patent_number
stringlengths 0
9
| section
stringclasses 4
values | raw_text
stringlengths 0
954k
|
|---|---|---|
description | This is a Continuation of International Application PCT/EP2017/080645, which has an international filing date of Nov. 28, 2017, and which claims the priority of German Patent Application 10 2016 224 200.8, filed Dec. 6, 2016. The disclosures of both applications are incorporated in their respective entireties into the present Continuation by reference. The present invention relates to a method for repairing reflective optical elements for EUV lithography which comprise a substrate and a coating that reflects at an operating wavelength in the range of between 5 nm and 20 nm. Furthermore, the present invention relates to a collector mirror for EUV lithography which comprises a substrate and a coating that reflects at an operating wavelength in the range of between 5 nm and 20 nm. In EUV lithography apparatuses, for the lithography of semiconductor components, use is made of reflective optical elements for the extreme ultraviolet (EUV) wavelength range (e.g. wavelengths between approximately 5 nm and 20 nm) such as, for instance, photomasks or mirrors on the basis of multilayer systems for quasi-normal incidence or mirrors having a metallic surface for grazing incidence. Since EUV lithography apparatuses generally have a plurality of reflective optical elements, they must have as high a reflectivity as possible to ensure sufficiently high overall reflectivity. The reflectivity and the lifetime of the reflective optical elements may be reduced by contamination of the optically used coating of the reflective optical elements, which arises on account of the short-wave irradiation together with residual gases in the operating atmosphere. Since a plurality of reflective optical elements are usually arranged one behind another in an EUV lithography apparatus, even relatively small contaminations on each individual reflective optical element already affect the overall reflectivity to a relatively great extent. Contamination can occur for example on account of moisture residues. In this case, water molecules are cleaved by the EUV radiation and the resulting oxygen radicals oxidize the optically active surfaces of the reflective optical elements. A further contamination source is hydrocarbons which can originate for example from the vacuum pumps used in EUV lithography apparatuses or from residues of photoresists which are used on the semiconductor substrates to be patterned and which, under the influence of the operating radiation, lead to carbon contaminations on the reflective optical elements. In the case of collector mirrors used in conjunction with a laser-based EUV plasma light source, the material which is excited to form a plasma, for example tin, occurs as an additional contamination source. While oxidative contaminations are generally irreversible, in particular carbon contaminations and possibly tin can be removed inter alia by treatment with reactive hydrogen, by virtue of the reactive hydrogen reacting therewith to form volatile compounds. Reactive hydrogen can be hydrogen radicals or else ionized hydrogen atoms or molecules. It has been observed, however, that under the influence of reactive hydrogen which is used for cleaning or which can arise on account of the interaction of the EUV radiation with hydrogen present in the residual atmosphere, blistering at the reflective coating and even detachment of layers or individual plies can occur, in particular close to the surface of multilayer systems. Macroscopic blistering or delamination is observed in particular in the case of collector mirrors, which are especially exposed to reactive hydrogen compared with other reflective optical elements of an EUV lithography apparatus. Blistering or delamination can occur in particular at defects in the coating of the reflective optical elements. The delamination is caused by the penetration of reactive hydrogen into the reflective coating, in particular at mechanical defects or defects that occurred during the coating. The indiffused reactive hydrogen can recombine to form molecular hydrogen and thus lead to blistering and, in the worst case, breaking up or peeling of the coating. Damaged locations of this type may have a high reflection in the infrared wavelength range. This is problematic particularly in the case of collector mirrors. This is because the highest thermal load occurs in the case of collector mirrors, inter alia on account of the infrared lasers that can be used in the radiation source, and upon reflection of the thermal radiation in the direction of the beam path of the EUV lithography apparatus it is possible, in particular, for the downstream reflective optical elements to be damaged. The previous approach has hitherto consisted in repairing reflective optical elements damaged in particular by hydrogen-induced blistering by completely removing the damaged coating and coating the substrate anew. It is an object of the present invention to provide an alternative way of repairing reflective optical elements for EUV lithography that have been damaged by hydrogen. This object is achieved with a method for repairing reflective optical elements for EUV lithography which comprise a substrate and a coating that reflects at an operating wavelength in the range of between 5 nm and 20 nm, comprising: localizing a damaged location in the coating; covering the damaged location with one or more materials by applying a covering element to the damaged location, wherein the covering element is embodied with a surface structure, a convex or concave surface or a coating corresponding to the coating of the reflective optical element, or a combination thereof. Coating should be understood to mean both coatings on the basis of multilayer systems which are suitable particularly for normal and quasi-normal incidence and are based on Bragg reflection, and coatings having only one or a few layers which are suitable for grazing incidence and are based on total internal reflection. Moreover, the coating can comprise additional layers such as, inter alia, protective layer systems as vacuum seal, polishing or smooth layers on the substrate or spectral filter layers for deflecting undesired radiation wavelength ranges such as infrared radiation, for instance. The process of localizing damaged locations, in particular blisters, spalling, scratches and cracks, can take place manually with close visual inspection, since these damaged locations have a macroscopic extent in many cases. It can also take place with the assistance of inspection systems that scan the surface of the coating. It has been found that as a result of the targeted covering of the damaged locations with a covering element composed of one or more materials, in particular having low hydrogen permeability, it is possible to achieve a sufficiently permanent repair of damaged reflective optical elements with low temporal and monetary expenditure in order to be able to withstand operation of an EUV lithography apparatus. Moreover, the covering elements can already be prepared as items in stock and, if a damaged location is localized during an inspection, can be applied immediately or, if appropriate, adapted rapidly to the surface shape in order to achieve the best possible covering. This allows very fast repair. A surface structure can contribute to the fact that undesired radiation components such as from the ultraviolet or infrared wavelength range, for example, are reflected in a different direction than the radiation in the operating wavelength range. This can also be achieved with convex or concave surfaces. Covering units in the form of convex caps are particularly preferred. They additionally have the advantage that they can cover blisters and spalling equally well. A coating corresponding to the reflective coating on the surface of the covering element can lead to an increased reflectivity in the operating wavelength range at the repaired location; the reflectivity is ideally as high as at an undamaged location. Advantageously, the covering element is secured on the coating of the reflective optical element with an adhesive. The covering element can be secured over the whole area or by applying adhesive spots or partial areas or lines. Preference is given to using adhesives which are heat-resistant and/or outgas as little as possible in a vacuum. Further suitable possibilities for securing covering elements are, inter alia, soldering, welding, in particular spot welding, or wringing. Preferably, the covering element is embodied as a film or a covering unit. A covering unit has the advantage of greater mechanical stability and that it can be prefabricated. A film can be better adapted ad hoc to the damaged location to be repaired and to the surface profile of the coating in the region of the damaged location. Preferably, the covering element is embodied with an angular and/or curved boundary. In particular, the covering element can have a round, angular, polygonal or totally free shape. Advantageously, in this case, the boundary is adapted to the shape of the damaged location. Particularly preferably, the covering element has an ellipsoidal or elongate shape. By means of a suitable choice of the orientation relative to the scanning direction of an EUV lithography apparatus in which the reflective optical element is used, it is thereby possible to reduce the influence of the covering element in the form of an abrupt bright-dark transition, such that the imaging performance of the EUV lithography apparatus is detrimentally affected to a lesser extent by the repair of the reflective optical element with a covering element. Preferably, a covering element is applied which comprises one or more materials of the group comprising metal, steel, high-grade steel, Invar, aluminum, molybdenum, tantalum, niobium, silicon, titanium, zirconium, hafnium, scandium, yttrium, lanthanum, cerium, copper, silver, gold, platinum, rhodium, palladium, ruthenium, glass, ceramic and aluminum oxide. In the case of these materials, it has been found that particularly little reactive hydrogen penetrates into them. Moreover, covering units or films can be fabricated well from these materials. Furthermore, there exist securing possibilities, in particular adhesives, in order to secure such covering elements well on the coating of the reflective optical element to be repaired. In preferred embodiments, a covering coating is applied to the damaged location. A covering coating is primarily suitable for reducing further delamination of the coating as much as possible in the event of blisters that have undergone spalling. Preferably, the covering coating is applied by tin plating, gold plating, electroplating, oxidation, nitriding and/or deposition by atmospheric pressure plasma. Tin plating and gold plating can take place for example with metal melts or films. The procedures mentioned have all proved to be worthwhile for applying to damaged locations of the coating of reflective optical elements material that covers the damaged location. In this regard, enlargement of the damaged location can be suppressed. The procedures can be combined with one another in order to apply different layers to the damaged location. Applying a covering coating can be carried out manually or in an automated manner with the aid of a robot arm, for example. Advantageously, as the covering coating, a metal layer comprising gold, platinum, rhodium, palladium, ruthenium, molybdenum, tantalum, niobium, silicon, titanium, zirconium, hafnium, aluminum, scandium, yttrium, lanthanum and/or cerium is applied by electroplating or a covering coating comprising one or more of the group comprising molybdenum, tantalum, niobium, silicon, titanium, zirconium, hafnium, aluminum, scandium, yttrium, lanthanum, cerium, oxides thereof, nitrides thereof, carbides thereof, borides thereof, gold, platinum, rhodium, palladium, ruthenium, carbon, boron carbide and boron nitride is applied by atmospheric pressure plasma. These materials firstly adhere well on the customary coating materials of reflective optical elements and secondly afford good protection against reactive hydrogen. In preferred embodiments, before the process of covering the damaged location, coating material is removed in the region of said damaged location. In particular before applying a film, a covering unit or a covering coating, expansion of the damaged location over time can be better avoided this pretreatment. The strength and the endurance of the covering elements or of the covering coating can also be increased as a result. Furthermore, the object is achieved with a collector mirror for EUV lithography which comprises a substrate and a coating that reflects at an operating wavelength in the range of between 5 nm and 20 nm, wherein the coating locally comprises a covering element, wherein the covering element comprises a surface structure, a convex or concave surface or a coating corresponding to the coating of the collector mirror, or a combination thereof. It has been found that collector mirrors which have been repaired with covering elements owing to hydrogen-induced damaged locations have a good resistance to further hydrogen-induced damaged locations at the repaired locations even after a cleaning cycle with reactive hydrogen or during ongoing operation together with a plasma radiation source. Moreover, the repair expenditure is lower than in the case of removing and reapplying the coating to the collector mirror. In particular, the outage times of an EUV lithography apparatus in which the collector mirror is used are significantly reduced. A surface structure can contribute to the fact that undesired radiation components such as from the infrared wavelength range, for example, are reflected in a different direction than the radiation in the operating wavelength range. This can also be achieved with convex or concave surfaces. Covering units in the form of convex caps are particularly preferred. They additionally have the advantage that they can cover blisters and spalling equally well and the latter reflect in particular long-wave radiation such as infrared radiation in no preferred direction. A coating corresponding to the reflective coating on the surface of the covering element can lead to an increased reflectivity in the operating wavelength range at the repaired location; the reflectivity is ideally as high as at an undamaged location. Further preferred configurations of covering units are laminae or thin sheets, for example. In preferred embodiments, the covering element is embodied as a film or a covering unit. A covering unit has the advantage of greater mechanical stability and that it can be prefabricated. A film can be better adapted ad hoc to the damaged location to be repaired and to the surface profile of the coating in the region of the damaged location. Preferably, the covering element comprises one or more of the materials of the group metal, steel, high-grade steel, Invar, aluminum, molybdenum, tantalum, niobium, silicon, titanium, zirconium, hafnium, scandium, yttrium, lanthanum, cerium, copper, silver, gold, platinum, rhodium, palladium, ruthenium, glass, ceramic and aluminum oxide. In the case of these materials, it has been found that particularly little reactive hydrogen penetrates into them. Moreover, covering units or films can be fabricated well from these materials. Furthermore, they can be secured well on the coating of a collector mirror for EUV lithography. Advantageously, the coating locally comprises a covering coating, in particular for sealing a damaged location. In preferred embodiments, the covering coating comprises one or more of the materials of the group molybdenum, tantalum, niobium, silicon, titanium, zirconium, hafnium, aluminum, scandium, yttrium, lanthanum, cerium, oxides thereof, nitrides thereof, carbides thereof, borides thereof, gold, platinum, rhodium, palladium, ruthenium, carbon, boron carbide and boron nitride. These materials firstly adhere well on the customary coating materials of collector mirrors for EUV lithography and secondly afford good protection against reactive hydrogen. FIG. 1 schematically shows an EUV lithography apparatus 10. Primary components are the illumination system 14, the photomask 17 and the projection system 20. The EUV lithography apparatus 10 is operated under vacuum conditions so that the EUV radiation in the interior thereof is absorbed as little as possible. A plasma source or a synchrotron can serve for example as the radiation source 12. In the example illustrated here, a plasma source is used. The emitted radiation in the wavelength range of approximately 5 nm to 20 nm is firstly focused by the collector mirror 13. The operating beam is then introduced into the illumination system 14. In the example illustrated in FIG. 1, the illumination system 14 has two mirrors 15, 16. The mirrors 15, 16 guide the beam onto the photomask 17 having the structure which is intended to be imaged onto the wafer 21. The photomask 17 is likewise a reflective optical element for the EUV and soft X-ray wavelength range, which is exchanged depending on the production process. With the aid of the projection system 20, the beam reflected from the photomask 17 is projected onto the wafer 21 and the structure of the photomask is thereby imaged onto said wafer. In the example illustrated, the projection system 20 has two mirrors 18, 19. It should be pointed out that both the projection system 20 and the illumination system 14 can have in each case only one or three, four, five or more mirrors. In the example illustrated here, the collector mirror 13 is a mirror 50 for quasi-normal incidence, the coating 52 of which is based on a multilayer system 54, as illustrated schematically in FIG. 2. This involves alternately applied layers of a material having a higher real part of the refractive index at the operating wavelength at which for example the lithographic exposure is carried out (also called spacer 57) and of a material having a lower real part of the refractive index at the operating wavelength (also called absorber 56), wherein an absorber-spacer pair forms a stack 55. In certain respects a crystal is thereby simulated whose lattice planes correspond to the absorber layers at which Bragg reflection takes place. The thicknesses of the individual layers 57, 56 and also of the repeating stacks 55 can be constant over the entire multilayer system 54 or vary, depending on what spectral or angle-dependent reflection profile is intended to be achieved. The reflection profile can also be influenced in a targeted manner by the basic structure composed of absorber 56 and spacer 57 being supplemented by further more and less absorbent materials in order to increase the possible maximum reflectivity at the respective operating wavelength. To that end, in some stacks absorber and/or spacer materials can be mutually interchanged or the stacks can be constructed from more than one absorber and/or spacer material. The absorber and spacer materials can have constant or varying thicknesses over all the stacks in order to optimize the reflectivity. Furthermore, it is also possible to provide additional layers as diffusion barriers between spacer and absorber layers 57, 56. A material combination that is customary for example for an operating wavelength of 13.4 nm is molybdenum as absorber material and silicon as spacer material. In this case, a stack 55 usually has a thickness of 6.7 nm, wherein the spacer layer 57 is usually thicker than the absorber layer 56. In the example illustrated here, the coating 52 also comprises a protective layer 53, which can also consist of more than one layers, and a spectral filter layer 58, which serves to filter radiation from undesired wavelength ranges, such as, for instance, ultraviolet radiation likewise emitted by the radiation source 12 or the infrared radiation with which the plasma of the radiation source 12 is excited, from the beam path of the operating radiation in the EUV wavelength range. To that end, the spectral filter layer 58 can have a diffraction grating structure, for example. In many cases, it is composed of metal alloys, in particular of readily processable metals that are readily able to be applied in the micrometers thickness range, such as nickel-phosphorus, copper, silver or gold. By way of example, in the case of a molybdenum-silicon multilayer system, the protective layer 53 can be constructed, inter alia, from a layer of silicon nitride and a layer of ruthenium as vacuum seal. The coating 52 is arranged on a substrate 51. Typical substrate materials for reflective optical elements for EUV lithography, in particular collector mirrors, are glass ceramic, quartz glass, doped quartz glass, silicon, silicon carbide, silicon-infiltrated silicon carbide, copper, aluminum and alloys thereof. In a variant that is not illustrated here, the collector mirror can also be configured as a mirror for grazing incidence. To that end, by way of example, on a substrate composed of a copper or aluminum alloy, said collector mirror can comprise a polishing layer composed, inter alia, of nickel-phosphorus or amorphous silicon and thereabove a ruthenium layer as coating. Optionally, said collector mirror can additionally comprise a spectral filter layer. In the case of a metallic substrate, the latter can also be structured in order to filter out ultraviolet or infrared radiation, for example, from the beam path. In the example illustrated here, the radiation source can be a plasma radiation source in which tin droplets are excited with a CO2 laser to form a plasma that emits radiation in the EUV wavelength range. In this case, tin can penetrate into the EUV lithography apparatus and deposit on, in particular, the surface of the collector mirror. In the case of the reflective optical elements disposed downstream in the beam path, the tin contamination is negligible and contamination on the basis of oxygen or carbon can primarily occur. In order to reduce in particular the tin and carbon contamination on the coatings of the reflective optical elements of an EUV lithography apparatus, they are operated in vacuo with an admixture of hydrogen at a low partial pressure. Under the influence of the EUV radiation, reactive hydrogen in the form of hydrogen radicals and hydrogen ions forms from the molecular hydrogen. Said hydrogen ions are largely converted into hydrogen radicals by wall collisions. The reactive hydrogen together with the contaminations forms volatile tin and/or carbon compounds that can be extracted by pumping. Particularly if the coating contains defects that arose during operation or as early as during production, such as, for instance, pores, inclusions, dislocations or mechanical damage, such as scratches or cracks, for instance, penetration of reactive hydrogen into the coating can be observed, said reactive hydrogen being able to recombine within the coating or at the boundary with respect to the substrate. The conversion into molecular hydrogen leads to an increase in volume. Blisters form below the surface, which can lead to local peeling of part of or the entire coating. Delaminated locations may have a high reflectivity in the infrared range. This is problematic particularly in the case of collector mirrors if they are used in conjunction with a laser plasma radiation source from which, owing to the laser, not only EUV radiation but also infrared radiation emerge. If too much infrared radiation is coupled into the further beam path, the downstream mirrors of the optical system and the photomask could be damaged. Hitherto, reflective optical elements damaged by the influence of hydrogen have had to be produced virtually anew by virtue of the need to remove the entire coating and coat the substrate anew. FIG. 3 illustrates by way of example and schematically hydrogen-induced damaged locations 63, 64, 65, 66 in a coating 62 of a reflective optical element 60 for EUV lithography, for instance a collector mirror, on a substrate 61. The coating 62 can be constructed for example as explained above in the case of FIG. 2, in particular for normal or quasi-normal angles of incidence, or else as explained for grazing incidence. In the example illustrated here, the coating 62 has not been damaged down to the substrate 61, but this may occur in the case of all damaged locations. The damaged location 63 is a blister caused by an accumulation of molecular hydrogen in the coating 62. A blister that has already burst open is illustrated as damaged location 65. In the case of the damaged location 64, that part of the coating 62 which underwent spalling has already broken away entirely and the underlying part of the coating 62 is exposed and may be damaged by contamination or indiffusing hydrogen. Disturbing infrared reflections can occur at the damaged locations 63, 64, 65. In order then to repair the reflective optical element 60 for EUV lithography which comprises a substrate 61 and a coating 62 that reflects at an operating wavelength in the range of between 5 nm and 20 nm, firstly it is necessary to localize a damaged location in the coating. The process of localizing in particular hydrogen-induced damaged locations, specifically blisters and spalling, can take place for example through close visual inspection, since they have a macroscopic extent, for instance in the submillimeters to centimeters range, in many cases. It can also take place with the assistance of inspection systems that scan the surface of the coating. Before the localized damaged location is then covered with one or more materials, preferably having low hydrogen permeability, coating material in the region of the damaged location can be removed before the covering process. This has taken place for example in the case of the damaged location 66 illustrated in FIG. 3 and can be carried out for example by grinding, drilling, milling or similar processes. In this case, it is possible for example to penetrate into non-delaminated regions of the coating 62 or only to open and/or remove a blister. The removal of coating material has the advantage that further delamination at the damaged location can be better prevented or the damaged location can be better covered. Various covering possibilities are illustrated in FIG. 4 by way of example and schematically for the now repaired reflective optical element 70, which can be embodied as a collector mirror, for instance. It should be pointed out that all covering possibilities can be combined arbitrarily with all types of damaged locations. By way of example, covering elements which can be embodied, inter alia, as a covering unit or a film can be applied to damaged locations. In the example illustrated in FIG. 4, the damaged location 63 in the form of a blister has been covered with a covering unit 71 in the form of a cap. The cap 71 is composed of a hydrogen-impermeable material such as e.g. ceramic, for example aluminum oxide, glass or metal, in particular aluminum, molybdenum, high-grade steel or Invar. The cap 71 can also be composed of tantalum, niobium, silicon, titanium, zirconium, hafnium, scandium, yttrium, lanthanum, cerium, copper, silver, gold, platinum, rhodium, palladium, ruthenium or any desired combination of two or more of these materials or the materials mentioned above or comprise one or more of the materials mentioned. The cap 71 was secured by adhesive bonding with an adhesive that exhibits little outgassing, such as, for instance, a mineral filled epoxy resin. The cap 71 can be adhesively bonded over the whole area or only in points or a ring. Overflowing adhesive is largely noncritical since it combusts during operation in the course of irradiation with EUV radiation in the presence of hydrogen. A gap in the adhesive bond should also be regarded as noncritical since the reactive hydrogen recombines to form harmless molecular hydrogen as a result of wall collisions in the gap between cap 71 and coating 62. The cap 71 has a convex top side. This has the advantage that infrared radiation is scattered diffusely at the cap 71. In order to intensify this effect, the cap surface can additionally be roughened by sanding, sandblasting, etching or the like. Furthermore, the cap 71 can be passivated by an galvanic layer. When choosing the cap material it is advantageous to choose the coefficient of thermal expansion to be as similar as possible to that of the substrate 61. Alternatively or additionally the cap cross section can be weakened by preferably rotationally symmetrically provided notches, grooves 711 or lamellae, as took place in the case of the cap 71 illustrated, in order to reduce thermal stresses of the cap material vis-à-vis the substrate material. In order to avoid stresses on account of different coefficients of thermal expansion, flexible cap materials may also be advantageous. Covering elements, in particular covering units, can be adhesively bonded onto the undamaged coating 62 around a damaged location 63, 64, 65. Precisely with cap-type covering units, even in the case of a concave base such as may often be present in the case of collector mirrors, even blisters and mounds can be covered. Particularly if the coating does not adhere very well on the substrate or a blister is too large, the coating can be removed at the corresponding damaged location partly, for example down to the spectral filter layer, or else entirely down to the substrate using, inter alia, grinding, etching, ion beam bombardment or plasma etching. The covering element, in particular a cap-type covering unit, can then be adhesively bonded on the substrate or a coating region with good adherence. It is advantageous if, in the edge region of the covering element, there are a few millimeters of undamaged coating that can be covered by the covering element in order that penetration of reactive hydrogen below the covering element is prevented as much as possible. To that end, the covering element can also comprise for example a cantilever as adhesive edge. The covering unit can moreover also be embodied for example as a lamina or a sheet. Instead of a cap-type covering unit, a film 72 can also be applied to a damaged location, as took place in the case of damaged location 64 in the example illustrated in FIG. 4. Suitable materials have proved to be aluminum, aluminum alloys, titanium, copper, steel, silver, gold, but also ceramics and glasses through which hydrogen radicals penetrate only to a very small extent. Further suitable materials are generally metals, high-grade steel, Invar, molybdenum, tantalum, niobium, silicon, zirconium, hafnium, scandium, yttrium, lanthanum, cerium, platinum, rhodium, palladium, ruthenium, combinations of the materials mentioned or materials which comprise them or the combinations thereof. They can have thicknesses in the range of from a few atomic layers, as in the case of gold leaf, to a few hundred micrometers. One advantage of films is that they can easily be cut to size and adapted to the shape of the damaged location to be covered. As a result, they are suitable in particular for elongated and irregularly shaped damaged locations, for example also for scratches. Moreover, owing to their rather small thickness, in the event of temperature changes, they exert shear forces on an adhesive bond to a lesser extent. The negative influence of different coefficients of thermal expansion on the adhesive strength can also be reduced as a result. Overall, they can be secured on the coating 62 using adhesives having lower adhesive strength than covering units. Furthermore, they can be removed again relatively easily if rework of the reflective optical element 70 occurs. They could be peeled off from the adhesive and adhesive residues could be removed by a cold shock. It is advantageous, particularly in the case of collector mirrors having a curved surface, to adhesively bond the film 72 in a manner following the shape of the reflective optical element 70. To that end, beforehand the film can for example be concavely preshaped or be shaped directly on the surface using an areal, soft tool, such as a cotton swab or a foamed material stamp, for instance. Depending on the degree of curvature, however, a planar piece of film or thin sheet can also be applied. By virtue of the film having a round shape, even damaged locations in coatings of reflective optical elements having a somewhat higher degree of curvature can be repaired in a hydrogen-tight manner. It has also proved to be worthwhile in particular to preshape the film concavely and to provide one circumferential collar section or at least two collar sections as adhesive edge. The securing of the film 72 can be carried out as explained above for the covering element 71 embodied as a cap. Preferably, a filled adhesive is used and the adhesive bonding can be carried out areally, at points or as an adhesive ring or sections thereof. Inorganic adhesive systems such as sodium silicate, for instance, can also be used. Particularly in the case of films, however, securing by electric welding, laser welding or soldering, for example, is also possible, which can in each case also be carried out at points. Using electrostatic attraction, for example, the film, in particular, can be provisionally fixed in order to facilitate securing by welding or soldering. It is also possible to prepare self-adhesive film pieces. By way of example, self-adhesive aluminum films with adhesive based on acrylic resin are commercially available. It is possible to apply in particular curable adhesive to a film or thin sheet or else a covering unit protected by a protective film, in order that the adhesive cures only after the removal of the protective film and after the application of the covering element in particular as a result of contact with air humidity, oxygen or UV radiation. Furthermore, a chemical activator can be sprayed on before application if the covering element, in particular in the embodiment as a film, does not comprise all the components of the adhesive and the missing component(s) must be added during application. In a further variant, the film to be applied can be covered with auxiliary films from both sides. Before the film is applied, the adhesive-side auxiliary film is removed. Afterward, the film is placed onto the damaged location to be repaired and, through pressure at points on the other auxiliary film, the adhesive-coated side of the film is secured on the coating around the damaged location. This procedure has the advantage that the size and shape of the film actually applied need only be defined at the instant of application. In order, particularly in the case of collector mirrors, to prevent as much as possible reflection of radiation in undesired wavelength ranges into the beam path of the EUV lithography apparatus, the films can be provided with a macroscopic surface structure, as indicated by way of example as surface structure 721 in the case of the covering element 72 for example in FIG. 4. For example, they can be creased or embossed in order to reduce directional reflection of UV or IR radiation. Coarsely embossed film is commercially available. Dedicated embossing dies can also be used. In particular embossed patterns of tetrahedra have proved to be suitable for avoiding UV or IR reflections into the further beam path for EUV lithography in the case of corresponding orientation. In order to reflect IR radiation, in particular, as diffusely as possible, the films or thin sheets can be provided with a layer that reflects infrared radiation poorly, for example via anodizing, oxidation, pickling or etching for instance using acid. In particular, covering elements can also comprise a coating corresponding to the coating of the reflective optical element to be repaired, that is to say for reflecting EUV radiation. A covering element 73 embodied as a lamina 732 having a coating 731 suitable for reflecting EUV radiation is indicated in FIG. 4. In terms of its curvature, it is advantageously adapted to the curvature of the surface of the reflective optical element 70. The lamina 732 can be produced for example from silicon, glass, sapphire or aluminum oxide or generally a metal. Depending on the material of which the coated lamina 73 is composed and the base, that is to say the part of the coating 62 or the substrate 61, on which said lamina is applied, the latter can be applied by adhesive bonding, soldering or wringing. In preferred variants, the coated lamina 73 additionally has a surface structuring in order to divert radiation from undesired wavelength ranges, in particular infrared radiation, out of the beam path. A further possibility of repair, which moreover can readily be combined with the procedures described above, consists in applying a covering coating to the damaged location, as indicated as 74 for instance in FIG. 4. In the present example, the damaged location 66 was prepared by virtue of the fact that before the process of covering the damaged location 66, coating material in the region thereof was removed. This can be done, inter alia, with grinding, drilling or milling. A first possibility for applying a covering coating consists in oxidizing the material exposed at the damaged location 66. This can be done for example with an acid treatment using an oxidizing acid such as nitric acid, for instance, which is suitable in particular if nickel-phosphorus is exposed. The oxidation can also be carried out by an atmospheric pressure air and/or oxygen plasma. By using an atmospheric pressure noble gas plasma, in particular comprising argon or helium, and the corresponding volatile compounds, it is also possible to apply protective coatings which comprise or consist of one or more of the materials of the group molybdenum, tantalum, niobium, silicon, titanium, zirconium, hafnium, aluminum, scandium, yttrium, lanthanum, cerium, oxides thereof, nitrides thereof, carbides thereof, borides thereof, gold, platinum, rhodium, palladium, ruthenium, carbon, boron carbide and boron nitride. With an atmospheric air plasma, exposed material at the damaged location can also be nitrided. A wide variety of commercially available atmospheric pressure plasma devices exist, inter alia ones in which the plasma unit is scarcely larger than a pin and can also be handled in this way. Such a plasma unit can be implemented manually or in an automated manner in combination with a robot arm. The second possibility is primarily preferred if gases that would be harmful to human beings are used. One particular advantage of the atmospheric pressure plasma is also that a very dense plasma can be provided in conjunction with a very low heating effect and even particularly sensitive coatings can thus be processed. Particularly if compressed air can be used as process gas for the atmospheric pressure plasma, the operating costs are very low. A damaged location can also be repaired by electroplating and be passivated against reactive hydrogen. One example is electroplating with the aid of commercially available devices, the electroplating unit of which is configured in principle as a kind of cotton wad, which can be energized via a power terminal. Particular preference is given to galvanically applying one or more noble or semi-noble metals, in particular gold, silver, platinum or ruthenium. Further suitable materials are rhodium, palladium, molybdenum, tantalum, niobium, silicon, titanium, zirconium, hafnium, aluminum, scandium, yttrium, lanthanum and cerium. Pure metals, combinations thereof or alloys or materials containing them can be applied. A damaged location can also be tin-plated. Particularly before the reflective optical element is intended to be intensively cleaned with hydrogen, a damaged location can be sealed by tin drops having a size in the millimeters range. To that end, the damaged location such as damaged location 66 can be prepared by ablation. A blister such as damaged location 63 can also be incipiently drilled or milled, such that the tin penetrates into the open blister. A damaged location that has already been covered with tin can additionally be covered with further layers or covering elements. It is also particularly advantageous for the tin-plated damaged location additionally to be gold-plated, for example by applying gold leaf and, if appropriate, for the latter to be secured by soldering or welding, or by galvanically applying the gold. Some other noble or semi-noble metal can also be applied instead of gold. FIG. 5A schematically illustrates a further reflective optical element embodied as a collector mirror 80. The collector mirror 80 has a damaged location 67 in its coating 62 on the substrate 61. The damaged location 67 was repaired by applying a covering element 75 embodied as a covering unit having a concave surface. The covering element 75 can be shaped in various ways in different variants. Exemplary variants are illustrated schematically in FIGS. 5B to 5E. The covering element 75a from FIG. 5B has a rectangular boundary; the covering element 75b from FIG. 5C has an elliptic boundary; the covering element 75c from FIG. 5D has a polygonal boundary; and the covering element 75d from FIG. 5E has a freeform-shaped, predominantly curved boundary. The shape of the boundary can be adapted to the shape of the respective damaged location. Particularly in the case of covering elements shaped in elongate fashion, given suitable orientation relative to the scanning direction of an EUV lithography apparatus in which the reflective optical element is used, it is possible to reduce the influence of the covering element in the form of an abrupt bright-dark transition. As a result, the imaging performance of the EUV lithography apparatus is detrimentally affected by the repair to a lesser extent. Collector mirrors for EUV lithography which are operated with tin plasma sources and repaired in the manner described above do not exhibit hydrogen-generated blister growth at the repaired damaged locations, either after tin cleaning using hydrogen radicals or after lengthy operation with a tin plasma source. It should be pointed out that the repair method presented here may also be suitable for repairing damaged locations in the form of scratches or cracks. 10 EUV lithography apparatus 12 EUV radiation source 13 collector mirror 14 illumination system 15 first mirror 16 second mirror 17 mask 18 third mirror 19 fourth mirror 20 projection system 21 wafer 50 reflective optical element 51 substrate 52 coating 53 protective layer 54 multilayer system 55 pair of layer 56 absorber 57 spacer 58 spectral filter layer 60 collector mirror 61 substrate 62 coating 63 damaged location 64 damaged location 65 damaged location 66 damaged location 67 damaged location 70 collector mirror 71 covering element 711 groove 72 covering element 721 surface structure 73 covering element 731 coating 732 lamina 74 covering coating 75 covering element 75a covering element 75b covering element 75c covering element 75d covering element 80 collector mirror |
|
044252960 | abstract | Probe-holding apparatus for holding a probe for checking steam generator tubes particularly in a nuclear reactor installation. The apparatus comprises a telescopic arm supported via a ball and socket joint from a support mounted in or near an access aperture in a chamber at one end of the steam generator. A probe guide is carried by a carriage pivotally mounted at the other end of the telescopic arm. The carriage includes an endless belt having a series of spaced projections which engage into the ends of the tubes, the projections being spaced by a distance equal to the tube pitch or a multiple thereof. The belt is driven by a stepping motor in order to move the carriage and place the probe guide opposite different ones of the tubes. |
047479957 | claims | 1. With a cruciform shaped radioactive control rod of the type having four substantially equidistantly spaced plate-like sheaths extending from and along a large portion thereof so as to provide a first set of opposed sheaths and a second set of opposed sheaths, each sheath containing at least one radioactive rod, and a velocity limiter at one end thereof, apparatus for separating said velocity limiter from the remainder of said control rod, said apparatus comprising: shearing means for simultaneously shearing each set of two opposed sheaths adjacent the velocity limiter, said shearing means including a first shearing head operative from a first direction to shear one of the sheaths of a respective set and a second shearing head operative from a second direction substantially opposite to said first direction to shear the other of the sheaths of the respective set; rotating means for providing relative rotation of the sheaths with respect to said shearing means such that said shearing means can simultaneously shear the other set of two opposed sheaths, to thereby separate the velocity limiter from the remainder of the control rod. 2. Apparatus according to claim 1; wherein said rotating means includes rotatable turntable means for supporting the control rod thereon in a vertical arrangement with the velocity limiter resting thereon, and control means for controlling rotation of said rotatable turntable means. 3. Apparatus according to claim 2; further including aligning means associated with said rotatable turntable means for selectively aligning each set of opposed sheaths with said first and second shearing heads. 4. Apparatus according to claim 1; wherein the control rod includes at least one hole at a position adjacent the velocity limiter and at a position at which there are no radioactive rods, and said shearing means is positioned in line the said at least one hole to shear the sheaths thereat. |
claims | 1. An efficient turbine system that utilizes nuclear thermal energy in a unique combined Carnot cycle and Rankine cycle in a closed cogenerative and regenerative cycle, comprising:a multi-stage gas turbine having multiple turbine stages;a condensible working fluid, heated by a thermal energy source to a superheated gas and delivered in a main path to the internals of the multi-stage gas turbine and in an auxiliary path to each stage of the multi-stage gas turbine as a superheated steam for isothermal expansion, wherein a portion of the condensed working fluid is injected as a liquid into the multi-stage gas turbine before and between the turbine stages for a regenerative cogeneration expansion as a gas that supplements and combines with the primary working fluid in the multi-stage gas turbine; anda multi-stage recovery turbine wherein the combined working fluid is delivered to the multi-stage recovery turbine with a final adiabatic expansion in the multi-stage recovery turbine with work extracted by electric generators connected to at least one of the turbines. 2. The turbine system of claim 1 wherein the multi-stage gas turbine has a shroud over the multiple turbine stages that forms a high pressure chamber with passages to each of the multiple stages of the turbine for feeding supplemental superheated gas to the multi-stage gas turbine. 3. The turbine system of claim 2 wherein the passages are perforations in the shroud at the turbine stages. 4. The turbine system of claim 2 wherein the working fluid is water. 5. The turbine system of claim 4 wherein the shroud has water injection nozzles for injecting water over the shroud for cooling the shroud wherein the water flashes to steam and adds to the working fluid in the multi-stage gas turbine. 6. The turbine system of claim 1 wherein the multi-stage gas turbine has turbine blades and stators and the portion of the condensed working fluid injected as a liquid into the multi-stage gas turbine before and between the turbine stages is injected onto the turbine blades and stators of the multi-stage gas turbine for cooling the turbine blades and stators. 7. An efficient turbine system that utilizes a thermal energy source in a combined Carnot cycle and Rankine cycle in a closed cogenerative and regenerative cycle comprising:a multi-stage gas turbine having multiple turbine stages;a condensible working fluid, heated by the thermal energy source to a superheated gas and delivered in a main path to the internals of a multi-stage gas turbine and in an auxiliary path to each stage of the multi-stage gas turbine for isothermal expansion wherein a portion of the condensed working fluid is injected as a liquid into the multi-stage gas turbine before and between the turbine stages for a regenerative cogeneration expansion as a gas that supplements and combines with the primary working fluid in the multi-stage gas turbine; and,a recovery turbine wherein the combined working fluid is delivered to the recovery turbine with a final adiabatic expansion in the recovery turbine with work extracted by electric generators connected to at least one of the turbines. 8. The turbine system of claim 7 wherein the multi-stage gas turbine has a shroud over the multiple turbine stages that forms a high pressure chamber with passages to each of the multiple stages of the turbine for feeding supplemental superheated gas to the multi-stage gas turbine. 9. The turbine system of claim 8 wherein the passages are perforations in the shroud at the turbine stages. 10. The turbine system of claim 8 wherein the working fluid is water. 11. The turbine system of claim 8 wherein the shroud has water injection nozzles for injecting water over the shroud for cooling the shroud wherein the water flashes to steam and adds to the working fluid in the multi-stage gas turbine. 12. The turbine system of claim 7 wherein the multi-stage gas turbine has turbine blades and stators and the portion of the condensed working fluid injected as a liquid into the multi-stage gas turbine before and between the turbine stages is injected onto the turbine blades and stators of the multi-stage gas turbine for cooling the turbine blades and stators. 13. The turbine system of claim 7 wherein the thermal energy source is nuclear thermal energy. 14. The turbine system of claim 7 wherein the recovery turbine is connected to an electrical generator. 15. The turbine system of claim 7 wherein the working fluid is expanded in the recovery turbine and condensed for return to the cycle. 16. The turbine system of claim 7 wherein the turbine system has a high pressure pump and condensed working fluid is returned to a fluid supply system by the high pressure pump. |
|
062890719 | summary | FIELD OF THE INVENTION The present invention relates to a positron source capable of generating a positron beam of high intensity, a method of preparing the positron source, and an automated system for supplying the positron source. RELATED BACKGROUND ART Slow positron beams have been commonly used in positron microscopes, for research in physical properties and for crystal defect evaluation of the surfaces or interfaces of semiconductors and metallic materials, and recently have become useful more and more. At present, slow positron beams are generated by emitting from positron emitters (radioisotopes), or by ejecting positrons that are generated through pair creation with a braking radiation into a moderator to be slowed down the positrons. A positron emitter is often prepared by irradiating a solid target (e.g., aluminum or boron nitride) with a beam of charged particles (e.g., protons) accelerated with a cyclotron or the like; thus a positron emitter can be generated in the solid target. A braking radiation is usually generated by irradiating a heavy metal target with an electron beam accelerated with a linear accelerator or the like. Upon the utilization of positron beams, a strong point source for a positron emitter is required. Various approaches have been proposed for increasing the intensity of positron beams, such as the improvement in moderator efficiency and the use of a stronger positron source. As a moderator, one formed of a tungsten foil which is annealed at 2000.degree. C. is currently used. However, such moderator cannot achieve an efficiency of the order of 10.sup.-4 or more. Although many efforts are being made to improve moderators, drastic and practical improvements could hardly be expected. On the other hand, for preparing a strong positron source, the use of a large-scale and expensive device is needed. In the preparation process for a strong positron source using a solid target, there is a serious problem that heat generated during the passage of a large electric current should be removed. The process also has another problem as follows. A solid target is placed nearby a moderator for the purpose of causing to emit positrons from a positron emitter generated in the target and increasing the incident efficiency of positrons generated through pair creation with a braking radiation into the moderator. When such solid target is irradiated with an electron beam or an ion beam, the moderator sustains a radiation damage or is radioactivated by a secondary radiation other than the positrons. In order to overcome this problem, it is proposed an approach for avoiding the influence of the secondary radiation during the irradiation of the target, which comprises: irradiating a solid target at a place a distance away from a moderator thereby generating a positron emitter; transferring the irradiated solid target to the place where the moderator is placed; and ejecting a beam of positrons emitted from the positron emitter in the solid target into the moderator. However, such approach is not practical. This is because the use of a solid target usually needs a cooling device for removing heat generated as a result of the irradiation and, therefore, if a solid target is to be transferred, the system as a whole will inevitably become a large scale due to the integration of the cooling device. In the process utilizing a braking radiation generated with an electron beam, it is impossible in principle to separate a heavy metal target and a moderator. Moreover, in this process, it is necessary to automate the supply of a positron source to a positron beam-generating unit for the purpose of avoiding the harmful irradiation exposure of operators. SUMMARY OF THE INVENTION Under these situations, the present invention is made. That is, the object of the present invention is to provide a positron source capable of generating a positron beam of high intensity without damaging a moderator, a method of preparing the positron source, and an automated system for supplying the positron source. The present inventors have found that the positron source can be prepared using a liquid target containing H.sub.2.sup.18 O [.sup.18 O(H.sub.2 O)] as a target for generating a positron emitter, by irradiating the liquid target with a proton beam to generate a positron emitter .sup.18 F through a .sup.18 O(p,n).sup.18 F reaction, and causing to bind the .sup.18 F onto a carbon member to trap the .sup.18 F on the carbon member. This finding leads the accomplishment of the present invention. Therefore, the present invention provides a positron source comprising a carbon member having .sup.18 F bound onto the surface thereof. The-carbon member is preferably made of graphite or glassy carbon. The carbon member preferably has a rod-like or strip-like geometry onto an end of which .sup.18 F is bound. The present invention also provides a method of preparing a positron source comprising: irradiating a liquid target containing H.sub.2.sup.18 O with a beam of charged particles to generate .sup.18 F; and passing an electric current through the liquid target using a carbon member as an anode to cause to bind the .sup.18 F onto the surface of the carbon member. The liquid target may contain a small amount of natural fluorine ions, for example, by the addition of a fluoride of an alkali metal which is soluble in the liquid target and is a strong electrolyte (e.g., NaF, NaHF.sub.2 and KF). The reason for the pre-addition of a small amount of natural fluorine ions to a liquid target [.sup.18 O(H.sub.2 O)] is as follows. The number of the .sup.18 F atoms generated through a nuclear reaction in the liquid target is at most 3.5.times.10.sup.15 atoms, which corresponds to only 1.1.times.10.sup.-8 g in terms of the weight of fluorine atoms. Such extremely trace amount of .sup.18 F atoms might result in insufficient current for electrodeposition. In order to prevent this problem, natural fluorine ions are added to the liquid target at a concentration of 2.mu./ml so that the number of the .sup.18 F atoms becomes about 100 times greater than that without natural fluorine ions. This ensures the chemical behavior of the generated .sup.18 F as F.sup.31 in an aqueous solution (a liquid target). Since the amount of the fluorine ions added is very small, it is necessary for the fluorine ions to be added to the liquid target prior to the irradiation. In the present invention, it is preferable that the carbon member (i.e., an anode) have a rod-like or strip-like geometry and an electric current be passed through the liquid target while contacting an end surface of the carbon member with the liquid target so that the .sup.18 F is concentratedly bound onto the end surface of the carbon member. It has not been made clear yet whether the bonding of the .sup.18 F onto the surface of the carbon member is via a direct bonding between the .sup.18 F and a carbon atom in the carbon member (e.g., generation of a C-F bonding) or via intercalation of the .sup.18 F into a graphite-type crystal structure of the carbon member (i.e., formation of an intercalation compound). The present invention also provides an automated system for supplying a positron source comprising: means for moving a container with a solution containing .sup.18 F to the position where an electric current is to be passed through the solution; means for passing an electric current through the solution at that position using a carbon member as an anode; and means for transferring the carbon member after the passage of the electric current to a positron beam-generating unit. In this system, the solution containing .sup.18 F is fed to a container placed in another room, and an electric current is then passed through the solution at that place. This system may further comprise means for recovering the solution after the passage of electric current. The present invention further provides an automated system for supplying a positron source comprising: a rotary table for rotating a container mounted thereon; means for supplying a solution containing .sup.18 F into the container; first drive means for rotationally driving the rotary table so that the container moves between the position where the solution is to be supplied into the container and the position where an electric current is to be passed through the solution in the container; a rotary member on which a carbon member is mounted; second drive means for rotationally driving the rotary member so that the carbon member moves between the position opposed to the liquid surface of the solution in the container placed in the position where an electric current is to be passed to the solution and the position opposed to a positron source-receiving section of a positron beam-generating unit; hoisting-and-lowering means for moving the rotary member up and down; and a power supply for passing an electric current through the solution in the container using the carbon member as an anode; wherein the carbon member onto the surface of which .sup.18 F is caused to bind by passing an electric current through the solution in the container using the carbon member as an anode, is attached to the positron source-receiving section of the positron beam-generating unit. This system may further comprise contact-detection means for detecting the contact of the carbon member with the solution in the container, which enables a precise control of the depth of the carbon member immersed in the solution. The contact-detection means may also be serve as means for detecting a micro-current passing through the solution at the instant when the carbon member is contact with the liquid surface of the solution. In the system, a plurality of containers may be mounted on the rotary table and the same numbers of carbon members as that of the containers may be mounted on the rotary member so that a continuous operation becomes possible for a long time of period. The H.sub.2.sup.18 O-containing liquid target can be fed to any place readily through a pipe. Therefore, if it is possible to irradiate the H.sub.2.sup.18 O-containing liquid target to generate a positron emitter .sup.18 F, transfer the .sup.18 F-containing solution by remote control to the place where the positrons are used, and trap the .sup.18 F on the carbon member at that place in the state that the .sup.18 F binds onto a very small area of the carbon member, then undesirable damage of a moderator or background noise of the measurements caused by the secondary radiation during the irradiation of the liquid target can be prevented by transferring only the carbon member (i.e., the positron source) to the place where the moderator is set. In addition, by confining the surface area of the carbon source onto which the positron emitter .sup.18 F is intended to be bound within narrow limits, the density of the positron source in the surface area can be increased and, consequently, a positron beam of high intensity can be generated. According to the present invention, since the irradiation of the target is performed at a place a distance away from the moderator, the influence of the secondary radiation caused by the irradiation can be eliminated. In the present invention, it is also preferable to immediately recover the H.sub.2.sup.18 O remaining in the solution after the preparation of a positron source is completed, because H.sub.2.sup.18 O is a very expensive material and the amount of .sup.18 O converted into .sup.18 F in one irradiation is extremely small. If the H.sub.2.sup.18 O is not recovered immediately and allowed to leave in the solution, it is not only evaporated as water vapor, but also normal water is dissolved into the H.sub.2.sup.18 O-containing solution to reduce the concentration of the H.sub.2.sup.18 O. This specification includes part or all of the contents as disclosed in the specifications and/or drawings of Japanese Application Nos. 10-248611 and 10-308533, which are priority documents of the present application and incorporated herein by reference in their entirety. The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings. |
claims | 1. A confinement system comprising:an enclosure comprising:a first end and a second end that is opposite from the first end; anda midpoint that is substantially equidistant between the first and second ends of the enclosure;two internal magnetic coils suspended within an interior of the enclosure and co-axial with a center axis of the enclosure, the two internal magnetic coils each having a toroidal shape;a plurality of encapsulating magnetic coils co-axial with the center axis of the enclosure, the encapsulating magnetic coils having a larger diameter than the internal magnetic coils;a center magnetic coil co-axial with the center axis of the enclosure and located proximate to the midpoint of the enclosure;one or more heat injectors coupled to the enclosure; andtwo mirror magnetic coils co-axial with the center axis of the enclosure;wherein the magnetic coils are operable, when supplied with electrical currents, to form magnetic fields for confining plasma within a magnetic sheath inside the enclosure, the magnetic sheath configured to allow recirculation of plasma between edges of adjacent cusps formed within the enclosure;wherein each of the one or more heat injectors is operable to inject a beam of neutral particles into the enclosure through the magnetic sheath; andwherein the center magnetic coil is disposed outside the interior of the enclosure. 2. The confinement system of claim 1, wherein at least one of the one or more heat injectors is aligned substantially perpendicular to the center axis of the enclosure. 3. The confinement system of claim 2, wherein the at least one of the one or more heat injectors aligned substantially perpendicular to the center axis of the enclosure is operable to inject a circular-shaped beam of neutral particles into the enclosure. 4. The confinement system of claim 1, wherein the at least one of the one or more heat injectors is aligned at an angle different from ninety degrees from the center axis and operable to inject an non-circular, elliptical-shaped beam of neutral particles into the enclosure. 5. The confinement system of claim 1, wherein the one or more heat injectors are operable to focus the beam of neutral particles toward a focal point within the enclosure. 6. The confinement system of claim 1, wherein the one or more heat injectors are operable to cause the beam of neutral particles to diverge as it propagates in the enclosure based on one or more of an alignment of the one or more heat injectors, a shape of the beam of neutral particles, and a beam energy of the beam of neutral particles injected by the one or more heat injectors. 7. A confinement system comprising:two internal magnetic coils suspended within an interior of an enclosure;a center magnetic coil coaxial with the two internal magnetic coils and located proximate to a midpoint of the enclosure;a plurality of encapsulating magnetic coils coaxial with the internal magnetic coils, the magnetic coils being operable, when energized, to preserve the magnetohydrodynamic (MHD) stability of the fusion reactor by maintaining a magnetic sheath within the enclosure that prevents plasma within the enclosure from expanding, wherein the magnetic sheath is configured to allow recirculation of plasma between edges of adjacent cusps formed within the enclosure;two mirror magnetic coil coaxial with the internal magnetic coils; andone or more heat injectors operable to inject a beam of neutral particles toward the center of the enclosure through the magnetic sheath;wherein the center magnetic coil is disposed outside the interior of the enclosure. 8. The confinement system of claim 7, wherein at least one of the one or more heat injectors is substantially perpendicular to a center axis of the enclosure. 9. The confinement system of claim 8, wherein the at least one of the one or more heat injectors aligned substantially perpendicular to the center axis is operable to inject a circular-shaped beam of neutral particles into the enclosure. 10. The confinement system of claim 7, wherein the at least one of the one or more heat injectors are aligned at an angle different from ninety degrees from a center axis of the enclosure and operable to inject a non-circular, elliptical-shaped beam of neutral particles into the enclosure. 11. The confinement system of claim 7, wherein the one or more heat injectors are operable to focus the beam of neutral particles toward a focal point within the enclosure. 12. The confinement system of claim 7, wherein the one or more heat injectors are operable to cause the beam of neutral particles to diverge as it propagates in the enclosure based on one or more of an alignment of the one or more heat injectors, a shape of the beam of neutral particles, and a beam energy of the beam of neutral particles injected by the one or more heat injectors. 13. A method comprising:energizing two internal magnetic coils suspended within an interior of an enclosure;energizing a center magnetic coil coaxial with the two internal magnetic coils and located proximate to a midpoint of the enclosure;energizing a plurality of encapsulating magnetic coils coaxial with the internal magnetic coils, the magnetic coils being operable, when energized, to preserve the magnetohydrodynamic (MHD) stability of the fusion reactor by maintaining a magnetic sheath within the enclosure that prevents plasma within the enclosure from expanding, wherein the magnetic sheath is configured to allow recirculation of plasma between edges of adjacent cusps formed within the enclosure;energizing two mirror magnetic coil coaxial with the internal magnetic coils; andinjecting a beam of neutral particles toward the center of the enclosure;wherein the center magnetic coil is disposed outside the interior of the enclosure. 14. The method of claim 13, wherein injecting the beam of neutral particles toward the center of the enclosure increases the average energy of the plasma confined within the magnetic sheath. 15. The method of claim 13, wherein injecting the beam of neutral particles toward the center of the enclosure comprises forming fully ionized plasma in the enclosure during a start-up phase. 16. The method of claim 15, wherein injecting the beam of neutral particles toward the center of the enclosure comprises injecting at least partially ionized plasma. 17. The method of claim 15, wherein the beam of neutral particles comprises deuterium particles. 18. The confinement system of claim 1, wherein the two mirror magnetic coils comprise a first mirror magnetic coil and a second mirror magnetic coil disposed on opposite sides of the center magnetic coil. 19. The confinement system of claim 1, further comprising:a center coil system configured to supply first electrical currents flowing in a first direction through the center magnetic coil;an internal coil system configured to supply second electrical currents flowing in a second direction through each of the two internal magnetic coils;an encapsulating coil system configured to supply third electrical currents flowing in the first direction through each of the plurality of encapsulating magnetic coils; anda mirror coil system configured to supply fourth electrical currents flowing in the first direction through each of the two mirror magnetic coils. 20. The confinement system of claim 1, wherein each of the two internal magnetic coils comprises at least a first shielding surrounding the internal magnetic coil and each of the two internal magnetic coils is suspended within the enclosure by at least one support. |
|
055531083 | claims | 1. In a fuel bundle assembly for a nuclear reactor wherein a plurality of fuel rods and at least one water rod extend between an upper tie plate and a lower tie plate, the improvement comprising a fixed connection between said water rod and the lower tie plate, the fixed connection including a threaded lower end plug on the water rod and a threaded hole in a boss formed in the lower tie plate adapted to receive said threaded lower end plug, said threaded lower end plug formed with a diametrical slot therein and said boss formed with a pair of slots extending from opposite sides of said hole such that said diametrical slot and said pair of slots are alignable when said threaded lower end plug is threaded into said boss; and a key insertable within the aligned diametrical slot and pair of slots to thereby fix said water rod against rotational movement. 2. The fuel bundle of claim 1 wherein said key is secured within said aligned slots. 3. The fuel bundle of claim 1 wherein said key is secured by welding. 4. The fuel bundle of claim 1 wherein said one or more water rods comprise a pair of water rods and wherein only one of the water rods incorporates said improvement. |
summary | ||
055132294 | claims | 1. A method for removing a control rod drive from a control rod drive housing in a nuclear reactor from a position below a reactor pressure vessel, said control rod drive comprising a position indicator probe installable along a centerline axis of and removable from said control rod drive, comprising the steps of: uncoupling a control rod from said control rod drive while said position indicator probe is in place inside said control rod drive and electrically connected to a control room of the reactor; verifying in the control room that said control rod is uncoupled from said control rod drive from electrical signals received from said position indicator probe; electrically disconnecting said position indicator probe from said control room; electrically connecting an indicating tool to said position indicator probe; supporting said control rod drive from below using a mechanical support without removing said position indicator probe; removing a plurality of mounting bolts to mechanically disconnect said control rod drive from said control rod drive housing; lowering said mechanical support to slide said control rod drive out of said control rod drive housing; and verifying that said control rod is uncoupled from said control rod drive from electrical signals received by said indicating tool from said position indicator probe while said control rod drive is sliding out of said control rod drive housing. placing a support means underneath said control rod drive in contact therewith; removing a plurality of mounting bolts to disconnect said control rod drive from said control rod drive housing; lowering said support means to slide said control rod drive out of said control rod drive housing; wherein all of said steps are performed while said position indicator probe is in place in said control rod drive; monitoring the state of a plurality of position switches inside said position indicator probe while said support means is being lowered; and generating an indicating signal in response to all of said plurality of position switches being in an open state, said indicating signal indicating that said control rod drive is coupled to said associated control rod. 2. The method as defined in claim 1, further comprising the step of monitoring the state of first and second position switches inside said position indicator probe while said support means is being lowered. 3. The method as defined in claim 2, further comprising the steps of generating a first indicating signal in response to closing of said first position switch and generating a second indicating signal in response to closing of said second position switch, said first indicating signal indicating that said control rod drive is uncoupled from an associated control rod and said second indicating signal indicating that said control rod drive is coupled to said associated control rod. 4. The method as defined in claim 1, further comprising the step of monitoring the state of a plurality of position switches inside said position indicator probe while said support means is being lowered. 5. A method for removing a control rod drive from a control rod drive housing in a nuclear reactor, said control rod drive comprising a position indicator probe arranged along a centerline axis of said control rod drive, comprising the steps of: 6. The method as defined in claim 5, wherein said indicating signal is a flashing light source. 7. The method as defined in claim 5, wherein said indicating signal is a pulsed sound source. |
050009079 | abstract | A nuclear reactor is provided with an emergency cooling water injection device, comprising a vessel through which pass not only the cooling water inlet and outlet pipes under normal operating conditions but also a conduit for injecting pressurized water coming by an emergency reservoir, should a breakage of the primary circuit occur. A thermally insulated duct of the side wall of the vessel, at least at the level of the core, conveys the injected water below the core support plate. |
044410255 | description | DESCRIPTION OF PREFERRED EMBODIMENTS Radiation protective aprons, per se, are known. In this connection, reference is made to U.S. Pat. Nos. 3,404,225 (Green); 2,451,282 (Feibel); 2,494,664 (Lubow); 2,642,542 (Weinberg); 3,052,799 (Hollands); 3,093,829 (Maines); 3,233,248 (Bushnell); and German Pat. No. 1078279 and French Pat. No. 1145614. Referring first to FIG. 1, there is depicted, laid out flat, in a plan view, an x-ray protective apron 10 which embodies the present invention. Although this particular embodiment will be discussed at length here, it is to understood that this invention is not restricted to this particular embodiment or use, but instead is applicable to any apparel. Thus, for example, it is not restricted to use on x-ray protective equipment, but is applicable as well to equipment for use in protecting against other forms of radiation, as well as for such things as bullet-proof vests and the like, particularly where the weight of the equipment is a significant factor. The apron apparel shown in FIG. 1 may be made from a wide variety of known per se protective materials, such as lead filled vinyl, laminated fabrics, etc. As shown, it includes a main body portion 11, a neck portion 12, and flap members 14, 16. The insides of the flaps 14, 16, (i.e., the portions which ultimately face juxtaposed to the outer surface of the apron) include Velcro surfaces 15, 17 (respectively), for interengagement with the Velcro surfaces 18, 20 (respectively) affixed to the front of the main body 11 of the apron 10. Although other forms of length (and therefore tautness) adjustable fasteners, such as hooks and eyes (not shown) may also and/or alternatively be used, Velcro fasteners have been found to be particularly advantageous for use with embodiments of this invention because of the ease with which they may be attached and removed, and because of the small and variable increments of length adjustment which they afford, as contrasted with the more limited and fixed positioning afforded by other fastening means. In this connection, reference is made to Maines U.S. Pat. No. 4,196,355. It should be noted particularly that in preferred embodiments of this invention, the flaps are so that, and the corresponding fastener means 18, 20 on the main body 11, are so oriented that when the flaps 14, 16 are fastened in position as hereinafter described, their outermost ends, and therefore their axial orientation, will be at least slightly downward. By this means, the weight transfer hereinafter described, may be achieved easier and more effectively as this tends to transfer the apron's weight downward onto the pelvis, rather than straight across the small of the back. Referring to FIG. 2, it will be seen that when the user puts the apron on, the flaps 14, 16 are crossed approximately in the region of the lower back; i.e., near the top of the pelvis structure, where the size of the body normally increases above the buttocks. The user has virtually unlimited choice as to the degree of length of the flaps as they are brought around the sides and, as shown in FIG. 3, secured to the front of the apron by means of the associated fastening means. It will be apparent, therefore, from FIG. 4 in particular, that by means of so regulating the length of the flaps, and therefore their degree of tautness, part or even substantially all of the weight of the apron may be taken off of the wearer's shoulders and concentrated on the wearer's lower body region. The looser the flaps, the greater the share of the weight that will be borne by the shoulders. The tighter the flaps are drawn, the greater the share of the weight that will be borne by the lower body region; i.e., the hips and pelvis. The latter, structurally as well as by virtue of being at a lower center of gravity, is more well suited for weight bearing, particularly over extended periods of time. Another feature of this, in terms of user comfort, is the ready ability which it affords to change the weight distribution of the apron at any time and from time to time; such change, per se, being well known as a means to make weight bearing more tolerable and comfortable, particularly over extended periods of time. Thus, it will be apparent that through practice of this invention, it is possible to produce a wide variety of apparel which is as fully protective as desired, of "full" cut and adaptably contoured, roomy, non-binding, and yet, even when made from heavy materials, adjustable so as to redistribute its weight and to minimize fatigue. Accordingly, it is to be understood that the embodiments herein disclosed and described are by way of illustration and not of limitation, and that a wide variety of embodiments may be made without departing from the spirit or scope of this invention. |
abstract | A filter is disclosed for the spectral filtration of X-rays emanating from an X-ray source which cross an object under examination and are detected by an X-ray detector in at least two different spectral regions. After crossing the object under examination, the X-rays have an energy spectrum which displays a characteristic distribution for the anode material of the X-ray source. In an embodiment, the filter is configured to suppress part of the energy spectrum comprising the focal point of the energy spectrum. A corresponding X-ray system and method are also disclosed. |
|
048896845 | description | Referring to FIG. 1A, a fuel bundle S is shown in relation to a reactor core. The core includes two flow regions. One of these flow regions is interior of the fuel bundle, the remaining region is exterior of the fuel bundle and in core bypass region B. A simplified description of the fuel bundle can be presented. A lower tie-plate L is illustrated. The tie-plate supports a group of fuel rods R. Some of these rods are threaded at 16. These threaded rods extend between lower tie-plate L and upper tie-plate U. The threaded rods form connections between the respective tie-plates and maintain the remaining rods in side-by-side upstanding relation. Apertures in the region between the fuel rods permit flow of water into the fuel bundle. Extending between the two tie-plates L and U and on the outside of the fuel bundle is a channel C. Channel C forms a flow barrier between the inside of the fuel bundle F and the core bypass region B. At the bottom of the lower tie-plate are metering apertures A. The pressure difference between the inside of the fuel bundle and the bypass region causes water to flow through the metering apertures A into the bypass region B. As has been set forth, it is this pressure drop acting from the interior of the fuel bundle F to the core bypass region B that causes the channel C overlying the lower tie-plate L to bulge away from the sides. The prior art has prevented unreasonable flow rates in the interstices between the sides of the lower tie-plate L and the channel C by the use of fingers F. Fingers F are typically spring biased away from the sides of indentations 18 in the lower tie-plate. Such spring bias enables the fingers F to move into the volume between the lower tie-plate L and the channel C as the channel deflects away from the lower tie-plate. Unfortunately, such spring bias is an additional contributing factor to channel deflection. Referring to FIG. 1B, a section of the lower tie-plate L at the channel C is illustrated. This Figure shows how leakage flow occurs without finger springs, or other means for limiting leakage flow. Specifically, water under pressure enters aperture 14 flowing upwardly through a grid 20 for support of the individual fuel rods R. After passage through grid 20, some water finds its way into the interstitial flow volume 22 defined between the lower portion of the channel C and the overlapping portion of the channel tie-plate L. The pressure effect produced on this portion of the channel can be seen with respect to the coolant pressure diagram plotted with respect to the channel C. Remembering that a pressure P.sub.i is present on the interior of the fuel bundle F, it will be seen that channel C above the lower tie-plate L is under a complete pressure differential between the core bypass region B and the interior of the fuel bundle F. Water passing in the interstitial area 22 gradually loses its pressure until escape from the bottom of the channel at 25. Consequently, coolant pressure likewise falls gradually over the length of the channel as it is illustrated. Such pressure experiences an immediate drop at the entrance to the channel at 23 until an almost full drop is realized upon exit at 25. Referring to FIG. 2, an embodiment of this invention is illustrated. Lower tie-plate L is shown. The lower tie-plate includes first and second labyrinth seal rings 30, 32. These labyrinth seal rings define expanded flow areas 31, 33. Functions of labyrinth seals are well known. Specifically, the labyrinth seals provide expanded volumes for inefficient turbulent flow to occur immediately after each of the constricted apertures 30, 32. Such expanded and inefficient flow causes large and rapid pressure differentials across the labyrinth seal. Referring to the flow diagram, it can be seen that the labyrinth seal matrix of the respective seals 30, 32 produces a rapid and full pressure between the entrance to the seal 29 and the region below the seal 38. The portion 38 of the channel C underlying this rapid pressure drop area has no pressure load acting on it. The part of the channel which is not loaded can thereafter reinforce the overlying portions of the channel. Referring to FIG. 3, the reader can understand that it is possible for a labyrinth seal to be configured by both cooperative shaping of the lower tie-plate L and the channel C. According to this embodiment, channel C is provided in the vicinity of the lower tie-plate L with corrugations, which corrugations 40 define with respect to the lower tie-plate L successive contracted regions of flow 42, 44 followed by expanded regions of flow 43, 45. These respective regions of flow define a labyrinth seal along the length of the interstitial volume between the channel C and the lower tie-plate L. Referring to FIGS. 4A, 4B, and 4C, a preferred embodiment of this invention is illustrated. A lower tie-plate L and channel C are shown. The area of the improvement herein is shown by circular detail 50. Referring to FIG. 4B, a first detail is illustrated. Specifically, channel C against lower tie-plate L defines a diffuser volume 54, diffuser volume 54 includes an initial venturi flow 53. Referring to the diagram configured opposite to FIG. 4A, the effect of this can be seen. Specifically, at inflow area 51, pressure exceeds that of the core bypass region P.sub.o. However, between the region above the aperture 51 and the beginning of the aperture 55 there is a large increase in flow velocity and a corresponding decrease in pressure, in accordance with Bernoulli's theorem. Between the beginning of the aperture 55 and the beginning of the diffuser 53 there is an additional pressure drop caused by friction losses over the length of the aperture. Thereafter, and due to the action of the diffuser, pressure slowly increases until it equalizes to the pressure of the core bypass region at P.sub.o. In accordance with this aspect of the invention, not only does the lower unloaded portion of the channel C reinforce the overlying loaded portion of the channel but additionally, a negative pressure acts inwardly in the vicinity of the lower portion of the channel C at the tie-plate. It is important to notice that this negative pressure will increase upon increasing deflection. That is to say, the very effect of pressure induced deflection, which it is the purpose of this invention to combat, causes increased flow with increased negative pressure differential. The reader will also understand that by configuration of the lower tie-plate at 60 on FIG. 4C, the same effect can be reached. Specifically, a pressure drop at the aperture 53 is formed. Moreover, a diffuser 54 is present. Thus, by either the configuration of the lower tie-plate L or the bottom of the channel C, the hydraulic forces on the channel C counteract the bulging forces heretofore set forth. Having set forth the invention as relates to the sides of the channel adjacent the lower tie-plate, attention can now be directed to an improvement at the corners of the polygon sectioned (square sectioned) channel. Corners are an unavoidable leakage path. Because of manufacturing considerations, a gap is intentionally designed at the corners and a snug fit between channel and lower tie-plate is designed over the sides. Because of difficulty in maintaining tight tolerances there is uncertainty in this leakage. Referring to FIG. 5, a diffuser 70 is shown placed at the corner of the lower tie-plate L between the channel C and the tie-plate. FIG. 5A shows a top view of one corner of the lower tie-plate, and FIG. 5B show a section through the corner. This diffuser, however, is reversed. It includes an aperture 72 disposed towards the core bypass region B and a diffuser aligned to and towards the interior of the fuel bundle F. The purpose of this reverse diffuser can be easily understood. First, reference will be made to the aperture A in the prior art of FIG. 1A. Thereafter, and with a brief explanation, a return to FIG. 5 will illustrate the principles involved. In the prior art, and for the purposes of reflood of the fuel bundles F, aperture A serves two purposes. During normal reactor operation, aperture A permits a small and metered amount of water to pass from the interior of the fuel bundle F to the core bypass region B. In such passage, a pressure drop was experienced, which pressure drop enabled metered flow under low pressure to the core bypass region B. Upon a loss of coolant accident, aperture A is intended to have a reverse flow. In such a reverse flow it enables water flooding the core bypass region B to pass interior of the fuel bundles F. In such passage, the fuel rods R remained flooded and are not subjected to the consequences of overheating. Turning to FIG. 5B, the function of the reverse diffuser can be set forth. During normal operation, flow will typically be down the diffuser section 73 to the aperture 72. Thereafter, flow will pass through in a constant metered flow the length of the aperture 74 until discharged to the core bypass B occurs. Such flow can be relatively constant and metered. Thus, the reverse diffuser configuration can serve the function of metering water from the interior of the fuel bundle F to the core bypass region B. Upon reflood, the water flow will be reversed as shown by arrows 75. As is well known in the hydraulic arts, by aligning the diffuser with respect to flow, an efficient expansion of flow occurs with an accelerated passage. Thus, with the reverse diffuser here disclosed, reflood of the fuel bundle F from the core bypass region B will occur with greater efficiency. The reverse diffuser has very little effect on the leakage flow during normal operation. Some of the pressure drop is friction as the flow passes through the gap, most is the loss in energy as the exiting jet dissipates its energy in the bypass region. During reflood the diffuser acts as a diffuser. There is very little pressure loss as the flow exits from the gap through the diffuser, into the fuel bundle. Thus the time to reflood is reduced. Thus, the only new feature is the enhancement of reflooding provided by the corner diffusers. |
