deposited polyimide film. 17. An electron beam exposure system comprising: a vacuum column; at least a unit such as an electronic lens, a deflector or an electro-optical component housed in the vacuum column; a first insulating film provided on the unit; a wiring provided on the first insulating film; a wiring terminal provided at the wiring in a position for direct connection to another unit; and a second insulating film covering the wiring except for the wiring terminal. 18. An electron beam exposure system comprising: a vacuum column; an electromagnetic lens and an electrostatic deflector housed in the vacuum column; a lens stand for holding the electromagnetic lens thereon; a deflector stand for holding the electrostatic deflector; a first wiring provided on the electromagnetic lens via a first insulating film and including a first wiring terminal; a second wiring provided on the lens stand via the first insulating film, and including a second wiring terminal formed in a position for direct connection to the electromagnetic lens and electrically connected to the first wiring terminal; a third wiring provided on the electrostatic deflector via the first insulating film and including a third wiring terminal; and a fourth wiring provided on the deflector stand via the first insulating film, and including a fourth wiring terminal formed in a position for direct connection to the electrostatic deflector and electrically connected to the third wiring terminal. |
|
046801596 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION A terminal storage container 11 of steel (FIGS. 1 and 2) includes a circular storage space 13 to accommodate the individual fuel rods 15 of several irradiated nuclear reactor fuel elements. The fuel rods 15 are tightly packed in four circular-segmental fuel-rod cans 17. These cans 17 are closed after being loaded. The fuel-rod cans 17 are placed in a cage 19 which is inserted into the circular storage space 13. When viewed in cross-section, this insert cage 19 includes a centrally located square shaft 21 from the corners of which diagonal partition walls 23 extend to the container inner wall 24 of the storage space 13. This results in the provision of four storage compartments 25 for receiving the fuel-rod cans 17. The fuel-rod cans 17 are of circular-segmental configuration. The rear walls 27 of cans 17 abutting the container inner wall 24 are curved and have a curvature corresponding to the curvature of the container inner wall 24. The radially extending sides 29 of the cans 17 are parallel to the partition walls 23. The inwardly facing wall 31 of each fuel-rod can is of a lattice configuration and extends parallel to a corresponding one of the sides of the square central shaft 21. A chamfer forms the transition between the radial sides 29 of the fuel-rod cans 17 and their curved rear wall 27. Each fuel-rod can 17 is capable of holding the fuel rods of two disassembled irradiated nuclear reactor fuel elements. Loading takes place with the can 17 lying on its rear wall 27. The latticed wall 31 is not yet set in place at this stage. The fuel rods are loaded into the can 17 through the opening. Following loading, the wall 31 is welded to the can. The loading opening of the terminal storage container 11 is closed by a stepped cap 33 (FIG. 1) which is fastened onto a suitable step 37 of the loading opening by means of threaded bolts 35. A seal (not shown) is placed between cap 33 and container 11. Another cap 41 is arranged on top of the screw-on cap 33 which is inserted into the loading opening and welded to the container wall 43. In the assembly shown in FIGS. 1 and 2, the terminal storage container 11 is placed into a shielded transport container 45. The loading opening of the shielded transport container 45 is closed by a closure cover 47 which is secured by threaded fasteners. A polyethylene layer 49 is inserted into the inner wall of the shielded transport container 45 for shielding neutrons. The shielded transport container 45 is equipped with carrying lugs 51 secured to its outer periphery. The loaded fuel-rod cans 17 are each equipped with a handling block 55 on the upper end faces thereof for the application of suitable lifting gear. Hold-down springs 57 bear with one end against the upper end surfaces 53 of the fuel-rod cans 17 and bear with the other end against the cover 33. The mode of operation of the arrangements described above will now be explained. The individual fuel rods 15 are loaded into the segmental fuel-rod cans 17 which are then closed. The fuel-rod cans 17 are then seized by the handling block 55 and placed into corresponding ones of compartments 25 of the insert cage 19. Hold-down springs 57 are placed on the upper end faces 53 of the fuel-rod cans 17. As the first cap 33 is fastened to the container 11, the springs will bear against the fuel-rod cans 17 thereby causing the fuel-rod cans 17 to be in constant abutment with the container bottom. The fuel-rod cans 17 lie against the container inner wall 24 with their curved rear walls 27 and a good heat transfer to the container body is thereby ensured. The empty square center shaft-like compartment 21 in the middle of the storage container 11 is loaded with fuel element structural parts 63 which were separated at the time of disassembly of the fuel elements. These parts include top and bottom pieces as well as the spacers including the control rod guide tubes. The fuel element structural parts are compacted. FIG. 3 shows the cross-section of a circular storage chamber 71 of a terminal storage container 73 in a modified embodiment. Inserted into the storage chamber 71 is a modified cage 75 which likewise has a square center shaft-like compartment 77 in the middle of the storage chamber 71. This square central shaft-like compartment 77 is held in position by pairs of partition walls (78, 79) which extend from the compartment corners and bear radially against the container inner wall 81. The partition walls (78, 79) of each pair are interconnected by a curved rear wall 83. Further pairs of partition walls (87, 89) extend from the center of the sides 85 of the square central compartment 77 to the container inner wall 81. The ends of the walls (87, 89) of each partition wall pair are connected by a short rear wall 91. The rear walls 83 and 91 of the partition wall pairs (78, 79) and (87, 89), respectively, are curved as shown and face the container inner wall 81. A circular-segmental fuel-rod can 93 is arranged between a pair of partition walls (78, 79) which extend from a corner of cage 75 and a pair of partition walls (87, 89) which extend from the center of a side 85 thereof. These fuel-rod cans 93 each have curved rear wall 95. The radial sides 97 of the fuel-rod cans 93 extend parallel to the adjacent pairs of partition walls (78, 79) and (87, 89). The inwardly facing wall 99 of the fuel-rod cans 93 is slightly curved. The embodiment of FIG. 3 shows eight fuel-rod cans 93 arranged in a circle. Each can 93 is capable of accommodating the fuel rods 101 of a single fuel element. The fuel-rod cans of this embodiment are loaded at the end face thereof. The cross-sections of the fuel-rod cans 93 are preferably identical in order not to complicate the front-loading procedure of the cans 93 and to be able to carry out the procedure without modification. Following loading, the upper end wall is welded to its fuel-rod can 93. For wet loading the fuel-rod cans 93, that is, for loading the same under water, a suction pipe 103 is provided in the circular storage space 81 so that the water can be removed from the container 73 following loading. FIGS. 4 to 6 illustrate another embodiment of the insert cage and the fuel-rod cans of FIG. 3. Like parts are assigned like reference numerals, with a prime being added. Inclined guides 105 are provided in the upper region on the radial sides 79' of each fuel-rod can 93'. These upper guides 105 cooperate with inclined engagement surfaces 106 provided in the adjacent partition walls of partition pairs (78', 79') and (87', 89'), respectively, of the insert cage 75'. At the lower end of the insert cage 75', outwardly extending inclined guide surfaces 109 are provided in the vicinity of the bottom of the storage container 73'. The guideways 105 and the guide surfaces 109 urge the fuel-rod cans 93' against the container inner wall 81' as they are being inserted. It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. |
abstract | The invention concerns a method of monitoring the operation of a reactor of a nuclear plant. The reactor is operated at a given total reactor power during a normal fuel operation cycle. The radioactivity level in the off-gas stream is continuously measured to detect a possible release of fission gases from the fuel rods as a consequence of a fuel leakage due to a defect on the cladding of any of the fuel rods in any of the fuel assemblies. An instantaneous power distribution is regularly established in the core and a power distribution pattern over time is established based on the instantaneous power distributions. The release of fission gases and the established power distribution pattern are then combined and correlations between changes in the release of fission gases and in the power distribution pattern are observed in order to determine a position of the defect. |
|
summary | ||
description | This application claims priority of German application No. 10 2007 003 853.6 filed Jan. 25, 2007, which is incorporated by reference herein in its entirety. The invention relates to a multileaf collimator, in particular for a radiation therapy device, and to a radiation therapy device having a multileaf collimator of said kind. A multileaf collimator is used in radiation therapy for treating tumors. A multileaf collimator of such kind is described in, for instance, DE 196 39 861 A1 and WO 00/46813. A tumor is irradiated during radiation therapy with energy-rich beams, usually high-energy X-radiation from a linear accelerator. The multileaf collimator is therein brought into the path of the X-ray beam. The multileaf collimator has a plurality of leaves that can be mutually displaced under motorized control for the purpose of establishing an opening whose contour corresponds to that of the tumor. Thus, only the tumor and not adjacent healthy body tissue will be irradiated with the X-rays. Two sets of leaves are for that purpose arranged mutually opposite such that they can be moved with their front sides toward or away from each other. Virtually any tumor contour can be reproduced in that way. Said leaves can each be positioned by means of an electric motor embodied as a stepping motor. The positioning accuracy of a stepping motor of said type has, though, proved disadvantageous. Moreover, a stepping motor has a starting behavior that does not allow slight adjustment in positioning. The object of the invention is to disclose a multileaf collimator having an improved positioning device. Said object is inventively achieved by means of a multileaf collimator as claimed in the claims. Each leaf is for that purpose assigned at least one linear drive having at least one piezoelectric actuator, which can be driven by a control device, for displacing the leaf in an adjusting direction. A high degree of positioning and repetition accuracy can be achieved through employing a piezoelectric actuator for displacing a leaf. It is hence possible to dispense with a complex measuring and control system for compensating positioning inaccuracies of the kind needed even for highly accurate stepping motors. Moreover, the displacement of the piezoelectric actuator is proportional to the applied supply voltage. By specifying the supply voltage it is thus possible to precisely and simply specify how far the leaf will be displaced by means of the piezoelectric actuator. A successive linear movement of the leaf can thus be achieved by driving the piezoelectric actuator repeatedly. The piezoelectric actuator furthermore consumes little current while moving the leaf. The piezoelectric actuator is otherwise virtually currentless so that its current consumption is close to zero. Accordingly, a transformer requiring to be provided for electrically powering the piezoelectric actuator can furthermore be of low-power design. The energy requirements of the piezoelectric actuator are low so that the operating costs of the linear drive are low compared with a motor-driven linear drive. The noise produced while the transformer is operating is low owing to the low power consumption. A linear drive of said type can have very small dimensions because a piezoelectric actuator occupies little structural space. It can therefore be significantly more compact in structural design than a conventional linear drive for a multileaf collimator having electric motors that can be individually driven. The piezoelectric actuator expediently has a piezoelectric element and a transducer coupled to the piezoelectric element. The transducer can in terms of its geometry in that way be matched exactly to the leaf requiring to be moved. In an advantageous development a frictional engagement is embodied for transmitting a driving force between the transducer and the leaf requiring to be moved, with the frictional force being adjustable as a function of direction. In other words, when frictional contact has been established with the transducer the displaceably mounted leaf is moved thereby by means of static friction. The mechanical coupling between the transducer and leaf due to frictional engagement is purely passive in nature. There is hence no need to control the coupling force. Because the transducer is linked directly to the leaf by means of frictional engagement there is no mechanical play whatever between the transducer and leaf. A particularly high degree of positioning and repetition accuracy can hence be achieved. A complex control system for compensating positioning inaccuracies of the kind needed even for highly accurate stepping motors does not have to be employed. Force is transmitted directly to the leaf requiring to be moved by means of the transducer via frictional engagement. Gearing for force transmission is hence not needed so that driving can be implemented simply and economically. The transducer engages on the leaf virtually without sound so that very little noise is produced while the leaf is being moved. The current consumption of the piezoelectric actuator is furthermore close to zero while the leaf is being held in a holding position by means of frictional engagement so that a particularly low energy consumption will be insured especially when the multileaf collimator is in standby mode. The control device expediently drives the piezoelectric actuator in such a way that, exploiting the leaf's mass inertia, the leaf will be moved compliantly during an excursion in the direction of motion and, in the opposite direction, the transducer wilt slide across the leaf. In other words the frictional engagement between the transducer and leaf is produced solely by the interplay between the leaf's mass inertia and direction-dependent driving of the transducer. Selective moving of the leaf will have been achieved thereby in a simple manner and with little control effort. The control unit is advantageously set up for driving the piezoelectric actuator in such a way that the transducer's speed will be lower in the direction of motion than in the opposite direction. Rapid buildup or cleardown of the supply voltage will cause the piezoelectric element to expand or contract rapidly. The transducer secured to the piezoelectric element will thus overcome the static frictional force being applied to its friction surface through frictional engagement. The transducer will be moved in the direction counter to the direction of motion by means of sliding friction on the leaf's surface. The transducer's contact point on the leaf can be changed in that way. What is therein exploited is that the leaf requiring to be moved has a significantly greater mass than the transducer and so will retain its position owing to its mass inertia. Slow buildup or cleardown of the supply voltage will cause the piezoelectric element to expand or contract slowly. A frictional engagement between the transducer and leaf will be produced in that way. The leaf's mass inertia will be overcome by the static frictional force between the transducer and leaf. The leaf will be displaced in the direction of motion by means of the transducer engaging on it. Thus, a linear leaf movement in the direction of motion can be achieved in a simple manner with a periodic supply voltage that rises rapidly and falls slowly. A reversal of the direction of motion can be achieved just as simply with a periodic supply voltage that falls rapidly and rises slowly. A bilateral linear movement can accordingly be implemented using an asymmetric supply voltage. For example a periodic voltage having the nature of an asymmetric saw tooth is suitable as the supply voltage. In an advantageous development, a plurality of piezoelectric actuators are provided for moving the leaf. Thus, a leaf having a high mass and hence a high mass inertia can also be moved by means of the linear drive. The piezoelectric actuators can be moved jointly by means of the control device so that the static frictional force transmitted by means of static friction to the leaf will suffice to displace it by means of frictional engagement. Moving of a leaf by means of a plurality of simultaneously moved piezoelectric actuators is particularly significant if a leaf having a high mass is to be moved. That is the case with, for example, a multileaf collimator employed in radiation therapy. A multileaf collimator of said type has leaves made of a radiation-shielding material, usually a tungsten alloy, of very high density so that the individual leaves have a high mass. The control device is advantageously set up for operating the piezoelectric actuators in succession. That will enable the individual transducers' contact points to be changed successively by means of sliding friction exploiting the leaf's mass inertia and allow the leaf to be displaced continuously without interruption. The piezoelectric actuators are therein expediently arranged on the leaf's narrow and/or flat sides. Different advantageous arrangements are therein possible. Thus a plurality of piezoelectric actuators can be arranged in each case in pairs on opposite narrow sides or opposite flat sides. The force applied to a linear guide holding and guiding the leaf can in that way be reduced. In another advantageous variant a plurality of piezoelectric actuators can be arranged on a narrow or flat side. Structural space for the piezoelectric actuator will then have to be provided only on said narrow or flat side. The linear drive can then be of particularly compact design. The leafs linear guide will on the other hand have to be embodied in such a way that the leaf can be displaced smoothly notwithstanding the force being applied unilaterally thereto. The object is further achieved by means of a radiation therapy device having a multileaf collimator as claimed in one of the preceding claims. The claims directed to the multileaf collimator along with their advantages are therein applicable analogously to the radiation therapy device. Since the multileaf collimator has very precisely positionable leaves, a contour for the irradiating of a tumor can be specified precisely. That will allow radiation therapy to be performed with high precision. The risk of either not including parts of the tumor tissue during irradiating or of damaging healthy body tissue through irradiating is therefore significantly less compared with a motor-driven multileaf collimator according to the prior art. FIG. 1 is a schematic top view of a multileaf collimator 2 that includes a number of plate-type leaves 4 arranged substantially mutually parallel. Said leaves 4 can be adjusted in the adjusting direction 6. For adjusting, in each case two mutually opposite leaves 4 are with their front sides 10 moved toward or away from each other by means of a control device 8. It is in that way possible to set virtually any contour 12 for the irradiating of a tumor by means of an X-ray beam traversing the multileaf collimator 2 in the beam direction 14. In FIG. 1, as viewed from the plane of the figure said X-ray beam traverses the irradiating contour 10 from top to bottom through the multileaf collimator 2. FIG. 2a shows a leaf 4 mounted longitudinally displaceably in the adjusting direction 6 by means of a linear guide 16. For displacing the leaf 4, a linear drive 18 for displacing a leaf 4 is provided with two piezoelectric actuators 20,20′ that can be driven by the control unit 8. Bach piezoelectric actuator 20,20′ includes a piezoelectric element 22,22′ and a transducer 24,24′ coupled thereto that are shown schematically in FIG. 2a. Both transducers 24,24′ of the piezoelectric actuators 18,18′ are in frictional contact with the opposite narrow sides 26,26′ of the leaf 4. A frictional force 28,28′ therein acts on the surface of the narrow side 26,26′. The leaf 4 is displaced in a direction of motion 30 as follows. The supply voltage V of the piezoelectric element 22 of the first piezoelectric actuator 20 is first rapidly increased by means of the control device 8. The transducer 24 of the piezoelectric actuator 20 slides by means of sliding friction across the surface of the narrow side 26. It therein covers the travel interval 34 in the direction 32 counter to the direction of motion 30 and thus changes its contact point. The supply voltage of the piezoelectric element 22′ of the piezoelectric actuator 20′ is then rapidly increased by means of the control device 8 shown in FIG. 2b. The transducer 24′ of the piezoelectric actuator 20′ will thus also be displaced in the opposite direction 32 on the surface of the narrow side 26′ by the extent of the travel interval 34. The transducers 24,24′ of both piezoelectric actuators 20,20′ will then both have a new contact point displaced in the opposite direction 32 by the extent of the travel interval 34. Finally, according to FIG. 2c, the supply voltages of the two piezoelectric elements 22,22′ are slowly simultaneously reduced by means of the control device 8. The transducers 24,24′ are both moved by the piezoelectric elements 22,22′ in the direction of motion 30 by the extent of the travel interval 34. Thus the frictional forces 28,28′ of both friction surfaces of the transducers 24,24′ will engage jointly via frictional engagement on both narrow sides 26,26′. Since both transducers 24,24′ are, moreover, moved slowly, the leaf 4 will by means of frictional engagement also be moved compliantly with the transducers 24,24′ in the direction of motion 30 by the extent of the travel interval 34. The contact point of both transducers 24,24′ is then in turn changed again as described for FIGS. 4a and 4b. A continuous linear movement of the leaf 4 in the direction of motion 30 will have been achieved thereby. Described in FIGS. 3a-c is the movement of the leaf 4 by means of the linear drive 1 in the direction of motion 30 counter to the direction of motion shown in FIGS. 2a-c. According to FIG. 3a, the supply voltage of the piezoelectric element 22′ is first rapidly reduced by means of the control device 8. The transducer 24′ of the piezoelectric actuator 20′ moves by the extent of the travel interval 34 in the direction 32 counter to the direction of motion 30. According to FIG. 3b, the supply voltage of the piezoelectric element 22 of the first piezoelectric actuator 20 is then reduced by means of the control device 8. The transducer 24 of the piezoelectric actuator 20 thus also moves by means of sliding friction by the extent of the travel interval 34 in the opposite direction 32. The contact point of both transducers 24,24′ of both piezoelectric actuators 20,20′ will in each case have been changed by the extent of the travel interval 34, Finally, according to FIG. 3c, the supply voltages of the two piezoelectric actuators 22,22′ are slowly simultaneously increased by means of the control device 8. The transducers 24,24′ are both displaced in the direction of motion 32 by the extent of the travel interval 34. Because said displacement takes place slowly and, moreover, both friction surfaces of both transducers 24,24′ transmit a frictional force 28,28′ to the leaf 4 by means of frictional engagement, the leaf 4 will likewise be moved by means of static friction in the direction of motion 30 by the extent of the travel interval 34. Because both piezoelectric actuators 20,20′ engage with their transducers 24,24′ on both opposite narrow sides 26,26′ of the leaf 4, the leaf 4 will not be subjected to any additional force. The linear guide 16 can hence be embodied in a simple manner. The movement, described in FIGS. 2a-c and FIGS. 3a-c, of the leaf 4 is intended solely to elucidate an interaction among a plurality of piezoelectric actuators 20,20′. Leaves 4 having a very large mass can basically be moved as a result of employing a larger number of piezoelectric actuators 20,20′. Moreover, the piezoelectric actuators 20,20′ will in that case not have to be individually driven consecutively but can also be driven in groups. If the leaf 4 has a very high mass, then owing to its mass inertia individual transducers 24,24′ will also be displaceable if driven relatively slowly. The number of piezoelectric actuators 20,20′, the driving thereof, and their friction surfaces will hence be mutually coordinated to obtain an even movement. According to FIG. 4, a second linear drive 18 for a leaf 4 has two piezoelectric actuators 20,20′. The opposite flat sides 36,36′ of the leaf 4 are each assigned a piezoelectric actuator 20,20′. Each piezoelectric actuator 20,20′ exerts a frictional force 28,28′ on the flat side 36,36′ assigned to it. The only difference compared with FIG. 2a is that both piezoelectric actuators 20,20′ are now assigned to the flat sides 36,36′ and no longer to the narrow sides 26,26′ of the leaf 4. The leaf 4 is moved in the adjusting direction 6 in a manner analogous to that described for FIGS. 2a-c and FIGS. 3a-c. According to FIG. 5, a third linear drive 18 for a leaf 4 again has two piezoelectric actuators 20,20′. The piezoelectric actuators 20,20′ are both arranged on a narrow side 18 of the leaf 4. Each piezoelectric actuator 20,20′ exerts a frictional force 28,28′ with its transducer 24,24′ on the narrow side 18. The leaf 4 is again moved in the manner described for FIGS. 2a-c and FIGS. 3a-c. The arrangement of the piezoelectric actuators 20,20′ on the one hand makes an especially compact structural design possible; on the other hand, however, the linear guide 16 must be embodied in such a way as to absorb the unilaterally acting frictional force 28,28′. FIG. 6 is a schematic side view of a radiation therapy device 38 which by means of a retaining device 40 includes a multileaf collimator 2 arranged in a housing. By means of an automatic focusing system not shown in FIG. 6, the X-ray beam 42 traverses the multileaf collimator 2 in the beam direction 14 for the purpose of irradiating a tumor 44 of a person 46. By means of its individually displaceable leaves 4 (not shown in the figure) the multileaf collimator 2 therein establishes the contour 10 for irradiating the tumor 44, as shown in FIG. 1. Because the person 46 is at a distance of the order of magnitude of around one meter or more in the beam direction 14 from the multileaf collimator 2, the X-ray beam 42 will widen along its path from the multileaf collimator 2 to the tumor 44. In other words, even slight positioning inaccuracies in the millimeter range will mean that either diseased tissue within the tumor 44 will not be covered by the X-ray beam 42 or that healthy tissue surrounding the tumor 44 will be covered by the X-ray beam 42 and damaged by it. Particularly selective radiation therapy is hence made possible by the improved positioning of the leaves 4. |
|
054669430 | description | DESCRIPTION OF THE INVENTION The invention is an evacuated testing device 100 utilizing infrared (IR) radiation for testing semi-conductor devices as shown in the FIGURE. The evacuated testing device 100 provides a test chamber 101 which includes a test dewar 102 and an infrared (IR) blackbody radiating source 104. The test dewar 102 includes an outer structure 106 and a base 108 each of which can be comprised of aluminum. The base 108 serves as part of the support structure of the test dewar 102 as shown in the FIGURE. The entire test chamber 101 is under vacuum. Positioned within the test dewar 102 and attached to the base 108 is a cold shield 110. An aperture 112 is formed within the cold shield 110 for admitting the IR radiation from the IR blackbody radiating source 104. Mounted to the dewar base 108 and extending into the test chamber 101 is a cold finger 114. The cold finger 114 provides a platform for mounting a semiconductor device under test such as a focal plane array 116. The cold finger 114, which is connected to a refrigerated system (not shown), also cools the focal plane array 116 by drawing heat therefrom during cryogenic testing. The focal plane array 116 is an infrared sensing device that senses uniform IR radiation emitted from, for example, the IR blackbody source 104. The focal plane array 116 can be comprised of a detector and associated signal processing equipment (not shown). The detector serves to sense the photon radiation from the blackbody source 104 and converts the photons into electrical signals. The electrical signals are then processed by the signal processing equipment (not shown) associated with the focal plane array 116 which provides an output signal. The output signal is then transmitted to, for example, a computer system for subsequent processing. The size of the aperture 112 formed within the cold shield 110 and the temperature of the IR blackbody source 104 determines the amount of radiation impinging upon the focal plane array 116. The cold shield 110 can also be comprised of aluminum. The test dewar 102 thus incorporates the cold shield 110, the aperture 112, the cold finger 114 and the focal plane array 116. Butted against and hermetically sealed to the test dewar 102 is a housing 118 for the IR blackbody radiating source 104 as shown in the FIGURE. The blackbody housing 118 can be comprised of aluminum and the hermetic seal between the test dewar 102 and the housing 118 is established and maintained by methods known in the art. A hermetically sealed feedthru connector 120 passes through the blackbody housing 118. The feedthru connector 120 is utilized to route electrical cabling between a control box (not shown) located external to the test chamber 101 and the IR blackbody radiating source 104. The IR blackbody radiating source 104 is a uniform radiometric source exhibiting extremely low reflectivity and is an efficient emitter of IR radiation. The radiating source 104 is generally employed for testing and evaluating IR sensitive devices such as the focal plane array 116 shown in the FIGURE. The radiating source 104, which replaces the vacuum shroud of prior art test dewars, includes a two-stage thermoelectric cooler 122, an IR sensor 124 and an emissive surface 126. The thermoelectric cooler 122 comprises two ceramic plates 128 and 130 as shown in FIG. 1. The ceramic plates 128 and 130 include a plurality of semiconductors positioned therein as is known in the art. The ceramic plates 128 and 130 are electrically connected to a direct current voltage source (not shown) via a plurality of conductors 132 routed through the feedthru connector 120. By applying different D.C. voltages to the ceramic plates 128 and 130, the thermoelectric cooler 122 can act as a hot plate or a cold plate. For example, when a D.C. voltage is applied to the ceramic plates 128 and 130 that results in positive current flow, the thermoelectric cooler 122 functions as a hot plate. Likewise, when a D.C. voltage is applied to the ceramic plates 128 and 130 that results in negative current flow, the thermoelectric cooler 122 functions as a cold plate. Thus, the thermoelectric cooler 122 operates as a heat pump to vary the temperature of the emissive surface 126 shown in the FIGURE. The emissive surface 126 thermally communicates with the thermoelectric cooler 122 and functions as the blackbody radiator. The emissive surface 126 is fabricated from copper and is coated with a painted surface as is known in the art. The temperature of the emissive surface 126 is logarithmically proportional to the IR radiation generated and emitted by the surface. By varying the voltage applied to the thermoelectric cooler 122, the temperature of the emissive surface 126 is changed. By varying the temperature of the emissive surface 126, the amount of IR radiation generated and transmitted is also varied. Positioned between the thermoelectric cooler 122 and the emissive surface 126 is the IR sensor 124. In particular, the IR sensor 124 is mounted to the backside of the emissive surface 126 and can be a commercially available thermistor. The thermistor is a calibrated resistor used to measure the differences in temperature between two surfaces. Electrical energy is delivered to the sensor 124 via the plurality of conductors 132 routed through the feedthru connector 120 as shown in the FIGURE. The sensor 124 on the IR blackbody radiating source 104 functions to provide feedback signals to the control box (not shown) necessary to maintain a specific temperature by the thermoelectric cooler 122 and thus the emissive surface 126. Attached to the blackbody housing 118 is a heat sink 134 as shown in the FIGURE. The heat sink 134 serves to cool the hot side of the thermoelectric cooler 122 which pumps heat into and out of the IR blackbody radiating source 104. Excess heat or cooling is removed from the structure of the thermoelectric cooler 122 via the heat sink 134 which can be, for example, a finned metallic extrusion. A cooling fan 136 is employed to draw air over the heat sink 134 to assist in removing the excess heat or cooling. The cooling fan 136 is connected to the heat sink 134 and thus the blackbody housing 118 via a shroud 138 at a mechanical interface 140. The evacuated testing device 100 of the present invention comprises a thermoelectrically temperature stabilized blackbody radiating source 104 for use within an evacuated environment of the test chamber 101 for testing semiconductor devices. The radiating source 104 is a uniform radiometric source capable of maintaining to within 0.05.degree. C. any temperature between -40.degree. C. to +80.degree. C. This extended temperature range is very useful in testing a focal plane array 116. Because the blackbody radiating source 104 is mounted within-an evacuated environment, performance is not adversely affected by air currents or moisture condensing on the surface of the source 104. Further, since the blackbody radiating source 104 is mounted within the test chamber 101, there are no intervening optical elements between the source 104 and the focal plane array 116 under test. Thus, any window for viewing the IR radiating source 104 is eliminated. Finally, the IR blackbody radiating source 104 can be slewed between temperatures within the test range (e.g., -40.degree. C. to +80.degree. C.) in a short time period. This is true because the evacuated environment (e.g., approximately 10.sup.-4 torr) eliminates any interference and degradation due to the atmosphere and extends the range of the blackbody radiating source 104. The slewing and temperature control of the blackbody radiating source 104 ensure rapid increment stepping across the test temperature range of interest. Thus, with the proper control, the blackbody source 104 can be automatically ramped. Therefore, the focal plane array 116 can be accurately characterized over all radiometric backgrounds of interest within the test chamber 101 without significant reconfiguration of the testing device 100. The evacuated testing device 100 of the present invention simplifies the task of testing a focal plane array 116. It enables the simulation of very high background flux conditions and extremely low background flux conditions within a few minutes. A very high background flux condition is generated by a highly emissive photon source having a temperature of greater than +80.degree. C. while an extremely low background flux condition is generated by a highly emissive photon source with a temperature less than -40.degree. C. The invention exhibits a unique design in that the IR blackbody radiating source 104 and the test dewar 102 incorporating the focal plane array 116 are each contained within the test chamber 101 of the evacuated testing device 100. Further, the present invention can be computer controlled and enhances the ability to determine the operating characteristics of the focal plane array 116 over a large scene dynamic range. Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. It is therefore intended by the appended claims to cover any and all such modifications, applications and embodiments within the scope of the present invention. Accordingly, |
summary | ||
summary | ||
description | The present specification is a continuation of U.S. patent application Ser. No. 13/523,604, of the same title, filed on Jun. 14, 2012, which, in turn, relies on U.S. Provisional Patent Application No. 61/497,024, of the same title, and filed on Jun. 14, 2011, for priority and is incorporated herein by reference in its entirety. The present specification is also a continuation-in-part of U.S. patent application Ser. No. 13/368,202, entitled “Covert Surveillance Using Multi-Modality Sensing”, and filed on Feb. 7, 2012, which relies on U.S. Provisional Patent Application No. 61/440,834, of the same title and filed on Feb. 8, 2011, for priority. The aforementioned application is incorporated herein by reference in its entirety. The present invention also relies on U.S. patent application Ser. No. 12/916,371, entitled “Mobile Aircraft Inspection System” and filed on Oct. 29, 2010, for priority, which is herein incorporated by reference in its entirety. The present specification generally relates to the field of covert surveillance for detecting threat items and contraband, either in a vehicle or on a person, and more specifically to a covert mobile inspection vehicle which combines a plurality of detection and prevention components that may be deployed rapidly to a threat zone to aid detection and prevention of subversive activities. More specifically, the present specification relates to an inspection system and method for simultaneous active backscatter and passive radiation detection. To counter the threat of terrorism, there is a requirement for systems to be put in place to detect and address subversive activity. Some of such systems known in the art are purely designed to detect subversive activity; others are designed to prevent subversive activity; while still other known systems are designed purely as a deterrent. For example, some systems are primarily physical (such as barriers and security agents), some rely on networks of sensors (such as CCTV systems) while others involve dedicated installations (such as radio jamming mast or X-ray scanning machines). What is needed, however, are covert surveillance systems that are highly mobile, can be rapidly deployed and allow the use of a plurality of surveillance data to enable more informed, robust and intelligent threat detection and prevention. Accordingly, there is need for a covert mobile inspection vehicle that uses a plurality of prevention and detection components or sensors. There is also need for a system that intelligently integrates and/or correlates surveillance information from the plurality of multi-modality sensors to detect and prevent subversive activities. Further, among detection systems that provide for efficient non-invasive inspection, X-ray imaging systems are the most commonly used. Transmission based X-ray imaging systems are traditionally used to inspect trucks and cargo containers for contraband. Inspection of a certain larger structures, such as complete aircraft, however, can be challenging with a transmission-based geometry wherein, typically, the source is located on one side of the aircraft and detectors are located on the other side of the aircraft. This geometry has many challenges, and in particular, when scanning around the landing gear and engines there is difficulty in placing detectors and thus, in producing radiographic images. In backscatter-based inspection systems, X-rays are used for irradiating a vehicle or object being inspected, and rays that are scattered back by the object are collected by one or more detectors. The resultant data is appropriately processed to provide images which help identify the presence of contraband. Since aircraft are typically made of lighter materials, a backscatter-based detection system would provide adequate penetration in most cases and thus would only require equipment to be placed on one side of the aircraft. However, backscatter technology may not be suitable when all areas of the aircraft have to be penetrated with a high detection probability, such as is the case with nuclear materials detection. Areas of high attenuation as measured by the backscattered radiation include fuel tanks, transformers, counterweights, among other aircraft components. In addition, backscatter technology cannot effectively discriminate between typical metals and special nuclear materials. Aircraft inspection calls for unique requirements such as the capability of inspecting large aircraft from more than one side. In addition, varying aircraft sizes would require the inspection head to scan at different heights, and several sections of the aircraft, such as the wings and tails, would require different head and detector scanning configurations. Conventional X-ray backscatter and transmission systems, however, do not have adequate scanning robustness, ability to work in various orientations, scanning range, or field of view for aircraft inspection applications. There is also a need to detect partially shielded or un-shielded special and radiological materials using passive detection technology. There is an even greater need to perform active and passive measurements simultaneously to prevent re-scanning the object or to avoid having two separate screening systems. In passive radiation-based detection systems, radiation emitted from special and radiological materials is measured without active interrogation. It is challenging, however, to combine both active backscatter inspection and passive radiation detection while still ensuring that the backscatter beam signals do not interfere with passive detection techniques, because the high backscatter radiation will impinge upon passive detectors at the same time the low-intensity passive signals are measured. Therefore, what is needed is a method and system for detection of both active backscatter and passive radiation, and in particular, simultaneous inspection. What is also needed is an active and passive detection system that is easily transportable, mobile, and non-intrusive, that is capable of operating even in rugged outdoor conditions such as airport environments. In one embodiment, the present specification discloses a covert mobile inspection vehicle comprising: a backscatter X-ray scanning system comprising an X-ray source and a plurality of detectors for obtaining a radiographic image of an object outside the vehicle; at least one sensor for determining a distance from at least one of the plurality of detectors to points on the surface of the object; a processor for processing the obtained radiographic image by using the determined distance of the object to obtain an atomic number of each material contained in the object; and one or more sensors to obtain surveillance data from a predefined area surrounding the vehicle. In an embodiment, the sensor is a scanning laser range finder causing a beam of infra-red light to be scattered from the surface of the object wherein a time taken for the beam of infra-red light to return to the sensor is indicative of the distance to the surface of the object. In one embodiment, the present invention is an inspection system and method for simultaneous active backscatter and passive radiation detection. In one embodiment, the present invention is a simultaneous low energy backscatter (100-600 kV) and passive radiation (gamma rays and neutrons) detection system and method. In one embodiment, the present invention is a non-intrusive inspection system that includes an inspection head having an x-ray source, a scanning wheel, a dual-purpose detector and associated electronics. The dual purpose detector can detect both backscatter x-rays and passive radiation. In one embodiment, the x-ray and gamma ray detectors are combined in the same module. In another embodiment, the x-ray detector is different from the gamma-ray detector. In one embodiment, the x-ray source of the present invention is constantly on, producing x-rays in a fan beam. In one embodiment, a spinning wheel having a plurality of pinholes therein is employed to produce a pencil beam of radiation through at least one pinhole. In one embodiment, the spinning wheel is employed to “block” the x-ray fan beam (and resultant pencil beam) from exiting, by blocking the slits in the spinning wheel, during which time passive radiation detection is active. In another embodiment, a beam chopping mechanism is employed, wherein the beam chopping mechanism is designed to present a helical profile shutter (aperture), formed on a cylinder, for X-ray beam scanners. In one embodiment, a radiation shield is provided on a radiation source such that only a fan beam of radiation is produced from the source. The fan beam of radiation emits X-rays and then passes through the spin-roll chopper, which acts as an active shutter. Thus, when the spin-roll chopper and therefore, helical aperture(s) is rotating, there is only a small opening for the X-ray fan beam to pass through, which provides the moving flying spot beam. In this embodiment, at least one gap between the spin-roll slits is used to block the exiting radiation to allow for passive measurements. In yet another embodiment, a scanning pencil beam is generated by any one of the approaches described above or any other approach as is known to those of ordinary skill in the art and deactivated by turning off the X-ray source (in contrast with previous embodiments, where the source is “blocked” by use of the spinning wheel or spin-roll chopper). Examples of suitable x-ray sources include, but are not limited to gridded sources, field emission electron sources (e.g. carbon nanotubes) or any other source that can switch the beam on-off within a few microseconds. In one embodiment, the present invention is a system for detecting concealed threats in an object by simultaneously performing active and passive radiation detection, the system comprising: an X-ray source with a modulating device to produce a pencil beam of radiation for scanning the object, said modulating device capable of blocking the pencil beam at regular intervals; a detector module for detecting both radiation backscattered by the object when scanned with the pencil beam of radiation and passive radiation emitted from threats within said object when the pencil beam of radiation is blocked, wherein said detector module comprises at least one detector; and a controller to measure backscattered radiation only when the x-ray pencil beam is on, and to measure only passive radiation when the x-ray pencil beam is blocked. In another embodiment, the present invention is a system for detecting concealed threats in an object by simultaneously performing active and passive radiation detection, the system comprising: an X-ray source with a modulating device to produce a pencil beam of radiation for scanning the object; a controller for switching the X-ray source on and off at regular intervals; and a detector module comprising an X-ray detector for detecting radiation backscattered by the object when scanned with the pencil beam, and a passive radiation detector for detecting radiation emitted from threats inside said object when the pencil beam is switched off. The system further comprises control electronics to measure backscattered radiation only when the beam is on, and to measure only passive radiation when the x-ray pencil beam is off. In one embodiment, the detector module comprises a detector array, wherein said detector array is capable of detecting both backscattered x-rays and passive radiation. In one embodiment, the passive radiation detector is at least one of a gamma ray detector, a neutron detector, or a gamma-neutron detector. In one embodiment, the neutron detector is used to passively measure neutrons simultaneously with backscatter radiation and passive gamma rays. In one embodiment, the modulating device comprises a disc with at least one pinhole. In another embodiment, the modulating device comprises a cylindrical chopper with at least one helical slit. In one embodiment, the modulating device is rotated to produce a pencil beam that is blocked at regular intervals and the system does not illuminate the object with radiation when the pencil beam is blocked. In one embodiment, the X-ray source is switched on and off at least once in a time period determined by a rotational frequency of the X-ray source, on the order of less than 1% of the rotational time. In another embodiment, the present invention is a method for detecting concealed threats in an object by simultaneously performing active and passive radiation detection, the method comprising: modulating an X-ray source to produce a pencil beam of radiation for scanning the object, such that the pencil beam is blocked at regular intervals; and detecting radiation backscattered by the object when scanned with the pencil beam, and detecting passive radiation emitted from threats inside said object when the pencil beam is blocked. In one embodiment, radiation is detected by using a dual-purpose detector adapted to detect both backscattered x-rays and passive radiation. In another embodiment, passive radiation is detected using a separate passive radiation detector that is at least one of a gamma ray detector, a neutron detector, or a combined gamma-neutron detector. In one embodiment, the neutron detector passively measures neutrons simultaneously with backscatter radiation and passive gamma rays. In one embodiment, backscattered radiation is measured when the x-ray pencil beam is on, and only passive radiation is measured when the beam is blocked. In one embodiment, the X-ray beam is modulated using a modulating device that comprises a disc with at least one pinhole. In another embodiment, the beam is modulated using a modulating device that comprises a cylindrical chopper with helical slits. In one embodiment, the modulating device is rotated to produce a pencil beam and is adapted to block said pencil beam at regular intervals. In one embodiment, the measured backscatter radiation and passive radiation data is combined to determine the presence of threats. In yet another embodiment, the present invention is a system for detecting concealed threats in an object by simultaneously performing active and passive radiation detection, the system comprising: an X-ray source with a modulating device to produce a pencil beam of radiation for scanning the object; a detector module comprising a detector for detecting radiation backscattered by the object when scanned with the pencil beam and radiation emitted from threats inside said object; and control electronics to measure a resultant backscatter signal having energies less than a first threshold and to measure passive gamma rays above a second threshold that is set at approximately the first threshold. In one embodiment, the system further comprises a processor, wherein said processor is programmed to subtract background noise produced by the high-energy gamma rays from the backscatter signal. In one embodiment, the system comprises a neutron detector to passively measure neutrons simultaneously with the backscatter radiation and passive gamma rays. In one embodiment, a processor is employed to analyze both the x-ray image and the passive gamma and neutron information for potential threats. The aforementioned and other embodiments of the present shall be described in greater depth in the drawings and detailed description provided below. The present specification is directed towards a covert mobile inspection system, comprising a vehicle, which is equipped with a plurality of multi-modality sensors. Surveillance information from the plurality of sensors is utilized to detect and prevent subversive activities. Thus, the present specification describes a system and method for providing covert and mobile surveillance/inspection of subversive activities using a plurality of multi-modality surveillance sensors. In addition, the present specification is directed toward using a backscatter X-ray scanning system that has improved threat detection capabilities as at least one of the plurality of surveillance sensors utilized. Accordingly, in one embodiment, the present specification describes a covert mobile inspection vehicle having an improved on-board backscatter X-ray scanning system and further equipped with a plurality of prevention and inspection components or devices. In one embodiment, the backscatter X-ray scanning system includes a sensor, such as a scanning laser range finder, that measures the distance of the detectors from the surface of the object under inspection. Because it is possible to map the equivalent distance between the X-ray beam at any angle and the surface of the object by determining the relative positions of the X-ray source and the laser sensor, in one embodiment, the present specification describes an improved method of generating a radiographic image of the object under inspection, using this known distance to generate an intensity-corrected image at a given equivalent distance. The corrected image is then used to map an effective atomic number of all materials in the radiographic image. Additionally, this distance data is also used to provide an accurate geometric correction in the image to produce a true likeness of the shape of the object under inspection. In another aspect of the improved method of generating a radiographic image of the object under inspection, adaptive region based averaging is applied (such as by using a statistical filter and/or median filter). This results in an image which has equivalent statistical properties useful in determining an accurate effective atomic number for all regions in the object under investigation. Optionally, the knowledge of effective atomic numbers and their ranges or variations is used to colour code the radiographic image. In another embodiment, the present specification describes a method for measuring individual X-ray energies as they interact within at least one detector in order to form an analysis of the spectral content of the scattered X-ray beam. In another embodiment, the backscatter X-ray scanning system additionally uses a multi-element scatter collimator to allow use of fan-beam X-ray irradiation to generate the backscatter image. Therefore, scattered X-rays which lie within an acceptance angle of, for example, the collimator element are detected and associated to the appropriate corresponding part of the generated radiographic X-ray image. Apart from the X-ray scanner/sensor, the plurality of multi-modality surveillance sensors comprise any or all combinations of components such as GPS receivers, scanning lasers, CCTV cameras, infra-red cameras, audio microphones, directional RF antennas, wide-band antennas, chemical sensors, jamming devices. In accordance with another embodiment, the present specification describes an automated detection processor for integrating and analysing all surveillance information from the plurality of sensors, in real-time, to highlight threat items for review by an operator seated inside the covert vehicle and/or remotely through a secured wireless network. The present specification discloses multiple embodiments. The following disclosure is provided in order to enable a person having ordinary skill in the art to practice the invention. Language used in this specification should not be interpreted as a general disavowal of any one specific embodiment or used to limit the claims beyond the meaning of the terms used therein. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention. FIG. 1A shows a covert mobile inspection system 100 in accordance with an embodiment of the present invention. The system 100 comprises a relatively small vehicle 102, such as a van, which is equipped with a plurality of detection and prevention sensors 104 such as scanning, listening and broadcasting devices. In an embodiment, the vehicle is a 3.5 ton chassis having a height less then 3 m above road level, length ranging from 4 m to 6 m and width ranging from 2.2 m to 2.5 m. In other embodiments, the vehicle may comprise small vans having a weight ranging from 1.5 T to 3.5 T. One aspect of the embodiments disclosed herein is the use of surveillance data from these multi-modality sensors in correlation and/or aggregation with data from an on-board X-ray scanning sensor. In one embodiment of the present invention, the X-ray scanning system on-board the surveillance vehicle of FIG. 1A also comprises a sensor in order to measure its distance to the scattering object, material or point. In one embodiment, the X-ray sensor generates a backscatter radiographic image of an object from a single side utilizing Compton scattering. This allows the vehicle 105 to collect scan data, in a covert fashion, at a low dose to allow scanning of individuals, small as well as large vehicles/cargo for detection of threat devices, materials and individuals. In another embodiment, the X-ray scanning system allows for scanning of several sides of a vehicle under inspection. For example, U.S. patent application Ser. No. 12/834,890 and Patent Cooperation Treaty (PCT) Application Number US10/41757 both entitled “Four-Sided Imaging”, and filed on Jul. 12, 2010 by the Applicant of the present specification, both herein incorporated by reference in their entirety, describe “[a] scanning system for the inspection of cargo, comprising: a portal defining an inspection area, said portal comprising a first vertical side, a second vertical side, a top horizontal side, and a horizontal base defined by a ramp adapted to be driven over by a vehicle; a first X-ray source disposed on at least one of the first vertical side, second vertical side or top horizontal side for generating an X-ray beam into the inspection area toward the vehicle; a first set of transmission detectors disposed within the portal for receiving the X-rays transmitted through the vehicle; a second X-ray source disposed within the ramp of said portal for generating an X-ray beam towards the underside of the vehicle; and a second set of detectors disposed within the ramp of said portal for receiving X-rays that are backscattered from the vehicle. FIG. 1B is a schematic representation of one embodiment of the four-sided X-ray imaging system 100B disclosed in U.S. patent application Ser. No. 12/834,890 and Patent Cooperation Treaty (PCT) Application Number US10/41757. As shown in FIG. 1B, vehicle 105 drives over a ramp 110 and underneath an archway 115, which defines an inspection portal. Specifically, the portal is defined by a first (left) side, a second (right) side, a top side and a bottom platform, which is a portion of the ramp 110. In one embodiment, ramp 110 comprises a base, a first angled surface leading upward to a flat transition point defining the highest part of the ramp, which also functions as the bottom platform, and a second angled surface leading back down to the ground. The highest part of the ramp is typically between 50 and 150 mm in height. In one embodiment, archway 115 houses multiple X-ray transmission detectors 117 and at least one X-ray source 119, housed within an enclosure, shown as 220 in FIG. 2. While FIG. 1B depicts the X-ray source 119 as being on the left side of the portal, one of ordinary skill in the art would appreciate that it could be on the right side, with an appropriate reconfiguration of the detectors 117. Preferably, the enclosure housing the X-ray is physically attached to the exterior face of the first side and is approximately 1 meter tall. The position of the enclosure depends upon the size of the inspection portal. In one embodiment, the enclosure occupies 20% to 50% of the total height of the first side. In one embodiment, a slit or opening is provided on first side, through which X-rays are emitted. Slit or opening extends substantially up first side to approximately 100% of the height. In one embodiment, slit or opening is covered with a thin coating that is substantially transparent to an X-ray. In one embodiment, the thin coating is comprises of a material such as aluminium or plastic and further provides an environmental shield. In one embodiment, the enclosure and X-ray unit further comprise a first collimator close to the source of X-rays and a second collimator close to the exit, described in greater detail below. Where the X-ray source enclosure is so positioned, detectors 117 are positioned on the interior face of the second side and the interior face of top side and occupy the full height of second side and the full length of top side, proximate to second side. In another embodiment, the enclosure housing the X-ray is physically attached to the exterior face of the second side and is approximately 1 meter tall. The position of the enclosure depends upon the size of the inspection portal. In one embodiment, the enclosure occupies 20% to 50% of the total height of the first side. As described above with respect to first side, if the enclosure housing the X-ray is on second side, a slit or opening is similarly provided on second side. The detectors are also similarly positioned on the interior faces of top side and first side when the enclosure is on second side. In one embodiment, with a dual-view system, an enclosure housing an X-ray source can be provided on both the first side and second side. As shown in FIG. 2, the X-ray scanning system 200 comprises an X-ray source 205 collimated by a rotating disk with a small aperture which allows X-rays to scan in at least one pencil beam 206, and preferably a series of “moving” pencil beams, within a substantially vertical plane from the X-ray source 205 to the object 210. X-rays 207 scatter back from the object 210 under inspection and some of these reach at least one detector array 215 located adjacent to the X-ray source 205 but outside the plane described by the moving X-ray beam 206. The intensity of the backscatter signal 207 is representative of the product of distance to the object and atomic number of the object. Persons of ordinary skill in the art would appreciate that the signal size due to Compton scattering from objects varies as the inverse fourth power of distance between the X-ray source and the scattering object. It is also known to persons of ordinary skill in the art that low atomic number materials are less efficient at scattering X-rays than high atomic number materials while high atomic number materials are more efficient at absorbing X-rays of a given energy than low atomic number materials. Therefore, the net result is that more X-rays having a greater intensity are scattered from low atomic number materials than from high atomic number materials. However, this effect varies approximately linearly with atomic number while the X-ray signal varies as the inverse fourth power of distance from the source to the scattering object. This also implies that known Compton scatter based radiographic images are essentially binary in nature (scattering or not scattering) since the small but quantitative variation of the signal size due to variation in atomic number is lost in the gross variation in signal intensity caused due to varying distances from X-ray source to scattering points. To correct for distance, a sensor 220 is provided (adjacent to the X-ray source and detectors) which is capable of detecting the distance to each point at the surface of the object 210. In one embodiment, the sensor 220 is advantageously a scanning laser range finder in which a beam of infra-red light 221 is scattered from the surface of the object 210 and the time taken for the pulsed beam to return to the sensor 220 is indicative of the distance to the surface of the object 210. For example, U.S. patent application Ser. No. 12/959,356 and Patent Cooperation Treaty Application Number US10/58809, also by the Applicant of the present specification, entitled “Time of Flight Backscatter Imaging System” and filed on Dec. 22, 2010, both of which are herein incorporated by reference in their entirety, describes a method in which the time of flight of the X-ray beam to and from the surface of the object under inspection is used to determine the distance between the source and scattering object. One of ordinary skill in the art would note that the distances between the surface of the object and the planar detector arrays are variable, since the object is not straight sided. Further, since the distance from the X-ray source to the object under inspection is not known in general, an assumption is generally made that the object is planar and at a fixed distance from the source. Thus, if the object is closer than assumed, then the object will appear smaller in the image and conversely, if the object is further away then it will appear to be larger. The result is an image which is representative of the object under inspection but not with correct geometry. This makes it difficult to identify the precise location of a threat or illicit object within the object under inspection. U.S. patent application Ser. No. 12/959,356 and Patent Cooperation Treaty Application Number US10/58809 address the above problem by integrating time of flight processing into conventional backscatter imaging. X-rays travel at a constant speed which is equal to the speed of light (3×108 m/s). An X-ray will therefore travel a distance of 1 m in 3.3 ns or equivalently, in 1 ns (10−9 s) an X-ray will travel 0.3 m. Thus, if the distance between a backscatter source and the object under inspection is on the order of 1 m, it corresponds to around 3 ns of transit time. Similarly, if the backscatter X-ray detector is also located around 1 m from the surface of the object, it corresponds to an additional 3 ns of transit time. Thus, the signal received at the detector should be received, in this example, 6 ns after the X-ray beam started its transit from the X-ray tube. In sum, the X-ray's transit time is directly related to the detectors' distance to or from the object. Such times, although quite short, can be measured using detection circuits known to those of ordinary skill in the art. The minimum distance is practically associated with the time resolution of the system. Objects can be proximate to the source, but one will not see much scattered signal since the scatter will generally be directed back to the X-ray source rather than to a detector. A practical lower limit, or the minimum distance between the plane of the system and the nearest part of the object to be inspected, is 100 mm. The further away the object is from the detector, the smaller the signal size and thus a practical upper limit for distance is of the order of 5 m. In the systems of the present application, as shown diagrammatically in FIGS. 2A and 2B, the distance between the X-ray source and the object under inspection is determined precisely by recording the time taken for an X-ray to leave the source and reach the detector. FIG. 2A depicts a representation, as a step function, of an X-ray source being switched rapidly from its beam-off condition to its beam-on condition. While 201 represents the step function at the source, 202 represents the detector's response. Thus, as can be seen from 201 and 202, after the beam is switched on from its off state at the source, the detector responds with a step-function like response after a time delay Δt 203. Referring to FIG. 2B, as the source 209 emits a pencil beam 211 of X-rays towards the object 212, some of the X-rays 213 transmit into the object 212, while some X-rays 214 backscatter towards the detectors 217. It may be noted that there are different path lengths from the X-ray interaction point (with the object) to the X-ray detector array. Therefore if a large detector is used, there will be a blurring to the start of the step pulse at the detector, where the leading edge of the start of the pulse will be due to signal from the part of the detector which is nearest to the interaction spot, and the trailing edge of the start of the pulse will be due to signal from parts of the detector which are further away from the interaction spot. A practical system can mitigate such temporal blurring effects by segmenting the detector such that each detector sees only a small blurring and the changes in response time each provide further enhancement in localisation of the precise interaction position, hence improving the determination of the surface profile of the object under inspection. The detector size (minimum and/or maximum) that would avoid such blurring effects described above is commensurate with the time resolution of the system. Thus, a system with 0.1 ns time resolution has detectors of the order of 50 mm in size. A system with 1 ns time resolution has detectors of the order of 500 mm in size. Of course, smaller detectors can be used to improve statistical accuracy in the time measurement, but at the expense of reduced numbers of X-ray photons in the intensity signal, so there is a trade-off in a practical system design which is generally constrained by the product of source brightness and scanning collimator diameter. Referring to FIG. 2, it should be appreciated that knowing the relative positions of the X-ray source 205 and the laser sensor 220 the equivalent distance between the X-ray beam 206 at any angle and the surface of the object 210 is mapped using a geometric look up table (for computational efficiency). This known distance is then used to apply an intensity correction to the measured X-ray scatter data to produce a radiographic image at a given equivalent distance of, say, 1 m. Thus, objects that are closer than 1 m will have their intensity reduced by a factor of 1/(1-distance)4 while objects farther away than 1 m will have their intensity increased by a factor of 1/(1-distance)4. The quantitatively corrected image so produced is then used to map an effective atomic number of all materials in the radiographic image, as shown in FIGS. 3A through 3C. As shown in FIG. 3A, radiographic image 305 represents an image of two objects obtained using an X-ray scanning system without intensity or effective atomic number scaling, the lower one 302 being close to the X-ray source and the upper one 304 being farther away from the source. The lower object 302 is shown to be bright while the upper image 304 is seen to be faint. Referring now to FIG. 3B, image 310 shows the result of scaling intensity for distance where the lower object 307 is now lighter than in image 305 while the upper object 308 is now brighter than the lower object 307. This suggests that the upper object 308 is of lower atomic number than the lower object 307. This is in contrast to the original image 305, wherein the relative atomic numbers are typically prone to misrepresentation. In accordance with another aspect of the present application, it is recognized that signal scattered due to objects farther from the X-ray source have poorer signal-to-noise ratio than signal from scattering objects closer to the source. This implies that the distance measurement can be further utilized to implement an adaptive region based averaging method whereby signal from regions far from the source are averaged over a larger region, such that the linear dimension of these regions is scaled as the square of the distance from source to object. This effect is shown in image 315 of FIG. 3C. In FIG. 3C, the upper object 313 has been averaged over larger regions than the lower object 312 thereby resulting in equivalent statistical properties useful in determining an accurate effective atomic number for all regions in the object under investigation. In a preferred embodiment, the adaptive region averaging method is implemented using a statistical filter to determine if a given pixel is likely to be a part of the main scattering object, or part of an adjacent object in which this value should not be used to compute the region average. In one embodiment, a suitable statistical filter lists all pixel values within a region (for example a 7×7 block), ranks them in order and then determines the mean value and standard deviation of the central range of values. Any pixel within the whole block whose intensity is more than 2 standard deviations from the mean value within that block is considered to be part of an adjacent object. A range of statistical filters can be developed which may use higher order statistical attributes, such as skewness, to refine the analysis. Alternate methods, such as median filtering, which can mitigate against boundary effects between image features are well known to persons of ordinary skill and all such methods can be suitably applied within the scope of the present invention. In accordance with yet another aspect described in the present specification, in one embodiment, the individual pixels in image 310 are colored according to the values in the quantitative image 315 scaled by effective atomic number. Here, the distance normalized pixels are colored on an individual basis (to ensure a sharp looking image) based on results from the region averaged image 315 with improved statistics. Alternative schemes can also be used for pixel coloring. For example, pixels with effective atomic number below 10 are colored orange (corresponding to organic materials such as explosives), pixels with effective atomic numbers between 10 and 20 are colored green (corresponding to low atomic number inorganic materials such as narcotics) while materials with effective atomic numbers greater than 20, such as steel, are colored blue. Still alternatively, a rainbow spectrum can be used in which pixel colored changes from red through yellow, green and blue as effective atomic number increases. Many other color tables can be selected depending on preference and application. In accordance with further aspect of the present specification, it is recognized that the beam from the X-ray source is diverging from a point which is generally located at least one meter from ground level. This implies that the raw image 305 is actually distorted—with regions at the centre of the image being unnaturally wide compared to regions at the top and bottom of the image which are unnaturally narrow. In conventional methods, a geometric correction is applied according to a cosine-like function which makes the assumption of a flat sided object at a fixed distance from the source. In contrast, in an embodiment of the present invention, the distance data from the scanning laser sensor 220 of FIG. 2 is used to provide an accurate geometric correction to produce a true likeness of the shape of the object under inspection. The present invention also lays focus on spectral composition of the X-ray beam that is incident on the object under inspection. Accordingly, in one embodiment it is advantageous to create the X-ray beam using an X-ray tube with cathode-anode potential difference in the range 160 kV to 320 kV with tube current in the range of 1 mA to 50 mA depending on allowable dose to the object under inspection and weight and power budget for the final system configuration. Regardless of tube voltage and current, a broad spectrum of X-ray energies is produced as shown in FIG. 4. Here, a broad Bremsstrahlung spectrum 405 is visible complimented by fluorescence peaks 410 at 60 keV with a typical tungsten anode tube. It should be noted that as a result of Compton scattering, the X-rays backscattered towards the detectors are generally of lower energy than those interacting in the object itself, and so the scattered beam has a lower mean energy than the incident beam. Further, the impact of the scattering object is to preferentially filter the X-ray beam—removing more and more of the lower energy components of the beam the higher the effective atomic number of the scattering object. This phenomenon is shown in FIG. 5 where a high atomic number (Z) material represents higher mean energy spectrum 505 while a lower atomic number (Z) material is represented by the relatively lower mean energy spectrum 510, thereby enabling discerning of low Z items from relatively high Z items. Referring back to FIG. 2, the detectors 215 measure the energy of the X-rays 207 that arrive at the detectors 215 after being scattered by the object 210. In one embodiment, each detector 215 comprises an inorganic scintillation detector such as NaI(Tl) or an organic scintillator such as polyvinyl toluene coupled directly to one or more light sensitive readout devices such as a photomultiplier tube or a photodiode. In an alternate embodiment, the detectors comprise semiconductor sensors such as semiconductors having a wide bandgap including, but not limited to, CdTe, CdZnTe or HgI which can operate at room temperature; or semiconductors having a narrow bandgap such as, but not limited to, HPGe which needs to be operated at low temperatures. Regardless of the detector configuration chosen, the objective is to measure individual X-ray energies as they interact in the detector in order to form an analysis of the spectral content of the scattered X-ray beam 207. Persons of ordinary skill in the art would appreciate that the data acquisition module (typically comprising detectors, photomultipliers/photodiodes and analog-to-digital converter circuitry and well known to persons skilled in the art) will be synchronized to the position of the primary X-ray beam 206 in order to collect one spectrum for each interacting X-ray source point. For example, the X-ray system 200 may be configured to collect 300 lines per second with 600 pixels per image line. In this case, the equivalent dwell time of the primary X-ray beam at each source point is 1/180000 sec=5.5 μs per point and the detectors need to be capable of recording several hundred X-rays during this time. To achieve the necessary count rates, one embodiment uses a small number of fast responding detectors (such as polyvinyl toluene plastic scintillators with photomultiplier readout) or a larger number of slow responding detectors (such as NaI scintillators with photomultiplier readout), depending upon factors such as cost and complexity. Given the acquisition of the X-ray spectrum at each sample point and the phenomena described with reference to FIGS. 4 and 5, it would be evident to those of ordinary skill in the art that the statistical properties of the X-ray spectrum can provide additional information on the effective atomic number of the scattering material at each primary beam interaction site. Using the known distance information, the area of the spectrum may be corrected to yield an improved quantitative result (as discussed earlier), while properties such as mean energy, peak energy and skewness of the spectrum provide the quantitative parameters that are required for accurate materials analysis. As an example, a scattering object far from the detector will produce a naturally faint signal, with the displayed brightness of this object being corrected through the use of known distance information, such as that provided by a scanning laser. Given that the signal for the region is formed from a limited number of scattered X-ray photons, the properties of the signal can be described using Gaussian statistics. Gain correction to account for distance from the source is applied in a linear fashion, and so the region still maintains its original statistical properties even though its mean value has been scaled to a larger value. As identified in FIG. 5, the spectral composition of the scattered beam is dependent on effective atomic number of the scattering material. FIG. 7 is a flowchart illustrating a method of obtaining an atomic number of each material contained in an object being scanned by the covert mobile inspection vehicle of the present invention. At step 702, a true extent of each region of the radiographic image is obtained by using a suitable statistical filter as described earlier. A true extent of a region enables determining a boundary of each constituent material. Thus, the true extent refers to the physical area over which the object extends. It is desirable to find the point at which one object finishes and at which the next object begins so that only pixels for the current object are used in quantitative imaging, without the effects of contamination from adjacent objects. At step 704, a mean energy of each detected signal is calculated along with a standard deviation and skewness of energies of pixels present in each region. At step 706, a product of the calculated standard deviation and a mean energy of the pixels energies of pixels present in each region is calculated. At step 708, the calculated product is compared with a pre-determined scale where a low value of the product corresponds to a low atomic number material and a high value of the product corresponds to a high atomic number material. In one embodiment, the present invention is directed towards a combination of active low-energy backscatter radiation (100-600 kV) detection and passive radiation (gamma rays and neutrons) detection for non-intrusive inspection of vehicles, trucks, containers, railcars, aircraft and other objects for nuclear, radiological and other contraband materials. It should be appreciated that the X-ray scatter data is generally at low energy and often below 100 keV in magnitude. In contrast, gamma-rays from radioactive sources, that may be present in the object under inspection, will typically be at much higher energy (for example Co-60 has gamma-rays at 1.1 and 1.3 MeV while Cs-137 emits gamma rays at 662 keV). As shown in FIG. 6, it is therefore possible to discriminate these high energy gamma rays, represented by spectrums 605 and 606, from the low energy scattered X-rays 610 thereby allowing simultaneous acquisition of active X-ray backscatter signals along with passive gamma-ray detection in accordance with an aspect of the present invention. In one embodiment, control electronics are employed to measure the resultant backscatter signal 610 having an upper threshold 611 set at or near the highest backscatter energy and to measure passive gamma rays 606, 605 above a threshold level 608 that is at or around the upper backscatter threshold 607. It should be noted that the low-energy backscatter spectrum is contaminated with the Compton background produced in the detector from incomplete energy deposition. In general, this background is very low compared to the backscatter signal. However, if needed, this background can be subtracted based on the signals measured at high energy. In one embodiment, the non-intrusive inspection system includes an inspection head having an x-ray source, a mechanism for producing a scanning pencil beam, a dual-purpose detector and associated electronics. The dual purpose detector can detect both backscatter x-rays and passive radiation. In one embodiment, the x-ray source of the present specification is constantly on, producing x-rays in a fan beam. In one embodiment, a spinning wheel having a plurality of “slits” or “pinholes” therein is employed to “block” the x-ray fan beam (and resultant pencil beam) from exiting, during which time passive radiation detection is active. In another embodiment, a beam chopping mechanism, such as a spin-roll chopper, is employed, wherein the beam chopping mechanism is designed to present a helical profile shutter (aperture), formed on a cylinder, for X-ray beam scanners. In this embodiment, the slits are configured in such a way that there is at least one gap where no pencil beam is produced and the beam is effectively turned “off”. In one embodiment, the present invention employs X-ray backscatter imaging, although one of ordinary skill in the art would appreciate that screening of the object may be performed using any available radiation imaging technique. For the purpose of inspection based on backscatter technology, in one embodiment the X-ray energy delivered by the source is optimized to be in the range of 150 kV to 600 kV. This range allows adequate penetration of the object under inspection. For better quality of imaging and to allow for shorter inspection times, the beam current is maximized, especially since the dose of radiation delivered to the object under inspection is less of a concern. In one embodiment, the beam scanning mechanism further comprises a beam chopper, and is designed to include shielding material as well. In one embodiment, the angle of the X-ray beam with respect to the normal to the front of the detector head is kept preferentially at about 10 degrees. This angle avoids the beam having to travel through the full length of an object which is commonly vertical, and provides some depth information to the screener. It should be appreciated that other ranges of energy levels may be used and other forms of radiation or energy can be used, including gamma, millimeter wave, radar or other energy sources. Any imaging system that has the potential for displaying object detail may be employed in the system and methods of the present invention. FIG. 8 is a cross-sectional view of an inspection head used in one embodiment of the present invention. In one embodiment, backscatter module 800 comprises X-ray source 801, a mechanism for producing a scanning pencil beam 802, and detectors 803. A front panel 804 of backscatter module 800 employs a scintillator material 805, which detects the backscattered X-rays resultant from a pencil beam of X-rays 806 that is scanned over the surface of the object (and in this example, aircraft) 807 being inspected. In one embodiment, detector 803 is a dual-purpose detector capable of detecting both backscatter x-rays and passive radiation. In a preferred embodiment, the x-ray and gamma-ray detectors are combined in the same module, and therefore, the same detector is employed for detecting both the backscatter x-rays and passive gamma rays. In another embodiment, the x-ray detector is different from the gamma-ray detector, especially in cases when the preferred gamma-ray detector has a response slower than few microseconds such that the detector is not appropriate for backscatter inspection. Gamma-ray detectors and neutron detectors are also employed for passive measurements along with x-ray inspection. The passive detector consists of at least one gamma-ray detector and an optional moderated 3He or other neutron detectors. In one embodiment of operation, the system scans the object employing the inspection module. The object, or part of the object, is then rescanned using a passive detector. U.S. patent application Ser. No. 12/976,861, also by the Applicant of the present invention, entitled “Composite Gamma Neutron Detection System” and filed on Dec. 22, 2010, describes a method for simultaneous detection of gamma-rays and neutrons with pulse shape discrimination to discriminate between the two effects. This method is also applicable to the current invention and is incorporated herein by reference. As described in U.S. patent application Ser. No. 12/976,861, several nuclei have a high cross-section for detection of thermal neutrons. These nuclei include He, Gd, Cd and two particularly high cross-section nuclei: Li-6 and B-10. In each case, after the interaction of a high cross-section nucleus with a thermal neutron, the result is an energetic ion and a secondary energetic charged particle. For example, the interaction of a neutron with a B-10 nucleus can be characterized by the following equation:n+B-10→Li-7+He-4 (945 barns, Q=4.79 MeV) Equation 1: Here, the cross section and the Q value, which is the energy released by the reaction, are shown in parenthesis. Similarly, the interaction of a neutron with a Li-6 nucleus is characterized by the following equation:n+Li-6→H-3+He-4 (3840 barn, Q=2.79 MeV) Equation 2: It is known that charged particles and heavy ions have a short range in condensed matter, generally travelling only a few microns from the point of interaction. Therefore, there is a high rate of energy deposition around the point of interaction. In the present invention, molecules containing nuclei with a high neutron cross section are mixed with molecules that provide a scintillation response when excited by the deposition of energy. Thus, neutron interaction with Li-6 or B-10, for example, results in the emission of a flash of light when intermixed with a scintillation material. If this light is transported via a medium to a photodetector, it is then possible to convert the optical signal to an electronic signal, where that electronic signal is representative of the amount of energy deposited during the neutron interaction. Further, materials such as Cd, Gd and other materials having a high thermal capture cross section with no emission of heavy particles produce low energy internal conversion electrons, Auger electrons, X-rays, and gamma rays ranging in energy from a few keV to several MeV emitted at substantially the same time. Therefore, a layer of these materials, either when mixed in a scintillator base or when manufactured in a scintillator, such as Gadolinium Oxysulfide (GOS) or Cadmium Tungstate (CWO) will produce light (probably less than heavier particles). GOS typically comes with two activators, resulting in slow (on the order of 1 ms) and fast (on the order of 5 μs) decays. CWO has a relatively fast decay constant. Depending on the overall energy, a significant portion of the energy will be deposited in the layer, while some of the electrons will deposit the energy in the surrounding scintillator. In addition, the copious X-rays and gamma rays produced following thermal capture will interact in the surrounding scintillator. Thus, neutron interactions will result in events with both slow and fast decay constants. In many cases, neutron signals will consist of a signal with both slow and fast components (referred to as “coincidence”) due to electron interlacing in the layer and gamma rays interacting in the surrounding scintillator. The scintillation response of the material that surrounds the Li-6 or B-10 nuclei can be tuned such that this light can be transported through a second scintillator, such as a plastic scintillator in one embodiment, with a characteristic which is selected to respond to gamma radiation only. In another embodiment, the material that surrounds the Li-6 or B-10 is not a scintillator, but a transparent non-scintillating plastic resulting in a detector that is only sensitive to neutrons. Thus, the plastic scintillator is both neutron and gamma sensitive. When a neutron is thermalized and subsequently captured by the H in the detector, a 2.22 MeV gamma ray is also emitted and often detected. In this manner, the invention disclosed in U.S. patent application Ser. No. 12/976,861 achieves a composite gamma-neutron detector capable of detecting neutrons as well as gamma radiation with high sensitivity. Further, the composite detector also provides an excellent separation of the gamma and neutron signatures. It should be noted herein that in addition to charged particles, B-10 produces gamma rays. Therefore, in using materials that produce gamma rays following neutron capture, the result may be a detection that looks like gamma rays. Most applications, however, want to detect neutrons; thus, the disclosed detector is advantageous in that it also detects the neutrons. FIG. 9 is a flowchart illustrating serial X-ray backscatter and passive gamma ray detection. Referring to FIG. 9, in the first step 901, the X-ray source is turned on and the beam chopping mechanism is started. In the next step 902, the system is moved to the location where scan is to be started. Thereafter, the backscatter passive inspection module is moved relative to the object for scanning, as shown in step 903. In the next step 904, the object is scanned and backscatter data is received. The X-ray source is then turned off, as shown in step 905. The area is then rescanned with passive detectors, as shown in step 906. After this, image generated from backscatter data and passive measurement results are displayed, as shown in step 907. The system then checks if the scan is complete, as shown in step 908. In cases where the scan is not complete, the system moves to the next scanning location, as shown in step 909. The X-ray source is then turned back on, as shown in step 910, and the scan process is repeated until complete. In another embodiment, the backscatter and passive detector works in an interleaved mode, in such a way that there is no need to rescan the object. In this mode, the backscatter measurement is performed when the beam of radiation impinges on the object. During the time the pencil-beam impinges unto the object, the X-ray system (via the inspection head) collects data to produce images. When the pencil beam is blocked and there is no radiation beam exiting from the beam chopping mechanism, the passive detectors are enabled to collect gamma-rays and neutrons. The main advantage of simultaneous inspection is the reduced logistic complexity and shorter scan time compared with performing X-ray and passive detection separately. FIG. 10 is a flowchart illustrating interleaved X-ray backscatter and passive gamma ray detection. Referring to FIG. 10, in the first step 1001, X-ray is turned on and the beam chopping mechanism is started. The beam chopping mechanism comprises, in one embodiment, a spinning wheel that can be rotated to periodically block the beam. In the next step 1002, the backscatter passive inspection module is moved relative to the object for scanning Next, neutron data is collected passively, as shown in step 1003. Thereafter, the system checks if X-rays are being emitted, in step 1004. Thus, if X-ray beam is being emitted, and is not blocked, the system collects backscatter data, as shown in step 1005. However, if the beam chopping mechanism is currently blocking the X-ray beam, the system collects data pertaining to passive gamma rays emitted from the object. This is shown in step 1006. In the end, image generated from backscatter data and passive measurement results are displayed, as shown in step 1007. The results of the passive detection measurements and the X-ray images are data fused to improve detection of nuclear and radioactive materials. For example, dark areas in the backscatter image may indicate the presence of partially shielded nuclear or radioactive materials. If higher levels of radiation occur in these dark areas, there is a stronger indication of the presence of these threat materials. In one embodiment, a spinning wheel having a plurality of pinholes therein is employed to produce a pencil beam of radiation through at least one pinhole, during which time backscatter radiation detection is active. In one embodiment, the spinning wheel effectively “blocks” the x-ray fan beam (and resultant pencil beam) from exiting, due to the position of the pinholes in the spinning wheel, during which time passive radiation detection is active. Thus, passive radiation measurement proceeds when the beam is “off” or blocked by the spinning wheel geometry, where there is no pinhole for the radiation to exit. FIG. 11 is an illustration of an embodiment of a spinning wheel as used in the system of the present invention, showing the pencil beam in an “on” position, wherein a backscatter measurement is taken. As shown in FIG. 11, spinning wheel 1100 comprises a disc fabricated from shielding material defining at least one pinhole 1105 through which a fan beam 1110 “exits” through the spinning wheel as pencil beam 1115. In one embodiment, spinning wheel 1100 comprises two pinholes 1105. The pencil beam radiation, and thus backscatter measurement capability, is “on” when the fan beam 1110 exits the spinning wheel as a pencil beam 1115. FIG. 12 is an illustration of one embodiment of a spinning wheel as used in the system of the present invention, showing the pencil beam in an “off” position, wherein a passive measurement is taken. As shown in FIG. 12, as spinning wheel 1200 is rotated, there are times when the fan beam 1210 does not coincide with at least one slit 1205. During this time, the fan beam 1210 is shielded by the spinning wheel 1200, and therefore, no radiation exits the system. It is during these times when the fan beam 1210 is “off” that a passive radiation measurement is taken. It should be noted herein that employing a spinning wheel having two pinholes is only exemplary and that the basic approach can use any number of pinholes in the spinning wheel geometry as long as a passive measurement is performed when the pencil beam is off. In another embodiment, a beam chopping mechanism is employed, wherein the beam chopping mechanism is designed to present a helical profile shutter (aperture), formed on a cylinder, for X-ray beam scanners. In one embodiment, a radiation shield is provided on a radiation source such that only a fan beam of radiation is produced from the source whereby the fan beam of radiation emits X-rays which then pass through the spin-roll chopper, which acts as an active shutter. Thus, when the spin-roll chopper and therefore, helical aperture(s) is rotating, there is only a small opening for the X-ray fan beam to pass through, which provides the moving flying spot beam. In this embodiment, the slits are configured in such a way that there is at least one gap where no pencil beam is produced. U.S. patent application Ser. No. 13/047,657, entitled “Beam Forming Apparatus” and assigned to the Applicant of the present invention, is herein incorporated by reference in its entirety. FIG. 13A illustrates an exemplary design for one embodiment of the spin-roll chopper, as used in various embodiments of the present invention. Beam chopper 1302 is, in one embodiment, fabricated in the form of a hollow cylinder having helical slits 1304 for “chopping” the X-ray fan beam. The cylindrical shape enables the beam chopper 1302 to rotate about the Z-axis and along with the helical apertures 1304, create a spin-roll motion, which provides effective scanning and therefore good image resolution, as described below, while at the same time keeping the chopper lightweight and having less moment of inertia as the spin-roll mass is proximate to the axis of rotation. Stated differently, the radius of the spin-roll chopper is small compared to spinning wheel or disc beam chopping mechanisms, and is advantageous in some cases. It should be noted that the helical twist angle 1325 represents the angle of motion of the helical aperture from the y-axis (center line) when the cylinder is spun about the z-axis a total of 90 degrees. Thus, an X-ray beam scanner employing the spin-roll chopper as in one embodiment of the present invention effectuates beam chopping by rotating the hollow cylinder 1302 machined with at least two helical slits 1304, enabling X-ray beam scanning with both constant and variable linear scan beam velocity and scan beam spot size. The spin-roll chopper enables both constant and variable linear scan beam velocity by manipulating the geometry of the helical apertures. In one embodiment, the velocity is varied or kept constant by manipulating the pitch and roll of the helical apertures along the length of the spin-roll chopper. Thus, it is possible to have a constant speed or to slow the scan down towards areas where more resolution is desired. The spin-roll chopper as described with respect to the present invention also enables variable and constant beam spot size by manipulating the geometry of the helical apertures, thus varying the resultant beam power. In one embodiment, the actual width of the aperture is manipulated to alter the beam spot size. In one embodiment, the width of the helical aperture varies along the length of the spin-roll chopper cylinder to compensate for the varying distance of the aperture from the center of the source and allow for uniform beam spot projection along the scan line. Thus, in one embodiment, the farther the aperture is away from the source, the narrower the width of the helical aperture to create a smaller beam spot size. In one embodiment, closer the aperture is to the source, wider the helical aperture to create a larger beam spot size. Helical slits 1304 are fabricated to ensure that the projection of the X-ray beam is not limited by dual collimation of the two slits. Dual collimation refers to the concept whereby the X-ray beam will pass through two helical slits at any given point in time. The resultant X-ray beam trajectory 1330 is also shown in FIG. 13A. In one embodiment, a pair of helices will produce one travelling beam. In another embodiment, additional pairs of helices may optionally be added to produce additional travelling or flying spot beams depending upon scanning requirements. In an embodiment of the present invention a plurality of viewing angles ranging from sixty degrees to ninety degrees can be obtained through the helical slits in the spin-roll chopper. FIG. 13B illustrates a beam chopping mechanism using the spin-roll chopper described with respect to FIG. 13A. Referring to FIG. 13B, the cylindrical spin-roll chopper 1352 is placed in front of a radiation source 1354, which, in one embodiment, comprises an X-ray tube. In one embodiment, rotation of the chopper 1352 is facilitated by including a suitable motor 1358, such as an electromagnetic motor. The speed or RPM of rotation of the spin-roll chopper system is dynamically controlled to optimize the scan velocity. In one embodiment, the spin-roll chopper system is capable of achieving speeds up to 80K RPM. In yet another embodiment, a scanning pencil beam is generated by any one of the approaches described above or any other approach as is known to those of ordinary skill in the art and deactivated by turning off the X-ray source (in contrast with previous embodiments, where the source is “blocked” by use of the spinning wheel or spin-roll chopper). Examples of suitable x-ray sources include, but are not limited to gridded sources, field emission electron sources (e.g. carbon nanotubes) or any other source that can switch the beam on-off within a few microseconds. However, it should be noted that if the wheel or spin-roll chopper is spinning slower, then the time between switching the X-ray source on and off can be longer. Therefore, it can be stated that the time it takes for the X-ray source to be switched on and off is relative to the rotational frequency of the spinning wheel, on the order of a fraction of the rotational time of the source, which is in the range of less than 1%. By way of example, if the rotational frequency if 2400 rpm (rotations per minute) and there are four pinholes, the time would be 6.25 ms ON and 6.25 ms OFF. If the spinning wheel is rotating at 240 rpm, then the times would be 62.5 ms ON and 62.5 ms OFF. Thus, the expression for the preferred time is as follows:Time [ms]=((60/frequency [rpm])/number of pinholes)×1000 Equation 3: FIG. 14 is a block diagram 1400 showing signal processing with two different sets of electronics when the backscatter x-ray detector and passive gamma-ray detector are the same. That is, the detector is dual-purpose, capable of detecting both backscattered X-rays and passive radiation. The backscatter system uses integrating electronics 1405, while the passive detector uses spectroscopic electronics 1410. Both set of electronics 1405, 1410 are gated with a gating signal 1415 from the spinning wheel control 1417. This produces a high signal when the system emits a pencil beam of radiation. The backscatter integrating electronics 1405 employs an AND gate 1420 to measure backscatter radiation only when the beam is on, as described above with respect to FIG. 3A. The passive detector 1425 uses a NAND gate 1430 to measure only gamma rays when the x-ray pencil beam is off, as described above with respect to FIG. 13B. The optional neutron detector (not shown) need not be gated and can measure neutrons at all times. The resultant backscatter image and results of the passive gamma-ray and neutron measurements are then shown on the screen (separately or combined). The inspection system refers to any backscatter and passive radiation detection system that can be deployed in a scanning vehicle, portal, gantry, trailer, mobile platform or other scanning configurations. The system is also designed such that it can be moved relative to the object or such that the object can be moved relative to the system. Reference will now be made to a specific embodiment of an aircraft inspection system that employs the active and passive radiation techniques as described in the present specification. It should be noted herein that such embodiment is exemplary only and that any system can be designed such that it takes advantage of the methods described above. U.S. patent application Ser. No. 12/916,371, entitled “Mobile Aircraft Inspection System” and filed on Oct. 29, 2010, is herein incorporated by reference in its entirety. FIG. 15 illustrates the overall system design of one embodiment of the present invention. Referring to FIG. 15, aircraft inspection system 1500, in one embodiment, comprises inspection head 1501, vehicle or transport cart 1502, and manipulator arm 1503. In one embodiment, inspection head 1501 comprises an inspection module, further comprising an X-ray source, a beam scanning mechanism and X-ray detectors. The inspection module is described in greater detail above with respect to FIG. 8. In one embodiment, vehicle or transport cart 1502 is any standard vehicle suitable for movement about an aircraft 1505. In one embodiment, vehicle 1502 is movably connected to first, proximal end 1609a of manipulator arm 1503 and inspection head 1501 is movably connected to second, distal end 1509b of manipulator arm 1503 via a customized attachment 1504. Manipulator arm 1503 is described in greater detail below. In one embodiment, customized attachment 1504 is designed for use with the system of the present invention. In another embodiment, customized attachment 1504 may be available as an off-shelf component, as long as it achieves the objectives of the present invention, as described below. In one embodiment, the inspection head 1501 is mounted on manipulator arm 1503 in such a manner that it allows for scanning of a variety of aircraft sizes, shapes and configurations. The manipulator arm 1503 is also capable of rotating and moving the inspection head 1501 in all directions. In one embodiment, customized attachment 1504 is movably attached to manipulator arm 1503 at a first joint 1504a and movably attached to inspection head 1501 at a second joint 1504b. Thus customized attachment 1504 allows for the inspection head 1501 to be moved and rotated about first joint 1504a and second joint 1504b. In one embodiment, first joint 1504a and/or second joint 1504b is a ball and socket type joint that allows for at least one movement, such as but not limited to tilt, swivel and/or rotation at the joint, and in one embodiment, full motion. The ability to move and rotate the source at both the first attachment joint 1504a and at the second attachment joint 1504b allow for the system to follow the contour of the aircraft and thus, adjust to its shape using several degrees of movement freedom. In addition, manipulator arm 1503 has multiple articulation or pivot joints 1507 that allow for complex motions. In one embodiment, in order to avoid damage to the aircraft 1505 being inspected, the inspection head 1501 includes at least one proximity sensor 1506. In one embodiment, the sensors are redundant, so if one fails to operate, another sensor will still alert when the system is too close to the aircraft. The at least one proximity sensor 1506 is configured to avoid collision and keep the inspection head 1501 at a safe distance from the aircraft 1505. Therefore, once the at least one proximity sensor 1506 is triggered, the inspection system 1500 will cease operation. When inspection system 1500 ceases operation, the scanning head is refracted and the system cannot be operated until the sensor alarm is cleared. In one embodiment, the at least one proximity sensor 1506 is connected and controlled via hardware. In one embodiment, manipulator arm 1503 includes at least one proximity sensor. In one embodiment, vehicle 1502 also includes at least one proximity sensor. To select appropriate design specifications for the vehicle and the manipulator arm, the critical areas of focus are: a) the distance from the source/detector to the aircraft, b) the controlled motion of the source/detector, and c) collision avoidance for both the vehicle and the manipulator with the aircraft. In one embodiment, an optimal distance from the source/detector arrangement to the aircraft rages from ½ meter up to two meters. In one embodiment, the distance is chosen to provide optimal image resolution, inspection coverage and signal strength. The weight of the source/detector in conjunction with the maximum height and maximum reach that the manipulator arm must obtain further determines the dimensions of the vehicle platform. It should be understood by those of ordinary skill in the art that the weight of the source is largely dependent on source type, and that source type is chosen based on the object under inspection and scanning requirements. Scanning sequence, motion speed, and tolerances for position and vibration also direct the specifications for the manipulator arm and/or any special attachments or tooling. As mentioned earlier, in order to minimize development time and costs in one embodiment, any suitable off-the-shelf vehicle and/or manipulator arm may be employed and modified as per the design requirements of the present invention. In one embodiment, the height and reach of the manipulator arm and weight and/or dimensions of the inspection head are a function of the size of the airplane or large cargo containing entity being scanned. FIG. 16 illustrates an exemplary vehicle 1600 that is connected to a backscatter module (not shown), via manipulator arm 1601, for the aircraft inspection system of the present invention. In one embodiment, for example, the vehicle 1600 may be a wheeled excavator or a similar vehicle. FIG. 17 illustrates an exemplary manipulator arm 1700 that is used for mounting a backscatter module (not shown) for the aircraft inspection system of the present invention. In one embodiment, the manipulator arm 1700 comprises a multi-purpose hydraulic boom. The boom design allows for the flexibility of attaching the vehicle (not shown) to a first, proximal end 1709a while attaching standard or custom tools at its second, distal end 1709b. Second, distal end 1709b, in one embodiment, is modified to allow for attachment of a backscatter inspection module at joint 1703. In one embodiment, manipulator arm 1700 is operated using computer-controlled motion and has at least five degrees of freedom for positioning in all directions, including up-down, left-right, in/out and rotation. In one embodiment, the system further comprises a controller unit, which can be remote from the system or located within the vehicle, for communicating motion instructions to controllers located in the scanning head or gantry unit which, in turn, directs motors to move the scanning head and/or gantry unit in the requisite direction. One method of controlling motion of the vehicle and the manipulator arm using a computer involves referring to a database of airplane models, stored in a memory on the computing system. Each entry in the database corresponds to a plane contour. This database enables the motion-control program to generate a scan plan, which is used to control the motion of the arm and the head to scan the airplane according to the plan. Further, for some planes, it may not be possible to scan the entire plane from one vehicle position. Therefore, the motion control program analyzes the various positions required and the system scans the plane accordingly. In one embodiment, the arm is capable of full 360 degree rotation. The manipulator 1700 is linearly extensible and contractible, and the extension and contraction can be achieved with a complex motion of the various parts of the manipulator arm. The system scans the aircraft by moving the arm at a nearly constant distance from the surface of the aircraft. The manipulator arm 1700 is also equipped with the capability of source rotation at the joint 1703, as described above. The ability to rotate and move the source through several degrees of freedom at attachment joint 1703, allow for the system to follow the contour of the aircraft and thus, adjust to its shape. The manipulator arm of the present invention has multiple articulation or pivot points 1705 that allow for complex motions, including but not limited to extension and contraction. In one embodiment, the aircraft inspection system of the present invention is capable of producing high-resolution images that enable the operator to easily identify concealed threat and contraband items. In one embodiment, a database or threat library containing standard images of airplanes is employed to compare resultant scans of the aircraft under inspection with images collected from planes of the same model to determine anomalies. In one embodiment, depending on the size of the airplane, the images of parts of the planes are collected separately. These images can then be displayed separately, or they could be “stitched” together show a combined image. The aircraft inspection system of the present invention is capable of accurately detecting both organic materials, such as solid and liquid explosives, narcotics, ceramic weapons, as well as inorganic materials, such as metal. In one embodiment, the aircraft imaging system uses automated threat software to alert an operator to the presence of potential inorganic and organic threat items. In one embodiment, the system is capable of transmitting backscatter and photographic images to an operator or remote inspector wirelessly. The aircraft inspection system of the present invention is designed to be modular to enhance transportability and ease of assembly. In one embodiment, the individual modules—the vehicle, the manipulator arm, the scanning head, and optionally detector cart can be assembled on site and/or customized per application. In addition, in another embodiment, the system is ready to deploy and requires no assembly. The system is also designed to be rugged so that it can withstand harsh environments for outdoor deployments even in inclement conditions. In one embodiment, the power required to run the system is provided on-board allowing the system to operate anywhere on the airfield. In one embodiment, the aircraft inspection system of the present invention is scalable for inspecting any aircraft size from executive jets to Airbus 380. Thus, the size of the vehicle and arm can be scaled to the size of the aircraft. FIG. 18 shows another embodiment of the X-ray scanning system 1800 of the present invention that additionally uses a multi-element scatter collimator 1816 to allow use of fan-beam X-ray irradiation to generate the backscatter image. Here, the X-ray source 1805 emits a fan beam 1806 of radiation towards the object 1810. A segmented detector array 1815 is located behind a multi-element collimator 1816, one detector element per collimator section. The collimator 1816 is designed to permit X-rays to enter from a narrow angular range, typically less than +/−2 degrees to the perpendicular to the detector array 1815. X-rays 1807 scattering from various points in the object 810 which lie within the acceptance angle of, for example, the collimator element 1816 are detected and associated to the appropriate corresponding part of the generated radiographic X-ray image. Again, a sensor 1820 is provided to measure distance to the surface of the object 1810 in order to correct the X-ray backscatter signal and produce a quantitative image scaled by effective atomic number. U.S. patent application Ser. No. 12/993,831, also by Applicant of the present invention, entitled “High-Energy X-Ray Inspection System Using A Fan-Shaped Beam and Collimated Backscatter Detectors”, and filed on Nov. 19, 2010, discloses use of such a multi-element scatter collimator and is hereby incorporated by reference in its entirety. A system configuration according to an embodiment of the invention disclosed in U.S. patent application Ser. No. 12/993,831 is outlined in FIGS. 19 to 21. Here, an X-ray linear accelerator 20 is used to fire a collimated fan-beam of high energy (at least 900 keV) X-radiation through an object 22 under inspection and to a set of X-ray detectors 24 which can be used to form a high resolution transmission X-ray imaging of the item under inspection. The X-ray linear accelerator beam is pulsed, so that as the object under inspection moves through the beam, the set of one-dimensional projections can be acquired and subsequently stacked together to form a two-dimensional image. In this embodiment, an X-ray backscatter detector 26 is placed close to the edge of the inspection region on the same side as the X-ray linear accelerator 20 but offset to one side of the X-ray beam so that it does not attenuate the transmission X-ray beam itself. As shown in FIG. 10, it is advantageous to use two backscatter imaging detectors 26, one on either side of the primary beam. In some embodiments the backscatter detectors may be arranged differently. In some embodiments there may be only one backscatter detector. In other embodiments there may be more than two such detectors. In contrast to known backscatter imaging detectors which use the localisation of the incident X-ray beam to define the scattering region, the backscatter imaging detector described, is able to spatially correlate the intensity of backscattered X-ray signals with their point of origin regardless of the extended fan-beam shape of the X-ray beam. In the backscatter imaging detector 26, this spatial mapping is performed using a segmented collimator 28 in zone plate configuration as shown schematically in FIG. 21. Normally, a zone plate will comprise a series of sharply defined patterns whose impulse response function is well known in the plane of a two-dimensional imaging sensor that is located behind the sensor. In the present case, the energy of the X-ray beam to be detected is typically in the range 10 keV to 250 keV and so the edges of the zone plate pattern will not be sharp. For example, a zone plate fabricated using lead will require material of thickness typically 2 mm to 5 mm. Further, it is expensive to fabricate a high resolution two-dimensional imaging sensor of the size that is required in this application. However, it is noted that the radiation beam is well collimated in one direction (the width of the radiation fan beam) and therefore the imaging problem is reduced to a one-dimensional rather than a two-dimensional problem. Therefore a backscatter detector in the form of an effectively one dimensional imaging sensor 30 is provided behind the zone plate 28. To address this problem an elemental backscatter detector is used in this embodiment. As shown in FIG. 21, the detector 30 comprises a plurality of detector elements 32. FIG. 22 illustrates a detector element 32 suitable for use in this example. Here, the detector element 32 comprises a bar of scintillation material (about 100 mm long in this example) and is supplied with a photo-detector 34 at either end. The photo-detector 34 may advantageously be a semiconductor photodiode or a photomultiplier tube. X-ray photons that interact in the scintillation material emit light photons and these will travel to the two photo-detectors where they may be detected. It may be shown that the intensity of the light reaching each photo-detector is in proportion to the distance of the point of interaction from the face of the photo-detector. Therefore, by measuring the relative intensity at the two photo detectors, the point of interaction of the X-ray photon with the detector can be resolved. Referring back to FIG. 1A, the covert surveillance vehicle 105 is equipped with a plurality of other sensors 110, apart from the X-ray scanning system, in accordance with an aspect of the present invention. In one embodiment, the vehicle 105 is equipped with a GPS receiver the output of which is integrated with the on-board X-ray scanning system to provide the absolute location at which each scan line is conducted. Again, output from a scanning laser is reconstructed into a 2D image to provide a quantitative analysis of the scene around the vehicle. This 2D image is archived for subsequent analysis and review. The 2D laser scanner image may also be used to determine when the overall scan of a particular object should start and when the scan for that object is complete. Also, optical wavelength colour CCTV images are collected at the front and sides of the vehicle, ideally using pan-tilt-zoom capability, to allow clear review of all locations around the vehicle. In one embodiment, images from the CCTV cameras are analysed to read license plate and container codes and this data is also archived along with the X-ray, GPS and all other surveillance data. Similarly, infra-red cameras can also be used to monitor the scene around the vehicle to look for unexpectedly warm or cold personnel as indication of stress or presence of improvised explosive devices. This data is also archived along with X-ray and all other surveillance data. In one embodiment, audio microphones are also installed around the vehicle to listen for sounds that are being produced in the vicinity of the vehicle. Specialist microphones with pan-tilt capability are installed to listen to sounds from specific points at some distance from the vehicle, this direction being analysed from the CCTV and IR image data. Directional RF (Radio Frequency) antennas are installed in the skin of the vehicle to listen for the presence of electronic devices in the vicinity of the vehicle. This data is integrated with the rest of the surveillance data. Similarly, wide band antennas are installed with receiving devices that monitor communications channels that may be used by law enforcement, military and emergency services. Again, RF antennas are installed to monitor mobile phone communications including text messaging from the local region around the vehicle. In one embodiment, chemical sensors are also installed to monitor composition of the air around the vehicle to detect trace quantities of explosives, narcotics and other relevant compounds with this data being integrated with that generated by the imaging and other sensors. In accordance with another aspect of the present invention, an automated detection processor integrates and analyses all surveillance information from the plurality of sensors 110, in real-time, to highlight threat items for review by an operator seated inside the vehicle 105 and/or remotely through a secured wireless network. In one embodiment, data from the individual sensors is analysed for key signatures. For example, the X-ray data is analysed for detection of improvised explosive devices or for the presence of organic materials in unexpected places (such as the tyres of a car). CCTV data is analysed for license plates with cross-checking against a law enforcement database. Audio information is analysed for key words such as “bomb” or “drugs”, for unexpectedly fast or deliberate phrasing which may indicate stress, or for a non-native language in the presence of a native language background for example. Once a piece of information has been analysed to comprise a threat or risk, this is escalated up a decision tree and is then compared against automated risk analysis from other sensors. If correlated risks are detected, a significant threat alarm is raised for immediate action by a human operator. If no correlated risk is detected, a moderate threat alarm is raised for review by the operator. The result is a managed flow of information where all sensor surveillance information is analysed at all times, and only significant threat information is passed up the decision tree to reach the final level of an alert to a system operator. The detection processor, in one embodiment, is a microprocessor computer running relevant code programmed for managing information and decision flow based on correlation and aggregation of the plurality of surveillance information. Great Britain Provisional Patent Application Number 1001736.6, entitled “Image Driven Optimization”, and filed on Feb. 3, 2010, and Patent Cooperation Treaty (PCT) Application Number GB2011/050182 entitled “Scanning Systems”, and filed on Feb. 3, 2011 by the Applicant of the present specification, both herein incorporated by reference in their entirety disclose a scanner system comprising a radiation generator arranged to generate radiation to irradiate an object, and detection means arranged to detect the radiation after it has interacted with the object and generate a sequence of detector data sets. Referring to FIG. 23, a scanner system comprises an X-ray beam generation system which includes a shielded radiation source 10, a primary collimator set 12A and a secondary collimator set 12B, and a set of radiation detectors 14 configured into a folded L-shaped array 16, are disclosed. The primary collimator set 12 A acts to constrain the radiation emitted by the source 10 into a substantially fan-shaped beam 18. The beam 18 will typically have a fan angle in the range +/−20 degrees to +/−45 degrees with a width at the detector elements 14 in the range 0.5 mm to 50 mm. The second collimator set 12B is adjustably mounted and the position of the two second collimators 12B can be adjusted by means of actuators 20, under the control of a decision processor 22. The detectors 14 output detector signals indicative of the radiation intensity they detect and these form, after conversion and processing described in more detail below, basic image data that is input to the decision processor 22. The decision processor 22 is arranged to analyse the image data and to control the actuators 20 to control the position of the second collimator set 12B in response to the results of that analysis. The decision processor 22 is also connected to a control input of the radiation source 10 and arranged to generate and vary a control signal it provides to the control input to control the energy and timing of X-ray pulses generated by the radiation source 10. The decision processor 22 is also connected to a display 24 on which an image of the imaged object, generated from the image data, can be displayed. By way of example, the radiation source 10 may comprise a high energy linear accelerator with a suitable target material (such as tungsten) which produces a broad X-ray spectrum with a typical beam quality in the range from 0.8 MV to 15 MV from a relatively small focal spot typically in the range 1 mm to 10 mm diameter. The radiation source 10 in this case would be pulsed with a pulse repetition frequency generally in the range 5 Hz to 1 kHz where the actual rate of pulsing is determined by the decision processor 22. The detectors 14 in this case are advantageously fabricated from a set of scintillation crystals (generally high density scintillator such as Csl, CdW04, ZnW04, LSO, GSO and similar are preferred) which are optically coupled to a suitable light detector, such as a photodiode or photomultiplier tube. Signals from these detectors 14 converted to digital values by a suitable electronic circuit (such as a current integrator or trans impedance amplifier with bandwidth filtering followed by an analogue to digital converter) and these digital values of the sampled intensity measurements are transferred to the decision processor 22 for analysis. The primary 12 A and secondary 12B collimators in this case are advantageously fabricated from high density materials such as lead and tungsten. A plurality of active devices are installed on the vehicle 105 to help mitigate against threats that may be present proximate to the covert inspection vehicle itself. For example, a jamming device can be installed to block mobile phone communication. This device may be turned on automatically in certain situations based on results from the automated decision processor. For example, should an improvised explosive device be detected in the vicinity of the vehicle the jamming device is turned on automatically to block spoken commands to a subversive or to prevent direct communication to the trigger of the explosive device. A jamming device can also be installed to block satellite communications required in order to prevent satellite phone communications that may result in subversive activity. In one embodiment the covert inspection vehicle 105 is operated by a single person with the primary responsibility for driving the vehicle. Surveillance data can be broadcast back to a central intelligence location in real time, as required, with download of the full archived surveillance data once the vehicle returns to its home location. The automated decision processor can action or trigger appropriate events, depending upon the decision steps programmed therein, without operator intervention to avoid the driver loosing focus on their primary task. In another embodiment, the covert inspection vehicle 105 is also provided with space for another security operative whose task is to monitor the surveillance data stream as it arrives from the plurality of sensors either in parallel with the automated decision processor or as a consequence of information from the automated decision processor. This operator is provided with two way secure wireless communication back to a central intelligence location in order to transact instructions and actions as required. The above examples are merely illustrative of the many applications of the system of present invention. Although only a few embodiments of the present invention have been described herein, it should be understood that the present invention might be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention may be modified within the scope of the appended claims. |
