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047217383 | description | EXAMPLE 1 Polyethylene (45 g) is blended with 1% and 2%, by weight, of Zr(O.sub.3 PCH.sub.2 CH.sub.2 SH). These samples and a polyethylene control are processed in a Brabender mixer at 40 rpms at 160.degree. C. After 15 minutes the samples are removed from the mixer while still hot. The samples are compression molded at 325.degree. F. and 36 tons in a 21/4".times.5".times.1/8" plaque mold and the plaques are used to measure sensitivity to microwave energy in the RF region by irradiating the sample at 61-85 cm..sup.-1. (Unless indicated otherwise, all samples were tested for sensitivity to microwave heating by irradiation at 61-85 cm.sup.-1 using a Thermall EO-1 RF generator and made by W. T. LaRose Associates, Cohoes, N.Y.) Minor heat absorption of the samples is noted at 130 milliamps once a threshold temperature is reached; however, as shown below at higher powers much more heat absorption is obtained. EXAMPLE 2 Plaque samples of the formulations given in Table 1 are made up as in Example 1, except that the samples are of the dimensions 11/2".times.21/2".times.1/8". The temperature of the samples as a function of exposure to microwave radiation is measured as follows: Two plaques, one on top of the other, are supported on a 11/2".times.21/2".times.1/8" aluminum plate which acts as a heat sink. The temperature of the inner surfaces of the plaques is measured with a surface pyrometer for five successive 60 second pulses. The initial current is 370 milliamps. After each series the aluminum plate is cooled to room temperature. The results are summarized in Table 1. TABLE 1 ______________________________________ Pulse 1st 2nd 3rd 4th 5th Formulation .degree.F. .degree.F. .degree.F. .degree.F. .degree.F. ______________________________________ Polyethylene (Control) 68 81 87 94 101 2% Zr(O.sub.3 PCH.sub.2 CH.sub.2 SH).sub.2 White 86 93 102 109 115 2% Zr(O.sub.3 PCH.sub.2 CH.sub.2 SH).sub.2 Red 82 94 105 115 121 2% Zr(O.sub.3 PCH.sub.2 OH).sub.2 101 123 132 138 140 2% Ti(O.sub.3 PC.sub.6 H.sub.5).sub.2 87 102 110 118 129 5% Zr(O.sub.3 PCH.sub.2 CH.sub.2 SH).sub.2 98 117 132 144 150 Polyethylene (Control).sup.a 84 2% Zr(O.sub.3 PCH.sub.2 CH.sub.2 SH)White.sup.a 93 2% Zr(O.sub.3 PCH.sub.2 CH.sub.2 SH)Red.sup.a 80 ______________________________________ .sup.a Samples tested again to make sure repeated residual heat buildup has no bearing on the magnitude of the sensitivity to microwave RF heating. It is clear from the results of Table 1 that the particulate layered compounds utilized in this experiment sensitize polyethylene to microwave heating, in the RF range. EXAMPLE 3 The samples of Table 2 are made in a Brabender plsticorder using a polyethylene as the nonpolar polymer. Each is tested as in Example 2 and the results obtained are summarized in Table 2. TABLE 2 __________________________________________________________________________ Pulse Additive 1st .degree.F. 2nd .degree.F. 3rd .degree.F. 4th .degree.F. 5th .degree. F. __________________________________________________________________________ None 77 86 93 99 104 2% Et/CO Copolymer.sup.b 88 118 138 150 156 2% Asbestos 125 161(fusion) -- -- -- 5% Asbestos 144(fusion) -- -- -- -- 2% Zr(O.sub.3 PCH.sub.2 OH).sub.2 108 127 143 148 157 2% Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 120 153 166 186 186 2% Vinylalcohol 115 159 187 200 -- (fusion) 4% ET/CO Copolymer 141 178 197 -- -- Repeats (see footnote .sup.a above) None 86 103 115 121 128 2% Et/CO.sup.b 114 145 159 166 173 Copolymer __________________________________________________________________________ .sup.b An ethylenecarbon monoxide copolymer prepared by peroxidecatalyzed polymerization. The sample comprising 2% Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 is superior to the samples comprising the prior art microwave enegy sensitizers. Moreover, in addition to its safety advantage over asbestos, the current drift over a 60 second time period is very small (7%) while asbestos shows a greater than 10% current drift and premature fusion. EXAMPLE 4 The formulation of Table 3, using a polyethylene, available from Exxon, were made in a Bradbender Plasticcorder, molded, then subjected to microwave energy as in Example 2. TABLE 3 ______________________________________ Pulse 1st 2nd 3rd 4th 5th Additive .degree.F. .degree.F. .degree.F. .degree.F. .degree.F. ______________________________________ None 97 107 125 137 144 0.5% Asbestos 101 123 139 146 156 0.5% Zr(O.sub.3 PCH.sub.2 CHOH).sub.2 103 125 137 149 153 1.0% Asbestos 136 174 -- -- -- 1.0% Zr(O.sub.3 PCH.sub.2 CHOH).sub.2 117 142 150 162 164 0.75% Asbestos 110 139 168 189 -- 0.75% Zr(O.sub.3 PCH.sub.2 CH).sub.2 106 134 148 156 162 1.25% Zr(O.sub.3 PCH.sub.2 CH).sub.2 117 145 157 164 172 0.5% Ti(O.sub.3 PCH.sub.2 CH.sub.2 OH) 94 114 131 140 146 0.75% Ti(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 98 116 127 136 143 1.0% Ti(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 91 108 122 132 138 1.25 Ti(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 98 122 135 144 151 ______________________________________ Room Temperature 68.degree. F. Pulses are 60 seconds each at 376 milliamps Titanium layered compounds powder more easily and may be more compatible with polyethylene than is its zirconium cogener; however the titanium layered compounds are not quite as good as zirconium - especially for pulses less than 180 seconds. Nevertheless both compositions are efficient microwave sensitizers for polyethylene. In addition, the temperature rise magnitude for successive pulses decreases whith increasing temperature of the polymer compositions of this invention as compared to the asbestos-containing polymer compositions and the polymer alone. This property is, of course, desirable and unexpected. EXAMPLE 5 In this Example the plaques are shielded by a 1/4" Teflon.RTM. ring. The results are summarized in Table 4 below. TABLE 4 __________________________________________________________________________ Pulse Additive 1st 2nd 3rd 4th 5th __________________________________________________________________________ None 72 82 92 99 104 2 Teflon 0.5% Asbestos 87 102 111 120 127 ring shields None 84 95 101 107 113 2 Teflon 2% Zr(O.sub.3 PCH.sub.2 OH) 108 127 137 141 149 ring shields 2% Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 126 160 162 -- -- __________________________________________________________________________ It is hypothesized OH in that compound is less sterically hindered and can therefore vibrate more freely. All five pulses are done sequentially. Each sequence starts at ambient temperature (72.degree. F.) The aluminum plate is washed in water to remove heat buildup. In this experiment, the edges of the aluminum plates are rounded so that the bottom of the RF chamber won't be damaged by accidental arcing. The Teflon rings ensure that the sample plaques are affected only by direct radiation and not refracted energy. EXAMPLE 6 The formulations of Table 5 were made and tested as in Example 5. TABLE 5 ______________________________________ Pulse 1st 2nd 3rd 4th 5th Additive .degree.F. .degree.F. .degree.F. .degree.F. .degree.F. ______________________________________ None 84 95 104 114 119 0.5% Asbestos 99 114 125 130 137 0.75% Asbestos 124 157 166* -- -- 1.0% Asbestos 135 170 -- -- -- 0.5% Ti(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 92 103 112 126 125 0.75% Ti(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 97 111 120 127 131 1.0% Ti(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 96 113 124 132 140 1.25% Ti((O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 99 113 124 130 137 0.5% Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 91 104 111 118 119 0.75% Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 106 124 137 142 149 1.0% Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 112 130 140 143 153 1.25% Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 112 128 142 149 155 2.0% Ti(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 100 115 125 132 138 ______________________________________ *Sample melted This sample demonstrates, again, that the additives of this invention are superior to the prior art asbestos additive because of the observed temperature leveling phenomenon. EXAMPLE 7 Silica (325 mesh) and Frequon 3035 (at 2.0 percent, by weight polymer) were evaluated for their ability to impart microwave sensitization in dielectric plastics. A formulation containing 0.75% asbestos and one containing 2.0% zirconium hydroxyethylphosphonate [ZR(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 ] were also tested. It was found that the Frequon 3035 had a useful microwave sensitivity, but the silica did not. The sensitivity characteristics of the Frequon 3035 were further evaluated, and the results are tabulated in Tables 6 and 7. Frequon 3035 is more effective than Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 ; however, this may be due to Frequon 3035's, generally, smaller particle size. TABLE 6 ______________________________________ MICROWAVE SENSITIVITIES (.degree.F.) ONE PULSE AT 370 MILLIAMPS FOR 60 SEC. NO SHIELDING ROOM TEMPERATURE TEMPERA- AFTER ONE ADDITIVE TURE CYCLE ______________________________________ None 62 82 2% Frequon 64 163 2% Zr (O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 65 122 0.75% Asbestos 71 123 4% Frequon 3035 69 181 (melts) 2% 325 Mesh Silica 66 89 5% 325 Mesh Silica 68 88 ______________________________________ TABLE 7 ______________________________________ MICROWAVE SENSITIVITIES THREE CYCLES OF 300 MILLIAMPS FOR 30 SECONDS NO SHIELDING ROOM T.degree. F. TEMPERA- PULSE NUMBER ADDITIVE TURE 1 2 3 ______________________________________ None 64 75 88 91 1% Frequon 3035 67 93 111 124 1.5% Frequon 3035 67 105 129 145 2.0% Frequon 3035 65 116 160 195* 2.0% Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 67 100 116 131 0.75 Asbestos 67 96 124 141 ______________________________________ *Sample melted EXAMPLE 8 Microwave sensitivity measurements were made in a polyethylene matrix on zirconium phosphate [Zr(O.sub.3 POH).sub.2 ] zirconium hydroxyethylphosphate [Zr(O.sub.3 POCH.sub.2 CH.sub.2 OH).sub.2 ], and zirconium hydroxyethylphosphonate [Zr(O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 ], using asbestos and a matrix without any additive as reference samples. The plaques were subjected to 370 milliamps for 60 seconds each. There was no cooling to room temperature in between the various samples, and no Teflon shielding was used to prevent effects of refracted radiation from having an effect on the sample. Room temperature was 64.degree. F. and this was true only for first pulse of control sample. The data taken are given in Table 8. The hydroxyethylphosphonate performs the best followed by the hydroxyethylphosphate and the phosphate, respectively. Sensitivity of the hydroxyethylphosphonate is of approximately the same magnitude as that of asbestos. Nytal 99 is an industrial talc from R. T. Vanderbilt, Inc. Talc is chemically similar to asbestos, and to some extent, has been used as a substitute for asbestos in some commercial applications. Obviously, this particular grade of talc is not appreciably microwave sensitive. In Table 9, the samples were shielded, as above, and allowed to equilibrate to room temperature between pulses. Otherwise the conditions were the same as in Table 9. TABLE 8 ______________________________________ Pulse No. (.degree.F.) Additive 1 2 3 4 5 ______________________________________ None 82 103 122 131 138 2% Zr (O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 122 164 -- -- -- 2% Nytal 99 94 112 130 142 150 2% Zr (O.sub.3 POCH.sub.2 CH.sub.2 OH).sub.2 106 140 157 175 -- 2% Zr (O.sub.3 POH).sub.2 95 117 139 154 164 0.75% Asbestos 147 186 -- -- -- ______________________________________ TABLE 9 ______________________________________ Pulse No. (.degree. F.) 1 2 3 4 5 ______________________________________ None 78 91 101 112 118 2% Zr (O.sub.3 PCH.sub.2 CH.sub.2 OH).sub.2 116 143 165 -- -- 2% Nytal 99 83 97 110 118 127 2% Zr (O.sub.3 POCH.sub.2 CH.sub.2 OH).sub.2 98 127 139 151 163 2% Zr (O.sub.3 POH).sub.2 92 110 124 134 138 0.75% Asbestos 116 158 -- -- -- ______________________________________ While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto since many obvious modifications can be made and it is intended to include within this invention any such modifications as will fall within the scope of the appended claims. |
abstract | An improved grid for use in a fuel assembly of a nuclear reactor includes a plurality of straps connected in a lattice, with a plurality of mixing vanes being disposed on the straps and being arranged such that the hydraulic forces on the mixing vanes generally cancel one another out. The mixing vanes of diagonal quadrants of the grid are generally aligned with diagonally disposed imaginary alignment planes. Each strap includes a plurality of strap members, with each strap member including a spring and a pair of dimples. The spring includes a contoured spring embossment having a greater radius of curvature in a relaxed condition than the radius of a fuel rod. Each dimple includes a similarly configured contoured dimple embossment. The spring embossment is mounted on a pair of legs that extend nonlinearly between a first plate and a second plate of each strap member to increase compliance thereof. |
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046648712 | claims | 1. A nuclear power installation of compact construction, comprising: a high-temperature pebble bed reactor, having a core of spherical fuel elements, and a reflector which surrounds the core and which has a side section; a multicomponent cylindrical steel pressure vessel surrounding said reactor including a retracted upper section, a cover and a main body; a heat utilization system positioned in the retracted section of the pressure vessel, above the reactor in the pressure vessel, comprising only one steam generator, wherein said heat utilization system uses a cooling gas which flows from bottom to top through the core and the pressure vessel; at least two circulating blowers which are disposed on the cover of the vessel, which are connected with the heat utilization system, and which function in the direction of flow of the cooling gas; a first means for shutting down the reactor having an upper portion laterally disposed to the retracted upper section externally to the pressure vessel and a lower portion located within the main body of the pressure vessel; and a second means for shutting down the reactor having an upper portion laterally disposed to the upper retracted section externally to the pressure vessel and a lower portion located within the main body of the pressure vessel; wherein said first means for shutting down the reactor comprises a plurality of absorber rods, bores in said side section of said reflectors which function to contain said absorber rods, and rod drives disposed outside of said steel pressure vessel in the area of said retracted upper section, said rod drives functioning to insert the rods into the bores. wherein said said second means for shutting down the reactor comprises small absorber spheres, a plurality of storage containers disposed outside the steel pressure vessel in the area of the retracted upper section, for containing the small absorber spheres, annular conduits connected to said storage containers which are arranged inside the steel pressure vessel, projections on said side of said reflector which protrude into the core; and channels in said projections which are connected to said annular conduits and which serve to introduce the small absorber spheres. a high-temperature pebble bed reactor having a core of spherical fuel elements and a reflector which surrounds the core and which has a side section; a multicomponent cylindrical steel pressure vessel surrounding said reactor including a retracted upper section, a cover and a main body; a heat utilization system positioned in the retracted section of the pressure vessel, comprising only one steam generator with a centrally located sub-system and at least one annular sub-system independent from said centrally located sub-system wherein said annular sub-system surrounds said centrally located sub-system and wherein said heat utilization system uses a cooling gas which flows from bottom to top through the core and the pressure vessel; at least two circulating blowers which are disposed on the cover of the vessel, which are connected with the heat utilization system, and which function in the direction of flow of the cooling gas; a first means for shutting down the reactor; and a second means for shutting down the reactor. a plurality of absorber rods; bores in said side section of said reflectors which function to contain said absorber rods; and rod drives disposed outside of said steel pressure vessel in the area of said retracted upper section, said rod drives functioning to insert the rods into the bores. small absorber spheres; a plurality of storage containers disposed outside the steel pressure vessel into the area of the retracted upper section, for containing the small absorber spheres; annular conduits connected to said storage containers which are arranged inside the steel pressure vessel; projections on said side of said reflector which protrude into the core; and channels in said projections which are connected to said annular conduits and which serve to introduce the small absorber spheres. housings for the rod drives of the first means for shutting down; fittings in the region between the main body of the steel pressure vessel and the retracted upper section for fastening the housings to the steel pressure vessel; and flange means for attaching said housings to said fittings. fittings in the region between the main body of the steel pressure vessel and the retracted upper section for fastening the housings to the steel pressure vessel, wherein said housings are welded to said fittings. fittings on the cover of the steel pressure vessel for fastening the circulating blowers; and flange means on the circulating blowers for attaching the blowers to said fittings. a support base for said core; at least one outlet means for removing fuel elements from the core; and decollating means provided for said outlet means for isolating the fuel elements. a thermal side shield upon which said side section of said reflector rests; and raised support points on said thermal side shield which create gaps for the passage of cooling gas. 2. A nuclear power installation of claim 1, 3. A nuclear power installation, comprising: 4. A nuclear power installation as claimed in claim 3, wherein each independent sub-system comprises a distributor, a collector, an inlet line, and an outlet line. 5. A nuclear power plant according to claim 3, wherein the first means for shutting down the reactor comprises: 6. A nuclear power plant according to claim 5, wherein the second means for shutting down the reactor comprises: 7. A nuclear power palnt according to claim 6, wherein said rod drives are means for gravitational introduction of the absorber rods of the first shut-down arrangement and said first means for shutting down comprises means for rapid shut-down (scram) of the high-temperature pebble bed reactor, and wherein the second shut-down arrangement may optionally be used for said rapid shut-down. 8. A nuclear power plant according to claim 6, wherein the second means for shutting down the reactor is a means for long-term shut-down of the high-temperature pebble bed reactor. 9. A nuclear power plant according to claim 5, further comprising: 10. A nuclear power plant according to claim 5, further comprising housings for the rod drives of the first means for shutting down the reactor; and 11. A nuclear power plant according to claim 3, further comprising: 12. A nuclear power plant according to claim 3, wherein said heat utilization system further comprises means for removal of residual heat. 13. A nuclear power plant according to claim 12, wherein said circulating blowers cooperate with said heat utilization system for both steam generation and removal of residual heat. 14. A nuclear power plant according to claim 13, wherein one circulating blower is provided for each sub-system of said heat utilization system during both steam generation and removal of residual heat. 15. A nuclear power plant according to claim 12, further comprising a secondary cooling system with a plurality of components for recooling said heat utilization system during the removal of residual heat. 16. A nuclear power plant according to claim 12, further comprising a secondary cooling system for recooling each sub-system of said heat utilization system during the removal of residual heat. 17. A nuclear power plant according to claim 3, wherein said spherical fuel elements pass through the core only once, and wherein the nuclear power plant further comprises: 18. A nuclear power plant according to claim 3, further comprising: 19. A nuclear power plant according to claim 18, further comprising grooves on the side of said side section of said reflector for engaging said support points. 20. A nuclear power plant according to claim 18, wherein said support points are welded to said thermal side shield, and further comprising means for compensating for assembly tolerances. 21. A nuclear power plant according to claim 19, wherein said support points are screwed to said thermal side shield, and further comprising means for compensating for assembly tolerances. |
039649652 | description | DETAILED DESCRIPTION OF THE INVENTION Having reference to the above drawing, the reactor pressure vessel 1 contains the core 2, the coolant main pipeline loop is shown at 3 and the direction of the coolant flow is indicated by the arrow 4. The coolant flows from the pressure vessel 1 to the steam generator 5 and is returned to the pressure vessel under the force of the pump 6 which maintains the circulation in the loop 3. The secondary coolant pipeline loop 3a is shunted around the pump 6 so as to pass from 10 to 20% of the coolant through the coolant water purification system 10 which included the degassing facility 11 where the coolant is decompressed and cooled so that its gases are separated. The degassed water coolant returns to the pressure vessel 1 via the pipeline 12 which is part of the secondary loop 3a. The separated gases flow through the pipe 14. As previously mentioned, these gases are mainly hydrogen, nitrogen and oxygen but they also include small amounts of the noble gases krypton and xenon making the disposal of the gases a problem as previously indicated. According to the invention, these gases are passed by the pipe 14 into a recombiner 15 which is of the catalytic type, the amount of oxygen relative to the hydrogen being insufficient to support flame combustion. In this way the oxygen is removed from the gases, the output from the recombiner 15 going through a dryer or water separator 16 from which the water flows via a pipe 17 for return to the water system of the reactor installation or disposed of. The gases leaving the recombiner 16 then go into a gas separation facility generally indicated by 18. This gas separation facility may be of the type which through condensation and step-wise evaporation of the different gases effected via suitable heat exchangers, effects the separation according to the liquification temperatures of the gaseous components. Known equipment is capable of separating the major part of the noble gases in the gas mixture leaving the recombiner 16, particularly krypton and xenon, and these are fed via a pipe 20 to the previously referred to gas storage facility 21. The latter can be a steel bottle containing for better absorption, activated carbon. Its volumetric capacity need not be greater than 1m.sup.3 and preferably it is of much smaller size, such as less than 0.1m.sup.3. Such capacities are sufficient for storing the noble gases produced in the course of a years operation of a pressurized-water powered reactor of 1000 MWe. The separated hydrogen is sent through a pipe 23 and to the water coolant gas-charging system 24 which normally also includes a storage facility for the hydrogen, permitting its use as required. This facility 24 feeds into the secondary loop 3a as required to maintain the water coolant' s hydrogen concentration, or possibly used elsewhere. It is important to note that the purity requirements for the hydrogen with respect to radioactivity components are so low that the gas separation facility 18 need not operate with great efficiency and, therefore, can be constructed and operated inexpensively as compared to the expense that would be required for the complete removal of the noble gases. The condensed nitrogen and possibly some remaining portion of the noble gases are fed from the facility 18 via a pipe 25 to a unit 27 of the type which by partial evaporation or rectification entirely separates the nitrogen from any remaining noble gases, the latter going through a pipe 28 to the previously described noble gas storage bottle 12. The separation here should be adequate to remove all remaining noble gases to a degree permitting discharge of nitrogen to the atmosphere if desired. As shown, the nitrogen leaves 27 via a pipe 30, a valve 24a serving to send the nitrogen either to the gas-charging facility 24 or to a gas stack 32 discharging the nitrogen to the atmosphere, this being entirely safe from the environmental pollution viewpoint as it now or may potentially in the future exist. Neither of the facilities 11 and 18 are required to separate completely all of the noble gases. This is required in the case of the facility 27 but here the content of noble gases is already very small as compared to the initial content and they must be separated only from the nitrogen. It follows that the previously described problem is solved by this invention in an economical way while meeting the environmental requirements which the previously described prior art system could not do satisfactorily. |
claims | 1. A radiographic imaging system comprising:a scanning bay;a movable table configured to move a subject to be scanned fore and aft along a first direction within the scanning bay;an x-ray projection source configured to project x-rays in an x-ray beam toward the subject;a pair of generally cylindrically-shaped rotatable filters formed of attenuating matter, each filter rotatable about a line of rotation that extends along a long axis of the filter and is defined to be transverse to the x-ray beam; anda computer programmed to:determine a region-of-interest of the subject; androtate at least one rotatable filter of the pair of rotatable filters such that the pair of rotatable filters limit x-ray exposure outside the region-of-interest. 2. The radiographic imaging system of claim 1 wherein each cam filter has a length and an attenuation profile that varies as a function of filter length. 3. The radiographic imaging system of claim 1 wherein an attenuation profile of each filter is a function of filter thickness. 4. A cam filter assembly for use with a radiation emitting imaging system, the cam filter assembly including a pair of non-overlapping cam filters wherein each cam filter has a generally rod-shaped body and has an attenuation power that varies with thickness of the filter, the pair of cam filters being configured to be independently rotated to collectively manipulate a beam of radiation projected toward a subject to generate a desired radiation profile across a region-of-interest of the subject. 5. The cam filter assembly of claim 4 wherein each filter has a width situated along an x-axis and a length situated along a z-axis, the z-axis being parallel to a long axis of the subject, and wherein each filter has varying attenuation characteristics along its length. |
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047088222 | claims | 1. A method of solidifying radioactive waste which comprises embedding mirabilite pellets that are obtained by drying, granulating and pelletizing radioactive solid waste, directly in a solidifying material to provide a solidified package; the solidifying material being a crosslinked plastic resin with a large distance between crosslinked points and having a modulus of elasticity that is smaller than the modulus of elasticity of the mirabilite pellets and the plastic resin being not greater than an external pressure applied to the solidified package, wherein the plastic resin is a polymer consisting of a styrene and an unsaturated polyester which contains a polybutadiene glycol, and the mirabilite pellets have a modulus of elasticity on the order of 10.sup.3 Kg/cm.sup.2 and the plastic resin has a modulus of elasticity on the order of 10.sup.2 Kg/cm.sup.2. 2. A method of solidifying radioactive waste which comprises embedding mirabilite pellets that are obtained by drying, granulating and pelletizing radioactive waste, directly in a solidifying material to provide a solidified package, wherein the solidifying material is cement which contains a rubber-like binder and has a modulus of elasticity that is smaller than the modulus elasticity of said mirabilite pellets, and further a tangential stress .sigma. at a boundary between a solid mirabilite pellets and the cement is not greater than an external pressure applied to the solidified package; and the mirabilite pellets having a modulus of elasticity on the order of 10.sup.3 Kg/cm.sup.2 and the plastic resin having a modulus of elasticity on the order of 10.sup.2 Kg/cm.sup.2. |
056407041 | summary | BACKGROUND OF THE INVENTION Various industrial processes result in the production of waste streams containing toxic, hazardous, or radioactive waste species. Commonly these waste streams are in the form of aqueous solutions or dispersions that contain heavy metals and/or radionuclides in either dissolved or precipitated forms. These waste streams can also contain various other harmful compounds such as nitrates and phosphates. Examples of such waste streams are those wastes that result from plating operations for the aluminum plating of radioactive materials. Such plating operations result in a waste sludge material that contains nitrate compounds, nickel compounds, and radioactive compounds. These waste streams must be treated to meet various governmental regulations prior to disposal. One way of treating these waste streams is to admix the waste with cement to form a grout admixture. This admixture is then allowed to cure and the waste compounds are immobilized in the hardened mass to an extent. A way to test the efficiency of the immobilization is to perform a toxicity characteristic leaching procedure (TCLP) test. This form of waste treatment is useful; however, the toxic, hazardous, or radioactive species frequently is not immobilized sufficiently and the cured waste/cement mass falls to pass the TCLP testing. Other techniques used to treat such waste streams includes vitrification processes. In such processes the waste is added to a molten matrix, typically a glass matrix, where the aqueous and volatile matter is evaporated and the heavy metals, radioactive species, and other harmful compounds are entrapped in the glass material. The glass is then cooled and allowed to harden to solidify and immobilize the waste. However, such techniques are generally reserved for relatively higher level wastes due to the prohibitive costs of vitrification processing. Thus, there exists a need in the art to develop processes for the efficient, economical, and reliable waste stream solidification and immobilization of harmful species. Ideally such an improved process would utilize the cement solidification technology, which is relatively inexpensive and commercially available, and improve upon that technology to provide for superior immobilization results. SUMMARY OF THE INVENTION The present invention provides methods and processes for immobilizing and solidifying harmful heavy metal and radioactive species within a waste material. The processes of the present invention are also particularly advantageous for immobilizing and solidifying nitrate compounds with a waste material. One embodiment of the present invention is a method that can be carried out by admixing the waste material with cement and a complexant compound to form a grout admixture. Preferably, the complexant compound is an iron compound that can form a hydrated iron oxide in the presence of an aqueous solution. This grout admixture is then allowed to cure and solidify. Preferably, the grout admixture is treated to remove excess aqueous fluid from the admixture, such as by way of filtration. The grout admixture is placed within a suitable containment vessel for final storage and disposal. In particular, one embodiment of the present invention is a method for the immobilization of hazardous and/or radioactive species present within a waste material. The method is practiced by blending 100 parts by weight of a waste material comprising water and at least one heavy metal species or at least one radioactive species with from about 5-50 parts by weight of cement and a complexant comprising an iron compound, wherein the weight ratio of elemental iron to cement is from about 1:3 to about 1:50, to form a grout material. Excess aqueous fluid is separated from said grout material to form a condensed grout waste, and this condensed grout waste is allowed to cure and solidify. The presence of the complexant compound provides for superior immobilization and solidification of the various potentially harmful species, such as heavy metals, radionuclides, and nitrates. In particular, iron has been found to greatly enhance the immobilization and solidification performance of the cement. |
claims | 1. A doorless radiation attenuation corridor through which patients pass through to a room containing a source of radiation, said corridor comprising:an entry corridor having walls, a ceiling and a floor made of radiation resistant materials, said entry corridor defining a first axis along which said patients pass from a safe region;an intermediate corridor attached to said entry corridor, said intermediate corridor having walls, a ceiling and a floor made of radiation resistant materials, said intermediate corridor defining a second axis along which said patients pass,said walls of said intermediate corridor having portions which are substantially parallel to one another, said substantially parallel portions of said walls of said intermediate portions forming angles with said second axis of between 10° and 45°;a final corridor leading to said room containing said radiation source, said final corridor having walls, a ceiling and a floor made of radiation resistant materials, said final corridor defining a third axis along which patients pass said third axis being at substantially a 90° angle to said second axis;wherein radiation from said radiation source is substantially attenuated between said radiation source and said safe region in a doorless corridor. |
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047568674 | abstract | The remote measurement device comprises a supporting structure (5) consisting of a plane annular base connected to the end of a handling pole of great length, and a movable measuring assembly carried by the base (5) and consisting of a stage (30) movable in all directions of the plane of the base coming to rest on the plate (3). The stage (30) is integral with a tubular sleeve (36) the axis of which is perpendicular to the plane of the stage (30), and the supporting structure (5) has a thrust assembly (18) abutting against the outer surface of the sleeve (36). A tracer (38) with a movable rod is mounted on the sleeve (36), with its rod (40) in a radial direction and pointed towards the interior of the sleeve (36). For measurement, the sleeve (36) is slipped onto the cylindrical element (4), and the thrust assembly (18) moves the sleeve (36) and the stage (30) forming the movable measuring assembly as a result of a radial thrust exerted on the sleeve (36) in a zone diametrically opposite the tracer (38). The position or movements of the rod (40) of the tracer (38) are measured. |
040100693 | claims | 1. A vented nuclear fuel rod comprising a tubular casing having upper and lower ends and which is integral throughout between said ends, a lower end cap closing said lower end, said upper end having an upper end cap having a substantially central, axially extending hole formed therethrough and a flange which is welded to said upper end, said casing having an inside and said upper end cap having a tubular stub projecting into said casing and radially spaced from said inside, a tubular filter casing inside of the first-named casing and having an upper end which is welded to said tubular stub, said filter casing having a lower end and a filter end cap welded thereto and through which a hole extends axially, said filter casing having an inside in which filter material is pressed to a degree preventing gas by-passing between the material and the inside of the filter casing, and nuclear fuel positioned within the first-named casing's said inside between said filter end cap and said lower end cap of the first-named casing. |
abstract | Disclosed is an installation (1) for sterilizing objects (8) by means of a radiation source (50). The installation (1) comprises an irradiation zone (5) in which the radiation source (50) is arranged. An entry zone (3), which is preceded by a feed zone (2), is mounted in front of the irradiation zone (5) while an exit zone (4), which is followed by a subsequent processing zone (9), is mounted behind the irradiation zone (5). A transportation line (6) that is used for conveying the objects (8) extends through the installation (1). One respective shield (7) is associated with the entry zone (3) and the exit zone (4). The entry zone (3) encompasses a first inlet opening (31) that has a passage to the feed zone (2) as well as a second inlet opening (32) which has a passage to the irradiation zone (5). The exit zone (4) has a first outlet (41) that has a passage to the irradiation zone (5) as well as a second outlet opening (42) which has a passage to the subsequent processing zone (9). The transportation line (6) extends in alignment through all inlet openings and outlet openings (31,32;41,42). The shields (7) are movable. In each position of the shields (7) in which the objects (8) that are conveyed through the installation (1) can penetrate one of the two inlet openings (31,32) or one of the two outlet openings (41,42), the other inlet opening (32,31) and the other outlet opening (42,41) are covered by the associated shield (7). |
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claims | 1. A process for hydrogen combination in nuclear power stations, reprocessing plants, or fuel element stores, comprising:providing a nuclear power station, a nuclear fuel reprocessing plant or a nuclear fuel element store, in which hydrogen is generated by the contact of nuclear fuel with water, or by the contact of hot metal with water; andcontacting the hydrogen generated in the nuclear power station, the nuclear fuel reprocessing plant or the nuclear fuel element store and oxygen with a catalyst to form water, wherein the catalyst comprises an intrinsically hydrophobic BEA zeolite having a SiO2/Al2O3 ratio greater than 100, the BEA zeolite not being hydrophobicized with an organosilicon compound, the BEA zeolite containing a catalytically-active noble metal. 2. A process of claim 1, further comprising, after contacting the hydrogen with the catalyst, regenerating the catalyst by burning off organic deposits by heating. 3. A process of claim 1, wherein the noble metal is selected from the group consisting of rhodium, iridium, palladium, platinum, ruthenium, osmium, gold, silver and combinations thereof. 4. A process of claim 1, wherein the BET surface area of the catalyst is from 300 to 900 m2/g, and the integral pore volume of the catalyst is greater than 100 mm3/g. 5. A process of claim 1, wherein the noble metal is disposed essentially in pores of the BEA zeolite. 6. A process of claim 1, wherein the noble metal is platinum, palladium, or a combination thereof. |
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047145820 | claims | 1. For use in a nuclear reactor having an upper stationary structure, a lower stationary structure and a core under said lower stationary structure, an actuating device for vertically moving a cluster of control elements between an upper position in engagement with said upper stationary structure and a lower position where said cluster is retained by said lower stationary structure, said actuating device comprising: a vertical shaft movable along its axis and comprising gripping means at the lower end thereof, grab means fast with said cluster and located at a top end thereof, said grab means having resilient fingers arranged to engage said gripping means and to be latched by snap fitting on the upper stationary structure in a predetermined position, said gripping means being so shaped as to engage with said resilient fingers when the latter are unlatched from said upper structure and when said gripping means are raised beyond the predetermined position which causes locking of the grab on the upper stationary structure, whereas said lower fixed structure is arranged for causing forced disengagement of said gripping means when the latter are lowered by said shaft beyond a rest position of the grab means on said lower stationary structure, raising of the gripping means then driving the grab means by a simple abutment force. an actuating and locking device for vertically moving a cluster of control elements between an upper position in engagement with said upper stationary structure and a lower position where said cluster is retained by said lower stationary structure, said actuating device comprising: a longitudinally movable vertical drive shaft; gripping means fast with the lower end of said drive shaft and including a plurality of upwardly directed rigid blades having radial locking lips at an upper free end thereof, grab means fast with said cluster, located at a top end thereof and including a plurality of upwardly directed resilient fingers, said fingers having radially directed latching projections, recess means formed in said upper structure and dimensioned to receive said latching projections for resiliently locking said grab means in said upper structure, wherein said blades and gripping means are mutually proportioned for said lips to abut said latching projections in an abutment position and to carry said grab means and cluster upon upward movement of said gripping means; for said lips to upwardly force said latching projections into said upper structure until they snap into said recess; and for said lips to slide over said latching projections and to resiliently bend said fingers inwardly upon continued upward movement of the gripping means from the abutment position while said latching projectons are retained in said recess for forcing said latching projections radially inwardly and disengaging said latching projections from said recess. an actuating and locking device for vertically moving a cluster of control elements between an upper position in engagement with said upper stationary structure and a lower position where said cluster is retained by said lower stationary structure, said actuating device comprising: a longitudinally movable vertical drive shaft; gripping means fast with the lower end of said drive shaft and including a plurality of upwardly directed rigid blades having radial locking lips at an upper free end thereof, grab means fast with said cluster, located at a top end thereof and including a plurality of upwardly directed resilient fingers, formed with groove means shaped to receive said lips and to exert a radial expansion force on said fingers for mutually locking said fingers and blades with a predetermined resilient force, said fingers having radially directed latching projections, recess means formed in said upper structure and dimensioned to receive said latching projections for resiliently lockings said grab means in said upper structure, wherein said blades and gripping means are mutually proportioned for said lips to abut said latching projections in a predetermined relative abutment position and to carry said grab means and cluster upon upward movment of said gripping means; for said lips to upwardly force said latching projections into said upper structure until they snap into said recess; and for said lips to slide over said latching projections and to resiliently bend said fingers inwardly upon continued upward movement of the gripping means from the abutment position while said latching projections are retained in said recess for radially inwardly disengaging said latching projections from said recess, and wherein said lower fixed structure has a plurality of pins arranged for abutting connection with said gripping means and for causing forced disengagement of said groove means from said lips when said gripping means are lowered by said shaft beyond a rest position of said gripping means. 2. A device according to claim 1, wherein the gripping means comprise a rigid nipper comprising rigid blades for connection with said resilient finger and a bottom wall formed with passages for pins fast with an upper end nozzle of a fuel assembly and arranged to force out the grab means. 3. A device according to claim 2, wheren said grab means comprise a tubular body split up so as to form said resilient fingers and having a lower part cooperating with said pins and a resilient stop intended to bear on the nipper and having a prestress force greater than the weight of the grab means and greater than the snap engagement force of the latter end of the cluster and wherein the upper stationary structure comprises a grab housing having an annular recess defined by a downwardly facing shoulder on which the resilient fingers bear and by a flange for locking projections of the fingers. 4. A device according to claim 3, further comprising grooves formed in said flange for allowing the passage of the rigid blades, wherein said blades comprise endmost lips intended to cause bending of the fingers during raising of the nipper when the grab is resting thereon, until the lips are engaged in a groove of the fingers, the bending being sufficient for freeing the fingers from the recess and from the flange. 5. A device according to claim 3, wherein said cluster is formed of a plurality of independent sub-clusters, distributed about the vertical shaft and each associated with a grab supported by a cross piece fixed to the shaft and constituting part of said grab means. 6. A device according to claim 2, wherein the pins are carried by the upper core plate of the reactor. 7. A device according to claim 2, wherein said pins are carried by an upper end nozzle of a fuel assembly associated with the cluster. 8. A device according to claim 1, wherein said cluster is formed of elements containing neutron absorbing material. 9. A device according to claim 1, wherein said cluster is formed of elongated elements containing fertile material. 10. A device according to claim 5, wherein said vertical shaft is disposed coaxially with a second shaft connected to a cluster of elements for controlling the reactivity of the reactor. 11. For use in a nuclear reactor having an upper stationary structure, a lower stationary structure and a core under said lower stationary structure, 12. For use in a nuclear reactor having an upper stationary structure, a lower stationary structure and a core under said lower stationary structure, 13. An actuating device according to claim 12, wherein each of said radially directed latching projections is separated by said groove means into a lower portion having a first radial distance from an access of said grab means and an upper portion having a greater distance to said axis. |
description | The Government has certain rights in the invention pursuant to Work for Others Agreement No. 854V0. This application claims priority to U.S. Provisional Patent Application No. 61/306,754, filed Feb. 22, 2010; the content of which is incorporated by reference herein in its entirety. This application incorporates by reference in its entirety U.S. patent application Ser. No. 12/696,851, filed Jan. 29, 2010; the content of which is incorporated by reference herein in its entirety now U.S. Pat. No. 8,571,167. The present invention relates to nuclear power plants, and, more particularly, to fast neutron spectrum, sodium cooled reactors with metallic fuel. World electricity demand is expected to as much as double by 2030 and quadruple by 2050. The world electricity demand increase is forecasted to come from developed countries but to an even larger extent from developing countries. To meet rapid growth in developing countries, nuclear energy should be packaged in a configuration tailored to meet their specific needs. A fast neutron spectrum, sodium cooled reactor with metallic fuel is described. FIG. 1 illustrates an exemplary Small Modular Reactor (“SMR”) system 501 of the present invention. The SMR system may include a uranium-fueled core 503. The core composition may be enriched (<20%) uranium/zirconium alloy for the initial core and recycled uranium/transuranic zirconium for subsequent cores. Uranium 235/thoruim/zirconium alloys may also be used in some embodiments. The core 503 may be submerged in a tank 505 of ambient pressure liquid sodium 507. The tank 505 may be thin-walled stainless steel, and may be sized for shipment by barge or rail. The tank 505 may be positioned in a guard vessel 517 and a deck 521 of the tank 505 that may be enclosed by a removable dome 519. The guard vessel 517 and dome 521 together may create a containment 523. The SMR system 501 may be encased in a concrete silo 515. The core 503 and its containment 523 may be emplaced in a concrete silo with a concrete cover. The silo and its cover may create a shield structure to protect the reactor system 501 and the containment 523 from external hazards. The shield structure and/or the containment 523 and reactor 503 may be seismically isolated. The SMR system 501 may also include control rods 513. The liquid sodium 507 from the tank 505 may be pumped by one or more pumps 509 through the core 503 to carry heat away from the core 503. The liquid sodium 507 may carry the heat to one or more sodium to sodium heat exchangers 511. The liquid sodium 507 may be heated from about 350° Celsius to about 510° Celsius. FIG. 2 shows the SMR system 501 within a larger energy generation system 601. The heated sodium 507 may pass through the heat exchanger 511 to heat secondary sodium, which in turn passes through a secondary heat exchanger 603 where the secondary sodium heats supercritical (almost liquid) carbon dioxide. The supercritical CO2 is compressed to 21 MPa, just above its critical point at approximately 7 MPa and approximately 31° C. It is then recuperated to ˜350° C. in regenerative heat exchangers 609; then further heated to ˜500° C. in the Na-to-CO2 heat exchanger. The recuperation and compression of a nearly-liquid fluid allow for an approximately 40% energy conversion at a relatively low temperature compared to ideal gas Brayton cycles. The heated supercritical carbon dioxide may then be used to spin a gas turbine 605 to make electricity in an electrical generator 608 in a carbon dioxide Brayton cycle building 607. The turbine 605 and compressor 606 rotating machinery is very compact owing to the high density of the CO2. “Printed circuit” heat exchangers used for recuperations and for sodium to supercritical carbon dioxide heat exchange 603 are of extremely high power density. Altogether the supercritical CO2 Brayton cycle is much more compact than comparable Rankine steam cycle energy converters. The Brayton cycle may provide the SMR a thermal efficiency (heat energy converted to electricity) of approximately 39% to approximately 41% or more, an efficiency much higher than conventional light water reactor (“LWR”) steam driven turbines. Furthermore, in certain embodiments of the present invention waste heat can be used to meet lower-temperature needs, such as space heating, water desalination, industrial process heat, or can be dissipated through cooling towers. Small sodium-cooled fast reactors may demonstrate important inherent safety characteristics. These reactors may operate with simplified, fail-safe controls that may facilitate rapid licensing by regulatory authorities. For example, in response to an accident condition, such as loss of coolant flow, overcooling in the heat exchanger, control rod runout or loss of ability to reject heat, embodiments of the reactor may shut themselves down without human or safety-system intervention. For instance, as the reactor coolant heats up, the core structures may thermally expand causing increased neutron leakage from the core, in turn causing power levels to decrease in a self-correcting fashion. SMR operation requirements may be significantly simpler than conventional nuclear systems due to a characteristic that allows the reactor to innately follow load requirements brought upon by varying levels of electricity demand. Metal alloy fuel is well demonstrated, both from performance and fabrication perspectives, and can straightforwardly meet long refueling time interval requirements. Additionally, a cermet fuel may be used, while the cermet fuel none-the-less retains metallic alloy fuel attributes. The reactor core may have a long life, up to about 20 years or more. The reactor may not have or require permanent onsite refueling equipment or fuel storage capability. Refueling may be done by an outside service provider that brings refueling equipment with a new core, changes the core out, and takes both used core and refueling equipment away when completed. Fuel handling and shipping can commence at a very short time after reactor shutdown owing to the derated specific power (kwt/kg fuel). One or more multi-assembly clusters in a reactor core may have derated specific power (kwt/kg fuel) for enabling long refueling intervals while remaining in the existing fuels database. This may also enable refueling operations very shortly after reactor shutdown. Refueling operations may start within approximately two weeks of overall reactor shutdown, and may finish within approximately 1 month of overall reactor shutdown. The whole reactor core may be replaced at one time, about every 20 years. As such, the reactor system may have no requirement that the operator handle fuel. The overall unit may be sealed, physically and with electronic monitors, so that any intrusion attempt is easily detected. The elimination of any need or the ability to gain direct access to the fuel and use of smart monitoring systems not only reduces operator requirements, but also addresses proliferation concerns. Additionally, the SMR is small enough to be located below ground, which enhances containment and protection from terrorist activities. Finally, embodiments of the system are small enough that they can be shipped by barge, rail, and truck and installed at the site using modular construction techniques: this ability to remotely manufacture and obtain economies of serial production is a desirable benefit. When the fuel cartridges are returned to the manufacturer/designer/fabricator's facility, nearly all of the used nuclear material can be recycled and used as fuel in future cartridges, greatly reducing the volume and radio-toxicity of the final waste to be stored in a geologic repository. Unlike used fuel from conventional light water reactors, material from SMR's need not be stored for tens of thousands of years. Non-recyclable materials from SMR's require only a few hundred years of storage before the waste decays to levels of radiation associated with the original uranium ore. The reactor concept and its supporting fuel cycle infrastructure may offer a configuration of nuclear energy tailored to meet the needs of emerging electricity markets in developing countries as well as imminent global need for carbon-free non-electric energy sources. This configuration of nuclear energy may rely on the huge energy density of nuclear fuel (>106 times that of fossil fuel) to enable a distributed fleet of small fast reactors of long (20 year) refueling interval, providing local energy services supported by a small number of centralized facilities handling fuel supply and waste management for the entire fleet. The reactors may be sized for local and/or small grids, and are standardized, modularized and pre-licensed for factory fabrication and rapid site assembly. Correspondingly, the centralized fuel cycle infrastructure may be sized for economy of scale to support a large fleet of reactors in the region and may be operated under international safeguards oversight. The configuration is tailored to meet the tenets of sustainable development. FIG. 3 illustrates an exemplary nuclear energy infrastructure in its mature stage. A regional center 701 may supply/ship reactor fuel and/or accept spent fuel returns from sub-regions, such as countries 703. Various regional centers 701 may trade in fissile and fertile material to level out regional surpluses and/or shortages. Reactor Overview Embodiments of the present invention may include an approximately 50 MWe (125 MWt) to approximately 100 MWe (260 MWt) sodium-cooled fast reactor operating on a long (approximately 15 to approximately 20 year) whole core refueling interval. An initial fuel load may be enriched uranium (<20% enriched) in the form of metal alloy fuel slugs, sodium or helium bonded to ferritic-martinsitic cladding. The reactor may exhibit an internal breeding ratio near unity such that its reactivity burnup swing is small and its core is fissile self-sufficient. A burnup swing of less than approximately 1% Δk/k may facilitate passive safety and passive load follow. Embodiments of the present invention may attain 80 MWtd/kg or more fuel average burnup, and upon pyrometallurgical recycle at completion of its 20 year burn cycle, depleted uranium makeup feedstock may be all that is required for the reload core. Upon multiple recycles, the core composition may gradually shift to an equilibrium transuranic fuel composition, which is also fissile self sufficient, and thus requiring only U238 makeup upon recycle. A forced circulation heat source reactor may deliver heat at ˜500° C. through a sodium intermediate loop that drives a supercritical CO2 (S—CO2) Brayton Cycle power converter attaining ˜40% conversion efficiency and may be capable of incorporating bottoming cycles for desalination, district heat, etc. Other embodiments might drive a Rankine steam cycle. Embodiments of the present invention may employ passive decay heat removal; achieve passive safety response to Anticipated Transients Without Scram (ATWS); and employ passive load follow. The balance of plant may have no nuclear safety function. The plant may be sized to permit factory fabrication of rail and barge shippable modules for rapid assembly at the site. Embodiments of the present invention may have features targeted to meet infrastructure and institutional needs of rapidly growing cities in the developing world as well as non-electric industrial and/or municipal niche applications in all nations. Targeting Emerging Markets Nuclear energy is a well-established industrial business that, over the past 35 years, has attained 13,000 reactor years of operating experience and 16% market share of world electricity supply. Nuclear energy is being deployed primarily in the form of large size (greater than or approximately equal to 1200 MWe) plants in industrialized nations. There are currently 436 reactors deployed in 30 countries. Future growth in nuclear deployments is projected to be as much as 66% or even 100% additional capacity by 2030. The majority of the growth is projected to take place in developing countries where institutional and infrastructure conditions often differ from those that, in the past, favored large scale plants and a once through fuel cycle. Developing nations often have small, local grids of under a few tens of GW, which are unable to accommodate a 1.2 to 1.5 GWe sized plant. Embodiments of the present invention operating at 100 MWe, are not only compatible with smaller grid size but additionally, the smaller capital outlay required for its installation is compatible with a developing country's necessity for sharing limited financing across multiple development projects during the early decades of its rapid economic growth. A twenty year refueling interval with fuel supply, recycle, and waste management services outsourced to a regional center enable a nation to attain unprecedented energy security even absent a need to first emplace a complete indigenous fuel cycle/waste management infrastructure. Moreover, centralization of fuel cycle facilities for economy of scale in technical and institutional safeguards operations may facilitate an international nonproliferation regime even for widespread worldwide deployment of nuclear-based energy supply. The energy supply growth rate in industrialized countries is projected to be slower than in developing countries. Nonetheless, new nuclear plants are needed for replacements of coal and nuclear plants as they are decommissioned at end of life. The large capacity interconnected grids in industrialized nations are compatible with large power rating plants. Niche markets, however, are expected to rapidly emerge in both developed and developing nations for non-electric and/or cogeneration applications of carbon-emission-free nuclear energy. Among these markets may be water desalination, oil sands/oil shale recovery and upgrading, and coal or bio to liquids synthetic fuel production. Passive safety posture precludes any safety function being assigned to the balance of plant and along with the reactor's reduced source term favor siting adjacent to industrial and municipal installations. Features of the Fuel Cycle First, the core power density (kwt/liter) and fuel specific power kwt/kg fuel may be derated so as to achieve a 20 year refueling interval while remaining within the bounds of the established metallic alloy fuels experimental database. This may provide a client long term energy security and a high level of reliable availability. Second, the once in 20 year whole-core refueling may be conducted by factory personnel who bring the refueling equipment and fresh fuel from offsite, conduct the refueling operations, and then return the used core and the refueling equipment to the factory. This may provide the client a way to attain energy security absent a prior need to emplace indigenous facilities for enrichment, fuel fabrication, reprocessing, and waste repositories. Third, the refueling operations may be done on the basis of a fuel handing assembly that may include multiple sub-components. Various numbers of sub-components may be included and may or may not be clustered. As an example, see an exemplary core made of seven fuel assembly clusters 801 in FIG. 4. FIG. 4 shows an exemplary arrangement of core components. For example, an outer layer of shield assemblies 803 may cover a layer of reflector 805, which may cover a layer of outer core 807. Middle core 809 of a lower enrichment may generally surround inner core 811 of still lower enrichment with primary control 813 and secondary control 815 assemblies placed within the core 801. As shown, the fuel, reflector, shield and control rod assemblies are grouped into seven-assembly clusters to speed the rate of core refueling. During operations, the seven-assembly cluster may be transferred after a very short cooling period following reactor shutdown so as to minimally interrupt energy supply availability. The short cooling period and seven-assembly cluster features may be possible due to the derated fuel specific heat (kwt/kg fuel). Fourth, the first fuel loading may be enriched uranium (enrichment <20%) and the core may be fissile self-sufficient such that at the end of the 20 year operation interval, the core contains as much bred-in fissionable content as has been burned out. Upon pyrometallurgical recycle of the used core, only U238 feedstock and fresh cladding may be required for refabrication of a replacement core. Fifth, over multiple recycles, the composition of the core may gradually transition from a U235-rich composition towards an equilibrium transuranic-rich composition that is also fissile self sufficient. The fuel cycle waste stream may exclusively include fission products, which require only 200 to 300 years of sequestration before decaying to background levels of radioactivity, whereas all transuranics may be returned to the reactor as fuel where they are converted to fission products. Sixth, after the first core loading, all subsequent cores may require only U238 as feedstock. This may extend the world's ore resource potential to nearly 100% productive use, and yielding at least a millennium of energy supply. Capability to use thorium-based metallic alloy fuel extends the world's resource base to multi millennia. Seventh, the fuel fabrication technology may offer the option of incorporating LWR used fuel crushed oxide particles onto a metallic alloy to form a cermet. This option, when combined with an added (oxide reduction) step in the pyrometallurgical recycle process may offer a route to cost effective management of LWR used fuel by subsuming it into the fast reactor closed fuel cycle. Features of a Heat Source Reactor First, a core layout may include assembly clusters of individually ducted and orifaced fuel assemblies. As described above, see FIG. 4 for exemplary seven-assembly clusters in a core layout. In other embodiments, other numbers and arrangements may be contemplated. The assemblies may be grouped into clusters for fuel handling while preserving individual fuel assemblies so as to retain the orificing and the limited free bow reactivity feedback characteristics. Replaceable reflector and shield assemblies may be grouped into 3 or 4 assembly clusters. Second, a “limited free bow” core clamping approach may be used. The clamping approach may utilize a removable and vertically adjustable horizontal wedge 901 located in a central assembly position of a core layout of ducted fuel assemblies 913 at an elevation approximately at above-core load pads 903, as shown in FIG. 5A. Note that radial displacement as shown in FIGS. 5A and 5B is exaggerated. The wedge 901 may be attached to a driveline 905 coupled to a vertical positioning mechanism 907 on a reactor deck 909. Preferably, the wedge 901 is at a lower end of the driveline 905, where the driveline 905 is in a vertical orientation. The wedge 901 can be removed/withdrawn to loosen the core for fuel handling, as shown in FIG. 5B. The wedge 901 can be re-inserted to clamp the core 915 and top load pads 917 outward against a core former ring 911 at a top load pad elevation once refueling is completed. Preferably the top load pads 917 may surround one or more ducted fuel assemblies 913 at approximately a top end of the ducted fuel assemblies 913. The above-core load pads 903 may surround one or more ducted fuel assemblies 913 above a fuel elevation, but below the top load pads 917. A grid plate elevation may approximately correspond with a bottom end of the ducted fuel assemblies 913. Third, a core may retain performance parameters, both operational and safety, even as the fuel composition evolves over the 20 year burn cycle and further evolves from one recycle loading to another. Fourth, embodiments of the present invention may include a strategy to monitor reactivity feedbacks throughout core life and to fine-tune their values using the vertical position adjustment of the wedge, should they drift as the core ages over its 20 year burn cycle. The integral reactivity feedbacks may be measured in situ by non-intrusive small adjustments of coolant flow rate, inlet coolant temperature, and control rod position. The rest position of the core clamping wedge 901 may be used to adjust the value of a core radial expansion component of the inherently negative power coefficient of reactivity, as shown in FIGS. 6A-6C. Note that radial displacement as shown in FIGS. 6A-6C is exaggerated. As shown in FIG. 6A, increasing power may increase outward (towards the right in FIGS. 6A-6C) bowing 951 of fuel assemblies 913. Unrestrained flowering upon an increase in core power may result from an increase a radial thermal gradient on the ducted fuel assemblies 913. Inboard ducted fuel assemblies 913 may push outward, as shown in FIG. 6B. Limited free bow core restraint may enhance radial dilation at fuel zone elevation of ducted fuel assemblies 913. As shown in FIG. 6C, an increase in coolant outlet temperature may bathe the wedge driveline 905 with increased temperature such that the driveline's thermal expansion may drive the wedge 901 downward/deeper. This may in turn amplify the radially outward bowing of core fuel assemblies 913 at a fuel zone elevation, which then may increase axial leakage and reduce reactivity. By adjusting a rest position of the wedge 901 at full power and full flow, the amplitude of the bowing enhancement can be fine tuned. Fifth, a passive safety response may be provided for loss of flow, loss of heat sink, chilled coolant inlet temperature and single rod runout transient overpower (ATWS) transient initiators without scram. The innate reactivity feedbacks with respect to power and fuel and coolant temperatures, when combined with a nearly zero reactivity burnup swing and with natural circulation capability at decay heat levels, may take the reactor to an undamaged safe state for all ATWS initiators, i.e., no damage may be incurred and a stable state may be reached for these initiators even if the rods fail to scram. Sixth, a passive decay heat removal channel may be provided to the ambient atmosphere ultimate heat sink always operating as a backup to active decay heat removal channels. The passive channel may always be operating at less than or approximately equal to 1% full power and can be confirmed to be functioning at all stages of core life by in situ non-intrusive measurements. The heat capacity of the core and internal structure is sufficient to safely absorb the initial transient of decay heat in excess of the passive channels' capacity. Features of a Power Plant First, a heat source reactor driving a S—CO2 Brayton cycle energy converter may attain nearly 40% or more heat to electricity conversion efficiency while operating in the working fluid range of ˜500° C., 21 MPa to 31° C., ˜7 MPa. This converter may use rotating machinery of extraordinarily high power density and recuperative heat exchangers of exceptionally high power density. Second, a heat source reactor may passively load follow the energy converter demand for heat. The reactor may sense the balance of plant demand communicated via flow rate and return temperature of the intermediate heat transport loop. The reactor's innate reactivity feedbacks may maintain heat production in balance with heat removal through the intermediate loop within tens of seconds and without need for active adjustments of control rods. Third, a Balance of Plant (BOP) may be provided that carries no nuclear safety function and can be built, operated and maintained to normal industrial standards. The reactor can passively accommodate all physically attainable combinations of flow rate and return temperature returning from the BOP through the intermediate heat transport loop. The passive decay heat removal channel may have no dependence on the BOP, and the nearly zero burnup control swing makes a rod runout TOP resulting from a control system error a no damage event. So the BOP need not carry any nuclear safety function. Fourth, embodiments of the present invention may include a potential to tie a broad diversity of BOP configurations to a standard, pre-licensed heat source reactor since the BOP carries no nuclear safety function. The S—CO2 Brayton cycle may reject ˜60% of supplied heat and may do so between ˜100° C. and 31° C. Many cogeneration options may exist for such a temperature range, including multi-effect distillation desalinization; district heat; district chilled water; ice production and others. Alternately, diverse non-electric industrial processes may be co-sited closely with the heat source reactor, given its self-protection features, small source term, passive load following feature, and high level of availability. Although the foregoing description is directed to the preferred embodiments of the invention, it is noted that other variations and modifications will be apparent to those skilled in the art, and may be made without departing from the spirit or scope of the invention. Moreover, features described in connection with one embodiment of the invention may be used in conjunction with other embodiments, even if not explicitly stated above. |
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052727424 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is generally related to nuclear reactor fuel assemblies and particularly to springs used in end fittings of the assemblies. 2. General Background Typically, a nuclear reactor for the generation of electrical power includes a core of fissionable material to heat a coolant flowing up therethrough. The fissionable material is enclosed in elongated fuel rods assembled in a square array called fuel assemblies. The fuel rods are held in spaced parallel relationship by a number of spacer grids distributed at intervals along the length of the assembly. The fuel assemblies are held in an array by core grid plates at the top and bottom and are provided with upper and lower end fittings for mating with the grid plates. Typically, holddown spring means is provided between the upper end fitting and the upper core grid plate. This is necessary to provide sufficient holddown force against hydraulic lift forces in the core generated by coolant flow. The springs also allow for axial dimensional growth of the fuel assembly due to either differential thermal expansion or irradiation induced material change. The problems of design, therefore, are in the ability to provide sufficient holddown force against hydraulic lift while allowing sufficient room for growth. Sufficient material strength and stiffness must be available within a limited volume area. The stiffness/volume efficiency of a spring becomes very important when used for nuclear fuel holddown. Known devices which address this problem include the following. U.S. Pat. No. 4,551,300 entitled "Nuclear Reactor Fuel Assembly End Fitting" discloses an end fitting having a plurality of rigid levers and elastic means in recesses in the end fitting which exert a restoring torque on corresponding levels. U.S. Pat. Nos. 4,072,562 and 4,072,564 disclose the use of torsion bars as holddown means. U.S. Pat. Nos. 4,671,924; 3,801,453; 4,427,624; 4,631,166; and 4,420,457 disclose the use of leaf springs as holddown means. U.S. Pat. No. 4,986,960 discloses the use of an end fitting having hairpin shaped springs along each side of the end fitting. U.S. Pat. Nos. Re 31,583; 3,475,273; 3,515,638; 3,600,276; 3,689,358; 3,770,583; 4,076,586; 4,078,967; 4,192,716; 4,208,249; 4,278,501; 4,534,933; 4,560,532; and 4,729,868 disclose the use of a variety of holddown devices including helical springs and are representative of the general state of the art. In certain reactor designs, the upper end fitting also has a pedestal attached to the grillage. The pedestal serves as a resting point for control rod and axial power shaping rod assemblies. It is from this location that the reactor control component drives as well as other handling systems (not in the reactor) connect with the control rod and axial power shaping rod assemblies. The force of the helical holddown spring used in these designs is transmitted to the reactor internals by way of a spring retainer. The holddown function of the spring and the interface function of the pedestal are independent. Helical springs present two problems. They are fully exposed to coolant flow which subjects the springs to the dynamic stresses of flow induced vibration. Also, reconstitution of a fuel assembly utilizing helical springs is a relatively complex operation. Known structures that use a pedestal affixed to the upper end fitting grillage do not permit the use of a central leaf spring and the advantages it affords relative to the helical holddown spring. SUMMARY OF THE INVENTION The present invention addresses the above need in a straightforward manner. What is provided is an upper end fitting that combines the function of the control assembly pedestal of the end fitting and the connecting bolt and nut of a leaf holddown spring assembly. Leaf springs are bolted together such that the exterior radius of the leaf springs are facing each other. The nut and bolt used to connect the leaf springs together are sized to extend above the leaf springs and serve as the pedestal that will properly position the control assemblies. A spring retainer above the leaf springs is provided with a hole that allows passage of the nut and bolt as the system is deflected by the reactor internals upon installation. |
abstract | A charged particle beam apparatus can be constructed with a smaller size (resulting in a small installation space) and a lower cost, suppress vibration, operate at higher speed, and be reliable in inspection. The charged particle beam apparatus is largely effective when a wafer having a large diameter is used. The charged particle beam apparatus includes: a plurality of inspection mechanisms, each of which is mounted on a vacuum chamber and has a charged particle beam mechanism for performing at least an inspection on the sample; a single-shaft transfer mechanism that moves the sample between the inspection mechanisms in the direction of an axis of the single-shaft transfer mechanism; and a rotary stage that mounts the sample thereon and has a rotational axis on the single-shaft transfer mechanism. The single-shaft transfer mechanism moves the sample between the inspection mechanisms in order that the sample is placed under any of the inspection mechanisms. The rotary stage positions the sample such that a target portion of the sample can be inspected by the inspection mechanism under which the sample is placed, and the inspection mechanisms inspect the sample. |
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043812813 | description | DESCRIPTION OF A PREFERRED EMBODIMENT Referring now especially to FIGS. 1, 1-A and 1-B there is seen the active core 1 of the reactor in which are positioned the active, or driver fuel elements of the type shown in FIG. 2-A. Also forming a part of this component is our core baffle 2 positioned around the periphery of the central core and comprising fuel elements of the type shown on FIG. 2-B. The latter is shown more clearly in FIG. 1-A and conceptually in FIG. 1-B, the broken lines A-A and B-B denoting the geometric limitations of the active core. It can be seen that the core baffle 2 actually surrounds and delimits the active core. Core barrel 3 and thermal shield 4 are clearly indicated as located inside pressure vessel shell 5. Positioned around the central active core are shown the blanket elements which in general comprise fuel elements of the type shown in FIG. 2-B and containing primarily the fertile thorium fuel. The first two series of elements positioned between the outside of the core baffle and the inside of the core barrel are shown at 6 and 7 respectively. A second series positioned on the outside of the core barrel and the inside of the thermal shield are shown at 8 and 9 respectively. All of these are best seen on FIG. 1-B in their relative positions and are shown in combined form on FIG. 1-A. It is seen how the elements shown at 2 form both a part of the blanket arrays and part of the active core, the reason for which is evident from the description of operation given below. The upper and lower ends of the fuel elements 32 of FIG. 2-A comprising as they do fertile thorium serve also to form the top and bottom portions of a complete blanket around the active core. A lower support grid plate 10 is of a more or less conventional type and serves to hold the fuel elements comprising the active core. An upper grid plate 11 which is removable is also of a more or less conventional type. Circular openings 12 in the grid plates serve to accommodate the fuel elements. The coolant inlet to the reactor is shown at 13 and the outlet at 14, the direction of flow being indicated by the arrows inside the reactor vessel. The method of mechanical positioning or support of the elements comprising the outer blanket arrays may be by a separate grid plate not shown, but disposed for removal and reinsertion of the fuel elements in the course of operation of the reactor after removal of the vessel head (also not shown). As thus arranged and positioned the components of our reactor combine to function and permit the operation of our reactor in the novel manner and produce the novel results set forth and claimed below. Referring now to FIG. 2 and first to FIG. 2A there is shown diagrammatically the relative position of the various components of an individual fuel rod. At 31 there is seen diagrammatically the active fuel which may comprise enriched uranium oxide (UO.sub.2) pellets encased in reactor fuel tubing. The tubing may be of zircaloy, stainless steel or other material having similar nuclear properties. There is also seen at 32 the fertile fuel which may comprise thorium oxide (ThO.sub.2) pellets likewise enclosed in the reactor fuel tubing. In plenum chambers 33 there is positioned a spring 33a and a spacer 33b. The spring may be of helical configuration. This component of our invention serves to provide necessary expansion for the collection of fission gases, as well as for the separation of the active or fissile fuel from the fertile fuel for reasons which are developed more fully below. Where further separation of the kind is required, we replace the fertile material and/or active fuel with inert or neutron moderating material at 35. The above described fuel rods represent the fuel rods located throughout the active core. The position of the fertile material at the top and bottom of the rods serves to form a top and bottom blanket of thorium in the core. Referring now to FIG. 2B there is seen another fuel rod in which like numbers represent like components. In this case the rod consists entirely of thorium pellets 32 and this is the fertile material which is shown located as part of the blanket at positions 6, 7, 8, and 9 of FIG. 1. In addition, as noted previously, we provide for an outer annular blanket of thorium within the active core by replacing the active fuel rods adjacent to the core baffle 2 with fertile thorium rods of FIG. 2B. For these blanket arrays, only one, each, of which is shown in FIG. 1, we install rod holders on the outside of the core baffle, inside the core barrel, outside the core barrel, and inside the thermal shield to hold the thorium-filled rods. We locate these rods in contiguous arrays; or we space them out (depending upon the neutron flux and time of irradiation at each specific location). The pellets contained in these rods may be hollow or solid or a mixture of solid and hollow pellets 34 corresponding in a roughly inverse manner to the reactor flux profile; the significance of the hollow pellets is detailed below. FIG. 2C represents an alternate embodiment of the fuel rod of FIG. 2A. In this embodiment we utilize hollow pellets of thorium 34 and active fuel 36 to form an annulus within which at 34a moderating material may be included, e.g., water from the reactor coolant system. Thorium pellet sizing and configuration described above is for the purpose of minimizing fast neutron reactions in thorium due to fissioning of the uranium 233 after it is formed. This allows us to maximize uranium 233 formation per unit thorium prior to significant build-up of uranium 232. Specifically, we have discovered that these pellet geometries allow a major fraction of the fast neutrons to escape from the thorium before they have a chance to interact with it. We refer to this as the escape probability for the fast neutrons of concern, i.e., those with energies greater than 6 Mev. Thus, we have discovered this escape probability to be approximately 90% for an infinite array of zircaloy rods containing solid thorium (ThO.sub.2) pellets one-half inch in diameter. Specifically, about 90% of all neutrons from internal U-233 fissioning leave the thorium pellet before interacting. Of the remaining 10% that do interact, only a small fraction are energetic enough to result in the conversion of thorium to U-232; and of these a smaller fraction still (.about.20%) actually produce the (n,2n) reactions of equation (1) above. We have discovered further that we can increase and enhance the fast neutron escape probability (and, hence, minimize [n,2n] reactions on thorium) by employing hollow thorium pellets as described above, and by introducing neutron moderating material such as the water coolant from the reactor into the hollow space. Specifically, we have discovered that for hollow cylindrical pellets as we thin down the cylinder wall the probability increases that internally born fast neutrons escape before interacting with thorium. We have calculated the reduction in fast (above 6 Mev) neutron reactions accomplished by hollowing out the pellets and inserting neutron moderator. For one-half inch cylindrical thorium pellets contained within zircaloy tubing as above, with two-thirds of the internal pellet volume replaced by light-water, reactions within the thorium pellet attributable to neutrons greater than 6 Mev are reduced 33.2% relative to formation of the U-233 product. That is, for a given rate of U-233 production per unit weight of thorium charge, reactions due to neutrons greater than 6 Mev are reduced 33.2%; or, aproximately one-third more fast neutrons escape (and are reduced below 6 Mev in energy by the intervening moderator) than was the case for the solid pellet (90% escape probability). Our calculations show that with further thinning of the pellet wall the fast neutron escape probability continues to increase relative to the U-233 production rate, ultimately approaching 100% for very thin-walled pellets. Our discovery of these methods whereby we can maximize the fast neutron escape probability preferentially relative to U-233 production in thorium target material is important for the successful production of clean U-233 in quantity under our invention. Finally, the segregated thorium embodiment described above performs an additional function important to our invention. Many of the neutrons from the core of the reactor are normally absorbed in the surrounding moderator (water) or absorbed in the structural components. By placing thorium fertile material in these locations the life of the structural components is increased by the reduced neutron absorptions and many of the neutrons are usefully utilized (to form U-233). Of course, some of the neutrons that leak from the core sustain repeated atomic collisions and re-enter the core (are reflected). These neutrons likewise will be reduced because of the thorium absorptions. However, this subtraction of neutrons can be compensated for rather easily by removing some of the neutron absorbers (poison) that are inserted in the core to control the chain reaction after charging undepleted fuel. In other cases, fuel containing slightly higher enrichment can be used. Also, by configuring the in-core top and bottom thorium blankets in predetermined ways we achieve useful flux and power distribution functions in the active core region. Operation The method of charging and operating our reactor comprises an important part of our invention. To demonstrate the effectiveness of our invention a typical example will be analyzed. 1. Period of Irradiation Under average conditions we irradiate for a period of one year using a power density of 50 kilowatts thermal per liter of core volume in the case of a boiling water reactor and 100 kilowatts thermal per liter of core volume in the case of a pressurized water reactor. We charge thorium into the reactor during regular annual refueling outages for power generating purposes. For a reactor delivering 1000 MW of electrical power, a twenty-ton (metric) charge of thorium (as metal or ThO.sub.2) can be accommodated using the embodiments and configurations previously described. This amount of thorium constitutes a practicable charge size for purposes of producing U-233; depending upon U-233 yield requirements, lesser or greater amounts can be charged. We have found that best results are obtained by utilizing an average driver fuel rod power output of approximately 7 KW (thermal) per foot. We discharge thorium from the reactor during normal refueling outages also. We replace the in-core rods with new charge combinations depending upon location and length of desired irradiation. We replace the extra-core radial blanket rods less frequently, allowing 2 to 3 years irradiation for these. 2. Yield and U-232 Contamination After 300,000 MWD (electrical) of normal reactor operation for power generating purposes (over a one-year period), the U-233 yield in our charge will be 100 to 125 kilograms. At present-day nuclear power costs a reasonable value for this U-233 is approximately $5 to $6 million. Using the above embodiments and thorium irradiation methods, we have discovered that the average U-232 content in the irradiated thorium charge will not be greater than 300 to 500 ppm (on an atom ratio, U-232/U-233, basis). However, when U-233 is used as driver fuel the U-232 content tends to build up on repeated recyclings, reaching an asymptotic value four to five times that of the first cycle. The existence of this equilibrium condition is based on the fact that U-232 ultimately is destroyed (by continuous neutron irradiation in the reactor) as rapidly as it is formed or added in by recycling. These and other possible sources of U-232 build-up are countered by the dilution effect, described below, as U-233 is processed and recycled as fuel. (Other sources of U-232 include neutron reactions on the naturally-occurring isotope, Th-230, similar to equations (1) to (3) above, Th-230 sometimes being present as a natural constituent of thorium ores.) Thus, in the final driver fuel embodiment (where the U-233 content is of the order of 2 to 3%) the U-232 contamination will not exceed 10 ppm based on the total uranium present. 3. Chemical Processing and Fuel Use Following irradiation of the thorium charge in the LWR, we chemically process it for direct incorporation of the U-233 into uranium for use as a reactor fuel. We have discovered that the most efficient and safest way to use our clean U-233 product is to co-process the irradiated thorium charge with uranium. The uranium may be in the form of irradiated reactor fuel (from the same or other LWR plants), depleted uranium tailings from U-235 isotopic enrichment process, or natural uranium. Since the U-233 and accompanying U-232 are both diluted 33 to 50 times in the process (the final fuel product containing 2 to 3% U-233), the U-232 content of the final uranium fuel product will not exceed 10 ppm based on the total uranium present, giving due allowance for possible Th-230 contamination of the original thorium ore and repeated recycling U-232 build-up. The major steps in the post-irradiation processing of our thorium-uranium charge are as follows: Step 1--Charge Preparation After a fuel cooling period, we section the fuel rods by guillotining or similar technique. That is, we cut off the ends of the rods so as to include all of the irradiated thorium plus a predetermined amount of the ends of the active fuel sections. We combine these end sections and selected rods from the radial arrays and with uranium from one or more of the sources cited above. Step 2--Co-dissolution of Thorium and Uranium The combined thorium-uranium charge is co-dissolved for chemical processing. Dissolution requires nitric acid treatment with the assistance of hydrofluoric acid. Other processes under development, involving use of volatilization methods, may be appropriate here also. Also, the limited solubility of thorium may be used to advantage in processing to segregate it from streams containing uranium (and plutonium, when present). Step 3--Thorium Separation The outermost thorium blankets are lowest in U-232 content. Therefore, significant amounts of Th-228 (the progeny of U-232) are not present. We are thus able to recover that thorium and prepare it directly for recycle and production of additional U-233. The remainder of the thorium charge must be stored for several years to permit the Th-228 to decay before recycling. For complete extraction of the U-233 from the thorium charge one year out-of-reactor is required to permit completion of the reaction: EQU Pa-233 .beta./27.4d U-233 (4) Step 4--Uranium Separation After blending all of the uranium isotopes together (U-233 from our thorium charge, U-235 and U-238 from natural and/or depleted uranium), we extract and separate the entire isotopic mixture, as uranium, in preparation for fabrication as reactor fuel. By proper proportioning of the driver isotopes, U-233 and U-235, in this processing step we achieve the precise level of enrichment (or driver fuel concentration) desired in the final fuel embodiment. Additional processing steps are added to remove fission products and plutonium, when present. Step 5--Fuel Fabrication In the final step of our fuel processing, the combined uranium isotope matrix (containing<10 ppm U-232) is concentrated and converted to reactor fuel in normal uranium fuel fabricating facilities. Plutonium may be combined with thorium and recycled as fuel in a similar manner to the process we use for combining U-233 and uranium. Depending upon the material inputs and fuel products desired, we vary the method of incorporating the clean U-233 into the uranium fuel matrix. The essential features of our process in all cases are: (1) We produce a thorium-free uranium fuel using U-233. This is important in order to prevent future build-up of U-232 from thorium as is the case with present fuels where U-233 and other driver fuels are burned in the presence of thorium. (2) We produce U-233 relatively free from the contaminating U-232 isotope. Dilution with uranium during processing produces a clean reactor fuel as defined above. (3) We produce a new and novel fuel that utilizes a uranium matrix with the fissile isotopes, U-233 and U-235, as driver; plutonium can be added, also. (4) We produce a fuel that can be fabricated and handled in the same manner as U-235 enriched uranium and which is a more efficient fuel for LWR's than the latter. Thus, we estimate that the total heat generating capacity can be increased as much as 25% when U-233 is substituted for U-235, and up to 50% when U-233 is substituted for Pu-239. If the neutronic properties are fully utilized in a "hardened spectrum" reactor (i.e., a LWR in which the average neutron energy is increased), the total heat generating capacity is increased by an additional 20% in both cases. This includes the fissioning of all progeny in every case. (5) We produce a clean U-233 driver fuel which can be combined directly with uranium so as to reduce or eliminate costly requirements for U-235 enrichment by the gaseous diffusion process and its accompanying process steps, all of which are time-consuming and require large quantities of power. also, using U-233 in place of U-235 conserves the latter as the only naturally-occurring fissile fuel. (6) By guillotining or sectioning the rods to include the irradiated thorium together with the ends of the active uranium fuel columns, we optimally blend the U-233 with the least depleted uranium from the core. Since the costs for uranium enrichment per unit include fixed and variable charges we minimize enrichment costs associated with the spent uranium fuel that is not processed with thorium: i.e., the unit uranium enrichment costs (which are maximum for the fuel of the least depletion or burnup) are decreased. (7) With each successive mixed fuel enrichment with U-233 the synthetic fuel gains efficiency because the naturally occurring U-235 is burned out and replaced with the more efficient U-233. Once uranium has been enriched with U-233, it must be re-enriched upon reactor depletion with U-233 or relatively pure U-235. (8) In uranium-fueled reactors a neutron multiplication is obtained from the fast fissions of U-238. This phenomenon is enhanced with U-233 because the fission-to-absorption ratio is not reduced by energetic neutrons as much as the fission-to-absorption ratio with U-235. (9) In the ultimate U-233 fuel embodiment (represented by FIG. 2C) we have found that the value of improved fuel performance to the reactor operator exceeds that from the concomitant production of U-233. Thus, in this embodiment, we not only achieve optimum moderation (using reactor water coolant) for the top and bottom thorium blankets; but, in addition, we approach optimum utilization of U-233 as a nuclear fuel. By utilizing internal and external cooling of the fuel rods we can harden the spectra by slightly increasing the diameter of the fuel rod and thus increasing the fuel to moderator ratio. By effectively using internal and external cooling we remove the melting point of fuel as a reactor limit and can increase the specific power of the fuel. Such an increase would allow a reduction in reactor size for a given rated power. With U-233 in uranium fuel and a hardened neutron spectra, breeding in light-water reactors would be approached (as noted in the previously cited literature reference to Lang). The above listed design features and earlier description should not be construed as limiting since various modifications can be made as previously noted without departing from the scope of the invention. It is intended that the invention be limited in scope only by the appended claims. The novelty of this invention lies in the deliberate segregation and distribution of fertile thorium with respect to the driver fuel in the fabrication and charging of the fuel assemblies, followed by dilution of any U-232 formed by coprocessing the irradiated thorium with uranium. The effect is to minimize the occurrence of (n,2n) reactions due to neutrons greater than 6 Mev in energy which in turn minimizes production of unwanted U-232. Minimum U-232 production consistent with good power generating performance can be achieved with the invention described herein. U-232 dilution further reduces the problem for the remaining U-232 formed. This results in a U-233 driver fuel that can be more safely and efficiently utilized than previously achievable. |
description | Embodiments of the present invention will be explained hereunder, referring to the drawings. FIG. 1 shows an embodiment of the present invention. In this embodiment, in a boiling water type nuclear reactor in which a plurality of fuel assemblies 2 each surrounded by a channel box 1 are loaded, and a plurality of control rods having control rod blades each disposed between the channel boxes, long blade control rods 6 each having control rod blades extending latitudinally in four directions, respectively, are arranged between the channel boxes on a diagonal of each of square bundle regions each formed of a plurality of (four in this embodiment) the fuel assemblies 2, and short blade control rods 7 each are arranged between channel boxes of each of the square bundle regions at the center of the region, each of which short e blade control rods 7 has a blade length (in a lateral or latitudinal, direction) of about one half of the width of one of the square bundle regions, for example, substantially the same as the width of each of the above-mentioned fuel assemblies. With this construction, as mentioned above, in the long blade control rod 6 arranged between the channel boxes on the diagonal, the control rod worth per one rod increases and the number of control rods and the number of control rod driving devices can be reduced by the number corresponding to an increment of the control rod worth, so that the cost can be reduced. Quantitatively, the number of the control rods can be reduced by 25% as compared with the conventional lattice. FIG. 2 shows an arrangement of the control rods, over the whole reactor core. Symbols ∘ denote the latitudinal long blade control rods 6 and symbols xe2x97xaf denote the latitudinal short blade control rods 7. Moreover, as clearly shown in both FIGS. 1 and 2, the long blade control rods each have a blade length in a latitudinal direction which is about twice as long the blade length in a latitudinal directional of the short blade control rods. It is found that the number of control rods and the number of the control rod driving devices can be reduced largely as compared with the conventional arrangement and the control rod system can be simplified. Further, as explained previously in the summary of the invention, the reactor shutdown margin can be secured easily and the number of control rods is reduced. As a result, Gd for securing a reactor shutdown margin does not remain and low inventory fuel is not loaded, whereby economy is improved greatly. Further, in this embodiment, by sharing the role of the control rods such that the long blade control rods on the diagonal serve for reactor shutdown and the short blade control rods at central portions are for controlling reactivity during operation and at time of scram, the system can be rationalized and simplified, and the cost of the whole plant can be reduced. Further, in the short blade control rods for controlling reactivity, by using a neutron absorber of material (B10) which has a high reactivity effect, the control rod worth of the short blade control rods increases, and scram characteristic and reactivity control characteristic can be increased. Further, since the long blade control rods on the diagonal are not used for scram, a control system of high speed scram, etc. can be omitted, which enables use of a hydraulic driving system of a low cost, whereby a cost is reduced largely. Further, in the above-mentioned embodiment, it is possible to share the role of the control rods such that the long blade control rods 6 on the diagonal are used for controlling reactivity during operation and for shutdown of the reactor and the central short blade control rods 7 are used scram. In this case, the system is rationalized and simplified as mentioned above, so that reduction of the cost can be expected. Further, in the arrangement as shown in FIG. 1, another embodiment, in which the reactivity worth of a control rod is improved at an upper region thereof, is explained hereunder with respect to a neutron absorber used in a control rod. In this embodiment, in particular, enrichment of B10 in the short blade control rod arranged at the central portion of the square bundle is made relatively high at the upper region. In general, in a boiling water type nuclear reactor, since a void ratio is higher at an upper region of the reactor during operation, neutron spectrum is hardened, and production of Pu239 by neutron absorption is promoted. Therefore, the enrichment of fissionable materials becomes high at an upper portion of the reactor and the reactor shutdown margin in the region decreases relatively. In this embodiment, the enrichment of B10 in the upper region of the length of the control rod is increased for the upper region of the nuclear core in which a reactor shutdown margin decreases relatively, whereby the reactor shutdown margin can be increased, as shown in FIG. 4 which is a graph showing the ratio of the high B10 enriched region of the control rod to the reactor shutdown margin. Further, since an amount of used B10 can be reduced, a manufacturing cost can be reduced. Therefore, a cost of the whole plant can be reduced in total. FIGS. 5 and 6 show a conventional core in part and a core in part according to the present invention, each of which is adopted for fuel assemblies of fuel rod lattice structure of 9xc3x979. FIG. 6 shows an embodiment of the present invention in which a large-sized fuel assembly is formed by 4 mini-bundles each of which has a bundle width of about 12 inches (30.5 cm) as used in BWR and, ABWR at present. As in the previous embodiments, in this embodiment in FIG. 6, a cost of the plant can be reduced largely by reduction of the number of control rods. Further, by role sharing of the control rods, a control rod system can be simplified, and a cost the whole plant can be reduced largely. Although not illustrated, fuel rod lattice structures of 8xc3x978 and 10xc3x9710 also can be applied. FIGS. 7A and 7B show another embodiment of the present invention. In this embodiment, fuel assemblies 2 constituting a square bundle region as shown in FIG. 1 each have nine (9) water rods 11 as shown in FIG. 7A. As shown in FIG. 7B, each water rod 11 has an ascending flow path 12 and a descending flow path 13, the ascending and descending flow paths 12, 13 are connected to an inflow hole 14 and an outflow hole 15, respectively, and the inflow hole 14 is positioned at a portion lower than the outflow hole 15. The density of water in each water rod in this embodiment changes largely according to a flow rate of water passing through the fuel assembly. That is, under the condition that a flow rate of water in the core is small, since an amount of steam generated in the water rod becomes larger than an amount of water flowing in the control rod, the water rod inside is filled with steam. When the flow rate of water increases, an amount of water flowing in the water rod goes beyond an amount of steam generated therein, so that the water rod inside is filled with water. Therefore, the water rod inside is filled with steam in operating at a low flow rate in an initial burning stage, whereby an average density of water inside the fuel assembly decreases, so that neutron spectrum is hardened, whereby production of Pu239 is promoted. On the other hand, since the water rod inside is filled with water in operation at a high flow rate in a final burning stage and the average density of water inside the fuel assembly increases, the neutron spectrum is and it is possible to effectively burn Pu239 produced in the operation at a low flow rate, and fuel economy is raised. That is, since excessive neutrons in the initial burning stage can be used for production of Pu239, the number of short blade control rods can be reduced by a decrease in reactivity control by absorption of excessive neutrons during operation, so that further cost reduction is realized. Further, since a lot of the water rods can be arranged by making the fuel assembly large in size, an effect of effective use of Pu239 increases and fuel economy can be improved greatly. In this invention, since the fuel assemblies each are made large in size as the fuel assemblies in FIG. 1, it is effective from a viewpoint of fuel economy to provide, inside each fuel assembly, water rods the cross-sectional area of each of which corresponds to that of several fuel rods. Further, the reactor shutdown margin can be improved by using such material that control rod worth becomes high at a portion facing central side portions of the fuel assembly 2, as a neutron absorber arranged inside the control rod blades. According to the present invention, the number of control rods can be drastically reduced without decreasing control rod worth. Further, since the role of the control rod can be shared, the control system can be simplified and rationalized and a cost of the plant can be reduced. |