claims | 1. A nuclear reactor comprising a depressurization system for a pressurized container, comprising a main valve which comprises:a pneumatic actuator, andan opening spring,wherein:the main valve is configured to be fluidly connected at one side to a pressurized container in which contains a gas and at the other side to the atmosphere, andthe opening spring is adjusted to set a predetermined mechanical pressure such that when a pressure inside the pressurized container is bigger than the predetermined mechanical pressure, the main valve remains closed, and that when the pressure inside the pressurized container is lower than the predetermined mechanical pressure, the main valve opens to establish a fluid communication so as to allow the pressurized gas from the pressurized container be discharged into the atmosphere. 2. The nuclear reactor according to claim 1, wherein the depressurization system further comprises at least one solenoid valve configured to be connected between the pressurized container and the main valve. 3. The nuclear reactor according to claim 1, wherein the depressurization system further comprises at least one manual valve configured to be connected between the pressurized container and the main valve. 4. The nuclear reactor according to claim 1, wherein the depressurization system further comprises a pneumatic line which can connect an output of the main valve with a pneumatic motor of an isolation valve configured to be connected to an output of the pressurized container. 5. The nuclear reactor according to claim 1, wherein the main valve is disposed inside a housing, the housing comprises:a connection to the pressurized container;a pressurized chamber where the gas from the pressurized container is accumulated;a shut-off element which receives the gas pressure from the pressurized chamber and that is associated with the opening spring; andat least one gas outlet,wherein:when the pressure inside the pressurized chamber is bigger than the predetermined mechanical pressure from the opening spring, the shut-off element closes the fluid communication between the pressurized chamber and the gas outlet, against the action of the opening spring, andwhen the pressure inside the pressurized chamber is lower than the predetermined mechanical pressure from the opening spring, the pressurized chamber is in fluid communication with the gas outlet or outlets and the gas from the pressurized container will be discharged to the atmosphere. 6. The nuclear reactor according to claim 5, wherein the pressurized chamber comprises a floater that closes the communication from the connection of the pressurized container with the outlet gas when a certain amount of liquid comes inside the pressurized chamber. 7. The nuclear reactor according to claim 5, wherein the depressurization system further comprises a closing piston associated with a second spring closing the communication connection of the pressurized container with the gas outlet or outlets by injecting air through a first air inlet. 8. The nuclear reactor according to claim 5, wherein the depressurization system further comprises an opening piston associated with a third spring which opens the communication from the connection of the pressurized container with the gas outlet or outlets by injecting air through a second air inlet. 9. The nuclear reactor according to claim 5, wherein the depressurization system further comprises an adjusting disk associated with the shut-off element and with the opening spring so that a relative position to the shut-off element of the adjusting disk defines the default mechanical pressure for the opening spring. 10. The nuclear reactor according to claim 5, wherein the depressurization system further comprises at least three threaded parts placed inside the housing and a plurality of screws housed in threaded holes made in the at least three threaded parts, such that the plurality of screws are configured to adjust the relative position of the at least three threaded parts. |
|
claims | 1. An apparatus for making a gap between first and second objects, said apparatus comprising:a light introducing unit configured to introduce light to a first entry window formed in the first object;a first detection unit configured to detect a total intensity of light from a first exit window formed in the first object with respect to each of a plurality of values of the gap, the first exit window being at such a position that light would enter through the first entry window of the first object, reflect off the second object, and then enter the first exit window if the gap has a predetermined value;a second detection unit configured to detect a total intensity of light from a second exit window formed in the first object with respect to each of a plurality of values of the gap, the second exit window being at such a position that light would enter through a second entry window of the first object, reflect off the second object, and then enter the second exit window if the gap has the predetermined value; anda positioning mechanism configured to obtain a position of the second object, with respect to a direction of the gap, where the gap has the predetermined value based on a plurality of total intensities of light detected by said first detection unit and a plurality of total intensities of light detected by said second detection unit, and to position the second object at the obtained position,wherein said positioning mechanism is configured to obtain a first position of the second object, with respect to the direction of the gap, where said first detection unit detects the maximum total intensity of light and a second position of the second object, with respect to the direction of the gap, where said second detection unit detects the maximum total intensity of light, and to position the second object at an average position of the first and second positions. 2. A method of making a gap between first and second objects have a predetermined value, said method comprising the steps of:a first introduction step of introducing light into a first entry window on the first object;a first detection step of detecting a first total intensity of light from a first exit window on the first object with respect to each of a plurality of values of the gap, the first exit window being at such a position that light would enter through the first entry window of the first object, reflect off the second object, and then enter the first exit window if the gap has the predetermined value;a second introduction step of introducing light into a second entry window on the first object;a second detection step of detecting a second total intensity of light from a second exit window on the first object with respect to each of a plurality of values of the gap, the second exit window being at such a position that light would enter through the second entry window of the first object, reflect off the second object, and then enter the second exit window if the gap has the predetermined value;an obtaining step of obtaining a position of the second object, with respect to a direction of the gap, where the gap has the predetermined value based on a plurality of total intensities of light detected in said first detection step and a plurality of total intensities in said second detection step; anda position step of positioning the second object at the position obtained in said obtaining step,wherein the obtaining step obtains a first position of the second object, with respect to the direction of the gap, where the maximum total intensity of light is detected in said first detection step and a second position of the second object, with respect to the direction of the gap, where the maximum total intensity light is detected in the second detection step, and obtains the position of the second object where the gap has the predetermined value by averaging the first and second positions. 3. A method of making a gap between first and second objects have a predetermined value, said method comprising the steps of:a first introduction step of introducing light into a first entry window on the first object;a first detection step of detecting a first total intensity of light from a first exit window on the first object with respect to each of a plurality of values of the gap, the first exit window being at such a position that light would enter through the first entry window of the first object, reflect off the second object, and then enter the first exit window if the gap has the predetermined value;a second introduction step of introducing light into a second entry window on the first object;a second detection step of detecting a second total intensity of light from a second exit window on the first object with respect to each of a plurality of values of the gap, the second exit window being at such a position that light would enter through the second entry window of the first object, reflect off the second object, and then enter the second exit window if the gap has the predetermined value;an obtaining step of obtaining a position of the second object, with respect to a direction of the gap, where the gap has the predetermined value based on a plurality of total intensities of light detected in said first detection step and a plurality of total intensities in said second detection step; anda position step of positioning the second object at the position obtained in said obtaining step,wherein said obtaining step includes the steps of:calculating a first approximate curve for a first graph of the plurality of total intensities of light detected in said first detection step;calculating a second approximate curve for a second graph of the plurality of total intensities of light detected in said second detection step; anddetermining a first position of the second object corresponding to a peak of the first approximate curve;determining a second position of the second object corresponding to a peak of the second approximate curve; andobtaining the position of the second object where the gap has the predetermined value by averaging the first and second positions. |
|
043436820 | claims | 1. A plant having feed water heating means for a nuclear steam supply unit during plant start up where said plant has a nuclear steam supply unit for changing water to steam, a turbine, a main steam delivery line connecting said turbine with said unit, a condenser connected to a discharge of said turbine, a feed water delivery line extending from said condenser to said unit, a feed water pump in said feed water delivery line, at least one high pressure heater in said feed water delivery line between said feed water pump and said unit, a high pressure heater steam delivery line extending between a steam extraction point on said turbine and said high pressure heater, a heater operation valve in said high pressure heater steam delivery line and a drain extending from said high pressure heater; the improvement comprising in having a start up steam line extending from said main steam delivery line to said high pressure heater, and a start up valve in said start up steam line whereby when said start up valve is opened, steam from said main steam delivery line will be admitted to said high pressure heater to heat feed water entering the unit during a plant start up and whereby when said start up valve is closed after plant start up, said operation valve may be opened to admit steam to said high pressure heater from said extraction point. 2. A plant according to claim 1, the improvement further comprising in that a plurality of high pressure heaters are provided in said feed water delivery line with each heater being connected to said main steam delivery line by a start up steam line having a start up valve therein and being connected to a high pressure heater steam delivery line having a heater operation valve therein, and wherein a drain line from a high pressure heater located in the feed water delivery line further from said feed water pump is connected in series with a high pressure heater located in the feed water delivery line closer to said pump. 3. A method of start up of a plant having a nuclear steam supply unit, a turbine, a main steam delivery line connecting said turbine with said unit, a condenser connected to a discharge of said turbine, a feed water delivery line extending from said condenser to said unit, a feed water pump in said feed water delivery line, at least one high pressure heater in said feed water delivery line between said feed water pump and said unit, a high pressure heater steam delivery line extending between an extraction point on said turbine and said high pressure heater, a heater operation valve in said high pressure heater steam delivery line, a drain line extending from said high pressure heater, a start up steam line extending from said main steam delivery line to said high pressure heater, and a start up valve in said start up line, comprising the steps of opening said start up valve during start up of the plant to allow steam to pass from said main steam delivery line to said high pressure heater whereby feed water entering into said nuclear steam supply unit is heated. 4. A method of start up according to claim 3 wherein said plant has a plurality of high pressure heaters each of which is connected to said main steam delivery line by a start up steam line having a start up valve therein and each of which is connected to a high pressure heater steam delivery line having a heater operation valve therein, and wherein a drain line from said heater located further from said pump is connected in series with a heater located closer to said pump, comprising the additional step of opening the start up valve in the start up steam line leading to a first heater located closest to said pump until the feed water passing through said first heater approaches its design limit, then opening the start up valve in the start up steam line leading to a second heater located further from said pump than said first heater to obtain further heating of the feed water. 5. A method of start up according to claim 4 including the additional step of admitting steam to said turbine to start and partially load the same, then partially closing the start up valves in said start up steam lines to reduce the steam pressure in each heater to that equal to the steam pressure at an extraction point on said turbine and then opening the heater operation valves whereby steam is supplied to said heaters from the extraction points, and then completely closing said start up valves. |
abstract | The disclosed embodiments relate to ion delivery mechanisms, e.g., for fusion power. Particularly, some embodiments relate to systems and methods for delivering ions to a fuel source in such a manner to initiate fast ignition. The ions may be accumulated into “microbunches” and delivered to the fuel with considerable energy and velocity. The impact may compress the fuel while delivering sufficient energy to begin the fusion reaction. |
|
description | With reference to FIG. 1, an electron accelerator 10 produces high energy electrons. In the preferred embodiment, the electron accelerator 10 generates electrons with potentials of 1 to 10 MeV. The accelerator 10 is controlled from a remote control room 12 where an operator manipulates variables such as the potential of the electrons, the destination of the electrons, and the like. The electrons from one accelerator are selectively directed to various treatment areas. The electrons are directed to an x-ray producing device 14 where they are converted into x-rays for use in a product sterilization or other treatment process. The produced x-rays irradiate a region 16, through which a product conveyer 18 conveys packages of product 20 to be sterilized or treated. An entry gate 22 controls the rate of entry of product onto the conveyer 18. This allows the product conveyer 18 to be operated at different speeds relative to other conveyers that bring product to and from the product conveyer 18 depending on the application. For products that need more irradiation, the conveyer 18 is run at a slower speed, if appropriate. Likewise, the conveyer 18 is accelerated, if appropriate, for product that needs less irradiation. In an alternate embodiment, the product conveyer always runs at a constant speed and the radiation intensity, and therefore the dose is changed. This embodiment varies the amount of radiation transmitted into the treatment region 16 as a result of more intense radiation. An exit gate 24 channels irradiated product onto another conveyer for removal from the system. This further allows the product conveyer to be operated independently of its surroundings. For safety purposes most of the conveyer 18 is within a radiation shield 26 which allows no ambient radiation to exit. The gates 22, 24 can be toggled in the preferred embodiment to allow product 20 to be irradiated multiple times if desired. For example, the product can be irradiated once from each side before being discharged and replaced. With reference to FIG. 2 and continuing reference to FIG. 1, a high energy electron beam 28 generated by the accelerator 10 is converted into x-rays 30. These x-rays 30 irradiate the product 20 which is passing on the conveyer 18. In the preferred embodiment, there is an optical or other sensor 32 that senses when the product 20 is in the treatment region 16. The optical senor 32 is coordinated with the electron accelerator control 12 such that the treatment region 16 is only irradiated when there is product 20 present. The optical sensor 32 helps extend the life of a target 34. When the x-ray source 14 is in operation, it is constantly generating heat, and is constantly cooled. By toggling the source 14 on and off, while still cooling it, the target 34 cools down more efficiently. As an option, a shield 36 made of heavy metal, such as lead or iron, is disposed behind the conveyer 18 opposite the x-ray source. This shield terminates most of the radiation that has passed through the product 20 and the conveyer 18, making the surrounding area safer. The shield 36 is preferred when the beam is directed horizontally or the installation is not on the ground floor, to protect the rooms next to or below the x-ray source. With reference to FIG. 3 and continuing reference to FIG. 2, the x-ray source target 34 is made of metal that is capable of producing x-rays when bombarded with high energy electrons. In the preferred embodiment, the target 34 is made of tantalum mounted to a substrate 40 having high thermal conductivity. Aluminum, copper, and their alloys are preferred, but other thermally conductive materials are also contemplated. When electrons cross a vacuum and hit the target 34, much of their energy is converted into heat. The conductive substrate 40 conducts the heat away from the target 34. Coolant fluid, water in the preferred embodiment for simplicity of handling, flows through tubes, bores, or other cavities 42 in the substrate to conduct heat away from the system. Other fluids, such as coolant oil are also contemplated. Preferably, the coolant fluid does not come into direct contact with the target 34. Because of this, the target is protected from oxidation and corrosion as a result of exposure to the coolant. Alternately, the coolant could flow directly over the target 34. Preferably corrosion inhibitors are added to reduce corrosion and extend the life of the target. The x-ray source 14 includes deflection plates 44 located along a periphery of an accelerator horn 46. The deflection plates 44 electrostatically or magnetically manipulate a direction of the electron beam 28 such that the electron beam 28 does not always hit the same spot on the target 34. More specifically, the control 12 controls the deflection plates in accordance with dimensions of the product. Typically, the scan horn is elongated, for example, about a meter long. The electron beam is swept back and forth over a distance commensurate with the corresponding dimension of the passing product. To promote cooling of the target, the electron beam is also moved side to side. For example, the electron beam is swept along one line in a first sweep and along a parallel line on the return sweep. More complex sweep patterns such as following a multiplicity of parallel, shifted sweep paths, sinusoidal or other non-linear sweep paths, oval loops, and other two dimensional paths are also contemplated. In the preferred embodiment, the deflection plates 44 are electrostatic plates which, when negatively charged, repel the electron beam. Positively charged plates to attract the beam are also contemplated. Alternately, they may be magnetic plates. The plates can be located inside or outside of the vacuum. If electrostatic plates are located inside the vacuum, hermetic feedthroughs for electrical leads are provided. With reference to FIG. 4, a detailed view of a preferred target 34 is provided. The target 34 is divided into multiple layers, three in the preferred embodiment. The target layers are sandwiched between by layers of the thermally conductive substrate 40. When the x-ray source 14 of the preferred embodiment is in operation, the electron beam 28 strikes a first layer 34a of tantalum foil. Some of the electrons are converted into x-rays and some pass through the first layer of target. Those electrons which pass through strike a second layer 34b of target, where some are converted and some pass through. The process is again repeated for a third layer 34c. The target layers in the preferred embodiment are films or coatings of the target material adhered to layers of substrate material. As illustrated in FIG. 4, the target layers 34a, 34b, 34c are progressively thinner. Each layer has a different capability of stopping electrons. Typically, different energies are stopped in different layers. As a result, different x-ray spectra result from each layer. Further, the second and third layers filter out low energy x-rays generated in the upstream target layers. This is an advantage of having multiple layers of target as opposed to one thick layer of target. It is to be understood that the x-rays generated in the preferred embodiment have a direction of propagation that is generally the same as the electron beam. To help focus the x-rays in a forward direction, the substrate is shaped with forward extending side flanges. The greater material thickness at the flanges absorbs more x-rays than the thinner central window portion. Optionally, a layer of filter material, such as stainless steel, is positioned between one or more target layers and the treatment region to absorb low energy x-rays. Typically, the best conventional x-ray targets only convert approximately 15% of the kinetic energy of the incumbent electrons into x-rays. The target 34 of the present invention converts about 80% of the electrons"" energy into x-rays. This is done by supporting a very wide variety of energies in the target. What would not get used in a conventional target, passes through the first layer 34a and interacts with the second, and so on. Since more of the electrons are being used, less are being converted into heat. This makes cooling the target a somewhat easier proposition. In an alternate embodiment, one thick layer of target could be used instead of multiple thinner ones and achieve the same electron stopping power. Because common target materials, such as tantalum and tungsten are relatively poor heat conductors, the heat from the anode target is removed more slowly. The invention has been described with reference to the preferred embodiment. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. |
|
description | This application is National Phase application of PCT International Application PCT/US2016/031736, filed on May 11, 2016, which claims priority under 35 U.S.C. 119(e) of U.S. provisional application Ser. No. 62/197,873, filed on Jul. 28, 2015, and U.S. provisional application Ser. No. 62/268,720, filed on Dec. 17, 2015, the contents of both of which are hereby incorporated by reference in their entirety and for all purposes. The present disclosure relates to a source wire assembly for radiographic applications, particularly for guiding a gamma ray source through a tubular path, such as with a radiographic projector. The source wire assembly includes a core of flexible metal cable, such as, but not limited to, aircraft cable, which may include wires and/or strands which are woven, helix wound, twisted or braided. In the prior art, it is known to drive a gamma or other radiographic source though a tubular path in order to produce radiographic scans with respect to the integrity of a structure, such as a pipe or similar construction. This may be done in connection with a radiographic projector or similar device. Representative prior art includes U.S. Published Patent Application 2011/0309272 entitled “Radiographic Projector”, published on Dec. 22, 2011 on behalf of Cole; U.S. Pat. No. 6,627,908 entitled “Radiation Source Assembly and Connector Press Used in Producing Such Assemblies”, issued on Sep. 30, 2003 to Han et al.; U.S. Pat. No. 6,481,914 entitled “Radiographic Source Connector with Improved Coupling Mechanism”, issued on Nov. 19, 2002 to Grenier et al.; and U.S. Pat. No. 4,827,493 entitled “Radiographic Source”, issued on May 2, 1989 to Parsons et al. Typically, it is desired that a source wire assembly be somewhat stiff or rigid, but with flexibility to accommodate curvature within the tube path and elasticity so that the source wire assembly is not permanently deformed by the curvature within the path. It is therefore an object of the present disclosure to provide a source wire assembly which is stiff or rigid, but having sufficient flexibility to accommodate curvature within the tube path of a radiological projector (or similar equipment) and with sufficient elasticity to avoid permanent deformation within the curved path. This and other objects are attained by the present disclosure of a source wire assembly which includes a core of flexible metal cable, such as, but not limited to, aircraft cable, which may include strands which are woven, helix wound, twisted, braided, or otherwise intertwined, the strands further including a plurality of metallic wires which may be woven, helix wound, twisted, braided or otherwise intertwined. This flexibility of the core provides the desired elasticity and eliminates or reduces any permanent deformation of the source wire assembly when driven through curved paths. Referring now to the figures in detail, wherein like numerals indicate like elements throughout the several views, one sees that FIG. 1 is a cross-sectional view of an embodiment of the source wire assembly 10 of the present disclosure. Source wire assembly 10 is substantially rotationally symmetric about longitudinal axis 11 and is intended for radiographic uses such as, but not limited to, a radiographic projector which includes a curved or serpentine path. The curved or serpentine path of the radiographic projector is typically bounded by heavy radiological shielding. The curved or serpentine path, in combination with the heavy radiological shielding, provides for substantially reduced radiation emitted through the path to the exterior, particularly if there is no line of sight from the exterior of the radiological projector to the radiological source of the source wire assembly 10. The total shielding is further increased, and the emitted radiation to the exterior of the radiographic projector is decreased, by the various metallic or otherwise shielding elements comprising the source wire assembly 10. Source wire assembly 10 includes an interior cylindrical core 12 of flexible metal cable. An exemplary, but non-limiting, embodiment of the flexible metal cable is shown in FIG. 2, wherein aircraft-type cable is presented with seven strands 13, each of the strands including seven metallic wires, resulting in what is commonly known as 7×7 aircraft cable. The wires are twisted, helix wound, woven, or braided together within each strand and the strands are likewise twisted, helix wound, woven or braided together to form the resulting cable. However, as will be appreciated by those skilled in the art after review of this disclosure, other configurations of aircraft cable or flexible metallic cable may be substituted for 7×7 aircraft cable. The various components of the source wire assembly 10 are mounted, directly or indirectly, on the cylindrical core 12. This allows the source wire assembly 10 to operate with freedom of movement in multiple planes and degrees of motion. Radioactive source capsule assembly 14 includes a radioactive gamma ray source 16 encased within a housing 18. The housing 18 includes a blind aperture 20 for receiving, surrounding and securing the distal end 22 of the cylindrical core 12. It is intended that a wide range of prior art or standard radioactive source capsule assemblies 14 may be adaptable to this embodiment. Typically, the source capsule assembly 14 is permanently attached to the cylindrical core 12. The source capsule assembly 14 being attached at the end of cylindrical core 12 allows for axial radiographic applications of the radiographic projector (not shown). A cylindrical spacer sleeve 24, typically metallic, coaxially surrounds a portion of the cylindrical core and is used to space the radioactive source assembly 14 from the shield beads 26 and maintain the proper axial alignment of the various components. The shield beads 26 are metallic toroidal rings with a central passageway through which the cylindrical core 12 passes. The shield beads 26 provide radiological shielding from the source capsule assembly 14. The cylindrical spacer sleeve 24 further assures that all gaps are filled between the shield beads 26, thereby eliminating or reducing any catch points. The cylindrical spacer sleeve 24 further aids in the permanent attachment process by preventing shield beads 26 from falling into the swaging assembly and further allows the active source capsule assembly 14 to be cut off when the assembly is returned for disposal. Shield beads 26, which are made from a gamma shielding material, such as, but not limited to, tungsten, are illustrated in FIG. 1 as a series of ten individual toroidal rings abutting each other, with a hollow passageway through which cylindrical core 12 passes. Those skilled in the art, after review of the present disclosure, will recognize that a range of equivalent shielding materials may be used, depending upon the application. Shield beads 26 radiologically shield the proximal end of the source wire assembly 10, as well as any attached equipment such as the rear port of a radiographic projector (not shown), from the radioactive source 16. Shield beads 26 may further include beveled outer circular edges to aid in the flexure of the source wire assembly 10. The leftmost or most distal shield bead 26 is of a reduced diameter and has a more pronounced chamfered face. The purpose of this profile is to gradually transfer from the larger diameter of the shield beads 26 to the smaller diameter of the sleeve 24. This helps to prevent or minimize “hang-up” incidents or accidents from occurring. However, the remaining shield beads 26 have a diameter for a tight tolerance within the passageway of the radiographic projector in order to provide sufficient radiological shielding. Spacer beads 28 and coil spring 30 sequentially engage the interior cylindrical core 12. The spacer beads 28 are typically made from a metal, such as, but not limited to, stainless steel. Those skilled in the art, after review of the present disclosure, will recognize that a range of equivalent materials may be used, depending upon the application. A first end of coil spring 30 may be engaged within undercut cylindrical slot 29 of rightmost spacer bead 28, radially outwardly adjacent from cylindrical core 12, in order to prevent coil spring 30 from riding over the chamfered surface of the rightmost spacer bead 28 and likewise eliminates or reduces any snagging of the first end of coil spring 30 during operation of the source wire assembly 10 (commonly known as a “hang-up incident” or “hang-up accident”). The capturing of the interior cylindrical core 12 of flexible metal cable by cylindrical spacer sleeve 24, coil spring 30 and beads 26, 28 eliminates or reduces the risk of “bird caging”, or inelastic curved deformation, during repeated use. Furthermore, the chamfered faces on the shield beads 26 and spacer beads 28 allow for minimal bend radii of the overall source wire assembly 10. Coil spring 30 further engages against connector housing 32 whereby a second end of coil spring 30 enters a cylindrical slot 33 formed by an indented relationship between sleeve 35 (swaged onto cylindrical core 12) and connector housing 32. This configuration is intended to eliminate or reduce any snagging of the second end of coil spring 30 during operation of the source wire assembly 10 (commonly known as a “hang-up incident” or “hang-up accident”). Connector housing 32 includes an enlarged distal lip 34 to further provide a diameter similar to or greater than that of shield beads 26 and spacer beads 28. This ensures that the source assembly adequately activates the source locking mechanism inside the radiographic projector (not shown) during operation. Cylindrical core 12 is engaged within the hollow interior 36 of connector housing 32 so that the proximal end of the cable 12 is surrounded by the enlarged distal lip 34 and sleeve 35. Hollow interior 36 further houses cylindrical connector shield 38, which may be made from tungsten, which provides further shielding to any attached equipment such as the rear port of a radiographic projector (not shown), from the radioactive source 16. Connector shield 38 may be biased in position by internal coil spring 40. Connector housing 32 further provides a standard connection device 42 for attachment to driving equipment, such as, but not limited to, a push-pull operation associated with a radiographic projector, which may include source wire locking and safety mechanisms. In the alternative embodiment of the source wire assembly 10 of FIGS. 3 and 4, the two spacer beads 28 after the rightmost spacer bead 28 have been replaced by four additional shield beads 26 (with a single spacer bead 28 remaining in the rightmost position). This alternative embodiment of the source wire assembly 10 is expected to provide for increased shielding efficiency in the associated radiography projector (not shown) by reducing the radioactive dose emanating from the rear port of the projector (not shown) when the source wire assembly 10 is in the locked secure position. This results in increased safety to the operator or handler of the device and further provides a safety factor to avoid potential non-conforming shield efficiency profiles when the projector and the source wire assembly 10 enter the production stage of manufacture. Thus the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby. |
|
053295692 | summary | BACKGROUND OF THE INVENTION The present invention relates generally to a window structure for transmitting x-ray radiation and for shielding undesirable debris resulting from the x-ray radiation generation process. A variety of window systems have been developed for irradiating samples. By way of example, Forsyth et al. in U.S. Pat. Nos. 4,980,896 and 4,697,934; Riordan et al. in U.S. Pat. No. 4,837,794 and Grobman in U.S. Pat. No. 4,408,338 each describe a method of x-ray lithography of semiconductor chips. In fact, the use of x-ray lithography is often times preferred because of its ability to produce line widths less than one micron. Soft x-rays (i.e. relatively long wavelengths and low penetrating power) are particularly useful for such applications. Soft x-rays can be generated by a variety of known techniques; however, such x-ray generation processes can also produce unwanted debris which can adversely interfere with the x-ray lithography process. In one x-ray lithography system, a pulsed plasma source is used for x-ray generation. Such sources convert an electrical input into x-rays using the phenomena of gas jet z-pinch. In this method of x-ray generation, a burst of a gas (e.g. nitrogen, krypton, or argon) is expanded using a nozzle in concert with the fast discharge of a capacitor bank through the expanding gas. A high current discharge and the resulting intense magnetic field radically compresses the plasma. The result is a dense, high temperature plasma which is a very intense source of desirable x-rays with comparatively long wavelengths and hence, low penetrating power (i.e. soft x-rays). Unfortunately, generated along with the x-rays are hot gases, charged particles and other debris having instantaneous accelerations exceeding 100 g's. Consequently, a need exists for a window structure which allows transmission of the x-rays, yet blocks or shields the sample from undesirable radiation generated debris. For electromagnetic radiation above about 1000 .ANG. in wavelength, or below about 1 .ANG. in wavelength, practical transmissive debris shield materials exist, (e.g. quartz and beryllium). However, for electromagnetic radiation between about 1000 and 1 .ANG. in wavelength, no single practical window material exists. Known durable window materials are not sufficiently transparent to electromagnetic radiation within this range while window materials which are sufficiently transparent within of this range are not very durable. Unfortunately, this is precisely the range in which high resolution microcircuit lithography is contemplated. Satisfying these dual, competing requirements has been greatly impeded because no one material or structure has been discovered which exhibits both the required transmissivity for x-rays and the structural strength to withstand the impact of debris. As such typical x-ray lithography systems employ a first structure as a window and a second, spaced apart structure as a debris shield. See e.g. Riordan et al., Grobman. More recently, Perkins et al. in U.S. Pat. Nos. 4,960,486 and 4,933,557 have proposed a structure composed of an x-ray transmissive film material overlaid onto a structural support. In spite of such advances, a need still exists for a single window structure combining both transmissive and debris shielding capabilities. The present invention provides a novel x-ray transmissive shield composed of materials having complementary properties so as to overcome the limitations of existing window and debris shield systems. SUMMARY OF THE INVENTION The present invention relates generally to a window structure for transmitting radiation and for shielding undesirable radiation generated debris. More specifically, a composite window comprising thin film layers of first and second materials laminated together is described. By selecting materials having complementary properties, a novel x-ray window is produced having superior structural strength and high radiation fluence capabilities compared to those either material by itself. Preferably, materials are selected from a first group having high tensile strength and low melting points and from a second group having low tensile strength and high melting points. In one embodiment, a layer of a highly x-ray transmissive material is laminated to a layer of an x-ray transmissive polymeric material. In an alternative embodiment, a layer of highly x-ray transmissive material is laminated to both faces of each layer of polymeric material. |
summary | ||
abstract | An electron beam sterilizer has a bottle holder 28 provided with a rotation shaft 38, a neck gripper 70 mounted to a lower end of the rotation shaft 38, a rotating body 30 for rotating and moving the neck gripper 70 and a rotator revolver (segment gear 54, pinion gear 46, disc-shaped cam 66, etc.), and while conveying the resin bottle 2 in the state of being held, the resin bottle 2 is sterilized by irradiation with the electron beam through the irradiation window 19 of the electron beam irradiation device 18. The entire surface of the resin bottle 2 is completely sterilized by being rotated by the rotator during the movement in front of the irradiation window 19 and, thereafter, the rotator is inverted in position to return the neck gripper to thereby discharge the bottle. |
|
048779628 | description | In the drawings, the same reference numerals indicate the same or corresponding parts. DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinbelow, an example of ion implantation performed in accordance with the method of the present invention will be described while referring to FIGS. 3 and 4 of the accompanying drawings. FIG. 3 is a schematic view of a silicon substrate in the form of a silicon wafer 7 which is mounted on a rotatable base 5 of an electrostatic scanning ion implantation apparatus like the one illustrated in FIG. 1. FIG. 4 is a front view of the wafer 7. The wafer 7 is made of (100) Si and has a flat 7a lying in a (110) crystal plane. The base 5 is able to tilt the wafer 7 with respect to incident ion beams 6, and it is able to rotate the wafer 7 in its own plane. The angle of tilt of the wafer 7 is indicated by T, and the angle of rotation of the wafer flat 7a with respect to a horizontal plane 8 is indicated by R. In this example, the direction of the ion beam 6 is such that when the wafer flat 7a is horizontal, the (110) crystal planes of the wafer 7 are aligned with the ion beam 6, and therefore the angle of rotation R is measured with respect to the horizontal plane 8. In order to perform ion implantation in accordance with the present invention, the base 5 is tilted by a tilt angle T of about 7.degree. and is rotated with respect to the horizontal plane 8 by a rotational angle R of 15.degree. to 75.degree.. Most preferably, the angle of rotation R is about 45.degree.. When the wafer 7 is secured in this first position, indicated by P1, the wafer 7 is irradiated with a dose of ions equal to approximately 1/4 of the total dose with which it is to be irradiated. In this position, the (110) crystal planes of the wafer 7 are not aligned with the ion beam 6, so planar channeling is largely prevented. After performing ion implantation in this first position, the wafer 7 is then rotated by the base 5 in the plane of the wafer 7 by 90.degree. in the counterclockwise direction in FIG. 4 to a second position P2. At this second position, the wafer 7 is again irradiated with approximately 1/4 of the total dose of ions. Next, the wafer 7 is again rotated counterclockwise by 90.degree. in its own plane to a third position P3 and irradiated with approximately 1/4 of the total dose, after which it is rotated counterclockwise by 90.degree. to a fourth position P4 and irradiated with the remaining approximately 1/4 of the total dose. After irradiation at the fourth position, the total dose of ions has been implanted, and ion implantation of the wafer 7 is complete. The (100) crystal plane of silicon has four-fold symmetry, so a wafer 7 having a flat 7a lying in a (110) crystal plane has <110> crystal axes which are parallel to and perpendicular to the flat 7a. If the angle between the flat 7a and a horizontal plane 8 is 0.degree. for such a wafer 7, during ion implantation, planar channeling occurs along the (110) planes, as was the case with the wafer 7 of FIG. 2. However, in the method of the present invention, as a wafer 7 is rotated in its own plane by an intitial angle of 15.degree. to 75.degree. away from a position in which the (110) crystal planes would be aligned with an incident ion beam, the (110) crystal planes are no longer aligned with an incident ion beam and little planar channeling takes place. Furthermore, as the wafer is rotated by 90.degree. at a time to four different positions and ion implantation is performed with the same dose of ions at each position, planar channeling is yet further decreased. Therefore, the uniformity of the depth of implantation of ions in the surface of a wafer is greatly increased. In the above-described example, the initial angle of rotation R of the wafer 7 was 15.degree.-75.degree., but as the wafer 7 is rotated four times by 90.degree. at a time to four different positions, the same effects can be obtained if the initial angle of rotation is (R+90.degree.), (R+180.degree.), or (R+270.degree.). |
048287920 | description | DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, a fuel assembly 10 has a support structure having grids 12 which retain fuel rods 14 according to a square lattice, two upper 15 and lower 18 end pieces and guide tubes holding the other components of the support structure in position. The top part only of the fuel rods is illustrated. The top part only of the fuel rods is illustrated. The guide tubes, forming tie rods, are distributed between two groups. The guide tubes 20 of the first group are fixed permanently to grids 12, as shown schematically by a cross (X) in the figure. The guide tubes of the first group are also connected permanently to a plate 22 formed with outlet openings for the coolant, forming the bottom of the upper end piece 16. The permanent connections may be of any appropriate type and selected depending on the nature of the material forming the pieces to be assembled together. Welding, threaded connections or connections by deformation of a thin wall may be used as is well known in the art. The guide tubes 20 of the first group are received in the lower end piece 18 in which they may slide vertically. The guide tubes 24 of the second group are rigidly fixed to the lower end piece 18. They project through cells in grid 12 in which they are slidably received. The guide tubes 24 pass through the bottom wall 22 of the upper end piece 16 and project inside piece 16. Their upper end is fixed by a permanent connection 26 to a perforated plate 28 mounted in a frame belonging to the upper end piece 16, above the bottom wall 22. As shown in FIG. 1, four springs 30 are located between the plate 28 and flanges 32 at the upper part of the frame of the upper end piece 16. The springs are under a precompression so as to exert on plate 28 a force biasing it into contact with the bottom wall 22. Plate 28 advantageously includes studs 34 for holding the springs 30 in position and, possibly, for limiting their amount of compression by abutting flanges 32. A first substructure, formed of the first group of guide tubes 20, grids 12 and the upper end piece 16, carries the fuel rods: it is subjected to about 90% of the hydraulic thrust received by the fuel assembly. A second substructure, comprising the lower end piece 18 and the guide tubes 24, receives about 10% of the hydraulic thrust. Consequently, springs 30 may be dimensioned so as to take up only 10% of the total thrust of the coolant on the fuel assembly. When the assemblies are loaded into the reactor, the lower end piece of each assembly rests on the core support plate 36. Springs 30 bias the upper end piece 16 upwardly with a force which is less than the weight of the first substructure and the rods which it carries; the first substructure consequently remains in abutment on the second substructure. The upper core plate 38 may then be positioned. The whole of the weight of the assembly will be applied to the core support plate, directly for the second substructure, through the second substructure in so far as the first is concerned. During start up and operation of the reactor, an upwardly directed thrust is exerted by the coolant. That force lifts the first substructure until the upper end piece 16 is in contact with the upper core plate. Then about 90% of the thrust will be directly applied to plate 38 by direct abutting connection rather than via resilient means. Due to the direct contact and the omission of the springs found in the prior art assemblies and which have their own resonance frequency, amplification of the vibration of the upper internal equipments (which the resilient means of conventional assemblies may generate on the fuel rod bundle 14) is avoided. Attenuation of the vibration of the fuel rods is an essential factor in improving the life of the sheath of the fuel rods and the life and efficiency of the springs provided in the grids for exerting on the fuel rods a force holding them in position. The fraction of the thrust of the coolant which is exerted on the second substructure tends to raise the lower end piece 18 and to lift it off from the core support plate 36. Since however the fraction of the total thrust which is exerted on the second substructure is small, springs 30 having a low precompression, typically between 100 and 200 decanewton, are sufficient for holding the lower end piece 18 in contact with the core support plate 36. That direct contact again attenuates the vibrations of the fuel rod bundle. Referring to FIGS. 2A, 2B and 3, the connection of the guide tubes 20 and 24 with the end pieces are illustrated. The guide tubes 20 are enlarged at their upper end into passages of bottom wall 22 formed with indentations and their lower portions are slidably received in the lower end piece 18. On the other hand, guide tubes 24 are crimped at their upper end in plate 24, slidably received in bottom wall 22, and fixed at their lower end, for example by screws, to the lower end piece 18. The screws may comprise a thin skirt for deformation into a cavity of end piece 18 for preventing them from rotating. The sliding fit of the guide tubes in the end pieces ensures mutual guidance of the two subassemblies and participates in the mechanical strength of the assembly. Referring to FIG. 4 (where the elements corresponding to those of FIG. 1 are designated by the same reference number) a modified embodiment includes an upper end piece designed so that the springs 30 are disposed between two plates. For that, the end piece 16 consists of a bottom wall 22, having passages (not shown) for coolant flow, extended upwardly by a frame with gripping flanges 32 and downwardly by a skirt 40 having an abutment flange 42. The upper part of each guide tube 24 slides within the bottom wall 22 whereas the upper end of each guide tube 20 is securely connected to the bottom wall. A plate 28 with coolant flow apertures is slidably mounted in skirt 40. The guide tubes 24 are fixed to plate 28, but the exterior of each guide tube 24 which slides in bottom wall 22 is beyond the connection zone 26. The guide tubes 20 have a sliding fit in plate 28. Springs 30 are disposed concentrically to the end parts of the guide tubes 24 and bias the two substructures into the abutment position as shown in FIG. 4. When the upwardly flowing coolant exerts on the substructures an upwardly directed force, the major part of this force is absorbed, as in FIG. 1, by direct contact of the end piece 16 with the upper core plate 38, whereas spring 30 exerts on plate 28 a sufficient force for maintaining the lower end piece 18 in contact with the core support plate 36. In the modified embodiment shown in FIG. 5, where the elements already described again have the same reference numbers, springs 30 which tend to spread the end pieces apart are disposed in the lower part of the assembly. The first substructure includes the grids 12, the guide tubes 20 fixed to the bottom wall 22 of the upper end piece 16 and an apertured plate or grid 44 slidably mounted on the guide tubes 24. The second substructure includes the guide tubes 24 fixed to the lower end piece 18 and slidable in the upper end piece 16. Stop means may be provided for limiting the extent of movement of parts 16 and 18 away from each other under the action of springs 30 and/or during handling of the fuel assemblies suspended by the upper end piece 16. As shown in FIG. 5, the stop means are formed by enlarged sockets 46 permanently fixed to the guide tubes 24 and arranged for contact with plate 44. Springs 30 are disposed about the portion of the guide tubes 24 situated between plate 44 and the lower end piece 18. The embodiment which has just been described has the advantage that the upper end piece 16 has no spring, which facilitates movement of the control rod clusters used for controlling the core reactivity and facilitates handling of the assembly. Finally, the assembly shown schematically in FIG. 6 is of the floating grid type, in which some of the grids are not connected to the guide tubes of the first substructure. Referring to FIG. 6, the assembly has a general construction similar to that shown in FIG. 1. But some of the grids 12a are slidably mounted on the fuel rods 20 and 24. Some of the fuel rods, such as those shown at 46 are provided with resilient means additional to the springs 30 and increasing the force biasing the end pieces 16 and 18 away from each other. The number of such rods 46 will depend on the additional force to be exerted. Each of the fuel rods 46 has a lower end plug 48 bearing on the lower end piece 18. At its upper end, each such rod carries resilient means which will now be described (the arrangement being reversed if required). Referring to FIG. 8 which is a view of the part of the fuel rod shown in a dash dot line in FIG. 7 at an enlarged scale, such resilient means include a tubular push rod 50 whose frusto-conical end part engages in a hole 52 in the bottom wall of the upper end piece 16. Push rod 50 is slidably received on a bolt 54 carried by end plug 56 of rod 46. A helical spring 58 is disposed within the push rod 50 between the end part of the push rod and a spacer 60 retained by an internal shoulder of push rod 50. The spacer 60 prevents loss of the spring 58 before the push rod is mounted on the bolt 54. Each spring 58 transmits from one end piece to the other a force participating in the hold down function and completing the action of the springs 30. Each spring 58 may for example exert a precompression force of 1 decanewton. If each fuel rod of a typical fuel assembly, whose rods are distributed at the 17.times.17 nodes of a square lattice is provided with such resilient means, the total force may reach about 250 daN, i.e. about 25% of the force exerted by a conventional hold down device. Such a contribution allows transmission of part of the hydraulic forces due not only to the bundle of fuel rods, but also to the floating grids 12a. The arrangement which has just been described is applicable not only to "floating grid" assemblies, but also to assemblies in which all grids are fixed to guide tubes. |
053226445 | abstract | A process for decontaminating radioactive material comprises the step of contacting the material with a dissolving composition to dissolve the contaminants in the material, said composition comprising a dilute solution of about 0.05 molar ethylene diamine tetraacetic acid, about 0.1 molar carbonate, about 10 grams per liter hydrogen peroxide and an effective amount of sodium hydroxide to adjust the pH of the composition to a pH from about 9 to about 11. Also included are the steps of separating the dissolving composition containing the dissolved contaminants from the contacted material and recovering dissolved contaminants from the dissolving composition that has been separated from the material. A composition for dissolving radioactive contaminants in a material, comprising a dilute solution having a basic pH and effective amounts of a chelating agent and a carbonate sufficient to dissolve radioactive contaminants is also provided. |
abstract | An X-ray fluorescence analysis apparatus in which a collimator for defining a range of passage of X-rays, can be safely and simply attached and detached by providing a right-hand screw thread for attachment of the collimator to a housing, an X-ray generator, or an X-ray detector, and further providing a left-hand screw thread on a side of the collimator opposite to that of the right-hand screw thread. An attachment jig having a left-hand screw thread corresponding to the left-hand screw thread provided on the collimator is used to attach and detach the collimator. |
|
claims | 1. A synchrotron that accelerates and decelerates a charged particle beam that circulates in the synchrotron, comprising:a first extraction deflector and a second extraction deflector that are used to extract the accelerated or decelerated beam from the synchrotron;a plurality of deflection magnets and a first single quadrupole magnet that are arranged between the first and second extraction deflectors, the first single quadrupole magnet being arranged between any deflection magnets among the plurality of deflection magnets;a second quadrupole magnet that is arranged on the upstream side of the first extraction deflector in a traveling direction of the charged particle beam on a path of the circulating charged particle beam; anda third quadrupole magnet that is arranged on the downstream side of the second extraction deflector in the traveling direction of the charged particle beam on the path of the circulating charged particle beam. 2. The synchrotron according to claim 1,wherein the first quadrupole magnet is a defocusing quadrupole magnet, and the second quadrupole magnet and the third quadrupole magnet are focusing quadrupole magnets. 3. The synchrotron according to claim 1,wherein the plurality of deflection magnets arranged between the first and second extraction deflectors are a first deflection magnet and a second deflection magnet, andthe first deflection magnet, the first quadrupole magnet and the second deflection magnet are arranged in this order from the upstream side in the traveling direction of the charged particle beam. 4. The synchrotron according to claim 1,wherein the plurality of deflection magnets arranged between the first and second extraction deflectors are a first deflection magnet, a second deflection magnet and a third deflection magnet, andthe first deflection magnet, the first quadrupole magnet, the second deflection magnet and the third deflection magnet are arranged in this order from the upstream side in the traveling direction of the charged particle beam. 5. The synchrotron according to claim 1,wherein the plurality of deflection magnets arranged between the first and second extraction deflectors are a first deflection magnet, a second deflection magnet and a third deflection magnet, andthe first deflection magnet, the second deflection magnet, the first quadrupole magnet and the third deflection magnet are arranged in this order from the upstream side in the traveling direction of the charged particle beam. 6. The synchrotron according to claim 1,wherein a combined function magnet is used instead of the deflection magnet and the first quadrupole magnet that are arranged between the first and second extraction deflectors. 7. The synchrotron according to claim 6,wherein the second quadrupole magnet and the third quadrupole magnet are focusing quadrupole magnets. 8. A particle therapy system comprising:the synchrotron according to claim 1, anda beam transport/irradiation system that transports the charged particle beam extracted from the synchrotron to a target and irradiates the target with the charged particle beam. 9. A particle therapy system comprising:the synchrotron according to claim 2, anda beam transport/irradiation system that transports the charged particle beam extracted from the synchrotron to a target and irradiates the target with the charged particle beam. 10. A particle therapy system comprising:the synchrotron according to claim 3, anda beam transport/irradiation system that transports the charged particle beam extracted from the synchrotron to a target and irradiates the target with the charged particle beam. 11. A particle therapy system comprising:the synchrotron according to claim 4, anda beam transport/irradiation system that transports the charged particle beam extracted from the synchrotron to a target and irradiates the target with the charged particle beam. 12. A particle therapy system comprising:the synchrotron according to claim 5, anda beam transport/irradiation system that transports the charged particle beam extracted from the synchrotron to a target and irradiates the target with the charged particle beam. 13. A particle therapy system comprising:the synchrotron according to claim 6, anda beam transport/irradiation system that transports the charged particle beam extracted from the synchrotron to a target and irradiates the target with the charged particle beam. 14. A particle therapy system comprising:the synchrotron according to claim 7, anda beam transport/irradiation system that transports the charged particle beam extracted from the synchrotron to a target and irradiates the target with the charged particle beam. |
|
description | This application is related to co-pending patent application Ser. No. 13/444,932, filed concurrently herewith. 1. Field This present invention relates to a passive containment cooling system for a nuclear reactor power plant and more specifically to a passive containment air cooling system that relies on natural circulation of air over the surface of a metal containment. 2. Related Art Nuclear power has played an important part in the generation of electricity since the 1950s and has advantages over thermal electric and hydraulic power plants. The generation of electricity by nuclear power is accomplished by the nuclear fission of radioactive materials. Due to the volatility of the nuclear reactions, nuclear power plants are required by practice to be designed in such a manner that the health and safety of the public is assured even for the most adverse accident that can be postulated. For plants utilizing water as a coolant, the most adverse accident is considered to be a double ended break of the largest pipe in the reactor cooling system and is termed a loss of coolant accident (LOCA). For accident protection, these plants utilize containment systems that are designed to physically contain water, steam and any entrained fission products that may escape from the reactor cooling system. The containment system is normally considered to encompass all structures, systems and devices that provide ultimate reliability and complete protection for any accident that may occur. Engineered safeguard systems are specifically designed to mitigate the consequences of an accident. Basically, the design goal of a containment system is that no radioactive material escapes from the nuclear power plant in the event of an accident so that the lives of the surrounding populous are not endangered. Recently, reactor manufacturers have offered passive plant designs, i.e., plants that will shut down in the event of an accident without the operator intervention or off-site power. Westinghouse Electric Company LLC offers the AP1000 passive plant design that employs a passive containment cooling system that uses a large steel shell. The containment cooling system suppresses the rise in pressure that will likely occur within the containment in the unlikely event of a loss of coolant accident. The passive containment cooling system is an engineered safety feature system. Its objective is to reduce the containment temperature and pressure, following a loss of coolant accident or steam line break accident inside the containment, by removing thermal energy from the containment atmosphere. The passive containment cooling system also serves as a means of transferring heat for other events resulting in a significant increase in containment pressure and temperature. The passive containment cooling system also limits release of radioactivity (post accident) by reducing the pressure differential between the containment atmosphere and the external environment, thereby diminishing the driving force for leakage of fission products from the containment to the atmosphere. The passive containment cooling system also provides a source of make-up water to the spent fuel pool cooling water. To achieve the foregoing objectives, the containment building is made of steel to provide efficient heat transfer from within to outside of the containment. During normal operation, heat is removed from the containment vessel by continuous natural circulation of air. During an accident, however, more heat removal is required and air cooling is supplemented by evaporation of water, provided by a passive containment cooling system water storage tank and gravity feed. An AP1000 containment system 10 is schematically illustrated in FIG. 1, surrounding an AP1000 reactor system including a reactor vessel 12, steam generator 14, pressurizer 16 and main coolant circulation pump 18; all connected by the piping 20. The containment system 10 in part comprises a steel dome containment vessel enclosure 22 surrounded by a concrete shield building 24 which provides structural protection for the steel dome containment vessel 22. The major components of the passive containment cooling system are a passive containment cooling water storage tank 26, an air baffle 28, air inlet 30, air exhaust 32 and water distribution system 34. The passive containment cooling water storage tank 26 is incorporated into the shield building structure 24, above the steel dome containment vessel 22. An air baffle 28 located between the steel dome containment vessel 22 and the concrete shield building 24 defines the cooling air flow path which enters through an opening in the shield building 24 at an elevation approximately at the top of the steel dome containment vessel 22. After entering the shield building 24, the air path travels down one side of the air baffle 28 and reverses direction around the air baffle at an elevation adjacent the lower portion of the steel dome containment vessel. The air path then flows up between the baffle and the steel dome containment vessel 22 and exits at the exhaust opening 32 in the top of the shield building 24. The exhaust opening 32 is surrounded by the passive containment cooling water storage tank 26. In the unlikely event of an accident, the passive containment cooling system provides water that drains by gravity from the passive containment cooling water storage tank 26 and forms a film over the steel dome containment vessel 22. The water film evaporates thus removing heat from the containment building 22. The passive containment cooling system is capable of removing sufficient thermal energy, including subsequent decay heat, from the containment atmosphere following a Design Basis event resulting in containment pressurization such that the containment pressure remains below the design value with no operator action required for at least 72 hours. The air flow path that is formed between the shield building 24, which surrounds the steel dome containment vessel 22, and the air baffle 28 results in the natural circulation of air upward along the containment vessel's outside steel surface. This natural circulation of air is driven by buoyant forces when the flowing air is heated by the containment steel surface and when the air is heated by and evaporates water that is applied to the containment surface. The flowing air also enhances the evaporation that occurs from the water surface. In the event of an accident, the convective heat transfer to the air by the heated containment steel surface only accounts for a small portion of the total heat transfer that is required, such total heat transfer being primarily accomplished by the evaporation of water from the wetted areas of the containment steel surface, which cools the water on the surface which then cools the containment steel, which then cools the inside containment atmosphere and condenses steam within the containment. Water is continuously applied via gravity from the passive containment cooling water storage tank 26 to the containment vessel steel surface 22 for the first seventy two hours following a Design Basis event. The application of water to the containment vessel steel surface 22 enhances heat transfer through the vessel and aids in condensing the steam within the containment, therefore also limiting the pressure increase within the containment. After the first seventy two hours, active onsite pumping methods will provide makeup water to the passive containment cooling water storage tank 26 for at least an additional four days. Additional onsite and offsite water sources and pumping methods continue to provide makeup water to the passive containment cooling water storage tank 26 after seven days. It is an object of this invention to enable air cooling alone of the containment vessel to provide sufficient decay heat removal to maintain acceptably low containment pressure after the initial three days. Furthermore, it is an object of this invention to enable air cooling of the containment vessel to provide such sufficient decay heat removal with no reliance on active components, operator actions, or non-safety onsite or offsite water supplies. Additionally, it is an object of this invention to provide sufficient air cooling of the containment vessel that will enable a reduction in the size of the passive containment cooling water storage tank that is required. These and other objects are achieved in accordance with the embodiments set forth hereafter which include the application of swirl generators, guide vanes, and a vortex engine. More particularly, the embodiments set forth include a solid metal nuclear containment shell having sides and a cover, sized to surround at least a portion of the primary coolant loop of a nuclear reactor system. An outer housing having sides and a roof substantially surrounds and is spaced from an exterior surface of the solid metal shell forming an annular cooling fluid passage around the exterior surface of the sides of the solid metal shell that communicates with a passage between the cover and the roof. A fluid intake communicates between the outside of the outer housing and a lower portion of the annular passage and a fluid exit extends through a portion of the roof. A swirl vane assembly is supported in the annular passage between an interior of the sides of the housing and the exterior surface of the sides of the metal shell to enhance the turbulence and mixing of the air rising in the annular passage along the solid metal shell as the air is heated by the heat transmitted through the solid metal shell. Preferably, a swirl vane assembly, comprising at least two swirl vanes which are positioned at approximately the same elevation and proximate each other with at least two swirl vanes arranged in a counter rotating pair to enhance the mixing of the air as it rises along the solid metal shell. In a preferred embodiment, the swirl vane assembly comprises a plurality of the counter rotating pairs of swirl vanes, which are circumferentially spaced around the exterior surface of the sides of the solid metal shell at approximately the same elevation. Desirably, the same elevation is in a lower portion of the annular passage. In one embodiment, the swirl vane assembly is supported from the wall opposite the exterior surface of the solid metal shell and, preferably, a baffle is interposed between the sides of the housing and the exterior surface of the solid metal shell so that the baffle extends approximately from a lower surface of the roof of the housing to an elevation juxtaposed to a lower portion of the sides of the solid metal shell below the swirl vane assembly so that the cooling air intake through the housing communicates cooling air between the baffle and the housing and into the annular passage below the swirl vane assembly. Desirably, the swirl vane assembly is supported on an interior of the baffle. As a further improvement, the swirl vane assemblies comprise at least two swirl vane assemblies supported at two spaced elevations, one above the other. In still another embodiment, the nuclear reactor containment includes a vortex engine 42 supported proximate to or within the air exhaust 32. In still another embodiment, directional guide vanes 44 are supported in the passage between the cover and the roof, that are oriented to direct the cooling fluid from the annular passage to an intake on the vortex engine. As previously mentioned, in an AP1000® passive cooling containment system, the convective heat transfer to the air by the heated containment steel surface only accounts for a small portion of the total heat transfer; such total heat transfer being primarily accomplished by the evaporation of water from the wetted areas of the containment steel surface, which cools the water on the surface, which then cools the containment steel, which then cools the inside containment atmosphere and condenses steam. It is an object of the embodiment described herein to enable air cooling alone to provide sufficient heat removal to maintain acceptably low containment pressure with no reliance on active components, operator actions, or auxiliary water supplies, after the initial three days when the initial water volume in the passive containment cooling water storage tank 26 has been exhausted. The foregoing objective is achieved in related co-pending application Ser. No. 13/444,932, filing date Apr. 12, 2012, by creating a tortuous air path and in effect creating an increased surface area over the steel containment vessel over which cooling air flows. The embodiments described herein achieve the same objective by promoting better mixing of the air within the annular passage 34 between the baffle 28 and the steel dome shell 22 and by drawing more air per unit time through that passage. Either of these concepts can be used alone or they can be used together to promote more efficient cooling of the reactor containment. Though, the dome containment shell 22 is identified as being constructed out of steel it should be appreciated that the containment vessel can be constructed out of other materials that have relatively good thermal conductivities and the necessary integrity and strength. Also, it should be appreciated that the water film during the discharge of the passive containment cooling water storage tank 26 will follow a flow path over the steel dome containment vessel that is opposite to the direction of flow of the air path. The design of the AP1000 nuclear power plant passive containment cooling system utilizes the steel containment vessel 22, the shield building 24 and the air baffle 28 to form an air flow path driven by natural circulation. The cooler outside air is drawn into the sides of the shield building 24 through inlet vents 30 and directed downward around the baffle 28. The cool air then turns back upwards and travels countercurrent to water flowing down the containment vessel shell 22. Heat is transferred from the vessel steel to the water and finally to the air flowing up and out the chimney 32. The buoyancy of the warm air leaving the chimney helps to drive the air flow through the annulus 34. The AP1000 passive containment cooling system utilizes water from the passive containment cooling system storage tank 26 on the top of the shield building 24, a safety related source, for the first 72 hours. Traditionally, from 72 hours to seven days, water is supplied by an ancillary tank on the plant site, although this action requires operator intervention as well as AC power. It is the object of this embodiment to enhance the air flow through the annulus 34 such that continued water cooling after 72 hours can be replaced with passive air-only cooling that will maintain the pressure within the containment within design limits. To accomplish the foregoing objective, the preferred embodiment employs a swirl generator such as the swirl vane assembly 36 shown in FIG. 2 to improve decay heat removal from the containment vessel 22 by passively rotating the air in the annulus so that the cooler air adjacent the baffle 28 is rotated towards the steel dome enclosure 22 as the air moves up the annulus to disrupt the thermal boundary layer and enhance the heat transfer across the steel dome enclosure. The term “passive” is employed to indicate that there are no moving parts and the action is accomplished without any need for an outside power source. The swirl generator illustrated in FIG. 2 is a swirl vane assembly 36 that has a tubular housing that supports a number of curve vanes whose arc transforms an axial intake of air into a swirling pattern. The embodiment employed herein may also employ a vortex engine such as the one illustrated in FIGS. 3 and 4 to generate a virtual chimney in combination with the air exhaust exit 32 on top of the shield building 24 and use this virtual chimney to improve decay heat removal. The combination of the swirl generators 36 with a vortex engine 42 can be further enhanced with the use of guide vanes 44 in the space between the underside of the roof of the shield building 24 and the cover of the steel dome enclosure 22. None of the swirl generators, vortex engine or guide vanes require moving parts or are maintenance intensive. Nevertheless, this combination of elements enhances the natural draft through the annulus of the shield building without the use of fans or AC power, or physically increasing the height of the shield building chimney. Preferably, the swirl generators 36 are arranged in counter-rotating pairs in the annulus 34. Thus, in accordance with this embodiment, swirl generators 36 are attached to the inside surface of the baffle 28 adjacent to the steel dome enclosure 22 in a lower portion of the annular passage 34. The purpose of the swirl generators 36 is to make the air flow rising up the annulus region 34, counter current to the water flow streaming down the surface of the steel dome enclosure 22, turbulent by means of rotating the air. This mixing of the warmer air near the vessel 22 with cooler air adjacent the baffle 28 using a swirling motion will thin the thermal boundary layer, thereby reducing resistance to heat transfer. Preliminary testing suggests the vortices produced by the swirl generators 36 will travel for an extensive distance before dissipating. An additional bank of swirl generators 36, as illustrated in FIG. 6, higher up in the annulus 34, may be employed to regenerate the vortices as necessary. Each swirl vane assembly 36 comprises two swirl vanes oriented to establish counter rotating air paths, i.e., air paths that rotate in opposite directions. At each elevation where the swirl vane assemblies are supported, the assemblies are equidistantly spaced circumferentially around the outer surface of the steel dome enclosure vessel 22. By use of the swirl generators 36, heat transfer from the containment steel enclosure 22 to the water and then to the air is improved. However, adding any device in the air flow path through the annulus 34 will tend to impose a penalty on pressure drop and air velocity. This embodiment further contemplates that these losses can be recouped by increasing the thermal buoyancy of the system. This can be accomplished by the development of a virtual chimney, figuratively illustrated by reference character 46 in FIG. 6. The virtual chimney 46 extends from the top of the shield building chimney 48. The virtual chimney 46 is a high velocity cylinder of air rotating in tornado-like fashion that will help to pull air through the annulus region 34 and increase air velocity such that losses incurred by the swirl generators 36 are compensated for and heat transfer is further increased. A vortex generator is an aerodynamic surface consisting of a small vane or vanes that create a vortex. A vortex engine works on the principal that mechanical energy is produced when water descends or when warm air rises. The atmospheric vortex engine captures the energy produced when warm air rises by creating a river of rising air using an air vortex which acts as a vertical conduit. The vortex is produced by admitting warm or humid air tangentially into a circular arena. Tangential entries cause the warm moist air to spin as it rises forming an “anchored vortex.” Centrifugal forces in the vortex prevents the rising air from becoming diluted by cooler ambient air and thereby losing its buoyancy. Once the turbulent air flow produced by the swirl generators 36 in the annulus 34 has progressed to the dome region between the steel containment vessel 22 and the shield building 24, guide vanes 44 will aid in “pre-swirling” the air flow towards the shield building chimney 48 in a favorable swirling motion. The guide vanes 44 assist in developing the larger vortex required to be generated by the vortex engine 42. The vortex engine 42 is positioned within, on or near the chimney 48 of the shield building 24 and may, in principal, be a larger scale version of a swirl generator. The air entering the inlet 50 of the vortex engine 42 will do so in a tangential fashion and will produce a high velocity cylinder of air that will extend some distance above the top of the shield building chimney 48 into the outside air with the portion of the extension above the shield building chimney making up the virtual chimney 46. This virtual chimney will extend the effective height of the shield building chimney 48, thereby increasing buoyancy and increasing the driving force for air flow. A plan view of a vortex engine that can be employed for this purpose is illustrated in FIG. 3 with FIG. 4 showing a side view exposing the inlet to the vanes 52 that are capped by a base plate 54 having a central opening 56 and a cover 58. The air enters the vanes 52 and accelerates as it moves around to the arena and up the chimney drawing more air into the intake 50 as it extends upward and out the virtual extension of the chimney. Accordingly, more air is drawn through the system to overcome the pressure drop imparted by the swirl vane banks 36. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
|
abstract | A method using statistical parameters (e.g. mean, standard deviation, exceptional values) of performance monitoring metrics to substantially reduce the quantity of performance monitoring data collected and reported, make system performance monitoring scalable and enhance the readability of the system performance display. The number of metrics monitored may be reduced by monitoring only one of any two metrics that are closely correlated. |
|
061987867 | abstract | A method of controlling the system pressure in a power generating system, having a turbine-generator and a BWR, that modulates the core thermal power of the reactor while maintaining the main turbine control valves in a constant steady position is described. The core thermal power may be adjusted by adjusting the control rod density within the reactor core or by adjusting the flow rate through the reactor which may be accomplished by modulating the speed of variable frequency recirculation pumps or by modulating recirculation flow control valves. The method includes transferring the power generation system from normal turbine control valve modulation pressure control to core thermal power modulation pressure control. Additionally the method includes modifying the bypass valve closure bias and the power control bias to accommodate the variances from core power modulation pressure control over normal pressure control. If pressure transients are outside of predetermined safety ranges, the method provides for transferring system pressure control back to the standard turbine control valve modulation pressure control. |