|
summary | ||
039986934 | abstract | A monitoring system for providing warning and/or trip signals indicative of the approach of the operating conditions of a nuclear steam supply system to a departure from nucleate boiling or coolant temperature saturation. The invention is characterized by calculation of the thermal limit locus in response to signals which accurately represent reactor cold leg temperature and core power; the core power signal being adjusted to compensate for the effects of both radial and axial peaking factor. |
050733346 | summary | BACKGROUND OF THE INVENTION The present invention relates to a self-actuated nuclear reactor shutdown system wherein a control rod suspended by a temperature sensitive electromagnet (TSEM) is automatically separated or detached from the TSEM and is inserted into a reactor core to effect an emergency shutdown of the reactor when the temperature of a coolant rises in an extraordinary manner. In the present invention, a temperature sensitive magnetic material (TSMM) is located in the wall of wrapper tubes adjacent to a control rod guide tube and constitutes a part of a magnetic circuit of the TSEM. Therefore, the response to the thermal transient can be improved and the stability in the actuation of the TSEM can also be expected. The reactor shutdown system of the present invention can be utilized for fast breeder reactors, light water reactors and the like. Nuclear reactors of various types are provided with some back-up control rods to be inserted into a reactor core when anything unusual occurs, in addition to control rods for power control, in order to enhance the reliability of the reactor shutdown. For a reactor shutdown system, it has been proposed that a TSEM in which a TSMM is provided as a part of the magnetic circuit thereof is installed inside the reactor core so as to implement the retention and separation of the control rod. As for the TSEM, a ferromagnetic material which has a suitable Curie point is employed to break the magnetic circuit by decreasing saturation flux density when the temperature of the TSEM is close to the Curie point. During a normal operation of the nuclear reactor, the control rod is suspended at the upper part of the control rod guide tube by the TSEM. When the temperature of the coolant flowing through a fuel assembly rises due to an extraordinary accident, the TSMM transforms from a ferromagnetic substance to a nonmagnetic one. Therefore, the magnetic circuit of the electromagnet is broken at the TSMM and the TSEM no longer exerts its holding force. Consequently, the control rod can be spontaneously unlatched from the TSEM and inserted into the reactor core and the reactor is shut down. It has been proposed in the prior art to provide some structure to introduce hot coolant from the fuel assembly to the TSEM such as, for example, a coolant introduction pipe, in order to prospectively obtain a quick response of the TSEM to thermal transient of the coolant. Such a prior art structure as described above, however, employs a complicated mechanism for introducing the coolant flowing through an adjacent fuel assembly into the control rod guide tube, and cannot provide high reliability. Besides, it is expected that a response time will be longer when the flow rate of the coolant decreases, because the flow rate of the coolant at a high temperature introduced into the control rod guide tube cannot be increased in comparison with the mass of the TSMM. Moreover, in the structure wherein the control rod guide tube is used as a part of the magnetic circuit, the vertical relative position between the electromagnet and the control rod guide tube must always be controlled with high precision, and this impairs the intrinsic feature of the self-actuated shutdown system which is to actuate without any external control. SUMMARY OF THE INVENTION An object of the present invention is to provide a self-actuated nuclear reactor shutdown system which improves the thermal transient response and reduces the influence of the flow of the coolant to thereby enhance the reliability of an actuation characteristic of the system. Another object of the present invention is to provide a self-actuated nuclear reactor shutdown system which dispenses with the control of the relative position between the electromagnet and the control rod guide tube and prevents the occurrence of a spurious actuation or a non-actuation of the control rod. The present invention provides an improvement in a self-actuated nuclear reactor shutdown system which comprises a control rod, a temperature sensitive electromagnet (TSEM) disposed above the control rod for causing the control rod to latch thereto and unlatch therefrom, and a control rod insertion portion around which a plurality of wrapper tubes each receiving a fuel assembly are arranged. According to the present invention, in order to accomplish the above-described objects, an upper part of a wall of each of the wrapper tubes arranged around the control rod insertion portion is made of a temperature sensitive magnetic material (TSMM) having a characteristic whereby the saturation flux density thereof will be reduced when there is an extraordinary rise in the temperature of a coolant flowing through the fuel assembly. The TSMM constitutes a part of a magnetic circuit of the electromagnet. It is also possible to accomplish the above-described objects by connecting an extension tube made of the TSMM to the upper end of the wrapper tube, so that the TSMM of the extension tube constitutes a part of the magnetic circuit of the electromagnet. The upper part of the wall of the wrapper tube or the extension tube made of the TSMM may have a length equal to the vertical stroke of the electromagnet. It is also possible that the TSMM is provided only in an area in which the electromagnet is set during a normal operation of a nuclear reactor and the part of the wall of the wrapper tube below the area is made of a ferromagnetic material extending over the range of the vertical stroke of the electromagnet. The electromagnet has an iron core and an armature capable of latching with an unlatching from the iron core, and a coil wound on the iron core. A nonmagnetic material is incorporated in a part of the iron core in the proximity of the TSMM. In the present invention, since the upper part of each wrapper tube arranged around the control rod insertion portion or the extension tube of the wrapper tube is made of the TSMM, the TSMM can be heated directly by the coolant at a high temperature coming out of the fuel assembly. Therefore, it is unnecessary to worry about uncertain factors such as the unstable flow of the coolant and the like, and extraordinary rise in the coolant temperature can be detected rapidly. The operation of the TSEM retaining the control rod is basically the same as that in the prior art. During normal operation of the reactor, the TSMM exhibits a ferromagnetic property, and the TSEM can support the control rod. In the case of an accident wherein the coolant temperature rises in an extraordinary manner in the reactor, the coolant at a high temperature coming out of the fuel assembly raises the temperature of the TSMM and therefore the saturation flux density of the material decreases. Consequently, the supporting force exerted by the TSEM is terminated. Therefore, the control rod is released and inserted into the core and thus the reactor is shut down. |
claims | 1. An assembly for mounting a fuel assembly in a nuclear reactor comprising:a fuel assembly including fuel rods within the fuel assembly, the fuel assembly including a lower tie plate with a fuel assembly mating fixture on a bottom portion of the fuel assembly; anda fuel support including a fuel support mating fixture, the fuel support mating fixture and the fuel assembly mating fixture shaped to fit into one another at only one, only two, or only three orientations of the fuel assembly relative to the fuel support,wherein the fuel assembly mating fixture forming a bottom portion of the fuel assembly is configured to align and mate with the fuel support mating fixture as the fuel assembly is vertically lowered into the fuel support. 2. The assembly of claim 1 wherein the fuel support is configured for elevating the fuel assembly unless the fuel assembly mating fixture is engaged with the fuel support mating fixture at the only one, only two, or only three orientations. 3. The assembly of claim 1 wherein the fuel assembly mating fixture is positioned about a radial from an axis defined by the fuel assembly at one of the only one, only two, or only three orientations of fuel assembly mating fixture relative to the fuel rods within the assembly. 4. The assembly of claim 3 wherein the fuel support mating fixture is configured from a portion of a body of the fuel support defining an aperture for receiving the lower tie plate. 5. The assembly of claim 1 wherein the fuel assembly mating fixture includes an outer shape of the lower tie plate providing the only one, only two, or only three orientations of the fuel assembly and to a lattice contained therein, and wherein the fuel support mating fixture includes an aperture with a corresponding shape defined by the fuel support for receiving the lower tie plate and maintaining the only one, only two, or only three orientations of the fuel assembly to the fuel support upon installation of the fuel assembly onto the fuel support. 6. The assembly of claim 5 wherein the outer shape of the lower tie plate and the corresponding shape of the aperture are selected from the group consisting of a triangle, a quadrilateral, a pentagon, a heptagon, and a star. 7. The assembly of claim 1 wherein the fuel assembly mating fixture includes a male member, and wherein the fuel support mating fixture includes a female member configured to receive and secure the male member to provide the only one, only two, or only three orientations. 8. The assembly of claim 7 wherein the female member includes a beveled cavity for guiding the lower tie plate into the cavity and appropriately mating the fuel assembly mating fixture with the fuel support mating fixture. 9. The assembly of claim 1 wherein the fuel support mating fixture includes a male member, and wherein the fuel assembly mating fixture includes a female member configured to receive and secure the male member to provide the only one, only two, or only three orientations. 10. The assembly of claim 1 wherein the fuel rods within the fuel assembly are arranged to have a predetermined pattern with the only one, only two, or only three orientations within the fuel assembly. |
|
abstract | An X-ray CT apparatus, as one example, includes at least one X-ray irradiation source configured to irradiate an X-ray to a volume of interest, at least one X-ray detector including a plurality of detection element segments configured to detect the X-ray penetrated through the volume of interest, at least one collimator configured to create an opening that is movable in at least one of a slice direction and a channel direction, at least one image processing part configured to extract a portion of the volume data, a controller configured to set the opening of the at least one collimator to a second opening size according to a cylinder-like second scanning range that is set to limit the volume of interest and configured to perform a second scan, and at least one reconstruction part configured to reconstruct image data based on data collected by the second scan. |
|
description | This application is a divisional application of U.S. patent application Ser. No. 10/821,658, filed Apr. 8, 2004, which claims priority to U.S. Provisional Patent Application No. 60/461,624 filed Apr. 8, 2003, the disclosures of which are hereby incorporated by reference herein. A part of this invention was made with United States Government support from Contract No. DE-AC03-76SF00098 between the U.S. Department of Energy (DOE) and the Lawrence Berkeley National Laboratory. The United States has certain rights in this invention. The present invention relates in general to the detection of special nuclear materials (“SNM”) in suspect containers. In particular, the present invention uses high-energy gamma rays emitted from fission products or fragments to identify SNM (i.e., 235U and 239Pu) in cargo containers and other potential sites. Special nuclear material (SNM) is defined by Title I of the Atomic Energy Act of 1954 as plutonium, uranium-233, or uranium enriched in the isotopes uranium-233 or uranium-235. The definition includes any other material which the Nuclear Regulatory Commission determines to be special nuclear material, but does not include source material. The Nuclear Regulatory Commission (“NRC”) has not declared any other material as SNM. SNM is only mildly radioactive, but it includes some fissile material, uranium-233, uranium-235, and plutonium-239, that, in concentrated form, can be the primary ingredients of nuclear explosives. These materials, in quantities greater than formula quantities, are defined as “strategic special nuclear material” (SSNM). The uranium-235 content of low-enriched uranium can be concentrated (i.e., enriched) to make highly enriched uranium, the primary ingredient of a nuclear weapon. Since Sep. 11, 2001, an increased urgency has been associated with the development of new and improved means for the detection and prevention of the clandestine transport of nuclear weapons materials and other materials for producing weapons of mass destruction. A particularly difficult problem is posed by highly-enriched uranium (e.g., 235U) and plutonium (e.g., 239Pu) that might be hidden in large sea-going cargo containers, which may be filled with masses approaching 27 MT and which might represent areal densities of more than 50 g cm−2 through which an identifying signal must penetrate to reach a detector. Passive detection methods (e.g., see “Passive Nondestructive Assay of Nuclear Materials,” edited by D. Reilly, N. Ensslin, and H. Smith, Jr., NUREG/CR-5550, LA-UR-90-732 (1991)) based on measurements of neutrons and/or photons are either inapplicable or impractical in many such cases. Traditional methods of radiography are unlikely to provide a unique signature of highly-enriched 235U and 239Pu. Active interrogation with neutrons or high-energy photons in a variety of forms (e.g., see “Ionizing Radiation Imaging Technologies for Homeland Security,” D. J. Strom and J. Callerame, Proceedings of the 36th Midyear Topical Meeting, Health Physics Society, Jan. 26-29, 2003, San Antonio, Tex., and “A Review of Neutron Based Non-Intrusive Inspection Technologies,” T. Gozani, Conference on Technology for Preventing Terrorism, Hoover Institution, Mar. 12-13, 2002, Stanford University, Stanford, Calif.) currently depends upon the observation of β-delayed neutrons following induced fission to provide a unique signature for 235U and 239Pu. However, the shielding provided by a thick hydrogenous cargo can be so large that this method will fail or will have very low detection sensitivity. In addition, considering that millions of cargo and other containers enter the United States each year, and considering that SNM might be hidden in some of these containers, in order to prevent the entry of any hidden SNM into the United States, a detection method needs to be effective without having to open and unload the containers. Furthermore, not only does a detection system need to be non-invasive, it must be able to perform its detection function in as short a time as possible, so as to not overly burden the flow of goods into the U.S. via these containers. There is therefore a need for a system and a method of detecting special nuclear materials (“SNM”) in suspect containers that does not suffer from the above described shortcomings. The present invention is directed to methods and systems that use either neutrons or high-energy photons (e.g., gamma-rays) to irradiate a fully loaded cargo or other container. Such neutrons or gamma-rays have a sufficient flux and energy level to induce fission in any SNM inside the container. After the neutron or photon irradiation is completed, a detector, or an array or arrays of detectors are used to interrogate the container for high energy (e.g., above 3 MeV) gamma rays that are produced by radioactive decays of fission products. In one embodiment, the present invention is directed to a method of detecting the presence of special nuclear materials in a suspect container. The method includes irradiating the suspect container with a beam of neutrons, so as to induce a thermal fission in a portion of the special nuclear materials; detecting the gamma rays that are emitted from the fission products formed by the thermal fission, to produce a detector signal; comparing the detector signal with a threshold value to form a comparison; and detecting the presence of the special nuclear materials using the comparison. In another embodiment, the present invention is directed to a system for detecting the presence of special nuclear materials in a suspect container. The system includes a neutron beam source configured for irradiating the suspect container with a beam of neutrons, so as to induce a thermal fission in a portion of the special nuclear materials; a detector configured for detecting the gamma rays that are emitted from the fission products formed by the thermal fission, to produce a detector signal; a comparator for comparing the detector signal with a threshold value to form a comparison; and a presence detector for detecting the presence of the special nuclear materials using the comparison. For a further understanding of the nature and advantages of the invention, reference should be made to the following description taken in conjunction with the accompanying drawings. The embodiments of the present invention are directed to methods and systems that use either neutrons or high-energy photons (e.g., gamma-rays) to irradiate a fully loaded cargo or other container. Such neutrons or gamma-rays have a sufficient flux and energy level to induce fission in any SNM inside the container. After the neutron or photon irradiation is completed, a detector, or an array or arrays of detectors are used to interrogate the container for high energy (e.g., above 3 MeV) gamma rays that are produced by radioactive decays of fission products. The inventors herein have shown that the yields of high-energy gamma rays following the thermal neutron-induced fission of 235U and 239Pu are large enough to permit the detection of kilogram-sized quantities of SNM hidden inside of cargo or other containers. The inventors herein have also shown that the energy spectrum of gamma rays emitted by fission products is qualitatively different from that produced by other material that would be commonly found in cargo or other containers. In addition, the inventors herein have determined the effective half-life of these gamma rays to be approximately 20 seconds. The energy spectrum and/or the time dependence (i.e., half-life) and/or the combination of the energy spectrum and the time dependence of the gamma-ray spectrum provides a unique signature for the SNM and its detection. The embodiments of the method and system of the present invention enable a fully loaded cargo container to be screened for SNM in a period on the order of one minute or less. Furthermore, the embodiments of the method and system of the present invention are easily scalable to enable the screening of smaller sized packages such as luggage items at airports for SNM in a period on the order of one minute or less. This ability of the embodiments of the present invention to detect the presence of SNM in suspect containers is quite remarkable considering that such containers come in an enormous range of sizes and loadings. For example, such containers are closed and randomly loaded where one is unaware whether the contents are apricots, bubblegum, bombs, fabrics, metals, plastics, steel, SNM, or wood. In particular, the embodiments of the present invention use the high-energy gamma rays emitted from short-lived fission fragments to identify SNM in cargo containers and other potential sites. As used herein high-energy gamma rays refer to gamma rays having an energy level higher than approximately 3-4 million electron volts (MeV). Also as used herein, short-lived fission fragments refer to fission fragments having a half that is less than approximately one minute. The active interrogation of a mass of highly enriched uranium (“HEU”), Pu, or SNM, embedded in a cargo container, with either 2.5 MeV deuterium-deuterium (“D-D”) neutrons or 14 MeV deuterium-tritium (“D-T”) neutrons, has been studied by some. A cargo container as used herein, refer to standard containers that are commonly made of steel that are typically available in the 20-foot or 40-foot lengths and which are approximately 8-foot wide by 8.5-foot high, that are used to transport goods on cargo ships. Some containers are larger and some are smaller. In those studies, a reasonable worst-case scenario assumes that the cargo container is otherwise filled with hydrogenous material at a water-equivalent density of about 0.4 gm cm−3. As an example of the effectiveness of the embodiments of the present invention, this worse-case scenario has been considered here with the further constraint that the SNM is located at the center of the container and that a distance of 1.5 m must be penetrated before radiations can reach a detector. It is known that some effort has been expended to investigate the possible use of delayed neutrons as the signal carrier for the presence of SNM. To demonstrate the advantages of the embodiments of the present invention, an evaluation of the relative merits of signals from delayed neutrons and the high-energy gamma rays from short-lived fission products is presented below. This evaluation shows the effectiveness of the embodiments of the present invention for the worst-case scenario, and clearly demonstrates that high-energy gamma rays from the decay of fission products offer a significant advantage in comparison to the signals from delayed neutrons. Delayed Neutrons The yields of delayed neutrons from thermal fission of 235U and 239Pu are about 0.017 and 0.0065 per fission, respectively. The half lives of the delayed neutron precursors lie in the range of about 0.1-56 s, and the ENDFB-IV nuclear data set energy spectra are shown in FIG. 1. The data on the yield of delayed neutrons shows that approximately half of the intensity has an energy less than 0.6 MeV and there are very few neutrons with energies above about 1.5 MeV. Because of thermalization and capture of the neutrons in hydrogen, there may be a very small probability for escape of delayed neutrons to an external detector. The results of calculations using nuclear engineering texts show that the root mean squared distance from birth of a 2 MeV neutron at the target until its absorption in hydrogen is about 15 cm in water at normal density, and thus the effective distance that must be traversed through normal water from the target to the detector is approximately 60 cm. The probability for escape of neutrons to a detector can be approximately estimated in two ways. Beyond about 40 cm from a point source of fission neutrons in water, the flux of neutrons with energies En>1 MeV is approximately G ( r ) = 0.12 ⅇ - 0.103 r w 4 π r 2 cm - 2 ( source particle ) - 1 , where rw is the distance penetrated in water at normal density. The quantity 4πr2 G(r), representing the probability of survival per source particle independent of the 1/r2 flux loss that will affect all radiations emitted from the source, is found to be about 2.5×10−4 (source particle)−1. Because the average thermal neutron will be captured in hydrogen within a few cm of where it is produced, this is a measure of the probability that any fission neutron will produce a thermal neutron that escapes to a detector. A second estimate is obtained from the Fermi-age approximation. This gives the spatial distribution of the neutron density of a given energy that has slowed down from some source energy as q ( r , τ ) = ⅇ - r 2 / 4 τ ( 4 π τ ) 3 / 2 cm - 3 ( source particle ) - 1 , where τ is the Fermi age in cm2. The approximate value of τ for thermal neutrons slowing down from a fission source is 31 cm2 in water. Estimating the velocity of a thermal neutron as 2200 m s−1, the quantity 4πr2 q(r,τ) v is about 2.0×10−6 (source particle)−1. Although both estimates are rather rough approximations, they clearly indicate a very low probability of a fission neutron producing a thermal neutron that can escape to a detector. Because of their smaller average energies, the attenuation of delayed neutrons is expected to be significantly larger than for fission neutrons and thus the probability that they can produce a thermal neutron that can escape to a detector is expected to be smaller yet. The conclusion is that the direct observation of delayed neutrons under the assumed limiting conditions will likely afford a very low sensitivity for detecting SNM. On the other hand, indirect observation of the delayed neutrons is possible via their capture by hydrogen (“H”) to produce 2.2 MeV gamma rays (or by capture by other nuclides in more realistic situations). The attenuation coefficient for 2 MeV gamma rays in water is about 0.049 cm−1. Neglecting the size of the target and the 1/r2 flux loss, the probability for escape of such photons to a detector uncollided would be about 0.053. So, in effect, the direct or indirect observation of delayed neutrons under the assumed limiting conditions will likely afford a very low sensitivity for detecting SNM. Considering that delayed neutrons afford a very low sensitivity for detecting SNM in cargo or other containers, the inventors herein have focused their efforts on the detection of gamma rays from short-lived fission products. The inventors herein have demonstrated that gamma rays from short-lived fission products escape to a detector with significantly higher probability than the delayed neutrons or the capture gamma rays that result from them. Delayed Gamma Rays from Short-Lived Fission Products It is known that approximately 90% of the total yield of fission products from thermal fission of 235U is contained in 32 mass chains located at A=88-103 and A=131-146. For thermal fission of 239Pu, the light-massed peak increases in mass number by about 8-10 but the heavy massed peak remains fixed. Because the charge distribution is so narrow (FWHM˜1.4 e), the majority of the chain yield will be found in one or two nuclides. A nuclide produced with Z=ZP, where ZP is the most probable atomic number for a given mass number, has a yield of about 0.5 of the chain yield. The values of ZP for 239Pu fission are 0.2-0.3 e greater than for 235U fission and thus essentially the same nuclides are considered for a fixed mass number in the two cases. For orientation purposes, only those nuclides with half lives less than a few minutes, and for which the probability for emission of a gamma ray with Eγ>4.0 MeV is at least 10−2 per decay, are directly considered. In Table 1 are the nuclides of interest and their relevant properties. TABLE 1Short-lived, high-yield fission products with probability > 0.01for emission of γ-rays with Eγ > 4.0 MeVHalf-235U239PuLifeEγ—Iγ—235U*239Pu*Iγ— f−1Iγ— f−1Nuclide(s)(keV)(%)CY (%)CY (%)(%)(%)Br-8655.11.60.48954074.60.0007360.00022555192.80.0004480.00013762110.580.00009282.84E−05Br-8755.62.030.69418140.0008120.00027646452.20.00044660.00015247841.80.00036540.000124496220.0004060.00013851950.530.000107593.66E−0552010.550.000111653.8E−0554740.380.000077142.62E−05Br-8816.31.780.5140221.510.000268787.7E−05414840.0007120.00020444951.20.00021366.12E−0545633.20.00056960.00016347221.760.000313288.98E−0549861.950.00034719.95E−0550201.510.000268787.7E−0551970.950.00016914.85E−0552120.640.000113923.26E−0552960.720.000128163.67E−0554560.640.000113923.26E−05Br-894.351.090.3540861.80.00019620.00006341663.80.00041420.00013343541.20.00013080.00004245020.880.000095923.08E−05Rb-901584.51.2841366.70.0030150.000858436680.00360.00102446462.250.00101250.00028851871.170.00052650.00015Rb-90m2581.240.74241931.140.000141368.46E−0544541.180.000146328.76E−05Rb-9158.45.582.140784.10.00228780.00086142651.40.00078120.000294Rb-924.54.821.9246382.20.00106040.00042248091.10.00053020.000211483610.0004820.00019249231.10.00053020.00021151882.50.0012050.0004852151.10.00053020.00021152491.10.00053020.00021155841.70.00081940.000326563220.0009640.00038457390.70.00033740.00013458790.70.00033740.00013459010.90.00043380.00017360040.590.000284380.00011360300.790.000380780.00015261150.80.00038560.000154Sr-9523.95.273.0140751.220.0006430.000367Y-980.551.921.5244508.90.001710.001353I-136m46.91.261.6545601.410.000177660.00023348892.20.00027720.00036350910.540.000068048.91E−0551871.040.000131040.00017252550.580.000073089.57E−05Totals31.014.30.031060.0122 The fifth and sixth columns of Table 1 provide cumulative yields of the nuclides, and the seventh and eight columns provide the absolute intensity of gamma rays per fission. As is shown above, eleven nuclides are listed in the table with half lives in the range 0.55-158 s. All but one have half lives in essentially the same range as the delayed neutrons. For most of the nuclides, the cumulative yield is significantly larger than the independent yield and that implies that an additional ten or so nuclides with comparable or shorter half lives might have significant probabilities for emission of high-energy gamma rays. The total of the cumulative yields of the eleven nuclides is approximately twice as large for fission of 235U as it is for 239Pu. The total probability per fission for observing a gamma ray with Eγ>4.0 MeV from decay of these nuclides is about 0.031 and 0.012, respectively, for the two fission systems. These are about a factor of two larger than the delayed neutron yields and represent conservative estimates. The attenuation coefficient for 4 MeV gamma rays in H2O is 0.034 cm−1, and thus 13% of such gamma rays would escape from the container (e.g., 1.5 m distance) uncollided as compared to about 5.3% for 2 MeV gamma rays. If the 2.2 MeV photons from neutron capture on hydrogen were used as a surrogates for delayed neutrons, the high-energy gamma rays from the fission products offer, conservatively, a factor of about 5 larger probability for escape to a detector. While the capture photons are monoenergetic, the fission product gamma rays vary considerably in energy. Unless one used a high-resolution instrument, such as a germanium (“Ge”) detector, one will not be able to resolve these lines but one would also be unlikely to distinguish the capture photons either. Thus, what one is looking for is an elevated continuum that lasts for a few minutes following the neutron burst. The use of gamma ray detection for discovering illicit SNM may be limited by both the natural background and by the decay of activation products, especially those with half lives on the order of seconds or minutes. The natural background is dominated by a gamma ray at 1.461 MeV (40K) and the highest energy line of high intensity is that at 2.614 MeV (208Tl). Apart from very weak lines resulting from neutron capture of the terrestrial neutron background and rare high-energy interactions, no gamma ray lines with energies exceeding 4 MeV are found. The characteristics of short-lived activation products with lifetimes comparable to the fission products listed in Table 1 are shown in Table 2. TABLE 2Neutron activation products with short half livesHalfAct.Eγ—LifeIγ—I— > 2.0Thresh%Prod.Reaction(MeV)(sec)(abs)MeV (abs)(MeV)abundC-1518O(n, a)5.32.40.635.290.2N-1616O(n, p)6.17.10.6710.2599.87.10.049Na-2626Mg(n, p)2.521.1.070 > 2.08.86112.54Al-3030Si(n, p)2.233.61.05 > 2.08.043.12.63.5K-4444Ca(n, p)2.151326>0.44.992.092.52(>2.0)3.66S-3736Ar(n, γ)3.13000.9400.3440Ar(n, a)2.5699.6 With the exception of the (n,γ) and (n,α) reactions on the Argon (Ar) isotopes, all of the other reactions have thresholds greater than about 5.0 MeV, and, if D-D neutrons are used as the interrogation source, these reactions will not take place. Ar comprises about 0.93% of air. The (n,α) excitation function on 40Ar shows a maximum of 0.02 b at an energy of about 8.7 MeV and drops to less than about 0.001 b at 5.0 MeV. Thus, with D-D neutrons, the source produced by this reaction is expected to be very weak. Therefore, in the zeroth order, the (n,γ) cross section on 36Ar may be neglected because of its low atomic abundance. If D-T neutrons are used, the production of these interfering nuclides will take place only in that volume where the neutrons have not been moderated enough to drop their energies below about 5 MeV. While attractive from the point of view of minimizing interference from activation products, the use of D-D neutrons comes with the handicap of a production cross section of about a factor of 100 less than that possible with D-T sources, a deficit that may be too large to incur. However, by using a partially moderated D-T source the fraction of incident neutrons that lies above 5 MeV is substantially reduced. As an example, it may be possible to surround the D-T source with Be of an optimum thickness determined by detailed Monte Carlo calculations. Therefore, the intensity enhancement from a D-T target may be maintained without undue production of neutron activation products. Regardless of which neutron source is chosen, the average neutron that can penetrate to the target will be thermal or very nearly so. In order to detect the presence of SNM using high-energy gammas emitted from fission products, the characteristic energy spectrum and time dependence of these high-energy gammas was measured. In order to do so, it was advantageous to have a switchable high-intensity source of neutrons of variable energy that can be used to irradiate targets of 235U and/or 239Pu. The 88″ Cyclotron at Lawrence Berkeley National Laboratory (“LBNL”) provides such a beam, measurement and shielding facility. At the 88″, neutrons were produced in large numbers by deuteron fragmentation. The 88″ provided deuteron beams up to 60 MeV with currents up to 10 μA. The neutrons were produced on average with half the deuteron energy and their angular distribution was forward peaked. In this manner, a large number of neutrons were directed onto a suitable moderator and then onto the target of interest. A target delivery and transfer system (e.g., rabbit system) was also used at the LBNL facility that enabled the irradiation of the target inside an existing cave and then the transfer of the target to a remote shielded counting station where Ge, sodium iodide (“NaI”), or plastic scintillator detectors were located. In addition, appropriate electronics and data acquisition systems necessary for such measurements, were used to make the measurements. Using the system described above, the feasibility of the methodology and system of the embodiments of the present invention was demonstrated by conducting the following exemplary experiment. A deuteron source (e.g., 1 μA of 16-MeV such as the LBNL's 88″ Cyclotron) was used to bombard a beryllium (“Be”) source to produce source of neutrons. The neutrons were then moderated (i.e., slowed down) using a combination of steel and polyethylene. Highly enriched 235U, depleted U, and 239Pu targets were irradiated with the neutrons and then transported to a shielded counting station using a pneumatic transfer system, as is known to those skilled in the art of nuclide detection. Gamma ray counting was performed with large germanium (“Ge”) scintillator detectors. Time-based data was acquired using an ORTEC NOMAD system running GAMMAVISION. Using this bombardment and detection setup, many gamma particles above 4 MeV were detected and decay curves as a function of energy were determined. These as well as other aspects of the embodiments of the present invention and how it is generalized for containers in general and cargo containers in particular are described below in further detail. The measurement methodology disclosed above describes a method that provides unequivocal signatures of 235U and 239Pu that provides high sensitivity in the presence of thick hydrogenous and other cargos. The system and method in accordance with the embodiments of the present invention is based in part on the relatively high intensity of γ rays with Eγ≧3.0 MeV that are emitted from short-lived fission fragments (e.g., see Chu, S. Y. F., Ekstrom, L. P., and Firestone, R. B., WWW Table of Radioactive Isotopes, http:ie.lbl.gov/toi (1999), and England, T. R. and Rider, B. F., ENDF-349, LA-UR-94-3106 (1994)). These β-delayed γ rays have yields in fission that are approximately an order of magnitude larger than the corresponding β-delayed neutron intensities from the thermal fission of 235U and 239Pu. They are likely to be transmitted through thick hydrogenous material with 102-103 times the probability likely for β-delayed neutrons. Their energies lie above interferences from normal environmental radioactivity. In addition, the energy spectra and time dependencies for emission of the β-delayed γ rays provide unique signatures for 235U and 239Pu. In order to capture the main properties of the high-energy delayed γ rays, the γ-ray spectra following thermal neutron induced fission of 235U and 239Pu was measured. Using the setup and facility described above, neutrons were produced by bombarding a 1-inch thick water-cooled Be target with 16-MeV deuterons from the Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. Neutrons were then moderated using a 15 cm cube of steel surrounded by up to 45 cm of polyethylene. The steel cube was located immediately downstream of the Be target. A pneumatic transfer system shuttled targets between an irradiation location inside the polyethylene and a remote shielded counting station with a transit time of 2-3 s. The thermal neutron flux at the irradiation site was approximately 1.5×106 cm−2 s−1. 235U (93% isotopic content), 239Pu (95% isotopic content) and, as representative of the characteristics of some cargo loadings, wood, polyethylene, aluminum, sandstone, and steel were irradiated. In each case, targets were repeatedly subjected to cycles of 30-s irradiations followed by 30-s counting periods, during which 10 sequential 3.0-s γ-ray spectra were acquired. Counting began 3 s after the end of irradiation. γ-rays were detected with an 80% relative efficiency coaxial high purity Ge (“HPGe”) detector and with a 30-cm×30-cm×10-cm plastic scintillator. Data were acquired and sorted using ORTEC PC-based electronics and software. FIG. 2 is a γ-ray spectra observed in the HPGe detector in 30 seconds of live time following the neutron irradiation of 0.568 grams of 239Pu and of 115 grams of steel. In order to display these two spectra on the same plot, offsets of 30 and 10 counts per channel were added to the data obtained from the 239Pu and steel targets, respectively. FIG. 2A (inset) is a graph of background-corrected decay curves for gamma rays in the energy intervals 3000-4000keV and 4000-8000 keV observed from the 239Pu target. Similar results were obtained from a 235U target. FIG. 2 shows γ-ray spectra for E≧1.0 MeV acquired with the HPGe detector from irradiation of 0.568 grams of 239Pu and 115 grams of steel. The temporal behavior of detected high-energy events is shown in the inset, FIG. 2A. Both the energy and temporal distributions of the high-energy γ rays from thermal fission of 235U are quite similar to those shown for 239Pu but their intensity per fission is about a factor of 3 larger. Also, results similar to those shown for steel were found from the irradiation of wood, polyethylene, aluminum and sandstone in the most important characteristic, i.e., no spectrum indicated the presence γ rays with energies exceeding 3.0 MeV. From the steel target, a small number of lower-energy γ rays produced by the decays of long-lived isotopes such as 56Mn (t1/2=2.58 hours) were observed. To the contrary, the spectrum from 239Pu is indicative of fairly intense γ-ray emission at E≧3.0 MeV that extends to at least 5.5-6.0 MeV. It is also clear, as expected, that the high-energy intensity is spread over a relatively large number of lines rather than concentrated in only a few. Thus, a simple and sensitive method to identify fissile material may integrate the total number of events in a wide energy interval, regardless of whether the events represent full- or partial-energy depositions. The results from this type of analysis for the energy intervals 3-4 MeV and 4-8 MeV are shown in FIG. 2A (inset). The integrated numbers of events from irradiated 235U and 239Pu showed decays with a short effective half-life of approximately 25 seconds, whereas those from all other materials tested showed much longer decay times. The two features—large numbers of γ rays with energies above 3.0 MeV and a short effective half-life—are unique signatures of 235U and 239Pu. Because of the high-density of γ-ray lines produced by the decay of fission fragments, a practical system for interrogating large objects does not necessarily require high-resolution detectors, such as the above HPGe detector. For example, the energy spectrum shown in FIG. 2 was generated using a high-resolution detector and thus various sharp energy counts are displayed. However, had a low-resolution detector been used, then the overall triangular shape of the spectrum of FIG. 2, without the sharp lines would have been produced. In fact, essentially the same results shown in FIG. 2 were obtained with the low-resolution plastic scintillator described above. This is particularly significant because such scintillators are sufficiently low in cost that allow one to form a large array of such devices surrounding a cargo container to provide a large solid angle for detecting photons. To demonstrate that a system and method as described above is easily scalable, even all the way up to a large container, and thus yields practical results in reasonable times, the response of an array of detectors following a 30-s irradiation of a cargo container with a source producing 1011 14 MeV neutrons s−1 is estimated as follows. As a worse-case scenario, in the full-scale system, the cargo is assumed to be wood with a 5-cm (diameter) sphere of 239Pu located at its center. An embodiment of such a full-scale system 300 is shown in FIG. 3. FIG. 3 shows neutron beam source 302 directing neutrons at a cargo container 304 that is suspected of containing SNM 306. Any beam generating system that is capable of providing such a flux may be used with the system of the present invention. For example, a compact linear accelerator, such as a LINAC and an appropriate target (e.g., Be) may be configured to provide the necessary flux. Preferably the beam emits neutrons isotropically so as to adequately scan the container. Alternately, the beam may be an anisotropic beam that is scanned across the container using a scanning system. The neutron beam may be a D-D or a D-T produced beam. The cargo container 304 is surrounded by an array of detectors 308 that are used to detect high-energy gammas that are emitted from fission products produced by the thermal fission of the SNM nuclei by the neutrons that have been moderated on their way to the SNM target 306. The detector or detectors, or array of detectors may be Ge or HPGe detectors or liquid or plastic scintillators, or other suitable gamma ray detectors. In one embodiment, the cargo container 304 is moved on a rail car in position relative to the beam source 302 and the detectors 308. The cargo is then irradiated for a time period (e.g., 30 sec.) and then after the irradiation, counting is conducted for another time period (e.g., 30 sec.). Alternately, the cargo container 304 is placed on a moving conveyor and it is irradiated and counted in a continually moving configuration. The counting period is not limited to a 30-second period, so long as the period is capable of adequately capturing gamma rays having a half-life on the order of 20 to 30 seconds. For a worse-case determination, the 1011 14 MeV neutrons s−1 beam is considered to be approximately 15 feet away from the container 304. With no attenuation, the neutron flux at a distance of approximately 15 feet will be approximately 3.84 neutrons/cm2-sec (e.g. 1/r2 attenuation). Based on a very conservative estimate that 90% of all neutrons are absorbed by other cargo, then the resulting flux at the SNM target will be approximately 3.83 neutrons/cm2-sec. Integrated over a 30-second irradiation window, the resulting neutron fluence is approximately 1.1×105 n/cm2. Referring to FIG. 4, and considering that a thermal neutron has an attenuation length in 235U or 239Pu of on the order of 1 mm, then the available target mass for a 5 cm diameter target is approximately 500 grams. Using conservative text book calculations, the resulting gamma yield of gamma particles above 3 MeV that are emitted in a 30 second window is approximately 1.0×105 gamma particles. Again using a very conservative estimate and estimating that approximately 10% of the high-energy gammas escape the container, then it is estimated that approximately 1000 high-energy gamma events are expected to be detected in a 30-second counting window following the thermal fission of 239Pu, and approximately 350 detected γ-ray events above 3 MeV for 235U. These very conservative scaling calculations show that with currently available technology, an entire cargo container may be scanned for 235U and 239Pu and other SNM in approximately less than one minute. Possible interferences from activities induced in other materials are few and can be negated substantially by appropriate choice of the interrogating source, as is known to those of skill in the detection of radio nuclides. Furthermore, the system in accordance with the embodiments of the present invention, when combined with a radiographic imaging system, is even more attractive for rapid identification of 235U and 239Pu and other fissile materials in a wide range of applications. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. For example, the source of neutrons may be any source including a D-D or a D-T source that gets moderated on its way to the SNM target to induce a thermal fission in a portion of the SNM. Or that the detectors and their signal processing software and devices may be any setup that is capable of obtaining a time-dependant energy spectrum for the high-energy gamma rays that have been emitted from the fission products of the thermal fission of a portion of the SNM. These other embodiments are intended to be included within the scope of the present invention, which is set forth in the following claims. |
|
description | This patent application is a continuation of U.S. patent application Ser. No. 11/749,540, filed May 16, 2007 now abandoned, which claims priority benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60/801,038, filed May 16, 2006, the contents of which are incorporated by reference herein in their entirety. The present invention relates to systems and methods for diagnostic analysis, and, more particularly, to systems and methods for the diagnosis of undesirable events and/or lack of desirable events representing product or process malfunctions. Products and processes, including machines, generally perform at least one of four functions related to energy. They can convert energy, transmit energy, contain energy or direct energy. Recognizing that energy can be either destructive or useful, there are generally five energy paths in and out of a specific energy function. These energy paths include: (i) the path of input energy used or purchased to achieve the energy function, (ii) the path of output energy for performing useful work, i.e., the work the machine was intended to perform, (iii) the path of waste energy, or energy loss, typically a function of the second law of thermodynamics, while attempting to perform the useful work, (iv) the path of any input signal energy used to direct other energy paths, and (v) the path of any external input energy from the environment. At times, a machine product or process may generate energy losses or leaks that manifest themselves in the form of vibrations, noise, fluid leaks, overheating or wear. For these energy leak problems, conventional diagnostic and measurement systems typically measure the waste energy itself by measuring the magnitude of vibrations or noise, the leak rate, the time to overheat or the amount of wear. For example, using a traditional approach for diagnosing the cause of a product or process malfunction, the presence of an undesirable event (or the lack of a desirable event), such as a fluid leak in a bolted flange and seal arrangement (FIG. 1), is detected and measured directly with respect to the magnitude of the leak in order to determine the feature or property of the particular component responsible for causing the event. As a result of using this direct measurement approach, two systems that do not leak would appear to have no difference with respect to their tendency to leak. Traditional approaches for determining the potential reliability of a product or process often expose a group of products or processes to a specific test environment and compare their performance to a requirement. This requirement is often in a “no failures allowed” format. The presence of an undesirable event, such as the fluid leak in the bolted flange and seal arrangement as described above, at any point during the test would be categorized as a failure. As a result, systems which do not experience a leak would appear to have no difference with respect to their tendency to leak and would therefore be thought of as reliable. Events can be catastrophic (e.g., something breaks) or they can be simple malfunctions. It is possible that a catastrophic failure at a component level can cause a malfunction at a system level. All events, whether catastrophic or malfunctions, are driven by four energy functions, and each of those four energy functions is in turn driven by individual features and/or properties of a product or process, or combinations thereof. Catastrophic events are traditionally difficult to measure because they have occurred in the past. Moreover, traditional methods, including those described above, often rely solely on an attribute measurement system for catastrophic failures (i.e., broken vs. not broken) providing little leverage to converge onto the root cause of the failure. Therefore, there is a long felt yet unmet need for systems and methods that use an energy function model to identify questions concerning a product or process malfunction, rapidly and easily answer those questions, and isolate the root cause of a malfunction event to a subset of the product or process represented by the energy function model. A series of the questions identified act as a progressive search to converge on the feature or property that can be changed or controlled to manage the energy responsible for the malfunction. These and other long-felt but previously unmet needs are addressed, at least in part, by various aspects of the present invention. In one of its primary aspects, the present invention provides systems and methods for identifying the cause of a product or process malfunction by measuring how the product or process is intended to perform in terms of the four basic energy functions and five energy paths. The systems and methods of the present invention convert malfunction events, which may otherwise be difficult to measure, into measurements of energy which are then used to contrast how the product or process is actually performing with how it is intended to perform. A variety of progressively convergent search methods can be applied to the contrast with the specific goal of identifying the key features or properties that control the critical energy functions corresponding to the malfunctions. Unlike the conventional approaches which only measure the magnitude of an energy leak itself, the systems and methods of the present invention may also measure input energy or useful work output energy to detect contrasts. One aspect of the present invention is an embodiment of a diagnostic method for determining a cause of an event in a product or process. In some embodiments of the present invention, the event comprises a malfunction event. The method provides a schematic of the product or process which can cover the narrowest scope known to contain the root cause of the event, or, if nothing is known, the entire product or process. The method also detects an energy function of the product or process according to how the product or process manages energy during operation. Generally, a product or process can direct energy, transmit energy convert energy or contain energy. With respect to the detected energy function, the method identifies a plurality of energy paths that may include an input energy path corresponding to the energy used or purchased to achieve the detected energy function, an output energy path corresponding to the performance of useful work, a waste energy path corresponding to energy loss, an input signal energy path and an environmental energy path. The method then selects, from the plurality of energy paths, an energy for measurement to detect a contrast between how the product or process is actually performing and how the product or process was intended to perform. The method may obtain these measurements through direct measurement of the selected energy or through indirect measurement of the selected energy via at least one of its component factors. Finally, the method conducts a progressive search on the contrast to identify a feature or property of the product or process responsible for causing the event. In different embodiments of this aspect of the present invention, the product or process may comprise prototype products or processes, or production products or processes. In the case of a prototype product or process, a feature or property identified by the method of the present invention may correspond to a design under consideration for which a contrast in the direct measurement of the malfunction event is not detected. In one embodiment of this aspect of the present invention, if no contrast is detected using the plurality of measurements for the first selected energy, a second energy may be selected for measurement from the plurality of energy paths. In yet another embodiment of this aspect of the present invention, the identified feature or property of the product or process may be changed or controlled to prevent the future occurrence of the event. In still another embodiment of this aspect of the present invention, the contrast between how the product or process is actually performing and how the product or process is intended to perform is detected by generating a plurality of energy measurements for a second product or process that is not experiencing a malfunction event. Another aspect of the present invention is an embodiment of a method for identifying evidence of deviation from a specification for a product or process. The method provides a schematic of the product or process which can cover the narrowest scope known to contain the root cause of the event, or, if nothing is known, the entire product or process. The method also detects an energy function of the product or process according to how the product or process manages energy during operation. With respect to the detected energy function, the method identifies a plurality of energy paths. The method then selects, from the plurality of energy paths, an energy for measurement to detect a contrast between how the product or process is actually performing and how the product or process was intended to perform. The method then generates the plurality of measurements for the selected energy. The method next compares the plurality of generated measurements to a respective target range of values and, based on the comparison, infers the existence of an alert condition for the deviation. Yet another aspect of the present invention is an embodiment of a method for ascertaining the reliability of a product or process. First, the method provides a plurality of samples of a given product or process and exposes those samples to an environmental stress. The method provides a schematic of the product or process which can cover the narrowest scope known to contain the root cause of the event, or, if nothing is known, the entire product or process. The method also detects an energy function of the product or process according to how the product or process manages energy during operation. With respect to the detected energy function, the method identifies a plurality of energy paths. The method then selects, from the plurality of energy paths, an energy for measurement to detect a contrast between how the product or process is actually performing and how the product or process was intended to perform. The method then generates the plurality of measurements for the selected energy. The method next compares the plurality of generated measurements of the plurality of exposed samples to identify a contrast and conducts a progressive search on the contrast to identify a feature or property of the plurality of samples that can be used to control the energy function that is not being achieved. The method also compares the plurality of generated measurements to a plurality of energy measurements of an unstressed product or process and, based on the comparison, infers the useable life of a similar unstressed product or process. Another aspect of the present invention is a method for diagnosing a cause of a malfunction event in a product or process. The method selects from a plurality of energy paths existing during operation of the product or process, a first energy for measurement to detect a contrast between how the product or process is actually performing and how the product or process is intended to perform. The method conducts a progressive search on the contrast to identify a feature or property of the product or process that can be sued to control an energy function that is malfunctioning. The identified feature or property can then be controlled or changed to prevent future malfunction events. Still another aspect of the present invention is a diagnostic computer system for determining a cause of an event in a product or process. The diagnostic computer system comprises a processor for detecting a first energy function of the product or process according to how the product or process manages energy during operation and for identifying, for the first energy function, a plurality of energy paths. The diagnostic computer system also comprises a user interface for accepting input from a user and for transmitting the input to the processor over a communications medium. The user selects from the plurality of energy paths, a first energy for measurement to detect a contrast between how the product or process is actually performing an how the product or process is intended to perform. The diagnostic computer system further comprises a sensor system operatively coupled to the processor for generating a plurality of measurements of the selected first energy, a storage device operatively coupled to the processor for storing the plurality of generated measurements, and a display for presenting a schematic of the product or process provided by the processor over the communications medium for viewing by the user. The display may also be configured to present graphic representations of the plurality of generated measurements. The user can operate the diagnostic computer system to conduct a progressive search on the contrast to identify a feature or property of the product or process responsible for causing the event. An additional aspect of the present invention is an embodiment of a computer-readable medium having stored thereon computer-executable program instructions for diagnosing a cause of an event in a product or process. When executed by a computer processor, the computer-executable program instructions cause the computer processor to perform several diagnostic steps. The method provides a schematic of the product or process which can cover the narrowest scope known to contain the root cause of the event, or, if nothing is known, the entire product or process. The method also detects an energy function of the product or process according to how the product or process manages energy during operation. With respect to the detected energy function, the method identifies a plurality of energy paths. The method then selects, from the plurality of energy paths, an energy for measurement to detect a contrast between how the product or process is actually performing and how the product or process was intended to perform. Finally, the method conducts a progressive search on the contrast to identify a feature or property of the product or process responsible for causing the event. A further aspect of the present invention is an embodiment of a computer system for training a user to diagnose and apply corrective action to a malfunctioning product or process. The computer system comprises a server with a processor for executing an interactive training program and a client computer coupled to the server via a communications medium. The training program comprises a plurality of downloadable training modules. When executed, the training program identifies a malfunction in a product or process, requires the user to diagnose a cause of the malfunction, and allows the user to download selected training modules. The downloadable training modules are downloaded from the server over the communications medium for access by the user at the client computer. At least one downloadable training module of the plurality of downloadable training modules trains the user to perform one of several tasks involved in diagnosing a cause of a malfunction in a product or process. The training program includes downloadable training modules that train users to (i) create a schematic of the product or process; (ii) label a plurality of functions performed by the product or process during operation of the product or process according to how the product or process manages energy; (iii) draw, for at least one function of the plurality of functions, a plurality of energy paths; (iv) connect at least two functions of the plurality of functions with respect to a “how” direction, an opposite “why” direction and a perpendicular “when” direction; (v) limit the scope of the schematic to at least one function known to contain a root cause of the event; (vi) select an energy path to measure to determine a contrast between how the product or process actually works and how the product or process is supposed to work; (vii) generate a plurality of measurements of the selected energy paths; (viii) select an alternative energy path for measurement if no contrast is detected; (ix) conduct a progressive search on the contrast to identify a property of the product or process that can be sued to control an energy function not being achieved; or (x) adjust the property to prevent the malfunction. Other embodiments, objects and advantages of the present invention will be apparent from the following description, the accompanying figures and the appended materials, which are incorporated herein by reference in their entirety. This description, including the figures and any material incorporated herein, describe embodiments that illustrate various aspects of the present invention. These embodiments are not intended to, and do not, limit the scope of the invention to particular details, but provide bases for supporting the claims to the invention. Methods described herein can be implemented using a computer system in an embodiment of the present invention. Furthermore, it may be useful to practice of the invention with the recited steps in a different order from the order provided in the listed methods. One aspect of the present invention relates to an embodiment of a method for use in a system for diagnosing the causes of product or process malfunctions. The diagnostic method can reveal potential risks of malfunction in a newly designed product or process. The methods and systems of the present invention use combinations of function models, which describe how a product is supposed to work, and energy accounting principles. The function models are drawn based on how the product or process is supposed to manage energy during operation. Generally, the function models include a box which represents the specific energy function the product or process is intended to perform, an arrow to the right of the box representing the input energy source, an arrow with text to the left of the box representing the useful work performed by the product or process, and an arrow below the box representing the energy losses, or leaks. FIG. 2A illustrates five possible energy paths for an energy function performed by a machine. These energy paths include: (i) the path of input energy used or purchased to achieve the energy function (E1) 201, (ii) the path of output energy for performing useful work, i.e., the work the machine was intended to perform (E2) 202, (iii) the path of waste energy, or energy loss, typically a function of the second law of thermodynamics, while attempting to perform the useful work (E3) 203, (iv) the path of any input signal energy used to direct other energy paths (E4) 204, and (v) the path of any external input energy from the environment (E5) 205. This method aids in the development of additional measurement systems, beyond the original which signaled the problem in the first place. These additional measurement systems are useful in applying a convergent strategy to narrow the search of potential causes of a malfunction, and in evaluating the malfunction risks of competing designs which do not demonstrate a difference with respect to direct measurement of the malfunction. Various embodiments of aspects of the present invention use function models to develop strategies for handling events such as malfunctions (e.g., energy leaks). FIG. 3 shows a flow chart of an embodiment of a diagnostic method for determining a cause of a product or process malfunction event, or other undesirable event, by characterizing how the product or process manages energy. Alternatively, the method may diagnose a cause of the lack of a desirable event. At step 301, a user creates, or otherwise provides, a schematic of the product or process. At step 302, the user labels or assigns each function performed in the operation of the product or process within the scope of the schematic according to how it manages energy. Each energy function includes one of directing energy, transmitting energy, converting energy or containing energy. For each of these energy management functions the user identifies, or labels, the appropriate energy paths at step 303. The energy paths may comprise (i) the path of the input energy used or purchased to achieve the energy function, (ii) the path of the output energy performing the useful work, (iii) the path of energy losses, (iv) the path of any input signal energy, or (v) the path of any input environmental energy. At step 304, the user connects, or associates, each energy function in relation to each other on the schematic. The connecting of energy functions will relate to a “how” direction (e.g., right), an opposing “why” direction (e.g., left) and a perpendicular “when” direction (e.g., up and down). If appropriate, at step 305 the user limits the schematic to the narrowest scope known to contain the root cause of the malfunction. If nothing is known, the schematic will contain the entire product or process. From the energy paths previously drawn, the user, at step 306, selects an energy for measurement for one of the identified energy functions to show how a product or process is actually performing in contrast to how that product or process was intended to perform. These measurements can be ranked by input energy, output energy, waste energy, signal energy or environmental energy. Alternatively, or additionally, the measurements can be ranked according to contrast criteria specific to the operation of the product or process. At step 307, the user generates a set of energy measurements either directly (i.e., Joules) or indirectly, through its component factors such as force through a distance. The energy measurements may be displayed on a display device such as, though not limited to, a computer monitor or a printer to aid the user in using the measurements to identify a contrast. The energy measurements may also be stored on a computer data storage device. At step 308, following the measurement based on the selected energy path, a user determines whether a contrast has been found. If no contrast is found, the user proceeds back to step 306 to select an alternative energy path for measurement. At step 310 the user conducts a progressive search on the contrast to identify a feature or property of specific components of the product or process that is responsible for the malfunction. Once identified, the user may, at step 311, correct and/or control the appropriate feature or property to prevent future malfunction and control the energy action not properly being achieved. In one embodiment of the present invention, the contrast between how a product or process is actually performing and how it is intended to perform is identified by making a similar set of energy measurements of a second product or process that is not malfunctioning (309), rather than identifying the contrast within various measurements of the malfunctioning product or process itself. In yet another embodiment of the present invention, the measurements are made on prototype products or processes, rather than production products or processes. In this embodiment, the features or properties identified refer to competing designs under consideration that do not show any difference in the direct measurement of the malfunction. FIG. 4 illustrates an example of a schematic for diagnosing the cause of a malfunction in a rotating pump using the methodology described above with respect to FIG. 3. Using the method outlined above, in the example of a fluid leak in a bolted flange and seal arrangement (FIG. 1), an energy function model of how the arrangement performs its intended function of containing fluid is provided (FIG. 2B). The energy paths of the input energy 211 (i.e., bolt torque through some angle of turn), output energy 212 (i.e., compression of a seal), and waste energy 213 (i.e., friction in the threads) are identified and quantified. The possible energy measurements are considered based on their ability to show a contrast between how the system is actually performing relative to how it is supposed to perform. In this example, the input energy is chosen to reveal this contrast. The input energy measurements can be represented graphically as shown in FIG. 5A, allowing for the calculation of spare energy stored in the compressed seal. The spare energy is represented as the area under the torque x displacement curve from the point at which the system stops leaking to the minimum torque limit, resulting in an estimate of the system's ability to resist the specific malfunction at hand, leakage. By measuring the input energy (i.e., torque and angle of turn), it is also possible to see the effects of the various components of the system, such as friction in the threads as the bolt is run down, compression of the seal and stretching of the bolt. This measurement can be used to contrast the variability between similar systems, none of which have actually leaked under the specified torque requirements. FIG. 5B shows the measurements of a poorly performing system. Using this now apparent contrast, a progressive search can be conducted to determine the feature or property which is the true cause of the variation of spare energy. Once identified, this feature can be changed or controlled to prevent similar products or processes from experiencing this malfunction. Neither of the two systems shown in FIGS. 5A and 5B experienced a leak at the required torque value, thus detection of a difference with conventional approaches (i.e., leak or no leak) would not have been possible. In another embodiment of an aspect of the present invention, a method for identifying evidence of deviation from a specification in a product or process, such as a manufacturing process, is provided. This deviation may give rise to an alert condition in the product or process. An alert condition can be any condition recognized for the product or process as one that may trigger an observation or other response from an entity with responsibility for at least some aspect of the process. An alert condition may be inferred, for example, if a deviation exceeds a defined threshold based on a preselected rule. The rule may vary depending upon the input energy required to achieve a specific function. For example, for a product with a bolted flange seal arrangement, the rule may say that the test limits of the input bolt torque and angle of turn required to turn off a fluid leak are below a certain energy threshold, thus assuring adequate spare energy to resist malfunctions once put into application. Products not meeting the minimum specification can be rejected, and attention can be given to determining the feature or property of the specific component responsible for the rejection using the process outlined below. FIG. 6 shows a flow chart of an embodiment of a method for identifying evidence of deviation from a specification for a product or process. At step 601 a user creates, or otherwise provides, a schematic of the product or process within the narrowest scope known to contain the root cause of the malfunction. If nothing is known, the schematic will contain the entire product or process. At step 602, the user labels or assigns each function in the operation of the product or process within the scope of the schematic according to how it manages energy. Each energy function includes one of directing energy, transmitting energy, converting energy or containing energy. For each of these energy functions the user identifies, or labels, at step 603, the appropriate energy paths. The energy paths may comprise (i) the path of the input energy used or purchased to achieve the energy function, (ii) the path of the output energy performing the useful work, (iii) the path of energy losses, (iv) the path of any input signal energy, or (v) the path of any input environmental energy. The user then connects, or associates, each energy function in relation to each other on the schematic. The connecting of energy functions will relate to a “how” direction (e.g., right), an opposing “why” direction (e.g., left) and a perpendicular “when” direction (e.g., up and down). From the energy paths previously drawn, the user selects, at step 604, an energy for measurement to show how a product or process is working in contrast to how that product or process is supposed to work. At step 605, the user generates a set of energy measurements either directly (i.e., Joules) or indirectly, through its component factors such as force through a distance. At step 606 the user compares each set of measurements to a respective target range of values and, at step 607, based on the comparison, infers the existence of evidence of an alert condition for the deviation. In an embodiment of this aspect of the present invention, a computer system may transmit a signal indicative of an alert condition for the deviation to notify the user that corrective action is needed. If an alert condition exists, the user can then take appropriate corrective action (608). Data relating to the existence of the alert condition may be stored on a computer data storage device or displayed on a display device including, though not limited to, a computer monitor or printer. FIG. 7 shows a flow chart of an embodiment of a method for ascertaining the reliability of products or processes exposed to an environmental stress. At step 701, a user creates, or otherwise provides, a set number of samples of a given product. At step 702, the user then exposes the sample products to the appropriate stresses and environments likely to be experienced during the products' intended applications, either through a series of tests or actual field use. At step 703, the user creates, or provides, a schematic of the product or process within the narrowest scope known to contain the root cause of the potential malfunction. If nothing is known, the schematic will contain the entire product or process. At step 704, the user labels or assigns each function in the operation of the product or process within the scope of the schematic according to how it manages energy. Each energy function includes one of directing energy, transmitting energy, converting energy or containing energy. For each of these energy functions the user identifies, or labels, at step 705, the appropriate energy paths. The energy paths may comprise (i) the path of the input energy used or purchased to achieve the energy function, (ii) the path of the output energy performing the useful work, (iii) the path of energy losses, (iv) the path of any input signal energy, or (v) the path of any input environmental energy. The user may then connect, or associate, each energy function in relation to each other on the schematic. The connecting of energy functions will relate to a “how” direction (e.g., right), an opposing “why” direction (e.g., left) and a perpendicular “when” direction (e.g., up and down). From the energy paths previously drawn, at step 706, the user selects an energy for measurement to show how a product or process is working in contrast to how that product or process is supposed to work. At step 707, the user generates a set of energy measurements either directly (i.e., Joules) or indirectly, through its component factors such as force through a distance. These measurements may be taken on prototype products or processes, or on production products or processes. At step 708, the user compares each set of measurements for all the exposed products tested to identify contrasts, or variations. At step 709, the user uses the measurements to conduct a progressive search on the contrasts to identify a feature or property of specific components of the product or process responsible for the malfunction. Once identified, the user may correct and/or control the appropriate feature or property to prevent future malfunction and may control the energy action not properly being achieved. At step 710, the user compares each set of measurements to energy measurements of an unstressed product or process and, at step 711, based on this comparison, infers the useable life of similar unstressed products or processes. Data relating to the inferred useable life of similar unstressed products or processes may be stored on a computer data storage device. This data may also be displayed on a display device including, though not limited to, a computer monitor or printer. Using the method outlined above, in the example of the fluid leak in the bolted flange and seal arrangement previously described (FIGS. 1 and 2B), the input energy 211 (i.e., bolt torque through some angle of turn), output energy 212 (i.e., compression of a seal), and waste energy 213 (i.e., friction in the threads) are identified and quantified. The measurements can be represented graphically as shown in FIG. 5A, allowing for the calculation of spare energy stored in the compressed seal and resulting in an estimate of the system's ability to resist the specific malfunction at hand, leakage. By measuring the input energy (i.e., torque and angle of turn), for example, it is also possible to detect the effects of the various components of the system, such as friction in the threads as the bolt is run down, compression of the seal and stretching of the bolt. This measurement can be used to contrast the variability between new and degraded systems (i.e., product at the start of the test and end of the test), none of which have actually leaked under the specified torque requirements. FIG. 5B shows the measurements of a poorly performing, degraded system. Using this now apparent contrast, a progressive search can be conducted to determine the feature or property which is the true cause of the variation. Once identified, this feature can be changed or controlled to prevent similar products or processes from experiencing this malfunction. Neither of the two systems shown in FIGS. 5A and 5B experienced a leak at the required torque value, thus detection of a difference with conventional approaches (i.e., leak or no leak) would not have been possible. Another aspect of the invention provides for systems and methods of training users to accomplish the methods described herein with respect to other embodiments of various aspects of the present invention. A training method presents portions of the diagnostic method with actual or theoretical examples of its use to groups of trainees in a conference room or classroom setting. Each trainee, either individually or in teams, is assigned a specific problem. The system then provides a qualified coach to guide the trainees through the solution of the problem. A written description of the diagnostic method as applied to the assigned problem is prepared which includes the detailed solution and the steps required to implement the solution by the trainee or trainee team to solve the problem. The qualified coach then reviews, in detail, the written description and interviews the trainee, either individually or as part of the team, to determine the depth of understanding of the diagnostic method. In one embodiment of this aspect of the present invention the training method is implemented in a computer system comprising a computer or computers coupled with a network wherein the trainee participates either interactively or through downloadable modules. In a preferred embodiment the computer system comprises a server with a processor for executing an interactive training program and a client computer coupled to the server via a communications medium. The training program comprises a plurality of downloadable training modules. When executed, the training program identifies a malfunction in a product or process, requires the user to diagnose a cause of the malfunction, and allows the user to download selected training modules. The downloadable training modules are downloaded from the server over the communications medium for access by the user at the client computer. At least one downloadable training module of the plurality of downloadable training modules trains the user to perform one of several tasks involved in diagnosing a cause of a malfunction in a product or process. The training program includes downloadable training modules that train users to (i) create a schematic of the product or process; (ii) label a plurality of functions performed by the product or process during operation of the product or process according to how the product or process manages energy; (iii) draw, for at least one function of the plurality of functions, a plurality of energy paths; (iv) connect at least two functions of the plurality of functions with respect to a “how” direction, an opposite “why” direction and a perpendicular “when” direction; (v) limit the scope of the schematic to at least one function known to contain a root cause of the event; (vi) select an energy path to measure to determine a contrast between how the product or process actually works and how the product or process is supposed to work; (vii) generate a plurality of measurements of the selected energy paths; (viii) select an alternative energy path for measurement if no contrast is detected; (ix) conduct a progressive search on the contrast to identify a property of the product or process that can be sued to control an energy function not being achieved; or (x) adjust the property to prevent the malfunction. In another embodiment of the present invention, a method for diagnosing a cause of a malfunction event in a product or process comprises conducting a progressive search on a contrast to identify a feature or property of the product or process that can be used to control an energy function not being achieved. The identified feature or property can then be corrected and/or controlled to prevent future malfunctions. The systems and methods of the present invention can be applied to catastrophic failures (i.e., something breaks or is permanently altered because of how energy was managed) as well as malfunction-type failures (i.e., the desired performance is not achieved). The systems and methods of the present invention can be applied at different scopes, from entire systems, to components that make up a system, to individual features or properties of a product or process. In various embodiments of the present invention, the energy measurements described herein are stored in a computer data storage device. In various embodiments of the present invention, methods described herein may also be performed by a computer with or without a user. FIG. 8 provides a schematic of a diagnostic computer system for determining a cause of an event in a product or process according to the methods of the present invention. The diagnostic computer system comprises a processor 801 on a server 800 for detecting a first energy function of the product 807 or process 808 according to how the product 807 or process 808 manages energy during operation and for identifying, for the first energy function, a plurality of energy paths. The diagnostic computer system also comprises a user interface 802 for accepting input from a user (e.g., a keyboard) and for transmitting the input to the processor 801 over a communications medium 803. The user selects from the plurality of energy paths, a first energy for measurement to detect a contrast between how the product 807 or process 808 is actually performing and how the product or process is intended to perform. The diagnostic computer system further comprises a sensor system 804 operatively coupled to the server 800 for generating a plurality of measurements of the selected first energy, a storage device 805 operatively coupled to the processor for storing the plurality of generated measurements, and a display 806 for presenting a schematic of the product or process provided by the processor over the communications medium for viewing by the user. The display 806 may also be configured to present graphic representations of the plurality of generated measurements. The user can operate the diagnostic computer system to conduct a progressive search on the contrast to identify a feature or property of the product 807 or process 808 responsible for causing the event. Systems according to the present invention, such as are shown in FIG. 8, may comprise any type of conventional computer system and operating system. The aspects of the present invention may be practiced using any suitable, conventionally available input, display and data storage devices and may also include an optional communications access device such as a modem, network interface card or port, or wireless transmitter for providing computer-to-computer communication capabilities. It may further involve a web server that would provide connectivity to a network such as an intranet, extranet, or the Internet, allowing for remote access to the software supporting the methods of the present invention. In such a case, a client device may run any suitable web browsing programs or other software that would permit a user to access the network. The system may also include additional software components that would allow a user to view data and information in a range of formats. The instruction set that is used to direct a system to perform functions according to the present invention may be present as software in memory or implemented as hardware or firmware. The instruction set may be written in any computer language or combination of languages selected by a service provider, coder or programmer. The instruction set may also be a macro or template in a spreadsheet, or a custom-designed and implemented application. A service provider may also choose to implement the invention as an applet within a web page. Other suitable approaches may be used. A service provider on a publicly-accessible site, location, or web page, or on a restricted-access site may host the invention. A user may, for example, access the software by running a web browser on a client device and entering a uniform resource locator (“URL”) corresponding to the web address of a server system, which may be running a web server which then allows access to the software application. While the invention has been shown and described with reference to particular embodiments, those skilled in the art will understand that various changes in form and details of the methods according to the present invention may be made without departing from the spirit and scope of the invention. All aspects of this invention that involve recording, transmitting, modifying, updating, manipulating, calculating, displaying and reporting information, and all other associated processing, can be performed on one or more computing devices that may be coupled by one or more networks, which may be the public internet, wide-area and/or local networks, public and/or private. Specific arrangements and embodiments described above provide examples of the principles covered by the appended claims and their equivalents, but also include many other embodiments and variations, as well as objects and advantages, that may not be explicitly described in this document but that would nevertheless, be appreciated by those skilled in the field of this invention. For example, but without limitation, structural or functional elements might be rearranged, or method steps reordered, consistent with the present invention. Similarly, processors or databases may comprise a single instance or a plurality of devices coupled by network, databus or other information path. Similarly, principles according to the present invention, and systems and methods that embody them, could be applied to other examples, which, even if not specifically described here in detail, would nevertheless be within the scope of the appended claims. |
|
summary | ||