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description | The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Grant No. DE-FG02-04ER83944 awarded by the U.S. Department of Energy. 1. Field of Invention The present invention relates to a method and system for treating a workpiece using a charged particle beam, and more particularly to a method and system of using a charged particle beam to treat an interior surface of a workpiece. 2. Description of Related Art Gas-cluster ion beams (GCIB's) are used for etching, cleaning, smoothing, and forming thin films. For purposes of this discussion, gas clusters are nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such gas clusters may consist of aggregates including a few to several thousand molecules, or more, that are loosely bound together. The gas clusters can be ionized by electron bombardment, which permits the gas clusters to be formed into directed beams of controllable energy. Such cluster ions each typically carry positive charges given by the product of the magnitude of the electronic charge and an integer greater than or equal to one that represents the charge state of the cluster ion. The larger sized cluster ions are often the most useful because of their ability to carry substantial energy per cluster ion, while yet having only modest energy per individual molecule. The ion clusters disintegrate on impact with the workpiece. Each individual molecule in a particular disintegrated ion cluster carries only a small fraction of the total cluster energy. Consequently, the impact effects of large ion clusters are substantial, but are limited to a very shallow surface region. This makes gas cluster ions effective for a variety of surface modification processes, but without the tendency to produce deeper sub-surface damage that is characteristic of conventional ion beam processing. Conventional cluster ion sources produce cluster ions having a wide size distribution scaling with the number of molecules in each cluster that may reach several thousand molecules. Clusters of atoms can be formed by the condensation of individual gas atoms (or molecules) during the adiabatic expansion of high pressure gas from a nozzle into a vacuum. A skimmer with a small aperture strips divergent streams from the core of this expanding gas flow to produce a collimated beam of clusters. Neutral clusters of various sizes are produced and held together by weak inter-atomic forces known as Van der Waals forces. This method has been used to produce beams of clusters from a variety of gases, such as helium, neon, argon, krypton, xenon, nitrogen, oxygen, carbon dioxide, sulfur hexafluoride, nitric oxide, nitrous oxide, and mixtures of these gases. Several emerging applications for GCIB processing of workpieces on an industrial scale are in the semiconductor field. Although GCIB processing of a workpiece is performed using a wide variety of gas-cluster source gases, many of which are inert gases, many semiconductor processing applications use reactive source gases, sometimes in combination or mixture with inert or noble gases, to form the GCIB. Conventional GCIB processing techniques suffer from a general inability to process all surfaces on workpieces having a complex topology. For example, certain types of workpieces include internal cavities bounded by interior surfaces. These interior surfaces are difficult to treat using conventional GCIB processing techniques because of difficulties represented in presenting these interior surfaces to the GCIB for impingement by the ionized clusters. Certain workpiece topologies may render it impossible to expose the interior surfaces to the GCIB using conventional GCIB processing techniques. Embodiments of the present invention relates to a method and system for treating a workpiece using a charged particle beam. Furthermore, the method and system provide for using a gas cluster ion beam (GCIB) to treat an interior surface of a workpiece. According to one embodiment, a method of treating an interior surface on an internal cavity of a workpiece using a gas cluster ion beam (GCIB) is described. The method comprises positioning the workpiece in a GCIB processing system and positioning a beam deflector within the internal cavity of the workpiece. Thereafter, the workpiece is exposed to a GCIB formed in the GCIB processing system, and the GCIB is re-directed by the beam deflector to the interior surface of the internal cavity of the workpiece to treat the interior surface. According to another embodiment, a processing system is configured to treat a workpiece having an internal cavity with an interior surface. The processing system may comprise a charged particle beam source disposed in a vacuum vessel and a beam deflector disposed in the vacuum vessel. The charged particle beam source is configured to produce a charged particle beam. The processing system may further comprise a workpiece holder configured to support the workpiece inside the vacuum vessel for treatment by the charged particle beam. A positioning system is mechanically coupled with the beam deflector. The positioning system is configured to position a beam deflector surface of the beam deflector inside the internal cavity of the workpiece. The positioning system is also configured to move the beam deflector relative to the internal cavity of the workpiece so that the beam deflector surface intercepts and re-directs the charged particle beam toward the interior surface. According to yet another embodiment, a beam deflector is provided for use in a gas cluster ion beam (GCIB) processing system to treat a workpiece having an internal cavity with an interior surface. The beam deflector may include an arm member and a positioning system mechanically coupled with the arm member. The positioning system is configured to position the arm member such that a beam deflector surface of the arm member is inside the internal cavity of the workpiece. The positioning system is configured to move the arm member relative to the internal cavity of the workpiece so that the beam deflector surface intercepts and re-directs the GCIB toward the interior surface. A method and system for treating a workpiece using a charged particle beam, such as a gas cluster ion beam (GCIB), is disclosed in various embodiments. However, one skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without specific details. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale. In the description and claims, the terms “coupled” and “connected,” along with their derivatives, are used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other while “coupled” may further mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but do not denote that they are present in every embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. Various additional layers and/or structures may be included and/or described features may be omitted in other embodiments. There is a general need for treating various surfaces on a workpiece and, in particular, there is a general need for treating complex surfaces on a workpiece using a charged particle beam, such as a GCIB. Such complex surfaces on a workpiece can include an interior surface on an internal cavity of the workpiece, wherein accessibility to the interior surface or surfaces by the GCIB is limited. For example, the workpiece may include a tubular workpiece, such as a waveguide member for electromagnetic (EM) wave propagation or an accelerator member for a linear accelerator. Moreover, these workpieces may comprise complex topographies for their interior surfaces, i.e., high degrees of curvature. Although the embodiments to follow describe the use of a GCIB to treat the surfaces of a workpiece, other charged particle beams are contemplated including, for example, an ion beam or an electron beam. According to one embodiment, a method and system of treating an interior surface on an internal cavity of a workpiece using a gas cluster ion beam (GCIB) is described. The method and system comprise positioning the workpiece in a GCIB processing system and positioning a beam deflector within the internal cavity of the workpiece. Thereafter, the workpiece is exposed to a GCIB formed in the GCIB processing system, and the GCIB is re-directed by the beam deflector to the interior surface on the internal cavity of the workpiece to treat the interior surface. The treatment of the interior surface or interior surfaces may include sputtering the surface, etching the surface, depositing material on the surface, smoothing the surface, hardening the surface, chemically treating the surface, or physically treating the surface, or any combination of two or more thereof. For example, the GCIB may be utilized to smooth sub-micron-scale roughness and remove particulate contamination that can cause emission and breakdown of high-voltage electrodes and that are limitations in the development of high gradient EM wave technology. By adjusting the orientation of the beam deflector relative to the workpiece, and optionally, the workpiece and/or beam deflector relative to the GCIB, the interior surface or surfaces of the workpiece can be treated by the GCIB. One or more properties of the GCIB, including the beam composition, beam dose, beam intensity, etc., can be adjusted or controlled or both in order to facilitate treatment of the interior surface or surfaces of the workpiece. With reference to FIG. 1 and in accordance with an embodiment, a representative GCIB processing system 100 includes a vacuum vessel 102, workpiece holder 150, upon which a workpiece 152 to be processed is affixed, and vacuum pumping systems 170A, 170B, and 170C. GCIB processing system 100 is configured to produce a GCIB to treat workpiece 152. The vacuum vessel 102 comprises three communicating chambers, namely, a source chamber 104, an ionization/acceleration chamber 106, and a processing chamber 108 to define a reduced-pressure enclosure. Gas clusters can be formed as a gas jet 118 in the source chamber 104. A gas cluster ion beam (GCIB) 128 is formed in the ionization/acceleration chamber 106 wherein gas clusters from the gas jet 118 admitted from the source chamber 104 are ionized and accelerated. The GCIB 128 is subsequently filtered in the ionization/acceleration chamber 106 to generate a filtered GCIB 230 that is communicated from the ionization/acceleration chamber 106 to the processing chamber 108. The filtered GCIB 230 is utilized to treat the workpiece 152 in the processing chamber 108. The chambers 102, 104, 106 are evacuated to suitable operating pressures by vacuum pumping systems 170A, 170B, and 170C, respectively. Vacuum pumping systems 170A, 170B, and 170C can include turbo-molecular vacuum pumps (TMP) capable of pumping speeds up to about 5000 liters per second (or greater) and a gate valve for throttling the chamber pressure. In conventional vacuum processing devices, a TMP with a pumping speed of about 1000 liters per second to 3000 liters per second can be employed. TMPs are useful for low pressure processing, typically less than about 50 mTorr. Furthermore, a pressuring-measuring device for monitoring chamber pressure (not shown) can be coupled to the vacuum vessel 102 or to any of the individual vacuum chambers 104, 106, 108. The pressure-measuring device can be, for example, a capacitance manometer or an ionization gauge. A first gas composition 111, which is stored in a first gas source 112, is admitted under pressure through a first gas control valve 113A to a gas metering valve or valves 113. Additionally, an optional second gas composition 111A, which is stored in a second gas source 112B, is admitted under pressure through a second gas control valve 113B to the downstream gas metering valve or valves 113. According to one example, the first gas composition 111 can include a condensable inert gas. For example, the inert gas can include a noble gas, i.e., He, Ne, Ar, Kr, Xe, or Rn. Additionally, according to another example, the second gas composition can comprise a film forming gas composition, an etching gas composition, a cleaning gas composition, a smoothing gas composition, etc. Furthermore, the first gas source 111 and the second gas source 112B may be utilized either alone or in combination with one another to produce ionized clusters comprising helium, neon, argon, krypton, xenon, nitrogen, oxygen, hydrogen, methane, nitrogen trifluoride, carbon dioxide, sulfur hexafluoride, nitric oxide, or nitrous oxide, or any combination of two or more thereof. Alternatively, the first gas composition 111 and the second gas composition 111A may be pre-mixed or pre-diluted or both, and may be delivered from a single gas source. The high pressure, condensable gas comprising the first gas composition 111, the second gas composition 111A, or both, is introduced through gas feed tube 114 into stagnation chamber 116 and is ejected into the substantially lower pressure vacuum through a properly shaped nozzle 110. As a result of the expansion of the high pressure, condensable gas from the stagnation chamber 116 to the lower pressure region of the source chamber 104, the gas velocity accelerates to supersonic speeds and gas jet 118 emanates from nozzle 110. The inherent cooling of the jet as static enthalpy is exchanged for kinetic energy, which results from the expansion in the jet, causes a portion of the gas jet 118 to condense and form clusters, each consisting of from several to several thousand weakly bound atoms or molecules. A gas skimmer 120, positioned downstream from the exit of the nozzle 110 between the source chamber 104 and ionization/acceleration chamber 106, partially separates the gas molecules on the peripheral edge of the gas jet 118, that may have not condensed into a cluster, from the gas molecules in the core of the gas jet, that may have formed clusters. Among other reasons, this selection of a portion of gas jet 118 can lead to a reduction in the pressure in the downstream regions where higher pressures may be detrimental (e.g., ionizer 122, suppressor electrode, and processing chamber 108). Furthermore, gas skimmer 120 defines an initial dimension for the gas cluster beam entering the acceleration/ionization chamber 106. After the gas jet 11 8 has been formed in the source chamber 104, the constituent gas clusters in gas jet 118 are ionized by an ionizer 122 to form GCIB 128. The ionizer 122 may include an electron impact ionizer that produces electrons from one or more filaments 124, which are accelerated and directed to collide with the gas clusters in the gas jet 118 inside the ionization/acceleration chamber 106. Upon collisional impact with the gas cluster, electrons of sufficient energy eject electrons from molecules in the gas clusters to generate ionized molecules. The ionization of gas clusters can lead to a population of charged gas cluster ions, generally having a net positive charge. Beam electronics 130 are utilized to ionize, extract, accelerate, and focus the GCIB 128. The beam electronics 130 includes a set of suitably biased high voltage electrodes 126, an anode power supply 134, a filament power supply 136, an extraction power supply 138, an accelerator power supply 140, and lens power supplies 142, 144. The filament power supply 136 provides voltage VF to heat the ionizer filament 124. The high voltage electrodes 126, which are located in the ionization/acceleration chamber 106, extract the cluster ions from the ionizer 122. The high voltage electrodes 126 then accelerate the extracted cluster ions to a desired energy and focus them to define GCIB 128. The kinetic energy of the cluster ions in GCIB 128 typically ranges from about 1000 electron volts (1 keV) to several tens of keV. The anode power supply 134 provides voltage VA to an anode of ionizer 122 for accelerating electrons emitted from filament 124 and causing the electrons to bombard the gas clusters in gas jet 118, which produces cluster ions. The extraction power supply 138 provides voltage VE to bias at least one of the high voltage electrodes 126 to extract ions from the ionizing region of ionizer 122 and to form the GCIB 128. The accelerator power supply 140 provides voltage VAcc to bias one of the high voltage electrodes 126 with respect to the ionizer 122 so as to result in a total GCIB acceleration energy equal to about VAcc electron volts (eV). The lens power supplies 142,144 bias some of the high voltage electrodes 126 with potentials (e.g., VL1 and VL2) to focus the GCIB 128. By way of example of the biasing potentials, extraction power supply 136 may provide a voltage to a first electrode of the high voltage electrodes 126 that is less than or equal to the anode voltage of ionizer 122 and the accelerator power supply 140 may provide a voltage to a second electrode of the high voltage electrodes 126 that is less than or equal to the anode voltage of ionizer 122 and the extraction voltage of the first electrode. The lens power supply 142 may provide a voltage to a third electrode of the high voltage electrodes 126 that is less than or equal to the anode voltage of ionizer 122, the extraction voltage of the first electrode, and the accelerator voltage of the second electrode. The lens power supply 144 may provide a voltage to a fourth electrode of the high voltage electrodes 126 that is less than or equal to the anode voltage of ionizer 122, the extraction voltage of the first electrode, the accelerator voltage of the second electrode, and the first lens voltage of the third electrode. A beam filter 146 in the ionization/acceleration chamber 106 can be utilized to eliminate monomers, or monomers and light cluster ions from the GCIB 128 to define the filtered process GCIB 230 that enters the processing chamber 108. A beam gate 148 is disposed in the path of GCIB 128 in the ionization/acceleration chamber 106. Beam gate 148 has an open state in which the GCIB 128 is permitted to pass from the ionization/acceleration chamber 106 to the processing chamber 108 to define process GCIB 230, and a closed state in which the GCIB 128 is blocked from entering the processing chamber 108. A control cable conducts control signals from a control system 190 to the beam gate 148. The control signals controllably switch beam gate 148 between the open or closed states. Alternatively, other ways to turn on or turn off the GCIB 128, and thereby the process GCIB 230, may be employed. Workpiece 152 can be affixed to the workpiece holder 150 via a clamping system (not shown), such as a mechanical clamping system. Furthermore, workpiece holder 150 can include a heating system (not shown) or a cooling system (not shown) that is configured to adjust and/or control the temperature of workpiece holder 150 and workpiece 152. The workpiece 152 is disposed in the path of the process GCIB 230 in the processing chamber 108 when affixed to the workpiece holder 150. The workpiece 152 may be a workpiece having an interior surface on an internal cavity or a tubular workpiece, or other workpiece to be processed by GCIB processing wherein the process GCIB 230 is to be re-directed. Because most applications contemplate the processing of large workpieces or workpieces with complex surface topography, a scanning system may be desirable to adjust the position and/or orientation of the workpiece 152 relative to the process GCIB 230. Referring still to FIG. 1, a scan actuator 160 provides linear motion of the workpiece holder 1 50 in the direction of X-scan motion (into and out of the plane of the paper) and Y-scan motion 164, which is orthogonal to the X-scan motion. The combination of X-scanning and Y-scanning motions translates the workpiece 152, held by the workpiece holder 150, relative to the process GCIB 230, and may be utilized to effect the treatment of the interior surfaces of workpiece 152. Additionally, the scan actuator 160 may be configured to provide Z-scan motion for workpiece 152 (motion that is substantially parallel with the principal axis of the process GCIB 230). The workpiece holder 150 positions the workpiece 152 with the process GCIB 230 at an angle with respect to the axis of the process GCIB 230 so that the process GCIB 230 has an angle of beam incidence with respect to a workpiece surface. The angle of beam incidence may be 90° or some other angle. As described above, the workpiece 152 can be a workpiece having at least one interior surface on an internal cavity. For example, the interior surface of workpiece 152 may include a singly connected domain, or a multiply connected domain. Additionally, for example, workpiece 152 may include a tubular workpiece. The tubular workpiece 152 may include a circular cross-section, a rectangular cross-section, a square cross-section, a triangular cross-section, or a cross-section of arbitrary cross-sectional shape. Additionally, the interior surface or surfaces of the workpiece 152 may include low degrees of curvature (i.e., substantially flat), or it may include high degrees of curvature (i.e., concave and convex undulations, etc.). According to an embodiment and as shown in FIG. 1, the GCIB processing system 100 includes a beam deflector 162 for re-directing the process GCIB 230 towards a surface 154 on workpiece 152, such as an interior surface on an internal cavity. The beam deflector 162, which is located inside the processing chamber 108, comprises an arm member 169 having a beam deflector surface configured to extend into an internal cavity of workpiece 152 to be processed in the GCIB processing system 100. The beam deflector surface is configured to interact with the process GCIB 230 and, as a consequence of the interaction, re-direct the process GCIB 230 towards the interior surface of the workpiece 152. In one embodiment, the beam deflector 162 and beam deflector surface may be electrically coupled with an electrical bias system 220 (FIG. 2). The electrical bias system 220 is configured to electrically bias the beam deflector 162 and beam deflector surface relative to the workpiece 152 and the process GCIB 230. Alternatively, the beam deflector 162 and the beam deflector surface may be electrically self-biased by the GCIB 230. In one embodiment, the GCIB 230 is electrostatically re-directed by the beam deflector surface of the beam deflector 162 toward the surface 154 of the workpiece 152. The electrical biasing of the beam deflector surface of the beam deflector 162 is effective to electrostatically repulse or repel the approaching GCIB 230 toward the interior surface. As illustrated in FIG. 1, the arm member 169 is configured to position the beam deflector surface within the workpiece 152 and, thereby, to position the beam deflector surface of the beam deflector 162 relative to the process GCIB 230. A beam deflector scan actuator 166 provides linear motion of the beam deflector 162 in the direction of Z-scan motion 165 (relative to the workpiece 152). Additionally, the beam deflector scan actuator 166 provides linear motion of the beam deflector 162 in the direction of X-scan motion (into and out of the plane of the paper) and Y-scan motion, which is orthogonal to the X-scan motion. The combination of X-scanning, Y-scanning, and Z-scanning motions translates the beam deflector 162 within workpiece 152 relative to interior surface 154 and process GCIB 230, and may be utilized to effect the treatment of the interior surfaces of workpiece 152. An auxiliary scan actuator 168 may be configured to provide rotational motion 167 of the beam deflector surface on beam deflector 162. In one embodiment, the rotational motion 167 may be about an axis 129 substantially parallel with the principal axis of the process GCIB 230. In another embodiment, the rotational motion 167 may be about an axis 129 substantially perpendicular with the principal axis of the process GCIB 230 (i.e., a tilt angle). A beam current sensor 180 may be disposed beyond the workpiece holder 150 and in the path of the process GCIB 230 so as to intercept a sample of the process GCIB 230 when the workpiece holder 150 is scanned out of the path of the process GCIB 230. The beam current sensor 180 is typically a Faraday cup, or the like, which is closed except for a beam-entry opening. The beam current sensor 180 is typically affixed to the wall of the vacuum vessel 102 with an electrically insulating mount 182. As shown in FIG. 1, the control system 190 connects to the scan actuator 160, the beam deflector scan actuator 166, and the auxiliary scan actuator 168 through one or more electrical cables (or wireless systems). Control system 190 controls the scan actuator 160, the beam deflector scan actuator 166, and the auxiliary scan actuator 168 in order to adjust the position of the workpiece 152 and the beam deflector 162 relative to one another and relative to the process GCIB 230. Control system 190 receives the sampled beam current collected by the beam current sensor 180 by way of an electrical cable. Based upon the collected beam current, the control system 190 monitors the process GCIB 230. When a predetermined dose (i.e., integrated beam current) of gas cluster ions has been delivered, the control system 190 controls the dose of gas cluster ions received by the workpiece 152 by removing the workpiece 152 from the path of the process GCIB 230 or by actuating the beam gate 148 to block the delivery of the process GCIB 230 to the workpiece 152, as described below. In operation, the control system 190 signals the opening of the beam gate 148 to irradiate the workpiece 152 with the process GCIB 230. When the dose received by the workpiece 152 reaches a predetermined dose, the control system 190 closes the beam gate 148 and processing of the workpiece 152 is complete. Based upon measurements of the GCIB dose received for a given area of the workpiece 152, the control system 190 can adjust the scan velocity in order to achieve an appropriate beam dwell time to treat the interior surface 154 of workpiece 152 to pre-specified conditions. For example, the pre-specified conditions can include a degree of polishing. The degree of polishing can be characterized by a surface roughness, such as a maximum roughness (Rmax), an average roughness (Ra), or a root-mean-square (rms) roughness (Rq). Alternatively, the process GCIB beam 230 may be scanned at a constant velocity in a fixed pattern across the interior surface 154 of the workpiece 152; however, the GCIB intensity is modulated (may be referred to as Z-axis modulation) to deliver an intentionally non-uniform dose to the sample. The GCIB intensity may be modulated in the GCIB processing apparatus 100 by any of a variety of methods, including varying the gas flow from a GCIB source supply; modulating the ionizer by either varying a filament voltage VF or varying an anode voltage VA; modulating the lens focus by varying lens voltages VL1 and/or VL2; or mechanically blocking a portion of the gas cluster ion beam with a variable beam block, adjustable shutter, or variable aperture. The modulating variations may be continuous analog variations or, alternatively, may be time modulated switching or gating. Control system 190 comprises a microprocessor, memory, and a digital I/O port capable of generating control voltages sufficient to communicate and activate inputs to GCIB processing system 100 as well as monitor outputs from GCIB processing system 100. Moreover, control system 190 can be coupled to, and can exchange information with, vacuum pumping systems 170A, 170B, and 170C, first gas source 112, second gas source 112B, first gas control valve 113A, second gas control valve 113B, beam electronics 130, beam filter 146, beam gate 148, the scan actuator 160, the beam deflector scan actuator 166, the auxiliary scan actuator 168, the beam deflector electrical bias system 220 (FIG. 2), and beam current sensor 180. For example, a program stored in the memory can be utilized to activate the inputs to the aforementioned components of GCIB processing system 100 according to a process recipe in order to perform a GCIB process on workpiece 152. One example of control system 190 is a DELL PRECISION WORKSTATION 610™, available from Dell Corporation, Austin, Tex. However, the control system 190 may be implemented as a general purpose computer system that performs a portion or all of the microprocessor based processing steps of the invention in response to a processor executing one or more sequences of one or more instructions contained in a memory. Such instructions may be read into the controller memory from another computer readable medium, such as a hard disk or a removable media drive. One or more processors in a multi-processing arrangement may also be employed as the controller microprocessor to execute the sequences of instructions contained in main memory. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, embodiments are not limited to any specific combination of hardware circuitry and software. The control system 190 can be used to configure any number of processing elements, as described above, and the control system 190 can collect, provide, process, store, and display data from processing elements. The control system 190 can include a number of applications, as well as a number of controllers, for controlling one or more of the processing elements. For example, control system 190 can include a graphic user interface (GUI) component (not shown) that can provide interfaces that enable a user to monitor and/or control one or more processing elements. Control system 190 can be locally located relative to the GCIB processing system 100, or it can be remotely located relative to the GCIB processing system 100. For example, control system 190 can exchange data with GCIB processing system 100 using a direct connection, an intranet, and/or the internet. Control system 190 can be coupled to an intranet at, for example, a customer site (i.e., a device maker, etc.), or it can be coupled to an intranet at, for example, a vendor site (i.e., an equipment manufacturer). Alternatively or additionally, control system 190 can be coupled to the internet. Furthermore, another computer (i.e., controller, server, etc.) can access control system 190 to exchange data via a direct connection, an intranet, and/or the internet. With reference to FIG. 2, a beam deflector 200 is illustrated that is constructed according to a representative embodiment of beam deflector 162 (FIG. 1) for use with GCIB processing system 100. The beam deflector 200 comprises an arm member 210 configured to extend into an internal cavity 253 of a workpiece 252 to be processed by the GCIB 230, and an end member 216 having a beam deflector surface 217 coupled to the arm member 210 and configured to interact with the GCIB 230 and re-direct the GCIB 230 as re-directed GCIB 232 traveling in a trajectory toward an interior surface 254 of the workpiece 252. The arm member 210, which may be identical to arm member 169 (FIG. 1), may comprise one or more mechanical elements 218 that are designed for extension into and out of the internal cavity 253 of workpiece 252. A positioning system (not shown) is coupled to the arm member 210. For example, the positioning system mechanically coupled with arm member 210 may be identical to beam deflector scan actuator 166 and the auxiliary scan actuator 168 coupled with arm member 169 (FIG. 1). The positioning system is configured to adjust the position of the beam deflector surface 21 7 relative to the interior surface 254 and the GCIB 230 by translating the beam deflector surface 217 along, for instance, a translational axis 212, or rotating the beam deflector surface 217 about, for instance, a rotational axis in a rotational direction 214. The positioning system can be implemented to perform translation of the beam deflector surface 217 in any one of or combination of the three orthogonal translational degrees of freedom (X-axis, Y-axis, or Z-axis). In an alternative embodiment, the positioning system can be implemented to rotate the beam deflector surface 217 in any one of or combination of the three orthogonal rotational degrees of freedom (about the X-axis, Y-axis, or Z-axis). In one embodiment, an electrical bias system 220 may be coupled to the arm member 210 and the beam deflector surface 217. The electrical bias system 220 is configured to electrically bias the arm member 210 and the beam deflector surface 217 relative to the workpiece 252 and the GCIB 230. The electrical bias system 220 may comprise a power supply, such as a direct current (DC) power supply. In one embodiment, the DC power supply can include a variable DC power supply. Alternatively, the DC power supply can include a bipolar DC power supply. The DC power supply can further include a system configured to perform monitoring, adjusting, or controlling the polarity, current, voltage, or on/off state of the DC power supply, or any combination thereof. For example, the DC voltage applied to arm member 210 and beam deflector surface 217 by the electrical bias system 220 may have an absolute value ranging from approximately 0 volts (V) to approximately 200 kV (kilovolts). In one embodiment, the absolute value of the voltage has a value ranging from approximately 1 kV to approximately 100 kV. In another embodiment, the absolute value of the voltage has a value ranging from approximately 10 kV to approximately 60 kV, e.g., 20 kV. Additionally, for example, the electrical bias system 220 can be configured to be electrically isolated from the beam deflector 200 so that beam deflector 200 can be used to measure beam currents. Specifically, with the bias voltage switched off, the beam deflector 200 can be used as a collector to measure the GCIB current of process GCIB 230. For instance, this measurement may be useful for GCIB alignment. The beam deflector 200 may further comprise a shield member 222 disposed proximate the interior surface 254. The shield member 22 may include an aperture 226 to permit the passage of the re-directed GCIB 232 from the beam deflector surface 217 to the interior surface 254. The shield member 222 can define a collection space 224 for collecting debris 234 from the interaction of re-directed GCIB 232 with interior surface 254. Specifically, the debris 234 may be collected on a surface of the shield member 222. In one embodiment, the shield member 222 can be coupled to a shield temperature control system for adjusting or controlling the temperature of the shield member 222 in order to promote the collection of debris 234 on the surface of shield member 222. The shield temperature control system can include either a heating system (not shown) or a cooling system (not shown) that is configured to adjust and/or control the temperature of shield member 222. For example, shield member 222 can be fabricated from a thermally conductive material and a portion of the shield member can be coupled to a heating device, such as a resistive heating device, or coupled to cooling device, such as a thermo-electric cooling device or cryogenic cooling device. In one embodiment, the shield member 222 can be coupled to an electrical bias. For example, electrical bias system 220 may be coupled to the shield member 222, and configured to electrically bias the shield member 222 relative to the beam deflector surface 217 and the workpiece 252. For example, the DC voltage applied to shield member 222 by the electrical bias system 220 may have an absolute value ranging from approximately 0 volts (V) to approximately 500 V and, desirably, an absolute value ranging from approximately 0 volts (V) to approximately 100 V. The beam deflector surface 217 can comprise a substantially flat surface oriented at an angle relative to the incident GCIB 230 (FIG. 2) and oriented in a plane inclined at a non-perpendicular angle, θ, relative to a longitudinal axis 211 of the arm member 210. Additionally, the angle of orientation θ of the beam deflector surface 217 relative to the incident GCIB 230 may be variable. For example, the beam deflector surface 217 may tilt on a manually or automatically adjustable pivot joint at the end of the arm member 210. One or more openings (not shown) may be formed through the end member 216 carrying beam deflector surface 217 in order to permit the passage of gaseous material through the beam deflector 200. In an alternative embodiment, the end member 216 may include a screen or biasable screen. Alternatively, as shown in FIG. 3A, a beam deflector 210A may comprise a substantially flat surface 217A oriented substantially perpendicular to the incident GCIB 230 and oriented in a plane that is substantially perpendicular to the longitudinal axis 211 of the arm member 210. In an alternative embodiment and as shown in FIG. 3B, a beam deflector 210B may comprise a substantially convex surface 217B oriented in front of the incident GCIB 230. The GCIB 230 impinges the substantially convex surface 217B at an impingement position dependent angle of incidence. In another alternative embodiment and as shown in FIG. 3C, a beam deflector 210C may comprise a substantially concave surface 217C oriented in front of the incident GCIB 230 so as to intercept the GCIB 230. The GCIB 230 impinges the substantially concave surface 217C at an impingement position dependent angle of incidence. With reference to FIG. 4, a section of a gas cluster ionizer 300 for use in ionizing a gas cluster jet is shown. The section is viewed from a perspective normal to the axis of GCIB 128. The gas cluster ionizer 300 may be used as the ionizer 122 in the GCIB processing system 100 (FIG. 1). For typical gas cluster sizes (2000 atoms to 15000 atoms), clusters leaving the skimmer aperture 120 (FIG. 1) and entering the ionizer 122 (FIG. 1) will travel with a kinetic energy of about 130 electron volts (eV) to about 1000 eV. At these low energies, any departure from space charge neutrality within the ionizer 122 will result in a rapid dispersion of the jet with a significant loss of beam current. Gas cluster ionizer 300 is a self-neutralizing ionizer. As with other ionizers, gas cluster ionizer 300 ionizes gas clusters by electron impact. Accordingly, gas cluster ionizer 300 includes multiple linear thermionic filaments 302a, 302b, and 302c (typically tungsten) that emit thermo-electrons (seven examples indicated by 310) and electron-repeller electrodes 306a, 306b, and 306c and beam-forming electrodes 304a, 304b, and 304c that supply suitable electric fields that focus the thermo-electrons. Thermo-electrons 310 pass through the gas cluster jet and the jet axis and then strike the opposite beam-forming electrode 304b to produce low energy secondary electrons (312, 314, and 316 indicated for examples). Although not shown for simplicity of description, linear thermionic filaments 302b and 302c also produce thermo-electrons that subsequently produce low energy secondary electrons. All the secondary electrons help ensure that the ionized cluster jet remains space charge neutral by providing low energy electrons that can be attracted into the positively ionized gas cluster jet as required to maintain space charge neutrality. Beam-forming electrodes 304a, 304b, and 304c are biased positively with respect to linear thermionic filaments 302a, 302b, and 302c and electron-repeller electrodes 306a, 306b, and 306c are negatively biased with respect to linear thermionic filaments 302a, 302b, and 302c. Insulators 308a, 308b, 308c, 308d, 308e, and 308f electrically insulate and support electrodes 304a, 304b, 304c, 306a, 306b, and 306c. For example, this self-neutralizing ionizer is effective and achieves over 1000 μAmps argon GCIBs. Alternatively, other types of ionizers may be employed to ionize the GCIB 128. With reference to FIG. 5, a method of treating a workpiece using a gas cluster ion beam (GCIB) processing system is described. The method comprises a flow chart 500 beginning in block 510 with positioning a workpiece in a gas cluster ion beam (GCIB) processing system configured to produce a GCIB. For example, the workpiece may comprise a workpiece having an internal cavity with an interior surface, such as a tubular workpiece. In particular, the workpiece may be workpiece 152 (FIG. 1) or workpiece 252 (FIG. 2). Additionally, for example, the GCIB processing system may comprise the GCIB processing system 100 (FIG. 1). In block 520, a beam deflector is positioned within the internal cavity of the workpiece, and it is positioned to interact with the GCIB. The beam deflector can be any one of the beam deflectors described in FIGS. 1, 2, 3A, 3B, and 3C. In block 530, the workpiece is exposed to the GCIB. In block 540, the beam deflector is utilized to re-direct the GCIB towards an interior surface of the workpiece. During the treatment, the position of the workpiece may be adjusted relative to the GCIB or, alternatively, the position of the beam deflector may be adjusted relative to the workpiece. With regard to the latter alternative, the beam deflector may be translated relative to the workpiece, rotated relative to the workpiece, or a combination of these positional adjustments. Although only certain embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. |
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052951693 | abstract | A reactor containment facility having a reactor pressure vessel containing a core; a dry well in which the reactor pressure vessel is arranged; a suppression chamber holding suppression-pool water and forming above the suppression-pool water a wet well; and a plurality of vent pipes allowing the dry well to communicate with the suppression-pool water; a steel wall which is in contact with the suppression-pool water of the suppression chamber and which surrounds at least the pool water so as to form a containment vessel which houses the dry well and the suppression chamber; and an outer peripheral pool containing cooling water in contact with the outer peripheral surface of the steel wall. The facility further includes: a dividing structure for dividing the wet well of the suppression chamber into a first space which is in contact with the water surface of the suppression-pool water and a second space which is not in contact therewith; a first passage which allows the first space to communicate with the second space and which has an area smaller than that of the dividing device; and a cooling device for keeping the second space at a temperature lower than that of the first space. |
summary | ||
description | (First Embodiment) A description is made of a first embodiment in which the present invention is applied to replacement of a reactor vessel in a pressurized water reactor plant (hereinafter abbreviated to a xe2x80x9cPWR plantxe2x80x9d). In this embodiment, after removing a polar crane within a reactor containment vessel (simply called a containment vessel), a reactor vessel (hereinafter abbreviated to xe2x80x9cRVxe2x80x9d) and core internals are carried out together and replaced with a new set of reactor vessel and core internals. FIG. 2 is a schematic vertical sectional view of a reactor shielding building in the PWR plant to which the present invention is applied. As shown in FIG. 2, a reactor shielding building 1 is of a reinforced concrete structure, and a steel-made containment vessel (hereinafter abbreviated to xe2x80x9cCVxe2x80x9d) 3 is installed inside the reactor shielding building 1. Walls and floors of a reinforced concrete structure or a steel-framed concrete structure are provided in a lower portion of the CV 3 to define a reactor cavity 5, and the RV 2 is installed at the center of a bottom portion of the reactor cavity 5. An operation floor 7, on which various kinds of works in the CV 3 are performed, is formed in an upper portion of the reactor cavity 5. An equipment carrying-in opening 4 is provided on the upper side of the operation floor 7 so that various types of equipment may be carried out to the exterior of the reactor shielding building 1 through the opening 4. A steam generator (hereinafter abbreviated to xe2x80x9cSGxe2x80x9d) 8 is arranged in a space surrounded by a shied wall 6. An annular rail 10 is installed just below a dome-shaped ceiling of the CV 3, and a polar crane 9 is mounted on the annular rail 10. The polar crane 9 is an overhead traveling crane comprising a girder 9a and a trolley 9b, and it is used-to move large-weight components in the CV 3. FIG. 3 is a perspective view, partly broken away, of the RV 2 shown in FIG. 2. As shown in FIG. 3, an upper lid 2a is fixed to a body of the RV 2 through a flange 2b using bolts 2c. The RV 2 has a height of about 10 m and a diameter of about 4 m. Core internals 50, described later, are installed inside the RV 2. A core tank 12 is arranged at the center of the RV 2, and a fuel assembly 13 is arranged inside the core tank 12. The core tank 12 is a cylindrical core internal arranged in the RV 2 so as to surround a rector core. An upper core support plate 17 is detachably provided at an upper end of the core tank 12 and is attached to an upper core plate 16 by a plurality of upper core support posts 19. The upper core plate 16, the upper core support plate 17, a control rod cluster 18, and the upper core support posts 19 constitute upper core internals 20. A lower core support plate 14 and a lower core plate 15 are provided in a lower portion of the core tank 12. The core tank 12, the lower core support plate 14, and the lower core plate 15 constitute lower core internals 21. The core internals 50 comprise the upper core internals 20 and the lower core internals 21. The core internals 20 and 21 can be separately taken out to the exterior of the RV 2. An inlet nozzle 22 and an outlet nozzle 23 both provided in the RV 2 are connected via pipes to the SG 8 installed in the CV 3. FIG. 1A and FIG. 1B are flowchart showing a method for replacing the RV according to the first embodiment. First, work for making the reactor open is performed in step S1. In the reactor opening work, the upper lid 2a of the RV 2 is removed. FIG. 4 is a schematic vertical sectional view of the RV 2 and surroundings thereof during the reactor opening work. Numeral 18a denotes a control rod driving mechanism. Then, in step S2, the upper core internals 20 are removed. This work is performed in a state in which a core water level is raised to fully fill the reactor cavity 5 with water. FIG. 5 is a schematic vertical sectional view of the RV 2 and surroundings thereof during the work for removing the upper core internals 20. The upper core plate 16, the upper core support plate 17, the control rod cluster 18, and the upper core support posts 19, which constitute the upper core internals 20, are removed together. Then, in step S3, all fuel is taken out and moved to a fuel pool. This work is performed while the core water level is kept raised to fully fill the reactor cavity 5 with water. FIG. 6 is a schematic vertical sectional view of the RV 2 and surroundings thereof during the work for taking out a fuel assembly 13 with a fuel replacing apparatus 13a. Then, in step S4, the upper core internals 20 are returned into the RV 2 and mounted in place. When the upper core internals 20 are not replaced, this step can be omitted. Then, in step S5, the interior of the RV 2 is decontaminated to eliminate radioactive materials deposited on an inner wall of the RV 2 and the core internals 50. Chemical decontamination using chemicals is one example of decontaminating methods. Performing the decontamination makes it possible to simplify a shield that is used when carrying out the RV 2 to the exterior of the reactor shielding building 1. When the decontamination is not performed, this step can be omitted. Then, in step S6, pipes 24 and 25 connected to the inlet nozzle 22 and the outlet nozzle 23 respectively are cut off. On that occasion, for reducing an exposure rate of workers engaged in the pipe cutting work, water sealing plugs 22a and 23a are attached to the inlet nozzle 22 and the outlet nozzle 23 respectively from the inside of the reactor while the reactor cavity 5 is kept fully filled with water. Subsequently, the reactor water level is lowered to a position of the flange 2b in the upper portion of the RV 2. Thereafter, for shutting off radiations from the inner side of the reactor, a shield lid 26 having a radiation shielding capability is attached to the flange 2b by bolts 26a. Then, after securing a space for the pipe cutting work, structural members, such as sealing materials, located above the nozzles and thermal insulating materials located around the nozzles are removed. With removal of those materials, the RV 2 is prevented from interfering with the nozzles when it is carried out. FIG. 7 is a schematic vertical sectional view of the RV 2 and surroundings thereof, showing a state after cutting off the pipes 24 and 25 connected respectively to the inlet nozzle 22 and the outlet nozzle 23. To prevent radioactive materials in the reactor from flowing out to the exterior of the RV 2, closure plates 22b and 23b are attached to the respective nozzles after the pipe cutting work from the outer side of the RV 2. Then, in step S7, a radiation shielding material, such as mortar, is filled in the reactor. The shielding material is filled through a hose or the like inserted in a hole, which is formed in the shield lid 26 beforehand, Filling the shielding material into a reactor bottom portion makes it possible to omit a bottom plate of a radiation shield 28, described later, for the RV 2. After filling the shielding material, the hole formed in the shield lid 26 is plugged. When the radiation dose from the reactor bottom portion is not more than a transport standard value, this step may be omitted. Then, in step S8, cables 37 connected to the bottom portion of the RV 2 for in-core instrumentation are removed. In step S9, a heavy-duty crane 30 for carrying out (in) the RV 2 is set up outside the reactor shielding building 1. Then, in step S10, a temporary opening 31, through which the RV 2 can be carried out (in), is formed in the ceiling (top wall) of the reactor shielding building 1 and the containment vessel 3. A shutter 32 capable of opening and closing is provided above the temporary opening 31 for protection against rain. FIG. 8 is a schematic vertical sectional view of the reactor shielding building 1 after setting up the heavy-duty crane 30 and forming the temporary opening 31. Then, in step S11, the polar crane 9 is removed and, in step S12, the radiation shield 28 is carried in. When carrying in the radiation shield 28, reinforcing members 27 are first placed at the bottom of the reactor cavity 5 so as to surround the RV 2. The reinforcing members 27 serve to distribute the weight of the radiation shield 28 over the bottom of the reactor cavity 5. Subsequently, the shutter 32 is opened, and the radiation shield 28 is carried into the CV 3 through the temporary opening 31 and temporarily placed on the reinforcing members 27 by using the heavy-duty crane 30. To that end, the temporary opening 31 is set to a size allowing the radiation shield 28 to be carried in (out) through it. The radiation shield 28 has a cylindrical shape and is provided at its upper end with a shield upper lid 28a in the form of a disk. The radiation shield 28 serves to shut off radiations from the RV 2. FIG. 9 is a schematic vertical sectional view of the RV 2 and surroundings thereof, showing a state in which the radiation shield 28 is temporarily placed in the reactor cavity 5 and a sling 30a is attached to the shield lid 26. Then, in step S13, the RV 2 is lifted up and united with the radiation shield 28. The strongback (sling) 30a as a jig for lifting up the RV 2 is attached to the shield lid 26 using eight to ten pieces of bolts 26a. The sling 30a is suspended by the heavy-duty crane 30. The shield upper lid 28a has a slit-like opening through which the sling 30a is able to pass, and has hooks 28b provided on its upper side for hanging the radiation shield 28. By raising the sling 30a with the heavy-duty crane 30, the RV 2 is lifted up. The RV 2 is combined with the radiation shield 28 just by lifting up the RV 2 such that the shield lid 26 is brought into abutment with the shield upper lid 28a. Subsequently, the opening of the shield upper lid 28a is covered with a protective sheet 28c, and ends of the protective sheet 28c are fixedly attached in a sealed-off manner using a sealing tape. Likewise, a lower end of the radiation shield 28 is covered with a protective sheet 28d whose ends are also fixedly attached in a sealed-off manner using a sealing tape. Each of the protective sheets 28c and 28d can be formed of, e.g., a polyvinyl chloride sheet. FIG. 10 is a schematic vertical sectional view of the RV 2 and surroundings thereof, showing a state in which the RV 2 is lifted up and united with the radiation shield 28. Thus, the radiation shield 28 can be easily combined with the RV 2 in a surrounding relation in a short time just by lifting up the core internals 50 together (in union) with the RV 2. Also, since the openings of the radiation shield 28 are sealed off with the protective sheets 28c and 28d, radioactive dust deposited on the surface of the RV 2 can be prevented from scattering to the exterior. Next, in the state of the radiation shield 28 being combined with the RV 2, the surfaces of the shield and the protective sheets are decontaminated. The fact that the surface dose rate has been lowered to such a level as not affecting an external environment of the containment vessel is confirmed by a contamination test. FIG. 11 is a schematic vertical sectional view of the CV 3, showing a state immediately before lifting up a large-size block 51, which includes the radiation shield 28 and the RV 2 united into one, by the heavy-duty crane 30 and carrying out the large-size block 51 through the temporary opening 31. As shown in FIG. 11, the radiation shield 28 covers the whole of the RV 2 from the top to the bottom thereof. Since the bottom portion of the RV 2 generates a lower radiation dose than a core portion located above the bottom portion of the RV 2 and is filled with the radiation shielding material, it is not required to attach a radiation shield to the bottom portion of the RV 2 in most cases. When it is required to attach such a shield to the bottom portion of the RV 2, the shield is attached to the reactor bottom portion in step S13. A method for attaching the shield is now described with reference to FIGS. 12A and 12B. FIG. 12A shows a state before attaching a bottom shield 29, and FIG. 12B shows a state after attaching the bottom shield 29. As shown in FIG. 12A, the large-size block 51 is lifted up by the heavy-duty crane 30 to a level above the operation floor 7, rails 29a are set at the top of the reactor cavity 5, and a flatcar 29b including the bottom shield 29 laid thereon is rested on the rails 29a. Then, as shown in FIG. 12B, the flatcar 29b including the bottom shield 29 laid thereon is moved to a position right below the large-size block 51, and the large-size block 51 is descended to a height at which it contacts the bottom shield 29. Thereafter, the large-size block 51 and the bottom shield 29 are joined to each other by, e.g., bolts. In such a way, when carrying the RV 2 out of the reactor shielding building 1, the surface dose rate of the radiation shield 28 can be reduced to a level lower than a reference value (limit value). Then, in step S14, the RV 2 is carried out. More specifically, the RV 2 is lifted up as the large-size block 51 in union with the radiation shield 28 and the core internals 50. The large-size block 51 is carried out to the exterior through the temporary opening 31 of the reactor shielding building 1. After carrying out the large-size block 51 to the exterior of the reactor shielding building 1, the shutter 32 is closed. FIG. 13 is a view showing a state in which the large-size block 51 is carried out by the heavy-duty crane 30 through the temporary opening 31 of the reactor shielding building 1. Then, in step S15, the large-size block 51 carried out of the reactor shielding building 1 is carried into a storage container 40. On that occasion, a fore end 30b of the heavy-duty crane 30 is moved from a position right above the temporary opening 31 of the reactor shielding building 1 to a position right above the storage container 40 while keeping the large-size block 51 hanged by the heavy-duty crane 30. Thereafter, the large-size block 51 is descended and carried into the storage container 40. FIG. 14 is a view showing a state immediately before carrying the large-size block 51 into the storage container 40 in step S15. The storage container 40 is provided under the ground near the reactor shielding building 1, and has a structure capable of containing the large-size block 51 in an upright posture. Thus, the large-size block 51 can be carried into the storage container 40 by using the heavy-duty crane 30 while the large-size block 51 is kept in the same state as that just after being carried out of the reactor shielding building 1. After carrying the large-size block 51 into the storage container 40, a lid is attached to the storage container 40 for bringing it into a sealed-off condition. As an alternative, in step S15, the large-size block may be loaded on a trailer, transported to the storage container, and then carried into it. This method is effective when the storage container is remote from the reactor shielding building. Also, the storage container may be provided in a building of a ridge continuation with the reactor shielding building. The storage container may be provided on the ground to be able to contain the large-size block in a horizontally laid state. A method for loading the large-size block on a trailer (flatcar) in a horizontally laid state is now described. The large-size block 51 hanged by the heavy-duty crane 30 is moved to a tilting-down apparatus provided on a trailer 34, which is stopped near the reactor shielding building 1. Then, the large-size block 51 is horizontally laid by the tilting-down apparatus to be loaded on the trailer 34. FIG. 15A is a view showing a state in which the large-size block 51 is tilted down to be laid on the trailer 34, and FIG. 15B is a view showing one example of the tilting-down apparatus provided on the trailer for tilting down the large-size block. In such a case, a tilting-down shaft 28g is attached to the radiation shield 28 beforehand. The large-size block 51 is slowly descended toward a tilting-down bearing 35 while being vertically hanged by heavy-duty crane wires 30c, and at the same the trailer 34 is slowly moved in a direction corresponding to the direction in which the large-size block 51 is to be tilted down. As a result, the radiation shield 28 is rotated about the tilting-down shaft 28g, and the large-size block 51 is gradually tilted down from the vertically hanged state. On that occasion, the distance and speed by and at which the trailer 34 is moved and the distance and speed by and at which the large-size block 51 is descended, are adjusted in a proper combination so that the weight imposed on the tilting-down shaft 28g is reduced to, e.g., about a half the total weight of the large-size block. In such a way, the large-size block 51 is gradually horizontally laid on a platform 36 of the trailer 34 while avoiding excessive loads from being imposed on the tilting-down shaft 28g and the tilting-down bearing 35. After horizontally laying the large-size block 51 on the platform 36 of the trailer 34, the large-size block 51 is fixed in place by, e.g., wires. The work for tilting down the large-size block is thus completed. Through the procedures described above, the work for carrying out, as the large-size block 51, the RV 2 in union with the radiation shield 28 and the core internals 50 is completed. Then, in step S16, a new reactor vessel (new RV) 2 is lifted up by the heavy-duty crane 30 and is carried in to a predetermined position within the containment vessel 3 (i.e., the bottom portion of the reactor cavity 5) through the temporary opening 31. At this time, the new RV 2 is carried in together with the lower core internals 21 mounted in the new RV 2. Alternatively, the new RV 2 and the lower core internals 21 may be carried in separately. Then, in step S17, the removed polar crane 9 is carried into the containment vessel 3 through the temporary opening 31 for restoration to the same state as that before removal. Subsequently, the temporary opening 31 is closed in step S18, and the heavy-duty crane 30 is dismantled in step S19. Further, in step S20, an outlet pipe and an inlet pipe to be connected to the new RV 2 are connected respectively to the outlet nozzle and the inlet nozzle for restoration to the same state as that before replacement. In step S21, the cables are attached to a bottom portion of the new RV 2 for restoration to the same state as that before replacement. Then, fuel is charged in step S22 and the upper core internals 20 are mounted in step S23 for restoration to the same state as that before removal. Thereafter, in step S24, the operation of the reactor is started. A series of work steps for replacing the reactor vessel is completed through the procedures described above. Another example of the radiation shield 28 to be combined with the RV 2 will be described below with reference to FIGS. 16A and 16B. A radiation shield 28 of this example differs from that shown in FIG. 9 in having, instead of the shield upper lid 28a, stopper beams 28e that are brought into abutment with the upper lid of the RV 2. The remaining structure is the same as that shown in FIG. 9, and hence a description thereof is omitted here. FIG. 16A and FIG. 16B show a state in which the RV 2 is lifted up and combined with the radiation shield 28 of this example. Specifically, FIG. 16A is a side view, partly broken away, showing details of an attachment unit for the radiation shield 28, and FIG. 16B is a top plan view of FIG. 16A. As shown in FIG. 16B, opposite ends of each of four stopper beams 28e are fixed to an upper surface of the radiation shield 28 by set bolts 28f. The stopper beams 28e are arranged at positions almost evenly spaced from each other in the circumferential direction such that the stopper beams will not interfere with the sling 30a. A hook 28h for hanging the radiation shield 28 is provided at the center of each stopper beam 28e. In the radiation shield 28 of this example, since central portions of the stopper beams 28e are brought into abutment with the shield lid 26, the radiation shield 28 can be easily combined with the RV 2 just by lifting up the RV 2. Depending on cases, the height of the radiation shield 28 can be reduced to a height enough to cover nearly a level of-the outlet nozzle (or the inlet nozzle) by filling a shielding material in the RV 2. In such a case, the height of the radiation shield 28 may be reduced to such an extent that the stopper beams 28e are brought into abutment with the outlet nozzle (or the inlet nozzle). In that case, the radiation shield 28 can also be easily combined with the RV 2 in a short time just by lifting up the RV 2. With the embodiment described above, the reactor vessel can be carried out and in with high efficiency in a short time in a state where the polar crane is removed. It is therefore possible to shorten the term of work for replacing the reactor vessel and hence to shorten the downtime of the nuclear power plant. Further, when carrying out the reactor vessel, the surface dose rate of the shield for the reactor vessel can be reduced to a level lower than the limit value. Moreover, since workers are less required to access the reactor vessel when the shield is combined with the reactor vessel, the radiation exposure rate of the workers can be reduced during the work for carrying out the reactor vessel. Additionally, in the embodiment described above, work for draining reactor water in the RV 2 after the end of step S6 may be omitted. In that case, the remaining reactor water is effective to shut off radiations from the core internals 50. It is therefore possible to further reduce the surface dose rate of the RV 2, and hence to omit the step S7 of filling mortar (shielding material). Also, instead of mortar, powder (or fine particles) of, e.g., lead or steel may be sealed off in the reactor. While, in the embodiment described above, the polar crane is removed in step S11, this step is not limited to removal of the polar crane. For example, the polar crane may be operated to move aside for creating a space, through which the reactor vessel and the shield are able to pass, in an area within the reactor containment vessel where the polar crane is installed. In that case, the polar crane is restored to the original state in step S17. (Embodiment 2) Next, a description is made of a second embodiment in which the present invention is applied to replacement of a reactor vessel in a PWR plant. In this embodiment, after reinforcing a polar crane, a large-size block including a reactor vessel (RV) is lifted up by the reinforced polar crane and then carried out through an opening formed so as to penetrate side walls of a containment vessel (CV) and a reactor shielding building for replacement with a new reactor vessel. FIG. 17A and FIG. 17B are flowchart showing a method for replacing the RV according to the second embodiment. Steps T1-T8 and T21-T25 in FIGS. 17A and 17B are the same as steps S1-S8 and S20-S24 in FIGS. 1A and 1B. This second embodiment differs from the first embodiment in steps T9-T20 in FIGS. 17A and 17B. Other procedures are the same as those in the first embodiment and a description thereof is omitted here. Steps T9-T20 in this embodiment will be described below. In step T9, a temporary opening 4a is formed so as to penetrate side walls of a CV 3 and a reactor shielding building having 1, the temporary opening 4a having a size allowing a large-size block 51 including an RV 2 to be carried out through it in a horizontally laid state. FIG. 18 shows a state in which the temporary opening 4a enabling the large-size block 51 (not shown in FIG. 18) to be carried out therethrough is formed in the side wall of the CV 3 at a level above an operating floor 7. Although an equipment carrying-in opening 4 is provided in the CV 3 for carrying out/in large-size equipment through it, the size of the equipment carrying-in opening 4 is not enough to carry out the large-size block 51 including a radiation shield 28 and the RV 2, as described above. Therefore, the temporary opening 4a is newly formed so as to penetrate both the CV 3 and the reactor building 1. A shutter 4b capable of opening and closing is provided to close the temporary opening 4a. The temporary opening 4a may be formed at a different position from the equipment carrying-in opening 4, but the term necessary for the work can be cut down by enlarging the existing equipment carrying-in opening 4 to such an extent that the temporary opening 4a is formed. Then, in step T10, a polar crane 9 is reinforced. The existing polar crane has a capacity of about 100 tons. On the other hand, the weight of the large-size block 51 including core internals 50, the RV 2 and the radiation shield 28 amounts to 400 to 500 tons. For that reason, the polar crane 9 is reinforced to be capable of lifting up the large-size block 51 having such a large weight. FIG. 19 shows a state in which the polar crane 9 is reinforced by erecting reinforcing members 33 on the operating floor 7 in the CV 3. The reinforcing members 33 may be provided with pulleys or the likes so that the reinforcing members are able to freely move on the operating floor 7 in conjunction with the polar crane 9. Then, in step T11, an auxiliary trolley 9c with a reinforced lifting apparatus is mounted. More specifically, the auxiliary trolley 9c comprising a chain jack (or a hydraulic jack, etc.), which has a capacity capable of lifting up the large-size block with the weight of 400 to 500 tons, is mounted on a girder 9a. Then, in step T12, the radiation shield 28 is carried in through the temporary opening 4a. As with step S12 in the first embodiment, the radiation shield 28 is temporarily placed on the RV 2 (or reinforcing members 27) in a bottom portion of a reactor cavity 5. The radiation shield 28 is provided with a tilting down shaft 28g, which is similar to that shown in FIGS. 15A and 15B, for tilting down the RV 2. Then, in step T13, the RV 2 and the radiation shield 28 are combined with each other. The RV 2 is lifted up by the reinforced polar crane 9. As with step S13 in the first embodiment, the RV 2 and the radiation shield 28 can be easily united into one in a short time by just lifting up the RV 2 to such an extent that a shield lid 26 of the RV 2 is brought into abutment with a shield upper lid 28a. Then, in step T14, a flatcar (trailer) 34a provided with a tilting-down bearing 35 is carried into the CV 3 and set up on the operating floor 7 for tilting down the RV 2. Then, in step T15, the large-size block 51 including the RV 2 combined with the radiation shield 28 is tilted down. The tilting-down of the large-size block 51 is performed in a similar manner as described above in connection with FIGS. 15A and 15B. FIG. 20 is a view showing a state in which the large-size block 51 is tilted down in the CV 3 to be laid on the flatcar 34a. Then, in step T16, the large-size block 51 in a state of being horizontally laid on the flatcar 34a is carried out of the reactor shielding building 1 through the temporary opening 4a. In step T17, while keeping the large-size block 51 horizontally laid on the flatcar 34a, the large-size block 51 is transported to a storage container 40 for the RV 2, which is installed in, e.g., the nuclear power plant site, and then carried into the storage container 40. Then, in step T18, a new reactor vessel (new RV) 2 is carried into the CV 3 through the temporary opening 4a by using the flatcar 34a. After carrying the new RV 2 into the CV 3, the new RV 2 is tilted up by the reinforced polar crane 9 in accordance with the procedure reversal tot that in step T15. Further, the new RV 2 is lifted up by the reinforced polar crane 9 and is installed in the reactor cavity 5. Then, the reinforcing members 33 and the auxiliary trolley 9c for the polar crane 9 are removed in step T19, and the temporary opening 4a is closed in step T20. Subsequent steps T21 to T25 are performed in the same manners as in steps S20 to S24 shown in FIGS. 1A and 1B. The work for carrying out the large-size block 51, which includes the core internals 50, the RV 2 and the radiation shield 28 united into one, and the work for carrying the new RV 2 are thereby completed. With this embodiment, carrying-out and -in of the reactor vessel can be implemented in a short time with high efficiency by using the reinforced polar crane. It is therefore possible to shorten the term of work for replacing the reactor vessel and hence to shorten the downtime of the nuclear power plant. Further, as with the first embodiment, when carrying out the reactor vessel, the surface dose rate of the shield for the reactor vessel can be reduced to a level lower than the limit value, and the radiation exposure rate of workers can be reduced. |
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052395634 | summary | BACKGROUND OF THE INVENTION This invention relates to an instrument for quantifying the interaction between atomic, ionic, and/or plasma jets with solid or liquid materials surfaces. In particular, this invention relates to an apparatus for the measurement of particle, momentum, and energy fluxes of a plasma stream where forces onto surfaces defining the plasma boundary are transmitted by ionic and neutral particles with 10's of eV's of kinetic energy, are accompanied by high heat fluxes, and are pulsed. Work toward the goal of fusion energy production is progressing in a number of laboratories throughout the world. In the area of magnetic confinement fusion, the major effort is focused on the "tokamak" device, which consists of a toroidal vessel that contains a high temperature plasma, surrounded by magnetic field coils that confine and position the plasma. Design and operation of these devices requires quantitative study of the interaction between an intense plasma stream and surfaces of different materials immersed in dense plasmas. In the prior art, momentum and energy flows and pressures are calculated using the kinetic theory of gases from measurements of density with ionization, thermocouple, or manometer gauges. The prior art methods are unsuitable, however, for surfaces immersed dense plasmas (n>10.sup.12 cm.sup.-3); little experimental data are available on the effects of ionic impacts, in the energy range <100 eV, onto surfaces; and the theory of plasmas is sufficiently complex (due, for example, to varying collisionality) that single-point measurements of plasma temperature and density in the plasma interior, as by probes or Thomson scattering, do not readily yield an accurate prediction for the particle, momentum, or energy fluxes at the boundaries of the plasma. It is therefore a primary object of this invention to provide a diagnostic instrument to measure the absolute pressure (momentum flux) from an intense plasma stream where forces onto surfaces defining the plasma boundary are transmitted by ionic and neutral particles with 10's of eV's of kinetic energy and are accompanied by high heat fluxes. In the accomplishment of the foregoing object, it is another important object of this invention to provide an instrument for measuring momentum flux of a plasma stream in an intense magnetic field and pulsed plasma environment. It is another important object of this invention to provide an instrument for measuring momentum flux which may be calibrated in situ, without the need to vent to air. It is a further object of this invention to present an instrument for measuring pulsed momentum flux which gives a response time of approximately 1 ms. Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention. SUMMARY OF THE INVENTION To achieve the foregoing and other objects, this invention comprises an instrument in which momentum flux onto a biasable target plate is transferred via a suspended quartz tube onto a sensitive force transducer--a capacitance-type pressure gauge. The transducer is protected from thermal damage, arcing and sputtering, and materials used in the target and pendulum are electrically insulating, rigid even at elevated temperatures, and have low thermal conductivity. The instrument enables measurement of small forces (10.sup.-5 to 10.sup.3 N) accompanied by high heat fluxes which are transmitted by energetic particles with 10's of eV of kinetic energy in an intense magnetic field and pulsed plasma environment. |
039649679 | summary | BACKGROUND This invention relates generally to gas tagged nuclear fuel elements and more specifically to a capsule for introducing tag gas into nuclear fuel elements. During the operation of nuclear reactors there may be a failure of the cladding resulting in release of radioactive fission products to the coolant and ultimately to the environment. Moreover, coolant may enter the failed fuel element and react with the fuel, causing further damage. It is therefore highly desirable to have some means of detecting a cladding failure. It is also highly desirable to locate, as nearly as possible, the fuel element which has failed. In liquid metal cooled fast reactors the coolant is blanketed by an inert cover gas. In water-cooled reactors there is a gradual evolution of non-condensable off-gases produced in part by dissociation of the water. Other reactors are cooled by gas, e.g., carbon dioxide or helium. One method detecting a fuel cladding failure in any of these types of reactors is by analysis of the gas. In order to indicate and identify a fuel element failure, it is known to introduce specific mixtures of different isotopes of, e.g., neon, xenon or krypton into the fuel elements. By using different isotopic mixtures in different subassemblies of the reactor core it is possible to determine the location of the failed fuel element. This is done by subjecting the gas to mass spectrometric analysis. It is then possible to remove the fuel assembly containing the defective fuel element. The above method is described in U.S. Pat. No. 3,632,470 to Rubin et al., U.S. Pat. No. 3,663,363 to Crouthamel et al., and U.S. Atomic Energy Commission report BNWL-1200-4, pages 4.38 to 4.44. This method has come to be known as "tagging" and the isotopic mixture has come to be known as the "tag gas." One problem in connection with the tagging has been the manner of introduction of the tag gas into the fuel element. The fuel elements ordinarily contain a fill gas, usually helium, in addition to the nuclear fuel. The helium is normally introduced by placing the fuel tube containing nuclear fuel in a chamber which contains a welding apparatus, evacuating the chamber, backfilling with helium, inserting the end cap into the end of the fuel tube, then welding the end cap to the fuel tube. While the tag gas can be added to the helium during the backfilling step, this is wasteful of the tag gas, which is relatively expensive. Moreover, in some cases, the tag gas may include a radioactive isotope which should not be released into the helium which escapes from the chamber after the welding step. To avoid this problem, the tag gas has been, in one prior art method, enclosed in a capsule fitted with a punch attached to a bimetallic element which causes the punch to penetrate the capsule when a certain temperature is reached in the reactor. See Henault et al., American Nuclear Society Transactions, Vol. 13, page 798 ( 1970). However, since the puncturing does not take place until the fuel is in the reactor, there is no way to be sure that the intended release of the gas from the capsule has actually taken place. It is an object of this invention to provide a means for releasing tag gas from a capsule within a fuel element which will be positive in operation, which can be operated before the fuel element is placed in the reactor, and which is subject to nondestructive inspection to verify its operation. SUMMARY OF THE INVENTION According to the present invention, the above and other objects are attained by providing within a nuclear reactor fuel element a ferromagnetic punch which is actuated by external electro-magnets and driven against a thin rupturable end wall of a sealed capsule, penetrating the capsule and releasing a sealed tag gas into the fuel element. Preferably, the punch is slidably mounted within a sealed non-magnetic tag gas capsule and has a double-ended penetrating portion. Advantageously, the standard nondestructive testing of the weld quality between the end cap and the fuel tube, such as by X-ray or radiographic inspection, serves to verify penetration of the sealed capsule and release of the tag gas around the loosely-fitting capsule into the fuel element. |
047956062 | description | DESCRIPTION OF A PREFERRED EMBODIMENT The apparatus is primarily intended to provide visual inspection of the outer surface of an internal tank for liquid metal in the primary circuit of a liquid metal fast breeder nuclear reactor but the apparatus may find use in other situations requiring remote visual inspection. A liquid metal-containing primary vessel in the form of an open-topped generally cylindrical tank 10 (only part shown) has wall 11 and a guard vessel 12 with roof 13 surrounds the tank 10 for containment of any liquid which may escape from the tank 10. It is required periodically to inspect the outer surface 14 of the wall 11 to check for leaks. For this purpose in the present case the containment vessel roof 13 is provided with a small number of access apertures 15, each normally closed by a respective removable plug, each aperture having an upstanding tube 16 extending to an upper structure 9 and from the lower end of which extends a rigid curved guide tube 17. A horizontal guide track 18 extends completely around and slightly outside the upper end region of the wall 11 being supported on circumferentially spaced brackets 19 each secured to the wall 11 adjacent the upper end of the wall 11. The track 18 comprises two laterally spaced depending arms 20, 21 the upper ends of which are secured to the lower ends of spaced arms 19a, 19b forming part of the brackets 19 having converging portions 20a, 21a leading to radially spaced vertical portions 20b, 21b. The track 18 is typically 19 meters in diameter. The apparatus further comprises a deployment device 22 comprising a series of rigid tubular units 23, adjacent units being connected by flexible bellows 24 so that the units can articulate relative to each other. Each unit 23 carries guide rollers 25, one on each side, for engaging the inner surfaces of portions 20b, 21b (FIG. 2) and also carries wheels 27 (two on each side) for running on the lower regions of portions 20a, 21a. The device 22 is introduced through an aperture 16 and tube 17 and can move along the track 18 to bring the leading end of the device 22 to the region of track near the next aperture 16. An umbilical cable 28 extends along and inside the device 22 and carries a camera 29 at its leading end. The camera 29 can be lowered between track portions 20b, 21b as shown chain-dotted. Thus, the device 22 is inserted on to the track 18, the camera 29 is lowered to enable inspection of a vertical strip of the surface 14, the camera is raised, the device 22 pushed further along the track 18, the camera 29 again lowered to inspect the next adjacent vertical strip of the surface 14, and so on until the surface 14 between apertures 16 has been inspected. The device is then inserted in the next aperture 16 and this process repeated until the whole of the surface 14 has been inspected. The inner surface 30 of structure 12 can also be viewed and also the roof insulation in annular region 31, FIG. 4. The camera 29 may be connected to a video display unit (not shown) and the cable 28 includes means for carrying a supply of coolant gas (for example argon, helium, nitrogen or carbon dioxide) to the camera 29. Light for the camera may be supplied through the umbilical cable 28. In modified arrangements the camera is responsive to nuclear radiation, for example, from a leak in the wall 11, or to infrared radiation. The position of the camera can be assessed from a knowledge of how many units 23 have been inserted into aperture 16 and how much cable 28 has been inserted into the device 22. The camera can be arranged to view around the track, before the camera is lowered between track portions 20b, 21b. The apparatus is convenient and avoids a multiplicity of guide tubes around the vessel each for directing an inspection device to a selected region of the vessel outer surface and the relative simplicity of deployment improves confidence in the reliability of operation and retrieval. Modifications are possible. Thus the wheels 27 may in some cases be replaced by low friction sliders to form, as do the wheels, guide means for engaging the track. The bellows 24 can be replaced by other mechanisms permitting adjacent tubes to articulate relative to each other. The track 18 could take the form of a monorail with the deployment device 22 being guided on the monorail by suitable means. The device could be used to inspect the outer surface of a tube and the term "vessel" is to be understood as including this. The vessel may be closed or open-topped. Further the track 18 need not be circular as seen in plan but could take other shapes e.g. sinusoidal or alternate straight portions and curved portions. Also the surface 11 being inspected need not be circular as viewed axially. The track 18 could be other than horizontal and could for example be attached to depend from a roof structure or be otherwise supported than from a wall 12 adjacent the wall being inspected. The guide 17 could be in the form of a track rather than a tube. Instead of being permanently shaped into a curved deployment form as shown, the tube or guide 17 could be flexible and resilient so as to be initially curved but capable of being generally straightened to be inserted through aperture 16 and, after insertion, to regain the curved form. The rollers 25 could be replaced by a single roller engaging both portions 20b, 21b. In some cases the track 18 is shaped to enable the rollers 25 to be omitted. The number of guide wheels 27 can be varied to suit requirements. Instead of scanning the surface of the wall 11 in a series of adjacent vertical strips, the surface can be scanned in a series of adjacent horizontal strips by moving the device round the wall, and repeating this with the camera lowered a little further for each scan. The camera could be a still camera and in any case the camera could form part of a closed circuit television system. A fiberscope could be extended through the tubes 23 to inspect the wall surface. The camera could include lighting means to illuminate the wall 11 rather than or in addition to supplying light along the umbilical cable system. In some cases the camera may be external to the tubes 23. The umbilical cable system may carry tools for effecting repairs, the tools being manipulable from outside the roof 13. In general, inspection units other than or additional to the camera could be deployed by the device. |
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abstract | A scintillator module includes a substrate, a columnar scintillator crystal layer formed on the substrate, and a non-adhesive moisture-proof member having a given hardness and opposing a crystal growing side of the columnar scintillator crystal layer. The moisture-proof member ensures a void between the moisture-proof member and individual conic peak portions of columnar scintillator crystals forming the columnar scintillator crystal layer under vacuum sealing, and holds the columnar scintillator crystal layer in a moisture-proof state between a moisture-proof layer and the substrate. |
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description | This non-provisional application claims priority benefit of Provisional application No. 61/873,143 filed Sep. 3, 2013 entitled “Use of Intermediate Fluids as to the Mechanisms in the system & Method to Mitigate Migration of Contaminates” the entirety of which is hereby incorporated by reference. On Mar. 11, 2011, the Fukushima nuclear reactor site in Japan was severely crippled, with major radiation leakage, as a consequence of a massive earthquake at Tsunami which struck Japan. On Apr. 5, 2011, within one month after the onset of the Fukushima disaster, the undersigned Harry V. Lehmann, caused to be filed a Provisional Patent Application, being No. 61/471,967, which set forth the invention upon which US Non-Provisional Patent Application US 2012/0310029, as published on Dec. 12, 2012. The undersigned works as the CEO of Green Swan Inc. (www.greenswan.org), a California-based firm concerned with human health in relation to radiation. The above filings, on Apr. 5, 2011, and the later US Non-Provisional Patent Application filed on Apr. 5, 2012, contemplate the use of super-cooled fluids circulated in the Figures which are integrated into both filings, particularly as illustrated in FIG. 1 of US 2012/0310029. The super-cooled fluids as discussed hi the above Provisional and Non-Provisional filings while specifically mentioning the use of fluids other than N2, contemplated the use of extreme low boiling point fluids, so that extreme cold could be brought to bear immediately below the crippled reactor site, and similar sites, including that further removal of heat (and consequent increased rapidity of “ice-basket” riming) would result from an increased rate of boil off of the submitted fluids, due to increased pipe aperture at the mid-points of the doubled barreled shallow ice basket, or shallow ice bowl, approach contemplated in those patents applications. Prior to the above filings, previous experimental and very limited practical deployment had been made of Liquid Nitrogen for the purposes of ground stabilization, most famously, circa 1995, in regard to the drilling and N2 filling of 178 holes around the Leaning Tower of Pisa so that the Tower could be stabilized in place without tipping over while restoration work was undertaken. Prior to the above filings, previous experimental and very limited practical deployment had been made of other super-cooled fluids for the establishment of an “ice wall” barrier: Prior purposes of such “ice wall” approaches have included the establishment of a vertical ice wall surround to protect against radioactive ground water migration at a contaminated nuclear site in the United States, and a similar use of a deployed vertical ice wall surround was made, but not activated, for containment of water away from an active gold mine in Canada, and, also prior to the above patent application filings by the undersigned in April of 2011 and April of 2012, there were other attempts made to stabilize ground, or to mitigate ground water migration, through the use of vertical ice walls. All of the prior Art, meaning all known Art in existence prior to the above filings in April of 2011 and April of 2012 was based upon the drilling of vertical holes, and the filling of those holes with super-cooled solutions, or the circulation of super-cooled solutions within such vertical holes, typically to obtain containment of ground water migration by the drilling of and filling of such super-cooled holes down to an impermeable or less-permeable sub-strata, including strata of harder clay or bedrock. In practical effect, all known prior attempts in this area had been to create a containment tank, with a surface circumference defined by the ring of drilled and super-cooled vertical hole, and a bottom circumference defined by the bottoms of such holes, hoped to be at points interfacing with the expected less-permeable sub-strata constituting the bottom of the large ice walled holding tank defined by the so-drilled and so-cooled holes, often in recent iterations contemplated to be taken to and maintained at a super-cooled state by the circulation of super-cooled saline solution. The disclosed subject matter is directed to a System and Method for retarding and controlling the speed of flow of contaminated water, from a nuclear reactor or other contamination source from which such contaminated water is issuing. The subject matter advantageously uses micro-tunneling, coupled with pipe insertion, coupled with insulated pipe insertion, so that liquids with very low boil points, such as Liquid Nitrogen, or other refrigerant gasses, may be inserted in the liquid state, to vaporize upon release from the insulated containment, so that heat energy is absorbed from the water table, resulting in a reduction in flow rate, thereby impeding the capacity of the water under flow to carry particulate matter. The subject matter also discloses a “laced” approach, in which twin barreled pipes, as herein set forth, may be inserted an non-conflicting depths, but in such proximity to mutually contribute to water sludge accumulation, ice rime, and, with sufficient evaporation process, the formation of an ice lens, sufficient to retard the escape of contaminated water. The effect of this System and Method is to control and slow the release of contaminated water as it is possible to rapidly obtain the freezing the ground water, including salt water, which permeates the area underneath the melted reactors, so that the resulting ice lens will mitigate the extent to which radioactive water is released into the environment. The method here described may be used for this purpose through the accomplishment of two goals; first, a resulting reduction in the quantum of radioactive water released, per se, and secondly, a reduction in the level of particulate radiation reaching the environment due to slowed water flow velocities. It is advantageous to appreciate the existence of “trenchless excavation” for pipe installation. “Direct Jacking,” and the “Micro-tunneling” are approaches widely deployed in the civil engineering context, and similar approaches are used for waste water treatment pipe installation. Direct Jacking is a tunneling process whereby a single new pipe is installed in one pass. A bore head begins the tunnel excavation from an access shaft and is pushed along by hydraulic jacks that remain in the shaft. The link to the boring head is maintained by adding jacking pipe between the jacks and the head. By this procedure, the pipe is laid as the tunnel is bored. Micro-tunneling is defined as a trenchless construction method for installing pipelines. The North American definition of microtunneling describes a method and does not impose size limitations on such method; therefore, a tunnel may be considered a microtunnel if all of the following features apply to construction: Remote Controlled: The microtunneling boring machine (MTBM) is operated from a control panel, normally located on the surface. The system simultaneously installs pipe as spoil is excavated and removed. Personnel entry is not required for routine operations. Guided: The guidance system usually references a laser beam projected onto a target in the MTBM, capable of installing gravity sewers or other types of pipelines to the required tolerances, for line and grade. Pipe Jacked: The pipeline is constructed by consecutively pushing pipes and the MTBM through the ground using a jacking system for thrust. Continuously supported: Continuous pressure is provided to the face of the excavation to balance groundwater and earth pressures. The above citations are inserted merely to acquaint the reader with the fact that in the modem context it is possible to obtain rapid remote controlled boring of pipe holes, so as to facilitate installation of pipe suitable for such installation. The remainder of the “ice lens” approach as herein stated are based upon the availability of such boring technology. No sophisticated explanation of the Rankine Cycle is attempted nor necessary here, but a baseline discussion will speed appreciation for those who have not seen their high school or college texts for a while. It is understood that it takes energy to convert any type of matter from its liquid state to its vapor state. Rather than getting esoteric, just consider the tea kettle; the kettle and its contents are heated, the boiling point is reached, at the boiling point the water reaches its vapor state, and leaves the kettle. It almost immediately precipitates to what we see as “steam,” although close examination of the spout will show a gap, perhaps we could call it a vapor gap, which is a view through the transparent water in its true vapor state. That water in the vapor state is invisible is known to those who have visited the engine rooms of steam turbine aircraft carriers, where in olden days, when a leak was suspected, a broomstick would be swung before a worker as he walked, as the thin vapor stream would cut the stick in half, thereby saving the man. Those turbines, of course, took immense amounts of fuel to operate, originally fuel oil, later nuclear. Bottom line, to take a fluid to the vapor state requires heat. Our common experience may cause us to first visualize this as a one-way street of analysis; we apply heat, the fluid eventually reaches the boiling point as a result of the input of the heat, the heat having forced sufficient molecular vibratory activity that the vapor state is reached as a result of the heat. However, as Lord Kelvin taught, the system is a two-way thoroughfare. That is why we have working refrigerators. In that context, the evaporation cycle of a gas, chosen for its low boiling point (an issue which will be shown as relevant to the macro-machine here contemplated for radioactive containment) can, through compression of that gas (thus the “compressor” of a refrigerator) result in the use of the evaporative cycle, which is called the Rankine Cycle, for the extraction of heat, through the forcing of the cycle by compression of the vapor (gaseous state) so that the liquid state is reached, and then the carefully controlled evaporation of the subject liquid, thereby drawing heat at that point of conversion, from the surrounding material world. These are well understood baseline concepts with which all readers of this paper will have been familiar, but it is suggested that a quick review will enhance appreciation of the feasibility of the macro-application as hereafter explained. The super-cooling of the circulated saline solution or other super-cooled liquid so-placed or so-circulated in such holes used an intermediary fluid to cool the affected earth, with the actual cooling obtained by Rankine Cycle cooling, yet without direct contact between the super-low boiling point fluids lined holes used to create the vertical ice wall which has been the aim of all known work prior to the filing of the Lehmann patent applications of April 2011 and April 2012. It is advantageous to integrate the use of intermediary cooling fluids, including saline solutions, into the “ice basket” approach first articulated by the Lehmann. In the last week prior to the filing of the Provisional Patent Application of Sep. 3, 2013, widely circulated news reports have indicated that those charged with responsibility for the attempted remediation of the natural disaster-caused nuclear contamination events at Fukushima are now seeking to adopt and deploy the older, ice wall” technologies previously used or experimented with in the United States and elsewhere as a means of ground water migration mitigation at toxic sites. The prior “nice basket” filings of Lehmann, as incorporated herein by reference because of the creation of a shallow ice bowl for containment purposes, present clear energy consumption and speed of-construction advantages over the older “vertical ice wall surround 11 approach currently under discussion for remediation of the disaster at Fukushima. The disclosed subject matter further explains the very considerable energy consumption and speed-of-construction advantages of the previously filed Lehmann patents, and for the additional purpose of asserting Claims for the use of intermediary cooling fluids, such as saline solutions, as part of the “shallow ice basket, or “shallow bowl” approach contemplate in the April 2011 and April 2012 patent filings. The prior art did not contemplate the use of computer controlled horizontal and mixed angle drilling, whereas such modem computer controlled mixed angle drilling was an inherent feature in the prior Provisional and Non-Provisional patent filings which have above been incorporated by reference into this document. As to Fukushima, and in terms of application to any similar ground water migration mitigation system, the current, unexecuted, “ice wall” approach involves the establishment of a very deep ice walled cylinder, which would wall in the contaminated water with ice and frozen soil, such that the fence would run all the way down to bedrock or clay (far more than a hundred feet) at which point it is believed that the contaminants would hopefully be stopped from further ground water migration due to the “impermeable clay later” which is stated as residing at that subterranean level. This approach in comparison to the “ice basket” outlined in the previously filed Lehmann patent filings, results in a vastly larger volume of contaminated water containment, resulting in a vastly greater use of energy for cooling, than will occur of the “ice basket” approach outlined in the prior Lehmann filings is chosen instead. The presently contemplated “ice wall” approaches, using vertical shafts, does not make use of modem computer controlled horizontal and mixed” angle drilling technique, and the result of this is that a vastly larger pool of contaminated water is contained by the “ice wall” system than is the case if the more shallow “ice basket” or “ice bowl” as contemplated in the prior Lehmann patent filings is deployed. The value of the “shallow bowl of ice” approach is very quickly and clearly illustrated with simple kitchen tools. The experimenter seeking to verify the advantages of the “shallow ice bowl” approach needs only one large cooking pot and one salad bowl having a diameter larger than the diameter of the pot. By taking the large bowl, one with a diameter at the top larger than the diameter of the cooking pot, and placing the bowl the big metal pot, the experimenter will see demonstrated that only the bottom sixth or so of the salad bowl volumetrically, intrudes within the cylinder of volume described by the interior dimension of the large pot. In fact, due to the curvatures of the line of the bowl from a starting position at the “ground level” emulated by the top of the pot, the actual volumetric displacement represented by the interior dimension of the bowl, when compared to the volume of the pot, may be considerably less than a sixth of the volume of the pot. In practical operation, at Fukushima, this results in a several positive advantages over the “ice wall” approach currently under consideration; A) the evacuation of the contaminated water from a smaller starting volume means that vastly less ground water is contaminated during operation, which means that: B) Far less groundwater need be pumped out, and further that: C) Due to decreased interior volume of the pipes used for this purpose, coupled with the smaller volume of contaminated groundwater perpetually evacuated, the energy required for pump operation is very substantially diminished, and: D) Pump strain is reduced, and: E) Construction time, due to the use of computer guided micro-tunneling is much less, and: F) Volume of extracted soils is diminished, and: G) Immediate production of the ice bowl does not prohibit the construction of the ice fence, using the more traditional ice wall, approaches, such that a failsafe system would automatically evolve, and: H) The currently announced “ice wall” approach contemplates forty years of accumulation of heavy contaminants at the allegedly impermeable clay layer at the bottom of the cylindrical area hoped to be described by the currently anticipated “ice fence.” Eventually, so it is hoped, four or five decades down the road, the site is to have been decontaminated. As a result, it would appear that the need for the ice fence would abate. Even if not the case, an assumption that there will be an ice fence, in site at a coastline, which will somehow remain in perpetuity is optimistic. The contaminants involved by their atomic weight nature heavier than their surrounding milieu, such that the accumulation of a substantial contaminant layer at the bottom of the proposed cylinder is unavoidable the “bottom of the pot,” see above). The contaminants generate heat when accumulated, and the character of interaction with the hypothetical clay layer is not known, and: Assuming the very best case with the clay layer (hardening by heat), upon the cessation of the “ice fence” cooling process, the result of the cylindrical “ice fence” is a huge residue of impermissibly dangerous contaminants, residing in perpetuity, and inevitably capable of lateral migration. In comparison to all of the above disadvantages of a large cylindrical trice wall” the “ice basket” approach as articulated in the previously filed Lehmann patent applications, if deployed, would require the constant handling of only about a sixth of the volume, or perhaps a far smaller fraction, of the amount of contaminated water which would have to be constantly evacuated and treated if the more “classic ice wall” approach is pursued. The use of the “ice basket” approach will result in faster construction, less construction materials, and far less contaminate water to be handled, resulting in a substantial reduction in energy use needed to keep the pumps going, as well as far less equipment strain, and far less necessary storage of contaminated water J this last perhaps being the largest advantage of the previously filed Lehmann approach, per Apr. 5, 2011 and Apr. 5, 2012. The present subject matter also addresses an unusual situation where there has been contamination into the earth and groundwater beneath a site, but where due to changed circumstances (such as the sinking of ground level from an earthquake, as happened at Fukushima) there are persistent or intermittent situations where hydrostatic pressures are greater beneath a site than at ground level for that site. Fukushima currently stands as an example of this peculiar and difficult situation, where a combination of gravity, great heat and great weight have caused penetration of radioactive materials through concrete containment and into the ground below and groundwater, while simultaneously there may be greater hydrostatic pressure below, such that there is a radioactive artesian effect. These and many other objects and advantages of the present subject matter will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments. It is within existing engineering technology to create what amounts to a macro-refrigerator through very carefully sited drilling of the earth around the reactors suffering from meltdown, so as to create an “ice basket” beneath the reactor cores involved. The formation of such an ice lens, or basket in its fullest application, will result in diminished levels of radioactive water reaching the sea. This is what can be done: One embodiment to prevent such migration of contaminates is the drilling of a multiple twined lateral tunnels beneath the affected reactors. The tunnels, probably six twin bores, should be drilled, first, down at a 45 or so degree angle (or such shallower angle as may be necessary for pipe insertion), to then a level bore, at a drilled position centered below each melting reactor. For example to use an arbitrary figure of a thousand foot radius from the center of the containment, may define an appropriate balance between exposure avoidance needs and practical necessities relating to the boring and pipe insertion process. Obviously, commencement of operations from a threshold outside the ambit of severe cumulative exposure risks would be wise, but at the edge, so as to minimize the amount of drilling involved. Preferably the boring should be a downward drilling on a 45 degree angle, to, again, here for illustration, about one hundred feet below or lower than the base of the reactor, or whatever is left of it as in the case of an accident. The construction of the containment grid could also be done preemptively during construction of the reactor or other source of contaminates, or as a matter of course before any such emergency. There may be a lateral portion. These lateral portions are well within the capacity fairly commonly available robotic pipe insertion drilling equipment as alluded to above. It is suggested that due to various factors, multiple holes should be commenced as equipment and staffing become available. It is known that 24 inch micro-tunneling is available in industry. For the instant illustrative purposes, it is envisioned using a 18 inch pipe. There should be the insertion of insulated pipe through the resulting tunnel. It is preferable to keep this as simple as possible. There are means of cooling the frontal area of the insertion sans pumping, but believed this to be a bit more complex than likely justified. Preferably there should be two twin pipes drilled, think of it as a “double barreled” approach. This is necessary because the currently escaping radioactive sea water is at or near sea level, and not solely at lower elevations, though this will of course inevitably become a deepening problem. The desirability for twin bores will be shortly examined. Upon the insertion of the insulated pipe, which at the least must have telemetry for heat, there should be the insertion of a low boiling point gas. Preferably liquid nitrogen. It is noted that while venting of the nitrogen post use is likely, this need not involve any particulate radiation. There is the need to control the post evaporation venting of the gas, which can involve compression and reuse, however such is not the focus, the focus here will be on cooling, and not re-circulation. The baseline is that a cold non-explosive gas, here liquid nitrogen may be inserted via a well-insulated interior casing, or pipe, which is in turn inserted inside the pipe originally inserted into the bore. This method mimics a repair method already in wide use for the repair of deteriorated pipe via the insertion of a pipe of lesser dimension, which in current sewer pipe repair scenarios is called “re-lining.” When spot repairs of old pipe lines, mainly sewers, are no longer viable, local authorities are faced with the problem of rehabilitating or replacing pipelines in the course of time. Replacement has the disadvantage of being very costly and disruptive to urban areas where the largest sewer networks are located. HOBAS pipes are inserted in the existing pipeline with grout cementing them in place. In view of the savings municipal authorities are now allocating as much as 50% of budgets to rehabilitation. These types of products are ideal for this application being lightweight, corrosion resistant, quality-assured, easily jointed and rigid to resist grouting forces. It is noted that there are several indications at the HOBAS site of the use of resins to obtain near-perfect interior smoothness, coupled with entire leakage prevention, using modem materials. So long as the bore can be made at a level sufficient that heat ruin of the piping systems here contemplated is avoided (this may ultimately involve “leapfrog” installations of the “pipe basket”), there may and should be the capacity to entirely insulate the low boiling point gas (here, nitrogen) from contact with radioactive fluid. This would result in a clean vent, although the potential for compression and re-circulation (a true “mega-fridge”) is obvious. In this contemplated system of twin, or paired, bores, each twin bore will have a “nominal” end (where temperatures exterior to the insulation are consistent with ambient OAT), and a “cold end” which will be the area from the point of release just to the near side of bottom dead center from the reactor. It is preferable that the point of N2 release be prior to the position in the pipe directly below bottom dead center of the reactor, so that direct cooling from the N2 can come prior to, or without, pipe insertion directly below the heat source. The reasons for this will be fairly apparent thus no fuller explanation is furthered here. Thus, half the each pipe is “ambient,” and half of each pipe, from bottom dead center to the exterior gas release (or compression) point, is very cold. This will cause ice to rime upon the pipe, and so long as gas release is continued, cooling of the surrounding rock/water substrate to occur, to the extent that ice will migrate out from the pipe. This is why a twin bore is advantageous, since the result will be cooling all the way from bottom dead center to the surface, with the insulated pipe having been installed from opposing positions on the circle which defines the drill origination circumference around the affected reactor(s). One such installation, of just one twin pipe system, would, if well engineered, result in some reduction of rate of radioactive water loss to the environment, due to water viscosity increase and resulting reduction in velocity of migration. Thus, a resulting “ice lens” beneath the affected reactor. However, the next set of twin pipe bores, each “fueled” in opposing directions of super-cool liquid insertion, would commence the formation not just of an “Ice Lens” but rather the building up of an ice web, or “Ice Basket” should result. It would be essential to drill each succeeding twin bore system to an elevation above or below all preceding bores, so as to avoid one drilled system from ruining its predecessor. These are matters of intricate field detail, but quite manageable for one of skill in the art. There are two methods of freezing involved. First, the liquid nitrogen (the world's supply could if necessary be devoted to this, a unifying effort, though I recognize that this as a melodramatic statement) will, at the least, if there is continuation, cause a freezing of the ground water, just because it is a super-cold liquid. However, it will inevitably evaporate, also thus causing “heat drain” from the Rankine process from the surrounding rock/water milieu. If this groundwater freezing is thus brought to equilibrium with the heat output, time will be bought. There are other applications, but there are problems with loss of ductility at every turn. Still, a desperate situation may sometimes only be surmounted through recognition of the need for an inventive approach. As with some other suggestions, this is sent along for reasons of citizenship. Rather than evaluating this, it is suggested that it be forwarded and evaluated by others more formally qualified than the undersigned. FIGS. 1 and 2 illustrate the proposed drilling, and the results of actuation of the system as herein described. This is a method through which the leakage of radioactive water into the ocean can be reduced in magnitude and stalled at such a reduced rate for a protracted period of time. FIG. 1 is a side view of an embodiment 100 showing a simple drawing of a nuclear reactor 10 of a general type, the earth 28 upon which it is situated, the water table 26, an inlet casing pipe 12, through which an ultra-low boil point fluid is inserted within an insulated pipe 16, so that, at aperture 18, vaporization of the gas 20 occurs. This results in contact cooling of the soil proximate the cooling channels 24, from the N2, or other chosen refrigerant itself, but also draws heat, from the evaporative cooling process inherent in the involved vaporization. An ice region 22 is thereby produced at the exterior of the casing. Care must be taken to assure that the N2 or other suitable gas is utterly dry, to avoid aperture contamination. Hydraulic process is noted as one possible adjunct to insertion. As noted previously the channels may be formed during the construction of the site and thus other techniques may be available. The potential for capture at vent 14 is recognized, with possible re-compression and delivery of the compressed liquid and gas to the inlet 12 as discussed above. However release to the atmosphere is acceptable if tight seam is obtained, infiltration of the contaminate is avoided, in which case the N2 in the gaseous state would have no toxic character, already being roughly 78% of the ambient air. FIG. 2 is a top view of an embodiment 200 of the subject matter illustrating the use of multiple non-intersecting pipes, separated by differing but near depth levels, so that, post aperture 18, as to each such pipe, there is cooling effect from the direct contact with the super-cooled liquid form of the N2 (or other) involved, and to a greater effect, continuing up pipe 24 (and in this instance downstream) the vaporization draws heat into the N2, which is then exhausted 14. This results in cooling of the surrounding water, the viscosity increase resulting therefrom thereby slowing velocity, and thereby reducing capacity for the carrying of particulate matter. In addition, with precise modeling before the fact and precise calibration in execution, the overlapping instances of evaporating cooling will cause an ice lens 22 formation below the reactor 10, which should migrate upwards in accordance with the exhaust pipes and their associated cooling effect. A partial ice lens 22 is shown in FIG. 2. It is noted that while these drawings have tended to illustrate the placing of the aperture near bottom dead center, it likely will work better towards ice lens formation if the aperture point is directly below the first encountered edge from the vantage point of the insulated pipe, so that there will be a resulting four cold pipe confluence below the partial melt, so as to assist in ice web propagation. To assist in evaporation, a vacuum may also be created in the cooling channels. Temperature control would be advantageous. Multiple configurations of the cooling channels are envisioned in defining the boundary of the containment area, such shapes may include bowl shapes, saucer shapes, hyperbolic, parabolic, cylindrical or rectangular shape. Another aspect of the present subject matter is the uses of throttling of the gas rather than evaporation. In such case a compressed gas would be provided and then expanded through the aperture 18 into the cooling channels 24 at a much lower pressure and temperature. Still another aspect of the disclosed subject matter is the use of computer controlled drilling to accomplish both a mouth-up ice bowl beneath the contaminated site and directly beneath it a mouth-down bowl of similar shape but larger circumference, emulating an “hourglass shape” in the resulting intertwine of computer-controlled micro-tunnels, with an aperture at the juncture between the mouth-up bowl and the mouth-down bowl, such that higher hydrostatic pressure in the bowl beneath will concentrate contaminates and contaminated groundwater of higher pressure below and channel them upward through such aperture, at rates which may be varied in accordance with adjustable variation in aperture size by chosen aperture perimeter, varied by operators decision through the use of chilled tunnels at varying distances from the center of the aperture involved. The aperture may be of a physical valve, or more advantageously be defined by the ice shield by controlling the cooling passages to allow for an permeable area 21. Due to the application of Bernoulli's Principle, a greater or lesser level of artesian flow may be regulated in addition by variation of the circumference and thickness of the chill formed mouth-down bowl, in illustrative allegory being “the bottom half of the hourglass.” This will thus allow the use of naturally occurring pressure phenomena, coupled with aperture variation bowl size modulation to both contain sunken contaminates and move them via such hydrostatic pressure differential up to the surface, while still, via the top and “mouth-up” bowl serving to contain such contaminants in order to increase the predictability of managing them. Thus use of controlled aperture shielding resulting from shaped frozen groundwater through the use of modem micro-tunneling technique coupled with inserted super-cooled fluids as a mechanism of establishing sustaining and modifying such shield may be undertaken. Computer directed micro-tunneling technique may establish pathways for the introduction of super-cooled fluids, or intermediary cooled fluids, towards the establishment of an “ice basket,” progressing to an “ice shield” or “ice bowl” beneath a contaminated site in order to mitigate migration from one side of the so-constructed bowl or shield to the other side of the same so-constructed emplacement, and such prior submitted Art, as referenced by the identification numbers thereupon as here stated are here used for the limited purpose of illustration, and the prior applications are not incorporated herein as though more fully set forth. One embodiment differs in that it proposes not a shield like previously proposed, but instead here submit a Bernoulli-effect-based flow-rate adjustable shield and hydrostatic pump combination machine, of particular utility in situations where, for example changes in geomorphology have resulted in an aberration of prior groundwater migration patterns, including in situations such that there is a resulting net flow upward into the original contamination source area. Moreover, the present subject matter allows for the gradual dissipation of contaminated water, as well as control dilution of contaminated water. FIGS. 3 and 4 illustrate a system for creation of an ice region 22 (ice shield) having a variable water permeable region 21. As shown the cooling passages 24 for all but the inner most ring cause the ground water to freeze resulting in an ice region in which a water permeable region remains which may allow water to enter or leave the boundary of the ice shield 22. By selecting the cooling passages 24 to engage the size of the permeable region may be changed. For example if the inner passage 24 where activated the permeable region could be reduced to zero and effectively present any water to pass through the boundary. Similarly, if the inner two passages 24 would closed the permeable region 21 would increase. A sensor 19 is shown in the figures allowing the contaminate level to be determined within the ice shield 22 and also proximate the water permeable region 21 to aid in the control of the variable aperture 21. The sensor may also extend to outside the ice shield 22. Information regarding the relative contamination of water in/outside or passing through the aperture 21 may be used to control the aperture 21. FIGS. 5 and 6 illustrate various arrangements of the ice shields and the water permeable regions 21. In FIG. 5, a binary water permeable region 21 is shown. The application of cooling fluid or gas through the input pipe 12 closes the aperture 21, and ceasing to provide the cooling fluid opens the aperture 21. The cooling channels shown in FIG. 5 demonstrate the various patterns in which the channels may be constructed. FIG. 6 shows the addition of a variable water permeable region 21 to a traditional ice shield 22, characterized by vertical wells with in the permeable layer 103 for the cooling of the ground water. In FIG. 6, the bottom of the containment shield is shown as Clay 105 and thus cooling passages are not required to bound the contaminated water. As in FIG. 5, the permeable region 21 is shown as a binary system, however a variable aperture as described above is also envisioned. FIGS. 8A and 8B shows the present subject matter in which the ice shield 22 forms and internal hour glass shape. By selectively choosing the cooling channels 24 to activate the water permeable region 21 may be expanded or narrowed to control the flow of water into the ice shield 22 as shown in FIG. 8A or out of the ice shield 22 as shown in FIG. 8B. The release of contaminated water through the variable aperture 21 may be a function of the contamination determined by the sensor 19. The contaminated water may be slowly released over time at safe level. Alternatively, the contaminated water can be diluted by allowing ground water up through the variable aperture 21 over time. The aperture may also be cycled, allowing water in during the dry season, and water out during the wet seasons, or vice versa to slowly dilute and disperse the contaminates. The variable aperture 21 may also serve as a safety value, in that an influx of surface water via rain or snow may result in an overflow of the ice shield 22 which would immediately effect the biosphere with contaminated water, whereas if the overflow was released from the aperture some natural filtering, dilution and filtering would likely mitigate the resultant contamination compared with a surface release. While the cooling fluid and pipe placement has been primarily described using expanding gas as the working fluid, the use of an cooled intermediate fluid as described above is equally envisioned. A heat exchanger not shown cools the intermediate fluid which enters into inlet 12 and exits from outlet 14. With the use of an intermediate fluid the apertures 18 would not be needed to expand the working gas and the portions of the passages outside of the desired freezing zone would advantageously be insulated to prevent heat absorption. FIG. 7 illustrates the use of a heat exchanger for providing the supper cooled intermediate fluid. The intermediate fluid enters from outlet 14 passes through the coils of the heat exchanger where it is cooled an exits as a super cooled fluid to inlet 12. The cooling unit provides the working fluid typically low boiling point fluid and expands it through the aperture 18 which absorbs heat from the intermediate fluid and then returns to the compressor of the cooling unit which removes the absorbed heat. The general construction of heat exchangers is well known and thus will not be further described. For the use and the resulting tunnels from lateral or horizontal or mixed angle drilling, and the installation of piping in the resulting tunnels, through the use of modem micro-tunneling technique, including but not limited to remote controlled micro-boring machinery (MTBM) for the establishment of radii channels underneath a toxic site or a site with potential for toxicity, including as illustrated in FIG. 1 where cooling of the earth and water within it results from the circulation of a super-cooled liquid within pipes installed in the resulting channels, including but not limited to channels drilled in overlapping radii form, such that a “shallow ice bowl” effect results, such that the migration of contaminated groundwater beyond such ice bowl is mitigated and where the cooling fluid used within such shallow radii channels includes intermediary fluids (as opposed to super low boiling point fluids as may be used to obtain the cooling of such intermediary fluids) including but not limited to saline solutions with resulting lowered freezing points. The shallow angle frozen ice barrier, including in radii shape, and including in shapes as shown in FIG. 1, where cooling of the earth and water within has resulting in the establishment of such frozen ice barrier, from the circulation of a super cooled intermediary liquid within pipes installed in the resulting channels, including but not limited to intermediary fluids such as saline solutions which have a low freezing point. Regarding the insertion of pipes for the circulation of super-cooled fluids, including fluids with very low boiling points, and also including intermediary fluids with very low freezing points, the use of pipes which are composed of corrosion resistant metals or plastics or other corrosion resistant materials, but that such pipe is in turn enclosed within an exterior pipe or casing, with spacers keeping a constancy of distance between the exterior of the interior pipe and the interior of the exterior casing, and that the intervening space between the interior side of the exterior casing and the exterior side of the interior pipe is filled with lead or other radiation migration impairing materials, such that the contamination is avoided of the super-cooled fluid or gas used for cooling purposes as shown herein and in FIG. 1 where cooling of the earth and water within it results from the circulation of a super-cooled liquid within pipes installed in the resulting channels. While preferred embodiments of the present invention have been described, it is to be understood that the embodiments described are illustrative only and that the scope of the invention is to be defined solely by the appended claims when accorded a full range of equivalence, many variations and modifications naturally occurring to those of skill in the art from a perusal hereof. |
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056152450 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to accompanying drawings. The present invention, however, is not to be limited to the details given herein. FIG. 4 shows a monochromator for radiant X-rays according to an embodiment of the present invention. The monochromator is composed of a first crystal 10 which has a first surface of incidence 12 having a concave letter V-shaped groove 11 and a second crystal 20 which has a second surface of incidence 22 having a letter V-shaped convex 21. The first crystal 10, as shown in FIG. 5, internally includes a transport pipe 30 (cooling means) for flowing a cooling material 31 behind the first surface of incidence 12 along the concave letter V-shaped groove 11. The transport pipe 30 extends toward the bottom portion (intensely heated zone) 13 of the concave letter V-shaped groove 11 from the bottom portion of the first crystal 10, branches off in opposed directions just under the intensely heated zone 13 so as to run substantially along the inclined surfaces 12, which are the first surface of incidence of the letter V-shaped groove, and reaches side walls of the first crystal 10, from which the cooling material 31 is discharged outside. Stainless steel or Teflon which is heat-resistant and pressure resistant is used as material for the transport pipe 30, and water or liquid gallium having a good cooling efficiency is used as the cooling material 31, and also the cooling material 31 is applied to the intensely heated zone 13 in the form of a water jet. FIG. 6 is a schematic showing a lattice distortion of the first crystal 10 caused by heat when a pencil of radiant X-rays enters the monochromator for radiant X-rays of the present invention. In FIG. 6, horizontal lines 40 denote lattice planes. Initial lattice planes before entry of a pencil of X-rays are represented with dotted lines, and thermally deformed lattice planes are represented with solid lines. As seen from FIG. 6, a portion (denoted by 42) of the inclined surface 12 near the intensely heated zone 13 expands in an inward direction of the concave letter V-shaped groove 11, but a deformation of lattice planes themselves is slight. That is, lattice planes deform in such a manner that ends thereof slightly rise with resect to a virtual line extended from the bottom portion 13 of the concave letter V-shaped groove 11. However, thus deformed lattice planes do not deviate too much from initial lattice planes. Also, in the intensely heated zone 13, since the inclined surfaces of the concave letter V shaped groove 11 converge, thermally generated stresses cancel out each other and are attenuated, whereby thermal distortion is suppressed. In a zone 44 subject to a deformation which is directed toward the inside of the first crystal 11 underneath the intensely heated zone 13, the deformation terminates within the crystal without reaching the bottom portion and side surfaces of the crystal. Accordingly, the influence of the thermal deformation concentrates on the periphery of the intensely heated zone 13, and the influence on the entire crystal can be minimized. Thus, the influence of thermal deformation on lattice planes is very small which is observed with the monochromator for radiant X-rays of the present invention, and hence any large warp of lattice planes does not take place which is observed with conventional plate type monochromators. FIG. 7 shows a path of a parallel pencil of X-rays which enters the first crystal and then exits the second crystal. A parallel pencil of radiant X-rays enters the first crystal 10 at the first surface of incidence 12 having the concave letter V-shaped groove 11 (angle between the letter V-shaped inclined surfaces: 2.alpha.). The first surface of incidence 12 is inclined at an angle of .theta. from a pencil of incident X-rays A.sub.0 B.sub.0 C.sub.0 (minor axis 2S.sub.v, major axis 2S.sub.h), and thus the shade A.sub.1 B.sub.1 C.sub.1 of X-rays on the surface of incidence elongates to a half-ellipse (minor axis 2s.sub.v /sin.theta., major axis S.sub.h /{tan.alpha. sin.theta.}. Then, the X-rays which have expanded on the first surface of incidence 12 reflect therefrom. Thus reflected X-rays enter the second crystal 20 at the second surface of incidence 22 having the letter V-shaped convex 21 (angle between the letter V-shaped inclined surfaces: 2.alpha.). The concave letter V-shaped groove 11 and the letter V-shaped convex 21 fit into each other and are positioned so as to align with each other. As a result, the first surface of incidence 12 and the second surface of incidence 22 are arranged in parallel with each other and spaced by D. Accordingly, a pencil of X-rays reflecting from the first surface of incidence 12 impinges in parallel on the second surface of incidence 22, thereby forming a half-elliptical shadow A.sub.2 B.sub.2 C.sub.2 of X-rays having the same size on the second surface of incidence 22. As a result of arranging the first surface of incidence 12 and the second surface of incidence 22 in parallel with each other, a pencil of X-rays impinging on the second surface of incidence 22 exits at the same angle .theta. as the Bragg angle .theta. to the first surface of incidence 12. Thus, a pencil of emissive X-rays A.sub.3 B.sub.3 C.sub.3 (minor axis 2S.sub.v, major axis 2S.sub.h) is obtained which has the same size and parallelism as the initial parallel pencil of X-rays. In this case, a cross section of the pencil of incident X-rays is seen from FIG. 8, and a cross section of the pencil of emissive X-rays is seen from FIG. 9. FIG. 8 is a distribution diagram showing a power distribution of the first beam from an undulator, representing a pencil of incident X-rays which enters the first crystal. FIG. 9 is a distribution diagram showing a power distribution of the emissive beam which exits the monochromator, representing a pencil of emissive X-rays which exits the second crystal. As seen from the figures, both cross sections agree well with each other, indicating that the pencil of emissive X-rays accurately reproduces the pencil of incident X-rays. Since the pencil of emissive X-rays is useful as a light for X-ray structural analysis, material evaluation and the like, it is found that high-accuracy X-ray spectroscopic performance can be obtained. To obtain useful light which accurately has the same size and parallelism as a pencil of radiant X-rays, it is preferable that the first crystal 10 and the second crystal 20 be arranged in such a manner that the centerline of the bottom portion 13 of the concave letter V-shaped groove aligns with the centerline of a tip portion 23 of the letter V-shaped convex 21. Suppose that the first crystal 10 and the second crystal 20 deviate from each other by spacing b. In this case, as shown in FIG. 10, X-rays which reflect from the first crystal 10 do not impinge in parallel on the second surface of incidence 22 of the second crystal 20. Unlike an initial parallel pencil of X-rays, resultant emissive X-rays become an unparallel pencil of X-rays, whose cross section is a stepped cross section having a shear of 2b cos.theta./tan.alpha., as shown in FIG. 11. For example, in a test under the conditions in which the angle, .theta., (Bragg angle) between a pencil of incident X-rays and a surface of incidence is 15 degrees, an angle of a V groove is 2.alpha., and the deviation, b, between the first and second crystals is 0.1 mm, the result is that an intensity distribution of a pencil of emissive X-rays, i.e., an intensity distribution of monochromatic light is found to have a stepped cross section as shown in FIG. 12. FIG. 13 is a graph in which a shear of the cross section of an emissive beam is plotted as the Bragg angle, .theta., and the angle, 2.alpha., of the letter V-shaped groove are varied at 0.1 mm in the deviation between the first and second crystals. As seen from FIG. 13, as .theta. and 2.alpha. approach 90 degrees, a shear of the cross section of the emissive beam becomes smaller. In other words, in order to obtain a pencil of emissive X-rays which is substantially equal to a pencil of incident X-rays at high accuracy, the deviation between the first and second crystals can also be compensated by bringing an angle of the letter V-shaped groove closer to 90 degrees. According to a monochromator for radiant X-rays of the present invention, a heat flux per unit area of incident X-rays can be reduced on the surface of a crystal, and cooling characteristics equivalent to those of a commonly used water cooled or liquid gallium cooled monochromator can be obtained. Also, the structure is such that thermal stresses due to incident X-rays cancel each other out, whereby a thermal deformation can be suppressed. Furthermore, two crystal surfaces of incidence are provided which are in the shape of concave letter V and convex letter V combined, and thus a longitudinal size can be halved as compared with conventional inclined crystal monochromators, thereby attaining a compact structure. Also, this structure is less likely to be subjected to mechanical deformation. Even when any deformation takes place, the deformation can be directed so as not to affect optical performance. In addition, cooling means extends from the bottom portion of a crystal and runs behind the surface of incidence, whereby cooling efficiency can be increased. Thus, the monochromator for radiant X-rays of the present invention is compact, suppresses a fluctuation in the position of a pencil of incident X-rays, allows easy adjustment, provides a pencil of emissive X-rays stably and highly accurately, is easy to use and economical, and allows easy maintenance. As has been stated above, having good cooling and excellent distortion characteristics, being compact and easy to use, providing a stable pencil of emissive X-rays at high accuracy, and allowing easy installation, adjustment, and maintenance, the monochromator for radiant X-rays of the present invention fully exhibits capabilities thereof when used in third-generation radiant beam facilities. From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skilled of the art are intended to be covered by the appended claims. |