description | This application is a division of U.S. patent application Ser. No. 11/109,064, filed Apr. 18, 2005 now U.S. Pat. No. 8,135,106, which claims benefit of U.S. Provisional Application No. 60/564,894 filed Apr. 23, 2004. The teachings of those applications are incorporated herein by reference in their entirety. The present invention relates to Boiling Water Reactor nuclear power plants. In particular, the present invention relates to protecting Boiling Water Reactor cores from unstable density wave oscillations that may cause the reactor core to exceed thermal limits and cause fuel damage. Boiling Water Reactors (BWR's) designed for power generation utilize fuel assemblies arranged inside vertical channels through which water coolant flows. Each of the fuel assemblies consists of a plurality of vertical rods arrayed within the vertical channels. The vertical rods are sealed cylindrical tubes which have ceramic pellets of fissionable material, (e.g., uranium oxide), stacked inside. The water flows upward in the channels and removes the heat generated in the pellets by the fission of the heavy isotopes. In addition to its cooling function, the water serves as a neutron moderator. The moderator function is achieved as the neutrons produced in the fission process collide with the hydrogen atoms in the water molecules and slow down to lower energies which increase the probability of inducing further fission reactions and the fission chain reaction is sustained. In Boiling Water Reactors, the water is allowed to boil as it travels up in the fuel assembly channel. The density of water is reduced by the boiling process and the moderating function is reduced accordingly. In the normal mode of operation of Boiling Water Reactors, the coolant flow rate through the fuel channels is steady and stable. However, departure from steady configuration is likely under reduced coolant flow operation, particularly when power levels are relatively high. Such operating conditions are encountered during reactor startup and as a result of recirculation pumps tripping an anticipated transient. The mechanism of the instability is associated with the so called density waves and is described as follows. Boiling Water Reactor fuel assemblies have a vertical boiling channel with initially steady inlet water flow rate. The density profile of the two phase mixture is one of monotonically decreasing density as function of elevation and is fixed in time. The density of the coolant at the exit of the channel is higher for higher coolant flow rate and is lower for higher power. Given a small perturbation in inlet flow rate, a corresponding perturbation in coolant flow density takes place at the boiling boundary and the density perturbation travels up the channel with the coolant flow, causing the density wave. The resistance to coolant flow increases substantially with decreasing flow density for the same mass flow rate. The density wave therefore affects the distribution of flow resistance along a boiling channel. In the specific case where the density wave travel time to the upper part of the channel coincides with the reversal of the inlet flow perturbation, a resonance effect results and the flow resistance change reinforces the original perturbation. The magnitude of the reinforcement is larger for high net density change, i.e. power to flow ratio, and can be sufficiently large to cause diverging flow oscillations, where the ratio of the magnitude of flow change at the peak of one cycle to that of the previous cycle (known as decay ratio) exceeds unity. In a Boiling Water Reactor, the density waves cause corresponding changes in the moderating function of the coolant and periodically alter the reactivity of the core. The alternating reactivity results in corresponding neutron flux and power oscillations. These power oscillations filter through the fuel pellets, with damping and time delay caused by the heat diffusion process, and result in fuel surface heat flux oscillations. The heat flux oscillations interact with the density wave and generally reinforce it. It is noted that fuel rods of smaller diameter reduce the filtering effect and have an adverse effect on stability. Early Boiling Water Reactor fuel designs utilized a simple array of 7×7 rods in a regular square lattice. The power density was relatively low, as the linear heat generation rate was relatively high, which forced the reactor power level to remain low to avoid set thermal limits. Newer designs use larger numbers of rods, specifically 8×8, 9×9, and 10×10 rod arrays. The increased number of rods resulted in decreasing the linear heat generation rate and permitted the fuel channel power density to increase, however, the increased number of rods resulted in two adverse effects: The first adverse effect of increasing the number of rods is that the diameter of each rod is reduced. This results in proportional reduction in heat conduction time constant and reduces its stabilization effect. The second adverse effect of the increase of the number of fuel rods in later designs is the increase of the coolant pressure drop as the hydraulic diameter of the subchannels is reduced. The two phase flow resistance in the upper part of the flow channel is increased, which results in reduced hydraulic stability. The development of large magnitude flow oscillations due to unstable density waves cannot be tolerated in a Boiling Water Reactor as it results initially in cyclical dryout and rewetting of the fuel surface and may lead to irreversible dryout. The occurrence of irreversible dryout leads to clad temperature increase and clad failure and release of radioactive material from therein. For this reason, Boiling Water Reactor plants take measures to guard against instabilities. These measures are: 1. Define by using computer simulations the boundaries of one or more exclusion zones on the power flow map, where neutron coupled density wave instabilities of the global or regional types are possible, and restrict operation in said zones. 2. Install hardware that accesses the neutron flux signals, and use these signals to determine if oscillatory behavior is present, in which case protective measures such as reactor scram are taken. There is therefore a need to provide a design that prevents density waves in Boiling Water Reactors while not exclusively dependent on their coupling to neutron flux signals. It is therefore an objective of the present invention to prevent density waves in Boiling Water Reactors. The present invention provides a method of operating a Boiling Water Reactor comprising analyzing LPRM (Local Power Range Monitor) signals for oscilliatory behavior indicative of neutron-flux-coupled density wave oscillations, determining if oscilliatory behavior is present in the signals; initiating a reactor protective corrective action if the oscilliatory behavior is determined, locating operating power and coolant flow relative to a boundary of an exclusion zone above which neutron-flux-uncoupled oscillations are possible, and initiating a reactor protective corrective action if neutron flux uncoupled oscillations are possible. The present invention also provides a method of operating a Boiling Water Reactor, comprising the steps of analyzing LPRM signals for oscilliatory behavior indicative of neutron-flux-coupled density wave oscillations, determining if oscilliatory behavior is present in the signals, initiating a reactor protective corrective action if the oscilliatory behavior is determined, analyzing several channels of high power using a stability program on-line at actual operating conditions and checking to determine if neutron flux uncoupled oscillations are possible, and initiating a reactor protective corrective action if neutron flux uncoupled oscillations are possible. Compliance with General Design Criteria GDC 10 and 12 of 10 C.F.R. 50 Appendix A precludes operating a Boiling Water Reactor under oscillatory conditions. Detect and Suppress systems have been installed in many Boiling Water Reactor such systems issue scram signals upon detecting oscillatory neutron flux signals using grouped Local Power Range Monitors (LPRM). These systems neglect protection against pure thermal hydraulic unstable density waves which are virtually uncoupled to neutron signals and are therefore virtually undetectable using LPRM's. The discovery of the existence of such unstable waves and their decoupling from the detection system is the impetus behind the present invention. The present invention relates to the unstable thermal hydraulic density waves virtually uncoupled to neutron flux variations and a method for protecting Boiling Water Reactors against same. The new system offers complete protection by combining two concepts, namely “Detect and Suppress” and “Anticipate and Suppress” where each protection concept targets specific modes of oscillations. The “Anticipate and Suppress” function relies on computerized methods for defining conditions under which growing single channel hydraulic oscillations may occur, and issues a scram signal to suppress the same. Other operating conditions for which single channel oscillations are not possible while coherent core wide or regional mode oscillations coupled with neutron flux are possible, are left to the “Detect and Suppress” function to recognize and issue scram signals to prevent their growth beyond safe operating limits. In accordance with the present invention, a mode of operating Boiling Water Reactors is identified in which unstable hydraulic density wave oscillations grow in magnitude while being virtually uncoupled to the neutron flux or the signal derived therefrom owing to its frequency being generally different from the frequency of the prevailing coherent oscillation modes which are coupled with neutron flux and power oscillations. This invention also offers an arrangement for protecting against said neutron-uncoupled density waves by separating them from the coherent oscillation types. According to this invention, the detect and suppress methods are simplified to account for neutron coupled modes only, while explicit protection from the neutron uncoupled mode is left to computerized analytical methods which are described hereafter in detail. FIG. (1) represents a power coolant flow operating map of a typical BWR. The nearly straight line (A) is defined as a control rod line, which represents a power flow relationship as flow forced by running pump(s) changes for a fixed control rod pattern. The curved line (B) represents the power coolant flow relationship under natural circulation, where the pumps are not running Curve (C) represents the boundary of the exclusion zone typical of the prior art, which divides the power coolant flow map into a stable region under the curve and potentially unstable region above the curve, where unstable regions are defined by neutron coupled modes. Curve (N) represents the boundary of the new exclusion zone according to the present invention, which divides the power coolant flow map into a stable region under the curve and potentially unstable region above the curve, where unstable is defined by a neutron uncoupled density wave mode. The advantage of the present invention lies in the size of the restricted or excluded region being smaller than that of the prior art which allows for greater operation flexibility. FIG. (2) is a logical flow diagram of an algorithm for protecting Boiling Water Reactor plants against the growth of all possible unstable modes in the first embodiment. The first step 10 is analyzing a set of LPRM neutron signals and issue a scram 20 (or any other corrective action such as power reduction) if the neutron flux signals indicate oscillatory behavior as determined in step 15. In case the neutron flux signals were not found to be oscillatory beyond noise levels, which indicates that neutron coupled modes are not excited, the algorithm goes to step 30. Step 30 is a check of whether the operating power and coolant flow point lie above the exclusion boundary denoted by (N) in FIG. (1), and issue a corrective action accordingly 20 when instability is anticipated as provided in step 35. When the algorithm passes through the two logical checks with negative indication of instabilities, the process is repeated 40 periodically at a period sufficiently small to preclude the growth of instabilities within a period to a degree sufficient to challenge the thermal operating limits of the plant. It must be noted that the above mentioned steps can be applied to run in sequence or in parallel, on the same computer processor or on separate one. FIG. (3) is a logical flow diagram of an algorithm for protecting BWR plants against the growth of all possible unstable modes in the second embodiment. Step 100 comprises analyzing a set of LPRM neutron signals and issuing a scram (or any other corrective action such as power reduction) 120 if the neutron flux signals indicate oscillatory behavior as determined in step 115. In the instance that neutron flux signals are not found oscillatory beyond noise levels, which means neutron coupled modes are not excited, the algorithm proceeds to the next step 130. Step 130 is a check of whether the operating conditions (power, axial power profile, coolant flow, inlet temperature and pressure) of any of a preset number of channels characterized by relatively high power can undergo neutron uncoupled density wave oscillations. The operating conditions are obtained from the on line monitoring computer programs. In the case the density wave stability algorithm indicates possible instability in any of the channels as queried in step 135, a scram signal or any other corrective action such as power reduction is issued in step 120. When the algorithm passes through the two logical checks with negative indication of instabilities, the process is repeated periodically at a period sufficiently small to preclude the growth of instabilities within a period to a degree sufficient to challenge the thermal operating limits of the plant in step 140. It must be noted that the above mentioned steps can be applied to run in sequence or in parallel, on the same computer processor or on separate one. Similarly, the stability calculation for each of the identified channels can be executed in sequence or in parallel using more than one computer processor. The present invention also provides a protection against a mode of operating a Boiling Water Reactor where the flow entering a single or few fuel channels undergoes growing oscillations due to unstable density waves along the channels where the magnitude of the density variations is too small for effective coupling to neutron flux modulation via feedback mechanisms which makes neutron detectors ineffective in detecting the oscillations. The present invention also provides a method for protecting Boiling Water Reactors from neutron uncoupled hydraulic oscillations by automatically issuing a shut down scram or power reduction signal upon reaching conditions where said oscillations are deemed possible by analytical means. The present invention also defines the conditions under which neutron uncoupled hydraulic oscillations is possible in at least one channel of a Boiling Water Reactor in which the boundaries of an exclusion zone on the operating power coolant flow map is calculated using computer programs simulating hydraulic density waves, inside the exclusion zone the simulated decay ratio is greater than a preset limit. The present invention also provides a method for defining the conditions under which neutron uncoupled hydraulic oscillations are possible in at least one channel of a Boiling Water Reactor in which the so called decay ratio for each of several top candidate channels characterized by high power relative to other co resident channels is calculated on line using computer simulations, and a scram or power reduction signal is issued in case any of the calculated channel decay ratios exceed a pre set limit. The present invention detects power oscillations and suppresses them via control rod insertions where the system protection parameters are tuned to allow sufficient time for suppressing coherent neutron flux coupled hydraulic oscillations while excluding neutron uncoupled channel oscillation modes. This tuning is achieved by using computer simulations of reactor oscillations to produce a relationship between the power oscillation magnitude and critical power ratio (“CPR”) where the neutron uncoupled hydraulic oscillations are excluded. Unstable density waves can grow to a large magnitude sufficient to challenge the thermal safety limit, while being virtually undetectable via neutron flux signals due to the weak level of interaction given that only a relatively small numbers of channels undergo such oscillations and the excited neutron flux levels are below or comparable to the noise level customary found in neutron signals. This fact identifies a major deficiency in the prior art which depends on neutron signals exclusively to identify oscillations. According to the present invention, the Detect and Suppress solution is improved fundamentally by performing the Delta CPR/Initial CPR Vs. Oscillation Magnitude (DIVOM) analysis to account exclusively for the neutron coupled modes known as the global and regional modes of power oscillations. This results in a calculated DIVOM curve of relatively small slope that allows the Detect and Suppress functions to be performed smoothly with a high degree of reliability without the problem of false identification of oscillations that can impact the continuity of operation of the power plant. The Detect and Suppress function is augmented by an additional function to prevent the neutron uncoupled oscillation mode. This augmentation cannot rely on the LPRM signals by virtue of the fundamental nature of the instability being virtually uncoupled to the neutron flux signals. Rather, the protection relies on analytical simulations and the protection is that of Anticipate and Suppress. This can be done in several methodologies, two of which are described herein. In the first embodiment, analytical simulations are performed a priori for each operating cycle or on generic basis for each plant where a sufficient number of possible operational conditions are covered. The analytical simulations identify a zone on the power coolant flow map where neutron uncoupled oscillations are possible. This zone lies above the curve (N) in FIG. (1). The exclusion zone above the curve is smaller than the one of the prior art shown in the same figure as curve (C), which improves the operational flexibility considerably. By using this analytically based exclusion method to avoid neutron uncoupled oscillations and in the same time using the Detect and Suppress to guard against the neutron coupled modes, this invention provides for complete protection against all possible oscillation modes. The flow chart of the first embodiment is given as FIG. (2). The second embodiment differs from the first embodiment in that an on line algorithm is used to calculate the stability of the neutron uncoupled modes instead of calculating the same in advance to create an a priori exclusion zone. In that manner the exclusion zone is determined on actual conditions instead of the worst of all possible operating conditions and thus relieves the plant operator from additional unnecessary conservatism. The stability algorithm receives input from the plant monitoring computer, and the input for each analyzed channel consists primarily of the power, power profile, coolant flow rate, inlet flow temperature, and system pressure. The selection of the channels to be analyzed on line is based on their relative power level and the channels of the highest power will be selected. The number of selected channels is determined a priori by off line analysis to make sure that the proper number of candidate channels are selected for on line analysis. There is no limit however to the number of channels selected, and virtually all channels in the core can be analyzed provided that the analysis is complete within a time period sufficiently small that an incipient oscillation does not have enough time to grow to a level that may challenge the thermal safety limits. Use of parallel processing is a preferred way to ensure that all channels where oscillations are possible are analyzed within the time period. The flow chart of the second embodiment is given as FIG. (3). |
|
description | This invention was made with U.S. government support under grant number CCF-0524673 awarded by the National Science Foundation. The U.S. government has certain rights in this invention. Embodiments of the present invention relate to a method and an apparatus for using entangled particles and, more particularly, to a microscope and a lithography apparatus. In order to implement an N-fold increase in resolution in imaging and lithography, the following ingredients are conventionally needed: either (a) creation of an entangled state of the form |Ψ(N)with high photon number N, or (b) the availability of an N-particle absorbing medium able to detect N photons at a given position simultaneously, or both. As of yet, no measures were known to overcome these disadvantages. Thus, what is needed are techniques to allow for an N-fold increase over the classical resolution limit which overcome these restrictions. Embodiments of the present invention use an entirely different scheme to achieve an optical resolution of λ/N when compared to the prior art. The method may involve neither of the requirements of the prior art as described above. As with path-entangled number states, such techniques may allow for an N-fold increase in resolution compared to the first order intensity correlation function G(1)(r) while keeping a contrast of 100%. Because the N particles may be recorded by distinct analyzers, only a single particle may be registered at each detector. This means that an N-particle absorbing material is most likely not needed in this scheme, only detectors suitable to detect one-particle events. One embodiment of the present invention is a method for using one particle out of N particles for irradiating a target. The method generally includes providing a radiation source with N incoherent emitters detecting particles emitted from said radiation source by using N−1 detectors located at N−1 different positions, and opening a particle barrier based on an occurrence of single detections on all N−1 detectors within a predetermined time period to allow said one particle to reach said target. Another embodiment of the present invention provides an apparatus for irradiating a target. The apparatus generally includes a radiation source with N incoherent emitters, N−1 particle detectors located at N−1 different positions, a discriminator adapted for identifying single particle detection events on all N−1 detectors within a predetermined time period from other particle detection events, and a particle barrier adapted to be opened based on the discriminator. Yet another embodiment of the present invention is a method for using N particles for investigating an object, wherein N is greater than or equal to 2. The method generally includes fixing the position of the object, detecting particles of a radiation emitted by the object by using N detectors located at N different positions, and discriminating single particle detections detected on all N detectors within a predetermined time period from other particle detection events. Yet another embodiment of the present invention provides an apparatus for investigating an object. The apparatus generally includes a fixing unit for fixing the position of the object, N particle detectors located at N different positions for detecting particles of a radiation emitted by the object, wherein N is greater than or equal to 2, and a discriminator adapted for discriminating single particle detection events on all detectors within a predetermined time period from other particle detection events. Reference will now be made in detail to the various embodiments of the invention, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation of the invention, and is not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present invention includes such modifications and variations. In order to describe embodiments of the present invention, a theoretical approach to a specific example is provided below. The specific example includes the use of atoms as emitters and photons as radiation particles. However, it is important to note that the invention is not limited to the described system of photons and atoms. Rather, various kinds of radiation may be employed, including photons, electrons, protons, neutrons, alpha particles, atoms, molecules and ions. At the same time, the emitters or scattering sites may be selected from the group consisting of atoms, ions, molecules, quantum dots, and Josephson circuits. It is known that nonclassical correlations exist in the radiation of two atoms that are coherently driven by a continuous laser source. These include second order intensity correlations of spontaneously emitted photons, which are proportional to the conditional probability to detect a photon at r2 and time t+τ, given that a photon has been recorded at r1 and time t. It can be shown analytically that those photons can exhibit a spatial interference pattern (in the second order correlation function) not present in a classical treatment so that bunched and antibunched light is emitted in different spatial directions, even when the atoms are initially uncorrelated. The phenomena show up even without any interatomic interaction. The spatial interference patterns for the second order correlation function are of particular interest. One of the ideas underlying embodiments of the present invention was finding spatial interference patterns of higher order correlations in the fluorescence radiation emitted by trapped particles and utilizing them for imaging and manipulation purposes. As described herein, this may allow surpassing the resolution limits of classical optics. This may be achieved by applying technical measures which may be much easier to implement than methods known from the art. FIG. 6 shows a schematic view of Young's double slit experiment. Shown are a light source 100, a collimation slit 110, a double slit 120, light beams 140, 150 as examples, and a far-field interference pattern I(r)˜G(1)(r) 130. In this experiment (or in a Mach Zehnder interferometer), the probability G(1)(r) to detect a photon at position r results from the interference of the two possible paths a single photon can take to reach the detector. This may be expressed by the state |Ψ(1)=1/√{square root over ( )}2(|1U|0L+|0U|1L) where the subscript L(U) denotes the lower (upper) arm of the interferometer. Variation of the detector position may lead to a modulation of the form G(1)(r)=1+cos δ(r), where δ(r)=kd sin θ(r) is the optical phase difference of the waves emanating from the two slits and k, d, and θ(r) are the wave number, slit separation, and scattering angle, respectively. Obviously, the fringe spacing of the modulation (in units of d sin θ(r)) may be determined by the optical wavelength, corresponding to the Rayleigh criterion which restricts the pattern size of the interfering beams to λ. Quantum entanglement is able to bypass the Rayleigh limit. If one considers, for example, the path-entangled two-photon state |Ψ(2)=1/√{square root over (2)}(|2U|0L+|0U|2L), the two-photon state |2 may have twice the energy of the single photon state |1 in a given mode. Hence, it may accumulate phase twice as fast when propagating through the setup. This may give rise to a two-photon absorption rate of the form G(2)(r, r)=1+cos 2δ(r) exhibiting a fringe spacing half that of G(1)(r). Correspondingly, for the entangled N-photon state |Ψ(N)=1/√{square root over (2)}(|NU|0L+|0U|NL) the N photon absorption rate may read G(N)(r, . . . , r)=1+cos Nδ(r), displaying a fringe spacing of λ/N. This gain in resolution by a factor of N with respect to G(1)(r) may be fruitfully applied for a wide range of applications (e.g., in microscopy, lithography, spectroscopy, and magnetometry). N identical two-level atoms excited by a single laser pulse may be considered. After the spontaneous decay, the N resulting photons may be registered by N detectors at positions r1, . . . rN. In case of detection within a predetermined time interval, the Nth order correlation function may be written (up to an insignificant prefactor) asG(N)(rL, . . . , rN)=(D†(r1) . . . D†(rN)D(rN) . . . D(r1) (1)where D ( r i ) = 1 N ∑ α = 1 N σ α - ⅇ - ⅈ kn ( r i ) · R α . ( 2 ) Here, D is the detector operator which links the detection of a photon at ri to the emission of a photon by one (unknown) atom of all atoms situated at Rα, where α=1, . . . , N. n(ri)=ri/ri stands for the unit vector in the direction of detector i, the sum is over all atom positions Rα, k=ω0/c, where ω0 is the transition frequency, and σα−gαe| is the lowering operator of atom for the transition |e|g. For all atoms initially prepared in the excited state |e, one obtains from Eqs. (1) and (2): G ( N ) ( r 1 , … , r N ) = 1 N N γ ( r 1 , … , r N ) 2 , where ( 3 ) γ ( r 1 , … , r N ) = ∑ ε 1 , … , ε N = 1 ε 1 ≠ … ≠ ε N N ∏ α = 1 N ⅇ - ⅈ kn ( r ε α ) · R α . ( 4 ) Equations (3) and (4) show that G(N)(r1, . . . , rN) results from the interference of N! terms, associated with all possibilities to scatter N photons from N identical atoms which are subsequently registered by N detectors. To simplify further calculations, the case of N equidistant atoms may be assumed. Choosing the origin of the coordinate system in the center of the atomic chain leads toRα=jαdu (5)with u being the unit vector along the chain axis, d the interatomic spacing, and jα=−(N−1)/2, . . . , (N−1)/2 for α=1, . . . , N (see FIG. 1). By definingδ(ri)=kdn(ri)·u=kd sin θi (6)where θi is the angle between n(ri) and the direction normal to the atomic chain (see FIG. 1), it may be found that G ( N ) ( r 1 , … , r N ) = 1 N N ( ∑ N 1 permutations of the j components cos ( j - δ ) ) 2 ( 7 ) Here, j is the vector of the distances of the atoms from the origin in units of d:j=(j1, . . . , jN) (8)andδ=(δ(r1), . . . , δ(rN)). (9) Due to the symmetry of the configuration, the function G(N)(r1, . . . , rN) contains N!/2 cosine terms, each oscillating in general with a different spatial frequency. Obviously, the complexity of the expression rises rapidly with the atom number N. However, if, for example, the N detectors are placed in such a manner that all terms in Eq. (7) interfere to give a single cosine term, a modulation oscillating at a unique spatial frequency would be left. A set of particular detector positions may be found that lead to the following general result: for arbitrary even N and choosing the detector positions such that δ ( r 2 ) = - δ ( r 1 ) , δ ( r 3 ) = δ ( r 5 ) = … = δ ( r N - 1 ) = 2 π N , δ ( r 4 ) = δ ( r 6 ) = … = δ ( r N ) = - 2 π N , ( 10 ) the Nth order correlation function G(N) as a function of detector position r1 may be reduced toG(N)(r1)=AN[1+cos(Nδ(r1))], (11)where AN is a constant which depends on N. For arbitrary odd N, and choosing the detector positions such that δ ( r 2 ) = - δ ( r 1 ) , δ ( r 3 ) = δ ( r 5 ) = … = δ ( r N ) = 2 π N + 1 , δ ( r 4 ) = δ ( r 6 ) = … = δ ( r N - 1 ) = - 2 π N + 1 , ( 12 ) the Nth order correlation function G(N) as a function of r1 may be reduced toG(N)(r1)=AN[1+cos((N+1)δ(r1))]. (13) According to Eqs. (11) and (13), for any N a correlation signal with a modulation of a single cosine may be obtained, displaying the same contrast and similar fringe spacing as in the case of the maximally entangled N-photon state |Ψ(N): for even N the fringe spacing corresponds to λ/N, for odd N it corresponds to λ/N+1). However, in contrast to |Ψ(N), both the necessity to generate path-entangled Fock states and the need to detect a faint multi-photon absorption signal may be avoided. Since in this scheme the N photons may be registered by N distinct detectors, only a single photon may be recorded at each detecting device. It should be emphasized that as the photons are created by spontaneous emission, the interference signal may be generated by incoherent light. An achievable contrast of 100% may prove the underlying quantum nature of the process (i.e., the existence of non-local correlations between the detected photons). The quantum correlations may be generated by the measurement process after the detection of the first photon. In fact, just before the detection of the Nth photon, the atomic system may be in an N-particle W-state with one excitation. The non-classical characteristics of this scheme may thus be an example of detection induced entanglement of initially uncorrelated distant particles. To exemplify the method, the simplest situation is considered, i.e., the case of N=2 atoms. With j=(−½, +½), Eq. (7) may be used to obtain: G ( 2 ) ( r 1 , r 2 ) = 1 2 [ 1 + cos ( δ ( r 1 ) - δ ( r 2 ) ) ] . ( 14 ) The modulation of the G(2)(r1, r2)-function may depend on the relative position of the two detectors (see FIG. 1): for δ(r2)=δ(r1), the second order correlation function is a constant, whereas for fixed r2 the two photon coincidence as a function of δ(r1) exhibits the same phase modulation and fringe spacing as G(1)(r) in the Young's double slit experiment. The increased parameter space available for the detector positions in case of two detectors may also allow determining the relative orientation δ(r2)=−δ(r1). This case may lead to G ( 2 ) ( r 1 ) = 1 2 [ 1 + cos ( 2 δ ( r 1 ) ) ] , ( 15 ) exhibiting a phase modulation as a function of r1 with half the fringe spacing of G(1)(r) while keeping a contrast of 100%. This may correspond to the fringe pattern achieved with the maximally entangled two-photon state |Ψ(2). The assumed condition for the direction of emission of the two photons, (i.e., δ(r2)=−δ(r1)) may correspond to a space-momentum correlation of the photons identical to the one present in spontaneous parametric down conversion (SPDC). This process is presently widely used for producing entangled photon pairs. Adding a beam splitter may also allow transforming the space-momentum entangled photon pair generated by SPDC into the maximally path-entangled two-photon state |Ψ(2). By using either correlated states, (i.e., space-momentum entangled photon pairs or maximally path-entangled photon number states), sub-wavelength resolution may be obtained, surpassing the Rayleigh limit by a factor of two, three and four. However, extending these schemes to states with higher numbers of entangled photons may appear to be difficult since the use of, for example, an X(N) nonlinearity or, alternatively, N−1 nonlinear X(2) crystals in a cascaded arrangement results in very low efficiencies, dropping rapidly with increasing N. By contrast, the present scheme may be extended to N>2 atoms straightforwardly in view of single atom trapping techniques known from the art. The complexity to produce path-entangled Fock states with high photon number N, as well as the necessity of an N-photon absorbing material can thus be circumvented. Next, the third order correlation function G(3)(r1, r2, r3) for three equidistant atoms will be examined. For arbitrary detector positions r1, r2, and r3 it may be derived from Eq. (7): G ( 3 ) ( r 1 , r 2 , r 3 ) = 4 27 [ cos ( δ ( r 1 ) - δ ( r 2 ) ) + cos ( δ ( r 1 ) - δ ( r 3 ) ) + cos ( δ ( r 2 ) - δ ( r 3 ) ) ] 2 . ( 16 ) By positioning, for example, the two detectors according to Eq. (12), Eq. (16) may be reduced to G ( 3 ) ( r 1 ) = 2 27 [ 1 + cos ( 4 δ ( r 1 ) ) ] . ( 17 ) Obviously, G(3) as a function of r1 exhibits a modulation of a single cosine with a contrast of 100%, in this case with a fringe spacing of λ/4. Similarly, G(4)(r1) may be determined where the detectors are placed according to Eq. (10): G ( 4 ) ( r 1 ) = 1 8 [ 1 + cos ( 4 δ ( r 1 ) ) ] . ( 18 ) Finally, the result may be compared with the modulation of the far field intensity G(1)(r1) obtained in the case of a chain of N equidistant atoms. If each atom is initially prepared in the state |Φ>=1/√{square root over (2)}(|g+|e), it may be derived from Eqs. (1) and (2) G ( 1 ) ( r 1 ) = 1 2 [ 1 + 1 N ∑ α = 1 N - 1 ( N - α ) cos ( α δ ( r 1 ) ) ] . ( 19 ) Equation (19) shows that, apart from an offset, G(1)(r1) equals the outcome of the classical grating. As is well known from this classical device, a term cos((N−1) δ(r1)) indeed appears in the intensity distribution, oscillating in space with N−1 times the modulation of the two-slit interference pattern. However, lower spatial frequencies may appear as well and contribute to G(1)(r1). From the point of view of microscopy, the resolution is determined by the Rayleigh limit: an object can be resolved only if at least two principal maxima of the diffraction pattern are included in the image formation (Abbe's theory of the microscope). According to this criterion, the use of G(1)(r1) for imaging the N atoms may allow at best resolving an interatomic spacing equal to λ. By contrast, the use of the Nth order correlation function with N detectors positioned according to Eq. (10) (or Eq. (12)) may allow resolving an atom-atom separation as small as λ/N (or λ/N+1)) [see Eqs. (11) or (13)]. In conclusion, it was shown that N photons of wavelength λ spontaneously emitted by N atoms and coincidentally recorded by N detectors at particular positions may exhibit correlations and interference properties similar to classical coherent light of wavelength λ/N. The method requires neither initially entangled states nor multi-photon absorption, only common detectors suitable for single-photon detection. Embodiments of the present invention make use of the findings described above. However, it is important to note that the invention is not limited to the described system of photons and atoms. Rather, various kinds of radiation may be used, including photons, electrons, protons, neutrons, alpha particles, atoms, molecules and ions. At the same time, the emitters or scattering sites may be selected from the group consisting of atoms, ions, molecules, quantum dots, and Josephson circuits. FIG. 2 shows an embodiment of the invention, in which an apparatus is provided to use one particle out of N quantum entangled particles for irradiating a target. The apparatus may comprise a radiation source (10) with a plurality of N incoherent emitters (20). In this example, N is chosen to be 4. These emitters may be, for example, atoms, ions, molecules, quantum dots or Josephson circuits. They are preferably, but not necessarily arranged in a row. Typically, the emitters may be kept in the evacuated chamber (30), wherein their positions are maintained, for example, by means of an atom or ion trap. The emitters may emit radiation particles which may be chosen from the group consisting of photons, phonons, electrons, protons, neutrons, alpha particles, atoms or ions. The apparatus may further comprise N−1 detectors (40) to detect the emitted radiation, which may be arranged in a plane with the emitters. The detectors may be chosen from the various types known from the art in accordance with the type of radiation. The detectors may be connected to a discriminating device (60), which is adapted to discriminate particle detection events on all detectors within a predetermined time period. Typically, but not necessarily, the discriminating device (60) is an electronic device. Furthermore, the apparatus may comprise a particle barrier (70), which may be adapted to be opened depending on a discriminated detection on all N−1 detectors. The type of the particle barrier may be chosen depending on the type of radiation used. In the case of photons, for example, the particle barrier may be a liquid crystal display (LCD) device. The barrier should be suitably designed to allow short opening switching times. In case of photons, these times lie in a range of nanoseconds. A target for interaction with the emitted radiation is provided so that the particle barrier may be located between the radiation source and a target (90). In an embodiment of the invention, a second radiation source (80) may serve to irradiate the emitters with radiation. Depending on the desired kind of radiation, the second source may, for example, comprise a laser, an electron source like a tube or an electron accelerator, a source of radioactive radiation of various types or a plasma device to produce ions. A part of the applied radiation may interact with the emitters and be scattered. Accordingly, these can be regarded to re-emit the radiation. The source for the applied radiation is typically, but not necessarily, a laser. In an embodiment, the applied radiation may be pulsed. Typically, but not necessarily, the combination of emitters and the applied radiation is suitably chosen such that no more than two energetic states of the emitters are selected in the scattering process. In an embodiment of the invention, the N−1 detectors and the particle barrier may be positioned in accordance with the findings described above. Hence, by arranging the setup in the manner described below, a modulation of a signal generated by the accumulation of multiple detection events on the target may take the form of a pure sinus when at least one detector and/or the particle barrier are moved circumferentially around the target during an irradiation process. The N−1 detectors and the particle barrier may be positioned about defined angular positions with respect to the radiation source. The distances of the detectors from the radiation source may be substantially similar. The angular positions θi of the detectors with respect to an axis perpendicular to the row of emitters may be derived from the calculations as described above. In particular, they may be calculated from Eq. (10) in case of an even number of N, from Eq. (12) in case of an odd number of N, and by taking into account the relation of Eq. (6). The first terms of Eqs. (10) and (12) may determine the angles of the first of the N−1 detectors and the particle barrier (which can be regarded as a replacement of the Nth detector in the theoretical scenario above) to be of equal amount, but of opposite sign. Hence, these may be positioned symmetrically about an axis perpendicular to the row of emitters by an arbitrarily chosen angle θi. Both the first detector and the target may be adapted to be movable in a circumferential direction with respect to the radiation source, whereby their movement is controlled in order to maintain the previously described angular relation (see FIG. 2). The positions of the remaining N−2 detectors may also be determined by Eqs. (10) and (12). The results of Eq. (10) or (12) for δ(ri), which depend only on the number N of detectors used, may be used to calculate the angles of the detectors by applying Eq. (6), according to whichδ(ri)=kd sin θi Because d is the spacing between the emitters of the radiation source and k is the wave number of the emitted radiation, the angles θi may be derived by a simple calculation from the results of Eq. (10) or (12). θi refers to the angle between the position vector of detector i and the axis perpendicular to the row of emitters (see FIG. 2). For small N, there are solutions according to which each of the N−1 detectors and the particle barrier have different angular positions θi. Thus, the N−1 detectors may be disposed in one plane, which includes the row of emitters, at different angular positions θi, as is shown in the example of FIG. 2. For any N, there are generally solutions where two or more of the detectors share the same angle θi. Thus, detectors with the same angle θi may be disposed in a second plane perpendicular to the plane defined by the row of emitters, the first detector and the particle barrier. This further plane may share the angle θi with respect to an axis perpendicular to the row of emitters. The detectors may be arranged on the further plane about arbitrary angles φi, however taking into account the spontaneous emission pattern of the considered atomic transition. By doing so, several detectors may be deployed sharing the same θi, which is exemplarily shown in FIG. 5 for three detectors. In an embodiment of the invention, one detector and the target may be moved along an angular range in opposite angular directions during an irradiation process. The size of this range may depend on several individual parameters including the properties of the radiation source and the target. It may need to be set up experimentally in order to achieve best results. In a following discrimination step, particle detections detected on all N−1 detectors within a predetermined time interval may be discriminated from other particle detection events using a discrimination device. If an occurrence of detection events on all N−1 detectors is recognized, the particle barrier may be opened to allow passage of a particle. In an embodiment, the particle barrier may only be locally opened. After passing the opened barrier, the particle may be used to interact with the target. In an embodiment of the invention, particles passing the particle barrier may be used for physical manipulation of a target object by means of interaction between the particle and the target object after their passage through the opened barrier. This manipulation may include lithography purposes, such as in the production of semiconductors. A pattern to be reproduced on a semiconductor substrate may be composed using sinusoidal modulations of different frequencies according to a Fourier decomposition of the structure of the pattern to be achieved. FIG. 3 shows an embodiment of the invention with two scattering sites (N=2), a detector 40, and a target 90. Given Eq. (14), it can be seen that when choosing δ2=(1−m) δ1, where m can take arbitrary values, the G(2) function takes the following form: G ( 2 ) ( δ 1 ) = 1 2 + 1 2 · cos [ m δ 1 ] . Given the relation δi=kd sin θi (Eq. (6)), wherein each phase δi is limited within the interval [−kd, +kd] as the term sin θi runs from −1 to +1 while θi can take all values within [−π/2, +π/2], solutions exist for the interval δ1=[−kd/m, +kd/m]. Within these boundaries, the movement of the detector and the target (respective to the particle barrier) may yield an accumulated signal at the target shown in FIG. 3 for various values of m. As is shown in the figure, the angular interval of the target (determined by θ1) decreases with growing m. However, the number of modulations within the corresponding angular interval may be kept constant. Thus, the optical resolution of the apparatus used for lithographic purposes may increase with growing m. FIG. 4 shows another embodiment of the invention, in which an apparatus is provided to use N quantum entangled particles for investigating an object. In this example, N is chosen to be 4. The apparatus may comprise an object which acts as a radiation source (10) with a plurality of N incoherent emitters (20). These emitters may be, for example, atoms, ions, molecules, quantum dots, or Josephson circuits. They are preferably, but not necessarily arranged in a row. Typically, they are kept in the evacuated chamber, wherein their positions may be maintained, for example, by means of an atom or ion trap. The emitters may emit radiation particles, which may be chosen from the group consisting of photons, phonons, electrons, protons, neutrons, alpha particles, atoms, molecules, or ions. The apparatus may further comprise N detectors (40) located at N different positions to detect emitted radiation, which may be arranged in a plane with the object comprising the emitters. The detectors may be chosen from the various types known from the art in accordance with the type of radiation used. A limitation on the type of detector may be that it is suitable to detect single particles of the radiation. The detectors may be connected to a discriminating device (60), which may be adapted to discriminate particle detection events taking place on all detectors within a predetermined time interval. Typically, but not necessarily, the discriminating device (60) is an electronic device. In an embodiment of the invention, a second radiation source (80) may serve to irradiate the emitters with radiation. Depending on the desired type of radiation, the second source may, for example, comprise a laser, an electron source such as a tube or an electron accelerator, a source of radioactive radiation of various types, or a plasma device to produce ions. A part of this radiation may interact with the emitters and be scattered. Accordingly, these may be regarded as emitters re-emitting radiation. The source for the applied radiation is typically, but not necessarily a laser. For some embodiments, the applied radiation may be pulsed. Typically, it is chosen in a way so that no more than two energetic states of the emitters are selected in the scattering process. The N detectors may be positioned about defined angular positions with respect to the radiation source. The distances of the detectors from the object may be chosen substantially arbitrarily, but should lie in the same order of magnitude for reasons of experimental practicability. The angular positions of the detectors with respect to an axis perpendicular to the object may be derived from the calculations as described above. In particular, they may be calculated from Eq. (10) in case of an even number of N, from Eq. (12) in case of an odd number of N, and by taking into account the relation of Eq. (6). The first terms of Eq. (10) and (12) may determine the angles of the first and second of the N detectors to be of equal amount, but of opposite sign. Hence, these may be positioned symmetrically about an axis perpendicular to the row of emitters about an arbitrarily chosen angle. Both the first and second detectors may be adapted to be movable in a circumferential direction with respect to the object, whereby their movement may be controlled in order to maintain the previously described angular relation. The positions of the remaining N−2 detectors may also be determined by Eqs. (10) and (12). The results of Eq. (10) or (12) for δ(ri), which depend only on the number N of detectors used, may be used to calculate the angles of the detectors by applying Eq. (6), according to whichδ(ri)=kd sin θiBecause d is the spacing between the emitters of the object and k is the wave number of the emitted radiation, the angles θi may be derived by a simple calculation from the results of Eq. (10) or (12). θi refers to the angle between the position vector of detector i and the axis perpendicular to the row of emitters. For small N, there may be solutions according to which each of the N detectors have different angular positions θi. Thus, they may be disposed in one plane, which includes the row of emitters, at different angular positions θi, as is shown in the example of FIG. 4. For any N, there are generally solutions where two or more of the detectors share the same angle θi. Thus, detectors with the same angle θi may be disposed in a second plane perpendicular to the plane defined by the row of emitters, the first detector, and the particle barrier. This further plane may share the angle θi with respect to an axis perpendicular to the row of emitters. The detectors may be arranged on the further plane about arbitrary angles φi. By doing so, several detectors may be deployed sharing the same θi, which is exemplarily shown in FIG. 5 for three detectors. In an embodiment of the invention, the first and second detector may be moved along an angular range in opposite angular directions during an irradiation process. The size of this range may depend on several individual parameters, such as the properties of the radiation source and the object. Best results for this range may be empirically determined. During irradiation, particle detections detected within a predetermined time interval on all N detectors may be discriminated using a discrimination device. If an occurrence of detection events on all N detectors within a specific time interval is recognized, this event may be counted by a counting device. By arranging the N detectors in the angular relation described above, a modulation of a signal generated by the accumulation of multiple N-particle detection events may take the form of a pure sinus-oscillation when the object consists of N incoherent emitters and at least one of the detectors is moved. By analyzing the modulation of the accumulated radiation, calculations may be carried out on the structure of the object (e.g., the interatomic spacing). Thus, the apparatus and the described method may be suitable for microscopic investigations into the object constituted by the emitters. Embodiments of the invention may also be directed to an apparatus for carrying out the disclosed methods including apparatus parts for performing each described method step. These method steps may be performed by way of hardware components, a computer programmed by appropriate software, by any combination of the two, or in any other manner. Furthermore, embodiments of the invention may also be directed to methods by which the described apparatus operates, including method steps for carrying out every function of the apparatus. |
|
description | This application claims priority to co-pending German Patent Application Ser. No. 10 2008 061 631.1, filed Dec. 11, 2008, the entirety of which is incorporated by reference herein. The present invention relates to a method for the determination of the coefficient of performance of a refrigeration machine, in particular of a heat pump, which includes a closed circuit which has a refrigerant and in which an evaporator, a compressor, a condenser and an expansion valve are arranged. The quotient from the heat output of the refrigeration machine and the taken up electrical power of the refrigeration machine is called the coefficient of performance (COP) of a refrigeration machine. Conventionally, the electrical power take-up of the refrigeration machine is detected via an electricity meter, whereas the heat output of the refrigeration machine is determined by a temperature measurement and a volume flow measurement on the water side of the refrigerant circuit, i.e. that is behind the condenser. A method is also known in which the temperatures and the pressures of the refrigerant are detected using two pressure sensors and three temperature sensors at different points of the circuit and are used for the calculation of the coefficient of performance. The electrical power take-up of the refrigeration machine is also detected by means of an electricity meter. The heat output of the refrigeration machine can then be calculated by multiplying the coefficient of performance by the taken up electrical power. It proves to be problematic with the known methods or refrigeration machines that both the electricity meter and the pressure sensors represent a not unsubstantial cost factor. In a method in accordance with the invention, at least three temperatures of the refrigerant are determined for the determination of the coefficient of performance of a refrigeration machine, in particular of a heat pump, which includes a closed circuit which has a refrigerant and in which an evaporator, a compressor, a condenser and an expansion valve are arranged, using at least three temperature sensors which are arranged in the circuit. Enthalpies and pressures of the circuit are calculated from the determined refrigerant temperatures and both the heat output and the taken up electrical power of the refrigeration machine are calculated from differences of the calculated enthalpies. The coefficient of performance is finally determined from the quotient of the calculated heat output and the calculated taken up electrical power. In a method in accordance with the invention, the coefficient of performance of the refrigeration machine is in other words determined only with reference to temperature values which are delivered by three temperature sensors arranged in the refrigerant circuit, with a specific knowledge of the thermodynamic properties of the system, in particular of the refrigerant and of the compressor, being required. A minimum of information on the refrigerant circuit which is required to be able to determine the coefficient of performance of the refrigeration machine is determined by the measurement of the refrigerant temperatures at three different points of the refrigerant circuit. A use of additional sensors, e.g. of further temperature sensors or pressure sensors, which are typically approximately ten times more expensive than temperature sensors, is thus generally not required. The use of a costly electricity meter can in particular be dispensed with. The use in accordance with the invention of a minimal number of temperature sensors therefore makes it possible to determine the coefficient of performance of a refrigeration machine with a minimal cost effort. In accordance with an advantageous embodiment of the method, a first temperature is measured in the region of the inlet of the compressor, a second temperature is measured in the region of the outlet of the condenser and a third temperature is measured in the region of the outlet of the expansion valve. The refrigerant temperatures measured at these points of the refrigerant circuit are generally sufficient to determine the enthalpies of the circuit and ultimately to determine the coefficient of performance of the refrigeration machine from them. Alternatively, a fourth temperature can additionally be determined by means of a fourth temperature sensor and can be used for the determination of the coefficient of performance, with the fourth temperature preferably being determined in the region of the outlet of the compressor. By the measurement of the refrigerant temperature at the compressor outlet, this temperature no longer has to be calculated by a compressor model, but it can rather be determined exactly. The coefficient of performance can be determined more simply, faster and more precisely in this manner. In the method in accordance with the invention in accordance with claim 4, at least two temperatures and one pressure of the refrigerant are determined for the determination of the coefficient of performance of a refrigeration machine using at least two temperature sensors and at least one pressure sensor which are arranged in the refrigerant circuit. Enthalpies of the circuit are calculated from the determined refrigerant temperatures and the determined refrigerant pressure and the heat output and the taken up electrical power of the refrigeration machine are calculated from differences between the enthalpies. The coefficient of performance of the refrigeration machine is then determined from the quotient of the calculated heat output and the calculated taken up electrical power. In this variant of the method in accordance with the invention, the coefficient of performance of the refrigeration machine can also be determined using a minimal number of sensors and in particular without an electricity meter and thus particularly cost-effectively. In this case, the determination of the coefficient of performance takes place only with reference to the measured values delivered by the two temperature sensors and by the one pressure sensor, with specific knowledge of the system, in particular of the thermodynamic properties of the refrigerant and of the compressor, also having to be required here. In accordance with an advantageous embodiment of the method, a first temperature is measured in the region of the inlet of the compressor, a second temperature is measured in the region of the outlet of the condenser and a first pressure is measured in the region of the outlet of the evaporator. In addition, a third temperature can be determined and can be used for the determination of the coefficient of performance, with the third temperature preferably being determined in the region of the outlet of the compressor. Due to the additional measurement of a third temperature, it is possible to replace calculations which are required on the use of only three sensors for the determination of the enthalpies, in particular for the determination of the coolant temperature at the compressor outlet, by an actual measurement, whereby the determination of the coefficient of performance of the refrigeration machine can take place more simply, faster and with a higher precision. Alternatively or additionally, a second pressure can be determined and can be used for the determination of the coefficient of performance, with the second pressure preferably being determined in the region of the outlet of the condenser. The measurement of the second pressure also contributes to a faster and more precise determination of the coefficient of performance in that the calculation of the pressure value required without the direct measurement can be dispensed with. Further subject matters of the invention are moreover the refrigeration machines disclosed herein. The methods in accordance with the invention can be carried out particularly easily and the above advantages can be achieved correspondingly using these refrigeration machines. A first embodiment of a refrigeration machine in accordance with the invention is shown in FIG. 1. The refrigeration machine includes a closed circuit 10 which has a refrigerant and in which an evaporator 12, a compressor 14, a condenser 16 and an expansion valve 18 are arranged. For the determination of the refrigerant temperature, a temperature sensor 28 is arranged in the region of the inlet of the compressor 14, a temperature sensor 30 is arranged in the region of the outlet of the condenser 16 and a temperature sensor 32 is arranged in the region of the outlet of the expansion valve 18. The temperature sensors 28, 30, 32 are connected to an evaluation unit 26 which can be integrated in a control of the refrigeration machine. The refrigeration machine is described here in its function as a heat pump. FIG. 2 shows for this purpose a log p-h diagram of the refrigerant used in the refrigeration machine, with the pressure p of the refrigerant being entered logarithmically as the function of the enthalpy H. In addition, the limits of saturated liquid 20 and saturated gas 22 are drawn. The point E in FIG. 2 designates the state of the refrigerant after the expansion through the expansion valve 18. An evaporation (E-A) and overheating (A-B) of the refrigerant takes place in the evaporator 12. The compressor 14 provides a compression (B-C) of the refrigerant which is accompanied by a corresponding temperature increase. The temperature of the refrigerant can be increased, for example, from approximately +10° C. at the outlet of the evaporator 12 up to approximately +90° C. by the compressor 14. A condensing (C-D) of the refrigerant takes place in the condenser 16, with the condensation temperature being able to amount, for example, to +50° C. The now liquid refrigerant which is only 50° C. warm is subsequently expanded by the expansion valve 18 (D-E), with it cooling down to approximately 0° C., for example. In the following, the temperature of the gaseous refrigerant at the inlet of the compressor 14 is designated as T1; the temperature of the liquid refrigerant at the outlet of the condenser 16 as T2; the temperature of the expanded refrigerant at the outlet of the expansion valve 18 as T3; and the temperature of the gaseous refrigerant at the outlet of the compressor 14 as T4. The evaporation pressure, i.e. that is the pressure of the gaseous refrigerant at the outlet of the evaporator 12 is designated as P1 and the condensing pressure, i.e. that is the pressure of the liquid refrigerant at the outlet of the condenser 16 as P2. First the enthalpy H1 is determined at the outlet of the condenser 16, the enthalpy H2 at the inlet of the compressor 14 and the enthalpy H3 at the outlet of the compressor 14 to determine the coefficient of performance of the refrigeration machine. In this respect, the enthalpy H1 is a function of the refrigerant temperature T2 at the outlet of the condenser, the enthalpy H2 is a function of the refrigerant temperature 11 at the inlet of the compressor 14 and of the refrigerant pressure P1 at the outlet of the evaporator 12; and the enthalpy H3 is a function of the refrigerant temperature T4 at the outlet of the compressor 14 and of the refrigerant pressure P2 at the outlet of the condenser 16:H1=f(T2) (1)H2=f(P1,T1) (2)H3=f(P2,T4) (3) In the embodiment shown in FIG. 1, the determination of the temperatures T1, T2, T3 takes place by measurement using the temperature sensors 28, 30 and 32 respectively. The temperature values T1, T2, T3 detected by the temperature sensors 28, 30, 32 are communicated to the evaluation unit 26. Using the pressure equation of the refrigerant used, the evaluation unit 26 calculates the pressure P2 from the received value for the temperature T2 at the outlet of the condenser 16 and the pressure P1 from the temperature value T3 at the outlet of the expansion valve 18. The generally known Clausius-Clapeyron equation can be used, for example, as the pressure equation. With knowledge of the temperatures T1 and T2 and of the pressure P1, the enthalpies H1 and H2 can now be determined by equations (1) and (2). The enthalpy H3 is calculated from the compressor model since the temperature T4 is not known. It is assumed for this purpose that approximately 95% of the electrical power taken up by the compressor 14 is induced into the refrigeration circuit. The electrical power Qe1 taken up by the compressor 14 is in this respect not determined by an electricity meter, but is rather calculated by a model describing the thermodynamic properties of the compressor 14, e.g. a 10-coefficient model. Not only the electrical power taken up by the compressor 14 can be calculated using this model, but also the refrigerating capacity Q0 of the compressor 14, the electrical current I taken up by the compressor 14 and the mass flow m° of the refrigerant flowing through the compressor 14. In this respect, the values calculated only apply to the documented operating point of the compressor 14 either at a constant overheating or at a constant suction gas temperature, i.e. at a constant temperature T1 of the refrigerant at the compressor inlet. To calculate the values of the real operating point, the values have to be corrected in dependence on the real compressor inlet temperature T1. The electrical power Qe1 taken up by the compressor 14 is divided by the mass flow m° to determine the enthalpy difference H3-H2.Qe1/m°=H3−H2 (4) Since the enthalpy H2 is known from equation (2), the enthalpy H3 can be calculated easily from the enthalpy difference H3−H2. For control, the refrigerant temperature T4 at the compressor outlet is calculated from the point of intersection of the line of enthalpy H3 with the line of the pressure P2 in the log p-h diagram of FIG. 2. Subsequently, the heat output Qh of the refrigeration machine is calculated from the difference of the calculated enthalpies H3 and H1 in accordance with the equationQh=m°*(H3−H1) (5). The electrical power Qe1 taken up by the compressor 14 was already determined using the compressor model and is preoperational to the difference of the enthalpies H3 and H2 in accordance with equation (4). To determine the coefficient of performance COP or the efficiency of the refrigeration machine, subsequently only the quotient of the heat output Qh and of the electrical power Qe1 still has to be formed:COP=Qh/Qe1=(H3−H1)/(H3−H2) (6). In addition, the annual performance index of the refrigeration machine can be determined by an integration of the coefficient of performance over time. Accordingly, the heat output Qh and the electrical power Qe1 can be integrated over time to indicate the heating energy and the taken up electrical energy. The power take-up of additional devices such as pumps, electronics, etc. can in this respect be taken into the calculation through suitable parameters. A second embodiment of a refrigeration machine in accordance with the invention is shown in FIG. 3 which differs from the embodiment described above in that a fourth temperature sensor 34 connected to the evaluation unit 26 is arranged in the region of the compressor 14 to determine the refrigerant temperature T4 at the compressor outlet. In this embodiment, the refrigerant temperature T4 at the compressor outlet therefore does not need to be estimated using a compressor model, but is rather measured directly. In accordance with the first embodiment, while using the pressure equation of the refrigerant used, the evaluation unit 26 calculates the pressure P2 from the received value for the temperature T2 at the outlet of the condenser 16 and the pressure P1 from the temperature T3 at the outlet of the expansion valve 18. Subsequently, in accordance with equations (1) to (3), the enthalpies H1, H2 and H3 are determined from the measured temperatures T1, T2, T4 and from the calculated pressures P1, P2 and the coefficient of performance is determined from these in accordance with equation (6). A third embodiment of a refrigeration machine in accordance with the invention is shown in FIG. 4 which differs from the first embodiment described with reference to FIG. 1 in that, instead of the third temperature sensor 32, a pressure sensor 36 is arranged in the region of the outlet of the evaporator 12 to measure the pressure P1 of the refrigerant there. The pressure sensor 36 is connected to the evaluation unit 26 to communicate the measured refrigerant pressure P1 to it. In this embodiment, the pressure P1 therefore does not need to be calculated from the refrigerant temperature T3 at the outlet of the expansion valve 18, but is rather measured directly. Only the pressure P2 has to be calculated using the pressure equation of the refrigerant used from the temperature T2 at the outlet of the condenser 16 and the refrigerant temperature T4 at the compressor outlet has to be calculated, as explained with reference to FIG. 1, using a compressor model so that the enthalpies H1, H2 and H3 can be determined in accordance with equations (1) to (3) and, in accordance with equation (6), the coefficient of performance of the refrigeration machine can be determined from them. A fourth embodiment of a refrigeration machine in accordance with the invention is shown in FIG. 5 which differs from the third embodiment shown in FIG. 4 in that a fourth temperature sensor 34 connected to the evaluation unit 26 is arranged in the region of the outlet of the compressor 14 to determine the refrigerant temperature T4 at the compressor outlet. Unlike in the third embodiment, the refrigerant temperature T4 at the compressor outlet therefore does not have to be calculated using a compressor model in this embodiment, but is rather measured directly in a similar manner to the second embodiment shown in FIG. 2. As in the embodiments described above, the pressure P2 is also calculated from the refrigerant temperature T2 at the outlet of the condenser 16 here. Subsequently, the enthalpies H1, H2 and H3 are calculated in accordance with equations (1) to (3) from the measured temperatures T1, T2, T4 and the measured pressure P1 as well as the calculated pressure P2, and the coefficient of performance is determined therefrom in accordance with equation (6). A fifth embodiment of a refrigeration machine in accordance with the invention is shown in FIG. 6 which differs from the third embodiment shown in FIG. 4 in that a second pressure sensor 38 connected to the evaluation unit 26 is arranged in the region of the outlet of the condenser 16 to determine the refrigerant pressure P2 at the condenser outlet. Unlike in the third embodiment, the pressure P2 therefore does not have to be calculated using the pressure equation of the refrigerant used from the temperature T2 at the outlet of the condenser 16 in this embodiment, but it is rather measured directly. Only the refrigerant temperature T4 at the compressor outlet is calculated using a compressor model in this embodiment as described with reference to FIG. 1. Subsequently, in accordance with equations (1) to (3), the enthalpies H1, H2 and H3 are calculated from the measured temperatures T1, T2 and the measured pressures P1, P2 and from the calculated temperature T4 and the coefficient of performance is determined therefrom in accordance with equation (6). A sixth embodiment of a refrigeration machine in accordance with the invention is shown in FIG. 7 which differs from the fifth embodiment shown in FIG. 6 in that a third temperature sensor 34 connected to the evaluation unit 26 is arranged in the region of the outlet of the compressor 14 to determine the refrigerant temperature T4 at the compressor outlet. Unlike in the fifth embodiment, the refrigerant temperature T4 at the compressor outlet therefore does not need to be estimated using a compressor model in this embodiment, but is rather measured directly. Subsequently, in accordance with equations (1) to (3), the enthalpies H1, H2 and H3 are calculated from the measured temperatures T1, T2 and T4 and the measured pressures P1, P2 and the coefficient of performance is determined therefrom in accordance with equation (6). |
|
claims | 1. An injection system for injecting a chemical solution into a nuclear power reactor while the reactor is in a normal operating condition to treat the reactor's internal surfaces, cracks and crevices with one or more chemical species, and thereby mitigate intergranular stress corrosion cracking, the injection system comprising:a vessel external to the reactor that stores the concentrated chemical solution for mitigating intergranular stress corrosion cracking in the reactor's internal surfaces,first and second valves external to the reactor and connectable to a common transit tube that, in turn, is connectable to the reactor's injection tap through which feedwater enters the reactor,a first injection pump external to the reactor and connected between the vessel and the first valve that pumps the concentrated chemical solution from the vessel through the first valve into the common transit tube connected to the reactor's injection tap,an apparatus external to the reactor and supporting the vessel that measures by gravimetric method the rate at which the concentrated chemical solution is pumped from the vessel by the first injection pump,a source of deionized water external to the reactor,a second injection pump external to the reactor and connected between the source of deionized water and the second valve that pumps the deionized water from the source of said water through the second valve into the common transit tube, to dilute the concentrated chemical solution within the common transit tube before it is injected into the reactor,the first and second injection pumps pumping the concentrated chemical solution and the deionized water, respectively, into the common transit tube, causing the diluted chemical solution to be fed through the reactor's injection tap into the power reactor's internals during normal operation of the power reactor, anda logic controller external to the reactor and connected to the external gravimetric measuring apparatus, the first and second injection pumps and the first and second valves, the logic controller receiving from the external gravimetric measuring apparatus chemical solution weight loss measurements and using the measurements to calculate the rate at which the concentrated chemical solution is pumped from the vessel to control the first and second valves and the first and second injection pumps and thereby control the rate at which the diluted chemical solution is injected into the power reactor,the logic controller injecting the diluted chemical solution into the reactor at a rate whereby the reactor water chemical concentration during application is kept at parts per trillion levels and the conductivity increase is at a level that enhances the convection, eddy and diffusion transport of the injected chemical into the cracks and crevices in the reactor. 2. The injection system of claim 1, wherein the chemical species are selected from the group consisting of platinum, alcohol, hydrazine, titanium, zirconium, tungsten, vanadium and tantalum. 3. The injection system of claim 1 further comprising a recirculation and storage system, external to the reactor, that stores and circulates a buffer solution through the first injection pump to flush the first injection pump's wetted moving parts to prevent solid deposition and precipitation on components of the first injection pump,the system comprising a canister for storing the buffer solution, a sealed flush housing surrounding a piston of the first injection pump and lines for delivering the solution to the flush housing and for returning the solution to the canister. 4. The injection system of claim 3, wherein the buffer solution consists of sodium carbonate and sodium bicarbonate powder in a 1:1 ratio, resulting in a flush solution with 0.025 equal molar of each and with a pH˜10. 5. The injection system of claim 1, wherein the first and second injection pumps are positive displacement pumps that regulate injection capacity-to control the rate of injection of the diluted chemical solution into the reactor. 6. The injection system of claim 1, wherein the apparatus for determining the rate at which the concentrated chemical solution is being pumped from the solution vessel includes at least one load cell that measures a reduction in weight of the amount of chemical solution stored in the vessel using a gravimetric method. 7. The injection system of claim 6, wherein the apparatus that determines the rate at which the concentrated chemical solution is pumped from the solution vessel is further comprised of a data acquisition system that calculates the chemical solution weight reduction using a signal from at least one load cell. 8. The injection system of claim 1, wherein the injection rate is a function of increases in the reactor's main steam line radiation, concentration of the chemical solution in the reactor's water and chemical species deposited on the reactor's internal surfaces, and corrosion potential measured by at least one electrochemical corrosion potential (“ECP”) probe. 9. The injection system of claim 1, wherein the chemical solution injected into the reactor is either a noble metal, alcohol, hydrazine, titanium, zirconium, tungsten, tantalum, vanadium or any combination thereof. 10. The injection system of claim 1, wherein the logic controller controls the injection of the diluted chemical solution into the reactor vessel over a time period of about 1 to 3 weeks. 11. The injection system of claim 1, wherein the chemical solution injected into the reactor is a solution of a platinum compound. 12. The injection system of claim 11, wherein the logic controller controls the injection rate of the platinum compound into the reactor vessel through the feedwater system so that the rate is less than 10 g/h. 13. The injection system of claim 11, wherein the logic controller controls the injection rate of the platinum compound into the reactor vessel through the feedwater system so that the rate is less than 4 g/h. 14. The injection system of claim 11, wherein the logic controller controls the injection rate of the platinum compound into the reactor vessel according to the platinum compound's concentration in, and the conductivity of the reactor's water. 15. The injection system of claim 14, wherein the platinum compound is Na2Pt(OH)6 and its concentration in the reactor's water is 500 ppt, and wherein the reactor's water conductivity during injection of the chemical solution into the reactor vessel is maintained at a level of less than 0.3 μS/cm, and not to exceed 1.0 μS/cm. 16. The injection system of claim 14, wherein the platinum compound is Na2Pt(OH)6 and its concentration in the reactor's water is less than 100 ppt and wherein the reactor's water conductivity during injection of the chemical solution into the reactor vessel is maintained at a level of less than 0.3 μS/cm, and not to exceed 1.0 μS/cm. 17. The injection system of claim 14, wherein the platinum compound is re-injected into the reactor at six-month to twelve-month intervals. 18. The injection system of claim 14, wherein the deposition of the platinum compound on the reactor vessel's inner surfaces is at least 0.001 μg/cm2. 19. The injection system of claim 14, wherein the deposition of the platinum compound on the reactor vessel's inner surfaces is greater than 0.01 μg/cm2. 20. An injection system for injecting a diluted chemical solution into a nuclear power reactor while the reactor is operating at full power and temperature to treat the reactor's internal surfaces causing intergranular stress corrosion cracking to be mitigated, the injection system comprising:at least one tank external to the reactor that stores a concentrated chemical solution that will be injected into the reactor for mitigating intergranular stress corrosion cracking in the reactor's internal surfaces,first and second valves external to the reactor and connectable to a transit tube that is connectable to the reactor's tap for the feedwater system,a first injection pump external to the reactor and connected between the at least one tank and the first valve that pumps the concentrated chemical solution from the at least one tank and that meters the concentrated chemical solution's flow through the first valve into the transit tube,at least one load cell external to the reactor and supporting the at least one tank that determines reductions in the weight of the concentrated chemical solution stored in the at least one tank in response to the solution being pumped from the at least one tank by the first injection pump,a source of deionized water external to the reactor,a second injection pump external to the reactor and connected between the source of deionized water and the second valve that pumps the deionized water from the source of said water and that meters the deionized water's flow through the second valve into the transit tube to dilute the concentrated chemical solution in the transit tube before it is injected into the reactor, and causing the residence time of the chemical solution within the transit tube before delivery of the solution to the reactor to be reduced,the first and second pumps pumping the concentrated chemical solution and the deionized water, respectively, to the transit tube, causing the diluted chemical solution to be fed through the reactor's feedwater injection tap into the power reactor's internals during normal operating condition of the power reactor,a logic controller external to the reactor and connected to the at least one load cell, the first and second injection pumps and the first and second valves, the logic controller receiving from the least one load cell weight chemical solution loss measurements and using the measurements to calculate the rate at which the concentrated chemical solution is pumped from the at least one tank to thereby control the first and second valves and the first and second injection pumps and thereby control the rate at which the diluted chemical solution is injected into the power reactor's feedwater injection tap,the logic controller injecting the diluted chemical solution into the reactor at a rate whereby the reactor water concentration during application is kept at parts per trillion levels and the conductivity increase is at a level that enhances the convection, eddy and diffusion transport of the injected chemical into the cracks and crevices in the reactor, anda recirculation and storage system external to the reactor that stores and circulates through the first injection pump a buffer solution to flush the first injection pump's wetted moving parts to prevent solid deposition and precipitation on components of the second injection pump, the system comprising a canister for storing the buffer solution, a sealed flush housing surrounding a piston of the first injection pump and lines for delivering the solution to the flush housing and for returning the solution to the canister. |
|