description | In FIG. 1, reference 10 refers to a cylindrical metallic drum in which nuclear waste of very low radioactivity is placed beforehand. More precisely, these nuclear wastes are in the form of flat cakes 12, piled one on top of the other inside the drum 10. Each of these flat cakes 12 is constituted of a cylindrical metallic packaging filled with nuclear waste of very low activity, then compacted inside a press. As indicated above, the invention concerns a process and an installation making it possible to carry out a blocking operation, during which a blocking material 14 such as cement plaster is injected successively into each drum 10, to immobilise the flat cakes 12 there by filling as far as possible the free space inside the drum 10. According to the invention, the process and installation are designed in such a way that the blocking operation is carried out while avoiding any dispersion of the contaminated air initially contained in the drum 10 into the atmosphere of the processing workshop and in particular on the external wall of the drum. The installation according to the invention comprises an intermediary lid 16, which is mounted on the open upper end of the drum 10 as soon as the cakes have been placed in it. The intermediary lid 16 is then crimped. As shown more clearly in FIG. 2, the intermediary lid is fixed in a sealed fashion to the upper part of the drum 10. In order to do this, it can in particular be fitted into an annular sealing joint 18 which covers the curl 10a forming the upper end of the drum 10, and then crimped. The intermediary lid 16, made out of sheet metal, comprises at its centre a circular opening 20. The diameter of this opening is, for example, 164 mm in the case of a drum 10 of 570 mm diameter. The circular central opening 20 of the intermediary lid 16 is initially closed in a sealed fashion by a metallic cap 22, for example in aluminum, glued on the upper face or external to the intermediary lid 16. The metallic cap 22 is constituted of a temporary closing pellet for the drum. At its centre, on its lower surface turned towards the inside of the drum 10, it is provided with a ballast domino 24 constituting ballast means whose function will be made clear below. As a non-limiting example, the mass of the ballast domino 24 can be about 50 gm. On its lower face turned towards the interior of the drum 10, the intermediary lid 16 comprises at least one anti-float organ such as three lugs 26 soldered on the lid 16 and arranged at 120xc2x0 one after the other around a circle centered on the axis of the intermediary lid 16. As a non-limiting example, the circle around which the lugs 26 are arranged can have a diameter of 350 mm. The lugs 26 stick out downwards inside the drum 10, of a determined length, for example 45 mm. Thus they maintain a minimum free space of the same height between the intermediary lid 16 and the top of the pile of cakes 12 placed in the drum 10. This space favors later flow of the blocking material 14 when it is injected into the drum. The installation according to the invention also comprises a dynamic containment hood 28 (FIG. 1) under which is placed the upper part of the drum 10 closed by the intermediary lid 16, when the blocking operation is carried out. In the embodiment represented, the dynamic containment hood 28 is fixed. More precisely, it is fixed under a horizontal partition 30 equipping the processing workshop. The setting of the upper part of the drum 10 under the dynamic containment hood 28 is obtained by placing the drum 10 on the upper plate of a jack 32 comprising lifting means. When lifting of the drum 10 is completed, its upper end is received inside the dynamic containment hood 28, as illustrated in FIG. 1. In order to improve filling of the drum 10 by the blocking material 14 during the blocking operation, means 34 (FIG. 3) able to make the drum 10 vibrate are associated with the jack 32. In other terms, the latter is a vibrating jack. In FIG. 1, lines of dots and dashes represent diagrammatically an anti-fall system constituted of fingers 35 linked by arms 37 to the horizontal partition 30. When the drum 10 is in the upper position, the fingers 35 arrive under the upper plate of the jack and ensure that it is maintained in this position, even in the case of failure of the jack 32. As shown diagrammatically in FIG. 3, the drums 10 are moved one after the other above the jack 32 by a conveyor belt 36, to be submitted to the blocking operation. They are then moved on from this post by the same conveyor belt 36. According to the invention, the dynamic containment hood 28 supports in its centre the collar 39, terminated at its lower part by a toothed crown 38 (FIG. 1). This toothed crown 38 is placed along the axis of the opening 20 formed at the centre of the intermediary lid 16 and its diameter is slightly smaller than that of this opening. The toothed crown 38 is provided around the length of its boundary with pointed and long saw-teeth directed downwards. These saw-teeth ensure the perforation of the cap 22 at the end of the lifting of the drum 10 under the dynamic containment hood 28, just before the beginning of injection of the blocking material 14. Holes 37 are pierced all around the cylindrical support of the toothed crown 38, at such a level that they are below the intermediary lid 16, at the end of the piercing operation of the cap 22. These holes 37 avoid negative pressure application to the cap 22 after piercing and allow good air circulation. When perforation is carried out, the ballast domino 24 placed at the centre of the cap 22 drags downwards, by gravity, the disc cut out in the cap by the toothed crown 38. The ballast domino 24 ensures that the disc falls in the drum and thus prevents this disc remaining inside the toothed crown 38 and closing the piping opening inside the crown. It also avoids the risk of it floating on the surface of the blocking material 14. The installation according to the invention also comprises means 40, for injecting the blocking material 14 in the drum 10. These means of injection 40, which will be described in more detail below with reference to FIG. 3, comprise in particular an injection nozzle 42 which opens inside the toothed crown 38, as shown in FIG. 1. The injection nozzle 42 is oriented downwards and is preferably arranged along the axis of the toothed crown. When the cap 22 has been perforated by the toothed crown 38, the operation of the means of injection 40 makes it possible to inject blocking material 14 directly inside the drum 10 without rupture of the containment of the latter. The installation according to the invention also comprises means 44 of negative pressure application onto the drum 10 and the interior of the dynamic containment hood 28. These means for negative pressure application 44 comprise in particular one or several air suction tubes 46, which open inside the collar 39 carrying the toothed crown 38. The air suction tube or tubes 46 are linked to suction means 47 able to extract the contaminated air pushed out of the drum 10, while blocking material 14 is injected, still maintaining negative pressure in the drum and inside the dynamic containment hood 28, compared to the outside environment. As a non-limiting illustration, the depression produced by the negative pressure application means 44 is, for example, about 2660 Pa. The negative pressure application means 44 also comprise very high efficiency filters 49 able to retain the totality of the contaminated dusts contained in the air sucked out. Advantageously, the means of suction 47 are doubled, in order to avoid any loss of containment in the event of deterioration of the main suction system or a loss of electricity supply. Advantageously and as shown schematically in FIG. 1, a deflector 48 is placed inside the toothed crown 38, immediately below the injection head 42, so as to direct the blocking material 14 towards the periphery of the drum 10. Thus any risk of clogging, even temporary, is avoided for the air suction tubes 46. In fact, in the absence of a deflector, a bank of blocking material could be formed on the top of the pile of cakes 12. Outside the collar 39 carrying the toothed crown 38, the upper wall of the dynamic containment hood 28 supports a laser detector 50 directed towards the intermediary lid 16. The laser detector 50 makes it possible to measure the distance separating the containment hood 28 from the intermediary lid 16. Linked to a control circuit (not shown) of the lifting jack 32, the laser detector 50 thus forms means for positioning the lower end of at least one bubble tube 52 at a predetermined level below the cap 22, after perforation of the latter (preferably, two bubble tubes 52 are used, as shown in FIG. 1). In other terms, when the distance measured by the laser detector 50 reaches a predetermined value, the upward movement of the drum 10 assured by the lifting jack 32 is stopped. The lower ends of the bubble tubes 52 are then at a predetermined level below the intermediary lid 16. The control of this positioning makes it possible to pilot precisely the filling level of the drum 10 with the blocking material 14, by using the bubble tubes 52. For this, the lower parts of the bubble tubes 52 (FIG. 1) are placed inside the collar 39 carrying the toothed crown 38. The level of the lower ends of the bubble tubes 52 is such that, when the lifting of the drum 10 has been stopped in response to the measurement made by the laser detector 50, these ends are situated at a level slightly lower than that of the intermediary lid 16. As an example, the lower ends of the bubble tubes 52 can be at 4 mm below the level of the intermediary lid 16. The bubble tubes 52 thus constitute means for detecting the filling of the drum 10. In other terms, when the bubble tubes 52 are closed by the blocking material 14 at the end of filling, one is sure that the drum is completely filled. The filling of the drum is thus stopped. When two bubble tubes 52 are used as shown in FIG. 1, advantageously they are placed in positions diametrically opposite each other relative to the vertical axis of the dynamic containment hood 28. Thus they ensure redundancy of detection. In FIG. 3, a diagram is shown of means of level detection 54 to which the bubble tubes 52 are connected. These means of level detection 54 pilot the automatic closing of two level-detection valves 56a and 56b, placed in a circuit for feeding the nozzle 42 with blocking material 14. This supply circuit constitutes, with the injection nozzle 42, the injections means 40. A third valve 56c, located immediately above the injection nozzle 42, serves as a safety valve and enables piloting of the rinsing of the supply circuit. It is controlled from the operations room, by an on-off control. As shown in FIG. 3, the supply circuit for the nozzle 42 comprises a closed circuit 58 connected to the injection nozzle 42 by a pipe 60 in which the valves 56b and 56c are placed. The closed circuit 58 comprises a hopper 62 for filling and storing the blocking material 14. The capacity of the hopper 62 is designed to allow at least one drum 10 to be filled. The hopper 62 is filled with the desired volume of blocking material, from a mixer (not shown), let in through a pipe 64 through a valve 66. The closed circuit 58 allows the blocking material 14 to circulate continuously in a loop, to avoid it all setting, to increase its lifetime and to limit the effects of clogging the tubing, until this material is injected into the drum 10. For this, it is equipped with pumping means such as a peristaltic pump 68. The valve 56a piloted by the level detection system 54 is placed in the closed circuit 58, immediately below the branch linking the circuit 58 to the injection nozzle 42 through the pipe 60. A pipe 74, provided with a valve 76, links the water distribution network to the pipe 60 between the two valves 56b and 56c placed on it. This pipe 74 makes it possible, by injecting water under pressure, to carry out the rinsing of the central and lower parts of the injection nozzle 42 when the drum which has just been filled has been emptied. It is set in action before the following drum arrives underneath the dynamic containment hood 28. The recuperation of rinsing effluents is carried out by a retractable plate (not shown) which comes into place against the dynamic containment hood 28, in place of the drum. The effluents are then directed towards a specialised installation for treating polluted water. Other valves 82 are set in different locations around the closed circuit 58. In addition, a pipeline 84 provided with a valve 86 opens into the circuit 58, near the suction of the pumping means 68. This pipeline makes it possible to ensure the cleaning of the whole circuit, in particular by introducing a foam ball, through the piping 84, thus ensuring evacuation of the residual blocking material through emptying tubing 87, provided with a stop valve 88. The final rinsing of the closed circuit is carried out by injecting clean water into the hopper 62 (with pumping means 68 in operation) and recuperating the effluents in the retractable plate then set in place under the hood 28. Only a part of the closed circuit 58 is inside the processing workshop in which the filling of the drums 10 is carried out. A portion of the containment partition 88 defining this workshop is shown diagrammatically in FIG. 3. The part of the circuit 58 located outside the processing workshop includes in particular the hopper 62 and the pumping means 68. Advantageously, the whole of the installation is piloted by automatic control-command means (not shown). When a drum 10 is brought up to the filling post in which the blocking operation is carried out according to the invention, it contains cakes 12 and its upper end is closed in a sealed fashion by the intermediary crimped lid 16 whose central opening 20 is closed by the cap 22. As soon as the drum 10 is set on the lifting jack 32 by the conveyor belt 36, its horizontal displacement is stopped and the drum is lifted up to the position shown in FIG. 1. In this position, controlled by laser detectors 50, the cap 22 is perforated by the toothed crown 38. The disc cut out in the cap falls immediately onto the pile of cakes 12, by gravity, because of the mass of the ballast domino 24. Despite this perforation, the containment of the drum 10 remains intact, until the end of filling, by the dynamic containment hood 28 under negative pressure application by means 44 for negative pressure application. The injection of the filling material 14 into the drum then begins under the action of the pumping means 68, after opening valves 56a and 56c placed in the piping 60. Simultaneously, the drum is made to vibrate by means 34 for creating vibration, associated with the jack 32. The injection of the filling material 14 continues until the bubble tubes 52 detect the arrival of the free level of the blocking material immediately next to the intermediary lid 16. The level detection means 54 then automatically close the valves 56a and 56b and the injection is stopped. Next, the jack 32 is once again activated to re-lower the drum 10 onto the conveyor belt and to carry it to the following post where an external lid (not shown) is set in place. More precisely, the external lid is set on the drum above the intermediary lid 16 and crimped on the curl 10a of the drum. The process and installation which have just been described make it possible to carry out the blocking operation while still ensuring complete control of containment. Any dispersion of contamination into the atmosphere of the workshop, and in particular any contamination of the external wall of the drum is thus avoided. |
|
051986787 | abstract | Polymerization devices having an irradiation space in an irradiation chamber, the space being accessible via at least one pivotable or displaceable wall, and having a light conductor and a radiation source unit, wherein the light conductor feeds the radiation from the radiation source into the irradiation space of the irradiation chamber and forms a releasable connection between the irradiation chamber and the radiation source unit, are known. To create a polymerization device that makes it possible to operate an irradiation chamber for curing plastic dental parts by means of a hand-held polymerization unit, with the capability of easy conversion from a hand-held polymerization unit to a stationary polymerization device, the radiation source unit is a hand-held polymerization unit, which is retained by its housing part on a first support, disposed on a support plate of a support frame; the light conductor is guided in a second support of the support plate; and the irradiation chamber is supported on a part of the support frame. |
047175346 | claims | 1. A nuclear fuel cladding having a predetermined concentration of burnable absorber integrally incorporated therein, for use in containing a nuclear fuel in a reactor, the cladding formed as a hollow composite tube comprising: an outer tubular layer, having a first thickness of at least 15 mils, consisting essentially of a first zirconium alloy; an intermediate layer bonded to the inner wall of said outer tubular layer, having a second thickness less than said first thickness, consisting essentially of a mixture of a boron-containing material having a predetermined enrichment of boron and a second zirconium alloy, said second thickness being defined by said predetermined enrichment of boron in said boron-containing material and by the predetermined concentration of burnable absorber incorporated into said fuel cladding; and an inner layer of zirconium metal, having a third thickness less than said second thickness, bonded to said intermediate layer, said third thickness being sufficient to isolate said intermediate layer from said nuclear fuel. an outer tubular layer, having a first thickness of at least 15 mils, consisting essentially of a zirconium alloy; an intermediate layer bonded to the inner wall of said outer tubular layer, having a second thickness less than said first thickness, of about 3-5 mils, consisting essentially of a mixture of a zirconium boride and a zirconium alloy; and an inner layer of zirconium metal, having a thickness less than said second thickness, of about 1-2 mils, bonded to said intermediate layer. 2. A nuclear fuel cladding as defined in claim 1 wherein said first and said second zirconium alloys are selected from the group consisting of Zircaloy-2, Zircaloy-4 and a zirconium alloy containing about 2.5 percent by weight niobium. 3. A nuclear fuel cladding as defined in claim 1 wherein said boron-containing material is selected from the group consisting of natural boron, enriched boron, zirconium boride, boron nitride, boron carbide, or mixtures thereof. 4. A nuclear fuel cladding as defined in claim 1 wherein said outer tubular layer is at least twice the thickness of the sum of the thicknesses of the intermediate layer and the inner layer. 5. A nuclear fuel cladding as defined in claim 1 wherein said composite cladding has a wall thickness of between 18-22 mils. 6. A nuclear fuel cladding as defined in claim 1 wherein said intermediate layer has a thickness of between 3-5 mils. 7. A nuclear fuel cladding as defined in claim 6 wherein said inner layer has a thickness of between 1-2 mils. 8. A nuclear fuel cladding having a burnable absorber integrally incorporated therein, for use in containing a nuclear fuel in a reactor, the cladding formed as a hollow composite tube comprising: 9. In a nuclear fuel rod comprising a metallic tubular cladding formed from a metal selected from zirconium and a zirconium alloy, containing a nuclear fuel, and having end sealing means thereon to hermetically seal said nuclear fuel within said metallic tubular cladding, the improvement wherein said metallic tubular cladding is a composite, said cladding having integrally incorporated a predetermined concentration of burnable absorber material, said cladding comprising an outer tubular layer having a first thickness, sufficient to provide the mechanical integrity and strength to contain the nuclear fuel, said first thickness being at least about 15 mils, said outer tubular layer consisting essentially of a first zirconium alloy; an intermediate layer bonded to the inner wall of said outer tubular layer, having a second thickness less than said first thickness, consisting essentially of a mixture of a boron-containing material having a predetermined enrichment of boron and a second zirconium alloy, said second thickness being determined by the predetermined concentration of burnable absorber incorporated into said cladding and the predetermined enrichment of boron in said boron-containing material; and an inner layer of zirconium metal, having a third thickness less than said second thickness, said third thickness being between about 1-2 mils, bonded to said intermediate layer. 10. A nuclear fuel rod as defined in claim 9 wherein said first and said second zirconium alloys are selected from the group consisting of Zircaloy-2, Zircaloy-4 and a zirconium alloy containing about 2.5 percent by weight niobium. 11. A nuclear fuel rod as defined in claim 9 wherein said boron-containing material is selected from the group consisting of natural boron, enriched boron, zirconium boride, boron nitride, boron carbide, or mixtures thereof. 12. A nuclear fuel rod as defined in claim 9 wherein said outer tubular layer is at least twice the thickness of the sum of the thicknesses of the intermediate layer and the inner layer. 13. A nuclear fuel rod as defined in claim 9 wherein said composite cladding has a wall thickness of between 18-22 mils. 14. A nuclear fuel rod as defined in claim 9 wherein said intermediate layer has a thickness of between 3-5 mils. 15. In a nuclear fuel rod comprising a metallic tubular cladding formed from a metal selected from zirconium and a zirconium alloy, containing a nuclear fuel, and having end sealing means thereon to hermetically seal said nuclear fuel within said metallic tubular cladding; the improvement wherein said metallic tubular cladding is a composite of an outer tubular layer having a first thickness of at least 15 mils consisting essentially of a zirconium alloy; an intermediate layer bonded to the inner wall of said outer tubular layer having a second thickness less than said first thickness, of about 3-5 mils, consisting essentially of a mixture of zirconium boride and a zirconium alloy; and an inner layer of zirconium metal, having a thickness less than said second thickness, of about 1-2 mils, bonded to said intermediate layer. |
046684662 | description | DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views. Also, in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. In General Referring now to the drawings, and particularly to FIG. 1, there is shown an elevational view of a fuel assembly, represented in vertically foreshortened form and being generally designated by the numeral 10. The fuel assembly 10 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 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 nuclear reactor. 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 heat generated therein for the production of useful work. To control the fission process, a number of control rods 32 are reciprocally movable in the guide thimbles 14 located at predetermined positions in the fuel assembly 10. Specifically, the top nozzle 22 includes a rod cluster control mechanism 34 having an internally threaded cylindrical member 36 with a plurality of radially extending flukes or arms 38. Each arm 38 is interconnected to a control rod 32 such that the control mechanism 34 is operable to move the control rods 32 vertically in the guide thimbles 14 to thereby control the fission process in the fuel aassembly 10, all in a well-known manner. Grid Cell Spring Force Measurement Apparatus For precisely maintaining the spacing between the fuel rods 18 in the reactor core and preventing both lateral and longitudinal movement thereof, the grids 16 are conventionally designed to impose spring forces on the fuel rods 18 directed from around the circumference of the individual rod radially inwardly toward the longitudinal axis of the rod. Referring now to FIGS. 2 to 4, it is seen that each of the grids 16 includes a multiplicity of interleaved inner straps 40 having an egg-crate configuration designed to form cells, indicated as 42, a majority of which individual accept one fuel rod 18 (for purposes of clarity only one cell 40 is shown in FIG. 2 with a fuel rod 18 disposed through it) and a minority of which accept one control rod guide thimble 14. The cells 42 of each grid 16 which accept and support the fuel rods 18 at a given axial location therealong typically use relatively resilient springs 44 and relatively rigid protrusions or dimples 46 formed into the metal of the interleaved inner straps 40 to generate the spring forces needed to hold the fuel rods therein. Also, the inner straps 40 are generally flexible such that they bow somewhat when the fuel rods 18 are disposed through the grid cells 42. In the illustrated embodiment, there are two springs 44 on two adjacent sides of each cell 42 containing a fuel rod 18 and two dimples 46 on each of two adjacent sides of the cell facing each spring. The springs 44 and dimples 46 of each grid cell 42 frictionally engage or contact the respective fuel rod 18 extending through the cell. Additionally, outer straps 48 are attached together and peripherally enclose the grid inner straps 40 to impart strength and rigidity to the grid 16. Thus, the actual spring force imposed on a given fuel rod 18 results from interaction with one another of the resilient springs 44, rigid dimples 46 and flexible interleaved straps 40 comprising the cell 42 which receives the fuel rod. In order to properly characterize the holding capability of an individual grid 16, it is this spring force that must be measured. Turning finally to FIGS. 5 to 7, for measuring the spring force, resulting from the combined action of the system of resilient springs 44, rigid dimples 46 and flexible interleaved grid straps 40, imposed on a given fuel rod 18 when disposed through one cell 42 in one of the support grids 16 of the fuel assembly 19, the present invention provides a grid cell force measuring apparatus, generally designated 50. The measuring apparatus 50 includes a pair of front and rear elongated members 52,54 having respective mid-sections 56,58 and respective upper and lower end portions 60,62 and 64,66 extending in opposite directions from the respective mid-sections 56,58. The members 52,54 are pivotally connected together at their mid-sections 56,58 such that as the upper end portions 60,64 of the members, being juxtaposed in spaced apart relation to one another, are moved toward and away from each other the lower end portions 62,66 of the members, also being juxtaposed in spaced apart relation to one another, are moved away from and toward each other. More particularly, the elongated members 52,54 of the measuring apparatus 50 take the form of a pair of front and rear bars. The upper and lower end portions 64,66 of the rear bar 54 extend in opposite directions from the mid-section 58 thereof and in generally linear alignment with one another, whereas the upper and lower end portions 60,62 of the front bar 52 extend in opposite directions from the mid-section 56 thereof but in a transversely offset relationship. Due to such offset relationship, the upper end portion 60 of the front bar 52 is spaced farther or remote from the upper end portion 64 of the rear bar 54 while the lower end portion 62 of the front bar 52 is spaced closer or adjacent to the lower end portion 66 of the rear bar 54. Additionally, a pair of transversely spaced tabs 68,70 are attached to the rear bar 54 at its mid-section 58 and extend generally parallel to one another and outwardly from a side thereof facing the front bar 52. The tabs 68,70 have respective aligned holes 72,74 defined therethrough, whereas a hole 76 is defined through the midsection 56 of the front bar 52. A pivot pin 78 extends through the aligned holes 72,74 in the spaced tabs 68,70 on the rear bar 54 and through the hole 76 in the front bar 52 so as to mount the front bar on the tabs for pivotal movement relative to the rear bar. Further, the measuring apparatus 50 includes force generating means, generally designated 80, coupling the upper end portions 60,64 of the front and rear elongated bars 52,54 together and being operable to apply a progressively increasing force so as to draw the upper end portions toward one another and thereby, via the pivotal connection of the bars, push the lower end portions 62,66 apart from one another. In particular, the force generating means 80 includes a shaft 82 rotatably connected to one of the upper end portions 60,64 of the bars 52,54, such as the upper end portion 60 of the front bar 52, and threadably connected to the other thereof, such as the upper end portion 64 of the rear bar 54. A knob 84 is attached to an end of the shaft 82 disposed adjacent the front bar 52 for facilitating rotation of the shaft through manual turning of the knob in either of two opposite directions in order to move the upper end portions 60,64 of the elongated bars 52,54 toward and away from each other. Thus, the rotatable shaft 82 and knob 84 of the force generating means 80 are used to generate an increasing force at a first location along the elongated bars 52,54 which will be external of the given one grid cell 42 when the lower end portions 62,66 of the bars 52,54 are inserted in the cell to the position seen in FIG. 7 for carrying out the measuring procedure. The elongated bars then serve as means for transmitting that increasing force from the first location therealong and applying the force at a second location displaced from the first location and internal of the one grid cell 42. The elongated bars 52,54 of the measuring apparatus 50 can be adjusted to simulate fuel rods of various diameters. Toward this end, means in the form of a set screw 86 is attached to the lower end portion 62 or 66 of the one of the elongated bars 52,54 and can be adjusted to preset the displacement between the lower end portions of the bars. Specifically, by rotating the set screw 86, which in the illustrated embodiment is threadably attached to the lower end portion 66 of the rear bar 54, and by simultaneously adjusting the shaft 82 on the upper end portion 60 of the front bar 52, the set screw 86 is operable to coact with the lower end portion 62 of the front bar 52 to preset a minimum displacement between the bars at the respective lower end portions thereof and thereby a minimum combined cross-sectional dimension of the bars at their lower end portions. Then, when the lower end portions of the bars are inserted into a given one grid cell 42, such as seen in FIG. 7, they will simulate a fuel rod 18 disposed through the cell having a predetermined outside diameter. Other features of the measuring apparatus 50 comprise an adjustable stop 88, guide means 90 and limit means 92. The adjustable stop 88 includes a strip 94 having an elongated slot 96 and being attached to one of the bars, such as the mid-section 58 of the rear bar 54 along the rearwardly facing side thereof, by a bolt 98 inserted through the slot. The strip 94 extends downwardly a short distance and has a lower terminal end 100 for engaging the top of a grid strap 40, as seen in FIG. 7, to provide correct positioning of the lower end portions 62,66 of the bars 52,54 in the one grid cell 42 for applying the increasing force to one of the springs 44 in the cell. The position of the terminal end 100 of the strip 94 can be vertically adjusted by untightening the bolt 98 and then sliding the strip 94 relative thereto. The guide means 90, being coupled between the upper end portions 60,64 of the front and rear bars 52,54 to assist in maintaining alignment of the bars with one another as they are pivotally moved relative to one another, includes a guide pin 102 and a guide bore 100. The guide pin 102 is anchored in the upper end portion 60 or 64 of one of the elongated bars 52,54, such as the rear bar 54, and extends transversely toward the upper end portion of the other elongated bar, such as the front bar 52. The guide bore 104 is formed through the upper end portion of the other of the elongated bars, such as the front bar 52 for slidably receiving the guide pin 96 therethrough as the bars 52,54 are pivotally moved relative to one another. The limit means 92, being a set screw threadably received through the upper end portion of one of the elongated bars, such as the front bar 52, extends transversely toward the upper end portion of the other of the elongated bars, such as the rear bar 54 for engagement therewith upon relative pivotal movement of the bars toward one another. The set screw 92 is adjustable for presetting the minimum displacement between the upper end portions 60,64 of the elongated bars 52,54 and thereby defining a maximum force which can be applied at their lower end portions 62,66 to the resilient spring 44 in the grid cell 42. Finally, the grid force measuring apparatus 50 includes means for sensing and recording the spring force of the grid cell 42. First, means in the form of a strain gauge 106 is attached to the lower end portion of one of the elongated bars, such as the front bar 52, a short distance below its mid-section 56. The strain gauge 106 senses the level of the increasing force being applied to the spring 44 within the one grid cell 42 into which the bars 52,54 are inserted. Although the bars 52,54 are made of metal, the lower end portion 62 of the front bar 52 is thin enough in cross-section so as to have sufficient flexure to give a meaningful strain gauge readout. Also, the measuring apparatus 50 has means, generally designated 108, in the form of a pair of electrical contacts being coupled between the lower end portions 62,66 of the front and rear bars 52,53 and capable of breaking contact with one another when application of the increasing force to the spring 44 in the cell 42 causes deflection of the spring to occur. The pair of electrical contacts 108 includes a circuit element in the form of an electrically conducting plate 110 attached to and electrically insulated from the lower end portion of one of the elongated bars, such as the front bar 52, and the set screw 86 attached to the lower end portions of the other of the elongated bars, such as the rear bar 54. As mentioned earlier, one function of the set screw 86 is to preset the displacement between the lower end portions 62, 66 of the elongated bars 52,54. The second function is to provide electrical contact with the circuit element 110 when the elongated bars 52,54 are initially inserted into the grid cell 42. Lastly, as seen in FIG. 7, the measuring apparatus 50 has means in the form of a readout 112, preferably a suitable digital type, coupled across the terminals 114,116 of the strain gauge 106, being preferably in a bridge arrangement, and in parallel with the contacts 108. The readout 112 indicates the level of force at the instance deflection of the spring 44 occurs. Specifically, a pair of lead lines 118,120 couples the readout in series with the strain gauge terminals 114,116. However, the contacts 108, i.e., the circuit element 110 and set screw 86, are also connected by lead lines 122,124 in series with the strain gauge terminals. When the contacts 108 are closed, the terminals 114,116 of the strain gauge 106 are effectively short circuited and no force level signal is conducted to the readout 112. However, when the force applied to the grid cell spring 44 is marginally greater than the spring force, the spring 44 deflects and the electrical contacts 108 go from a closed to an open condition. Then the strain gauge terminals 114,116 are no longer shorted and a signal is generated by the strain gauge 106 and received and recorded by the readout 112 at the instance the contacts 108 are opened. This provides a determination of the spring force for the preselected fuel rod 18 outside diameter. In FIG. 7, the pivotally connected elongated bars 52,54 of the measuring aparatus 50 are shown placed vertically in the grid cell 42 to be measured, with the rear bar 54 in contact with both grid dimples 46 and the front bar 52 in contact with the grid spring 44, With the bars preset by the set screw 86 at the selected fuel outside diameter dimension and rotatable shaft 82 in a loosened condition, the depth of insertion into the grid cell is preset by the adjustable positioning stop 88. By turning the knob 84, the shaft 82 is gradually tightened until electrical contact between the set screw 86 and the insulated conducting circuit element 110 is broken. The contact break is monitored electrically such that at the instance the break occurs the strain gauge 106 reading is recorded by readout 112. This reading determines the spring force for one spring 44 and its associated pair of dimples 46 at the preset dimension across the bars 52,54. The same steps are repeated to measure the spring force for the other spring and pair of dimples in the same cell. The two readings are added together to get the total spring force in the given cell. By increasing or decreasing the preset dimension between the bars 52,54 by, for example, increments of two thousands of one inch, the bars may be reinserted into the cell 42 and the spring force again determined. Using differences in spring force for the incremental changes in preset dimensions, the spring rate characteristic of the cell can be derived over the total required range. 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. |
050892126 | summary | The invention relates to an apparatus for controlling the power output of a nuclear reactor, in particular for the reactor core of an advanced pressurized water reactor, having a number of control elements each being movable by a drive mechanism, and each of the control elements including a plurality of control rods and a support structure joining the control rods to one another. When taking the existing, time-tested technology of pressurized water reactors used in many nuclear power plants as a point of departure, substantially better utilization of the raw material used as a source of energy is attained in a so-called advanced pressurized water reactor by using novel fuel assemblies, along with slight changes to the pressurized water reactor core. In order to accomplish this, the average neutron energy in the reactor core must be increased. Since the water that moderates neutrons continues to be used simultaneously as a coolant, the average neutron energy in an advanced pressurized water reactor is shifted beyond the thermal range by reducing the ratio between the moderator volume and the fuel volume. In a liquid-cooled reactor core, the fuel assemblies are disposed vertically in a generally cylindrical reactor pressure vessel that has a rounded or partly spherical cover or dome and a rounded or partly spherical bottom. The coolant flows from bottom to top through the reactor pressure vessel and simultaneously acts as a moderator. Each fuel assembly includes a bundle of fuel rods, which are guided in a grid or lattice assembled from spacers and are movably supported in a shared top and bottom piece. The fuel rods can expand between the top and bottom pieces retained in grid or lattice plates and are therefore not hindered in their axial temperature expansion. In order to enable the fuel rods to receive uranium oxide as a fuel, they are constructed as tubes within which the fuel is hermetically sealed in pellet form. Controlling the power output of the nuclear reactor is performed, among other means, by control rods that are driven to a variable depth into the active part of the reactor core. To this end, certain fuel assemblies include guide rods, inside which the control rods can be driven. However, during operation of the nuclear reactor, only a selected number of fuel assemblies is equipped with control rods. In order to reduce the number of control rod drive mechanisms, the control rods that are all associated with the same fuel assembly are coupled to a single drive rod above the fuel assembly through a shared support structure, known as a "spider". The drive rods of the control elements pass through the cover of the reactor pressure vessel to individual control element drive mechanisms at the outside. The locations of the control elements are typically symmetrically distributed over the cross-sectional area of the reactor core. The number of control elements is limited by the maximum allowable number of bores that can be provided in the reactor pressure vessel cover for the passage of the drive rods therethrough. In contrast to the square cross-sectional structure of the fuel rod grid or lattice of the conventional pressurized water reactor, the fuel rod grid or lattice structure in the advanced pressurized water reactor is hexagonal in cross section. This permits a very small spacing between the fuel rods, so that on average more fuel is contained per unit of reactor core volume in an advanced pressurized water reactor than in the core of a conventional pressurized water reactor. Given unchanged dimensions of the reactor pressure vessel, the necessary compactness of the reactor core of an advanced pressurized water reactor makes for twice the number of fuel rods, as compared with a conventional pressurized water reactor, at only approximately half the active core height. In order to ensure reliable regulation and/or shutoff of the advanced pressurized water reactor, it is therefore necessary to provide a larger number of control elements per unit of cross-sectional area of the reactor core than in a conventional pressurized water reactor. On the other hand, as shown by such a configuration described in the journal "Kernreaktoren" [Nuclear Reactors] by H.-J. Zech, in Deutsches Atomforum, Bonn 1988, if the dimensions of the reactor pressure vessel are unchanged, then the number of drive rods for the control elements is limited, particularly because of the predetermined number of bores in the reactor pressure vessel cover. It is accordingly an object of the invention to provide an apparatus for controlling the power output of a nuclear reactor, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and with which more control elements can be actuated in the reactor core of an advanced pressurized water reactor per unit of cross-sectional area than in a pressurized water reactor of the previously typical type, for a given number of control element drive mechanisms. The control elements should be distributed in such a way that they cover the area uniformly and symmetrically over the entire cross section of the reactor core, in order to compel uniform power distribution in the core. With the foregoing and other objects in view there is provided, in accordance with the invention, a nuclear reactor, especially an advanced pressurized water reactor, with controlled power output, comprising a reactor core having a cross section in a given plane with a center of area and axes of symmetry passing through the center of area, a multiplicity of control elements disposed in groups, each of said groups having at least one of said control elements, said control elements of each of said groups with more than one control element being joined together, said groups being symmetrical to at least two of the axes of symmetry, drive mechanisms each moving a respective one of said groups of control elements, each of said control elements having a plurality of control rods, a support structure joining said control rods of a group to one another, fuel assemblies disposed in groups, each of said groups of control elements having a given number of control elements being associated with one of said groups of fuel assemblies having said given number of fuel assemblies, and other fuel assemblies with which said control elements are not associated, said other fuel assemblies surrounding said groups of fuel assemblies. In accordance with another feature of the invention, each of said groups of control elements has 1, 2 or 3 control elements, and each of said groups of fuel assemblies has 1, 2 or 3 fuel assemblies. In accordance with a further feature of the invention, the cross section of said reactor core is approximately circular, and each two of said axes of symmetry define an angle therebetween being an integral multiple of 30.degree.. In accordance with an added feature of the invention, the cross section of said reactor core is substantially circular, and said reactor core has a hexagonal fuel rod grid structure. In accordance with an additional feature of the invention, the groups of control elements are a total of 61 groups of control elements having a total of 151 control elements, 13 of said groups of control elements each have one control element, 6 of said groups of control elements each have two control elements, and 42 of said groups of control elements each have three control elements. In accordance with yet another feature of the invention, there are provided connecting pieces each having said control elements of a respective one of said groups detachably retained thereon and each being movable by a respective one of said drive mechanisms. In accordance with yet a further feature of the invention, there is provided a multi-armed guide plate in which said connecting piece is guided. In accordance with a concomitant feature of the invention, the multi-armed guide plate has adjacent arms defining an angle therebetween being a fraction of 360.degree., said fraction corresponding to the number of said arms. An advantage of the apparatus for controlling the power output of a nuclear reactor according to the invention, is that with little engineering effort or expense, substantially more control elements per unit of cross-sectional area can be installed in the reactor core, for an unchanged number of control element drive mechanisms, by joining the control elements into groups. A distribution of the control elements that covers the area and is symmetrical over the cross section of the reactor core is attained in accordance with the invention by providing that the drive rods of two or three control elements are joined together by being converted, through one connecting piece each, into one drive rod. Along with individually driven control elements, this enables a particularly advantageous geometrical configuration of the control elements to be provided over the reactor core cross section, with six axes of symmetry between which the angle is an integral multiple of 30.degree.. Thus, in calculating the layout and monitoring the reactor core, a 30.degree. portion can be used as the basis and then extrapolated for the entire core cross section. It is moreover possible for a number of fuel assemblies that suits given requirements to be provided with control rods, through the formation of groups having more than three control elements, locally or over the entire core cross section. The apparatus according to the invention is especially advantageous when a pressurized water reactor system is being converted into an advanced pressurized water reactor, because neither the reactor pressure vessel cover nor the control element drive mechanisms need be replaced. 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 an apparatus for controlling the power output of a nuclear reactor, 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. |
description | In FIG. 1A, in the preferred embodiment, an incoming particle beam 1 impacts a target mass 9 through its containment surface 23 resulting in a nuclear reaction or collision and the generation of GW exhibiting an axis 21, which can propagate radially or in either direction. The reaction or collision also produces back scattered particles 2, nuclear reaction products 3 moving in the preferred direction of target nuclei alignment 22, high-energy photons 4 (for example, x-ray emissions) also moving primarily in the preferred direction 22, sputtered particles 7, and recoil atoms 8. A typical target atom 11 when impacted by the particle beam is jerked by the release of nuclear-reaction products or by collision or by other means and produce GW similar to or in simulation of a sub-microscopic star explosion or collapse discussed by Geoff Burdge, Deputy Director for Technology and Systems of the National Security Agency, written communication dated Jan. 19, 2000 and incorporated herein by reference. This axis is described and illustrated co-pending patent application, Ser. No. 09/616,683, filed Jul. 14, 2000, now U.S. Pat. No. 6,417,597. In the case of nuclear-reaction-produced jerks, the radius of gyration at the reactants is significantly smaller than the GW wavelength so that the quadrupole approximation holds. The energizing process can also result in harmonic oscillation or a quadrupole radiator. In this case the GW propagates radially or cylindrically as discussed by Albert Einstein and Nathan Rosen (1937, Journal of the Franklin Institute, 223, pp. 43-54). The target""s characteristic length, absorption depth, or approximate radius of gyration of the extensive emulated target mass 10 is utilized in the quadrupole approximation to compute the power of the GW that is generated. In FIG. 1B, the particle bunches 12 are shown impacting or colliding with an incoming particle bunch 13 of another particle beam at a collision angle 14, which could be any value including zero. In this case, the incoming target bunch is contemplated to be spin-polarized noble gas, such as helium II or odd-nuclear isotopes of xenon, etc. in order to exhibit a preferred direction in space 22. In FIG. 2 is exhibited a medium in which the GW speed is reduced 34, the new direction of GW 35 caused by the GW passing through a boundary of a medium 38 at an oblique angle 36 with respect to a normal to the surface of such a medium 37 produces GW refraction. The back surface of the medium in which the GW speed is again changed 39 is shown, but for clarity no refractive bending of the GW is exhibited. Examples of suitable media are superconducting media. In FIGS. 3A, 3B, 3C, and 3D are exhibited the build up or accumulation of GW along the radially expanding cylindrical GW wave fronts created by and normal to the motion direction 42 of the energizable particle or quadrupole radiator axis. In FIG. 3A a typical central target-mass particle 40 is energized by an incoming particle 41 of the particle-beam bunch. The radially expanding GW wave front 43 moves out at local GW speed. In FIG. 3B, which is at a time xcex94t later, where xcex94t is the time between the arrival of the first and second particle bunch, that is, inversely proportional to the beam-chopping frequency. In this case GW 43 emanating from the first typical target-mass particle 40 is reinforced or constructively interferes with the GW generated by other target-mass particles 44 situated at the distance VGWxcex94t radially out from target-mass particle 40, where VGW is the local GW speed. For clarity only two particles 44 are exhibited out of a ring of such target particles in the target mass in a plane normal to the direction of the energizing motion. Their location will be such as to cause their GW 45 to constructively interfere with and reinforce the originally expanding GW 43. In FIG. 3C, which is at time 2xcex94t later, the GW 43 emanating from the first particle 40 and the second particles 44 are reinforced by another set of particles 46 and their attendant GW 47. FIG. 3D is at time 3xcex94t and typical target-mass particles 48 add their GW 49 to the accumulating and radially expanding GW. Each arriving beam bunch initiates additional expanding rings of coherent GW until the target-mass particles are exhausted or until their replacements are unavailable. There are large numbers of energizable particle sites that are simultaneously energized so that the GW permeates the target mass as the GW are superimposed. As noted by Pinto and Rotoli (op cit, p. 567) xe2x80x9c . . . the quadrupole formula is only valid provided a suitable surface integral vanish(es), which is the case for an assembly of point sources, . . . xe2x80x9d. In the context of the previous application, Ser. No. 09/616,683, now U.S. Pat. No. 6,417,597, the typical target-mass, particles such as 40, 44, 46, and 48 are considered to be energizable elements. Such elements can be permanent magnets, electromagnets, solenoids (or nanosolenoids) current-carrying plates, piezoelectric crystals, nanomachines including harmonic oscillators, nanomotors and nanoselenoids or microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) in general, etc. In the case of solenoids (or nanosolenoids), some nanomachines, nanoelectromechanical systems, current-carrying plates, etc. the energizing and enegizable elements can be colocated, for example the energizing coil around the energizable central magnetic core in the case of the nanosolenoids. The energizing elements in the context of the ""683 application would include coils, current pulses moving in conductors, biomolecular motors, etc. that operate under the control of an Individual Independently Programmable Coil System (IIPCS), described in the parent U.S. Pat. No. 6,160,336 of which the previous Application, now U.S. Pat. No. 6,417,597, is a continuation-in-part, in order to activate or energize the energizable elements in a sequence as the ring of GW, whose propagation plane is normal to the direction of the energizable elements quadrupole radiator axis, moves radially out at local GW speed. In this case directivity can be achieved in both l:he orientation of the GW ring""s plane, the sector of that expanding ring where the GW wave front is reinforced or constructively interfered with by energizing the energizable elements and/or by destructive interference of one GW with another (as in the astrophysical case of a uniformly, isotropically exploding or collapsing star). The collector elements, in the context of the previous application, Ser. No. 09/611,683, now U.S. Pat. No. 6,417,597 would be at the same locations as the energizable elements and interrogated in a sequence by the IIPCS to detect or receive specific GW frequencies, that is, tuned to the GW frequency. In FIG. 4 the constructive interference or reinforcement or amplification of a GW by energizable elements is over a linear pattern 50, 54, 56, and 58 produced by a micro mass explosion or collapse which simulate a macro star explosion or collapse, with GW directed along its axis as predicted by Burdge, op. cit. 2000 is illustrated (but directed in both directions along the axis. The reinforcement of GW is illustrated schematically by the arrows 53, 55, 57, and 59. The GW builds up to a larger amplitude 62 as the beam bunch and the GW crest or front move with the same speed together through the particles comprising the target mass and generate coherent GW pulses. The target particles or energizable elements 50, 54, 56 and 58 are VGW xcex94t apart where VGW is the GW speed and xcex94t is the time between energization. Thus an extensive mass composed of all of the energized target particles is emulated. In the context of the ""597 patent the typical target mass particles 50, 54, 56 and 58 are considered to be energizable elements. As already discussed, such elements can be magnets, conductors, piezoelectric crystals, harmonic oscillators, nanomachines, etc. The collector elements, in the context of ""597, would be at the same locations as the energizable elements and interrogated in a sequence by the IIPCS to detect or receive GW having a particular frequency and phase. In FIG. 5, of the preferred embodiment a particle source 15, which could be a laser or a nuclear reaction, produces particles that can be accelerated by an acceleration device 16 (unless the particles are photons), focused by a focusing device 17 such as a superconducting medium or electromagnetic field and separated into bunches by a beam chopper 18. The target mass can be a solid, a liquid (including a superfluid such as liquid helium II), a gas (including electron gas), or another particle beam. Alternately, the beam can be separated into bunches and modulated as to frequency and number of particles in each bunch at the particle source 15. The particle source 15 or beam chopper 18 is controlled by computer 19, an information-processing device 20 and transmitter 71. The particle beam bunches 1 impact the target particles 9 and produce a nuclear reaction, generating GW 21, which can be received at receiving device 70. The information processing device 20 can be, for example, a Kalman filter and/or a table look up for identifying the element to be energized. In FIG. 6A, are illustrated a plan view of a typical stack of elements or array of element sets or subsets, which could be GW collectors or could be energizable elements such as target atoms or nuclei. The indices, which describe the location or address of these elements, 27 are denoted by i, j, xcfx86k. For example, the top element 28 has an index i=0 (0th column), j=4 (4th row), and xcfx86k represents the directivity of this individual element, either produced by an active element or element set alignment or by connecting a specific, kth member of an underlying stack of elements, having the appropriate orientation fixed, of which the figure shows only the top member. As another example element 29 has an index ixe2x88x921 (xe2x88x921st column), j=1 (1st row), and xcfx86k. In FIG. 6B the directivity angle to the preferred direction 22 is 180xc2x0 and the prior locations of the GW crests 61 are behind the GW crest 25. The distance between the lines (or planes comprising the GW wave crests) at elements in the GW direction 21 is 24. The elements 26 on the;anticipated GW crest 25 of the GW 21 are connected to an information processing device, that is interrogated (detection mode) or energized (generation mode). In FIG. 6C the future locations of the GW crests 60 is in front of the GW crest 25 and the directivity angle is 135xc2x0, in FIG. 6D it is 90xc2x0, in FIG. 6E it is 45xc2x0 and in FIG. 6F it is 0xc2x0. In FIG. 7 is illustrated a spherical set of element sets or subsets or electrodes 31 comprising an element having directivity angles xcex1k and xcex4k for a kth member of the element set or subset 32 distributed over a sphere 33. A propulsion system utilizing a gravitational wave generator is shown in block diagram form in FIG. 8. As shown therein, the propulsion system provides a gravitational wave generator 67 disposed within a vehicle housing 75. The generator includes a particle-beam source 69 energizing elements and nuclear-reaction chamber 72, which includes the target-mass energizable elements. Such elements could involve high-energy, nuclear-particle collisions whose products are distribut d asymmetrical in the direction of tab particle-beam energizing element""s motion (as discussed by Charles Seife (2000), Science, Volume 291, Number 5504, p. 573 and incorporated herein by reference). Alternatively, the energizable nuclear elements could be constrained to a preferred orientation yielding a preferred direction of the collision products and again, a nuclear jerk in a preferred direction. Such GW directivity is illustrated schematically in FIGS. 8A and 8B of the parent patent, U.S. Pat. No. 6,160,336. The rearward moving gravitational waves 62 exit the rear of the vehicle propelling the vehicle in the desired direction of travel 74. The target-mass energizable elements in the nuclear-reaction chamber 72 build up, by constructive interference or reinforcement, the coherent GW 62 as exhibited in FIG. 4. The system of energizable elements comprising the target emulates a more extensive mass having a longer effective radius of gyration 10 exhibited in FIG. 1A and, therefore, stronger GW and more momentum to cause the forward motion in the desired direction of travel 74. A refractive medium can intercept the oppositely or forward-directed GW and those rays can be bent or refracted to the side in order to reduce the forward component of GW momentum and, thereby promote forward propulsion in the desired direction of travel. The forward-moving portion of the GW generated by the jerks associated with the energization of the elements comprising the target mass is not coherent. This GW portion is the result of the smaller actual radii of gyration of each individual energizable element. Thus weaker GW is generated and as previously mentioned, can be bent to the side by a GW refractive medium and far less momentum is carried away to counter the propulsion in the desired forward direction of travel so that forward propulsion dominates. The present invention relies upon the fact that the rapid movement or jerk or oscillation of a mass or collection of submicroscopic particles such as nuclei will produce a quadrupole moment and generate useful high-frequency, for example, up to QuadraHertz (Qhz) or higher-frequency, GW. The device described herein accomplishes GW generation in several ways based upon the interaction of energizing and energizable submicroscopic particles. In a preferred embodiment a collection of target nuclei or target-beam particles are jerked or otherwise set in motion, for example, harmonic oscillatory motion, in concert, in response to the impact of a particle beam, which is a directed flow of particles or waves that carries energy and information. The particle beam moves with the same speed as the local speed of the gravitational waves. According to Ning Li and Douglas Torr (1992), Physical Review B, Volume 64, Number 9, p.5491, if the target is a superconductor, then the GW are estimated to be two orders of magnitude slower than the speed of GW in a vacuum or the speed of light. Specifically, they state: xe2x80x9cIt should be pointed out that since nothing is known of the phase velocity of a gravitational wave . . . propagating within a superconductor, it is usually presumed to be equal to the velocity of light. We argue that the interaction of the coupled electromagnetic and gravitoelectromagnetic fields with the Coop r pairs in superconductors will form a superconducting condensate wave characterized by a phase velocity xcexdxcfx81xcex7xe2x88x92. Since . . . the phase velocity can be predicted for the first time as xcexdxcfx81xcex7xe2x88x92m . . . 106 [m/s]xe2x80x83xe2x80x83(30) which is two orders of magnitude smaller than the velocity of light.xe2x80x9d The target will exhibit an absorption thickness, that is, a length over which many of the impacting particles interact with the target nuclei to produce a nuclear reaction whose collision products move in a preferred direction resulting in a jerk or oscillation. The particle beam is composed of bunches of particles generated in a cylindrical beam pipe, each bunch enters the target material and interacts with a cylinder of target nuclei or target beam particles, comprising the target mass, having a length that is associated with the radius of gyration of the emulated target mass. The results of the interaction, in addition to the jerk or oscillation imparted to the target mass by nuclear reaction or collision, include back-scattered particles 5, secondary electrons 6, sputtered particles, forward-scattered particles (channeling) and recoil atoms as well as ion implantation. The jerk-producing or oscillation-producing collisions involve elastic (single Coulomb) and inelastic (bresstrahlung) scattering impacts on nuclei and particles and sometimes result in a nuclear reaction, the products of which move out in a preferred direction based upon the alignment of the target 22. The particle beam bunch""s front edge strikes the nuclei or particles in the cylindrical target-mass volume at a speed equal to the local GW speed. As each nucleus or other particle-beam target is impacted and is jerked or otherwise set in motion by the reaction to a nuclear products emission or collision, it generates GW in the direction of or normal to the beam""s velocity and/or the alignment direction at the target nuclei and the GW grows in amplitude and emulates a large target mass having an effective radius of gyration larger than that of any single energizable element. The GW can also be generated in the direction normal to a quadrupole (harmonic-oscillator) axis or in the direction of a is jerk, so that the particle-beam directed GW builds up or accumulates and generates a coherent GW as the beam particles progress through the target nuclei and thereby, emulates an extensive target mass. According to Douglas Torr and Ning Li (1993), Foundation of Physics Letters, Volume 6. Number 4, p.371 xe2x80x9c . . . the lattice ions, . . . must execute coherent localized motion consistent with the phenomenon of superconductivity.xe2x80x9d Thus, a preferred embodiment is to have the target nuclei constrained in a cylindrical superconductivity state. As the particle-beam bunch moves down the cylinder of target nuclei, it strikes one target nuclei after another, creating a GW and adding to the forward-moving or radially-directed GW""s amplitude as it progresses in step with the bunch""s particles in the preferred direction in space of FIG. 1A22 thereby emulating an extensive target mass. The particle-beam bunches are modulated by a particle-emission and/or chopper-control computer to impart information by modulating the generated GW. In addition, since the GW can be slowed by virtue of passing through a medium such as a superconductor (Li and Torr op. cit. 1992) and, therefore, refracted by it, as in a lens, the GW can be focused and intensified. The GW can also be venerated in a direction normal to a dipole axis. According to Joseph Weber (1964), Gravitation and Relativity, W. A. Benjamin Inc., New York, p. 91, a summation of charge times acceleration gives rise to dipole radiation, which also can be accomplish d gravitationally in a superconductor according to Li and Torr, op. Cit. 1992, pp. 5489ff and Torr and Li, op. Cit. 1993, pp. 371ff. In another embodiment electron transfer dynamics between incident particle-beam gas molecule energizing elements, for example, nitric oxide, NO and a metal target surface composed of energizable elements such as Au (111) has been discussed by Yuhui Huang et al. (2000), Science, Volume 290, No. 5489, pp. 111-114. The large-amplitude vibrational motion associated with the energizable target molecules in high vibrational states strongly modulates the energy driving force of the energizing electron-transfer reaction. In this regard, although not discussed in any connection with GW generation, according to Huang, et al. (ibid, p. 113), xe2x80x9c . . . the multiquantum vibrational transfer occurs on the subpicosecond time scale.xe2x80x9d In order to accomplish experiments or communication with a GW generation or transmitter device, it is necessary to detect or receive GW. In this regard application Ser. No. 09/616,683, filed Jul. 14, 2000, now U.S. Pat. No. 6,417,597, describes such a detection device in which the collector elements replace the energizable elements of the present invention. The GW receiver is oriented in a direction from which the GW is known to be generated. The GW can be focused on the detection device by means of a refractive medium exhibiting a lense shape, as shown in FIG. 2, in order to amplify the GW intensity. Furthermore, since the GW frequency is also known, the collector elements of the GW receiver can be interrogated, that is, selectively connected by the control computer to an information-proc ssing device, in a sequence at the anticipated incoming GW frequency, that is, tuned. Thus, as the incoming GW pass through the ensemble of the GW receiver""s collector elements, utilizing piezoelectric crystals, or capacitors, or strain gauges, or transducers, or parametric transducers, or nanomachines, etc., these elements are interrogated at the anticipated time of passage of the GW crest past them. The uncertainty is in the determination of the GW phases. Within, for example, a subpicosecond time resolution, all of the possible GW phases (or times that the GW crest hits the leading rows of collector elements) are initially swept through by the control computer to establish the phase that correlates best with the maximum amplitude of the received GW signal, that is, tuned to the GW signal. After this initialization the GW phase is tracked by, say, a Kalman filtering technique described on pp. 384-392 of Robert M. L. Baker, Jr. (1967) Astrodynamics, Applications and Advanced Topics, Academic Press, New York. The small voltages and currents produced by some of the alternative collector elements can be measured, for example, by a superconducting quantum interference device (SQUID) using Josephson junctions (described in U.S. Pat. No. 4,403,189) and/or by quantum non-demolition (QND) techniques utilized in optics but applied to the problem of reducing quantum-noise limitations for high-frequency GW. The QND technique was first suggested by Vladimir Braginsky of the Moscow State University and published by A. M. Smith (1978) in xe2x80x9cNoise Reduction in Optical Measurement Systems)xe2x80x9d IEE Proceedings, volume 125, Number 10, pp. 935-941. Superconductors are also contemplated for use in connection with the collection elements as discussed in the previous application, Ser. No. 09/616,683, filed Jul. 14, 2000, so that the collection elements can be in a superconducting state. Referring again to U.S. Pat. No. 6,417,597 describes collector elements that can detect GW through the same conductors as are attached to the energizable elements for GW generation and are connected by an Individual Independently Programmable Coil System (IIPCS), a device that acts as a transceiver. The IIPCS is more fully described in U.S. Pat. No. 6,610,336. Such a control computer can connect the collector elements together and interrogate them in a pattern that will effectively sense GW incoming from a specific direction and, in like fashion, it can connect the energizer elements and energize them in a pattern that will effectively direct the radially or linearly propagating GW or steer them in a specific direction. It is valuable, therefore, both to scan for GW from a given set of directions, and to steer GW in a given set of directions, that is, to provide for directivity in both reception and transmission of GW. The control computer, acting in concert with the information-processing device, establishes a communications link between a GW receiver and a GW transmitter or, alternatively, among GW transceivers and establishes point to multipoint communication. The aforementioned directivity can be best illustrated by FIG. 6. FIG. 6A exhibits a plan view of a typical section of an array of elements or element sets or subsets, the elements with indices 27, i, j, xcfx86k. xcfx86k represents the directivity angle, measured relative to some arbitrary fixed direction in space 30, of an individual element, either produced by active element alignment (by being in an electromagnetic field, in a superconducting state, spin polarized, etc.) or being an element set or subset, or by connecting to a specific member of an underlying stack of elements having the appropriate orientation fixed, of which the figures shows only the top member. In this latter case the i, j element stack may, for example, be 180 members high, each member offset from the next by one degree k=1 to 180) in the three-dimensional ensemble of elements. The central or control computer or information processing function is, therefore, a table look up of the indices that should be xe2x80x9conxe2x80x9d for a given directivity and also located on the crest of the specific GW of interest (incoming or outgoing). An xe2x80x9conxe2x80x9d element is one that is interrogated (for reception) or energized (for transmission). In FIG. 6B the directivity angle to the preferred direction 22 is 180xc2x0. The elements on the anticipated GW crest 25 of interest of the GW 21 are communicated to collectors and interrogated (detection mode) or energized (generation mode). The prior locations of the GW crests 61 are behind the crest 25. In FIG. 6C the directivity angle is 135xc2x0, and the future locations of the crests 60 are in front of the crest 25. In FIG. 6D the directivity angle is 90xc2x0, in FIG. 6E it is 45xc2x0, and in FIG. 6F it is 0xc2x0. A coordinate rotation will afford directivity in three dimensions. In this latter regard, the elements could be arrays of elements or element sets or subsets and those arrays could be spherically isotropic in their activity as either collectors or energizable elements. In one embodiment, the element sets or subsets consist of piezoelectric crystals in a spherical configuration or array. Thus, GW can be sensed or generated in any direction. In this case, the piezoelectric crystals would be spread out evenly over the surface of a sphere 33 exhibited in FIG. 7. In a preferred embodiment each element would consist of a spherical piezoelectric crystal 33 with electrodes 31 spread out evenly over its surface and interrogated or energized in opposite pairs to achieve directivity in detection or generation of GW. FIG. 7 illustrates the sphere 33 and the elements 31 (collectors or energizable) comprising the element sets or subsets. A typical member of this element set or subset, 32, has its directivity angles xcex1k and xcex4k for the kth member of the element sets or subsets defined by the notation xcfx86k (xcex1k, xcex4k). In one embodiment, the elements are piezoelectric crystals. In a preferred embodiment the elements are electrodes 31 attached to the surface 33 of a single, spherical piezoelectric crystal. Thus the propagation of the GW can be steered as opposite pairs of the electrodes are energized and detected from specific directions as the opposite pairs of electrodes, acting as collectors, are interrogated. Collectively the myriad of such spherical piezoelectric crystals can generate or detect a coherent GW by energizing or interrogating them in an appropriate pattern or sequence as illustrated in FIGS. 6B, 6C, 6D, 6E, and 6F. The specific relationship for GW generation by energizing elements, such as particle-beam particles, colliding with energizable elements, such as aligned target nuclei, will be an outcome of the use of the present invention described herein. To better understand that relationship, it is helpful to refer to the standard quadrupole approximation, Eq. (110.16), p.355 of L. C. Landau and E. M. Lifshitz, The Classical Theory of Fields, Fourth Revised English Edition, Pergamon Press, 1975 or Eq. (1), p.463 of J. P. Ostriker, (xe2x80x9cAstrophysical Source of Gravitational Radiation in Sources of Gravitational Radiation,xe2x80x9d Edited by L. L. Smarr, Cambridge University Press. 1979) which gives the GW radiated power (watts) as P=xe2x88x92dE/dt=xe2x88x92(G/45c5)K(d3Dxcex1xcex2/dt3)2 [watts]xe2x80x83xe2x80x83(1) where E=energy [joules], t=time [s], G=6.67423xc3x9710xe2x88x9211 [m3/kgxe2x88x92s2] (universal gravitational constant, not the Einstein tensor), c=3xc3x97108 [m/s] (the speed of light), and Dxcex1xcex2[kgxe2x88x92m2] is the quadrupole moment-of-inertia tensor of the mass of the target particles, and the xcex4 and xcex2 subscripts signify the tensor components and directions. The quantity (d3Dxcex1xcex2/dt3)2 is the kernel at the quadrupole approximation. Equation (1) can also be expressed as: P=KI3dot(d3I/dt3)2/5 c2 [watts]xe2x80x83xe2x80x83(2) where I=(xcexa3m)r2 [kgxe2x88x92m2], the moment of inertia, (xcexa3m)=sum of the masses of the individual target nuclei that are impacted by the particle beam, expel nuclear-reaction products, and caused to jerk or recoil in unison, [kg], (or, at least jerk or oscillate as the forward-moving GW front moves by), r=the effective radius of gyrations of the ensemble of target nuclei that constitute the target mass [m], and KI3dot=a dimensionless constant or function to be established by experiment. The third derivative of the moment of inertia is d3I/dt2=(xcexa3m)d3r2/dt3=2r(xcexa3m)d3r/dt3+ . . . xe2x80x83xe2x80x83(3) and d3r/dt3 is computed by noting that 2r(xcexa3m)d2r/dt2=n2rfn [Nxe2x88x92m] (equation of motion)xe2x80x83xe2x80x83(4) where n is the number of beam particles, which interact with target nuclei to emit nuclear-reaction products, and is the nuclear reactive force on a given target nuclei caused by the release of nuclear-reaction products. The third derivative is approximated by d3I/dt3=n2rxcex94fn/xcex94txe2x80x83xe2x80x83(5) in which xcex94 fn is the nearly instantaneous increase in the force on the ensemble of nuclei caused by the release of nuclear-reaction products or the collision impulse over the brief time interval, xcex94t. The xcex94t is the nuclear-reaction time for a typical individual collision, taken here to be 10xe2x88x9212 [s]. We will also take, for convenience of calculation, the time between emission of particle bunches also to be xcex94t. Thus the chopping frequency would be one THz. As a bunch of beam particles strike the target nuclei material, the particles impact on the target nuclei, with, for example, 10% of them causing a nuclear reaction. In this regard, the characteristic length (or emulated or effective radius of gyration, r) of the target mass could be considered to be the thickness of the target mass or the distance that the particle-beam bunch moves at local GW speed before the number of particles in a given bunch is reduced by half or by some other measure of the effective radius of gyration of the target mass as the ensemble of energized particles comprising the target mass move in concert at local GW speed and emulate a cohesive target mass. The target nuclei are held in place by intermolecular forces that propagate at the local sound speed, that is, during the xcex94t interval while the beam particles interact with the target nuclei and create aligned nuclear-reaction products, the particles move a distance vxcex94t, where v is the particle speed that is made equal to the local GW speed, VGW, but the nuclei move more slowly and influence one another at sound speed. Thus, alternative characteristic lengths could be either vxcex94t or the distance local sound travels in at or the length of the target-mass cylinder, or the absorption thickness, etc. For the numerical example we will choose r=1 [cm]=0.01 [m] and the beam itself to have a cross-sectional area of one square centimeter. Thus for the numerical example the target mass is a cube one centimeter on a side and the generated GW rings from harmonic oscillation that move out in a plate or slab one centimeter thick. With KI3dot=32, as in the case of the GW radiated by the centrifugal-force jerk of a spinning rod, from Eq. (1), p.90 of Joseph Weber (1964), xe2x80x9cGravitational Waves in Gravitation and Relativity,xe2x80x9d Chapter 5, W. A. Benjamin, Inc., New York and Introducing Eq. (5), Eq. (2) becomes P=1.76xc3x9710xe2x88x9252(n2r xcex94fn/xcex94t)2 [watts]xe2x80x83xe2x80x83(6) The number of particles in a typical bunch is estimated to be approximately that of the Stanford Linear Collider (SLC) or 4xc3x971010 particles. It is estimated that 10% of the particles impact target nuclei and result in nuclear reaction (that is, a 10% harvest), so n=4xc3x971010. Inserting these numbers into Eq. (6) we have P=1.76410xe2x88x9252(4xc3x971010xc3x972xc3x970.01xcex94fn/xcex94t)2 [watts]xe2x80x83xe2x80x83(7) and, subject to further verification as to the mass defect and impulsive nuclear force, that is verification of the magnitude of the jerk, we take xcex94fn=1xc3x9710xe2x88x926 [N] and xcex94t=10xe2x88x9212 [s] resulting in P=1.13xc3x9710xe2x88x9222 [watts]. The reference area is either the rim of a disk one centimeter thick and one centimeter in diameter or 3.14xc3x9710xe2x88x924 [m2] for a GW flux of 3.6xc3x9710xe2x88x9219 [watts/m2] for a harmonic oscillation of the target elements or one square centimeter for a linear jerk of the target elements (there is a factor of 0.5 since the GW is bifurcatedxe2x80x94half moving in the direction of the jerk and half in the opposition direction). The former leads to a forward component of GW flux of 5.65xc3x9710xe2x88x9219 [watts/m2]. A lens system composed of a media in which the GW is slowed (such as a superconducting media) could concentrate or focus the GW from, say, a one square centimeter, to 10 micrometers2 for an increase in GW flux of 105 to 5.65xc3x9710xe2x88x9213 [watts/m2]. Note that in the refraction medium the GW wavelength is significantly smaller than 10 micrometers2 at THz frequencies, so that GW diffraction, if present, is not very significant. All of the foregoing quadrupole equations are approximations to P. Due to the slowness of the GW, about one hundredth of light speed, the GW wavelength in the superconducting target is about xcexGW 0.01cxcex94t=3xc3x97105xc3x9710xe2x88x9212=3xc3x9710xe2x88x926[m], but still larger than the radius of the target nuclei, beam particles, or nuclear-reaction products, so xcexGW is much greater than the radius of the target particles and also, due to the slow propagation speed, all speeds are much less than c. Thus the quadrupole approximation is good, but still KI3dot will be further refined as will the harvest and other details of the energizing and jerk-producing or harmonic-oscillation-producing mechanism of the invention such as xcex94fn and xcex94t. The GW produced also is xe2x80x9c . . . itself the source of some additional gravitational fieldxe2x80x9d as noted by Landau and Lifshitz (op cit, 1979, p. 349) and discussed in the Propulsion section of U.S. Pat. No. 6,417,597. Thus attendant to the GW is a change in gravity that can be effectively utilized for the movement of mass and, hence, as a propulsion means. Analysis of Binary Pulsar PSR 1913+16 As discussed in the Prior application Ser. No. 09/616,663, now U.S. Pat. No. 6,417,597, since binary pulsar PSR 1913+16 represents the only experimental confirmation of GW, the features and advantages of the present invention will be better understood by a further analysis of this double-star system. According to Robert M. L. Baker, Jr., p. 3 of xe2x80x9cPreliminary Tests of Fundamental Concepts Associated with Gravitational-wave Spacecraft Propulsion,xe2x80x9d Paper No. 2000-5250 in the CD-ROM proceedings of the American Institute of Aeronautics and Astronautics Space 2000 Conference and Exposition, AIAA Dispatch: [email protected], or www.aiaa.org/publications, Sep. 19-21, 2000, the double star exhibits a mass of m=2.05xc3x971030 [kg], a semi-major axis, a, of 2.05xc3x97109 [m], and a mean motion, n (or xcfx89) of 2.25xc3x9710xe2x88x924 [radians/s]. The average centrifugal force component or force-vector component subject to cage during the star pair""s orbit, xcex94fcfx,y, is man2=(5.56xc3x971030)(2.05xc3x97109)(2.25xc3x9710xe2x88x924)2=5.77xc3x971032[N],xe2x80x83xe2x80x83(8) From Eq. (1), p. 90 of Joseph Weber, (op cit. 1964) and from Eq. (2) herein, one has for Einstein""s formulation (1918, Sitzungsberichte, Preussische Akademi der Wisserschaften, p. 154) of the gravitational-wave (GW) radiated power of a rod spinning about an axis through its midpoint, having a moment of inertia, I [kgxe2x88x92m2], and an angular rate, xcfx89 [radians/s]: xe2x80x83P=xe2x88x9232GI2xcfx896/5c5=xe2x88x92G(Ixcfx893)2/5(c/2)5 [watts]xe2x80x83xe2x80x83(9) or P=xe2x88x921.76xc3x9710xe2x88x9252(Ixcfx893)2=xe2x88x921.76xc3x9710xe2x88x9252(r[rmxcfx892]xcfx89)2xe2x80x83xe2x80x83(10) where using classical (not relativistic) mechanics, [rmxcfx892]2 can be associated with the square of the magnitude of the rod""s centrifugal-force vector, fat, for a rod of mass, m, and radius of gyration, r. This vector reverses every half period at twice the angular rate of the rod (and a component""s magnitude squared completes one complete period in halt the rod""s period). Thus the GW frequency is 2xcfx89 and the time-rate-of-change of the magnitude of, say, the x-component of the centrifugal force, fcfx is xcex94fcfx/xcex94txe2x88x9d2fcfxxcfx89.xe2x80x83xe2x80x83(11) (Note that frequency, "ugr"=xcfx89/2xcfx80.) The change in the centrifugal-force vector itself (called a xe2x80x9cjerkxe2x80x9d when divided by a time interval) is a differential vector at right angles to fct and directed tangentially along the arc that the dumbbell or rod moves through. As previously mentioned, Equation (9) is an approximation and only holds accurately for r less than less than xcexGW (wave length of the GW) and for speeds of the GW generator far less than c (the speed of light). Equation (9) is the same equation as that given for two bodies on a circular orbit on p. 356 of Landau and Lifshitz, op. cit., 1975, (I=xcexcr2 in their notation) where xcfx89=n, the orbital mean motion. As a validation of the use of a jerk to estimate gravitational-wave power, let us utilize the jerk approach for computing the gravitational-radiation power of PSR 1913+16. We computed in Equation (8) that each of the components of force change, xcex94fcfx,y=5.77xc3x971032 [N] (multiplied by two since the centrifugal force reverses its direction each half period) and xcex94t=(xe2x85x9) (7.75 hrxc3x9760 minxc3x9760 sec)=1.395xc3x97104 [s]. Thus using the jerk approach: P=xe2x88x921.76xc3x9710xe2x88x9252{(2rxcex94fcfx/xcex94t)2+(2rxcex94fcfy/xcex94t)2}=xe2x88x921.76xc3x9710xe2x88x9252(2xc3x972.05xc3x97105xc3x975.77xc3x971032/1.395xc3x97104)3xc3x972=xe2x88x9210.1xc3x971024 [watts]xe2x80x83xe2x80x83(12) versus 9.296xc3x971024 [watts] using Landau and Lifshitz""s (op. cit., 1975, p. 356) more exact formulation given by the analyses of Baker (op. cit., 2000, p. 4) integrating using the mean anomaly. The stunning closeness of the agreement is, of course, fortuitous since due to orbital eccentricity there is no symmetry among the xcex94fcfx,y components around the orbit. Nevertheless, the value of the jerk approach is well demonstrated. Since the present invention produces waves or ripples in the conjectured spacetimeuniverse (STU) continuum or fabric (see U.S. Pat. No. 6,160,336), it can be used to explore cosmological conjectures and theories. According to a thumbnail sketch of Einstein""s theory of general relativity, time and space disappear with material things. That is, matter (stars to atomic nuclei) are inseparably connected to time and space and vice versa. xe2x80x9cThingsxe2x80x9d are all but hills, valleys, and holes in the fabric of Einstein""s spacetime. It is conjectured that the equivalence of inertial and attractive mass and the unification of all forces, gravitational, centrifugal, electromagnetic, nuclear, etc. is that they are all simply undulations in the multidimensional STU fabric. We may consider a centrifugal force field to be a gravitational force field and elastic, thrust, drag, etc., force fields to be electromagnetic in origin. Thus force is a property of STU and vice versa. Such a concept is similar to that expressed by Schrxc3x6dinger in 1946 (reported in Denis Brian""s Einstein a life, 1996, John Wiley and Sons, p. 351) in his theory that xe2x80x9c . . . purely wave theory, in which the structure of space-time would yield gravitation, electromagnetism, and even a classical analog of strong nuclear (forces)xe2x80x9d. In fact, the term xe2x80x9cgravitational wavesxe2x80x9d could be replaced by the term xe2x80x9cforce wavesxe2x80x9d or xe2x80x9cinertia wavesxe2x80x9d since it is the change in force, any force or attraction, or jerk of an inertial mass that results in the waves or ripples in the STU fabric. Gravitational waves are related directly to an inertial mass in motion (caused by either a change in attraction or forcexe2x80x94a jerk or harmonic oscillation) and not directly related to a gravitational field. In this regard, the wave/particles for such a force wave are proposed to be defined as xe2x80x9cgravitational instantonsxe2x80x9d or xe2x80x9cinstantonsxe2x80x9d. Such wave/particles would be analogous to photons associated with electromagnetic waves, gravitons associated with gravitational attraction, and gluons associated with strong nuclear forces. For historical reasons the term gravitational waves should be retained, whereas to avoid confusion with gravitons and the erroneous association of GW exclusively with gravitational attraction the term xe2x80x9cinstantonsxe2x80x9d is used. There is a fundamental difference between photons, gravitons, gluons, etc., and instantons. The former are manifested by the curvature of the multidimensional STU fabric created by the attractions or forces associated with charge, mass, nuclear particles, etc. (all conjectured to be similar to gravity, that is, not really xe2x80x9cforcesxe2x80x9d, but motion along convergent or divergent geodesics in the multidimensional STU), whereas the latter is manifested by the rapid changes in the forces or jerk or oscillation associated with the formerxe2x80x94like xe2x80x9ccracking a whipxe2x80x9d or xe2x80x9cstriking a drum headxe2x80x9d of STU fabric to produce ripples in the STU fabric as Landau and Lifshitz (op cit, p. 355) suggest, such STU fabric distortions caused by high-frequency gravitational waves (expressed as instantons) change gravity (expressed as gravitons) itself. Thus all the properties of wave/particles, like diffraction and dispursion, may not be present in the instantons. Continuing with the thumb-nail-sketch conjectures of the STU continuum at the most elementary level, the inherent uncertainty in position and velocity (as opposed to the practical, experimental inability to exactly define position and velocity simultaneously) is simply a reflection of the fact that you can""t xe2x80x9cseexe2x80x9d the entire STU panorama from any one single vantage point. Thus there can be complete determinism, cause and effect can prevail, and xe2x80x9cGod does not have to play dicexe2x80x9d, because everything is in the STU fabric, for example, in different universes at different times everything cannot be xe2x80x9cseenxe2x80x9d. A xe2x80x9clinexe2x80x9d cannot connect xe2x80x9cpointsxe2x80x9d in the STU fabric, but the xe2x80x9cpointsxe2x80x9d are still there and their xe2x80x9cmotionxe2x80x9d on the fabric is predictable; but, unfortunately, they can""t be xe2x80x9cseenxe2x80x9d or predicted simultaneously. The more conventional spacetime continuum is embedded in the multidimensional STU, which is a multidimensional manifold. As far as quantum mechanics is concerned, the detailed surface of the STU fabric can be thought of as ribbed or like stepsxe2x80x94essentially quantum steps. According to this conjecture the intractable frontier between xe2x80x9c . . . a smooth spacial geometry . . . xe2x80x9d and xe2x80x9c . . . the violent fluctuations of the quantum world on short distances . . . the roiling frenzy of quantum foam.xe2x80x9d (Brian Greene, 1999, the elegant universe, Norton, New York, p. 129) is nothing more or less than the interface between osculating universes on small scales in which entities shift back and forth at willxe2x80x94actually smooth transitions with mass/energy and momentum conserved and entropy constant. Thus the measurement of the fundamental constants in a given universe are subject to a very small variation depending upon xe2x80x9cwherexe2x80x9d (or xe2x80x9cwhenxe2x80x9d) they are measured. In this regard, xe2x80x9cwherexe2x80x9d has a more global meaning. In the STU xe2x80x9cwherexe2x80x9d is similar to position in conventional space (but a continuum of dimensions). On the other hand xe2x80x9cwherexe2x80x9d and what are time-like universe dimensions. In xe2x80x9courxe2x80x9d universe its simply xe2x80x9ctime-when.xe2x80x9d These extremely simplified general cosmological conjectures would require very complicated mathematics in order to obtain quantitative results and make them more than just superficial fantasies. Thus the present invention would be useful in obtaining experimental insights concerning the foregoing conjectures and confirmation of quantitative cosmological theories and predictions. Also the receiver aspect of the invention, as it relates to the detection of high-frequency GW, would be useful in studying the xe2x80x9cBig Bangxe2x80x9d information imprinted on GW background between about 10xe2x88x9225 and 10xe2x88x9212 [s] after its start. |
|
description | An Application Data Sheet is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed Application Data Sheet is incorporated by reference herein in its entirety and for all purposes. The present inventions relate to methods, apparatuses, devices, and systems for creating, controlling, conducting, and optimizing fusion activities of nuclei. In particular, the present inventions relate to, among other things, fusion activities that are conducted individually or collectively on a very small scale, preferably on the nano-scale or smaller such as pico to femto scales, for the utilization of energy produced from these activities in smaller devices and for aggregation into larger devices. Controlled fusion devices, methods and systems are taught and disclosed in US Patent Application Publication Nos. 2010/0294666, 2011/0188623, U.S. patent application Ser. Nos. 13/663,751, 14/205,337, 13/952,826, 61/925,114, 61/925,131, 61/925,122, 61/925,148, 61/925,142, 61/210,383, and 61/843,015 the entire disclosures of each of which are incorporated herein by reference. As used herein, unless expressly stated otherwise, the term fusion should be given its broadest possible meaning, and would include interactions between two or more nuclei whereby one or more new or different nuclei are formed, as well as subsequently induced or derivative reactions and energy generation associated therewith. As used herein, unless expressly stated otherwise, the terms formation, formation of material, and similar terms should be given their broadest possible meaning, and would include transmutation, and the modification or creation of a nucleus or nuclei, such as, for example, nuclides, and isotopes having value in medical, imaging, testing, and other useful applications. As used herein, unless expressly stated otherwise, the term light element means an element or ion with atomic mass of 62 or less. As used herein, unless expressly stated otherwise, the term physical confinement, physical containment, and similar such terms mean the use of a physical structure that passively confines the fusion reaction as opposed to the use of directed energy, including shockwaves, EM fields such as from lasers, or electromagnetic fields to confine the fusion interaction. As used herein, unless expressly stated otherwise, the term strongly ionized plasma means a plasma whereby the ratio of ions to neutrals is at least about 1:1. As used herein, unless expressly stated otherwise, the term weakly ionized plasma means a plasma whereby the ratio of ions to neutrals is less than about 1:100. The terms plasma, ionized material, and similar such terms includes all degrees and ratios of ionization. As used herein, unless expressly stated otherwise, the term neutrals means atoms, molecules or clusters with no net charge. As used herein, unless expressly stated otherwise, the terms fusion fuel, reactants, fusion reactions and similar terms are to be given their broadest possible means and would include hydrogen-1, boron-11, lithium-6, lithium-7, deuterium, tritium, helium-3, nitrogen-15, and any other elements, materials and compounds, including isotopes, that may be identified to be useful fusion fuels, and combinations and variations of the foregoing. For 60 years the science and technology communities have been striving to achieve controlled and economically viable fusion. The commonly held belief in the art is that another 25-50 years of research remain before fusion is a viable option for power generation-“As the old joke has it, fusion is the power of the future—and always will be” (“Next ITERation?”, Sep. 3, 2011, The Economist). Further, until the present inventions, it was believed that a paradigm existed in that achieving fusion of reactants was unobtainable without incredibly high temperatures for even the most likely reactants and even higher temperatures for other reactants. As a consequence, it was further believed that there was no reason to construct, or investigate the composition of, a nuclear fusion reactor with lower temperature reactant confinement. Prior to the present inventions it was believed that the art in controlled fusion reactions taught that temperatures in excess of 150,000,000 degrees Centigrade were required to achieve favorable gross energy balance in a controlled fusion reactor. Gross energy balance, Q, is defined as: Q = E fusion E i n , a . where Efusion is the total energy released by fusion reactions and Ein is the energy used to create the reactions. The Joint European Torus, JET, claims to have achieved Q≈0.7 and the US National Ignition Facility recently claims to have achieved a Q>1 (ignoring the very substantial energy losses of its lasers). The condition of Q=1, referred to as “breakeven,” indicates that the amount of energy released by fusion reactions is equal to the amount of energy input. In practice, a reactor used to produce electricity should exhibit a Q value significantly greater than 1 to be commercially viable, since only a portion of the fusion energy can be converted to a useful form. Conventional thinking holds that only strongly ionized plasmas, are necessary to achieve Q>1. These conditions limit the particle densities and energy confinement times that can be achieved in a fusion reactor. Thus, the art has looked to the Lawson criterion as the benchmark for controlled fusion reactions—a benchmark, it is believed, that no one has yet achieved when accounting for all energy inputs. The art's pursuit of the Lawson criterion, or substantially similar paradigms, has led to fusion devices and systems that are large, complex, difficult to manage, expensive, and economically unviable. A common formulation of the Lawson criterion is as follows: N τ E * > 3 ( 1 - η i n η out ) H η i n η out 〈 σ v 〉 ab ( H ) Q ab 4 ( 1 + δ ab ) - ( 1 - η i n η out ) A br H All of the parameters that go into the Lawson criterion will not be discussed here. But in essence, the criterion requires that the product of the particle density (N) and the energy confinement time (τE*) be greater than a number dependent on, among other parameters, reaction temperature (H) and the reactivity σνab, which is the average of the product of the reaction cross section and relative velocity of the reactants. In practice, this industry-standard paradigm suggests that temperatures in excess of 150,000,000 degrees Centigrade are required to achieve positive energy balance using a D-T fusion reaction. For proton-boron fusion, as one example, the criterion suggests that the product of density and confinement time must be yet substantially higher. It should be noted that current fusion schemes using D-T fuels, which produce radioactive materials, should have shielding and take steps and precautions, such as the use of robotic operating systems to maintain safety. An aspect of the Lawson criterion is based on the premise that thermal energy must be continually added to the plasma to replace lost energy to maintain the plasma temperature and to keep it fully or highly ionized. In particular, a major source of energy loss in conventional fusion systems is radiation due to electron bremsstrahlung and cyclotron motion as mobile electrons interact with ions in the hot plasma. The Lawson criterion was not formulated for fusion methods that essentially eliminate electron radiation loss considerations by avoiding the use of hot, heavily ionized plasmas with highly mobile electrons. Because the conventional thinking holds that high temperatures and strongly ionized plasma are required, it was further believed in the art that inexpensive physical containment of the reaction was impossible. Accordingly, methods being pursued in the art are directed to complex and expensive schemes to contain the reaction, such as those used in magnetic confinement systems (e.g., the ITER tokamak) and in inertial confinement systems (e.g., NIF laser). In fact, at least one source in the prior art expressly acknowledges the believed impossibility of containing a fusion reaction with a physical structure: “The simplest and most obvious method with which to provide confinement of a plasma is by a direct-contact with material walls, but is impossible for two fundamental reasons: the wall would cool the plasma and most wall materials would melt. We recall that the fusion plasma here requires a temperature of ˜108 K while metals generally melt at a temperature below 5000 K.” (“Principles of Fusion Energy,” A. A. Harms et. al.) The present inventions break the prior art paradigms by, among other things, increasing the reactant density, essentially eliminating electron radiation losses, and combinations of these, by avoiding the use of a strongly ionized plasma, modifying the Coulomb barrier and thus increasing the reaction cross section, and essentially eliminating the need for confinement to contain the fusion reaction. Such approaches make Lawson's criterion inapposite. The importance and value of achieving economically viable controlled fusion has long been recognized and sought after in the art. Controlled fusion may have applications in energy production, propulsion, material creation, material formation, the production of useful isotopes, generation of directed energetic beams and particles, and many other key fields and applications. In the energy production area, controlled fusion has been envisioned to provide a solution to global energy and environmental challenges, including supply, distribution, cost, and adverse effects from using hydrocarbon or other alternative fuel sources. Accordingly, there has been a long-standing and unfulfilled need for a controlled fusion reaction, and the clean energy and other benefits and beneficial uses that are associated with such a reaction. This need, however, has primarily focused on using controlled fusion for larger, or macro applications, such as providing power to a city, factory or building. There has further been a long-standing need for reliable and dependable small power sources for use in small devices such as cell phones, robotics, hearing aids, pace makers, laptop computers, smart phones, hand held electronic devices and the like, as well as for newer, smaller, and emerging technologies, such as, nano-technologies, micro-circuits, nano-circuits and micro-robotics. While battery technologies and other power sources have been rapidly evolving and becoming smaller, and smaller, in many instances they have failed to keep up with the needs of smaller and smaller devices, and the need for having power supplies that do not readily become depleted. Unfortunately, in many cases, battery technology may be becoming the limiting factor to the further advancement of these small electronic technologies. The present methods, devices and systems for conducting fusion reactions solve these and other problems, deficiencies, and inadequacies associated with prior attempts to create a viable controlled fusion system, and short comings in conventional small, micro-, nano-, and sub-nano-electronic devices. Further, the present inventions avoid the risks associated with conventional fission power generation. Moreover, available aneutronic embodiments of controlled fusion avoid the potential issues associated with managing neutrons produced in other fusion reactions, and make devices utilizing these embodiments readily usable in devices that are closely associated with living entities, e.g., a pace maker. Thus, the present inventions, among other things, solve these needs by providing the articles of manufacture, devices and processes taught, disclosed and claimed herein. Thus, there are provided the methods, systems, articles and devices of the present specification, drawings and claims. In general, the present inventions relate to methods, apparatuses, devices, and systems for creating, measuring, controlling, conducting, and optimizing fusion activities of nuclei. In particular, the present inventions relate to, among other things, fusion activities that are conducted individually on a very small scale; and for the utilization of the energy, materials, and particles that are produced from these small-scale fusion activities. The present inventions further related to, among other things, small devices for causing and controlling these small fusion activities, and utilizing the products of these fusion activities, as well as, the aggregation of these smaller devices and the utilization of the aggregation. Generally, the present methods, apparatuses, and systems utilize the creation of submicron regions, and preferably nano regions (e.g., about one cubic nanometer, nm3, 10−27 m3), or smaller, of high charge densities to provide for controlled fusion reactions, and preferably with simple containment schemes (without the need for any complicated containment schemes), and more preferably without the need for any magnetic fields. Further, embodiments of the present inventions create or modify quantum and other effects to provide for, or enhance, the fusion reaction. In general, embodiments of the controlled fusion devices cause electrons to form an area of high charge density associated within a base structure containing the reactants. In an embodiment the base structure has, is, or forms a lattice, mesh, cage, pores, other substructures, and combinations and variations of these. The base structure, and preferably the substructure, holds, carries, encapsulates, encompasses, replenishes, exposes, contains, supports, maintains and combinations and variations of these reactants. The high charge density associated with the base structure can be provided by causing the electrons to move in a manner that results in their collection, agglomerating, coming together, increasing density and combinations and variation of these. Embodiments of the base structure material include, for example palladium, tungsten, boron hydride, titanium, tantalum, getter materials for hydrogen and low molecular weight gasses, and other materials that can support or carry the fusion fuel. The base structure may be a composite material, an alloy, a metal-ceramic, it may contain layers, the layers may be of the same or different materials, the layers may have the same or different substructures, initially underlying layers may over time become exposed to the reaction as the device operates, and combinations and variations of these and other configurations. Coatings may be used on the surface of the base structure, for example, gold, copper, silver or other conducting materials, and preferably materials having good conductivity, and having low resistance. Embodiments of the base structure have a discontinuity. This discontinuity can be an area of discontinuity, or more preferably one or more points of discontinuity (It being understood that the point(s) may still have some area, but as used herein the point(s) of discontinuity generally refers to a generally circular shape, generally square shape, generally rectangular shape, generally elliptical shape or other shape having an area of about 1 μm2 or less, about 500 nm2 or less, about 100 nm2 or less, 50 nm2 or less and preferably about 10 nm2 or less). Generally, this discontinuity is associated with, preferably adjacent, and more preferably central to the area of high electron charge density. The discontinuity may be a knife edge, it may be an annular knife edge, and preferably it may be the tip, e.g., point, of a tapered member, such as a solid or tubular nano-needle. The base structure may contain one, two or more discontinuities. When multiple discontinuities are present they may be the same or different, for example, in terms of shape configuration, intended reactants or other attributes. The fusion fuel may be any of the materials identified in this specification, as suitable for a fusion reaction or known to be useful in such a reaction, or later discovered to be useful, that can be loaded or otherwise incorporated into, or held by, the base structure, and more preferably the substructure of the base structure. Preferably, the fusion fuel is, for example hydrogen, deuterium, Boron-11, Helium-3, and mixtures of these. The fusion fuel is loaded or reloaded into the base structure. Preferably, the fusion fuel is loaded or reloaded into the discontinuity, and most preferably is load into the area where the high electron density will be present. Thus, in a preferred embodiment the fusion fuel is heavily loaded into the volume of the base structure that is in the area of the discontinuity and the area of high electron density, with the fusion fuel being held by the substructure. It addition to the fusion fuel being preloaded into the base structure, the fusion fuel can be added continuously, batch wise, generated in situ during the fusion reaction (e.g., generation of 3He), between operations and combinations and variations of these. Thus, for example, a palladium tubular nano-needle base structure, having a closed tip to a needle point, can have its inner space filled with excess hydrogen (or in fluid communication with a source of hydrogen) so that as the hydrogen is depleted during operation the excess hydrogen will migrate, e.g., getter, into the base structure and thus re-load the structure with fusion fuel. In an embodiment, the device can be operated without reloading or replenishing of the fusion fuel in the base structure. The device could be created with many base structures, only some of which operate at any given time, wherein the additional base structures would be activated when the fusion fuel is fully or partially depleted from the base structures that had previously been activated. Such an device would include a monitoring and control mechanism to successively turn off and on base structures in a desired manner. The volume of fusion fuel, e.g., hydrogen to the volume of base structure material, e.g., palladium, can be significantly larger, providing advantages to the fusion reaction. The volume of fusion fuel can be 2× larger or more than the volume of base structure material, it can be 3× larger or more, it can be 5× larger or more, and it can be 7× larger or more, depending upon, among other things, the particular fusion fuel(s) used, base material used, and substructure present. For hydrogen fuel, palladium base structure embodiments, the hydrogen can be loaded to 8× the volume of the palladium. Preferably, the fusion fuel can be loaded or reloaded into the base structure to particle densities of 1015/cc or more, 1018/cc or more, 1020/cc or more, 1022/cc or more, and more preferably about 1023/cc. It being noted that the fusion fuel densities of the present inventions are substantially greater than the densities obtained in the larger magnetic containment fusion devices, such as the Tokamak reactors (reported to be limited to particle densities of 1014/cc). The fusion fuel can be loaded or reloaded into the base structure by gettering, provided that the base structure-fusion fuel type exhibit this effect. The fusion fuel can be loaded or reloaded by any means or technique known to the art, or later developed, to incorporate or include smaller atomic scale particles into a larger matrix or supporting structure. The fusion fuel itself, may also be the base structure. The region of high electron density can be provided by using a microwave generator, radio frequency (RF) wave generator, or similar device, associated with the base structure. In operation, the high electron density generator causes the electrons to move in a first direction along generally the surface of the base structure toward the discontinuity (forward electron flow), and then quickly reverses the flow of the electrons away from the discontinuity (reverse electron flow). In this manner the forward and reverse electron flows along generally the surface of the substructure creates a high electron density at the discontinuity. The base structure can be coated with a material to enhance or facilitate this flow of electrons along its surface, such as a gold coating, copper coating, silver coating or a coating of other conducting materials, and preferably materials having good conductivity, and having low resistance. This area of high electron density is present, e.g., exists, at its peak periodically. Typically the periodicity of the high electron density peak is at about the same frequency as that of the high electron density generator; although there may be doubling, and other effects that result in a differences between the two. For example the generator may operate at a wavelength of from about 10 microns to about 0.1 micron. The generator can also operate at wavelengths of x ray and gamma ray to reach higher electron densities. The power for these generators is minimal, requiring about 1 mW to about 10 mW, and generally less than about 1 mW per discontinuity. A laser may also be directed on the discontinuity and establish a similar forward and reverse flow of electrons to establish an area of high electron density peaks. Laser wavelengths of from about_10 microns_ to about_0.1 micron_, The laser power for the laser beam can be from about_1_nW to_1_mW, about_1_mW to about_10_mW and generally less than about_1_mW. The base structure can be coated with, or made from a material, that is selected to optimize the laser material interaction and more preferably to optimize both the laser material interaction and the flow of electrons. In addition to the laser, microwave generator and RF generator, other manners of, devices for, generating the region of high density electrons can be used, for example magnetrons with cavities which can bundle electrons together to high densities or nonlinear effects in an electron-beam plasma where the electron wave can collapse three dimensionally to very small locations with high electron densities. The region of high density electrons, in particular embodiments, can have particle densities of 1015/cc or more, 1018/cc or more, 1020/cc or more, 1022/cc or more, and about 1023/cc or more. The electric field for these regions can be greater than about 108 V/m (volts/meter), greater than about 109 V/m, greater than about 1010 V/m and greater than about 1011 V/m. The fusion fuel material may be, for example, hydrogen-1, boron-11, lithium-6, lithium-7, deuterium, helium-3, nitrogen-15, tritium. It may be advantageous to use molecular compounds that are good electron emitters, for example boron nitride or lanthanum hexaboride or cerium hexaboride and combinations and variations of these and other types of materials. It should be understood that the figures in this specification are generally representative of very small components (e.g., micron, nano, and pico sizes). Thus, the figures are not to scale, and are illustrative of the relationships, structures and components of the various embodiments, and should be viewed as part of, and in the context of, the entirety of the teachings of this specification. Turning to FIG. 1 there is shown a perspective view of a section of an embodiment of a base structure 110 for use in an embodiment of a fusion device of the present invention. The base structure 110 is a tubular electrode 100, which has a tapering section 101, to form a tip 102, e.g., a point, which is a discontinuity. When a high-density electron generator (not shown) is applied to the electrode 100, electron movement as shown by double arrow 103 occurs. With the arrow 103a toward the tip 102 being the forward electron movement and the arrow 103b toward the tubular section being the reverse electron movement. The area of high electron density is shown as 102 and the high electric field region is 104. Although it is presently believed that this is primarily a surface effect, the scope of protection to the present inventions should not be so limited. The movement of the electrons is preferably collective, coherent, and both. Thus, it is theorized that this collective and coherent motion of electrons is similar to, and may be, the type of electron movement exhibited in superconductive materials. This collective and coherent electron motion, of the present inventions, takes place at room and elevated temperatures. Thus, the present invention provides for ambient temperature and above superconductivity, and superconductivity like behaviors in the movement of electrons. Turning to FIG. 1A there is shown a cross sectional schematic view of the tip 102 and tapering section 101 of electrode 100. The substructure 105 of the base structure 110, has fusion fuel materials, e.g., 106a, 106b, 106c, 106d. In operation it is believed that the creation of the area of high electron density enables, facilitates, or furthers the fusion reaction of the fusion fuel. It is theorized that among other things, the presence of the high electron density lowers the coulomb barrier, and preferably creates a negative well, that permits the fusion fuel, e.g., 106b, 106c, to fuse. Further, it is theorized that the highly localized electron density, creates a ponderomotive force that drives the fusion fuel together, and also drives the electrons into the substructure of the base material, enhancing the fusion reaction of the fusion fuel. In one of the embodiments of the present invention, as shown in FIG. 7, there is a three layer structure that will produce large electric field enhancement. The geometry of generalized discontinuity is shown in FIG. 7. By using a femtosecond laser, the local surface plasmon (LSP) is excited. By optimizing parameters, a large field enhancement at resonant frequency was observed. Calculation result shows that near the Pd layer, the field enhancement induced high electric potential which have the same magnitude of coulomb barrier between two deuterium nucleis, which means it can overcome the coulomb repulsion and extremely enhance the probability of fusion reaction. In another embodiment, the excitation source, e.g. laser, diode laser, or RF/microwave generator, is integrated in or near the base structure of the device to optimizing coupling of radiation and miniaturization of the device. The submicron controlled fusion device can be associated with a device for generating electricity. The devices would include, for example, sensor chips that have been adapted to generate a current, voltage or both in response to the heat generated by the fusion reaction, in response to the charged fusion product particles generated by the fusion reaction and both. Thus, as examples, (A) a radiation detection type diode can be adapted to produce electricity from the fusion products, (B) a thermoelectric device could convert a portion of the heat energy into electric current, (C) a fluid could be forced to flow, expand or incur a phase change so as create some electricity or other useful energy. The devices for generating electricity from the controlled fusion reaction could also include (D) mechanisms to slow the resulting charged particles by an electromagnetic field so as to effect a direct conversion to electricity and (E) mechanisms to put small electrodes adjacent to the discontinuity so as to have charged particles collide with one or the other of the electrodes and thereby induce a current or to recharge a connected battery or capacitor. The foregoing means could include combinations of the foregoing. For example, if the means of direct conversion to electricity was only partially efficient, it could be deployed in combination with a thermoelectric device to create electricity from the heat remaining after deployment of the direct conversion mechanism. Although not required, the electrodes of the device could also be located in, or have a source of fusion fuel around their exterior, such as being contained in a closed micro-vessel, filled with, or having hydrogen flowed through it. Generally, the term “about” is meant to encompass a variance or range of ±10%, the experimental or instrument error associated with obtaining the stated value, and preferably the larger of these. Embodiments of the present inventions may utilize quantum, electrostatic, mechanical, or other effects including, among other things, large E-fields, high electron densities, ponderomotive