claims | 1. A transportable nuclear battery comprising:a sealed reactor shell;a reactor core;a nuclear fuel in the reactor core, the nuclear fuel comprising plutonium, carbon, hydrogen, zirconium, and thorium, the hydrogen contained in glass microspheres coated with a burnable poison; anda generator;wherein the hydrogen is stored in the glass microspheres as a moderator to control reactivity of the reactor core. 2. The nuclear battery of claim 1, wherein the burnable poison comprises a thermal neutron absorber selected to increase absorption of neutrons in the thorium, such that depletion of the burnable poison during operation of the reactor core shifts an energy spectrum of the neutrons toward low neutron energy. 3. The nuclear battery of claim 2, wherein neutron hydrogen collisions inside the glass microspheres improve utilization of fissile material generated from the absorption of neutrons in the thorium. 4. The nuclear battery of claim 1, wherein the burnable poison comprises boron, boron carbide or erbium. 5. The nuclear battery of claim 1, further comprising a coating on the glass microspheres, the coating configured to aid in keeping the hydrogen within the glass microspheres at high temperature. 6. A high temperature gas cooled reactor comprising the nuclear battery of claim 5. 7. The nuclear battery of claim 1, wherein the nuclear fuel comprises a mixture of the hydrogen containing glass microspheres and fuel microspheres, the fuel microspheres comprising the uranium and plutonium. 8. The nuclear battery of claim 7, wherein the mixture of hydrogen containing glass microspheres and fuel microspheres is comprised within a fuel rod inserted into a moderator block. 9. The nuclear battery of claim 8, further comprising a plurality of fertile material pellets surrounding the fuel rod in the moderator block, the fertile material pellets comprising the thorium. 10. The nuclear battery of claim 9, wherein the reactor core is assembled with a plurality of such moderator blocks inside the reactor shell, the moderator blocks comprising graphite. |
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claims | 1. A method of measuring aberrations by the use of an electron microscope having a function of displaying an image of a specimen by focusing an electron beam onto the specimen, scanning the beam over the specimen, detecting electrons transmitted through the specimen by an electron detector, and visualizing the output signal from the detector in synchronism with the electron beam scanning, said method comprising the steps of:taking autocorrelation of local regions on a Ronchigram of the specimen that is amorphous;detecting aberrations in the electron beam formed from local angular regions on an aperture plane from the autocorrelation or from Fourier analysis of the autocorrelation; andcalculating the aberrations based on results of the detection. 2. A method of measuring aberrations as set forth in claim 1, wherein a Gaussian function is used as a function representing said autocorrelation. 3. A method of measuring aberrations as set forth in claim 1, wherein when said autocorrelation is analyzed, an isocontrast portion of said autocorrelation is fitted using an elliptical function. 4. A method of measuring aberrations as set forth in any one of claims 1 to 3, wherein parameters indicating variations in the aberrations in the electron beam are normalized using an amount of positional deviation from a focal point when said Ronchigram is derived and a distance to a just focus, in order to find absolute values of the aberrations in the electron beam. 5. A method of measuring aberrations as set forth in any one of claims 1 to 3, wherein two Ronchigrams providing different focal points are obtained and parameters indicating variations in the aberrations in the electron beam are normalized using the differential distance between the focal points, in order to find absolute values of the aberrations in the electron beam. 6. A method of measuring aberrations as set forth in any one of claims 1 to 3, wherein variations in geometrical aberrations caused when energy of the electron beam directed at the specimen are detected as variations in local regions of the Ronchigram, and a chromatic aberration coefficient is measured from a variation in the energy of the electron beam and from an amount of focal shift. 7. A method of correcting aberrations using a method of measuring aberrations as set forth in any one of claims 1 to 3. 8. An electron microscope having a function of displaying an image of a specimen by focusing an electron beam onto the specimen, scanning the beam over the specimen, detecting electrons transmitted through the specimen by an electron detector and visualizing the output signal from the detector in synchronism with the electron beam scanning, and an aberration corrector for use in an illumination system, said electron microscope comprising:first calculation means for taking autocorrelation of minute regions on a Ronchigram of the specimen that is amorphous;detection means for detecting aberrations in the electron beam formed from local angular regions on an aperture plane from the autocorrelation or from Fourier analysis of the autocorrelation;second calculation means for calculating aberrations based on results of the detection; andcontrol means for the aberration corrector in the illuminating system for correcting the aberrations based on results of calculations performed by the second calculation means. |
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abstract | Systems and methods for storing radioactive materials that afford adequate ventilation of the cavity in which the radioactive materials are stored. In one aspect, the invention is a method of storing radioactive materials comprising: a) positioning a system comprising a shell forming a cavity and at least one inlet ventilation duct extending from an inlet to an outlet at a bottom portion of the cavity in a below grade hole so that the inlet of the inlet ventilation duct is above grade and the outlet of the inlet ventilation duct into the cavity is below grade; b) introducing engineered till into the hole to circumferentially surround the shell; c) lowering a canister containing radioactive materials into the cavity; and d) subsequent to the canister being lowered into the cavity, placing a lid on the shell. |
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claims | 1. A method of determining a global core reactivity bias for a nuclear reactor core and bringing the nuclear reactor core to a critical reactor state, the method comprising:predicting a combination of parameters expected to yield the critical reactor state of the nuclear reactor core, wherein the parameters comprise control rod position, soluble boron concentration, and coolant temperature;operating a nuclear reactor at a first subcritical state;measuring, using a source range detector, a first measured neutron flux value while the nuclear reactor is operating at the first subcritical state;adjusting the nuclear reactor to operate at a second subcritical state by repositioning at least one control rod of the nuclear reactor;measuring, using the source range detector, a second measured neutron flux value while the nuclear reactor is operating at the second subcritical state;predicting a first spatially-corrected neutron flux value for the first subcritical state and a second spatially-corrected neutron flux value for the second subcritical state;comparing each of the measured neutron flux values with the corresponding spatially-corrected neutron flux values to determine the global reactivity bias;wherein a spatial correction factor is not applied to the measured neutron flux values;updating the predicted combination of parameters by adjusting at least one of the parameters according to the global reactivity bias; andbringing the nuclear reactor core to the critical reactor state using the updated combination of parameters. 2. The method of claim 1, further comprising performing a regression analysis to determine a relationship between the measured neutron flux values and the corresponding spatially-corrected neutron flux values to determine the global reactivity bias;wherein the determined global reactivity bias is used to detect an anomaly associated with the nuclear reactor core without operating the reactor at a critical state. 3. The method of claim 1, wherein the first subcritical state and the second subcritical state are steady-state conditions. 4. The method of claim 1 wherein the predicted combination of parameters are updated without operating the nuclear reactor at the critical reactor state. 5. The method of claim 1, wherein operating the reactor at the first subcritical state occurs after an initial construction of the nuclear reactor. 6. The method of claim 1, wherein operating the nuclear reactor at the first subcritical state occurs after a refueling of the nuclear reactor. 7. The method of claim 2, wherein the anomaly associated with the nuclear reactor core is an anomalous reactivity behavior. 8. A processing device programmed to carry out the method of claim 1. 9. A machine readable medium comprising instructions for carrying out the method of claim 1. |
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048667447 | summary | BACKGROUND OF THE INVENTION This invention relates to a device for an X-ray CT apparatus, which eliminates a scattering beam in the slice direction of an X-ray. In an X-ray CT apparatus, X-ray beam 12 from X-ray source 10 is formed through collimators 14 into a fan-shaped pattern, as shown in FIG. 1. The fan-shaped X-ray beam 12 has a proper circumferential length in fan-out direction 2 and a somewhat small width in slice direction 1. On the optical path of X-ray beam 12, a patient, not shown, lies on a bed and an X-ray passed through the patient enters into, for example, arcuate X-ray gas detector 16. X-ray gas detector 16 is curved in fan-out direction 2 with X-ray source 10 as a center. A high pressure xenon gas is sealed into X-ray detector 16 and plate-like electrodes, not shown, are arranged at a proper interval along fan-out direction 2 such that they are located in a substantially parallel fashion. Upon the entry of the X-ray into an area between the adjacent electrodes, a xenon gas is ionized to yield Xe ions and electrons. The Xe ions and electrons are detected by the corresponding electrodes as an ion current so that an amount of X-ray entering into the area between the respective electrodes is converted to an electric signal. In the X-ray CT apparatus, X-ray source 10 and X-ray detector 16 are rotated around a rotation axis which passes through the patient and is parallel to slice direction 1. Signals are produced in accordance with the amounts of X-ray during the rotation of X-ray source 10 and X-ray detector 16 and processed through computation to obtain a patient's slice image. In such an X-ray CT apparatus, the X-ray from X-ray source 10 penetrates the patient and enters directly into detector 16. In addition to the X-ray beam, a scattering beam is also produced. Due to the scattering beam an error is introduced into the X-ray detection signal, impeding the formation of an exact image. In fan-out direction 2, since the parallel electrodes of X-ray detector 16 function as a grid, the incidence of the scattering beam is suppressed to such an extent that it can practically be disregarded. In slice direction 1, however, the scattering beam is incident to gas detector 16 without being eliminated. In the prior art, no countermeasure has been taken so as to eliminate such a scattering beam in the slice direction. This is because, in the slice direction, an X-ray incident to X-ray detector 16 is one which has almost totally been transmitted through the patient, and less of the scattering beam is incident thereto. Recently, there is a tendency for the slice width of the X-ray to be decreased in order to improve spatial resolution in an X-ray CT image. However, a problem arises due to an increase in the penumbra area of the X-ray and in the amount of incident scattering beam. FIGS. 2 and 3 are views each showing a relation between the X-ray beam in the slice direction and the area to which the X-ray beam is incident. In the prior art, since, as shown in FIG. 2, diaphragms 14 are located with a broader spacing therebetween and since X-ray beam 12 illuminated from the focus of X-ray source 10 has a broader width as a slice width S (the width taken in the slice direction of X-ray 12 at the position of the patient), penumbra area 24 is narrowed so that less dosage of X-ray is incident to X-ray detector 16. As shown in FIG. 3, however, if the slice width S of X-ray 12 is narrowed by an upper collimator, penumbra area 24 is increased and, for this reason, a greater amount of scattering beam 26 coming from the patient is incident to X-ray detector 16, thus degrading the resultant image. In this way, if the slice width of the X-ray is narrowed so as to enhance the spatial resolution, an image degradation problem arises due to the scattering beam, thus prominently reducing the spatial resolution enhancement effect. SUMMARY OF THE INVENTION It is accordingly the object of this invention to provide a scattering beam eliminating device for an X-ray CT apparatus, which effectively eliminates the scattering component of an X-ray beam in the slice direction to improve both the spatial resolution and image accuracy. According to this invention there is provided a scattering beam eliminating device for an X-ray CT apparatus including an X-ray irradiation device for irradiating a fan-shaped X-ray beam to a patient, the fan-shaped X-ray beam having an X-ray illumination area defined in a fan-out direction and slice direction, and an X-ray detector having an X-ray entrance surface and X-ray detection elements arranged in the fan-out direction to detect the X-ray incident thereto through the X-ray entrance surface, the detector detecting the X-ray which has penetrated the patient. The scattering beam eliminating device has a scattering beam eliminating member comprising an array of plate-like grids made of an X-ray-absorbing material and arranged substantially parallel to each other, a plurality of X-ray transmission areas each located between the grids and made of an X-ray transmitting material, and an X-ray exit surface positioned on the X-ray entrance surface and fixed to the X-ray entrance surface. According to this invention, since the scattering portion of an X-ray which is produced in the slice direction is absorbed by the grid of the scattering beam eliminating member, the incidence of the scattering beam to the X-ray detector in the slice direction is suppressed. The scattering of the X-ray in the fan-out direction is suppressed under the action of the grid of the X-ray detector per se. Since the X-ray detector is not affected by the scattering beam in both the fan-out direction and the slice direction, the amount of X-ray transmitted is detected with high accuracy. It is, therefore, possible to obtain an image of high accuracy and an improved spatial resolution. |
description | This application is a continuation-in-part of International Patent Application No. PCT/CA2013/050090 filed Feb. 6, 2013, which claims the benefit of U.S. Provisional Application No. 61/633,071, filed Feb. 6, 2012. The present continuation-in-part claims the benefit of U.S. Provisional Application 61/862,378, filed on Aug. 5, 2013. The contents of International Patent Application No. CA2013/050090, of U.S. Provisional Application No. 61/633,071, and of U.S. Provisional 61/862,378 are incorporated herein by reference. The present disclosure relates generally to nuclear reactors. More particularly, the present disclosure relates to molten salt nuclear reactors. Molten salt reactors (MSRs) were primarily developed from the 1950s to 1970s but, as of late, there has been increasing world interest in this type of reactor. Older concepts are being re-evaluated and new ideas put forth. This class of nuclear reactor has a great deal of advantages over current nuclear reactors, the advantages including potentially lower capital costs, overall safety, long lived waste profile and resource sustainability. With MSRs advantages also come some significant technological challenges which lead to difficult basic design decisions. The first and likely foremost is whether and how a neutron moderator may be employed. Graphite has, in almost all cases, been chosen as a moderator as it behaves very well in contact with the fluoride salts used in MSRs. These salts are eutectic mixtures of fissile and fertile fluorides (UF4, ThF4, PuF3 etc) with other carrier salts such as LiF, BeF2 or NaF. Using graphite as a bulk moderator within the core of the MSR has many advantages. For example, it gives a softer or more thermalized neutron spectrum which provides improved reactor control and a greatly lowered starting fissile inventory. As well, using graphite throughout the core of a MSR allows the ability to employ what is known as an under-moderated outer zone which acts as a net absorber of neutrons and helps shield the outer reactor vessel wall from damaging neutron exposure. The vessel, which contains the nuclear core, has typically been proposed as being made of a high nickel alloy such as Hastelloy® N; however, other materials are possible. The use of graphite within the core of the MSR (i.e., within the neutron flux of a MSR) can have a serious drawback however. That is, that graphite will first shrink and then expand beyond its original volume as it is exposed to a fast neutron flux. Overall expansion of graphite (graphite core) occurs when the volume of the graphite (graphite core) is larger than its original volume, i.e., the volume preceding any neutron irradiation. An upper limit of total fast neutron fluence can be calculated and operation of the MSR is such that this limit is not exceeded. This limit determines when the graphite would begin to expand beyond its original volume and potentially damage surrounding graphite elements or the reactor vessel itself. How long graphite can be used within the reactor core is thus directly related to the local power density and thus to the fast neutron flux it experiences. A low power density core may be able to use the same graphite for several decades. This is the case for many previous reactors employing graphite such as the British gas cooled Magnox and AGR reactors. They were extremely large and had a low power density for thermohydraulic reasons but, this permitted an extremely long graphite lifetime. However, MSRs would benefit from having a far higher power density and thus graphite lifetime can become an issue. The scientists and engineers designing MSRs have long been faced with important design options. A first option is to simply design the reactor to be quite large and very low power density in order to get a full 30 year or more lifetime out of the graphite. Thus one can seal all the graphite within the vessel and the graphite can remain in the vessel for the design life of the nuclear plant. Examples of this choice can be found in the studies of Oak Ridge National Laboratories (ORNL) in the late 1970s and early 1980s. For example, ORNL™ 7207 proposes a 1000 MWe reactor which was termed the “30 Year Once Through” design which would have a large reactor vessel of approximately 10 meters in diameter and height in order to avoid the need for graphite replacement. Much of the later work by Dr. Kazuo Furukawa of Japan, on what are known as the FUJI series of reactor designs, also chose this route of large, low power nuclear cores. These very large cores have obvious economic disadvantages in terms of the sheer amount of material required to fabricate the core and reactor vessel, and in the excessive weight of the core. These challenges increase the cost and complexity of the surrounding reactor building as would be understood by those trained in the field. It should be added that a 30 year nuclear plant lifetime was quite acceptable in the 1970s but by today's standards would be thought short. 50 or 60 years is now desired and would mean a still larger core to allow this lifetime without graphite replacement. A second option often proposed is to employ a much smaller, higher power density core but to plan for periodic replacement of the graphite. This approach was commonly assumed in the work at Oak Ridge National Laboratories (ORNL) in the design of the Molten Salt Breeder Reactor from about 1968 to 1976 before the program was cancelled. This 1000 MWe reactor design had an outer vessel of Hastelloy® N that would contain hundreds of graphite elements fitting together and filling the vessel but with passage channels for the molten salt fuel to flow and exit the core to external heat exchangers. In this second option, the reactor has much smaller dimensions which are of approximately 6 meters in diameter and height. In this case the graphite, particularly in the center of the core with the highest fast neutron flux, only had an expected lifetime of 4 years. Thus the reactor had to be designed to be shut down and opened up every 4 years to replace a large fraction of the graphite elements. This may not sound overly difficult to those not trained in the field but with molten salts, the fission products, some of which are relatively volatile, are in the fuel salt and can also embed themselves onto a surface layer of graphite and, for example, the inner metal surfaces of the reactor vessel. Thus just opening the reactor vessel was known to be an operation that could be difficult to perform without allowing radioactive elements to spread into the surrounding containment zone. As well, the design of the reactor vessel itself is more complex when it needs to be periodically opened. These challenges are why the route of larger, lower power density cores were often chosen. A third option is to try to omit the use of graphite altogether. This is possible and results in reactors typically with a much harder neutron spectrum. An example of this choice is the Molten Salt Fast Reactor (MSFR) proposed by a consortium of French and other European researchers starting around year 2005. It has very serious drawbacks however. For example it requires upwards of five times the starting fissile load and any accidental exposure of the salt to a moderator, such as water or even hydrogen content in concrete, could lead to criticality dangers. Beyond the issue of graphite lifetime, there are also the somewhat related issues of the lifetime of the reactor vessel itself and of the primary heat exchangers. The reactor vessel wall may also have a limited lifetime due to neutron fluence with both thermal and fast neutrons potentially causing problems. The most commonly proposed material being a high nickel alloy, such as Hastelloy® N, with reasonably well understood behaviour and allowed limits of neutron fluence. As such, a great deal of effort goes into core design to limit the exposure of neutrons and/or lower the operating temperature of the vessel wall. As well, adding thickness to the wall may help as strength is lost with increased neutron exposure. This adds both weight and expense. It is thus a challenge to have a 30 to 60 year lifetime of the reactor vessel itself. Another design challenge is the primary heat exchangers which transfer heat from the radioactive primary fuel salt to a secondary coolant salt. This coolant salt then typically transfers heat to a working media such as steam, helium, CO2 etc. In some cases these heat exchangers are outside or external the reactor vessel itself, which appears to be the case for all 1950s to 1980s ORNL designs. They also may be located within the reactor vessel itself which has its own set of advantages and challenges. One great advantage of internal heat exchangers is no radiation of significance need leave the reactor itself as only secondary coolant salt enters and leaves the vessel. For both internal and external heat exchangers, the great challenge is in either servicing or replacing them. When a MSR is opened up, it can potentially lead to radioactivity being released into a containment zone or space. ORNL for example proposed common tube in shell heat exchangers external to the core, four heat exchanger units per 1000 MWe reactor. In the case of any tube leaks the operation was not to fix or plug tubes but to open the shell and remove the entire tube bundle and replace with a new bundle. Only after a cooling period would a decision be made on repair and reuse of the bundle or simple disposal. Thus it is clear that primary heat exchanger service and/or replacement techniques are a great challenge in MSR design. Further, when either graphite or heat exchangers are replaced, then the issue of their safe storage must be also addressed as they will become significantly radioactive during operation. This represents yet another challenge in MSR overall plant design. It should be further highlighted that the related nuclear design field of Fluoride salt cooled, High temperature Reactors (known as FHRs) has very similar issues. In this work the reactor design can be very similar but instead of the fuel being in the fluoride salt, it is in solid form within the graphite moderator using the fuel form known as TRISO. In this case the limited graphite lifetime is also a function of the lifetime of the solid TRISO fuels; however, all other design issues and challenges are very similar to MSR design work. In FHRs, the primary coolant salt is not nearly as radioactive but does typically contain some radioactive elements such as tritium and a similar set of challenges are present when planning to use solid block TRISO fuels and periodically replace them. A subset of FHR design involves using a pebble fuel form which does ease fuel replacement without opening up the reactor vessel; however, this type of design has its own set of issues The decay heat that follows the shutdown of a nuclear reactor following the loss of external cooling has been a long-standing industry challenge. The incident at Fukushima Japan indicates the seriousness of the issue. If the decay heat is not removed quickly from the reactor, the temperature in the reactor rises to unacceptable levels. Thus the speed with which the initial decay heat can be removed from the reactor is critical. Therefore, improvements in nuclear reactors are desirable. The present disclosure relates to the integration of the primary functional elements of graphite moderator and reactor vessel and/or primary heat exchangers and/or control rods into a single replaceable unit having a higher and more economic power density while retaining the advantages of a sealed unit. Once the design life of such an Integral Molten Salt Reactor (IMSR) is reached, for example, in the range of 3 to 10 years it is disconnected, removed and replaced as a unit and this unit itself may also potentially function as the medium or long term storage of the radioactive graphite and/or heat exchangers and/or control rods and/or fuel salt itself. The functions of decay heat removal and volatile off gas storage may also be integrated in situ. The present disclosure also relates to nuclear reactor that has a reactor vessel surrounded by a buffer material. The buffer material can absorb decay heat when external cooling is lost. The absorption of decay heat is effected by the buffer material phase transition latent heat, the phase transition being that of solid phase to liquid phase. The absorption is also effected by convective heat transfer when the buffer material is in the liquid state. The convective heat transfer occurs between the reactor vessel and a heat sink in thermal contact with the buffer material. In a first aspect of the disclosure, there is provided a method of operating a nuclear power plant, the nuclear power plant comprising a nuclear reactor to produce heat, a heat exchanger system, and an end use system, the heat exchanger system to receive heat produced by the nuclear reactor and to provide the received heat to the end use system. The method comprising steps of: operating the nuclear reactor, the nuclear reactor comprising a vessel and a graphite moderator core positioned in the vessel, the heat exchanger system having an inside portion located inside the vessel and an outside portion located outside the vessel; shutting down the nuclear reactor upon occurrence of a shutdown event, to obtain a shutdown nuclear reactor; severing all operational connections between the inside portion of the heat exchanger system and the outside portion of the heat exchanger system to obtain a severed, shutdown nuclear reactor; obtaining a replacement nuclear reactor having an inner heat exchanger system portion; and operationally connecting a replacement nuclear reactor to the outside portion of heat exchanger system by connecting the inner heat exchanger system portion of the replacement nuclear reactor to the outside portion of the heat exchanger system. In a second aspect of the disclosure, there is provided a nuclear reactor unit that comprises: a containment vessel; a nuclear reactor located in the containment vessel, the nuclear reactor having a reactor vessel that has a reactor vessel wall; and a buffer salt contained in the containment vessel. The buffer salt is in thermal contact with the reactor vessel wall. The nuclear reactor, when running, is to generate a heat output that produces a first reactor vessel wall temperature. The buffer salt is in a solid state when at a temperature equal to or below the first reactor vessel wall temperature. The nuclear reactor, when shutdown, is to generate decay heat that produces a second reactor vessel wall temperature greater than the first reactor vessel wall temperature. The buffer salt is to absorb a portion of the decay heat, an absorption of the portion of the decay heat to raise the temperature of the buffer salt, the buffer salt is to melt and become a liquid buffer salt when at the second reactor wall temperature. The containment vessel to maintain the liquid salt in thermal contact with the reactor vessel wall. In a third aspect, the present disclosure provides a nuclear power plant that comprises: a molten salt reactor (MSR) to produce heat, the MSR reactor comprising a vessel and a graphite moderator core positioned in the vessel; a heat exchanger system having a coolant salt circulating therein; a strain sensor arranged to measure strain in the graphite moderator core; and an end use system, the heat exchanger system to receive heat produced by the nuclear reactor and to provide the received heat to the end use system, the strain sensor to provide a signal indicative of excessive strain when the strain in the graphite moderator core exceeds a strain threshold value. In a fourth aspect, the present disclosure provides a nuclear power plant that comprises: a molten salt reactor (MSR) to produce heat; a heat exchanger system; radioactivity detectors positioned outside the vessel; shutoff mechanisms positioned outside the vessel; and an end-use system, the MSR comprising a vessel, a graphite moderator core positioned in the vessel, and a molten salt circulating at least in the vessel, the molten salt to transfer the heat produced by the MSR to the heat exchanger system, the graphite moderator core defining one or more than one through hole, the heat exchanger system to receive the heat produced by the MSR and to provide the received heat to the end use system, the heat exchanger system comprising a plurality of heat exchangers in fluid communication with the one or more than one through hole of the graphite moderator core, each heat exchanger having associated thereto a respective radioactivity detector, each radioactivity detector arranged to detect radioactivity present in the coolant salt circulating in the respective heat exchanger, each shutoff mechanism arranged to shut off circulation of the coolant salt circulating in the respective heat exchanger when radioactivity beyond a threshold amount is detected, by the respective radioactivity detector, in the respective heat exchanger. Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures. The present disclosure provides an integral Molten Salt Reactor (IMSR). The IMSR of the present disclosure has a graphite core that is permanently integrated with the vessel of the IMSR, which means that the graphite core is in the vessel of IMSR for the lifetime of the IMSR. As such, in the IMSR of the present disclosure, the graphite core is not a replaceable graphite core and remains within the IMSR for the operational lifetime of the IMSR. The graphite core is fixedly secured within the vessel of the IMSR. Advantageously, this eliminates the need for any apparatus that would be required for replacing the graphite core at pre-determined moments as per a pre-determined schedule. A further advantage is that the IMSR does not require any access port to allow access to the graphite core for replacement of the graphite core. An additional advantage of the IMSR of the present disclosure is that, after expiration of the design lifetime of the IMSR, the IMSR serves as a storage container for any radioactive matter within the IMSR. The components of the IMSR include the reactor vessel itself and any graphite elements of the nuclear core. Other components can include the primary heat exchangers which can be installed, in the reactor vessel, during fabrication of the IMSR. The IMSR is built to operate (produce electricity) for a design lifetime, which takes into account the reactor's graphite core expansion over time and the structural integrity of the graphite core. That is, as mentioned above in the background section, the graphite core will eventually expand beyond its original volume under neutron flux. Operation of MSRs in the presence of such expansion is not desirable as the graphite core can suffer breaks. The IMSR of the present disclosure is simply shut down and replaced after expiration of its design lifetime. Further components of the IMSR can include piping such as coolant salt inlet conduits and outlet conduits, and the pump shaft and impeller for moving (pumping) the coolant salt (primary coolant fluid) when a pump is employed. In some embodiments of the present disclosure, an IMSR that has been shut down can simply remain in its containment zone (hot cell) that can act as a heat sink for the decay heat generated by the shut down IMSR. The decay heat simply radiates out the IMSR through the IMSR's vessel wall and into the containment zone and ultimately to the outside environment. MSRs typically operate at temperatures in the region of 700 degrees C., radiant heat is very effective in removing decay heat. Further, to accelerate decay heat removal, the IMSR of the present disclosure, a buffer salt can be added in the containment zone to surround the IMSR; this allows faster heat extraction from the IMSR to the containment zone. In certain embodiments the IMSR can have a frozen plug of salt that can be melted to allow the primary coolant drain to decay heat removal tanks. In some other embodiment, during operation of the IMSR and after shut down of the IMSR, the IMSR can be a sealed unit that simply retains produced fission gases within the IMSR sealed vessel or, the fission gases can be release slowly to any suitable fission gases treatment system. In the present disclosure, elements can be said to be operationally connected to each other when, for example, information in one element can be communicated to another element through a connection between the elements. The connection can be an electrical connection. Further, elements can be said to be operationally connected when state of one element can be controlled by, or related to a state of another element. Further, in the present disclosure, elements can be said to be in fluid communication when fluid present at one element can flow to the other element. FIG. 1A shows the frontal view of an embodiment of an IMSR 90 of the present disclosure. 100 is the reactor vessel itself, made of Hastelloy® N, a high nickel alloy, or any other suitable material such the molybdenum alloy TZM (titanium-zirconium-molybdenum alloy). The reactor vessel 100 can be referred to as a sealed reactor vessel in the sense that any graphite core within the reactor vessel 100 is sealed therein; that is, it meant to remain within the reactor vessel 100, and not be replaced during the operational lifetime of the IMSR. As the IMSR 100 of the present disclosure can have a short design life (e.g., 5 years), the walls of the reactor vessel 100 can be thinner than required for MSRs that have a 30+ year design life and can be allowed to operate in a much higher neutron fluence, or at a higher operating temperature than such long lifetime MSRs. 102 shows the core or core region which can be a simple mass of graphite defining channels 115 for a molten salt fuel 108 to flow through. The channels can also be referred to as through holes. The core 102 can also be referred to as core region, a graphite moderator core, and a graphite neutron moderator core. As the core 102 of the embodiment of FIG. 1A does not need to be replaced, the construction of the core 102 can be simplified in that it does require any structural features that would allow and/or facilitate its removal from the vessel 100 or its replacement. 104 shows a reflector (neutron reflector) to reflect neutrons toward the core 102 and to shield the primary heat exchanger unit 106 from excessive neutron flux. The reflector 104 can be optional. In the absence of the reflector 104 any metallic structure, for example, conduits and heat exchangers located in the IMSR above the core 102 would likely suffer neutron damage. The reflector 104 can be made of stainless steel as it serves no structural purpose so irradiation damage of the reflector 104 is of little concern. The reflector 104 has channels 99 or piping defined therein to allow the molten salt fuel 108 to flow from the primary heat exchanger unit 106 through the channels 115 defined by the core 102. The channels 115 can be varied in either diameter or lattice pitch in different areas of the core 102 to create, for example, an undermoderated region as well as an outer reflector zone in the graphite, as would be understood by those trained in the field. In the IMSR example of FIG. 1A, the flow of the molten salt fuel 108 in the vessel 100 is shown by the arrows 109. The primary heat exchanger unit 106 has an opening 117 that receives the fuel salt 109 provided by the drive shaft and impeller unit 116, which is driven by a pump 118. The primary heat exchanger unit 106 contains a series of heat exchangers. Such a heat exchanger is shown at reference numeral 119. Each heat exchanger 119 is connected to an inlet conduit 114 and an outlet conduit 112 that propagate a coolant salt 113 (which can also be referred to as a secondary coolant salt) from the outside of the vessel 100, through the heat exchanger 119, to the outside of the vessel 100. The coolant salt 113 flows through the inlet conduit 114, heat exchanger 119, and outlet conduit 112 in the direction depicted by arrows 111. The coolant salt 113 receives heat from heat exchanger 119, which receives the heat from the fuel salt 108 that flows on, or circulates around, the heat exchanger 119. The secondary coolant salt 113 is pumped by a pump or pumping system (not shown). For clarity purposes, the heat exchanger 119 is shown as a straight conduit connecting the inlet conduit 114 to the outlet conduit; however, as would be understood by the skilled worker, the heat exchanger 119 can be of any suitable shape and can include any number of conduits connecting the inlet conduit 114 to the outlet conduit 112. As an example, a heat exchanger can have a manifold structure where coolant salt circulating in a main conduit is divided into a plurality of conduits stemming from the main conduit. Further, each heat exchanger can be individually shut down upon occurrence of a heat exchanger fault and the nuclear reactor can continue to operate with a reduced number of functioning heat exchangers. The heat exchanger unit 106, the heat exchangers 119 it comprises, and the inlet conduits 114 and outlet conduits 112 connected to the heat exchangers 119 are all part of a heat exchanger system that is used to transfer heat from the IMSR to a system (an end use system) or apparatus such as, for example, a steam generator. Such a heat exchanger system is shown elsewhere in the disclosure, in relation to a nuclear power plant. The inlet conduits 114 and the outlet conduits 112 are operationally connected to a pump system—not shown—which is also part of the heat exchanger system. That is, the pump system circulates the coolant salt through the inlet conduits 114, the outlet conduits 112, and the heat exchangers 119. The inlet conduits 114 and the outlet conduits 112 can be operationally connected to additional heat exchangers that provide the heat of the coolant salt circulating the heat exchangers 119, the inlet conduits 114 and the outlet conduits 112 to another medium, such as, for example, another fluid such as water. In the example of FIG. 1A, the heat exchanger system is partly comprised in the vessel 100 as the heat exchangers 119 and a portion of inlet conduit 114 and the inlet conduit 112 are inside the vessel 100. Further, the heat exchanger system is partly outside the vessel 100 in that another portion of the inlet conduit 114 and the outlet conduit 112 are outside the vessel 100, as are the aforementioned pump system and any additional heat exchanger. That is to say, that the heat exchanger system has an inside portion located inside the vessel 100, and an outside portion located outside the vessel 100. Also in the example of FIG. 1A, the molten fuel salt circulates only in the vessel 100. That is, under normal operating conditions, that is, conditions in which no break in equipment occurs, the molten fuel salt 108 does not leave the vessel 100. The IMSR 90 is positioned in a hot cell whose function is to prevent radiation or radioactive elements, present or generated in the IMSR 90, from traversing the hot cell walls. Such a hot cell cell wall is partly shown at reference numeral 130. The outlet conduit 112, and the inlet conduit 114, can pass through openings in the hot cell wall 130 and can reach a secondary heat exchanger (not depicted) giving heat to either a third loop of working fluid or to the final working media such as steam or gas. The level of molten fuel salt 108 within the reactor vessel is depicted by reference numeral 122. Fission gasses will collect above this liquid level 112 and may be retained in the vessel 100 or be allowed to transit, through an off gas line 120, to an off gas sequestration area (not depicted). These off gasses can be moved to the sequestration area by a helium entrainment system (not depicted). An example of the dimensions of the IMSR of FIG. 1A may be 3.5 meters in diameter, 7-9 meters in height, and may provide a total power of 400 MWthermal (up to about 200 MWelectrical). This power density would give a graphite lifetime and thus design lifetime of the IMSR of somewhere between 5 and 10 years. These dimensions of the IMSR 90 make transport and replacement of the IMSR 90 manageable and the power density allows many years of usage of any graphite employed. The geometry of the core 102 and vessel 100 can be cylindrical. The core 102 can be fitted with, or connected to, one or more stress monitors 902 that monitor the stress (shear stress, normal stress, or both) that may develop in the core 102 over time, as the core is subjected to neutrons. The stress monitors are operationally connected to a control system 901 and, upon the stress measured by the stress monitors 902 exceeding a predetermined threshold value, the monitoring system can shut down the IMSR 90. The one or more stress monitors (stress sensors, strain sensors, stress detectors, stress gauges, strain gauges) can include, for example, a ring surrounding the core with a strain gauge connected (mounted) to the ring. Any overall expansion of the graphite will create stress in the ring. The stress in the ring is be detected by the strain gauge mounted on the ring. The one or more stress monitors can also include a stress monitor mounted on any other part that is secured to the core. For example, in instances where the core is mounted to a mounting plate, a stress monitor can be secured to the mounting plate. Stress in the core will transfer to the mounting plate and will be sensed by the stress sensor. The stress monitors can be, for example, electrical in nature in that the resistance of the stress monitor will change as a function of stress. The stress monitors may also be mechanical or optical (e.g., optical fiber stress gauge). In some embodiments, it is possible to determine the neutron fluence on the core 102. That is, it is possible to determine the number of neutrons per cm2 received by the core 102. It may also be possible to monitor the fluence only for fast neutrons, e.g., for neutrons having an energy above a particular energy level (e.g., 50 KeV). One possible method of determining the neutron fluence would be by inferring the neutron fluence by determining (measuring) local power density which is directly related to both fission power and fast neutron fluence. For example by placing simple thermocouples separated by a short distance within a single salt channel in the core, the temperature difference and flow rate could be used to infer local power density. The IMSR can be shut down automatically or manually when the total neutron fluence meets a threshold criteria. For example, the IMSR can be shut down when the neutron fluence approaches a pre-determined value beyond which the core graphite 102 would likely deform or crack. The IMSR 90 can be shutdown in any suitable manner. For example, and with reference to FIG. 1B, upon occurrence of a shutdown event such as excessive strain in the core 102 or excessive neutron fluence on the core 102, the molten fuel salt 108 can be dumped in a dump tank 903 located below the vessel 90. Such dump tanks can have any suitable geometry, provided the geometry in question does not give rise to criticality. The dump tank 903 can be connected to the vessel through any suitable valve mechanism 904. One such valve mechanism is freeze plug, which comprises a portion of a conduit connecting the vessel 30 to the dump tank. The portion of the conduit is filled with a material that is maintained in the solid state by powered cooling (not shown). The material can be a portion of the fuel salt itself. When the cooling stops, for whatever reason such as controlled shutdown or a loss of external cooling of the reactor, the material melts, opening the valve mechanism 902, and the molten fuel salt 108 falls into the dump tank 903. Another example of a valve mechanism 904 is that of a mechanical valve held in the open position by springs, and held in the closed position by powered solenoids (not shown). As with power of the powered cooling being remove or lost when power is cut or lost in the solenoids, the solenoids will de-energize and the valve will revert to its open position, under the force of the springs, and the molten fuel salt will fall into the dump tank. In the freeze plug example and the mechanical valve example, the control system 901 would cut-off power to, respectively, the cooling unit and the solenoids upon occurrence of a shutdown event such as stress in the core 102, or excessive neutron fluence at the core 102, or when external cooling is lost (failure/shutdown of the heat exchanger system). As another example, upon detection of a shutdown event, the control system 901 can cause a control rod 902 to be lowered in the vessel 90. The control rod 905 can be maintained out of the vessel 90 by a powered device 906 (e.g., a powered solenoid arrangement) as long as there is power provided to the powered device. Upon occurrence of a shutdown event or loss of external cooling of the reactor, the control system 901 shuts off the power to the powered device and the control rod lowers in the vessel 90. FIG. 2 shows a top down view of the top of an example of an IMSR of the present disclosure. FIG. 2 shows the pump motor 118, and the off gas line 120. As well, FIG. 2 shows a series of four inlet conduits 114 and four outlet conduits 114 passing from the reactor vessel 100 through the primary hot cell wall 130. Four separate pairs of lines (one pair of lines has one inlet conduit 114 and one outlet conduit 112) are depicted; however, any suitable number of such pairs of lines (and associated heat exchanger 119) is also within the scope of the present disclosure. Each pair of lines is connected to a heat exchanger comprised in the heat exchanger unit 106. An advantage of keeping primary heat exchangers within the IMSR and simply replacing the IMSR after its design lifetime, is that techniques for heat exchanger repair, removal, and/or replacement need not be developed. However plans must be made for potential failure and leakage between the primary fuel salt and secondary coolant. By compartmentalising the primary heat exchanger unit 106 into multiple independent heat exchangers 119, any failure of the heat exchangers 119 and/or leakage of molten fuel salt 108 into the coolant 113 can be effectively managed. FIG. 3 shows an embodiment of a disconnect arrangement to cut off the flow of the secondary coolant 113 though the inlet conduits 114 and outlet conduits 112 in the direction given by arrows 111. For clarity purposes, only one pair of lines (one inlet conduit 114 and one outlet conduit 112) is shown in FIG. 3. In the example of FIG. 3, a radioactivity detector 300, for example, a Geiger counter is placed next to an outlet line 112 and can detect any leak of radioactive primary fuel salt into the outlet line 112. When radioactivity beyond a pre-determined level is detected by the radioactivity detector 300, a controller 301, connected to the radiation detector 301, controls shutoff mechanisms 304 that are connected to the outlet conduit 112 and the inlet conduit 114, to shut the outlet conduit 112 and its corresponding inlet conduit 114. The shutoff mechanisms are to isolate the individual heat exchanger 119 (not shown in FIG. 2) connected to the now shut inlet conduit 114 and outlet conduit 112. The shutoff mechanisms 304 can also be to sever the physical connection along the inlet conduit 114 and the outlet conduit 112. The shutoff mechanisms can include any suitable type of shutoff valves and any suitable type of crimping devices, the latter to crimp shut the inlet conduit 114 and the inlet conduit 112. The shutoff mechanisms 304 can also include a refrigerating unit that can cool and freeze the coolant salt circulating in a compromised inlet conduit or a compromised outlet conduit. Such freezing would occur in a segment of the compromised conduit (inlet or outlet) and stop the flow of coolant salt. In some embodiments, where the inlet and/or outlet conduits are substantial in diameter and hence difficult to freeze, the conduits can be mechanically stretched to reduce their diameter and the sections of the conduits having the reduced diameter can be frozen. Further, if a leak of secondary coolant fluid 113 into the molten fuel salt 108 occurs, it can be detected by measuring a drop in pressure, using one or more pressure detectors 303 mounted in or otherwise operationally connected to the inlet conduit 114, the outlet conduit 112 or both. The one or more pressure detectors are operationally connected to the controller 301, which can shut off the shutoff mechanisms 304 upon determining that a drop in pressure (or any abnormal change in pressure) has occurred in the coolant salt 113 circulating in the inlet conduit 114, outlet conduit 112, or both. Furthermore, when a leak of secondary coolant fluid 113 into the molten fuel salt 108 occurs, it can be detected by monitoring (e.g., periodically monitoring) the level of molten salt in the reactor vessel. If the level of molten salt rises, then it can be attributed to a leak of secondary coolant salt. In some embodiments, each pair or group of pairs of inlet conduit and outlet conduit can be connected to a distinct coolant pump. When a fault is detected in one of the pairs, the pump to which the pair is associated can be shut down and the conduit in question can be crimped, frozen or otherwise disabled by a shutoff mechanism. Provided that all the coolant pumps are not shutdown, the nuclear reactor can still function. By choosing compatible primary carrier salts for the molten fuel salt 108 and the secondary coolant salt 113, mixing of these fluids can be tolerated. For example, if the primary carrier salt is LiF—BeF2 and/or NaF—BeF2, then a secondary coolant salt of LiF—BeF2 and/or NaF—BeF2 would be compatible with the primary carrier salt in cases of limited mixing, i.e. in cases where the volume of coolant salt 113 leaked in into the molten fuel salt 108 is tolerable in terms of its effects on neutron production and absorption. By having many, perhaps 4 but even up to 10 or more pairs of inlet conduits/outlet conduits (and corresponding heat exchangers 119), the loss of one or more individual heat exchangers may do little to the overall ability to transfer heat from the primary heat exchanger unit 106 to the coolant salt 113 as the other remaining pairs of inlet conduits/outlet conduits can simply take the added heat exchange load or the IMSR can lower its power rating slightly. Heat exchangers are unlike many other systems in that there is very little economy of scale such that 10 smaller pairs of inlet/outlets or tube bundles will not have a combined cost much more than one large unit. FIG. 4 shows another embodiment of an IMSR 92 in accordance with the present disclosure. As in the IMSR 90 of FIG. 1A, the IMSR 92 of FIG. 4 comprises a vessel 100, a reflector 104 and a core 102. Additionally, the IMSR 92 comprises a control rod 400 (which can be optional) and a series of heat exchanger units 106. Each heat exchanger unit has a drive shaft and impeller unit 116 to pump molten fuel salt 108 through the heat exchanger units 106. For clarity purposes, pump motors that drive the shaft and impeller units 116 are not shown. Also for clarity purposes, inlet conduits and outlets conduits propagating a coolant salt through the heat exchanger units 106 are not shown. The molten salt fuel 108 that is pumped through the heat exchanger units 106 is directed downwards, towards the periphery of the core 102 by a baffle structure 402. The molten fuel salt flows towards the bottom of the vessel 100 and then upwards through the channels 115 of the core 102. Although two channels 115 are shown in FIG. 4, any suitable number of channels 115 is within the scope of the present disclosure. FIG. 5 shows a top, cross-sectional view of the MSR 92 shown at FIG. 4. The top view of FIG. 5 shows 8 heat exchanger units 106, each having an inlet conduit 114, an outlet conduit 112, and a pump shaft and impeller unit 116. Also shown is the control rod 400. FIG. 6 shows a side perspective view of the IMSR of FIG. 4. The IMSR 92 comprises six heat exchanger units 106, each having an inlet conduit 114, outlet conduit 112, and shaft and impeller unit 116. The heat exchanger units 106 are positioned above the core 102 and about a longitudinal axis of the vessel, the longitudinal axis being parallel to the control rod 400. The direction of flow of the molten fuel salt 108 is indicated by arrow 109. After exiting the individual heat exchangers 106, the molten fuel 108 flows obliquely down, guided by the baffle structure 402 and, optionally, by partitions 404 that separate the outputs of the individual heat exchanger units. The flow of the molten fuel salt 108 through the core 102 may be in different directions in different embodiments, for example upwards as shown in the embodiment of FIG. 4 or downwards as shown in the embodiment of FIG. 1A. There are advantages and disadvantages to both upwards and downwards flow directions. An upward flow through the core as shown in FIG. 4 has the advantage of being in the same direction as natural circulation but can make the use of pumps (the pumps pumping the coolant salt through the heat exchanger units) slightly more difficult to direct the flow through the primary heat exchangers. In some embodiments of the present disclosure, the pumps and the shaft and impeller units can be omitted and the MSR can instead use natural circulation to circulate the molten fuel salt 108. As such, the pumps and the shaft and impeller units can be optional in embodiments where natural circulation suffices to circulate the molten salt fuel 108. FIG. 7 shows an embodiment where natural circulation of the molten fuel salt 108 is used. The MSR 94 of FIG. 7 is similar to the MSR 92 of FIG. 6 with the exception that no pumps or shaft an impeller units are required. Rather, the molten fuel salt 108 present in the channels 115 heats up through nuclear fission reaction and flows upwards towards the top region of the vessel 100. Once outside the channels 115, the molten salt cools down and begins to flow downwards, through the heat exchangers 105, and towards the bottom of the vessel 100 where the cooled molten fuel salt re-enters the channels to be heated up. FIG. 8 shows another embodiment of an IMSR in accordance with the present disclosure. The IMSR 96 of FIG. 8 has a vessel 100 in which is positioned a graphite moderator core 102, which can have one or more channels 115 defined therein. The vessel 100 is connected to a heat exchanger unit 106 that is located outside the vessel 100. The heat exchanger unit 106 contains a plurality of heat exchangers (not shown); each heat exchanger includes an inlet conduit 114 and an outlet conduit 112 that circulate coolant salt though the heat exchanger. Each inlet conduit 114 and outlet conduit 112 is operationally connected to a coolant salt pump system (not shown). The inlet conduit 114 and the outlet conduit 112 are shown traversing a hot cell wall 130. The vessel 100 is connected to the heat exchanger unit 106 through conduits 700 and 702. A pump 704 circulates a molten fuel salt 706 through the vessel 100, the channels 115, and the heat exchanger 106. The same configuration of radioactivity detector, pressure detectors 303, shut-off mechanisms, and controller shown at FIG. 3, can also be applied to the embodiment of FIG. 8. The core 102 can be fitted with one or more stress monitors 902 that monitor the stress (shear stress, normal stress, or both) that may develop in the core 102 over time, as the core is subjected to neutrons. The stress monitors are operationally connected a monitoring system (not shown and, upon the stress measured by the stress monitors 902 exceeding a predetermined threshold value, the monitoring system can shut down the IMSR 96. Upon the graphite moderator core 102 reaching its operational lifetime, the conduits 700 and 702 can be severed to physically disconnect the vessel 100 from the remainder of the IMSR. After sealing the cut-off portion of the conduits 700 and 702 attached to the vessel 100, the vessel 100 can be disposed in a containment facility and a new vessel with a new graphite moderator core can be attached to the conduits 700 and 702. The IMSR embodiments shown at FIGS. 1-8 were described has having a molten fuel salt (108 or 706) circulating therein. However, modifications to the embodiments of FIGS. 1-8 would allow the IMSRs shown therein to operate on a solid nuclear fuel comprised within the core 102 as opposed to being comprised in the molten fuel salt. For example, in the embodiment of FIG. 1A, the molten fuel salt can be replaced by a fuel-free (nuclear fuel-free) molten salt and the core 102 can comprise solid nuclear fuel such as TRISO fuels. Further, as no fission gasses are released in such solid fuel IMSRs, there would be no need for the off gas line 120. As previously described however, there are similar advantages to the invention of integrating a sealed solid fuel core into the replaceable IMSR unit. FIG. 9 shows a block diagram of an embodiment of a nuclear power plant 2000 that includes an MSR 2002 such as, any one of IMSR 90, 92, 94, and 96 described above in relation to FIGS. 1, 4, 6, 7, and 8. The MSR 2002 generates heat and provides the generated heat to a heat exchanger system 2004. The heat exchanger system 2004 can include the heat exchanger unit 106 disposed in the vessel 100, which also includes a graphite moderator core 102 and is discussed above in relation FIGS. 1, 4, 6, and 7. With respect to MSR 96 shown at FIG. 8, the heat exchanger system 2004 can include the heat exchanger unit 106, which is located outside the vessel 100 that includes the graphite moderator core 102. Additionally, the heat exchanger system 2004 of FIG. 9 can include additional heat exchangers that receive the heat from the above noted heat exchanger units 106. The nuclear power plant 2000 of FIG. 9 includes an end-use system 2006 that receives heat from the heat exchanger system 2004 and uses that heat to do work. For example, the end-use system 2006 can include a heat exchanger apparatus that transport the heat received from the heat exchanger system 2004 to an industrial apparatus that uses that heat. An example of such an industrial apparatus includes a cement kiln. In other embodiments, the end-use system 2006 can include a steam generator that uses the heat received from the heat exchanger system 2004 to produce steam that powers a turbine system, which can be used to power an electrical generator. In further embodiments, the end-use system 2006 can include a steam generator that uses the heat received from the heat exchanger system 2004 to produce steam that is used for bitumen extraction from bituminous sands (e.g., steam assisted gravity drainage). FIG. 10 shows a flowchart of a method according to certain examples of the present disclosure. The method shown at FIG. 10 is a method of operating a nuclear power plant. The nuclear power plant comprises a nuclear reactor (e.g., an MSR) that generates heat (thermal energy) and a heat exchanger system. The nuclear reactor comprises a vessel, a graphite moderator core positioned in the vessel, and a molten salt circulating at least in the vessel. In embodiments where the nuclear reactor is an MSR, the molten salt is a molten fuel salt. The nuclear reactor heats the molten salt and the heat exchanger system receives the heat from the molten salt. The method of FIG. 10 includes, at action 1000, operating the nuclear reactor. At action 1002, the MSR is shut down upon occurrence of a shutdown event. Shutdown events can include, for example, a detection of strain in the graphite moderator core the neutron fluence on the graphite moderator exceeding a maximum fluence level, and an operation duration of the nuclear reactor exceeding a pre-determined operation duration. The pre-determined duration of operation is determined in relation to maintaining the structural integrity of the graphite moderator core positioned in the vessel of the MSR and in relation to the operation conditions under which the MSR operates. For a given graphite moderator core, when the pre-determined operation conditions are such that the graphite moderator core is subjected to low peak power densities and low average power densities, the pre-determined duration of operation will be longer than when the pre-determined operation conditions are such that the graphite moderator core is subjected to high peak power densities and high average power densities. An MSR having a peak power density of 20 MWthermal/m3 would result in the pre-determined duration of operation being about 11.5 years when running at full capacity, and about 15 years when running at 75% capacity. It is envisaged that the operational time (duration) of a practical IMSR will be less than 15 years and thus, will have a peak power density higher than 20 MWthermal/m3. At action 1004, all operational connections between the inside portion of the heat exchanger system and the outside portion of the heat exchanger system are severed. This results in a severed, shut-down nuclear reactor. That is, any type of conduit connected to the nuclear and used to transfer heat from the nuclear reactor to any part of the heat exchanger system located outside the vessel is severed. Further, electrical connections for pump motors and monitoring instrumentation, small conduits for makeup fuel salt addition, salt sampling, off gas removal and a dip line for the removal of the fuel salt can also be severed when, for example, the severed shutdown nuclear reactor is to be moved or sequestered At action 1006, a replacement nuclear reactor can be obtained and, at action 1008, the inner heat exchanger system portion of the replacement nuclear reactor is connected to the outside portion of the heat exchanger system. If applicable, any other electrical connections for pump motors and monitoring instrumentation, small conduits for makeup fuel salt addition, salt sampling, off gas removal and a dip line for the removal of the fuel salt of the replacement nuclear reactor can be made. At action 1001, if fault in a heat exchanger is detected, the flow of coolant salt in the faulty heat exchanger can be stopped. At action 1005, the severed, shutdown nuclear reactor can be sequestered. To shut down the nuclear reactor, a control rod (shutdown rod) can be used or, in embodiments where the nuclear reactor is an MSR, by draining the molten fuel salt to an external storage such as a dump tank. The coolant lines can then be sealed and/or crimped and disconnected along with any other lines such as off gas lines. Examples of coolant lines are shown in FIG. 1 as inlet conduit 114 and outlet conduit 112. After disconnecting these lines the spent nuclear reactor, i.e., the reactor vessel and all remaining conduit segments attached thereto, can be removed, for example, by using an overhead crane. Such operations might be done after a period of in situ cool down for radiation levels to diminish. In such a mode, likely the next unit (i.e., the replacement nuclear reactor) can be installed adjacent the spent IMSR such that, long term, while one unit operates, the other is cooling down and then replaced before the operating unit is finished its cycle. Using an overhead crane for removal may involve some mechanism to breach the primary hot cell. The pump motor (see reference numeral in FIG. 1), when present, can be recycled, for example by, cutting it from the shaft of the impeller to which the pump motor is connected. The rest of the spent nuclear reactor can be transferred off site or to another area of the nuclear power plant, perhaps even within the primary hot cell. As an option, the unit might also be used for the short, medium or even long term storage of the primary fuel salt itself, perhaps after some or all actinides are removed for recycle or alternate storage. Thus the spent nuclear reactor may act as a storage and/or disposal canister for the internal graphite, primary heat exchangers and even the salt itself. At some point a decision on long term sequestration would have to be made but potentially the entire unit could be lowered into an underground location such as deep borehole made on site or transported to a salt cavern for safe long term sequestration. Some comment on the overall economic viability is perhaps of use as it goes against the often imposed logic of attempting to get the longest service life as possible from all components. The advantages seem to greatly outweigh any economic penalty of decreased capital amortization time. First, there may be little change in the overall need of graphite over the lifetime of the nuclear plant itself as would be understood by those trained in the field. Second, the components now having a shorter design life such as the reactor vessel and/or primary heat exchangers typically make up only a small fraction of the nuclear plant costs. In studies by Oak Ridge National Laboratories, such as in ORNL 4145 the cost of the reactor vessel and primary heat exchangers were only around 10% of the plant cost. The ability to lower the cost of these items by the great simplifications allowed by having a sealed replaceable unit would seem to more than make up for the lowered amortization time. When the decreased research and development costs are factored in, the advantage of this disclosed design seem clear. FIG. 11 shows a top, cross-sectional view of a further embodiment of a nuclear reactor 1100 of the present disclosure. The nuclear reactor 1100 has a nuclear reactor vessel, which has a nuclear reactor vessel wall 1104 and, the nuclear reactor vessel 1102 is contained in a containment vessel 1106, which has a containment vessel wall 1108. Between the nuclear reactor vessel wall 1104 and the containment vessel wall 1108 is a buffer salt 1110. The nuclear reactor wall 1104 is made of a thermally conductive material, for example, a nickel-base alloy such as Hastelloy® N. The buffer salt 1110 is in thermal contact with the nuclear reactor wall 1104. Upon loss of electrical power to the heat exchanger system, the pumps pumping the coolant salt through the heat exchangers located inside the vessel will stop functioning. However, some of decay heat will continue to be transferred out the reactor vessel through natural circulation: that is, the coolant salt in the reactor vessel will heat up and circulate through the secondary heat exchangers (secondary heat exchanger loops) system by convection. As such, provided the heat exchanger system remains able to shed some of the heat received by nuclear reactor, severe consequences, such as damaging the metallic structure of the nuclear reactor vessel, can be avoided. However, upon a catastrophic event, for example an earthquake, where the heat exchanger system becomes thoroughly defective, i.e., is no longer able to transfer any significant heat from the nuclear reactor 1102, the nuclear reactor 1102 can no longer transfer the decay heat generated therein and failure to properly manage the decay heat can lead to severe consequences. In accordance with the present disclosure, the decay heat can be safely managed by selecting a buffer salt 1110 that acts as a phase transition heat sink. When used in MSRs, the buffer salt provides an alternative to the freeze plug and dump tank approach often used in MSRs. The virtue of the embodiment of FIG. 11 is the ability to passively dissipate the decay heat that is produced by nuclear reactors after the loss of external cooling (i.e., when the heat exchanger system can no longer transfer any significant heat from the nuclear reactor). The embodiment of FIG. 11 enables the dissipation of the decay-heat surge even when there is loss of external cooling, thereby avoiding severe consequences. As an example, the nuclear reactor 1100 can be considered to be an MSR that runs at about 650° C. and produces thermal energy at a rate of 80 MWth (full power value) and the nuclear reactor vessel wall 1104 is at 650° C. Upon shutdown, the decay heat generated by the nuclear reactor will be, averaged over the first two days, about 0.5% of the full power value and the temperature of the nuclear reactor vessel wall 1104 will increase. When the buffer salt 1110 is 53% NaF-47% AlF3 (density of 2.4 t/m3 with 400 kJ/kg latent heat, melting point of 695° C.) and is 1 meter thick, the total mass of the buffer salt is about 177 tons and provides a latent heat of melting of 7.1×1010 joules. In this example, the buffer salt 1110 provides approximately 2 days of initial decay heat absorption even with an adiabatic assumption of no other heat loss. That is, it will take about two days for the buffer salt 1110 to melt, i.e., about two days for the temperature of the nuclear reactor vessel wall 1104 and of the buffer salt 1110 to reach the buffer salt's melting point of 695° C. After the buffer salt has melted it remains in the containment vessel 1106, surrounding the nuclear reactor 1102, the decay heat is no longer absorbed by the buffer salt and needs to me managed otherwise. Several options of managing the decay heat are available. For example, the containment vessel can be surrounded by water (a water jacket) 1112 that will be boiled off by the decay heat. In the present example the water 1112 will boil off at a rate of about 8 liters/minute (this boil-off rate will decrease with time as less and less decay heat is generated). The boiled off water can be replenished by a water reservoir (not shown). A modest reservoir can supply water for many months, especially in view of the unrealistic adiabatic assumption; clearly, radiant and conductive heat will be dissipated into the building housing the nuclear and in the environment surrounding the water jacket. As such, the realistic water boil-off rate will be less that 8 liters/minute. The water jacket can be in the form of coiled piping surrounding the containment vessel and in thermal contact with the containment vessel wall 1108. The coiled piping is connected to the water reservoir. In other embodiments, an air jacket can be used. The air jacket can be in the form of coiled piping surrounding the containment vessel and in thermal contact with the containment vessel wall 1108. As will be understood by the skilled worker, in some embodiments, providing cooling to the containment vessel may cause a relatively thin layer of the buffer salt adjoining the outside wall of the containment vessel to remain in the solid state when the temperature at the wall in question is at, or below, the freezing point of the buffer salt. Such embodiments are within the scope of the present disclosure. The buffer salt 1110 can be selected to be a thermal insulator when in the solid state and a thermal conductor when in the liquid (molten buffer salt) state. Specifically, the solid state thermal conductivity of the selected buffer salt is lower than the heat transfer capability of the liquid state buffer salt. That is, convective heat transfer in the liquid state is significantly higher than conductive heat transfer in the solid state. 53% NaF-47% AlF3 is such a buffer salt. Having the buffer salt 1110 acting as a thermal insulator during operation of the nuclear reactor reduced loss of heat generated by the nuclear reactions taking place in the nuclear reactor vessel 1102. FIG. 12 shows a top, cross-sectional view of a further embodiment of a nuclear reactor 1114 of the present disclosure. As in the nuclear reactor 1100 of FIG. 11, the nuclear reactor 1114 has a nuclear reactor vessel 1102, which has a nuclear reactor vessel wall 1104 and, the nuclear reactor vessel 1102 is contained in a containment vessel 1106, which has a containment vessel wall 1108, which can be referred to as an outer wall or as a containment vessel outer wall. Additionally, the containment vessel has an inner wall 116 (shown with dashed line) that is in thermal contact with the nuclear reactor vessel wall 1104. Between the inner wall 1116 and the containment vessel wall 1108 is the buffer salt 1110. The inner wall 1116 is thermally conductive and, as such, the buffer salt 1110 is in thermal contact with the nuclear reactor wall 1104. Advantageously, the nuclear reactor 1114 allows for removal of the nuclear reactor vessel 1102 from the containment vessel 1106 without having to remove the buffer salt 1110. Also, a replacement nuclear reactor can be inserted in the containment vessel 1106. Even though the above examples use 53% NaF-47% AlF3 as a buffer salt, any other suitable buffer salt can be used. That is, salts that have a melting point above the operating temperature of the nuclear reactor and that can act as a thermal insulator in the solid state and as a thermal conductor (by convection) in the liquid state can be used. Other examples of salts that can be used as buffer salts include: other fluoride salts such as 66% NaF-34% ZrF4 (melting point of 640° C.) and 26% KF-74% Zr4 (melting point of 700° C.); bromide salts such as NaBr (melting point of 747° C., latent heat of melting: 250 KJ/Kg) and KBr (melting point of 734° C.; and other salts such as MgCl (melting point of 714° C., latent heat of melting: 360 kJ/Kg). Even though the nuclear reactors of FIGS. 11 and 12 are shown with buffer salts, other embodiments may use a buffer material other than a buffer salt. For example, the buffer salt 1110 of FIGS. 11 and 12 can be replaced by pure aluminum (melting point of 660° C., latent heat of melting: 397 kJ/Kg). In this case, to avoid having excessive heat transfer between the nuclear vessel and the containment vessel during normal operation of the nuclear reactor, the aluminum can be in the form of balls, which allows for only some thermal contact between neighbouring balls and the nuclear reactor vessel wall and the containment vessel. As with other nuclear reactors described herein, the nuclear reactors shown at FIGS. 11 and 12 can also be disconnected, removed, and replaced as a unit, with or without the containment vessel. In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However it will be apparent to one skilled in the art that these specific details are not required. The above described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those skilled in the art without departing from the scope, to be defined solely in the accompanying claims. |
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059603682 | claims | 1. A process for preparing radioactive, hazardous, or mixed waste for storage, comprising: (A) contacting radioactive, hazardous, or mixed waste starting material comprising at least one organic carbon-containing compound and at least one radioactive or hazardous waste component with nitric acid and phosphoric acid for a period of time sufficient to oxidize at least a portion of said organic carbon-containing compound to gaseous products, thereby producing a residual concentrated waste product comprising substantially all of said radioactive or hazardous metal waste components; and (B) immobilizing said residual concentrated waste product in a solid phosphorus-containing ceramic or glass form. (A) contacting radioactive, hazardous, or mixed waste starting material comprising at least one organic carbon-containing compound and at least one radioactive or hazardous waste component with nitric acid and phosphoric acid for a period of time sufficient to oxidize at least a portion of said organic carbon-containing compound to gaseous products, thereby producing a residual concentrated waste product comprising substantially all of said radioactive or hazardous metal waste components; and (B) immobilizing said residual concentrated waste product in a solid form, wherein said solid form comprises a glass or ceramic matrix selected from the group consisting of iron phosphate glass, ferric phosphate ceramic, and magnesium phosphate ceramic. 2. The process according to claim 1, wherein said radioactive, hazardous, or mixed waste starting material comprises low level radioactive waste or low level mixed waste. 3. The process according to claim 2, wherein said low level radioactive waste or low level mixed waste comprises material selected from the group consisting of job control waste, ion exchange resins, and reactor coolant system cleaning streams. 4. The process according to claim 3, wherein said organic carbon-containing compound is selected from the group consisting of neoprene, cellulose, EDTA, tributylphosphate, polyethylene, polypropylene, polyvinylchloride, polystyrene, oils, resins, and mixtures thereof. 5. The process according to claim 1, wherein said radioactive or hazardous waste component contains an element selected from the group consisting of U, Th, Cs, Sr, Am, Co, Tc, Hg, Pu, Ba, As, Cd, Cr, Pb, Se, Ag, Zn, and Ni. 6. The process according to claim 5, wherein said radioactive waste component is Pu. 7. The process according to claim 1, wherein said nitric acid and said phosphoric acid are present in molar quantities of about 0.03 to about 2.0 moles of HNO.sub.3 and of about 12.8 to 14.77 moles of H.sub.3 PO.sub.4. 8. The process according to claim 1, wherein oxygen is provided by introducing air into a mixture of said radioactive, hazardous, or mixed waste starting material, said nitric acid and said phosphoric acid. 9. The process according to claim 1, wherein said contacting temperature is in the range of about 140.degree. C. to about 210.degree. C. 10. The process according to claim 1, wherein said organic carbon-containing compound is selected from the group consisting of polyethylene, polypropylene, and polyvinylchloride, said contacting temperature is in the range of about 185.degree. C. to about 190.degree. C., and wherein said contacting is carried out at a pressure in the range of about 10 to about 15 psig. 11. The process according to claim 1, wherein said gaseous products comprise carbon oxides, water, and nitrogen oxides. 12. The process according to claim 11, further comprising oxidizing said nitrogen oxides to form nitric acid and recycling said nitric acid to said contacting step. 13. The process according to claim 11, wherein said carbon oxides comprise carbon monoxide and carbon dioxide, and wherein said carbon monoxide formation is suppressed by the presence of a catalytic amount of a Pd.sup.+2 containing catalyst. 14. The process according to claim 1, wherein said immobilizing said residual concentrated waste product in a solid phosphorus-containing ceramic or glass form comprises preparing an iron-phosphate waste glass comprising said radioactive or hazardous waste component stabilized in a matrix of iron-phosphate glass. 15. The process according to claim 14, wherein preparing said iron-phosphate waste glass comprises mixing said residual concentrated waste product, iron oxide, and a glass former, and vitrifying said mixture at a temperature between about 1050.degree. C. and about 1300.degree. C. 16. The process according to claim 1, wherein said immobilizing said residual concentrated waste product in a solid phosphorus-containing ceramic or glass form comprises preparing a magnesium phosphate ceramic from said residual concentrated waste product. 17. The process according to claim 16, wherein said preparing said magnesium phosphate ceramic comprises mixing said residual concentrated waste stream with magnesium oxide and boric acid to form a slurry, and allowing the slurry to set. 18. The process according to claim 1, wherein said immobilizing said residual concentrated waste product in a solid phosphorus-containing ceramic or glass form comprises preparing a ferric phosphate ceramic from said residual concentrated waste product. 19. The process according to claim 1, wherein substantially all of said organic carbon-containing compound is oxidized into gaseous components. 20. A process for preparing radioactive, hazardous, or mixed waste for storage, comprising: |
042697280 | summary | FIELD OF THE INVENTION This invention relates to the storage of spent fuel in repositories in which sulfur is used as the storage medium. More particularly, the invention relates to an improvement in the method for the storage of radioactive wastes in repositories in which the storage medium is liquid sulfur and the repositories are made self-sealing. DESCRIPTION OF THE PRIOR ART In view of the fact that nuclear energy will be increasingly used to supply the world's energy, the nuclear industry is faced with the problem of developing a method for safely disposing of radioactive wastes. It must especially be ensured that the radioactivity from such wastes will not contaminate the environment. Up until a short time ago, storage facilities were expected to hold spent fuel for less than 10 years. However, new policy guidelines require that the fuel may have to be stored for periods of up to 100 years. A number of factors must be taken into consideration in the development of a method for safely storing radioactive wastes for this length of time. For example, the question of storage cost must be considered. In this connection, it will be appreciated that it is always possible to arrange a large number of so-called barriers around the radioactive wastes to be stored. On the other hand, a large number of such barriers will significantly increase the storage costs and, in turn, make the production of nuclear energy less competitive when compared to other sources of energy. The most common storage medium for spent fuel elements has been water. However, water presents problems in that over long periods of time, e.g., up to ten years, it exerts a corrosive effect on the containers and parts of the repositories in contact with the water. This ultimately results in various metallic salts from the repositories and the elements being dissolved in the water. Such salts do possess a level of radioactivity. Consequently, should an accident occur wherein a leak results, the water with the radioactive salts dissolved therein can leak out and is easily absorbed into the ground or evaporates into the atmosphere leaving the radioactive contaminants. Thus, water is not suitable for a long term storage medium. In the past, a variety of methods for storing radioactive materials have been utilized. In U.S. Pat. No. 4,131,564, a process for preparing solid wastes containing radioactive or toxic substances for safe handling, transportation and permanent storage has been described. A similar method is disclosed in U.S. Pat. No. 3,838,061. U.S. Pat. No. 3,824,673 discloses a method for the treatment of irradiated fuel elements, particularly for transporting the fuel elements wherein a molten alloy material is deposited between the fuel rods and the alloy is allowed to solidify. The concept of making containers self-sealing for long-term storage is described in U.S. Pat. No. 3,983,050. In this case, the radioactive material is stored in a container in which powdered cement is added so that any leak will cause hardening of the cement when the storage container is in a moisture-containing environment, such as, open air or a water tank storage. SUMMARY OF THE INVENTION Applicants have discovered that long-term storage requirements which are now considered to be necessary can be met by utilizing, as the storage medium, elemental sulfur. The use of the sulfur avoids the disadvantages of the water previously used and further provides extremely long term storage capability, e.g., up to and even more than 100 years. |
description | This disclosure is a national stage of International Patent Application PCT/US2019/047745, filed on Aug. 22, 2019, which claims priority to and benefit from U.S. Provisional Patent Application Ser. No. 62/721,273 titled “Systems and Methods for Data Processing for Real-Time Emergency Planning,” filed on Aug. 22, 2018, which are herein incorporated by reference in their entirety. This invention was made with government support under Sponsor Award No. DE-NE0008710 awarded by the U.S. Department of Energy. The government has certain rights in the invention. This disclosure generally relates to systems and methods for real-time data processing and for emergency planning. An emergency is an unplanned situation or event (e.g., an accident) that when occurs increases a risk of injury to the well-being of people, animals, and/or property. Emergencies necessitate prompt action to mitigate a hazard or adverse consequence for human health, safety, quality of life, property or the environment. A computer-implemented method and a neural network may include receiving scenario test data that may be representative of a plurality of different test scenarios for a system. The scenario test data may be collected in real-time based on monitoring local or regional data to ascertain any anomaly phenomenon from scenarios which may be applicable to any one of: nuclear power plant, hydro-electric dam, coal-fired generator plant, power grid instability, water pumping station, food contamination sampling, biohazards, disease outbreak, communication network traffic, network denial attacks, oil refinery, off-shore drill platform, chemical plant, weather patterns, tides level, people movement, facial recognition, to name a few. Any anomaly from the scenario data analysis may be an indication of an imminent danger that may lead to catastrophe, a criminal act or a behavioral change that may result in a disruption to the population or a surrounding community. In an embodiment, each test scenario may be characterized by a set of observable parameters of the system. A computer-implemented method may include filtering a plurality of different test scenarios to identify a sub-set of test scenarios from the plurality of different test scenarios that may have similar behavior characteristics. The computer-implemented method may include providing a sub-set of test scenarios to a trained neural network to identify one or more sub-set of test scenarios. The one or more identified sub-set of test scenarios may correspond to one or more anomaly test scenarios from the sub-set of test scenarios that is most likely to lead to an undesirable outcome associated with an emergency causing event. In another example, a system as shown and/or described herein. In an even further example, a product as shown and/or described herein. In another example, a method as shown and/or described herein. In an example, a device as shown and/or described herein. In another example, an apparatus as shown and/or described herein. The summary is provided merely for purposes of summarizing some example embodiments so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described examples should not be construed to narrow the scope or spirit of the disclosure in any way. Other examples, embodiments, aspects, and advantages will become apparent from the following detailed description taken in conjunction with the accompanying drawings. Emergencies are undesirable and in many instances may be prevented had circumstances leading up to an accident been recognized, and acted upon, prior to the accident's occurrence. The actions taken in the initial moments of an emergency are critical. For example, a prompt warning to humans to evacuate, shelter or lockdown may save lives. Action by employees with knowledge of building and process systems may help mitigate a leak and minimize damage to the facility and the environment. Response strategies (or plans) may be developed to tackle the emergency and provide guidelines for humans on how to respond to the occurrence of an emergency. For example, accidents resulting at a nuclear facility (e.g., anyone of nuclear power plants, nuclear waste repositories, etc.) may have profound effects on the environment, including the well-being of people, animals, and/or property. In an example wherein an accident occurs at a nuclear facility, personnel would be responsible for returning the nuclear facility to a normal operating state (e.g., safe state). The plant staff should be supported in taking these actions with Emergency Operating Procedures (EOPs) for which they receive extensive training and take corrective actions to mitigate or to prevent occurrence of a nuclear facility melt down accident. EOPs are for maintaining fundamental safety functions and preventing a hazard or adverse consequence for human health, safety, quality of life, property or the environment. The scope of EOPs is to provide procedural guidance for stake-holders to handle emergency conditions. Thus, EOPs generally provide actions for a wide spectrum of operating conditions, ranging from abnormal operation up to accidents far exceeding the design basis of the setting the data is collected, such as sensory data in a nuclear power plant. Severe accident conditions may include accident conditions involving significant damage to the environment. For example in nuclear power plants, severe accident conditions begin when significant fuel damage occurs or is anticipated. From the perspective of EOPs, severe accident conditions occur when the provisions and guidance of EOPs are no longer effective in preventing the hazard. EOPs concentrate on protecting integrity of the setting the data is acquired. It is only after this fails or is imminent that personnel rely on severe accident guidelines (SAG), which focus on maintaining other barriers for public protection, typically the containment or confinement of effects and/or results of an emergency causing event. Guidelines referred to as severe accident management guidelines (SAMG) have been developed for each level. SAMG may include directions on how to terminate core damage once it has started, to maintain the capability of the containment as long as possible, to minimize on-site and off-site releases, to return the plant to a safe operating state, etc. If there is a potential for a significant release of radioactive material into the environment as may be inferred from PRA, the personnel must declare a level of site emergency. However, offsite response, such as evacuation, is ordered not by the personnel but by State personnel (e.g., the Governor). In making offsite response decisions, States must rely on the expertise of the personnel, their understanding of the current state of the nuclear facility, and their projection (or predictions) as to the likely outcomes of the event (e.g., results and/or effects of the event). An event tree (ET)/fault tree (FT) methodology may be traditionally used for PRA to account for uncertainties in accident progression. The ET may be used to model the sequence of events to possible end states. When there is uncertainty in the occurrence of an event, the ET branches into two (or more) ETs where each ET follows the consequences associated with the uncertain event. For example, if a valve is designed to open when the pressure in the reactor vessel exceeds a pre-specified set point, the ET may need to follow the consequences of the valve opening or failing to open. The uncertainties associated with the events occurring or not occurring are estimated using FTs. The traditional ET/FT approach has challenges in modeling the interaction among hardware/process/software/human behavior and may have subsequently challenges in adequately supporting the declaration of a site emergency, as well as assisting in emergency response. In particular, scenarios that may lead to catastrophic events may not be identified and personnel may not be able to properly and efficiently respond to the emergency causing event. Effective real-time SAMGs to be constructed necessitates accurate identification of scenarios are most likely to lead to undesirable radiological impact. Systems, methods, devices, apparatuses, and products (referred to herein more generally as “systems”) are described herein for data processing for real-time emergency planning. The systems described herein can process data and assist personnel in assessing an event sequence probabilistically as an Unusual Event (UE), an Alert, a Site Area Emergency (SAE) or a General Emergency (GE) as the accident evolves and may reduce the level of exposure of the population, as well as the negative impacts of possible evacuation. Using the systems described herein, State personnel may be better equipped with technical guidance in undertaking emergency response activities associated with an evacuation. In an example, the systems described herein may project levels of radiological exposure in a surrounding environment, including humans, and their likelihoods based on observable parameters from personnel and environmental devices (e.g., instrumentation) at a nuclear facility. In some examples, the systems described herein may be configured to construct a real-time SAMGs based on dynamic event trees (DETs) to support a declaration of a site emergency and to guide off-site response. In DET analysis, the systems described herein may be configured to characterize alternative scenarios or pathways by branching points in a tree as the accident progresses in time for which branching probabilities may be assigned in a similar manner to ETs. However, unlike the traditional ET/FT approach, the temporal behavior of all stages of a severe accident may be reflected by DETs, including the interaction among hardware/process/software/human behavior. In that respect, with data from observed variables that may be monitored by facility personnel, DETs may be used to estimate a likelihood of different levels of offsite release of radionuclides based on deep learning methodologies described herein based on the training data set. Accordingly, the systems described herein may assist personnel in predicting the likelihood of future states of the nuclear facility to support the declaration of a site emergency and to assist in the emergency response. The systems described herein may be configured to project the radiological outcomes to the public based on a deep learning network. Input data to the system described herein includes temporal behavior of monitored data in a control room, along with the training of the tool based on output of MELCOR/RASCAL codes (as an example) obtained from the simulation of a large set of possible accident scenarios representing potential outcomes of a given initiating event. Accordingly, the systems described herein have particular advantages over existing techniques, which will become more readily apparent according to the examples described herein. FIG. 1 illustrates an exemplary environment that includes a tool 102 for data processing for real-time emergency planning. The tool 102 may be implemented on a tangible hardware, such as a computer, such as a laptop computer, a desktop computer, a server, a tablet computer, a workstation, or the like. In some examples, the tool 102 may be implemented on a mobile device, for example, a cellular device. The tool 102 may include memory 104 for storing data and machine-readable instructions. The memory 104 may be implemented, for example, as a non-transitory computer storage medium, such as volatile memory (e.g., random access memory), non-volatile memory (e.g., a hard disk drive, a solid-state drive, flash memory or the like) or a combination thereof. In an alternate embodiment, the tool 102 may be implemented on a distributed cloud network, such as Amazon Web Services (AWS), Microsoft's Azure, Google Cloud or a similar cloud network service. The tool 102 may include a processing unit 106 (e.g., a Central Processing Unit (CPU), a Graphical Processing Unit (GPU) or similar) that may be configured to access the memory 104 and execute the machine-readable instructions stored in the memory 104. The processing unit 106 may be implemented, for example, as one or more processor cores. In the present example, although the components of the tool 102 are illustrated as being implemented on the same system, in other examples, the different components could be distributed across different systems and communicate, for example, over a network. The processing unit 106 may be configured to receive scenario data 108. The scenario data 108 may be generated based on a DET (dynamic event trees) evaluation associated with an emergency causing event. The scenario test data 108 may be representative of a plurality of different test scenarios for a system at a nuclear facility. For example, the scenario data 108 may be generated based on a DET study performed for a station blackout (SBO) in a three-loop pressurized water reactor (PWR). In an embodiment, part or all of the DET scenario data 108 may be also generated by the Analysis of Dynamic Accident Progression Trees (ADAPT) system (not shown in FIG. 1). The ADAPT system may be programmed to determine an evolution of possible scenarios for a system model (e.g., the three-loop PWR) based on branching and stopping rules, which may be user-defined. The ADAPT system may be programmed to keep track of scenario likelihoods and may graphically display the DETs and simulator outputs as a function of time. The ADAPT system may be programmed to interface with severe accident analysis code for simulation of the emergency event (not shown in FIG. 1). In some examples, the severe accident analysis code may be part of the ADAPT system (e.g., as a module). A severe accident analysis code may include a simulation data generator. As an example, MELCOR may be used to model a behavior of a system associated with an emergency causing initiating event. MELCOR is a fully integrated, software code that may be to simulate the progression of accidents in light water reactor nuclear power plants. MELCOR may provide a best-estimate code for severe accident analysis. A wide range of accident phenomena may be modeled in MELCOR including, but not limited to, thermo-hydraulic response in a reactor coolant system, reactor cavity, containment and confinement buildings, core heat-up, degradation, and relocation, ex-vessel debris behavior, core-concrete attack, hydrogen production, transport, and combustion; fission product release and transport, impact of engineered safety features on thermal-hydraulic and radionuclide behavior. For example, the ADAPT system may be programmed to provide input data (e.g., branching rules, stop conditions, etc.) to the severe accident analysis code for DET analysis of the system model for an emergency causing initiating event. The input data may be provided at a user input device (not shown in FIG. 1). The severe accident analysis code may be programmed to simulate the system model based on the input data from the ADAPT system, as well as to advance the emergency event through predetermined time steps until a pre-specified end time may be achieved. The data from simulation results data may correspond to the scenario data 108. The scenario data 108 may include a plurality of scenario datasets that may represent a plurality of different scenarios for the system (and/or the plant facility). Each scenario dataset may include branching combination results, which may be associated with the emergency causing event. For each scenario dataset, the severe accident analysis code (or the ADAPT system) may be programmed to calculate probabilities of radionuclide release fractions. Each scenario may be characterized by a set of observable parameters of the system in response to the emergency causing event. In some examples, each scenario may be characterized by a combination of the observable parameters, as disclosed in Table 1 of FIG. 2. FIG. 2 illustrates an exemplary table that includes a set of observable parameters of the system at a nuclear facility. For training the neural network engine 112 in FIG. 1, the observable parameters for each scenario may be obtained from the severe accident analysis code for a given number of time divisions over multiple simulations of the system. Each scenario may be represented by a matrix, n×m, wherein n is a number of the observable parameters and m is the given number of time divisions. In some examples, the tool 102 may include a consequence system, such as a radiological assessment system for consequence analysis (RASCAL) or a MELCOR Accident Consequence Code System (MACCS) (not shown in FIG. 1). The consequence system may be programmed to determine associated offsite dosage for each scenario. The consequence system may be programmed to characterize environment impacts for each scenario based on key radionuclides (e.g., Cs-137 and I-131), or other radionuclides. In some examples, a single pre-defined meteorology may be used in the assessment of environmental impact. The consequence system may be used to assess the radiation dosage at user-defined time that may be experienced by an individual located within a given amount of miles of the nuclear facility (e.g., within two miles and ten miles of the nuclear facility) for each scenario. The tool 102 may further include a scenario filter 110. The scenario filter 110 may be programmed to filter the plurality of different scenarios to identify a sub-set of scenarios having similar behavior characteristics. The scenario filter 110 may be programmed to define the first bin (e.g., first range) and a second bin (e.g., second range). For example, the first bin may correspond to a total effective dose equivalent (TEDE) that is greater than 10 rem (referred to herein as “Bin over 10 rem”). The second bin may correspond to a TEDE less than or equal to 10 rem (referred to herein as “Bin 0-10 rem”). The scenario filter 110 may be programmed to assign the identified sub-set of scenarios to one of the first and the second bin. In some examples, the scenario filter 110 may be programmed to apply a clustering process to different scenarios to determine to which bin each scenario may be assigned. The clustering process may be used to identify scenarios (e.g., scenario datasets—observable parameters for the system) with similar behavior or when classifying their characteristics. In an example, the scenario filter 110 may be programmed to apply the mean shift methodology (MSM) to assign each point in the state space (e.g., scenario at each instance of time) to a cluster centroid based on a bandwidth of a defined kernel through a set of local averaging calculations. The idea is to consider all the points that are inside the centroid and determine the center of mass m(sA) of these points as shown in Eq. (1): m ( S A ) = ∑ i = 1 I x i → g ( S A - x i → h 2 ) ∑ i = 1 I g ( S A - x i → h 2 ) ( 1 ) In Eq. (1), xi may correspond to a data point (scenario) of location in the space of possible scenarios and I may represent a total number of scenarios. The SA in Eq. (1) may correspond to an initial estimation of location (original point). A Gaussian kernel gg(x→) may be used for weighing the distance between SA and xi and may be defined by: g ( x → ) = e - x → 2 / h 2 ( 2 ) FIG. 3 illustrates clustering of exemplary two-dimensional data into a number of bins with radius or bandwidth h. The process may be repeated until the centroids of clusters converge within a given error. From each cluster, the centroid and specific scenarios within that cluster may be identified and assigned to a respective bin. For example, Bins over 10 rem and 0-10 rem may use the same bandwidth. The scenario filter 110 may be programmed to partition the plurality of different scenarios into three sets: a training set (consistent of Bins over 10 rem and 0-10 rem), a testing set (consisting of Bins over 10 rem and 0-10 rem), and a validation set (Bin over 10 rem) according to the clustering process. For the set of exposures in the proximity of the nuclear facility (e.g., within two miles) the Bin over 10 rem of the training set was constructed by random sampling 3% of each cluster, and Bin 0-10 rem by random sampling 90% of each cluster for balancing the number of scenarios in each bin. The remaining scenarios in Bin over 10 rem constituted the validation set. In a similar manner for the region extending to a greater distance from the nuclear facility (e.g., 10 miles from the nuclear facility), Bin over 10 rem of the training set was constructed by 21% of each cluster and Bin 0-10 rem by 90% of each cluster. FIG. 4 illustrates exemplary tables characterizing a distribution of the plurality of scenarios in the proximity of the nuclear facility based on the clustering process. In Table 2, the training set has 186 scenarios, the testing set has 52 scenarios, and the validation set has 2418 scenarios. Table 3 illustrates the distribution of the plurality of scenarios for the set of exposures extending to a greater distance from the nuclear facility, wherein the training set has 871 scenarios, the testing set has 138 scenarios, and the validation set has 1647 scenarios. The tool 102 may further include a neural network engine 112. The neural network engine 112 may be programmed to generate a neural network object 116 that may include an input layer and an output layer between which one or more hidden layers may be generated. In some examples, the neural network object 116 may communicate to one of: a convolutional neural network (CNN) and a generalized custom neural network. FIG. 5 illustrates an exemplary convolutional neural network (CNN) 502 and FIG. 10 illustrates an exemplary generalized custom neural network. In some examples, the CNN 502 may be realized by a hardware and software tool, such as the tool 102, as illustrated in FIG. 1. Additionally, or alternatively, the CNN 502 may correspond to the neural network object 116, as illustrated in FIG. 1. The CNN 502 may be generated by the neural network engine 112 based on user input (e.g., a number of convolution layers, pooling layers, output layers, fully connected layers, etc.). The CNN 502 may include a plurality of convolution layers, a plurality of fully connected layers, a plurality of max-pooling layers, an output layer and an input layer. In some examples, the CNN 502 may include six convolutional layers and three fully-connected layers stacked aside that may include two different classes, as shown in FIG. 5. In an example, the CNN 502 may be programmed to receive input data 504 (e.g., scenarios test data from a nuclear power plant) and process the input data to produce a plurality of output labels 506. In some examples, the plurality of output labels 506 may include the Bin 0-10 rem and the Bin over 10 rem. In this example, the last fully-connected layer of the CNN 502 may be programmed to produce resultants of 2 output labels 506, which may be the Bin 0-10 rem and the Bin over 10 rem. A first convolutional layer of the CNN 502 may be programmed to process the input data with 20 kernels of size 1×1 with a stride 1. The output of the first layer may be used as an input of the second layer and a second convolutional layer of the CNN 502 may be programmed with 52 kernels of size 5×5 with a pad 2. A third convolutional layer of the CNN 502 may be programmed to process the input data with 71 kernels of size 2×2 with a pad 1. A fourth convolutional layer of the CNN 502 may be programmed to process the input data with 72 kernels of size 2×2 with a pad 1, a fifth convolutional layer of the CNN 502 may be programmed to process the input data with 52 kernels of size 2×2 with a pad 1, and a sixth convolutional layer of the CNN 502 can be programmed to process the input data with 22 kernels of size 2×2 with a pad 1 are applied. The neural network engine 112 may be programmed to train the CNN 502 based on scenario training data comprising a plurality of training scenarios. In some examples, the plurality of training scenarios may correspond to the scenario training set. The neural network engine 112 may be programmed to train parameters of the CNN 502 based on the scenario training data. After training the CNN 502, the neural network engine 112 may be programmed for testing different scenarios for the system in connection with the emergency causing event. In an example, the CNN 502 may be programmed to receive scenario test data representative of a plurality of different scenarios for the system. In some examples, the scenario test data may correspond to the scenario test set. The neural network engine 112 may be programmed to provide the scenario test data to the CNN 502 for classification of the plurality of different scenarios. The CNN 502 may be programmed to classify each of the plurality of different scenarios as having a TEDE less than or equal to 10 rem or having a TEDE greater than 10 rem. Each scenario of the plurality of different scenarios classified as having the TEDE greater than 10 rem may correspond to one or more scenarios that is most likely to lead to the undesirable outcome associated with the emergency causing event. In an example, the undesirable outcome may correspond to a release of ionizing radiation. In some examples, the tool 102 may be programmed to generate a real-time emergency plan for real-time emergency planning based on the one or more scenarios classified as having the TEDE greater than 10 rem. In some examples, the neural network engine 112 may be programmed to communicate with a display generator 114 stored in the memory 104. The display generator 114 may be programmed to provide data to a display 118. The display generator 114 may be programmed to generate display data characterizing the one or more scenarios classified as having the TEDE greater than 10 rem. The display 118 may be configured to render the display data to provide visualization of the one or more of scenarios classified as having the TEDE greater than 10 rem. In some examples, the rendered display data may be used by a human for real-time emergency planning. The resulting number of false negatives (FNs) (belonging to Bin over 10 rem but identified as belonging to Bin 0-10 rem), false positives (FPs) (belonging to Bin 0-10 rem but identified as belonging to Bin over 10 rem), true negatives (TNs) (belonging to Bin 0-10 rem and identified as belonging to Bin 0-10 rem), and true positives (TPs) (belonging to Bin over 10 rem and identified as belonging to Bin over 10 rem) for testing, validation, and testing plus validation cases are presented in Table 4, as shown in FIG. 6. FIGS. 7-8 show the testing+validation set of TPs, TNs, FPs, and FNs for the 2-mile and the 10-mile transport. In some examples, the numbers of FNs, FPs, and TNs may be substantially smaller than TPs. In the testing set of 2-mile transport, there was 1 false positive out of a total of 2418 scenarios and the rest of data were identified correctly. The validation set of 2-mile transport contains one misidentified scenario, a FN, which was incorrectly identified as Bin 0-10 rem instead of Bin over 10 rem. There were 10 false negatives and 10 false positives out of a total 138 testing scenarios in 10-mile transport. There were 142 false negatives in the validation set. In view of the foregoing structural and functional features described above, a method that may be implemented will be better appreciated with reference to FIG. 9. While, for purposes of simplicity of explanation, the method of FIG. 9 is shown and described as executing serially, it is to be understood and appreciated that such method is not limited by the illustrated order, as some aspects could, in other embodiments, occur in different orders and/or concurrently with other aspects from that shown and described herein. Moreover, not all illustrated features may be required to implement a method. FIG. 9 depicts an example of a flow diagram illustrating an exemplary method 900 for identifying a scenario of a plurality of scenarios that is likely to lead to an undesirable outcome. In some examples, the method 900 may be executed by a tool (e.g., the tool 102, as illustrated in FIG. 1). The method may begin at 902 by receiving scenario test data representative of a plurality of different test scenarios for a system. Each test scenario may be characterized by a set of observable parameters for the system. At 904, the method may include filtering the plurality of different test scenarios to identify a sub-set of test scenarios from the plurality of different test scenarios having similar behavior characteristics. At 906, the method may include providing the sub-set of test scenarios to a trained neural network to identify one or more sub-set test scenarios. The one or more identified sub-set of test scenarios may correspond to one or more anomaly test scenarios from the sub-set of test scenarios that is most likely to lead to an undesirable outcome associated with an emergency causing event. It should be noted that the filtering of the plurality of different test scenarios to identify a sub-set of test scenarios from the plurality of different test scenarios having similar behavior characteristics to search for the one or more anomaly test scenarios from the sub-set of test scenarios that is most likely to lead to an undesirable outcome associated with an emergency causing event may require deep learning of neural networks processing massive amount of annotated data which is expensive and time consuming. Several methods including domain adaptation, differential geometry and modular networks may be utilized to simplify such time consuming tasks. FIG. 10 illustrates an overview of different techniques in topology modularization utilized in neural network data processing. A new type of architecture called “Aggregate Network” is proposed to solve a complicated task that has many learnable parameters. The Aggregate network is very similar to typical convolutional neural networks but deviates from common networks in its core ‘agents’. In fact, the Aggregate network consists of several ‘bulks’, which are composed of multiple ‘blocks’. Each block in a bulk can be considered as an agent that is specialized to perform a certain task. These tasks are often more complicated than tasks that a filter can learn. This agent-based network easily learns complicated task and breaks them down into simpler tasks. Modularization of neural network may be broken down into the following parts: (a) Domain: Extracting certain information from the input data, e.g., applying image processing technique to extract a specific part of an object; (b) Topology: The recipe to connect different modules and parts of a network to each other; (c) Formation: Primarily concerned with the method used for connecting and constructing modules; (d) Integration: The final step to fuse different modules into a cohesive system. The overall topology of a network is defined by how different nodes and modules are connected. Throughout the research on neural networks, neuroscience has been the source of inspiration for topological modularity. A subtle yet important note on modularization is the difference between topological modularity and functional modularity. Topological modularity is a necessary but not sufficient condition of functional modularity, i.e., functional specialization is only possible with having a learning algorithm present along with topological modularity. The overall topology of a network is defined by how different nodes and modules are connected (see FIGS. 11A-B, 12A-D). For instance, highly-clustered non-regular (HCNR) is a modular topology which has dense connections within its modules. A multi-architectural topology may include several different network architectures wired in certain ways to create a more complex network architecture. A repeated block topology consists of smaller blocks that compose the entire architecture by a certain repetition rule. The repeated block topology can be multi-path (multiple subnetworks, which are semi-independently connected), sequential (based on construction by composition, i.e., a series of similar blocks connected to one another compose the architecture), recursive, or modular node (similar to regular monolithic neural networks except that some single neurons are replaced with a module) as shown in FIG. 10 above. The following describes the topological modularity techniques in more details: Highly-clustered non-regular (HCNR) (see FIG. 11A): is a modular topology which has dense connections within its modules. Connections within a module are also nonregular, i.e., a repeating template can describe the topology. Although dense within modules, connections between different modules are sparse. HCNR share some properties with a viable network in neuroscience, small-world networks, where nodes are not one another's neighbors in general, but the neighbors of a given node are most likely neighbors. Properties such as short average path between two nodes and sparse connectivity reduces the computation complexity of HCNR and equipped them with short-term memory. Multi-Architectural (see FIG. 11B): A multi-architectural topology may include several different network architectures wired in certain ways to create a more complex network architecture. Multi-architectural topology is often complex and time consuming to train. However, the ensemble of various architecture improves the performance and increases the error tolerance. Repeated block (see FIGS. 12A-D): As it is also understood from the title, a repeated block topology consists of smaller blocks that compose the entire architecture by a certain repetition rule. Smaller blocks could be entirely identical or similar to some degree. There is a large body of scientific work that connects the repeated block notion to biology. One can also more intuitively decipher repeated blocks due to their structural characteristics. The most common repeated block topologies are categorized by how they are used in a network: Multi-path (see FIG. 12A): multi-path are multiple subnetworks, which are semi-independently connected (FIG. 5.5a). Each path receives and processes the input in parallel with other paths. Perhaps one of the most cited problems in computer vision is how the visual system of an animal can be translated into a network. It is believed that each type of retinal ganglion cells independently tiles the entire visual canvas. Each cell perceives a visual context through its different aperture and sensitivity to features of that stimulus. Thus, multi-path topology is in accord with biology. Parallelism in multi-path topology provides two unique characteristics that regular deep neural networks do not possess. One, extending multiple paths both in the direction of depth and width is easier that regular deep neural networks, in which later layers are dependent on the earlier layers. Second, various modes and type of input data can be fed into multi-path networks. The renowned Siamese network is often used for finding similarity between objects over time, fusing different sources of data such as depth and RGB image in semantic segmentation, etc. Multi-path topology can be integrated into other topologies as well. For instance, ResNetXt is the improved version of ResNet, which is a sequential topology. ResNetXt modules have multi-path structure. In summary, multi-path topology provides parallelism and multi-model fusion at the cost of additional hyper-parameters. Modular Node (see FIG. 12B): Modular node is very similar to regular monolithic neural networks except that some single neurons are replaced with a module. Modular nodes increase the computational capacity of a neural network but requires a careful design for each module. Block-Based Neural Network (BBNN) is an example of such topology that was originally designed for hardware configuration but later was used in others tasks, as well. Long Short-Term Memory (LSTM), which is a popular recurrent neural networks (RNN), also has a modular node. Yet another well-known network architecture that benefits from modular node structure is CapsNet [110] that attempts to overcome the limitation of CNNs by using vectors of instantiation parameters instead of nodes to represent objects. Nevertheless, such representation is pose invariant, while the use of regular CNNs only provides translation invariance. Recursive topology (see FIG. 12C): Recursive topology is mainly designed to study and process temporal input data. Building blocks are often being repeated through a nested loop. FractalNet is an example of such topology. The claim of FractalNet is that residual representation is not the reason that very deep neural networks outperform their competition but it is the path length and therefore how gradient is effectively propagated. Sequential topology is based on construction by composition, i.e., a series of similar blocks connected to one another compose the architecture. Sequential topology (see FIG. 12D): Sequential topology has a similar notion to deep networks in which concepts that are more complex are dependent on lower level concepts but instead of units, modules appear in the sequential topology. Inception and Xception are among the more famous networks with sequential topology. LSTM can also be considered as a temporal sequential topology. Perhaps the main downside of networks with sequential topology is the training part, which could be difficult. However, many deep network architectures share this disadvantage. Empirical tricks for training deep networks such as batch normalization could potentially be used for networks with sequential topology as well. Another embodiment of modular neural network architecture called Aggregate network (see FIG. 13) is disclosed as an alternate embodiment of the neural network for real-time data processing to detect anomaly scenarios. An overview of Aggregate architecture is shown in FIG. 13. The architecture may be modular with shallow depth towards to a front of the architecture. A block depth increases as the data flows to the back of the architecture. In an embodiment, the Aggregate network may be built of specialized agents (i.e., blocks) for processing micro tasks. A bulk of blocks is a unit that hosts specialized blocks, thus becoming a unit of agents specialized for processing certain macro tasks. The key operators in each block may be convolution kernels, activation functions, and batch normalization layers. Certain blocks may also include other operations such as transposed convolution kernels. An Aggregate network may be warm started with another backbone architecture, as well. Blocks may include a 3DConv with variable number of strides, filters, and kernel size depending on where in the architecture they appear. To make blocks level-set friendly, Tan h may be chosen as the activation function to produce a range of values between −1 and 1 for the normalized distance field. Prior to passing feature maps from the convolution kernel to the activation function, they are passed to a batch normalization layer. The input data, which is a set of sequential RGB images—for instance, 8 consecutive frames—may be fed to a block with 64 filters, a kernel size of (t:3; w:3; h:3), and a stride of size (t:1;w:1;h:1). The architecture has 4 bulks (1302 to 1304) in the first segment S1 and another 4 bulks (1305-1308) in the second segment S2. The first segment S1 may be responsible for learning special tasks, which will be used in the second segment S2 to reconstruct a volumetric input. The first bulk (1301) in the first segment has 16 blocks, each block has 4 filters, stride of size (t:1;w:1;h:1). The kernel size varies from one block to another in order to capture entities with various scale and size. Such design ensures scale invariancy in addition to addressing the dilemma of choosing the appropriate kernel size. A kernel size can take on any of the following sizes: [t, w, h]→[1, 3, 3], [2, 5, 5], [2, 7, 7], [2, 9, 9], [2, 11, 11]. A circular assignment scheme may be used to choose a kernel size. Thus, the 1st; 6th; 11th, and 16th blocks may have the same size kernels. Similarly, the 2nd; 7th and 12th blocks may share the same design. Following this pattern, the first bulk has 4 different style blocks ranging from smaller to large receptive field. At the end, all the filters for a bulk may be concatenated, e.g., the shape of feature maps coming out the first bulk is (T, W, H, 64). It should be noted that there are no inner connections in a bulk, and every block in a bulk shares the same input. When the data flow leaves the first bulk (1301), a maxpool layer with kernel size [2, 2, 2] and stride of size [2, 2, 2] is applied. The second bulk (1302) has a similar set of blocks but with different number of filters. In the second bulk (1302), blocks will have 16 filters each. The number of blocks may be set to 8, which results to 128 different filters coming out of the second bulk (1302). The kernel size follows the same circular assignment scheme in the previous bulk (1302). Then, the output of this bulk has the following shape: [T=2, H=2, W=2, 128]. In the second segment S2, bulks and blocks are slightly different, which may be called transpose bulk and transpose block. The first transpose bulk (1305) has 1 block and 1 transpose block. The block has 512 filters, stride [1, 1, 1], and kernel size of [2, 3, 3]. The output of block is the input of transpose block with 512 filter, kernel size of [2, 2, 2], and stride [1, 1, 1]. Similarly, the second transpose bulk (1306) includes a block and a transpose block, as well. The block has 256 filters, stride [1, 1, 1], and kernel size of [2, 3, 3]. The transpose block has 256 filter, kernel size of [2, 2, 2], and stride [2, 2, 2]. Bulks (1301-1304) in the first segment S1 are connected to their corresponding bulks (1305-1308) in the second segment S2. Skip connections transfer features extracted in the early stage to bulks deeper in the network. Such wiring attenuates flaws in the reconstruction compared to the case when no feature from earlier stages is passed along. At the last layer, the output of the last bulk (1304 or 1308) is fed to a 3DConv with Tan h activation and 1 filter with [1, 1, 1] kernel size. This will provide distance values for the objects in a sequence of images. In an aspect of deep learning, cost functions play a vital role. In the literature, cost functions have been studied from a statistical point of view, in great detail. The nature of cost functions from a geometric point of view is considered. Cost functions may induce certain geometries on the domain of data. For instance, a Kullback-Leibler (KL) divergence function may induce a flat structure on a manifold of data. This flatness, however, is never satisfied in the neural networks. Thus, a regularizer term may be added to ensure that both implicit and explicit assumptions are made during a design of cost functions won't be violated. For instance, for the KL divergence, one may use the Brouwer degree as a regularizer, which counts a number of twists and orientation of a manifold of data under a mapping function f (see FIG. 14). In another aspect of deep learning, Geometric cost functions may be implemented in the Aggregate network. Each block in the network may learn a specific micro task that is best described by a certain primitive geometry. This micro task is different from another micro task learned by a different block in the same bulk. The composition of these modular tasks and primitive geometries may create more complex tasks. For instance, the manifold of all human faces may share a specific geometry in general (the shape of a face, the location of eyes, lips, nose, etc.). However, the manifold of male faces is different from the manifold of female faces. Both manifolds are different from the manifold of baby faces. Once the manifolds of male and female faces are learned by the Aggregate network, one may generate baby faces from the aforementioned manifolds. The geometric cost function ensures that the spatial relationship between facial features is kept. As mentioned, Aggregate network may be implemented in anomaly scenarios detection. For instance, when a group of people are walking toward a stadium, while a smaller group is walking out of the stadium, it may be desirable to detect which group dominates the flow and the direction of the crowd. The walking pattern of a human in various scenarios may be learned by the Aggregate network. For example, the trajectory of the person may calculated and predicted over time. In such case, the Aggregate network is equipped with three dimensional operators. Thus, the learned trajectory is temporally consistent, i.e., both time and space information may simultaneously be used during learning and prediction. A geometric formulation of a cost function that performs classification on the manifold of all the walking patterns and trajectories may easily differentiate a direction of individuals as shown in FIG. 15. What have been described above are examples. It is, of course, not possible to describe every conceivable combination of elements, components, or methods, but one of ordinary skill in the art will recognize that many further combinations and permutations are possible. Accordingly, the disclosure is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims. Additionally, where the disclosure or claims recite “a,” “an,” “a first,” or “another” element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements. As used herein, the term “includes” means includes but not limited to, and the term “including” means including but not limited to. The term “based on” means based at least in part on. |