047612614 | summary | FIELD OF THE INVENTION This invention is concerned with an improved liquid metal nuclear reactor for the production of steam. More particularly, this invention is directed to a liquid metal nuclear reactor comprised of a reactor core in a vessel that is connected to one or a plurality of discrete satellite tanks which house thermal hydraulic equipment such as pumps and heat exchangers. BACKGROUND OF THE INVENTION Nuclear reactors have required and have been provided with cooling means since the early days of nuclear reactor development. Various coolants have been tried. In the past liquid metal nuclear reactors have been made which have been cooled with mercury, liquid sodium or a liquid sodium-potassium mixture. There are two basic types of liquid metal reactors which have been under development for commercial nuclear power applications. These reactors have been described as loop reactors such as the Fast Flux Test Reactor and the Clinch River Breeder Reactor in the United States or the pool type reactor such as the Phenix in France. These reactors have used liquid metal sodium as the primary coolant. In the loop reactor, the core, pumps and intermediate heat exchangers are located in separate vessels and connected with pipes. The sodium is pumped from the core to the heat exchanger and back to the core. There is no pool of liquid metal in this reactor as there is in a pool reactor. The pool reactor comprises a large vessel or pot containing liquid sodium in which the reactor core, intermediate heat exchangers and the primary circulating pumps are located. In this configuration, the cool liquid sodium is pumped to the core from which it flows into a pool of hot sodium and then through the heat exchanger and is discharged into a pool of cool sodium, prior to entry to the pumps. In the prior art, alternate designs of the loop reactors have been described wherein the intermediate heat exchanger and the pump have been housed in an auxilliary vessel which is connected to the main reactor vessel by a duct having a coaxial pipe. The prior art loop reactors have required complex pipe arrangements including snubbers, hangers, heating systems, insulation, inspection capability means and usually a check valve and flow measuring device. The entire primary system is enclosed within an inert atmosphere and a steel lined concrete cell compartment. Guard vessels or some other means such as siphon breakers are provided to insure a safe minimum level of sodium within the reactor vessel in the event of a leak in the piping system. The prior art pool reactors have been difficult to fabricate and have presented engineering difficulties due to the relatively confined area of the main reactor vessel which contains the reactor core, intermediate heat exchangers and pumps as well as reactor core shielding. The size of these vessels requires a complex fabrication and assembly process with the accompanying quality control problems. The relatively crowded interior of the pool reactor provides little design flexibility and may necessitate compromises in the design of the pump, heat exchanger and associated structures. The amount of primary coolant embodied by the pool concept is usually larger than the loop plant thus providing an added margin for safety in the event all decay heat removal systems fail. For Superphenix I, a separate containment structure is provided for the atmosphere above the vessel head because safety authorities have postulated that conditions may occur which can cause the primary coolant to be ejected through the seals of the vessel head. A steel cover may be provided above the vessel to act as a containment barrier but such a cover is difficult to provide because of the large size of the head, the many penetrations required for completing the circuits of the secondary coolant and the need to remove, for maintenance and repair, the primary pump or the primary heat exchanger. The pool type of design does not require separate primary cells, a primary cell inerting and cooling system and primary piping hangers or snubbers. In addition the pool reactor due to the multiplicity of pumps hydraulically connected to a common pool has the advantage of not requiring fast acting check valves in the primary circuit and the operational flexibility of not requiring immediate trip of the pumps during a reactor shutdown. SUMMARY OF THE INVENTION This invention provides a liquid metal reactor wherein the primary pump and heat exchanger are in a separate satellite tank that is connected to the main reactor vessel with upper and lower conduit means that minimize the distance between the reactor vessel and the satellite tank. The size of the separate satellite tank is such that the satellite tank and the reactor provide a sufficiently large volume of liquid metal so that space is provided for a sufficient volume of liquid metal that is capable of dampening temperature transients resulting from abnormal operating conditions. The advantages of this invention are that the reactor vessel may be made much smaller than in the pool arrangement and yet the system will have the advantage of having a very substantial thermal inertia due to the relatively large amount of available liquid metal. The satellite tank which contains the pump and heat exchanger may be fabricated as a module and multiple modules may be used in combination with a single reactor. The design provides a great deal of flexibility for advancements since the modules may include optimized pumps and heat exchangers that are designed without including the constraints that are dictated by the dimensions of a pool reactor. It is therefore a primary object of the invention to provide a novel liquid metal reactor system that eliminates the piping problems inherent in the design of a loop type liquid metal reactor and the design, fabrication and construction difficulties associated with a pool type reactor vessel. It is also an object of this invention to provide a liquid metal reactor that has a novel containment system. It is a further object of this invention to provide a liquid metal reactor that inherently accommodates thermal expansion forces. It is also an object of this invention to provide a liquid metal reactor that operates in a similar fashion as a pool plant, can utilize pool plant type of primary pumps and intermediate heat exchangers and has the advantages associated with small and less complex reactor vessels. It is also an object of this invention to provide diverse, independent means of decay heat removal in a liquid metal reactor in which the decay heat removal systems are not susceptible to liquid metal slug formation due to a core disruptive accident. The liquid metal reactor of the invention comprises a reactor vessel having a core, at least one satellite tank; pump means in said satellite tank; heat exchanger means in said satellite tank; an upper liquid metal conduit extending between said reactor vessel and said satellite tank; a lower liquid metal conduit extending between said reactor vessel and said satellite tank and said satellite tank having space for a volume of sodium that is sufficient to dampen temperature transients resulting from abnormal operating conditions. |
claims | 1. A heating apparatus comprising an alumina bath supplied with one or more external heating elements, wherein the alumina bath defines a cavity into which a reactor may be placed, the reactor comprising an oxidising agent for the oxidation of hydrogen gas into water. 2. The heating apparatus of claim 1, wherein the oxidising agent comprises copper oxide. 3. The apparatus of claim 2, wherein the oxidising agent is diluted with an inert diluent. 4. The heating apparatus of claim 3, wherein the oxidising agent is diluted 50% by weight with the inert diluent. 5. The heating apparatus of claim 2, wherein hydrogen gas is passed into the CuO reactor in which the hydrogen gas is oxidised into water while the CuO is converted into Cu. 6. The heating apparatus of claim 5, wherein a stream of air-containing nitrogen gas (N2/air) is fed into the CuO reactor to oxidise Cu in order to regenerate CuO. 7. The heating apparatus of claim 2, wherein the oxidising agent is selected from R3-11G and R3-17 catalysts. 8. The heating apparatus of claim 1, wherein the reactor is at least partially immersed in the alumina bath. 9. The heating apparatus of claim 8, wherein the reactor is completely immersed in the alumina bath. 10. The heating apparatus of claim 1, wherein the one or more external heating elements is selected from a collar, a jacket, and a heating coil. 11. The heating apparatus of claim 1, wherein the external heating elements are electrically heated. 12. The hearing apparatus of claim 1, wherein the alumina bath is a heat exchanger. 13. The heating apparatus of claim 1, wherein the alumina bath heats up the reactor to an initial reaction temperature with no deleterious effects to the oxidising agent material. 14. The heating apparatus of claim 13, wherein the initial reaction temperature is 200° C. 15. The heating apparatus of claim 1, wherein the alumina bath comprises outer walls taking the form of a substantially cylindrical or cuboidal container. 16. The heating apparatus of claim 15, wherein the outer walls of the alumina bath comprise stainless steel or aluminum. 17. The heating apparatus of claim 1, wherein the reactor comprises less than 12 kg of the oxidising agent. 18. An apparatus for treating hydrogen gas liberated from the acid or alkaline dissolution of a metal, the apparatus comprising a reactor comprising an oxidising agent for the oxidation of hydrogen gas into water, wherein the reactor is heated with one or more heating elements positioned in contact with the reactor, wherein the liberated hydrogen gas is passed through the reactor followed by regeneration of the oxidising agent, and wherein the oxidising agent comprises a metal oxide in bulk form or a metal oxide finely dispersed on the surface of an inert support. 19. The apparatus of claim 18, wherein the one or more heating elements are selected from one or more heated clamps or bands. 20. The apparatus of claim 19, wherein the bands may be in the form of a single helical band which runs along at least part of a length of the reactor. 21. The apparatus of claim 18, wherein the heating elements are electrically heated. 22. The apparatus of claim 18, wherein the one or more heating elements heat up the reactor to an initial reaction temperature with no deleterious effects to the oxidising agent material. 23. The apparatus of claim 22, wherein the initial reaction temperature is 200° C. 24. The apparatus of claim 18, wherein the oxidising agent comprises copper oxide. 25. The apparatus of claim 24, wherein the oxidising agent is selected from R3-11G and R3-17 catalysts. 26. The apparatus of claim 18, wherein the oxidising agent is diluted with an inert diluent. 27. The apparatus of claim 26, wherein the inert diluent comprises stainless steel pellets. 28. The apparatus of claim 26, wherein the oxidising agent is diluted 50% by weight with the inert diluent. 29. The apparatus of claim 18, wherein the reactor further comprises a first conduit. 30. The apparatus of claim 29, wherein the liberated hydrogen gas enters the reactor through the first conduit. 31. The apparatus of claim 29, wherein a mixture of nitrogen and air is introduced to the reactor through the first conduit for the regeneration of the oxidising agent. 32. The apparatus of claim 18, wherein the reactor further comprises a venting conduit. 33. The apparatus of claim 32, wherein gaseous water exits the reactor through the venting conduit. 34. The apparatus of claim 32, wherein waste nitrogen gas exist the reactor through the venting conduit after the regeneration of the oxidising agent. 35. The apparatus of claim 18, wherein the reactor comprises less than 12 kg of the oxidising agent. 36. An apparatus for treating hydrogen gas liberated from the acid or alkaline dissolution of a metal, the apparatus comprising a reactor comprising an oxidising agent diluted with an inert diluent for the oxidation of hydrogen gas into water, wherein the reactor is at least partially immersed in an alumina bath supplied with one or more external heating elements, and wherein the liberated hydrogen gas is passed through the reactor followed by regeneration of the oxidizing agent. 37. The apparatus of claim 36, wherein the one or more heating elements are selected from a collar, a jacket, and a heating coil. 38. The apparatus of claim 36, wherein the heating elements are electrically heated. 39. The apparatus of claim 36, wherein the alumina bath heats up the reactor to an initial reaction temperature with no deleterious effects to the oxidising agent material. 40. The apparatus of claim 30, wherein the initial reaction temperature is 200° C. 41. The apparatus of claim 36, wherein the oxidising agent comprises copper oxide. 42. The apparatus of claim 41, wherein the oxidising agent is selected from R3-11G and R3-17 catalysts. 43. The apparatus of claim 36, wherein the oxidising agent is diluted with an inert diluent. 44. The apparatus of claim 43, wherein the inert diluent comprises stainless steel pellets. 45. The apparatus of claim 43, wherein the oxidising agent is diluted 50% by weight with the inert diluent. 46. The apparatus of claim 36, wherein the reactor further comprises a first conduit. 47. The apparatus of claim 46, wherein the liberated hydrogen gas enters the reactor through the first conduit. 48. The apparatus of claim 46, wherein a mixture of nitrogen and air is introduced to the reactor through the first conduit for the regeneration of the oxidising agent. 49. The apparatus of claim 36, wherein the reactor further comprises a venting conduit. 50. The apparatus of claim 49, wherein gaseous water exits the reactor through the venting conduit. 51. The apparatus of claim 49, wherein waste nitrogen gas exist the reactor through the venting conduit after the regeneration of the oxidising agent. 52. The apparatus of claim 36, wherein the reactor comprises less than 12 kg of the oxidising agent. 53. A process for treating hydrogen gas liberated from the acid or alkaline dissolution of a metal using the apparatus of claim 18, the process comprising passing the liberated hydrogen gas through the reactor and regenerating the oxidising agent. 54. The process of claim 53, wherein the oxidation of hydrogen gas into water is greater than 95%. 55. The process of claim 53, wherein the regeneration of the oxidising agent is greater than 90%. 56. The process of claim 53, wherein the reactor reaches steady state conditions in 3 hours. 57. A process for treating hydrogen gas liberated from the acid or alkaline dissolution of a metal using the apparatus of claim 36, the process comprising passing the liberated hydrogen gas through the reactor and regenerating the oxidising agent. 58. The process of claim 57, wherein the oxidation of hydrogen gas into water is greater than 95%. 59. The process of claim 57, wherein the regeneration of the oxidising agent is greater than 90%. 60. The process of claim 57, wherein the reactor reaches steady state conditions in 3 hours. |
|
description | This application is a continuation of U.S. patent application Ser. No. 15/584,692 filed May 2, 2017, which is a continuation of U.S. patent application Ser. No. 14/912,754 filed Feb. 18, 2016, which is a U.S. national stage application under 35 U.S.C. § 371 of PCT Application No. PCT/US2015/027455, filed Apr. 24, 2015, which claims the benefit of U.S. Provisional Application No. 61/983,606 filed Apr. 24, 2014; the entireties of which are all incorporated herein by reference. The present invention relates generally to nuclear fuel containment, and more particularly to a capsule and related method for storing or transporting individual nuclear fuel pins or rods including damaged rods. Reactor pools store used fuel assemblies after removal and discharge from the reactor. The fuel assemblies and individual fuel rods therein may become damaged and compromised during the reactor operations, resulting in cladding defects, breaking, warping, or other damage. The resulting damaged fuel assemblies and rods are placed into the reactor pools upon removal and discharge from the reactor core. Eventually, the damaged fuel assemblies, rods, and/or fuel debris must be removed from the pools, thereby allowing decommissioning of the plants. The storage and transport regulations in many countries do not allow storage or transport of damaged fuel assemblies without encapsulation in a secondary capsule that provides confinement. Due to the high dose rates of used fuel assemblies post-discharge, encapsulating fuel assemblies is traditionally done underwater. Furthermore, some countries may require removal of individual damaged fuel rods from the fuel assembly and separate storage in such secondary capsules. Processes already exist for removing single rods from a used fuel assembly and encapsulation. Subsequent drying of damaged fuel after removal from the reactor pool using traditional vacuum drying is exceedingly challenging because water can penetrate through cladding defects and become trapped inside the cladding materials. An improved fuel storage system and method for drying, storing, and transporting damaged fuel rods is desired. A nuclear fuel storage system and related method are provided that facilitates drying and storage of individual fuel rods, which may be used for damaged and intact fuel rods and debris. The system includes a capsule that is configured for holding a plurality of fuel rods, and further for drying the internal cavity of the capsule and fuel rods stored therein using known inert forced gas dehydration (FGD) techniques or other methods prior to long term storage. Existing forced gas dehydration systems and methods that may be used with the present invention can be found in commonly owned U.S. Pat. Nos. 7,096,600, 7,210,247, 8,067,659, 8,266,823, and 7,707,741, which are all incorporated herein by reference in their entireties. In one embodiment, a storage capsule for nuclear fuel rods includes: an elongated body defining a vertical centerline axis, the body comprising an open top end, a bottom end, and sidewalls extending between the top and bottom ends; an internal cavity formed within the body; a lid attached to and closing the top end of the body; and an array of axially extending fuel rod storage tubes disposed in the cavity; wherein each storage tube has a transverse cross section configured and dimensioned to hold no more than one fuel rod. In one embodiment, a fuel storage system for storing nuclear fuel rods includes: an elongated capsule defining a vertical centerline axis, the capsule comprising a top end, a bottom end, and sidewalls extending between the top and bottom ends; an internal cavity formed within the capsule; a lid attached to the top end of the capsule, the lid including an exposed top surface and a bottom surface; an upper tubesheet and a lower tubesheet disposed in the cavity; a plurality of vertically oriented fuel rod storage tubes extending between the upper and lower tubesheets; and a central drain tube extending between the upper and lower tubesheets; wherein each storage tube has a transverse cross section configured and dimensioned to hold no more than one fuel rod. A method for storing nuclear fuel rods is provided. The method includes: providing an elongated vertically oriented capsule including an open top end, a bottom end, and an internal cavity, the capsule further including a plurality of vertically oriented fuel rod storage tubes each having a top end spaced below the top end of the capsule, the storage tubes each having a transverse cross section configured and dimensioned to hold no more than a single fuel rod; inserting a first fuel rod into a first storage tube; inserting a second fuel rod into a second storage tube; attaching a lid to the top end of the capsule; and sealing the lid to the capsule to form a gas tight seal. A method for storing and drying nuclear fuel rods includes: providing an elongated vertically oriented capsule including an open top end, a bottom end, and an internal cavity, the capsule further including a plurality of vertically oriented fuel rod storage tubes each having a top end spaced below the top end of the capsule, the storage tubes each having a transverse cross section configured and dimensioned to hold no more than a single fuel rod; inserting a fuel rod into each of the storage tubes; attaching a lid to the top end of the capsule, the lid including a gas supply flow conduit extending between top and bottom surfaces of the lid and a gas return flow conduit extending between the top and bottom surfaces of the lid; sealing the lid to the capsule to form a gas tight seal; pumping an inert drying gas from a source through the gas supply conduit into the cavity of the capsule; flowing the gas through each of the storage tubes; collecting the gas leaving the storage tubes; and flowing the gas through the gas return conduit back to the source. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. All drawings are schematic and not necessarily to scale. The features and benefits of the invention are illustrated and described herein by reference to exemplary embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. Accordingly, the disclosure expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. As used throughout, any ranges disclosed herein are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. In addition, all references cited herein are hereby incorporated by referenced in their entireties. In the event of a conflict in a definition in the present disclosure and that of a cited reference, the present disclosure controls. nuclear fuel assemblies (also referred to as “bundles” in the art) each comprise a plurality of fuel pins or rods mechanically coupled together in an array which is insertable as a unit into a reactor core. The fuel assemblies traditionally have a rectilinear cross-sectional configuration such as square array and contain multiple fuel rods. A reactor core contains multiple such fuel assemblies. The fuel rods are generally cylindrical elongated metal tubular structures formed of materials such as zirconium alloy. The tubes hold a plurality of vertically-stacked cylindrical fuel pellets formed of sintered uranium dioxide. The fuel rod tubes have an external metal cladding formed of corrosion resistant material to prevent degradation of the tube and contamination of the reactor coolant water. The opposite ends of the fuel rod are sealed. FIGS. 1-9B show a damaged nuclear fuel storage system 100 according to the present disclosure. The system includes a vertically elongated fuel rod enclosure capsule 110 configured to hold multiple damaged fuel rods and a closure lid 200 mounted thereto. The lid 200 is configured for coupling and permanent sealing to the capsule 200, as further described herein. Capsule 110 has an elongated and substantially hollow body formed by a plurality of adjoining sidewalls 118 defining an internal cavity 112 that extends from a top end 114 to a bottom end 116 along a vertical centerline axis Cv. The bottom end 116 of the capsule is closed by a wall. The top end 114 of the capsule is open to allow insertion of the damaged rods therein. The sidewalls 118 are sold in structure so that the cavity 112 is only accessible through the open top end 114 before the lid is secured on the capsule. In one embodiment, capsule 110 may have a rectilinear transverse cross-sectional shape such as square which conforms to the shape of a typical fuel assembly. This allows storage of the capsule 110 in the same type of radiation-shielded canister or cask used to store multiple spent fuel assemblies, for example without limitation a multi-purpose canister (MPC) or HI-STAR cask such as those available from Holtec International of Marlton, N.J. Such canisters or casks have an internal basket with an array of rectilinear-shaped openings for holding square-shaped fuel assemblies. It will be appreciated however that other shaped capsules 110 may be used in other embodiments and applications. The body of the capsule 110 may be formed of any suitable preferably corrosion resistant material for longevity and maintenance of structural integrity. In one non-limiting exemplary embodiment, the capsule 110 may be made of stainless steel and have a nominal wall thickness of 6 mm. In certain embodiments, the capsule 110 may further include a laterally enlarged mounting flange 111 disposed at and adjacent to the top end 114, as shown in FIGS. 1-3 and 7-9A. Mounting flange 111 extends laterally outwards from the sidewalls 118 on all sides and vertically downwards from top end 114 along the sidewalls for a short distance. The mounting flange 111 is configured and dimensioned to engage a mounting opening 302 formed in a storage canister 300, thereby supporting the entire weight of a loaded capsule 110 in a vertically cantilevered manner as shown in FIGS. 11-13 and further describe herein. In other embodiments, different methods may be used to support the capsule 110 in the storage canister and mounting flange 111 may be omitted. Referring now particularly to FIGS. 3, 7, 8 and 9A, the capsule 110 further includes an internal basket assembly configured to store and support a plurality of damaged fuel rods. The assembly includes an upper tubesheet 120 and lower tubesheet 122 spaced vertically apart therefrom. The upper and lower tubesheets are horizontally oriented. The lower tubesheet 122 is separated from the interior bottom surface 116a of bottom end 116 of the capsule 110 by a vertical gap to form a bottom flow plenum 124. The upper tubesheet 120 is spaced vertically downwards from the top end 112 of the capsule 110 by a distance D1 sufficient to form a top flow plenum 126 when the closure lid 200 is mounted on the capsule as shown in FIG. 15. Top plenum 126 is therefore formed between the bottom 204 of the lid 200 and top surface 128 of the upper tubesheet 120. Both the bottom and top plenums 124, 126 are part of flow paths used in conjunction with the gas fuel rod drying/dehydration process after the capsule is closed and sealed, as further described herein. A plurality of fuel rod storage tubes 130 are each supported by the upper and lower tubesheets 120, 122 for holding the damaged (i.e. broken and/or leaking) fuel rods. In certain embodiments, intermediate supporting tubesheets or other support elements (not shown) may be used to provide supplementary support and lateral stability to the storage tubes 130 for seismic events. In one embodiment, the storage tubes 130 each have a diameter and internal cavity 131 with a transverse cross section configured and dimensioned to hold no more than a single fuel rod. Accordingly, the tubes 130 extend vertically along and parallel to the vertical centerline axis Cv of the capsule 110 from the upper tubesheet 120 to the lower tubesheet 122. Each of the tubes 130 is accessible through the upper tubesheet 120 (see, e.g. FIG. 9A). In one embodiment, the tubes 130 each have an associated machined lead-in guide in the upper tubesheet 120 to support the insertion of the fuel rods. An annular tapered or chamfered entrance 136 is therefore formed in the upper tubesheet 120 adjacent and proximate to the top open end 132 of each tube 130. The obliquely angled surface (with respect to the vertical centerline axis Cv) of the chamfered entranceways 136 help center and guide loading of the damaged fuel rods into each of the storage tubes 130. The top end 132 of the tubes may therefore be spaced slightly below the top surface 128 of the upper tubesheet 120 as shown. The bottom ends 134 of the fuel rod storage tubes 130 may rest on the bottom interior surface 116a of the capsule 110. Each storage tube 130 includes one or more flow openings 133 of any suitable shape located proximate to the bottom ends 134 of the tubes below the bottom tubesheet 122. The openings 133 allow gas to enter the tubes from the bottom plenum 124 during the forced gas dehydration process and rise upward through the tubes to dry the damaged fuel rods. The fuel rod storage tubes 130 may be mounted in the upper and lower tubesheets 120, 122 by any suitable method. In certain embodiments, the tubes 130 may be rigidly coupled to upper and/or lower tubesheets 120, 122 such as by welding, soldering, explosive tube expansion techniques, etc. In other embodiments, the tubes 130 may be movably coupled to the upper and/or lower tubesheets to allow for thermal expansion when heated by waste heat generated from the decaying fuel rods and heated forced gas dehydration. Accordingly, a number of possible rigid and non-rigid tube mounting scenarios as possible and the invention is not limited by any particular one. The fuel rod storage tubes 130 may be arranged in any suitable pattern so long as the fuel rods may be readily inserted into each tube within the fuel pool. In the non-limiting exemplary embodiment shown, the tubes 130 are circumferentially spaced apart and arranged in a circular array around a central drain tube 150 further described below. Other arrangements and patterns may be used. Referring now to FIGS. 7, 8, 9A, 9B, and 15, the central drain tube 150 of the capsule 110 may be mounted at approximately the geometric center of the upper tubesheet 120 as shown. The center drain tube 150 in one arrangement is supported by and extends vertically parallel to and coaxially with centerline axis Cv of the capsule from the upper tubesheet 120 to the bottom tubesheet 122. The drain tube 150 may be rigidly coupled to the tubesheets 120, 122 using the same techniques described herein for the fuel rod storage tubes. Drain tube 150 is a hollow structure forming a pathway for introducing insert drying gas into the tube assembly to dry the interior of capsule 110 following closure and sealing, as further described herein. The drain tube 150 includes an open top end 151 and an open bottom end 152. The top end functions as a gas inlet and the bottom end functions as a gas outlet, with respect to the dehydration gas flow path further described herein. The bottom end 152 is open into and may extend slightly below the bottom surface of the lower tubesheet 122 to place the drain tube in fluid communication with the bottom plenum 124 of the capsule 110, as shown for example in FIGS. 9A-B. This forms a fluid pathway for introducing drying gas into the bottom of the capsule 110. The outlet end 152 of the drain tube 150 is spaced vertically apart from the interior bottom surface 116a of the capsule 110. Drain tube 150 may include a sealing feature configured to form a substantially gas-tight seal between the closure lid 200 and drain tube for forced gas dehydration process. In one embodiment, the sealing feature may be a spring-biased sealing assembly 140 configured to engage and form a seal with the bottom of the closure lid 200 for gas drying. The sealing assembly 140 includes a short inlet tube 141, an enlarged resilient sealing member 142 disposed on top of the inlet tube, and spring 143. Inlet tube 141 has a length less than the length of the drain tube 150. Spring 143 may be a helical compression spring in one embodiment having a top end engaging the underside 142b of the sealing member 142 which extends laterally (i.e. transverse to vertical centerline axis Cv) and diametrically beyond the inlet tube 141, and a bottom end engaging the top surface 128 of the upper tubesheet 120. The inlet tube 141 is rigidly coupled to the sealing member 142 and has a diameter slightly smaller than the drain tube 150. This allows the lower portion of the inlet tube 141 to be inserted into the upper portion of the drain tube 150 through the top inlet end 151 for upward/downward movement in relation to the drain tube. Spring 143 operates to bias the sealing member 142 and inlet tube 141 assembly into an upward projected inactive position away from the upper tubesheet 120 ready to engage the closure lid 200, as further described herein. Accordingly, the sealing assembly 140 is axially movable along the vertical centerline axis from the upward projected inactive position to a downward active sealing position. In one embodiment, the sealing member 142 may have a circular shape in top plan view and a convexly curved or domed sealing surface 142a in side transverse cross-sectional view (see, e.g. FIGS. 9A and 9B). The curved sealing surface 142a ensures positive sealing engagement with a gas supply outlet extension tube 210 in the capsule closure lid 200 (see FIG. 6) to compensate for irregularities in the extension tube end surface edges and less than exact centering of the extension tube with respect to the sealing member 142, thereby preventing substantial leakage of drying gas when coupled together. The sealing member 142 includes a vertically oriented through-hole 144 to form a fluid pathway through the sealing member to the drain tube 150. In one embodiment, the sealing member 142 may be made of a resiliently deformable elastomeric material suitable for the environment of a radioactive damaged fuel rod storage capsule. The elastomeric seal provides sufficient sealing and a leak-resistant interface between the central drain tube 150 and closure lid 200 to allow the inert drying gas (e.g. helium, nitrogen, etc.) to be pumped down the central drain tube to the bottom of the capsule 110 during the forced gas dehydration process. It will be appreciated that other types of seals and arrangements may be used. Accordingly, in some embodiments metal or composite metal-elastomeric sealing members may be used. The sealing member may also have other configurations or shapes instead of convexly domed, such as a disk shaped with a flat top surface or other shape. In other embodiments, a non-spring activated sealing assembly may be used. Accordingly, the invention is not limited by the material of construction or design of the seal and sealing assembly so long as a relatively gas-tight seal may be formed between the closure lid gas outlet extension tube 210 and the drain tube 150 for forced gas dehydration of the capsule 110. The fuel rod basket assembly, including the foregoing tubesheets, rod storage tubes, central drain tube, and sealing assembly may be made of any suitable preferably corrosion resistant material such as stainless steel. Other appropriate materials may be used. The closure lid 200 will now be further described. Referring to FIGS. 1-6 and 15, lid 200 in one embodiment may have a generally rectilinear cube-shaped body to complement the shape of cavity 112 in capsule 110 in which at least a portion of the lid is received. Accordingly, in one embodiment the lid 200 and capsule 110 may have a square shape in top plan view. Lid 200 further has a substantially solid internal structure except for the gas flow conduits formed therein, as further described below. The lid 200 is formed of a preferably corrosion resistant metal, such as stainless steel. Other materials may be used. Lid 200 includes a top surface 202, bottom surface 204, and lateral sides 206 extending between the top and bottom surfaces. The lateral sides 206 of the lid have a width sized to permit insertion of a majority of the height of the lid into the cavity 112 of the capsule. The bottom of the lid 200 includes a peripheral skirt 212 extending around the perimeter of the bottom surface 204 that engages and rests on the top surface 128 of the upper tubesheet 120 of the capsule 110 when the lid is mounted in the capsule. In one embodiment, the skirt 212 is continuous in structure and extends around the entire perimeter without interruption. The skirt 212 projects downward for a distance from the bottom surface 204 of the lid which is recessed above the bottom edge 212a of the skirt. The forms a downwardly open space 211 having a depth commensurate with the height of the skirt 212. When the bottom edge 212a of skirt 212 rests on top surface 128 of the upper tubesheet 120, the top plenum 126 is formed between the bottom surface 204 of lid 200 and the upper tubesheet inside and within the skirt 212. The bottom edge 212a of the skirt 212 thereby forms a seal between the upper tubesheet 120 and lid 200 for forced gas dehydration of the capsule 110. An enlarged seating flange 208 extends around the entire perimeter of the lid 200 adjacent to top surface 202 and projects laterally beyond the sides 206. The top surface 202 may be recessed below the top edge 208a of the seating flange 208 as shown. A stepped shoulder 213 is formed between seating flange 208 and sides 206 which engages and seats on a mating shoulder 113 formed inside the mounting flange 111 of capsule 110 in cavity 112 (see particularly FIG. 15A). Both mating shoulders 213 and 113 extend around the entire perimeter regions of the lid 200 and capsule 110 respectively and limit the insertion depth of the lid into the capsule. In one embodiment, the top edges 111a and 208a of the mounting flange 111 and seating flange 208 respectively are flush with each other and lie in approximately the same horizontal plane when the closure lid 200 is fully mounted in the capsule 110 (see, e.g. FIGS. 10A, 10B, and 15A). This facilitates formation of an open V-groove weld 205 to hermetically seal the lid to the capsule. The mounting and seating flanges 111, 208 each include opposing beveled faces 115, 208 respectively to form the V-groove. Because of the recessed top surface 202 of the lid 200 and mounting flange 111, access is available to both sides of finished weld which advantageously permits full volumetric inspection of the weld such as by ultrasonic non-destructive testing or other methods. The source and detector of the ultrasonic test (UT) equipment may therefore be placed on opposite sides of the weld for full examination. A multi-pass welding process may be used which prevents any potential through-cracking of a single weld line in the case of an undetected defect. This parallels welding processes used in the United States for Multi-Purpose Canisters (MPCs), but is modified to allow volumetric weld examination (a key consideration for acceptance of weld integrity by some international regulators). Each pass is followed by a Liquid Penetrant Test (LPT) to identify defects in the weld layer as the weld is formed. The finished weld is then volumetrically tested using UT. Unlike a bolted joint sealed with gaskets, a welded joint with volumetric inspection typically does not require leak-monitoring or checks prior to future transport. FIGS. 10A and 10B show the lid 200 and capsule 110 before and after welding, respectively. This does not limit the capsule to having a bolted lid, similar to dual-purpose metal casks used for storage and transport of spent nuclear fuel. In such embodiment, the capsule would have one more seals, for example elastomeric or metallic, that would be compressed during tightening of the lid bolts on the capsule, forming a hermetic seal. According to another aspect of the invention, the closure lid 200 is configured to permit forced gas dehydration of the capsule 110 and plurality of damaged fuel rods contained therein after the lid is seal welded to the capsule. Accordingly, the lid 200 includes a combination of gas ports and internal fluid conduits to form a closed flow loop through capsule 110. Referring now to FIGS. 1-6 and 15, lid 200 includes a gas supply port 220 and gas return port 222 formed in the top surface 202 of the lid, and a gas supply outlet 224 and gas return inlet 226 formed in the bottom surface 204 of the lid. In one configuration, the gas supply outlet 224 and return inlet 226 may be located at diagonally opposite corner regions of the top surface 202 of the lid 200 proximate to the lateral sides 206. The gas supply port 220 is fluidly coupled to the gas supply outlet 224 via an internal flow conduit 228. The gas return port 222 is fluidly coupled to the gas return inlet 226 via another separate internal flow conduit 230 which is fluidly isolated from flow conduit 228. In one embodiment, the flow conduits 228, 230 each follow a torturous multi-directional path through the lid to prevent neutron streaming. In one configuration, flow conduit 228 includes a vertical section 222a connected to gas supply outlet 224, first horizontal section 228b connected thereto, second horizontal section 228c connected thereto, and second vertical section 228d connected thereto and gas supply port 220. The flow conduit sections 228a-d may be arranged in a rectilinear pattern. Flow conduit 228 includes a vertical section 230a connected to gas return port 222, horizontal section 230b connected thereto, and second vertical section 230c connected thereto and gas return inlet 226. The flow conduit sections 230a-c may also be arranged in a rectilinear pattern. Because the lid 200 has a solid internal structure, the flow conduits may be formed by drilling or boring holes through the lateral sides 206 and top and bottom surfaces 202, 204 of the lid to points of intersection between the conduits as best shown in FIGS. 5 and 15. After formation of the flow conduits, the penetrations 232 in the lateral sides 206 of the lid may be closed using threaded and/or seal welded metal caps applied before mounting and welding the lid 200 to the capsule 110. The penetrations 232 in the bottom surface 204 of the lid may remain open. The gas supply and return port penetrations 232 in the top surface 202 of the lid may be threaded and closed using threaded caps 234 to permit removal and installation of remote valve operating assemblies 240 (RVOAs) for forced gas dehydration of the capsule, as shown in FIGS. 14 and 15. It should be noted that the gas supply outlet 224 in lid 200 is fluidly coupled to the gas supply outlet extension tube 210. The extension tube 210 compensates for the height of the lid bottom skirt 212 to allow physical coupling of the tube to the sealing assembly 140 when the skirt rests on the top surface 128 of the upper tubesheet 120. In one embodiment, the extension tube 210 and gas supply outlet 224 are centered on the bottom surface 204 of the lid 200. In certain other embodiments, the extension tube may be omitted and the gas supply outlet 224 penetration may be directly coupled to the sealing assembly 140. A method for storing and drying fuel rods using capsule 110 will now be briefly described. The method may be used for storing intact or damaged fuel rods, either of which may be stored in capsule 110. The process begins with the top of the capsule 110 being open so that the storage tubes 130 are accessible for loading. The loading operation involves inserting the fuel rods into the storage tubes 130. After the capsule is fully loaded, the lid 200 is attached to the top end 114 and sealed to the capsule. In one preferred embodiment, the lid is sealed welded to the capsule as described elsewhere herein to form a gas tight seal After lid 200 is seal welded to the capsule 110, the interior of the capsule and fuel rods therein may be dried using heated forced gas dehydration (FGD) system such as those available from Holtec International of Marlton, N.J. Commonly owned U.S. Pat. Nos. 7,096,600, 7,210,247, 8,067,659, 8,266,823, and 7,707,741, which are all incorporated herein by reference in their entireties, describe such systems and processes as noted above. The remote operated valve assemblies 240 are first installed in the gas supply and gas return ports 220, 222. The valves are then connected to the gas supply and return lines from the FGD system. The next steps, described in further detail herein, include pumping the inert drying gas from the FGD system or source through the gas supply conduit into the cavity 112 of the capsule 110 and into the bottom plenum 124, flowing the gas through each of the storage tubes 130 to dry the fuel rods, collecting the gas leaving the storage tubes in the top plenum 126, and flowing the gas through the gas return conduit back to the FGD source. The process continues for a period of time until analysis of the drying gas shows an acceptable level of moisture removal from the capsule 110. Referring now to FIGS. 5, 9A, 14, and 15, threaded caps 234 may first be removed from the gas supply and return ports 220 and 222 in the lid 200 which is welded to the capsule 110. A remote valve operating assembly 240 is then threadably coupled to each port 220, 222. The gas supply and return lines from the FGD skid which holds the dehydration system equipment are then fluidly coupled to the valve assemblies. The dehydration and drying process is now ready to commence by pumping the inert and heat drying gas from the FGD system through the capsule 110 to dry the fuel rods in the storage tubes 130, as further described herein. Gas supplied from the FGD system first flows through the first valve assembly 240 into the lid 200 through the gas supply port 220. The supply gas then flows through flow conduit 228 to the gas supply outlet 224 and then into gas supply outlet extension tube 210. The supply gas enters the sealing assembly 140 and flows downwards through the central drain tube 150 into the bottom plenum 124 of the capsule 110. The gas in the bottom plenum enters the bottom of the fuel rod storage tubes 120 through openings 133 formed in and proximate to the bottom ends 134 of the tubes. The gas flows and rises upwards through each of the storage tubes 120 to dry the damaged fuel rods stored therein. The gas then enters the top plenum 126 above the upper tubesheet 120 beneath the lid 200. From here, the gas leaves the top plenum and enters the gas return inlet 226 in the lid. The gas flows through flow conduit 230 to the gas return port 222 and into the remote valve operating assembly 240 connected thereto. The return gas then flows through the return line back to the FGD system skid to complete the closed flow loop. Advantageously, the present invention allows drying of multiple damaged fuel rods in the capsule 110 simultaneously instead of on an individual, piece-meal basis. This saves time, money, and operator dosage of radiation. According to another aspect of the invention, the lid 200 includes a threaded lifting port 340 configured for temporary coupling to a lifting assembly 342 that may be used for moving and transporting the capsule 110 around the fuel pool and loading into transport casks or multi-purpose canisters. The lifting assembly 342 in one embodiment may include a lifting rod 344 including a bottom threaded end 346 for rotatable coupling to the threaded lifting port 340 and an opposite top operating end 348 configured for rigging to equipment such as a crane that may be used to lift and maneuver the capsule 110. According to yet another aspect of the invention, a lid-based capsule storage system is provided which is configured for holding and supporting a plurality of capsules 110. The capsule storage system includes a cask loading lid 400 which may be configured to retrofit and replace lids used in existing transport or transfer casks used for loading, storing, and transporting undamaged fuel bundles. Using the temporary lid, the existing casks may used to provide radiation shielding during the capsule 110 drying and closure operations described herein. Referring to FIGS. 11-15, the loading lid 400 can be designed for any dual-purpose metal casks, such as those supplied by Holtec, TNI, or GNS or transfer casks, such as the HI-STRAC used by Holtec International in Marlton, N.J. Loading lid 400 may have multiple mounting cutouts or openings 302 extending completely through the lid each of which are designed to allow insertion of a single capsule 110. The mounting openings 302 are sized smaller than the mounting flange 111 of the capsule 110 so that the flange remains above the top surface 402 of the lid 400. A shoulder 404 is formed beneath each mounting flange 111 between the flange and sidewalls 118 of the capsule which engages the top surface 402 of the lid 400. This allows the capsules to hang from the lid 400 in a vertically cantilevered manner. The top of the capsule 110 therefore sites about 10-15 mm above the lid surface 402 in one representative non-limiting embodiment to enable workers to easily access the top of the capsules to perform the closure operations. The location of the mounting openings 302 can be optimized to allow easy worker access to the capsules during the drying and closure operations. According to another aspect of the invention shown in FIG. 16, a leak testing lid 500 is provided which can be coupled and sealed to the mounting flange 111 of the capsule 110. The lid 500 attached to the mounting flange 111 of capsule 110 and includes a piping connection assembly 502 which allows hook-up to leak testing equipment for performance of an integrated leak test of the entire sealed capsule 110. Although the fuel rod encapsulation capsule is described herein for use with damaged fuel rods, it will be appreciated that the capsule has further applicability for use with intact fuel rods or debris storage as well. Accordingly, the invention is expressly not limited for use with damaged fuel rods alone. While the foregoing description and drawings represent some example systems, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope and range of equivalents of the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. In addition, numerous variations in the methods/processes described herein may be made. One skilled in the art will further appreciate that the invention may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims and equivalents thereof, and not limited to the foregoing description or embodiments. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention. |
|
abstract | The invention relates to a process for reprocessing a spent nuclear fuel and for preparing a mixed uranium-plutonium oxide, which process comprises: a) the separation of the uranium and plutonium from the fission products, the americium and the curium that are present in an aqueous nitric solution resulting from the dissolution of the fuel in nitric acid, this step including at least one operation of coextracting the uranium and plutonium from said solution by a solvent phase; b) the partition of the coextracted uranium and plutonium to a first aqueous phase containing plutonium and uranium, and a second aqueous phase containing uranium but no plutonium; c) the purification of the plutonium and uranium that are present in the first aqueous phase; and d) a step of coconverting the plutonium and uranium to a mixed uranium/plutonium oxide. |
|
summary | ||
summary | ||
claims | 1. A method of automatically correcting aberrations in a charged-particle beam, comprising the steps of:storing image data into a memory, the image data being obtained by scanning a specimen with the charged-particle beam;reading the image data from said memory and blurring regions close to four sides of an image represented by the image data;extracting a profile of a probe formed by said charged-particle beam from the image that has been blurred by the immediately preceding step;extracting line profiles from the extracted profile of the probe;performing extraction of amounts of features, calculations of aberrations, judgments on corrections of the aberrations, and setting of an amount of feedback about the obtained line profiles; andcorrecting conditions under which an aberration corrector is driven, based on the obtained amount of feedback, the aberration corrector acting to correct the aberrations in the charged-particle beam. 2. An apparatus for automatically correcting aberrations in a charged-particle beam, said apparatus comprising:an aberration corrector for correcting the aberrations in the charged-particle beam;a memory for storing image data obtained by scanning a specimen with the charged-particle beam;a four-sided region-blurring device for reading the image data from said memory and blurring regions close to four sides of an image represented by said image data;a probe profile extractor for extracting a probe profile of the charged-particle beam from the image which has been blurred by the immediately preceding step;a line profile extractor for extracting line profiles from the extracted probe profile;correction amount-calculating means for performing extraction of amounts of features, calculations of aberrations, judgment on corrections of the aberrations, and setting of an amount of feedback about the extracted line profiles; andcorrecting means for correcting conditions under which the aberration corrector is driven, based on the amount of feedback obtained by said correction amount-calculating means. 3. A method for automatically correcting aberrations in a charged-particle beam as set forth in claim 1, wherein background noise contained in the probe profile is removed by automatically adjusting an amount by which the regions close to the four sides are blurred by said four-sided region-blurring device. |
|
summary | ||
summary | ||
063242583 | description | FIG. 1A schematically shows a perspective view of a conventional arrangement for making combined emission/transmission recordings. Arranged on a table (not shown for the sake of simplicity) is an object 1, for instance (a part of) a human being. Located in the object 1 is a portion 2, for instance an organ, to which a radioactive substance has been supplied, so that the portion 2 radiates gamma radiation, as indicated by the arrows 3. It is noted that the portion 2 radiates the radiation 3 in all directions. Arranged next to the object 1 is a camera 10, which is sensitive to the gamma radiation 3. Since the nature and construction of the camera 10 are not a subject of the present invention, and a knowledge thereof is not necessary for a skilled person to properly understand the present invention, it will not be further described. Suffice it to note that gamma radiation-sensitive cameras are known per se, and that use can be made of such a camera known per se. Arranged in front of the camera 10 is a collimator 21. A collimator can be regarded, in general, as a transmission means with a direction-selective transmission characteristic, which ensures that a detection segment of the detection surface of the camera 10 can only be irradiated by radiation with a predetermined direction. In one possible embodiment, the collimator 21 is a substantially plate-shaped element of a material with a high degree of absorption, for instance lead, which is provided with a pattern of a multiplicity of bores or passages 31 with a slight diameter, the direction of each passage 31 determining the direction in which the passage can be passed by radiation. In one possible embodiment, the collimator has a thickness of about 2-8 cm, the passages have a diameter of about 2 mm, and the wall portions between adjacent passages have a thickness of about 0.2 mm. Further, next to the object 1, opposite the camera 10, a radiation source 50 is arranged. The radiation source 50 emits radiation, in this example gamma radiation, as indicated by the dotted arrows 5. The radiation 5 has a particular spatial distribution; in FIG. 1, however, all arrows 5 have been indicated as being mutually parallel, for reasons to be discussed hereinafter. Generally, the camera 10 with the collimator 21 on the one hand and the radiation source 50 on the other are mounted on a common subframe, which can rotate relative to the table bearing the object 1, for the purpose of obtaining images of the object 1 from different points of view. For the sake of simplicity, this has not been represented in the drawings. In the conventional arrangement shown in FIG. 1, the radiation source 50 is a so-called planar source, and the collimator 21 is a parallel collimator, that is, all the passages 31 of the collimator 21 are parallel to each other, as illustrated in FIG. 1B. An important disadvantage of the combination of a parallel collimator and a planar radiation source is that each surface element of the planar radiation source 50 radiates radiation in all directions within a particular solid angle, but that only a very limited portion is utilized in making the transmission image, namely, only the portion that is directed in the direction of the passages of the collimator 21. Conversely, this implies that a relatively strong source is needed for making a transmission image with a predetermined brightness. An improvement in this regard is provided by the arrangement shown in FIG. 2. There the parallel collimator 21 has been replaced with a focused collimator 22, and the planar radiation source 50 has been replaced with a line source 60. In the focused collimator 22 the passages 32 are directed towards a single focus line 33, which substantially coincides with the line-shaped radiation source 60. More particularly, each centerline of a passage 32 intersects the line-shaped radiation source 60 at an angle of substantially 90.degree.. Such a collimator is also referred to as fan beam collimator. Alternatively, the passages of the collimator can be directed in two mutually perpendicular directions towards two different focus lines (astigmatic collimator), as is known per se, in which case the line-shaped radiation source 60 is positioned along one of those focus lines. The use of a line source 60 together with a fan beam collimator 22 provides an advantage over the combination of a planar source 50 and a parallel collimator 21 in that the radiation produced is better utilized, and hence the amount of radioactive matter of the radiation source can be less. Further, the emission recording is improved because converging collimators count more photons than do parallel collimators. Furthermore, converging collimators, in comparison with parallel collimators, provide the advantage that a "point" illuminates several pixels, which can be designated as a magnifying effect, so that a greater definition is obtained both in the projection image and in the tomography image. Another improvement in this regard is provided by the arrangement shown in FIG. 3. There the parallel collimator 21 has been replaced with a focused collimator 23, and the planar radiation source 50 has been replaced with a point source 70. In the focused collimator 23 the passages 34 are directed towards a single focus point 35, which coincides substantially with the point-shaped radiation source 70. Such a collimator is also referred to as a cone beam collimator. In the combination of a cone beam collimator 23 and a point source 70, the radiation energy of the source is used even more efficiently than in a fan beam collimator. Thus a converging collimator makes it possible to use a compact (line or point) source, so that the amount of radioactivity that is needed for making a recording can be limited. Further, it can be stated in general that images made with a converging collimator have much better definition and noise properties than do images made with a parallel collimator. A problem playing a role in producing a combined emission/transmission recording is that photons coming from the external source may end up in the emission image, and that photons emitted by the object itself may end up in the transmission image. Such incorrectly interpreted photons signify a reduction of the accuracy or quality of the images obtained (image degradation). In the publication "A scanning Line Source for Simultaneous Emission and Transmission Measurements in SPECT" by P. Tan et al in The Journal of Nuclear Medicine, vol. 34, no. 10, October 1993, p. 1752, an arrangement is described which enables obtaining a separation between the emission-derived radiation and the transmission-derived radiation. That known arrangement is schematically represented in FIG. 4. There the collimator 24 is a parallel collimator, which entails the above-described disadvantages, compared with converging collimators. The radiation source 80 in FIG. 4 is a line-shaped radiation source, which is provided with a shielding 81 to ensure that the radiation 82 that leaves the line source 80 and strikes the camera 10 is located in a single plane 83 which includes the line source 80. The line source 80, whose longitudinal direction is directed parallel to the front face of the collimator 24, is so directed that the plane 83 is perpendicular to the collimator 24. Thus, during the making of a recording the collimator is illuminated according to a line-shaped irradiation pattern 25 (line-shaped "light spot") (projection of the radiation beam on the camera), which is defined by the line of intersection of the plane 83 and the front face of the collimator 24. The radiation 82 that strikes the collimator 24 at right angles is allowed to pass by the passages 36 in the collimator 24 and reaches the camera 10. Thus a line-shaped area of the camera 10 is irradiated with transmission photons. Photons that strike the camera 10 outside this line-shaped area are emission photons. The line source 80 which, as already mentioned hereinabove, is mounted in a subframe (not shown), is moved relative to the subframe, and hence relative to the camera 10, in a direction parallel to the front face of the collimator 24, perpendicular to its longitudinal direction, as indicated by the arrow P. Thus the line-shaped irradiation pattern 25 of the camera 10 is moved in a direction perpendicular to the longitudinal direction of that line-shaped area 25, to scan the surface of the camera 10. As schematically illustrated in FIG. 4B, a control element 84 is present, which receives information regarding the position of the line source 80 and calculates therefrom what detection elements (pixels) of the camera 10 receive transmission radiation; the image signals of those pixels are added to an image memory 85 for the transmission image, while the image signals of the other pixels are added to an image memory 86 for the emission image. Thus, as it were, with respect to the pixels of the camera 10 a moving transmission window 87 is defined, which window 87 defines the pixels that contribute to the transmission image, and hence corresponds to the moving irradiation pattern 25. The above-discussed technique will therefore be referred to hereinafter, for short, as "moving transmission window". Although this known method as such is capable of rendering the emission image less sensitive to transmission photons, there is yet an important inherent disadvantage, associated with the use of a parallel collimator. In fact, it is found in practice that the number of photons that, starting from the line source 80, reaches the pixels of the camera 10 as defined by the transmission window 87 is particularly small. The result is that the transmission image is of low light intensity, unsharp and contains much noise, while being particularly sensitive to photons coming from the object 1 itself (which really belong in the emission image.) The present invention proposes a construction which does not have the disadvantages mentioned, at least does so to a much lesser extent, and combines the advantages mentioned. A first embodiment 100 of the apparatus according to the present invention is illustrated in FIG. 5. What this apparatus 100 has in common with the known devices is that a camera 10, a collimator 120 and a radiation source 150 are present, with the camera 10 and the collimator 120 on the one hand and the radiation source 150 on the other being arranged on opposite sides of an object 1. In this embodiment 100 the collimator 120 is a converging collimator with at least one focal line or convergence line 121. Preferably, the collimator 120 is a fan beam collimator. The radiation source 150 is a substantially line-shaped source, which is arranged adjacent the focal line 121 and preferably coincides with the focal line 121. The line source 150 is provided with radiation-directing means 151 which ensure that the radiation 152 is emitted only in a plane 153 which contains the line source 150; these radiation-directing means 151 can be equal to the means 81 discussed in the publication mentioned. In the figure, the radiation-directing means 151 are illustrated as a shield 155 extending around the line source 150, which shield 155 can be a cylindrical shield whose cylinder axis coincides with the focal line 121 of the fan beam collimator 120. The shield 155 is provided with an elongate passage slit 156 parallel to the line source 150, which elongate passage slit 156 defines the direction in which radiation 152 coming from the line source 150 is allowed to pass through the shield 155. Preferably, the shield 155 comprises a radiation-absorbing material. Thus, for the purpose of the transmission image, the camera 10 is illuminated with an elongate irradiation pattern 125, which is defined by the line of intersection of the plane 153 and the camera 10. According to an important aspect of the present invention, means are provided for moving the elongate irradiation pattern 125, perpendicularly to the longitudinal direction of the irradiation pattern 125, in such a manner that the transmission radiation 152 always comes from the direction of the focal line 121 of the collimator 120. Within the scope of the concept of the invention, this can be effected in different ways. FIG. 5B illustrates a first variant. There the line source 150 is fixedly positioned at the focal line 121 of the collimator 120, and the slit 156 of the shield 155 is movable in a direction perpendicular to the longitudinal direction thereof. In the embodiment shown, the shield 155 is arranged for rotation relative to the focal line 121 of the collimator 120, as indicated by the arrow P2. It is also possible, however, that the shielding comprises a screen plate, arranged between the line source and the collimator, with a passage slit provided therein, which screen plate is linearly moveable. Since the manner in which the rotatable arrangement of the shield 155 is accomplished is of no importance for a good understanding of the present invention, and those skilled in the art will be able without any problems to design such a rotatable arrangement, that arrangement will not be further discussed here. FIG. 5C illustrates a second variant. There the combination of the line source 150 and the shield 155 is in a position removed from the focal line 121, in the example shown between the focal line 121 and the camera 10. The line source 150, the passage slit 156 in the shield 155, and the focal line 121 are disposed in one plane 153. The combination of the line source 150 and the shield 155 is mounted in the subframe (not shown), in such a manner that the combination is rotatable relative to the focal line 121, as indicated by the arrow P3, so that the plane 153 performs a swinging motion relative to the focal line 121. A second embodiment 200 of the apparatus according to the present invention is illustrated in FIG. 6. What this apparatus 200 has in common with the above-discussed apparatus 100 of the first embodiment is that a camera 10, a collimator 220 and a radiation source 250 are present, with the camera 10 and the collimator 220 on the one hand and the radiation source 250 on the other being arranged on opposite sides of an object 1, and that the collimator 220 is a converging collimator with at least one focal line or convergence line 221, preferably a fan beam collimator. In this embodiment 200 the radiation source 250 is a substantially point-shaped source, which is arranged adjacent or in that focal line 221. The point source 250 is provided with radiation-directing means 251 which ensure that the radiation 252 is emitted only in a plane 253 which is perpendicular to the focal line 221. In the figure, the radiation-directing means 251 are illustrated as a shield 255 extending around the point source 250, which shield 255 can be a spherical shield whose center lies on the focal line 221 of the fan beam collimator 220. The shield 255 comprises an elongate passage slit 256 perpendicular to the focal line 221, which elongate slit 256 defines the direction in which radiation 252 coming from the point source 250 is allowed to pass by the shield 255. Preferably, the shield 255 comprises a radiation-absorbing material. Accordingly, as in the first embodiment 100, in the second embodiment the camera 10, for the purpose of the transmission image, is illuminated with an elongate irradiation pattern 225, which is defined by the line of intersection of the plane 253 and the camera 10. According to an important aspect of the present invention, means are provided for displacing the elongate irradiation pattern 225, perpendicularly to the longitudinal direction of the irradiation pattern 225, in such a manner that the transmission radiation always comes from the direction of the focal line 221 of the collimator 220. In the illustrated embodiment, this is accomplished in that the combination of the point source 250 and the shield 255 is mounted in the subframe (not shown), in such a manner that the combination is movable along the focal line 221, as indicated by the arrow P4. Since the manner in which this movable arrangement is accomplished is no importance for a good understanding of the present invention, and those skilled in the art will be able without any problems to design such a movable arrangement, that arrangement will not be further discussed here. An important advantage of this second embodiment 200 over the first embodiment 100 is that a point source can be used, so that the amount of radioactive material that is needed for making a recording can be reduced considerably, while the local intensity can be high, so that a transmission image is only to a slight extent affected by emission radiation. It is noted that in the example discussed the illumination pattern is a line-shaped pattern, but that the pattern being line-shaped, though preferable, is not essential to the present invention. In principle, the illumination pattern may have an arbitrary shape, as long as that shape is known beforehand, in order that the control device "knows", at any rate can compute, what pixels of the detector at any given time contribute to the transmission image. A third embodiment 300 of the apparatus according to the present invention is illustrated in FIG. 7. What this apparatus 300 has in common with the above-described apparatus 200 of the second embodiment is that a camera 10, a collimator 320 and a radiation source 350 are present, with the camera 10 and the collimator 320 on the one hand and the radiation source 350 on the other being arranged on opposite sides of an object 1; that the collimator 320 is a converging collimator; and that the radiation source 350 is a substantially point-shaped source. In this embodiment 300 the collimator 320 is a converging collimator with a single convergence point 321 (cone beam collimator). The radiation source 350 is arranged adjacent that convergence point 321 and is preferably disposed in that convergence point 321. The point source 350 is provided with radiation-directing means 351 which ensure that the radiation 352 is only emitted in a plane 353 which contains the convergence point 321. In the figure, these radiation-directing means 351 are illustrated as a shield 355 extending around the point source 350, which shield 355 can be a spherical shield whose center coincides with the convergence point 321 of the cone beam collimator 320. The shield 355 is provided with an elongate passage slit 356, which defines the direction in which radiation 352 coming from the point source 350 is allowed to pass by the shield 355. Preferably, the shield 355 comprises a radiation-absorbing material. Accordingly, as in the first embodiment 100 and the second embodiment 200, in the third embodiment 300, the camera 10, for the purpose of the transmission image, is illuminated with an elongate irradiation pattern 325, which is defined by the line of intersection of the plane 353 and the camera 10. According to an important aspect of the present invention, means are provided for moving the elongate irradiation pattern 325, perpendicularly to the longitudinal direction of the irradiation pattern 325, in such a manner that the transmission radiation 352 always comes from the direction of the convergence point 321 of the collimator 320. In the illustrated embodiment, this is accomplished in that the combination of the point source 350 and the shield 355 is mounted in the subframe (not shown), in such a manner that the shield 355 is rotatable relative to an axis of rotation 357 which intersects the convergence point 321 of the cone beam collimator 320 and which lies in the plane 353, as indicated by the arrow P5. Since the manner in which this rotatable arrangement is accomplished is of no importance for a good understanding of the present invention, and those skilled in the art will be able without any problems to design such a rotatable arrangement, that arrangement will not be further discussed here. As in the first embodiment 100, it is possible in the third embodiment 300 too, that the shielding comprises a screen plate, arranged between the point source and the collimator, with a passage slit provided therein, which screen plate is linearly movable in a direction perpendicular to the longitudinal direction of the passage slit. Further, with reference to FIG. 5C, it is noted that in this third embodiment 300 too, it is not necessary that the point source 350 coincides with the convergence point 321 of the collimator 320. Accordingly, all three of the embodiments discussed involve, in accordance with the present invention, a planar radiation beam which illuminates the camera 10 according to an elongate illumination pattern 125; 225; 325, and that elongate illumination pattern is moved over the camera 10. In a similar manner to that described in the article by P. Tan et al (see FIG. 4) mentioned earlier, a transmission window moving along with that elongate illumination pattern can be defined in that a control element (not shown for the sake of simplicity) calculates from, respectively, the orientation (FIGS. 5 and 7) and position (FIG. 6) of the radiation source what pixels of the camera contribute to the transmission image. Since this is known per se, this will not be further explained here. FIG. 8 illustrates a side elevation of a fourth embodiment of the apparatus according to the present invention, in which a further improvement is embodied. This fourth embodiment 400 comprises two cameras 410 and 410', which are arranged at an angle relative to each other; in the example shown, the two cameras 410 and 410' are at right angles to each other. Each camera 410, 410' is provided with a fan beam collimator 420, 420', respectively. Each fan beam collimator 420, 420' has a focal line 421, 421', respectively, which is perpendicular to the plane of the paper. Arranged at each focal line 421, 421' is a point source 450, 450', respectively, which is movable substantially along the corresponding focal line 421, 421'. The operation of the combination of the camera 410, the collimator 420 and the movable point source 450 is similar to the operation of the combination of the camera 10, the collimator 220 and the movable point source 250 as described with reference to FIGS. 6A and 6B; likewise, the operation of the combination of the camera 410', the collimator 420' and the movable point source 450' is similar to the operation of the combination of the camera 10, the collimator 220 and the movable point source 250 as described with reference to FIGS. 6A and 6B. According to an important aspect of this fourth embodiment 400 the position of the focal line 421, 421', respectively, is not symmetrical with respect to the corresponding collimator 420 and 420', respectively. As is clearly illustrated in FIG. 8, the focal line 421 of the one collimator 420 has been moved in the direction of the other collimator 420', and the focal line 421' of the other collimator 420' has been moved in the direction of the one collimator 420. In the example shown, each focal line 421 and 421', respectively, lies in a plane perpendicular to an edge of the corresponding collimator 420 and 420', respectively, so that each collimator 420 and 420', respectively, can be designated as a "half" fan beam collimator. An advantage of the fourth embodiment 400 is that it obviates situations where, if a portion of the object 1 is located close to a camera, that portion is not imaged at all ("truncated"). FIGS. 9A and 9B illustrate two mutually perpendicular side elevations of a fifth embodiment according to the present invention, in which a further improvement is embodied. This fifth embodiment 500 comprises two cameras 510 and 510', which are arranged at an angle relative to each other; in the example shown, the two cameras 510 and 510' are at right angles to each other. Each camera 510, 510' is provided with a cone beam collimator 520 and 520', respectively. Each cone beam collimator 520, 520' has a convergence point 521, 521', respectively. Arranged adjacent each convergence point 521, 521', respectively, is a point source 550, 550', respectively, which is rotatable about an axis perpendicular to the plane of the paper of FIG. 9A. The operation of the combination of the camera 510, the collimator 520 and rotatable point source 550 is similar to the operation of the combination of the camera 10, the collimator 320 and rotatable point source 350 as described with reference to FIGS. 7A and 7B; likewise, the operation of the combination of the camera 510', the collimator 520' and rotatable point source 550' is similar to the operation of the combination of the camera 10, the collimator 320 and rotatable point source 350 as described with reference to FIGS. 7A and 7B. According to an important aspect of this fifth embodiment 500 the position of the convergence point 521, 521' is not symmetrical with respect to the corresponding collimator 520, 520'. As is clearly illustrated in FIGS. 9A and 9B, the convergence point 521 of the one collimator 520 has been moved in the direction of the other collimator 520', and the convergence point 521' of the other collimator 520' has been moved in the direction of the one collimator 520. In the example shown, each convergence point 521, 521' lies on a line perpendicular to a corner point of the corresponding collimator 520, 520', so that each collimator 520, 520' can be designated as a "quarter" cone beam collimator. The use of cone beam collimators has utility in particular in imaging smaller organs or parts of the body, such as for instance brains. For obtaining a sharper image it is desirable that the distance between the object and the camera be made as small as possible. With two cameras at right angles to each other, a half cone beam is not adequate to optimally image the head of a patient, because the distance between the head and one of the cameras must then increase and therefore entails unsharpness. The fifth embodiment 500 solves this problem. The object can be placed closer to the cameras, while avoiding that a portion of the object 1 that is located close to a camera is not imaged at all ("truncated"). In FIGS. 9A and 9B a possible axis of rotation for the cameras 510, 510', respectively, is designated by the reference numeral 599. Asymmetries other than an exact quarter-cone can also be used, for instance at other angles between the cameras. FIG. 10 illustrates a further improvement, proposed by the present invention, for increasing the definition of the image in transmission tomography. This definition is to an important extent determined by the size of the source used. In practice, it is difficult to reduce the size of the source while yet retaining a good radiation strength of the source: this would mean inter alia that the source would have to be very concentrated. According to the present invention, effectively a very small source size is achieved (virtual point source 650) by arranging a source 651 with spatial dimensions behind a strongly absorbing screen plate 652, in which a preferably conical hole 653 is formed, the size of the hole 653 corresponding to the desired size of the source. This further provides the advantage that it is possible to regulate the strength of the radiation in a direction-dependent manner; this results in a certain intensity profile that can be determined through the choice of the source shape. In FIG. 10 it is further illustrated that a moving radiation beam can be provided by moving a screen plate 655 with a slit 656 of a desired shape in front of the virtual point source 650. A camera 610 receives radiation solely from the direction defined by the hole 653 and the slit 656, which direction is indicated in FIG. 10 by a dotted line 660. The amount of radiation in this direction corresponds substantially to the length L of the three-dimensional source 651 proper, measured along this dotted line 660. It will be clear that it is possible so to choose the three-dimensional shape of the three-dimensional source 651, through the addition/removal of radioactive material at the back of the three-dimensional source 651, that the desired radiation profile is achieved. The beam width and emission strength can be regulated inter alia by the magnitude of the hole 653 in the absorbing plate 652, the shape of the source 651, and the mutual distances between the source, the absorbing plate 652 and the moving screen plate 655. The obliqueness of the conical hole 653 at the front of the highly absorbent plate 652 partly determines what portion of the camera 610 is still irradiated. It will be clear to those skilled in the art that the scope of protection of the present invention as defined by the claims is not limited to the embodiments discussed and represented in the drawings, but that it is possible to change or modify the represented embodiments of the tomography device according to the invention within the scope of the concept of the invention. Thus, it is possible, for instance, to determine in a different way what pixels furnish transmission image signals. In general, the energy of the transmission photons is different from the energy of the emission photons (for instance, 100 keV and 140 keV, respectively); it is therefore possible for the detected photons to be selected according to energy. Further, it is noted that in nuclear medicine normally the combination of an emission recording with a transmission recording is desired. However, the present invention is also applicable in situations where only a transmission recording is desired. The present invention is also applicable in PET systems (Positron Emission Tomography). In these systems, a radioactive substance is injected into the patient, which substance radiates positrons. The emitted positrons annihilate with electrons present in the body of the patient. The distance traveled by a positron in the body before it annihilates is generally only a few millimeters. Upon annihilation two gamma quants are released, each of 511 keV, which quants move in exactly opposite directions. As illustrated in FIG. 11, these two quants 703.sub.1 and 703.sub.2 are detected with two oppositely arranged position-sensitive detectors 710.sub.1, 710.sub.2. The signals of these detectors are assessed for coincidence in a processing circuit: when from the two detectors two signals arise simultaneously, it is assumed that these signals "belong together", that is, are caused by quants released upon the same annihilation. The two positions where those two quants strike the two detectors define a line on which the annihilation must have taken place. Because this line is fixed through the coincidence of the two detections, no collimator is needed in a PET system. A consequence of this is that PET is much more sensitive than SPECT. Further, PET is sometimes operated with a SPECT system with two detectors without collimators (see FIGS. 11A and 11B). It is also possible to use several detectors 710.sub.1, 710.sub.2, 710.sub.3 (see FIG. 11C). PET too can be combined with transmission sources 750 as described in the foregoing with regard to SPECT. In that case, too, it is desired to perform a correction for attenuation. As has been described in the foregoing, for this purpose use can be made of a linearly movable point source on the convergence line of a fan beam collimator, or a rotary point source adjacent the convergence point of a cone beam collimator. In the case of a PET system, however, it is important that at the location of the moving irradiation pattern a collimator is arranged before the camera, while no collimator is arranged before the positions of the camera that are located next to the irradiation pattern. What is thus accomplished is that at the location of the transmission window unnecessary emission radiation is blocked. According to a particular aspect of the present invention, for that purpose use can be made of a line-shaped collimator element 720, whose construction and operation are substantially the same as those of the above-discussed collimator arranged stationarily in front of the entire detection surface of the camera, with the understanding that the collimator element 720 has a strip-shaped appearance, that is, a length dimension substantially corresponding to the dimension of the detection surface of the camera and a width substantially corresponding to the width of the irradiation pattern. The collimator element 720 is movably arranged, and is moved perpendicularly to its longitudinal direction in conjunction with the displacement of the irradiation pattern. In the case wherein the moving irradiation pattern is generated by a linearly moving point source 750.sub.A (see FIG. 11B; FIGS. 6A-B), it suffices to move the collimator element 720 linearly. In the case where the moving irradiation pattern is generated by a rotary line source 750.sub.B (see FIG. 11A; FIGS. 5A-C), the longitudinal direction of the collimator element is parallel to its convergence line, and the collimator element 720 should further be rotated in such a manner that its convergence line remains substantially stationary. Summarizing, the present invention provides a device for obtaining tomography images, which on the one hand provides a very good separation between transmission images and emission images and on the other hand provides an improved image strength (counts per pixel) in the transmission image, so that the images provided have an improved signal-to-noise ratio over the prior art. |
047117575 | summary | BACKGROUND OF THE INVENTION The present invention relates to position indicating devices, particularly for indicating the position of a linear element which is inaccessible to direct visual observation. More specifically, the invention is directed to devices for indicating the position of a component, such as a control rod, in a nuclear reactor. The operation of a nuclear reactor, and particularly control of the core activity and monitoring of the core state, is effected by various elements which are mounted on drive rods which are movable to permit the elements to penetrate the core to a selected depth. While it is essetial to continuously and accurately monitor the vertical position of each such drive rod, this cannot be accomplished directly because all of the components associated with the core are enclosed in a pressure vessel preventing direct visual observation. Heretofore, various position indicating devices for this purpose have been proposed and utilized. One class of known devices employs an array of annular sensing coils spaced apart along a vertical path and arranged to produce output signals in response to the movement of a body, such as the upper end of a drive rod, along the path, the rod being displaceable within the cylindrical region enclosed by the coils. This body is of a material selected to effect a variation in the impedance, which includes inductive and resistive components, of a coil as the body passes into the cylindrical region of the coil. The coils are arranged in series-connected pairs and the coils of each pair can be spaced apart along the vertical path in such a manner that coils of other coil pairs are interposed between the coils of a given pair. An a.c. operating voltage is applied across each coil pair and the point of connection between the coils of the pair constitutes an output at which a position indicating signal can appear. All the coils are electrically identical so that if only one coil of a pair is penetrated by the impedance-influencing body, a detectable voltage change will appear at the associated output. If both coils are penetrated or both coils are not penetrated, the coil pair will be electrically balanced, and no voltage will appear at the output. Each coil pair output is connected to a signal producing element, such as a differential amplifier having a reference input connected to a reference potential, so that the signal producing element will produce an output signal when the detectable voltage appears at the output of its associated coil pair. With such an arrangement, the number of signal producing elements must be equal to the number of coil pairs, which is equal to one-half the number of incremental positions that can be sensed. Thus, if twenty different positions must be sensed, ten signal producing elements are required. The output signals from the position-sensing elements are generally processed as respective bits of a binary code so that, in the exemplary case mentioned above, a 10-bit Gray code is established. Since it is generally desired to process such position information digitally, it would be advantageous to convert the group of signals produced by such an arrangement to an 8-bit code and a translation from a 10-bit pattern to an 8-bit code is not always a simple task. Moreover, the number of positions to be sensed varies from one system to another so that a separate conversion scheme is required for each such system. Even within a given system, the number of positions to be sensed can vary from one movable structure to another. In the case of one proposed nuclear power system, it will be necessary to accurately detect up to 23 incremental positions. SUMMARY OF THE INVENTION It is an object of the present invention to directly convert positional information into an 8-bit Gray code representing a number of incremental positions which can have a wide range of values. Another object of the present invention is to permit standardization of the circuitry for producing the 8-bit code regardless of the number of incremental positions to be monitored. Another object of the invention is to monitor a large number of incremental positions with a circuit utilizing only 8 output components, each producing an output associated with a respective bit position. Yet another object of the invention is to reduce the number of circuit components required to produce the desired 8-bit output. The above and other objects are achieved, according to the invention, by a novel position indicating device for producing an indication of the position of a displaceable structure, the device comprising: a position representing member mounted for movement in response to displacement of the structure and movable along a defined path from a starting point such that the distance to which the member extends from the starting point corresponds to the position of the structure; a plurality of sensing elements extending along the defined path such that each element is associated with a respective location along the defined path, each element being operative to respond to the presence of the member when the member extends from the starting point to the respective location associated with that element; means operatively coupling the elements into respective pairs of elements and having, for each pair of elements, an output producing a signal only when a single element of its respective pair is responding to the presence of the member; a plurality of signal producing members each operative for producing a signal representing a predetermined logic state in response to a predetermined input signal; and circuit means operatively connecting the outputs to the signal producing members for causing a signal at each output to produce a predetermined input signal at a corresponding signal producing member and for causing a predetermined input signal to be produced at at least one signal producing member by a signal at at least two outputs. |