forces, modification or change of the Coulomb barrier, modification or change of the reaction cross section, space charge or electron shielding effects, the use of neutrals, ion-neutral coupling, nuclear magnetic moment interaction, spin polarization, magnetic dipole-dipole interaction, high particle density materials, compression forces associated with centrifugal forces or ponderomotive forces, phase transitions of hydrogen, positive feedback mechanisms, and modification and variations of these and other effects. All references in this specification to modifying, changing, lowering, reducing or eliminating the barrier include means by which the Coulomb barrier is offset by, or its effect is reduced by, the presence of one or more other features (e.g., high electron densities) even though the Coulomb barrier itself (independent of such features) remains unchanged. It is noted that there is no requirement to provide or address the theory underlying the novel and groundbreaking fusion methods, devices and systems that are the subject of the present inventions. Nevertheless, these theories are provided to further advance the art in this important area. The theories put forth in this specification, unless expressly stated otherwise, in no way limit, restrict or narrow the scope of protection to be afforded the claimed inventions. These theories many not be required or practiced to utilize the present inventions. It is further understood that the present inventions may lead to new, and heretofore unknown theories to explain the fusion methods, devices and system of the present inventions, and such later developed theories shall not serve to diminish or limit the scope of protection afforded the claimed inventions. Modification or Change of the Coulomb Barrier In order to fuse, two nuclei must come into contact; however, nuclei are very small (on the order of 10−15 m), and because they are positively charged, they are electrostatically repulsed by one another. The potential energy curve of a two particle system 501 in which a first nucleus 502 is approaching a second nucleus is illustrated in FIG. 5A. On the horizontal axis, x is the distance between the two nuclei. The system potential 501 is near zero when the first nucleus is located far away from the second nucleus, and increases as the first nucleus approaches the second nucleus. The system potential 501 is the sum of the repulsive (positive) Coulomb potential and the attractive (negative) strong nuclear force potential. Once the two nuclei are very close, at distance xn apart (where xn is approximately equal to the sum of the radii of the two fusing nuclei), the system potential 501 becomes negative due to the effect of the strong nuclear force. Thus, the term “Coulomb barrier” is used to describe the difficulty of bringing the two nuclei into contact, either by getting through or getting above the potential curve shown in FIG. 5A. FIG. 5A labels the kinetic energy of the two-nucleus system, “ϵ,” as expressed by:ϵ=½mrν2 where ν=ν1−ν2, ν1 and ν2 are the velocities of the two nuclei, and mr is the reduced mass of the system, given by: m r = m 1 m 2 m 1 + m 2 where m1 and m2 are the masses of the two nuclei. Classical mechanics holds that, when the nuclei are approaching one another, ϵ must be greater than the height of the Coulomb barrier for the nuclei to come into contact. However, quantum mechanics allows for “tunneling” through a potential barrier, thus making fusion reactions possible when ϵ is below this threshold. However, the magnitude of the barrier still presents an impediment to tunneling, such that reactions with larger Coulomb barriers (e.g., higher, wider, or both) are generally less likely to occur than those with smaller barriers. Embodiments of the present invention may lower or reduce the Coulomb barrier, and may eliminate it to the extent of creating a well, by creating, modifying, or utilizing effects that have negative (attractive) potentials. Such a negative potential is illustrated in FIG. 5B. In this figure, a negative potential 505 is shown, and the additive effect of the negative potential 505 and the initial system potential 503 creates a new, resultant system potential 504, in which the Coulomb barrier is lower. Thus, for example, embodiments of the present invention may lower or reduce the Coulomb barrier through the use of effects such as: space charge or electron shielding effects; large E-fields, high electron densities, the use of neutrals; ion-neutral coupling; or nuclear magnetic moment interaction, spin polarization, or dipole-dipole interaction effects; and combinations and variations of these and other effects. FIG. 5C illustrates the resultant system potential 504 that arises from combining the initial system potential 503 with ponderomotive force 506, an electron shielding potential, e.g., the high density electrons and large E-field 507, and a nuclear magnetic moment interaction potential 508. Each of these alone and in combination reduces the Coulomb barrier, which makes it easier for the nuclei to tunnel through or overcome the potential barrier, thus increasing the probability that the fusion reaction will take place. Ponderomotive Force In general, a ponderomotive force is a force that is created from an oscillating electric field. The ponderomotive force affects both positive and negative charged particles the same, i.e., moving them in the same direction. Thus, the ponderomotive force is a rare case where the sign of the particle charge does not change the direction of the force, unlike the case with the Lorentz force. Thus, in embodiments of the present invention the ponderomotive force has the effect of crushing, or compacting the substructure containing the fusion fuel forcing the fusion fuel into contact and to fuse. The ponderomotive force Fp is expressed by Fp = e 2 ∇ E 2 4 m ω 2 where e is the electrical charge of the particle, m is the mass, ω is the angular frequency of oscillation of the field, and E is the amplitude of the electric field. From this equation it is readily seen that the high E results in a strong ponderomotive force. However if the E field is at a high frequency, such as above the ion plasma frequency, then only the light electrons will be influenced by these fields. The heavier ions will nonetheless be influenced by the electron motion through the ambipolar electric field, which is the DC field generated when electrons are separated from the ions. Electron Shielding An advantage of using weakly ionized plasma is that the reactants largely comprise neutral atoms. The electrons interposed between the nuclei shield the repulsive Coulomb force between the positively charged nuclei. This phenomenon affects the Coulomb repulsion and may reduce the Coulomb barrier. In addition, using reactants that are highly efficient electron emitters introduces a cloud of electrons, a negative space charge, between the positively charged reactants, which further enhances this shielding effect. In an embodiment of the present invention, the high density electrons are driven by ponderomotive forces into the substructure, amongst the fusion fuel. It is believed that these electrons in the substructure provide an electron shielding effect which reduces the Coulomb barrier and enhances the fusion reaction rate. In a further embodiment, there is present in the system a material with a geometry or surface profile that creates non-uniform electric fields. Thus, by way of example, a surface with a dendritic profile may be desirable to generate very high localized electric fields for fusion. Nuclear Magnetic Moment Interactions Many nuclei have an intrinsic “spin,” a form of angular momentum, which is associated with their own internal spinning motion and resultant current. The magnetic field lines form as though one end of the nucleus were a magnetic north pole, and the other end were a magnetic south pole, leading the nucleus to be referred to as a “magnetic dipole,” and the strength and orientation of the dipole described as the “nuclear magnetic moment”, which is represented as a vector. Nuclear magnetic moments play a role in quantum tunneling. Specifically, when the magnetic moments of two nuclei are parallel, an attractive force between the two nuclei is created. As a result, the total potential barrier between two nuclei with parallel magnetic moments is lowered, and a tunneling event is more likely to occur. The reverse is true when two nuclei have antiparallel magnetic moments, the potential barrier is increased, and tunneling is less likely to occur. When the magnetic moment of a particular type of nucleus is positive, the nucleus tends to align its magnetic moment in the direction of an applied magnetic field. Conversely, when the moment is negative, the nucleus tends to align antiparallel to an applied field. Most nuclei, including most nuclei which are of interest as potential reactants, have positive magnetic moments (p, D, T, 6Li, 7Li, and 11B all have positive moments; 3He, and 15N have negative moments). In an embodiment of a controlled fusion device a magnetic field may be provided that aligns the magnetic moments in approximately the same direction at every point within the device where a magnetic field is present. This results in a reduction of the total potential energy barrier between nuclei when the first and second working materials have nuclear magnetic moments which are either both positive or both negative. It is believed that this leads to an increased rate of tunneling and a greater occurrence of fusion reactions. This effect may also be referred to as spin polarization or magnetic dipole-dipole interaction. In addition, the gyration of a nucleus about a magnetic field line also contributes to determining the total angular momentum of the nucleus. Hyperpolarization of Nuclei. Nuclei such as 3He can be polarized by collisions with alkali metal vapors or directly by RF fields in a weak magnetic field. This process can bring more than 90% of 3He atoms all aligned along the same direction, thereby increasing the attractiveness among them. The 3He 3He fusion reactions lead to the formation of 4He atom plus two energetic protons, a very desirable fusion reaction, because there are no neutrons in the product and the energy yield is very high, above 10 MeV. Thus, although magnetic fields are not necessary with preferred embodiments of the present invention, e.g., “amagnetic”—a device free of additional, induced or provided magnetic fields, to obtain a controlled fusion reaction, they may be utilized to enhance, or optimize the fusion reaction and the performance of the device. Modification or Change of the Reaction Cross Section The probability of a fusion reaction between a pair of nuclei is expressed by the reaction cross section, “σ.” The cross section is typically measured in experiments as a function of ϵ (energy) by bombarding a stationary target of nuclei with a beam of nuclei. The cross section is normally defined such that: σ = B I where B is the number of reactions per unit time per target nucleus, and I is the number of incident particles per unit time per unit target area. When cross section is defined and measured in this way, each fusion reaction will have a certain, specific cross section at a particular ϵ for a given system. The fusion reaction rate per unit volume in a particular reactor is normally described by: R = n 1 n 2 1 + δ 12 〈 σ v 〉 where δ12=1 if the first nucleus and the second nucleus are the same type of nuclei (e.g., deuterium is being fused with deuterium) and δ12=0 otherwise, and σν is the “averaged reactivity” of the system, defined as:σν=∫0∞σ(ν)νƒ(ν)dνwhere ƒ(ν) is the distribution function of the relative velocities, normalized in such a way that ∫0∞ƒ(ν)dν=1. When the second nucleus is at rest, σν=σν; however, the preceding definition accounts for situations in which the second nucleus moves, and each pair of interacting nuclei may have a different relative velocity ν. The rate of fusion energy release is then given by: dW dt = REwhere W is the total fusion energy per unit volume released and E is the energy released by a single reaction (E=8.68 MeV in the case of p-11B fusion). The probability of the two nuclei coming into contact through a quantum tunneling event is described by the tunneling barrier transparency, “T,” such that a higher value of T corresponds to greater likelihood of tunneling. Since tunneling is the primary mechanism by which fusion occurs, cross section is proportional to T (σ∝T). T is approximated by: T ≈ e - ϵ G ϵ where e is Euler's number, and ϵG is the modified energy of the Coulomb barrier. When the two nuclei are a distance x≥xT apart, ϵG is described by:ϵG∝∫xnxTq1φ(x)dx where, q1 is the charge of the first nucleus, φ(x) is the potential expressed as a function of x, and xT is the classical turning point at which φ(xT)=ϵ. As a result of these relationships, a higher value of φ (e.g., larger Coulomb barrier) will tend to translate into higher ϵG, which in turn will tend to lead to lower T, lower σ, lower R, and, when E>0, lower dW dtfor any specific system. Thus, systems in which potential φ is high will tend to experience fewer fusion events and lower fusion energy release rates, and systems in which potential φ is low will tend to experience more fusion events and higher fusion energy release rates. As discussed above, reducing the Coulomb barrier is equivalent to reducing potential φ, and embodiments of the present invention may employ these techniques to generally increase the cross section, σ; this also increases the fusion reaction rate.High Particle Density An embodiment of the present invention, instead of creating a strongly ionized plasma to obtain a high particle density, loads the substructure with significantly more, e.g., high density of, particles than is believed to be obtainable by any plasma. As the particles are essentially held in a solid, or are a solid material, this approach does not give rise to plasma instabilities, and so particle density (n1 and n2) can be many orders of magnitude higher than with a strongly ionized plasma, and many orders of magnitude higher than obtainable with weakly ionized plasma where its neutral density is at least 1017/cm3. In an embodiment of the present invention, particle density is throughout the entire volume of the device. Further, the compression induced by the centrifugal force leads to an increased density of particles in the region in which fusion events are expected to be concentrated, leading to densities of about 1018/cm3 or higher in the region of the device where reactants are concentrated. In addition, an embodiment of the present invention uses boron compounds in a solid form, which have a particle density on the order of 1023/cm3. Thus, in the region where fusion reactions are thought to be concentrated, the present invention achieves particle densities in a physical container many orders of magnitude greater than other methods known in the art (for example, it is believed that Tokamak reactors have not achieved sustained particle densities greater than about 1014/cm3). An advantage of the present inventions is that they effectively suppress radiation losses due to electron bremsstrahlung. Conventional fusion reactors such as Tokamaks employ hot, highly ionized plasma. Electron-ion interaction, resulting in bremsstrahlung and cyclotron radiation, is a significant source of energy loss and is one of the reasons such systems have not been able to satisfy the Lawson criterion. However, the high-density, lightly ionized, and colder plasma employed in embodiments of the present inventions suppresses electron mobility and greatly reduces radiative losses. Phase Transition of Hydrogen Under High Pressures Hydrogen atoms under high pressure compression can become liquid or solid metals, depending on the compressional forces and their states of rotation. In either the liquid or solid states, the density is many orders of magnitude higher than that in the gaseous state. The total reaction rate will be correspondingly higher according to the product of the particle densities of the two reactants. In addition, metallic hydrogen becomes highly conductive or even a superconductor with zero resistance. This increases the overall conductivity of the entire system, lowering the resistive loss and the input energy required. Thus, the overall efficiency of such a system is greater, making it easier to attain a large Q factor and the corresponding energy gain. Positive Feedback The present invention may generate particles during operation. In some cases these particles may provide benefit to the device's function. In embodiments utilizing ionized particles, the creation of ionizing radiation may further enhance additional fusion by increasing, modifying, maintaining, or improving the ionization or a working material or plasma. The key feature of this new fusion concept depends on the screening effect of electrons around the neutrals. It is expected that the fusion process will release more electrons through heating or collisions with fusion products. These processes could cause larger electron density fluctuations, including Langmuir collapses [1, 12]. This type of positive feedback generates stronger screening effects and could create sustainable fusion process for energy production. The following examples are provided to illustrate various embodiments of controlled submicron fusion methods, devices and systems of the present inventions. These examples are for illustrative purposes, and should not be viewed as, and do not otherwise limit, the scope of the present inventions. Turning to FIG. 2 there is shown a schematic of a submicron controlled fusion device 200. The device 200 has an electrode 201a, which is part of the base structure 201. The device 200 has a second electrode 201b, which is also part of the base structure 201. The electrodes 201a and 201b have substructures that contain the fusion fuel. The electrodes 201a, 201b, have tips 203a, 203b, which are discontinuities. Electrode 201a is connected to high density electron generator 204 by lead line 202a. Electrode 201b is connected to high density electron generator 204 by lead line 202b. The high density electron generator 204, in the embodiment of this example is an RF generator operating at 1.63 GHz. The dimensions for the device 200 are provided in the figure and are in inches. Turning to FIG. 3 there is shown a schematic representation of the electron fields that will be generated by the device 200. FIG. 3 is a plan view, looking down the y-axis, of the tip 203b and electrode 201b. It being understood that a similar electron field will be generated by electrode 201a. The E fields generated are represented by the various color areas, area 220 is 3000 αV/m, 221 is 2500 αV/m, 222 is 2350 αV/m, 223 is 1500 αV/m, and 224 is 650 αV/m where α is a proportional constant which depends on the generator voltage. The embodiment of example 1, has the electrodes made from palladium, and are coated with a thin layer of gold. The fusion fuel is a 50:50 mixture of hydrogen-1 and deuterium, and loaded to a particle density of 1022−/cc. The device of Example 2 has been operated in a cloud chamber to test the behavior of electrons. According to theory and past experiments the cloud chamber will show the emission of fusion product particles from the electrodes. The fusion products will include helium-3. A submicron controlled fusion device is associated with a detection chip that has been adapted to convert the fusion product particles into electricity. The electrical generation assembly of Example 4 powers a circuit in an electronic device. The electronic device can be a cell phone, a hearing aid, a pace maker, a glucose pump, an in situ diagnostic and metering system for the sensing of conditions, and delivery of medicaments. In embodiments, the device could be an independent unit with a primary function of providing electricity and/or heat to some other device (e,g., computers, cars, homes, etc.) including, by being connected to provide electricity and/or heat temporarily to one device (e.g., a car) and then disconnected from that device and connected to another device (e.g., a home). The development of such independent devices could also allow the rollout of electricity to lesser developed countries without the concurrent need to build transmission and distribution systems in the same way that lesser developed countries were able to build communications networks primarily by wireless means without having to build the wire infrastructure that the developed countries had built for communications prior to the development of wireless technologies. Turning to FIG. 4, there is shown a schematic diagram of a submicron fusion device of the present inventions in a vacuum chamber testing assembly. Turning to FIG. 6, there is shown a perspective schematic view of an array 600 of several hundred substrates e.g., 601a, 601b that have been arranged on a planer support structure 603. The substrates each have a discontinuity, e.g., 602, which in this embodiment is a micro-point or tip. Each substrate, which in this embodiment is an electrode loaded with a fusion fuel, is subjected to a high electron density generator, which when activated drives the fusion reaction. The collective energy from the array can then be converted into electrical energy, or other forms of energy as may be required. The substrate in this embodiment can be Silica, Silicon carbide, or other suitable substrate. We assume a model of a dipole antenna driven by an oscillating source of peak voltage of Vosc=300V at a frequency of 2 GHz. During each cycle electrons are driven to the tapered tip of a dipole which has a radius of a=10 nm and a lateral area of A=0.1 u×0.1 u (where u is one micron). The oscillating electric field, Eosc, is given approximately by Vosc/a. This high frequency field acts only on electrons and gives rise to a ponderomotive force Fe as a result of the gradient of the electric field intensity7 Fe=−ωpe2/ω2[grad εoEosc2/2] newtons/m3 Electrons undergoes a drift motion driven by this ponderomotive force Fe; the ambipolar electric field generated by the separation between electrons and ions transmit the same force to ions. The force experienced by an ion, fion, is obtained by dividing the ponderomotive force, Fe, by the density of ions:fion=−ne/ninf[grad εoEosc2/2] newtons, where nf=εoω2me/e2 For ne/ni˜1,nf=1.6×1025/m3, taking gradient length˜10 nmfion˜8.8×10−121030/3.2×102510−8˜27 N. The equivalent potential felt by the ion is then D=fionx/q=2.7×106 volts, the distance x between two D atoms being taken to be 10−14 m where the repulsion barrier is greatest. The equivalent potential is 2.7×106 volts which is of the order of the Coulomb barrier, resulting in fusion through quantum tunneling. Consider nano-Au particles of 30 nm diameters. Lasers of wavelengths corresponding to 2-4 eV energy are used to excite surface plasmons. Laser was focused onto surface of nano-particles and excite Surface Plasmons. Enhancement of near electric field was observed to be 100 from plasma resonance. Consider a pulsed 1 ns and 1 J laser focused to 50 nm: from balance of energy flowcεoE2osc=Po/A watt/m2 E2osc˜1.5×1026 V2/m2 Taking the observed enhancement of E by 102 via SP resonance E2osc˜1030 V2/m2 Laser-excited E2 is 109 larger than previous electric dipole excitation at microwave frequencies. However the number density of ions is larger. The laser excitation might be more efficient than microwave excitation. It can also be more easily implemented experimentally. In an embodiment the fuel loaded into the base structure is a radioisotope. In this embodiment the decay of the radioisotope is regulated. In general, the Coulomb barrier acts as an impediment to the decay of radioisotopes. The mechanisms described in these embodiment could be deployed to reduce the Coulomb barrier so as to cause the decay of a radioisotope to occur at a faster rate than the natural “half-life” for such radioisotope. The ability to increase the rate of decay of a radioisotope could be useful for the treatment of fission nuclear waste. One particularly favorable application would be to isolate and treat the most dangerous materials (whether elements or isotopes) with long half-lives so as to reduce such materials to stable (or at least less dangerous) elements or isotopes and to avoid having to construct storage mechanisms that need to be effective for very long periods (often many generations). The ability to increase the rate of decay of a radioisotope could also be useful to create a device that would rely on the release of charged energetic particles for the production of electricity. By being able to increase the rate of decay of a radioisotope, the power output of the device could be materially increased without having to increase the amount of radioisotope that would need to be loaded into the device. In an embodiment a computer simulation program is used to simulate fusion reactions, determine the characteristic of such reactions, determine candidates for fusion reactions, simulate and model the events arising from utilization of the sub-micron and other fusion processes and devices disclosed herein and incorporated herein by reference. The computer simulation system has a computer, having a processor, a memory or storage and a human machine interface. The system has a program, data and both, associated with (e.g., the program, and the data, could be resident on the machine, on a server, in the cloud, etc.) it. Preferably the program has the following packages to provide calculations and present predictive data and information. These packages may be based upon actual data that is provided or stored in the system, from published data and from observed data. The program preferably has the following: a package for utilizing, modeling and both, high speed cylindrical rotation, and associated centrifugal forces; a package for utilizing, modeling and both, an array of electron emitters, which can be programmed to control the number of emitted electrons; a package for utilizing, modeling and both, fusion reactions and interactions, in the sub-atomic domain, including the collective behavior of electrons, ions and neutrals, the dynamics and interrelationship of the particles; a package for utilizing, modeling and both, diagnostics such as NMR, mass analyzers, chemical analyzers, and optical analyzers; a package for utilizing, modeling and both, electromagnetic radiations, basic interactions and controls for these radiations; a package for utilizing, modeling and both, energy production products to be (that are capable of, or their capability to be) transformed to electricity; a package for utilizing, modeling and both, heat energy and accounting for this energy and its management and utilization; and package for utilizing, modeling and both, the transformation between heat and electrical power, which would include thermoelectric effects. The various embodiments of devices, methods and systems set forth in this specification may be used for various operations, other energy production, including the formation of materials. Additionally, these embodiments, for example, may be used with systems and operations that may be developed in the future; and with existing systems and operations that may be modified, in-part, based on the teachings of this specification. Further, the various embodiments set forth in this specification may be used with each other, in whole or in part, and in different and various combinations. Thus, for example, the configurations provided in the various embodiments of this specification may be used with each other; and the scope of protection afforded the present inventions should not be limited to a particular embodiment, configuration or arrangement that is set forth in a particular embodiment, example, or in an embodiment in a particular Figure. The invention may be embodied in other forms than those specifically disclosed herein without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. |
|
abstract | A new nuclear fuel element has been developed to be used in particular in fourth generation gaseous heat exchanger reactors working with a fast neutron flow. |
|
051630788 | summary | BACKGROUND OF THE INVENTION a) Field of the Invention This invention relates to a multilayer film reflecting mirror suitable to an optical element for use in an X-ray optical system. b) Description of the Prior Art Recently, attention has come to be attracted to an artificial grating, as a reflecting mirror for soft X rays, comprising thin films laminated with film thicknesses between several and several hundred angstroms. It is usual for the lamination technique of the artificial grating to alternately laminate the thin film of a substance A with a low refractive index and that of a substance B with a high refractive index, over the range of several tens of layers to several hundred layers, in a soft X-ray region. For instance, W (tungsten), Ni (nickel) or Mo (molybdenum) is known as the substance A, while C (carbon), B (boron), Be (beryllium) or Si (silicone) as the substance B [T. Namioka, Revue Phys. Appl., Vol. 23 (1988), pp. 1711-1726]. In the case where the substances A and B are alternately built up, various methods are known, for example, of laminating periodically individual substance layers whose film thicknesses are made constant and of laminating the film layers which are optimized for each layer [Takeshi Namioka et al., "Developments of Light Sources and Optical systems for Soft X-ray Lithography", Report of Research by Scientific Research-Aid Fund for the 1985 Fiscal Year (Test Research (2)), pp. 1-36, 1986]. Additionally, for the purpose of preventing individual substances from diffusing at the interface between the layers of the substances A and B, an artificial grating is also devised which comprises at least three kinds of substances by providing a buffer layer, between the layers of the substances A and B, constructed of other substance (U.S. Pat. No. 4,693,933). For a film fabrication, approaches, such as electronic beam evaporation, sputtering and laser beam techniques, are known and the examples of the artificial grating using these film fabrication techniques are also reviewed [H. Yamashita, O plus E, Feb., 1987, pp. 67-83; T. Namioka et al., Journal of the Japanese Society of Precision Engineering, Vol. 11 (1986), pp. 16-18]. To secure a sufficient reflectance in the soft X-ray region, however, a working technique with a high degree of accuracy is required and hence there is the report that a surface roughness of 1 nm or less is required for a substrate and that of 1.4 .ANG. or less for the interfaces between individual layers (U.S. Pat. No. 4,727,000). Consideration is also given to theoretically design and evaluate the reflectance of the multilayer film reflecting mirror making use of the artificial grating mentioned above, and in general, when X rays in a long wavelength region are incident and in a grazing incidence region, the difference in reflectance between a design value and a measured value is small. In such instances, it is effective to apply Fresnel's recurrence formula as a theoretical model. FIG. 1 shows an optical model of the multilayer film reflecting mirror, in which reference symbol R.sub.m-1 represents the complex amplitude reflectance in the case where the substances are laminated to the (m-1)-th layer for film fabrication and N.sub.m-1 the complex index of refraction of the (m-1)-th layer. The complex amplitude reflectance in the case where the substance having a complex index of refraction N.sub.m is further laminated thereon, with a thickness of d.sub.m, is designated by R.sub.m, which is given by ##EQU2## where r.sub.m is the Fresnel coefficient relating to a vacuum of the m-th layer of a new lamination, .delta..sub.m is the phase difference between both ways in the m-th layer, and i is the unit of the imaginary number [T. Namioka, Revue Phys. Appl., Vol. 23 (1988), pp. 1711-1726]. For the p-polarized light component. ##EQU3## For the s-polarized light component, ##EQU4## where .phi. is the angle of incidence at which X rays are incident on the multilayer film through the vacuum and .phi..sub.m is the complex angle of refraction. Also, when the wavelength is taken as .lambda., the phase difference .delta..sub.m is given by ##EQU5## If, therefore, the substrate not shown is taken as m=0 and Equation (1) is used, in turn, from the 0-th layer to the m-th layer to determine R.sub.m, a desired reflectance of the multilayer film reflecting mirror can be calculated. FIG. 2 shows the design value and the measured value of the reflectance in the case where X rays with a wavelength of 1.5 .ANG. are incident while the angle of diffraction is made to change, on the multilayer film reflecting mirror comprising W of a film 17.3 .ANG. thick and C of a film 34.7 .ANG. thick, built on the substrate into 11 layers. In this case, as will be obvious from FIG. 2, the difference in reflectance between the design value and the measured value is extremely small. If, however, the wavelength of X rays to be incident is shorter or X rays enter at the normal incidence, the difference will become larger. This is attributed to two points indicated below. (a) In the case of the incidence of X rays having a shorter wavelength or at the normal incidence, the film thickness per layer must be diminished. This makes it difficult to uniform the film thickness with the deterioration of reflectance. (b) In the case of the incidence of X rays having a shorter wavelength or at the normal incidence, the interference condition of the X rays become severe, with the result that the roughness of each interface is more liable to affect the X rays. Most of the multilayer film reflecting mirrors of the prior art mentioned above have been fabricated in view of the case where X rays are incident principally at a grazing angle of 20.degree. or less in the grazing incidence region or where X rays having long wavelengths of 100 .ANG. or more are incident in the normal incidence region. These mirrors can bring about the reflectance close to the design value if the roughness of the interface is sufficiently controlled. When X rays of short wavelengths are incident in the normal incidence region, however, problems are caused by the property of interference of X rays, due to the reasons of the above points (a) and (b), within the multilayer film reflecting mirror. In a multilayer film reflecting mirror illustrated in FIG. 3 which comprises the thin films of two kinds of substances A and B different in refractive index from each other, laminated alternately with the thicknesses of d.sub.1 and d.sub.2, respectively, when the thickness of a pair of layers (which will be hereinafter referred to as periodic thickness) is represented by d, the wavelength of an X ray by .lambda., and the grazing angle by .theta., Bragg's condition becomes EQU 2d sin .theta.=.lambda. (5) and the periodic thickness d is expressed by ##EQU6## In other words, the periodic thickness reduces as the wavelength .lambda. becomes short and the incident angle is small. Consequently, incident X rays interfere within the multilayer film reflecting mirror, so that the highest reflectance needs to control correctly the thickness of the multilayer film with the accuracy corresponding to the periodic thickness d. In the above case, however, no discussion is made in detail as to how the accuracy of the film thickness should be controlled under any condition. FIG. 4 depicts the design example of the multilayer film reflecting mirror comprising Ni and Sc built up of 201 layers, with the film thicknesses of 8.2 .ANG. and 11.8 .ANG., respectively. It is constructed so that when the reflecting mirror is fabricated, an actual film thickness generally have a tolerance .DELTA.d with respect to the design value of each film thickness. The tolerance .DELTA.d may be assumed to arise at random in the probability according to the normal distribution given by ##EQU7## where .sigma. is the deviation. According to Equation (7), the value of .DELTA.d of -.sigma..ltoreq..DELTA.d.ltoreq..sigma. appears in the probability of 68%. FIG. 5 shows the results of simulation of the reflectances in the cases where X rays having a wavelength of 39.8 .ANG. are incident while the incident angle is made to change, on the multilayer film reflecting mirror fabricated so that the film thickness has the tolerance .DELTA.d for the design value and where the deviation .sigma., that is, the accuracy of the film fabrication is changed. According to FIG. 5, as the deviation .sigma. increases from 0 .ANG. to 0.4 .ANG., the reflectance materially reduces, and consequently, there is the feasibility that even the reflecting mirror fabricated with a deviation of about 0.4 .ANG. cannot be utilized as a useful one. In the case where, as mentioned above, the film thickness deviates at random from the design value in accordance with the normal distribution, some multilayer film reflecting mirrors fabricated will exhibit remarkably low reflectances in view of the theory of probability. Thus, the multilayer film reflecting mirrors of the prior art in practical fabrication have been difficult to bring about the stabilization of their qualities and the improvement in a product yield. SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a multilayer film reflecting mirror which has a practical reflectance and can be fabricated in a high probability, with the resultant improvement of a product yield. To achieve this object and in accordance with the present invention, the multilayer film reflecting mirror comprises a plurality of substance layers built on a substrate to be applied to X rays having wavelengths of 100 .ANG. or less so that a deviation .DELTA. from the design value of the film thickness of each layer is controlled within a range defined by ##EQU8## where .theta. is the grazing angle of an X ray being incident and .lambda. is the wavelength of the X ray. The foregoing will be explained in detail below. FIG. 6 is a conceptional view showing the reflecting action where X rays are incident on the multilayer film reflecting mirror comprising substances A and B alternately laminated, in which reference symbols L.sub.1 and L.sub.2 designate X rays. In this figure, in order that X rays having the wavelength .lambda. interfere within the multilayer film reflecting mirror to secure a full reflectance, it is necessary to satisfy the following relationship, from Bragg's condition: EQU .lambda.=2d sin .theta. (9) where d is the periodic thickness (the sum of thicknesses of the substances A and B) and .theta. is the grazing angle. That is, in order that the optical path difference between the X rays L.sub.1 and L.sub.2 is made equal to .lambda., it is necessary to control each periodic thickness. The accuracy of this thickness control is indicated by an optical path length S along which the X ray travels one period within the multilayer film, from Equation (9), and which corresponds to the length connecting points F, G, and H in FIG. 6. Since the refractive index of the multilayer film reflecting mirror is nearly unity in the X-ray region, the optical path length S is expressed by ##EQU9## If Equation (9) is used, ##EQU10## The goodness of the interference and reflectance of the multilayer film reflecting mirror depends basically on how the thickness of each layer is accurately formed with respect to the optical path length S calculated from the incidence condition of the X ray. Further, the accuracy in fabricating the multilayer film is determined relative to the optical path length S. Hence, if the optical path length S to be calculated is obtained, the optimum design value of each film thickness will be determined, and by defining the deviation of each film thickness in the film fabrication, within a certain range, produced at random from the optimum design value on the basis of the optical path length S, the fabrication of the multilayer film reflecting mirror which has practical use can be realized in a high probability. That is, Equation (8) is obtained. Equation (8) allows the deviation from the design value, up to 3% of the optical path length S along which the X ray travels one period within the multilayer film. Thus, even though the tolerance of each film thickness is produced at random in the film fabrication while having the deviation of .DELTA. from the optimum design value, in the probability according to the normal distribution given by Equation (7), the multilayer film reflecting mirror having the reflectance of at least 50% of the design value can be fabricated in the probability of 30% or more. Also, even in a method for the design of a nonperiodic structure in which the thickness of each layer of the multilayer film reflecting mirror is optimized, the practical multilayer reflecting mirror can be fabricated on the same condition as the design of the periodic structure, provided the film thickness of each layer is set within the tolerance defined by Equation (8). Additionally, in actual coatings applied by the approaches such as electronic beam evaporation and sputtering techniques, the film thickness can be monitored within 0.1 .ANG. tolerance by the use of a crystal oscillator and an ellipsometer, so that the film fabrication is possible within the tolerance defined by Equation (8). The structure of this type of the multilayer film reflecting mirror is peculiarly suitable for the case where the reflecting mirror is formed by the multilayer film with which the substrate having a curvature is coated. As the examples of optical systems constructed using the reflecting mirrors according to the present invention, the soft X-ray imaging elements of typical Schwarzschild and Walter optical systems are illustrated in FIGS. 7A and 7B, respectively. The Schwarzschild optical system is constructed by the combination of two concave mirrors with a convex mirror, while on the other hand, the Walter optical system uses the combination of the reflecting mirrors comprised of curved surfaces represented by secondary functions of paraboloids and ellipsoids. For the soft x-ray region, each surface is coated with the multilayer film mirror in the attempt to improve the transmission efficiency of the entire optical system. With 60 .ANG. or smaller wavelengths in particular, the surface is coated with the multilayer film which utilizes W and C, and Ni excellent in optical constant as in Ni and Ti, and Ni and Sc. Each optical system of the foregoing reflects soft X rays at least twice, so that the deviation of the thickness of the multilayer film from the design value will remarkably decrease the transmission efficiency of the entire optical system. As such, the present invention contributes also to the solution of such a problem. This and other objects as well as the features and the advantages of the present invention will become apparent from the following detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings. |
054401879 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to radionuclide-emitter, voltaic-junction batteries, and, more particularly, to compact electric batteries that are powered by the combination of a nuclear radiation emitting source and a responsive semiconductor voltaic-junction for service in many applications where chemical batteries are unsatisfactory or inferior. 2. The Prior Art Compact long-life energy sources have wide applications in such fields as aerospace systems, cardiac pacemakers, computer memory maintenance, remote instrumentation, etc. Chemical batteries suffer generally from theoretical limits in the energy density that they can accommodate. Radionuclide-emmiter, voltaic-junction cells have much higher theoretical limits in energy density, in some cases more than a factor of 1,000 greater, but, in the past, have not achieved desirable high energy density and long life in practice. Major problems have been encountered in adapting such prior art cells for practical use at relatively low temperature. Silicon p-n junction cells for directly converting radiation, either visible or ionizing, to electricity were developed in the early 1950's. Specific use of radio-isotopes to power silicon p-n cells, known as betavoltaic cells, were extensively studied in the 1970's for applications where low power but high energy density were important, for example, in cardiac pacemakers. A primary motivation for these studies was that the theoretical energy density is much higher in betavoltaic cells than in the best chemical batteries, 24.3 W-h/cm.sup.3 versus 0.55 W-h/cm.sup.3 for mercury-zinc batteries. Unfortunately, isotopes that could be employed with silicon had to be limited to low energy beta emitters because of radiation damage. For example, a typical threshold energy for electron damage is about 0.180 MeV assuming an atomic displacement damage threshold of 12.9 eV. Alpha particles were known to cause so much damage that they were not seriously considered at any energy. This constraint excluded the most potent nuclide sources, and thus restricted maximum power of such devices because of limits to the specific activity achievable at maximum concentration with reasonable half-lives. In the aforementioned co-pending patent application of the inventors hereof, the invention is directed to a relatively powerful battery that operates at a temperature above the point at which damage is rectified by annealing in the voltaic-junction. In some applications, particularly some applications involving prosthetic inserts for the human body, batteries that operate at relatively low temperatures are required. BRIEF DESCRIPTION OF THE INVENTION The primary object of the present invention is to provide a novel high energy density electric cell comprising a nuclear source of relatively high energy radiation fluence, a semiconductor voltaic-junction characterized by a logarithmic curve for this fluence relating minority carrier diffusion length and a damage constant, and an enclosure having a sufficiently low thermal impedance for dissipation of sufficient heat from the nuclear source to permit predetermined degradation of the minority carrier diffusion length initially and predetermined maintenance of the minority carrier diffusion length thereafter. The nuclear radiation includes energetic radiation such as alpha, beta and gamma emissions or combinations thereof. Preferred inorganic crystalline materials characteristically incorporated in the semiconductor junction are selected from the class consisting of cadmium telluride, indium phosphide, silicon carbide and synthetic diamond. The semiconductor junction, for example, is differentially treated with n or p dopants. The thermal impedance is composed of a thermal insulator such as a ceramic electrical non-conductor. The arrangement is such that damage to the semiconductor junction, resulting from the highly energetic emissions of the nuclear source, at first occurs rapidly and thereafter substantially stabilizes at an operative electrical output for an operative predetermined period. Other objects of the present invention will in part be obvious and will in part appear hereinafter. |
048633119 | abstract | To store radioactive materials in bore holes of salt domes these bore holes are lined with superimposed tubular sections made of metallic material including in each case of an outer ring and an inner ring which are securely joined together by an intermediate ring of an electrochemically nobler material; the joining of the tubular section with each other is carried out by welding the intermediate rings and by inserting support rings in corresponding recesses of the outer rings. |
abstract | Systems and methods are provided in which an extreme ultraviolet (EUV) light generation apparatus used with a laser apparatus is configured to detect an image of a laser beam by which a target has been irradiated. The EUV light generation apparatus may also be configured to control the position at which a laser beam is to be focused and the position of a target, based on the detection result. |
|
054935903 | claims | 1. A fuel element assembly for use in a nuclear reactor using pressurized water as a coolant flowing in a plurality of fuel channels, said fuel element comprising: an elongated fuel element containing fissionable material, said fuel element having opposed ends and a peripheral surface extending the length between said opposed ends; and at least one CHF enhancement appendage attached along the length of said fuel element and projecting outwardly from the peripheral surface of said fuel element for generating turbulence in said coolant flowing along said length of said fuel element downstream of the locations of said CHF enhancement appendage. a fuel bundle containing a plurality of elongated fuel elements, each of said fuel elements having opposed ends and a peripheral surface extending the length between said opposed ends; at least one spacer for separating said fuel elements from each other; at least one bearing pad attached to outer fuel elements for providing load bearing to said fuel bundle; and at least one CHF enhancement appendage attached to each of certain fuel elements along said length thereof and projecting outwardly from the peripheral surface of said each fuel element for generating turbulence in said coolant flowing along said length of said fuel bundle downstream of the locations of said CHF enhancement appendage. an elongated pressure tube defining a fuel channel therethrough, said pressure tube having a length, an inlet for introducing said coolant into said fuel channel, and an outlet for discharging said coolant from said fuel channel; a plurality of elongated fuel bundles contained within said pressure tube, each of said fuel bundles containing a plurality of fuel elements therein, each of said fuel elements having opposed ends and a peripheral surface extending the length between said opposed ends, said length of each fuel element being parallel to said length of said pressure tube; a plurality of spacers for separating said fuel elements from each other; a plurality of bearing pads attached to outer fuel elements for providing load bearing to said fuel bundles; and at least one appendage provided on each of certain fuel elements along said length thereof and projecting outwardly from the peripheral surface of said each fuel element into coolant flow space within said fuel channel surrounded by fuel elements, for generating turbulence in said coolant flowing along said length of each of said fuel bundle downstream of the locations of said CHF enhancement appendages. a pressure tube defining a fuel channel therethrough, said pressure tube having a length, an inlet for introducing said coolant into said fuel channel, and an outlet for discharging said coolant from said fuel channel; a plurality of fuel bundles contained within said pressure tube, said fuel bundles being separated from each other forming water gaps therebetween, through which said coolant flows, each of said fuel bundles comprising a plurality of fuel elements separated from each other forming water gaps therebetween, through which said coolant flows, each of said fuel elements having opposed ends and a peripheral surface extending the length between said opposed ends, said length of each fuel element being parallel to said length of said pressure tube; a plurality of spacers for separating said fuel elements from each other; a plurality of bearing pads attached to outer fuel elements for providing load bearing to said fuel bundles; a plurality of CHF enhancement appendages having a cylindrical shape and being attached to each of certain locations of certain said fuel elements along said length thereof and projecting outwardly from the peripheral surface of said each fuel element into said fuel channel for generating turbulence in said coolant flowing along said length of each of said fuel bundles within said fuel channel downstream of the locations of said CHF enhancement appendages; each of said CHF enhancement appendages having a bottom where said CHF enhancement appendage is attached to one of said certain fuel elements, the cross-sectional area of each of said CHF enhancement appendage at said bottom thereof being in a range of 3 mm.sup.2 to 11 mm.sup.2, and the height of said CHF enhancement appendage from said bottom being in a range of 0.6 mm to 2.3 mm, each of said CHF enhancement appendages being attached at said bottom to one of said fuel elements and having no contact with the other fuel elements, one to four appendages being provided in each sub-channel defined by a space surrounded by some of said fuel elements; the locations of said CHF enhancement appendages within said fuel bundle being such that the turbulence generated by said CHF enhancement appendages occurs at locations within the fuel bundle where CHF is most likely to occur. 2. A fuel element assembly according to claim 1, wherein at least two CHF enhancement appendages are positioned symmetrically about the length of said fuel element. 3. A fuel element assembly according to claim 1, wherein said CHF enhancement appendage has a cylindrical shape having a top end and a bottom end where said CHF enhancement appendage is attached to said fuel element. 4. A fuel element assembly according to claim 3, wherein the cross-sectional area of said CHF enhancement appendage at said bottom end thereof is in a range of 3 mm.sup.2 to 11 mm.sup.2, and the height of said CHF enhancement appendage from said bottom end is in a range of 0.6 mm to 2.3 mm. 5. A fuel element assembly according to claim 1, wherein the distance between said CHF enhancement appendage and a nearest end of said fuel element is in a range of 5 cm to 20 cm. 6. A fuel bundle assembly for use in a nuclear reactor using pressurized water as a coolant flowing in a plurality of fuel channels, said fuel bundle assembly comprising: 7. A fuel bundle assembly according to claim 6, wherein at least two CHF enhancement appendages are positioned symmetrically about the length of each of said certain fuel elements. 8. A fuel bundle assembly according to claim 6, wherein said CHF enhancement appendage has a cylindrical shape having a top end and a bottom end where said CHF enhancement appendage is attached to one of said fuel elements. 9. A fuel bundle assembly according to claim 8, wherein the cross-sectional area of said CHF enhancement appendage at said bottom end thereof is in a range of 3 mm.sup.2 to 11 mm.sup.2, and the height of said CHF enhancement appendage from said bottom end is in a range of 0.6 mm to 2.3 mm. 10. A fuel bundle assembly according to claim 6, wherein the distance between said CHF enhancement appendage and a nearest one of said ends of said fuel elements is in a range of 5 cm to 20 cm. 11. A pressurized fuel channel type nuclear reactor which uses pressurized water as a coolant, said reactor comprising: 12. A pressurized fuel channel type nuclear reactor according to claim 11, wherein said CHF enhancement appendage is attached on each of said certain fuel elements at a location where said CHF enhancement appendages generates the turbulence at locations within the fuel bundle where CHF is most likely to occur. 13. A pressurized fuel channel type nuclear reactor according to claim 11, wherein one to four CHF enhancement appendages are provided in each of certain subchannel defined by a coolant flow space surrounded by some of said fuel elements which are adjacent to each other, and said coolant flow space excludes any inter-fuel element gap defined by the closest distance between any two neighbouring fuel elements. 14. A pressurized fuel channel type nuclear reactor according to claim 11, wherein said CHF enhancement appendage is attached to one of said certain fuel elements and has no contact with the other fuel elements. 15. A pressurized fuel channel type nuclear reactor according to claim 11, wherein at least two CHF enhancement appendages are positioned symmetrically about the length of each of said certain fuel elements. 16. A pressurized fuel channel type nuclear reactor according to claim 11, wherein said CHF enhancement appendage has a cylindrical shape having a top end and a bottom end where said CHF enhancement appendage is attached to said fuel element. 17. A pressurized fuel channel type nuclear reactor according to claim 16, wherein the cross-sectional area of said CHF enhancement appendage at said bottom end thereof is in a range of 3 mm.sup.2 to 11 mm.sup.2, and the height of said CHF enhancement appendage from said bottom end is in a range of 0.6 mm to 2.3 mm. 18. A pressurized fuel channel type nuclear reactor according to claim 14, wherein distance between said CHF enhancement appendage and a nearest end of said fuel elements is in a range of 5 cm to 20 cm. 19. A critical power enhancement system for a nuclear reactor which uses pressurized water as a coolant, said system comprising: 20. A fuel bundle assembly according to claim 6, wherein said CHF enhancement appendage has no contact with any other fuel elements. |
summary | ||
description | The present disclosure generally relates to work machines and, more particularly, relates to cab-less autonomous track-type tractors. Track-type tractors, earth-moving machines and other work machines generally may contain parts which are often integrated as one self-contained assembly. Many parts of the work machine are often used to perform certain functioning. For instance, a blade and ripping unit at the front and back of the work machine, respectively, may be configured to cut and rip material encountered by the work machine on its path. A power unit within the work machine may include a battery and an engine and may provide the power within the work machine. In typical work machines or track-type tractors, the parts described above may often be integrated with the work machine, wherein the entire work machine may be one self-contained assembly in which the parts of the work machine cannot be separated from another or separately removed from the work machine. More specifically, parts such as the engine, battery, generator, inverter, and cooling package are all integrated within a typical work machine. Further, other parts such as a blade at the front of the work machine, and the ripper at the back of the work machine are often integrated with the typical work machine. Accordingly, a problem associated with typical work machines is that there often a high number of connections and interface points within the machine. As such, access to the various parts and components within the work machine may be cumbersome as a result. Maintenance of the work machine may be more difficult given the number of connections and interface points within the work machine. It may often be difficult to access and successfully maintain the various parts of the work machine given the high number of connections and interface points within the work machine. Another problem associated with a work machine that typically has integrated parts and a high number of connection points is that it may be often difficult to remove various parts for service and testing. Parts which may need service and maintenance such as the engine or battery cannot be separately removed from the work machine while leaving the other parts of the work machine intact. Accordingly, if the engine or battery needs maintenance, the entire work machine would need to be taken to a maintenance facility, service station, or the like to provide maintenance or service to the battery or engine. Further, providing maintenance or testing on either the battery or engine may also involve having to navigate or work around the other parts of the work machine since parts cannot typically be removed from a typical work machine or the like. Accordingly, the testing of and maintenance of the work machine can be very tedious, cumbersome and time-consuming as a result. Various configurations may exist to purportedly allow easier access to parts and maintenance and testing of various components of track-type tractors and work machines. For example, U.S. Pat. No. 7,938,847, entitled “Radiator Arrangement,” discloses how a radiator arrangement may be present within an engine compartment, wherein the radiator arrangement includes a first radiator and a second radiator. However, such configurations face the common challenge that the all of the parts of the work machine are integrated within the work machine and cannot be separately removed from the work machine. As a result, such configurations do not address the problem of easy access to parts within the machine, and timely maintenance and testing of the various parts of the work machine. In view of the foregoing disadvantages associated with known work machines, a need exits for a cost effective solution which would not drastically alter the physical structure of the work machine, and yet still allow for easy access to the various parts within the work machine. In addition, a need exits for various parts of the work machine to be separately removed from the work machine should maintenance or testing of the various parts be required. The present disclosure is directed at addressing one or more of the deficiencies and disadvantages set forth above. However, it should be appreciated that the solution of any particular problem is not a limitation on the scope of the disclosure or of the attached claims except to the extent expressly noted. In one aspect of the present disclosure, a work machine is provided. The work machine may include a power module configured to provide power and including a battery and an engine coupled to a folding heat exchange device. The work machine may also include a drive module configured over a track roller frame with one or more motors. The work machine may also include a hydraulic module including one or more devices in a front region and one or more devices in a rear region to cut or rip encountered material. In another aspect of the present disclosure, an electric drive machine is provided. The electric drive machine may include a front module configured with a blade to cut and rip encountered material. The electric drive machines may include a power module with a battery and an engine to provide power. The electric drive machines may also include a drive module positioned on a plurality of tracks with at least one motor. The electric drive machines may also include a rear module with one or more ripping devices to rip the encountered material. In yet another aspect of the present disclosure, a power modular device is provided. The power modular device may include an engine coupled to an intake manifold and an exhaust manifold, and including an exhaust system with an exhaust inlet and an exhaust outlet and a turbocharger, and configured to provide electrical power. The power modular device may also include a battery connected to a fuel pump. Further, the power modular device may also include a folding heat exchange device positioned over the battery and the engine and configured to be folded in the vertical direction to allow access to the battery and the engine. These and other aspects and features will be more readily understood when reading the following detailed description in conjunction with the accompanying drawings. While the following detailed description is given with respect to certain illustrative embodiments, it is to be understood that such embodiments are not to be construed as limiting, but rather the present disclosure is entitled to a scope of protection consistent with all embodiments, modifications, alternative constructions, and equivalents thereto. Referring now to the drawings and with specific reference to FIG. 1, a machine 10 is depicted. With continued reference to FIG. 1, the machine 10 may be an electrically powered track-type tractor 10, truck, earth-moving machine, work machine or the like. The machine 10 is illustrated in the context of a track type machine that may be used in construction, mining, road building, or the like. The machine 10 is nevertheless not limited to just performing construction, mining, or road building, and may be used for other purposes. The machine 10 may include a mobile electric drive machine having a frame 12. The frame 12 may have an electrical power system 14 mounted therein. The electrical power system 14 may include an engine 16 that provides electrical power for the machine 10. The machine 10 may also include one or more tracks 18. The machine 10 may also include a drive coupling 20 between the engine 16 and a generator 22. An electric motor 24 may be provided that is coupled to the generator 22 and configured to drive the tracks 18. The electric motor 24, the tracks 18, the drive coupling 20, and the electrical power system 14 can comprise a propulsion system for the machine 10. The drive coupling 20 may transmit torque between the engine 16 and the generator 22. The drive coupling 20 may be driven by an engine output shaft 28. The generator 22 may rotate and generate electrical power. The drive coupling 20 may also include a reaction plate 34. The reaction plate 34 may rotate with the engine 16. The generator 22 may include an input shaft 36 that is coupled with a friction plate 38. Accordingly, the machine 10 described above is comprised of various modules. As will be described below, the major components of the machine 10 are broken into easily assembled, and easily accessible modules to allow for the modules of the machine 10 to be tested separately and to reduce the number of unnecessary connections within the machine 10. FIG. 2 illustrates a schematic diagram of the engine 16 described in FIG. 1. The engine 16 includes an intake manifold 40 and an exhaust manifold 42. An exhaust system 50 is included within the engine 16 as well. The exhaust system 50 includes an exhaust inlet 52 and an exhaust outlet 54. A turbocharger 56 may be disposed within the exhaust system 50. A battery 70 is provided and electrically connected to a fuel pump 72. Referring to FIGS. 3-4, one module of the machine 10 is depicted as a modular power unit 80. The modular power unit 80 may include the battery 70 and the engine 16 described above. With typical machines, power units are integrated into a core of the machine 10, and the servicing of the power unit that is integrated into the machine 10 may be cumbersome and time consuming. Such a power unit may not be easily removed or attended to if it is integrated with the machine 10. In addition, if a new type of power source became available, it may be difficult to place the new power unit into the machine 10. Accordingly, it may be harder for the machine 10 be fitted with the new power source. In the present disclosure, on the other hand, the modular power unit 80 is not integrated within the core of the machine 10. As a result, the modular power unit 80 minimizes its interfaces with the other units in the machine 10 to allow for easy service and future adaptability. The modular power unit 80 is part of the machine 10, but is not integrated as one single unit with the other units of the machine 10. The modular power unit 80 may be removed apart from the machine 10 should the modular power unit 80 require testing, service or if it was needed to be used in another machine or the like. Moreover, the modular power unit 80 could also be adapted to different technologies. The modular power unit 80 may include a folding heat exchange device 90. The folding heat exchange device 90 may be positioned atop of the battery 70 and the engine 16. The folding heat exchange device 90 can either be placed over both the engine 16 and the battery 70, or in the alternative, the folding heat exchange device 90 may be lifted or folded up as shown in FIG. 4 to allow for access to the engine 16 and battery 70 or other parts within the modular power unit 80. As illustrated in FIG. 4, the advantages of the folding heat exchange device 90 is easy access to the engine 16 or battery 70 or other parts within the modular power unit 80. For instance, if any of the parts of the modular power unit 80 needed to be repaired, the modular power unit 80 can be easily removed from the machine 10. In addition, the mobility of the folding heat exchange device 90 can allow the parts which need to be serviced within the modular power unit 80 to be easily accessible. Another advantage of the folding heat exchange device 90 is that it is easier to test the battery 70 or engine 16 or other parts within the modular power unit 80. There is simple access to any parts within the modular power unit 80 that need to be serviced. The modular power unit 80 can also be used for different machines. Overall, having the modular power unit 80 not being integrated with the machine 10 allows the modular unit 80 to be easier to repair and service and to use in other machines or the like. Referring to FIG. 5, another module of the present disclosure, a drive module 100, is illustrated to fit over a track roller frame 110. The track roller frame 110 is a large structure positioned on the outside of the machine 10 as shown in FIG. 5. Designing the drive module 100 to fit about the track roller frame 110 will allow for easy assembly, service and general access. The drive module 100 or track roller frame 110 is not integrated with the rest of the machine 10. As a result, the drive module 100 can be easily removed from the machine 10 without affecting the other modules of the machine 10, and also be serviced when necessary. The drive module 100 may be provided in various embodiments, with two being depicted. FIG. 6 illustrates one embodiment, wherein the drive module 100 may have a dual motor trapezoidal track configuration. The dual motor with dual sprocket design may be chosen so that the torque and power requirements could be met without exceeding the length and width envelope of the current track roller frame 110. FIG. 7 illustrates another embodiment in which the drive module 100 may have a single motor design. In the single motor design, the track 18 may extend beyond the back of the track roller frame 110. In the single and dual drive configuration, the drive module 100 is bolted to a top portion of the track roller frame 110. The drive module 100 can be disconnected from the machine 10 by unwrapping the track 18 and unbolting it from the track roller frame 110. With either embodiment, the benefits from the drive module 100 fitting over the track roller frame 110 include being able to service either the drive module 100 or the track roller frame 110 apart from the machine 10 and provide easy care and maintenance for the drive module 100. As stated above, the drive module 100 and track roller frame 110 are not integrated with the machine 10. Accordingly, both the drive module 100 and track roller frame 100 may be serviced apart from the machine 10, or used in another work machine or the like. Another module type is depicted in FIG. 8. As shown therein, hydraulic modules with a front unit 140 and a rear unit 150 are illustrated. Normally, hydraulic units or modules are fully integrated onto work machines. As a result, although part redundancy within a machine may be minimized, a high number of interface points within a machine may exist. In addition, maintenance on the hydraulic units may be cumbersome when the hydraulic units are integrated with the machine. As a result, the entire machine would need to be brought in even if only the hydraulic units needed to be serviced. To remedy this problem, the present disclosure has separated the hydraulics of the machine into two units. The front unit or module 140 is positioned in front of the machine 10, and includes a blade. The rear unit 150 or module is positioned at the back of the machine 10 and includes a plurality of ripping devices. The front unit 140 and the rear unit 150 are connected to the engine by a power take off (PTO) shaft. The benefits for the front unit 140 and the rear unit 150 are similar to the other modules of the machine 10 described above. If either the front unit 140 or the rear unit 150 needs to be serviced, the entire front unit 140 or rear unit 150 can be pulled from the machine 10 without removing any other modules from the machine 10. Only PTO shafts or hydraulic line connections which connect the front unit 140 or rear unit 150 to the machine need to be removed. In other embodiments, the front unit 140 and the rear unit 150 could be designed to fit up to a shop test unit. As a result of having the front unit 140 and the rear unit 150 not being integrated with the machine 10, both units 140, 150 may be tested apart from the machine. Accordingly, the service of both units 140, 150 and also the rest of the machine 10 becomes simpler, and the downtime in which the entire machine 10 faces is drastically reduced. Turning to FIG. 9, another module, a ripping module 160 of the machine 10, is illustrated. The ripping module 160 is located at rear portion of the machine 10. The ripping module 160 may include a ripping device 165. Another machine 210 with similar configurations to the machine 10 also includes a ripping module 260 as shown in FIG. 10. The ripping module 260 may also include a ripping device 265. The ripping devices 165, 265 shown in FIG. 11 are designed to rip material that may typically require the weight and power of a larger machine through assisted ripping. Such material may include large rocks, dirt, gravel or the like which the machines 10, 210 may encounter when in use. During a ripping procedure, the ripping device 165 of the machine 10 performs assisted ripping by being coupled within the ripping device 265 of machine 210 as shown in FIG. 11. Assisted ripping involves providing smaller machines such as the ripping module 160 the capability to rip material that would typically require the weight and power of larger machines. Ordinarily, large rocks or a large amount of dirt or gravel found within the earth may typically require a large ripping unit or module. An overall benefit of assisted ripping is that it allows for smaller devices to be used to rip bigger and harder material through assisted ripping between the ripping devices 165, 265. In general, the present disclosure may find applicability in various industrial work machines or the like. Such machines may be employed as prime movers, earth movers, rail, marine devices or the like. The present disclosure includes a machine configured with various modules which are not integrated with the machine 10 to allow each of the modules to be easily removed from the machine 10 when the modules need service or maintenance. The machine 10 is configured with easily assembled and easily accessible modules that are not integrated with the machine 10. In the present disclosure, the modular power unit 80 minimizes its interfaces with the other units in the machine 10 to allow for easy service and future adaptability. In addition, the folding heat exchange device 90 may be lifted or folded up as shown in FIG. 3 to allow for access to the engine 16 and battery 70 or other parts within the modular power unit 80 that may require service. The drive module 100 is not integrated with the rest of the machine 10. As a result, the drive module 100 with either of the two designs described above can be easily removed from the machine 10 without affecting the other modules of the machine 10, and also be serviced when necessary. Through assisted ripping, both the ripping devices 165, 265 are able to rip a larger and heavier amount of rock, gravel or the like that would typically require a larger ripping unit or module. Turning now to FIG. 12, an exemplary method 300 for performing a ripping procedure in accordance with the present disclosure is illustrated. Starting in block 301, a rear portion of the machine 10 may be aligned with a rear portion of the machine 210. In a next block 302, the ripping device 165 of the machine 10 may be coupled to the ripping device 265 of the machine 200. In block 303, the work machines 10, 210 then move in the same horizontal direction, and a ripping procedure is performed by the ripping devices 165, 265. The ripping device 165 may transfer all of its weight and tractive force onto the ripping device 265 to perform assisted ripping. Next in block 304, the ripping devices 165, 265 are then repositioned. In block 305, the ripping procedure is performed in another horizontal direction, wherein the machines 10, 210 still move in the same direction to enable another ripping procedure to be performed. During this ripping procedure, the weight and tractive force of the ripping device 265 is transferred onto the ripping device 165. While the preceding text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of protection is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the scope of protection. |
|
description | The invention relates generally to nuclear reactors, and more specifically, to a debris exclusion and retention device for a reactor fuel assembly. Nuclear reactors, such as boiling water reactors (BWR), have a core that contains fuel assemblies that enclose fuel rods. As the nuclear reactor is a closed circulation system, debris tends to accumulate within the system. Debris in this context refers to any solid material entrained in the fluid flow. Debris can include materials left over from reactor construction, corrosion byproducts, and detritus introduced or dislodged during outages and repair services. Accumulation of debris within a fuel assembly is potentially damaging to fuel rods. For example, as debris particles lodge against the fuel rods, coolant traveling through the fuel bundle creates turbulence which causes the captured debris particles to vibrate rapidly against the fuel rod cladding, resulting in its perforation or rupture. Fuel rods with damaged cladding are sometimes referred to as “leakers.” If a sufficient number of leakers are present, the plant may be forced to shut down or to operate at less than optimum efficiency in compliance with regulations and to address safety concerns. In either case, it is highly desirable to minimize the entrance of foreign debris into the fuel assemblies. To prevent debris from entering a fuel assembly, coolant that flows through the fuel assembly is typically filtered at the lower tie plate of the fuel assembly. In this fashion, debris can be prevented from entering into the fuel assembly depending on the effectiveness of the selected filter. This impeded debris simply accumulates within the lower tie plate, but only so long as there is sufficient forward coolant flow through the fuel assembly. The debris that has accumulated within the cavity of the lower tie plate during reactor operations becomes dislodged due to reverse or stagnant coolant flow conditions, or in reaction to an internal or external vibration source. Escape is very likely to occur, for example, as a fuel assembly is moved above the reactor core, which is common during reactor shut down and refueling. As the fuel assembly is lifted upward, the speed of its ascent causes coolant to flow back through the fuel assembly, thereby dislodging (i.e., backwashing) debris that had accumulated in the filter. Once dislodged, the debris falls out of the lower tie plate of the fuel assembly that is being transported and into the lower plenum, or worse, into the vulnerable upper ends of fuel assemblies that are positioned below, in the reactor core. Debris that has been filtered and has accumulated within the lower tie plate cavity during reactor operations can also backwash out of the lower tie plate upon significant reduction of flow, for example, where reactor flow is reduced at low or no power. This debris will be reintroduced to the lower tie plate in subsequent reactor operation, allowing for a subsequent opportunity for infiltration of the debris into the fuel assembly. Accordingly, although highly effective filters have been developed, the problem of retaining the debris that has been impeded by the filters remains. Previous attempts to address the debris retention problem employ various filtering structure designs that attempt to prevent debris from being dislodged from the lower tie plate. However, to do so the prior designs substantially change the direction and the momentum of the normal flow pattern of coolant through the lower tie plate, which creates an undesirable pressure drop within the fuel assembly, which adversely affects reactor operation. Further, prior attempts to redesign the structure of conventional lower tie plates resulted in devices that are costly and complicated to manufacture. The various embodiments of the invention provide a retention device that advantageously utilizes natural flow paths within a lower tie plate of a fuel assembly to entrap filtered debris within the lower tie plate. The problem of retention of the debris is solved, as the retention device entraps debris that has been impeded by an exclusion device, such as an independent or integral debris filter. Together, the exclusion device and the retention device cooperate to continuously flush the internal cavity of the lower tie plate, thereby mitigating undesirable levels of flow resistance. This “backwash” flushing removes debris trapped or embedded within cracks and crevices of the lower tie plate, all the while using the coolant flow that is present in the fuel assembly during normal reactor core operations. In addition, by using the natural coolant flow patterns, the retention devices have, at most, minimal impact on the pressure drop in the core. More specifically, according to one aspect, the exemplary retention devices are configured such that the coolant flow through the center opening of an inlet nozzle of the lower tie plate has a higher flow velocity than the coolant flow in low flow zones that naturally form along the internal walls of the lower tie plate, which results in the diversion and accumulation of debris along the internal walls and corners of the lower tie plate. In certain embodiments, this flow dynamic is accomplished by expanding an interior cavity of the lower tie plate. One embodiment is a debris retention assembly for a fuel assembly, the debris retention assembly including a debris filter that is disposed across a flow path along which coolant travels into the fuel assembly. The debris filter is configured to impede the flow of debris that is propelled by the flow of coolant, so as to prevent introduction of the debris into the fuel assembly. The debris retention assembly also includes a debris retention device that is positioned upstream from the debris filter with respect to the direction of coolant flow and also disposed across the flow path. The debris retention device is configured to entrap debris that has been impeded by the debris filter to prevent escape of the debris from the debris retention assembly. Moreover, the debris retention device entraps debris without redirecting coolant flow. Rather, the debris retention device utilizes the vortices that naturally exist in a BWR lower tie plate to resist backwash and to retain loose debris carried by the vortices to the periphery of the debris retention device. To do so, the debris retention device includes a forward flow channel that resists debris escape under reverse flow, such as with an array of cylindrical cells that allow flow that is normal to the plane of the forward flow channel and resists tangential flow. A straining plate, or series of straining plates, encircles the forward flow channel, such that backwater and vortices carrying debris deposit the debris onto the straining plates. Each straining plate is perforated, and impervious dead zones may be disposed between straining plates or may interrupt perforated sections of a straining plate. Another embodiment is a lower tie plate for a fuel assembly that incorporates a debris retention assembly. The lower tie plate includes an inlet nozzle for receiving coolant into the fuel assembly along a flow path, a housing that expands outwardly with respect to the inlet nozzle to define a lower tie plate cavity, and the debris retention assembly, which is permanently or removably enclosed within the housing. Again, the debris retention assembly includes a debris filter and a debris retention device that is positioned upstream from the debris filter. According to one aspect of the embodiments, a debris retention cavity is defined between debris retention device and the debris filter, the debris retention cavity extending into the low flow zones that naturally result from the flow dynamics and geometries of the lower tie plate. To entrap debris, the debris retention device includes a forward flow channel that resists reverse flow of coolant without impeding coolant flow, and is disposed in a high flow zone that is surrounded by the peripheral low flow zones. In certain embodiments, the forward flow channel is configured to divert debris that is released from the debris filter under low flow or reverse flow conditions, or that avoids the debris filter by flowing into a low flow zone, by directing the debris into at least one straining plate in the low flow zone. In certain embodiments, the exemplary retention devices can be retrofitted in to existing fuel assembly designs, either independently to cooperate with an existing debris filter, or as part of an assembly that includes both elements. The foregoing has broadly outlined some of the aspects and features of the various embodiments, which should be construed to be merely illustrative of various potential applications. Other beneficial results can be obtained by applying the disclosed information in a different manner or by combining various aspects of the disclosed embodiments. Other aspects and a more comprehensive understanding may be obtained by referring to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings, in addition to the scope defined by the claims. As required, detailed embodiments are disclosed herein. It must be understood that the disclosed embodiments are merely exemplary of and may be embodied in various and alternative forms, and combinations thereof. As used herein, the word “exemplary” is used expansively to refer to embodiments that serve as illustrations, specimens, models, or patterns. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. In other instances, well-known components, systems, materials, or methods that are known to those having ordinary skill in the art have not been described in detail in order to avoid obscuring the present disclosure. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art. Exemplary Environment The exemplary environment in which the various embodiments of the invention will be described is a boiling water reactor (BWR). Referring to FIG. 1, the general structure of a reactor pressure vessel (RPV) 10 is illustrated. The RPV 10 includes a reactor pressure vessel head 20, a steam dryer 22, a steam separator 24, a top guide 26, a core shroud 28, a core support plate 30, fuel assemblies 32, control rods 34, fuel support members 36, control rod guide tube 38, a lower plenum 40, reinforcing beams 42, recirculation pumps 44, and main steam lines 46. Coolant flow F cools the components of the RPV 10. Pressure is generated in the lower plenum 40 by the recirculation pumps 44 such that coolant (e.g., water) flows from the lower plenum 40 into the fuel assemblies 32. In the fuel assemblies 32, the coolant is heated to produce a two-phase flow including steam and liquid components. The steam and liquid components are separated from the flow by the reactor systems including the steam separators 24 and the steam dryers 22. For example, steam is separated from the coolant flow by the steam separators 24 and then directed into the steam dryers 22 to remove additional moisture that may remain. Thereby, pressurized steam is produced that is now directed by way of the main steam line 46 into the reactor's turbine building (not shown). The pressurized steam that has been generated is then directed into the turbine. Water that is separated from the flow by the steam separators 24 and the steam dryers 22 is re-directed back down and into the recirculation pumps 44. Fuel Assembly and Fuel Support Referring to FIG. 1, the upper ends of the fuel assemblies 32 are supported by the top guide 26 and the lower ends of the fuel assemblies 32 are supported by the fuel support members 36. Generally described, the fuel support member 36 is configured so as to support four fuel assemblies 32 in a lattice arrangement and to direct coolant flow from the lower plenum 40 upwards and into each of the four nuclear fuel assemblies 32, individually. The fuel support member 36 is inserted into the upper end of the control rod guide tube 38 so as to be positioned at the upper end of the control rod guide tube 38. Referring to FIGS. 2 and 3, the fuel assembly 32 includes a hollow metal channel 50, expansion springs 51, full length fuel rods 52, part-length fuel rods 53, fuel spacers 54, water rods 55, an upper tie plate 56 with a handle 57, and a lower tie plate 58. The hollow metal channel 50 has an elongated shape with a square cross-section and upper and lower open ends in which the upper tie plate 56 and lower tie plate 58 are received. The full length fuel rods 52 and the part-length fuel rods 53 are arranged in parallel and contain fissionable material. The fuel spacers 54 support both the full length fuel rods 52, the part-length fuel rods 53, and the water rods 55 at several positions along the entire length of the fuel assembly once the assembly is placed within the hollow metal channel 50. The upper and lower tie plates 56, 58 secure the upper and the lower ends of the full length fuel rods 52, while the lower ends of the part-length rods 53 are secured only to the lower tie plate 58. This assembly ensures that the coolant can pass through and around each of the fuel rods 52 and 53. In FIGS. 2 and 3, the fuel assembly 32 may also include at least one water rod 55. In operation, the hollow metal channel 50 is vertical within the reactor's core, the upper tie plate 56 is positioned at the top opening of the hollow metal channel 50, which contains the components of each fuel assembly 32. The lower tie plate 58 is positioned at the bottom opening of the hollow metal channel 50, and the fuel spacers 54 are positioned at various locations along the interior length of the hollow metal channel 50. The fuel spacers 54 and the tie plates 56, 58 are configured so as to allow coolant flow through the fuel assembly 32. During normal operation, coolant flows in the flow direction F through the lower tie plate 58, over the fuel rods 52 and 53, along the interior length of the hollow metal channel 50 and then out through the top of the upper tie plate 56. Debris from reactor 10 systems can be entrained in the coolant flow and introduced to the fuel assembly 32 during normal operation. Lower Tie Plate Referring to FIGS. 2-4, the lower tie plate 58 includes an inlet nozzle 60 that leads to a lower tie plate cavity 62, in which a filter cartridge 63 is disposed below a lower tie plate grid 64. The lower tie plate grid 64 is located at an upper end of the lower tie plate cavity 62 and supports the lower end plugs for the fuel rods 52 and 53. The lower tie plate grid 64 directs the flow of coolant into the fuel assemblies 32 and between all of the fuel rods 52 and 53 and the water rods 55. The lower tie plate 58 further includes a bail 59, which extends outward and across the inlet nozzle 60. Generally, the bail 59 is configured to facilitate directing the lower end of the lower tie plate 58 of the fuel assembly 32 so as to be received by the fuel support member 36. Fuel Support Member Referring to FIG. 2, the fuel support member 36 includes a lower side entry orifice 82 that is configured to direct flow F from the lower plenum 40, upwards and through the support chamber 80 and into the fuel assembly 32. The support chamber 80 leads from a lower side entry orifice 82 where direct flow F enters from below. When the lower tie plate 58 is received within the support chamber 80, the bail 59 extends into the conical portion of the support chamber 80 through the receiving orifice 84. The outer inclined surface of the lower tie plate 58 forms a mechanical seal against a lip of the receiving orifice 84. As such, the support chamber 80, the lower tie plate 58, and the hollow metal channel 50 provide a substantially continuous channel that directs the coolant flow from the lower plenum 40 through the support chamber 80 and upwards through the fuel assembly 32 resting atop of each fuel support 36. Filter Cartridge Referring to FIGS. 6-12, various exemplary embodiments of a debris retention assembly 63 for use in a lower tie plate 58 is further described. For purposes of comparison, and not of limitation, an exemplary prior art debris filter cartridge 67 (shown in FIGS. 4 and 5) is a single stage filter system that is positioned across the coolant flow F as it enters the inlet nozzle 60 of the lower tie plate, moves through the housing 62, and exits through the lower tie plate grid 64. As discussed above, the debris filter 67 may function well under steady flow conditions to impede debris from migrating into the fuel assembly, but if flow ceases or reverses, the debris can escape and become mobile again. Also, flow resistance may divert some backwater down through the inlet nozzle 60, allowing debris to evade filtration. The various aspects of the present invention beneficially eliminate the problem of escaping debris with an integrated debris retention assembly 63 that both filters the flow and entraps the debris, thereby preventing its escape once its flow through the lower tie plate is impeded. In contrast to the prior art devices, the exemplary debris retention assembly 63 is at least a dual stage entrapment system that includes a debris filter 65 and debris retention device 66. FIG. 7 is an exploded cross-sectional view of a lower tie plate 58 with a fully assembled debris retention assembly 63 for a nuclear fuel assembly 32. The debris retention device 66 contains a debris tray 68, which is defined in part by a peripheral band 93 and one or more straining plates 92 interrupted by dead zones 70 (see FIG. 12). The straining plates 92, which may be integral to the peripheral band 93, have perforations 78 in certain embodiments, as will be discussed. The debris retention device 66 is further defined by a forward flow channel 90 that provides structure to the debris retention assembly 63, resists reverse flow of debris, and adds additional filtering capability, without adversely impacting performance in forward flow conditions. A peripheral band 93 encompasses all of these components as it defines the walls of the debris retention assembly 63. The peripheral band 93 has an outer surface that may be contoured with features, such as raised detents 72, which aid positioning, stability, and retention within the lower tie plate 58. Best shown in FIGS. 6, 7 and 8, the illustrated debris retention assembly 63 is configured to be inserted through a slot 74 and positioned within the lower tie plate cavity 62 between the inlet nozzle 60 and the lower tie plate grid 64. In this fashion, it is contemplated that an existing fuel assembly can be retrofitted with a debris retention assembly 63, and that a debris retention assembly 63 can be removed and cleaned or replaced during maintenance operations. A machined metal cover plate 69 is used to seal slot 74 into which the filter cartridge is first inserted and also used to further maintain the debris retention assembly 63 positioning within the lower tie plate 58. Referring to FIGS. 6 and 12, depressions (not shown) in the interior casting of the lower tie plate 58 correspond to detents 72 that protrude from one or more edges P along the periphery of the debris retention assembly 63. The detents 72 are configured to be received in the depressions to locate and secure the debris retention assembly 63 in position. In certain embodiments, the inside wall of the housing 62 that houses the debris retention assembly 63 within a lower tie plate 58 is cast larger than most conventional designs, to achieve desired flow dynamics. Specifically, the high velocity of the flow through the inlet nozzle 60 encountering the relatively sudden area expansion in the enlarged housing 62 creates a jet impingement flow pattern that direct debris towards low flow zones Z around the inner periphery of the lower tie plate cavity 62. The low flow zones Z within the debris retention assembly 63 are less extensive than the low flow zones Z that would exist inside the lower tie plate 58 in the absence of the debris retention assembly 63. FIG. 5 shows a cross-sectional diagram showing the housing 62 as enlarged in accordance with this aspect of certain embodiments, but with a prior art debris filter cartridge 67 installed within a lower tie plate 58, to demonstrate the pattern of vortices that are created by jet impingement of the coolant flow F on the filter cartridge 67. Low flow zones Z are created as the direct coolant flow F moves through the enlarged housing 62. Debris particles accumulate on surfaces 61 in the low flow zone Z. FIG. 7 illustrates an exploded view of the same housing 62 with an exemplary debris retention assembly 63, and FIG. 8 shows the debris retention assembly in operation in the housing 62. The central forward flow channel 90 allows coolant flow F to enter the debris retention assembly 63 in an unobstructed, relatively linear path and does not substantially change the direction or momentum of the coolant flow F. Any openings in the forward flow channel 90 can be much coarser by design, as compared to the size of openings in the debris filter 65. Consequently, forward coolant flow F may be sufficiently forceful to propel debris D through the forward flow channel 90 where the debris D then encounters and is impeded by the debris filter 65. Under stagnant or reverse flow R/F conditions, however, the forward flow channel 90 impedes the release of debris from the debris retention assembly 63, as these conditions generally do not generate sufficient force to propel the debris back through the forward flow channel 90. Accordingly, the forward flow channel 90 impedes backwash flow and the escape of debris D from the debris retention cavity 76 of the debris retention assembly 63, without substantially impacting normal flow dynamics within the lower tie plate cavity 62. In certain embodiments, for example, this backwash restrictive functionality can be achieved as shown in FIG. 9, wherein the forward flow channel 90 includes a matrix of cylindrical cells 94 that resist backwash and divert debris D to the periphery of the cavity 76 to be captured by the straining plates 92. As shown in FIG. 12, each cell 94 has a hexagonal cross-sectional shape, although other shapes may be suitable. In any event, the height, size, and thickness of the cells 94 is selected to allow linear flow (i.e., flow normal to the plane of forward flow channel 90) to pass unimpeded. In certain other embodiments, the cylindrical cells in the forward flow channel 90 may be replaced with apertures (not shown) the diameter of which is small enough to stop low velocity debris D but large enough to have negligible impact on flow of coolant under any conditions. Referring to FIGS. 8 and 9, as the coolant flow F moves through forward flow channel 90, after exiting the surface of the forward flow channel 90, coolant flow F creates a pattern of vortices in the housing 62. In general, low flow zones Z are areas of low velocity, reverse flow R/F in the enlarged cavity 62 and are created at least in part by the vortices that naturally exist in the lower tie plate 58. The low flow zone is a volume where debris D that is blocked by the debris filter 65 can be collected in the straining plates 92 of the debris retention device 66. Referring to FIGS. 7-9 and 11, the debris retention device 66 includes forward flow channel 90 that allows coolant flow F to flow substantially unobstructed into the debris retention device 66, and straining plates 92 that are positioned to extend at least partially across the low flow zones Z. Due to flow impingement, debris D (FIG. 11) propelled by the flow will be directed to the low flow zone Z resulting in an optimal position for the debris retention assembly 63. The forward flow channel 90 geometries (FIGS. 9 and 12) inhibit local flow and allow the entrapment of debris, preventing its release under stagnant, forward flow, and reverse flow conditions. Further, the dead zones 70 attract the debris as the sections with fine perforations 78 allow any back-water to cycle out of the cavity 76 without carrying the debris away. The perforations 78 in the debris retention cavity 76 may be directed to enhance the flushing characteristics of the debris off the surfaces 61, within the low flow zone Z, that accumulates within the cavity 62 of the lower tie plate 58 (see FIG. 8). Operation Referring to FIGS. 3, 7, and 8, during normal operation, coolant flows in direction F through the inlet nozzle 60, into the enlarged housing 62, through the debris retention assembly 63, and through the lower tie plate grid 64 before entering the fuel assembly 32. Debris passes into the debris retention assembly 63 through the forward flow channel 90 of the debris retention device 66 and is blocked by the debris filter 65 before the debris can enter the fuel assembly 32 and damage fuel rods 52 and 53. The flow impingement at the surface of the debris filter 65 pushes the debris to the low flow zones Z in the interior of the debris retention assembly 63. As the debris reaches the low flow zones Z, the debris falls into the straining plates 92 of the debris retention device 66 that is positioned within the low flow zone Z. Debris that is impeded and that is held by the flow F proximate the center of the debris filter 65 may fall to the debris retention device 66 during stagnant or reverse flow, also known as a “backwash,” such as when the fuel assembly 32 is moved. The forward flow channel 90 resists the release of debris under backwash. Although described in the context of an integrated cartridge style debris retention assembly 63, the debris filter 65 and the debris retention device 66 can alternatively be separate devices that are installed in series within the lower tie plate housing. In such embodiments, individual components can be interchanged or replaced separately. This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. |
|
abstract | A spacer for a fuel assembly of a boiling water reactor has a frame formed of outer webs and inner webs disposed crosswise relative each other. Gills are disposed on the exterior of the outer webs. The exterior of the outer webs of the spacer is provided with a plurality of projections in the form of bulges in the wall. The bulges project outwardly by a greater distance than the gills. |
|
summary | ||
claims | 1. A multi-beam source for generating a plurality of beamlets of energetic electrically charged particles, the multi-beam source comprising:an illumination system; anda beam-forming system,wherein the illumination system is adapted to generate energetic electrically charged particles and to form said particles into a wide illuminating beam, andthe beam forming system is configured to be illuminated by the illuminating beam emerging from the illumination system and is adapted to form a plurality of beamlets of energetic particles out of the beam, said beam forming system comprising:a beam-splitting means having a plurality of apertures transparent to the energetic particles of the particle beam to form the plurality of beamlets out of the beam, andan electrical zone device, said electrical zone device comprising a composite electrode being positioned along a two-dimensional plane oriented orthogonally to an optical axis of the electrical zone device and having lateral dimensions covering at least an area permeated by the particle beam, said composite electrode being composed of a plurality of substantially planar partial electrodes, said partial electrodes being arranged adjoining to each other according to a partitioning of the surface area of the electrical zone device and said partial electrodes being adapted to be applied different electrostatic potentials, the electrical zone device further comprising a plurality of openings transparent to the energetic particles of the particle beam. 2. The multi-beam source of claim 1, wherein the beam-splitting means and the electrical zone device are arranged in consecutive order and the openings of the electrical zone device are aligned with the apertures of the beam-splitting means. 3. The multi-beam source of claim 1, wherein the beam-splitting means is integrated in the electrical zone device. 4. The multi-beam source of claim 1, wherein the plurality of beamlets produced by the multi-beam source are substantially homocentric. 5. The multi-beam source of claim 1, wherein the plurality of beamlets produced by the multi-beam source are substantially telecentric. 6. The multi-beam source of claim 1, wherein the electrically charged particles are ions. 7. The multi-beam source of claim 1, further comprising at least one additional electrode, in particular an annular electrode, said electrode being positioned in proximity of the electrical zone device but out of the plane of the composite electrode of said electrical zone device. 8. The multi-beam source of claim 7, wherein the at least one additional electrode comprises at least one multi-pole electrode, the at least one multi-pole electrode being positioned out of the plane of the composite electrode of the electrical zone device. 9. The multi-beam source of claim 1, wherein the partial electrodes of the electrical zone device are arranged such that each opening of the electrical zone device is associated with a set of partial electrodes being located adjoining to the respective opening. 10. The multi-beam source of claim 9, wherein the set of partial electrodes comprises four partial electrodes. 11. The multi-beam source of claim 1, wherein the partial electrodes of the electrical zone device are shaped as concentric rings, centered at an optical axis of the electrical zone device. 12. The multi-beam source of claim 1, wherein the partial electrodes of the electrical zone device are shaped as sectors arranged around an optical axis of the electrical zone device. 13. The multi-beam source of claim 1, wherein the partial electrodes of the electrical zone device are sector-shaped and arranged around a central area of the electrical zone device, said central area being formed by at least one further central partial electrode. 14. The multi-beam source of claim 1, wherein a resistive material is provided in the gaps between neighboring partial electrodes of the electrical zone device. 15. The multi-beam source of claim 1, wherein openings of the plurality of openings of the electrical zone device are present only within the areas of each of the partial electrodes of the electrical zone device. 16. The multi-beam source of claim 1, wherein a CMOS-layer is provided within the electrical zone device, containing electronic circuitry for controlling the partial electrodes of the electrical zone device by applying different electrostatic potentials. 17. The multi-beam source of claim 1, wherein the partial electrodes of the electrical zone device are controlled via direct wiring which is adapted to apply different electrostatic potentials to the partial electrodes. 18. The multi-beam source of claim 1, wherein said electrical zone device is at least one of said electrical zone devices. 19. The multi-beam source of claim 18, wherein at least one of said electrical zone devices is positioned immediately in front of or after a beam-splitting means as seen along the direction of the particle beam. 20. The multi-beam source of claim 18, wherein a first electrical zone device of the plurality of electrical zone devices is positioned immediately in front of the beam-splitting means as seen along the direction of the particle beam and a second electrical zone device is positioned immediately after the beam-splitting means as seen along the direction of the particle beam. 21. The multi-beam source of claim 20, wherein the partial electrodes of at least one of the plurality of electrical zone devices are arranged such that each opening of the plurality of openings of the electrical zone device is associated with a set of said partial electrodes being located adjoining to the respective opening. 22. The multi-beam source of claim 1, further comprising a blanking device for switching off the passage of selected beamlets, said blanking device having a substantially plate-like shape, comprising a plurality of openings, each opening being provided with at least one controllable deflection means for deflecting particles radiated through the opening off their nominal path. 23. The multi-beam source of claim 22, wherein the blanking device has a CMOS-layer for controlling the deflection means. 24. The multi-beam source of claim 1, further comprising at least one correction lens arrangement for the correction of geometric aberrations of the multi-beam source, the correction lens arrangement having a substantially plate-like shape and comprising a plurality of orifices, the orifices widening to opening spaces at the beginning or the end of the orifice as seen in the direction of the particle beam, said opening spaces configured to act as correction lenses upon receiving the respective beamlets, said opening spaces further having a width varying over the area of the correction lens arrangement, thus defining a varying correction lens strength, the correction lens arrangement being located in front of or after the electrical zone device as seen in the direction of the particle beam. 25. The multi-beam source of claim 24, wherein the correction lens arrangement is located adjacent to said electrical zone device, the electrical zone device being arranged in front of or after the correction lens arrangement as seen along the direction of the particle beam. 26. The multi-beam source of claim 1, wherein the electrical zone device is provided with a cover. 27. The multi-beam source of claim 26, wherein the cover layer is made of electrically conductive material. 28. An electrical zone device for use in a multi-beam source according to claim 1, said electrical zone device comprising a composite electrode having lateral dimensions covering the whole of the electrical zone device, said composite electrode being composed of a plurality of substantially planar partial electrodes, said partial electrodes being arranged adjoining to each other according to a partitioning of the surface area of the electrical zone device and said partial electrodes being adapted to be applied different electrostatic potentials, the electrical zone device further comprising a plurality of openings. 29. The electrical zone device of claim 28, wherein the partial electrodes of the electrical zone device are arranged such that each opening of the plurality of openings of the electrical zone device is associated with a set of partial electrodes being located adjoining to the respective opening. 30. The electrical zone device of claim 29, wherein the set of partial electrodes comprises four partial electrodes. 31. The electrical zone device of claim 28, wherein the partial electrodes are shaped as concentric rings. 32. The electrical zone device of claim 28, wherein the partial electrodes are shaped as sectors arranged around an optical axis of the electrical zone device. 33. The electrical zone device of claim 28, wherein the partial electrodes are sector-shaped and arranged around a central area of the electrical zone device, said central area being formed by at least one further central partial electrode. 34. The electrical zone device of claim 28, wherein a resistive material is provided in the gaps between neighboring partial electrodes. 35. The electrical zone device of claim 28, wherein openings of the plurality of openings of the electrical zone device are present only within the areas of each of the partial electrodes of the electrical zone device and not in the gaps between the partial electrodes. 36. The electrical zone device of claim 28, wherein a CMOS-layer is provided within the electrical zone device to allow for controlling the partial electrodes of the electrical zone device by applying different electrostatic potentials. 37. The electrical zone device of claim 28, wherein the partial electrodes are controlled via direct wiring which is adapted to apply different electrostatic potentials to the partial electrodes. 38. The electrical zone device of claim 28, further comprising a cover layer to protect subsequent structures of the electrical zone device. 39. The electrical zone device of claim 38, wherein the cover layer is made of electrically conductive material. 40. An apparatus for multi-beam lithography for irradiating a target by means of a beam of energetic electrically charged particles, comprising:the multi-beam source of claim 1 for generating a plurality of substantially telecentric/parallel beamlets out of the beam of energetic electrically charged particles, anda multi-beam optical system positioned after the multi-beam source as seen in the direction of the beam for focusing the beamlets onto the surface of the target. 41. The apparatus of claim 40, further comprising at least one blanking means for switching off the passage of selected beamlets, said blanking means having a plurality of openings, each opening corresponding to a respective aperture of the beam-splitting means of the multi-beam source, each opening being provided with a controllable deflection means for deflecting particles radiated through the opening off their path to an absorbing surface within the multi-beam lithography apparatus, said blanking means being located before the multi-beam optical system as seen in the direction of the particle beam and/or being integrated in the multi-beam optical system. 42. The apparatus of claim 40, wherein the multi-beam source has a blanking device having a substantially plate-like shape, comprising a plurality of openings, each opening being provided with at least one controllable deflection means for deflecting particles radiated through the opening off their nominal path. 43. The apparatus of claim 40, wherein for each beamlet a deflection unit is provided, said deflection unit being positioned within or before the multi-beam optical system as seen in the direction of the beam, said deflection unit being adapted to correct individual imaging aberrations of its respective beamlet with respect to a desired position on the target and/or to position its respective beamlet during a writing process on the target. 44. The apparatus of claim 40, wherein an electrostatic lens array is placed within the multi-beam optical system. 45. The apparatus of claim 40, wherein for each beamlet an electrostatic lens arrangement is provided as a means to adjust the diameter of the beamlet and/or the position of the beamlet on the target. |