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claims | 1. A system for delivering and harvesting irradiation targets through a nuclear reactor, the system comprising:a loading/offloading system providing irradiation targets, wherein the loading/offloading system is outside of an access barrier of the nuclear reactor;a penetration pathway connecting the loading/offloading system to one of a plurality of instrumentation tubes extending into the nuclear reactor inside the access barrier, wherein the penetration pathway is traversable by the irradiation targets to the instrumentation tube; anda storage cask connected to the penetration pathway via the loading/offloading system, wherein the storage cask includes,an irradiation target receiving facility,a removable surface that seals the storage cask and the facility within the storage cask,a hood secured about the removable surface, wherein the hood includes a top opening with a flange, and wherein the removable surface and hood are shaped so that the removable surface forms a seal about the flange when drawn up through the hood, andan engagement hole, wherein the irradiation target receiving facility can be reached via the engagement hole only when the removable surface is drawn up through the hood and seated against the flange. 2. The system of claim 1, wherein the storage cask is connected to the loading/offloading system via a closed path. 3. The system of claim 1, further comprising:an exhaust system configured to clean and vent gas, wherein the storage cask is connected to the loading/offloading system via tubing connected to the exhaust system. 4. The system of claim 3, wherein the exhaust system includes a plurality of filters configured to remove substantially all radioactive particulate matter from a gas flowing through the exhaust system, and wherein the exhaust system is configured to flow the gas to atmospheric pressure. 5. The system of claim 3, wherein the tubing includes a powered moving structure configured to move the tubing among different destinations and to connect the tubing to the storage cask. 6. The system of claim 1, wherein the storage cask is connected to the loading/offloading system via tubing, and wherein the irradiation target receiving facility is sealed inside of and separate from the storage cask. 7. The system of claim 6, wherein the facility includes an engagement port that is self-sealing except when penetrated by the tubing. 8. The system of claim 7, wherein the engagement port includes,an opening configured to receive the tubing, anda plunger biased against the opening so as to seal the opening except when depressed by the tubing. 9. The system of claim 3, wherein the tubing includes a plurality of distinct paths, wherein a first of the distinct paths is connected to and transports irradiation targets into the facility, and wherein a second of the distinct paths is connected to and transports only gas from the facility. 10. The system of claim 9, wherein the second distinct path further exclusively connects to the exhaust system. 11. The system of claim 7, wherein the engagement hole is sized to receive and seal around the tubing, and wherein the engagement hole is at an angle that matches an angle of the engagement port in the facility such that the tubing will extend in a straight line to engage both the engagement hole and the engagement port. 12. The system of claim 1, wherein the storage cask connects to the loading/offloading system through tubing shaped to pass through the engagement hole. 13. The system of claim 12, wherein the tubing contains a depositing path for the irradiation targets to enter the cask and an exhaust path for venting waste gas from the cask, and wherein the depositing and the exhaust paths are separate tubes. 14. The system of claim 1, wherein the storage cask is outside the access barrier. 15. The system of claim 3, wherein the hood is in pneumatic communication with the exhaust system. 16. A system for delivering and harvesting irradiation targets through a nuclear reactor, the system comprising:a loading/offloading system providing irradiation targets, wherein the loading/offloading system is outside of an access barrier of the nuclear reactor;a penetration pathway connecting the loading/offloading system to one of a plurality of instrumentation tubes extending into the nuclear reactor inside the access barrier, wherein the penetration pathway is traversable by the irradiation targets to the instrumentation tube;a storage cask connected to the penetration pathway via a tubing to the loading/offloading system such that irradiation targets may be deposited in the storage casks from the instrumentation tube, wherein the storage cask includes,an irradiation target receiving facility sealed inside of and separate from the storage cask,a removable surface that seals the storage cask and the facility within the storage cask when not removed,a hood secured about the removable surface, wherein the hood includes a top opening with a flange, and wherein the removable surface and hood are shaped so that the removable surface forms a seal about the flange when drawn up through the hood, andan engagement hole, and wherein the facility can be reached via the engagement hole only when the removable surface is drawn up through the hood and seated against the flange; andan exhaust system configured to clean and vent gas, wherein the tubing is connected to the exhaust system. 17. The system of claim 16, wherein the exhaust system includes a plurality of filters configured to remove substantially all radioactive particulate matter from a gas flowing through the exhaust system, and wherein the exhaust system is configured to flow the gas to atmospheric pressure. 18. The system of claim 16, wherein the tubing includes a powered moving structure configured to move the tubing among different destinations and to connect the tubing to the storage cask. 19. The system of claim 16, wherein the irradiation target receiving facility includes an engagement port that is self-sealing except when penetrated by the tubing. 20. The system of claim 19, wherein the engagement port includes,an opening configured to receive the tubing, anda plunger biased against the opening so as to seal the opening except when depressed by the tubing. |
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052727432 | description | DETAILED DESCRIPTION OF THE INVENTION FIGS. 1 and 2 depict an inner key member for use in insertion and removal of fuel rods in accordance with an embodiment of the present invention. The key member, generally designated by 1, comprises an elongated key body 2 having a pair of opposite side faces and having a plurality of first projections 3 and a plurality of second projections 4 formed alternately on the opposite side faces in staggered relation to one another. Each first projection 3 is of a trapezoidal shape having an inclined surface 3a directing toward the proximal end of the key body 2, and is adapted to be held in engagement with the peripheral end around an opening 5a formed in each inner strap 5. Each second projection 4 has inclined surfaces 4a and 4b facing the proximal and distal ends thereof, respectively, and is adapted to deflect a spring 5b in a direction away from a dimple 5c opposing thereto when the key member 1 is inserted through the opening 5 into the grid cells of the grid and is operated in a manner as will be described later. In conjunction with the disassembling of a nuclear fuel assembly, the method of insertion and removal of the fuel rods using the aforesaid key member will now be described. First, a nuclear fuel assembly 10 as illustrated in FIG. 8 is horizontally placed on an assembly base which may be the same one as that used during the assembling operation or may be another similar base. The nuclear fuel assembly 10 placed on the assembly base includes a pair of top and bottom nozzles 11 and 12 spaced apart from each other, and a plurality of, e.g., nine grids G1, G2, G3-G9 arranged between the top and bottom nozzles 11 and 12 in a spaced relation to each other. Each of the grids G1 to G9 includes a plurality of inner straps 5 intersecting generally perpendicular to each other to define a plurality of grid cells therein and a plurality of outer straps 6 intersecting perpendicular to each other and covering the inner straps 5 to complete outermost grid cells defined by the inner straps. Provided on the strap walls defining a respective grid cell are opposed pairs of dimple 5c and spring 5b which cooperate with each other to constrict the fuel rod 15 therein. In each of the grids G1 to G9, an opening 5a is formed at each of the intersections of the inner straps 5 for enabling the insertion of the inner key member 1, whereas openings 16 are also formed in the outer straps 6 for enabling the insertion of the key members therethrough. A plurality of control-rod guide pipes 13 are inserted through the grid cells of the grids G1-G9, and are secured at their one ends to the grid G1 through inserts or sleeves I and at the other ends to the bottom nozzle 12. In addition, a plurality of measuring instrument pipes 14 are inserted through the grid cells disposed at the central portion of the grids, and are secured at their one ends to the grid G1 through the inserts I and at the other ends to the bottom nozzle 12. Specifically, each of the control rod-guide pipes 13 and the instrumentation pipes 14 is provided with a bulged or enlarged portion, and is secured to each of the grids G2 to G9 with the bulged portion being fixed to the grid through a sleeve S1 or S2. In each of the control rod-guide pipes 13, that portion between the top nozzle 11 and a position displaced a predetermined distance from the grid G3 toward the bottom nozzle 12, as well as those upper and lower portion (left and right portions in FIG. 8) sandwiching the grid G2, are formed into larger-diameter portions 13a, whereas the remaining portions are formed into a smaller-diameter portions 13b. Furthermore, a plurality of fuel rods 15 are inserted through the grid cells of the grids and held by the grids by being urged by the springs formed on the straps of the grids G1 to G9 towards the dimples opposing thereto. The nuclear fuel assembly 10 thus constructed is secured on the assembly support in a horizontal manner, and the top nozzle 11 is removed from the control-rod guide pipes 13 and the measuring instrument pipes 14. Subsequently, a cutter 20 or a cutting device is secured on a support (not shown) which is arranged adjacent to the top nozzle 11 disposed on the aforesaid base. As depicted in FIG. 9, the cutter 20 includes an elongated outer tube 20a; a pushing rod 20b inserted through the outer tube 20a for sliding movement therealong; a spring-accommodating tube 20c threaded on the forward end of the outer tube 20a and having an end plate; a spring-retaining member 20d of a rod-like shape disposed in the spring-accommodating tube 20c for sliding movement therealong and having an enlarged portion at a side adjacent to the outer tube 20a; and a coil spring 20e disposed around the spring-retaining member 20d so as to act between the end plate of the spring-accommodating tube 20c and the enlarged portion of the spring-retaining member 20d to urge the retaining member 20d away from the end plate. A tubular guide member 20f, which has an elongated aperture 20i formed therein so as to extend longitudinally thereof, is threaded on the forward end of the spring-accommodating tube 20c. In addition, a pushing member 20g, which is provided with a radially outwardly protruding member 20h threaded thereon, is threaded on the forward end of the spring-retaining member 20d, and is accommodated in the tubular guide member 20f for sliding movement therealong with the protruding member 20d being engaged with the elongated aperture 20i. Furthermore, a cutter blade 20j is accommodated in the tubular guide member 20f for rotation about a shaft 20k which is journaled on the guide member 20f so as to extend transversely thereof. The pushing member 20g has an inclined face 201 formed at its forward portion, and is adapted to engage with the rearward end of the cutter blade 20j. In operation, the pushing rod 20b is forwarded, the inclined face 201 of the pushing member 20g is brought into engagement with the cutter blade 20j to bring the cutting edge portion of the cutter blade into engagement with the inner peripheral surface of the control rod-guide pipe 13 or the measuring instrument pipe 14, and the outer tube 20a and hence the spring-accommodating tube 20c and the guide member 20f are rotated circumferentially to turn the cutter blade along the inner peripheral surface of the control rod-guide pipe 13 or the measuring instrument pipe 14, whereby the control rod-guide pipe 13 or the measuring instrument pipe 14 is cut by the blade in its circumferential direction. In the cutting operation of the control rod-guide pipe 13 or the instrument pipe 14 by means of the cutter 20, the cutter 20 is inserted into the control rod-guide pipe 13 or the instrumentation pipe 14 from the upper end thereof (from the left end in FIG. 8), and that portion of the pipe which is located at a position slightly displaced from the opening 16 of the grid G1 toward the bottom nozzle 12 is first cut. Thereafter, the cutting is successively carried out at a respective position displaced slightly from the opening 16 of each of the grids G2 to G9 toward the top nozzle 11. In the foregoing, different kinds of the guide member 20f are prepared in advance so as to be used for pipes of different diameters. Specifically, in the cutting of the smaller diameter portions 13b of the control rod-guide pipes 13, a guide member 20f of a smaller diameter is mounted on the cutter, whereas in the cutting of the larger diameter portions 13a of the control rod-guide pipes 13 and the instrumentation pipe 14, a guide member of a larger diameter is used. Thus, after each of the control rod-guide pipes 13 or each of the measuring instrument pipes 14 is cut into a plurality of cut pipes A1 to A8 or B1 to B8, the inner peripheral surfaces of the cut pipes are examined with an endoscope to confirm that the cutting is properly carried out, following which the cutter 20 is removed from the base. Subsequently, a bulging apparatus, not shown, is secured on the base, and the cut pipes are subjected to bulging operations, in the order of from A1 to A8 B1 to B8), thereby reducing the longitudinal length of each cut pipe. As a result, the cut pipes A1 to A8 and B1 to B8 are deformed away from the openings 16 for inserting the key members. Thereafter, outer key members for deflecting the springs on the outer straps 6 and the inner key members 1 for deflecting the springs on the inner straps 5 are detachably attached to the outer straps 6 and the inner straps 5. In operation, the inner key member 1 is inserted through the opening 16 into a respective one of the openings 5a (see FIG. 3). Then, the inner key member 1 is turned 90 degrees about its longitudinal axis (see FIG. 4), and is caused to move forwardly (see FIG. 5). With this movement, the inclined surface 3a of each first protrusion 3 formed on the one side of the inner key member 1 is guided by the peripheral end of the opening 5a, and the first protrusion 3 is brought into engagement therewith, whereas the inclined surface 4a of the second protrusion 4 is brought into abutment with the spring 5b to be urged thereagainst, and finally the protruding surface of the second protrusion 4 is brought into abutment with the spring 5b to deflect the spring 5b in a direction away from the dimple 5c opposing thereto. The above operation is repeatedly carried out to insert a great number of inner key members 1 into the grids G1 to G9 (see FIGS. 6 and 7), and hence the springs 5b on the inner straps 5 can be reliably deflected without damaging the fuel rods 15. Furthermore, in order to confirm that the fuel rods 15 may be removed easily from each of the grids G1 to G9, a force to hold the fuel rod, i.e., force to draw out the fuel rod, is measured, and then the bulging apparatus is removed from the base, following which the bottom nozzle 12 is removed. Subsequently, after drawing the fuel rods 15 out of the grids G1 to G9 using a pull-in device (not shown), the inspection of the thus drawn fuel rods 15 is commenced. In the foregoing, in conjunction with the method for drawing out the fuel rods, there is disclosed a method which comprises, prior to the removal of the fuel rods from the grid cells of the grids, cutting the prescribed portions of the control-rod guide pipes and the measuring instrument pipes, and shortening the pipes by enlarging them to thereby ensure the spacings for the insertion of the key members. This method may be modified as follows. More specifically, a cutter 40 modified from the aforesaid cutter 20 is prepared. The modified cutter 40 is similar to the cutter 20 in that it includes the outer tube 20a; the pushing rod 20b inserted through the outer tube 20a for sliding movement therealong; the spring-accommodating tube 20c threaded on the forward end of the outer tube 20a; the spring retaining member 20d disposed in the spring-accommodating tube 20c for sliding movement therealong; the spring 20e acting between the spring-accommodating tube 20c and the retaining member 20d to urge the retaining member 20d away from the end plate of the spring-accommodating tube 20c; the guide member 20f detachably threaded on the spring-accommodating tube 20c; and the pushing member 20g with the protruding member 20h secured to the spring-retaining member 20d. However, a pair of cutter blades 20p and 20p, each of which has a cutting edge portion at its forward end and an inclined surface 20m at its rearward end, are secured to the guide member 20f for rotation about the common shaft 20k which is journaled on the guide member 20f. In addition, the pushing member 20g includes a pair of inclined faces 20q and 20q sloping so as to approach each other in a forward direction, and the cutter blades 20p are arranged so that the cutting edge portions as well as the inclined surfaces 20m are directed in different directions, whereby the inclined faces 20q of the pushing member 20g are adapted to be in engagement with the inclined surfaces 20m, respectively. Thus, in the modified cutter 40, when the pushing rod 20b is forwarded, the inclined faces 20q of the pushing member 20g are brought into pressing engagement with the inclined surfaces 20m of the cutter blades 20j, thereby bringing the forward cutting edge portions of both of the cutter blades 20j into engagement with the inner peripheral surface of the control rod-guide pipe 13 or the measuring instrument pipe 14. Then, the outer tube 20a, and hence the spring accommodating tube 20c and the guiding portion 20f, are caused to move backward in a longitudinal direction of the pipe to thereby form an opposed pair of slits 41 in the pipe. In the formation of slits 41 in the bulged portion 42 of each of the control rod-guide pipes 13 and the instrument pipes 14, the cutting operation is repeated twice to provide circumferentially equally distributed four slots in each pipe (see FIG. 12). Furthermore, each slit 41 is formed such that when the bulged portion 42 is pressed into a smaller diameter, the width of the slit 41 becomes smaller than the inner diameter of the sleeve S1 or S2. Thus, the slits are formed in the bulged portion of each of the control rod-guide pipes 13 and the instrument pipes 14, and then the control rod-guide pipes 13 and the instrument pipes 14 are removed from the grids by just pulling them out. Thereafter, the same procedures as mentioned above are repeated. As described above, since the key member in accordance with the present invention includes a plurality of first projections adapted to be held in engagement with the opening of the strap and a plurality of second projections adapted to be held in engagement with the spring to deflect the spring away from the dimple facing thereto, the key member can be employed to release the constrictive engagement of the fuel rods with the springs and dimples. Therefore, sufficient cell space required for the assembling and/or disassembling of the nuclear fuel assembly can be ensured without using a special device such as a spring-deflecting jig of an expander type. Furthermore, inasmuch as the aforesaid key member can be employed in both for insertion and removal of fuel rods, the insertion and removal of fuel rods, or the disassembling or assembling of the nuclear fuel assembly can be effected very efficiently without damaging the fuel rods. |
summary | ||
description | This invention was made with Government support under Grant No. DE-FG02-03ER83658 awarded by the Department of Energy. The Government has certain rights in this invention. The present invention relates generally to electrically resonant cavities, and in particular to resonant cavities of the type used in electron beam and other charged particle accelerators. The invention described and claimed herein has application to accelerators used to produce charged particle beams, primarily electron beam accelerators. While the present invention is described herein primarily with reference to electron beam accelerators, the invention also has application to accelerators designed to produce beams of protons or other charged particles. All of the references cited herein are hereby incorporated by reference. In most charged particle accelerators there is a need to determine the size, position, cross-sectional shape, and other characteristics of the beam of charged particles produced by the accelerator, usually at various points along the path of the beam as it is accelerated along an evacuated beam tube. Such a determination is necessary in order to enable appropriate adjustments to be made to the structures and operating parameters of the accelerator, for the purpose of optimizing the size, shape, position and other characteristics of the beam. Since the particles constituting the beam are electrically charged, they interact with an electrically resonant cavity interposed along the beam path. This interaction provides the basis for accelerating the particles, by applying a radio frequency signal to the cavity from an external source. In this regard, a particle beam accelerator will typically have a substantial number of resonant cavities, up to hundreds or thousands, positioned in sequence along the beam path. The purpose and function of each such cavity is to accelerate the particles as they pass through the cavity. At each stage additional energy is imparted to the charged particles, to the extent that in an electron beam accelerator the electrons are typically accelerated to a velocity that is a substantial fraction of the speed of light. Acceleration is not the only use of resonant cavities in a particle accelerator. The interaction between the charged particles and any resonant cavity through which they pass also provides a basis for using a resonant cavity as a diagnostic tool, for determining the size, shape and other characteristics of the beam as it passes along the beam line; and it is to this purpose that the present invention is directed. An electrically conductive structure acts as a resonator, or oscillator, when it has appropriate capacitative and inductive elements electrically connected in series in a loop. A simple oscillator can consist of an inductor and a capacitor connected to one another so as to form closed electrical loop. Resonance of such a circuit consists of alternating accumulations of an electric field in the capacitor and a magnetic field in the inductor. The frequency at which such an oscillator resonates is determined by the inductance (L) of the inductor and the capacitance (C) of the capacitor. Such a circuit is known as an LC network and its resonant frequency is given by the formula: f = 1 2 π LC A conductive structure as simple as a hollow tube that is closed at both ends can act as a resonant oscillator, and such an oscillator is known as a resonant cavity. In the ideal case of a cylindrical tube closed at both ends by parallel end plates, the spaced apart, parallel end plates act as a capacitor and the cylindrical wall of the tube acts as a single-turn inductor. In such a structure the periodic accumulation, discharge, and reversal of an axially extending electrical field, which extends between the capacitative end plates, alternates 90 degrees out of phase with the accumulation, discharge and reversal of a circular magnetic field that is centered on and extends along a circular path around the axis of the cylindrical tube, and which is largely contained within the cylindrical walls of the tube. The full cycle of the reversing electrical and magnetic fields repeats at the resonant frequency of the cavity. Electrical energy can be introduced into such a cavity in the form of an RF signal transmitted into the cavity through a waveguide, to thereby maintain the cavity in a continuously resonant mode by overcoming ordinary losses due to power dissipation in the LC circuit. In a charged particle accelerator, beams of charged particles, typically electrons or protons, are formed and are accelerated along a beam path. As noted above, resonant cavities are used to accelerate the particles in such beams. In such accelerators an evacuated beam tube defines a beam line that extends axially through multiple, spaced resonant cavities that are positioned along the beam line. The charged particles are accelerated in bunches as they pass through the successive resonant cavities. Each cavity must be appropriately positioned along the beam path and its interaction with the charged particles must be appropriately timed and otherwise optimized in several respects to achieve effective acceleration of the charged particles. In particular, at each cavity the periodic formation of the electrical field must be properly phased and timed so that both its direction and its maximum strength coincide with the arrival of a bunch of charged particles at the center of the cavity. Further, the axial length of the particle bunch must be short compared with the wavelength of the RF signal used to excite the cavity. Finally, the axial length of the cavity in the direction of the beam must be sufficiently short that the electrical field extends in the same direction during the entire time required for the particle bunch to pass through the cavity. A continuing challenge in the design and operation of particle accelerators is the determination of the precise characteristics of the particle beam at various points along the beam path. Such characteristics as the beam current, the cross-sectional shape of the beam, and the position of the beam relative to the axis of the beam tube are all affected by multiple factors related to the physical characteristics of the particle source and the beam line, including its accelerating cavities, as well as the operating parameters of the accelerator. The ability to accurately and precisely diagnose the characteristics of the particle beam at various points is necessary in order to make the operating adjustments that are in turn required to optimize the quality of the beam. For this purpose, diagnostic resonant cavities may be interposed in the beam line at various points. Diagnostic cavities resonate in a manner similar to the resonance of the accelerating cavities. However, in the case of a diagnostic cavity the charged particle beam passing through the cavity generates a signal which can be transmitted out of the cavity through an appropriate waveguide. The nature and strength of this signal depend on the intensity, shape and position of the particle beam and thus can be used for diagnostic purposes. Various techniques have been used to monitor the characteristics of a particle beam. See for example J. Ross et al., “Very High Resolution RF Cavity BPM” (beam position monitor), Proceedings of the 2003 Particle Accelerator Conference, p. 2545. A cavity intended as a beam position monitor is characterized by a voltage pattern which is, for example, positive in one side of the cavity and negative in the opposite side of the cavity. Such a cavity is useful for measuring the average displacement of the particle beam to one side of the cavity or the other. As another example, a method of measuring the quadrupole moment of a beam with stripline beam position monitors for the purpose of determining the beam emittance was developed by Miller et al. (R. H. Miller, J. E. Clendenin, M. B. James, J. C. Sheppard, Proc. 12th Int. Conf. On High Energy Acc. (Fermilab, Batavia, 1983), SLAC-PUB-3186). In a related method, Whittim and Kolomensky disclosed the concept of using a resonant cavity to measure the beam dipole, quadrupole and higher moments. (D. H. Whittum and Y. K Kolomensky, Rev. Sci. Instr. 70 (1999), p 2300.) The idea of using a resonant cavity to measure the beam quadrupole moment was further developed by Kim et al. (J. S. Kim, C. D. Nantista, R. H. Miller, A. W. Weidemann, “A Resonant Cavity Approach to Non-Invasive Pulse-to-Pulse Emittance Measurement,” submitted to Rev. Sci. Instr.) The use of a cavity mode to measure the beam quadrupole moment has a much better signal to noise ratio than either the stripline or button pickup techniques, and can be used to measure much smaller beam features. In a quadrupole mode, the cavity is split into four quadrants, such that the cavity voltage alternates between positive and negative between adjacent quadrants and the cavity voltage is proportional to x2−y2. The quadrupole-mode cavity measures <x2−y2>=σx2−σy2+<x>2−<y>2, where the angle brackets (< >) indicate an average over the particle beam population. Nearby dipole cavities measuring <x> and <y> can be used to subtract the two rightmost terms from this expression in order to give a measurement of σx2−σy2, where σx and σy are the root mean square beam widths in the x and y directions, respectively. In the absence of beam coupling between the x and y phase spaces, an emittance measurement can be performed by measuring the quadrupole moment at six locations along the beamline interspersed along the beamline focusing elements. Also, another cavity can be tilted by 45 degrees to measure <xy>, which can be used to diagnose and correct coupling between the x and y beam dimensions. Quadrupole-mode beam position monitor cavities typically generate a much weaker signal than dipole-mode beam position monitor cavities. In order to make accurate measurements of low-emittance, high-energy beams, the measurement cavity should be optimized as much as possible. One way to improve measurement sensitivity is to use a multi-cell standing-wave cavity, for example a 9-cell structure as disclosed by J. S. Kim et al. (J. S. Kim, R. H. Miller, C. D. Nantista, “Design of a Standing-Wave Multi-Cavity Beam-Monitor for Simultaneous Beam Position and Emittance Measurement,” Rev. Sci. Instr. 76, 1 (2005)). In the disclosure of Kim et al., the shunt impedance as a function of beam offsets x and y is approximately R≃800 (x2−y2)2 Ω, where x and y are in units of millimeters. We define the shunt impedance as R=V2/P, where V is the voltage gained by a relativistic particle crossing a cavity containing a reference mode, and P is the power dissipated in the cavity walls. For a high-current train of pulses such as is expected to be used in future collider designs, such a diagnostic can adequately resolve the quadrupole moment of a beam with σx=1 μm, and σy<<σx. In order to make an accurate measurement in this case, the beam should be relatively close to the cavity axis, within a few microns. Multi-cell structures are, however, more difficult to fabricate and tune. In order to obtain adequate shunt impedance for the mode, the structure is typically designed to operate in the π-mode. However, improper cell-to-cell transverse alignment can couple power to all modes in the quadrupole band, with phase advance ranging from 0 to π. (N. Barov, J. S. Kim, A. W. Weidemann, R. H. Miller, C. D. Nantista, “High-Precision Resonant Cavity Beam Position, Emittance and Third-Moment Monitors,” Proc. of the 2005 Particle Accelerator Conference.) This power must eventually be filtered out, which is more difficult in the case of small inter-mode spacing. A resonant cavity incorporating two conductive rods extending into the cavity has been disclosed as having an approximately 100-fold increase in shunt impedance and has been suggested as being useful primarily as a beam deflector, and incidentally as a potential dipole-mode beam position monitor. (C. Leemann and C. G. Yao, “A Highly Effective Deflecting Structure,” Proceedings of the 1990 Linac conference, p. 232.) However, beam deflection in any particular direction requires only a dipole-mode structure, and thus there is no suggestion in the disclosure of Leemann and Yao of applications of more complex cavities based on higher-order resonant modes. Moreover, when the cavity of Leeman and Yao is optimized to function as a high-frequency (>5 GHz) diagnostic cavity with a reasonably large beam tube diameter, the effect of the rods is greatly diminished. For example, an 8.6 GHz cavity with a 1 cm diameter beam tube and the two rods of Leeman and Yao produces only approximately 40% more output power than a comparable cavity without the rods. Consequently beam position monitors based on resonant cavities and designed for electron accelerators operating at higher frequencies have consisted of simple resonant cavities without the two conductive rods suggested by Leeman. In this regard, many electron accelerators operate with very short electron bunches, on the order of 10 picoseconds or less. In order to maximize the cavity output signal of such an accelerator, the diagnostic cavity frequency should be as high as possible, yet while also maintaining the condition that the cavity field should not change appreciably during the time period of the electron bunch. This favors a cavity frequency of at least 5 GHz. For these reasons the two-rod cavity design of Leeman and Yao has not found acceptance as a beam position monitor, and there is nothing in the Leeman and Yao disclosure to suggest that increasing the number of rods would improve the performance of the cavity as a diagnostic cavity. Accordingly, it is the object and purpose of the present invention to provide a resonant cavity that is useful for measuring and diagnosing the characteristics of a charged particle beam produced in a charged particle accelerator. More particularly, it is the object and purpose to provide an improved apparatus and method for measuring the cross-sectional shape and dimensions of a charged particle beam. The present invention provides a diagnostic resonant cavity for use in determining characteristics of a charged particle beam traveling along a beam line of a charged particle accelerator. The cavity includes two electrically conductive, opposing end walls that are spaced apart from one another by an electrically conductive tubular wall. The walls have centered openings for interposition of the cavity in the beam line of an accelerator by connection to a beam tube, wherein the longitudinal axis of the beam tube defines the nominal path of travel of the charged particle beam. The cavity further includes an even plurality of at least four pairs of electrically conductive rods extending inwardly into the cavity from the end walls, with each pair of rods consisting of two rods that extend inwardly and coaxially toward one another from the two opposing end walls, in a direction parallel to the axis of the beam tube. The rods of each pair of rods are spaced from one another so as to form a capacitative gap between one another. The pairs of rods are equally spaced azimuthally in a symmetrical array around the central longitudinal axis of the beam tube. The rods effectively increase the shunt impedance of the cavity and thus increase the strength of a resonance signal emitted from the cavity upon passage of a particle beam through the cavity. Increased signal strength enables increasingly accurate determinations of the shape of the particle beam passing through the cavity. Cavities having higher order resonant modes, for example, a cavity based on a sextupole mode and utilizing six pairs of spaced rods, are also useful for attaining more detailed information on the cross-sectional shape of the beam passing through the cavity. In another embodiment of the invention, the cavity includes an even plurality of at least four rods which extend from only one end wall of the cavity, for a length greater than the major fraction of the length of the cavity, and which are equally spaced azimuthally in a symmetrical array around the central longitudinal axis of the beam tube. These and other aspects of the invention will be more apparent upon consideration of the accompanying drawings, taken with the following detailed description of preferred embodiments. The drawings constitute part of this specification and are best understood with reference to the following detailed description of the invention. The term “resonant cavity” is used herein to mean a hollow electrically resonant structure that defines an interior volume through which a charged particle beam may be passed. The electrons in high-energy research electron accelerators travel at nearly the speed of light and are bunched in time so that the bunch duration is only a small fraction of the period of one oscillation of the resonant cavities through which the electrons pass. The electron beam may be made up of many such bunches spaced at a regular time interval, or it may consist of a single bunch of electrons. As noted above, the electric and magnetic fields within a resonant cavity oscillate at frequencies that are determined by the capacitance and inductance of the cavity. A resonant cavity typically has many harmonic resonances, or modes, each of which must be considered separately. A mode is characterized by the voltage it can impart to a charged particle traveling generally parallel to the beam tube axis but offset by some distance from the beam tube axis. That voltage will be distributed over the cross sectional area of the cavity in a pattern that is a function of the transverse coordinates perpendicular to the beam direction. If the pattern is a dipole, with for example a positive voltage in the left half of the cavity and a negative voltage in the right half, it can be used to diagnose an offset of the beam position from one side of the cavity to the other. If a greater portion of the beam overlaps with the voltage pattern of the positive region than that of the negative region, there is a net positive interaction and power is deposited into the cavity. If there is a net negative interaction, power will be deposited with the opposite phase. A single electron bunch passing through a cavity with no resonating RF field will deposit energy in several modes according to the overlap with the voltage profile of each mode. This energy can be coupled out of the cavity into an external circuit by means of a conventional waveguide connected to the cavity. Only some of the modes, typically one or two of them, will be required for making the measurement, and the remaining modes may be suppressed. This can be done with a well-known combination of coupler design and filtering. Diagnostic cavities can be used in either a single bunch or a bunch train mode of accelerator operation. In single bunch operation the cavity is initially free of microwave energy, and interaction between the electron bunch and the cavity deposits a particular amount of energy into the cavity, which can then be measured. In bunch train operation, a series of bunches passes through the cavity, such that the bunch repetition frequency is a subharmonic of the cavity frequency and microwave energy is resonantly accumulated in the cavity. In bunch train operation the power coupled out of the cavity is proportional to the shunt impedance R of the cavity, and this parameter serves as the figure of merit in bunch train operation. In single bunch operation, the detected microwave signal is generally proportional to R/Q, where Q is known as a quality factor and is defined as the ratio of the energy stored in the cavity to the average energy dissipated in the cavity during one radian (approximately 57 degrees) of cavity oscillation. In single bunch operation there is the concern that too low a value of Q can diminish the efficiency with which the deposited energy is coupled to the waveguide. FIGS. 1 through 3 illustrate a preferred embodiment of a quadrupole resonant cavity 10 constructed in accordance with the present invention. The cavity 10 is interposed in a beam tube 12 having a diameter of approximately 1.0 cm and a resonant frequency of 11.424 GHz. The cavity 10 has parallel end walls 14 and 16 which are connected by a cylindrical outer wall 18. The axis of the beam tube 12 is centered on the end walls 14 and 16 and is coaxial with the axis of the cylindrical cavity wall 18. The cavity 10 includes four solid metallic rods 20, 22, 24 and 26, which extend inwardly from end wall 14, and four identical rods 28, 30, 32 and 34, which extend inwardly from end wall 16 in opposition to rods 20–26. Rods 20–26 and 28–34 are coaxial with one another, respectively, and are spaced apart to form a capacitative gap between them. In the illustrated embodiment the diameter of the cylindrical cavity wall 18 is approximately 3 centimeters and the spacing between the end walls 14 and 16 is approximately 1 centimeter. The rods 20 through 34 are approximately 3 millimeters in length and approximately 2 to 3 millimeters in diameter. They are preferably positioned as illustrated so as to be tangential to the beam tube 12. The four pairs of rods 20–26 and 28–34 are positioned azimuthally equidistantly around the beam tube 12 and form capacitative gaps which are aligned with the areas of highest voltage magnitude in the quadrupole pattern. The cavity shunt impedance R of a cavity such as that shown in FIGS. 1 through 3 is optimized by selecting the length and diameter of the rods 20 through 34, along with the length and diameter of the cylindrical wall 18 of the cavity 10. Although a cavity having a cylindrical outer wall 18 is illustrated, the outer wall may have a square, octagonal, or any other tubular cross section. The cross sectional shape of the outer wall has an influence on the frequencies of the remaining cavity modes. The optimum rod length for the cavity 10 illustrated in FIGS. 1 through 3 has been determined by numerical modeling of the field conditions within the cavity 10. For different rod lengths, the cavity outer wall 18 is adjusted so that the quadrupole mode resonant frequency is maintained at 11.424 GHz. As FIG. 4 indicates, the shunt impedance R rises quickly as a function of the rod length until the rod length reaches approximately 3.2 mm, and then rapidly diminishes at greater rod lengths. Rod lengths greater than approximately 3.2 mm correspond to cavity geometries where the diameter of the outer wall 18 is too small, i.e., less than approximately 1.26 cm. The maximum shunt impedance for an embodiment as shown in FIGS. 1 through 3 is approximately 5.3 times larger, and the maximum R/Q value is approximately 11.5 times larger, that of a bare cavity having the same resonant frequency, but not having the rods 20 through 34. The effect of rod diameter on shunt impedance of the cavity has also been determined by numerical modeling, and is illustrated in FIG. 5. For each of the several diameters listed in FIG. 5, the optimum shunt impedance R occurs at a different value of the rod length. The outer wall diameter of each cavity configuration was again adjusted to reach the target 11.424 GHz resonance frequency. Although the 2 mm diameter rods outperform the 3 mm rods in terms of enhanced shunt impedance by about 5%, the larger diameter 3 mm rods are preferred because of greater ease of fabrication. The shunt impedance R can be further optimized by adjusting the cavity length, as measured by the length of the cylindrical wall 18. The shunt impedance R at each value of cavity length is optimum near the same value of the cavity outer radius of wall 18, so simulations were performed at a fixed outer radius of 1.77 cm and the cavity frequency was corrected by altering the length of the rods. By this technique the optimum length of the cavity is determined to be approximately 1.1 cm. The primary effect of the rods of the embodiment shown in FIGS. 1 through 3 is to increase the shunt impedance R and thereby increase the strength of the output signal. However an unintended consequence of the rods is to concentrate the electric field locally so that it deviates from a pure quadrupole pattern. For a beam greater than about 1 mm in radius, this has the undesirable consequence that the resulting output signal represents a combination of the beam quadrupole moment as well as the dodecapole, or 12-pole moment, of the beam. However, so long as the beam confined within a 1 mm radius, which is usually the case, these undesirable higher order moments are negligible. The performance of a quadrupole-mode cavity is partly determined by the spacing between the desired mode, and the remaining cavity modes. Analysis of a rectangular pillbox cavity by Kim et al. indicates that a combination of TM310 and TM130 modes can couple on-axis. (J. S. Kim, C. D. Nantista, R. H. Miller, A. W. Weidemann, “A Resonant Cavity Approach to Non-Invasive Pulse-to-Pulse Emittance Measurement.” submitted to Rev. Sci. Instr.) These modes tend to be close in frequency at 12.6 GHz and 13.4 GHz, and the tail of the frequency distribution can extend to 11.424 and thus limit resolution. For a cavity 10 as illustrated, the fundamental mode is at 5.6 GHz, and the dipole modes are at 8.7 GHz. A TE-like mode appears at 13.8 GHz, but will not couple for a beam propagating parallel to the cavity axis. The orthogonal quadrupole mode with electric field maxima rotated 45 degrees from the posts is at 14.2 GHz. With slightly larger rods and smaller cavity outer radius, this mode can easily be made to resonate at >18 GHz if needed. The mode which corresponds to a TM200 mode in a cylindrical cavity occurs at 15 GHz. The frequency of this mode can also be increased, if needed. The signal generated by interaction of a particle beam with the resonant field in the cavity 10 can be transmitted out of the cavity 10 through a conventional waveguide assembly, which is well known and is not further described here. The optimization of shunt impedance and R/Q has been determined as a function of several cavity parameters, but with a fixed beam tube radius. Some further optimization may be possible by rounding both inside and outside corners of the cavity, canting the end faces of the rods, and optimizing the cross-sectional shape of the rods. In the case of a quadrupole cavity with four gaps, errors in rod length and placement can result in frequency shift and mode translation, as well as a baseline (monopole-like) shift in the mode pattern. The mode sensitivity to cavity geometry is also subject to fabrication variations. As noted above, a cavity geometry similar that disclosed in FIGS. 1 through 3, but with only two pairs of rods, was suggested by Leemann and Yao for the purpose of using a 500 MHz dipole mode cavity as a beam deflector. The geometry of the Leeman and Yao structure essentially consists of putting two quarter-wave resonators side-by side. Such a cavity design has an approximately 100-fold increase in shunt impedance. The disclosure of Leeman and Yao suggests that such a design can also be used for the purpose of making a beam position monitor cavity. However, when such a design is applied to a high-frequency (>8 GHz) beam position monitor cavity with a sufficiently large beam pipe (>1 cm), the 100-fold improvement in shunt impedance observed at lower frequencies diminishes almost entirely, to around 40%. FIGS. 6 through 8 disclose a second preferred embodiment of the invention. As in the embodiment described above, a resonant cavity 40 is interposed in a beam tube 42 and includes end walls 44 and 46 connected by cylindrical wall 48. However this embodiment includes six identical rods 50 which extend inwardly from end wall 44, and six opposing rods 52 which extend inwardly from end wall 46. As in the previous embodiment, the rods 50 and 52 are positioned tangentially to the beam tube 42 and are equally spaced azimuthally around the beam tube 42. The six sets of opposing, spaced rods 50 and 52 form a sextupole resonant cavity. A sextupole mode enables detection of an asymmetric component of the beam distribution. One application of such an embodiment is to detect the presence of a beam tail, for providing an early warning of beam breakup due to short-range wakes in a linear accelerator. The embodiment of FIGS. 6 through 8 consists of a cavity geometry with a 1.0 cm cavity length, a 1.7 cm outer radius and rods each having a diameter of 3 mm and a length of 3 mm, spaced at 60 degree intervals around the cavity and positioned tangentially to the beam tube having a radius of 5 mm. The resonant frequency of this cavity is 14.28 GHz. The shunt impedance near the axis is given by:R(x,y)=11.15(x3−3xy2)2 Ωwhere distances x and y are measured in mm. For the purpose of comparing to a similar cavity with no rods, comparison can be made to a standing-wave cavity operating in the 3 π/4-mode. With a cavity length of 11 mm, longitudinal centers spaced 13.1 mm apart, and a beam pipe tube with a diameter of 1 cm, the combined shunt impedance for two cells (one active and one inactive) is determined to be 0.45 Ω at a 1 mm offset. By comparison, the shunt impedance for the same cavity but with the six rods is approximately 25 times larger, and the R/Q ratio is approximately 70 times larger. These enhancements are significant and can be combined with the use of multiple cavities and further optimization of the beam tube radius. Such measures can partially overcome the inherently lower sensitivity of a sextupole mode cavity. The cavity geometries described above offer improved shunt impedance for the measurement of beam quadrupole, sextupole, and higher order moments. These geometries also have advantages in that the remaining cavity modes can be spaced further apart from the mode of interest. FIGS. 9 and 10 illustrate another preferred embodiment of the invention. A resonant cavity 60 having end walls 62 and 64 connected by a cylindrical wall 66 is interposed in a beam tube 68. Four elongated rods 70, 72, 74 and 76 extend inwardly from end wall 62 for a distance greater than the major length of the cavity 60, as measured by the distance between end walls 62 and 64, but less than the length of the cavity 60, so as to provide a capacitative gap between the exposed ends of the rods 70 through 76 and the end wall 64. In the preferred embodiment the length of the rods 70–76 is approximately 90 percent of the length of the cavity 60. As with the previous embodiments, the rods 70 through 76 are positioned tangentially to the beam tube 68 and are spaced equidistantly around the beam tube 68. Although the present invention is directed to optimizing a design with a 1 cm diameter beam tube resonating at 11.424 GHz, it may be adapted to other operating conditions. The invention can be adapted to a different frequency by proportionally scaling all the structural dimensions, including the beam tube, where the frequency is inversely proportional to the scaled dimension. In this regard the performance of the cavity varies rapidly with the diameter of the beam tube. For example, in the case of an accelerator with an 8 mm beam tube diameter, the shut impedance R is improved by a factor of 2.1 over the 1 cm beam tube embodiment, and in the case of a beam tube having a 1.2 cm diameter the shut impedance is decreased by a factor of 1.8 relative to the 1 cm beam tube embodiment. The present invention is described and illustrated herein with reference to preferred embodiments that constitute the best mode known to the applicant for making and using the invention. It will be appreciated that various modifications, alterations and substitutions may be apparent to one skilled in the art and may be made without departing from the invention. Accordingly the scope of the invention is defined by the following claims. |
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description | This application is based on Japanese patent application No. 2006-046,140 and 2006-346,385, the contents of which are incorporated hereinto by reference. 1. Technical Field The present invention relates to an ion implanting apparatus that is capable of irradiating an ion beam over a semiconductor wafer to implant ion species, and in particular, relates to an ion implanting apparatus that is capable of forming a beam geometry by passing an ion beam through a through hole of a member. 2. Related Art Currently, an ion implanting apparatus is utilized for implanting ion species into a semiconductor wafer. Such ion implanting apparatus is described as follows in reference to FIG. 10 and FIG. 11. An ion implanting apparatus 100 shown here includes a main part that comprises an ion gun 110, an aperture member 120, a wafer holding unit 130 or the like, which are linearly arranged. The ion gun 110 produces ion species supplied from an ion source (not shown) to create an ion beam. The aperture member 120 is formed by, for example, machining carbon graphite, and is provided with a slit-shaped through hole 122 formed in a flat member body 121. The wafer holding unit 130 includes a rotation stage 131 and a slide mechanism (not shown), and the rotation stage 131 holds a plurality of silicon wafers 140 that are to be processed. The rotation stage 131 revolves a plurality of silicon wafers 140 that are held thereon, and the slide mechanism reciprocates the rotation stage 131 along a vertical direction. In the ion implanting apparatus 100 having the above-described configuration, an ion beam emitted by the ion gun 110 passes through the through hole 122 of the aperture member 120, so that a beam is shaped to have the corresponding geometry. A plurality of silicon wafers 140 that are revolved and vertically reciprocated by the wafer holding unit 130 are consecutively exposed over the ion beam having such beam geometry, so that the ion species is equivalently injected over the entire surfaces of a plurality of silicon wafers 140. The aperture member 120 as described above may alternatively be referred to as, for example, a resolving aperture, a beam aperture, a slit member or the like, and, regardless of the name of the member, the member is composed of a flat member provided with a slit-shaped through hole 122 formed therein, as shown in FIG. 11. Currently, various proposals for ion implanting apparatuses as described above are made (see, for example, Japanese Patent Laid-Open No. H10-25,178 (1998), Japanese Patent Laid-Open No. H11-149,898 (1999) and Japanese Patent Laid-Open No. H11-283,552 (1999)). Further, an ion implanting apparatus is also proposed which is configured such that at least a surface of various members located in paths for an ion beam is formed of high purity silicon (not shown). In this ion implanting apparatus, even if particles of contaminants are generated from the members in the paths for the ion beam, the particle is necessarily composed of high purity silicon, and, therefore, a contamination of a silicon wafer can be prevented. In addition to above, it is disclosed in the related art documents that the above-described high purity silicon may be composed of amorphous silicon deposited on the member surface by a chemical vapor deposition (CVD) process, amorphous silicon deposited by a sputter process, a silicon grown by an epitaxy process or the like (see, for example, Japanese Patent Laid-Open No. H03-269,940 (1991). Since a gas of ion species is constantly generated in a periphery of an ion beam in the ion implanting apparatus 100 as described above, the ion species is deposited to form a thin film on an inner surface of the through hole 122 of the aperture member 120, as shown in FIG. 12, during the long term operation. Then, the thin film deposited on the inner surface of the through hole 122 of the aperture member 120 may be peeled off by exposing thereof with the ion beam, and may be eventually scattered to a silicon wafer 140 as a contaminant, as shown in FIG. 13. In this case, the above-described contaminant may adhere onto a surface of the silicon wafer 140, or may generate damage in the surface of the silicon wafer 140 by a collision of the contaminant, eventually necessitating the disposal of the silicon wafer 140. For example, a high-current ion implanting apparatus (not shown) or the like utilizes a batch system that retains a large number (e.g., 13 pieces) of silicon wafers 140 therein, and therefore, once a failure is generated as described above, a large number of silicon wafers 140 should be disposed at the same time. In addition to above, while contaminants generated from the member are composed of silicon in the case of employing the ion implanting apparatus described in the aforementioned Japanese Patent Laid-Open No. H03-269,940, when the contaminants collide with a surface of a silicon wafer, damages may be generated therein. Even if no damage is generated, the presence of contaminants of silicon adhered onto the surface of the silicon wafer may cause a failure in the later semiconductor process. According to one aspect of the present invention, there is provided an ion implanting apparatus, which is capable of forming a beam geometry by passing an ion beam through a through hole of a member, wherein at least an inner surface of the through hole of the member is coated with a thermal spraying film. Such configuration provides an adsorption of ion species of the ion beam on the porous thermal spraying film of the member, and an unoriented poly-crystalline structure for a deposition layer generated on the inner surface of the through hole in the unoriented poly-crystalline structure of the member. According to another aspect of the present invention, there is provided an ion implanting apparatus, which is capable of forming a beam geometry by passing an ion beam through a through hole of a member, wherein at least an inner surface of the through hole of the member is formed to be porous. Such configuration provides an adsorption of the ion species of the ion beam on a porous inner surface of the through hole of the member or the like. According to yet other aspect of the present invention, there is provided an ion implanting apparatus, which is capable of forming a beam geometry by passing an ion beam through a through hole of a member, wherein at least an inner surface of the through hole of the member is formed have an unoriented poly-crystalline structure. Such configuration provides an unoriented poly-crystalline structure for a deposition layer generated on the inner surface of the through hole in the unoriented poly-crystalline structure of the member. In addition to above, the “member that forms a beam geometry” according to the present invention may be satisfied if it serves as forming a beam geometry of an ion beam with an aid of a through hole, and more specifically, a typical member that forms a beam geometry may be achieved by having various types of structures of, for example, a flat plate provided with a through hole formed therein, a cylindrical member provided with a through hole formed therein, a plurality of boards combined so as to form a through hole therein, or the like. In addition, the term “porous” used in the present invention describes a condition in which a plurality of pores are formed in a predetermined range from at least an outer surface to an inside thereof. The term “porous film” means a film having a predetermined film thickness and being provided with a plurality of pores formed in the interior therein. Further, such “porous” indicates a structure, in which, for example, a plurality of concave portions are formed on the surface thereof and a plurality of pores are formed in the interior thereof, and at least a portion of a plurality of the concave portions connect with at least some of a plurality of the pores, and at least some of the plurality of pores mutually connect. Since at least an inner surface of the through hole of the above-described member is coated with a thermal spraying film or at least an inner surface of the through hole of the member having a through hole and being capable of forming a beam geometry is formed to be porous in the ion implanting apparatus according to the present invention to provide a suitable adsorption of the ion species of the ion beam on a porous inner surface of the through hole of the member or the like, unwanted generation of the deposition layer on the inner surface of the through hole is inhibited and a failure of the processing object caused by a scattering of the particles peeled-off from the deposition layer is prevented. Further, since at least an inner surface of the through hole of the above-described member is coated with a thermal spraying film or at least the inner surface of the through hole of the above-described member is formed to have unoriented poly-crystalline structure in the ion implanting apparatus according to the present invention to provide a deposition film generated on the inner surface in the through hole of the member to have unoriented poly-crystalline structure that exhibits extremely high inter-layer adhesiveness, a failure of the processing object caused by a scattering of the particles peeled-off from the deposition layer is prevented. The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposed. An embodiment of the present invention will be described as follows in reference to FIG. 1 to FIG. 6. In the following description, an identical element appeared in the above descriptions of the related art is referred to as the identical name, and a detailed description is not presented. An ion implanting apparatus 200 of the present embodiment includes a main part that comprises an ion gun 210, an aperture member 220, a wafer holding unit 230 or the like, and the ion gun 210 is capable of emitting ion species supplied from an ion source (not shown) to create an ion beam. The wafer holding unit 230 comprises a rotation stage 231 and a slide mechanism (not shown). The rotation stage 231 is capable of revolving a plurality of silicon wafers 140 that are retained thereon, and the side mechanism is capable of reciprocating the rotation stage 231 in a vertical direction or the like. The aperture member 220 has a flat member body 221, and the member body 221 is formed by, for example, machining carbon graphite. Such a member body 221 is provided with a slit-shaped through hole 222 formed therein, and an inner surface of such through hole 222 and a front and a rear surface of an outer surface thereof are coated with a coating film 223 that is a porous film. Such a coating film 223 is formed to have a thermal spraying film thickness of about 150 (μm) by, for example, a thermal spraying of silicon. As shown in FIGS. 2A to 2C, the surface thereof is formed to have a porous rough surface with random concave and convex portions of not larger than several micrometers. In the more detail, a number of concave portions and convex portions are formed in the surface of the above-described coating film 223, and a number of pores are formed in the interior thereof. At least some of the larger number of concave portions connect with at least some of the larger number of pores, and at least some of the larger number of pores mutually connect. Further, the concave portions, the convex portions and the pores of the coating film 223 are not influential in forming the beam geometry, and are formed to have dimensions of not larger than several micrometers, which are adopted for adsorbing ion species. In addition to above, FIGS. 2A to 2C are electron microscope photographs, showing conditions of the observed coating film 223 that were experimentally produced by a thermal spraying of silicon. In addition to above, the member body 221 composed of carbon graphite is formed to have an oriented poly-crystalline structure, as shown in FIG. 3. On the other hand, the coating film 223 that is deposited on such member body 221 by a thermal spraying of silicon is formed to have an unoriented poly-crystalline structure, as shown in FIG. 4. In the configuration as described above, in the ion implanting apparatus 200 of the present embodiment, an ion beam emitted by the ion gun 210 passes through the through hole 222 of the aperture member 220, so that a beam is shaped to have the corresponding geometry. A plurality of silicon wafers 140 that are revolved and vertically reciprocated by the wafer holding unit 230 are consecutively exposed over the ion beam having such beam geometry, so that the ion species is equivalently injected over an entire surface of a plurality of silicon wafers 140. Since the inner surface and the outer surface of the through hole 222 of the aperture member 220 are coated with the porous coating film 223 in the ion implanting apparatus 200 of the present embodiment, a gas of the ion species that is constantly generated around the ion beam is adsorbed by the porous coating film 223, as shown in FIG. 5. Therefore, even if the operation is continued for longer periods of time, a deposition of the ion species on the inner surface of the through hole 222 or the like scarcely occurs, and a failure of the silicon wafer 140 caused by a scattering of the deposited particles flaked off can be well prevented. Moreover, since the coating film 223 has the unoriented poly-crystalline structure, the deposition layer disposed on the surface thereof generated by ion species has an unoriented poly-crystalline structure, as shown in FIG. 6. As described above, the deposition layer having the unoriented poly-crystalline structure exhibits extremely high inter-layer adhesiveness, as compared with the conventional deposited layer. Thus, flaking off from the deposition layer can be well prevented. When the aperture member 220 as described above is manufactured, the member body 221 having the through hole 222 of the geometry that corresponds to the beam geometry formed therein is preferably formed by machining carbon graphite or the like, and the inner surface of the through hole 222 of such member body 221 is preferably coated with a porous coating film 223 by a thermal spraying process. In addition to above, when the present inventors experimentally produced the actual ion implanting apparatus 200 as described above and experiments were performed, it was confirmed that number of particles generated on the surface of the silicon wafer 140 was reduced to about one-tenth of that found in the conventional technologies. In the experiment, number of particles adhered onto the surface of the silicon wafers 140 and number of scratches that are considered to be generated by striking the particles thereto were counted. In addition, an aperture member, which was formed by the present inventors by machining carbon graphite and had a roughened inner surface of a through hole of a member body roughened by a blast treatment, was experimentally produced (not shown), and it was found that advantageous effects as described above were not achieved by employing the aperture member having such configuration. It is considered that this is because, although the surface is roughened by such blast treatment, the inside thereof is not porosified by such blast treatment, and therefore the ion species can not be well adsorbed. Further, it is considered that another reason is that, since the member body formed by machining carbon graphite or the like has an oriented poly-crystalline structure as discussed later in detail, the deposition layer generated thereon has also the oriented poly-crystalline structure having lower inter-layer adhesiveness. In addition, the above-described Japanese Patent Laid-Open No. H10-25,178 discloses that a coating film composed of carbon is formed on a surface of an aperture member by carbonization of a thermosetting resin impregnated into the aperture member or the like. However, the present inventors have identified that, since the thus-formed coating film is not porous and is formed to have the oriented poly-crystalline structure, the advantageous effects as described above are not obtained. Here, advantageous effects obtainable by employing the crystal structure as described above will be described as follows. The present inventors have investigated a flaking-off mechanism of a thin film deposited on an inner surface of a through hole of an aperture member during ion beam irradiation, by direct observation using a scanning electron microscope (SEM) and by a crystal structure analysis employing X-ray diffraction (XRD) method. When the surface of the thin film deposited on the inner surface of the through hole of the aperture member having a conventional structure was observed by enlarging the image with a scanning electron microscope, surface conditions of being cracked or almost causing flaking-off were confirmed, as shown in FIG. 7. Further, when the cross sections of the deposited thin film was observed by enlarging the image with a scanning electron microscope, it was confirmed that the film was deposited to be composed of layers and the film had peeled portions between the layers, as shown in FIG. 8. Further, a crystal structure analysis of the deposited thin film was performed by X-ray diffraction method, and it was found from the analysis that a crystal structure of carbon graphite was C-axis oriented. A schematic representation of such condition presents that a crystal structure having C-axis orientation along a direction normal to the deposited surface is estimated, as shown in FIG. 3. FIG. 9 represents an enlarged view of such crystal structure. While the deposited thin film has the crystal structure having C-axis orientation, longer carbon interatomic distance between the layers of 3.40 angstroms is presented in such structure (carbon interatomic distance in the layer plane of 1.42 angstroms), and such structure provides a condition that a layer weakly attracts another layer with a van der Waals attraction, and thus the structure exhibits an easy peeling along the layer direction. In particular, thicker deposition layers are formed by conducting repeated depositions of the film. A stress exerted onto the layer (or layer boundary) is increased, so that film pieces are easily flaked off. Conditions of causing a crack, peeling or flaking-off of the deposition layer as shown in FIG. 8 support the above-described estimation. Then, the present inventors investigated that an aperture member having a coating film deposited on a member body composed of carbon graphite is incorporated into an ion implanting apparatus by a thermal spraying of silicon, and then an ion beam of ion species required for the wafer was irradiated, as described above. Then, it was confirmed that a film having an unoriented poly-crystalline structure is deposited and adhered on the surface of the through hole in the aperture member in every ion implanting operation. The deposition layer having such unoriented poly-crystalline structure exhibits extremely physically higher adhesiveness between the layer, as compared with the deposition layer having the oriented poly-crystalline structure deposited by a conventional technology. Thus, it was confirmed that the aperture member with the coating film of the unoriented poly-crystalline structure deposited thereon by a thermal spraying of silicon provides a prevention for a flaking-off of the deposition layer. In addition to above, while the deposition layer is composed of crystal of carbon as described above, carbon is not contained in ion species. Thus, it can be estimated that the deposited layer is formed of carbon and ion species, which are precipitated from the aperture member by an exposure to ion beam. It should be noted that the present invention is not particularly limited to the present embodiment, and various types of modifications are allowed without departing from the scope and the spirit of the present invention. For example, while it is illustrated that the coating film 223 is composed of silicon in the above-described configuration, the coating film may alternatively be formed of tungsten. It is apparent that the present invention is not limited to the above embodiment, and may be modified and changed without departing from the scope and spirit of the invention. |
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abstract | A Thorium fuel rod assembly is disclosed that includes first and second support elements and a number of Thorium fuel rods positioned between support elements. Each of the Thorium fuel rod includes an outer fuel element containing a solid Thorium an inner core element containing Beryllium that is positioned within an interior cavity defined by the outer fuel element. In an exemplary disclosure, the inner core element also defines an inner cavity such that a beam of high energy particles may be directed into the inner cavity of the inner core element to impinge upon a Beryllium nucleus within the inner core element to produce a (p, n) reaction resulting in the emission of a neutron, where the emitted neutron may interact with a Thorium nucleus in the outer fuel element to cause the Thorium nucleus to fission. |
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claims | 1. A method for storing and drying nuclear fuel rods, the method comprising:providing an elongated vertically oriented capsule including an open top end, a bottom end, and an internal cavity including a plurality of vertically oriented fuel rod storage tubes, 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 at least one of the storage tubes;attaching a lid to the top end of the capsule, the lid including a gas supply flow conduit extending internally between top and bottom surfaces of the lid and a gas return flow conduit extending internally 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 flow conduit of the lid into the cavity of the capsule;flowing the gas through each of the storage tubes;collecting the gas leaving the storage tubes; andflowing the gas through the gas return conduit which exits the lid. 2. The method according to claim 1, wherein the gas flowing through the gas supply conduit is pumped directly to a bottom plenum in the capsule through a central drain tube and bypasses the storage tubes. 3. The method according to claims 2, wherein the storage tubes are vertically oriented and the gas enters a bottom end of each storage tube and leaves through a top end of each storage tube. 4. The method according to claims 3, wherein the collecting step includes flowing the gas leaving the top ends of the storage tubes into a top plenum formed between the top ends of the tubes and the lid. 5. The method according to claim 4, wherein the top plenum is fluidly isolated from the central drain tube. 6. The method according to claim 2, wherein the step of attaching the lid further comprises compressing an axially movable spring-loaded sealing assembly on a top end of the central drain tube with the bottom of the lid, the sealing assembly fluidly coupling the gas supply flow conduit of the lid to the central drain tube. 7. The method according to claim 1, wherein the gas flows through the gas supply and return flow conduits following a multi-directional path through the lid configured to prevent neutron streaming. |
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description | The present application is a continuation of U.S. patent application Ser. No. 13/736,452, filed Jan. 8, 2013, which is a continuation of U.S. patent application Ser. No. 13/094,498, filed Apr. 26, 2011, now U.S. Pat. No. 8,351,562, which in turn is a continuation of U.S. patent application Ser. No. 11/953,207, filed Dec. 10, 2007, now U.S. Pat. No. 7,933,374, which in turn is a continuation-in-part of U.S. patent application Ser. No. 11/123,590, filed May 6, 2005, now U.S. Pat. No. 7,330,526, which in turn claims the benefit of U.S. Provisional Patent Application Ser. No. 60/665,108, filed Mar. 25, 2005 and U.S. Provisional Patent Application Ser. No. 60/671,552, filed Apr. 15, 2005, the entireties of which are hereby incorporated by reference. The present invention relates generally to the field of storing high level waste (“HLW”), and specifically to methods for storing HLW, such as spent nuclear fuel, in ventilated vertical modules. The storage, handling, and transfer of HLW, such as spent nuclear fuel, requires special care and procedural safeguards. For example, in the operation of nuclear reactors, it is customary to remove fuel assemblies after their energy has been depleted down to a predetermined level. Upon removal, this spent nuclear fuel is still highly radioactive and produces considerable heat, requiring that great care be taken in its packaging, transporting, and storing. In order to protect the environment from radiation exposure, spent nuclear fuel is first placed in a canister. The loaded canister is then transported and stored in large cylindrical containers called casks. A transfer cask is used to transport spent nuclear fuel from location to location while a storage cask is used to store spent nuclear fuel for a determined period of time. In a typical nuclear power plant, an open empty canister is first placed in an open transfer cask. The transfer cask and empty canister are then submerged in a pool of water. Spent nuclear fuel is loaded into the canister while the canister and transfer cask remain submerged in the pool of water. Once fully loaded with spent nuclear fuel, a lid is typically placed atop the canister while in the pool. The transfer cask and canister are then removed from the pool of water, the lid of the canister is welded thereon and a lid is installed on the transfer cask. The canister is then properly dewatered and filled with inert gas. The transfer cask (which is holding the loaded canister) is then transported to a location where a storage cask is located. The loaded canister is then transferred from the transfer cask to the storage cask for long term storage. During transfer from the transfer cask to the storage cask, it is imperative that the loaded canister is not exposed to the environment. One type of storage cask is a ventilated vertical overpack (“VVO”). A VVO is a massive structure made principally from steel and concrete and is used to store a canister loaded with spent nuclear fuel (or other HLW). VVOs stand above ground and are typically cylindrical in shape and extremely heavy, weighing over 150 tons and often having a height greater than 16 feet. VVOs typically have a flat bottom, a cylindrical body having a cavity to receive a canister of spent nuclear fuel, and a removable top lid. In using a VVO to store spent nuclear fuel, a canister loaded with spent nuclear fuel is placed in the cavity of the cylindrical body of the VVO. Because the spent nuclear fuel is still producing a considerable amount of heat when it is placed in the VVO for storage, it is necessary that this heat energy have a means to escape from the VVO cavity. This heat energy is removed from the outside surface of the canister by ventilating the VVO cavity. In ventilating the VVO cavity, cool air enters the VVO chamber through bottom ventilation ducts, flows upward past the loaded canister, and exits the VVO at an elevated temperature through top ventilation ducts. The bottom and top ventilation ducts of existing VVOs are located circumferentially near the bottom and top of the VVO's cylindrical body respectively, as illustrated in FIG. 1. While it is necessary that the VVO cavity be vented so that heat can escape from the canister, it is also imperative that the VVO provide adequate radiation shielding and that the spent nuclear fuel not be directly exposed to the external environment. The inlet duct located near the bottom of the overpack is a particularly vulnerable source of radiation exposure to security and surveillance personnel who, in order to monitor the loaded overpacks, must place themselves in close vicinity of the ducts for short durations. Additionally, when a canister loaded with spent nuclear fuel is transferred from a transfer cask to a storage VVO, the transfer cask is stacked atop the storage VVO so that the canister can be lowered into the storage VVO's cavity. Most casks are very large structures and can weigh up to 250,000 lbs. and have a height of 16 ft. or more. Stacking a transfer cask atop a storage VVO/cask requires a lot of space, a large overhead crane, and possibly a restraint system for stabilization. Often, such space is not available inside a nuclear power plant. Finally, above ground storage VVOs stand at least 16 feet above ground, thus, presenting a sizable target of attack to a terrorist. FIG. 1 illustrates a traditional prior art VVO 2. Prior art VVO 2 comprises flat bottom 17, cylindrical body 12, and lid 14. Lid 14 is secured to cylindrical body 12 by bolts 18. Bolts 18 serve to restrain separation of lid 14 from body 12 if prior art VVO 2 were to tip over. Cylindrical body 12 has top ventilation ducts 15 and bottom ventilation ducts 16. Top ventilation ducts 15 are located at or near the top of cylindrical body 12 while bottom ventilation ducts 16 are located at or near the bottom of cylindrical body 12. Both bottom ventilation ducts 16 and top ventilation ducts 15 are located around the circumference of the cylindrical body 12. The entirety of prior art VVO 2 is positioned above grade. As understood by those skilled in the art, the existence of the top ventilation ducts 15 and/or the bottom ventilation ducts 16 in the body 12 of the prior art VVO 2 require additional safeguards during loading procedures to avoid radiation shine. It is an object of the present invention to provide a system and method for storing HLW that reduces the height of the stack assembly when a transfer cask is stacked atop a storage VVO. It is another object of the present invention to provide a system and method for storing HLW that requires less vertical space. Yet another object of the present invention is to provide a system and method for storing HLW that utilizes the radiation shielding properties of the subgrade during storage while providing adequate ventilation of the high level waste. A further object of the present invention is to provide a system and method for storing HLW that provides the same or greater level of operational safeguards that are available inside a fully certified nuclear power plant structure. A still further object of the present invention is to provide a system and method for storing HLW that decreases the dangers presented by earthquakes and other catastrophic events and virtually eliminates the potential of damage from a World Trade Center or Pentagon type of attack on the stored canister. It is also an object of the present invention to provide a system and method for storing HLW that allows for an ergonomic transfer of the HLW from a transfer cask to a storage container. Another object of the present invention is to provide a system and method for storing HLW below or above grade. Yet another object of the present invention is to provide a system and method of storing HLW that reduces the amount of radiation emitted to the environment. Still another object of the present invention is to provide a system and method of storing HLW that eliminates the dangers of radiation shine during loading procedures and/or subsequent storage. A still further object of the present invention is to provide a system and method of storing HLW that locates openings for both the inlet and outlet vents in a removable lid. A yet further object of the present invention is to provide a system and method of storing HLW that leads to convenient manufacture and site construction. These and other objects are met by the present invention which, in some embodiments, is a system for storing high level waste comprising: an inner shell forming a cavity for receiving high level waste, the cavity having a top and a bottom; an outer shell surrounding the inner shell so as to form a space between the inner shell and the outer shell; at least one opening in the inner shell at or near the bottom of the cavity, the at least one opening forming a passageway from the space into the cavity; a lid positioned atop the inner and outer shells, the lid having at least one inlet vent forming a passageway from an ambient atmosphere to the space and at least one outlet vent forming a passageway from the cavity to the ambient atmosphere. Depending on the exact storage needs, the apparatus can be adapted for either above or below grade storage of high level waste. In other embodiments, the invention is a method of storing high level waste comprising: (a) providing an apparatus comprising an inner shell forming a cavity having a top and a bottom, an outer shell concentric with and surrounding the inner shell so as to form a space therebetween, and at least one opening in the inner shell at or near the bottom of the cavity, the at least one opening forming a passageway from the space into the cavity; (b) placing a canister of high level waste into the cavity; (c) providing a lid having at least one inlet vent and at least one outlet vent; (d) positioning the lid atop the inner and outer shells so that the at least one inlet vent forms a passageway from an ambient atmosphere to the space and the at least one outlet vent forms a passageway from the cavity to the ambient atmosphere; and (e) cool air entering the cavity via the at least inlet vent and the space, the cool air being warmed by the canister of high level waste, and exiting the cavity via the at least one outlet vent in the lid. In still other embodiments, the invention is a system for storing high level waste comprising: an inner shell forming a cavity for receiving high level waste, the cavity having a top and a bottom; an outer shell surrounding the inner shell so as to form a space between the inner shell and the outer shell; a floor plate, the inner and outer shells positioned atop and connected to the floor plate; and at least one opening in the inner shell at or near the bottom of the cavity, the at least one opening forming a passageway from the space into the cavity. In yet another embodiment, the invention can be a system for storing high level radioactive waste comprising: an outer shell having an open top end and a hermetically closed bottom end; an inner shell forming a cavity, the inner shell positioned inside the outer shell so as to form a space between the inner shell and the outer shell; at least one passageway connecting the space and a bottom portion of the cavity; at least one passageway connecting an ambient atmosphere and a top portion of the space; a lid positioned atop the inner shell, the lid having at least one passageway connecting the cavity and the ambient atmosphere; and a seal between the lid and the inner shell so at form a hermetic lid-to-inner shell interface. In still another embodiment, the invention can be a system for storing high level radioactive comprising: a metal plate; a first metal tubular shell having a top end and a bottom end, the metal plate connected to the bottom end of the first metal tubular shell so as to hermetically close the bottom end of the first metal tubular shell; a second metal tubular shell forming a cavity, the second metal tubular shell positioned within the first metal tubular shell so as to form a space between the first metal tubular shell and the second metal tubular shell; at least one opening in the second tubular shell that forms a passageway connecting the space and a bottom portion of the cavity, a lid comprising a plug portion and a flange portion surrounding the plug portion, the plug portion extending into the cavity and the flange portion resting atop the inner shell and the outer shell; at least one passageway connecting the cavity and the ambient atmosphere; and at least one passageway connecting the space and the ambient atmosphere. In a further embodiment, the invention can also be a system for storing high level radioactive comprising: a metal plate; a first metal tubular shell having a top end and a bottom end, the metal plate seal welded to the bottom end of the first metal tubular shell so as to hermetically close the bottom end of the first metal tubular shell; a second metal tubular shell forming a cavity and having a top end and a bottom end having at least one cutout; and the second metal tubular shell located within the first metal tubular shell so as to form an annular space between the first metal tubular shell and the second metal tubular shell, the at least one cutout forming a passageway connecting the space and a bottom portion of the cavity. In a still further embodiment, the invention can be a method of storing high level radioactive waste comprising: (a) providing a container comprising an outer shell having an open top end and a hermetically closed bottom end, an inner shell forming a cavity, the inner shell positioned within the outer shell so as to form a space between the inner shell and the outer shell, and at least one opening in the inner shell that connects the space and a bottom portion of the cavity; (b) lowering a hermetically sealed canister holding high level radioactive waste into the cavity via the open top end; (c) providing a lid having at least one inlet vent and at least one outlet vent; (d) positioning a lid atop the inner and outer shells so that the at least one inlet vent forms a passageway from an ambient atmosphere to the space and the at least one outlet vent forms a passageway from the cavity to the ambient atmosphere, the lid substantially enclosing the open top end; and (e) cool air entering the cavity via the at least outlet vent and the space, the cool air being warmed by the canister of high level waste, and exiting the cavity via the at least one outlet vent in the lid. In a yet further aspect, the invention can be a method of storing high level radioactive waste comprising: (a) providing a body portion comprising a floor, an open top end, an inner shell extending upward from the floor and forming a cavity, an outer shell extending upward from the floor and surrounding the inner shell so as to form a space therebetween, and at least one opening in the inner shell that forms a passageway from a bottom of the space into a bottom of the cavity; (b) placing a canister containing high level radioactive waste into the cavity; and (c) positioning a lid having at least one outlet vent atop the inner and outer shells so as to enclose the open top end of the body portion and the at least one outlet vent forms a passageway from a top of the cavity to the ambient atmosphere; and wherein at least one inlet vent forms a passageway from an ambient atmosphere to a top of the space to facilitate natural convective cooling of the canister containing high level radioactive waste. In another aspect, the invention can be a spent nuclear fuel storage facility comprising: an array of storage containers, each of the storage containers comprising: a body portion having a storage cavity configured to hold a canister containing spent nuclear fuel; and a lid that rests atop and is detachably coupled to the body portion, the lid comprising an inlet vent and an outlet vent; and wherein each of the storage containers is configured to draw air through the inlet vent and into the storage cavity and pass the air through the outlet vent as heated air. In still another aspect, the invention can be a spent nuclear fuel storage facility comprising: an array of storage containers, each of the storage containers comprising: a first portion positioned below grade, the first portion having a cavity configured to hold a canister containing spent nuclear fuel; and a second portion positioned above grade, the second portion comprising an inlet vent for drawing ambient air into cavity of the first portion and an outlet vent for passing heated air out of the cavity. In yet another aspect, the invention may be a spent nuclear fuel storage facility comprising: a plurality of storage containers arranged in rows in a closely spaced apart manner to form an array, each of the storage containers comprising: a body portion having a storage cavity extending along a longitudinal axis and having an open top end, the storage cavity configured to hold a canister containing spent nuclear fuel; and a lid detachably coupled to the body portion and enclosing the open top end, the lid comprising a sidewall, a bottom surface, and a top surface, an inlet vent comprising a plurality of inlet openings formed into the sidewall of the lid and an outlet vent comprising a plurality of first openings in the bottom surface of the lid, a common second opening in the top surface of the lid, and a plurality of passageways extending from the plurality of first openings and converging at the common second opening; wherein each of the storage containers is configured to draw air through the inlet vent and into the storage cavity and pass the air from the storage cavity through the outlet vent via thermosiphon flow. FIG. 2 illustrates a high level waste (“HLW”) storage container 100 designed according to an embodiment of the present invention. While the HLW storage container 100 will be described in terms of being used to store a canister of spent nuclear fuel, it will be appreciated by those skilled in the art that the systems and methods described herein can be used to store any and all kinds of HLW. The HLW storage container 100 is designed to be a vertical, ventilated dry system for storing HLW such as spent fuel. The HLW storage container 100 is fully compatible with 100 ton and 125 ton transfer casks for HLW transfer procedures, such as spent fuel canister transfer operations. All spent fuel canister types engineered for storage in free-standing, below grade, and/or anchored overpack models can be stored in the HLW storage container 100. As used herein the term “canister” broadly includes any spent fuel containment apparatus, including, without limitation, multi-purpose canisters and thermally conductive casks. For example, in some areas of the world, spent fuel is transferred and stored in metal casks having a honeycomb grid-work/basket built directly into the metal cask. Such casks and similar containment apparatus qualify as canisters, as that term is used herein, and can be used in conjunction with the HLW storage container 100 can as discussed below. The HLW storage container 100 can be modified/designed to be compatible with any size or style of transfer cask. The HLW storage container 100 can also be designed to accept spent fuel canisters for storage at an Independent Spent Fuel Storage Installations (“ISFSI”). ISFSIs employing the HLW storage container 100 can be designed to accommodate any number of the HLW storage container 100 and can be expanded to add additional HLW storage containers 100 as the need arises. In ISFSIs utilizing a plurality of the HLW storage container 100, each HLW storage container 100 functions completely independent from any other HLW storage container 100 at the ISFSI. The HLW storage container 100 comprises a body portion 20 and a lid 30. The body portion 20 comprises a floor plate 50. The floor plate 50 has a plurality of anchors 51 mounted thereto for securing the HLW storage container 100 to a base, floor, or other stabilization structure. The lid 30 rests atop and is removable/detachable from the body portion 20. As will be discussed in greater detail below, the HLW storage container 100 can be adapted for use as an above or below grade storage system. Referring now to FIG. 3, the body portion 20 comprises an outer shell 21 and an inner shell 22. The outer shell 21 surrounds the inner shell 22, forming a space 23 therebetween. The outer shell 21 and the inner shell 22 are generally cylindrical in shape and concentric with one another. As a result, the space 23 is an annular space. While the shape of the inner and outer shells 22, 21 is cylindrical in the illustrated embodiment, the shells can take on any shape, including without limitation rectangular, conical, hexagonal, or irregularly shaped. In some embodiments, the inner and outer shells 22, 22 will not be concentrically oriented. As will be discussed in greater detail below, the space 23 formed between the inner shell 22 and the outer shell 21 acts as a passageway for cool air. The exact width of the space 23 for any HLW storage container 100 is determined on a cases-by-case design basis, considering such factors as the heat load of the HLW to be stored, the temperature of the cool ambient air, and the desired fluid flow dynamics. In some embodiments, the width of the space 23 will be in the range of 1 to 6 inches. While the width of space 23 can vary circumferentially, it may be desirable to design the HLW storage container 100 so that the width of the space 23 is generally constant in order to effectuate symmetric cooling of the HLW container and even fluid flow of the incoming air. The inner shell 22 and the outer shell 21 are secured atop floor plate 50. The floor plate 50 is square in shape but can take on any desired shape. A plurality of spacers 27 are secured atop the floor plate 50 within the space 23. The spacers 27 act as guides during placement of the inner and outer shells 22, 21 atop the floor plate 50 and ensure that the integrity of the space 23 is maintained throughout the life of the HLW storage container 100. The spacers 27 can be constructed of low carbon steel or another material and welded to the floor plate 50. Preferably, the outer shell 21 is seal joined to the floor plate 50 at all points of contact, thereby hermetically sealing the HLW storage container 100 to the ingress of fluids through these junctures. In the case of weldable metals, this seal joining may comprise welding or the use of gaskets. Most preferably, the outer shell 21 is integrally welded to the floor plate 50. A ring flange 77 is provided around the top of the outer shell 21 to stiffen the outer shell 21 so that it does not buckle or substantially deform under loading conditions. The ring flange 77 can be integrally welded to the top of the outer shell 21. The inner shell 22 is laterally and rotationally restrained in the horizontal plane at its bottom by the spacers 27 and support blocks 52. The inner shell 22 is preferably not welded or otherwise permanently secured to the bottom plate 50 or outer shell 21 so as to permit convenient removal for decommissioning, and if required, for maintenance. The bottom edge of the inner shell 22 is equipped with a tubular guide (not illustrated) that also provides flexibility to permit the inner shell 22 to expand from its contact with the air heated by the canister in the cavity 24 without inducing excessive upward force on the lid 30. The inner shell 22, the outer shell 21, the floor plate 50, and the ring flange 77 are preferably constructed of a metal, such as a thick low carbon steel, but can be made of other materials, such as stainless steel, aluminum, aluminum-alloys, plastics, and the like. Suitable low carbon steels include, without limitation, ASTM A516, Gr. 70, A515 Gr. 70 or equal. The desired thickness of the inner and outer shells 22, 21 is matter of design and will be determined on a case by case basis. However, in some embodiments, the inner and outer shells 22, 22 will have a thickness between ½ to 3 inches. The inner shell 22 forms a cavity 24. The size and shape of the cavity 24 is not limiting of the present invention. However, it is preferred that the inner shell 22 be selected so that the cavity 24 is sized and shaped so that it can accommodate a canister of spent nuclear fuel or other HLW. While not necessary to practice the invention, it is preferred that the horizontal cross-sectional size and shape of the cavity 24 be designed to generally correspond to the horizontal cross-sectional size and shape of the canister-type that is to be used in conjunction with that particular HLW storage container 100. More specifically, it is desirable that the size and shape of the cavity 24 be designed so that when a canister containing HLW is positioned in cavity 24 for storage (as illustrated in FIG. 8), a small clearance exists between the outer side walls of the canister and the side walls of the cavity 24. Designing the cavity 24 so that a small clearance is formed between the side walls of the stored canister and the side walls of the cavity 24 limits the degree the canister can move within the cavity during a catastrophic event, thereby minimizing damage to the canister and the cavity walls and prohibiting the canister from tipping over within the cavity. This small clearance also facilitates flow of the heated air during HLW cooling. The exact size of the clearance can be controlled/designed to achieve the desired fluid flow dynamics and heat transfer capabilities for any given situation. In some embodiments, for example, the clearance may be 1 to 3 inches. A small clearance also reduces radiation streaming. The inner shell 22 is also equipped with equispaced longitudinal ribs (not illustrated) at an elevation that is aligned with the top lid of a canister of HLW stored in the cavity 24. These ribs provide a means to guide a canister of HLW down into the cavity 24 so that the canister properly rests atop the support blocks 52. The ribs also serve to limit the canister's lateral movement during an earthquake or other catastrophic event to a fraction of an inch. A plurality of openings 25 are provided in the inner shell 22 at or near its bottom. The openings 25 provide a passageway between the annular space 23 and the bottom of the cavity 24. The openings 25 provide passageways by which fluids, such as air, can pass from the annular space 23 into the cavity 24. The opening 25 are used to facilitate the inlet of cool ambient air into the cavity 24 for cooling stored HLW having a heat load. In the illustrated embodiment, six opening 25 are provided. However, any number of openings 25 can be provided. The exact number will be determined on a case-by-case basis and will be dictated by such consideration as the heat load of the HLW, desired fluid flow dynamics, etc. Moreover, while the openings 25 are illustrated as being located in the side wall of the inner shell 22, the openings 25 can be provided in the floor plate 50 in certain modified embodiments of the HLW storage container 100. In some embodiments, the openings 25 may be symmetrically located around the bottom of the inner shell 22 in a circumferential orientation to enable the incoming cool air streaming down the annular space 23 to enter the cavity 24 in a symmetric manner. The opening 25 in the inner shell 22 are sufficiently tall to ensure that if the cavity 24 were to become filled with water, the bottom region of a canister resting on the support blocks 52 would be submerged for several inches before the water level reaches the top edge of the openings 25. This design feature ensures thermal performance of the system under any conceivable accidental flooding of the cavity 24 by any means whatsoever. A layer of insulation 26 is provided around the outside surface of the inner shell 22 within the annular space 23. The insulation 26 is provided to minimize the heat-up of the incoming cooling air in the space 23 before it enters the cavity 24. The insulation 26 helps ensure that the heated air rising around a canister situated in the cavity 24 causes minimal pre-heating of the downdraft cool air in the annular space 23. The insulation 26 is preferably chosen so that it is water and radiation resistant and undegradable by accidental wetting. Suitable forms of insulation include, without limitation, blankets of alumina-silica fire clay (Kaowool Blanket), oxides of alumina and silica (Kaowool S Blanket), alumina-silica-zirconia fiber (Cerablanket), and alumina-silica-chromia (Cerachrome Blanket). The desired thickness of the layer of insulation 26 is matter of design and will be dictated by such considerations such as the heat load of the HLW, the thickness of the shells, and the type of insulation used. In some embodiments, the insulation will have a thickness in the range ½ to 6 inches. A plurality of support blocks 52 are provided on the floor (formed by floor plate 50) of the cavity 24. The support blocks 52 are provided on the floor of cavity 24 so that a canister holding HLW, such as spent nuclear fuel, can be placed thereon. The support blocks 52 are circumferentially spaced from one another and positioned between each of the openings 25 near the six sectors of the inner shell 22 that contact the bottom plate 50. When a canister holding HLW is loaded into the cavity 24 for storage, the bottom surface of the canister rests atop the support blocks 52, forming an inlet air plenum between the bottom surface of the HLW canister and the floor of cavity 24. This inlet air plenum contributes to the fluid flow and proper cooling of the canister. The support blocks 52 can be made of low carbon steel and are preferably welded to the floor of the cavity 24. In some embodiments, the top surfaces of the support blocks 52 will be equipped with a stainless steel liner so that the canister of HLW does not rest on a carbon steel surface. Other suitable materials of construction for the support blocks 52 include, without limitation, reinforced-concrete, stainless steel, plastics, and other metal alloys. The support blocks 52 also serve an energy/impact absorbing function. In some embodiments, the support blocks 52 are preferably of a honeycomb grid style, such as those manufactured by Hexcel Corp., out of California, U.S. The lid 30 rests atop and is supported by the tops edges of the inner and outer shells 22, 21. The lid 30 encloses the top of the cavity 24 and provides the necessary radiation shielding so that radiation can not escape from the top of the cavity 24 when a canister loaded with HLW is stored therein. The lid 30 is specially designed to facilitate in both the introduction of cool air to the space 23 (for subsequent introduction to the cavity 24) and the release of warmed air from the cavity 24. In some embodiments, the invention is the lid itself, independent of all other aspects of the HLW storage container 100. FIGS. 4 and 5 illustrate the lid 30 in detail according to an embodiment of the present invention. In some embodiments, the lid 30 will be a steel structure filled with shielding concrete. The design of the lid 30 is preferably designed to fulfill a number of performance objectives. Referring first to FIG. 4, a top perspective view of the lid 30 removed from the body portion 20 of the HLW storage container 100 is illustrated. In order to provide the requisite radiation shielding, the lid 30 is constructed of a combination of low carbon steel and concrete. More specifically, in constructing one embodiment of the lid 30, a steel lining is provided and filled with concrete (or another radiation absorbing material). In other embodiments, the lid 30 can be constructed of a wide variety of materials, including without limitation metals, stainless steel, aluminum, aluminum-alloys, plastics, and the like. In some embodiments, the lid may be constructed of a single piece of material, such as concrete or steel for example. The lid 30 comprises a flange portion 31 and a plug portion 32. The plug portion 32 extends downward from the flange portion 31. The flange portion 31 surrounds the plug portion 32, extending therefrom in a radial direction. A plurality of inlet vents 33 are provided in the lid 30. The inlet vents 33 are circumferentially located around the lid 30. Each inlet vent 33 provides a passageway from an opening 34 in the side wall 35 to an opening 36 in the bottom surface 37 of the flange portion 31. A plurality of outlet vents 38 are provided in the lid 30. Each outlet vent 38 forms a passageway from an opening 39 in the bottom surface 40 of the plug portion 32 to an opening 41 in the top surface 42 of the lid 30. A cap 43 is provided over opening 41 to prevent rain water or other debris from entering and/or blocking the outlet vents 38. The cap 43 is secured to the lid 30 via bolts 70 or through any other suitable connection, including without limitation welding, clamping, a tight fit, screwing, etc. The cap 43 is designed to prohibit rain water and other debris from entering into the opening 41 while affording heated air that enters the opening 41 to escape therefrom. In one embodiment, this can be achieved by providing a plurality of small holes (not illustrated) in the wall 44 of the cap 43 just below the overhang of the roof 45 of the cap. In other embodiments, this can be achieved by non-hermetically connecting the roof 45 of the cap 43 to the wall 44 and/or constructing the cap 43 (or portions thereof) out of material that is permeable only to gases. The opening 41 is located in the center of the lid 30. By locating both the inlet vents 33 and outlet vents 38 in the lid 30, there is no lateral radiation leakage path during the lowering or raising of a canister of HLW in the cavity 24 during loading and unloading operations. Thus, the need for shield blocking, which is necessary in some prior art VVOs is eliminated. Both the inlet vents 30 and the outlet vents 38 are preferably radially symmetric so that the air cooling action in the system is not affected by the change in the horizontal direction of the wind. Moreover, by locating the opening 34 of the inlet vent 30 at the periphery of the lid 30 and the opening 41 for the outlet vents 38 at the top central axis of the lid, mixing of the entering cool air stream and the exiting warm air stream is essentially eliminated. In order to further protect against rain water or other debris entering opening 41, the top surface 42 of the lid 30 is curved and sloped away from the opening 41 (i.e., downward and outward). Positioning the opening 41 away from the openings 34 helps prevent the heated air that exits via the outlet vents 38 from being drawn back into the inlet vents 35. The top surface 42 of the lid 30 (which acts as a roof) overhangs beyond the side wall 35 of the flange portion 31, thereby helping to prohibit rain water and other debris from entering the inlet vents 33. The overhang also helps prohibit mixing of the cool and heated air streams. The curved shape of the increases the load bearing capacity of the lid 30 much in the manner that a curved beam exhibits considerably greater lateral load bearing capacity than its straight counterpart. The outlet vents 38 are specifically curved so that a line of sight does not exist therethrough. This prohibits a line of sight from existing from the ambient air to an HLW canister that is loaded in the HLW storage container 100, thereby eliminating radiation shine into the environment. In other embodiments, the outlet vents may be angled or sufficiently tilted so that such a line of sight does not exist. The inlet vents 33 are in a substantially horizontal orientation. However, the shape and orientation of the inlet and outlet vents 33, 38 can be varied. The inlet and outlet vents 30, 38 are made of “formed and flued” heads (i.e., surfaces of revolution) that serve three major design objectives. First, the curved shape of the inlet and outlet vents 30, 38 eliminate any direct line of sight from the cavity 24 and serve as an effective means to scatter the photons streaming from the HLW. Second, the curved steel plates 78 that form outlet vent passageway 38 significantly increase the load bearing capacity of the lid 30 much in the manner that a curved beam exhibits considerably greater lateral load bearing capacity in comparison to its straight counterpart. This design feature is a valuable attribute if a beyond-the-design basis impact scenario involving a large and energetic missile needs to be evaluated for a particular ISFSI site. Third, the curved nature of the inlet vents 30 provide for minimum loss of pressure in the coolant air stream, resulting in a more vigorous ventilation action. In some embodiments it may be preferable to provide screens covering all of the openings into the inlet and outlet vents 30, 38 to prevent debris, insects, and small animals from entering the cavity 24 or the vents 30, 38. Referring now to FIG. 5, the lid 30 further comprises a first gasket seal 46 and a second gasket seal 47 on the bottom surface 37 of the flange portion 31. The gaskets 46, 47 are preferably constructed of a radiation resistant material. When the lid 30 is positioned atop the body portion 20 of the HLW storage container 100 (as shown in FIG. 3), the first gasket seal 46 is compressed between the bottom surface 37 of the flange portion 31 of the lid 30 and the top edge of the inner shell 22, thereby forming a seal. Similarly, when the lid 30 is positioned atop the body portion 20 of the HLW storage container 100, the second gasket seal 47 is compressed between the bottom surface 37 of the flange portion 31 of the lid 30 and the top edge of the outer shell 21, thereby forming a second seal. A container ring 48 is provided on the bottom surface 35 of the flange portion 31. The container ring 48 is designed to extend downward from the bottom surface 35 and peripherally surround and engage the outside surface of the top of the outer shell 22 when the lid 30 is positioned atop the body portion 20 of the HLW storage container 100, as shown in FIG. 3. Referring again to FIG. 3, the cooperational relationship of the elements of the lid 30 and the elements of the body portion 20 will now be described. When the lid 30 is properly positioned atop the body portion 20 of the HLW storage container 100 (e.g., during the storage of a canister loaded with HLW), the plug portion 32 of the lid 30 is lowered into the cavity 24 until the flange portion 31 of the lid 30 contacts and rests atop the inner shell 22 and the flange ring 77. The flange portion 31 eliminates the danger of the lid 30 falling into the cavity 24. When the lid 30 is positioned atop the body portion 20, the first and second gasket seals 46, 47 are respectively compressed between the flange portion 31 of the lid 30 and the top edges of the inner and outer shells 22, 21, thereby forming hermetically sealed interfaces. The first gasket 46 provides a positive seal at the lid/inner shell interface, prohibiting mixing of the cool air inflow stream through the annular space 23 and the warm air outflow stream at the top of the cavity 24. The second gasket 47 provides a seal at the lid/outer shell interface, providing protection against floodwater that may rise above the flange ring 77 itself. The container flange 48 surrounds and peripherally engages the flange ring 77. The flange ring 77 restrains the lid 30 against horizontal movement, even during design basis earthquake events. When so engaged, the lid 30 retains the top of the inner shell 22 against lateral, axial movement. The lid 30 also provides stability, shape, and proper alignment/orientation of the inner and outer shells 22, 21. The extension of plug portion 32 of the lid 30 into the cavity 24 helps reduce the overall height of the HLW storage container 100. Because the plug portion 32 is made of steel filled with shielding concrete, the plug portion 32 blocks the skyward radiation emanating from a canister of HLW from escaping into the environment. The height of the plug portion 32 is designed so that if the lid 30 were accidentally dropped during its handling, it would not contact the top of a canister of HLW positioned in the cavity 24. When the lid 30 is positioned atop the body portion 20, the inlet vents 33 are in spatial cooperation with the space 23 formed between the inner and outer shells 22, 21. The outlet vents 38 are in spatial cooperation with the cavity 24. As a result, cool ambient air can enter the HLW storage container 100 through the inlet vents 33, flow into the space 23, and into the bottom of the cavity 24 via the openings 25. When a canister containing HLW having a heat load is supported within the cavity 24, this cool air is warmed by the HLW canister, rises within the cavity 24, and exits the cavity 24 via the outlet ducts 38. Because the openings 34 (best visible in FIG. 4) of the inlet vents 30 extend around the circumference of the lid 30, the hydraulic resistance to the incoming air flow, a common limitation in ventilated modules, is minimized. Circumferentially circumscribing the openings 34 of the inlet vents 30 also results in the inlet vents 30 being less apt to becoming completely blocked under even the most extreme environmental phenomena involving substantial quantities of debris. Similar air flow resistance minimization is built into the design of the inlet vents 38 for the exiting air. As mentioned above, the HLW storage container 100 can be adapted for either above or below grade storage of HLW. When adapted for above grade storage of HLW, the HLW storage container 100 will further comprises a radiation absorbing structure/body surrounding the body portion 20. The radiation absorbing structure will be of a material, and of sufficient thickness so that radiation emanating from the HLW canister is sufficiently absorbed/contained. In some embodiments, the radiation absorbing structure can be a concrete monolith. Moreover, in some embodiment, the outer shell may be formed by an inner wall of the radiation absorbing structure itself. Referring now to FIGS. 6 and 7, the adaptation and use of the HLW storage container 100 for the below grade storage of HLW at an ISFSI, or other location will be described, according to one embodiment of the present invention. Referring to FIG. 6, a hole is first dug into the ground at a desired position within the ISFSI and at a desired depth. Once the hole is dug, and its bottom properly leveled, a base 61 is placed at the bottom of hole. The base 61 is a reinforced concrete slab designed to satisfy the load combinations of recognized industry standards, such as ACI-349. However, in some embodiments, depending on the load to be supported and/or the ground characteristics, the use of a base may be unnecessary. The base 61 designed to meet certain structural criteria and to prevent long-term settlement and physical degradation from aggressive attack of the materials in the surrounding sub-grade. Once the base 61 is properly positioned in the hole, the HLW storage container 100 is lowered into the hole in a vertical orientation until it rests atop the base 61. The floor plate 50 contacts and rests atop the top surface of base 61. The floor plate 50 is then secured to the base 61 via anchors 51 to prohibit future movement of the HLW storage container 100 with respect to the base 61. The hole is preferably dug so that when the HLW storage container 100 is positioned therein, at least a majority of the inner and outer shells 22, 21 are below ground level 62. Most preferably, the hole is dug so that only 1 to 4 feet of the inner and outer shells 22, 21 are above ground level 61 when the HLW storage container 100 is resting atop base 61 in the vertical orientation. In some embodiments, the hole may be dug sufficiently deep that the top edges of the inner and outer shells 22, 21 are flush with the ground level 62. In the illustrated embodiment, about 32 inches of the inner and outer shells 22, 21 protrude above the ground level 62. An appropriate preservative, such as a coal tar epoxy or the like, can be applied to the exposed surfaces of outer shell 21 and the floor plate 50 in order to ensure sealing, to decrease decay of the materials, and to protect against fire and the ingress of below grade fluids. A suitable coal tar epoxy is produced by Carboline Company out of St. Louis, Mo. under the tradename Bitumastic 300M. In some embodiments, it may be preferable to also coat all surfaces of both the inner shell 22 and the outer shell 21 with the preservative, even though these surfaces are not directly exposed to the elements. Once the HLW storage container 100 is resting atop base 61 in the vertical orientation, soil 60 is delivered into the hole exterior of the HLW storage container 100, thereby filling the hole with soil 60 and burying a major portion of the HLW integral structure 100. While soil 60 is exemplified to fill the hole and surround the HLW storage container 100, any suitable engineered fill can be used that meets environmental and shielding requirements. Other suitable engineered fills include, without limitation, gravel, crushed rock, concrete, sand, and the like. Moreover, the desired engineered fill can be supplied to the hole by any means feasible, including manually, dumping, and the like. The soil 60 is supplied to the hole until the soil 60 surrounds the HLW storage container 100 and fills the hole to a level where the soil 60 is approximately equal to the ground level 62. The soil 60 is in direct contact with the exterior surfaces of the HLW storage container 100 that are below grade. A radiation absorbing structure, such as a concrete pad 63, is provided around the portion of the outer shell 21 that protrudes above the ground level 62. The ring flange 77 of the outer shell 21 rests atop the top surface of the concrete pad 63. The concrete pad 63 is designed so as to be capable of providing the necessary radiation shielding for the portion of the HLW storage container 100 that protrudes from the ground. The top surface of the pad 63 also provides a riding surface for a cask crawler (or other device for transporting a transfer cask) during HLW transfer operations. The soil 60 provides the radiation shielding for the portion of the HLW storage container 100 that is below the ground level 62. The pad 63 also acts as a barrier membrane against gravity induced seepage of rain or flood water around the below grade portion of the HLW storage container 100. A top view of the concrete pad 63 is shown in FIG. 7. While the pad 63 is preferably made of a reinforced concrete, the pad 63 can be made out of any material capable of suitably absorbing/containing the radiation being emitted by the HLW being stored in the cavity 24. Referring again to FIG. 6, when the HLW storage apparatus 100 is adapted for the below grade storage of HLW and the lid 30 removed, the HLW storage apparatus 100 is a closed bottom, open top, thick walled cylindrical vessel that has no below grade penetrations or openings. Thus, ground water has no path for intrusion into the cavity 24. Likewise, any water that may be introduced into the cavity 24 through the inlet and outlet vents 33, 38 in the lid 30 will not drain out on its own. Once the concrete pad 63 is in place, the lid 30 is placed atop the inner and outer shells 22, 21 as described above. Because the lid 30, which includes the openings of the inlet and outlet vents 33, 38 to the ambient, is located above grade, a hot canister of HLW can be stored in the cavity 24 below grade while still affording adequate ventilation of the canister for heat removal. Referring now to FIG. 8, the process of storing a canister 90 loaded with hot HLW in a below grade HLW storage container 100 will be discussed. Upon being removed from a spent fuel pool and treated for dry storage, a canister 90 is positioned in a transfer cask. The transfer cask is carried by a cask crawler to a desired HLW storage container 100 for storage. While a cask crawler is exemplified, any suitable means of transporting a transfer cask can be used. For example, any suitable type of load-handling device, such as without limitation, a gantry crane, overhead crane, or other crane device can be used. In preparing the desired HLW storage container 100 to receive the canister 90, the lid 30 is removed so that cavity 24 is open. The cask crawler positions the transfer cask atop the underground HLW storage container 100. After the transfer cask is properly secured to the top of the underground HLW storage container 100, a bottom plate of the transfer cask is removed. If necessary, a suitable mating device can be used to secure the connection of the transfer cask to the HLW storage container 100 and to remove the bottom plate of the transfer cask to an unobtrusive position. Such mating devices are well known in the art and are often used in canister transfer procedures. The canister 90 is then lowered by the cask crawler from the transfer cask into the cavity 24 until the bottom surface of canister 90 contacts and rests atop the support blocks 52, as described above. When resting on support blocks 52, at least a major portion of the canister is below grade. Most preferably, the entirety of the canister 90 is below grade when in its storage position. Thus, the HLW storage container 100 provides for complete subterranean storage of the canister 90 in a vertical configuration inside the cavity 24. In some embodiments, the top surface of the pad 63 itself can be considered the grade level, depending on its size, radiation shielding properties, and cooperational relationship with the other storage modules in the ISFSI. Once the canister 90 is positioned and resting in cavity 24, the lid 30 is positioned atop the body portion 20 of HLW storage container 100 as described above with respect to FIG. 3, thereby substantially enclosing cavity 24. An inlet air plenum exists below the canister 90 while an outlet air plenum exists above the canister 90. The outlet air plenum acts to boost the “chimney” action of the heated air out of the HLW storage container 100. The lid 31 is then secured in place with bolts that extend into the concrete pad 63. As a result of the heat emanating from canister 90, cool air from the ambient is siphoned into the inlet vents 33, drawn through the space 23, and into the bottom of cavity 24 via the openings 25. This cool air is then warmed by the heat from the canister 90, rises in cavity 24 via the clearance space between the canister 90 and the inner shell 22, and then exits cavity 24 as heated air via the outlet vents 38 in the lid 30. It should be recognized that the depth of the cavity 24 determines the height of the hot air column in the annular space 23 during the HLW storage container's 100 operation. Therefore, deepening the cavity 24 has the beneficial effect of increasing the quantity of the ventilation air and, thus, enhancing the rate of heat rejection from the stored canister 90. Further lowering the canister 90 into the cavity 24 will increase the subterranean depth of the radiation source, making the site boundary dose even more miniscule. Of course, constructing a deeper cavity 24 will entail increased excavation and construction costs. A multitude of HLW storage containers 100 can be used at the same ISFSI site and situated in arrays as shown in FIG. 9. Although the HLW storage containers 100 are closely spaced, the design permits a canister in each HLW storage container 100 to be independently accessed and retrieved easily. While the invention has been described and illustrated in sufficient detail that those skilled in this art can readily make and use it, various alternatives, modifications, and improvements should become readily apparent without departing from the spirit and scope of the invention. |