053274717 | claims | 1. A nuclear reactor fuel assembly, comprising: a) at least one coolant tube with an upper end having an opening formed therein and an upper end piece and a lower end having an opening formed therein and a lower end piece; b) a bottom plate being supported by said coolant tube and joined to said lower end piece in a dimensionally rigid manner, said bottom plate having inlet openings formed therein for liquid coolant; c) a cover plate retaining said upper end piece and having outlet openings formed therein for a liquid/steam mixture of coolant; d) gridlike spacers defining meshes therein, means for retaining said spacers on said coolant tube between said plates; and e) a plurality of fuel rods each being guided through a respective one of said meshes, each of said fuel rods being filled with nuclear fuel and each of said fuel rods being joined to at most one of said plates. a) a bundle of mutually parallel fuel rods containing nuclear fuel; b) a fuel assembly head being disposed above said bundle and having a top with a bundle; c) a bottom plate being disposed under said bundle and being permeable to liquid coolant; and d) a coolant tube being disposed in said bundle, being parallel to said fuel rods and having upper and lower open ends; e) said coolant tube having a lower end piece on said lower end being supportingly retained on said bottom plate for retaining said coolant tube on said bottom plate; and f) supporting means for attaching said coolant tube to said fuel assembly head, said coolant tube having an upper end piece on said upper end being supportingly retained on said fuel assembly head and protruding from below into a recess formed substantially in a center portion of said fuel assembly head, said supporting means consisting essentially of said upper end piece and said recess. a) a laterally outer fuel assembly case having an interior and open upper and lower ends; b) a cover plate covering said upper end of said case and having coolant outlets formed therein; c) a bottom plate covering said lower end of said case and having coolant inlets formed therein; d) a coolant tube extending in axial direction in the interior of said case and having upper and lower ends, each of said upper and lower ends having at least one opening formed therein for the passage of water, said coolant tube having a lower end piece joined to said bottom plate with a rigid connection transmitting substantially all forces exerted upon said bottom plate to said lower end piece and to said coolant tube, and said coolant tube having an upper end piece, and a releasable connection supporting said upper end piece at said cover plate; e) a plurality of spacers being substantially perpendicular to and retained on said coolant tube at predetermined axial positions, said spacers containing support ribs; f) a plurality of fuel rods being parallel to said case, being respectively supported on said support ribs and having lower ends, some of said fuel rods extending substantially as far as said cover plate; and g) lower closure caps standing unscrewed on said bottom plate and being disposed on said lower ends of at least all of said fuel rods extending substantially as far as said cover plate. 2. The fueld assembly according to claim 1, including a stop body mounted on said upper end piece, said cover plate being detachably retained on said stop body, and a lower closure cap disposed on said bottom plate, said fuel rods including longer and shorter fuel rods, and only said shorter fuel rods being retained by said lower closure cap on said bottom plate. 3. A nuclear reactor fuel assembly, comprising: 4. The fuel assembly according to claim 3, wherein said bottom plate and said fuel assembly head are supports for said coolant tube, one of said end pieces is longitudinally displaceably supported on one of said supports, and including a stop body on said fuel assembly head defining a maximal spacing between said supports, and at least one spring disposed between said supports for pressing one of said supports against said stop body. 5. The fuel assembly according to claim 4, including a stop shoulder formed onto said one displaceably supported end piece, said shoulder defining a minimal spacing between said fuel assembly head and said bottom plate. 6. The fuel assembly according to claim 4, wherein said spring is disposed on one of said fuel rods. 7. The fuel assembly according to claim 4, wherein said spring is disposed on one of the said pieces. 8. The fuel assembly according to claim 4, wherein said spring is disposed on said upper end piece. 9. The fuel assembly according to claim 3, wherein said fuel assembly head has a part being formed onto said handle, being secured against rotation, and being screwed on from above, and said upper end piece is passed through said part. 10. The fuel assembly according to claim 3, wherein said upper end piece carries a socket pin, said fuel assembly head carries a cover plate having coolant outlet openings formed therein, and said socket pin extends through said cover plate and carries a detachably mounted stop body for said cover plate. 11. The nuclear reactor fuel assembly according to claim 10, wherein said cover plate is mounted on said upper end piece, and including a supporting mechanical connection securing said bottom plate to said lower end piece, a spring under pressure pressing said cover plate against said stop body, and said fuel rods having upper ends with upper closure caps. 12. The nuclear reactor fuel assembly according to claim 11, wherein said upper closure caps are loosely guided on said cover plate in an appropriate receiving position. 13. The nuclear reactor fuel assembly according to claim 11, wherein said upper closure caps do not touch said cover plate in an appropriate receiving position. 14. A fuel assembly of a boiling water reactor, comprising: 15. The fuel assembly according to claim 14, wherein at least two of said spacers are penetrated by all of said fuel rods, said fuel rods include first and second groups of fuel rods, each of said fuel rods at least in said first group extend from said bottom plate as far as said cover plate and carry one of said lower closure caps on said lower end, said bottom plate has an upper surface facing toward said cover plate, said lower closure caps stand on said upper surface of said bottom plate, said fuel rods of said first group have upper ends, and including upper closure caps on said upper ends being loosely disposed on said cover plate at given receiving positions. 16. The fuel assembly according to claim 15, wherein each of said fuel rods in said second group is shorter than a fuel rod in said first group and carries one of said lower closure caps on said lower end being retained on said bottom plate, said fuel rods of said second group have upper ends, and including upper closure caps on said upper ends being disposed in the vicinity of one of said spacers and being spaced apart from said cover plate. 17. The fuel assembly according to claim 16, including a plug connection joining said lower closure caps of said fuel rods of said second group to said bottom plate. 18. The fuel assembly according to claim 16, wherein said coolant outlets in said cover plate are outlet openings disposed between said given receiving positions of said fuel rods of said first group and enlarged outlet openings disposed in a projection of said shorter fuel rods. 19. The fuel assembly according to claim 16, wherein said fuel rods of said second group are each disposed along diagonals of the cross section of said case. 20. The fuel assembly according to claim 16, wherein said case has walls, some of said fuel rods are adjacent said walls, and each of said fuel rods adjacent said walls belongs to said first group. 21. The fuel assembly according to claim 20, wherein said support ribs of said spacers define first through eleventh rows and first through eleventh columns of meshes between said support ribs, counting from said wall inward, and said fuel rods of said second group are each disposed in one of said third row and said third column. 22. The fuel assembly according to claim 14, wherein said upper end piece of said coolant tube passes through said cover plate from below and is screwed to said cover plate from above. 23. The fuel assembly according to claim 14, including a handle, said upper end piece of said coolant tube being passed through said cover plate from below and screwed to said cover plate and to said handle from above. 24. The fuel assembly according to claim 14, including a handle, said upper end piece of said coolant tube being passed through said cover plate from below and screwed to said handle from above. 25. The fuel assembly according to claim 23, wherein said handle is undetachably secured to said cover plate. 26. The fuel assembly according to claim 24, wherein said handle is undetachably secured to said cover plate. 27. The fuel assembly according to claim 14, including a part formed onto said bottom plate into which said lower end piece of said coolant tube is introduced, and a securing bolt securing said lower end piece to said part, to protect against relative rotation of said bottom plate and said coolant tube. 28. The fuel assembly according to claim 14, wherein said cover plate is resiliently supported against said bottom plate. 29. The fuel assembly according to claim 14, wherein said coolant inlets in said bottom plate are flow openings having cross sections creating a uniform flow through the fuel assembly with a pressure loss being negligible as compared to a pressure loss at said coolant outlets in said cover plate. 30. The fuel assembly according to claim 1, wherein said fuel rods have upper and lower ends, and including threadless closure caps disposed on said upper and lower ends of all of said fuel rods. 31. The fuel assembly according to claim 3, wherein said fuel rods have upper and lower ends, and including threadless closure caps disposed on said upper and lower ends of all of said fuel rods. 32. The fuel assembly according to claim 14, wherein said lower closure caps are disposed on said lower ends of all of said fuel rods, said fuel rods have upper ends, and including upper closure caps disposed on all of said upper ends of said fuel rods, all of said closure caps disposed on said upper and lower ends of all of said fuel rods being threadless. |
046630937 | claims | 1. An internal gelation process for the preparation of nuclear fuels, comprising: (a) moving a volume of hot perchloroethylene through a trough; (b) directing droplets of a nuclear fuel solution into the moving volume of hot perchloroethylene, the droplets of nuclear fuel solution gelling to form gelled spheres while the droplets are floating on the surface of the moving volume of perchlorethylene; (c) dropping the resultant gelled spheres into a vertical column of perchloroethylene, wherein the gelled spheres of nuclear fuel age as a floating bed in the vertical column; and (d) separating the aged gelled spheres of nuclear fuel from the perchlorethylene. 2. Process as claimed in claim 1 wherein the hot perchloroethylene solution of step (a) has a temperature between about 7.degree. and about 90.degree. C. 3. Process as claimed in claim 1 wherein the hot perchloroethylene solution has a temperature of about 85.degree. C. 4. Process as claimed in claim 1 wherein the nuclear fuel solution used in step (b) is a (UPu)O.sub.2 (U-Pu) solution. 5. Process as claimed in claim 1 wherein the vertical column of step (c) is an ager. 6. Process as claimed in claim 1 wherein the aged gel spheres from step (d) are transported on a moving screen, the entrained perchloroethylene draining off of the aged gel spheres, the drained gel spheres are washed in an aqueous wash column, the wash water is drained from the gel spheres and the aged gel spheres are dried. 7. Process as claimed in claim 1 wherein the wash water contains ammonium hydroxide. 8. The aged gel spheres of nuclear fuel prepared by process of claim 1. 9. The aged gel spheres of (UPu)O.sub.2 prepared by the process of claim 4. |
062529390 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to an X-ray examination apparatus which includes an X-ray source, PA1 an X-ray detector, PA1 an X-ray filter which includes a plurality of filter elements and is arranged between the X-ray source and the X-ray detector, PA1 an electric voltage source and a control system for selectively applying electric voltages to individual filter elements, PA1 which control system includes voltage lines, and PA1 the filter elements are formed by spaces between plates which are locally attached to one another, and PA1 the voltage lines are provided at least partly on one or more of the plates. the filter elements being connected to the electric voltage source by way of voltage lines, and PA2 the X-ray absorptivity of the individual filter elements being adjustable by adjustment of a quantity of X-ray absorbing liquid in individual filter elements on the basis of the electric voltages applied to the individual filter elements. 2. Description of Related Art An X-ray examination apparatus of this kind is known from international patent application WO 97/03449. The X-ray examination apparatus is used to form an X-ray image of an object to be examined, for example a patient to be radiologically examined. The X-ray source irradiates the object by means of an X-ray beam and an X-ray image is formed on the X-ray detector due to local differences in the X-ray absorption within the object. The X-ray filter ensures that the range of brightness values of the X-ray image remains limited. The X-ray filter is adjusted in such a manner that on the one hand parts of the X-ray beam which are only insignificantly attenuated by the object are slightly attenuated by the X-ray filter and that, on the other hand, parts of the X-ray beam which are significantly attenuated by the object are transmitted by the X-ray filter practically without attenuation. Because the brightness values of the X-ray image lie within a limited range, the X-ray image can be very readily processed further in order to achieve a good rendition of even small details of low contrast. The X-ray filter of the known X-ray examination apparatus is provided with a bundle consisting of a very large number of capillary tubes, each of which communicates with the X-ray absorbing liquid by way of one end. The quantity of X-ray absorbing liquid present in the individual capillary tubes is influenced by the electric voltage applied to the wall of the capillary tubes. It has been found that the adhesion between the wall of the capillary tubes and the X-ray absorbing liquid is dependent on the electric potential difference between the wall of such a capillary tube and the X-ray absorbing liquid. The voltage lines extend between the capillary tubes in the X-ray filter of the known X-ray examination apparatus. The capillary tubes are connected to one of the voltage lines by way of a respective field effect transistor. The field effect transistors are arranged between the capillary tubes. It is a drawback of the X-ray filter of the known X-ray examination apparatus that a rather large amount of space is required for the voltage lines to extend between the capillary tubes. Consequently, the active surface area of the known X-ray filter is significantly smaller than the overall surface area of the X-ray filter. Moreover, the field effect transistors are arranged in a region which is exposed to X-rays during operation of the X-ray examination apparatus. The X-rays may affect the field effect transistors so that the service life of the known X-ray filter is limited. Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed. SUMMARY OF THE INVENTION It is an object of the invention to provide an X-ray examination apparatus which includes an X-ray filter which is adjustable on the basis of respective quantities of X-ray absorbing liquid in individual filter elements and has an active surface area which is larger than that of the known X-ray filter. It is a further object of the invention to provide an X-ray filter whose service life is significantly longer than that of the known X-ray filter. This object is achieved by means of an X-ray examination apparatus according to the invention which is characterized in that: The filter elements have the shape of capillary tubes which are formed by spaces between the plates. Preferably, the plates are provided with separating members. The separating members separate neighboring filter elements from one another between neighboring plates. The separating members are formed, for example by protrusions which are formed transversely of the plates. Alternatively, use can be made of corrugated plates; the corrugations of the plates then constitute the separating members. The individual filter elements are provided with respective electrodes which are arranged on the parallel plates, for example on the side of the parallel plates which faces the inner side of the relevant filter elements. If desired, the electrodes can be covered with an electrically insulating dielectric layer and/or with a hydrophobic coating layer. The electrodes receive the electric voltage whereby the quantity of X-ray absorbing liquid present within the respective filter elements is influenced. The electric voltages are applied to the electrodes via the voltage lines. Because the voltage lines extend across the plates, between the filter elements hardly any additional space is required for the voltage lines. Consequently, the voltage lines do not take up any active space of the X-ray filter so that the active surface area of the X-ray filter is larger than that in the known X-ray examination apparatus. The active surface area of the X-ray filter is the surface area of the X-ray filter via which the absorption of the X-rays can be controlled. The voltage lines can be readily continued across the parallel plates so as to reach a region which is not traversed by the X-ray beam during operation of the X-ray examination apparatus. Switching elements can then be positioned in such a region which is not traversed by the X-ray beam and the electrodes can be connected to the switching elements by way of the voltage lines extending across the parallel plates. In that case the switching elements are not exposed to X-rays during operation of the X-ray examination apparatus. Degrading of the switching elements by the X-rays is thus avoided and hence the service life of the X-ray filter is prolonged. The switching elements form part of the control unit and the voltage lines are connected to the electric voltage source via the switching elements. The respective electrodes of the individual filter elements are thus connected to the electric voltage source via the respective voltage lines and the switching elements. The electric voltage is applied to the associated filter element, specifically to the electrode of said filter element, by closing a switching element as desired. Preferably, the switching elements are formed by thin-film transistors which can be switched by applying a gate voltage to a gate contact of such a thin-film transistor. Furthermore, the individual thin-film transistors are connected to the electrodes of the filter elements, for example by way of their respective drain contact, and to the voltage lines by way of their respective source contact. The switching elements may also be constructed as integrated circuits in semiconductor technology, for example silicon. The corrugated plates are preferably formed by flexible wall foils. In that case the filter elements are preferably formed by locally attaching the wall foils in a stack of wall foils to one another and by subsequently expanding the stack of wall foils essentially transversely of the surface of the wall foils, for example by stretching. Between neighboring, essentially parallel wall foils, spaces are thus formed at the areas where the neighboring wall foils are not attached to one another, which spaces act as filter elements. When the neighboring wall foils are locally attached to one another along narrow, continuous bonding seams, the spaces are formed as capillary tubes. The dimensions of the tubes, notably the cross-section thereof, are determined by the spacing and the width of the bonding seams and by the degree of expansion of the stack of wall foils. Like the electrodes, the voltage lines are preferably provided on the wall foils already before the wall foils are stacked and the stack is expanded. This makes it possible to provide the voltage lines and the electrodes on the wall foils as metallization patterns while the wall foils are still loose from one another and still have a flat shape. In such circumstances the metallization patterns can be provided in a simple and uncomplicated manner. For example, the metallization patterns can be simply formed by means of a laser ablation process. It is notably not necessary to guide the voltage lines between the filter elements after the filter elements have already been formed. Instead, the voltage lines are provided already before the formation of the filter elements and, when the filter elements are formed by the stretching of the stack of wall foils, the voltage lines on the wall foils are distorted together with the wall foils so that the voltage lines will automatically extend between the spaces between the wall foils constituting the filter elements. Preferably, in parts of the stack of foils a number of intermediate foils is inserted between the wall foils. The intermediate foils are preferably provided between the filter elements and the region where the voltage lines emerge from the stack of foils. The intermediate foils preferably extend into the region where the voltage lines emerge for the foil stack. The intermediate foils may continue until the angle of the foil stack. The intermediate foils changes the distance between voltage lines on separate wall foils. The intermediate foils are provided notably at the edge of the stack of wall foils in order to ensure that in the region where the voltage lines emerge from the stack of foils the distance between the voltage lines on separate wall foils differs from the distance between the voltage lines on neighboring foils which are not separated by intermediate foils. Depending on the size of the filter elements, i.e. the spaces between the wall foils and the thickness and number of intermediate foils the distance between separate wall foils in the region where the voltage lines emerge from the stack of foils is larger or smaller than the distance between wall foils where they are not separated by the intermediate foils and form the filter elements. Because the intermediate foils increase the distances between the voltage lines on separate wall foils in the region where the voltage lines emerge from the stack of wall foils, the voltage lines can be readily connected to an electronic control circuit outside the X-ray filter; this electronic control circuit includes inter alia the switching elements whereby the electric voltages are selectively applied to the electrodes of the filter elements. When the intermediate foils are provided only in the region where the voltage lines emerge from the stack of wall foils, but not in the region in the stack of wall foils where the filter elements are formed as capillary tubes between the wall foils, the distance between neighboring wall foils where they form the filter elements is much smaller than the distance between the wall foils in the region where the voltage lines emerge from the stack of wall foils. Thus, an X-ray filter can be realized which includes a large number of small capillary tubes which are also arranged very close to one another and in which the voltage lines can also be simply connected to the electronic control circuit which is arranged outside the X-ray filter. Advantageously, the distances between the voltage lines on separate wall foils can be accurately adapted to the distances between connection contacts of the electronic control circuit outside the X-ray filter. Furthermore, the voltage lines on one and the same wall foil preferably fan out slightly in the region where the voltage lines emerge from the stack of foils. It is thus achieved that the distance between the foils in the plane of the relevant wall foil accurately corresponds to the connection contacts of the electronic control circuit with the switching elements. The intermediate foils are preferably made of the same material as the wall foils, but neither voltage lines nor electrodes are provided thereon. Because the same foil material is used for the intermediate foils and the wall foils, the intermediate foils are bonded to one another and to the wall foils in the same circumstances as those in which the wall foils are locally bonded to one another. This avoids the necessity of a complex process in which, for example the circumstances such as temperature and pressure must be frequently varied in order to treat the stack of wall foils with the locally inserted intermediate foils. The wall foils are notably locally bonded to one another and the intermediate foils are bonded to one another and to the wall foils in the same circumstances. Preferably, the stack of wall foils with the inserted intermediate foils is bonded in a single process step, for example by heating the assembly under pressure. Preferably, structured separating layers are provided between the wall foils. Openings are recessed in said structured separating layers so that neighboring wall foils can contact one another at the area of the openings in the separating layer when a pressure is exerted on the stack of foils. When the stack of foils is heated under pressure, the neighboring wall foils are locally fused at the areas where they contact one another via the openings in the separating layers. The wall foils remain separated at the areas where they are kept apart by the material of the separating layers. The bonded stack of wall foils with the intermediate foils is subsequently stretched in the direction transversely of the foils so that the capillary tubes are formed between the wall foils. Preferably, the separating layers are formed as a number of preferably mutually parallel metal tracks. The metal tracks also act as the electrodes via which the electric voltages are applied to the individual capillary tubes in order to control the quantity of X-ray absorbing liquid in the capillary tubes. Preferably, the voltage lines extend across the foils approximately transversely of or even perpendicularly to the longitudinal axis of the capillary tubes. The voltage lines thus follow the shortest path from the individual capillary tubes in the stack of wall foils and from the region which is exposed to X-rays during operation of the X-ray examination apparatus. Via the shortest possible voltage lines, the capillary tubes are electrically connected to the switching elements and, when the X-ray examination apparatus is in operation, the capillary tubes are situated in the X-ray beam but the switching elements remain outside the X-ray beam. The voltage lines in a further embodiment extend partly transversely of the capillary tubes until they are out of reach of the X-ray beam and outside the reach of the X-ray beam they extend, more or less parallel to or at an angle relative to the longitudinal axis of the capillary tubes, to a region adjacent the X-ray beam and above the stack of wall foils. The electronic control circuit with the switching elements can be arranged in said region adjacent the X-ray beam and above the stack of wall foils without risk of exposure to X-rays. Preferably, the stack of wall foils is mechanically reinforced at least at one of the edges extending transversely of the surface of the wall foils. This facilitates the connection of the voltage lines, emerging from the stack of foils at the mechanically reinforced edge, to the electronic control circuit with the switching elements. The mechanical reinforcement ensures that the voltage lines accurately remain at the correct distance from one another upon emerging from the stack of wall foils in order to be connected to the connection contacts of the electronic control circuit. The correct distance between the voltage lines upon leaving the stack of wall foils is exactly equal to the corresponding distance between the connection terminals. Preferably, those edges of the wall foils are reinforced which extend essentially parallel to the longitudinal axis of the capillary tubes. Electrically conductive supply lines are provided on the intermediate foils in an embodiment of the X-ray filter of the X-ray examination apparatus according to the invention. The supply lines are electrically connected to the voltage lines on the wall foils. The electric voltages are applied to the individual filter elements via the supply lines and the voltage lines under the control of the switching elements. Preferably, a plurality of groups of intermediate foils with supply lines are provided and the voltage lines are connected to supply lines of the group of intermediate foils situated nearest to the relevant filter elements. The required length of the voltage lines becomes shorter, because a part of the electrical path from the individual filter elements to the outside of the stack of wall foils extends via the supply lines. For a suitable electrical contact the voltage lines are provided with voltage contact pads and the supply lines are provided with supply contact pads. The voltage contact pads are provided at an end of the voltage lines where the voltage lines reach the intermediate foils across the wall foils. The supply contact pads are provided at an end of the supply lines where the supply lines reach, across the intermediate foils, the ends of the voltage lines on the wall foils. As a result of the use of separate supply lines and voltage lines on the intermediate foils and the wall foils, respectively, the supply lines and the voltage lines can be made to extend in different directions. This enables random selection of the location where the supply lines emerge from the stack of wall foils in the region which is not exposed to X-rays during operation of the X-ray examination apparatus. It has been found that suitably electrically conductive connections are readily realized between the supply lines and the voltage lines by connecting the supply contact pads and the voltage contact pads to one another by way of a clamping contact. For example, the intermediate foils with the supply lines are inserted into the stack of wall foils in such a direction that during insertion the supply lines are essentially parallel to the voltage lines on the wall foils. Hence, the supply lines are easily brought into correspondence with the voltage lines. Furthermore, one supply line may be connected to several voltage lines so that various filter elements are activated together. Several supply lines may be connected to a signal voltage so that a lower electrical resistance is achieved between the voltage lines and a control circuit (e.g. a driver IC) which controls the selection of voltage lines to be energized. |
summary | ||
summary | ||
abstract | An edge-curing device may comprise a cylindrical lens, a linear array of light-emitting elements, and an aperture, each aligned symmetrically about a longitudinal plane in a housing, wherein the cylindrical lens is positioned between the linear array of light-emitting elements and the aperture, the aperture spans the length of the cylindrical lens and is positioned directly adjacent to an emitting face of the cylindrical lens, and light emitted from the linear array of light-emitting elements and passing through the cylindrical lens is emitted from the emitting face and focused by the aperture within a beam width centered about the longitudinal plane. |
|
summary | ||
045487820 | abstract | An intense, space-charge-neutralized, pulsed ion beam is used to heat a magnetically-confined plasma, such as tokamak plasma, by injecting the ion beam into the plasma along a trajectory that is generally tangential to the confining magnetic field. The intense ion beam is injected into the tokamak before the plasma is fully formed, the remainder of the plasma is formed around the beam, and the beam transfers its energy to the plasma by classical collisions with the electrons and ions of the plasma. Heating of the plasma can be sufficient to produce breakeven or ignition. |
summary | ||
047626763 | summary | CROSS REFERENCE TO RELATED APPLICATION Reference is hereby made to the following copending application dealing with related subject matter and assigned to the assignee of the present invention: "Integral Reusable Locking Arrangement For A Removable Top Nozzle Subassembly Of A Reconstitutable Nuclear Fuel Assembly" by Robert K. Gjertsen et al, assigned U.S. Ser. No. 857,675 and filed Apr. 30, 1985. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to fuel assemblies for nuclear reactors and, more particularly, is concerned with an adapter plate of a fuel assembly top nozzle which has a fuel rod capture grid with an adjustable flow feature for tailoring the top nozzle pressure drop to the specific reactor core location of the fuel assembly. 2. Description of the Prior Art In most nuclear reactors, the reactor core is comprised of a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include a multiplicity of fuel rods held in an organized array by grids spaced along the fuel assembly length. The grids are attached to a plurality of control rod guide thimbles. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the guide thimbles which extend above and below the opposite ends of the fuel rods. At the top end of the fuel assembly, the guide thimbles are attached in openings provided in the lower adapter plate of the top nozzle. It is conventional practice to design the adapter plate of the fuel assembly top nozzle to accommodate three requirements. First, the adapter plate must satisfy a structural criteria, that is, it must be capable of lifting the fuel assembly under a 6 g load. Second, it must serve a fuel rod capture function in which the fuel rods are mechanically restrained by the adapter plate from ejections upwardly from the core. Third, from a functional standpoint, the adapter plate must have sufficient open area to permit reactor coolant flow to pass through the top nozzle with minimum pressure drop. U.S. Pat. No. 4,427,624 proposes a composite nozzle for a fuel assembly adapted for installation on the upper or lower end thereof which is constructed from two components. The first component of the nozzle is a casting weldment or forging designed to carry handling loads, support fuel assembly weight and flow loads, and interface with structural members of both the fuel assembly and reactor. In short, the first component is designed to satisfy the structural criteria. The second component of the nozzle is a thin stamped bore machine flow plate adapted for removable attachment to the first component. The plate is designed to limit upward movement of the fuel rods and thus ejection thereof from the core. The plate also has multiple openings or orifices of varying size and configuration to help direct coolant flow in a predetermined path through the fuel assembly and to assure that a pressure drop of predetermined magnitude will take place across the assembly. In short, the second component is intended to fulfill the two requirements of rod capture and coolant flow with minimum pressure drop. Notwithstanding the overall acceptability of the above-described basic approach to end nozzle construction, the second flow plate component proposed in the aforesaid patent has been found incapable of achieving both functions. In order to provide sufficient coolant flow through it to attain the minimum pressure drop desired, the plate must be built with insufficient structure to perform the fuel rod capture function. Consequently, a need remains for an alternative design of a component which will satisfy the dual requirements of minimum pressure drop and fuel rod capture. SUMMARY OF THE INVENTION The present invention provides a top nozzle adapter plate construction designed to satisfy the aforementioned needs. The present invention provides an adapter plate which has separate components for carrying out the structural and functional features of the adapter plate. The functional requirements of fuel rod capture and coolant flow with low pressure drop are carried out by a grid of interleaved straps which form a large number of coolant flow channels and a large number of intersections for restraining fuel rod movement, and by means for adjusting the pressure drop to tailor it to the specific distribution desired across the fuel assembly. The pressure drop through the grid can be changed without affecting the structural design and integrity of the adapter plate which is established by another component thereof with which the grid is connected. The top nozzle adapter plate of the present invention is really important in reload operations for matching coolant flow output of different fuel assemblies. In each reload operation, approximately one-third of the fuel assemblies are changed. Thus, the reactor will ordinarily contain different fuel assemblies with different amounts of spent fuel. With the ability of changing the direction of flow through the top nozzle and thereby the pressure drop, one can match the outputs of two different fuel assemblies which are located adjacent to one another. Accordingly, the present invention is directed to a top nozzle adapter plate for use in a fuel assembly of a nuclear reactor. The fuel assembly has a plurality of elongated structural members and a multiplicity of fuel rods disposed in a predetermined array. The fuel rods are supported in a manner which permits the possibility of upward movement thereof from the fuel assembly when acted upon by hydraulic forces occurring in upward coolant flow through the fuel assembly in the reactor. The adapter plate comprises: (a) an upper structural component capable of rigid connection to the elongated structural members; and (b) a lower functional component connected to the upper structural component. The lower component includes a grid composed of a plurality of spaced and interleaved straps which are capable of restraining upward movement of the fuel rods from the fuel assembly while defining open channels through the grid which are capable of allowing passage of coolant flow therethrough. The lower component also includes coolant flow directing means being operable to establish a predetermined desired pressure drop across the top nozzle of the fuel assembly. More particularly, the interleaved straps of the grid cross one another to form intersections capable of alignment with individual fuel rods in the array thereof. Further, the coolant flow directing means can take either of two embodiments. First, it can be in the form of a plurality of tabs connected to predetermined ones of the grid straps and extending outwardly therefrom, with the tabs being adjustable into various desired positional relationships with respect to the grid channels for controlling coolant flow therethrough. Or, the coolant flow directing means can be in the form of a thin flat plate having holes of predetermined desired sizes and shapes formed therein, with the plate extending along the interleaved straps of the grid and its holes generally aligned with the open flow channels of the grid. Additionally, the upper structural component includes a plurality of spaced and interconnected hubs and ligaments arranged to define substantial open areas for coolant flow therethrough while providing a rigid framework capable of transmitting lifting loads imposed by the fuel assembly. The hubs are capable of connection to the elongated structural members of the fuel assembly. Also, the grid includes void areas through which the hubs of the upper component extend when the grid is connected to the upper component. Finally, the upper component includes a plurality of open flanges connected to and extending outwardly of the hubs, whereas the grid includes upstanding corner strips for attachment to the flanges of the upper component. |
051695669 | claims | 1. A method for preparing a contaminant barrier from a hydraulically bonded cement composition, the method comprising the steps of: (a) deliberately positioning a powdered hydraulic cement composition and at least one getter into a near net final position substantially corresponding to a desired contaminant barrier shape, said getter being capable of preventing passage of a contaminant through the barrier; and (b) hydrating the powdered hydraulic cement composition without substantial mechanical mixing of the cement and water. 2. A method for preparing a contaminant barrier as defined in claim 1, wherein the at least one getter includes an ion getter. 3. A method for preparing a contaminant barrier as defined in claim 1, wherein the at least one getter includes a liquid getter. 4. A method for preparing a contaminant barrier as defined in claim 1 wherein the at least one getter includes a gas getter. 5. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement composition is hydrated by contacting the powdered hydraulic cement composition with gaseous water. 6. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement composition is hydrated in a controlled gaseous environment including carbon dioxide. 7. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement composition is hydrated by contacting the powdered hydraulic cement composition with an aqueous solution. 8. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement composition has a predetermined polymodal size distribution. 9. A method for preparing a contaminant barrier as defined in claim 1, further comprising the step of deliberately positioning an aggregate within the powdered hydraulic cement composition prior to hydrating the cement. 10. A method for preparing a contaminant barrier as defined in claim 9, wherein the aggregate comprises a plurality of aggregate particles having a predetermined polymodal size distribution. 11. A method for preparing a contaminant barrier as defined in claim 9, wherein the aggregate includes a plurality of fibers. 12. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement composition and the at least one getter are compressed into the near net final position by isostatic compression in a mold. 13. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement includes a mixture of chemically different hydraulic cements. 14. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement includes a Portland cement. 15. A method for preparing a contaminant barrier as defined in claim 1, wherein the contaminant includes a radioactive waste. 16. A method for preparing a contaminant barrier as defined in claim 1, wherein the contaminant includes a heavy metal ion. 17. A method for preparing a contaminant barrier as defined in claim 1, wherein the contaminant includes a gas generator. 18. A method for preparing a contaminant barrier as defined in claim 1, wherein the contaminant includes both radioactive and hazardous waste. 19. A method for preparing a contaminant barrier as defined in claim 1, wherein the at least one getter includes a zeolite. 20. A method for preparing a contaminant barrier as defined in claim 1, wherein the at least one getter includes a mixture of different zeolites. 21. A method for preparing a contaminant barrier as defined in claim 1, wherein the at least one getter includes a layered clay. 22. A method for preparing a contaminant barrier as defined in claim 1, wherein the at least one getter includes a mixture of layered clays. 23. A method for preparing a contaminant barrier as defined in claim 1, wherein the at least one getter includes a mixture of at least one zeolite and at least one layered clay. 24. A method for preparing a contaminant barrier as defined in claim 1, wherein the at least one getter includes a mixture of different getters. 25. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement composition includes a water-containing compound, such that at least a portion of the water necessary for hydrating the powdered hydraulic cement is capable of being provided by the water-containing compound. 26. A method for preparing a contaminant barrier as defined in claim 1, wherein a portion of the powdered hydraulic cement composition remains substantially unhydrated. 27. A method for preparing a contaminant barrier as defined in claim 1, wherein the powdered hydraulic cement composition and the at least one getter are deliberately positioned in substantially separate layers. 28. A method for preparing a contaminant barrier as defined in claim wherein the powdered hydraulic cement composition and the at least one getter are deliberately positioned as a mixture. 29. A method for preparing a contaminant barrier as defined in claim 1, wherein the desired contaminant barrier shape is in the form of a waste container. |
summary | ||
051184664 | 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 a prior art nuclear reactor core vessel 10 and coolant system 12 connected thereto. The reactor coolant system 12 includes two coolant loops, generally indicated by the numerals 14A and 14B. Each of the coolant loops 14A, 14B includes a single steam generator 16, a pair of high inertia canned motor pumps 18, a single hot leg pipe 20, and a pair of cold leg pipes 22. The pair of prior art pumps 18 in each coolant loop 14A, 14B are hermetically sealed and mounted in inverted positions to the one steam generator 16 in the respective coolant loop. Each pump 18 has a casing 24 which is attached, such as by welding, directly to the bottom of a channel head 26 of the steam generator 16 so as to effectively combine the two components into a single structure. The hot leg pipes 20 extend between and interconnect the reactor vessel 10 and the respective steam generators 16 for routing high temperature reactor coolant from the vessel 10 to the steam generators 16. The cold leg pipes 22 extend between and interconnect the pumps 18 and the reactor vessel 10 for routing lower temperature reactor coolant from the steam generators 16 via the pumps 18 back to the reactor vessel 10. Further, a pressurizer tank 28 is connected by a surge line 30 to one of the hot leg pipes 20. Prior Art Coolant Pump With External Heat Removal Arrangement Referring to FIG. 2, there is illustrated in greater detail one of the prior art reactor coolant pumps 18. In addition to its casing 24, the pump 18 has a central rotor 32 extending axially through the casing 24 and rotatably mounted to the casing adjacent a lower end 32A by a pivot pad bearing 34 and adjacent an upper end 32B by a thrust bearing 36. A canned motor 38 is located about the pump rotor 32 between the opposite lower and upper bearings 34, 36. The motor 38 includes a rotor section 40 mounted to the pump rotor 32 for rotation therewith and a stator section 42 mounted stationarily to the casing 24 about the rotor section 40. For removing heat to cool the lower and upper bearings 34, 36 and the motor 38, the pump 18 also includes a heat removal arrangement 44 which is separate from the reactor coolant water circulated through the coolant loop 14A, 14B. Further, the pump 18 has an impeller 46 mounted at the upper end 32B of the rotor 32 which rotates therewith. One end 24A, such as the upper end, of the pump casing 24 has a central inlet nozzle 48, a peripheral outlet nozzle 50 and an annular passage 51 which interconnects the inlet and outlet nozzles 48, 50. The pump impeller 46 is disposed across the annular passage 51 and in flow communication with reactor coolant water flowing in a main stream therethrough. Operation of the motor 38 causes rotation of the rotor 32 and the impeller 46 therewith. Rotation of the impeller 46 draws water axially through the central inlet nozzle 48 from the steam generator 16 and discharges the water tangentially through the outlet nozzle 50 to the respective one of the cold leg pipes 22, after flowing through the annular passage 51. In such manner, operation of the pumps 18 creates lower pressure at their inlet nozzles 48 which sucks or draws water from the reactor vessel 10 via the respective hot leg pipes 20 to and through the steam generators 16 and positive pressure at their outlet nozzles 50 which pumps water through the cold leg pipes 22 back to and through the reactor vessel 10. The heat removal arrangement 44 includes an annular hollow jacket 52 surrounding the motor 38, a set of coils 54 contained in the jacket 52 and surrounding the motor 38, and other respective sets of coils (not shown) located adjacent the lower and upper bearings 34, 36. The multiple sets of coils are connected in flow communication so as to define a closed path for circulation of an internal coolant fluid therein for cooling the bearings 34, 36 and motor 38. The annular hollow jacket 52 of the heat removal arrangement 44 has an inlet 52A and an outlet 52B connected in flow communication with an external source (not shown) of a secondary coolant fluid which can then flow through the jacket 52 over the set of coils 54 contained therein. The secondary coolant fluid is typically at a temperature much lower than the temperature of the internal coolant fluid circulating about the closed path such that the heat carried by the internal coolant fluid gained from cooling the bearings 34, 36 and motor 38 is readily transferred to the secondary coolant fluid through the set of coils 54 in the jacket 52. Improved Coolant Pump With Self-Cooling Arrangement Turning to FIGS. 3 and 4, there is illustrated an improved version of the pump 18 having a self-cooling arrangement 56 in accordance with the principles of the present invention. The self-cooling arrangement 56 employs some of the reactor coolant water to cool the pump rotor bearings 34, 36 and pump motor 38. Only a fraction, for example one percent, of the reactor coolant water is diverted from the main stream of coolant water flowing through the annular passage 51 by the self-cooling arrangement 56 before return to the main stream. The self-cooling arrangement 56 can be used in reactor applications where the temperature of the reactor coolant water entering the pump 18 is below approximately 200.degree. F. Reactor coolant water at that temperature can readily remove motor heat generated by electrical losses and bearing heat generated by friction, eliminating the need for use of the external secondary coolant fluid and separate internal closed path coolant fluid as in the case of the prior art heat removal arrangement 44. Referring to FIG. 3, the self-cooling arrangement 56 provided in the pump 18 defines a fluid flow loop 58, with the arrows in FIG. 3 identifying the direction of coolant water flow about the loop 58. The fluid flow loop 58 provides flow of reactor coolant water from the annular passage 51 into a heat transfer relationship with the bearings 34, 36 and the motor 38 before returning the flow back to the annular passage 51. As mentioned above, the self-cooling arrangement 56 is operable for diverting only a fraction, such as approximately one percent, of the reactor coolant water from and back to the main stream through the annular passage 51 to cool the bearings and motor. The fluid flow loop 58 of the self-cooling arrangement 56 is composed of outer and inner annular loop portions 60, 62. The outer loop portion 60 extends generally coaxial with, but is located farther radially outwardly from, the central rotor 32 than is the inner loop portion 62. The annular configurations of the outer and inner loop portions 60, 62 promote uniform flow of the coolant water about the loop 58 and past the bearings 34, 36. The coolant water flows from the lower end toward the upper end of the pump 18 along the outer annular loop portion 60 and in the opposite direction along the inner annular loop portion 62. The fluid flow loop 58 also includes a plurality of entry and exit ports 64, 66 which open respectively into and from the outer and inner loop portions 60, 62. The entry and exit ports 64, 66 are defined in flow communication with the annular passage 51. Particularly, the entry ports 64 are defined in the casing 24, whereas the exit ports 66 are defined through the rotor 32. Also, the entry ports 64 are located downstream of the exit ports 66. Thus, the entry ports 64 are defined at the high pressure discharge side of the pump 18 or at points of greater pressure in the main stream of the coolant water through the annular passage 51, whereas the exit ports 66 are defined at the low pressure suction side of the pump 18 or at points of lesser pressure in the main stream of water flow through the passage 51. The outer portion 60 of the fluid flow loop 58 is formed by an outer annulus 68 which surrounds the exterior of the motor 38 and a plurality of channels 70 which extend between the outer annulus 68 and the entry ports 64. More particularly, the casing 24 has the cylindrical hollow jacket 52 which surrounds and is spaced outwardly from the exterior of the stator section 42 of the motor 38 to define the outer annulus 68. The inner portion 62 of the fluid flow loop 58 is formed by an inner annulus 72 which surrounds the exterior of the central rotor 32 and motor rotor section 40 and is defined by the clearance between rotary rotor and stationary stator sections 40, 42 of the motor 38. The inner loop portion 62 also includes lower and upper pathways 74, 76 defined along and past the lower and upper bearings 34, 36. The lower pathways 74 interconnect in flow communication the lower end of the inner annulus 72 with the exit ports 66, whereas the upper pathways 76 interconnected in flow communication the upper end of the inner annulus 72 with the upper end of the outer annulus 68. The outer and inner loop portions 60, 62 thus generally extend coaxially with the central rotor 32. Further, the self-cooling arrangement 56 includes foreign particle deflectors provided with respect to the fluid flow loop so as to minimize passage of particles into the fluid flow loop 58 and to collect those particles which do pass into the loop 58 at a desired location along the loop 58. More particularly, one form of the foreign particle deflectors is a plurality of deflector elements 78 mounted to casing 24 adjacent entry ports 64 and projecting into the annular passage 51 upstream of the entry ports 64 for impeding particles entrained in the main stream of fluid flow from leaving the main stream and passing through the entry ports 64 into the outer portion 60 of the fluid flow loop 58. Most particles moving at greater momentum will tend to pass the entry ports 64 or be deflected downstream past the ports 64. Another form of the foreign particle deflectors is a centrifugal separator element 80 mounted to the rotor 32 upstream of the lower bearing 34 for rotation with the rotor. The separator element 80 extends across the inner loop portion 62 for striking particles still entrained in the flow of fluid in loop 58 and flinging the particles outwardly thereof. An annular deadend cavity 82 is defined in a radial portion of the casing 24 radially spaced outwardly from and surrounding the rotational path of the separator element 80 which is capable of receiving and trapping particles flung therein by the separator element 80 upon rotation of the rotor 32. Such collected particles are thus prevented from entering the lower bearing 34 where they could cause damage. 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. |
054141974 | summary | FIELD OF THE INVENTION The present invention relates to methods of containing and isolating toxic or hazardous wastes by forming an aggregate of the waste in asphalt or other polymers and subsequently incorporating the aggregate in a cementitious matrix. More particularly, the present invention relates to a method of containing low-level radioactive wastes comprising encapsulating the waste in asphalt to form an aggregate, mixing the aggregate in portland cement and exerting a centrifugal force on the mixture before hardening of the portland cement. BACKGROUND OF THE INVENTION Standard practice in the disposal of toxic wastes or low-level radioactive wastes requires incorporating the wastes into a non-leaching or low-leaching wasteform and burying the wasteform in a permitted site. The usual strategies for producing a wasteform involve blending the solid (sludge or salt) and liquid waste as a slurry in a dry mixture that contains a filler and a cementitious product such as portland cement or fly ash and lime. Because cement-based wasteforms have some porosity and may leach salts, an alternate strategy has involved mixing dry waste salts into a thermosetting polymer such as asphalt or polyethylene. Neither technique is totally satisfactory when used alone. Portland cement-based wasteforms present problems due to the interaction of the waste and the cement, which can prevent the wasteform from solidifying; cause the wasteform to solidify too quickly; or cause the wasteform to lose strength after initially hardening. The problems related to interferences with the cementing reactions are so great that with a typical sulfate or nitrate waste, the salt loading is typically less than 15 percent of the mass of the wasteform. If detergents or surfactants are present the loading may have to be even lower. Although the wasteforms made as cement-based composites can be manufactured as strong, coherent masses, they still show porosity that is typically in the range observed in concrete. Soluble salts will be leached from these wasteforms if they are exposed to groundwater. Asphalt-based wasteforms have been widely used for disposal of low-level radioactive wastes, especially those containing soluble salts. This is because the wasteform can be manufactured with dried salts and because leaching rates are generally very low due to the hydrophobic nature of the material. When asphalt, polyethylene, or other polymers are used to encapsulate waste, problems arise from the combustibility of organic materials when mixed with strong oxidizers, such as chlorates and nitrates. Radiation from the enclosed wastes can degrade the polymer and generate hydrogen gas. As the hydrogen gas accumulates it pressurizes the containers holding the asphalt thus creating an explosive potential. In past applications of solidification in waste disposal, the accepted approach to forming a solid from a waste has been to mix the waste as a slurry, solution or dry solid with an organic or inorganic cementing or encapsulating medium and to create conditions that would allow the cementing medium to harden. This technology has been documented for both radioactive wastes (Dlouhy, Zdenek, 1982. Disposal of Radioactive Wastes, Elsevier Scientific Publ. New York, and conventional industrial wastes (U.S. EPA 1980. Guide to the Disposal of Chemically Stabilized and Solidified Waste, SW-872, U.S. EPA, Washington, D.C.). Waste composites have been fabricated using organic polymers and portland cement-based mortars; but in prior applications, the mortar and the polymers have been mixed together to let the organic polymer fill the void space in the hardened mortar. For example, SYNCRETE, a polymer-portland cement mixture developed for waste disposal involves mixing water, a polymer emulsion, portland cement, wastes and a catalyst to produce a hardened block containing wastes (Cohen, S., P. Crouzet, 1986. "SYNCRETE: A highly efficient polymer cement embedding matrix for waste processing". Waste Management '86, Waste Isolation in the US.Proceedings of the Symposium, March 2-6, 1986, Tucson, AZ, pp 583-588). The polymer interpenetrating the matrix produced by the hydration of the calcium silicate in the portland cement is thought to produce the exceptional strength observed in this composite. Unfortunately, the polymer does not isolate the waste and the components in the waste can prevent the polymerization of the polymer and also stop the hardening reactions that occur in the portland cement. The present invention differs significantly from the SYNCRETE approach because the new system isolates the waste in a polymer and coats the polymer-waste mixture before the waste is added to the portland cement-based mortar. The new technology represents a significant improvement over the prior art because it prevents any of the components in the waste from interfering with the setting reactions that occur in the portland cement hydration. Dlouhy (1982) describes another wasteform that is manufactured by mixing the waste with portland cement to form a weak block that is then strengthened by impregnating the block with organic polymer. Unfortunately, this technique requires that the block be vacuum dried at 165 degrees C. and soaked in the heated polymer. In the example cited, the block is held in liquid styrene at 85 degrees C. for 40 hours. (Dlouhy, Zdenek 1982 . Disposal of Radioactive Wastes, Elsevier Scientific Publ. Co. New York, NY p. 138). The new technique does not involve polymer impregnation and can proceed faster with the advantage that the wastes will not weaken the portland cement matrix, and no final impregnation will be required. The polymer impregnation also has a significant disadvantage in that it is difficult to insure that the polymer in the waste block has polymerized without breaking or coring the block. Both of these steps destroy the integrity of the waste block. In the new system the condition of the waste-polymer composite can be determined by inspection prior to the addition of the pellets of composite to the portland cement-based matrix. An alternate method for encapsulating wastes in polyethylene was proposed by Lubowitz et. al., in 1977. In the method discussed by Lubowitz et. al., dried wastes were stirred into an acetone solution of modified 1,2-polybutadiene for five minutes and then the waste/polymer mixture was allowed to set for two hours. The polymer-impregnated particles are placed in a mold and subjected to mechanical pressure and heated to between 120 and 200 degrees C. to produce fusion. A polyethylene jacket approximately 3.5 mm (1/2 in.) thick is fused over the solid block. The proposed disposal method would use 800 to 1000 lb. blocks (Lubowitz, H. R., R. L. Denham, and G. A. Zakrzewski, 1977 Development of a Polymeric Cementing and Encapsulating Process for Managing Hazardous Wastes. U.S. EPA Publ. EPA-600/2-77-045, U.S. EPA, Cincinnati, Ohio,. This technique has serious drawbacks in that all of the organic polymers and solvents used are flammable. If an oxidizer (such as chlorate or nitrate) is mixed with acetone and polybutadiene and heated, care must be taken to avoid a fire. Also the polyethylene jacket can deform (squeeze thin) under pressure and can be punctured. Damage in handling and stacking can compromise the integrity of the outer polyethylene jacket. In contrast, the new technique avoids these problems by using only thermoplastic media and techniques that have been routinely used with oxidizing salts and embeds coated pellets of organic polymer in a portland-cement mortar mix that will not flow or deform plasticly and poses no risk of fire. Furthermore, the organic polymer is distributed through an inorganic matrix that separates the pellets and destroys the physical continuity of the combustible material. SUMMARY OF THE INVENTION According to the present invention many of the problems associated with the wasteforms discussed above can be eliminated by providing a new waste form which benefits from the advantages of both those prior art wasteforms. According to the present invention, pellets of asphalt-encapsulated or polymerencapsulated wastes are used as an aggregate in a concrete mixture that has the low-leaching characteristics of an asphalt or organic polymer wasteform; and the strength, durability, and desirable chemical characteristics of a portland cement-based wasteform. Organic polymers such as asphalt or polyethylene are compatible with concrete. Asphalt has typically been used as a sealer over concrete. Naturally brittle asphaltenes, such as gilsonite, have been used as an aggregate to produce low-density concrete. Because of the plastic nature of asphalt-based wasteforms, they are enclosed in a shippable container (usually a steel drum) for transportation and disposal. The drum adds to the cost of the wasteform and provides only temporary (15-20 year) containment if the drums are buried. By incorporating asphalt particles in concrete, containment can be extended well beyond what would be the predicted life of a buried steel drum. The elimination of the drum lowers the cost of the wasteform. Waste salts that are oxidizers (nitrates, chlorates, etc.) can form potentially flammable mixtures that can burn without access to air. Salts such as nitrates mixed with asphalt may result in the equivalent of a solid rocket fuel. Using the new technology of the present invention and isolating the asphalt as pellets in a concrete matrix greatly reduces the potential for ignition of the asphalt-oxidizer mixture. With the contact between pellets reduced, a large, continuous fire also becomes much less likely; although individual exposed pellets may burn if ignited. It has been shown that when radioactive wastes are incorporated in asphalt or other organic polymers, the radiation breaks down the organic polymer and generates hydrogen gas. I the wasteform is sealed in a drum, hydrogen gas can accumulate and pressurize the drum creating a serious safety problem. The mortar matrix of the present invention allows hydrogen gas to diffuse out of the wasteform without producing dangerous gas accumulations or pressurized containers. Asphalt wasteforms are developed for long-term containment of wastes that will be hazardous for hundreds of years. The wasteforms may be excavated at some future date when the nature of the material is long forgotten. Subsequent use of the wastes may expose humans to hazards of toxicity or radioactivity. If the new technique is employed and the asphalt is dispersed through a mortar matrix, it is far less likely that the asphalt will ever be reclaimed and reintroduced into the environment. |
abstract | A single piece fuel element and fast spectrum boiling water reactor using such a single piece fuel element. The single piece fuel element is formed from coated fissile particles embedded in a matrix made from a material such as SiC that is inert to all fissile and fertile heavy nuclei and to the coolant fluid circulating in and around this element. Furthermore, the fuel element includes parallel plates delimiting spaces between them. A ratio between the thickness of the plates and the width of the spaces is set so that the fuel element can be put in fast spectrum or thermal spectrum at will. An application of the single piece fuel element to a fast spectrum boiling water nuclear reactor operating with natural circulation in which the above mentioned ratio is approximately equal to 1 enables a high consumption of plutonium. |
|
048470430 | summary | The disclosure relates to jet pumps that move liquid from a low (suction) pressure to a high (discharge) pressure. More specifically, the invention discloses a liquid jet pump implemented in velocity and total momentum by a condensing jet of high velocity steam utilizable to assist jet pumping. BACKGROUND OF THE INVENTION Conventional jet pumps include a body having three distinct regions. These regions are a converging inlet section, a mixer section of substantially uniform cross-sectional area throughout its length, and a diffuser section which diverges or increases in cross-sectional area in the flow direction. If desired, a short tailpipe having a uniform cross-sectional area equal to the cross-sectional area of the diffuser exit may be included on the end of the diffuser. A jet pump is typically powered by a jet of fluid. A nozzle is positioned in the inlet section to convert a high-pressure stream of driving fluid into a high-velocity, low-pressure jet of driving fluid. This high velocity, low pressure jet of driving fluid flows axially through the inlet section of the jet pump and into the mixing section of the jet pump. In virtually all jet pump applications, fluid termed as "drive fluid" is pumped to the region of the jet pump nozzle. This pumping occurs via piping of a size generally optimized to balance the captial costs of the piping against the operating costs of the pumping energy. The flow passage of the driving fluid stream begins with the generally-always-larger cross-sectional area drive fluid supply piping, sized to mitigate fluid flow loss. At the nozzle this flow passage then gradually reduced, allowing drive flow that is initially at high pressure to accelerate smoothly until it attains the static pressure corresponding to the nozzle exit. The drive nozzle may be comprised of a single jet or may be represented as a plurality of jets. When a single jet is used, the nozzle is positioned to discharge the jet in a downstream direction along the longitudinal axis of the jet pump body. When the drive flow is subdivided into multiple jets, these jets are usually positioned equally spaced to some radius between the jet pump body longidutinal axis and the inside diameter of the mixing section and are oriented to discharge coaxially. The high-velocity jet or jets entrains fluid surrounding the nozzle in the inlet section as well as in the entrance region of the mixer section by conventional driving stream to driven stream momentum transfer. This momentum transfer continuously induces the surrounding or "driven" fluid to flow into and through the inlet section. The velocity of the entrained driven fluid increases due to the decreasing cross-sectional flow area as the driven fluid moves through the converging inlet. Thus, the pressure of the combined driving and driven fluids are reduced to a low value. The converging inlet section surrounding the nozzle directs the driven fluid into the mixing section. Within the mixing section, the high-velocity jet of driving fluid gradually widens as an entrainment-mixing process takes place with the driven fluid. During mixing, momentum is transferred from the high-velocity driving stream to the driven fluid, so pressure of the combined stream increases. The mixing process ends in the mixer. This end occurs, in theory, after the velocity taken across an area perpendicular to the longitudinal axis of the mixer becomes nearly constant (except in the boundary layer close to the walls). When this velocity profile occurs, it is said that a nearly "flat" velocity profile has been attained. Generally, it is assumed that this flat profile occurs shortly after the jet expands to touch the walls of the mixing section. From the mixing section, the mixed driving and driven fluids flow into a diffuser of increasing cross-sectional area in the flow direction. This diffuser has two functions. First, it further increase inlet section to diffuser exit pump discharge pressure. Second, the velocity of the mixed fluids exhausting from the jet pump is reduced. Thus, a jet pump operates on the principle of the conversion of momentum to pressure. The driving fluid issuing from the nozzle has low pressure, but high velocity and momentum. By a process of momentum exchange, driven fluid from the inlet or suction section is entrained and the combined flow enters the mixing section. In the mixing section, the velocity profile, i.e., a curve showing fluid velocity as a function of distance from the longitudinal axis of the mixing section, is changed by mixing. Momentum decreases and the velocity profile becomes nearly flat, i.e., perpendicular to the longitudinal axis of the mixing chamber. The decrease in momentum results in an increase in fluid pressure. The flat velocity profile gives minimum momentum with a resulting highest pressure increase in the mixing section. In the outwardly diverging diffuser, the relatively high velocity of the combined stream is smoothly reduced and converted to a still higher pressure. When the term "jet pump" is used, convention implies that both suction fluid and drive fluid are in the same fluid states. The fluid states can be liquid state, or the gaseous state. When the application involves the gaseous state, convention in the continued use of the term "jet pump" implies that compressible effects are not significant in the design. Otherwise, such terms as "ejectors", "injectors", "educators", "pressure amplifiers" and the like are used to more clearly describe the application and the device characteristics. Jet pumps are useful in many systems. Often, such system applications involve pumping large quantities of fluid at high rates. Thus, small improvements in pump performance can have major effect on system performance and economy. One application for which liquid jet pumps are especially suited is the recirculation of coolant in a nuclear reactor of the boiling water reactor (BWR) type. In a typical large boiling water reactor about 270,000 gallons/minute of coolant is recirculated by jet pumps. Thus, it is apparent that small increases in jet pump efficiency will produce important improvements in system performance and economy. It is desirable in certain BWRs to accomplish the nuclear reactor coolant recirculation process by forced-circulation, as opposed to natural circulation, to gain an overall more compact reactor pressure vessel with concomitant savings in nuclear steam supply system costs and containment costs. One such forced-circulation system is employed in the General Electric Company BWR/3 through BWR/6 product line of forced-circulation reactors. This system uses jet pumps mounted inside the reactor vessel. The motive flow driving the jet pump is supplied by external mechanical (centrifugal) pumps. These external recirculation pumps take suction from the downward flow in the annulus between the core shroud and the reactor vessel wall. This downward flow consists of feedwater mixed together with separated liquid that has been separated out from the two-phase mixture produced by the nuclear reactor core. The separated liquid is produced at the steam separator and steam dryer drains and is recirculated back to the entrance to the core. The feedwater represents coolant inventory returning to the reactor. This returning coolant inventory balances the reactor-produced steam which is supplied to the power station turbine. In order to drive the motive flow, approximately one third of the downcomer recirculation flow is taken from the vessel through two recirculation nozzles. Thereafter, it is pumped to higher pressure, distributed in a manifold to which a number of riser pipes are connected, and returned to the vessel via inlet nozzles. Inside the reactor, piping connects from each of these inlet nozzles to one or more jet pumps. In the jet pump this now-high-pressure flow is discharged in the jet pump nozzle, inducing the remainder of the downcomer flow. In the jet pump, the flows mix (producing exchange, and unification of momentum), diffuse (an action which converts momentum into higher pressure), and discharge into the core lower plenum. Forced circulation of the entire reactor coolant results. One of the disadvantages of the above jet pump recirculation system is that jet pumps have characteristically poorer mechanical efficiency than do centrifugal pumps. Consequently, the electrical power (assuming motor-driven centrifugal pumps) required to drive the entire recirculation flow is greater than that for non-jet-pump recirculation systems. Those familiar with boiling water reactor design will appreciate that a non-jet-pump system often entails many other, much more costly disadvantages. Hence, the non-jet-pump system is not necessarily the indisputably preferred modern BWR recirculation system. Certain improved BWR recirculation systems seek to eliminate the external recirculation loops associated with existing jet-pump-type BWRs. This saves capital equipment costs, enables compacting the reactor containment, and reduces the personnel radiation exposure that occurs during maintenance servicing on the drive pumps and during inservice inspections of the coolant piping weld integrity. Among the several practical means of eliminating these external loops, one such conceptual means long under design study is to use feedwater-driven jet pumps (FWDJPs). In the FWDJP recirculation system design concept, a substantial portion--such as 80%--of the feedwater is raised to extra-high pressures--such as 2700 psig--by mechanical pumps in the feedwater train. This high-pressure feedwater is piped to the nozzles of jet pumps mounted as before in the reactor downcomer annulus. The high-pressure feedwater is accelerated in the convergent-flow-area FWDJP nozzle to high velocities and discharged at the jet pump nozzle. This induces the balance of the recirculation flow--which now consists of the mixture of liquid returning from the steam separators plus the residual (20%) portion of the feedwater--to be pumped through the FWDJP and discharged at requisite higher pressure into the core lower (entrance) plenum. One of the disadvantages remaining with the FWDJP recirculation system described above, is that the resulting FWDJP must operate with a high proportion of induced flow per unit of drive flow. (The ratio of induced flow/drive flow is termed the "M-ratio"). A performance disadvantage with jet pumps is that when M-ratios exceed 1.5, approximately, the jet pump efficiency becomes increasingly poorer. The application described in the paragraph above produces an M-ratio of about 8.6. The FWDJP efficiency is substantially diminised below the best-possible-efficiency at which jet pumps--given lower M-ratios--are capable of operating. Yet another disadvantage of the FWDJP recirculation system described above is that an extra mechanical pump(s) is required (if total feedwater pumping power is to be minimized) in the feedwater train(s) to boost the FWDJP drive flow beyond the 1250 psig pressure (at conventional BWR feedwater pump discharge) to the 2700 psig needed to accomplish FWDJP recirculation. Yet another disadvantage is that piping design pressures (and thus pipe wall thicknesses and thus piping costs) are raised in the feedwater delivery piping running between feedwater pump discharge into the reactor. SUMMARY OF THE INVENTION This invention provides an improved steam-assisted liquid jet pump in which the high potential energy represented by steam is used, in nozzle mixing section located upstream of the jet pump body, to accelerate the jet pump liquid drive system. The steam, at a pressure exceeding the saturated pressure corresponding to the bulk temperature of the liquid drive stream, is expanded through a converging/diverging nozzle--down to the saturation pressure. This expansion results in conversion of steam pressure to steam velocity. In a preferred configuration, the steam nozzle accomplishing the steam expansion is configured to surround a central jet of drive liquid which itself has been accelerated, via its own nozzle, from supply pressure down to saturated pressure. The steam, travelling with higher velocity than the liquid, simultaneously mixes and condenses as the two flows proceed downstream in a nozzle mixing section that continuously converges. This process of mixing and condensing also produces momentum exchange between the two steam and water streams. The converging nozzle mixing section ends at a point just downstream of the point where nominally complete condensation has occurred. The higher momentum of the jet of fluid emerging from this nozzle mixing section is manifested as a higher velocity than can be obtained without the action of the steam. The total jet momentum emerging from the nozzle mixing section of the steam-assisted jet pump is yet-higher because of the mass addition represented by the condensed steam. This emergent jet flow is, in turn, positioned in the suction inlet of the main jet pump body so that it discharges analogous to the the positioning of the discharging drive fluid from a conventional jet pump. Because this emergent stream in the steam-assisted jet pump has greater momentum than is available to a conventional jet pump having same drive stream supply pressure and flow rate, this steam-assisted jet pump possesses correspondingly improved capabilities to induce suction fluid through the jet pump body. In an alternate configuration, the steam may be presented to the nozzle-mixing-section so that it discharges downstream centrally at the longitudinal axis, with the colder drivewater surrounding this jet of expanded, high-velocity steam. In either case, this steam-assisted jet pump, individually optimally designed for each of the nuclear reactor recirculation flow applications described above, will require less electrical energy per unit of net recirculation flow than for their corresponding standard BWR/3-BWR/6 applications or the FWDJP applications currently devised. This improved jet pump will improve the effective system pumping efficiency as measured by comparative net plant heat rates. Furthermore, in the case of the FWDJP application, this steam-assisted jet pump can result in eliminating the need for a special feedpump to boost pressure from 1250 psig to 2700 psig. Because the device internals in this latter case fit totally inside the reactor, there is no extra-high-pressure external piping required. Finally, because the steam adds to the mass flow rate discharged from the nozzle of the steam-assisted FWDJP, to perform a fixed amount of recirculation flow the M-ratio of the FWDJP can be reduced, thus enabling its operating point to be at a more favorable, higher, efficiency. OTHER OBJECTS, FEATURES AND ADVANTAGES An object of this invention is to disclose an apparatus and a process for increasing the velocity of a jet pump's liquid driving stream with an inflow of steam. Accordingly, the jet pump is provided with a nozzle mixing section. The nozzle mixing section includes at its inlet end a water inlet nozzle and a steam inlet nozzle--the steam inlet nozzle preferably surrounding the water jet and exhausting in the same direction. The steam jet is produced by the presence of a pressure differential existing across the steam nozzle. The steam passes through a converging and diverging shaped passage (nozzle) where the steam flow experiences a decrease in pressure and conversion to high velocity. In the central region of the nozzle mixing section, steam comes into contact with the liquid stream. This produces steam condensation, which maintains the pressure differential across the steam nozzle. Momentum transfer occurs from the high velocity steam to the slower water stream. There ultimately issues from the nozzles of the nozzle mixing section a steam-accelerated fluid stream. This steam-accelerated fluid stream emerges from the nozzle mixing section as a fluid jet containing significantly enhanced momentum. This momentum-enhanced jet has the capability of providing improved jet pumping by the jet pump. A further object of this invention is to disclose the use of such a steam-assisted jet pump in combination with a nuclear reactor, such as a nuclear boiling water reactor. According to this aspect, a plurality of steam-assisted jet pumps forcing circulation within the nuclear reactor are each powered by a stream of drivewater, the drivewater being well below the saturation temperature of the discharged saturated steam from the reactor. Each of these steam-assisted jet pumps is provided with a nozzle mixing section as previously disclosed. Steam is mixed with the drivewater in the nozzle mixing section of the reactor jet pumps. Thereafter, the combined, condensed and accelerated fluid stream is utilized to drive the jet pumps effecting forced circulation in the reactor. An advantage of this aspect of the invention is that the steam-assisted jet pump extracts a lesser energy penalty from the nuclear power station than conventional water driven jet pumps now realize. A further additional advantage is that the improved jet pump by producing acceleration of the fluid stream at the mixing section within the nozzle can reduce the drivewater pump head supplied to the jet pump. In other words, the velocity added by the steam jet immediate the nozzle of the jet pump obviates the requirement that a drivewater pump--such as a feedwater pump--remote from the jet pump be used to supply additional head. Consequently the inefficiencies associated with remote pumps and their piping losses are reduced. A further advantage of the disclosed pumping system is that the mixing of the steam with the water affects contact heat exchange. Heat is added to the jet pump nozzle outflow and ultimately to the jet pump outflow. Consequently the water flow interior of the reactor is rendered more efficient. Yet another advantage of the disclosed system is that the requirement for a discretely separate loop for recirculation jet pump drive is eliminated. Consequently, associated problems relating to construction and maintenance of such loops are likewise eliminated. For example, the hazard of impurities lodging in such piping admitting radioactivity to maintenance personnel is avoided. Simply stated, required exterior coolant recirculation piping loops from the reactor vessel are reduced or eliminated all together. |