|
summary | ||
description | The present patent application is a non-provisional application claiming the prioirty of a provisional application of Application No. 60/717,856, filed Sep. 16, 2005. The present invention relates to a lithography system for projecting an image pattern onto a target surface such as a wafer, wherein control data are coupled to a control unit for controlling exposure projections by means of light signals, using a free space interconnect. The present invention relates in particular to a system wherein such control unit is included in close proximity to or within the projection space, more in particular to a multi-beam mask-less lithography system. The current invention in principle relates all the same to charged particle and to light projection based lithography systems Such a system is known, e.g. from the international patent publication WO2004038509 in the name of Applicant, i.e. from the particular embodiment provided by FIG. 14 thereof. The known system comprises a computer system for providing pattern data of an image to be projected by a so called beam column for projecting charged particles, in particular electrons on to a target surface such as a wafer and an inspection tool. The beam column comprises a vacuum chamber in which one or more charged particle sources are accommodated, which emit particles in a manner known per se, using amongst others an electric field for withdrawing particles from said source or sources. The beam column further comprises charged particle optic means for converging an emitted bundle of charged particles, for splitting up the same into a multiplicity of charged particle beams, further referred to as writing beams, and forming exposure projections. A control unit for controlling the exposure projections is included in the form of charged particle optical means for shaping or directing such writing beams, here showing a blanker optical part or modulator array comprising blanking deflectors, as well as a writing deflector array for deflecting writing beams for the purpose writing of a pattern using writing beams not blanked by said blanking deflectors. The blanker optic part, known per se, e.g. from international patent publication WO2004107050 in the name of Applicant, deflects, depending on a computer provided signal a writing beam away from a straight trajectory parallel with other writing beams, to such amount of inclination that no part of the writing beam effectively passes the opening provided for each writing beam in a stopping plate, thereby effecting an “off” state of the particular writing beam. All optic parts in the beam column are shaped with an array of openings, the openings of the separate parts being mutually aligned so as to enable the passage of a writing beam in said column towards said target surface in a controlled manner. The known mask-less multi-beam system is further typically provided with blanking deflectors having both the source and the target surface arranged in a conjugate plane thereof, i.e. it may easily be combined with the subject matter of WO2004/0819010. In this manner the lithography system favorably realizes an optimal brightness of the source on the target surface. Also, in this manner a minimum amount of space is required for the blanker array. The target surface for a writing beam is held on a stage included in the beam column. The stage, induced by an electronic control unit of the system, moves together with said surface perpendicularly relative to said emitted writing bundles, preferably solely in a direction transverse to a direction in which such writing bundles are finally deflected for writing purposes. Writing of a pattern by the known lithography system is thus effected by the combination of relative movement of the target surface and a timed “on” and “off” switching of a writing beam by said blanker optics upon signaling by said control unit, more in particular by a so-called pattern streamer thereof. Signaling for on/off switching, i.e. modulating of a writing beam is in the related known system performed by using light optics. The blanker optics thereto comprises light sensitive parts such as photodiodes, for receiving light signals, which are converted into electronic signals, e.g. applying the measures as provided by the international patent publication WO2005010618 in the name of Applicant. The light signals are produced by electronic to light conversion by said control unit for the system, and are transported to the beam column by means of an optical carrier, in casu a bundle of glass fibers that finally projects from “e.g. a transparent part of the vacuum boundary”. Light signals are projected to said blanker optics using a lens system, which in the known system is disclosed to be comprised of a converging lens located in between a transmitter part and the light sensitive parts of deflectors included in the blanker optic part. The arrangement of deflector, light sensitive parts and light to electric conversion is produced using both so-called MEMS- and (Bi-) CMOS-technology. So as to prevent the use of mirroring parts, in the related known system the signaling light beams are projected from a far upper side relative to the blanking optic part, so as to achieve an angle of incidence of the pattern information carrying light signals on the light sensitive elements, as small as possible. The publication in which the related embodiment is comprised, teaches however, that other locations of projection may be realized when using mirrors for correcting the larger angles of incidence occurring at most of such alternative locations. Although general set up of the above described lithography system has proven to be satisfactory, drawbacks are noticed at the oblique illumination system disclosed, in that it suffers from non-optimal transmission of light, at least less than expected and in that it suffers from relatively large aberrations. The present invention therefore seeks to improve the known mask-less multi-beam lithography system in general, however, in particular as to the light optics system (LOS) thereof. The present invention further has for an object to improve the lithography system by either increasing the light transmission efficiency thereof and/or by reducing the chance of aberrations in the light optic part thereof. The present invention solves, at least to a significant extent eliminates the above said problems encountered in lithography systems by using a mirror for redirecting light beams, provided with one or more holes for letting through exposure, e.g. writing projections of said lithography system part. In particular a free space optical interconnect of such systems according to the invention comprises a holey, i.e. holed mirror incorporated in the projection trajectory of said plurality of writing beams, wherein said mirror is arranged relative to said emitter part and said light sensitive elements to realize an on-axis, i.e. an at least virtually perpendicular incidence of said light beams on said light sensitive elements, said mirror being provided with at least one hole allowing passage of one or more of said writing beams. Alternatively provided, in accordance with further insight underlying the present invention, a lithography in which an electronic image pattern may be delivered to a exposure tool for projecting an image to a target surface, said exposure tool comprising a control unit for controlling exposure projections, said control unit at least partly being included in the projection space of said exposure tool, and being provided with control data by means of light signals, said light signals being coupled to said control unit by using a free space optical interconnect comprising modulated light beams that are emitted to a light sensitive part of said control unit, wherein the modulated light beams are coupled to said light sensitive part using a holed, alternatively denoted holey mirror for on axis incidence of said light beams on said light sensitive part, the one or more holes of said mirror being provided for passage of said exposure projections. Using a system according to the present invention minimizes the presence of aberrations by remaining on-axis at projection of light signals, without, at least noticeably interfering with, i.e. hampering the exposure projections of the exposure tool of the lithography system. With the presently claimed solution, the invention is realized in a new, in advance expectedly impossible, though in hindsight relatively simple to perform highly favorable manner. The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications. In the figures, corresponding structural features, i.e. at least functionally, are referred to by identical reference numbers. FIG. 1 represents an overall side view of the prior art lithography system that is improved by the current invention, in which a light emitter, or an array of fiber ends 2 of a light carrier Fb, in case embodied by optical fibers Fb, projects light beams 8 onto modulator array 24 using an optical system represented by lenses 54. Modulated light beams 8 from each optical fiber end are projected on a light sensitive element, i.e. light sensitive part of a modulator of said modulator array 24. In particular, ends of the fibers Fb are projected on the modulator array. Each light beam 8 holds a part of the pattern data for controlling one or more modulators, the modulation thereof forming a signaling system for transferring pattern data based modulator array instructions for realizing a desired image on said target surface. FIG. 1 also shows a beam generator 50, which generates a diverging charged particle beam 51, in this example an electron beam. Using an optical system 52, in casu an electron optical system, this beam 51 is shaped into a parallel beam. The parallel beam 51 impinges on beam splitter 53, resulting in a plurality of substantially parallel writing beams 22, directed to modulator array 24, alternatively denoted blanker array. Using modulators in the modulator array 24, comprising electrostatic deflector elements, writing beams 27 are deflected away from the optical axis of the litho system, and writing beams 28 pass the modulators undeflected. Using a beam stop array 25, the deflected writing beams 27 are stopped. The writing beams 28 passing stop array 25 are deflected at deflector array 56 in a first writing direction, and the cross section of each beamlet is reduced using projection lenses 55. During writing, the target surface 49 moves with respect to the rest of the system in a second writing direction. The lithography system furthermore comprises a control unit 60 comprising data storage 61, a read out unit 62 and data converter 63, including a so-called pattern streamer. The control unit 60 is located remote from the rest of the system, for instance outside the inner part of a clean room. Using optical fibers Fb, modulated light beams 8 holding pattern data are transmitted to lenses 54 which project the ends of the fibers on to the modulator array 24. FIG. 2 figuratively represents the light optic system of the improved lithography system according to a first embodiment. It entails the use of a holey mirror 104, which is applied for realizing an in-axis incidence of light beams 8 on the light sensitive elements of modulator array 24. The holey mirror thereto comprises one relatively large hole through which all for blanking deflected writing beams 27 and all undeflected writing beams 28 may pass, or a plurality of relatively small holes 105, one for each deflected or undeflected writing beam. According to preference, the mirror 104 comprises a substantially flat reflecting surface which is included in the system under angle of 45 degrees, so that while maintaining perpendicular incidence of light beams 8 on modulator 24, an axially minimal amount of space is required for the light optic system. With such minimized axial space requirement, design freedom is attained for locating the LOS either to the upper, or to the bottom side of the modulator array 24, which in turn enhances manufacturing freedom of the array modulator 24, which is a highly complex part, manufactured using CMOS and MEMS technology. With the use of a holey mirror 104, a focusing lens 106, preferably embodied by a lens system performing a focusing function, is included as close as possible to the latter, at least closer to the mirror than to the fiber ends 2. By locating said focusing lens 106 in close proximity of the holey mirror 104, it is favorably realized that the holey mirror can be applied without undue loss in light signal intensity, which might otherwise be due to the presence of holes 105. In accordance with the present invention the array of fiber ends 2 are completed with a micro lens array 101, forming a virtual fiber array 103, in fact an array of spots in the focal plane for the micro lenses 101. In line with a particular and independent aspect of the invention, a micro lens of the micro lens array 101, here according to preferred embodiment performs a magnifying function on the light signals transmitted by a particular fiber of the fiber array Fb. The lens system according to the present invention thus sets forth a dual imaging system comprising a magnification of each signal by means of a micro-lens, and a subsequent focusing of the signal by means of said lens 106, common to all of the emitted light signals. In this manner, independence is favorably attained in setting, in casu increasing, an effective spot size of each fiber, and setting, in casu decreasing a fiber pitch. As to the first effect hereabove, it is according to the present invention preferred to cover an area as large as possible of a light sensitive element, so as to obviate the need for strong focus of the light signal 8, thereby reducing the chance of aberration and thereby reducing the need for further optical elements, which enhances the transmission of light, i.e. reduces the loss thereof. The desired and created light spot is not much larger than the light sensitive area so as to minimize loss of light by projecting light on surrounding, inert parts. This arrangement implies however that the projection of light is relatively sensitive for positioning errors of a light beam 8, in that small displacement thereof implies a reduction in the amount of light than is received by the relevant light sensitive element, e.g. photodiode. Thus, by sizing the incidence spot 24i larger, but not much larger than the light sensitive area, it is according to the invention prevented that expensive or complex optical elements are required in the free space interconnect of the LOS, while on the other hand sensitivity as to misalignment of the incident light beam part is reasonably reduced. In this respect misalignment may be due to actual conditions of the litho system, to structural inaccuracy, or to a combination thereof. As to the second effect mentioned here above, the pitch of the ends of fibers Fb is incompatible with, in particular larger than the pitch of the light sensitive elements on the modulator array 24, unless undue, and consequently uneconomic manufacturing efforts are made. With the present dual lens and dual imaging system independence in setting both parameters is attained in a favorable manner. FIG. 3 represents the arrangement for preferred incorporation of the light optics system shown in FIG. 2, in the lithography system, according to the invention. It shows a holder 24S for the above mentioned blanker or modulator array 24, by means of which holder the modulator array 24 is placed in a charged particle column. Such charged particle column is, together with the holder for holding a wafer or other kind of target surface, included in a housing Hv by means of which a vacuum condition for said column and target stage is realized. The array of fibers Fb is fed through an opening in a demountable part of said housing Hv, here by using a significant amount of vacuum compatible sealing material for realizing an air tight sealing of the fibers in said opening. An inner housing end part Fbv of said fibers is thereby also to a significant extent secured from outside mechanical impulses that might act thereon. The end part Fbv of the array of fibers is at its end 2 further secured mechanically to a housing Hl for the lens and mirror part of the light optics system. In turn the housing Hl is secured to said modulator array holder 24S. In this manner it is in a favorable, mechanical manner secured that the positions of the fiber ends 2 and the modulator array, in particular the light sensitive areas thereof are fixed relative to one another. In turn, the array holder 24S is connected to an undepicted frame for elements such as collimator 52, and splitter 53, and as further discussed under FIG. 1, constituting the charged particle column. As illustrated in one dimension in FIG. 3, the holey mirror 104 covers the entire area of a modulator array, while in the same manner the lens 106 covers the entire area of the tilted mirror 104. The lens 106 is thereby incorporated axially in close proximity to the holder 24S. It may be clear from the above, that the principles of the dual lens system, mechanical fixation of a lens housing Hl to the blanker 24 and the specific application of a holey mirror 104 may all be applied independently from one another. Further to the latter, the principle of dual imaging can be applied while using an off-axis projection instead of the presently preferred perpendicular projection. FIG. 4 figuratively represents the light optic system of the improved lithography system according to a second embodiment. It entails the use of a holey mirror 107, which is applied for realizing an in-axis incidence of light beams 8 on the light sensitive elements of modulator array 24. The holey mirror thereto comprises one relatively large hole 108 through which all writing beams 27 deflected for blanking and all undeflected writing beams 28 may pass, or a plurality of relatively small holes, one for each deflected or undeflected writing beam. According to preference, the mirror 104 comprises a focusing reflecting surface, said reflecting surface in particular being placed at an angle for reflecting the incident light beams 8 towards the modulator 24 and said reflecting surface in particular being a concave surface for simultaneous focusing the incident light beams 8 onto the modulator 24. With the use of a holey mirror with a focusing reflecting surface 107, a focusing lens 106, may be omitted. It is favorably realized that any loss in light signal intensity, in particular due to reflections at the surfaces of the focusing lens 106, can be further reduced. Furthermore, it is realized that the focusing element in this second embodiment, in particular the concave reflecting surface of the holey mirror 107, can be much closer to the modulator array 24, than the lens 106 in the first embodiment. Due to this close distance, the light optical system of this second embodiment can be designed with a larger numerical aperture and thus with an increased resolving power of the light optical system. Also in the second embodiment of FIG. 4, the array of fiber ends 2 is completed with a micro lens array 101, forming a virtual fiber array 103, in fact an array of spots in the focal plane for the micro lenses 101. A micro lens of the micro lens array 101 performs a magnifying function on the light signals transmitted by a particular fiber of the fiber array Fb. The concave reflecting surface of the holey mirror 107 according to the second embodiment thus sets forth a dual image system comprising a magnification of each signal by means of a micro-lens, and a subsequent focusing of the signal by means of said concave reflecting surface of the holey mirror 107, common to all of the emitted light signals. Furthermore, it is realized that a holey mirror with a focusing reflecting surface 107 as shown in FIG. 4 may also be combined with a focusing lens 106 as shown in FIG. 3. In this case the focusing element 106, 107 comprises two optical parts and both optical parts may contribute to the focusing effect and/or can be used to further reduce optical aberrations. Apart from the concepts and all pertaining details as described in the preceding the invention also relates to all features as defined in the following set of claims as well as to all details as may be directly and unambiguously be derived by one skilled in the art from the above mentioned figures, related to the invention. In the following set of claims, rather than fixating the meaning of a preceding term, any reference numbers corresponding to structures in the figures are for reason of support at reading the claim, included solely as an exemplary meaning of said preceding term. |
|
048225525 | abstract | A method and apparatus for passively scanning for the gamma radiation emission count of nuclear fuel contained within a nuclear fuel rod to determine enrichment uniformity are enclosed, and wherein a nuclear fuel rod containing a nuclear fuel is advanced along a linear path of travel and its natural gamma radiation emission count is repeatedly detected at each of a plurality of regularly spaced apart discrete segments along the length of the rod. The outputs from each of the detecting steps are summed to obtain a total gamma radiation count for each segment from which the enrichment values for each segment as well as the average enrichment of said fuel rod may be calculated. |
abstract | Embodiments of the invention describe methods and apparatus for assigning a beam intensity profile to a gas cluster ion beam and processing workpieces using a gas cluster ion beam. One embodiment includes generating a gas cluster ion beam in a gas cluster ion beam processing apparatus, collecting parametric data relating to the spatial intensity of the gas cluster ion beam, and generating a beam intensity profile describing the spatial intensity of the gas cluster ion beam by fitting a mathematical functional shape to the parametric data. Another embodiment describes a method for processing a workpiece using a gas cluster ion beam. |
|
summary | ||
description | Controls for combustion boilers allow combustion engineers to optimize boiler performance. To optimize the performance of a boiler, a combustion engineer balances and lowers emissions, e.g., oxygen (O2), nitrogen oxides (NOx) and carbon monoxide (CO), from the boiler. The boiler has a series of controls to adjust, for example, the amount of fuel and air supplied to a primary combustion zone in the boiler, a reburn zone, and an overfire air zone. A boiler typically has various emissions sensors distributed in its flue gas path. The sensors generate data indicating the emission levels at the sensor locations in the boiler. For example, carbon monoxide (CO) and oxygen (O2) sensors have been arranged in a grid at a downstream location of the boiler. The grid of sensors generates data indicating a profile of emissions at a plane of the flue gases where the grid is located. Sensor grid data has not been previously processed in a manner to provide real time plots of sensor grid data. Traditionally, engineers adjust the controls for a boiler combustion system without receiving immediate feedback as to the consequences of their adjustments on emissions. Engineers do not see the results of their adjustments until after the data on emissions subsequent to the adjustments becomes available for review. It would be desirable for engineers to receive prompt emission feedback to view the influence on emissions due to adjustments being made to a boiler. The invention may be embodied as a method of presenting a changing combustor condition including: sensing the combustor condition in real time using a sensor array in a gas path of the combustor; generating data from the sensor array representative of the combustor condition at a plurality of positions in the gas path; transmitting the generated data to a computer system proximate to a controller for the combustor; generating a graphical representation of the real time showing combustor conditions in the gas path, and displaying the graphical representation in real time on the computer system. The invention may be further embodied as a method of presenting a changing combustor condition comprising: sensing the combustor condition in real time using a sensor array in a gas path of the combustor; generating data from the sensor array representative of the combustor condition at a plurality of positions in the gas path; transmitting the generated data in real-time to a computer system proximate to a controller for the combustor; capturing the real-time data on the computer system at a location proximate to boiler controls; generating a graphical representation of the real time showing combustor conditions in the gas path, and displaying the graphical representation in real time on the computer system. The invention may also be embodied as a system for collecting and presenting a changing combustor condition comprising: a sensor grid located in the combustion, said grid sensing the combustor condition in real time using a sensor array in a gas path of the combustor and generating data representative of the combustor condition at a plurality of positions in the gas path; a network for communicating electronic data; a computer system coupled to the network and further comprising a controller and a display, wherein said controller receives the generated data and generates a graphical representation of the real time showing combustor conditions in the gas path, and said graphical representation is presented on said display. The invention may be also embodied as a method of adjusting a boiler having a flue gas duct comprising: sensing flue gas emissions in the gas duct with a plurality of emission sensors arranged in an array; generating a multidimensional graphical depiction of the flue gas emissions by plotting sensor data captured from the emission sensor; adjusting the boiler to modify the distribution of flue gases in the gas duct; generating a subsequent multidimensional graphical depiction of the flue gas emissions by plotting sensor data captured subsequent to the boiler adjustment, and repeating until the graphical depiction displays an acceptable plot of flue gas emissions. FIG. 1 is a schematic cross-sectional diagram of a combustor 10, e.g., a boiler. Several in-situ carbon-monoxide (CO), oxygen (O2) and temperature sensors 12 are positioned across a flue gas duct 14 of a combustor to monitor hot flue gases flowing through a post-flame zone 20. The sensors 12 may, for example, be a planer grid of solid-electrolyte sensors which measure the concentration of (or changes in the concentration of) CO, O2 and temperature in the flue gases. Other sensors may also be used to measure other component gas concentrations in the flue gas or other conditions of the flue gas. The sensors generate signals indicative of the concentration of or changes in the concentration of one or more gases present in the flue gases or of the temperature of the flue gas. In practice, any number of sensors 12 may be installed across a plane in the flue gas duct 14. The sensors may be arranged in a horizontal or vertical row, in a two-dimensional (2D) or 3D grid, or in some other effective sensor pattern. The sensor may extend at varying depths into the duct to monitor a distribution profile of gaseous combustibles in the flue gas. The combustor 10 may be a large structure, such as more than one, two or even three hundred feet tall. The combustor 10 may include a plurality of combustion devices, e.g., an assembly of combustion fuel nozzles and air injectors 16, which mix fuel and air to generate flame in a flame envelope 18 within the combustor 10. The combustion device 16 may include burners, e.g., gas-fired burners, coal-fired burners and oil-fired burners, etc. The burners may be situated in a wall-fired, opposite-fired, tangential-fired, or cyclone arrangement, and may be arranged to generate a plurality of distinct flames, a common fireball, or any combination thereof. Alternatively, a combustion device called a “stoker” which contains a traveling or vibrating grate may be employed to generate flame within the combustor 10. When the combustion device(s) 16 in the combustor 10 are actively burning fuel, two distinct locations can be identified within the combustor 10: (1) a flame envelope 18, and (2) a “post-flame” zone 20, which is the zone downstream of the flame envelope 18 spanning some distance toward the flue gas exit 22. Downstream of the flame envelope 18, hot combustion gases and combustion products may be turbulently thrust about. These hot combustion gases and products, collectively called “flue gas,” flow from the flame envelope 18, through the “post-flame” zone and towards the exit 22 of the combustor 10. Water or other fluids (not shown) may flow through the walls 24 of the combustor 10 where they may be heated, converted to steam, and used to generate energy, for example, to drive a turbine. The sensors 12 are located in the post-flame zone 20 of the combustor 10. The sensors 12 alternatively may be disposed in the flame envelope 18 if constructed to withstand the harsh, high-temperature environment thereof. The sensors are, in this example, a 2D grid of CO, O2 and/or temperature sensors arranged at the post-flame zone 20 and in a particular plane of the flue gas path. The sensors generate data indicative of the CO, O2 and/or temperature concentration at various points in a plane of the flue gas at the sensor location. Based on the data generated from each sensor, a profile can be generated of the CO emissions in the plane of the flue gas at the sensor grid location. FIG. 2 is a block diagram of computer and electronic components for sensing combustion emissions; generating and processing sensor data, and plotting and otherwise presenting the sensor data. The sensor grid 30 (see exemplary sensor grid 12 in FIG. 1) is positioned at a location in the combustor to sense a condition of the combustion process and associated emissions. For example, the sensor grid may include sensors for CO, O2, and/or temperature measurements of the flue gases. Each sensor in the grid 30 generates data indicative of a characteristic of the combustion process, such as the level of CO or O2 emissions in the flue gas or of the temperature at a particular location in a plane of the flue gas. The data from the sensor grid is electronically captured by data acquisition hardware 32 and associated data acquisition software 34. The sensor data is outputted by the hardware/software 32, 34 in a continuous data stream. The data may be output every ten seconds, every second, or every 1/10th of a second (for example), to provide a real-time data output of the sensor grid. Alternatively, the data acquisition hardware 32 may include an electronic memory to store the data generated by the sensor grid and the time at which each sensor measurement is taken. The data acquisitions hardware operates under the supervision of data acquisition software 34 to capture the sensor grid data, time stamp the data and store the data, such as in a database, for subsequent processing by a computer system 36. The sensor data stored in the data acquisition hardware 32, and accessible using the data acquisition software 34 may be formatted such that each of the sensor output values for the grid at a particular period of time is stored in a database. The data may include both (real time) data regarding the sensor output values, and historical data of prior sensor readings with associated time of reading information). Accordingly, the sensor data stored in the memory of the data acquisition hardware/software provides both real time information on sensor readings taken of the flue gases and historical sensor readings of flue gas measurements. The computer 36 may receive a real-time output of sensor data or (alternatively) access the sensor data in the data acquisition hardware 32 by interrogating the data using the data acquisition software. The data acquisition hardware and software are well known and conventional software products. The data acquisition hardware may be a conventional computer system with electronic memory. The data acquisition software may be conventional database measurement software and software for interfacing with the sensor outputs and capturing the data in usable data form. For example, the sensor interface software may convert sensor readings into data indicative of CO and/or O2 levels, and temperature levels within the flue gas stream. The computer 36 may be, for example, a personal computer laptop computer which is carried by the boiler engineer to the control panel for the boiler, and to the side of a boiler having burner adjustment controls. The computer 36 may have a wired or wireless network connection 38 that links the computer to the data acquisition hardware/software storing the sensor data. For example, the laptop may be connected via a wired CATS Ethernet network (which may include a link through the Internet) to the data acquisition hardware/software unit. The computer 36 may transmit a database interrogation request to the data acquisition software 34 to download certain sensor data stored in the data acquisition hardware. The requested sensor data may include real time sensor level outputs and historical sensor output levels. The requested data is transferred from the data acquisition hardware/software, over the network connection 38 and to the computer 36. The computer 36 may temporarily store the sensor data. The computer 36 may include conventional software modules including a display software module 40 and a mapping or graphing software module 42. The display software and graphing software in combination plots the sensor data in a contour graph or other graphical map to show the sensor data as points on the graph and arrange in a pattern substantially the same as the sensor pattern of the sensors in the grid 30. In general, data collected from the sensor grid flows into the computer 36 which is available to the boiler engineer when adjusting the combustion conditions within the combustor. The computer 36 processes the sensor data to display to the engineer the sensor data in easily readable form, such as in a contour map showing emission levels at the sensor grid location. In addition, the computer 36 may perform other processes on the sensor data, such as calculating average emission levels based on all of the sensor output levels from the grid 30. The sensor data processed by the computer 30 is presented in a graphical display or output as calculated data which is available to the combustion engineer while adjusting the combustor. FIG. 3 is a flow chart that generally shows the data processing operations performed by the computer 36. The process steps shown in FIG. 3 are performed by the display software 40 and contour graphing software 42, in conjunction with other software modules executed by the computer. Suitable display software, contour graphing software and other software executed by the computer are either conventional and commercially available software programs or may be developed using well-known software programming techniques. The sensor data flow is downloaded into the computer 36 using a software data input module 44. The data import module imports sensor measurement data, e.g., data regarding CO, O2 and/or temperature. Once imported into the computer 36, the sensor data is available for graphing and calculations. Further, the data import module may interrogate the database of sensor readings and time of readings stored in the data acquisition hardware/software 32, 34. The data input module may also include software for downloading sensor data flow over the network connection 38. The downloaded sensor data is formatted into a database or other form usable by the display software and contour graphing software by a data loader module software program 46. The data loader module temporarily stores the downloaded sensor data and time data so as to provide a database of sensor data usable to generate contour maps of emission levels in the boiler and to calculate emission conditions, such as an average emission level based on an average of sensor readings during a particular period of time. A controller module 48 in the computer 36 provides control functions for manipulating and calculating the sensor data provided by the data loader module 46. The controller module is provides an interface between the other software modules to allow the modules to function together. The controller module interrogates the other modules and controls the flow data and commands between these modules. In addition, the controller module includes user interface functions which allow the boiler engineer to select a type of graph or map to be used in presenting the data, select a time (or period of times) corresponding to the sensor data to be presented, and select calculations to be performed on the sensor data. For example, a combustion engineer may request contour maps to be prepared based on real time sensor data flow. Further, maps of historical sensor data may be read in from a data file representing data collected at earlier time periods, such as at fifteen minute intervals during a preceeding four hour period. The historical contour maps may be displayed sequentially. The controller module accesses the data loader module 36 to collect real time sensor data and historical sensor data for each fifteen minute period during a proceeding four hour period. A timer software module 50, may be used to provide a timing function for a real-time sensor data stream and to continually update, e.g., every ten seconds, every second, every 1/10th of a second (for example), graphs and plots of the boiler emissions. In addition, the timer 50 may provide timing information to be associated with a real time data flow from the sensor data, if the data acquisition hardware 32 and data acquisition software 34 does not already provide such a timing function. The time module 50 provides timing control for contour plot updates and sets a delay period between each update. A configuration module 52 works in conjunction with the controller module 58 to format the sensor data and timing information in a manner suitable for either a graphing software module 54 and a data calculation module 56. A certain amount of configuration is needed to, for example, correlate sensor data points from the sensor grid to points on a contour plot or other graph. The configuration module may also establish a graphing update rate, and other parameters needed to be configured. A configuration data file may be stored regarding the sensor points on the grid, refresh rate and other information needed for plotting contour plots. The configuration module 52 may also perform standard data formatting processes to place the sensor data and timing information in a format suitable for graphing the data onto a contour map or presenting the data to a calculation function that generates, for example, average emission levels. The graphing module 54 generates a map or graph of the sensor data which is viewable by the boiler engineer. By viewing the map or graph of the sensor data, the boiler engineer sees a graphical representation of the actual emission conditions at the plane of the flue gas corresponding to the sensor grid 30. By interacting with the controller module 48, the boiler engineer may alternately view a real time contour map of current sensor data and a sequence of contour maps of prior sensor data readings, such as taking at fifteen minute intervals during the proceeding two hour period. The boiler engineer may view calculated emission values, such as average emission levels based on an average of all sensor data readings from the grid 30 at current levels and proceeding time intervals, by viewing the output of the calculation module 56. Further, a data export module 57 enables the boiler engineer to export calculated values regarding emissions and based on sensor data from the computer 36 to another computer or, a printer, or other data output devices. FIGS. 4 and 5 are exemplary contour plot graph of CO emission levels taken by a grid of CO sensors in the flue gas path of a boiler. The plot graphically shows the CO emissions across a flue gas plane of a boiler having a rectangular cross section. The contour plot 60, 62 indicates different levels of CO emissions by shaded or colored regions. A color or gray scale bar 64 at the top of the contour provides a correlation between plot color/shading and emission levels. The individual sensors in the sensor grid 30 are represented by point 66 on the contour plot. The sensor point 66 are arranged similarly to the arrangement of sensors in the grid 30 in the boiler. The contour plot may also display the actual sensor value 68 for each sensor in the grid. An average sensor reading 70 may be presented below the grid. The contour graphing module may make available to the boiler engineer a series of contour plots taken at certain intervals, such as every one second, to enable the boiler engineer to see a sequence of changes made to the emission levels as the boiler engineer adjusts combustion conditions in the boiler. In addition, the contour graphing software program may enable a moving picture display 72 which sequentially shows the contour plots over a period of time. The moving picture display readily shows how changes in emission levels occur as adjustments are made to the combustion conditions. Using the contour plots and cumulative CO average emission level, a boiler engineer is aided in adjusting the combustion conditions to balance the sensor readings 68 in the grid 30 and minimize the cumulative average 70 of the sensor readings. The boiler engineer may use the contour plots and calculated average of the sensor readings to perform other optimization procedures on the boiler. For example, the engineer may adjust boiler controls to reduce smooth the emission gradients shown in a real-time contour plot. By smoothing the gradients on the plot, the tendency can be minimized of the boiler to foul due to reduce pressure zones in the gas duct 14. Real time CO grid sensor data is presented a graphical form to boiler engineer as they make adjustments to optimize boiler performance. Data from a grid of Reuter-Stokes™ CO sensors 30 is imported into a system through a Reuter-Stokes™ data acquisition unit 34. Once the data is in computer 36, a contour-plotting program will be launched. The plotting application will read the CO data and plot a contour diagram for the sensors in the grid. The plotting software will continuously update this plot with live data. The plot will be arranged with the data points in the same configuration as the CO grid. A single point on the plot will correspond to a single CO sensor in the grid. This graphical representation of the CO sensor data can be used to make adjustments to the boiler to optimize the efficiency of the boiler and to reduce NOx emissions. A service engineer could take a laptop, utilizing CatS Ethernet or wireless networking technology, and stand in front of the boiler controls while viewing the data. The engineer could make adjustments to the boiler and watch the changes in the plots to visually see how his changes affected the boiler performance. The data would be updated in a matter of seconds, providing rapid feedback to the engineer, and thus, minimizing the time to optimize the boiler settings. The plots will allow the engineers to adjust the combustion fuel nozzles and air injectors (see device 16 in FIG. 1) until the CO sensor values are balanced, and the average CO value is minimized. Achieving balanced sensor values and a minimized averaged sensor value optimizes the combustion conditions for the boiler. To make the adjustments, the engineer may access live sensor data from the data acquisition system, plot the data, calculate an overall CO sensor value, and provide current and historical plots of sensor data in a display package that can be installed on a laptop computer that the boiler engineer carries when making the adjustments at the boiler. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. |
|
summary | ||
055747582 | claims | 1. A method for measuring selectively gamma-rays of radionuclides, in primary water of a nuclear reactor, which further contains radionuclides each emitting a pair of annihilation gamma-rays in diametrically opposite directions, by the use of a gamma-ray spectrometric system which includes a primary detector for detecting photons of the gamma-rays and photons of the one annihilation gamma-rays in the one direction, a secondary detector for detecting at least photons of the other annihilation gamma-rays in the opposite direction, a shield detector for detecting Compton-scattered photons of the gamma-rays escaped from the primary detector to the shield detector, and an anticoincidence circuit connecting with the primary, secondary, and shield detectors, the primary detector and the secondary detector being located in opposed manner relative to the axis of a coolant pipe through which the primary water flows, the shield detector surrounding the primary detector except for its portion facing the pipe on which the gamma-rays and the annihilation gamma-rays are incident, which method comprises: detecting the photons of the gamma-rays and the photons of the one annihilation gamma-rays on the primary detector as pulses while detecting the photons of the other annihilation gamma-rays on the secondary detector as pulses; counting the pulses of the secondary detector in anticoinci- dence with the pulses of the primary detector thereby to reject the recording of the pulses of the annihilation gamma-rays from the primary detector, thus minimizing the annihilation gamma-rays on the primary detector; and subsequently determining count numbers of the gamma-rays. 2. A method for measuring selectively gamma-rays of radionuclides, in primary water of a nuclear reactor as set forth in claim 1, which further comprises simultaneously detecting the Compton-scattered photons of the gamma-rays on the shield detector as pulses; and counting the pulses of the shield detector in anticoincidence with the pulses of the primary detector thereby to reject the recording of the Compton-scattered gamma-rays from the primary detector, whereby the Compton-scattered gamma-rays on the primary detector are also diminished. 3. The method for measuring selectively gamma-rays of radionuclides as set forth in claim 1, which comprises using a semiconductor detector or a scintillation detector as the primary detector, and scintillation detectors as the secondary and shield detectors. 4. The method for measuring selectively gamma-rays of radionuclides as set forth in claim 2, which comprises using a semiconductor detector or a scintillation detector as the primary detector, and scintillation detectors as the secondary and shield detectors. 5. A method for measuring selectively gamma-rays of radionuclides as set forth in claim 3, wherein the semi-conductor detector is selected from a germanium detector, lithium drift silicon detector and cadmium telluride detector; and the scintillation detector is selected from a detector of sodium iodide activated by thallium, detector of cesium iodide activated by thallium, and bismuth germanate detector. 6. A method for measuring selectively gamma-rays of radionuclides as set forth in claim 4, wherein the semi-conductor detector is selected from a germanium detector, lithium drift silicon detector and cadmium telluride detector; and the scintillation detector is selected from a detector of sodium iodide activated by thallium, detector of cesium iodide activated by thallium, and bismuth germanate detector. |
abstract | A focused ion beam apparatus, including: a sample holder provided with a fixing surface for fixing, via a deposition film, a micro-specimen extracted from a specimen using a method for fabrication by a focused ion beam, in which a width of the fixing surface is smaller than 50 microns; a specimen transferring unit having a probe to which the specimen can be joined through the deposition film, and transferring the micro-specimen extracted from the specimen by the focused ion-beam fabrication method, to the sample holder; and a sample chamber in which the sample, the sample holder and the probe are laid out, wherein, in the sample chamber, the micro-specimen extracted from the specimen by the focused ion-beam fabrication method is fixed to the fixing surface of the sample holder through the deposition film, and the micro-specimen fixed to the fixing surface is fabricated by irradiating the focused ion beam. |
|
041486080 | abstract | Method and apparatus for the processing of fluid materials, particularly in the preparation of samples for radioactive isotope tracer studies by combustion of starting materials containing such isotope tracers. The sample is burned in a combustion chamber which tapers upwardly and inwardly above the sample receptacle so as to approximate the shape of the flame of a burning sample, and the combustion products are continuously exhausted from the combustion chamber and passed through a heat exchanger which condenses the condensable vapors in the combustion products. The condensed vapors are then separated from the gases, and the gases are passed into a reaction column if there is a radioactive isotope tracer remaining in gas form. Oxygen is fed into the combustion chamber at a controlled rate during combustion, and after combustion nitrogen gas is fed into the combustion chamber and exhausted therefrom through the heat exchanger and into the separating means, so as to purge the system of any remaining gaseous production products. A liquid scintillator, and a liquid solvent if desired, are passed through the heat exchanger into the separating means after each combustion so as to recover any residual condensed vapors. In the reaction column, the gas containing the radioactive isotope tracer is reacted with a trapping agent in a column comprising a series of smoothly contoured reaction chambers interconnected by smoothly contoured necked down portions. After all the gases have been passed through the column, the direction of gas flow is reversed in the column so as to discharge the reaction product into a counting vial. A liquid scintillator, and a liquid solvent if desired, are then passed through the reaction column following the same procedure as followed previously for the trapping agent, thereby recovering all the reaction product from the column. |
claims | 1. A reactor core monitoring system, comprising:an information retention portion configured to retain a regular cycle time interval and a short cycle time interval used for calculating reactor core performance data, the time interval of the short cycle being shorter than the regular cycle thereof;a first data storage portion configured to store the reactor core performance data calculated in the timing of the regular cycle, the reactor core performance data including at least one information of power distribution, thermal limits, and amount of fuel consumed;a second data storage portion configured to store the reactor core performance data calculated in the timing of the short cycle asynchronous to the regular cycle;a signal processing portion configured to create heat balance data based on a process signal in a cycle which is shorter than the short cycle, the process signal including at least one information of reactor pressure, temperature, flow rate, control rod position, average power range modeling signals, and local power range modeling signals;a data acquisition portion configured to acquire, in a timing of the regular cycle, latest heat balance data from the signal processing portion and reactor core performance data which was calculated in a previous timing of the regular cycle from the first data storage portion, while also being configured to acquire, in a timing of the short cycle asynchronous to the regular cycle, latest heat balance data from the signal processing portion and reactor core performance data from either the first data storage portion or the second data storage portion which was calculated most recently regardless of whether calculated in the regular cycle or the short cycle; anda data calculation portion configured to calculate new reactor core performance data indicating an updated amount of fuel consumed based on the acquired reactor core performance data and the heat balance data, the new reactor core performance data being stored in the first data storage portion or the second data storage portion. 2. The reactor core monitoring system according to claim 1, further comprising an input portion configured to receive input information corresponding to the regular cycle time interval, the short cycle time interval, and an activation time of the short cycle, wherein activation of the short cycle time interval is started/stopped arbitrarily. 3. The reactor core monitoring system according to claim 1, wherein the information retention portion is also configured to retain storage address information on the reactor core performance data calculated in the data calculation portion. |
|
053902190 | summary | FIELD OF THE INVENTION The invention relates to steam generators used in nuclear installations for electric power generation, particularly those using one or more pressurized water reactors. The invention more particularly relates to a device placed in the secondary circuit of the steam generator. Prior Art In a nuclear power station, in which the power supplying means is constituted by a pressurized water nuclear reactor, a primary circuit is used for removing the energy produced by the reactor. Pressurized water is enclosed within the the primary circuit. Use is made of a heat exchanger, such as a steam generator, for utilizing the thermal energy extracted by the primary circuit from the nuclear reactor. Such a steam generator is shown in FIG. 1. The primary circuit has an inlet 1 and an outlet 2 located at the lower end of the steam generator. The pressurized water flowing in the primary circuit traverses, within the steam generator, a tube bundle 3, in the lower part of the steam generator. The inlet for the water for the secondary circuit 4 is lateral and is positioned in the upper part. The outlet 5 of the secondary circuit is located in the upper part of the steam generator. After entering through the inlet of the secondary circuit 4, the water from the latter is distributed by a supply ring 6 and is piped between the pressure envelope 7 of the steam generator and the envelope 8 of the tube bundle 3. It then rises along the latter and is vaporized by contact with it. On reaching the upper end 9 thereof, it is collected by the upper part 10 of the envelope 7 and by discharge pipes 12 equipped with centrifugal separators for separating the water from the steam. The steam is then discharged through the outlet 5 after passing through one or more dryers 13, which complete the separation of the water from the steam. The water in saturated form separated in this way from the steam is known as recirculated water and is piped via the pipe or pipes 15 before being mixed with the water from the supply ring 6. Bearing in mind the structure of that part of the secondary circuit traversing the steam generator, it is readily apparent that relatively small objects, enclosed within the secondary circuit may follow the path of the latter within the steam generator and may thus be jammed or wedged in the narrow passages. constituted by the spaces separating the tubes of the tube bundle 3. Bodies foreign to the steam generator and having different shapes, sizes and forms, referred to as migrating bodies, can be accidentally introduced into the steam generator via the secondary water supply system, or during maintenance operations. During the operation of the steam generator, these bodies may be carried along by the secondary fluid and then become fixed at different points of the steam generator, such as the tube plate 31, or enter the tubes of the bundle 3. These objects can damage the walls of the tubes by impact or friction. SUMMARY OF THE INVENTION It is an object of the invention is to limit the size and number of migrating bodies coming from the secondary water supply system and the upper part of the steam generator and which are liable to reach the tubular plate and damage the bundle of tubes. The subject of the invention is a device for trapping migrating bodies within the secondary circuit of a steam generator of a nuclear power generation installation, constituted by a plurality of grids or equivalent mechanical filtering systems which, for optimum efficiency, occupy the entire annular section of the secondary circuit, downstream of the water supply tubes for the secondary circuit and upstream of the introduction of the water into the bundle of tubes of the primary circuit. When the tubes of the bundle of tubes are spaced by a given distance, the efficiency of the device according to the invention increases if the grids have meshes whose maximum width is smaller than such distance, so as to not allow the passage of objects or bodies liable to jam between the tubes. In the main construction of the device according to the invention, the grids or the like are constituted by circular sectors fitted on two radial brackets common to two adjacent sectors and welded to the envelope of the tube bundle. In this case, the grids are preferably screwed to the brackets so as to be dismantlable. In the preferred embodiment of the device according to the invention, the width of the grids is slightly less than the width of the annular section of the secondary circuit at the point where the grids are installed so as to leave a clearance of a few millimeters, thus permitting expansions between the pressure envelope and the tube bundle envelope of the steam generator. In this case, first outer strips can be placed on the inner wall of the steam generator pressure envelope in the annular section in order to fill the external circular clearance between the grids and the pressure envelope. Second circular strips fixed on the outer periphery of the grids make it possible to avoid the reintroduction into the space between the pressure envelope and the tube bundle envelope of objects trapped on the grids. In the same way, inner strips can be placed between the grids and the outer wall of the tube bundle envelope. In order to be able to withstand the possible impacts of migrating bodies, the various hydraulic stresses and the weight of operators, the grids have a thickness of a few centimeters, so as to have an adequate mechanical strength. |
summary | ||
048030414 | claims | 1. A process for the recycling of nuclear fuel pellets contained in a first metal can in which these pellets and said first metal can have previously been irradiated in a fast neutron nuclear reactor, wherein the process comprises extracting the pellets from the first irradiated can and introducing these pellets into a second unirradiated metal can before irradiating again said pellets contained in said unirradiated second metal can in a fast neutron reactor, said unirradiated metal can having a larger internal diameter than the internal diameter of the first can when said first can was in an unirradiated state, wherein the pellets are extracted from the first can by progressively melting the first can from one of its ends, the thus exposed pellets being maintained in their orientation and position in the stack and then being immediately introduced into the new can. 2. A process according to claim 1, wherein the first can is melted by means of a coil supplied by a high frequency electric current producing a skin effect by induction. 3. A process according to claim 1, wherein the first can is removed immediately after it has melted. 4. A process according to claim 3, wherein the first can is removed by means of a refractory material deflector and to which the first can does not adhere after melting. 5. A process according to claim 3, wherein the first can is removed by blowing a neutral gas. 6. A process according to claim 1, wherein the pellets are introduced into the new can after preheating the latter. 7. A process according to claim 1, wherein the new can is placed in a sleeve or jacket limiting the contamination thereof. |
summary | ||
046541942 | claims | 1. A nozzle assembly for directing coolant into the duct tube of a fuel assembly attached thereto compising: an elongated shell having inlet openings adjacent one end thereof for admitting coolant thereinto, an orifice plate assembly in said shell downstream of said inlet openings, neutron shielding means in said shell downstream of said orifice plate assembly, diffusing means in said shell downstream of said neutron shielding means for dispersing said coolant uniformly through said duct tube, said orifice plate assembly comprising a plurality of separable stacked orifice plates having differently configurated and sized openings, respectively, for directing said coolant therethrough in a predetermined flow pattern, and wherein one of said orifice plates includes means for imparting a spiral flow to said coolant, and said shielding means includes a shield block having a central passage for conveying said coolant in a spiral path therethrough, said central passage having at one end thereof a converging inlet adjacent said one orifice plate, and further wherein said shield block is formed with an annular well surrounding said central passage, and a partition defining in part said central passage and separating said well from said passage. 2. A nozzle assembly according to claim 1, wherein said openings in each of said plates are offset from the openings in adjacent plates. 3. A nozzle assembly according to claim 1 said partition formed with slots establishing communication between said passage and said well for passing particulates entrained in said spiraling coolant flow therethrough for entrapment in said well. 4. A nozzle assembly according to claim 1 including an insert removably mounted in said shield block against the distal end of said partition, said insert having a bore communicating with said central passage. 5. A nozzle assembly according to claim 1 wherein said means for imparting a spiral flow to said coolant comprises a plurality of circumferentially spaced curved vanes. 6. A nozzle assembly according to claim 1, wherein said shell comprises a major portion and a lower portion detachably connected to said major portion and sealing means interposed between said major portion and said lower portion 7. A nozzle assembly according to claim 6, including means for threading said lower portion on said major portion, and means for locking said lower portion to said major portion in the assembled relation thereof. 8. A nozzle assembly according to claim 1, wherein said neutron shielding means comprises a shield block and a shield plug disposed in an abutting stacked relation and having passages therethrough for conveying said coolant from said orifice plate assembly to said diffusing means. 9. A nozzle assembly according to claim 8, wherein said diffusing means comprises an individual block having a central bore and a plurality of bores in radial spaced relation to said central bore for conveying coolant from said neutron shielding means into said duct tube for uniform distribution therethrough. 10. A nozzle assembly according to claim 9 wherein said last mentioned block is threaded within said shell in abutting engagement against said shield plug to secure said shield plug, said shield block and said orifice assembly in place in a stacked relation. |
059563818 | abstract | A method and an apparatus detect the dropping of at least one control element in a reactor core of a power station by delaying signals output by detectors disposed along a fall path of the control element in such a way that they are approximately simultaneous. This improves a registration of the dropping of the control element by improving a ratio between a useful signal and a noise signal. |
summary | ||
051320770 | summary | BACKGROUND OF THE INVENTION The invention relates to pressurized water nuclear reactors and is for use in the same environment as U.S. patent application Ser. No. 07/582,589, filed substantially concurrently herewith, by the same inventor, for "Bottom Nozzle to Lower Grid Attachment". More specifically, the device relates to the lower core plate to fuel assembly interface. The invention is a design created more evenly to distribute the flow within and above the lower end fitting to decrease the jet flow impingement on fuel rods. This improves reactor performance by improving the performance diffusing lower core plate flow jets. The desired result sought and achieved is a decrease of flow induced vibration of the fuel rods and stiffening and lightening of the lower end fitting. In the past, flow induced vibration of fuel rods in their lower spans has caused high fuel rod wear rates. This has resulted in the use of a stronger grid support system in the lower section of the fuel assemblies. The current and prior art practice of using inconel lower grids, with their high neutron capture, is to achieve these required supporting forces. The need for the improved lower end fitting thus also results from the desire for vibration elimination which would allow use of a low parasitic material such as Zircaloy 4. Use of an integral wear-reduction-shield of the type taught in U.S. Pat. No. 4,888,149 issued to the inventor of the present invention also provides strength to the new lower end fitting. SUMMARY OF THE INVENTION The novel bottom nozzle or end fitting device of the invention is constructed of stainless steel and is located immediately above the lower core plate flow holes. The device is circular and has a curved profile. The geometry of the devices, their number and height, is dependent on the reactor core plate geometry and the size of the lower end fitting. The devices are rigidly held in place by members extending from the edges of the device to the lower end fitting support legs and the thimble flux shield. This stiffens the end fitting and permits a reduced thickness of the flow plate and legs. The curved shapes are parabolic type and are adjusted to optimize the diffusion of the jet to lower pressure drop. The diffusers are bell mouth in type and have a unique shape dictated by the reactor and fuel assembly design. Based on the lower core plate flow hole geometry, lower end fitting design, and the reactor flow rate, the diffuser shapes are optimized to achieve maximum jet diffusion and resultant reduction in damaging vibration of fuel rods and pressure drop due to turbulence. The device acts as bell mouth annular diffusers causing the lower core plate flow hole jets to be diffused and evenly spread before impingement on fuel rods located above the end fitting. This results in a calculated 10% to 15% lower pressure drop for the lower end fitting. It also lowers the jet flow impingement on the assembly's fuel rods. Less jet flow impingement results in lower fuel rod wear due to flow induced vibration of the fuel rods. The addition of these devices are also used as structural members of the end fitting. The devices and members and their placement results in thinner lower end fitting legs, smaller lower end fitting gussets, and thinner flow plates while still maintaining the original strength of the lower end fitting. |
description | The present patent application claims the benefit of U.S. Provisional Application No. 62/290,427, which was filed on 2 Feb. 2016, and which is hereby incorporated by reference. The disclosure relates generally to curing polymer materials, and more specifically, to a solution for curing ultraviolet sensitive polymer materials (e.g., polymer inks, coatings, adhesives, and the like). Ultraviolet curing, commonly known as UV curing, is a type of curing that involves a photochemical process in which high-intensity ultraviolet light is used to create a photochemical reaction that instantly cures or “drys” polymer inks, coatings or adhesives. Benefits of UV curing include that it is a low temperature process, a high-speed process, and a solventless process, as the cure is by polymerization rather than by evaporation. These benefits make UV curing suitable for printing, coating, decorating, stereolithography and assembling of a variety of products and materials. Mercury vapor lamps have traditionally been the industry standard for curing products with ultraviolet light. Mercury vapor lamps typically have a small-fused quartz arc tube mounted within a larger bulb. An electric arc is discharged through mercury in the arc tube to produce light by emitting a spectral output in the ultraviolet region of the light spectrum. The light intensity generated from mercury vapor lamps generally occurs in the 240 nm to 270 nm range and the 350 nm to 380 nm range, which can cause rapid curing. Fluorescent lamps are another type of ultraviolet source used for UV curing applications. Generally, fluorescent lamps are a low pressure, mercury vapor gas-discharge lamp that uses fluorescence to produce visible light. In operation, an electric current in the gas excites mercury vapor which produces short-wave ultraviolet light that causes a phosphor coating on the inside of the lamp to glow. The fluorescent lamps are suitable for UV curing because of their ability to operate at specific frequencies. In the last few years, ultraviolet light emitting diodes (UV LEDs) have been used in UV curing applications. UV LED curing technology offers many benefits over traditional broad-spectrum UV curing modalities like mercury vapor lamps and fluorescent lamps, such as lower operating costs and environmental attributes that eliminate mercury and ozone safety risks. Because UV LED curing is a relatively new type of UV curing technology, it is desirable to attain solutions that enable more effective curing of ultraviolet sensitive polymer materials such as inks, coatings, and adhesives. This Summary Of The Invention introduces a selection of certain concepts in a brief form that are further described below in the Detailed Description Of The Invention. It is not intended to exclusively identify key features or essential features of the claimed subject matter set forth in the Claims, nor is it intended as an aid in determining the scope of the claimed subject matter. Some aspects of the present invention are directed to utilizing ultraviolet light at different wavelength emissions that are arranged in a random, mixed, sequential or simultaneous arrangement to cure ultraviolet sensitive polymer materials such as polymer inks, coatings, and adhesives. These ultraviolet sensitive polymer materials can have varying thicknesses. In addition, the ultraviolet sensitive polymer materials can have liquid monomers and oligomers mixed with a small percent of photoinitiators. Also, the ultraviolet sensitive polymer materials can have selected pigments and additives. Exposure to ultraviolet energy causes the inks, coatings or adhesives that form the ultraviolet sensitive polymer materials to instantly harden. The UV curing system of the illustrative embodiments described herein can include an ultraviolet illuminator including an ultraviolet light C (UV-C) radiation emitter having a set of UV-C sources configured to emit UV-C radiation at a predetermined UV-C duration and intensity, an ultraviolet light B (UV-B) radiation emitter having a set of UV-B sources configured to emit UV-B radiation at a predetermined UV-B duration and intensity, and an ultraviolet light A (UV-A) radiation emitter having a set of UV-A sources configured to emit UV-A radiation at a predetermined UV-A duration and intensity. A control unit is configured to direct the curing of the ultraviolet sensitive polymer material on a substrate with the UV-C radiation emitter and at least one of the UV-B radiation emitter and the UV-A radiation emitter. In one embodiment, the control unit directs the UV-C radiation emitter to perform surface pinning of the ultraviolet sensitive polymer material, and one of the UV-B radiation emitter and the UV-A radiation emitter to perform a final curing of the ultraviolet sensitive polymer material after the surface pinning by the UV-C radiation emitter. The control unit can further direct the UV-C radiation emitter and at least one of the UV-B radiation emitter or the UV-A radiation emitter to cure the ultraviolet sensitive polymer material inhomogeneously at different lateral locations, wherein the UV-C radiation emitter cures the ultraviolet sensitive polymer material at a first location with the UV-C radiation at the predetermined UV-C duration and intensity, while one of the UV-B radiation emitter or the UV-A radiation emitter cures the ultraviolet sensitive polymer material at a second location with a different intensity and wavelength. In one embodiment, the ultraviolet sensitive polymer material can include a multi-layered film formed on the substrate. In this manner, the UV-C radiation emitter can perform surface pinning of each layer formed on the substrate, while one of the UV-B radiation emitter or the UV-A radiation emitter can perform a final curing of the multi-layered film after the surface pinning of the outermost layer. In one embodiment, the multi-layered film can include droplets of the ultraviolet sensitive polymer material. For example, the droplets can be injected onto the substrate by a nozzle prior to forming any of the other layers. In one embodiment, the UV-C radiation emitter can cure the droplets of the ultraviolet sensitive polymer material with UV-C radiation at the predetermined UV-C duration and intensity, and one of the UV-B radiation emitter or the UV-A radiation emitter can perform the final curing of the droplets, thereby enabling the other layers of the multi-layered film to be formed thereon. In another embodiment, an infrared light source can apply infrared heating to the droplets for coalescing into a larger domain of ultraviolet sensitive polymer material. An acoustic vibrational source can also be used with the infrared light source to promote the coalescing of the droplets through mechanical excitation. The infrared light source and the acoustic vibrational source can be used in place of the various ultraviolet emitters or these components can be used in conjunction with the emitters. In one embodiment, a curing monitor can monitor the optical properties of the ultraviolet sensitive polymer material during the curing performed by the UV-C radiation emitter and at least one of the UV-B radiation emitter or the UV-A radiation emitter. The curing monitor, which can include a visible light source and a camera, can generate signals of the optical properties and send these signals to the control unit. The control unit can use these signals to monitor the curing of the ultraviolet sensitive polymer material. For example, the control unit can adjust the duration, intensity, wavelength and sequence of operation of the UV-C radiation emitter, UV-B radiation emitter, and/or UV-A radiation emitter in accordance with the optical properties. In another embodiment, a reflectivity measuring device can be operatively coupled with the ultraviolet sensitive polymer material, the UV-C radiation emitter, the UV-B radiation emitter, the UV-A radiation emitter and the control unit. In this manner, the reflectivity measuring device can generate reflectivity measurement signals from the ultraviolet sensitive polymer material during the curing by the UV-C radiation emitter and one of the UV-B radiation emitter or the UV-A radiation emitter. In one embodiment, the reflectivity measurements are taken at a wavelength coincident with a characteristic thickness of the film of the ultraviolet sensitive polymer material. The control unit can use these reflectivity measurement signals to infer a quality of the curing of the ultraviolet sensitive polymer material. For example, the quality of the curing can be determined in relation to predetermined quality reflectivity values that are representative of a targeted curing. In one embodiment, the reflectivity measuring device can include a light source and a sensor for measuring reflectivity data from that specific light source. In an embodiment, the light source can comprise a focused beam directed at a specific angle towards the ultraviolet sensitive polymer. In another embodiment, the angle of the beam can be varied. In addition, the location of the sensor and its orientation also can be adjusted to measure reflection at different reflection angles to evaluate diffusive properties for reflected light. In another embodiment, the light source can comprise a laser sensor that is configured to scan a surface of the ultraviolet sensitive polymer material with a laser beam and obtain reflectivity measurements at different locations of the ultraviolet sensitive polymer material. A first aspect of the invention provides a system, comprising: a substrate having a film of an ultraviolet sensitive polymer material; an ultraviolet light C (UV-C) radiation emitter including a set of UV-C sources configured to emit UV-C radiation at a predetermined UV-C duration and intensity; an ultraviolet light B (UV-B) radiation emitter including a set of UV-B sources configured to emit UV-B radiation at a predetermined UV-B duration and intensity; an ultraviolet light A (UV-A) radiation emitter including a set of UV-A sources configured to emit UV-A radiation at a predetermined UV-A duration and intensity; and a control unit configured to direct curing of the ultraviolet sensitive polymer material with the UV-C radiation emitter and at least one of the UV-B radiation emitter or the UV-A radiation emitter. A second aspect of the invention provides a system, comprising: a substrate having a film of an ultraviolet sensitive polymer material; an ultraviolet illuminator including an ultraviolet light C (UV-C) radiation emitter having a set of UV-C sources configured to emit UV-C radiation at a predetermined UV-C duration and intensity, an ultraviolet light B (UV-B) radiation emitter having a set of UV-B sources configured to emit UV-B radiation at a predetermined UV-B duration and intensity, and an ultraviolet light A (UV-A) radiation emitter having a set of UV-A sources configured to emit UV-A radiation at a predetermined UV-A duration and intensity; a curing monitor configured to monitor the optical properties of the ultraviolet sensitive polymer material during the curing performed by the UV-C radiation emitter and at least one of the UV-B radiation emitter or the UV-A radiation emitter; a reflectivity measuring device configured to generate reflectivity measurements from the ultraviolet sensitive polymer material during curing thereof; and a control unit operatively coupled with the ultraviolet sensitive polymer material, the UV-C radiation emitter, the UV-B radiation emitter, the UV-A radiation emitter, the curing monitor and the reflectivity measuring device configured to direct curing of the ultraviolet sensitive polymer material with the UV-C radiation emitter and at least one of the UV-B radiation emitter or the UV-A radiation emitter, wherein the control unit directs the UV-C radiation emitter to perform surface pinning of the ultraviolet sensitive polymer material and the at least one of the UV-B radiation emitter or the UV-A radiation emitter to perform final curing of the ultraviolet sensitive polymer material after surface pinning by the UV-C radiation emitter as a function of the optical properties and reflectivity measurements, wherein the control unit monitors optical properties of the ultraviolet sensitive polymer material during the curing and adjusts the duration, intensity, wavelength and sequence of operation the UV-C radiation emitter, UV-B radiation emitter, and UV-A radiation emitter in accordance with the optical properties, and wherein the control unit infers a quality of the curing of the ultraviolet sensitive polymer material from the reflectivity measurement signals obtained by the reflectivity measuring device. A third aspect of the invention provides a method, comprising: forming a film of an ultraviolet sensitive polymer material on a substrate; directing an ultraviolet light C (UV-C) radiation emitter including a set of UV-C sources to emit UV-C radiation to the ultraviolet sensitive polymer material on the substrate at a predetermined UV-C duration and intensity for curing; and directing one of: an ultraviolet light B (UV-B) radiation emitter including a set of UV-B sources configured to emit UV-B radiation at a predetermined UV-B duration and intensity or an ultraviolet light A (UV-A) radiation emitter including a set of UV-A sources configured to emit UV-A radiation at a predetermined UV-A duration and intensity, to emit radiation to the ultraviolet sensitive polymer material for further curing thereof. The illustrative aspects of the invention are designed to solve one or more of the problems herein described and/or one or more other problems not discussed. It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. As indicated above, some aspects of the present invention are directed to utilizing ultraviolet light at different wavelength emissions, arranged in a random, mixed, sequential or simultaneous arrangement to cure ultraviolet sensitive polymer materials. As used herein, ultraviolet sensitive polymer materials is inclusive of any film including an ultraviolet sensitive polymer component. Illustrative films include polymer inks, coatings, and adhesives. The ultraviolet sensitive polymer materials can have liquid monomers and oligomers mixed with a small percent of photoinitiators. Also, the ultraviolet sensitive polymer materials can have selected pigments and additives. Exposure to ultraviolet energy causes the ultraviolet sensitive polymer materials to react and instantly harden to form a solid plastic. The UV curing system of the illustrative embodiments described herein generally includes an ultraviolet illuminator having an ultraviolet radiation range that covers ultraviolet light C (UV-C), ultraviolet light B (UV-B), and ultraviolet light A (UV-A). Ultraviolet radiation, which can be used interchangeably with ultraviolet light, means electromagnetic radiation having a wavelength ranging from approximately 10 nm to approximately 400 nm, wherein UV-C encompasses electromagnetic radiation having a wavelength ranging from approximately 210 nm to approximately 280 nm, UV-B spans electromagnetic radiation having a wavelength ranging from approximately 280 nm to approximately 315 nm, and UV-A includes electromagnetic radiation having a wavelength ranging from approximately 315 nm to approximately 400 nm. As used herein, a material/structure is considered to be “reflective” to ultraviolet light of a particular wavelength when the material/structure has an ultraviolet reflection coefficient of at least 30 percent for the ultraviolet light of the particular wavelength. A highly ultraviolet reflective material/structure has an ultraviolet reflection coefficient of at least 80 percent. Furthermore, a material/structure/layer is considered to be “transparent” to ultraviolet radiation of a particular wavelength when the material/structure/layer allows at least ten percent of radiation having a target wavelength, which is radiated at a normal incidence to an interface of the material/structure/layer to pass there through. The curing systems described herein can include a number of components described below in more detail, some of which may be optional, that facilitate the curing of ultraviolet sensitive polymer materials. The modalities used with the various curing systems described herein including its respective components can include any now known or later developed approaches that incorporate the concepts of the embodiments described below in more detail. The description that follows may use other terminology herein for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. For example, unless otherwise noted, the term “set” means one or more (i.e., at least one) and the phrase “any solution” means any now known or later developed solution. The singular forms “a,” “an,” and “the” include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “including”, “has”, “have”, and “having” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Turning to the drawings, FIG. 1 shows a schematic of an illustrative UV curing system 10 for curing a film of an ultraviolet sensitive polymer material 12 on a substrate 14 with an ultraviolet illuminator 16 having an ultraviolet radiation range that covers UV-C, UV-B, and UV-A. In one embodiment, the ultraviolet illuminator 16 includes a UV-C radiation emitter 18 comprising a set of UV-C sources 20 configured to emit UV-C radiation at a predetermined UV-C duration and intensity. In addition, the ultraviolet illuminator 16 can further include a UV-B radiation emitter 22 comprising a set of UV-B sources 24 configured to emit UV-B radiation at a predetermined UV-B duration and intensity. The ultraviolet illuminator 16 can also include a UV-A radiation emitter 26 comprising a set of UV-A sources 28 configured to emit UV-A radiation at a predetermined UV-A duration and intensity. It is understood that the number of UV sources in each of the UV-C radiation emitter 18, the UV-B radiation emitter 22 and the UV-A radiation emitter 26 as depicted in FIG. 1 is only illustrative and is not meant to the limit the various embodiments described herein. Generally, the ultraviolet illuminator 16 can comprise any combination of one or more ultraviolet radiation emitters, each of which can be configured with one or more UV sources. Examples of ultraviolet sources include, but are not limited to, high intensity ultraviolet lamps (e.g., high intensity mercury lamps), discharge lamps, UV LEDs, super luminescent LEDs, laser diodes, and/or the like. In one embodiment, the ultraviolet illuminator can include a set of UV sources, such as UV LEDs, manufactured with one or more layers of materials selected from the group-III nitride material system (e.g., AlxInyGa1−X−YN, where 0≤x, y≤1, and x+y≤1 and/or alloys thereof). Additionally, the ultraviolet illuminator can comprise one or more additional components (e.g., a wave guiding structure, a component for relocating and/or redirecting ultraviolet radiation emitter(s), etc.) to direct and/or deliver the emitted radiation to a particular location/area, in a particular direction, in a particular pattern, and/or the like. Illustrative wave guiding structures include, but are not limited to, a wave guide, a plurality of ultraviolet fibers, each of which terminates at an opening, a diffuser, and/or the like. Intensity, radiation wavelength, and duration of radiation are all parameters that have a role in the UV curing provided by the UV-C radiation emitter 18, the UV-B radiation emitter 22, and the UV-A radiation emitter 26 that can form the ultraviolet illuminator 16. These parameters for each of the ultraviolet radiation emitters can vary based on the ultraviolet sensitive polymer material 12 and the particular target UV curing that is desired. A proper setting of these parameters for each of the ultraviolet radiation emitters can ensure UV curing in a target manner that can include among other things, the lateral location of the curing, the pattern of the curing and the desired amount of polymerization of the ultraviolet sensitive polymer material 12. Those skilled in the art will appreciate that each of the radiation emitters in the ultraviolet illuminator 16 can have more or less than the three UV sources (e.g., LEDs) depicted. Further, it is understood that each of the radiation emitters in the ultraviolet illuminator 16 can have different amounts of UV sources and is not necessary for each to have the same number. Also, it is understood that although the ultraviolet illuminator 16 is depicted in FIG. 1 as having three stations of ultraviolet radiation emitters, the illuminator can have one station that incorporates the UV-C radiation emitter 18, the UV-B radiation emitter 22, and the UV-A radiation emitter 26, or the UV-C radiation emitter 18 and only one of the UV-B radiation emitter 22 and the UV-A radiation emitter 26. Examples of polymer inks, coatings, and adhesives that are suitable for use as the ultraviolet sensitive polymer material 12 that has liquid monomers and oligomers mixed with a small percent of photoinitiators in this embodiment as well as others described herein, can include, but are not limited to, acrylated resins, epoxies, aliphatic and aromatic urethanes, polyesters, and printing inks. In one embodiment, additional ink additives can be added to the ultraviolet sensitive polymer material 12 to facilitate curing and sensing such as for example, ultraviolet scattering powder, ultraviolet transparent nanoparticles, ultraviolet reflective nanoparticles, and electrically conductive elements or particles. As shown in FIG. 1, a control unit 30 can be operatively coupled to the ultraviolet illuminator 16 to effectuate a UV curing operation of the ultraviolet sensitive polymer material 12 on the substrate 14. In one embodiment, the control unit 30 can be configured to direct curing of the ultraviolet sensitive polymer material 12 with the UV-C radiation emitter 18 and at least one of the UV-B radiation emitter 22 or the UV-A radiation emitter 26. In this manner, the control unit 30 can direct the UV-C radiation emitter 18 to perform surface pinning of the ultraviolet sensitive polymer material 12 and one of the UV-B radiation emitter 22 or the UV-A radiation emitter 26 to perform final curing of the ultraviolet sensitive polymer material after surface pinning by the UV-C radiation emitter. For example, the UV-C radiation emitter 18 can perform the surface pinning of the ultraviolet sensitive polymer 12 material by cross-linking the polymer at the surface of the polymer, while the UV-B radiation emitter 22 or the UV-A radiation emitter 26 can perform the final curing of the ultraviolet sensitive polymer material by cross-linking deeper into the polymer coating. In one embodiment, the intensity of radiation emitted by the UV radiation emitters 18, 22, 26 can be on the order of hundreds of mW/cm2. Regardless, depending on the type and/or thickness of the ultraviolet sensitive polymer material 12 radiated, the intensity of UV radiation and time for radiating an ultraviolet sensitive polymer material can be optimized. In general, the control unit 30 can direct the ultraviolet illuminator 16 to perform the UV curing of the ultraviolet sensitive polymer 12 material by controlling a plurality of operating parameters associated with the UV-C radiation emitter 18, the UV-B radiation emitter 22, and/or the UV-A radiation emitter 26. The operating parameters can include a wavelength of the ultraviolet radiation that is emitted from each of the ultraviolet radiation emitters, an intensity or dosage of the ultraviolet radiation delivered to the ultraviolet sensitive polymer material 12 on the substrate 14 by the emitters, and a time duration that the emitters delivers the ultraviolet radiation to the material. Other parameters can include, but are not limited to, a power setting for operating each of the ultraviolet radiation emitters, a selected subset of the ultraviolet sources to be operated on an emitter, and a maximum operating temperature of the emitters. It is understood that the control unit 30 can take the form of a device separate from the ultraviolet illuminator 16 as depicted in FIG. 1, or it can take the form of multiple components with each ultraviolet radiation emitter of the illuminator having a control unit integrated therein to control its specific operation. Although not shown in this embodiment, information regarding the operating parameters can be obtained from a variety of sensors which can provide signals representative of those parameters to the control unit 30. These sensors as described below can include optical sensors, reflectivity measuring devices and the like. Furthermore, it is understood that a multitude of other types of sensors can implemented with the various embodiments described herein. For example, other sensors can include, but are not limited to, a temperature sensor, a chemical sensor, a radiation sensor, a transparency sensor, etc. Each of these sensors could detect the level or amount of a particular parameter that each is intended to measure and send signals thereof to the control unit 30. In this manner, the control unit 30 can invoke a feedback electrical control module that can monitor and adjust various parameters of the curing process. Using the UV-C radiation emitter 18 to perform the surface pinning of the ultraviolet sensitive polymer material 12 and the UV-B radiation emitter 22 or the UV-A radiation emitter 26 to perform the final curing is advantageous because each of the different UV radiations has a different penetration depth. In particular, UV-C radiation has the lowest penetration depth and can be used for pinning the ultraviolet sensitive polymer material 12 prior to its complete curing using UV-B and/or UV-A radiation. The exact wavelength, intensity and duration of radiation depend on the particular application at hand. It is understood that the UV-C radiation emitter 18 can be used to perform both the surface pinning and the final pinning of the ultraviolet sensitive polymer 12 material. Similarly, it is possible to have the UV-B radiation emitter 22 or the UV-A radiation emitter 26 perform both the surface pinning and the final pinning of the ultraviolet sensitive polymer 12. In another embodiment, one of the UV-B radiation emitter 22 and the UV-A radiation emitter 26 can be used to perform the surface pinning of the ultraviolet sensitive polymer 12, while the other can be used to perform the final pinning. Further, the curing operations performed by the UV-C emitter, the UV-B emitter and/or the UV-A emitter at varying wavelengths of radiation can occur simultaneously or at separate times. FIGS. 2A-2B show schematics of an illustrative UV curing system 31 for curing a single layer of film 32 and a multi-layered film 34 of an ultraviolet sensitive polymer material, respectively, on a substrate 14 with an ultraviolet illuminator 36 according to an embodiment. In FIG. 2A, the single layer of film 32 includes a layer 38 of the ultraviolet sensitive polymer material, which can include any of the aforementioned polymer inks, coatings, and adhesives, and/or pigments and additives. FIG. 2A further depicts a top surface 40 of the layer 38 of the ultraviolet sensitive polymer material that is cured by the ultraviolet illuminator 36. In one embodiment, the ultraviolet illuminator 36 can have an ultraviolet radiation range that covers UV-C, UV-B, and UV-A. For clarity in this embodiment and others that follow, the ultraviolet illuminator 36 is illustrated with a single station that is configured with UV-C, UV-B, and UV-A emitters, however, it is understood that the illuminator can include multiple stations of ultraviolet radiation emitters. Also, for clarity, in this embodiment and others that follow, the control unit is not depicted with the ultraviolet illuminator 36. The control unit can be assumed to be integrated with the ultraviolet illuminator 36, however, it is understood that the control unit can be a component separate from the illuminator. In a UV curing operation of the single layer of film 32 of the ultraviolet sensitive polymer depicted in FIG. 2A, the ultraviolet illuminator 36 can direct UV-C radiation onto the top surface 40 of the layer 38 of the ultraviolet sensitive polymer material for surface pinning of the material. The ultraviolet illuminator 36 can then follow up the surface pinning with a final curing of the layer 38 of the ultraviolet sensitive polymer material with the UV-B radiation and/or UVA radiation. In this manner, the ultraviolet illuminator 36 can cure just the top surface 40 of the layer 38 with the UV-C radiation (i.e., surface pinning) without curing the bulk of the ultraviolet sensitive polymer material (i.e., the layer 38). The ultraviolet illuminator 36 can then final cure both the top surface 40 and the bulk of the layer 38 with UV-B radiation and/or UVA radiation. In FIG. 2B, the multi-layered film 34 of ultraviolet sensitive polymer material is depicted with a second layer 42 of the material having a top surface 44 formed on the first layer 38 and its top surface 40. This second layer 42 of the ultraviolet sensitive polymer material can include any of the aforementioned polymer inks, coatings, and adhesives, and/or pigments and additives. The second layer 42 of the ultraviolet sensitive polymer material can include the same material as that of the first layer 38 or it can be of a different type. To perform a UV curing operation of the multi-layered film 34 of ultraviolet sensitive polymer material depicted in FIG. 2B, the ultraviolet illuminator 36 can use the UV-C radiation emitter to perform surface pinning of each layer of the ultraviolet sensitive polymer material and one of the UV-B radiation emitter or the UV-A radiation emitter to perform final curing of the multi-layered film after surface pinning an outer layer of the ultraviolet sensitive polymer material. For example, in the embodiment depicted in FIG. 2B, the top surface 40 of the first layer 38 can be cured with UV-C radiation. Then the second layer 42 of the ultraviolet sensitive polymer material can be formed over the cured top surface 40 of the first layer 38. This sequence ensures that the layers of films do not mix. The top surface 44 of the second layer 42 can then be cured with UV-C radiation. Although FIG. 2B depicts the multi-layered film 34 as only having two layers, it is understood that additional layers are possible and within the scope of the various embodiments of the present invention. Each additional layer that is applied to form the multi-layered film 34 can undergo surface pinning with UV-C radiation prior to application of the next layer. After all of the layers have been applied and undergone surface pinning, the ultraviolet illumination can emit UV-B radiation and/or UV-A radiation to the multi-layered film for final curing as these ranges of radiation can penetrate through the multiple layers to perform the curing. FIGS. 3A-3B show schematics of an illustrative curing system 46 for curing a multi-layered film 48 of an ultraviolet sensitive polymer material along with droplets 50 of a material placed between the multi-layered film and the substrate 14 according to an embodiment. In one embodiment, the droplets 50 can include ultraviolet sensitive polymer material of any of the aforementioned polymer inks, coatings, and adhesives, and/or pigments and additives. In one embodiment, the droplets 50 of ultraviolet sensitive polymer material can include, but are not limited to, printable ink, resins, epoxies, and/or the like. Although not shown in FIGS. 3A-3B, these droplets can be injected on the substrate 14 prior to the formation of the multi-layered film 48 by a nozzle. In one embodiment, a curing operation of the multi-layered film 48 of ultraviolet sensitive polymer material and the droplets 50 can be performed with an infrared source 52. The infrared source 52 can comprise any type of infrared radiation emitter, such as one or more infrared LEDs, incandescent lamps, and/or the like. The infrared source 52 can emit radiation towards the multi-layered film 48 and the droplets 50 with a wavelength in the range of about 800 nanometers to about 1 micron. The infrared radiation emitted from the infrared source 52 can cure both the multi-layered film 48 which is shown in FIGS. 3A-3B with a layer 38 of ultraviolet sensitive polymer material with its top surface 40, and the droplets 50. FIG. 3B shows the infrared radiation from the infrared source can cause the droplets 50 to coalesce and form a large domain 54 of ultraviolet sensitive polymer material between the multi-layered film 48 and the substrate 14 prior to ultraviolet curing as described herein. FIG. 4 shows a schematic of an illustrative curing system 56 for curing droplets 50 of a material with an infrared light source 52 and an acoustic vibrational source 58 according to an embodiment. In this embodiment, a nozzle 60 can inject droplets 50 of ultraviolet sensitive polymer material onto the substrate 14. The nozzle 60 can be any conventional material nozzle that is configured to inject droplets of material on a substrate for subsequent curing. The nozzle 60 can be controlled by an integrated control unit or by an external control unit configured to control the infrared light source 52 and the acoustic vibrational source 58 in addition to the nozzle 60. The droplets 50 of ultraviolet sensitive polymer material can include any of the aforementioned materials. As shown in FIG. 4, the nozzle 60 can inject a multiple of different types of droplets 50 of material onto the substrate 14, which can lead to polymer mixing (such as ink mixing, for example) and chemical interaction of different droplets for improved curing. The acoustic vibrational source 58 can mix the different droplets 50 of material through mechanical excitation of the substrate 14. This mixing of the different droplets 50 cause these individual droplets to coalesce into a larger domain of ultraviolet sensitive polymer material. This mechanical excitation imparted by the acoustic vibrational source 58 can occur simultaneously with the injection of the droplets 50 by the nozzle 60, or it can occur after all of the material has been deposited on the substrate 14. Examples of the acoustic vibrational source 58 can include, but are not limited to, a piezoelectric actuator, a mechanical sound actuator, and/or the like. After mixing of the droplets, the infrared light source 52 can be used to cure the larger domain of coalesced ultraviolet sensitive polymer material. In one embodiment, the infrared source 52 can emit infrared radiation towards the larger domain of coalesced ultraviolet sensitive polymer material in the aforementioned wavelength range. The infrared radiation emitted from the infrared source 52 in this range will cure the domain of coalesced ultraviolet sensitive polymer material. In another embodiment, an ultraviolet illuminator of the types described herein can be configured to operate cooperatively with the nozzle 60, the acoustic vibrational source 58, and the infrared source 52. For example, the ultraviolet illuminator can be used to emit UV-C radiation after a layer of droplets 50 have been deposited on the substrate and then followed up with either UV-B or UV-A radiation. If more than one layer is applied to the substrate, the ultraviolet illumination can emit UV-C radiation to each layer before a subsequent layer is formed thereon. After all of the layers have been applied and the last outer layer has been irradiated with UV-C radiation, then the ultraviolet illuminator can perform a final cure of the layers with UV-B and/or UV-A radiation. In one embodiment, the acoustic vibrational source 58 can be used to mix up the injected droplets prior to or in conjunction with the operation of the ultraviolet illuminator, while the infrared source 52 can be used to apply an additional cure as a complement to the curing provided by the illuminator. It is understood that other arrangements of operation of the ultraviolet illuminator with the nozzle 60, the acoustic vibrational source 58, and the infrared source 52 are possible. FIG. 5 shows a schematic of an illustrative UV curing system 62 for a multi-layered film 34 of an ultraviolet sensitive polymer material having a curing monitor 64 to monitor the optical properties of the ultraviolet sensitive polymer material during the curing according to an embodiment. The curing monitor 64 is generally an optical system that can determine the curing progress and the success of the curing of the multi-layered film 34 of ultraviolet sensitive polymer material, which includes a first layer 38 and top surface 40, and a second layer 42 and top surface 44, by the ultraviolet illuminator 36. In one embodiment, the curing monitor 64 can include a visible light source 66 that directs visible light towards the multi-layered film 34 on the substrate 14 during the curing provided by the ultraviolet illuminator 36, while a camera 68 records images of the surfaces of the various layers of the film while being irradiated with UV-C, UV-B, and UVA radiation. In this manner, the visible light source 66 and the camera 68 can serve as an optical sensor for evaluating the success or progress of the UV curing system 62. Although not shown in FIG. 5, a control unit can control operation of the UV curing performed by the ultraviolet illuminator 36 and the curing monitor 64. The control unit can be remote from the ultraviolet illuminator 36 and the curing monitor 64, or have components integrated with each. In one embodiment, the optical properties that can be monitored from the curing monitor 64 can include, but are not limited to, transparency of the polymer, reflection and/or scattering from the polymer surface, polymer color, and/or the like. These optical properties can be monitored while an UV-C radiation emitter of the ultraviolet illuminator 36 emits UV-C radiation to each of the layers during surface pinning, while an UV-B radiation emitter and/or UV-A radiation emitter emits UV-B radiation and UV-A radiation, respectively, to the layers during final curing of the film. The curing monitor 64 can generate signals of these optical properties and transmits these signals to the control unit. The control unit can monitor the curing of the multi-layered film 34 of ultraviolet sensitive polymer material as a function of the signals of the optical properties. For example, the control unit can adjust the duration, intensity, wavelength and sequence of operation of the UV-C radiation emitter, the UV-B radiation emitter, and the UV-A radiation emitter of the ultraviolet illuminator 36 in accordance with the optical properties sensed by the curing monitor 64. By monitoring the curing of the multi-layered film 34 in this manner, the control unit can then determine whether the changes in applied wavelength or changes in intensity of applied wavelength resulted in an optimal curing. Those sequences of wavelengths, intensities and duration of illuminating sources that resulted in optimal quality curing can be noted as a good curing “recipe” or “regime” and stored into a data system for future use and reference as a database that allows for recalling of the curing regimes corresponding to different image qualities. For printing applications, the curing regimes can be stored as functions of a position on piece of paper. In this manner, the curing regimes can contain information on the curing of different parts of the image in a different color gamut. The control unit can also record the characteristics of the images from the curing monitor 64 that are produced during the curing and be used as part of the database. In another embodiment, the curing monitor 64 can be used to monitor the curing process of ultraviolet sensitive polymer materials that can change color. For example, some polymer inks can change color during the curing process. In one embodiment, part of an ink can be cured to have a color image wherein part of the image is cured to be black and white, grey or sepia. Other inks can contain additives that change color during curing, and some inks can have fluorescent material that indicate where the UV-C or UV-A radiation is being deposited. In another example, the inks can be cured to be only visible under ultraviolet exposure for applications such as authentication purposes. In these examples, the different colors of the inks can be cured using different wavelengths of UV-C, UV-B, and/or UV-A radiation. The curing monitor 64 can be used to monitor the color changes of these inks in various ways, e.g., through the use of a camera. FIG. 6 shows a schematic of an illustrative UV curing system 70 depicting inhomogeneous curing of an ultraviolet sensitive polymer material 12 on a substrate 14 at different lateral locations according to an embodiment. The UV curing system 70 can include multiple ultraviolet illuminators 36 that emit ultraviolet radiation towards the ultraviolet sensitive polymer material 12. In one embodiment, as shown in FIG. 6, the UV curing system 70 can include two ultraviolet illuminators 36 each configured to emit ultraviolet radiation of different intensity and/or wavelength that is deposited at different portions of the ultraviolet sensitive polymer material 12. For example, one of the ultraviolet illuminators 36 can include an UV-C radiation emitter that emits UV-C radiation to one location of the ultraviolet sensitive polymer material 12, while the other illuminator can include either an UV-B radiation emitter or an UV-A radiation emitter that emits UV-B radiation and UV-A radiation, respectively, to a different location of the material, at predetermined wavelength-specific intensities and durations. This configuration enables the UV curing system 70 to cure the ultraviolet sensitive polymer material 12 inhomogeneously at different lateral locations. In addition, this configuration allows for improved mixing or confinement of the ultraviolet sensitive polymer material 12 depending on its application. As shown in FIG. 6, one ultraviolet illuminator 36 can be centered over the ultraviolet sensitive polymer material 12, while the other ultraviolet illuminator 36 can located along an edge or peripheral location of the material in relation to the substrate 14. In one embodiment, the ultraviolet illuminator 36 centered over the ultraviolet sensitive polymer material 12 can include a UV-A radiation emitter, while the ultraviolet illuminator 36 located along an edge of the material can include a UV-C radiation emitter. In this configuration, the UV-C radiation emitter can be used to confine the ultraviolet sensitive polymer material 12 to a certain location 72 along the surface of the substrate 14, while the UV-A radiation emitter can be used to cure the overall domain 74 of the ultraviolet sensitive polymer material 12. It is understood that the rate of curing can be different for the UV-C radiation emitter and the UV-A radiation emitter. This difference in the rate of curing enables the UV-C radiation emitter to define the domain of the ultraviolet sensitive polymer material 12, and the UV-A radiation emitter to finalize the curing application for the material. In general, the UV-C radiation emitter can cure the ultraviolet sensitive polymer material 12 at a much higher rate as it is only cures the thin surface of the material. In another embodiment, the UV-C radiation emitter can emit UV-C radiation towards the ultraviolet sensitive polymer material 12 in a range having an absorption length that is no more than 10% of the absorption length in the range of UV-A radiation for the UV-A radiation emitter. This same range is also applicable in embodiments where a UV-B radiation emitter is used in place of or in addition to the UV-A emitter. That is, the UV-C radiation emitter can emit UV-C radiation in a range having an absorption length that is no more than 10% of the absorption length in the UV-B radiation for the UV-B radiation emitter. It is understood that other configurations for curing lateral locations of the ultraviolet sensitive polymer material 12 are possible. In one embodiment, the ultraviolet illuminators can be fixed in specific locations with respect to the ultraviolet sensitive polymer material 12 and the substrate 14, or the illuminators can be configured to scan the material in a predetermined pattern to achieve the desired curing. Also, it is possible to replace the UV-A radiation emitter with a UV-B radiation emitter. Furthermore, it is understood that more than two ultraviolet illuminators can be used to cure the ultraviolet sensitive polymer material 12. Also, instead of having ultraviolet illuminators of a single range wavelength, it is possible to use illuminators that integrate multiple ranges that include UV-C, UV-B and/or UV-A radiation, that scan across the ultraviolet sensitive polymer material 12. FIG. 7 shows a schematic illustrating a feedback control process 76 for a UV curing process of an ultraviolet sensitive polymer material 12 placed on a substrate 14 with an ultraviolet illuminator 36 having an UV-C radiation emitter, an