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053751493 | abstract | An apparatus and method of extracting power from energetic ions produced by nuclear fusion in a toroidal plasma to enhance respectively the toroidal plasma current and fusion reactivity. By injecting waves of predetermined frequency and phase traveling substantially in a selected poloidal direction within the plasma, the energetic ions become diffused in energy and space such that the energetic ions lose energy and amplify the waves. The amplified waves are further adapted to travel substantially in a selected toroidal direction to increase preferentially the energy of electrons traveling in one toroidal direction which, in turn, enhances or generates a toroidal plasma current. In an further adaptation, the amplified waves can be made to preferentially increase the energy of fuel ions within the plasma to enhance the fusion reactivity of the fuel ions. The described direct, or in situ, conversion of the energetic ion energy provides an efficient and economical means of delivering power to a fusion reactor. |
042773067 | description | Generally, the present invention is directed to methods for the control of impurity flow in toroidal plasma systems by providing a magnetic confinement system having outer flux lines which are axisymmetrically bound with respect to the plasma. In this connection, a confining field is provided which has outer flux lines bound in a zone adjacent the plasma and displaced from the plasma in a direction along the major toroidal axis opposite the direction of positive ion toroidal drift. This may be accomplished by providing a relocatively high flux value in the plasma confinement zone, and a relatively low flux value in the adjacent flux binding zone. By further providing a particle sink such as a vacuum pumping zone in the zone adjacent the plasma, in which outer magnetic flux lines of the plasma are bound to vacuum chamber walls, a plasma diffusion pump may be provided which is adapted to control impurities, but which does not require complicated poloidal divertor structures using internal coils. Apparatus which may be adapted for performance of the present invention comprises the elements of toroidal plasma confinement systems, preferably of Tokamak design and more preferably of Tokamak design and having a noncircular plasma cross section which is elongated in a direction along the major toroidal axis. Such tokamak systems for the containment of high-temperature plasmas comprise means for providing a strong, toroidal magnetic field in which the plasma ring is to be embedded, and which is generally provided by electrical current in one or more conductive coils encircling the minor toroidal axis. Such systems also comprise means for providing a toroidal electric field to maintain a toroidal current flowing in the plasma, and this plasma current in turn generates a magnetic field component which is poloidal. The combination of the poloidal magnetic field with the toroidal magnetic field with the toroidal magnetic field produces resultant magnetic field lines that lie on closed, nested magnetic surfaces, and the plasma is subjected to confining, constricting forces generated by the current flowing in it. The toroidal confinement systems may also include various means to generate, heat or otherwise control the plasma, such as neutral beam injection systems. Examples of apparatus which may be utilized in connection with the present invention include the Doublet III apparatus of General Atomic Company and the ISX tokamak system of Oak Ridge National Laboratory. The invention will now be more particularly described with specific reference to the toroidal plasma confinement system 10 illustrated in FIGS. 1 and 2 of the drawings. The plasma generation and confinement apparatus 10 may be a toroidal fusion reactor for producing high energy neutrons by nuclear reaction occasioned by the fusion of deuterium and tritium nuclei, or may utilize the light hydrogen isotope in provision of a high temperature plasma for study of plasmas or any other use to which hydrogen plasmas may be put. The apparatus 10 has a large toroidal reaction chamber 12 for plasma generation and confinement. A plasma may be created in the vacuum chamber 12 by an appropriate poloidal field, established by E-coils 14. When the E-coils are energized, they produce a time varying magnetic flux linking the chamber 12. The electric field induced by this flux variation initiates and maintains the toroidal discharge current required for plasma confinement and ohmic heating. F-coils 16a, b control the magnetic configuration and position of a plasma discharge in a predetermined manner. The F-coil system establishes the magnetic boundary conditions for the plasma 40 in the upper zone of vacuum chamber 12 and may be varied to control the position and other parameters of the plasma 40. Also provided around the chamber 12 are toroidal B-coils 18, which establish an azimuthal magnetic field for stable plasma confinement. The F-coils 16a, b are programmed to provide a higher flux .psi. value in the upper chamber, such that the outer magnetic lines of flux intersect with the vacuum chamber walls in the lower zone of the vacuum chamber adjacent the plasma, and such that a "D" shaped plasma is provided in the upper zone of chamber 12. The .psi. flux values and outer, bound flux lines 44 are shown in more detail in FIG. 2, where the plasma zone comprising the predominant amount of the plasma [e.g., at least 90% of the plasma mass] is shown as shaded plasma region 40. As indicated, the .psi. value of the upper portion 46 of the vacuum chamber 12 is greater than the .psi. value of the lower portion 48 of the chamber, such that the outermost magnetic flux lines (indicated by lines 44) adjacent the walls of the chamber 12 in the upper portion 46, are directed to intersect the chamber walls in the lower portion 48. Of course, inner flux lines in the upper chamber are closed, or continuous, such that charged particles of the plasma 40 which are influenced by electromagnetic forces to follow the flux lines will experience force tending to confine the plasma in the zone 40. However, ionized particles adjacent the chamber 12 walls which tend to follow the outer flux lines, will experience a charge particle path which intersects with the wall in the lower portion 48 of the chamber 12. The plasma conditions are initiated at relatively low pressures. Hence, the chamber 12 is constantly pumped out by vacuum pumps through ports 30 located at the bottom of the vacuum chamber 12 and corresponding conduits 32. At the high temperatures thus produced in the reaction region containing the plasma, the dueterium and tritium nuclei may undergo fusion, producing helium nuclei and high energy neutrons. Such neutrons at energies of about 14 MeV may penetrate the first wall 22 and pass into a blanket 24 surrounding the chamber 12. The blanket 24, formed in part of carbon and lithium, is used for extracting the energy from the neutrons, raising the temperature of the blanket 24. Helium gas may be circulated through the blanket 24 from a conduit 26. Cool helium is introduced into the conduit 26, and heated helium is withdrawn from a conduit 28. The helium provides a safe, yet effective, heat transfer function, carrying heat from the reactor to an external heat exchanger, and recirculated through conduit 26. A radiation shield 34 may be provided to limit the escape of harmful radiation. By providing a particle sink such as a vacuum pump system in the lower chamber zone, impurity particles adjacent the chamber walls may thus be collected at the lower zone and removed from the system. By providing a hydrogen source in the upper chamber zone, such as the neutral beam system input, the net impurity flow into the lower zone is enhanced. The illustrated apparatus 10 may be regarded as an axisymmetrical plasma diffusion pump. Magnetic flux lines 44 are bound between two walls (i.e., intersect the lower walls of the vacuum chamber at two places). Hydrogen gas is introduced in the middle and r-f power from a suitable source (not shown) is applied to ionize the gas. Resulting plasma flows along the outer flux lines towards the wall in the lower portion of the chamber at sound velocity. Because the impurity atoms produced at the wall are ionized in a much shorter distance than the distance to the main plasma, the plasma flow will push the impurity ions back towards the wall by collisional and/or electrostatic interaction. In the case of collisional pumping, the conditions that the impurity ions are ionized in a short distance may be represented by ##EQU1## The condition that the collisions between protons and impurity ions are sufficiently frequent to produce collisional pumping may be represented as: ##EQU2## where v.sub.o is the velocity of sputtered atom, n is the plasma density, <.sigma.v> is the ionization probability, a is the distance from the wall to the main plasma, .nu..sub.iz is the proton-impurity collision frequency, T.sub.i is the plasma ion temperature, m.sub.p is the proton mass, v.sub.s is the sound velocity of the plasma, and l is the distance along a line of magnetic induction from the main plasma to the intersection of that line of magnetic induction with the vacuum chamber wall. By utilizing the following relationship of .nu..sub.iz ; EQU .nu..sub.iz .apprxeq.nZ.sup.2 10.sup.-12 (T.sub.i /e).sup.-3/2 sec.sup.-1 ( 3) Equation (2) may be rewritten as: EQU nl>2.times.10.sup.16 (T.sub.i /e).sup.2 (T.sub.i /T.sub.e).sup.1/2 Z.sup.-2 (4) where T.sub.e is the electron temperature and Z is the charge of impurity ions. The ion temperature T.sub.i may be estimated from the energy balance, i.e., EQU .nu..sub.ei (T.sub.e -T.sub.i)=2T.sub.i v.sub.s /l (5) or ##EQU3## There are two regimes depending on plasma density, as follows: ##EQU4## For the high density case, where ln is greater than 4.times.10.sup.17 (T.sub.e /e).sup.2, the electron temperature T.sub.e is approximately equal to the plasma ion temperature T.sub.i, and Equation (4) is satisfied for Z less than 5. For the low density case where ln is less than 4.times.10.sup.17 (T.sub.e /e).sup.2, the ion temperature T.sub.i may be represented as: ##EQU5## By combining Equation (8) with Equation (4), EQU nl<3.times.10.sup.18 (T.sub.e /e).sup.2 Z.sup.4/3 (9) This condition is automatically satisfied. The lower limit of the density is given by Equation (4) by utilizing the lowest value for the ion temperature and by Equation (7). For an electron temperature equal to ionization potentials, Equation (1) becomes EQU n>>2.times.10.sup.12 (v.sub.o /a) (10) By assuming the sound velocity v.sub.o to be approximately equal to 1.times.10.sup.3 meters per second, we have EQU n>>2.times.10.sup.15 a.sup.-1 m.sup.-3 (11) As indicated, the pumping interaction may be collisional and/or electrostatic, and in a substantially collisionless system, the pumping is done by electrostatic potential. When the hydrogen plasma flows towards the lower vacuum chamber wall at sound velocity and where the electron temperature T.sub.e is very much greater than the plasma ion temperature T.sub.i (T.sub.e >>T.sub.i) there is an electrostatic potential accelerating the protons. The potential is of the order of about T.sub.e /e. The impurity atoms, after becoming ionized, are repelled by the potential barrier, if the electron temperature T.sub.e is greater than W.sub.z /Z, where W.sub.z is the kinetic energy of the impurity atoms. The condition on the plasma density in this case is that the plasma flow be substantially unaffected by the impurity flux, that is, that the proton density shall be much higher than the impurity density. The impurity density n.sub.z may be estimated from the sputtering yield, by the following relationship: ##EQU6## where .alpha. is the sputtering yield, n.sub.h is the plasma density of hot plasma, .tau..sub.h is the particle confinement time of hot plasma, and .delta. is the ratio of volume of hot plasma, and volume of divertor space. For typical plasma parameters of the illustrated apparatus 10, n.sub.h =10.sup.20 m.sup.-3, .tau..sub.h =0.5 sec, a=0.5 m, .delta.=1, .alpha.=0.1, and v.sub.o =10.sup.3 m/sec. Accordingly, from Equation (12) the impurity density n.sub.z under such conditions is about 1.times.10.sup.16 m.sup.-3. The condition for ionization as set forth in Equation (1) is: ##EQU7## Accordingly, it will be appreciated that these two conditions are not very different. The power P required to maintain the divertor plasma may be represented as: ##EQU8## where R is the major radius. By substituting a plasma length which is approximately equal to Rq (q is the safety factor), the power P may be represented as: ##EQU9## For typical plasma parameters of the illustrated embodiment, n=2.times.10.sup.17, q=3, T.sub.e =20 eV, a=0.5 m, and v.sub.s =4.5.times.10.sup.4 m/sec, the power P may be seen from Equation (15) to be about 30 kW. Turning back to the drawings of FIGS. 1 and 2, a D-shaped plasma 40 is produced in the top half of the chamber 12. The flux surfaces 44 that are not closed in the chamber are made to intersect with the wall in the bottom half. As indicated previously, pure hydrogen gas may be supplied to the upper portion of the vacuum chamber containing the plasma 40 and the vacuum pump ports are in the bottom half. However, a separate gas supply may not be needed, if sufficient gas is introduced to the plasma 40 by means of the neutral beam injector utilized for heating of the plasma 40. A 50 kW r-f power system is applied to maintain the low temperature plasma in the bottom half of the chamber 12. The low temperature plasma has a density of about 10.sup.11 cm.sup.-3 and temperature of about 20 eV. The r-f heating system may be lower hybrid resonance type operating at a frequency of about 1 GHz. The pumping speed of the bottom half of the chamber around the torus of the illustrated embodiment is approximately 10.sup.9 cc/sec. Therefore, the neutral gas density is of the order of 10.sup.-5 Torr. Coating of the wall with titanium may be used to increase the pumping speed. The density and the temperature of the pumping plasma in the illustrated embodiment generally corresponds to the temperature and density of plasma present near the wall or behind the limiter of typical tokamak plasma systems. The heating power utilized to maintain the pumping plasma is a very small fraction of the power throughput of the tokamak plasma 40 in the upper chamber. As is the case of conventional divertors, the design constraint is mainly due to pumping speed. While the method has been particularly described with respect to utilization with Doublet III apparatus, the method may also be used with other apparatus such as the ISX apparatus of ORNL. Furthermore, while the method has been particularly described with respect to a specific operational embodiment, it will be appreciated that various modifications, adaptations and variations will become apparent from the present disclosure and are considered to be within the spirit and scope of the present invention as defined by the following claims. Various of the features of the invention are set forth in the following claims. |
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abstract | A radiation detector system/method that simultaneously detects alpha/beta, beta/gamma, or alpha/beta/gamma radiation within an integrated detector is disclosed. The system incorporates a photomultiplier tube with radiation scintillation materials to detect alpha/beta/gamma radiation. The photomultiplier tube output is then shape amplified and fed through discriminators to detect the individual radiation types. The discriminator outputs are fed to an anti-coincidence and pulse width and timing analysis module that determines whether individual alpha/beta/gamma pulses are valid and should be counted by corresponding alpha/beta/gamma pulse radiation counters. The system may include a radiation detection method to affect alpha/beta/gamma radiation detection in a variety of contexts. The system/method may be implemented in a variety of applications, including but not limited to whole body radiation contamination detectors, laundry radiation scanners, tool/article radiation detectors, and the like. |
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description | The present application claims priority from Japanese application serial no. 2006-051501, filed on Feb. 28, 2006, the content of which is hereby incorporated by reference into this application. The present invention relates to a natural circulation boiling water reactor and a handling method thereof. The conventional natural circulation boiling water reactor is known in which a chimney is disposed above the core inside the reactor pressure vessel (see Japanese Patent Publication No. Hei 7-27051 for example). The chimney has a function for promoting natural circulation of the coolant in the reactor pressure vessel by introducing the coolant which is two-phase flow including gas and liquid and is exhausted from a core, to an upper portion in the reactor pressure vessel. This conventional chimney is formed of flow path partitions that are disposed in the reactor pressure vessel. FIG. 8a is a perspective view showing the conventional chimney and FIG. 8b shows cross section taken along a line Z-Z in FIG. 8a. As shown in FIG. 8a, the conventional chimney 211 forms flow paths 211a of the coolant by a plurality of division of the inside of the reactor pressure vessel (not shown), along the vertical direction thereof. As shown in FIG. 8b, the flow path partition walls 211b form grids in the cross sectional view and the flow paths 211a form a square shape. The flow path partition walls 211b are assembled as a grid of plate members of stainless steel for example and are integrally formed by welding at the position of intersection of each plate member It is to be noted that as shown in FIG. 8b, edges of each of four corners of the chimney 211 (flow path partition walls 211b) in the conventional natural circulation boiling water reactor are welded. However, stress tends to concentrate at the edges of the flow path 211a due to flow-induced vibration (FIV) and the like. There is a possibility that stress corrosion cracking (SCC) will occur at the welded portion 240 where the stress has concentrated. Thus a natural circulation boiling water reactor in which the chimney 211 has a reduced number of welded portions 240 is desired. Furthermore, generally when the chimney in the natural circulation boiling water reactor is repaired or replaced, the chimney is taken out from the reactor pressure vessel. However, in the chimney of the conventional natural circulation boiling water reactor, because the flow path partition wall is heavy and has a length of a few meters in the vertical direction, and are integrally formed by welding the plate members, removing the flow path partition walls from the reactor pressure vessel requires a great amount of stress and time. In the natural circulation boiling water reactor when maintenance and inspection such as checking, repair and processing of the parts around the core such as a core shroud and the like is performed, the chimney is taken out from the reactor pressure vessel. Thus, handling of the natural circulation boiling water reactor at the time of maintenance and inspection such as this checking, repair and processing is extremely complicated. The object of the present invention is to provide a natural circulation boiling water reactor in which a number of welded portions of a chimney can be reduced and the chimney can be easily detached from the reactor pressure vessel. The present invention for attaining the above object is characterized in that the natural circulation boiling water reactor provides to a chimney with a plurality of tubes. That is to say, each of the plurality of tubes partitions the coolant flow path above a core. Thus, unlike the conventional natural circulation boiling water reactor providing the flow path partition wall grid in which the plate members are made integral by welding and coolant flow paths are partitioned, the chimney of the natural circulation boiling water reactor of the present invention can reduce the number of welded portions because the edges of the four corners of each flow path do not need to be welded. The natural circulation boiling water reactor of the present invention can avoid removal as a single unit, as in the case of the flow path partition wall grid in the conventional natural circulation boiling water reactor, by detaching each tube. According to the present invention, because the number of welded portions can be reduced, the number of productions steps and the manufacturing cost when manufacturing the natural circulation boiling water reactor can be reduced, and generation of stress corrosion cracking and the like can be prevented. According to the present invention, because the tubes which form the chimney can be removed individually, maintenance and inspection of the chimney itself as well as structure members around the core can perform easily. A natural circulation boiling water reactor according to an embodiment of the present invention will be described in details with reference to FIG. 1 to FIG. 3. After outlines of the natural circulation boiling water reactor are described, the chimney included in the natural circulation boiling water reactor will be described. (Natural Circulation Boiling Water Reactor Outline) Generally, two types of boiling water reactors are used based on the difference in the method for supplying the coolant (cooling water) to a core. In one method, the coolant is circulated by force using a recirculation pump, and in the other method, a recirculation pump is not used and the coolant is circulated naturally. The boiling water reactor of the present embodiment is the natural circulation boiling water reactor of the latter case. FIG. 1, which will be used here, is an explanatory diagram showing the natural circulation boiling water reactor according to the present embodiment. As shown in FIG. 1, the natural boiling water reactor (referred to as reactor hereinafter) 1 obtains the required circulation force for natural circulation of the coolant due to specific gravity difference between coolant of low density being two-phase flow including gas and liquid and coolant of the liquid phase. The liquid phase coolant includes feed water from a feed water pipe 16b and the low density coolant separated by a steam separator 12. The coolant of the two-phase flow includes mixed the void, or in other words the steam (gas phase) generated in the core 7 stored in a reactor pressure vessel (referred to as pressure vessel) 6 hereinafter and coolant being the liquid phase coolant at saturation temperature. As shown in FIG. 1, The reactor 1 provides the pressure vessel 6 and a cylindrical core shroud 8 disposed so as to be concentric inside the pressure vessel 6. The core shroud 8 has a circular space formed between an outside surface thereof and an inside surface of the pressure vessel 6. A downcomer 9 is formed by this circular space and another circular space formed between the inside surface of the pressure vessel 6 and an outside surface of the chimney shell 11d. The core 7 loading a plurality of fuel assemblies 21 is disposed in the core shroud 8. A circular feed water sparger (not shown) is above the downcomer 9 inside the pressure vessel 6. The circular feed water sparger feeds coolant into the pressure vessel 6 after the coolant is pumped into a feed water heater 5 from a condenser 3 by a feed water pump 4 and heated and then supplied into the pressure vessel 6 through a feed water nozzle 17 connected to the feed water pipe 16b. The core 8 is supported by shroud support legs 8a. The coolant which descends the downcomer 9 is introduced to a core lower plenum (called lower plenum hereinafter) 10 located under the core 8 from the flow paths between the shroud support legs 8a. A core plate 22 is provided under the core 7. A first grid support plate 11f which forms the chimney 11 described hereinafter is provided above the core 7. As described below, this first grid support plate 11f functions as the top guide of the conventional reactor and determines the cross-direction position of the core support plate 22 as well as the fuel assemblies 21 and control rods 24. The core plate 22 has circular penetration holes (not shown) at prescribed intervals and the control rod guide tubes 25 are inserted into these penetration holes. The lower portion of the control rod guide tube 25 combines with the upper portion of a control rod drive mechanism housing (called CRD housing hereinafter) 26a which installs a control rod drive mechanism (called CRD hereinafter) 26. The CRD 26 penetrates the bottom of the pressure vessel 6, joins the control rod 24 and moves the control rod 24 in the vertical direction. Four fuel assemblies 21 is supported by a fuel support (not shown) that is mounted on the upper end portion of the control rod guide tube. Load of the fuel assemblies 21 is transmitted to the bottom of the pressure vessel 6 via the control rod guide tube 25 and the CRD housing 26a. As is known, the fuel support (not shown) has four coolant inlets at the side wall. Orifices that are provided at the coolant inlets respectively limit the coolant flow rate. The control rod guide tube 25 has four openings at a position corresponding to the coolant inlets of the fuel support respectively. By flowing through this opening, the coolant supplied to the lower plenum 10 is further introduced in each fuel assembly 21 via the fuel support through the orifice and the opening of the control rod guide tube 25. Each fuel assembly 21 has a fuel bundle and a channel box (not shown) being square cylinder. The fuel bundle is enclosed by square cylinder channel box. Individual flow paths are formed in each channel box in the vertical direction thereof. Because the upper ends of the channel box are bound at the lower portion of the first grid support plate 11f, the fuel assembly 21 determines the cross-direction position as described above. The control rod 24 comprises an effective portion which includes a neutron absorber (not shown) and the effective portion is inserted between the fuel assemblies 21 by being guided at the outer surface of the channel box. A plurality of local power range monitor (LPRM) detector assemblies (simply called LPRM hereinafter) 33 are arranged in the core 7. The LPRM has a plurality of neutron detectors and measures the neutron flux of the power region. The lower portion of the LPRM 33 is housed at the in-core monitor housing 33a which passes through the penetration hole formed at the bottom of the pressure vessel 6 and the signal cable (not shown) comes out from the lower end of the in-core monitor housing 33a. A chimney 11 which will be described in detail hereinafter is disposed above the core 7. The upper end of the chimney shell 11d which forms the chimney 11 is closed by the shroud head 12a. At the upper portion in the chimney shell 11d, the upper plenum 11c is partitioned between the shroud head 12a and the second grid support plate 11e which forms the chimney 11a. The coolant is come in the upper plenum 11c through grid holes 41b described hereinafter (see FIG. 2b) formed in the second grid support plate 11e. A plurality of holes (not shown) through which the coolant is passed are formed in the shroud head 12a. The holes connect with the steam separator 12 via the stand pipe 12b. The steam separator 12 separates the coolant coming out of the holes formed in the shroud head 12a in the flow state of two-phase flow including saturated steam and saturated water. A steam dryer 13 is disposed above the steam separator 12. The steam dyer 13 removes the moisture content being included in the saturated steam separated at the steam separator 12. The saturated steam exhausted from the steam dryer 13 is supplied to the turbine 2 via a steam dome 14, a steam outlet nozzle 15, and a main steam pipe 16a. It is to be noted that the shroud head 12a, stand pipe 12b and steam separator 12 are assembled as a single unit and at the time of fuel exchange, they can be removed from the chimney 11 as one unit. (Chimney) As shown in FIG. 1, the chimney 11 introduces the coolant exhausted from the core 7 in the flow state of two-phase flow including gas and liquid above the pressure vessel 6. Natural circulation of the coolant in the pressure vessel 6 is thereby promoted. The chimney 11 mainly comprises the chimney shell 11d, the square tube 11b, the first grid support plate 11f (grid support plate) and the second grid support plate 11e. It is to be noted that the square tubes 11b are the “tubes” referred to in the scope of the claims and the first grid support plate 11f is the “grid support plate”. As shown in FIG. 1, the chimney shell 11d is disposed above the core 7 in the pressure vessel 6, and is formed of a cylindrical member. The chimney shell 11d is disposed so as to be concentric with the pressure vessel 6. A plurality of square tubes 11b is disposed in the chimney shell 11d so as to extend in the vertical direction. As described hereinafter, an upper ends of the square tubes 11b are supported around the circumference of grid holes 41b (see FIG. 2b) formed in the second grid support plate 11e. The lower ends of the square tubes 11b are supported around the circumference of the grid holes 41a (see FIG. 2b) formed in the first grid support plate 11f. Next, the arrangement of the square tubes 11b in the chimney shell 11d will be described in further detail. FIG. 2a shows a cross-section of the chimney taken along a line X-X in FIG. 1. FIG. 2b is a disassembled perspective view of the chimney. FIG. 2c shows a cross-section taken along a line Y-Y in FIG. 2a. However, in FIGS. 2a-2c the chimney shell is omitted for the sake of convenience. As shown in FIG. 2a, the square tubes 11b of this embodiment are formed such that the outline is that of a square in the cross-section and are disposed at W2 intervals exceeding the width W1 of each square tube in the rows and columns. More specifically, by arranging a square tube 11b in every other grid hole 41a formed in the first grid support plate 11f, the interval W2 between the square tubes 11b comes to exceed the width W1 of each square tube so that as illustrated in FIG. 2a, the arrangement of the square tubes 11b of one row are offset with respect to the arrangement of the squares tubes 11b of an adjacent row. The square tubes 11b are arranged in this manner, so leaving space S between the edges of the adjacent square tubes 11b. As shown in FIG. 2b, the first grid support plate 11f is formed of a disc-like member. The grid hole 41a is formed which penetrates this member in the thickness direction. The planar configuration of the grid hole 41a has substantially the same configuration as the cross-section configuration of the inside space of the square tube 11b, or in other words, is square-shaped. There is a plurality of grid holes 41a so as to be aligned in the surface of the first grid support plate 11f. The interval of the grid hole 41a is set to be a distance at which the square tubes 11b do not interfere with each other when the adjacent grid holes 41a support the square tubes 11b. At the opposite surface (lower surface) of one surface (upper surface) of the first grid support plate 11f which supports the square tubes 11b, the upper end portion of the fuel assembly 21 (channel box) is fit into the opening of the grid hole 41a, to thereby bind the fuel assembly 21 at the first grid support plate 11f. As shown in FIG. 1, the first grid support plate 11f is disposed in the pressure vessel 6, and thus the coolant exhausted from the core 7 in the flow state of two-phase flow including gas and liquid will be introduced in the chimney shell 11d via the grid hole 41a. This type of structure in which the first grid support plate 11f supports the square tubes 11b is preferably a structure in which the square tubes 11b are supported so as to be detachable. As shown in FIG. 2c, one example comprises the circular groove H which is formed in the first grid support plate 11f and the protruding rib P of the square tube 11b which fits into the groove H. The groove H is formed around the circumference of the grid hole 41a of the first grid support plate 11f so as to be along the outline of its square shape. The protruding rib P is formed at the lower end of the square tube 11b so as to correspond to the groove H. By the square tube 11b being supported at the first grid support plate 11f, the inside of the square pipes 11b and the grid hole 41a are connected. It is to be noted that the structure in which the first grid support plate 11f supports the square tubes 11b may be one in which the first grid support plate 11f and the square tube 11b are fastened by fastening devices such as bolts. As shown in FIG. 2b, the second grid support plate 11e supports the upper end portion of the square tubes 11b and has a similar structure to that of the first grid support plate 11f. That is to say, a plurality of grid holes 41b is formed at the second grid support plate 11e. A structure (not shown) for supporting the upper end portion of the square tubes 11b is provided at one surface (lower surface) of the side where the square tubes 11b are disposed. This structure is formed in the same manner as the structure of the first grid support plate 11f which supports the lower end portions of the square tubes 11b. After the core 7 (without fuel assembly) is formed in the pressure vessel 6 shown in FIG. 1, this type of chimney 11 is installed above the core 7. At this time, the chimney 11 may be assembled inside the pressure vessel 6, or the chimney 11 may assembled in advance at the outside of the pressure vessel 6 and then installed inside the pressure vessel 6. Also, the material of the members forming the chimney 11 (the first grid support plate 11f, the second grid support plate 11e, the square tubes 11b, the chimney shell 11d and the like) may be that used in the conventional reactor, and any material with excellent heat resistance and anticorrosive properties may be suitably selected and used. Examples of the material include stainless steel, zirconium alloys, titanium alloys and the like. The square tubes 11b may for example be formed by processing a plate-like member. (a)-(d) of FIG. 3 which will be referred to here shows the steps for manufacturing the square tubes. As shown in (a) of FIG. 3, four parallel bending lines 43a with intervals corresponding to the width W1 of the square tube 11b (see FIG. 2b) are established on the standard plate member 43. Then, as shown in (b) of FIG. 3, the plate member 43 is bent inward at 90 degrees along the bending lines 43a. As a result, as shown in (c) of FIG. 3, a square tube 11b is formed which has the seam 40a of the plate member 43 at one side surface. The seam 40a extends along the longitudinal direction of the square tube 11b. As shown in (d) of FIG. 3, a square tube 11b with a width W1 is obtained by welding the plate members along the seam 40a. In the square tube 11b obtained in this manner, the welding line 40 which is aligned with the seam 40a (see (c) of FIG. 3) is set. The welding line 40 is preferably set at a position which is ⅛ to ⅜ of the width W1 from the edge of the square 111b to the side surface. Next, the operation of the reactor 1 of this embodiment will be described with reference to FIG. 1 and FIG. 2a to FIG. 2c as appropriate, and the operational effects of this reactor 1 will be described. As shown in FIG. 1, in this reactor 1, the coolant supplied from the feed water inlet nozzle 17 to the reactor pressure vessel 6 is mixed with the saturated water separated by the steam separator 12. The coolant descends the downcomer 9 in the direction indicated by the arrow A and flows into the core shroud 8 from the flow path formed by the space (not shown) in the shroud leg 8a. As a result, the coolant is heated in the core 7. The heated coolant flows in the flow state of saturated two-phase flow including gas and liquid in the direction indicated by the arrow B. That is to say, the coolant is introduced in the chimney shell 11d (see FIG. 1) via the grid hole 41a (see FIG. 2b) of the first grid support plate 11f of the chimney 11. Then, as shown in FIG. 2a, the coolant that flows into the grid hole 41a in which there are no square tubes 11b passes through the region enclosed by the side surfaces of four square tubes 11b (side walls of the square tubes 11b) and is introduced into the upper plenum 11c (see FIG. 1) through the grid hole 41b of the second grid support plate 11e in which there are no square pipes 11b. Meanwhile, the coolant passed through the grid holes 41a in which there are square tubes 11b (see FIG. 2a and FIG. 2c) is supplied into the square pipes 11b and then flows into the upper plenum 11c from the grid hole 41b of the second grid support plate 11e shown in FIG. 2b in which there are square tubes 11b. In this chimney 11, as shown in FIG. 2a, because the edges of the adjacent square tubes 11b are separated and the space S is formed in between the adjacent square tubes 11b, when the coolant passes through the regions that is enclosed by side surfaces of four square tubes 11b (side walls of the square pipes 11b) inside the chimney shell 11d, the stress originating at the square tubes 11b due to generation of the flow-induce vibration (FIV) is reduced compared with the case where the edges of the square pipes 11b are connected. As shown in FIG. 1, the coolant of two-phase flow introduced to the upper plenum 11c flows into the standpipe 12b and further is supplied into the steam separator 12. The steam separator 12 separates the coolant of two-phase flow into saturated steam that flows in the direction of arrow C, and saturated water that flows in the direction of arrow D. This separated saturated steam flows through the steam dryer 13 and is then supplied to the turbine 2 through the main steam pipe 16a via the steam outlet nozzle 15 and used for power generation. Also, the separated saturated water is mixed with the coolant in the pressure vessel 6 and then further mixed with the coolant supplied from the feed water inlet nozzle 17. Then the coolant descends the downcomer 9 again to circulate in the pressure vessel 6. According to the reactor 1 of this embodiment which was described above, when the coolant flows inside the chimney shell 11d, the stress being applied to the square tubes 11b by flow-induce vibration (FIV) is reduced. Thus, the possibility of stress corrosion cracking (SCC) being generated at the square tubes 11b is reduced. This effect is most remarkable at the edges of the square tubes 11b. According to this reactor 1, the first grid support plate 11f which forms the chimney 11, also functions as the top guide of the conventional reactor, and thus this top guide may be omitted, or may be simplified (made thinner). As a result, the construction cost for the top guide can be eliminated. Furthermore, in the reactor 1, because each square tubes 11b divides the inside of the chimney shell 11d and is formed a plurality of partitioned flow paths of the coolant above the core 7, unlike the conventional reactor having the flow path partition wall grid in which the plate members are made integral by welding and coolant flow paths are partitioned, the edges of the four corners of each flow path does not need to be welded. Thus, in this reactor 1, the number of welded parts in the chimney 11 can be reduced and therefore the possibility that the SCC will be generated at the welded portions is reduced. Also, the number of productions steps and the manufacturing cost when manufacturing the reactor 1 can be reduced. According to the reactor 1, by removing the square tubes 11b, removal as one unit as is the case of the flow path partition wall grid in the conventional reactor is avoided. As a result, in this reactor 1, removal of the chimney 11 can be easily performed. Furthermore, according to the reactor 1, because the square tube 11b which forms the chimney 11b can be easily formed by bending the plate member 43, the chimney 11 itself can be easily produced. In the reactor 1, because the square tube 11b which forms the chimney 11b is formed by bending the plate member 4, it is sufficient for the welding line 40 for forming the square pipe 11b to be at one location. As a result, the possibility of the SCC being generated is reduced. Also, in the reactor 1, because the welding line 40 on the square pipe 11b which forms the chimney 11b is set on the side surface of the square pipe 11b, the possibility of the SCC being generated is reduced compared with the case where the welding line is set on the edge of the square tube 11b. In the reactor 1, because the welding line 40 on the square tube 11b which forms the chimney 11b is set at a position which is ⅛ to ⅜ of the width W1 from the edge of the square tube 11b to the side surface, the possibility of the SCC being generated is further reduced. It is to be noted that the present invention is not to be limited by the above embodiments, and various modifications are possible. In the above embodiment, the square tubes 11b in the chimney 11 are arranged such that one is in every other grid hole 41, but the square tubes 11b may be arranged so that there is one in every 2 or more grid holes 41. In this embodiment, the chimney 11 is formed of square tubes 11b, but the cross-sectional configuration of the tube is not particularly limited. The outline of the outer side of the cross-section may for example, be circular, elliptical or polygonal (not square). Also, in this embodiment, square tube 11b is formed by bending one plate member 43, but a pair of plate members 43 which have been bent to form a C-shape may be welded to each other. In addition, in this embodiment, the upper ends of the square tubes 11b are supported by the second grid support plate 11e, but the member for supporting the square tubes 11b is not particularly limited, and may for example, be flanges formed on the square tubes 11b and these flanges may be joined to each other. (Handling Method for the Natural Circulation Boiling Water Reactor) Next, the handling method for the reactor 1 of this embodiment will be described with reference mainly to FIG. 1 and FIG. 4 to FIG. 7b. First, the case in which a square pipe 11b which is a part of the chimney 11 is replaced in the reactor 1 is used as an example for describing the handling method for the reactor 1. FIG. 4 which is used here is a process chart for replacing the square tube, while FIG. 5 shows the state where the square tubes are removed from the reactor. As shown in FIG. 4, in the case where a predetermined square pipe 11b needs to be replaced, first the operation of the reactor 1 is shut down (Step S1). Then, as shown in FIG. 5, a predetermined water level is maintained in the temporary storage/cutting pool 42 which is a structure attached to the reactor 1. Next, as shown in FIG. 4, the pressure vessel 6 (see FIG. 1) is opened (Step S2). In-reactor devices such as the steam separator 12 and the shroud head 12a and the like (see FIG. 1) which will interfere with the operation of replacing the square tube 11b are taken out from the pressure vessel 6 (Step S3). Next, fuel assembly 21 is taken out from the core 7 (see FIG. 1) via the grid holes 41b (see FIG. 2(b)) of the second grid support plate 11e which becomes visible when the shroud head 12a is detached (Step S4). The second grid support plate 11e is then taken out from the pressure vessel 6. Next, the square tube 11b being replaced (inscribed old square tube in FIG. 4) is taken out from the pressure vessel 6 (Step S5). The square tube 11b that has been taken out is carried into the temporary storage/cutting pool 42 and temporarily put in the temporary storage/cutting pool 42 (Step S6). The processes from Step 2 through Step 6 are all performed in the state where the temporary storage/cutting pools 42 (see FIG. 5) are filled with water. As shown in FIG. 5, crane 42b is used in order to take out each of the members from the pressure vessel 6. This is not shown but all of the members that are taken out are temporarily placed in the temporary storage/cutting pool 42. Next, the square tubes 11b that is temporarily placed in the temporary storage/cutting pool 42 shown in FIG. 5 are cut in the temporary storage/cutting pool 42 for disposal (Step S7), as shown in FIG. 4. The cut pieces are accommodated in a specified cask (not shown), and then conveyed from the temporary storage/cutting pool 42 (Step S8). The cask is transferred to a storing pool (not shown) (Step S9). On the other hand, the new square tube 11b (inscribed “new square tube” in FIG. 4) is placed inside the pressure vessel 6 using the crane 42b (Step S10). Subsequently, the fuel assembly 21 is placed in the core 7 (see FIG. 1) via the grid hole 41b (see FIG. 2b) of the second grid support plate 11e by the crane 42b (Step S11). The in-reactor devices such as the steam separator 12, the shroud head 12a and the like (See FIG. 1) that have been taken out from the reactor vessel 6 in Step S3 are installed in the reactor vessel 6 and restored to the original state (Step S12). Then the reactor vessel 6 is closed (Step S13). After the water in the temporary storage/cutting pool 42, that is, at least above the reactor vessel 6 has been exhausted, the reactor 1 starts up (Step S14), and thus a series of steps in the method for handling the reactor 1 ends. Next, a handling method for the reactor 1 using the example of the case where maintenance and inspection of the reactor 1 is performed, will be described with reference mainly to FIG. 6 and FIGS. 7a and 7b. FIG. 6 shows a process for performing maintenance and inspection. FIG. 7a and FIG. 7b show the state in which the square tubes are switched. It is to be noted that the steps before Step S21 shown in FIG. 6 are the same as Step S1 to Step S4 in FIG. 4 and the steps after Step S23 shown in FIG. 6 are the same as Step S11 to Step S14 in FIG. 4. Thus, these steps are omitted in FIG. 6 and detailed descriptions of these steps are also omitted. In the handling method for the reactor 1 herein, after the fuel assembly 21 is taken out from the core 7 (see FIG. 1 and Step S4 in FIG. 4), as shown in FIG. 6, the square tubes 11b are shifted (Step S21). More specifically, as shown in FIG. 2a, the predetermined square tubes 11b supported by the first grid support plate 11f are moved in the direction of the broken line arrow. Thus prescribed square tubes 11b are moved into the grid holes 41a which appear between the square tubes 11b. The step of shifting the square tubes 11b is equivalent to the “first step” referred to in the scope of the claims. As shown in the example of FIG. 7a, three square tubes 11b are shifted. As a result, the predetermined square pipes 11b indicated by the broken lines in FIG. 7a are shifted and grid holes 41a appear at the position from which the predetermined square pipes 11b are removed, and space for placing devices used in the maintenance/inspection is secured by removing predetermined square tubes 11b. The maintenance and the inspection of the members in the circumference of the core 7 such as the core shroud 8 and the like (see FIG. 1) can be performed via the grid holes 41a and 41b that was formed (Step S22). “The maintenance and the inspection” herein includes inspection, repair and processing of the members comprising the reactor 1. It is to be noted this step is equivalent to the “second step” referred to in the scope of the claims. Next, after the maintenance and the inspection of the reactor 1 are completed, by moving each square tube in the direction of the broken line arrow (arrow in a direction of arrow opposite to the direction of the broken line arrow shown in FIG. 2a) shown in FIG. 7a, as shown in FIG. 6, reinstallation of the square tubes 11b is performed (Step S23). That is to say, the square tubes 11b are reinstalled so as to be disposed as shown in FIG. 2a. Subsequently, this series of steps in the handling method for the reactor 1 ends by performing the steps from Step S11 to Step S14 shown in FIG. 4. It is to be noted that this handling method is not limited to the case where the square tube 11b which is disposed so as to enclose one grid hole 41a is shifted, as shown in FIG. 7a, but as shown in FIG. 7b, the square tubes 11b at the position close to the chimney shell 11d may be shifted in the direction of the broken line arrow. According to the handling method for the reactor 1 described above, because the square tubes 11b can be removed individually, there is no need for them to be taken out as one unit as is the case of the flow path partition wall grid in the conventional reactor. As a result, according to this handling method, replacement and repair of the structural members (square tubes 11b and the like) of the chimney 11 as well as maintenance and inspection of the structural members of the reactor 1, particularly the members around the core 7, can be performed easily. |
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abstract | Because a mirror electron imaging type inspection apparatus for obtaining an inspection object image with mirror electrons has been difficult to optimize inspection conditions, since the image forming principles of the apparatus are different from those of conventional SEM type inspection apparatuses. In order to solve the above conventional problem, the present invention has made it possible for the user to examine such conditions as inspection speed, inspection sensitivity, etc. intuitively by displaying the relationship among the values of inspection speed S, inspection object digital signal image pixel size D, inspection object image size L, and image signal acquisition cycle P with use of a time delay integration method as a graph on an operation screen. The user can thus determine a set of values of a pixel size, an inspection image width, and a TDI sensor operation cycle easily with reference to the displayed graph. |
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claims | 1. A method to clean or replace a debris shield in a nuclear reactor fuel bundle assembly for a nuclear reactor core, the assembly including a bundle of fuel rods mounted below an upper tie plate and housed in a channel, the method comprising:(a) inserting a debris shield in the upper tie plate;(b) maintaining the shield in the upper tie plate and above the fuel rods, while the fuel assembly is in the operating nuclear reactor core;(c) flowing coolant through the bundle and the debris shield during operation of the nuclear reactor core;(d) capturing or deflecting debris falling down to the fuel assembly with the debris shield;(e) after steps a to d, removing the fuel bundle assembly from the nuclear reactor core, and(f) after step (e) removing the debris shield from the upper tie plate. 2. The method in claim 1 further comprising after step (f) inserting at least one of the debris shield and another debris shield in the upper tie plate and positioning the fuel bundle assembly into the nuclear reactor core. 3. The method in claim 1 wherein debris is captured or deflected while coolant flow is stagnant or reversing. 4. The method in claim 1 wherein after step (e) the fuel bundle assembly is moved to a maintenance or fuel inspection pool and step (f) is performed while the fuel bundle assembly is in the maintenance pool. 5. The method in claim 4 further comprising:after step (f) and while the fuel bundle assembly is in the maintenance or fuel inspection pool inserting at least one of the debris shield or and another debris shield in the upper tie plate, and positioning the fuel bundle assembly into the nuclear reactor core, andafter step (f) moving the fuel bundle assembly from the maintenance or fuel inspection pool to the nuclear reactor core. 6. The method in claim 1 wherein step (f) includes removing the debris shield from a slot in a frame of the upper tie plate. 7. The method in claim 6 wherein the debris shield is removed by being slid horizontally from the slot. 8. The method in claim 1 wherein step (f) further includes removing the upper tie plate while the debris shield remains attached to the fuel rods and thereafter removing the debris shield. 9. The method in claim 1 wherein the upper tie plate includes a rectangular frame and the method further comprises supporting a tie rod in the rectangular frame of the upper tie plate, wherein the frame defines a generally horizontal open area and the debris shield covers the open area. 10. A method to capture and remove debris falling into a nuclear reactor fuel bundle assembly a nuclear reactor core, the assembly including a bundle of fuel rods mounted below an upper tie plate and housed in a channel, the method comprising:inserting a debris shield in the upper tie plate;maintaining the shield in the upper tie plate and above the fuel rods, while the fuel bundle assembly is in an operating nuclear reactor core;flowing coolant through the fuel rods and the debris shield during operation of the nuclear reactor core;capturing debris falling in the fuel assembly on the debris shield;after capturing the debris, removing the fuel bundle assembly with the inserted debris shield from the nuclear reactor core to a maintenance or fuel inspection pool and thereafter removing the debris shield from the upper tie plate, performing at least one of (a) removing the captured debris from the removed debris shield and thereafter reinserting the debris shield into the upper tie plate and (b) inserting another debris shield into the upper tie plate, andafter the reinsertion of the debris shield or the insertion of the another debris shield, moving the fuel bundle assembly from the maintenance or fuel inspection pool to the nuclear reactor core. 11. The method of claim 10 wherein the reinsertion of the debris shield or the insertion of another debris shield includes sliding the debris shield in a horizontal slot in the upper tie plate. 12. The method of claim 10 wherein the reinsertion of the debris shield or the insertion of another debris shield includes lifting the upper tie plate up and off of the debris shield while the debris shield remains attached to the fuel rods, and thereafter removing the debris shield from the fuel rods. 13. The method in claim 10 wherein debris is captured while coolant flow is stagnant or reversing. 14. The method in claim 10 wherein inserting the debris shield includes positioning the debris shield in an opening of the upper tie plate. 15. The method in claim 10 wherein the debris shield includes an aperture and the method further comprises supporting a tie rod in an aperture of the debris shield. 16. The method of claim 10 wherein the insertion of the debris shield includes positioning the debris shield below and adjacent a lower surface of the upper tie plate. 17. A method to seat an upper tie plate in a fuel bundle assembly for a nuclear reactor, wherein the fuel bundle assembly includes fuel rods, at least one water rod, tie rods, and a channel, the method comprising:attaching a debris shield to upper portions of the fuel or water rods, wherein the debris shield includes openings to receive the upper portions and apertures narrower than the openings, and the openings extend through an area of the debris shield having the apertures, andafter attaching the debris shield, seating the upper tie plate over the debris shield and securing the upper tie plate to the tie rods of the fuel bundle assembly. 18. The method of claim 17 wherein the upper tie plate includes a lower cavity and the seating step includes fitting the lower cavity in the upper tie plate over the debris shield. 19. The method of claim 17 further including removing the upper tie plate while the debris shield remains attached to the upper portions of the fuel or water rods. 20. The method of claim 19 further including removing at least one of the fuel rods through one of the openings in the debris shield while the upper tie plate is removed and while the debris shield remains attached to one the upper portions of at least one of the fuel rods. 21. The method of claim 17 wherein the upper portions of the fuel rods include end plugs and the end plugs are attached to the debris shield. 22. A method to remove a fuel rod from a fuel bundle for a nuclear reactor, wherein the fuel bundle includes a bundle of fuel rods and a water rod mounted below the upper tie plate, the method comprising:removing the upper tie plate from the fuel bundle, while the debris shield remains attached to an upper portion of at least one of the fuel rods or of a water rod, andafter removing the upper tie plate, removing the fuel rod by lifting the rod up through the debris shield, while the debris shield remains attached to an upper portion of at least one of the fuel rods or of the water rod. 23. The method of claim 22 wherein the removed fuel rod is not threaded and the fuel rod or water rod attached to the debris shield is threaded. 24. The method of claim 22 wherein the at least one of the fuel rods is configured to receive an expansion spring, and the at least one of the fuel rods is removed with the expansion spring mounted on the removed fuel rod. 25. The method of claim 24 wherein the expansion spring extends up through the debris shield and abuts the upper tie plate before the upper tie plate is removed. 26. The method of claim 22 further comprising moving the fuel bundle from a nuclear reactor core to a maintenance or inspection pool, and removing a metal channel from the fuel bundle. 27. The method of claim 22 further comprising inserting a fuel rod through the debris shield in place of the removed fuel rod, and thereafter seating the upper tie plate on the debris shield. |
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claims | 1. An ion implanter for implanting a substrate with a material comprising:an ion source;a beam line assembly configured to extract ions from said ion source to form an ion beam and direct said ion beam toward a substrate disposed on a substrate support;a mask disposed in front of said substrate, said mask having a plurality of apertures to allow respective portions of said ion beam through said mask toward said substrate; anda scanning assembly configured to move said substrate support with respect to said ion beam at a first scan rate when first portions of said substrate are aligned with said plurality of apertures and at a second scan rate when second portions of said substrate are aligned with said plurality of apertures wherein said first scan rate is faster than said second scan rate and said second scan rate corresponds to point contacts of a solar cell. 2. The ion implanter of claim 1 wherein said mask is fixedly disposed, with respect to said ion beam, in front of said substrate. 3. The ion implanter of claim 1 wherein said ion beam has a height dimension, said apertures having a length corresponding to said height dimension. 4. The ion implanter of claim 1 further comprising a cooling subassembly connected to said mask for maintaining a temperature of said mask. 5. The ion implanter of claim 1 wherein said second portions of said substrate have a higher dose rate of ions from said ion beam as compared to said first portions of said substrate. 6. The ion implanter of claim 5 wherein said second portions of said substrate correspond to said point contacts in said solar cell. |
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041697588 | abstract | Apparatus for the in situ inspection of a nuclear reactor vessel to detect the location and character of flaws in the walls of the vessel, in the welds joining the various sections of the vessel, in the welds joining attachments such as nozzles, elbows and the like to the reactor vessel and in such attachments wherein an inspection head carrying one or more ultrasonic transducers follows predetermined paths in scanning the various reactor sections, welds and attachments. |
046631127 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method for determining the contents of a fuel rod within a test range extending along the length of the fuel rod. The objective in particular is to distinguish fuel pellets of pure uranium dioxide from those which are doped with oxides of rare earths, for instance, with gadolinium oxide, Gd.sub.2 O.sub.3. 2. Description of the Prior Art Heretofore, for this purpose, the closed fuel rod has been irradiated with a neutron source and subsequently, the secondary radiation of the fuel rod was recorded over its length. This secondary radiation of differently doped fuel pellets can be distinguished from the radiation of pure UO.sub.2 in the fuel rod. However, this so-called "rod scanning" requires considerable equipment in the form of a large number of measuring devices and radiation protection measures which represent a substantial investment. SUMMARY OF THE INVENTION An object of the invention is to provide a method for distinguishing doped fuel pellets from those of pure UO.sub.2 in fuel rods with materially less investment cost than the method heretofore used, and in particular without the requirement for the radiation protection measures previously needed. With the foregoing and other objects in view, there is provided in accordance with the invention a method for determining the contents of a fuel rod containing fuel pellets of pure uranium dioxide and doped fuel pellets within a test range extending along the length of the fuel rod which comprises concentrically surrounding the fuel rod with a test coil and moving the test coil from the beginning to the end of the test range, measuring the impedance of the test core as a function of its position during movement, and feeding the test coil an a-c voltage with a frequency sufficiently low to produce a measurement value in the region of a fuel pellet of pure uranium dioxide which clearly distinguishes from a measurement value in the region of a doped fuel pellet. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a method for determining the contents of a fuel rod, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. |
description | This application is a continuation of U.S. application Ser. No. 10/695,504 filed on Oct. 29, 2003 now abandoned and also claims Paris Convention priority of DE 102 54 026.8 filed Nov. 20, 2002 the complete disclosures of which are hereby incorporated by reference. The invention concerns a reflector for X-ray radiation which is curved in a non-circular arc shape along a first cross-section in a plane containing an x-direction (tangential curvature), wherein the reflector is also curved along a second cross-section in a plane perpendicular to the x-direction (sagittal curvature). An X-ray mirror of this type is disclosed e.g. in DE 44 07 278 A1. X-ray radiation is electromagnetic radiation as is visible light. Due to the higher energy on the order of keV, the interaction between X-ray radiation and matter is significantly different than with visible light. Considerable difficulties were found in providing effective optical structural elements such as mirrors or lenses for X-ray radiation. The structural elements realized up to now are based mainly on Bragg diffraction and total reflection, both under grazing incidence. In a flat embodiment, an X-ray mirror on the basis of the Bragg diffraction can only reflect a very small portion of the incident divergent X-ray radiation, since the Bragg condition requires relatively accurate angles of incidence. To solve this problem, curved mirror surfaces and also a locally variable planar separation were suggested. The curvature of the mirror surface and the planar separation may thereby vary along a first direction x which corresponds approximately to the main propagation direction of the X-ray radiation (under grazing incidence). For normal dimensions of X-ray analysis devices, the local radius of curvature is on the order of meters and usually has a parabolic or elliptical shape. It is technically relatively easy to produce. To realize a variable planar separation, a multi-layer mirror design has been used. This type of X-ray mirror is referred to as a “Goebel Mirror” (DE 44 07 278 A1). The reflectivity of the Goebel mirror is limited in that the divergence of the beam perpendicular to the x-direction in the mirror plane cannot be satisfactorily taken into consideration. Two-dimensional focusing is feasible through a rotationally symmetrical design i.e. a second circular arc-shaped mirror curvature in the plane perpendicular to the x-direction. For typical dimensions of X-ray analysis devices, the mirror must have radii of curvature perpendicular to the x-direction in the millimeter range. It has not been previously possible to produce such a strongly curved X-ray mirror with sufficient accuracy, since sufficiently precise reduction in the surface roughness and waviness of such a strongly curved mirror is difficult. Moreover, it has not been possible up to now to prevent layer thickness errors for multi-layer mirrors in the region of large radii of curvature (i.e. at the mirror edge) using conventional coating techniques (sputtering, molecular beam epitaxy etc.), with a reasonable degree of effort. These coating errors reduce the reflectivity of the X-ray mirrors for the desired X-ray wavelength and introduce scattered rays of other wavelengths. To still obtain two-dimensional focusing, two one-dimensionally focusing Goebel mirrors, which are rotated relative to each other through approximately 90°, must be used in series. This causes considerable intensity loss. Another disadvantage of rotationally symmetrical Goebel mirrors is the circular annular beam profile of the reflected X-ray radiation outside of the focus. Either the sample or the detector is usually in the focus and therefore either the detector or the sample must be disposed in the region of the annular beam profile. This reduces the intensity, and the optical path of such an X-ray analysis device lacks flexibility due to the annular beam profile. Rotationally symmetrical total reflection mirrors with two-dimensional focusing are also known. Due to the reduced light collecting capacity, the very small maximum angle of incidence, the associated adjustment difficulties, and the lack of monochromatization, total reflection mirrors are no practical alternative. In contrast thereto, it is the object of the present invention to make the design of X-ray mirrors and the beam shape of reflected X-ray radiation more flexible, to facilitate production of X-ray mirrors with high efficiency (i.e. high reflection capacity and good focusing properties). This object is achieved in a surprisingly simple but effective fashion by a method for manufacturing a reflector for X-ray radiation (X-ray mirror) of the above-presented type which is characterized in that the reflector has a curvature along the second cross-section which is also not circular arc-shaped. The curvature along the second cross-section (sagittal curvature) is particularly critical for the production of two-dimensional focusing mirrors. In accordance with the invention, this second curvature is not circular arc-shaped. In particular, deviations, which reduce the curvature of the reflector along the second cross-section and in particular in the edge region of the reflector, are of particular importance. The polishing processes for reducing the roughness or waviness of the reflector surface can be greatly facilitated. A deviation from the rotationally symmetrical shape also offers new design possibilities for the beam shape of the reflected X-rays outside of the focus. The circular annular shape outside of the focus can be eliminated and appropriate design of the curvature of the inventive reflector along the second cross-section can be used to adjust the beam shape to the requirements of a particular experiment. Possible alternative beam shapes include an elliptical, annular shape and a lens-type shape. The beam shape can, in particular, be adjusted to the shape of a sample to be examined, to an X-ray detector, or an entrance slit thereof. The deviation from the curvature along the second cross-section permits compensation of coating errors in multi-layer mirrors, without reducing the reflectivity of the X-ray mirror (see below). In an advantageous embodiment of the inventive reflector, the curvature of the reflector along the second cross-section adjusts the focusing properties of the reflector, in particular in the plane perpendicular to the x-direction. The curvature of the reflector along the second cross-section determines the direction of the outgoing X-rays, which, upon incidence initially diverge in the reflector plane perpendicular to the x-direction. The focusing effect of the curvature along the second cross-section can preferably be selected such that the focus of both curvatures of the reflector coincide e.g. at the detector or at infinity (parallel beam). One embodiment of the inventive reflector is particularly advantageous wherein the reflector focuses or renders parallel in two dimensions. This produces a high intensity of the outgoing X-rays since only one loss-causing reflection on the inventive reflector is required for two-dimensional focusing or parallelization of the X-rays. In a further advantageous embodiment, the reflector is curved parabolically, hyperbolically or elliptically along the first cross-section (tangential curvature). The parabolic shape is the basic shape of the Goebel mirror and permits parallelization of the outgoing X-rays, which exhibit a beam divergence when incident on the reflector across the mirror surface in the x-direction. An elliptical shape permits focusing of the initially divergent beam to a specific focal spot. The preferred embodiment of the inventive reflector is characterized in that the reflector has a periodically repeating sequence of layers of materials A, B, . . . with different refractive indices, wherein the sum d=dA+dB+ . . . of the thicknesses dA, dB, . . . of sequential layers of materials A, B, . . . changes continuously along the x-direction, in particular, monotonically. This embodiment corresponds to a Goebel mirror whose curvature along the second cross-section is not circular arc-shaped. Up to now it has not been technically possible to produce Goebel mirrors with rotationally symmetrical second curvature of satisfactory quality. The above-mentioned embodiment is far easier to produce than a rotationally symmetrical Goebel mirror and has comparable X-ray optical properties. The change in the angle of incidence on the multi-layer across the length of the X-ray mirror from the front to the back (in the x-direction) is compensated for with respect to the Bragg condition through adjusting the layer separation (planar separation) to ensure good reflectivity for the X-ray radiation of a given wavelength over the entire length of the X-ray mirror. Focusing of the beam divergence perpendicular to the x-direction in the mirror plane is adjusted via the non-circular arc shaped curvature along the second cross-section, a shape which generally produces incomplete focusing. This may be desired for certain applications and is therefore explicitly part of the present invention. A further particularly advantageous development of this embodiment is characterized in that the sum d changes along the second cross-section, in particular by more than 2%. The change in the sum d along the second cross-section is an almost unavoidable error when coating strongly curved surfaces. The curvature is particularly strong in the edge region of the reflector and for this reason, in conventional coating methods, the layer thickness there is smaller than at non-curved, flat locations. When the layer thickness changes, the angle of incidence of the radiation must be adjusted to ensure further fulfillment of the Bragg equation and thereby ensure sufficient reflectivity for a given wavelength. The angle of incidence is a function of the local curvature of the reflector. When the curvature dependence of the coating thickness is known (e.g. by model calculation described below, or experimentally) the actual reflection and focusing behavior of the finished multi-layer reflector can be determined and adjusted through precise previous setting of the curvature of the mirror. In one particularly advantageous embodiment of this further development, the curvature of the reflector along the second cross-section effects focusing and reflectivity properties of a reflector having changes in the sum d along the second cross-section which correspond to those of a reflector having circular curvature along its second cross-section and a constant sum d. This design realizes an X-ray optical component whose properties correspond to a rotationally symmetrical Goebel mirror. Realization of a functioning rotationally symmetrical Goebel mirror has not been possible up to now. Production of this inventive embodiment is easier since the curvature along the second cross-section is reduced and the unavoidable layer thickness errors can be accepted. In another advantageous embodiment, the reflector has an elliptical curvature with different semi-axis lengths or a parabolic curvature along the second cross-section. The elliptical structure is particularly suited for focusing the divergence of radiation perpendicular to the x-axis in the mirror plane. The parabolic shape promotes formation of a parallel beam. In an advantageous embodiment of the inventive reflector, the reflector has a reflecting surface of a width of more than 2 mm, in particular at least 4 mm (measured perpendicular to the x direction). In conventional rotationally symmetrical Goebel mirrors, the reflectivity decreases towards the edge for a given wavelength. In particular, for conventional dimensions of an X-ray analysis device, reflecting widths are limited to less than 2 mm. The inventive reflector has a high reflectivity for much larger widths. This increases the reflected intensity in accordance with the invention, to first approximation, in proportion to the reflecting surface. The present invention also concerns an X-ray analysis device with an X-ray source, a sample to be analyzed, an X-ray detector, beam-forming and/or beam-delimiting means and the inventive reflector described above. The inventive reflector is particularly advantageous when used in such an X-ray analysis device. In addition to an X-ray tube, the X-ray source may comprise a separate monochromator. The sample may be disposed on a goniometer. The detector may be designed to resolve energy or be integrally event counting. In a preferred embodiment of the inventive X-ray analysis device, the X-ray radiation impinges on the reflector at an angle of less than 5° with respect to the x-direction. Bragg diffraction is particularly effective under these circumstances, since, for conventional X-ray radiation in the region of some keV (e.g. Cu—Kα), the associated layer thickness is technically easy to realize. In another advantageous embodiment, the curvature of the reflector along the second cross-section is designed such that the reflectivity of the reflector is maximum for the wavelength of the radiation generated by the X-ray source. This leads to high reflecting intensities and therefore shorter measuring times in the X-ray analysis device. In particular, different reflectors may be exchanged for use with different X-ray wavelengths. One embodiment is particularly advantageous wherein the reflector focuses X-ray radiation incident thereon to a point-like region (focal spot), in particular onto the sample or the X-ray detector. These are the most frequent applications for an optical path, since the counting rate on the detector is thereby maximized. One embodiment of an inventive X-ray analysis device is also advantageous with which the reflector generates an X-ray beam from the incident X-ray radiation having a desired beam divergence, in particular a parallel beam. Parallel beams can illuminate samples with high uniformity and a similar beam profile can be projected on both the sample and the detector. Further advantages of the invention can be extracted from the description and the drawing. The features mentioned above and below can be used in accordance with the invention either individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration, rather have exemplary character for describing the invention. The invention is shown in the drawing and is explained in more detail with reference to embodiments. FIG. 1 schematically shows the structure of an inventive X-ray analysis device. The X-ray source 1 emits X-ray radiation. FIG. 1a shows two beams 2 and 3 of this X-ray radiation. Both beams 2, 3 pass a collimator 4 and are incident on the reflecting surface of the inventive reflector 5. An orthogonal coordinate system X, Y, Z is associated with the reflector 5. The reflector is a gradient multi-layer mirror. The reflecting surface in the z-direction is formed by a periodic sequence of at least two layers of materials A, B with different refractive indices for the incident X-ray radiation. The respective layers extend approximately in neighboring XY planes. The reflecting surface of the reflector 5 is curved in two dimensions (see FIGS. 2a and 2b). In accordance with the invention, neither of the two curvatures has the shape of a circular arc. The beams 2, 3 are reflected on the reflector 5, penetrate through the sample 6 and are registered in the X-ray detector 7. The beams 2, 3 have a divergence 8 in the XZ plane of typically 0.2 to 2°. The angle of incidence 9 of the two beams 2, 3 is thereby approximately 0.5 to 2.5° with respect to the X direction or the X′ direction (the angle of incidence 9 is exaggerated in FIG. 1a and also in FIG. 1b for reasons of clarity). The X-direction is the main direction of extension of the reflector 5. Apart from the angle of incidence 9, the direction of incidence of the X-ray radiation on the reflector 5 coincides with the X-direction. The divergence 8 of impinging X-ray radiation in the XZ plane is focused through the curvature of the reflector along its first cross-section (tangential curvature) in the XZ plane, i.e. the plane containing the x-direction (see FIG. 2a). In FIG. 1a, the curvature of the reflector along the first cross-section is parabolic. FIG. 1b shows the same X-ray analysis device as FIG. 1a, however, comprising two other beams 10 and 11. Both beams have a divergence 12 in the YZ plane. The order of magnitude of this divergence 12 is approximately 1–2°. The beams 10, 11 are reflected at the surface of the reflector 5, penetrate through the sample 6 and are registered in the detector 7. The divergence 12 of the incident X-ray radiation in the YZ plane is focused by the curvature of the reflector along a second cross-section (sagittal curvature) in the YZ plane, i.e. perpendicular to the x-direction (see FIG. 2b). In contrast to the conventional Goebel mirror, the inventive reflector 5 has a curvature, which is not circular arc shaped, but approximately elliptical. The curvature of the reflector 5 is shown in FIGS. 2a and 2b. Both figures show the reflector 5 of FIG. 1a/b in an enlarged scale. The intersection line 13 of the reflecting surface of the reflector 5 and XZ plane (which contains the X direction) illustrates the curvature of the reflector in a first dimension. In FIG. 2a, this curvature is parabolic. The first curvature represents the curvature of the reflector along the first cross-section. The intersection line 14 of the reflecting surface of the reflector 5 in the YZ plane illustrates the curvature of the reflector in a second dimension. In FIG. 2b, this curvature is elliptical. This second curvature represents the curvature of the reflector along the second cross-section and, in accordance with the invention, does not have the shape of a circular arc. In this embodiment, the reflector surface is mirror-symmetrical relative to a central XZ plane. This is generally advantageous for the invention to obtain uniformly illuminating reflected X-rays. The inventive device is explained in detail below for X-rays incident on two-dimensionally curved X-ray reflectors, in particular multi-layer X-ray reflectors with a shape other than rotationally symmetrical. X-ray radiation reflectors having a multi-layer structure have been used in different X-ray analysis instruments for some time. These multi-layers typically consist of some ten to some hundred individual alternating layers of two or more materials, with individual layer thickness of typically 1–20 nm. These multi-layers deflect and monochromatize incident X-rays through diffraction in correspondence with the Bragg equation. The reflectivity of these multi-layers may be very high for X-rays. Reflectivities of up to 90% were theoretically predicted and also obtained in experiments through continuous improvements in manufacturing coating techniques. For actual spatially extended X-ray sources (in contrast to theoretical, ideal point sources) the reflectivities are reduced to typically 30–70%, depending on the source size. For use in the region of hard X-ray radiation (wavelengths typically 0.05–0.25 nm), the deflection angles are typically in the region between 0.5–2.5 degrees: within the range of grazing incidence. Substantial improvements in such X-ray reflectors were obtained e.g. in U.S. Pat. No. 6,226,349 and in M. Schuster, H. Göbel, L. Brügemann, D. Bahr, F. Burgäzy, C. Michaelsen, M. Störmer, P. Ricardo, R. Dietsch, T. Holz and H. Mai “Laterally graded multi-layer optics for X-ray analysis”, Proc. SPIE 3767, pp. 183–198, 1999 by curving the reflectors in one dimension (parabolically, elliptically, etc.). The requirements for the shape accuracy of these reflectors are high and are in a region of considerably less than 1 micrometer. To obtain high reflectivity for such reflectors at all locations of the reflector, the multi-layer coatings must vary in a highly defined manner over the surface of the reflector according to the conditions e.g. disclosed in U.S. Pat. No. 6,226,349 and the above cited Schuster publication. The requirements for precision of the coating of such reflectors are quite high and are typically 1–3% of the individual layer thicknesses. These tolerances result from the widths of the multi-layer Bragg reflections, which are typically in the region of 1–3% of the Bragg angle. This results in tolerance requirements for the coating, which are typically in the region of some tens of picometers. Despite these extreme requirements, such reflectors have been recently produced using different methods and have been commercially available for several years. Since these reflectors are operated with small angles of incidence, the shape is substantially flat (in the range of some ten micrometers) and the radii of curvature are typically a few meters. Macroscopically seen, the reflectors are substantially flat. Due to the curvature of the reflectors, coating of these macroscopically flat reflectors produces no additional problems compared to flat reflectors and the coating of these reflectors is also substantially flat. Two-dimensionally curved rotationally symmetrical reflectors (rotational ellipsoid, rotationally paraboloid, etc. or segments of these shapes) also coated with multi-layers have been suggested many times for X-rays, e.g. U.S. Pat. No. 4,525,853, U.S. Pat. No. 4,951,304, U.S. Pat. No. 5,222,113. However, they were never realized. Reasons therefor are the enormous technical problems with coating (tangentially varying according to U.S. Pat. No. 6,226,349 and at the same time extremely homogeneous (1–3%) in a transverse direction in which the optics is now also curved). The principal reason therefor is that these reflectors must be substantially flat in one direction (radii of curvature in the meter range), but strongly curved perpendicular thereto (sagittal) with typical curvature radii of only a few millimeters, since the reflectors are operated at small angles of incidence. In addition to the need for extremely precise coating in the tangential direction (specified in U.S. Pat. No. 6,226,349), the considerable angles of inclination in the transverse direction lead to coating errors, since the reflectors are no longer flat but macroscopically curved. Since the layer thicknesses of typical coating methods change with the angle of inclination with respect to the coating source, the additional requirement that the layer thickness be homogeneous in a transverse direction (in the range of a few tens of picometers) is an additional technical challenge. The required coating has not been obtained up to now. For this reason, two-dimensionally collimating or focusing multi-layer X-ray reflectors have been realized up to now only according to U.S. Pat. No. 6,014,423 and U.S. Pat. No. 6,014,099 and earlier studies [M. Montel, X-ray Microscopy and Microradiography, Academic Press, New York, pp. 177–185, 1957; V. E. Cosslett and W. C. Nixon, X-Ray Microscopy, Cambridge, At The University Press, p. 108 ff, 1960; Encyclopedia of Physics, ed. S. Flügge, Vol. XXX: X-Rays, Springer Berlin, p. 325 ff, 1957; Kirkpatrick-Baez, see e.g. FIG. 1 in U.S. Pat. No. 6,041,099] through combination of two macroscopically substantially flat reflectors, i.e. through double reflection. Since at least two reflectors must be used which must be precisely mutually aligned, the costs and the adjustment effort are substantial. Moreover, the use of two reflectors results in intensity loss. Since even the best multi-layer reflectors lose efficiency, in particular when used with extended X-ray sources (e.g. rotary anodes), an intensity loss of 50% per reflection is relatively normal for increased extension of the sources. However, these reflectors are up to now the only two-dimensionally collimating or focusing multi-layer X-ray reflectors according to prior art. For these reasons, all conventional two-dimensionally collimating or focusing rotationally symmetrical X-ray reflectors with sagittal curvature radii in the millimeter range are total reflection mirrors (e.g. WO 0138861 or MICROMIRROR™ Bede Scientific). The requirements for the coating are minimal (only one individual layer is required e.g. gold and the layer must only have a sufficient thickness >approximately 30 nm: a homogeneous layer thickness is not required) and meet much lower requirements for the micro roughness of the reflector compared to a multi-layer reflector (for total reflection approximately 1 nm, wherein multi-layer mirrors require a roughness of <0.3 nm according to U.S. Pat. No. 6,226,349). Total reflectors have several substantial disadvantages over multi-layer reflectors. They require even smaller irradiation angles (approximately three times smaller), have corresponding reduced light collecting capacity, and lack monochromaticity. Such total reflectors have no monochromatizing properties but only suppress high-energy X-rays for which the total reflection angle is exceeded at certain geometries. For these reasons, it is extremely desirable to provide improved methods and processes for producing two-dimensionally collimating or focusing multi-layer coated X-ray reflectors. This is achieved in accordance with the invention by using two-dimensionally curved multi-layer coated bodies, which are not rotationally symmetrical. The advantages that result from the omission of the auxiliary condition of rotational symmetry, are not obvious and are therefore described in the following examples. The change from a rotationally symmetrical to a non-rotationally symmetrical reflector is initially disadvantageous. This is shown in FIGS. 3 and 4 with the example of a focusing reflector. While the cross-section of rotationally symmetrical reflectors 30 (FIG. 3) is circular and all rays 31 are reflected perpendicularly to the tangent, to a point 32, this is not the case with non-rotationally symmetrical reflectors 40 (FIG. 4). Non-rotationally symmetrical reflectors therefore produce a focusing loss. The free selection of the cross-section offers some additional possibilities as explained by way of example below. It is important (as shown through calculations) that the focusing loss is horizontal (in width) but not vertical (in height). The reason therefor is that the magnification ratio (source size to image size) of such reflectors is nearly independent of the cross-sectional shape of the reflector. This surprising property can finally be traced back to the high eccentricity of the reflectors relevant in this case (see below). FIG. 5 shows a typical application (a so-called monocrystal diffractometer). The X-ray radiation 52 emanating from an X-ray source 51 (with collimator 200 μm) is focused onto the two-dimensional detector 54 by a rotationally symmetrical reflector 53 (e.g. MICROMIRROR). Due to the finite size of the X-ray source (e.g. 0.1 mm diameter), the beam image at the image focus 61 (see FIG. 6) is also typically some 0.1 mm. The sample 55 typically has a diameter of 0.5 mm and is typically located 10 cm in front of the detector 54. The beam shape 62 is annular at this location. The sample 55 is thereby not optimally illuminated. Conversely, disadvantages occur when the sample is placed at the focus, since the scattered radiation is not point-like at the detector. The fundamentally annular beam profile 62 outside of the image focus is generally disadvantageous. For this reason, it is sufficient or even advantageous to use only a part (only a segment) of the entire reflector for such applications. FIG. 7 shows that the beam image in the focus 71 (detector) and outside of the focus 72 (sample) has approximately the same size for this section of the reflector. Suitable selection of the reflector and size of the reflector section leads to beam dimensions which are appropriate for the application at hand. An ellipsoidal reflector section 81 corresponding to FIG. 8 is described by way of example below. The shape of the ellipsoid 82 is described by ( x - a ) 2 a 2 + y 2 b 2 + z 2 c 2 = 1b=c produces a rotationally symmetrical ellipsoid with circular cross-section (prior art). b≠c produces an inventive non-rotationally symmetrical ellipsoid with elliptical cross-section (all cross-sectional shapes are possible in accordance with the invention). Typical values for a, b and c are a=250 mm, b=5 mm, and c=5 mm. This produces a separation between source and image focus of 2a=500 mm and a maximum diameter of the reflector 2b=10 mm. As described above, the necessity of the short curvature radius in the y-z plane results from the auxiliary requirements for small angles of incidence. FIGS. 9 and 10 show the corresponding depth profiles along x and y for a 4 mm wide reflector section. The curves are substantially flat in the x direction (FIG. 9) and have a drop depth (in the z direction) of some ten micrometers over a length of some ten millimeters, i.e. have a large radius of curvature of typically several meters. The curves along y in accordance with FIG. 10 are macroscopically curved and have a drop depth of several hundred micrometers over a width of 4 mm, i.e. have a small radius of curvature in the range of several millimeters. FIG. 11 shows that this strong curvature in the y-z plane produces considerable inclination of the edge of the reflector relative to the horizontal. At the edge of the 4 mm wide reflector, angles of inclination β of approximately 30 degrees occur. This edge inclination produces considerable problems for coating, which must be homogeneous in the y-z plane for a rotationally symmetrical body (in addition to the already mentioned layer thickness gradient along x according to prior art and the extremely high precision required and described therein). The coating methods used for producing X-ray reflectors such as “sputtering” according to U.S. Pat. No. 6,226,349 generally use coating sources with a more or less directed material beam. This has the consequence that, when inclined or tilted surfaces are coated, less material condenses per unit surface than with frontal coating, in dependence on the angle of inclination β (see FIG. 12 with coating source 120, material ray 121, mirror substrate 122 and angle of inclination β). Sputtering produces e.g. approximately a layer thickness distribution which varies with cos(β) wherein β is defined according to β=arctan(dz/dy) (more generally, a dependence with (cos β)″ is observed, wherein n depends on the details of the coating process used. The following is based on a process with n=1, without limiting the general case). FIG. 13 shows that with such a coating error (deviation from uniform thickness), the reflector meets the above-mentioned acceptable layer thickness errors of <2% only over a width of less than 2 mm. As shown in FIG. 14, detailed examinations with the Monte-Carlo method (ray tracing) confirm this result (reflectivity for two wavelengths, Cu—Kα and Cu—Kβ, over the surface of a reflector of 60×4 mm2 assuming a cos(β) coating error; light points indicate high reflectivity). These studies also show that the reflector no longer reflects the desired X-ray wavelength in the edge regions (e.g. Cu Kα, FIG. 14a), but also starts to reflect another wavelength in these edge regions due to the decreasing layer thicknesses (e.g. Cu Kβ, FIG. 14b). The reflector loses intensity and also its monochromatic effect. For coating such a reflector, additional apparative measures are required to generate a uniform layer thickness along the strongly curved surface. FIG. 15 (coating source 151, material flow 152) shows two possible ways of making the layer uniform. Movement of a diaphragm 153 or suitable pivoting, reciprocating or other turning motions of the mirror substrate 154 or a combination of these measures can lead to a layer which is homogeneous along the strongly curved surface. It is still necessary to keep to the required layer thickness gradient along the x-direction in a likewise extremely precise fashion as described above. Meeting of this condition in the conventional substantially flat reflectors requires considerable effort with regard to the apparatus (see e.g. DE 19701419) since they generally require, in addition to at least one rotary motion or diaphragm shift, measures to stabilize the temperature or other relevant parameters without impairing the substantially high quality of the vacuum. Controlled coating of strongly curved surfaces additionally requires at least one further rotary motion or diaphragm motion, as described above. The additional apparative effort to meet all these requirements for precision coating in the region of some ten picometers over a three-dimensionally curved surface is extremely high and has not been realized up to now. In contrast thereto, the inventive solution does not require any modification of the conventional coating apparatus. Rather, the deviation from uniform thickness in the coating is compensated for by modification of the curvature of the substrate. Coating systems such as e.g. that of FIG. 10 of U.S. Pat. No. 6,226,349 for producing X-ray reflectors can therefore be used without modification for producing the inventive reflectors. In correspondence with the inventive solution, the semi-axis b of the substrate is changed such that the above-described coating errors are perfectly compensated for non-normal incidence. This Is described In more detail below. The rotational ellipsoid is preferably expressed in cylindrical coordinates: ( x - a ) 2 a 2 + r 2 b 2 = 1 wherein z=r·cos α and y=r·sin α. To ensure optimum reflection of a rotationally ellipsoidal mirror, the coating thickness d must be:d(α)=const. When a coating error occurs, it can be corrected through variation of b with α. The rotational ellipsoid becomes the general non-rotationally symmetrical ellipsoid ( x - a ) 2 a 2 + r 2 b 2 ( α ) = 1.b(α) is calculated from d ( f , α ) = λ · b ( α ) · f · f ′ 2 · ( b 2 ( α ) - δ · f · f ′ ) [ see M. Schuster, H. Gobel L. Brügemann, D. Bahr. F. Burgäzy, C. Michaelsen, M. Störmer. P. Ricardo, R. Dietsch, T. Holz and H. Mai “Laterally graded multi-layer optics for X-ray analysis”, Proc. SPIE 3767, pp. 183–198, 1999]. One obtains b ( α ) = 1 2 · ( λ · f · f ′ d ( f , α ) · 2 ) + 1 4 · ( λ · f · f ′ d ( f , α ) · 2 ) 2 + δ · f · f ′ . f is the separation between source focus and the observed mirror segment, f′ is the separation between the observed mirror segment and image focus. Due to the high eccentricity (a>>b,c) of the reflectors observed herein, f≈x and f′≈2a−x. δ is the dispersion coefficient of the multiple layers used (see e.g. U.S. Pat. No. 6,226,349). If the irregularity of the coating as described above can be described e.g. by d(f,α)=d0(f)·cos β with β = arc tan ⅆ z ⅆ y . The angular dependence of the elliptic semi-axis b can be described by b ( β ) = 1 2 · ( λ · f · f ′ d 0 ( f ) · cos β · 2 ) + 1 4 · ( λ · f · f ′ d 0 ( f ) · cos β · 2 ) 2 + δ · f · f ′ The ellipsoidal equation then becomes ( x - a ) 2 a 2 + r 2 ( 1 2 · ( λ · f · f ′ d 0 ( f ) · cos β · 2 ) + 1 4 · ( λ · f · f ′ d 0 ( f ) · cos β · 2 ) 2 + δ · f · f ′ ) 2 = 1. For the further analysis 1 - ( x - a ) 2 a 2 = r 0 2 b 0 2 can be defined, which leads to the following equation r 0 · ( 1 2 · ( λ · f · f ′ d 0 ( f ) · cos β · 2 ) + 1 4 · ( λ · f · f ′ d 0 ( f ) · cos β · 2 ) 2 + δ · f · f ′ ) = r · b 0 which, solved for cos β, gives cos β = 1 d 0 ( f ) · λ · r · b 0 r 0 · f · f ′ 2 · ( r 2 · b 0 2 - δ · f · f ′ · r 0 2 ) To determine the cross-sectional shape z=f(y) a numerical solution is recommended—with the initial conditions β(0)=0 and z(0)=−r0. The algorithm is ( ⅆ z ⅆ y ) i = tan β i z i + 1 = z i + ( ⅆ z ⅆ y ) i · Δ y y i + 1 = y i + Δ y cos β i + 1 = 1 d 0 ( f ) · λ · y i + 1 2 + z i + 1 2 · b 0 · r 0 · f · f ′ 2 · ( ( y i + 1 2 + z i + 1 2 ) b 0 2 - δ · f · f ′ · r 0 2 ) Refined numerical solutions according to known methods are possible. Ray tracing simulations however show that this solution is sufficiently accurate. The calculated cross-sectional shape is shown in FIG. 16. In contrast to the rotationally symmetrical shape (b=c=5 mm), the shape described herein is flatter and corresponds with good approximation to an ellipsoid with b=6.4 mm and c=5 mm. Ray tracing calculations confirm that an ellipsoid modified in this manner reflects the desired X-ray line over the entire cross-section, despite the coating error. In contrast to FIG. 14b, the desired monochromatic effect is also completely maintained. The flatter shape of the inventive solution has moreover only approximately half the edge inclination than the rotationally symmetrical ellipsoid. For this reason, one can expect that the coating problems and the production problems of the curved shape be additionally substantially reduced by the low roughness requirements. Production of the inventive reflectors is therefore simpler and less expensive. FIGS. 17 and 18 show embodiments of the invention in which a periodic sequence of layers of materials (in this case two materials, A and B) have thicknesses whose sum changes continuously in the x (FIG. 17) and y (FIG. 18) directions. FIG. 19 shows an embodiment in which the inventive mirror 5 reflects X-rays from a source 1 to form an parallel outgoing beam 200. Analog to the above-described method, a non-rotationally symmetrical paraboloid can be calculated to parallelize rather than focus the beam. The rotation paraboloid with the parabolic parameter p is preferably expressed in cylindrical coordinates:r2=2·p·xwherein z=r·cos α and y=r·sin α. To ensure optimum reflection of a rotationally paraboloid mirror, the following must be true for the coating thickness d:d(α)=const. A coating error can be corrected through variation of p with α. The paraboloid of rotation then becomes the generally non-rotationally symmetrical paraboloid.r2=2·p(α)·x. p(α) is calculated according to d ( f , α ) = λ · 2 · p ( α ) · f 2 · ( p ( α ) - 2 · δ · f ) [ see M. Schuster. H. Göbel. L. Brügemann, D. Bahr. F. Burgäzy. C. Michaelsen, M. Störmer. P. Ricardo. R. Dietsch, T. Holz and H. Mai “Laterally graded multi-layer optics for X-ray analysis”, Proc. SPIE 3767pp. 183–198, 1999]. One obtains p ( α ) = 1 2 · ( λ · 2 · f d ( f , α ) · 2 ) + 1 4 · ( λ · 2 · f d ( f , α ) · 2 ) 2 + 2 · δ · f . If the irregularity of the coating can again be described as d(f,α)=d0(f)·cos β, wherein β=arctan dz/dy, the angular dependence of the parabolic parameter p is given by p ( β ) = 1 2 · ( λ · 2 · f d 0 ( f ) · cos β · 2 ) + 1 4 · ( λ · 2 · f d 0 ( f ) · cos β · 2 ) 2 + 2 · δ · f The paraboloid equation then becomes r 2 = 2 · ( 1 2 · ( λ · 2 · f d 0 ( f ) · cos β · 2 ) + 1 4 · ( λ · 2 · f d 0 ( f ) · cos β · 2 ) 2 + 2 · δ · f ) 2 · x For further analysis x = r 0 2 ( x ) 2 · p 0 can be defined. The result is r 0 · ( 1 2 · ( λ · 2 · f d 0 ( f ) · cos β · 2 ) + 1 4 · ( λ · 2 · f d 0 ( f ) · cos β · 2 ) 2 + 2 · δ · f ) = r · p 0 ,which, solved for cos β, becomes cos β = 1 d 0 ( f ) · λ · 2 · r · p 0 · r 0 · f 2 · ( r · p 0 - 2 · δ · f · r 0 ) To determine the cross-sectional shape z=f(y) a numerical solution is recommended—with the initial conditions β(0)=0 and z(0)=−r0. The algorithm is: ( ⅆ z ⅆ y ) i = tan β i z i + 1 = z i + ( ⅆ z ⅆ y ) i · Δ y y i + 1 = y i + Δ y cos β i + 1 = 1 d 0 ( f ) · λ · 2 · y i + 1 2 + z i + 1 2 · p 0 · r 0 · f 2 · ( y i + 1 2 + z i + 1 2 · p 0 - 2 · δ · f · r 0 ) Refined numerical solutions according to conventional methods are possible. Ray tracing simulations, however, show that the solution shown herein provides sufficient accuracy. The two approaches described above are to be understood as examples only and analog approaches are possible for other coating errors (e.g. parabolic, (cos β)n) and other reflector shapes (e.g. spherical, hyperboloid, . . . ). The curved reflector substrates can be produced in a manner known per se e.g. by grinding, polishing, and lapping of solid bodies of quartz, Zerodur, glass or other materials. Roughnesses below 0.1 nm (already 0.3 nm is satisfactory for multi-layers) and curvature errors below 5 μrad (already less than 25 μrad produces very good mirrors) were routinely obtained for reflectors according to U.S. Pat. No. 6,226,349 using such methods. These values lead to exceptional optical properties. Further shaping techniques of the reflector substrates are bending technologies [e.g. DE 19935513] or copying/replication techniques [U.S. Pat. No. 4,525,853 claim 12]. The advantages of the inventive teaching can be summarized as follows: a) the production of the shape is facilitated since flatter shapes with less curvatures and edge angles can be used. The flatter shape facilitates polishing to reduce roughness. b) Selection of the cross-sectional shape permits further favorable influence on the radiation properties (beam size, divergence), e.g. to produce a wider beam depending on the application. To determine mechanical tensions or textures of materials with X-ray diffractometric methods, it is desired to illuminate a larger sample surface (in contrast to monocrystal diffractometry). Selection of a non-rotationally symmetrical reflector provides a larger selection of optics optimized for the application. The optical design permits more flexibility. c) Especially for multi-layer X-ray mirrors the following is also true: Coating errors in a transverse direction can be completely compensated for through (free!) selection of the cross-sectional shape of the body in this direction. The coating becomes then “very” simple” or becomes possible for the first time with the same techniques which are currently used for substantially flat optics. d) Intensity is considerably increased since, in contrast to prior art, only one reflection is required (intensity loss per reflection approximately 50%) and since a larger mirror surface can be used. Conventional reflectors are used within a width of only approximately 1 mm. In contrast thereto, a 4 mm wide reflector was described (without limitation of the general case). In total, an intensity gain by a factor of 8 can be expected. e) Only one mirror is required instead of the optics according to prior art having 2 mirrors (cost factor). f) Adjustment of the reflector is much easier than for a Kirkpatrick-Baez arrangement according to prior art. Due to the particularly advantageous embodiment of the inventive reflector as a Goebel mirror with a non-rotationally symmetrical curvature transverse to the x direction (which corresponds approximately to the main irradiation direction of the X-ray radiation) the design of such an embodiment or of an associated X-ray analysis device is explained in more detail below. The preferred inventive X-ray analysis device comprises a source emitting X-ray radiation a sample to be analyzed a detector which responds to X-ray radiation optical shaping and/or delimiting means; and a curved multi-layer Bragg reflector which is disposed in the optical path between the source and the sample and comprises a periodically repeating sequence of layers, wherein one period consists of at least two individual layers A, B which have different diffraction index decrements δA≠δB and thicknesses dA and dB, wherein the period thickness, i.e. the sum d=dA+dB+ . . . of the individual layers A, B, . . . of a period changes continuously along an x-direction, and wherein the reflector is curved such that it forms a partial surface of a paraboloid or ellipsoid in the focal line or focal point at which the source or an image of the source is located, wherein the paraboloid or ellipsoid is curved along a cross-section in a plane perpendicular to the x-direction in a shape which is not that of a circular arc. The paraboloid or ellipsoid is not a rotational paraboloid or ellipsoid, rather a non-rotationally symmetrical paraboloid or ellipsoid. The embodiments of the inventive X-ray analysis device with parabolic reflector shape have the following properties: the layers of the reflector are vacuum-evaporated, sputtered or grown directly on a concavely curved suiface of a parabolic hollowed substrate, wherein the curvature of the concave substrate surface in a xz plane follows the formula z2=2px with 0.02 mm<p<0.5 mm, preferably p≈0.1 mm; the concave substrate surface facing the reflector has a maximum admissible shape deviation of Δp=√{square root over (2px)}·ΔΘR, wherein ΔΘR is the half-width of the Bragg reflection of the reflector and is in the range 0.01°<ΔΘR<0.5°, preferably 0.02°<ΔΘR<0.20°, the concave substrate surface facing the reflector has a maximum admissible waviness of Δ z Δ x = 1 2 ΔΘ R , the concave substrate surface facing the reflector has a maximum admissible roughness of Δ z = d 2 π ,preferably Δz≦0.3 nm, the X-ray radiation impinges on the curved surface of the reflector at an angle of incidence of 0°≦Θ≦5°, the periodic thickness d along the x-direction changes such that the X-ray radiation of a certain wavelength λ of a point X-ray source always experiences a Bragg reflection irrespective of the point of incidence (x, z) on the reflector in that the periodic thickness d increases in x-direction towards the paraboloid opening according to d = λ 2 1 ( 1 - δ _ / sin 2 Θ ) sin Θ and Θ = arccot 2 px p ,wherein δ is the decrease of the average refractive index of the multi-layer Bragg reflector, the deviation Δd/Δx of the periodic thickness d at each point of the multi-layer Bragg reflector along the x direction is smaller than Δ d Δ x = 1 2 d X , the following is true for the periodic thickness d: 1 nm≦d≦20 nm, for the number N of periods 10<N<500, preferably 50≦N≦100, and the energy E of the light quantum of the X-ray radiation is: 0.1 keV<E<0.1 MeV. Use of amorphous or polycrystalline substrate material is also advantageous, in particular glass, amorphous Si, polycrystalline ceramic material or plastic material. With regard to the number of individual layers per period, 2, 3 or 4 layers are particularly recommended. The layer thicknesses of the individual layers differ from material to material, preferably by at most 5%. Conventional (rotationally symmetrical) Goebel mirrors according to prior art are described e.g. in DE 198 33 524 A1 the entire disclosure of which is hereby incorporated by reference. |