summary | ||
summary | ||
abstract | A tool for patterning a disk such as a magnetic media disk for use in a disk drive system. The tool includes a chamber and a first and second series of magnets, each evenly spaced about the chamber wall. An ion beam source at an end of the chamber emits an ion beam toward the disk which is held within the chamber. The first series of magnets deflect the ion beam away from center and toward the chamber wall. The second ion beam source deflects the ion beam back toward the center so that the ion beam can strike the disk at an angle. In addition, to bending the ion beam, the magnets also rotate the bent ion beam so the movement of the ion beam revolves within the chamber. |
|
summary | ||
claims | 1. A liquid fuel combinatorial medical isotope production reactor arrangement, comprising:a. a modular reactor core having groups of symmetric homogeneous fuel assemblies interlinked together by a common upper plenum in a heterogeneous lattice arranged in a regular lattice;b. an individual and removable cooling arrangement, reflux condenser, and sweep gas circuit for each homogeneous fuel assembly group;c. a closed fuel circulation region within the reactor core;d. a closed loop reactor cooling arrangement; ande. a semi-closed loop radiolytic gas management arrangement being in fluid communication with the upper plenum. 2. The reactor arrangement of claim 1, wherein the fuel assemblies in each of the groups are interlinked by a common lower plenum. 3. The reactor arrangement of claim 1, wherein the fuel assemblies in all of the groups are interlinked by a common lower plenum. 4. The reactor arrangement of claim 1, wherein the fuel assemblies are arranged in a rectangular array lattice. 5. The reactor arrangement of claim 1, wherein the fuel assemblies are arranged in a triangular pitch lattice. 6. The reactor arrangement of claim 1, wherein the upper plenum comprises a disk-shaped housing having flat bottom surface, a flat top surface, an inlet opening for each of the fuel assemblies formed in the flat bottom surface and at least one outlet opening formed in the flat top surface and connected to the semi-closed loop radiolytic gas management arrangement. 7. The reactor arrangement of claim 1, wherein the removable cooling arrangement comprises a tubing coil which extends over each of the fuel assemblies. 8. The reactor arrangement of claim 7, wherein the removable cooling arrangement further comprises an inlet header and an outlet header, wherein the tubing coil and the reflux condenser are connected to form a continuous coil that is in communication with the inlet header and the outlet header. 9. The reactor arrangement of claim 8, further comprising a central umbilical support tube which houses the inlet header and the outlet header. 10. The reactor arrangement of claim 1, wherein the sweep gas circuit comprises a nozzle positioned above the individual and removable cooling arrangement. 11. The reactor arrangement of claim 10, wherein the individual and removable cooling arrangement comprises a tubing coil which extends over each of the fuel assemblies, and the nozzle is centrally aligned with the tubing coil. 12. The reactor arrangement of claim 1, wherein the sweep gas circuit further comprises an entrainment trap in fluid communication with the upper plenum, a hydrogen recombiner upstream from and in fluid combination with the entrainment trap and a gas cooler-condenser upstream from and in fluid combination with the hydrogen recombiner. 13. The reactor arrangement of claim 12, wherein the hydrogen recombiner comprises an axial bed having catalytic particles encased in a housing. 14. The reactor arrangement of claim 13, wherein the housing has an inlet and an outlet. 15. The reactor arrangement of claim 14, further comprising a pressure relief valve positioned at the inlet and the outlet of the housing and a pressure relief container in fluid communication with the pressure relief valves. 16. The reactor arrangement of claim 12, further comprising a gas filtering system in fluid communication with the gas cooler-condenser, the gas filtering system having a filter bed, a positive displacement compressor in fluid communication with the filter bed, a gas holding tank in fluid communication with the positive displacement compressor, a NOx removal system in fluid communication with the holding tank and a radioactive gas disposal system in fluid communication with the NOx removal system. 17. The reactor arrangement of claim 1, further comprising a 99Mo processing system having a first plurality of columns in fluid communication with the reactor core, and a plurality of separator columns containing a sorbent, the plurality of separator columns being in fluid communication with the first plurality of columns. 18. A liquid fuel combinatorial medical isotope production reactor arrangement, comprising:a. a modular reactor core having homogeneous fuel assemblies;b. an upper plenum which interlinks the fuel assemblies in a heterogeneous lattice, the upper plenum having a disk shaped housing with a flat bottom surface, a flat top surface, an inlet opening for each of the fuel assemblies formed in the flat bottom surface and at least one outlet opening formed in the flat top surface;c. a cooling arrangement, reflux condenser, and sweep gas circuit for each of the homogeneous fuel assemblies;d. a closed fuel circulation region within the reactor core;e. a closed loop reactor cooling arrangement; andf. a semi-closed loop radiolytic gas management arrangement being in fluid communication with the outlet opening of the upper plenum. 19. The reactor arrangement of claim 18, wherein the fuel assemblies are interlinked by a common lower plenum. 20. The reactor arrangement of claim 18, wherein the removable cooling arrangement comprises a tubing coil which extends over each of the fuel assemblies, the sweep gas circuit comprises a nozzle positioned above the individual and removable cooling arrangement, the nozzle being centrally aligned with the tubing coil. 21. A liquid fuel combinatorial medical isotope production reactor arrangement, comprising:a. a modular reactor core having groups of symmetric homogeneous fuel assemblies interlinked together by a common upper plenum in a heterogeneous lattice arranged in a regular lattice, wherein the common upper plenum links together at least two individual symmetric fuel assemblies;b. an individual and removable cooling arrangement, reflux condenser, and sweep gas circuit for each homogeneous fuel assembly group;c. a closed fuel circulation region within the reactor core;d. a closed loop reactor cooling arrangement; ande. a semi-closed loop radiolytic gas management arrangement being in fluid communication with the upper plenum. |
|
abstract | A fuel assembly for a pressurized water nuclear reactor contains a multiplicity of fuel rods which are guided in a plurality of axially spaced spacers which in each case form a square grid, composed of grid webs, with a multiplicity of cells arranged in rows and columns. In each case one control rod guide tube is guided through a number of these cells. At least one spacer is configured to be mechanically stronger in a first partial region than in a second partial region. In this second partial region, the spacer is provided with at least one resisting element which protrudes into a flow sub-channel formed between the fuel rods and increases the flow resistance. The resisting element counteracts a reduction associated with the mechanically weaker configuration, in the flow resistance in the second partial region and in this manner effects a homogenization of the hydraulic behavior of a spacer which is mechanically inhomogeneous on account of the varying mechanical configuration. |
|
summary | ||
051223333 | summary | This invention relates to an apparatus for eliminating aerosols from air escaping from a nuclear reactor containment vessel. As is known, various types of apparatus have been used for the elimination of aerosols contained in air which has escaped from the containment vessel of a nuclear reactor plant, for example, in the event of an excess pressure occurring in the containment vessel. In such apparatus, the air is usually ID feed to a water bath by means of a conduit connected to the containment vessel. In one known apparatus of this kind, venturi scrubbers have been disposed in a water bath with each having a venturi tube to which the aerosol-laden air is feed while water is added to the air flowing through each venturi tube at the narrowest point of such tube. The purpose of such scrubbers is to fix a considerable proportion of the aerosols in the water by mixing the water and air. In addition, above the water bath in a tank containing the same, there is disposed a filter of high-grade steel fibers, through which the air emerging from the water bath has to pass before being discharged to atmosphere via a chimney. The purpose of this filter is to retain the residual aerosols in the air. In the known apparatus, separate containers are required to accommodate the water bath and the filter. Further, the extremely fine high-quality steel fibers of the filter have a thickness of 2 .mu.m and require special protective steps to guard against corrosion. After any trial runs of the apparatus, each of the filters normally has to be replaced. In addition, the filter retention power is restricted. Further, the venturi scrubbers disposed vertically in the water bath take up a relatively considerable height. The constructional requirements and overall volume of the known apparatus are therefore quite large. Accordingly, it is an object in the invention to reduce the expense of removing aerosols from air vented from a nuclear reactor containment vessel. It is another object of the invention to reduce the constructional outlay for an apparatus for eliminating aerosols from the air of a nuclear reactor containment vessel. It is another object of the invention to provide a relative simple apparatus for eliminating aerosols from air vented from a nuclear reactor containment vessel. Briefly, the invention provides an apparatus for eliminating aerosols from air escaping from a nuclear reactor containment vessel. In this respect, the apparatus includes a water basin for holding a bath of water and a conduit for delivering a flow of aerosol-laden air into the water bath from a containment vessel of a nuclear reactor plant, for example, in response to an excess pressure in the containment vessel. In addition, a plurality of nozzles are disposed in the basin and are connected in parallel with the air delivery conduit in order to discharge jets of aerosol-laden air into the water bath for entrainment of water therein. Also, a baffle plate extends over the nozzles and has perforations therein for mixing the water-entrained aerosol-laden air passing therethrough. Still further, a plurality of static mixer elements are disposed in stacked array within the water bath above the baffle plate for conducting the mixture of water-entrained aerosol-laden air therethrough. These static mixer elements have intersecting flow passages for splitting up elongating and re-arranging the components of the water and air mixture in order to disperse the air in the water while separating the aerosols into at least one of the water and the static mixer elements. The apparatus also includes a jacket which circumferentially surrounds the mixer elements. This jacket may also extend downwardly into a zone of the nozzles. A further conduit is also connected to the basin above the water bath and the static mixer elements for discharging a flow of aerosol-depleted air therefrom. The use of a plurality of nozzles with a perforated baffle plate reduces the overall height required of the aerosol-eliminating apparatus considerably as compared with known venturi scrubbers. Hence, the space requirements for the apparatus are reduced. The use of static mixer elements enables practically all the aerosols to be fixed. Thus, the air emerging from the water bath can be discharged directly to the surroundings, that is, without having to pass through a filter. Also, there is no need to provide a special closed container for the apparatus. The nozzles, baffle plates and static mixer elements can be accommodated in a water basin which, in any case, is present in a nuclear reactor plant. The apparatus permits trials to be carried out at any time without any need to subsequently replace any parts. Further, the parts of the apparatus can be easily inspected an the static mixer elements can be easily removed, and, if necessary, cleaned by conventional processes. |
abstract | A collimator according to an embodiment is a collimator for use in an X-ray CT apparatus and includes a collimator module and resin. The collimator module includes a first scattered ray eliminating part and a second scattered ray eliminating part. The resin is provided between the first scattered ray eliminating part and the second scattered ray eliminating part and is configured to hold the first scattered ray eliminating part and the second scattered ray eliminating part. |
|
abstract | In a scanning probe apparatus capable of always effectively canceling an inertial force to suppress vibration even in repetitive use while replacing a sample holding table or a probe, a stage for a sample or the probe includes a drive element for moving the sample holding table and movable portions movable in a direction in which an inertial force generated during movement of the sample holding table. The stage is configured so that the drive element, the movable portions, and the sample holding table or the probe are integrally detachably mountable to a main assembly of the scanning probe apparatus. |
|
053612795 | description | DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a boiling water reactor pressure vessel suitable for housing the internal control rod drive of the present invention. The pressure vessel 20 has a top head 21 and a bottom head 22. The nuclear core 25 is positioned on a core plate 26. A matrix of fuel bundles 28 is arranged within the core. The bundles are spaced sufficiently so that a cruciform shaped control rod blade 32 of control rod 31 can be slid back and forth in the region between the channels to control the reactor output. A top guide plate 35 is positioned near the top end of the fuel bundles to help position the channels. The channels may extend well above the fuel bundles to form a chimney 37. Of course, the invention can be used with other conventional reactors designs, as for example, designs wherein the chimneys are eliminated and/or larger channels are provided that contain a plurality of fuel bundles and/or in conjunction with a cluster type core wherein finger type control rods are used. An open control rod drive grid 40 is positioned a distance above the top guide plate 35. The spacing between the tops of the fuel bundles and the grid 40 is sufficient so that substantially the entire control rod blade 32 can be lifted above the core 25. A multiplicity of control rod drives (CRDs) 30 are mounted on the control rod drive grid as best seen in FIG. 2. Specifically, one CRD 30 is positioned above each control rod 31. In the embodiment of the invention shown in FIG. 1, a multiplicity of standpipes 42 are positioned somewhat above the control rod drive grid 40 with each standpipe being arranged to receive the jack rod 34 of an associated control rod drive 30. The standpipes 42 are provided with an internal guide tube to contain the jack rods and to control flow, induced vibration in the jack rods. In alternative embodiments, these guide tubes could be arranged between the standpipes. Conventional steam separators 44 are positioned above the stand pipes 42 and a conventional steam dryer 45 is positioned above the steam separators and typically within the top head 21. Referring next to FIG. 2, the construction of a first embodiment of the control rod drives 30 will be described. Each control rod drive 30 includes a jack rod 34, a connector 36 and a hydraulic jack 38. The connector 36 is arranged to couple the jack rod 34 to the control rod 31. In alternative embodiments, the jack rod could be formed integrally with the control rod. The jack rod 34 takes the form of a notched shaft which is designed to cooperate with the latches of the hydraulic jack 38 to create a ratchet type mechanism. The hydraulic jack 38 includes a holding mechanism 50 for holding the jack rod 34 in a stationary position and a lifting mechanism 60 for lifting and lowering the jack rod 34. Both the lifting mechanism and the holding mechanism are housed within a casing 59 and are hydraulically operated. The holding mechanism 50 includes a pair of pivotally mounted latch fingers 51 that are respectively coupled to sliding members 53 by pivotal linkages 52 and to a fixed support 57 by pivots 58. The latch fingers 51 each include a holder 54 that is adapted to engage the notches in the jack rod 34. In the described embodiment, the holders 54 take the form of holding pins, but it should be appreciated that latches, pins or other suitable mechanism may all be used as holders within the scope of this invention. The sliding members 53 are biased in a downward direction by biasing spring 55. A hold piston 56 is positioned under the sliding members 53 for pushing the sliding members upward. The hold piston 56 in turn is supplied by a hydraulic holding line 71. Thus, the sliding members 53 are biased downward by the biasing spring 55, and forced upward by the hold piston 56 when the holding line 71 is pressurized. When no pressure is exerted by the hold piston 56 against the sliding members 53, then the biasing spring 55 will push the sliding members downward. This movement will release the latch fingers 51 which in turn release the jack rod. When a significant pressure is applied in the hydraulic holding line 71, then the hold piston 56 pushes the sliding members 53 upward against the force of the biasing spring 55, thereby causing the latch fingers 51 to pivot into the engaging position which firmly holds the jack rod in place. The lifting mechanism 60 has a pair of latch fingers 61 that are respectively pivotally mounted to a pair of sliders 63 by pivots 62. The latch fingers 61 each have a lifter 69 thereon that is adapted to engage the notches in the jack rod 34. Like the holders 54, the lifters 69 in the described embodiment are lifting pins but may take the form of latches or other suitable mechanisms. The sliders 63 are free to move a limited distance within casing 59. The free end of each latch finger 61 is coupled to a sliding member 65 by a linkage 64 that is pivotal on each end. The sliders 63 are biased in a downward direction by biasing spring 66. The sliding members 65 are each biased in a downward direction by a biasing spring 67 positioned between the housing and the lifting mechanism. A lift piston 68 is positioned under the sliding members 65 such that when actuated, it can push the sliding members upward against the force of biasing spring 67. This action serves to pivot the latch fingers from a release position into an engaging position. When no pressure is exerted by the lift piston 68 against the sliding members 65, then the biasing spring 67 will push the sliding members 65 downward. This movement will release the latch fingers 61 which in turn will release the jack rod. When a significant pressure is applied in the hydraulic lifting line 73, then the lift piston 68 pushes the sliding members 65 upward against the force of the biasing spring 67, thereby causing the latch fingers 61 to pivot into the engaging position. When the holding pins 54 are released and the lifting pins 69 are engaged, then the movement of the jack rod can be controlled by the pressure within lifting line 73. Specifically, if a high pressure is applied against the lift piston 68, then the piston will stroke upward with the lifting pins 69 engaged, thereby moving the sliders upwards against the springs 66, which lifts the jack rod by a notch. On the other hand, if only a moderate pressure is applied against the lift piston 68, then the weight of the control rod combined with the force of spring 66 will push the sliders 63 downward and thus the lift piston will stroke downward. In this manner the jack rod can be lowered by a notch. The described embodiment requires two hydraulic lines to operate each jack mechanism. By way of example, in a reactor that employs two hundred cruciform shaped control rods, two hundred control rod drives may be used. In such an embodiment, four hundred hydraulic lines would be necessary. An alternative embodiment of the invention which uses an addressing system to reduce the number of hydraulic lines required will next be described referring to FIG. 3. In this embodiment, modified holding and lifting mechanisms are used and a hold control valve 180 is added to each drive. Specifically, the hold control valve 180 has a piston 182 that is biased in a first direction by biasing spring 184. The side of the piston opposite the biasing spring has a plunger 186 that has a much narrower diameter then the piston 182. The position of the piston is influenced by three factors. They include the biasing spring 184, the pressure in lifting line 73 which acts against the piston 182 in a direction opposite the biasing spring, and the pressure of the holding line 71 which also acts against the plunger 186 in a direction opposite to the biasing spring. The piston is moveable between open and closed positions. In the open position, a communication path is formed between the holding line 71 and a control line 175. The piston 156 in holding mechanism 150 is influenced by three forces as well. These forces include a biasing spring 155, the pressure in control line 175 and the pressure in holding line 71. The biasing spring 155 and the pressure in control line 175 urge the hold piston 156 towards a disengaged position while the pressure in holding line 71 urges the piston towards a closed position. The surface area of the piston 156 that is influenced by the control line 175 is somewhat larger than the area influenced by holding line 71. The pressure in control line 175 will be very similar to the pressure in holding line 71 when the hold control valve 180 is opened. Therefore, the position of the hold piston 156 will effectively be determined by whether the hold control valve 180 is open, as long as there is pressure in holding line 71. If all pressure is removed from the holding line, the biasing spring 155 will move the piston to the withdrawn position. The lifting mechanism 160 effectively includes a lifting piston 165 and a lift cylinder 168. The position of each of these components is influenced by the pressure in lifting line 73. The pin positioning piston 165 is influenced by a biasing spring 164 and the pressure in lifting line 73. Specifically, as long as there is a significant pressure within the lifting line, the pin positioning piston will remain in the engaged position. When pressure is removed from the lifting line, the lifting pins 169 will move to the disengaged position under the influence of biasing spring 164. The lift cylinder 168 is influenced by a biasing spring 166 and the pressure in lifting line 73, as well as the engagement of the holding pins 154. Specifically, when the holding pins 154 are engaged, the jack rod will remain in place regardless of the pressure exerted in the lifting line 73. However, when the holding pins 154 are disengaged and the lifting pins 169 are engaged, then the full weight of the jack rod 34 and the control rod will be borne by the lift cylinder 168. In this case, if a high pressure is applied in lifting line 73, then the lift cylinder will stroke upward and the jack rod 34 will be lifted a notch. On the other hand, if a medium pressure is applied to the lifting line 73, then the weight of the control rod would cause the lift cylinder 168 to stroke downward, thereby lowering the control rod a notch. With the described logic, if a high pressure is applied to both the lifting and holding lines, the jack rod 34 will be lifted one notch. Specifically, the hold control valve 180 is opened against the force of biasing spring 184, which introduces a high pressure in the region behind the holding piston 156. Thus, the holding piston 156 will stroke towards the disengaged position, which serves to release the holding pin 154 from the jack rod 34. On the other hand, the high pressure on the lifting piston 165 and the lift cylinder 168 causes the lifting pins 169 to engage the jack rod and the lifting cylinder to stroke upwards, thereby moving the jack rod upwards. The jack rod 34 may be lowered a notch by keeping the pressure in the holding line 71 high while asserting a medium pressure in the lifting line 73. In this condition, the hold control valve is again opened by the combined forces of the pressures within the holding and lifting lines acting against the biasing spring 184. However since a medium pressure is asserted against the lifting piston, the weight of the control rod will stroke the lift cylinder downwards, which will step the jack rod down a notch. If no pressure is applied to the lifting line, then the lifting piston 165 will disengage. At the same time, the hold control valve 180 will close and the pressure in the holding line will stroke the hold piston 156 which serves to lock the holding pin 154 in place. This is true regardless of whether a high or medium pressure is applied in the holding line 73. On the other hand, if no significant pressure is present on either the holding line or the lifting line, then the force of biasing spring 155 will stroke the holding piston to the right (as seen in FIG. 3) which releases the holding pin 154. Thus, when no pressure is applied to either line, both pins will release and gravity will cause the control rod to fall into the core. Thus, the system is failsafe in that in the event of a power loss or other control failure, the control rods will automatically descend into the core. Any time that a medium pressure is applied to the holding line, the hold control valve 180 will be closed. Thus, the pressure of the holding line 71 will stroke the holding piston in a manner that moves the holding pin 154 into the engaged position. In this condition, regardless of the pressure on the lifting line, the jack rod will be firmly held in place. Any time that the holding line does not have any pressure, the holding pin will disengage from the jack rod. In this condition the jack rod could be lifted or lowered by varying the pressure in the lifting line 73 between the high and medium pressures. However, in the current embodiment, this type of control is not used. With the described arrangement, it can be seen that an addressing system can be arranged that would provide individual control of the control rod drives, but eliminate the need to use dedicated holding and lifting lines. Specifically, in such an addressing grid arrangement, a plurality of holding line are provided with each holding line being connected to a row of drives. Similarly, a plurality of lifting lines are provided with each lifting line being connected to a column of drives. In the steady state, the holding lines would be pressurized with a medium pressure, while the lifting lines would not be pressurized at all. As explained above, with this arrangement, all of the drives would hold their associated jack rod firmly in place. When a particular control rod is to be lifted or lowered, the pressure in its associated holding line is increased to a high pressure. The remaining holding lines remain at the medium pressure. The pressure in the selected control rods lifting line is then adjusted to either lift the control rod (by applying a high pressure) or to lower the control rod (by applying a medium pressure. The remaining lifting lines will remain unpressurized. It is noted that since all of the holding lines other than the selected holding line are at a medium pressure, their associated drives in the selected column will not move, regardless of the pressure in the selected lifting line. Similarly, since all of the lifting lines other than the selected lifting line are unpressurized, the unselected drives in the selected row will not move. Thus, with the described arrangement, true addressing can be used to control the control rod drives. With this arrangement, a total of 30 hydraulic lines (15 lifting lines and 15 holding lines) can be used to control a system having over 200 drives. It will be appreciated by those skilled in the art that this is a significant improvement and would substantially simplify the system's plumbing. Referring next to FIGS. 4-6, a variety of control rod drive mounting arrangements will be described. The first described embodiment is suitable for use in a reactor that employs cruciform shaped control rods. As seen in FIG. 4, the grid 40 is an open matrix of beams 81 having mounting surfaces 80 formed at each beam intersection. The mounting surfaces are designed to correspond in shape to the shape of the bottom end of the control rod drive. A cruciform slot 83 is formed in each mounting surface 80 for receiving an associated control rod blade 32. Each control rod drive 30 also has a corresponding cruciform slot 84 through which the jack rod and the control rod blade may pass. In the illustrated embodiment, the cross section of the control rod drive casings 59, and the mounting surface are substantially cruciform in shape as seen in the drawings. The lifting and holding mechanisms are positioned in the region 85 formed between adjacent arms 86 of the cruciform casing. The mounting surface 80 includes a pair of raised hydraulic ports 90 and a pair of raised mounting guides 92. The hydraulic ports 90 are designed to fit into matching female ports on the bottom surface of the control rod drive. Similarly, the mounting guides are received by matching indentations in the bottom surface of the control rod drive. Thus, the raised ports 90 and the raised mounting guides 92 cooperate to position the drive 30 on the mounting surface. Then a plurality of bolts or other fasteners (not shown) are used to secure the drive to the mounting surface. The hydraulic supply lines 93 (which include holding lines 71 and lifting lines 73) may be strung along the sides of the beams 81. An alternative embodiment of the grid 40 is shown in FIG. 5. This embodiment also has an open matrix structure and is adapted for use in a system having large channels with chimneys extending therefrom and wherein each channel houses a group of four fuel bundles. The control rods used in this embodiment are designed to extend into the spaces between adjacent fuel channels, as seen in FIG. 5. In this embodiment, the grid 40 takes the form of a top beam grid having a multiplicity of mounting surfaces 80 that are similar to those described above with respect to the previous embodiment. A plurality of side beams 95 extend downward from the top beams 94. The side beams extend outward in pairs that run in the direction of each arm 86 of the cruciform drive casing. The parallel side beams are spaced apart a distance that is slightly wider than the walls of chimney 37 and have flared lowered ends 97 that insure an easy fit over the top end of the chimneys. The grid is positioned such that the top of the chimneys are positioned slightly below the top beams 94. With this arrangement, during installation the grid can simply be lowered into place over the top edge of the chimney walls. This permits replacement of the chimneys upon removal of the top beam grid. Another alternative grid structure is shown in FIGS. 6 and 7. This embodiment is particularly well adapted for use in cluster type core configurations. In such configurations, it is advantageous if each jack rod 34 carries a plurality of finger type control rods 100 using a spider 102 positioned below the grid 40, as best seen in FIG. 7. The holes in the center of the mounting surface 80 and the drive 30 are each cylindrical in nature. As such, they only pass the jack rod itself. As best seen in FIG. 7, a hydraulic coupling 105 can be used to connect the jack rod 34 to the spider 102. The grid takes the form of an open matrix formed by I-beams. The positioning and mounting of the drive is accomplished in the same manner as the previously described grids wherein raised mounting guides 92 and raised hydraulic ports 90 cooperate with matching recesses and recessed ports on the drive to position the drive and bolts or other fasteners are used to secure the drive. The hydraulic lines 93 are strung along the web portion of the I-beam. In other respects, the grid is similar to those previously described. The described hydraulic jack can be very compact in size. By way of example, a suitable overall drive height is about two feet. The reduced size of the CRD permits a substantial decrease in the required pressure vessel and containment building heights. By way of example, the described control rod drive system has the potential of reducing the containment height by three times the core height (i.e. approximately 36 feet) and the pressure vessel height by one core length when compared to conventional BWR control rod drive systems. The use of internal jacks also has the advantage of significantly reducing the vessel penetrations in both size and number. By way of example, four penetrations of less than 10 inches in diameter around the periphery of the pressure vessel would be sufficient to handle all of the required hydraulic lines for an array of 200 control rod drives even if two lines are provided for each drive. This must be compared with the 200 six-inch-diameter penetrations that would be required for conventional CRDs. This reduces vessel fabrication costs and significantly reduces the amount of in service inspection required. The size of the openings is even further reduced if the described addressing system is used. By way of example, just two four-inch-diameter penetrations would be sufficient to control 200 control rod drives if the addressing system were used. The described control rod drive is failsafe in operation. Thus, in the event of a rupture of one of the lines or a loss of pressure, the control rods would automatically fall into the core. Since the drive is internal to the reactor pressure vessel, none of the components need to be pressure retaining, which serves to substantially reduce the cost of the drives themselves. Although only a few embodiments of the invention have been described, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims. |
description | The invention relates to a highly heat-resistant laminated component for a fusion reactor. The component has at least one plasma-facing area made of tungsten or a tungsten alloy with a tungsten concentration of >90% by weight, a heat-dissipating area made of copper or a copper alloy with conductivity of >250 W/mK and a mean grain size of >100 μm, and an area lying in between and being formed of a refractory-metal-copper composite. For stationary fusion reactor operation, power flows of up to 10 MW/m2 can be expected in the area of the surface of first-wall components, which are also referred to as PFCs (plasma facing components). In the event of plasma breakdown, approximately 20 GJ may be released at certain points within only a few milliseconds. The development of PFCs designed specifically for use in areas of maximum energy concentration, such as diverter, baffle and limiter areas, represents a key element in the technological implementation of the results of fusion research. The material requirements applicable to PFC components are diverse and often conflict with one another. In addition to physical and mechanical properties such as high thermal conductivity, high melting point, low vapor pressure, good thermal-shock resistance and suitability for processing, use in nuclear fusion poses special requirements, including low activation and transmutation under heavy neutron exposure, low continuous tritium absorption, low erosion by plasma ions and neutron particles, low sputter rate and erosion resulting from local effects such as arcs and hotspots as well as low cooling of core plasma through characteristic radiation. Depending upon the specific load conditions, the preferred materials for PFCs are beryllium, carbon-fiber-reinforced carbon (CFC), and tungsten. Tungsten is particularly well suited for use in the first wall, where relatively low plasma temperatures and high particle densities prevail. Tungsten has very good thermal properties such as high thermal conductivity (165 W/mK at room temperature). Moreover, its high melting point, low tritium absorption capacity, low vacuum gas rate and low sputter rate virtually predestine tungsten for use in PFCs. In order to achieve effective heat removal in areas of extreme energy density, PFCs must be actively cooled. This can be accomplished with the aid of copper components filled with circulating coolant, which are combined as a heat sink with the tungsten components. To achieve sufficiently high mechanical stability and rigidity, it is advantageous to join the copper heat sink with a highly rigid metallic structural material. Austenitic steels and particle-reinforced copper alloys, such as age-hardened Cr—Zr alloyed copper alloys (Cu—Cr—Zr) or ODS (oxide-dispersion-strengthened) copper materials (e.g. Cu—Al2O3, Cu—ZrO2, Cu—Y2O3, Cu-rare-earth-oxide) are suitable for reinforcing elements of this kind. Two design variations are considered for PFCs to be used in areas of high energy density. In so-called flat tiles, the transitions between the individual materials are nearly uniform. In monoblock components, sufficient structural stability and rigidity are provided by the tube filled with circulating coolant, which may consist, for example, of an age-hardened copper alloy or ODS copper. Toward the outside, the other materials are arranged in a configuration comparable to that of the flat-tile variation. The tungsten segment is a cube-shaped body that surrounds the cooling tube, whereby a buffer layer consisting of a soft, ductile materials, preferably pure copper with a low oxygen content (OFHC copper) is placed between the cooling tube and the tungsten segment. A particular difficulty encountered in the production of laminated parts for fusion reactors, such as flat-tile or monoblock components, is that tungsten and copper exhibit very different heat expansion behavior. The heat expansion coefficient of tungsten at room temperature is 4.5×10−6 K−1, while that of copper is 16.6×10−6 K−1. Technologies recommended for bonding tungsten to copper include diffusion welding and back-casting. Diffusion welding can be performed using hot isostatic pressing (HIP) as described in European patent specification EP 1 025 938. The processes cited above are performed within a temperature range of approximately 700 to 1300° C. During cooling, stress builds up in the vicinity of the joint as a result of the different heat expansion coefficients of tungsten and copper. Stresses are also induced when PFCs are used, however, as they are exposed to cyclical heat loads. These stresses can cause cracking or separation at the tungsten to copper interfaces. This hinders thermal dissipation and thus poses the danger that the laminated component will melt. Extensive development programs have been initiated, some of which have already been completed, for the purpose of realizing a laminated component consisting of a plasma-facing tungsten segment bonded form-fitting with an actively cooled copper heat sink which exhibits low bonding stresses in the interface area. A significant reduction in stresses was achieved by designing the tungsten segment as a group of individual small cubes or rods with side lengths or a diameter of several millimeters, whereby the cubes or rods are inserted into a copper segment. This form of segmentation reduces thermal stresses resulting from the bonding process and from cyclical operation. However, the design also poses a high risk of fatigue cracking in the tungsten-copper interface. Numerous attempts have been made to reduce tensions in the interface by incorporating a graded interlayer between the tungsten and copper segments. Thus, U.S. Pat. No. 5,126,102, for example, describes a method for producing a tungsten-copper FGM (functionally graded material) in which a tungsten segment with graded porosity, produced by thermal plasma spraying, for example, is infiltrated with copper. U.S. Pat. No. 5,988,488 also describes a production process in which thermal plasma spraying is used to achieve a graded interlayer between the tungsten and copper segments. In contrast to the process described in U.S. Pat. No. 5,126,102, the copper phase is also separated by thermal plasma spraying, whereby the specific powder blend added contains corresponding proportions of tungsten and copper. A thin metallic film between the tungsten and the FGM promotes adhesion. U.S. Pat. No. 5,988,488 also contains a description of an attempt to insert a layer consisting of a blend of copper and tungsten between the tungsten and the copper heat sink by brazing or diffusion bonding. However, the difference in the heat expansion coefficients was too great. No further detailed explanations are provided in this patent. It can be assumed that the production processes described in both, U.S. Pat. No. 5,126,102 and U.S. Pat. No. 5,988,488 produce laminated parts that exhibit significantly higher resistance to thermally induced cracks. However, the disadvantage of the processes described in these patents is that they are complicated and, consequently, the parts produced in the manner described are very expensive. Moreover, due to process engineering constraints, the technologies cited above are applicable to flat-tile structures only. Generally speaking, their use in the production of monoblock geometries is impossible for geometric reasons. It is accordingly an object of the invention to provide a laminated component for a fusion reactor which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for laminated components for fusion reactors consisting at least in part of tungsten or a tungsten alloy and copper or a copper alloy which exhibit sufficient functional capacities, particularly with respect to thermal fatigue, which can be produced cost-effectively, and which are suitable for monoblock geometries. With the foregoing and other objects in view there is provided, in accordance with the invention, a highly heat-resistant laminated component for a fusion reactor, comprising: a plasma-facing area made of tungsten or a tungsten alloy with a tungsten concentration of >90% by weight, a heat-dissipating area of copper or a copper alloy with a thermal conductivity of >250 W/mK and a mean grain size of >100 μm, and an area in between the plasma-facing area and the heat-dissipating area of a refractory-metal-copper composite; the refractory-metal-copper composite having a macroscopically uniform copper and tungsten concentration progression and a refractory metal concentration x of 10 vol. %<x<40 vol. % throughout a thickness d of 0.1 mm<d<4 mm, and a refractory metal phase forming a virtually continuous skeleton. Refractory-metal-copper components are used in many industrial applications as heat sinks or heat spreaders, in electronic packages, for example. Refractory metals are elements in groups IVb and Vb of the periodic table of elements which have a melting point above 1800° C.—specifically the metals Nb, Ta, Cr, Mo, and W. Contrary to the widespread conception that stresses in tungsten-copper laminated components for fusion reactors can be reduced only with the use of FGMs, experiments surprisingly showed that interlayers composed of refractory-metal-copper materials with a macroscopically uniform copper-refractory-metal concentration progression can also be used effectively. A macroscopically uniform concentration progress is defined as the concentration progression throughout the thickness of the refractory-metal-copper composite without regard for microscopic differences in concentration. Microscopic differences in concentration always appear in refractory-metal-copper composites, since refractory metals and copper are insoluble or soluble only to a small extent in each other. Thus one finds copper and refractory-metal phase areas next to one another in sizes of between 5 and 50 μm. An effective reduction of stresses in the interface area is can only be achieved if the layer consisting of a refractory-metal-copper composite is at least 0.1 mm thick. Thinner layers do not provide for sufficient tension reduction. While thicknesses of 4 mm and above do not impair the functional capacity of the laminated part in terms of resistance to separation and thermally induced fatigue cracking, heat dissipation is reduced by virtue of the poorer thermal conductivity of the refractory-metal-copper composite to the extent that the functional reliability of the laminated part is not longer ensured. A further prerequisite for sufficient functional capacity is that the refractory metal concentration in refractory-metal-copper composites must lie between 10 and 40% by volume. Process reliability is not sufficiently ensured at either higher or lower refractory metal concentrations. Furthermore, the refractory-metal-copper composite must be produced in such a way that the refractory-metal phases form a nearly continuous skeleton. This requirement is met by refractory-metal-copper composites produced using power-metallurgical processes, such as the infiltration of a porous refractory-metal body with copper. The porous refractory-metal body can be a shaped or sintered object. Refractory-metal-copper composites with nearly continuous skeletons can also be produced by pressing powder mixtures or composite powders and sintering. Aside from W—Cu and Mo—Cu composites produced in this way, the use of rolled or extruded Mo—Cu composites has proven to be particularly advantageous. Furthermore, the copper or copper-alloy segment must be capable of sufficiently reducing thermally induced stresses. Given the selection criterion of “thermal conductivity >250 W/mK”, only copper materials with a low concentration of alloy elements and a correspondingly low yield strength can be used. In addition, the copper or copper-alloy segment must have a mean particle size of more than 100 μm in order to ensure effective stress reduction. The bonding of the copper or copper-alloy segment using OFHC (oxygen-free-high-conductivity) copper by back-casting it to the refractory-metal-copper composite has proven highly advantageous. This process ensures that the mean particle size in the copper/copper-alloy segment is always greater than 100 μm. The bonding of the tungsten/tungsten-alloy segment with the refractory-metal-copper composite segment by melting the copper phase can be accomplished during the same process phase. It has proven advantageous to introduce a copper foil or sheet with measuring between 0.005 and 0.5 mm in thickness between the tungsten and the refractory-metal-copper composite. In order to improve the bond between tungsten and copper, it is also advantageous to introduce a metallic element or alloy—by coating the tungsten substrate, for example—which is soluble in both tungsten and copper or which reacts with these two materials. Elements or alloys of the ferrous metals group, such as nickel, are suitable for this purpose. Suitable tungsten materials for the plasma-facing segment include monocrystalline tungsten, pure tungsten, AKS (aluminum-potassium-silicate doped) tungsten, UHP (ultra-high-purity) tungsten, nanocrystalline tungsten, amorphous tungsten, ODS (oxide-dispersion-strengthened) tungsten, W-Re, ODS-W-Re and carbide-, nitride, or boride-precipitation-hardened tungsten alloys with preferred a carbide, nitride or boride concentration of between 0.05 and 1 vol. %. Segmentation of the tungsten/tungsten-alloy components is advantageous. As the crack propagation rate of the tungsten components is significantly higher in the direction of deformation than perpendicular to it, it may be advisable in the case of parts exposed to high levels of stress to produce the tungsten parts in such a way that the direction of deformation is perpendicular to the plasma-facing surface. In order to achieve sufficient structural stability and rigidity, a component consisting of a metallic material with a strength of more than 300 MPa is bonded to the copper segment. Particularly suitable metallic materials include age-hardened Cu—Cr—Zr, and ODS-Cu materials as well as austenitic steels. The selection of the most suitable bonding method depends upon the type of materials paired. Copper-copper or copper-steel pairings are best bonded using hard soldering or diffusion bonding techniques, such as hot isostatic pressing. Also suitable for copper-copper pairings are such melt-welding processes as high-energy electron-beam welding. 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 laminated component for fusion reactors, 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 and examples, when read in connection with the accompanying drawings. A diverter plate 1 for fusion reactors was produced as a flat tile (see FIG. 1). In the first step, tungsten tiles 2 measuring 20×40×6.5 mm were cut from a tungsten rod with a diameter of 60 mm. The tiles were cut from the rod in such a way that the tile height (6.5 mm) is parallel to the rod axis. Thus the particles are aligned in the direction of subsequent main heat flow. An intermediate tile 3 with a thickness of 2 mm, a width of 20 mm and a length of 40 mm was then cut from a plate consisting of a tungsten-copper composite with a copper concentration of 15% by weight (designation T 750). In a suitable casting unit, a tungsten tile 2, an OHFC copper foil measuring 0.10 mm in thickness 6, the T 750 intermediate tile 3 and an OFHC-copper block 4 measuring 20×40×10 mm were stacked. The stack was then back-cast with OHFC copper in an inert-gas oven in a hydrogen atmosphere at a temperature of 1250° C. That temperature was maintained for 30 minutes, ensuring sufficient coverage of the molten copper on all of the solid components of the structure. Following removal of the back-cast stack from the back-casting unit, the stack was milled on all sides. In the process, the back-cast copper was milled down to a residual thickness of 2 mm (see FIG. 3). In order to remove undesired copper deposits, the other surfaces were also milled on all sides. Subsequent ultrasonic testing and a metallographic probe taken from a the joint zone of a parallel sample showed that a solid material bond was formed in the entire stack during the cooling phase once the temperature fell below the copper melting point. Using the process described in the above-noted European patent specification EP 1 025 938, the laminated tiles produced in the back-casting process described above were joined with a Cu—Cr—Zr heat sink 5 in which the cooling structure 7 was worked in mechanically after removal from the HIP unit. The material sequence of the components is illustrated schematically in FIG. 2. The diverter plate 1 shown in FIG. 4 was produced in monoblock design in a similar process. A passage with a length of 10 mm and a diameter of 15.2 mm was bored through the center a block of tungsten 2 measuring 30×20×10 mm. A ring 3 with an outside diameter of 15 mm, a wall thickness of 1 mm and a length of 10 mm was made from a plate consisting of a tungsten-copper composite with a copper concentration of 20% by weight (designation T 800). An OHFC copper foil with a thickness of 0.1 mm, the ring 3 made from T 800 and a 15 mm long OFHC copper rod with a diameter of 13 mm were introduced into the passage bored through the tungsten block in accordance with the material sequence shown in FIG. 2. The tile bore was then back-cast with OFHC copper in an inert-gas oven in a hydrogen atmosphere at a temperature of 1250° C. for 30 min. After removal of the back-cast monoblock, a bore with a diameter of 12 mm concentric with the bore in the tungsten block was drilled into the back-cast copper. Upon completion of this processing phase, the laminated block exhibited an OFHC copper layer 4 with a thickness of 0.50 mm in the bore (see FIG. 5). The components produced in this way were joined with a Cu—Cr—Zr tube 5 with an outside diameter of 12 mm in an HIP process. The cooling structure 7 was introduced mechanically following removal from the HIP unit. Subsequent ultrasonic testing and metallographic analysis showed perfect bonding of the parts of the laminated component produced in this way. This application claims the priority, under 35 U.S.C. § 119, of Austrian patent application AT/GM 228/2003, filed Apr. 2, 2003; the disclosure of the prior application is herewith incorporated by reference in its entirety. |
|
06178219& | claims | 1. A method for repairing a holder for fuel elements in a reactor, which comprises removing a core grid from an upper end of a core shroud and replacing the core grid with a forged core grid connected to the core shroud via an adapter ring without a welding operation. 2. The method as claimed in claim 1, wherein the reactor is a boiling water reactor. 3. The method as claimed in claim 1, which comprises loosely inserting the adapter ring between the core grid and the core shroud. 4. The method as claimed in claim 1, which comprises shrink-fitting the adapter ring onto the core grid. 5. The method as claimed in claim 1, which comprises securing the connection of the adapter ring to the core grid by connecting elements. |
abstract | A guide thimble plug for a nuclear fuel assembly is provided, in which an internal threaded hole is formed through a main body so that the main body is coupled to a bottom nozzle by a screw coupling. An upper insert part is formed in the upper end of the main body. The upper insert part is inserted into a shock absorption tube. A thermal deformation prevention part is formed on the main body below the upper insert part and is recessed inward from the outer surface of the main body such that, when the main body is coupled to the guide thimble, a gap is defined between the thermal deformation prevention part and the guide thimble. The guide thimble and the shock absorption tube can be reliably fastened to the bottom nozzle, and thermal deformation of the guide thimble can be minimized. |
|
054815797 | claims | 1. In a fuel bundle assembly for a nuclear reactor wherein a plurality of fuel rods and at least one water rod extend between an upper tie plate and a lower tie plate, the improvement comprising: an upper end plug secured to the at least one water rod and having a recessed portion defined by upper and lower shoulders; and a latching mechanism for securing the at least one water rod to the upper tie plate comprising a latch bar mounted on an upper surface of the upper tie plate and rotatable into and out of said recess portion in said end plug when said end plug extends above said upper surface of said tie plate upon installation of said upper tie plate on the fuel bundle assembly. 2. The improvement of claim 1 wherein said at least one water rod comprises a pair of water rods and respective end plugs in side-by-side relationship, and wherein said upper tie plate includes a double water rod boss having a pair of apertures enabling at least said end plugs of said pair of water rods to pass through and extend above said upper tie plate, and wherein said latch bar includes laterally opposite portions simultaneously rotatable into and out of opposed recessed portions on the end plugs of said pair of water rods. 3. The improvement of claim 2 wherein said latch bar is free to rock from side to side when the latch bar is rotated into said cut-outs to thereby accommodate radiation growth of said pair of water rods. 4. The improvement of claim 3 wherein a lower surface of said latch bar is formed with a projecting rib extending perpendicular to a centerline between centers of said pair of water rods, said rib in engagement with said upper surface of said tie plate thereby serving as a pivot axis for said latch bar. 5. The improvement of claim 1 and further including a locking pin engageable between said latch bar and said upper tie plate to prevent said latch bar from rotating out of said cut-out. 6. The improvement of claim 2 and further including a locking pin engageable between said latch bar and said upper tie plate to prevent said latch bar from rotating out of said recessed portions. 7. The improvement of claim 5 wherein said locking pin is spring loaded. 8. The improvement of claim 5 wherein said locking pin includes a pair of spring fingers. 9. The improvement of claim 2 wherein said water rod double boss includes a hole located between said apertures for receiving a centering post passing through said latch bar, thereby enabling rotation of said latch bar relative to said upper tie plate. 10. The improvement of claim 2 wherein said water rod double boss includes a projection and a first through hole therein extending parallel to said apertures, and wherein said latch bar includes a second through hole alignable with said first through hole when said latch bar is rotated into said recessed portions: and a locking pin insertable within said first and second through holes to thereby prevent rotation of said latch bar out of said recessed portions. 11. The improvement of claim 1 wherein said at least one water rod comprises a pair of water rods and respective end plugs in side-by-side relationship, and wherein said upper tie plate includes a double water rod boss having a pair of apertures enabling at least said end plugs of said pair of water rods to pass through and extend above said upper tie plate, said laterally opposed recessed portions comprise circumferential grooves in the respective end plugs, and further wherein said latch bar includes a pair of hooks facing in opposite directions and simultaneously rotatable into engagement with said circumferential grooves. 12. The improvement of claim 11 wherein said pair of hooks are provided with rounded water rod engagement surfaces. 13. The improvement of claim 11 wherein said circumferential grooves are each defined by a square base and each hook has a corresponding generally square shaped water rod engagement surface. 14. A fuel bundle assembly for a nuclear reactor including a plurality of fuel rods and a pair of water rods extending between upper and lower tie plates, said fuel rods and said water rods passing through said upper tie plate; a latch bar mounted on said upper tie plate for securing said pair of water rods to said upper tie plate, said latch bar including means for accommodating differential thermal growth of said pair of water rods. 15. The fuel bundle of claim 14 wherein said water rods include end plugs having laterally recessed opposed portions located above said upper tie plate, and wherein said latch bar includes laterally opposite portions simultaneously rotatable into and out of said opposed recessed portions. 16. The fuel bundle of claim 15 wherein said means includes an elongated rib on a lower surface of said latch bar in engagement with said upper tie plate and forming a pivot axis for said latch bar. 17. The fuel bundle of claim 15 and including means for locking said latch bar in a locked position when said laterally opposite portions are located within said opposed recessed portions. 18. The fuel bundle of claim 14 and including means for biasing said upper tie plate away from said plurality of fuel rods and said pair of water rods. 19. The fuel bundle of claim 15 wherein said laterally opposed recessed portions comprise 360.degree. circumferential grooves, and wherein said latch bar is formed with a pair of hooks having rounded water rod engagement surfaces facing in opposite directions. 20. The fuel bundle of claim 15 wherein said laterally opposed recessed portions comprise 360.degree. circumferential grooves, a base of each groove having a substantially square profile, and wherein said latch bar is formed with a pair of hooks having substantially squared slob opening in opposite directions. |
abstract | A charged particle beam writing apparatus and a charged particle beam writing method capable of shortening the time necessary to generate shot data and improving writing throughput. A graphic pattern defined in write data is divided into graphics represented in shot units. The divided graphics are temporarily stored in a memory and are distributed to their corresponding subfield areas while developing position information defined in a state of being compressed to write data. When each pattern is written by multi-pass writing, graphics divided at a first pass are used for distribution to subfield areas after a second pass. |
|
058728252 | claims | 1. An apparatus for inerting and venting the containment atmosphere in a nuclear power station, comprising: a supply line for an inerting agent communicating with a containment vessel of a nuclear power station; a vent line for containment atmosphere communicating with the containment; and a joint reversible activity holdup device communicating with said vent line and with said supply line. a line for supplying an inerting agent to and for venting containment atmosphere from a containment of a nuclear power station, said line communicating with the containment; and a reversible activity holdup device inserted in said line. 2. The apparatus according to claim 1, wherein said activity holdup device includes a filter element mounted rotatably about an axis. 3. The apparatus according to claim 1, wherein said activity holdup device includes adsorption material selected from the group consisting of activated charcoal and a molecular sieve. 4. The apparatus according to claim 1, wherein said activity holdup device includes adsorption material having an inner exchange surface of at least 1000 m.sup.2 /m.sup.3. 5. The apparatus according to claim 1, which further comprises an aerosol separating device communicating with said activity holdup device for separating aerosols from the containment atmosphere. 6. The apparatus according to claim 1, which further comprises a superheater connected upstream from said activity holdup device in a flow of the inerting agent. 7. The apparatus according to claim 1, which further comprises a control device for setting a temperature of an inerting agent entering said activity holdup device. 8. The apparatus according to claim 1, wherein the inerting agent comprises water vapor. 9. The apparatus according to claim 1, which further comprises a stack communicating with said vent line. 10. The apparatus according to claim 1, which further comprises a selfclosing shutoff fitting connected in said supply line. 11. An apparatus for inerting and venting a containment atmosphere in a nuclear power station, comprising: 12. The apparatus according to claim 11, wherein said activity holdup device includes adsorption material selected from the group consisting of activated charcoal and a molecular sieve. 13. The apparatus according to claim 11, wherein said activity holdup device includes adsorption material having an inner exchange surface of at least 1000 m.sup.2 /m.sup.3. 14. The apparatus according to claim 11, which further comprises an aerosol separating device communicating with said activity holdup device for separating aerosols from the containment atmosphere. 15. The apparatus according to claim 11, which further comprises a superheater connected upstream from said activity holdup device in a flow of the inerting agent. 16. The apparatus according to claim 11, which further comprises a control device for setting a temperature of an inerting agent entering said activity holdup device. 17. The apparatus according to claim 11, which further comprises a stack communicating with said vent line. 18. The apparatus according to claim 11, which further comprises a selfclosing shutoff fitting connected in said supply line. 19. A method of inerting and venting a containment atmosphere in a containment of a nuclear power station, which comprises: feeding inerting agent into a containment in a feed flow, venting a containment atmosphere from the containment in a vent flow, and alternatingly conducting the feed flow and the vent flow through a reversible activity holdup device. 20. The method according to claim 19, which comprises, in the activity holdup device, separating radioactive material out of the vent flow of the vented containment atmosphere and conveying the radioactive material back into the containment with the feed flow of the inerting agent through the activity holdup device. 21. The method according to claim 19, which further comprises regulating a temperature of the inerting agent. 22. The method according to claim 19, which further comprises superheating the inerting agent. |
051075296 | claims | 1. Apparatus comprising: (a) a plurality of juxtaposed members, each member having a surface defining a filter for attenuating electromagnetic radiation, the filter of each member being comprised of a plurality of adjacent and unique preselected attenuation patterns, the attenuation provided by the filter varying throughout at least selected portions of the surface, at least a portion of the filter of each member overlapping a portion of the filter of all other members; (b) motive means operatively coupled to the members for independently moving each member relative to an electromagnetic radiation emitter, the emitter being disposed to emit radiation along a path intersected by the overlapping portions of the filters, movement of a member altering attenuation of the radiation along the path; and, (c) control means operatively coupled to the motive means for controlling the operation of the motive means to alter attenuation provided by the overlapping portions of the filters. a) a plurality of juxtaposed disks, each having an annular filter region for attenuating electromagnetic radiation according to preselected patterns defining attenuation patterns, the attenuation patterns varying throughout at least selected angular positions along the filter region of each disk, at least a portion of the filter region of each disk overlapping a portion of the filter region of all other disks; b) motive means operatively coupled to the disks for independently rotating each disk relative to an electromagnetic radiation emitter disposed to emit radiation along a path that is intersected by the overlapping portions of the filter regions, rotation of a disk relative to the emitter attenuating emitted radiation according to a selected combination of attenuation patterns, the attenuated radiation having a pattern defining a radiation pattern that corresponds to the selected combination of attenuation patterns; and c) control means operatively coupled to the motive means for automatically selecting the combinations of attenuation patterns to alter attenuation provided by the overlapping portions of the filter regions. a) a plurality of juxtaposed disks, each having an annular filter region for attenuating x-rays according to preselected patterns defining attenuation patterns, the attenuation patterns varying throughout at least selected angular positions along the filter region of each disk, the attenuation patterns being defined by one of a plurality of discrete cells or a substantial continuum of irregularities in a surface of each disk, at least a portion of the annular region of each disk defining a constant attenuation region for providing substantially constant attenuation to x-ray, at least a portion of the filter region of each disk overlapping a portion of the filter region of all other disks; b) motive means operatively coupled to the disks for independently rotating each disk relative to an x-ray emitter, the emitter being disposed to emit x-ray along a path intersected by the overlapping portions of the filter regions, rotation of a disk relative to the emitter attenuating emitted radiation according to a selected combination of attenuation patterns, the attenuated radiation having a pattern defining a radiation pattern that corresponds to the selected combination of attenuation patterns, the motive means being operative to substantially align the constant attenuation region of each disk with the path to define a parked position for irradiating a subject to obtain a preliminary radiographic image; and, c) control means operatively coupled to the motive means for automatically selecting the combinations of attenuation patterns to alter attenuation provided by the overlapping portions of the filter regions, the control means being operatively coupled to receive and process the preliminary image, the control means further comprising means for determining locations and magnitudes of at least overexposures in the preliminary image, the control means rotating the disks to select one of the unique combinations of attenuation patterns to compensate for the overexposures. a) providing a plurality of juxtaposed disks, each having an annular filter region for attenuating electromagnetic radiation according to preselected patterns defining attenuation patterns; b) rotating the disks to a preselected angular position; c) irradiating a subject with electromagnetic radiation directed through the annular regions of each disk when the disks have been rotated to the preselected angular position to obtain a preliminary image; d) determining locations and magnitudes of at least overexposures in the preliminary image; and, e) rotating, based upon step (d), at least one disk to select a unique combination of attenuation patterns and irradiating the subject with electromagnetic radiation directed through the selected patterns, the attenuated radiation having a pattern corresponding to the selected combination of attenuation patterns, the combination of attenuation patterns being selected to compensate for the overexposures in the preliminary image. 2. Apparatus according to claim 1 wherein each member is a disk, the surface is an annulus of the disk and the movement provided by the motive means is rotation of a disk. 3. Apparatus according to claim 2 wherein each disk has an area in the annulus that provides substantially constant attenuation to electromagnetic radiation and defining a constant attenuation region, and the disks are rotatable to substantially align the constant attenuation regions of each disk with the path to define a parked position. 4. Apparatus according to claim 3 wherein the control means is operative to rotate the disks to the parked position for irradiating a subject to obtain a preliminary radiographic image. 5. Apparatus according to claim 4 wherein the control means is operative, based upon the preliminary image, to rotate the disks and thereby alter the attenuation provided by the overlapping filters to adjust for at least overexposures in the preliminary image. 6. Apparatus according to claim 2 wherein the electromagnetic radiation comprises x-rays. 7. Apparatus according to claim 6 wherein rotation of a disk results in a selected, unique combination of attenuation patterns along the path, the attenuated radiation having a pattern that corresponds to the selected combination of attenuation patterns. 8. Apparatus according to claim 7 wherein the control means is operative to rotate the disks to a selected position for irradiating a subject to obtain a preliminary radiographic image and being operatively coupled to receive and process the preliminary image, the control means further comprising means for determining locations and magnitudes of at least overexposures in the preliminary image, the control means rotating the disks to select one of the unique combinations of attenuation patterns to compensate for the regions of overexposure. 9. Apparatus according to claim 8 wherein each disk has an area in the annulus that provides substantially constant attenuation to electromagnetic radiation and defining a constant attenuation region, and the disks are rotatable to substantially align the constant attenuation regions of each disk with the path to define said selected position. 10. Apparatus according to claim 1 wherein each pattern is defined by a plurality of discrete cells in a surface of the disk. 11. Apparatus according to claim 1 wherein each pattern is defined by a substantially continuum of irregularities in a surface of the disk. 12. Apparatus according to claim 10 or 11 wherein the patterns are formed by variations in a thickness of the filter. 13. Apparatus according to claim 2 wherein the disks are substantially concentric. 14. Apparatus according to claim 2 wherein the disks are non-concentric but are disposed in substantially parallel planes. 15. Apparatus comprising: 16. Apparatus according to claim 15 wherein each disk has an annular area that defines a constant attenuation region for providing substantially constant attenuation to electromagnetic radiation, and the disks are rotatable to substantially align the constant attenuation regions of each disk with the path to define a parked position, the control means being operative to rotate the disks to the parked position for irradiating a subject to obtain a preliminary radiographic image. 17. Apparatus according to claim 16 wherein the control means is operatively coupled to receive and process the preliminary image, and the control means further comprises means for determining locations and magnitudes of at least overexposures in the preliminary image, the control means rotating the disks to select one of the unique combinations of attenuation patterns to compensate for the overexposures. 18. Apparatus according to claim 16 wherein the filter of each disk is comprised of plurality of adjacent and unique preselected attenuation patterns. 19. Apparatus according to claim 19 wherein each pattern is defined by a plurality of discrete cells in a surface of the disk. 20. Apparatus according to claim 18 wherein each pattern is defined by a substantial continuum of irregularities in a surface of the disk. 21. Apparatus according to claim 19 or 20 wherein the patterns are formed by variations in thickness of the filter. 22. Apparatus comprising: 23. Apparatus according to claim 22 wherein the patterns are formed by variations in thickness of the filter. 24. Method comprising: 25. Article comprising a disk having an annulus at least a portion of which defines a filter for attenuating electromagnetic radiation according to preselected radiation patterns, the patterns varying throughout angular positions along the annulus, the attenuation patterns being defined by one of a plurality of discrete cells or a substantial continuum of irregularities in a surface of the disk. 26. Article according to claim 25 wherein a portion of the annulus of the disk contains a region defining a constant attenuation region for providing substantially constant attenuation to electromagnetic radiation. 27. Article according to claim 25 wherein the patterns are defined by variations in a thickness of the filter. 28. Article according to claim 27 wherein the variations in the thickness of the filter are defined by stamped depressions and peaks of varying thickness in the annulus. 29. Article according to claim 27 wherein the variations in the thickness of the filter are defined by milled depressions and peaks of varying thickness of the annulus. |
claims | 1. A system for storing spent nuclear fuel comprising:a shell forming a cavity, the shell having an open top end, a hermetically closed bottom end, a height and an opening in a side wall of the shell;a canister storing spent nuclear fuel positioned in the cavity, the cavity having a horizontal cross-section that accommodates no more than one of the canister;an inlet ventilation duct having an inlet opening, the inlet ventilation duct connected to the shell so as to enclose the opening of the shell, the inlet ventilation duct forming a hermetically sealed passageway from the inlet opening to the opening of the shell, the hermetically sealed passageway excluding the cavity; andthe opening of the shell positioned at a first vertical height above the bottom end of the shell and the inlet opening positioned at a second vertical height above the bottom end of the shell, wherein the second vertical height is greater than the first vertical height. 2. The system of claim 1 further comprising:a lid positioned atop the shell so as to substantially enclose the open top end of the shell, the lid being non-unitary with respect to the shell; andwherein the lid comprises an outlet ventilation duct forming a passageway from a top of the cavity to an ambient atmosphere. 3. The system of claim 1 further comprising an outlet ventilation duct forming a passageway from a top of the cavity to an ambient atmosphere. 4. The system of claim 3 wherein the outlet ventilation duct is hermetically connected to the shell. 5. The system of claim 1 further comprising a bottom plate, the shell positioned atop the bottom plate so that the bottom plate forms the hermetically closed bottom end, and wherein the bottom plate, the shell, and the inlet ventilation duet form an integral structure. 6. The system of claim 1 further comprising a concrete body surrounding the shell, the inlet ventilation duct extending through the concrete body. 7. The system of claim 1 further comprising a first of the inlet ventilation duct and a second of the inlet ventilation duct, wherein each of the first and second inlet ventilation ducts are substantially S-shaped. 8. The system of claim 1 further comprising means for insulating the inlet ventilation duct from the shell. 9. The system of claim 1 further comprising a base positioned below a grade, the shell and the inlet ventilation duct positioned atop the base. 10. The system of claim 1 further comprising:a ground having a grade; andwherein a major portion of the shell is positioned below the grade so that the opening in the side wall of the shell is below the grade, and the inlet opening is above the grade. 11. The system of claim 10 further comprising:a lid positioned atop the shell so as to substantially enclose the open top end of the shell, the lid being non-unitary with respect to the shell; andwherein an outlet air plenum is created between the lid and the canister, and an outlet ventilation duct that forms a passageway from the outer air plenum to an ambient atmosphere above the grade. 12. The system of claim 1 wherein the shell and the inlet ventilation duct are constructed of steel, the inlet ventilation duct being seal welded to the shell. 13. The system of claim 1 further comprising one or more support blocks located on a floor of the cavity. 14. The system of claim 1 further comprising:a lid positioned atop the shell so as to substantially enclose the open top end of the shell, the lid being non-unitary with respect to the shell;a first of the inlet ventilation duct and a second of the inlet ventilation duct, wherein each of the first and second inlet ventilation ducts are substantially S-shaped;one or more support blocks located on a floor of the cavity; the lid secured to a top of the shell, the lid comprising an outlet ventilation duct;a bottom plate; wherein the bottom plate, the shell, and the first and second inlet ventilation ducts form an integral structure;a concrete body surrounding the shell, the first and second inlet ventilation ducts extending through the concrete body;means for insulating the inlet ventilation duct from the shell;a ground having a grade;the shell positioned sufficiently below the grade so that the entire canister is below the grade;a base positioned below the grade, the shell and inlet ventilation duct positioned atop the base;wherein the shell, the inlet ventilation duct, and the bottom plate are constructed of steel and seal welded together; andwherein an outlet air plenum is created between the lid and the canister. 15. The system of claim 1 further comprising a lid positioned atop the shell so as to substantially enclose the open top end of the shell, the lid being non-unitary with respect to the shell. 16. The system of claim 1 further comprising:the shell and the inlet ventilation ducts being constructed of metal; anda concrete body surrounding the shell, the inlet ventilation duct extending through the concrete body. 17. A system for storing spent nuclear fuel comprising:a shell forming a cavity, the shell having an open top end, a hermetically closed bottom end, a height and an opening in a side wall of the shell;a multi-purpose canister storing spent nuclear fuel positioned in the cavity so that an annular space exists between the shell and the multi-purpose canister, the cavity having a horizontal cross-section that accommodates no more than one of the multi-purpose canister;an inlet ventilation duct extending from an outside surface of the shell and having an inlet opening, the inlet ventilation duct connected to the shell so as to enclose the opening of the shell, the inlet ventilation duct forming a hermetically sealed passageway from the inlet opening into the annular space via the opening of the shell;the opening of the shell positioned at a first vertical height above the bottom end of the shell and the inlet opening positioned at a second vertical height above the bottom end of the shell, wherein the second vertical height is greater than the first vertical height; andwherein a line of sight does not exist through the hermetically sealed passageway from the inlet opening to the opening. 18. A system for storing spent nuclear fuel comprising:a shell forming a cavity, the shell having an open top end, a hermetically closed bottom end, a height and an opening in a side wall of the shell;a canister storing spent nuclear fuel positioned in the cavity, the cavity having a horizontal cross-section that accommodates no more than one of the canister;an inlet ventilation duct having an inlet opening, the inlet ventilation duct connected to the shell so as to enclose the opening of the shell, the inlet ventilation duct forming a hermetically sealed passageway exclusive of the cavity that extends from the inlet opening into the cavity via the opening of the shell; andthe opening of the shell positioned at a first vertical height above the bottom end of the shell and the inlet opening positioned at a second vertical height above the bottom end of the shell, wherein the second vertical height is greater than the first vertical height. 19. The system of claim 1 wherein the open top end of the cavity has a horizontal cross section through which the canister can pass. 20. The system of claim 17 wherein the open top end of the cavity has a horizontal cross section through which the multi-purpose canister can pass. 21. The system of claim 18 wherein the open top end of the cavity has a horizontal cross section through which the canister can pass. |
|
claims | 1. A 99mTc generator comprising:(a) a body portion having an inlet and an outlet; and(b) an ion exchange housed within said body portion, said ion exchange comprising carbon or graphite fibers impregnated with an acidic organophosphorus extractant selected from the group consisting of DEHPA, EHEHPA, and DTMPPA, and said ion exchange further comprising ions of 99Mo bound to said extractant. 2. A 99mTc generator according to claim 1, further comprising:(c) an aqueous solution having a pH of from about 1 to about 2 within said body portion and in contact with said ion exchange, said aqueous acid solution containing 99mTc that has been produced by radioactive decay of said 99Mo. 3. A 99mTc generator according to claim 2, wherein the pH of said aqueous solution is about 1. 4. A 99mTc generator according to claim 2, wherein the pH of said aqueous solution is about 2. 5. A 99mTc generator according to claim 2, wherein said aqueous solution is selected from the group consisting of hydrochloric acid and nitric acid. 6. A 99mTc generator according to claim 1, wherein said acidic organophosphorus extractant comprises DEHPA. 7. A 99mTc generator according to claim 1, wherein said acidic organophosphorus extractant comprises EHEHPA. |
|