UV-B radiation emitter, and an UV-A radiation emitter, and a control unit 30 according to an embodiment. Each of the UV-C radiation emitter, the UV-B radiation emitter, and/or the UV-A radiation emitter can emit radiation at the ultraviolet sensitive polymer material 12 at a specific intensity, radiation wavelength, and duration. The ultraviolet illuminator 36 can cure the ultraviolet sensitive polymer material 12 using any of the aforementioned approaches. During the UV curing operation of the ultraviolet sensitive polymer material 12, data can be obtained at 78 through the aforementioned curing monitor or any other type of sensors that can be used to obtain data on a plurality of operating parameters associated with the UV-C radiation emitter, the UV-B radiation emitter, and the UV-A radiation emitter. As mentioned above, the operating parameters can include a wavelength of the ultraviolet radiation that is emitted from each of the ultraviolet radiation emitters, an intensity or dosage of the ultraviolet radiation delivered to the ultraviolet sensitive polymer material 12 on the substrate 14 by the emitters, and a time duration that the emitters deliver the ultraviolet radiation to the material. Other parameters can include, but are not limited to, a power setting for operating each of the ultraviolet radiation emitters, and a maximum operating temperature of the emitters. The control unit 30 can monitor the curing of the ultraviolet sensitive polymer material 12 as a function of the signals representative of the operating parameters monitored by the curing monitor and/or various other sensors. For example, the control unit 30 can adjust the duration, intensity, wavelength and sequence of operation of the UV-C radiation emitter, the UV-B radiation emitter, and/or the UV-A radiation emitter of the ultraviolet illuminator 36 in accordance with the sensed operating parameters at 80. The process of monitoring and adjusting operating parameters of the ultraviolet illuminator 36 continues until the control unit 30 determines that the curing is successful. Those sequences of wavelengths, intensities and duration of illuminating sources that result in optimal quality curing can be noted by the control unit 30 as a good curing “recipe” or “regime” and stored into a database for future use and reference. U.S. Pat. No. 8,277,734 describes a feedback control approach for modifying ultraviolet radiation according to the sensing of a system and is incorporated herein by reference. It is understood that the processing approach illustrated in FIG. 7 is illustrative of only one approach of curing the ultraviolet sensitive polymer material and that other possibilities exist. For example, the method could include more or less steps than that described. Also, it is understood that some of these steps can be performed in a different order than that described. FIG. 8 shows a schematic of an illustrative UV curing system 84 operating in conjunction with a reflectivity measuring device 86 to generate reflectivity measurement signals from a multi-layered film 88 of ultraviolet sensitive polymer material 90 during curing of the material by an ultraviolet illuminator 36 according to an embodiment. In one embodiment, the reflectivity measuring device 86 can generate reflectivity measurement signals from the multi-layered film 88 of ultraviolet sensitive polymer material, which can include any of the aforementioned materials, during a curing process by the UV-C radiation emitter and one or both of the UV-B radiation emitter and the UV-A radiation emitter that is associated with the ultraviolet illuminator 36. The control unit, which is not illustrated in FIG. 8 for clarity, can infer a quality of the curing of the multi-layered film 88 of ultraviolet sensitive polymer material from the reflectivity measurements. In one embodiment, the control unit can infer a quality of the curing of the multi-layered film 88 of ultraviolet sensitive polymer material as a function of the reflectivity measurements, wherein the quality of the curing is determined in relation to predetermined quality reflectivity values representative of a targeted curing. For example, when the reflectivity values observed are in close proximity to the recorded reflectivity values, then the curing can be evaluated as being successful. An exact matching range will be evaluated depending on the type of material that is being cured. The top portion of FIG. 8 illustrates an example of the reflectance of the multi-layered film of ultraviolet sensitive polymer material 88 as a function of time in relation to a target reflectance that achieves a targeted curing. In particular, the reflectance of the film 88 will approach an asymptotic value when the film 88 is cured. As illustrated, the measured reflectance of the film can be a combination of reflectance from multiple layers of the film 88. After processing the reflectivity measurements, the control unit can then record the data associated with each of the various curing operations. In one embodiment, the reflectivity measuring device 86 can include a laser sensor that is configured to scan a surface of the multi-layered film 88 of ultraviolet sensitive polymer material with a laser beam and obtain reflectivity measurements at different locations of the ultraviolet sensitive polymer material. Scanning the surface of the multi-layer film at different points with the laser beam ensures that all points of the film undergo the curing. In one embodiment, the reflectivity measurements obtained by the laser sensor can be taken at a wavelength coincident with a characteristic thickness of the multi-layered film 88 of ultraviolet sensitive polymer material 90. It is understood that the reflectivity measurements are one type of parameter that can be obtained from the UV curing operation and used to infer information on the state of the film 88 of ultraviolet sensitive polymer material 90 being cured and is not meant to limit the scope of the various embodiments described herein. It is understood that other parameters can be used to infer information on the state of the film. For example, electrical means, such as, lateral or vertical resistivity of the film 88, can be used to measure the resistivity of the film 88 of ultraviolet sensitive polymer material 90. In this manner, the control unit can infer the state of the material being cured from the resistivity measurements. For example, the resistivity values will approach a slowly varying asymptotic value when the film is cured. FIG. 9 shows a schematic block diagram representative of an overall processing architecture of a curing system 800 that is applicable to any of the systems described herein according to an embodiment. In this embodiment, the architecture 800 is shown including sources 802 (e.g., ultraviolet sources including an ultraviolet illuminator having ultraviolet radiation emitters, infrared sources, visible sources, vibrational sources) and the sensors 804 (e.g., curing monitor, optical systems, reflectivity measuring devices, etc.) for the purposes of illustrating the interaction of all of the components that can be used to cure ultraviolet sensitive polymer material. As depicted in FIG. 9 and described herein, the curing system 800 can include a control unit 30. In one embodiment, the control unit 30 can be implemented as a computer system 820 including an analysis program 830, which makes the computer system 820 operable to manage the sources 802 and the sensors 804 in the manner described herein. In particular, the analysis program 830 can enable the computer system 820 to operate the sources 802 and process data corresponding to one or more attributes regarding the sources and the ultraviolet sensitive polymer material, which can be acquired from the sensors 804, and/or historical data 840. The computer system 820 can individually control each source 802 and sensor 804 and/or control two or more of the sources and the sensors as a group. In an embodiment, during an initial period of operation, the computer system 820 can acquire data from at least one of the sensors 804 regarding one or more attributes of the sources 802 and the ultraviolet sensitive polymer material and generate data 840 for further processing. The computer system 820 can use the data 840 to control one or more aspects of the curing process of the ultraviolet sensitive polymer material. Furthermore, one or more aspects of the operation of the sources 802 can be controlled or adjusted by a user 812 via an external interface I/O component 826B. The external interface I/O component 826B can be used to allow the user 812 to selectively turn on/off the sources 802. The external interface I/O component 826B can include, for example, a touch screen that can selectively display user interface controls, such as control dials, which can enable the user 812 to adjust one or more of: an intensity, scheduling, and/or other operational properties of the sources 802 (e.g., operating parameters, radiation characteristics). In an embodiment, the external interface I/O component 826B could conceivably include a keyboard, a plurality of buttons, a joystick-like control mechanism, and/or the like, which can enable the user 812 to control one or more aspects of the operation of the set of sources 802. The external interface I/O component 826B also can include any combination of various output devices (e.g., an LED, a visual display), which can be operated by the computer system 820 to provide status information pertaining to the curing process for use by the user 812. In an embodiment, the external interface I/O component 826B can include a speaker for providing an alarm (e.g., an auditory signal), e.g., for signaling that the curing of the ultraviolet sensitive polymer material has finished. The computer system 820 is shown including a processing component 822 (e.g., one or more processors), a storage component 824 (e.g., a storage hierarchy), an input/output (I/O) component 826A (e.g., one or more I/O interfaces and/or devices), and a communications pathway 828. In general, the processing component 822 executes program code, such as the analysis program 830, which is at least partially fixed in the storage component 824. While executing program code, the processing component 822 can process data, which can result in reading and/or writing transformed data from/to the storage component 824 and/or the I/O component 826A for further processing. The pathway 828 provides a communications link between each of the components in the computer system 820. The I/O component 826A and/or the external interface I/O component 826B can comprise one or more human I/O devices, which enable a human user 812 to interact with the computer system 820 and/or one or more communications devices to enable a system user 812 to communicate with the computer system 820 using any type of communications link. To this extent, during execution by the computer system 820, the analysis program 830 can manage a set of interfaces (e.g., graphical user interface(s), application program interface, and/or the like) that enable human and/or system users 812 to interact with the analysis program 830. Furthermore, the analysis program 830 can manage (e.g., store, retrieve, create, manipulate, organize, present, etc.) the data, such as data 840, using any solution. In any event, the computer system 820 can comprise one or more general purpose computing articles of manufacture (e.g., computing devices) capable of executing program code, such as the analysis program 830, installed thereon. As used herein, it is understood that “program code” means any collection of instructions, in any language, code or notation, that cause a computing device having an information processing capability to perform a particular function either directly or after any combination of the following: (a) conversion to another language, code or notation; (b) reproduction in a different material form; and/or (c) decompression. To this extent, the analysis program 830 can be embodied as any combination of system software and/or application software. Furthermore, the analysis program 830 can be implemented using a set of modules 832. In this case, a module 832 can enable the computer system 820 to perform a set of tasks used by the analysis program 830, and can be separately developed and/or implemented apart from other portions of the analysis program 830. When the computer system 820 comprises multiple computing devices, each computing device can have only a portion of the analysis program 830 fixed thereon (e.g., one or more modules 832). However, it is understood that the computer system 820 and the analysis program 830 are only representative of various possible equivalent monitoring and/or control systems that may perform a process described herein with regard to the control unit, the ultraviolet radiation sources and the sensors. To this extent, in other embodiments, the functionality provided by the computer system 820 and the analysis program 830 can be at least partially be implemented by one or more computing devices that include any combination of general and/or specific purpose hardware with or without program code. In each embodiment, the hardware and program code, if included, can be created using standard engineering and programming techniques, respectively. In another embodiment, the control unit can be implemented without any computing device, e.g., using a closed loop circuit implementing a feedback control loop in which the outputs of one or more sensors are used as inputs to control the operation of the curing process. Illustrative aspects of the invention are further described in conjunction with the computer system 820. However, it is understood that the functionality described in conjunction therewith can be implemented by any type of monitoring and/or control system. Regardless, when the computer system 820 includes multiple computing devices, the computing devices can communicate over any type of communications link. Furthermore, while performing a process described herein, the computer system 820 can communicate with one or more other computer systems, such as the user 812, using any type of communications link. In either case, the communications link can comprise any combination of various types of wired and/or wireless links; comprise any combination of one or more types of networks; and/or utilize any combination of various types of transmission techniques and protocols. All of the components depicted in FIG. 9 can receive power from a power component 845. The power component 845 can take the form of one or more batteries, a vibration power generator that can generate power based on magnetic inducted oscillations or stresses developed on a piezoelectric crystal, a wall plug for accessing electrical power supplied from a grid, and/or the like. In an embodiment, the power source can include a super capacitor that is rechargeable. Other power components that are suitable for use as the power component can include solar, a mechanical energy to electrical energy converter such as a piezoelectric crystal, a rechargeable device, etc. FIG. 10 shows a schematic of an illustrative environment 900 in which the architecture of the curing system depicted in FIG. 9 can be used to facilitate curing of an ultraviolet sensitive polymer material 12 according to an embodiment. In this embodiment, the computer system 820 of the control unit 30 can be configured to control the sources 802 during the curing as described herein. The sensors 804 are configured to acquire data processed by the computer system 820 to monitor a set of attributes regarding the curing of the ultraviolet sensitive polymer material 12. As illustrated, the sensors 804 can acquire data used by the computer system 820 to monitor the set of attributes (e.g., operating parameters, ultraviolet radiation characteristics). In one embodiment, the computer system 820 can be configured to control and adjust a direction, an intensity, a pattern, and/or a spectral power (e.g., wavelength) of the set of ultraviolet radiation sources, based on data received from any of the sensors. The computer system 820 can control and adjust each property of the set of ultraviolet radiation sources independently. For example, the computer system 820 can adjust the intensity, time duration, and/or time scheduling (e.g., including duration (e.g., exposure/illumination time)), duty cycle, time between exposures/illuminations, and/or the like) of the ultraviolet radiation sources for a given wavelength. Each of the properties of the ultraviolet radiation sources can be adjustable and controlled by the computer system 820 according to data provided by the sensors 804. It is understood that the environment 900 may include the power component 845 to supply power to one or more of the various components depicted in FIG. 10, such as the sources 802, the sensors 804, the computer system 820, and/or the like. The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to an individual in the art are included within the scope of the invention as defined by the accompanying claims. |
|
054523346 | claims | 1. A nuclear reactor fuel assembly for a pressurized water reactor comprising: (a) an upper tie plate; (b) a lower tie plate; (c) a plurality of substantially parallel fuel rods extending longitudinally; (d) a spacer grid for supporting the plurality of fuel rods; wherein the upper tie plate has a first portion adapted to form an alignment bore to receive a corresponding alignment pin of the upper core support plate of said pressurized water reactor to align the fuel assembly with respect to the upper core support plate; wherein the first portion further includes means for disengaging from the upper tie plate so that the first portion is disengaged from the upper tie plate when a predetermined mechanical force is transmitted to the first portion, said force resulting from at least a portion of the weight of the fuel assembly being transmitted by the alignment pin being wedged against the alignment bore of the first portion. and wherein the upper tie plate further includes a plurality of vertical sidewalls and at least one flange extending horizontally from one of the plurality of vertical sidewalls, and at least one of the plurality of sidewalls adapted to form a slot; and wherein the break-away pin is at least two break-away pins, a first of the at least two break-away pins securing the tab of the corner post to the slot in the one of the plurality of sidewalls of the upper tie plate, and a second of the at least two break-away pins securing a second of the plurality of walls of the corner post to the flange of the upper tie plate. wherein the upper tie plate further includes a plurality of vertical sidewalls, and at least one of the plurality of sidewalls adapted to form a groove to receive the rib of the corner post; and wherein the break-away pin is at least two break-away pins, a first one of the at least two breakaway pins secures the corner post to one of the plurality of sidewalls of the upper tie plate. (a) an upper tie plate; (b) a lower tie plate; (c) a control rod guide tube extending longitudinally between the upper tie plate and the lower tie plate; (d) a plurality of substantially parallel fuel rods extending longitudinally; (e) a spacer grid extending transversely to the at least one guide tube for supporting the plurality of fuel rods; (f) a disengaging upper tie plate corner post adapted to form an alignment bore to receive a corresponding alignment pin of the upper core support plate of said pressurized water reactor to align the fuel assembly with respect to the upper core support plate; wherein the corner post further includes a securing-disengaging means for securing the corner post to the upper tie plate and for disengaging from the upper tie plate so that the corner post is disengaged from the upper tie plate when a predetermined mechanical force is transmitted to the corner post, said force resulting from at least a portion of the weight of the fuel assembly being transmitted by the alignment pin being wedged within the alignment bore of the corner post. 2. A nuclear fuel assembly as in claim 1 wherein the upper tie plate is adapted to form a recess and wherein the first portion comprises a disengaging upper tie plate corner post adapted to be received in the recess formed in the upper tie plate. 3. A nuclear fuel assembly as in claim 2 wherein the means for disengaging comprises a break-away pin securing the corner post to the upper tie plate, the break-away pin fractures when the predetermined mechanical force results in shear stresses in the pin corresponding to less than the buoyance weight of the fuel assembly. 4. A nuclear fuel assembly as in claim 2 wherein the means for disengaging comprises a break-away pin securing the corner post to the upper tie plate, the break-away pin fractures when the predetermined mechanical force results in shear stresses in the pin corresponding to less than about 30% to about 45% of the buoyance weight of the fuel assembly. 5. A nuclear fuel assembly as in claim 3 wherein the disengaging upper tie plate corner post includes a plurality of walls which are adapted to conform to the recess in the upper tie plate, a first one of the plurality of walls further includes a tab; 6. A nuclear fuel assembly as in claim 2 wherein the means for disengaging comprises a break-away pin securing the corner post to the upper tie plate, the break-away pin fractures when the predetermined mechanical force results in tensile stresses in the pin corresponding to less than the buoyancy weight of the fuel assembly. 7. A nuclear fuel assembly as in claim 2 wherein the means for disengaging comprises a break-away pin securing the corner post to the upper tie plate, the break-away pin fractures when the predetermined mechanical force results in tensile stresses in the pin corresponding to less than about 30% to about 45% of the buoyancy weight of the fuel assembly. 8. A nuclear fuel assembly as in claim 6 wherein the disengaging upper tie plate corner post includes a plurality of walls which are adapted to conform to the recess in the upper tie plate, a first one of the plurality of walls further includes a rib; 9. A nuclear fuel assembly as in claim 8 wherein the upper tie plate includes a flange extending horizontally from one of the sidewalls, and a second one of the at least two break-away pins securing a second of the plurality of walls of the corner post to the flange of the upper tie plate. 10. A fuel assembly as in claim 9 wherein the first one of the at least two break-away pins extends longitudinally and secures the corner post to a one of the plurality of sidewalls of the upper tie plate. 11. A nuclear fuel assembly as in claim 10 wherein a second of the at least two break-away pins extends longitudinally and secures the corner post to a second one of the plurality of sidewalls of the upper tie plate. 12. A nuclear reactor fuel assembly for a pressurized water reactor comprising: 13. The fuel assembly as in claim 12 wherein the upper tie plate includes a flange extending horizontally from a sidewall of the tie plate, and the securing-disengaging means comprises at least one break-away pin for securing the corner post to the flange and which fractures when the predetermined mechanical force results in tensile stresses corresponding to less than the buoyance weight of the fuel assembly. 14. The fuel assembly as in claim 12 wherein the upper tie plate includes a flange extending horizontally from a sidewall of the tie plate, and the securing-disengaging means comprises at least one break-away pin for securing the corner post to the flange and which fractures when the predetermined mechanical force results in tensile stresses corresponding to about 30% to about 45% of the buoyance weight of the fuel assembly. 15. The fuel assembly as in claim 14 wherein the at least one break-away pin is at least two pins extending longitudinally from the corner post into the flange of upper tie plate. |
summary | ||
055880363 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus and a radiographing method for setting radiographing conditions at a time of radiographing by using the X-ray CT apparatus. 2. Related Prior Art An X-ray CT (computerized tomography) apparatus has been widely used as a medical diagnosis apparatus for providing a tomographic image of a body of a subject such as a patient. When radiographing operation is performed by using an X-ray CT apparatus, various radiographing conditions such as a scan speed, tube voltage, tube current, slicing width, scan pitch, and tilt angle are entered in advance as previous informations, and a scanning operation is then carried out in accordance with the entered radiographing conditions to obtain a desired tomographic image. In such medical use, there is a case where a particular region of a patient is repeatedly radiographed at regular intervals in order to determine time-dependent changes such as progress or healing of a disease of a patient. In such a case, the radiographing has been often carried out under nearly the same radiographing conditions as those by which the previous radiographing was carried out for the reason that the subject, the region to be diagnosed, the type of disease, etc. are the same. In a conventional X-ray CT apparatus, however, the radiographing conditions must be reset each time the radiographing is performed. This is extremely troublesome to an operator and causes the examination efficiency to be lowered. SUMMARY OF THE INVENTION An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art and to provide an X-ray CT apparatus and a radiographing method using the X-ray CT apparatus capable of automatically setting radiographing conditions in accordance with past exposure information of a subject. This and other objects can be achieved according to the present invention by providing, in one aspect, an X-ray CT apparatus for performing a radiographing operation to a subject lying on a bed, comprising: a bed drive means for moving a bed to a predetermined position; PA1 an X-ray tube irradiating an X-ray to the subject; PA1 a detecting means for detecting an irradiated X-ray; PA1 a gantry means on which the X-ray tube and the X-ray detecting means are mounted; PA1 a gantry drive means for rotationally driving the gantry means; PA1 an exposure information file means into which past exposure information for the subject is stored; and PA1 a main controller for setting a radiographing condition in accordance with the past exposure information stored in the exposure information file and for controlling at least one of the X-ray tube, the bed drive means and the gantry drive means in accordance with the set radiographing condition. PA1 preparing an information of the subject; PA1 entering the information into the main controller; PA1 indexing the past exposure information of the subject from the exposure information file; PA1 confirming whether the past exposure information is indexed; PA1 displaying the indexed past exposure information as numerical data in a case where the past exposure information is indexed; PA1 confirming whether a radiographing condition is set in accordance with the displayed exposure information; PA1 setting and storing the radiographing condition in a case where the radiographing condition is set in accordance with the displayed exposure information; and PA1 performing a scan operation with the set radiographing condition. PA1 preparing an information of the subject; PA1 entering the information into the main controller; PA1 carrying out a scanographing operation and displaying the scanographic image on the monitor; PA1 indexing the past exposure information of the subject from the exposure information file; PA1 confirming whether the past exposure information is indexed; PA1 converting a slice information in the indexed past exposure information into a slice information image data in a case where the past exposure information is indexed; PA1 displaying the indexed past exposure information as numerical data and displaying the slice information as slice information image data; PA1 confirming whether a radiographing condition is set in accordance with the displayed exposure information; PA1 inversely converting the slice information image data into the slice information; PA1 setting and storing the radiographing condition in a case where the radiographing condition is set in accordance with the displayed exposure information; and PA1 performing a scan operation with the set radiographing condition. In a preferred embodiment in this aspect, the apparatus further comprises a bed drive means controller, a gantry drive means controller and a high-voltage controller, through which the bed drive means, the gantry drive means and the X-ray tube are controlled, respectively, by the main controller. The main controller comprises a central processing unit, a scan control means for controlling the high-voltage controller, the bed drive means controller and the gantry drive means controller, an input/output control means for the exposure information file means and means for converting a slice information data within the exposure information into a slice information image data and controlling the data for display, the scan control means, the input/output control means and the converting means are operatively connected to the central processing unit. A monitor is operatively connected to the data converting and controlling means of the main controller, the monitor means including a main monitor for displaying a scanographic image and a sub-monitor for displaying the exposure information as numerical data. In another aspect of the present invention, there is provided a method for performing a radiographing operation by using an X-ray CT apparatus of the characters described above, wherein a radiographing condition according to which the radiographing operation is performed is set in accordance with a past exposure information stored in the exposure information file and at least one of the bed, the X-ray tube, and the gantry in accordance with the set radiographing conditions. In one preferred embodiment, the radiographing operation is performed by the steps of: In this embodiment, the radiographing operation further comprises the steps of modifying a numerical data of the radiographing condition in the displayed exposure information. In a case where the past exposure information is not indexed, the radiographing condition is set manually and stored and the scan is then performed with the set radiographing condition. In a case where the radiographing condition is not set, it is confirmed whether further index is to be continued and in a case where the index is continued, another past exposure information for the subject is further indexed, and in a case where the index is not continued, the radiographing condition is set manually and stored. In another preferred embodiment, the radiographing operation is performed through a previous setting of a radiographing position and region of the subject by the steps of: In this embodiment, the radiographing operation further comprises the step of modifying a numerical data of the radiographing condition and the slice information image data in the displayed exposure information. In a case where the past exposure information is not indexed, the radiographing condition is set manually and stored and the scan is then performed with the set radiographing condition. In a case where the radiographing condition is not set, it is confirmed whether further index is to be continued and in a case where the index is continued, another past exposure information for the subject is further indexed, and in a case where the index is not continued, the radiographing condition is set manually and stored. In the above embodiments, a predetermined number of a plurality of past exposure informations for the subject are stored in accordance with the time order and when a new radiographing condition is stored as exposure information, an oldest past exposure information automatically vanishes. According to the embodiments of the present invention, the past exposure information on a particular subject such as a patient is indexed from the exposure information file, which stores exposure information. Then, the radiographing conditions are set based on the indexed past exposure information. Scan is then carried out while controlling at least one of the bed, the X-ray tube, and the gantry in accordance with the set radiographing conditions. According to the preferred embodiment of the present invention, scanography is performed to produce a scanographic image before implementing the scan. The slice information such as the slicing pitch in the slicing operation and the tilt angle of the gantry is converted to slice information image data, and the converted slice information image data are displayed on a monitor as an image which is superimposed on the scanographic image. At this point, no relationship of relative position has been established between the slice information image and the scanographic image on the monitor. Next, the slice information image is modified so that the radiographing will be carried out at a desired point on the scanographic image and at a desired tilt angle. As a mode of modifying the slice information image, the whole slice information image is moved on the monitor with respect to the scanographic image. Such a modifying operation on the monitor establishes the relationship of relative position between the slice information image and the scanographic image. Then, the modified slice information image data are inversely converted to the slice information data, and the inversely converted slice information data and numerical data, which have been modified separately, are used as the radiographing conditions for carrying out the scan. During the scan, the gantry, the bed, and the X-ray tube are controlled in accordance with the radiographing conditions. The nature and further features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings. |
summary | ||
050154370 | abstract | A reactor core for a gas-cooled reactor, which core is composed of a plurality of prismatic bodies (2) of graphite containing nuclear fuel and having a top wall, a bottom wall and a plurality of vertically extending side walls, each graphite body (2) being provided with a plurality of first coolant flow channels (4) extending vertically between the top wall and the bottom wall, and with a plurality of second coolant flow channels (6) extending transversely to the first channels (4) and each interconnecting a plurality of the first channels (4). |
051695960 | abstract | The movable air baffle shield means in accordance with the present invention provides an efficient method of cooling the space surrounding the containment vessel while also providing the capability of being moved away from the containment vessel during inspection. The containment apparatus comprises a generally cylindrical sealed containment vessel for containing at least a portion of a nuclear power generation plant, a disparate shield building surrounding and housing the containment vessel therein and spaced outwardly thereof so as to form an air annulus in the space between the shield building and the containment vessel, a shield baffle means positioned in the air annulus around at least a portion of the sides of the containment vessel providing a coolant path between the baffle means and the containment vessel to permit cooling of the containment vessel by air, the shield baffle means being movable to afford access to the containment vessel. |
052271226 | claims | 1. A display device for indicating the value of a parameter in a process plant having an indicator and alarm system, comprising: a display screen; digital processing means for producing a plurality of display fields on the display screen, receiving input signals originating from sensors responsive to changes in the parameter, computing derived values from the input signals, and producing output value images in some of the display fields commensurate with respective input signals and derived values; some of said fields defining touch-sensitive selection means for selecting particular of said fields and particular of said values for display on said screen; wherein a first set of said fields define a first display page and a second set of fields define a second display page, 2. The device of claim 1, wherein the sensor fields include displays which identify at least one sensor for each of at least two different range of values of the parameter. 3. The device of claim 1, wherein the quality field can display one of at least three categories, including a first category indicating that the process parameter value has been derived form a plurality of sensor inputs and is deemed validated, a second category indicating that the process parameter value has been derived from a plurality of sensor inputs but cannot be validated, and a third category indicating that the process parameter value is one of the sensor values. |
claims | 1. An ex-core nuclear instrumentation system, comprising:neutron detectors which measure neutron flux leaked from a reactor vessel and convert the neutron flux into a current value,a detector signal processing circuit which converts the converted current value into a voltage value,a signal processing card which performs arithmetic processing using a voltage value which is converted in the detector signal processing circuit so as to input the state of neutron flux during the operation of the reactor,and an operation panel having a man machine interface,wherein the signal processing card includes a CPU, a FPGA, an electrically rewritable nonvolatile memory and a key switch,wherein the signal processing card has general-purpose logic, which is connected directly to the key switch and controls a write signal of the electrically rewritable nonvolatile memory, that is configured to prevent the writing to electrically nonvolatile memory when a key is removed from the key switch,and when the key is engaged with the key switch the CPU retrieves rewrite data from the operation panel through the FPGA to the electrically rewritable nonvolatile memory to rewrite the data in the electrically rewritable nonvolatile memory. 2. The ex-core nuclear instrumentation system as claimed in claim 1, wherein the signal processing card and the operation panel are constituted by separate electronic substrates, and the signal processing card and the operation panel are connected by a serial communication line. 3. The ex-core nuclear instrumentation system as claimed in claim 1, wherein signals which are outputted from the operation panel include signals other than rewriting data to the electrically rewritable nonvolatile memory. 4. The ex-core nuclear instrumentation system as claimed in claim 1, wherein the electrically rewritable nonvolatile memory is configured to be reset. 5. The ex-core nuclear instrumentation system as claimed in claim 1, wherein the man machine interface includes an input key. |
|
description | The present invention relates generally to the field of diagnostic radiography and, more particularly, to an anti-scatter X-ray grid device and a method of making the same. Anti-scatter grids are widely used in X-ray imaging to enhance image quality. X-rays emitted from a point source pass through a patient or object and are then detected in a suitable X-ray detector. X-ray imaging works by detecting the intensity of X-rays as a function of position across the X-ray detector. Darker areas with less intensity correspond to regions of higher density or thickness in the object, while lighter areas with greater intensity correspond to areas of lower density or thickness in the object. This method relies on X-rays either passing directly through the object or being totally absorbed. However, X-rays may also undergo scattering processes, primarily Compton scattering, in the patient or object. Such X-rays generate image noise and thus reduce the quality of the image. In order to lessen the impact of such scattered X-rays, an anti-scatter grid is employed. The grid preferentially passes primary X-rays (those that do not scatter) and rejects scattered X-rays. This is done by interleaving materials of low X-ray absorption, such as graphite or aluminum, with layers of high X-ray absorption, such as lead or tungsten. Scattered X-rays are then preferentially stopped before entering the X-ray detector. However, a fraction of primary X-rays are also absorbed in the grid. One of the primary metrics for anti-scatter grid performance is the quantum improvement factor (QIF), wherein QIF=Tp2/Tt. Tp is the primary X-ray transmission through the grid and Tt is the total transmission. This equation shows the importance of achieving a high primary transmission. If primary X-rays are lost, imaging information is also lost and thus either the X-ray dose must be increased or a degradation in image quality accepted. A QIF of 1 or greater indicates an improvement in image quality, while a QIF of <1 indicates that the grid actually harms the quality of the image. The principal design metrics for an anti-scatter grid are the line frequency, the line thickness, and the grid height, often expressed as the ratio. The line frequency, typically expressed in units of lines/cm, gives the number of absorbing strips of material in a given distance. The line thickness is just the thickness of the absorbing lines, often expressed in units of microns. The grid ratio is the ratio of the grid height to the interspace distance (the amount of low-absorbing material between a pair of grid lines). Grid performance is also influenced by the material used in manufacturing the grid and the type and thickness of grid covers, which are non-active sheets encasing the grid to provide mechanical support. In designing an anti-scatter grid, the degree of scatter rejection must be balanced with the primary transmission in order to maximize the quantum improvement factor. However, this is not always possible because of manufacturing limitations. For example, in a low-energy procedure, such as mammography, the grid lines are often thicker than required because of limitations in manufacturing grids with very thin lines. Moreover, in such low energy procedures, the interspace material can be a significant absorber of primary X-rays. Traditional methods of grid manufacture involve laminating lead foils onto interspace material or using a fine saw to cut grooves in a graphite substrate and filling the grooves with lead. Molding has also been suggested as a method of grid manufacture, for example as disclosed in U.S. Patent Publication Number US20090272874. Accordingly, there is an ongoing need for improving upon existing X-ray grid design and manufacturing techniques. The present invention overcomes at least some of the aforementioned drawbacks by providing an anti-scatter X-ray grid device, and a method of making an anti-scatter X-ray grid device, that ultimately provides improved grid performance. More specifically, the present invention is directed to a grid manufacturing technique that provides grids with extremely thin grid lines, and highly transparent interspace material, that is fast, inexpensive and highly repeatable. Therefore, in accordance with one aspect of the invention, a method of making an anti-scatter X-ray grid device comprises: providing a substrate comprising a first material substantially non-absorbent of X-rays, the substrate having a plurality of channels therein; applying a layer onto a sidewall of the plurality of channels, wherein the layer comprises a second material substantially non-absorbent of X-rays; and applying a third material substantially absorbent of X-rays into a portion of the plurality of channels, thereby defining a plurality of X-ray absorbing elements. In accordance with another aspect of the invention, an anti-scatter X-ray grid device comprises: a substrate comprising a first material substantially non-absorbent of X-rays, the substrate having a plurality of channels therein; a second material substantially non-absorbent of X-rays, lining sidewalls of the plurality of channels; and a third material substantially absorbent of X-rays, at least partially resident in the plurality of channels, thereby defining a plurality of X-ray absorbing elements. Various other features and advantages of the present invention will be made apparent from the following detailed description and the drawings. Aspects of the present invention have been shown to offer advantages over previous methodologies of making anti-scatter X-ray grid devices. Aspects of the present invention provide a manufacturing technique that allows for thinner grid lines and highly X-ray transparent interspace material in a cost effective and well-controlled process. Amongst other advantages, use of grid devices 10 employing the present invention will provide for better imaging results for mammographic and other low energy (e.g., about 26-33 kVp) X-ray systems. FIG. 1 is a sectional side view of a conventional radiographic imaging arrangement employing an embodiment of the present invention. A tube 50 generates and emits x-radiation 52 which travels toward a body 90. Some of the x-radiation 54 is absorbed by the body 90 while some of the radiation penetrates and travels along paths 56 and 58 as primary radiation, and other radiation is deflected and travels along path 60 as scattered radiation. Radiation from paths 56, 58, and 60 travels toward an image receptor such as photosensitive film 62 where it will become absorbed by intensifying screens 64 which are coated with a photosensitive material that fluoresces at a wavelength of visible light and thus exposes photosensitive film 62 (the radiograph) with the latent image. When an anti-scatter grid 10 is interposed between body 90 and photosensitive film 62, radiation paths 56, 58, and 60 travel toward the anti-scatter grid 10 before film 62. Radiation path 58 travels through translucent material 14 of the grid 10, whereas both radiation paths 56 and 60 impinge upon absorbing material 12 and become absorbed. The absorption of radiation path 60 constitutes the elimination of the scattered radiation. The absorption of radiation path 56 constitutes the elimination of part of the primary radiation. Radiation path 58, the remainder of the primary radiation, travels toward the photosensitive film 62 and becomes absorbed by the intensifying photosensitive screens 64 which expose photosensitive film 62 with the latent image. While the configuration shown in FIG. 1 contemplates a film-based detection system, other image receptors may be used without departing from the present invention. For example, the image receiving portion of the system may instead comprise a digital system using either direct or indirect conversion methods. In the indirect method, the X-rays would be absorbed in a scintillator layer which emits visible light that is subsequently detected in an array of photodiodes. In the direct method, the X-rays would be converted directly into an electrical signal in a suitable direct conversion material, such as amorphous selenium. Referring to FIG. 2, a sectional elevation view of a portion 16 of an anti-scatter X-ray grid device is shown. An embodiment of a method of making a grid may start with providing this portion 16. The portion 16 comprises a substrate 14 having a plurality of channels 18 therein. The substrate 14 may be made of a first material that is substantially non-absorbent of X-rays. As shown, the plurality of channels 18 may include sidewalls 20 and a channel bottom or end. The plurality of channels 18 may be made by a variety of techniques. For example, the plurality of channels 18 may be made in the substrate 14 by at least one of injection molding, laser, mechanical, plasma etching, and the like. The substrate 14 may be made of any suitable material that is substantially non-absorbent of X-rays such as thermoplastic, PEEK, graphite, aluminum, and combinations thereof. As shown for example in FIGS. 1 and 2, the axial orientation of the plurality of channels 18 may be non-parallel so the cone of X-rays emitted from the source 50 (FIG. 1) approximately align with the axes of the plurality of channels 18. While FIG. 2 shows a substrate 14 portion of an embodiment of an anti-scatter grid, clearly there are other embodiments available without departing from aspects of the invention. For example, while only five channels 18 are shown, the totally quantity of channels 18 may be virtually any suitable number. Similarly, the cross sectional shape, dimensions, and configuration can vary from that shown. Referring to FIG. 3, a sectional elevation view of the portion 16 of an anti-scatter X-ray grid device is shown undergoing a second step in a method of making the grid device. As shown, a second material 34 substantially non-absorbent to X-rays is placed within the plurality of channels 18. The second material 34 may be provided via a reservoir or source 30 so that the second material 34 may be applied 32 as a layer onto the sidewalls 20 of the plurality of channels 18. For example, the second material 34 may be any suitable conformal coating that may be applied via a variety of suitable methods including at least one of vacuum deposition, evaporation, chemical vapor deposition, sputtering, and the like. Similarly, the conformal coating comprises an oxide, a nitride, a polymer, an acrylic, an epoxy, a urethane, silicone, and combinations thereof. In an embodiment, the conformal coating may comprise Parylene. Parylene is a tradename for a variety of chemical vapor deposited poly (p-xylylene) polymers. As shown, any suitable material may be used as the second material 34 that both narrows the width of the plurality of channels 18 and does not fully fill the width of the plurality of channels 18. In this manner, the application of the second material 34 provides for a remaining channel 36. While FIG. 3 shows the substrate 14 portion of an embodiment of an anti-scatter grid undergoing an application of the second material 34, clearly there are other embodiments available without departing from aspects of the invention. For example, the second material 34 may be applied as a layer on only one of the two sidewalls 20 and ends or bottoms of the plurality of channels 18. Suitable quantities of the second material 34 may be applied in the plurality of channels 18 so that a width of the remaining channels 36 is less than about 20 μm. In other embodiments, the width of the remaining channels 36 may be in a range from about 5 μm to about 10 μm. Referring to FIG. 4, a sectional elevation view of the portion 16 of an anti-scatter X-ray grid device is shown undergoing a third step in a method of making the grid device 10. As shown, a third material 42 substantially absorbent to X-rays is applied within a portion of the remaining channels 36, thereby defining a grid device 10. The third material 42 may be provided via a reservoir or source 40 such that the third material 42 may be applied 44 into a portion of the remaining channels 36 thereby defining a plurality of X-ray absorbing elements 12. The third material 42 may be any suitable material that is substantially absorbent of X-rays such as a material that contains lead, tungsten, uranium, gold, and/or a polymer (e.g., epoxy, etc.) containing lead, tungsten, and/or gold. As shown, the third material 42 may be applied in the remaining channels 36 so that the third material 42 substantially fills the plurality of channels 18. In this manner, the application of the third material 42 ultimately defines a plurality of X-ray absorbing elements 12 that may have an angular orientation (see e.g., FIGS. 1 and 5). In an embodiment, a top surface 49 of the grid device 10 may be planarized by any suitable means including, for example, mechanical grinding and the like. As FIG. 5 shows, a portion of the grid device 10 may be constructed employing aspects of the methods disclosed herein. The grid device 10 includes a plurality of X-ray absorbing elements 12 having a width, w, and height, h1 that are distributed a space, d, apart. The height of the grid device 10, denoted as h, is generally greater than h1 and may be about 1 mm or any other suitable height. Similarly, h1 may be partially through the height of the grid device, and be, for example, 0.5 mm. The width, w, of the plurality of X-ray absorbing elements 12 may be in a range of about 20 μm to about 30 μm. In other embodiments, the width, w, of the plurality of X-ray absorbing elements 12 may be in a range of about 5 μm to about 10 μm. Similarly, the spacing, d, between adjacent X-ray absorbing elements 12 may be in a range of about 100 μm to about 300 μm. The X-ray absorbing elements 12 are located within X-ray non-absorbent materials comprising the substrate 14 and second material 34. The footprint of the completed grid device 10 may be virtually any suitable size. For example, the grid device 10 may be a rectangle having dimensions (i.e., length and/or width) that are in a range from about 12 cm to at least about 40 cm. Similarly, the distribution of the plurality of channels 18, and concomitantly the plurality of elements 12, may be in a range from about 30 elements/cm to about 100 elements/cm. As shown in FIG. 5 and FIG. 1, for example, the plurality of X-ray absorbing elements 12 may have an angular orientation. That is a longitudinal axis of each the plurality of X-ray absorbing elements 12 may vary from being normal to the X-ray source 50 (FIG. 1) by an offset angle, θ. As shown in FIG. 1, the offset angle, θ, may vary and increase in the various plurality of X-ray absorbing elements 12, from 0 degrees to any suitable angle (e.g., 15 degrees, etc.). The location within the grid device 10 of the X-ray absorbing elements 12 that have various offset angles can vary depending on the geometry of the X-ray system. For example, in an embodiment, the center of the grid device 10 may include X-ray absorbing elements 12 that are about 0 degrees. In another embodiment (e.g., mammographic systems), at least one of the edge regions of the grid device 10 may include X-ray absorbing elements 12 that are about 0 degrees. The precise angular orientation of the various X-ray absorbing elements 12 may depend on the location and distance of the X-ray source(s). In this manner, the grid device 10 is a focused grid. Therefore, according to one embodiment of the present invention, a method of making an anti-scatter X-ray grid device comprises: providing a substrate comprising a first material substantially non-absorbent of X-rays, the substrate having a plurality of channels therein; applying a layer onto a sidewall of the plurality of channels, wherein the layer comprises a second material substantially non-absorbent of X-rays; and applying a third material substantially absorbent of X-rays into a portion of the plurality of channels, thereby defining a plurality of X-ray absorbing elements. According to another embodiment of the present invention, an anti-scatter X-ray grid device comprises: a substrate comprising a first material substantially non-absorbent of X-rays, the substrate having a plurality of channels therein; a second material substantially non-absorbent of X-rays, lining sidewalls of the plurality of channels; and a third material substantially absorbent of X-rays, at least partially resident in the plurality of channels, thereby defining a plurality of X-ray absorbing elements. The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims. |
|
053655613 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown a major portion of an X-ray exposure apparatus to which the present invention is applied. In FIG. 1, a wafer 101 has a surface to which a radiation-sensitive material (resist) is applied. Mask 102 has formed thereon a pattern for manufacture of semiconductor devices. Mask stage 112 is adapted to hold the mask 102 parallel to the wafer 101 with a clearance (mask-to-wafer gap) of about 40 microns in a Z-axis direction. Wafer moving stage 103 is adapted to hold the wafer 101 and to move the same in each of the X-axis and Y-axis directions. The exposure apparatus of the present embodiment is arranged such that, by means of the stage 103, different shot areas (exposure regions) of a wafer 101 are placed, in a predetermined order, to be opposed to an irradiation field 120 (see FIG. 2), whereby the whole surface of the wafer 101 is exposed with radiation. At any one time, a pattern bearing portion of the mask 102 and one exposure region of the wafer 101 are placed at the irradiation field 120. In other words, the exposure apparatus of this embodiment is structured as a step-and-repeat type exposure apparatus, called a "stepper". Sensor 104 is provided on the wafer moving stage 103 and is movable in the X and Y directions with the movement of the moving stage 103 so as to measure the illuminance at each of desired points in the irradiation field 120. Denoted generally at 105 is a main shutter mechanism having a movable aperture member. In this embodiment, the movable aperture member is provided by an endless belt having openings (apertures). The main shutter mechanism cooperates with an auxiliary shutter mechanism 106, to provide an exposure shutter device. The operation of each of the main shutter mechanism 105 and the auxiliary shutter mechanism 106 is controlled by a controller 113. More specifically, this controller 113 operates to control the main shutter mechanism 105, in a manner which will be described later, on the basis of the illuminance at each point within the irradiation field 120 as measured by use of the sensor 104. Also, the controller 113 operates to control the auxiliary shutter 106 so as to open the same before initiation of the exposure control by the main shutter mechanism 105 and to close the auxiliary shutter 106 after completion of the exposure control. Denoted at 107 is a beryllium thin film (partition film). The mask 102 side of this beryllium film 107 is maintained, for example, in a reduced-pressure He gas ambience, while a high-vacuum ambience is maintained on a radiation-source side of the film 107. Denoted at 108 is a radiation emitting point of a synchrotron orbitration radiation (SOR) ring which functions as an X-ray source. The synchrotron radiation (X-rays) from the emission point 108 has a uniform intensity distribution in a direction (X-direction in this embodiment) parallel to the orbital plane of an electron beam 110 (see FIG. 2), but has a substantially symmetric intensity distribution with respect to a direction (Y direction) perpendicular thereto. As best seen in FIG. 2, a convex-surface cylindrical mirror 109 functions to expand the synchrotron radiation from the emission point 108 in the direction (Y direction) in which the radiation has a substantially symmetric intensity distribution. The cylindrical mirror 109 is used to provide an irradiation field 120 of a required dimension, at the position at which the mask 102 and one exposure region of the wafer 101 are placed. Usually, when a cylindrical mirror whose reflection surface has a single curvature is used, there occurs in the irradiation field 120 a one-dimensional (Y direction) illuminance distribution (non-uniformness) having one peak. An example of such an illuminance distribution is illustrated in FIG. 6. The curve in FIG. 6 has been drawn by plotting the results of the calculation of the illuminance distribution as weighted in consideration of the dependency, upon wavelength, of the sensitivity of a resist material applied to a wafer 101. The axis of the abscissa denotes the position, while the axis of the ordinate denotes a specific illuminance in which the illuminance is standardized by using the illuminance I.sub.L or I.sub.U (=I.sub.L) at the position Y.sub.1 or Y.sub.N as a reference (=1). Reference character I.sub.P denotes a peak illuminance, and reference character Y.sub.P denotes the position in the Y direction corresponding to the peak Y.sub.P. FIG. 3 exemplifies a specific structure of a main shutter mechanism usable in the FIG. 1 embodiment. Belt 105 having an aperture 204 comprises a thin metal belt made of stainless steel, for example. This thin metal belt has a thickness sufficient for intercepting X-rays from the source. The belt 105 is wound around rollers 201 and 202. By rotating one of these rollers by a driving motor 203, the aperture 204 of the belt 105 can operate as a movable aperture. Arrow 210 corresponds to the Y direction and denotes in FIG. 3 the direction of movement of the aperture 204, which direction is coincident with the direction in which the synchrotron radiation has non-uniformness in intensity. The belt 105 is provided with two apertures, one of which is denoted at 204, and another of which is denoted at 208. The aperture 204 functions as a movable aperture which is operable to locally control, along the Y direction, the exposure time for the exposure region. The aperture 204 has a leading edge 206 and a trailing edge 207. When the leading edge and the trailing edge of the aperture 204 moves through the exposure region in the Y direction, their moving speeds are controlled independently by the controller 113. The other aperture 208 is defined by an opening of a size and shape necessary for avoiding interception of the radiation from the source in a time period in which the movable aperture member provided by the opening 204 is in an open state. Photosensor 209 is operable to detect the position of the aperture 204 and is used to determine the timing of passage of the aperture 204 through the exposure region. FIG. 4 exemplifies the manner of movement of the leading edge 206 and the trailing edge 207 of the aperture 204 (movable aperture). In FIG. 4, the axis of the abscissa denotes the time and the axis of the ordinate denotes the position of the movable aperture in its moving direction, namely, the position coordinate in the direction of non-uniformness in intensity of the radiation being projected. The zone as depicted at L.sub.O (from Y.sub.1 to Y.sub.N) corresponds to the exposure region (irradiation field) in FIG. 4, while reference character L.sub.E denotes the interval between the leading edge 206 and the trailing edge 207 of the aperture 204 in the Y direction. It is an important feature that, within the exposure region L.sub.O, the moving speeds of the leading edge 206 and the trailing edge 207 change independently of each other. In an initial state, the aperture 204 is located at a position under the exposure region (exposure field), in FIG. 4. When exposure start is instructed, the controller 113 operates to actuate the motor 203 to move the belt 105 with the cooperation of the rollers 202 and 203, so that the positions of the leading edge 206 and the trailing edge 207 of the aperture 204 are changed with the lapse of time along the curves shown in FIG. 4. When the leading edge 206 reaches the position Y.sub.1, the exposure starts. The leading edge 206 displaces between the positions Y.sub.1 and Y.sub.N in such manner that the position of the leading edge 206 changes relatively slowly in the neighborhood of the position Y.sub.1 whereas it changes relatively quickly in the neighborhood of the position Y.sub.N. At this time, the trailing edge 207 has not reached the exposure region, because there is a relationship "L.sub.O <L.sub.E ", After this and when a middle portion of the aperture 204 reaches the exposure region, the controller 113 stops the drive of the motor 203 and, thereafter, restarts the drive of the motor 203 at a suitable timing. When the trailing edge 207 reaches the position Y.sub.N, the exposure is completed, and, thereafter, the drive of the motor 203 is stopped. The trailing edge 207 displaces such that the position of trailing edge 207 changes relatively quickly in the neighborhood of the position Y.sub.1, whereas it changes relatively slowly in the neighborhood of the position Y.sub.N. The reason for controlling the moving speed (displacement) of each of the leading edge 206 and the trailing edge 207 will be explained later. FIG. 7 shows changes in the position of each of the leading edge 206 and the trailing edge 207, moving between the positions Y.sub.1 and Y.sub.N in FIG. 4. The axis of the abscissa denotes the position coordinate in the Y direction, while the axis of the ordinate denotes time. FIG. 8 shows the exposure time (T.sub.E -T.sub.F) at each point Y.sub.i between the positions Y.sub.1 and Y.sub.N. In these Figures, reference character T.sub.F denotes the time at which the leading edge 206 reaches the point Y.sub.i, and reference character T.sub.E denotes the time at which the trailing edge 207 passes the point Y.sub.i. It is seen from FIG. 8 that, in the FIG. 4 example, the exposure time is shorter at the central portion of the exposure region (zone between Y.sub.1 and Y.sub.N) than that at marginal portions. In FIG. 9, the illustrated curve shows the illuminance at each point Y.sub.i (FIG. 6) as multiplied by the exposure time at each point Y.sub.i (FIG. 8). Namely, the graph of FIG. 9 shows the amount of exposure at each point Y.sub.i within the exposure region (actually, this corresponds to the amount of radiation absorbed by a resist material). It is seen from FIG. 9 that, by the provision of a speed-controlled movable aperture of the present embodiment, the amount of exposure can be made substantially uniform throughout the exposure region irrespective of that the radiation contains non-uniformness as shown in FIG. 6. In the above-described example, the movable aperture moves through the exposure region by a constant acceleration motion. To be exact, accordingly, the amount of exposure in the exposure region is not completely uniform. However, depending on the manner of control of the movable aperture, it is in principle possible to make the amount of exposure completely uniform, over every point Y.sub.i. An example of this will be described below in detail. Assume that, within the exposure region, a coordinate is set in the direction in which the illuminance changes. Points in the exposure region of a number N are selected and reference characters Y.sub.1, Y.sub.2, . . . and Y.sub.n are assigned to these points. Actual illumination intensity at a position Y.sub.i, as calculated on the basis of the data obtained by the measurement by the sensor 104 and having been weighted in accordance with the sensitivity-to-wavelength characteristics of a resist material on a wafer, is denoted by I.sub.i. Assuming that the required amount of exposure is E, then a correct exposure time at the position Y.sub.i in the exposure region can be expressed as follows: EQU T.sub.i =E/I.sub.i (1) On the other hand, the time at which the leading edge 206 of the movable aperture passes the point Y.sub.i is denoted by T.sub.Fi (P.sub.1, P.sub.2, . . . ). These reference characters P.sub.1, P.sub.2, . . . are parameters for controlling the operation of the movable aperture. Similarly, the time at which the trailing edge 207 of the movable aperture passes the point Y.sub.i is denoted by T.sub.Ei (P.sub.1, P.sub.2, . . . ). For each parameter P.sub.k, such a one by which the value E, determined by the following equation, becomes minimum is determined by the following calculation: ##EQU1## The motion of the movable aperture is controlled accordingly. By doing so, it is possible to minimize the error caused in relation to the control of the movable aperture. If control parameters of a number not less than N are set, it is possible to establish the following relationship with respect to each point Y.sub.i on the exposure region: EQU T.sub.Ei -T.sub.Fi -T.sub.i .+-.0 (3) In this case, it is possible to provide the same amount of exposure at every point Y.sub.i in the exposure region. Therefore, it is possible to assure, at high precision, uniform exposure over the whole exposure region. Taking this case as an example, a moving method by which the exposure can be completed in the shortest time will be explained below. It is assumed now that Y.sub.1 and Y.sub.N denote the ends of the exposure region; the movable aperture is moved in the direction from the point Y.sub.1 to the point Y.sub.N ; an illuminance distribution such as shown in FIG. 6 is provided; I.sub.p denotes the peak of the illuminance distribution in the exposure region; Y.sub.p denotes the position which provides the peak; I.sub.L =I.sub.1 ; and I.sub.U =I.sub.N. In an example when, as shown in FIG. 4, the movable aperture is provided by one endless belt having an aperture 204, and if the length L.sub.E of the aperture satisfies the following relation: EQU L.sub.E .gtoreq.max(.vertline.Y.sub.P -Y.sub.1 .vertline.,.vertline.Y.sub.N -Y.sub.P .vertline.), then, the movable aperture may be moved such a manner that the time T.sub.Fi and the time T.sub.Ei at which each point Y.sub.i is passed by the leading edge 206 and the trailing edge 207 of the aperture 204, with a maximum speed Vmax of the movable aperture, can be expressed by the following equations: ##EQU2## wherein T.sub.F0 is the time at which the leading edge 206 passes the point Y.sub.1 (T.sub.F1 =T.sub.F0). The manner of motion of the leading edge 206 and the trailing edge 207 as determined by equations (4), (5), (6) and (7) is shown in FIG. 10. Also, in this example, like the FIG. 7 example, the leading edge 206 displaces relatively slowly in the neighborhood of the point Y.sub.1. The moving speed gradually increases and, in the neighborhood of the position Y.sub.N, the leading edge moves relatively quickly. On the other hand, the trailing edge 207 moves relatively quickly in the neighborhood of the position Y.sub.1 and the moving speed gradually decreases, such that the trailing edge moves relatively slowly in the neighborhood of the position Y.sub.N. Also, the exposure time (T.sub.Ei -T.sub.Fi) in the exposure region is shortest at the position Y.sub.P. In this case, the time period .DELTA.T from the entrance of the leading edge 206 of the aperture 204 into the exposure region to the exit of the trailing edge 207 of the aperture 204 from the exposure region is given by the following equation: ##EQU3## Among various types of the motion of the movable aperture, satisfying equation (3), the above-described is the one that provides the minimum of the time (.DELTA.T). Particularly, when L.sub.O .ltoreq.L.sub.E, the leading edge 206 and the trailing edge 207 do not exist in the exposure region at the same time. Therefore, the maximum speed Vmax can be determined as desired within a range of E/I.sub.L >L.sub.O /Vmax. The motion according to equations (4) to (7) provides a minimum time .DELTA.T. However, it should be noted that the motion represented by these equations is not the sole solution. Any motion may be adopted, provided that equations (5) and (7) are satisfied. Further, according to another important feature of the present invention, as long as the illuminance distribution is continuous, uniform exposure is attainable with regard to any illuminance distribution. Equations (4) to (7) show one solution for such a moving method. Namely, the leading edge 206 may be moved in accordance with equation (4) in such a region wherein T.sub.i decreases in the moving direction, whereas the leading edge may be moved in accordance with equation (6) in such a region wherein T.sub.i increases. Referring now to FIG. 5, another embodiment of a shutter device will be described. Denoted in FIG. 5 by reference numerals 211 and 212 are two separate movable aperture members each being in the form of a belt member, in this embodiment. The movable aperture member 211 is wound around driving rollers 216 and 219, while the other aperture member 212 is wound around driving rollers 217 and 218. Arrow 215 denotes the moving direction of these aperture members for the exposure control. In this embodiment, the origin sensor and the driving actuator of the FIG. 3 embodiment are omitted. Reference numeral 214 denotes an edge of an opening of the aperture member 212, and this edge has a function substantially the same as that of the leading edge 206 of the FIG. 3 embodiment. Reference numeral 213 denotes an edge of an opening of the aperture member 211, and this edge has a function substantially the same as that of the trailing edge 207 of the FIG. 3 embodiment. When the leading edge and the trailing edge of a shutter device is provided by two separately movable members, as in the present embodiment, an auxiliary shutter member such as at 106 in FIG. 1 may be omitted. Further, in the present embodiment, the length L.sub.E of the opening in the FIG. 4 example can be made apparently variable. Therefore, a higher degree of freedom is provided with respect to the control. In the extension of the method of the present invention, which assures uniform exposure by use of movable aperture means, equation (8) provides an optimization method for the design of the illumination system shown in FIG. 2. This will be described below in greater detail. FIG. 11 shows the illuminance distribution in the exposure region which varies with the change in the curvature 1/R of the convex-surface cylindrical mirror 109 of the illumination system shown in FIG. 2. In the particular example shown in FIG. 11, calculations were made under the conditions that: the critical wavelength .lambda..sub.L of the synchrotron radiation was 10.2 .ANG.; the intrinsic diversive angle .sigma. at the critical wavelength .lambda..sub.L was 0.44 mrad; the distance between the emission point 108 of the synchrotron radiation and the reflection center of the mirror 109 was about 5 m; the distance between the reflection center of the mirror 109 and the movable aperture 105 was about 7 m; and the size L.sub.O of the exposure region in the Y direction was about 30 mm (the Y direction is substantially vertical, although the inclination is emphasized in FIG. 1). Under these conditions, and while taking into account the angle of incidence of the radiation upon the mirror 109, the calculations were made. FIG. 12 is a graph wherein the axis of the abscissa denotes 1/R while the axis of the ordinate denotes .eta. which, on an occasion when the movable aperture means is moved in accordance with equations (4) to (7), can be expressed by the following equation (9): EQU .eta.=1/I.sub.U +1/I.sub.L -1/I.sub.P (9) EQU .DELTA.T=.eta.E+L.sub.0 /Vmax (10) As seen in this Figure, there exists such a radius of curvature (Rc) of the convex-surface cylindrical mirror 109 that provides the minimum ordinate value. While the value Rc is variable depending on the profile of the synchrotron radiation source and the size of the exposure field as well as the disposition of the radiation source, the mirror and the mask, for example, it is possible to assure an exposure system having a shortest opening time for the shutter and having a good efficiency with respect to time, by selecting, as the radius of curvature of the convex-surface cylindrical mirror, such an Rc that provides the minimum of .eta. as represented by equation (9). However, upon actual determination of the radius of curvature, the selection of Rc does not always provide a best result. In the method of the present invention making the exposure uniform, error factors which affect the same include an error in the measurement of illuminance, an error in the control of the moving speed of the movable aperture, and so on. The tolerances for these errors are determined with respect to the required precision for the amount of exposure. Each error can be reduced more easily, with smaller non-uniformness in the intensity of radiation. This is in the tendency to reduce the radius of curvature of the cylindrical mirror and, therefore, increases the exposure time. To enlarge the radius of curvature of the cylindrical mirror beyond Rc causes larger non-uniformness in the radiation and, additionally, the prolongation of the exposure time. Therefore, to do so provides no merit. As will be understood from the above, it is desirable to take the value Rc as an upper limit for the radius of curvature of the cylindrical mirror and to select a smaller radius of curvature within a range that does not increase the exposure time beyond a tolerable level. When the radius R is small, on the other hand, the non-uniformness in the intensity of radiation becomes small and the effectiveness of the present invention, making uniform the exposure by the action of the movable aperture means, may be reduced. But, the illuminance itself becomes too low. In consideration of this, when the radius of curvature of the cylindrical mirror that provides the minimum .eta. min is denoted by Rc, the radius R may desirably be within the limit of about 3.times..eta. min. In the particular example of FIG. 12, the radius R=30 m defines an intensity distribution which provides "3.6.times..eta. min". In the foregoing embodiments, the motion of the movable aperture has been described with reference to an example wherein the illuminance distribution has one peak. However, as long as the illuminance distribution is one dimensional and the illuminance changes continuously, the present invention is applicable to any profile of distribution and assures uniform exposure. Thus, the present invention is applicable not only to an illumination system having a cylindrical mirror, but also to any other illumination system using any other optical component such as a non-cylindrical mirror, for example. With regard to the illuminance distribution I, it may be measured after execution of actual exposure and development. Alternatively, it may be detected by calculations based on the ray tracing the synchrotron radiation. In accordance with the present invention, as described hereinbefore, a speed-controllable movable aperture means is provided, as an exposure shutter, in an exposure apparatus having an illumination system which provides radiation containing non-uniformness in the illuminance within an exposure field, and the aperture means is controlled to locally control the exposure time. By this, the non-uniformness in the amount of exposure (the amount of radiation absorbed by the resist material) resulting from the non-uniformness in the illuminance can be reduced remarkably, with the result that the resolution of the exposure apparatus can be improved significantly. Further, since the precision itself for the uniformness in the exposure as required from the point of resolution in the exposure process can be satisfied by the local exposure time control of the present invention using the movable aperture means, the tolerance for the non-uniformness in illuminance as can be set for the illumination system side is determined by the performance of this local exposure time control, and a significantly wider tolerance is allowed as compared with that for the non-uniformness as allowed conventionally. Usually, the magnitude of the illuminance and the uniformness thereof are somewhat incompatible factors with respect to the design of an illumination system. Therefore, if the tolerance for the non-uniformness becomes wider, as in the present invention, the illuminance can be made higher correspondingly. This makes it possible to reduce the exposure time and to reduce the exposure error due to the variation with time during the exposure. Additionally, this makes it possible to increase the processing speed of the apparatus, called "throughput". In the foregoing, it is shown that an exposure apparatus according to the present invention having a movable aperture means can accomplish more precise and correct exposure even when it is used with an illumination system that provides a much higher intensity of illumination than that of prior art illumination systems. By using the exposure time as an evaluation function, an index is given in the optimum designing of an illumination system. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. |
abstract | A method and apparatus for inspecting the upper portion of a core shroud of a nuclear power plant is provided. The upper shroud scanner mounts on an arcuic section of a steam dam of the core shroud and moves back and forth there along. A vertical arm with transducers thereon extend down from a Y-car portion of the upper shroud scanner. Transducers adjacent the core shroud emit and receive an ultrasonic sound to inspect for flaws and defects in the core shroud. |
|
062597604 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the nuclear steam supply system (NSSS) 1 of the invention includes a pressure vessel 3 which is an upright cylinder with an integral bottom head 5 and a removable upper head 7. The upper head 7 is only removable for the insertion of the internals and is then permanently sealed to make the vessel proliferation resistant. This is possible because, as will be seen below, the internals are designed to have a useful life at full power of at least ten years and preferably fifteen years or more. The pressure vessel 3 has a lower section 9 and an upper section 11. The reactor core 13 is centrally positioned in the lower section 9 on a core support structure 15 spanning the lower section. A core chimney 17 surrounds the reactor core 13 and extends upward into the upper section 11 of the pressure vessel 3 to form a central passage 19 extending upward from the reactor core 13 and an annular passage 21 between the chimney 17 and the inner surface 22 of the pressure vessel. A plurality of steam generators 23 are circumferentially spaced around the annular passage 21. Each of these steam generators 23 has a secondary circuit 25 which includes a feed water inlet pipe 27 and a steam outlet pipe 29, both of which extend out of the pressure vessel 3, in this case through the upper head 7. The pressure vessel 3 contains a pool of reactor coolant 31 which fills the vessel up to the level 33, leaving a steam expansion space 35 above. Thus, the reactor core 13 and steam generators 23 are fully immersed in the pool of reactor coolant 31. The steam generators 23 have reactor coolant inlets 36 at their upper ends and outlets 37 at their lower ends. The reactor core 13 has fuel assemblies 39, each containing a number of fuel rods 41. As will be described in more detail, the reactor core 13 has fast or epithermal spectrum neutronics. The heat generated by the fuel contained in the fuel rods 41 heats the reactor coolant which, as shown by the arrows, rises in the central passage 19 formed by the chimney 17, flows over the top of the chimney and through optional openings 42 near the top of the chimney into the annular passage 21. The reactor coolant then flows downward through the steam generator 23 to heat the feed water in the secondary circuit 25 and thereby produce steam, which can be used to drive a steam turbine-generator set (not shown). The reactor coolant exits the lower end of the steam generators 23 and continues down through the annular passage 21, through the core support structure 15 and then back upward through the reactor core 13. As will be seen, the conditions are such that this flow in the pool of reactor coolant can be produced by 100% by natural circulation, even at 100% core power. However, in order to assure adequate flow, and to promote mixing, a number of reactor coolant pumps 43 can be provided in the annular passage 21 at the core support structure 15. These pumps 43 have an impeller section 45 mounted in the annular passage 21, while the drive motors 47 are mounted on the outside of the pressure vessel, where they can be reached for change out or maintenance. A number of reactor coolant pumps 43 can be circumferentially spaced around the lower end of the annular passage 21 at the core support structure 15. As pointed out, one of the primary objectives of the NSSS 1 is proliferation resistance. A high degree of proliferation resistance is achieved by providing a reliable unit with a long life which does not require access to the internals. However, it was also discussed that the steam generators are a prime source of failures. Therefore, in accordance with the invention, a plurality of steam generators 23 in excess of a predetermined number of steam generators which are required to operate the reactor core at 100% power are provided in the pressure vessel 3. In the particular embodiment of the NSSS 1, shown in FIGS. 1 and 2, for example, where the predetermined number of steam generators required for full-power operation of the reactor core 13 is four, a plurality of eight steam generators is provided, so that there is 100% redundancy. At any one time, no more than four of the steam generators are activated. The steam generators are activated by circulating feed water through the secondary circuit 25, so that the steam generator draws heat from the pool of reactor coolant 31. The 100% redundancy is only exemplary, and more or less redundancy of the steam generators can be provided. Similar redundancy is provided for the reactor coolant pumps. Also by way of example only, six reactor coolant pumps could be provided where a maximum of three pumps would ever be run simultaneously. Less redundancy of the reactor coolant pumps may be needed as the motors are accessible from outside the pressure vessel for maintenance and replacement. The pool configuration also contributes to enhanced safety, as it virtually eliminates the loss of coolant accidents and piping rupture events. It also contributes to the capability of 100% natural circulation by greatly reducing the pressure drop attributable to piping losses. The reactor core 13 is provided with control rods 49 which can be inserted and removed from the core by drivelines 51 which extend upward through the upper head 7 and can be raised and lowered by control rod drives 53 located outside the pressure vessel 3. The control rods are used to shut down the reactor, and although the reactor may be run at 100% power for base loading, the control rods can also be partially inserted for reactivity control during load following. As mentioned, an important feature of the invention is that the reactor core 13 has a core life of at least 10 years and preferably at least fifteen years without refueling or fuel shuffling. This is achieved with a fast or epithermal spectrum reactor core. In order to achieve the high conversion ratio required for a fast or epithermal neutron spectrum, a tight lattice core which minimizes the water volume fraction is necessary. A tight lattice core means that the fuel rods are spaced close together. Quantitatively, a p/d (pitch to diameter) ratio of less than about 1.1 is needed. As is known, such a small p/d ratio is achieved by use of the known triangular lattice. As is also known, the fuel for such a fast or epithermal spectrum reactor core is uranium enriched with plutonium though a thorium based fuel can also be used. Reactivity is controlled by burnable poison added to the fuel. Initially, the excess neutrons are captured by the poison. As the reactivity decreases, the burnable poisons also are depleted. As can be seen from FIG. 3, with a 20% enrichment (the maximum allowed under the proliferation resistance requirement), criticality is maintained well beyond 5,952 FPD (full power days), or about 20 years at 80% CF (capacity factor). At 15 years (5,475 days), there is still 15% excess reactivity with a core burn-up of 74,000 MWd/t (megawatt days thermal). Based on these preliminary results, it is expected that a reactivity lifetime of about fifteen years could be achieved with a U/235 enrichment between 12 and 15% at the p/d assumed. This preliminary analysis shows that a water-cooled fast or epithermal spectrum core can last, from a criticality point of view, about fifteen years in a straight burn mode. When a realistic core configuration is considered, including the effects of leakage and parasitic losses, fuel forms other than the .sup.235 UO.sub.2 used in the example of FIG. 3 may show better performance with regard to burn-down behavior, cycle length and required p/d ratio. Adoption of a fast or epithermal spectrum allows the use of more robust cladding materials, such as stainless steel or advanced alloys, because the good neutronics properties of Zircaloy.RTM. are no longer necessary. Stainless steel and advanced (e.g., refractory) alloys are very reliable at high temperatures and in the presence of boiling. In addition, the stainless steel cladding will better be able to resist the swelling of the fuel and containment of the fission gases over the fifteen-year life span than the zirconium-based materials. As mentioned above, a tight lattice fuel configuration is needed for the fast or epithermal spectrum neutronics. However, this increases flow resistance which is detrimental to achieving natural circulation. Natural circulation is enhanced by a minimum pressure drop and a high driving head. As already discussed, the pool configuration eliminates the piping losses inherent in a loop system. In order to minimize the pressure drop, we have opted to decrease the required core mass flow rate by using a much larger core .DELTA.T than is conventionally used in the typical PWR. Since the temperature of the light water exiting the reactor core is dictated by the pressure level, which we have kept comparable to that in conventional PWRs at about 160 bar, the core inlet temperature was decreased. Thus, we have a core exit temperature of about 320 degrees C (without boiling) and a core inlet temperature of 235 degrees C, to provide a .DELTA.T of 85 degrees C (without boiling). This is compared to a similar exit temperature, but with only a 35 degree C .DELTA.T in a conventional PWR. The pressure drop can be further limited by keeping the core height to a minimum necessary to ensure the required degree of natural circulation. To maximize the driving head, chimney channels 55 are provided in the chimney 17 above the reactor core to channel water at different enthalpies. This raises the level at which the heated water from the core mixes with the pool of coolant. As shown in FIG. 1, the chimney channels vary in height. This is because the temperature across the core varies. In the example shown, the channels 55 at the center are higher than those at the periphery. This optimizes the conditions near the end of the fuel cycle. At the beginning, the reverse would be true. It may be more suitable to make all the chimneys the same height to average the effect over the life of the core. The driving head can be further increased by allowing partial boiling at the top of the core to further decrease the density in the hot leg. For instance, a steam fraction of from about 5-20%, with a preferred value of about 10%, achieves this increase in driving head. Another consideration for enhanced natural circulation is a fuel rod configuration with an enhanced heat transfer area to achieve simultaneously the conflicting requirements of tight pitch and high natural circulation. A high heat transfer area offsets the decrease in heat transfer coefficient caused by the low flow rate which is necessary to keep the pressure drop low. The following Table I sets forth the major reactor parameters used in feasibility studies performed to address key neutronic and thermal hydraulic issues. TABLE I Major reactor parameters used in feasibility assessment Reactor thermal power - 500 MW Core inlet temperature - 235.degree. C. Core exit temperature - 320*, 347.sup.+.degree. C. Exit quality - 0*,0.1.sup.+ Primary loop pressure - 160 bar Fuel rod type - solid, annular Fuel rod outside diameter - 7, 9, 11 mm Fuel rod inside diameter - 0, 2, 3, 4 mm P/D ratio - 1.1 Total primary loop pressure drop - 2.5 times the core pressure drop Core height - 1 m Chimney height - 5 m Steam generator height - 4 m Natural circulation head - 0.05*, 0.14.sup.+ bar Fuel type - oxide Maximum nominal fuel temperature - 1200.degree. C. *No boiling .sup.+ With boiling In addition to the standard solid rod, annular rod configurations were analyzed to assess the effect of increasing the heat transfer area. Thermal conductivities assumed for rod temperature calculations were stainless steel cladding, helium gap and oxide fuel. Note that lower fuel temperatures can be achieved with a fuel/cladding heavy liquid metal (e.g., Pb, Pb--Bi, or Sn) bond, which is not reactive with water. Of course, the use of metal fuel will also yield lower temperatures. All calculations were for nominal conditions and the maximum normal fuel limiting temperature of 1200.degree. C. was estimated by assuming a conservative maximum hot spot of 2500.degree. C. (.about.4500.degree.F.) and a cumulative (and conservative) uncertainty factor of 2.5. The calculated performance parameters were: natural circulation ratio (defined as the ratio of the natural convection head to the total pressure drop); core diameter (calculated from the total number of rods and assuming 217 rods per assembly); and, maximum nominal fuel temperature. The cases where the maximum temperature exceeded 1200.degree. C., and/or the natural circulation ratio dropped below 0.35, and/or the core diameter exceeded 1.5 m were discarded. These were of course rather arbitrary limits and in a couple of cases we kept configurations which were not quite satisfying all constraints, but were still judged overall attractive. Table II summarizes the configurations which satisfy all the above constraints. TABLE II Many configurations can be the starting point for an optimized, attractive design Core Max Rod Type OD (mm) ID (mm) Boiling NCR D (m) T (.degree. C.) Annular 7 2 Yes 1.09 1.41 482 Annular 7 2 Yes 0.37 1.01 608 Annular 9 3 Yes 1.18 1.30 552 Annular 9 3 Yes 0.61 1.13 653 Annular 9 3 Yes 0.38 0.95 782 Annular 9 3 No 0.33 1.30 521 Solid 9 -- Yes 0.81 1.30 1041 Annular 11 4 Yes 1.50 1.38 622 Annular 11 4 Yes 0.97 1.16 712 Annular 11 4 Yes 0.67 0.95 802 Annular 11 4 Yes 0.49 0.95 892 Annular 11 4 No 0.57 1.38 550 Annular 11 4 No 0.39 1.38 614 Annular 11 4 No 0.93 1.59 505 Solid 11 -- Yes 2.00 1.59 1010 Solid 11 -- No 0.31 1.38 1130 Other fuel rod configurations can be considered, which may be more effective than the annular rod in enhancing the heat transfer area, such as, for example, finned elements both straight and twisted, petal-lobe elements, and an inverted fuel bundle geometry, where flow channels are within solid fuel blocks which was used, and tested, in the NERVA space reactor. Also, the imposed limit of 1200.degree. C. is very conservative and more detailed calculations will allow its relaxation, thus allowing more latitude in the geometry selection. The key conclusion of these preliminary analyses performed for the disclosed reactor concept is that a hard neutron spectrum, tight lattice water cooled core is indeed feasible from the point of view of long core life and high level of natural circulation. The fact that a number of different configurations satisfied the rather arbitrary and restrictive imposed limits indicated that ample room exists for a satisfactory point design and future optimization. A second embodiment of the invention is illustrated in FIG. 4. In this NSSS 1', the control rods 49 are inserted and withdrawn from the core by drivelines 51' which extend through the bottom head 5 of the reactor. This makes room for additional steam generators 23' in the upper section 11 of the pressure vessel 3, where, as shown, they extend downward into the central passage 19. This provides more redundancy for the steam generators. Alternatively, it makes it possible to reduce the height, and therefore the pressure drop, of the steam generators, as they contribute about one half of the total pressure drop. It also opens the opportunity to profile the steam generators by adjusting the height, size, flow resistance and steam temperature to optimize performance. For example, steam generators on the periphery might generate steam at a slightly lower temperature than those in the center and can therefore be used for reheat. This configuration also enhances proliferation resistance, as the steam generators 23' must be removed to access the fuel. As a further refinement, the chimney channels 55 could be extended all the way up to the steam generators 23' with each assembly servicing a separate steam generator. In this arrangement, the cold water will mix after exiting the individual steam generators. The reactor coolant pumps 43' can be mounted with the impellers 45' supported on the core support structure 15 and with the external motor drive 47' penetrating through the bottom head 5. Small NSSS like that described above obviously cannot claim economies of scale, but actually can be built in multiple modules thus offering cost reductions through multiple identical units. This concept can be further exploited by adoption of multiple components in a single unit and a "once through" approach. This has significant beneficial effects also on maintenance and waste disposal. For an appreciation of the advantages of multiple components in a single unit, consider the following example. Assume that a 600 MWe "plant" is requested by a customer; this translates into roughly 1800 MWt or four NSSS 1 modules of 450 MWt each. To convert the heat from each 450 MWt unit, assume that we employ nine steam generators rated at 50 MWt each. Note that by using a pool reactor, versus the conventional loop arrangement of today's reactors, there is really no separate piping, pumps, valves, etc. for each steam generator. Now we line up 18 steam generators along the pool wall rather than the required nine. This provides 100% redundancy, that is, throughout the life of the plant we can replace failed generators (which experience shows has a good probability of happening) with a simple on-line "plug out/plug in" procedure rather than having long out-of-service repairs. It should also be remembered that with a 15-year fuel life there are no outages for fuel refueling which can be used for repairs and maintenance; thus minimization of maintenance is economically imperative. An additional advantage of this arrangement is that extra steam generators can be activated for handling peak power production. From the point of view of economy of construction, in the above example a 600 MWe plant will require 72 steam generators, or 144 for the equivalent of a four-loop 1200 MWe plant. It is obvious that a mini-mass production is indeed feasible, especially if more than one unit is deployed (current schemes call for about ten units to be deployed concurrently worldwide). Along the same logic, the NSSS 1 will have a lifetime equal to that of its fuel loading, i.e., around 15 years. When the fuel life is exhausted, the entire reactor is replaced without ever taking the fuel out. In terms of economics, this is the opposite of current practice; instead of having a single large plant where lifetime is stretched as long as possible, we have a fleet of smaller plants replaced relatively frequently and whose components are built in large numbers. From the point of view of proliferation resistance and environmental acceptance there is no spent fuel to deal with. The entire reactor, after draining the water, is removed and buried in a permanent repository. The reduction in waste disposal of spent fuel is dramatic because of the five-fold increase in fuel lifetime and the elimination of low level waste generated during normal refueling operations. It is envisioned that the NSSS 1 will also be delivered as an assembled unit to the host country, thus precluding access to the fuel at any time. Economically, the target for this system is to produce power at a total cost less than 2C/kWhr. It is expected to achieve this because of the following: 1. Elimination of entire reactor systems such as emergency core cooling (because of passive safety against loss of coolant and loss of flow), refueling (because of long core life) and coolant poison control (because of the use of burnable poisons) PA1 2. Simplification and compactness of reactor and primary system, because of the use of the pool configuration PA1 3. Reduction in fuel cycle cost, because of the 15-year single charge PA1 4. Minimization of maintenance, though the use of modularity and redundancy PA1 5. Increase in capacity factor, reduction in O/M costs and reduced need for supporting infrastructure, because of the elimination of refueling outage and minimized maintenance PA1 6. Use of "mini-mass" factory production and assembly of components PA1 7. No spent fuel separation, storage and disposal. PA1 8. No site decommissioning costs, because the entire reactor is taken back. In summary, the NSSS of the invention will be safer, cheaper and environmentally friendlier than the presently available or proposed systems. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given tile full breadth of the claims appended and any and all equivalents thereof. |
summary | ||
042008034 | summary | This invention concerns a multiple collimator apparatus for determining the distribution of radiation from a radioactive source. Such devices generally include a shield block or plate having spaced bores through it in which measuring probes may be inserted for measuring the radiation collimated by the respective bores. Such multiple collimator apparatus are used in nuclear medical diagnosis when radioactive marking substances have been incorporated in the organs or other body parts to be explored and the radiation for this purpose is generally gamma-ray radiation. It is intended that the radioactive radiation registered in each of the detectors or probes should be related to the respective locations at which the detectors are aimed by the respective bores through the shield plate or block through which they "look." Collimators of various kinds of construction are known. Thus there are collimators for individual probes or detectors (cf. G. J. Hine "Instrumentation in Nuclear Medicine," Academic Press, New York/London, 1967, vol. I, pages 429 to 460) providing a generally cylindrical or sometimes conical bore through a lead shield. The lead shield prevents radioactive rays from regions outside the scope of view of the bore from reaching the measuring detector and thereby affecting the measurement. This function is also served when two or more bores each with a different field of view and each serving a separate detector are provided through the same lead shield. Multiple collimators are known in which a multiplicity of similar bores are arranged at regular spacing in a lead plate. Such collimators, which are called multiple collimators, make possible the coverage of a large region of an object to be investigated by a search raster and thereby to provide an image of the entire object field with gamma-ray cameras (cf. H. O. Anger, "Scintillation camera with multi-channel collimators," J. Nucl. Med., 1964, page 515). Combined collimators are also known in which several individual collimators are combined into a collimator block (cf. H. W. Pabst, G. Hor, H.A.E. Schmidt; Nuclear Medicine "Fortschritte der Nuclear-Medizin in klinischer and technologischer Sicht," S. K. Schattauer-Verlag, Stuttgart/New York, 1975, pages 74 to 77). In a particular case it may be sought to reduce the extent of space occupied by such a combination of collimators. In such a way it has been successful to measure object fields and also functional studies of individual organs, for example of the heart, where separate time-activity measurements can be made for different regions of the organ. Such combined collimators, however, just as the other kinds of collimators mentioned above, do not in all cases meet the requirements of medical diagnosis, for a fixed combination of several collimators in one block has the disadvantage that it is not possible to fit the various individual characteristics of organs under investigation. This is already evident because the organs, as for example the heart, are different for each patient with regard to size, shape, position and configuration to an extent that cannot be neglected. Multiple collimators available up to now have the disadvantage that they are not usable for masking out all but a discrete measuring field from a larger field or are usable in that way only with additional provisions which must be depended on in order to assure a shielding effect with respect to everything outside the selected field of view. Furthermore, the cost of the required precautions does not stand in any acceptable ratio to the experimental results desired. If individual collimators are used that are movable with respect to each other in order to cover a discrete object field, the disadvantage arises that the necessary shielding for each individual device tends to interfere with the other devices, as a result of which the detectors cannot be collected together so closely as would be desirable for the measurement. It is an object of the present invention, therefore, to provide a collimator device for the simultaneous use of several detector probes that permit the setting of the detector probes, appropriately for the organ to be investigated, to conditions closely fitting the requirements of diagnosis work in nuclear medicine, while at the same time providing adequate shielding against disturbing rays. SUMMARY OF THE INVENTION Briefly, detectors and collimator tubes through which they "look" are mounted so as to pivot either about an axis or a point in their mounting within a shield plate or block, generally referred to as a shield plate. One of the probes can "look" in a fixed direction without loss of flexibility of the arrangement, since if all the others can be swung, the relation, among the probes, of their various directions of sensitivity is fully adjustable. The pivoted mounting in the shield plate is so organized that a particular region of a body organ under examination can be brought within the optical scope of all of the measuring probes or detectors under a wide range of variable conditions (for example, spacing from the shield plate) and nevertheless in each position of the measuring probes there is sufficient shielding against disturbing radiation from directions not relevant to the measurement. On the basis of the foregoing principle, bores are made in the shield plate having a bearing shell-shaped widened portion for providing an articulated joint with a collimator tube and the remaining portion of the bore as it leads away from the widened portion is divergent in at least one transverse direction. A collimator tube into which a detector probe can be fitted is provided in each bore of the kind just described having a bearing portion fitting the shape of the bearing shell-shaped widened portion of the bore, so that the remainder of the collimator tube can swing through an angle limited by the divergent portion of the bore. If the articulation is a ball joint, the collimator tube can swing through a solid angle and the divergent portion of the bore is essentially conical, but it is also practical to provide a roller joint articulation, in which case the divergence of the diverging part of the bore need diverge only in one plane and the collimator tubes swing through a plane angle. In any case the shielding, provided by the part of the shield plate not hollowed out for the purposes described and by the bearing-forming portions of the collimator tubes, is made sufficiently great so that no disturbance rays can get into the collimator tubes. The pivoted arrangement of the collimator tubes in the shield plate make it possible to aim the respective detectors at the same target portion of the object to be examined. If desired, the direction of observation of each of the individual detectors in the object field can be made visible by sighting lights. In spite of the movability of the collimator tubes about their pivots, a fully effective shielding is provided against disturbing rays in every position of the collimator tubes. In cases in which it is important to locate the detectors of a multiple collimator according to the invention as close to each other as possible, the diameter of the articulated joints of the shield plate and collimator tubes must be kept as small as possible. In such cases it is practical to put the articulated joints on the side of the multiple collimator apparatus that faces the object to be observed and thereby to assure that the shield plate together with the bearings provides sufficient mass for screening off disturbing rays. In particular cases it can also be practical to constitute the collimator tubes in such a way that they project beyond the shield plate towards the object. The multiple collimator of the present invention is provided by fitting a body rotatably mounted for rotation about its axis of symmetry into a bore of corresponding shape with the rotatable body having a cavity for a collimator tube mounted so as to be pivoted or rotatable therein, the collimator tube and the cavity for it fitting each other in shape. The cavity and the collimator tube fitted into it can be made in different ways according to the particular application in which it is desired to use the apparatus. One of the possible variations of the last-mentioned kind of construction of the multiple collimator according to the invention is the provision of a prismatically shaped cavity in the rotatable body, into which a collimator tube having a rectangular stem is pivoted so that it can swing about an axis running perpendicular to the axis of rotation of the rotatable body. Another variation consists in providing, in the rotatable body, a conical cavity with an axis of symmetry running eccentrically in the rotatable body, while the bore through the collimator tube rotatably mounted in the cavity is arranged eccentrically to the axis of rotation of the collimator tube. In both cases essentially four degrees of freedom of rotation are provided for the adjustment of the movable collimator tube through two simple bearings, so that the setting of the movable collimators can be read by use of two scales. It is therefore appropriate to provide scale graduations on the shield plate and/or on the body rotatable in the bore for determining the angular position of the rotatable body and also scale graduations on the body rotatable in the bore and/or on the collimator tube for determining the position of the collimator tube. The various embodiments of the multiple collimator with collimators adjustable in their respective positions have the advantage that--apart from the reproducibility of the adjustment--statistical data can readily be obtained from which a normal setting, the typical deviations and an optimization of the adjustment procedure can be derived. Thus, for example, the two breast nipples of the patient can for example serve as reference points. With approximately point-shaped radiation regions, the space coordinates of the latter can also be determined. The multiple collimator according to the invention has the great advantage that the detectors can be fitted in an optimum fashion taking account of the object to be measured. A further advantage is that the fields of view of the collimator tubes can be compressed substantially closer together and in the case of combinations of individual collimators, without impairing the effectiveness of shielding. The apparatus, moreover, is particularly well suited for functional analysis of individual organs or segments of organs in using a procedure making use of radioactive marker materials. The invention is further described by way of example with reference to the annexed drawings, in which: FIG. 1 is a top view of a first embodiment of the multiple collimator by which basic principles are explained; FIG. 2 is a section through the multiple collimator apparatus of FIG. 1 along the line A-B; FIG. 3 is a section through the multiple collimator apparatus of FIG. 1 along the line C-D; FIG. 4 is a top view of an embodiment of the multiple collimator according to the invention; FIG. 5 is a section through the multiple collimator apparatus of FIG. 4 along the line A-B; FIG. 6 is a partial top view of a second embodiment of the multiple collimator apparatus according to the invention; and FIG. 7 is a section through the portion of the multiple collimator apparatus shown in FIG. 6, through the line A-B of FIG. 6. |
abstract | Marking of the cuts which have to be made, cutting of the section at two ends, removal of the section which has to be replaced, bevelling of the joint ends of the parts remaining after the section has been cut out from the pipe, adjustment of a new or replacement section for length and bevelling of its joining ends and positioning and narrow bevel welding of the ends joining the replacement section to the ends of the remaining parts of the pipe are performed outside the pipe. Within the pipe operations of machining and inspecting an internal part of the joining ends welded together are performed by remote control in a programmed way by introducing and positioning means for working within the pipe from a component of the primary circuit. The procedure is in particular used to effect the replacement of a section of a cold leg of the primary circuit using means for carrying out work comprising a robot arm secured to a supporting chassis borne by a carriage which moves the means for carrying out work within the cold leg inserted into the cold leg through the volute of the primary pump of the nuclear reactor. |
|
summary | ||