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description | This is a Continuation-In-Part Application of international application PCT/EP03/007304 filed Jul. 8, 2003 and claiming the priority of German patent application 102 35 116.3 filed Aug. 1, 2002. The invention relates to a screened therapy Chamber for ion therapy, the chamber being for shielding neutrons having an energy up to GeV, wherein the therapy Chamber is shielded at all but one side, which includes a labyrinth-like shielded access. In Germany and other European countries, therapeutic medical accelerators for highly energetic ion radiation are under development [I]. For the design of such high energy ion accelerators for cancer therapy, however, there is a problem in that ion accelerators produce secondary radiation during slowing down of the ions in the accelerator structures, in biological and other targets, in particular in the patient when irradiated. The main component of the secondary radiation is neutron radiation. The primary beam is accelerated and transported to the target. The following processes result in the production of neutrons forming secondary radiation: beam losses by charge conversion, beam losses by charge transfer, beam losses by interaction with the residual gas in a partial vacuum, losses during deflection and inflection procedures extraction and injection, during slowing down of the ion beam in the tissue or another material. The unavoidable secondary radiation, that is, the neutron radiation must be shielded. The radiation levels generated as source radiation are substantial; they are at a level of up to Sv/h. The radiation level tolerable outside the radiation shield is at a μSv/h level, depending on the definition for the areas outside the radiation shield, for example, according to German radiation protection rules surveillance or control areas. Consequently, the neutron radiation dose must be reduced by about 6 orders of magnitude. A heavy ion therapy unit in a hospital environment needs to comply with the requirements of the radiation protection rules, that is, areas adjacent to the therapy rooms are to be defined as surveillance areas, in which the 1-mSv-limit per year is met with negligible emissions from radioactive materials. Conventional therapy installations wherein patients are irradiated with X-ray or gamma radiation are arranged in radiation bunkers in such a way that concrete walls shield the primary radiation such as the stray radiation in such a way that the surrounding areas do not have an increased radiation level. Radiation therapy has been performed so far using radiation from gamma radiation sources such as 137-Cs, 60-Co, or X-radiation generated by electron accelerators. The radiation protection obtained by walls serves therefore for the shielding of gamma and X-radiation. For electron accelerators with high end energies of up to 50 MeV, the neutron radiation generated by the nuclear photo effect must be shielded. Authoritative control rules for the design of the neutron shields are the DIN norms (German Industry Norms) DIN 6847/part 2 [II], the publication of the NCRP (National Council on Radiation Protection and Measurements) and, for high energy particle accelerators in basic research, the reference book Landolt-Börnstein [III]. The general procedure for the shielding of neutron radiation is the use of hydrogen-containing substances such as water, concrete and water-containing minerals. Materials such as lead or iron used for the shielding of X- and gamma radiation are not particularly suitable to absorb or moderate neutrons. For direct neutron radiation in accordance with DIN 6847, part 2, [II], the following tenth-value layer thickness for the area of mechanical irradiation units are given for a limit of 1 mSv per year, with negligible emissions of radioactive materials: MaterialWater paraffinConcreteIron, lidTenth value thickness10-15 cm16-25 cm42 cm Because of insufficient absorption and moderation of neutrons with energies of up to 3 MeV, the effectiveness of metals is insufficient so that additional hydrogen-containing absorbers must be used. The shielding effect H(d)/H0 of a wall with a thickness of d and a minimum thickness of (d>d0) is for a neutron beam with an energy En: H ( d ) Ho = 1 r 2 · exp ( - d λ ( E n , ϑ ) With the characteristic moderating constant 2, which depends on the energy En of the neutron radiation and the angle relative to the incident beam, the distance r to the source location the shield thickness d and the source strength H0, which depends on the primary beam and the target. Generally, the shielding effect is higher with copper than with concrete except for neutrons with energies of 3 MeV or less. The shielding however should be such that it is effective for all neutron energies as they may occur with the transport of the source neutrons through the shield so that shielding must be present which is effective for all neutron energies. The radiation protection arrangements of the radiation therapy installations built up to now concentrate in the shielding of neutron components in the energy range of the neutrons of about 10 MeV. Herein, concrete alone is generally a sufficiently effective radiation protection for all types of radiation. The difference in the shielding effectiveness of metals and concrete is small over a wide energy range that is an energy range of 3 to 30 MeV. The newest radiation protection plans for the Italian ion therapy project TERA were done by Agosteo et al. [IV]. Herein the planning is based on carbon ions. For the design of the radiation protection features, neutron spectra are used as they are used also in the present case. Agosteo developed on the basis of the measured neutron spectrums and the transport of the neutrons—using the radiation transport program FLUKA [V]—with a simplified geometry, for example, a spherical geometry, a model which permits an estimation of the attenuation of the neutron radiation in such simplified arrangements. The model describes essentially the dose caused by direct radiation. increased doses to be expected as a result of stray radiation are difficult to estimate with such models. Heavy ion therapy installations which provide depth therapy with carbon ions require accelerated ions with energies of up to about 400 MeV per nucleon. The neutron radiation generated during moderation of the ions in the tissue has energies of up to about 1000 MeV. Such high-energetic neutron radiation is difficult to shield particularly with conventional shielding materials. The attenuation length of neutrons with energies in excess of 100 MeV in normal concrete of the density of 2.3 g/cm3 is 45 to 52 cm. The tenth value thickness is about 100 cm. The physical parameters of an ion therapy installation differ substantially from those of a conventional X-ray irradiation installation. The primary beam including protons, carbon ions, oxygen ions is precisely guided from the generation during the acceleration up to the deposition in the tissue and is not much scattered like X-ray beams, but, during moderation, highly energetic neutrons are generated. For example, a carbon ion with an energy of 400 MeV per nucleon produces about 5 neutrons on average when being slowed down. Another basic difference with regard to conventional X-ray therapy installations resides in the higher spatial requirements and the spatial disturbance of the beam generation up to the application of the beam in the patient. Therefore the shielding expenses already of the beam transport system are higher than with conventional installations. Furthermore, the access to the treatment rooms is more difficult since large areas around the therapy unit are occupied by the beam guide structure. Conventional shielding concepts for X-ray irradiation installations utilize mainly the shielding effects of concrete with attenuation lengths (concrete wall thicknesses) which are applicable for MeV neutron radiation. Radiation protection shields have been developed so far only with the consideration of hydrogen-containing moderators for the utilization of the elastic scattering of neutrons on protons, whose effective cross-sections become smaller with increasing neutron energy. Concepts for the shielding of high-energy neutron radiation should, according to the calculations of the inventors, also consider physical processes, such as spallation and fragmentation reactions. The advantage is that they have constant effective cross-sections and constant interaction probabilities for high energies. In comparison with concrete, there are materials which result in changed moderating lengths and which may require less space than concrete shields. In order to be able to effectively dimension, the therapy units, compact shielding arrangements are of great interest. These include: Areas adjacent to the therapy rooms should be so designed that nobody needs to be there over extended periods; The therapy room sizes should be limited so that only small areas need to be shielded; The shielding itself should be efficient so that relatively little space is required therefor, Shielding doors should be relatively small as a result of the previous measure, so they can be moved also without power assistance within an acceptable period. It is the object of the present invention to provide an efficient and effective shielding arrangement of a relatively small volume. In a shielded chamber for ion therapy including a therapy room 6 which has a main axis 11 as determined by the direction of a high-energy ion therapy beam 9 surrounded by shielding 1 and includes at said one end a labyrinth entrance with at least two shielding wall sections 14 displaced longitudinally along the main axis and extending into the room from opposite side walls, the wall sections include means for causing spallation of the incident high energy neutrons to thereby generate from the high energy neutrons in the high energy neutron beam a plurality of low energy neutrons which are then moderated. The solution is based on the principle of a spatially structured multi-layer component shield, that is a combination shield for high energy neutron radiation. Essential is the introduction of a layer 8 which first causes an interaction between high energy neutrons of the neutron radiation cone 10 in spallation reactions with heavy atom nuclei. In this process, several low energy neutrons are generated from a high-energy neutron. These low-energy neutrons can then be absorbed or moderated with conventional hydrogen containing shielding materials, the combination shield is effective in two steps: initiation of spallation and fragmentation reactions in the first layer 8; absorption of the secondary radiation being generated in the first layer 8, by a second low energy neutron moderating and absorbing layer 2. In connection with the combination shielding, generally referred to as 14 and comprising said first layer 8 and said second layer 2, (illustrated in FIG. 1 as 14′, 14″, and 14′″; 8′, 8″, and 8′″; and 2′, 2″, and 2′″, respectively; and further illustrated in FIG. 3 as 8′, 8″, and 8′″; and 2′, 2″, and 2′″, respectively) an optimization in various areas of the radiation protection is important. In spallation reactions, not only neutrons are generated but also nuclear fragments, among them radio nuclides which again are a source of possible radiation. The selection of the heavy target nuclei determines which spectrum of radio nuclides can be produced. The selection of the heavy target nucleus consequently optimizes the conversion of highly energetic neutrons to low energy neutrons and the generation of beta and gamma radiation emitting radio nuclides. The use of heavy spallation neutron converters such as lead, bismuth, etc., provides for a correspondingly large spectrum of generated radio nuclides some of which have a longer life. Lighter spallation neutron converters have a lower spallation efficiency, but the possibilities and the effective cross-sections for the production of radio nuclides are smaller, since, in accordance with the nuclide map, fewer radio nuclides can be generated. This is an advantage in connection with radiation protection considerations with respect to the exposure to beta and gamma radiation when the accelerator is turned off. The combination shielding 2, 8 for the patient treatment area 6 can be summarized with measures for the spatial structuring in the following way: i) the introduction of combination shields 2, 8, for example, metal 8 with 0.5 to 1 m layer thickness and a hydrogen containing layer 2 of a 1.5 to 2 or 3 m layer thickness, wherein, in the first layer 8, high energy neutron spallation reactions are initiated and neutrons of mostly lower energy are generated which are moderated in the second and further layers 8, for example, 0.5 m Fe and 1.5 m concrete. ii) the introduction of transverse webs 4 extending from the ceiling down vertically toward the floor and consisting of concrete for example, iii) the introduction of transversely extending walls arranged behind one another,iv) a radiation protection door 5 of hydrogen containing substances such as Polyethylene, water, paraffin etc. v) another measure comprises a back stray chamber for neutrons with walls in combination shielding 14 and a side exit into the labyrinth, vi) beam stop reinforcements 3 for the location where the primary beam is dumped.An additional measure is: a movable cover for example of metal such as Pb for the area in which the primary beam is dumped, in order to shield the gamma radiation emitted by radio nuclides created when the primary ion beam hits the beam stop reinforcements 3 during quality assurance beam operation. The cover can be moved during irradiating procedures into a shield in order to avoid its activation. After shutting off the primary beam 9, the movable cover can be moved. Further possible measures are: The mobile shields in the radiation treatment room, so-called set-up walls. The above measures must be combined in order to achieve the required shielding effects. The use of the combination shielding 14 is part of an optimized radiation protection arrangement. The individual measures are known in the art or are used in praxis of accelerators in basic research. However in combination for optimizing shielding effects, they are novel. In combination, they reduce the dose of the secondary radiation by about 6 orders in magnitude from the radiation source to the entrance. An important aspect is the reduction of the part of direct radiation from the source as well as the part of stray radiation. Shields used so far for shielding neutron radiation utilize only the prevalent neutron absorption reactions in the shields by moderating incident neutrons via hydrogen containing moderators. The measures proposed herein provide for a combined interaction in that first, by way of spallation reactions of the incident radiation, neutrons of smaller energy than that of the incident neutrons are generated. These lower energy neutrons are then moderated in a conventional way and absorbed in the shielding by neutron absorption reactions. Furthermore, new geometric elements for strategic shielding are provided in a labyrinth arrangement, for example the back stray dead end path, for the reduction of the stray radiation. Depending on the application of the above-mentioned measures, the above-mentioned strategies result in an optimized shielding of the generated neutron and photon radiation under the following aspects: Reduction of the radiation level caused by direct radiation, that is, non-stray radiation; Reduction of the stray radiation; Optimization of the use of the spatial arrangements of the shielding units; Reduction of the production of radio nuclides by secondary radiation, and reduction of the radiation exposure by the gamma- and beta radiating nuclides generated; The combination of the first three measures in such a way that for example access shielding door 5 is not strictly required, but may be employed. The essential advantages of the invention reside in the realization of radiation protection by construction features. Those are: Optimization of the shielding with regard to material and geometry; Combination of the optimized measures to fulfill the requirements of the radiation protection regulations with regard to installations for the treatment of Cancer by means of heavy ion therapy using protons, carbon ions and other ions; The proposed measures are suitable to provide adequate shielding even under the most unfavorable condition wherein the entrance direction to the treatment location of the patient is along the beam axis; A more efficient and effective moderation of the direct and stray radiation for high energy neutron radiation; A compact shielding for a two-mode operation in connection with patient irradiation and quality assurance with beam deposition in the shielding wall; Consideration of the generation of radioactive materials during radiation and the shielding of these materials. The present prototype planning of a heavy ion therapy installation at a radiological university hospital is based on carbon ion radiation and proton radiation. The plans were examined by the TÜV Süddeutschland (Technical Surveillance Association of Southern Germany) with respect to the shielding arrangements and effects and was approved as to its principal design. The invention will be described below on the basis of a schematic representation of the horizontal irradiation location of the heavy ion therapy installation designed for this university hospital. The heavy ion therapy installation is operated with either protons, carbon ions, neon ions or heavy ions forming the primary beam for the cancer treatment of patients, thereby producing secondary neutron radiation. The reason for this is the described nuclear physical fragmentation process of the primary ions or of the target nucleus during the moderation procedure of the primary ions in the material, in particular in the patient's tissue being irradiated. For example, per carbon ion with the energy of 400 MeV per nucleon on average 5 neutrons are released. In addition to the beam transportation system from the synchrotron to the patient which involves minimal losses, particularly the area 6 of the patient treatment is a location with relatively high neutron radiation dose. With the arrangement of such therapy installations, the access to the treatment area 6 is located in some cases opposite the primary beam 9 along the beam path 11, i.e. in zero degree forward direction. The neutrons are emitted spatially in such a way that the main part of the neutron radiation is emitted forwardly peaking in zero degree direction. This requires that the access area 7 includes means which sufficiently attenuate the radiation. (See FIGS. 1 and 2). The effectiveness of the shielding arrangements for an irradiation location can be determined most accurately by means of radiation transport programs. In the exemplary embodiment, the results of Monte-Carlo radiation transport calculations based on measured neutron spectra are summarized. The estimation of the radiation level was calculated for the horizontal radiation locations using the radiation program FLUKA on the basis of measured neutron spectra. A carbon ion beam 9 with an energy of 400 MeV per nucleon was considered. As target 12 for the measurements, a graphite block of 100×100×200 mm3 was used. The neutron spectra were measured at the angles 0°, 7.5°, 15°, 30°, 60° and 90°. There are basically two radiation modes for such therapy installations: Irradiation of patients where the full primary beam is deposited in the patient. Verification of irradiation plans for quality assurance wherein the beam may also be deposited in a beam catcher. For the calculation, the spectra measured with a carbon target were considered as being representative of an exposure of a patient or respectively, the spectra measured with a copper target were considered to be representative of the radiation exposure, for quality assurance measurement programs. For the FLUKA simulation calculations of the labyrinth, the two geometries are treated as follows: patient geometry, P; geometry Q (quality assurance) for control measurements. In the first case, the beam 9 is destroyed in the target 12 about 3.5 m ahead of the first labyrinth wall element 14; in the latter cases, most of the beam is destroyed directly in the first wall element 14 of the labyrinth (see FIGS. 1 and 2). The neutrons generated are transported through the labyrinth toward the entrance area 7 and the dose generated along the labyrinth is determined. For the intensity of the ion beam, averaged during operation over a 10 min. time interval, maximum values of 107 ions per second are expected. The theoretical maximum value is at 3×108 ions per second. For source neutrons which are emitted backwardly, the neutron spectra measured at less than 90° are used. For optimizing the shielding effect, the following measures are introduced. labyrinth techniques for reducing the stray radiation; in addition to conventional concrete shields, the use of combination shieldings 14; the introduction of transverse webs 4 extending from the ceiling down to a level of 2.5 m in the labyrinth passage 16 in the area of the intermediate walls 14; local reinforcement 3 of the iron shielding 8 in the first wall of 0.5 m to 1.0 m for the dump function in an area of 1 m2 for quality assurance; the use of an iron shielding layer 8 also in the third transverse wall (0.5 m), the use of a polyethylene door 5 closing the outer end of the entrance area 7 (0.5 m thickness) the use of iron shielding in the ceiling area over the target 12 (0.5 m iron). The determination of the doses concentrates on the entrance area 7 to the labyrinth 16, where the waiting areas 15 for the personnel are and on the adjacent rooms. The dose values are calculated for a primary beam 9 of maximum intensity with 3×108 ions per second (see FIG. 2). The table 1 below gives an overview of the calculations performed. Geometry P means patient geometry, geometry Q indicates the radiation for quality assurance measurements. Geometry D means ceiling geometry, in the present case with iron reinforcement of 0.5 m iron as a combination shield instead of a 2 m thick concrete shield above the target location. The characteristic feature of the planned arrangement—that is the forward straying of the neutron cone 10 into the access area 7—has so far not been taken into consideration in the literature for the kind of radiation treatment installations. TABLE1Overview of the geometries as computed with FLUKA employing the various radiation parameters and geometries.BeamDose Rategeometry3 × 108neutronsP3 × 108photonsP1 × 107neutronsP3 × 108neutronsQ1 × 107neutronsQ3 × 108neutronsD1 × 107neutronsD Listing of Reference Numerals1Shielding walls2 Second shield layer (neutron moderation)3 Beam stop reinforcement4Webs extending from ceiling5 Access shielding door6 Treatment area7 Access area8 First shield layer (initiates spallation)9 Primary ion beam10Neutron cone11Primary ion beam central axis12Target14The combination shielding15Preparation and control room16Labyrinth passage [I]. J. Debus; Proposal for a dedicated Ion Beam Facility for Cancer Therapy. DKFZ, GSI and FZR Report 1998 [II]. DIN 6847/Teil 2 (Strahlenschutzregeln für die Errichtung von medizinischen Elektronenbeschleunigeranlagen, Kapitel 8.7, Bemessung der Abschirmung von Neutronenstrahlung), März 1990. [III]. A. Fasso, K. Goebel, M. Höfert, J. Ranft, G. Stevenson in Landolt-Börnstein, Gruppe 1: Kern- and Teilchenphysik; Band 11: Abschimmung gegen hochenergetische Strahlung, Herausgeber H. Schopper, Springer-Verlag, Berlin, 1990. [IV]. S. Agosteo; Radiation Protection at Medical Accelerators; Radiation Protection Dosimetrie, Vol. 96 No. 4, 393-406 (2001). [V]. A. Fasso, A. Ferrari, J. Ranft, P. R. Sala: New developments in FLUKJ modelling hadronic and EM interactions Proc. 3rd Workshop on Simulating Accelerator Radiation Environments, KEK, Tsukuba (Japan) 7-9 May 1997. Ed. H. Hirayama, KEK Proceedings 97-5 (1997), p. 32-4 |
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053596331 | abstract | In a method of assembling a nuclear fuel assembly, a deflecting jig is inserted into grid cells in each of a plurality of grids. The diameter of the deflecting jig is enlarged to urge a spring of at least one pair of dimples and spring associated with the grid cell to deflect the springs away from the dimple. A plurality of elongated key members are inserted into the grid cells through a plurality of openings defined at intersections between the straps forming walls of the grid cells. Each key member is rotated about its axis to cause hooks of the key member to project from a wall surface of the strap in a direction opposite to the projecting direction of the springs. The key member is then moved in a direction to engage the hooks with the wall surface of the strap. Urging of the spring by the deflecting jig is released to allow the same to be withdrawn from the grid cells and, subsequently, the fuel rods are inserted into the respective grid cells. The key member is then moved in a direction to bring the springs into pressure contact with the fuel rods. The key members are then withdrawn from the grid cells. |
046831088 | claims | 1. A locking screw assembly for securing together first and second structures in the internal region of a nuclear reactor core, wherein the first structure has a screw bore therethrough with a counterbore portion formed in an outer surface thereof, said assembly comprising: a lateral recess formed in the counterbore portion and spaced from said outer surfaces; an elongated screw receivable through the screw bore for threaded engagement with the second structure, said screw having an enlarged shoulder flange dimensioned for seating in the counterbore portion and for rotation with respect thereto, and an angular drive head projecting axially from said shoulder flange and having a lateral width substantially less than that of the counterbore portion; and a locking member disposed in the counterbore portion against said shoulder flange, said locking member having an angular opening therein shaped to receive said angular drive head therein for engagement with said locking member to prevent rotation with respect thereto, said locking member having a lateral projection engaged in said recess to prevent movement of said locking member with respect to the first structure. 2. The assembly of claim 1, wherein the counterbore portion has a plurality of said lateral recesses formed therein. 3. The assembly of claim 1, wherein said lateral recess is part-spherical in shape and extends radially outwardly of the counterbore portion. 4. The assembly of claim 1, wherein said drive head is hexagonal in shape. 5. The assembly of claim 4, wherein said locking member has a hexagonal opening therein for receiving said drive head therein in close fitting relationship. 6. The assembly of claim 1, wherein said locking member includes a cup-shaped member having a circular end wall with a central opening therethrough for receiving said drive head and a cylindrical side wall integral with said end wall and projecting therefrom around the entire circumference thereof coaxially therewith, said lateral projection being formed on said cylindrical side wall. 7. The assembly of claim 6, wherein said drive head is hexagonal in shape, said opening in said circular end wall being hexagonal in shape for receiving said drive head therethrough in close fitting relationship. 8. Locking screw apparatus for securing together first and second structures in the internal region of a nuclear reactor core, wherein the first structure has a screw bore therethrough with a counterbore portion formed in an outer surface thereof, said apparatus comprising: a lateral recess formed in the counterbore portion and spaced from said outer surface; an elongated screw receivable through the screw bore for threaded engagement with the second structure, said screw having an enlarged shoulder flange dimensioned for seating in the counterbore portion and rotation with respect thereto and an angular drive head projecting axially from said shoulder flange and having a lateral width substantially less than that of the counterbore portion; a locking member disposed in the counterbore portion against said flange, said locking member having an angular opening therein shaped to receive said angular drive head therein for engagement with said locking member to prevent rotation with respect thereto, said locking member having a deformable portion disposed adjacent to said lateral recess; and means for deforming said deformable portion into said recess for engagement therewith to prevent movement of said locking member with respect to the first structure. 9. The apparatus of claim 8, wherein said counterbore portion has a plurality of said lateral recesses formed therein. 10. The apparatus of claim 8, wherein said deforming means includes means movable axially of said screw for effecting the deforming operation. 11. The apparatus of claim 8, wherein said locking member includes a cup-shaped member having a circular end wall disposed against said shoulder flange and having a central opening therein for receiving said drive head, and a cylindrical side wall integral with said end wall and projecting therefrom around the entire circumference thereof substantially coaxially therewith, said side wall forming said deformable portion. 12. The apparatus of claim 11, wherein said drive head is hexagonal in shape, said opening in said circular end wall being hexagonal in shape for receiving said drive head therein in close fitting relationship. 13. The apparatus of claim 11, wherein said deforming means includes a die member engageable with the first structure and having a die portion receivable in said cup-shaped member, and a drive member movable axially of said screw within said die member for laterally moving said die portion into deforming engagement with said side wall. 14. The apparatus of claim 13, wherein said counterbore portion has a plurality of said lateral recesses formed therein, said die member being bifurcated to define two legs, each of said legs having a die portion thereon for simultaneously deforming said side wall into two of said lateral recesses. 15. The apparatus of claim 11, wherein said locking member is formed of metal. 16. The apparatus of claim 15, wherein said side wall is substantially thinner than said end wall. 17. A method for locking in place a screw which secures together first and second structures in the internal region of a nuclear reactor core, wherein the first structure has a screw bore therethrough with a counterbore portion formed in an outer surface thereof, said method comprising the steps of: forming a lateral recess in the counterbore portion and spaced from said outer surface, providing an elongated screw having an enlarged shoulder flange and an angular drive head with a lateral width substantially less than that of the counterbore portion, disposing the screw through the screw bore in threaded engagement with the second structure and with the shoulder rotatably seated in the counterbore portion, providing a locking member having an angular opening therein and disposing it in the counterbore portion against the flange with the drive head received in the opening for engagment with the locking member to prevent rotation with respect thereto, and deforming a portion of the locking member into the recess for engagement therewith to prevent movement of the locking member with respect to the first structure. 18. The method of claim 17, wherein said forming step includes a rotary cutting step. 19. The method of claim 17, wherein said forming step includes formation of a plurality of said lateral recesses in the counterbore portion. 20. The method of claim 17, wherein the deforming step includes the steps of providing a die member and positioning it adjacent to said locking member, and displacing the die member into deforming engagement with the locking member. |
description | This application claims the benefit of priority of U.S. Provisional Application Ser. No. 60/278,359, filed Mar. 23, 2001, which is incorporated in its entirety by this reference. The disclosed devices, apparatuses, methods, assays, and processes relate generally to applying radiant electromagnetic energy to biological material, and, more particularly, relate to the application of radiant electromagnetic energy in the far-infrared (FIR) region of the electromagnetic spectrum to biological material with minimal contamination by radiation in other electromagnetic bands (such as X-rays and microwaves). The term “far infrared” (FIR) identifies the range of the electromagnetic spectrum with free space wavelengths of about 100 to 1000 microns, or with wavenumbers from about 100 to 10 cm−1. Humans have developed extensive technology to generate and detect electromagnetic waves or vibrations throughout the electromagnetic spectrum—from the very short wavelengths and very high frequencies of gamma rays to the very long wavelengths and very low frequencies of radio waves—with the exception of the FIR gap in the spectrum existing between infrared light and millimeter wavelength microwaves. For use in the FIR gap there exists various sources and detectors, but this technology is much less well developed than the technology available for use in the other parts of the spectrum. In the late 1980's, the research of the late Professor John Walsh at Dartmouth College and others led to the development of tunable, electron beam driven radiation sources to produce electromagnetic radiation at FIR frequencies in a flexible, tunable and affordable fashion. See U.S. Pat. No. 5,263,043 to Walsh and U.S. Pat. No. 5,790,585 to Walsh, both of which are incorporated in their entireties by this reference. This work showed that a small, compact and relatively inexpensive table top free electron laser could be a commercially practiced device to generate FIR electromagnetic waves. Previously in the art, the common wisdom was that large biomolecules could not support vibrations, especially considering that they were always in water. Physicists thought that any possible mode of vibration would be seriously overdamped. That is to say, proteins were seen (from a mechanical point of view) more as sponges that would just go “thunk” if struck (i.e., exposed to mechanical perturbation or electromagnetic radiant energy), rather than as bells or springs which would ring or vibrate when struck. In the terminology of classical physics, it was believed that a protein structure, while having restoring forces which tend to pull the structure back towards its equilibrium conformation when the structure is forced away from its equilibrium conformation or physical shape by external forces of any nature, would not oscillate about its equilibrium conformation because the damping forces inherent in the structure and its environment would be sufficiently strong to preclude any oscillation. However, several practitioners in the art have reported evidence that proteins are capable of vibration, even in aqueous environments. Furthermore, a number of practitioners have reported that certain proteins vibrate in the FIR band. In 1994, it was reported that the first event following impact of a visible photon on the retinal chromophore of rhodopsin was the initiation of a vibration at wavenumber 60 cm−1 (corresponding to a far infrared wavelength of about 166 microns) (Wang Q et al, “Vibrationally coherent photochemistry in the femtosecond primary event of vision,” Science, Vol. 266, 21 October 1994, p. 422). Also in 1994, researchers reported that “breathing modes” of myoglobin oscillate at FIR frequencies in association with ligand binding (binding of the oxygen which is transported by myoglobin) and that the vibrations are not overdamped (Zhu L et al, “Observation of coherent reaction dynamics in heme proteins,” Science, Vol. 266, 21 October 1994, p.629). Other experimentalists observed low frequency modes (near 20 cm−1) (Diehl M et al, “Water-coupled low-frequency modes of myoglobin and lysozyme observed by inelastic neutron scattering,” Biophysical Journal, 1997 November; 73(5): 2726–32). Such results have generated further interest in the existence of vibrational modes in proteins, and, more particularly, vibrational modes in the FIR frequency range. Other recent work reinforces earlier findings that proteins and water can have modes in the FIR range (Xie A et al., Phys. Rev. Ltr. (2002) 88:1, 018102-1; Boyd JE et al., Phys. Rev. Ltr. (2001) 84:14, 147401-1). There are also suggestions that water associated with the KcsA potassium channel may be structured (Zhou Y et al., Nature (2001) 414:43–48). However, no practical means exists in the art to produce and apply electromagnetic energy selectively from the FIR band to biological matter (i.e., with minimal contamination by energy from other bands, such as X-rays and microwaves). Bohr et al, in U.S. Pat. No. 6,060,293, the entire disclosure of which is incorporated herein by reference, teach methods of application of Gigahertz frequency radiation to biological matter. However, delivery of FIR radiation to biological matter requires methods and apparatus for the generation, filtering, and focusing of the FIR radiation clearly distinct from those taught by Bohr et al. The instantly disclosed subject matter enhances the art by providing devices, apparatuses, methods, assays, and processes for delivering FIR band radiation with minimal contamination by energy in other electromagnetic bands to biological matter. In a first embodiment, a method of irradiating a biological sample with far infrared (FIR) irradiation includes providing tunable FIR irradiation, removing X rays from the irradiation, and irradiating at least one biological sample with the tunable FIR irradiation, wherein at least a component of the biological sample undergoes at least one of a conformational change or a phase change in response to the irradiating. In a second embodiment, an assay includes providing tunable FIR irradiation, removing X rays from the irradiation, irradiating at least one biological sample with the tunable FIR irradiation, providing compounds, allowing the biological sample to bind to at least one compound, and measuring a binding affinity between the at least one biological sample and the at least one compound. In a related embodiment, the irradiating disrupts an interaction between the biological sample and the at least one compound. In a third embodiment, a method of detecting an impurity in an article includes providing FIR irradiation having a characteristic that is selective for the impurity, removing X rays from the irradiation, irradiating at least a component of the article with the irradiation, and detecting a residual irradiation emitted from at least the component of the article. In a fourth embodiment, a diagnostic method includes providing tunable FIR irradiation, removing X rays from the irradiation, irradiating at least a component of a biological sample with the irradiation, and detecting a residual irradiation emitted from at least the component of the biological sample. In a fifth embodiment, a free-electron laser process for generating coherent stimulated electromagnetic radiation includes passing a beam of electrons along a path extending over a diffraction grating element to produce interaction electromagnetic radiation, at least a first mode of the interaction electromagnetic radiation being directed along a selected axis substantially parallel to the path of the beam, providing feedback of at least the first mode of the interaction electromagnetic radiation, controlling the current of the beam of electrons for selectively increasing the current at least up to a feedback beam current level to provide feedback from a resonator element of at least the first mode of the interaction electromagnetic radiation for achieving the stimulated radiation, and removing X rays from the stimulated radiation. In a sixth embodiment, a far infrared (FIR) irradiation device includes an FIR source producing an FIR irradiation having a tunable wavelength, the source being capable of continuous-wave output, and a filter receiving the irradiation from the source. In a seventh embodiment, a laser apparatus for generating coherent electromagnetic laser radiation includes resonator means for defining a resonant cavity in which stimulated radiation can propagate to generate coherent electromagnetic laser radiation, the resonator means including at least a first diffraction grating means for defining a geometrically periodic coupling structure, means for directing a beam of electrons over the diffraction grating means to excite an electromagnetic field through which the electron beam propagates, the beam of electrons having a beam thickness selected relative to the wavelength of the coherent electromagnetic laser radiation, the grating means and the beam directing means being adapted to produce interaction between the beam and the electromagnetic field for generating stimulated radiation, so that the stimulated radiation propagates in the resonant cavity to generate coherent electromagnetic laser radiation, and filter means for removing X rays from the stimulated radiation. In an eighth embodiment, a free-electron laser apparatus for generating coherent stimulated electromagnetic radiation includes a source of a beam of electrons, diffraction grating means, means for directing a beam of electrons along a path extending over the grating means so that the beam interacts with the grating to produce interaction electromagnetic radiation, at least a first mode of the interaction electromagnetic radiation being directed along a selected axis substantially parallel to the path of the beam, resonator means for providing feedback of at least the first mode of the interaction electromagnetic radiation, means for controlling the current of the beam of electrons for selectively increasing the current at least up to a feedback beam current level to provide feedback from the resonator means of at least the first mode of the interaction electromagnetic radiation for achieving the stimulated radiation, and filter means for removing X rays from the stimulated radiation. For any of the foregoing embodiments, in an additional embodiment, the biological sample is in a sample cell. For any of the foregoing embodiments, in an additional embodiment, the sample cell is selected from the group consisting of polymethylpentene, polyester, polypropylene, polyethylene, single crystal quartz, or sapphire, styrene, or any combination thereof. For any of the foregoing embodiments, in an additional embodiment, the biological sample is suspended in at least one of an aqueous solution or an aqueous gel within the sample cell. For any of the foregoing embodiments, the biological samples, compounds, or components thereof may be provided in a library. The biological samples, compounds, or components thereof may be disposed on a microarray. The biological samples, compounds, or components thereof may include nucleic acid and/or protein. In any of the foregoing embodiments, an additional embodiment further includes subjecting the biological sample to an assay. In any of the foregoing embodiments, an additional embodiment further includes determining at least one of a power of the irradiation, a wavelength of the irradiation, a duration of the irradiation, a pulse rate of the irradiation, a pulse shape of the irradiation, a duty cycle of the irradiation, or a bandwidth of the irradiation at least in part in response to feedback from the assay. In any of the foregoing embodiments, an additional embodiment further includes receiving a residual quantity of the irradiation by a detector. In any of the foregoing embodiments, an additional embodiment further includes setting a characteristic of the irradiation at least in part in response to feedback from the detector. For any of the foregoing embodiments, in an additional embodiment, the characteristic of the irradiation is selected from the group consisting of a power of the irradiation, a wavelength of the irradiation, a duration of the irradiation, a pulse rate of the irradiation, a pulse shape of the irradiation, a duty cycle of the irradiation, or a bandwidth of the irradiation, or any combination thereof. In any of the foregoing embodiments, an additional embodiment further includes receiving spectroscopic data from the detector in response to the residual quantity of the irradiation. In any of the foregoing embodiments, an additional embodiment further includes receiving image data from the detector in response to the residual quantity of the irradiation. In any of the foregoing embodiments, an additional embodiment further includes directing a portion of the irradiation to a detector. In any of the foregoing embodiments, an additional embodiment further includes determining a characteristic of the irradiation at least in part in response to feedback from the detector. For any of the foregoing embodiments, in an additional embodiment, the characteristic of the irradiation is selected from the group consisting of a power of the irradiation, a wavelength of the irradiation, a duration of the irradiation, a pulse rate of the irradiation, a pulse shape of the irradiation, a duty cycle of the irradiation, or a bandwidth of the irradiation, or any combination thereof. In any of the foregoing embodiments, an additional embodiment further includes receiving spectroscopic data in response to the portion of the irradiation. In any of the foregoing embodiments, an additional embodiment further includes receiving image data from the detector in response to the portion of the irradiation. For any of the foregoing embodiments, in an additional embodiment, the source is capable of emitting continuous-wave irradiation. For any of the foregoing embodiments, in an additional embodiment, the irradiation has continuously tunable power. For any of the foregoing embodiments, in an additional embodiment, the irradiation has continuously tunable wavelength. For any of the foregoing embodiments, in an additional embodiment, the irradiation has continuously tunable bandwidth. For any of the foregoing embodiments, in an additional embodiment, the irradiation has continuously tunable pulse rate. For any of the foregoing embodiments, in an additional embodiment, the irradiation has continuously tunable pulse shape. For any of the foregoing embodiments, in an additional embodiment, the irradiation has continuously tunable duty cycle. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a power in the range of about 1 milliwatt per square centimeter to about 1000 milliwatts per square centimeter. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a power of about 100 milliWatts per square centimeter. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a power in the range of about 1 picoWatt to about 1 Watt. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a power in the range of about 0.1 microWatts to about 10 milliwatts. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a wavelength in the range of about 10 microns to about 3,000 microns. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a wavelength in the range of about 60 microns to about 1,000 microns. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a wavelength in the range of about 100 microns to about 500 microns. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a wavelength in range of about 430 microns to about 480 microns. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a duration in the range of about 1 microsecond to about 1 hour. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a duration in the range of about 100 microseconds to about 1 second. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a duration in the range of about 1 second to about 1 minute. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a duration in the range of about 1 minute to about 10 minutes. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a duration of about 3 minutes. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a bandwidth equal to approximately 0.03 times a center wavenumber of the irradiation. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a bandwidth in the range of about 0.01 cm−1 to about 100 cm−1. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a bandwidth in the range of about 0.01 cm−1 to about 1 cm−1. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a bandwidth in the range of about 0.6 cm−1. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a bandwidth in the range of about 1 cm−1 to about 100 cm−1. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a pulse rate in the range from continuous wave to about 1 GigaHertz. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a pulse rate in the range from about 25 Hz to about 55 Hz. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a duty cycle in the range of about 5 per cent to about 100 per cent. For any of the foregoing embodiments, in an additional embodiment, the irradiation has a pulse shape comprising at least one of rectangular, triangular, sawtooth, sinusoidal, rectified, or constant. In any of the foregoing embodiments, an additional embodiment further includes tuning the irradiation to couple selectively with the component of the biological sample. For any of the foregoing embodiments, in an additional embodiment, the component comprises an organelle. For any of the foregoing embodiments, in an additional embodiment, the organelle is selected from the group consisting of a nucleus, a cytoskeleton, a centriole, an endoplasmic reticulum, a golgi apparatus, a mitochondrion, a chloroplast, a cell membrane, a nuclear membrane, a cell wall, a lysosome, a vacuole, a vesicle, a ribosome, or a peroxisome, or any combination thereof. For any of the foregoing embodiments, in an additional embodiment, the component is selected from the group consisting of a mitotic spindle, a DNA polymerase complex, a transcription complex, a protein replication complex, a gene, or a centromere, or any combination thereof. For any of the foregoing embodiments, in an additional embodiment, the gene is selected from the group consisting of an immunoglobulin gene, a T cell receptor gene, a p53 gene, a retinoblastoma gene, or a proto-oncogene, or any combination thereof. For any of the foregoing embodiments, in an additional embodiment, the component is selected from the group consisting of a cytoskeleton, a centriole, a nuclear lamin, an intermediate filament, a neurofilament, a nucleic acid, a lipid, a fatty acid, a triglyceride, a phospholipid, a steroid, a polyisoprenoid, a glycolipid, a peptide, a polypeptide, an amino acid, an amino acid-coupled transfer RNA, a nucleotide, a nucleoside, a protein, a heat-shock protein, a histone, an enzyme, a lipoprotein, a monosaccharide, a disaccharide, a polysaccharide, a lipopolysaccharide, a proteoglycan, a glycoprotein, a water molecule, a water cluster, a region of gelled vicinal water, actin, myosin, titin, troponin, tropomyosin, a microtubule, or a microfilament, or any combination thereof. For any of the foregoing embodiments, in an additional embodiment, the biological sample is an organism. For any of the foregoing embodiments, in an additional embodiment, the organism is a microorganism. For any of the foregoing embodiments, in an additional embodiment, the component comprises an organ. For any of the foregoing embodiments, in an additional embodiment, the organ is selected from the group consisting of a skin, a brain, a meninx, an artery, a vein, an eye, an optic nerve, a cochlea, an olfactory nerve, an oculomotor nerve, a trochlear nerve, a trigeminal nerve, an abducent nerve, a facial nerve, a vestibulocochlear nerve, a glossopharyngeal nerve, a vagus nerve, a spinal accessory nerve, a hypoglossal nerve, a brainstem, a spinal cord, a nerve root, a neuron, a bone, a muscle, a nasopharynx, an oropharynx, an esophagus, a stomach, a duodenum, a jejunum, an ileum, a colon, a rectum, an anus, a heart, an aorta, a femoral artery, a popliteal artery, a common carotid artery, an internal carotid artery, a capillary, blood, a thymus, a thyroid, a parathyroid gland, an adrenal gland, a pituitary gland, a kidney, a lung, a trachea, a brochiole, an alveolus, a pancreas, a hand, an arm, a forearm, a leg, a foot, a thigh, a ligament, a tendon, a cartilage, connective tissue, a hair follicle, a liver, a lymph node, a gallbladder, a bile duct, a lymphatic duct, a tongue, a spleen, a ureter, a urethra, a prostate, a uterus, an ovary, a testis, a fallopian tube, a reproductive organ, or a bladder, or any combination thereof. For any of the foregoing embodiments, in an additional embodiment, the component comprises a neoplasm. For any of the foregoing embodiments, in an additional embodiment, the biological sample comprises a neoplasm. In any of the foregoing embodiments, an additional embodiment further includes collimating the irradiation. In any of the foregoing embodiments, an additional embodiment further includes focusing the irradiation onto a target. For any of the foregoing embodiments, in an additional embodiment, the target receives substantially all of the FIR irradiation. For any of the foregoing embodiments, in an additional embodiment, the target has a diameter in the range of about 1 micron to about 2 meters. For any of the foregoing embodiments, in an additional embodiment, the target has a diameter in the range of about 1 micron to about 1 millimeter. For any of the foregoing embodiments, in an additional embodiment, the target has a diameter in the range of about 10 microns to 100 microns. For any of the foregoing embodiments, in an additional embodiment, the target has a diameter in the range of about 100 microns to 1 millimeter. For any of the foregoing embodiments, in an additional embodiment, the target has a diameter in the range of about 1 centimeter to about 10 centimeters. For any of the foregoing embodiments, in an additional embodiment, the target comprises a microarray. In any of the foregoing embodiments, an additional embodiment further includes positioning the biological sample proximate to a distal end of a waveguide, and directing the irradiation through the waveguide to the biological sample. For any of the foregoing embodiments, in an additional embodiment, the waveguide further comprises a proximal end, and a diameter of the waveguide decreases from the proximal to the distal end. For any of the foregoing embodiments, in an additional embodiment, the diameter of the waveguide decreases from about 1 cm at the proximal end to about 50 microns at the distal end. For any of the foregoing embodiments, in an additional embodiment, the waveguide further comprises a reflective coating on an inner surface of the waveguide. For any of the foregoing embodiments, in an additional embodiment, the reflective coating is selected from the group consisting of aluminum, silver, or gold, or any combination thereof. The aluminum, silver, or gold may also be alloyed with appropriate metals, such as with chromium or tin. For any of the foregoing embodiments, in an additional embodiment, wherein the FIR irradiation is provided by a source, the source including resonator means for defining a resonant cavity in which stimulated radiation can propagate to generate coherent electromagnetic laser radiation, the resonator means including at least a first diffraction grating means for defining a geometrically periodic coupling structure, means for directing a beam of electrons over the diffraction grating means to excite an electromagnetic field through which the electron beam propagates, the beam of electrons having a beam thickness selected relative to the wavelength of the coherent electromagnetic laser radiation, and the grating means and the beam directing means being adapted to produce interaction between the beam and the electromagnetic field for generating stimulated radiation, so that the stimulated radiation propagates in the resonant cavity to generate coherent electromagnetic laser radiation. For any of the foregoing embodiments, in an additional embodiment, the FIR irradiation is provided by a source, the source including a source of a beam of electrons, diffraction grating means, means for directing a beam of electrons along a path extending over the grating means so that the beam interacts with the grating to produce interaction electromagnetic radiation, at least a first mode of the interaction electromagnetic radiation being directed along a selected axis substantially parallel to the path of the beam, resonator means for providing feedback of at least the first mode of the interaction electromagnetic radiation, and means for controlling the current of the beam of electrons for selectively increasing the current at least up to a feedback beam current level to provide feedback from the resonator means of at least the first mode of the interaction electromagnetic radiation for achieving the stimulated radiation. For any of the foregoing embodiments, in an additional embodiment, wherein removing includes removing substantially all X rays. For any of the foregoing embodiments, in an additional embodiment, the filter comprises an off-axis collimating reflector. For any of the foregoing embodiments, in an additional embodiment, the collimating reflector is sized, shaped, and positioned to remove X-rays from the irradiation. For any of the foregoing embodiments, in an additional embodiment, the filter comprises a first mirror. For any of the foregoing embodiments, in an additional embodiment, the first mirror is sized, shaped, and positioned to remove X-rays from the irradiation. For any of the foregoing embodiments, in an additional embodiment, a reflective surface of the first mirror is flat. For any of the foregoing embodiments, in an additional embodiment, a reflective surface of the first mirror is curved. In any of the foregoing embodiments, an additional embodiment further includes a second mirror. For any of the foregoing embodiments, in an additional embodiment, the filter comprises an electrostatic decelerating grid. In any of the foregoing embodiments, an additional embodiment further includes a sample cell, receiving the irradiation from the filter. For any of the foregoing embodiments, in an additional embodiment, wherein the sample cell is selected from the group consisting of polymethylpentene, polyester, polypropylene, polyethylene, single crystal quartz, styrene, or sapphire, or any combination thereof. For any of the foregoing embodiments, in an additional embodiment, the sample cell contains a biological sample. For any of the foregoing embodiments, in an additional embodiment, the irradiation is tuned to couple selectively with a component of the biological sample. For any of the foregoing embodiments, in an additional embodiment, the detector emits spectroscopic data in response to the residual quantity of the irradiation. For any of the foregoing embodiments, in an additional embodiment, the detector emits image data in response to the residual quantity of the irradiation. For any of the foregoing embodiments, in an additional embodiment, at least one of a power of the irradiation, a wavelength of the irradiation, a duration of the irradiation, a pulse rate of the irradiation, a pulse shape of the irradiation, a duty cycle of the irradiation, or a bandwidth of the irradiation is determined at least in part in response to feedback from an assay. For any of the foregoing embodiments, in an additional embodiment, the source and the filter are disposed in a common housing. For any of the foregoing embodiments, in an additional embodiment, the common housing comprises an output window. For any of the foregoing embodiments, in an additional embodiment, the common housing comprises an output lens. For any of the foregoing embodiments, in an additional embodiment, the output lens collimates the irradiation. Certain embodiments provide systems and methods for the generation and the application of FIR band electromagnetic radiant energy onto biological matter with minimal contamination by energy from other bands in the electromagnetic spectrum. In certain embodiments, the presently disclosed subject matter provides devices, apparatuses, methods, assays, and processes for the generation, filtration, delivery to biological matter, and detection of FIR band radiant energy with minimal contamination by radiation from other bands of the electromagnetic spectrum. In certain embodiments, the presently disclosed subject matter provides devices, apparatuses, methods, assays, and processes for applying FIR band electromagnetic radiation to biological matter with minimal contamination by radiation from other bands of the electromagnetic spectrum. In one embodiment, at least one of the disclosed devices, apparatuses, methods, assays, and processes includes an FIR source producing an FIR irradiation, a filter receiving the irradiation from the source, a sample cell receiving the irradiation from the filter and containing a biological sample, and optionally, a detector, receiving a quantity of the irradiation from the sample cell. In an embodiment, a pellicle or thin film beamsplitter is placed in the beam before the sample. The beam splitter diverts a fraction of the beam to a detector for monitoring. Monitoring can take place before the sample or after or both. In a related embodiment, the FIR source produces an irradiation with a power in the range of 1 picoWatt to 1 Watt, a wavelength in the range of 10 microns to 3000 microns, and a bandwidth of 0.01 cm−1 to 100 cm−1. In another related embodiment, the filter comprises an off-axis parabaloid collimating reflector and at least one mirror. In yet another related embodiment, the sample cell is at least one of polymethylpentene, polyester, polypropylene, polyethylene, single crystal quartz, styrene, and sapphire. In another embodiment, at least one of the disclosed devices, apparatuses, methods, assays, and processes provides a method for irradiating a biological sample with FIR radiation, comprising the steps of providing an FIR irradiation device as described in the first embodiment above, suspending a biological sample in an aqueous solution and/or aqueous gel, placing the solution containing the sample in the sample cell of the irradiation device, causing the FIR source to produce the irradiation, and allowing the sample to receive the irradiation. A related embodiment further comprises the step of subjecting the sample to an assay. Another related embodiment further comprises the step of receiving a quantity of FIR radiant energy by the detector. FIR irradiation can be provided and/or detected at the same frequency as the original source, or might be at any other frequency within the electromagnetic spectrum, e.g. as the result of fluorescence type effects. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising proteins within living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising cytoskeletal proteins within living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising nucleic acids within living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising deoxyribonucleic acids within living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising ribonucleic acids within living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising proteins isolated from living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising cytoskeletal proteins isolated from living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising nucleic acids isolated from living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising deoxyribonucleic acids isolated from living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising ribonucleic acids isolated from living cells. In another embodiment, FIR of selected wavelengths is delivered to biological matter comprising a tissue of a human or animal organism. In another embodiment, FIR of selected wavelengths is delivered to a site within a human or animal organism. Another embodiment provides a method for treating blood or blood products, comprising removing temporarily blood or blood products from a subject, exposing the blood or blood products to FIR radiant energy of selected wavelengths to induce changes in the biological matter within the blood, and returning the blood or blood products to the subject. Such an embodiment may be practiced in a continuous fashion, i.e., the blood or blood products are continuously pumped out of the body, through a fixture providing exposure to an effective amount of FIR radiant energy, and back into the body. As understood herein, the term “biological matter” refers to any living organism and any substance found within, purified from, or derived from any living organism, or any substance synthesized in vitro to recapitulate or resemble any substance found within, purified from, or derived from any living organism. The FIR source has several important features. First, it offers continuous tunability, so that any and every frequency in the FIR band may be produced and used, continuous control of bandwidth (or continuous control of the degree of monochromaticity), so that any arbitrary bandwidth from 0.01 cm−1 to 100 cm−1 could be produced and used, continuous control of the pulse shape, width and repetition rate, and continuous control of the power level from 1 picoWatt to 1 Watt. As understood herein, “continuous” means that the value of a parameter (frequency, bandwidth, pulse shape, width or repetition rate, duty cycle, or power level) can be set to any arbitrary value within an implied or expressed range of values. The source can also produce continuous-wave (CW) output, which corresponds to a 100 per cent duty cycle, although in some embodiments, a smaller duty cycle may be preferred. That any combination of parameters can be used is important because this means that in principle all biological effects can be addressed. Continuous tunability facilitates accessing biological effects, since all frequencies in the band may be reached. Thus, one or more of the FIR frequencies associated with a particular biological effect may be achievable and the effect in question will be accessible to the technology. In order for vibrations at FIR frequencies to influence the function of biomolecules, it is understood that there must be a physical mechanism by which these vibrations can be induced in proteins and other biomolecules. At least one of the herein disclosed devices, apparatuses, methods, assays, and processes provides such a mechanism. An embodiment according to at least one of the herein disclosed devices, apparatuses, methods, assays, and processes generates electromagnetic radiation in the FIR band that may be tuned, removes radiation from other electromagnetic bands, for example, by filtration, delivers the radiation to biological matter, detects a portion of the radiation during delivery, and analyzes the biological matter for any changes resulting from irradiation. An embodiment according to at least one of the disclosed devices, apparatuses, methods, assays, and processes may induce specific changes in the function or activity of any article of biological matter in a tuned or resonant fashion. Practices of the disclosed devices, apparatuses, methods, assays, and processes can analyze, test, modify, and treat the biological material as a result of such application of FIR electromagnetic energy, among other scientific and commercial applications. An embodiment according to at least one of the disclosed devices, apparatuses, methods, assays, and processes may induce such changes because the FIR band radiant energy delivered to the biological matter will be converted into vibrational phonon energy at a frequency the same as or related to the incident FIR radiation. This vibrational energy in the FIR frequency range is received, stored and re-transmitted by biomolecules, in particular by the microtubule and actin based structures of the cytoskeleton and/or associated proteins and molecules which have been shown to permeate all living organisms. (For a non-specialist's description of the cytoskeleton and of microtubules, see Ingbar D E, “The architecture of life,” Scientific American, January 1998). It has been reported that single-wall carbon nanotubes support a quantized spectrum of phonon vibrations in the FIR frequency range (Hone J et al, “Quantized phonon spectrum of single-wall carbon nanotubes,” Science, Vol. 289, 8 September 2000, p. 1730). A similar effect can occur in microtubules due to the similarity of microtubules to carbon nanotubes. An embodiment according to at least one of the disclosed devices, apparatuses, methods, assays, and processes may be used to induce phonon vibrations or modify existing phonon vibrations in biological matter. Such vibrations in the FIR frequency range are sustained by and can be transmitted through the cytoskeleton. Research cited above suggests that much of the information and energy transfer in living organisms is effected through this support by, and transmission through, the cytoskeleton of phonon vibrations in the FIR frequency range. Furthermore, an embodiment according to at least one of the disclosed devices, apparatuses, methods, assays, and processes may modify other biomolecules directly or indirectly interacting with the cytoskeleton elements (including but not limited to centrioles, nuclear lamins, filaments, neurofilaments, DNA, RNA, lipids, fatty acids, triglycerides, phospholipids, steroids, polyisoprenoids, glycolipids, peptides, polypeptides, amino acids, amino acid-coupled transfer RNA, nucleotides, nucleosides, proteins, heat shock proteins, histones, enzymes, lipoproteins, monosaccharides, disaccharides, polysaccharides, lipopolysaccharides, and proteoglycans, glycoproteins, microtubules, microfilaments, and all monomer substituents of these molecules). Biomolecules may be naturally derived or synthesized. Such modification induced by an embodiment according to at least one of the disclosed devices, apparatuses, methods, assays, and processes may variously effect resonant energy transfer within and throughout a living organism via the cytoskeleton and the organized clusters of water molecules (which clusters may or may not also be adjacent to or intermixed with dissolved ions of K, Na and Ca among other elements) surrounding the cytoskeleton. Such transfers may supply energy for the occurrence, activation of, and deactivation of many of the biomolecular interactions, reactions and processes in a living organism. Such interactions, reactions, and processes include, for example, DNA synthesis and replication, RNA synthesis, protein synthesis, protein degradation, protein folding and conformation, enzymatic activity as a consequence of protein conformation, vesicle transport, carcinogenesis, apoptosis, cell differentiation, cell migration, and cell division (mitosis and meiosis). An embodiment according to at least one of the disclosed devices, apparatuses, methods, assays, and processes may affect a given biomolecule or class of biomolecules selectively by delivering FIR radiation within a specific range of frequencies. Further applications of the disclosed devices, apparatuses, methods, assays, and processes are contemplated. For example, the FIR irradiation may be focused upon a neoplasm, such as a benign or malignant tumor, to ablate the tumor. Alternatively, imaging and/or spectroscopic data may be obtained from living tissue to detect and localize neoplastic tissue by identifying particular spectral characteristics in FIR imaging or spectral data that distinguish the neoplastic tissue from normal tissue. In an embodiment, such a device could be positioned outside an organism to detect, e.g., tumors, located within the organism. Applications of the disclosed devices, apparatuses, methods, assays, and processes to geophysics are contemplated. For example, FIR irradiation may be used to detect ground faults and other types of structures, such as bodies of water or particular rock types. FIR irradiation may be used to detect clouds and the presence, type, composition, and propensity to rain of the clouds. Further, FIR may be used to perturb organized water in clouds, thereby causing rainfall. For example, millimeter-sized microdroplets of structured water in clouds may be disrupted by application of FIR irradiation, thereby causing rainfall. One possible use of FIR radiation is in the triggering of biological processes. Many biological processes appear to be mediated by phase-transitions. An hypothesis has been put forth, supported by appreciable evidence, that the phase-transition is, in fact, a generic mechanism underlying basic cell function (Pollack, 2001). Within this paradigm, an organelle carries out its fiction through the phase-transition. Phase-transitions can involve interaction between solute and solvent, so if FIR radiation affects the solvent, e.g., perturbs water from a structured to a disordered state, either by interacting directly with the water, or by interacting with proteins in such a way that the proteins perturb the water, it will inevitably shift the phase-transition equilibrium. Hence, FIR radiation could be a useful approach to trigger any of a number of intracellular processes, such as intracellular signaling. Of many examples, a practical one is that of cancer cells. Cell division involves a sequence of sub-processes, each of which is thought to involve some kind of phase-transition. If any one of these sub-processes could be blocked, division might be inhibited. Thus, focused FIR radiation could be used to block the growth of tumors. With disclosed devices, apparatuses, methods, assays, and processes, the frequency and pulse width could be selected to optimize the result. Another illustrative example is in the area of muscle contraction. In dystrophic disease states, muscles progressively lose their ability to contract. Both the triggering of contraction and the contractile event appear to involve phase-transitions. Hence, contraction should be triggerable by an FIR source. Currently, this is done by electrodes, but the triggering current is rather diffuse. A focused FIR source, optimally tuned, could be used to trigger local contraction, thereby “exercising” the target muscle and increasing its vigor. Particular molecular targets within the muscle can include, e.g., actin, myosin, titin, troponin, and tropomyosin. Myosin can cause water destructuring by using energy from hydrolysis of ATP. In hydrolizing ATP, myosin can vibrate to destructure the water. Other proteins in contact with the myosin, such as actin, tropomyosin, dystrophin, and alpha actinin, may also establish vibrations that destructure water. The water may be vicinal water. In neurons, neurofilaments and spectrin can vibrate, thereby destructuring water. Another biological example is in the artificial release of drugs. In smart drug-delivery systems, the active substance is typically embedded in a gel. When the gel undergoes a phase-transition, and becomes permeable, the substance is released. Release could therefore be triggered by an FIR pulse. The gel could be designed such that the drug is responsive to radiation at a particular frequency, thereby allowing specificity of release targets. In additional embodiments, FIR irradiation can be delivered to DNA within living cells where the DNA is in the form of chromatin. FIR irradiation can be delivered to centrioles within living cells. FIR irradiation can be delivered to living cells in order to modify the activity of the DNA. FIR irradiation can be delivered to living cells in order to modify rate of DNA replication. FIR irradiation can be delivered to living cells in order to modify rate of DNA transcription into RNA. FIR irradiation can be delivered to living cells in order to modify rate of progress of cell mitosis. FIR irradiation can be delivered to living cells in order to modify the process of morphogenesis of an organism. FIR irradiation can be delivered to living cells in order to modify the cells' rate of progress of cell mitosis. FIR irradiation can be delivered to living cells in order to modify the DNA rearrangement process during antibody generation. FIR irradiation can be delivered to cytoskeleton elements including, e.g., microtubules and actin fibers within living cells in order to modify transfer of cellular components along these elements. FIR irradiation can be delivered to neurons within living organisms in order to modify the activity of the neurons. FIR irradiation can be delivered to the olfactory system within living organisms in order to modify the organisms ability to smell. FIR irradiation can be delivered to living cells in order to modify the rate of cell division. FIR irradiation can be delivered to living cells in order to modify the rate of low level photon emission in visible frequencies (e.g., 300–800 nm wavelength). FIR irradiation can be delivered to living cells in order to modify the rate of low level photon emission in visible frequencies (e.g., 300–800 nm wavelength) in order to determine the health of the cells. FIR irradiation can be delivered to DNA and centrioles within living cells in order to modify a Bose Einstein condensate of phonons in the centriole and DNA of a living cell. The disclosed devices, apparatuses, methods, assays, and processes can facilitate the induction of resonant effects in some system at a specific frequency. The disclosed devices, apparatuses, methods, assays, and processes contemplate techniques to facilitate drug discovery. Compounds may be screened for sensitivity to particular FIR frequencies shared by a target molecule. Similar or related frequencies may suggest similar chemical and/or physical properties shared by the target and the compound. For example, the FIR sensitivities of drugs or drug targets could be noted, and then a library of compounds could be screened to find similar sensitivities among candidate drugs or targets. Alternatively, binding strength and/or binding kinetics between candidate drugs and targets could be determined by measuring how much FIR irradiation of a selected frequency is necessary and/or sufficient to disrupt the binding of a drug candidate to a target. In another alternative, FIR irradiation can be used to monitor the catalytic rate of an enzyme, by detecting a conformational or phase change in the enzyme, a cofactor, a reactant, or a product. In an embodiment, a waveguide can be provided to deliver the FIR irradiation to an area smaller than the diffraction limit typical for FIR wavelengths. The FIR beam can be introduced into the proximal end of the waveguide, the proximal end having a diameter in one embodiment of about 1 cm. The inside of the waveguide is preferably coated with a reflective coating (e.g. aluminum, silver, and/or gold). The waveguide can be drawn (in, e.g., a flame) so that it gradually tapers from, e.g., 1 centimeter diameter down to, e.g., about a tenth of a wavelength in diameter at the distal end. In an embodiment, the distal end diameter can be about 50 microns. A target placed right at the tip of the waveguide is impinged upon by the “near field” of the FIR irradiation, which is evanescent from the tip of the waveguide. In this exemplary embodiment, the FIR energy is concentrated to a small target diameter. One can use the energy in the evanescent field to measure absorption by the target sample at the frequency of the FIR field. One can also use the FIR energy in the near filed at the tip of the waveguide to influence a resonant system within the target sample. This type of delivery system allows delivery of FIR energy to areas with, e.g., up to ten times smaller diameter than the diameter of focus allowed by the diffraction limit. Thus for wavelengths around 500 microns, the FIR irradiation can be concentrates to a spot with a diameter of about 50 microns. This exemplary embodiment could greatly enhance the localization of the delivery of the FIR energy to a biological sample. In an embodiment, such highly concentrated localization could facilitate Photo Dynamic Therapy (PDT). Normally PDT uses visible or near infrared light from a laser to interact with a dye which has been injected in, e.g., a tumor. The light is absorbed preferentially by the dye which has been preferentially taken up by the tumor so that any heating induced by the absorption of the laser light is in the tumor. In principle, this would kill the tumor while having little effect on surrounding tissue. In an embodiment, a tumor having a resonant frequency in the FIR band that is not shared by normal tissue or is substantially weaker in normal tissue, could be ablated by delivery of concentrated FIR selectively to the tumor. Delivery would be selective, e.g., because the normal is not sensitive to the chosen frequency of FIR irradiation. In an embodiment, FIR irradiation may be applied to an enzyme to increase the reaction rate of the enzyme, or to substitute for a cofactor, reactant, or intermediate during the enzymatic reaction. Increasing reaction speed or efficiency can facilitate protein expression and may increase the yield of product for a given amount of enzyme or within a given period of time. Conversely, FIR irradiation may be delivered to an enzyme to impede its reaction, thereby providing a method to, e.g., control a process or prevent formation, maintenance, or progression of a disease. In an embodiment, FIR irradiation of a sample can provide a “fingerprint” of the sample by identifying particular FIR frequencies or sub-bands to which the sample is sensitive. Thus, the presence of one article may be detected with another article, if the two articles differ in their FIR spectra. In an embodiment, apertures of the optical elements can be smaller than those used with microwaves. In an embodiment, reflective elements for practice of the disclosed devices, apparatuses, methods, assays, and processes, are preferentially adapted for use with FIR irradiation. In an embodiment, reflective elements for practice of the disclosed devices, apparatuses, methods, assays, and processes, are preferentially adapted for use with FIR irradiation may be those designed for use with radiation from other regions of the spectrum, such as with visible light. In an embodiment, at least one of the disclosed devices, apparatuses, methods, assays, and processes, provides a filter to remove X rays. When a high energy electron beam (for example, a beam having an energy of 30 KeV (30,000 electron Volts) impinges on and is stopped or slowed by some material (i.e. the grating or the walls of a chamber) x-rays can be emitted as a result. The energy of the high speed electrons can be dissipated in the form of, e.g., x-radiation or heat. X rays thereby produced can contaminate the irradiation produced by directing the electron beam past, e.g., a grating. The x-ray contamination can interact with, e.g., an operator, an observer, or the article to which the irradiation is directed. The x-rays may cause damage, especially if they contact biological matter. Therefore, the disclosed devices, apparatuses, methods, assays, and processes, contemplate filters for removing x-rays from the FIR irradiation. In an embodiment, an electrostatic decelerating grid is provided to receive the electron beam and to dissipate the energy of the electrons without generating x-rays. In another embodiment, the FIR irradiation is directed away from its origin through a “maze” or convoluted optical path. The maze may located inside a common housing with the FIR source. For example, the filter may be positioned inside the vacuum chamber that contains the grating and the region of interaction between the electron beam and grating. In an embodiment, the filter may be located outside the housing. In an embodiment, the filter may be located partly inside the housing and partly outside the housing. In an embodiment, the housing may include a part of the filter. In an embodiment, the filter includes one or more mirrors. In an embodiment, the mirrors can reflect FIR while blocking x-rays. X rays impinging on a mirror may give rise to secondary (or tertiary, etc.) x-rays, which can then propagate in a direction different from that of the FIR irradiation, thereby removing the x-rays from the FIR irradiation. A second mirror repeating the process can facilitate the removal of x-rays from the FIR irradiation. In an embodiment, the mirror is sized with sufficient thickness to stop the x-rays. In an embodiment, the mirror includes a material having a density sufficient to stop x-rays. In an embodiment, the mirror includes at last one of lead or aluminum. In an embodiment, reflective surfaces are applied to the at least one of lead or aluminum. In an embodiment, the reflective surface comprises aluminum. As described herein, the mirrors, including flat mirrors and curved mirrors, can be used to create a path change for the FIR irradiation that excludes X-rays. X-rays may not reflect from surfaces, and can create secondary X-rays of lower energy that are related to the surface from which they emit. More surfaces may further reduce the chance that energetic X-rays will be able to follow the FIR irradiation. In an embodiment, one mirror surface is provided. In an embodiment, two mirror surfaces are provided. In an embodiment, three mirror surfaces are provided. In another embodiment, more than three mirrors are provided. As described herein, the mirrors, including flat mirrors and curved mirrors, can be used to act as focusing elements with cylindrical, spherical or parabolic surfaces. Combinations of variously sized and shaped mirrors can be used to create the desired beam shape. In an embodiment, the FIR irradiation beam can be emitted from the grating divergently at about, e.g., f=5, but may be astigmatic, having different f numbers in different axes. The beam could be made divergent, collimated, convergent, asymmetric (having astigmatism). In an embodiment, the mirror system can be sufficiently small to be contained within the vacuum chamber. Sizing the mirror system small enough to fit within a small vacuum chamber can help avoid requiring a large vacuum pump to maintain a typical vacuum chamber pressure of about 1·10−6 Torr and thereby keep the laser system, in an embodiment, small and/or compact. In an embodiment, the vacuum chamber can contain the grating and also the mirrors and be about 2 cc to about 5 cc in volume. As described herein, the mirrors, including flat mirrors and curved mirrors, can be fabricated from, e.g., metals or substrates covered with metals. Materials from which the mirrors can be fabricated include but are not limited to, e.g., aluminum, brass, copper, metalcoated plastic, or glass coated with, e.g., silver or aluminum. In an embodiment, mirrors can have an anti-reflection coating. In an embodiment, mirrors designed for or appropriate for visible light may be used for FIR irradiation. In an embodiment, mirrors placed in the vacuum chamber can be low-outgassing materials. In an embodiment, a lens can be provided in the optical path of the FIR irradiation. The lenses could be made of any FIR-transparent or semi-transparent material, including but not limited to, polymethylpentene, polyester, polypropylene, polyethylene, single crystal quartz, or sapphire, styrene, or any combination thereof. In an embodiment, the vacuum chamber has an output window through which the FIR irradiation can leave the vacuum chamber. In an embodiment, the output window can be plano. The output window can be fashioned with any of the materials described above. In an embodiment, the output window can be made from polymethylpentene and can have an electrically conductive coating on the vacuum side that may be transparent to the FIR. In an embodiment, the material from which the output window is made can maintain the integrity of the vacuum inside the vacuum chamber. In an embodiment, the output window may be any optical element to focus, collimate, diverge, or perform any optical change on the FIR irradiation as described above or known in the art. In a preferred embodiment, a tunable, narrow-band source is provided. Such a source facilitates driving a resonance of a biological sample or a component thereof because the source can emit FIR irradiation of a specified frequency, power, and bandwidth. In an embodiment, an FIR source can produce FIR irradiation can have a peak power of about 100 milliwatts per square centimeter. In an embodiment, FIR irradiation having power of about 1 microwatt can be focused on a target having an area of about 10−5 square cm The figures illustrate equipment for the practice of the disclosed devices, apparatuses, methods, assays, and processes. FIG. 1 shows a functional block diagram according to an embodiment of the disclosed devices, apparatuses, methods, assays, and processes for the irradiation of biological matter with FIR radiation. A source (2) emits FIR radiation, preferably with a power in the picoWatt to Watt range, preferably with a tunable frequency in the 10 to 3000 micron range, and preferably with a bandwidth in the range from 0.01 cm−1 to 100 cm−1, more preferably in the range from 0.01 cm−1 to 1 cm−1, most preferably approximately 0.6 cm−1. This radiation is directed through a filter (4) to dissipate or deflect any X-radiation or radiation at any other unwanted frequencies produced as a by-product of the operation of the source (2). The radiation then impinges on a sample of biological material (8). The sample (8) may then be subjected optionally to an assay (10) to measure any changes in the sample (8) induced by the radiation. A detector (12) may be employed optionally to measure any residual radiation following impingement on the sample (8). Feedback may be sent from the detector (12) and/or the assay (10) to the source (2) to modulate or otherwise modify the output of the source (2). FIG. 2 is an orthogonal projection view of one illustrative embodiment. FIGS. 2A-1 and 2A-2 are top and front views, respectively, of the same embodiment. The FIR source corresponds to the source (2) of FIG. 1. The illustrated filter (4) in FIG. 1 can include by way of example an off-axis parabaloid collimating reflector 14 and a mirror 16, both of which can be in optical alignment with the path of the source output. The radiation 17 can be focused to impinge on the sample in the sample cell 20 by a lens 18. The radiation 17 may be deflected by a second mirror 22. The sample cell 20 may contain the biological matter to be irradiated. A residual radiation 24 (e.g., a portion of the source output not absorbed by the optical components, the sample cell 20, the sample, or the aqueous solution and/or aqueous gel in which the sample may be suspended) may be then reflected by a third mirror 26 and optionally focused by one or more lenses 28 to be detected optionally by the detector 12. FIGS. 2B-1 and 2B-2 show top and front views, respectively, of an exemplary embodiment in which a mirror 30 deflects a small portion 32 of the source output 17, for example 5%, to the detector 12. Alternatively, a beamsplitter or pellicle could be used to direct a portion of the irradiation to a detector. This has the advantage of removing the detector from the area of the sample to allow more flexibility in engineering the sample area. It may also be used to normalize the output (which varies over time) of the FIR source when using the apparatus to perform absorption spectroscopy. The FIR source may be directed through a filter comprising by way of example a combination of refractive (i.e., lens) and reflective (i.e. mirror) optical components to a sample target. The system may be optimized to place all FIR available on a target area preferably no larger than about 1 mm in diameter. It is also preferable for the target area to be no larger than the diffraction limit will allow for the wavelengths being used. Such placement minimizes waste of available FIR and also permits selective delivery of FIR to multiple articles of biological matter, to a single article, or even to one portion of an article of biological matter with minimal delivery to other portions of the same article. However, one of ordinary skill in the art would appreciate that the target area size need not be so limited, but may be of any size, given the application. The sample comprises a quantity of biological matter, for example, living cells suspended in an aqueous solution and/or aqueous gel. The FIR source can be operated continuously or pulsed, illustratively, at about 100 Hz with a 10–15% duty cycle to prevent heating of components within the FIR source and of the biological sample as well as to eliminate the need for a chopper in the optical path. A variety of pulse shapes obvious to those skilled in the art can be employed to enhance the effects of the FIR and/or minimize collateral damage to the target during irradiation. A device according to an embodiment Of the disclosed devices, apparatuses, methods, assays, and processes may be used to determine experimentally optimal wavelengths for interactions with the targeted cellular components. While the optimum wavelengths for certain cellular components are known in the art, many others are currently being elucidated, and many more have yet even to be investigated. As used herein, “optimum wavelength” refers to a wavelength of FIR radiant energy selected for its ability to elicit the expected or desired effect more quickly or efficiently than other frequencies, for its ability to evade absorption by water and specifically elicit vibrational energy in a specific article of biological matter, or for its ability to induce vibrational energy in water molecules or chains of water molecules as a method to enhance the coupling of the FIR into a specific article of biological matter. The refractive elements (for example, the lenses 18 and 28) can be made of materials that are in the range of about 50% to 95% transparent to the FIR. Examples of such materials include polyester, polypropylene, polyethylene, polymethylpentene (PMP), styrene, single crystal quartz, and sapphire. PMP has the advantage of being transparent to visible light (VIS) as well as to the FIR, and it also has nearly the same refractive index at both wavelengths. Fabricating the refractive elements with PMP greatly facilitates aligning the FIR optical system with visible light, as well as permitting the sharing of the optical path by both FIR and VIS. This can also permit application of the FIR while simultaneously making VIS observations of the target, or simultaneously applying VIS (lasers, lamps) to the target by similar means such as dichroic mirrors and interference filters such as are currently used for fluorescence microscopy. Sapphire is also transparent to both VIS and FIR, and can be fabricated with optical surfaces suitable for high resolution microscopy, however sapphire in these thicknesses has more absorption losses than PMP. There are other materials (described in the book Far Infrared Techniques, by Maurice Kimmitt, Pion Limited, 1970, SBN 85086 009 1) that act as longpass and shortpass filters. The reflective elements of the optical system of FIG. 2 can be typically made of glass or other ceramics, metals and plastics, as described above. The ceramics and metals are usually aluminized front surface mirrors of the type commonly used in optical systems, however any metal with a surface polished sufficiently to reflect FIR will suffice. An advantage of using optical quality front surface metallized reflectors (plano, concave, convex, parabaloid, parabolic) is that, in combination with, e.g., PMP or sapphire, the whole optical system can be shared by both VIS and FIR as required. Metals can also form grids and screens which are selectively reflective of the FIR depending upon the spatial frequency of the elements of the grid/screen. Partially reflective elements can be made of most the above materials to be used as beam splitters and/or polarizers, as well as the type of wire grid polarizer/beamsplitter made by Sciencetech in Canada, and others. In an embodiment, a 50% beamsplitter includes a thin polyester sheet (e.g., DuPont Mylar). Any of the non-conductive optical elements exposed to the electron beam in the FIR source (PMP window in one embodiment, high molecular weight polyethylene in another embodiment) preferably has a conductive coating, more preferably metallic, applied to bleed off any electrical charge that might develop otherwise. A charge build-up can deflect the electron beam and make source operation difficult. Metal coatings can be applied by vacuum deposition, or, alternatively, a weak solution of colloidal graphite suspended in alcohol may be applied to create a layer of conductive carbon that is sufficient to carry any electrons to ground, but not so thick as to interfere with the FIR transmission through the optical element. The graphite works adequately, and is simple to apply. FIG. 3 is an exploded view of the sample cell 20. The sample cell may be a microscope slide composed of a material that is non-toxic to biological matter, transparent or semitransparent to FIR radiation, and, preferably, transparent to both FIR radiation and visible light. Examples include those materials described above as being appropriate for the refractive elements of an embodiment of the disclosed devices, apparatuses, methods, assays, and processes. In the upper surface of the sample cell can be a recessed reservoir 32 for containing an article of biological matter. The reservoir 32 may have a slot 36 to hold fluid. The reservoir 32 may be produced by milling, etching, or any other method familiar to one skilled in the art. The reservoir 32 may be covered by a cover glass 34, comprising a thin wafer of a material which may be transparent to VIS and partially or fully transparent to FIR, preferably sapphire. The sample cell 20 and/or the cover glass 34 themselves may function as additional refractive elements, further focusing the source output on the sample. FIGS. 4A and 4B depict front and side views, respectively, of an exemplary embodiment in which the source 2 and filter 4 are contained in a common housing 38. The common housing 38 may be a vacuum chamber. A portion of source 2 is shown, including an electron optical lens 40 and a grating 42. An electron beam 44 is directed past the grating 42, thereby generating output from the grating including FIR irradiation 46. The FIR irradiation 46 can be directed to a first mirror 48, from which it reflects. In the depicted embodiment, the mirror 48 is oriented at 45 degrees relative to the direction of the incident irradiation 46, but one of ordinary skill in the art will recognize that any of the mirrors may be oriented to reflect the irradiation 46 through any angle. The irradiation 46 may optionally be directed to a second mirror 50, and, again optionally, to a third mirror 52. The total number of mirrors is not limited, as described above. The irradiation 46 may then be directed out of the common housing 38 through an output window 54. In the embodiment depicted in FIGS. 4A and 4B, the mirrors 48, 50, 52, can be piano, or flat, as can be the output window 54. FIGS. 5A and 5B depict an exemplary embodiment similar to that in FIGS. 4A and 4B except that the output window 54′ in this case can be a lens. In an embodiment, output window 54′ can collimate the irradiation 46′. In an embodiment, output window 54′ can focus the irradiation 46. FIGS. 6A and 6B depict an exemplary embodiment similar to that in FIGS. 4A and 4B except that one of the mirrors can be curved. In the depicted embodiment, the third mirror 52′ is curved so as to collimate the irradiation 46′. Other mirrors, such as 48 and 50, could be additionally or alternatively curved to, e.g., collimate, focus, correct or induce asymmetry, or any other optical manipulation known in the art. In an embodiment according to at least one of the disclosed devices, apparatuses, methods, assays, and processes, the biological matter is retained in the sample cell throughout the duration of the irradiation, detection, and assay steps. In another embodiment according to at least one of the disclosed devices, apparatuses, methods, assays, and processes, the biological matter is removed from the sample cell after irradiation and detection and placed in a container more convenient for the assay to be performed. For example, if the sample cell is composed of a material that is not transparent to visible light, then the sample might be moved from the sample cell to a borosilicate glass microscope slide following irradiation to facilitate its examination in a light microscope. Examples of other assay systems with specific container means include but are not limited to nuclear magnetic resonance (NMR), X-ray crystallography, infrared, visible, and/or ultraviolet light spectroscopy, mass spectrometry, fluorescence microscopy, and others. In one embodiment, the output of the tunable FIR source having a line shape peaked at about the wavelength 445 microns and having a full width at half power of approximately 20 microns, having a duty cycle of 10% and a repetition rate of approximately 100 Hz, and having peak power of approximately 1 microWatt (or a peak signal strength of approximately one volt as detected by a helium cooled silicon bolometer manufactured by Infrared Laboratories operated on the low gain setting of the preamplifier) can be focused on an article of biological matter, for example the surface of an individual green algae multicellular organism of the species Volvox globator, held in a reservoir of a sample cell composed of, for example, polymethylpentene. The source output photon energy will be converted to phonon vibrations of a frequency equivalent or related to the output energy frequency in the biological matter or elements of the biological matter therein, inducing changes in the biological matter, for example changes of the transmission and reflection and fluorescence of visible light of specific wavelengths as measured by light spectrospcopy and or fluorescence microscopy. In an embodiment, contamination in a biological sample or other article can be detected by measuring FIR absorption or emission characteristic of the contaminant but not of the biological sample or other article. In an embodiment, an article can be sterilized by exposing it to FIR irradiation to which the contaminant is sensitive but the article or biological sample is not, or to which the article or biological sample is less sensitive than is the contaminant. This might be particularly useful in places where sterilization or decontamination is important, such as in hospitals or other medical venues, clean rooms, water treatment plants, food processing plants, or in spacecraft. Measuring binding affinity may include, e.g., determining an affinity or equilibrium constant. The range of FIR wavelengths used may be from about 10 to 3000 microns, preferably about 100 to 500 microns, most preferably 430 to 480 microns. The range of FIR wavelengths used may be from about 10 microns to about 100 microns. The range of FIR wavelengths used may be from about 100 microns to about 200 microns. The range of FIR wavelengths used may be from about 200 microns to about 300 microns. The range of FIR wavelengths used may be from about 300 microns to about 400 microns. The range of FIR wavelengths used may be from about 400 microns to about 500 microns. The range of FIR wavelengths used may be from about 410 microns to about 420 microns. The range of FIR wavelengths used may be from about 420 microns to about 430 microns. The range of FIR wavelengths used may be from about 430 microns to about 440 microns. The range of FIR wavelengths used may be from about 440 microns to about 450 microns. The range of FIR wavelengths used may be from about 450 microns to about 460 microns. The range of FIR wavelengths used may be from about 460 microns to about 470 microns. The range of FIR wavelengths used may be from about 470 microns to about 480 microns. The range of FIR wavelengths used may be from about 480 microns to about 490 microns. The range of FIR wavelengths used may be from about 490 microns to about 500 microns. The range of FIR wavelengths used may be from about 500 microns to about 600 microns. The range of FIR wavelengths used may be from about 600 microns to about 700 microns. The range of FIR wavelengths used may be from about 700 microns to about 800 microns. The range of FIR wavelengths used may be from about 800 microns to about 900 microns. The range of FIR wavelengths used may be from about 900 microns to about 1000 microns. The range of FIR wavelengths used may be from about 1000 microns to about 2000 microns. The range of FIR wavelengths used may be from about 2000 microns to about 3000 microns. Duration of irradiation may be in the range from about 1 microsecond to 1 year. The duration of irradiation may be in the range of about 1 second to 1 hour. The duration of irradiation may be in the range of about 1 microsecond to about 10 microseconds. The duration of irradiation may be in the range of about 10 microseconds to about 100 microseconds. The duration of irradiation may be in the range of about 100 microseconds to about 1 second. The duration of irradiation may be in the range of about 1 second to about 2 seconds. The duration of irradiation may be in the range of about 2 seconds to about 3 seconds. The duration of irradiation may be in the range of about 3 seconds to about 4 seconds. The duration of irradiation may be in the range of about 4 seconds to about 5 seconds. The duration of irradiation may be in the range of about 5 seconds to about 6 seconds. The duration of irradiation may be in the range of about 6 seconds to about 7 seconds. The duration of irradiation may be in the range of about 7 seconds to about 8 seconds. The duration of irradiation may be in the range of about 8 seconds to about 9 seconds. The duration of irradiation may be in the range of about 9 seconds to about 10 seconds. The duration of irradiation may be in the range of about 10 seconds to about 1 minute. The duration of irradiation may be in the range of about 1 minute to about 10 minutes. The duration of irradiation may be in the range of about 10 minutes to about 1 hour. The duration of irradiation may be about 3 minutes. Pulse rate of the irradiation may be in the range of continuous wave to about 1 GigaHertz. Pulse rate of the irradiation may be in the range of continuous wave to about 1 MegaHertz. Pulse rate of the irradiation may be in the range of continuous wave to about 1 kiloHertz. Pulse rate of the irradiation may be in the range of continuous wave to about 100 Hertz (Hz). Pulse rate of the irradiation may be in the range of about 10 Hz to about 100 Hz. Pulse rate of the irradiation may be in the range of about 25 Hz to about 55 Hz. Pulse rate of the irradiation may be about 40 Hz. In an embodiment of at least one of the disclosed devices, apparatuses, methods, assays, and processes, as illustrated, e.g., in FIGS. 1, 2, the detector comprises a helium cooled bolometer (manufactured by Infrared Laboratories Inc.) to keep track of the FIR signal delivered. Some part of the signal can be absorbed by the optical components, the target, and the aqueous solution and/or aqueous gel; the remainder, typically 10–30% of the FIR is transmitted through the entire fixture/target and is seen by the detector. In an embodiment of at least one of the disclosed devices, apparatuses, methods, assays, and processes, the filter (4) of FIG. 1 comprises metal reflective surfaces arranged in a labyrinth-like form in the path of the radiation emitted by the source before the radiation impinges on the sample. The filter absorbs and deflects both the primary and secondary X-rays produced by the source electron beam in such a manner as to prevent the X-rays from entering the vicinity of or impinging upon the sample. Various alternative embodiments are envisioned and within the scope of the disclosed devices, apparatuses, methods, assays, and processes, such as those comprising other FIR sources, arrangements of reflective and refractive elements contained within the filter, types of biological matter subject to FIR irradiation, designs of the sample cell, types and methods of assays to be performed on samples following irradiation, types of detectors, and the like. Therefore, while the disclosed devices, apparatuses, methods, assays, and processes have been particularly shown and described with reference to a number of embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosed devices, apparatuses, methods, assays, and processes. |