055330894 | description | DETAILED DESCRIPTION OF THE INVENTION Reference is now directed to the accompanying drawing, wherein there is shown in FIG. 1 apparatus disclosing the invention and illustrating its mode of use. An instrument, indicated generally by the numeral 1, embodies the invention. It comprises a rack 2 and a unit 3 supported by the rack. The function of the rack is to support and position the unit between an x-ray emitting device or source 4 and the body 5 of a patient. The function of the unit is to collimate and limit rays 6 issuing from the source to a particular area of the body, and also to shield from the rays areas of the body surrounding the particular area. A photographic film 7 is disposed below a conventional table 8 supporting the body to obtain a representation of the x-rayed area of the body. As a means for supporting the unit relative to the source of x-rays and the body of the patient, the rack 2 may, accordingly, take various forms for such purpose. Here, a practical form of the rack for such purpose is illustrated. The rack 2 has a rear element 9 mounted for swivel movement relative to a support 10. A strut 11, pivoted at its rear end 12 to the element 9, is pivoted at its opposite end 13 to a second strut 14. The latter is pivoted at its forward end 15 to a universal joint 16, which in turn is swiveled upon a short rod 17 extending from a side 18 of a frame member 19 of the unit 3. Key elements defined by the pivots at the various joints of the rack are manipulative to make secure adjusted positions of the related components of the rack to one another. The rack is manually adjustable and extendible to position and support the unit 3 between the source 4 of x-rays and the body 5 of the patient. The frame member 19 of the unit 3 is multi-sided, preferably rectangular in configuration; and it is formed of cylindrical rod of aluminum or other lightweight material. The frame defines a continuous perimeter about an aperture 20, which aperture serves for passage of x-rays from the source 4 to a body 5 located beneath the unit. Depending from each of the sides 18 of the frame 19 of the unit 3 are separate panels 21 of flexible radio-opaque material, such as is provided by lead sheeting, or lead impregnated vinyl. Each panel is pivotally supported by a hinge 22 to the related side of the frame. The several panels may, accordingly, be selectively pivoted to one another about the frame to vary the size opening of the aperture at its bottom end. The panels are preferably rectangular in form and serve, when adjustably pivoted relative to one another, to define and limit as needed the dimension of the bottom or outlet end of the aperture 20, whereby x-rays issuing from the source 4 through the aperture are concentrated, limited and collimated as desired to impinge upon a particular area of the body of a patient underlying the aperture of the unit 3. Impingement of any of the rays upon a panel defining the aperture is absorbed by the radio-opaque material of the panel and, accordingly, is shuttered from contact with surrounding areas of the body of the patient; and only that portion of the rays intended to impinge upon the body of the patient passes through the aperture of the unit. In effect, as the panels about the frame of the unit are selectively pivoted to adjusted positions relative to one another, the direction of x-rays issuing from the source through the aperture of the unit to the body of a patient may be collimated, limited and beneficially controlled. The flexible nature of the panels enables portions of the panels which may be in contact with the body of the underlying patient to be flexed about the body. The several panels of the unit are provided with translucent perforations 24 along their lower ends. X-rays which may pass through these perforations and register upon the film 7 below the patient provide a scale indication of the size of the exit end of the aperture from which the rays project to the body of the patient. The several hinges 22 supporting the panels to the frame 19 of the unit 3 have a friction engagement with the frame, whereby they are held in their pivoted positions about the frame until the panels are re-pivoted to other positions. In FIG. 4 is shown a modified form of a hinge 25 which may be employed in supporting a panel to the frame of the unit. This hinge is in the form of a band which sleeves a ring of closely spaced holes 26 formed in the related tubing of the frame. A ball detent 27 disposed in a hole of the hinge is adapted under the load of a leaf spring 28 mounted to the hinge to engage in part in one of the holes 26 of the frame accordingly as the panel is pivoted about the frame, whereby the pivoted position of the related panel is adapted to be secured. And, it is apparent that as the panel is manually pivoted, its pivoted position and detent engagement about the frame may be readjusted, and the dimension of the aperture for passage of x-rays from the source to the body of the patient may be varied. While an embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes of form, design and arrangement may be made in its components without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art; and it is my intent, therefore, to claim the invention not only as shown and described, but also in all such forms and modifications thereof as may be reasonably construed to fall within the spirit of the invention and the scope of the appended claims. |
summary | ||
043552366 | claims | 1. An adjustable strength multipole permanent magnet comprising a plurality of axial layers of magnetic material wherein one layer can be angularly displaced with respect to an adjacent layer, each of said axial layers comprising a plurality of segments comprising an oriented, anisotropic permanent magnet material arranged in a ring so that there is a substantially continuous ring of permanent magnet material, each segment having a predetermined easy axis orientation within a plane perpendicular to the axis of the magnet. 2. The multipole permanent magnet of claim 1 wherein said magnetic material comprises a rare earth cobalt material. 3. The multipole permanent magnet of claim 2 wherein said rare earth cobalt material is samarium cobalt. 4. The multipole permanent magnet of claim 1 wherein said magnetic material comprises a ceramic ferrite. 5. The multipole permanent magnet of claim 1 wherein said magnet is a quadrupole magnet. 6. The quadrupole magnet of claim 5 having four axial layers. 7. The quadrupole magnet of claim 5 wherein each axial layer comprises sixteen segments. 8. The quadrupole magnet of claim 5 wherein each segment is essentially rectangular in cross-sectional shape. 9. The quadrupole magnet of claim 5 wherein the direction of the easy axis of each segment in each layer is determined by the formula: EQU .alpha.=2.theta. 10. The quadrupole magnet of claim 9 further having four axial layers wherein each axial layer comprises sixteen segments and wherein said anisotropic magnetic material comprises a rare-earth cobalt material. 11. The quadrupole magnet of claim 10 wherein said rare earth cobalt material is samarium cobalt. 12. The quadrupole magnet of claim 9 further having four axial layers wherein each axial layer comprises sixteen segments and wherein said anisotropic magnetic material comprises a ceramic ferrite. 13. An adjustable strength multipole permanent magnet assembly comprising a multipole permanent magnet having a plurality of axial layers of magnetic material wherein one layer can be angularly displaced with respect to an adjacent layer and means connected to at least two adjacent axial layers for angularly displacing one layer with respect to the adjacent layer, each of said axial layers comprising a plurality of segments comprising an oriented, anisotropic, permanent magnet material arranged in a ring so that there is a substantially continuous ring of permanent magnet material, each segment having a predetermined easy axis orientation within a plane perpendicular to the axis of the magnet assembly. 14. The magnet assembly of claim 13 wherein said material comprises a rare-earth cobalt material. 15. The magnet assembly of claim 13 wherein said material comprises a ceramic ferrite. 16. The magnet assembly of claim 13 wherein said adjustable means comprises means for varying the aperture field strength to said magnet in an approximately linear manner. 17. The magnet assembly of claim 13 wherein said magnet is a quadrupole magnet. 18. The magnet assembly of claim 17 wherein the direction of the easy axis of each segment in each layer is determined by the formula: EQU .alpha.=2.theta. 19. The magnet assembly of claim 17 having four axial layers wherein each axial layer comprises sixteen segments wherein said anisotropic magnetic material comprises a rare-earth cobalt material. 20. The magnet assembly of claim 19 wherein said adjustment means comprises means for rotatably displacing the two outer layers of the magnet with respect to the two inner layers of the magnet. 21. An adjustable strength multipole permanent magnet assembly comprising a multipole permanent magnet having a plurality of axial layers of magnetic material wherein one layer can be angularly displaced with respect to an adjacent layer and means connected to at least two adjacent axial layers for angularly displacing one layer with respect to the adjacent layer, each of said axial layers comprising a plurality of segments comprising an oriented, anisotropic, permanent magnet material arranged in a ring so that there is a substantially continuous ring of permanent magnet material, each segment having a predetermined easy axis orientation within a plane perpendicular to the axis of the magnet assembly, said assembly having four axial layers wherein said adjustment means comprises means for rotatably displacing the two outer layers of the magnet with respect to the two inner layers of the magnet and wherein said adjustment means further comprises a rod moveable in a direction perpendicular to the axis of the magnet, a first lever arm connected at one end to the rod and at the other end to one outer axial layer of the magnet, a second lever arm connected at one end to the rod and at the other end to the two inner axial layers of the magnet, and a third lever arm connected at one end to the rod and at the other end to the other outer axial layer of the magnet so that upon inward movement of the rod, the two other axial layers of the magnet are rotatably displaced in one direction and the two inner axial layers of the magnet are displaced angularly in the opposite direction. 22. The magnet assembly of claim 21 wherein the angular displacement of the outer layers is equal to the angular displacement of the inner layers. 23. The magnet assembly of claim 21 wherein all of said lever arms are equal in length and said length is equal to the distance from the point of attachment of the arm to the axial layer to the axial center of the quadrupole. 24. A method for focusing a charged particle beam, said method comprising focusing said charged particle beam by passing the beam through the aperture of an adjustable strength multipole permanent magnet, said magnet comprising a plurality of axial layers of magnetic material wherein one layer can be angularly displaced with respect to an adjacent layer, each of said axial layer comprising a plurality of segments comprising an oriented, anisotropic permanent magnet material arranged in a ring so that there is a substantially continuous ring of permanent magnet material, each segment having a predetermined easy axis orientation within a plane perpendicular to the axis of the magnet. 25. The method according to claim 24 wherein said magnetic material comprises a rare earth cobalt material. 26. The method according to claim 25 wherein said rare earth cobalt material is samarium cobalt. 27. The method according to claim 24 wherein said magnetic material comprises a ceramic ferrite. 28. The method according to claim 24 wherein said magnet is a quadrupole magnet. 29. The method according to claim 28 wherein said magnet comprises four axial layers. 30. The method according to claim 28 wherein each axial layer comprises sixteen segments. 31. The method according to claim 28 wherein each segment is essentially rectangular in cross-sectional shape. 32. The method according to claim 28 wherein the direction of the easy axis of each segment in each layer is determined by the formula; EQU .alpha.=2.theta. 33. The method according to claim 32 wherein each axial layer comprises sixteen segments and wherein said anisotropic magnetic material comprises a rare-earth cobalt material. 34. The method according to claim 33 wherein said rare-earth cobalt material is samarium cobalt. 35. The method according to claim 32 wherein said anisotropic magnetic material comprises a ceramic ferrite. 36. A method for focusing a charged particle beam, said method comprising passing the beam through the aperture of an adjustable strength multipole permanent magnet assembly, said assembly comprising a multipole permanent magnet having a plurality of axial layers of magnetic material wherein one layer can be angularly displaced with respect to an adjacent layer and means connected to at least two adjacent axial layers for angularly displacing one layer with respect to the adjacent layer, each of said axial layers comprising a plurality of segments comprising an oriented, anisotropic, permanent magnet material arranged in a ring so that there is a substantially continuous ring of permanent magnet material, each segment having a predetermined easy axis orientation within a plane perpendicular to the axis of the magnet assembly. 37. The method in accord with claim 36 wherein said material comprises a rare-earth cobalt material. 38. The method in accord with claim 36 wherein said material comprises a ceramic ferrite. 39. The method in accord with claim 36 wherein said adjustable means comprises for varying the aperture field strength of said magnet in an approximately linear manner. 40. The method in accord with claim 36 wherein said magnet is a quadrupole magnet. 41. The method in accord with claim 40 wherein the direction of the easy axis of each segment in each layer is determined by the formula; EQU .alpha.=2.theta. 42. The method in accord with claim 40 wherein each axial layer comprises sixteen segments wherein said anisotropic magnetic material comprises a rare-earth cobalt material. 43. The method in accord with claim 42 wherein said adjustment means comprises means for rotatably displacing the two inner layers of the magnet with respect to the two inner layers of the magnet. 44. The method in accord with claim 43 wherein said adjustment means further comprises a rod moveable in a direction perpendicular to the axis of the magnet, a first lever arm connected at one end to the rod and at the other end to one outer axial layer of the magnet, a second lever arm connected at one end to the rod and at the other end to the two inner axial layers of the magnet, and a third lever arm connected at one end to the rod and at the other end to the other outer axial layer of the magnet so that upon inward movement of the rod, the two other axial layers of the magnet are rotatably displaced in one direction and the two inner axial layers of the magnet are displaced angularly in the opposite direction. 45. The method in accord with claim 44 wherein the angular displacement of the outer layers is equal to the angular displacement of the inner layers. 46. The method in accord with claim 44 wherein all of said lever arms are equal in length and said length is equal to the distance from the point of attachment of the arm to the axial layer to the axial center of the quadrupole. |
description | This application claims priority to U.S. Provisional Patent Application No. 63/023,385, filed on May 12, 2020, which is incorporated herein by reference. The present application is related to x-ray windows. X-ray windows are used in expensive systems requiring high reliability. High system requirements result in demanding characteristics of the x-ray window. The following definitions, including plurals of the same, apply throughout this patent application. As used herein, the term “identical material composition” means exactly identical or identical within normal manufacturing tolerances. As used herein, the term “g/cm3” means grams per cubic centimeters. As used herein, the term “minimum thickness” means the smallest/minimum thickness of the specified material in the aperture 15 or 35. As used herein, the terms “on”, “located at”, and “adjacent” mean located directly on or located over with some other solid material between. The terms “located directly on”, “adjoin”. “adjoins”, and “adjoining” mean direct and immediate contact. As used herein, the term “nm” means nanometer(s). As used herein, the term “parallel” means exactly parallel, parallel within normal manufacturing tolerances, or nearly parallel such that any deviation from exactly parallel would have negligible effect for ordinary use of the device. As used herein, the terms “top-side” and “bottom-side” refer to top and bottom-sides or faces in the figures, but the device may be oriented in other directions in actual practice. The terms “top” and “bottom” are used for convenience of referring to these sides or faces. 10, 30, 50, 60, and 70 are x-ray window embodiments. The support-frame 11 can encircle an aperture 15. The support-frame 11 can include an inner-side 11i facing the aperture 15 and an outer-side 11o facing outward and opposite of the inner-side 11i. The support-frame 11 can include a top-side 11T and a bottom-side 11B opposite of each other. The boron-film 12 can include a near-side 12N (nearer the support-frame 11) and a far-side 12F (farther from the support-frame 11). Method step 90 shows an upper-boron-film 12u and a lower-boron-film 12L. The annular-film 32 can include an aperture 35, a near-side 32N (nearer the support-frame 11) and a far-side 32F (farther from the support-frame 11). The thin-film 52 can be an aluminum-film or a film made of another material. The thin-film 52 can be a stack of multiple layers/multiple thin-films. 80 and 90 are steps in a method of making x-ray windows. Wafer 81 has a top-side 81T and a bottom-side 81B. Wafer 81 is located in an oven 82. Useful characteristics of x-ray windows include low gas permeability, low outgassing, high strength, low visible and infrared light transmission, high x-ray flux, made of low atomic number materials, corrosion resistance, high reliability, and low-cost. Each x-ray window design is a balance between these characteristics. An x-ray window can combine with a housing to enclose an internal vacuum. The internal vacuum can aid device performance. For example, an internal vacuum for an x-ray detector (a) minimizes gas attenuation of incoming x-rays and (b) allows easier cooling of the x-ray detector. Permeation of a gas through the x-ray window can degrade the internal vacuum. Thus, low gas permeability is a desirable x-ray window characteristic. Outgassing from x-ray window materials can degrade the internal vacuum of the device. Thus, selection of materials with low outgassing is useful. The x-ray window can face vacuum on one side and atmospheric pressure on an opposite side. Therefore, the x-ray window may need strength to withstand this differential pressure. Visible and infrared light can cause undesirable noise in the x-ray detector. The ability to block transmission of visible and infrared light is another useful characteristic of x-ray windows. A high x-ray flux through the x-ray window allows rapid functioning of the x-ray detector. Therefore, high x-ray transmissivity through the x-ray window is useful. Detection and analysis of low-energy x-rays is needed in some applications. High transmission of low-energy x-rays is thus another useful characteristic of x-ray windows. X-rays can be used to analyze a sample. X-ray noise from surrounding devices, including from the x-ray window, can interfere with a signal from the sample. X-ray noise from high atomic number materials are more problematic. It is helpful, therefore, for the x-ray window to be made of low atomic number materials. X-ray windows are used in corrosive environments, and may be exposed to corrosive chemicals during manufacturing. Thus, corrosion resistance is another useful characteristic of an x-ray window. X-ray window failure is intolerable in many applications. For example, x-ray windows are used in analysis equipment on Mars. High reliability is a useful x-ray window characteristic. X-ray window customers demand low-cost x-ray windows with the above characteristics. Reducing x-ray window cost is another consideration. The present invention is directed to various x-ray windows, and methods of making x-ray windows, that satisfy these needs. Each x-ray window or method may satisfy one, some, or all of these needs. As illustrated in FIGS. 1-7, x-ray windows 10, 30, 50, 60, and 70 can include a boron-film 12 on a support-frame 11, and spanning an aperture 15 of the support-frame 11. These x-ray windows 10, 30, 50, 60, and 70 can include the following characteristics: low gas permeability, low outgassing, high strength, low visible and infrared light transmission, high x-ray flux, made of low atomic number materials, corrosion resistance, high reliability, and low-cost. The boron-film 12 can be the main support structure spanning the aperture 15 of the support-frame 11, and can be thicker than any other material spanning the aperture 15. Example lower limits of a minimum thickness Th12 of the boron-film 12 across the aperture include: Th12≥25 nm, Th12≥50 nm, Th12≥100 nm, Th12≥300 nm, or Th12≥500 nm. Example upper limits of a minimum thickness Th12 of the boron-film 12 across the aperture include: and Th2≤500 nm, Th12≤750 nm, ≤1200 nm, Th12≤1500 nm, Th12≤3000 nm, or Th12≤10,000 nm. The support-frame 11 can have a ring shape, can encircle the aperture 15, or both. The support-frame 11 can have a top-side 11T and a bottom-side 11B, which can be opposite of each other and parallel with respect to each other. The support-frame 11 can have an inner-side 11i facing the aperture 15 and an outer-side 11o opposite of the inner-side 11i. The inner-side 11i and the outer-side 11o can extend between and can join the top-side 11T and the bottom-side 11B. The support-frame 11 (and the wafer 81 described below) can comprise silicon, such as for example ≥30, ≥50, ≥90, or ≥95 mass percent silicon. The support-frame 11 (and the wafer 81 described below) can comprise silicon dioxide, such as for example ≥30, ≥50, ≥90, or ≥95 mass percent silicon dioxide. The boron-film 12 can have a near-side 12N (nearer the support-frame 11) and a far-side 12F (farther from the support-frame 11), opposite of each other. The near-side 12N of the boron-film 12 can adjoin and/or be hermetically-sealed to the top-side 11T of the support-frame 11. The hermetic-seal can be a direct bond between the top-side 11T of the support-frame 11 and the boron-film 12. The hermetic-seal can be free of aluminum or an aluminum-film. Example weight percentages of boron, throughout the entire boron-film 12, include ≥80, ≥90, ≥95, ≥97, ≥98, or ≥99 weight percent. Example weight percentages of hydrogen, throughout the entire boron-film 12, include ≥0.01, ≥0.05, ≥0.1, ≥0.5, ≥0.9, ≥2, or ≥4 weight percent hydrogen. Example density, throughout the entire boron-film 12, includes ≥1.94 g/cm3, ≥2.04 g/cm3, or ≥2.1 g/cm3 and ≤2.18 g/cm3, ≤2.24 g/cm3, or ≤2.34 g/cm3. For example, the boron-film 12 can have 99.1 weight percent boron, 0.9 weight percent hydrogen, and density of 2.14 g/cm3. A window with these material properties can be manufactured as noted in the METHOD section below. The aperture 15 of the support-frame 11 can consist of thin films spanning the entire aperture. The aperture 15 of the support-frame 11 can be free of material of the support-frame 11, free of ribs, or both. As illustrated in FIGS. 3-4 and 7, x-ray windows 30 and 70 can further comprise an annular-film 32 on the bottom-side 11B of the support-frame 11. The annular-film 32 can be hermetically-sealed to the support-frame 11. The annular-film 32 can adjoin the bottom-side 11B of the support-frame 11. An aperture 35 of the annular-film 32 can be aligned with the aperture 15 of the support-frame 11. The annular-film 32 can be absent from, not extend into, and not cross the aperture 15 of the support-frame 11. The annular-film 32 can have material composition as described above for the boron-film 12. The boron-film 12 and the annular-film 32 can have an identical material composition. The boron-film 12 and the annular-film 32 can have similar thickness. For example |Th12−Th32|/Th12, where Th12 is a minimum thickness of the boron-film 12 and Th32 is a minimum thickness of the annular-film 32. Addition of the annular-film 32 can improve the ability of the x-ray window to withstand thermal stress during rapid or large temperature changes and can improve bonding of the x-ray window to a housing. The above benefits are particularly applicable if the annular-film 32 is similar in material and thickness to the boron-film 12, X-ray windows 30 and 70, with the annular-film 32, can be combined with any other x-ray window examples described herein, including those shown in any of FIGS. 1 and 5-6. As illustrated in FIGS. 5-7, a stack of films, including the boron-film 12 and a thin-film 52, can span the aperture 15 of the support-frame 11. The thin-film 52 can be an aluminum-film. Example material compositions of the aluminum-film include ≥25, ≥50, or ≥75 weight percent aluminum throughout the entire aluminum-film. Addition of the aluminum-film can improve the ability of the x-ray window to block visible light. The aperture 15 can consist only of the boron-film 12 and the aluminum-film. The thin-film 52 can be located on the far-side 12F of the boron-film 12, as illustrated in FIG. 5. Because of superior corrosion resistance of the boron-film 12, a more likely location for the thin-film 52 is on the near-side 12N, as illustrated in FIGS. 6-7. The thin-film 52 can adjoin a central portion of the near-side 12N of the boron-film 12. The thin-film 52 on the far-side 12F of the boron-film 12 can be combined with the annular-film 32 (FIGS. 3 and 7). The thin-film 52 on the far-side 12F of the boron-film 12 can be combined with the thin-film 52 on the near-side 12N (FIGS. 6-7). An outer portion or outer ring of the near-side 12N of the boron-film 12 can be attached to or adjoin the support-frame 11. A junction of the boron-film 12 and the support-frame 11 can be free of the thin-film 52. The thin-film 52 can extend onto, cover, or adjoin the inner-side 11i and the bottom-side 11B of the support-frame 11, as illustrated in FIG. 6. The thin-film 52 can extend onto, cover, or adjoin the inner-side 11i of the support-frame 11 and the far-side 32F of the annular-film 32, as illustrated in FIG. 7. Because aluminum has a higher atomic number than boron, it can be useful to have a relatively thin layer of aluminum. Thus for example, Th52≤0.5*Th12, Th52≤0.3*Th12, Th52≤0.1*Th12, where Th52 is a minimum thickness of the thin-film 52 in the aperture 15 and Th12 is a minimum thickness of the boron-film 12 in the aperture 15. Other example relationships, for the thin-film 52 to have sufficient thickness, include Th52≥0.001*Th12, Th52≥0.01*Th12, or Th52≥0.1*Th12. The boron film 12 can be the primary film or only film spanning the aperture 15. Thus, for example, ThF≤1.1*Th12, ThF≤1.25*Th12, ThF≤1.5*Th12, or ThF≤2*Th12. The aluminum-film and the boron-film 12 can be the only solid structures spanning the aperture 15 of the support-frame 11. The boron film 12 and the aluminum-film can be the primary films, or only films, spanning the aperture 15. Thus, for example, ThF≤1.1*(Th12+Th52), ThF≤1.25*(Th12+Th52), ThF≤1.5*(Th12+Th52), or ThF≤2*(Th12+Th52). ThF is a minimum thickness of the films in the aperture 15. The x-ray window can be hermetically sealed to a housing, with an internal vacuum. The boron-film 12 can face atmospheric pressure and the aluminum-film can face a vacuum. Method A method of manufacturing an x-ray window can comprise some or all of the following steps, which can be performed in the following order. There may be additional steps not described below. These additional steps may be before, between, or after those described. The method can comprise placing a wafer 81 in an oven 82; introducing a gas into the oven 82, the gas including boron, and forming boron-film(s) 12 on the wafer 81 (step 80 in FIG. 8 or step 90 in FIG. 9). The gas can include diborane, such as for example ≥5 molar percent diborane and ≥70 molar percent argon. Deposition temperature can be adjusted to control percent hydrogen and percent boron. Lower (higher) temperature can result in in increased (decreased) hydrogen in the boron-film 12. For example, a temperature of 390° C. can result in about 1% H in the boron-film 12. Other example temperatures in the oven 82, during formation of the boron-film(s) 12, include ≥50° C., ≥100° C., ≥200° C., ≥300° C., or ≥340° C., and ≤340° C., ≤380° C., ≤450° C., ≤525° C., ≤550° C., or ≤600° C. Formation of the boron-film 12 can be plasma enhanced, in which case the temperature of the oven 82 can be relatively lower. A pressure in the oven can be relatively low, such as for example 60 pascal. Higher pressure deposition might require a higher process temperature. As illustrated in FIG. 9, the wafer 81 can have a top-side 81T and a bottom-side 81B. The top-side 81T and the bottom-side 81B can be opposite of each other and can be parallel with respect to each other. Both the top-side SIT and the bottom-side 81B can be exposed to the gas (mount or hold the wafer at its outer edges). Forming the boron-film(s) 12 can include forming an upper-boron-film 12U on the top-side 81T of the wafer 81 and forming a lower-boron-film 12L on the bottom-side 81B of the wafer 81. Here is an example of deposition to form boron-film(s) 12 with about 99.1 weight percent boron, 0.9 weight percent hydrogen, and density of 2.14 g/cm3: A wafer 81 is loaded into the oven 82. The furnace is evacuated (about 450 mTorr) and temperature stabilized at ˜390° C. A gas with 15 molar percent diborane and 85 molar percent argon is introduced into the oven, resulting in deposition of the boron-film(s) 12. Oven 82 pressure is controlled by an adjustable butterfly valve at the vacuum inlet. After step 80, the method can further comprise etching through a center of the wafer 81 at the bottom-side 81B to form a support-frame 11 encircling an aperture 15 (see FIGS. 1-2). After step 90, the method can further comprise etching through a center of the lower-boron-film 12S to form an annular-film 32 and etching through a center of the wafer 81 at the bottom-side 81B to form a support-frame 11 encircling an aperture 15 (see FIGS. 3-4). The annular-film 32 can be used as a mask to etch the wafer 81 to form the support-frame 11. Etch of the wafer can continue up to the boron-film 12 or upper-boron-film 12U. A resist can be used to form the desired annular-shape of the annular-film 32 or the support-frame 11. A solution of potassium ferricyanide, a fluorine plasma (e.g. NF3, SF6, CF4), or both, can be used to etch the lower-boron-film 12S. Example chemicals for etching the wafer 81 include ammonium hydroxide, cesium hydroxide, potassium ferricyanide, potassium hydroxide, sodium hydroxide, sodium oxalate, tetramethylammonium hydroxide, or combinations thereof. The resist can then be stripped, such as for example with sulfuric acid and hydrogen peroxide (e.g. Nanostrip). Some (e.g. ≥25%, ≥50%, ≥75%, or ≥90%) of the near-side 12N and the far-side 12F of the boron-film 12 can both face atmospheric pressure, a gas, or both at this step in the process (after etch and before the deposition of thin-film 52/aluminum-film). A thin-film 52 (e.g. an aluminum-film) can be deposited on the far-side 12F of the boron-film 12 (FIG. 5). A thin-film 52 (e.g. an aluminum-film) can be deposited on the near-side 12N of the boron-film 12 (or the near-side 12N of the upper-boron-film 12U), on the inner-side 11i of the support-frame 11, on the bottom-side 11B of the support-frame 11, or combinations thereof (FIG. 6). If the x-ray window includes the annular-film 32, then deposition can occur on an inside surface and the far-side 32F of the annular-film 32 instead of on the bottom-side 11B of the support-frame 11 (FIG. 7). The method can further comprise applying an adhesion layer (e.g. Cr, Si, Zn) on the boron-film 12 before applying, or during application of, the aluminum-film. The x-ray window can then be sealed to a housing with a vacuum inside of the housing. The boron-film 12 (or upper-boron-film 12U) can face atmospheric pressure outside of the housing, and the aluminum-film can face the vacuum. The support-frame 11, boron-film(s) 12, annular-film 32, and the thin-film(s) 52 can have properties as described above. |
|
051494949 | abstract | An apparatus for protecting personnel and the environment from harmful emissions of radiation from a source thereof includes a plurality of shielding parts so located as to be in the path of the radioactive emissions and to absorb them (one such part being located farther away from the source of emissions than the other) so that an electrical potential difference between the shielding parts is established, due to different absorptions of radiation by them, means for consuming electrical power at a location remote from the radioactive source, and electrical conductors communicating the consuming means (or load) with such shielding parts. Although the invention is primarily intended for protecting personnel and the environment against emissions from radiation sources, such as radioactive wastes, it is also useful for shielding other sources of harmful radiated emissions. Also within the invention are processes for protecting personnel and the environment against radiation hazards. |
description | The present invention relates generally to ion implantation systems, and more particularly to a biased electrostatic deflector that selectively removes energy contaminants from an ion beam. Ion implantation systems are used to dope semiconductors with impurities in integrated circuit manufacturing. In such systems, an ion source ionizes a desired dopant element, which is extracted from the source in the form of an ion beam of desired energy. The ion beam is then directed at the surface of a semiconductor wafer in order to implant the wafer with the dopant element. The ions of the beam penetrate the surface of the wafer to form a region of desired conductivity, such as in the fabrication of transistor devices in the wafer. A typical ion implanter includes an ion source for generating the ion beam, a beamline assembly including a mass analysis apparatus for mass resolving the ion beam using magnetic fields, and a target chamber containing the semiconductor wafer or workpiece to be implanted by the ion beam. In order to achieve a desired implantation for a given application, the dosage and energy of the implanted ions may be varied. The ion dosage controls the concentration of implanted ions for a given semiconductor material. Typically, high current implanters are used for high dose implants, while medium current implanters are used for lower dosage applications. The ion energy is used to control junction depth in semiconductor devices, where the energy levels of the beam ions determine the degree to which ions are implanted or the depth of the implanted ions. The continuing trend toward smaller and smaller semiconductor devices requires a mechanism, which serves to deliver high beam currents at low energies. The high beam current provides the necessary dosage levels, while the low energy permits shallow implants. The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. The present invention is directed towards an angular energy filter that employs biased electrostatic deflectors to mitigate or remove energy contaminants from a generated ion beam. The angular energy filter employs the biased electrostatic deflectors to select a specific energy of ions and exclude non-selected energies from reaching a target. Angular deflectors and methods of filtering that remove energy contaminants from a ribbon shaped ion beam are provided. In one aspect, an angular electrostatic filter comprises a top deflection plate and a bottom deflection plate extending from an entrance side to an exit side of the filter. The bottom deflection plate is substantially parallel to the top deflection plate and includes an angle portion. An entrance focus electrode is positioned on the entrance side of the filter and an exit focus electrode is positioned on the exit side of the filter and both serve to focus the ion beam. Edge electrodes are positioned between the top and bottom deflection plates and at sides of the filter to mitigate edge effects. Other filters, assemblies, and methods are provided. To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout. The illustrations and following descriptions are exemplary in nature, and not limiting. Thus, it will be appreciated that variants of the illustrated systems and methods and other such implementations apart from those illustrated herein are deemed as falling within the scope of the present invention and the appended claims. Many ion implantations performed in current semiconductor fabrication processes are shallow and/or ultra-shallow implants that form shallow and/or ultra-shallow junction depths in formed devices. These shallow and/or ultra-shallow implants typically employ low energies (e.g., 1 keV), but require relatively high beam current. Generally, it is appreciated that high current low energy ion beams are obtained by extracting the ion beam from an ion source at a relatively high energy. Then, the ion beam is mass purified and transported to a position relatively close to a target wafer. Subsequently, the ion beam is decelerated to a selected low energy level and is then transported to the target wafer. However, the ion beam can include energy contaminants that are unaffected by the deceleration and, therefore, penetrate target wafers deeper than desired. As a result, the energy contaminants can damage underlying components and/or other portions of the target wafer, resulting in a potential loss of process control. The present invention facilitates ion implantation by mitigating or removing energy contaminants from ion beams, and particularly low energy ion beams. An ion implantation system of the present invention employs an angular energy filter that mitigates or removes the energy contaminants from a generated ion beam. The angular energy filter employs biased electrostatic deflectors to select a specific energy of ions and exclude non-selected energies from reaching a target. A path of the selected ions is altered by a selected angle and the selected ions pass through a slit or opening towards a target wafer. Path(s) for energy contaminants are not altered by the selected angle and, therefore, do not generally pass through the slit or opening towards the target wafer. One mechanism for removing energy contaminants is to apply a voltage potential between two infinitely sized parallel plates that, as a result of being infinite, can generate a perfectly uniform electric field there between. However, such sized plates are not feasible and deflection plates of limited sizes are, therefore, employed. These deflection plates of limited size result in electric fields that are substantially non-uniform near edges of the plates resulting in undesired horizontal and edge focusing. As a result, the plates can undesirably operate as a dipole lens. The present invention employs a bottom deflection plate with an angled portion, edge electrodes, entrance focus electrodes, and/or exit focus electrodes in order to compensate for edge focusing effects. Referring initially to FIG. 1, an ion implantation system 100 suitable for implementing one or more aspects of the present invention is depicted in block diagram form. The system 100 includes an ion source 102 for producing an ion beam 104 along a beam path. The ion beam source 102 includes, for example, a plasma source 106 with an associated power source 108. The plasma source 106 may, for example, comprise a relatively long plasma confinement chamber from which an ion beam is extracted. A beamline assembly 110 is provided downstream of the ion source 102 to receive the beam 104 therefrom. The beamline assembly 110 includes a mass analyzer 112, an acceleration structure 114, which may include, for example, one or more gaps, and an angular energy filter 116. The beamline assembly 110 is situated along the path to receive the beam 104. The mass analyzer 112 includes a field generating component, such as a magnet (not shown), and operates to provide a field across the beam path so as to deflect ions from the ion beam 104 at varying trajectories according to mass (e.g., charge to mass ratio). Ions traveling through the magnetic field experience a force which directs individual ions of a desired mass along the beam path and which deflects ions of undesired mass away from the beam path. The acceleration gap or gaps within the acceleration structure 114 are operable to accelerate and/or decelerate ions within the beam to achieve a desired depth of implantation in a workpiece. Accordingly, it will be appreciated that while the terms accelerator and/or acceleration gap may be utilized herein in describing one or more aspects of the present invention, such terms are not intended to be construed narrowly so as to be limited to a literal interpretation of acceleration, but are to be construed broadly so as to include, among other things, deceleration as well as changes in direction. It will be further appreciated that acceleration/deceleration means may be applied before as well as after the magnetic analysis by the mass analyzer 112. It is appreciated that contaminating particles, also referred to as energy contaminants, include neutral and/or other non-selected energy ranges, may be produced within the ion beam 104 by collisions among ions and background or residual particles. Such encounters can cause some of the ions to exchange charges with the background or other particles thereby becoming neutral particles or contaminants. These neutral particles can be implanted onto the wafer in areas that are to be doped with ions, thereby diluting the intended level of doping and adversely affecting the doping process. More importantly, because these particles are electrically neutral they can pass through the accelerator, and more particularly through electrostatic fields generated by the electrodes unaffected (e.g., without being accelerated, decelerated, focused, bent or otherwise altered in speed and/or direction). As such, these particles can be implanted into the wafer at undesired depths as their (unaffected) energy levels will likely differ from the energy levels of the bent, focused, accelerated and/or decelerated ions in the ion beam that have passed through and been adjusted by the accelerator. This neutral particle contamination can severely degrade the desired performance of resulting semiconductor devices. An angular energy filter 116 receives the accelerated/decelerated ions from the acceleration gap(s) 114 and selects ions within a specific energy range and excludes contaminating particles, including neutrals and ions having other energies, from the ion beam 104. The angular energy filter 116 employs deflection plates, focusing electrodes, and edge electrodes, discussed infra, to alter a path of ions within the specific energy range and allows those ions to pass through a slit or aperture. Otherwise, the non-selected ions do not pass through the slit and are thereby prevented from contaminating the wafer. The deflection plates cause the selected ions to be deflected at a selected angle (e.g., about 5 to 25 degrees) from the path of the energy contaminants, which also happens to be the original path of the ion beam 104 as the neutral energy contaminants are unaffected by the deflection plates since the contaminants are electrically neutral. The beam of ions is directed onto the workpiece to encounter select areas of the workpiece to be doped. It will be appreciated that some type of barrier can, for example, be placed in front of the stream of energy contaminants to prevent the contaminants from encountering the workpiece or wafer. The angular energy filter 116 also mitigates beam blow up, which occurs as a result of the repulsive properties of like charged particles. Positively charged ions which form the ion beam repulse each other because of a so-called “space-charge force”. Space-charge effects increase with decreasing ion beam energy, and thus may increase as the ions in the beam are decelerated, making the beam more prone to dispersal or blow up. Because of the space-charge force, the lateral spread of an ion beam is proportional to: ( m / q ) × ( Iz 2 / U 3 / 2 ) where m is an ion mass, q is an ion charge, I is a beam current, U is beam energy, and z is the traveling distance of the ion beam, assuming that the ion beam is uniform and has a circular cross section. Thus, it can be appreciated that the likelihood of beam blow up increases as the distance that the beam travels increases. Accordingly, if an ion beam travels over a long distance to a wafer, it becomes more difficult for all ions to reach the wafer, particularly where the beam is decelerated and there is a large beam current or concentration of ions within the beam. The angular energy filter 116 mitigates beam blow up by arranging/configuring the deflection plates and other electrodes within the angular energy filter 116 so as to reduce the distance that the ion beam 104 has to travel to reach the target and by focusing the ion beam 104 to oppose space charge induced beam dispersion and by allowing the beam to maintain a somewhat higher energy, which reduces the space charge forces while in the presence of electrostatic fields. An end station 118 is also provided in the system 100 to receive the mass analyzed decontaminated ion beam 104 from the beamline assembly 110. The end station 118 supports one or more workpieces such as semiconductor wafers (not shown) along the beam path for implantation using the mass analyzed decontaminated ion beam 104. The end station 118 includes a target scanning system 120 for translating or scanning one or more target workpieces and the ion beam 104 relative to one another. The target scanning system 120 may provide for batch or serial implantation, for example, as may be desired under given circumstances, operating parameters and/or objectives. FIG. 2 is a graph illustrating exemplary energy contamination for ion implantation. The graph compares ion beams with known energy contamination with an ion beam without substantial energy contamination, such as one filtered with an angular energy filter of the present invention. The values of the graph were obtained using secondary ion mass spectroscopy (SIMS). An x-axis depicts depth from a surface of a target wafer and a y-axis represents measured dopant concentration. The ion implantations performed to obtain the graph were 0.5 keV B+ implants. Line 201 depicts measured dopant concentration for an ion implantation relatively free of energy contaminants that may be obtained using an angular electrostatic deflector of the present invention. Line 202 depicts measured dopant concentrations for an implant done in the conventional way in which there is no deflection to eliminate energy contamination after decel and there is a significant drift length prior to the decel gap in which charge exchange collisions can lead to neutrals at a higher energy. By comparing lines 201 and 202, it is noted that energy contamination has resulted in a noticeable difference in dopant concentration. This difference is the result of the energy contaminants being implanted and being implanted with energies exceeding the desired 0.5 keV of the B+ ions. FIGS. 3 and 4, discussed below, illustrate focusing properties of exemplary electrodes in accordance with the present invention. They are provided to facilitate a better understanding of the invention by describing focusing and accelerating properties of an exemplary pair of electrodes. FIG. 3 is a diagram illustrating ion beam focusing properties of a pair of electrodes 300 that decelerate an ion beam in accordance with one or more aspects of the present invention. First 302 and second 304 electrodes are provided which have first 306 and second 308 apertures formed therein, respectively. The first 302 and second 304 electrodes are substantially parallel to one another, and the apertures 306, 308 define a gap 310 between the electrodes 302, 304 through which an axis 312 substantially normal to the electrodes 302, 304 may pass so as to intersect the first 306 and second 308 apertures. The gap 310 has a width 314 substantially equal to the distance between the first 302 and second 304 electrodes, and a height 316 substantially equal to that of the first 306 and second 308 apertures. It will be appreciated, however, that the elements, features, components and/or items illustrated in the FIG. 3 (as well as in all of the other figures included herewith) may not be shown to scale nor with correct proportions relative to one another. By way of example, the gap 310 and apertures 306, 308 may be significantly magnified in FIG. 3 relative to their actual size. In operation, an electrostatic field 318 is generated between the electrodes 302, 304 by applying different biases 320, 322 to the first 302 and second 304 electrodes. The apertures 306, 308 affect the electric field distribution because the internal electric field leaks through the apertures 306, 308. As such, field lines 324 bow out into the gap 310 as the electrostatic field curls around ends 326 of the electrodes 302, 304 which define the apertures 306, 308. It will be appreciated that in the example illustrated in FIG. 3, the electrodes 302, 304 are biased to decelerate ions passing through the gap 310 as the field lines are directed from the second electrode 304 to the first electrode 302 as indicated by the direction of the arrows on the field lines 324. Two trajectories 328, 330 of ions in an ion beam passing though the gap are depicted in FIG. 3 to illustrate focusing effects. It will be appreciated that these trajectories are exemplary in nature and that trajectories of actual ions may differ from these trajectories 328, 330 somewhat. During deceleration, as the ions enter the gap 310 through the first aperture 306, the field lines 324 push the positive ions away from the axis 312 running through the gap 310. However, when the ions initially enter the gap 310, they still possess a great deal of energy and momentum as they have not been significantly decelerated. The field lines 324 thus have a small effect on the trajectories of the ions at this point and the ions are pushed away from the axis 312 only slightly as indicated at 332 and 334. As the ions continue through the gap, however, they are decelerated to a greater and greater degree and the field lines 324 thus have a greater affect on their respective trajectories. When the ions are approximately half way through the gap 310, the field lines 324 push the ions toward the axis 312 running through the gap 310 as indicated at 336 and 338. As the ions approach the second aperture 308, they have been significantly decelerated and have greatly reduced momentums. As a result, the field lines 324 affect their trajectories to a much greater degree causing them to converge towards the axis 310 as indicated at 340. The overall net effect, thus, is convergence or focusing of the ion beam. It will be appreciated that the amount of convergence illustrated in FIG. 3 may be exaggerated for purposes of illustration. FIG. 4 is a diagram illustrating ion beam focusing properties of a pair of electrodes 300 that accelerate an ion beam in accordance with one or more aspects of the present invention. It will be appreciated that the overall net effect of ion beam focusing holds true where the ion beam is accelerated as well. This is illustrated in FIG. 4 where the first 302 and second 304 electrodes are biased such that the field lines 324 point in a direction from the first electrode 302 toward the second electrode 304 to accelerate ions thorough the gap 310. As ions enter the gap 310 through the first aperture 306, they are pushed in toward the axis 312 by the field lines 324 as indicted at 342 and 344. At this point they are pushed in rather significantly as the ions are initially moving rather slowly and have little momentum. As the ions continue to pass through the gap, however, they are continually accelerated and pick up increased momentum. As such, once the ions reach about the halfway point of the gap 310, the field lines have little affect on their trajectories as the ions speed through the gap 310 and out the second aperture 308. The overall net effect is thus once again convergence of the ion beam as indicated at 346, which may likewise be exaggerated for purposes of illustration. FIG. 5 is a horizontal cross sectional view of a beamline assembly in accordance with an aspect of the present invention. The beamline assembly causes an incident ion beam to reduce its energy levels to a desired level, removes energy contaminants from the ion beam, and directs the ion beam toward a target (e.g., target wafer). The beamline assembly comprises an acceleration component 502, a tube focus component 504, and an angular electrostatic filter 505. The acceleration component 502 comprises a number of stages that successively decelerate an incoming ion beam 520 as it travels through the component 502. The stages comprise electrodes arranged and biased to decelerate (or accelerate) ions. The tube focus component 504 is supported by insulators from the acceleration component 502, so that it can be biased independently to a negative potential that focuses the ion beam 520 in a vertical direction, and allows the ion beam to decelerate more but maintain an energy higher than the final energy by the potential of the tube focus voltage while the ions are substantially within component 504. The tube focus component 504 is rectangular in shape and is wider in the horizontal direction. A grounding plate 506 is present on the other side of the tube focus component 504 that terminates electric fields from the tube focus component 504. The angular electrostatic filter 505 is operatively coupled to the tube component 504 and filters energy contaminants from the ion beam. The angular electrostatic filter 505 comprises an entrance electrode 508, an exit electrode 510, a top deflection plate 512, a bottom deflection plate 514, an edge electrode 516, and an exit slit 518. The entrance electrode 508 and exit electrode 510 comprise apertures that permit passage of the ion beam there through. The top deflection plate 512 is parallel to a path of the ion beam and the bottom deflection plate 514 includes a first portion parallel to the path of the ion beam and the top deflection plate and an angled portion. The edge electrode 516 is positioned about halfway between the top deflection plate 512 and the bottom deflection plate 514. The exit slit 518 is located at an exit end of the filter 505 and permits selected ions of the ion beam to pass toward a target. The entrance electrode 508 and the exit electrode 510 are operative to accelerate the ion beam into the deflecting region and decelerate the beam after the deflecting region. As a result, the entrance electrode 508 and the exit electrode 510 can improve beam bend angle accuracy. The entrance electrode 508 and the exit electrode 510 are therefore set to a deflection bias value (as will be discussed in greater detail infra), but can also be set to other values. The top deflection plate 512 and the bottom deflection plate 514 operate as an electrode pair to desirably deflect selected ions, which comprise desired energy values, within the ion beam at a specific angle that permits them to pass through the exit slit 518. Energy contaminants, including neutral contaminants, do not bend or do not bend at the specific angle and, as a result, do not pass through the exit slit 518 and/or a more limiting slit closer to the target. The angled portion of the bottom deflection plate 514 facilitates proper deflection of the selected ions so that a relatively large beam can bend to the desired path without hitting the bottom plate. The exit slit 518 is typically biased to 0 V or ground, which causes the beam to decelerate after passing the exit focus electrode 510. The beam is decelerating to the final energy as it exits the fields of the deflecting plates 512 and 514 and the exit focus electrode 510. It is also completing the bend of the deflection. There are only short segments of these trajectories in which ions can be neutralized while at higher potentials and still have completed the bend enough to pass through blocking slits. This shorter path mitigates the possibility of neutral ions heading towards the target compared to conventional devices, which have a significant drift distance at a constant energy preceding the decel gap. A top deflection voltage is applied to the top deflection plate 512 and a bottom deflection voltage is applied to the bottom deflection plate 514 thereby causing an electric field to develop there between. These voltages can be of equal magnitude with the top plate positive and bottom plate negative voltages. Alternatively, both plates can be operated at negative potentials by using a negative bias voltage. Generally, the bottom deflection voltage is more negative than the top deflection voltage. The deflection bias value is the average of the top deflection voltage and the bottom deflection voltage. Typically, the edge electrodes 516 are set to the deflection bias value voltage. As a result, the edge electrodes 516 mitigate edge effects associated with the finite width of the deflection plates, in other words they mitigate undesired deflection of the ion beam by reducing field penetration at the ends of the plates. The voltages applied to the tube focus component 504 and the top and bottom deflection plates 512 and 514 can allow the ion beam to maintain a higher energy than it will have once it fully decelerates to ground potential to mitigate space charge forces while in the presence of the generated electrostatic fields. The ion beam is generally stripped of neutralizing electrons by the generated electrostatic fields. As a result, energy is employed to reduce the perveance of the ion beam. The following description provides exemplary values and settings for a typical operation of the beamline assembly in order to facilitate a better understanding of the present invention. It is appreciated that the present invention is not limited to the exemplary values and settings described below. As an example of normal operation, the ion beam 520 enters the acceleration component 502 after a mass analyzer (not shown) with a relatively high energy level of 53.36 keV. The stages of the acceleration component 502 successively reduce the energy level or decelerate the ion beam 520. A final stage 522 of the acceleration component is at about −10.5 kV, which decelerates the ion beam 520 to an energy level of about 11.5 keV. The tube focus component 504 is set to about −5 kV, which causes the energy level of the ion beam 520 to drop further, but not to ground potential so that the beam energy stays somewhat elevated at 6 keV within this electrode and also focuses the ion beam 520 in the vertical direction. In this example, the edge electrode 516, the entrance electrode 508, and the exit electrode are set to the deflection bias, which is −3.5 kV. The bottom plate 514 is set to a voltage of −5 kV and the top deflection plate 512 is set to a voltage of −2 kV, which causes selected ions within the ion beam 520 to deflect at a desired angle toward the bottom deflection plate 514 and ultimately pass through the exit slit 518. The exit slit 518 is at a potential of 0 V, which results in the ion beam dropping to a final energy level of 1 keV, in this example. FIG. 6 is a simplified horizontal, side view 600 of an angular electrostatic filter in accordance with an aspect of the present invention. The filter removes energy contaminants, including neutral contaminants, from an ion beam while causing ions having selected energies to deflect at a particular angle towards a target or target workpiece. The angular electrostatic filter includes an entrance focus electrode 602, an exit focus electrode 604, a top deflection plate 606, a bottom deflection plate 608, and an edge electrode 610 (one for each side of a ribbon shaped ion beam). The entrance focus electrode 602 is positioned on an entrance side of the filter and mitigates edge focus effects and focuses an incoming ion beam. The entrance focus electrode 602 is relatively thin due to its relatively small aperture 612 that permits passage of the incoming ion beam. The exit focus electrode 604 is positioned on an exit side of the filter and also mitigates edge focus effects and re-focuses the ion beam as it is exiting the filter. The exit focus electrode 604 is relatively thick in order to ensure that a negative potential is achieved along the desired path or axis 618. The top deflection plate 606 is parallel to an initial path or axis 616 of the ion beam and extends from the entrance side of the filter to the exit side of the filter. The bottom deflection plate 606 is also substantially parallel to the initial path 616, but has an angled portion 620 that deflects away from the path 616. The edge electrodes 610 extend from the entrance focus electrode 602 to the exit focus electrode 606 and mitigate edge focus effects. During operation, an ion beam enters the entrance electrode 602 through the aperture 612 along the path or axis 616. The top deflection plate 606 and the bottom deflection plate 608 generate an electric field generally extending from the top deflection plate 606 toward the bottom deflection plate 608. This field causes positively charged ions to deflect towards the bottom deflection plate 608. Generally, selected ions or ions having a selected energy deflect at a selected angle 624. Other ions, ions with non-selected energies, are deemed energy contaminants and deflect at other angles or fail to deflect. For example, neutral energy contaminants are not affected by the energy field and continue to travel along the original path or axis 616. The angled portion 620 of the bottom deflection plate 608 facilitates a controlled deflection of the selected ions by shaping the electric field, discussed below, to reduce a path length for the ion beam that is susceptible to energy contamination. The entrance electrode 602 and the exit electrode 604 are typically set to a deflection plate bias, which is an average of the voltages applied to the top deflection plate 606 and the bottom deflection plate 606. However, the entrance electrode 602 and the exit electrode 604 can be set to other voltages according to desired beam shaping properties. Generally, the entrance electrode 602 and the exit electrode 604 facilitate shaping and focusing of the ion beam by causing the electric field to be more uniform. The edge electrode 610, which also includes an angled portion 622, follows the desired path 618 of the selected ions and reduces edge effects and is also typically set to the deflection plate bias. The bottom deflection plate 608 is set to a bottom voltage and the top deflection plate 606 is set to a top voltage. Generally, the bottom voltage is more negative than the top voltage in order to attain the selected angle of deflection 624. The magnitude of the difference between the bottom voltage and the top voltage relates to the strength of the generated electric field. As a result, a larger magnitude between the top and bottom voltages yields a greater electric field and, therefore, a greater deflection angle. FIG. 7 is a side view 700 of the angular electrostatic filter of FIG. 6 in accordance with an aspect of the present invention. This view 700 more clearly shows the edge electrodes 610 and is presented as viewed from the exit end of the angular electrostatic filter. The components shown in FIG. 7 are described more fully with respect to FIG. 6. Here, the edge electrodes 610, the top deflection plate 606, and the bottom deflection plate 608 are shown. The entrance focus electrode 602 and the exit focus electrode 604 are not shown so as to further illustrate the present invention. An angled portion 620 of the bottom deflection plate 608 and an angled portion 622 of the edge electrodes 610 can be seen in this view. It is noted that the width of the angular electrostatic filter is larger than its height in order to accommodate ribbon shaped ion beams. FIG. 8 is another horizontal, side view 800 of an angular electrostatic filter in accordance with an aspect of the present invention. The filter removes energy contaminants, including neutral contaminants, from an ion beam while causing ions having selected energies to deflect at a particular angle towards a target or target wafer. This view 800 depicts electrostatic fields that may be generated during operation of the angular electrostatic filter. An infinitely long pair of parallel plates can, with different voltages applied, generate an electric field that is uniformly orthogonal to the planes of the parallel plates. However, angular electrostatic filters are unable to employ infinitely long plates and are, therefore, susceptible to fringe or edge effects near edges of the top and bottom deflection plates 606 and 608 as shown at 630. The entrance electrode 602, the exit electrode 604, and the edge electrodes 610 are biased so as to mitigate these fringe or edge effects and generate a more uniform electric field. Additionally, the entrance electrode 602 and the exit electrode 604 can be employed to focus the ion beam in the vertical dimension as discussed supra. The exit electrode 604 is substantially thicker than the entrance electrode 602 because its aperture 614 is substantially larger than the aperture 612 of the entrance electrode 602. FIG. 9 is a perspective view of an angular electrostatic filter 900 in accordance with an aspect of the present invention. This view is presented to more clearly illustrate an exemplary arrangement of components within the angular electrostatic filter 900. It is appreciated that this filter 900 is exemplary in nature and that the present invention contemplates filters with other arrangements, configurations, spacings, and the like. The filter 900 removes energy contaminants, including neutral contaminants, from an ion beam while causing ions having selected energies to deflect at a particular angle towards a target or target wafer. Operation of the components within the filter 900 is generally as described above. The angular electrostatic filter includes an entrance focus electrode 902, an exit focus electrode 904, a top deflection plate 906, a bottom deflection plate 908, an edge electrode 910 (one for each side of a ribbon shaped ion beam), and an exit slit 918. During operation, an ion beam enters an entrance side of the filter 900 through the entrance electrode 902 via an aperture 912 within the entrance electrode 902. The top deflection plate 906 and the bottom deflection plate 908 generate an electric field generally extending from the top deflection plate 906 toward the bottom deflection plate 908. This field causes positively charged ions to deflect towards the bottom deflection plate 908 at a vertex point about where an angled portion of the bottom deflection plate 908 begins. Generally, selected ions or ions having a selected energy deflect at a selected angle. Other ions, ions with non-selected energies, are deemed energy contaminants and deflect at other angles or fail to deflect. For example, neutral energy contaminants are not affected by the energy field and continue to travel along the original, line of sight path. The selected ions are deflected and pass through the exit slit 918 whereas the energy contaminants are not so deflected and fail to pass through the exit slit 918. FIG. 10 is a graph illustrating exemplary energy contamination for ion implantation. The graph compares ion beams with varying levels of energy contamination, but filtered with an angular energy filter of the present invention. The graph was obtained using secondary ion mass spectroscopy (SIMS). An x-axis depicts depth from a surface of a target wafer and a y-axis represents measured dopant concentration. The ion implantations performed to obtain the graph were 1 keV B+ implants. Potentials of −5 kV on the tube focus and −3.5 kV on the AEF bias and −5 kV on AEF focus electrodes might make one suspect that charge exchange within some of these potentials could lead to higher energy ions that could get to the wafer. However there is a relatively small fraction of the path length of the desired ions in which charge exchange can create a neutral that can get to the wafer with a higher energy. Line 1001 depicts measured dopant concentration for an ion implantation in which there is no risk of energy contaminants. Line 1002 depicts measured dopant concentrations for an ion implantation comprising 1 sccm Xe and subjected to biasing and line 1003 depicts measured dopant concentrations for an ion implantation subjected to biasing without added gas. It can be seen from lines 1001, 1002, and 1003 that lines are similar. Accordingly, the intentional addition of Xe and/or biasing with the angular electrostatic filter do not introduce substantial amounts of energy contaminants. In view of the foregoing structural and functional features described supra, methodologies in accordance with various aspects of the present invention will be better appreciated with reference to the above figures and descriptions. While, for purposes of simplicity of explanation, the methodologies described below are depicted and described as executing serially, it is to be understood and appreciated that the present invention is not limited by the illustrated order, as some aspects could, in accordance with the present invention, occur in different orders and/or concurrently with other aspects from that depicted and described herein. Moreover, not all illustrated features may be required to implement a methodology in accordance with an aspect the present invention. Referring now to FIG. 11, an exemplary methodology 1100 is illustrated for removing energy contaminants from a ribbon shaped ion beam in accordance with an aspect of the present invention. Although the methodology 1100 is illustrated and described hereinafter as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with one or more aspects of the present invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methodologies according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated. The method 1100 begins at block 1102, wherein a ribbon shaped ion beam is provided. The ion beam is relatively wide in a horizontal direction and relatively thin in a vertical direction. The method 1100 continues at block 1104, wherein an angle of deflection for a selected energy range of ions within the ion beam is selected. The selected energy range is dependent upon the ions to be employed in an implantation and are typically positive (e.g., B+ ions, BF2+ ions, and the like). The angle of deflection can vary, but is typically a relatively small value (e.g., 15 to 25 degrees). An entrance focus field is applied along a path of the ion beam that focuses the ion beam in a vertical dimension at block 1106. An entrance focus electrode comprising an aperture is typically employed to apply the entrance focus field. The ion beam path travels through the aperture. Continuing at block 1108, a deflection field, which is substantially in the vertical direction, is applied to the ion beam according to the selected angle of deflection to deflect ions within the selected energy range at about the selected angle of deflection. Energy contaminants are generally not deflected (e.g., neutral contaminants) or at another angle. A negative voltage bias is superimposed on the deflection field by using negative voltage on the top deflection plate and a more negative voltage on the bottom deflection plate, wherein the ion beam travels between the top and bottom deflection plates. Space charge blowup of the ion beam is mitigated at block 1109. The negative bias potential applied to deflection plates allows the ion beam to maintain a higher energy while being deflected in the electrostatic field, which reduces space charge blow up of the ion beam. The negative bias potential can lead to undesirable edge focusing near each end of the top and bottom plate. This undesirable edge focusing is limited at block 1111 by applying a potential, nominally equal to the bias potential, to electrodes at the edge of the plates spaced along the middle of the gap between the top and bottom plates. Generally, edge electrodes, as discussed above, are employed to limit the undesirable edge focusing near each end of the top and bottom plate. An exit focus field that focuses the ion beam in a vertical direction is applied to the ion beam after applying the deflection field at block 1112. The exit focus field is applied by using an exit focus electrode with an aperture that permits passage of the ion beam through the aperture. Subsequently, energy contaminants are blocked while the ions deflected at about the selected angle pass through toward a target wafer at block 1114. A block or piece of material can be employed to absorb the energy contaminants while an exit slit has an opening that permits passage of the ion beam towards the target wafer. Although the invention has been illustrated and described above with respect to a certain aspects and implementations, it will be appreciated that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary implementations of the invention. In this regard, it will also be recognized that the invention may include a computer-readable medium having computer-executable instructions for performing the steps of the various methods of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes”, “including”, “has”, “having”, “with” and variants thereof are used in either the detailed description or the claims, these terms are intended to be inclusive in a manner similar to the term “comprising”. Also, the term “exemplary” as utilized herein simply means example, rather than finest performer. |
|
abstract | An apparatus for use in a radiation procedure includes a radiation filter having a first portion and a second portion, the first and the second portions forming a layer for filtering radiation impinging thereon, wherein the first portion is made from a first material having a first x-ray filtering characteristic, and the second portion is made from a second material having a second x-ray filtering characteristic. An apparatus for use in a radiation procedure includes a first target material, a second target material, and an accelerator for accelerating particles towards the first target material and the second target material to generate x-rays at a first energy level and a second energy level, respectively. |
|
abstract | Provide a particle beam transport system that contribute to reduction of construction period and cost for a particle beam treatment facility including plural treatment rooms accommodating a particle-beam irradiation equipment. |
|
description | A radiation imager system 10, such as a computed tomography (CT) system, incorporating the device of the present invention is shown in schematic form in FIG. 1. CT system 10 comprises a radiation point source 20 and a radiation detector 30 and a collimator 50 disposed between radiation source 20, typically an x-ray source, and detector panel 40. Radiation detector 30 typically comprises a panel 40 having an array of photosensor pixels 42 (only a few of which are shown in phantom for purposes of illustration) coupled to a scintillator (not shown) that together convert incident radiation into electrical signals. The detector elements in conventional CT systems are arranged in a one-dimensional array. Advanced volumetric CT systems have detector elements arranged in two-dimensional array, as illustrated in FIG. 1. The radiation detector elements are coupled to a signal processing circuit 60 and thence to an image analysis and display circuit 70. This FIG. 1 arrangement allows an object or subject 90 to be placed at a position between the radiation source and the radiation detector, for examination or inspection of the object or subject. Collimator 50 is positioned over radiation detector panel 40 to allow passage of radiation beams that emanate along a direct path from radiation source 20, through exam subject 90, and to radiation detector panel 40, while absorbing substantially all other beams of radiation that strike the collimator. The construction of embodiments of the present invention for collimator 50, as well as the details of the fabrication of these collimators, are discussed in detail below. FIG. 2 is a cross-sectional view of a representative portion of a first embodiment of the collimator of the present invention. FIG. 3 is a slightly larger cross-sectional view of collimator 100. Collimator 100 is preferably fabricated from a solid, monolithic block or slab of a radiation absorbent material, such as tungsten. A plurality of channels or passages 102 are formed in the slab, extending completely through the slab from a first surface 104 to a second surface 106. The channels 102 extending through collimator 100 are xe2x80x9cfocally alignedxe2x80x9d, meaning that each of the channels has a central longitudinal axis L aligned or collinear with a respective orientation angle of the radiation source, such that extensions of the longitudinal axes L converge at a point corresponding to the position of radiation point source 20 in the imager assembly, as shown by the converging lines in FIG. 2. In that way, the channels 102 permit radiation originating at the radiation point source to pass through the collimator 100 to impinge upon detector 40. At the same time, the channels are oriented such that scattered or stray radiation not originating at or traveling directly from the radiation point source will impinge upon a portion of the collimator 100, such as first surface 104, or a wall 108 of a channel, and be absorbed by the collimator material prior to the radiation reaching a detector element 42. As a result, substantially the only radiation reaching the detector 40 will be radiation emanating directly from the radiation source 20 which passes through the object or subject 90, and which continues through to the detector. The image obtained is therefore minimally degraded by detection of scattered radiation. The fabrication process for producing collimators in accordance with the FIG. 2 embodiment advantageously permits custom design or tailoring of the collimator for different imaging situations, or for use in imaging devices having different configurations. As noted previously, the collimator is preferably formed from a single monolithic slab of a high atomic number material (e.g., an atomic number of about 72 or greater) which can absorb radiation of the type intended to be employed in a particular radiation detector or imager. This slab may be of a thickness on the order of several millimeters (e.g., 2-10 mm), with the thickness depending upon the energy of the radiation to be used and the imaging precision required, for example. As seen in the flow diagram of FIG. 4, the fabrication process begins with the use of a CAD (computer aided design) program, which generates a drawing of a two-dimensional collimator based upon overall imager system parameters, including the distance at which the collimator 100 will be placed from the radiation point source 20 in the imaging device, the size and position or location of the detector elements 42 on detector 40, and the spacing distance, if any, between the collimator 100 and detector 40. The CAD program preferably generates digital data files referred to as stereo-lithographic (STL) files. The CAD drawing or STL files contain information which defines the position, size, and orientation of the channels 102 which will extend through collimator 100 once fabrication is completed. In general, the size, orientation and position of the channels is determined by the distance of the collimator 100 from the radiation point source 20 in a given imager system, the size and location of the individual detector elements 42 on the detector panel 40, and the distance, if any, between the collimator 100 and the detector panel 40. The exit opening 110 of each of the channels 100 typically is sized and shaped to correspond to the size of the detector element 42 disposed adjacent to that channel. Where the collimator is not disposed in intimate contact with the detector panel 40, the sizing of the exit opening typically is also designed to account for spacing between the collimator 100 from the detector panel so as to allow the radiation passing from the collimator to be incident over the surface area of the respective detector elements 42. Based on the size and shape of the exit openings 110, the channel will generally have tapered walls which extend along imaginary planes defined by the respective edges of the exit opening 110 and the radiation point source 20. The size and position of the entrance openings 112 to the channels of the collimator 100 are thus dictated by the tapering walls 108 (that is, the dimensions of the channel are greater at first surface 104 of the collimator than at second surface 106 of the collimator) of the channels at the point that the channels reach the first or front surface 104 of the collimator. The exit and entrance openings 110, 112, respectively, on a collimator 100 designed for use with a two dimensional array of detector elements are schematically illustrated in FIG. 5. This figure shows entrance openings 112 in solid lines and exit openings 110 in broken lines. The geometric complexity of the channels and the differences in geometry from channel to channel can be better appreciated in this view as well. The generated STL files are typically used for control of a machining device, such as an electro-deposition machining (EDM) device, to machine out the material from block 101 to create the geometrically complex channels 102 which extend through the finished collimator. The geometric complexity of the channels is a result of the fact that the entrance and exit openings of the channels, and angles of orientation of the channels relative to the front and rear surfaces 104, 106 (respectively) of the collimator may all vary as a function of their distance from a central axis extending from the front surface of the collimator through a center of the radiation source 20. The CAD program and STL files generated permit the precise machining of these highly complex channels. In addition, a significant advantage of using CADISTL files is that collimators having different channel characteristics can readily be made by revising the drawings or files or creating new drawings or files based on the device parameters which may be different for different imaging devices or for different imaging conditions in the same imaging device. As a result, this focally-aligned 2D collimator design and fabrication process have a great deal of flexibility despite the complexity of machining the many different channel configurations, and of machining at compound angles relative to the surfaces of the collimator. Collimators can thus be fabricated which are optimized for varying end uses. Generally, high energy (approximately 320-450 KeV) industrial x-ray imagers will be larger and have greater slab thicknesses and wall thicknesses (thickness of the material separating adjacent channels) to enhance the ability of the collimator to block the undesired radiation from reaching the detector 40. Collimators optimized for use with somewhat lower x-ray energies, used in medical imaging (approximately 120 KeV), for example, may have one or more of the following characteristics so as to be adapted for use in a medical system: a smaller slab thickness, or a thinner wall thickness. Two-dimensional collimators 100 as described above serve to reduce or suppress detection of scatter radiation. Due to the fact that such collimators have a substantial thickness (as noted above), as compared with thin sheets having collimation openings therein (e.g., openings over one or more detector columns or rows) and due to the fact that the web 150 of the collimator remaining after the channels have been machined is also of relatively substantial thickness (e.g., about 2 mm to about 10 mm of a high atomic number material for high energy x-rays in an industrial CT system), if the collimator is installed in a stationary position in the imager system, it is necessary to conduct an oversampling of the source distribution (e.g., a 4xc3x97 sampling) to ensure that the detector elements of pixels 42 obtain an accurate image of the entire object being imaged, and not one with discrete sections corresponding to the grid of channels. Optionally, the imager system can be designed such that the collimator 100 is mounted to a vibrating platform 300 (FIG. 3) that will move the collimator 100 relative to the detector panel 40 such that the exit openings of the channels move to expose the detector elements to non-scattered radiation that otherwise would have been blocked or absorbed by the web portion 150 of the collimator. The platform vibration would be set such that each detector pixel sees the collimator walls and the exit opening of the channel for the same amount of time to ensure evenness (that is, uniformity) of exposure. An alternative embodiment of the present invention is schematically illustrated in FIGS. 6, 7 and 8. This alternative embodiment approximates the performance of the focally aligned 2D collimator of FIG. 2 by performing a one-dimensional (1D) collimation in a first plane, immediately followed by a further 1D collimation in a second plane which is orthogonal to the first plane. The net effect of the two collimations approximates the effectiveness and performance of a 2D collimator, and is generally superior to the effectiveness of a 1D collimator. Collimator 200 comprises first collimation section 204, which is made up of a plurality of first plate sets 201 (a representative one of which is illustrated in FIG. 6) of collimator plates 202. Each of the first plate sets 204 define a focally aligned (as that term is used herein) passage 206 adapted to allow to pass therethrough incident radiation emanating from a radiation point source. The axis of the passage is defined in a plane between the radiation point source and an underlying row (or other configuration) of detectors. In a conventional 1D collimator, scattered x-ray photons are prevented from reaching the detector in the plane of collimation of the collimator, but scattered photons originating in the plane orthogonal to that are not suppressed from reaching the detector elements. In this embodiment, collimator 200 further comprises a second collimation section 212. Second collimation section comprises a plurality of second plate sets 203. Second plate sets comprise collimator plates 210 that are positioned to create a respective focally aligned passages 216 arranged to collimate in a plane orthogonal to the plane of collimation of the first collimation section. The structure of the second collimation section will be essentially identical to that of the first collimation section, with the possible exception that the plates may be arranged such that passages 216 are adjusted to account for the different distance or spacing from the point source 20. Otherwise, the second collimation section appears, in end view, essentially identical to the first collimation section illustrated in FIG. 7. Collimator plates comprise a material selected to provide a desired level of attenuation given design information on energy level of x-ray radiation in the system and the imaging geometry used. Commonly, materials such as tungsten, lead, and natural uranium are efficacious collimator materials for use in imaging systems of the present invention. As seen in the substantially schematic illustrations in FIGS. 7 and 8, the plates of each of the first and second collimation sections are joined in fixed relationship to each other by a plurality of brackets 220 which make up a frame 222. The first and second collimation sections are also preferably secured in position relative to each other by brackets which also make up part of frame 222. One example of frame 222 comprises a box-type structure of a material transparent to the x-ray radiation (e.g., plastic or the like) that is fabricated to provide brackets (or grooves) 220 that receive collimator plates. For the 2-D arrangement, each of first and second collimator sections 204, 212, comprise a respective frame 222. The frames are disposed orthogonal to one another to provide the desired 2-D collimator structure. The collimator sections are typically fastened to the detector assembly (e.g., with bolts, snaps, or the likes) such that the sections can be removed and repositioned, if necessary. The collimator 200 is structured such that radiation passes successively through first collimation section 204 and second collimation section 212, with the effect that radiation not emanating directly from the radiation point source is, in large part, absorbed by plates of either the first or second collimation section. Collimator 200 thus is often referred to as a pseudo-2D or hybrid-2D collimator. FIG. 8, which illustrates the orthogonal orientation of plates 202 of first collimation section 204 and plates 210 of second collimation section 212, shows that passages 206 and 216, in combination and in succession, approximate the channels 102 of the collimator 100 according to the first preferred embodiment. For the purposes of clarity, only the leading edges 220, 222 of plates 202, 210, respectively, are shown in the view of FIG. 8. The broken lines illustrate that plates 210 are disposed underneath plates 202 in this illustration. In simulations conducted using a model of the collimator 200 shown in FIGS. 6, 7 and 8, this embodiment of the collimator demonstrated performance comparable to a true 2D collimator under moderate scatter conditions, such as are experienced in medical x-ray imaging. For example, for a given workpiece and energy of x-rays, the amount of the scatter signal reaching the detector array is typically less than about 20% of the primary x-ray signal reaching the array, and generally is between about 5% to about 10% of the primary signal reaching the array. The amount of scatter (e.g., the scatter signal as a percent of primary signal, is commonly less is medical imaging than in industrial imaging, where the composition and the geometry of parts being imaged generally contribute to a higher amount of scatter of incident x-rays. In extreme scatter conditions, such as are experienced in industrial x-ray imaging, the performance of collimator 200 is degraded. Nonetheless, given the relatively more complex design and fabrication of a true 2D collimator, there are many applications where the pseudo-2D collimator 200 would provides a desirable combination of performance and production cost. While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. |