048760609 | summary | BACKGROUND OF THE INVENTION The present invention relates to a control blade for use in a nuclear reactor which is adapted to be inserted into and extracted from a nuclear reactor core for the purpose of controlling the power of the nuclear reactor. More particularly, the invention is concerned with a long-life flux-trap type control blade suitable for use in a boiling water reactor (BWR). In general, a control blade for use in a boiling water reactor has a central tie rod and a plurality of wings formed by U-shaped sheath plates attached to the tie rod, each wing containing a multiplicity of neutron absorber rods. Each neutron absorber rod is composed of a clad tube made of a steel such as stainless steel and grain of boron carbide (B.sub.4 C) charged in the clad tube. In order to prevent the grain of boron carbides from moving freely within the clad tube, partition balls are placed at a predetermined interval within the clad tube. The boron carbides in the form of grain charged in the neutron absorber rod progressively decreases its neutron absorption power (capacity) due to absorption of neutrons, and generates He gas as a result of reaction between boron-10 (.sup.10 B) and neutrons resulting in a rise of the pressure within the clad tube. The lifetime of the control blade determined by the neutron absorption power is referred to as "nuclear lifetime", while the lifetime determined by the internal gas pressure of the clad tube is referred to as "mechanical lifetime". The control blade, which is adapted to be inserted into and extracted from the nuclear reactor core, is not uniformly exposed to neutrons. For instance, the rate of neutron exposure rate is high at the side edges and upper end of each wing. This means that these portions of the control blade absorb greater amounts of neutron than other portions of the control blade and, therefore, the nuclear lifetime is reached earlier in these portions than in other portions of the control blade. In consequence, the control blade has to be disposed of as a radioactive waste, even though sufficient lifetime is left in other portions thereof. In order to obviate this problem, the present inventors have developed an improved control blade in which long-life neutron absorbers are disposed in the vicinity of side edges of wings where the degree of neutron exposure is high, as disclosed in Japanese Patent Laid-Open No. 74697/1978. This improved control blade, however, is still unsatisfactory from the view point of prolongation of lifetime of control blades, because it exhibits a lifetime which is only twice as long as that of ordinary control blades containing B.sub.4 C. In order to cope with the demand for prolongation of lifetime of control blades, the present inventors have developed a long-life control blade capable of operating much longer than the above-mentioned improved control blade. This long-life control blade has, as disclosed in Japanese Patent Laid-Open No. 55887/1983, solid neutron absorption plates made of a long-life neutron absorber and disposed in each wing thereof. The neutron absorption plate has apertures or recesses whose sizes and distribution are so determined that the amount of material removed by the presence of such apertures or recesses is comparatively small in the portion where the axial distribution of the shut down margin is small and is comparatively large in the portion where the axial distribution of the shut down margin is large. This long-life control blade, however, suffers from the following disadvantage, due to the use of hafnium (Hf) sheet as the neutron absorber. Namely, hafnium is expensive and has a large specific gravity (13.3 g/cm.sup.3) so that the cost and the weight of the control blade are increased undesirably. The increased weight of the control blade in turn requires a design of a control rod drive mechanism which can safely operate such heavy control blades because conventional control rod drive mechanism cannot withstand such heavy weight of the control blades. The inventors, however, have confirmed that there still is a margin for the removal of material in the hafnium sheet which is used as long-life neutron absorber for the purpose of reducing the weight of the hafnium sheet, and that ordinary control blade drives are still usable provided that the weight of the control blade is reduced by the removal of the material. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a long-life control blade for use in a nuclear reactor such as BWR in which the weight of the long-life neutron absorber and, hence, the overall weight of the control blade are effectively reduced so as to enable conventional control rod drive mechanism to safely drive such a long-life control blade, thereby overcoming the above-described problems of the prior art. Another object of the present invention is to provide a long-life control blade having almost the same size, shape and total weight as those of ordinary B.sub.4 C control blades and, hence, usable in existing boiling water reactors. Still another object of the present invention is to provide a long-life control blade for nuclear reactors, suitable for use in operation of the reactor at a high burn-up and in long-term operation of the reactor. A further object of the present invention is to provide a long-life control blade for nuclear reactors, which is improved in such a way as to effectively avoid damaging due to electrochemical corrosion. A still further object of the present invention is to provide a hybrid-type long-life control blade for nuclear reactors, which is improved in such a way as to avoid damaging due to electrochemical corrosion and to increase mechanical strength so as to exhibit greater resistance to deformation by any external force. A still further object of the present invention is to provide a long-life control blade for nuclear reactors, which is improved such as to exhibit a greater resistance to buckling while reducing the weight of sheaths, thus reducing the total weight of the control blade. According to the present invention, these and other objects can be achieved in one aspect by providing a control blade for nuclear reactors comprising: an upper structure; a lower structure; a central tie rod having radial projections and interconnecting the upper and lower structures together; and wings composed of sheath plates each having a substantially U-shaped cross-section and secured to the end of each projection of the central tie rod, and long-life neutron absorber charged in each of the sheath plate; wherein the neutron absorber in each sheath is divided into a plurality of neutron absorber elements (sections) along the axis of the central tie rod, each neutron absorber element (section) being composed of neutron absorber plates spaced from and opposing each other such that a water gap for guiding the flow of a moderator is defined between these neutron absorber plates. In this control blade, the reactivity worth is increased by virtue of the water gap for guiding the flow of a moderator (coolant) between the opposing neutron absorber plates. The provision of the water gap also enables the thickness of the neutron absorber plates to be reduced in accordance with the amount of the neutron exposure. For these reasons, the control blade can have almost the same size, shape and weight as those of ordinary B.sub.4 C type control blades, even though a heavy long-life neutron absorber such as hafnium sheets is used. Therefore, the control blade can be used in existing nuclear reactors without requiring modification of the control rod drive mechanism, and can operate for a period which is much longer than those offered by known control blades. In another aspect, the present invention provides, in order to avoid any electrochemical corrosion due to contact between different metals, a control blade for nuclear reactors comprising: an upper structure; a lower structure; a central tie rod having radial projections and interconnecting the upper and lower structures together; and wings composed of sheath plates each having a substantially U-shaped cross-section and secured to the end of each projection of the central tie rod, and long-life neutron absorber charged in each of the sheath plate; wherein the neutron absorber in each wing is composed of a plurality of neutron absorber plates such as of hafnium which are spaced from each other in the thicknesswise direction of the wing by means of supporting spacers, such that a water gap for guiding the flow of a moderator is defined between opposing neutron absorber plates, and wherein a water passage is formed between the external surface of each neutron absorber plate and the adjacent inner surface of the sheath. In still another aspect, the present invention provides, in order to prevent buckling through enhancement of strength to lateral bending force, a control blade for nuclear reactors comprising: an upper structure; a lower structure; a central tie rod having radial projections and interconnecting the upper and lower structures together; and wings composed of sheath plates each having a substantially U-shaped cross-section and secured to the end of each projection of the central tie rod, and long-life neutron absorber charged in each of the sheath plate; wherein the neutron absorber in each wing is divided into a plurality of neutron absorber elements along the axis of the tie rod, each the element being composed of a plurality of neutron absorber plates spaced from and opposing each other; and wherein a plurality of spacers are disposed between the opposing neutron absorber plates such that a linear flow passage for a moderator is defined so as to extend in the axial direction of the tie rod, the spacers being arranged at a substantially constant interval along the axis of the tie rod but the interval is slightly reduced in the regions between adjacent neutron absorber plates. These and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments when the same is read in conjunction with the accompanying drawings. |
description | The invention relates to testing of a device under test. In particular, the invention relates to diagnostic test systems and tests to be used therewith. Testing of a device is normally an integral part of the design, manufacture and maintenance of the device. Testing is routinely employed during the design of a new device to establish reliability and an operational capability of the device. In manufacture, testing establishes and/or quantifies operability of the device as well as facilitates yield improvements through failure diagnosis. Once the device is deployed, testing helps to maintain the device by detecting potential failures and diagnosing the cause or causes of failures of the device or its components. In most cases, testing comprises performing a set or sequence of tests on the device under test (DUT). Such a set of tests or test suite typically employs one or more pieces of test equipment. Together, the test equipment and the test suite are referred to as a testing system. In some cases the testing system comprises a complex, integrated and highly automated system. In other cases, the testing system is only loosely integrated and many, if not all, of the tests are performed manually. In yet other cases, a testing subsystem is built into the DUT and functions as a built-in self-test for the DUT. As used herein, the term ‘testing system’ includes all such testing systems including a built-in testing subsystem of the DUT. However, while testing systems vary widely according to the DUT and the application of the testing system, at some basic level all testing systems generally attempt to determine whether a given DUT is GOOD or BAD. A GOOD DUT is one that passes the tests administered by the testing system while a BAD DUT is one that fails one or more of the tests. Since DUTs generally are made up of one or more components, a secondary goal of many testing systems is to diagnose which component or components of the DUT is responsible the DUT being BAD. Thus, many testing systems include some form of a diagnostic system that performs a component or subsystem level diagnosis of failures encountered during testing. A DUT with a built-in test subsystem also may feature a built-in self-diagnostic capability. For example, a given DUT typically includes a variety of components. Such components include, but are not limited to, integrated circuits, electrical components, battery subsystems, mechanical components, electrical buses, wiring components, and wiring harnesses. Any one or more of these components may fail and cause the failure of the DUT. The role of the diagnostic system portion of the testing system is to attempt to pinpoint the component or components that most likely caused the encountered failure or failure mode of the DUT. Typically, diagnostic systems of testing systems either employ a fault tree approach to produce a diagnosis or attempt to extract a diagnosis from a combination of results of functional tests used to verify DUT functionality. In simple terms, a fault tree is a flow chart of tests to perform and related diagnoses. Tests are performed at each of a series of decision blocks of the flow chart. At each decision block, results of the test performed determine which of a plurality of branches leading out of the decision block is to be taken. Branches either lead to additional decision blocks or to stop blocks. Stop blocks give a diagnosis and represent an end point of the fault tree. Typically the stop blocks are annotated with the diagnosis (e.g., a name of a failed component) or with “no diagnosis is possible” indication. Thus, when a stop block is reached, the annotation gives the diagnosis. In general, only enough tests necessary to reach a stop block giving a diagnosis are performed when a fault tree is employed. Typically, fault trees are designed to mimic a decision-making process followed by a skilled test technician. On the other hand, diagnostic systems based on the results of functional tests typically require that all tests of a predetermined set or test suite be performed before an attempt at a diagnosis can be made. Moreover, many such diagnostic systems employ a model or models of the DUT. As used herein, a model-based diagnostic system is defined as a diagnostic system that renders conclusions about the state or failure mode of the DUT using actual DUT responses to applied functional tests that are compared to expected responses to these tests produced by a model of the DUT. Often, the model is a computer-generated representation of the DUT that includes specific details of interactions between components of the DUT. Selecting a suite of tests to perform is an important step in using model-based diagnostic testing systems. Performing too few tests or performing the wrong tests can lead to an inability to arrive at a diagnosis or even an incorrect diagnosis. In other words, a poorly designed test suite may not provide a particularly effective or reliable diagnosis of a DUT failure. In particular, for a given test suite, simply adding tests may not improve the diagnostic efficacy of the test system. Thus, often the problem is how to choose additional tests to add to the suite to increase diagnostic efficacy. On the other hand, performing too many tests is potentially costly in terms of time and test equipment needed to arrive at a diagnosis. Moreover, some of the tests may be redundant and add little if anything to the diagnostic accuracy of the test system. In particular, many tests performed on a DUT can take an appreciable amount of time to perform and/or require the use of expensive equipment. If performing such tests does not increase the diagnostic efficacy of the testing system, the tests might just as well be eliminated. In such situations, the problem is one of determining which tests of a test suite may be eliminated without significantly reducing diagnostic efficacy. Accordingly, it would be advantageous to be able to examine a test suite to determine what tests might be added to improve the diagnostic efficacy of the testing system. Likewise, it would be useful to be able to determine which tests in a test suite are redundant or have little added diagnostic value and, therefore, can be safely eliminated from the suite. Such abilities would address a longstanding need in the area of model-based diagnostic testing systems. According to the present invention, a revision of a test suite of a diagnostic testing system is determined by evaluating diagnostic efficacy and accuracy of the test suite. In particular, the present invention suggests tests to add to the test suite that may improve diagnostic efficacy and accuracy of the testing system. Adding the suggested test or tests improves the ability of the testing system to accurately diagnosis a failure detected in a device under test (DUT). The present invention alternatively or further establishes a relative diagnostic value of tests in a test suite of the testing system. The diagnostic value of the tests identifies tests that may be deleted from the test suite with minimal impact on an overall diagnostic efficacy of the test suite. In particular, tests determined to have a low relative efficacy value may be eliminated without adversely affecting overall diagnostic efficacy to reduce a cost, a complexity, and/or a redundancy of the tests performed by the testing system according to the present invention. The present invention is applicable to virtually any model-based diagnostic testing system, but is particularly well suited for use in conjunction with automated testing systems, especially those used to test electronic systems. In an aspect of the present invention, a method of suggesting a test to add to a test suite of a diagnostic testing system is provided. In particular, the method suggests a potential test to add to the test suite and provides an indication of a relative increase in an overall diagnostic efficacy of the test suite associated with adding such a test to the test suite. In some embodiments, the suggested test is defined by a coverage that the test provides over one or more components in the DUT. The relative increase in overall diagnostic efficacy is provided as a ‘score’ for each suggested test. In some embodiments, a list of suggested tests is generated that includes an assigned score for each suggested test in the list, thereby enabling a choice of which test or tests to add based on the score and other factors, such as constraints imposed by the DUT and/or available test equipment. The method of suggesting a test to add comprises creating a simulation database for the DUT and the test suite. The method of suggesting a test to add further comprises determining from the simulation database a probability of correct and incorrect diagnoses for the test suite. The probabilities of correct and incorrect diagnoses are preferably determined for as many combinations of correct and incorrect diagnoses as are possible for the DUT. The method of suggesting a test to add further comprises suggesting a test to add from the determined probabilities. Suggesting comprises creating a list of suggested tests to be added to the test suite. In some embodiments, each suggested test on the list is provided in terms of what component(s) of the DUT it covers. In another aspect of the present invention, a method of identifying a test to delete from a test suite is provided. Advantageously, the method determines diagnostic efficacies of tests of the test suite. In particular, the method of identifying generates a list of tests, each test on the list being associated with a relative diagnostic efficacy or diagnostic value of the test. The list may be used to identify the test that may be safely eliminated as having low diagnostic efficacy. The method of identifying a test to delete comprises creating a simulation database for the DUT and the test suite. The method further comprises determining a probability of a correct diagnosis using the test suite. The method further comprises determining a probability of a correct diagnosis for a modified test suite. The modified test suite is the test suite with a selected test deleted from the suite. Determining a probability of correct diagnosis for the modified test suite is preferably repeated with a different one of the tests in the test suite being the selected test that is deleted. The method further comprises computing an efficacy value for each of the tests in the test suite. The method further comprises identifying a test to delete from the determined probabilities and computed efficacy values. Identifying comprises generating a list of the tests and associated efficacy values. Tests with low efficacy values may be deleted from the suite without significantly reducing the overall diagnostic efficacy of the test suite. In yet another aspect of the present invention, a system that determines a diagnostic efficacy of a test suite of a testing system is provided. The system determines an efficacy of tests in a test suite and either or both suggests tests to add and identifies tests to delete from the test suite. The system comprises a processor, a memory and a computer program stored in the memory. The processor accesses the computer program from memory and executes the computer program. The computer program comprises instructions that when executed determine the efficacy of tests in a test suite. The instructions may further suggest tests to add and/or identify a test to delete from the test suite. In a preferred embodiment, the instructions implement the method of the present invention. The system of the present invention may be a stand-alone system or may be incorporated into a testing system for testing a DUT. A key advantage of the present invention is that it provides quantitative information upon which to base decisions about which test(s) to add or remove from a test suite. In particular, the present invention effectively ‘discovers’ problems associated with diagnostic accuracy of a test suite and automatically suggests tests to add to the test suite to address those problems. Moreover, the present invention associates a relative amount of improvement in diagnostic accuracy with suggested tests facilitating an evaluation of the advantages of adding such tests. Furthermore, the present invention quantifies the efficacy of tests in the test suite, thereby enabling the identification of test(s) that can be removed from a test suite while minimally reducing the effectiveness of the suite. Removing identified tests may result in reducing test time while minimally impacting the effectiveness of the test suite. Certain embodiments of the present invention have other advantages in addition to and in lieu of the advantages described hereinabove. These and other features and advantages of the invention are detailed below with reference to the following drawings. The present invention determines a revision of a test suite of a testing system used for diagnostic testing of a device under test (DUT) using an evaluation of diagnostic efficacy of the test suite and constituent tests thereof. In particular, the present invention can suggest a test or tests to add to the test suite to improve diagnostic efficacy of the test suite. Furthermore, the present invention can identify a test or tests of the test suite that have low diagnostic efficacy and therefore may be deleted from a test suite with minimal reduction in overall diagnostic efficacy. The present invention employs a measure of diagnostic effectiveness or efficacy of the test suite and of tests that make up the test suite. The measure of efficacy according to the present invention enables the identification of characteristics of a test that, when added to the test suite, improves the overall accuracy of diagnostic testing performed by the testing system. Similarly, the measure of efficacy facilitates identifying a test of the test suite that has low relative diagnostic value compared to the test suite as a whole. A test with low diagnostic value often may be eliminated or deleted from the test suite without significantly reducing the diagnostic efficacy of the test suite. A DUT, as used herein, refers to any of a variety of devices, systems or subsystems, including mechanical, electrical, and chemical systems as well as combinations thereof. Examples of such DUTs include, but are not limited to, circuit boards, entire systems having a plurality of circuit boards, automobiles, satellite receiving systems, chemical manufacturing plants, and even test equipment. In general, a test of the DUT comprises applying a stimulus to one or more inputs of the DUT and measuring a response at one or more outputs of the DUT. A group or set of one or more tests applied to the DUT, and in part, used to diagnose a failure of the DUT, is referred to herein as a ‘test suite’. To facilitate discussion hereinbelow, a DUT is assumed to be made up of one or more (n) separate, well-defined components, where n is an integer greater than or equal to one. For example, such separate, well-defined components in an electrical system include, but are not limited to, integrated circuits, multichip modules, discrete electrical devices, wiring buses, wiring harnesses, power supplies, and circuit boards. A discrete electrical device includes, but is not limited to, a resistor, capacitor, inductor, diode and transistor. Thus, the DUT has n components where n is equal to or greater than one. Each of the n components of the DUT has two states or operational conditions with respect to testing performed on the DUT. The two states are referred to herein as GOOD and BAD. A component that is in the GOOD state is operating properly while a component that is in the BAD state is not operating properly. In other words, each of the components either is operating properly (i.e., GOOD) or is not operating properly (i.e., BAD) according to the component's specifications. Moreover, it is assumed for the purposes of discussion that the component state does not change during testing by the testing system. There are m tests in the test suite where m is an integer having a value of zero or more. Each of the m tests acts upon or ‘covers’ a subset of one or more of the n components of the DUT. The subset of components covered by a particular test may overlap with another subset covered by others of the m tests in the test suite. Thus for m≧1, if the DUT fails a particular test, it is assumed that at least one of the components of the DUT covered by that particular test is BAD. Furthermore, a ‘test coverage’ is the subset of components acted upon or covered by a particular test of a test suite. It is also assumed herein that each of the m tests either passes or fails when applied to the DUT. Therefore, a given test generates one of only two results, namely PASS or P if the test passes and FAIL or F if the test fails. Restricting the test results of a test to only two states, PASS and FAIL, is not limiting since tests that inherently generate a finite number of states greater than two can be treated as a finite number of separate tests each having only two states. The list of tests in a test suite along with the state of the test after it is applied to the DUT is referred to as the ‘test results’. Moreover, the tests of the test suite are predefined or given and are typically designed to test DUT functionality. The DUT and its interaction with the test suite are modeled by a probability of failure of each of the n components, the test coverages of the m tests on the n components, and joint coverages of the m tests on the n components. A joint coverage is an intersection of the coverages of a pair of tests. The probability of failure of each component may be based on a priori information or derived from actual historical data for the component. A model is employed to generate a statistical simulation of the DUT with respect to the tests of the test suite in the form of a ‘prediction table’ or ‘simulation database’. A Monte Carlo simulation is a type of statistical simulation known in the art. In a preferred embodiment, the simulation database contains a set of entries each having a field for a frequency-of-occurrence value, a field for a test result pattern, and a field for a component state pattern. Such a model and a Monte Carlo simulation database computed from such a model is described in Kanevsky and Barford, U.S. Pat. No. 6,167,352, incorporated herein by reference. In an alternate embodiment, the simulation database is made up of actual experimental data reflecting historical results of prior tests and component failures. In this embodiment, the model is a count of actual DUTs and the relationships between test failures and actual device failures. In yet another embodiment, the simulation database may be based on a failure mode-effects analysis. Hereinafter, the term ‘random number’ is meant to include the output of a pseudo-random number generator as well as numbers chosen through some stochastic process. In an aspect of the invention, a method 100 of suggesting a test to add to a test suite of a diagnostic testing system is provided. The suggested test, if added to the test suite, improves overall diagnostic efficacy of the test suite. FIG. 1 illustrates a flow chart of the method 100 of suggesting a test to add to the test suite according to a preferred embodiment. The method 100 comprises creating 110 a simulation database for the DUT and the test suite. A computer model of the DUT, actual failure data for the DUT, or a combination thereof are employed to create 110 the simulation database. The simulation database, whether based on the computer model, actual failure data, or a combination thereof, preferably includes a field for a component state pattern, a field for a test result pattern, and a field representing a frequency-of-occurrence or number-of-occurrences value for each combination of component state pattern and test result pattern. A preferred embodiment of the creation 110 of the simulation database is described in Kanevsky et al. In the preferred embodiment, a model-based simulation is performed to create 110 the simulation database. The simulation repetitively generates a component state pattern and determines a test result pattern based on the component state pattern. Each component pattern includes a state for each component (e.g., GOOD or BAD) in the DUT. The state pattern is generated randomly such that whether a given component is GOOD or BAD is based on a random number. Preferably, the state pattern is also based on a probability of failure for each component in the DUT. The state pattern is then applied to the model to determine which test passes or fails based on the state pattern. Each occurrence of a unique pair of component state pattern and test result pattern is counted during the simulation to produce the number-of-occurrences value for the pair. Thus, the database complied from the simulation ultimately comprises a large number of rows, each row having a component pattern, a test pattern and a number-of-occurrences value. The method 100 of suggesting a test to add further comprises determining 120 from the simulation database a probability of a correct diagnosis and a probability of an incorrect diagnosis. Equivalently, a number-of-occurrences for each of the diagnoses, correct and incorrect, may be determined 120′ instead of a probability. The diagnoses are produced using the test patterns of the simulation database. The accuracy of the diagnoses, whether a given diagnosis is correct or incorrect, is determined by comparing the diagnosis produced from the test pattern to an associated component pattern. For example, a correct diagnosis labels a b-th component as BAD when the b-th component is actually BAD according to the component pattern. On the other hand, an example of an incorrect diagnosis labels a d-th component as BAD when, in fact, the b-th component is BAD according to the component pattern. The probability or number-of-occurrences of correct and incorrect diagnoses are preferably determined 120, 120′ for as a many combinations of correct and incorrect diagnoses as are represented in the simulation database. Essentially, determining 120, 120′ comprises counting a number-of-occurrences of each of the correct and incorrect diagnoses included in the simulation database. A probability of a given diagnosis may be computed from the count by dividing the number-of-occurrences of the diagnosis by a total number-of-occurrences of all diagnoses included in the determination 120, 120′. In some embodiments, only the probability of incorrect diagnoses is determined 120, 120′. The method 100 of suggesting a test to add further comprises creating 130 a list of suggested tests. In a preferred embodiment, the list of suggested tests is provided in terms of characteristics of each of the suggested tests. Preferably, the test characteristics include a coverage that the test has on one or more components of the DUT. The list is created 130 by choosing from the diagnoses of the simulation database those incorrect diagnoses having the highest probability or equivalently the highest number-of-occurrences. The list may include one or more suggested tests. Thus, if five suggested tests are desired, the list is created 130 by choosing five incorrect diagnoses in the simulation database having the five highest probabilities. The list is created 130 by further using information from the chosen incorrect diagnoses to determine a test coverage for each suggested test. For example, information regarding an incorrectly diagnosed BAD component versus an actual BAD component may be used to determine a coverage for a suggested test. In general, a given suggested test coverage preferably has little or no coverage on one component and high coverage on another component. Thus, in a preferred embodiment, the suggested test may be defined by a pair of components and a respective coverage level of the test on these components (e.g., high or low). The suggested test is preferably provided in terms of coverages since the method advantageously ‘discovers’ that in some cases, the diagnostic test system employing the test suite has difficulty distinguishing between certain pairs of components. In some other cases, the difficultly in distinguishing may be due to a lack of sufficient coverage of a particular component and not a conflict in the coverages between component pairs. In such cases, the test suggested by the present invention may be defined by a single component needing additional test coverage. A second component is not considered and thus, if pairs of components are reported, a ‘don't care’ may be used instead of a second component. Thus according to the present invention, the suggested test preferably defines one component for which the suggested test provides high coverage and either another component for which the suggested test should have low coverage or a ‘don't care’ when another component is not considered. The extension of the method 100 of the present invention to additionally handle suggesting tests involving sets of more than one component is straightforward for one of ordinary skill in the art given the discussion herein. All such extensions are within the scope of the present invention. In the preferred embodiment, a score is given for each suggested test that shows a relative amount of improvement in diagnostic accuracy that is obtained by adding a suggested test. The score is an approximation to the probability of the ‘high coverage’ component being the true BAD component when the ‘low coverage’ component is given as the diagnosis. In addition, the preferred embodiment of the method 100 may also output an estimate of overall diagnostic accuracy of the test suite in the form of a probability of a correct diagnosis to assist in determining an improvement that may result from adding one or more of the suggested tests. It should be noted that a best suggested test to add to the test suite may be impossible or at least difficult to perform on a given DUT. For example, there may be constraints on the DUT or test equipment that make it impossible to conduct a specific suggested test with the recommended ‘high coverage’ and ‘low coverage’ characteristics with respect to the DUT components. Therefore, the method 100 of the present invention preferably produces a list containing more than one suggested test as an output. The user of the present invention advantageously may choose to add to the test suite one or more of the highest scored tests from the list based on a practicality and cost effectiveness of each suggested test. Moreover, the list of suggested tests produced by the present invention may be represented either in human readable form or in machine-readable form. The human-readable form of the list of suggested tests may take any of several common textual or graphical forms known in the art. The machine-readable form may be used by other computer programs or automated systems. Such other computer programs or automated systems may design a test from the suggested test characteristics and/or implement a designed test, for example. To better understand the method 100 of the present invention, consider an example of an implementation of the preferred embodiment of the method 100 using a matrix representation for storing intermediate results generated by the method 100. The use of matrix notation hereinbelow is intended to facilitate discussion and in no way limits the scope of the present invention. In addition, for the purposes of discussion hereinbelow, it is assumed that a model of the DUT, its components, test coverages, and a priori probabilities of component failure are available. Using the model, a Monte Carlo simulation is performed and a simulation database is created 110. The model incorporates probabilities of failure for each of the components of the DUT. The example simulation database consists of a table with three columns and a large number of rows. A first column of the table contains component pattern bit strings ω(e.g., ω=ω1, ω2, . . . , ωn) that encode which component or components are BAD. Each of the components of the DUT is represented by a unique position i within the component pattern bit string ω as indicated by the subscripts. The component pattern bit string ω of the first column is also referred to as a ‘failed component’ bit string ω or simply a component pattern ω hereinbelow. A ‘1’ in an i-th position of the component pattern bit string ω indicates that an i-th component is BAD while a ‘0’ in the i-th position indicates that the i-th component is GOOD. For example, given a component pattern bit string ω having a value of a second bit ω2 equal to ‘1’, a second component is BAD according to that component pattern. A second column of the table contains test result pattern bit strings Δ encoding which of the tests of the test suite failed or passed. The bit string Δ (e.g., Δ=Δ1, Δ2, . . . , Δm) is also referred to as a ‘failed test’ bit string Δ or simply a ‘test pattern’ Δ herein. Each test in the test suite is represented by a unique position i within the test pattern bit string Δ. A ‘1’ in an i-th position of the test pattern bit string Δ indicates that an i-th test failed while a ‘0’ in the i-th position indicates the i-th test passed. For example, a test pattern bit string Δ having values of a third bit Δ3 and a fifth bit Δ5 equal to ‘1’ indicates that a third test and a fifth test of the test suite failed. A third column v of the table records a number of occurrences of a given combination of component pattern bit string ω and test pattern bit string Δ represented by a given row produced during the course of a simulation. The number of occurrences v is an integer greater than or equal to 0. Thus, if a given component pattern bit string ω and test pattern bit string Δ pair is produced twenty times during the simulation, the corresponding number of occurrences v=20. Each row in the table corresponds to a different, unique pattern of GOOD and BAD components or component pattern bit string ω and an associated of test pattern bit string Δ produced by the Monte Carlo simulation. An example of a portion of such a simulation database is presented in Table 1. TABLE 1Component PatternTest PatternNumber of Occurrences00100000000000000000012010000001000101010101149101001000100100000011351000000011000100101011781000001101010111100013180010000000000001000002400010000000000000000029. . . . . . . . . In addition to generating the above-described simulation database, the example described herein employs a variable E to accumulate a total number of occurrences from which a probability of correct diagnosis is calculated and employs a matrix M having m+1 rows and m columns where m is the number of tests in the example test suite (i.e., number of bits in the test pattern bit string Δ). The matrix M will eventually contain a count of a number of occurrences of each possible diagnosis based on the simulation database. In particular, for d≦m, M(d,b) will contain a number of occurrences in which a d-th component is diagnosed as the BAD component when a b-th component is the actual BAD component. The variable E and all elements of the matrix M are initially set to zero during creating 110. In the example, determining 120 probabilities of correct and incorrect diagnoses begins by producing a copy of the simulation database containing only those rows from the simulation database that have one and only one BAD component. In other words, the copied database comprises only those rows of the original simulation database for which the component pattern bit string ω contains only a single ‘1’, all other bits being ‘0’. The database copy preferably is sorted on the test pattern column. The sorting produces a sorted database in which all rows with a given test pattern bit string Δ are adjacent to one another. The adjacent rows with a given test pattern are called a group or sequence. Each such group or sequence of adjacent rows having identical test pattern bit strings Δ begins at an i-th row. A next sequence in the sorted database begins at a j-th row. Copying and sorting are not essential since other embodiments of the present invention can be realized without theses steps, as one skilled in the art will readily recognize. However, copying and sorting result in a more efficient implementation of the method 100, and in particular, copying and sorting, as described hereinabove, assist in performing later steps in the example. Determining 120 probabilities of correct and incorrect diagnoses continues by examining each of the sequences. For each sequence, in turn, a row is identified having a largest value for the number of occurrences v. A position number of the single BAD component in the component pattern for that row is then referred to as d. Note that copying the database, as described above, has insured that each component pattern in the copied database has one and only one BAD component. Thus, a unique position number may always be assigned to d for each sequence by following the approach outlined hereinabove. Next, if the test pattern bit string Δ of the sequence being examined has no failed tests (i.e., Δk=0∀k=1, . . . , m) perform the following operations for each row r in the sequence of rows i to j−1. First, set a variable b equal to the BAD component position number of row r. Second, set a variable vr equal to the number of occurrences v of the row r. Third, let a current value of M(m+1, b) equal a former value of M(m+1, b) plus vr (i.e., M(m+1, b)=M(m+1, b)+vr). Fourth, let a current value of E equal E plus vr (i.e., E=E+vr). Thus, if considering the seventh row of Table 1, b=4 and vr=29 where m=14, M(15, 4)=M(15, 4)+29 and E=E+29. On the other hand, if considering row r=1 of Table 1, b=2 and vr=12 so that M(15, 3)=M(15, 3)+12 and E=E+12. Otherwise, if the test pattern bit string Δ of the sequence being examined has at least one failed test (i.e., Δk=1 for one or more k=1, . . . , m) perform the following operations for each row r in the sequence of rows i to j−1. First, set a variable b equal to the BAD component position number of row r. Second, set a variable vr equal to the number of occurrences v of the row r. Third, let a current value of M(d, b) equal a former value of M(d, b) plus vr (i.e., M(d, b)=M(d, b)+vr). Fourth, let a current value of E equal E plus vr (i.e., E=E+vr). Thus, if considering the second row of Table 1 where b=2 and vr=149, M(d, 2)=M(d, 2)+149 and E=E+149. On the other hand, if considering row r=6 of Table 1, b=3 and vr=24 so that M(d, 3)=M(d, 3)+24 and E=E+24. The value of d, of course, depends on finding a row in a sequence within the sorted databases (not shown) that has a highest value of number of occurrences vr as previously described. Once each sequence has been examined a probability of producing a correct diagnosis may be calculated. To calculate the probability of correct diagnosis let Pcorr equal a sum of diagonal elements of the matrix M. Then, divide the sum Pcorr by the accumulated total number of occurrences E. In other words, let Pcorr=0, for i=1, . . . , m, perform Pcorr=Pcorr+M(i,i), and then let Pcorr=Pcorr/E. The matrix M thus filled is used to create 130 a list of tests to suggest. In particular, a set of the s largest elements of M, excluding diagonal elements is found. Thus, if s =3 is the number of suggested tests to be included in the list, the M matrix is examined and the three elements M(d,b), d≠b, having the three largest values are found. Preferably, the s elements, once found, are ordered and processed in descending value of M(d,b). For each of the s elements M(d,b) perform the following. First, if d≦m, set a ‘Low Coverage’ field of a suggested test to component d, otherwise (i.e., when d=m+1) set the low coverage field to ‘don't care’. Second, set a ‘High Coverage’ field of the suggested test to component b. Third, set a ‘score’ field of the suggested test to a value computed by dividing the element value M(d,b) by the total occurrences E (i.e., Score=M(d,b)/E). Fourth, write the suggested test to an output such as a display or a machine-readable file in memory. For example, consider a sample output of method 100 shown in Table 2. The sample output provides a list of three suggested tests according to the present invention. Each of the suggested tests is represented by a row in Table 2 and comprises a low coverage component, a high coverage component and a score. The low coverage component is either represented by a specific component number (e.g., 2) or is labeled using ‘don't care’. The high coverage component is represented by a component number (e.g., 5). The score (e.g., 0.021) is an estimate of an improvement in the probability of correct diagnosis that would occur if the suggested test were added to the test suite. In addition to the list of suggested tests, an estimate of a probability of correct diagnosis (i.e., Pcorr) is included in the sample output of Table 2. TABLE 2Low CoverageHigh CoverageScoredon't care30.021250.021160.017Estimated Probability of correct diagnosis = 0.879 In another aspect of the invention, a method 200 of identifying a test to delete from a test suite is provided. FIG. 2 illustrates a flow chart of the method 200 of identifying tests to delete. The method 200 advantageously determines diagnostic efficacy of tests in a test suite. The method 200 of identifying generates a list of tests, each test being associated with a relative diagnostic efficacy. The generated list is used to identify one or more tests in a test suite that may be deleted. In particular, tests that are in some way redundant or do not otherwise significantly contribute to an overall diagnostic accuracy or efficacy of the test suite may be eliminated. The method 200 quantifies a relative diagnostic efficacy making it possible to identify tests that may be safely deleted from a test suite. The method 200 of identifying tests to delete comprises creating 210 a simulation database for a DUT and a test suite T. A computer model of the DUT or actual failure data for the DUT, or a combination thereof are employed to create 210 the simulation database. Creating 210 a simulation database is essentially identical to creating 110 a simulation database described hereinabove with respect to method 100. Likewise, as with creating 110 in the method 100, in a preferred embodiment of method 200, a model-based simulation is performed to create 210 the simulation database. The method 200 further comprises determining 220 a probability of correct diagnosis Pcorr for the test suite T. The probability of correct diagnosis Pcorr may be determined 220, as described hereinabove with respect to method 100. In particular, determining 220 comprises counting a number of occurrences of each of the correct diagnoses included in the simulation database. A probability of a given diagnosis may be computed from the count by dividing the number of occurrences of the diagnosis by a total number of occurrences of all diagnoses included in the determination 220. In some embodiments, the probability of incorrect diagnoses is determined also. The method 200 further comprises determining 230 a probability of correct diagnosis Pcorr,t for a modified test suite T. The modified test suite T is a test suite including all tests but a selected test t of the test suite T, (i.e., t∈T and t∈T) The probability of correct diagnosis Pcorr,t for the modified test suite T may be determined in a manner analogous to that used in determining 220 for the test suite T. Preferably, determining 230 a probability of correct diagnosis Pcorr,t is repeated for m different modified test suites T wherein m is a number of tests in the test suite T and each different modified test suite T is associated with a different selected test t. Thus, a unique probability of correct diagnosis Pcorr,t is determined 230 for each of m modified test suites T associated with m different tests t. The method 200 further comprises computing 240 an efficacy value for each of the tests in the test suite T. The efficacy value ε(t) is a metric that relates the diagnostic accuracy or effectiveness of a particular modified test suite T to the test suite T. A preferred metric ε(t) for a given test t is a difference between the determined 230 probability of a correct diagnosis Pcorr,t and the determined 220 probability of correct diagnosis Pcorr,t (i.e., ε(t)=Pcorr,t−Pcorr). In some embodiments, a cost c(t) associated with a test t may also be incorporated in the efficacy value metric ε(t). For example, the cost c(t) of a test t may be incorporated by multiplying the difference between probabilities of correct diagnoses by the cost (i.e., ε(t)=c(t)·(Pcorr,t−Pcorr)) The method 200 further comprises generating 250 a list of the tests and associated efficacy values. The generated 250 list may include efficacy values ε(t) for some or all of the tests t in the test suite T. Moreover, the list of tests and associated efficacy values thus generated 250 by the present invention may be represented either in human readable form or in machine-readable form. The human-readable form may take any of several common textual or graphical forms known in the art. The machine-readable form may be used by other computer programs or automated systems. The other computer programs or automated systems may use the list to further modify a test suite or implement a modified test suite, for example. Among other things, the generated 250 list of tests may be used to identify tests that may be deleted or eliminated from the test suite T. In particular, tests with low efficacy values ε(t) may be deleted from the suite T without significantly reducing the overall diagnostic efficacy of the test suite T. Therefore, using the list, tests with low efficacy values ε(t) may be identified that can be safely deleted from the test suite. While minimally reducing the diagnostic efficacy of the test suite, removal of tests with low efficacy values ε(t) may reduce the time and associated costs of testing the DUT. To better understand the method 200 of the present invention, consider an example of an implementation of a preferred embodiment of the method 200 using a matrix representation for storing intermediate results generated by the method 200. The use of matrix notation hereinbelow is intended to facilitate discussion and in no way limits the scope of the present invention. In addition, for the purposes of discussion hereinbelow it is assumed that a model of the DUT, its components, test coverages, and a priori probabilities of component failure are available. A simulation database is created 210 for this example in a form and in a manner analogous to that the example of method 100 described hereinabove. In particular, the database comprises multiple rows, each row having a field for a component pattern ω, a test pattern Δ, and a number of occurrences v. A first copy of the database is produced including only those rows from the simulation database having one BAD component. The first copied database is sorted according to test pattern. As described for method 100, the sorting produces sequences or groups of rows having the same test pattern and each sequence begins at an i-th row and a next sequence begins at a j-th row. A matrix M and a variable E are created and initialized to zero (i.e., M=0 and E=0). The M matrix is filled and the total occurrence variable E is likewise used to accumulate a count of the total number of occurrences as described hereinabove with respect to method 100. Once each sequence in the first copied database has been examined, a probability of a correct diagnosis is determined 220. To determine 220 the probability of correct diagnosis, let Pcorr equal a sum of diagonal elements of the M matrix. Then, divide the Pcorr by the accumulated total number of occurrences E. In other words, let Pcorr=0, for i=1, . . . , m, perform Pcorr=Pcorr+M(i,i), and then let Pcorr=Pcorr/E. Next a probability of correct diagnoses Pcorr,t for modified test suites T′ associated with each of the tests t in the test suite T is determined 230. In particular, for each test t in the test suite, a modified test suite T′ is identified by selecting a test t to remove from the test suite T. Once a test t is selected, a second copied database is produced from the first copied database by first deleting the bit from the each of the test pattern bit strings Δ associated with the selected test t. Then, the second copied database is generated by sequentially copying rows of the first copied database into the second copied database while simultaneously combining together any rows that have identical bit string values for the component pattern ω and the test pattern Δ. In each row in the second database representing a set of combined rows, the number of occurrence value v is the sum of the number of occurrence values v for the combined rows. For example, consider five rows of a first copied database as shown in Table 3. TABLE 3Component PatternTest PatternNumber of Occurrences001000001100101010101120010000010001010101011490010000001000100101013500100000110001000010115001000000000010010101178If a third test t is selected, then a third bit Δ3 of each of the test patterns Δ is deleted. Upon deleting the third bit Δ3 of each test pattern Δ, it is evident that a first and a second row in Table 3 have identical component and test patterns. Likewise a third and a fifth row of Table 3 have identical component and test patterns. A portion of a second copied database corresponding to the rows shown in Table 3 is shown in Table 4. Note that the number of occurrence values for the combined rows is the sum of the number occurrence values of the individual rows prior to combining and copying. TABLE 4Component PatternTest PatternNumber of Occurrences00100000100101010101161001000000000100101012130010000010001000010115 A probability of correct diagnosis Pcorr,t for each test t may then be computed, as was done for the case of the test suite T in which the M matrix was filled, except that for the correct diagnosis Pcorr,t, the matrix M is filled from the second copied database representing the modified test suite T′ for each test t. Alternatively, a simpler approach to computing the probability of correct diagnosis Pcorr,t for each test t comprises performing the following operations. First, initialize a variable St to equal 0 (i.e., St=0). Second loop through the rows of the other second database and sum a largest number of occurrences value vmax found for each unique test pattern value Δ with a current value of the variable St (i.e., St=St+vmax for each unique test pattern Δ). The probability of correct diagnosis Pcorr,t for the modified test suite T′ for test t is then computed by dividing the variable St by the total number of occurrences Et (i.e., Pcorr, t=St/Et). Note that the total number of occurrences Et is simply the sum of all numbers of occurrences v in the second copied database. Moreover, one skilled in the art will readily recognize that this simpler approach may also be employed to compute the probability of correct diagnosis Pcorr for the test suite T from the first copied database, if so desired. A metric ε(t) representing a diagnostic efficacy value of each of the tests t may then be computed 240. In particular for each test t, the metric ε(t) is computed by subtracting from the probability of correct diagnosis Pcorr,t for the test t the probability of correct diagnosis Pcorr for the test suite T. A list is generated 250 from the metrics ε(t). An example of such a list is shown in Table 5. The efficacy value ε(t) in the example of method 200 represents a estimated improvement in the diagnostic accuracy of the test suite T. The estimated improvement values are typically negative numbers since in general, deleting a test will reduce the accuracy of the resulting test suite. However, since the reduction in accuracy may be very small compared to the cost of doing the deleted test, the reduction in accuracy may be acceptable in many instances. TABLE 5TestEst. Improvement1−0.1052−0.1063−0.1324−0.138 A key advantage of the present invention is that it provides quantitative information upon which to base decisions about which test(s) to add or remove from a test suite. In particular, the present invention effectively ‘discovers’ problems associated with diagnostic accuracy of a test suite and automatically suggests tests to add to the test suite to address those problems. Moreover, the present invention associates a relative amount of improvement in diagnostic accuracy with suggested tests, facilitating an evaluation of the advantages of adding such tests. Furthermore, the present invention quantifies the efficacy of tests in the test suite, thereby enabling the identification of test(s) that can be removed from a test suite while minimally reducing the effectiveness of the suite. Removing identified tests may result in reducing test time while minimally impacting the effectiveness of the test suite. The method 100 of suggesting a test to add to a test suite of a diagnostic testing system and/or the method 200 of identifying a test to delete from a test suite of the present invention also may be employed when testing a DUT for which a specific diagnosis of component failure is not needed. For example, in some cases a cost of repair of a DUT is more than the cost of the DUT. In such a case, it is sufficient to determine from testing whether the DUT, as a whole, is GOOD or BAD. However in such cases, it still may be desirable to optimize a given test suite such that the test suite maximizes coverage and minimizes test costs. Test costs are often measured in terms including, but not limited to, test time, cost of test equipment, and/or number of tests. Given the discussion hereinabove, one skilled in the art can readily realize that the method 100 and/or the method 200 can be employed in such a case where a diagnosis beyond a GOOD/BAD determination for the DUT, as a whole, by simply defining the DUT to have a single component, namely the DUT itself. In particular, for those situations in which no component level diagnosis is to be performed by the testing system, the methods 100 and 200 may be used by simply setting the number of components to equal one. For the examples described hereinabove with respect to methods 100 and 200, after creating 110, 210 a simulation database, set the number of components n equal to one (i.e., n=1). Next, replace the component pattern of each row of the simulation database with a bit string having a single bit equaling ‘1’. Then continue with the examples as described. In yet another aspect of the present invention, a system 300 that determines an efficacy of tests in a test suite of a testing system is provided. In some embodiments, the system 300 suggests tests to add to the test suite to improve the overall efficacy and/or accuracy of a testing system employing the test suite. In other embodiments, the system 300′ provides an effect on overall efficacy of one or more tests in the test suite and facilitates identification of test that may be deleted from the test suite with minimal reduction in the overall efficacy of the testing system. In yet other embodiments, the system 300, 300′ may provide a combination of suggested tests to add and an identification of tests to delete. FIG. 3 illustrates a block diagram of the system 300, 300′, 300″ of the present invention. The system 300, 300′, 300″ comprises a processor (CPU) 310, a memory 320 and a computer program 330, 330′ stored in the memory 320. The CPU 310 accesses the computer program 330, 330′, 330″ from memory and executes the computer program 330, 330′, 330″. The system 300, 300″, 300″ may be a stand-alone system or may be part of a testing system that employs the test suite to test a DUT. In a preferred embodiment, the CPU 310 is a general-purpose processor such as a microprocessor or microcontroller capable of executing the computer program 330, 330′, 330″. However in other embodiments, the CPU 310 may be a specialized processor, such as might be found in an application specific integrated circuit (ASIC). The memory 320 may be any form of computer memory including, but not limited to, random access memory (RAM), read only memory (ROM), and disk memory. In some embodiments, the memory 320 is separate from the CPU 310 while in other embodiments the memory may be incorporated in the CPU 310. As with the CPU 310, the memory may be a portion of an ASIC. The computer program 330, 330′, 330″ comprises instructions that, when executed, determine the efficacy of tests in a test suite and one or both suggest tests to add and identify tests to delete from the test suite. In a preferred embodiment, the instructions of the computer program 330 implement the method of determining a revision of a test suite of a model-based diagnostic testing system of the present invention. More preferably, the computer program 330 implements both the method 100 and the method 200 of the present invention. In particular, the computer program 330, 330′ creates a simulation database, determines a probability of correct and incorrect diagnoses, and creates a list of suggested tests to add to the test suite. In the preferred embodiment, the list of suggested tests comprises a user-selected number or quantity of suggested tests. Each suggested test comprises one or more of a component of the DUT identified as needing high coverage in the test to be added, a component of the DUT identified as having low coverage in the test to be added, and a score for the test. The score indicates a relative improvement in an efficacy of the test suite for diagnosing a correct, failed component in the DUT being tested. In addition, a measure of an overall probability of correct diagnosis for the test suite is provided. As for the computer program 330, the computer program 330′ preferably implements the method 100 of the present invention. In another embodiment, the computer program 330, 330″, when executed by the CPU 310, creates a simulation database, determines a probability of correct diagnosis for the test suite, determines a probability of correct diagnosis for a modified test suite that excludes a test of the test suite, and computes an efficacy value for the modified test suite. The determination of a probability of correct diagnosis and the computation of the efficacy value for the modified test suite that excludes a test are repeated for more than one modified test suite wherein each different test suite excludes a different test. Preferably, an efficacy value associated with every test in the test suite is computed. The computer program 330, 330″ also generates a list of tests and their relative effect on overall test suite efficacy. The list may be used to identify tests to delete from the test suite. As for the computer program 330, the computer program 330″ preferably implements the method 200 of the present invention. Thus, there has been described a novel method 100, 200 of determining a revision of a test suite of a model-based diagnostic testing system. In addition, a system 300, 300′, 300″ that determines an efficacy of tests in a test suite and either or both suggests tests to add and identifies tests to delete from the test suite has been described. It should be understood that the above-described embodiments are merely illustrative of the some of the many specific embodiments that represent the principles of the present invention. Clearly, those skilled in the art can readily devise numerous other arrangements without departing from the scope of the present invention. |
|
description | 1. Field of the Invention The present invention relates to a container, and particularly relates to a radioactive contaminant container for containing radioactive contaminants. 2. Background Art In the related art, a radioactive contaminant container for safely containing radioactive contaminants has been known (for example, refer to Japanese Unexamined Patent Application Publication No. 2007-147580). Japanese Unexamined Patent Application Publication No. 2007-147580 discloses a mobile radiation shielding container formed in order to safely reserve radioactive wastes generated in a medical field for waste treatment or to store radioactive materials. The mobile radiation shielding container is a heavy radiation shielding container formed by heavy metals such as lead in order to contain a radioactive waste introducing receptacle or a radioactive material storing bucket. The radiation shielding container disclosed in Japanese Unexamined Patent Application Publication No. 2007-147580 has an opening and closing lid on an upper surface or a lateral surface thereof in order to insert the radioactive waste introducing receptacle. The upper surface of the lid of the radiation shielding container has an introducing hole for introducing the radioactive waste into the radioactive waste introducing receptacle, and is formed to cover a surface of the introducing hole with the lid for shielding radiation generated from the inside. In order for the radiation shielding container to be movable, a caster is attached to a lower portion of the radiation shielding container. However, the mobile radiation shielding container disclosed in Japanese Unexamined Patent Application Publication No. 2007-147580 is proposed on the premise that the container is used in a medical field, and is not intended to store a large amount of radioactive contaminants. For example, when an accident of a nuclear power plant results in a large amount of the radioactive contaminants, all of the radioactive contaminants cannot be immediately purified. Accordingly, it becomes necessary to store the radioactive contaminants for temporary isolation from a living space or for permanent isolation for the purpose of disposal. When the mobile radiation shielding container disclosed in Japanese Unexamined Patent Application Publication No. 2007-147580 is used to store a large amount of the radioactive contaminants, lead is used in the mobile radiation shielding container in order to enhance radiation shielding efficiency. Accordingly, it is apprehended that the lead adversely affects the environment. In addition, in order to move a container which becomes heavy due to use of heavy metals such as lead, a caster is attached to the above-described mobile radiation shielding container. Therefore, when the mobile radiation shielding container disclosed in Japanese Unexamined Patent Application Publication No. 2007-147580 is used to store the radioactive contaminants, it is necessary to have an extra space inside a storing space in order to contain the caster portion. In addition, in order to store a large amount of the radioactive contaminants, it is necessary to provide many containers. In this case, in order to save the storing space, it is required to store the containers by stacking the container thereon. However, since the mobile radiation shielding container disclosed in Japanese Unexamined Patent Application Publication No. 2007-147580 has the attached caster, it is difficult to safely stack the container thereon. Therefore, the present invention aims to provide a radioactive contaminant container which can enhance radiation shielding efficiency even by using materials of low environmental load and can save a storing space, when storing radioactive contaminants by using multiple containers. In order to achieve the above-described object, a radioactive contaminant container according to the present invention includes a wall that defines a containing space for containing radioactive contaminants and shields at least a portion of radiation irradiated from the radioactive contaminants, and the wall has an outer shape of a hexagonal cylinder or a substantially hexagonal cylinder. The term “radioactive contaminants” means a substance contaminated by radioactive substances. The term “wall” does not depend on a positional relationship when the radioactive contaminant container is placed on a predetermined plane. For example, when the radioactive contaminant container is placed on a predetermined plane so that an axial direction of the hexagonal cylinder or the substantially hexagonal cylinder is perpendicular to the plane, the wall is configured to include all of an upper surface, a lateral surface and a bottom surface of the hexagonal cylinder or the substantially hexagonal cylinder. Similarly, for example, even when the radioactive contaminant container is placed on a predetermined plane so that the axial direction of the hexagonal cylinder or the substantially hexagonal cylinder is parallel to the plane, the wall is configured to include all of the upper surface, the lateral surface and the bottom surface of the hexagonal cylinder or the substantially hexagonal cylinder. For example, the wall includes a first protrusion extending along the axial direction of the hexagonal cylinder or the substantially hexagonal cylinder and protruding outward; and a first recess extending along the axial direction and recessed inward, and the first recess can be fitted to the first protrusion formed in the other radioactive contaminant container. In the description of the invention, the term “outward side” represents a farther side from the center of the radioactive contaminant container unless otherwise described, and the term “inward side” represents a closer side from the center of the radioactive contaminant container unless otherwise described. As an example, the wall may include a first surface and a second surface, each extending in a direction intersecting with the axial direction of the hexagonal cylinder or the substantially hexagonal cylinder, and each shape being hexagonal or substantially hexagonal. Any one surface of the first surface and the second surface may include a second protrusion protruding outward, and the other surface may include a second recess recessed inward. The second recess may be fitted to the second protrusion formed in the other radioactive contaminant container. The wall may include a metal plate having multiple through-holes. For example, a portion of the wall may be formed to be attachable to and detachable from the other portion of the wall, or to be openable and closeable in order to contain the radioactive contaminants in the containing space. As an example, the wall may include a layer containing radiation shielding materials having at least silicon, strontium, magnesium, europium and dysprosium as essential elements. The wall may further include a layer formed of stainless steel. The layer containing the radiation shielding materials may be a layer in which the radiation shielding materials are added to resin or rubber. As another example, the wall may be formed of stainless steel. For example, the radioactive contaminant container according to the present invention may contain a reverse osmosis membrane used to purify radioactively contaminated water. In addition, a radioactive contaminant container according to the present invention may be configured such that a containing space for containing radioactive contaminants contains multiple radioactive contaminant containers according to the present invention. As an example, the first recess may be disposed on three surfaces which are not adjacent to each other within six surfaces extending in the axial direction of the hexagonal cylinder or the substantially hexagonal cylinder, and a handle for attaching a wire rope for transportation may be disposed in the first recess. In a radioactive contaminant container according to the present invention, since a wall has an outer shape of a hexagonal cylinder or a substantially hexagonal cylinder, when multiple radioactive contaminant containers are juxtaposed, it is possible to juxtapose the adjacent radioactive contaminant containers by bringing the containers into close contact with each other. In addition, the radioactive contaminant containers can be not only juxtaposed, but also stacked. Therefore, when storing the radioactive contaminant containers containing radioactive contaminants, it is possible to save storing space for the radioactive contaminant containers, which is disposed under the ground or on the ground. In addition, it is possible to juxtapose or stack the radioactive contaminant containers by bringing the containers into close contact with each other. Accordingly, a radiation shielding function obtained by the wall is enhanced by increased thickness at horizontally or vertically adjacent places of the two walls. This can further reduce air dose inside the container and the storing space of the radioactive contaminant container. That is, in order to enhance radiation shielding efficiency of the radioactive contaminant container, it is not necessary to form the radioactive contaminant container by using lead which adversely affects the environment. If the multiple radioactive contaminant containers according to an aspect of the present invention are brought into close contact with each other and are juxtaposed or stacked, it is possible to further enhance the radiation shielding efficiency. In this manner, according to the radioactive contaminant container of the present invention, the radiation shielding efficiency can be enhanced even by using materials of low environmental load and a storing space can be saved, when storing the radioactive contaminants by using the multiple radioactive contaminant containers. If the wall includes the first protrusion extending along the axial direction of the hexagonal cylinder or the substantially hexagonal cylinder and protruding outward; and the first recess extending along the axial direction and recessed inward, and if the first recess can be fitted to the first protrusion formed in the other radioactive contaminant container, when juxtaposing multiple radioactive contaminant containers, it is possible to connect the multiple radioactive contaminant containers according to an aspect of the present invention by allowing the first protrusion and the first recess of the adjacent radioactive contaminant containers to be fitted to each other. Therefore, the multiple radioactive contaminant containers can be further brought into close contact with each other and can be stably stored. In addition, by connecting the radioactive contaminant containers to each other, it is possible to reduce a risk that the radioactive contaminant containers may fall down due to a shock of an earthquake. If any one surface of the first surface and the second surface in the wall, each shape of which is hexagonal or substantially hexagonal, includes a second protrusion protruding outward, and the other surface includes a second recess recessed inward, and if the second recess can be fitted to the second protrusion formed in the other radioactive contaminant container, when stacking multiple radioactive contaminant containers, it is possible to allow the second protrusion of the lower radioactive contaminant container to be fitted to the second recess of the upper radioactive contaminant container. Therefore, even when the radioactive contaminant containers are stacked, the multiple radioactive contaminant containers can be further brought into close contact with each other, and can be stably stored by connecting the upper and lower containers. Accordingly, it is possible to reduce a risk that the radioactive contaminant containers may fall down due to a shock of an earthquake. If the wall is configured to include the metal plate having multiple through-holes, strength of the wall is increased. In addition, since the metal plate has the multiple through-holes, even when a stretching force, a compression force or an impact is applied to the wall, it is possible to mitigate these forces. Therefore, it is possible to increase overall strength of the radioactive contaminant container. As an example, the term “metal plate having multiple through-holes” represents a metal mesh plate. If in order to contain the radioactive contaminants in the containing space, a portion of the wall is formed to be attachable to and detachable from the other portion of the wall or to be openable and closeable, a portion of the wall functions as a lid. Accordingly, it is possible to facilitate introducing and containing of the radioactive contaminants. If the wall includes the layer containing the radiation shielding materials having at least silicon, strontium, magnesium, europium and dysprosium as essential elements, it is possible to further enhance the radiation shielding function of the radioactive contaminant container by using the radiation shielding materials of the low environmental load. Similarly, if the layer containing the radiation shielding materials is a layer in which the radiation shielding materials are added to resin or rubber, it is also possible to further enhance the radiation shielding function of the radioactive contaminant container by using the radiation shielding materials of the low environmental load. If the wall is configured to further include a layer formed of stainless steel or the wall is formed of the stainless steel, since the wall is unlikely to rust, the strength of the wall can be maintained. In addition, it is possible to further enhance the radiation shielding function. If the radioactive contaminant container according to the present invention is configured to contain a reverse osmosis membrane (RO membrane) used to purify radioactively contaminated water, it is possible to contain and store the reverse osmosis membrane (RO membrane) which becomes the radioactive contaminants through the purification of the radioactively contaminated water, in the radioactive contaminant container having the radiation shielding function. If the containing space of the radioactive contaminant container according to the present invention is configured to contain other multiple radioactive contaminant containers according to the present invention, the radioactive contaminants contained inside the multiple radioactive contaminant containers are doubly contained in the radioactive contaminant container. Accordingly, it is possible to further enhance the radiation shielding efficiency. Furthermore, the outer shape of the wall in the radioactive contaminant container containing the multiple containers is the hexagonal cylinder or the substantially hexagonal cylinder. Accordingly, the thickness of the wall of the adjacent places is increased by the juxtaposition. Therefore, as described above, it is possible to further enhance the radiation shielding efficiency. If the first recess is disposed on three surfaces which are not adjacent to each other within six surfaces extending in the axial direction of the hexagonal cylinder or the substantially hexagonal cylinder, and if the handle for attaching the wire rope for transportation is disposed in the first recess, when lifting, transporting and installing the radioactive contaminant container, the radioactive contaminant container can be lifted, transported and installed with a good balance. Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 illustrates a perspective view of a radioactive contaminant container according to the first embodiment, and FIG. 2 illustrates a front view of the radioactive contaminant container 1. A radioactive contaminant container 1 includes walls 2 which define a containing space for containing radioactive contaminants 3 such as radioactively contaminated soil and radioactively contaminated ashes. The walls 2 shield at least a portion of radiation irradiated from the radioactive contaminants 3. The walls 2 of the radioactive contaminant container 1 have an outer shape of a substantially hexagonal cylinder. The walls 2 include a detachable lid 2a disposed to be capable of introducing the radioactive contaminants 3 and a main body 2b. In the radioactive contaminant container 1 according to the first embodiment, as illustrated in FIG. 2, in a positional relationship when the walls 2 of the substantially hexagonal cylinder are placed in an upright position so that an axial direction y is perpendicular to a placement surface, the wall 2 configuring an upper surface of the substantially hexagonal cylinder is the lid 2a, and the wall 2 configuring a bottom surface and lateral surfaces is the main body 2b. In the radioactive contaminant container 1 according to the first embodiment, since widths of lateral surfaces 5 of the main body 2b (width in a direction perpendicular to the axial direction y) are coincidental with each other, the walls 2 have the outer shape of a substantially regular hexagonal cylinder. In the radioactive contaminant container 1 according to the first embodiment, as an example, a length in the axial direction of the substantially regular hexagonal cylinder configured to have the outer shape of the walls 2 is approximately 1 m, and a length of a diagonal line passing through a center of the substantially regular hexagon in a plane of the substantially regular hexagon is approximately 1 m. As illustrated in FIGS. 1 and 2, each lateral surface 5 of the main body 2b has either a lateral surface protrusion 6 extending along the axial direction y of the substantially hexagonal cylinder or a lateral surface recess 7 extending along the axial direction. In the radioactive contaminant container 1 according to the first embodiment, the lateral surface protrusion 6 or the lateral surface recess 7 is arranged in the center of each lateral surface 5. The lateral surface 5 having the lateral surface protrusion 6 and the lateral surface 5 having the lateral surface recess 7 are configured to be adjacent to each other. As illustrated in FIG. 1, the lateral surface protrusion 6 includes an outward protrusion 6b protruding outward from the radioactive contaminant container 1 and an inward protrusion 6a protruding inward to the radioactive contaminant container 1. The outward protrusion 6b is formed so that the width becomes narrower as it goes outward, and the inward protrusion 6a is formed so that the width becomes narrower as it goes inward. The lateral surface recess 7 is formed so that the width becomes narrower as it goes inward to the radioactive contaminant container 1. In the radioactive contaminant container 1 according to the first embodiment, when multiple radioactive contaminant containers 1 are juxtaposed, the outward protrusion 6b can be fitted to the lateral surface recess 7 disposed on the other radioactive contaminant container 1. The lid 2a has a lid protrusion 9 corresponding to the shapes of the lateral surface protrusion 6 and the lateral surface recess 7, and a lid recess 10. When the lid 2a is attached to the main body 2b, the lid protrusion 9 is formed so that an outer edge thereof matches the outward protrusion 6b, and the lid recess 10 is formed so that the outer edge matches the lateral surface recess 7. A lid center projection 11 projecting outward from the radioactive contaminant container 1 is formed in the center of the lid 2a. In a positional relationship illustrated in FIG. 1, when the radioactive contaminant container 1 is placed on any plane, the lateral surface protrusion 6 and the lateral surface recess 7 are formed to have a gap with the plane. FIG. 3 illustrates a perspective view when viewed from a bottom surface direction of the radioactive contaminant container 1, and FIG. 4 illustrates a bottom view. The bottom surface has a bottom surface projection 14. The bottom surface projection 14 is continuously formed from an edge portion of the lateral surface 5 where the lateral surface protrusion 6 and the lateral surface recess 7 are not formed. The bottom surface projection 14 is formed at each substantially hexagonal corner which appears on the bottom surface of the radioactive contaminant container 1. As illustrated in FIG. 3, in a positional relationship where the radioactive contaminant container 1 is arranged so that the bottom surface is placed to face upward, the bottom surface projection 14 includes an upper surface 14a formed on the same plane, a pair of first lateral walls 14b extending toward a direction of the center from an edge portion of the radioactive contaminant container 1, and a pair of second lateral walls 14c formed integrally with the lateral surface 5. A plane 15 formed in an inner side surrounded by the bottom surface projection 14 and a plane 16 formed in an outer side of the bottom surface projection 14 are on the same plane. The upper surface 14a of the bottom surface projection 14 is located further in the outer side of the radioactive contaminant container 1 than the plane 15 and the plane 16, and extends parallel to the plane 15 and the plane 16. The first lateral wall 14b is disposed to be tilted to the plane 15 and the plane 16. The first lateral wall 14b is tilted so that a cross-sectional surface of the bottom surface projection 14 becomes narrower as it goes outward from the radioactive contaminant container 1. As illustrated in FIG. 4, a pair of the first lateral walls 14b mutually extends to the direction of the center and comes into contact with each other to form a corner portion 18 at the junction. When the radioactive contaminant containers 1 are stacked on one another, a recess of the bottom surface which is formed by the bottom surface projection 14 and the plane 16 is formed so as to be fitted to the lid center projection 11 formed in the radioactive contaminant container 1. FIG. 5 illustrates a plan view of the lid 2a. The lid center projection 11 includes a projection 20 of a substantially regular hexagonal cylinder which has a predetermined height width, and a notched portion 21 formed at a corner portion which is the regular hexagon when the projection 20 is viewed from the upper surface. When the radioactive contaminant containers 1 are stacked on one another, the corner portion 18 of the bottom surface projection 14 is fitted to the notched portion 21. A pair of lateral walls 20a of the projection 20 is tilted so that a pair of the lateral walls 20a of the projection 20, which defines a pair of the first lateral walls 14b forming the corner portion 18, and the notched portion 21 is in close contact with each other. Next, FIG. 6 illustrates an opening shape of the main body 2b when the lid 2a is opened. The outer shape of the cross-sectional surface of the lateral surface protrusion 6 in a width direction (cross-sectional surface perpendicular to the axial direction y) is hexagonal, and in the opening of the main body 2b, the outer shape of an end surface of the lateral surface protrusion 6 is hexagonal. Among sides configuring the hexagon, three sides protruding inward are configured to have inward protrusions 6a, and three sides protruding outward are configured to have outward protrusions 6b. In the opening of the main body 2b, the lateral surface recesses 7 appear as an end surface of three consecutive sides. The shape of the inner wall surface of the inward protrusion 6a and the shape of the inner wall surface of the lateral surface recess 7 are coincidental with each other. In addition, in the inner side of each substantially hexagonal corner portion which appears on the opening surface, an inner wall 25 extending along the axial direction y of the radioactive contaminant container 1 is disposed. As illustrated in FIG. 6, the inner wall 25, when viewed from the opening surface, includes a first inner wall 25a extending inward from the inner side wall surface of the lateral surface 5, a second inner wall 25b formed continuously with the first inner wall 25a and extending parallel to the opposed lateral surface 5, a third inner wall 25c formed continuously with the second inner wall 25b and extending parallel to the opposed lateral surface 5, and a fourth inner wall 25d extending between the third inner wall 25c and the lateral surface 5. A space 24 is defined between the inner wall 25 and the lateral surface 5. In the lateral surface protrusion 6, a space 27 is defined between a wall surface configuring the inward protrusion 6a and a wall surface configuring the outward protrusion 6b. Since the space 24 and the space 27 are disposed, it is possible to further reduce the weight of the radioactive contaminant container 1 as compared to a case where these spaces are filled. The containing space 23 of the radioactive contaminant container 1 is defined by the inner wall surface of a portion of the lateral surface 5 and the inner wall surface of the inner wall 25 and the inward protrusion 6a which are extended from the portion of the lateral surface 5. As illustrated in FIG. 5, a rear surface of the lid 2a has a lid placing projection 29 which is fitted to the inside of the inner wall surface defining the containing space 23 when the main body 2b is closed by the lid 2a, that is, the inside of the inner wall surface of the portion of the lateral surface 5 and the inner wall surface of the inner wall 25 and the inward protrusion 6a which are extended from the portion of the lateral surface 5. In a plan view illustrating a surface of the lid 2a in FIG. 5, the lid placing projection 29 disposed on the rear surface of the lid 2a is virtually illustrated. When the lid 2a is used for closing, it is possible to stably place the lid 2a on the main body 2b by using the lid placing projection 29. In the radioactive contaminant container 1 according to the first embodiment, the walls 2 configuring the radioactive contaminant container 1 are reinforced, thereby increasing the strength of the radioactive contaminant container 1. FIG. 7 illustrates an enlarged view of a portion along the line A-A′ illustrated in FIG. 6. A reinforcing metal plate 28 having multiple through-holes is embedded on the lateral surface 5 of the main body 2b and inside the inner wall 25. The thickness widths of the lateral surface 5 of the main body 2b in which the reinforcing metal plate 28 is embedded and the inner wall 25 are respectively 10 mm as an example. Multiple circular through-holes are arranged in regular mesh in the reinforcing metal plate 28. As an example, the reinforcing metal plate 28 is a metal mesh plate. Since the reinforcing metal plate 28 has the multiple through-holes, even when a stretching force, a compression force or an impact is applied thereto, it is possible to mitigate these forces. In the radioactive contaminant container 1 according to the first embodiment, the reinforcing metal plate 28 is also embedded along the lid 2a and the bottom surface inside the lid 2a and the bottom surface. The reinforcing metal plate 28 is also embedded inside the lid center projection 11, the bottom surface projection 14, the lateral surface protrusion 6 and the lateral surface recess 7. That is, in the radioactive contaminant container 1 according to the first embodiment, the reinforcing metal plate 28 is embedded throughout the entire walls 2. FIG. 8 illustrates a cross-sectional view along the line B-B′ illustrated in FIG. 6. In the cross-sectional view of FIG. 8 along the line B-B′, the reinforcing metal plate 28 is not illustrated. As illustrated by the cross-sectional view along the line B-B′, in the radioactive contaminant container 1 according to the first embodiment, the walls 2 include multiple layers. An outer layer 30 is formed of stainless steel, an intermediate layer 31 is a layer of a radiation shielding materials which is molded in a plate shape, and an inner layer 32 is formed of stainless steel. The radiation shielding materials have at least silicon, strontium, magnesium, europium and dysprosium as essential elements. The radiation shielding materials will be described later in detail. A width ratio of the outer layer 30, the intermediate layer 31 and the inner layer 32 can be appropriately selected depending on an amount of radiation to be shielded. FIG. 9 illustrates a perspective view in a state where multiple radioactive contaminant containers 1 are juxtaposed and stacked. In the radioactive contaminant container 1 according to the first embodiment, the outer shape of the walls 2 is the substantially hexagonal cylinder. Accordingly, when the multiple radioactive contaminant containers 1 are juxtaposed, it is possible to juxtapose or stack the adjacent radioactive contaminant containers 1 by bringing the containers into close contact with each other. Therefore, when storing the radioactive contaminant containers 1 containing the radioactive contaminants 3 (refer to FIG. 1), it is possible to save a storing space for the radioactive contaminant containers 1, which is disposed under the ground or on the ground. In addition, it is possible to juxtapose or stack the radioactive contaminant containers 1 by bringing the containers into close contact with each other. Accordingly, the thickness is increased at horizontally or vertically adjacent places of the walls 2. Therefore, a radiation shielding function is enhanced by the walls 2. This can further reduce air dose inside the container and the storing space of the radioactive contaminant container 1. In addition, the lateral surface of the radioactive contaminant container 1 has the outward protrusion 6b and the lateral surface recess 7 which can be fitted together. When the multiple radioactive contaminant containers 1 are juxtaposed, the outward protrusion 6b and the lateral surface recess 7 of the adjacent radioactive contaminant container 1 are fitted together, thereby enabling the connection between the radioactive contaminant containers 1. Therefore, it is possible to further bring the multiple radioactive contaminant containers 1 into close contact with each other and to stably store the containers. In addition, by connecting the radioactive contaminant containers 1, it is possible to reduce a risk that the radioactive contaminant containers 1 may fall down due to a shock of an earthquake. In addition, in the radioactive contaminant container 1 according to the first embodiment, the inward protrusion 6a is formed inside the outward protrusion 6b. Therefore, when the outward protrusion 6b and the lateral surface recess 7 of the adjacent radioactive contaminant containers 1 are fitted together, the wall thickness of the fitted portion further becomes thicker than the wall thickness of the other portion. Therefore, it is possible to further enhance the radiation shielding function. Furthermore, the lid 2a and the bottom surface of the radioactive contaminant container 1 have the lid center projection 11 and the multiple bottom surface projections 14. When the multiple radioactive contaminant containers 1 are stacked, the corner portion 18 of the bottom surface projection 14 can be fitted to the notched portion 21 of the lid center projection 11. That is, since the bottom surface projection 14 is formed, the lid center projection 11 can be fitted to a recess of the bottom surface which is formed by the first lateral wall 14b of the bottom surface projection 14 and the plane 16. Therefore, even when the radioactive contaminant containers 1 are stacked, the multiple radioactive contaminant containers 1 can be further brought into close contact with each other, and can be stably stored by connecting the upper and lower containers. Accordingly, it is possible to reduce a risk that the radioactive contaminant containers 1 may fall down due to a shock of an earthquake. Further, as illustrated in FIG. 9, in order to more stably store the containers, multiple container placing rod-shaped members 40 may be arranged in the storage space. The container placing rod-shaped member 40 is fitted to the recess of the bottom surface which is formed by the first lateral wall 14b of the bottom surface projection 14 and the plane 16. In this manner, it is possible to more stably juxtapose the lowermost radioactive contaminant container 1. Radiation Shielding Materials Hereinafter, the above-described radiation shielding materials will be described in detail. The radiation shielding materials have at least silicon, strontium, magnesium, europium and dysprosium as essential elements. It is possible to shield X-rays in a practicable level by combining the elements. In addition, ultraviolet rays can also be absorbed. Further, since silicate-based compound is used, the specific gravity is lighter than lead and workability is also excellent. The content of silicon (Si) is preferably 5 to 30 mass %, and more preferably 10 to 20 mass %. The content of strontium (Sr) is preferably 30 to 60 mass %, and more preferably 40 to 50 mass %. The content of magnesium (Mg) is preferably 1 to 20 mass %, and more preferably 5 to 10 mass %. The content of europium (Eu) is preferably 0.1 to 5 mass %, and more preferably 0.5 to 3 mass %. The content of dysprosium (Dy) is preferably 0.1 to 5 mass %, and more preferably 0.5 to 3 mass %. The above-described radiation shielding materials may contain an oxygen atom (preferably 10 to 50 mass %, and more preferably 20 to 40 mass %) in addition to the above-described essential elements. In addition, a boron atom and a radiation absorbing atom other than the above-described atoms (for example, lanthanoid elements such as erbium) may be contained therein, and further inevitable impurities in production may be contained therein. In view of maleficence, it is preferable that lead elements be not substantially contained therein. For example, the content of the lead is 5 mass % or less, and preferably 1 mass % or less. The shape of the above-described radiation shielding materials can be appropriately determined depending on the usage of the shielding materials, and for example includes a granular shape (powder), a pellet shape, a block shape, a film shape and a plate shape. The above-described radiation shielding materials can be obtained through powder processing, and can be mixed with other organics (powder shape and fiber shape) to be used in various shielding applications. For example, in a case of the granular shape, an average particle size may be set to 0.1 μm to 1,000 μm, and preferably 1 μm to 100 μm. In addition, the above-described radiation shielding materials may be independently used as the compound containing the above-described essential elements, or may be used in conjunction with additives such as water, an organic solvent (alcohol, ethers and the like), surfactants, a resin binder, inorganic particles, organic particles and other radiation shielding materials. In addition, it is preferable to use titanium compounds of titanium, titanium oxide simultaneously and the like. This can further improve a shielding performance of ultraviolet rays. A preferred manufacturing method of the above-described radiation shielding materials includes a calcination process of mixing and baking silicon compounds, strontium compounds, magnesium compounds, europium compounds and dysprosium compounds. More specifically, for example, the radiation shielding materials can be manufactured through mixing and sintering processes of silicon oxide, strontium carbonate (SrCO3), magnesium oxide (MgO), europium oxide (Eu2O3), and dysprosium oxide (Dy2O3). As the silicon oxide, either silicon dioxide (SiO2) or silicon monoxide (SiO) may be used, but silicon dioxide (SiO2) is preferably used in the radiation shielding materials. A mixing ratio is not particularly limited. For example, it may be set in which silicon oxide is 20 to 60 mass % (preferably 30 to 50 mass %), strontium carbonate is to 60 mass % (preferably 30 to 50 mass %), magnesium oxide is 5 to 40 mass % (preferably 10 to 30 mass %), europium oxide is 0.1 to 5 mass % (preferably 0.2 to 1 mass %) and dysprosium oxide is 0.1 to 5 mass % (preferably 0.2 to 1 mass %). In addition to the above-described raw materials, boron compounds of boric acid (H3BO3) may be further added thereto. This facilitates electron transfer between metals during the firing, thereby enabling acceleration in an oxidation-reduction effect. A mixing amount of boric acid is not particularly limited, but is preferably 0.1 to 5 mass %, and more preferably 0.5 to 3 mass %. After being mixed, the above-described raw materials may be pulverized by using a grinder such as a ball mill and a rod mill. The materials may not be pulverized, but in a case of the above-described radiation shielding materials, it is preferable to pulverize the materials. For example, a firing temperature may be set to 500° C. to 2,000° C. in an electric furnace, and preferably 1,000° C. to 1,500° C. Firing atmosphere may be either air atmosphere or an inert gas, but is preferably air atmosphere. The firing time may be appropriately determined depending on a firing temperature and firing atmosphere, but for example, may be set to 10 minutes to 10 hours, and preferably 30 minutes to 5 hours. After the firing process, it is preferable to further add a plasma sintering process. This can improve X-ray absorption to be obtained from the radiation shielding materials. The plasma sintering may be performed according to the related art, and for example, may be performed at 500° C. to 2,000° C. (preferably 700° C. to 1500° C.) by using a plasma sintering machine. The sintering time may be appropriately determined depending on a sintering temperature, but for example, may be set to 5 minutes to 2 hours, and preferably 10 minutes to 1 hour. The above-described radiation shielding materials will be further described in detail by using the following examples. Incidentally, the above-described radiation shielding materials are not limited to the following examples. Example 1 of Radiation Shielding Materials SiO2 (manufactured by Iwai Chemicals Co., Ltd) of 40 mass %, SrCO3 (manufactured by Honjo Chemical Corporation) of 38.2 mass %, MgO (manufactured by Ube Material Industries, LTD.) of 20 mass %, Eu2O3 (manufactured by NeoMag Co., Ltd.) of 0.4 mass %, Dy2O3 (manufactured by NeoMag Co., Ltd.) of 0.4 mass % and H3BO3 (manufactured by Iwai Chemicals Co., Ltd) of 1 mass % were placed in a ball mill mixer, and were mixed for one hour. Then, the materials were placed in an electric furnace, and firing was performed under the conditions of air atmosphere, 1,300° C. and two hours. After the firing, the materials were naturally cooled to a room temperature, and were pulverized by using the ball mill mixer so that an average particle size thereof became 7 μm. In this manner, the radiation shielding materials in Example 1 were obtained. A composition ratio of the radiation shielding materials in Example 1 was measured. The measured result was Si of 13.3 mass %, Sr of 42.4 mass %, Mg of 6.23 mass %, Eu of 0.84 mass % Dy of 1.83 mass %, 0 (oxygen atom) of 31.3 mass %, and the remaining was impurities. The measured result of the specific gravity was 3.7 g/cm3. A qualitative analysis and a fluorescent X-ray analysis were performed in measurement by using an X-ray diffraction apparatus. As a result, Example 1 described above estimated the radiation shielding materials to be Sr2MgSi2O7.Eu3+,Dy3+. Example 2 of Radiation Shielding Materials For the radiation shielding materials obtained in Example 1, sintering was further performed at 1,000° C. for approximately 30 minutes by using a plasma sintering machine (manufactured by SPS Syntax Inc., Model No.: SPS-1030). After the sintering, the radiation shielding materials were naturally cooled to a room temperature, and radiation shielding materials (pellet shape and thickness of 3 mm) in Example 2 were obtained. Comparative Examples of Radiation Shielding Materials A lead plate (thickness of 0.3 mm, commercially available) and an aluminum plate (thickness of 3 mm, commercially available) were respectively used in Comparative Example 1 and Comparative Example 2. X-ray Shielding Performance of Radiation Shielding Materials (X-ray Transmission Measurement) The radiation shielding materials in Example 1 were further processed in a pellet shape (thickness of 3.95 mm) by using a press machine. According to a transmission method, an X-ray transmittance rate was measured for samples of Examples 1 and 2 and Comparative Examples 1 and 2 under a condition in which measured energy was 50 keV, and then a linear absorption coefficient was calculated by using the transmittance rate. The linear absorption coefficient is calculated by dividing the thickness of the sample (cm) from a value obtained by taking natural logarithm of the transmittance rate. The obtained measurement results are illustrated in Table 1. TABLE 1ThicknessTransmit-Linear Absorptionof Sampletance RateCoefficient (μ/cm)Example 13.95 mm0.0627.0(pellet)Example 23 mm0.0559.7(pellet)Comparative0.3 mm0.06491.8Example 1(leadplate)Comparative3 mm0.741.0Example 2(aluminumplate) Ultraviolet Shielding Performance of Radiation Shielding Materials (UV Transmission Measurement) A transmission rate of ultraviolet rays in Example 1 was measured by using an ultraviolet and visible spectrophotometer (manufactured by Shimadzu Corporation, Model No.: UV2400PC). As a result, in a wavelength of 250 nm to 400 nm, the transmittance rate was 20% or less. The above-described result shows an excellent linear absorption coefficient, since in Examples 1 and 2 of the radiation shielding materials, it is possible to obtain a sufficiently low transmittance rate with a practical thickness, although the radiation shielding materials cannot compete with lead which is excellent as the X-ray shielding material in Comparative Example 1. In particular, when compared to aluminum in Comparative Example 2, it is appreciated that the radiation shielding materials sufficiently have an excellent linear absorption coefficient. In addition, in Example 1 of the radiation shielding materials, it is appreciated that the ultraviolet shielding performance is excellent since the transmittance rate of the ultraviolet rays is low. Furthermore, there is an advantageous effect against electron beams. In addition, the radiation shielding materials have the significantly lower specific gravity than the specific gravity of lead (11.34), and are excellent in workability since the radiation shielding materials can be easily deformed in a granular shape or a plate shape. Therefore, it is appreciated that the radiation shielding materials can be used in various applications or forms. The radioactive contaminant container 1 may directly contain the radioactive contaminants according to the first embodiment, or may contain the other radioactive contaminant containers after the radioactive contaminants are contained in the other radioactive contaminant containers. FIG. 10 illustrates a state where the radioactive contaminant container 1 according to the first embodiment contains multiple radioactive contaminant containers 42 according to a second embodiment. FIG. 11 illustrates a perspective view of the radioactive contaminant container 42 according to the second embodiment. As illustrated in FIG. 11, the radioactive contaminant container 42 according to the second embodiment includes a wall having a main body 43 and a lid 45. The outer shape of the wall is a substantially regular hexagonal cylinder. The lid 45 is attachable to and detachable from the main body 43. A containing space defined by the main body 43 and the lid 45 can contain the radioactive contaminants. FIG. 12 illustrates the cross-sectional view along the line C-C′ illustrated in FIG. 10 together with the lid 2a on the assumption that the lid 2a is in a closed state. The lid placing projection 29 (refer to FIG. 5) of the lid 2a according to the first embodiment is omitted in the illustration. As an example, the radioactive contaminant container 42 according to the second embodiment contains a reverse osmosis membrane (RO membrane) 47 contaminated by the radioactive materials. In some cases, the reverse osmosis membrane (RO membrane) 47 is used when purifying water contaminated by the radioactive materials. The reverse osmosis membrane (RO membrane) 47 becomes the radioactive contaminants after purifying the contaminated water. In the radioactive contaminant container 42 according to the second embodiment, the outer shape configured to have the lid 45 and the main body 43 is a substantially hexagonal cylinder. Accordingly, when multiple radioactive contaminant containers 42 are juxtaposed, the adjacent radioactive contaminant containers 42 can be juxtaposed in close contact with each other. Therefore, as illustrated in FIG. 10, it is possible to contain more radioactive contaminant containers 42 by using a specified space. In addition, the length of one side of the substantially hexagon appearing on the plane side and the bottom surface side of the radioactive contaminant container 42 according to the second embodiment is substantially the same as the length of each side of the inner side appearing on the cross-sectional surface of the inner wall surface which defines the containing space 23 (refer to FIG. 6) in the radioactive contaminant container 1 according to the first embodiment. Accordingly, without causing an extra empty space to be made in the containing space 23 of the radioactive contaminant container 1 according to the first embodiment, it is possible to contain more radioactive contaminant containers 42 according to the second embodiment. In order to smoothly contain the radioactive contaminant containers 42 according to the second embodiment, as an example, a space of approximately 3 mm may be disposed between the adjacent radioactive contaminant containers 42. Hitherto, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and can be modified and changed in various forms based on the technical spirit of the present invention. For example, in the radioactive contaminant container 1 according to the first embodiment, the shape of the inner wall surface which defines the containing space 23 is not limited to the shape (refer to FIG. 6 and the like) illustrated as above. For example, the illustrated example in FIG. 10 adopts the shape of the inner wall surface which allows fifty five pieces of the radioactive contaminant container 42 according to the second embodiment which is to be contained, but may adopt the shape of the inner wall surface which allows fewer pieces of the radioactive contaminant container 42 according to the second embodiment which is to be contained without causing the extra empty space to be made in the containing space 23. An example is illustrated in FIG. 13. In the example illustrated in FIG. 13, each area of the radioactive contaminant container 42 according to the second embodiment which occupies the opening area of the radioactive contaminant container 1 according to the first embodiment is larger than the area of the example illustrated in FIG. 10. Therefore, an inner wall surface 48 continuous with the inner wall 25 is further disposed inside the radioactive contaminant container 1 according to the first embodiment. The length of each side of the inside appearing on the cross-sectional surface of the further disposed inner wall surface 48 which defines the containing space 23 is designed to be substantially the same as the length of one side of the substantially hexagon appearing on the plane and the bottom surface side of the radioactive contaminant container 42 according to the second embodiment in FIG. 13. In addition, as another example, the shape of the inner wall surface which allows more radioactive contaminant containers 42 according to the second embodiment than the example illustrated in FIG. 10 to be contained may be adopted as another example. The radioactive contaminant container 1 according to the first embodiment can contain various radioactive contaminants or containers which contain radioactive contaminants, in addition to the radioactive contaminant container 42 according to the second embodiment. Therefore, depending on a shape and a nature of materials to be contained, it is possible to appropriately determine which form is suitable for the opening of the containing space in the radioactive contaminant container 1 according to the first embodiment. The wall of the radioactive contaminant container 1 according to the first embodiment includes the outward protrusion 6b extending along the axial direction and protruding outward, and the lateral surface recess 7 extending along the axial direction and recessed inward, but without being limited thereto, and may not include the outward protrusion 6b and the lateral surface recess 7. FIGS. 14 and 15 illustrate a perspective view of a radioactive contaminant container 50 according to another embodiment. FIG. 14 is a perspective view when viewed from the plane side, and FIG. 15 is a perspective view when viewed from the bottom surface side. The radioactive contaminant container 50 according to another embodiment does not include the outward protrusion 6b extending along the axial direction and protruding outward, and the lateral surface recess 7 extending along the axial direction and recessed inward. The other configurations are the same as those of the radioactive contaminant container 1 according to the first embodiment. The shape of the wall of the radioactive contaminant container 50 which is configured to have a lid 52a and a main body 52b is a substantially regular hexagonal cylinder. A bottom surface end portion recess 57 is formed on the bottom surface side of the place corresponding to the outward protrusion 6b and the lateral surface recess 7 of the radioactive contaminant container 1 according to the first embodiment. The radioactive contaminant container 1 according to the first embodiment includes the bottom surface recess formed by disposing the bottom surface projection 14, and the lid center projection 11, but without being limited thereto, may not include the above-described bottom surface recess and the lid center projection 11. In addition, even when the bottom surface recess and the lid center projection 11 are included, the shapes thereof are not limited thereto. FIG. 16 illustrates a plan view of a radioactive contaminant container 60 according to further another embodiment. FIG. 17 illustrates a cross-sectional view along the line D-D′ in FIG. 16. The outer shape of the radioactive contaminant container 60 is a substantially regular hexagonal cylinder. A lid center projection 61 whose cross-sectional surface parallel to an upper surface of the lid is a regular hexagon is disposed on the upper surface of the lid. The lateral surface of the lid center projection 61 is tilted so that the area of the above-described cross-sectional surface of the lid center projection 61 becomes narrower as it goes outward. A bottom surface recess 62 whose cross-sectional surface is a hexagon is formed on the bottom surface of the radioactive contaminant container 60. Accordingly, the lid center projection 61 of the other radioactive contaminant container 60 can be fitted to the bottom surface recess 62. In addition, as another example, without disposing the projections and the recesses such as the outward protrusion 6b, the lateral surface recess 7, the lid center projection 11 and the bottom surface recess on the walls 2 of radioactive contaminant container 1, a radioactive contaminant container may be configured to include a wall of a hexagonal cylinder including a regular hexagonal cylinder. The radioactive contaminant container 42 according to the second embodiment does not include the projection and the recess for being connected to the other radioactive contaminant container 42, but is not limited thereto. Similarly to the radioactive contaminant container 1 according to the first embodiment, the projection and the recess for being connected to the other radioactive contaminant container 42 may be included. In the first and second embodiments, the lids 2a and 45 are disposed to be attachable to and detachable from the main bodies 2b and 43, but are not limited thereto. For example, the lids 2a and 45 may be disposed to be openable and closeable with respect to the main bodies 2b and 43. In the first and second embodiments, the description has been made for clarity of the description by defining the upper surface and the bottom surface, in the positional relationship when the wall of the substantially hexagonal cylinder is placed in the upright position so that the axial direction y in FIG. 2 is perpendicular to the placement surface, but is not limited thereto. Multiple radioactive contaminant containers may be juxtaposed or stacked on one another so that the axial direction y is perpendicular to the placement surface. In this case, it is preferable that the lid be bonded to the main body after the radioactive contaminants are contained or the lid be formed on the surface located above when the radioactive contaminant container is placed. The wall 2 of the radioactive contaminant container 1 according to the first embodiment adopts a three-layer structure where the intermediate layer 31 formed of the radiation shielding material is interposed between the outer and inner stainless steel layers 30 and 32, but is not limited thereto. For example, a two-layer structure may be adopted where a stainless steel layer is arranged outside and a radiation shielding material-added layer formed by adding a radiation shielding material to a resin or rubber is arranged inside. Similarly, the wall of the radioactive contaminant container 42 according to the second embodiment may also adopt the three-layer structure where the intermediate layer 31 formed of the radiation shielding material is interposed between the outer and inner stainless steel layers 30 and 32, or may also adopt the two-layer structure where the stainless steel layer is arranged outside and the radiation shielding material-added layer formed by adding the radiation shielding material to the resin or rubber is arranged inside. The other configuration may be adopted. In addition, without using the radiation shielding material, the wall 2 of the radioactive contaminant container 1 may be formed of other materials such as stainless steel. For example, even when the wall 2 of the radioactive contaminant container 1 is formed of only the stainless steel, depending on the thickness of the wall 2, it is possible to shield at least a portion of radiation. When multiple radioactive contaminant containers 1 are juxtaposed, total thickness of the adjacent walls 2 are twice the thickness of the single wall 2, thereby further improving the radiation shielding function. Similarly, without using the radiation shielding material, the wall of the radioactive contaminant container 42 according to the second embodiment may be formed of other materials such as the stainless steel. In addition, with regard to the radiation shielding materials, the radiation shielding material has been described which has been independently developed by the applicant, but without being limited thereto, other materials having the radiation shielding function may be used as the radiation shielding material. In the radioactive contaminant container 1 according to the first embodiment described above, when the lid 2a is attached to the main body 2b, the outer edge of the lid recess 10 of the lid 2a may be formed so as to expose a portion of the plane side end portion of the lateral surface recess 7, and a handle may be attached to the plane side end portion of the exposed lateral surface recess 7. The handle is sometimes referred to as a lifting point. When lifting, transporting and installing the radioactive contaminant container 1, it is possible to lift the radioactive contaminant container 1 by attaching a wire rope to the handle. The handle is attached to the three places of lateral surface recess 7 which are disposed on three surfaces not adjacent to each other among six surfaces extending in the axial direction of the substantially hexagonal cylinder. Accordingly, the radioactive contaminant container 1 can be lifted, transported and installed with a good balance. Furthermore, when a partition is disposed in the storing space of the radioactive contaminant container 1, it is possible to fix the handle to the partition in order to prevent falling of the radioactive contaminant container 1. As an example, the shape of the handle is a U-shape, but without being limited thereto, may be any shape if the wire rope can be attached thereto. It is preferable that the height width of the handle be configured so as not to interfere with the fitting to the other radioactive contaminant container 1 when stacking the radioactive contaminant containers 1 on one another. |