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description | The present application is a continuation application of U.S. application Ser. No. 10/359,236 filed on Feb. 6, 2003, now U.S. Pat. No. 7,164,126 which in turn is a continuation application of U.S. application Ser. No. 10/239,062 filed on Oct. 22, 2002, now U.S. Pat. No. 7,034,296 the disclosures of each of which are incorporated herein by reference in their entirety. The present invention relates to a method of forming a sample image and a charged particle beam apparatus, and particularly to a method of forming a sample image and a charged particle beam apparatus which are suitable for obtaining a high resolution image in a high magnification and not influenced by image drift. In a charged particle beam apparatus typical of which is a scanning electron microscope, desired information (for example, a sample image) is obtained from a sample by scanning a thinly converged charged particle beam on the sample. In such a charged particle beam apparatus, the resolution becomes higher year by year, and the required observation magnification becomes higher as the resolution becomes higher. As the beam scanning method for obtaining a sample image, there are a method which obtains a final objective image by adding a plurality of images obtained by high speed scanning and a method which obtains a final objective image by once of low speed scanning (acquiring time of one frame image: approximately 40 seconds to 80 seconds). The influence of the drift of a view area on the acquired image becomes more serious as the observation magnification becomes higher. For example, in the method of acquiring the objective image by adding image signals obtained by the high speed scanning pixel by pixel (frame addition), when there is drift caused by charge-up of the sample during adding the images, the objective image after adding has blurs in a direction of the drift because displaced pixels of the view area are added. Reducing the influence of the drift may be attained by reducing number of adding frames and shortening the adding time, but this method can not obtain a sufficient S/N ratio. On the other hand, in the method of acquiring the image by the low speed scanning, when there is drift during acquiring the image, the image is deformed because the view area flows in a direction of the drift. A technology is disclosed in Japanese Patent Application Laid-Open No. 62-43050. The technology is that a pattern for detecting drift is stored, and a beam irradiating position is corrected by periodically acquiring an image of the pattern to detect a displacement between the acquired image and the stored pattern. A technology is disclosed in Japanese Patent Application Laid-Open No. 5-290787. The technology is that two images are acquired based on electron beam scanning on a specified observed area, and pattern matching is performed in order to specify an amount of displacement and a direction of displacement between the both images, and pixels are added by moving the pixels by the specified amount of displacement and the specified direction of displacement. In the technology disclosed in Japanese Patent Application Laid-Open No. 62-43050, the accuracy of controlling the beam irradiating position becomes insufficient when the observation magnification becomes several hundred thousand times. For example, when an image of 1280×960 pixels is tried to be acquired with an observation magnification of 200 thousand times, the size of one pixel on the observation view area (on the sample) is approximately 0.5 nm. Measurement and evaluation with a higher magnification become necessary as the scale-down of a measured object is progressed. Under such a condition, when the technology is applied to an apparatus for forming a final image by adding a plurality of images, image shift (drift) below several nm causes “blurs” in a flame added image. Although the technology disclosed in Japanese Patent Application Laid-Open No. 62-43050 suppresses the image shift by controlling the scanning position of the electron beam to correct the drift, the correcting accuracy of the position by such control is limited to several nm to several tens nm. Accordingly, it is almost impossible to correct the position (correct the drift) of an image having a magnification the position above several hundred thousand times with a pixel level. In addition, there is a problem in that the through-put is decreased because stabilization of the drift takes a long time. On the other hand, the technology disclosed in Japanese Patent Application Laid-Open No. 5-290787 can be appreciated in the point that the position between the images can be corrected in the pixel level, but there is the following problem. Because an S/N ratio of image data before processing image adding is low and accordingly the displacement between the images is difficult to be detected, it is difficult to correct the displacement with high accuracy. Further, it can be considered that the S/N ratio is improved by increasing the probe current (the electron beam current) to increase the amount of secondary electron emission. However, in a case of an easily charged sample, the displacement between the images acquired at different timing is further increased by movement of the view area of the electron beam due to charging, and as the result, it has been difficult to correct the displacement with high accuracy. Furthermore, in a case where a sample weak against electron beam damage is irradiated by an electron beam having a large beam current, there is a problem in that the sample may be broken or evaporated. An object of the present invention is to provide a sample image forming method and a charged particle beam apparatus which are suitable for realizing suppressing of the view area displacement with high accuracy while the influence of charging due to irradiation of the charged particle beam is being suppressed. In order to attain the above object, the present invention provide a method of forming a sample image by scanning a charged particle beam on a sample and forming an image based on secondary signals emitted from the sample, the method comprising the steps of forming a plurality of composite images by superposing a plurality of images obtained by a plurality of scanning times; and forming a further composite image by correcting positional displacements among the plurality of composite images and superposing the plurality of composite images, and a charged particle beam apparatus for realizing the above method. As described above, since positional displacements can be detected among images having a sufficient S/N ratio without increasing beam current by forming composite images and then correcting the positional displacements, “blurs” of an image at adding the frames can be suppressed because the positional displacements are corrected with high accuracy. The other objects of the present invention and the other detailed construction of the present invention will be described in the section “DESCRIPTION OF THE PREFERRED EMBODIMENTS” in the present specification. Embodiments of the present invention will be described below, referring to the accompanied drawings. FIG. 1 is a block diagram showing an embodiment of a scanning electron microscope in accordance with the present invention. A voltage is applied between a cathode 1 and a first anode 2 by a high voltage control power source 20 controlled by a computer 40 to extract a primary electron beam 4 with a preset emission current from the cathode 1. An acceleration voltage is applied between the cathode 1 and a second anode 3 by the high voltage control power source 20 controlled by the computer 40, and the primary electron beam 1 emitted from the cathode 1 is accelerated and travels to a lens system in the rear stage. The primary electron beam 4 is focused by a focusing lens 5 controlled by a lens control power source 21. Then, after unnecessary regions of the primary electron beam are removed by an aperture plate 8, the primary electron beam 4 is focused on a sample 10 as a very small spot by a focusing lens 6 controlled by a lens control power source 22 and an objective lens 7 controlled by an objective lens control power source 23. The objective lens 7 may be of various type such as an in-lens type, an out-lens type, a snorkel type (a semi-in-lens type) etc. Further, each of the lenses may be constructed of an electrostatic lens which is composed of a plurality of electrodes. The primary electron beam 4 is two-dimensionally (in X-Y directions) scanned on the sample 10 by a scanning coil 9. Current is supplied to the scanning coil 9 from a scanning coil control power source. Secondary signals 12 generated from the sample 10 by irradiation of the primary electron beam are travel to the upper portion of the objective lens 7, and then are separated from the primary electrons by a secondary signal separation orthogonally-crossing electromagnetic field generator 11 to be detected by a secondary signal detector 13. The signals detected by the secondary signal detector 13 are amplified by a signal amplifier 14, and then transmitted to an image memory 25 and displayed on an image display unit 26 as a sample image. The secondary signal detector may be a detector for detecting secondary electrons or reflected electrons, or a detector for detecting light or X-rays. An address signal corresponding to a memory area of the image memory 25 is generated in a computer 40, and converted to an analogue signal, and than supplied to the scanning coil 9 though the scanning coil control power source 24. The address signal in X-direction is a digital signal repeating, for example, 0 to 512 in a case where the image memory 25 is 512×512 pixels, and the address signal in Y-direction is a digital signal repeating 0 to 512 which is added by 1 when the address signal in X-direction reaches 512 from 0. The signals are converted to the analogue signals. Since the address of the image memory 25 corresponds to the address of the reflection signal for scanning the primary electron beam, a two-dimensional image of the deflection region of the primary electron beam by the scanning coil 9 is recorded in the image memory 25. The signals in the image memory 25 can be sequentially and successively read out using a read-out address generating circuit (not shown) synchronized by a read-out clock. The signal read-out corresponding to the address is converted to an analogue signal, and becomes a brightness modulated signal for the image display unit 26. The image memory 25 has a function for superposing (adding) the images (image data items) in order to improve the S/N ratio and then storing the composite image. For example, by superposing images obtained by 8 times of two-dimensional scanning and then storing the composite image, one frame of complete image is formed. That is, a final image is formed by adding images which are formed by once or more times of X-Y scanning. Number of images (number of adding frames) for forming one frame of the complete image may be arbitrarily set, and an appropriate number is set in taking into consideration conditions such as secondary electron generating efficiency and so on. Further, by superposing a plurality of frames each of which is formed by adding the plurality of images, a finally desired image may be formed. By executing blanking of the primary electron beam at the time when a desired number of image frames are stored or after the time, information input to the image memory may be interrupted. Further, in a case where the number of adding frames is set to 8, it is possible to provide such a sequence that the first frame of image may be deleted when a ninth frame of image is input so that 8 frames of image remain as the result. Otherwise, it is possible to perform weighted addition averaging. That is, when a ninth frame of image is input, an added image stored in the image memory is multiplied by ⅞ and then the ninth frame of image is added to the added image after being multiplied by ⅞. A two-stage deflecting coil 51 (an image shift deflector) is arranged at a position the same as that of the scanning coil 9, and thereby, the position of the primary electron beam 4 (the observed area) on the sample 10 can be two-dimensionally controlled. The deflecting coil 51 is controlled by a deflecting coil control power source 31. A stage 15 can move the sample 10 at least in 2 directions (X-direction and Y-direction) on a plane normal to the primary electron beam. From an input unit 42, an image acquiring condition (scanning speed, number of adding flames of image) and a method of correcting view area can be specified, and outputting and storing of the images can be also specified. Further, the embodiment of the apparatus in accordance with the present invention comprises a function for forming a line profile based on detected secondary electrons or detected reflected electrons. The line profile is formed based on an amount of detected electrons when the primary electron beam is one-dimensionally or two-dimensionally scanned or based on brightness information of the sample image, and the obtained line profile is used for dimension measurement of a pattern formed, for example, on a semiconductor wafer. The embodiment of the apparatus in accordance with the present invention may further comprise an interface 41 for transmitting image data to an external unit or the like, and a recording unit 27 for storing image data to an appropriate memory medium. In the explanation of FIG. 1, the control unit is described as a unit integrated with the scanning electron microscope or the like, but it is, of course, not limited to such a unit. A control processor separately provided from the scanning electron microscope may be used to execute the processing as described below. At that time, a transmitting medium for transmitting signals from the control processor to the scanning electron microscope and input and output terminals for inputting and outputting the transmitted signals through the transmitting medium are necessary. Further, it is possible that a program for executing the processing to be described below is registered in a memory medium, and the program is executed by the control processor for supplying necessary signals to the scanning electron microscope having an image memory. That is, the embodiments of the present invention to be described below also hold as the invention of program which can be employed to a charged particle beam apparatus such as a scanning electron microscope having an image processor. In an embodiment of a method of improving an S/N ratio by adding TV scanned images, the processing flow of FIG. 2 will be described below in detail. FIG. 5 is a view schematically showing the processing of FIG. 2. First Step (S2001): Number N0 of adding frames for each acquired image and number N1 of acquired image sheets are specified. At that time, total number of adding frames of the final image is N0×N1. In general, by setting the number N0 to 2 frames to 8 frames and the number N1 to 10 sheets to 50 sheets, a necessary S/N ratio can be obtained depending on the purpose. In a case where each of image is acquired with slow scanning slightly slower than the TV scanning, the number N0 may be set to 1 frame. In a case of TV scanning of interlace type, the number N0 can be set to 2. In regard to the condition setting, it is preferable that the plurality of sample images are formed by fixing the optical conditions (a focusing condition of the electron beam and a scanning condition) in order to make detection of positional displacement easy. Second Step (S2002): As starting of acquiring image is instructed from the input unit 42, N1 sheets of images of frame adding number N0 (F1, F2, . . . , FN1) in the same view area are successively acquired. Third Step (S2003): F1 is set to a memory area of the objective image F0. Forth Step (S2004): A sharpened image F0a is produced from the objective image F0. As the sharpening processing, a technique using an image filter for emphasizing edges in the image may be used. Fifth Step (S2005): A sharpened image F2a is produced from the image F2. Sixth Step (S2006): A positional displacement between the sharpened image F2a of F2 and the sharpened image F0a is detected. Calculation processing such as image correlation may be applied to the detection of the positional displacement. However, of course, the present invention is not limited to the above, and all the image processing methods capable of detecting the positional displacement are applicable. Seventh Step (S2007): Pixels of the original image F2 is shifted by the amount of the displacement of view area detected in the Sixth Step and added to the image of F0, and then the formed image is returned as the objective image F0 again. Eighth Step (S2008): By repeating the Fourth Step to the Sixth Step Substituting F3 for F2, the adding processing with the correction of positional displacement is executed to all the N1 sheets of images. In the present embodiment, the finally obtained image is an image formed by adding N0×N1 frames, but the image is blurred by the drift only when N0 frames are added. Therefore, the blur of the image by the drift is reduced to 1/N1 compared with the case of directly adding N0×N1 frames. By employing such a sequence, it is possible to remove the positional displacement in a direction on the two-dimensional image plane between images acquired at different timing due to charge-up on the sample, and accordingly, image blurs of the image can be suppressed or eliminated. FIG. 3 shows an example of a result obtained by this embodiment. FIG. 3 (a) is an image obtained through commonly adding the frames (1280×960 pixels, 200 thousands times of magnification), and drifts are accumulated during adding the images to form conspicuous “blur” in the final image. FIG. 3 (b) is an image obtained by acquiring 10 sheets of images having frame adding number 1/10 times as small as the frame adding number of FIG. 3 (a), and adding these 10 sheets of the images while the positional displacements are being corrected. In FIG. 3 (b), though the total frame adding number of images is the same as that of FIG. 3 (a), the “blur” in the final image caused by the drift is also reduced to 1/10 times as small as that in FIG. 3 (a) because only the drift accumulated each of the added image becomes “blur” in the final image and the acquiring time for each image is 1/10 times as short as that in FIG. 3(a). Since the amount of drift changes depending on the kind of the sample, the optical condition and so on, it is preferable that N0 and N1 are set corresponding to the S/N ratio. Since number of scanning times (number of images) required for securing a required S/N ratio is determined based on the quality of obtained image and the efficiency of generating secondary electrons, N0 and N1 may be determined in taking the degree of drift into consideration. Further, it is also possible to construct the sequence that by inputting a parameter expressing conditions of the sample (easiness of charge-up etc) and at least one of total adding number, number of adding frames (N0) and number of acquired images (N1), the other two parameters are determined. According to such a construction, the apparatus condition can be easily set only by inputting specification necessary for observation. In the present embodiment, although the positional displacement between the frame-added images is corrected, the present invention is not limited to the above. Correction of the positional displacement may be executed by the unit of an arbitrary number of frames or by the unit of arbitrary number of acquired sheets. At that time, unless an image to be compared with for detecting the positional displacement has an S/N ratio larger than a certain value, the drift detecting accuracy will be decreased. Therefore, it is preferable that number of images necessary for securing a desired S/N ratio is set as the frame adding number (N0), and then number of acquired image sheets (N1) for obtaining a necessary S/N ratio for the final sample image is set. In the present invention, the image may be stored in the image memory 25 after correcting the positional displacement. Otherwise, by preparing a frame memory corresponding to (frame adding number)×(acquired images), the positional displacement among sample images may be corrected when the sample image is displayed, or when the sample image is transferred to an external image memory element, or before the sample image is transferred to the external image memory element. Otherwise, the positional displacement among sample images may be corrected in the external image memory element. By preparing at least an image memory for storing a composite image, an image memory for storing images before executing superposing processing and an image memory for storing an image to be acquired, images acquired one after another by the electron beam scanning can be successively superposed. In the present embodiment, in order to make the setting of N0 and N1 for specified samples easier, the system may be constructed in such that a reference image for each combination of N0 and N1 is stored, and the reference image can be read out at setting N0 and N1. By doing so, an operator can set appropriate N0 and N1 by referring to the reference image. It is preferable that when drift is fast, number of displacement corrections is increased by decreasing number of frames N0, and that when drift is nor so fast, number of frames N0 is increased in order to improve the quality of the image to be compared with. For example, it is preferable that as a means for appropriately setting numbers of N0 and N1, a means for adjusting N0 and N1 stepwise is provided. In a case where the total adding frame is set to 50, the combinations of N0 and N1 are 1×50, 2×25, 5×10, 10×5, 25×2 and 50×1. However, by providing a means for adjusting the combination and a means for displaying an actually added image, the operator can set appropriate N0 and N1 from the superposed image without detailed knowledge on the technology in regard to the present invention. By providing the adjusting means described above, not only in the case of correcting the displacement, but also in a case where the quality of image is changed by changing the combination of N0 and N1, an appropriate combination of N0 and N1 can be easily selected. Further, the same effect can be attained by providing a means for adjusting the degree of displacement correction which sets N1 to a larger value when “the degree of displacement correction is large” is selected, and sets N0 to a smaller value when “the degree of displacement correction is small” is selected. A processing flow of FIG. 4 will be described below in detail. First Step (S4001): Number N0 of adding frames for each acquired image and number N1 of acquired image sheets are set. Second Step (S4002): Two sheets of images of the frame adding number N0 are successively acquired. Third Step (S4003): Sharpened images are generated from the acquired two sheets of images, and a positional displacement between the sharpened images is calculated. Therein, when the amount of this displacement exceeds a preset allowable value, each of the images before correcting the position and being added conspicuously includes “blurs” due to drift. Therefore, the processing is stopped, and a display function may notify the operator that the drift is too large. Fourth Step (S4004): The two sheet of images after correcting the positional displacement are added to each other, and the added image is registered as F0. Fifth Step (S4005): The view area is moved in a direction canceling the positional displacement obtained in the process of S4003. Therein, as the shifting means, each of a method of using an electric view-area shifting means (an image shift deflector) and a method of using a stage is available depending on the amount of shifting. In general, when the amount of shifting is small, both of the image shift deflector and the stage are used. When the amount of shifting is large, the stage is used or the image shift deflector is used if necessary. By canceling the displacement of the view area using image shift deflector and the stage, the displacement between the images can be compressed even if there is a comparatively large drift. Therefore, it is possible to solve the problem that an effective view area (an area where view areas of images are overlapped with one another) after correcting the positional displacement by the image processing becomes narrow. Sixth Step (S4006): The next image is acquired. Seventh Step (S4007): By forming a sharpened image of the acquired image and a sharpened image of F0, a positional displacement between the sharpened images is calculated. Eighth Step (S4008): The image F0 and the image acquired in S4006 are added by correcting the positional displacement between the images, and the added image is newly set as F0. Ninth Step (S4009): The view area is moved in a direction canceling the positional displacement obtained in the process of S4008. Tenth Step (S4010): By repeating the process S4006 to the process S4009, N1 sheets of images are obtained, and the obtained images are added. According to the above construction, a large drift component can be corrected by the stage and the beam deflection, and very small drift of pixel level can be corrected at adding the images. Therefore, a high resolution image can be obtained by effectively correcting even a comparatively large drift. On the other hand, in order to minimize the effect of drift, it is necessary to minimize the acquiring time of each of the images for correcting the positional displacements and then being added to the limit. However, the limit is determined by the S/N ratio of the images necessary for detecting the positional displacement. Therefore, if the amount of the drift exceeds a certain value, each of the images itself for detecting the positional displacement becomes blurred due to drift. When an amount of drift causing such a result is detected, a means for displaying that a high resolution image is difficult to be acquired or for stopping the measurement may be provided. By doing so, it is possible to solve a problem of uselessly operating the apparatus under a state that acquiring of the sample images is clearly difficult. A processing flow of FIG. 6 will be described below in detail. First Step (S6001): A first image F1 for detecting drift is acquired. Second Step (S6002): An objective image F0 is acquired under an appropriate slow scanning condition. By acquiring the image under such a slow scanning condition, a high contrast image can be obtained because secondary electrons can be generated more compared to the case of fast scanning. Third Step (S6003): A second image F2 for detecting drift is acquired. Fourth Step (S6004): A displacement ΔF (ΔFx, ΔFy) between the images F1 and F2 is detected. Fifth Step (S6005): Amounts of deformations in the horizontal direction and the vertical direction of the objective image are calculated from the amount of image displacement ΔF. Sixth Step (S6006): A new image F0′ is formed by deforming the objective image F0. Here, the processing of Fifth Step will be described below in detail, referring to FIG. 7. Letting the amount of displacement between the drift detecting images F1 and F2 acquired into the image memory be ΔF (ΔFx, ΔFy), and a time difference between acquiring the image F1 and acquiring the image F2 be ΔT, drift speeds (Vx, Vy) in X-direction and Y-direction can be calculated by the following equations.Vx=ΔFx/ΔT, Vy=ΔFy/ΔT On the other hand, letting an acquiring time of the objective image F0 be T0, a displacement of view area of the image F0 generated during the time period from starting scanning to ending scanning can be expressed as follows. X-directionΔF0x = Vx × T0Y-directionΔF0y = Vy × T0 Therefore, as shown in FIG. 7, by deforming the objective image F0 in the image memory by F0x (Y-direction) and ΔF0y (X-direction) toward the directions of correcting the drift, it is possible to reproduce the estimated image F0′ which would be obtained if the drift did not occur. In the present embodiment, the images F1 and F2 for detecting drift are acquired before and after acquiring the objective image F0, respectively, but, of course, the present invention is not limited to the above. The images F1 and F2 may be successively acquired before acquiring the image F0 or after acquiring the image F0. In that case, the deformation is estimated from the displacement between the images F1 and F2 at the time when the image F0 is acquired, and then the estimated image F0′ can be reproduced. Each of the images F1, F2 and F0 is stored in the image memory, and the images F1 and F2 are read out based on judgment on necessity of image reproduction, and then the reproduction processing is performed. According to the construction described above, the shape of an observed object deformed by drift can be accurately known. Particularly, in the case of slow scanning, the electron beam is being irradiated on the sample, and accordingly deformation of the sample image due to charging of the sample becomes large. Therefore, application of the technology of the present embodiment is very effective in slow scanning. Further, although the present embodiment has been described on the case of two images for correcting drift and one image to be corrected, the present invention is not limited to the above and arbitrary number of images may be used. Further, in order that the operator judges the necessity of image reproduction, in the apparatus of the present embodiment, option buttons for selecting necessity of image reproduction are provided on a graphical user interface (GUI), as shown in FIG. 16. Although FIG. 16 shows the example of performing selection using a pointing device or the like on the image display unit, the present invention is not limited to this method. Setting may be performed using another well-known input setting means. In the observation using an electron beam apparatus such as a scanning electron microscope, there is a need that the sample image is highly accurately formed. On the other hand, there is also a need that damage of the sample is reduced by suppressing irradiation of the electron beam as low as possible. In the case of the embodiment of the apparatus in accordance with the present invention, the sample image can be firmed with high accuracy if the deformation of the sample due to drift can be suppressed, but the electron beam scanning for acquiring at least the images F1 and F2 is further required, which is different from the case of simply forming the image F0. That is, since the scanning time of the electron beam is increased, possibility of the sample damage caused by the electron beam irradiation is increased, By providing the option described above, the operator can select necessity of the reproduction taking a status of the observed object or the condition for forming an appropriate sample image into consideration, and can form the sample image which the operator desires. Further, by making a graph on what extent the deformation is corrected and registering the graph, the information can be used for setting the scanning speed and for judgment of necessity of drift correction. Further, by storing and displaying number of scanning times of the electron beam and amount of correction and the amount of deformation versus the irradiation time, it is possible to know the sample image is deformed by how long the electron beam is scanned. An embodiment of applying the drift correction technology to addition of line profiles will be described below, referring to FIG. 8. In general, measurement of dimension of a pattern on a wafer uses a signal distribution (a line profile) which is obtained when an electron beam is line-scanned on a pattern of a measured object. In a case where the sample is an insulator, high speed scanning is performed in order to prevent disturbance caused by charging. Therefore, since a signal obtained by once of line scanning is bad in the S/N ratio, it is difficult to perform highly reproducible measurement. Accordingly, in general, signal distributions obtained from several times of scanning are added to form a profile of the measured object. At that time, if drift occurs in the direction of line scanning, the added line profile becomes dull, and accordingly the accuracy of measurement is decreased. Therefore, each of the profiles obtained by plural times of line scanning is stored, and positional correction of the profiles is performed so that the correlation among the profiles becomes highest, and then the profiles are added. In this case, a signal acquired by once of scanning may be used as each of the profiles before addition. However, when the scanning speed is high, the signal acquired by once of scanning is too bad in the S/N ratio. Therefore, signals obtained by minimum number of scanning times within a range capable of correlating among the profiles are simply added, and the added signal may be used as each of the profiles before addition. By this method, the problem of dullness of the profile is improved even if there is drift, and a profile having a high S/N ratio can be produced. Therefore, it is possible to perform highly reproducible measurement. Further, the apparatus may be constructed in such that the setting page described in FIG. 16 is also used for selecting the necessity of positional correction. A semiconductor inspection apparatus or the like may be constructed in such that reliability of the measurement can be checked later by sounding an alarm or setting a flag to the measurement when an amount of positional correction exceeds a threshold and clearly increases. Therein, in a case where an amount of correction, a added profiler and profiles before adding are stored, or in a case where the line profile is formed based on a two-dimensional scanned image, the apparatus may be constructed in such that the added image or the images before adding are stored and displayed on an image display unit later. According to the construction described above, when a measured object is erroneously measured in a repetitive pattern or the like where patterns of the same type are adjacently arranged, the erroneous measurement can be easily checked. Particularly, in the case where a line profile is formed through one-dimensional scanning, the measurement can be rapidly performed compared to the case of two-dimensional scanning. However, it is impossible to check the accuracy of measurement by referring the sample image. In the present embodiment, the line profile can be formed with high accuracy even in the case of one-dimensional scanning by which the measurement can be rapidly performed. For example, even in an apparatus measuring length of a pattern based on a line profile, the length can be measured with high accuracy based on the line profile formed with high accuracy. In a case where a pattern width of a line pattern having roughness is measured, the measuring length range is expanded toward directions perpendicular to the direction of measuring length, and measurement of length based in the line profile is performed using a plurality of different positions within the measuring length range. Then, the plurality of obtained measured length values are averaged, or the dispersion values of roughness are measured based on the plurality of measured length values obtained within the expanded measuring length range. The present embodiment is also applicable to this case. For example, by performing addition of line profile with the above-mentioned positional correction for each of the plurality of the length measuring positions, and then by measuring the average value or the dispersion value of roughness, these resultant values can be obtained with high accuracy. Even in a case where the line profiles are displaced depending on the length measuring position due to charge-up or the like, the added line profile can be appropriately formed and the length can be accurately measured by performing positional correction, using one reference line profile, to the line profiles in the other positions, not by performing positional correction for each of the plurality of the length measuring positions. According to the construction described above, reliability evaluation of electric property of a semiconductor element pattern can be easily realized regardless of existence of roughness. Further, in the case of measuring lengths of a plurality of positions, when a measured length value of one of the positions is extremely different from the measured length values of the other of the positions, there is a possibility that a part of the line pattern is extremely thinned, or that a failure of the length measurement occurs. In such a case, the apparatus may be constructed in such that an error message is output or that the measured results such as the sample image and the line profile are registered together with the measuring conditions so as to check the results later by read out the data. FIG. 9 is a graph for explaining an example of estimating an accurate dimension from time-varying pattern dimensions by repeating measurement of the same pattern plural times. The object to be measured using an electron beam is damaged to be shrunk or evaporated depending on the material by irradiation of the electron beam. In such a case, since the pattern dimension is decreased as the amount of beam irradiation increases, the measurement itself is an error cause. In order to evaluate the correct dimension by estimating the error caused by the measurement itself, the same pattern is measured plural times. Since the amount of beam irradiation is increased in proportion to number of measuring times, deformation of the pattern is also increased as the number of measuring times is increased. Therefore, the pattern dimension before irradiating the beam or before shrinking at starting the beam irradiation can be estimated by obtaining the relationship between the number of measuring times (in proportion to the amount of beam irradiation) and the dimension measured value. In the embodiment of the apparatus in accordance with the present invention, a sequence for automatically executing the above-described dimension estimation is installed. The apparatus may be constructed in such that in order to judge later whether or not the dimension estimation is correctly performed, a table graphing number of measuring times versus measured value is stored, and then output to the display unit or an external output unit. For example, in a case where an observed object is shrunk and at the same time drift also occurs, the dimension estimation may be not appropriately performed by influence of the drift, the operator can check by referring to the above-described graph whether or not the dimension estimation is correct. By storing a sample image obtained at that time corresponding to the stored graph, the correctness of the dimension estimation can be checked referring to the sample image. The apparatus may be constructed in such that when the above-described graph records an abnormal trend, the graph is selectively stored or a preset flag is set. For example, when an abnormal change is observed in a graph expressing the trend of dimension change, something may occur in the electron beam apparatus at that time, and accordingly the dimension measurement may be not correctly performed. If the apparatus is constructed so that the graph or the sample image can be selectively checked at that time, the operator can efficiently check the correctness of the dimension estimation without performing useless check. Although the abscissa of the graph expresses “number of measuring times” in the present embodiment, the abscissa may express another parameter such as “number of scanning times” or “time”. The ordinate is not limited to express “measured value” either, and the ordinate may express a ratio of a measured value to a normal value (a design value). By forming a dummy pattern having a condition equivalent to a measured object pattern at a position near the measured object pattern when the present embodiment is applied to an apparatus for measuring length of a semiconductor pattern, measurement of length can be accurately performed without shrinking the pattern which affect operation of the semiconductor element. FIG. 10 is a view showing an example in which images, each of which has number of pixels larger than number of pixels of an objective image, are acquired, and displacements among the acquired images are corrected. In the present embodiment shows a case where the number of pixels of the objective image is, for example, 512×512 pixels. In this example, the number of pixels of the acquired image is 1024×1024 pixels. When the acquired images are added by correcting the positional displacements, there appears a region which can not be used as the objective image due to displacement among the images. In the present embodiment, the images each having a region wider than the number of pixels of the objective image are acquired in advance, and a region of 512×512 pixels in the central portion is cur out after adding the acquired images to obtain the final objective image. Since such slightly larger images are acquired, as described above, it does not occur that the peripheral portion of the final image is lost by being cut off when drift occurs. FIG. 11 shows an embodiment in which images are added by removing an abnormal image. In a case where an abnormally displaced image or an abnormally blurred image is formed by a sporadic disturbance during acquiring a plurality of images, or in a case where images acquired after acquiring a specific image show abnormal contrast due to charge during irradiating the beam, the abnormal image can be removed from the original images to be added by detecting the abnormality through image processing of these images. In regard to displacement, the abnormality can be detected by presetting an amount of displacement of view area to be judged as abnormal. In regard to blur, the abnormal image can be removed by executing image differential processing or the like, and setting a threshold to be judged as abnormal. In regard to the abnormal contrast, the abnormal image can be removed by judging on a histogram or by judging on abnormal decrease in the value of correlation with another image after correcting view area. By removing the abnormal information as described above, high resolution image can be stably acquired even if an unexpected cause occurs. Although the image judged to be abnormal can be removed, in order to search the cause of abnormality later, the image judged to be abnormal is stored in the image memory together with the optical conditions (acceleration voltage of the electron source, emission current and so on) at the time when the abnormality is recognized, or before and after the time when the image is judged to be abnormal. According to the construction described above, it is easy to check what reason the abnormal image is produced by. For example, if the timing that over current flows to the cathode of the electron source agrees with the timing that the abnormal image is produced, the cause exists in the electron source, which can be used as an index of replacing of the electron source. Changes of current and voltage applied to the optical element such as the extracting electrode, the acceleration electrode or the scanning coil of the electron microscope are displayed by a time chart, and the timing that the abnormality occurs is superposed on the time chart. By doing so, the operator can visually specify the cause. The abnormal frame removing technology explained by the present embodiment can be applied to the line profile addition explained in Embodiment 4. Although the example of mainly automatically removing the abnormal image has been described in the present embodiment, the present invention is not limited to the above. For example, it is possible to provide a function that images before adding are displayed on the image display unit, and an image judged to be abnormal by the operator can be selectively removed. Therein, if the apparatus is constructed in such that some of images can be selected using a pointing device or the like from the plurality of images before adding arranged and displayed on the image display unit, the operator can be visually select images to be removed from the plurality of images before adding. The apparatus may be constructed in such that not only the images before adding are displayed, but also the plurality of added images are displayed in order to ascertain abnormal images using the images having a some degree of S/N ratio. FIG. 12 shows an embodiment in which view area displacements among a plurality of images acquired by a plurality of image signals are corrected, and then the images are added. For example, when an added image using reflected electron signal is tried to be acquired, a lot of frames must be acquired for each of the original images because the amount of the reflected electron signal is generally little. The reason is that if an original image is formed by acquiring a small number of image frames acquired by the small signal amount, the view area displacement among the images can not detected because the S/N ratio of the original image is extremely decreased. On the other hand, if number of the original image frames is increased, the original image itself is blurred due to drift because the time acquiring the original images becomes long. In the present embodiment, the original images are acquired by the reflected electron signal, and at the same time original images having a good S/N ratio are acquired using secondary electron signal, and view area displacement among the original images acquired by the secondary electron signal is detected, and then the amount of the detected view area displacement is applied to the view area displacement among the plurality of images obtained by the reflected electron signal. Since the secondary electron image and the reflected electron image are acquired at the same time, the view area of the reflected electron image completely agrees with the corresponding secondary electron image. Therefore, the view area displacement of the original reflected electron images having a bad S/N ratio can be accurately corrected through the method of the present embodiment. Since the secondary electron signal image having a high S/N ratio is used as the image for detecting the view area displacement, number of frames composing the original image can be minimized. Therefore, the original image itself is not blurred by drift. As examples of signal having a bad S/N ratio, there are, for example, X-ray signal and sample absorption current. The embodiment of the present invention can be applied to various kinds of signals. Particularly, in a case where an element distribution (an X-ray image) of a thin film sample is acquired with high resolution, the secondary electron signal in the present embodiment may be replaced by transmission electron signal. In general, occurrence of X-rays scattering inside a sample can be prevented by making the sample into a foil having a thickness of several tens nm, and accordingly a high resolution element distribution image can be obtained. As the detection system for detecting secondary electrons and reflected electron at the same time, a construction shown in FIG. 17 is considered. According to this construction, two kinds of electrons (reflected electrons 1706, secondary electrons 1707) emitted from a sample 1705 can be detected at the same time using a reflected electron detector 1703 and a secondary electron detector 1704 arranged at an upper position and at a lower position of an objective lens 1702 for focusing a primary electron beam 1701, respectively. Further, secondary electrons and reflected electrons can be detected together using a detection system shown in FIG. 18. In the case of the construction of FIG. 18, secondary electrons and reflected electrons 1803 are accelerated by a retarding voltage 1802 applied to a sample 1801, and collide against a secondary electron converting electrode 1805 arranged above an objective lens 1804. At the collision, the accelerated secondary electrons and the accelerated reflected electrons 1803 produce secondary electrons 1806, and the secondary electrons 1806 are attracted to a secondary electron detector 1807 to be detected. An energy filter 1808 is applied with an energy filter voltage 1809 which is equal to or slightly higher than the retarding voltage 1802 applied to the sample. By applying such a voltage, only the reflected electrons are selectively pass through the energy filter 1808. In the construction described above, the secondary electrons and the reflected electrons are alternatively acquired by switching the voltage of the energy filter 1809 on-off or strong-weak every acquiring of predetermined number of two-dimensional image frames. Then, the positional displacement is detected using the secondary electron images, and the positional displacement of the reflected electron image is corrected using the detected positional displacement information, and then the reflected electron image is stored in the image memory. By doing so, in the scanning electron microscope employing the retarding technology, the reflected electron image without blur can be obtained. Although the reflected electrons and the reflected electrons are clearly separated in the present embodiment, the present invention is not limited to the above. The amount of electrons detected by the secondary electron detector 1809 may be increased by applying an energy filter voltage 1809 lower than the retarding voltage 1802 to the energy filter 1808. Since most of the electrons emitted from the sample have energy smaller than 50 eV, number of frames composing the original image can be minimized by using electrons having energy smaller than 50 eV for the images for detecting the view area displacement. The applied voltage to the energy filter 1808 may be changed depending on the purpose of analysis. The reflected electron detector and the secondary electron detector are not limited to those described in the present embodiment, but various types of detectors may be employed. Although the X-ray detector has not been illustrated, all of the existing X-ray detectors are applicable. FIG. 13 shows an embodiment in which positional displacements of a plurality of acquired images are corrected only in a specified direction on a sample surface, and then the images are added. In a case where an image has a pattern only in a specified direction in the image, positional displacement in a direction perpendicular to the pattern can be detected with high accuracy, but accuracy of detecting positional displacement in a direction parallel to the pattern is extremely low. In regard to such an image, by adjusting view areas only in the direction perpendicular to the pattern and adding the images, the error in the view area adjusting can be reduced. The direction of the pattern can be specified by analysis of frequency components of the image or line profiling of the image by binarization. In an apparatus for measuring line width of a pattern on a semiconductor wafer, accuracy of a result of length measurement can be maintained even when view area displacement is corrected only a specified direction as described above. Most of patterns on a semiconductor wafer are formed in linier shapes, and line widths in everywhere on a single line pattern are almost the same. Therefore, measurement of length can be accurately performed unless displacement occurs only in the direction perpendicular to the pattern. In a case where an objective image is a line pattern, and there is a view area displacement shown in FIG. 20 (a) between two frames of the images to be added, the relationship between shifting amount and degree of agreement becomes as shown in FIG. 20 (b). Referring to FIG. 20 (b), blur in the added image is corrected by overlapping the images under a condition of maximizing the degree of agreement, but the condition of maximizing the degree of agreement exists not only at one position, but at positions distributed in a line shape. Accordingly, the condition overlapping the images (the condition of maximizing degree of agreement) can not determine uniquely. Therefore, since the blur of the pattern can be corrected with the minimum shifting amount between the images when the shifting direction of the image is selected in the direction perpendicular to the pattern, there is an effect in that the effective view area of the added image is maximized. FIG. 14 shows a method of detecting the amount of positional displacement and adding the corrected images. In an input image 1401 and an input image 1402, a region 1403 having an adequate size is put, for example, in the central portion of the input image 1401, and template matching is performed to the input image 1402 using the area 1403 as a template. Assuming that a region 1404 matches with the region 1403 as the result, the region 1403 and the region 1404 are overlapped on each other, and a rectangular region (an AND region) 1405 of overlapping the input image 1401 and the input image 1402 on each other is set, and a portion not overlapping with the AND region in each of the input image 1401 and the input image 1402 is cut off to form a post-position-adjusting input image 1406 or 1407, respectively. Adding processing is performed by inputting the post-position-adjusting input images 1406 and 1407. This example shows the case of two input images, but it is easy to extend to a case of three or more input images. As an example of the template matching, there is a method of executing normalized correlation processing between two images based on the following equation, where the size of the input image is assumed to be 512×512 pixels and the size of the template in the center is assumed to be 256×256 pixels. Therein, a position where the calculated correlation value becomes the maximum is defined as a matching position. r ( x , y ) = [ N ∑ i , j P ij M ij - ( ∑ i , j P ij ) ( ∑ i , j M ij ) ] [ N ∑ i , j P ij 2 - ( ∑ i , j P ij ) 2 ] [ N ∑ i , j M ij 2 - ( ∑ i , j M ij ) 2 ] ,Therein, r(x, y) is a correlation value at (x, y), Mij is a density value at a point (i, j) inside the template, Pij is a density value at a corresponding point (x+1, y+1) of the input image, and N is number of pixels of the template. FIG. 15 shows another embodiment of a method of adding corrected images. Similarly to FIG. 14, in an input image 1401 and an input image 1402, a region 1403 having an adequate size is put, for example, in the central portion of the input image 1401, and template matching is performed to the input image 1402 using the area 1403 as a template. Assuming that a region 1404 matches with the region 1403 as the result, the region 1403 and the region 1404 are overlapped on each other, and a rectangular region (an OR region) 1501 including both of the input image 1401 and the input image 1402 is set, and a portion not overlapping with the OR region in each of the input image 1401 and the input image 1402 is added, and each of the added portions is filled with number of pixels of 0 or an average value of each of the input images to form a post-position-adjusting input image 1502 or 1503, respectively. Adding processing is performed by inputting the post-position-adjusting input images 1502 and 1503. This example shows the case of two input images, but it is easy to extend to a case of three or more input images. Description will be made below on an example in which the drift correction technology in accordance with the present invention is applied to automatic operation of a semiconductor inspection scanning electron microscope. In general, in order to automatically operate the semiconductor inspection scanning electron microscope, a recipe file to which information such as measuring positions and observing conditions is registered is formed in advance, and then measurement positioning, observation and measurement are performed according to the file. In the present method, an environment set before executing the recipe file is registered. FIG. 19 shows a recipe execution environment page. Main sequence of executing the recipe is as follows. That is, initially, alignment for detecting a position of a wafer on a stage is executed. At that time, image recognition is performed according to an image registered at forming the recipe. Next, the wafer is moved to the measuring position using the stage, and an image is acquired with a comparatively low magnification. Positioning of the measured pattern (called as addressing) is performed with high accuracy by image recognition, and pattern dimension measurement is performed by electrically deflecting the electron beam and zooming up to the measuring magnification. Automatic focus adjustment is performed before the positioning of the pattern or before the measurement. When test execution of the recipe or in a case where there are a plurality of measured wafers, an amount of drift during the time period from acquiring of an image for positioning the pattern to acquiring an image for measurement is measured for each of the measured points using the first wafer. In the case of alignment, an amount of drift at several minutes after the alignment is measured and stored. At executing the recipe, an amount of drift at each of the measured points or the alignment point is added to the image as an offset after positioning. In the case of addressing, the electron beam is deflected to a position added with the offset and the magnification is zoomed up to the measuring magnification. By doing so, the drift after positioning can be reduced, and the plurality of samples can be measured with high throughput because it is unnecessary to detect the amount of drift at the actual measurement using the recipe or at measuring the second wafers and wafers after the second. Whether or not the drift correction is executed at alignment, at addressing or at measurement is judged by ON or OFF of a drift correction switch 1901 for alignment, a drift correction switch 1902 for addressing or a drift correction switch 1903 for measurement, respectively. By providing the environment setting page to be described in the present embodiment, it is possible to set a concrete method of drift correction which changes depending on a measurement condition and a status of a sample. In recent manufacturing and inspection of semiconductors, a plurality of semiconductor wafers are usually dealt by the cassette unit by containing the semiconductor wafers in a cassette. An apparatus for continuously measuring such a plurality of measured objects is provided with a means for selecting whether or not drift correction is performed based on an amount of correction registered at forming the recipe and a means for selecting whether or not drift correction is performed based on an amount of drift actually measured each wafer. By constructed as described above, when there is individual difference of the semiconductor wafers in the cassette, the operator judges whether or not the measurement accuracy takes precedence over the throughput, and the selection can be reflected to the measurement. In a case of performing offset correction, a means for selecting whether or not offset correction is performed based on a value registered at forming the recipe and a means for selecting whether or not offset correction is performed using a value used for detecting the amount of drift in the first wafer in the cassette and registered are provided. By constructed as described above, when there is a manufacturing error between a test pattern or a design value and an actual pattern, the operator judges whether or not the measurement accuracy takes precedence over the throughput, and the selection can be reflected to the measurement. Although the above description is the example in which the operator selects the concrete correcting method, the present invention is not limited to the above. For example, it is possible to provide a sequence which automatically sets the concrete method described above by inputting a magnitude of manufacturing error or presence of manufacturing error. Although the above embodiments have been described on the cases of using the scanning electron microscope, the present invention is not limited to the scanning electron microscope. The present invention can be applied to a charged particle beam apparatus of another type in which a sample image is displaced due to some drift producing cause. |
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claims | 1. A nuclear fuel particle, comprising:a fuel kernel;a buffer graphitic carbon layer;an inner pyrolytic carbon layer;a multilayer pressure vessel including at least three layers in which a pyrolytic graphite layer is present between two layers of silicon carbide, wherein a thickness of the silicon carbide layers of the multilayer pressure vessel is at least 2 times a thickness of the pyrolytic graphite layers of the multilayer pressure vessel; andan outer pyrolytic carbon layer. 2. The nuclear fuel particle according to claim 1, wherein the multilayer pressure vessel includes at least two additional pairs of pyrolytic graphite layer and silicon carbide layer between the pyrolytic graphite layer and one of the two layers of silicon carbide. 3. The nuclear fuel particle according to claim 1, wherein the multilayer pressure vessel includes at least one additional pair of pyrolytic graphite layer and silicon carbide layer between the pyrolytic graphite layer and one of the two layers of silicon carbide. 4. The nuclear fuel particle according to claim 3, wherein the pyrolytic graphite layer(s) and the silicon carbide layer(s) alternate throughout the multilayer pressure vessel, thereby the pyrolytic graphite layers separate layers of silicon carbide. 5. The nuclear fuel particle according to claim 1, wherein each of the pyrolytic graphite layers of the multilayer pressure vessel has a thickness from 20 nm to 1000 nm. 6. The nuclear fuel particle according to claim 1, wherein the fuel kernel includes fissile and/or fertile materials in an oxide, carbide, or oxycarbide form. 7. The nuclear fuel particle according to claim 1, wherein the fuel kernel includes low enriched uranium (LEU). |
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abstract | A containment cooling apparatus includes a cooling water tank disposed above a containment; a spray header connected to the cooling water tank via a first communicating pipe, wherein the spray header is disposed on an outside of the containment for spraying cooling water to an outer wall of the containment; a bell shaped shield covering the containment, wherein the cooling water tank is disposed on a top portion of the shield; a space formed between an inner wall of the shield and the outer wall of the containment, wherein the spray header is disposed in the space; an exhaust hole disposed on the top portion of the shield; and a water separator disposed in the exhaust hole and/or the space. The containment cooling apparatus has higher utilization of coolant. |
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059404647 | abstract | A zirconium alloy tube for forming the whole or the outer portion of a nuclear fuel pencil housing or a nuclear fuel assembly guide tube. The zirconium alloy contains 0.8-1.8 wt. % of niobium, 0.2-0.6 wt. % of tin and 0.02-0.4 wt. % of iron, and has a carbon content of 30-180 ppm, a silicon content of 10-120 ppm and an oxygen content of 600-1800 ppm. The tube may be used when recrystallized or stress relieved. |
claims | 1. A method comprising:forming, on a substrate having an error of shape, a multilayer film stack of alternating layers of high refractive index material and low refractive index material and that reflects radiation in a range from vacuum ultraviolet through X-ray; andcutting away at least one cycle of alternating layers from a portion of the multilayer film stack so that the multilayer film stack, having said at least one cycle cut away, corrects a wavefront aberration of a wavefront phase of a light reflected by the multilayer film stack that would have been caused by the error of share of the substrate if said at least one cycle of alternating layers were not cut away. 2. The method according to claim 1, wherein the multilayer film stack is formed in a number of cycles of alternating layers of high refractive index material and low refractive index material larger than that necessary to saturate a reflectance. 3. The method according to claim 1, wherein said cutting away is controlled by detecting a difference in a material that forms the multilayer film stack. 4. The method according to claim 3, wherein a difference in material is detected by monitoring a secondary electron discharge. 5. The method according to claim 3, wherein a difference in material is detected by monitoring an optical change of characteristics. 6. The method according to claim 5, wherein said optical change of characteristics monitored is a change in an optical constant of visible rays or a change based on ellipsometry. 7. A method for forming an optical element that reflects radiation in a range from vacuum ultraviolet through X-ray, comprising:forming on a substrate a multilayer film having a stack of alternating layers of high refractive index material and low refractive index material in a number of cycles larger than necessary to saturate reflectance;forming a correction film on the multilayer film; andcutting away a portion of the correction film and the multilayer film stack in accordance with an amount of adjustment of a wavefront phase of emerging rays. 8. A multilayer film reflection mirror that reflects radiation in a range from vacuum ultraviolet through X-ray comprising:a substrate having an error of shape; anda multilayer film formed on the substrate for reflecting the radiation, wherein the multilayer film is formed by a plurality of repeated pairs of layers, layers of each pair of layers having different refractive indexes from each other, at least one pair of layers successively arranged from an outermost surface of the multilayer film having a predetermined portion in which material of the respective layers of the respective pair does not exist so that the respective layers are thereby non-uniform across the multilayer film, and so that the multilayer film thereby corrects a wavefront aberration of a wavefront phase of a light reflected by the multilayer film that would have been caused by the error of shape of the substrate if said at least one pair of layers successively arranged from the outermost surface of the multilayer film did not have said predetermined portion. 9. The multilayer film reflection mirror according to claim 8, wherein said wavefront aberration is corrected with more than one layer among said plurality of repeated pairs. 10. The multilayer film reflection mirror according to claim 8, wherein the multilayer film is formed by repeated pairs of layers whose number exceeds a number at which reflectivity is substantially saturated. 11. The multilayer film reflection mirror according to claim 10, wherein the wavefront aberration is corrected with more than one layer among the pairs of layers where the reflectivity is already saturated being partially removed. 12. The multilayer film reflection mirror according to claim 10, wherein reflectivity of said multilayer film is between about 15% and about 80%. 13. The multilayer film reflection mirror according to claim 8, wherein said light is an EUV light. 14. The multilayer film reflection mirror according to claim 8, wherein said multilayer film is formed by pairs of molybdenum and silicon layers. 15. The multilayer film reflection mirror according to claim 8, wherein said multilayer film is multilayer film formed by pairs of ruthenium and silicon layers, a multilayer film formed by pairs of rhodium and silicon layers, a multilayer film formed by pairs of ruthenium and carbon layers, or a multilayer film formed by pairs of rhodium and carbon layers. 16. An exposure apparatus comprising: a mirror comprising:a substrate having an error of shape; anda multilayer film formed on the substrate and reflecting radiation in a range from vacuum ultraviolet through X-ray, the multilayer film formed by a plurality of repeated pairs of layers, layers of each pair of layers having different refractive indexes from each other, at least one repeated pair of layers successively arranged from an outermost surface of the multilayer film having a predetermined portion in which material of the respective layers does not exist so that the respective layers are thereby non-uniform across the multilayer film and so that the multilayer film thereby corrects a wavefront aberration of a wavefront phase of a light reflected by the multilayer film that would have been caused by the error of shape of the substrate if said at least one repeated pair of layers successively arranged from the outermost surface of the multilayer film did not have said predetermined portion. 17. A method of manufacturing a multilayer film reflection mirror, comprising;forming a substrate having an error of shape; andforming a multilayer film on the substrate, the multilayer film having a plurality of repeated pairs of layers and reflecting radiation in a range from vacuum ultraviolet through X-ray, each pair of layers having layers with different refractive indexes from each other, at least one pair of layers successively arranged from an outermost surface of the multilayer film having a predetermined portion in which material of the respective layers does not exist so that the respective layers are thereby non-uniform across the multilayer film, so that the multilayer film thereby corrects a wavefront aberration of a wavefront phase of a light reflected by the multilayer film that would have been caused by the error of shape of the substrate if said at least one pair of layers successively arranged from the outermost surface of the multilayer film did not have said predetermined portion. 18. The method according to claim 17, further comprising partially removing at least one layer among said plurality of repeated pairs of layers, to thereby provide said at least one pair of layers successively arranged from an outermost surface of the multilayer film having a predetermined portion in which material of the respective layers does not exist. 19. The method according to claim 18, wherein the removing of the multilayer film is stopped at a portion of a layer having a relatively higher refractive index among said layers in a pair having different refractive indexes from each other. 20. The method according to claim 19, wherein said layer having a relatively higher refractive index is made of silicon. 21. The method according to claim 17, wherein said multilayer film is formed by repeated pairs whose number exceeds a number at which reflectivity substantially is saturated. 22. The method according to claim 21, further comprising partially removing more than one layer among the pairs of layers of the multilayer film where the reflectivity is already saturated, to thereby provide said at least one pair of layers successively arranged from an outermost surface of the multilayer film having a predetermined portion in which material of the respective layers does not exist. 23. The method according to claim 21, wherein reflectivity of said multilayer film is between about 15% and about 80%. 24. The method according to claim 17, wherein said light is an EUV light. 25. The method according to claim 17, wherein said multilayer film is made from molybdenum and silicon layers. 26. The method according to claim 17, wherein said multilayer film is multilayer film formed with pairs of ruthenium and silicon layers, a multilayer film formed with pairs of rhodium and silicon layers, a multilayer film formed with pairs of ruthenium and carbon layers, or a multilayer film formed with pairs of rhodium and carbon layers. 27. An optical element comprising:a substrate having an error of shape;a multilayer film formed on the substrate, the multilayer film having a stack of alternating layers of high refractive index material and low refractive index material in a number of cycles larger than necessary to saturate reflectance; anda correction film on the multilayer film,wherein the multilayer film reflects radiation in a range from vacuum ultraviolet through X-ray, and the correction film and the stack each have a cut away portion with at least one cycle of alternating layers being cut away in the cut away portion of the stack, so that the stack having said cut away portion corrects a wavefront aberration a wavefront phase of a light reflected by the multilayer film that would have been caused by the error of shape of the substrate if the stack did not have said cut away portion. 28. A multilayer film reflection mirror comprising:a substrate having an error of shape; anda multilayer film formed on the substrate and reflecting radiation in a range from vacuum ultraviolet through X-ray, wherein at least one cycle of a predetermined portion of the multilayer film corrects a wavefront aberration of a wavefront phase of a light reflected by the multilayer film that would have been caused by the error of shape of the substrate if said at least one cycle did not make a correction. |
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claims | 1. A working method which performs a deposition working or an etching working to a workpiece by irradiating a focused ion beam to the workpiece, comprising:a first working process performing a deposition working or an etching working to the workpiece by face-irradiating the focused ion beam to an actual working range entering inside an edge part of a working range of the workpiece, anda second working process performing the deposition working or the etching working to the workpiece by irradiating the focused ion beam to an edge of an edge part or an edge part vicinity, which is left in the workpiece after the first working process and which is smaller than the irradiation width of the focused ion beam. 2. A focused ion beam working apparatus that performs a deposition working or an etching working to a workpiece by irradiating a focused ion beam to the workpiece, comprising:scanning means for scanning a focused ion beam on a workpiece; andcontrol means for controlling the scanning means to perform a deposition working or an etching working to the workpiece by face-irradiating the focused ion beam to an actual working range entering inside an edge part of a working range of the workpiece, and subsequently controlling a dose quantity of the focused ion beam by irradiating the focused ion beam to an edge of an edge part which is left in the workpiece after the first working and which is smaller than the irradiation width of the focused ion beam. 3. A working method of deposition processing or etching processing a workpiece using a focused ion beam, the method comprising the steps:providing a workpiece that has a missing portion which extends inwardly from an edge of the workpiece or that has an excess portion which extends outwardly from an edge of the workpiece;performing a first deposition processing or a first etching processing to the workpiece by face-irradiating a focused ion beam onto the workpiece and scanning the focused ion beam in a working range that does not overlap the workpiece edge by a distance smaller than the irradiation width of the focused ion beam so that a part of the missing portion or a part of the excess portion remains along the workpiece edge; and thereafterperforming a second deposition processing or a second etching processing to the workpiece by edge-irradiating a focused ion beam onto the workpiece edge and scanning the focused ion beam to eliminate the remaining missing portion or the remaining excess portion along the workpiece edge. 4. A working method according to claim 3; further including a step of controlling the dose quantity of the focused ion beam during the step of performing the second deposition processing or etching processing. |
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052884341 | abstract | A process for dissolution of spent high efficiency particulate air (HEPA) filters and then combining the complexed filter solution with other radioactive wastes prior to calcining the mixed and blended waste feed. The process is an alternate to a prior method of acid leaching the spent filters which is an inefficient method of treating spent HEPA filters for disposal. |
abstract | The invention relates to a method for eliminating neutrons from fission, fusion or aneutronic nuclear reactions in a reactor (100), in particular in a laser-driven nuclear fusion reactor (100) which operates with hydrogen and the boron-11 isotope, in which method at least some moderated neutrons are made to undergo a nuclear reaction with tin (11). As a result of the nuclear reactions with tin, the neutrons convert the tin nuclei into stable nuclei having a higher atomic weight resulting from neutron capture. The invention also relates to a reactor (100) which is designed for energy conversion by means of fission, fusion or aneutronic nuclear reactions and for generating electric energy, wherein the reactor contains a neutron elimination device (50) which contains tin and is arranged such that at least some moderated neutrons are made to undergo a nuclear reaction with the tin. |
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abstract | The present invention relates to rigid structures and composite materials thereof for providing radiation attenuation/shielding. Some embodiments pertain to a radiation shielding apparatus including: a plurality of positionable radiation-shielding stacks of tiles. The stacks are subsequently and adjacently arranged in a contiguous configuration. A tile positioning mechanism allows movement of tiles within a stack between a stacked (retracted) position and an extended position. In the extended position, the tiles of each of the plurality of radiation shielding stacks at least partially overlap tiles of subsequent and adjacent tile stack at corresponding opposing side-margins thereof. |
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050248014 | summary | CROSS REFERENCES TO RELATED APPLICATIONS This application is related to U.S. Pat. Nos. 4,774,050; 4,642,213 and 4,711,753 incorporated by reference herein. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a system for automatically and periodically updating and adjusting an on-line pressurized water reactor core analytical model, which consists of a data file of parameters that describe the reactor core, to insure that at all times the model (data file) closely matches the then current characteristics of the modeled and monitored core, so that real-time and anticipating graphics displays representative of the operating characteristics of the actual core can be generated for a plant operator's use and an attached core parameter predictor can be reliably initialized by a user at any time, even through only minimal core monitoring and analytical capabilities are available. 2. Description of the Related Art An analytical core model has, in the context of the present invention, three essential components. The first of these is the broad collection of facts that encompasses the physical description of the core and the nuclear cross section data sets that describe the relative rates at which various nuclear reactions will occur in the core. The second of these several components is the current set of spatial distributions of time varying concentrations of certain transient nuclear isotopes that significantly affect local neutron balances throughout the core. Typical isotopes of concern are xenon-135 and samarium-149 precursors, iodine-135 and promethium-149, and, on a longer time scale, long term burn-up. The last essential component of the model is that small set of coefficients that, coupled with certain algorithms embedded in neutronics calculation sequences, allows complex nuclear phenomenom that are known to be operative in the reactor core to be replicated with a sufficient degree of accuracy by very simple approximation. The concept of updating the analytical core model relates to the tracking in time of the changes that occur in the local concentrations of the several nuclides that are of primary consideration in satisfying the second component of the analytical core model. The concept of adjusting the analytical core model relates to modifying one or more of the co-efficients that make up the third component of the analytical core model, so that the simple approximations used to replicate the affects of complex nuclear processes in the core provide the best available replication. With respect to the above components, two distinct problems pose themselves. The first problem relates to obtaining, on-line, sufficient information regarding the current distribution of nuclear power, iodine-135 and xenon-135 to be able to supply the reactor operator with reliable, concise indicators both of actual current core conditions and of trends in current core conditions, so that the operator can effectively and efficiently exercise control functions using xenon distribution displays as described in U.S. Pat. No. 4,642,213. In this context, the reactor operator can well include dedicated automatic control systems that carry out nominally human control functions. Various known approaches to successfully solving this problem include the use of the responses of many strings of fixed incore detectors to synthesize full three dimensional core power distributions from which the needed indicators are readily extracted, the use of on-line three dimensional analytical core models, augmented by a modest number of plant instrumentation signals, again to generate a comparably useable three dimensional core power distribution, and the use only of the signals from conventional plant instrumentation, filtered through empirically derived correlations, to produce detailed one dimensional core average axial power distributions and the needed derivative indicators such as is described in the U.S. Pat. No. 4,774,050. The use of many strings of fixed incore detectors necessarily commits the plant owner to relatively high initial and ongoing equipment costs. The use of three dimensional analytical models is highly computer resource intensive. The use of purely empirical correlations requires frequent careful calibration of the plant instrumentation and of the correlations themselves. The second problem relates to insuring that the analytical core model be sufficiently well matched to the operating characteristics of the corresponding reactor core, so that the predictions of core behavior remain stable and realistic over periods of tens of hours in the future, granted a valid initialization of a core predictor. Attempts have been made in the past using conventional core models to track certain operating parameters (power level, control bank position, etc.) in pressurized water reactors as plant operations proceed and to periodically update the analytical core models by, in affect, making projections of core response as the core actually responds. In none of these cases was an attempt made to adjust online any of the set of coefficients in the third component of the core model to force the model to match the actual nuclear characteristics of the core. In all such cases in which the reactor core involved was unstable or nearly unstable to spatial xenon oscillations, deviations between the calculated core average axial power distribution and the actual measured core average axial power distribution, as inferred by comparison of calculated axial offset with measured offset, for example, set in quickly and grew rapidly to a point where the current analytical results were useless and any subsequent predictions of core response would be, at best, suspect. The recently demonstrated use of a full, three dimensional nodal core model, that is at least weakly coupled to the plant instrumentation and that has provision for periodically adjusting the actual neutronics characteristics of the model to force reasonable agreement of the calculated core characteristics for the measurable values of those characteristics, offers the only currently known avenue that could lead to solving this second problem, albeit at a rather high commitment of computer resources. In the face of the foregoing, it is evident that what is needed is a simple on-line, one-dimensional analytical core model, which is far less computer resource intensive than a full three dimensional analytical core model, that can utilize the responses of conventional reactor instrumentation both to periodically update the model data file to account for ongoing plant operations and to, when deemed necessary, adjust the actual neutronics characteristics of the core model to ensure that calculated axial power distributions continue to closely track measured axial power distributions, as indicated by comparing calculated and measured values of axial offset and axial pinch. The close match of the core model to the actual reactor obtained by utilizing monitored reactor instrumentation responses both to continuously update the axial power, iodine, xenon, promethium, samarium and long term burn-up distributions in the core model and to concurrently adjust the nuclear characteristics of the model to match the nuclear characteristics of the core then provides a relatively inexpensive, readily implemented method for solving both of the problems identified above. U.S. Pat. No. 4,711,753 describes a scheme for utilizing the results obtained from an equilibrium full core flux map to calibrate or adjust certain elements of the analytical model (or data filed) to be used by a core response predictor. In particular, the axial distribution of the transverse buckling values, B.sup.2.sub.xy (Z) is adjusted, so that the calculated axial power distribution in the core model closely approximates the core average axial power distribution derived from the flux map. The constraint that the flux map be taken under stable equilibrium core conditions is imposed because no information regarding transient iodine, xenon promethium or samarium distributions can be derived from a single flux map. In this approach the axial distribution of the transverse buckling values takes the form: ##EQU1## which when expanded becomes: EQU B.sup.2.sub.xy (Z)=A.sub.1 F.sub.1 (Z)+A.sub.4 F.sub.4 (Z)+A.sub.5 F.sub.5 (Z)+. . . (2) The calibration or adjustment process consists in determining the values of the set of expansion coefficients, A.sub.n, that results in the best matching of a series of integral parameters characterizing the calculated axial power distributions to the corresponding parameters characterizing the core average axial power distribution derived from the flux map. The particular parameters include the well known axial offset parameter (AO) and other progressively higher order terms involving integrals over thirds, quarters and fifths of the core height. Due to the complex relationship of calculated axial power distribution to the core model, of which transverse buckling is only one of several components, the values of the expansion coefficients must be found by a guided trial and error search process involving several nested levels of search, details of which are given in the referenced patent. The whole procedure is feasible only because the particular set of expansion functions used, the F.sub.n (Z) functions, has the unique property of effectively decoupling the searches for the successive expansion coefficient values. Thus, the A.sub.1 coefficient influences the reactivity balance, but does not significantly affect any aspect of power distribution. The A.sub.2 coefficient controls the axial offset aspect of the power distribution but does not materially affect axial pinch (AP), etc. aspects, and so on. That the decoupling is effective has been demonstrated theoretically, and by repeated application of the calibration procedure to a variety of analytical core models. However, the calibration procedure described in U.S. Pat. No. 4,711,753 is applicable only when the results of a recent flux map taken under equilibrium core conditions are available. This occurs typically once a month in a conventional operating pressurized water reactor. Therefore, the needed system must be able to readjust the values of at least the dominant transverse buckling coefficients, specifically the A.sub.2 and A.sub.3 coefficients of equation (2) on-line and on a nominally continuous basis until the next monthly calibration becomes available to compensate for minor defects in the analytical core model and/or the neutronics algorithms being used. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for continuously updating the current distribution and related parameters of a nuclear reactor core analytical model. It is an additional object of the present invention to provide a method for continuously, on line adjusting aspects of an analytical core model to closely reflect the actual characteristics of the monitored reactor core, thereby insuring that the other initialization parameters of the model are correctly and validly updated as reactor operations proceed. It is a further object of the present invention to provide an updating and adjusting capability without requiring the availability of a complex core power distribution synthesis facility. It is still another object of the present invention to provide a system that functions in the background, updating and adjusting the model without intervention by the user, so that the model will be accurate when needed. The above objects can be attained by a system that updates and adjusts an analytical core model periodically using measured values available for normal core instrumentation. An initial reference calibration of the core model is made using results from an equilibrium flux map and a concurrently measured reactor coolant system boron concentration value. Thereafter, the analytical model is updated and adjusted on-line to replicate actual core operations as they progress. To accomplish this, changes are made in the model to track measured changes in the core power level, control bank position, core inlet temperature and so forth, and the model is depleted over progressive, short time steps to update the calculated values of axial power distribution and axial iodine, xenon, promethium, samarium and long term burn-up distribution at each update. Concurrently, values of the axial offset and axial pinch parameters are extracted from the calculated axial power distribution and are compared with estimates of the actual core average axial offset and axial pinch parameters, derived directly from conventional core instrumentation responses without intermediate core average axial power distribution synthesis, to determine whether an adjustment of certain of the analytical core model coefficients is needed. If either the calculated axial offset or calculated axial pinch parameter differs from the measured value of the axial offset or axial pinch by more than a preset tolerance, the adjustment process, operating on the second and third coefficients of the analytical transverse buckling expansion is set in motion. These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. |
claims | 1. A waste form formed by a method comprising the steps of:sorbing a hazardous radioactive material in nanopores of a nanoporous material;fixing the sorbed hazardous radioactive material with an alkaline reagent or alkaline silicate to render it less volatile/soluble by converting the sorbed hazardous material into a sorbed, anionic hazardous radioactive material;mixing the nanoporous material with a glass-forming component; andvitrifying the mixed nanoporous material and glass-forming component to form the waste form;wherein the waste form comprises nanometer precipitates comprising the hazardous radioactive material; andwherein the waste form excludes clay. 2. The waste form of claim 1 wherein the nanoporous material comprises alumina with pore sizes up to maximum of about 50 nm. 3. The waste form of claim 1 wherein the nanoporous material comprises derivatives of mesoporous alumina with pore sizes up to maximum of about 50 nm. 4. The waste form of claim 3 wherein the derivatives comprise one or more oxides of transition metals selected from the group consisting of silver (Ag), copper (Cu), iron (Fe), nickel (Ni), zinc (Zn), cobalt (Co), zirconium (Zr), and bismuth (Bi). 5. The waste form of claim 1 wherein the glass-forming component comprises one or more glass-forming oxides. 6. The waste form of claim 5 wherein the one or more glass forming oxides are selected from the group consisting of SiO2, Na2O, K2O, CaO, MgO, B2O3, Li2O, and P2O5. 7. The waste form of claim 5 wherein the one or more glass forming oxides are in percentages by weight about 0-2% Al2O3, 12-15% B2O3, 7-9% Li2O, 7-9% Na2O, and 68-72% SiO2. 8. The waste form of claim 1 wherein the hazardous radioactive material comprises one or more gaseous or soluble ions. 9. The waste form of claim 1 wherein the hazardous radioactive material is selected from the group consisting of 129I and 99Tc. 10. The waste form of claim 1 wherein the vitrifying step occurs at a temperature lower than 1100 ° C. 11. The waste form of claim 1 wherein the vitrifying step occurs at a temperature between about 75 ° C. and about 950 ° C. 12. The waste form of claim 1 wherein the vitrifying step occurs at a temperature between about 800 ° C. and about 900 ° C. 13. The waste form of claim 1 wherein the vitrifying step occurs at a temperature between about 850 ° C. and about 950 ° C. 14. The waste form of claim 1 further comprising one or more components that stabilize the nanometer precipitates in stable crystals. 15. The waste form of claim 14 wherein the one or more components comprise lithium oxide. 16. The waste form claim 1 wherein the fixing step comprises reacting the hazardous radioactive material with an alkaline reagent. 17. The waste form of claim 1 wherein the fixing step comprises reacting the hazardous radioactive material with alkaline metal hydroxide. 18. The waste form of claim 1 wherein the fixing step comprises reacting the hazardous radioactive material with sodium or potassium silicate. 19. The waste form of claim 1 wherein the hazardous radioactive material comprises one or multiple hazardous species. 20. The waste form of claim 19 wherein the one or more hazardous radioactive species comprise one or both of 129I and 99 Tc. |
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description | This application is a continuation of U.S. application Ser. No. 10/721,032 filed Nov. 24, 2003, now U.S. Pat. No. 7,091,508, which is a divisional of U.S. application Ser. No. 09/990,073 filed Nov. 21, 2001, now U.S. Pat. No. 6,653,648, which is a continuation-in-part of U.S. application Ser. No. 09/638,772 filed Aug. 15, 2000, now U.S. Pat. No. 6,448,571, all of which are incorporated herein by reference to the extent permitted by law. This invention relates generally to radiation protection systems and, more particularly, to radiation shielding systems with integrated procedural environments for use in the course of diagnostic or therapeutic procedures as well as methods for the use of such systems. X-rays are used in a wide variety of medical procedures, many of which require medical personnel to be in direct contact with the patient, thereby exposing such personnel to radiation. As presently configured, x-ray laboratories produce x-ray exposure to the patient and to the operator and associated technicians. Since patients undergo a limited number of exposures, cumulative radiation exposure to the individual patient is rarely a significant health concern. However, operators and health care personnel performing numerous procedures per year over many years may be exposed to significant cumulative radiation doses over time, which may have adverse effects. See David A. Clark, Editorial Comment, 51 Catheterization and Cardiovascular Interventions 265 (2000); Stephen Balter, An Overview of Radiation Safety Regulatory Recommendations and Requirements, 47 Catheterization and Cardiovascular Interventions 469 (1999). For this reason, both fixed and mobile lead shields are employed in fluoroscopic procedures to minimize radiation exposure. Such shields typically are constructed of radiation resistant plates suspended on bars that are adjusted to be interposed between the operators and the patient on the x-ray table. Despite the use of these shields, medical personnel are still exposed to radiation. It is therefore imperative that personnel wear leaded protective clothing (including full lead aprons, thyroid collars and leaded glasses). In addition, the doctors or other operators perform these radiologic procedures many hours per day and several days per week over many years throughout their medical careers. This long term, cumulative exposure may cause adverse effects. Furthermore, the wearing of heavy lead aprons may have long term deleterious effects resulting in disabling disorders of the spine in a significant number of operators. See Allan Mr. Rose, et al., Prevalence of Spinal Disc Disease Among Interventional Cardiologists, 79 American Journal of Cardiology 68 (1997). There are patents teaching systems for protecting and shielding against radiation in x-ray laboratories. The patents describe various shields made of radiation resistant material that are either mobile or attached to the x-ray table and can be adjusted between the operators and the x-ray source. Though there are numerous shapes and designs for these shields, and although they may be constructed of various materials, they do not sufficiently protect against radiation exposure, and medical personnel must still wear heavy and encumbering leaded protective clothing. Furthermore, such leaded protective aprons, collars and glasses do not fully protect the operator as they leave substantial portions of legs, arm and head exposed. Despite dramatic technological evolution of the imaging systems employed for diagnostic and therapeutic radiological procedures, the fundamental architecture of the radiological x-ray laboratory and its ancillary components have not changed appreciably over the last 50 years. For example, in the present configuration of a typical cardiac catheterization laboratory, there is a fixed floor or ceiling mounted radiological C-arm along with the ancillary electrical and computer equipment necessary to run the x-ray system. However, in order to perform diagnostic and therapeutic procedures, such a laboratory requires multiple other capital equipment items, as well as disposables. These items may include a fluoroscopy table, manual controls for the table, fluoroscopy monitors positioned some distance away from the procedure site and out of the operator's preferred line of site, physiological sensors and instruments for monitoring the patient, at least one staging area often located behind the surgeon or at the patient's groin area, and various other surgical tools and medical disposables. In the present configurations, neither these items nor the laboratory itself are optimized for procedural efficiency or radiation protection of the medical personnel within the laboratory. When working with a patient on an x-ray table, doctors and other medical personnel can be exposed to primary radiation that emanates directly from the source or can be exposed to secondary radiation that is reflected or scattered by an object such as the x-ray detector, the x-ray table, and even the patient. No prior invention has sufficiently reduced the primary and secondary radiation exposure of operators in an x-ray laboratory and addressed its inefficiencies of such a lab by using a radiation protection system comprising a shielding cubicle, screen, flexible interface and integrated operations environment. It is in view of the above that the present invention was developed. A preferred embodiment of the invention is a radiation protection system for shielding medical personnel from x-rays from an x-ray emitter while working on a patient, comprising an x-ray table having a first side, a second side and a top surface, the top surface for supporting a patient; a radiation-shielding cubicle having an interior defining a medical personnel region, the cubicle having a ceiling, floor, a first wall for separating the medical personnel from an x-ray emitter disposed outside of the cubicle, a second wall extending from one end of said first wall adjacent to a first side of the x-ray table and a third wall extending from the first wall adjacent to a second side of the x-ray table, the first wall having an opening for locating a portion of the x-ray table into the interior of the cubicle; a radiation-shielding screen attached to the x-ray table for covering the portions of the patient and the top surface of the x-ray table located in the interior of the cubicle; a radiation-shielding flexible interface for joining the x-ray table to the cubicle, the flexible interface having a flexible radiation-resistant skirt sealing the opening; and an integrated procedural environment. Among the objects and features of the invention is reducing the radiation exposure of staff in an x-ray laboratory. A second object of the invention is substantially reducing exposure to primary radiation around an x-ray table and thereby permitting doctors to perform fluoroscopic based medical and surgical procedures with access to a patient without being exposed to excessive amounts of radiation. A third object of the invention is reducing exposure to secondary radiation in the region around an x-ray table where medical professionals operate on a patient. A fourth object of the invention is to minimize radiation leaking into a cubicle while the x-ray table moves relative to the cubicle. Another object of the present invention is to improve the architecture, configuration and design of the equipment items in an x-ray procedure laboratory as well as the efficiency and flow of such laboratories. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. Referring to the accompanying drawings in which like reference numbers indicate like elements, FIG. 1 illustrates a radiation protection system 10 that covers a patient 12 on an x-ray table 14 and separates an operating region 16 from a C-arm x-ray emitter 18. The radiation protection system 10 includes a radiation-shielding wall 20, a radiation-shielding screen 22 on the x-ray table, and a radiation-shielding flexible interface 24 connecting the screen 22 and x-ray table 14 with the wall 20. The wall 20 is constructed from well-known radiation-blocking materials and is preferably transparent, thereby permitting visual contact between operators (not shown) in the medical personnel region 16 and the patient 12. An opening 26 is provided in the wall 20 so that it can be moved over the x-ray table 14. A mobility device, such as casters 28 or tracks (not shown) permits the wall 20 to be rolled into place, and retracting the casters 28 sets the wall in place. The top of the wall 30 is preferably higher than the C-arm 32 at its highest extension. The radiation-shielding screen 22 is movably attached to the x-ray table 14. The screen 22 may have a plurality of screen supports 34 (see also FIG. 6) attached to the x-ray table 14 and a radiation-resistant partition 36 attached to the supports 34. When extended, the screen 22 covers the x-ray table 14 in the personnel region 16 and the partition 36 is interposed between the patient 12 and the operators. The flexible interface 24 may have flexible joints 38 and a flexible, radiation-resistant skirt 40. The flexible joints 38 connect the wall 20 with the x-ray table 14 and hold the skirt 40. The skirt 40 joins the wall 20 to the screen 22 and covers the opening 26 in the wall. The flexible joints 38 and skirt 40 may extend, thereby allowing movement of the x-ray table 14 during the medical procedure without moving the wall 20. Thus, the connections between the screen 22, table 14, interface 24 and wall 20 (or cubicle 100 in other embodiments) creates a radiation-resistant seal. Transferring the patient 12 to and from the x-ray table 14 is facilitated by detaching the flexible interface 24 from the wall 20 and moving the wall, and by retracting the screen 22 to the foot 42 of the x-ray table 14. During fluoroscopic procedures, it is preferable for the screen 22 to extend over the patient 12 from the foot 42 to the patient's mid abdomen region 44. The partition 36 may be formed from a flexible sheet of radiation-resistant material, permitting the screen 22 to fold like a curtain as the screen supports 34 slide along the table. It will be evident to those skilled in the art that other movable devices can be substituted for the sliding mechanism, including a screen that can rotate like an awning (not shown). Alternatively, the screen 22 may be constructed from rigid panels or segments. Also, screen segments may be hingedly attached like an accordion or rollably attached like a roll-top desk or a pool cover, or conformably attached like a Venetian blind. As shown in FIGS. 1, 5 and 6, 7 and 8, the screen 22 preferably includes at least one instrument port 46 through which physicians may operate on the patient 12 with procedural equipment (not shown), including threading a catheter through the port 46 and inserting the catheter into the patient 12. For fluoroscopic procedures in which a catheter is inserted into the patient 12, it is preferable to have access to the patient through ports 46 over the patient's groin region near the femoral vessels. Each access port 46 can be covered by a radiation-shielding cloak 48 that is attached to the screen 22 around catheters. The cloaks, generally 48, help protect the doctors operating around the x-ray table 14 from radiation scattering through their respective ports 46. The screen 22 may also have control ports 50, allowing connections and access to controls on the x-ray table (not shown). The x-ray table 14 may also have a user interface 52 external or internal to the screen 22. Access to the x-ray table's controls allows the operators to adjust the position of the table throughout the procedure. It may also permit the operators to control the position and orientation of the C-arm 32 and catheterization system monitors 54. As with other procedural equipment, the wall 20, screen 22, interface 24, and cloaks 48 can be sterilized. Alternatively to or in combination with removing the screen 22 from the x-ray table 14 and the interface 24 from the wall 20 for sterilization, such elements and the partition 36 and the skirt 40 may be covered by disposable, sterile covers (not shown). With the radiation protection system 10 set in place, operators and other medical personnel in the operating region 16 are shielded from the x-ray emitter 18 and x-ray scattering during radiologic procedures. The radiation-shielding wall 20 separates the operating region 16 from the x-ray emitter 18 to protect the operators from exposure to most, if not all, primary radiation from the x-ray emitter 18 and from secondary radiation that could be scattered through the patient 12 or other sources. The radiation-shielding screen 22 is interposed between the doctors and the patient 12 to protect against most x-ray scattering from the patient 12 and the x-ray table 14. The radiation-shielding flexible interface 24 covers the opening 26 in the wall 20 and joins the wall with the x-ray table 14 and the screen 22 to protect against most radiation leaking into the operating region 16 when the x-ray table is moved. FIG. 2 illustrates the unassembled sections of another embodiment of a radiation protection system 10. As in the first embodiment, the radiation protection system 10 includes a radiation-shielding screen 22 and a radiation-shielding flexible interface 24. In the second embodiment, the radiation protection system 10 has a radiation-shielding cubicle 100, and the flexible interface 24 is mounted circumferentially around the x-ray table 14. As illustrated in FIGS. 3 and 4, the cubicle 100 encloses the operating region 16 when the system 10 is assembled. The entire cubicle 100 can be constructed from well known radiation-blocking materials and it can be constructed to allow for repeated disassembly and reassembly for portability and storage. A first wall 102 is interposed between the personnel and the C-arm x-ray emitter 18. The first wall 102 is structurally and functionally similar to the radiation-shielding wall 20 in the first embodiment. Within the cubicle 100, the medical personnel region 16 preferably provides adequate space for two physicians to operate on the patient 12. A third cubicle wall 104, shown here as a half-wall, separates the personnel region 16 from the x-ray table 14. As with the wall 20 in the previous embodiment, the cubicle 100 is preferably supported by a mobility device such as casters 28 that can be retracted when the cubicle is in place over the x-ray table 14. The cubicle 100 may also have at least one door 106. The cubicle 100 may contain access panels 108 for transferring equipment between the operating region 16 and the x-ray laboratory. The cubicle may also have tubing ports 110 for running catheters, tubes and other surgical equipment (not shown) from the patient 12 and the x-ray table 14 to other components in the x-ray laboratory. The cubicle may have its own ventilation system to maintain optimal ventilation and sterility, and may include shelves 112 for procedural equipment. Shelves 112 in the cubicle 100 may serve as a general staging table and shelves 112 suspended over the x-ray table 14 could serve as platform, allowing quick access to equipment by a doctor or other medical personnel 114. As in the previous embodiment, the cubicle 100 may also have monitors 54 to display fluoroscopic and other physiologic information, and the cubicle 100 may include an audio and/or video system for optimal communication between the medical personnel 114 and the rest of the laboratory. In this embodiment, each corner 116 of the flexible interface 24 may be attached to the cubicle 100 through the flexible joint 38. As in the previous embodiment, the flexible radiation-resistant skirt 40 may be held between the joints 38 to cover an opening 118 in the wall 102 and to join the wall 102 with the x-ray table 14 and the screen 22. In the second embodiment, the skirt 40 may also circumferentially join the x-ray table 14 to the cubicle 100. As in the previous embodiment, the flexible joints 38 and skirt 40 permit the x-ray table 14 to be moved during the procedure. Extending and retracting the radiation screen 22 is performed in a manner that is similar to the previous embodiment, and transferring the patient 12 to and from the x-ray table is also performed a similar manner. In the second embodiment, the flexible interface 24 may be detached around its circumference so that the cubicle 100 can be moved and the screen 22 can be retracted to the foot 42 of the x-ray table 14. FIG. 4 illustrates that these embodiments use much the same system for shielding operators and other medical personnel 114 from the x-ray emitter 18 and x-ray scattering when working in the personnel region 16 adjacent to the patient 12 on the x-ray table 14. In particular, operators are shielded from most x-ray radiation by isolating the personnel region 16 from the x-ray emitter 18 with the radiation-shielding wall 102 and the radiation-shielding flexible interface 24, covering the patient with a radiation-shielding screen 22 adjacent to the personnel region, and joining the wall 102 and the screen 22 with the flexible interface 24. The wall 102 and the flexible interface 24 isolate the personnel region 16 from the x-ray emitter 18. The flexible interface 24 attaches the x-ray table 14 to the wall 20, 102 through flexible joints 38, 116 and joins the screen 22 to the wall 20, 102 through a flexible radiation-resistant skirt 40. The second embodiment further isolates the operating region 16 with the half-wall 104 adjacent to the x-ray table 14 and uses the skirt 40 to circumferentially join the x-ray table 14 with the cubicle 100. A preferred embodiment of the present invention is shown in FIG. 5 as a radiation protection system for shielding medical personnel from x-rays from an x-ray emitter while working on a patient, comprising an x-ray table 14 having a first side 14a, a second side 14b and a top surface, the top surface for supporting a patient 12; a radiation-shielding cubicle 100 having an interior defining a medical personnel region 16, the cubicle 100 having a ceiling 101, floor 103, a first wall 102 for separating the medical personnel from an x-ray emitter 18 disposed outside of the cubicle 100, a second wall 505 extending from one end of said first wall 102 adjacent to a first side 14a of the x-ray table 14 and a third wall 104 extending from the first wall 102 adjacent to a second side 14b of the x-ray table 14, the first wall 102 having an opening 26 for locating a portion of the x-ray table 14 into the interior of the cubicle; a radiation-shielding screen 22 attached to the x-ray table 14 for covering the portions of the patient and the top surface of the x-ray table located in the interior of the cubicle 100; a radiation-shielding flexible interface 24 for joining the x-ray table 14 to the cubicle 100, the flexible interface 24 having a flexible radiation-resistant skirt 40 sealing the opening 26; and an integrated procedural environment. The present invention may include a control module 501 integrated into an operator's chair 504, however, the module 501 may be mounted in other suitable locations within the cubicle 100. The control module 501 may comprise controls for movement of the table 14, adjustments and movement of the chair 504 itself, as well as the C-arm, monitor 54a position, environmental conditions (lights, heating and air conditioning, etc.) and other various components. In addition, the control module 501 may comprise foot pedals on the chair 504 for more convenient access to various switches. FIG. 10 depicts a cross-section of the system 10 along the line 10-10 in FIG. 5. As such, it illustrates another view of wall 104 disposed between the medical personnel and the table 14 as well as the connection 910 between the interface 24 and the wall 14 which is shown from above in FIG. 4. The operator's chair 504 is designed for optimal comfort and ease of access to the patient so that the operator is positioned in an ergonomically designed adjustable chair positionable within the personnel region 16 with freedom of motion for hand movement control of all the operating functions of the integrated procedural environment at the touch of a finger, and to give the operator optimal ergonomic access to the patient and the medical equipment needed for the procedure. Alternatively, the chair 504 design may have a “stand-up” configuration as is known in the art to allow the operators to stand yet be supported orthopedically. As shown in FIG. 5, the integrated procedural environment may also include the inside surface 502 of a cubicle 100 wall 505 across from the personnel region 16. As will be described herein, this surface 502 may be used to support various integrated elements including monitor displays 54a and staging platforms 500 for instruments. On the interior surface 502 of wall 505, fluoroscopic/cine screens and physiologic monitors 54a may be provided. In the integrated environment, the fluoroscopic monitors 54a may be placed in close proximity to the operator 114, which is in dramatic difference to previously available systems where the monitors are often positioned at an unnecessarily far distance and an orthopedically awkward angle relative to the operators. The interior surface 502 may support monitor displays 54a including fluoroscopic monitors, as well as physiologic monitors including, for example, EKG and blood pressure, for heart rate and oxygen measurements (pulse oximetry). The monitors may also include a display 506 of video from a patient video camera that includes both video as well as audio of the patient's head from a camera placed on the x-ray C-arm that tracks and angles towards the patient's head in order to keep visual monitoring of the patient, as well as two way microphone system to monitor and communicate with the patient during the procedure. As shown in FIGS. 6 and 7, the radiation protection screen 22 may comprise a radiation protection vascular access drape or drape portion 22a composed of a soft, pliable, light, but radiation resistant material having ports 46 placed within the design of the overall screen 22 such that the position and size of the ports 46 allows full access to the correct aspect of the patient regardless of his size and weight. The shape and size of each port 46 are variable depending on the procedure being performed but in a preferred embodiment are substantially round and approximately 10 to 20 cm in diameter. The drape 22a may have a circumferential pleated portion 22b that may allow for attachment to the various other components including the flexible interface 24, table 14, cubicle 100, and the rest of the screen 22, if so constructed. As shown in FIGS. 7 and 8, the drape 22a may also have one or more channels 710 in continuity with the cephalad (head) side of the ports 46 and overlaying the groin region of the patient. The channels 710 may be constructed of the same radiation resistant material as the drape 22a and may comprise a flap 712. The flaps 712 may comprise overlapping portions of drape material connected by hook and loop or other suitable fasteners. The channels 710 may be unflapped (opened) in order to allow a radiolucent area to be exposed in the occasional cases in which passage of the guide-wire from a needle through the groin region is difficult and requires fluoroscopic monitoring. Once the wire has been successfully advanced past this region, the flaps 712 can be reclosed to recomplete the radiation resistant seal over the channels 710. This system may also include a radiation-shielding cloak 48, as shown in FIG. 9A. This cloak may be made of the same radiation resistant material as the drape 22a and constructed in a circular fashion with a radial slit 902 and a small diameter central orifice 904. This cloak 48 may be placed over a port 46 employed for the procedure and is applied once vascular access has been achieved and procedural equipment, such as a vascular sheath, is positioned in the patient. The cloak may then be opened at slit 902, encircled around the sheath and positioned to fully cover the port 46 so that the only component of the patient that is not fully covered by a radiation protection device is the minutely small diameter of the access sheath that exits through the protector orifice 904. Additional components of the drape 22a may include a radiation shielding cloak 49 shown in FIG. 9B. This cloak 49 may be placed over an unused port 46. Cloaks (48, 49) may be covered or enclosed within a sterile drape which may have a hook and loop, adhesive strip or some other suitable fastener on one side that can then be attached to the drape 22a to maintain secure cloak (48, 49) positioning. FIG. 7 also illustrates other novel aspects of the present invention. The table 14 of the present invention may incorporate conduit or similar built-in retention systems 750 for the consolidation and orderly routing procedural equipment including of the leads from various physiological monitoring sensors 752 attached to the patient 12. Similarly, intravenous fluid bags 507 may be hung within the cubicle 100 and their lines 754 may be routed within conduit in the table 14 so as to facilitate the orderly and efficient maintenance of the procedural laboratory. In addition, the table 14 may include at least one arm rest 762 which may have integrated restraints 761 and physiological sensors such as temperature, pulse meter, blood pressure cuff 760 and pulse oximeter. Leads from these sensors may be internally routed within the table 14 or routed within the table's conduit 750 as described above. The patient arm rest 762 may also serve to restrict hand and arm movement of the patient to aid in reducing contamination. During fluoroscopic procedures, there are numerous disposable items employed including wires, sheaths, catheters, balloons, procedure dependent fluid administration, syringes, needles, hemostats, and many others. At present, such items are typically kept on a table behind the surgeon, with some items kept in the patient's groin or lap. The inefficiency of this system has been detailed in U.S. Pat. No. 5,586,163 which discloses and claims a novel platform and method for convenient access to such items. The integration of such a platform 500 into the present invention is illustrated in FIG. 5 attached to the inside surface 502 of the cubicle 100. Adapted in this way, the platform 500 will hold procedural equipment within the medical professional's reach in the operating region yet outside of the immediate surgical site and off of the patient. In addition, the system 10 may include a radiation detector in operative connection with the fluoroscopy system for the automatic detection of radiation exposure above baseline levels and the subsequent automatic shutting down of the x-ray emitter and fluoroscopy system. To use the invention, the patient would be prepped and draped and the radiation protection system 10 employed in the following manner: (1) The patient would be placed and sterily prepared on the table 14 in the standard fashion; (2) the sterily covered screen 22 is scrolled up from the foot of the table 14 to just below the patient's knees and the drape 22a (if used) is positioned from the patient's knees to waist or chest level; (3) the vascular access drape 22a is positioned such that the ports 46 are located over the right and left femoral vascular access regions of the patient; (4) the circumferential pleated connecting border 22b of the vascular access drape 22a is then connected to the flexible interface 24 as well as to the screen 22, if separate from the drape 22a; (5) a rectangular cloak 49, within a sterile drape, is placed over the unused vascular access ports; (6) vascular access is achieved; (7) a cloak 48 is placed around the inserted vascular sheath and positioned to fully cover the vascular access port 46 employed for the procedure. In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. For example, the wall 20 in the first embodiment can be curved or hinged to partially surround the operating region 16. As another example, the cubicle 100 can be wider to extend over the foot 42 of the x-ray table 14, thereby enlarging the operating region 16 within the cubicle 100. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents. |
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062467409 | abstract | A cylindrical thin-wall sleeve including an SiC fiber-reinforced SiC composite material (SiC/SiC), which has a porosity of 40% or less and a wall thickness of 5 mm or less. |
claims | 1. A target supply unit to be used in an extreme ultraviolet light source apparatus for generating extreme ultraviolet light by irradiating a target material with a laser beam to turn the target material into plasma, said target supply unit comprising:a target container configured to accommodate the target material;a target nozzle configured to inject the target material supplied from said target container;a reducing gas supply unit configured to supply a reducing gas into said target container;an exhaust pipe configured to exhaust a gas within said target container;a gas analysis unit configured to measure concentration of a reaction product of the reducing gas in said exhaust pipe to output a signal representing the concentration of the reaction product of the reducing gas; anda control unit configured to control said reducing as supply unit to stop supply of the reducing gas when the concentration of the reaction product of the reducing gas becomes not more than a predetermined value according to the signal outputted from said gas analysis unit. 2. The target supply unit according to claim 1, further comprising:a heater attached to said target container and electrically connected to said control unit. 3. The target supply unit according to claim 1, wherein said reducing gas contains at least one of hydrogen gas, hydrogen radical, and carbon monoxide gas. 4. The target supply unit according to claim 3, further comprising:a radicalizing unit configured to radicalize the hydrogen gas contained in said reducing gas. 5. The target supply unit according to claim 1, further comprising:a gasifying unit configured to gasify a reducing agent, which is in a liquid state at room temperature, to generate said reducing gas. 6. The target supply unit according to claim 5, wherein said reducing agent, which is in a liquid state at room temperature, contains an acid solution. 7. The target supply unit according to claim 1, further comprising:a pressurization gas supply unit configured to supply a pressurization gas for adjusting pressure within said target container and diluting said reducing gas. 8. The target supply unit according to claim 1, further comprising:a pressure container configured to accommodate the target material supplied from said target container,wherein said target nozzle injects the target material supplied from said target container via said pressure container. 9. The target supply unit according to claim 1, wherein said reducing gas supply unit includes at least one mass flow controller electrically connected to said control unit. 10. The target supply unit according to claim 1, further comprising:a heater provided to a pipe connected to said target container. 11. The target supply unit according to claim 1, further comprising:a temperature sensor provided to said target container. 12. The target supply unit according to claim 1, further comprising:a pressure sensor configured to measure pressure within said target container. 13. The target supply unit according to claim 1, wherein said gas analysis unit includes one of a dew-point meter and a Fourier transform infrared spectrophotometer. 14. The target supply unit according to claim 4, wherein said radicalizing unit includes one of a microwave plasma unit and a high-temperature heating unit using a filament. 15. The target supply unit according to claim 6, wherein said reducing agent contains one of formic acid, acetic acid, and hydrochloric acid. |