|
051739305 | abstract | An x-ray monochromator, wherein a housing supports a plurality of mirrors forming a plurality of opposed mirror faces in parallel with each other and having thereon multilayer coatings, with each of said pairs of mirror faces being provided with identical coatings which are different from the coatings on the other pairs of mirror faces such that each pair of mirror faces has a peak x-ray reflection at a different wavelength regime. The housing is moveable to bring into a polychromatic x-ray beam that pair of mirror faces having the best x-ray reflection for the desired wavelength, with the mirrors being pivotable to move the mirror faces to that angle of incidence at which the peak reflectivity of the desired wavelength x-rays occurs. |
039403092 | abstract | A coupling is provided for holding and releasing a safety and a safety-and-control rod in a nuclear reactor which coupling comprises three pairs of electromagnets, said electromagnets being arranged in a circular row and act upon a single armature attached to the rod; the electromagnets of each pair being disposed at diametrically opposed position with respect the the rod axis. The signal from each sensor of a set of multiple sensors of each relevant parameter of the reactor operation is supplied to a meter of the parameter. The signals from one of each set of meters are conjointly supplied to a logic circuit which is connected to an amplifier. Finally the power from each amplifier is separately supplied to each pair of electromagnets for controlling the hold and release of the rod. The electromagnets of the coupling are arranged in a circular row and act upon a single armature attached to the rod. |
043127045 | summary | The invention concerns a shut-off device for tubular conduits, particularly for the downwards-leading quick core emptying of nuclear reactors of the bulk type, especially the pebble bed reactor type, designed for spontaneous discharge of the fuel elements when the conduit is not shut off. In the operation of nuclear reactors, it is extremely important to assure the afterheat removal in the case of a failure of reactor cooling. Therefore, high-temperature reactors utilizing spherical fuel elements (like in pebble bed reactors) are provided with a quick core-discharge system to prevent excessive core heating in the case of a failure of all available apparatus for removal of heat developed in the core. Such systems lead the spherical fuel elements in such an emergency to emptying conduits that are distributed around the periphery of the core bottom, inclined downwards, and running generally radially, leading the fuel elements out of the core into a cooled reception cavity which may particularly be a ring chamber surrounded by water and located at a level beneath that of the core. These emptying conduits could even lead perpendicularly downward, but they are preferably inclined about 30.degree. to the horizontal and usually branch out from the conventional fuel element extracting conduits of the core. In such quick spontaneous core discharge systems, the mechanical shut-off devices that are located in the downward leading discharge conduits must be sure to function. Repeated testing of their function in every case under full load is, therefore, required without producing a substantial discharge or emptying of the reactor core and without resulting in a noticable modification of the original condition of the shut-off device in question. These requirements are not met from a practical standpoint by the known shut-off devices. In process engineering technology, cut-off devices such as diaphragms, insertion discs, flaps, and rupture-type safety discs operated by levers are known. These are either are not capable of, or accessible for, repeated testing (rupture discs) or are insufficient even in a combination of several similar devices, one behind the other, for effectively providing repeated functional testing without appreciable modification of the original condition as above mentioned. If the first shut-off device directly adjacent to the core is opened, a substantial volume of fuel elements drops into the space between the first and second shut-off device of a series of successive gate discs or blocking flaps, as the result of which a precise closing of the open first shut-off device is either completely prevented or is possible only at the price of a higher rate of breakage of the spherical fuel elements. On the otherhand, elimination of the quantities of fuel elements getting into the region between the shut-off devices in functional testing produces difficulties. It is an object of this invention to develop a new shut-off device to avoid the difficulties described, which will permit repeated functional testing, without resulting in an appreciable modification of the initial state and without compromising or making doubtful, by a modification of the system, the readiness condition established as a result of the functional test. SUMMARY OF THE INVENTION Briefly, two interfitting rod combs, each movable into the conduit cross-section, are individually actuatable and combine to form a load-bearing wall running transversely across the conduit and the gap between the individual rods of each set of comb rods (which rods may be constituted either as solid or as hollow rods of suitable cross-section) is smaller than the diameter of the fuel elements (balls). Preferably, the respective sets of rods of the two interfitting combs or grids combine to form a load-bearing wall with ball-fitting grooves on the upstream side of this gate wall, running in a direction aligned with the rods, with the bottom portion of each groove being formed by the upstream face of a rod of one of the combs and the side portions of the groove being completed in adjoining portions of the two rods adjacent on either side and belonging to the other of the combs. Preferably, a symmetrical forming of the ball-fitting grooves is provided by correspondingly formed longitudinal sides of the rods. Apart from the difference in the cross-sectional shape of the rods of the respective combs necessary to provide the grooves, the interfitting rods of the two combs could have basically similar configurations. A particularly favorable arrangement mechanically is obtained by approximately I-shaped cross-sections of the rods of the first comb which provide the bottoms of the ball-fitting grooves, while the complementary cross-sectional shapes of the rods of the second comb fitting in between are provided by hollow rods, as further described below with reference to FIG. 3. In this preferred configuration, the width of the rods of both combs, as particularly seen on the (downstream) side of the structure opposite the side with the ball grooves, is substantially equal. The ball grooves formed by the cooperation of the rods of the two combs of the shut-off device prevent a change of position of the balls, which are fuel element balls of uniform diameter, upon the operation of one or the other of the combs, particularly if care is taken upon the initial complete loading of the system, to pack the first three layers of balls adjoining the shut-off device as closely and as free of voids as possible. It can, accordingly, be useful to pack these first layers of balls by hand, but even if that is not done, the spontaneous ordered arrangement of the balls is favored by the grooves and, also, by a cooperating profiling of the rods of the second comb, so that the connecting surfaces between the surfaces forming the edges of the ball grooves is, preferably, roof-shaped. Furthermore, the ordered gapless ball filling in the region of the conduit adjacent to the shut-off device can be aided by a shaping of the joining conduit wall section on the "upstream" side of the combs, which shaping should favor the gapless filling of each of the grooves with fuel balls. By means of the present invention, it is basically possible to perform repeated functional tests of the shut-off device by successively opening and again closing the first and then the second of the combs. The direction of the rods has practically no special significance in this connection. If one proceeds, however on the basis that the system should remain unimpairedly capable of operation even after a serious accident that previously has been only simulated, without requiring any entry from outside, it is useful to have the generally I-shaped rods of the first comb arranged to be movable from above downwards and the complementary rods of the second comb from below upwards to reach their interfitting closed positions. In this manner the opening up of the comb rod guideways can be prevented so that the balls could fall into them when the shut-off device is opened. This is particularly so if the rod lengths and the closed-off end surfaces of the rods of the second comb are so constituted that when the second comb is moved downward into its open position, a flush closing of the guideways in the conduit walls is provided. Furthermore, in order to prevent the possibility that balls could be pressed upwards into corresponding holes, the second comb preferably includes a slotted cover plate of half-ring-shaped configuration so that it is complementary to the inner conduit wall, as is further show, for example, in FIG. 5. The approximately I-shaped rods of the first comb that is moved down from above into its closed position preferably have at their free ends extensions that engage, in the closed position, into corresponding cavities in the duct wall. In this manner, a supplementary supporting of the I-shaped rod is obtained which raises the load-bearing ability of the rods with respect to the column of balls lying against them. Upon opening this first comb, it is moved so far upward that these extensions no longer project into the duct cross-section. The above-described oppositely directed movements of each of the combs and the closing off of the passages can be readily constituted mechanically if the connecting webs or bridges of the combs are offset from the closure plane, which can be provided by having the rods of the two combs fastened by extensions projecting away at right angles to the closure plane over to the connecting webs or bridges. Hydraulic, pneumatic, or electrically operating systems can be provided that work by means of pistons, spindles, or other mechanical drives for the separate actuation of the individual rod combs. A spindle drive is particularly suitable in which the connecting bridges of the combs are guided, for example, by four roller bearings on corresponding rails that run in the direction of movement of the combs and are mounted laterally with respect to the tubular conduit, or else, in particular, are fastened to the inside of a pressure container that serves as a supporting construction. The entire shut-off equipment is enclosed in a double pressure container with pressure-tight spindle guides leading thereto. Within the emptying or discharge duct, three gas-blocking valves, particularly in the form of wedge valves are connected to the spindle guides. |
042082480 | abstract | A typical embodiment of the invention provides a nuclear fuel assembly lock structure for control rod guide tubes. Illustratively, a sleeve telescopes over an end portion of a control rod guide tube which bears against an internal shoulder of the tube. The upper end of the sleeve protrudes beyond the control rod guide tube spider and is locked in place by means of a resilient cellular lattice or lock that is seated in a mating groove in the outer surface of the sleeve. A special tool is provided for disengaging the entire lock structure, washer, spider, spring and grill from the end of the fuel assembly in order to enable these components to be removed in an assembled state and subsequently replaced on the fuel assembly after inspection and repair. |
description | 1. Field of the Invention The present invention relates to an projection imaging type electron microscope which observes or inspects object surfaces by illuminating sample surfaces with an electron beam and using the secondary electrons, reflected electrons, or the like that are generated as a result. 2. Description of the Related Art Mapping type electron microscopes are electron microscopes in which sample surfaces are observed in two dimensions by using an electron beam optical system to illuminate the sample surface with an electron beam, and using an electron beam optical system to focus an image of the secondary or reflected electrons generated as a result on the detection surface of a detector. Unlike an SEM, such an electron microscope makes it possible to reduce the number of times that scanning is performed; accordingly, the required sample observation time can be shortened, so that this type of microscope has attracted attention as an inspection device for micro-devices such as semiconductors. An example of a microscope that is conceivable as such an projection imaging type electron microscope is shown in FIG. 5. An illuminating beam 34 emitted from a cathode 31 passes through a Wehnelt electrode 44, a first anode 45, a second anode 46 and an illumination electron optical system 32, and is incident on an electromagnetic prism 33. After the optical path of the illuminating beam 34 is altered by the electromagnetic prism (E×B) 33, the beam 34 passes through an objective electron optical system 37, and illuminates the surface of a sample 36. When the illuminating beam 34 is incident on the sample 36, secondary electrons, backscattered electrons and reflected electrons with a distribution corresponding to the surface shape, distribution of materials, variation in potential and the like (referred to collectively as generated electrons 38) are generated from the sample 36. These generated electrons 38 pass through the objective electron optical system 37, electromagnetic prism 33 and image focusing electron optical system 39, and are projected onto an MCP (micro channel plate) detector 40; accordingly, an image is formed on the CCD camera 43 via an optical image projection optical system 42. Furthermore, 35 indicates a sample stage. The optical path of the electron beam in the essential parts of such an projection imaging type microscope is shown in FIG. 6. In FIG. 6, the objective electron optical system 37 is shown as consisting of lenses 37a and 37b, and an aperture diaphragm 37c, and the image focusing electron optical system 39 is shown as consisting of lenses 39a, 39b, 39c and 39d. After being caused to converge by the action of the lens 37a, the illuminating beam 34 diverges, and is caused to illuminate the sample 36 in a perpendicular (telecentric) manner by the action of the lens 37b. The position where the illuminating beam converges is the first crossover position in the projection image focusing optical system. The generated electrons 38 that are generated from a point on the optical axis of the sample 36 converge at the position of the electromagnetic prism 33 after leaving the objective electron optical system 37; subsequently, these electrons are acted upon by the lenses 39a, 39b, 39c and 39d, and are focused as an image on the MCP detector. The generated electrons 38b (principal rays) that are emitted in a direction parallel to the optical axis from points that are off the optical axis of the sample 36 pass through the first crossover position, and are acted upon by the lenses 39a, 39b, 39c and 39d so that these electrons cross the optical axis twice as shown in the figures. The position where these electrons initially cross the optical axis following the first crossover position is called the second crossover position. Since the aperture diaphragm 37c is disposed in the first crossover position, the generated electrons 38 constitute the principal rays, and the opening angle of the projection electron optical system including the objective electron optical system and image focusing electron optical system is determined by the aperture diaphragm 37c. Furthermore, the illuminating beam 34 is arranged so that this beam illuminates the sample 36 by Koehler illumination. Specifically, the system is arranged so that the aperture diaphragm (not shown in the figures) disposed in the illumination electron optical system 32 in FIG. 5 is in a conjugate relationship with the first crossover position. The aperture diaphragm 37c is disposed in order to determine the opening angle of the projection electron optical system, and may be omitted as far as the inherent illumination electron optical system is concerned. Furthermore, the lenses 39a and 39b act as zoom lenses, and the image focusing magnification can be varied by altering the applied voltage so that the power balance of the lenses 39a and 39b is altered. Moreover, the lenses 39c and 39d act as projection lenses. [Problems to Be Solved by the Invention] However, the following problems have been encountered in optical systems of the type shown in FIG. 6. Specifically, in cases where the opening of the aperture diaphragm 37c disposed at the first crossover is small, there is a possibility that the illuminating beam from the illumination electron optical system will be knocked out by this aperture diaphragm. Accordingly, the illumination electron optical system must be designed while taking the conditions of the projection electron optical system into account; this is one factor that limits the degree of freedom in the design of the illumination electron optical system. The present invention was devised in light of such circumstances; it is an object of the present invention to provide an projection imaging type electron microscope which alleviates the restrictions imposed on the design of the illumination electron optical system by the conditions of the projection image focusing electron optical system, and which increases the degree of freedom in the design of the illumination electron optical system. [Means Used to Solve the Problems] The first means used to solve the problems described above is a projection imaging type electron microscope in which a sample surface is observed by causing an illuminating electron beam emitted from an electron beam source to be incident on an electromagnetic prism via an illumination electron optical system. The sample surface is illuminated via an objective electron optical system with the illuminating electron beam that passes through the electromagnetic prism, and electrons generated from the sample surface are conducted to the electromagnetic prism via the objective electron optical system. The electrons that pass through the electromagnetic prism are conducted to a detector via an image focusing electron optical system, and an image of the sample surface is focused on the detection surface of the detector. The system is devised so that the sample surface is illuminated with the illuminating electron beam by Koehler illumination, and such that the objective electron optical system is formed as an object-side telecentric optical system. Moreover, an aperture diaphragm is provided the projection image focusing electron optical system (including the objective electron optical system, electromagnetic prism and image focusing optical system) that focuses an image of the sample surface on the image focusing surface of the detector. The aperture diaphragm is disposed at the position of the second electron beam crossover (second crossover) (as counted from the object surface constituting the sample surface) in the projection image focusing optical system. In this means, the aperture diaphragm of the projection image focusing optical system is disposed at the second crossover position. Accordingly, since there is no need to dispose an aperture diaphragm in the first electron beam crossover (first crossover) position, the imposition of a design restriction on the illumination electron optical system by the aperture diaphragm is eliminated. The second means used to solve the problems described above is the first means, wherein a diaphragm with a size that does not block the effective range of the illuminating electron beam, and that does not block the electron beam passing through the aperture diaphragm of the projection image focusing optical system, is disposed at the first electron beam crossover (first crossover) position (as counted from the object surface) in the projection image focusing optical system. In the first means, in cases where the aperture diaphragm conventionally disposed at the first crossover position is completely removed, large quantities of generated electrons reach the optical system on the rear side of the first crossover position, and these electrons may collide with the optical elements such as lenses, so that these optical elements are contaminated; furthermore, the image focusing characteristics may deteriorate as a result of the Coulomb effect produced by these generated electrons. Accordingly, in this second means, a diaphragm with a size that does not block the effective range of the illuminating electron beam, and that does not block the electron beam passing through the aperture diaphragm of the projection image focusing optical system, is disposed in the first crossover position. Since this diaphragm has the size described above, this diaphragm does not affect the illuminating electron beam, and does not cause any knocking out of the electron beam that is considered to be necessary for the projection image focusing optical system. Furthermore, subsequent contamination of the optical elements or an increase in the Coulomb effect can be prevented by cutting the excess electron beam at the first crossover position. The third means used to solve the problems described above is the first means or second means, wherein a stigmator that corrects the astigmatic aberration of the electromagnetic prism is disposed between the electromagnetic prism and the aperture diaphragm. Since the electromagnetic prism causes the light beam passing through to converge in the electric field direction, the convergence position of the electron beam differs in the electric field direction and magnetic field direction of the electromagnetic prism. Since there is only one position in which an aperture diaphragm is disposed, electrons that are emitted from the sample parallel to the optical axis may not pass through the center of the aperture diaphragm depending on the electric field direction and magnetic field direction of the electromagnetic prism. Accordingly, telecentric image focusing of points outside the optical axis on the side of the sample becomes impossible, so that the aberration is aggravated. In the present means, the positional separation of the second crossover generated mainly by the electromagnetic prism (i.e., the fact that the second crossover position differs in the electric field direction and magnetic field direction of the electromagnetic prism) is corrected by means of a stigmator, so that the aperture diaphragm is disposed in the second crossover position in this case. Accordingly, all of the electrons emitted from the sample parallel to the optical axis pass through the center of the aperture diaphragms, so that the problem described above is solved. The fourth means used to solve the problems described above is any of the first through third means, wherein the projection image focusing electron optical system has a zoom lens, and has a relay optical system between the zoom lens and the electromagnetic prism, and the second crossover is disposed in the relay optical system. In a conventional projection imaging type electron microscope, as is shown in FIG. 6, the second crossover position is formed inside the zoom lens system. However, because of the nature of a zoom lens, this crossover position moves when the magnification is varied; accordingly, in such an optical system, it is difficult to ensure that the aperture diaphragm is disposed in the second crossover position. Accordingly, in the present means, a relay optical system is installed between the zoom lens and the electromagnetic prism, and the second crossover is formed inside this relay optical system, so that the aperture diaphragm is disposed in this position. The fifth means used to solve the problems described above is the fourth means, wherein the relay optical system is a system which focuses a first intermediate image of the sample surface as a second intermediate image by means of a first lens, and in which a second lens is disposed in the position of the second intermediate image. As will be described later in the embodiment of the present invention, by forming the relay optical system with such a construction, it is possible to increase the distance between the first intermediate image plane and the first lens compared to relay optical systems that have been widely used in the past, so that a stigmator can easily be installed in this position. Or conversely speaking, in cases where a stigmator is installed, the length of the relay optical system can be shortened compared to the length of relay optical systems used in the past, so that the overall length of the projection imaging type electron microscope can be reduced, and the Coulomb effect can be reduced. Furthermore, by performing adjustments in combination with the zoom optical system, it is possible to improve the telecentric properties at the third intermediate image focusing plane. Furthermore, in the present means, the first intermediate image plane, first lens, and the like are referred to using ordinal numerals. However, this is done in order to distinguish these parts from other parts, and does not mean (for example) that the first intermediate image is the initial intermediate image in the optical system, or that the first lens is the initial lens in the optical system. The sixth means used to solve the problems described above is any of the first through fifth means, wherein the zoom lens consists of two lenses, and these two lenses are constructed with plane symmetry in which a plane oriented at right angles with respect to the optical axis is the plane of symmetry. In this means, the two lenses that constitute the zoom optical system are constructed so that these lenses show plane symmetry with a plane oriented at right angles with respect to the optical axis taken as the plane of symmetry; accordingly, these lenses act in such a direction that the aberrations cancel each other, thus preventing an aggravation of the aberration. [Effect of the Invention] The present invention alleviates the restrictions imposed on the design of the illumination electron optical system by the conditions of the projection electron optical system, thus making it possible to provide an projection imaging type electron microscope in which the degree of freedom in the design of the illumination electron optical system is increased. 1: Illuminating beam; 2: Electromagnetic prism; 3: Optical axis; 4a: Cathode lens; 4b: Cathode lens; 5: Sample; 6a: Generated electrons; 6b: Generated electrons; 7: Stigmator; 8a Relay lens; 8b: Relay lens; 9a: Zoom lens; 9b: Zoom lens; 10a: Projection lens; 10b: Projection lens; 11: Aperture diaphragm; 12: Auxiliary diaphragm; 21: Intermediate image plane; 22: Intermediate image plane; 23: Relay lens; 24: Relay lens; 25: Zoom lens; 26: Zoom lens; 27: Intermediate image plane; 28: GND electrode; 29: Application electrode; 30: GND electrode. An embodiment of the present invention will be described below with reference to the figures. However, the overall construction of the projection imaging type electron microscope in this case is the same as that of the conventional electron microscope shown in FIG. 5, and the illumination electron optical system up to the point of the electromagnetic prism is the same as that in a conventional microscope; accordingly, in the following description, only the projection image focusing electron optical system including the objective electron optical system will be described. FIG. 1 is a diagram showing an outline of the projection image focusing electron optical system in an projection imaging type electron microscope constituting an embodiment of the present invention. This figure shows a state in which the zoom system is set at a magnification that results in 1× image focusing. The orientation of the illuminating beam 1 from the illumination electron optical system is bent along the optical axis 3 of the projection image focusing optical system by the action of an electromagnetic prism 2. The illuminating beam 1 is caused to converge by the action of a cathode lens 4a, and then diverges and is caused to illuminate the sample 5 in a perpendicular (telecentric) manner by the action of a cathode lens 4b. The system is devised so that the position where the illuminating beam 1 converges is the first crossover position in the projection image focusing optical system. The generated electrons 6a that are generated from a point on the optical axis of the sample 5 are caused to be parallel to the optical axis 3 by the cathode lens 4b, and are focused at the position of the electromagnetic prism 2 by the cathode lens 4a. Then, these electrons pass through the stigmator 7, are relayed by the relay lenses 8a and 8b, and are incident on the zoom lens 9a. In this case, the system is devised so that the generated electrons 6a cross the optical axis at the position of the relay lens 8b. The generated electrons 6a are parallel to the optical axis 3 between the zoom lenses 9a and 9b. The generated electrons 6a that have left the zoom lens 9b perform a third image focusing at the projection lens 10a, and are further projected onto the MCP by the projection lens 10b. Meanwhile, the generated electrons 6b that are emitted from the sample 5 parallel to the optical axis (principal rays) are focused by a cathode lens and cross the optical axis 3 at one point. This point is the first crossover. The generated electrons 6b are caused to be parallel to the optical axis by the cathode lens 4a, and are focused as an image at the position of the electromagnetic prism 2; these electrons 6b pass through the stigmator 7 and are incident on the relay lens 8a. These electrons are then again focused so that the electrons cross the optical axis 3 at one point. This position is the second crossover. An aperture diaphragm 11 is disposed in this second crossover position. Subsequently, the generated electrons 6b are oriented parallel to the optical axis by the relay lens 8b. These electrons pass through the zoom lenses 9a and 9b, and are again oriented parallel to the optical axis; then, these electrons are caused to cross the optical axis 3 at the position of the projection lens 10b by the projection lens 10a, and are subsequently incident on the MCP. Furthermore, in the state shown in the figure, the generated electrons 6b that have left the zoom optical system are parallel to the optical axis, and are incident on the projection lens system in a perpendicular (telecentric) orientation. However, if the zoom magnification is varied, this relationship is altered, so that such a relationship is not maintained. This point will be described later. An auxiliary diaphragm 12 is disposed in the first crossover position. This auxiliary diaphragm prevents generated electrons that make absolutely no contribution to image focusing from being incident on the subsequent optical system and contaminating the optical elements such as lenses, and prevents any increase in the Coulomb effect; accordingly, this diaphragm has an opening which is large enough so that there is no blocking of generated electrons that contribute to image focusing, and no blocking of the effective illuminating beam 1. As was described above, the deviation of the second crossover position caused by the electromagnetic prism 2 is corrected by the stigmator 7, and an aperture diaphragm 11 is disposed in the second crossover position. In a conventional projection imaging type electron microscope, an aperture diaphragm is disposed in the first crossover position; accordingly, there is no need to correct the positional deviation of the second crossover position. However, in the present invention, in which an aperture diaphragm is installed at the second crossover, it is necessary to provide such correction. In the optical system shown in FIG. 1, a second crossover is formed by the relay lens 8a, and an image plane (plane conjugate with the sample 5) is disposed in the position of the relay lens 8b. The technical significance of this will be described with reference to FIG. 2. FIG. 2 shows diagrams that compare a conventionally used relay optical system with the relay optical system used in FIG. 1. In FIG. 2, (a) is a diagram showing a conventional relay optical system; this system relays the image of an intermediate image plane 21 to another intermediate image plane 22. For this purpose, the image of the intermediate image plane 21 is inverted and focused at a magnification of M on the intermediate image plane 22 by using the relay lenses 23 and 24. The distance L2 between the intermediate image plane 21 and the relay lens 23 is equal to the focal length f1 of the relay lens 23. The distance L1 between the intermediate image plane 21 and the intermediate image plane 22 is 2f1(1+M). On the other hand, (b) in FIG. 2 is a diagram which shows the relay optical system used in FIG. 1. This is an optical system that relays an image of the intermediate image plane 21 to another intermediate image plane 22; this system is the same as the conventional relay optical system shown in (a) in that an image of the intermediate image plane 21 is inverted and focused at a magnification of M on the intermediate image plane 22, but differs in that image focusing is performed only by the relay lens 23, and in that the relay lens 24 is disposed in the same position as the intermediate image plane 22. Accordingly, as is shown in the figures, L1=L2(1+M). In a case where the distance L1 between the intermediate image plane 21 and intermediate image plane 22 and the image focusing magnification M are set at the same values, the length of L2 in (b) can be set at twice the length of L2 in (a), so that a space for the installation of the stigmator can be formed between these image planes. Accordingly, even if a stigmator is installed, the apparatus can be constructed without increasing the length of the relay optical system. By devising the relay optical system as shown in (b), it is also possible to alleviate the collapse of telecentric properties at the image focusing plane caused by the variation of the image magnification in the zoom optical system. This will be described with reference to FIG. 3. FIG. 3(a) is a diagram showing the optical path in a case where the image magnification is 1×. The principal rays passing through the relay optical system shown in FIG. 2(b) advances in parallel, and an image of the intermediate image plane 22 is inverted and focused on the intermediate image plane 27 by the action of the zoom lens 25 and zoom lens 26. In this case, the telecentric properties of the intermediate image plane 27 are maintained. FIG. 3(b) is a diagram showing the optical path in a case where the image magnification is set at 3×. In this case, the power of the zoom lens 26 is zero. In this state, if the power of the relay lens 24 is set at the same value as in FIG. 3(a), the principal rays emitted via the relay lens 24 remain parallel to the optical axis, and the principal rays reach the intermediate image plane 27 via the optical path indicated by a solid line. As is shown in the figure, the telecentric properties at the intermediate image plane 27 collapse. In this state, if the power of the relay lens is strengthened, the principal rays advance along the optical path indicated by a broken line in the figure, so that telecentric properties at 27 are improved. As a result, distortion and transverse aberration at points not on the optical axis can be ameliorated. FIG. 4 is a diagram showing the electrode construction of the zoom lenses 9a and 9b in FIG. 1; this figure is a sectional view cut along a plane that includes the optical axis 3. The respective zoom lenses 9a and 9b are formed by a combination of a GND electrode 28, an application electrode 29 and a GND electrode 30; each of these electrodes has a circular shape in a section cut along a plane perpendicular to the optical axis 3. The zoom lens 9a and zoom lens 9b are the same; however, the disposition of the electrodes of these lenses is in a mirror-image relationship with respect to a plane oriented at right angles to the optical axis 3. The construction of a zoom system in which the same electrodes are thus disposed in a mirror-image relationship offers the following merits. In cases where low-magnification image focusing is performed, a large visual field size is used; generally, therefore, distortion and transverse chromatic aberration are increased. The present embodiment assumes that a zoom of 1× to 3× will be performed; however, in the case of low-magnification image focusing, i.e., in the case of a magnification of 1×, the electron tracks are almost completely symmetrical with respect to the third crossover position as shown in FIG. 3(a), so that the optical system is close to an optical system that is telecentric on the entry and exit sides. In this case, the distortion and transverse chromatic aberration of the two zoom lenses 9a(25) and 9b(26) cancel each other, so that the aberration in the case of low-magnification image focusing is reduced. Furthermore, it is desirable that the length of the zoom system be as short as possible. However, if an attempt is made to shorten this length, then it is necessary to shorten the focal length of the zoom lenses 9a and 9b; as a result, it is necessary to reduce the internal diameters of the respective electrodes or to increase the voltage that is applied to the anode 29. If the applied voltage is increased, the cost of the power supply device is correspondingly increased; in actuality, therefore, it is more preferable to deal with this problem by reducing the internal diameters of the respective electrodes. In this case, since the region near the axis is narrowed, the aberration is aggravated. However, if the electrodes are disposed as shown in FIG. 4, the aberrations of the two zoom lenses 9a(25) and 9b(26) cancel each other, so that the aggravation of the aberration is alleviated. Moreover, by making the two zoom lenses 9a and 9b the same, it is possible to facilitate assembly and the procurement of parts, so that the cost is reduced. |
|
048435376 | summary | BACKGROUND OF THE INVENTION The present invention generally relates to a safety control system such as for a nuclear power plant, and more particularly to a safety control system provided with two independent actuating means. In nuclear power plants, it is a common practice to provide the plant with a safety and safeguard system for protecting the plant as well as a nuclear reactor against any possible abnormal transients and other unwanted phenomena for the purpose of assuring the safety of the nuclear reactor. By way of example, Japanese Laid-open Patent publication No. 118801/1986 (JP-A No. 61-118801) corresponding to U.S. Patent Application No. 666,696 filed Oct. 30, 1984 discloses a nuclear reactor safety and protection or safeguard system which includes sensors and channel signal processors connected in series, respectively, in a quadruple array and two logic circuits to which the outputs of the four channel signal processors are inputted. Each of the logic circuits is implemented in the form of two-out-of-four (2-out-of-4) voting logic circuit configuration, where one of the logic circuits is designed to produce a signal for activating a protecting system which can respond to the signal by opening a circuit breaker inserted in an electric power supply line leading to an electromagnetic device incorporated in a control rod controller unit to thereby scram the reactor, while the other logic circuit is designed to produce another safety system activating signal which brings about operation of an emergency borated water injection system and a spray system installed within a containment vessel of the reactor. In connection with the 2-out-of-4 voting logic, typical examples thereof are found in a Japanese publication entitled "Nuclear Power Handbook", (1976), p.p. 263-267 and in particular on page 264, Table 9.6. The aforementioned Japanese patent publication thus teaches the use of logic circuits implemented in the form of a 2-out-of-4 voting logic. However, no concrete circuit configuration of the 2-out-of-4 logic circuit is disclosed in this publication, although the abovementioned handbook shows in the Table 9.6 a typical example of the configuration of the 2-out-of-4 logic circuit. More specifically, the Japanese Laid-open Patent Publication No. 118801/1986 concerns a safety control safegurd system for a pressurized water reactor (PWR). According to the safety control safeguard system for the reactor disclosed in this publication, one of the 2-out-of-4 logic circuits is utilized for activating the coil or solenoid incorporated in the control rod controller unit. In this conjunction, it is however noted that in the case of a control rod drive controller unit provided for assuring the safety of a boiling water reactor (BWR) known heretofore, the scramming electromagnetic valve for operating the controller unit is equipped with a pair of excitation coils. Consequently, according to the teachings disclosed in the Japanese patent publication mentioned above, the 2-out-of-4 logic circuit has to be provided for each of the excitation coils. For implementing the 2-out-of-4 logic circuit, the circuit configuration shown in the Table 9.6 on page 264 of the aforementioned handbook may be adopted. Needless to say, when two independent manipulating or actuating means are provided for a single control system in concern (e.g. when two independent excitation coils are provided as in the case of the BWR), the two-out-of-four logic circuit has to be provided for each of the actuating means for activation thereof, which in turn means that the structure of the safety control safeguard system becomes very complicated, to disadvantage. SUMMARY OF THE INVENTION It is an object of the present invention to provide a control system of a simplified structure. Another object of the present invention is to provide a control system which includes two-out-of-four logic circuits having no common mode therebetween and which can enjoy a significantly imroved reliability. A further object of the present invention is to provide a control system in which a status signal processor or maintenance signal processor which suffers an abnormality can be easily disconnected. In view of the above objects, there is provided according to an aspect of the present invention a control system which comprises sensors disposed in a quadruple array, first, second, third and fourth signal processing channels disposed in parallel and each including signal processing means having an input supplied with an output signal from the associated sensor, two independent actuating means, an apparatus whose operation is controlled by the actuating means, and switch means communicated with the first, second, third and fourth signal processing channels for activiating operation of the two independent actuating means in response to the inputting of a trip signal produced in response to at least two outputs of the signal processing channels. By virtue of the inventive arrangement in which the switch means for the control system is so arranged as to operate the two independent actuating means in response to the trip signals produced from at least two of four signal processing channels and constitutes in cooperation with the two actuating means a two-out-of-four logic circuit, the system structure can be significantly simplified. |
053023242 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for the decontamination of a substance contaminated with radioactivity produced in a nuclear power station or the like, and to a method and an apparatus for the decontamination of a material used for said decontamination. 2. Description of the Prior Art Heretofore, in a nuclear power station, with the passage of time substances contaminated with radioactivity are produced due to contact of apparatus and the parts thereof with radioactivity. Such contaminated apparatus or parts are generated as replaced or disposed forms at the time when the apparatus are subjected to routine inspection or overhaul. Otherwise, there occurs no replacement of the part, however, some apparatus contaminated are generated to be necessarily coated. The degree of contamination of these contaminated substances can be out of the specified range according to safety standards. To dispose of these substances large size substances are cut into small size substances, contained in metal drums, and then they are usually confined in abandoned mines or the like, or kept or dumped in storage places which are constructed in regions with few inhabitants located apart from urban areas. In the present invention, said terms "keeping and dumping" are unified as one word "dumping" for convenience. The amount of substances contaminated with radioactivity stated above increases every year by the operation of nuclear power stations, resulting in lack of places to dump these substances. New waste-dumping places, therefore, become necessary. Then when a new waste-dumping place is selected, however, the inhabitants near the place tend to make an opposition movement leading to social problems. The present invention is intended to solve such troubles. The object of the invention is to provide a method and an apparatus for the decontamination of substances contaminated with radioactivity which comprises decontaminating substances contaminated with radioactivity as mentioned above, enabling the decontaminated substances to have less radioactivity than that required by safety standard, therefore, allowing the substances to be dealt with as general industrial wastes, and enabling the use of a greatly reduced area of waste-dumping place. Another object of the invention is to to provide a method and an apparatus for the decontamination of materials used for the decontamination of the substance mentioned above which comprise decontaminating fully said materials, regenerating the materials, and permitting the re-use thereof. BRIEF SUMMARY OF THE INVENTION The present invention is directed to provide a method for the decontamination of substance contaminated with radioactivity which comprises applying shotblast or sandblast to the substance to remove matters adhered to the surface of the substance, then cleaning the surface of the substance using liquid, washing the grit of said shotblast or sandblast with an organic solvent, filtering the organic solvent used for the washing, vaporizing the organic solvent comprising residue removed by heating, liquefying and recovering the vaporized solvent, and washing the washed grit with a solution containing a chelate compound. In addition, as far as the decontaminating apparatus of the present invention is concerned, it is an apparatus for the decontamination of the substance contaminated with radioactivity comprising means for shotblasting or sandblasting; means for washing the grit of the shotblast or sandblast with an organic solvent; means for filtering washing liquid used for the washing; means for purifying which comprises heating said filtered washing liquid, liquefying and purifying by cooling; and means for washing using a liquid containing chelate compound. Further, a method for decontaminating the material used for the decontamination mentioned above which comprises washing the grit of shotblast or sandblast, being applied to the substance contaminated with radioactivity, with an organic solvent, filtering the organic solvents used for the washing, vaporizing the filtered organic solvent by heating, liquefying and purifying the vaporized organic solvent by cooling, and washing said washed grit with a liquid containing chelate compound. Further, as for a decontaminating apparatus for the material used for the decontamination of the substance contaminated with radioactivity, the apparatus comprising means for filtration being made corresponding to a means for washing the grit of shotblast or sandblast; means for purifying organic solvent which comprises evaporizing the organic solvent by heating and liquefying the solvent by cooling; and means for washing a chelate liquid using a solution containing chelate compound. Further, a method of the decontamination of substances contaminated with radioactivity which comprises washing said substance by the use of a washing apparatus containing a liquid as well as having means for ultrasonic vibration. Further, an apparatus for the decontamination of substances contaminated with radioactivity comprising a vessel containing a liquid as well as having means for ultrasonic vibration. |
046817069 | abstract | A nuclear waste packaging facility for receiving both contact and remote handled nuclear waste in portable shipping containers and encapsulating this waste into ground-disposable modules is disclosed herein. The facility generally comprises a separately shielded section for processing remote handled waste including various remotely-controlled winches and conveyors, as well as a second, separately shielded section for processing contact handled waste. A module transportation and loading section is disposed between the remote and contact handled waste sections of the facility, and places empty module containers in a loading position adjacent each of the two, separately shielded sections of the facility. Both the contact and remote handled waste sections include radiation and ultrasonic detectors for determining the radioactive level of the waste, and whether or not any of this waste is in liquid form. The outputs of these detectors are connected to a central computer, which generates a signal indicating how much of the contact or non-contact handled waste may be loaded into a particular module container before the surface radiation of the completed module will exceed a certain, preselected limit. Additionally, the computer actuates an alarm circuit when either of the ultrasonic detectors generates a signal indicating that any of the waste is in liquid form. Finally, a common grouting station having an extendable trough may be used to grout modules loaded from either the contact or remote handled waste sections of the facility. The facility is preferably close to a land burial site to minimize the distance the completed modules must be transported before they are permanently buried. |
054992770 | summary | FIELD OF THE INVENTION The present invention relates generally to liquid metal-cooled nuclear reactors and to air cooling thereof. In particular, the invention relates to the passive removal of reactor decay and sensible heat from a liquid metal reactor and the transport of the heat to a heat sink (i.e., atmospheric air) by the inherent processes of conduction and radiation of heat and natural convection of fluids. BACKGROUND OF THE INVENTION In the Advanced Liquid Metal Reactor (ALMR), a reactor core of fissionable fuel is submerged in a hot liquid metal, such as liquid sodium, within a reactor vessel. The liquid metal is used for cooling the reactor core, with the heat absorbed thereby being used to produce power in a conventional manner. A known version of an ALMR plant has a concrete silo which is annular or circular. The silo is preferably disposed underground and contains concentrically therein an annular containment vessel in which is concentrically disposed a reactor vessel having a nuclear reactor core submerged in a liquid metal coolant such as liquid sodium. The annular space between the reactor and containment vessels is filled with an inert gas such as argon. The reactor and containment vessels are supported or suspended vertically downward from an upper frame, which in turn is supported on the concrete silo by a plurality of conventional seismic isolators to maintain the structural integrity of the containment and reactor vessels during earthquakes and allow uncoupled movement between those vessels and the surrounding silo. Operation of the reactor is controlled by neutron-absorbing control rods which are selectively inserted into or withdrawn from the reactor core. During operation of the reactor, it may be necessary to shut down the fission reaction of the fuel for the purpose of responding to an emergency condition or performing routine maintenance. The reactor is shut down by inserting the control rods into the core of fissionable fuel to deprive the fuel of the needed fission-producing neutrons. However, residual decay heat continues to be generated from the core for a certain time. This heat must be dissipated from the shut-down reactor. The heat capacity of the liquid metal coolant and adjacent reactor structure aid in dissipating the residual heat. For instance, heat is transferred by thermal radiation from the reactor vessel to the containment vessel. As a result, the containment vessel experiences an increase in temperature. Heat from the containment vessel will also radiate outwardly toward a concrete silo spaced outwardly therefrom. These structures may not be able to withstand prolonged high temperatures. For example, the concrete making up the walls of the typical silo may splay and crack when subjected to high temperatures. To prevent excessive heating of these components, a system for heat removal is provided. One of the heat removal systems incorporated in the ALMR is entirely passive and operates continuously by the inherent processes of conduction and radiation of heat and natural convection of fluids. This safety-related system, referred to as the reactor vessel auxiliary cooling system (RVACS), is shown schematically in FIG. 1. Heat is transported from the reactor core to the reactor vessel 15 by natural convection of liquid sodium. The heat is then conducted through the reactor vessel wall. Heat transfer from the reactor vessel outside surface to the colder containment vessel 7 across a gap space 16 filled with an inert gas, such as argon, is almost entirely by thermal radiation. A heat collector cylinder 4 is disposed concentrically between the containment vessel 7 and the silo 5 to define a hot air riser 6 between the containment vessel and the inner surface of the heat collector cylinder, and a cold air downcomer 3 between the silo and the outer surface of the heat collector cylinder. Heat is transferred from the containment vessel 7 to the air in the hot air riser 6. The inner surface of heat collector cylinder 4 receives thermal radiation from the containment vessel, with the heat therefrom being transferred by natural convection into the rising air for upward flow to remove the heat via air outlets 9. Heat transfer from the containment vessel outer surface is approximately 50% by natural convection to the naturally convecting air in the hot air riser 6 and 50% by radiation to the heat collector cylinder 4. Heating of the air in the riser 6 by the two surrounding hot steel surfaces induces natural air draft in the system, with atmospheric air entering through four air inlets 1 above ground level. The air is ducted to the cold air downcomer 3 via the inlet plenum 2, then to the bottom of the concrete silo 5, where it turns and enters the hot air riser 6. The hot air is ducted to the four air outlets 9 above ground level via the outlet plenum 8. The outer surface of heat collector cylinder 4 is covered with thermal insulation (not shown) to reduce transfer of heat from heat collector cylinder 4 into silo 5 and into the air flowing downward in cold air downcomer 3. The greater the differential in temperature between the relatively cold downcomer air and the relatively hot air within the riser, the greater will be the degree of natural circulation for driving the air cooling passively, e.g., without motor-driven pumps. The overall heat removal rate of the RVACS increases with temperature and is controlled to a large degree in the air riser gap by convective heat transfer from enclosing surfaces. Thus, if it were possible to increase the convective heat transfer on these surfaces or increase the exposed surface area, a larger decay heat load would be rejected by the RVACS at any given reactor assembly temperature. Two methods of enhancing the RVACS performance by such means are respectively described in U.S. Pat. No. 5,043,135 to Hunsbedt et al., entitled "Method for Passive Cooling Liquid Metal Cooled Nuclear Reactors and Systems Thereof", and in U.S. Pat. No. 5,339,340 to Hunsbedt, entitled "Method for Enhancing Air-Side Heat Transfer to Achieve Improved Reactor Air-Cooling System Performance". U.S. Pat. No. 5,043,135 describes an air-side heat transfer surface preparation technique that results in a higher air-side convective heat transfer rate. It involves the creation of surface roughness by placement of protrusions 10 (see FIG. 2) that disturb the thermal boundary layer near the hot steel walls. An additional enhancement method described in U.S. Pat. No. 5,339,340 utilizes the air-side enhancement method of U.S. Pat. No. 5,043,135 in combination with an additional, perforated collector cylinder 11 (see FIG. 2) placed in the air stream. The use of a perforated steel cylinder is unique in that the degree and shape of the perforations can be adjusted and selected such that optimum air-side heat transfer is achieved. The supplementary decay heat removal system which is the subject of the present invention can be used by itself but is more effective when used in combination with the enhancements of U.S. Pat. Nos. 5,043,135 and 5,339,340. This approach is assumed in the following discussion. SUMMARY OF THE INVENTION The present invention is an improvement which seeks to enhance the performance of the aforementioned prior art passive air cooling system. In the enhanced decay heat removal method described herein, heat is removed from the annular region filled with an inert gas between the outside surface of the reactor vessel and the inside surface of the containment vessel. This heat removal is in addition to the heat removed by the RVACS. The enhanced method is unique in that multiple cooling ducts in flow communication with the inert gas-filled gap space are added to provide multiple flow paths for the inert gas to circulate to heat exchangers. Heat in the inert gas is removed in these heat exchangers, thereby introducing natural convection flows in the inert gas, which in turn absorbs heat directly from the reactor vessel by natural convection heat transfer and acting in unison with the conventional decay heat removal system. The total passive convective heat transfer of the resulting dual decay heat removal system is thereby increased since heat is removed directly from both the reactor and containment vessel surfaces by natural convection. The use of the prior art enhancement methods described above along with the enhancement heat removal means of the present invention can result in improved temperature margins in the reactor design. In the alternative, the reactor core size could be increased for a particular vessel size to the extent other design constraints will permit. This could lead to a more compact and economical reactor design for future LMR systems. Also, the passive cooling system concept could be adapted to future, large-size reactors for which this type of passive heat removal system has to date been shown to be less than satisfactory because of the relatively low heat fluxes achievable. |
description | This application is a divisional of U.S. patent application Ser. No. 15/069,302, filed Mar. 14, 2016, which is a divisional of U.S. patent application Ser. No. 12/843,037, filed Jul. 25, 2010, the contents of each of which are incorporated by reference in its entirety. As shown in FIG. 1, a conventional fuel assembly 10 of a nuclear reactor, such as a Boiling Water Reactor (BWR), may include an outer channel 12 surrounding an upper tie plate 14 and a lower tie plate 16. A plurality of full length fuel rods 18 and/or part length fuel rods 19 may be arranged in a matrix within the fuel assembly 10 and pass through a plurality of spacers (also known as spacer grids) 15 axially spaced one from the other and maintaining the rods 18, 19 in the given matrix thereof. The fuel rods 18 and 19 are generally continuous from their base to terminal, which, in the case of the full length fuel rod 18, is from the lower tie plate 16 to the upper tie plate 14. Outer channel 12 encloses the fuel rods 18/19 within the assembly 10 and maintains water or other coolant flow within assembly 10 about fuel rods 18/19 and in contact with the fuel rods 18/19 to facilitate heat transfer from the fuel to the coolant. Outer channel 12 is traditionally uniform in mechanical design and material for each other assembly 10 provided to a particular core, to aid in assembly design standardization and manufacturing simplicity. Outer channel 12 may be fabricated conventionally of a material compatible with the operating nuclear reactor environment, such as a Zircaloy-2. As shown in FIG. 2, a conventional reactor core, such as a BWR core, may include a plurality of cells 40 in the reactor core. Each cell may include four fuel assemblies 10 having adjacent fuel channels 12. Other fuel assemblies 10 may be placed in the reactor core outside of cells 40 and not adjacent to control blades. The fuel assemblies 10 in FIG. 2 are shown in section to illustrate control blades 45, which are conventionally cruciform-shaped and movably-positioned between the adjacent surfaces of the fuel channels 12 in a cell 40 for purposes of controlling the reaction rate of the reactor core. Conventionally, there is one control blade 45 per cell 40. As a result, each fuel channel 12 has two sides adjacent to the control blade 45 and two sides with no adjacent control blade. The control blade 45 is formed of materials that are capable of absorbing neutrons without undergoing fission itself, for example, boron, hafnium, silver, indium, cadmium, or other elements having a sufficiently high capture cross section for neutrons. Thus, when the control blade 45 is moved between the adjacent surfaces of the fuel channels 12, the control blade 45 absorbs neutrons which would otherwise contribute to the fission reaction in the core. On the other hand, when the control blade 45 is moved out of the way, more neutrons will be allowed to contribute to the fission reaction in the core. Conventionally, only a fraction of all control blades 45 within a core will be exercised to control the fission reaction within the core during an operating cycle. As such, only a corresponding fraction of fuel assemblies will be directly adjacent to an extended control blade, or “subject to control,” during an operating cycle. After a period of time, a fuel channel 12 may become distorted as a result of differential irradiation growth, differential hydrogen absorption, and/or irradiation creep. Differential irradiation growth is caused by fluence gradients and results in fluence-gradient bow. Differential hydrogen absorption is a function of differential corrosion resulting from shadow corrosion on the channel sides adjacent to the control blades 45 and the percent of hydrogen liberated from the corrosion process that is absorbed into the fuel channel 12; this results in shadow corrosion-induced bow. Irradiation creep is caused by a pressure drop across the channel faces, which results in permanent distortion called creep bulge. As a result, the distortion (bow and bulge) of the fuel channel 12 may interfere with the movement of the control blade 45. Channel/control blade interference may cause uncertainty in control blade location, increased loads on reactor structural components, and decreased scram velocities. Conventionally, if channel/control blade interference has become severe, the control blade is declared inoperable and remains fully inserted. Example embodiments are directed to fuel assemblies useable in nuclear reactors and methods of optimizing and fabricating the same. Example embodiment fuel assemblies include an outer channel having a physical configuration determined based on a position of the fuel assembly within a core of the nuclear reactor, such as the position of the fuel assembly with respect to a control blade in the nuclear reactor that will be used to control core reactivity. When example embodiment fuel assemblies are to be directly adjacent to an inserted control blade, the outer channel may be thickened, reinforced, and/or fabricated of a material more resistant to deformation than Zircaloy-2, such as Zircaloy-4, NSF, and VB, so as to reduce or prevent distortion of the channel against the control blade and interfering with operation of the same. When example embodiment fuel assemblies are not in a controlled location, the outer channel may be thinned so as to increase water volume and reactivity in the assembly. As such, a reactor core including example embodiment fuel assemblies will include fuel assemblies having unique outer channels, in thickness, material, etc., unlike conventional power reactor cores. Example methods of configuring fuel assemblies include determining operational characteristics of the fuel assembly, such as the likelihood that the fuel assembly is controlled via control blade insertion in the nuclear reactor in a current or future fuel cycle, and physically selecting or modifying the outer channel of the fuel assembly based thereon. For example, if the fuel assembly is in a controlled location during the fuel cycle, the outer channel may be fabricated of a material more resistant to deformation than Zircaloy-2, such as Zircaloy-4, NSF, or VB, and/or thickened. Or, for example, if the fuel assembly is not in a controlled location, the outer channel may be approximately 20 mils (thousandths of an inch) or more thinner than outer channels of conventional fuel assemblies. Example methods are useable with or may further include configuring outer channel characteristics in order to meet desired neutronic properties of the fuel assembly. Hereinafter, example embodiments will be described in detail with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may be embodied in many alternate forms and should not be construed as limited to only example embodiments set forth herein. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” or “fixed” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the language explicitly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, “channel,” “outer channel,” and the like are defined in accordance with the conventional fuel assembly structures shown and described in FIG. 1 as element 12, subject to the modifications discussed hereafter. As used herein, “distortion” or “channel distortion” includes both channel bow and channel bulge in nuclear fuel assemblies that may cause interference with control blade operation. It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures or described in the specification. For example, two figures or steps shown in succession may in fact be executed in parallel and concurrently or may sometimes be executed in the reverse order or repetitively, depending upon the functionality/acts involved. The inventors of the present application have identified several potential fuel channel characteristics and/or modifications to reduce or prevent fuel channel distortion. The inventors of the present application have further identified the effect these characteristics, in combination with other fuel assembly parameters, have on whole core performance. Example embodiments and methods discussed below uniquely address these previously-unidentified effects to achieve several advantages, including improved core performance, increased energy generation, reduced control blade error, materials conservation, and/or other advantages discussed below or not, in commercial nuclear power plants, while departing from total fuel channel uniformity purposefully used in conventional commercial nuclear power plants. Example embodiment fuel assemblies include fuel channels with optimized physical properties. Example embodiment fuel assemblies may include one or more channel characteristics to decrease fuel channel distortion. For example, the fuel channel may be thickened in its shortest dimension or reinforced with additional material. The thicker or reinforced fuel channel has greater resistance to distortion from differential irradiation growth, differential hydrogen absorption, and/or irradiation creep experienced in operating nuclear reactor environments. The percent reduction in deformation is approximately proportional the percentage increase in channel thickness. Or, for example, materials may be used in the channel that are resistant to distortion. For example, Zircaloy-4, a known zirconium alloy excluding nickel, may replace Zircaloy-2, which contains nickel. The reduced nickel content in Zircaloy-4 reduces differential hydrogen absorption and resultant channel bow. Other materials more resistant to deformation than Zircaloy-2 may additionally be used in whole or in part in addition to Zircaloy-4. For example, additional materials more resistant to deformation than Zircaloy-2 are described in co-pending application Ser. No. 12/153,415 “Multi-layer Fuel Channel and Method of Fabricating the Same,” incorporated herein by reference in its entirety. That document discloses alloys hereinafter called “NSF” having about 0.6-1.4% niobium (Nb), about 0.2-0.5% iron (Fe), and about 0.5-1.0% tin (Sn), with the balance being essentially zirconium (Zr) and alloys hereinafter called “VB” having about 0.4-0.6% tin (Sn), about 0.4-0.6% Fe, and about 0.8-1.2% chromium (Cr), with the balance being essentially zirconium (Zr). Other configurations for decreasing fuel channel distortion are useable with example embodiment fuel assemblies. Example embodiment fuel assemblies may use multiple mechanisms in combination to further reduce fuel channel distortion. Configurations and fuel channel characteristics in example embodiment fuel channels may be selected in accordance with example methods, discussed in the following section. Example embodiment fuel assemblies may further include channel characteristics that improve fuel neutronic characteristics, decrease material usage and costs, and/or improve other fuel assembly parameters. Such characteristics may include, for example, a thinner channel that permits greater water volume and neutron moderation within example embodiment fuel assemblies. The thinner channel may consume less material in fabrication and improve fuel assembly reactivity, heat transfer characteristics, etc. Example embodiment fuel assemblies having thicker, reinforced, and/or thinner channels, different alloys, or other channel modification may be used instead of conventional fuel assemblies having standardized channels throughout an entire core. Example embodiment fuel assemblies may thus significantly improve performance of a core including example embodiment fuel assemblies and/or reduce fuel resource consumption. For example, thinning the channels of 75% of the fresh conventional fuel assemblies for a particular fuel cycle by approximately 20 mils (20 thousandths of an inch) in the thinnest dimension may result in a reduction in volume of approximately 16,500 in3 zirconium alloy used. In the same example, assuming 8 channels would not need to be replaced because they include channel mechanisms to decrease fuel channel deformation, an additional ˜2,000 in3 zirconium alloy volume may be saved. In the same example, assuming 8 channels are not needed to be fabricated because 8 fewer fuel assemblies are required in a fuel cycle with fuel savings from channel characteristics that improve fuel neutronic characteristics of example embodiment fuel assemblies, an additional ˜2,000 in3 zirconium alloy volume may be conserved. Thus, example embodiment fuel assemblies, having different channel characteristics selected and implemented in accordance with example methods discussed below, may result in significant materials savings and improved core performance. Example Methods As discussed above, increasing channel thickness decreases water volume and overall reactivity of an assembly having a thicker channel. Lower reactivity results in less optimal fuel usage and less power production in a nuclear core of a nuclear power reactor. Increasing channel thickness further increases costs of fuel assemblies having thicker channels. Increasing channel thickness also reduces the risk and/or magnitude of channel distortion and interference with control blade function. Decreasing channel thickness has a generally opposite effect of increasing water volume and overall reactivity of an assembly having a thinner channel, while also increasing distortion likelihood. Zircaloy-4 has similar fluence bow and creep bulge characteristics compared to Zircaloy-2. Zircaloy-4, however, resists channel bow caused by differential hydrogen absorption. NSF and VB are additionally resistant to other forms of bow and bulge causing channel deformation. Example methods uniquely leverage the above advantages and disadvantages of fuel channel modification to reduce or prevent channel distortion while minimizing negative effects on fuel economy, control blade function, and other core performance metrics. As shown in FIG. 3, example methods include an operation S100 of determining fuel assembly characteristics, including whether a fuel assembly is placed or will be located in a cell such that the fuel assembly will be directly adjacent to a control blade that will be operated in a current and/or future fuel cycle to control the fission reaction in the core. A fuel assembly positioned directly adjacent to a control blade that is likely to be exercised to control the fission reaction is herein defined as a “controlled fuel assembly” or in a “controlled location,” because it is most subject to control blade negative reactivity and most likely to affect control blade performance. The determination of whether a fuel assembly is subject to control may be based on one or more fuel assembly operational characteristics that determines placement/position of the fuel assembly within the reactor core over one or more fuel cycles, in addition to overall plant characteristics such as core size, thermal power rating, etc. For example, an operational characteristic may be reactivity of the fuel assembly. Reactivity determines the degree to which the fuel can contribute to the fission chain reaction during power operations. Reactivity is directly controllable with control blade insertion, due to the blades' neutron-absorbing properties. As such, fuel with higher reactivity may be placed in controlled locations to enhance core-wide overall control of the neutron chain reaction. Similarly, fuel with lower reactivity may be less likely to be subject to control. Although location with regard to utilized cruciform control blades is described in connection with example embodiments and methods, it is understood that other sources of negative reactivity may additionally be accounted for in example methods and embodiments. For example, proximity to burnable poisons or proximity to a control rod present in some plant designs may be accounted for by determining operational characteristics of the fuel assembly that determine the likelihood that the fuel assembly will be placed in that proximity. Controlled locations may also be determined in S100 by known core modeling and mapping methods and software. For example, a program may receive input of several fuel assembly operational characteristics for several fuel assemblies and determine an optimum core configuration with corresponding fuel assembly positions. Because example methods and embodiments may themselves affect fuel assembly operational characteristics as discussed below, such known core modeling and mapping methods may be alternatively and repetitively executed before and following fuel assembly modification in example methods to ensure optimized core performance. Following the determination in S100, one or more fuel assembly channels are configured based on the position determination. The configuring generally increases assembly reactivity, decreases distortion potential, and/or reduces material consumption in the configured assembly/assemblies. If it is determined from S100 that the assembly will be placed in a cell adjacent to an employed control blade, i.e., subject to control, then a first configuration S210 is pursued. S210 configures the assembly channel to reduce or eliminate channel distortion during power operations. For example, in S210, channel thickness may be increased by several hundredths of an inch or more to ensure decreased channel distortion. The degree of thickening may further be based on decreased reactivity or other operational characteristics desired of the assembly during operation in the nuclear reactor core. Or, channel thickness may be increased or the channel may be reinforced on only a side or wall directly adjacent to the control blade that will be operated, while remaining fuel channel sides may be unmodified or modified in accordance with S220. Additionally, or in the alternative, in S210, the channel may be fabricated out of a material more resistant to distortion than Zircaloy-2, including shadow-corrosion-bow-resistant Zircaloy-4, or fluence-gradient-bow and/or-creep-bulge-resistant NSF or VB. In this way, only assemblies determined to be at a position benefiting from a thicker or reinforced channel or a channel including Zircaloy-4, NSF, and/or VB, such as a controlled assembly likely to be placed in a cell adjacent to an employed control blade, are configured with channel features that decrease or eliminate distortion while leveraging other characteristics such as reactivity or fabrication expense. Further, because assemblies in a controlled core position typically possess higher excess reactivity, a thicker or reinforced channel that may decrease reactivity is not a significant disadvantage for the overall core reactivity; indeed, such reactivity-decreasing configuration may aid in balancing core power production and/or simplifying control blade operations. If it is determined from S100 that the assembly will be placed in an uncontrolled core position, such as an edge position in the core or adjacent to a control blade that will not be utilized, then a second configuration S220 is pursued. S220 configures the assembly channel to increase fuel assembly neutronic characteristics for the assembly in the operating core and decrease manufacturing burden in fabricating the assembly, without regard to distortion risk. For example, in S220, channel thickness may be decreased by several hundredths of an inch or more to increase water or moderator volume in the assembly, thereby increasing reactivity and fuel usage in the assembly. Reducing channel thickness in S220 further decreases an amount of expensive zirconium alloy or other channel material required to fabricate the assembly. In S220, assembly channel thickness may be reduced by a margin that takes into account the increased reactivity; the channel may be thinned such that the assembly has a determined or desired reactivity or other operational property when in use in the nuclear reactor core. In this way, a core may contain fuel assemblies with several different, unique channel thicknesses and other characteristics as determined in S210 and S220. Assemblies may be configured in S210 and S220 in several different manners and timeframes. For example, the configuring in S210 and S220 may be selecting a pre-existing assembly or ordering an assembly having the configuration determined in S210 and S220, by a power plant operator, for insertion or re-insertion during an upcoming fuel cycle in the nuclear reactor core. Alternatively, the configuring in S210 and S220 may be a physical fabricating or modifying of the fuel assembly to match the configuration determined in S210 and S220 by a fuel assembly manufacturer or refitter, for example. Example methods including S100 and S210/S220 may address fuel assembly location and configuration for use in an immediately approaching fuel cycle, a future fuel cycle, and/or multiple fuel cycles. For example, S100 may determine that a fuel assembly will be in a controlled position adjacent to an employed control blade in a first fuel cycle, and the same or later analysis may determine that the fuel assembly will be relocated to a position away from a control blade in a second layer fuel cycle. The assembly may be configured under S210 for the first cycle, and then reconfigured under S220 for the second cycle. Such reconfiguring may include re-channeling the fuel assembly by removing and replacing the channel used in the first fuel cycle with a channel having the configuration determined in S220 for use in the second fuel cycle. Similarly, a reverse determination may result in the reverse configuration. Or, for example, S100 may determine, based on multi-cycle operating parameters, that a particular fuel assembly will not be placed in a controlled location in its lifetime. Configuration of the assembly may then proceed under S220, without further modification of the assembly during its lifetime in the reactor. FIG. 4 is an illustration of an example reactor core 400 containing example embodiment fuel assemblies 100 and 200 modified in accordance with example methods. As shown in FIG. 4, four example embodiment assemblies 100 are in controlled locations about a control blade 45a that is anticipated to be used to control the fission chain reaction in the core. According to example methods, assemblies 100 about blade 45a have channels 120 configured in accordance with S210. For example, channels 120 may be thickened, reinforced, and/or fabricated of a material more resistant to deformation than Zircaloy-2. Or, for example, only select sides or walls 120b directly adjacent to control blade 45a may be configured in accordance with S210, including being thickened, reinforced, and/or fabricated of a material more resistant to deformation than Zircaloy-2. Other walls 120a may be unmodified or thinned and/or fabricated of a material equally or less resistant to deformation than Zircaloy-2, in accordance with S220. Example assemblies 200, adjacent to blade 45b that is not to be operated during the fuel cycle or adjacent to no control blade, may be configured in accordance with S220. For example, channels 121 in assemblies 200 may be thinned and/or fabricated of a material equally or less resistant to deformation than Zircaloy-2. Example methods including S100 and S210/S220 may be executed for each assembly to be placed within a core. Alternatively, example methods may be executed only with respect to particular assemblies in order to optimize core operating characteristics. For example, if example fuel assembly channel configuring methods are used in conjunction with other known core configuration methods, the calculated or desired fuel assembly locations and characteristics may require no fuel assembly channel configuring or reconfiguring as in S210 or S220. Example methods may be used as an integral part of core design or as a separate step performed alternatively and/or iteratively with other known methods of core design. For example, a known core design program may output a core map using fuel assembly characteristics with fuel having uniform channel properties. Example methods including S100 and S210/S220 may then be performed on some or all fuel assemblies involved in the map, changing their operational characteristics. The core design program may then be re-executed with the modified fuel assembly characteristics, and this alternating core configuring between example and known methods may continue until no further optimization is possible or desired. Or, example methods may be used as an integral part of otherwise known core design methods, treating reactivity, bow likelihood, and other fuel assembly parameters affected by channel configuring in S210 and S220 as additional variables in the core design process. Example embodiments and methods thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied through routine experimentation and without further inventive activity. Variations are not to be regarded as departure from the spirit and scope of the example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.