|
summary | ||
abstract | Systems and methods for assessing the quality of a digital slide image. In an embodiment, the digital slide image is divided into a plurality of image regions. For each of a subset of the plurality of image regions, a quality of the image region is determined based on a determined spatial frequency of the image region. In addition, a visual depiction of the digital slide image may be generated that, for each of the subset of the plurality of image regions, indicates the determined quality of that image region. |
|
summary | ||
description | The present invention relates to thermonuclear fusion; the process of producing energy by fusing lighter elements into heaver elements. More particularly the present invention relates to a device configured to create an environment in which thermonuclear fusion may occur using two opposing cathodes, separated by a gap, with an anode positioned outside the gap. The invention, in operation, forms and contains a plasma in which fusion may occur. Thermonuclear fusion produces energy by fusing lighter elements into heaver elements. The mass of the new element is lighter than the two original nuclei; the difference in mass is converted to energy E=mc2. At this time a useful thermonuclear fusion reactor that can satisfy Lawson's criterion has not been built because of the technical difficulties and inefficiencies of the current designs being pursued. There are currently two main types of fusion reactors being explored: Tokamaks and Inertial Confinement Fusion. Tokamaks are a toroidal reactor used in thermonuclear experiments, in which a strong helical magnetic field keeps the plasma from contacting the external walls. The magnetic field is produced partly by current-carrying coils and partly by a large inductively driven current through the plasma. These devices that create a torus shaped magnetic field are difficult and expensive to build and maintain and as of yet, is not a useful fusion reactor. Inertial confinement fusion (ICF) is a type of fusion energy research that attempts to initiate nuclear fusion reactions by heating and compressing a fuel target, typically in the form of a pellet that most often contains a mixture of deuterium and tritium. The fuel pellet is then hit from multiple directions with lasers compressing and heating the fuel and initiating fusion. At this time ICF has had only minor success. Both tokamaks and ICF systems use considerable energy just to create and maintain the environment for fusion to occur. Both “machines” are extremely expensive and difficult to build and are as of yet, not useful. Therefore, what is needed is a device that may more efficiently create, contain, and maintain plasma in which a fusion reaction may occur. The subject matter of this application may involve, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of a single system or article. In one aspect, a device and system for the creation and containment of plasma is provided. The device has a chamber defining its primary structure. The chamber defines an interior volume and surrounds this volume. During operation, at least a partial vacuum is drawn on the chamber interior volume. Two cathodes are positioned within the volume of the chamber. The two cathodes each comprise an electrode end to which an electricity source may be connected, a quantity of ceramic insulation along a length of the two cathodes, and a cathode tip comprising an exposed portion of metal, typically tungsten. The cathode tip is in electrical communication with the electrode end by a conductor passing through the insulation. The cathode tips are arranged facing each other and separated by a gap. An anode is positioned within the chamber, outside of the gap separating the two cathode tips. Further, a fuel source is configured to provide a quantity of ions, or material to be ionized, within the volume. In some aspects, an interior wall of the chamber adjacent to the interior volume is configured to have a positive charge to operate as a secondary anode. This configuration may aid in the containment of plasma generated during the device's operation. An electricity source is connected to the two cathodes and the anode. When an electric current is applied, the system is configured to hold a quantity of ions in an orbital path about the two cathodes separated by the gap at temperatures such that the ions form a plasma. The system is similarly configured to heat the ions sufficiently to form the plasma by the same application of electric current. A video showing an embodiment of the present invention in use can be seen on YouTube at: https://www.youtube.com/watch?v=t1_4Nc4-IX4. In another aspect, under the appropriate electrical application quantities and fuel usage (deuterium and/or tritium), thermonuclear fusion may be achieved using this device. The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention and does not represent the only forms in which the present invention may be constructed and/or utilized. The description sets forth the functions and the sequence of steps for constructing and operating the invention in connection with the illustrated embodiments. Generally, the present invention concerns a device for creating an environment in which fusion can occur. In its most basic embodiment, the present invention comprises two opposing cathodes separated from each other by a gap. An anode is positioned outside of the gap on a horizontal plane from the vertically positioned cathodes. This cathode and anode structure is positioned within a chamber with a vacuum drawn. Into the chamber, a quantity of fuel such as hydrogen, deuterium, and/or tritium fuel may be introduced. In a particular embodiment, a fuel source may inject this material into the chamber at a controlled rate selected based on desired reaction rate and operational conditions. In a further embodiment, walls of the enclosing chamber may be used as an anode, thereby providing additional assistance in confinement of the plasma. The cathodes contemplated herein may be any structure capable of conducting a negative charge. In a particular embodiment, the cathodes may each be a tungsten electrode insulated with an aluminum oxide ceramic. While placement of the cathodes within the chamber may vary, in many embodiments, the cathodes are positioned approximately within the center of the chamber. Further, the cathodes may be parallel and aligned with each other in some embodiments. The fuel for a fusion embodiment of the present invention will be hydrogen, deuterium, and/or tritium, introduced into the chamber. In one embodiment, the fuel may be pre-ionized. In other embodiments, other gasses and ionized elements and compounds may be used without straying from the scope of the present invention. In these embodiments, plasma may be created using various materials to, for example, generate lighting, heating, and the like. Upon the application of a current to the electrode configuration discussed above, the two cathodes, from a distance, create a virtual point charge that attracts positively charged ions. The current applied may vary depending on application. Typically the voltages and current applied to the two cathodes will be the same, in different embodiments it may be different between the two cathodes. In another embodiment, the voltage and/or current may be oscillated or varied during a usage to, for example, assist in heating and/or controlling plasma. Further, these cathodes may be electrically bonded in one embodiment, and may be electrically isolated from one another in another embodiment. In one embodiment, the applied voltage will be 15 kv or greater. During application of the voltage, positively charged ions are accelerated towards the negatively charged electric field created by the cathode. At a distance relative to the ion, the two cathodes appear as a single point charge. In the case of positively charged particles, which are used in the present invention, the force on these charged particles due to the electric field is directed parallel to the electric field vector, and does not depend on the velocity of the particle. As ions accelerate towards both cathodes, their combined influence appears as a single point charge. As ions get close, their combined attraction causes them to pass between the cathodes without colliding into the cathodes. In fact, there is a point between the cathodes that the combined influence on the positively charged ions is in equilibrium and the ions drift between the two cathodes. After a period of operation, the majority of these ions will pass through this equilibrium and between the cathodes. Ions having passed between the cathodes are influenced by the cathodes' attractive negative charge combined with interactions in the ion cloud impart an angular momentum to the ions causing them to enter an orbit around and between the cathodes. Additional plasma heating may be accomplished by pulsing or oscillating the DC voltage or other external means. In other embodiments, additional cathodes may be used and positioned about the gap. For example, cathodes in other planes from the primary two may be utilized to provide additional orbiting guidance. In a particular embodiment, four cathodes may be used, two in one plane, and two in a perpendicular plane. As ions heat through friction and/or other external means, their orbits become larger, reducing the probability of colliding with the cathodes. Voltages and/or current may be varied or oscillated during operation to assist heating of the plasma. Similarly, the gap between the electrodes may be adjusted. All of this adjustment may be performed automatically using a computerized control system coupled with one or a plurality of sensors, such as a temperature sensor, optical sensor, electrical flow and current sensors, and the like. During experiments, dense plasma clouds have been observed, having coherent stable plasma structures. In a thermonuclear fusion embodiment, collisions between deuterium and tritium require a temperature of approximately 40 million kelvin to overcome the Coulomb barrier to fuse and release energy. Collisions fusing deuterium and tritium will release an energy of 17.6 MeV. As is known, for every volt that an ion of +/−1 charge is accelerated across, it gains 11,604 kelvin in temperature. In a particular example of a magnetic confinement fusion plasma is 15 KeV, or approximately 174 mega-kelvin is generated. Accordingly, an ion with a charge of +/−1 can reach this temperature by being accelerated across a fifteen thousand volt drop. As such, using the present invention and appropriate voltage, a plasma may be created. In some instances, using necessary voltage and appropriate fuel (deuterium or tritium) thermonuclear fusion may be acheived. A particular embodiment of the present invention was constructed for testing purposes. In this embodiment, two 15 kV transformers were connected to two bridge rectifiers in series, which in turn were connected to a capacitor bank. The anode and two cathodes were connected to these capacitor banks to provide an electrical current to the system. This configuration is capable of providing 15 kV direct current between the anode and two cathodes. The anode and cathodes are positioned within a chamber, and a vacuum is drawn thereon using a vacuum pump. The cathodes are selected to be 1/16″ insulated tungsten electrodes. Turning now to FIG. 1, a view of an embodiment of the present invention is provided. An anode a and two cathodes b are positioned within a chamber j, which contains a volume of deuterium and/or tritium fuel, provided by fuel source k, shown in FIG. 3. The two cathodes b are positioned across from each other, having a gap f in between. The anode a is positioned outside of this gap f. In varying embodiments, gap f may be either adjustable, or fixed. Insulation e about the cathodes b restricts the flow of current to the electrode tip d of the cathodes b from source of electricity l, shown in FIG. 3. In a further embodiment, walls enclosing the chamber j may be used as a primary or secondary anode by having a positive charge. This additional charging of the walls of the chamber facilitate a three dimensional containment of the plasma created when voltage is applied to the system. FIG. 2 shows a frontal view of an embodiment of the cathode b. The exposed electrode tip c can be seen surrounded by insulation e. FIG. 3 provides a view of an embodiment of the invention in use, showing an ion path. This figure shows a hypothetical path g of an ion accelerating from anode to cathode without the influence of an opposing cathode. This path demonstrates how the system would work without the second cathode b. As can be seen, the ion's path directly connects anode a and cathode b. Path h however shows a view of the ion path in of the present invention when current is applied. Specifically, path h shows a path of an ion i from anode a to the electric field generated by opposing cathodes b. The combined influence of opposing cathodes b causes the ions i to pass between the two cathodes and enter an orbit around them. In some embodiments, when enough of these ions in orbit about the cathodes b can generate sufficient energy densities in a plasma to achieve thermonuclear fusion. Further, with an increased ion density collisions between the ions further increase the temperature of the plasma. In operation of the present invention, initially an arc may be created between anode and cathode to create the plasma. However, once this plasma is created, the plasma cloud is held in place orbiting about the two central cathodes. It should be understood that in some embodiments, more than one anode and more than two cathodes may be used, in various configurations, to produce different electric fields and plasma structures. In some embodiments, multiple anodes and cathodes may be utilized for some three-dimensional plasma confinement shapes. Regardless of cathode and anode orientation however, the concept of the present invention remains the same: a gap is created between two or more cathodes, and one or more anode is positioned outside of that gap, causing ions to orbit between and around cathodes. In some embodiments, the device may also generate different types of electromagnetic radiation depending on the type of gasses used such as neon, sodium, xenon, or other reactive gas. Such embodiments can be used as a usable light source, or may be positioned between mirrors to produce electromagnetic radiation for a laser. In some further embodiments, some or all of this excess energy generated as electromagnetic radiation may be used productively in a power embodiment using photo-voltaic cells and the like. Accordingly, it can be seen that the present invention provides a number of distinct advantages over the prior art. For example, the present invention utilized the power consumed by the device to simultaneously and directly hold and heat the plasma, increasing efficiency and limiting energy loss. Further, mechanical pressure may be applied to the fuel to increase ion densities so long as a corresponding voltage increase is applied. Scale up of the present invention may be very straightforward because there is no theoretical limit as to how much current can be used in the device. Further, compared to the complex solutions and attempts at solutions of the prior art, the present invention is comparatively simple and inexpensive to construct and maintain. The production of energy from hydrogen fusion has the potential to benefit humanity. It produces little to no pollution. The fuel is easily obtained and essentially limitless. It can break dependency on fossil based fuels, and the corresponding dependence on countries that control fossil fuel production. Further, it has the potential to slow man-made climate change and benefit economic development. While several variations of the present invention have been illustrated by way of example in preferred or particular embodiments, it is apparent that further embodiments could be developed within the spirit and scope of the present invention, or the inventive concept thereof. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention, and are inclusive, but not limited to the following appended claims as set forth. |
|
abstract | A heel effect compensation filter is configured to have a thickness distribution that uniforms an X-ray intensity angular distribution that is nonuniform in the body axis direction of a subject in an X-ray flux irradiated space. The space is formed by an X-ray flux diverging from an anode in a body width direction of the subject and diverging in a shape of an approximate sector in the body axis direction due to the heel effect, when the X-ray flux generated on the anode by irradiating a thermoelectron beam flux from a cathode to the anode is irradiated on the subject. The thickness distribution can be obtained using a predetermined formula. |
|
summary | ||
abstract | An integrated circuit vehicle diagnostics interface adapter includes a semiconductor substrate with two integral gateway conductors. A set of paired switches on the substrate link any two of a first set of contacts to the gateway conductors, and another set of paired switches on the substrate link the two gateway conductors to any pair of a second set of contacts corresponding to a particular vehicle network communications protocol circuit in a vehicle diagnostics device. Both sets of switches are controlled by an integrated switch control module. |
|
description | The present application is a continuation of co-pending U.S. patent application Ser. No. 11/897,644, filed on Aug. 31, 2007, entitled Gas Management System For A Laser Produced Plasma EUV Light Source, the disclosure of which is hereby incorporated by reference. The present application is related to co-pending U.S. patent application Ser. No. 11/358,992 filed on Feb. 21, 2006, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, co-pending U.S. patent application Ser. No. 11/827,803 filed on Jul. 13, 2007, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE HAVING A DROPLET STREAM PRODUCED USING A MODULATED DISTURBANCE WAVE, co-pending U.S. patent application Ser. No. 11/786,145 filed on Apr. 10, 2007, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, co-pending U.S. patent application Ser. No. 11/107,535 filed on Apr. 14, 2005, entitled EXTREME ULTRAVIOLET LIGHT SOURCE, which is a continuation of U.S. patent application Ser. No. 10/409,254 filed on Apr. 8, 2003, entitled EXTREME ULTRAVIOLET LIGHT SOURCE, co-pending U.S. patent application Ser. No. 11/358,988 filed on Feb. 21, 2006, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE WITH PRE-PULSE, co-pending U.S. patent application Ser. No. 11/067,124 filed on Feb. 25, 2005, entitled METHOD AND APPARATUS FOR EUV PLASMA SOURCE TARGET DELIVERY, co-pending U.S. patent application Ser. No. 11/174,443 filed on Jun. 29, 2005, entitled LPP EUV PLASMA SOURCE MATERIAL TARGET DELIVERY SYSTEM, co-pending U.S. SOURCE MATERIAL DISPENSER FOR EUV LIGHT SOURCE, co-pending U.S. patent application Ser. No. 11/358,992 filed on Feb. 21, 2006, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, co-pending U.S. patent application Ser. No. 11/174,299 filed on Jun. 29, 2005, and entitled, LPP EUV LIGHT SOURCE DRIVE LASER SYSTEM, co-pending U.S. patent application Ser. No. 11/406,216 filed on Apr. 17, 2006 entitled ALTERNATIVE FUELS FOR EUV LIGHT SOURCE, co-pending U.S. patent application Ser. No. 11/580,414 filed on Oct. 13, 2006 entitled, DRIVE LASER DELIVERY SYSTEMS FOR EUV LIGHT SOURCE, and co-pending U.S. patent application Ser. No. 11/644,153 filed on Dec. 22, 2006 entitled, LASER PRODUCED PLASMA EUV IGHT SOURCE, co-pending U.S. patent application Ser. No. 11/505,177 filed on Aug. 16, 2006, entitled EUV OPTICS, co-pending U.S. patent application Ser. No. /452,501 filed on Jun. 14, 2006 entitled DRIVE LASER FOR EUV LIGHT SOURCE, co-pending U.S. Pat. No. 6,928,093, issued to Webb, et al. on Aug. 9, 2005, entitled LONG DELAY AND HIGH TIS PULSE STRETCHER, U.S. application Ser. No. 11/394,512, filed on Mar. 31, 2006 and titled CONFOCAL PULSE STRETCHER, U.S. application Ser. No. 11/138,001 filed on May 26, 2005 and titled SYSTEMS AND METHODS FOR IMPLEMENTING AN INTERACTION BETWEEN A LASER SHAPED AS A LINE BEAM AND A FILM DEPOSITED ON A SUBSTRATE, and U.S. application Ser. No. 10/141,216, filed on May 7, 2002, now U.S. Pat. No. 6,693,939, and titled, LASER LITHOGRAPHY LIGHT SOURCE WITH BEAM DELIVERY, U.S. Pat. No. 6,625,191 issued to Knowles et al on Sep. 23, 2003 entitled VERY NARROW BAND, TWO CHAMBER, HIGH REP RATE GAS DISCHARGE LASER SYSTEM, U.S. application Ser. No. 10/012,002, U.S. Pat. No. 6,549,551 issued to Ness et al on Apr. 15, 2003 entitled INJECTION SEEDED LASER WITH PRECISE TIMING CONTROL, U.S. application Ser. No. 09/848,043, and U.S. Pat. No. 6,567,450 issued to Myers et al on May 20, 2003 entitled VERY NAROW BAND, TWO CHAMBER, HIGH REP RATE GAS DISCHARGE LASER SYSTEM, U.S. application Ser. No. 09/943,343, co-pending U.S. patent application Ser. No. 11/509,925 filed on Aug. 25, 2006, entitled SOURCE MATERIAL COLLECTION UNIT FOR A LASER PRODUCED PLASMA EUV LIGHT SOURCE, the entire contents of each of which are hereby incorporated by reference herein. The present disclosure relates to extreme ultraviolet (“EUV”) light sources which provide EUV light from a plasma that is created from a target material and collected and directed to an intermediate region for utilization outside of the EUV light source chamber, e.g. by a lithography scanner/stepper. Extreme ultraviolet light, e.g., electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13.5 nm, can be used in photolithography processes to produce extremely small features in substrates, e.g., silicon wafers. Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has at least one element, e.g., xenon, lithium or tin, with one or more emission lines in the EUV range. In one such method, often termed laser produced plasma (“LPP”) the required plasma can be produced by irradiating a target material, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam. One particular LPP technique involves irradiating a target material droplet with one or more high energy pulses. In this regard, CO2 lasers may present certain advantages as a drive laser producing high energy pulses in an LPP process. This may be especially true for certain target materials such as molten tin droplets. For example, one advantage may include the ability to produce a relatively high conversion efficiency e.g., the ratio of output EUV in-band power to drive laser input power. In more theoretical terms, LPP light sources generate EUV radiation by depositing laser energy into a source element, such as xenon (Xe), tin (Sn) or lithium (Li), creating a highly ionized plasma with electron temperatures of several 10's of eV. The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma in all directions. In one common arrangement, a near-normal-incidence mirror (often termed a “collector mirror”) is positioned at a distance from the plasma to collect, direct (and in some arrangements, focus) the light to an intermediate location, e.g., focal point. The collected light may then be relayed from the intermediate location to a set of scanner optics and ultimately to a wafer. In a typical setup, the EUV light must travel within the light source about 1-2 m from the plasma to the intermediate location, and as a consequence, it may be advantageous, in certain circumstances, to limit the atmosphere in the light source chamber to gases having relatively low absorptance of in-band EUV light. For EUV light sources designed for use in high volume manufacturing (HVM) environments, e.g. exposing 100 wafers per hour or more, the lifetime of the collector mirror can be a critical parameter affecting efficiency, downtime, and ultimately, cost. During operation, debris are generated as a by-product of the plasma which can degrade the collector mirror surface. These debris can be in the form of high-energy ions, neutral atoms and clusters of target material. Of these three types of debris, the most hazardous for the collector mirror coating is typically the ion flux. Generally, for the configuration described above, the amount of neutral atoms and clusters from the droplet target impinging onto the collector may be small since most of the target material moves in a direction pointing away from the collector surface, (i.e., in the direction of the laser beam). In the absence of debris mitigation and/or collector cleaning techniques, the deposition of target materials and contaminants, as well as sputtering of the collector multilayer coating and implantation of incident particles can reduce the reflectivity of the mirror substantially. In this regard, co-pending, co-owned U.S. patent application Ser. No. 11/786,145 filed on Apr. 10, 2007, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, discloses a device in which a flowing buffer gas such as hydrogen at pressures at or above about 100 mTorr is used in the chamber to slow ions in the plasma to below about 30 eV before the ions reach the collector mirror, which is typically located about 15 cm from the plasma. It is currently envisioned that about 100 W of EUV power, or more, will need to be delivered to a scanner/stepper to allow for efficient high volume EUV photolithography. To obtain this output power, a 5-20 kW drive laser, e.g. CO2 laser, may be used to irradiate a source material such as a stream of tin droplets. Of the 5-20 kW of power delivered within the EUV light source chamber, calculations indicate that about 20%-80% of this power may be transferred to a buffer gas in the chamber. With the above, in mind, Applicants disclose a Gas Management System for a Laser-Produced-Plasma EUV Light Source, and corresponding methods of use. In a first aspect, a device is described herein which may comprise an enclosing structure defining a closed loop flow path; a system generating a plasma at a plasma site, the site being in fluid communication with the flow path; a gas disposed in the enclosing structure; a pump forcing the gas through the closed loop flow path; a heat exchanger removing heat from gas flowing in the flow path; and a filter removing at least a portion of a target species from gas flowing in the flow path. In one application of this aspect, the plasma may comprise tin and the filter may remove a compound selected from the group of compounds comprising tin hydrides, tin oxides, tin bromides and combinations thereof. In one embodiment of this aspect, the enclosing structure may be formed with an inlet and an outlet, and the device may further comprise a gas source connected to the inlet and a conditioner connected to the outlet to condition gas exiting the enclosing structure, the conditioner being selected from the group of conditioners consisting of a gas dilution mechanism, a scrubber or a combination thereof. In one implementation of this aspect, the enclosing structure may comprise a vessel in fluid communication with a guideway, the guideway being external to the vessel. In another aspect, a device is described herein which may comprise an EUV reflective optic formed with a through-hole; an enclosing structure defining a closed loop flow path passing through the through-hole; a system generating a plasma at a plasma site, the site being in fluid communication with the flow path; a gas disposed in the enclosing structure; and a pump forcing the gas through the closed loop flow path. In one implementation of this aspect, the enclosing structure may comprise a vessel in fluid communication with a guideway, the guideway being external to the vessel. In one embodiment of this aspect, the device may further comprise a gas flow restriction member establishing first and second compartments in the vessel, the closed-loop flow path extending from the first compartment through the through-hole formed in the optic to the second compartment, and in a particular embodiment, the optic may be formed with an edge, the vessel may formed with a vessel wall and the restriction member may be disposed between the collector edge and vessel wall to restrict flow therebetween. In one arrangement of this aspect, the gas may pass through a temperature controlled, multi-channel structure prior to reaching the pump. In another aspect, a device is described herein which may comprise an enclosing structure; a system generating a plasma producing EUV radiation at a plasma site in the enclosing structure and releasing at least 5 kW of power into the chamber; a gas disposed in the chamber at a pressure exceeding 100 mTorr at at least one location in the enclosing structure; and a closed-loop circulation system circulating gas through the enclosing structure, the circulation system including at least one heat exchanger cooling the gas on each pass through the loop. In one implementation of this aspect, the gas may flow through the closed-loop circulation system at an average flow rate greater than 50 standard liters per minute. In one embodiment of this aspect, the enclosing structure may comprise a vessel and the heat exchanger may be positioned in the vessel. In one arrangement of this aspect, the heat exchanger may be a temperature controlled, multi-channel structure. In one embodiment of this aspect, the closed-loop circulation system may maintain an average gas temperature of less than 1000 degrees Celsius in the system. In another aspect, a device is described herein which may comprise an enclosing structure; a system generating a plasma at a plasma site in the enclosing structure, the plasma producing EUV radiation and ions exiting the plasma; an optic distanced from the site by a distance, d; a gas disposed between the plasma and optic, the gas establishing a gas number density sufficient to operate over the distance, d, to reduce ion energy below 100 eV before the ions reach the optic; and a closed-loop circulation system circulating gas through the enclosing structure, the circulation system including at least one heat exchanger removing heat from gas flowing through the loop. In one implementation of this aspect, the optic may direct EUV radiation to an intermediate location and the device may further comprise a multi-channel structure disposed between the plasma site and the intermediate location. In one embodiment of this aspect, the gas may comprise greater than 50 percent hydrogen by volume. In one arrangement of this aspect, the gas may comprise an etchant gas selected from the group of etchant gases consisting of HBr, HI, Br2, Cl2, HCl, or combinations thereof. In one embodiment of this aspect, the gas may establish a gas number density, n, sufficient to operate over the distance, d, to reduce ion energy below 30 eV before the ions reach the optic. In one arrangement of this aspect, the system may comprise a droplet generator providing droplets, the droplets comprising tin, and a laser illuminating droplets to create the plasma, the laser comprising a gain medium comprising CO2. With initial reference to FIG. 1 there is shown a schematic view of an EUV light source, e.g., a laser produced plasma EUV light source 20 according to one aspect of an embodiment. As shown in FIG. 1, and described in further detail below, the LPP light source 20 may include a system 22 for generating a train of light pulses and delivering the light pulses into a chamber 26. For the source 20, the light pulses may travel along one or more beam paths from the system 22 and into the chamber 26 to illuminate one or more targets at an irradiation region 28. Suitable lasers for use in the device 22 shown in FIG. 1 may include a pulsed laser device, e.g., a pulsed gas discharge CO2 laser device producing radiation at 9.3 μm, 9.6 μm or 10.6 μm, e.g., with DC or RF excitation, operating at relatively high power, e.g., 10 kW or higher and high pulse repetition rate, e.g., 50 kHz or more. In one particular implementation, the laser may have a MOPA configuration with multiple stages of axial-flow RF-pumped CO2 amplification and having a seed pulse that is initiated by a Q-switched Master Oscillator (MO) with low energy and high repetition rate, e.g., capable of 50 kHz operation. From the MO, the laser pulse may then be amplified, shaped, and/or focused before entering the LPP chamber. Continuously pumped CO2 amplifiers may be used for the system 22. For example, a suitable CO2 laser device having an oscillator and three amplifiers (O-PA1-PA2-PA3 configuration) is disclosed in co-pending U.S. patent application Ser. No. 11/174,299 filed on Jun. 29, 2005, and entitled, LPP EUV LIGHT SOURCE DRIVE LASER SYSTEM, the entire contents of which are hereby incorporated by reference herein. Depending on the specific application, other types of lasers may also be suitable, e.g., an excimer or molecular fluorine laser operating at high power and high pulse repetition rate. Examples include, a solid state laser, e.g., having a fiber or disk shaped active media, a MOPA configured excimer laser system, e.g., as shown in U.S. Pat. Nos. 6,625,191, 6,549,551, and 6,567,450, an excimer laser having one or more chambers, e.g., an oscillator chamber and one or more amplifying chambers (with the amplifying chambers in parallel or in series), a master oscillator/power oscillator (MOPO) arrangement, a power oscillator/power amplifier (DOPA) arrangement, or a solid state laser that seeds one or more excimer or molecular fluorine amplifier or oscillator chambers, may be suitable. Other designs are possible. As further shown in FIG. 1, the EUV light source 20 may also include a target material delivery system 90, e.g., delivering droplets of a target material into the interior of a chamber 26 to the irradiation region 28 where the droplets will interact with one or more light pulses, e.g., zero, one or more pre-pulses and thereafter one or more main pulses, to ultimately produce a plasma and generate an EUV emission. The target material may include, but is not necessarily limited to, a material that includes tin, lithium, xenon or combinations thereof. The EUV emitting element, e.g., tin, lithium, xenon, etc., may be in the form of liquid droplets and/or solid particles contained within liquid droplets or any other form which delivers the EUV emitting element to the irradiation region 28 in discrete, semi-continuous and/or continuous amounts. For example, the element tin may be used as pure tin, as a tin compound, e.g., SnBr4, SnBr2, SnH4, as a tin alloy, e.g., tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or a combination thereof. Depending on the material used, the target material may be presented to the irradiation region 28 at various temperatures including room temperature or near room temperature (e.g., tin alloys, SnBr4) at an elevated temperature, (e.g., pure tin) or at temperatures below room temperature, (e.g., SnH4), and in some cases, can be relatively volatile, e.g., SnBr4. More details concerning the use of these materials in an LPP EUV source is provided in co-pending U.S. patent application Ser. No. 11/406,216 filed on Apr. 17, 2006 entitled ALTERNATIVE FUELS FOR EUV LIGHT SOURCE, the contents of which are hereby incorporated by reference herein. Continuing with FIG. 1, the EUV light source 20 may also include an optic 30, e.g., a collector mirror in the form of a truncated ellipsoid having, e.g., a graded multi-layer coating with alternating layers of Molybdenum and Silicon on a substrate, e.g. SiC, polycrystalline Si, single crystal Si, etc. FIG. 1 shows that the optic 30 may be formed with a through-hole to allow the light pulses generated by the system 22 to pass through the optic 30 to reach the irradiation region 28. As shown, the optic 30 may be, e.g., an ellipsoidal mirror that has a first focus within or near the irradiation region 28 and a second focus at a so-called intermediate region 40 where the EUV light may be output from the EUV light source 20 and input to a device utilizing EUV light, e.g., an integrated circuit lithography tool (not shown in FIG. 1). Also shown, the optic 30 may be positioned such that the closest operable point on the optic 30 is located at a distance, d from the irradiation region 28. It is to be appreciated that other optics may be used in place of the ellipsoidal mirror for collecting and directing light to an intermediate location for subsequent delivery to a device utilizing EUV light, for example the optic may be parabolic or may be configured to deliver a beam having a ring-shaped cross-section to an intermediate location, see e.g. co-pending U.S. patent application Ser. No. 11/505,177 filed on Aug. 16, 2006, entitled EUV OPTICS, the contents of which are hereby incorporated by reference. For the device 20, a temperature control system may be used to maintain the optic 20 within a pre-selected operational temperature range. The temperature control system may include heating, e.g. one or more ohmic heaters placed on the collector mirror substrate backside, and/or cooling, e.g. one or more cooling channels formed in the collector mirror substrate to pass a heat exchange fluid, e.g. water or liquid gallium. As used herein, the term “optic” and its derivatives includes, but is not necessarily limited to, components which reflect and/or transmit and/or operate on incident light and includes, but is not limited to, lenses, windows, filters, wedges, prisms, grisms, gradings, etalons, diffusers, transmission fibers, detectors and other instrument components, apertures, stops and mirrors including multi-layer mirrors, near-normal incidence mirrors, grazing incidence mirrors, specular reflectors and diffuse reflectors. Moreover, as used herein, the term “optic” and its derivatives is not meant to be limited to components which operate solely or to advantage within one or more specific wavelength range(s) such as at the EUV output light wavelength, the irradiation laser wavelength, a wavelength suitable for metrology or any other particular wavelength or wavelength band. Continuing with reference to FIG. 1, the EUV light source 20 may also include an EUV controller 60, which may also include a drive laser control system 65 for triggering one or more lamps and/or laser devices in the system 22 to thereby generate light pulses for delivery into the chamber 26, and/or for controlling beam delivery, e.g. optics moveable via actuator to adjust beam focusing, beam steering, beam shape, etc. A suitable beam delivery system for pulse shaping, focusing, steering and/or adjusting the focal power of the pulses is disclosed in co-pending U.S. patent application Ser. No. 11/358,992 filed on Feb. 21, 2006, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, the contents of which are hereby incorporated by reference herein. As disclosed therein, one or more beam delivery system optics may be in fluid communication with the chamber 26. Pulse shaping may include adjusting pulse duration, using, for example a pulse stretcher and/or pulse trimming. The EUV light source 20 may also include a droplet position detection system which may include one or more droplet imagers 70 that provide an output indicative of the position of one or more droplets, e.g., relative to the irradiation region 28. The imager(s) 70 may provide this output to a droplet position detection feedback system 62, which can, e.g., compute a droplet position and trajectory, from which a droplet error can be computed, e.g., on a droplet by droplet basis or on average. The droplet error may then be provided as an input to the controller 60, which can, for example, provide a position, direction and/or timing correction signal to the system 22 to control a source timing circuit and/or to control a beam position and shaping system, e.g., to change the location and/or focal power of the light pulses being delivered to the irradiation region 28 in the chamber 26. Also for the EUV light source 20, the target material delivery system 90 may have a control system operable in response to a signal (which in some implementations may include the droplet error described above, or some quantity derived therefrom) from the controller 60, to e.g., modify the release point, release timing and/or droplet modulation to correct for errors in the droplets arriving at the desired irradiation region 28. For the EUV light source 20, the droplet delivery mechanism may include, for example, a droplet dispenser creating either 1) one or more streams of droplets exiting the dispenser or 2) one or more continuous streams which exit the dispenser and subsequently break into droplets due to surface tension. In either case, droplets may be generated and delivered to the irradiation region 28 such that one or more droplets may simultaneously reside in the irradiation region 28 allowing one or more droplets to be simultaneously irradiated by an initial pulse, e.g., pre-pulse to form an expanded target suitable for exposure to one or more subsequent laser pulse(s), e.g., main pulse(s), to generate an EUV emission. In one embodiment, a multi-orifice dispenser may be used to create a “showerhead-type” effect. In general, for the EUV light source 20, the droplet dispenser may be modulating or non-modulating and may include one or several orifice(s) through which target material is passed to create one or more droplet streams. More details regarding the dispensers described above and their relative advantages may be found in co-pending U.S. patent application Ser. No. 11/358,988 filed on Feb. 21, 2006, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE WITH PRE-PULSE, co-pending U.S. patent application Ser. No. 11/067,124 filed on Feb. 25, 2005, entitled METHOD AND APPARATUS FOR EUV PLASMA SOURCE TARGET DELIVERY, and co-pending U.S. patent application Ser. No. 11/174,443 filed on Jun. 29, 2005, entitled LPP EUV PLASMA SOURCE MATERIAL TARGET DELIVERY SYSTEM, co-pending U.S. patent application Ser. No. 11/827,803 filed on Jul. 13, 2007, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE HAVING A DROPLET STREAM PRODUCED USING A MODULATED DISTURBANCE WAVE, the contents of each of which are hereby incorporated by reference herein. The EUV light source 20 may include one or more EUV metrology instruments (not shown) for measuring various properties of the EUV light generated by the source 20. These properties may include, for example, intensity (e.g., total intensity or intensity within a particular spectral band), spectral bandwidth, polarization, etc. For the EUV light source 20, the instrument(s) may be configured to operate while the downstream tool, e.g., photolithography scanner, is on-line, e.g., by sampling a portion of the EUV output, e.g., using a pickoff mirror or sampling “uncollected” EUV light, and/or may operate while the downstream tool, e.g., photolithography scanner, is off-line, for example, by measuring the entire EUV output of the EUV light source 20. As indicated above, irradiation of a target at the irradiation region 28 produces a plasma and generates an EUV emission. In addition, as a by-product of this process, ions may be generated which exit the plasma, typically, in all directions. Generally, the ion's initial energy exiting the plasma will vary over a range, with the range being affected by a number of factors including, but not limited to, the wavelength, energy, intensity and pulse-shape of the irradiating light, and the composition, size, shape and form of the target material. Also indicated above, these ions may, if unabated, degrade nearby optics, such as mirrors, laser input windows, metrology windows, filters, etc. FIG. 1 shows that a flowing gas may be disposed between the plasma (irradiation region 28) and optic, the gas establishing a gas number density, n, (i.e. number of molecules/volume) sufficient to operate over the distance, d, to reduce ion energy to a target maximum energy level before the ions reach the optic. For example, a gas number density sufficient to reduce ion energy to a target maximum energy level between about 10-200 eV, and in some cases below 30 eV may be provided. For operation of the device shown in FIG. 1, it is contemplated that the flowing gas establishing a target gas number density over the distance, d, will be present, and flowing, during EUV light generation. Factors which may be considered in selecting a suitable gas composition and gas number density include the ion stopping power of the gas composition (e.g. slowing ions below about 30 eV over a distance of about 10-30 cm) and the EUV absorption of the gas as a function of number density (e.g. providing an acceptable in-band EUV absorption over a distance of about 1-2 m as the EUV light travels from the plasma to the collector mirror and then on to the intermediate region 40. Suitable gases may, depending on the specific application, include hydrogen e.g., greater than 50 percent hydrogen (protium and/or deuterium isotopes), helium and combinations thereof. For example, for a plasma generating ions having a maximum initial ion energy and distance, d, of about 15 cm from the plasma, a suitable gas for reducing ion energy below about 30 eV may be hydrogen gas at a pressure of about 500 mtorr at room temperature may be suitable. For some arrangements, pressures in the range of about 500 mtorr to 2000 mtorr may be employed. SRIM (Stopping and Range of Ions in Matter) software (available at www-srim-org website) can be used to determine the gas number density (operable over a given distance, d) that is required to reduce the energy of an ion (having an initial ion energy) to below a selected energy. From the number density, the expected EUV absorption by the gas can be calculated. It is to be further appreciated that gas introduced into the chamber may react with chamber conditions, ions and/or the plasma to dissociate and/or create ions, e.g. atomic hydrogen and/or hydrogen ions which may be effective for cleaning/etching and/or ion slowing. FIG. 1 further shows that the light source 20 may include a gas management system including a regulated gas source 100 for introducing one or more gas(ses) into the chamber 26, an adjustable pump 102 for removing gas from the chamber 26, and an external guideway 104 for establishing a closed loop flow path. FIG. 1 also shows that the light source 20 may include a pump 106 forcing gas through the closed loop flow path, a heat exchanger 108 removing heat from gas flowing in the flow path, and a filter 110 removing at least a portion of a target species, e.g. contaminants, from gas flowing in the flow path. These contaminants may degrade optical components and/or absorb EUV light. A valve 112, regulator(s), or similar device may be provided to meter the amount of gas which is directed to pump 102 or 106. As shown, a conditioner 114 may be provided to dilute and/or scrub the gas prior to release. With this arrangement, a flowing gas may be disposed between the optic 30 and irradiation region 28. Removal of gas from the chamber 26 via pump 102 may be performed to maintain a constant gas pressure in the chamber 26 in response to gas additions from the gas source 100, and/or to remove contaminants, vapor, metal dust, etc. from the chamber 26, and/or to establish a pressure gradient in the chamber 26, e.g. to maintain a relatively large pressure between the optic 28 and irradiation region 28 and a smaller, relatively low pressure between the irradiation region 28 and the intermediate region 40. In addition, pump 106, heat exchanger 108 and filter 110 may cooperate to remove heat and thereby control the temperature within the chamber 26, to control the temperature of the optic 30 and/or to remove contaminants, vapor, metal dust, etc. from the chamber 26 and/or to provide a pressure gradient in the chamber 26, e.g. to maintain a relatively large pressure between the optic 28 and irradiation region 28 and a smaller, relatively low pressure between the irradiation region 28 and the intermediate region 40. Control of the gas source 100 and pumps 102, 106 may be used, concertedly, to maintain a selected gas pressure/pressure gradient and/or to maintain a selected flow rate through the chamber 26 and/or to maintain a selected gas composition, e.g. a selected ratio of several gases, e.g. H2, HBr, He, etc. Typically, the selected flow rate may depend, among other things, on the light source power input to the chamber, the amount of gas mixing, the efficient of the heat exchanger 108 and the efficiency of other component cooling systems, e.g. the collector mirror cooling system. By way of example, for a Sn target and CO2 laser system with the optic 30 positioned about 15 cm from the irradiation site 28, a laser pulse energy of about 500 mJ and an EUV output repetition rate in the range of 10-100 kHz, a flow rate of about 200-400 slm (standard liters per minute) or greater, may be employed. For the light source 20, the gas source 100 may introduce several gases, for example H2, He, Ar and HBr, either separately and independently, or the gas may be introduced as a mixture. Moreover, although FIG. 1 illustrates the gas being introduced at one location, it is to be appreciated that the gas may be introduced at multiple locations, may be removed at multiple locations and/or may be evacuated for circulation at multiple locations. The gas may be supplied via a tank or may be generated locally. For example, the gas source 100 may include an on-demand hydrogen/deuterium generator. Several types are available including a device with extracts hydrogen/deuterium from water/heavy water using a proton exchange membrane. Such a device is marketed and sold by Domnick Hunter under the product name Hydrogen Generator, for example see the www-domnickhunter-com website for details. Depending on the gas used, conditioner 114 may provide an appropriate chemical scrubber, e.g to scrub etchant gas vapors, and/or a source of a diluent gas to dilute the exiting gas prior to release into the atmosphere. For example, when H2 is used (which tends to be explosive at number densities of 4-25%), a diluent gas such as N2, or air may be used to reduce the H2 concentration before release (generally below 4% and more preferably below 0.4%). Alternatively, or in addition to the use of a diluent gas, a catalytic converter, possibly having a Platinum catalyst may be used to convert hydrogen to water. Suitable gases for reducing ion energy may include, but are not limited to, hydrogen (protium and deuterium isotopes), helium and combinations thereof. In addition, a cleaning/etching gas for removing contaminants that have deposited on surfaces of optics may be included such as a gas having a halogen. For example, the etchant gas may include HBr, HI, Br2, Cl2, HCl, or combinations thereof. By way of example, a suitable composition when Sn or a Sn compound is used as the target material may include 50-99% H2 and 1-50% HBr. FIG. 2A shows a calculated plot using SRIM software illustrating that ions having an initial energy of 10 keV are significantly scattered but are not stopped in Argon gas at 50 mTorr over a distance, d, of 200 mm. On the other hand, FIG. 2B shows a calculated plot using SRIM software illustrating that ions having an initial energy of 10 keV have less scattering (compared to FIG. 2A) and may be effectively stopped in Hydrogen gas at 400 mTorr at a distance, d, of about 170 mm. FIG. 3 shows measured plots illustrating ion stopping at three different hydrogen pressures. As shown, in the absence of any stopping gas, e.g. hydrogen, the distribution of ion energies is represented by curve 150 which shows that the maximum initial ion energy is about 3 keV. These ions where generated by irradiating a flat Sn target with CO2 laser pulse at optimal intensity for in-band conversion (e.g. CE ˜4.5%). Measurements were conducted using a Faraday Cup (Model FC-73A from Kimball Physics) positioned about 16.5 cm from the irradiation zone and positioned to receive ions at an angle of about 45 degrees from the input laser beam axis. Curve 152 shows that for ions having an initial maximum ion energy of about 3 keV, maximum ion energy is reduced to about 1.5 keV over a distance, d, of 16.5 cm in uniform, non-flowing Hydrogen gas at 120 mTorr. Curve 154 shows that for ions having an initial maximum ion energy of about 3 keV, maximum ion energy is reduced to about 0.9 keV over a distance, d, of 16.5 cm in uniform, non-flowing Hydrogen gas at 210 mTorr. Curve 156 shows that for ions having an initial maximum ion energy of about 3 keV, maximum ion energy is reduced to about 0.25 keV over a distance, d, of 16.5 cm in uniform, non-flowing Hydrogen gas at 290 mTorr. FIG. 3 also shows calculated EUV transmissions over a 2 m path for the three hydrogen pressures, with Hydrogen gas at 120 mTorr having 96% transmission, Hydrogen gas at 210 mTorr having 93% transmission, and Hydrogen gas at 290 mTorr having 90% transmission. FIG. 4A shows a plot of maximum observed energy versus hydrogen pressure for ions having initial ion energies as shown in curve 150 of FIG. 3 using a Faraday Cup positioned 16.5 cm from the irradiation zone and at an angle of about 45 degrees from the input laser beam axis. FIG. 4B shows a measured normalized in-band EUV signal after passing through a distance of 145 cm as a function of Hydrogen pressure; and ion flux as a function of Hydrogen pressure with ion flux calculated as ∫I(E)dE. FIG. 4C shows a plot of ion range (in cm) as function of gas pressure for various initial ion energies and for Hydrogen and Helium gases as calculated using SRIM simulation software (as described above). The above data demonstrate an ion mitigation technique which may be used to suppress ion flux (i.e., the energy-integrated signal) by at least 4 orders of magnitude with an acceptable level of EUV absorption. In some cases, the collector mirror reflective coating may have about 500 sacrificial layers and still provide full EUV reflectivity. Taking into account a measured erosion rate of 0.2 layers per Million pulses (in the absence of ion mitigation) and the suppression factor of 104 (due to the above-described mitigation), a collector lifetime exceeding 1012 pulses is estimated corresponding to about 1 year of operation of the collector mirror in a high volume manufacturing environment. The use of an ion stopping gas and/or etchant gas(es) as described above, may, depending on the specific application, be used alone or in combination with one or more other ion mitigation techniques such as the use of a foil shield (with or without a slowing or deflecting gas), and the use of an electric and/or magnetic fields) to deflect or slow ions and/or the use of pulse shaping to reduce ion flux, see e.g. co-pending U.S. patent application Ser. No. 11/786,145 filed on Apr. 10, 2007, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, the contents of which are hereby incorporated by reference. FIG. 5 shows the gas management components of a light source 200 having a chamber 26 in which an optic 30 formed with a through-hole is disposed, e.g. a near-normal incidence, ellipsoidal collector mirror for directing EUV light from an irradiation region 28, e.g. where a target material droplet is irradiated by a drive laser (not shown) producing EUV radiation, to an intermediate region 40 for subsequent use by a scanner 202. As shown in FIG. 5, the gas management system may include an enclosing structure defining one or more closed loop flow paths, the enclosing structure having a vessel, e.g. chamber 26, in fluid communication with one or more guideways 204a,b, each guideway 204a,b being external to the chamber 26. Although FIGS. 5 and 5A illustrate a gas management system having four external guideways 204a-d, it is to be appreciated that more than four and as few as one external guideway may be used. Continuing with FIG. 5, it can be seen that within each closed loop flow path, gas is directed through the through-hole formed in the optic 30 and toward the irradiation region 28. From the through-hole, a portion of the gas flows through heat exchanger 206 and into pumps 208a,b. For the optic 30 shown in FIG. 5, the through-hole also functions to pass a laser beam from a laser source (not shown) to the irradiation region 28, although, as discussed below, other through-holes may be used to flow gas through the optic 30. For the source 200 shown, heat exchanger 206 may consist of a plurality of spaced apart, parallel, annularly shaped metal plates, with each plate extending around the circumference of the chamber 26. One, some or all of the plates may be formed with one or more internal passages to pass a heat exchange fluid, e.g. water, to cool each plate. The heat exchanger 206 may function to cool gas flowing through the exchanger 206 and/or to condense target material vapors that may undesirably absorb EUV radiation and/or foul optics, e.g. tin vapor when tin is used as a target material. Once cooled, the gas may pass through pumps 208a,b, which may be, for example, a turbo-pump or a roots-type booster, and thereafter be directed through an external guideway to a location where the gas will, once again flow through the through-hole formed in the optic 30. It is to be appreciated that one or more flow regulators (not shown) may be provided, e.g. one regulator near each pump, to balance flow throughout the gas management system. FIGS. 5 and 5B also show that a portion of the gas from the through-hole may flow within chamber 26 through multi-channel structure 210. As seen there, the multi-channel structure 210 may be disposed between the irradiation location 28 and the intermediate point 40 and may include a plurality of concentric, conical shaped vanes 212 that are arranged to allow light to travel from the optic 30 to the intermediate region 40 and may be designed to minimize EUV light obscuration. In addition, vane location may be selected to correspond to light paths which are unusable by the scanner 202, due, e.g. to obstructions in the scanner. One or more radial members 213 may be provided to support the concentric, conical shaped vanes. FIG. 5C shows another embodiment in which the vanes 212″ consist of flat plates converging toward the intermediate region 40, as shown. A flange 211 may be provided to restrict flow between the wall of the chamber 26 and the multi-channel structure 210, as shown. FIGS. 6 and 7 show an alternative arrangement for a multi-channel structure 210′ which includes a plurality of radially oriented vanes 212′. Alternatively, a multi-channel structure having both concentric conical and radial vanes may be employed. For the multi-channel structures, 210, 210′, 210″ shown in FIGS. 5-7, one, some or all of the vanes may be formed with internal passages to flow a heat exchange fluid, e.g. water or liquid gallium, to cool each vane. The multi-channel structures, 210, 210′, 210″ may function to cool gas flowing through the multi-channel structures, 210, 210′, 210″ and/or to condense target material vapors that may undesirably absorb EUV radiation, e.g. tin vapor when tin is used as a target material and/or to provide significant resistance to gas flow, thus, establishing a pressure gradient in the chamber 26 with a relatively high gas pressure upstream of the multi-channel structures, 210, 210′, 210″, e.g. between the irradiation region 28 and optic 30 to e.g. provide ion stopping and/or etching power, and a relatively low gas pressure downstream of the multi-channel structures, 210, 210′, 210″, e.g. between the multi-channel structures, 210, 210′, 210″ and the intermediate region 40, to e.g. minimize EUV absorption. For the device shown, the multi-channel structures, 210, 210′, 210″ may be positioned to receive source material from irradiation zone 28. As disclosed herein, depending on the specific application, the structure 210, 210′, 210″ may be used alone or in combination with one or more other debris mitigation techniques such as the use of an ion slowing gas as described above, the use of a foil shield (with or without an ion slowing or deflecting gas), the use of an electric and/or magnetic field(s) to deflect or slow ions, and the use of a pulse-shaped beam. A beam stop may be provided which may be separate from, attached to or formed integral with the multi-channel structure 210, 210′, 210″. In the operation of the device, a target material, such as a droplet, is irradiated by one or more pulses to generate plasma. Typically, irradiated target material moves along the beam direction and spreads into a wide solid angle. A large portion of the material may be collected by the multi-channel structure 210, 210′, 210″, which also may be temperature controlled. For example, a temperature controlled beam stop for collecting and directing LPP target material is disclosed and claimed in co-pending U.S. patent application Ser. No. 11/509,925 filed on Aug. 25, 2006, entitled SOURCE MATERIAL COLLECTION UNIT FOR A LASER PRODUCED PLASMA EUV LIGHT SOURCE, the entire contents of which are hereby incorporated by reference herein. See also co-pending U.S. patent application Ser. No. 11/786,145 filed on Apr. 10, 2007, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, the entire contents of which are hereby incorporated by reference herein. By-products of the target material irradiation may include metal dust, target material vapor and micro-droplets or clusters and can be in several forms, for example, when tin, e.g., pure tin, or a tin compound, e.g., SnBr4, SnH4, SnBr2 etc, is used as the source material, the by-products may include tin and tin compounds including oxides. Dusts and other contaminates, e.g., from collector mirror erosion, etc. may also be present in the chamber. These by-products may, among other things, damage optics and absorb/scatter EUV radiation. By way of example, and not limitation, the multi-channel structure 210, 210′, 210″ may function to collected liquids and solids (in some cases remelting solids) and/or condensing vapors. For a target material containing Sn, some or all of the operable surfaces of the multi-channel structure 210, 210′, 210″ may be maintained at a temperature above the melting point of Sn, e.g., above about 230 C. At this temperature, micro-droplets may stick to the surface of the multi-channel structure 210, 210′, 210″, and in some cases, flow downwardly by gravitational force. Solidified metal dust may be re-melted into the molten material and also flow downward. The compounds of Sn (e.g., oxides) may also be trapped by the liquid flow and removed from the chamber. The multi-channel structure 210, 210′, 210″ may have inter-connecting channels (not shown) for directing liquid metal flow from surfaces to the bottom where the liquid metal may be collected. The location and direction of the channels may be configured relative to the EUV source orientation (e.g. the light source axis may be tilted relative to horizontal at about 28 degrees) to ensure proper flow of liquid on the multi-channel structure 210, 210′, 210″. On the other hand, in some applications, some or all of the operable surfaces of the multi-channel structure 210, 210′, 210″ may be maintained at a temperature below the melting point of Sn, e.g., below about 230 C (for a target material containing Sn). At these temperatures, condensation is promoted and liquids and solids may be allowed to accumulate on the multi-channel structure 210, 210′, 210″. The multi-channel structure 210, 210′, 210″ may also function as a cold trap condensing vapors, e.g., Sn vapor present in the chamber. FIG. 5 shows that from the multi-channel structures, 210, gas flows generally in the direction of the intermediate region 40. FIG. 5 also shows that some, a portion, or all of the gas exiting the multi-channel structures, 210 may pass through heat exchanger 214 and into pumps 216a,b. For the source 200 shown, heat exchanger 214 may consist of a plurality of spaced apart, parallel, annularly shaped metal plates that extend around the circumference of the chamber 26. One, some or all of the plates may be formed with one or more internal passages to pass a heat exchange fluid, e.g. water, to cool each plate. The heat exchanger 214 may function to cool gas flowing through the exchanger 214 and/or to condense target material vapors that may undesirably absorb EUV radiation, e.g. tin vapor when tin is used as a target material. Once cooled, the gas may pass through pumps 216a,b, which may be, for example, a turbo-pump or a roots-type booster, and thereafter be directed through an external guideway 204a,b to a location where the gas will, once again flow through the through-hole formed in the optic 30. It is to be appreciated that one or more flow regulators (not shown) may be provided, e.g. one regulator near each pump, to balance flow throughout the gas management system. One or both of the guideways 204a,b may include an optional filter 218a,b and/or an additional, optional, heat exchanger 220a,b. For the light source 200, the filters 218a,b may function to removing at least a portion of a target species, e.g. contaminants that may degrade optical components and/or absorb EUV light, from gas flowing in the flow path. For example, when a tin containing material is used as a source material to generate the plasma, contaminants such as tin hydrides, tin oxides and tin bromides may be present in the gas which may degrade optical components and/or absorb EUV light. These contaminants may be removed using one or more suitable filters, e.g. zeolite filters, cold traps, chemical absorbers, etc. The heat exchangers 220a,b may, for example, consist of a plurality of parallel metal plates, spaced apart and internally cooled, as described above, and may function to cool the gas in the guideway 204a,b and/or condense and thereby remove vapors, e.g. tin vapors from the gas stream. FIG. 5 further shows that the gas management system may include a regulated gas source 222 for selectively introducing, either continuously or in discrete amounts, one or more gas(ses) into the chamber 26, e.g. for ion stopping (e.g. H2, (protium and/or deuterium isotopes) and/or He), and/or etching plasma generated debris deposits from surfaces in the chamber 26, such as the surface of optic 30, (e.g. HBr, HI, Br2, Cl2, HCl, H2, or combinations thereof). It is to be appreciated that the gas source 222 may include one or more flow regulators (not shown). FIG. 5 further shows that the gas management system may include an adjustable pump 224, e.g. turbopump or roots booster, and optional conditioner 226, (e.g. to dilute and/or scrub the gas prior to release, as described above, with reference to conditioner 114 shown in FIG. 1) for selectively removing some or all of the gas from the chamber 26, and/or other portions of the gas management system, e.g. guideways 204a,b etc. either continuously or in discreet amounts. In some cases, a heat exchanger (not shown) may be placed upstream of the pump 224 to protect the pump from high temperature gas. Addition of fresh gas to the chamber 26 via gas source 222 and/or removal of gas via pump 224 from the chamber 26 may be performed to remove heat and thereby control the temperature within the chamber 26, and/or to remove contaminants, vapor, metal dust, etc. from the chamber 26, and/or to provide a pressure gradient in the chamber 26, e.g. to maintain a relatively large pressure between the optic 30 and irradiation region 28 and a smaller, relatively low pressure between the irradiation region 28 and the intermediate region 40. Control of the gas source 222 and pumps 216a,b and 224 may be used to maintain a selected gas number density in a selected area of the chamber and/or pressure gradient and/or to maintain a selected flow rate through the chamber 26 and or to maintain a selected gas composition, e.g. a selected ratio of several gases, e.g. H2, HBr, He, etc. FIG. 5 further shows that one of more gas monitors 228 measuring one or more gas characteristic including, but not limited to, gas temperature, pressure, composition, e.g. He/H2 ratio, HBR number density, etc. may be disposed in the chamber 26 or placed in fluid communication therewith to provide one or more signals indicative thereof to a gas management system controller 230, which, in turn, may control the pumps, regulators, etc. to maintain a selected gas temperature, pressure and/or composition. For example, a mass-spectrometer residual gas monitor may be used to measure HBR number density. FIG. 5 also shows that the gas management system may include provisions for maintaining pre-selected flows (flow rates and/or flow directions), temperatures, gas number densitys and/or contaminant levels at or near the intermediate region 40. In particular, the gas management system may be designed to meet specifications for one or more of these parameters that are developed by scanner manufacturers, etc. As shown, gas management near the intermediate region 40 may include the maintenance of a pressure below the pressure at the scanner input such that gas flows from the scanner 202 and toward the intermediate region 40. FIG. 5 also shows that the gas management system may include a gas source 232 providing a stream of gas that flows from the intermediate region 40 toward the irradiation zone 28 and a pump 234 and optional conditioner 236, as described above, for selectively evacuating the intermediate region 40. FIG. 8 shows another embodiment of a gas management system for an LPP EUV light source having an enclosing structure defining a closed loop flow path, the enclosing structure having a vessel, e.g. chamber 26, in fluid communication with a guideway 204′, the guideway 204′ being external to the chamber 26. As shown, the flow path directs gas through the irradiation region 28 normal to the axis 248 of the optic 30 and between the optic 30, e.g. ellipsoidal collector mirror, as described above, and a multi-channel structure 210, 210′, 210″ (as described above and having flow restricting flange 211, as described above). Also shown, the gas management system may include a pump 208, as described above, and a heat exchanger 250, e.g. having a plurality of spaced apart, metal plates, arranged in parallel, with one or more of the plates being formed with internal passages to allow a cooling fluid for flow through. An optional filter (not shown), as described above, may also be employed in the closed loop system. FIG. 9 shows another embodiment of a gas management system for an LPP EUV light source having an enclosing structure defining a closed loop flow path in which the gas in introduced into the volume surrounding the irradiation region to create a vortex and thereby increase gas mixing and the transfer of heat from the plasma to the gas and, in some cases, minimize stagnation zones. As shown, gas is directed into the chamber 26 from one or more guideways 204a″, b″, c″, d″ with a tangential component to create a vortex within the chamber 26 and near the irradiation region 28. FIG. 10 shows another embodiment of a gas management system for an LPP EUV light source having an enclosing structure defining a closed loop flow path, the enclosing structure having a vessel, e.g. chamber 26, in fluid communication with a guideway 204″, the guideway 204″ being external to the chamber 26. It can also be seen that a pump 208, as described above, may be provided to circulate gas through the closed loop. FIG. 10 further shows that an optic 30, e.g. ellipsoidal collector mirror, may be disposed in the chamber 26, the optic 30 formed with a central through-hole allowing a laser beam to pass through and reach an irradiation region 28. It can further be seen that a gas flow restriction member 280 may be disposed in the chamber 26 extending from a location at or near the edge of the optic 30 to a location at or near the wall of the chamber 26 to establish compartments 282, 284 in the chamber 26. Gap(s) may be provided between the optic 30/restriction member 280 and/or restriction member 280/chamber wall, e.g. 1-3 mm to allow for expansion/contraction of the optic 30 while maintaining suitable gas flow restriction. For the device, the gas flow restriction member 280 may be integrally formed with the optic 30 or may be a separate component. With this arrangement, it can be seen that the closed-loop flow path may extend from the compartment 282 through the through-hole formed in the optic 30 and into the compartment 284. Also shown, the device may include a multi-channel structure 210, 210′, 210″, as described above, having flow restricting flange 211, as described above. Note: a heat exchanger (not shown) and/or filter (not shown), both as described above, may also be employed in the closed loop system. FIG. 10 further shows that a shroud 300 may be positioned in the through-hole which may function, among other things, to reduce the amount of plasma generated debris reaching beam delivery optics 302a,b, which, as shown, are disposed in fluid communication with the chamber 26 and irradiation region 28. For the device shown, the shroud 300 may be conical shaped having a small diameter end facing the irradiation zone. The shroud 300 may be positioned a suitable distance from the irradiation zone to prevent shroud overheating. Beam delivery optics 302a,b may be coupled to actuators (which may or may not be positioned in the compartment 282) and may be used for pulse shaping, focusing, steering and/or adjusting the focal power of the pulses delivered to the irradiation region 28 and may function to allow the laser input window 304 to be positioned at a remote location relative to the irradiation region 28 such that a line-of-sight debris path between the irradiation region 28 and window 304 is not established, thereby reducing debris deposition on the window 304. Although two reflective optics are shown, it is to be appreciated that more than two and as few as one optic may be employed. A suitable beam delivery system for pulse shaping, focusing, steering and/or adjusting the focal power of the pulses is disclosed in co-pending U.S. patent application Ser. No. 11/358,992 filed on Feb. 21, 2006, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE, the contents of which are hereby incorporated by reference herein. As disclosed therein, one or more beam delivery system optics may be in fluid communication with the chamber 26. FIG. 11 shows another embodiment of a gas management system for an LPP EUV light source having one or more components in common with the arrangement shown in FIG. 10 and described above, to include an enclosing structure defining a closed loop flow path, the enclosing structure having a vessel, e.g. chamber 26, in fluid communication with a guideway 204″, the guideway 204″ being external to the chamber 26, a pump 208, an optic 30, e.g. ellipsoidal collector mirror, may be formed with a central through-hole, a shroud 300 may be positioned in the through-hole, beam delivery optics 302a,b disposed in fluid communication with the chamber 26 and irradiation region 28 and a remotely located laser input window 304. For the embodiment shown in FIG. 11, a gas flow restriction member 280′ may be disposed in the chamber 26 extending from a location at or near the outer surface of the shroud 300 to a location at or near the wall of the chamber 26 to establish compartments 282′, 284′ in the vessel. For the device, the gas flow restriction member 280′ may be integrally formed with the shroud 300 or may be a separate component. With this arrangement, it can be seen that the closed-loop flow path may extend from the compartment 282′ through the through-hole formed in the optic 30 and in to the compartment 284′. FIG. 11A illustrates another possibility in which the optic 30 is formed with a plurality of relatively small through-holes, (of which through-holes 375a,b,c have been labeled), allowing gas flowing within a closed loop flow path to flow through the holes in the optic to reach the space between the optic and irradiation region 28. FIG. 11B illustrates yet another possibility in which one or more tube(s) 380 are positioned near, e.g. within about 1-2 mm, of the reflective surface of the optic 30, with each tube formed with a plurality of relatively small holes to release gas onto the surface of the optic 30. Either of these configurations may be employed with or without gas flow through the central through-hole (described above). For these configurations, placement of the tubes and/or through-holes may be selected to correspond to light paths which are unusable by the scanner, due, e.g. to obstructions in the scanner and/are otherwise blocked by other structures, e.g. debris mitigation structures, multi-channel structures, etc. FIG. 12 shows another embodiment of a gas management system for an LPP EUV light source having an enclosing structure defining a closed loop flow path, the enclosing structure having a vessel, e.g. chamber 26, in fluid communication with a guideways 204a′, 204b′, the guideways 204a′, 204b′being external to the chamber 26, as described above. As shown, the chamber 26 may include a plasma irradiation module 400, pump/heat exchanger module 402, pump/heat exchanger module 404 and scanner interface module 406. For the device, the chamber 26 may consist of separate modules assembled together or one integrally formed unit. For the device shown, an optic 30 may be positioned in the chamber 26, e.g. an ellipsoidal collector mirror formed with a central through-hole to allow a laser beam from a laser source (not shown) to pass through and reach an irradiation region 28. Also shown, the optic may focus light from the irradiation region 28 to an intermediate region 40, generating a cone of EUV light extending through the chamber 26 having an apex at the intermediate region 40. FIG. 12 further shows that pump/heat exchanger module 402 includes pumps 208a′,b′, as described above, and heat exchanger 214a, and pump/heat exchanger module 404 includes pumps 208c′d′, as described above and heat exchanger 214b. For the device, and heat exchangers 214a,b may consist of a plurality of spaced apart, parallel, annularly shaped metal plates that extend around the EUV light cone and with each plate individually sized to extend to an inner circular edge that is near or at the edge of the EUV light cone (defined by the ellipsoidal optic 30), as shown. One, some or all of the plates may be formed with one or more internal passages to pass a heat exchange fluid, e.g. water, to cool each plate. The heat exchangers 214a,b may function to cool gas flowing through the exchanger 214a,b and/or to condense target material vapors that may undesirable absorb EUV radiation, e.g. tin vapor when tin is used as a target material. Once cooled, the gas may pass through pumps 208a′-d′, which may be, for example, turbo-pumps and/or roots-type boosters, and thereafter be directed through external guideways 204a′,b′ to locations in the a plasma irradiation module 400. As shown, a space may be provided between the outer diameter of the heat exchanger plates and the pump to form a vacuum cavity. For the device, the plates may nearly fill the entire length of the chamber, thus resistance of such structure to gas flow may be fairly small, not limiting the pumping speed of the pumps. At the same time, the working area of the plates will be large to provide high efficiency for gas cooling. It is to be appreciated that one or more flow regulators (not shown) may be provided, e.g. one regulator near each pump, to balance flow throughout the gas management system. For the device, one or both of the guideways 204a′,b′ may include an optional filter 218a,b (as described above) and/or an additional, optional heat exchanger 220a,b (as described above). Continuing with FIG. 12, it can be seen that a multi-channel structure 210a′ is positioned along the gas flow path between the plasma irradiation module 400 and pump/heat exchanger module 402, a second multi-channel structure 210b′ is positioned along the gas flow path between the pump/heat exchanger module 402 and the pump/heat exchanger module 404 and a third multi-channel structure 210c′ is positioned along the gas flow path between the pump/heat exchanger module 404 and the scanner interface module 406. For the device shown, each multi-channel structure may include a plurality of concentric, conical shaped vanes (see FIG. 5B) plate shaped vanes (see FIG. 5C) and/or radially oriented vanes (see FIG. 7) that are arranged to allow light to travel from the optic 30 to the intermediate region 40 and may be designed to minimize EUV light obscuration. In addition, vane location may be selected to correspond to light paths which are unusable by the scanner 202, due, e.g. to obstructions in the scanner. Each multi-channel structure may be positioned in an opening formed in the respective module housing, as shown, to restrict flow between the multi-channel structure and respective module housing. While the particular embodiment(s) described and illustrated in this patent application in the detail required to satisfy 35 U.S.C. §112 are fully capable of attaining one or more of the above-described purposes for, problems to be solved by, or any other reasons for or objects of the embodiment(s) above described, it is to be understood by those skilled in the art that the above-described embodiment(s) are merely exemplary, illustrative and representative of the subject matter which is broadly contemplated by the present application. Reference to an element in the following Claims in the singular is not intended to mean nor shall it mean in interpreting such Claim element “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to any of the elements of the above-described embodiment(s) that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present Claims. Any term used in the Specification and/or in the Claims and expressly given a meaning in the Specification and/or Claims in the present Application shall have that meaning, regardless of any dictionary or other commonly used meaning for such a term. It is not intended or necessary for a device or method discussed in the Specification as an embodiment to address or solve each and every problem discussed in this Application, for it to be encompassed by the present Claims. No element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the Claims. No claim element in the appended Claims is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited as a “step” instead of an “act”. |
|
claims | 1. Proximity exposure method in which alignment of a workpiece and a mask and irradiation of the workpiece are performed with obliquely angled exposure light, comprising the following process steps: positioning a workpiece in vertical alignment with a mask on which a mask pattern is formed with light directed toward the workpiece and mask vertically from above; arranging the workpiece spaced from the mask with a gap of a predetermined size therebetween moving the workpiece out of said vertical alignment for aligning the workpiece relative to the mask based on an angle of incidence and an irradiation angle of the obliquely angled exposure light with respect to the mask and based on the size of said gap; and irradiating the workpiece with obliquely angled exposure light via the mask and exposing the mask pattern onto the workpiece. 2. Proximity exposure method as claimed in claim 1 , wherein an amount of deviation between a projection site of the mask pattern on the workpiece in vertical irradiation of the mask with light and a projection site of the mask pattern on the workpiece with oblique irradiation of the mask with light is computed, and based on this computed amount of deviation the aligning is performed. claim 1 3. Proximity exposure method as claimed in claim 1 , wherein said aligning comprises the following steps: claim 1 X=Xn+xcex94Xxe2x88x92G xc2x7tan xcex4xc2x7cos "PHgr" Y=Yn+xcex94Yxe2x88x92G xc2x7tan xcex4xc2x7sin "PHgr" measuring the gap between the mask and the workpiece with a gap measuring device; determining locations of mask alignment marks and workpiece alignment marks by an alignment microscope viewed from a position perpendicular to the mask; moving the workpiece alignment marks by moving a workpiece carrier in X-Y-"THgr" directions, from first position coordinates to second position coordinates, the second position coordinates being (X, Y) determined by the formulas: where, for any X-Y coordinates, (Xn, Yn) are the position coordinates of the determined locations of the workpiece alignment marks, (Xn+xcex94X, Yn+xcex94Y) are the position coordinates of the workpiece alignment marks of the workpiece which has been re-positioned relative to the mask alignment marks by moving the workpiece carrier in the X-Y-"THgr" directions, G is the size of the gap between the mask and the workpiece, xcex4 is angle of incidence of the obliquely angled light into the mask, and "PHgr" is the irradiation angle of the irradiation light which is incident in the X-direction of the mask pattern. |
|
summary | ||
abstract | An improved radiation shielding material and storage systems for radioactive materials incorporating the same. The PYRolytic Uranium Compound (xe2x80x9cPYRUCxe2x80x9d) shielding material is preferably formed by heat and/or pressure treatment of a precursor material comprising microspheres of a uranium compound, such as uranium dioxide or uranium carbide, and a suitable binder. The PYRUC shielding material provides improved radiation shielding, thermal characteristic, cost and ease of use in comparison with other shielding materials. The shielding material can be used to form containment systems, container vessels, shielding structures, and containment storage areas, all of which can be used to house radioactive waste. The preferred shielding system is in the form of a container for storage, transportation, and disposal of radioactive waste. In addition, improved methods for preparing uranium dioxide and uranium carbide microspheres for use in the radiation shielding materials are also provided. |
|
description | The present invention relates to an illumination system, to a lithographic apparatus comprising such an illumination system and a method for manufacturing a device. A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. A photolithographic apparatus requires an illumination system that supplies a beam of radiation that is used to impart a pattern to the substrate. Of course, illumination systems for forming beams may also be used in applications other than photolithography where a beam or radiation is needed. An embodiment of such an illumination system contains mirrors to reflect the beam. In particular when an EUV beam is used mirrors are preferred over lenses. Preferably metal mirrors are used. Metal mirrors may be used that comprise a thick metal layer to reflect all of the radiation at a grazing angle of incidence, or alternatively mirrors may be used, comprising a stack alternating layers of metal and layers of non-metal. Metal mirrors with a thick metal layer are mostly used with a grazing incidence beam. Metal mirrors with a stacked structure are also used under other angles of incidence, even under (near) normal incidence conditions. Typical metals used in such mirrors are Molybdenum and Ruthenium. In the stacked structures the layers between metal layers are often made of silicon. However, the use of such mirrors has its problems. Molybdenum and Silicon are susceptible to oxidation when exposed at the surface. Therefore mirrors containing layers of these materials are often provided with a top layer, which protects against oxidation (for example ruthenium may be used for this). Also the mirrors tend to get contaminated during use. From US patent application publication No 20060278833, assigned to the same assignee, it is known that use of a gas containing hydrogen (in particular hydrogen radicals) can be used to remove contamination from an optically reflective surface in a EUV lithographic apparatus. It has been found that Sn and C contamination can be effectively removed from reflective surfaces in this way. Unfortunately atomic hydrogen can also cause cracks in the reflective surface when the mirror has a layer of certain metals, such as an exposed ruthenium or molybdenum layer, that can be reached by the hydrogen radical. This effect has been described in a US patent application assigned to the assignee of the present application (assignee docket P 2263.000). In this patent application it was described that a coating of Si3N4 can be used to protect against cracking. However, such a coating detracts from reflection and may be difficult to deposit for certain mirror configurations An EUV mirror containing a stack of layers of alternately Si and MoSi2 is known from an article titled “High-temperature MoSi2/Si and Mo/C/Si/C multilayer mirrors High-temperature MoSi2/Si and Mo/C/Si/C multilayer mirrors”, published in a poster session of the 3rd International EUVL Symposium 01-04 November 2004 Miyazaki, Japan. This reference is limited to multilayer mirrors and it does not mention hydrogen cleaning. Moreover a MoSi2/Si mirror has a relatively low peak reflection (approx. 40%) at 1.5 degrees to the perpendicular. It is desirable to provide for an illumination system wherein a reflective surface that is protected from cracking with a minimum detrimental effect on reflectivity. According to an aspect of the invention, there is provided an illumination system configured to condition a radiation beam, comprising a mirror comprising a layer made of metal non-metal compound adjacent a reflection surface of the mirror and a hydrogen radical source configured to supply gas containing hydrogen or hydrogen radicals to the reflection surface. According to another aspect of the invention, there is provided a radiation source comprising such an illumination system. According to an aspect of the invention, there is provided a lithographic apparatus comprising an illumination system configured to condition a radiation beam and a hydrogen radical source configured to supply gas containing hydrogen or hydrogen radicals into the illumination system, the illumination system comprising a mirror comprising a layer made of metal non-metal compound adjacent a reflection surface of the mirror. According to an aspect of the invention, there is provided a mirror for use in a hydrogen or hydrogen radical environment, comprising a protection layer made of a metal non-metal compound adjacent a reflection surface of the mirror. According to an aspect of the invention, there is provided a method of removing contamination from a mirror with a reflecting metal containing layer, the method comprising supplying a hydrogen radicals to a reflection surface of the mirror and protecting the mirror against damage due to the supply of the hydrogen radicals by using a layer made of a metal non-metal compound in the mirror adjacent the reflection surface. According to an aspect of the invention, there is provided a device manufacturing method comprising projecting a patterned beam of radiation onto a substrate, wherein the radiation that goes into the beam is reflected by a mirror, the method comprising a step of removing contamination from a mirror using a supply of a gas containing hydrogen radicals to a reflection surface of the mirror, wherein the mirror comprises a layer made of a metal non-metal compound adjacent the reflection surface. According to an aspect of the invention, there is provided a EUV mirror comprising a protection layer made of a metal non-metal compound adjacent a reflection surface of the mirror. According to an aspect of the invention, there is provided a method of removing contamination from a mirror with a reflecting metal containing layer, the method comprising supplying a hydrogen radicals to a reflection surface of the mirror and protecting the mirror against damage due to the supply of the hydrogen radicals by using a layer made of a metal non-metal compound in the mirror adjacent the reflection surface. According to an aspect of the invention, there is provided a device manufacturing method comprising projecting a patterned beam of radiation onto a substrate, wherein the radiation that goes into the beam is reflected by a mirror, the method comprising a step of removing contamination from a mirror using a supply of a gas containing hydrogen radicals to a reflection surface of the mirror, wherein the mirror comprises a layer made of a metal non-metal compound adjacent the reflection surface. FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or EUV radiation). a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. The support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines 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 exposure. The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure. Referring to FIG. 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system. The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies. The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed FIG. 2 schematically shows source SO and part of an illumination system, including a mirror 20. Although an embodiment is shown wherein the illumination system and the source are separate units, it should be appreciated that in another embodiment the source may be part of the illumination system, in a single apparatus, which may be a lithographic apparatus or an apparatus for another application. The mirror 20 may be configured for grazing incidence or normal-incidence reflection. In an embodiment mirror 20 is the first mirror encountered along a radiation path from source SO to the substrate (not shown), i.e. the mirror that is exposed to most radiation and particles from radiation source SO. Furthermore the lithographic apparatus comprises a hydrogen radical source 22 configured to supply hydrogen radicals (atomic hydrogen) to the surface of mirror 20 for cleaning purposes. In an embodiment the source SO is a plasma source, which is known per se. One reason for using a plasma source is that it is suitable for producing very short wavelength radiation of use in the beam, e.g. in the EUV range. Mirror 20 EUV mirror, which means that it has reflectivity to reflect a sufficient part of the EUV beam to be useful for photolithography. Conventionally, mirror 20 (and other mirrors not shown) which function as EUV mirrors in the lithographic apparatus can be made of, metals like Molybdenum or Ruthenium (for example a grazing incidence beam is used) or mirror 20 may comprise a plurality of layers in a stack of alternate layers of different materials. Metals like Mo and Ru provide for efficient reflection of radiation in the EUV range. As used herein such metal layers will be termed reflecting metal layers, both when a single such layer provides for substantially all reflection on its own and when reflections is provided by a stack containing such metal layers. Unfortunately the use of EUV radiation has the effect that such a mirror 20 in the lithographic apparatus (and other mirrors, not shown, elsewhere in the apparatus) can become contaminated by carbonaceous deposits. Moreover, certain suitable plasma sources SO produce Sn ions which can also lead to contamination of the mirrors. Hydrogen radical source 22 is provided to remove this type of contamination. During a cleaning step hydrogen radical source 22 supplies atomic hydrogen to mirror 20 (and optionally to other mirrors not shown). In an embodiment a stream of hydrogen radicals is supplied in situ in the apparatus during the cleaning step, for example between two successive pattern projection operations. Alternatively, the hydrogen radicals may even be supplied during projection. As an alternative the mirror may be removed or replaced to perform cleaning. Unfortunately, it has been found that with conventional metal mirrors exposure of the mirror to hydrogen radicals leads to damage to the mirror. Such exposure may arise during cleaning, but also when traces of hydrogen gas are present during irradiation with an EUV beam, because the beam can dissociate hydrogen. In another embodiment a hydrogen source is present in the photolithographic apparatus to create a buffer gas to suppress effects of ions introduced into the photolithographic apparatus, for example by a plasma radiation source, or to create a gas curtain against gasses emerging from photoresist on substrate W. During exposure to a EUV beam of radiation, the beam may dissociate hydrogen molecules into radicals, which give rise to similar problems as the hydrogen radicals supplied by hydrogen radical source 22. Hence, when a hydrogen source is present in the photolithographic apparatus, these problems may occur whether a hydrogen radical source is present or not. FIG. 3 shows an embodiment of mirror 20 in cross section. Mirror 20 is specifically designed for use in a photolithographic apparatus that contains a hydrogen source and/or a hydrogen radical source, but such a mirror may also be used in other contexts. Mirror 20 comprises a stack of layers of alternating mutually different materials on a substrate 38. A stack is typically used to make it possible to reflect EUV beams at (near) normal incidence on the surface of the mirror. The stack comprises first layers 30 made of for example Mo2Si (i.e Mo and Si in a ratio of two to one), which function as protection layers, second layers 32 made of for example substantially pure Mo and third layers 34 made of, for example, substantially pure Si. As used herein “substantially pure” includes purity levels as can be obtained by sputtering from a Mo or Si target, and at least so pure that the Mo properties with respect to hydrogen radicals are not significantly affected by any impurities. The first layers 30 are closer to the reflection surface 36 of mirror 20 than second layers 32. Third layers 34 are provided between successive first and second layers 30, 32. Second and third layers 32, 34 form an EUV reflective multilayer stack. Without protection layers of Mo2Si such stacks are known per se. The thickness of the layers is selected in order to provide for constructive interference of reflected radiation when mirror 20 is used. First layers 30 may have thickness in a range of 0.5 to 5 nm, for example. First layers 30 made of Mo2Si are added to protect mirror 20 against cracking effects due to hydrogen radicals. Although an embodiment has been shown with two first layers 30 of Mo2Si and a larger number of second layers 32 in the multilayer stack, it should be appreciated that a different number of first layers 30 of Mo2Si may be used, for example only one first layer of Mo2Si nearest reflection surface 36, followed by layers of Mo, with third layers 34 in between (as shown in FIG. 4), or three or more layers of Mo2Si nearest reflection surface 36, followed by layers of Mo. In a further embodiment (FIG. 5) no layers of Mo may be used at all, alternate layers of Mo2Si and Si being used. However, it is preferred that the ratio between the number of layers of Mo2Si and the number of layers of Mo is less than 50% and preferably less than 10%. Thus the reducing effect of the lower reflectivity of Mo2Si is minimized. In another embodiment, shown in FIG. 7 reflection is provided substantially entirely (e.g. by more than 90%) by a single, thick protection layer of Mo2Si (i.e. much thicker than the layer thickness used for obtaining interference), or another compound of a metal and Si. Typically, at EUV wavelengths such a mirror is used for grazing incidence reflection, at an angle of, say, five degrees with the surface. As used herein “protection layer” refers to a layer between the reflection surface of the mirror and one or more layers of a different material that is vulnerable to damage by hydrogen (or hydrogen radicals), such as shown in FIG. 3, but in the case of mirror with only a single layer next to the reflection surface to provide all reflectivity the term “protection layer” refers to that single layer, as shown in FIG. 6, because this protects vulnerable layers by making them redundant. FIG. 6 shows or by a single layer of a metal that provides substantially for all reflection (e.g. >90%) capped by a protection layer of a compound of a metal and Si as shown. Typically, at EUV wavelengths such a mirror is used for grazing incidence reflection, at an angle of, say, five degrees with the surface. A protection layer of at least 2 nm thickness may be used for protecting the underlying substrate in this embodiment, but preferably a thickness of at least 12 nm is used to achieve high reflectivity. There is no limit on the maximum thickness of the mirror, a thickness of >1 micrometer may be used, as long as the surface roughness is still acceptable (<1 nm for EUV radiation). Note that it is also possible to use a layer 32 made of a metal Si compound in combination with an additional thin protective layer of another material, such as Si3N4 between the metal-Si compound layer and the reflection surface. In this case the thin protective layer with a low thickness (˜2 nm) may be used, for example to increase performance of the hydrogen cleaning technique. Previously, it has been shown that for example a thin coating of Si3N4 can significantly increase the Sn cleaning rate from a Ru surface. It is expected to be similar when a Ru/Si compound is used instead of Si3N4. As shown in the preceding figures a protection layer of Mo2Si is used to protect against detrimental effects of hydrogen cleaning. This protection layer may be a first layer on top of a stack of alternating layers, a layer on to top of a layer with a thickness to provide all reflectively of the mirror on its own, or the protective layer itself may have a thickness to provide all reflectively of the mirror on its own. The layer is a compound of Mo and Si. As used herein the term “metal non-metal compound” is used to signify that Mo and Si (or any other combination of a metal and a non-metal) are mixed at an atomic level, i.e. so that the layer is not made up of separate crystals of Mo and Si, or separate sub-layers that each contain only one of these materials, for example by simultaneous sputtering from Mo and Si targets or by growing from Mo2Si molecules. As used herein, the term “metal non-metal compound” encompasses such mixtures at atomic level in all concentration ratios, not necessarily limited to stoichiometric ratios. It has been found that Mo2Si combines the properties of good EUV reflectivity and reduced susceptibility to cracking when exposed to hydrogen radicals. The reflectivity of Mo2Si is about 95.3% at 5 degrees grazing incidence, which is only slightly worse than the reflectivity of Mo under the same conditions (96.3%). A possible explanation is that Mo is a metal with high atomic weight, which provides for good EUV reflectivity, whereas the presence of Si in the lattice reduces or blocks migration of hydrogen atoms through the Mo2Si lattice. Migration through metal-only lattices is assumed to contribute to the cracking effect of cleaning with hydrogen radicals. In an embodiment mirror 20 is manufactured using sputtering to deposit the layers. When the protection layer (or one of the protection layers) is deposited Mo and Si targets are activated concurrently so that Mo and Si are deposited in a ratio of 2:1 to form a lattice of Mo2Si. Although an embodiment using layers of Mo and Mo2Si has been shown, it should be appreciated that other materials may be used. In principle any metal may be used instead of Mo in the reflective layers, preferably transition metals are used. For example, instead of Mo another transition metal such as ruthenium (Ru), tungsten (W), Rhodium (Rh), Niobium (Nb) or Zirconium (Zr) may be used. In the protection layers instead of Mo2Si, one may use another compound of metal and non-metal, such as a transition metal carbide, nitride boride or silicide or mixtures thereof. Preferably, a combination of metal with silicon is used, as it has been found that this very effectively reduces problems due to hydrogen cleaning. Preferably a stoichiometric ratio of metal and Si. For example, it has been found that Ru2Si3 (Ru and Si in a ratio of two to three) may be used instead of Mo2Si. Ru2Si3 has a reflectivity of 89.9% compared to Ru (94.8) at 5 degree grazing incidence. Damage due to cracking is also less when Ru2Si3 is used instead of Ru. It may be noted that the proposed ratios are stoichiometric ratios, i.e. ratios that correspond to ratios of the metal and non-metal in molecules. This provides for a more stable compound layer with a well defined lattice. However, it may also be contemplated to use non-stoichiometric ratio's. In view of the dramatic reduction of the problems with hydrogen radical found in experiments with stoichiometric ratios it is expected that a significant reduction of these problems will also occur with other ratios, due to the fact that Si will also block hydrogen significant hydrogen uptake at such other ratio's. The main limitation on the amount of silicon is its effect on reflectivity. FIG. 8 shows a theoretical relation between reflectivity and silicon content when Si is added to Ruthenium (the stoichiometric ratio corresponds to 60%). It can be seen that a Ru/Si compound will have a lower reflectivity compared to pure Ru surface. The difference depends on the reflection angle, but a typical reflection angle in practice is 7 degrees. When using a maximum allowed reflection loss of 10% compared to a normal Ru surface, the maximum allowed Si concentration is around 80%. As can be seen, quite high silicon concentrations can be used with acceptable reflectivity. Thus, sufficient silicon can be provided to reduce the effect of hydrogen. Preferably at least 10% silicon is used. More preferably Si concentration of at least 30% is used. As alternatives for Si, other materials may be added to the metal. The introduction of any non metal that can be combined with metal in the top layer before it is exposed to hydrogen is expected to reduce the effects of hydrogen. Be, BN, or B4C may be contemplated for example. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured. The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams. The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.