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description | The present application claims priority from Japanese patent application No. JP 2005-188345 filed on Jun. 28, 2005, the content of which is hereby incorporated by reference into this application. The present invention relates to a method and apparatus for applying charged particle beams and, particularly, to a technology effectively applied to a high-speed and high-accuracy apparatus for applying charged particle beams, which is used for semiconductor manufacturing devices and semiconductor inspection apparatuses. Examples of technologies studied by the present inventors are as follows in a charged electron beam applied technology for use in a semiconductor manufacturing process. In the semiconductor manufacturing process, an electron beam lithography system is used for drawing a desired circuit pattern on a wafer or mask as a subject. Also, electron microscopes, electron-beam inspection devices, and other devices are used for irradiating the subject with electron beams and checking, from signals of secondary electrons or the like produced, the shape of a pattern formed on the subject or the presence or absence of a defect of the pattern. In these semiconductor manufacturing devices applying electron beams, it is an important problem that the speed of processing the subject, i.e., throughput is improved along with accuracy. To solve this problem, in Japanese Patent Laid-Open Publication No. 2001-267221 and Japanese Patent Laid-Open Publication No. 2002-319532, for example, there is proposed a multibeam method in which: a test sample is irradiated with a plurality of electron beams; these electron beams are deflected for scanning on the test sample; and, depending on the pattern to be drawn, the plurality of electron beams are individually turned on/off to draw the pattern. One example of such an electron beam lithography system of this type is described by using a schematic drawing of FIG. 13. In FIG. 13, a one-dot-chain line represents a beam axis, which is an axis on which axes of symmetry of an electron gun and an electromagnetic lens formed in approximately rotation symmetry should coincide with each other, the beam axis serving as a reference of a beam path. In this example, a thermal electron gun obtaining easily a large current and stable in electron emission is used. The thermal electron gun heats a cathode 101 made of a material with a low work function to provide electrons with energy enough to overcome a barrier of a cathode surface, and accelerates the electrons toward an anode 103 with a higher potential with respect to the cathode 101. The reference numeral “104” denotes a crossover of electron beams. The “crossover” is an image formed when electron beams emitted in the same direction from different positions in the same cathode cross one another. The size (diameter) of the crossover is called a crossover diameter, and a position where the crossover is formed on the beam axis is called a crossover height. A source forming lens 105 is an electromagnetic lens having a function of forming an image by reducing the crossover 104. That is, a first intermediate image of the crossover 104 is formed. Herein, since the crossover is used as a light source, it is called a source crossover 106. Note that as shown in FIG. 14, the electron beams emitted from the electron gun may be incident on the source forming lens 105 without forming a crossover. Also in this case, if a track of the electron beams is extrapolated linearly from a side of the source forming lens and a point 104b crossing on the beam axis is virtually handled as a crossover, this situation is similar to that as described above. Therefore, the point 104b is referred to as a virtual crossover. By using this source crossover 106 as a light source, a condenser lens 107 produces an approximately parallel electron beam. The condenser lens 107 is an electromagnetic lens. The reference numeral “108” represents an aperture array formed by two-dimensionally arranging apertures. “109” a lens array formed by two-dimensionally arranging electrostatic lenses having the same focal length. “110” and “111” each a deflector array formed by two-dimensionally arranging electrostatic deflectors capable of being driven individually. “112” a blanker array formed by two-dimensionally arranging electrostatic blankers capable of being driven individually. The approximately parallel electron beam produced by condenser lens 107 is divided by the aperture array 108 into a plurality of electron beams. The divided electron beams are converged at the height of the blanker array 112 by lens action of the corresponding lens array 109. That is, a second intermediate image of the crossover is formed. At this time, the deflector arrays 110 and 111 individually adjust paths of respective electron beams so that the corresponding beams pass through desired positions in the corresponding blankers. The blanker array 112 controls whether the test sample is irradiated with the corresponding electron beam. That is, the electron beams deflected by the blankers are intercepted by a blanking aperture 114, and does not reach onto the test sample. On the other hand, the beams not deflected by the blanker pass through the blanking aperture 114 to reach onto the test sample 119. Reducing glasses 113 and 115 and objective lenses 116 and 118 project, on a test sample 119 mounted on a stage 120, the reduced second intermediate image of the crossover formed at the height of the blanker array 112. The position of the reduced projected image is determined depending on a deflection amount by a deflector 117. Meanwhile, as a result of studies by the present inventors regarding the above-described charged particle beam applying technology, the following has been revealed. For example, in the above-described multibeam lithography method, the beams formed by the aperture array 108 preferably pass through a desired position of the corresponding electrostatic lens at a desired angle. In the example of FIG. 13, the beams preferably pass through a center of the electrostatic lens in parallel with respect to a beam axis. To achieve this for all electron beams formed, it is necessary that an array interval between the apertures of the aperture array 108 and an array interval between the electrostatic lenses of the lens array 109 are equal to each other and further the aperture array 108 and the lens array 109 are positioned in appropriate alignment. Furthermore, the electron beam with which the aperture array 108 is irradiated is required to have high parallelism. By contrast, in the specification of the prior application (Japanese Patent Application No. 2004-262830) by the present applicant, a front focal plane of the condenser lens is made coincide with the height of the intermediate image of the crossover serving as a light source. Therefore, adjustment is made so that the aperture array is irradiated with the electron beams in parallel. On the other hand, characteristics of the electron beams emitted from the thermal electron gun are determined by a work function of the cathode material, cathode temperature, intensity of an electric field on a cathode surface, and other factors. Of these, the work function of the cathode material is difficult to freely manipulate, so that the cathode temperature is controlled by an amount of currents passing through a heater for heating the cathode 101. Also, the characteristics of the electron beams are controlled by a voltage applied to a Wehnelt cylinder 102 placed so as to control a potential distribution near the cathode 101. Therefore, the characteristics of the electron beams emitted from the thermal electron gun can be predicted to some extent through simulation, for example. In practice, however, in addition to an assembling error of the electron gun and thermal expansion by heating, for example, the cathode 101 heated at high temperatures are changed in shape by evaporation with time. Therefore, it is difficult to accurately predict an electric field distribution in the electron gun. Moreover, variations and temporal changes of resistance of the heater for heating the cathode are also factors in causing errors in cathode temperature. From these reasons, it is difficult to accurately obtain the height of the crossover through only guesses based on simulation and previous data. Also, there are strong possibilities that the height of the crossover 104 will change before and after replacement of the cathode 101 and/or adjustment of the electron gun and that the height of the crossover 104 will gradually change due to use for a long time. Therefore, even if the above-mentioned method and apparatus disclosed in the specification of the prior application (Japanese Patent Application No. 2004-262830) are used to make the front focal plane of the condenser lens 107 coincide with the height of the intermediate image (source crossover 106) of the crossover 104, the height of the intermediate image of the crossover is changed due to the above-described reasons and thus is displaced from the front focal plane of the condenser lens 107. Accordingly, since the condenser lens 107 has to be again adjusted, an adjustment time until drawing is started is increased and throughput of the lithography system is decreased. Furthermore, a ratio in size between the source crossover 106 and the intermediate image of the crossover converged at the height of the blanker array 112 is determined by an inverse ratio between a distance from the source crossover 106 to a main surface of the condenser lens 107 and a distance from a main surface of the lens array 109 to the blanker array 112. Therefore, if the front focal plane of the condenser lens 107 is aligned with the displaced source crossover 106, the size of the intermediate image of the crossover converged at the height of the blanker array 112 may be changed. This means to vary the size of each beam reaching onto the test sample, so that such variation affects drawing accuracy. Still further, although the electromagnetic lens is more controllable as compared with the electron gun, the resistance of a coil may be varied due to a change in ambient temperature and the focal length of the lens is varied in some cases. Thereby, the following phenomena occur. (1) When the focal length of the source forming lens 105 is fluctuated from a desired value, the source crossover 106 is formed at a desired height, that is, a height displaced from the front focal plane of the condenser lens 107. Thereby, the parallelism of the electron beams with which the aperture array 108 is irradiated deteriorates. (2) Fluctuations of the focal length of the condenser lens 107 means fluctuations of the front focal plane. Therefore, as with (1), since the front focal plane of the condenser lens 107 is shifted with respect to the source crossover 106, the parallelism of the electron beams with which the aperture array 108 is irradiated deteriorates. Therefore, an object of the present invention is to provide, in a charged particle beam applying apparatus such as an electron beam lithography system, a technology that can facilitate a positional adjustment of a crossover and improve throughput of the apparatus. The above and other objects and novel features of the present invention will become apparent from the description of the specification and the accompanying drawings. Outlines of representative ones of the inventions disclosed in the present application will briefly described as follows. The present invention is to solve the problems described above, and has a feature of providing an end face to the front focal plane of the condenser lens. By using this end face to measure the shape of the electron beams, the shape of the beams on the front focal plane of the condenser lens can be always checked even if the height of the crossover formed by the electron gun or the resistance of the source forming lens is varied. Furthermore, by using that end face to adjust a focal length of the source forming lens so that the shape of the beams becomes the sharpest, adjustment can be made so that the intermediate image of the crossover is formed on the front focal plane of the condenser lens. Note that since the end face is an obstacle on the beam path at a time of drawing, the present invention is configured to be removable from a beam axis without deteriorating a near vacuum state. Also, the present invention is characterized by, for a plurality of electron beams, measuring a relative position with respect to the corresponding lens or blanker and by comparing the measured relative position with a relative position at a time of initial adjustment. That is, a change in focal length of the condenser lens is monitored, and adjustment is made if the change in focal length exceeds a tolerance. Thereby, the parallelism of the electron beams with which the aperture array is irradiated can be appropriately managed. Effects obtained by representative ones of the inventions disclosed in the present application will be briefly described as follows. The positional adjustment of the crossover is facilitated and the throughput of the charged particle beam applying apparatus can be improved. Embodiments of the present invention will be detailed below based on the drawings. Note that, throughout in all of the drawings for describing the embodiments, the same members are denoted in principle by the same reference numerals and repetitive description thereof will not be omitted. FIG. 1 is a view showing a schematic structure of a multibeam electron-beam lithography system according to a first embodiment of the present invention. Members shown in FIG. 1 and having the same reference numerals as those in FIG. 13 indicate the same members as those in FIG. 13. Firstly, with reference to FIG. 1, one example of the multibeam electron-beam lithography system according to the first embodiment will be described. The multibeam electron-beam lithography system according to the first embodiment includes, for example, an electron gun composed of a cathode 101, a Wehnelt cylinder 102, and others; an anode 103; an aligner 207; a source forming lens 105; a movable stage 209 equipped with a crossover regulation edge 208; a condenser lens 107; an aperture array 108; a lens array 109; deflector arrays 110 and 111; a blanker array 112; reducing glasses 113 and 115; a blanking aperture 114; objective lenses 116 and 118; a deflector 117; a stage 120; a Faraday cup 210; a controller 201; and others. Also, this electron-beam lithography system includes a vacuum pump for keeping a charged particle beam path in a vacuum state. The controller 201 includes an electron-gun control unit 202, a mechanism control unit 203, an optical-system control unit 204, a blanker control unit 205, a data processing unit 206, and others. The electron-gun control unit 202 is electrically connected to the electron gun. The mechanism control unit 203 is electrically connected to the movable stage 209 and the stage 120. The optical-system control unit 204 is electrically connected to the aligner 207, the source forming lens 105, the condenser lens 107, the lens array 109, the deflector arrays 110 and 111, the reducing glasses 113 and 115, and the objective lenses 116 and 118. The blanker control unit 205 is electrically connected to the blanker array 112. The data processing unit 206 is electrically connected to the Faraday cup 210. As mentioned also in the column of SUMMARY OF THE INVENTION, in the electron beam lithography system according to the present embodiment, it is important to form the source crossover 106 on a front focal plane of the condenser lens 107 and keep, with high accuracy, parallelism of electron beams with which the aperture array 108 is irradiated. However, due to an assembly error of the thermal electron gun, thermal expansion of the electron gun by heating, evaporation of the cathode 101, variations in heater resistance among systems, changes with time, and other factors, it is difficult to form the crossover 104 at a desired height. In particular, the height of the crossover 104 is varied in many cases before and after replacement and/or adjustment of the cathode 101. The height of the source crossover 106 is also varied in many cases accordingly. Therefore, in the present embodiment, the height of the source crossover 106 is adjusted with high accuracy after replacement and adjustment of the cathode 101. After replacement of the cathode 101 or after adjustment of the electron gun, an acceleration voltage of the electron gun is set at a desired value through the electron-gun control unit 202 of the controller 201. Also, a voltage applied to the Wehnelt cylinder 102 is set so that a current of the electron beam emitted from the electron gun has a desired value. FIG. 2 is a view showing a structure of the crossover regulation edge 208. The crossover regulation edge 208 is a shielding plate equipped with a sharp end face for regulating an imaging plane of a crossover imaging lens and, for example, includes a molybdenum base 301 and an aperture 302 provided in the molybdenum base 301 and is supported by the movable stage 209. Also, the crossover regulation edge 208 is placed on the front focal plane of the condenser lens 107. By driving the movable stage 209 by the mechanism controller 203, the crossover regulation edge 208 can be inserted on and extracted from a beam axis without substantially impairing a vacuum state of a beam path. When the height of the source crossover 106 is adjusted in the present embodiment, the crossover regulation edge 208 is inserted on the beam axis and is then scanned on the beam axis with an electron beam. To the crossover regulation edge 208, the electron beam before being divided by the aperture array 108 is converged. Therefore, the crossover regulation edge 208 is irradiated with the electron beam with a high current density. For this reason, using a material with a high melting point is required for a portion irradiated with the electron beam. Such a high melting point is preferably equal to or higher than 1000 degrees Celsius, for example. In the first embodiment, as shown in FIG. 2, since the aperture 302 is formed in the molybdenum base 301, an end face of the aperture 302 is used as a crossover regulation edge. Tungsten, tantalum, or the like has a high melting point and is therefore suitable as a material other than that of molybdenum. Also, using a sufficiently thick base is required for allowing heat to escape to the outside. The thickness thereof is preferably equal to or larger than 50 microns. In the present embodiment, the thickness is set at 100 microns. Furthermore, a member that is the crossover regulation edge 208 is preferably conductive and non-magnetic. For scanning with electron beam, the aligner 207 is used, which has been conventionally used as an electromagnetic deflector for optimizing an angle of the electron beam emitted from the electron gun with respect to a downstream electron-optical system. That is, a scanning signal generated from the optical-system control unit 204 is inputted to the aligner 207 to be one-dimensionally or two-dimensionally scanned with electron beam, and then an amount of electron beams passing through the aperture 302 is measured by using the Faraday cup 210 provided on the stage 120. In the present embodiment, the Faraday cup with a sufficiently large aperture is used to keep detection efficiency constant irrespectively of a scan distance by the aligner 207. Alternatively, for example, a semiconductor detector with a large detection area can be used to achieve the same function. FIG. 3 is a view showing a measurement example at a time of measuring a one-dimensional profile of a detection signal of the Faraday cup 210. A horizontal axis represents a scan distance by the aligner 207, whilst a vertical axis represents a detection signal amount of the Faraday cup 210. In FIG. 3, three profiles denoted by the reference numerals “401”, “402”, and “403” are ones obtained when the current flowing through the source forming lens 105 is varied to have three different values. Under the condition of obtaining the profile 401 whose waveform is the sharpest, the electron beam is converged best to the crossover regulation edge 208. That is, the optical-system control unit 204 sequentially changes the focal length of the source forming lens 105 and, based on the signal from the Faraday cup 210, the data processing unit 206 determines the shape of the electron beam under individual conditions. By this procedure, the beam is converged on the crossover regulation edge 208, and conditions for forming an intermediate image of the crossover are obtained. Thereby, since the height of the intermediate image of the crossover has been made coincide with the front focal plane of the condenser lens 107 with high accuracy, the mechanism control unit 203 drives the movable stage 209 to remove the crossover regulation edge 208 from the electron beam path. Then, after other optical parameters are adjusted, the controller 201 starts drawing. Note that, in the present embodiment, the crossover regulation edge 208 is one-dimensionally scanned with a beam for measuring a one-dimensional profile. Alternatively, scanning may be two-dimensionally performed with an electron beam, and conditions under which the sharpest two-dimensional image can be obtained by being two-dimensionally scanned with the electron beam may be taken as those under which the beam is converged most. Furthermore, in the present embodiment, as shown in FIG. 2, the aperture of the crossover regulation edge 208 has a rectangular shape. Alternatively, other shapes, such as a polygon or a circle, can achieve similar effects as long as the end face of the aperture is sufficiently sharp in comparison with the size of the electron beam that is a measurement object. Still further, a one-dimensional sharp end face may be used. Also, in the present embodiment, the Faraday cup 210 provided on the stage 120 is used to obtain a signal required for profile measurement. Alternatively, other means may be used as long as the amount of the electron beams passing through the aperture 302 can be measured. For example, a downstream optical-system element such as the aperture array 108 may measure the amount of electrons reflected, or a measuring element such as a photodiode may be inserted in the beam path. Still further, if the crossover regulation edge 208 is electrically suspended, that is, insulated with respect to an electron-optical lens tube, the flowing current can be directly measured and therefore this may be used for profile measurement. As a result of the above-described adjustment performed after adjustment of the electron gun including replacement of the cathode, conditions under which the aperture array is irradiated with the electron beam in parallel can be obtained with high accuracy. Thereby, since positional accuracy of the electron beam reaching onto the wafer is improved, a time required for correction can be shortened. Thus, throughput is improved in device manufacturing. Note that the procedure according to the present embodiment may be carried out not only after adjustment of the electron gun but also at the time of regular adjustment of optical parameters. FIG. 4 is a view showing a schematic structure of a multibeam electron-beam lithography system according to a second embodiment of the present invention. Components shown in FIG. 4 and having the same reference numerals as those in FIGS. 1 and 13 are identical to those in FIGS. 1 and 13. In the second embodiment, two-stage electromagnetic lenses, that is, a first source forming lens 501 and a second source forming lens 502 are provided between the front focal plane of the crossover 104 and the front focal plane of the condenser lens 107. By using these lenses, the crossover formed by the electron gun is reduced to form an image on the front focal plane of the condenser lens 107. Since the first source forming lens 501 and the second source forming lens 502 are used together as a zoom lens, the crossover is reduced with an arbitrary magnification to form an image relative to the source crossover 106 on the front focal plane of the condenser lens 107. Therefore, in the present embodiment, the size of the light source can be freely determined in accordance with the conditions required from the process. For example, the light source is made small in order to obtain high resolution, whilst the light source is made large in order to improve throughput. Thereby, it is preferable to make each beam current large. What is important in using the first source forming lens 501 and the second source forming lens 502 as a zoom lens is that the intermediate image of the crossover is formed on the front focal plane of the condenser lens 107 irrespectively of the zoom condition and that the parallelism of the electron beam with which the aperture array 108 is irradiated is kept with high accuracy. The focal length of the electromagnetic lenses can be obtained through simulation with a certain degree of accuracy. However, particularly, when excitation of the electromagnetic lens is intensified, for example, when non-linearity of the relation between the current and the magnetic field is intensified, the accuracy of simulation has a limit. To get around this problem, for several types of zoom conditions, currents to be applied to the first source forming lens 501 and the second source forming lens 502 are obtained in advance through simulation. Then, in order to make the front focal plane of the source crossover 106 and the front focal plane of the condenser lens 107 coincide with each other with higher accuracy, the following procedure is taken for adjustment. FIG. 5 is a flowchart of a method for obtaining image forming conditions in the second embodiment. In step S601, the movable stage 209 is driven via the mechanism control unit 203, and the crossover regulation edge is set on the electron beam path. In step S602, standard currents fulfilling a first zoom condition obtained through the simulation (N=1) are applied to the first source forming lens 501 and the second source forming lens 502. In step 603, while the aligner 207 is used to scan the crossover regulation edge 208 with electron beams, the amount of the passing electron beams is measured by using the Faraday cup 210, whereby the size of the electron beam on the crossover regulation edge 208 is obtained. In step S604, one of setting currents of the first source forming lens 501 and the second source forming lens 502 is sequentially varied until an image forming condition, that is, a condition under which the size of the beam has a minimum value is obtained. Steps S602 through S604 are repeated to find a lens condition under which a source crossover is image-formed on the front focal plane of the condenser lens 107 under the first zoom condition. In step S605, the size of the source crossover under the obtained lens condition is measured. That is, the waveform obtained by scanning the crossover regulation edge 208 with electron beams is subjected to primary differentiation to measure the profile of the source crossover 106. Alternatively, the size of the electron beam reduced and projected on the stage 120 may be measured. Steps S602 through S605 are performed on a plurality of zoom conditions. Thereby, the setting currents of the first source forming lens 501 and the second source forming lens 502 and the size of the source crossover can be determined correspondingly to each zoom condition. In step S606, the image forming conditions of the first source forming lens 501 and the second source forming lens 502 obtained through steps S602 to S604 and the size of the crossover obtained in step S605 are stored in a memory incorporated in the controller 201. Steps S602 through S606 are then performed for a second zoom condition (N=2). The same steps are repeated until all of the image forming conditions are found. Note that “N” is a natural number and represents the number of image forming conditions. In step S607, the movable stage 209 is driven via the mechanism control unit 203 to remove the crossover regulation edge 208 from the electron beam path. FIGS. 6A and 6B are graphs of one example of measurement results obtained through the above-described procedure, and represent optimum currents for the first source forming lens 501 and the second source forming lens 502 corresponding to respective source crossovers. FIG. 6A depicts a relation between the size of the source crossover and an optimum current of the first source forming lens 501, whilst FIG. 6B depicts a relation between the size of the source crossover and an optimum current of the second source forming lens 502. In FIGS. 6A and 6B, curve lines represent results obtained after fitting based on a measurement point where N=5. To make the source crossover small, it can be seen that the current flowing through the first source forming lens 501 is increased to decrease the focal length, whilst the current flowing through the second source forming lens 502 is decreased to increase the focal length. At the time of drawing, based on these measurement results, a lens current corresponding to a desired crossover diameter is obtained. If no measurement point corresponding to the desired crossover diameter is obtained, the current obtained by fitting is used. By making the above-described adjustment, the intermediate image (source crossover 106) of the crossover 104 is formed on the front focal plane of the condenser lens 107, whereby the parallelism of the electron beam with which the aperture array 108 is irradiated is kept with high accuracy irrespective of the zoom conditions. Therefore, the size of the source crossover that is optimum for the process can be achieved, and almost the same yield and throughput as those in the first embodiment can be also obtained. In the above first and second embodiments, a single crossover regulation edge regulating the height of the crossover has been used. By contrast, in a third embodiment, a plurality of crossover regulation edges are used. FIG. 7 is a view showing a structure of crossover regulation edges for use in the third embodiment. The reference numerals “801”, “802”, and “803” denote crossover regulation edges with different heights supported by one movable stage 804. In the third embodiment, in place of the crossover regulation edge 208 and the movable stage 209 as shown in FIGS. 1 and 4, the crossover regulation edges 801, 802, and 803 are placed between the crossover 104 and the condenser lens 107. In the present embodiment, through the same method as that according to the first embodiment, a condition under which an intermediate image of the crossover is formed for each of three crossover regulation edges 801, 802, and 803 is obtained. That is, a current for the source forming lens 105 corresponding to the height of each crossover regulation edge is obtained. FIG. 8 is a graph depicting results experimentally obtained regarding a relation between the height of the crossover regulation edge and the current for the optimum source forming lens 105. A straight line represents fitting results. The present embodiment is suitable in the case where the crossover regulation edge cannot be placed on the front focal plane of the condenser lens 107 due to space limitations. In such a case, from the relation between the height of the crossover regulation edge and the current of the source forming lens 105 shown in FIG. 8, the current of the source forming lens 105 corresponding to the front focal plane of the condenser lens 107 can be obtained through interpolation or extrapolation. Note that, in the present embodiment, one-dimensional shape edges with sharp end faces are provided at a plurality of heights. Alternatively, as shown in FIG. 9, apertures 805, 806, and 807 with apertures of circles or the like may be placed at a plurality of heights while being eccentric to one another. Note that, in FIG. 9, a positional relation is such that the aperture 805 is at a top, the aperture 806 is at a middle, and the aperture 807 is at a bottom. Also, the present embodiment is effective even when the height of the front focal plane of the condenser lens 107 has to be moved due to a change in projection conditions. In the first to third embodiments, the electron beam lithography system of a type in which the reduced image of the crossover formed by the electron gun is transferred onto the test sample for drawing has been described, and their object is to keep the height of the crossover serving as an object point at a desired position. By contrast, in a fourth embodiment, an electron beam lithography system of a type which is called generally a variable shaped beam method and in which the crossover is not transferred onto the test sample will be described. FIG. 10 is a view showing a schematic structure of an electron beam lithography system according to the fourth embodiment of the present invention. Components shown in FIG. 10 and having the same reference numerals as those in FIGS. 1 and 13 are identical to those in FIGS. 1 and 13. As shown in FIG. 10, an electron beam emitted from the cathode 101 is accelerated toward the anode 103, and is then incident on a condenser lens 1002. The voltage of the Wehnelt cylinder 102 is kept constant. By the action of convergence of a condenser lens 1002, a crossover 1003 is formed near the exit of the condenser lens. The reference numeral “1001” denotes a blanking electrode, which bends track of the electron beam so as to intercept the electron beam with respect to the test sample. That is, the electron beam deflected by the blanking electrode 1001 is intercepted by the blanking aperture 114, thereby not reaching onto the test sample 119. On the other hand, the beam not deflected by the blanking electrode 1001 passes through the blanking aperture 114 to reach onto the test sample 119. The beam once forming the crossover 1003 spreads again and then irradiates a first mask 1004. Since the first mask 1004 is provided with a single rectangular aperture, an aperture image can be obtained from the irradiated electron beam. The aperture image of the first mask 1004 is formed on a second mask 1009 through the shaping lens 1007. The second mask 1009 is provided with a rectangular aperture for performing a variable shaped beam method and a shaping aperture for performing a character projection method. The image forming position on the second mask 1009 is controlled by a beam shaping deflector 1008, whereby the shape and area of the electron beam are determined. The electron beam passing through the aperture of the second mask 1009 is projected onto the test sample 119 placed on the stage 120 by a reducing lens 1010 and an objective lens 1011. Inside the objective lens 1011, a deflector group is placed. By this deflector group, the image forming position of the electron beam on the test sample is determined. The deflector group according to the present invention includes a main deflector 1012 with a largest deflection area of 5 millimeters, a sub-deflector 1013 with a second-largest deflection area of 500 microns, and a sub-sub-deflector 1014 with a smallest deflection area of 80 microns. This is a structure of the electron beam lithography system for use in the fourth embodiment. Here, the reference numeral “1005” denotes an image forming line for the crossover, and “1006” an image forming line for the mask. This means that an aperture image of the first mask 1004 is formed by a shaping lens 1007 on the second mask 1009, reduced by the reducing lens 1010, and is then eventually formed by the objective lens 1011 on the test sample. On the other hand, in the electron beam lithography system of this method, the beam size is required to be not varied when the height of a test sample surface is varied. To achieve this, it is preferable to realize a so-called Koehler illumination, and its realization will be explained with reference to a schematic view of FIG. 11. In FIG. 11, the reference numeral “1101” denotes a light source, which corresponds to an intermediate image of a crossover in the present embodiment. “1102” a light-gathering lens for gathering light emitted from the light source, which corresponds to a part of a reducing lens in the present embodiment. “1103” an image plane, which corresponds to an intermediate image plane of a mask in the present embodiment. “1104” an aperture stop, which corresponds to a blanking aperture in the present embodiment. Depending on the size of the aperture stop, an open angle is determined. The reference numeral “1105” denotes an objective lens and has an effect of transferring an image formed on the image plane 1103 onto a test sample surface 1106 which is an object surface. Here in FIG. 11, a distance from the aperture stop 1104 to the objective lens 1105 is equal to a focal length f of the objective lens. Therefore, if the aperture stop is caused to form an image from the light source 1101, the image of the light source is formed on the front focal plane of the objective lens 1105. Therefore, as shown by a combination of solid lines and dotted lines, a light beam emitted from one point of the light source passes through the objective lens and then becomes parallel beams. That is, the so-called Koehler illumination is achieved. At this time, since a principal ray is vertically incident on the test sample surface, the size of the image of the mask is not varied in accordance with variations of the height of the test sample surface 1106. To achieve the Koehler illumination as shown in FIG. 11 in the present embodiment, an intermediate image of the crossover is image-formed on the front focal plane of the objective lens 1011 in FIG. 10, and it is preferable to provide the blanking aperture 114 at a position of the formed intermediate image. As such, in this method, an image forming relation of the crossover is very important. In FIG. 10, the reference numeral “1005” is an ideal image forming line for the crossover. The crossover is image-formed on the front focal plane of the objective lens, whereby the Koehler illumination is achieved. However, as described in the column of “SUMMARY OF THE INVENTION, due to an assembly error of the thermal electron gun, thermal expansion of the electron gun by heating of cathode, evaporation of the cathode, variations in heater resistance among systems, changes with time, and other factors, the height of the crossover 1003 is varied before and after replacement of the cathode and/or adjustment of the electron gun in many cases. To get around this problem, in the present embodiment, the crossover regulation edge 208 is scanned with the beam by using an aligner (not shown) located near the anode 103 and the beam profile is measured. Therefore, excitation of the condenser lens 1002 is adjusted so that the crossover 1003 is formed at a desired height. Note that, in the electron beam lithography system of this method, the magnification of the image on the test sample with respect to the aperture image of the second mask 1009 may be varied for each test sample. In such a case, it is preferable that the focal length is adjusted by excitation of the reducing lens 1010 and the objective lens 1011. Depending on such adjustment, however, the image forming relation of the crossover is also varied. This means that the height at which the crossover 1003 is to be formed is also varied. In such a case, it is preferable that the crossover regulation edge 208 is configured to be movable in a height direction. Alternatively, as with the third embodiment, a plurality of edges different in height as shown in FIG. 7 may be used. Thereby, a relation between the height of the crossover regulation edge 208 and the current of the condenser lens 1002 can be experimentally obtained. Thus, through interpolation or extrapolation, the current of the condenser lens 1002 corresponding to a desired crossover height can be obtained. In other words, irrespectively of the magnification, an intermediate image of the crossover can be formed on the front focal plane of the objective lens 1011, whereby the Koehler illumination can be achieved. The present embodiment is more effective when the condenser lens 1002 is formed of two-stages of lenses and acts as a zoom lens. That is, while the crossover diameter is adjusted for each test sample or even each pattern within the same test sample, the crossover can be image-formed at a desired position. For this reason, since the beam current can be varied according to desired accuracy of the current density on the test sample, throughput can be improved. A fifth embodiment relates to the multibeam electron bean lithography system shown in FIG. 1. The first to fourth embodiments have aimed at calibrating, for variations in the height of the crossover that are generated in the multibeam drawing method, in particular, generated before and after replacement of the cathode and/or adjustment of the electron gun, the height of the crossover by using the crossover regulation edge. These embodiments have been able to achieve similar effects also for variations near a focal point of a source forming lens. By contrast, the fifth embodiment solves a problem of variations in the focal length of the condenser lens. A method of adjusting the focal length of the condenser lens is disclosed in the specification of the above-mentioned prior application. In the above specification, the aperture of the blanker array is simultaneously scanned with a plurality of beams to acquire an overlapped image by a plurality of aperture images. By using this overlapped image as an indicator, astigmatism correction of the focal length of the condenser lens and the irradiation optical system is performed. By using this method, the aperture array is irradiated with the electron beam in approximately parallel, so that the method is effective for adjusting the focal length of the condenser lens. It takes some time for this adjustment. Therefore, decreasing the frequency of this adjustment is effective in order to improve throughput of the lithography system. In practice, however, the resistance of the coil of the condenser lens may be varied due to a change in ambient temperature to cause the focal length of the lens to be varied. To get around this problem, in the present embodiment, after astigmatism correction of the focal length of the condenser lens and the irradiation optical system, only a specific beam is used to acquire the overlapped image of the aperture images, so that the acquired overlapped image is used as a reference aperture image. Then, every time drawing of each predetermined unit, such as each sheet of test sample or each lot, is finished, an overlapped image of aperture images of a specific beam is acquired through a method similar to that immediately after adjustment, so that the acquired overlapped image is compared with the reference aperture image. FIGS. 12A through 12C are views each depicting an overlapped image of apertures for four-corner beams. FIG. 12A illustrates an overlapped image of apertures acquired by using four-corner beams of multibeam arrangement immediately after adjustment. To obtain this image, the blanker control unit 205 of the controller 201 shown in FIG. 1 may be used to apply a blanking voltage not to blankers corresponding to the four-corner beams but to blankers corresponding to the other beams for interception with respect to the test sample. Then, the blanker array 112 is scanned with those four-corner beams not subjected to blanking, and a current reaching onto the stage 120 is measured by the Faraday cup 210. Note that, for scanning with the four-corner beams, an aligner (not shown) for alignment of the beam emitted from the lens array 109 with respect the blanker array 112, or a deflector array may be used. Note that, in FIGS. 12A to 12C, the amount of electron beams is large at light-colored portions. A reason for the fact that the aperture images obtained from the four-corner beams do not completely coincide with one another is due to distortion aberration of the condenser lens 107. That is, even if the formed multibeam has the most ideal arrangement on the whole, when only the four-corner beams are considered, the aperture images do not necessarily coincide with one another. After adjustment, drawing is started, and then an overlapped image of the aperture images for the four-corner beams is acquired for each lot with the same method. As a result, after drawing for several lots, as shown in FIG. 12B, it has been found that an overlapped image of the aperture images is changed. Although not exceeding a tolerance, this change has been thought to be an early sign of a change in the focal length of the lens, so that the condenser lens 107 is again adjusted. Then, after drawing for further several lots, as shown in FIG. 12C, the overlapped image of the aperture images has been changed. Therefore, astigmatism correction of the irradiation optical system is performed through the method disclosed in the specification of the above-mentioned prior application, and then the aperture image as shown in FIG. 12A can be obtained. Note that whether adjustment is made may be determined by an operator. However, such adjustment can be made automatically if an image processing is used to obtain a degree of overlapping of the aperture images and take this degree as an indicator. Therefore, this will be more convenient. Note that, in the present embodiment, four beams are used for monitoring an irradiation state of the aperture array 108 because at least four beams are required to see variations of three parameters, that is, the focal length of the condenser lens 107 and astigmatism aberration (in a 0-degree direction and in a 45-degree direction). Alternatively, more beams may be used. Another reason is that variations in the focal length of the condenser lens 107 and distortion due to astigmatism aberration are most significant with the four-corner beams. By carrying out the method of the present embodiment, the focal length of the condenser lens and astigmatism aberration of the irradiation optical system can be achieved at optimum frequencies, whereby the throughput of the lithography system is kept excellent. As described above, although the invention made by the inventors has been specifically described on the basis of the embodiments, the present invention is not limited to the above embodiments and, needless to say, can be variously modified and altered within the scope of not departing from the gist thereof. For example, although the apparatus that applies an electron beam has been described in the above embodiments, the present invention is not limited to it. The present invention can be applied to an apparatus that applies other charged particle beams such as ion beams. The present invention can be applied to a lithography system, a microscope, and an inspection apparatus that apply an electron beam, an ion beam, or the like. |
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abstract | The invention relates to a method for reducing the radioactive contamination of the surface of a component used in a nuclear reactor, which component is in contact with radioactively contaminated water, in which method a hydrophobic film is produced on the surface of a component by virtue of the surface being wetted with an aqueous solution which contains a film-forming amphiphilic substance. |
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054147468 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 15, a cross-sectional view of the first embodiment of the X-ray exposure mask of the present invention is shown. The X-ray exposure mask 7 has major components including an X-ray transmission layer (membrane) 1 and an X-ray absorption layer 8 fabricated on the membrane 1. In this embodiment, two kinds of X-ray absorber patterns having different plane sizes are formed, that is, a pattern 9 having a single absorber 8A with relatively large plane width and a pattern 10 including absorbers 8B with small pules size and windows 5. Absorbers 8B and windows 5 are so arranged that their interval is maintained to be constant in a repetitive manner. This embodiment shown in FIG. 15 improves the prior art shown in FIG. 5 and FIG. 7. The absorber 8 is composed of tantalum (Ta) and the membrane 1 is composed of silicon nitride (SiN) and its thickness is 2 .mu.m. The width W of the absorber 8A is 1 .mu.m, the width W3 of the absorber 8B is 0.2 .mu.m and its adjacent window width W2 is also 0.2 .mu.m. The thicknesses T1 and T2 of absorbers 8A and 8B corresponding to each of the patterns 9 and 10 are 0.65 .mu.m and 0.3 .mu.m, respectively. The X-ray exposure mask shown in FIG. 15 was fabricated in the following steps. At first, after forming a 2 .mu.m thick silicon nitride layer on the both surfaces of the silicon substrate by CVD (Chemical Vapor Deposition), a tantalum layer with a thickness of 0.65 .mu.m was formed on the silicon nitride layer on one surface of the substrate and furthermore, a silicon dioxide layer with thickness of 0.3 .mu.m was formed on the tantalum layer by ECR (Electron Cyclotron Resonance). An EB (Electron Beam) resist was coated on the silicon dioxide layer, and the resist material was exposed by the electron beam and developed to remove the resist except on the absorbers 8A. Using this resist pattern as an etching mask, the silicon dioxide layer was etched by RIE (Reactive Ion Etching). And furthermore, using the etched silicon dioxide layer as an etching mask, the 0.65 .mu.m thick tantalum layer is etched until the thickness of the tantalum layer gets to 0.3 .mu.m by RIE. The silicon dioxide layer was removed with thin hydrofluoric acid (HF) solution and a 0.3 .mu.m-thick silicon dioxide layer was again formed on the substrate by ECR. EB resist was coated on the silicon dioxide layer and the resist was exposed by electron beam and developed to remove it except on the absorbers 8A and 8B. This exposed resist pattern was used as an etching mask in order to remove the silicon dioxide layer by RIE etching. And furthermore, using the etched silicon dioxide layer as an etching mask, the 0.3 .mu.m-thick tantalum layer was etched by RIE except for the absorber patterns 8A and 8B. Finally, the silicon nitride layer on the backside of the silicon substrate except its edge parts was removed by etching processing, and the remaining silicon nitride layer was used as an etching mask in order to remove the silicon substrate by wet etching processing. As the thickness of the tantalum layer used for forming the absorber pattern 10 in the exposure mask of this embodiment is so small as 0.3 .mu.m, the etching performance is good, problems in prior art such as broken patterns and irregular pattern edge shapes can be eliminated, and furthermore, the pattern shape and size can be regulated precisely in fabricating process in spite of using such a narrow pattern width as 0.2 .mu.m. Using the above described X-ray exposure mask 7, pattern replication processing is performed in an X-ray exposure apparatus using synchrotron radiation having a peak wavelength of 0.8 nm. The gap between the mask and the wafer is controlled to be 30 .mu.m. Positive resist FBM-G (made by Daikin Co. Ltd.) with thickness of 1 .mu.m was coated as exposure resist. In case of using the X-ray exposure mask of this embodiment, the optimal exposure dose to control the deviation of the resist pattern size corresponding to the absorber pattern 10 within .+-.10% of 0.2 .mu.m was 100.+-.20 mJ/cm.sup.2 and the large exposure dose margin could be obtained to be .+-.20%. With respect to the absorber pattern 9, the deviation of the resist patterns size corresponding to the pattern 9 could be controlled within .+-.10% with the exposure dose between 80 and 160 mJ/cm.sup.2. In contrast, in case of using conventional exposure masks, the optimal exposure dose to control the deviation of the resist pattern size corresponding to the absorber pattern 10 within .+-.10% was 150 .+-.15 mJ/cm.sup.2 where the exposure dose margin was reduced to be less than half of the margin given by the present invention. With respect to the absorber pattern 9, in using the dose of 150 mJ/cm.sup.2, the size of the replicated pattern was reduced by 10% from the design value 1 .mu.m, and so, the absorber patterns 9 and 10 could not be replicated exactly at the same time in accordance with the designed value. In addition, in case of using the X-ray exposure mask of the present invention, the necessary exposure dose for replicating patterns was so small as 100 mJ/cm.sup.2, and in contrast, in case of using conventional exposure masks, the exposure intensity was required to be as large as 150 mJ/cm.sup.2. As a result, in using the X-ray exposure mask of the present invention, the exposure time could be reduced by 2/3 and the throughput could be attained to be 1.5 times as large as that in using conventional exposure masks. The reason why the higher pattern transfer performance can be obtained by the X-ray exposure mask of the present invention is described below. In FIG. 16, the transmitted X-ray exposure intensity distribution is shown when using the X-ray exposure mask of the present invention. In FIG. 17, the transmitted X-ray exposure intensity distribution is shown when using the conventional X-ray exposure mask. The X-ray transmitted through the membrane diffracts in response to the proximity gap of 30 .mu.m. The phase of the X-ray transmitted through the absorption layer shifts and the intensity of the X-ray is reduced. In addition, the X-rays transmitted through the absorption layer and the membrane interfere each other. The region where the diffraction and the interference occur is determined by the X-ray wavelength and the proximity gap, and in case of using the X-ray wavelength and the proximity gap in this embodiment, the region where the diffraction and the interference show a highest effect is extended at most 0.2 .mu.m from the pattern edge. Hence, the smaller the pattern size, the larger the effect of diffraction and interference which leads to the deviation of the transmitted X-ray intensity distribution. By using these characteristics and by determining optimally the thickness of the absorption layer with respect to the fine pattern region to obtain the optimum X-ray intensity distribution, an effective exposure contrast for fine absorber patterns can be improved. That is, in this embodiment, by making the absorber thickness of fine lines-and-spaces patterns of 0.2 .mu.m small enough to be 0.3 .mu.m, the effective contrast can be increased. The transmitted X-ray intensity distribution with respect to lines-and-spaces pattern shown in FIG. 16 will be described in detail later. While, where the thickness of the absorption layer including large-sized, for example 1 .mu.m-width patterns are made as thin as 0.3 .mu.m, the X-ray intensity distribution within 0.2 .mu.m from the edge attained is good, but since the X-ray intensity distribution further inside is influenced by the mask contrast as described above, the intensity of the transmitted X-ray is increased because of the low contrast. As a result, the fog occurs on the resist pattern. In case of making the thickness of the absorption layer including both the large-sized patterns and the fine patterns 0.65 .mu.m which is used in prior art, the X-ray intensity distribution in the region corresponding to the large-sized patterns obtained is good, but as shown in FIG. 17, the X-ray intensity distributes in reverse mode in the region of 0.2 .mu.m fine patterns or has unfavorable peaks in the region within pattern. Owing to this, the exposure dose margin becomes smaller which leads to the deterioration of the pattern replication performance. In order to replicate precisely both of the large-sized patterns and the fine patterns, this embodiment of the present invention is effective where the thickness of the absorption layer corresponding to the large-sized patterns is controlled to be equivalent to that of prior art and only the thickness of the absorption layer corresponding to the fine patterns is taken to be small. In other words, it is proved to be valid to give such an intensity distribution so that the peaks of the distribution may correspond to the regions without X-ray absorbers and the bottoms of the distribution may correspond to the regions with absorbers, in which the intensity distribution is defined in the direction along the horizontal line on FIG. 16, that is, the direction parallel to the direction along which the width of absorber is defined. As a second example the X-ray exposure mask having lines-and-spaces patterns with W3 and W2 shown in FIG. 15 being 0.15 .mu.m, respectively, is fabricated in the following manner. The thickness T2 of the absorption layer 10 is controlled to be 0.3 .mu.m so that the phase shift defined by .vertline.360 (1-n)T2/.lambda..vertline. may be 83.degree. and the mask contrast defined by 1/exp(-.mu.T2) may be 2.45 with respect to the synchrotron radiation having a peak power wavelength of 0.8 nm. In this configuration, the refractive index n of tantalum is 0.99939 and the linear absorption coefficient .mu. is 0.002987 (nm.sup.-1). This mask is fabricated by the same process as that for the mask shown in FIG. 15. In the fabricating process, there are no problems such as broken patterns and irregular pattern edge shapes, and desired fine patterns having small-sized shape such as 0.15 .mu.m are formed precisely. Using the X-ray exposure mask including lines-and-spaces patterns fabricated by the above mentioned process, patterns are transferred with an X-ray exposure apparatus using synchrotron radiations having a peak power wavelength of 0.8 nm. The gap between the mask and the wafer is controlled to be 30 .mu.m. A positive resist FBM-G is coated to a thickness of 0.6 .mu.m on the wafer and patterns are replicated. An example of scanning electron microphotograph of the replicated resist pattern is shown in FIG. 18. In case of using this mask, the range of the X-ray exposure dose can be taken to be large enough from 80 to 110 mJ/cm.sup.2. The reason why the higher pattern transfer performance can be obtained by the X-ray exposure mask of the present invention is described below. In FIG. 19, a cross-sectional view of the X-ray mask and the intensity and the phase of the transmitted X-ray are shown. In FIG. 20, a general example of the transmitted X-ray intensity distribution is shown. In FIGS. 19 and 20, the X-ray intensity is normalized by the X-ray intensity transmitted through the membrane without absorber patterns. The X-ray transmitted through the membrane diffracts at the absorber edge in response to the proximity gap of 30 .mu.m. The intensity of the X-ray transmitted through the absorber pattern is reduced by {1-exp(-.mu.t) } and the phase of the X-ray is shifted by {360(1-n)t/.lambda.} degrees, wherein t is a thickness of the absorber. In addition, the X-ray transmitted through the absorber and membrane interfere with each other. The region where the diffraction and the interference occur is determined by the X-ray wavelength and the proximity gap, and in case of the X-ray wavelength and the proximity gap in this embodiment, the region where the diffraction and the interference occur significantly is extended at most 0.2 .mu.m from the pattern edge. Hence, the smaller the pattern size, the larger the effect of diffraction and interference which leads to the deviation of the transmitted X-ray intensity distribution. In some cases, the X-ray intensity distribution shows a reverse intensity pattern as (a) and (b) shown in FIG. 20, which leads to the inability to replicate resist patterns exactly in accordance with the mask patterns. However, when the phase shift and the decrease of X-ray intensity is controlled optimally in accordance with the present invention, the effect of the X-ray diffraction and interference can be effectively used to obtain an optimum X-ray intensity distribution for replicating exactly the mask patterns. That is, the minimum value of the X-ray intensity at the position (a) in FIG. 20 can be increased, the maximum value of the X-ray intensity at the position (b) in FIG. 20 can be decreased, and as a result, the difference (c) between them can be increased. Owing to this configuration, it will be appreciated that the effective exposure contrast can be increased even with respect to fine patterns less than 0.3 .mu.m. In the case that the region where the X-ray intensity distribution can exactly capture the mask pattern is defined by the exposure dose margin M and that the minimum value at (a) is assumed to be a and the minimum value at (b) is assumed to be b, then the following relationships can be established; (i) M=a/b if a is less than 1, and (ii) M=1/b if a is equal to or greater than 1. In FIGS. 21A and 21B, the relationship between the exposure dose margin and the mask contrast and the relationship between the exposure dose margin and the phase shift are shown. As for FIG. 21A, the proximity gap is 30 .mu.m, and as for FIG. 2lB, the proximity gap is 20 .mu.m. In FIGS. 21A and 2lB, curves A, B and C correspond to the line width and the space width, 0.2 .mu.m, 0.15 .mu.m and 0.1 .mu.m, respectively. As found in FIGS. 21A and 21B, the exposure dose margin has the maximum value when the mask contrast is about 2.5 and the phase shift is about 80.degree. and the exposure dose margin has relatively high values where the mask contrast is between 1 and 4, and the phase shift within a range from 30.degree. to 120.degree.. Hence, by controlling the thickness of the absorber so that these conditions may be satisfied, fine patterns including the lines-and-spaces patterns of 0.1 .mu.m to 0.2 .mu.m can be replicated exactly even if the proximity gap is as large as 20 .mu.m to 30 .mu.m. In the case that the material used for the absorption layer is tantalum, the thickness of the absorber is within a range from 75 nm to 450 nm so that the above mentioned conditions may be satisfied. In FIG. 22, a cross-sectional view of the third embodiment of the X-ray exposure mask of the present invention is shown. The X-ray exposure mask 11 has major components including a 2 .mu.m-thick X-ray transmission layer (membrane) 1 composed of silicon nitride and an X-ray absorption layer 12 which is formed on the membrane 1 and composed of tantalum. Specific patterns are formed in the X-ray absorption layer 12 so that a window 3 may be formed between a couple of the X-ray absorbers 12A. Absorber 12A is composed of the first part 12B with its thickness T1 and the second part 12C with its thickness T2 being less than T1. As an example, T1 is 0.65 .mu.m and T2 is determined by considering the X-ray wavelength. As described before, T2 is 0.3 .mu.m when the peak wavelength of the X-ray is 0.8 .mu.m. The distance between a couple of the second parts 12C, that is, the width of the window 3 is 0.1 .mu.m. The width L of the second part 12C is taken to be less than Lq=1.2 (G.lambda.)1/2, where .lambda. is a peak wavelength and G is a proximity gap. Since the thickness of the second part 12C is less than the thickness of the first part 12B, the X-ray intensity transmitted through the second part 12C is greater than the X-ray intensity transmitted through the first part 12B, and the phase shift of the former X-ray is less than the phase shift of the latter X-ray. In FIGS. 23A and 23B, X-ray intensity distributions in the case of placing the mask shown in FIG. 22 on the sample with the proximity gap of 30 .mu.m, respectively, and 20 .mu.m and exposing the X-ray having the peak wavelength of 0.8 nm are shown. By controlling the phase shift of the X-ray transmitted through the X-ray absorber neighboring the window 3 and by restricting the mutual interference between the X-rays diffracted from the window 3 and the X-rays transmitted through the absorber, the high effective exposure contrast and the high exposure dose margin can be attained even if the width of the window 3 is as small as 0.1 .mu.m. In addition, as the X-ray exposure intensity distribution captures exactly the mask patterns, the high precision mask pattern replication can be established. FIGS. 24A and 24B show dependence of the exposure dose margin M on the width L of the second part 12C, that is, the part having the thickness of 0.3 .mu.m, with the width W1 of the window 3 as a parameter. As for FIG. 24A, the proximity gap G is 30 .mu.m, and as for FIG. 24B, the proximity gap G is 20 .mu.m. The exposure dose margin M increases as the width L increases from the starting point L0, that is L=0, and M reaches the maximum value when the width L gets to Lm, and M decreases as L increases beyond Lm. As shown in FIGS. 24A and 24B, the value of L to make the exposure dose margin M greater than 1.5 are 0.18 .mu.m and 0.15 .mu.m in the case that G are 30 .mu.m and 20 .mu.m, respectively. In the above cases, the refractive index of the X-ray absorption layer 12 is 0.99939, the linear absorption coefficient is 0.002987(nm.sup.-1), the relative X-ray transmittance at the second part 12C is 40% when the X-ray transmittance at the window 3 is defined to be 100%, and the phase shift is -83.degree. when the phase shift at the window 3 is defined to be 0.degree.. That is, k is calculated to be 1.2 from the equation Lq=k(G.lambda.).sup.1/2. In other words, to obtain the sufficient exposure dose margin, it is required to make the width L of the second part 12C satisfy the following equation; L.ltoreq.1.2 (G.lambda.).sup.1/2. Let G2 be the maximum X-ray exposure intensity at the sample position corresponding to the window 3, and let G3 be the maximum X-ray exposure intensity at the sample position corresponding to the X-ray absorber, both of which are normalized by the X-ray exposure intensity transmitted through the membrane, in this case if G2 is greater than or equal to 1, the exposure dose margin M is 1/G3, and if G2 is less than 1, M is G2/G3. FIG. 25 is a cross-sectional view of the fourth embodiment of the X-ray exposure mask of the present invention. The X-ray absorption layer 14 in the mask 13 is formed to be lines-and-spaces patterns. Absorber 14A at both ends has the first part 14B with its thickness of T1 and the second part 14C with its thickness T2 being less than T1, and the thickness of the absorber 14D placed between both of 14A is T2. For example, T1 may be 0.65 .mu.m, and T2 may be 0.3 .mu.m in the case of using the X-ray with peak wavelength of 0.8 .mu.m. The width of the second part 14C is less than or equal to 1.2(G.lambda.).sup.1/2 similarly to the embodiment shown in FIG. 22. The distance between the absorbers 14A and 14D, and the distance between a couple of absorbers 14D, that is, the width W2 of the window 5 and the width W3 of the absorber 14D are 0.1 .mu.m, respectively. FIG. 26 shows the X-ray exposure intensity distribution on the sample in the case where the mask 13 is placed on the sample with the proximity gap of 20 .mu.m and where the peak wavelength of the X-ray is 0.8 .mu.m. Since each of the absorber 14A is controlled to be two different thicknesses and the thickness of absorber 14D has also controlled, the higher exposure contrast and the higher exposure dose margin can be attained because of the similar reason explained in the second and third embodiments. In addition, there is no fog at the periphery of the mask pattern and the pattern defined by the absorber can be replicated precisely. FIG. 27 shows a cross-sectional view of the fifth embodiment of the X-ray exposure mask of the present invention. The material used for the absorption layer 16 in the mask 15 is tantalum and the width W4 of the absorber 16 is 0.2 .mu.m. The absorber 16 is composed of the first part 16A with the thickness T1 at its center and of the second parts 16B with the thickness T2 being less than T1 at the both end parts of the absorber 16. T1 and T2 are 0.65 .mu.m and 0.3 .mu.m, respectively, and the width of the second part 16B is less than 1.2(G.lambda.).sup.1/2. FIG. 28, shows the X-ray exposure intensity distribution in the case of placing the mask 15 on the sample with the proximity gap of 20 .mu.m and using the X-rays having the peak wavelength of 0.8 .mu.m. In this embodiment, the higher exposure contrast and the higher exposure dose margin can be attained, and the pattern defined by the absorber can be replicated precisely onto the sample. FIG. 29 shows the cross-sectional view of the sixth embodiment of the X-ray exposure mask of the present invention. The X-ray absorption layer 18 of the mask 17 contains patterns 12, 14 and 16 shown in FIGS. 22, 25 and 27. Used materials and thickness of the X-ray transmission layer 1 and the absorption layer 18 are similar to those used in the previously described embodiments. Therefore, the mask 17 brings an overall effect summing up an individual effect given by each mask defined in the previously described embodiments. Next, by referring to FIGS. 30A through 30K, the fabricating process of the mask shown in FIG. 29 is described. At first, the X-ray transmission layer 1, for example, made of silicon nitride is formed on the main surface 20a of the substrate 20, for example, made of silicon, and the silicon nitride layer 1A is formed on another main surface 20b behind the main surface 20a of the substrate 20 by known low pressure CVD method, the thicknesses of which are 2 .mu.m respectively, (FIG. 30A). Next, the X-ray absorption layer 18 which is, for example, composed of tantalum and is used to form X-ray absorbers 12, 14 and 16 of X-ray exposure masks, is formed on the X-ray transmission layer 1, for example, by known magnetron spattering deposition method and has the thickness of 0.65 .mu.m (FIG. 30B). Next, the mask material layer 21 for absorber etching, for example, made of Si02 and being 0.3 .mu.m-thick, is formed on the X-ray absorption layer 18 by deposition method using a known electron cyclotron resonance apparatus (FIG. 30C). Next, the mask layer 23 for etching of the layer 21, for example, made of photo resist, is formed on the mask layer 21 and exposed in specific patterns shown by 22, 24 and 26 by known lithographic method. Patterns 22, 24 and 26 correspond to plane geometry of the absorber patterns 12, 14 and 16, respectively, defined on the X-ray absorption layer shown in FIG. 29 (FIG. 30D). Next, using the mask layer 23 shaped in specific patterns as a mask, the mask material layer 21 is etched by known unisotropic etching method and after that, the mask layer 23 is removed. Thus, specific patterns as shown by 32,34 and 36 are formed as a mask layer 25 (FIG. 30E). Next, using the mask 25 as a mask, the X-ray absorption layer 18 is etched by unisotropic etching method and channels 27 are formed. The depth of the channel 27 is so determined that the thickness of the X-ray absorption layer 18 below the bottom of the channel 27 may be less than or equal to T2 which was defined before (FIG. 30F). Next, the mask layer 25 is etched by known isotropic etching method. That is, the mask layer 28 having mask layer members 42, 44 and 46, the shape of which corresponds to the plane geometry of the thick absorber parts 12B, 14B and 16A, respectively, as shown in FIG. 29 (FIG. 30G). In this step, in the case where the mask layer is composed of SiO2, the isotropic etching method can be performed by wet etching process with etchant composed of a mixture of 50% hydrofluoric acid solution and 40% ammonium fluoride solution. In this etching process, the relationship between the etching depth measured in nm in the mask layer 25 and the etching time measured in seconds can be defined by a linear function as shown in FIG. 31, and hence, the mask layer 28 can be formed precisely. Next, using the mask layer 28 as a mask, the X-ray absorption layer 18 is etched by unisotropic etching method so that the bottoms of channels 27 may reach the X-ray transmission layer 1 and that specific patterns 12, 14 and 16 may have 0.3 .mu.m-thick parts 12C, 14C and 16B of the X-ray absorber (FIG. 30H). And next, on the silicon nitride film 1A formed on the main surface 20b of the substrate 20, a mask layer 51 having a window 52 which enables the region, where absorber patterns 12, 14 and 16 are formed, to direct toward outside through the substrate 20, and the X-ray transmission layer 1 is formed (FIG. 30I). And next, using the mask layer 51 as a mask, and by unisotropic etching method, the substrate 20 is removed except for its peripheral portion to the lower face of the X-ray transmission layer 1 (FIG. 30J). Finally, according to demand, the mask layers 28 and 51 may be removed (FIG. 30K). Thus, the X-ray exposure mask as shown in FIG. 29 is made. According to the above mentioned method, if only at first, the first X-ray absorption layer 1 is formed on the substrate and furthermore the first etching mask layer is formed on the first X-ray absorption layer, next an X-ray absorber pattern having parts with their thickness different from one another can be formed in self-aligning by etching the first X-ray absorption layer using the unisotropic etching method and the first etching mask layer as a mask to form the second X-ray absorber, and then by etching the first etching mask layer by isotropic etching method to form the second etching mask layer, and finally by etching the second X-ray absorption layer by unisotropic etching method and by using the second etching mask layer as a mask. In using the X-ray mask of the present invention, the resolution and the process margin with respect to patterns including lines and spaces less than 0.2 .mu.m can be improved, even if the proximity gap is relatively larger, in comparison with the patterning characteristics using conventional X-ray masks. And furthermore, various kinds of patterns including different sizes and geometries can be simultaneously and precisely replicated. Additionally, the fabrication method of the above mentioned X-ray mask of the present invention, high precision X-ray masks can be fabricated in a simplified process. At the same time, manufacturing cost may be reduced with the above mentioned fabrication method. Though in the above described embodiments materials used for absorption layers is taken to be tantalum by way of example. Gold, tungsten and other metallic materials can be used to attain the same effect as that given by tantalum only if specific characteristics on the phase shift and the mask contrast in absorption layers can be satisfied at a certain level. The present invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the intention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention. |
040627268 | claims | 1. A reactor system comprising a pressure vessel having at least one inlet and one outlet nozzle, a distribution hoop located within the vessel, the hoop having an opening facing the outlet nozzle, an impervious means interposed between the vessel and the hoop to define a fluid flow channel extending from the opening to the outlet nozzle, said means including a seal ring abutting the vessel and a bellows interposed between the ring and the hoop, said bellows urging the ring toward the vessel to maintain sealing contact therebetween. 2. A reactor system according to claim 1 wherein the impervious means includes a compression ring abutting the hoop and fixedly connected to said bellows. 3. A reactor system according to claim 2 wherein the compression ring includes a circular flange disposed in spaced surrounding relation to said bellows. 4. A reactor system according to claim 2 wherein the compression ring includes a circular flange disposed within said bellows in spaced relation therewith. |
summary | ||
summary | ||
description | The following relates to the nuclear reactor arts, nuclear power generation arts, nuclear safety arts, and related arts. Nuclear reactor safety centers upon maintaining the radioactive core in an immersed condition with adequate heat removal. During normal operation, the reactor core is disposed in a sealed reactor pressure vessel that is filled (or mostly filled) with primary coolant (e.g., light water, in the case of a light water reactor). Heat removal is provided by circulation of the primary coolant through a “heat sink”. In the case of a nuclear power plant, the “heat sink” usually takes the form of a steam generator or turbine. For example, in a boiling water reactor (BWR) the primary coolant boils in the pressure vessel and primary coolant steam isolated by a steam separator/dryer assembly is sent to a turbine where the act of performing useful work on the turbine cools the steam. The condensed steam flows back into the pressure vessel of the BWR to complete the primary coolant circuit. The turbine, in turn, drives an electrical power generator so as to generate the electrical output of the BWR-based power plant. In the case of a pressurized water reactor (PWR), the primary coolant is maintained in a subcooled liquid phase (except possibly in a steam bubble at the top of the pressure vessel). The subcooled liquid primary coolant is pumped through a steam generator located external to the pressure vessel where heat is transferred to secondary coolant that in turn drives the turbine. The primary coolant exiting the steam generator flows back into the pressure vessel to complete the primary coolant circuit. In a variant “integral” PWR design, the steam generator is located internally within the pressure vessel. In a typical integral PWR design, an annular riser is disposed in the pressure vessel to define inner “riser” and outer annular “downcomer” regions. The primary coolant flows upward (away from the reactor core) in the riser region and back downward in the outer annular downcomer region to complete the primary flow circuit. The internal steam generator is typically disposed in the downcomer region, and comprises tubes having primary coolant flowing downward inside the pipes and secondary coolant flowing upward outside the pipes (or, alternatively, the secondary coolant may flow upward inside the tubes and the primary coolant downward outside the tubes). Safety systems are designed to remediate various possible events that could compromise the objective of keeping the reactor core immersed in primary coolant and adequately cooled. Two possible events that are addressed by the safety systems are: a loss of coolant accident (LOCA); and a loss of heat sinking accident. Conventionally, safety systems include a steel containment structure surrounding the pressure vessel and of sufficient structural strength to contain released primary coolant steam. Condensers are disposed inside the containment structure in order to condense the primary coolant steam so as to reduce pressure inside containment. An ultimate heat sink comprising a large body of water located externally from the containment structure provides the thermal sink for heat captured by the condensers. A refueling water storage tank (RWST) located inside the containment structure provides water during refueling operations, and also serves as a source of water in emergencies. In a LOCA, a rupture in the pressure vessel or in connecting piping (e.g., pipes conducting primary coolant to/from an external turbine or steam generator) causes the pressure vessel to depressurize and possibly leak primary coolant. Remediation of a LOCA includes (1) containing and condensing primary coolant steam in order to depressurize the system; and (2) replenishing water to the pressure vessel in order to keep the reactor core immersed. The RWST provides replenishment water, while the condensers located inside the containment structure provide a mechanism for recondensing the escaped primary coolant steam. In a loss of heat sinking event the “heat sink” is lost. In a BWR, this can occur if the flow of primary coolant steam to the turbine is interrupted (for example, because the turbine must be shut down unexpectedly or abruptly fails). In a PWR, the corresponding event is interruption of subcooled primary coolant flow through the external steam generator. In an integral PWR, the corresponding event is loss of secondary coolant flow through the internal steam generator. In any loss of heat sinking event, the response includes venting steam from the pressure vessel to the condensers located inside the containment structure in order to remove heat and controllably depressurize the pressure vessel. Ideally this will be performed using a closed system in which steam from the pressure vessel is vented into the condensers. However, if the pressure rise due to loss of heat sinking is too rapid it may be necessary to vent into the containment structure (in effect, converting the loss of heat sinking event into a controlled LOCA). In one aspect of the disclosure, an apparatus comprises: a nuclear reactor including a pressure vessel and a nuclear reactor core disposed in the pressure vessel; a subterranean containment structure containing the nuclear reactor; and an ultimate heat sink pool disposed at grade level wherein an upper portion of the subterranean containment structure defines at least a portion of the bottom of the ultimate heat sink pool. In some embodiments, the upper portion of the subterranean containment structure comprises an upper dome. In some embodiments, the apparatus further comprises: a condenser comprising a heat exchanger including hot and cold flow paths disposed inside the subterranean containment structure; and cooling water lines operatively connecting the condenser with the ultimate heat sink pool. In another aspect of the disclosure, an apparatus comprises: a pressurized water reactor (PWR) including a pressure vessel and a nuclear reactor core disposed in the pressure vessel; a subterranean containment structure containing the nuclear reactor; and an ultimate heat sink pool having a bottom defined at least in part by an upper portion of the subterranean containment structure. In some embodiments, the upper portion of the subterranean containment structure comprises an upper dome. In some such embodiments, the upper dome protrudes above the surface of the ultimate heat sink pool to define an island surrounded by the ultimate heat sink pool. In another aspect of the disclosure, an apparatus comprises: a nuclear reactor including a pressure vessel and a nuclear reactor core disposed in the pressure vessel; a containment structure containing the nuclear reactor; an ultimate heat sink pool disposed on top of the containment structure wherein the containment structure defines a bottom of the ultimate heat sink pool; a condenser comprising a heat exchanger including hot and cold flow paths disposed inside the containment structure; and cooling water lines operatively connecting the condenser with the ultimate heat sink pool. Disclosed herein are improved emergency safety systems which have advantages of passive operation and reduced susceptibility to being compromised by external influences such as flooding, earthquakes, hostile assault, and so forth. With reference to FIG. 1, an illustrative nuclear reactor of the pressurized water reactor (PWR) type 10 includes a pressure vessel 12, which in the illustrative embodiment is a cylindrical vertically mounted vessel. A nuclear reactor core 14 is disposed in a lower portion of the pressure vessel 12. (Note that in diagrammatic FIG. 1 the reactor care 14 is revealed by a cutaway 16 in the pressure vessel 12). The reactor core 14 includes a mass of fissile material, such as a material containing uranium oxide (UO2) that is enriched in the fissile 235U isotope, in a suitable matrix material. In a typical configuration, the fissile material is arranged as “fuel rods” arranged in a core basket. The pressure vessel 12 contains primary coolant water (typically light water, that is, H2O, although heavy water, that is, D2O, is also contemplated) in a subcooled state. The PWR 10 includes other components known in the art that are not shown, such as a “basket” or other structure supporting the reactor core 14 in the pressure vessel 12, neutron-absorbing control rods selectively inserted into the reactor core 14 by a control rod drive mechanism (CRDM) to control the nuclear chain reaction, and central riser that defines a primary coolant circulation path inside the pressure vessel 12, primary coolant pumps, or so forth. These various components may be variously disposed inside or outside the pressure vessel. For example, the CRDM may be external, as is conventionally, the case, or may be located internally inside the pressure vessel as described in Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, U.S. Pub. No. 2010/0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety; and Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, Intl Pub. WO 2010/144563 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. The reactor coolant pumps may be internal or external, and in some embodiments may be omitted entirely in which case heat generated by the reactor core 14 drives primary coolant flow via natural circulation. The illustrative PWR 10 is an integral PWR design, by which it is meant that an internal steam generator is disposed in the pressure vessel 12. The installed steam generator is not shown; however, FIG. 1 diagrammatically shows a removed internal steam generator 20 that has been removed from the pressure vessel 12 for maintenance, or is located as shown prior to installation into the pressure vessel 12, or so forth. Additional conventional components are not shown, such as a crane for lifting an upper pressure vessel section in order to open the pressure vessel 12 and for moving the steam generator 20; various scaffolding, walkways or the like for movement of personnel, various auxiliary equipment and electronics, and so forth. The PWR 10 is contained in a containment structure 22. The containment structure 22 is typically a steel structure in order to provide structural strength and high thermal conductivity (to facilitate heat removal techniques as disclosed herein). Additionally or alternatively, portions or all of the containment structure 22 may be made of steel-reinforced concrete, a composite material such as a steel host with embedded nanoparticles to enhance thermal conductivity, or so forth. The illustrative containment structure 22 is generally cylindrical, and further includes a lower flood well 24 and an upper dome 26. The lower flood well contains the lower portion of the pressure vessel 12 including the reactor core 14. This flood well enables the lower region to be flooded with water in certain emergency situations in order to assist in cooling the reactor core 14. As disclosed herein, the upper dome 26 provides enhanced structural strength and serves as a steam condensation surface in certain emergency situations. The containment structure 22 is large enough to accommodate the PWR 10 and to additionally provide space for operations such as removing the steam generator 20 during installation and/or maintenance. The containment structure 22 is subterranean, by which it is meant that the containment structure 22 lies below grade, that is, below the ground level 30 (except possibly for an uppermost extremity of the upper dome 26). A secondary containment structure 32 contains the (primary) containment structure 22. The secondary containment structure 32 is typically made of concrete, steel-reinforced concrete, or another suitably robust building material. In embodiments disclosed herein the secondary containment structure 32 is not a thermal pathway and hence the thermal conductivity of the material constituting the secondary containment structure 32 is not a design consideration (thus, making concrete one suitable material). The secondary containment structure 32 is mostly subterranean in order to “contain” the subterranean primary containment structure 22; however, an upper “roof” 34 of the secondary containment structure 32 is above-ground. The subterranean arrangement of the containment structure 22, as well as its relatively large size, facilitates employing a passive emergency cooling system comprising an at-grade (that is, at ground level) ultimate heat sink (UHS) pool 40 in thermal communication with the upper dome 26 of the containment structure 22. The upper dome 26 has an outside surface 42 that serves as at least a portion of the “bottom” of the UHS pool 40, and an inside surface 44 that serves as a condensation surface that is cooled by the UHS pool 40. The UHS pool 40 is contained by the upper dome 26 defining at least a portion of the “bottom” of the pool 40 along with sidewalls 46 and, in the illustrative embodiment, an additional bottom portion 48 that is welded with (or otherwise in sealed connection with) the upper dame 26. In some embodiments the additional bottom portion 48 may be omitted and the sidewalls are instead welded directly with (or otherwise in direct sealed connection with) the upper dome 26. By “at grade” or “at ground level” it is meant that the water in the UHS pool 40 is mostly or entirely at or below ground level, and the surface of the water when the UHS pool 40 is at its maximum capacity is about at ground level. The surface may be slightly below ground level, but it should not be so far below ground level that an earthquake, explosion, or other disruption could cause the surrounding ground to cave into the UHS pool 40 and obliterate the pool. Similarly, the surface may be slightly above ground level (for example, by constructing the sidewalls to extend above-grade), but it should not be so far above ground level that an above-ground leak could result in the UHS pool being drained. The upper portion (i.e., roof 34) of the secondary containment structure 32 is optionally omitted. Including the roof 34 enables better control over the composition (e.g., chemistry) of the UHS pool 40, and prevents debris from falling into the UHS pool 40. In some embodiments the UHS pool is provided with a cover that is separate from the secondary containment structure. On the other hand, in some embodiments the sidewalls 46 and optional bottom portion 48 of the UHS pool may form part of the secondary containment structure. More generally, various levels and degrees of integration and/or separation between the walls and bottom of the UHS pool 40, on the one hand, and the secondary containment 32 on the other hand, are contemplated. It is also contemplated to omit the secondary containment structure 32 entirely, if such an omission does not compromise safety and does not violate applicable nuclear regulatory standards. The UHS pool 40 provides passive heat removal as follows. Primary coolant released from the pressure vessel 12 (whether in an uncontrolled LOCA or in a controlled fashion such as may be performed in a loss of heat sinking event) naturally rises and contacts the inside surface 44 of the dome 26. The UHS pool 40 in contact with the outside surface 42 of the dome 26 keeps the dome 26 at outside ambient temperature (or, more precisely, at about the temperature of the water in the UHS pool 40, which is at or close to outside ambient temperature). The high thermal conductivity of the steel (or other suitably chosen material) of the dome 26 ensures that the outside and inside surfaces 42, 44 are at about the same temperature. Thus, the inside surface 44 is cold (e.g., at or below 40° C. for most climates) as compared with the steam (which is at or above 100° C.). The primary coolant steam thus condenses onto the inside surface 44 of the dome 26, and its latent heat and any additional kinetic energy is transferred through the (high thermal conductivity) dome 26 to the UHS pool 40. The condensed primary coolant is in the form of water (or water droplets) adhering to the inside surface 44 of the dome 26. In some embodiments this water is simply allowed to fall or run downward along the surface under the influence of gravity. Advantageously, this may result in a substantial portion of the condensed water flowing into the flood well 24 to contribute to flooding the flood well 24. Alternatively, baffles 50 are provided to guide the flow of the condensed water. In the illustrative embodiment the baffles 50 are arranged to guide the condensed water into a refueling water storage tank (RWST) 52 which is used in some emergency conditions (such as some LOCA events) to replenish water in the pressure vessel 12. In some embodiments, the UHS pool 40 is also used as the source of cooling water for a condenser 60 disposed inside the containment structure 22. The condenser 60 provides an additional mechanism for condensing primary coolant steam. In some embodiments, and in some emergency conditions, the condenser 60 inlet is coupled directly with the inside of the containment structure 22 in order to condense primary coolant steam that has been released into the containment structure 22. In some embodiments, and in some emergency conditions, the condenser 60 may be connected with the pressure vessel 12 (connection not illustrated) in order to condense primary coolant steam inside the pressure vessel 12. This latter approach may be useful, for example, in the case of a loss of heat sinking event in which the sealing integrity of the pressure vessel 12 has not been compromised but pressure inside the pressure vessel 12 is rising (and primary coolant being converted to steam) due to the loss of heat sinking. The condenser 60 comprises a heat exchanger 61 including hot and cold flow paths (indicated diagrammatically in FIG. 1). The primary coolant steam flows in the hot path, while cooling water flows through the cold path. The hot and cold flow paths are in fluid isolation from one another but are in thermal communication with each other. For example, the condenser 60 may include tubes in a manifold, where the tubes form one flow path and the manifold the other flow path. In another contemplated configuration, the hot and cold flow paths may be two intertwined tubes. Cooling water flows from the UHS pool 40 into the condenser 60 via an inlet pipe 62, and heated cooling water (which may still be water, or may be steam, or may be some mixed steam/water phase) flows via an outlet pipe 64 back to the UHS pool 40. The illustrative pipes 62, 64 have open ends in fluid communication with the UHS pool 40; alternatively, these ends may connect with a heat exchanger coil 66 (shown in phantom in FIG. 1) disposed in the UHS pool 40 such that the cooling water is in fluid isolation from both the primary coolant steam and the UHS pool 40. The embodiment of FIG. 1 includes the condenser 60 comprising the heat exchanger 61 including hot and cold flow paths disposed inside the subterranean containment structure 22, with cooling water lines 62, 64 operatively connecting the condenser 60 with the UHS pool 40. While the single condenser 60 is illustrated, it is to be understood that one, two, three, four, or more condensers 60 may be disposed in the subterranean containment structure 22 with suitable connecting cooling water lines 62, 64. The use of multiple condensers 60 can provide redundancy, and may be required by applicable nuclear regulatory rules. Moreover, when multiple condensers 60 are provided the hot flow paths may be connected with different locations. For example, one or more condensers may be connected with the pressure vessel 12 to provide condensation action for primary coolant steam that is contained inside the pressure vessel 12, and one or more condensers be arranged to operate on the interior volume of the subterranean containment structure 22 to provide condensation action for primary coolant steam that escapes from the pressure vessel 12 during a LOCA. It is also to be understood that in some embodiments the condensers may be omitted, or may have their cold flow paths connected with a cooling water source other than the UHS pool 40. In some such embodiments, the only heat transfer path from the interior of the subterranean containment structure 22 to the UHS pool 40 is via the upper dome 26 of the containment structure 22. Configuration of the upper portion of the containment structure 22 as the illustrated upper dome 26 has certain advantages. The dome shape has advantageous structural strength which is useful in supporting the weight of the UHS pool 40, since the upper dome 26 serves as at least a portion of the bottom of the UHS pool 40. The dome shape also provides a larger surface area as compared with a flat roof. Nonetheless, it is contemplated for the upper portion of the containment structure supporting the UHS pool to have a configuration other than a dome shape, such as being a flat roof, angled roof, or so forth. With brief reference to FIGS. 2-4, the illustrative upper dome 26 optionally includes grooves or undulations 70 that increase the surface area for condensation. FIG. 2 provides an overhead view of the upper dome 26 illustrating an advantageous configuration in which the grooves or undulations run “downward” along the general direction that the condensate is expected to flow. FIGS. 3 and 4 show two suitable configurations for the grooves or undulations 70. FIGS. 3 and 4 show sections through a small portion of the upper dome 26 with the sectioning plane oriented transverse to the direction of the grooves or undulations 70. In the embodiment of FIG. 3 the grooves or undulations 70 are formed on both the outside surface 42 and the inside surface 44 of the upper dome 26. This configuration can have manufacturing advantages in that the thickness of the upper dome 26 is constant (albeit undulating or including grooves). In the embodiment of FIG. 4 the grooves or undulations 70 are formed only on the inside surface 44 of the upper dome 26 (and hence would not actually be visible in the overhead view of FIG. 2). This configuration recognizes that the surface area of interest for condensation, which is to be made as large as practicable, is the inside surface 44 whereas the upper surface 42 can be of smaller area. The configuration of FIG. 4 can provide improved structural rigidity and robustness due to the additional material retained by not including the grooves or undulations in the outside surface 42. With reference back to FIG. 1, during a LOCA primary coolant steam is released into the subterranean containment structure 22. The primary coolant steam condenses at the inside surface 44 of the upper dome 26, and its latent heat and any additional kinetic energy is transferred through the (high thermal conductivity) dome 26 to the UHS pool 40. This raises the temperature of the water comprising the UHS pool 40, and causes increased evaporation from the surface of the UHS pool 40. If the heat transfer is of sufficient rate and magnitude the water comprising the UHS pool 40 may actually boil to produce steam emanating from the surface of the UHS pool 40. The secondary containment structure 32 containing the subterranean containment structure 22 and the UHS pool 40 has vents 80 arranged to allow water evaporated or boiled off of the UHS pool 40 to escape from the secondary containment structure 32. The UHS pool 40 should have sufficient water to maintain cooling for a design time without any refilling of the UHS pool 40, such as at least three days in accordance with some nuclear regulatory rule paradigms, or up to 14 days in some more aggressive regulatory rule paradigms. In some embodiments it is contemplated that the UHS pool 40 may comprise hundreds of thousands of gallons of water or more. However, the quantity of water sufficient for a given operational period is expected to depend upon various factors such as thermal power, design pressure, and so forth, and accordingly this is to be understood as being merely an illustrative example. More generally, heat transfer from the interior of the containment structure 22 to the UHS pool 40 is via the area of the portion of the bottom of the UHS pool 40 that is defined by (and hence in contact with) the upper portion 26 of the subterranean containment structure 22. The wetted area and tank volume should be sufficient to remove decay heat generated in the reactor core 14 and thereby maintain suitably low pressure and temperature conditions within the containment structure 22. The heat transfer q from the containment 22 to the UHS pool 40 is given by: q=U·Awet·ΔT where Awet denotes the wetted area, U denotes the overall heat transfer coefficient for heat transfer from the containment 22 to the UHS pool 40, and ΔT denotes the temperature difference between the containment 22 and the UHS pool 40. To provide sufficient cooling, q≧Qdecay heat should hold, where Qdecay heat denotes the heat generated by the reactor core 14 due to fission product decay following reactor shutdown. Solving U·Awet·ΔT≧Qdecay heat for the wetted area Awet (that is, for the area of the portion of the bottom of the UHS pool 40 that is defined by, and hence in contact with, the upper portion 26 of the subterranean containment structure 22) yields: A wet ≥ Q decay heat U · ( T max - T UHS ) . ( 1 ) In the above Criterion (1), Awet denotes the wetted area, Tmax denotes the maximum allowable temperature inside the containment, TUHS denotes the maximum allowable temperature of the UHS pool 40, Qdecay heat denotes the highest postulated value for heat generated by the reactor core 14 due to fission product decay following reactor shutdown, and U denotes the overall heat transfer coefficient for heat transfer from the containment 22 to the UHS pool 40. More particularly, components that contribute to the overall heat transfer coefficient U include: heat transfer by condensation and convection from the interior of the containment 22 to the inside surface of the upper portion 26 of containment 22; heat conduction through the containment shell; and heat transfer from the outside surface of the upper portion 26 of containment 22 into the UHS pool 40 by boiling and/or convection of water of the UHS pool 40. The generated decay heat Qdecay heat decreases with time following reactor shutdown and is dependent upon the reactor operating power history (that is, the history of operating power as a function of time prior to shutdown). As indicated by Criterion (1), the minimum permissible wetted area should scale with the amount of decay heat to be dissipated. To be conservative, the UHS pool 40 should be designed for the largest value of Qdecay heat postulated for any accident scenario under consideration. The maximum allowable temperature Tmax is the maximum long-term temperature desired for the containment 22. The initial energy release resulting from a loss of coolant accident (LOCA) may cause a brief temperature transient during which the temperature inside the containment 22 briefly exceeds Tmax. The maximum temperature Tmax should be kept low enough to ensure that electrical wiring, valve actuators, instrumentation, and other critical devices inside the containment 22 continue to operate. The temperature TUHS is the maximum allowable temperature of the water in the UHS pool 40. The temperature of the water in the UHS pool 40 is expected to vary with time after reactor shutdown as heat is transferred through the upper portion 26 of the subterranean containment 22 into the UHS pool 40. A limitation TUHS≦100° C. is imposed by the boiling point of water at atmospheric pressure. As heat transfer decreases with increasing temperature TUHS of the UHS pool 40, a conservative value is TUHS=100° C. Yet another consideration in the design is that the wetted area Awet may decrease over time after reactor shutdown as water boils off or evaporates from the UHS pool 40. In some cases this concern may be obviated by the fact that the decay heat output is highest just after reactor shutdown at which time the water level of the UHS pool 40 has not yet been depleted. Also, for a LOCA credit can be taken for the effect of the thermal capacitance of equipment within the containment 22, and of the containment structure 22 itself, in order to reduce pressure and temperature immediately following an energy release. The UHS pool 40 can reduce or stabilize pressure in the containment 22 provided that Criterion (1) is met. The values for the parameters Awet, U, Qdecay heat, Tmax, and TUHS used in designing in accord with Criterion (1) can be assessed in various ways. In one approach, Qdecay heat is set to its initial, highest value (i.e., the value just after any brief transient accompanying the LOCA or other shutdown event). The maximum allowable temperature Tmax should be set to a conservatively low value (note that a lower value of Tmax drives the minimum permissible wetting area higher). Similarly, a conservatively high value of TUHS should be used (a higher value decreases ΔT and hence drives the minimum permissible wetting area higher). A conservative approach is to set TUHS=100° C. The overall heat transfer coefficient U can be adjusted to some extent by controlling parameters such as the wall thickness of the upper portion 26 of the containment 22 (but, that wall bears weight from the UHS pool 40 and this limits on how thin the wall can be made). Similarly, the wetted area Awet can be adjusted based an the overall structural design geometry or layout. Note that an alternative formulation of Criterion (1) is U·Awet·ΔTmin≧Qdecay heat where ΔTmin denotes the minimum temperature difference between the containment 22 and the UHS pool 40 postulated to occur during any accident scenario under consideration. Although not illustrated, it is contemplated for the vents 80 to include screens, bends, or other features to reduce the likelihood of becoming clogged by debris. It is also contemplated for one or more of the vents 80 to take the form of one or more chimney stacks, while other openings serve as air inlets in order to set up a draught within the volume defined between the surface of the UHS pool 40 and the roof 34 of the secondary containment structure 32. Operation of the illustrative safety systems shown in FIG. 1 are as follows. In a LOCA, a breach in the pressure boundary of the pressure vessel 12 causes primary coolant water to escape from the vessel. The reactor coolant system (RCS) responds by depressurizing the pressure vessel 12 and containment 22 using the one or more condensers 60 and the additional condensation provided by the cooling of the dome 26 by the UHS pool 40. Once depressurization reduces the pressure to a sufficiently low level, additional water is injected into the pressure vessel 12 from the refueling water storage tank (RWST) 52 located inside the containment 22. Decay heat from the reactor core 14 boils this water and continues to release it to the containment 22 until active systems (not shown) are brought online to provide normal cooling. The passive cooling systems 26, 40, 60 are designed to remove much of this energy for at least 72 hours (in accordance with regulations of the Nuclear Regulatory Commission, NRC, in the United States) to prevent excessive pressures inside containment. The water stored in the UHS pool 40 above the containment dome 26 is in direct contact with the steel containment surface to provide a large surface for heat transfer. The energy inside the containment 22 heats the water of the UHS pool 40, possibly up to boiling temperature so as to boil the water of the UHS pool 40. The steam generated is vented to the atmosphere by the vents 80. This venting does not release any radioactivity because the water of the UHS pool 40 is not contaminated. In a loss of heat sinking event, the RCS pressurizes initiating the emergency core cooling system (ECCS) emergency condenser 60. Primary coolant steam is vented to the inlet of the condenser 60 and the condensate is returned to the reactor pressure vessel 12 (piping not illustrated). The condenser 60 is cooled by low pressure water from an UHS tank 40. The illustrative safety systems have numerous advantages. Placement of the UHS pool 40 at grade level reduces the likelihood of damage as compared with an elevated ultimate heat sink pool (for example, mounted atop a conventional reactor building). Moreover, even if the containment structures 26, 46, 48 of the UHS pool 40 were to be breached, the result would be that the water comprising the UHS pool 40 would flow downward either into the (primary) containment structure 22 (in the case of a breach of the upper dome 26) or into the secondary containment structure 32 (in the case of a breach of the sidewalls 46 or additional bottom portion 48). In the former case the water would contribute to filling the flood well 24 while in the latter case the water would continue to surround the primary containment structure 22 and hence would continue to act (at least to some degree) as a condensation mechanism. Another advantage is that the UHS pool 40 can be replenished without elevating the refilling water above grade level 30. FIG. 1 shows illustrative refilling inlets 82 passing through the secondary containment structure 32 and the sidewalls 46. These inlets 82 can be connected with various replenishment water supplies. For example, a natural or artificial lake at higher elevation than the grade level 30 of the nuclear facility could be plumbed to the inlets 82 with suitable parallel manual/electronic valving to enable opening the replenishment line via an automated system or manually (if, for example, electrical power is lost for an extended period). Indeed, the UHS pool 40 can even be replenished by rainwater, flood water, or other naturally occurring surface water, for example by configuring the inlets 82 as gutters (preferably including suitable screening or the like to avoid clogging by debris). The combination of the subterranean containment structure 22 and the UHS pool 40 disposed above and supported by the containment 22 has the yet further advantage of substantially reducing susceptibility to damage by hostile action. The subterranean arrangement of the containment 22 is a substantial barrier to attack, and the UHS pool 40 provides an additional surface barrier shielding the containment structure 22 (and the nuclear reactor 10 contained within) from projectiles, explosives, or other attack mechanisms. This reduced access to the subterranean containment structure 22 due to the UHS pool 40 can raise some difficulties during maintenance operations such as refueling. In the illustrative embodiment, this is solved by constructing the upper dome 26 of the subterranean containment structure 22 with sufficient height so as to protrude above the surface of the UHS pool 40 so that the top of the dome 26 defines an island surrounded by the UHS pool 40. A hatch or other access can be provided in this “island” for delivering fresh fuel or other components. Alternatively, if the top of the upper dome is below the water level of the UHS pool, then the UHS pool can be partially drained in order to expose the top of the dome to provide access for maintenance. The illustrative nuclear reactor 10 is a pressurized water reactor (PWR) with an integral steam generator (integral PWR). However, the disclosed safety systems are also applicable to reactors of other types, such as a PWR with external steam generators, or a boiling water reactor (BWR). In the latter case, the BWR is conventionally contained in a more compact containment structure than that used in PWR designs, and the compact conventional BWR containment may not provide sufficient surface area for contact between the UHS pool and the containment structure. This can be remedies by using a larger containment structure for the BWR reactor, and/or by including the surface area enhancing grooves or undulations 70 in the dome of the BWR containment. The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. |
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043354653 | claims | 1. An apparatus for producing and accelerating electrons and ions under the application of a voltage, said apparatus comprising: 2. The apparatus of claim 1 wherein said voltage supply means supplies a potential to said electrodes which is inversely proportional to the cube of the product of the gas pressure and the distance between said electrodes. 3. The apparatus of claim 2 or 1, wherein said electrodes are planar and parallel with respect to each other. 4. The apparatus of claim 2 or 1 wherein said means defining at least one aperture defines at least two apertures in each of said electrodes, said apertures being aligned to define at least two convergent gas-discharge paths. 5. The apparatus of claim 1 or 1 wherein there is provided a trigger means connected to at least two electrodes for time wise triggering said spark-like gas-discharge. 6. The apparatus of claim 1 or 1 wherein one of said electrodes is an anode and another is a cathode. 7. The apparatus of claim 6 wherein additional electrodes are provided with the cathode separating said additional electrodes from said anode and a negative voltage supply means connected to said additional electrodes for the purpose of accelerating ions flowing from said anode towards said cathode. 8. The apparatus of claim 6 wherein additional electrodes are provided with the anode separating said additional electrodes from said cathode and a positive voltage supply means connected to said additional electrodes for the purpose of accelerating said electrons flowing from said cathode towards said anode. 9. The apparatus of claim 6 wherein adjacent said anode there is provided a chamber filled with low pressure gas, said chamber including a holder means for supporting a work piece for treatment. 10. The apparatus of claim 6 wherein adjacent the anode there is provided a terminal electrode means, having a small outflow opening, for constricting the electron flow. 11. The apparatus of claim 6 wherein additional electrodes are provided adjacent the cathode and have a potential applied thereto equal to that of an electrode in the center area of the accelerator such that an extensively neutral particle flow is produced. 12. The apparatus of claim 11 wherein the neutral particle flow is utilized in an ion-rocket and means are provided for electrically neutralizing said ions prior to their exit from the ion-rocket engine. 13. The apparatus of claim 6 wherein adjacent said cathode there is provided a chamber for the containing of a material which produces neutrons under the application of ions traveling along said spark-like gas-discharge path. 14. The apparatus of claim 1 wherein there is additionally provided means for mounting target material along said spark-like gas-discharge path, for releasing the heat of thermo-nuclear fusion. 15. The apparatus of claim 14 wherein a plurality of particle accelerators are arranged around a covered spherical bowl such that a central point in said spherical bowl is along the gas-discharge paths of each particle accelerator and a target means is provided at the central point of the spherical bowl, said target being covered by thin metallic skin. 16. The apparatus of claim 1 wherein said gas becomes luminous during said spark-like gas-discharge. 17. The apparatus of claim 6 wherein adjacent said anode, there is located a means for emitting X-ray beams when bombarded with electrons. 18. A method for producing and accelerating ions and electrons in response to an applied voltage, said method comprising the steps of: 19. The method according to claim 18, wherein the pressure of said ionizable gas is on the order of 0.5 mbar. 20. The method according to claim 18, wherein the spacing between adjacent ones of said plural spaced electrodes is approximately one mm. 21. The method according to claim 18, wherein said spark-like gas discharge has a duration of only a few nanoseconds. 22. The apparatus according to claim 1, wherein the pressure of the ionizable gas is approximately 0.5 mbar. 23. The apparatus according to claim 1, wherein the spacing between said at least two spaced electrodes is approximately 1 mm. |
047553456 | abstract | A resonant double loop radio frequency (rf) antenna for radiating high-power rf energy into a magnetically confined plasma. An inductive element in the form of a large current strap, forming the radiating element, is connected between two variable capacitors to form a resonant circuit. A real input impedance results from tapping into the resonant circuit along the inductive element, generally near the midpoint thereof. The impedance can be matched to the source impedance by adjusting the separate capacitors for a given tap arrangement or by keeping the two capacitances fixed and adjustng the tap position. This results in a substantial reduction in the voltage and current in the transmission system to the antenna compared to unmatched antennas. Because the complete circuit loop consisting of the two capacitors and the inductive element is resonant, current flows in the same direction along the entire length of the radiating element and is approximately equal in each branch of the circuit. Unidirectional current flow permits excitation of low order poloidal modes which penetrate more deeply into the plasma. |
052992519 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS A structure of an embodiment according to the invention is show in FIG. 4 to FIG. 6. One of the different points as compared to the conventional apparatuses shown in FIG. 1 and FIG. 2 is that three moving bases are arranged in the same plane. These moving bases are the X position alignment system moving base 16a, the Y position alignment system moving base 16b and the .theta. position alignment system moving base 16c as shown in FIG. 4. Three optical alignment systems, which are X position optical alignment system 11a, Y position optical alignment system 11b and .theta. position optical alignment system 11c are installed on the three bases 16a, 16b and 16c respectively. Therefore, these three optical alignment systems 11a, 11b and 11c are also arranged in the same plane. Common parts such as optical parts can be used in these systems. Three half-mirrors 14a, 14b and 14c, and three reflective mirrors 15a, 15b and 15c, are included in the three optical alignment systems 11a, 11b, and 11c, respectively, as shown in FIG. 4. The distance h.sub.1 is defined as a length between the optical axis of the optical alignment system 11a and the X-ray mask 6. The distance h.sub.2 is defined as a length between the optical axis of the optical alignment system 11b and the X-ray mask 6. The distance h.sub.3 is defined as a length between the optical axis of the optical alignment system 11c and the X-ray mask 6. These three distances h.sub.1, h.sub.2 and h.sub.3 become equal to each other because of the arrangement of these three systems in the same plane. The distance h.sub.1 ', h.sub.2 ' and h.sub.3 ' are also defined as lengths between the object lenses 12a, 12b and 12c, and the prisms 13a, 13b and 13c respectively. When the distances h.sub.1 ', h.sub.2 ' and h.sub.3 ' are made the same, the focal length f.sub.1 (=h.sub.1 +h.sub.1 ') of the optical alignment system 11a, f.sub.2 (=h.sub.2 +h.sub.2 ') of the optical alignment system 11b, and f.sub.3 (=h.sub.3 +h.sub.3 ') of the optical alignment system 11c can be made the same value. Therefore, the widths of the alignment marks 6a, 6b and 6c become the same C1=C2=C3) and the alignment detecting accuracies in the optical alignment systems 11a, 11b and 11c are made even with each other. Three narrow portions 106a, 106b and 106c are shaped in front of the moving bases 16a, 16b and 16c respectively. In this embodiment, by cutting both sides of the base, the narrow front portion is rectangle-shaped (as shown in FIG. 4) and the maximum width "a" of the moving base is larger than the maximum width "b" of the narrow front portion as Shown in FIG. 5 and FIG. 6. The moving bases 16a, 16b and 16c can move individually on the same plane without interferences with each other because of the narrow front portions as described above. When the chip size of the X-ray mask 6 is d.times.d length and breadth, a method to search for the marks on the mask by use of the alignment system is described hereunder. In the case of d.gtoreq.b (d is already defined above and b is the width of the narrow front portion), the search for the marks starts from the center of the chip to the edge of the chip as shown in FIG. 5. In the case of d<b, the search for the marks starts from the edge of the chip as shown in FIG. 6. When the bases move to search for the marks, an interlock mechanism is necessary to prevent the clashing of the moving bases against each other. A software control is generally used as the interlock mechanism. First a interlock map is made The map shows the lashing points of the three moving bases 16a, 16b and 16c each other. Next, the actual locations of the three bases are compared with the points on the map, and the moving bases are stopped before the bases clash against each other. Thus, the interference of the optical alignment system is prevented. However, the software control has some problems. When the software control or a hardware control system including the software is broken, the moving bases may clash against each other. Under the software control, the X-Y positions of the moving bases always must be observed by the computer. This is one of the causes for increases in cost. Another preferred embodiment which doesn't have the problems as described above is shown in FIG. 7 and FIG. 8. As shown in these Figures, X interference blocks 17a and 17b are attached at both sides of the notches in the moving base 16a. In a similar way, Y interference block 17c and .theta. interference block 17d are attached to moving bases 16b and 16c, respectively. The size of these blocks 17a, 17b, 17c and 17d is slightly larger the size of the narrow front portions of the moving bases 11a, 11b and 11c, respectively. The shape of these blocks is the same as the narrow front portions of the moving bases (shown as A--A', B--B and C--C'). When the moving bases 16a, 16b and 16c on which the alignment systems 11a, 11b and 11c are installed move, the interference blocks 17a, 17b and 17d clash against each other before the optical alignment systems clash against each other, that is to say, the interference blocks work as a mechanical interlock. Another mechanical interlock is shown in FIG. 9. In this case, interference block 17d' shaped as shown in FIG. 9 is attached on the moving base 16c. The block 17d' can rotated on a axis 18. When the interference block 17a clashes against the interference block 17d' at the P1 or P2 position of the block 17a and 17d', which depends on the movement of the moving base 16a and 16c, the rotatable block 17d' rotates and a sensor 19 detects the movement of the block 17d' and the bases 16a or 16c are stopped before the clashing between the moving base 16a and 16c occurs. Another preferred embodiment shown in FIG. 10 is described hereunder. A interference block 17d" is attached to the moving base 16b. The interference block 17d" can also rotate on a axis. An interference block 17b is attached on the other side of the moving base 16a. A sensor 20 for detecting the clashing of the blocks is installed on the block 17d". Moreover limit sensors (not shown) are installed on each moving base 16a, 16b and 16c. The moving base 16a has two limit sensor detecting in two directions individually. One direction is described as X1+-X1-, and the other is described as X2+-X2-. The moving base 16b has two limit sensors detecting in the directions as described in Y1+-Y1- and Y2+-Y2-. The moving base 16c also has two limit sensors detecting in the directions as described in .theta.1+-.theta.1- and .theta.2+-.theta.2-. The moving bases cannot continue to move when the limit sensor signal is received. However, the moving base can move in the direction required to switch off the limit sensor. The limit sensor restricts the area in which each moving base can move around by electric mechanisms. The movement of this system as described above is as follows. In FIG. 11, the input signals from the limit sensors or the sensors 19, 20 are described in the left line, on the other hand the output signals to stop the movements of the bases are described in the right line. For example, when a signal of the YL from the sensor 20 is put on, movement in the directions of Y1+, Y2+, X1+ and X2- is locked as shown in FIG. 11 and the clashing between the moving base 16a and 16b is prevented. The movement in the direction of X1+ is locked when at least an input signal X1+ or .theta.L (from the sensor 19) is put on. The present invention has been described with respect to specific embodiments. However, other embodiments based on the principles of the present invention should be obvious to those of ordinary skill in the art Such embodiments are intended to be covered by the claims. |
048812471 | abstract | Disclosed is a method and apparatus for measuring the burnup of nuclear fuel. A curve giving the calculated relationship between the fast neutron emission rate and the burnup of fuel is prepared. The fast neutron counting rate from a sample of nuclear fuel of known burnup is measured and the proportionality ratio between that measurement and the fast neutron emission given by the curve for the same burnup is determined. The fast neutron counting rate of nuclear fuel of unknown burnup is then measured and multiplied by the proportionality ratio to determine the fast neutron emission rate, from which the unknown burnup is then determined by means of the curve. |
047073276 | description | Referring now to the figure of the drawing in detail, there is seen a concrete structure 1 serving as a radiation shield, and a steel pressure vessel 2 in the concrete structure which is provided with a detachable cover 3 at its upper end. A core barrel 4 which is also metallic is disposed within the pressure vessel 2. The metallic core barrel 4 has a support or mounting in the form of a circular projection 5 which rests on a similarly circular flange 6 formed at the inside of the pressure vessel 2. The circular projection and flange divide the space between the core barrel 4 and the pressure vessel 2 into an upper space 8 and a lower space 7. The contact surfaces between the circular projection and flange are constructed with respect to their size and type of surface in such a manner as to form a gas-tight seal which is effective even for small pressure differences, between the lower space 7 and the upper space 8 between the pressure vessel and the core barrel. The core barrel 4 contains ceramic internal parts 9 formed of carbon blocks and/or graphite which surround a space for accommodating a fission zone 10 formed of a multiplicity of spherical fuel elements. Among other things, canals 11 are extended through the internal parts 9. Absorber rods can be moved through the canals 11 for controlling the fission zone, by means of conventional drives 12 disposed on the ceiling of the core barrel 4. The internal parts 9 also contain canals 13, through which cooling gas enters the space 7 from a non-illustrated heat sink through a hot-gas line 16. The cooling gas is conducted to an upper plenum 14, thereby cooling the internal parts 9, and is sent from the plenum 14 through the fission zone from top to bottom. The hot cooling gas flows together into a lower plenum 15 and is conducted to the heat sink through the hot-gas line 16 coaxially disposed in a nozzle 17 of the pressure vessel 2. The upper space 8 is likewise filled with helium which is preferably used as the cooling gas. However, the cooling gas in the space 8 is stagnant and can therefore be kept at a slight overpressure relative to the lower space, so as to prevent contamination of the gas by impurities which are unavoidably present in the cooling gas proper and can be further activated while passing through the fission zone. Since the core barrel 4 is gas-tight above the support 5, 6, the nuclear reactor cover 3 can be removed for repair and servicing purposes (such as to provide service on the absorber rod drives 12), without impairing the accessibility of the parts which will then be exposed due to radioactive contamination and without the danger of the air which than fills the upper space 8 from reaching the internal parts 9 and corroding them. The lower space 7 and the upper space 8 are in connection with each other through a first schematically-illustrated equalization line 18 which can be shut off by a valve 19. The line 18 provides the mutual matching of the respective pressures corresponding to the different operating conditions, required in normal reactor operation. However, the line 18 is not sufficient for equalizing the pressure differences suddenly occurring in the event of a major leak in the pressure vessel 2. For this purpose, a second equalization line 20 is provided. The line 20 begins near the lower end of the core barrel 4 and is brought through the gap between the core barrel 4 and the internal parts 9 to the upper end of the core barrel 4 where it is provided with a schematically-illustrated rupture disc protector 21. If required, the protector 21 quickly releases a flow cross section sufficient for pressure equalization and thus prevents a possible lifting of the core barrel 4 from its mounting 5, 6. The decay heat still developing even if the reactor is then shut down, sets the cooling gas contained in the interior of the core barrel 4 in a convective flow, which carries out the decay heat removal from the fission zone 10. The second equalization line 20 which is then open, carries the cold and therefore heavier air which has penetrated into the upper space 8, into the lower space 7, filling it. However, the air cannot enter into the interior of the core barrel 4 because this is prevented by the temperature stratification between the air and the hot gas. The foregoing is a description corresponding, in substance, to German Application No. P 33 45 457.4, dated Dec. 15, 1983, International priority of which is being claimed for the instant application, and which is hereby made part of this application. Any material discrepancies between the foregoing specification and the specification of the aforementioned corresponding German application are to be resolved in favor of the latter. |
054917328 | claims | 1. In a nuclear reactor including a primary system, a fuel storage building, a primary auxiliary building and a chemical decontamination clean-up system including a chemical injection system for use in cleaning primary system fluids flowing through the nuclear reactor primary system, a layout plan for locating various components of said chemical decontamination cleanup system in said nuclear reactor, comprising the steps of: a) locating a plurality of first demineralizer banks formed from three banks of cation demineralizers connected in parallel flow relationship and a single bank of anion demineralizers connected in series flow relationship with said three banks of cation demineralizers in a shielded room within said fuel storage building and flow coupling said plurality of first demineralizer banks to said nuclear reactor primary system for receiving said primary system fluids from said primary system; b) locating a second demineralizer bank in a shielded room within said primary auxiliary building and flow coupling said second demineralizer bank to said plurality of first demineralizer banks for receiving said primary system fluids from said plurality of first demineralizer banks; and c) locating a return means in said primary auxiliary building and flow coupling said return means to said second demineralizer bank for directing said primary system fluids from said second demineralizer bank to said nuclear reactor primary system. 2. The layout plan for locating various components of a chemical decontamination cleanup system in a nuclear reactor as recited in claim 1, including the substep of forming each of said three banks of cation demineralzers from three individual cation demineralizers connected in parallel flow relationship and positioning each of said cation demineralizers on an individual skid in said shielded room within said fuel storage building. 3. The layout plan for locating various components of a chemical decontamination cleanup system in a nuclear reactor as recited in claim 1, including the substep of forming said single bank of anion demineralizers from three individual anion demineralzers connected in parallel flow relationship and positioning each of said anion demineralizers on an individual skid in said shielded room within said fuel storage building. 4. The layout plan for locating various components of a chemical decontamination cleanup system in a nuclear reactor as recited in claim 1, including the substep of forming said return means from a pair of resin traps located downstream from said second demineralizer bank and positioning said pair of resin traps within said shielded room within said primary auxiliary building and a pair of filters downstream from said at least one resin trap and positioning said pair of filters within said shielded room within said primary auxiliary building. 5. The layout plan for locating various components of a chemical decontamination cleanup system in a nuclear reactor as recited in claim 4, including positioning said pair of resin traps in side-by-side relationship on a skid in said shielded room within said primary auxiliary building. 6. The layout plan for locating various components of a chemical decontamination cleanup system in a nuclear reactor as recited in claim 4, including positioning said pair of filters on a skid in said shielded room in said primary auxiliary building adjacent to said pair of resin traps. 7. The layout plan for locating various components of a chemical decontamination cleanup system in a nuclear reactor as recited in claim 1, including forming said second demineralizer bank from two individual finish demineralzers connected in parallel flow relationship and positioning each of said finish demineralizers on a skid in said shielded room within said primary auxiliary building. 8. The layout plan for locating various components of a chemical decontamination cleanup system in a nuclear reactor as recited in claim 1, including positioning said chemical injection system outdoors between said fuel storage building and said primary auxiliary building and flow coupling said chemical injection system to said primary system upstream from said plurality of first demineralzer banks. |
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